Permeability And Selectivity Properties Of Pillared-graphene

Pillared-graphene inherits the excellent hydrophobic,mechanical,chemical and electrical properties of graphene and carbon nanotubes,which provide natural advantages for fluid flow in pillared-graphene nanochannels.The study of the flow characteristics of water in nanochannels provides a theoretical basis for the design of nanodevices such as drug delivery,seawater desalination,sensors,and nano pumps.In this thesis,pillared-graphene was considered as a nanochannel,and the permeability and selectivity of pillared-graphene were investigated by means of the classical molecular dynamics simulation.Study on the permeability of pillared-graphene,three nanochannel models were first constructed,and the infiltration behaviour of water passing through the three nanochannels was compared.The results show that the funnel-shaped structure at the entrance of pillared-graphene nanochannels can effectively improve the permeation environment near the entrance of the channel and increase the permeability of water.At the same time,The distribution of energy barriers near the inlet of the nanochannel also indicates that water is more prone to enter the columnar graphene nanochannel.Secondly,the effects of pressure,temperature and electric field strength on the permeability of pillared-graphene were investigated.The simulation results show that the permeability of water passing through pillared-graphene nanochannels increases with the increase of pressure,and has excellent continuous permeability during the simulation.Different pressures will lead to differences in the density distribution of water near the inlet,which in turn will cause differences in the distribution of energy barriers.Energy barrier decreases with increasing the pressure.Under the same pressure conditions,the temperature has a significant influence on the permeability of water,and the permeability of the water in the pillared-graphene increases with the temperature.The mechanism is that the high temperature can improve the activity of water,resulting in the increase of the kinetic energy of water molecules in the simulation system,so that it is easier to overcome the barrier of energy and accelerate the penetration of water.As for the effect of electric field intensity on the permeability of water,accordingto the method of adding electric field adopted in this thesis,the electric field plays an impediment to the penetration of water,and the permeability of water decreases with the increase of the electric field strength.No water molecules can successfully pass through the nanochannels when the charge exceeds 0.8 e.Finally,the influences of the axial spacing of the two CNTs in the pillared-graphene on the water permeability is considered.The permeability of the water in the nanochannel decreases with the increase of the axial spacing and the water permeability even approaches two times of the permeability in the case of the pillared-graphene with a single CNT channel.In order to explore the sieving properties of pillared-graphene,the thesis first used(6,6)pillared-graphene as nanochannels to study the influence of pressure and salt concentration on the sieving characteristics.The results show that as the pressure increases,the permeability of water passing through(6,6)pillared-graphene nanochannel is gradually increased,and the salt rejection is always 100 %.In addition,there is no obvious correlation between the permeability and the concentration of the salt solution,i.e.,the permeability of water molecules will not have significantly interfered with the change of the salt solution concentration.Secondly,this paper also explored the permeability and selectivity of(9,9)pillared-graphene nanochannels.Due to the enlarged pore size,not only the permeability of water molecules has been dramatically improved,but also the salt rejection has been reduced.From the comparison of(9,9)pillared-graphene with(6,6)pillared-graphene,it can be found that when the internal pressure of the salt solution is maintained at 100 MPa,(9,9)pillared-graphene can obtain high the permeability and salt rejection.Finally,the sieving properties of pillared-graphene with the axial spacing of 0.98 nm were investigated.The results show that while the permeability of water molecules has been increased by more than twice,it is still able to obtain a 100% salt rejection.