Preparation And Properties Of Macro-sized Graphene Oxide Functional Films

Since the 21st century,with the rapid development of modern industry and the over-exploitation of natural resources,the pollution of water resources and the shortage of safe water have become increasingly serious,which has become one of the severe crises faced by the development of human society.Compared with traditional water treatment technology,membrane separation technology has the advantages of high efficiency,environmental protection,simplicity and energy saving,and has been widely used in water treatment and other fields.As an oxidation derivative of graphene,graphene oxide(GO)has attracted extensive attention due to its unique one-atom thickness and two-dimensional structure,as well as its versatility in antibacterial,amphiphilic and processability.GO layered array membrane is considered as a membrane material with a variety of application prospects.However,in fact,due to the high hydrophilicity of the lamellar,the layered GO membrane exhibits an inherent tendency of expansion in water,which leads to the significant expansion of the interlayer distance and even structural collapse,thus losing its separation performance,which seriously limits their practical application.Therefore,in this paper,the GO/polymer composite dispersion with good viscosity was constructed,and then the macroscopically sized and structure-stable GO composite membrane materials were mass-prepared by combining dip coating method and chemical crosslinking method,and the microstructure,stability,membrane separation performance and photothermal evaporation performance of GO matrix composite membrane were systematically studied.The specific research content is divided into the following two parts:The first part is the preparation of GO/polyvinyl alcohol(PVA)composite film by dip coating and its properties.The relationship between the viscosity of GO/PVA composite dispersion and GO concentration and PVA ratio was studied.It was found that the viscosity and film-forming properties of GO dispersion were significantly improved after mixing with PVA.The GO/PVA composite dispersion was applied to commercial qualitative filter paper by dip coating method to obtain large-size composite film,and the stability of composite film was enhanced by borate crosslinking reaction.The microstructure study shows that the surface of the composite film is smooth and uniform,and there is no defect.Membrane separation tests confirmed that the composite membrane has the potential to separate organic solvents/water mixtures and has good resistance to protein contamination.The water flux and MWCO of the GO/SA composite membrane can be easily adjusted by changing the content of GO or SA in the mixed dispersion solution.Multiple cycle tests showed that the GO/PVA composite membrane could recover about 86%of water flux after 4 cycles of protein contamination,showing good anti-protein contamination performance.The antibacterial test showed that the antibacterial rate of the composite membrane against Escherichia coli was above 99.99%.In addition,the composite membrane also showed good acid-base stability,organic solvent resistance,organic dye removal ability.It is worth mentioning that the composite film also shows considerable photothermal evaporation performance,and the evaporation rate of pure water can reach 1.28 kg/m~2/h under 1 sunlight intensity.The second part is also the preparation of GO/sodium alginate(SA)composite membrane by dip coating and its properties.The relationship between the viscosity of GO/SA composite dispersion and GO concentration and SA ratio was studied.The viscosity and film formation of GO/SA composite dispersion are significantly improved compared with GO.Calcium chloride crosslinked GO/SA composite film coated on commercial qualitative filter paper enhances the stability of the composite film by double crosslinking sodium alginate(SA)and calcium ions.The microstructure study shows that the surface of the composite film is smooth and has no defects,and presents obvious lamination structure.Membrane separation tests confirmed that the water flux and MWCO of the GO/SA composite membrane could be easily adjusted by changing the content of GO or SA in the mixed dispersion solution.Multiple cycle tests and organic solvent related tests show that the composite membrane has the potential to separate organic solvent/water mixture and has good resistance to protein contamination.The acid and alkali resistance test shows that the composite membrane can almost keep its original properties after soaking in HCl(1 mol/ml)or Na OH(1mol/ml)solution,which reflects the good acid-base stability of the composite membrane.It is worth mentioning that in the photothermal evaporation experiment,the evaporation rate of G9S1.8 membrane reached 1.37 kg/m~2/h under the condition of 1sunlight intensity,and after 7 days of continuous illumination in the simulated seawater environment,the efficiency was still stable at more than 80%.The above research results prove that GO/polymer composite dispersion,combined with dip coating method and chemical crosslinking method(borate ester crosslinking or ion crosslinking)can be used to mass-prepare macroscopically sized GO composite membrane materials,and obtain better structural stability,membrane separation performance and photothermal evaporation performance.The research work on the construction of GO composite dispersion with good viscosity and the mass preparation of macro-size GO composite membrane in this topic is expected to promote the promotion and application of GO composite membrane in the separation fields of substance separation,wastewater treatment,desalination and so on.