Microwave synthesis of metal-doped ZnS photocatalysts and applications on degrading 4-chlorophenol using heterogeneous photocatalytic ozonation process

Photocatalysts can produce active species in the heterogeneous photocatalytic ozonation (HPO) process, which can efficiently degrade and mineralize organic pollutants. In this study, pristine ZnS and metal-doped (Cu, Ag, Bi, Ga, In) ZnS were synthesized by microwave method. The degradation rate of 4-chlorophenol (4-CP) in HPO process is ranked as Cu/ZnS > Bi/ZnS > Ag/ZnS > In/ZnS > Ga/ZnS > ZnS, which is attributed to the following reasons: (1) the schottky junction formed between ZnS and doped metal can effectively capture electrons as an electron trap, thus inhibiting the recombination of electron-hole pairs; (2) narrow bandgap of Cu/ZnS can enhance electron transport; (3) the valence bands of Ag/ZnS, Bi/ZnS, Ga/ZnS and In/ZnS were more positive than that of pristine ZnS to enhance the oxidization ability of holes. The experimental results showed that the optimal water-intake ozone dose optimal influent ozone dosage was 32 mg/l.min(-1) under the optimal initial solution pH of 7. In addition, the possible mechanism of HPO process was proposed and clarified. We believe that metal-doped ZnS has a promising potential to be the photocatalyst for the degradation of organic pollutants.