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.     

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.     

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.     

g-C3N4 coated SrTiO3 as an efficient photocatalyst for H2 production in aqueous solution under visible light irradiation

A highly active photocatalyst based on g-C₃N₄ coated SrTiO₃ has been synthesized simply by decomposing urea in the presence of SrTiO₃ at 400 °C. The catalyst demonstrates a high H₂ production rate ∼440 μmol h⁻¹/g catalyst in aqueous solution under visible light irradiation, which is much higher than conventional anion doped SrTiO₃ or physical mixtures of g-C₃N₄ and SrTiO₃. The improved photocatalytic activity can be ascribed to the close interfacial connections between g-C₃N₄ and SrTiO₃ where photo-generated electron and holes are effectively separated. The newly synthesized catalyst also exhibited a stable performance in the repeated experiments.     

TiO2 nanotubes incorporated with CdS for photocatalytic hydrogen production from splitting water under visible light irradiation

The CdS/TiO₂ composites were synthesized using titanate nanotubes (TiO₂NTs) with different pore diameters as the precursor by simple ion change and followed by sulfurization process at a moderate temperature. Some of results obtained from XRD, TEM, BET, UV–vis and PL analysis confirmed that cadmium sulfide nanoparticles (CdSNPs) incorporated into the titanium dioxide nanotubes. The photocatalytic production of H₂ was remarkably enhanced when CdS nanoparticles was incorporated into TiO₂NTs. The apparent quantum yield for hydrogen production reached about 43.4% under visible light around λ = 420 nm. The high activity might be attributed to the following reasons: (1) the quantum size effect and homogeneous distribution of CdSNPs; (2) the synergetic effects between CdS particles and TiO₂NTs, viz., the potential gradient at the interface between CdSNPs and TiO₂NTs.     

Heterostructured boron doped nanodiamonds@g-C3N4 nanocomposites with enhanced photocatalytic capability under visible light irradiation

Boron doped nanodiamonds (BDND) were coupled with graphitic carbon nitride (g-C₃N₄) nanosheets to form a heterojunction via a facile pyrolysis approach. The BDND@g-C₃N₄ heterojunction exhibits enhanced visible-light absorbance, improved charge generation/separation efficiency and prolonged lifetime of carriers, which lead to the enhanced photocatalytic activities for the hydrogen evolution and organic pollution under visible-light irradiation. The optimal H₂ evolution rate and apparent quantum efficiency at 420 nm of the BDND@g-C₃N₄ heterojunction is 96.3 μmol h⁻¹ and 6.91%, which is about 5 and 2 times higher than those of pristine g-C₃N₄ nanosheets (18.2 μmol h⁻¹ and 3.92%). No obvious decrease in hydrogen generation rate is observed in the recycling experiment due to the high photo-stabilization of the BDND@g-C₃N₄ composite. The degradation kinetic rate constant of organic pollution of the BDND@g-C₃N₄ structure is 0.1075 min⁻¹, which is 3 times higher compared to pristine g-C₃N₄. This work may provide a promising route to construct highly efficient non-metal photocatalysts for hydrogen evolution and organic pollution degradation under visible light irradiation.     

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).     

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.     

Construction of ternary hybrid layered reduced graphene oxide supported g-C3N4-TiO2 nanocomposite and its photocatalytic hydrogen production activity

