The Study On The Preparation And Performance Of Graphene Oxide Based Composite Membrane

The graphene oxide (GO) has 2D structure, good hydrophilicity and tunable physicochemical properties, which made it be an ideal membrane material in the field of separation membrane. GO can combine with functional molecules by covalent bonding or non-covalent bonding, thereby changing the structures and separation performance of the membrane.In this paper, the GO membranes were prepared by vacuum filtration. By grafting polydopamine, the membrane structure was tuned to exhibit good performance in pervaporation dehydration of organics. Moreover, we prepared a high positively charged nanofiltration (NF) membrane by electrostatic self-assembly with GO and polyethyleneimine (PEI) to apply in desalination. The membrane structure was adjusted with different assembly conditions to achieve high desalination performance. The main work includes the following aspects:1. GO was reacted with dopamine under certain condition, and a series of polydopamine grafted GO (PDA-g-GO) was synthesized at different reaction time. The PDA-g-GO composite membranes were successfully fabricated by vacuum filtration on the hydrolyzed polyacrylonitrile ultrafiltration membrane (h-PAN), and the composite membranes were used to separate ethanol/H2O and isopropyl alcohol/H2O mixture by pervaporation. The results indicated that the separation performance of membranes for isopropyl alcohol/H2O was better than ethanol/H2O, which was mainly because of the size exclusion. Moreover, the size of nano-channel in membranes was efficiently adjusted by grafting of polydopamine. The composite membranes showed markedly different performance with various polydopamine loading amount. When the reaction time was 2 h, the PDA-g-GO composite membrane presented great separation performance for isopropyl alcohol/H2O with a permeation flux of 2273 g/m2h which was 39.0%higher than GO composite membrane, and kept a high water concentration in permeate of 99.7 wt%.2. High positively charged NF membranes have been prepared via a electrostatic self-assembly technique using graphene oxide (GO) and PEI. The high aspect ratio and unique 2D structure of GO nanosheets made them easily to be assembled on the membrane surface, and the intrinsic low resistant channels within the GO nanosheets resulted in a high water flux of the membrane. By assembled a PEI layer on the membrane outer surface, the composite membrane exhibited high positive charge and resulted in the high rejections to multivalent ions. The effects of deposition time, PEI and GO concentrations on separation performance of the NF membranes were detailed studied. The best performance among all the membranes was achieved with salt rejection of 93.9% for Mg2+ and a water flux of 20.8 L/m2·h at 30℃ and 0.5 MPa.