Oxidation of As(Ⅲ)in water by visible light/methylene blue/ascorbic acid activated molecular oxygen
The oxidation process and mechanism for As(Ⅲ)oxidation in water with visible light/methylene blue(MB+)/ascorbic acid(H2A)activated molecular oxygen(visible light/MB+/H2A system)were systematically investigated in this work.The effects of light,pH,H2A 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 H2A increase,the oxidation of As(Ⅲ)was promoted first and then remained unchanged.The optimum dosages of H2A and MB+were 300 μmol·L-1 and 5 mg·L-1,respectively.H2O2 is the main active species for the oxidation of As(Ⅲ)in the visible light/MB+/H2A system.MB+enhances H2O2 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/H2A system.
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