Synthesis of a Ga-doped La5Ti2Cu0.9Ag0.1O7S5 photocatalyst by thermal sulfidation for hydrogen evolution under visible light

Abstract

Ga-doped La5Ti2Cu0.9Ag0.1O7S5 absorbs visible light up to 710 nm and can serve as a H2 evolution photocatalyst in Z-scheme water splitting systems. This material is typically obtained in the form of rod-like particles that exhibit one-dimensional conductivity along their long axis. However, these relatively long particles (10–20 µm) require charge carriers migrate over significant distances to participate in photocatalytic reactions, which limits reaction efficiency. In the present study, Ga-doped La5Ti2Cu0.9Ag0.1O7S5 particles approximately 2 µm in length were prepared by thermal sulfidation. The as-formed particles had rod-like morphology but contained a lot of burrs that could be eliminated by annealing in the presence of sulfur vapor. Rh cocatalyst particles could be deposited on the tips of these particles in a dense, widely dispersed manner by stepwise impregnation-reduction and post-photodeposition. These treatments enhanced the photocatalytic H2 evolution activity of the Ga-doped La5Ti2Cu0.9Ag0.1O7S5 particles in aqueous solutions containing electron donors by a factor of seven and increased the apparent quantum efficiency of the process to 3.1% at 420 nm. This work demonstrates that thermal sulfidation is an effective approach to reducing the particle size of an oxysulfide photocatalyst. With appropriate post-treatment and cocatalyst loading processes, such photocatalysts can efficiently evolve hydrogen from aqueous solutions.