Synthesis And Photocatalytic Activity Of Noble-Metal/Semiconductor Hybrid Photocatalysts

In the past decades, environmental problem and energy shortage are increasingly serious because of the continuous development of global industrialization, and they have become two major challenges to be addressed for the current world. Semiconductors used for photocatalysts can both degrade pollutants in the environment and convert solar energy into other clean energy under sunlight, which can restore the environment and use solar energy directly. In this thesis, some nanohybrid photocatalysts composed of noble metal nanoparticles with surface plasmon resonance effect such as Ag and Au as well as metal oxide semiconductors with different morphologies were synthesized, to enhance the photocatalytic activity, and the mechanism for the enhancement in photocatalytic activity was discussed. The main research results in this thesis are listed as follows:1. Three typical MMO semiconductors including ZnO, TiO2and CeO2were synthesized via the general route integrating evaporation-inducedself-assembly and in situ pyrolysis of metal precursors, and a series of Ag/MMO composite photocatalysts with different loading amounts of Ag nanoparticles (i.e.1wt.%,2wt.%, and5wt.%) were prepared by a facile and general photodeposition process. The as-synthesized samples were characterized with XRD, BET, SEM, TEM, HRTEM, XPS, and UV-vis DRS, etc. The results indicated that the MMO samples are mesoporous structure with large specific surface area and narrow pore distribution, and the as-obtained Ag/MMO nanocomposites are composed of Ag nanoparticles with sizes of50-100nm and surrounded by small nanoparticles of metal oxides. When used for photodegrading the typical organic pollutants of MB and phenol solution under a simulated sunlight (λ=350-780nm), the as-synthesized mesoporous ZnO and mesoporous TiO2shouwed enhanced photocatalytic activity than commercial ZnO and TiO2, and the Ag/MMO composites showed greatly enhanced photocatalytic activity than their corresponding pure MMO semiconductors. The photocatalytic activity of the composite initially increases and then decreases with the Ag loading amount increasing. The Ag(5)/MMO composite exhibits the highest photocatalytic activity. The enhancement in the photocatalytic activity of Ag/MMO composites can be attributed to the synergetic effect of the mesoporous structures for efficient mass transfer as well as the Ag nanoparticles providing plasmonic enhancement of light absorption.2. Ultrathin WO2.72nanowire (WO) with high aspect ratio and its WO3-x/RGO composite (WGO) were synthesized via a solvothermal process of WCl6alcoholysis in ethanol. Moreover, the corresponding NM/WO and NM/WGO composite photocatalysts loading noble metal nanoparticles (NM=Ag, Au) were prepared by a in-situ redox reaction between the reductive WO2.72and the oxidative noble-metal salt in aqueous solution. The as-synthesized samples were characterized with XRD, SEM, TEM, HRTEM, Zeta Probe, and UV-vis spectrophotometer, etc. The results indicated that noble-metal particles with sizes<50nm were successfully reduced by in-situ redox reaction, and attached on the surface of WO ultrathin nanowire and WGO composite closely. The properties of the as-synthesized nanomaterials were evaluated by adsorbing MB and MO solution as well as phodegrading MB solution under visible light irradiation. The results indicated that the NM/WO and NM/WGO samples exert selective adsorption for cationic dye such as MB, and huge adsorption capacity for MB (220μmol/g). Moreover, the as-synthesized NM/WO and NM/WGO photocatalysts present enhanced photocatalytic activity under visible light irradiation. The selective adsorption is attributed to the surface electro-negativity of the WO naniwires, and the huge adsorption benefits from the huge specific surface area of ultrathin nanowire structure as well as the addition of RGO nanosheets. The enhancement in the photocatalytic activity of NM/WGO can be attributed to the synergetic effect of RGO nanosheets for the efficient charge transportation and separation as well as the noble metal nanoparticles for plasmonic enhancement of light absorption.