Study On The Design And Preparation Of Graphene Oxide-based Membranes And Their Application

Graphene oxide (GO) membranes, featured with high flexibility, compact structure and excellent separation performance, possess huge potential applications in the construction of 2D materials, sensor, energy storage and conversion, as well as environmental protection. In recent years, the study on the graphene oxide membrane mainly focuses on the applications in the fields of water treatment and gas separation, however, the poor mechanical property of the membranes limits their application seriously. The good solution to the improvement of mechanical property is the introduction of various forces between the GO sheets, such as van der waals’ force, hydrogen bonding, electrostatic interactions and covalent bonding, in which covalent bonding is known as the most effective interaction among them. In addition, the poor channels in the GO membranes limit their application in the oil-water separation. Therefore, the tuning of the structure and the surface chemistry of GO membrane becomes essential. Herein, the present thesis aims at making solutions to these problems mentioned above. Firstly, GO membrane with excellent mechanical property is fabricated with D400 as covalent cross-linking agent. Secondly, using filter paper as template matrix for GO and methyltrichlorosilane (MTS) as surface modifying agent, superhydrophobic surface was achieved over the membrane surface. The obtained hybrid membrane enables the oil-water separation with high selectivity. Details are summarized as follows:1. Covalent cross-linking was used for the construction of GO hybrid membrane with good mechanical properties by means of the combination of vacuum-induced assembly and low temperature cross-linking reaction. By introducing polyetheramine D400 into the GO suspension the cross-linking effect can be generated by the ring-opening reaction between epoxy groups on the surface of GO and the amine groups at the ends of D400 molecules, as a result, the ultimate strength of the membrane is reinforced. The strength of the membranes increases with the increasing of D400 content and then decreases, which can be attributed to the competition between reinforcement by covalent cross-linking and extinction effect by the increasing of d-spacing between the GO sheets, and the ultimate strength of the membrane is approximately 2.73 times higher than that of pure GO membrane, indicating the superiority of the covalent cross-linking for the mechanical property improvement of the membrane.2. A two-step impregnation method in GO suspension and MTS solution is used for the creation of FP@GO@MTS with superhydrophobic property for efficient oil-water separation, in which the filter paper (FP) acts as the porous matrix, providing the micro channels for the fluids and altering the assembly manner of GO sheets. The methyltrichlorosilan acts as the modifying agent to lower the surface energy of GO and increase the roughness of the hybrid membrane. The GO sheets connect the filter paper by hydrogen bond through oxygen-containing groups and contribute to the additional membrane surface roughness by their wrinkles. The synergistic effect between the hierarchical structures and surface chemistry from low surface energy agent endows the resultant membrane with superhydrophobic property. Therefore, the as-prepared membrane possesses superior oil-water separation selectivity and long duration lifetime. The strategy of the materials design and synthesis open a new avenue for the GO membrane application in oil-water separation.