【作者】 陈志；

【导师】 俞书宏；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2022， 博士

【摘要】 金属-有机骨架(MOFs)是一类新兴的多孔有机-无机复合晶体,相比其他传统多孔材料具备独特的竞争优势,如极高的孔隙率、极大的比表面积、可调节的孔径、多样性拓扑结构等,在多相催化、气体储存与分离、化学传感、药物运输、环境净化等方面显示出广泛的应用前景。MOFs宏观上多为微晶粉末,具有本征脆性、不溶性、成型困难等问题,使得其难以加工成宏观组装体材料,而这限制了进一步商业化应用。此外,不同微纳尺度的组织形式也会影响性能。基于此,本文着眼于MOFs宏观组装体材料的制备及性能研究,首先概述了 MOFs的发展历史及结构性能特征,接着总结了 MOFs二维、三维宏观组装方法及应用研究。随后,针对MOFs宏观组装手段不足、工艺粗糙、缺乏多级精细结构调控的现状,本论文发展了系列简单、高效、宏量的喷涂再结晶、原位生长和取向冷冻铸造等MOFs多尺度宏观组装方法,开发了一系列的新型MOFs宏观组装体材料,探究其在电子器件、环境净化、催化等方面的应用。取得的主要研究成果如下:1.发展了一种简便、快速且经济高效的制备方法,获得厚度可控(44～5100纳米)、尺寸较大(60×80平方厘米)、致密连续的高质量MOFs二维宏观薄膜。本工作首次制备了分散均匀的非晶MOFs前驱体溶胶;该前驱体溶胶具有优异的流变性能及良好的粘性,能够通过简单喷涂的方式,在多种基底(如氟掺杂的氧化锡(FTO)、玻璃、二氧化硅、氧化铝、硅片、铜片甚至柔性聚碳酸酯等)上形成连续涂层;通过加热连续涂层能原位转化为致密均匀的高质量MOFs薄膜。作为展示,本工作进一步报道了沉积在FTO基底上的具有良好热稳定性(300摄氏度)的MOFs晶体薄膜,并以之组装了具有高介电常数的电子器件。这种粘性无定型前驱体溶胶的通用性和可规模化特性,拓宽了金属有机框架的应用范围,预示其在电子器件、气体分离、电池隔膜等领域的工业化应用。2.发展了一种简便、可规模化生产的原位制备策略,获得了大尺寸(60×40平方厘米)的MOFs@密胺海绵三维宏观组装体材料。本工作通过将海绵基底修饰诱导MOFs原位生长和前驱体溶胶在海绵骨架上原位沉积转化这两种方法,在海绵骨架表面制备了均匀、致密的MOFs涂层。通过调控表面活性剂种类、反应物配比、多次生长等方法实现了优化的包覆效果和材料性能,获得的c-ZIF-67@海绵可以在1000毫升每分钟的高通量气体流速下实现对PM2.5高达95.9%的单次过滤效率(空白海绵仅为25.8%),过滤阻力与空白海绵相比几乎一致(低于25帕)。本工作通过发展新型的简单、高效、宏量的MOFs涂覆方法,显著提高了廉价商用海绵的综合过滤性能,为解决包括PM2.5在内的常见空气污染问题提供了新思路。3.发展了一种高效、可拓展的取向冷冻铸造组装方法,获得了具有多级孔结构的MOFs三维宏观组装体材料。本工作通过将MOFs与羧甲基纤维素混合悬浮液单向冷冻制备出具有多级孔结构的MOFs三维宏观组装体材料,多级孔结构包括石英毛细管形成的毫米级大孔、取向冷冻获得的微米级孔道和纳米级MOFs框架孔道,这种孔道有利于富集反应物和暴露反应活性位点。作为展示,我们以掺铜ZIF-8为前驱体,热解后可获得具有多级孔结构的三维二氧化碳还原电催化剂。它以Cu单原子和Cu纳米颗粒为活性物质,在49.3毫安每平方厘米的电流密度下将CO2转化为乙醇的法拉第效率接近27.8%。此外,制备出的具有多级孔结构的轻质高强MOFs/海藻酸盐宏观组装体可实现水污染处理,对低浓度甲基橙的过滤效率可达到95%。通过这种跨尺度多级孔道结构设计,MOFs的结构和性能优势得以充分发挥,为MOFs在包括催化和污水净化等多个领域提供了新思路。更多还原

