光催化体系中噻虫胺降解动力学及机制

Kinetics and Mechanistic Investigation of the Photocatalytic Degradation of Clothianidin

利用光催化技术探讨了烟碱类杀虫剂噻虫胺在水体环境中降解的可行性,不同催化剂浓度、反应温度、底物浓度、溶液初始p H值和不同阴阳离子等因素对其光催化降解动力学的影响,及其初步的光催化降解机制.结果表明噻虫胺的光催化降解符合L-H动力模型,其降解假一级动力学速率常数为0.050 6 min-1.当催化剂用量(TiO_2)为3.0 g·L^(-1)时,噻虫胺的光催化降解速率最大;高温和较低的底物浓度有利于噻虫胺的光催化降解;溶液的初始p H值为5时噻虫胺的降解速率最大,强酸和强碱均不利于其光催化降解.而无机阴、阳离子对噻虫胺降解均有明显的抑制作用.最后,通过GC/MS对噻虫胺光催化降解中间产物进行了初步鉴定,研究发现在活性氧物种的作用下噻虫胺降解途径主要有母体化合物的羟基化,硝基胍基团中N—N的断裂,以及连接硝基胍和噻唑环的C—N键的裂解等.

Clothianidin was selected as a model compound for kinetics and mechanistic investigation of the photocatalytic degradation of nicotine insecticides. We assessed the feasibility of the degradation process,and systematically explored the effects of catalyst amount,reaction temperature,substrate concentration,initial solution pH value,and the presence of inorganic anions and cations on the reaction. The results revealed a Langmuir-Hinshelwood interaction of pseudo-first-order kinetics,showing a rate constant of 0. 050 6min～（-1）. The photocatalytic degradation rate was the highest when the amount of catalyst（ TiO2） was 3 g·L^-1. It was observed that an increase of reaction temperature or lowering of substrate concentration was beneficial to clothianidin degradation. Additionally,the initial pH value of the solution had an obvious effect on the degradation process. Strong acid and alkali were not conducive and the degradation rate constant was the largest at pH = 5. Furthermore,most of the inorganic anions and cations significantly hindered the degradation of clothianidin. Finally,the degradation intermediates were identified by GC / MS,and the reaction pathways at the initial stage of the photocatalytic process were proposed： hydroxylation of parent compound,cleavage of N—N bond in the nitroguanidine group,and cleavage of the C—N bond connected to the nitroguanidine and thiazole rings.