Studies of Model Photocatalysts: Stochastic, Electrochemical and Solution Analysis of Colloidal Nanoparticles
AuthorBarakoti, Krishna Kumar
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This dissertation covers photocatalytic and stochastic photoelectrochemical studies of colloidal semiconducting nanomaterials. Photocatalytic properties of colloidal titanium dioxide nanoparticles (TiO2 NPs) and stochastic interaction of colloidal dye sensitized nanoparticles (DSNPs) with Pt ultramicroelectrode are studied. These nanostructured materials are potentially useful substances in solar energy based photovoltaics and water-splitting devices. In this dissertation, we present the photoelectrochemical study of bare TiO2 nanoparticles, sensitized nanoparticles and cadmium selenide (CdSe) materials, suspended in methanol as a model system. Methanol oxidation reaction is studied as a model reaction of photocatalysis that provides a comprehensive view of the process. Mechanistic and kinetic details of the process and their relationship with colloidal properties are described based on our findings. To accomplish this, we adapted analytical methods for quantitative analysis of formaldehyde, formic acid and carbon dioxide present in neat methanol. Our observations reveal formaldehyde is the predominant reaction product in controlled conditions that minimize the content of oxygen and water. Methanol oxidation to formaldehyde is consistent with two-electron oxidation mechanism. The photoelectrochemical study of dye sensitized TiO2 NPs shows stochastic interaction between DSNPs, suspended in methanol with a Pt ultramicroelectrode. In the dark, the current steps observed are anodic, consistent with the oxidation of dye “N719” at the Pt electrode surface. Under illumination, cathodic steps are observed as a dominant step response and are assigned to the reduction of the oxidized form of dye that is generated after electrons are injected into the TiO2 NPs. We also present preliminary results for stochastic photoelectrochemical study of quantum dots, CdSe and CdSe/ZnS materials.