Preparation And Characterization Of Functionalized Graphene Oxide Composite Membranes And Their Separation Performance For Dye Wastewater Treatment

With the rapid industrialized and economic development,industrial wastewater pollution has become an increasingly serious problem.Among them,dye wastewater poses a serious threat to human health and water ecosystems.As a new two-dimensional material,graphene oxide?GO?has many features including oxygen-containing functional groups,large specific surface area,and strong adsorption capacity.It is widely modified as an adsorbent for dye wastewater treatment.Compared with common treatment processes such as adsorption,membrane separation technology has the advantages of high efficiency,environmental protection and energy conservation.However,there are few reports on high-flux GO-based membranes with high-rejection performance for dye wastewater treatment.In this dissertation,two kinds of functionalized graphene oxide composite membranes were prepared by GO functionalized modification and vacuum filtration method.Preparation and characterization of GO-based composite membranes and their separation performance for dye wastewater treatment were systematically investigated,and the separation mechanism through these membranes was studied details.Graphene oxide/attapulgite?GO/APT?composite membranes were fabricated by the assembly of natural clay of APT nanorods incorporating into the interlayers of GO sheets via chemical graft modification.By characterization of FTIR,XPS,Raman,XRD and FESEM,APT nanorods were confirmed to be incorporated into GO laminar layers via grafting modification to form a C-O-Si bond.Therefore,a composite membrane was constructed with a three-dimensional network laminate structure,which would influence GO interlayer distance?d-spacing?,membrane surface microstructure and separation performance.Comparison of those of pristine GO membrane,the calculated d-spacing of GO/APT composite membranes increased from 0.90 nm to 1.07 nm,while water contact angles of membrane surface decreased from 71.0° to 43.3°.The water permeated flux increased from 3.4 of pristine GO membrane to 13.3 L m^-22 h^-1 of GO/APT membrane with preserving high rejection over99.9%for 7.5 mg L^-1 Rhodamine B wastewater under optimized conditions.Similarly,membrane thickness,dye concentrations and separating dye species with positive and negative charges in feed solutions were also found to affect separation performance of this composite membrane.Such these GO/APT composite membranes exhibited high rejection performance for dye molecules.Dye molecules were efficiently rejected through these membranes by the synergistic separation mechanism of molecular sieving?size exclusion effect?and electrostatic interaction.These GO/APT membranes provided additional insight into the potential applications in water purification and dyes wastewater treatment.GO/EDTA and GO/EDTAS composite membranes with three-dimensional graphene oxide framework?GOF?structure were prepared by covalent crosslinking reaction with ethylenediaminetetraacetic acid?EDTA?and N-?trimethoxysilylpropyl?-ethylenediaminetriacetic acid?EDTAS?as crosslinking agents,respectively.The results of XRD,FTIR,XPS,Raman and FESEM showed that the functionalized modification of GO nanosheets with EDTA?EDTAS?produced a three-dimensional network structure with covalent bonds,which effectively improved membrane stability,and regulated the membrane d-spacing and membrane surface hydrophilicity thus enhancing separation performance of membrane.Pure water flux of GO/EDTA composite membranes increased from 5.1 L m^-2 h^-1 for pristine GO membrane to 90.0L m^-2 h^-1 under optimized conditions,which were more than 16 times higher than that of pristine GO membrane.And the rejection performance was maintained with higher rejection rate for dye molecules such as coomassie brilliant blue.Moreover,membrane thickness,pH and ionic strength in the dye solutions,chemical structure of dye species with positive and negative charges also affected the separation performance of these membranes.Such these GO/EDTA and GO/EDTAS composite membranes exhibited high separation performance for organic dye molecules through the synergistic separation mechanism:molecular sieves,electrostatic interactions and?-?interactions between dye molecules and the membrane surface.It could be effectively solved the trade-off problems between permeated flux and rejection performance of membranes,which provided a reference for the application in high-salt dye wastewater treatment for graphene oxide-based membranes.