Photocatalytic Activity For Water Decomposition Research Articles

A 4e-–2e- cascaded pathway for highly efficient production of H2 and H2O2 from water photo-splitting at normal pressure

Overall water solar-splitting is one of the most attractive candidates to break water down into hydrogen peroxide (H2O2) and hydrogen (H2) in a cheapest and cleanest way (i.e., 2H2O →H2O2+ H2). However, the generated intermediate H2O2 in the 2e− process would poison the catalysts. Hence, it is an ideal pathway to generate H2O2 by 4e−–2e− cascaded process (H2O→O2→H2O2), which is more thermodynamically advantageous and can also avoid the catalyst poisoning by the intermediate product of H2O2. Herein, we report CoP modified by carbon dots (CoP/CDs composite) to realize simultaneous generation of H2 and H2O2 via a 4e−–2e− cascaded pathway, coupling photocatalytic water oxidation (4e−) and oxygen reduction reaction (2e−). The optimal CoP/CDs sample displays a prominent H2 yield of 239 μmol/h/g and H2O2 production rate of 466 μmol/h/g without sacrificial agent at normal pressure. It exhibits the highest photocatalytic activity for water decomposition to produce H2 and H2O2 simultaneously. Moreover, the quantum efficiency of the as-prepared sample is 2.05 % at 535 nm. This work offers a novel approach to achieve high-efficiency production of H2 and H2O2 by photocatalytic water splitting.

Highly Efficient Photocatalytic Hydrogen on CoS/TiO2 Photocatalysts from Aqueous Methanol Solution

The photocatalyzed water splitting reaction in aqueous methanol solution is an efficient preparation method for hydrogen and methanal under mild conditions. In this work, metal sulfide-loaded TiO2 photocatalysts for hydrogen and methanol production were synthesized by hydrothermal method (180°C/12 h) and characterized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The crystal structures of the samples are the typical anatase phase of TiO2 and exhibit a spherical morphology. When TiO2 was loaded with CoS, ZnS, and Bi2S3, respectively, the resulting catalysts showed photocatalytic activities for water decomposition to hydrogen in aqueous methanol solution under 300 W Xe lamp irradiation. Among the photocatalysts with various compositions, the 20 wt% CoS/TiO2 sample with a 2.1 eV band gap showed the maximum photocatalytic activity for the photocatalytic reaction, which indicated that CoS improved the separation ratio of photoexcited electrons and holes. The enhanced activity can be attributed to the intimate junctions that are formed between CoS and TiO2, which can reduce the electron-hole recombination. The production rate of hydrogen with 20 wt% CoS/TiO2 photocatalyst was about 5.6 mmol/g/h, which was 67 times higher than that of pure TiO2. The formation rate of HCHO was 1.9 mmol/g/h with 98.7% selectivity. Moreover, the CoS/TiO2 photocatalyst demonstrated good reusability and stability. In the present study, it is demonstrated that CoS can act as an effective cocatalyst to enhance the photocatalytic hydrogen and methanal production activity of TiO2. The highly improved performance of the CoS/TiO2 composite was mainly ascribed to the efficient charge separation.

Facile synthesis of nano-structured magnetite in presence of natural surfactant for enhanced photocatalytic activity for water decomposition and Cr (VI) reduction

Nano-structured magnetites (C-Fe3O4, G-Fe3O4 and Au/G-Fe3O4) were synthesized in the absence and presence of aqueous leaf extract of Averrhoa carambola, a natural, nontoxic surfactant and reductant. The magnetites were characterized by XRD, BET surface area, UV–vis DRS, TEM, FESEM, FT-IR, XPS and PL for structural, morphological and optical properties. The photocatalytic activities of magnetites were evaluated for the hydrogen generation by decomposition of water and reduction of Cr (VI) under visible light irradiation. Nano-structured magnetite (G-Fe3O4 and Au/G-Fe3O4) prepared in the presence of bio-surfactants showed higher photocatalytic activity compared to magnetite (C-Fe3O4) synthesized in absence of it. Among all the prepared catalysts, the in situ loaded Au nanoparticles over G-Fe3O4 (Au/G-Fe3O4) showed higher catalytic activity due to its surface plasmon resonance effect. The novelty of this present study is the synthesis of highly efficient photoactive magnetites of high surface area using a natural surfactant at room temperature in a one step method without using any external stabilizing agent and reducing agent.

