Tunable NiOₓ-MoO₃-MoS₂ nanocomposites: synthesis, structural insights, and enhanced photocatalytic performance

Tunable NiOₓ-MoO₃-MoS₂ nanocomposites: synthesis, structural insights, and enhanced photocatalytic performance | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Tunable NiOₓ-MoO₃-MoS₂ nanocomposites: synthesis, structural insights, and enhanced photocatalytic performance Hila Shalom, Shifra Tahover, Olga Brontvein, Iddo Pinkas, Raanan Carmieli, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7802560/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Mar, 2026 Read the published version in Scientific Reports → Version 1 posted 12 You are reading this latest preprint version Abstract We report the synthesis, structural characterization, and photocatalytic activity of NiOₓ-MoO₃-MoS₂ nanocomposites (NCs) with different ratios of MoO₃-MoS₂ (labeled as NMOS, N = NiOₓ, MO = MoO₃, S = MoS₂). NiOₓ nanoparticles (NPs) were synthesized via a sol–gel method and subsequently annealed with different Mo-precursor ratios to form NMOS NCs. Structural analyses (XRD, TEM, XPS, Raman) confirmed a non-stoichiometric NiOₓ core with mixed Ni valence states and oxygen defects, encapsulated by MoO₃-MoS₂ domains. Optical studies showed band gap tuning from 3.53 eV (NiOₓ) to 2.92 eV (NMOS-III), enhancing visible-light absorption. Photocatalytic activity, evaluated through methylene blue (MB) degradation, revealed NMOS-I's superior efficiency due to balanced phase composition and efficient radical generation, with rapid adsorption and degradation in the first 5 minutes, followed by slower equilibrium adsorption. In contrast, excessive Mo-precursor loading in NMOS-III formed a secondary phase (e.g., NiS), leading to recombination losses and reduced efficiency. The synthesis used a unique sol-gel and annealing method, enabling tunable phase ratios and enhanced photocatalysis, with no prior reports on this ternary system. These findings highlight the role of phase distribution and interfacial chemistry, offering new possibilities for tailoring NMOS NCs for photocatalytic and environmental applications. Physical sciences/Chemistry Physical sciences/Materials science Physical sciences/Nanoscience and technology NiO nanoparticles MoO₃ MoS₂ nanocomposites dye degradation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction In recent years, the demand for advanced nanomaterials with a wide range of applications, such as photodegradation,[ 1 ] energy storage, and catalysis,[ 2 ] has increased. Nanocomposites (NCs) have garnered significant attention for their ability to combine unique properties of individual components, enhancing performance and enabling multifunctional applications.[ 3 , 4 ] Transition metal oxides are promising due to their chemical stability, natural abundance, cost-effectiveness, and relatively simple synthesis routes.[ 5 ] Nickel oxide (NiO) nanoparticles (NPs) are one of the most common metal oxides that have been extensively studied due to their mechanical,[ 6 ] electronic,[ 7 ] magnetic[ 8 ], optical[ 9 , 10 ], and p-type conductivity properties. Therefore, NiO NPs have been used in a variety of applications: gas sensors,[ 11 ] fuel cells,[ 12 , 13 ] catalysts,[ 14 , 15 ] battery materials,[ 16 , 17 ] and supercapacitors.[ 18 , 19 ] NiO NPs crystallize in a cubic structure, with their size and defect concentration, such as nickel vacancies and oxygen interstitials, influencing their magnetic[ 8 ] and electronic[ 7 ] properties. The NiO NPs can be synthesized using a variety of methods: hydrothermal synthesis,[ 20 ] electrodeposition,[ 21 ] sol-gel method[ 22 ], and thermal decomposition.[ 23 ] Despite these benefits, NiO NPs tend to aggregate due to strong interparticle binding energy,[ 24 ] exhibit low electrical conductivity due to a wide bandgap (3.5–3.9 eV),[ 25 ] and face challenges in defect control during synthesis, leading to inconsistent performance.[ 26 ] To overcome these limitations, NiO is commonly incorporated with other metal oxides like molybdenum trioxide (MoO₃). MoO₃ has a layered structure of double MoO₆ octahedra stacked by van der Waals forces,[ 27 , 28 ] high surface area,[ 29 ] remarkable electronic properties,[ 30 , 31 ] and oxidizing characteristics. As an n-type semiconductor, MoO₃ exhibits an indirect band gap of 3.16 eV (with a direct band gap of 2.27 eV),[ 32 , 33 ] MoO₃ supports stable photogenerated charge carriers at room temperature.[ 34 ] Moreover, MoO₃ is thermally stable,[ 35 ] low-toxicity,[ 36 ] and highly catalytic, making it suitable for the hydrogen evolution reaction (HER),[ 37 ] gas sensor applications,[ 38 , 39 ] energy storage devices,[ 40 ] and other functional applications.[ 41 ] MoO₃ can be easily synthesized in various forms, including powder,[ 42 ] 2D nanosheets,[ 43 ] and nanotubes.[ 44 ] Incorporating MoS₂ into NiO-MoO₃ introduces a layered structure of molybdenum atoms between sulfur layers, enhancing electrical conductivity,[ 45 , 46 ] active edge sites,[ 47 ] visible-range light absorption,[ 48 ] charge separation, and photocatalytic performance. MoS₂, an n-type semiconductor with an indirect bandgap of 1.2 eV (direct 1.8 eV),[ 48 ] exhibits stable photogenerated excitons at room temperature due to high exciton binding energy (several hundred meV).[ 49 ] Moreover, MoS₂ is thermally stable,[ 50 ] not toxic[ 51 , 52 ], and highly catalytically active,[ 53 ] making it promising for HER,[ 54 ] gas sensor,[ 55 ] lithium-ion battery[ 56 ], and other functional applications.[ 57 , 58 ] MoS₂ can be synthesized as powder, 2D nanosheets, or nanotubes.[ 59 ] NiO-MoO₃-MoS₂ NCs (labeled as NMOS, N = NiOₓ, MO = MoO₃, S = MoS₂) hold significant potential due to the synergistic interplay between their individual components. Despite the lack of direct investigations into the full NMOS system, existing studies on NiO-MoO₃ and MoO₃-MoS₂ composites highlight the potential benefits of their integration.[ 60 , 61 ] Several studies of MoO₃-MoS₂ NCs or nanowires achieved through hydrothermal synthesis exhibit enhanced optoelectronic and catalytic properties.[ 60 ] Additionally, research on NiO-MoO₃ and nickel molybdate (NiMoO₄) synthesized by spin coating sol–gel techniques, focusing on its physical and electrochemical properties with polymer additives, highlights the growing interest in Ni-Mo-based hybrids.[ 61 ] This study introduces a novel approach by synthesizing NiO NPs via a sol-gel method and fabricating NMOS NCs with varying molar ratios of (NH₄)₂MoS₄ as a Mo precursor, an underexplored strategy for optimizing NCs performance. The NMOS NCs were characterized using X-ray diffraction (XRD) for composition and crystalline structure, transmission electron microscopy (TEM) for morphology, composition, and particle size, X-ray photoelectron spectroscopy (XPS) for surface elemental composition and chemical states, and Raman spectroscopy confirmed the vibrational modes and structural features of the MoO₃-MoS₂ domains. Optical properties assessed via UV-Vis spectrophotometry and photoluminescence (PL) measurements. The strength of this work lies in its comprehensive multi-technique characterization and detailed evaluation of photocatalytic performance through dye degradation experiments, with electron paramagnetic resonance (EPR) spectroscopy providing insights into reactive radical species and the underlying catalytic mechanism. 2. Results and Discussion 2.1. Synthesis The first step in the preparation of NMOS NCs is the NiO x (X = 0–1) NPs synthesis. The NiO NPs were synthesized using the sol-gel method, in which nickel(II) nitrate hexahydrate (Ni(NO₃)₂6H₂O) was first dissolved in distilled water (DI). Subsequently, a sodium hydroxide (NaOH) solution was added dropwise. This resulted in the formation of a light green nickel hydroxide (Ni(OH)₂) precipitate, which was subsequently centrifuged, washed three times with DI water, and dried to yield a pale green paste. The chemical reaction is shown in Reaction 1. Reaction 1 : \(\:\:\varvec{N}\varvec{i}{\left({\varvec{N}\varvec{O}}_{3}\right)}_{2}6{\varvec{H}}_{2}\mathbf{O}+2\varvec{N}\varvec{a}\varvec{O}\varvec{H}\to\:\varvec{N}\varvec{i}{\left(\varvec{O}\varvec{H}\right)}_{2}6{\varvec{H}}_{2}\mathbf{O}\downarrow\:+2\varvec{N}\varvec{a}{\varvec{N}\varvec{O}}_{3}\) Upon annealing at 270°C for 2 hours, the Ni(OH)₂ transformed into black non-stoichiometric NiOₓ NPs. The chemical reaction involved in the process is shown in Reaction 2 [ 62 ]: Reaction 2 : \(\:\:\varvec{N}\varvec{i}{\left(\varvec{O}\varvec{H}\right)}_{2}\to\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{x}}+{\varvec{H}}_{2}\varvec{O}\) The second step in the synthesis of NiOₓ–MoO₃–MoS₂ NCs involves the growth of a MoO₃–MoS₂ layer encasing the NiOₓ NPs. Ammonium tetrathiomolybdate ((NH₄)₂MoS₄) was employed as the molybdenum precursor (Mo-precursor), enabling the initial ionic interaction with the NiOₓ surface and leading to the formation of the NiOₓ–MoS₄²⁻ structure. Different molybdite concentrations (referred to as I, II, and III) were added by varying the molar ratios of (NH₄)₂MoS₄. The NCs formation process consisted of sonicating the NiOₓ NPs in an aqueous solution of (NH₄)₂MoS₄ to ensure homogeneous dispersion and promote surface interaction between the Mo–S species and the NiOₓ NPs. This was followed by overnight stirring, allowing sufficient time for uniform deposition of MoS₄²⁻ onto the NiOₓ surface, as shown in Reaction 3 . The driving force for the formation of NiOₓ–MoS₄²⁻ intermediate is likely the combination of electrostatic interactions and the mildly acidic environment generated when (NH₄)₂MoS₄ is dissolved in DI. The NiOₓ NPs are p-type semiconductors, due to intrinsic defects such as nickel vacancies or extra oxygen,[ 63 ] which results in a positive surface character at acidic pH.[ 64 ] These electrostatic interactions ensure close contact between the NiOₓ NPs and the surrounding MoS₄²⁻ species, which is crucial for their subsequent crystallization during the annealing step. Reaction 3 : \(\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{x}}+{\left({\varvec{N}\varvec{H}}_{4}\right)}_{2}{\varvec{M}\varvec{o}\varvec{S}}_{4}\to\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{x}}-{{\varvec{M}\varvec{o}\varvec{S}}_{4}}^{-2}+2{{\varvec{N}\varvec{H}}_{4}}^{+}\) The last phase of the NCs was the 15-minute annealing, which promoted the crystallization of the MoO₃-MoS₂ phase and the removal of the ammonia (NH₃) and sulfur-based residues. First, the NiOₓ–MoS₄⁻² solution was centrifuged to remove the excess salt residues, and the resulting precipitates were vacuum-dried. Subsequently, the dried powders were placed in quartz ampoules and continuously vacuumed to promote the removal of NH₃ and sulfur-based residues. The ampoule was placed in a horizontal two-zone tube furnace with the powder-containing region positioned in the higher-temperature zone at 520°C (hot zone), while the opposing end remained at 350°C (cold zone). This dual-temperature configuration was deliberately chosen based on the known decomposition temperature of (NH₄)₂MoS₄.[ 65 ] In the higher-temperature zone (520°C), intermediate species such as amorphous MoS₃ begin to form, while NH₃ and hydrogen sulfide (H₂S) are simultaneously released and evacuated under vacuum ( Reaction 4 ).[ 65 ] The cooler zone (350°C) facilitates the directional migration and condensation of these volatile byproducts, ensuring their safe and gradual removal while preventing uncontrolled sulfur release or recombination. Afterwards, the remaining intermediate species, such as MoS₃, are converted into crystalline MoS₂, while further crystallization and restructuring of the NMOS NCs occur ( Reaction 5 ). Moreover, the annealing step plays a crucial role in repairing structural defects within the non-stoichiometric NiOₓ. It also enhances the NiOₓ crystallinity and stability by reducing structural defects such as nickel vacancies and excess oxygen.[ 66 ] Reaction 4 : \(\:{\left({\varvec{N}\varvec{H}}_{4}\right)}_{2}{\varvec{M}\varvec{o}\varvec{S}}_{4}\to\:2{\varvec{N}\varvec{H}}_{3}+{\varvec{H}}_{2}\varvec{S}+{\varvec{M}\varvec{o}\varvec{S}}_{3}\) Reaction 5 : \(\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{x}}-{{\varvec{M}\varvec{o}\varvec{S}}_{4}}^{-2}+2{{\varvec{N}\varvec{H}}_{4}}^{+1}\to\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{x}}{-\varvec{M}\varvec{o}\varvec{S}}_{2}+2{\varvec{N}\varvec{H}}_{3}+{\varvec{H}}_{2}\varvec{S}+\varvec{S}\) The annealing time of 15 minutes was chosen based on several considerations. First, the decomposition of (NH₄)₂MoS₄ into intermediate MoS₃, followed by its conversion into MoS₂ and MoO₃, is known to occur rapidly at 520°C.[ 65 ] Literature studies indicate that these transformations initiate within minutes, making 15 minutes an appropriate and controlled thermal window.[ 67 ] Second, under vacuum conditions at high temperatures, prolonged heating can lead to the excessive evaporation of sulfur species (e.g., S₂, H₂S), which may reduce the formation of crystalline MoS₂.[ 68 ] Limiting the annealing time helps to minimize sulfur loss while still allowing essential phase transitions. Additionally, extended exposure to sulfur residues increases the likelihood of side reactions between sulfur and NiOₓ, potentially resulting in the formation of undesired nickel sulfide (NiS) phases.[ 67 ] A short annealing time helps suppress such secondary reactions, ensuring better phase purity and structural integrity of the final NiOₓ–MoO₃–MoS₂ NCs. The presence of NiOₓ within the NMOS NCs during the annealing process at 520°C may cause additional side reactions to occur during the thermal decomposition of MoS₃ to MoS₂. Although NiOₓ does not serve as a direct oxidant, it can release lattice oxygen under high temperature, thereby acting as a catalytic or surface-active species that modifies the local redox environment and facilitates reaction pathways.[ 69 ] During the decomposition of MoS₃ under vacuum, sulfur residues are released as a byproduct ( Reaction 6 ). Those sulfur residues can react with the NiOₓ surface, leading to the partial formation of nickel sulfide (NiS) as a secondary phase and oxygen (O₂) released ( Reaction 7 (. The sol-gel synthesis of NiOₓ produces NaNO₃ as a byproduct ( Reaction 1) , which may not be entirely removed during the washing procedure and can persist in the final product. As NaNO₃ is highly water-soluble, completely removing Na⁺ and NO₃⁻ ions can be difficult because of their adsorption on the surface of extremely fine Ni(OH)₂/NiO fine particles. Therefore, even after three rounds of washing with DI, some ions may remain adsorbed on the particle surfaces or become trapped within an evolving gel-like network, where NaNO₃ can be physically entrapped and shielded from removal.[ 70 ] As a result, NaNO₃ residues may remain in the dried and calcined NiOₓ powder. During the subsequent annealing step in the encapsulation process, this residual NaNO₃ can decompose to form reactive oxygen species such as sodium nitrite (NaNO₂) and O₂ ( Reaction 8 ).[ 71 ] Since all the reactions occur within the same 15-minute annealing window, the O₂ released during this period ( Reaction 7–8 ) can effectively oxidize the MoS₃ to MoO₃, particularly under vacuum, where molecular oxygen availability is otherwise limited ( Reaction 9 ). The relatively low O₂ content ensures controlled and stepwise oxidation. Reaction 6 : \(\:{\varvec{M}\varvec{o}\varvec{S}}_{3}\to\:{\varvec{M}\varvec{o}\varvec{S}}_{2}+\frac{1}{2}{\varvec{S}}_{2}\uparrow\:\) Reaction 7 : \(\:\frac{1}{2}{\varvec{S}}_{2}+{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{x}}\to\:\varvec{N}\varvec{i}\varvec{S}+\frac{1}{2}{\varvec{O}}_{2}\uparrow\:\) Reaction 8 : \(\:\varvec{N}\varvec{a}{\varvec{N}\varvec{O}}_{3}\to\:\varvec{N}\varvec{a}{\varvec{N}\varvec{O}}_{2}+\frac{1}{2}{\varvec{O}}_{2}\uparrow\:\) Reaction 9 : \(\:{2\varvec{M}\varvec{o}\varvec{S}}_{3}+4{\varvec{O}}_{2}\to\:2{\varvec{M}\varvec{o}\varvec{O}}_{3}+2{\varvec{S}\varvec{O}}_{2}\) 2.2 Structural Analysis The X-ray diffraction (XRD) patterns in Fig. 1 display the structural characteristics of NiOₓ and NMOS-I-III NCs. The successful synthesis of NiOₓ NPs in the cubic phase (PDS 00-073-0450) is evident from prominent diffraction peaks at 37.2°, 43.3°, 62.8°, 75.4°, and 79.36°, which correlate to the 111 , 200 , 220 , 311 , and 222 planes, respectively.[ 72 ] In addition to the characteristic XRD pattern of NiO, we observe an additional peak at 29.29° that can be assigned to NaNO₃, which constitutes ~ 8% of the total. (PDS 98-000-0333). The presence of NaNO 3 is likely a residual byproduct from the sol-gel process utilized in the synthesis of NiOₓ NPs ( Reaction 1 ). The XRD pattern for the NMOS-I and NMOS-II NCs shows that the samples contain ~ 96% NiO, ~ 3% MoO₃ (PDS 04-008-4547), and traces of molybdenum disulfide. The oxidation pathway leading to the formation of MoO₃ involves a reaction between MoS₃, formed during the decomposition of (NH₄)₂MoS₄, and residual NaNO₃ that remains trapped within the gel-like network formed during the sol–gel synthesis of NiOₓ. During the annealing process at 520°C, this residual NaNO₃ decomposes to produce reactive oxygen species, such as NaNO₂ and O₂, as shown in Reaction 8 .[ 71 ] Indeed, while the NiOₓ XRD pattern shows approximately ~ 8% of NaNO₃, it's completely absent in the NCs' patterns, which further supports the proposed transformation pathway. Namely, the decrease in NaNO₃ suggests it was consumed by the oxidation reactions, likely through the release of oxygen species that facilitated MoS₃ oxidation to MoO₃. As expected, at low initial concentrations of MoS₄¯², only trace amounts of MoS₂ (PDF 04-026-7897) were detected, partly due to the presence of oxidation-promoting species in the reaction environment. The low molybdate content observed in the XRD patterns can be attributed to several factors. First, the Ni:Mo precursor ratios were relatively low, approximately 4:1 for NMOS-I and 2:1 for NMOS-II, which limited the availability of molybdenum for MoS₂ formation. Second, the oxidation of MoS₃ to MoO₃ during annealing by the byproducts of O₂ and NaNO₃. Additionally, the relatively short annealing time (15 min at 520°C) may be insufficient for the complete conversion of MoS₃ into well-crystallized MoS₂, resulting in the partial formation of amorphous MoS₂ that is undetectable by XRD. Moreover, if only a small percentage of MoS₂ is formed, it will be extremely difficult to detect by XRD due to its minimal thickness, insufficient mass, and weak diffraction intensity.[ 73 ] Indeed, the characteristic (002) reflection, which indicates the layered structure, is often very weak or completely absent in monolayer and few-layer samples.