Effects of Bi-dopant and co-catalysts upon hole surface trapping on La₂Ti₂O₇ nanosheet photocatalysts in overall solar water splitting

Pristine and Bi-doped lanthanum titanium oxide (La₂Ti₂O₇) nanosheets have been synthesized as photocatalysts for overall solar water splitting. The surface hole trap is a critical factor that limits the photocatalytic activity of pristine La₂Ti₂O₇. Deposition of cobalt phosphate (Co-Pi) and platinum (Pt) nanoparticles on La₂Ti₂O₇ cannot remove the surface traps although they are essential for enabling the oxygen and hydrogen evolution reactions. It is interesting that doping bismuth (Bi) into La₂Ti₂O₇ nanosheets has eliminated the surface traps due to surface enrichment of Bi. The Co-Pi/Bi-La₂Ti₂O₇/Pt nanosheets exhibit increasing photocatalytic activity toward overall water splitting with increasing the Bi-dopant level up to 5 at.%. Further increasing the Bi-dopant level leads to the formation of localized states above the valence band, leading to the lifetime reduction of photogenerated charge-carriers, and jeopardizing the photocatalytic activity. This work proposes an effective strategy to address the surface trapping and surface catalysis issues in the nanostructured metal oxide photocatalysts.