Institut de Chimie des Milieux et des Matériaudx de Poitiers IC2MP, UMR 7285 CNRS Université de Poitiers, 1 rue Marcel Doré, TSA 41105, 86073 Poitiers Cedex 9, France.
Institut de Chimie des Milieux et des Matériaudx de Poitiers IC2MP, UMR 7285 CNRS Université de Poitiers, 1 rue Marcel Doré, TSA 41105, 86073 Poitiers Cedex 9, France.
Chemosphere. 2018 Jun;201:425-431. doi: 10.1016/j.chemosphere.2018.03.021. Epub 2018 Mar 6.
The manganese oxide birnessite adsorbed and catalyzed the transformation of the anthelminthic drug niclosamide (NIS) into 2-chloro-4-nitroaniline (CNA) and 5-chlorosalicylic acid (CSA) at acidic pH. The adsorption of NIS was fitted using a linear isotherm for all conditions and reaction times. Linear adsorption constant K was 103 000 L kg at pH 5.0. The rate of transformation was first order with respect to both MnO and NIS. At pH 5.0, the second order rate constant was 3.3 (±0.3) × 10 M s. The adsorption constants and the rates of transformation decreased when pH increased from 4.0 to 5.5 because of increasing electrostatic repulsions between both negatively charged manganese oxide surface (pH = 2.5) and NIS (pKa = 6.38). The presence of natural organic matter (NOM) extracted from surface water also significantly decreased the adsorption and the rates of transformation of NIS. The rate of transformation decreased by a factor of 20 in presence of 1.6 mgC L even though significant amounts of NIS were adsorbed onto MnO. The interactions between NOM and NIS were investigated by using the fluorescence quenching method and would explain that NIS adsorbed on the surface of manganese oxide was stable in presence of NOM. Thus, hydrolysis catalyzed by manganese oxide is probably not an important process compared to biodegradation and adsorption because of the presence of organic matter and pH values usually >5.5 in aquatic environment.
在酸性 pH 值条件下，氧化锰矿水钠锰矿吸附并催化驱虫药硝氯酚（NIS）转化为 2-氯-4-硝基苯胺（CNA）和 5-氯水杨酸（CSA）。所有条件和反应时间下，NIS 的吸附均符合线性等温线。在 pH 5.0 时，吸附常数 K 为 1030000 L kg。转化速率与 MnO 和 NIS 均呈一级关系。在 pH 5.0 时，二级反应速率常数为 3.3(±0.3)×10 M s。当 pH 值从 4.0 增加到 5.5 时，吸附常数和转化速率均降低，这是因为带负电荷的锰氧化物表面（pH=2.5）和 NIS（pKa=6.38）之间的静电排斥作用增加。地表水提取的天然有机物（NOM）的存在也显著降低了 NIS 的吸附和转化速率。即使有大量的 NIS 被吸附到 MnO 上，在 1.6 mgC L 的存在下，转化速率也降低了 20 倍。通过使用荧光猝灭法研究了 NOM 和 NIS 之间的相互作用，这可以解释在 NOM 存在下，吸附在锰氧化物表面的 NIS 是稳定的。因此，与生物降解和吸附相比，由于有机物的存在和 pH 值通常大于 5.5，氧化锰矿的水解催化可能不是一个重要的过程。