[ 74 ] In addition, turbostratic disorder and poor crystallinity further reduce XRD visibility. As a result, XRD cannot reliably confirm the presence of MoS₂; this reflection becomes discernible only as the number of layers increases and crystallinity improves. The XRD pattern for the NMOS-III sample reveals a more complex composition: 56.8% NiO, 25.3% MoO₃, 9.6% NiS (PDS 98-000-0308), and 8.3% MoS₂. NiS forms due to a reaction between the NiO and the sulfur in MoS₂ ( Reactions 6–7 ). These results indicate that increasing MoS 4 − 2 concentration makes the formation of various Mo-based oxides and NiS more pronounced, suggesting complex interactions between NiOₓ and MoS₄¯² at the interface. The synthesis of non-stoichiometric NiOₓ NPs resulted in oval-shaped NPs with an average diameter of approximately 8 ± 3 nm (Fig. 2 A-B). Figure 2 A displays a representative TEM image of the NPs, while Fig. 2 B shows the corresponding size distribution. A representative HR-TEM image of a single NiOₓ NP is shown in Fig. 2 A - insert . The image reveals well-defined lattice fringes with an interplanar spacing of 0.241 nm, corresponding to the ( 111 ) plane of cubic-phase NiO.[ 72 ] The crystallinity of the NPs was further confirmed by the Selected Area Electron Diffraction (SAED) pattern shown in Fig. 2 C, which displays distinct concentric diffraction rings. These rings can be indexed to the ( 111 ), ( 200 ), ( 220 ), and ( 311 ) planes, confirming the face-centered cubic structure of NiO.[ 72 ] The EDS analysis ( Table 1 and Figure S1 ) revealed that the NiOₓ NPs contain ~ 57 at% Ni and ~ 43 at% O, corresponding to a Ni:O atomic ratio of 1:0.75. This deviation from the ideal stoichiometry of NiO (1:1) suggests the presence of nickel-rich phases or oxygen vacancies.[ 66 ] Table 1 Results of the semi-quantitative EDS analysis from TEM images Nickel (Ni) (at%) Oxygen (O) (at%) Molybdenum (Mo) (at%) Sulfur (S) (at%) Ni: O NiOₓ 57.3 ± 3.6 42.7 ± 3.6 1: 0.75 NMOS-I 56.8 ± 3.6 43.2 ± 3.4 1:0.76 25.7 ± 3.5 59.0 ± 4.8 11.1 ± 4.0 4.2 ± 2.7 NMOS-II 22.0 ± 2.6 58.6 ± 3.1 13.5 ± 2.3 5.9 ± 2.9 NMOS-III 13.8 ± 3.4 52.2 ± 3.2 18.2 ± 3.4 15.7 ± 3.6 During the synthesis of NMOS NCs, the NiOₓ NPs underwent an additional 15-minute annealing step at 520°C to crystallize the MoO₃-MoS₂. This temperature is significantly higher compared to the formation temperature of the NiOₓ NPs (270°C). The elevated thermal treatment not only facilitated the crystallization of the MoO₃-MoS₂ mixture but also induced further growth and enhanced crystallinity within the NiOₓ NPs.[ 66 , 75 ] Consequently, the annealed NiOₓ NPs exhibited an increased average particle size of approximately 13 ± 4 nm, as shown in Fig. 2 D-E. Clear lattice fringes are observed with an interplanar spacing of 0.241 nm, corresponding to the ( 111 ) plane of cubic-phase NiO, confirming the improved crystallinity following the high-temperature annealing (Fig. 2 D – insert ) .[ 72 ] In Fig. 2 F, the SAED pattern shows distinct concentric diffraction rings of the FCC structure of NiO.[ 72 ] EDS measurements (Table 1 ) revealed that the non-stoichiometric NiOₓ NPs contain 57 at% Ni and 43 at% O, corresponding to a Ni:O atomic ratio of 1:0.76. HR-STEM analyses of the NMOS NCs (Fig. 2 ) reveal well-defined NiOₓ NPs embedded within molybdate-derived structures. Orthorhombic MoO₃ crystallites are distinguished by lattice fringes with an interplanar spacing of 0.366 nm corresponding to the (001) plane. The NiOₓ NPs display lattice fringes with a spacing of 0.241 nm, assigned to the (111) plane of cubic NiO.[ 72 ] In all cases, EDS elemental mapping (Fig. 2 G-H, J-K, M-N) demonstrates the presence of Ni, O, Mo, and S, and the semi-quantitative analysis (Table 1 ) confirms their presence in agreement with the designed composite structure. The differences among the samples with a varied amount of molybdate precursor are manifested in the change of MoO₃ NP size, composition, and crystallinity, each directly correlated with precursor concentration. In the NMOS-I sample (Fig. 2 I), MoO₃ crystallites are relatively small (~ 5–7 nm) and display the (011) plane with a spacing of 0.255 nm. In the NMOS-II sample (Fig. 2 L), MoO₃ NPs grow to ~ 21 nm, reflecting the effect of increased (NH₄)₂MoS₄ loading in promoting the development of larger domains. In the NMOS-III sample (Fig. 2 O), the MoO₃ NP size further increases to ~ 33 nm, demonstrating that precursor concentration strongly drives nucleation and coarsening of MoO₃ crystallites. The compositional trends follow the same pattern: the NMOS-I NCs contains 25.7% Ni, 59.0% O, 11.1% Mo, and 4.2% S, the NMOS-II NCs shows increased Mo and S (13.5% Mo, 5.9% S) with reduced Ni (22.0%), while the NMOS-III NCs exhibits the most pronounced enrichment in Mo (18.2%) and S (15.7%) alongside a decrease in Ni (13.8%) and O (52.2%). These differences are consistent with XRD analysis (Fig. 1 ), where MoO₃ reflections intensify and sharpen from the NMOS-I to NMOS-III samples, confirming the enhanced crystallinity and higher fraction of the MoO₃ phase at increasing precursor concentrations. The X‑ray photoelectron spectroscopy (XPS) spectra of NiOₓ and NMOS-I-III NCs are shown in Fig. 3 , providing insight into their electronic structure, chemical composition, and surface states. Depth profiling was performed on the NCs to obtain representative information from both the NiOₓ NPs and their interface with the MoO₃–MoS₂ domains. For NiOₓ NPs (Fig. 3 A-B), the Ni 2p and O 1s peaks are clearly observed. Background subtraction was performed using the Shirley method. The O 1s spectrum, deconvoluted with Shirley background subtraction, shows two main components: a peak at 530.03 eV corresponding to lattice oxygen (M–O) in NiO, and a higher binding energy peak at 532.09 eV associated with surface hydroxyl groups or adsorbed species (C–O/Ni–OH). Notably, nickel species are progressively reduced during XPS depth profiling with Al Kα radiation, revealing lower oxidation states and even the presence of metallic Ni. The Ni 2p spectrum displays a complex envelope arising from multiple oxidation states and satellite features. The main Ni²⁺ peaks appear at 855.01 eV (2p₃/₂) and 872.40 eV (2p₁/₂), with shake-up satellites at 860.78 eV and 879.91 eV, characteristic of Ni²⁺ in NiO. Peaks at 857.07 eV (2p₃/₂) and 873.82 eV (2p₁/₂), with additional shake-up at 864.00 eV and 883.50 eV, indicate Ni³⁺ species with minor Ni⁺ contributions appear at 853.70 eV and 870.78 eV. These multiple valence states confirm the non-stoichiometric nature of NiOₓ, consistent with oxygen vacancies or partial surface reduction/oxidation. TEM–EDS analysis further supports this interpretation, showing a Ni:O atomic ratio of ~ 1:0.75. XPS quantification yields Ni and O atomic percentages of 62.5% and 37.5%, respectively ( Table S2 ), confirming the nickel-rich composition. In the NMOS-I NCs ( Figure S2A-B and Fig. 3 C), the Ni 2p and O 1s peaks remain at similar binding energies but with reduced intensities (54.8% Ni and 37.8% O). This reduction reflects surface modification caused by Mo incorporation. In the Mo 3d region, the peaks at 232.7 eV and 235.6 eV correspond to Mo⁶⁺ (Mo 3d₅/₂ and 3d₃/₂), indicative of MoO₃ or related oxides. Additional peaks at 228.6 eV and 230.6 eV are characteristic of Mo⁴⁺ in MoS₂, while the small peak at 225.9 eV corresponds to the S 2s signal. These results confirm the coexistence of MoO₃ and MoS₂ phases, with partial oxidation of MoS₂ likely occurring during annealing or through interactions with NiOₓ. The quantified contributions from Mo⁶⁺, Mo⁴⁺, and S 2s are 4.5%, 2.2%, and 0.7%, respectively. Increasing the Mo-precursor to NMOS-II NCs changes the relative intensities of the peaks without shifting their binding energies ( Figure S2C-D and Fig. 3 D). XPS quantification reveals atomic percentages of 59.7% Ni, 31.7% O, 4.3% Mo⁶⁺, 3.3% Mo⁴⁺, and 1.0% S. These results confirm that NiOₓ remains the dominant phase, but the sample is increasingly enriched in the composite with Mo⁴⁺/Mo⁶⁺ species and sulfur, yielding a mixed MoO₃–MoS₂ composition. The partial oxidation of MoS₂ is consistent with annealing-induced oxidation processes. For the NMOS-III NCs ( Figure S2E-F and Fig. 3 E), the Ni, O, Mo, and S signals undergo further redistribution. The atomic percentages are 43.4% Ni, 28.9% O, 7.9% Mo⁶⁺, 13.4% Mo⁴⁺, and 6.4% S. The higher S 2s intensity compared to the NMOS-I and NMOS-II samples suggests increased incorporation of MoS₂, along with the possible formation of NiS as a secondary phase due to chemical interactions between NiOₓ and the MoS₄²⁻ precursor. The simultaneous presence of NiOₓ, MoO₃, and MoS₂ phases, along with traces of NiS, highlights the complex chemical interplay occurring during precursor decomposition and annealing. In summary, XPS analysis shows that increasing Mo-precursor concentration leads to higher Mo and S content, reflecting enlarged MoO₃ and MoS₂ formation. The NiOₓ phase remains dominant but undergoes surface modification, with evidence of partial MoS₂ oxidation and possible NiS formation at higher concentrations. This confirms the tunable composition and complex interfacial chemistry of the nanocomposites. 2.3. Spectroscopic Analysis Raman spectra of NiOₓ and NMOS-I-III NCs are shown in Fig. 3 F, providing characteristic vibrational signatures, structural features, and phase composition. The corresponding peak assignments are summarized in Table S2 . Across all samples, NiO-related modes are detected, though their intensity and visibility decrease progressively with increasing precursor concentration. At the same time, MoO₃-related peaks are consistently observed in the composites, and their number, position, and intensity evolve with Mo precursor loading. These observations confirm the coexistence of NiOₓ and Mo-derived phases, with variations in spectral features reflecting changes in nanoparticle size, structural integration, and phase composition. The differences between the samples are evident in both the identity and relative intensities of the Raman bands. The spectrum of pristine NiOₓ (Fig. 3 F - black ) is dominated by Ni–O vibrations, with sharp features at ~ 514 and ~ 1077 cm⁻¹ corresponding to the first-order longitudinal optical (LO) and second-order longitudinal optical (2LO) modes, respectively, and additional peaks at ~ 398 and ~ 725 cm⁻¹ assigned to first-order transverse optical (TO) and second-order transverse optical (2TO) modes.[ 76 , 77 ] The sharp peak at 514 cm⁻¹ is particularly significant, as it is commonly associated with Ni-related defects,[ 77 ] reflecting the non-stoichiometric nature of the synthesized NiOₓ. In the NMOS-I sample (Fig. 3 F - red ), the NiO signals decrease in intensity and shift slightly (~ 538 and ~ 1093 cm⁻¹), which can be explained by the growth of larger NiO NPs during annealing,[ 78 ] as confirmed by TEM. At the same time, six new bands emerge that are characteristic of MoO₃: ~356 cm⁻¹ (Mo–O bending), ~ 765 cm⁻¹ (O–Mo–O bridge stretching), ~ 819 and ~ 851 cm⁻¹ (Mo–O–Mo symmetric stretching), ~ 891 cm⁻¹ (terminal Mo = O stretching), and ~ 940 cm⁻¹ (polyoxometalate-type Mo–O stretching).[ 79 , 80 ] These features confirm the coexistence of NiO and MoO₃, in agreement with XRD and XPS results. In the NMOS-II spectrum (Fig. 3 F - blue ), the NiO contribution is further reduced, with only a weak LO mode at ~ 545 cm⁻¹ detected. In contrast, MoO₃-related signals intensify, including peaks at ~ 364 cm⁻¹ (Mo–O bending), ~ 756–763 cm⁻¹ (Mo–O–Mo stretching), ~ 816 cm⁻¹ (Mo = O stretching), ~ 858 and ~ 888 cm⁻¹ (Mo–O stretching and bending), and ~ 940 cm⁻¹ (polyoxometalate-type stretching). These results show that higher precursor loading enhances the vibrational contributions of MoO₃ while masking most NiO modes, consistent with the structural integration suggested by XRD and XPS. Finally, in the NMOS-III sample (Fig. 3 F - green ), the NiO-related modes disappear entirely, indicating their suppression by Mo-rich and sulfide phases. Strong MoO₃ vibrations are observed at ~ 707, 824, 863, 905, 953, and 1007 cm⁻¹, several of which are shifted to lower wavenumbers due to lattice softening caused by the growth of larger MoO₃ NPs (~ 33 nm, TEM). In addition, MoS₂ fingerprints are clearly detected at ~ 376 cm⁻¹ (E¹₂g), ~ 403 cm⁻¹ (A₁g), and ~ 460 cm⁻¹ (A₁u), consistent with the increased MoS₂ fraction at this loading.[ 81 ] A low-frequency band at ~ 344 cm⁻¹ is also present, assigned to NiS vibrations,[ 82 ] confirming partial sulfide formation via interaction between NiOₓ and the MoS₄²⁻ precursor during annealing. Together, these observations highlight the progressive transition from NiO-dominated spectra to MoO₃- and MoS₂-rich vibrational signatures, with additional NiS contributions at the highest precursor concentration. The absorption spectra of NiOₓ and NMOS-I-III NCs are displayed in Fig. 4 A. All the spectra exhibit absorption in the UV–visible region, with an absorption edge around 300 nm corresponding to the presence of NiOₓ NPs.[ 83 , 84 ] As the Mo content increases, the spectra show clear broadening and splitting of the absorption band, indicating changes in the electronic structure. Deconvolution of the absorbance spectra (Fig. 4 B-E) enables a more detailed interpretation of these features and allows us to trace the individual spectral contributions of MoO₃ and MoS₂. The NiOₓ NPs deconvolution (Fig. 4 B) reveals three distinct peaks at 248, 298, and 300 nm. The peaks in 248 and 298 nm are characteristic of NiOₓ NPs with an average size of ~ 8 nm.[ 83 – 85 ] The third broad peak at 300 nm is typical of NaNO₃ and corresponds to the weak n→π* electronic transition within the nitrate ion.[ 86 ] The presence of NaNO₃, a byproduct of the sol–gel synthesis of NiOₓ, is further supported by XRD analysis. The absorbance spectrum of NMOS-I NCs displays more pronounced and sharper peaks at 262 nm and 303 nm (Fig. 6 A). Moreover, the first one appears to be more intense with reduced FWHM. The 262 nm peak, associated with NiOₓ, exhibits a red shift compared to pristine NiOₓ, likely due to increased particle size (~ 13 ± 4 nm, confirmed by TEM) and reduced quantum confinement effects (Fig. 2 B,E). In addition, the shift and the narrowing of the NiO x pick can also be ascribed to the annealing process, as well as the formation of the additional Mo-related phases. Namely, the electronic interactions between NiOₓ and MoO₃–MoS₂ modify the transition energies. Indeed, the absorbance peak at 303 is most likely attributed to the presence of MoO₃,[ 87 ] which forms during the annealing process with the Mo-precursor ( Reaction 9 ). That ascription is further supported by the comparatively higher dielectric function of MoO₃, which enhances its optical response in this region, resulting in a more intense and distinct absorbance peak.[ 88 , 89 ] Spectrum deconvolution supporting this interpretation (Fig. 4 C), as it resolves additional broad spectral contribution at 310 nm, which is assigned to the defects within the NCs as well as MoO₃.[ 90 ] As the concentration of the Mo-precursor increases to NMOS-II NCs, the characteristic NiOₓ-related absorption features diminish markedly, with the NiOₓ peak nearly disappearing from the spectrum. Instead, the absorption is dominated by an edge around 300 nm, corresponding to MoO₃. This shift occurs as the NiOₓ is embedded within a MoO₃–MoS₂ matrix, which suppresses its optical response. The latter observation is supported by TEM, XRD, and Raman analysis, showing increased MoO₃ and reduced NiOₓ signals. Similar to the NMOS-I NCs, spectral deconvolution of the NMOS-II absorption profile (Fig. 4 D) resolves three peaks at 262, 303, and 315 nm, with the latter two attributed to MoO₃. As observed in TEM, the red shift of the third peak from 310 nm to 315 nm suggests further MoO₃ growth and dielectric enhancement, consistent with larger MoO₃ domains. For the NMOS-III sample, the absorption spectrum exhibits extended absorption into the visible region (400–800 nm), which is a result of the higher MoS₂'s concentration.[ 91 ] The absorption's deconvolution presents a complex mixture of multiple peaks at 262, 272, 305, and 728 nm (Fig. 4 E). The band at 262 nm is associated with NiOₓ, and the decrease in its full width at half maximum (FWHM) indicates changes in its local electronic environment within the Mo-rich matrix. The peak at 272 nm corresponds to NiS,[ 92 ] formed through interaction of NiOₓ with the Mo-precursor during annealing, while the 305 nm band is attributed to MoO₃, and is consistent with its stronger crystallinity and dielectric response.[ 87 , 90 , 93 ] The broad peak at 728 nm arises from overlapping contributions of MoS₂ and Mo-based sub-oxides. These results confirm the multiphase nature of the NMOS-III nanocomposite, consistent with the phase distribution observed in Raman, XRD, and XPS analyses. To summarize, NiOₓ and NMOS-I-II NCs samples exhibit a clear absorption edge in the UV region, dominated by NiOₓ and MoO₃ contributions, with negligible absorption above 400 nm. By contrast, NMOS-III exhibits extended visible-light absorption due to MoS₂ and secondary Mo phases, reflecting its multiphase character. The band gap values of NiO and NMOS-I-III NCs are shown in Figure S3 . Pure NiOₓ NPs exhibit a band gap of 3.53 eV, consistent with reported values.[ 94 ] Upon introducing the Mo-precursor, the band gap increases to 3.66 eV in the NMOS-I sample. This shift can be attributed to the growth and improved crystallinity of NiOₓ during annealing, together with the formation of MoO₃ domains. As the NiOₓ is most likely embedded within the MoO₃–MoS₂ matrix, this results in a modified electronic structure and a slight blue shift of the absorption edge. Interestingly, at a 2x Mo-precursor concentration, the band gap of NMOS-II NCs red shifts back to 3.53 eV. This red shift is attributed to the growth of separated MoO₃ domains, which increase the NiO-MoO₃ phase segregation and separation. This interpretation is further supported by XRD, which reveals intensified MoO₃ reflections, Raman spectra show suppression of NiOₓ vibrational modes by Mo-rich phases, and XPS data confirm increased Mo⁶⁺/Mo⁴⁺ contributions. In contrast, for NMOS-III, the band gap shifts to 2.93 eV. The profound shift can be ascribed to the MoS₂ and NiS formation. The presence of MoS 2 introduces broad band-edge transitions that extend optical absorption into the visible range. The emission spectra of NiOₓ and NMOS-I-III NCs at an excitation wavelength (λ ex ) of 250 nm and 532 nm are shown in Fig. 5 A-B, respectively. The 250 nm excitation is for the NiOₓ component, while the 532 nm excitation is selective for the Mo-component. Under excitation at 250 nm, the PL spectra of all samples display the same emission profile with varying intensities (Fig. 5 A). Deconvolution reveals three main peaks at 380, 497, and 601 nm, together with a broad band at 463 nm ( Figure S4 ). Since the spectral shape remains essentially unchanged across all samples, only the NiOₓ deconvolution is shown in Figure S4 , while the fitting parameters for the composites are summarized in Table S3 . The emission at 380 nm represents near-band-edge (NBE) transitions typical in wide-bandgap semiconductors like NiOₓ. This strong peak is attributed to excitonic recombination between the conduction and valence bands within the band edge.