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随着世界人口的不断增加和经济发展需求的攀升,世界上越来越多的地区出现了缺水的现象[1]。2020年,全球超过20亿人生活在水资源紧张的国家,无法获得安全的饮用水,到2050年全球将有50亿人面临水资源短缺问题[2]。我国水资源总量虽然大,但我国人口众多,且水资源分布不平衡,导致我国约1/4的省份面临严重缺水问题。我国也是水资源污染严重的国家之一。中国的污废水排放量极大,2019年全国污水排放量554.65亿立方米,同比增长6.4%[3]。水污染加剧和水资源减少已成为制约经济社会发展的瓶颈,亟须发展水污染治理的新原理和新技术。
纳米材料与技术为高效、低成本的水环境中污染物去除开辟了新的途径[4],其在吸附[5-6]、催化[7-8]、氧化还原处理[9-11]和膜分离[12-14]方面的应用越来越多。纳米科技将对开发更清洁、更环保的水处理技术产生重大影响,如何基于纳米材料开发更高效的水处理技术是环境领域的热点问题[15]。与微米级或更大粒径的材料相比,纳米材料由于其具有较高的比表面积在吸附工艺中表现出卓越的水处理能力[16],如黏土[17]、沸石[18]、金属氧化物[19-20]、聚合膜[21-22]、多孔纳米纤维[23-24]和零价铁[25-26]等吸附材料在对重金属离子、有机物、染料和病原体等常见污染物的吸附过程中表现出了反应速度快、选择性高和去除能力强等优势[27-28]。尽管基础研究成果众多,但是纳米材料的工程化应用仍存在技术瓶颈,如何提高纳米材料的分散性、稳定性和安全性是纳米材料大规模应用的基础和前提[29-31]。
大量研究表明,将纳米材料负载在合适的基体材料上是解决上述问题的有效方法之一[32-33]。选用合适的基体物质可以将具有反应活性的纳米材料分隔在离散但接近的空间内,基体材料的选择性通道可以提供隐蔽的环境,不仅可以使分子扩散得到良好的控制,还能使纳米材料不受其他反应成分的干扰而保持活性[34-36]。用磁性物质作基体可以使得材料在磁场作用下快速从水介质中分离[37],与传统的过滤法相比,操作过程简单,且不容易引起堵塞或材料的流失[38]。限域空间内生长的纳米材料还显示出了优越的目标污染物净化功能[39-40]。本文综述了空间限域型纳米复合材料的合成方法,阐述了由多孔材料构成的限域空间内活性纳米颗粒尺寸、污染物富集对吸附过程的影响,总结了限域空间内物质分子微观结构和晶型等纳米材料表面特性,从分子水平揭示孔材料限域空间对吸附剂吸附性能、吸附反应过程、反应产物和吸附剂再生性能的作用机制,最后对空间限域型纳米复合材料在水处理领域的应用前景进行了展望,以期为纳米吸附剂制备、吸附过程的理论模拟、吸附剂和吸附作用的原位动态表征和纳米吸附剂的水处理应用等方面提供理论指导和技术支撑。
限域结构纳米复合材料及其吸附性能研究进展
Research progress of confined space-constructed environment nanocomposites and their adsorption properties
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摘要: 纳米材料因其比表面积大和表面活性高,在水处理领域表现出了极具潜力的发展前景。利用空间限域结构来固定和分散纳米材料可有效解决纳米材料易团聚失活、操作分离困难和潜在环境风险等问题。文章综述了具有限域结构的纳米复合材料制备方法及其对水中污染物吸附性能的研究进展,从限域空间内纳米颗粒的尺寸调控与污染物的富集、限域空间中特异性的污染物分子结构和纳米材料晶体结构等多方面详细分析了纳米限域效应的环境行为及其对水环境中污染物去除的重要意义。根据分析可知,限域结构中的吸附机理、纳米复合材料在真实环境体系下的应用、材料的环境与健康风险等是未来该领域研究的重要方向和热点内容。Abstract: Nanomaterials show a great potential in the field of water treatment due to their large specific surface area and high surface activity. The use of spatially confined structures to fix and disperse nanomaterials can effectively solve the problems of easy agglomeration and deactivation of nanomaterials, difficulty in operation and separation, and potential environmental risks. In this paper, the preparation methods of nanocomposites with confined structures and their research progress on the adsorption performance of pollutants in water are reviewed. The environmental behavior of the nanoconfinement effect and its significance to the removal of water pollutants are analyzed in detail from several aspects, including the specific molecular structure of pollutants and crystal structures of nanomaterials in the confined space. The adsorption mechanism in the confined space, application of the confined structure nanocomposites in real environmental systems, and the environmental and health risks of materials are the key directions and hot topics of future research in this field.
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表 1 各合成方法的适用条件和优缺点
Table 1. Applicable conditions, advantages and disadvantages of each synthesis method
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