| With industrialization and urbanization,the shortage of fresh water resources has become one of the biggest challenges for modern society.The application of reverse osmosis for desalination can separate water and salt ions by external pressure and semi-permeable membranes to obtain pure fresh water.Among them,carbon-based two-dimensional porous membranes,due to their unique atomic thickness,smooth surface(surface fouling resistance),high solvent resistance,non-toxicity and non-hazardousness,excellent thermodynamic and chemical stability,and high mechanical strength are considered as a new generation of high-performance desalination membrane candidates.However,the development of nanoporous structures with good mechanical properties and electronic characteristics remains extremely challenging.Furthermore,simulating the behavior of salt ions and water molecules in a restricted space from a microscopic scale can help to understand the properties and physical mechanisms of two-dimensional porous materials for desalination,thus providing theoretical guidance for the screening and design of membrane materials with superior performance and wider applications.Therefore,in this study,two carbon-based two-dimensional porous materials(Kust-I and graphdiyne)are used to investigate the potential of Kust-I and graphite acetylene membranes for seawater desalination applications using first-nature principles and molecular dynamics methods,to elucidate the effects of the interaction between salt ions and water in seawater and the filtration membrane on water and salt transport,and to reveal the water fluxes and the physical mechanisms behind the salt ion retention rates.physical mechanism behind its water flux and salt rejection rate.The main conclusions obtained in this thesis are as follows:(1)Based on density-functional theory,a high-performance stable two-dimensional graphene-based material(Kust-I)with a nanometer pore size of 0.45 nm is cleverly constructed with decagonal,hexagonal,and pentagonal carbon rings.First-principles and classical molecular dynamics simulation results indicate that ten-membered and pentagon rings act in parallel in Kust-I to provide sufficient salt-ion selective adsorption sites and the electron concentration and desalination effect of this material is satisfactory.The mechanical and electronic properties result further suggest that the periodic pore structure and electron distribution can effectively overcome the stress concentrations,improve the service life,and produce a self-cleaning effect that facilitates recycling.Highly anticipated,a potentially facile Kust-I synthesis route was proposed.These findings show the material’s tremendous potential in addressing the significant challenge of achieving a mechanical stability,long service life,ease of recycling,and large-scale application of current two-dimensional carbon materials.(2)The results further suggested that synthesizable graphdiyne was one of the most promising potential desalination membranes by virtue of its periodic pore structure,electronic properties,and structural stability.Graphdiyne membranes have a salt rejection rate close to 100%and require less pressure compared to other 2D materials.We then found that the transition-state energy of Na~+in a graphdiyne membrane was satisfactory(0.03 e V)due to significant charge-transfer between the carbon atoms in the periodic pores and Na~+in the pz orbitals.This blocked the filtration and agglomeration of Na~+,while imparting the graphdiyne membrane with metallicity.Therefore,in striking contrast to conventional polymeric thin films,the periodic conductive network is expected to enable the reuse of reverse osmosis membranes through the application of an electric field,thereby increasing their service life.We present herein a new approach for the design and screening of next-generation desalination membranes,which is only one step away from solving the problem of introducing periodic nanopores in two-dimensional carbon materials. |
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