[ 95 ] The board 463 nm peak and 497 nm peak are associated with structural defects such as oxygen vacancies and interstitials in NiOₓ.[ 96 ] Whereas the 601 nm band is attributed to transitions from the conduction band to the d -band within NiOₓ's band structure, aligning with its estimated Fermi level energy.[ 97 ] For NMOS-I, the emission intensity is nearly doubled compared to pristine NiOₓ, probably due to energy transfer from MoO₃ defect states, as supported by XRD, TEM, XPS, and Raman analyses. In contrast, the emission of NMOS-II NCs is only slightly enhanced compared to the NiOₓ. This enhancement is attributed to MoS₂ contributions, which extend absorption but also introduce non-radiative pathways that partially suppress emission.[ 98 ] NMOS-III exhibits significantly reduced PL compared to the NiOₓ, which can be attributed to the presence of a multiphase composition (NiO, NiS, MoO₃, and MoS₂), as confirmed by the other results. This complex phase mixture introduces non-radiative recombination centers and contending energy transfer pathways that quench emission. Namely, the lower PL intensity likely arises from defect states and electronic transitions specific to the NiS and MoS₂ phases, which differ from pure NiOₓ transitions and contribute weaker overall emissions. When excited at 532 nm, the emission is much lower in intensity due to the low Mo-content (Fig. 5 B-F and Table S4 ). The pristine NiOₓ exhibits weak emission with a broad background and a shoulder-like peak at 633 and 661 nm (Fig. 5 B-F and Table S4 ). The background is attributed to deep-level defects, particularly oxygen vacancies, while the shoulder features originate from defect-related states associated with the non-stoichiometric NiOₓ lattice.[ 96 ] In NMOS-I NCs, the emission intensity increased, and the broad background is blue-shifted. The 633 nm peak becomes more distinct, and the 661 nm shoulder-like feature broadens and strengthens. These enhancements are attributed to the presence of Mo-based additives. In NMOS-II NCs, the broad background is red-shifted with additional peaks at 629, 670, and 723 nm. The 629 nm feature corresponds to the MoS₂ B exciton with a blue shift due to defect-induced lattice distortions. The 670 nm peak is attributed to the MoS₂ A exciton, arising from direct electron–hole recombination in MoS₂,[ 99 , 100 ] and its red shift results indicate a subtle increase in MoS₂ layer thickness. The 723 nm band is likely related to defect-bound excitons, which become more pronounced in few-layer and defect-rich Mo-S phases. In NMOS-III NCs, the overall emission is reduced compared to NMOS-I NCs and NMOS-II NCs, reflecting the complex multiphase composition (NiO, NiS, MoO₃, MoS₂) as confirmed by XRD, TEM, XPS, and Raman analyses. Deconvolution reveals a blue-shifted background with additional peaks at 633 and 670 nm, corresponding to MoS₂ B and A excitons, respectively.[ 99 , 100 ] The slight shifts of these excitonic peaks also suggest enhanced defect–exciton interactions, where defects act as trapping or recombination sites that perturb excitonic transitions. 2.4. Photocatalysis Analysis Our findings demonstrate that NMOS NCs exhibit exceptional potential as a photocatalytic system. The unique architecture integrates p-type NiOₓ NPs, known for their high theoretical capacitance, with n-type MoO₃-MoS₂ phases. This combination forms efficient p–n junctions at their interfaces, facilitating enhanced charge separation and transfer. Additionally, the combined effect of these phases should improve electronic conductivity and chemical stability, creating an optimal platform for visible-light-driven photocatalysis. These properties position the nanocomposites as a highly promising material for photocatalytic applications. To elucidate whether Mo-based structures enhance the radical-mediated photocatalytic activity of the NCs, we employed electron paramagnetic resonance (EPR) spectroscopy. This technique enables the detection and identification of radicals generated in the presence of NCs through the use of spin-trapping agents such as dimethyl sulfoxide (DMSO) and or 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO), a nitrone-based spin trap effective for both hydroxyl (·OH⁻) and superoxide (·O₂⁻) radicals. To evaluate the formation of the reactive radicals in NiOₓ and NMOS-I-III NCs, EPR measurements were conducted in the dark and under visible-light illumination (Fig. 6 A and Figure S4 ). For both NiOₓ and NMOS-III NCs, no EPR signals were observed under dark conditions or visible light irradiation (Fig. 6 B), suggesting that no stable radicals were generated. This behavior can be explained by their optical properties: NiOₓ NPs have a wide band gap of approximately 3.53 eV, allowing them to absorb light primarily at the ultraviolet rather than visible. Similarly, NMOS-III NPs NCs contain a high fraction of MoO₃, and also predominantly absorb ultraviolet light. As a result, both NiOₓ and NMOS-III exhibit limited photoactivity under visible light, consistent with their relatively poor photocatalytic performance in dye degradation experiments, as will be shown below. For NMOS-I-II NCs, no signals were observed under dark conditions. However, after exposure to visible light, the EPR spectrum exhibits a distinct pattern centered around g = 2, with four lines indicative of interactions with hydroxyl radicals (·OH⁻).[ 101 ] Notably, the radical signal intensity of NMOS-II exhibits the strongest response under illumination (Fig. 6 A). Notably, using BMPO as a spin trapping agent in EPR spectroscopy effectively detects reactive oxygen species like ·OH⁻ and ·OOH (·O₂⁻) despite their short half-lives.[ 102 ] DMSO traps mainly the ·OH⁻ radicals, thus can be used to distinguish between the signals induced by oxygen species.[ 103 ] Hence, to verify the formation of ·OH⁻ radicals, DMSO was added to the samples during the EPR measurements. The presence of DMSO resulted in a quenched EPR signal for NMOS-II compared to samples without DMSO, see Fig. 6 B. The latter result indicates that the main active radical species formed under illumination of the NMOS-I and NMOS-II is the ·OH⁻. This specific species is the most favorable for advancing oxidation processes, especially in applications such as pollutant and wastewater treatment, soil remediation, and sterilization.[ 104 ] To evaluate the NCs' photocatalytic efficacy, we examined the ability of NiOₓ and NMOS-I-III NCs to degrade methylene blue (MB) dye under visible-light irradiation. MB is an aromatic heterocyclic cationic dye [ 105 ], and is considered to be one of the most popular clothing colorants in the textile industry,[ 106 ] known for its environmental persistence and toxicity. Effective degradation of MB demonstrates the NCs' ability to break down complex organic pollutants, highlighting their potential for environmental remediation applications, such as wastewater treatment, by leveraging visible-light-driven photocatalysis to address industrial dye pollution. Figure 7 shows the change in the absorbance of the MB dye at different time intervals for all the examined catalysts (NiOₓ and NCs) in aqueous solutions. The reduction of the MB characteristic absorption maxima \(\:\left({\lambda\:}_{max\:}\sim665\:nm\right)\) was used to track the progression of dye degradation. In addition, we assessed the photocatalytic efficiency of all NPs and NCs by comparing the degradation rate \(\:\left(D\%\right)\) , and the kinetics of the photocatalytic reactions, as detailed in the methods section ( Figure S5A ). Following 90 minutes of illumination, the degradation rates of MB dye are as follows: 35% with NiO NPs, 82% with NMOS-I, 73% with NMOS-II, and 42% with NMOS-III, Figure S5A . NMOS-I and NMOS-II NCs demonstrated the highest photocatalytic efficiency compared to NiOₓ and NMOS-III NCs. The superior performance of NMOS-I can be attributed to the optimal balance between NiOₓ and Mo-related phases (1:0.02, as confirmed by XRD). This combination facilitates efficient charge separation and suppresses electron–hole recombination. In contrast, excessive Mo- and S-content in the NMOS-III NCs introduces additional recombination centers (e.g., NiS). Two second-order kinetic models of the photocatalytic process provided the best fit for the experimental results. The rate constants for the rapid initial phase (0–5 min) and the slower phase (5–90 min) are detailed in Table S5 and Figure S5B . The faster dye degradation within the first 5 minutes is promoted by the fast adsorption of dye molecules onto the active sites of the NCs. For NMOS-I and NMOS-II NCs, this process is much more efficient and fast, with NMOS-I NCs exhibiting the fastest kinetic rate of 0.575 min⁻¹. The process proceeds more rapidly because ·OH⁻ radicals are generated alongside adsorption, which promotes dye molecule degradation and thereby regenerates the active sites on the surface of the NCs. This observation is supported by the EPR analysis, where only the NMOS-I and NMOS-II NCs were shown to exhibit radical formation. In the following degradation phase, for the pristine NiO and NMOS-III, this process is extremely slow, with a kinetics rate of 0.003 and 004 min⁻¹, respectively. This slow degradation occurs mainly due to slow equilibrium adsorption. Conversely, for the NMOS-I and NMOS-II, this process is faster, 0.015 and 0.018 min⁻¹, respectively. Here again, due to the higher Mo-content, there is a synergistic effect between the adsorption process and radical-promoted photocatalysis. The photodegradation processes involving NMOS-I-II NCs and their interaction with dyes are detailed in Equations 1–4 . Under illumination with visible light, photons with energy greater than or equal to the band gap of the semiconductor components (NiOₓ, MoO₃, or MoS₂) excite electrons from the valence band (VB) to the conduction band (CB), generating electron-hole pairs. The photogenerated electrons and holes react with adsorbed species (oxygen, water, or hydroxide ions) to produce reactive oxygen species, such as ·O₂⁻ and ·OH⁻, which are responsible for dye degradation. The ·OH⁻reacts with the adsorbed MB, breaking their chromophores and leading to mineralization.[ 107 ] Equation 1 : \(\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{X}}-\varvec{x}1-2{\varvec{M}\varvec{o}\varvec{O}}_{3}-{\varvec{M}\varvec{o}\varvec{S}}_{2}+\varvec{h}\varvec{v}\to\:\varvec{N}{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{X}}-\varvec{x}1-2{\varvec{M}\varvec{o}\varvec{O}}_{3}-{\varvec{M}\varvec{o}\varvec{S}}_{2}\left({\varvec{e}}_{\varvec{C}\varvec{B}}^{-}+{\varvec{h}}_{\varvec{V}\varvec{B}}^{+}\right)\) Equation 2 : \(\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{X}}-\varvec{x}1-2{\varvec{M}\varvec{o}\varvec{O}}_{3}-{\varvec{M}\varvec{o}\varvec{S}}_{2}\left({\varvec{h}}_{\varvec{V}\varvec{B}}^{+}\right)+\:{\varvec{H}}_{2}\varvec{O}\to\:\varvec{N}\varvec{i}\varvec{O}@1-2\varvec{L}-{\varvec{M}\varvec{o}\varvec{S}}_{2}+{\bullet\:\varvec{O}\varvec{H}}^{-}+{\varvec{H}}^{+}\) Equation 3 : \(\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{X}}-\varvec{x}1-2{\varvec{M}\varvec{o}\varvec{O}}_{3}-{\varvec{M}\varvec{o}\varvec{S}}_{2}\left({\varvec{h}}_{\varvec{V}\varvec{B}}^{+}\right)+\:{\bullet\:\varvec{O}\varvec{H}}^{-}\to\:\varvec{N}\varvec{i}\varvec{O}@1-2\varvec{L}-{\varvec{M}\varvec{o}\varvec{S}}_{2}+\bullet\:\varvec{O}\varvec{H}\) Equation 4 : \(\:{\varvec{N}\varvec{i}\varvec{O}}_{\varvec{X}}-\varvec{x}1-2{\varvec{M}\varvec{o}\varvec{O}}_{3}-{\varvec{M}\varvec{o}\varvec{S}}_{2}\left({\varvec{e}}_{\varvec{C}\varvec{B}}^{-}\right)+{\varvec{O}}_{2}\to\:\varvec{N}\varvec{i}\varvec{O}@1-2\varvec{L}-{\varvec{M}\varvec{o}\varvec{S}}_{2}+{\bullet\:{\varvec{O}}_{2}}^{-}\) 3. Conclusions The NMOS NCs were synthesized via a novel approach of sol-gel synthesis of non-stoichiometric NiOₓ NPs, followed by annealing with different molar ratios of Mo-precursor, enabling tunable multiphase compositions. Comprehensive characterization through XRD, TEM, XPS, and Raman confirmed the formation of multiphase NCs, where NiOₓ retained its non-stoichiometric nature, while MoO₃ and MoS₂ fractions increased with Mo-precursor concentration in NMOS I and II. Interestingly, NMOS-III NCs exhibited a complex multiphase composition, including NiS formation due to interactions between NiOₓ and MoS₄²⁻. Absorbance and PL analyses revealed that increasing Mo content shifted the optical properties of the NCs. NMOS-I and NMOS-II NCs showed dominant absorption in the UV range, while NMOS-III NCs extended absorption into the visible region due to higher MoS₂ and NiS content. Band gap values ranged from 3.66 eV (NMOS-I) to 2.93 eV (NMOS-III), reflecting the influence of MoS₂ and phase segregation on electronic structure. The NMOS-I NCs exhibited the highest photocatalytic efficiency for MB degradation under visible-light irradiation, achieving an 82% degradation rate after 90 minutes. This superior performance is attributed to an optimal balance of NiOₓ and MoO₃–MoS₂ phases, forming efficient p–n junctions that enhance charge separation and minimize electron–hole recombination. In contrast, NMOS-III showed reduced efficiency (42%) due to recombination centers introduced by NiS and excess MoS₂. EPR measurements confirmed that NMOS-I and NMOS-II NCs generate ·OH⁻ radicals under visible-light irradiation, driving MB degradation. The absence of radicals produced by NiOₓ is attributed to its limited visible-light absorption. On the contrary, the lack of produced radicals in NMOS-III can be mainly attributed to the presence of NiS. In both cases, the lack of radical signals under visible light is consistent with their wider band gaps. These properties restrict their visible-light absorption and confine their photoactivity. Kinetic analysis revealed that MB degradation in NMOS-I and NMOS-II proceeds via dual stages: a rapid initial stage dominated by dye adsorption and degradation by ·OH⁻ radicals, followed by a slower stage controlled by slow equilibrium adsorption. NMOS-I showed the fastest overall kinetics due to efficient interaction between adsorption and photocatalysis, while higher Mo loadings (NMOS-III) diminished this effect. In conclusion, this study's innovative synthesis and multi-technique characterization demonstrate that NMOS NCs, particularly NMOS-I and NMOS-II, offer a promising platform for visible-light-driven photocatalysis. The novel tunable phase compositions enhance charge separation and optical properties, while detailed kinetic modeling of adsorption-photocatalysis interplay provides actionable insights for designing heterostructured NCs. These findings suggest potential applications in environmental remediation, such as dye degradation, and pave the way for further optimization of heterostructured nanomaterials for advanced photocatalytic systems. 4. Methods 4.1. Experimental 4.1.1 Sol-gel synthesis of NiOₓ NPs: 3.635 g of nickel(II) nitrate hexahydrate (Ni(NO₃)₂6H₂O, Merck, 97%) dissolved in 5 mL of distilled water (DI). Meanwhile, 2 g of sodium hydroxide (NaOH, Bio-Lab, 97%) was dissolved in 5 mL of DI. Then, 0.9 mL of NaOH solution was added dropwise to the Ni solution. The resulting light green mixture was centrifuged at 5000 RPM for 5 minutes. The precipitation was washed 3 times with DI and dried in a vacuum oven at 80 ˚C for 1h. The obtained green powder was annealed at 270°C for 2 h under a nitrogen atmosphere to yield dark-black powder. 4.1.2 Synthesis of NMOS NCs: The dark-black NiOₓ NPs powder was divided into four vials (with one vial serving as a reference). Three different molar ratios of ammonium tetrathiomolybdate ((NH₄)₂MoS₄) were added to each vial to control the relative MoO₃–MoS₂ content (labeled as I, II, and III). The molar ratios were as follows: NMOS-I: 0.276 mol NMOS-II: 0.552 mol NMOS-III: 0.828 mol 15 mL of DI was added to each vial, and the mixtures were sonicated for 5 minutes. All solutions were then mixed overnight in an oil bath at 55°C. To finalize the coating of NiO NPs with the MoS₂ layer, each sample was centrifuged at 11,000 RPM for 20 minutes. Subsequently, each sample was sonicated for 5 minutes in 3 mL of ethanol and transferred to ampoules. The ampoules were dried in a vacuum oven at 80°C for 1 hour. Finally, the ampoules were vacuum-sealed and placed in a horizontal oven with two heat zones (350°C and 520°C) for 15 minutes. 4.2. Characterization Techniques 4.2.1 X-ray diffraction (XRD): XRD patterns of the NiOₓ NPs and NMOS-I-III NCs were collected in a step − scan mode at room temperature using Rigaku SmartLab SE diffractometer with 40 kV X-ray generator (Cu Kα radiation, 10 − 50° 2θ range, step width 0.03°). The XRD data were analyzed with the assistance of MDI Jade 8.8 software. 4.2.2 High-resolution Transmission Electron Microscopy (HR-TEM): HR-TEM analysis of the NiOₓ NPs and NMOS-I-III NCs was performed using a Talos F200X S/TEM microscope (Thermo Fisher Scientific, USA) with an accelerating voltage of 200kV, X-FEG Electron source. An energy-dispersive X-ray spectroscopy (EDS) detector (super-X EDS system) was attached to the TEM instrument, which allowed the chemical composition of the nanocrystals to be determined. The samples were prepared by dropping 5 µL of a highly diluted sample solution in ethanol onto a copper grid covered by formvar carbon. 4.2.3 X‑ray photoelectron spectroscopy (XPS): XPS spectra of the NiOₓ NPs and NMOS-I-III NCs were collected using a Thermo Scientific ESCALAB QXi. The samples were irradiated with monochromatic Al Kα radiation with a spot size of 400µm. The survey scans were collected at a pass energy of 200 eV and an energy step size of 1.0 eV. High-resolution scans were collected at a pass energy of 40 eV and an energy step size of 0.1 eV. A dual-beam neutralization was used to manage charge effects. All data was processed and analyzed using Avantage software version 6.4. 4.2.4 Raman measurements Raman anlysisi of NiOₓ NPs and NMOS-I-III NCs were collected using a LabRAM HR Evolution system (Horiba, France) equipped with a 532 laser to minimize fluorescence interference. Spectra were acquired using an 800 mm spectrograph, offering high sensitivity, high spectral resolution, and low stray light. A 600 gr/mm grating was employed, yielding a spectral resolution of less than 1.0 cm⁻¹ per pixel. Imaging and spectral acquisition were conducted using a BXFM Olympus modular optical microscope with a PlanFL N ×100 objective lens (NA 0.9). Each spectrum was collected with an exposure time of 0.25–0.5 seconds, averaged over 10 accumulations. 