Photocatalytic H2 generation from spinels ZnFe2O4, ZnFeGaO4 and ZnGa2O4

Enhanced Acetone-Sensing Performance of a Bilayer Structure Gas Sensor Composed of a ZnO Nanorod Top Layer and a ZnFe2O4 Nanoparticle Decorated ZnO Nanorod Bottom Layer

In this study, we report a high-performance acetone gas sensor utilizing a bilayer structure composed of a ZnO nanorod top layer and a ZnFe2O4 nanoparticle-decorated ZnO nanorod bottom layer. ZnO nanorods were synthesized via a water-bath method, after which the ZnFe2O4 nanoparticle-decorated ZnO nanorods were prepared using a simple immersion and calcination method. SEM and TEM revealed the porous morphology of the samples and the formation of ZnO-ZnFe2O4 heterojunctions. XPS analysis demonstrated an increase in oxygen vacancy content with the introduction of ZnFe2O4 nanoparticles. Compared to pure ZnO nanorods, ZnFe2O4-decorated ZnO nanorods showed a 3.9-fold increase in response to 50 ppm acetone. Covering this layer with ZnO nanorods further increased the response by an additional 1.6 times, and simultaneously enhanced the selectivity to acetone. The top layer improves gas sensing performance by introducing heterojunctions with the bottom layer, partially blocking acetone gas at the bottom layer to facilitate a more complete reaction, and filtering ethanol interference.

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

The transformation of renewable bio-oil into value-added 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, thereby 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 tailored specifically for upgrading bio-oil. Its objective is to shed light on their potential to address the limitations of conventional catalysts, thereby advancing sustainable biofuel production. Initially, a comprehensive analysis is conducted on different metal oxide composites in terms of their similarity and dissimilarity on properties. Subsequently, the synthesis methodologies of spinels are scrutinised and potential avenues for their modification are explored. Following this, an in-depth discussion ensues regarding the utilisation of spinels as catalysts or catalyst precursors for catalytic cracking, ketonisation, catalytic hydrodeoxygenation, steam and aqueous-phase reforming, as well as electrocatalytic upgrading of bio-oil, with a specific emphasis on elucidating their catalytic reactivity, and underlying structure-activity correlation and catalysis mechanisms. Finally, the challenges and potential prospects in utilising spinels for the catalytic valorisation of renewable biofuel are addressed, with a specific focus on the use of 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.

A Superhydrophilic, Light/Microwave-Absorbing Coating with Remarkable Antibacterial Efficacy

Driven by the overuse of antibiotics, pathogenic infections, dominated by the rapid emergence of antibiotic resistant bacteria, have become one of the greatest current global health challenges. Thus, there is an urgent need to explore novel strategies that integrate multiple antibacterial modes to deal with bacterial infections. In this work, a Co(Ni,Ag)/Fe(Al,Cr)₂O₄ composite duplex coating was fabricated using template-free sputtering deposition technology. The phase constitution of the coating was estimated to be 79 wt % Fe(Al,Cr)₂O₄ phase and 21 wt % of an Ag-containing metallic phase. The composite coating consisted of a ∼10 μm-thick porous outer-layer and a ∼6 μm-thick compact inner-layer, in which the outer-layer is composed of a densely stacked array of microscale cones. After exposure to ambient air for 14 days, the composite coating showed a wettability transition from a superhydrophilic nature to exhibit adhesive superhydrophobic behavior with a water contact angle of 142° ± 2.8°, but it reverted to its initial superhydrophilic state after annealing in air at 200 °C for 5 h. The absorption rate of the as-received composite coating exceeds 99% in a broad band spanning both the visible and NIR regions and showed a high photothermal efficiency to convert photon energy into heat. Similarly, the composite coating showed microwave absorption behavior with a minimum reflection loss value of 38 dB at 4.4 GHz. In vitro antibacterial tests were used to determine the antibacterial behavior of the composite coating against Escherichia coli and Staphylococcus aureus after 60 min of visible light irradiation. After this exposure, the as-prepared composite coating exhibited nearly 100% bactericidal efficiency against these bacteria. The antibacterial behavior of the coating was attributed to the synergistic effects of the superhydrophilic surface, the release of Ag⁺ ions, and the photothermal effect. Therefore, this composite coating may be a promising candidate to efficiently combat medical device-associated infections.

