Simulation Studies For Hydrogen-bonding,Structure,Transport Behaviors,and Their Coupling Mechanisms Of Confined Water In Carbon Nanochannels

In the past decades,confined water has always received intensive attention since for their unusual properties in the nanoscale confinement.At present,the experiments mainly explore the properties of confined water through different characterization methods and have made some progress.However,it still has to fight against enormous challenges for experimental observations to provide a comprehensive understanding of the unique microscopic properties of confined water.Furthermore,many studies on confined water have only concentrated on 1-D or 2-D confinement.In particular,there is a tremendous lack of research on water confined in the different dimensions,scales and shapes.Based on this research background,the research object is confined water and the main research content is to explore the HB,structure,transport behaviors and coupling mechanism of water molecules in carbon nanochannels from dimension,scale and shape by using MD simulation and machine learning is used to construct the confined water MLFF in carbon nanochannel,so as to better help researchers understand the special behaviors of confined water from the molecular level.In Chapter 2,we reported a series of classical MD simulations to explore confined water in the sub-nanometer-sized and nanometer-sized heterostructures by adjusting 1-D CNTs with different diameters and 2-D graphene sheets with different interlayer distances.We found that in the 1-D confinement,the sub-nanometer scale leads to a significant decrease in the HBs of water molecules,which leads to a significant increase in the transport rate.However,in the 2-D confinement,the transport behavior of water molecules at different sizes is almost the same as that of HB.Through further analysis,we knew that in the 1-D confinement,the transport rate of water molecules is opposite at the two scales,mainly because the HB plays a dominant role in the transport behavior of water molecules at the sub-nanometer scale,while the environment at the lower confined of the nanometer scale determines the transport behavior of water molecules.More importantly,through the comparison of our results,it is found that the 1-D confinement plays a more important role than the2-D confinement in determining the structure,dynamic and HB properties of water molecules in the 1-D/2-D heterojunction at both the sub-nano scale and the nano scale.In Chapter 3,we continue to perform a series of classical MD simulation methods to explore the behavior of confined water in the triangular carbon nanoparticles with different sizes.The transport behavior of water molecules in the three triangular nanochannels did not show a single change with the size,but that of graphyne-4 > graphyne-5 > graphyne-3.In addition,we also found that water molecules have two distinct orientations in the nanochannel,which have periodic reversal behavior in the transport direction.We further analyzed the frequency of HB breakage of water molecules in the orientation reversal process,and found that the size of the three systems was still graphyne-4 > graphyne-5 > graphyne-3.This result indicated that the larger the frequency of HB breakage of water molecules in the graphyne triangle nanochannel,the less HB is bound to the transmission process,resulting in a faster transmission rate.Based on the above results,we can see that in the graphyne triangle confinement,water molecules have an obvious periodic inversion transport behavior,and the transmission rate depends on the frequency of HB breaking and the variation of the number of HB.In Chapter 4,we adopted a combination of first-principles computing,molecular dynamic,and machine learning to develop a MLFF for water molecules confined in 1-D CNT(6,6)to further explore the structural and diffusion behavior of confined water molecules.The energy and force of atom calculated by DFT and predicted by MLFF appear being linear identical,namely the relationship between the two meet = curve trend,indicating that the MLFF of confined water molecules with high accuracy.Besides,the MLFF is further applied to explore the structural and diffusion behavior of confined water molecules.And according to the diffusion coefficient formula got its α value of 1.62,which means that the mode of diffusion is not fully ballistic mode compared with the value of the classical water molecular force field.The research work in the postgraduate stage is mainly from two aspects: The first is molecular dynamic;the second is first-principles calculation,molecular dynamic and machine learning coupling.From the perspective of molecular level,the structure,dynamics and HB properties of confined water molecules in carbon materials are comprehensively explored,which has important guiding significance for experimental scientists to further design and prepare high-performance new carbon materials.