Research On Mechanical Properties And The Application In Seawater Desalination Of Graph-N-Yne

Since the discovery of two dimensional(2D)structure-graphene in 2004,recent dozen years 2D materials gain a rapid evolution and investigation,many novel 2D materials rising from traditional materials have been reported with diverse structures and unique capabilities.As a 2D crystal,graph-n-yne(n=1,2,3,4,5)had been theoretically demonstrated in stability and graph-2-yne was synthesized in 2010.Graph-n-yne is constructed by sp-hybridized acetylene linkages conjugating sp2-ybridized benzene rings as a planar lattice structure.Due to its uniformly distributed pores and plentiful carbon bonds,graph-n-yne holds outstanding electronic,optical and photoelectrical properties as an excellent semiconductor,indicating that graph-n-yne has potentially important application in purification,electron,energy,catalysis and photoelectricity.There are many fundamental studies on graph-n-yne at present including some mechanical investigations,but the mechanical work is incomplete.Based on ab initio first principle calculation and molecular dynamics simulation,this thesis calculates the mechanical properties of graphyne to graph-5-yne,respectively.Firstly,lattice parameters of the primitive cells of graph-n-yne are obtained by utilizing ab initio calculations.The ideal mechanical properties and cohesive energies of primitive cells of graph-n-yne are calculated.These results indicate that the increasing number of acetylene linkages lead to the varying lattice parameters,reducing cohesive energy and decreasing structural stability.Secondly,using molecular dynamics(MD)simulations based on AIREBO potential,critical uniaxial tension of graph-n-yne nanosheets and nanotubes are implemented at room temperature.Initial in-plane stiffness,fracture stress and fracture strain of graph-0-yne(graphene)to graph-5-yne nanosheets and nanotubes under larger nanoscale are obtained.Graph-n-yne nanosheets and nanotubes show mechanical anisotropy.Moreover,the increasing number of acetylene linkages in graph-n-yne nanostructures have significantly attenuate influence on initial in-plane stiffness,fracture stress and fracture strain.Before and after structure failure,the behavior and crack propagation of nanostructures in different directions are analyzed and discussed,respectively.These results not only contribute to bond characterization of graph-n-yne,but also provide the guidance of structure and mechanics for the successful synthesis of other graph-n-yne members and their applications on related fields or nano-devices.Finally,the seawater desalination of single-layer graph-3-yne to graph-5-yne are further investigated based on MD method.Desalination speed and salt rejection rate of membranes are calculated with different pressure gradient along permeation directions at room temperature.The calculated results demonstrates that the desalination ratio increases with the dimensions of Vdw pores in membranes increasing.However,the salt rejection ratio of graph-4-yne and graph-5-yne decreases with the pore sizes and water pressure increasing.The calculated seawater desalination ratio of graph-3-yne is higher than that of traditional reverse osmosis membranes by two orders of magnitude.Further,the effect of membranes with partial charges on the process of seawater desalination was calculated.The membranes with partial charges can keep high salt rejection ratio.In conclusion,graph-3-yne and graph-4-yne membranes perform exceptional desalination and salt rejection.These theoretical calculations would have an instructive guidance for the future application of graph-n-yne membranes on seawater desalination.