Spinel ferrites (MFe2O4): Synthesis, improvement and catalytic application in environment and energy field

To develop efficient catalysts is one of the major ways to solve the energy and environmental problems. Spinel ferrites, with the general chemical formula of MFe₂O₄ (where M = Mg²⁺, Co²⁺, Ni²⁺, Zn²⁺, Fe²⁺, Mn²⁺, etc.), have attracted considerable attention in catalytic research. The flexible position and valence variability of metal cations endow spinel ferrites with diverse physicochemical properties, such as abundant surface active sites, high catalytic activity and easy to be modified. Meanwhile, their unique advantages in regenerating and recycling on account of the magnetic performances facilitate their practical application potential. Herein, the conventional as well as green chemistry synthesis of spinel ferrites is reviewed. Most importantly, the critical pathways to improve the catalytic performance are discussed in detail, mainly covering selective doping, site substitution, structure reversal, defect introduction and coupled composites. Furthermore, the catalytic applications of spinel ferrites and their derivative composites are exclusively reviewed, including Fenton-type catalysis, photocatalysis, electrocatalysis and photoelectro-chemical catalysis. In addition, some vital remarks, including toxicity, recovery and reuse, are also covered. Future applications of spinel ferrites are envisioned focusing on environmental and energy issues, which will be pushed by the development of precise synthesis, skilled modification and advanced characterization along with emerging theoretical calculation.

Achieving cadmium selenide-decorated zinc ferrite@titanium dioxide hollow core/shell nanospheres with improved light trapping and charge generation for photocatalytic hydrogen generation

We report the rational design and fabrication of magnetically separable zinc ferrite@titanium dioxide (ZnFe₂O₄@TiO₂) hollow core/shell nanospheres as photocatalysts for efficient H₂ evolution by loading the TiO₂ shell layer on the prepared ZnFe₂O₄ hollow nanospheres using the kinetics-controlled coating method. Meanwhile, the incident light absorption, photogenerated charge transfer and separation and photocatalytic hydrogen evolution activity were remarkably improved by well anchoring cadmium selenide (CdSe) quantum dots on the ZnFe₂O₄@TiO₂ hollow core/shell nanospheres. This unique design integrates the structural and functional merits of the ZnFe₂O₄, TiO₂, and CdSe quantum dots into porous hollow nanospheres with the double-shell heterostructure. This design significantly accelerates the separation and transport of photogenerated charge carriers, enhances the light absorption, and offers more active sites for the photocatalytic H₂ evolution reaction. Benefitting from the unique structural and component merits, the optimized magnetically separable ZnFe₂O₄@TiO₂/CdSe hollow core/shell nanospheres exhibit excellent photocatalytic hydrogen evolution performance with a high H₂ generation rate (266.0 μmol h^-1·g^-1) and high stability.

High Selectivity to Aromatics by a Mg and Na Co-modified Catalyst in Direct Conversion of Syngas

The demand for aromatics, especially benzene, toluene, and xylene, has been increased in recent years as the crucial feedstocks of coatings and pharmaceutical industry. In this work, a modified Fischer-Tropsch synthesis (FTS) catalyst FeNaMg was fabricated via a sol-precipitation method and integrated with an HZSM-5 aromatization catalyst for the aromatics synthesis from syngas by a one-step process. Syngas was first converted to lower olefins as intermediates on the active component of the FeNaMg catalyst followed by aromatization on zeolite. Different characterization approaches, such as BET, XRD, XPS, hydrogen temperature-programmed reduction, temperature-programmed desorption of CO, TG, and SEM, revealed that Mg efficiently optimized physicochemical properties of the Fe-based catalyst by generating a MgFe2O4 spinel structure. Further investigation demonstrated that the MgFe2O4 spinel structure could increase the syngas adsorption area, facilitating the reduction and carburization of the Fe phase, while Mg decreased CO2 selectivity (31.26 to21%) by restraining the water-gas shift reaction and improved the utilization efficiency of carbon. At the same time, alkali metal Na changed the surface electronic environment of the FTS catalyst to enhance CO adsorption as an electronic promoter, which suppressed methane formation by restraining over hydrogenation. Therefore, the synergism that existed between Mg and Na during the reaction escalated the CO conversion and aromatics selectivity to 96.19 and 51.38%, respectively.

