Photocatalytic Activity for Water Decomposition of RuO2-Dispersed Zn2GeO4 with d10 Configuration

Exploring the Photocatalytic Mechanism of BiTi4GaO11: Insights from the Electronic Structure and Chemical Bonding

Photocatalytic water splitting and CO2 reduction offer sustainable solutions to energy and environmental issues, but efficient semiconductor photocatalysts are still limited. Oxide photocatalysts with d0 and/or d10 metals often have wide bandgaps, and incorporating d10ns2 metals can raise the valence band maximum (VBM) and narrow the bandgap. Here, we synthesized BiTi4GaO11 (BTGO), a new photocatalyst containing d106s2, d0, and d10 metals. Structural analysis via powder X-ray and neutron diffraction confirmed BTGO crystallizes in the space group Cmcm, with Ga cooccupying all three Ti sites. Density functional theory calculations revealed that the conduction band minimum (CBM) of BTGO is primarily composed of Ti t2g - O 2p antibonding orbitals. Hybridization between Bi 6s and O 2p orbitals leads to the formation of antibonding orbitals, which further interact with Bi 6p orbitals to form the VBM. This interaction shifts the VBM upward, narrows the bandgap (Eg = 2.82 eV), and enables the visible-light absorption. Experimental results demonstrated that BTGO efficiently catalyzes photocatalytic H2 production and CO2 reduction. Furthermore, the incorporation of cocatalysts suppressed the recombination of photogenerated charge carriers, enhancing photocatalytic activity. This work highlights the importance of electronic structure and bonding analysis in understanding the fundamental mechanisms of photocatalysis.

Ba3SnGa10-xInxO20 (0 ≤ x ≤ 2): site-selective doping, band structure engineering and photocatalytic overall water splitting

Developing new photocatalysts and deciphering the structure-property relationship are always the central topics in photocatalysis. In this study, a new photocatalyst Ba3SnGa10O20 containing two d10 metal cations was prepared by a high temperature solid state reaction, and its crystal structure was investigated by Rietveld refinements of monochromatic X-ray powder diffraction data for the first time. There are 2 Ba, 4 metal cations and 6 O independent atoms in a unit cell. Sn4+ and Ga3+ co-occupy the octahedral cavities named M1 and M2 sites, and the other two metal sites are fully occupied by Ga3+. Rational In3+-to-Ga3+ substitution was performed to reduce the potential of the conduction band minimum and enhance the light absorption ability, which was indeed confirmed using UV-vis diffuse reflectance spectra and Mott-Schottky plots for Ba3SnGa10-xInxO20 (0 ≤ x ≤ 2). Interestingly, In3+ exhibits site selective doping at M1 and M2 sites exclusively. With the light absorption ability enhanced, the photocatalytic overall water splitting activity was also improved, i.e. the photocatalytic H2 generation rate was 1.7(1) μmol h-1 for Ba3SnGa10O20, and the optimal catalyst Ba3SnGa8.5In1.5O20 loaded with 1.0 wt% Pd exhibited the H2 generation rate of 27.5(4) μmol h-1 and the apparent quantum yield at 254 nm was estimated to be 2.28% in pure water.

Combined Analyses on Electronic Structure and Molecular Orbitals of d10 Bimetal Oxide In2Ge2O7 and Photocatalytic Performances for Overall Water Splitting and CO2 Reduction

