Spinel Metal Oxide Research Articles

A spinel MnCo2O4/NG 2D/2D hybrid nanoarchitectures as advanced electrode material for high performance hybrid supercapacitors

Supercapacitors suffer from lack of energy density and to achieve better energy density, a new class of hybrid architectures with controlled morphology is prerequisite. Here, a facile polyol method is successfully used for the synthesis of MnCo2O4/nitrogen doped graphene 2D/2D hybrid nanoarchitectures and this combination successfully avoids the restacking and agglomeration of nitrogen−doped graphene nanosheets. The formation of MnCo2O4/NG 2D/2D hybrid nanoarchitectures are confirmed by state−of−art techniques. This combination leads to a large conducting network that improves the exposure of active sites at the electrode−electrolyte interface for the transportation of electrons and ions. The synergistic effect of 2D MnCo2O4 nanoflakes over the 2D nitrogen−doped graphene serves the capacitance of ca. 1170 F g−1 at 1 A g−1 with an excellent rate capability of 818 F g−1 at 20 A g−1. An asymmetric supercapacitor is successfully fabricated using these MnCo2O4/NG 2D/2D hybrid nanoarchitectures as the cathode and 2D nitrogen−doped graphene as the anode electrodes, which exhibits better performance than previously reported spinel metal oxide materials. The asymmetric supercapacitor exhibits excellent energy density (∼48.5 Wh kg−1 at ∼808 W kg−1) and power density (∼16000 W kg−1 at ∼32.1 Wh kg−1), with an outstanding cyclic durability of 85.9% retention after 10,000 cycles.

(Invited) Realizing the Electro(photo)Chemical Behavior in Liquid Electrolyte through in-Situ Methodology

Metal oxide of spinel family has performed great potential toward oxygen evolution reaction (OER), but the fundamental mechanism of spinel oxides is still far from being completely understood especially for the role of metal ions. Owing to various coordinated sites of divalent/trivalent metals ions and surface condition (morphology and defects), it’s a great challenge to have a fair assessment of electrocatalytic performance of spinel system. Herein, we demonstrated a series of MFe2O4 (M = Fe, Co, Ni, Zn) family with a well-controlled morphology to achieve comprehensive study of electrocatalytic activity toward OER, in which most of the divalent metals (M2+) of MFe2O4 were located at octahedral sites. By utilizing several analyses, we could conclude a universal rule toward the spinel metal oxide for oxygen evolution. The activities for OER in spinel metal oxide system were determined by the occurrence of phase transformation rather than electronic state of metal ions, and this structural transformation could work well in both crystallographic sites (Td and Oh sites). Additionally, the divalent metal ion significantly dominated the formation of oxyhydroxide through an epitaxial relationship which depended on the atomic arrangement in the interface of spinel and metal oxyhydroxide, while trivalent metal ions were likely to be hosts lattices. The metal oxyhydroxide was formed during redox occurrence rather than OER, while the redox occurrence with remarkable increase in resistance and capacitance might result from the structural transformation from spinel to metal oxyhydroxide. We believed that the approaching strategies and information obtained in present study can offer a guide to design a promising electrocatalytic system toward oxygen evolution reaction and other fields.

Rate-dependent electrochemical reaction mechanism of spinel metal oxide anode studied by in situ TEM

Spinel Co3O4, as conversion-type transitional metal oxide, has attracted extensive interest for LIBs anode due to its high theoretical capacity. The application of transitional metal oxide including Co3O4 anode has been proved challenging due to voltage hysteresis, bad rate capability, extremely low initial Coulombic efficiency (typically 65∼70%), and volume change induced mechanical failure. Among the facing problems, the fundamental understanding of severe capacity fading at high C-rate is clearly needed to be unveiled. In this paper, we utilized in situ transmission electron microscopy (TEM) to study the electrochemical reaction process of spinel Co3O4 anode and firstly unveiled the rate-dependent morphological and structural evolution process. It has been demonstrated that the structural evolution from pristine Co3O4 phase to the formation of Co/Li2O composites during lithiation (bias = −3 V). Impressively, the Co/Li2O composites could fully delithiated into pure tightly-contacted CoO crystals (∼1.45 nm) at lower delithiated bias (+3 V); while the lithiated products partially transformed into the CoO crystals, and further suffered a severe aggregation (∼6 nm) at higher delithiated bias (+8 V). These findings advance the understanding of the mechanism of capacity fading at high current density (C-rate) in conversion-type spinel Co3O4 anode for lithium ion batteries.

