Research On The Adsorption And Diffusion Of SO₂/N₂ In Functionalized Carbon Nanotubes

The use of traditional fossil fuels will produce a variety of air pollution gases.Among them,as a kind of combustion product harmful to the environment and toxic to human body,SO₂ has attracted more and more attention.Carbon nanotubes?CNTs?are a kind of high performance gas adsorption materials,which plays an important role in the field of gas adsorption.In this work,the adsorption and diffusion of SO₂/N₂ mixture gas in pristine carbon nanotubes,carbon nanotubes with port modification and carbon nanotubes with inner surface modification are studied by molecular dynamics?MD?and grand canonical Monte Carlo?GCMC?simulation.The results are as follow:In pristine carbon nanotubes,the adsorption amount of SO₂ is much higher than that of N₂ due to the strong interaction between SO₂ and carbon nanotubes.With the diameter of carbon nanotubes increasing,the adsorption amount of SO₂ increased gradually,but the adsorption of N₂ decreased.With the temperature increasing,both of the adsorption of SO₂ and N₂ are decreasing.The adsorption selectivity of SO₂/N₂ in carbon nanotubes is increases with the diameter of tube increasing.However,with the temperature increasing,the adsorption selectivity of SO₂/N₂ is decreases.In the process of adsorption,the adsorption heat of SO₂ is decreases with the increasing of temperature.In general,the self-diffusion coefficient of SO₂ in carbon nanotubes increases with the temperature increasing.With the diameter of carbon nanotubes increasing,the diffusion characteristic of SO₂ in the tube is more and more close to the bulk phase and the“limited effect”becomes weakly when the molecule in the large diameter nanotubes,which will decrease the value of self-diffusion coefficient.The migration frequency of molecules at the port of carbon nanotubes is increasing with the temperature increases and the migration frequency of SO₂ is much higher than that of N₂ because of a mount of SO₂ molecule in nanotubes.The modification of dangling bonds at the end of carbon nanotubes could not change the surface characteristics and internal volume of the nanotubes,so it is had no significant effect on the adsorption performance of the gas.However,the groups which modifying the end of the nanotubes will undoubtedly reduce the effective area of the end of the nanotubes during the thermal movement,which has a great impact on the molecule diffusion.In this work,the results shows that SO₂ has the highest diffusion coefficient in the carbon nanotubes modified with-OH and the lowest in the carbon nanotubes modified with-COOH.Compared with the pristine carbon nanotubes,the addition of-OH can promote the diffusion of SO₂ in carbon nanotubes slightly.As-COOH has a longer chain than-OH and-NH₂,the effective area of the carbon nanotubes port with-COOH is reduced more than-OH and-NH₂ modified nanotubes,thus hindering the diffusion of SO₂ molecules in the port.The influence of port functional groups on the port migration frequency of gas molecules SO₂ and N₂ was follow the order of-H>-OH>-NH₂>-COOH.The inner surface of carbon nanotubes was modified with-OH,-NH₂ and-COOH functional groups,which had a certain impact on the surface characteristics and internal volume of carbon nanotubes.In this work,it can be found that the adsorption amounts of the SO₂/N₂ in the carbon nanotubes are significantly reduced and the adsorption amounts of the mixture gases in the carbon nanotubes follow the order of-COOH<-NH₂<-OH<-H.However,the selectivity of SO₂/N₂ in carbon nanotubes is significantly enhanced.In addition,the adsorption heat of SO₂ in the adsorption process follows the same rule as the adsorption amount.Surface modification has no significant effect on the end of the nanotube,so the diffusion characteristics of gas molecules at the end of the nanotube are almost unchanged.