Stable NiO–ZnFe2O4 p–n heterojunction nanocomposite for dualfunctional photocatalysis and sensor applications

Stable NiO–ZnFe2O4 p–n heterojunction nanocomposite for dualfunctional photocatalysis and sensor applications | 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 Research Article Stable NiO–ZnFe2O4 p–n heterojunction nanocomposite for dualfunctional photocatalysis and sensor applications Dhanyashree Savitha Vishwakumar, Jagadish Krishnegowda, Jahnavi Hunasekatte Katamallappa, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8906372/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract The design of single semiconductor nanocomposite for combined photocatalytic and sensing applications has gained considerable global attention. Herein, a NiO–ZnFe₂O₄ (NZF) nanocomposite was synthesized via a simple combustion method and systematically investigated photocatalytic and electrochemical properties. X-ray confirmed the coexistence of cubic NiO and spinel ZnFe₂O₄ phases, while SEM and EDX revealed a porous nanostructure. The band gap energy 1.6 eV, attributed to p–n heterojunction and interfacial interaction. The BET surface area of 205 m²g⁻¹ further enhanced the catalytic activity. Consequently, the NZF nanocomposite achieved 91% photocatalytic degradation of Brilliant Blue FCF under optimized conditions. Electrochemical sensing studies toward hydrogen peroxide using NZF electrodes demonstrated with a wide linear range (0.1–200 µM) and a low detection limit of 2 µM attributed to synergistic charge transfer and reduced overpotential at the heterojunction interface. Hence the NZF nanocomposite is a promising multifunctional material for environmental remediation and electrochemical sensing. NiO–ZnFe₂O₄ nanocomposite p–n heterojunction Photocatalytic degradation Brilliant Blue dye Hydrogen peroxide sensor Electrochemical sensing Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction The extensive use of organic dyes in textile, food, and pharmaceutical industries has led to their increased release into wastewater (Lin J et al. 2023 and Islam T et al. 2023 ). Insufficient treatment of these dyes poses serious environmental and health concerns due to their toxicity, persistence, and potential carcinogenic effects (Singha K et al. 2021). Brilliant Blue FCF is a synthetic organic dye widely used in textile, food, cosmetic, and pharmaceutical industries (Guo J et al. 2013 ). It is commonly applied as a coloring agent because of its strong color and high chemical stability (Dalmaz A et al. 2025). Due to its large-scale industrial use, this dye is often released into the environment through untreated or partially treated effluents (Nascimento VX et al. 2023 ). As a result, it accumulates in wastewater and natural water bodies (Al-Gethami W et al. 2024 ). The complex aromatic structure of Brilliant Blue FCF makes it resistant to natural degradation (Flury M et al. 1994). Its presence in aquatic systems can reduce light penetration and disturb photosynthetic activity. It may also lower dissolved oxygen levels and exhibit toxic effects on aquatic organisms (Gupta VK et al. 2006 ). Therefore, efficient wastewater treatment methods are required to remove persistent dyes such as Brilliant Blue FCF. Advanced oxidation processes, particularly sunlight-driven photocatalysis, are effective and environmentally friendly wastewater treatment methods that utilize low-cost and abundant solar energy (Vilar VJ et al. 2020 and Kumari H et al. 2023 ). In this process, semiconductor photocatalysts absorb sunlight to generate electron–hole pairs, which react with oxygen and water to produce reactive oxygen species such as hydroxyl and superoxide radicals (Nosaka Y et al. 2017). The generated radicals can efficiently break down stable organic pollutants. As a result, complex dye molecules are converted into simpler and less harmful products (Rauf MA et al. 2009). In many cases, the pollutants are further mineralized into carbon dioxide and water. Therefore, sunlight-driven photocatalysis is regarded as a promising strategy for treating dye-polluted wastewater (Abou Zeid S et al. 2024 and E1 Golli A et al. 2023 ). Semiconductor photocatalysts enable environmental remediation by converting light energy into electron–hole pairs that drive surface redox reactions for pollutant degradation (Zhu D et al. 2019 and Hagfeldt A et al. 1995). The efficiency of photocatalysis depends on properties such as band gap energy, charge separation, and available active sites (Yanagi R et al. 2021 ). Designing semiconductor heterostructures is an effective strategy to improve light absorption and reduce charge recombination (Balapure A et al. 2024 ). A key drawback of pristine semiconductor photocatalysts is the rapid recombination of photogenerated electron–hole pairs, which limits their catalytic efficiency (Tan HL et al. 2019 and Jiang L et al. 2018 ). This issue can be addressed by forming heterojunctions between semiconductors with different band gap energies, creating favorable interfacial band alignment (Smith AM et al. 2010 and Zheng B et al. 2018 ). This structure facilitates efficient charge separation and directed charge transfer. Consequently, electron–hole recombination is suppressed, leading to improved photocatalytic activity (Zhou W et al. 2018). Several studies have reported the synthesis and use of nanocomposite semiconductors for the photocatalytic degradation of dyes. Qaiser Khan et al., has synthesized TiO 2 /rGO nanocomposites by hydrothermal technique and invesitigated the degradation of Brilliant Green under UV light. The results reviealed the 2% TiO 2 /rGO nanocomposite with the addition of PMS (peroxymonosulfate) shows 99.9% of degradation (Khan Q et al. 2023 ). CuO–TiO₂ nanocomposites have shown 90–95% electrochemical photocatalytic degradation of Brilliant Blue FCF dye under UV and visible light due to heterojunction-enhanced charge separation (Li Y 2021 ). Ultrasonically synthesized PEG-assisted Yb₂O₃/ZnFe₂O₄ nanocomposites have been applied for dye and herbicide degradation and electrochemical sensing of catechol (Fatima N et al. 2026 ). A solution-combustion-derived ZnFe₂O₄/ZnO composite achieved nearly 80% degradation of methylene blue and remazol brilliant blue under UV and visible light due to heterojunction-induced visible-light absorption and enhanced charge separation (Zouhier M et al. 2020 ). In addition to developing new semiconductors, evaluating existing materials under combined advanced oxidation processes is essential for gaining mechanistic insight and designing improved multifunctional photocatalytic and electrochemical systems (Hong J et al. 2022 and Ali H et al. 2025 ). NiO and ZnFe₂O₄ are metal oxide semiconductors that show photocatalytic activity under visible light due to their suitable band gap energies. NiO generally exhibits a wide band gap in the range of 3.2–3.8 eV (Mustafa F et al. 2017 ), whereas ZnFe₂O₄ has a narrower band gap of about 1.9–2.3 eV, which allows efficient visible-light absorption (Kumar P et al. 2025 ). The selection of NiO and ZnFe₂O₄ is further supported by their favorable properties, including visible-light responsiveness, low toxicity, and good electrical conductivity. ZnFe₂O₄ exhibits high electronic conductivity (≈ 10⁵ Ω⁻¹ cm⁻¹) and a large dielectric permittivity (~ 1.7 × 10¹¹) in the bulk state. In contrast, NiO is a p-type semiconductor with good electrical conductivity arising from nickel vacancies and hole carriers (Kaya D et al. 2021 ). These complementary electrical characteristics make NiO and ZnFe₂O₄ attractive for catalytic and energy-related applications, especially when combined to form heterostructured systems (Bohra M et al 2021 and Zahra SE et al. 2025 ). Hydrogen peroxide is an important industrial chemical and reactive oxygen species whose concentration must be carefully monitored due to its environmental and biological effects (Duca G et al 2020 and Ciriminna R et al. 2016 ). Electrochemical sensing provides a simple, rapid, and cost-effective method for H₂O₂ detection, and the limitations of enzyme-based sensors have driven the development of stable non-enzymatic sensors based on metal oxide nanomaterials (Thatikayala D et al. 2020 and Hu Y et al. 2021 ). In particular, metal oxide heterostructures exhibit enhanced electrocatalytic activity due to improved charge transfer, reduced overpotential, and increased active surface area (Xia C et al. 2021 ), making H₂O₂ a widely used model analyte for evaluating semiconductor-based sensors. From a synthesis perspective, the combustion method offers a fast and scalable route to produce porous metal oxide composites with abundant active sites suitable for photocatalytic and electrochemical applications (Li FT et al. 2015 ). However, systematic studies on combustion-derived NiO–ZnFe₂O₄ nanocomposites with dual functionality remain limited. In this study, a NiO–ZnFe₂O₄ (NZF) nanocomposite was synthesized using a simple combustion method and examined for its structural, optical, photocatalytic, and electrochemical properties. The roles of p–n heterojunction formation, band gap narrowing and increased surface area were investigated in relation to the photocatalytic degradation of Brilliant Blue FCF dye and the electrochemical detection of hydrogen peroxide. This work establishes a clear structure–property–performance relationship and highlights the potential of NZF nanocomposites as multifunctional materials for environmental remediation and sensing applications. 2. Materials and Methodology 2.1. Materials The materials utilized in this study were Nickel nitrate hexahydrate (Ni (NO 3 ) 2 ·6H 2 O), Zinc nitrate hexahydrate (Zn (NO 3 ) 2 ·6H 2 O), Iron (III) nitrate nanohydrate (Fe (NO 3 ) 3 ·9H 2 O), and Citric acid (C 6 H 8 O 7 .H 2 O). These chemicals are analytical research grade high-quality powders procured from Sigma-Aldrich. 2.2. Synthesis of NiO/ZnFe 2 O 4 (NZF) nanocomposite by Combustion method 0.02 M of Nickel nitrate hexahydrate and 0.01 M of citric acid are first mixed in 10 mL of water to prepare a precursor solution. The solution is stirred continuously for two hours to ensure homogeneity. Subsequently, it is placed in a preheated muffle furnace at temperature 300°C for 10 minutes. The resulting material is subjected to calcination at 500°C for 2 hours. 2Ni(NO)⋅6HO + CHO​ → 2NiO + 6CO​ + 3N​ + 14H​O Following the synthesis of nickel oxide, it is incorporated into a solution mixture containing 0.01 M zinc nitrate hexahydrate, 0.02 M iron nitrate nanohydrate and 0.01 M citric acid in a stoichiometric ratio. The resulting mixture is stirred for three hours to ensure uniformity, followed by sonication for 30 minutes to enhance dispersion. The prepared solution is then transferred to a crucible and placed in a preheated muffle furnace at 300°C for 10 minutes. After initial combustion, the material is calcinated at 600°C for 3 hours. This process results in the formation of the final product, NiO/ZnFe 2 O 4 nanocomposite. Zn(NO 3 ​) 2 ​⋅6H 2 ​O + 2Fe(NO 3 ​) 3 ​⋅9H 2 ​O + C 6 ​H 8 ​O 7 ​ + NiO → NiO/ZnFe 2 ​O 4 ​ + 6CO 2 ​ + 3N 2 ​+ H 2 ​O 2.2.3. Characterization X-ray diffraction (XRD) patterns were recorded using a Rigaku Ultima III diffractometer equipped with Cu Kα radiation (λ = 1.5406 Å). The surface morphology of the synthesized samples was examined using scanning electron microscopy (SEM, JEOL JSM-6390LV), while their microstructural features were further analyzed by transmission electron microscopy (TEM, Hitachi H-9000 NAR). The optical properties were investigated through UV–Vis diffuse reflectance spectroscopy (DRS) using a JASCO V-670 spectrophotometer operating in the range of 350–1500 nm to estimate the band gap energy. Room-temperature photoluminescence (PL) spectra were acquired on a Jobin Yvon Fluorolog-3-11 spectrofluorometer equipped with a xenon excitation source. 