Boosting oxygen reduction activity of spinel CoFe2O4 by strong interaction with hierarchical nitrogen-doped carbon nanocages

The unique hierarchical nitrogen-doped carbon nanocages (hNCNC) are used as a new support to homogeneously immobilize spinel CoFe2O4 nanoparticles by a facile solvothermal method. The so-constructed hierarchical CoFe2O4/hNCNC catalyst exhibits a high oxygen reduction activity with an onset potential of 0.966V and half-wave potential of 0.819V versus reversible hydrogen electrode, far superior to the corresponding 0.846 and 0.742V for its counterpart of CoFe2O4/hCNC with undoped hierarchical carbon nanocages (hCNC) as the support, which locates at the top level for spinel-based catalysts to date. Consequently, the CoFe2O4/hNCNC displays the superior performance to the CoFe2O4/hCNC, when used as the cathode catalysts in the home-made Al-air batteries. X-ray photoelectron spectroscopy characterizations reveal the more charge transfer from CoFe2O4 to hNCNC than to hCNC, indicating the stronger interaction between CoFe2O4 and hNCNC due to the nitrogen participation. The enhanced interaction and hierarchical morphology favor the high dispersion and modification of electronic states for the active species as well as the mass transport during the oxygen reduction process, which plays a significant role in boosting the electrocatalytic performances. In addition, we noticed the high sensitivity of O 1s spectrum to the particle size and chemical environment for spinel oxides, which is used as an indicator to understand the evolution of ORR activities for all the CoFe2O4-related contrast catalysts. Accordingly, the well-defined structure-performance relationship is demonstrated by the combination of experimental characterizations with theoretical calculations. This study provides a promising strategy to develop efficient, inexpensive and durable oxygen reduction electrocatalysts by tuning the interaction between spinel metal oxides and the carbon-based supports.

Structural regulation of ZnGa2O4 nanocubes for achieving high capacity and stable rate capability as an anode material of lithium ion batteries

Increasing demand for high energy capability Li rechargeable batteries has promoted extensive research on the development of electrode materials. Multi-component spinel metal-oxide is considered to be promising anode material owing to their better electrical conductivity and higher electrochemical activity. Herein, a facile one-pot strategy without further thermal annealing treatment is successfully developed for preparation of well-defined ZnGa2O4 nanocubes. To the best of our knowledge, this is the first report on the synthesis of ZnGa2O4 nanocubes through wet chemical method and applied as anode material. Galvanostatic charge and discharge results indicate ZnGa2O4 nanocubes electrode is capable of delivering a higher capacity and better cycling stability than ZnO/Ga2O3 mixture electrode. Noteworthily, ZnGa2O4 nanocubes electrode also exhibites superior capacity compared with ZnGa2O4 nanospheres electrode which is consisted of secondary nanoparticles. Large amount of ZnGa2O4 nanocubes could retain their morphology after 160 charge/discharge cycles and further surface elemental analysis illustrates elements distributions has no changes in the surface. The unique structure and high crystallinity is responsible for higher capacity and better cycling stability.

Cyano-Bridged Trimetallic Coordination Polymer Nanoparticles and Their Thermal Decomposition into Nanoporous Spinel Ferromagnetic Oxides.

