A Computational Study On Post-Synthesis Modification Of Metal-Organic Frameworks

Metal-Organic Frameworks (MOFs), commonly recognized as "soft" analogues of zeolites, is a new class of nanoporous materials. Due to their large surface areas, adjustable pore sizes and controllable properties, as well as acceptable thermal stability, MOFs are promising candidates for a wide range of applications in gas storage, separation, catalyst, biochemistry, and pharmacy, etc. The study of MOFs has become a research frontier area of materials, and hotspots. Due to the chemical diversity and complex structure of MOFs, purely experimental approach is insufficient to conduct systematic studies. Computational chemistry can provides theoretical guidance for the design of optimal adsorbents and the determination of optimal industrial operation conditions, which also saves a lot of time for complicated experimental works. In this work, a systematic molecular simulation study for gas adsorption and penetration separation in a modified MOF was carried out, and its performance was compared in detals with the mother MOFs as well as other commonly used MOFs. The main contents and findings are summarized as follows.1. In this work, the new IRMOF-3-AM1was constructed based on the mother IRMOF-3using Materials Studio. A multiscale approach combining grand canonical Monte Carlo simulation and density functional theory calculation was adopted to investigate the adsorptive separation of CO2/CH4, CO2/CO and CO2/N2mixtures in both MOFs. The results show that the selectivity of CO2from gas mixtures in the AM1-modified MOF is greatly improved, due to the enhancement of electrostatic potential in the materials by the presence of the carboxylic group. The simulations also show that the pore size and structure of the modified MOF also have some influences on the separation selectivity, although the key influence comes from the enhancement of electrostatic field.2、Grand canonical Molecular Dynamics simulations were performed to study the permeability selectivity of CO2/CH4mixture in five MOFs at room temperature. The results show that the adsorption selectivity of CO2in the catenated MOFs is much higher than that in its non-catenated counterparts, on the contrary, the permeability of CO2of the former is lower than that in the latter, due to smaller free volume in them. Our simulations also show that the permeability of CO2from the gas mixtures in the IRMOF-3-AM1is better than that in the other MOFs considered in this work.3、This work shows that the introduction of groups in MOFs with large pores is a good modification method to improve both adsorption selectivity and permeability of MOFs, which may find applications in designing new MOFs for CO2capture.