Semiconducting photocatalytic overall water splitting and CO2 reduction are possible solutions to the emerging worldwide challenges of oil shortage and continual temperature increase, and the key is to develop an efficient photocatalyst. Most photocatalysts contain the d0, d10 or d10ns2 metals, and a guiding principle is desired to help to distinguish outstanding semiconductors. Here, the d10 bimetal oxide In2Ge2O7 was selected as the target. First, density functional theory (DFT) calculations point out that the nonbonding O 2p orbitals dominate the valence band maximum (VBM), and In 5s-O 2s and Ge 4s-O 2s antibonding orbitals are the major components of conduction band minimum (CBM). Moreover, the molecular orbitals were analyzed to consolidate the DFT calculations and make it more understandable for chemists. Due to the very small specific surface area (0.51 m2/g) and wide band gap (4.14 eV), as-prepared In2Ge2O7 did not exhibit any overall water splitting activity; nevertheless, when loading with 1 wt% cocatalyst (i.e., Pt, Pd), the surficial charge recombination can be greatly eliminated and the overall water splitting activity is significantly improved to 33.0(4) and 17.2(7) μmol/h for H2 and O2 generation, respectively. The apparent quantum yield (AQY) at 254 nm is 8.28%. This observation is proof that the inherent electronic structure of In2Ge2O7 is beneficial for the charge migration in bulk. Moreover, this catalyst also exhibits an observable CO2 reduction activity in pure water, which is a competition reaction with water splitting, anyway, the CH4 selectivity can be enhanced by loading Pd. This is a successful attempt to unravel the structure-property relationship by combining the analyses on electronic structure and molecular orbitals and is enlightening to further discover good candidates to photocatalysts.

Suppressing Nonradiative Recombination by Electron-Donating Substituents in 2D Conjugated Triphenylamine Polymers toward Efficient Perovskite Optoelectronics

Highly efficient perovskite optoelectronics (POEs) have been limited by nonradiative recombination. We report a strategy to inhibit the nonradiative recombination of 2D triphenylamine polymers in the hole transport layer (HTL) via introducing electron-donating groups to enhance the conjugation effect and electron cloud density. The conjugated systems with electron-donating groups present smaller energy level oscillation compared to the ones with electron-absorbing groups, as confirmed by nonadiabatic molecular dynamics (NAMD) calculation. Further study reveals that the introduction of low-frequency phonons in the electron-donating group systems shortens the nonadiabatic coupling and inhibits the nonradiative recombination. Such electron-donating groups can decrease the valence band maximum of 2D polymers and promote hole transport. Our report provides a new design strategy to suppress nonradiative recombination in HTL for application in efficient POEs.

Investigation of multicolor emitting Cs3GdGe3O9:Bi3+,Eu3+ phosphors via energy transfer for WLEDs

Bi³⁺/Eu³⁺ doped Cs₃GdGe₃O₉ luminescent materials were prepared by a solid-state reaction. The energy band and density of states of Cs₃GdGe₃O₉ were calculated by density functional theory. The Cs₃GdGe₃O₉ host presents a broadband emission peaking at 520 nm. Systemic measurement and analysis of luminescence properties were performed to confirm the energy transfer in Cs₃GdGe₃O₉:Bi³⁺,Eu³⁺. The multicolor modulated emission from blue (0.1678, 0.1568) to red (0.5931, 0.3251) can be achieved by varying the doping ratio of bismuth to europium. A white light-emitting diode (WLED) was produced by combining the Cs₃GdGe₃O₉:0.05Bi³⁺,0.1Eu³⁺ phosphor, a commercial green phosphor, and a 310 nm ultraviolet chip. The color rendering index of the WLED driven by 20 mA bias current is 89.6 with the CIE coordinates of (0.3520, 0.3626). The results reveal that the Cs₃GdGe₃O₉:Bi³⁺,Eu³⁺ phosphor is a potential material that can be used in multicolor tunable luminescence and WLEDs.

Recent Advances in Ternary Metal Oxides Modified by N Atom for Photocatalysis

Ternary metal oxides (TMOs) with flexible band structures are of significant potential in the field of photocatalysis. The efficient utilization of renewable and green solar energy is of great importance to developing photocatalysts. To date, a wide range of TMOs systems has been developed as photocatalysts for water and air purification, but their practical applications in visible light-assisted chemical reactions are hindered mainly by its poor visible light absorption capacity. Introduction of N atoms into TMOs can narrow the band-gap energy to a lower value, enhance the absorption of visible light and suppress the recombination rate of photogenerated electrons and holes, thus improving the photocatalytic performance. This review summarizes the recent research on N-modified TMOs, including the influence of N doping amounts, N doping sites, and N-induced phase transformation. The introduced N greatly tuned the optical properties, electronic structure, and photocatalytic activity of the TMOs. The optimal N concentration and the influence of N doping sites are investigated. The substitutional N and interstitial N contributed differently to the band gap and electron transport. The introduced N can tune the vacancies in TMOs due to the charge compensation, which is vital for inducing different activity and selectivity. The topochemical ammonolysis process can convert TMOs to oxynitride with visible light absorption. By altering the band structures, these oxynitride materials showed enhanced photocatalytic activity. This review provides an overview of recent advances in N-doped TMOs and oxynitrides derived from TMOs as photocatalysts for environmental applications, as well as some relevant pointers for future burgeoning research development.

