Preparation Of Graphene-Based Photocatalysts And Exploratory Study On Their Photocatalytic Performance

Graphene (GR) has become a sparkling rising star on the horizon of material science. Due to its unique planar structure, excellent transparency, superior electron conductivity and mobility, high specific surface area, and high chemical stability, GR is regarded as an ideal high performance candidate to prepare GR-based nanocomposites for energy storage and conversion. In the thesis, we reporte preparation of TiO2-graphene, ZnS-graphene and Au-Pd/graphene nanocomposites and exploratory study on their photocatalytic performance. The different roles of graphene and graphene oxide in these graphene-based nanocomposite photocatalysts have been investigated. The findings are following:I:We show that the TiO2-GR nanocomposites exhibit much higher photoactivity than bare TiO2 toward the gas-phase degradation of benzene and the liquid-phase degradation of dyes. By investigating the effect of different weight addition ratios of graphene on the photoactivity of TiO2-GR systematically, we find that the photoactivity of the TiO2-GR nanocomposites is enhanced when an appropriate amount of GR in introduced; however, the higher weight addition ratio of GR in TiO2-GR will decrease the photoactivity. In addition, the key features for TiO2-GR due to the integration of GR including enhancement of adsorptivity of pollutants, light absorption intensity, electron-hole pairs lifetime, and extended light absorption range have also been found in the composite of TiO2 and carbon nanotubes (TiO2-CNT). Therefore, when using the hard integration of GR with solid semiconductor particles, our present work strongly highlights that TiO2-GR is in essence the same as TiO2-CNT composite materials on enhancement of photoactivity of TiO2.Ⅱ:We conceptually demonstrate how to synthesize a more efficient TiO2-GR nanocomposite as a visible light photocatalyst toward selective oxidation of alcohols under mild conditions. Comparison between TiO2-GR and TiO-CNT discloses the prominent advantage of GR over CNT on both controlling the morphology of TiO2-GR nanocomposite and enhancing the photocatalytic activity of TiO2. This work clearly highlights the importance and necessity for a comparison investigation between GR- and CNT-semiconductors as photocatalysts, which will promote our in-depth fundamental understanding on the analogy and difference between GR and its forebears on controlling the morphology of carbon-semiconductor nanocomposites and enhancing the photocatalytic performance.Ⅲ:We show a proof-of-concept study on improving the photocatalytic performance of TiO2-GR nanocomposite via a combined strategy of decreasing defects of GR and improving the interfacial contact between GR and the semiconductor TiO2.The TiO2-GR nanocomposite fabricated by this approach is able to make more sufficient use of the electron conductivity of GR, by which the lifetime and transfer of photoexcited charge carriers of TiO2-GR upon visible light irradiation will be improved more efficiently.Ⅳ:The ZnS-GR nanocomposites exhibit visible light photoactivity toward aerobic selective oxidation of alcohols and epoxidation of alkenes under ambient conditions. In terms of structure-photoactivity correlation analysis, we for the first time propose a new photocatalytic mechanism where the role of GR in the ZnS-GR nanocomposites acts as an organic dye-like macromolecular "photosensitizer" for ZnS instead of an electron reservoir. This novel photocatalytic mechanism is distinctly different from all previous research on GR-semiconductor photocatalysts, for which GR is claimed to behave as an electron reservoir to capture/shuttle the electrons photogenerated from semiconductor.V:We report the direct synthesis of stabilizing-molecules-free bimetallic Au-Pd nanoalloys promoted by graphene oxide (GO) in an aqueous phase. The formation of Au-Pd nanoalloys and loading onto the reduced GO (denoted as GR) are accomplished simultaneously. Controlled experiments suggest that GO vividly acts as a unique "solution processable macromolecular surfactant" and 2D "flat-mat" support to promote the formation and loading of alloyed Au-Pd bimetallic nanoparticles onto the GR sheet. The as-formed Au-Pd/GR exhibits higher photocatalytic activity than both monometallic Au/GR and Pd/GR, prepared by the same approach, toward degradation of dye, Rhodamine B (RhB), which thus demonstrates the promising potential of bimetallic nanoalloys than monometallic one in promoting visible light photocatalysis.