Photocatalytic Activity of R3MO7 and R2Ti2O7 (R = Y, Gd, La; M = Nb, Ta) for Water Splitting into H2 and O2

In situ SEIRAS analysis of enhanced photocatalytic carrier transfer to a Pt cocatalyst induced by sacrificial reagents

In situ SEIRAS analyses revealed a peak shift of adsorbed CO on Pt cocatalysts supported on TiO2 photocatalysts in the presence of sacrificial reagents. This observation suggests that charge separation from the photocatalysts to the cocatalysts was enhanced, leading to negative potential shifts that promote hydrogen evolution.

Refined structural studies on the fluorite-related polymorphs of sol-gel undoped and Eu3+-doped yttrium tantalates

Compounds with the general formula RE3MO7 (RE = rare earth ions; M = Ta, Nb, Sb, Ru, Ir, Os, Re, etc.), crystallize as a fluorite-related structure, forming polymorphs with different space groups. The space group strongly depends on the RE3+ and M5+ ionic radii and processing conditions. Structural characterization is well-established for the lanthanide series, but literature studies have divergent views about how to attribute yttrium tantalate (Y3TaO7) space groups-some authors have described the Y3TaO7 structure as orthorhombic and belonging to space group C2221 or Ccmm, whereas others have assigned a cubic Fm3̄m structure to it. Here, we have characterized the structure of undoped and Eu3+-doped Y3TaO7 (0.1 to 50 mol% of Eu3+) samples synthesized by the sol-gel method that crystallized as a cubic disordered fluorite-type structure, space group Fm3̄m. Their powder X-ray diffraction measurements, Rietveld analyzes and Raman spectra were used as a conclusive technique of the structural properties. We have also investigated whether a secondary phase (M'-YTaO4) emerged in the samples and compared the phase composition of each sample to their Raman spectra. Low-temperature photoluminescence measurements (∼15 K) using Eu3+ as a structural probe helped us analyze the inhomogeneous broadening observed in the emission spectra. These measurements can be used as an important tool to attribute the crystalline phases of rare earth tantalates and niobates.

Layered KTO/BiOCl nanostructures for the efficient visible light photocatalytic degradation of harmful dyes

Novel KTO/BiOCl nanostructured photocatalysts with various weight proportions were synthesized using a simple hydrothermal process. The as-prepared nanostructured composite catalysts were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, UV-vis diffused reflectance spectroscopy, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy with high resolution, X-ray photoelectron spectroscopy, and photoluminescence (PL). The photocatalytic activity of prepared catalysts was examined using Rhodamine B (RhB) and Congo Red (CR) as the aimed pollutants. BiOCl nanoparticles were distributed uniformly on the surface of the K₂Ti₄O₉ nanobelts. The optical properties showed that the layered titanate with BiOCl nanostructured photocatalyst displayed improved photoresponsivity due to the narrowed bandgap. The PL results showed that the greater inhibition of the electron-hole recombination process and KTO/BiOCl with a mass proportion of 20% revealed the most favorable photocatalytic behavior. The rate constant of RhB and CR degradation was five times as high as that of the bare BiOCl and titanate. The superior photocatalytic performance was attributed to the advancement of heterojunction between the KTO nanobelt and BiOCl. The KTO/BiOCl nanostructure is a promising visible, active photocatalyst, and the photocatalytic mechanism is discussed using the possible band structures of BiOCl and KTO.

Charge Transfer-Triggered Bi3+ Near-Infrared Emission in Y2Ti2O7 for Dual-Mode Temperature Sensing

