Synthesis of Spinel-Type MCo2O4 (M = Cu, Ni, Fe, Mn) Adsorbents and Their Performance in Trace H2S Capture for Cultural Heritage Preservation

Synthesis of Spinel-Type MCo2O4 (M = Cu, Ni, Fe, Mn) Adsorbents and Their Performance in Trace H2S Capture for Cultural Heritage Preservation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Synthesis of Spinel-Type MCo 2 O 4 (M = Cu, Ni, Fe, Mn) Adsorbents and Their Performance in Trace H 2 S Capture for Cultural Heritage Preservation Nan Jia, Xinying Che, Peng Fu, Juxiang Yang, Ke Huang, Pengna Li, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9000416/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Trace hydrogen sulfide (H 2 S) causes irreversible deterioration of cultural relics even at low concentrations. To address the limitations of existing adsorbents in conservation environments, we developed Ni-doped Co 3 O 4 spinel nanosheets using a metal-organic framework precursor. The substitution of tetrahedral Co 2+ sites with Ni 2+ modulates the surface electronic structure, resulting in an adsorbed-to-lattice oxygen ratio O ads /O latt of 1.21. Density functional theory (DFT) calculations combined with experimental data indicate that these surface oxygen species promote electron transfer from H 2 S and facilitate oxidative dissociation. The NiCo 2 O 4 material exhibits a saturation capacity of 4.2 mmol g -1 at 25 °C, compared to 2.0 mmol g -1 for commercial activated carbon, and maintains 92% capacity after ten regeneration cycles. Crucially, in accelerated aging environments, the material achieves near-total suppression of sulfidation on silver coupons and lead white pigments, demonstrating its potential as a high-efficiency safeguard for cultural heritage. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Cultural relics are physical vestiges of human history and culture, embodying profound historical narratives and cultural significance. The long-term accumulation of trace hydrogen sulfide (H 2 S) in the microenvironments where cultural relics are preserved accelerates the irreversible deterioration of cultural heritage [1] [2]. Metallic relics are particularly vulnerable [3]. Upon interaction with H 2 S, the surface of bronze artifacts reacts to form thermodynamically stable copper(I) sulfide (Cu 2 S, K sp = 2.5 × 10 -48 ) [4]. The unit cell volume of Cu 2 S expands by approximately 26% compared to elemental copper, inducing internal stress, cracking in the substrate, and the formation of a black, powdery corrosion layer [5]. In the presence of chloride ions, this process evolves into the characteristic deterioration known as "bronze disease," where copper(I) chloride (CuCl) is sulfidized into a porous Cu 2 S structure, ultimately leading to the structural disintegration of the artifact. Organic cultural relics are also threatened [6]. When the relative humidity exceeds 60%, H 2 S dissolves into the thin film of adsorbed water on their surfaces. The subsequent ionization (H 2 S ⇌ H + + HS - ) creates a localized weakly acidic environment with a pH of approximately 5.6 [7]. This acidity catalyzes the hydrolysis of the β-1,4-glycosidic bonds in cellulose, causing the degree of polymerization (DP) of paper to decrease from an initial value of 2000 ± 300 to about 500 ± 80 after aging, accompanied by a reduction in tensile strength exceeding 65% [8]. A more insidious form of biochemical erosion occurs on stone substrates. Sulfur-oxidizing bacteria, such as acidithiobacillus thiooxidans, utilize H 2 S as an electron donor in their metabolism, producing sulfuric acid (2H 2 S + 4O 2 → 2H 2 SO 4 ) [9]. The resulting strongly acidic environment (pH < 2.0) dissolves calcite (CaCO 3 ), leading to the crystallization of gypsum (CaSO 4 ·2H 2 O) [7]. The crystallization pressure associated with a volume expansion of about 135% can fracture rock pores. Concurrently, lead-based pigments, such as lead white [2PbCO 3 ·Pb(OH) 2 ] [10], are converted into friable lead sulfate (PbSO 4 ), causing the detachment of painted layers in murals. These pervasive erosive effects render H 2 S, even at parts-per-billion (ppb) levels [11], a latent threat to the long-term preservation of cultural relics. There is an urgent need to develop ambient-temperature purification materials with high adsorption capacity and selectivity to mitigate this risk [12]. Existing adsorption systems still face significant limitations in addressing the specific requirements for H 2 S purification in cultural heritage preservation environments, including the need for ambient temperature operation, effectiveness at low concentrations, and high selectivity [13]. While wet scrubbing and thermal catalytic oxidation are suitable for industrial desulfurization, their high energy consumption (requiring temperatures >150°C) and tendency to generate byproducts that may damage artifacts restrict their use [14]. Although activated carbon and molecular sieves offer potential for room-temperature adsorption, their surface chemical inertness and sensitivity to humidity result in poor selectivity (H 2 S adsorption capacity typically <50 mg/g). In contrast, spinel-type transition metal oxides (AB 2 O 4 ) stand out due to the intrinsic tunability of their crystal structure [15]. The topological coupling between tetrahedral (A-site) and octahedral (B-site) interstices in their lattice enables the construction of a gradient network of Lewis acid sites, significantly enhancing the capture capability for the lone-pair electrons in H 2 S molecules [16]. More importantly, the selective occupation of A- or B-sites by heterovalent transition metal ions (e.g., Ni 2+ , Cu 2+ ) allows for targeted regulation of oxygen vacancy (V O ) concentration and electron transfer pathways [17]. For instance, the substitution of tetrahedral Co 2+ (ionic radius r = 0.74 Å) by Ni 2+ (r = 0.69 Å) induces lattice contraction, promoting the conversion of surface lattice oxygen (O 2 − ) into chemically adsorbed oxygen species (O 2 − /O − ). This process enhances the low-temperature oxidation activity toward H 2 S. In this study, a defect engineering strategy is developed to construct high‑performance H 2 S scavengers based on Ni‑doped Co 3 O 4 spinel nanosheets (Figure 1). Through selective substitution of tetrahedral Co 2+ sites with Ni 2+ , the surface electronic structure is effectively modulated, and the ratio of surface adsorbed oxygen (O ads ) to lattice oxygen (O latt ) is optimized. Combined experimental characterization and density functional theory calculations elucidate a distinct surface oxygen activation–electron transfer mechanism. The results indicate that the enhanced Lewis acidity and increased oxygen vacancy concentration promote the rapid oxidative dissociation of H 2 S molecules. Furthermore, standard accelerated aging tests, namely Oddy tests, confirm the exceptional performance of the material in inhibiting sulfidation of sensitive cultural heritage materials, such as silver and lead white, under trace H 2 S exposure. This work not only offers atomic level insights into the gas solid interfacial reactions of spinel oxides, but also establishes an efficient and reliable paradigm for the preventive conservation of museum collections. Experimental section Adsorbent Synthesis. Synthesis of Co 3 O 4 Spinel: The Co 3 O 4 spinel was synthesized via a metal–organic framework-derived route. First, cobalt(II) acetate tetrahydrate ((CH 3 COO) 2 Co·4H 2 O, 0.25 mmol, ca. 62.2 mg) was dissolved in 15 mL of deionized water to form Solution A. Separately, terephthalic acid (H 2 BDC, 0.125 mmol, 20.8 mg) was dissolved in 15 mL of N,N-dimethylacetamide (DMA) to form Solution B. Under stirring, Solution B was added dropwise into Solution A, and the mixture was stirred for 10 min to obtain a homogeneous solution. The resulting mixture was transferred into a 50 mL Teflon-lined stainless-steel autoclave and heated at 150 °C for 3 h. After natural cooling, the precipitate was collected, washed several times with water and methanol, and dried at 60 °C for 12 h to obtain the precursor. Finally, the precursor was placed in a tube furnace and calcined at 500 °C for 4 h under air atmosphere with a heating rate of 5 °C min -1 , yielding the final Co 3 O 4 product. Synthesis of Doped Spinel Oxides (MCo 2 O 4 , M = Cu, Ni, Fe, Mn): The procedure for preparing the doped spinels was essentially the same as that described for Co 3 O 4 , except that corresponding metal salts were added to Solution A together with cobalt acetate in stoichiometric ratios. For CuCo 2 O 4 , copper(II) acetate monohydrate (Cu 2 (OAc) 4 (H 2 O) 2 , 0.125 mmol, ca. 34.9 mg) was introduced. For NiCo 2 O 4 , nickel(II) acetate tetrahydrate (Ni(CH 3 COO) 2 ·4H 2 O, 0.125 mmol, ca. 31.1 mg) was added. For CoFe 2 O 4 , basic iron(III) acetate (Fe(OH)(CH 3 COO) 2 , 0.5 mmol, ca. 119.0 mg) was used. For CoMn 2 O 4 , manganese(II) acetate tetrahydrate ((CH 3 COO) 2 Mn·4H 2 O, 0.5 mmol, ca. 122.5 mg) was incorporated. All subsequent steps, including hydrothermal reaction, washing, drying, and calcination, were carried out under identical conditions to those employed for the pure Co 3 O 4 sample. Adsorption Performance Evaluation. Static Adsorption Isotherms: H 2 S adsorption isotherms were acquired at 0 °C, 25 °C, and 40 °C under pressures ranging from 0 to 1 bar using a Micromeritics 3Flex analyzer coupled with a thermostatic bath (Laboto CC‑2020E). Before measurement, each sample (50 mg) was degassed under vacuum at 180 °C for 6 h to remove physisorbed water and residual impurities [18]. Dynamic Breakthrough Tests: The dynamic H 2 S adsorption performance of NiCo 2 O 4 was examined in a fixed‑bed reactor system. The setup included: (i) a gas‑blending station with calibrated mass‑flow controllers delivering 50 ± 2 ppm H 2 S in N 2 ; (ii) a quartz adsorption column (8 mm i.d.) packed with adsorbent supported on a sintered quartz frit; and (iii) a laser gas analyzer monitoring the effluent H 2 S concentration with 0.1 ppm resolution. Prior to testing, 50 mg of the adsorption was activated in situ under N 2 flow (50 mL·min -1 ) at 120 °C for 8 h. Quartz‑wool plugs ensured uniform gas distribution, and PID‑controlled heating maintained isothermal conditions at 25 ± 0.5 °C. The H 2 S/N 2 mixture (300 ± 5 mL·min -1 ) was passed through the adsorbent bed at atmospheric pressure. The breakthrough time was defined as the point when the outlet H 2 S concentration reached 5% of the inlet value, following ASTM D6646‑14. Cyclic Regeneration Performance: Ten consecutive H 2 S adsorption–regeneration cycles were performed at 0 °C to assess the recyclability of the materials. Before each adsorption run, the samples were regenerated by vacuum degassing at 180 °C for 4 h to restore active sites and minimize experimental scatter. Identical initial conditions (50 ppm H 2 S/N 2 , 300 mL·min -1 flow rate) were used in all trials to ensure reproducibility. The adsorption‑capacity retention rate was calculated after each regeneration step to quantify any performance loss. Modified Oddy Test Methodology. An optimized Oddy‑test protocol was employed to evaluate the H 2 S‑suppression capability of NiCo 2 O 4 under conditions relevant to cultural‑heritage conservation. Custom‑designed, sealed borosilicate‑glass reactors (50 mL nominal volume) were placed in a precision climatic chamber providing tight environmental control (±1 °C, ±2% RH, calibrated per NIST SP 260‑136) [19]. Simulated artifact specimens consisted of: (i) mirror‑polished silver coupons (>99.9% purity, 10 × 10 × 0.1 mm) cleaned by sequential ethanol ultrasonication and N 2 ‑jet drying, and (ii) glass slides uniformly coated with lead‑white pigment (PbCO 