Effects of MnO2 of different structures on activation of peroxymonosulfate for bisphenol A degradation under acidic conditions
Effects of MnO2 of different structures on activation of peroxymonosulfate for bisphenol A degradation under acidic conditions
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DOI：
10.1016/j.cej.2019.03.238
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发表时间：
2019-08-15
影响因子：
15.1
通讯作者：
Zhang, Huichun
中科院分区：
文献类型：
--
作者：
Huang, Jianzhi;Dai, Yifan;Zhang, Huichun
合成了具有不同结构的MnO2，包括三种隧道结构（α -, 1 β -, γ -MnO2）和层状结构（MnO2），并研究了过氧单硫酸盐（PMS）的活化。不同结构的MnO2对污染物降解中PMS活化的影响，通过双酚A （BPA）氧化的准一级速率常数来量化，顺序为：α -MnO2> -MnO2> -MnO2> δ -MnO2。结果表明，在酸性条件下，PMS-MnO2的催化氧化和MnO2的直接氧化均可降解BPA，且不同MnO2对这两种降解机制的相对重要性不同。α -、β -、γ -和δ - mno2的直接氧化反应活性分别占总反应活性的25.2%、7.4、34.1和94.5%。表征了MnO2的物理化学性质，包括晶体结构、形貌、表面Mn氧化态、表面积、氧种类和电导率，并将其与催化活性相关联。结果表明，MnO2的结晶度是影响反应活性的主要因素，因此结晶度最小的δ -MnO2的反应活性最低。对于结晶MnO2，催化活性与Mn平均氧化态、Mn（III）含量和电导率呈线性相关。电子自旋共振（ESR）和乙醇和叔丁醇的猝灭实验表明，硫酸盐自由基（SO4中心点-）在体系中起主导作用，羟基自由基（OH）起次要作用。此外，单线态氧（O-1(2)）等非自由基机制也有助于双酚a的降解，特别是当δ - mno2为催化剂时。这些发现为PMS-MnO2的污染物降解机制提供了新的见解，并为开发具有成本效益的水/废水处理催化剂提供了指导。
MnO2 with various structures, including three tunnel structures (alpha-, 1 beta-, gamma-MnO2) and a layered structure (MnO2), were synthesized and investigated for peroxymonosulfate (PMS) activation. The effects of different structured MnO2 on PMS activation in contaminant degradation, as quantified by the pseudo-first order rate constants of bisphenol A (BPA) oxidation, followed the order: alpha-MnO2> gamma-MnO2> beta-MnO2> delta-MnO2. Results showed that under acidic conditions, BPA was degraded by both catalytic oxidation by PMS-MnO2 and direct oxidation by MnO2, and the relative importance of the two mechanisms differed for different MnO2. The direct oxidation accounted for 25.2, 7.4, 34.1, and 94.5% of the total reactivity of alpha-, beta-, gamma-, and delta-MnO2, respectively. Physicochemical properties of MnO2 including crystal structure, morphology, surface Mn oxidation states, surface area, oxygen species and conductivity were characterized and correlated with the catalytic reactivity. The results demonstrated that the crystallinity of MnO2 was the dominant factor in the catalytic reactivity, resulting in the lowest reactivity for the least crystalline delta-MnO2. For the crystalline MnO2, the catalytic reactivity linearly correlated with Mn average oxidation state, Mn(III) content, and conductivity. Electron spin resonance (ESR) and quenching experiments with ethanol and tert-butanol suggested that sulfate radicals (SO4 center dot-) were the dominant radicals in the systems, while hydroxyl radicals (OH) played a minor role. In addition, nonradical mechanisms such as singlet oxygen (O-1(2)) also contributed to the BPA degradation, especially when delta-MnO2 was the catalyst. These findings offered new insights into the contaminant degradation mechanisms in PMS-MnO2 and provided guidance to develop cost-effective catalysts for water/wastewater treatment.