Synthesis and Photocatalytic Activity of Rhodium-Doped Calcium Niobate Nanosheets for Hydrogen Production from a Water/Methanol System without Cocatalyst Loading

Rhodium-doped calcium niobate nanosheets were synthesized by exfoliating layered KCa2Nb3–x Rh x O10−δ and exhibited high photocatalytic activity for H2 production from a water/methanol system without cocatalyst loading. The maximum H2 production rate of the nanosheets was 165 times larger than that of the parent Rh-doped layered oxide. The quantum efficiency at 300 nm was 65%. In this system, the methanol was oxidized to formaldehyde (main product), formic acid, and carbon dioxide by holes, whereas electrons cause the reduction of water to H2. The conductivity of the parent layered oxide was decreased by doping, which indicates the octahedral RhO6 unit in the lattice of the nanosheet functions as an electron trap site. The RhO6 units in the nanosheet probably also act as reaction sites for H2 evolution.