Controlled Fabrication Of Chemically Modified Graphene Films And Their Applications

Graphene is a single layer of two-dimensional carbon lattice.Defect-free graphene possesses excellent mechanical,electrical,and optical properties,while its processability is poor.Chemically modified graphene(CMG)including graphene oxide(GO)and reduced graphene oxide(rGO)are dispersible in various solvents and partly retain the structure and properties of perfect graphene.Therefore,CMG has potential applications in a variety of fields,such as composite materials,energy related systems,and catalysis,etc.Two-dimensional CMG sheets are unique building blocks for self assembly and they can be readily assembled into functional CMG films.In this dissertation,CMG films with controlled microstructures were developed and their applications in high-strength structural materials,flexible supercapacitor,and molecular separation were explored.The main content is listed as follows.Silk fibroin(SF)/GO composite films were prepared by intercalating SF chains between the interlayers of GO sheets.The strong electrostatic and hydrogen bonding interactions between both components improved the mechanical properties of the composite films.The as-prepared SF/GO composite film containing 15 wt% of SF showed a high tensile strength of 221.3 ± 16.4 MPa,about twice that of pure GO film(114.1 ± 24.1 MPa).The restacking of rGO sheets was effectively prevented by intercalating poly(vinyl pyrrolidone)(PVP)chains between adjacent rGO sheets.The PVP/rGO composite film containing 45 wt% of PVP is mechanical strong(121.5 ± 10.8 MPa)and highly conductive(247.9 S/m).The solid-state supercapacitor based on this composite film showed excellent flexibility,high volumetric specific capacitance(67.4 F/cm3 at a current density of 1 A/g),and good rate capability.This flexible supercapacitor retained a high volumetric specific capacitance of 51.2 F/cm3 even at an ultrahigh current density of 100 A/g.The semipermeability of GO films in organic solvents and its modulating methods were studied.GO films can be swollen by organic solvents and the degrees of solvation depend on the properties of solvents.By carefully choosing solvents,the nanochannel sizes in GO films can be regularly modulated.For example,pyrene molecules are ableto penetrate GO film when using ethanol as solvent,but they will be blocked as n-hexane or toluene was used as the solvent.Thermal annealing can also tune the nanochannel sizes in GO film,thus modulating its semipermeability.The permeation rates of solutes dissolved in ethanol decrease with the increase of annealing temperature.An ultrathin layer of solvent solvated r GO(S-r GO)was deposited on a Nylon microfiltration film by vacuum filtration.In methanol solvent,the resultant S-r GO composite films showed high rejections to small-size negatively charged solutes and neutral molecules with sizes larger than 3.4 nm,while retaining their high methanol permeance(~75 L/m2·h·bar).Moreover,these S-r GO composite films are stable in organic solvents,and strong acidic,alkaline,or oxidative media,showing promise for organic solvent nanofiltration of practical significance.