Reduced graphene oxide (rGO) supported g-C₃N₄-TiO₂ ternary hybrid layered photocatalyst was prepared via ultrasound assisted simple wet impregnation method with different mass ratios of g-C₃N₄ to TiO₂. The synthesized composite was investigated by various characterization techniques, such as XRD, FTIR, Raman Spectra, FE-SEM, HR-TEM, UV vis DRS Spectra, XPS Spectra and PL Spectra. The optical band gap of g-C₃N₄-TiO₂/rGO nanocomposite was found to be red shifted to 2.56 eV from 2.70 eV for bare g-C₃N₄. It was found that g-C₃N₄ and TiO₂ in a mass ratio of 70:30 in the g-C₃N₄-TiO₂/rGO nanocomposite, exhibits the highest hydrogen production activity of 23,143 μmol g^?1h^?1 through photocatalytic water splitting. The observed hydrogen production rate from glycerol-water mixture using g-C₃N₄-TiO₂/rGO was found to be 78 and 2.5 times higher than g-C₃N₄ (296 μmol g^?1 h^?1) and TiO₂ (11,954 μmol g^?1 h^?1), respectively. A direct contact between TiO₂ and rGO in the g-C₃N₄-TiO₂/rGO nanocomposite produces an additional 10,500 μmol g^?1h^?1 of hydrogen in 4 h of photocatalytic reaction than the direct contact between g-C₃N₄ and rGO. The enhanced photocatalytic hydrogen production activity of the resultant nanocomposite can be ascribed to the increased visible light absorption and an effective separation of photogenerated electron-hole pairs at the interface of g-C₃N₄-TiO₂/rGO nanocomposite. The effective separation and transportation of photogenerated charge carriers in the presence of rGO sheet was further confirmed by a significant quenching of photoluminescence intensity of the g-C₃N₄-TiO₂/rGO nanocomposite. The photocatalytic hydrogen production rate reported in this work is significantly higher than the previously reported work on g-C₃N₄ and TiO₂ based photocatalysts.     

Structure characteristics of CdS/H1.9K0.3La0.5Bi0.1Ta2O7 and photocatalytic activity for hydrogen evolution under visible light

Visible-light-driven CdS/HKLBT photocatalyst was prepared by ion exchange of Cd²⁺ in aqueous Cd(CH₃COO)₂ solutions, then by sulfurization in aqueous N₂H₈S solutions. The characterization by XRD, SEM, HRTEM and XRS revealed that CdS nanoparticles exist both on the surface and in the interlayer of HKLBT. The composite CdS/HKLBT showed higher photocatalytic activity for hydrogen evolution (504.2 μmol/h) than that of pure CdS (187.3 μmol/h), even than that of 0.5 wt%Pt/CdS (496.0 μmol/h) under visible light (λ > 400 nm) in the presence of lactic acid as sacrificial reagent. The enhancement of photocatalytic activity is attributed to the strong contact between CdS and HKLBT in CdS/HKLBT as well as the effective separation of photogenerated carrier in CdS through electron rapid injection into CB of HKLBT.     

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.     

Heterojunction composites of g-C3N4/KNbO3 enhanced photocatalytic properties for water splitting

In this paper, g-C₃N₄/KNbO₃ heterojunction composites were prepared and used to water splitting for hydrogen production under simulated sunlight. The morphology and structure of the composites were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-Ray spectroscopy and high resolution transmission electron microscopy. The g-C₃N₄/KNbO₃ composites exhibited the better photocatalytic performance for water splitting more than 2 and 1.8 times of the pure g-C₃N₄ and KNbO₃. Meanwhile, the Pt nanoparticles as a co-catalyst were deposited on the surface of g-C₃N₄/KNbO₃ as Pt-g-C₃N₄/KNbO₃ composites for water splitting which enhanced photocatalytic properties almost 74 and 14 times than that of Pt-KNbO₃ and Pt-g-C₃N₄. Such a significant improvement of the photocatalytic activity was mainly ascribed to the photoinduced electron-holes in the interface of g-C₃N₄/KNbO₃ composites rapid separation and the co-catalysis effect of Pt nanoparticles. These present study work may provide a useful method for water splitting using an effective composites photocatalysts.     

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。     

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.     

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%.     

