二氧化锰氧化降解金霉素的动力学研究

研究了金霉素(CTC)在二氧化锰(MnO2)作用下的氧化降解过程,并讨论了初始MnO2浓度、体系pH及温度对降解反应的影响.无MnO2存在时,CTC没有发生降解.但是当体系中存在MnO2时,CTC浓度开始迅速下降,反应后期降解速率逐渐变慢;同时体系中二价锰离子(Mn2+)浓度逐渐升高,表明MnO2可以降解CTC,该过程是一个氧化还原反应.采用草酸溶解MnO2和过滤2种不同的方法终止反应,对比2种方法所得的结果,可以发现该反应过程中,开始阶段降解作用占主导地位,在反应达到平衡后吸附作用才明显.CTC的降解速率随着MnO2初始浓度的增加和体系温度的升高均显著加快.反应体系的pH能强烈影响CTC的氧化降解,降解速率随着pH的升高而明显降低.这是由于CTC随体系pH由3.77升高到7.41时,分别以阳离子、中性形态和阴离子的形式存在;而-δMnO2(pHzpc=2.25)表面在pH3.77的整个范围内均呈现为负电性.因此随pH升高,阴离子形态的CTC逐渐增多,导致其在MnO2表面的吸附作用减弱,从而使降解速率变缓.

Oxidative Kinetics of Chlortetracycline by Manganese Dioxide

To better understand the transformation of chlortetracycline (CTC) under the oxidation of manganese dioxide (MnO₂), kinetics of CTC reaction with MnO₂ were investigated and the effects of MnO₂ initial concentration, pH, and temperature on kinetics were also discussed. Results showed that loss of CTC was not detected in the absence of MnO₂. But CTC was rapidly degraded along with the generation of Mn²⁺ in the presence of MnO₂, which indicated that this process was an oxidation-reduction reaction. In order to explain the adsorption of CTC on MnO₂ surface, two different approaches (filtration and oxalic acid addition) were used to quench the reactions. Oxidation was observed dominantly in the initial stage compared with adsorption, and adsorption become noticeable after the reaction reached an equilibrium level. The reaction rate of CTC increased with the increase of MnO₂ initial concentration and temperature of the reaction system. In addition, the reaction rate of CTC also decreased significantly as the pH of reaction mixture increased from 3.77 to 7.41, which was caused by the decreased adsorption of CTC on MnO₂ with the increase of pH. Over the entire pH range (3.77-7.41), the speciation of CTC transited from cation and then zwitterion to anion, however, the MnO₂ surface exhibited all with negative charges because its zeta-potential (pH point of zero charge) was 2.25. Thus, pH increase would result in the decline of the adsorption force between CTC speciation and the MnO₂ surface.