Characterization of structural and optical properties of Mn2+ doped Zn2 GeO4 nanorods as an efficient green phosphor for solid-state lighting

A series of Mn²⁺ doped zinc germinate ZGO:xMn²⁺ (x = 0-0.05) nanorods were synthesized successfully by the hydrothermal method. X-ray diffraction, Rietveld refinement were used to describe the structural information of the ZGO:xMn²⁺ nanocrystals. XRD revealed that crystal phases of the ZGO:xMn²⁺ is rhombohedral and in the R-3 space group. The unit cell size did not significantly change as the concentration of Mn²⁺ doping increased. The Williamson-Hall equation was also used to explain the strain, nanocrystalline size, and stacking fault. Green LEDs were successfully fabricated by coating ZGO:Mn²⁺ nanorods onto UV-LEDS chip. High color purity, CIE coordinates of the fabricated green LEDs are (0.2404, 0.5428) which is one of the promising candidate for fabrication of UV-based green LEDs.

Metal-Coordinated Supramolecular Self-Assemblies for Cancer Theranostics

Metal-coordinated supramolecular nanoassemblies have recently attracted extensive attention as materials for cancer theranostics. Owing to their unique physicochemical properties, metal-coordinated supramolecular self-assemblies can bridge the boundary between traditional inorganic and organic materials. By tailoring the structural components of the metal ions and binding ligands, numerous multifunctional theranostic nanomedicines can be constructed. Metal-coordinated supramolecular nanoassemblies can modulate the tumor microenvironment (TME), thus facilitating the development of TME-responsive nanomedicines. More importantly, TME-responsive organic-inorganic hybrid nanomaterials can be constructed in vivo by exploiting the metal-coordinated self-assembly of a variety of functional ligands, which is a promising strategy for enhancing the tumor accumulation of theranostic molecules. In this review, recent advancements in the design and fabrication of metal-coordinated supramolecular nanomedicines for cancer theranostics are highlighted. These supramolecular compounds are classified according to the order in which the coordinated metal ions appear in the periodic table. Furthermore, the prospects and challenges of metal-coordinated supramolecular self-assemblies for both technical advances and clinical translation are discussed. In particular, the superiority of TME-responsive nanomedicines for in vivo coordinated self-assembly is elaborated, with an emphasis on strategies that enhance the accumulation of functional components in tumors for an ideal theranostic outcome.

Rationalize the Significantly Enhanced Photocatalytic Efficiency of In3+-doped α'-Ga2S3 by Bond Theory and Local Structural Distortion

Mechanistic understanding on the electronic structure of α'-Ga₂S₃ unravel that the electrons in nonbonding 3p_z orbitals of two-coordinated S^2- anions are photoexcited to the adjacent σ-type antibonding orbitals (Ga-4s and S-3p) and migrate thereafter to the surface along the a-axis. By introduction of the In-S antibonding on the one hand and modifying the local dipole moment on the other hand, the light absorption ability and charge separation efficiency can be both enhanced by In³⁺-to-Ga³⁺ substitution, and the photocatalytic H₂ evolution rate can be significantly promoted. Local geometric distortion is common in solid solutions, but its effect on charge migration behavior has yet been considered in semiconducting photocatalysis. Our case study on In³⁺-doped Ga₂S₃ is a good reminder of such the importance.

