Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Water Res. 2017 Jun 1;116:126-134. doi: 10.1016/j.watres.2017.03.028. Epub 2017 Mar 18.
Aromatic organoarsenic compounds tend to transform into more mobile toxic inorganic arsenic via several processes, and can inadvertently spread toxic inorganic arsenic through the environment to water sources. To gain insight into the transformation mechanisms, we herein investigated how the process of para arsanilic acid (p-ASA) transformation works in detail on the surface of adsorbents by comparing it with phenylarsonic acid (PA) and aniline, which have similar chemical structures. In contrast to the values of 0.23 mmol g and 0.68 mmol g for PA and aniline, the maximum adsorption capacity was determined to be 0.40 mmol g for p-ASA at pH 4.0. The results of FTIR and XPS spectra supported the presence of a protonated amine, resulting in a suitable condition for the oxidation of p-ASA. Based on the combined results of UV-spectra and UPLC-Q-TOF-MS, we confirmed that the adsorbed p-ASA was first oxidized through the transfer of one electron from p-ASA on MnO surface to form a radical intermediate, which through further hydrolysis and coupling led to formation of benzoquinone and azophenylarsonic acid, which was identified as a major intermediate. After that, p-ASA radical intermediate was cleaved to form arsenite (III), and then further oxidized into arsenate (V) with the release of manganese (Mn) into solution, indicating a heterogeneous oxidation process.
芳香有机砷化合物往往通过多种过程转化为更具移动性的有毒无机砷，并可能无意中通过环境将有毒无机砷传播到水源中。为了深入了解转化机制，我们通过比较与具有相似化学结构的对氨基苯磺酸（p-ASA）和苯胺，详细研究了对氨基苯磺酸在吸附剂表面的转化过程。与苯胂酸（PA）和苯胺的最大吸附容量值 0.23mmol g 和 0.68mmol g 相比，在 pH 值为 4.0 时，p-ASA 的最大吸附容量被确定为 0.40mmol g。FTIR 和 XPS 光谱的结果支持存在质子化的胺，从而为 p-ASA 的氧化提供了合适的条件。基于紫外光谱和 UPLC-Q-TOF-MS 的综合结果，我们证实吸附的 p-ASA 首先通过 p-ASA 在 MnO 表面上的单电子转移被氧化，形成自由基中间体，然后通过进一步的水解和偶联形成苯醌和偶氮苯砷酸，这被鉴定为主要的中间产物。之后，p-ASA 自由基中间体被裂解形成亚砷酸盐（III），然后进一步氧化成砷酸盐（V），同时锰（Mn）释放到溶液中，表明这是一个多相氧化过程。