Preparation of Bi0.5Y0.5VO4 Solid Solution by Polymerized Complex Method and Photocatalytic H2 Evolution

Bi0.5Y0.5VO4 solid solution was successfully prepared by polymerized complex (PC) method and characterized by X-ray diffraction, scanning electron microscopy, UV–Vis diffuse reflectance spectroscopy, nitrogen adsorption–desorption, respectively. The relationships between the calcination temperature and the photocatalytic activity for water decomposition were investigated. The optimal calcination temperature as well as Pt loading was optimized to achieve the best photocatalytic performance. It was found that Bi0.5Y0.5VO4 via 800 °C calcination for 4 h and loaded with 0.5 wt% Pt exhibited a high photocatalytic activity, by which the amounts of hydrogen produced was about 744 μmol h−1 g−1. In comparison with conventional solid state reaction method, the samples prepared by PC method showed much higher activity. The solid solution that prepared by PC method is a feasible and effective method to adjust the band structure of semiconductors materials.

High photocatalytic hydrogen production from methanol aqueous solution using the photocatalysts CuS/TiO2

Photocatalysts CuS/TiO2 for hydrogen production were synthesized by hydrothermal method at high temperature and characterized by XRD, UV–visible DRS, XPS, EDX, SEM and TEM. When TiO2 was loaded with CuS, it showed photocatalytic activities for water decomposition to hydrogen in methanol aqueous solution under 500 W Xe lamp. Among the photocatalysts with various compositions, the one with 1 wt% CuS-loaded TiO2 showed the maximum photocatalytic activity for water splitting, which indicated CuS could improve the separation ratio of photoexcited electrons and holes. What's more, the amounts of the produced hydrogen was about 570 μmol h−1, which had exceeded pure titania (P25) 32 times. In the present paper, it is proven that CuS can act as an effective co-catalyst to enhance the photocatalytic H2 production activity of TiO2.

Photocatalytic water splitting into hydrogen and research on synergistic of Bi/Sm with solid solution of Bi–Sm–V photocatalyst

Photocatalyst Bi1−xSmxVO4 were prepared by solid phase reaction and characterized by XRD, UV–visible DRS, BET, and SEM. Bi1−xSmxVO4 showed two structures with the component content. When the composition was above x = 0.3, Bi1−xSmxVO4 were of single phase with tetragonal type and can be regarded as solid solutions of was BiVO4 and SmVO4. When Bi1−xSmxVO4 was loaded with 0.3 wt% Pt, the samples showed photocatalytic activities for water decomposition to hydrogen under UV light. Among these catalysts, Bi0.5Sm0.5VO4 showed the best photocatalytic activity for water splitting, which indicated synergistic of Bi/Sm enhanced the photocatalysis efficiency. What's more, Bi0.5Sm0.5VO4 loaded with other co-catalysts was found to act as a photocatalyst for water decomposition to hydrogen and oxygen under UV light irradiation, and the photocatalyst loaded with Pt/Cr2O3 had the best photocatalytic property. The amounts of the produced hydrogen and oxygen, respectively, were about 188.25 μmol h−1 g−1 and 95.90 μmol h−1 g−1. This study indicated that the formation of solid solution was the feasible method to adjust energy band and synergistic of Bi/Sm can enhance the photocatalytic activities of water decomposition.

ChemInform Abstract: Photocatalytic Properties of M2Ti6O13 (M: Na, K, Rb, Cs) with Rectangular Tunnel and Layer Structures: Behavior of a Surface Radical Produced by UV Irradiation and Photocatalytic Activity for Water Decomposition.

