水体中二氧化钛(P25)光催化降解甲芬那酸的机理

Photo-catalytical degradation of mefenamic acid by TiO_2(P25) in aqueous solution

本文研究了甲芬那酸(MEF)在UV-P25光催化降解下的行为和产物.结果表明,在紫外光照下P25能够快速催化降解MEF,实验浓度下很好地符合准一级动力学模型,速率常数为0.338 min^(-1).碱性溶液有利于MEF的降解,随着p H值从5.0增加到10.0,速率常数从0.271 min^(-1)增加到了0.388 min^(-1).采用硝基苯作为分子探针鉴定了P25光催化降解MEF过程中生成的羟基稳态浓度为0.58×10^(-1)2mmol·L^(-1),通过异丙醇猝灭计算出羟基自由基贡献率为95.7%,由此推算MEF与羟基的实际二级反应速率常数为1.04×1010L·(mol·s)^(-1).采用UPLC/MS/MS鉴定了MEF降解产物,推测MEF的光催化降解途径主要涉及脱氢反应、羟基化反应和酮化反应.发光菌急性毒性试验评价MEF降解过程中中间产物的毒性变化表明,UV-P25是一种有效降低MEF毒性的方法.

Massive and prolonged use of pharmaceutical and personal care products （PPCPs） lead to their frequent occureace in surface water and waste water. Here the process and products of MEF degradation catalyzed by TiO2（P25） were studied. The results demonstrated that P25 could quickly catalyze the degradation of MEF, which followed pseudo-first-order kinetics with a rate constant of 0.338 min-1. The reaction rate increased, from 0.271min-1 to 0.338 min-1 as the pH values was elevated from 5.0 to 10.0. The actual second-order rate constant for the reaction of MEF with .OH was 1.04×10^10L· （mol·s）-1 according to the calculated steady state .OH concentration of 0.58× 10-12 mmol·L-1 and the ·OH contribution rate of 95.7%. The primary photo-catalytical products of MEF were identified using UPLC/MS/MS, and possible degradation pathways were proposed by dehydrogenation, hydroxylation and ketonized reactions. The toxicity of the photo-catalytical products was evaluated using the Microtox test, which revealed that UV-P25 was an effective method for reducing the toxicity of MEF.