4.2.5 UV-Vis Spectrophotometer: The absorbance spectra of the NiOₓ NPs and NMOS-I-III NCs solutions were recorded in the range of 250–800 nm using a V-750 UV-visible spectrophotometer (Jasco, Japan) equipped with 60 mm integrating spheres. 4.2.6 Spectrofluorometer: The photoluminescence (PL) spectra of the NiOₓ NPs and NMOS-I-III NCs were recorded using FP-8350 Spectrofluorometer (Jasco, Japan). Here, lasers with 250 nm wavelength were used for excitation, and the PL was measured in the range 300–800 nm using FP-8350 Spectrofluorometer (Jasco, Japan). 4.2.7 Electron Paramagnetic Resonance (EPR): Spectra of the NiOₓ NPs and NMOS-I-III NCs were recorded on a Bruker ELEXSYS 500 X-band spectrometer equipped with a Bruker ER4119HS resonator operating at a microwave frequency of 9.5 GHz. The EPR device operated at a microwave frequency of 100 kHz. Spectra were recorded using a microwave power of 20 mW with a sweeping range of 200 mT and a modulation amplitude of 0.1 mT. 5 mg of each sample was dispersed in DI. Each sample (200 µl) was inserted into a flat cell Suprasil for aqueous solutions (WG-808-Q, Wilmad) at room temperature. A stock solution was prepared by sonicating 25 mg 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO) spin trap in 5 mL Di. Each sample consisted of a 40 µL dispersed solution with NiO and NMOS-I-III NCs in DI (5 mg in 1mL), with 160 µL BMPO stock solution. 4.2.8 Photocatalysis Dye degradation was performed to study the photocatalytic activity of the NiOₓ NPs and NMOS-I-III NCs. A stock solution was prepared by dispersing 5 mg of methylene blue (MB) dye in 10 mL DI. 10 mg of each NPs sample (the NiO and NMOS-I-III NCs) was dispersed in 29 mL of DI. For each sample, 1 mL of MO stock solution was added to 29 mL of DI water of the NiO and NMOS-I-III NCs. Each sample was placed in front of a solar simulator 10500 model (1 sun, Abet-technologies, USA) at a 10 cm distance. 2.5 ml of the sample was collected every 10 minutes and centrifuged at 11000 rpm for 1 minute before measuring the absorption spectrum. The degradation rate \(\:\left(D\text{\%}\right)\) was calculated using Eq. 1 and Eq. 2 , where, \(\:{C}_{0}\) and \(\:{C}_{t}\) is the dye concentration at \(\:t=0\:min\) (initial concentration) and \(\:t=t\:min\) , respectively. Equation 5 \(\::\:D\%=\left(1-\frac{{C}_{t}}{{C}_{0}}\right)x100\%\) The first-order kinetic equation is given by: Equation 6 : \(\:\varvec{l}\varvec{n}\left(\frac{{\varvec{C}}_{\varvec{t}}}{{\varvec{C}}_{0}}\right)={\varvec{k}}_{1}\varvec{t}\) Here, \(\:{k}_{1}\) (min –1 ) represents the reaction first-order rate constant derived from the slope of the \(\:ln\left(\frac{{C}_{t}}{{C}_{0}}\right)\) versus time (t) plot. Declarations Funding: This research was funded by the Israel Ministry of Energy and the Israel Ministry of Innovation, Science, and Technology. Author Contribution H.S. conceptualized the experiment(s), developed methodology, conducted investigation, curated data, performed analysis, wrote the manuscript, and contributed to writing – review & editing. S.T. assisted with synthesizing and measuring absorbance, photoluminescence, and dye degradation. O.B. performed TEM experiments. I.P. conducted Raman spectroscopy. R.C. conducted EPR experiments. L.Y. supervised, handled project administration, and contributed to writing, review & editing. All authors reviewed the manuscript. Acknowledgement We sincerely thank Pini Shekhter from the Center for Nanoscience and Nanotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel, for his invaluable assistance with the XPS measurements. We also express our sincere gratitude to Iddo Pinkas from the Department of Chemical Research Support at the Weizmann Institute of Science for his invaluable assistance with the Raman measurements. His expertise was instrumental in the analysis presented in this work. We also extend our deep appreciation to all colleagues whose contributions were essential to the success of this research. Their time, expertise, and collaborative efforts were greatly valued. Data Availability The data supporting the conclusions of this paper are available within the manuscript and its supplementary information. References Saeed, M., Muneer, M. & Haq, A. Akram, N. Photocatalysis: an effective tool for photodegradation of dyes—a review. Environ. Sci. Pollut Res. 29 , 293–311 (2022). Joshi, N. C., Gururani, P. & Gairola, S. P. Metal oxide nanoparticles and their nanocomposite-based materials as photocatalysts in the degradation of dyes. Biointerface Res. Appl. Chem. 12 , 6557–6579 (2022). Feng, H. et al. Core-shell nanomaterials: Applications in energy storage and conversion. Adv. Colloid Interface Sci. 267 , 26–46 (2019). Shafiee, A. et al. 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06:46:54","extension":"png","order_by":95,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":23928,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigureXPSC.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/b3a4c8b20adc4f339a2f7b71.png"},{"id":94823391,"identity":"30f04d03-e8b9-4869-bd1e-888ea8544be4","added_by":"auto","created_at":"2025-10-31 06:47:17","extension":"png","order_by":96,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":24694,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigureXPSD.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/c86187291f5919362bc4098f.png"},{"id":94823232,"identity":"cf7bd4f9-b0b1-450f-bb3d-7fd146fa69da","added_by":"auto","created_at":"2025-10-31 06:46:50","extension":"png","order_by":97,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":24808,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigureXPSE.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/e40736c3d0356a2df5959207.png"},{"id":94824241,"identity":"e267ed49-8fc4-4526-9b78-4d1b07701133","added_by":"auto","created_at":"2025-10-31 06:48:41","extension":"png","order_by":98,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":223681,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/600f79e2eff79c6943c89dc0.png"},{"id":94823956,"identity":"8ea372c1-6de1-4b02-835a-826a1c0adac1","added_by":"auto","created_at":"2025-10-31 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06:46:33","extension":"png","order_by":101,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":66263,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/600244036840bd2df97788fa.png"},{"id":94750456,"identity":"c2733f58-d008-438b-889a-3a34047584aa","added_by":"auto","created_at":"2025-10-30 10:12:16","extension":"png","order_by":102,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":171388,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/2aa7b3f96e269efbce0e136c.png"},{"id":94750455,"identity":"487ca1c7-feab-4ff8-a6d5-6d1069975402","added_by":"auto","created_at":"2025-10-30 10:12:16","extension":"png","order_by":103,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":86556,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/7c1ef27d1c6dbc7ec8f90a31.png"},{"id":94823389,"identity":"aff21907-b5e0-4906-81e0-d4d8eeef1e2b","added_by":"auto","created_at":"2025-10-31 06:47:17","extension":"png","order_by":104,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":505222,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/f706104c3383041b46284c1e.png"},{"id":94824158,"identity":"8a85ea3b-04ef-4419-a1ce-8d427fa853f6","added_by":"auto","created_at":"2025-10-31 06:48:34","extension":"xml","order_by":105,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":237172,"visible":true,"origin":"","legend":"","description":"","filename":"a53495df920f473c86e7ff67e2b539fc1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/689588cceb901e96620f7a6b.xml"},{"id":94750466,"identity":"2ca0afde-7492-4332-93a6-4fb0c1e13a42","added_by":"auto","created_at":"2025-10-30 10:12:17","extension":"html","order_by":106,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":258323,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/7a6bfcc968d199645bb65922.html"},{"id":94750357,"identity":"fc45bf78-f78d-4a1e-83bc-662bfce3366b","added_by":"auto","created_at":"2025-10-30 10:12:14","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":196999,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/bf93465bb2ca6bcbcb5f4ecd.png"},{"id":94750360,"identity":"ded010e4-d9c4-4f71-9d30-cca122f0ff8b","added_by":"auto","created_at":"2025-10-30 10:12:14","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":758340,"visible":true,"origin":"","legend":"\u003cp\u003eHR-TEM images and related analyses of NiOₓ NPs and NMOS-I-III NCs are presented as follows: (A) NiOₓ NPs, with an inset showing a high-resolution image of a single NP; (B) Size distribution histogram of NiOₓ NPs; (C) SAED pattern of NiOₓ NPs; (D) annealed NiOₓ NPs, with an inset showing a high-resolution image of a single NP; (E) Size distribution histogram of annealed NiOₓ NPs; (F) SAED pattern of annealed NiOₓ NPs; (G, J, M) HR-TEM images of NMOS-I-III NCs displaying particle morphology; (H, K, N) corresponding EDS mapping for NMOS-I-III NCs; and (I, L, O) images of the lattice fringes for NMOS-I-III NCs, respectively.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/9a2747975416b4ca73abe927.png"},{"id":94823198,"identity":"5ce33c60-c0d6-4651-bec5-965ff0ef246e","added_by":"auto","created_at":"2025-10-31 06:46:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":342106,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectra of (A) Ni 2p and (B) O 1s for NiOₓ, Mo 3d spectrum for (C) NMOS-I NCs, (D) NMOS-II NCs, and (E) NMOS-III NCs\u003cstrong\u003e. \u003c/strong\u003e(F) Raman spectra of NiOₓ NPs (black) and NMPS NCs prepared with different Mo-precursor ratios: NMOS-I (red), NMOS-II (blue), and NMOS-III (green).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/7bcb5e718d6bf986d563be3e.png"},{"id":94750364,"identity":"f45431bd-5971-45ee-9ac4-1fe6261a2126","added_by":"auto","created_at":"2025-10-30 10:12:14","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":227482,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Absorption spectra of NiOₓ NPs and NMOS-I-III NCs with various Mo-precursor ratios; (B–E) spectral deconvolution of NiOₓ and NMOS-I-III NCs.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/62f8daac7b36a6b5ab11eae1.png"},{"id":94823193,"identity":"86d210d1-75b0-40c0-a5ca-343cb1ababed","added_by":"auto","created_at":"2025-10-31 06:46:41","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":312705,"visible":true,"origin":"","legend":"\u003cp\u003eEmission spectra of NiO NPs, NMOS-I, NMOS-II, and NMOS-III NCs measured at excitation wavelengths of 250 nm (A) and 532 nm (B). Deconvoluted PL spectra of (C) NiOₓ and (D-F) NMOS-I-III NCs at an excitation wavelength of 532 nm.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/f470b006944649ab45d19062.png"},{"id":94750361,"identity":"c0a83cb6-9b02-4baf-aa11-430d292f889e","added_by":"auto","created_at":"2025-10-30 10:12:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":209871,"visible":true,"origin":"","legend":"\u003cp\u003eEPR spectra acquired under visible-light illumination of (A) NiOₓ and NMOS-I-III with BMPO as a \"spin-trap\" and (B) NMOS-II NCs under light illumination with and without the addition of DMSO.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/899477f511aec470ddfa222e.png"},{"id":94750375,"identity":"3c35a273-a712-4c53-9e12-976027f337ea","added_by":"auto","created_at":"2025-10-30 10:12:14","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":325228,"visible":true,"origin":"","legend":"\u003cp\u003e3D UV-visible spectra of MB photodegradation after different light irradiation times using NiOₓ and NMOS-I-III NCs in aqueous solutions. Note: spectra are shown with an offset for clarity.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/373d0489e3b244ea2d5fcee6.png"},{"id":104250730,"identity":"d220c868-eb5d-4b11-8090-ad0d976a75f1","added_by":"auto","created_at":"2026-03-09 16:07:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3335427,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/fff7892e-5823-4786-aa57-c4529a70d7f2.pdf"},{"id":94750368,"identity":"8155a61a-c99b-4c41-8b4c-756f5e7f1fdc","added_by":"auto","created_at":"2025-10-30 10:12:14","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":3239567,"visible":true,"origin":"","legend":"","description":"","filename":"NiOMoS2SI10.03.25.docx","url":"https://assets-eu.researchsquare.com/files/rs-7802560/v1/42c9f7681b768db7bb9e17b5.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Tunable NiOₓ-MoO₃-MoS₂ nanocomposites: synthesis, structural insights, and enhanced photocatalytic performance","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn recent years, the demand for advanced nanomaterials with a wide range of applications, such as photodegradation,[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] energy storage, and catalysis,[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] has increased. Nanocomposites (NCs) have garnered significant attention for their ability to combine unique properties of individual components, enhancing performance and enabling multifunctional applications.[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] Transition metal oxides are promising due to their chemical stability, natural abundance, cost-effectiveness, and relatively simple synthesis routes.[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eNickel oxide (NiO) nanoparticles (NPs) are one of the most common metal oxides that have been extensively studied due to their mechanical,[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] electronic,[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] magnetic[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], optical[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and p-type conductivity properties. Therefore, NiO NPs have been used in a variety of applications: gas sensors,[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] fuel cells,[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] catalysts,[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] battery materials,[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and supercapacitors.[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] NiO NPs crystallize in a cubic structure, with their size and defect concentration, such as nickel vacancies and oxygen interstitials, influencing their magnetic[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and electronic[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] properties. The NiO NPs can be synthesized using a variety of methods: hydrothermal synthesis,[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] electrodeposition,[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] sol-gel method[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], and thermal decomposition.[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] Despite these benefits, NiO NPs tend to aggregate due to strong interparticle binding energy,[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] exhibit low electrical conductivity due to a wide bandgap (3.5\u0026ndash;3.9 eV),[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] and face challenges in defect control during synthesis, leading to inconsistent performance.[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eTo overcome these limitations, NiO is commonly incorporated with other metal oxides like molybdenum trioxide (MoO₃). MoO₃ has a layered structure of double MoO₆ octahedra stacked by van der Waals forces,[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] high surface area,[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] remarkable electronic properties,[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] and oxidizing characteristics. As an n-type semiconductor, MoO₃ exhibits an indirect band gap of 3.16 eV (with a direct band gap of 2.27 eV),[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] MoO₃ supports stable photogenerated charge carriers at room temperature.[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] Moreover, MoO₃ is thermally stable,[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] low-toxicity,[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] and highly catalytic, making it suitable for the hydrogen evolution reaction (HER),[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] gas sensor applications,[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] energy storage devices,[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] and other functional applications.[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] MoO₃ can be easily synthesized in various forms, including powder,[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] 2D nanosheets,[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] and nanotubes.[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eIncorporating MoS₂ into NiO-MoO₃ introduces a layered structure of molybdenum atoms between sulfur layers, enhancing electrical conductivity,[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] active edge sites,[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] visible-range light absorption,[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] charge separation, and photocatalytic performance. MoS₂, an n-type semiconductor with an indirect bandgap of 1.2 eV (direct 1.8 eV),[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] exhibits stable photogenerated excitons at room temperature due to high exciton binding energy (several hundred meV).[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] Moreover, MoS₂ is thermally stable,[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] not toxic[\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], and highly catalytically active,[\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e] making it promising for HER,[\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e] gas sensor,[\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e] lithium-ion battery[\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e], and other functional applications.[\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e] MoS₂ can be synthesized as powder, 2D nanosheets, or nanotubes.[\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eNiO-MoO₃-MoS₂ NCs (labeled as NMOS, N\u0026thinsp;=\u0026thinsp;NiOₓ, MO\u0026thinsp;=\u0026thinsp;MoO₃, S\u0026thinsp;=\u0026thinsp;MoS₂) hold significant potential due to the synergistic interplay between their individual components. Despite the lack of direct investigations into the full NMOS system, existing studies on NiO-MoO₃ and MoO₃-MoS₂ composites highlight the potential benefits of their integration.[\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e] Several studies of MoO₃-MoS₂ NCs or nanowires achieved through hydrothermal synthesis exhibit enhanced optoelectronic and catalytic properties.