The synthesis of a novel family of cyano-bridged trimetallic coordination polymers (CPs) with various compositions and shapes has been reported by changing the compositional ratios of Fe, Co, and Ni species in the reaction system. In order to efficiently control the nucleation rate and the crystal growth, trisodium citrate dihydrate plays an important role as a chelating agent. After the obtained cyano-bridged trimetallic CPs undergo thermal treatment in air at three different temperatures (250, 350, and 450 °C), nanoporous spinel metal oxides are successfully obtained. Interestingly, the obtained nanoporous metal oxides are composed of small crstalline grains, and the grains are oriented in the same direction, realizing pseudo-single crystals with nanopores. The resultant nanoporous spinel oxides feature interesting magnetic properties. Cyano-bridged multimetallic CPs with various sizes and shapes can provide a pathway toward functional nanoporous metal oxides that are not attainable from simple cyano-bridged CPs containing single metal ions.

Mesoporous Spinel Metal Oxides As High Performance Cathode in Aqueous Rechargeable Lithium Ion Battery

1. Introduction – Secondary Li ion batteries, regarded as the current benchmark for new battery technologies, are under extensive development throughout the world [1]. However, their requirement that organic electrolytes be used limits the rate capacity and specific power the cell can achieve and present several safety hazards and cost limitations that prevent their application in medium to large-scale storage systems [1, 2]. Here, aqueous rechargeable lithium ion batteries (ARLBs) utilizing mesoporous spinel metal oxide cathodes are investigated, due to their high capacity, cycling stability and high rate capability [3, 4]. 2. Fabrication procedures – LiMn2O4 (LMO) anode is fabricated by solid state reaction of 5 mmol Li2CO3 and 10 mmol Mn2O3 at 750 °C for 24 hrs. Activated carbon (AC, Kureha BAC) is utilized as received. Electrochemical testing was performed on Teflon sealed CR2032 coin cells utilizing type 304 S.S. mesh as electrode substrates. 6 M LiNO3 in D.I. water is used as the electrolyte, with addition of 0.01 M HNO3 and LiOH to create acidic and basic electrolytes, respectively.3. Experimental setup and results – Average mass loadings of 5 mg cm-2 are utilized. Charge and discharge is done at a rate of 2 mA cm-2 between potentials of 0 and 2 V. HiRes TEM images, EDX spectrum and discharge capacity results of three LMO based cells are shown in Figure 1(a-d). Evidence of the pH dependence of the development of a porous nanoscale layer of Fe2O3 is shown in Figure 1(a-c), and is reflected in the superior performance of the basic cell, as shown in Figure 1(d). Capacity fading characteristic of the development of mixed material phases and Jahn-Teller distortion is observed in the two cells that do not show the development of this porous Fe2O3 layer (acidic and neutral), while the introduction of the new coating creates a capacity increase of ~ 50 % with high stability up to 500 cycles. 4. Conclusions – Influence of the creation of a porous nanoscale Fe2O3 layer on the LMO cathode is directly responsible for observed increases in cell discharge capacity and the stabilization of material capacity fade, greatly increasing the performance of both functional indicators. Future work aims to develop an inexpensive and efficient way to create mesoporous and nanoporous microstructures of Fe2O3 and other spinel metal oxides with high porosity and active surface area, thereby increasing material capacity and rate capability of ARLBs required by medium and large scale energy storage. 5. References –[1] G.X. Wang, S. Zhong, D.H. Bradhurst, S.X. Dou, H.K. Liu, Journal of Power Sources, 74 (1998) 198-201. [2] X. Zeng, Q. Liu, M. Chen, L. Leng, T. Shu, L. Du, H. Song, S. Liao, Electrochimica Acta, 177 (2015) 277-282. [3] W. Tang, S. Tian, L.L. Liu, L. Li, H.P. Zhang, Y.B. Yue, Y. Bai, Y.P. Wu, K. Zhu, Electrochemistry Communications, 13 (2011) 205-208.[4] J. Zhang, T. Huang, Z. Liu, A. Yu, Electrochemistry Communications, 29 (2013) 17-20. Figure 1

Hybrid supercapacitor devices based on MnCo2O4 as the positive electrode and FeMn2O4 as the negative electrode

