ADSORPTION OF SMALL GASES IN MIL-127 METAL ORGANIC FRAMEWORKS

Abstract

Material of Institut Lavoisier -127 (MIL-127) is one of series of porous metal-organic frameworks (MOFs) that have many potential applications such as gas storage and separation, catalysis, and biological applications. MIL-127 is composed of trimers of iron(III) and 3,3’,5,5’ - azobenzenetetracarboxylate anions. To gain insight into the adsorption behavior and the dynamic behavior of small gases in MIL-127, we carried out Gibbs Ensemble Monte Carlo (GEMC) and Molecular Dynamics (MD) simulations. Firstly, the structure of MIL-127(Fe) was constructed from XRD result. Force field parameters were carefully selected. Different parameter sets from both quantum calculations and literatures have been employed. Their results were compared with each other and with experiments to find the one that can well reproduce the adsorption isotherm of small gases in MIL-127(Fe). Radial distribution functions (RDFs) and probability density were done to elucidate behavior of small gases. From simulations, the preferential adsorption sites of carbon dioxide is around the metal cluster zone of MIL-127(Fe) in contrast to adsorption sites of carbon monoxide which prefers to adsorb around organic linker zone. Finally, selected parameters were used to investigate the structure and self-diffusion of the guest molecules in the MIL-127(Fe). The self-diffusion coefficient of carbon dioxide is in the range of 1-3×10-9 m2/s and the self-diffusion coefficient of carbon monoxide is in the range of 4-14×10-9 m2/s.