2.2.4. Photocatalytic Activity The photocatalytic activity of the NZF nanocomposite toward the degradation of BB FCF dye under natural sunlight was evaluated by preparing aqueous BB FCF solutions with concentrations ranging from 0 to 50 ppm. To establish adsorption–desorption equilibrium, an appropriate amount of the catalyst was added to the dye solution and stirred in the dark for 15–30 min. The suspension was then transferred to a photocatalytic reactor and continuously stirred while exposed to direct sunlight. All experiments were conducted on clear sunny days on the rooftop of Davanagere University, Davanagere, Karnataka, India (≈ 14.441° N, 75.921° E; elevation ~ 580 m), where the average daily solar irradiance is approximately 215 W m⁻². To monitor the progress of dye degradation, aliquots were withdrawn from the reaction mixture at predetermined time intervals, centrifuged to separate the catalyst, and analyzed using a UV–Visible spectrophotometer (Shimadzu UV-1800; λ = 190–1100 nm) by measuring the absorbance at 630 nm. Optimization studies were performed by systematically varying catalyst dosage, solution pH, initial dye concentration, and irradiation time. The reusability of the catalyst was assessed by recovering, washing, and employing it in successive degradation cycles under identical conditions. All photocatalytic experiments were conducted in triplicate to ensure reliability. The results showed excellent reproducibility, with degradation efficiencies varying by only ± 3%. The degradation efficiency (η) was calculated using Eq. (1): η(%) = \(\frac{{C}_{0}-{C}_{t}}{{C}_{0}}\) x 100 = \(\frac{{A}_{0}-{A}_{t}}{{A}_{0}}\) x 100 Eq….. (1) where C 0 and A 0 are the initial dye concentration and absorbance before irradiation, and C t and A t ​ are the corresponding values at irradiation time t. The apparent first-order rate constant (k r ​) was determined using Eq. (2): Ln \(\left(\frac{{C}_{0}}{{C}_{t}}\right)\) = k r t Eq….. (1) where k r ​ is obtained from the slope of the linear plot of ln (C 0 /C t ) versus t (Li Y et al. 2005). 3. Results and discussion 3.1. X-ray Diffraction (XRD) analysis of NZF The crystalline structure and phase purity of the synthesized NZF nanocomposite were investigated using X-ray diffraction (XRD). Figure 1 a shows the XRD pattern of NZF, recorded in the 2θ range of 8° to 90°. The diffraction peaks located at 2θ values of ~ 37.24°, ~ 43.28°, ~ 62.85°, ~ 75.40°, ~ 79.37° can be indexed to the (101), (012), (110), (113) and (202) planes confirmed the rhombohedral structure of NiO according to the standard JCPDS card number 00-044-1159 and space group R-3m/166. Similarly, the diffraction peaks ~ 30°, ~ 35.34°, ~ 53.28°, ~ 56.79° corresponding to the planes of (220), (311), (422) and (511) confirmed the cubic structure of ZnFe 2 O 4 , in good agreement with JCPDS card number 01-077-0011 and space group Fd-3m/227. The XRD pattern exhibits sharp diffraction peaks, indicating the high crystallinity. The XRD pattern of NZF nanocomposite confirmed the presence of NiO and ZnFe 2 O 4 , as indicated by the presence of bothpeaks of NiO and ZnFe 2 O 4 . 3.2. The Energy Dispersive X-ray (EDX) Spectroscopy of NZF Figure 1 b presents the EDX spectrum of the NZF nanocomposite synthesized by the combustion method, along with the corresponding quantitative elemental analysis shown in the inset table. The spectrum exhibits distinct and intense peaks corresponding to Ni, Zn, Fe, and O, confirming the successful formation of the composite material. The absence of any additional impurity peaks indicates the high purity of the synthesized nanocomposite. As summarized in the inset table, the weight percentages of Ni, Zn, Fe, and O are 37.2%, 16.4%, 31.3%, and 15.1%, respectively, while the corresponding atomic percentages are 26.5%, 10.5%, 23.5%, and 39.6%. These values are in good agreement with the expected stoichiometry of the NZF system, confirming the coexistence of both NiO and ZnFe₂O₄ phases. The relatively higher oxygen content is attributed to the oxide nature of the composite. Overall, the EDX analysis verifies the elemental composition and uniform distribution of Ni, Zn, Fe, and O within the NZF nanocomposite, supporting the structural and functional integrity of the material. 3.3. Scanning Electron microscope (SEM) images of NZF Figures 1 (c) and 1(d) show the SEM micrographs of the NZF nanocomposite synthesized via the combustion method at different magnifications. The low-magnification image (Fig. 1 c) reveals the formation of irregularly shaped, loosely agglomerated clusters composed of fine particles, which is a typical characteristic of combustion-derived materials. These agglomerates arise from the rapid release of gases during the combustion process, leading to a highly porous structure. The high-magnification image (Fig. 1 d) clearly shows interconnected nanosized grains with rough surfaces and interparticle voids. The particle size is found to be in the range of approximately 150–230 nm, as indicated in the micrograph. Such a porous and rough morphology provides a high surface area and abundant active sites. This structural feature is highly beneficial for photocatalytic and electrochemical sensing applications, as it facilitates efficient mass transport and enhanced interfacial charge transfer. 3.4. Photocatalytic Brilliant Blue (BB) Dye degradation Figure 2 a shows the photocatalytic degradation of Brilliant Blue FCF dye as a function of irradiation time using NiO, ZnFe₂O₄, and the NZF nanocomposite. The degradation efficiency increases rapidly during the initial stages due to abundant active sites and efficient generation of reactive species. Among the catalysts, the NZF composite exhibits the highest degradation efficiency at all-time intervals. The enhanced performance of the composite is attributed to the synergistic effect and improved charge separation at the NZF heterojunction. In contrast, pure NiO and ZnFe₂O₄ show comparatively lower degradation efficiency due to faster charge recombination. 3.5. Band Gap Energy Figure 2 b shows the Tauc plots (αhν) 2 (eV) 2 versus photon energy (hν) (eV) used to estimate the optical band gap energies of NiO, ZnFe₂O₄ and the NZF nanocomposite. The band gap values were determined by extrapolating the linear portion of the plots to the energy axis. Pure NiO exhibit relatively higher band gap energy 3.4 eV and ZnFe₂O₄ exhibit 2.3 eV, whereas the NZF nanocomposite shows a reduced band gap 1.6 eV. This narrowing of the band gap can be attributed to strong interfacial interaction and p–n heterojunction formation between NiO and ZnFe₂O₄. The reduced band gap enhances visible-light absorption and promotes efficient charge separation, leading to improved photocatalytic performance of the nanocomposite. 3.6. Effect of Catalyst, dye concentration, Temperature and pH on BB dye degradation The effect of initial Brilliant Blue FCF dye concentration on the photocatalytic degradation efficiency of the NZF nanocomposite is shown in Fig. 3 a. High degradation efficiency (> 91%) is observed at lower dye concentrations (5–20 ppm) due to sufficient availability of active catalytic sites and reactive oxygen species. As the dye concentration increases, the degradation efficiency gradually decreases, reaching about 78% at 40 ppm. This reduction is mainly attributed to saturation of active sites on the catalyst surface and the light screening effect caused by higher dye concentration. Increased competition among dye molecules for reactive radicals also contributes to the lowered degradation efficiency at higher concentrations. Nevertheless, the NZF nanocomposite maintains appreciable photocatalytic activity over a wide concentration range, indicating its potential for practical wastewater treatment applications. Figure 3 b illustrates the effect of NZF photocatalyst loading on the degradation efficiency of Brilliant Blue FCF dye. The degradation percentage increases significantly with increasing catalyst dosage from 0.1 to 0.9 g due to the availability of a larger number of active surface sites and enhanced generation of reactive oxygen species. This increase facilitates improved adsorption of dye molecules and more effective photocatalytic reactions. The maximum degradation efficiency (~ 91%) is achieved at an optimal catalyst loading of around 0.9–1.0 g. Beyond this optimum, a slight decrease in degradation efficiency is observed with further increase in catalyst amount. This decline can be attributed to catalyst particle agglomeration, which reduces the effective surface area. Additionally, excess catalyst causes light scattering and shielding effects, limiting light penetration into the reaction medium. As a result, the generation of electron–hole pairs is suppressed at higher catalyst loadings. Overall, the results indicate the existence of an optimal catalyst dosage for efficient dye degradation. These findings highlight the importance of catalyst loading optimization for achieving maximum photocatalytic performance. Figure 3 c shows the effect of pH on the photocatalytic degradation of Brilliant Blue FCF dye using the NZF nanocomposite. The degradation efficiency increases from acidic to near-neutral conditions and reaches a maximum around pH 5–6. This enhancement is attributed to favorable surface charge interactions and efficient generation of reactive oxygen species. At alkaline pH values, the degradation efficiency decreases due to reduced dye adsorption and scavenging of hydroxyl radicals. These results indicate that mildly acidic to neutral pH conditions are optimal for dye degradation. Figure 3 d illustrates the effect of temperature on the photocatalytic degradation of Brilliant Blue FCF dye using the NZF nanocomposite. The degradation efficiency increases with temperature from 20 to around 26–30°C due to enhanced reaction kinetics and improved mass transfer. Maximum degradation (~ 91%) is observed near ambient temperature. Beyond this range, a slight decrease in efficiency occurs at higher temperatures. This decline may be attributed to increased charge carrier recombination and reduced adsorption of dye molecules on the catalyst surface. 3.7. BET Surface Area Analysis The specific surface areas (SBET) of pure NiO, ZnFe 2 O 4 and the NZF nanocomposite were determined from nitrogen adsorption–desorption isotherms measured at 77 K using a NOVA 3200 BET surface area analyzer (Quantachrome Corporation, USA). Prior to analysis, all samples were degassed under vacuum at 300°C for 3 h to remove physisorbed species. Surface areas were calculated using the Brunauer–Emmett–Teller (BET) method (Sinha P et al. 2019 ). Pore size distribution analysis (BJH) was not performed in the present study. The nitrogen adsorption–desorption isotherms of NiO, ZnFe 2 O 4 and the NZF nanocomposite are shown in Fig. 4 a. Both samples exhibit type IV isotherms with H3-type hysteresis loops, which are characteristic of mesoporous materials. The NZF nanocomposite displays a higher BET surface area of 220 m²/g, whereas pure NiO and ZnFe₂O₄ shows a slightly lower value of 160 and 150 m²/g respectively. The reduction in surface area for NiO is attributed to the partial occupation of its mesopores by ZnFe₂O₄ nanoparticles during composite formation. Despite this effect, the nanocomposite retains a well-developed porous structure and a high specific surface area, both of which are advantageous for catalytic applications. The incorporation of NiO leads to the formation of a hybrid heterostructure with intimate interfacial contact, facilitating enhanced charge separation and improved light absorption. These heterojunction interfaces increase the accessibility of active sites and promote more efficient adsorption of dye molecules. Consequently, the high surface area and mesoporous architecture of the NZF nanocomposite play a pivotal role in improving the photocatalytic degradation of BB FCF dye by providing an expanded reaction interface and accelerating redox processes under light irradiation. 3.8. Rate Constant and order of photodegradation reaction The photocatalytic decolorization kinetics of BB FCF dye were evaluated using a pseudo-first-order kinetic model, as commonly applied for the degradation of organic pollutants (Eq. 1). A control experiment carried out in the absence of the catalyst exhibited no observable degradation of BB FCF, even after 2 h of light irradiation, confirming that photolysis alone does not contribute significantly to the removal of the dye. \(\frac{-dc}{dt}\) = k app C ………….. Eq. 1 where kₐₚₚ (min⁻¹) represents the apparent rate constant. By integrating Eq. 1 under the appropriate boundary conditions, the relationship between the dye concentration at time t (Cₜ) and the initial concentration (C₀) can be expressed as: C t = C 0 at t = 0 (Eq. 2). \(\text{ln}\left(\frac{Co}{Ct}\right)=\) k app t ………………. Eq. 2 The apparent rate constants (kₐₚₚ) for each experiment were determined from the linear plots of ln(C₀/Cₜ) versus reaction time t ( Figue 4b ). Among the tested pH conditions, the kinetic data exhibited the best fit to the pseudo–first-order model at pH 5. Notably, the system at pH 5 also showed the highest kₐₚₚ value, indicating the most favorable photocatalytic degradation rate under this condition (3.56 X 10 − 2 min − 1 ). 