A Critical Review of the Synthesis and Applications of Spinel-Derived Catalysts to Bio-Oil Upgrading.

The transformation of renewable bio-oil into platform chemicals and bio-oil through catalytic processes embodies an efficient approach within the realm of advancing sustainable energy. Spinel-based catalysts have garnered significant attention owing to their ability to precisely tune metals within the framework, facilitating adjustments to structural, physical, and electronic properties, coupled with their remarkable thermal stability. This review aims to provide a comprehensive overview of recent advancements in spinel-based catalysts for upgrading bio-oil. Its objective is to shed light on their potential to address the limitations of conventional catalysts. Initially, a comprehensive analysis is conducted on different metal oxide composites in terms of their similarity and dissimilarity on properties. Subsequently, the synthesis methodologies are scrutinised and potential avenues for their modification are explored. Following this, an in-depth discussion ensues regarding the spinels as catalysts or catalyst precursors for catalytic cracking, ketonisation, catalytic hydrodeoxygenation, steam and aqueous-phase reforming, and electrocatalytic upgrading of bio-oil. Finally, the challenges and potential prospects are addressed, with a specific focus on the machine learning - based approaches to optimise the structure and activity of spinel catalysts. This review aims to provide specific directions for further exploration and maximisation of the spinel catalysts in the bio-oil upgrading field.

Unraveling the Impact of Oxygen Vacancy on Electrochemical Valorization of Polyester Over Spinel Oxides.

Electrochemical upcycling of end-of-life polyethylene terephthalate (PET) using renewable electricity offers a route to generate valuable chemicals while processing plastic wastes. However, it remains a huge challenge to design an electrocatalyst with reliable structure-property relationships for PET valorization. Herein, spinel Co3O4 with rich oxygen vacancies for improved activity toward formic acid (FA) production from PET hydrolysate is reported. Experimental investigations combined with theoretical calculations reveal that incorporation of VO into Co3O4 not only promotes the generation of reactive hydroxyl species (OH*) species at adjacent tetrahedral Co2+ (Co2+ Td), but also induces an electronic structure transition from octahedral Co3+ (Co3+ Oh) to octahedral Co2+ (Co2+ Oh), which typically functions as highly-active catalytic sites for ethylene glycol (EG) chemisorption. Moreover, the enlarged Co-O covalency induced by VO facilitates the electron transfer from EG* to OH* via Co2+ Oh-O-Co2+ Td interaction and the following C─C bond cleavage via direct oxidation with a glyoxal intermediate pathway. As a result, the VO-Co3O4 catalyst exhibits a high half-cell activity for EG oxidation, with a Faradaic efficiency (91%) and productivity (1.02 mmol cm-2 h-1) of FA. Lastly, it is demonstrated that hundred gram-scale formate crystals can be produced from the real-world PET bottles via two-electrode electroreforming, with a yield of 82%.

A detailed investigation of rare earth lanthanum substitution effects on the structural, morphological, vibrational, optical, dielectric and magnetic properties of Co-Zn spinel ferrites.

In this work, Co0.5Zn0.5LaxFe2-xO4 (0.00 ≤ x ≤ 0.10) spinel ferrites were synthesized using the sol-gel auto-combustion method. X-ray diffraction (XRD) analysis and Rietveld refinement confirmed the presence of a cubic spinel structure. The crystallite size was estimated to be between 17.5 nm and 26.5 nm using Scherrer's method and 31.27 nm-54.52 nm using the Williamson-Hall (W-H) method. Lattice constants determined from XRD and Rietveld refinement ranged from (8.440 to 8.433 Å and 8.442 to 8.431 Å), respectively. Scanning electron microscopy (SEM) revealed a non-uniform distribution of morphology with a decrease in particle size. The bandgap values decreased from 2.0 eV to 1.68 eV with increasing rare earth (La3+) doping concentration. Fourier-transform infrared (FT-IR) spectroscopy confirmed the presence of functional groups and M-O vibrations. The dielectric constant and dielectric loss exhibited similar behavior across all samples. The maximum tan δ value obtained at lower frequencies. Regarding magnetic behavior, there was a decrease in magnetization from 55.84 emu/g to 22.08 emu/g and an increase in coercivity from 25.63 Oe to 33.88 Oe with higher doping concentrations. Based on these results, these materials exhibit promising properties for applications in microwave and energy storage devices.

