| As a widely used photocatalyst, TiO2 is chemically stable, cheap, nontoxic and easy to recycle. Modification of titania aims to effectively separate electron-hole pairs and thus enhance the photocatalytic activity. In this dissertation, Pt-Cu/TiO2、Ag/TiO2 and TiO2 nanosheet were synthesized and characterized by X-ray diffraction (XRD), BET, transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and UV-Vis etal and their photocatalytic activity were studied. The main conclusions are summaried as follows:(1) Pt-Cu/TiO2 was prepared using the conventional wet impregnation method and the photocatalytic nitrate reduction over metallized TiO2 catalysts was investigated using benzene as the hole scavenger. The results showed that Pt-Cu alloy was formed in TiO2 supported bimetallic catalysts except for the bimetallic catalyst with TiO2 calcined at 700℃ as the support. For photocatalytic nitrate reduction in the presence of benzene, nitrate was mainly converted to ammonia or nitrite over Pt/TiO2 or Cu/TiO2 respectively, whereas TiO2 supported Pt-Cu bimetallic catalysts exhibited a considerable N2 selectivity for photocatalytic nitrate reduction. The catalytic activity and N2 selectivity of the supported bimetallic catalyst was strongly dependent on TiO2 calcination temperature, Pt/Cu ratio and metal loading amount. The bimetallic catalyst with TiO2 calcined at 300℃ as the support, Pt loading amount of 5 wt.% and Pt/Cu ratio of 4/1 displayed the optimized nitrate conversion and N2 selectivity compared with other bimetallic catalysts. The present results demonstrate the selective nitrate reduction over Pt-Cu/TiO2 catalysts with benzene as the hole scavenger, highlighting the validity of simultaneous removal of aqueous nitrate and benzene by photocatalysis.(2) Ag/TiO2 catalysts were prepared by the photo-deposition method and photocatalytic Pb(Ⅱ) reduction over TiO2 and Ag/TiO2 catalysts in the presence of formic acid was investigated. Ag deposition on TiO2 led to enhanced photocatalytic Pb(Ⅱ) reduction and the Ag/TiO2 catalyst with a Ag loading amount of 0.99 wt.% exhibited the optimum photocatalytic activity. For Pb(Ⅱ) reduction over Ag/TiO2 with a Ag loading amount of 0.99 wt.%, initial Pb(II) reduction rate was found to be dependent on the initial concentrations of formic acid and Pb(Ⅱ). Increasing initial Pb(Ⅱ) concentration led to linearly increased initial Pb(Ⅱ) reduction rate. At low formic acid concentration, in parallel, initial Pb(Ⅱ) reduction rates increased with formic concentration, but remained nearly identical at high formic acid concentration. Solution pH impacted the photocatalytic Pb(Ⅱ) reduction and after irradiation for 100 min Pb(Ⅱ) was removed by 11.8%,91.2% and 98.6% at pH of 0.8,2.0 and 3.5, respectively, indicative of enhanced Pb(Ⅱ) reduction with pH in the tested pH range.(3) TiO2 nanosheet (NS) with exposed (001) facets was synthesized via a hydrothermal approach using titanate nanotube (NT) as the precursor and NaF as the shape controlling agent. Photocatalytic phenol degradation over the catalysts was investigated. Results showed that upon hydrothermal treatment NT was transformed to anatase NS with high (001) facets. In comparison with NT, NS displayed much higher photocatalytic activity for phenol degradation, and the catalytic activity increased with the hydrothermal temperature. Phenol degradation over NS followed first-order kinetics, and NS prepared at 200℃ had the highest rate constant of 0.083 min-1. Moreover, the dependency of phenol degradation rate on initial phenol concentration obeyed the Langmuir-Hinshelwood model, indicative of an adsorption controlling reaction mechanism. |
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