The photocatalytic properties of RuO2-dispersed M2Ti6O13 (M=Na, K, Rb, Cs) were investigated as to the photoexcitation ability of the hexatitanates and the role of the dispersed RuO2. An EPR signal with g=2.020, g=2.018 and g=2.004 produced by UV irradiation of the hexatitanates at 77 K had a short life time in vacuum but remained stable upon exposure to gaseous molecules such as H2, He, N2, O2 and Ar. These gases brought about different stability and pressure dependence of the signal intensity, by which the radical is assigned to O- resulting from the surface lattice oxygen. The efficiency of the radical formation is associated with the presence of internal fields in the distorted TiO6 octahedra forming the rectangular tunnels of M2Ti6O13 (M=Na, K, Rb). RuO2 was dispersed on the hexatitanates by impregnation with either RuCl3(aq) solution or Ru3(CO)12 in tetrahydrofuran and the subsequent oxidation in the temperature range 573–823 K. The photocatalytic activity for water decomposition was higher for RuO2/M2Ti6O13 (M=Na, K, Rb) photocatalysts prepared using Ru3(CO)12 than for RuCl3. High resolution transmission electron microscopic images showed that uniformly distributed smaller RuO2 particles were formed for the former photocatalyst, which is considered to be responsible for the higher activity. The correlation between the concentration of the O- radical and photocatalytic activity is established, thus indicating that the O- radical is proposed to work as a hole site in the photocatalytic reaction, and the ability to separate photoexcited charges reflects the photocatalytic activity order of M2Ti6O13.

Photocatalytic Activity of Bismuth Layered Perovskite Treated with Acid

We synthesized Sr0.7La0.2[ ]0.1Bi2Ta2O9 (SBTL , [ ] vacancy), and measured their photocatalytic activity for water decomposition under UV light irradiation after acid treatment. They showed the high photocatalytic activity under UV light irradiation (H2 evolution (213μmol / h) , O2 evolution (82μmol / h)).

Synthesis of CaIn2O4 Rods and Its Photocatalytic Performance Under Visible-light Irradiation

A type of CaIn2O4 particle was synthesized at a relatively low temperature by a solution-combustion method using calcium nitrate and indium nitrate as oxidizers and glycine as a fuel, followed by a high-temperature postannealing, during which the nanometric grains of the as-combusted CaIn2O4 powder self-assembled into nano-capsules, and subsequently the nano-capsules linked end to end to form the regular CaIn2O4 rods with the diameter of 300 nm and the length of about 2 μm. The CaIn2O4 rods showed significantly higher photocatalytic activity for methylene blue degradation and toluene oxidation under visible-light irradiation than that of the sample synthesized by the conventional solid-state reaction. Particularly, the Pt-dispersed CaIn2O4 rods exhibited excellent photocatalytic activity for water decomposition under visible-light irradiation. The high crystallization degree, low impurity level and relatively large surface area of CaIn2O4 rods were considered as the important factors for its high photocatalytic performance.

Photocatalytic Activity for Water Decomposition to Hydrogen over Nitrogen‐doped TiO2 Nanoparticle

AbstractNitrogen‐doped TiO2 nanoparticle photocatalysts were obtained by an annealing method with gaseous ammonia and nitrogen. The influence of dopant N on the crystal structure was characterized by XRD, XPS, BET, TEM and UV‐Vis spectra. The results of XRD indicate that, the crystal phase transforms from anatase to rutile structure gradually with increase of annealing temperature from 300 to 700 °C. XPS studies indicate that the nitrogen atom enters the TiO2 lattice and occupies the position of oxygen atom. Agglomeration of particles is found in TEM images after annealing. BET results show that the specific surface areas of N‐doped samples from 44.61 to 38.27 m2/g are smaller than that of Degussa TiO2. UV‐Vis spectra indicate that the absorption threshold shifts gradually with increase of annealing temperature, which shows absorption in the visible region. The influence of annealing condition on the photocatalytic property has been researched over water decomposition to hydrogen, indicating that nitrogen raises the photocatalytic activity for hydrogen evolution, and the modified TiO2 annealed for 2 h at 400 °C under gas of NH3/N2 (V/V=1/2) mixture shows better efficiency of hydrogen evolution. Furthermore, the N‐doped TiO2 nanoparticle catalysts have obvious visible light activity, evidenced by hydrogen evolution under visible light (λ>400 nm) irradiation. However, the catalytic activity under visible light irradiation is absent for Degussa as reference and the N‐doped TiO2 annealed at 700 °C.