3 ) at 50 ± 5 μm thickness to mimic historical paint layers. Six experimental groups were compared: a blank control (no adsorbent), NiCo₂O₄ (50 mg), commercial activated carbon (AC, 50 mg), CuCo 2 O 4 (50 mg), CoFe 2 O 4 (50 mg) and CoMn 2 O 4 (50 mg). All specimens were subjected to accelerated aging at 30 °C and 60% relative humidity for 28 days, simulating long‑term conservation environments. Metallic and pigmented samples were mounted vertically inside the reactors using inert polytetrafluoroethylene holders, avoiding direct contact with adsorbents while allowing free diffusion of gaseous H 2 S. This configuration isolated vapor‑phase corrosion‑inhibition mechanisms, excluding potential artifacts from direct material contact. Colorimetric Analysis of Simulated Specimens. Color variations in the pigment layers of simulated specimens were quantified using the CIE L*a*b* colorimetric system. In this system, the L* coordinate indicates lightness, with higher values corresponding to brighter surfaces [20]. The a* and b* coordinates represent chromaticity: a* denotes position along the red‑green axis (positive for red, negative for green), and b* denotes position along the yellow‑blue axis (positive for yellow, negative for blue). The total color difference (ΔE) was calculated using the following expression: where ΔL , Δa, and Δb* are the differences between the initial and final values of each coordinate. The ΔE value thus provides a single metric for the overall magnitude of color change. DFT theoretical calculations. To elucidate the atomic‑scale adsorption mechanism and electronic‑structure evolution during H 2 S interaction with NiCo 2 O 4 , density functional theory (DFT) calculations were carried out using the DMol 3 module in Materials Studio 2020 (BIOVIA Inc.) [14]. The Perdew–Burke–Ernzerhof (PBE) generalized‑gradient approximation (GGA) functional was employed, and Grimme’s DFT‑D3 method with Becke–Johnson damping was included to account for van der Waals interactions. Norm‑conserving pseudopotentials described the core electrons, while valence electrons were expanded in a double‑numeric polarized (DNP) basis set with a real‑space cutoff of 5.0 Å. Geometry optimizations were considered converged when the energy change was below 1×10 -5 Ha, the maximum force component <0.002 Ha/Å, and the maximum atomic displacement <0.005 Å. The Brillouin zone was sampled with a 4×4×1 Monkhorst–Pack k‑point grid for structural relaxation and an 8×8×1 grid for static electronic‑property calculations, ensuring energy convergence within 1 meV/atom. The Fermi level was treated using the Methfessel–Paxton smearing scheme with a width of 0.005 Ha. Instruments. The structural and chemical features of the samples were examined using a combination of complementary techniques. Crystal phases were identified by X‑ray diffraction (XRD, Rigaku D/max‑rC, Cu Kα radiation). Surface elemental states and depth‑resolved composition were analyzed with X‑ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250, Al Kα source) combined with Ar + sputtering. Morphology and elemental distribution were visualized by field‑emission scanning electron microscopy (FE‑SEM, Hitachi SU‑8020). Results and Discussion Structural characterization of doped spinel oxides All samples exhibit nanoparticle morphologies derived from the MOF‑precursor route. As Figure 2, the Co 3 O 4 particles show relatively uniform quasi‑spherical shapes with slight aggregation. NiCo 2 O 4 and CuCo 2 O 4 display more homogeneous particle‑size distributions and smoother surfaces. CoMn 2 O 4 presents a porous, interconnected network. CoFe 2 O 4 consists of notably larger, well‑faceted polyhedral particles. The crystal structure and phase purity of the synthesized series of spinel oxide catalysts were systematically investigated by XRD, as shown in the Figure 3A. The diffraction peaks of pure-phase Co 3 O 4 NPs are located at 19.1 o , 31.3 o , 36.8 o , 44.8 o , 55.7 o , 59.3 o , and 65.2 o , which correspond perfectly to the standard pattern of the spinel structure (JCPDS No. 42-1467) and are indexed to the (111), (220), (311), (400), (422), (511), and (440) crystal planes, respectively. This confirms the successful synthesis of well-crystallized Co 3 O 4 nanoparticles. After the introduction of secondary metals (Ni, Cu, Mn, Fe), the XRD patterns of the resulting samples still exhibit a dominant spinel phase, with systematic shifts in peak positions due to lattice distortion induced by the Jahn–Teller effect [21]. Additionally, weak secondary diffraction peaks are observed in some patterns: around 44.5 o for the Ni-doped sample, near 34.8 o and 38.9 o for the Cu-doped sample, around 33.8 o and 60.1 o for the Mn-doped sample, and near 34.8 o and 50.2 o for the Fe-doped sample [22]. These signals are assigned to NiO, CuO, (Co,Mn) 2 O 4 , and Fe 2 O 3 phases, respectively. These results indicate that the heterometal atoms have been successfully introduced into the material system, confirming the incorporation of Ni, Cu, Fe, and Mn into the spinel lattice and the successful preparation of Co 3 O 4 , CuCo 2 O 4 , NiCo 2 O 4 , CoFe 2 O 4 , and CoMn 2 O 4 . As shown in the Figure 3B, the chemical structure of the catalysts was further analyzed by FT-IR. For Co 3 O 4 NPs, CuCo 2 O 4 , NiCo 2 O 4 , CoFe 2 O 4 , and CoMn 2 O 4 , two characteristic absorption bands attributed to M–O (where M represents metal ions) are observed in the range of 568–668 cm -1 . The band near 668 cm -1 is assigned to the vibrational stretching of M 2+ –O bonds in tetrahedral sites, while the band around 568 cm -1 corresponds to M 3+ –O vibrations in octahedral sites [23]. Notably, compared with pure Co 3 O 4 NPs, distinct changes in the characteristic spinel bands are observed upon the introduction of different heteroatoms, reflecting the influence of doping on the spinel structure of Co 3 O 4 . To elucidate the intrinsic relationship between adsorption performance and material composition as well as surface oxygen chemistry, the elemental composition and chemical states of all catalysts were systematically characterized using XPS [23, 24]. Figure 4 presents the XPS spectra of Co 3 O 4 , CuCo 2 O 4 , NiCo 2 O 4 , CoFe 2 O 4 , and CoMn 2 O 4 , including the fine structures of O 1s, Co 2p, Ni 2p, Cu 2p, Fe 2p, and Mn 2p. First, the composition of surface oxygen species was resolved by analyzing the O 1s spectra (Figure 4A). Taking Co 3 O 4 as an example, its spectrum can be deconvoluted into three peaks: the binding energies at 533.89 eV, 532.12 eV, and 530.59 eV are assigned to surface hydroxyl groups/adsorbed water molecules (O w ), chemically adsorbed oxygen (O ads ), and lattice oxygen (O latt ) [25], respectively. The ratio of the peak area of O ads to that of O latt (O ads /O latt ) was calculated for each material and is listed in Figure 4G. This ratio varies significantly with the doped metal, following the order: NiCo 2 O 4 (1.21) > CuCo 2 O 4 (0.77) > CoMn 2 O 4 (0.67) > Co 3 O 4 (0.57) > CoFe 2 O 4 (0.21). This order aligns well with their activity trends in H 2 S catalytic oxidation, indicating that surface adsorbed oxygen (O ads ) plays a dominant role in the reaction. Second, the Co 2p spectra (Figure 4B) reveal the valence distribution of cobalt ions. All samples exhibit characteristic doublet peaks for Co 2+ and Co 3+ . Quantitative analysis shows that the introduction of Fe and Mn increases the relative content of Co 3+ (with Co 3+ fractions of 0.59 in CoFe 2 O 4 and 0.61 in CoMn 2 O 4 ), suggesting that Fe and Mn tend to occupy low-valent cobalt sites [26]. Conversely, the introduction of Ni and Cu increases the proportion of Co 2+ (with Co 3+ fractions decreasing to 0.33 in NiCo 2 O 4 and 0.23 in CuCo 2 O 4 ), indicating that Ni and Cu primarily occupy high-valent cobalt sites. This result is consistent with the variations in oxygen species activity reflected in the O 1s spectra. The occupancy of different metal ions in the spinel structure significantly alters the local chemical environment of Co ions, thereby exerting a decisive influence on the adsorptive performance. Furthermore, the 2p spectra of other metal elements (Figure 4C–F) confirm the successful incorporation of heteroatoms. NiCo 2 O 4 shows characteristic peaks of Ni 2+ at 855.3 eV and 872.8 eV; CuCo 2 O 4 shows characteristic peaks of Cu 2+ at 933.5 eV and 953.4 eV; CoMn 2 O 4 shows characteristic peaks of Mn 3+ at 641.9 eV and 653.2 eV; and CoFe 2 O 4 shows characteristic peaks of Fe 3+ at 710.8 eV and 724.3 eV [27]. These signals indicate that the heterometal atoms have been successfully incorporated into the spinel lattice, forming structurally uniform solid solutions rather than simple physical mixtures. A comparative analysis of the surface chemical states of a series of spinel oxides (Figure G–H) reveals that NiCo 2 O 4 exhibits unique surface characteristics: its ratio of surface adsorbed oxygen to lattice oxygen (O ads /O latt ) is as high as 1.21, the highest among all materials, indicating the enrichment of highly reactive adsorbed oxygen species (e.g., O 2 ⁻, O⁻) on its surface [28]. Concurrently, its lattice oxygen binding energy is as low as 529.52 eV, suggesting weak bonding between O latt and the substrate, higher reactivity, and a greater propensity to participate in oxidation reactions. Additionally, its Co 3+ /(Co 3+ + Co 2+ ) and Ni 2+ /(Ni 3+ + Ni 2+ ) ratios are 0.33 and 0.54, respectively, constituting an ideal mixed-valence system that provides a platform for rapid electron transfer. These experimental data collectively demonstrate that NiCo 2 O 4 possesses a “highly active and dynamic” surface, laying a structural foundation for its efficient adsorption and oxidation of H 2 S. Characterization of H 2 S adsorption performance The H 2 S adsorption performance of the prepared series of doped Co 3 O 4 -based spinel materials (including Co 3 O 4 , CuCo 2 O 4 , NiCo 2 O 4 , CoFe 2 O 4 , and CoMn 2 O 4 ) was systematically evaluated using static volumetric and dynamic breakthrough methods, with commercial activated carbon (AC) included for comparison. The study focused on the adsorption capacity, kinetic behavior, cyclic stability, and the influence of temperature on adsorption performance. The equilibrium H 2 S adsorption capacity of the materials was measured at 25 °C and 1 bar using a Micromeritics 3Flex analyzer. As shown in Figure 5A, different cation dopants significantly affected the adsorption performance. NiCo 2 O 4 nanosheets exhibited the highest adsorption capacity of 4.2 mmol g -1 , substantially exceeding that of pure-phase Co 3 O 4 (2.2 mmol g -1 ) and commercial AC (2.0 mmol g -1 ). The capacities of CuCo 2 O 4 , CoMn 2 O 4 , and CoFe 2 O 4 were 3.2 mmol g -1 , 2.7 mmol g -1 , and 2.3 mmol g -1 , respectively. This performance trend (NiCo 2 O 4 > CuCo 2 O 4 > CoMn 2 O 4 > CoFe 2 O 4 > Co 3 O 4 ) aligns closely with the relative abundance of surface active oxygen species (O ads /O latt ratio) obtained from prior XPS characterization (Figure 3G), confirming the dominant role of surface chemisorbed oxygen (O ads ) in the capture and oxidative conversion of H 2 S. Under lower partial-pressure conditions (0.1 bar), which better simulate actual conservation environments, NiCo 2 O 4 maintained a capacity of 0.9 mmol g -1 , demonstrating its potential for low-concentration H 2 S purification. Dynamic breakthrough tests are essential for evaluating adsorbent performance under practical flow conditions. The breakthrough curves of the materials were measured at 25 °C, 50 % RH (Figure 5B). NiCo 2 O 4 showed the best performance, with a long breakthrough time (C/C₀ = 5 %) of 55 min and a steep, well-defined