A facile solid state synthesis route to tantalum oxynitride, β-TaON

Tantalum oxynitride is a prospective pigment and has attracted considerable recent attention as a photocatalyst for the overall splitting of water under visible light irradiation. Conventionally, TaON is synthesised by the thermal ammonolysis of Ta₂O₅, a process in which remains challenging to scale up. The use of ammonia/water or ammonia/oxygen within a narrow temperature window is required to produce high purity TaON material; otherwise Ta₃N₅ forms as the favoured ammonolysis product. It would be highly beneficial to develop a reliable, simpler and reproducible synthesis route to TaON without the use of gaseous ammonia under such complex conditions. This paper describes a facile synthesis route to monoclinic β-TaON (space group P2₁/c) using Ta₃N₅ itself as a solid state nitrogen source. After 6 h of reaction at 900 °C under vacuum followed by post-synthesis calcination at 580 °C for 30 min, the bright yellow oxynitride is produced as spherical particles ca. 80 nm in diameter with a direct band gap of 2.9 eV.