3.9. Radical-Scavenging analysis To elucidate the contribution of different reactive oxygen species (ROS) in the photocatalytic degradation of BB FCF, radical scavenging experiments were carried out using specific quenchers. Isopropanol (IPA, 1 mM), benzoquinone (BQ, 1 mM), and ammonium oxalate (AO, 1 mM) were employed as scavengers for •OH, O₂•⁻ and h⁺, respectively. As illustrated in Fig. 5 a, the degradation efficiency decreased from 91% in the absence of scavengers to 66% with IPA, 53% with BQ, and 51% with AO. The pronounced inhibition observed with BQ indicates that O₂•⁻ is the dominant reactive species responsible for dye degradation, whereas •OH radicals and photogenerated holes play subsidiary roles. These results suggest that electrons in the conduction band of the NZF nanocomposite readily interact with adsorbed O₂ to generate O₂•⁻ species, which act as the principal oxidizing agents driving the degradation of BB FCF molecules. 3.10. Catalyst reusability/cycle performance The NZF nanocomposite demonstrated excellent reusability, maintaining more than 90% degradation efficiency even after 10 successive photocatalytic cycles ( Figure. 5b ). This high level of retention confirms the catalyst’s structural stability and suitability for repeated use, underscoring its potential as a cost-effective and durable material for environmental remediation applications. 3.11. Mechanism of Photocatalytic Degradation by NZF nanocomposite The NZF nanocomposite exhibit excellent potential for visible-light-driven photocatalysis, particularly within the 400–800 nm range of the solar spectrum. This enhanced activity primarily arises from the narrow band gap of ZnFe 2 O 4 (~ 2.3 eV), which enables efficient absorption of visible photons, and from the incorporation of NiO, which improves charge carrier separation, structural stability, and the uniform distribution of active sites. The photocatalytic performance of the synthesized samples was evaluated using BB FCF as a model organic pollutant under visible-light irradiation (λ = 630 nm) (Tran HD et al. 2023). Upon illumination, ZnFe 2 O 4 absorbs visible light, promoting electrons (e⁻) from its valence band to the conduction band and generating holes (h⁺) in the valence band. However, in pure ZnFe 2 O 4 , these photogenerated electron–hole pairs tend to recombine rapidly, limiting photocatalytic efficiency (Hou W et al. 2011 ). Introducing NiO (an n-type semiconductor) forms a p–n heterojunction with p-type ZnFe 2 O 4 at their interface, which induces an internal electric field that drives directional charge transfer and effectively suppresses e⁻/h⁺ recombination. Consequently, the NZF nanocomposites exhibited significantly higher photocatalytic degradation efficiency (~ 91%). Under visible-light irradiation, the photogenerated electrons in NiO migrate to the composite surface, where they react with dissolved oxygen to produce superoxide radicals (•O₂⁻). Simultaneously, the photogenerated holes in ZnFe₂O₄ oxidize adsorbed water molecules or hydroxide ions to form hydroxyl radicals (•OH). These highly reactive species can non-selectively degrade BB FCF dye molecules by breaking their chromophoric structures, ultimately leading to mineralization into CO₂ and H₂O. In this study, the band gap energies of NiO, ZnFe 2 O 4 and NZF were estimated to be ~ 3.4, ~ 2.3 eV and ~ 1.3 eV, respectively, enabling efficient visible-light activation. Additionally, the NiO-ZnFe 2 O 4 particles possess a slightly positive surface charge, which favors the adsorption of anionic BB CFC molecules and enhances interfacial contact. The synergistic effects of improved charge separation, enhanced radical generation, and preferential dye adsorption contribute to the superior photocatalytic performance of the NiO-ZnFe 2 O 4 nanocomposites (Van Hoang O et al. 2024 ). A schematic representation of the proposed p–n heterojunction mechanism is shown in Fig. 6 . 3.12. Electrochemical characteristics of the unmodified NiO, ZnFe 2 O 4 and modified NZF nanocomposite electrode The electrochemical activities of the unmodified NiO, ZnFe 2 O 4 and NZF nanocomposite electrodes were investigated via CV technique by using [Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− as the model redox couple (Ahmad T et al. 2022 and Murugan P et al. 2022 ). Figure 7 a depicts the CV curves of the bare NiO, ZnFe 2 O 4 and NZF nanocomposite in 5 mM [Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− containing 0.1 M KCl at a scan rate of 70 mV s − 1 . There was a pair of well-defined and reversible redox peaks that corresponded to the one-electron transfer process of Fe 2+ reversibly into Fe 3+ . Comparing the oxidation and reduction peak current responses at the bare NiO, ZnFe 2 O 4 and NZF nanocomposite, it can be concluded that the modification of working electrode can significantly increase the electron transfer rate. Namely, the calculated results show that the oxidation and reduction peak currents of the NZF nanocomposite is (255.2 and 274.3 mA) were higher than those of the bare NiO (158.3 and 169.2 mA) and ZnFe 2 O 4 (200.5 and 223.4) respectively (Fig. 7 b). 3.13. Electrochemical behaviours of Hydrogen peroxide at the NiO, ZnFe 2 O 4 and modified electrode NZF nanocomposite. The electrochemical performance of the NiO, ZnFe 2 O 4 and modified electrode NZF nanocomposite electrodes towards the determination of H 2 O 2 was investigated by the CV technique in 0.1M PBS (pH10) containing 50 mM H 2 O 2 at a scan rate of 70 mV s − 1 (Fig. 8 a). The electrochemical parameters extracted from the CV curves further confirm the superior performance of the NZF composite electrode. The anodic peak potential (Epa) of the NZF nanocomposite (285.3 mV) is significantly lower than that of pure NiO (391.3 mV) and ZnFe₂O₄ (370.5 mV), indicating a reduced overpotential for H₂O₂ oxidation. Moreover, the composite exhibits the highest anodic peak current (Ipa = 4.92 µA) and cathodic peak current (Ipc = 4.22 µA), compared to NiO (Ipa = 3.05 µA, Ipc = 2.22 µA) and ZnFe₂O₄ (Ipa = 3.12 µA, Ipc = 2.25 µA) (Fig. 8 b). The enhanced current response demonstrates faster charge transfer and improved electrocatalytic activity at the composite electrode. The cathodic peak potentials (Epc) remain nearly similar for all electrodes, suggesting that the main improvement arises from facilitated anodic oxidation kinetics. These results clearly indicate that the formation of a p–n heterojunction between NiO and ZnFe₂O₄ plays a crucial role in lowering the oxidation potential and enhancing the electrochemical response toward H₂O₂. The electrochemical kinetics of the H 2 O 2 redox reactions were further clarified by exploring the influence of scan rate on the anodic and cathodic peak currents. Figure 9 a demonstrate the CV curves of the NZF nanocomposite–modified electrode at different scan rates from 10 to 70 mV s − 1 in 0.1 M PBS (pH 10) containing 50 µM H 2 O 2 . With increasing scan rate, both anodic and cathodic peak currents increase progressively, indicating enhanced electrochemical activity. The linear increase in peak current with scan rate suggests that the electrochemical oxidation of H₂O₂ is predominantly a surface-controlled process at the modified electrode. Additionally, a slight shift in peak potentials toward positive and negative directions is observed at higher scan rates, which is characteristic of quasi-reversible electron transfer kinetics. The well-defined redox peaks even at higher scan rates demonstrate the good electrochemical stability of the NZF nanocomposite. Overall, these results confirm efficient charge transfer and strong electrocatalytic behavior of the composite toward H₂O₂ sensing. Furthermore, there is a good linear relationship between the redox peak currents vs. scan rate (Fig. 9 b), indicating that both the oxidized and reduced forms are confined to the surface, confirming the surface controlled pseudocapacitive behaviour. 3.14. Optimization of electrochemical parameters: In order to achieve high electrochemical sensitivity, wide linear range, and low limit of detection for the determination of H 2 O 2 , the DPV technique was used (Ning et al. 2018 and Zhou X et al. 2013 ). Prior to the optimization stage, the DPV oxidation peak current and DPV reduction peak current of H 2 O 2 need to be compared due to the electrochemical reaction of H 2 O 2 occurring at the NZF nanocomposite electrode being a reversible process. Figure 10 a depicts the DPV behaviors of electrochemical oxidation and reduction of H 2 O 2 at the NZF nanocomposite electrode. The two peaks at 0.41 V and 0.5 V can be attributed to the electro-oxidation and electro-reduction of H 2 O 2 molecules, respectively. As shown in Fig. 10 b, the oxidation peak current of H 2 O 2 (12.15 mA) was ∼1.3-fold larger than that of the reduction peak current of H 2 O 2 (9.0 mA). Therefore, the electrochemical oxidation process using the DPV technique was chosen to achieve the highest analytical performance toward the detection of H 2 O 2 . Figure 11 a illustrates the effect of solution pH on the DPV response of the NZF nanocomposite toward H₂O₂ detection over the pH range 7–13. The oxidation peak current increases gradually from pH 7 and reaches a maximum around pH 10, indicating enhanced electrocatalytic activity in alkaline medium. This improvement is attributed to the increased availability of OH⁻ ions, which facilitates faster H₂O₂ oxidation kinetics. Beyond pH 10, a slight decrease in peak current is observed, possibly due to excessive OH⁻ adsorption and partial surface passivation of the electrode. Additionally, the peak potential shifts with pH, confirming the involvement of proton-coupled electron transfer in the sensing mechanism. Overall, the results indicate that mildly alkaline conditions (around pH 10) are optimal for sensitive H₂O₂ detection using the NZF nanocomposite. 3.15. Electrochemical determination of H 2 O 2 at the NZF nanocomposite electrodes. The electrochemical sensing performance of the proposed NZF nanocomposite electrodes towards the H 2 O 2 detection was evaluated by the DPV technique under the optimized conditions. Figure 11 b shows the DPV curves of different concentrations of H 2 O 2 ranging from 5 to 500 mM. As expected, the oxidation peak current of H 2 O 2 increased with the rising concentrations. The resulting calibration plots exhibited a good linear relationship between the oxidation peak currents and concentrations of H 2 O 2 . The limit of detection (LOD) of the proposed electrochemical sensor was determined to be 2 µM. Furthermore, from the obtained slope value, the electrochemical sensitivity of the ZnFe 2 O 4 -based electrochemical sensor was calculated to be 5 µA mM − 1 cm − 2 . The analytical parameters of the NZF nanocomposite based electro chemical sensor for the detection of H 2 O 2 are compared with those reported in the recent literature (Tables 1 ). These outcomes indicate that the proposed NZF nanocomposite based electrochemical sensor exhibited an excellent performance towards the electro-oxidation of H 2 O 2 with high electrochemical sensitivity, comparatively low limit of detection, and wide linear response ranges. Table 1 Comparison of NZF with other H 2 O 2 sensors based on different materials Electrode Detection limit Sensitivity (µA mM − 1 cm − 2 ) Linear range Ref. Pt/ZnFe 2 O 4 /rGO 0.1 µM 87.13 0.0005-10.2 µM (Ning L et al. 2018 ) AuNPs@Gr/NiF 1 µM 47.4 0.05–1.75 µM (Wang X et al. 2017 ) Ag@ TiO 2 0.43 µM -- 0.001-10 µM (Khan MM et al. 2013 ) Pd/ZnFe 2 O 4 /rGO 2.12 µM -- 0.025–10.2 µM (Ning L et al. 2017 ) Zn 0.7 Ni 0.3 Fe 2 O 4 /GCE 5 µM 3.88 0.02–10 µM (Zhao X et al. 2013) NiO/ZnFe 2 O 4 2 µM 5 0.1–200 µM Present work Conclusion In summary, a dualfunctional NZF nanocomposite was synthesized by low