Liu Dahuan

Diffusion Rates of Gas Molecules Adsorbed in Metal-Organic Frameworks

A systematic equilibrium molecular dynamics study was performed to investigate the diffusion rates of gas molecules as a function of the pressure in metal-organic frameworks(MOFs) with different structures.Methane was chosen as the probe molecule.The self-diffusion coefficients in eight typical MOFs were calculated at room temperature.Combined self-diffusion coefficients with the contour plots of the center of mass(COM) probability densities of methane,the relationship between the diffusion rates of gas molecules and the structure of the pores in the MOFs is discussed.Results show that methane tends to adsorb in pockets in MOFs with pocket and channel pores(P-C materials) at low pressure.With an increase in pressure,the gas molecules move to the channel and the self-diffusion coefficient increases.However,the diffusion coefficient of methane changes a little in the low and middle pressure range in the IRMOFs(isoreticular MOFs) with only one kind of pore.With a further increase in pressure,the self-diffusion coefficient of methane decreases in all the studied MOFs.Therefore,the difference in diffusion rates of methane in different MOFs may be mainly attributed to the pore structures of the materials.In addition,diffusion rates of the gas molecules in the P-C materials could be controlled in a wide range by varying the pressure,providing useful information for the application of MOFs in gas storage and separation.

Application of thermodynamics and computational chemistry to structure-property relationship study and design of nano-structured materials

Nano-structured materials have played an important role in chemical process intensification with the development of chemical technology. Metal-organic frameworks (MOFs) built up from inorganic subunits and organic moieties have been recognized as a new family of nanoporous materials with potential applications in different fields including gas storage, separation, catalysis, sensing and drug delivery. In this paper, MOFs were adopted as an example to introduce how thermodynamics and computational chemistry can help to study the structure-property relationships and design of nano-structured materials.

Stepped Behavior of Carbon Dioxide Adsorption in Metal-Organic Frameworks

Grand canonical Monte Carlo (GCMC) simulations were performed to study the stepped behaviors of carbon dioxide adsorption in the following five isoreticular metal-organic frameworks (IRMOFs): IRMOF-1, -8, -10, -14, -16. The simulation results show that the stepped phenomenon occurs easily when the temperature is low and the pore size is large for these IRMOFs. The critical pressure and temperature where the stepped behavior occurs show a linear relationship with the pore size. The results also further indicate that the electrostatic interaction between CO2 and CO2 molecules plays a dominant role on the stepped behavior. All these findings may provide useful information for the design and modification of MOFs for the adsorption and separation of carbon dioxide in gas mixtures.