MnCo2O4 nanosheets and FeMn2O4 nanospheres were synthesized using a hydrothermal method. Choline chloride was used as the capping agent during the preparation of the nanoparticles. XRD patterns confirmed the spinel structure of MnCo2O4 and FeMn2O4. XPS measurements were used to determine the oxidation state of the prepared spinel metal oxides. HRTEM images revealed the formation of hexagonal nanosheets of MnCo2O4 and nanospheres of FeMn2O4. Electrochemical measurements were made for both positive and negative electrodes using three electrode systems. MnCo2O4 Exhibits 282Cg−1 and FeMn2O4 yields 110Cg−1 at a specific current of 1Ag−1. Hybrid supercapacitor device was fabricated using MnCo2O4 as the positive and FeMn2O4 as the negative electrode material. The hybrid supercapacitor device was delivered a maximum power of 37.57kWkg−1.

Novel Nanostructured Materials for Metal-Air Batteries

This talk will focus on the design and synthesis of nanostructured non-precious metal-based hybrid catalysts for metal-air batteries. The presentation will describe some our works in nanostructured hybrid bifunctional electrocatalysts as air electrode for Zn-air rechargeable batteries, as well as nanostructured porous perovskite and spinel metal oxide catalytic materials as air electrode for Li-air batteries. In this presentation, I will introduce the fundamental and the most recent and significant scientific progresses made in the fields relevant to Zn-air and Li-air batteries, with emphasis placed on air electrodes. The preparation of MnO2 nanotubes functionalized with Co3O4 nanoparticles and their use as bifunctional air cathode catalysts for oxygen reduction reaction and oxygen evolution reaction in rechargeable zinc-air batteries will be reported. These hybrid MnO2/Co3O4 nanomaterials exhibit enhanced catalytic reactivity toward oxygen evolution reaction in alkaline conditions compared with that in the presence of MnO2 nanotubes or Co3O4 nanoparticles alone. Other bifunctional catalysts for oxygen reduction and evolution reactions in Zn-air batteries include spinel MnCo2O4/ nanocarbon hybrids, perovskite lanthanum cobalt manganese oxides/nanocarbon hybrids (LCMO/NC), Co3O4 nanoparticles decorated carbon nanofiber and cobalt sulphide/N- or S-doped grapheme etc. I also will report porous cobalt-manganese oxide nanocubes derived from metal organic frameworks and porous perovskite LaNiO3 nanocubes as cathode catalysts for rechargeable Li-O2 batteries.

Synthesis of Nickel and Zinc-Doped Aluminogallate Nanocomposite Spinels with the Hydrothermal Method and Wet Atomization for NO Reduction

The levels of nitrogen oxides (NOx = NO + NO2) released from both portable and standing combustion devices are on the increase, which contributes to serious environmental problems such as global warming and air pollution. The selective catalytic reduction (SCR) of NOx by hydrocarbons (HCs) is very effective, so there have been many studies of the performance of various catalysts for HC-SCR. In this study, Ga2O3–Al2O3–NiO–ZnO (GANZ) nanocomposite metal oxides were tested as catalysts for NOx reduction by C2H4. The spinel metal oxide powders were prepared with the hydrothermal reaction method. Aluminum, gadolinium, nickel, zinc nitrate, and ammonium carbonate salts are highly water soluble and were used in these syntheses. The hydrothermally synthesized powders were then processed with wet atomization to obtain highly dispersed fine particles. Finally, the spinel powders were tested in NOx reductions performed in the presence of high levels of oxygen and at a high space velocity, which are demanding conditions since most reported catalysts are not active in this environment. The synthesized product is an uncontaminated spinel phase of GANZ and was found to exhibit high catalytic activity even in the presence of 10 % H2O vapor and SO2 at a high space velocity. GANZ catalysts were also synthesized with the co-precipitation and sol–gel methods for comparison.

