Preparation And Characterization Of Graphene Oxide-based Self-assembled Materials

Graphene oxide (GO) is a kind of two dimensional layer-structured nanomaterials with functional groups such as hydroxyl and so on. Graphene oxide can combine with organic molecules and semiconductor nanoparticles to form functional nanocomposites via self-assembly approach. Graphene oxide has received much attention in the past a few years because Graphene oxide-based novel functional materials are believed to be promising for future potential applications in solar cell, catalysis, sensing and so on. In the present paper, graphene oxide and graphene (G) were prepared. Self-assembled thin films composed of graphene oxide and organic electrolytes were built up, and hybrid materials of grahene and metal sulfides were prepared. The obtained composites were characterized using a transmission electron microscope, a scanning electron microscope, a UV-vis spectrophotometer and a fluorescence spectrophotometer. The main content and research results in this thesis are summarized as follows:The graphite oxide was prepared by a modified Hummers method and the graphene oxide was achieved by ultrasonication and centrifugation of the graphite oxide dispersion. The results of XRD and FTIR show that spacing of graphite oxide become larger and the surface containe a large amount of functional groups including carboxyl, hydroxyl, epoxy and so on. The graphite oxide with these functional groups is hydrophilic. A Organic Dye, Alcian Blue 8GX (AB), and a polyelectrolyte, Poly(ethyleneimine) (PEI), were used to prepared multi-layered films composed of graphene oxide by using the electrostatic self-assembly technique. Photoluminescence can be observed on the self-assembled GO/AB composite films. The fluorescence peak of composites drifts compared with that of AB. The photoluminescence may result from the charge-transfer between AB molecules and the GO. The properties of the GO/PEI composite films were investigated, and the results show that the multi-layer self-assembled films have flat surface and good electrical insulation properties. The graphite oxide was used as precursor to prepare graphene by using a solvothermal method. The results of FTIR show the graphene oxide was transformed to graphene completely. The results of TEM observation show that the wrinkles on the grapheme sheets are clearly observed. GO was also used as precursor to prepare CdS/G and ZnS/G hybrid materials. The results of TEM observation show the CdS nanoparticles with an average size of 10 nm are uniformly attached onto the the surface of graphene. On the UV-vis absorption spectrum of the CdS/G dispersed in ethanol, an absorption peak of G at 270 nm and a shoulder of CdS NPs around 478 nm can be observed. In the fluorescence spectrum of the CdS/G, the highest peak around 520 nm which can be attributed to sulfur vacancies and defects. In the TEM images, it is observed that the ZnS nanoparticles with an average size of 23 nm are attached onto the surface of graphene. The UV-vis absorption spectrum of the ZnS/G NPs dispersed in ethanol has an absorption peak of G at 261 nm and a weak shoulder of ZnS NPs around 320 nm. In the fluorescence spectrum of the ZnS/G, the highest peak around 386 nm which can be attributed to zinc vacancies.The result of electrochemical measurement showed that the specific capacitance of G is 25 times as large as that of GO. The specific capacitance of the CdS/G hybrid particles is 3 times as large as that of CdS. The specific capacitance of ZnS/G is 6 times as large as that of ZnS.