Study On Synthesis And Visible-light-driven Photocatalytic Performance Of Hybrid Nanocatalysts Enhanced By SPR Effect Of Silver Nanoparticles

Controllable synthesis of visible-light induced photocatalysts has far-reachingsignificance in the new environmental management and energy sector. Carry thispoint, in this thesis, TiO2and AgX were chosen as the matrix to synthesizeAg@semiconduct plasmonic photocatalysts using photoreducing methods. Details areas follows.（1） Ag@TiO2（P25） nanocrystals were synthesized by a photoreducing methodin the presence of commercial TiO2（P25） nanoparticles. The TEM observationsindicate that the Ag nanoclusters （NCs） with a size range of1–3nm were uniformlyanchored on the surfaces of P25nanoparticles. The Ag@P25nanocomposites withvarious amounts of Ag NCs （0.5–10%in mass） were synthesized by changing theconcentrations of Ag+in the precursors. The photocatalytic activity of theas-synthesized Ag@P25nanocomposites was investigated by photodegradating RhBdye under visiblelight irradiation （λ≥400nm）. The results show that the as-obtainedAg@P25nanocomposites show a novel Ag-loading-density-dependent photocatalyticactivity, and that the Ag@TiO2photocatalyst with1%Ag NCs has the bestphotocatalytic performance with a high rate constant,22times higher than that of P25under the same condition. The photocatalytic mechanism was discussed in detail.（2） Anatase, rutile and brookite TiO2nanoparticles （marked as A-TiO2, R-TiO2,and B-TiO2, respectively） were synthesized using hydrothermal method. TheAg@TiO2nanocrystals with1%Ag NCs were synthesized by a photoreducingmethod using the above TiO2nanoparticles as the substrates. The samples werecharacterized by XRD, UV-vis, SEM, EDS. The photocatalytic performance of theAg-doped samples were measured by degrading RhB under the visible light (λ≥420nm,¹00mW cm^-2). The results indicate that the phases of the TiO2nanopariticleshighly influence the photocatalytic performance in photoderading RhB dye molecules,and the Ag@A-TiO2sample has the best property. （3） Silver-decorated TiO2nanoparticles （Ag@A-TiO2, Ag@P25） weresynthesized by photoreducing Ag+species in the presence of the anatase TiO2nanocrystals and P25, respectively. The TEM observations indicated that Ag speciesanchored on the surfaces of A-TiO2nanoparticles as Ag0（1–3nm） and AgO （10–15nm） nanoclusters （NCs）. The Ag NCs on the surface of P25have a size range of5–7nm, and no AgO species was found. The photocatalytic performance of theAg@syn-TiO2and Ag@P25samples were evaluated by degradating RhB undervisible-light irradiation （λ≥420nm）. In the RhB/Ag@A-TiO2system, thedegradation of RhB molecules has two stages:（i） N-deethylation of RhB molecules,and （ii） cycloreversion. For the RhB degradation in the presence of Ag@P25photocatalysts, the cycloreversion play a major role in the whole degradation.（4） AgBr/AgCl@Ag nanocrystals with various molar RBr/Agratios （0,1,1/3,1/2,2/3） were synthesized via stepwise liquid-solid reactions using freeze-dried PVP-Ag+compounds as Ag source, followed by a photoreduction reaction （0-20min）. TheAgBr/AgCl@Ag7.5（1:2） nanocrystals obtained take on a spherical morphology with aparticle-size range of58±15nm. The photocatalytic performance ofAgBr/AgCl@Ag nanocrystals was evaluated by photodegrading organic dyes,4-chlorophenol and isopropanol under artificial visible light （λ≥420nm,100mWcm2）. For the decomposition of rhodamine B, the AgBr/AgCl@Ag7.5（1:2）nanocrystals has a photodegradation rate of⁰.87min^-1,¹59times higher than that(⁰.0054min^-1) of TiO2（P25）, while the AgCl@Ag and AgBr@Ag nanocrystals hasa photodegradation rate of0.35min^-1and0.45min^-1, respectively. Thephotodegradation efficiency of isopropanol after an irradiation of60min is up to⁵9%. The enhancement in photocatalytic performance can be attributed to the highabsorbance of visible light and the efficient separation of photogeneratedelectron-hole pairs in the ternary system consisting of AgBr, AgCl and Ag species,besides their small particle-sizes.