Preparation And Characterization Of Graphene Nanomaterials And Research And Application For Watertreatment

Water shortage is a world-wide problem due to dwindling water resources and increasing water consumption. Graphene (GN) is a two-dimensional sheet of sp2-bonded carbon atoms in a hexagonal honeycomb lattice with atomic thickness and high mechanical strength. Attractive advantages of GN over membranes enable faster water transport, low pressure requirements, and a wider range of operating conditions than previously possible. Graphene oxide (GO) nanosheets are the highly oxidized form of GN with carboxyl, epoxy and hydroxyl groups in the plane and the edges. These oxygen-containing functional groups endow GO nanosheets with good hydrophilicity and provide possibilities for the reactions with amino groups. Based on its good hydrophilicity and chemical properties, GO nanosheets possess promising potentials for water purification, membrane preparation, adsorption and so on.Spongy GN and GO materials are applied as environmental pollutant adsorbents by utilizing the characteristics of ultralarge surface area, electrostatic interactions or hydrogen bonds of oxygen-containing functional groups and strong π-πinteraction on the surface. Graphene sponge (GS) has been made by reducing graphene oxide platelets in suspension followed by shaping via moulding and heating and shows highly efficient absorption of not only petroleum products and fats, but also toxic solvents such as toluene and chloroform.Nanofiltration (NF) membranes is nowadays an appropriate choice for brackish and seawater treatment. NF membranes with high retention of multivalent anion salts, low operational pressure and high water flux can considerately reduce the investment and energy costs of separation processes. Thus, it is of great interest to develop novel NF membranes assuring high salt rejections, as well as high water permeability.GO as a novel nanomaterial has been used for membrane fabrication via phase inversion, layer-by-layer deposition and surface functional ization to improve inversion, layer-by-layer deposition and surface functionalization to improve antifouling properties, permeability and mechanical strength of membranes. Surface functionalization is a feasible approach to change the surface properties of membranes in a defined selective way while preserving its porous structure. GO nanosheets should be covalently and irreversibly bonded on the membrane surface without aggregation to improve separating properties. Using ring-opening polymerization between epoxy groups in GO nanosheets and amino groups in the OCMC active layer, GO nanosheets can be irreversibly bound to the membrane surface. Furthermore, the mass transport process through GO-OCMC NF membranes is explored for the first time. To date, surface functionalization of the OCMC membranes with GO nanosheets that enhances desalting properties has not been investigated.In this work, the application of GO materials was demonstrated as environmental pollutant scavengers by utilizing unique porous structure with ultralarge surface area, electrostatic interactions or hydrogen bonds of oxygen-containing functional groups and π-π interaction on the surface and a novel OCMC NF membrane surface functionalized with GO nanosheets is synthesized to enhance desalting properties. GO sheets are prepared using improved Hummer’s method and generated GO sponge from GO suspension through freeze-drying process, and explored the potential application of GO sponge to remove TCP. The structural features of GO sheets and GO sponge have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Atomic Force Microscope (AFM) and scanning electron microscopy (SEM). Kinetic study and adsorption mechanism on TCP adsorption were also investigated. A novel OCMC NF membrane surface functionalized with GO nanosheets is synthesized to enhance desalting properties. GO nanosheets are covalently bound to the OCMC active layer of membranes, yielding both higher permeability and better separating property, compared with the pristine membrane and the commercial NF membranes. Moreover, the concentration of GO nanosheets has a remarkable influence on the morphology and separating performances of membranes, including hydrophilicity, surface roughness, mechanism of separation and permeation is also inverstigated for OCMC NF membranes surface functionalized with GO nanosheets.The results suggest that GO sponge presented higher adsorption capacity than GO sheets due to large specific surface areas and TCP had optimum adsorption capacity on both GO sheets and GO sponge at pH 2.0～6.0. Adsorption isotherms and kinetics curves of TCP on GO sheets and GO sponge were nonlinear, indicating the homogeneous monolayer chemical adsorption. In addition, GO-OCMC NF membranes exhibit not only higher permeability but also better salt rejections than the pristine membranes and the commercial NF membranes; besides, the desalting properties are enhanced with the concentration of GO nanosheets increasing. Furthermore, the transport mechanism of GO-OCMC NF membranes reveals that the nanoporous structure of GO-OCMC functional layer and size exclusion and electrostatic repulsion of water nanochannels formed by GO nanosheets lead to the membranes possessing enhanced desalting properties.