MAl2O4 (M=Ba, Mg) photocatalytic activity dependence on annealing atmosphere

Aluminate spinel type ${{\rm MAl}_2}{{\rm O}_4}$MAl₂O₄ (M=Ba or Mg) materials prepared using the combustion synthesis method were annealed either in an air or carbon atmosphere. The materials were characterized using X-ray diffraction, scanning electron microscopy, diffuse reflectance spectra, electrochemical impedance spectroscopy, and photoluminescence (PL) measurements. Their photocatalytic activity was evaluated for the dye degradation and hydrogen evolution. Methylene blue (15 ppm) was completely degraded using the air-annealed barium aluminate after 90 min, while a maximum hydrogen generation rate of $97 . 0 \;{\rm\unicode{x00B5}{\rm mol}\cdot{\rm h}^{ - 1}\cdot{\rm g}^{ - 1}}$97.0µmol⋅h^-1⋅g^-1 was achieved using the carbon-annealed magnesium aluminate. The results suggest that air-annealed photocatalysts are suitable for oxidation-dependent reactions, while carbon annealing may enhance reduction-dependent reactions.

Synthesis of a GaOOH/ZnBiTaO5heterojunction photocatalyst with enhanced photocatalytic performance toward enrofloxacin

In this work, a GaOOH/ZnBiTaO₅ heterojunction photocatalyst was synthesized innovatively and characterization techniques including XRD, SEM-EDS, XPS, FT-IR, PL and UV-Vis DRS were carried out to analyse the structural and morphological properties of the GaOOH/ZnBiTaO₅ heterojunction photocatalyst. The GaOOH is dispersed on the surface of ZnBiTaO₅ to form a heterojunction structure according to the SEM image. The band gaps of 10 wt%, 25 wt% and 50 wt% GaOOH/ZnBiTaO₅ heterojunction photocatalysts were calculated to be 3.21 eV, 3.22 eV and 3.23 eV, respectively, which were between the band gaps of pure ZnBiTaO₅ (3.19 eV) and pure GaOOH (4.76 eV). The photocatalytic performance of the GaOOH/ZnBiTaO₅ heterojunction photocatalyst was investigated by degrading enrofloxacin under ultraviolet light. The results showed that the as-prepared 25 wt% GaOOH/ZnBiTaO₅ presented optimal photocatalytic performance and could remove 58.27% of enrofloxacin in 60 min, which was higher than that of pure ZnBiTaO₅ (53.7%) and pure GaOOH (35.4%). In addition, it was confirmed that ˙O₂⁻, h⁺ and ˙OH were all the active radicals during the degradation process. Finally, the possible degradation mechanism of enrofloxacin was discussed in detail. This work provided a viable strategy for improving the photocatalytic performance of wide band gap semiconductors.

A GaOOH/ZnBiTaO₅ heterojunction photocatalyst was synthesized innovatively and characterized by XRD, SEM-EDS, XPS, FT-IR, PL and UV-Vis DRS to analyse the structural and morphological properties of the GaOOH/ZnBiTaO₅ heterojunction photocatalyst.

Progress on ternary oxide-based photoanodes for use in photoelectrochemical cells for solar water splitting

Solar water splitting using photoelectrochemical cells (PECs) has emerged as one of the most promising routes to produce hydrogen as a clean and renewable fuel source. Among various semiconductors that have been considered as photoelectrodes for use in PECs, oxide-based photoanodes are particularly attractive because of their stability in aqueous media in addition to inexpensive and facile processing compared to other types of semiconductors. However, they typically suffer from poor charge carrier separation and transport. In the past few years, there has been tremendous progress in developing ternary oxide-based photoelectrodes, specifically, photoanodes. The use of ternary oxides provides more opportunities to tune the composition and electronic structure of the photoelectrode compared to binary oxides, thus providing more freedom to tune the photoelectrochemical properties. In this article, we outline the important characteristics to analyze when evaluating photoanodes and review the major recent progress made on the development of ternary oxide-based photoanodes. For each system, we highlight the favorable and unfavorable features and summarize the strategies utilized to address the challenges associated with each material. Finally, by combining our analyses of all the photoanodes surveyed in this review, we provide possible future research directions for each compound and an outlook for constructing more efficient oxide-based PECs. Overall, this review will provide a critical overview of current ternary oxide-based photoanodes and will serve as a platform for the design of future oxide-based PECs.

