Fabrication And Desalination Performance Of Ether-Functionalized Graphene Oxide Based Composite Membranes

The shortage of fresh water resources has become one of the most concerned problems in the world.Seawater desalination and salt-containing wastewater treatment is one of the effective ways to solve this problem.Membrane technology is considered as one of the most promising desalination technologies because of its high efficiency,potential energy saving,ease of integration and scale-out.Pervaporation desalination technology,as a new desalination technology,has attracted more and more attention in recent years,because it can process high concentration brine without high pressure driving force.However,membrane materials with high water flux and high salt rejection??99.9%?at room temperature are rarely reported.Graphene oxide?GO?is suitable for surface functionalization modification due to its surface containing a variety of oxygen-containing functional groups.For the treatment and application of high-salinity wastewater and heavy metal wastewater,in this thesis,GO composite membrane was prepared by using ether-containing molecules as covalent cross-linking agent to conduct cross-linking modification with GO.The preparation,characterization and desalination performance of GO composite membranes were systematically investigated.Specific research contents are as follows:?1?Four kinds of ether-diamine molecules with different chain lengths were used to modify GO nanosheet,and the GO/ether-diamine composite membrane with a membrane thickness of about 25 nm was prepared by vacuum filtration method.By optimizing the GO/ether-diamine composite membrane,the optimal preparation conditions of the composite membrane were obtained as follows:?-Al₂O₃ support was modified twice by?-AlOOH sol,ether-diamine was 1,2-Bis?2-aminoethoxy?ethane,the solution concentration of GO/BAE2 composite was 0.08 g L^-1,the mass ratio between GO and BAE2 was 1/10.For pure water,3.5 wt%and 20.0 wt%NaCl solutions at 30 ^oC,the GO/BAE2 composite membrane prepared under the optimal conditions had permeated fluxes of 34.0,18.1 and 8.7 kg m^-2 h^-1,respectively,and their NaCl rejection were both nearly 100%.The composite membrane showed excellent separation performance for both heavy metal wastewater and rare earth wastewater.The presence of the ether group in BAE2 molecule effectively improved the hydrophilicity of the composite membrane,Diamine molecules covalent cross-linking with GO could effectively inhibit the substantial increase of membrane layer spacing?d-spacing?in the water,increase the binding force between the GO nanosheets and stability,and in the simulated seawater desalination?3.5 wt%NaCl solution?stability test in more than 30 days could still maintain excellent permeation flux(18.2±0.2 kg m^-2 h^-1),desalination performance was stable.The GO/BAE2composite membrane will have an important application prospect in wastewater treatment of high-salinity and heavy metal smelting wastewater.?2?GO/EGTA composite membranes were prepared by crosslinking GO nanosheets with ethylene glycol-bis?2-aminoethyl ether?-N,N,N',N'-tetraacetic acid?EGTA?.It can be proved by various characterization methods that:Through the functionalization modification of GO by EGTA,the morphology of the membrane surface could be effectively changed,and the membrane layer spacing could be precisely regulated.The introduction of ethers in EGTA improved the hydrophilicity of the membrane and the desalination performance of the membrane,which also could effectively separate heavy metals and rare earth wastewater.The results of membrane characterization and desalination performance test showed that:The test results of pervaporation desalination showed that:when the mass ratio of GO and EGTA was1/4,the composite membrane had the lowest water contact angle and the strongest hydrophilicity compared with the membrane prepared under other preparation conditions.The water flux of the composite membrane for 3.5 wt%NaCl solution was19.3 kg m^-2 h^-1 at 30 ^oC,and the rejection of the composite membrane for different heavy metals and rare earth ions were almost 100%.After covalently crosslinking EGTA with GO,the GO/EGTA composite membrane still exhibited excellent hydrothermal stability under acidic and alkaline conditions?pH=3.00¹1.00?.Ether-functionalized GO composite membrane has potential application value in the treatment of high-salinity wastewater and heavy metal smelting wastewater.