【作者】 王三跃；

【导师】 仲崇立；

【作者基本信息】 北京化工大学 ， 化学工程， 2007， 博士

【摘要】 金属—有机骨架材料（Metal-Organic Frameworks，MOFs）是一种类似于沸石的新型纳米多孔材料，具有结构组成的多样性、较大的比表面积和孔隙率、热稳定性好、可裁剪性的孔等特点，可应用在气体储存、分离、催化等领域。计算化学（包括量子化学与分子模拟）不仅可以突破传统方法中的局限性，而且还可为最佳吸附材料的设计和最优操作工况的确定提供理论依据，实现从以经验为主向定量、定向制备的转变，从而节省大量繁杂的实验研究。因此，开展对MOFs中流体的吸附、扩散等性质的理论研究，具有非常重要的实际意义。本文对MOFs中流体的吸附、分离、扩散等性质，采用量子化学计算与分子模拟两种方法，进行了系统的理论研究。主要内容如下：1、基于量子化学计算的方法，对甲烷在IRMOF-1和IRMOF-6中的吸附机理近行了系统的理论研究。得出甲烷在这两种MOF材料中的吸附能分为四个部分：大、小胞孔内的OZn₄簇的角落处和有机连接体苯环面上及侧边位。OZn₄簇是最佳吸附位，吸附最优构型是甲烷中C—H键指向氧或苯环面正上方。增长有机连接体，或在苯环引入给电子基团和含氧等极性官能团，有利于增强甲烷与MOFs的相互作用，从而有利于提高甲烷与MOF材料之间的吸附能。2、通过GCMC方法，对甲烷在各种MOFs中的吸附行为进行了模拟，得出影响MOF材料吸附量的主要因素是比表面积(S_acc)、自由体积份数(V_free)和无限释稀吸附热(q_st^∞)等，并且相互影响。同一系列的MOFs，其吸附规律具有相似性。从压力关系考虑，吸附量明显分为三个区间：在低、中和高压区间，吸附量分别与吸附材料的q_st^∞、S_acc和V_free相关联。3、采用GCMC方法研究了Cu-BTC在气体吸附分离中的应用，得出Cu-BTC是一种吸附分离的潜在MOF材料。孔径尺寸的大小、吸附质与吸附剂之间的静电力，是吸附选择性改善的重要原因。4、采用量子化学计算与GCMC模拟相结合的方法，研究了具有连锁结构和非连锁结构的MOFs对气体吸附储存、分离的影响。得出在较低压力下，具有连锁结构的MOFs比非连锁结构的MOFs有较高的吸附量，和较好的分离效果。5、采用柔性和刚性两种结构模型，通过分子力学与分子动力学相结合的方法，研究了甲醇分子在MOF-E[Ni₂（4，4’-Bipyridine）₃（NO₃）₄]中的吸附、扩散行为。得出每Ni₂结构单元稳定吸附量是2个甲醇分子，多于2个甲醇分子时骨架发生明显变形，出现吸附等温线的梯级现象；柔性模型下的结合能和扩散势垒值更加接近实际，说明宜采用柔性骨架模型模拟计算此类材料。更多还原

【Abstract】 Metal-Organic Frameworks （MOFs）, "soft" analogues of zeolites, is a new class of nanoporous materials. MOFs having extremely high porosities, chemical diversity and tailored materials as robust solids with high thermal stability and well-defined pore sizes are promising materials for gases storage, separation, and catalyst. Computational chemistry, including molecular simulation and quantum chemistry, can not only overcome the limitations of traditional methods, but also provide theoretical guidance for the design of optimal adsorbents and the determinations of optimal industrial operations. It saves a lot of time for complicated experimental work and realizes the transformation from the experimental to quantification. So, theoretical studies of fluid behaviors in MOFs will be very useful for the application of these materials.In this work, gas storage, separation and diffusion in MOFs have been carried out using quantum chemical calculations and molecular simulations. The main contents and findings are summarized as follows.1. Quantum chemical calculations were used to study the adsorption of methane in IRMOF-1 and IRMOF-6. The results show that there are four adsorption sites including the corners of cell and the sides or upsides of the linkers in MOFs, and the OZn₄ clusters are the preferential adsorption sites. It could be concluded that the adsorption energy between methane and frameworks could be increased by increasing the length of the linkers and introducing electron-donor functional or polar functional groups to the organic linkers.2. A systematic Monte Carlo simulation study has been performed on the adsorption of CH₄ in a series of MOFs to confirm the desired characteristics of an optimal adsorbent for methane storage. The simulations show that isosteric heat of adsorption, accessible special area, free volume are all influence properties for a material with adsorption capacity. However, not all these properties are compatible. The same series MOFs have the similar characteristics of gas adsorption from the simulations. The results reveal the existence of three adsorption regimes: at low pressure, methane uptake correlates with the heat of adsorption; at intermediate pressure, methane uptake correlates with the surface area; and at the highest pressures, methane uptake correlates with the free volume.3. GCMC simulations were conducted to systematically evaluate the gas adsorption separation in Cu-BTC. The results show that Cu-BTC could be potentially used for the gas purification and separation. Pore sizes in Cu-BTC and the electrostatic actions between adsorbent and absorbate improve the selective adsorption behaviors.4. Quantum chemical calculations and GCMC simulations were performed to investigate the effects of catenation on gas storage and separation in IRMOF-9 and IRMOF-10. The results show that the interpenetrating MOFs have higher capacity and selective factor than those non-interpenetrating MOFs at lower pressure or loading.5. Adsorption and diffusion behaviors of methanol in MOF-E were obtained with flexible and rigid models by using molecular mechanics and molecular dynamics. The results indicate that per Ni₂ unit can sorb two methanol molecules stably and the structure undergo obvious deformation when the loading is above two molecules, which resulted in methanol adsorption isotherm step. The calculated adsorption energy and diffusion barrier are agreement with the experiment well by flexible model. It could be concluded that flexible model should be considered to study the adsorption and diffusion characterizations of adsorbate in such MOFs.更多还原