Controlled Synthesis And Photocatalytic Performance Of Graphene-based Semiconductor Nanocomposites

Since its discovery in 2004, graphene (GR) has become a sparkling rising star on the horizon of material science. Due to its unique two-dimensional planar structure and excellent physicochemical properties, it has been regarded as an important component for making various functional composite materials. Especially, synthesis of graphene-based (GR-based) semiconductor photocatalysts and its applications in environmental and energy field have attracted extensive attention. In the aspect of fabrication, it is necessary to further improve the interfacial contact between GR and the semiconductor and maximize the advantages over GR in structure and properties. Thus, increasing interest should be devoted to fabricating GR-based semiconductor nanocomposites by developing new efficient synthetic strategies. As to its applications, so far, GR-based semiconductor nanocomposite photocatalysts are mainly focused on photocatalytic degradation of organic pollutants, water splitting, destruction of bacteria, selective oxidation of various alcohols and reduction of CO2 In contrast, it is still not available for the utilization of GR-based semiconductor composites photocatalysts for liquid phase selective reduction of nitro organics, which would promote us to further explore its application in the field of photocatalysis. In the present situation, the exploration of the facile and efficient synthsis of GR-based semiconductor composites, further expanding its applications and improving its photoactivity and photostability have been inspiring ever-increasing research interest.In this thesis, GR/ZnO nanorods and GR/CdS nanospheres nanocomposites have been synthesized and the crystal phase, morphology, photoresponse, specific surface area and electrochemical properties of the as-prepared samples are characterized by a series of techniques, including X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption, electrochemical analysis and photoluminescence spectra (PL). In addition, photocatalytic performance of these catalysts has been evaluated by photocatalytic degradation of organic dye and selective reduction of nitro organics to corresponding amino organics in water. The main results and conclusions obtained from the present research are as follows:I. GR/ZnO nanorods and GR/CdS nanospheres nanocomposites have been prepared via a simple hydrothermal method and an efficient electrostatic self-assembly approach, repectively. II. Compared with bare semiconductor, GR-based semiconductor nanocomposites exhibit much higher photocatalytic performance toward our selected model reactions under the light irradiation. The remarkably enhanced photoactivity for GR-based semiconductor nanocomposites can be ascribed to two integrative factors: The first one is the obvious adsorptivity enhancement over GR-based semiconductor nanocomposites than bare semiconductor, which results from the π-π conjugation between aromatic regions of graphene and the reactants; The second one is the introduction of GR with high conductivity and superior electron mobility into the semiconductor matrix, which would lead to the efficient separation and the prolonged lifetime of charge carriers photogenerated from semiconductor in GR-based semiconductor nanocomposites. III. The effective interfacial hybridization between ZnO nanorods and GR sheets could inhibit the photocorrosion of ZnO nanorods, thus improving the photostabiliry of GR/ZnO nanorods nanocomposites; IV. In the reaction of selective reduction of nitro organics, the utilization of hole scavenger significantly inhibits the the photocorrosion of CdS in which the S2- ion is highly prone to oxidation by photogenerated holes, thus making GR/CdS nanospheres be reusable catalysts for photocatalytic reduction of aromatic nitro compounds in water.