Simulations Of Carbon Nanotube Properties For Passing Water And Stopping Salt By Using CHARMM Force Field

Desalination technology is the key topic of current research.The organic permeable membrane doped with inorganic nanotubes can be used as a membrane material in desalination process.Carbon nanotubes are of particular interest to researchers because of their unique properties.The water-passing and salt rejection efficiency of carbon nanotubes with different diameters in different temperature conditions are two important factors affecting sea desalination.In this paper,carbon nanotubes were used as the research object.The molecular dynamics simulation method based on CHARMM force field was used.By adjusting the diameter of the tube,the concentration of the brine phase,and controlling the temperature,the water-passing efficiency and water molecular arrangements of the carbon nanotubes were investigated.Radial distribution function and root mean square displacement function of water molecules in the nanotubes is calculated and analyzed.The results show that the diameter of the pipe directly affects the microscopic motion configuration of the water molecules in the channel,and the water-passing and salt rejection efficiency is obviously different.Carbon nanotubes with small diameters hinder the passage of water molecules.As the diameter of the tube increases,the water molecules passing through the carbon tube exhibit a variety of arrangements.The salt rejection of carbon nanotubes with a diameter less than 1.09 nm is 100%,and the salt rejection rate decreases with increasing temperature.At the same time,the salt rejection rate is also related to the salt concentration,and the salt rejection rate increases with the increase of the concentration.For carbon nanotubes with a diameter greater than 1.09 nm,the salt rejection decreases with increasing nanotube diameter.In addition,salt rejection and salt concentration are correlated to some extent.In the carbon nanotubes with large diameter,the salt rejection of the carbon nanotubes can be significantly improved as the concentration of salt ions in the brine phase increases.For the saline solution,the water passing rate of the carbon nanotubes has a large correlation with the diameter of the carbon nanotubes.The larger the diameter,the stronger the water passing capacity.The water passing rate of carbon nanotubes with a diameter less than 1.09 nm is not affected by the salt phase salt concentration.As the concentration increases,the water passing rate does not change significantly.Carbon nanotubes with carbon nanotube diameters greater than or equal to 1.36 nm,with increasing tube diameter,the greater the salt ion concentration,the lower the water passing rate.The molecular dynamics simulation is used to explore the water-passing and salt rejection properties of carbon nanotubes,which provides a theoretical basis for the selection of doped carbon nanotubes during seawater desalination and provides theoretical support for the impro vement of seawater desalination technology.