Defect induced nickel, nitrogen-codoped mesoporous TiO2 microspheres with enhanced visible light photocatalytic activity

Nickel, nitrogen-codoped mesoporous TiO2 microspheres (Ni-N-TiO2) with high surface area, and an effective direct band gap energy of similar to 2.58 eV. Nickel sulfate used as the Ni source and ammonia gas as the N source here. The efficiency of the as-prepared samples was investigated by monitoring the degradation of Rhodamine B under visible light irradiation. The experimental results indicate that Ni-doped mesoporous TiO2 microspheres show higher photocatalytic activity than mesoporous TiO2 microspheres under visible light irradiation. It mainly due to that the electron trap level (Ni2+/Ni+) promoting the separation of charge carriers and the oxygen vacancies inducing the visible light absorption. In addition, Ni-N-TiO2 shows enhanced activity compared with Ni-TiO2. Codopants and dopants are found to be uniformly distributed in TiO2 matrix. Among the all samples the 0.5% molar quantity of Ni dopant and 500 degrees C 2 h nitriding condition gives the highest photocatalytic activity. The treatment of ammonia gas on Ni-TiO2 sample induced oxygen vancancies, substitutional and interstitial N. A suitable treatment by ammonia gas also promote separation of charge carriers and the absorption of visible light. The active species generated in the photocatalytic system were also investigated. The strategy presented here gives a promising route towards the development of a metal and non-metal codoped semiconductor materials for applied photocatalysis and related applications. (C) 2016 Elsevier Masson SAS. All rights reserved

Effect of nitridation on visible light photocatalytic behavior of microporous (Ag, Ag2O) co-loaded TiO2

A simple solvothermal approach with post-calcination is used to obtain (Ag, Ag2O) co-loaded TiO2 microspheres with high specific surface area (43.8 m(2)g(-1)) and desirable visible light photocatalytic degradation (64% after 2 h visible light irradiation). Generally, N-doping of TiO2 via nitridation using NH3 improves the visible light absorption property of material. However, nitridation of (Ag, Ag2O) co-loaded TiO2 results in a deleterious impact on the photocatalytic performance (around 20% after 2 h visible light irradiation). This is because nitridation of Ag-Ag2O-TiO2 results in (a) reduction of Ag2O to Ag and (b) Ag agglomeration and grain growth on TiO2 particles. These results in fact imply that in as-synthesized (Ag, Ag2O) co-loaded TiO2 systems, local surface plasmonic resonance (associated with of 5-12 nm Ag particles) aids in enhanced broad band visible light absorption; furthermore the heterojunction between TiO2 and Ag2O improves efficiency with which photogenerated carriers become available for photo catalysis. In all cases we show through selective radical quenching experiments that singlet oxygen is the primary reason for the dye degradation observed. (C) 2016 Elsevier Inc. All rights reserved

A facile two-step method for fabrication of plate-like WO3 photoanode under mild conditions

Fabrication of photoelectrodes on a large-scale, with low-cost and high efficiency is a challenge for their practical application in photoelectrochemical (PEC) water splitting. In this work, a typical plate-like WO3 photoanode was fabricated with chemical etching of the as-prepared mixed tungsten-metal oxides (W-M-O, M = Cu, Zn or Al) by a reactive magnetron co-sputtering technique, which results in a greatly enhanced PEC performance for water oxidation in comparison with that obtained from a conventional magnetron sputtering method. The current approach is applicable for the fabrication of some other semiconductor photoelectrodes and is promising for the scaling up of applications for highly efficient solar energy conversion systems

Visible light photocatalysts (Fe, N):TiO2 from ammonothermally processed, solvothermal self-assembly derived Fe-TiO2 mesoporous microspheres

Iron (III) and nitrogen co-doped mesoporous TiO2 microspheres (Fe-N-TiO2) are prepared using a self assembly based solvothermal process followed by an ammonothermal method. Among all samples, 1 mol.% of Fe dopants and 500 degrees C nitridation (for 2 h) gives the highest visible light photoactivity. Results imply that the Fe3+/Fe2+ dopant trap energy level introduced within the band gap in mildly Fe (similar to 1 at%) doped TiO2 and the mesoporous nature of the material, both aid in the observed catalytic performance. Subjecting Fe-TiO2 samples to ammonothermal process induces oxygen vancancies, and substitutional and interstitial N. This reduces optical band gap, and introduces local states. The lower band gap and local states together aid in the absorption of visible light and separation of charge carriers. Co-dopants are distributed uniformly in the best photocatalysts. The active species generated in the photocatalytic system is shown to be singlet molecular oxygen (O-1(2)) using selective radical quenchers. (C) 2017 Elsevier B.V. All rights reserved

Photoelectrochemical regeneration of all vanadium redox species for construction of a solar rechargeable flow cell

Energy storage is pivotal for the continuous utilization of solar energy suffering from the intermittency issue. Herein, we demonstrate a solar rechargeable flow cell (SRFC) based on photoelectrochemical regeneration of vanadium redox species for in-situ solar energy harvest and storage. In this device, TiO2 and MWCNT/acetylene black (MWCNT/AB) composite are served as the photoanode and the counter electrode, respectively, with all vanadium redox couples, VO2+/VO2+ and VO2+/V3+, as solar energy storage media. Benefitting from solar energy, the cell can be photocharged under a bias as low as 0.1 V, which is much lower than the discharge voltage of similar to 0.5 V. Photocharged under the optimized condition, the cell delivers a discharge energy of 23.0 mWh/L with 67.4% input electric energy savings. This prototype work may inspire the rational design for cost-effective solar energy storage devices. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved

