δ-MnO_2氧化降解苯酚的机理研究

Oxidative degradation of phenol by manganese dioxide

δ-MnO2以水羟锰矿和水钠锰矿的形式普遍存在于陆地和海洋环境中,是酚类等有机污染物发生非生物转化的重要氧化剂.本文研究了实验室制备的δ-MnO2悬浮液对苯酚的去除作用,同时讨论了pH、二氧化锰投加量、离子强度、共存金属离子和腐殖酸等不同影响因素对苯酚去除效率的影响.结果表明,苯酚氧化降解的最佳pH和δ-MnO2投加量分别为3.62和0.13mg·L-1.溶液中共存的Na+和Mn2+会对苯酚氧化降解产生抑制作用,而Mg2+和Ca2+对反应过程没有明显的影响.溶液中共存的腐殖酸也对苯酚的降解过程产生了抑制作用,随着腐殖酸的浓度由1mg·L-1增加到5mg·L-1,苯酚的去除率从96.9%降为78.9%.GC-MS分析发现,对苯二酚为该过程的主要中间产物,同时给出了苯酚在δ-MnO2存在时的可能降解机制.

Manganese dioxides （δ-MnO2） mainly exist in the form of vernadite and birnessite in the natural environment, which are considered to be important oxidants during the abiotic transformation of phenolic compounds. In this study, δ-MnO2 was synthesized by a facile method, and its ability for the degradation of aqueous phenol was investigated. Impacts of solution pH, δ-MnO2 loading, ionic strength, coexistence metal ions, and humic acid on the degradation of aqueous phenol were studied. The optimum solution pH and δ-MnO2 loading were determined to be 3.62 and 0.13 mg·L-1, respectively. The coexistence of Na＋ and Mn2＋ showed inhibition effect on the oxidative degradation process, while Mg2＋ and Ca2＋ did not show any obvious effect during the experimental process. The removal efficiency of phenol decreased from 96.9% to 78.9% when the concentration of humic acid in the reaction solution increased from 1 mg·L^-1 to 5 mg·L^-1. GC-MS was applied to identity the reaction intermediates, and hydroquinone was found to be the main reaction intermediate in the degradation system. Based on the above observations, the possible degradation pathway of phenol by δ-MnO2 was proposed.