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药品和个人护理品类污染物(如内分泌干扰物、抗生素等)导致的水体污染问题是生态安全和人类身体健康的一大威胁[1-3]。基于过硫酸盐的高级氧化技术可通过产生羟基自由基(OH•)、硫酸根自由基(SO4•−)、单线态氧(1O2)等活性氧物种降解水中多种类型的有机污染物,在药、护品类污染物处理方面受到了广泛关注[1]。与过一硫酸盐(peroxymonosulfate,PMS)相比,过二硫酸盐(peroxydisulfate,PDS)价格低廉、水溶性好、稳定性高便于储存和运输,已被广泛用于催化降解有机污染物[1]。PDS可通过热活化、碱活化、金属离子催化、金属氧化物催化等多种方法活化,其中基于纳米金属氧化物(如Co3O4等)的异相催化由于催化剂价格低廉、反应条件温和、催化活性高等优点,是目前研究的一个重要方向[2]。然而,纳米尺寸的金属氧化物分散于水中易团聚,导致催化剂活性位点暴露有限,并且分散于水中的纳米催化剂还存在难以分离和回收的问题,极大地限制了其应用。
将金属氧化物纳米催化剂负载于活性炭、泡沫金属、矿物颗粒以及陶瓷膜等三维载体的表面,不仅可以有效缓解氧化物纳米颗粒的团聚问题,而且便于分离和回收,对纳米金属氧化物活化过硫酸盐降解有机物具有重要意义[4]。现阶段,金属氧化物主要通过浆料涂覆的方式负载于载体表面,合成方法简单但稳定性较差[5]。添加高分子粘结剂可增强其稳定性,但催化体系中引入导电性较差的高分子不利于过硫酸活化过程中电子的转移,同时添加粘结剂也可能会带来二次污染[6]。因此,亟需发展一种可将金属氧化物原位负载于三维载体表面的绿色合成方法。植物多酚如单宁酸(tannic acid,TA)普遍存在于植物的根、茎、叶及果实中,是一种价格低廉的生物质[7]。TA分子富含邻二酚羟基,具有较强的金属离子络合能力和优异的表面粘附性能,可与多种金属离子(Co2+、Fe2+、Cu2+等)在聚乙烯球、陶瓷、玻璃等不同载体表面配位形成金属-多酚配合物[7]。作为由金属离子和有机配体组成的复合物,金属-多酚配合物可进一步热解制成不同种类的金属氧化物,并且研究表明有机配体TA分解还会产生多孔结构而形成多孔结构的金属氧化物[8]。
基于TA分子的金属离子络合能力和表面粘附性能,本研究以具有稳定物理化学性质且价格低廉的气泡石为载体,通过在其表面包覆Co2+与TA的配合物,进一步热解将纳米尺寸的Co3O4原位负载于气泡石表面,制备易分离回收的负载型Co3O4催化剂,通过SEM、XRD、ICP等详细分析了负载型Co3O4的结构和组成。利用负载型Co3O4催化剂活化PDS降解水中的双酚A(bis-phenol A,BPA)、磺胺甲恶唑(sulfamethoxazole,SMX)等药、护品类有机污染物,分析了溶液初始pH、PDS浓度、催化剂投加量、共存化学组分等对有机物降解性能的影响,并通过电子顺磁共振分析、化学淬灭实验、光谱分析等手段深入分析了PDS的活化机制和有机物的降解机理。
负载型Co3O4活化过二硫酸盐非自由基降解有机污染物
Nonradical oxidation of bis-phenol A by peroxydisulfate activated over immobilized Co3O4 nanoparticles
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摘要: 通过在三维矿物载体表面包覆金属-多酚配合物并煅烧实现了Co3O4纳米颗粒的原位负载,制得了易分离回收的负载型Co3O4催化剂,利用SEM、XRD以及XPS表征分析其形貌和微观结构,采用活化过二硫酸盐(PDS)降解药、护品类有机污染物以评价其催化性能。以双酚A为目标污染物,考察了初始pH、PDS浓度、催化剂投加量、共存阴离子(CO32−、SO42−、NO3−、Cl−)以及腐殖酸(HA)对BPA降解效率的影响。结果表明,负载型Co3O4能有效活化PDS降解有机物,在Co3O4投加量0.075 g·L−1,BPA初始浓度0.04 mmol·L−1,PDS初始浓度0.4 mmol·L−1以及初始pH=7的最优条件下,120 min内BPA可被完全去除。淬灭实验与EPR实验结果表明,负载型Co3O4活化PDS通过单线态氧(1O2)主导的非自由基途径氧化分解有机物。Abstract: Nanosized Co3O4 particles were in situ grown on the surface of three-dimensional mineral substrates by calcining surface-coated metal-phenolic coordination polymer. Immobilizing Co3O4 nanoparticles on the mineral substrate allows facile separation and recovery. SEM, XRD and XPS were performed to characterize the morphology and microstructure of the immobilized Co3O4 nanoparticles. The immobilized Co3O4 was applied to active peroxydisulfate (PDS) to degrade pharmaceutical and personal care products in water. The influence of initial pH, PDS concentration, catalyst dosage, inorganic ions (CO32−, SO42−, NO3−, Cl−) and humic acid (HA) on organics degradation was systematically investigated by using bis-phenol A(BPA) as a probe contaminant. The results showed that the immobilized Co3O4 could effectively active PDS to degrade BPA. Under the optimized conditions with a catalyst dosage of 0.075 g·L−1, PDS concentration of 0.4 mM, BPA with initial concentration of 0.04 mM and pH7 was completely removed within 120 min. Chemical scavenging experiments and EPR tests revealed the degradation of BPA followed a nonradical oxidation pathway based on singe oxygen (1O2).
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