K-Rich Spinel Interface of Air-Stable Layered Oxide Cathodes for Potassium-Ion Batteries.

Potassium-containing transition metal layered oxides (KxTmO2), although possessing high energy density and suitable operating voltage, suffer from severe hygroscopic properties due to their two dimensional (2D) layered structure. Their air sensitivity compromises structural stability during prolonged air exposure, therefore increasing the cost. The common sense for designing air-stable layered cathode materials is to avoid contact with H2O molecules. In this study, it is surprisingly found that P3-type KxTmO2 forms an ultra-thin, potassium-rich spinel phase wrapping layer after simply water immersion, remarkedly reduces the reaction activity of the material's surface with air. Combined with Density Function Theory (DFT) calculations, this spinel phase is found to be able to effectively withstand air deterioration and preserving the crystal structure. Consequently, the water-treated material, when exposed to air, can largely maintain its good electrochemical performance, with capacity retention up to 99.15% compared to the fresh samples. Such an in situ surface phase transformation mechanism is also corroborated in other KxTmO2, underscoring its effectiveness in enhancing the air stability of P3-type layered oxides for K+ storage.

The potential of Gd doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

The study shows that the addition of gadolinium ions has a significant impact on the structure, morphology, and adsorption properties of Ni-Co spinel ferrite that was synthesized by the sol-gel auto-combustion method. The research also indicates that the higher the Gd content, the greater the increase in the lattice parameter, which suggests that Gd3+ ions uniformly replaced the octahedral Fe3+ ions. The morphology and chemical composition of Gd-doped Ni-Co ferrites have been studied using SEM and EDS. Gd adding to the NiCoFe matrix increases the BET surface area by 50% (from 48 to 72 m2/g) and promotes the formation of mesopores with an average radius from 3.9 to 4.9 nm. The pHPZC values of Gd-doped ferrites are in the range of 7.22-7.39, which means that the ferrite surface will acquire a positive charge at natural pH, so this will promote the adsorption of Congo red anionic dye through electrostatic interaction forces. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to explain the mechanism of CR adsorption on the Ni0.5Co0.5GdxFe2-xO4 adsorbent surface. The ionic-covalent parameter has been estimated to describe the surface acid-base properties. Overall, this study highlights the potential of Gd3+ doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

Vacancy-rich heterogeneous MnCo2O4.5@NiS electrocatalyst for highly efficient overall water splitting.

Alkaline water electrolysis is regarded as a promising technology for sustainable energy conversion. Spinel oxides have attracted considerable attention as potential catalysts because of their diverse metal valence states. However, achieving the required current densities at low voltages is a challenge due to its limited active sites and suboptimal electron transport. In this study, we present a novel bifunctional catalyst composed of MnCo2O4.5 nanoneedles grown on NiS nanosheets for water electrolysis. Remarkably, MnCo2O4.5@NiS demonstrates exceptional catalytic activity, requiring 187 and 288 mV to achieve a current density of 100 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The impressive performance of MnCo2O4.5@NiS is demonstrated by the lower value of voltage 1.44 V needed to deliver the current density of 10 mA cm-2, which outperformed the 1.66 V required for a commercial Pt/C||RuO2 system. Detailed structure analysis and density functional theory (DFT) calculations reveal that the MnCo2O4.5@NiS heterostructure enhances electron transfer at the interface, promotes the formation of oxygen vacancies and tunes the electronic structures of Mn and Co. These findings underscore the potential of MnCo2O4.5@NiS as an efficient and cost-effective electrocatalyst for hydrogen production.

