Simulation Study On Gas Adsorption And Separation Characteristics Of Porous Carbon Nitrogen Material G-C₁₂N₈

With the rapid development of economy,the greenhouse effect caused by a large amount of CO₂produced by fossil fuel combustion is increasingly intensified.In order to solve this problem,CO₂needs to be captured and stored.It is found that porous carbon nitrogen materials can capture CO₂efficiently,but its microscopic mechanism needs further study.Therefore,Molecular Dynamics（MD）simulation、Density Functional Theory（DFT）and Grand Canonical Monte Carlo（GCMC）methods were used in this paper to study the adsorption principle of a new porous carbon nitrogen material g-C₁₂N₈for CO₂and the influencing factors of g-C₁₂N₈for the selective adsorption and separation of CO₂and N₂.（1）The adsorption properties of g-C₁₂N₈for N₂and CO₂were studied by DFT and GCMC simulation methods.The adsorption energy between CO₂and g-C₁₂N₈surface is significantly greater than that of N₂.The adsorption between N₂and g-C₁₂N₈surface is completely dominated by van der Waals force,while the adsorption between CO₂and g-C₁₂N₈surface is jointly contributed by electrostatic force and van der Waals force.Therefore,the adsorption energy between CO₂and g-C₁₂N₈surface is greater than N₂.With the increase of temperature,the diffusion coefficient of N₂and CO₂increases,and the diffusion coefficient of CO₂is lager than N₂,so the diffusion performance of CO₂is better.G-C₁₂N₈has a high selectivity coefficient S for N₂and CO₂,and the adsorption of CO₂on g-C₁₂N₈has significant advantages.In the mixed gas with low CO₂concentration,g-C₁₂N₈has a higher adsorption selectivity for CO₂.（2）MD simulation method was used to study the separation effect of g-C₁₂N₈on N₂/CO₂mixture under different temperature,strain and charge conditions.With the increase of temperature,the permeability of N₂and CO₂increases and the selectivity decreases slightly.Therefore,increasing temperature is not conducive to the selective separation of CO₂.Increasing strain increases the pore diameter of g-C₁₂N₈membrane and the permeability of N₂,while the permeability of CO₂does not change significantly,and the selectivity decreases sharply.When the strain increases to 8%or more,the selection for CO₂separation by g-C₁₂N₈almost disappears.Therefore,increasing strain is not conducive to the separation of CO₂.The introduction of charge can change the configuration of CO₂,and the permeability of CO₂increases with the increase of positive charge.With the increase of negative charge intensity,the permeability increases first and then decreases.When the charge reaches-6 e,the permeability of CO₂is the largest,so adding charge is conducive to the separation of CO₂.By revealing the research on the microscopic mechanism of adsorption of CO₂and N₂by g-C₁₂N₈material and the influence of temperature,strain and charge regulation on the separation performance of g-C₁₂N₈,it provides a theoretical basis for the development of porous carbon nitrogen materials with more efficient adsorption and separation of CO₂.