Xu Tielian, Cai Yong, O'Shea Kevin E
Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, USA.
Environ Sci Technol. 2007 Aug 1;41(15):5471-7. doi: 10.1021/es0628349.
Monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) are used as herbicides in the agriculture industry. We have demonstrated that MMA and DMA are readily degraded upon TiO2 photocatalysis. DMA is oxidized to MMA as the primary oxidation product, which is subsequently oxidized to inorganic arsenate, As(V). The adsorption of MMA and DMA on Ti02 surface was measured as a function of initial arsenic concentration and solution pH. The pH of the solution influences the adsorption and photocatalytic degradation to a similar degree, due to the speciation of the arsenic substrates and surface charge of TiO2 as a function of pH. The mineralization of MMA and DMA by TiO2 photocatalysis follows the Langmuir-Hinshelwood kinetic model. Addition of tert-butyl alcohol, a hydroxyl radical scavenger, during TiO2 photocatalysis dramatically reduces the rate of degradation, indicating that *OH is the primary oxidant. For dilute solutions, TiO2 may also be applicable as an absorbent for direct removal of a variety of arsenic species, namely As(III), As(V), MMA, and DMA, all of which are strongly adsorbed, thus eliminating the need for a multistep treatment process.
一甲基胂酸（MMA）和二甲基胂酸（DMA）在农业产业中用作除草剂。我们已证明MMA和DMA在二氧化钛光催化作用下易于降解。DMA被氧化为主要氧化产物MMA，随后MMA被氧化为无机砷酸盐As（V）。测量了MMA和DMA在TiO₂表面的吸附量与初始砷浓度和溶液pH值的关系。由于砷底物的形态以及TiO₂的表面电荷随pH值变化，溶液的pH值对吸附和光催化降解的影响程度相似。TiO₂光催化使MMA和DMA矿化遵循朗缪尔 - 欣谢尔伍德动力学模型。在TiO₂光催化过程中添加羟基自由基清除剂叔丁醇会显著降低降解速率，这表明·OH是主要氧化剂。对于稀溶液，TiO₂也可用作吸附剂直接去除多种砷物种，即As（III）、As（V）、MMA和DMA，所有这些物种都被强烈吸附，从而无需多步处理过程。
