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碘代消毒副产物是在水中含碘离子或含碘化合物的条件下,利用次氯酸钠,二氧化氯等消毒剂对饮用水或者污水进行消毒,与水中其他的化合物经过一系列复杂的反应生成的一类含碘的副产物。碘代消毒副产物的种类包括碘代三卤甲烷,碘代卤乙酸,碘代卤乙腈,碘代乙酰胺等[1-3]。碘代消毒副产物虽然在水中含量较低,但是大量的研究表明,其具有比常规的氯代和溴代消毒副产物更高的遗传毒性和细胞毒性[1]。我国的沿海地区和部分内陆地区水源中含有较高含量的碘离子,特别是北京、河南和河北部分浅层水中碘离子的含量高达1 000 µg·L−1,具有较高的碘代消毒副产物生成风险[4-5]。目前,针对碘代消毒副产物的控制研究大多集中在利用传统的混凝、沉淀,臭氧以及膜过滤等手段去除其前驱物,而对于碘代消毒副产物本身的降解研究较少[6]。
高级氧化技术是一种处理难降解有机废水的有效手段。芬顿氧化技术是应用最广泛和成熟的高级氧化技术,在处理印染、医药、石化等行业废水有重要的应用。但是传统的均相芬顿氧化技术还存在着pH适用范围窄、双氧水利用效率低以及存在铁泥二次污染等问题。多相芬顿催化氧化是近年来快速发展的一种改进型高级氧化技术,其目的在于克服均相芬顿技术的弊端。多相芬顿催化氧化主要是将自由的金属离子固相化,形成金属、金属氧化物、金属负载型以及金属离子掺杂型固体催化剂[7-11]。相比于传统的均相催化氧化技术,多相芬顿催化技术具有pH响应范围宽,不产生二次污染以及活性组分易分离的优点。但是,固液界面的存在使得多相芬顿催化氧化反应受到催化剂结构形貌、表面性质等自身特性影响,还受到污染物特性,氧化剂种类和浓度等反应条件的影响,其催化机理在当前尚未形成统一的认识,这极大增加了催化剂结构设计以及活性调控的难度[12-13]。这些催化剂的设计与调控大多依赖于催化剂内金属组分高价态与低价态之间的转换。因此,还存在着氧化剂利用率低,中性条件下催化效果不理想以及催化剂稳定性差等不足[14]。
双反应中心(dual-reactor centers,DRCs)催化剂是指通过在催化剂表面进行电子调控,构建具有贫富电子微区的双反应中心(DRCs),使得富电子中心可以为O2,H2O2等氧化剂提供电子,发生还原反应,生成活性氧物种 (包括·OH,O2·−等)。而缺电子中心则可以快速捕获体系中的污染物等作为电子供体,实现污染物多途径降解,并且两个中心之间通过化学键桥实现电子高效转移[15]。利用双反应中心原理构建的催化剂实现了突破了传统芬顿反应利用金属离子高低价态转换来实现H2O2的氧化还原,有效突破了反应的速率限制步骤,提高了H2O2的利用率,也大大提高了催化剂的稳定性[16]。有研究表明,利用阳离子-用键是构建高效双反应中心催化剂关键。比如,通过在CuAlO2催化剂表面嫁接CN(C3N4)有机配体,形成了C-O-Cu键桥,CN的引入一方面减少了CuAlO2的氧空穴的数量,另一方面大大的加速了电子在以C和Cu为贫富中心之间的传递,从而使得催化剂对双酚A的降解效率提高了25倍以上。但嫁接有机配体的方式存在有机配体脱落的风险,如何优化催化剂的合成方法,快速制备高效的双反应中心催化剂具有重要的意义。
之前的研究发现,氧空位的存在可以在一定程度上影响芬顿反应的发生,其对电子的转移以及污染物的捕获都有重要的意义。ZHAN等人将氧化钴掺杂到氧化锌(ZnO)纤锌矿晶格中,成功地在催化剂表面构建了富含未配对电子的氧空位富电子中心和Co(III)贫电子中心,催化效率提高了17倍以上。也有研究表明,铜系类芬顿催化剂在催化芬顿反应时,比铁系类芬顿催化剂具有更高的反应速率和更宽的pH适用范围。这是因为Cu (II) 被过氧化氢催化还原的速率(1.0×104 mol·s−1)要远高于Fe(III)(74 mol·s−1)。但是大部分的铜基的催化剂在污染物或者酸的作用下(0.5~10 mg·L−1),容易发生泄露,高于美国饮用水标准1.3 mg·L−1,从而造成一定的环境影响。因此,如何在保持铜元素高效催化效率的同时,提高铜元素的稳定性对于催化剂的设计和开发就显得尤为重要。
基于此,本文通过水热合成的方法在ZnO纤锌矿晶格中嵌入氧化铜(CuO),从而得到一种全新的双中心反应催化剂。通过XPS,EPR,FTIR等手段对催化剂的表面性质进行表征。并利用水中典型的碘代消毒副产物碘乙腈进行降解研究,重点研究了碘乙腈降解效果,影响因素以及矿化效果,同时根据EPR,XPS的分析结果推测了碘乙腈的降解机制。
Cu-ZnO双反应中心类芬顿催化剂降解水中碘乙腈性能与机制
Catalytic oxidation of iodoacetonitrile by Cu-ZnO dual-reaction center catalyst in water and its mechanism
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摘要: 多相芬顿催化虽然克服了均相芬顿pH适用范围窄,铁泥二次污染等问题,但还面临着稳定性差,H2O2利用率低的问题,从而限制了其实际应用。本文利用锌和铜的电负性差异制备了一种双反应中心催化剂Cu-ZnO,通过在催化剂表面构建贫富电子中心,从而诱导H2O2产生·OH降解污染物。采用TEM、EDS、XRD、FTIR、XPS以及EPR对催化剂进行表征,并研究了催化剂投加量、H2O2投加量、pH以及共存离子对碘乙腈降解效果的影响。结果表明,在催化剂投加量为1 g·L-1,双氧水投加量为10 mmol·L-1时,Cu-ZnO对碘乙腈的去除率在91%。大部分共存离子对催化剂的降解效果影响较小,且在酸性条件下催化剂稳定性较好,中性和碱性条件下金属离子基本无释放。催化剂诱导产生的•OH和HO2•/O2•−是碘乙腈(IAN)降解的主要活性物种,降解产物包括CO2,H2O,I-和IO3- 等。Abstract: The practical application of heterogeneous Fenton catalysis was limited by the instability and inefficiency of H2O2, even though which overcomes the problems such as narrow pH range and secondary pollution of iron sludge compared to homogeneous Fenton. In this study, a dual-reaction center catalyst Cu-ZnO was developed by taking advantage of the electronegativity difference between zinc and copper, and the rich and poor electron centers were constructed on the surface of the catalyst which could induce H2O2 and produce •OH for pollutants degradation. The catalysts were characterized by TEM, EDS, XRD, FTIR, XPS and EPR, and the effects of dosage of catalyst and H2O2, pH and coexisting ions on the degradation of iodoacetonitrile(IAN) were investigated. The results showed that 91% IAN was removed when the dosages of catalyst and H2O2 were 1 g·L-1 and 10 mM, respectively. Most coexisting ions had slight effects on IAN degradation by Cu-ZnO which showed a better stability under acidic conditions, and no metal ions released at neutral and basic pHs. •OH and HO2•/O2•− induced by catalyst are the main active species for IAN degradation, the degradation products included CO2, H2O, I-, IO3- and other organic products.
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Key words:
- heterogeneous Fenton /
- dual-reaction center /
- iodoacetonitrile /
- H2O2
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