Efficient visible-light-driven photocatalytic H2 production over Cr/N-codoped SrTiO3

Visible-light-response Cr/N-codoped SrTiO₃ was prepared by a sol–gel hydrothermal method. The comparison studies indicate that Cr-doped and Cr/N-codoped SrTiO₃ can be synthesized by this means, but not the N-doped SrTiO₃. The theoretical calculations exhibit the defect formation energy of the Cr/N codoping into SrTiO₃ is much smaller than that of the N doping into SrTiO₃, illuminating that the incorporation of Cr can promote the N doping into the O sites in the SrTiO₃. Compared to the Cr-doped SrTiO₃, the Cr/N-codoped SrTiO₃ photocatalyst shows the high photocatalytic activities for hydrogen production with the quantum efficiency of 3.1% at 420 nm, due to the smaller band gap and much less vacancy defects.     

Preparation of novel SrTiO3:Rh/Ta photocatalyst by spray pyrolysis and its activity for H2 evolution from aqueous methanol solution under visible light

SrTiO₃:Rh/Ta powder was prepared by spray pyrolysis from polymeric precursors containing citric acid and ethylene glycol. Co-doping Ta into SrTiO₃:Rh increased the presence of Rh³⁺ in the host material. The retention of balanced charges by the substitution of two Ti⁴⁺ ions in the host material by one ion each of Rh³⁺ and Ta⁵⁺ enhanced hydrogen evolution from aqueous methanol solution under visible light irradiation (λ > 415 nm) by 3.5 times (to 531 μmol h⁻¹) and reduced the induction period by 50% (to 1 h), when compared with SrTiO₃:Rh. Thorough mixing of the multi-component spray pyrolysis precursor solution resulted in highly dispersed Rh ions and porous photocatalyst particles, which showed enhanced hydrogen evolution rate.     

H2 evolution under visible light irradiation from aqueous methanol solution on SrTiO3:Cr/Ta prepared by spray pyrolysis from polymeric precursor

SrTiO₃:Cr/Ta powders were prepared by spray pyrolysis from polymeric precursors. Effects of the amount of co-dopant and additives on the photocatalytic activity for hydrogen evolution from aqueous methanol solution under visible light irradiation (λ > 415 nm) were investigated. For the photocatalyst prepared by spray pyrolysis from polymeric precursor, the hydrogen evolution rate was increased by a factor of ∼100 and induction period was decreased by a factor of 8 compared with a photocatalyst prepared by solid state reaction. These enhancements result from increased roughness of surface, and the compositional uniformity which are intrinsic characteristics of spray pyrolysis. In addition, photocatalyst prepared by spray pyrolysis from polymeric precursor have large BET surface area and small amount of Cr⁶⁺ ion which is responsible for long induction period. It should be noted that the reduction of Cr⁶⁺ ion was achieved without hydrogen reduction process.     

Photocatalytic H2 evolution on a novel CaIn2S4 photocatalyst under visible light irradiation

A novel visible-light-driven photocatalyst CaIn₂S₄ was synthesized using a facile hydrothermal method followed by a post-calcination process. The influence of the calcination temperature and time on the activities of the photocatalyst was investigated. CaIn₂S₄ exhibits optical absorption predominantly in visible region with an optical band gap of 1.76 eV. Considerable activity for hydrogen evolution from pure water was observed without any sacrificial agents or cocatalysts under visible light irradiation. The maximum hydrogen evolution rate achieved was 30.92 μmol g⁻¹ h⁻¹ without obvious deactivation of the photocatalytic activity for four consecutive runs of 32 h.     

In-situ growth of CdS quantum dots on g-C3N4 nanosheets for highly efficient photocatalytic hydrogen generation under visible light irradiation

Well dispersed CdS quantum dots were successfully grown in-situ on g-C₃N₄ nanosheets through a solvothermal method involving dimethyl sulfoxide. The resultant CdS–C₃N₄ nanocomposites exhibit remarkably higher efficiency for photocatalytic hydrogen evolution under visible light irradiation as compared to pure g-C₃N₄. The optimal composite with 12 wt% CdS showed a hydrogen evolution rate of 4.494 mmol h⁻¹ g⁻¹, which is more than 115 times higher than that of pure g-C₃N₄. The enhanced photocatalytic activity induced by the in-situ grown CdS quantum dots is attributed to the interfacial transfer of photogenerated electrons and holes between g-C₃N₄ and CdS, which leads to effective charge separation on both parts.     

