Mechanical Mechanism Of Ion Transport Through Angstrom-scale Graphene Channels

In recent years,the mass transport through nanochannels has received widespread attention from the academic and engineering communities,as well as industry,not only due to its cutting-edge significance in physical mechanics of surfaces and interfaces,but also because of its crucial application prospects in the fields of energy,environment,and health.With the continuous advancement of material preparation technology,the characteristic scale of nanochannel can be controlled under angstrom-scale For example,atomic smoothly graphene based two-dimensional channels,its characteristic scale can reach to angstrom scale.There are enormous application potentials of graphene channels in the field of pollution control,including desalination,hemodialysis,and ion batteries,and it is expected to achieve active regulation by screening different ions.In order to apply graphene channels to practical production and life as soon as possible,it needs not only the improvement of the level of preparation technology and experimental research,but also the urgent exploration and follow-up of theoretical research.In this paper,three mechanical problems,containing the mechanism of intermolecular forces among solid-liquid-ion interface,entry effect of two-dimensional channels on ionic dehydration and the mechanism of substance screening with angstrom channels are studied.The mechanical mechanism of ion transport in angstrom-scale graphene channels is systematically studied.Firstly,transport and friction behavior of ionic hydration layers in angstrom-scale channels are studied,the phenomenon of anion-cation charge asymmetry effect of mobility in channels is also interpreted.Structural and dynamic properties of ions confined in nanoslits are crucial to understand the fundamental mechanism underlying a wide range of chemical and biological phenomena.K+and Cl~show similar ion mobilities in a bulk aqueous solution,whereas they exhibit a remarkable difference when transporting through an angstrom-scale channel.Our molecular dynamics simulations uncover that such discrepancy originates from the subtle differences in their hydration structures and preferable locations across the channel.Opposite charge causes different water dipolar orientations around ions,mediating the distance and tribological interactions between hydrated ions and channel's walls.Hydrated Cl-ions experience a remarkable larger friction force inside the channel and consequently a smaller mobility compared with K+ ions.Secondly,the impeding mechanism of dehydration effect on ionic conductance in two-dimensional angstrom-scale channels are detected.There has been long-standing academic interest in the study of ion transport in nanochannel systems,owing to its vast implications in understanding the nature of numerous environmental,biological and chemical processes.Here,we investigate ion transport through two-dimensional slits using molecular dynamics simulations.These slits with angstrom-scale dimensions can be realistically replicated in the simulation,which leads to direct comparisons between simulations and experiments.In particular,this new confining geometry allows that the size exclusion effect can be unambiguously decoupled from other mechanisms.As the slit size approaches the ultimate scale,dehydration at the entry impedes the ionic conductance significantly,and even induces a complete ion rejection.We demonstrate that energy barriers required to accomplish the ion permeation can be theoretically connected to the partial dehydration process.The proposed model is further validated by simulations.Our results offer insights into the atomistic details of ion permeation,which may also cast light on developingFinally,the regulation mechanism of ionic screening and separation by monolayer graphene with different pore size is analyzed meticulously.Since the properties of hydration structures of lithium and potassium are similar,it is difficult to achieve high efficiency of screening and separation.Therefore,using the advantage of the molecular dynamics simulation method,detailed analysis of the ionic potential mean force and the dynamic variation of hydrate structures are researched,and the difference sieving mechanism of two kind of ions utilizing different porous graphene are compared and analyzed.Oh this basis,based on the lithium-ion battery with polymer-based porous graphene film,the shuttle inhibition effect of graphene pores on ions is discussed from the perspective of theoretical simulation analysis.Studies have shown that a monolayer graphene channel with suitable pore size and structure can effectively and selectively control the passage of lithium only,and prevent the migration of lithium polysulfide through the film,reducing the shuttle effect as a result.