Yuchao Hu

WO3/g-C3N4 composites: one-pot preparation and enhanced photocatalytic H2 production under visible-light irradiation

A series of WO3/g-C3N4 composites with different WO3 contents were prepared via a facile one-pot pyrolysis method, and showed notably enhanced visible-light-driven photocatalytic H2-evolution activities, with the highest rate of 400 μmol h-1 gcat-1 that was 15.0 times of that for pristine g-C3N4. Contents and sizes of WO3 crystallites in the composites were easily adjusted by changing the molar ratios of (NH4)2WS4 to C3H6N6 in the feed reagents, thereby successfully optimizing the Z-scheme system constructed by WO3 and g-C3N4 and thus effectively reducing the recombination of photogenerated charge carriers in g-C3N4. Moreover, pore volumes and surface areas of the composites were gradually enlarged by introducing WO3 into g-C3N4 via the one-pot preparation strategy, therefore promoting the redox reactions to evolve H2. This work presented an effective route to simultaneously optimize the phase compositions and textural structures of photocatalysts for enhanced H2 evolution.

Co3(OH)2(HPO4)2 as a novel photocatalyst for O2 evolution under visible-light irradiation

Cobalt phosphate has shown great potential as an electrocatalyst or a cocatalyst loaded on a photocatalyst for O2 evolution, but has not yet been successfully used as a photocatalyst for O2 evolution so far. Herein, a kind of cobalt phosphate, i.e., Co3(OH)2(HPO4)2 (Co3(PO4)2·2H2O), was prepared by a simple hydrothermal method, and was proved to be a novel, stable photocatalyst for O2 evolution under visible-light irradiation for the first time. The photocatalytic mechanism of Co3(OH)2(HPO4)2 was revealed by comprehensively comparing the physicochemical properties of Co3(OH)2(HPO4)2 with those of another kind of cobalt phosphate, i.e., Co3(PO4)2·8H2O, which was prepared by a precipitation method and showed little photocatalytic activity for O2 evolution under visible-light irradiation. The significantly improved photocatalytic activity of Co3(OH)2(HPO4)2, compared with that of Co3(PO4)2·8H2O, was mainly attributed to the synergistic promotion of the photocatalytic process by the following physicochemical properties of Co3(OH)2(HPO4)2, i.e., the distortion of Co2+ octahedra, the difference in electronic properties and the linkage of oxo bridges between the adjacent Co(1) and Co(2) octahedra. This work extended the application of cobalt phosphate in photocatalysis and presented an effective route to explore new O2-evolution photocatalysts by modifying the appropriate materials that were commonly employed as cocatalysts.

Rapid Preparation of Perovskite Lead Niobate Nanosheets by Ultrasonic‐Assisted Exfoliation for Enhanced Visible‐Light‐Driven Photocatalytic Hydrogen Production

Ultrathin perovskite lead niobate nanosheets, (TBA/H)Pb2Nb3O10, were rapidly prepared by novel high‐power ultrasonic exfoliation of layered HPb2Nb3O10, and were used as a photocatalyst for hydrogen production from methanol solution under visible light irradiation (λ>415 nm) for the first time. When compared with bulk HPb2Nb3O10, the nanosheets showed same tetragonal crystal structure, but dramatic decrease in thickness and two times higher photocatalytic hydrogen evolution activity. Enhanced photocatalytic performance resulted from the fact that the photoexcited electrons were more efficiently separated and utilized for H2 production on the nanosheets, owing to shorter migration distance of photoexcited electrons.

Continuous solid solutions of Na0.5La0.5TiO3–LaCrO3 for photocatalytic H2 evolution under visible-light irradiation

A series of continuous (Na0.5La0.5TiO3)1−x(LaCrO3)x solid solutions with orthorhombic-phase perovskite structure and with LaCrO3 contents (x) in the range from 0 to 1.0 were synthesized by a facile polymerized complex method, and were employed as photocatalysts for H2 evolution under visible-light irradiation. It was found that photocatalytic activities of the solid solutions significantly increased with the increase of x to 0.3, and reached the highest H2-evolution rate of 238.2 μmol h−1 gcat−1 on (Na0.5La0.5TiO3)0.7(LaCrO3)0.3, because the narrowed bandgaps of samples enhanced the generation of charge carriers and the increased lattice distortion of samples could promote the separation and migration of charge carriers. Nevertheless, photocatalytic activities of the solid solutions gradually decreased with the further increase of x from 0.3, since both the bandgaps and lattice distortion rarely changed but Cr6+ and defects gradually increased and thus accelerated the recombination of charge carriers.

Spatial summation of the short-term plasticity of a pair of organic heterogeneous junctions

Recent studies have found that responses to electrical stimulations in organic semiconductor and/or electrolyte heterogeneous junctions possess features in common with synaptic plasticity in neural networks. Spatial summation of short-term plasticity was then studied using a pair of such junctions, i.e., Pt/Mg-doped polyethylene oxide (PEO)/Pt and Pt/Mg-doped PEO/poly(3-hexylthiophene-2,5-diyl) (P3HT)/Pt devices. The former displayed short-term depression for charging peaks and short-term facilitation (STF) for discharging peaks, while the latter displayed STF for both the charging and discharging peaks. A simple integration of parallel connection showed that the system displayed frequency selectivity in the weight modification of the charging peaks, i.e., it facilitated below a frequency threshold but depressed at a higher frequency. The frequency threshold varied with input numbers from about 60 Hz to 100 Hz. In contrast, only STF was observed in the weight modifications of the discharging peaks. In addition, the weight modification could be linearly summed from those of the two source devices though the absolute peak currents could not. Our study demonstrates that synaptic computation are feasible for parallel connection system, depending on both input frequency and linear summation of weight modifications. Finally, we suggest that directional selectivity might be realized using the parallel system.

Molten Ag2SO4-based Ion-Exchange Preparation of Ag0.5La0.5TiO3 for Photocatalytic O2 Evolution

Ag0.5 La0.5 TiO3 with an ABO3 perovskite structure was synthesized by a newly developed ion-exchange method. Molten Ag2 SO4 instead of traditional molten AgNO3 was used as Ag+ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag+ for Na+ in Na0.5 La0.5 TiO3 with a stable ABO3 perovskite structure at a high ion-exchange temperature (700 °C). Under full-arc irradiation, the O2 -evolution activity of Ag0.5 La0.5 TiO3 was about 1.6 times that of Na0.5 La0.5 TiO3 due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag+ for Na+ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light-response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag+ for Na+ induced a lattice distortion of the ABO3 perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible-light irradiation, Ag0.5 La0.5 TiO3 displayed notable O2 evolution whereas Na0.5 La0.5 TiO3 showed little O2 evolution, thus demonstrating that the substitution of Ag+ for Na+ enabled the use of visible light to evolve O2 photocatalytically. This work presents an effective route to explore novel Ag-based photocatalysts.