Trivalent bismuth is a popular main group ion showing versatile luminescent behaviors in a broad spectral range from ultraviolet to visible, but barely in the near-infrared (NIR) region. In this study, we have observed unexpected NIR emission at ∼744 nm in a Bi³⁺-doped pyrochlore, Y₂Ti₂O₇ (YTOB). Our first-principles electronic structure calculation and analysis of the Bi local structure via extended X-ray absorption fine structure indicate that only Bi³⁺ species appears in YTOB and it has a similar local environment to that of Y³⁺. The NIR emission is assigned to a Ti⁴⁺ → Bi³⁺ metal-to-metal charge transfer process. Moreover, we have demonstrated dual-mode luminescence thermometry based on the luminescence intensity ratio (LIR) and lifetime (τ) in 0.5% Bi³⁺ and 0.5% Pr³⁺ co-doped Y₂Ti₂O₇ (YTOB0.5P0.5). It exhibits high thermometric sensitivity simultaneously in the cryogenic temperature range from 78 to 298 K based on τ of the NIR emission of Bi³⁺ at 748 nm and in the temperature range of 278-378 K based on the LIR of Bi³⁺ to Pr³⁺ emissions (I₇₄₈/I₆₁₅). As a novel LIR-τ dual-mode thermometric material over a wide temperature range, the maximum relative sensitivities of the YTOB0.5P0.5 reach 3.53% K^-1 at 298 K from the τ mode and 3.52% K^-1 at 318 K based on the LIR mode. The dual-mode luminescence thermometry with high responsivity from our Bi³⁺-based pyrochlore Y₂Ti₂O₇ phosphor opens a new avenue for more luminescent materials toward multi-mode thermometry applied in complex temperature-sensing conditions.

Optical Temperature Sensor Capabilities of the Green Upconverted Luminescence of Er3+ in La3NbO7 Ceramic Powders

We present a study of the Er3+ upconverted luminescence in erbium doped Lanthanum Niobium Oxide, La3NbO7, ceramic powder, prepared by solid state reaction. This study focuses on the analysis of the feasibility of this system as a temperature sensor. Efficient UC luminescence was observed under the 975 nm excitation showing intense green, red and NIR (850 nm) emission bands. The NIR luminescence centred at about 850 nm and lying on the first biological window is mainly insensitive to the temperature. In contrast, the upconverted green bands, associated with the (2H11/2,4S3/2) →4I15/2 transitions, showed a high sensibility to temperature. Their temperature dependence was studied from RT up to 525 K, paying special attention to the physiological range of temperature (303–318 K). The high thermal sensitivities obtained, in comparison with other Er3+ and Er3+-Yb3+ based optical temperature sensors in such ranges, suggest the potential application of this phosphor in thermal sensing, suitable for both biological systems and other industrial applications requiring higher temperatures.

Combinatorial Screening of Cu-W Oxide-Based Photoanodes for Photoelectrochemical Water Splitting

Metal oxide libraries for photoanodes for the oxygen evolution reaction (OER) were generated by printing a metal salt solution in an array layout, followed by calcination to yield 22 ternary metal oxide systems. The libraries included a ternary metal cation system based on CuWO₄ with one out of eight transition or posttransition metal ions Cr, Mn, Fe, Co, Ni, Zn, Bi, and Ga in different overall atomic ratios. The photocatalyst libraries were screened by scanning photoelectrochemical microscopy for the highest anodic photocurrents. Array elements that showed promising performance were printed in another set of eight libraries with smaller increments of overall composition. Improved performance with respect to CuWO₄ was found for Ga, Co, and Ni as the third element. A comparison of the most active composition of those arrays within one library showed the highest activity for Cu₄₈Ga₃W₄₉O_x. Printing spots of identical composition (Cu₄₈Ga₃W₄₉O_x, Cu₄₄Ni₉W₄₇O_x, and Cu₄₄Co₉W₄₇O_x) over a larger area facilitated further characterization by X-ray photoelectron spectroscopy ultraviolet photoelectron spectroscopy (UPS), X-ray diffraction, scanning electron microscopy, chopped light voltammetry, and scanning electrochemical microscopy for the OER. High and stable steady-state photocurrents were generated in a photoelectrochemical cell for all three electrodes even at a low constant bias voltage. The best overall photoanode composition Cu₄₈Ga₃W₄₉O_x showed currents that were 36 times higher than the currents of the binary Cu₅₀W₅₀O_x system. Significant n-doping was found by UPS valence band spectra for Ga-containing materials.

