Study Of Molecular Diffusion On Nanoporous Materials

With the rapid development of molecular simulation techniques, molecular computing is widely used in materials, physics, chemistry, biochemistry and medicine and other fields. In addition, by analyzing the simulation results with available experimental data can not be obtained, in particular, help to reveal the mechanism of the theory.In this paper, we have studied the molecular diffusion on nanoporous membranes using molecular dynamics simulation, specifically, the anisotropic diffusion of spherical molecules CF4 and CH4 on the nanopores of zeolite ITQ-3. By analyzing the simulation results and employing transition-state theory, we proposed a diffusion model of molecular diffusion in the narrow pores of zeolite ITQ-3. In this model, the movement of molecules is treated as hopping from one adsorption site to another in connected cavities and the potential barriers between them are thought to be large. This assumption could simplify the potential at the windows between the cavities as pure repulsive form, from which the formula for the dependence of diffusion upon temperature and Lennard-Jones parameters can be obtained analytically.The main results are summarized as:(1) A model of molecular diffusion in the narrow pores of zeolite ITQ-3 is proposed basing on transition-state theory.(2) The anisotropic diffusion of spherical molecules (CF4 and CH4) in the nanopores of zeolite ITQ-3 was investigated by molecular dynamic simulation.(3) The potential energy profiles of CF4 molecules along the pore axes in ITQ-3 can give an explicit explanation on the diffusive behaviors regarding the dependence of diffusivity on loadings.(4) Dependence of the diffusion coefficients of CH4 and CF4 on loading was investigated by molecular dynamic simulation. The establishment of the model was explained. In conclusion, the anisotropic diffusion of spherical molecules in the pores of zeolite ITQ-3 was investigated by molecular dynamic simulation. These provide new ideas and methods to measure the physical, chemical phenomena and processes which use the modern experimental methods to study and to explore the physical and chemical mechanism are difficult.