α-Arylation of oxindoles using recyclable metal oxide ferrite nanoparticles: Comparison between the catalytic activities of nickel, cobalt and copper ferrite nanoparticles

Three different spinel metal oxide catalytic systems including NiFe2O4, CuFe2O4 and CoFe2O4 were synthesized using co-precipitation technique and their catalytic activities were compared to each other in α-arylation of oxindole derivatives under the optimized reaction conditions. Both nickel ferrite and copper ferrite magnetic nanoparticles show approximately the same behavior in these reactions but cobalt ferrite ones indicate slightly different properties and were not as good as the other two catalysts. These superparamagnetic catalysts allowed that α-arylation of different types of oxindoles will occur in high yields under mild conditions and at very short times.

Nitrogen-doped graphene aerogel-supported spinel CoMn2O4 nanoparticles as an efficient catalyst for oxygen reduction reaction

Spinel CoMn2O4 (CMO) nanoparticles grown on three-dimensional (3D) nitrogen-doped graphene areogel (NGA) is prepared by a facile two-step hydrothermal method. The NGA not only possesses the intrinsic property of graphene, but also has abundant pore conformations for supporting spinel metal oxide nanoparticles, thus would be suitable as a good electrocatalysts' support for oxygen reduction reaction (ORR). The structure, morphology, porous properties, and chemical composition of CMO/NGA are investigated by X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, nitrogen adsorption–desorption measurements, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of catalysts is discussed by cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), and rotating disk electrode (RDE) measurements in O2-saturated 0.1 M KOH electrolyte. The CMO/NGA hybrid exhibits more positive onset potential and half-wave potential, faster charge transfer than that of CMO and NGA, and its electrocatalytic performance is comparable with the commercial 20 wt.% Pt/C. Furthermore, it mainly favors a direct 4e− reaction pathway, and has excellent ethanol tolerance and high durability, which is attributed to the unique 3D crumpled porous nanostructure of NGA with large specific area and fast electron transport, and the synergic covalent coupling between the CoMn2O4 nanoparticles and NGA.

One-pot synthesis of magnetic hybrid materials based on ovoid-like carboxymethyl-cellulose/cetyltrimethylammonium-bromide templates

A novel one-pot synthetic procedure to obtain magnetic hybrid nanostructured materials (HNM), based on magnetic spinel-metal-oxide (SMO) nanoparticles stabilized in ovoid-like carboxymethyl-cellulose (CMC)/cetyltrimethylammonium-bromide (CTAB) templates, is reported. The HNM were synthesized from the controlled hydrolysis of inorganic salts of Fe (II) and Fe (III) into aqueous dissolutions of CMC and CTAB. The synthesized HNM were characterized by transmission electron microscopy, Fourier transform infrared spectroscopy and static magnetic measurements. The experimental evidence suggests that, due to the competition between CTAB molecules and SMO nanoparticles to occupy CMC intermolecular sites nearby to its carboxylate functional groups, the size of both, SMO nanoparticles and ovoid-like CMC/CTAB templates can be tuned, varying the CTAB:SMO weight ratio. Moreover, it was found that the magnetic response of the HNM depends on the confinement degree of the SMO nanoparticles into the CMC/CTAB template. Hence, their magnetic characteristics can be adjusted controlling the size of the template, the quantity and distribution of the SMO nanoparticles within the template and their size.

Spinel Metal Oxide-Alkali Carbonate-Based, Low-Temperature Thermochemical Cycles for Water Splitting and CO2 Reduction

A manganese oxide-based, thermochemical cycle for water splitting below 1000 °C has recently been reported. The cycle involves the shuttling of Na+ into and out of manganese oxides via the consumption and formation of sodium carbonate, respectively. Here, we explore the combinations of three spinel metal oxides and three alkali carbonates in thermochemical cycles for water splitting and CO_2 reduction. Hydrogen evolution and CO_2 reduction reactions of metal oxides with a given alkali carbonate occur in the following order of decreasing activity: Fe_(3)O_4 > Mn_(3)O_4 > Co_(3)O_4, whereas the reactivity of a given metal oxide with alkali carbonates declines as Li_(2)CO_3 > Na_(2)CO_3 > K_(2)CO_3. While hydrogen evolution and CO_2 reduction reactions occur at a lower temperature on the combinations with the more reactive metal oxide and alkali carbonate, higher thermal reduction temperatures and more difficult alkali ion extractions are observed for the combinations of the more reactive metal oxides and alkali carbonates. Thus, for a thermochemical cycle to be closed at low temperatures, all three reactions of hydrogen evolution (CO_2 reduction), alkali ion extraction, and thermal reduction must proceed within the specified temperature range. Of the systems investigated here, only the Na_(2)CO_3/Mn_(3)O_4 combination satisfies these criteria with a maximum operating temperature (850 °C) below 1000 °C.