[\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e] Additionally, research on NiO-MoO₃ and nickel molybdate (NiMoO₄) synthesized by spin coating sol\u0026ndash;gel techniques, focusing on its physical and electrochemical properties with polymer additives, highlights the growing interest in Ni-Mo-based hybrids.[\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eThis study introduces a novel approach by synthesizing NiO NPs via a sol-gel method and fabricating NMOS NCs with varying molar ratios of (NH₄)₂MoS₄ as a Mo precursor, an underexplored strategy for optimizing NCs performance. The NMOS NCs were characterized using X-ray diffraction (XRD) for composition and crystalline structure, transmission electron microscopy (TEM) for morphology, composition, and particle size, X-ray photoelectron spectroscopy (XPS) for surface elemental composition and chemical states, and Raman spectroscopy confirmed the vibrational modes and structural features of the MoO₃-MoS₂ domains. Optical properties assessed via UV-Vis spectrophotometry and photoluminescence (PL) measurements. The strength of this work lies in its comprehensive multi-technique characterization and detailed evaluation of photocatalytic performance through dye degradation experiments, with electron paramagnetic resonance (EPR) spectroscopy providing insights into reactive radical species and the underlying catalytic mechanism.\u003c/p\u003e"},{"header":"2. Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Synthesis\u003c/h2\u003e\u003cp\u003eThe first step in the preparation of NMOS NCs is the NiO\u003csub\u003ex\u003c/sub\u003e (X\u0026thinsp;=\u0026thinsp;0\u0026ndash;1) NPs synthesis. The NiO NPs were synthesized using the sol-gel method, in which nickel(II) nitrate hexahydrate (Ni(NO₃)₂6H₂O) was first dissolved in distilled water (DI). Subsequently, a sodium hydroxide (NaOH) solution was added dropwise. This resulted in the formation of a light green nickel hydroxide (Ni(OH)₂) precipitate, which was subsequently centrifuged, washed three times with DI water, and dried to yield a pale green paste. The chemical reaction is shown in \u003cb\u003eReaction 1.\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 1\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:\\varvec{N}\\varvec{i}{\\left({\\varvec{N}\\varvec{O}}_{3}\\right)}_{2}6{\\varvec{H}}_{2}\\mathbf{O}+2\\varvec{N}\\varvec{a}\\varvec{O}\\varvec{H}\\to\\:\\varvec{N}\\varvec{i}{\\left(\\varvec{O}\\varvec{H}\\right)}_{2}6{\\varvec{H}}_{2}\\mathbf{O}\\downarrow\\:+2\\varvec{N}\\varvec{a}{\\varvec{N}\\varvec{O}}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eUpon annealing at 270\u0026deg;C for 2 hours, the Ni(OH)₂ transformed into black non-stoichiometric NiOₓ NPs. The chemical reaction involved in the process is shown in \u003cb\u003eReaction 2\u003c/b\u003e[\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]:\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 2\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:\\varvec{N}\\varvec{i}{\\left(\\varvec{O}\\varvec{H}\\right)}_{2}\\to\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{x}}+{\\varvec{H}}_{2}\\varvec{O}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eThe second step in the synthesis of NiOₓ\u0026ndash;MoO₃\u0026ndash;MoS₂ NCs involves the growth of a MoO₃\u0026ndash;MoS₂ layer encasing the NiOₓ NPs. Ammonium tetrathiomolybdate ((NH₄)₂MoS₄) was employed as the molybdenum precursor (Mo-precursor), enabling the initial ionic interaction with the NiOₓ surface and leading to the formation of the NiOₓ\u0026ndash;MoS₄\u0026sup2;⁻ structure. Different molybdite concentrations (referred to as I, II, and III) were added by varying the molar ratios of (NH₄)₂MoS₄. The NCs formation process consisted of sonicating the NiOₓ NPs in an aqueous solution of (NH₄)₂MoS₄ to ensure homogeneous dispersion and promote surface interaction between the Mo\u0026ndash;S species and the NiOₓ NPs. This was followed by overnight stirring, allowing sufficient time for uniform deposition of MoS₄\u0026sup2;⁻ onto the NiOₓ surface, as shown in \u003cb\u003eReaction 3\u003c/b\u003e. The driving force for the formation of NiOₓ\u0026ndash;MoS₄\u0026sup2;⁻ intermediate is likely the combination of electrostatic interactions and the mildly acidic environment generated when (NH₄)₂MoS₄ is dissolved in DI. The NiOₓ NPs are p-type semiconductors, due to intrinsic defects such as nickel vacancies or extra oxygen,[\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e] which results in a positive surface character at acidic pH.[\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e] These electrostatic interactions ensure close contact between the NiOₓ NPs and the surrounding MoS₄\u0026sup2;⁻ species, which is crucial for their subsequent crystallization during the annealing step.\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 3\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{x}}+{\\left({\\varvec{N}\\varvec{H}}_{4}\\right)}_{2}{\\varvec{M}\\varvec{o}\\varvec{S}}_{4}\\to\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{x}}-{{\\varvec{M}\\varvec{o}\\varvec{S}}_{4}}^{-2}+2{{\\varvec{N}\\varvec{H}}_{4}}^{+}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eThe last phase of the NCs was the 15-minute annealing, which promoted the crystallization of the MoO₃-MoS₂ phase and the removal of the ammonia (NH₃) and sulfur-based residues. First, the NiOₓ\u0026ndash;MoS₄⁻\u0026sup2; solution was centrifuged to remove the excess salt residues, and the resulting precipitates were vacuum-dried. Subsequently, the dried powders were placed in quartz ampoules and continuously vacuumed to promote the removal of NH₃ and sulfur-based residues. The ampoule was placed in a horizontal two-zone tube furnace with the powder-containing region positioned in the higher-temperature zone at 520\u0026deg;C (hot zone), while the opposing end remained at 350\u0026deg;C (cold zone). This dual-temperature configuration was deliberately chosen based on the known decomposition temperature of (NH₄)₂MoS₄.[\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e] In the higher-temperature zone (520\u0026deg;C), intermediate species such as amorphous MoS₃ begin to form, while NH₃ and hydrogen sulfide (H₂S) are simultaneously released and evacuated under vacuum (\u003cb\u003eReaction 4\u003c/b\u003e).[\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e] The cooler zone (350\u0026deg;C) facilitates the directional migration and condensation of these volatile byproducts, ensuring their safe and gradual removal while preventing uncontrolled sulfur release or recombination. Afterwards, the remaining intermediate species, such as MoS₃, are converted into crystalline MoS₂, while further crystallization and restructuring of the NMOS NCs occur (\u003cb\u003eReaction 5\u003c/b\u003e). Moreover, the annealing step plays a crucial role in repairing structural defects within the non-stoichiometric NiOₓ. It also enhances the NiOₓ crystallinity and stability by reducing structural defects such as nickel vacancies and excess oxygen.[\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 4\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\left({\\varvec{N}\\varvec{H}}_{4}\\right)}_{2}{\\varvec{M}\\varvec{o}\\varvec{S}}_{4}\\to\\:2{\\varvec{N}\\varvec{H}}_{3}+{\\varvec{H}}_{2}\\varvec{S}+{\\varvec{M}\\varvec{o}\\varvec{S}}_{3}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 5\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{x}}-{{\\varvec{M}\\varvec{o}\\varvec{S}}_{4}}^{-2}+2{{\\varvec{N}\\varvec{H}}_{4}}^{+1}\\to\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{x}}{-\\varvec{M}\\varvec{o}\\varvec{S}}_{2}+2{\\varvec{N}\\varvec{H}}_{3}+{\\varvec{H}}_{2}\\varvec{S}+\\varvec{S}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eThe annealing time of 15 minutes was chosen based on several considerations. First, the decomposition of (NH₄)₂MoS₄ into intermediate MoS₃, followed by its conversion into MoS₂ and MoO₃, is known to occur rapidly at 520\u0026deg;C.[\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e] Literature studies indicate that these transformations initiate within minutes, making 15 minutes an appropriate and controlled thermal window.[\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e] Second, under vacuum conditions at high temperatures, prolonged heating can lead to the excessive evaporation of sulfur species (e.g., S₂, H₂S), which may reduce the formation of crystalline MoS₂.[\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e] Limiting the annealing time helps to minimize sulfur loss while still allowing essential phase transitions. Additionally, extended exposure to sulfur residues increases the likelihood of side reactions between sulfur and NiOₓ, potentially resulting in the formation of undesired nickel sulfide (NiS) phases.[\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e] A short annealing time helps suppress such secondary reactions, ensuring better phase purity and structural integrity of the final NiOₓ\u0026ndash;MoO₃\u0026ndash;MoS₂ NCs.\u003c/p\u003e\u003cp\u003eThe presence of NiOₓ within the NMOS NCs during the annealing process at 520\u0026deg;C may cause additional side reactions to occur during the thermal decomposition of MoS₃ to MoS₂. Although NiOₓ does not serve as a direct oxidant, it can release lattice oxygen under high temperature, thereby acting as a catalytic or surface-active species that modifies the local redox environment and facilitates reaction pathways.[\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e] During the decomposition of MoS₃ under vacuum, sulfur residues are released as a byproduct (\u003cb\u003eReaction 6\u003c/b\u003e). Those sulfur residues can react with the NiOₓ surface, leading to the partial formation of nickel sulfide (NiS) as a secondary phase and oxygen (O₂) released (\u003cb\u003eReaction 7\u003c/b\u003e(.\u003c/p\u003e\u003cp\u003eThe sol-gel synthesis of NiOₓ produces NaNO₃ as a byproduct (\u003cb\u003eReaction 1)\u003c/b\u003e, which may not be entirely removed during the washing procedure and can persist in the final product. As NaNO₃ is highly water-soluble, completely removing Na⁺ and NO₃⁻ ions can be difficult because of their adsorption on the surface of extremely fine Ni(OH)₂/NiO fine particles. Therefore, even after three rounds of washing with DI, some ions may remain adsorbed on the particle surfaces or become trapped within an evolving gel-like network, where NaNO₃ can be physically entrapped and shielded from removal.[\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e] As a result, NaNO₃ residues may remain in the dried and calcined NiOₓ powder. During the subsequent annealing step in the encapsulation process, this residual NaNO₃ can decompose to form reactive oxygen species such as sodium nitrite (NaNO₂) and O₂ (\u003cb\u003eReaction 8\u003c/b\u003e).[\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eSince all the reactions occur within the same 15-minute annealing window, the O₂ released during this period (\u003cb\u003eReaction 7\u0026ndash;8\u003c/b\u003e) can effectively oxidize the MoS₃ to MoO₃, particularly under vacuum, where molecular oxygen availability is otherwise limited (\u003cb\u003eReaction 9\u003c/b\u003e). The relatively low O₂ content ensures controlled and stepwise oxidation.\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 6\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{M}\\varvec{o}\\varvec{S}}_{3}\\to\\:{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}+\\frac{1}{2}{\\varvec{S}}_{2}\\uparrow\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 7\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{1}{2}{\\varvec{S}}_{2}+{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{x}}\\to\\:\\varvec{N}\\varvec{i}\\varvec{S}+\\frac{1}{2}{\\varvec{O}}_{2}\\uparrow\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 8\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{N}\\varvec{a}{\\varvec{N}\\varvec{O}}_{3}\\to\\:\\varvec{N}\\varvec{a}{\\varvec{N}\\varvec{O}}_{2}+\\frac{1}{2}{\\varvec{O}}_{2}\\uparrow\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eReaction 9\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{2\\varvec{M}\\varvec{o}\\varvec{S}}_{3}+4{\\varvec{O}}_{2}\\to\\:2{\\varvec{M}\\varvec{o}\\varvec{O}}_{3}+2{\\varvec{S}\\varvec{O}}_{2}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cspan type=\"BoldUnderline\" class=\"BoldUnderline\" name=\"Emphasis\"\u003e2.2 Structural Analysis\u003c/span\u003e\u003c/p\u003e\u003cp\u003eThe X-ray diffraction (XRD) patterns in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e display the structural characteristics of NiOₓ and NMOS-I-III NCs. The successful synthesis of NiOₓ NPs in the cubic phase (PDS 00-073-0450) is evident from prominent diffraction peaks at 37.2\u0026deg;, 43.3\u0026deg;, 62.8\u0026deg;, 75.4\u0026deg;, and 79.36\u0026deg;, which correlate to the \u003cem\u003e111\u003c/em\u003e, \u003cem\u003e200\u003c/em\u003e, \u003cem\u003e220\u003c/em\u003e, \u003cem\u003e311\u003c/em\u003e, \u003cem\u003eand 222\u003c/em\u003e planes, respectively.[\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] In addition to the characteristic XRD pattern of NiO, we observe an additional peak at 29.29\u0026deg; that can be assigned to NaNO₃, which constitutes\u0026thinsp;~\u0026thinsp;8% of the total. (PDS 98-000-0333). The presence of NaNO\u003csub\u003e3\u003c/sub\u003e is likely a residual byproduct from the sol-gel process utilized in the synthesis of NiOₓ NPs (\u003cb\u003eReaction 1\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eThe XRD pattern for the NMOS-I and NMOS-II NCs shows that the samples contain\u0026thinsp;~\u0026thinsp;96% NiO, ~\u0026thinsp;3% MoO₃ (PDS 04-008-4547), and traces of molybdenum disulfide. The oxidation pathway leading to the formation of MoO₃ involves a reaction between MoS₃, formed during the decomposition of (NH₄)₂MoS₄, and residual NaNO₃ that remains trapped within the gel-like network formed during the sol\u0026ndash;gel synthesis of NiOₓ. During the annealing process at 520\u0026deg;C, this residual NaNO₃ decomposes to produce reactive oxygen species, such as NaNO₂ and O₂, as shown in \u003cb\u003eReaction 8\u003c/b\u003e.[\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e] Indeed, while the NiOₓ XRD pattern shows approximately\u0026thinsp;~\u0026thinsp;8% of NaNO₃, it's completely absent in the NCs' patterns, which further supports the proposed transformation pathway. Namely, the decrease in NaNO₃ suggests it was consumed by the oxidation reactions, likely through the release of oxygen species that facilitated MoS₃ oxidation to MoO₃.\u003c/p\u003e\u003cp\u003eAs expected, at low initial concentrations of MoS₄\u0026macr;\u0026sup2;, only trace amounts of MoS₂ (PDF 04-026-7897) were detected, partly due to the presence of oxidation-promoting species in the reaction environment. The low molybdate content observed in the XRD patterns can be attributed to several factors. First, the Ni:Mo precursor ratios were relatively low, approximately 4:1 for NMOS-I and 2:1 for NMOS-II, which limited the availability of molybdenum for MoS₂ formation. Second, the oxidation of MoS₃ to MoO₃ during annealing by the byproducts of O₂ and NaNO₃. Additionally, the relatively short annealing time (15 min at 520\u0026deg;C) may be insufficient for the complete conversion of MoS₃ into well-crystallized MoS₂, resulting in the partial formation of amorphous MoS₂ that is undetectable by XRD. Moreover, if only a small percentage of MoS₂ is formed, it will be extremely difficult to detect by XRD due to its minimal thickness, insufficient mass, and weak diffraction intensity.[\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e] Indeed, the characteristic (002) reflection, which indicates the layered structure, is often very weak or completely absent in monolayer and few-layer samples.[\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e] In addition, turbostratic disorder and poor crystallinity further reduce XRD visibility. As a result, XRD cannot reliably confirm the presence of MoS₂; this reflection becomes discernible only as the number of layers increases and crystallinity improves.\u003c/p\u003e\u003cp\u003eThe XRD pattern for the NMOS-III sample reveals a more complex composition: 56.8% NiO, 25.3% MoO₃, 9.6% NiS (PDS 98-000-0308), and 8.3% MoS₂. NiS forms due to a reaction between the NiO and the sulfur in MoS₂ (\u003cb\u003eReactions 6\u0026ndash;7\u003c/b\u003e). These results indicate that increasing MoS\u003csup\u003e4\u0026thinsp;\u0026minus;\u003c/sup\u003e\u0026thinsp;\u003csub\u003e2\u003c/sub\u003e concentration makes the formation of various Mo-based oxides and NiS more pronounced, suggesting complex interactions between NiOₓ and MoS₄\u0026macr;\u0026sup2; at the interface.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe synthesis of non-stoichiometric NiOₓ NPs resulted in oval-shaped NPs with an average diameter of approximately 8\u0026thinsp;\u0026plusmn;\u0026thinsp;3 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA-B). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA displays a representative TEM image of the NPs, while Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB shows the corresponding size distribution. A representative HR-TEM image of a single NiOₓ NP is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA \u003cb\u003e- insert\u003c/b\u003e. The image reveals well-defined lattice fringes with an interplanar spacing of 0.241 nm, corresponding to the (\u003cem\u003e111\u003c/em\u003e) plane of cubic-phase NiO.[\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] The crystallinity of the NPs was further confirmed by the Selected Area Electron Diffraction (SAED) pattern shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC, which displays distinct concentric diffraction rings. These rings can be indexed to the (\u003cem\u003e111\u003c/em\u003e), (\u003cem\u003e200\u003c/em\u003e), (\u003cem\u003e220\u003c/em\u003e), and (\u003cem\u003e311\u003c/em\u003e) planes, confirming the face-centered cubic structure of NiO.[\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] The EDS analysis (\u003cb\u003eTable\u0026nbsp;1\u003c/b\u003eand \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e) revealed that the NiOₓ NPs contain\u0026thinsp;~\u0026thinsp;57 at% Ni and ~\u0026thinsp;43 at% O, corresponding to a Ni:O atomic ratio of 1:0.75. This deviation from the ideal stoichiometry of NiO (1:1) suggests the presence of nickel-rich phases or oxygen vacancies.