Molecular Simulation And Quantum Chemical Calculation Of Methane Adsorption In Metal-organic Frameworks

Metal-Organic Frameworks (MOF) is a new class of porous materials that is similar to zeolite, which has high porosity, high adsorption, better thermal stability, etc. It has an attractive potential application in gas storage, adsorption, separation, optical properties, catalysis, sensors etc. Computational chemistry not only can overcome the limitations of traditional methods, but also could provide theoretical guidance for the design of optimal adsorbents and the determinations of optimal operations condition. It could save lots of time that spends in complex experiments and realize the transformation from the experimental to quantification. So it is useful to further the theoretical research on methane behaviors in MOF materials.In this work, gas adsorption in MOF materials has been studied by quantum chemical calculation and molecular simulation. The substance is as follows:1. A systematic Grand Canonical Monte Carlo simulation study has been performed on the adsorption of CH4 in a series of MOF materials. The conclusion got from well-studied MOF materials by Snurr group and Wang is also applicable to these newly-synthesized MOF materials. Besides, as pore topology is an indispensable factor in design materials, it will be more direct and clearer after classifying pore constructions in different types than directly when analyze the effects on adsorption from various factors.2. The research in adsorption properties of large aperture UMCM-2 has been done in the paper. The result shows that UMCM-2 will demonstrate step feature when at 100 K, 110 K, 120 K and 0.18 KPa, 0.74 KPa, 2.2 KPa, respectively.3. Comparing the adsorption sites of methane in new synthesized MOF with large pores with those with small ones by the center of mass probability distributions, the data show that gas molecules preferentially adsorb near metal element in small pores and move gradually from surface to channel or center of the materials with pressure increasing4. Quantum chemical calculations were used to study the adsorption of methane in a representative MOF material, UMCM-2. The results show that several adsorption sites, including corners of Zn4O cell, each side of BTB center and T2DC ring surface. The order of methane adsorption in UMCM-2 is the same as that in IRMOF-1 and IRMOF-6. Zn4O are the best adsorption sites, especially those sites near oxygen atom, as the electron-donating functional groups will enhance the interaction between methane and MOF. And the adsorption quality of BTB is weaker than that of benzene with -C6H6 group, as -C6H6 group is weaker electron-donating group comparing with -C2H4.5. The atoms charge of UMCM-2 is calculated by HF and B3LYP in DFT methods and four basis sets [STO-3Gg,6-31G,6-31G(D) and 6-311G]. Based on the system of UMCM-2, the effects on calculation results in different methods and basic sets are studied, as well as the effects on atomic charge correlation in the same basic sets but different methods.