Molecular Dynamics Study On Seawater Desalination Of New Ti₃C₂ MXene Structure

Solar interface evaporation seawater desalination（SSG）technology can limit heat to a thin layer of liquid in contact with the photothermal medium,avoid the overall heating of the bulk water,and effectively improve the light-steam conversion efficiency.It is expected to become a new way of seawater desalination in a low-carbon and green environment.The novel two-dimensional nanomaterials have excellent chemical stability and thermal stability.Smooth capillary pores are distributed on their surface,which is conducive to the rapid transmission of water molecules and is widely used in interfacial evaporation.However,the mechanism of water evaporation and ion exclusion in nanochannels is not clear.In this paper,MXene Ti₃C₂,MoS₂ and composite films were used as photothermal conversion materials to establish an interface evaporation system,and molecular dynamics simulation was used to explore its evaporation performance.The MXene Ti₃C₂ interface evaporation seawater desalination system was established to explore the effects of slit width,functional groups and layers on seawater desalination performance.The results show that the single-layer Ti₃C₂ with a slit width of 12（?）is the best desalination condition,the number of water molecules is 280,and the salt rejection rate is 95.6%.The end face of Ti₃C₂ is hydrophobic and the surface is hydrophilic,which reduces the interaction between water molecules and the interior of the channel and promotes the transport of water molecules.The water flux is related to the wettability of different functional groups.Adding functional groups makes water molecules need more energy through nanochannels,and the water flux decreases.The formation of hydrogen bonds between atoms and water molecules on the membrane surface is beneficial to the transport of water molecules,but the steric hindrance of Ti₃C₂（OH）₂ is the largest,and the water flux is lower than that of Ti₃C₂.Through the calculation of the average force potential,the free energy barrier of water molecules passing through the channel is lower than that of salt ions,so that water can pass through the nanochannel quickly and the salt rejection rate is high.The increase of Ti₃C₂ layers is not conducive to the passage of water molecules through the channel,and the water flux decreases.Hybrid deposition with MoS₂ to form a composite film can effectively solve the problems of pores and defects between MXene Ti₃C₂ materials,and has the advantages of both two-dimensional films.The MoS₂ interface evaporation system was constructed to study the effects of slit width,terminal group and layer number on seawater desalination performance.Under the combined action of hydrogen bond,steric hindrance and free energy barrier,the water flux of different terminal groups is:Mo-terminal>S-terminal>mixed-terminal;the difference in the amount of charge carried by the terminal group leads to inconsistent retention rates of Cl^-and Na⁺,but both are above 90%.Under the same slit width,the S-terminal system has the largest steric hindrance to water molecules,which is not conducive to the transport of water molecules,and the water flux is lower than that of the Mo-terminal system.The water flux and rejection rate of the Mo-terminal and S-terminal systems increase with the increase of the number of layers,and the water flux of the mixed-terminal system decreases.The three-layer Mo-terminated MoS₂ system has the best seawater desalination performance,with a water molecule number of 716 and a rejection rate of 100%.Ti₃C₂ and MoS₂ were used as photothermal conversion materials for interfacial evaporation seawater desalination system to explore the effects of slit width,Ti₃C₂ position and MoS₂ end group on seawater desalination performance.The results show that the addition of MoS₂ can improve the desalination performance of Ti₃C₂ system.When the slit width is 8（?）and Ti₃C₂ is located below the S-terminal MoS₂,the seawater desalination performance is the best,the water flux is 512 and the salt rejection rate is 100%.The fracture of hydrogen bonds between water molecules in the system with Ti₃C₂ located above MoS₂ leads to the discontinuity of water molecules transmission,the energy barrier through the channel increases,and the water flux is lower than that of the system with Ti₃C₂ located below MoS₂.The salt rejection rate of all research systems at 8（?）reached100%,and the rejection rate decreased with the increase of slit width.The water flux of different end-group systems is S-terminal>Mo-terminal>mixed-terminal.The Cl^-of the Mo-terminal system accumulates at the port to hinder the transmission of water molecules,and the spatial steric hindrance of the mixed-terminal is the largest.In this paper,molecular dynamics simulation is used to reveal the seawater desalination performance of MXene Ti₃C₂ and MoS₂ from the molecular level,which lays a theoretical foundation for the efficient seawater desalination of new two-dimensional nanomaterials.