(Y3+/Sm3+)-doped and co-doped CoFe2O4 for heterogeneous advanced oxidation process: structural, magneto-optical, and photocatalytic investigations.

The photocatalytic properties of CoFe2O4 nanoparticles were activated by the doping and co-doping of a low level of Y3+ and Sm3+ cations. After optimizing the annealing temperature, 900 °C was found to be the optimal temperature for the successful incorporation of Y3+ and Sm3+ into the spinel structure. The purity of our samples annealed at 900 °C was confirmed using several characterization methods, including PXRD, SEM, XPS, VSM, FTIR, and Raman spectroscopy. Thus, we were able to increase the photocatalytic degradation of orange G dye from 9.9 to 64.63% for the Sm3+-doped sample, 76.42% for the Y3+-doped sample, and even 85.81% for the co-doped sample under 60 min of UV-visible light irradiation. The beneficial effect of samarium and yttrium doping and co-doping is attributed to several factors: the first factor is doped and co-doped rare earth impurities induce distortion in the lattice, the larger the ionic radii of dopant element, the highest is the photocatalytic activity; second factor, upon doping and co-doping of rare earth impurities in the structure of CoFe2O4 leads to the creation of donor state level within the band gap, causing the Fermi energy to shift near the conduction band. Third factor, co-doping produced strong interactions, which accelerated photocarrier mobility and transport; lastly, longer electron-holes lifetime. We have provided a detailed study of the structural, vibrational, and optical properties to support our conclusions.

Efficient asymmetric diffusion channel in MnCo2O4 spinel for ammonium-ion batteries.

Transition metal oxides ion diffusion channels have been developed for ammonium-ion batteries (AIBs). However, the influence of microstructural features of diffusion channels on the storage and diffusion behavior of NH4+ is not fully unveiled. In this study, by using MnCo2O4 spinel as a model electrode, the asymmetric ion diffusion channels of MnCo2O4 have been regulated through bond length optimization strategy and investigate the effect of channel size on the diffusion process of NH4+. In addition, the reducing channel size significantly decreases NH4+ adsorption energy, thereby accelerating hydrogen bond formation/fracture kinetics and NH4+ reversible diffusion within 3D asymmetric channels. The optimized MnCo2O4 with oxygen vacancies/carbon nanotubes composite exhibits impressive specific capacity (219.2 mAh g-1 at 0.1 A g-1) and long-cycle stability. The full cell with 3,4,9,10-perylenetetracarboxylic diimide anode demonstrates a remarkable energy density of 52.3 Wh kg-1 and maintains 91.9% capacity after 500 cycles. This finding provides a unique approach for the development of cathode materials in AIBs.

Intrinsic exchange bias from interfacial reconstruction in an epitaxial NixCoyFe3-x-yO4(111)/α-Al2O3(0001) thin film family.

Intrinsic exchange bias is known as the unidirectional exchange anisotropy that emerges in a nominally single-component ferro-(ferri-)magnetic system. In this work, with magnetic and structural characterizations, we demonstrate that intrinsic exchange bias is a general phenomenon in (Ni, Co, Fe)-based spinel oxide films deposited onα-Al2O3(0001) substrates, due to the emergence of a rock-salt interfacial layer consisting of antiferromagnetic CoO from interfacial reconstruction. We show that in NixCoyFe3-x-yO4(111)/α-Al2O3(0001) films, intrinsic exchange bias and interfacial reconstruction have consistent dependences on Co concentrationy, while the Ni and Fe concentration appears to be less important. This work establishes a family of intrinsic exchange bias materials with great tunability by stoichiometry and highlights the strategy of interface engineering in controlling material functionalities.

