Enhancing the degradation of carbamazepine by UVA-LED/WO3 process with peroxydisulfate: Effects of light wavelength and water matrix

In this study, peroxydisulfate (PDS) was used as electron acceptor to improve the photocatalytic activity of WO3. The results indicated that the degradation of carbamazepine by UVA-LED/WO3/PDS process followed pseudo-first order and PDS addition significantly enhanced the degradation rate by inhibiting the recombination of electrons and holes. The observed pseudo-first order rate constant (kobs) was in linear relationship with the dosage of WO3, while inversely proportional to the initial concentration of CBZ. PDS decreased the kobs slightly when its concentration exceeded 0.5 mM. The 365 nm UVA-LED performed much better than 385 nm or 405 nm even though its energy efficiency was the lowest. Based on the steady-state kinetic model, sulfate radical was the dominant radical. The effects of water matrix were complex: bicarbonate ion and humic acid showed strong inhibitory effect; increasing the pH above 7 led to significant drop in CBZ removal; sulfate ion slightly decreased the kobs while 5 mM chloride ion more than doubled the kobs. The interactions between anions and WO3 surface were theoretically analysed to explain the effects of anions. The electrical energy per order values suggest that UVA-LED/WO3/PDS process is suitable for water with low organic carbon.