The photocatalytic performance of Ta and Rh co-doped TiO2 tuned by the average dopant valence

In order to reveal the effects of dopant average valence on the photocatalytic performance, Ta and Rh co-doped Ti 0.96 Ta 0.04−x Rh x O 2 (x = 0, 0.008, 0.016, 0.02, 0.024, 0.032, and 0.04) samples were crystallized at 450 °C and 800 °C, respectively; then the 800 °C crystallized x = 0.02 sample was subsequently reduced in the H 2 /N 2 mixture gases at 600, 700, 800, and 900 °C. Under different processing conditions, Ta remains the valence of +5, while the valence of Rh varies. Rh exhibits Rh 3+ and Rh 4+ in the 450 °C crystallized samples and is completely oxidized to Rh 4+ in the 800 °C crystallized samples. In the reduced samples, Rh exists in the forms of Rh, Rh 3+ and Rh 4+ . The optimal photocatalyst is obtained as the ratio of Rh 3+ /Rh 4+ is 2.11 or the average valence of doped Ta and Rh is closest to the +4 valence of substituted Ti.