Hierarchical Ternary Sulfides as Effective Photocatalyst for Hydrogen Generation Through Water Splitting: A Review on the Performance of ZnIn2S4

One of the major aspects and advantages of solar energy conversion is the photocatalytic hydrogen generation using semiconductor materials for an eco-friendly technology. Designing a low-cost efficient material to overcome limited light absorption as well as rapid recombination of photogenerated charge carriers is essential to achieve considerable hydrogen generation. In recent years, sulfide based semiconductors have attracted scientific research interest due to their excellent solar response and narrow band gap. The present review focuses on the recent approaches in the development of hierarchical ternary sulfide based photocatalysts with a special focus on ZnIn2S4. We also observe how the electronic structure of ZnIn2S4 is beneficial for water splitting and the various strategies involved for improving the material efficiency for photocatalytic hydrogen generation. The review places emphasis on the latest advancement/new insights on ZnIn2S4 being used as an efficient material for hydrogen generation through photocatalytic water splitting. Recent progress on essential aspects which govern light absorption, charge separation and transport are also discussed in detail.

Understanding Negative Thermal Expansion of Zn2GeO4 through Local Structure and Vibrational Dynamics

Zn₂GeO₄ is a multifunctional material whose intrinsic thermal expansion properties below ambient temperature have not been explored until now. Herein, the thermal expansion of Zn₂GeO₄ is investigated by synchrotron X-ray diffraction, with the finding that Zn₂GeO₄ exhibits very low negative (α_v = -2.02 × 10^-6 K^-1, 100-300 K) and positive (α_v = +2.54 × 10^-6 K^-1, 300-475 K) thermal expansion below and above room temperature, respectively. A combined study of neutron powder diffraction and extended X-ray absorption fine structure spectroscopy shows that the negative thermal expansion (NTE) of Zn₂GeO₄ originates from the transverse vibrations of O atoms in the four- and six-membered rings with ZnO₄-GeO₄ tetrahedra. In addition, the results of temperature- and pressure-dependent Raman spectra identify the low-frequency phonon modes (50-150 cm^-1) with negative Grüneisen parameters softening upon pressuring and stiffening upon heating during the lattice contraction, thus contributing to the NTE. This study not only reports the interesting thermal expansion behavior of Zn₂GeO₄ but also provides further insights into the NTE mechanism of novel structures.

Rocksalt-Zincblende-Wurtzite Mixed-Phase ZnO Crystals With High Activity as Photocatalysts for Visible-Light-Driven Water Splitting

Finding out the factors that dominate photocatalytic activity is always an essential topic toward the development of highly active photocatalysts. The increased photoactivity of ZnO:Ga (L) may be attributed to the existence of homojunctions and resultant oxygen vacancies in triphasic ZnO:Ga (L), which can reduce the recombination of photogenerated carriers and provide them higher doping efficiency and higher optical gain. Then, the photocatalytic behaviors of as-prepared N doped crystals have been studied and rationalized to understand the role of each of species played in light absorption and photo activation. The N-doped ZnO:Ga (L) sample which showed higher activity than N-doped ZnO:Ga (B) and ZnO:Ga (L), the high activity could be explained by increase of visible light absorption and presence of empty impurity levels introduced by N doping.

Zn2GeO4−x/ZnS heterojunctions fabricated via in situ etching sulfurization for Pt-free photocatalytic hydrogen evolution: interface roughness and defect engineering

The Zn₂GeO_4−x/ZnS intimate heterojunctions were synthesized by in situ etching sulfurization, which realized photocatalytic H₂ evolution from water without the Pt co-catalyst by the synergism between interface topology and oxygen defect control.

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.

