Complex perovskite A ₃NiNb ₂O ₉ (A = Mg, Ca, Sr and Ba) as photocatalysts for H ₂ production from aqueous solution under visible light irradiation

Developing photocatalysts that are capable of capturing and converting solar energy is an intriguing prospect, not only from environmental concerns but also from the energy security aspect. Perovskites (ABO ₃) containing transition metal cations (Ni ²⁺, Co ³⁺ and Fe ³⁺) have shown reasonable visible light absorption yet their photocatalytic activities under visible light irradiation are generally poor. Here we performed a brief investigation on a series of complex perovskites A ₃NiNb ₂O ₉ (A = Mg, Ca, Sr and Ba) with the aim to improve their photocatalytic activity by altering cation size at A sites. Their crystal structures and the effects upon light absorption were compared and discussed. Mg3NiNb2O9 was found to show the largest visible light absorption and highest photocatalytic activity (12.17 μmol h ^-1 /g catalyst) among the investigated perovskites. The shorter distance between the cations in the B sites is likely the reason for Mg3NiNb2O9 to be more photoactive.