Template synthesized nano-crystalline natrotantite: Preparation and photocatalytic activity for water decomposition

A new method for preparation of natrotantite (Na 2Ta 4O 11) by hydrothermal method using cetyl trimethyl ammonium bromide (CTAB) template is reported. The nano, mesoporous and crystalline natrotantite resulted during different methods adopted for surfactant removal. Nano-crystalline natrotantite was observed during template removal using ethanol. The meso and crystalline samples resulted during the high temperature calcination at 773 and 1373 K, respectively. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), UV–vis diffraction reflected spectra (DRS), N 2-adsorption isotherm and surface area measurements. Nano, mesoporosity of the sample was confirmed by TEM, N 2-adsorption isotherm studies. The band gaps of the nano, mesoporous and crystalline natrotantite were estimated to be 4.1, 4.3 and 3.9 eV with surface areas of 42.4, 133.6 and 6.21 m 2 g −1, respectively. Furthermore, nano-crystalline Na 2Ta 4O 11 is found to be highly efficient photocatalyst for water decomposition.

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

AbstractFor Abstract see ChemInform Abstract in Full Text.

Photocatalytic Activity for Water Decomposition of Indates with Octahedrally Coordinated d10 Configuration. II. Roles of Geometric and Electronic Structures

The effects of electronic and local structures on the photocatalytic activities for water decomposition of different kinds of indates [MIn2O4 (M = Ca, Sr), Sr0.93Ba0.07In2O4, and AInO2 (A = Li, Na)] were studied. Raman spectroscopic measurements were performed to characterize their structures. The geometric structures of InO6 octahedral units were compared among the indates, and it was shown that the photocatalytically active indates possessed distorted InO6 octahedra with dipole moment, and there was a correlation between the photocatalytic activities and the dipole moment. A plane-wave density function theory (DFT) was applied to calculate the density of state and band energy diagram for SrIn2O4. The valence band was composed of the O 2p orbital, whereas the conduction band consisted of the hybridized In 5s5p orbitals with large dispersion, indicative of large mobility of photoexcited electrons in the conduction band. The electronic feature of SrIn2O4 was compared with that of a representative transition metal oxide of BaTi4O9 with an octahedrally coordinated d0 metal ion. On the basis of the electronic and geometric consideration, a mechanism is proposed: internal fields due to the dipole moment promote the charge separation, while the broad sp conduction bands with large dispersion permit photoexcited electrons to move to RuO2 particles dispersed as a promoter.

Photocatalytic Activity for Water Decomposition of Indates with Octahedrally Coordinated d10 Configuration. I. Influences of Preparation Conditions on Activity

The photocatalytic properties for water decomposition of RuO2-dispersed alkaline earth metal and lanthanum indates with an octahedrally coordinated In3+ ion of d10 configuration were studied. The i...

Photocatalytic activities for water decomposition of RuO 2-loaded AInO 2 (A=Li, Na) with d 10 configuration

The photocatalytic activities for water decomposition of RuO 2-loaded alkaline metal indates, AInO 2 (A=Li, Na), with d 10 configuration were studied. Under Hg–Xe lamp illumination, RuO 2-loaded LiInO 2 had little activity, but RuO 2-loaded NaInO 2 showed the ability to photocatalytically decompose water to hydrogen and oxygen. The photocatalytic activity strongly depended on the calcination temperature of NaInO 2: with increasing calcination temperature, the activity increased, passed through a maximum, and sharply decreased. In case that a part of Na ion in NaInO 2 was replaced by Li or K ion, the photocatalytic activity decreased sharply with a small amount of Li and gradually with increasing content of K. The calculation based on a plane wave density function theory (DFT) was employed to elucidate the band structure of AInO 2 (A=Li, Na). The photocatalytic activities were compared with those of previously reported RuO 2-loaded MIn 2O 4 (M=Ca, Sr), and the activity differences among them are discussed.

