Xu Zhonghou, Jing Chuanyong, Li Fasheng, Meng Xiaoguang
Center for Environmental Systems, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
Environ Sci Technol. 2008 Apr 1;42(7):2349-54. doi: 10.1021/es0719677.
Photodegradation mechanisms of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) with nanocrystalline titanium dioxide under UV irradiation were investigated. In the presence of UV irradiation and 0.02 g/L TiO2, 93% MMA (initial concentration is 10 mg-As/L) was transformed into inorganic arsenate, [As(V)], after 72 h of a batch reaction. The mineralization of DMA to As(V) occurred in two steps with MMA as an intermediate product. The photodegradation rate of MMA and DMA could be described using first-order kinetics, where the apparent rate constant is 0.033/h and 0.013/h for MMA and DMA, respectively. Radical scavengers, including superoxide dimutase (SOD), sodium bicarbonate, tert-butanol, and sodium azide, were used to study the photodegradation mechanisms of MMA and DMA. The results showed that hydroxyl radicals (HO*) was the primary reactive oxygen species for the photodegradation of MMA and DMA. The methyl groups in MMA and DMAweretransformed into organic carbon, including formic acid and possibly methanol, also through photochemical reactions. The results showed that nanocrystalline TiO2 can be used for the photocatalytical degradation of MMA and DMA and subsequent removal of the converted As(V), since the high adsorption capacity of the material for inorganic arsenic species has been demonstrated in previous studies.
研究了紫外光照射下纳米晶二氧化钛对一甲基胂酸（MMA）和二甲基胂酸（DMA）的光降解机理。在紫外光照射和0.02 g/L TiO₂存在下，经过72 h的间歇反应后，93%的MMA（初始浓度为10 mg-As/L）转化为无机砷酸盐[As(V)]。DMA矿化生成As(V)分两步进行，中间产物为MMA。MMA和DMA的光降解速率可用一级动力学描述，其中MMA和DMA的表观速率常数分别为0.033/h和0.013/h。使用包括超氧化物歧化酶（SOD）、碳酸氢钠、叔丁醇和叠氮化钠在内的自由基清除剂来研究MMA和DMA的光降解机理。结果表明，羟基自由基（HO*）是MMA和DMA光降解的主要活性氧物种。MMA和DMA中的甲基也通过光化学反应转化为有机碳，包括甲酸和可能的甲醇。结果表明，纳米晶TiO₂可用于MMA和DMA的光催化降解以及随后对转化生成的As(V)的去除，因为在先前的研究中已证明该材料对无机砷物种具有高吸附能力。
