金属有机骨架材料在吸附分离大气污染物中的应用

大气污染问题是关系人民生命健康和经济社会和谐发展的重大问题。因此需要开发高效的吸附材料用于大气污染物的吸附和分离。金属有机骨架材料(MOFs)是一类新型的多孔材料,该材料具有结构多样、孔结构有序、大比表面积和高孔隙率等结构特点。MOFs通过调节有机配体的长度和官能团调节孔径和孔道尺寸,并进行功能化修饰在孔道中引入功能性位点来提高吸附性能和吸附选择性,从而表现出很好的结构稳定性、热稳定性、酸碱稳定性、可回收使用性及再生性等优势,在大气污染物的吸附中表现出优秀的吸附/分离性能。本文综述了以SO₂,NO₂,CO,VOCs等大气污染物的吸附去除为目标的MOFs材料,并对未来研究方向和研究前景进行展望。     

全氟酰基合成后修饰UiO-66用于吸附有机污染物（英文）

以三氟乙酰基和五氟丙酰基为修饰官能团,通过合成后修饰(PSM)的方法对金属-有机骨架(MOFs)改性,得到疏水骨架材料(UiO-66-F1和UiO-66-F2)。2个骨架材料均显示出亲油性,这说明它们是油性溶剂潜在的吸附材料。修饰后MOFs材料的结晶性、稳定性和多孔性较UiO-66-NH2仅有微小降低。UiO-66-F1和Ui O-66-F2的Brunauer-Emmett-Teller (BET)比表面积分别为810和610 m2·g-1。骨架材料因其合适的孔大小和疏水微环境,更容易吸附水中的有机污染物。此外,改性后材料对多种有机溶剂的吸附量显著提升,在经过10次的循环吸附后吸附量没有明显降低,具有出色的循环稳定性。     

多孔高分子材料对二氧化碳的捕获与转化

在温和的条件下,运用化学技术进行有效的碳捕获和碳转换是减少人为CO_2排放的重要途径。近年来,多孔有机聚合物(Porous organic polymers,POPs)由于其优异的CO_2吸附性能,被视为最具潜力的CO_2捕获材料而引起了广泛的关注。本文介绍了4种POPs的最新研究进展,包括金属有机骨架材料(Metalorganic frameworks,MOFs)、沸石咪唑酯骨架材料(Zeolitic Imidazolate Frameworks,ZIFs)、共轭微孔聚合物(Conjugated microporous polymers,CMPs)、共价有机骨架材料(Covalent organic frameworks,COFs),并对MOFs和CMPs作为催化剂和吸附剂在室温条件下CO_2的捕获与转化过程的相关实验研究工作进行了综述。     

金属有机框架材料的制备及在吸附分离CO_2中的应用

金属有机框架(MOFs)材料是当今的研究热点之一,是一类颇有潜力成为适用于CO2吸附和分离的重要材料。本文从MOFs的发展及其所具有的特点、MOFs用于CO2的吸附与分离所取得的突破性进展以及MOFs的传统合成及绿色制备方法三个方面展开论述。主要论述了MOFs适用于CO2吸附的原理,及其相对于传统的CO2吸附材料所具有的特点和优势,亦阐述了MOFs修饰与调变的方法。列出了MOFs用于单组分CO2吸附及CO2/CH4、CO2/N2吸附分离的结果。同时,针对传统MOFs制备方法不适宜大规模CO2捕集材料的生产,特别论述了机械化学合成法和新兴的潮湿矿物风化法,其均具有绿色化、无溶剂、低能耗和简单等特点,是一类较有研究价值和应用潜力的技术。随着温室效应和不可再生石化燃料的消耗等环境和能源问题的日趋严峻,研究及开发适用于CO2捕集与封存技术的MOFs新材料迫在眉睫,且任重而道远。     