Polymerizable Complex Synthesis of Pure Sr2NbxTa2‐xO7 Solid Solutions with High Photocatalytic Activities for Water Decomposition into H2 and O2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Photocatalysis for Water Decomposition by RuO2-Dispersed ZnGa2O4 with d10 Configuration

The photocatalytic activity for water decomposition of RuO2-dispersed ZnGa2O4 with an octahedrally coordinated Ga3+ ion was studied in order to examine the photocatalytic properties of p-block metal oxides with d10 configuration. ZnGa2O4 was impregnated with Ru3(CO)12 or Ru(C5H7O2)3 in THF and oxidized to convert them to RuO2. For RuO2-loaded ZnGa2O4, hydrogen and oxygen were stably produced from the initial stage of reaction under Hg−Xe lamp light irradiation. The activity dependence on the calcination temperature of ZnGa2O4, the amount of RuO2 loaded, and the oxidation temperature of RuO2 showed that the dispersion of small RuO2 particles leads to high photocatalytic activity. The electronic structure of ZnGa2O4 was calculated by a plane-wave-based density function theory (DFT). The valence bands were mainly composed of the O 2p orbitals, whereas the conduction bands were formed by hybridzation of Ga 4s4p and Zn 4s4p orbitals. Large dispersion observed in the conduction band indicated the large mobility...

Synthesis of RuO2-loaded BaTinO2n + 1 (n = 1, 2 and 5) using a polymerizable complex method and its photocatalytic activity for the decomposition of water

A polymerizable complex (PC) technique was utilized to prepare fine powders of high purity BaTinO2n + 1 with n = 1, 2 and 5 at lower temperatures than those used for the ordinary solid-state reaction procedure. The formation of pure BaTinO2n + 1 occurred when precursors obtained from PC-derived gel materials were heat-treated at 800–900 °C in static air for 2 h. BaTinO2n + 1 powders were subsequently converted to RuO2-loaded materials, and their photocatalytic activities for the decomposition of water were examined. While the RuO2–BaTi2O5 (n = 2) and RuO2–BaTi5O11 (n = 5) materials exhibited photocatalytic activity for water decomposition into H2 and O2 in approximately stoichiometric amounts (H2 ∶ O2 = 2 ∶ 1) under UV light irradiation with specific hydrogen gas evolution rates of 125 and 52 µmol h−1 g−1, respectively, the RuO2–BaTiO3(n = 1) exhibited a very low activity of less than 1 µmol h−1 g−1. The lack of a significant occurrence of photocatalysis in BaTiO3 was explained in terms of its crystal structure possessing only a very small polyhedral distortion.

Photocatalytic water decomposition by RuO 2-loaded antimonates, M 2Sb 2O 7 (M=Ca, Sr), CaSb 2O 6 and NaSbO 3, with d 10 configuration

The photocatalytic activity for water decomposition of alkaline earth metal and alkaline metal antimonates, M 2Sb 2O 7 (M=Ca, Sr), CaSb 2O 6 and NaSbO 3, was investigated. These antimonates were photocatalytically active when combined with RuO 2: both H 2 and O 2 were produced from the initial stage of reaction under UV irradiation, and the photocatalytic activity became stable as the reaction proceeded. The photocatalytic properties are discussed based on the distorted structures of SbO 6 octahedra.

Photocatalytic Activity for Water Decomposition of RuO2-Loaded SrIn2O4 with d10 Configuration

Abstract A p-block metal oxide of SrIn2O4 with d10 configuration was found to be a new photocatalyst for the overall splitting of water when combined with RuO2.