Interfacial Structure And Dynamics At Water-carbon Interface

Water and carbon are the two indispensable and fundamental substances in industrial applications and daily lives.The intricate and delicate interactions between them profoundly affect the human activities.Two-dimensional materials,such as graphene,exhibit superior molecular transport and molecular sieving properties,which is dependent on the nanopores on membrane planes or the slits between adjacent membranes.In realistic applications,graphene and graphene oxides exhibit nice water desalination,proton transport and gas separation properties.Graphyne,a newly discovered carbon allotrope,has attracted great attention due to the nanomesh structure and the potential in molecular sieving applications.At the same time,the nucleation ability of water on graphite surfaces greatly affect the nucleation rate of ice nuclei in atmosphere.Therefore,the understanding of water-carbon interaction is of great importance to realistic applications.In this thesis,using molecular dynamics simulations and density functional theory calculations we investigate the interfacial water structure and dynamics at water-carbon interface,including the molecular sieving properties of graphdiyne and the two-dimensional ice on graphite substrates.The main contents of this thesis are listed below.1)We discover the activated water flow through the nanopores on graphdiyne membrane,and revel the atomistic mechanism of transmembrane water transport.Graphdiyne is a newly discovered carbon allotrope in graphyne family.Compared with graphene,graphdiyne exhibits the intrinsic nanomesh structure with great uniformity and high nanopore density.Here using ab initio and classical molecular dynamics simulations we demonstrate that water can flow through graphdiyne.Water transports through subnanopores via a chemical-reaction-like activated process.The activated water flow can be precisely controlled through fine adjustment of working temperature and pressure.In contrast to a linear dependence on pressure for conventional membranes,here pressure directly modulates the activation energy,leading to a nonlinear water flow as a function of pressure.Consequently,high flux?1.6 L/Day/cm²/MPa?with 100%salt rejection efficiency is achieved at reasonable temperatures and pressures,suggesting graphdiyne can serve as an excellent membrane for water desalination.We further show that to get through subnanopores water molecule must break redundant hydrogen bonds to form a two-hydrogen-bond transient structure.2)Based on the researches above,we demonstrate that graphdiyne membrane shows superior proton conductivity and perfect selectivity thanks to its intrinsic nanomesh structure.The trans-membrane hydrogen bonds across graphdiyne serve as ideal channels for proton transport in Grotthuss mechanism.The free energy barrier for proton transfer across graphdiyne is?2.4 k J mol^-1,nearly identical to that in bulk water(2.1 k J mol^-1),enabling“transparent”proton transport at room temperature.This results in a proton conductivity of 0.6 S cm^-1 for graphdiyne,four orders of magnitude greater than graphene.Considering its ultimate pore size of 0.55 nm,graphdiyne membrane blocks soluble fuel molecules and exhibits superior proton selectivity.These advantages endow graphdiyne a great potential as proton exchange material.3)We discover the monolayer self-assembly ice on graphite substrate,and demonstrate that it is a two-dimensional variant of ice-II.The carbon nuclei from burning of fossil fuel are the main particle sources for ice nucleation in atmosphere.The nucleation and anti-nucleation of ice at the surface of carbon materials are of great importance to industrial applications.With combined theoretical and experimental explorations,we report discovery of a novel monolayer ice built exclusively from water hexamers but without shared edges,distinct from all conventional ice phases.Water grown on graphite crystalizes into a robust monolayer ice after annealing,attaining an exceeding high density of 0.134?^-2.Unlike chemisorbed ice on metal surfaces,the ice monolayer can translate and rotate on graphite terraces and grow across steps,endorsing its two-dimensional nature.We identify the monolayer ice structure as a variant of two-dimensional ice II at the surface.In this thesis,we investigate the interfacial water structure and dynamics at water-carbon interface.Two-dimensional carbon materials exhibit superior potential in molecular transport and molecular sieving,while the industrialization of these applications still need experimental and theoretical explorations.The modulation of nucleation ability at water-carbon interface is crucial in artificial rainfall and antifreeze.What's more,water-carbon interface gives rise to many novel physical and chemical properties.Water-carbon interaction is a fundamental and important type of interaction,the research of this interaction will benefit the human beings.