蒸气辅助合成PCN-6(M)双金属有机框架材料及其CH_(4)和CO_(2)吸附性能北大核心CSCD

以PCN-6(Cu_(3)TATB_(2))为母体材料,Co、Fe、Mn、Zn和Ni为第2种金属,将蒸气辅助法应用于双金属有机框架材料(MOFs)的合成中,并成功制备出PCN-6(M)(M=Co/Fe/Mn/Zn/Ni)系列双金属材料,采用粉末X射线衍射仪(PXRD)、扫描电子显微镜(SEM)、能谱仪(EDS)、电感耦合等离子发射光谱仪(ICP-OES)和气体吸附等技术手段对合成的材料进行了结构、形貌、组成和性能的表征,结果表明制备的PCN-6(M)系列双金属材料的PXRD衍射峰和形貌与母体材料PCN-6一致,交换的金属在材料中分布均匀,交换量(质量分数)分别为Co:12.1%,Fe:22.0%,Mn:16.1%,Zn:17.5%,Ni:16.8%,远高于相同条件下溶剂热法的金属交换量(5%左右),在气体吸附性能方面,PCN-6(Zn)、PCN-6(Ni)和PCN-6(Co)这3种双金属材料对CH_(4)和CO_(2)的吸附能力优于母体材料,理想吸附溶液理论(IAST)计算表明,PCN-6(Fe)对CO_(2)/CH_(4)的吸附选择性优于母体材料。通过蒸气辅助法制备双金属MOFs材料,可以提高金属的交换量并改变MOFs材料对不同气体分子的亲合力,进而提高材料对气体的吸附性能和选择性。蒸气辅助法为双金属MOFs材料的制备提供了新的思路,且有望用应于其它材料的制备中。     

金属有机框架(MOFs)基光催化剂的设计及其在太阳能燃料生产和污染物降解领域的研究进展（英文）

金属有机骨架(MOFs)具有较高的比表面积,丰富的金属/有机物种,较大的孔体积以及结构和成分可调节的特性,因此在太阳能燃料生产和污染物的光降解领域具有广泛的应用.根据其结构特点,研究者们主要从有机配体和孔道结构两方面对MOFs进行调控:(1)对有机配体进行修饰,如将杂原子、羟基、卤素原子、金属离子、生物大分子等引入MOFs结构;(2)将无机纳米粒子引入MOFs孔道内,如将贵金属、金属氧化物、多金属氧酸盐等纳米粒子封装在MOFs的孔道内.这些策略可有效增强MOFs的导电性、稳定性等,并进一步提高MOFs基催化剂的光催化性能.本文首先概述了四种经典MOFs类型,即UiO, ZIF, MIL和PCN系列的结构特点和催化性能.其次,总结了在设计MOFs基光催化材料过程中,根据不同类型MOFs特点着重考虑的五方面因素,即稳定性、能带结构、吸附作用、选择性和电导性.再次,讨论了提高MOFs基光催化剂活性的策略,如助催化剂修饰、构建异质结、配体或金属中心修饰和缺陷工程.最后,总结了MOFs基光催化材料在催化还原CO_2、分解水制氢和降解有机污染物反应中的应用进展及影响其催化性能的主要因素.尽管MOFs基光催化材料研究已经取得了令人瞩目的进展,但对MOFs基光催化剂进行可控设计制备仍然存在挑战.如何实现纳米MOFs基光催化材料的制备与规模化生产、可调缺陷MOFs基光催化材料的精准设计、开发高稳定性的MOFs基光催化材料等仍需进一步探索.因此,未来需要从MOFs的纳米化合成、复合材料界面结构的精准调控、催化活性机制与稳定性关系等方面对MOFs基光催化材料进行深入的研究.     

功能化金属有机骨架材料去除饮用水污染物的研究进展

金属有机骨架(MOFs)材料是一类以过渡金属为中心、含杂原子的有机物为配体、通过配位作用形成的周期性网络多孔晶体材料。与其他的多孔材料相比,MOFs配体种类繁多,比表面积极大,孔径大小可调控且具有特殊(饱和或不饱和)的金属位点,在气体存储、催化、吸附与分离等领域有广阔的应用前景。近年来,功能化MOFs对污染物的富集和去除成为学者关注的热点。这是由于通过对MOFs进行功能化修饰,能够改变MOFs的孔径大小、表面带电性质等物化性质,从而实现对目标物更高效的吸附。该文综述了近年来功能化MOFs对饮用水污染物吸附的研究进展,包括饮用水污染物的类型及危害、功能化MOFs的制备方法以及去除饮用水污染物的应用,并对今后的发展前景进行了展望。     

氨基修饰的金属有机框架Cu_3(BTC)_2的制备及其CO_2吸附性能研究

首先制备了嫁接氨基的均苯三甲酸,同时以其为原料通过溶剂热法合成了金属有机框架材料Cu_3(NH_2BTC)_2,利用XRD、N_2吸附-脱附、热重、红外、原位红外分析等表征手段对吸附剂进行了表征,并通过固定床测量穿透曲线的方法研究其CO_2吸附性能。结果表明,氨基被成功引入Cu_3(BTC)_2骨架中。氨基修饰的Cu_3(BTC)_2对CO_2有着较高的吸附容量,在10 kPa,50℃的条件下CO_2吸附量为1.41 mmol/g,这源于材料对于CO_2同时存在着物理吸附和化学吸附。     