S‑shaped breakthrough curve, indicating fast adsorption kinetics and superior mass transfer. CuCo 2 O 4 exhibited a breakthrough time of 46 min. In contrast, pure‑phase Co 3 O 4 and commercial AC showed significantly shorter breakthrough times of 31 min and 30 min, respectively. The AC curve displayed a shallower slope, suggesting higher mass‑transfer resistance. The excellent dynamic performance of NiCo 2 O 4 is attributed to its unique two‑dimensional nanosheet morphology, which provides abundant accessible surface sites and short diffusion pathways, together with its high O ads concentration that facilitates rapid surface reactions. The recyclability of an adsorbent is critical for practical application. The best‑performing NiCo 2 O 4 was subjected to ten consecutive adsorption‑regeneration cycles at 25 °C. After each saturation, the material was regenerated under a N 2 flow at 150 °C for 2 h. As shown in Figure 5C, after ten cycles, the H 2 S adsorption capacity of NiCo 2 O 4 decreased from an initial 4.2 mmol g -1 to 3.5 mmol g -1 , corresponding to a retention rate of 92.1 %, demonstrating good regeneration stability. This robust cycling performance stems from the excellent thermal and chemical stability of the spinel structure, which helps preserve active sites over repeated regeneration. Temperature plays a crucial role in adsorption processes. For NiCo 2 O 4 , the H 2 S adsorption capacity increased from 4.2 mmol g -1 at 0 °C to 4.8 mmol g -1 at 40 °C (Figure 5D). This positive correlation with temperature suggests that the adsorption is predominantly chemisorption‑driven, as the elevated temperature provides the necessary activation energy to overcome the energy barrier for surface reaction, thereby enhancing both the adsorption rate and capacity within this temperature range. Mechanistic investigation of H 2 S adsorption DFT calculations elucidated the electron transfer and H 2 S activation pathway during the initial adsorption stage. To understand the role of the aforementioned surface properties at the atomic scale, systematic DFT computations were performed. First, the differential charge density map (Figure 6A) visually illustrates the electron redistribution. After adsorption, the H 2 S molecule, particularly around the S atom, shows a clear reduction in electron density, while the neighboring O ads exhibits an increase in electron density. A continuous charge bridge forms between them, directly demonstrating electron transfer from the S atom of H 2 S to the surface O ads , accompanied by significant covalent interaction. Orbital-projected density of states (PDOS) analysis (Figure 6B) clarifies the orbital origin of this electron transfer from the perspective of band structure. After adsorption, the density of states near the Fermi level (EF) for the S 3p orbitals decreases markedly, whereas new occupied states appear near EF for the O ads 2p orbitals. This indicates strong hybridization between S 3p and O ads 2p, forming covalent bonding and promoting electron flow from H 2 S to the surface. Second, the XPS O 1s spectra (Figure 6C) provide further chemical evidence for the electron transfer. After adsorption, the binding energy of the characteristic peak assigned to O ads shifts significantly from 531.5 eV to 529.8 eV. The decrease in binding energy indicates that O ads gains electrons, leading to enhanced electron cloud density and a weaker shielding effect, which is consistent with the charge density analysis. Simultaneously, EPR measurements (Figure 6D) reveal changes in the unpaired electron state during adsorption. After adsorption, the signal intensity corresponding to oxygen vacancies and related defects (g = 2.003) decreases by more than 40%, indicating that the empty orbitals of O ads become occupied by electrons and their paramagnetism weakens, further supporting the conclusion of electron transfer from H 2 S to O ads . Integrating the above experimental and theoretical evidence, we propose a comprehensive adsorption-oxidation mechanism for H 2 S on NiCo 2 O 4 (Figure 6E). The mechanism begins with the strong chemisorption of the H 2 S molecule via its S atom onto the octahedral Co/Ni sites possessing a high d‑band center on the surface. Subsequently, the lone‑pair electrons from H 2 S rapidly transfer to neighboring O ads species, accomplishing initial activation and dissociation. The dissociation products are then deeply oxidized by adjacent highly reactive lattice oxygen (O latt ), generating oxygen vacancies. Finally, gaseous oxygen molecules fill these oxygen vacancies, regenerating the surface active oxygen species. This study clarifies that the outstanding performance of NiCo 2 O 4 originates from its unique Ni–Co synergistic effect, which optimizes the electronic structure of the material, endowing it simultaneously with strong H 2 S adsorption capacity, efficient initial oxidation activity, and sustainable deep oxidation and regeneration capability. Analysis of Oddy Test results To comprehensively evaluate the application safety and protective efficacy of the prepared doped Co 3 O 4 -based spinel materials in authentic cultural heritage preservation environments, this study employed a modified standard Oddy test method. Under accelerated aging conditions (30°C, 60% relative humidity), the materials' sustained H 2 S purification capacity and their protective effect on sensitive heritage simulants were systematically assessed. Polished silver coupons and simulated specimens coated with lead white pigment (2PbCO 3 ·Pb(OH) 2 ) were placed in sealed containers and co-exposed to a low-concentration H 2 S environment (initial concentration ~50 ppm) for 28 days. A blank control group (no adsorbent), a commercial activated carbon (AC) group, and experimental groups containing the best-performing NiCo 2 O 4 and CuCo 2 O 4 were established for comparison. As Figure 7A, after 28 days, the silver coupon in the blank control group was completely covered by black Ag 2 S, with its lightness value (ΔL*) plummeting from an initial 96.7 to 58.3, demonstrating the strong corrosiveness of H 2 S towards silver. The AC group provided limited protection, showing a ΔL* decrease of 22.5 (to 74.2) and the appearance of uneven dark spots on the surface, indicating insufficient adsorption capacity for long-term testing and localized H 2 S penetration. The CuCo 2 O 4 group showed significantly reduced corrosion with a ΔL* decrease of 9.8 (to 86.9), although slight discoloration was still visible. The NiCo 2 O 4 group exhibited near-complete protection, with a minimal ΔL* change of only 4.1 (to 92.6). The silver surface retained its metallic luster without significant visual difference from its initial state, proving this material's highly efficient and sustained capability to remove environmental H 2 S and completely block the silver sulfidation corrosion pathway. The corrosion of lead white samples manifested as a color change from white to black (Figure 7B). The blank control sample turned completely black by the test's end, with its yellow-blue coordinate (Δb*) dramatically decreasing from 26.1 to -3.5 (a change of -29.6). The AC group sample exhibited extensive blackening, with a Δb* decrease of 17.3 (to 8.8), indicating unsatisfactory protective performance. The CuCo 2 O 4 group offered some protection, resulting in a Δb* decrease of 10.5 (to 15.6), but scattered black spots were still observed. The NiCo 2 O 4 group again demonstrated the best protective performance. The lead white sample color remained stable with a negligible Δb* change (within ±1.0), and no blackening was visible to the naked eye, confirming that H 2 S in the environment was completely adsorbed and did not react with the pigment. XPS spectra of the silver surfaces corroborated the macroscopic corrosion observations (Figure 7C). A distinct S 2p signal, corresponding to a sulfur content of 7.2 at.%, remained evident in the AC group. In contrast, the silver coupon protected by NiCo 2 O 4 exhibited only a faint sulfur signal (1.8 at.%), confirming its superior corrosion inhibition at the chemical-state level. For the lead white samples, XPS analysis further tracked the evolution of their chemical states (Figure 7D). While the sulfur content reached 5.1 at.% in the AC group, the S 2p signal intensity in the NiCo 2 O 4 protected sample remained near the background level (<0.5 at.%). These results confirm at the molecular scale that NiCo 2 O 4 effectively suppresses the sulfidation reaction. Conclusion In summary, we have developed a high-performance H 2 S scavenger based on defect-rich NiCo 2 O 4 nanosheets via a solvothermal-calcination strategy. The substitution of tetrahedral Co 2+ with Ni 2+ successfully modulated the surface electronic environment, achieving an optimal O ads /O latt ratio of 1.21, which serves as the structural basis for enhanced reactivity. Consequently, the NiCo 2 O 4 scavenger exhibits a superior saturation adsorption capacity of 4.2 mmol/g at 25 °C, outperforming commercial activated carbon (1.6 mmol/g). Dynamic breakthrough experiments further confirmed its kinetic advantage, yielding a prolonged protection time of 55 min under continuous flow, significantly longer than the 48 min observed for activated carbon. Mechanistically, this performance is driven by the rapid electron transfer from H 2 S to surface oxygen species and the subsequent regeneration of oxygen vacancies, as evidenced by DFT calculations and XPS analysis. Most importantly, in simulated museum environments, the material demonstrated exceptional preventive conservation capabilities: the total color difference of silver artifacts was maintained at 4.1, and the chromaticity shift of lead white pigment was negligible, effectively blocking sulfidation pathways. This work provides a quantifiable, atomic-level paradigm for designing advanced functional materials for the preservation of cultural heritage. Declarations Acknowledgements Not applicable. Author contributions Conceptualization, N.J. and P.F.; resources, software, investigation, formal analysis, X.C. and P.L.; methodology, data curation, K.H.; writing-original draft preparation, N.J; visualization, K.H.; supervision, project administration, and funding acquisition, N.J. and J.Y.; All authors have read and agreed to the published version of the manuscript. Funding This research was supported by Young Talent fund of University Association for Science and Technology in Shaanxi, China (20230608), Shaanxi Provincial Natural Science Foundation (2024JC-YBQN-0148, 2023-JC-QN-1007), Special Research Project of Shaanxi Provincial Department of Education (22JKO531), Xi'an Science and Technology Program Project (25FWQY03, 25WTGJ02, 25PTZX09), the Natural Science Foundation of Shaanxi Province (2025JC-YBMS-177), Key Research and Development Project of Shaanxi Provincial Science and Technology Department (2024SF-YBXM-683), Undergraduate Innovation and Entrepreneurship Training Program Project (DC2026037), Xi'an University of Arts and Sciences Cultural Relics Microbiology Interdisciplinary Construction Platform. Availability of data and materials The datasets used and/or analysed during the current study are available fromthe corresponding author on reasonable request. 