Visible-light photocatalytic activity of NH ₃-heat-treated Ta ₂O ₅ to decompose rhodamine B in aqueous solution

Ta ₂O ₅ powder was heat treated in flowing NH ₃ at varying temperature for 2 h. When heat treated at 680-720 °C, nitrogen was doped to Ta ₂O ₅, but showed only a slight improvement of photocatalysis of rhodamine B dye in solution under visible light irradiation. From the heat treatment temperature of 740 °C, seeds of TaON and Ta ₃N ₅ formed newly and grew with the temperature. The optical absorption edge at 410-510 nm by TaON and absorption shoulder at 535 nm by Ta ₃N ₅ were observed. These specimens with N-doped Ta ₂O ₅, TaON, and Ta ₃N ₅ demonstrated notably improved photocatalytic performance, and the photocatalysis was facilitated by surface photosensitization.