Computational Chemical Study Of Hydrogen And Carbon Dioxide Adsorption In Metal Organic Frameworks

Metal organic frameworks(MOFs)are new kind of porous materials with several merits: strong functionality, great voidage and specific area, low crystalline density and high stability. MOFs show great dominant advantages and application prospect in energy gas storage and CO2 separation. However due to the various ligands, MOFs are early endless in its types. In order to find a suitable method on choosing MOFs with industial application value, it is necessary to conduct systematic research. Computational chemistry is a new developing research tool, it has superiority on structure function relationship study of complex systems, no only breaking through the boundedness of traditional research but also making explanation from mirco perspective, the tool can provide theoretical basis for the design of the optimum sorption material.With the theory of computational chemistry, a combination of Grand canonical Monte Carlo simulations and Density functional theory calculation was performed toward a deeper understanding of H2 adsorption in COFs and CO2 adsorption in MOF-399, meanwhile, the effects of gas impurities existence on CO2 adsorption in MOFs also were investigated. This work would give guides on the hydrogen storage and CO2 separation in MOFs.Aiming at the application value of energy gas storage in COFs, we studied the hydrogen adsorption property and mechanism on seven COFs. We found that 3D-COFs have a better adsorption capacity over 2D-COFs. Density functional theory was applied to investigate the adsorption mechanism of H2 on seven main clusters of COFs, the favorable adsorption sites were found. The increasing amount of carbon atoms on organic cluters would be beneficial to adsorption for H2. By calculating different adsorption configurations of two H2 moleculars on COF-10 and COF-105, it is found that H2 adsorption on these two COFs follows a cooperative mechanism. Alkali metals(Li, Na, K) doping and functional groups(methyl, sulfhydryl, amino) substitution of COFs can significantly enhance the adsoroption energy, indicating that chemical modification is an effcet ive way to enhance hydrogen adsorption capacity of COFs.Considering the feasibility of CO2 capture at higw pressure in MOF-399, we studied the CO2 adsorption property and mechanism on MOF-399 who has the lowest crystalline density. We investgated the effect of adsorption isotherm, temperature and electrostatic force. The results show that CO2 adsorption in MOF-399 is part of physical process and the main force include dispersion force and electrostatic force. CO2 adsorption amount in MOF-399 decrease with the increase of temperture and the electrostatic force account for 22% ~ 32%. When comparing stable configurations and adsorption energy, it is found that the bond angle of CO2 is changed and the unsaturated meta l site Cu is the most favorable site. The organic linkers show ability of CO2 adsorption in a certain degree when the pressure rises. Adsorption energy is effected by the interaction area between CO 2 and MOF-399.For further study of CO2 capture performance at low pressure in MOFs, we studied the adsporption property of Bio-MOF-11 in actual flue gas atmosphere. A systematic research on adsorption capacity of CO2, N2, SO2, H2 O and O2 on Bio-MOF-11 was performed. The CO2 adsorption capacity at 298 K and 1 bar is 4.167 mmol/g and Bio-MOF-11 has a good performance on CO2/N2 separation.We conducted the study of flue gas influence on CO2 searaption. The presence of H2 O is found to be good for the separation and SO2 is just on the opposite. Density functional theory calculation was performed to analyze the adsorption mechanism of CO2, SO2 and H2 O, the adsorption energy of SO2 and H2 O are larger than the adsorption energy of CO2.