An Unprecedented Tridentate-Bridging Coordination Mode of Permanganate Ions: The Synthesis of an Anionic Coordination Polymer-[CoIII(NH3)6]n[(K(κ1-Cl)2(µ2,2',2″-(κ3-O,O',O″-MnO4)2)n∞]-Containing Potassium Central Ion and Chlorido and Permanganato Ligands.

A unique compound (compound 1) with structural features including an unprecedented tridentate-bridging coordination mode of permanganate ions and an eight-coordinated (rhombohedral) κ1-chlorido and tridentate permanganato ligand in a potassium complex containing coordination polymer (CoIII(NH3)6]n[(K(κ1-Cl)2(µ2,2',2″-(κ3-O,O',O″-MnO4)2)n∞) with isolated regular octahedral hexamminecobalt(III) cation was synthesized with a yield of >90%. The structure was found to be stabilized by mono and bifurcated N-H∙∙∙Cl and N-H∙∙∙O (bridging and non-bridging) hydrogen bonds. Detailed spectroscopic (IR, far-IR, and Raman) studies and correlation analysis were performed to assign all vibrational modes. The existence of a resonance Raman effect of compound 1 was also observed. The thermal decomposition products at 500 °C were found to be tetragonal nano-CoMn2O4 spinel with 19-25 nm crystallite size and KCl. The decomposition intermediates formed in toluene at 110 °C showed the presence of a potassium- and chloride-containing intermediates combined into KCl during aqueous leaching, together with the formation of cobalt(II) nitrate hexahydrate. This means that the CoIII-CoII redox reaction and the complete decomposition of the permanganate ions occurred in the first decomposition step, with a partial oxidation of ammonia into nitrate ions.

Facet-Dependent Evolution of Active Components on Spinel Co3O4 for Electrochemical Ammonia Synthesis.

Spinel cobalt oxides (Co3O4) have emerged as a promising class of catalysts for the electrochemical nitrate reduction reaction (eNO3RR) to ammonia, offering advantages such as low cost, high activity, and selectivity. However, the specific role of crystallographic facets in determining the catalysts' performance remains elusive, impeding the development of efficient catalysts. In this study, we have synthesized various Co3O4 nanostructures with exposed facets of {100}, {111}, {110}, and {112}, aiming to investigate the dependence of the eNO3RR activity on the crystallographic facets. Among the catalysts tested, Co3O4 {111} shows the best performance, achieving an ammonia Faradaic efficiency of 99.1 ± 1.8% with a yield rate of 35.2 ± 0.6 mg h-1 cm-2 at -0.6 V vs RHE. Experimental and theoretical results reveal a transformation process in which the active phases evolve from Co3O4 to Co3O4-x with oxygen vacancy (Ov), followed by a Co3O4-x-Ov/Co(OH)2 hybrid, and finally Co(OH)2. This process is observed for all facets, but the formation of Ov and Co(OH)2 is the most rapid on the (111) surface. The presence of Ov significantly reduces the free energy of the *NH2 intermediate formation from 1.81 to -0.53 eV, and plentiful active sites on the densely reconstructed Co(OH)2 make Co3O4 {111} an ideal catalyst for ammonia synthesis via eNO3RR. This work provides insights into the understanding of the realistic active components, offers a strategy for developing highly efficient Co-based spinel catalysts for ammonia synthesis through tuning the exposed facets, and helps further advance the design and optimization of catalysts in the field of eNO3RR.

Electrical transport and dielectric relaxation mechanism in Zn0.5Cd0.5Fe2O4 spinel ferrite: A temperature- and frequency-dependent complex impedance study.