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Li, Fluorine Engineering Induces Phase Transformation in NiCo2O4 for Enhanced Active Motifs Formation in Oxygen Evolution Reaction, ADVANCED MATERIALS, 37 (2025) 2418058. J.X. Zheng, X.F. Peng, Z. Xu, J.B. Gong, Z. Wang, Cationic Defect Engineering in Spinel NiCo 2 O 4 for Enhanced Electrocatalytic Oxygen Evolution, ACS CATALYSIS, 12 (2022) 10245-10254. Y.Q. Bao, M. Qin, Y.K. Yu, L.M. Zhang, H.J. Wu, Facile fabrication of porous NiCo2O4 nanosheets with high adsorption performance toward Congo red, Journal of Physics and Chemistry of Solids, 124 (2019) 289-295. X.N. Li, Y.P. Li, L. Wang, J. Liu, L. Chen, X. Zhu, J.C. Hao, Y.L. Ma, J.H. Li, X. Wu, Efficient Regeneration of Waste Styrene Adsorption Carbon Catalyzed by Spinel NiCo 2 O 4 Active Sites and Cyclic VOC Adsorption and Desorption Performance, Langmuir, 41 (2025) 20579-20590. M.A. Bhatti, S. Kumar, A. Tahira, A.L. Bhatti, Z.A. Ujjan, M.A. Jakhrani, U. Aftab, R.H. Alshammari, A. Nafady, E. Dawi, M. Emo, B. Vigolo, A. 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Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 23 Apr, 2026 Reviews received at journal 15 Apr, 2026 Reviewers agreed at journal 26 Mar, 2026 Reviews received at journal 09 Mar, 2026 Reviewers agreed at journal 05 Mar, 2026 Reviewers invited by journal 05 Mar, 2026 Editor assigned by journal 04 Mar, 2026 Submission checks completed at journal 04 Mar, 2026 First submitted to journal 01 Mar, 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-9000416","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":603211471,"identity":"0e9d8efb-1d34-4401-82a4-8b7a72a8114c","order_by":0,"name":"Nan Jia","email":"","orcid":"","institution":"Xi'an University of Arts and Sciences","correspondingAuthor":false,"prefix":"","firstName":"Nan","middleName":"","lastName":"Jia","suffix":""},{"id":603211472,"identity":"14bcb05d-403f-40ae-a942-dd4ae135ddf0","order_by":1,"name":"Xinying Che","email":"","orcid":"","institution":"Xi'an University of Arts and Sciences","correspondingAuthor":false,"prefix":"","firstName":"Xinying","middleName":"","lastName":"Che","suffix":""},{"id":603211473,"identity":"b6d1a00d-bf74-4e07-8012-afb5952c7596","order_by":2,"name":"Peng Fu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyElEQVRIiWNgGAWjYBAC9gYwZQPlshGhhecAmEojXcthUrRI5B58XPDrvL25dI8Bw4eywwz8sxsIaclLNp7Zdztx55wzBowzzh1mkLhzAL8We4kcM2nentsJBjdyDJh52w4zGEgkELIlx/w3b885e7CWv0RqMWPm+XGAcQNICyNRWnjeJUvzNiQnbriRVnCw51w6j8QNQlrYcw9+5vljB3RY8sYHP8qs5fhnENAC1MTAwNgGYR6AcAkCkJo/RKgbBaNgFIyCkQsA+sxAi/m7v9AAAAAASUVORK5CYII=","orcid":"","institution":"Shaanxi Institute for the Preservation of Culture Heritage","correspondingAuthor":true,"prefix":"","firstName":"Peng","middleName":"","lastName":"Fu","suffix":""},{"id":603211474,"identity":"efd5c60f-3272-49cb-bce2-f75d542936cc","order_by":3,"name":"Juxiang Yang","email":"","orcid":"","institution":"Xi'an University of Arts and Sciences","correspondingAuthor":false,"prefix":"","firstName":"Juxiang","middleName":"","lastName":"Yang","suffix":""},{"id":603211475,"identity":"4710a588-360f-4cee-a6ef-7bc0bffe708d","order_by":4,"name":"Ke Huang","email":"","orcid":"","institution":"Xi'an University of Arts and Sciences","correspondingAuthor":false,"prefix":"","firstName":"Ke","middleName":"","lastName":"Huang","suffix":""},{"id":603211476,"identity":"6802c8b5-42b0-4d3c-893c-967eae848df1","order_by":5,"name":"Pengna Li","email":"","orcid":"","institution":"Xi'an University of Arts and Sciences","correspondingAuthor":false,"prefix":"","firstName":"Pengna","middleName":"","lastName":"Li","suffix":""},{"id":603211477,"identity":"1217c295-48af-4e19-9ade-972bbc62bc28","order_by":6,"name":"Kaili He","email":"","orcid":"","institution":"Shaanxi Institute for the Preservation of Culture Heritage","correspondingAuthor":false,"prefix":"","firstName":"Kaili","middleName":"","lastName":"He","suffix":""}],"badges":[],"createdAt":"2026-03-01 09:23:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9000416/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9000416/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104780116,"identity":"5e448182-f900-46a1-b43c-b8bb17e1b4f4","added_by":"auto","created_at":"2026-03-17 07:50:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1260507,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e preparation and application.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/83475882a8eb298209ee673f.png"},{"id":104780067,"identity":"11eb0500-cf6d-4103-ba3e-fe4a7383941f","added_by":"auto","created_at":"2026-03-17 07:50:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2915125,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic morphology of the as-prepared spinel oxides visualized by SEM. SEM images of (A) Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, (B) NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, (C) CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, (D) CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and (E) CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/5712394e7e89b3562b17c9ca.png"},{"id":104419288,"identity":"4904fdc8-ed25-4ed8-8044-dfc039f71db2","added_by":"auto","created_at":"2026-03-11 13:32:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2312198,"visible":true,"origin":"","legend":"\u003cp\u003eCrystal phase structure and chemical bonding characteristics of the synthesized spinel oxides analyzed by XRD and FT-IR spectroscopy. (A) XRD patterns and (B) FT-IR spectra of the synthesized spinel oxides (Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e NPs, CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e).\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/ccbf1ba13743f1a48464979a.png"},{"id":104779773,"identity":"a15e7c10-b35f-464d-98eb-3bef9a7fac95","added_by":"auto","created_at":"2026-03-17 07:46:04","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2549907,"visible":true,"origin":"","legend":"\u003cp\u003eSurface elemental chemical states, oxygen species composition and quantitative surface chemical parameters of the spinel oxides characterized by XPS. (A) O 1s, (B) Co 2p, (C) Ni 2p, (D) Cu 2p, (E) Fe 2p, (F) Mn 2p XPS spectra, (G-H) quantitative surface chemical parameters of the synthesized spinel oxides (Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e NPs, CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e).\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/22f73d95b99dbf9b5d9da307.png"},{"id":104419283,"identity":"9ff3a256-36af-41a5-b302-f38c480b35df","added_by":"auto","created_at":"2026-03-11 13:32:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1110396,"visible":true,"origin":"","legend":"\u003cp\u003eH\u003csub\u003e2\u003c/sub\u003eS adsorption performance of the synthesized spinel oxides systematically evaluated via static adsorption isotherms, dynamic breakthrough tests, cyclic regeneration experiments and temperature-dependent adsorption capacity tests. (A) H\u003csub\u003e2\u003c/sub\u003eS adsorption isotherms, (B) H\u003csub\u003e2\u003c/sub\u003eS breakthrough curves of Vulcan XC-72 and the synthesized spinel oxides, (C) cyclic adsorption capacity retention of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, (D) H\u003csub\u003e2\u003c/sub\u003eS uptake capacities at 0–40 °C.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/8c0b7414b611a89a8bc22b13.png"},{"id":104419289,"identity":"cca9d7b6-76e6-4531-91f9-e704aa352fd8","added_by":"auto","created_at":"2026-03-11 13:32:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1630829,"visible":true,"origin":"","legend":"\u003cp\u003eElectron transfer process, orbital hybridization characteristics and adsorption-oxidation mechanism of H\u003csub\u003e2\u003c/sub\u003eS on NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e revealed by DFT calculations and corresponding experimental characterizations. (A) Charge density map, (B) PDOS, (C) O 2p XPS spectra, (D) EPR spectra of pre-/post-adsorption NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e; (E) Comprehensive H\u003csub\u003e2\u003c/sub\u003eS Oxidation Mechanism on NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4 \u003c/sub\u003esurface.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/27c15e66891d921945645087.png"},{"id":104419285,"identity":"43f17a22-5a64-441f-a56e-6ee291e65794","added_by":"auto","created_at":"2026-03-11 13:32:12","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":650190,"visible":true,"origin":"","legend":"\u003cp\u003eProtective efficacy of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e adsorbent against sulfidation corrosion of silver coupons and lead white pigments evaluated by modified Oddy test and corresponding XPS analysis. (A) Silver, (B) lead white pigment of specimen visual comparison (Blank, AC, CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e); (C) S 2p XPS spectra of protected silver specimens by NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and AC; (D) S 2p XPS spectra of protected pigment by NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and AC.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/ea6de9f5a99cf68d92737f39.png"},{"id":104785737,"identity":"f25b94fa-705b-4c15-be0b-899fcc8384b2","added_by":"auto","created_at":"2026-03-17 08:12:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":13252536,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9000416/v1/e5f1270c-b964-4e9c-aa45-3cfdf812d0d2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eSynthesis of Spinel-Type MCo\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4 \u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e(M =\u003c/strong\u003e \u003cstrong\u003eCu, Ni, Fe, Mn) Adsorbents and Their Performance in Trace H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eS Capture for Cultural Heritage Preservation\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCultural relics are physical vestiges of human history and culture, embodying profound historical narratives and cultural significance. The long-term accumulation of trace hydrogen sulfide (H\u003csub\u003e2\u003c/sub\u003eS) in the microenvironments where cultural relics are preserved accelerates the irreversible deterioration of cultural heritage\u0026nbsp;[1]\u0026nbsp;[2]. Metallic relics are particularly vulnerable\u0026nbsp;[3]. Upon interaction with H\u003csub\u003e2\u003c/sub\u003eS, the surface of bronze artifacts reacts to form thermodynamically stable copper(I) sulfide (Cu\u003csub\u003e2\u003c/sub\u003eS, K\u003csub\u003esp\u003c/sub\u003e = 2.5\u0026nbsp;\u0026times;\u0026nbsp;10\u003csup\u003e-48\u003c/sup\u003e)\u0026nbsp;[4]. The unit cell volume of Cu\u003csub\u003e2\u003c/sub\u003eS expands by approximately 26% compared to elemental copper, inducing internal stress, cracking in the substrate, and the formation of a black, powdery corrosion layer\u0026nbsp;[5]. In the presence of chloride ions, this process evolves into the characteristic deterioration known as \u0026quot;bronze disease,\u0026quot; where copper(I) chloride (CuCl) is sulfidized into a porous Cu\u003csub\u003e2\u003c/sub\u003eS structure, ultimately leading to the structural disintegration of the artifact. Organic cultural relics are also threatened\u0026nbsp;[6]. When the relative humidity exceeds 60%, H\u003csub\u003e2\u003c/sub\u003eS dissolves into the thin film of adsorbed water on their surfaces. The subsequent ionization (H\u003csub\u003e2\u003c/sub\u003eS\u0026nbsp;⇌\u0026nbsp;H\u003csup\u003e+\u003c/sup\u003e + HS\u003csup\u003e-\u003c/sup\u003e) creates a localized weakly acidic environment with a pH of approximately 5.6\u0026nbsp;[7]. This acidity catalyzes the hydrolysis of the \u0026beta;-1,4-glycosidic bonds in cellulose, causing the degree of polymerization (DP) of paper to decrease from an initial value of 2000 \u0026plusmn; 300 to about 500 \u0026plusmn; 80 after aging, accompanied by a reduction in tensile strength exceeding 65%\u0026nbsp;[8]. A more insidious form of biochemical erosion occurs on stone substrates. Sulfur-oxidizing bacteria, such as acidithiobacillus thiooxidans, utilize H\u003csub\u003e2\u003c/sub\u003eS as an electron donor in their metabolism, producing sulfuric acid (2H\u003csub\u003e2\u003c/sub\u003eS + 4O\u003csub\u003e2\u003c/sub\u003e \u0026rarr;\u0026nbsp;2H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e)\u0026nbsp;[9]. The resulting strongly acidic environment (pH \u0026lt; 2.0) dissolves calcite (CaCO\u003csub\u003e3\u003c/sub\u003e), leading to the crystallization of gypsum (CaSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO)\u0026nbsp;[7]. The crystallization pressure associated with a volume expansion of about 135% can fracture rock pores. Concurrently, lead-based pigments, such as lead white [2PbCO\u003csub\u003e3\u003c/sub\u003e\u0026middot;Pb(OH)\u003csub\u003e2\u003c/sub\u003e]\u0026nbsp;[10], are converted into friable lead sulfate (PbSO\u003csub\u003e4\u003c/sub\u003e), causing the detachment of painted layers in murals. These pervasive erosive effects render H\u003csub\u003e2\u003c/sub\u003eS, even at parts-per-billion (ppb) levels\u0026nbsp;[11], a latent threat to the long-term preservation of cultural relics. There is an urgent need to develop ambient-temperature purification materials with high adsorption capacity and selectivity to mitigate this risk\u0026nbsp;[12].