【Abstract】 Metal organic frameworks(MOFs)are an emerging class of porous organic inorganic composite crystals with unique competitive advantages over other traditional porous materials,including extremely high porosity,ultrahigh specific surface areas,adjustable pore size,and diverse topology.MOFs exhibit important potential to enable disruptive technologies in application such as heterogeneous catalysis,gas storage and separation,chemical sensing,drug transport and environmental purification.MOFs are mostly macroscopically microcrystalline powders with intrinsic brittleness,insolubility,and molding difficulties,making them difficult to process into macroscopic assembled materials,and this limits further commercial applications.In addition,the organization form will also influence the performance.Based on this,this paper focuses on the preparation and performance study of MOFs macro-assembled materials.We firstly overviewed the development history,performance characteristics and synthesis methods of MOFs.Then,two-dimensional and three-dimensional macroscopic assembly methods and application studies of MOFs are summarized.In response to the current situation of insufficient means of MOFs macro-assembly,rough process and lack of multi-level fine structure regulation,this thesis develops a series of simple,efficient and macroscale macro-assembly methods of MOFs such as spray recrystallization,in situ growth and orientation freeze casting,develops a series of novel MOFs macro-assemblies materials and explores their applications in electronic devices,environmental purification,catalysis,etc.The main research results obtained are as follows:1.A facile,rapid and cost-effective preparation method is developed to obtain high-quality MOFs films with controllable thickness(44～5100 nm),large size(60×80 cm2),and continuous coating.This work is the first time to report a perfectly dispersed colloidal solution composed of amorphous MOFs precursor sols.The precursor sols are viscous and can be easily sprayed onto various substrates to form a continuous coating,such as fluorine-doped tin oxide(FTO),Glass,Silicon wafer,Silica,Alumina,Copper sheet,and even flexible polycarbonate.The continuous coating can be in-situ converted into dense and uniform high-quality MOFs thin films by heating.The MOFs films deposited on the FTO substrate have good thermal stability,and the electronic devices assembled from them have high dielectric constant.The versatility and scalability of this viscous amorphous precursor sol broaden the application range of MOFs and predict disruptive technologies of industrial application in the fields of electronic devices,gas separation,battery separator and so on.2.A facile and scalable in-situ fabrication strategy was developed to obtain largescale(60 × 40 cm2)MOFs@melamine sponge 3D macroscopic assemblies.In this work,a uniform and dense coating of MOFs was prepared on the surface of the sponge skeleton by two methods:in situ growth of MOFs induced by modification of the sponge substrate and in situ deposition and transformation of the precursor on the sponge skeleton.The optimized coating effect and material properties were achieved by adjusting the types of surfactants,the ratio of reactants,and multiple growths.It achieves a single filtration efficiency of up to 95.9%for PM2.5(the single filtration efficiency of bare sponge is only 25.8%),while the filtration resistance is almost the same as bare sponge(less than 25 Pa).Aiming to solve air pollution problems like PM2.5,multifunctional MOFs combined with cheap sponges endow great potential in the control of residential and industrial environments.3.An efficient and expandable assembly method of directed freeze casting was developed to obtain 3D macro assemblies of MOFs with hierarchic pore structure,including millimeter scale macropores formed by quartz capillary,micron scale pores obtained by directed freezing and nano scale MOFs framework pores,which is beneficial to enrich reactants and exposing reactive sites.As a demonstration,we use copper doped ZIF-8 as the precursor,pyrolyzed to acquire a 3D carbon dioxide reduction electrocatalyst with hierarchic pore structure.With copper singe atom and nanoparticles as active sites,the Faraday efficiency of CO2 to ethanol is close to 27.8%at current density of 49.7 mA/cm2.In addition,the prepared light-weight and highstrength MOFs/Alginate 3D macro assemblies can realize water pollution treatment,and the filtration efficiency of low concentration methyl orange can reach 95%Through this cross-scale hierarchic pore structure design,the performance advantages of MOFs can be brought into full play,providing new ideas for MOFs in many fields such as catalysis and environmental purification.更多还原