In the present study, the frequency-dependent dielectric relaxation and electrical conduction mechanisms in sol-gel-derived Zn0.5Cd0.5Fe2O4 (ZCFO) spinel ferrite were studied in the temperature range of 343-438 K. The formation of the ZCFO spinel ferrite phase with space group Fd3m was confirmed by X-ray diffraction analysis. The dielectric relaxation and electrical conduction mechanisms were studied using complex impedance spectroscopy (CIS). In the Nyquist plots, depressed semicircles were fitted with an equivalent circuit model with configuration (RGBQGB) (RGQG), signifying the contributions from grain boundaries and grains to the charge transport mechanism in the sample. The frequency-dependent AC conductivity was found to follow Jonscher's power law, and the frequency exponent term depicted the overlapping large polaron hopping (OLPH) model as the dominant transport mechanism. The activation energies for conductivity, electric modulus and impedance were calculated to identify the nature of the charge carriers governing the relaxation and conduction mechanisms in the prepared sample. Complex modulus studies confirmed the non-Debye type of dielectric relaxation, whereas tangent loss and dielectric constant analyses confirmed the thermally activated hopping mechanism of charge carriers in Zn0.5Cd0.5Fe2O4 spinel ferrite.

Synthesis of MnFe2O4 Spinel on Rusted Q235 Steel Surface and Its Corrosion Resistance Properties.

Corrosion of steel is an issue that cannot be ignored in contemporary society. Due to large-scale corrosion, it is urgent to develop a surface treatment process that enhances the corrosion resistance of steel, allowing for application in various scenarios as needed. This study aims to investigate a novel surface treatment process to extend the service life of corroded Q235 steel, reduce its sensitivity to corrosion, and enable its use in multiple environments. This study employs the sol-gel method, using manganese nitrate solutions of varying concentrations to treat the surface of Q235 steel after different electrolysis times. The optimal conditions for precursor preparation were found to be a Mn2+ concentration of 0.1 mol/L and an electrolysis time of 2 h. Electrochemical tests using NaCl solutions of different concentrations revealed a significant reduction in the corrosion current for the composite coating based on Q235 steel treated with this method in NaCl solutions with wt.% = 1, 2, 3, 4, 5. Furthermore, the resistance to corrosion was strongest in the NaCl solution with a concentration of 1 wt.% where the corrosion current decreased from 24.8 µA/cm2 to 6.79 µA/cm2. Additionally, the coating was found to be diffusion-controlled in the early stages of the corrosion process and charge transfer-controlled in the later stages. The MnFe2O4 spinel coating demonstrated the greatest enhancement in corrosion resistance in the wt.% = 1 NaCl solution.

Enhancing Lithium Conductivity Using High-Valence Cations in Cubic Spinel Halide Solid Electrolytes.

Halide solid electrolytes for all-solid-state batteries have recently emerged as competitors to oxide and sulfide solid electrolytes due to their excellent electrochemical properties. This ab initio study unveils the dynamic nature of Li2Sc2/3Cl4, a rare superionic conductor among cubic spinel halide materials. Li ions in Li2Sc2/3Cl4 prefer to occupy some of the tetrahedral 8a, octahedral 16c, and octahedral 16d sites, leading to disordered Li distribution. Li ions in Li2Sc2/3Cl4 diffuse through the single-ion diffusion mechanism rather than the concerted diffusion mechanism, providing a high conductivity of 1.36 mS cm-1. Li ions at the 16d site diffuse as actively as those at the 8a/16c site, an unexpected result that runs counter to the conventional view. In Li2MgCl4, the same cubic spinel as Li2Sc2/3Cl4, Li ions at the 8a/16c site diffuse actively, but those at the 16d site are almost immobile, resulting in a very low conductivity of 5.3 × 10-4 mS cm-1. The extremely higher conductivity in Li2Sc2/3Cl4 than in Li2MgCl4 is because the concentration of Sc3+/Mg2+ cations blocking the movement of Li ions at the 16d site is lower in Li2Sc2/3Cl4 than in Li2MgCl4. Designing cubic spinel materials containing high-valence cations is proposed as a way to increase conductivity by reducing the concentration of multivalent cations that impede Li diffusion. This study sheds new light on how to control conductivity using site-dependent Li mobility in solid electrolytes.

Spinel-Type Structured Phosphor Near-Infrared-II Emission: Intervalence Charge Transfer and Hetero-Valent Chromium Pairs.