Photocatalytic hydrogen production over CuGa2−xFexO4 spinel

Recovery of hydrogen from industrial H2S waste using spinel photocatalyst was studied. Spinel metal oxide photocatalysts (CuGa2−xFexO4 for x = 0.8, 0.6 and 0.4) were synthesized by ceramic route. They were loaded with 0.5 and 1 wt% noble metal oxide, RuO2. Their XRD pattern revealed a single phase cubic spinel crystalline structure for all the catalysts. SEM displayed small size cubic particles with the particle size decreasing with the decrease in iron content. 1 wt% RuO2 loaded CuGa1.6Fe0.4O4 decomposed H2S in aqueous 0.5 M KOH solution under visible light (λ ≥ 420 nm) irradiation and generated H2 to the tune of 10,045 μmol/h, giving rise to a high quantum efficiency of 21% at 510 nm.

Spinel ZnMn2O4 nanoplate assemblies fabricated via “escape-by-crafty-scheme” strategy

A two-step process that differs in important details from previous methods used to prepare ZnMn2O4 nanoplate assemblies has been reported. This material was prepared by thermal transformation of metal–organic nanoparticles into metal–oxide nanoparticles based on the “escape-by-crafty-scheme” strategy. Firstly, the nanoscale mixed-metal–organic frameworks (MMOFs) precursor, ZnMn2–ptcda (ptcda = perylene-3,4,9,10-tetracarboxylic dianhydride), containing Zn2+ and Mn2+, was prepared by the designed soft chemical assembly of mixed metal ions and organic ligands at a molecular scale. In a second step, the MMOFs are thermally transformed into spinel structured ZnMn2O4 with morphology inherited from the MMOFs precursors. The well-crystallized spinel structure can be formed by thermal treatment of ZnMn2–ptcda at 350 °C, and is formed at temperatures ≥450 °C using the co-precipitation method. This “escape-by-crafty-scheme” strategy can be extended to the preparation of other spinel metal–oxide nanoparticles, e.g. CoMn2O4, and NiMn2O4, with well-defined morphology inherited from the metal–organic precursors. The ZnMn2O4 nanoplate assemblies thermally treated at 450 °C have potential application in lithium ion batteries as anode materials, which show high specific capacity and good cyclability.

Surfactant-assisted synthesis and magnetic properties of monodispersed manganese ferrite nanocrystals

Monodispersed manganese ferrite (MnFe2O4) nanocrystals could be successfully synthesized in large quantities via a facile synthetic technique based on the pyrolysis of organometallic compound precursor, in which octadecene was used as solvent, and oleic acid and oleylamine were used as capping ligands. MnFe2O4 nanocrystals were obtained with size in a tunable range of 4–15 nm and their morphologies could be tuned from spherical to triangle-shaped by varying the surfactants. The phase structure, morphology, and size of the products were characterized in detail by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Magnetic properties of MnFe2O4 nanocrystals with different morphologies were measured using a superconducting quantum interference device (SQUID). Both monodisperse MnFe2O4 nanocrystals with spherical and triangle-shapes are superparamagnetic at room temperature while ferromagnetic at 2 K. The pyrolysis method may provide an effective route to synthesize other spinel ferrites or metal oxides nanocrystals.

