Preparation And Separation Performance Of Amino-Crosslinked Graphene Oxide Framework Composite Membranes

With the rapid development of the national economy and industrialization,the discharge of industrial wastewater is increasing rapidly.Among them,the discharge of high-salinity wastewater accounts for 5%of total wastewater volume in China and it keeps increasing by 2%every year.High-salinity wastewater has caused serious harm to both human health and the whole ecosystem.As a new type of two-dimensional carbon material,graphene oxide?GO?has attracted much attention due to its strong hydrophilicity,unique structure of oxygen-containing functional groups and large specific surface area,which is widely used as membrane separation material.Compared with other treatment technologies for high-salinity wastewater,membrane separation technology has the advantages of energy conservation,environmental protection and high efficiency.In this work,the amino-crosslinked graphene oxide framework?GOF?composite membranes were fabricated by GO functionalized modification with two crosslinking agents.The preparation,characterization and separation performance of GOF composite membranes were systematically studied.The details were as follows:?1?The graphene oxide/urea?GO/UR?composite was prepared by covalently modifying GO with UR,and then GO/UR composite membranes with GOF structure were fabricated with vacuum filtration method.The optimum membrane preparation conditions were obtained as follows:the mass ratio of GO to UR was 1/3.750 and the concentration of GO solution was 0.02 g L^-1 at room temperature.At 30 ^oC,the water permeated flux of GO/UR composite membrane were 36.1 kg m^-2 h^-1 and 21.2 kg m^-2h^-1 for pure water and 3.5 wt%NaCl solution,respectively,which were much higher than those of the pristine GO membrane.And at 60 ^oC in 3.5 wt%NaCl solution,the water permeated flux of GO/UR composite membrane was three times than of the pristine GO membrane,which was over 34.0 kg m^-2 h^-1,and the salt rejection rate was above 99.9%.The water permeated flux of 108.0,70.3 and 42.0 kg m^-2 h^-1 were achieved towards pure water,3.5 wt%and 20 wt%NaCl solutions at 90 ^oC,respectively,and the salt rejection rate were higher than 99.9%.According to the characterization results of FTIR,XPS,and XRD,it was also confirmed that GO and UR were successfully covalently reaction,which could effectively inhibit the GO swelling in aqueous solution.Moreover,such this membrane showed good long-term stability,which might be related to the interlayer spacing,surface hydrophilicity and three-dimensional laminar structure of the GOF membrane.?2?The graphene oxide/polyamidoamine?GO/PAMAM?composite membranes with GOF structure were prepared by cross-linking GO with PAMAM dendrimer.A series of studies on the membrane preparation conditions were investigated and the optimized conditions of GO/PAMAM composite membrane were obtained as followings:the mass ratio of GO to PAMAM was 1/1,the solvent was ethanol,and the GO solution concentration was 0.02 g L^-1.Thus,the highest water permeated flux and rejection rate above 99.99%were obtained for this membrane.By the characterization results of FTIR,XRD,TEM,Raman,XPS and AFM,GO and PAMAM could be successfully cross-linked to effectively improve the hydrophilicity and water channel structure of the membrane,thereby improving the separation performance of the GOF membrane.The GOF membrane exhibited good hydrothermal stability in different salt solutions at different concentrations of 30-75^oC.In addition,the membrane had good separation performance in wastewater treatment containing high-salinity?NaCl content of 10 wt%?and bisphenol A?BPA?,which is a typical representative of environmental endocrine disruptors.The GO/PAMAM composite membrane has potential application prospects in high-salinity wastewater treatment and water purification.