Photocatalytic water splitting on Au/HTiNbO5 nanosheets

The layered potassium titanium niobate, KTiNbO₅, is known as a photocatalyst for hydrogen production from water splitting under UV light. Here we show that titanium niobate nanosheets with a slit like framework can be obtained by exfoliation of KTiNbO₅ followed by proton exchange. Gold nanoparticles were deposited on the titanium niobate nanosheets using deposition-precipitation (DP), photo-deposition (PD) and impregnation (IMP) method in order to improve photocatalytic hydrogen production from water splitting.     

Factors affecting the production of H2 by water splitting over a novel visible-light-driven photocatalyst GaFeO3

A d¹⁰ photocatalyst, GaFeO₃ having a band gap of ∼2.7 eV, exhibits significant activity for the overall splitting of water under visible light (>395 nm) irradiation, in the absence of sacrificial reagent or a noble metal co-catalyst. The doping of an anion led to considerable enhancement in activity, the S-doped catalysts displaying better activity compared to the samples containing nitrogen. Even though the H₂/O₂ yields were affected by preparation-dependent grain morphology, no direct relationship was observed between the photoactivity of a sample and its specific surface area. The techniques of HRTEM, SEM, XPS, Laser Raman, UV–visible and photoluminescence spectroscopy have enabled to demonstrate that, besides the grain morphology, certain lattice imperfections and microstructure may also play a crucial role in water splitting activity of a photocatalyst. The factors responsible for catalyst deactivation are examined.     

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.     

Synthesis of carbon-doped SnO2 nanostructures for visible-light-driven photocatalytic hydrogen production from water splitting

Environmental issues: global warming, organic pollution, CO₂ emission, energy shortage, and fossil fuel depletion have become severe threats to the future development of humans. In this context, hydrogen production from water using solar light by photocatalytic/photoelectrochemical technologies, which results in zero CO₂ emission, has received considerable attention due to the abundance of solar radiation and water. Herein, a single-step thermal decomposition procedure to produce carbon-doped SnO₂ nanostructures (C–SnO₂) for photocatalytic applications is proposed. The visible-light-driven photocatalytic performance of the as-prepared materials is evaluated by photocatalytic hydrogen generation experiments. The bandgaps of the photocatalysts are determined by ultraviolet–visible diffused reflectance spectroscopy. The crystallinity, morphological features (size and shape), and chemical composition and elemental oxidation states of the samples are investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The proposed simple thermal decomposition method has significant potential for producing nanostructures for metal-free photocatalysis.     

Photocatalytic water splitting for hydrogen production on Au/KTiNbO5

Gold nanoparticles were deposited on potassium titanoniobate, KTiNbO₅ using deposition-precipitation (DP), conventional impregnation (IMP) and photodeposition method in order to improve photocatalytic hydrogen production from water splitting. The effect of synthesis pH value of a HAuCl₄ aqueous solution used in the DP process on the morphology of gold nanoparticles, optical property and photocatalytic activity of water splitting under UV light irradiation was investigated. These catalysts were characterized by powder X-ray diffraction patterns (XRD), inductively coupled plasma mass spectrometry (ICP-MS), UV–visible spectroscopy (UV–vis), and Transmission Electron Microscopy (TEM). The Au/KTiNbO₅ catalysts prepared by the DP method consisted of a good metal–semiconductor interface which allowed for a much higher efficient electron-hole separation. The 0.63 wt% Au/KTiNbO₅ catalyst prepared by the DP method at pH = 10 showed a uniform dispersion of gold nanoparticles with an average gold particle size of 4.2 nm and exhibited an ultra-high photocatalytic water splitting activity (3522 μmol g⁻¹ h⁻¹), about 47 times higher than that exhibited by the KTiNbO₅ photocatalyst.     

Zn-doped hematite modified by graphene-like WS2: A p-type semiconductor hybrid photocathode for water splitting to produce hydrogen

A p-type Zn-doped hematite (α-Fe₂O₃(Zn)) in spindle-shape with an acceptor density of ca. 4.21 × 10¹⁸ cm^?3 were synthesized by a facile hydrothermal method. After α-Fe₂O₃(Zn) was modified with graphene-like WS₂ (α-Fe₂O₃(Zn)/WS₂), the photoelectrochemical performances of the composite can be further enhanced. A photocell composed of the p-type α-Fe₂O₃(Zn)/WS₂ nanocomposite as photocathode and n-type α-Fe₂O₃ as photoanode was assembled to estimate the photocatalytic activity of α-Fe₂O₃(Zn)/WS₂. The amount of the hydrogen and oxygen produced from this tandem cell with the optimal electrodes under 2 h simulated solar light irradiation is 12.5 μmol and 4.3 μmol, respectively.     

