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近年来,药物和个人护理品(pharmaceutical and personal care products,PPCPs)在地下水、地表水和饮用水中被广泛检出,引起研究者们关注。双氯芬酸钠(diclofenac sodium,DCF)是一种典型的PPCPs,作为一种消炎止痛类药物已被广泛使用,因其具有难生物降解和生物积累性的特点,故给生态环境和人类健康带来极大的威胁。常规的处理技术无法有效地去除DCF,传统的生物处理技术对DCF的去除率只能达到30%左右[1]。因此,亟需寻找一种新型有效的处理方法去除水中的DCF。
近年来,基于硫酸根自由基(
$ {\rm{SO}}_4^{ \cdot {\rm{ - }}}$ )的高级氧化技术受到研究者们的广泛关注[2-3]。与·OH相比,$ {\rm{SO}}_4^{ \cdot {\rm{ - }}}$ 具有氧化还原电位高、pH适用范围广及半衰期长等优点,有利于污染物的降解。过硫酸盐(persulfate,PS)可在紫外光、热、碱、过渡金属离子(Mn2+)和零价铁等活化下产生$ {\rm{SO}}_4^{ \cdot {\rm{ - }}}$ 。然而,不同的方法具有各自的优点和缺点,如:热活化不产生二次污染,但在使用过程中会消耗很多能量;过渡金属离子可以在室温下活化PS,但是易受溶液pH影响而产生沉淀。零价铁可以在室温下活化PS产生$ {\rm{SO}}_4^{ \cdot {\rm{ - }}}$ ,其主要反应如式(1)和式(2)所示。零价铁的化学性质活泼,在制备和存储的过程中与氧气接触,会形成氧化膜覆盖在零价铁表面,从而影响其在反应过程中的活性。为了解决零价铁钝化问题,研究者们提出了一些改进方法,如利用纳米零价铁[4]、酸洗[5]、制备零价铁双金属[6]和氢气还原等[7]。这些方法可以在一定程度上改善零价铁去除污染物的活性,但是在实际应用方便仍然会存在一定的问题,如增加使用的成本、操作复杂等。有关磁场效应影响零价铁去除污染物的研究是近几年来新兴的研究方向,受到了研究者的广泛关注。KIM等[8]研究发现,在零价铁降解4-氯酚的过程中加入磁场时,可以提高4-氯酚的去除效率。研究者认为磁场可以加速零价铁的腐蚀作用,并促进氧气扩散到零价铁的表面,使其相互作用生成·OH降解污染物。一些研究对磁场强化零价铁降解污染物进行了一系列的探讨,证明了在不同的反应体系中,磁场均可以促进零价铁的腐蚀和Fe2+的溶出,可以不同程度地提高污染物的降解速率[9-13]。综上所述,磁场可以明显改善零价铁的反应活性,且操作简单、成本低、无二次污染。因此,将磁场与其他污染物处理技术相结合具有非常广泛的应用前景。由于零价铁是铁磁性物质,在磁场中磁化后离开磁场仍能保持剩磁,具有“磁记忆性”。因此,本研究利用零价铁的磁记效应来提高其反应活性,以DCF为模型污染物,采用预磁化零价铁活化PS体系对DCF进行降解,考察了零价铁投加量、PS投加量、pH等因素对DCF降解的影响,并探讨了DCF的降解机理,为DCF实际废水的降解提供了科学依据。
预磁化零价铁活化过硫酸盐体系降解双氯芬酸钠
Degradation of diclofenac sodium by premagnetized zero-valent iron-catalyzed persulfate
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摘要: 双氯芬酸钠(diclofenac sodium,DCF)是一种常用的消炎止痛药,已在地下水、地表水和饮用水中被广泛检出,成为一种新型微量污染物,具有潜在危害,基于此,采用预磁化零价铁/过硫酸盐(Pre-Fe0/PS)和零价铁/过硫酸盐(Fe0/PS)2种体系对DCF进行降解。考察了过硫酸盐(PS)投加量、零价铁投加量、初始pH对2种体系降解DCF的影响,探究了2种体系中铁离子的产生情况和pH的变化,并利用ESR技术检测了体系中生成的自由基。结果表明,与Fe0/PS体系相比,在不同PS量(0.125~1.0 mmol·L−1)、Fe0量(0.125~1.0 mmol·L−1)和初始pH 3.0~10.0下,Pre-Fe0/PS体系对DCF的降解速率常数提高了2.1~6.2倍;Pre-Fe0/PS体系中会产生更多的铁离子,且在反应过程中pH下降更快;Pre-Fe0/PS体系比Fe0/PS体系产生更多的
$ {\rm{SO}}_4^{ \cdot {\rm{ - }}}$ 和·OH,且能在较长的时间保持较高的浓度。Pre-Fe0/PS体系降解DCF可以适用更宽的pH范围,是DCF废水处理的有效途径。Abstract: Diclofenac sodium (DCF), a commonly used anti-inflammatory painkiller, has been widely detected in groundwater, surface water and drinking water. As an emerging pollutant, it can cause potential hazards. Based on this, the pre-magnetized Fe0 (pre-Fe0/PS) and Fe0/PS systems were used to degrade DCF. The effects of influencing operational parameters, including initial PS dosage, Fe0 dosage and pH, on the DCF degradation were investigated. The iron ions yield and pH changes in the both of systems were determined, and the generation of free radicals was also studied by using ESR. The results showed that pre-Fe0/PS process had 2.1~6.2 folds higher rate constant than Fe0/PS process for DCF degradation at different PS dosages (0.125~1.0 mmol·L−1), Fe0 dosages (0.125~1.0 mmol·L−1) and initial pH (3.0~10.0). More iron ions were generated and faster drop in pH occurred in pre-Fe0/PS process. EPR confirmed that stronger signals of DMPO-OH and DMPO-${\rm{SO}}_4^{-} $ adduct illustrated more and faster$ {\rm{SO}}_4^{ \cdot {\rm{ - }}}$ and ·OH radicals produced in pre-Fe0/PS system than those of Pre-Fe0/PS system, and could keep relative high content for a long duration. The pre-Fe0/PS process presents wide pH range to degrade DCF, and it is a promising approach to remove DCF.-
Key words:
- pre-magnetization Fe0 /
- persulfate /
- diclofenac sodium /
- degradation mechanism
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