In situ fabrication of two-dimensional g-C3N4/Ba5Ta4O15 nanosheet heterostructures with efficient charge separations and photocatalytic hydrogen evolution under visible light illumination

Separation of photo-generated electron-hole pairs plays a crucial role in determining the practical performance of semiconductor photocatalysts. Here we have successfully fabricated two dimensional g-C₃N₄/Ba₅Ta₄O₁₅ nanosheet heterostructures through an in situ urea degradation method. The so-formed nanosheet heterostructures demonstrate superior photocatalytic activities in H₂ evolution reactions over individual component. Further analysis using photoelectrochemical measurements suggests efficient charge separations at the interfaces of these heterostructures which contribute to a prolonged lifetime of photo-generated charges as well as the much enhanced photocatalytic activities. The in situ fabrication method adopted in this work ensures a firm anchorage of g-C₃N₄ onto Ba₅Ta₄O₁₅ nanosheets and a face-to-face contact between these two semiconductors. Such a peculiar microstructure is critical to the high photocatalytic activity and apparently outweighs the conventional ones that involve only physical mixtures of two semiconductors and a point-to-point contact.

SrCrxFe12-xO19 nanoceramics as an effective catalyst for desulfurization of liquid fuels: Green sol-gel synthesis, characterization, magnetic and optical properties

In this work, SrCr_xFe_12-xO₁₉ (x = 0.0, 0.5, 1.0, 1.5) nanostructures were successfully synthesized by sol-gel auto-combustion method, and different aminoacids were used as green reductants. Various analysis results show that SrCr_xFe_12-xO₁₉ nanoparticles synthesized successfully.The present study shows that SrCr_xFe_12-xO₁₉ nanoparticle could be used as adsorbent for the desulfurization of liquid fuels. Increasing of nanoparticles concentration was caused to increase the adsorption rate of sulfur contents of fuel. The adsorption rate of sulfur contents of fuel in various concentrations 4.5, 9.5, and 18.5 g. L ^-1 of SrCr_xFe_12-xO₁₉ nanoparticles in solution was estimated about 39, 50, and 62% for 30 min, respectively. The results of catalytic tests reveals that SrCr_xFe_12-xO₁₉ nanoparticles have the potential to be used as a new kind of semiconductor catalysts for the desulfurization of liquid fuels. Magnetic property of the final sample was measured at room temperature by a vibration sample magnetometer (VSM) and shown that the intrinsic coercivity of product is about 6000 Oe and it exhibits characteristics of single magnetic domains (M_r/ M_s = 0.53).

One-step synthesis, electronic structure, and photocatalytic activity of earth-abundant visible-light-driven FeAl2O4

The development of inexpensive visible-light-driven photocatalysts is an important prerequisite for realizing the industrial application of photocatalysis technology. In this paper, an earth-abundant FeAl₂O₄ photocatalyst is prepared via facile solution combustion synthesis. Density functional theory and the scanning Kelvin probe technique are employed to ascertain the positions of the energy bands and the Fermi level. Phenol is taken as a model pollutant to evaluate the photocatalytic activity of FeAl₂O₄. The scavenger experiment results, ˙OH-trapping fluorescence technique, and electron spin resonance measurements confirm that the superoxide anion radical is the main active species generated in the photocatalytic process, which also further corroborates the proposed electronic structure of FeAl₂O₄. The degradation experiments and O₂ temperature programmed desorption results over various samples verify that the crystallinity degree is a more important factor than the oxygen adsorption ability in determining photocatalytic activity.

Simultaneous bacterial inactivation and degradation of an emerging pollutant under visible light by ZnFe2O4co-modified with Ag and rGO

Simultaneous photo-inactivation ofE. coliand degradation of EE2 was achieved in the presence of ZnFe₂O₄-Ag/rGO. H₂O₂was mainly responsible for bacterial inactivation whereas, OH˙ was found to have more influence in EE2 degradation.

Robust, double-shelled ZnGa2O4 hollow spheres for photocatalytic reduction of CO2 to methane

Robust, double-shelled ZnGa₂O₄ hollow spheres were fabricated for photocatalytic reduction of CO₂ to methane.

Preparation and enhanced photocatalytic hydrogen-evolution activity of ZnGa2O4/N-rGO heterostructures

Schematic diagram of photocatalytic hydrogen-evolution of ZnGa₂O₄/N-rGO illustrating that N-rGO acted as a catalyst support and electron sink for promoting charge separation and transfer.