Visible light driven overall water splitting using cocatalyst/BiVO4 photoanode with minimized bias

BiVO4 and many other semiconductor materials are ideal visible light responsive semiconductors, but are insufficient for overall water splitting. Upon loading water oxidation cocatalyst, for example Co-borate (denoted as CoBi) used here, onto BiVO4 photoanode, it is found that not only the onset potential is negatively shifted but also the photocurrent and the stability are significantly improved. And more importantly, PEC overall water splitting to H-2 and O-2 is realized using CoBi/BiVO4 as photoanode with a rather low applied bias (less than 0.3 V vs. counter electrode) in a two-electrode scheme, while at least 0.6 V is needed for bare BiVO4. This work demonstrates the practical possibility of achieving overall water splitting using the PEC strategy under a bias as low as the theoretical minimum, which is the difference between the flat band and proton reduction potential for a photoanode thermodynamically insufficient for water reduction. As long as the water oxidation overpotential is overcome with an efficient cocatalyst, the applied bias of the whole system is only used for that thermodynamically required for the proton reduction

Enabling an integrated tantalum nitride photoanode to approach the theoretical photocurrent limit for solar water splitting

The feasibility of photoelectrochemical (PEC) water-splitting cells relies on the development of high-performance photoanodes. Significant progress has been made in the discovery of narrow bandgap semiconductors as promising photoanodes. However, the rational design of photoanode architecture that brings the potentials of narrow bandgap semiconductors into fruition for efficient PEC water oxidation still remains a key challenge. Herein, we show a highly efficient photoanode system consisting of a tantalum nitride (Ta3N5) semiconductor for light harvesting, hole-storage layers (Ni(OH)(x)/ferrhydrite) that mediate interfacial charge transfer from Ta3N5 to coupled molecular catalysts (Co cubane and Ir complex) for water oxidation and a TiOx blocking layer that reduces the surface electron-hole recombination. The integrated Ta3N5 photoanode exhibits a record photocurrent of 12.1 mA cm(-2) at 1.23 V vs. the reversible hydrogen electrode (RHE), which is nearly its theoretical photocurrent limit under sunlight (12.9 mA cm(-2)), suggesting that almost each pair of photogenerated charge carriers in Ta3N5 has been efficiently extracted and collected for solar water splitting

Development of Novel Perovskite-Like Oxide Photocatalyst LiCuTa3O9 with Dual Functions of Water Reduction and Oxidation under Visible Light Irradiation

Development of new visible-light-responsive materials is highly desirable in photocatalysis. Here, a novel oxide material LiCuTa3O9 (LCTO) with a characteristic perovskite-like structure, exhibiting a visible light absorption edge of approximate to 500 nm due to the hybridization of Cu 3d and O 2p orbitals, is reported. The structure of the as-obtained LCTO is experimentally characterized and theoretically simulated. UV-vis diffuse reflectance spectroscopy, Mott-Schottky, and density functional theory calculation results show that the LCTO is an n-type semiconductor with bandgap of approximate to 2.48 eV and exhibits suitable conduction band and valence band positions of approximate to-0.45 and 2.03 eV vs reversible hydrogen electrode, respectively. Based on initial optimization of preparative conditions and loading of cocatalysts, the as-modified LCTO sample can drive both water reduction and oxidation half reactions in the presence of corresponding sacrificial reagents under visible light irradiation (lambda >= 420 nm), demonstrating its promising application in solar water splitting. The dual functional features of LCTO render it a promising photocatalyst for one-step overall water splitting to produce hydrogen. In addition, the unobvious structural change of the LCTO photocatalyst during the reaction and repeated runs of the photocatalytic H-2 evolution reaction demonstrate its good photochemical stability

Synthesis of BaTaO2N oxynitride from Ba-rich oxide precursor for construction of visible-light-driven Z-scheme overall water splitting

Barium tantalum oxynitride (BaTaO2N) with an absorption edge of ca. 660 nm is one of the most promising photocatalysts for solar water splitting, and is usually synthesized by nitriding a mixture of Ba and Tacontaining compounds with a Ba/Ta molar ratio of unity under ammonia flow at high temperature, usually causing a high density of defect sites. Herein, we introduce a novel synthesis method for BaTaO2N (BTON) by employing Ba-rich LiBa4Ta3O12, prepared by a flux method, as a precursor of nitridation. As a comparison, BaTaOx was prepared by conventional solid state reaction and used as the precursor. The as-nitrided samples were correspondingly denoted as BTON-Flux and BTON-SSR. It was found that well-crystallized BTON oxynitride can be similarly obtained by both methods, but the BTON-Flux sample exhibits significantly decreased defect density and enhanced surface area relative to the BTON-SSR sample. As a result of their structural differences, the photocatalytic water splitting performance of the BTON-Flux sample, regardless of the H-2-evolving half reaction in the presence of methanol or Z-scheme overall water splitting, is much better than that of BTON-SSR. This study may open up a novel strategy for preparing oxynitride photocatalyst with decreased defect density for the promotion of solar water splitting