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 KCa ₂Nb _3-xRh _xO _10-δ and exhibited high photocatalytic activity for H ₂ production from a water/methanol system without cocatalyst loading. The maximum H ₂ 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 H ₂. The conductivity of the parent layered oxide was decreased by doping, which indicates the octahedral RhO ₆ unit in the lattice of the nanosheet functions as an electron trap site. The RhO ₆ units in the nanosheet probably also act as reaction sites for H ₂ evolution.