Thermochemical two-step water splitting cycles by monoclinic ZrO2-supported NiFe2O4 and Fe3O4 powders and ceramic foam devices

A thermochemical two-step water splitting cycle is examined for NiFe₂O₄ and Fe₃O₄ supported on monoclinic ZrO₂ (NiFe₂O₄/m-ZrO₂ and Fe₃O₄/m-ZrO₂) in order to produce hydrogen from water at a high-temperature. The evolution of oxygen and hydrogen by m-ZrO₂-supported ferrite powders was studied, and reproducible and stoichiometric oxygen/hydrogen productions were demonstrated through a repeatable two-step reaction. Subsequently, a ceramic foam device coated with NiFe₂O₄/m-ZrO₂ powder was made and examined as a water splitting device by the direct irradiation of concentrated Xe-light in order to simulate solar radiation. The reaction mechanism of the two-step water splitting cycle is associated with the redox transition of ferrite/wustite on the surface of m-ZrO₂. A hydrogen/oxygen ratio for these redox powder systems exhibited good reproducibility of approximately two throughout the repeated cycles. The foam device loaded NiFe₂O₄/m-ZrO₂ powder was also successful with respect to hydrogen production through 10 repeated cycles. A ferrite conversion of 24-76% was obtained over an irradiation period of 30 min.     

Facile synthesis of VS4/graphene nanocomposites and their visible-light-driven photocatalytic water splitting activities

VS₄/reduced graphene oxide (VS₄/rGO) composites are successfully synthesized via a one-step hydrothermal route. Then their photocatalytic activities are examined by water splitting reaction, and the morphology and structure are characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy and thermo gravimetric analysis, respectively. It is shown that graphene accelerates the nucleation during the growth period of VS₄. Main product is VS₄, not VS₂. Monoclinic VS₄ particles interact with graphene through chemical action. VS₄/rGO composites show excellent photocatalytic water splitting activities under visible-light irradiation. This excellent performance is due to the formation of π-conjugated structure, which can transmit electrons from S2_p to graphene rapidly. However, composites with excess graphene show poor dispersion, which leads to the best doping ratio of graphene is 5 wt%.     

Hydrogen production performance of active Ce/N co-doped SrTiO3 for photocatalytic water splitting

An efficient visible light responsive photocatalyst Ce/N co-doped SrTiO₃ was prepared via a hydrothermal method for hydrogen production. The phase structure, morphology, contents and valence states of the dopant elements, specific surface area, optical properties, and photocatalytic activity of the samples were characterized. The transient photocurrent response and electrochemical impedance spectra under visible light illumination indicated that Ce/N co-doped SrTiO₃ possessed a more intense photo-current response and lower surface resistance than N–SrTiO₃ and Ce–SrTiO₃. The water splitting rate of Ce/N-co-doped SrTiO₃ is 4.28 mmol/g/h, which is 84.49 times higher than that of pure SrTiO₃. The enhanced photocatalytic performance is due to the narrowing of the band gap of SrTiO₃ by Ce ion and N ion impurities.     

A new CdS/Bi1−xInxTaO4 heterostructured photocatalyst containing solid solutions for H2 evolution from water splitting

A new strategy has been put forward to improve the performance of photocatalytic H₂ evolution of tantalate-based catalysts through designing solid solutions Bi_1−xIn_xTaO₄ combined with CdS, among which the solid solutions Bi_1−xIn_xTaO₄ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) were firstly synthesized by the citrate method using cheap and environment-friendly Ta₂O₅. The experimental results reveal that the Bi_0.5In_0.5TaO₄ solid solution shows the best photocatalytic performance among the Bi_1−xIn_xTaO₄ solid solutions. And in the absence of noble metals, the 30% CdS/Bi_0.5In_0.5TaO₄ (30CBITO) catalyst exhibits good photocatalytic hydrogen evolution from water splitting with a rate of H₂ production of 511.75 μmol h⁻¹ g⁻¹ under simulated sunlight irradiation. And the rate of hydrogen evolution does not markedly change for 60 h. Their compositions, structures and morphologies were characterized by UV–vis diffusion reflectance spectroscopy (DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). A photocatalytic enhancement mechanism was put forward to elucidate the superior photocatalytic activity and long-term stability of the heterostructured CdS/Bi_0.5In_0.5TaO₄ composites.     