\u003c/p\u003e\n\u003cp\u003eExisting adsorption systems still face significant limitations in addressing the specific requirements for H\u003csub\u003e2\u003c/sub\u003eS purification in cultural heritage preservation environments, including the need for ambient temperature operation, effectiveness at low concentrations, and high selectivity\u0026nbsp;[13]. While wet scrubbing and thermal catalytic oxidation are suitable for industrial desulfurization, their high energy consumption (requiring temperatures \u0026gt;150\u0026deg;C) and tendency to generate byproducts that may damage artifacts restrict their use\u0026nbsp;[14]. Although activated carbon and molecular sieves offer potential for room-temperature adsorption, their surface chemical inertness and sensitivity to humidity result in poor selectivity (H\u003csub\u003e2\u003c/sub\u003eS adsorption capacity typically \u0026lt;50 mg/g).\u003c/p\u003e\n\u003cp\u003eIn contrast, spinel-type transition metal oxides (AB\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) stand out due to the intrinsic tunability of their crystal structure\u0026nbsp;[15]. The topological coupling between tetrahedral (A-site) and octahedral (B-site) interstices in their lattice enables the construction of a gradient network of Lewis acid sites, significantly enhancing the capture capability for the lone-pair electrons in H\u003csub\u003e2\u003c/sub\u003eS molecules\u0026nbsp;[16]. More importantly, the selective occupation of A- or B-sites by heterovalent transition metal ions (e.g., Ni\u003csup\u003e2+\u003c/sup\u003e, Cu\u003csup\u003e2+\u003c/sup\u003e) allows for targeted regulation of oxygen vacancy (V\u003csub\u003eO\u003c/sub\u003e) concentration and electron transfer pathways\u0026nbsp;[17]. For instance, the substitution of tetrahedral Co\u003csup\u003e2+\u003c/sup\u003e (ionic radius r = 0.74 \u0026Aring;) by Ni\u003csup\u003e2+\u003c/sup\u003e (r = 0.69 \u0026Aring;) induces lattice contraction, promoting the conversion of surface lattice oxygen (O\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e) into chemically adsorbed oxygen species (O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e/O\u003csup\u003e\u0026minus;\u003c/sup\u003e). This process enhances the low-temperature oxidation activity toward H\u003csub\u003e2\u003c/sub\u003eS.\u003c/p\u003e\n\u003cp\u003eIn this study, a defect engineering strategy is developed to construct high‑performance H\u003csub\u003e2\u003c/sub\u003eS scavengers based on Ni‑doped Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e spinel nanosheets (Figure 1). Through selective substitution of tetrahedral Co\u003csup\u003e2+\u003c/sup\u003e sites with Ni\u003csup\u003e2+\u003c/sup\u003e, the surface electronic structure is effectively modulated, and the ratio of surface adsorbed oxygen (O\u003csub\u003eads\u003c/sub\u003e) to lattice oxygen (O\u003csub\u003elatt\u003c/sub\u003e) is optimized. Combined experimental characterization and density functional theory calculations elucidate a distinct surface oxygen activation\u0026ndash;electron transfer mechanism. The results indicate that the enhanced Lewis acidity and increased oxygen vacancy concentration promote the rapid oxidative dissociation of H\u003csub\u003e2\u003c/sub\u003eS molecules. Furthermore, standard accelerated aging tests, namely Oddy tests, confirm the exceptional performance of the material in inhibiting sulfidation of sensitive cultural heritage materials, such as silver and lead white, under trace H\u003csub\u003e2\u003c/sub\u003eS exposure. This work not only offers atomic level insights into the gas solid interfacial reactions of spinel oxides, but also establishes an efficient and reliable paradigm for the preventive conservation of museum collections.\u003c/p\u003e"},{"header":"Experimental section","content":"\u003cp\u003e\u003cstrong\u003eAdsorbent Synthesis.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSynthesis of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e Spinel:\u0026nbsp;\u003c/em\u003eThe Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e spinel was synthesized via a metal\u0026ndash;organic framework-derived route. First, cobalt(II) acetate tetrahydrate ((CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003eCo\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO, 0.25 mmol, ca. 62.2 mg) was dissolved in 15 mL of deionized water to form\u0026nbsp;Solution A. Separately, terephthalic acid (H\u003csub\u003e2\u003c/sub\u003eBDC, 0.125 mmol, 20.8 mg) was dissolved in 15 mL of N,N-dimethylacetamide (DMA) to form\u0026nbsp;Solution B. Under stirring, Solution B was added dropwise into Solution A, and the mixture was stirred for 10 min to obtain a homogeneous solution. The resulting mixture was transferred into a 50 mL Teflon-lined stainless-steel autoclave and heated at 150 \u0026deg;C for 3 h. After natural cooling, the precipitate was collected, washed several times with water and methanol, and dried at 60 \u0026deg;C for 12 h to obtain the precursor. Finally, the precursor was placed in a tube furnace and calcined at 500 \u0026deg;C for 4 h under air atmosphere with a heating rate of 5 \u0026deg;C min\u003csup\u003e-1\u003c/sup\u003e, yielding the final Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e product.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSynthesis of Doped Spinel Oxides (MCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, M = Cu, Ni, Fe, Mn):\u0026nbsp;\u003c/em\u003eThe procedure for preparing the doped spinels was essentially the same as that described for Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, except that corresponding metal salts were added to Solution A together with cobalt acetate in stoichiometric ratios. For CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, copper(II) acetate monohydrate (Cu\u003csub\u003e2\u003c/sub\u003e(OAc)\u003csub\u003e4\u003c/sub\u003e(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e, 0.125 mmol, ca. 34.9 mg) was introduced. For NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, nickel(II) acetate tetrahydrate (Ni(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO, 0.125 mmol, ca. 31.1 mg) was added. For CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, basic iron(III) acetate (Fe(OH)(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e, 0.5 mmol, ca. 119.0 mg) was used. For CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, manganese(II) acetate tetrahydrate ((CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003eMn\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO, 0.5 mmol, ca. 122.5 mg) was incorporated. All subsequent steps, including hydrothermal reaction, washing, drying, and calcination, were carried out under identical conditions to those employed for the pure Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e sample.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdsorption Performance Evaluation.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eStatic Adsorption Isotherms:\u003c/em\u003e H\u003csub\u003e2\u003c/sub\u003eS adsorption isotherms were acquired at 0 \u0026deg;C, 25 \u0026deg;C, and 40 \u0026deg;C under pressures ranging from 0 to 1 bar using a Micromeritics 3Flex analyzer coupled with a thermostatic bath (Laboto CC‑2020E). Before measurement, each sample (50 mg) was degassed under vacuum at 180 \u0026deg;C for 6 h to remove physisorbed water and residual impurities\u0026nbsp;[18].\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eDynamic Breakthrough Tests:\u003c/em\u003e The dynamic H\u003csub\u003e2\u003c/sub\u003eS adsorption performance of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was examined in a fixed‑bed reactor system. The setup included: (i) a gas‑blending station with calibrated mass‑flow controllers delivering 50 \u0026plusmn; 2 ppm H\u003csub\u003e2\u003c/sub\u003eS in N\u003csub\u003e2\u003c/sub\u003e; (ii) a quartz adsorption column (8 mm i.d.) packed with adsorbent supported on a sintered quartz frit; and (iii) a laser gas analyzer monitoring the effluent H\u003csub\u003e2\u003c/sub\u003eS concentration with 0.1 ppm resolution. Prior to testing, 50 mg of the adsorption was activated in situ under N\u003csub\u003e2\u003c/sub\u003e flow (50 mL\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e) at 120 \u0026deg;C for 8 h. Quartz‑wool plugs ensured uniform gas distribution, and PID‑controlled heating maintained isothermal conditions at 25 \u0026plusmn; 0.5 \u0026deg;C. The H\u003csub\u003e2\u003c/sub\u003eS/N\u003csub\u003e2\u003c/sub\u003e mixture (300 \u0026plusmn; 5 mL\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e) was passed through the adsorbent bed at atmospheric pressure. The breakthrough time was defined as the point when the outlet H\u003csub\u003e2\u003c/sub\u003eS concentration reached 5% of the inlet value, following ASTM D6646‑14.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCyclic Regeneration Performance:\u0026nbsp;\u003c/em\u003eTen consecutive H\u003csub\u003e2\u003c/sub\u003eS adsorption\u0026ndash;regeneration cycles were performed at 0 \u0026deg;C to assess the recyclability of the materials. Before each adsorption run, the samples were regenerated by vacuum degassing at 180 \u0026deg;C for 4 h to restore active sites and minimize experimental scatter. Identical initial conditions (50 ppm H\u003csub\u003e2\u003c/sub\u003eS/N\u003csub\u003e2\u003c/sub\u003e, 300 mL\u0026middot;min\u003csup\u003e-1\u003c/sup\u003e flow rate) were used in all trials to ensure reproducibility. The adsorption‑capacity retention rate was calculated after each regeneration step to quantify any performance loss.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eModified Oddy Test Methodology.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAn optimized Oddy‑test protocol was employed to evaluate the H\u003csub\u003e2\u003c/sub\u003eS‑suppression capability of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e under conditions relevant to cultural‑heritage conservation. Custom‑designed, sealed borosilicate‑glass reactors (50 mL nominal volume) were placed in a precision climatic chamber providing tight environmental control (\u0026plusmn;1 \u0026deg;C, \u0026plusmn;2% RH, calibrated per NIST SP 260‑136)\u0026nbsp;[19]. Simulated artifact specimens consisted of: (i) mirror‑polished silver coupons (\u0026gt;99.9% purity, 10 \u0026times; 10 \u0026times; 0.1 mm) cleaned by sequential ethanol ultrasonication and N\u003csub\u003e2\u003c/sub\u003e‑jet drying, and (ii) glass slides uniformly coated with lead‑white pigment (PbCO\u003csub\u003e3\u003c/sub\u003e) at 50 \u0026plusmn; 5 \u0026mu;m thickness to mimic historical paint layers.