Tin oxide based nanostructured materials: synthesis and potential applications

In view of their inimitable characteristics and properties, SnO₂ nanomaterials and nanocomposites have been used not only in the field of diverse advanced catalytic technologies and sensors but also in the field of energy storage such as lithium-ion batteries and supercapacitors, and in the field of energy production such as solar cells and water splitting. This review discusses the various synthesis techniques such as traditional methods, including processes like thermal decomposition, chemical vapor deposition, electrospinning, sol-gel, hydrothermal, solvothermal, and template-mediated methods and green methods, which include synthesis through plant-mediated, microbe-mediated, and biomolecule-mediated processes. Moreover, the advantages and limitations of these synthesis procedures and how to overcome them that would lead to future research are also discussed. This literature also focuses on various applications such as environmental remediation, energy production, energy storage, and removal of biological contaminants. Therefore, the rise and journey of SnO₂-based nanocomposites will motivate the modern generation of chemists to modify and design robust nanoparticles and nanocomposites that can effectively tackle significant environmental challenges. This overview concludes by providing future perspectives on research into tin oxide in synthesis and its various applications.

Phase-sensitive radioluminescent and photoluminescent features in Tm3+-doped yttrium tantalates for cyan and white light generation

Radioluminescence and visible photoluminescent tunability features from a single Tm3+-doped yttrium tantalate phosphor prepared by a soft sol–gel method designed to afford cubic Y3TaO7 and monoclinic M’-YTaO4 crystalline phases are...

Pyrochlore-structural Nd2Ta2O5N2 Photocatalyst with Absorption Edge of over 600 nm for Z-scheme Overall Water Splitting

A pyrochlore-structural oxynitride Nd2Ta2O5N2 with a visible light absorption edge of ca. 620 nm was explored for photocatalytic water splitting. Dual functions of Nd2Ta2O5N2 were confirmed by proton reduction and...

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Dye-Sensitized Fe-MOF nanosheets as Visible-Light driven photocatalyst for high efficient photocatalytic CO2 reduction

Dye-sensitized system holds great potential for the development of visible-light-responsive photocatalysts not only because it can enhance the light absorption and charge separation efficiency of the systems but also because it can tune the band structure of catalysts. Herein, two-dimensional (2D) Fe-MOF nanosheets (Fe-MNS) with a LUMO potential of 0.11 V (vs. RHE) was prepared. Interestingly, it has been found that when the 2D Fe-MNS catalyst was functionalized with visible-light-responsive [Ru(bpy)]₃²⁺ as a dye-sensitizer, the electrons from the [Ru(bpy)]₃²⁺ can effectively inject into the 2D Fe-MNS, which resulted in a negative shift of the LUMO potential of the 2D Fe-MNS to -0.15 V (vs. RHE). Consequently, the [Ru(bpy)]₃²⁺/Fe-MNS catalytic system exhibits a sound photocatalytic CO₂-to-CO activity of 1120 μmol g^-1h^-1 under visible-light-irradiation. The photocatalytic CO production was further ameliorated by regulating the electronic structure of the 2D Fe-MNS by doping Co ions, achieving a remarkable photocatalytic activity of 1637 μmol g^-1h^-1. This work further supports that the dye-sensitized system is an auspicious strategy worth exploring with different catalysts for the development of visible-light-responsive photocatalytic systems.

High Eu3+ concentration quenching in Y3TaO7 solid solution for orange-reddish emission in photonics

We report the synthesis of a Y₃TaO₇ solid solution containing a high Eu³⁺ concentration (from 7 up to 50 mol%) and investigate how Eu³⁺ influences the Y₃TaO₇ crystallization process. To this end, we evaluate the Y₃TaO₇ structural features and photoluminescence properties after Eu³⁺ introduction into the Y₃TaO₇ lattice. The higher the Eu³⁺ ion concentration, the more stable the crystallization process of the Y₃TaO₇ phase seems to be. The Eu³⁺-containing Y₃TaO₇ displays intense orange-reddish, broad band emission because Eu³⁺ occupies different symmetry sites in the host and causes inhomogeneous broadening. Eu³⁺ emission quenching due to Eu³⁺ concentration is negligible up to 30 mol% and absolute quantum yield values of up to nearly 30% were obtained, making Eu³⁺-containing Y₃TaO₇ interesting materials for application as high-intensity emitters in photonics.

