UV/PMS体系硝基氯酚降解动力学及机理研究

采用紫外光(UV)/单过氧硫酸氢盐(PMS)体系可有效地氧化降解4-氯-2-硝基酚(4C2NP).考察了溶液pH值、底物初始浓度、PMS初始浓度和氯离子、硝酸根离子初始浓度对4C2NP降解效果的影响.在pH2~5时,体系中4C2NP的降解速率并未出现显著差异;随着pH值升高至近中性,其降解过程受到一定程度抑制.初始底物浓度和PMS浓度与体系中4C2NP的降解速率分别呈现负、正相关关系.外加氯离子对4C2NP降解呈现出双重作用,而硝酸盐离子对4C2NP降解抑制作用不显著.脱氯和脱硝过程是4C2NP主要的降解途径.被释放的氯离子会通过自由基反应进行再氯化过程,而脱落的硝基会很快被氧化生成稳定的硝酸盐,从而抑制了硝基的循环过程.最后,根据中间产物推断了4C2NP降解过程的反应机理.

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.