Theoretical Simulations Of The Capacitive Deionization Properties Of Graphene In Atomic And Electronic Levels

With the high-speed development of heavy industry and the improving demand of the people, the industrial wastewater and domestic wastewater cause serious environmental pollution to the limited freshwater resources. Obtaining economical freshwater resources from large amounts of seawater has become the focus of many scholars. Recently there are many approach to seawater desalination including distillation, electrodialysis, reverse osmosis and ion exchange, but those approaches all have their own deficiencies and weaknesses. The capacitive deionization(CDI) make it possible to realize a low-energy and non-pollution approach. Graphene with its high specific surface area and good electrical conductivity attracted many scholars to apply it to capacitive deionization by experiment, while the theoretical study is relatively lacking. This work using the method of computer simulations studied the interfacial capacitance and desalination performance.Firstly applying charge on the graphene to simulate the process of electrode charging, and calculated the interfacial capacitance of the pristine graphene by molecular dynamics simulation(LAMMPS) and density functional theory(CASTEP). The results show that the interfacial capacitance is about 70 F/g, which is well matched with the experimental value.The amount ratio of Na Cl and H2 O as the index, investigated the CDI performance of the pristine grapheme by molecular dynamics simulation, and combining the fluid flow velocity and the adsorbing capacity of the electrode surface, demonstrated the effects on desalination performance by different operating condition. The result showed that the lager electrode surface charge density, smaller electrode gap and lower flow velocity would improve the desalination performance.The interfacial capacitance of the defect graphene and N-doped garphene electrode with [BMIM][PF6] ionic liquid was investigated by molecular dynamics simulation and density functional theory. The result comparison with the pristine graphene showed that the interfacial capacitance gradually reduce with the increasing number of defect quantity, and gradually increasing with the increasing number of N-doped quantity. When the Ndoped ratio was 4.1%, the N-doped graphene electrode has larger interfacial capacitance about 122 F/g, which was well match with the experimental value. The desalination performance was studied using the defect graphene and the N-doped graphene by molecular dynamics simulation. The result showed that the defect graphene reduce the desalination rate and N-doped graphene increase the desalination rate.