全氟酰基合成后修饰UiO-66用于吸附有机污染物

以三氟乙酰基和五氟丙酰基为修饰官能团，通过合成后修饰（PSM）的方法对金属-有机骨架（MOFs）改性，得到疏水骨架材料（UiO-66-F1和UiO-66-F2）。2个骨架材料均显示出亲油性，这说明它们是油性溶剂潜在的吸附材料。修饰后MOFs材料的结晶性、稳定性和多孔性较UiO-66-NH₂仅有微小降低。UiO-66-F1和UiO-66-F2的Brunauer-Emmett-Teller（BET）比表面积分别为810和610 m²·g^-1。骨架材料因其合适的孔大小和疏水微环境，更容易吸附水中的有机污染物。此外，改性后材料对多种有机溶剂的吸附量显著提升，在经过10次的循环吸附后吸附量没有明显降低，具有出色的循环稳定性。     

离子液体功能化金属有机骨架材料催化CO2环加成反应研究进展

金属有机骨架(Metal-organic frameworks, MOFs)材料因具有超大比表面积、可修饰的化学结构、可调的孔隙形状和大小、开放的金属位点等独特的结构优越性而被广泛用于催化CO₂环加成反应的研究中。然而,大部分MOFs材料在此反应中往往需要在助催化剂或溶剂的存在下才能发挥其催化性能,这也导致了产物分离困难、资源浪费等问题。因此,开发能够单独催化CO₂环加成反应的MOFs材料成为当前科学家们研究的热点。在MOFs骨架上或孔腔内修饰离子液体是构筑此类催化体系的一种重要途径。本文对近年来这类MOFs的构筑策略、催化CO₂环加成反应的性能以及催化机理进行了总结,同时还对MOFs组成、形貌以及催化反应条件等因素对催化活性的影响进行了探讨。     

Revealing the Structure-Property Relationships of Metal-Organic Frameworks for CO(2) Capture from Flue Gas

It is of great importance to establish a quantitative structure-property relationship model that can correlate the separation performance of MOFs to their physicochemical features. In complement to the existing studies that screened the separation performance of MOFs from the adsorption selectivity calculated at infinite dilution, this work aims to build a QSPR model that can account for the CO(2)/N(2) mixture (15:85) selectivity of an extended series of MOFs with a very large chemical and topological diversity under industrial pressure condition. It was highlighted that the selectivity for this mixture under such conditions is dominated by the interplay of the difference of the isosteric heats of adsorption between the two gases and the porosity of the MOF adsorbents. On the basis of the interplay map of both factors that impact the adsorption selectivity, strategies were proposed to efficiently enhance the separation selectivity of MOFs for CO(2) capture from flue gas. As a typical illustration, it thus leads us to tune a new MOF with outstanding separation performance that will orientate the synthesis effort to be deployed.     

Progress in adsorption-based CO2 capture by metal-organic frameworks

Metal-organic frameworks (MOFs) have recently attracted intense research interest because of their permanent porous structures, large surface areas, and potential applications as novel adsorbents. The recent progress in adsorption-based CO(2) capture by MOFs is reviewed and summarized in this critical review. CO(2) adsorption in MOFs has been divided into two sections, adsorption at high pressures and selective adsorption at approximate atmospheric pressures. Keys to CO(2) adsorption in MOFs at high pressures and low pressures are summarized to be pore volumes of MOFs, and heats of adsorption, respectively. Many MOFs have high CO(2) selectivities over N(2) and CH(4). Water effects on CO(2) adsorption in MOFs are presented and compared with benchmark zeolites. In addition, strategies appeared in the literature to enhance CO(2) adsorption capacities and/or selectivities in MOFs have been summarized into three main categories, catenation and interpenetration, chemical bonding enhancement, and electrostatic force involvement. Besides the advantages, two main challenges of using MOFs in CO(2) capture, the cost of synthesis and the stability toward water vapor, have been analyzed and possible solutions and path forward have been proposed to address the two challenges as well (150 references).     

