AgI-BiOI-graphene composite photocatalysts with enhanced interfacial charge transfer and photocatalytic H2 production activity

BiOI-based photocatalysts were proved to exhibit photocatalytic H-2 production activity. AgI-BiOI-graphene showed better H-2 production activity than BiOI and BiOI-graphene. The surface chemistry, electronic property, phase structure, morphology, optical property and photocatalytic performance of these photocatalysts were studied. The interfacial electronic states of the photocatalysts were investigated through their C K-edge near-edge X-ray-absorption fine-structure (NEXAFS) spectra. Based on the in situ NEXAFS spectra measured with and without illumination, a mechanism about the transport of photoelectron from AgI to graphene through BiOI is proposed for the photocatalytic H-2 production process. The incorporation of graphene restricted the three-dimensional self-assembly of BiOI nanocrystals and led to the formation of less extensively crystallized BiOI domains through a confined-space effect. Addition of AgNO3 precursor altered the crystal structure of BiOI from flower-like to horizontally stacked flat plates. The results of NEXAFS spectra, photoluminescence spectra and photocurrent tests reveal that the improved photocatalytic activity of the AgI-BiOI-graphene photocatalyst is attributable to the interfacial interaction among AgI, BiOI and graphene, which enhanced the separation of photogenerated electrons to generate H-2. AgI-BiOI-graphene photocatalyst was a stable photocatalyst for the production of H-2. After three cycles, 86% activity of recycled photocatalysts was retained.