A mild H3BO3 environment for water splitting

A weakly acidic H₃BO₃ solution (pH = 5.1) was used to synthesize new oxygen-evolution catalysts for water splitting under mild conditions. Two novel oxygen-evolution catalysts, Co–BA_i and Mn–BA_i (BA_i = inorganic boric acid), were obtained in the H₃BO₃ solution with added Co²⁺ and Mn²⁺, respectively. The average oxygen evolution rate in the H₃BO₃ solution with Co²⁺ was 0.3133 μmol/h, about 70 times greater than the rate without a metal ion; the rate with Mn²⁺ was 1.13 μmol/h, about 250 times greater. The phases, morphologies, and compositions of the Co–BA_i and Mn–BA_i catalysts were analysed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy.     

TiO2 nanotubes for hydrogen generation by photocatalytic water splitting in a two-compartment photoelectrochemical cell

Highly ordered TiO₂ nanotube arrays for hydrogen production have been synthesized by electrochemical anodization of titanium sheets. Under solar light irradiation, hydrogen generation by photocatalytic water splitting was carried out in the two-compartment photoelectrochemical cell without any external applied voltage. The hydrogen gas and oxygen generated on Pt side and on TiO₂ nanotubes side respectively were efficiently separated. The effect of anodization time on the morphology structures, photoelectrochemical properties and hydrogen production was systematically investigated. Due to more charge carrier generation and faster charge transfer, a maximum photoconversion efficiency of 4.13% and highest hydrogen production rate of 97 μmol h⁻¹cm⁻² (2.32 mL h⁻¹cm⁻²) were obtained from TiO₂ nanotubes anodized for 60 min.     

Enhanced photocatalytic performance of chemically bonded SiC-graphene composites for visible-light-driven overall water splitting

Chemically bonded SiC-graphene composites were prepared by a chemical grafting method. The Si–C bonds between SiC and graphene can form a heterojunction interface. The chemical bonding and the heterojunction interface are beneficial to the quick transfer of photogenerated electrons from SiC to graphene and thus avoiding the recombination with holes. As a result, the composites show an enhanced activity (more than 90%) for photocatalytic splitting of water under visible light irradiation.     

Hierarchical spheres assembled from large ultrathin anatase TiO2 nanosheets for photocatalytic hydrogen evolution from water splitting

We report the synthesis of TiO₂ hierarchical spheres (THS) with large specific surface area via a facile one-pot solvothermal method. The as-prepared THS are self-assembled by ultrathin TiO₂ nanosheets with thickness of several nanometers and they show a uniform spherical morphology with an average size of 500–700 nm. However, the as-prepared light yellow THS exhibit inferior photocatalytic activity for hydrogen evolution from water splitting due to the poor crystallization of TiO₂ and the existence of oxygen vacancies. Significantly, a subsequent thermal treatment improves the crystallinity of THS, reduces the oxygen vacancies, and thereby enhances the photocatalytic performance. It demonstrates that the sample annealed at 550 °C (THS550) exhibits the highest photocatalytic activity, about 5 times higher than that of commercial TiO₂ nanoparticles (CTiO₂). Moreover, the THS550 sample loaded with 1 wt% Pt exhibits an hydrogen evolution rate as high as 17.9 mmol h^?1g^?1, and the corresponding apparent quantum efficiency has been determined to be 28.46% under 350 nm light irradiation.     

MoS2/CdS rod-like nanocomposites as high-performance visible light photocatalyst for water splitting photocatalytic hydrogen production

This study demonstrates a high-performance visible-light-driven photocatalyst for water splitting H₂ production. CdS nanorods (30 nm in diameters) with shorter radial transfer paths and fewer defects were prepared by a solvothermal method. To mitigate the recombination of electrons and holes, MoS₂ nanosheets with rich active sites were modified on the surface of CdS nanorods by a room-temperature sonication treatment. The photocatalytic water splitting tests show that the MoS₂/CdS nanocomposites exhibit excellent H₂ evolution rates. The highest H₂ evolution rates (63.71 and 71.24 mmol g^?1h^?1 in visible light and simulated solar light irradiation) was found at the 6% MoS₂/CdS nanocomposites, which was 14.61 times and 13.39 times higher than those of the corresponding pristine CdS nanorods in visible light and simulate solar light irradiation, respectively. The apparent quantum efficiency (AQE) of the 6% MoS₂/CdS nanocomposites at 420 nm was calculated to be 33.62%. The electrochemistry tests reveal that the enhanced photocatalytic activity is a result of extra photogenerated charge carries, greatly enhanced charge separation and transfer ability of the MoS₂/CdS composites. This study may give new insights for the rational design and facile synthesis of high-performance and cost-effective bimetallic sulfide photocatalysts for solar-hydrogen energy conversion.     

