纳米零价铁优化体系及其在环境中的应用研究进展

Nanoscale Zero Valent Iron-based Optimization System and Their Application in Environmental Remediation: a Review

零价铁材料作为近年来受到广泛关注和研究的环境原位修复介质,主要得益于自身的一些优势:(1)原料价廉易得,铁在自然界中广泛存在,含量占地壳元素的4.75%,丰富的储存量有利于降低其使用成本;(2)铁化学性质活泼,还原电势高,能与多种污染物发生反应,将其转化到无毒或低毒状态;(3)铁是一种环境友好的修复介质,不易造成二次污染等问题。此外,铁材料还具有较强的磁性,有利于分离回收。然而普通的零价铁颗粒比表面积相对较小,在一定程度上会影响零价铁的使用效果,尤其是去除速率较慢,同时较大的尺寸也使得零价铁材料不适用于土壤修复等对材料渗透性有一定要求的应用环境。为解决这一问题,纳米零价铁材料成为研究热点,其极大的比表面积可使材料反应速率提高到普通铁粉的10～100倍,反应活性极佳,且其颗粒粒径小、渗透性和流动性强,可通过注射的方式进入到地下污染体系中,能实现对土壤和地下水的污染修复,在各种污染环境的原位修复中有着广阔的应用前景。纳米零价铁的制备方法较多,主要可分为物理法(高能机械球磨法、物理气相冷凝法、溅射法和等离子体法等)和化学法(液相化学还原法、固相化学还原法、溶剂热法、气相化学反应法、电沉积法等)两大类。然而纳米零价铁材料性质过于活泼、表面能量高,且磁性较强又会导致其在使用中发生团聚、钝化等问题,严重降低电子效率,限制能效的充分发挥和使用寿命。为此,在纳米零价铁材料基础上进行优化改性是该领域的目前主要发展方向。本文将目前最常见的纳米零价铁优化体系归纳为三类:(1)纳米零价铁稳定化体系,又包括物理负载稳定化和表面化学改性稳定化两种;(2)纳米零价铁包埋体系,其中以生物材料固定化包埋最为常见;(3)纳米零价铁复合体系,例如铁/碳复合纳米材料、纳米双金属复合材料等。本文总结了各体系的特点和相应的制备技术,重点阐述了纳米零价铁优化体系在重金属、有机氯等污染环境中的最新应用进展,揭示了其修复机理和影响能效的因素。进一步提高纳米零价铁优化体系的使用效率、延长使用寿命、降低成本以及拓宽其应用领域,将是该领域未来的主要研究目标。

In recent years,zero-valent iron(ZVI)materials,as environmental in situ restoration agents,have received extensive attention and research.The superiority of ZVI materials can be concluded by the following aspects.Ⅰ.The raw material of ZVI iron,is cheap and easy to obtain,which is one of the most abundant elements in nature,accounting for 4.75%of the crustal elements,and the rich storage of iron is beneficial to reduce the cost of production.Ⅱ.Iron is active in chemistry and feature high reduction potential,which can react with diverse pollutants and convert them into non-toxic or low-toxic state.Ⅲ.Iron is a kind of environmental benign restoration agent,reducing the risk of secondary pollution.In addition,magnetic iron-based materials are in favor of recycling.Nevertheless,ordinary ZVI particles are not efficient in all cases because of their relatively small specific surface area,especially the large particle size of ZVI blocked its application in special environments(most part of underground water or unconsolidated aquifers)that requires the permeability of restoration agent.For the sake of making better use of ZVI,nanoscale zero valent iron(nZVI or nFe 0)is designed.Thanks to the large specific surface area,nZVI exhibits outstanding reactivity,10-100 times of that of ordinary ZVI,the small particle size,strong permeability and fluidity enables nZVI to directly inject into the underground pollution system,thus the remediation of soil and groundwater pollution can be realized.Therefore,nZVI possesses a broad prospect of application in the in-situ remediation of diverse polluted environments.There are many preparation approaches of nZVI,which can be divided into physical method(high-energy mechanical ball milling,physical vapor condensation,sputtering and plasma methods)and chemical method(liquid-phase chemical reduction,solid-phase chemical reduction,solvothermal,gas chemical reaction,electrodeposition methods,etc.).However,the excessive activity,high surface energy,nano size and strong magnetism of the nZVI will bring about the problems of agglomeration and fast surface passivation,which dramatically reduce the electronic efficiency,limit their function and shorten the life-time.Therefore,various kinds of nZVI-based nanocomposites have been developed to avoid these deficiencies.This paper reviews the recent modification technologies on nZVI,and classifies these nZVI-based nanocomposties into three categories:stabilized nZVI system(include physical load stabilization and surface chemical modification stabilization),immobilized nZVI system(the immobilization of biomaterials is most popular)and nZVI nanohybrids(such as iron/carbon nanocomposites,nano-bimetallic composites,etc.).The characteristics of each system and the corresponding preparation techniques are summarized,emphasis is put on their application in heavy metal and chlorine-containing organic polluted environment remediation,as well as remediation mechanism and influencing factors.It also suggests that the future research should be focused on further improvement of the efficiency,extending their lifespan,reducing economic cost,and enlarging the scope of application.