Eu³⁺ ions influence on the crystallization process of Y₃TaO₇ solid solution and this particular host has presented a high concentration quenching (30 mol%), displaying an intense orange-reddish emission, with color purity over 92.6%.

Energetics of Formation and Disordering in Rare Earth Weberite RE3TaO7 Materials

The recent finding of local weberite-like ordered domains in disordered and radiation damaged pyrochlore oxides has sparked interest in studying the structure, stability, and order-disorder in compounds that form in the weberite structure. In order to understand the relationships among the energetics, structure, and disordering, weberites of the formula RE₃TaO₇ (RE = La, Nd, Sm-Yb) were synthesized by conventional solid-state techniques. High temperature oxide melt solution calorimetry was used to determine their enthalpies of formation. Rietveld refinement of PXRD patterns shows that the La compound forms in the weberite La₃NbO₇ (Cmcm) structure; the Nd compound has both Y₃TaO₇ (C222₁)-type and La₃NbO₇-type polymorphs; the Sm-Ho compounds crystallize in the weberite Y₃TaO₇ (C222₁) structure; and the Ho-Yb compounds adopt the defect fluorite (Fm3̅m) disordered structure. Depending on the reaction temperature, Ho₃TaO₇ crystallizes in ordered Y₃TaO₇ (low temperature) or disordered defect fluorite (high temperature) structures. The formation enthalpy of weberites becomes more exothermic with increasing rare earth ionic radius, implying an increase in stability, i.e., La₃TaO₇ is most stable and Yb₃TaO₇ is least stable with respect to the component oxides. The calorimetric data also show that ordered Ho₃TaO₇ (Y₃TaO₇ structure) is energetically more stable by 9.2 ± 1.1 kJ/mol than disordered Ho₃TaO₇ (defect fluorite structure).

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

Solar-driven water splitting provides a leading approach to store the abundant yet intermittent solar energy and produce hydrogen as a clean and sustainable energy carrier. A straightforward route to light-driven water splitting is to apply self-supported particulate photocatalysts, which is expected to allow solar hydrogen to be competitive with fossil-fuel-derived hydrogen on a levelized cost basis. More importantly, the powder-based systems can lend themselves to making functional panels on a large scale while retaining the intrinsic activity of the photocatalyst. However, all attempts to generate hydrogen via powder-based solar water-splitting systems to date have unfortunately fallen short of the efficiency values required for practical applications. Photocatalysis on photocatalyst particles involves three sequential steps: (i) absorption of photons with higher energies than the bandgap of the photocatalysts, leading to the excitation of electron-hole pairs in the particles, (ii) charge separation and migration of these photoexcited carriers, and (iii) surface chemical reactions based on these carriers. In this review, we focus on the challenges of each step and summarize material design strategies to overcome the obstacles and limitations. This review illustrates that it is possible to employ the fundamental principles underlying photosynthesis and the tools of chemical and materials science to design and prepare photocatalysts for overall water splitting.

Preparation, characterization and investigation of sonophotocatalytic activity of thulium titanate/polyaniline nanocomposites in degradation of dyes

Thulium titanate/polyaniline nanocomposites were synthesized to observe the sonophotocatalytic degradation of dyes (widely used as a model pollutant) under ultrasonic irradiation and visible light. Based on our results, the synthesis process can improve sol-gel assisted sonochemical method in the presence of ultrasound and starch. To prepare pure thulium titanate nanostructures, the presence of starch and sonication treatment were concurrently obligatory. Therefore, sol-gel assisted sonochemical method can be used as a successful process for synthesis of thulium titanate nanostructures. According to the BET results, in the presence of ultrasound and starch surface area increased from 9.5305 m₂/g to 40.28 m₂/g. For verification of photacatalytic behavior of nanoparticles, several factors were studied. The nanocomposites/ultrasonic system showed greater photocatalytic activity for the degradation of Rh B rather than separately treatment of nanocomposites under visible light.

