Mechanistic studies on the oxidative degradation of Orange II by peracetic acid catalyzed by simple manganese(II) salts. Tuning the lifetime of the catalyst
Mechanistic studies on the oxidative degradation of Orange II by peracetic acid catalyzed by simple manganese(II) salts. Tuning the lifetime of the catalyst
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DOI：
10.1039/c2nj20852k
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发表时间：
2012-02
影响因子：
3.3
通讯作者：
Sabine Rothbart;E. Ember;R. Eldik
中科院分区：
文献类型：
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作者：
Sabine Rothbart;E. Ember;R. Eldik
在pH 9.5和25°C的温和反应条件下，观察到简单Mn（II）盐与绿色氧化剂过氧乙酸（PAA）联合使用时，水溶液中橙色II的催化氧化降解非常有效。为了进一步了解快速高效降解橙II的复杂反应网络，对催化降解反应进行了详细的动力学研究。用紫外/可见光谱法详细研究了催化剂、氧化剂和缓冲液浓度对反应过程的影响。降解速率随催化剂和PAA浓度的增加而增加，随碳酸盐缓冲液浓度的增加而降低，在pH≈9.4时反应活性最大。在没有底物的情况下进行的研究揭示了在选定的实验条件下各种高价锰中间体的连续形成。当PAA加入到pH为9.5的Mn（II）离子溶液中时，其紫外/可见光谱变化显示出双相行为，最终产物为MnVIIO4−和胶体MnIVO2。通过EPR和UV/Vis光谱的结合，观察到在反应的第一阶段存在Mn（IV）物质。如果在反应过程中在不同的延迟时间后向含有Mn(II)/PAA的反应混合物中添加染料，则观察到降解性能的显著变化表明催化剂组成随时间的变化。因此，在高价中间体形成和胶体MnIVO2发生之前，反应活性达到最高。用不同的原位形成的中间体所选择的催化实验表明，少量过氧化氢（普遍存在于商品过氧乙酸中，6 wt% H2O2）对于有效催化染料分解具有重要作用。H2O2作为还原剂在催化循环中发挥了至关重要的作用，避免了催化剂的过度氧化，从而延长了催化系统的寿命。对这些数据进行了评估，以获得在Mn（II）催化氧化染料与PAA降解过程中发生的复杂化学反应的机理。并与先前使用H2O2/HCO3−作为氧化剂的结果进行了比较。
A remarkably efficient, catalytic oxidative degradation of Orange II in aqueous solution was observed in the presence of simple Mn(II) salts used in combination with the green oxidant peracetic acid (PAA) under mild reaction conditions at pH 9.5 and 25 °C. In order to gain further insight into the complex reaction network responsible for the fast and efficient degradation of Orange II, detailed kinetic studies on the catalytic degradation reaction were performed. The influence of the catalyst, oxidant, and buffer concentrations on the reaction course was studied in detail by in situUV/Vis spectroscopy. The degradation rate increased with increasing catalyst and PAA concentration, decreased with increasing carbonate buffer concentration, and the reaction showed maximum reactivity at pH ≈ 9.4. Studies performed in the absence of substrate revealed the successive formation of various high valence manganese intermediates under the selected experimental conditions. The UV/Vis spectral changes observed upon addition of PAA to a Mn(II) ion containing solution at pH 9.5 showed biphasic behavior, and led to the formation of MnVIIO4− and colloidal MnIVO2 as final products. Through the combination of EPR and UV/Vis spectroscopy, the presence of a Mn(IV) species during the first phase of the reaction was observed. If the addition of a dye to the Mn(II)/PAA containing reaction mixture was carried out after different delay times during the course of the reaction, significant changes observed in the degradation performance pointed to changes in the catalyst composition with time. Thereby, the highest reactivity was reached just before the formation of the high valence intermediates and colloidal MnIVO2 occurred. Selected catalytic experiments with different in situ formed intermediates showed the essential role of a small amount of hydrogen peroxide (omnipresent in commercial peracetic acid, 6 wt% H2O2) for efficient catalytic dye decomposition. H2O2 was shown to play a crucial role as a reducing agent in the catalytic cycle, avoiding the over-oxidation of the catalyst, and thereby extending the lifetime of the catalytic system. The data were evaluated to gain mechanistic insight into the complex chemical reactions occurring during the Mn(II) catalyzed oxidative dye degradation with PAA. A comparison with earlier results concerning the use of H2O2/HCO3− as oxidant was made.