Study On Preparation Of Graphene Oxide, Graphene And Them-based Composite Membranes

Graphene, which was first prepared in2004, has attracted tremendous attention andbecome the leading edge and hotspot in various relative fields. Due to many intriguingphysical, chemical and mechanical properties, graphene has great potential appliedvalue. In this paper, we prepared graphene oxide (GO) and graphene firstly, and thenprepared them-based composite membranes and explored their performance.We provide a facile approach using graphene oxide colloidal suspension to preparegraphene nanosheets with concentrated sulfuric acid (H2SO4) as deoxidizing agent forthe first time. Results show that the higher the reaction temperature and the H2SO4concentration, the more complete the reduction. According to these two impactparameters, we found that the concentration of H2SO4is the key factor to determinethe degree of reduction. Only the concentration of sulfuric acid more than70wt%, thedegree of reduction would be more thoroughly.PVDF/Graphene composite membranes were prepared by a solution mixingmethod. As the content of graphene increased, the cross-section of the membranesshowed more and more scale-like stubble structure. The breaking strength of thecomposite membranes reached the maximum value as graphene content of0.5wt%,which increased34.2%compared to the pure PVDF membrane. The compositemembranes show low percolation threshold around1wt%graphene loading, theconductivity is0.001S/m.Graphene oxide was incorporated into the SPEEK matrix with relative high DS(67%) to prepare novle composite membranes for the first time. The strong interactionbetween the GO nanosheets and SPEEK molecular chains helps to reduce the swellingand methanol permeability of the composite membranes, and improve thedimensional stability. For the composite membranes, high conductivity can beachieved as the applicable temperature is improved.SPEEK ultrafiltration (UF) membranes with different DS were prepared byimmersion phase inversion method, methylsulfonic acid was used as solvent toaccommodate SPEEK. The water uptake, swelling and surface pore size wereincreased with the DS. Water flux was increased dramatically with the DS, flux of themembrane with60%DS was3.2times that of12%DS. For all the membranes,rejections of BSA were much higher, however, the rejections of PEG-20K and Rose Bengal were decreased with the DS dramatically. During the filtration of BSAsolution, all the SPEEK membranes showed lower permeate fluxes due to membranefouling, which produced by the protein molecules entrapping in the pores and blockthe channels under the trans-membrane pressure. Besides, the permeate flux wasrelevant to the feed pH. When feed pH was higher than7, the repulsion of chargesbetween BSA and membrane surface was enhanced, which suppressed the depositionof BSA, thus keep the permeate flux at a higher level.We prepared SPEEK nanofiltration (NF) membranes with7%DS and studiedtheir NF performance. The effects of several basic factors on performances, such asSPEEK concentration, coagulation-bath temperature and component, were explored.SPEEK NF membranes with excellent thermal stability can be used in hightemperature circumstance. In addition, we also prepared SPEEK/GO compositemembrane. Results show that the permeate flux decreases, the rejection and thedimensional stability increased with the rise of GO content.