Sr-doped LaTiO ₂ N photocatalyst for hydrogen evolution reaction synthesized from perovskite-type La–Ti oxide nanoparticles

LaTiO₂N responds to visible light up to a wavelength of 600 nm and so is a promising water splitting photocatalyst. However, structural defects and reduced titanium species generated in this material during the nitridation process promote the recombination of photoexcited electrons and holes, and so reduce its photocatalytic activity. The present work synthesized a Sr-doped La-Ti oxide <i>via</i> flame spray pyrolysis followed by heat treatment, and utilized this oxide as a starting material for the oxynitride. Sr doping promoted the formation of a La-Ti oxide having a perovskite-type structure similar to that of LaTiO₂N, whereas heat treatment prior to the nitridation enhanced the crystallinity of the resulting perovskite-type Sr-doped La-Ti oxide. These factors reduced the defect concentration in the LaTiO₂N, thereby improving the hydrogen evolution activity of the catalyst threefold. The present study demonstrates a means of suppressing the reduction of metal cations and thereby improving the photocatalytic activity of perovskite-type oxynitrides by controlling the structure and crystallinity of the oxide precursor.