\u003c/p\u003e\n\u003cp\u003eSix experimental groups were compared: a blank control (no adsorbent), NiCo₂O₄ (50 mg), commercial activated carbon (AC, 50 mg), CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (50 mg), CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u0026nbsp; (50 mg) and CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (50 mg). All specimens were subjected to accelerated aging at 30 \u0026deg;C and 60% relative humidity for 28 days, simulating long‑term conservation environments. Metallic and pigmented samples were mounted vertically inside the reactors using inert polytetrafluoroethylene holders, avoiding direct contact with adsorbents while allowing free diffusion of gaseous H\u003csub\u003e2\u003c/sub\u003eS. This configuration isolated vapor‑phase corrosion‑inhibition mechanisms, excluding potential artifacts from direct material contact.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eColorimetric Analysis of Simulated Specimens.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eColor variations in the pigment layers of simulated specimens were quantified using the CIE L*a*b* colorimetric system. In this system, the L* coordinate indicates lightness, with higher values corresponding to brighter surfaces [20]. The a* and b* coordinates represent chromaticity: a* denotes position along the red‑green axis (positive for red, negative for green), and b* denotes position along the yellow‑blue axis (positive for yellow, negative for blue). The total color difference (\u0026Delta;E) was calculated using the following expression:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/58895_8739fc6c57c1c19a/58895_custom_files/img1773235568.png\" width=\"305\" height=\"53\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u0026Delta;L\u003cem\u003e,\u003c/em\u003e \u0026Delta;a, and \u0026Delta;b* are the differences between the initial and final values of each coordinate. The \u0026Delta;E value thus provides a single metric for the overall magnitude of color change.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDFT theoretical calculations.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo elucidate the atomic‑scale adsorption mechanism and electronic‑structure evolution during H\u003csub\u003e2\u003c/sub\u003eS interaction with NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, density functional theory (DFT) calculations were carried out using the DMol\u003csup\u003e3\u003c/sup\u003e module in Materials Studio 2020 (BIOVIA Inc.)\u0026nbsp;[14]. The Perdew\u0026ndash;Burke\u0026ndash;Ernzerhof (PBE) generalized‑gradient approximation (GGA) functional was employed, and Grimme\u0026rsquo;s DFT‑D3 method with Becke\u0026ndash;Johnson damping was included to account for van der Waals interactions. Norm‑conserving pseudopotentials described the core electrons, while valence electrons were expanded in a double‑numeric polarized (DNP) basis set with a real‑space cutoff of 5.0 \u0026Aring;. Geometry optimizations were considered converged when the energy change was below 1\u0026times;10\u003csup\u003e-5 \u003c/sup\u003eHa, the maximum force component \u0026lt;0.002 Ha/\u0026Aring;, and the maximum atomic displacement \u0026lt;0.005 \u0026Aring;. The Brillouin zone was sampled with a 4\u0026times;4\u0026times;1 Monkhorst\u0026ndash;Pack\u0026nbsp;k‑point grid for structural relaxation and an 8\u0026times;8\u0026times;1 grid for static electronic‑property calculations, ensuring energy convergence within 1 meV/atom. The Fermi level was treated using the Methfessel\u0026ndash;Paxton smearing scheme with a width of 0.005 Ha.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInstruments.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe structural and chemical features of the samples were examined using a combination of complementary techniques. Crystal phases were identified by X‑ray diffraction (XRD, Rigaku D/max‑rC, Cu K\u0026alpha; radiation). Surface elemental states and depth‑resolved composition were analyzed with X‑ray photoelectron spectroscopy (XPS, Thermo Scientific ESCALAB 250, Al K\u0026alpha; source) combined with Ar\u003csup\u003e+\u003c/sup\u003e sputtering. Morphology and elemental distribution were visualized by field‑emission scanning electron microscopy (FE‑SEM, Hitachi SU‑8020).\u0026nbsp;\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003eStructural characterization of doped spinel oxides\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll samples exhibit nanoparticle morphologies derived from the MOF‑precursor route. As Figure 2, the Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles show relatively uniform quasi‑spherical shapes with slight aggregation. NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e display more homogeneous particle‑size distributions and smoother surfaces. CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e presents a porous, interconnected network. CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e consists of notably larger, well‑faceted polyhedral particles.\u003c/p\u003e\n\u003cp\u003eThe crystal structure and phase purity of the synthesized series of spinel oxide catalysts were systematically investigated by XRD, as shown in the Figure 3A. The diffraction peaks of pure-phase Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e NPs are located at 19.1\u003csup\u003eo\u003c/sup\u003e, 31.3\u003csup\u003eo\u003c/sup\u003e, 36.8\u003csup\u003eo\u003c/sup\u003e, 44.8\u003csup\u003eo\u003c/sup\u003e, 55.7\u003csup\u003eo\u003c/sup\u003e, 59.3\u003csup\u003eo\u003c/sup\u003e, and 65.2\u003csup\u003eo\u003c/sup\u003e, which correspond perfectly to the standard pattern of the spinel structure (JCPDS No. 42-1467) and are indexed to the (111), (220), (311), (400), (422), (511), and (440) crystal planes, respectively. This confirms the successful synthesis of well-crystallized Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles. After the introduction of secondary metals (Ni, Cu, Mn, Fe), the XRD patterns of the resulting samples still exhibit a dominant spinel phase, with systematic shifts in peak positions due to lattice distortion induced by the Jahn\u0026ndash;Teller effect [21]. Additionally, weak secondary diffraction peaks are observed in some patterns: around 44.5\u003csup\u003eo\u003c/sup\u003e for the Ni-doped sample, near 34.8\u003csup\u003eo\u003c/sup\u003e and 38.9\u003csup\u003eo\u003c/sup\u003e for the Cu-doped sample, around 33.8\u003csup\u003eo\u003c/sup\u003e and 60.1\u003csup\u003eo\u003c/sup\u003e for the Mn-doped sample, and near 34.8\u003csup\u003eo\u003c/sup\u003e and 50.2\u003csup\u003eo\u003c/sup\u003e for the Fe-doped sample [22]. These signals are assigned to NiO, CuO, (Co,Mn)\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e phases, respectively. These results indicate that the heterometal atoms have been successfully introduced into the material system, confirming the incorporation of Ni, Cu, Fe, and Mn into the spinel lattice and the successful preparation of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eAs shown in the Figure 3B, the chemical structure of the catalysts was further analyzed by FT-IR. For Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e NPs, CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, two characteristic absorption bands attributed to M\u0026ndash;O (where M represents metal ions) are observed in the range of 568\u0026ndash;668 cm\u003csup\u003e-1\u003c/sup\u003e. The band near 668 cm\u003csup\u003e-1\u003c/sup\u003e is assigned to the vibrational stretching of M\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;O bonds in tetrahedral sites, while the band around 568 cm\u003csup\u003e-1\u003c/sup\u003e corresponds to M\u003csup\u003e3+\u003c/sup\u003e\u0026ndash;O vibrations in octahedral sites\u0026nbsp;[23]. Notably, compared with pure Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e NPs, distinct changes in the characteristic spinel bands are observed upon the introduction of different heteroatoms, reflecting the influence of doping on the spinel structure of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eTo elucidate the intrinsic relationship between adsorption performance and material composition as well as surface oxygen chemistry, the elemental composition and chemical states of all catalysts were systematically characterized using XPS\u0026nbsp;[23, 24]. Figure 4 presents the XPS spectra of Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, including the fine structures of O 1s, Co 2p, Ni 2p, Cu 2p, Fe 2p, and Mn 2p. First, the composition of surface oxygen species was resolved by analyzing the O 1s spectra (Figure 4A). Taking Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e as an example, its spectrum can be deconvoluted into three peaks: the binding energies at 533.89 eV, 532.12 eV, and 530.59 eV are assigned to surface hydroxyl groups/adsorbed water molecules (O\u003csub\u003ew\u003c/sub\u003e), chemically adsorbed oxygen (O\u003csub\u003eads\u003c/sub\u003e), and lattice oxygen (O\u003csub\u003elatt\u003c/sub\u003e)\u0026nbsp;[25], respectively. The ratio of the peak area of O\u003csub\u003eads\u003c/sub\u003e to that of O\u003csub\u003elatt\u003c/sub\u003e (O\u003csub\u003eads\u003c/sub\u003e/O\u003csub\u003elatt\u003c/sub\u003e) was calculated for each material and is listed in Figure 4G. This ratio varies significantly with the doped metal, following the order: NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (1.21) \u0026gt; CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (0.77) \u0026gt; CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (0.67) \u0026gt; Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (0.57) \u0026gt; CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (0.21). This order aligns well with their activity trends in H\u003csub\u003e2\u003c/sub\u003eS catalytic oxidation, indicating that surface adsorbed oxygen (O\u003csub\u003eads\u003c/sub\u003e) plays a dominant role in the reaction.\u003c/p\u003e\n\u003cp\u003eSecond, the Co 2p spectra (Figure 4B) reveal the valence distribution of cobalt ions. All samples exhibit characteristic doublet peaks for Co\u003csup\u003e2+\u003c/sup\u003e and Co\u003csup\u003e3+\u003c/sup\u003e. Quantitative analysis shows that the introduction of Fe and Mn increases the relative content of Co\u003csup\u003e3+\u003c/sup\u003e (with Co\u003csup\u003e3+\u003c/sup\u003e fractions of 0.59 in CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and 0.61 in CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e), suggesting that Fe and Mn tend to occupy low-valent cobalt sites\u0026nbsp;[26]. Conversely, the introduction of Ni and Cu increases the proportion of Co\u003csup\u003e2+\u003c/sup\u003e (with Co\u003csup\u003e3+\u003c/sup\u003e fractions decreasing to 0.33 in NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and 0.23 in CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e), indicating that Ni and Cu primarily occupy high-valent cobalt sites. This result is consistent with the variations in oxygen species activity reflected in the O 1s spectra. The occupancy of different metal ions in the spinel structure significantly alters the local chemical environment of Co ions, thereby exerting a decisive influence on the adsorptive performance.