| With the dramatic increase of global population and the acceleration of modernized industries,the scarcity of freshwater resources has becoming one of the biggest challenges facing the world.Seawater desalination is an effective way to solve this problem,pervaporation desalination has received much attention on account of the advantages of thermal and membrane methods,and high efficiency in treating high-salinity wastewater.In recent years,graphene oxide（GO）has been widely used in pervaporation desalination due to its abundant oxygen-containing functional groups and strong hydrophilicity.However,pure GO is prone to swelling and poor stability in aqueous solutions,affecting the stability of membrane applications.Based on the application field of seawater desalination,the preparation,characterization and desalination performance of GO composite membranes which was functionalized GO with tris（2-hydroxyethyl）isocyanurate（THEIC）and tetramethylammonium-based caged polysesquioxane（POSS-O-NMe4+,POSS for short）was systematically investigated in this work.The details of this study are as follows:（1）GO/THEIC composite membranes with stable structure were prepared by cross-linking with tris（2-hydroxyethyl）isocyanurate using vacuum dip coating on ceramic supportα-Al2O3 tubes.By optimizing the GO/THEIC composite membranes,the pore size of the porous support was 200 nm,the mass ratio of GO/THEIC was 1/4,and the concentration of GO/THEIC complex solution was 0.02 g·L-1,resptectively.The permeate fluxes of the optimized GO/THEIC membranes at 30 oC were tested in pure water,0.3 wt%Na Cl and 3.5 wt%Na Cl solutions,resptectively.The fluxes of 35.3,28.1 and 23.0 kg·m-2·h-1,respectively,and Na Cl rejection over 99.9%were obtained.The characterization results of FTIR,XRD indicate the introduction of hydroxyl groups on THEIC improved the hydrophilicity of the membrane;meanwhile,the reaction between THEIC and GO nanosheets generated ester groups,which increased the membrane layer spacing GO interlayer bonding force and inhibited GO swelling,thus the water permeation flux and the stability of the membrane have been improved.The optimized GO/THEIC membrane can achieve accurate screening in the treatment of different salt solutions and heavy metal ions as well as keeping high pure water flux(31.1±1.0 kg·m-2·h-1)and desalination performance after 16 days of cycling in pure water-3.5 wt%Na Cl solution.The GO/THEIC composite membranes will have promising applications in seawater desalination,wastewater treatment.（2）GO/POSS composite membranes with high-performance were prepared by vacuum dip coating method using tetramethylammonium-based caged polysesquioxane as a cross-linking agent incorporated between graphene oxide layers.Various characterization,results confirmed that the incorporation of rigid structures containing Si-O-Si bonds between POSS and GO interlayer which were formed during the membrane formation process changed the microstructure of the membrane surface and reduced the membrane layer spacing,thus improved the desalination performance and stability.The best desalination performance of the GO/POSS composite membrane was achieved when the optimized preparation conditions were as follows:the mass ratio of GO/POSS was 5 wt%,the concentration of GO/POSS composite solution was 0.08 g L-1,the vacuum dip coating time was 20 s,and the p H of the composite solution was 8.The optimized GO/POSS composite membrane exhibited the best water permeated flux with 12.0 kg·m-2·h-1 and nearly 100%rejection in 3.5 wt%Na Cl solution at 60°C,meanwhile,it had good separation performance in high concentration salt solution and rare earth wastewater by size sieving.In addition,the GO/POSS composite membrane showed excellent separation performance and stability after 180 h test in simulated seawater（salinity:3.34 wt%）,as well as good acid resistance capacity during 15 days of continuous testing at 60 oC and p H=2-12.The GO/POSS composite membranes have great potential for seawater desalination and rare-earth wastewater treatment. |
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