表面硼酸化零价铁的制备及其重金属去除性能研究

The application of zero-valent iron (ZVI) for the heavy metal removal has become the focus in the field of pollution control. However, the scale-up utilization of ZVI is limited by its low electron transfer efficiency and poor electron selectivity. Modification of the surface iron oxide is an effective strategy to enhance the activity of ZVI. Recently, we interestingly found that the removal percentage of Cr(VI) by borated-ZVI (B-ZVI) could increase by 113 times compared with non-borated-ZVI. However, the specific mechanism for the improved heavy metal removal efficiency is still not clear. Therefore, the objectives of this project are to prepare different kinds of borated-ZVI, and characterize their structure and morphology systematically. Then Cr(VI) and Ni(II) are selected as the model contaminants to investigate the interaction between heavy metal and B-ZVI by monitoring the concentration and species variation of heavy metal, iron and boron. Meanwhile, with the help of theoretical calculation and modern characterization methods, we aim to reveal the effect of boron on the electron selectivity and surface coordination microstructure of ZVI. This project will provide theory guidance for the rational design of ZVI with high performance for environmental heavy metal remediation.

利用零价铁治理环境重金属污染是污染控制领域的研究热点，但零价铁大规模应用面临着电子传递效率低和选择性差的瓶颈问题。零价铁表面改性是突破这两个瓶颈问题的有效策略。我们最近发现，表面硼酸化能将零价铁去除六价铬的速率提高113倍，但尚不明确表面硼酸化零价铁高效去除重金属离子的内在机制。因此，本项目旨在制备不同表面硼酸化零价铁，系统表征表面硼酸化零价铁的结构与形貌，选取Cr(VI)与Ni(II)为模型污染物，通过监测表面硼酸化零价铁去除重金属过程中重金属、铁、硼等物种浓度与形态变化，考察重金属与表面硼酸化零价铁相互作用过程，同时借助理论计算与现代化表征手段，揭示硼酸对零价铁电子选择性以及表面配位微结构影响的内在机制，为进一步发展高效零价铁环境重金属治理技术提供理论指导。

尽管零价铁技术在治理环境重金属污染领域表现出巨大优势，但其大规模应用面临着电子传递效率低和选择性差的瓶颈问题。零价铁表面改性是突破这两个瓶颈问题的有效策略。在本项目中，我们对比了液相还原法、浸渍法、机械球磨法等零价铁表面硼酸化方法，系统表征了表面硼酸化零价铁的结构与形貌，考察了硼酸化零价铁去除水中重金属离子(Cr(VI)、Ni(II)、Cu(II))的性能，同时借助理论计算，阐明了表面硼酸化增强零价铁去除Cr(VI)、Ni(II)、Cu(II)的机制。具体研究结果如下：①硼酸表面修饰可改变零价铁表面等电点，增加Cr(VI)的吸附；同时硼元素空的p轨道可促使壳层铁原子与氧原子周围电子云发生离域，进而促使零价铁内部铁核电子向外传输，提升Cr(VI)的还原。此外，零价铁表面硼酸化还可增强吸附与还原途径去除Ni(II)。②与液相还原法与浸渍法相比，机械球磨改性方法在零价铁去除水中Cu(II)方面具有更优异的性能。通过密度泛函理论计算发现表面硼酸的存在可抑制氧气分子的吸附，进而减弱零价铁电子的无效利用，增强界面单电子传输途径，提升还原产物Cu(I)的占比。③通过比较外加硼单质、氧化硼、硼酸等不同形态含硼物质对零价铁去除六价铬性能的影响，发现仅有单质硼具有直接增强零价铁去除六价铬的性能。该增强性能主要依赖于硼单质可作为电子供给体，促进零价铁腐蚀过程的铁循环，进而提升二价铁还原六价铬的途径。本项目的研究结果为进一步发展高效零价铁环境重金属治理技术提供了理论指导。