二氧化锰氧化降解五氯酚的动力学模拟研究

研究了五氯酚(PCP)在二氧化锰(MnO2)氧化作用下的降解反应动力学,并讨论了无机离子和有机组分对PCP降解动力学的影响.采用n级反应速率模型对PCP降解动力学进行非线性拟合,结果显示n＞0.999,这表明一级反应速率模型适用于模拟PCP降解反应.在保证95%置信区间的条件下,采用准一级反应速率模型对0.5 h内的PCP降解动力学进行了非线性拟合,得到的离心法和维生素C破坏法下PcP降解表观速率常数kobs分别是2.86和2.14 h-1.二价金属离子的加入能降低PCP的kobs;当超过MnO2初始浓度2%以上的Mn2 存在时,Mn2 能对PCP的kobs产生显著影响,而其它不同类型和浓度的离子对kobs不产生显著影响.8种酚酸中的咖啡酸、丁香酸和五倍子酸对kobs的抑制作用达到了显著性水平;而肉桂酸、香豆酸、阿魏酸和邻(对)羟基苯甲酸的影响不明显.研究表明,降低PCP降解速率的主要原因是由于导致PCP在MnO2表面的吸附作用减弱或在MnO2表面与PCP发生竞争反应造成的.

Oxidation Kinetics of Pentachlorophenol by Manganese Dioxide

Experiments in the paper were conducted to determine oxidation kinetics of pentachlorophenol (PCP) using manganese dioxide (MnO2) as an oxidant. The influence of cosolutes (e.g. inorganic ions and organic substances) on the reaction kinetics was also assessed. When simulating the kinetics of PCP with n-order reaction model by a non-linear curve fitting approach, the reaction order n is over 0.999, which suggests that the first order reaction model fit the degradation kinetics of PCP. The apparent rate constant kobs values are 2.86 h-1 for the centrifugation method and 2.14 h-1 for the ascorbic acid method by non-linear fitting the kinetics of PCP for 0.5-hour reaction using pseudo-first-order model under the 95% confidence limits. The addition of bivalent metal ions causes the considerable reduction of the apparent rate constants. The significant effect on the kobs of PCP occurs when the concentration of Mn2+ above 2% of the initial MnO2 is added as the co-solute, but no significant influence on the kobs of PCP for the presence of other ions. The presence of caffeic acid, syringic acid or gallic acid reduces the reaction rate of PCP significantly. Oppositely, no considerable decrease of kobs is observed in experiments with the addition of cinnamonic acid, coumaric acid, ferulic acid or ortho (para)-hydroxybenzoic acid. These experimental results demonstrate that the decrease of PCP adsorbed to MnO2 considerably or the action of competing against PCP reacted with MnO2 is the dominant factor that slows down the transformed rate of PCP oxidation by MnO2.