Enhanced photocatalytic H-2-production activity of WO3/TiO2 step-scheme heterojunction by graphene modification

Sunlight-driven photocatalytic water-splitting for hydrogen (H-2) evolution is a desirable strategy to utilize solar energy. However, this strategy is restricted by insufficient light harvesting and high photogenerated electron-hole recombination rates of TiO2-based photocatalysts. Here, a graphene-modified WO3/TiO2 step-scheme heterojunction (S-scheme heterojunction) composite photocatalyst was fabricated by a facile one-step hydrothermal method. In the ternary composite, TiO2 and WO3 nanoparticles adhered closely to reduced graphene oxide (rGO) and formed a novel S-scheme heterojunction. Moreover, rGO in the composite not only supplied abundant adsorption and catalytically active sites as an ideal support but also promoted electron separation and transfer from the conduction band of TiO2 by forming a Schottky junction between TiO2 and rGO. The positive cooperative effect of the S-scheme heterojunction formed between WO3 and TiO2 and the Schottky heterojunction formed between TiO2 and graphene sheets suppressed the recombination of relatively useful electrons and holes. This effect also enhanced the light harvesting and promoted the reduction reaction at the active sites. Thus, the novel ternary WO3/TiO2/rGO composite demonstrated a remarkably enhanced photocatalytic H-2 evolution rate of 245.8 Fmol g(-1) h(-1), which was approximately 3.5-fold that of pure TiO2. This work not only presents a low-cost graphene-based S-scheme heterojunction photocatalyst that was obtained via a feasible one-step hydrothermal approach to realize highly efficient H-2 generation without using noble metals, but also provides new insights into the design of novel heterojunction photocatalysts. (C) 2020, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.