cost combustion method and investigated enhanced performance in both photocatalytic degradation and electrochemical sensing applications. Structural and morphological analyses confirmed the formation of a porous heterostructured composite with high surface area. The narrow band gap and p–n heterojunction formation enhanced visible light absorption and promote stable charge separation. As a result, the NZF nanocomposite exhibited high photocatalytic degradation efficiency toward Brilliant Blue FCF dye with favorable reaction kinetics. Further the synthesized NZF nanocomposite revealed good electrocatalytic activity for hydrogen peroxide sensing. NZF shows wide linear detection range, low LOD and reduced overpotential. In conclusion, the NZF highlight its dual functionality and becomes a promising material for both environmental sensing applications. Declarations Funding: The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Authorship contributions Dhanyashree Savitha Vishwakumar: Investigation, Methodology, Writing – original draft, Writing – review & editing. Rajendra Prasad Shivalingappa: Conceptualization, Supervision, acquisition, Methodology, Visualization, Formal analysis, Writing – review & editing. Jagadish Krishnegowda: Visualization, Formal analysis, review & editing. Jahnavi Hunasekatte Katamallappa: Review & editing. Acknowledgments I gratefully thank and deeply acknowledge anyone who gave a hand to make this new discovery and work coming out to light. Ethics Approval Not applicable. Consent for Publication Not applicable. Consent to participate Not applicable. Competing interests The authors declare no competing interests. Data Availability Statement All data supporting the findings of this study are included within the article. Additional data are available from the corresponding author upon reasonable request. References Abou Zeid S, Leprince-Wang Y (2024) Advancements in ZnO-based photocatalysts for water treatment: a comprehensive review. Crystals 14(7):611. https://doi.org/10.3390/cryst14070611 Ahmad T, Iqbal A, Halim SA, Uddin J, Khan A, El Deeb S, Al-Harrasi A (2022) Recent advances in electrochemical sensing of hydrogen peroxide (H 2 O 2 ) released from cancer cells. 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J Photochem Photobiol A 390:112305. https://doi.org/10.1016/j.jphotochem.2019.112305 Statements & Declarations Supplementary Files graphicalabstract.jpg Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Major Revision 08 Apr, 2026 Reviewers agreed at journal 09 Mar, 2026 Reviewers invited by journal 03 Mar, 2026 Editor invited by journal 03 Mar, 2026 Editor assigned by journal 01 Mar, 2026 First submitted to journal 27 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8906372","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":600206683,"identity":"029d30a2-fcea-4a33-9f56-fc153ad2fbf6","order_by":0,"name":"Dhanyashree Savitha Vishwakumar","email":"","orcid":"","institution":"Department of Chemistry, Davangere University, Davangere city, 577007, Karnataka State","correspondingAuthor":false,"prefix":"","firstName":"Dhanyashree","middleName":"Savitha","lastName":"Vishwakumar","suffix":""},{"id":600206684,"identity":"fcbd2ade-fc77-48b4-a14a-219705a8acfd","order_by":1,"name":"Jagadish 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\u003c/strong\u003enanocomposite.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/e419ae91970ef8dfc2accde4.jpg"},{"id":104203058,"identity":"964896a2-4563-4282-8cda-7f20b7436566","added_by":"auto","created_at":"2026-03-09 06:11:35","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":68587,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e Percentage degradation of BB FCF Dye and \u003cstrong\u003eb)\u003c/strong\u003e Band Gap Energy of NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and NZF nanocomposite\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/def9cc1d1cd5f3c1a7e824ff.jpg"},{"id":104203065,"identity":"fb4c7861-b12d-4f54-beb9-c647e1bc3a02","added_by":"auto","created_at":"2026-03-09 06:11:36","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":135619,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e Effect of Dye concentration, \u003cstrong\u003eb)\u003c/strong\u003e Effect of Catalytic concentration, \u003cstrong\u003ec)\u003c/strong\u003e Effect of pH, \u003cstrong\u003ed)\u003c/strong\u003e Effect of Temperature on BB FCF dye degradation\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/30d09db338b7e0c8e8427e5b.jpg"},{"id":104203057,"identity":"3969fd56-d084-44c9-b185-085203c90f7c","added_by":"auto","created_at":"2026-03-09 06:11:35","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":62303,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e BET surface area of NZF nanocomposite \u003cstrong\u003eb)\u003c/strong\u003e rate constant for the degradation of BB FCF dye.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/0c76bd28d8f02c7063f05e4a.jpg"},{"id":104203066,"identity":"e563da57-84d6-4b14-bb2f-ef96ff760353","added_by":"auto","created_at":"2026-03-09 06:11:37","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":76330,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea)\u003c/strong\u003e Radical Scavenger test and \u003cstrong\u003eb)\u003c/strong\u003e NZF Catalyst reusability on BB FCF dye degradation\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/a8edc3b744ddb4c6d2e480a0.jpg"},{"id":104405156,"identity":"1c79fabb-51b1-4296-9912-14316e9821d8","added_by":"auto","created_at":"2026-03-11 12:21:57","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":75168,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic mechanisms of BB FCF dye degradation under sunlight using NZF nanocomposite\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/82964df6ac0dd65c43fc6aec.jpg"},{"id":104403769,"identity":"ab73a1af-9908-4e41-81ef-406a7cd3accf","added_by":"auto","created_at":"2026-03-11 12:19:00","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":88342,"visible":true,"origin":"","legend":"\u003cp\u003e(a) CV curves and (b) the bar diagram of the oxidation/reduction peak currents of the NiO-ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in 20 µM [Fe(CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3−\u003c/sup\u003e/\u003csup\u003e4−\u003c/sup\u003e solution containing 0.1 M KCl at a scan rate of 70 mV s\u003csup\u003e−1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/195d52832045cd3e0bb0dd8e.jpg"},{"id":104203069,"identity":"f9411a26-6420-40ca-84d0-8d05d1127d8f","added_by":"auto","created_at":"2026-03-09 06:11:37","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":88241,"visible":true,"origin":"","legend":"\u003cp\u003e(a) CV curves and (b) the bar diagram of redox peak currents of 20 µM H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2 \u003c/sub\u003ein 0.1 M PBS (pH 10). The scan rate of CV is 70 mV s\u003csup\u003e−1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/d2e6430e76355610949e606e.jpg"},{"id":104404852,"identity":"11d4f416-9c78-45d0-928c-da720c096c8b","added_by":"auto","created_at":"2026-03-11 12:21:12","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":86306,"visible":true,"origin":"","legend":"\u003cp\u003eCV curves recorded at the surface of\u0026nbsp; NZF modified electrodes in 0.1 M PBS (pH10) containing 50 µM H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2 \u003c/sub\u003eat different scan rates (a) and(b) plots of peak current vs. scan rate.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/4f2b78f538ad415d5a01fe91.jpg"},{"id":104203059,"identity":"6da2441a-fb76-4284-89a0-4bac41820c14","added_by":"auto","created_at":"2026-03-09 06:11:35","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":101658,"visible":true,"origin":"","legend":"\u003cp\u003e(a) DPV oxidation/reduction curves and (b) the bar diagram of the oxidation/reduction peak currents of the NZF in 0.1 M PBS (pH 10) containing 250 µM H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/3b9ab1a3d547589957e03af8.jpg"},{"id":104404963,"identity":"96ed148a-7ea7-42b1-9369-f628648451b2","added_by":"auto","created_at":"2026-03-11 12:21:27","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":98431,"visible":true,"origin":"","legend":"\u003cp\u003e(a) DPV curves of 250 µM H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2 \u003c/sub\u003eat NZF with different pH values from 7.0 to 13.0; (b) DPV curves of 5–500 µM H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e in 0.1 M PBS (pH 10.0).\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/2199c39ad693eb4f4b37aac8.jpg"},{"id":104408858,"identity":"868fc8ef-c0e4-4cdc-8615-acb4a1ab9e64","added_by":"auto","created_at":"2026-03-11 12:43:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2290823,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/709a492d-e71e-4bef-b413-1769c9e743b3.pdf"},{"id":104404818,"identity":"21da6b4b-8b55-4648-b52f-80b7f817a141","added_by":"auto","created_at":"2026-03-11 12:21:09","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":111222,"visible":true,"origin":"","legend":"","description":"","filename":"graphicalabstract.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8906372/v1/fb40efcd267552ddeadbefc7.jpg"}],"financialInterests":"","formattedTitle":"Stable NiO–ZnFe2O4 p–n heterojunction nanocomposite for dualfunctional photocatalysis and sensor applications","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe extensive use of organic dyes in textile, food, and pharmaceutical industries has led to their increased release into wastewater (Lin J et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2023\u003c/span\u003e and Islam T et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Insufficient treatment of these dyes poses serious environmental and health concerns due to their toxicity, persistence, and potential carcinogenic effects (Singha K et al. 2021). Brilliant Blue FCF is a synthetic organic dye widely used in textile, food, cosmetic, and pharmaceutical industries (Guo J et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). It is commonly applied as a coloring agent because of its strong color and high chemical stability (Dalmaz A et al. 2025). Due to its large-scale industrial use, this dye is often released into the environment through untreated or partially treated effluents (Nascimento VX et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). As a result, it accumulates in wastewater and natural water bodies (Al-Gethami W et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The complex aromatic structure of Brilliant Blue FCF makes it resistant to natural degradation (Flury M et al. 1994). Its presence in aquatic systems can reduce light penetration and disturb photosynthetic activity. It may also lower dissolved oxygen levels and exhibit toxic effects on aquatic organisms (Gupta VK et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Therefore, efficient wastewater treatment methods are required to remove persistent dyes such as Brilliant Blue FCF.\u003c/p\u003e \u003cp\u003eAdvanced oxidation processes, particularly sunlight-driven photocatalysis, are effective and environmentally friendly wastewater treatment methods that utilize low-cost and abundant solar energy (Vilar VJ et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e and Kumari H et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In this process, semiconductor photocatalysts absorb sunlight to generate electron\u0026ndash;hole pairs, which react with oxygen and water to produce reactive oxygen species such as hydroxyl and superoxide radicals (Nosaka Y et al. 2017). The generated radicals can efficiently break down stable organic pollutants. As a result, complex dye molecules are converted into simpler and less harmful products (Rauf MA et al. 2009). In many cases, the pollutants are further mineralized into carbon dioxide and water. Therefore, sunlight-driven photocatalysis is regarded as a promising strategy for treating dye-polluted wastewater (Abou Zeid S et al. 2024 and E1 Golli A et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSemiconductor photocatalysts enable environmental remediation by converting light energy into electron\u0026ndash;hole pairs that drive surface redox reactions for pollutant degradation (Zhu D et al. 2019 and Hagfeldt A et al. 1995). The efficiency of photocatalysis depends on properties such as band gap energy, charge separation, and available active sites (Yanagi R et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Designing semiconductor heterostructures is an effective strategy to improve light absorption and reduce charge recombination (Balapure A et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). A key drawback of pristine semiconductor photocatalysts is the rapid recombination of photogenerated electron\u0026ndash;hole pairs, which limits their catalytic efficiency (Tan HL et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2019\u003c/span\u003e and Jiang L et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). This issue can be addressed by forming heterojunctions between semiconductors with different band gap energies, creating favorable interfacial band alignment (Smith AM et al. 2010 and Zheng B et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). This structure facilitates efficient charge separation and directed charge transfer. Consequently, electron\u0026ndash;hole recombination is suppressed, leading to improved photocatalytic activity (Zhou W et al. 2018).