可见光/亚甲基蓝/抗坏血酸活化分子氧氧化水中的As(Ⅲ)

Oxidation of As(Ⅲ)in water by visible light/methylene blue/ascorbic acid activated molecular oxygen

本文研究了可见光/亚甲基蓝(MB^(+))/抗坏血酸(H_(2)A)活化分子氧体系(可见光/MB^(+)/H_(2)A体系)氧化水中三价砷(As(Ⅲ))的过程与机理.考察了光照、pH、H_(2)A浓度、MB^(+)浓度、As(Ⅲ)初始浓度及水中常见阴离子和有机质的对As(Ⅲ)氧化效率的影响,通过自由基抑制实验和溶液光谱变化鉴定了体系中的活性物种及其生成机理.实验结果表明,光照对As(Ⅲ)的氧化有明显促进作用;在pH=8.0—9.5范围内,As(Ⅲ)的氧化随着pH的升高而加快;pH=9.5条件下,H_(2)A剂量的增加对As(Ⅲ)的氧化呈现先促进后趋于稳定的趋势,H_(2)A最佳投加量为300μmol·L^(-1);MB^(+)最佳投加量为5 mg·L^(-1).机理研究表明,H_(2)A和分子氧之间的双电子反应产生的H_(2)O_(2)是可见光/MB^(+)/H_(2)A体系活化分子氧体系中氧化As(Ⅲ)的主要活性物种.MB^(+)经可见光激发后通过促进A·-的产生进而产生H_(2)O_(2).基于同样机制,另外两种噻嗪染料(劳氏紫和天青B)在可见光/H_(2)A体系中也能促进As(Ⅲ)的氧化.

The oxidation process and mechanism for As(Ⅲ)oxidation in water with visible light/methylene blue(MB^(+))/ascorbic acid(H_(2)A)activated molecular oxygen(visible light/MB^(+)/H_(2)A system)were systematically investigated in this work.The effects of light,pH,H_(2)A concentration,MB^(+)concentration,initial concentration of As(Ⅲ),common anions and organic matter in water on the oxidation efficiency of As(Ⅲ)were examined.The active species and its formation mechanism in the system were identified by free radical inhibition assay and spectral changes.Results show that light can promote the oxidation of As(Ⅲ).In the range of pH 8.0—9.5,the oxidation rate of As(Ⅲ)increases with the increase of pH.At pH 9.5,as the dosage of H_(2)A increase,the oxidation of As(Ⅲ)was promoted first and then remained unchanged.The optimum dosages of H_(2)A and MB^(+)were 300μmol·L^(-1) and 5 mg·L^(-1),respectively.H_(2)O_(2) is the main active species for the oxidation of As(Ⅲ)in the visible light/MB^(+)/H_(2)A system.MB^(+)enhances H_(2)O_(2) generation by promoting the production of A·-via visible light excitation.Based on the same mechanism,two other thiazine dyes,thionine and Azure B,can also accelerate the oxidation of As(Ⅲ)in the visible light/H_(2)A system.