Insight into the photocatalytic mechanism of the optimal x value in the BiOBr x I 1− x , BiOCl x I 1− x and BiOCl x Br 1− x series varying with pollutant type

possessed the best photocatalytic activity towards TC and RhB degradation. Detailed characterization suggests that light absorption and charge separation efficiency are not the main factors behind this difference. Given that direct oxidation of the holes was dominant in the degradation process, the oxidation ability of the solid solutions was correlated with the oxidation behavior of the pollutant. The prerequisite condition for degrading a certain pollutant is that the valence band potential of the solid solution should be more positive than the oxidation potential of the pollutant, and yet, too big a difference between these two potentials does not benefit rapid degradation.