High capacity anode materials for Li-ion batteries based on spinel metal oxides AMn2O4 (A = Co, Ni, and Zn)

Manganites of transition and/or post-transition metals, AMn2O4 (where A was Co, Ni or Zn), were synthesized by a simple and easily scalable co-precipitation route and were evaluated as anode materials for Li-ion batteries. The obtained powders were characterized by SEM, TEM, and XRD techniques. Battery cycling showed that ZnMn2O4 exhibited the best performance (discharge capacity, cycling, and rate capability) compared to the two other manganites and their corresponding simple oxides. Further studies on the effect of different sintering temperatures (from 400 to 1000 °C) on particle size were performed, and it is found that the size of the particles had a significant effect on the performance of the batteries. The optimum particle size for ZnMn2O4 is found to be 75–150 nm. In addition, the use of water-soluble and environmentally friendly binders, such as lithium and sodium salts of carboxymethlycellulose, greatly improved the performance of the batteries compared to the conventional binder, PVDF. Finally, ZnMn2O4 powder sintered at 800 °C (<150 nm) and the use of the in-house synthesized lithium salt of carboxymethlycellulose (LiCMC) binder gave the best battery performance: a capacity of 690 mA h g−1 (3450 mA h mL−1) at C/10, along with good rate capability and excellent capacity retention (88%).

Synthesis and structural analysis of visible light photocatalyst, ZnBiGaO4 for photocatalytic solar hydrogen production

In this paper, we are reporting a novel spinel metal oxide photocatalyst, ZnBiGaO4 for the photocatalytic decomposition of hydrogen sulfide (H2S) to generate hydrogen. ZnBiGaO4 was prepared by two different methods. One is usual solid-state route and another is hydrothermal route, and this is the first time we are reporting ZnBiGaO4 synthesized by this route. The newly prepared ZnBiGaO4 was characterized for its crystal structure and microstructure by using XRD and Field Emission Scanning Electron Microscopy (FESEM), respectively. XRD analysis revealed that the structure of ZnBiGaO4 is cubic spinel structure. The photocatalyst was also characterized by using UV–Visible diffuse reflectance spectroscopy to determine its band gap and was estimated to be 2.8 eV. Our prima facie observations revealed that the formation of single-phase cubic spinel ZnBiGaO4 with significant photocatalytic activity under visible-light irradiations for solar hydrogen generation from H2S. Copyright © 2009 John Wiley & Sons, Ltd.

Visible light active pristine and [formula omitted] doped [formula omitted] spinel photocatalysts for solar hydrogen production

Spinel metal oxide photocatalysts, a rarely studied group in visible light driven photocatalytic decomposition of H 2 S and solar H 2 production, have been investigated in the present work. d 10 p-block element, Ga containing spinel CuGa 2 O 4 in pristine and Fe 3 + doped ( CuGa 2 - x Fe x O 4 , x = 0.6 ) states, was prepared by ceramic route without/with noble metal oxide, NiO / RuO 2 loading to the extent of 1 wt%. XRD analysis reveals a single-phase cubic spinel crystalline structure for all the catalysts. FESEM displays an irregular-shaped grain morphology for CuGa 2 O 4 and smaller size almost cubic particles for CuGa 2 - x Fe x O 4 . Energy dispersive X-ray spectroscopy suggests a chemical composition consistent with the stoichiometric molecular formula. Optically, the catalysts display an intensive light absorption in UV and visible regions with an onset at about 900 nm in the near IR region. Fe 3 + doping constructively influences the morphology and optical properties of pristine CuGa 2 O 4 . All these physico-chemical and material characteristics infuse a facile catalytic function into the prepared spinel oxides such that the naked CuGa 2 O 4 and CuGa 2 - x Fe x O 4 spinels exhibit a moderate to fairly good photocatalytic activity while the co-catalyst-loaded CuGa 2 - x Fe x O 4 spinel performs an exceedingly good photocatalytic activity with 15% quantum efficiency. Thus, the present work leads to the emergence of functionally high performance, stable and visible active ( λ ⩾ 420 nm ) photocatalysts in the spinel group for the production of solar hydrogen from H 2 S .