Synergistic Effect of Doping and Compositing on Photocatalytic Efficiency: A Case Study of La2Ti2O7

Charge generation and separation are two key issues in developing a high-efficiency semiconductor for the visible-light-driven photocatalysis. Here, we use the layered perovskite-type wide-gap semiconductor La₂Ti₂O₇ (LTO) as a model to systematically explore the synergistic effect of doping (with sulfur or nitrogen) and heterojunction (with graphitic C₃N₄) on improving visible light absorption and photoexcited charge separation by means of density functional theory calculations. It is found that the anion (N or S) doping into the LTO(010) surface can not only shift the optical absorption edge to the visible region, but also creates some partially occupied or unoccupied states in the band gap that would facilitate the formation of recombination centers. For the purpose of promoting electron-hole separation, the (N or S-doped) LTO(010) surfaces were hybridized with the monolayer g-C₃N₄. Interestingly, we found that the (S-doped) LTO/g-C₃N₄ heterostructure forms a type-II heterojunction, with the valence band maximum residing in the (S-doped) LTO and the conduction band minimum in g-C₃N₄, respectively. This band alignment feature facilitates efficient electron-hole separation. Moreover, we found that the S-doped LTO/g-C₃N₄ composite has a short interfacial distance (about 2.1 Å), implying that the interfacial interaction of this composite might be a chemical bond rather than a weak van der Walls interaction. The chemical bonding can enhance charge separation. Our theoretical findings provide design principles for optimizing the photocatalytic performance of the wide-gap photocatalysts and demonstrate that the S-doped LTO/g-C₃N₄ composite would be a potential candidate for the photocatalysis of water splitting.

Steering Charge Kinetics of Tin Niobate Photocatalysts: Key Roles of Phase Structure and Electronic Structure

Tin niobate photocatalysts with the phase structures of froodite (SnNb₂O₆) and pyrochlore (Sn₂Nb₂O₇) were obtained by a facile solvothermal method in order to explore the impact of phase structure and electronic structure on the charge kinetics and photocatalytic performance. By employing tin niobate as a model compound, the effects of phase structure over electronic structure, photocatalytic activity toward methyl orange solution and hydrogen evolution were systematically investigated. It is found that the variation of phase structure from SnNb₂O₆ to Sn₂Nb₂O₇ accompanied with modulation of particle size and band edge potentials that has great consequences on photocatalytic performance. In combination with the electrochemical impedance spectroscopy (EIS), transient photocurrent responses, transient absorption spectroscopy (TAS), and the analysis of the charge-carrier dynamics suggested that variation of electronic structure has great impacts on the charge separation and transfer rate of tin niobate photocatalysts and the subsequent photocatalytic performance. Moreover, the results of the X-ray photoelectron spectroscopy (XPS) indicated that the existent of Sn⁴⁺ species in Sn₂Nb₂O₇ could result in a decrease in photocatalytic activity. Photocatalytic test demonstrated that the SnNb₂O₆ (froodite) catalyst possesses a higher photocatalytic activity toward MO degradation and H₂ evolution compared with the sample of Sn₂Nb₂O₇ (pyrochlore). On the basis of spin resonance measurement and trapping experiment, it is expected that photogenerated holes, O₂^-•, and OH^• active species dominate the photodegradation of methyl orange.

