Study On Preparation,Separation And Stability Of Graphene Oxide Based Dense Membrane

Dense membrane has been widely investigated for gas separation,pervaporation?PV?,reverse osmosis and nanofiltration?NF?.However,its further applications have been greatly restricted by the trade-off between the selectivity and permeability.To break the trade-off bottleneck,it is needed to ultrathin the separation layer without sacrificing its integrity.Moreover,it is a challenge to make an ultrathin separation layer with desirable structural and separation stabilities.Thus,it is urgently to develop new materials for the preparation of novel membranes with suitable separation capability and stability.Due to its ultrathin 2-dimentional sheets,excellent mechanical strength and abundant of functional group,graphene and its derivatives have attracted a lot attentions as the most promising materials.In this work,the graphene oxide?GO?was employed to fabricate different membranes for NF and PV.Based on its oxygen-contained groups,the GO nanosheets have been assembly with polycations and hyperbranced polymers.Then,the confinement effects of the GO nanosheets on the structure,surface properties and separation performance membrane have been detailedly investigated via characterization and separation performance evaluation.Firstly,a polycations/GO multilayer membrane have been obtained via electrostatic driven layer-by-layer self-assembly.The feasibility of the preparation has been confirmed by the regular changes of the zeta potential,hydrophilicity,absorbance and the deposited mass during the assembly process.The mechanical strength has been obvious improved while comparing with pure polyelectrolyte multilayers.Then,the NF performance has been studied with a lab-made system.The?PDDA/GO?₄ membrane showed the most promising performance,namely,a flux of 6.42 kg?m^-2?h^-1?bar^-1 and a retention of 99.1%for methyl blue.Besides,the?PDDA/GO?₄ also performed competitive separation abilities for different dyes,different salts and different solvents when comparing with the membranes in literatures.Moreover,the GO incorporated membranes have more desirable stability,pressure-resistance,swelling-resistance and fouling resistance.Secondly,based on the present work,the stabilities of the GO incorporated multilayers in critical environments have been systematically studied by applying NaClO/NaOH/HCl treatments.The morphologies,structures and chemical properties of the multilayers before and after treatment were characterized.The dye retention performances of these multilayers membranes were also investigated.The results revealed that the introducing of GO could obviously enhanced the stabilities of multilayers.In addition,the behavior of multilayers during treatments were detected on the quartz crystals by QCM.The frequency shift curves indicated that the unique lamellar structure significantly inhibits the decomposition of the multilayers and improves the destruction resistance.Thus,we anticipate that this study can provide a comprehensive understanding of the variations in multilayers caused by the incorporation of 2D nanosheets and strengthen the design of novel ultrathin multilayer membranes.Finally,a GO/hyperbranced polymer?HPMA?hybrid membrane have been fabricated for methyl tert-butyl ether?MTBE?/methanol?MeOH?pervaporation.GO nanosheets were modified by in-situ polymerized HPMA through electrostatic interactions and the modification of GO and polymerization of HPMA were simultaneously achieved.The HPMA-modified GO nanosheets were then used to fabricate separation membranes on ceramic tubular substrates via a vacuum-assisted assembly method.The chemical structure of HPMA molecules and the HPMA-modified GO nanosheets were confirmed by FT-IR,Raman,and ¹H-NMR spectroscopy.Raman mapping verified that the GO nanosheets were dispersed well in the polymer matrix.The prepared HPMA-GO composite membranes were used to separate MTBE/MeOH mixture by pervaporation and the optimized MeOH content in permeation and flux could reach 99.5 wt.%and 0.41 kg·m^-2·h^-1,respectively.Furthermore,the operation stability of the GO-incorporated membrane was significantly improved because of the confinement effects of 2D GO nanosheets on HPMA.Thus,this study provides a facile route to design and fabricate novel GO-based membranes for their potential applications in organic/organic separations.