Study On The Preparation Of Graphene Oxide And Properties Of Loading Graphene Oxide Nanofiltration Membrane

The structure of graphene oxide(GO)is constituted by a monolayer carbon atoms in a two-dimensional grid.The special structure of GO provides a relatively ordered channel where water molecules can permeate through.Different kinds of oxygen-containing functional groups such as carboxyl,hydroxyl and epoxy may increase the hydrophilic performance of GO and also make GO molecular layer with unique negative performance,so GO shows a good application prospects in the field of water treatment and membrane separation.Composite nanofiltration membrane is generally formed by two parts including the supported layer and separating layer.This article is using flake graphite as raw material to compound graphene oxide with higher oxidation degree by improved Hummers method.Then pressure assisted self-assembly technology is used to prapare the GO-PVDF composite nanofiltration membrane loading GO,and the hydrophilic characteristics and desalination performance of nanofiltration membrane is explored.Firstly,the improved Hummers method is used to prepare graphene oxide,and various reaction conditions inclouding reaction time,reaction temperature,dosage of oxidant,ratio of mixed acid are respectively studied to the effect on the oxidation degree of GO.The FT-IR,TEM,XRD,Raman spectroscopy and others were used to characterize the prapared GO.The results show that the optimal technological conditions are as follows:the oxidation time is about 20 h,the reaction temperature is controlled at 90 ℃,the ratio of concentrated sulfuric acid and concentrated phosphoric acid is 17:3,and the ratio of KMnO4 and flake graphite is about 6:1.GO prapared by improved Hummers contains abudant oxygen-containing functional groups,the layer spacing of GO increases to 0.866 nm.The GO-PVDF composite nanofiltration membrane prapared through pressure assisted self-assembly method is characterized by the contact angle mete tester,SEM,AFM,etc.The results indicate that GO is loaded on PVDF membrane surface equably and forms a separation layer with thickness about 76～98nm.Different factors which effect on the rejection and flux of composite nanofiltration membrane including loading of GO,ultrasonic time,concentration of salt solution are investigated.The experimental results show that the rejection of GO nanofiltration membrane for different salt solutions is as follows:Na2SO4>NaCl>MgCl2,and higher removal rate is observed in low-concentration salt solution.Through experiments,it is can also be found that increasing the capacity of GO will improve desalting effect.When the loading capacity of GO is about 150 mg/m2,rejection of GO nanofiltration membrane to Na2SO4 is close to 80%.