\u003c/p\u003e\n\u003cp\u003eFurthermore, the 2p spectra of other metal elements (Figure 4C\u0026ndash;F) confirm the successful incorporation of heteroatoms. NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e shows characteristic peaks of Ni\u003csup\u003e2+\u003c/sup\u003e at 855.3 eV and 872.8 eV; CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e shows characteristic peaks of Cu\u003csup\u003e2+\u003c/sup\u003e at 933.5 eV and 953.4 eV; CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e shows characteristic peaks of Mn\u003csup\u003e3+\u003c/sup\u003e at 641.9 eV and 653.2 eV; and CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e shows characteristic peaks of Fe\u003csup\u003e3+\u003c/sup\u003e at 710.8 eV and 724.3 eV [27]. These signals indicate that the heterometal atoms have been successfully incorporated into the spinel lattice, forming structurally uniform solid solutions rather than simple physical mixtures.\u003c/p\u003e\n\u003cp\u003eA comparative analysis of the surface chemical states of a series of spinel oxides (Figure G\u0026ndash;H) reveals that NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e exhibits unique surface characteristics: its ratio of surface adsorbed oxygen to lattice oxygen (O\u003csub\u003eads\u003c/sub\u003e/O\u003csub\u003elatt\u003c/sub\u003e) is as high as 1.21, the highest among all materials, indicating the enrichment of highly reactive adsorbed oxygen species (e.g., O\u003csub\u003e2\u003c/sub\u003e⁻, O⁻) on its surface\u0026nbsp;[28]. Concurrently, its lattice oxygen binding energy is as low as 529.52 eV, suggesting weak bonding between O\u003csub\u003elatt\u003c/sub\u003e and the substrate, higher reactivity, and a greater propensity to participate in oxidation reactions. Additionally, its Co\u003csup\u003e3+\u003c/sup\u003e/(Co\u003csup\u003e3+\u0026nbsp;\u003c/sup\u003e+ Co\u003csup\u003e2+\u003c/sup\u003e) and Ni\u003csup\u003e2+\u003c/sup\u003e/(Ni\u003csup\u003e3+\u0026nbsp;\u003c/sup\u003e+ Ni\u003csup\u003e2+\u003c/sup\u003e) ratios are 0.33 and 0.54, respectively, constituting an ideal mixed-valence system that provides a platform for rapid electron transfer. These experimental data collectively demonstrate that NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e possesses a \u0026ldquo;highly active and dynamic\u0026rdquo; surface, laying a structural foundation for its efficient adsorption and oxidation of H\u003csub\u003e2\u003c/sub\u003eS.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization of H\u003csub\u003e2\u003c/sub\u003eS adsorption performance\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe H\u003csub\u003e2\u003c/sub\u003eS adsorption performance of the prepared series of doped Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-based spinel materials (including Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) was systematically evaluated using static volumetric and dynamic breakthrough methods, with commercial activated carbon (AC) included for comparison. The study focused on the adsorption capacity, kinetic behavior, cyclic stability, and the influence of temperature on adsorption performance.\u003c/p\u003e\n\u003cp\u003eThe equilibrium H\u003csub\u003e2\u003c/sub\u003eS adsorption capacity of the materials was measured at 25 \u0026deg;C and 1 bar using a Micromeritics 3Flex analyzer. As shown in Figure 5A, different cation dopants significantly affected the adsorption performance. NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanosheets exhibited the highest adsorption capacity of 4.2 mmol g\u003csup\u003e-1\u003c/sup\u003e, substantially exceeding that of pure-phase Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (2.2 mmol g\u003csup\u003e-1\u003c/sup\u003e) and commercial AC (2.0 mmol g\u003csup\u003e-1\u003c/sup\u003e). The capacities of CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e were 3.2 mmol g\u003csup\u003e-1\u003c/sup\u003e, 2.7 mmol g\u003csup\u003e-1\u003c/sup\u003e, and 2.3 mmol g\u003csup\u003e-1\u003c/sup\u003e, respectively. This performance trend (NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e \u0026gt; CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e \u0026gt; CoMn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e \u0026gt; CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e \u0026gt; Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) aligns closely with the relative abundance of surface active oxygen species (O\u003csub\u003eads\u003c/sub\u003e/O\u003csub\u003elatt\u003c/sub\u003e ratio) obtained from prior XPS characterization (Figure 3G), confirming the dominant role of surface chemisorbed oxygen (O\u003csub\u003eads\u003c/sub\u003e) in the capture and oxidative conversion of H\u003csub\u003e2\u003c/sub\u003eS. Under lower partial-pressure conditions (0.1 bar), which better simulate actual conservation environments, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e maintained a capacity of 0.9 mmol g\u003csup\u003e-1\u003c/sup\u003e, demonstrating its potential for low-concentration H\u003csub\u003e2\u003c/sub\u003eS purification.\u003c/p\u003e\n\u003cp\u003eDynamic breakthrough tests are essential for evaluating adsorbent performance under practical flow conditions. The breakthrough curves of the materials were measured at 25 \u0026deg;C, 50 % RH (Figure 5B). NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e showed the best performance, with a long breakthrough time (C/C₀ = 5 %) of 55 min and a steep, well-defined S‑shaped breakthrough curve, indicating fast adsorption kinetics and superior mass transfer. CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e exhibited a breakthrough time of 46 min. In contrast, pure‑phase Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and commercial AC showed significantly shorter breakthrough times of 31 min and 30 min, respectively. The AC curve displayed a shallower slope, suggesting higher mass‑transfer resistance. The excellent dynamic performance of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is attributed to its unique two‑dimensional nanosheet morphology, which provides abundant accessible surface sites and short diffusion pathways, together with its high O\u003csub\u003eads\u003c/sub\u003e concentration that facilitates rapid surface reactions.\u003c/p\u003e\n\u003cp\u003eThe recyclability of an adsorbent is critical for practical application. The best‑performing NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was subjected to ten consecutive adsorption‑regeneration cycles at 25 \u0026deg;C. After each saturation, the material was regenerated under a N\u003csub\u003e2\u003c/sub\u003e flow at 150 \u0026deg;C for 2 h. As shown in Figure 5C, after ten cycles, the H\u003csub\u003e2\u003c/sub\u003eS adsorption capacity of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e decreased from an initial 4.2 mmol g\u003csup\u003e-1\u003c/sup\u003e to 3.5 mmol g\u003csup\u003e-1\u003c/sup\u003e, corresponding to a retention rate of 92.1 %, demonstrating good regeneration stability. This robust cycling performance stems from the excellent thermal and chemical stability of the spinel structure, which helps preserve active sites over repeated regeneration.\u003c/p\u003e\n\u003cp\u003eTemperature plays a crucial role in adsorption processes. For NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, the H\u003csub\u003e2\u003c/sub\u003eS adsorption capacity increased from 4.2 mmol g\u003csup\u003e-1\u003c/sup\u003e at 0 \u0026deg;C to 4.8 mmol g\u003csup\u003e-1\u003c/sup\u003e at 40 \u0026deg;C (Figure 5D). This positive correlation with temperature suggests that the adsorption is predominantly chemisorption‑driven, as the elevated temperature provides the necessary activation energy to overcome the energy barrier for surface reaction, thereby enhancing both the adsorption rate and capacity within this temperature range.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMechanistic investigation of H\u003csub\u003e2\u003c/sub\u003eS adsorption\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDFT calculations elucidated the electron transfer and H\u003csub\u003e2\u003c/sub\u003eS activation pathway during the initial adsorption stage. To understand the role of the aforementioned surface properties at the atomic scale, systematic DFT computations were performed. First, the differential charge density map (Figure 6A) visually illustrates the electron redistribution. After adsorption, the H\u003csub\u003e2\u003c/sub\u003eS molecule, particularly around the S atom, shows a clear reduction in electron density, while the neighboring O\u003csub\u003eads\u003c/sub\u003e exhibits an increase in electron density. A continuous charge bridge forms between them, directly demonstrating electron transfer from the S atom of H\u003csub\u003e2\u003c/sub\u003eS to the surface O\u003csub\u003eads\u003c/sub\u003e, accompanied by significant covalent interaction. Orbital-projected density of states (PDOS) analysis (Figure 6B) clarifies the orbital origin of this electron transfer from the perspective of band structure. After adsorption, the density of states near the Fermi level (EF) for the S 3p orbitals decreases markedly, whereas new occupied states appear near EF for the O\u003csub\u003eads\u003c/sub\u003e 2p orbitals. This indicates strong hybridization between S 3p and O\u003csub\u003eads\u003c/sub\u003e 2p, forming covalent bonding and promoting electron flow from H\u003csub\u003e2\u003c/sub\u003eS to the surface.\u003c/p\u003e\n\u003cp\u003eSecond, the XPS O 1s spectra (Figure 6C) provide further chemical evidence for the electron transfer. After adsorption, the binding energy of the characteristic peak assigned to O\u003csub\u003eads\u003c/sub\u003e shifts significantly from 531.5 eV to 529.8 eV. The decrease in binding energy indicates that O\u003csub\u003eads\u003c/sub\u003e gains electrons, leading to enhanced electron cloud density and a weaker shielding effect, which is consistent with the charge density analysis. Simultaneously, EPR measurements (Figure 6D) reveal changes in the unpaired electron state during adsorption. After adsorption, the signal intensity corresponding to oxygen vacancies and related defects (g = 2.003) decreases by more than 40%, indicating that the empty orbitals of O\u003csub\u003eads\u003c/sub\u003e become occupied by electrons and their paramagnetism weakens, further supporting the conclusion of electron transfer from H\u003csub\u003e2\u003c/sub\u003eS to O\u003csub\u003eads\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eIntegrating the above experimental and theoretical evidence, we propose a comprehensive adsorption-oxidation mechanism for H\u003csub\u003e2\u003c/sub\u003eS on NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (Figure 6E). The mechanism begins with the strong chemisorption of the H\u003csub\u003e2\u003c/sub\u003eS molecule via its S atom onto the octahedral Co/Ni sites possessing a high d‑band center on the surface. Subsequently, the lone‑pair electrons from H\u003csub\u003e2\u003c/sub\u003eS rapidly transfer to neighboring O\u003csub\u003eads\u003c/sub\u003e species, accomplishing initial activation and dissociation. The dissociation products are then deeply oxidized by adjacent highly reactive lattice oxygen (O\u003csub\u003elatt\u003c/sub\u003e), generating oxygen vacancies. Finally, gaseous oxygen molecules fill these oxygen vacancies, regenerating the surface active oxygen species. This study clarifies that the outstanding performance of NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e originates from its unique Ni\u0026ndash;Co synergistic effect, which optimizes the electronic structure of the material, endowing it simultaneously with strong H\u003csub\u003e2\u003c/sub\u003eS adsorption capacity, efficient initial oxidation activity, and sustainable deep oxidation and regeneration capability.