g-C3N4/TiO2可见光催化降解磺胺甲恶唑的研究

以TiO₂颗粒和三聚氰胺为原料,采用高温煅烧法制备g-C₃N₄/TiO₂复合光催化材料,研究其对仿生生态系统中磺胺类抗生素的去除效果。利用扫描电子显微镜（SEM）、X射线衍射仪(XRD)、傅里叶变换红外光谱仪（FTIR）、紫外可见分光光度计（UV-vis DRS）对g-C₃N₄/TiO₂进行表征,并研究在可见光条件下g-C₃N₄/TiO₂对溶液中磺胺甲恶唑（SMX）的光催化降解效果。结果表明,g-C₃N₄/TiO₂具有良好的光催化活性,在可见光照射下,当g-C₃N₄/TiO₂投加量为0.2 g·L^-1时,对初始质量浓度为200 μg·L^-1的SMX的去除率可达84.3%。在相同条件下,而g-C₃N₄和TiO₂只能分别去除21.0%和16.0%的SMX,同时在仿生系统中12.37 g·m^-2 g-C₃N₄/TiO₂可以去除95.35%的SMX。通过质谱分析推测,SMX可能的降解路径分别为S—N键断裂、C—N键断裂、S—C键断裂、SMX的羟基化和SMX上氨基的硝化反应,两种可能的中间产物分别为对氨基苯磺酰胺和3-氨基-5-甲基异恶唑。     

Band gap engineering of SrTiO3 for water splitting under visible light irradiation

The electronic structures of pure, mono-doped (either Mo or N), and co-doped (Mo and N) SrTiO₃ are calculated by first principles with the Tran-Blaha modified Becke–Johnson potential. Results show that the calculated band gap of SrTiO₃ is improved from 1.87 to 3.27 eV by this new method, being in good agreement with the experimental value. Mo and N co-doping can prevent not only the partially occupied states from appearing at the band edge but also the two N atoms coupling. Therefore, the high activity of photocatalysis remains and the band edges are compatible with the redox potentials for water splitting. More importantly, the band gap of the most stable co-doped configuration is sharply narrowed to 2.07 eV. The defect formation energy calculations indicate that the co-doped systems are energetically favorable in Ti-poor and O-rich environments. These show that Mo and N co-doped SrTiO₃ should be a good candidate for water splitting using sunlight.     

Effects of charge balance with Na on SrTiO3:Mo prepared by spray pyrolysis for H2 evolution under visible light irradiation

Photocatalyst powders of SrTi_1−xMo_xO₃ and Sr_1−2xNa_2xTi_1−xMo_xO₃ were prepared by spray pyrolysis for hydrogen evolution for the first time from aqueous methanol solution under visible light irradiation. The co-doping of Mo⁶⁺/Na⁺ ions resulted in increase of BET surface area and pore volume, and formation of unique morphology with wrinkled, furrowed and porous surface, without significant distortion of lattice structure of host material. The hydrogen evolution rate of Sr_1−2xNa_2xTi_1−xMo_xO₃ photocatalyst was enhanced up to 1115.8 μmol g⁻¹ h⁻¹ with an induction period of 1 h under visible light irradiation, which was 1.5 times higher than that of SrTi_1−xMo_xO₃. The co-dopant Na⁺ ion contributed to the charge balance in the host material by compromising the excess positive charge of Mo⁶⁺, which was effective for enhancing the hydrogen evolution rate. The optimum composition of photocatalyst corresponding to the maximum hydrogen evolution rate was Sr_1−2xNa_2xTi_1−xMo_xO₃ (x = 0.004).     

Bimetallic PtNi/g-C3N4 nanotubes with enhanced photocatalytic activity for H2 evolution under visible light irradiation