Development and evaluation of porous materials for carbon dioxide separation and capture

The development of new microporous materials for adsorption separation processes is a rapidly growing field because of potential applications such as carbon capture and sequestration (CCS) and purification of clean-burning natural gas. In particular, new metal-organic frameworks (MOFs) and other porous coordination polymers are being generated at a rapid and growing pace. Herein, we address the question of how this large number of materials can be quickly evaluated for their practical application in carbon dioxide separation processes. Five adsorbent evaluation criteria from the chemical engineering literature are described and used to assess over 40 MOFs for their potential in CO(2) separation processes for natural gas purification, landfill gas separation, and capture of CO(2) from power-plant flue gas. Comparisons with other materials such as zeolites are made, and the relationships between MOF properties and CO(2) separation potential are investigated from the large data set. In addition, strategies for tailoring and designing MOFs to enhance CO(2) adsorption are briefly reviewed.     

In silico screening of metal-organic frameworks in separation applications

Porous materials such as metal-organic frameworks (MOFs) and zeolitic imidazolate frameworks (ZIFs) offer considerable potential for separating a variety of mixtures such as those relevant for CO(2) capture (CO(2)/H(2), CO(2)/CH(4), CO(2)/N(2)), CH(4)/H(2), alkanes/alkenes, and hydrocarbon isomers. There are basically two different separation technologies that can be employed: (1) a pressure swing adsorption (PSA) unit with a fixed bed of adsorbent particles, and (2) a membrane device, wherein the mixture is allowed to permeate through a micro-porous crystalline layer. In view of the vast number of MOFs, and ZIFs that have been synthesized there is a need for a systematic screening of potential candidates for any given separation task. Also of importance is to investigate how MOFs and ZIFs stack up against the more traditional zeolites such as NaX and NaY with regard to their separation characteristics. This perspective highlights the potency of molecular simulations in determining the choice of the best MOF or ZIF for a given separation task. A variety of metrics that quantify the separation performance, such as adsorption selectivity, working capacity, diffusion selectivity, and membrane permeability, are determined from a combination of Configurational-Bias Monte Carlo (CBMC) and Molecular Dynamics (MD) simulations. The practical utility of the suggested screening methodology is demonstrated by comparison with available experimental data.     

Molecular screening of metal-organic frameworks for CO2 storage

We report a molecular simulation study for CO2 storage in metal-organic frameworks (MOFs). As compared to the aluminum-free and cation-exchanged ZSM-5 zeolites and carbon nanotube bundle, IRMOF1 exhibits remarkably higher capacity. Incorporation of Na(+) cations into zeolite increases the capacity only at low pressures. By variation of the metal oxide, organic linker, functional group, and framework topology, a series of isoreticular MOFs (IRMOF1, Mg-IRMOF1, Be-IRMOF1, IRMOF1-(NH2)4, IRMOF10, IRMOF13, and IRMOF14) are systematically examined, as well as UMCM-1, a fluorous MOF (F-MOF1), and a covalent-organic framework (COF102). The affinity with CO2 is enhanced by addition of a functional group, and the constricted pore is formed by interpenetration of the framework; both lead to a larger isosteric heat and Henry's constant and subsequently a stronger adsorption at low pressures. The organic linker plays a critical role in tuning the free volume and accessible surface area and largely determines CO2 adsorption at high pressures. As a combination of high capacity and low framework density, IRMOF10, IRMOF14, and UMCM-1 are identified from this study to be the best for CO2 storage, even surpass the experimentally reported highest capacity in MOF-177. COF102 is a promising candidate with high capacity at considerably low pressures. Both gravimetric and volumetric capacities at 30 bar correlate well with the framework density, free volume, porosity, and accessible surface area. These structure-function correlations are useful for a priori prediction of CO2 capacity and for the rational screening of MOFs toward high-efficacy CO2 storage.     

Finding MOFs for highly selective CO2/N2 adsorption using materials screening based on efficient assignment of atomic point charges

Electrostatic interactions are a critical factor in the adsorption of quadrupolar species such as CO(2) and N(2) in metal-organic frameworks (MOFs) and other nanoporous materials. We show how a version of the semiempirical charge equilibration method suitable for periodic materials can be used to efficiently assign charges and allow molecular simulations for a large number of MOFs. This approach is illustrated by simulating CO(2) and N(2) adsorption in ~500 MOFs; this is the largest set of structures for which this information has been reported to date. For materials predicted by our calculations to have promising adsorption selectivities, we performed more detailed calculations in which accurate quantum chemistry methods were used to assign atomic point charges, and molecular simulations were used to assess molecular diffusivities and binary adsorption isotherms. Our results identify two MOFs, experimentally known to be stable upon solvent removal, that are predicted to show no diffusion limitations for adsorbed molecules and extremely high CO(2)/N(2) adsorption selectivities for CO(2) adsorption from dry air and from gas mixtures typical of dry flue gas.     