[\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eResults of the semi-quantitative EDS analysis from TEM images\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNickel\u003c/p\u003e\u003cp\u003e(Ni) (at%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eOxygen\u003c/p\u003e\u003cp\u003e(O) (at%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMolybdenum\u003c/p\u003e\u003cp\u003e(Mo) (at%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSulfur\u003c/p\u003e\u003cp\u003e(S) (at%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eNi: O\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eNiOₓ\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e57.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e42.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1: 0.75\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e\u003cb\u003eNMOS-I\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e56.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e43.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e1:0.76\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e25.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e59.0\u0026thinsp;\u0026plusmn;\u0026thinsp;4.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eNMOS-II\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e22.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e58.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e13.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e5.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eNMOS-III\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e13.8\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e52.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e18.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e\u003cp\u003e15.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eDuring the synthesis of NMOS NCs, the NiOₓ NPs underwent an additional 15-minute annealing step at 520\u0026deg;C to crystallize the MoO₃-MoS₂. This temperature is significantly higher compared to the formation temperature of the NiOₓ NPs (270\u0026deg;C). The elevated thermal treatment not only facilitated the crystallization of the MoO₃-MoS₂ mixture but also induced further growth and enhanced crystallinity within the NiOₓ NPs.[\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e] Consequently, the annealed NiOₓ NPs exhibited an increased average particle size of approximately 13\u0026thinsp;\u0026plusmn;\u0026thinsp;4 nm, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD-E. Clear lattice fringes are observed with an interplanar spacing of 0.241 nm, corresponding to the (\u003cem\u003e111\u003c/em\u003e) plane of cubic-phase NiO, confirming the improved crystallinity following the high-temperature annealing (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD \u0026ndash; insert\u003cb\u003e)\u003c/b\u003e.[\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF, \u003cb\u003ethe\u003c/b\u003e SAED pattern shows distinct concentric diffraction rings of the FCC structure of NiO.[\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] EDS measurements (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) revealed that the non-stoichiometric NiOₓ NPs contain 57 at% Ni and 43 at% O, corresponding to a Ni:O atomic ratio of 1:0.76.\u003c/p\u003e\u003cp\u003eHR-STEM analyses of the NMOS NCs (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) reveal well-defined NiOₓ NPs embedded within molybdate-derived structures. Orthorhombic MoO₃ crystallites are distinguished by lattice fringes with an interplanar spacing of 0.366 nm corresponding to the (001) plane. The NiOₓ NPs display lattice fringes with a spacing of 0.241 nm, assigned to the (111) plane of cubic NiO.[\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] In all cases, EDS elemental mapping (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG-H, J-K, M-N) demonstrates the presence of Ni, O, Mo, and S, and the semi-quantitative analysis (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) confirms their presence in agreement with the designed composite structure.\u003c/p\u003e\u003cp\u003eThe differences among the samples with a varied amount of molybdate precursor are manifested in the change of MoO₃ NP size, composition, and crystallinity, each directly correlated with precursor concentration. In the NMOS-I sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eI), MoO₃ crystallites are relatively small (~\u0026thinsp;5\u0026ndash;7 nm) and display the (011) plane with a spacing of 0.255 nm. In the NMOS-II sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eL), MoO₃ NPs grow to ~\u0026thinsp;21 nm, reflecting the effect of increased (NH₄)₂MoS₄ loading in promoting the development of larger domains. In the NMOS-III sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eO), the MoO₃ NP size further increases to ~\u0026thinsp;33 nm, demonstrating that precursor concentration strongly drives nucleation and coarsening of MoO₃ crystallites. The compositional trends follow the same pattern: the NMOS-I NCs contains 25.7% Ni, 59.0% O, 11.1% Mo, and 4.2% S, the NMOS-II NCs shows increased Mo and S (13.5% Mo, 5.9% S) with reduced Ni (22.0%), while the NMOS-III NCs exhibits the most pronounced enrichment in Mo (18.2%) and S (15.7%) alongside a decrease in Ni (13.8%) and O (52.2%). These differences are consistent with XRD analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), where MoO₃ reflections intensify and sharpen from the NMOS-I to NMOS-III samples, confirming the enhanced crystallinity and higher fraction of the MoO₃ phase at increasing precursor concentrations.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe X‑ray photoelectron spectroscopy (XPS) spectra of NiOₓ and NMOS-I-III NCs are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, providing insight into their electronic structure, chemical composition, and surface states. Depth profiling was performed on the NCs to obtain representative information from both the NiOₓ NPs and their interface with the MoO₃\u0026ndash;MoS₂ domains.\u003c/p\u003e\u003cp\u003eFor NiOₓ NPs (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA-B), the Ni 2p and O 1s peaks are clearly observed. Background subtraction was performed using the Shirley method. The O 1s spectrum, deconvoluted with Shirley background subtraction, shows two main components: a peak at 530.03 eV corresponding to lattice oxygen (M\u0026ndash;O) in NiO, and a higher binding energy peak at 532.09 eV associated with surface hydroxyl groups or adsorbed species (C\u0026ndash;O/Ni\u0026ndash;OH). Notably, nickel species are progressively reduced during XPS depth profiling with Al Kα radiation, revealing lower oxidation states and even the presence of metallic Ni. The Ni 2p spectrum displays a complex envelope arising from multiple oxidation states and satellite features. The main Ni\u0026sup2;⁺ peaks appear at 855.01 eV (2p₃/₂) and 872.40 eV (2p₁/₂), with shake-up satellites at 860.78 eV and 879.91 eV, characteristic of Ni\u0026sup2;⁺ in NiO. Peaks at 857.07 eV (2p₃/₂) and 873.82 eV (2p₁/₂), with additional shake-up at 864.00 eV and 883.50 eV, indicate Ni\u0026sup3;⁺ species with minor Ni⁺ contributions appear at 853.70 eV and 870.78 eV. These multiple valence states confirm the non-stoichiometric nature of NiOₓ, consistent with oxygen vacancies or partial surface reduction/oxidation. TEM\u0026ndash;EDS analysis further supports this interpretation, showing a Ni:O atomic ratio of ~\u0026thinsp;1:0.75. XPS quantification yields Ni and O atomic percentages of 62.5% and 37.5%, respectively (\u003cb\u003eTable S2\u003c/b\u003e), confirming the nickel-rich composition.\u003c/p\u003e\u003cp\u003eIn the NMOS-I NCs (\u003cb\u003eFigure S2A-B and\u003c/b\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC), the Ni 2p and O 1s peaks remain at similar binding energies but with reduced intensities (54.8% Ni and 37.8% O). This reduction reflects surface modification caused by Mo incorporation. In the Mo 3d region, the peaks at 232.7 eV and 235.6 eV correspond to Mo⁶⁺ (Mo 3d₅/₂ and 3d₃/₂), indicative of MoO₃ or related oxides. Additional peaks at 228.6 eV and 230.6 eV are characteristic of Mo⁴⁺ in MoS₂, while the small peak at 225.9 eV corresponds to the S 2s signal. These results confirm the coexistence of MoO₃ and MoS₂ phases, with partial oxidation of MoS₂ likely occurring during annealing or through interactions with NiOₓ. The quantified contributions from Mo⁶⁺, Mo⁴⁺, and S 2s are 4.5%, 2.2%, and 0.7%, respectively.\u003c/p\u003e\u003cp\u003eIncreasing the Mo-precursor to NMOS-II NCs changes the relative intensities of the peaks without shifting their binding energies (\u003cb\u003eFigure S2C-D and\u003c/b\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD). XPS quantification reveals atomic percentages of 59.7% Ni, 31.7% O, 4.3% Mo⁶⁺, 3.3% Mo⁴⁺, and 1.0% S. These results confirm that NiOₓ remains the dominant phase, but the sample is increasingly enriched in the composite with Mo⁴⁺/Mo⁶⁺ species and sulfur, yielding a mixed MoO₃\u0026ndash;MoS₂ composition. The partial oxidation of MoS₂ is consistent with annealing-induced oxidation processes.\u003c/p\u003e\u003cp\u003eFor the NMOS-III NCs (\u003cb\u003eFigure S2E-F and\u003c/b\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE), the Ni, O, Mo, and S signals undergo further redistribution. The atomic percentages are 43.4% Ni, 28.9% O, 7.9% Mo⁶⁺, 13.4% Mo⁴⁺, and 6.4% S. The higher S 2s intensity compared to the NMOS-I and NMOS-II samples suggests increased incorporation of MoS₂, along with the possible formation of NiS as a secondary phase due to chemical interactions between NiOₓ and the MoS₄\u0026sup2;⁻ precursor. The simultaneous presence of NiOₓ, MoO₃, and MoS₂ phases, along with traces of NiS, highlights the complex chemical interplay occurring during precursor decomposition and annealing.\u003c/p\u003e\u003cp\u003eIn summary, XPS analysis shows that increasing Mo-precursor concentration leads to higher Mo and S content, reflecting enlarged MoO₃ and MoS₂ formation. The NiOₓ phase remains dominant but undergoes surface modification, with evidence of partial MoS₂ oxidation and possible NiS formation at higher concentrations. This confirms the tunable composition and complex interfacial chemistry of the nanocomposites.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Spectroscopic Analysis\u003c/h2\u003e\u003cp\u003eRaman spectra of NiOₓ and NMOS-I-III NCs are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF, providing characteristic vibrational signatures, structural features, and phase composition. The corresponding peak assignments are summarized in \u003cb\u003eTable S2\u003c/b\u003e. Across all samples, NiO-related modes are detected, though their intensity and visibility decrease progressively with increasing precursor concentration. At the same time, MoO₃-related peaks are consistently observed in the composites, and their number, position, and intensity evolve with Mo precursor loading. These observations confirm the coexistence of NiOₓ and Mo-derived phases, with variations in spectral features reflecting changes in nanoparticle size, structural integration, and phase composition.\u003c/p\u003e\u003cp\u003eThe differences between the samples are evident in both the identity and relative intensities of the Raman bands. The spectrum of pristine NiOₓ (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF \u003cb\u003e- black\u003c/b\u003e) is dominated by Ni\u0026ndash;O vibrations, with sharp features at ~\u0026thinsp;514 and ~\u0026thinsp;1077 cm⁻\u0026sup1; corresponding to the first-order longitudinal optical (LO) and second-order longitudinal optical (2LO) modes, respectively, and additional peaks at ~\u0026thinsp;398 and ~\u0026thinsp;725 cm⁻\u0026sup1; assigned to first-order transverse optical (TO) and second-order transverse optical (2TO) modes.[\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e, \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e] The sharp peak at 514 cm⁻\u0026sup1; is particularly significant, as it is commonly associated with Ni-related defects,[\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e] reflecting the non-stoichiometric nature of the synthesized NiOₓ.\u003c/p\u003e\u003cp\u003eIn the NMOS-I sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF \u003cb\u003e- red\u003c/b\u003e), the NiO signals decrease in intensity and shift slightly (~\u0026thinsp;538 and ~\u0026thinsp;1093 cm⁻\u0026sup1;), which can be explained by the growth of larger NiO NPs during annealing,[\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e] as confirmed by TEM. At the same time, six new bands emerge that are characteristic of MoO₃: ~356 cm⁻\u0026sup1; (Mo\u0026ndash;O bending), ~\u0026thinsp;765 cm⁻\u0026sup1; (O\u0026ndash;Mo\u0026ndash;O bridge stretching), ~\u0026thinsp;819 and ~\u0026thinsp;851 cm⁻\u0026sup1; (Mo\u0026ndash;O\u0026ndash;Mo symmetric stretching), ~\u0026thinsp;891 cm⁻\u0026sup1; (terminal Mo\u0026thinsp;=\u0026thinsp;O stretching), and ~\u0026thinsp;940 cm⁻\u0026sup1; (polyoxometalate-type Mo\u0026ndash;O stretching).[\u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e, \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e] These features confirm the coexistence of NiO and MoO₃, in agreement with XRD and XPS results.\u003c/p\u003e\u003cp\u003eIn the NMOS-II spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF \u003cb\u003e- blue\u003c/b\u003e), the NiO contribution is further reduced, with only a weak LO mode at ~\u0026thinsp;545 cm⁻\u0026sup1; detected. In contrast, MoO₃-related signals intensify, including peaks at ~\u0026thinsp;364 cm⁻\u0026sup1; (Mo\u0026ndash;O bending), ~\u0026thinsp;756\u0026ndash;763 cm⁻\u0026sup1; (Mo\u0026ndash;O\u0026ndash;Mo stretching), ~\u0026thinsp;816 cm⁻\u0026sup1; (Mo\u0026thinsp;=\u0026thinsp;O stretching), ~\u0026thinsp;858 and ~\u0026thinsp;888 cm⁻\u0026sup1; (Mo\u0026ndash;O stretching and bending), and ~\u0026thinsp;940 cm⁻\u0026sup1; (polyoxometalate-type stretching). These results show that higher precursor loading enhances the vibrational contributions of MoO₃ while masking most NiO modes, consistent with the structural integration suggested by XRD and XPS.\u003c/p\u003e\u003cp\u003eFinally, in the NMOS-III sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF \u003cb\u003e- green\u003c/b\u003e), the NiO-related modes disappear entirely, indicating their suppression by Mo-rich and sulfide phases. Strong MoO₃ vibrations are observed at ~\u0026thinsp;707, 824, 863, 905, 953, and 1007 cm⁻\u0026sup1;, several of which are shifted to lower wavenumbers due to lattice softening caused by the growth of larger MoO₃ NPs (~\u0026thinsp;33 nm, TEM). In addition, MoS₂ fingerprints are clearly detected at ~\u0026thinsp;376 cm⁻\u0026sup1; (E\u0026sup1;₂g), ~\u0026thinsp;403 cm⁻\u0026sup1; (A₁g), and ~\u0026thinsp;460 cm⁻\u0026sup1; (A₁u), consistent with the increased MoS₂ fraction at this loading.[\u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e] A low-frequency band at ~\u0026thinsp;344 cm⁻\u0026sup1; is also present, assigned to NiS vibrations,[\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e] confirming partial sulfide formation via interaction between NiOₓ and the MoS₄\u0026sup2;⁻ precursor during annealing. Together, these observations highlight the progressive transition from NiO-dominated spectra to MoO₃- and MoS₂-rich vibrational signatures, with additional NiS contributions at the highest precursor concentration.\u003c/p\u003e\u003cp\u003eThe absorption spectra of NiOₓ and NMOS-I-III NCs are displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA. All the spectra exhibit absorption in the UV\u0026ndash;visible region, with an absorption edge around 300 nm corresponding to the presence of NiOₓ NPs.[\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e, \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e] As the Mo content increases, the spectra show clear broadening and splitting of the absorption band, indicating changes in the electronic structure. Deconvolution of the absorbance spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB-E) enables a more detailed interpretation of these features and allows us to trace the individual spectral contributions of MoO₃ and MoS₂.\u003c/p\u003e\u003cp\u003eThe NiOₓ NPs deconvolution (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB) reveals three distinct peaks at 248, 298, and 300 nm. The peaks in 248 and 298 nm are characteristic of NiOₓ NPs with an average size of ~\u0026thinsp;8 nm.[\u003cspan additionalcitationids=\"CR84\" citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e85\u003c/span\u003e] The third broad peak at 300 nm is typical of NaNO₃ and corresponds to the weak n\u0026rarr;π* electronic transition within the nitrate ion.[\u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e86\u003c/span\u003e] The presence of NaNO₃, a byproduct of the sol\u0026ndash;gel synthesis of NiOₓ, is further supported by XRD analysis.\u003c/p\u003e\u003cp\u003eThe absorbance spectrum of NMOS-I NCs displays more pronounced and sharper peaks at 262 nm and 303 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA). Moreover, the first one appears to be more intense with reduced FWHM. The 262 nm peak, associated with NiOₓ, exhibits a red shift compared to pristine NiOₓ, likely due to increased particle size (~\u0026thinsp;13\u0026thinsp;\u0026plusmn;\u0026thinsp;4 nm, confirmed by TEM) and reduced quantum confinement effects (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB,E). In addition, the shift and the narrowing of the NiO\u003csub\u003ex\u003c/sub\u003e pick can also be ascribed to the annealing process, as well as the formation of the additional Mo-related phases. Namely, the electronic interactions between NiOₓ and MoO₃\u0026ndash;MoS₂ modify the transition energies. Indeed, the absorbance peak at 303 is most likely attributed to the presence of MoO₃,[\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e87\u003c/span\u003e] which forms during the annealing process with the Mo-precursor (\u003cb\u003eReaction 9\u003c/b\u003e). That ascription is further supported by the comparatively higher dielectric function of MoO₃, which enhances its optical response in this region, resulting in a more intense and distinct absorbance peak.[\u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e88\u003c/span\u003e, \u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e89\u003c/span\u003e] Spectrum deconvolution supporting this interpretation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC), as it resolves additional broad spectral contribution at 310 nm, which is assigned to the defects within the NCs as well as MoO₃.