Study On Removing Harmful Ions From Water With Carbon Nanotube Membranes By Molecular Dynamics Simulation

In the 21st century,water resources have become a key issue in the world.The water that people drink is usually not a simple substance but a mixture that contains a variety of ions,and when some harmful ions are in excess,people will be at risk for disease.The current theoretical research shows that carbon nanotubes have the ability to transport water very quickly,the ability to drain and resist salt,and the ability to choose ions through nanotubes,so carbon nanotubes are often regarded as one of the ideal materials to simulate biological nano-channels and the potential materials to make seawater desalination membrane.Based on these properties,carbon nanotubes have the potential to remove excessive harmful ions from polluted water.Using classical molecular dynamics method,carbon nanotubes and graphene membranes are regarded as the research object,we used three types of pipe diameter of carbon nanotubes as a water channel that chiral parameters s respectively?7,7?,?8,8?and?9,9?,on one side of the membrane,0.5 mol/L ZnCl₂ solution aim to simulate polluted water,in which Zn²⁺simulate excessive harmful ion,the other side is pure water.water and ion fluxes by calculation to compare different purification ability of nanotube membrane,and the motion of ions in the simulation process was investigated.In addition,on the basis of the previous research,we simulated and simply analyzed the Double-wall carbon nanotube-graphene structural membrane.Filtering out the toxic ions to get clean water is the main purpose of our study,so we need to focus on two indicators,which respectively are the filtering rate of harmful ion and the water flux in the process simulation,simulation study show that,with the increase of single-walled carbon nanotube diameter,ion will more easily into carbon nanotubes,because in the process that the ions from the solution to the side of the nanotubes of the potential energy is increased,and in the process that ion from the nanotubes to the pure water potential energy is reduced.Under certain conditions?electric field and pressure?,ions cannot pass through the nanotube membrane with a small diameter,while water molecules can.In other words,harmful ions can be effectively filtered with a 100%removal rate,but its water transport capacity is limited.Beyond a certain condition,the ionic selective transmittance of the nanotube with a larger diameter will be weakened,resulting in the passage of certain harmful ions,it means that the harmful ion filtration rate will be reduced,but the water flux will be significantly improved.For simulation of Double-wall carbon nanotubes model that we founded,toxic ions filtering rate was 100%.in the aspect of water flux,multi-walled carbon nanotubes membrane are more excellent than single-walled carbon nanotubes membrane,water flux get a lot of ascension.By calculating potential of mean force of two kinds of ions in two water channel,inner tube and outer tube,we got PMF curve that belongs to two kinds of ions.in addition,we compared and analyzed water molecules whose position is internal pipe and outer pipes,for the future of new water treatment membrane basing on carbon nanotube provides some theoretical basis.