Bimetallic PtNi-decorated graphitic carbon nitride (g-C₃N₄) nanotubes were prepared through calcining the mixture of urea and thiourea in the presence of Pluronic F127, followed by deposition of bimetallic PtNi nanoparticles (NPs) via chemical reduction. It is found that the photocatalytic activity of PtNi/g-C₃N₄ nanotubes is strongly dependent on the molar ratio of Pt/Ni and the highest activity is observed for Pt₁Ni₁/g-C₃N₄. Under visible light (λ > 420 nm) irradiation, the H₂ generation rate over Pt₁Ni₁/g-C₃N₄ nanotubes is 104.7 μmol h^?1 from a triethanolamine (10 vol%) aqueous solution, which is higher than that of Pt/g-C₃N₄ nanotubes (98.6 μmol h^?1) and is about 47.6 times higher than that of pure g-C₃N₄ nanotubes. The cyclic photocatalytic reaction indicates that our Pt₁Ni₁/g-C₃N₄ nanotubes function as a stable photocatalyst for visible light-driven H₂ production. The effect of bimetallic PtNi NPs in the transfer and separation of photogenerated charge carriers occurring in the excited g-C₃N₄ nanotubes was investigated by performing photo-electrochemical and photoluminescence measurements. Our results reveal that bimetallic PtNi could replace Pt as a promising cocatalyst for photocatalytic H₂ evolution with better performance and lower cost.     

Stability of an H2-producing photocatalyst (Ru/(CuAg)0.15In0.3Zn1.4S2) in aqueous solution under visible light irradiation

Efficient photocatalytic water-splitting systems require stable photocatalysts that have photocatalytic activity with repeated consecutive use. This study investigated H₂ production under visible light irradiation with an Ru/(CuAg)_0.15In_0.3Zn_1.4S₂ photocatalyst and KI as an electron donor. In addition, the stability and reusability of the catalyst were evaluated over multiple cycles of H₂ production and catalyst regeneration. The results show that sintering temperature influenced the crystallinity and photocatalytic activity, as indicated by the X-ray diffraction analyses and H₂ production rates. In particular, the catalyst sintered at 873 K yielded the highest quantum yield of 4.6% at 420 ± 5 nm of wavelength. After seven consecutive reaction cycles, the quantum yield decreased from 4.6% to 3.0% at the end of the seventh cycle. The decrease probably occurred because (1) particles of the catalyst underwent pronounced aggregation, which led to the increase in particle size; and (2) a release of significant metal ions was observed during H₂ production, which led to a loss of the catalyst mass and potential changes in the photocatalytic activity. This study will help facilitate a search of stable photocatalysts for water splitting.     

Mesoporous nanocomposite Fe/Al2O3-MCM-41: An efficient photocatalyst for hydrogen production under visible light

The iron incorporated mesoporous Al₂O₃-MCM-41 nanocomposites, synthesized by sol-gel and followed by wetness impregnation method, were found to be active photocatalysts for evolution of hydrogen energy from water in the presence of sacrificial agent under visible light illumination (λ ≥ 400 nm). The key factors for water splitting are appropriate band gap energy, small particle size, high surface area and mesoporosity nature. The DRUV-vis spectra measured the band gap energy where as the particle sizes of the materials were evaluated by TEM. Beside these, the materials were characterized by small angle XRD, N₂ adsorption-desorption, FTIR and XPS. Moreover, among mesoporous support and mesoporous nanocomposites, 5Fe/Al₂O₃-MCM-41 exhibited highest water splitting ability and produced 146 μmol/h hydrogen gas with apparent quantum efficiency 6.1%. The textural properties (high surface area, narrow pore size, large pore volume and mesoporosity), visible light active band gap energy 1.90 eV and small particle size (47.95 nm) collectively contribute for high hydrogen production ability of 5Fe/Al₂O₃-MCM-41.     

SrS/CdS composite powder as a novel photocatalyst for hydrogen production under visible light irradiation

In this paper a novel SrS/CdS composite powders were prepared by coprecipitation method. The physicochemical properties of the photocatalysts were analyzed by XRD, UV–Vis, BET, PL and SEM. Photocatalytic hydrogen production results showed that these composite powders can work efficiently under visible light without loading noble metal, and it was found that the ratio of SrS/CdS equaling to 2/8 has the best performance among various SrS/CdS composite powders, and the hydrogen evolution rate amounted to 123 μmol/h under visible light irradiation. The apparent quantum yield for this photocalyst was calculated to be 2.85%, 4.59%, 9.63% at 420 nm, 440 nm and 480 nm respectively, and the apparent quantum yield under visible light was 5.83%. The reason for its high activity was analyzed.     