[\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e90\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eAs the concentration of the Mo-precursor increases to NMOS-II NCs, the characteristic NiOₓ-related absorption features diminish markedly, with the NiOₓ peak nearly disappearing from the spectrum. Instead, the absorption is dominated by an edge around 300 nm, corresponding to MoO₃. This shift occurs as the NiOₓ is embedded within a MoO₃\u0026ndash;MoS₂ matrix, which suppresses its optical response. The latter observation is supported by TEM, XRD, and Raman analysis, showing increased MoO₃ and reduced NiOₓ signals. Similar to the NMOS-I NCs, spectral deconvolution of the NMOS-II absorption profile (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD) resolves three peaks at 262, 303, and 315 nm, with the latter two attributed to MoO₃. As observed in TEM, the red shift of the third peak from 310 nm to 315 nm suggests further MoO₃ growth and dielectric enhancement, consistent with larger MoO₃ domains.\u003c/p\u003e\u003cp\u003eFor the NMOS-III sample, the absorption spectrum exhibits extended absorption into the visible region (400\u0026ndash;800 nm), which is a result of the higher MoS₂'s concentration.[\u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e91\u003c/span\u003e] The absorption's deconvolution presents a complex mixture of multiple peaks at 262, 272, 305, and 728 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE). The band at 262 nm is associated with NiOₓ, and the decrease in its full width at half maximum (FWHM) indicates changes in its local electronic environment within the Mo-rich matrix. The peak at 272 nm corresponds to NiS,[\u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e92\u003c/span\u003e] formed through interaction of NiOₓ with the Mo-precursor during annealing, while the 305 nm band is attributed to MoO₃, and is consistent with its stronger crystallinity and dielectric response.[\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e87\u003c/span\u003e, \u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e90\u003c/span\u003e, \u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e93\u003c/span\u003e] The broad peak at 728 nm arises from overlapping contributions of MoS₂ and Mo-based sub-oxides. These results confirm the multiphase nature of the NMOS-III nanocomposite, consistent with the phase distribution observed in Raman, XRD, and XPS analyses.\u003c/p\u003e\u003cp\u003eTo summarize, NiOₓ and NMOS-I-II NCs samples exhibit a clear absorption edge in the UV region, dominated by NiOₓ and MoO₃ contributions, with negligible absorption above 400 nm. By contrast, NMOS-III exhibits extended visible-light absorption due to MoS₂ and secondary Mo phases, reflecting its multiphase character.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe band gap values of NiO and NMOS-I-III NCs are shown in \u003cb\u003eFigure S3\u003c/b\u003e. Pure NiOₓ NPs exhibit a band gap of 3.53 eV, consistent with reported values.[\u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e94\u003c/span\u003e] Upon introducing the Mo-precursor, the band gap increases to 3.66 eV in the NMOS-I sample. This shift can be attributed to the growth and improved crystallinity of NiOₓ during annealing, together with the formation of MoO₃ domains. As the NiOₓ is most likely embedded within the MoO₃\u0026ndash;MoS₂ matrix, this results in a modified electronic structure and a slight blue shift of the absorption edge. Interestingly, at a 2x Mo-precursor concentration, the band gap of NMOS-II NCs red shifts back to 3.53 eV. This red shift is attributed to the growth of separated MoO₃ domains, which increase the NiO-MoO₃ phase segregation and separation. This interpretation is further supported by XRD, which reveals intensified MoO₃ reflections, Raman spectra show suppression of NiOₓ vibrational modes by Mo-rich phases, and XPS data confirm increased Mo⁶⁺/Mo⁴⁺ contributions. In contrast, for NMOS-III, the band gap shifts to 2.93 eV. The profound shift can be ascribed to the MoS₂ and NiS formation. The presence of MoS\u003csub\u003e2\u003c/sub\u003e introduces broad band-edge transitions that extend optical absorption into the visible range.\u003c/p\u003e\u003cp\u003eThe emission spectra of NiOₓ and NMOS-I-III NCs at an excitation wavelength (λ\u003csub\u003eex\u003c/sub\u003e) of 250 nm and 532 nm are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA-B, respectively. The 250 nm excitation is for the NiOₓ component, while the 532 nm excitation is selective for the Mo-component.\u003c/p\u003e\u003cp\u003eUnder excitation at 250 nm, the PL spectra of all samples display the same emission profile with varying intensities (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA). Deconvolution reveals three main peaks at 380, 497, and 601 nm, together with a broad band at 463 nm (\u003cb\u003eFigure S4\u003c/b\u003e). Since the spectral shape remains essentially unchanged across all samples, only the NiOₓ deconvolution is shown in \u003cb\u003eFigure S4\u003c/b\u003e, while the fitting parameters for the composites are summarized in \u003cb\u003eTable S3\u003c/b\u003e. The emission at 380 nm represents near-band-edge (NBE) transitions typical in wide-bandgap semiconductors like NiOₓ. This strong peak is attributed to excitonic recombination between the conduction and valence bands within the band edge.[\u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e95\u003c/span\u003e] The board 463 nm peak and 497 nm peak are associated with structural defects such as oxygen vacancies and interstitials in NiOₓ.[\u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e96\u003c/span\u003e] Whereas the 601 nm band is attributed to transitions from the conduction band to the \u003cem\u003ed\u003c/em\u003e-band within NiOₓ's band structure, aligning with its estimated Fermi level energy.[\u003cspan citationid=\"CR97\" class=\"CitationRef\"\u003e97\u003c/span\u003e] For NMOS-I, the emission intensity is nearly doubled compared to pristine NiOₓ, probably due to energy transfer from MoO₃ defect states, as supported by XRD, TEM, XPS, and Raman analyses. In contrast, the emission of NMOS-II NCs is only slightly enhanced compared to the NiOₓ. This enhancement is attributed to MoS₂ contributions, which extend absorption but also introduce non-radiative pathways that partially suppress emission.[\u003cspan citationid=\"CR98\" class=\"CitationRef\"\u003e98\u003c/span\u003e] NMOS-III exhibits significantly reduced PL compared to the NiOₓ, which can be attributed to the presence of a multiphase composition (NiO, NiS, MoO₃, and MoS₂), as confirmed by the other results. This complex phase mixture introduces non-radiative recombination centers and contending energy transfer pathways that quench emission. Namely, the lower PL intensity likely arises from defect states and electronic transitions specific to the NiS and MoS₂ phases, which differ from pure NiOₓ transitions and contribute weaker overall emissions.\u003c/p\u003e\u003cp\u003eWhen excited at 532 nm, the emission is much lower in intensity due to the low Mo-content (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB-F and \u003cb\u003eTable S4\u003c/b\u003e). The pristine NiOₓ exhibits weak emission with a broad background and a shoulder-like peak at 633 and 661 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB-F and \u003cb\u003eTable S4\u003c/b\u003e). The background is attributed to deep-level defects, particularly oxygen vacancies, while the shoulder features originate from defect-related states associated with the non-stoichiometric NiOₓ lattice.[\u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e96\u003c/span\u003e] In NMOS-I NCs, the emission intensity increased, and the broad background is blue-shifted. The 633 nm peak becomes more distinct, and the 661 nm shoulder-like feature broadens and strengthens. These enhancements are attributed to the presence of Mo-based additives.\u003c/p\u003e\u003cp\u003eIn NMOS-II NCs, the broad background is red-shifted with additional peaks at 629, 670, and 723 nm. The 629 nm feature corresponds to the MoS₂ B exciton with a blue shift due to defect-induced lattice distortions. The 670 nm peak is attributed to the MoS₂ A exciton, arising from direct electron\u0026ndash;hole recombination in MoS₂,[\u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e99\u003c/span\u003e, \u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e100\u003c/span\u003e] and its red shift results indicate a subtle increase in MoS₂ layer thickness. The 723 nm band is likely related to defect-bound excitons, which become more pronounced in few-layer and defect-rich Mo-S phases. In NMOS-III NCs, the overall emission is reduced compared to NMOS-I NCs and NMOS-II NCs, reflecting the complex multiphase composition (NiO, NiS, MoO₃, MoS₂) as confirmed by XRD, TEM, XPS, and Raman analyses. Deconvolution reveals a blue-shifted background with additional peaks at 633 and 670 nm, corresponding to MoS₂ B and A excitons, respectively.[\u003cspan citationid=\"CR99\" class=\"CitationRef\"\u003e99\u003c/span\u003e, \u003cspan citationid=\"CR100\" class=\"CitationRef\"\u003e100\u003c/span\u003e] The slight shifts of these excitonic peaks also suggest enhanced defect\u0026ndash;exciton interactions, where defects act as trapping or recombination sites that perturb excitonic transitions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Photocatalysis Analysis\u003c/h2\u003e\u003cp\u003eOur findings demonstrate that NMOS NCs exhibit exceptional potential as a photocatalytic system. The unique architecture integrates p-type NiOₓ NPs, known for their high theoretical capacitance, with n-type MoO₃-MoS₂ phases. This combination forms efficient p\u0026ndash;n junctions at their interfaces, facilitating enhanced charge separation and transfer. Additionally, the combined effect of these phases should improve electronic conductivity and chemical stability, creating an optimal platform for visible-light-driven photocatalysis. These properties position the nanocomposites as a highly promising material for photocatalytic applications.\u003c/p\u003e\u003cp\u003eTo elucidate whether Mo-based structures enhance the radical-mediated photocatalytic activity of the NCs, we employed electron paramagnetic resonance (EPR) spectroscopy. This technique enables the detection and identification of radicals generated in the presence of NCs through the use of spin-trapping agents such as dimethyl sulfoxide (DMSO) and or 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO), a nitrone-based spin trap effective for both hydroxyl (\u0026middot;OH⁻) and superoxide (\u0026middot;O₂⁻) radicals. To evaluate the formation of the reactive radicals in NiOₓ and NMOS-I-III NCs, EPR measurements were conducted in the dark and under visible-light illumination (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA and \u003cb\u003eFigure S4\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eFor both NiOₓ and NMOS-III NCs, no EPR signals were observed under dark conditions or visible light irradiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB), suggesting that no stable radicals were generated. This behavior can be explained by their optical properties: NiOₓ NPs have a wide band gap of approximately 3.53 eV, allowing them to absorb light primarily at the ultraviolet rather than visible. Similarly, NMOS-III NPs NCs contain a high fraction of MoO₃, and also predominantly absorb ultraviolet light. As a result, both NiOₓ and NMOS-III exhibit limited photoactivity under visible light, consistent with their relatively poor photocatalytic performance in dye degradation experiments, as will be shown below.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor NMOS-I-II NCs, no signals were observed under dark conditions. However, after exposure to visible light, the EPR spectrum exhibits a distinct pattern centered around g\u0026thinsp;=\u0026thinsp;2, with four lines indicative of interactions with hydroxyl radicals (\u0026middot;OH⁻).[\u003cspan citationid=\"CR101\" class=\"CitationRef\"\u003e101\u003c/span\u003e] Notably, the radical signal intensity of NMOS-II exhibits the strongest response under illumination (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA). Notably, using BMPO as a spin trapping agent in EPR spectroscopy effectively detects reactive oxygen species like \u0026middot;OH⁻ and \u0026middot;OOH (\u0026middot;O₂⁻) despite their short half-lives.[\u003cspan citationid=\"CR102\" class=\"CitationRef\"\u003e102\u003c/span\u003e] DMSO traps mainly the \u0026middot;OH⁻ radicals, thus can be used to distinguish between the signals induced by oxygen species.[\u003cspan citationid=\"CR103\" class=\"CitationRef\"\u003e103\u003c/span\u003e] Hence, to verify the formation of \u0026middot;OH⁻ radicals, DMSO was added to the samples during the EPR measurements. The presence of DMSO resulted in a quenched EPR signal for NMOS-II compared to samples without DMSO, see Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB. The latter result indicates that the main active radical species formed under illumination of the NMOS-I and NMOS-II is the \u0026middot;OH⁻. This specific species is the most favorable for advancing oxidation processes, especially in applications such as pollutant and wastewater treatment, soil remediation, and sterilization.[\u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e104\u003c/span\u003e]\u003c/p\u003e\u003cp\u003eTo evaluate the NCs' photocatalytic efficacy, we examined the ability of NiOₓ and NMOS-I-III NCs to degrade methylene blue (MB) dye under visible-light irradiation. MB is an aromatic heterocyclic cationic dye [\u003cspan citationid=\"CR105\" class=\"CitationRef\"\u003e105\u003c/span\u003e], and is considered to be one of the most popular clothing colorants in the textile industry,[\u003cspan citationid=\"CR106\" class=\"CitationRef\"\u003e106\u003c/span\u003e] known for its environmental persistence and toxicity. Effective degradation of MB demonstrates the NCs' ability to break down complex organic pollutants, highlighting their potential for environmental remediation applications, such as wastewater treatment, by leveraging visible-light-driven photocatalysis to address industrial dye pollution.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the change in the absorbance of the MB dye at different time intervals for all the examined catalysts (NiOₓ and NCs) in aqueous solutions. The reduction of the MB characteristic absorption maxima \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left({\\lambda\\:}_{max\\:}\\sim665\\:nm\\right)\\)\u003c/span\u003e\u003c/span\u003e was used to track the progression of dye degradation. In addition, we assessed the photocatalytic efficiency of all NPs and NCs by comparing the degradation rate \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left(D\\%\\right)\\)\u003c/span\u003e\u003c/span\u003e, and the kinetics of the photocatalytic reactions, as detailed in the methods section (\u003cb\u003eFigure S5A\u003c/b\u003e). Following 90 minutes of illumination, the degradation rates of MB dye are as follows: 35% with NiO NPs, 82% with NMOS-I, 73% with NMOS-II, and 42% with NMOS-III, \u003cb\u003eFigure S5A\u003c/b\u003e. NMOS-I and NMOS-II NCs demonstrated the highest photocatalytic efficiency compared to NiOₓ and NMOS-III NCs. The superior performance of NMOS-I can be attributed to the optimal balance between NiOₓ and Mo-related phases (1:0.02, as confirmed by XRD). This combination facilitates efficient charge separation and suppresses electron\u0026ndash;hole recombination. In contrast, excessive Mo- and S-content in the NMOS-III NCs introduces additional recombination centers (e.g., NiS).\u003c/p\u003e\u003cp\u003eTwo second-order kinetic models of the photocatalytic process provided the best fit for the experimental results. The rate constants for the rapid initial phase (0\u0026ndash;5 min) and the slower phase (5\u0026ndash;90 min) are detailed in \u003cb\u003eTable S5\u003c/b\u003e and \u003cb\u003eFigure S5B\u003c/b\u003e. The faster dye degradation within the first 5 minutes is promoted by the fast adsorption of dye molecules onto the active sites of the NCs. For NMOS-I and NMOS-II NCs, this process is much more efficient and fast, with NMOS-I NCs exhibiting the fastest kinetic rate of 0.575 min⁻\u0026sup1;. The process proceeds more rapidly because \u0026middot;OH⁻ radicals are generated alongside adsorption, which promotes dye molecule degradation and thereby regenerates the active sites on the surface of the NCs. This observation is supported by the EPR analysis, where only the NMOS-I and NMOS-II NCs were shown to exhibit radical formation. In the following degradation phase, for the pristine NiO and NMOS-III, this process is extremely slow, with a kinetics rate of 0.003 and 004 min⁻\u0026sup1;, respectively. This slow degradation occurs mainly due to slow equilibrium adsorption. Conversely, for the NMOS-I and NMOS-II, this process is faster, 0.015 and 0.018 min⁻\u0026sup1;, respectively. Here again, due to the higher Mo-content, there is a synergistic effect between the adsorption process and radical-promoted photocatalysis.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe photodegradation processes involving NMOS-I-II NCs and their interaction with dyes are detailed in \u003cb\u003eEquations 1\u0026ndash;4\u003c/b\u003e. Under illumination with visible light, photons with energy greater than or equal to the band gap of the semiconductor components (NiOₓ, MoO₃, or MoS₂) excite electrons from the valence band (VB) to the conduction band (CB), generating electron-hole pairs. The photogenerated electrons and holes react with adsorbed species (oxygen, water, or hydroxide ions) to produce reactive oxygen species, such as \u0026middot;O₂⁻ and \u0026middot;OH⁻, which are responsible for dye degradation. The \u0026middot;OH⁻reacts with the adsorbed MB, breaking their chromophores and leading to mineralization.