A visible-light-driven heterojunction for enhanced photocatalytic water splitting over Ta2O5 modified g-C3N4 photocatalyst

The photocatalytic water splitting for generation of clean hydrogen energy has received increasingly attention in the field of photocatalysis. In this study, the Ta₂O₅/g-C₃N₄ heterojunctions were successfully fabricated via a simple one-step heating strategy. The photocatalytic activity of as-prepared photocatalysts were evaluated by water splitting for hydrogen evolution under visible-light irradiation (λ > 420 nm). Compared to the pristine g-C₃N₄, the obtained heterojunctions exhibited remarkably improved hydrogen production performance. It was found that the 7.5%TO/CN heterojunction presented the best photocatalytic hydrogen evolution efficiency, which was about 4.2 times higher than that of pure g-C₃N₄. Moreover, the 7.5%TO/CN sample also displayed excellent photochemical stability even after 20 h photocatalytic test. By further experimental study, the enhanced photocatalytic activity is mainly attributed to the significantly improve the interfacial charge separation in the heterojunction between g-C₃N₄ and Ta₂O₅. This work provides a facile approach to design g-C₃N₄-based photocatalyst and develops an efficient visible-light-driven heterojunction for application in solar energy conversion.     

Facile route to achieve MoSe2-Ni3Se2 on nickel foam as efficient dual functional electrocatalysts for overall water splitting

Since the catalytic activity of present nickel-based synthetic selenide is still to be improved, MoSe₂-Ni₃Se₂ was synthesized on nickel foam (NF) (MoSe₂-Ni₃Se₂/NF) by introducing a molybdenum source. After the molybdenum source was introduced, the surface of the catalyst changed from a single-phase structure to a multi-phase structure. The catalyst surface with enriched active sites and the synergistic effect of MoSe₂ and Ni₃Se₂ together enhance the hydrogen evolution reactions (HER), the oxygen evolution reactions (OER), and electrocatalytic total water splitting activity of the catalyst. The overpotential of the MoSe₂-Ni₃Se₂/NF electrocatalyst is only 259 mV and 395 mV at a current density of 100 mA/cm² for HER and OER, respectively. MoSe₂-Ni₃Se₂/NF with a two-electrode system attains a current density of 10 mA/cm² at 1.60 V. In addition, the overpotential of HER and OER of MoSe₂-Ni₃Se₂/NF within 80000 s and the decomposition voltage of electrocatalytic total water decomposition hardly changed, showing an extremely strong stability. The improvement of MoSe₂-Ni₃Se₂/NF catalytic activity is attributed to the establishment of the multi-phase structure and the optimized inoculation of the multi-component and multi-interface.     

Ag2CO3-derived Ag/g-C3N4 composite with enhanced visible-light photocatalytic activity for hydrogen production from water splitting

In this paper, Ag-based g-C₃N₄ composites have been successfully fabricated through two deferent synthetic methods: (i) a facile and efficient precipitation-calcination strategy (denoted as D–CN–xAg, x represents the dosage of Ag₂CO₃, the same below), (ii) a calcination method (denoted as Z–CN–xAg). All Ag-based g-C₃N₄ composites exhibit the enhanced photocatalytic activities under visible-light irradiation. Moreover, the optimal dosage of Ag₂CO₃ in the D–CN–xAg composite is found to be 5%, the corresponding hydrogen production capacity is 153.33 μmol g⁻¹ h⁻¹, which is 4.6 times higher than that of Z–CN–5%Ag composite. This might be attributed to appropriate content of metallic Ag and more active sites exposed on the surface of D–CN–5%Ag composite. Meanwhile, combining with photoelectrochemical results, it could be inferred that LSPR effect and the intimate interfacial between metallic Ag and g-C₃N₄ in the system play also important role for the improvement of photocatalytic activity. These results demonstrate that the appropriate loading of metallic Ag originated from Ag₂CO₃ into g-C₃N₄ could accelerate the separation and transfer of photogenerated electron-hole pairs, leading to the improvement of photocatalytic activity for hydrogen production from water splitting. Finally, a possible photocatalytic mechanism is proposed.