| TiO2has remained as a favorable choice as a photocatalysis material due to itsremarkable photostability, nontoxicity and low cost. However, TiO2can only be exited byUV light due to the large band gap, which impedes its wide use. Moreover, the highrecombination rate of photogenerated electron-hole pairs during the photocatalytic processis also the main drawback of TiO2. In order to overcome these limitations, many studieshave been devoted to improve the photocatalytic activity by various methods, includingdoping non-metal ions, narrow bandgap semiconductor compositing, dye sensitizing andespecially, noble metals decorating. Among the above methods, the decorating noblemetals has been demonstrated to form Schottky barriers with TiO2, which significantlyenhance the separation of photogenerated carries and promotes the interfacial electrontransfer process. In addition, some noble metal nanoparticles (NPs) can strongly interactwith light in the visible region due to their extraordinary surface plasmon resonance (SPR)properties, which arise from the collective oscillations of the electrons close to the surfaceof the metal NPs. Such plasmonic properties of the noble metals have been used to extendvisible light responsive TiO2composite photocatalysts.Nano-structuring the TiO2is believed to be another possible technology forovercoming the disadvantages of TiO2due to the geometric–dependence of its properties.Most recently, photonic crystals with inverse opal structure have attracted a great deal ofattention because of their remarkable properties. Inverse opals offer a large internal surfacearea, supplying more reaction active sites. Furthermore, the ordered porous structurereduces the loss of light due to reflection, since photons that enter the inverse opals are lesslikely to escape due to multiple scattering by the walls. More importantly, photons in inverse opals propagate with strongly reduced group velocity at the frequency edges of thephotonic stop band (slow light effect), which can enhance the interaction between light andmaterial as a result of the increased effective optical path length. Therefore, consideringtheir respective advantages, the combination of photonic crystals and metal NPs may beregarded as an efficient strategy to enhance the light optical absorption of TiO2photocatalyst and the separation of photogenerated carriers, which thus can improve thephotocatalytic properties.There are two mainly chapter in this thesis:1. Fabrication of Ag/TiO2plasmonic photocatalyst and its enhanced photocatalyticactivity.We developed a pulsed current deposition method to fabricate TiO2inverse opals withhighly dispersed Ag nanoparticles (NPs) as a visible light driven plasmonic photocatalyst.It is observed that the incorporation of Ag NPs can significantly improve the photocatalyticactivity of TiO2inverse opals in all light spectrums, especially in the visible light region.With an appropriated deposition time of45s, the measured photocatalytic activity of thesample is the highest, and exceeds that of the Ag/TiO2inverse opals prepared byphotochemical reduction method. Such enhancement is ascribed to the optimized localizedsurface plasmon resonance property of the Ag NPs, and excellent separation of thephotoexcited electrons and Ag+ions, resulting from the uniform Ag NPs produced bypulsed current deposition. The proposed mechanism is further confirmed by hydroxylradical detection and electrochemical impedance spectroscopy analysis. Our study providesnew insight into the design and preparation of advanced visible light photocatalyticmaterials. This work was published in Journal of Materials Chemistry A,2014,2,824.2. Fabrication of Au/TiO2plasmonic photocatalyst and its photocatalytic activity.In this study, Au/TiO2photonic crystal photocatalyst with inverse opal structure werealso prepared by the pulsed current deposition method. The photonic stop bands of theseTiO2inverse opals were tuned by changing the pore size of inverse opal structures. It wasfound that when the red edge of the photonic stop band of TiO2inverse opals overlapped with the plasmonic peak of Au nanoparticles, the visible light photoelectric conversionperformance was better than that of sample, which the blue edge of the photonic stop bandof TiO2inverse opals overlapped with the plasmonic peak of Au nanoparticles. Suchphenomenon may be ascribed to a remarkable improvement in the light harvestingefficiency, which was due to the efficiency coupling effect of slow photon effect and theSPR effect. However, all samples decorated Au NPs showed weaker photoelectricconversion performance compared with the pure TiO2inverse opals, which may be relatedto the preparation method ofAu NPs. |
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