\u003c/p\u003e \u003cp\u003eSeveral studies have reported the synthesis and use of nanocomposite semiconductors for the photocatalytic degradation of dyes. Qaiser Khan et al., has synthesized TiO\u003csub\u003e2\u003c/sub\u003e/rGO nanocomposites by hydrothermal technique and invesitigated the degradation of Brilliant Green under UV light. The results reviealed the 2% TiO\u003csub\u003e2\u003c/sub\u003e/rGO nanocomposite with the addition of PMS (peroxymonosulfate) shows 99.9% of degradation (Khan Q et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). CuO\u0026ndash;TiO₂ nanocomposites have shown 90\u0026ndash;95% electrochemical photocatalytic degradation of Brilliant Blue FCF dye under UV and visible light due to heterojunction-enhanced charge separation (Li Y \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Ultrasonically synthesized PEG-assisted Yb₂O₃/ZnFe₂O₄ nanocomposites have been applied for dye and herbicide degradation and electrochemical sensing of catechol (Fatima N et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2026\u003c/span\u003e). A solution-combustion-derived ZnFe₂O₄/ZnO composite achieved nearly 80% degradation of methylene blue and remazol brilliant blue under UV and visible light due to heterojunction-induced visible-light absorption and enhanced charge separation (Zouhier M et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In addition to developing new semiconductors, evaluating existing materials under combined advanced oxidation processes is essential for gaining mechanistic insight and designing improved multifunctional photocatalytic and electrochemical systems (Hong J et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e and Ali H et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNiO and ZnFe₂O₄ are metal oxide semiconductors that show photocatalytic activity under visible light due to their suitable band gap energies. NiO generally exhibits a wide band gap in the range of 3.2\u0026ndash;3.8 eV (Mustafa F et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), whereas ZnFe₂O₄ has a narrower band gap of about 1.9\u0026ndash;2.3 eV, which allows efficient visible-light absorption (Kumar P et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). The selection of NiO and ZnFe₂O₄ is further supported by their favorable properties, including visible-light responsiveness, low toxicity, and good electrical conductivity. ZnFe₂O₄ exhibits high electronic conductivity (\u0026asymp;\u0026thinsp;10⁵ Ω⁻\u0026sup1; cm⁻\u0026sup1;) and a large dielectric permittivity (~\u0026thinsp;1.7 \u0026times; 10\u0026sup1;\u0026sup1;) in the bulk state. In contrast, NiO is a p-type semiconductor with good electrical conductivity arising from nickel vacancies and hole carriers (Kaya D et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These complementary electrical characteristics make NiO and ZnFe₂O₄ attractive for catalytic and energy-related applications, especially when combined to form heterostructured systems (Bohra M et al \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e and Zahra SE et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHydrogen peroxide is an important industrial chemical and reactive oxygen species whose concentration must be carefully monitored due to its environmental and biological effects (Duca G et al 2020 and Ciriminna R et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Electrochemical sensing provides a simple, rapid, and cost-effective method for H₂O₂ detection, and the limitations of enzyme-based sensors have driven the development of stable non-enzymatic sensors based on metal oxide nanomaterials (Thatikayala D et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e and Hu Y et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In particular, metal oxide heterostructures exhibit enhanced electrocatalytic activity due to improved charge transfer, reduced overpotential, and increased active surface area (Xia C et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), making H₂O₂ a widely used model analyte for evaluating semiconductor-based sensors. From a synthesis perspective, the combustion method offers a fast and scalable route to produce porous metal oxide composites with abundant active sites suitable for photocatalytic and electrochemical applications (Li FT et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). However, systematic studies on combustion-derived NiO\u0026ndash;ZnFe₂O₄ nanocomposites with dual functionality remain limited.\u003c/p\u003e \u003cp\u003eIn this study, a NiO\u0026ndash;ZnFe₂O₄ (NZF) nanocomposite was synthesized using a simple combustion method and examined for its structural, optical, photocatalytic, and electrochemical properties. The roles of p\u0026ndash;n heterojunction formation, band gap narrowing and increased surface area were investigated in relation to the photocatalytic degradation of Brilliant Blue FCF dye and the electrochemical detection of hydrogen peroxide. This work establishes a clear structure\u0026ndash;property\u0026ndash;performance relationship and highlights the potential of NZF nanocomposites as multifunctional materials for environmental remediation and sensing applications.\u003c/p\u003e"},{"header":"2. Materials and Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eThe materials utilized in this study were Nickel nitrate hexahydrate (Ni (NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), Zinc nitrate hexahydrate (Zn (NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), Iron (III) nitrate nanohydrate (Fe (NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO), and Citric acid (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e.H\u003csub\u003e2\u003c/sub\u003eO). These chemicals are analytical research grade high-quality powders procured from Sigma-Aldrich.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Synthesis of NiO/ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (NZF) nanocomposite by Combustion method\u003c/h2\u003e \u003cp\u003e0.02 M of Nickel nitrate hexahydrate and 0.01 M of citric acid are first mixed in 10 mL of water to prepare a precursor solution. The solution is stirred continuously for two hours to ensure homogeneity. Subsequently, it is placed in a preheated muffle furnace at temperature 300\u0026deg;C for 10 minutes. The resulting material is subjected to calcination at 500\u0026deg;C for 2 hours.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e2Ni(NO)⋅6HO + CHO​ → 2NiO + 6CO​ + 3N​ + 14H​O\u003c/h3\u003e\n\u003cp\u003eFollowing the synthesis of nickel oxide, it is incorporated into a solution mixture containing 0.01 M zinc nitrate hexahydrate, 0.02 M iron nitrate nanohydrate and 0.01 M citric acid in a stoichiometric ratio. The resulting mixture is stirred for three hours to ensure uniformity, followed by sonication for 30 minutes to enhance dispersion. The prepared solution is then transferred to a crucible and placed in a preheated muffle furnace at 300\u0026deg;C for 10 minutes. After initial combustion, the material is calcinated at 600\u0026deg;C for 3 hours. This process results in the formation of the final product, NiO/ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanocomposite.\u003c/p\u003e \u003cp\u003eZn(NO\u003csub\u003e3\u003c/sub\u003e​)\u003csub\u003e2\u003c/sub\u003e​\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003e​O\u0026thinsp;+\u0026thinsp;2Fe(NO\u003csub\u003e3\u003c/sub\u003e​)\u003csub\u003e3\u003c/sub\u003e​\u0026sdot;9H\u003csub\u003e2\u003c/sub\u003e​O\u0026thinsp;+\u0026thinsp;C\u003csub\u003e6\u003c/sub\u003e​H\u003csub\u003e8\u003c/sub\u003e​O\u003csub\u003e7\u003c/sub\u003e​ + NiO \u0026rarr; NiO/ZnFe\u003csub\u003e2\u003c/sub\u003e​O\u003csub\u003e4\u003c/sub\u003e​ + 6CO\u003csub\u003e2\u003c/sub\u003e​ + 3N\u003csub\u003e2\u003c/sub\u003e​+ H\u003csub\u003e2\u003c/sub\u003e​O\u003c/p\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003cdiv class=\"Heading\"\u003e2.2.3. Characterization\u003c/div\u003e \u003cp\u003eX-ray diffraction (XRD) patterns were recorded using a Rigaku Ultima III diffractometer equipped with Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;). The surface morphology of the synthesized samples was examined using scanning electron microscopy (SEM, JEOL JSM-6390LV), while their microstructural features were further analyzed by transmission electron microscopy (TEM, Hitachi H-9000 NAR). The optical properties were investigated through UV\u0026ndash;Vis diffuse reflectance spectroscopy (DRS) using a JASCO V-670 spectrophotometer operating in the range of 350\u0026ndash;1500 nm to estimate the band gap energy. Room-temperature photoluminescence (PL) spectra were acquired on a Jobin Yvon Fluorolog-3-11 spectrofluorometer equipped with a xenon excitation source.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003cdiv class=\"Heading\"\u003e2.2.4. Photocatalytic Activity\u003c/div\u003e \u003cp\u003eThe photocatalytic activity of the NZF nanocomposite toward the degradation of BB FCF dye under natural sunlight was evaluated by preparing aqueous BB FCF solutions with concentrations ranging from 0 to 50 ppm. To establish adsorption\u0026ndash;desorption equilibrium, an appropriate amount of the catalyst was added to the dye solution and stirred in the dark for 15\u0026ndash;30 min. The suspension was then transferred to a photocatalytic reactor and continuously stirred while exposed to direct sunlight. All experiments were conducted on clear sunny days on the rooftop of Davanagere University, Davanagere, Karnataka, India (\u0026asymp;\u0026thinsp;14.441\u0026deg; N, 75.921\u0026deg; E; elevation\u0026thinsp;~\u0026thinsp;580 m), where the average daily solar irradiance is approximately 215 W m⁻\u0026sup2;. To monitor the progress of dye degradation, aliquots were withdrawn from the reaction mixture at predetermined time intervals, centrifuged to separate the catalyst, and analyzed using a UV\u0026ndash;Visible spectrophotometer (Shimadzu UV-1800; λ\u0026thinsp;=\u0026thinsp;190\u0026ndash;1100 nm) by measuring the absorbance at 630 nm. Optimization studies were performed by systematically varying catalyst dosage, solution pH, initial dye concentration, and irradiation time. The reusability of the catalyst was assessed by recovering, washing, and employing it in successive degradation cycles under identical conditions. All photocatalytic experiments were conducted in triplicate to ensure reliability. The results showed excellent reproducibility, with degradation efficiencies varying by only\u0026thinsp;\u0026plusmn;\u0026thinsp;3%.\u003c/p\u003e \u003cp\u003eThe degradation efficiency (η) was calculated using Eq.\u0026nbsp;(1):\u003c/p\u003e \u003cp\u003eη(%) = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{{C}_{0}-{C}_{t}}{{C}_{0}}\\)\u003c/span\u003e\u003c/span\u003e x 100 = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{{A}_{0}-{A}_{t}}{{A}_{0}}\\)\u003c/span\u003e\u003c/span\u003e x 100 Eq\u0026hellip;.. (1)\u003c/p\u003e \u003cp\u003ewhere C\u003csub\u003e0\u003c/sub\u003e and A\u003csub\u003e0\u003c/sub\u003e are the initial dye concentration and absorbance before irradiation, and C\u003csub\u003et\u003c/sub\u003e and A\u003csub\u003et\u003c/sub\u003e​ are the corresponding values at irradiation time t.