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The rapid development of modern society leads to the inadequate supply of fresh water,which is a great challenge to the global sustainable development.Seawater desalination by reserves osmosis(RO)is an efficient technology to produce fresh water suitable for human consumption and irrigation.Presently,it comprises of 60%of desalination capacity worldwide and represents 75-85%of new desalination projects.A large number of studies have been conducted to develop novel membranes to cope with the high capital cost of current RO technology.In the last decade,dipeptide crystals have been utilized as permselective materials in gas separation.Particularly,crystalline hydrophobic dipeptides of Val-Ala(VA)class can form identical,parallel unidimensional nanoporous pores with average size ranging from 0.37 nm to 0.50 nm.The remarkable features of the pores imply good potential of hydrophobic dipeptides as RO membranes for water desalination.In this work,for the first time,molecular simulations are performed to investigate water desalination through eight membranes composed of Ala-Val(AV),Val-Ala(VA),Ala-Ile(AI),Ile-Ala(IA),Val-Ile(VI),Ile-Val(IV),Val-Val(VV)and Leu-Ser(LS)dipeptides.In all the eight membranes,100%salt rejection is achieved.Water permeability in VV,LS and AV dipeptides ranges from 5.78×10-7 to 7.15×10-7 kg.m/(m2.h.bar),much higher than that in commercial RO membranes.Water flux is influenced by both pore size and helicity.In AV,VV and LS,higher water flux is found primarily attributed to a larger pore size.Despite similar pore size in VA and AI,lower flux is observed in the former due to a higher helicity.The life time of hydrogen bonding in AV is the shortest than in IA and AI,which follows the order of water diffusion.An Arrhenius-type relationship is found between water flux and temperature in both AV and AI,and the activation energies are predicted to be 58.8 and 100.8 kJ/mol,respectively.Furthermore,the effect of force constant for position restraints is examined.Water flux in AV is not significantly affected when the force constant is > 500,but largely affected when the force constant < 500; this is attributed to the increasing fluctuation of pore size.The simulation study provides microscopic insights into water transport in dipeptide crystals and suggests the good potential of dipeptides as RO membranes for water desalination.