Enhanced Photocatalytic Degradation of 2-Butanone Using Hybrid Nanostructures of Gallium Oxide and Reduced Graphene Oxide Under Ultraviolet-C Irradiation

Hybrid nanostructures made of gallium oxide (Ga2O3) and reduced graphene oxide (rGO) are synthesized using a facile hydrothermal process method, where the Ga2O3 nanostructures are well dispersed on the rGO surface. The formed Ga2O3-rGO hybrids are characterized via Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), a diffuse reflectance Ultraviolet-visible-near infrared (UV-Vis-NIR) spectrophotometer, Brunauer–Emmett–Teller (BET), and photoluminescence (PL). Gas chromatography mass spectrometry (GC-MS) was used for analyzing volatile organic compounds (VOCs). The photocatalytic activity of the hybrid nanostructures is evaluated via the degradation of the 2-butanone, representing the VOCs under 254-nm radiation in the atmosphere. That activity is then compared to that of the Ga2O3 and commercial TiO2-P25. The Ga2O3-rGO hybrid shows enhanced photocatalytic degradation of 2-butanone compared to Ga2O3 and TiO2-P25, which is attributed to the enhanced specific surface area. The results indicate that the Ga2O3-rGO hybrid could be a promising method of enhancing photocatalytic activity and thereby effectively degrading VOCs, including the 2-butanone.

Novel magnetically separable of Fe3O4/Ag3PO4@WO3 nanocomposites for enhanced photocatalytic and antibacterial activity against Staphylococcus aureus (S. aureus)

BACKGROUND

Iron oxide nanocomposites have received a great attention for their application in various fields like physics, medicine, biology, and material science etc., due to their unique properties, such as magnetism, electrical properties, small size, biocompatibility and low toxicity.

METHODS

Fe3O4/Ag3PO4@WO3 nanocomposites with different weight percent of Ag3PO4 were successfully prepared through fabricated Ag3PO4/Fe3O4 with WO3 via in situ fabrication method, electrospinning involved precursor solution preparation and spinning to enhance photocatalyst performance under simulated sunlight for the degradation of methylene blue (MB) and antibacterial activity against Staphylococcus aureus (S. aureus).

RESULTS

The photocatalytic degradation of methylene blue (MB) under simulated light irradiation indicated that the nanocomposite with 0.25 mg of Ag3PO4 has the best activity. An additional advantage of these photocatalysts is magnetic recoverability, using external magnetic field and photocatalytic stability of the nanocomposites was evaluated for three cycles. In addition, using different scavengers, holes (h+) and superoxide radical (O 2 ·-) radicals and hydroxide radical (·OH) were identified the main oxidative species in the degradation reaction of methylene blue.

CONCLUSIONS

The results reveal that Fe3O4/Ag3PO4@WO3-0.25 nanocomposites have photocatalytic and antibacterial activity against S. aureus. The photocatalyst and mechanism based on the enhancement of electron transfer processes between Ag3PO4 and WO3 nanoparticles.

Inducing tunable host luminescence in Zn2GeO4 tetrahedral materials via doping Cr3

Zn₂GeO₄ consisting of tetrahedron, and it is a self-luminescent material due to the presence of the native defects and shows a bluish white emission excited by ultraviolet. Although Cr³⁺ doped in a tetrahedron generally cannot show luminescence, in this research, new defects are formed as Cr³⁺ doped in Zn₂GeO₄, hence a green emission band can be obtained. Meanwhile, the intensity of host emission is also decreased. Therefore, Zn₂GeO₄:Cr³⁺ are synthesized using a high-temperature solid-phase method. Thermoluminescence (TL) and luminescence decay curves are used to investigate the variation of native defects. The emission colour can be tuned from bluish white to green when Cr³⁺ doped in Zn₂GeO₄. This result has guidance for controlling the native emission of self-luminescent material.

Titanium dioxide (TiO2)-decorated silver indium diselenide (AgInSe2): novel nano-photocatalyst for oxidative dye degradation

Novel titanium-dioxide-decorated silver indium diselenide nano-photocatalyst for enhancement in photocatalytic dye degradation efficiency of three different dyes, namely, MB, MO, and RhB.