\u003c/p\u003e \u003cp\u003eThe apparent first-order rate constant (k\u003csub\u003er\u003c/sub\u003e​) was determined using Eq.\u0026nbsp;(2):\u003c/p\u003e \u003cp\u003eLn \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\left(\\frac{{C}_{0}}{{C}_{t}}\\right)\\)\u003c/span\u003e\u003c/span\u003e = k\u003csub\u003er\u003c/sub\u003et Eq\u0026hellip;.. (1)\u003c/p\u003e \u003cp\u003ewhere k\u003csub\u003er\u003c/sub\u003e​ is obtained from the slope of the linear plot of ln (C\u003csub\u003e0\u003c/sub\u003e/C\u003csub\u003et\u003c/sub\u003e) versus t (Li Y et al. 2005).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1. X-ray Diffraction (XRD) analysis of NZF\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe crystalline structure and phase purity of the synthesized NZF nanocomposite were investigated using X-ray diffraction (XRD). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea shows the XRD pattern of NZF, recorded in the 2θ range of 8\u0026deg; to 90\u0026deg;. The diffraction peaks located at 2θ values of ~\u0026thinsp;37.24\u0026deg;, ~\u0026thinsp;43.28\u0026deg;, ~\u0026thinsp;62.85\u0026deg;, ~\u0026thinsp;75.40\u0026deg;, ~\u0026thinsp;79.37\u0026deg; can be indexed to the (101), (012), (110), (113) and (202) planes confirmed the rhombohedral structure of NiO according to the standard JCPDS card number 00-044-1159 and space group R-3m/166. Similarly, the diffraction peaks\u0026thinsp;~\u0026thinsp;30\u0026deg;, ~\u0026thinsp;35.34\u0026deg;, ~\u0026thinsp;53.28\u0026deg;, ~\u0026thinsp;56.79\u0026deg; corresponding to the planes of (220), (311), (422) and (511) confirmed the cubic structure of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, in good agreement with JCPDS card number 01-077-0011 and space group Fd-3m/227. The XRD pattern exhibits sharp diffraction peaks, indicating the high crystallinity. The XRD pattern of NZF nanocomposite confirmed the presence of NiO and ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, as indicated by the presence of bothpeaks of NiO and ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. The Energy Dispersive X-ray (EDX) Spectroscopy of NZF\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb presents the EDX spectrum of the NZF nanocomposite synthesized by the combustion method, along with the corresponding quantitative elemental analysis shown in the inset table. The spectrum exhibits distinct and intense peaks corresponding to Ni, Zn, Fe, and O, confirming the successful formation of the composite material. The absence of any additional impurity peaks indicates the high purity of the synthesized nanocomposite. As summarized in the inset table, the weight percentages of Ni, Zn, Fe, and O are 37.2%, 16.4%, 31.3%, and 15.1%, respectively, while the corresponding atomic percentages are 26.5%, 10.5%, 23.5%, and 39.6%. These values are in good agreement with the expected stoichiometry of the NZF system, confirming the coexistence of both NiO and ZnFe₂O₄ phases. The relatively higher oxygen content is attributed to the oxide nature of the composite. Overall, the EDX analysis verifies the elemental composition and uniform distribution of Ni, Zn, Fe, and O within the NZF nanocomposite, supporting the structural and functional integrity of the material.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Scanning Electron microscope (SEM) images of NZF\u003c/h2\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e(c)\u003c/b\u003e and \u003cb\u003e1(d)\u003c/b\u003e show the SEM micrographs of the NZF nanocomposite synthesized via the combustion method at different magnifications. The low-magnification image (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) reveals the formation of irregularly shaped, loosely agglomerated clusters composed of fine particles, which is a typical characteristic of combustion-derived materials. These agglomerates arise from the rapid release of gases during the combustion process, leading to a highly porous structure. The high-magnification image (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) clearly shows interconnected nanosized grains with rough surfaces and interparticle voids. The particle size is found to be in the range of approximately 150\u0026ndash;230 nm, as indicated in the micrograph. Such a porous and rough morphology provides a high surface area and abundant active sites. This structural feature is highly beneficial for photocatalytic and electrochemical sensing applications, as it facilitates efficient mass transport and enhanced interfacial charge transfer.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Photocatalytic Brilliant Blue (BB) Dye degradation\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the photocatalytic degradation of Brilliant Blue FCF dye as a function of irradiation time using NiO, ZnFe₂O₄, and the NZF nanocomposite. The degradation efficiency increases rapidly during the initial stages due to abundant active sites and efficient generation of reactive species. Among the catalysts, the NZF composite exhibits the highest degradation efficiency at all-time intervals. The enhanced performance of the composite is attributed to the synergistic effect and improved charge separation at the NZF heterojunction. In contrast, pure NiO and ZnFe₂O₄ show comparatively lower degradation efficiency due to faster charge recombination.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5. Band Gap Energy\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb shows the Tauc plots (αhν)\u003csup\u003e2\u003c/sup\u003e (eV)\u003csup\u003e2\u003c/sup\u003e versus photon energy (hν) (eV) used to estimate the optical band gap energies of NiO, ZnFe₂O₄ and the NZF nanocomposite. The band gap values were determined by extrapolating the linear portion of the plots to the energy axis. Pure NiO exhibit relatively higher band gap energy 3.4 eV and ZnFe₂O₄ exhibit 2.3 eV, whereas the NZF nanocomposite shows a reduced band gap 1.6 eV. This narrowing of the band gap can be attributed to strong interfacial interaction and p\u0026ndash;n heterojunction formation between NiO and ZnFe₂O₄. The reduced band gap enhances visible-light absorption and promotes efficient charge separation, leading to improved photocatalytic performance of the nanocomposite.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.6. Effect of Catalyst, dye concentration, Temperature and pH on BB dye degradation\u003c/h2\u003e \u003cp\u003eThe effect of initial Brilliant Blue FCF dye concentration on the photocatalytic degradation efficiency of the NZF nanocomposite is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. High degradation efficiency (\u0026gt;\u0026thinsp;91%) is observed at lower dye concentrations (5\u0026ndash;20 ppm) due to sufficient availability of active catalytic sites and reactive oxygen species. As the dye concentration increases, the degradation efficiency gradually decreases, reaching about 78% at 40 ppm. This reduction is mainly attributed to saturation of active sites on the catalyst surface and the light screening effect caused by higher dye concentration. Increased competition among dye molecules for reactive radicals also contributes to the lowered degradation efficiency at higher concentrations. Nevertheless, the NZF nanocomposite maintains appreciable photocatalytic activity over a wide concentration range, indicating its potential for practical wastewater treatment applications.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb illustrates the effect of NZF photocatalyst loading on the degradation efficiency of Brilliant Blue FCF dye. The degradation percentage increases significantly with increasing catalyst dosage from 0.1 to 0.9 g due to the availability of a larger number of active surface sites and enhanced generation of reactive oxygen species. This increase facilitates improved adsorption of dye molecules and more effective photocatalytic reactions. The maximum degradation efficiency (~\u0026thinsp;91%) is achieved at an optimal catalyst loading of around 0.9\u0026ndash;1.0 g. Beyond this optimum, a slight decrease in degradation efficiency is observed with further increase in catalyst amount. This decline can be attributed to catalyst particle agglomeration, which reduces the effective surface area. Additionally, excess catalyst causes light scattering and shielding effects, limiting light penetration into the reaction medium. As a result, the generation of electron\u0026ndash;hole pairs is suppressed at higher catalyst loadings. Overall, the results indicate the existence of an optimal catalyst dosage for efficient dye degradation. These findings highlight the importance of catalyst loading optimization for achieving maximum photocatalytic performance.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec shows the effect of pH on the photocatalytic degradation of Brilliant Blue FCF dye using the NZF nanocomposite. The degradation efficiency increases from acidic to near-neutral conditions and reaches a maximum around pH 5\u0026ndash;6. This enhancement is attributed to favorable surface charge interactions and efficient generation of reactive oxygen species. At alkaline pH values, the degradation efficiency decreases due to reduced dye adsorption and scavenging of hydroxyl radicals. These results indicate that mildly acidic to neutral pH conditions are optimal for dye degradation.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed illustrates the effect of temperature on the photocatalytic degradation of Brilliant Blue FCF dye using the NZF nanocomposite. The degradation efficiency increases with temperature from 20 to around 26\u0026ndash;30\u0026deg;C due to enhanced reaction kinetics and improved mass transfer. Maximum degradation (~\u0026thinsp;91%) is observed near ambient temperature. Beyond this range, a slight decrease in efficiency occurs at higher temperatures. This decline may be attributed to increased charge carrier recombination and reduced adsorption of dye molecules on the catalyst surface.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.7. BET Surface Area Analysis\u003c/h2\u003e \u003cp\u003eThe specific surface areas (SBET) of pure NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the NZF nanocomposite were determined from nitrogen adsorption\u0026ndash;desorption isotherms measured at 77 K using a NOVA 3200 BET surface area analyzer (Quantachrome Corporation, USA). Prior to analysis, all samples were degassed under vacuum at 300\u0026deg;C for 3 h to remove physisorbed species. Surface areas were calculated using the Brunauer\u0026ndash;Emmett\u0026ndash;Teller (BET) method (Sinha P et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Pore size distribution analysis (BJH) was not performed in the present study. The nitrogen adsorption\u0026ndash;desorption isotherms of NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and the NZF nanocomposite are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. Both samples exhibit type IV isotherms with H3-type hysteresis loops, which are characteristic of mesoporous materials. The NZF nanocomposite displays a higher BET surface area of 220 m\u0026sup2;/g, whereas pure NiO and ZnFe₂O₄ shows a slightly lower value of 160 and 150 m\u0026sup2;/g respectively. The reduction in surface area for NiO is attributed to the partial occupation of its mesopores by ZnFe₂O₄ nanoparticles during composite formation. Despite this effect, the nanocomposite retains a well-developed porous structure and a high specific surface area, both of which are advantageous for catalytic applications. The incorporation of NiO leads to the formation of a hybrid heterostructure with intimate interfacial contact, facilitating enhanced charge separation and improved light absorption. These heterojunction interfaces increase the accessibility of active sites and promote more efficient adsorption of dye molecules. Consequently, the high surface area and mesoporous architecture of the NZF nanocomposite play a pivotal role in improving the photocatalytic degradation of BB FCF dye by providing an expanded reaction interface and accelerating redox processes under light irradiation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.8. Rate Constant and order of photodegradation reaction\u003c/h2\u003e \u003cp\u003eThe photocatalytic decolorization kinetics of BB FCF dye were evaluated using a pseudo-first-order kinetic model, as commonly applied for the degradation of organic pollutants (Eq.