Controlled Synthesis of CuS/TiO2 Heterostructured Nanocomposites for Enhanced Photocatalytic Hydrogen Generation through Water Splitting

Photocatalytic hydrogen (H₂) generation through water splitting has attracted substantial attention as a clean and renewable energy generation process that has enormous potential in converting solar-to-chemical energy using suitable photocatalysts. The major bottleneck in the development of semiconductor-based photocatalysts lies in poor light absorption and fast recombination of photogenerated electron-hole pairs. Herein we report the synthesis of CuS/TiO₂ heterostructured nanocomposites with varied TiO₂ contents via simple hydrothermal and solution-based process. The morphology, crystal structure, composition, and optical properties of the as-synthesized CuS/TiO₂ hybrids are evaluated in detail. Controlling the CuS/TiO₂ ratio to an optimum value leads to the highest photocatalytic H₂ production rate of 1262 μmol h^-1 g^-1, which is 9.7 and 9.3 times higher than that of pristine TiO₂ nanospindles and CuS nanoflakes under irradiation, respectively. The enhancement in the H₂ evolution rate is attributed to increased light absorption and efficient charge separation with an optimum CuS coverage on TiO₂. The photoluminescence and photoelectrochemical measurements further confirm the efficient separation of charge carriers in the CuS/TiO₂ hybrid. The mechanism and synergistic role of CuS and TiO₂ semiconductors for enhanced photoactivity is further delineated.

Proton and oxygen ion conductivity in the pyrochlore/fluorite family of Ln2-xCaxScMO7-δ (Ln = La, Sm, Ho, Yb; M = Nb, Ta; x = 0, 0.05, 0.1) niobates and tantalates

The tolerance factor is a good criterion to understand the structural transitions in Ln_2-xCa_xScMO_7-δ (Ln = La, Sm, Ho, Yb; M = Nb, Ta; x = 0, 0.05, 0.1). Decreasing the Ln ionic radius in Ln₂ScNb(Ta)O₇ leads to a morphotropic transition from a pyrochlore to a fluorite-like structure. Ca²⁺-doping leads to a pyrochlore-to-fluorite transition in Ln_2-xCa_xScMO_7-δ (Ln = La, Sm) and a fluorite-to-pyrochlore transition in Ho_2-xCa_xScNbO_7-δ. Proton contribution to the total conductivity was observed for Ln_2-xCa_xScNb(Ta)O_7-δ (Ln = La, Sm; x = 0, 0.05, 0.1) 3+/5+ pyrochlores and the maximum proton contribution was shown by Sm_1.9Ca_0.1ScMO_6.95 (M = Nb, Ta), which are located at the boundary between pyrochlores and fluorites (comparative study of electrical conduction and oxygen diffusion). Proton conduction of Sm_1.9Ca_0.1ScNbO_6.95 and Sm_1.9Ca_0.1ScTaO_6.95 pyrochlores persists up to 800 and 850 °C, respectively. The conductivity of fluorite-like Ho_2-xCa_xScNbO_7-δ (x = 0, 0.05) and Yb₂ScNbO₇ is dominated by the oxygen ion transport, in accordance with their energy activation values 1.09-1.19 eV. The dielectric permittivity and TG studies were used for the investigation of oxygen vacancy dynamics and water incorporation into the Ln_2-xCa_xScNb(Ta)O_7-δ (Ln = La, Sm, Ho, Yb; x = 0, 0.05, 0.1) lattice. It is shown that oxygen vacancy-related dielectric relaxation in the range of 550-650 °C (ambient air), typical of pyrochlores and fluorites with pure oxygen ion conductivity, decreases and disappears for proton-conducting oxides.

Combinatorial Discovery of Lanthanum-Tantalum Oxynitride Solar Light Absorbers with Dilute Nitrogen for Solar Fuel Applications

Oxynitrides with the photoelectrochemical stability of oxides and desirable band energetics of nitrides comprise a promising class of materials for solar photochemistry. Challenges in synthesizing a wide variety of oxynitride materials has limited exploration of this class of functional materials, which we address using a reactive cosputtering combined with rapid thermal processing method to synthesize multi-cation-multi-anion libraries. We demonstrate the synthesis of a La_xTa_1-xO_yN_z thin film composition spread library and its characterization by both traditional thin film materials characterization and custom combinatorial optical spectroscopy and X-ray absorption near edge spectroscopy (XANES) techniques, ultimately establishing structure-chemistry-property relationships. We observe that over a substantial La-Ta composition range the thin films crystallize in the same perovskite LaTaON₂ structure with significant variation of anion chemistry. The relative invariance in optical band gap demonstrates a remarkable decoupling of composition and band energetics so that the composition can be optimized while retaining the desirable 2 eV band gap energy. We also demonstrate the intercalation of diatomic nitrogen into the La₃TaO₇ structure, which gives rise to a direct-allowed optical transition at 2.2 eV, less than half the value of the oxide's band gap. These findings motivate further exploration of the visible light response of this material that is predicted to be stable over a wide range of electrochemical potential.