Near-infrared (NIR) emitting phosphors draw much attention because they show great applicability and development prospects in many fields. Herein, a series of inverse spinel-type structured LiGa5O8 phosphors with a high concentration of Cr3+ activators is reported with a dual emission band covering NIR-I and II regions. Except for strong ionic exchange interactions such as Cr3+-Cr3+ and Cr3+ clusters, an intervalence charge transfer (IVCT) process between aggregated Cr ion pairs is proposed as the mechanism for the ~1210 nm NIR-II emission. Comprehensive structural and luminescence characterization points to IVCT between two Cr3+ being induced by structural distortion and further enhanced by irradiation. Construction of the configurational energy level diagram enabled elucidation of this transition within the IVCT process. Therefore, this work provides insight into the emission mechanism within the high Cr3+ concentration system, revealing a new design strategy for NIR-II emitting phosphors to promote its response.

Near-Infrared Mechanoluminescence from Cr3+-Doped Spinel Nanoparticles for Potential Oral Diseases Detection.

Mechanoluminescence (ML) phosphors have found various promising utilizations such as in non-destructive stress sensing, anti-counterfeiting, and bio stress imaging. However, the reported NIR MLs have predominantly been limited to bulky particle size and weak ML intensity, hindering the further practical applications. For this regard, a nano-sized ZnGa2O4: Cr3+ NIR ML phosphor is synthesized by hydrothermal method. By improving the synthesis method and regulating the chemical composition, the NIR ML (600-1000 nm) intensity of such nano-materials has been further enhanced about four times. The reasons for the ML performance difference between micro-/nano- sized phosphors also have been preliminarily analyzed. Additionally, this work probes into the ML mechanism deeply in traps' aspect from band structure and defect formation energy, which can supply significant references for a new approach to develop efficient NIR ML nanoparticles. Finally, due to excellent tissue penetration capability, nano-sized ZnGa2O4:Cr3+ NIR ML phosphor shows great potential applications in biomedical fields such as for the detection of clinical oral diseases.

Entropy-induced high-density grain boundaries in Co-free high-entropy spinel oxides for highly reversible lithium storage.

Transition metal oxides (TMOs) with high discharge capacity are considered as one of the most promising anodes for lithium-ion batteries. However, the practical utilization of TMOs is largely limited by cycling stability issues arising from volume expansion, structural collapse. In this study, we synthesized a high-entropy spinel oxide material (FeCrNiMnZn)3O4 using a solution combustion method. With the implementation of five cations through high-entropy engineering, the agglomeration and expansion of the electrode materials during charging and discharging are suppressed, and the cycling stability is enhanced. The results demonstrate that entropy-induced high-density grain boundaries and the reversibility of spinel structure contribute to improved capacity and cycling stability. Herein, (FeCrNiMnZn)3O4 provides a high capacity (1374 mAh g-1) at 0.1 A g-1 and superior cycling stability (almost 100 %) during 200 cycles with a current density of 0.5 A g-1. The study provides valuable understanding for designing the high entropy oxides anode electrodes.

Enhancement of dielectric permittivity and Havriliak-Negami relaxation mechanism in MnFe2O4through Dy substitution.