\u0026nbsp;1). A control experiment carried out in the absence of the catalyst exhibited no observable degradation of BB FCF, even after 2 h of light irradiation, confirming that photolysis alone does not contribute significantly to the removal of the dye.\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\frac{-dc}{dt}\\)\u003c/span\u003e \u003c/span\u003e = k\u003csub\u003eapp\u003c/sub\u003e C \u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;.. Eq.\u0026nbsp;1\u003c/p\u003e \u003cp\u003ewhere kₐₚₚ (min⁻\u0026sup1;) represents the apparent rate constant. By integrating Eq.\u0026nbsp;1 under the appropriate boundary conditions, the relationship between the dye concentration at time t (Cₜ) and the initial concentration (C₀) can be expressed as: C\u003csub\u003et\u003c/sub\u003e = C\u003csub\u003e0\u003c/sub\u003e at t\u0026thinsp;=\u0026thinsp;0 (Eq.\u0026nbsp;2).\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\text{ln}\\left(\\frac{Co}{Ct}\\right)=\\)\u003c/span\u003e \u003c/span\u003e k\u003csub\u003eapp\u003c/sub\u003e t \u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;. Eq.\u0026nbsp;2\u003c/p\u003e \u003cp\u003eThe apparent rate constants (kₐₚₚ) for each experiment were determined from the linear plots of ln(C₀/Cₜ) versus reaction time t (\u003cb\u003eFigue 4b\u003c/b\u003e). Among the tested pH conditions, the kinetic data exhibited the best fit to the pseudo\u0026ndash;first-order model at pH 5. Notably, the system at pH 5 also showed the highest kₐₚₚ value, indicating the most favorable photocatalytic degradation rate under this condition (3.56 X 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.9. Radical-Scavenging analysis\u003c/h2\u003e \u003cp\u003eTo elucidate the contribution of different reactive oxygen species (ROS) in the photocatalytic degradation of BB FCF, radical scavenging experiments were carried out using specific quenchers. Isopropanol (IPA, 1 mM), benzoquinone (BQ, 1 mM), and ammonium oxalate (AO, 1 mM) were employed as scavengers for \u0026bull;OH, O₂\u0026bull;⁻ and h⁺, respectively. As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, the degradation efficiency decreased from 91% in the absence of scavengers to 66% with IPA, 53% with BQ, and 51% with AO. The pronounced inhibition observed with BQ indicates that O₂\u0026bull;⁻ is the dominant reactive species responsible for dye degradation, whereas \u0026bull;OH radicals and photogenerated holes play subsidiary roles. These results suggest that electrons in the conduction band of the NZF nanocomposite readily interact with adsorbed O₂ to generate O₂\u0026bull;⁻ species, which act as the principal oxidizing agents driving the degradation of BB FCF molecules.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.10. Catalyst reusability/cycle performance\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eThe NZF nanocomposite demonstrated excellent reusability, maintaining more than 90% degradation efficiency even after 10 successive photocatalytic cycles (\u003cb\u003eFigure. 5b\u003c/b\u003e). This high level of retention confirms the catalyst\u0026rsquo;s structural stability and suitability for repeated use, underscoring its potential as a cost-effective and durable material for environmental remediation applications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.11. Mechanism of Photocatalytic Degradation by NZF nanocomposite\u003c/h2\u003e \u003cp\u003eThe NZF nanocomposite exhibit excellent potential for visible-light-driven photocatalysis, particularly within the 400\u0026ndash;800 nm range of the solar spectrum. This enhanced activity primarily arises from the narrow band gap of ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (~\u0026thinsp;2.3 eV), which enables efficient absorption of visible photons, and from the incorporation of NiO, which improves charge carrier separation, structural stability, and the uniform distribution of active sites. The photocatalytic performance of the synthesized samples was evaluated using BB FCF as a model organic pollutant under visible-light irradiation (λ\u0026thinsp;=\u0026thinsp;630 nm) (Tran HD et al. 2023).\u003c/p\u003e \u003cp\u003eUpon illumination, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e absorbs visible light, promoting electrons (e⁻) from its valence band to the conduction band and generating holes (h⁺) in the valence band. However, in pure ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, these photogenerated electron\u0026ndash;hole pairs tend to recombine rapidly, limiting photocatalytic efficiency (Hou W et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Introducing NiO (an n-type semiconductor) forms a p\u0026ndash;n heterojunction with p-type ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e at their interface, which induces an internal electric field that drives directional charge transfer and effectively suppresses e⁻/h⁺ recombination. Consequently, the NZF nanocomposites exhibited significantly higher photocatalytic degradation efficiency (~\u0026thinsp;91%).\u003c/p\u003e \u003cp\u003eUnder visible-light irradiation, the photogenerated electrons in NiO migrate to the composite surface, where they react with dissolved oxygen to produce superoxide radicals (\u0026bull;O₂⁻). Simultaneously, the photogenerated holes in ZnFe₂O₄ oxidize adsorbed water molecules or hydroxide ions to form hydroxyl radicals (\u0026bull;OH). These highly reactive species can non-selectively degrade BB FCF dye molecules by breaking their chromophoric structures, ultimately leading to mineralization into CO₂ and H₂O.\u003c/p\u003e \u003cp\u003eIn this study, the band gap energies of NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and NZF were estimated to be ~\u0026thinsp;3.4, ~\u0026thinsp;2.3 eV and ~\u0026thinsp;1.3 eV, respectively, enabling efficient visible-light activation. Additionally, the NiO-ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles possess a slightly positive surface charge, which favors the adsorption of anionic BB CFC molecules and enhances interfacial contact. The synergistic effects of improved charge separation, enhanced radical generation, and preferential dye adsorption contribute to the superior photocatalytic performance of the NiO-ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanocomposites (Van Hoang O et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). A schematic representation of the proposed p\u0026ndash;n heterojunction mechanism is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.12. Electrochemical characteristics of the unmodified NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and modified NZF nanocomposite electrode\u003c/h2\u003e \u003cp\u003eThe electrochemical activities of the unmodified NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and NZF nanocomposite electrodes were investigated via CV technique by using [Fe(CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3\u0026minus;\u003c/sup\u003e/[Fe(CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e as the model redox couple (Ahmad T et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e and Murugan P et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea depicts the CV curves of the bare NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and NZF nanocomposite in 5 mM [Fe(CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e3\u0026minus;\u003c/sup\u003e/[Fe(CN)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e4\u0026minus;\u003c/sup\u003e containing 0.1 M KCl at a scan rate of 70 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. There was a pair of well-defined and reversible redox peaks that corresponded to the one-electron transfer process of Fe\u003csup\u003e2+\u003c/sup\u003e reversibly into Fe\u003csup\u003e3+\u003c/sup\u003e. Comparing the oxidation and reduction peak current responses at the bare NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and NZF nanocomposite, it can be concluded that the modification of working electrode can significantly increase the electron transfer rate. Namely, the calculated results show that the oxidation and reduction peak currents of the NZF nanocomposite is (255.2 and 274.3 mA) were higher than those of the bare NiO (158.3 and 169.2 mA) and ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (200.5 and 223.4) respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.13. Electrochemical behaviours of Hydrogen peroxide at the NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and modified electrode NZF nanocomposite.\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe electrochemical performance of the NiO, ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and modified electrode NZF nanocomposite electrodes towards the determination of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was investigated by the CV technique in 0.1M PBS (pH10) containing 50 mM H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at a scan rate of 70 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). The electrochemical parameters extracted from the CV curves further confirm the superior performance of the NZF composite electrode. The anodic peak potential (Epa) of the NZF nanocomposite (285.3 mV) is significantly lower than that of pure NiO (391.3 mV) and ZnFe₂O₄ (370.5 mV), indicating a reduced overpotential for H₂O₂ oxidation. Moreover, the composite exhibits the highest anodic peak current (Ipa\u0026thinsp;=\u0026thinsp;4.92 \u0026micro;A) and cathodic peak current (Ipc\u0026thinsp;=\u0026thinsp;4.22 \u0026micro;A), compared to NiO (Ipa\u0026thinsp;=\u0026thinsp;3.05 \u0026micro;A, Ipc\u0026thinsp;=\u0026thinsp;2.22 \u0026micro;A) and ZnFe₂O₄ (Ipa\u0026thinsp;=\u0026thinsp;3.12 \u0026micro;A, Ipc\u0026thinsp;=\u0026thinsp;2.25 \u0026micro;A) (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). The enhanced current response demonstrates faster charge transfer and improved electrocatalytic activity at the composite electrode. The cathodic peak potentials (Epc) remain nearly similar for all electrodes, suggesting that the main improvement arises from facilitated anodic oxidation kinetics. These results clearly indicate that the formation of a p\u0026ndash;n heterojunction between NiO and ZnFe₂O₄ plays a crucial role in lowering the oxidation potential and enhancing the electrochemical response toward H₂O₂.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe electrochemical kinetics of the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e redox reactions were further clarified by exploring the influence of scan rate on the anodic and cathodic peak currents. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea demonstrate the CV curves of the NZF nanocomposite\u0026ndash;modified electrode at different scan rates from 10 to 70 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in 0.1 M PBS (pH 10) containing 50 \u0026micro;M H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. With increasing scan rate, both anodic and cathodic peak currents increase progressively, indicating enhanced electrochemical activity. The linear increase in peak current with scan rate suggests that the electrochemical oxidation of H₂O₂ is predominantly a surface-controlled process at the modified electrode. Additionally, a slight shift in peak potentials toward positive and negative directions is observed at higher scan rates, which is characteristic of quasi-reversible electron transfer kinetics. The well-defined redox peaks even at higher scan rates demonstrate the good electrochemical stability of the NZF nanocomposite. Overall, these results confirm efficient charge transfer and strong electrocatalytic behavior of the composite toward H₂O₂ sensing. Furthermore, there is a good linear relationship between the redox peak currents vs. scan rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb), indicating that both the oxidized and reduced forms are confined to the surface, confirming the surface controlled pseudocapacitive behaviour.