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Interfacial Assembly of Nanoparticles for the Research and Application in Electrocatalysis and Spectroscopy

Author: LiuCai
Tutor: YangShiCheng
School: Hunan University
Course: Analytical Chemistry
Keywords: Nanoparticles Oil/water interface Self-assembly technique Surface-enhanced Raman scattering Interfacial etching Electrocatalysis
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Type: PhD thesis
Year: 2012
Downloads: 96
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Abstract


Nanoparticle thin-films are two-dimensional (2D) nanostructures involvingnanoparticles as building blocks, which have wide applications in the fields ofcatalysis, energy source, sensing, medical diagnosis and so on. Further,2Dnanostructured films can be employed as novel building blocks to designthree-dimensional nanostructures. Due to interactions between nanoparticles innanoparticle films, nanoparticle films usually exhibit unique collective propertiesdifferent from the single nanoparticle or bulk counterparts. It means that theproperties of as-prepared nanoparticle films can easily be tuned by controllingstructures of nanoparticle films. Thus, varied methods for fabricating nanoparticlefilms have been proposed so now, but among which, the oil/water interfacialassembly is paid a lot of attention because it is simple, convenient andinstrument-free. Therefore, it is a very meaningful, challenging task to developcontrollable interfacial assembly and exploit the relations between nanostructuresand their properties. Based on the above consideration, this thesis involves thefollowing contents:(1) Mechanism of oil/water interfacial assembly: Base on ethanol-mediatedinterfacial assembly, the energy change of single nanoparticle was caculated when itmigrated from the bulk solution onto oil/water interfaces. The theoretical andexperimental data indicate that thermodynamical states of sphere, cube and cylindernanoparticle are the stablest when they are located at oil/water interfaces, formingnanoprticle films, respectively. Additionally, the effects of the type of surfactant andoil on interfacial assembly were discussed roughly, respectively.(2) Machanical stability of nanoparticle monolayer films obtained by theinterfacial assembly: Take Pt nanoparticles as an example, oxygen reduction wascarried out on Pt nanoparticle monolayer films by cyclic voltammetrical and rotatingdisk electrode techniques. The results showed the Pt nanoparticle monolayer filmexhibited satisfactory electrocatalytic activity, and was still fixed firmly on theelectrode surface under a relative harsh condition ofelectrode rotation.(3) Gold nanoparticle films for CO electrooxidation: Gold nanoparticles canadsorp onto toluene/water interfaces by injecting a mixture of ethanol and tolueneinto Au aqueous colloid, and then gradually formed a Au nanoparticle monolayer film. The fine nanostructure of as-prepared Au nanoparticle monolayer film wascontrolled well simply by changing the ethanol:toluent volume ratio in the mixture.Carbon monoxide was used as a probe for testing the electrocatalytic performancesof the above Au nanoparticle film. The results indicate that, compared with isolatedAu nanoparticle monolayer film, the chain-like Au nanoparticle film showed anexcellent catalytical activity.(4) Au/Pt composit nanofilms for methanol electrooxidation: Two types ofAu nanosturctures, Au nanorods and gold nanospheres, were fabricated, respectively,by the above interfacial assembly, and then each Au nanoparticle film was modifiedby a platinum ultra-thin films using wet chemistry method. Pt thin films on goldnanomaterials show satisfactory electrocatalytic activities for methanolelectrooxidation. By comparison, the performance of catalyst is in this order: Pt-goldnanorod film>Pt-gold nanoparticle film>Pt-bare electrode. The results disclosed thecontribution of the synergitical effect of Au and Pt and the effect of the shape of Aunanoparticle on methanol electrooxidation.(5) Ag nanowire/carbon nanotube composite films for H2O2electrooxidation: Ag nanowire monolayer film and carbon nanotube film fabricatedat oil/water interfaces, respectively, were transferred alternatively onto galssycarbon surface without any linkers, forming a composite film. As-preparedcomposite film showed good electronic conductivity and catalytic activity. Due tothe linker-free merit, it responded quickly to H2O2, and may be used in rapiddetection of H2O2.(6) Ag nanowire “sandwich” structures for surface-enhanced Ramanscattering: Ag nanowire “sandwich” structures were fabricated by repeatedlytransfering Ag nanowire monolayer film locating at a oil/water interface onto thesame slide glass. Before repeating the transfer of Ag nanowire monolayer film, theslide galss covered with one layer of Au nanowire monolayer film was inmmersedinto a dye aqueous solution to absorb dye molecules. Due to the location of dyemolecules between two layers of Ag nanowire monolayer films, the “sandwith”structure showed better SERS activity than Ag nanowire monolayer film with dyemolecuels, which may result from enhancement of electromagnetic field betweentwo layers of Ag nanowire monolayer film.(7) Oriented etcting of Ag nanocube at oil/water interface: The theoreticalcalculations above show that the stablest state of each silver nanocube at theinterface is one of its sides in the oil phase and the opposite side was in the aqueous phase. According to this principle, in-situ etching of silver nanoparticles at oil/liquidinterfaces was done to prepare a concavity on the side of Ag nanocube.

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