Degradation kinetics and mechanisms of chloronitrophenol in UV/PMS system

The efficient removal of 4-chloro-2-nitrophenol (4C2NP) in ultraviolet (UV)/peroxymonosulfate (PMS) oxidation system was investigated. The effects of pH, PMS dosage and concentrations of 4C2NP, chloride and nitrate ions on the degradation efficiency of 4C2NP were evaluated. No significant differences in 4C2NP degradation rate were observed at pH 2.0~5.0, but a further increase in pH value would inhibit the substrate decomposition. In addition, PMS dosage positively correlated with degradation rates of 4C2NP, while 4C2NP concentration had a negative effect. A typical dual effect of chloride concentrations on the 4C2NP degradation kinetics was observed, whereas the increasing concentrations of nitrate showed an indistinctively inhibitory effect on 4C2NP degradation. Dechlorination and denitration were the dominant degradation pathways during the oxidative degradation of 4C2NP, followed by the formation of chloride and nitrate ions. The released chloride from chloro groups would be involved in re-chlorination through radical reactions. Nitro groups released would be oxidized to stable nitrate, preventing re-nitration. Degradation mechanism of 4C2NP in a UV/PMS system was proposed based on intermediates identified.