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过氧化氢作为一种绿色氧化剂[1],在催化剂作用下可产生氧化性极强的活性自由基,能够无选择地氧化降解水中的有机污染物,被广泛应用于有机物的氧化和工业废水的处理[2-3]。目前,常用的H2O2催化活化剂包括无机催化剂和有机活化剂。无机催化剂种类有金属离子、金属氧化物、金属配位体等。例如,金属离子催化剂Fenton试剂,Fe2+催化H2O2产生·OH把有机物氧化成CO2、H2O等小分子物质。Fenton反应对pH要求苛刻,并产生大量污泥,因此,类Fenton技术不断发展[4]。杨迦等[5]利用硫酸钠-过氧化氢-氯化钠加合物类芬顿试剂降解了苯胺。金属氧化物催化剂常用的有Fe、Mn、Cu、Ce、Ni、Co、Cr等的氧化物以及钼酸盐[6-7]。在中性条件下,钼酸根催化过氧化氢处理2,4,6-三氯酚和五氯酚废水,降解率可达95%以上[8]。但在酸性条件下,钼酸根催化过氧化氢的效率相对较低[9]。金属配合物催化剂包括酞菁配合物[10]、卟啉配合物、含氮大环配合物、席夫碱配合物[11]和杂多酸(盐)[12]。其中,合成的席夫碱镧系配位体LaL(NO3)3.xH2O和LnL2(NO3)3.xH2O催化H2O2降解苯胺具有很好的选择性[13]。DONG等[14]通过制备杂多酸盐Mg3Al-LDH-Nb6催化H2O2得到高活性氧化体系,对2-CEES(2-氯乙基乙基硫醚)有很好的降解效果。面对催化剂催化条件要求高的问题,寻找条件温和、活性高、适用范围广的过氧化氢催化剂显得尤为重要。
苯胺作为重要的工业原料主要用于制造染料、药物、树脂,还可以作为橡胶硫化促进剂,因此,在相关生产中不可避免地会产生大量苯胺污染水[15]。本文以苯胺为研究对象,依据上述相关文献和市售大宗化学品种类,从过氧化氢金属离子、金属氧化物和金属配位体等3类催化剂中选择了6种化合物(Fe、Cu、磷钼酸等),研究了其催化H2O2降解苯胺的效果;采用电子顺磁共振法、氧化还原电位测定法、化学发光法以及拉曼光谱法检测了PMA催化H2O2产生的活性物质及分布规律,探讨了H2O2催化机制;此外,进一步考察了催化剂用量、pH以及活性氧与苯胺的摩尔比对苯胺降解效果的影响,以获得H2O2/PMA催化体系的最佳反应条件;最后,利用GC/MS、LC/MS和IC等仪器分析方法检测苯胺的降解产物,探讨苯胺在H2O2/PMA催化体系中的降解途径。
过氧化氢/磷钼酸体系的催化机制及对苯胺的降解效果
Catalytic mechanism and performance of the hydrogen peroxide/phosphomolybdic acid system on aniline degradation
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摘要: 以苯胺为目标污染物,通过苯胺的降解实验从3类6种过氧化氢催化剂中筛选出催化效果较好的杂多酸催化剂磷钼酸(PMA)。利用氧化还原电位测定法、电子顺磁共振波谱法、化学发光法以及拉曼光谱法分析了H2O2/PMA催化体系的催化机制,初步推测PMA催化H2O2生成高活性的[Mo(OO)2]*和[Mo(OOH)2]*中间体。同时,考察了PMA用量、pH以及苯胺与活性氧的摩尔比对苯胺降解效果的影响,获得了H2O2/PMA体系最佳反应条件。当H2O2和PMA质量分数分别为1%和0.365‰、溶液pH为4,在1 min内对4 mg·mL−1苯胺的降解率可达98%以上。通过气相色谱质谱联用仪(GC/MS)、液相色谱质谱联用仪(LC/MS)和离子色谱(IC)等仪器分析方法检测确定苯胺的降解产物,推测其在H2O2/PMA催化体系的降解途径主要以N、C原子的氧化和聚合反应为主。Abstract: In this study, aniline was taken as a pollutant object, a heteropolyacid catalyst of phosphomolybdic acid(PMA) with better catalytic effect was screened out among six kinds of catalysts combined with hydrogen peroxide solution which could be divided as three types. The catalysis mechanism of H2O2/PMA system was anayzed through redox potential measurement, electron paramagnetic resonance, chemiluminescence and Raman spectroscopy. The experimental results indicated that H2O2 was catalyzed by PMA to produce highly active [Mo(OO)2]* and [Mo(OOH)2]* intermediate species. Meanwhile, the effects of PMA dosage, pH value and the molar ratio of aniline to reactive oxygen species on aniline degradation efficiency were studied to determine the optimum degradation conditions of H2O2/PMA system. When the mass concentrations of H2O2 and PMA were 1% and 0.365‰, respectively, over 98% aniline could be degraded within 1min for the solution with pH=4 and initial concentration of 4 mg·mL-1. The degradation products of aniline were determined by gas chromatography-mass spectrometry(GC/MS), liquid chromatography-mass spectrometry(LC/MS) and ion chromatography(IC), then it can be predicted that the main pathway of aniline degradation was oxidation and polymerization of N and C atom in H2O2/PMA oxidation system.
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Key words:
- hydrogen peroxide /
- phosphomolybdic acid /
- aniline /
- catalytic mechanism /
- degradation pathway
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