In this study, we constructed MnO₂/organic acid (OA) systems using MnO₂ colloid, the most reactive phase of Mn(IV), and two kinds of OA (oxalic acid and l-tartaric acid). We investigated the effect of OA on tetracycline (TC) degradation by MnO₂. The results show that both OA obviously accelerate TC degradation by MnO₂. Mn(III) formed during the reaction lead to the acceleration. Mn(III)-oxalate complex formed in oxalic acid system resulted in the lower degradation efficiency than that in l-tartaric acid system. The acceleration of oxalic acid was decreased when the concentration was more than 75 μM, and even completely disappeared with the concentration of 500 μM, owning to the fact that excess oxalic acid decreased the pH and some MnO₂ was fast reduced to Mn²⁺ by oxalic acid and unable to react with TC. The impact of pH on TC degradation resulted from the influences of H⁺ on MnO₂ redox potentials and TC deprotonation. And acidic conditions accelerated TC degradation. The addition of Mg²⁺, Ca²⁺, Fe³⁺ and Zn²⁺ exhibited an inhibitory effect in both systems for their occupying reactive sites on MnO₂ surface and blocking the access of TC to MnO₂. Similar intermediates in the two systems were detected, indicating a similar TC degradation mechanism including a series of reactions like dehydration, hydroxylation and oxidation. The MnO₂/OA system provides an efficient treatment of TC in wastewater. And it is also noticeable that MnO₂/OA system should also have an important effect on the fate of pollutants in environment, from our results.

在本研究中，我们使用MnO ₂胶体、Mn(IV) 中反应性最强的相和两种OA（草酸和l-酒石酸）构建了MnO ₂ /有机酸(OA) 系统。我们研究了OA 对MnO ₂对四环素(TC) 降解的影响。结果表明，两种OA均明显加速了MnO _{2 对}TC的降解。在反应过程中形成的 Mn(III) 导致加速。草酸体系中形成的Mn(III)-草酸盐络合物导致降解效率低于l-酒石酸系统。当浓度超过 75 μM 时，草酸的加速作用减弱，到 500 μM 时甚至完全消失，这是由于过量的草酸降低了 pH 值，部分 MnO ₂被快速还原为 Mn ²⁺。草酸，不能与TC反应。pH对TC降解的影响是由于H ⁺对MnO ₂氧化还原电位和TC去质子化的影响。酸性条件加速了TC降解。Mg ²⁺、Ca ²⁺、Fe ³⁺和Zn ²⁺的加入在两种体系中都表现出抑制作用，因为它们占据了MnO ₂上的反应位点表面并阻止 TC 进入 MnO ₂。在两个系统中检测到类似的中间体，表明类似的 TC 降解机制包括一系列反应，如脱水、羟基化和氧化。MnO ₂ /OA 系统可有效处理废水中的 TC。从我们的结果来看，MnO ₂ /OA 系统也应该对环境中污染物的归宿产生重要影响。