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基于有机金属框架、磁性Fe3O4及半胱氨酸的新型杂化纳米材料用于高效吸附Hg2+2020-04-27

重金属不可生物降解且易在环境中积累,会对环境造成严重污染。同时,重金属离子可以通过食物链进入人体,导致不同种类的疾病。在许多重金属离子中,Hg2+,Cd2+的毒性更大。因此,去除废水中的Hg2+和Cd2+非常重要。表面吸附技术是最普遍、使用最广泛的重金属脱除技术,具有环保、成本低、操作简便、可再生等优点。最近,纳米技术正在应用于吸附法,以提高其去除重金属离子的效率。

沸石咪唑酯骨架结构材料“(ZIFs)是多孔晶体材料,在其中,有机咪唑酯交联连接到过渡金属上,形成一种四面体框架。这种笼状结构可选择性地高效捕获和存储客体分子。Fe3O4作为一种磁性纳米粒,可利用外加磁场实现吸附材料的有效分离。此外,半胱氨酸的巯基可可与Hg2+高效螯合,实现对Hg2+有效的抓取。基于这些特性,中科院宁波材料所的吴爱国研究员及张玉杰副研究员提出利用Fe3O4纳米粒表面修饰聚丙烯酸(PAA)后与ZIF-90通过自组装形成核壳结构纳米粒,合成过程如Scheme 1所示。引入聚丙烯酸的目的主要有:阻止Fe3O4纳米粒聚集、利用PAA的羧基与ZIF-90中的Zn2+相互作用稳定纳米粒。随后利用亚胺键引入半胱氨酸,构建可高效吸附Hg2+的新型杂化纳米材料Fe3O4@ZIF-90-Cysteine。

Scheme 1. 新型杂化纳米吸附材料Fe3O4@ZIF-90-Cysteine的制备过程

新型杂化磁性材料Fe3O4@ZIF-90-Cysteine各组分之间的协同效应使其对于Hg2+的吸附能力可达到900 mg/g。XPS结果表明吸附机理主要基于巯基与Hg2+之间的弱酸-弱碱相互作用。此外,Fe3O4@ZIF-90-Cysteine对于Pb2+和Cd2+同样具有一定的吸附效果。这种新型杂化吸附剂具有以下优点:1)制备简单,可通过一锅煮的方法高效制备;2)Fe3O4@ZIF-90-Cysteine具有很好的Hg2+吸附能力;3)利用外加磁场,可实现磁性杂化吸附材料的快速分离;4)吸附机制是利用巯基与Hg2+间的弱相互作用实现对于Hg2+的抓取;5)多次使用后(3次)吸附效率仍能保持70%。
    该研究发表在Journal of Hazardous Materials,Available online 12 February 2020, 122288。https://doi.org/10.1016/j.jhazmat.2020.122288。

 

TitleA novel hybrid nanoadsorbent for effective Hg2+adsorption based on zeoliticimidazolate framework (ZIF-90) assembled onto polyacrylic acid capped Fe3O4 nanoparticles and cysteine

Abstract

This research reports a newmercury adsorbent in which Fe3O4 as a core wasembedded into the shell of ZIF-90 in a one-pot synthesis and the subsequent postsynthesis modification (PSM) of its surface with cysteine covalently, via aSchiff’s base reaction. Poly acrylic acid (PAA) was capped on the surface ofnanoparticles to prevent agglomeration of the nanoparticles. In addition, -COOHgroups of PAA coordinated with Zn2+ of ZIF-90 and this providedthe platform for ZIF-90 to grow on the nanoparticles forming the core-shellstructure. Based on the strong interactions between the thiol groups on theadsorbent and mercury ions as elucidated by the XPS analysis, theas-synthesized adsorbent showed selectivity for Hg2+. The sorbentexhibited high adsorption capacity of 900mgg-1 towards Hg2+ as calculated at pH 4and the adsorption kinetics followed pseudo-second-order kinetics model better.The Hg2+ loaded adsorbent was easily regenerated and itmaintained about 70% efficiency after the third use. Low-cost, readilyavailable and green materials, facile preparation, efficient removal and thebreakthrough in three times recyclability give the novel ZIF-90 based hybridnanoadsorbent wide prospects in the field of environmental remediation as agood adsorbent for Hg2+ removal in wastewater.

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