Microwave-assisted hydrothermal synthesis of transition-metal doped ZnIn2S4 and its photocatalytic activity for hydrogen evolution under visible light

Aiming at the enhancement of photocatalytic activity for hydrogen evolution over ZnIn₂S₄, different transition metals (Cr, Mn, Fe, Co) are doped into the lattices of ZnIn₂S₄ to narrow the band gap. The doped ZnIn₂S₄ is characterized by XRD, Raman, UV-vis spectra, photoluminescence spectra, SEM and XPS techniques. The photocatalytic evaluation shows that Mn-doped ZnIn₂S₄ performs photocatalytic activity 20% higher than undoped ZnIn₂S₄, while Cr-, Fe-, and Co-doped ZnIn₂S₄ perform poorer activities in an order of Cr > Fe > Co. Based on the combined characterization results, the band structures of doped ZnIn₂S₄ are schematically depicted, which illustrates the different effects of transition-metal doping on the photocatalytic activity for hydrogen evolution. For Mn-doped ZnIn₂S₄, the enhancement of photocatalytic activity could be due to narrowed band gap induced by Mn doping. However, for Cr-, Fe-, and Co-doped ZnIn₂S₄, the suppressed photocatalytic activities should be attributed to the dopant-related impurity energy levels localizing the charge carriers or acting as non-radiative recombination centers for photoexcited electrons and holes. Hence, this study indicates that it is of great importance to make the in-depth investigation on the effects of band structures on the photocatalytic activity, especially for the doped semiconducting photocatalysts.     

NiS2 Co-catalyst decoration on CdLa2S4 nanocrystals for efficient photocatalytic hydrogen generation under visible light irradiation

NiS₂ nanoparticles as noble metal-free co-catalysts were deposited onto the CdLa₂S₄ nanocrystals through a hydrothermal process. The loading of NiS₂ co-catalyst resulted in remarkable enhancement for H₂ production over the CdLa₂S₄ photocatalyst under visible light irradiation. The optimal hybrid photocatalyst with 2 wt% NiS₂ loading exhibited a H₂ production rate of 2.5 mmol h⁻¹ g⁻¹, which was more than 3 times higher than that of the pristine CdLa₂S₄ photocatalyst. The promoted photocatalytic H₂ production by NiS₂-loading is attributed to the enhanced separation of photogenerated electrons and holes as well as the activation effect of NiS₂ for H₂ evolution.     

In-situ growth of mesoporous Nb2O5 microspheres on g-C3N4 nanosheets for enhanced photocatalytic H2 evolution under visible light irradiation

Large-surface-area mesoporous Nb₂O₅ microspheres were successfully grown in-situ on the surface of g-C₃N₄ nanosheets via a facile solvothermal process with the aid of Pluronic P123 as a structure-directing agent. The resultant g-C₃N₄/Nb₂O₅ nanocomposites exhibited enhanced photocatalytic activity for H₂ evolution from water splitting under visible light irradiation as compared to pure g-C₃N₄. The optimal composite with 38.1 wt% Nb₂O₅ showed a hydrogen evolution rate of 1710.04 μmol h^?1 g^?1, which is 4.7 times higher than that of pure g-C₃N₄. The enhanced photocatalytic activity could be attributed to the sufficient contact interface in the heterostructure and large specific surface area, which leads to effective charge separation between g-C₃N₄ and Nb₂O₅.     

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.     

Solvothermal synthesis of SnNb2O6 nanoplates and enhanced photocatalytic H2 evolution under visible light

Well-defined SnNb₂O₆ nanoplates are synthesized here by a facile template-free solvothermal route in a mixed solvent of water and ethanol without an organic surfactant. The synthesized nanoplates have widths ranging from 200 to 400 nm and thicknesses in a range of 20–30 nm. The nanoplates were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV–Vis spectroscopy, Raman spectrometry, and by the Brunauer–Emmett–Teller method. The variation of the lattice parameters and the optical properties of the nanoplates were discussed in detail based on the crystal and electronic structure. The SnNb₂O₆ nanoplates exhibited greatly enhanced photocatalytic activity in terms of the reduction of water for H₂ generation under visible light irradiation as compared to the same compound prepared by a solid–state reaction method. This was mainly attributed to its higher surface area and extremely high two-dimensional anisotropy, which provided a short migration distance along the thickness direction.