Development of copper-doped TiO2 photocatalyst for hydrogen production under visible light

The advantage of copper doping onto TiO₂ semiconductor photocatalyst for enhanced hydrogen generation under irradiation at the visible range of the electromagnetic spectrum has been investigated. Two methods of preparation for the copper-doped catalyst were selected – complex precipitation and wet impregnation methods – using copper nitrate trihydrate as the starting material. The dopant loading varied from 2 to 15%. Characterization of the photocatalysts was done by thermogravimetric analysis (TGA), temperature programmed reduction (TPR), diffuse reflectance UV-Vis (DR-UV-Vis), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Photocatalytic activity towards hydrogen generation from water was investigated using a multiport photocatalytic reactor under visible light illumination with methanol added as a hole scavenger. Three calcination temperatures were selected – 300, 400 and 500 °C. It was found that 10 wt.% Cu/TiO₂ calcined at 300 °C for 30 min yielded the maximum quantity of hydrogen. The reduction of band gap as a result of doping was estimated and the influence of the process parameters on catalytic activity is explained.     

Effect of tri-doping on H2 evolution under visible light irradiation on SrTiO3:Ni/Ta/La prepared by spray pyrolysis from polymeric precursor

Tri-doped photocatalyst, SrTiO₃:Ni/Ta/La, was prepared by spray pyrolysis from aqueous and polymeric precursor solutions. The third dopant, La³⁺, contributed to the BET surface area and porous morphology by preventing crystal growth, and increased the Ni²⁺/Ni³⁺ ratio by affecting the electron configuration in the lattice structure, which is closely related to the hydrogen evolution rate. The hydrogen evolution rate of the tri-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%)/La(0.3 mol%), was increased by about 60%–895.2 μmol g⁻¹ h⁻¹ from the value of 561.2 μmol g⁻¹ h⁻¹ for the co-doped photocatalyst, SrTiO₃:Ni(0.2 mol%)/Ta(0.4 mol%), and was further enhanced to 2305.7 μmol g⁻¹ h⁻¹ when a polymeric precursor was used instead of an aqueous precursor in spray pyrolysis. The optimum additive content for polymeric precursor solution was 300 mol%.     

Improved photocatalytic H2 production assisted by aqueous glucose biomass by oxidized g-C3N4

Chemically modified g-C₃N₄ for the photocatalytic H₂ evolution from water was explored. Bulk g-C₃N₄ was treated in hot HNO₃ aqueous solution to obtain the oxidized material (o-g-C₃N₄), tested in water containing glucose as model water-soluble sacrificial biomass, using Pt as co-catalyst, under simulated solar light. The behaviour of o-g-C₃N₄ was studied in relation with catalyst amount, Pt loading, glucose concentration. Results showed that H₂ production is favoured by increasing glucose concentration up to 0.1 M and Pt loading up to 3 wt%, and it resulted strongly enhanced using small amount of o-g-C₃N₄ (0.25 g L^?1). o-g-C₃N₄ possesses superior photocatalytic activity (～26-fold higher) compared to pristine g-C₃N₄, with H₂ evolution further improved by ultrasound-assisted exfoliation and evolution rates up to ca. 1370 μmol h^?1 per gram of catalyst, with excellent reproducibility (RSD < 6%, n = 3). Significant production was observed also in river water and seawater, with results far better (up to ca. 2500 μmol g^?1 h^?1) compared to commercial AEROXIDE^® P25 TiO₂ under natural solar light.     

Synthesis of g-C3N4/TiO2 with enhanced photocatalytic activity for H2 evolution by a simple method

A photocatalyst composed of graphite-like carbon nitride (g-C₃N₄) and TiO₂ was fabricated by a simple method to calcine the mixture of melamine and TiO₂ precursor. The photocatalyst has enhanced photoactivity for hydrogen evolution from water. Characterization by XRD, FTIR, SEM and elemental analysis showed that the crystal structure and morphologies of composites were affected by the amount of melamine in the composite. The UV–Vis characterization displayed that the optical absorption range of g-C₃N₄/TiO₂ hybrid was broadened with a synergistic effect. The photoactivity for H₂ evolution was shown that the best result obtained from the composite with 67 wt% melamine has about 5 times improvement compared with bare TiO₂ or pure g-C₃N₄. The enhanced photoactivity might be related with the favorable structure resulted from heat-treatment temperature, and the content of g-C₃N₄ participating in wide optical absorption, separation and transportation of electronic-holes, as well as morphology of composite.     