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalysis of Oddy Test results\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo comprehensively evaluate the application safety and protective efficacy of the prepared doped Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-based spinel materials in authentic cultural heritage preservation environments, this study employed a modified standard Oddy test method. Under accelerated aging conditions (30\u0026deg;C, 60% relative humidity), the materials\u0026apos; sustained H\u003csub\u003e2\u003c/sub\u003eS purification capacity and their protective effect on sensitive heritage simulants were systematically assessed. Polished silver coupons and simulated specimens coated with lead white pigment (2PbCO\u003csub\u003e3\u003c/sub\u003e\u0026middot;Pb(OH)\u003csub\u003e2\u003c/sub\u003e) were placed in sealed containers and co-exposed to a low-concentration H\u003csub\u003e2\u003c/sub\u003eS environment (initial concentration ~50 ppm) for 28 days. A blank control group (no adsorbent), a commercial activated carbon (AC) group, and experimental groups containing the best-performing NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e were established for comparison.\u003c/p\u003e\n\u003cp\u003eAs Figure 7A, after 28 days, the silver coupon in the blank control group was completely covered by black Ag\u003csub\u003e2\u003c/sub\u003eS, with its lightness value (\u0026Delta;L*) plummeting from an initial 96.7 to 58.3, demonstrating the strong corrosiveness of H\u003csub\u003e2\u003c/sub\u003eS towards silver. The AC group provided limited protection, showing a \u0026Delta;L* decrease of 22.5 (to 74.2) and the appearance of uneven dark spots on the surface, indicating insufficient adsorption capacity for long-term testing and localized H\u003csub\u003e2\u003c/sub\u003eS penetration. The CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e group showed significantly reduced corrosion with a \u0026Delta;L* decrease of 9.8 (to 86.9), although slight discoloration was still visible. The NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e group exhibited near-complete protection, with a minimal \u0026Delta;L* change of only 4.1 (to 92.6). The silver surface retained its metallic luster without significant visual difference from its initial state, proving this material\u0026apos;s highly efficient and sustained capability to remove environmental H\u003csub\u003e2\u003c/sub\u003eS and completely block the silver sulfidation corrosion pathway.\u003c/p\u003e\n\u003cp\u003eThe corrosion of lead white samples manifested as a color change from white to black (Figure 7B). The blank control sample turned completely black by the test\u0026apos;s end, with its yellow-blue coordinate (\u0026Delta;b*) dramatically decreasing from 26.1 to -3.5 (a change of -29.6). The AC group sample exhibited extensive blackening, with a \u0026Delta;b* decrease of 17.3 (to 8.8), indicating unsatisfactory protective performance. The CuCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e group offered some protection, resulting in a \u0026Delta;b* decrease of 10.5 (to 15.6), but scattered black spots were still observed. The NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e group again demonstrated the best protective performance. The lead white sample color remained stable with a negligible \u0026Delta;b* change (within \u0026plusmn;1.0), and no blackening was visible to the naked eye, confirming that H\u003csub\u003e2\u003c/sub\u003eS in the environment was completely adsorbed and did not react with the pigment.\u003c/p\u003e\n\u003cp\u003eXPS spectra of the silver surfaces corroborated the macroscopic corrosion observations (Figure 7C). A distinct S 2p signal, corresponding to a sulfur content of 7.2 at.%, remained evident in the AC group. In contrast, the silver coupon protected by NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e exhibited only a faint sulfur signal (1.8 at.%), confirming its superior corrosion inhibition at the chemical-state level. For the lead white samples, XPS analysis further tracked the evolution of their chemical states (Figure 7D). While the sulfur content reached 5.1 at.% in the AC group, the S 2p signal intensity in the NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u0026nbsp;\u003c/sub\u003eprotected sample remained near the background level (\u0026lt;0.5 at.%). These results confirm at the molecular scale that NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e effectively suppresses the sulfidation reaction.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we have developed a high-performance H\u003csub\u003e2\u003c/sub\u003eS scavenger based on defect-rich NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanosheets via a solvothermal-calcination strategy. The substitution of tetrahedral Co\u003csup\u003e2+\u003c/sup\u003e with Ni\u003csup\u003e2+\u003c/sup\u003e successfully modulated the surface electronic environment, achieving an optimal O\u003csub\u003eads\u003c/sub\u003e/O\u003csub\u003elatt\u003c/sub\u003e ratio of 1.21, which serves as the structural basis for enhanced reactivity. Consequently, the NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e scavenger exhibits a superior saturation adsorption capacity of 4.2 mmol/g at 25 \u0026deg;C, outperforming commercial activated carbon (1.6 mmol/g). Dynamic breakthrough experiments further confirmed its kinetic advantage, yielding a prolonged protection time of 55 min under continuous flow, significantly longer than the 48 min observed for activated carbon. Mechanistically, this performance is driven by the rapid electron transfer from H\u003csub\u003e2\u003c/sub\u003eS to surface oxygen species and the subsequent regeneration of oxygen vacancies, as evidenced by DFT calculations and XPS analysis. Most importantly, in simulated museum environments, the material demonstrated exceptional preventive conservation capabilities: the total color difference of silver artifacts was maintained at 4.1, and the chromaticity shift of lead white pigment was negligible, effectively blocking sulfidation pathways. This work provides a quantifiable, atomic-level paradigm for designing advanced functional materials for the preservation of cultural heritage.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization, N.J. and P.F.; resources, software, investigation, formal analysis, X.C. and P.L.; methodology, data curation, K.H.; writing-original draft preparation, N.J; visualization, K.H.; supervision, project administration, and funding acquisition, N.J. and J.Y.; All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by Young Talent fund of University Association for Science and Technology in Shaanxi, China (20230608), Shaanxi Provincial Natural Science Foundation (2024JC-YBQN-0148, 2023-JC-QN-1007), Special Research Project of Shaanxi Provincial Department of Education (22JKO531), Xi\u0026apos;an Science and Technology Program Project (25FWQY03, 25WTGJ02, 25PTZX09), the Natural Science Foundation of Shaanxi Province (2025JC-YBMS-177), Key Research and Development Project of Shaanxi Provincial Science and Technology Department (2024SF-YBXM-683), Undergraduate Innovation and Entrepreneurship Training Program Project (DC2026037), Xi\u0026apos;an University of Arts and Sciences Cultural Relics Microbiology Interdisciplinary Construction Platform.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study are available fromthe corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing financial interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eD. 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Zhu, NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e with oxygen vacancies as better performance electrode material for supercapacitor, Chemical Engineering Journal, 334 (2018) 864-872.\u003c/li\u003e\n\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":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-heritage-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"hsci","sideBox":"Learn more about [Heritage Science](http://heritagesciencejournal.springeropen.com)","snPcode":"40494","submissionUrl":"https://submission.nature.com/new-submission/40494/3","title":"npj Heritage Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9000416/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9000416/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTrace hydrogen sulfide (H\u003csub\u003e2\u003c/sub\u003eS) causes irreversible deterioration of cultural relics even at low concentrations. To address the limitations of existing adsorbents in conservation environments, we developed Ni-doped Co\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e spinel nanosheets using a metal-organic framework precursor. The substitution of tetrahedral Co\u003csup\u003e2+\u003c/sup\u003e sites with Ni\u003csup\u003e2+\u003c/sup\u003e modulates the surface electronic structure, resulting in an adsorbed-to-lattice oxygen ratio O\u003csub\u003eads\u003c/sub\u003e/O\u003csub\u003elatt\u003c/sub\u003e of 1.21. Density functional theory (DFT) calculations combined with experimental data indicate that these surface oxygen species promote electron transfer from H\u003csub\u003e2\u003c/sub\u003eS and facilitate oxidative dissociation. The NiCo\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e material exhibits a saturation capacity of 4.2 mmol g\u003csup\u003e-1\u003c/sup\u003e at 25 °C, compared to 2.0 mmol g\u003csup\u003e-1\u003c/sup\u003e for commercial activated carbon, and maintains 92% capacity after ten regeneration cycles. Crucially, in accelerated aging environments, the material achieves near-total suppression of sulfidation on silver coupons and lead white pigments, demonstrating its potential as a high-efficiency safeguard for cultural heritage.\u003c/p\u003e","manuscriptTitle":"Synthesis of Spinel-Type MCo2O4 (M = Cu, Ni, Fe, Mn) Adsorbents and Their Performance in Trace H2S Capture for Cultural Heritage Preservation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-11 13:32:01","doi":"10.21203/rs.3.rs-9000416/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-23T04:05:01+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-15T15:47:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"165321185685311123592868907411655840764","date":"2026-03-27T00:20:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-09T14:37:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"179080454625807127885747481710461670164","date":"2026-03-05T23:24:01+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-05T14:44:42+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-04T12:36:39+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-04T05:09:48+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj Heritage Science","date":"2026-03-01T09:06:25+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-heritage-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"hsci","sideBox":"Learn more about [Heritage Science](http://heritagesciencejournal.springeropen.com)","snPcode":"40494","submissionUrl":"https://submission.nature.com/new-submission/40494/3","title":"npj Heritage Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9ba583ce-9a67-4e5c-8b9a-b4dd0fe2f96e","owner":[],"postedDate":"March 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-05T15:23:32+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-11 13:32:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9000416","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9000416","identity":"rs-9000416","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}