Photocatalytic hydrogen evolution using nanocrystalline gallium oxynitride spinel

Abstract

Photocatalytic hydrogen evolution from water was observed over nanocrystalline gallium oxynitride spinel under simulated solar light irradiation (320 nm < λ < 800 nm). Up to 8 μmol h⁻¹ of H₂ was evolved without co-catalyst loading. The photocatalyst was synthesized by the ammonolysis of gallium nitrate hydrate (Ga(NO₃)₃·xH₂O). Optical measurements indicate an indirect gap (E_g) in the visible region (E_g = 2.50 eV) which is ascribed to photoexcitations from the N 2p valence states. A direct gap has an onset at ultraviolet energies (E_g = 3.69 eV), which is ascribed to photoexcitations from lower energy O 2p valence states.