Degradation of diclofenac sodium in water by UV activated persulfate

To solve the deficiency of organic pollutants removal in traditional technologies, UV/persulfate (PS) process was employed to remove diclofenac, one of the typical pharmaceuticals and personal care products. The effect of various factors including initial diclofenac concentration, persulfate dosage, pH, inorganic anions and humic acidon the diclofenac degradation by UV/PS process was investigated. The proposed degradation pathways of intermediate products after reaction were also analyzed. The results showed that diclofenac degradation fitted the pseudo-first-order kinetics well (R²≥0.95). With the increase of the initial diclofenac concentration, the pseudo-first-order-constant gradually decreased. And the degradation rate of diclofenac quickly increased with the increase of the PS dosage. Different pH environment influenced the degradation rate of diclofenac to a certain extent. For the pH ranging from acidic to alkaline conditions, the degradation rate of diclofenac has an obvious increase. Inorganic anions in the solution had different degree of impact on the diclofenac degradation. The existence of bicarbonate ion accelerated the degradation but chloride ions had an adverse effect. Additionally, the existence of humic acid had an inhibition effect on the removal of diclofenac. Sulfate radicals activated by UV may react with diclofenac molecules, thereby removing carboxyl or hydroxyl herein. The main intermediate products were 2, 6-dichlorodiphenylamine, 1-(2, 6-dichlorophenyl)-2-indolinone, 2-indolinone and aldehydes or something.