Molecular Dynamics Simulation Of Diffusion Of Simple Molecules On Zeolite And Carbon Nanotubes

In this paper,the kinetic behavior of simple molecules in zeolite and carbon nanotubes was studied by means of molecular dynamics simulation.Firstly,the diffusion of methane and n-butane in one-component and different proportions of binary mixtures in the molecular structure of zeolite ITQ-3 was studied based on the transition state theory,the self-diffusion coefficients of the one-component molecules in the y?z direction and the diffusion behavior of the binary mixed molecules at each ratio were calculated,and the phenomena was explained by molecular projection of the frequency contours on the x-y and x-z planes of the zeolite ITQ-3.It was found that,in the zeolite ITQ-3,the diffusion of single component CH₄ and C₄H₁₀ showed two diffusion modes with the loading n:in the z direction of the channel,when the loading n increases,the self-diffusion coefficient also increases,and when it increased to a certain value,it began to decrease;while in the y direction channel,when the loading n increases,the self-diffusion coefficient is reduced continuously.The diffusion of mixed molecules CH₄ and C₄H₁₀ in zeolite ITQ-3shows that the diffusion of CH₄ in the mixed molecule is related to the total number of atoms:when the loading n is small,the diffusion coefficient of CH₄ is increased in the z and y directions as the total number of atoms increases;when the loading n is large,the diffusion coefficient of CH₄ decreases with the increase of the total number of atoms in the z direction,and in the y direction channel,the total number of atoms that makes the diffusion coefficient of CH₄ reduce caused by blocking effect in z direction channel is still in a transition state.Secondly,the diffusion behavior of water in carbon nanotubes was studied by means of molecular dynamics simulation.The limitations of the traditional calculation of diffusion of water in carbon nanotubes were discussed and a new method for the diffusion of water in carbon nanotubes was proposed:we treated water diffusion in carbon nanotubes as clusters delivering through channels and modeled clusters as Brownian motion particles.This method may also provide a new perspective in understanding diffusion of other polar molecules other than water confined in smooth channels.