Cobalt Oxide Nanoclusters on Rutile Titania as Bifunctional Units for Water Oxidation Catalysis and Visible Light Absorption: Understanding the Structure-Activity Relationship

The structure of cobalt oxide (CoO_x) nanoparticles dispersed on rutile TiO₂ (R-TiO₂) was characterized by X-ray diffraction, UV-vis-NIR diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, X-ray absorption fine-structure spectroscopy, and X-ray photoelectron spectroscopy. The CoO_x nanoparticles were loaded onto R-TiO₂ by an impregnation method from an aqueous solution containing Co(NO₃)₂·6H₂O followed by heating in air. Modification of the R-TiO₂ with 2.0 wt % Co followed by heating at 423 K for 1 h resulted in the highest photocatalytic activity with good reproducibility. Structural analyses revealed that the activity of this photocatalyst depended strongly on the generation of Co₃O₄ nanoclusters with an optimal distribution. These nanoclusters are thought to interact with the R-TiO₂ surface, resulting in visible light absorption and active sites for water oxidation.

Development of non-oxide semiconductors as light harvesting materials in photocatalytic and photoelectrochemical water splitting

This perspective summarizes recent advances in the use of (oxy)nitrides and oxysulfides as light harvesting semiconductors for photocatalytic or photoelectrochemical water splitting.

Amorphous Semiconductor Nanowires Created by Site-Specific Heteroatom Substitution with Significantly Enhanced Photoelectrochemical Performance

Semiconductor nanowires that have been extensively studied are typically in a crystalline phase. Much less studied are amorphous semiconductor nanowires due to the difficulty for their synthesis, despite a set of characteristics desirable for photoelectric devices, such as higher surface area, higher surface activity, and higher light harvesting. In this work of combined experiment and computation, taking Zn2GeO4 (ZGO) as an example, we propose a site-specific heteroatom substitution strategy through a solution-phase ions-alternative-deposition route to prepare amorphous/crystalline Si-incorporated ZGO nanowires with tunable band structures. The substitution of Si atoms for the Zn or Ge atoms distorts the bonding network to a different extent, leading to the formation of amorphous Zn1.7Si0.3GeO4 (ZSGO) or crystalline Zn2(GeO4)0.88(SiO4)0.12 (ZGSO) nanowires, respectively, with different bandgaps. The amorphous ZSGO nanowire arrays exhibit significantly enhanced performance in photoelectrochemical water splitting, such as higher and more stable photocurrent, and faster photoresponse and recovery, relative to crystalline ZGSO and ZGO nanowires in this work, as well as ZGO photocatalysts reported previously. The remarkable performance highlights the advantages of the ZSGO amorphous nanowires for photoelectric devices, such as higher light harvesting capability, faster charge separation, lower charge recombination, and higher surface catalytic activity.

Y(1-x)Sc(x)BaZn3GaO7 (0 ≤ x ≤ 1): Structure Evolution by Sc-Doping and the First Example of Photocatalytic Water Reduction in "114" Oxides

"114" oxides have shown intriguing physical properties while their performance in photocatalysis has not yet been reported probably due to the instability in aqueous solution. YBaZn3GaO7 is an exception, which is stable and indeed shows observable photocatalytic H2 evolution (∼2 μmol/h/g) in methanol aqueous solution under UV light. This activity was enhanced to 23.6 μmol/h/g by a full replacement of Y(3+) by Sc(3+). Optical absorption spectra and theoretical calculations show no significant difference upon Sc(3+)-doping. Instead, a systematic analysis of the structure evolution by Rietveld refinements for Y(1-x)Sc(x)BaZn3GaO7 (0 ≤ x ≤ 1) suggests that the increase of the catalytic activity is likely due to the decrease of the structural defects and thus the lower level of recombination rate of e(-) and h(+). In detail, Sc(3+) substitution leads to a shrinkage of YO6 octahedra, and successively the adjustment of the Zn(2+)/Ga(3+) occupancy behaviors in tetrahedra sites. The photocatalytic H2 evolution rate was further optimized to 118.2 μmol/h/g in methanol solution and 42.9 μmol/h/g in pure water for 1 wt % Pt-loaded ScBaZn3GaO7. Here, the relatively less investigated nonmagnetic "114" oxides were, for the first time, proved to be good candidates for photocatalytic water reduction.

