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

Abstract

Abstract To investigate the photocatalytic oxidation (PCO) of nitrite ions under visible light, Cr‐doped TiO 2 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 NO 2 – . 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 NO 2 – 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 NO 2 – , initial solution pH, the gas atmosphere, and cathodic reaction on the PCO of NO 2 – were studied as well. Furthermore, the PCO mechanism of NO 2 – was investigated by using tert‐butyl alcohol or benzoic acid as a diagnostic probe. It showed that the PCO of NO 2 – under visible light most probably proceeded indirectly via OH radicals, not directly via the valence‐band holes.