Co-doping schemes to enhance H2 evolution under visible light irradiation over SrTiO3:Ni/M (M = La or Ta) prepared by spray pyrolysis

Two photocatalysts, SrTiO₃:Ni/La and SrTiO₃:Ni/Ta, were prepared by continuous spray pyrolysis. The effects of the co-dopants on hydrogen evolution over the uncalcined photocatalysts were evaluated under visible light irradiation. The co-doping of La³⁺ into SrTiO₃:Ni transformed the charge structure and increased the presence of Ni²⁺ at the expense of Ni³⁺ in the host lattice structure. The co-doping of Ta⁵⁺ into SrTiO₃:Ni also increased the Ni²⁺/Ni³⁺ ratio around the Ti⁴⁺ ions. Compared with SrTiO₃:Ni, SrTiO₃:Ni/La showed a 3 times greater rate of hydrogen evolution under visible light irradiation and SrTiO₃:Ni/Ta, a 4 times greater rate. The co-doping levels required for optimized hydrogen evolution over SrTiO₃:Ni/La and SrTiO₃:Ni/Ta prepared by spray pyrolysis were smaller than those prepared by other methods. Spray pyrolysis also produced particles with large surface areas and high roughnesses.     

H2 evolution under visible light irradiation on La and Cr co-doped NaTaO3 prepared by spray pyrolysis from polymeric precursor

Photocatalysts of Na_1−xLa_xTa_1−xCr_xO₃ and NaTa_1−xCr_xO₃ were prepared by spray pyrolysis from aqueous and polymeric precursor solution. Apart from the contribution of La³⁺ ions co-doped into NaTa_1−xCr_xO₃ on the BET surface area and the surface morphology by preventing crystal growth, this co-doping contributed to the increased Cr³⁺ concentration by partially tuning the electron configuration from A⁺B⁵⁺O₃ to (A⁺A′³⁺)²⁺(B⁵⁺B′³⁺)⁴⁺O₃ in the lattice of the photocatalyst. Na_1−xLa_xTa_1−xCr_xO₃ prepared from polymeric precursor solution reduced the induction period to 33% and enhanced the hydrogen evolution rate 5.6-fold to 1467.5 μmol g⁻¹ h⁻¹ compared with the equivalent values of NaTa_1−xCr_xO₃ prepared from aqueous precursor. The optimum amounts of dopant and additives comprising the polymeric precursor to maximize the hydrogen evolution rate were x = 0.003 and 300 mol%, respectively.     

Photocatalytic H2 evolution under visible light from aqueous methanol solution on NaBixTa1−xO3 prepared by spray pyrolysis

Solid–solution NaBi_xTa_1−xO₃ photocatalyst powders were prepared by spray pyrolysis from aqueous and polymeric precursor solutions. The effects of Bi ions and additives in the precursors on the photocatalytic activities of the resulting catalysts were investigated by measuring hydrogen evolution rate from aqueous methanol solution under visible light irradiation (λ > 415 nm). The effects of NiO co-catalyst on hydrogen evolution rate are also tested. Hydrogen evolution rate was enhanced almost 20 times (to 1355 μmol g⁻¹ h⁻¹), with an induction period of 1 h, compared with a photocatalyst prepared by hydrothermal method because of the compositional uniformity and unique surface morphology with large BET surface area of the photocatalyst. Bi ions in the photocatalyst were confirmed by XPS to be mainly present as Bi⁵⁺. Polymeric additives to the precursors and NiO co-catalyst resulted in maximized hydrogen evolution rate when used at 300 mol% and 0.2 wt.%, respectively. The composition of the photocatalyst was optimized at NaBi_0.07Ta_0.93O₃.     

Self-doped Ti@TiO2 visible light photocatalyst: Influence of synthetic parameters on the H2 production activity

Self-doped TiO₂ shows visible light photocatalytic activity, while pristine TiO₂ is only UV responsive. Ti³⁺ has been demonstrated to be responsible for this improvement. We systematically studied various experimental parameters, such as the amount of reducing agent imidazole, types of imidazoles and Ti sources, and determined effects of these parameters on the combustion process and final materials. The phase composition, Ti³⁺ concentration, light absorption, surface area, and crystallinity of the product are significantly affected by the amount of imidazoles. Through comparing different imidazoles, we found that only flammable/combustible imidazoles are able to convert Ti⁴⁺ into Ti³⁺. This result is very helpful in understanding the mechanism and reactions in combustion process. Titanium precursors also have a great influence in production of Ti³⁺ doped TiO₂ materials. Titanium alkoxides allow the successful synthesis of blue partially reduced TiO₂, while TiCl₄ only lead to white pristine TiO₂.