In this work, the degradation kinetics and mechanism of diclofenac (DCF) by UV/peracetic acid (PAA) was investigated. The effects of pH, PAA dose and common water components such as inorganic ions and dissolved organic matter (DOM) on DCF degradation by UV/PAA were also evaluated. It was observed that the addition of PAA promoted the photodegradation of DCF due to the generation of reactive radicals in the photolysis of PAA, which was also confirmed by the radical scavenging experiment. The best degradation efficiency of DCF was obtained at pH 8.5. The removal of DCF was enhanced gradually with increasing PAA dose. Since NO₃ ⁻ is a photosensitive substance which can generate HO˙ under UV irradiation, its existence promoted the degradation of DCF. The presence of CO₃ ²⁻ could slightly improve DCF degradation, which might be due to the role of generated carbonate radicals. Cl⁻, SO₄ ²⁻ and Fe³⁺ had little effect on DCF removal, while Cu²⁺ could enhance DCF degradation because of its catalytic ability for PAA decomposition. An inhibition effect on DCF removal was observed in the presence of DOM, and it was more obvious in higher concentration of DOM. The elimination of total organic carbon (TOC) was low. According to the twelve reaction products detected in the UV/PAA system, the probable transformation mechanism of DCF was proposed exhibiting eight reaction pathways, i.e., hydroxylation, decarboxylation, formylation, dehydrogenation, dechlorination–hydrogenation, dechlorination–cyclization, dechlorination–hydroxylation and amidation. This study indicates that UV/PAA is a promising method for DCF removal from contaminated water.

In this study, peracetic acid (PAA) activated by Fe(Ⅱ) was proposed to remove diclofenac (DCF) in polluted water. It was found that Fe(Ⅱ)/PAA system could effectively remove DCF at neutral condition, which has a significant advantage over classical Fenton process. According to the result of scavenging experiment, both hydroxyl radical and peroxy radical were considered to be responsible for the degradation of DCF. The influence of several operational parameters including initial pH, Fe(Ⅱ) dosage, PAA concentration and common water matrix on DCF removal were investigated. 80% DCF was removed at mild condition (pH 6-7) within 60 s, and its removal rate could be enhanced with the increase in Fe(Ⅱ) dosage and PAA concentration. Presence of HCO₃^- and natural organic matter (NOM) was proved to have a significantly negative impact on DCF degradation. Four probable degradation pathways of DCF were proposed based on the detected reaction products, including hydroxylation, C-N bond cleavage, decarboxylation and dehydrogenation.

In this study, cobalt doped graphitic carbon nitride (Co–CN) was prepared and applied as a catalyst to activate peracetic acid (PAA) for sulfamethoxazole (SMX) degradation at neutral pH. PAA could be efficiently activated by Co–CN resulting in the efficient degradation of SMX. Characterization results of fresh and used Co–CN suggested that cobalt was successfully doped in graphitic carbon nitride (g-C₃N₄) through chemical bonding (Co–N bond) and the surface cobalt species in Co–CN (i.e., Co(II) and Co(III)) were the main activators for PAA. Organic radicals (i.e., CH₃C(O)O˙ and CH₃C(O)OO˙) were proved to be the dominant reactive species for SMX removal in the Co–CN/PAA system by radical scavenging experiments. The increase of cobalt doping content, PAA dosage or Co–CN dosage could accelerate SMX degradation and the neutral condition was highly favorable to SMX removal in Co–CN/PAA system. Co–CN exhibited a good stability and reusability for PAA activation in degrading SMX. Four possible degradation pathways of SMX (i.e., hydroxylation, nitration, bond cleavage and coupling reaction) were proposed in the Co–CN/PAA system according to eight identified transformation products.