Electrochemically Assisted Photocatalytic Oxidation of Nitrite over Cr‐Doped TiO2 under Visible Light

To investigate the photocatalytic oxidation (PCO) of nitrite ions under visible light, Cr‐doped TiO₂ supported on a titanium plate was used as a photoelectrode operated under anodic bias potential. The results showed that applying bias potential (E_appl) played an important role in the PCO of NO₂^–. Without bias potential the PCO reaction could not be initiated due to the rapid recombination rate of the photogenerated carriers, but when the potential was larger than 1.2 V (vs. saturated calomel electrode, SCE) the removal efficiency of NO₂^– increased up to 90 % within 3 h for an initial concentration of 8 mg L^–1. Zero‐order kinetics were observed at E_appl = 0.4 V (vs. SCE), while pseudo first order kinetics were found at E_appl ≥ 0.8 V (vs. SCE). The effects of the initial concentration of NO₂^–, initial solution pH, the gas atmosphere, and cathodic reaction on the PCO of NO₂^– were studied as well. Furthermore, the PCO mechanism of NO₂^– was investigated by using tert‐butyl alcohol or benzoic acid as a diagnostic probe. It showed that the PCO of NO₂^– under visible light most probably proceeded indirectly via OH radicals, not directly via the valence‐band holes.