Cooperative effect of temperature and linker functionality on CO2 capture from industrial gas mixtures in metal-organic frameworks: a combined experimental and molecular simulation study

In this work, the cooperative effect of temperature and linker functionality on CO(2) capture in metal-organic frameworks (MOFs) was investigated using experimental measurements in combination with molecular simulations. To do this, four MOFs with identical topology but different functional groups on the linkers and three important CO(2)-containing industrial gas mixtures were adopted. The interplay between linker functionality and temperature was analyzed in terms of CO(2) storage capacity, adsorption selectivity, working capacity of CO(2) in temperature swing adsorption (TSA) processes, as well as sorbent selection parameter (S(ssp)). The results show that the effect of linker functionality on CO(2) capture performance in the MOFs is strongly interconnected with temperature: up to moderate pressures, the lower the temperature, the larger the effect of the functional groups. Furthermore, the modification of a MOF by introducing more complex functional groups can not only improve the affinity of framework for CO(2), but also reduce the free volume, and thus may contribute negatively to CO(2) capture capability when the packing effect is obvious. Therefore, when we design a new MOF for a certain CO(2) capture process operated at a certain temperature, the MOF should be designed to have maximized affinity for CO(2) but with a negligible or small effect caused by the reduction of free volume at that temperature and the corresponding operating pressure.     

CO2 capture by metal-organic frameworks with van der Waals density functionals

We use density functional theory calculations with van der Waals corrections to study the role of dispersive interactions on the structure and binding of CO(2) within two distinct metal-organic frameworks (MOFs): Mg-MOF74 and Ca-BTT. For both classes of MOFs, we report calculations with standard gradient-corrected (PBE) and five van der Waals density functionals (vdW-DFs), also comparing with semiempirical pairwise corrections. The vdW-DFs explored here yield a large spread in CO(2)-MOF binding energies, about 50% (around 20 kJ/mol), depending on the choice of exchange functional, which is significantly larger than our computed zero-point energies and thermal contributions (around 5 kJ/mol). However, two specific vdW-DFs result in excellent agreement with experiments within a few kilojoules per mole, at a reduced computational cost compared to quantum chemistry or many-body approaches. For Mg-MOF74, PBE underestimates adsorption enthalpies by about 50%, but enthalpies computed with vdW-DF, PBE+D2, and vdW-DF2 (40.5, 38.5, and 37.4 kJ/mol, respectively) compare extremely well with the experimental value of 40 kJ/mol. vdW-DF and vdW-DF2 CO(2)-MOF bond lengths are in the best agreement with experiments, while vdW-C09(x) results in the best agreement with lattice parameters. On the basis of the similar behavior of the reduced density gradients around CO(2) for the two MOFs studied, comparable results can be expected for CO(2) adsorption in BTT-type MOFs. Our work demonstrates for this broad class of molecular adsorbate-periodic MOF systems that parameter-free and computationally efficient vdW-DF and vdW-DF2 approaches can predict adsorption enthalpies with chemical accuracy.     

Influence of Functional Groups and Modi cation Sites of Metal-Organic Frameworks on CO2/CH4 Separation: A Monte Carlo Simulation Study

In order to explore the in uence of modification sites of functional groups on landfill gas (CO₂/CH₄) separation performance of metal-organic frameworks (MOFs), six types of organic linkers and three types of functional groups (i.e. -F, -NH₂, -CH₃) were used to construct 36 MOFs of pcu topology based on copper paddlewheel. Grand canonical Monte Carlo simulations were performed in this work to evaluate the separation performance of MOFs at low (vacuum swing adsorption) and high (pressure swing adsorption) pressures, respectively. Simulation results demonstrated that CO₂ working capacity of the unfunctionalized MOFs generally exhibits pore-size dependence at 1 bar, which increases with the decrease in pore sizes. It was also found that -NH₂ functionalized MOFs exhibit the highest CO₂ uptake due to the enhanced Coulombic interactions between the polar -NH₂ groups and the quadrupole moment of CO₂ molecules, which is followed by -CH₃ and -F functionalized ones. Moreover, positioning the functional groups -NH₂ and -CH₃ at sites far from the metal node (site b) exhibits more significant enhancement on CO₂/CH₄ separation performance compared to that adjacent to the metal node (site a).