Quinary wurtzite Zn-Ga-Ge-N-O solid solutions and their photocatalytic properties under visible light irradiation

Wurtzite solid solutions between GaN and ZnO highlight an intriguing paradigm for water splitting into hydrogen and oxygen using solar energy. However, large composition discrepancy often occurs inside the compound owing to the volatile nature of Zn, thereby prescribing rigorous terms on synthetic conditions. Here we demonstrate the merits of constituting quinary Zn-Ga-Ge-N-O solid solutions by introducing Ge into the wurtzite framework. The presence of Ge not only mitigates the vaporization of Zn but also strongly promotes particle crystallization. Synthetic details for these quinary compounds were systematically explored and their photocatalytic properties were thoroughly investigated. Proper starting molar ratios of Zn/Ga/Ge are of primary importance for single phase formation, high particle crystallinity and good photocatalytic performance. Efficient photocatalytic hydrogen and oxygen production from water were achieved for these quinary solid solutions which is strongly correlated with Ge content in the structure. Apparent quantum efficiency for optimized sample approaches 1.01% for hydrogen production and 1.14% for oxygen production. Theoretical calculation reveals the critical role of Zn for the band gap reduction in these solid solutions and their superior photocatalytic acitivity can be understood by the preservation of Zn in the structure as well as a good crystallinity after introducing Ge.

Magnetite hybrid photocatalysis: advance environmental remediation

One of the main public concerns is the aquatic habitat and its corresponding issues because of the incessant contamination of the ecological water systems. In recent years, research attention has been focused on processes that lead to an improved oxidative degradation of organic pollutants. Therefore, semiconductor photocatalysis technology has aroused scientists’ interest in environmental remediation. Although several semiconductors have proven to be ideal candidates for the treatment of water pollution, the efficient separation and recycling of this fine-powdered photocatalyst is still a scientific problem when applied in practice, including separation process, selectivity, and dispersion. A photocatalyst with magnetic properties allows the use of the technique of magnetic separation, which is one of the most effective and simple methods for removing suspended solids from wastewater without the need for further separation processes. The magnetic photocatalyst allows its use as a suspended material, providing the advantage to have a high surface area for reaction. This review highlights the advantages and disadvantages of current photocatalyst systems. Moreover, it focuses on hybrid magnetic photocatalysts, including metals and nonmetals, metal oxides, carbon-based materials, and ceramics.

Corundum type indium oxide nanostructures: ambient pressure synthesis from InOOH, and optical and photocatalytic properties

A simple, cost effective, surfactant free and scalable synthesis of rh-In₂O₃ nanostructures showing intense blue light emission has been developed under ambient pressure.

Structural evolution of alkaline earth metal stannates MSnO3 (M = Ca, Sr, and Ba) photocatalysts for hydrogen production

The alkaline earth metal stannates MSnO₃ (M = Ca, Sr, and Ba) photocatalysts with different morphologies are successfully prepared by hydrothermal method and their photocatalytic activities are evaluated by photocatalytic reforming of ethanol/water solution to hydrogen.

Zn2−aGeO4:aRE and Zn2Ge1−aO4:aRE (RE = Ce3+, Eu3+, Tb3+, Dy3+): 4f–4f and 5d–4f transition luminescence of rare earth ions under different substitution

Generally, luminescent properties of rare earth ions doped host can be tuned by controlling the host composition, that is, when substituted for different cations of host, the rare earths ions can present different characteristics.

Facile synthesis of NiS/CdS nanocomposites for photocatalytic degradation of quinoline under visible-light irradiation

NiS/CdS nanocomposites with good visible-light-induced photocatalytic activity were successfully prepared via a facile two-step process.