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e3.14. Optimization of electrochemical parameters:\u003c/h2\u003e \u003cp\u003eIn order to achieve high electrochemical sensitivity, wide linear range, and low limit of detection for the determination of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the DPV technique was used (Ning et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018\u003c/span\u003e and Zhou X et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Prior to the optimization stage, the DPV oxidation peak current and DPV reduction peak current of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e need to be compared due to the electrochemical reaction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e occurring at the NZF nanocomposite electrode being a reversible process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea depicts the DPV behaviors of electrochemical oxidation and reduction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at the NZF nanocomposite electrode. The two peaks at 0.41 V and 0.5 V can be attributed to the electro-oxidation and electro-reduction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e molecules, respectively. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb, the oxidation peak current of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (12.15 mA) was \u0026sim;1.3-fold larger than that of the reduction peak current of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (9.0 mA). Therefore, the electrochemical oxidation process using the DPV technique was chosen to achieve the highest analytical performance toward the detection of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea illustrates the effect of solution pH on the DPV response of the NZF nanocomposite toward H₂O₂ detection over the pH range 7\u0026ndash;13. The oxidation peak current increases gradually from pH 7 and reaches a maximum around pH 10, indicating enhanced electrocatalytic activity in alkaline medium. This improvement is attributed to the increased availability of OH⁻ ions, which facilitates faster H₂O₂ oxidation kinetics. Beyond pH 10, a slight decrease in peak current is observed, possibly due to excessive OH⁻ adsorption and partial surface passivation of the electrode. Additionally, the peak potential shifts with pH, confirming the involvement of proton-coupled electron transfer in the sensing mechanism. Overall, the results indicate that mildly alkaline conditions (around pH 10) are optimal for sensitive H₂O₂ detection using the NZF nanocomposite.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e3.15. Electrochemical determination of H\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eat the NZF nanocomposite electrodes.\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eThe electrochemical sensing performance of the proposed NZF nanocomposite electrodes towards the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e detection was evaluated by the DPV technique under the optimized conditions. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb shows the DPV curves of different concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e ranging from 5 to 500 mM. As expected, the oxidation peak current of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e increased with the rising concentrations. The resulting calibration plots exhibited a good linear relationship between the oxidation peak currents and concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThe limit of detection (LOD) of the proposed electrochemical sensor was determined to be 2 \u0026micro;M. Furthermore, from the obtained slope value, the electrochemical sensitivity of the ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e -based electrochemical sensor was calculated to be 5 \u0026micro;A mM\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The analytical parameters of the NZF nanocomposite based electro chemical sensor for the detection of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e are compared with those reported in the recent literature (Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These outcomes indicate that the proposed NZF nanocomposite based electrochemical sensor exhibited an excellent performance towards the electro-oxidation of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e with high electrochemical sensitivity, comparatively low limit of detection, and wide linear response ranges.\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\u003eComparison of NZF with other H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e sensors based on different materials\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElectrode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDetection limit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSensitivity\u003c/p\u003e \u003cp\u003e(\u0026micro;A mM\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLinear range\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRef.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePt/ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/rGO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.1 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e87.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.0005-10.2 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Ning L et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAuNPs@Gr/NiF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.05\u0026ndash;1.75 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Wang X et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2017\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAg@ TiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.43 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e--\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.001-10 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Khan MM et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2013\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePd/ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/rGO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.12 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e--\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.025\u0026ndash;10.2 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Ning L et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2017\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZn\u003csub\u003e0.7\u003c/sub\u003eNi\u003csub\u003e0.3\u003c/sub\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e/GCE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.02\u0026ndash;10 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e(Zhao X et al. 2013)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNiO/ZnFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1\u0026ndash;200 \u0026micro;M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePresent work\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, a dualfunctional NZF nanocomposite was synthesized by low cost combustion method and investigated enhanced performance in both photocatalytic degradation and electrochemical sensing applications. Structural and morphological analyses confirmed the formation of a porous heterostructured composite with high surface area. The narrow band gap and p\u0026ndash;n heterojunction formation enhanced visible light absorption and promote stable charge separation. As a result, the NZF nanocomposite exhibited high photocatalytic degradation efficiency toward Brilliant Blue FCF dye with favorable reaction kinetics. Further the synthesized NZF nanocomposite revealed good electrocatalytic activity for hydrogen peroxide sensing. NZF shows wide linear detection range, low LOD and reduced overpotential. In conclusion, the NZF highlight its dual functionality and becomes a promising material for both environmental sensing applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthorship contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDhanyashree Savitha Vishwakumar: Investigation, Methodology, Writing \u0026ndash; original draft, Writing \u0026ndash; review \u0026amp; editing. Rajendra Prasad Shivalingappa: Conceptualization, Supervision, acquisition, Methodology, Visualization, Formal analysis, Writing \u0026ndash; review \u0026amp; editing. Jagadish Krishnegowda: Visualization, Formal analysis, review \u0026amp; editing. Jahnavi Hunasekatte Katamallappa: Review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eI gratefully thank and deeply acknowledge anyone who gave a hand to make this new discovery and work coming out to light.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Approval\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data supporting the findings of this study are included within the article. Additional data are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbou Zeid S, Leprince-Wang Y (2024) Advancements in ZnO-based photocatalysts for water treatment: a comprehensive review. Crystals 14(7):611. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/cryst14070611\u003c/span\u003e\u003cspan address=\"10.3390/cryst14070611\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAhmad T, Iqbal A, Halim SA, Uddin J, Khan A, El Deeb S, Al-Harrasi A (2022) Recent advances in electrochemical sensing of hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) released from cancer cells. 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J Photochem Photobiol A 390:112305. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jphotochem.2019.112305\u003c/span\u003e\u003cspan address=\"10.1016/j.jphotochem.2019.112305\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStatements \u0026amp; Declarations\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":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"NiO–ZnFe₂O₄ nanocomposite, p–n heterojunction, Photocatalytic degradation, Brilliant Blue dye, Hydrogen peroxide sensor, Electrochemical sensing","lastPublishedDoi":"10.21203/rs.3.rs-8906372/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8906372/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe design of single semiconductor nanocomposite for combined photocatalytic and sensing applications has gained considerable global attention. Herein, a NiO–ZnFe₂O₄ (NZF) nanocomposite was synthesized via a simple combustion method and systematically investigated photocatalytic and electrochemical properties. X-ray confirmed the coexistence of cubic NiO and spinel ZnFe₂O₄ phases, while SEM and EDX revealed a porous nanostructure. The band gap energy 1.6 eV, attributed to p–n heterojunction and interfacial interaction. The BET surface area of 205 m²g⁻¹ further enhanced the catalytic activity. Consequently, the NZF nanocomposite achieved 91% photocatalytic degradation of Brilliant Blue FCF under optimized conditions. Electrochemical sensing studies toward hydrogen peroxide using NZF electrodes demonstrated with a wide linear range (0.1–200 µM) and a low detection limit of 2 µM attributed to synergistic charge transfer and reduced overpotential at the heterojunction interface. Hence the NZF nanocomposite is a promising multifunctional material for environmental remediation and electrochemical sensing.\u003c/p\u003e","manuscriptTitle":"Stable NiO–ZnFe2O4 p–n heterojunction nanocomposite for dualfunctional photocatalysis and sensor applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-09 06:11:30","doi":"10.21203/rs.3.rs-8906372/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2026-04-08T09:23:53+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2026-03-09T07:33:49+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-03T20:45:56+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2026-03-03T12:54:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-02T04:49:31+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2026-02-27T05:41:39+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ce683e24-be59-4902-a6ad-287a3b422d37","owner":[],"postedDate":"March 9th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-08T09:37:31+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-09 06:11:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8906372","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8906372","identity":"rs-8906372","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}