Study On Tuning Interlayer Spacing Of Graphene Oxide Composite Nanofiltration Membranes And Dye Separation Performance

Owing to the development of textile industry,about 2.37 billion tons of dyeing wastewater with high salinity is produced every year,causing serious environmental pollution and waste of resources.The dyeing wastewater is highly toxic,complex in composition and difficult to handle.It is difficult to recycle dyes and inorganic salts by traditional water treatment technology.As a novel separation technology,nanofiltration?NF?with molecular weight cut-off of 200-1000 Da has the advantages of high efficiency,energy saving,mild working conditions,which has been used to effectively separate organic dyes.However,the traditional nanofiltration membranes?polymer-based and ceramic-based membranes materials?suffer from poor chemical durability,high cost,complex fabrication procedure or fragile.Graphene oxide?GO?,a type of two-dimensional material,has sufficient oxygen-containing groups,including epoxide,hydroxyl,and carboxylic acid groups.These functional groups lead to good hydrophilicity and allow excellent dispersion of GO nanosheets in water.GO has been used to fabricate nanofiltration membranes due to excellent chemical stability,high mechanical strength and strong hydrophilicity properties.GO-based membranes have controllable interlayer nanochannel,through which the selective permeation of dye molecules or inorganic salts would be achieved,thus realizing the recycling of dyes and inorganic salts.In this paper,amine modified Fe₃O₄ particles?NH₂-Fe₃O₄?,Ni-Fe layered double hydroxides?Ni-Fe-LDH?and metal organic frameworks?MOF?nanoparticles were selected to tune the interlayer spacing of GO-based membranes,and the GO-based composite nanofiltration membranes were fabricated using polyvinylidene fluoride?PVDF?porous membranes as support via vacuum filtration technique.The research contents and main conclusions are as follows:?1?Selecting 3-aminopropyltriethoxysilane?APTES?modified Fe₃O₄ particles as intercalation nanomaterial,GO/NH₂-Fe₃O₄ composite NF membranes were prepared by vacuum filtration,and the effect of addition amount of NH₂-Fe₃O₄ nanoparticles on nanofiltration performance was investigated.XRD,AFM,SEM and Zeta potential were adopted to characterize and analyze the structure of GO/NH₂-Fe₃O₄ composite NF membranes.The results showed that surface roughness of the membrane increased,and the membrane surface negative electronegativity decreased.It can be observed that with the increased addition of particles,the interlayer spacing of GO/NH₂-Fe₃O₄ membranes enlarged,which resulted in the improved water flux.The water flux of GO/NH₂-Fe₃O₄-8 membrane was up to 78 L/?m²h?,which was about 4.8 times more than that of pristine GO membrane,while the rejection rate to Congo red decreased only 1.8%than that of pristine GO membrane.The changed tight stacking structure enlarged nanochannel in GO-based membranes owing to the intercalation of NH₂-Fe₃O₄ nanoparticles,improving the separation performance on the Congo red/inorganic sodium salt mixed solution.The pristine GO membrane with low water flux had much higher rejection rates to Congo red and inorganic sodium salts,hardly to separate them.For Congo red/inorganic salts mixed solution,GO/NH₂-Fe₃O₄-8 composite NF membrane with high water flux showed a excellent Congo red rejection ratio?about 94%?and lower salts rejection,improving the dye desalination performance.In addition,the operating pressure increased from 0.2 MPa to 0.8 MPa,and the water flux of GO/NH₂-Fe₃O₄-8membrane showed a large enhancement in 208%?from 34.5 L/?m²h?to 106.4 L/?m²h??,while that of the pristine GO membrane was only increased by 142%.This result suggested that the embedded NH₂-Fe₃O₄ nanoparticles significantly improved the compaction resistance and structural stability of the GO-based composite membranes.?2?Ni-Fe-LDH particles were prepared by hydrothermal method,and the morphologies and structures were characterized by FT-IR,XRD and SEM.GO nanosheets and Ni-Fe-LDH uniformly dispersing in water,a series of GO/LDH composite membranes were prepared on dopamine-coated PVDF porous support.The results suggested that the hydrophilicity and Zeta potential of membranes surface increased with the introduction of LDH into membranes.As the amount of LDH increased introduction of LDH,the interlayer spacing of GO-based membranes became larger,obtaining a loose interlayer structure,which resulted in an enhancement of water flux.The water flux of GO/LDH-2 membrane was up to 54.6 L/?m²h?,which was about 3.1 times more than that of pristine GO membrane,while maintaining high dye rejection ratio?99%for Congo red,83.5%for methyl orange and 73.6%for methylene blue?.After continuous operating for 14 hours,flux and rejection to Congo red of GO/LDH-2membrane maintained at 37.3 L/?m²h?and 99%,respectively,indicating good long-term performance stability.?3?The NH₂-MIL-53?Al?porous nanoparticles were successfully prepared by solvothermal method,and their microstructures were characterized by FI-IR and XRD.Then GO/MOF composite membranes were prepared by vacuum filtration method.The results indicated that with the increase amount of NH₂-MIL-53?Al?nanoparticles,surface roughness of the composite NF membranes increased gradually,and the SEM images showed that the nanoparticles were uniformly embedded into the interspaces of graphene oxide nanosheets,leading to the increased interlayer spacing.As the addition amount of NH₂-MIL-53?Al?increased,the composite membrane showed a large enhancement in water flux.The water flux of GO/MOF-3 was up to 58.5 L/?m²h?,which was 3.4 times more than that of pristine GO membrane,while the rejection to Congo red,methyl orange and methylene blue remaining at 99.3%,86%and 77.2%,respectively.And GO/MOF-3 composite NF membrane showed the rejection decreased to 66.7%for Na₂SO₄ and 37.5%for NaCl.With transmembrane pressure increased from 0.2 MPa to 0.8 MPa,the water flux of GO/MOF-3membrane exhibited a large enhancement in 212%?from 25.2 L/?m²h?to 78.5 L/?m²h??,which indicated that the intercalation of NH₂-MIL-53?Al?nanoparticles into GO-based membranes enhanced the resistance to compaction obviously and maintained pore structural stability of composite NF membranes.