Homologous Compounds ZnnIn2O3+n (n = 4, 5, and 7) Containing Laminated Functional Groups as Efficient Photocatalysts for Hydrogen Production

Strong visible light absorption and high charge mobility are desirable properties for an efficient photocatalyst, yet they are hard to be realized simultaneously in a single semiconductor compound. In this work, we demonstrate that these properties coexist in homologous compounds Zn_nIn₂O_3+n (n = 4, 5, and 7) with a peculiar layered structure that combines optical active segment and electrical conductive segment together. Their enhanced visible light absorption originates from tetrahedrally or trigonal-bipyramidally coordinated In atoms in Zn(In)O₄₍₅₎ layers which enable p-d hybridization between In 4d and O 2p orbitals so that valence band minimum (VBM) is uplifted with a reduced band gap. Theoretical calculations reveal their anisotropic features in charge transport and functionality of different constituent segments, i.e., Zn(In)O₄₍₅₎ layers and InO₆ layers as being for charge generation and charge collection, respectively. Efficient photocatalytic hydrogen evolution was observed in these compounds under full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm). High apparent quantum efficiency ∼2.79% was achieved for Zn₄In₂O₇ under full range irradiation, which is almost 5-fold higher than their parent oxides ZnO and In₂O₃. Such superior photocatalytic activities of these homologous compounds can be understood as layer-by-layer packing of charge generation/collection functional groups that ensures efficient photocatalytic reactions.

Novel carbon-incorporated porous ZnFe2O4nanospheres for enhanced photocatalytic hydrogen generation under visible light irradiation

Surface hybridization of ZnFe₂O₄nanospheres with graphite-like carbon layers yields enhanced photocatalytic hydrogen production activity.

Structural dependence of the photocatalytic properties of double perovskite compounds A2InTaO6 (A = Sr or Ba) doped with nickel

Photocatalytic activity is greatly improved when there is no structural distortion, which guarantees maximal metal–oxygen–metal interactions.

Efficient charge separation based on type-II g-C3N4/TiO2-B nanowire/tube heterostructure photocatalysts

Separation of photo-generated charges has played a crucial role in controlling the actual performance of a photocatalytic system. Here we have successfully fabricated g-C3N4/TiO2-B nanowire/tube heterostructures through facile urea degradation reactions. Owing to the effective separation of photo-generated charges associated with the type-II band alignment and intimate interfacial contacts between g-C3N4 and TiO2-B nanowires/tubes, such heterostructures demonstrate an improved photocatalytic activity over individual moieties. Synthetic conditions such as hydrothermal temperatures for the preparation of TiO2-B and the weight ratio of TiO2-B to urea were systematically investigated. A high crystallinity of TiO2-B as well as the proper growth of g-C3N4 on its surface are critical factors for a better performance. Our simple synthetic method and the prolonged lifetime of photo-generated charges signify the importance of type-II heterostructures in the photocatalytic applications.

Synthesis, crystal structure, photodegradation kinetics and photocatalytic activity of novel photocatalyst ZnBiYO4

ZnBiYO4 was synthesized by a solid-state reaction method for the first time. The structural and photocatalytic properties of ZnBiYO4 were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV-Vis diffuse reflectance. ZnBiYO4 crystallized with a tetragonal spinel structure with space group I41/A. The lattice parameters for ZnBiYO4 were a=b=11.176479Å and c=10.014323Å. The band gap of ZnBiYO4 was estimated to be 1.58eV. The photocatalytic activity of ZnBiYO4 was assessed by photodegradation of methyl orange under visible light irradiation. The results showed that ZnBiYO4 had higher catalytic activity compared with N-doped TiO2 under the same experimental conditions using visible light irradiation. The photocatalytic degradation of methyl orange with ZnBiYO4 or N-doped TiO2 as catalyst followed first-order reaction kinetics, and the first-order rate constant was 0.01575 and 0.00416 min(-1) for ZnBiYO4 and N-doped TiO2, respectively. After visible light irradiation for 220 min with ZnBiYO4 as catalyst, complete removal and mineralization of methyl orange were observed. The reduction of total organic carbon, formation of inorganic products, SO4(2-) and NO3-, and evolution of CO2 revealed the continuous mineralization of methyl orange during the photocatalytic process. The intermediate products were identified using liquid chromatography-mass spectrometry. The ZnBiYO4/(visible light) photocatalysis system was found to be suitable for textile industry wastewater treatment and could be used to solve other environmental chemical pollution problems.

The role of surface Zn2+ ions in the transesterification of vegetable oils over ZnO supported on Al2O3 and Fe2O3

ZnO–Al₂O₃ and ZnO–Fe₂O₃ with different loadings of ZnO (5–20 wt%) along with ZnAl₂O₄ and ZnFe₂O₄ were prepared and tested in the transesterification of sunflower, waste cooking oil and Jatropha oil.