Synergetic effect of CuS@ZnS nanostructures on photocatalytic degradation of organic pollutant under visible light irradiation

Ultrafast visible light active CuS/ZnS nanostructured photocatalysts were synthesized by a hydrothermal method.

Synthesis and photocatalytic activity of K2CaNaNb3O10, a new Ruddlesden–Popper phase layered perovskite

The photocatalytic performance of a new layered perovskite K₂CaNaNb₃O₁₀ of the Ruddlesden–Popper phase was compared to Dion–Jacobson type KCa₂Nb₃O₁₀.

Structural and Near-Infrared Properties of Nd3+ Activated Lu3NbO7 Phosphor

Undoped and Nd³⁺ doped lutetium niobate phases have been prepared by a conventional solid state reaction method using lutetium acetate and niobium oxide at 1250 °C for 6 h. X-ray diffraction patterns of the 6 mol% Lu₃NbO₇ sample exhibited a cubic fluorite single phase. Phase structure exhibited interesting crystallization behaviour depending on increasing Nd³⁺ concentration which led to a Lu₃NbO₇ single phase formation during the heat treatment process. SEM investigations were also in agreement with the XRD results. Morphologies of Nd³⁺ doped lutetium niobate powders exhibited oval like shapes and grain sizes varied between 0.3 and 5 μm. Near-infrared luminescence properties of Nd³⁺ doped Lu₃NbO₇ were also studied. 1.06 μm laser transition characteristics of Nd³⁺ doped lutetium niobate have been observed. Concentration quenching phenomenon was not detected depending on increasing Nd³⁺ doping concentrations at room temperature.

Fabrication of novel p–n heterojunction BiOI/La2Ti2O7 composite photocatalysts for enhanced photocatalytic performance under visible light irradiation

A novel BiOI/La₂Ti₂O₇ composite photocatalyst with p–n heterojunctions was prepared for the first time. The as-obtained photocatalysts exhibit efficient activity under visible light irradiation for degradation of organic pollutants.

Synthesis and characterization of ZnS with controlled amount of S vacancies for photocatalytic H2 production under visible light

Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH₄ added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H₂ production under visible light were evaluated by gas chromatograph, and the midgap states of ZnS introduced by S vacancies were examined by density functional calculations. Our study reveals that the concentration of S vacancies in the ZnS samples can be controlled by varying the amount of the reducing agent NaBH₄ in the synthesis, and the prepared ZnS samples exhibit photocatalytic activity for H₂ production under visible-light irradiation without loading noble metal. This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value. Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.

Trends in non-metal doping of the SrTiO3 surface: a hybrid density functional study

N-, Br- and I-doped SrTiO₃ surfaces are theoretically found to be promising photocatalysts for water splitting in the visible region.

Band gap narrowing in nitrogen-doped La2Ti2O7 predicted by density-functional theory calculations

N_S co-existing with V_O in La₂Ti₂O₇ narrows the band gap and removes the localized energy state, leading to a strong visible light photocatalytic activity and enhancement of the UV performance.

Oxide-based nanostructures for photocatalytic and electrocatalytic applications

The enormous efforts on the design of efficient oxide-based materials towards photocatalysis & electrocatalysis have been highlighted in this article with emphasis on their size, structure & morphology.

An overview on visible light responsive metal oxide based photocatalysts for hydrogen energy production

The present review summarizes the recent development and challenges in visible light responsive metal oxide based photocatalysts for water splitting.