Pristine and Dy substituted MnFe2O4,MnFe2-xDyxO4(x= 0.00, 0.02, 0.04, 0.06, 0.08 & 0.10) were successfully synthesized by sol-gel method to investigate the dielectric properties of the system. MnFe2O4exhibits a high dielectric permittivity of order 104which is further augmented by 60% through Dy substitution. This is owing to the rise in interfacial polarization resulting from localized states, dipolar polarization arising from the multiple valence states of Fe and Mn ions, atomic polarization due to structural distortion induced by strain, and electronic polarization stemming from the concentration of free charge carriers. The enhancement of induced strain, mixed valence ratio of Fe2+/Fe3+and Mn4+/Mn2+, localized states, and free charge carrier concentration are confirmed from the XRD, XPS, and optical studies, respectively. The dielectric relaxation mechanism of MnFe2-xDyxO4follows a modified Havriliak-Negami relaxation model with conductivity contribution. Complex impedance analyses further validate the contribution of grain-grain boundary mechanisms to the dielectric properties confirmed through Nyquist plots. A comprehensive analysis of conductivity reveals the significant impact of Dy substitution on the electrical conductivity of MnFe2O4. This influence is strongly related to the variations in the concentration of free charge carriers within the MnFe2-xDyxO4system. The understanding of the underlying physics governing the dielectric properties of Dy-substituted MnFe2O4not only enhances the fundamental knowledge of material behavior but also opens new avenues for the design and optimization of advanced electronic and communication devices.

Tailoring structural and optical properties of Cu(II)-induced MgAl2O4 nanoparticles and their response to toxic dyes under solar illumination.

Worldwide environmental challenges pose critical problems with the growth of the global economy. Addressing these issues requires the development of an eco-friendly and sustainable catalyst for degrading organic dye pollutants. In this study, copper-doped magnesium aluminates (CuxMg1-xAl2O4) with x = 0.0-0.8 were synthesized using a citrate-based combustion route. The inclusion of Cu(II) significantly impacted the structural, microstructural, optical, and photocatalytic activity of the catalyst. Rietveld analysis of X-ray diffraction powder profiles revealed single-phase spinels crystallized in the face-centered cubic unit cell with Fd 3 ¯ m space group. Chemical states of the ions, surface morphology, and elemental investigation were analyzed by X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. UV-visible and diffuse reflectance spectroscopies confirmed the reduction of the band gap due to Cu(II) doping, validated by first-principle investigations using the WIEN2k code. The catalyst with x = 0.8 showed higher photocatalytic efficacy (90% and 93%) for removing two azo organic dye pollutants, rhodamine B and methyl orange, respectively, within 120 min. Degradation kinetics followed a pseudo-first-order mechanism. The doped (0.8) sample was structurally and morphologically stable and reusable under visible irradiation, retaining performance after three runs. Scavenger studies confirmed hydroxyl and superoxide radicals' involvement in the degradation. This work presents an effective approach to enhancing CuxMg1-xAl2O4 catalysts' photodegradation performance, with potential applications in pharmaceuticals and wastewater remediation.

Promoting Surface Reconstruction in Spinel Oxides via Tetrahedral-Octahedral Phase Boundary Construction for Efficient Oxygen Evolution.

Understanding the origin of surface reconstruction is crucial for developing highly efficient lattice oxygen oxidation mechanism (LOM) based spinel oxides. Traditionally, the reconstruction has been achieved through electrochemical procedures, such as cyclic voltammetry (CV), linear sweep voltammetry (LSV). In this work, we found that the surface reconstruction in LOM-based CoFe0.25Al1.75O4 catalyst was an irreversible oxygen redox chemical reaction. And a lower oxygen vacancy formation energy (EO-V) could benefit the combination of the activated lattice oxygen atoms with adsorbed water molecular. Motivated by this finding, a strategy of phase boundary construction from Co tetrahedral to octahedral was employed to decrease EO-V in CoFe0.25Al1.75O4. The results showed that as the Co octahedral occupancy ratio rose to 64 %, a 3.5 nm-thick reconstructed layer formed on the catalyst surface with a 158 mV decrease in overpotential. Further experiments indicated that the coexistence of tetrahedral-octahedral (O-T) phase would result in lattice mismatch, promoting non-bonding oxygen states and lowering EO-V. Then more active lattice oxygen combined with H2O molecules to generate hydroxide ions (OH-), followed by soluble cation leaching, which enhanced the reconstruction process. This work provided new insights into the relationship between the intrinsic structure of pre-catalysts and surface reconstruction in LOM-based spinel electrocatalysts.