Orange Zinc Germanate with Metallic Ge-Ge Bonds as a Chromophore-Like Center for Visible-Light-Driven Water Splitting

The efficiency of solar-energy-conversion devices depends on the absorption region and intensity of the photon collectors. Organic chromophores, which have been widely stabilized on inorganic semiconductors for light trapping, are limited by the interface between the chromophore and semiconductor. Herein we report a novel orange zinc germanate (Zn-Ge-O) with a chromophore-like structure, by which the absorption region can be dramatically expanded. Structural characterizations and theoretical calculations together reveal that the origin of visible-light response can be attributed to the unusual metallic Ge-Ge bonds which act in a similar way to organic chromophores. Benefiting from the enhanced light harvest, the orange Zn-Ge-O demonstrates superior capacity for solar-driven hydrogen production.

Recent progress in oxynitride photocatalysts for visible-light-driven water splitting

Photocatalytic water splitting into hydrogen and oxygen is a method to directly convert light energy into storable chemical energy, and has received considerable attention for use in large-scale solar energy utilization. Particulate semiconductors are generally used as photocatalysts, and semiconductor properties such as bandgap, band positions, and photocarrier mobility can heavily impact photocatalytic performance. The design of active photocatalysts has been performed with the consideration of such semiconductor properties. Photocatalysts have a catalytic aspect in addition to a semiconductor one. The ability to control surface redox reactions in order to efficiently produce targeted reactants is also important for photocatalysts. Over the past few decades, various photocatalysts for water splitting have been developed, and a recent main concern has been the development of visible-light sensitive photocatalysts for water splitting. This review introduces the study of water-splitting photocatalysts, with a focus on recent progress in visible-light induced overall water splitting on oxynitride photocatalysts. Various strategies for designing efficient photocatalysts for water splitting are also discussed herein.

A review of BiPO4, a highly efficient oxyacid-type photocatalyst, used for environmental applications

This review presents the recent progress on the oxyacid-type photocatalyst, BiPO₄, which possesses excellent UV-activity for environmental applications.

Facile synthesized highly active BiOI/Zn2GeO4 composites for the elimination of endocrine disrupter BPA under visible light irradiation

A high-performance BiOI/Zn₂GeO₄ visible light photocatalyst for the decomposition of organic pollutants was fabricated using a simple chemical bath approach.

Controllable Synthesis of Zn2GeO4Nanorods for Photocatalytic Reduction of Aqueous Cr(VI) and Oxidation of Organic Pollutants

Zn2GeO4nanorods were successfully synthesized by a simple hydrothermal method. The composition, morphology, and optical properties of as-synthesized Zn2GeO4samples were characterized by X-ray diffraction, scan electron microscopy, and UV-vis diffuse reflectance spectra. The photocatalytic properties of Zn2GeO4nanorods were evaluated by the reduction of Cr(VI) and oxidation of organic pollutants in aqueous solution. The effects of solution pH on Cr(VI) reduction by Zn2GeO4nanorods were studied in detail. The results indicated that the efficiency of Cr(VI) reduction was highest at pH 5.96. Moreover, Zn2GeO4nanorods also showed excellent photocatalytic ability for the oxidation of organic pollutants such as rhodamine B and 4-nitrophenol.

N,F-monodoping and N/F-codoping effects on the electronic structures and optical performances of Zn2GeO4

With N/F codoping, the optical absorption property of Zn₂GeO₄was improved under visible-light irradiation, which may promote the photocatalytic activity.

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.

Photocatalytic decomposition of humic acids in anoxic aqueous solutions producing hydrogen, oxygen and light hydrocarbons

Photocatalytic water splitting for hydrogen and oxygen production requires sacrificial electron donors, for example, organic compounds. Titanium dioxide catalysts doped with platinum, cobalt, tungsten, copper and iron were experimentally tested for the production of hydrogen, oxygen and low molecular weight hydrocarbons from aqueous solutions of humic substances (HS). Platinum-doped catalyst showed the best results in hydrogen generation, also producing methane, ethene and ethane, whereas the best oxygen production was exhibited by P25, followed by copper--and cobalt-containing photocatalysts. Iron-containing photocatalyst produced carbon monoxide as a major product. HS undergoing anoxic photocatalytic degradation produce hydrogen with minor hydrocarbons, and/or oxygen. It appears that better hydrogen yield is achieved when direct HS splitting takes place, as opposed to HS acting as electron donors for water splitting.