A Molecular Simulation Study of CO2 Adsorption in Metal-Organic Frameworks

摘要

The increasing carbon dioxide density in the atmosphere has led to the global warming and other environmental issues. Such increase in carbon dioxide comes mainly from the combustion of thousands of tons of fossil fuels (coal, oil and natural gas). Thus, the development of novel materials for CO2 capture, separation and sequestration is becoming critically essential. Many materials including aqueous amine solvent, micro and mesoporous solid substances have been extensively investigated for CO2 absorption/adsorption. It is found that quite a lot of distinct metal-organic frameworks (MOFs) have remarkable CO2 adsorption capacity in room temperature, particularly HKUST-1 and MIL-68(In). HKUST-1 (Hong Kong University of Science and Technology) is a MOF made up of copper nodes with 1,3,5-benzenetricarboxylic acid struts between them. MIL-68(In) is an indium-based MOF made up of the chains of InO4(OH)2 octahedral units which are interconnected with terephthalate ligands to form central triangle and hexagon channels. To understand the micromechanisms and hence to further improve their adsorption capacities, grand canonical Monte Carlo and molecular dynamics simulations have been employed in this study to explore CO2 adsorption uptake. The results show that both fluorinated HKUST-1 and MIL-68(In) have a superior CO2 adsorption performance than their unmodified structures. In addition, radial distribution function and mean square displacement analysis methods have been carried out to explore the CO2 adsorption sites and the self-diffusion within MOFs. The results indicate that CO2 molecules in HKUST-1 are more likely to attach to the metal sites with the pressure increase, however, the adsorbed CO2 in HKUST-1F and MIL-68F (In) are bound firmly to fluoride atoms, reducing their mobility.