[\u003cspan citationid=\"CR107\" class=\"CitationRef\"\u003e107\u003c/span\u003e]\u003c/p\u003e\u003cp\u003e\u003cb\u003eEquation 1\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{X}}-\\varvec{x}1-2{\\varvec{M}\\varvec{o}\\varvec{O}}_{3}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}+\\varvec{h}\\varvec{v}\\to\\:\\varvec{N}{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{X}}-\\varvec{x}1-2{\\varvec{M}\\varvec{o}\\varvec{O}}_{3}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}\\left({\\varvec{e}}_{\\varvec{C}\\varvec{B}}^{-}+{\\varvec{h}}_{\\varvec{V}\\varvec{B}}^{+}\\right)\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eEquation 2\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{X}}-\\varvec{x}1-2{\\varvec{M}\\varvec{o}\\varvec{O}}_{3}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}\\left({\\varvec{h}}_{\\varvec{V}\\varvec{B}}^{+}\\right)+\\:{\\varvec{H}}_{2}\\varvec{O}\\to\\:\\varvec{N}\\varvec{i}\\varvec{O}@1-2\\varvec{L}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}+{\\bullet\\:\\varvec{O}\\varvec{H}}^{-}+{\\varvec{H}}^{+}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eEquation 3\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{X}}-\\varvec{x}1-2{\\varvec{M}\\varvec{o}\\varvec{O}}_{3}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}\\left({\\varvec{h}}_{\\varvec{V}\\varvec{B}}^{+}\\right)+\\:{\\bullet\\:\\varvec{O}\\varvec{H}}^{-}\\to\\:\\varvec{N}\\varvec{i}\\varvec{O}@1-2\\varvec{L}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}+\\bullet\\:\\varvec{O}\\varvec{H}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eEquation 4\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\varvec{N}\\varvec{i}\\varvec{O}}_{\\varvec{X}}-\\varvec{x}1-2{\\varvec{M}\\varvec{o}\\varvec{O}}_{3}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}\\left({\\varvec{e}}_{\\varvec{C}\\varvec{B}}^{-}\\right)+{\\varvec{O}}_{2}\\to\\:\\varvec{N}\\varvec{i}\\varvec{O}@1-2\\varvec{L}-{\\varvec{M}\\varvec{o}\\varvec{S}}_{2}+{\\bullet\\:{\\varvec{O}}_{2}}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Conclusions","content":"\u003cp\u003eThe NMOS NCs were synthesized via a novel approach of sol-gel synthesis of non-stoichiometric NiOₓ NPs, followed by annealing with different molar ratios of Mo-precursor, enabling tunable multiphase compositions. Comprehensive characterization through XRD, TEM, XPS, and Raman confirmed the formation of multiphase NCs, where NiOₓ retained its non-stoichiometric nature, while MoO₃ and MoS₂ fractions increased with Mo-precursor concentration in NMOS I and II. Interestingly, NMOS-III NCs exhibited a complex multiphase composition, including NiS formation due to interactions between NiOₓ and MoS₄\u0026sup2;⁻.\u003c/p\u003e\u003cp\u003eAbsorbance and PL analyses revealed that increasing Mo content shifted the optical properties of the NCs. NMOS-I and NMOS-II NCs showed dominant absorption in the UV range, while NMOS-III NCs extended absorption into the visible region due to higher MoS₂ and NiS content. Band gap values ranged from 3.66 eV (NMOS-I) to 2.93 eV (NMOS-III), reflecting the influence of MoS₂ and phase segregation on electronic structure.\u003c/p\u003e\u003cp\u003eThe NMOS-I NCs exhibited the highest photocatalytic efficiency for MB degradation under visible-light irradiation, achieving an 82% degradation rate after 90 minutes. This superior performance is attributed to an optimal balance of NiOₓ and MoO₃\u0026ndash;MoS₂ phases, forming efficient p\u0026ndash;n junctions that enhance charge separation and minimize electron\u0026ndash;hole recombination. In contrast, NMOS-III showed reduced efficiency (42%) due to recombination centers introduced by NiS and excess MoS₂. EPR measurements confirmed that NMOS-I and NMOS-II NCs generate \u0026middot;OH⁻ radicals under visible-light irradiation, driving MB degradation. The absence of radicals produced by NiOₓ is attributed to its limited visible-light absorption. On the contrary, the lack of produced radicals in NMOS-III can be mainly attributed to the presence of NiS. In both cases, the lack of radical signals under visible light is consistent with their wider band gaps. These properties restrict their visible-light absorption and confine their photoactivity.\u003c/p\u003e\u003cp\u003eKinetic analysis revealed that MB degradation in NMOS-I and NMOS-II proceeds via dual stages: a rapid initial stage dominated by dye adsorption and degradation by \u0026middot;OH⁻ radicals, followed by a slower stage controlled by slow equilibrium adsorption. NMOS-I showed the fastest overall kinetics due to efficient interaction between adsorption and photocatalysis, while higher Mo loadings (NMOS-III) diminished this effect.\u003c/p\u003e\u003cp\u003eIn conclusion, this study's innovative synthesis and multi-technique characterization demonstrate that NMOS NCs, particularly NMOS-I and NMOS-II, offer a promising platform for visible-light-driven photocatalysis. The novel tunable phase compositions enhance charge separation and optical properties, while detailed kinetic modeling of adsorption-photocatalysis interplay provides actionable insights for designing heterostructured NCs. These findings suggest potential applications in environmental remediation, such as dye degradation, and pave the way for further optimization of heterostructured nanomaterials for advanced photocatalytic systems.\u003c/p\u003e"},{"header":"4. Methods","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e4.1. Experimental\u003c/h2\u003e\u003cp\u003e4.1.1 Sol-gel synthesis of NiOₓ NPs:\u003c/p\u003e\u003cp\u003e3.635 g of nickel(II) nitrate hexahydrate (Ni(NO₃)₂6H₂O, Merck, 97%) dissolved in 5 mL of distilled water (DI). Meanwhile, 2 g of sodium hydroxide (NaOH, Bio-Lab, 97%) was dissolved in 5 mL of DI. Then, 0.9 mL of NaOH solution was added dropwise to the Ni solution. The resulting light green mixture was centrifuged at 5000 RPM for 5 minutes. The precipitation was washed 3 times with DI and dried in a vacuum oven at 80 ˚C for 1h. The obtained green powder was annealed at 270\u0026deg;C for 2 h under a nitrogen atmosphere to yield dark-black powder.\u003c/p\u003e\u003cp\u003e4.1.2 Synthesis of NMOS NCs:\u003c/p\u003e\u003cp\u003eThe dark-black NiOₓ NPs powder was divided into four vials (with one vial serving as a reference). Three different molar ratios of ammonium tetrathiomolybdate ((NH₄)₂MoS₄) were added to each vial to control the relative MoO₃\u0026ndash;MoS₂ content (labeled as I, II, and III). The molar ratios were as follows:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eNMOS-I: 0.276 mol\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eNMOS-II: 0.552 mol\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eNMOS-III: 0.828 mol\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003e15 mL of DI was added to each vial, and the mixtures were sonicated for 5 minutes. All solutions were then mixed overnight in an oil bath at 55\u0026deg;C. To finalize the coating of NiO NPs with the MoS₂ layer, each sample was centrifuged at 11,000 RPM for 20 minutes. Subsequently, each sample was sonicated for 5 minutes in 3 mL of ethanol and transferred to ampoules. The ampoules were dried in a vacuum oven at 80\u0026deg;C for 1 hour. Finally, the ampoules were vacuum-sealed and placed in a horizontal oven with two heat zones (350\u0026deg;C and 520\u0026deg;C) for 15 minutes.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e4.2. Characterization Techniques\u003c/h2\u003e\u003cp\u003e4.2.1 X-ray diffraction (XRD):\u003c/p\u003e\u003cp\u003eXRD patterns of the NiOₓ NPs and NMOS-I-III NCs were collected in a step\u0026thinsp;\u0026minus;\u0026thinsp;scan mode at room temperature using Rigaku SmartLab SE diffractometer with 40 kV X-ray generator (Cu Kα radiation, 10\u0026thinsp;\u0026minus;\u0026thinsp;50\u0026deg; 2θ range, step width 0.03\u0026deg;). The XRD data were analyzed with the assistance of MDI Jade 8.8 software.\u003c/p\u003e\u003cp\u003e4.2.2 High-resolution Transmission Electron Microscopy (HR-TEM):\u003c/p\u003e\u003cp\u003eHR-TEM analysis of the NiOₓ NPs and NMOS-I-III NCs was performed using a Talos F200X S/TEM microscope (Thermo Fisher Scientific, USA) with an accelerating voltage of 200kV, X-FEG Electron source. An energy-dispersive X-ray spectroscopy (EDS) detector (super-X EDS system) was attached to the TEM instrument, which allowed the chemical composition of the nanocrystals to be determined. The samples were prepared by dropping 5 \u0026micro;L of a highly diluted sample solution in ethanol onto a copper grid covered by formvar carbon.\u003c/p\u003e\u003cp\u003e4.2.3 X‑ray photoelectron spectroscopy (XPS):\u003c/p\u003e\u003cp\u003eXPS spectra of the NiOₓ NPs and NMOS-I-III NCs were collected using a Thermo Scientific ESCALAB QXi. The samples were irradiated with monochromatic Al Kα radiation with a spot size of 400\u0026micro;m. The survey scans were collected at a pass energy of 200 eV and an energy step size of 1.0 eV. High-resolution scans were collected at a pass energy of 40 eV and an energy step size of 0.1 eV. A dual-beam neutralization was used to manage charge effects. All data was processed and analyzed using Avantage software version 6.4.\u003c/p\u003e\u003cp\u003e4.2.4 Raman measurements\u003c/p\u003e\u003cp\u003eRaman anlysisi of NiOₓ NPs and NMOS-I-III NCs were collected using a LabRAM HR Evolution system (Horiba, France) equipped with a 532 laser to minimize fluorescence interference. Spectra were acquired using an 800 mm spectrograph, offering high sensitivity, high spectral resolution, and low stray light. A 600 gr/mm grating was employed, yielding a spectral resolution of less than 1.0 cm⁻\u0026sup1; per pixel. Imaging and spectral acquisition were conducted using a BXFM Olympus modular optical microscope with a PlanFL N \u0026times;100 objective lens (NA 0.9). Each spectrum was collected with an exposure time of 0.25\u0026ndash;0.5 seconds, averaged over 10 accumulations.\u003c/p\u003e\u003cp\u003e4.2.5 UV-Vis Spectrophotometer:\u003c/p\u003e\u003cp\u003eThe absorbance spectra of the NiOₓ NPs and NMOS-I-III NCs solutions were recorded in the range of 250\u0026ndash;800 nm using a V-750 UV-visible spectrophotometer (Jasco, Japan) equipped with 60 mm integrating spheres.\u003c/p\u003e\u003cp\u003e4.2.6 Spectrofluorometer:\u003c/p\u003e\u003cp\u003eThe photoluminescence (PL) spectra of the NiOₓ NPs and NMOS-I-III NCs were recorded using FP-8350 Spectrofluorometer (Jasco, Japan). Here, lasers with 250 nm wavelength were used for excitation, and the PL was measured in the range 300\u0026ndash;800 nm using FP-8350 Spectrofluorometer (Jasco, Japan).\u003c/p\u003e\u003cp\u003e4.2.7 Electron Paramagnetic Resonance (EPR):\u003c/p\u003e\u003cp\u003eSpectra of the NiOₓ NPs and NMOS-I-III NCs were recorded on a Bruker ELEXSYS 500 X-band spectrometer equipped with a Bruker ER4119HS resonator operating at a microwave frequency of 9.5 GHz. The EPR device operated at a microwave frequency of 100 kHz. Spectra were recorded using a microwave power of 20 mW with a sweeping range of 200 mT and a modulation amplitude of 0.1 mT. 5 mg of each sample was dispersed in DI. Each sample (200 \u0026micro;l) was inserted into a flat cell Suprasil for aqueous solutions (WG-808-Q, Wilmad) at room temperature. A stock solution was prepared by sonicating 25 mg 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO) spin trap in 5 mL Di. Each sample consisted of a 40 \u0026micro;L dispersed solution with NiO and NMOS-I-III NCs in DI (5 mg in 1mL), with 160 \u0026micro;L BMPO stock solution.\u003c/p\u003e\u003cp\u003e4.2.8 Photocatalysis\u003c/p\u003e\u003cp\u003eDye degradation was performed to study the photocatalytic activity of the NiOₓ NPs and NMOS-I-III NCs. A stock solution was prepared by dispersing 5 mg of methylene blue (MB) dye in 10 mL DI. 10 mg of each NPs sample (the NiO and NMOS-I-III NCs) was dispersed in 29 mL of DI. For each sample, 1 mL of MO stock solution was added to 29 mL of DI water of the NiO and NMOS-I-III NCs. Each sample was placed in front of a solar simulator 10500 model (1 sun, Abet-technologies, USA) at a 10 cm distance. 2.5 ml of the sample was collected every 10 minutes and centrifuged at 11000 rpm for 1 minute before measuring the absorption spectrum. The degradation rate \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\left(D\\text{\\%}\\right)\\)\u003c/span\u003e\u003c/span\u003e was calculated using \u003cb\u003eEq.\u0026nbsp;1\u003c/b\u003e and \u003cb\u003eEq.\u0026nbsp;2\u003c/b\u003e, where, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{0}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{C}_{t}\\)\u003c/span\u003e\u003c/span\u003e is the dye concentration at \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:t=0\\:min\\)\u003c/span\u003e\u003c/span\u003e (initial concentration) and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:t=t\\:min\\)\u003c/span\u003e\u003c/span\u003e, respectively.\u003c/p\u003e\u003cp\u003e\u003cb\u003eEquation 5\u003c/b\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\::\\:D\\%=\\left(1-\\frac{{C}_{t}}{{C}_{0}}\\right)x100\\%\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eThe first-order kinetic equation is given by:\u003c/p\u003e\u003cp\u003e\u003cb\u003eEquation 6\u003c/b\u003e: \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{l}\\varvec{n}\\left(\\frac{{\\varvec{C}}_{\\varvec{t}}}{{\\varvec{C}}_{0}}\\right)={\\varvec{k}}_{1}\\varvec{t}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003cp\u003eHere, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{k}_{1}\\)\u003c/span\u003e\u003c/span\u003e (min\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) represents the reaction first-order rate constant derived from the slope of the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:ln\\left(\\frac{{C}_{t}}{{C}_{0}}\\right)\\)\u003c/span\u003e\u003c/span\u003e versus time (t) plot.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eThis research was funded by the Israel Ministry of Energy and the Israel Ministry of Innovation, Science, and Technology.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eH.S. conceptualized the experiment(s), developed methodology, conducted investigation, curated data, performed analysis, wrote the manuscript, and contributed to writing \u0026ndash; review \u0026amp; editing. S.T. assisted with synthesizing and measuring absorbance, photoluminescence, and dye degradation. O.B. performed TEM experiments. I.P. conducted Raman spectroscopy. R.C. conducted EPR experiments. L.Y. supervised, handled project administration, and contributed to writing, review \u0026amp; editing. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe sincerely thank Pini Shekhter from the Center for Nanoscience and Nanotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel, for his invaluable assistance with the XPS measurements. We also express our sincere gratitude to Iddo Pinkas from the Department of Chemical Research Support at the Weizmann Institute of Science for his invaluable assistance with the Raman measurements. His expertise was instrumental in the analysis presented in this work. We also extend our deep appreciation to all colleagues whose contributions were essential to the success of this research. Their time, expertise, and collaborative efforts were greatly valued.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data supporting the conclusions of this paper are available within the manuscript and its supplementary information.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSaeed, M., Muneer, M. \u0026amp; Haq, A. Akram, N. Photocatalysis: an effective tool for photodegradation of dyes\u0026mdash;a review. \u003cem\u003eEnviron. Sci. Pollut Res.\u003c/em\u003e \u003cb\u003e29\u003c/b\u003e, 293\u0026ndash;311 (2022).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJoshi, N. C., Gururani, P. \u0026amp; Gairola, S. P. Metal oxide nanoparticles and their nanocomposite-based materials as photocatalysts in the degradation of dyes. \u003cem\u003eBiointerface Res. Appl. 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Commun.\u003c/em\u003e \u003cb\u003e177\u003c/b\u003e, 114388 (2025).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"NiO, nanoparticles, MoO₃, MoS₂, nanocomposites, dye degradation","lastPublishedDoi":"10.21203/rs.3.rs-7802560/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7802560/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWe report the synthesis, structural characterization, and photocatalytic activity of NiOₓ-MoO₃-MoS₂ nanocomposites (NCs) with different ratios of MoO₃-MoS₂ (labeled as NMOS, N\u0026thinsp;=\u0026thinsp;NiOₓ, MO\u0026thinsp;=\u0026thinsp;MoO₃, S\u0026thinsp;=\u0026thinsp;MoS₂). NiOₓ nanoparticles (NPs) were synthesized via a sol\u0026ndash;gel method and subsequently annealed with different Mo-precursor ratios to form NMOS NCs. Structural analyses (XRD, TEM, XPS, Raman) confirmed a non-stoichiometric NiOₓ core with mixed Ni valence states and oxygen defects, encapsulated by MoO₃-MoS₂ domains. Optical studies showed band gap tuning from 3.53 eV (NiOₓ) to 2.92 eV (NMOS-III), enhancing visible-light absorption. Photocatalytic activity, evaluated through methylene blue (MB) degradation, revealed NMOS-I's superior efficiency due to balanced phase composition and efficient radical generation, with rapid adsorption and degradation in the first 5 minutes, followed by slower equilibrium adsorption. In contrast, excessive Mo-precursor loading in NMOS-III formed a secondary phase (e.g., NiS), leading to recombination losses and reduced efficiency. The synthesis used a unique sol-gel and annealing method, enabling tunable phase ratios and enhanced photocatalysis, with no prior reports on this ternary system. These findings highlight the role of phase distribution and interfacial chemistry, offering new possibilities for tailoring NMOS NCs for photocatalytic and environmental applications.\u003c/p\u003e","manuscriptTitle":"Tunable NiOₓ-MoO₃-MoS₂ nanocomposites: synthesis, structural insights, and enhanced photocatalytic performance","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-30 10:12:08","doi":"10.21203/rs.3.rs-7802560/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-20T07:03:55+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-17T05:55:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"326868723887452390748414334832099174175","date":"2025-11-06T03:59:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"119614315052473709541319455971733184352","date":"2025-11-05T10:52:13+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-25T10:46:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"190356946058046931275214971216206824094","date":"2025-10-18T11:44:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"228252236591114668415242495442236130414","date":"2025-10-16T12:41:07+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-16T11:36:57+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-10-16T07:27:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-15T04:26:08+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-10-15T04:25:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-10-07T20:46:32+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7d30b467-81ac-4b66-b64f-06f38e01fa90","owner":[],"postedDate":"October 30th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":56887982,"name":"Physical sciences/Chemistry"},{"id":56887983,"name":"Physical sciences/Materials science"},{"id":56887984,"name":"Physical sciences/Nanoscience and technology"}],"tags":[],"updatedAt":"2026-03-09T16:03:40+00:00","versionOfRecord":{"articleIdentity":"rs-7802560","link":"https://doi.org/10.1038/s41598-026-36921-4","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-03-06 15:59:35","publishedOnDateReadable":"March 6th, 2026"},"versionCreatedAt":"2025-10-30 10:12:08","video":"","vorDoi":"10.1038/s41598-026-36921-4","vorDoiUrl":"https://doi.org/10.1038/s41598-026-36921-4","workflowStages":[]},"version":"v1","identity":"rs-7802560","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7802560","identity":"rs-7802560","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}