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Title: Versatile applications of nanostructured metal oxides
Author: Li, Li
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2014
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This thesis explores applications of nanostructured metal oxides in photocatalysis, electrochromism and Raman spectroscopy. A variety of highly periodic nanoscale morphologies derived from block-copolymer self-assembly inspire the fabrication of well-ordered nanoporous metal oxide materials. Beginning with block-copolymer directed sol-gel chemistry, we have synthesized crystalline tungsten oxide consisting of micellar or cylindrical pores with uniform sizes. This porous structure reduced diffusion limitations of the reagents, allowing the easy access to a large surface area, therefore improving the photocatalytic activity compared to the non-structured material. This is followed by the fabrication of 3D highly interconnected gyroid-structured vanadium oxide via a simple, scalable and low cost replication strategy using a sacrificial polymer template derived from block-copolymer microphase separation. The electrochromic device fabricated using gyroid-structured vanadium oxide film showed significantly improved coloration responses, because the interconnected porous network greatly shortened the diffusion length of electrolyte ions. Then, the usage of metallic nanoparticles in enhanced Raman spectroscopy is explored. Au nanoparticles were employed as the Raman enhancer to probe the influence of interfacial reactions on the molecules adsorbed on a metal oxide (vanadium oxide) electrode. The spectral intensities and Raman shifts were found to be strongly dependent on the interfacial ion intercalation/extraction processes associated with the variations of the applied electric field. Next, the use of metal oxide nanoparticles in enhanced Raman spectroscopy is investigated. Metal oxide nanoparticles with high refractive indices when placed on top of metal surfaces can effectively enhance the Raman scattering field at the interface. This capability of Raman enhancement in combination with the range of functions of metal oxide nanoparticles opens up a novel approach to study the interfacial phenomena. Using this system, interfacial photocatalytic reactions of an organic dye catalyzed by titanium oxide nanoparticles were investigated by directly monitoring Raman scattering signals enhanced by the same nanoparticles. A diversion from metal oxides uses an Au nanoparticle on Au plane system as a surface- enhanced Raman scattering substrate. At the junction between an Au nanoparticle and an Au film, the electromagnetic field can be enhanced to an extent that single molecules can be detected. The use of such substrates to probe various molecules was also explored.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral