Electrodeposited nanoparticles: properties and photocatalytic applications

Abstract

The work presented in this thesis reports on fundamental studies into electrodeposition of gold and silver nanoparticulate spheroids on a conducting substrate, Fluorine-doped tin-oxide, and the manipulation of the electrodeposition conditions in order to influence and control the size and surface concentration of spheroids. Methods to control the deposition included chemical modification of the surface with an adsorbed monolayer of 3-aminopropyldimethylmethoxysilane, and manipulation of the potential pulse scheme, especially using a double pulse 'nucleation and growth' approach. The optimised method for production of silver and gold nanoparticulate surfaces was utilised to selectively create surfaces that yield strong surface enhanced Raman scattering (SERS) enhancements, as well as metal enhanced fluorescence. These enhancements have been quantified using the probe molecules Trans-1,2-bis(4-pyridyl)ethylene (BPE) and [Os(bpy)2Qbpy]2+ respectively (where bpy is 2,2’-bipyridyl and Qbpy is 2,2’:4,4’’:4’4’’-quarterpyridyl). Spontaneously formed, densely packed monolayers of [Os(bpy)2PIC]2+ have been formed on fluorine-doped tin-oxide (FTO) electrodes, and films of [Os(bpy)2Qby]2+ have been formed on silver nanoparticulate decorated FTO (where bpy is 2,2’-bipyridyl, PIC is 2-(4-carboxyphenyl)imidazo[4,5- f][1,10]phenanthroline, and Qbpy is 2,2’:4,4’’:4’4’’-quarterpyridyl). The quenching mechanism of the polyoxotungstate anion α-[S2W18O62] (POW) on the two osmium polypyridyl complexes in solution has been identified by analysis of the Stern-Volmer plots. The quenching of monolayers of these complexes by POW, coupled to the electrochemical regeneration of the ground state osmium complex by potential application at the FDTO electrode, has been used to photo-catalytically reduce methyl viologen. Finally a wireless gold bipolar electrode in a microchannel, whose potential is floating and managed by exerting potential control over the electrolyte solution rather than individual electrodes, has been used as the basis for an electrochemiluminescent DNA microsensor. The function of the DNA microsensor has been optimised to maximise signal intensity by altering the ECL solution, and by manipulating the pathway by which the ECL reaction proceeds. DNA binding has been detected based on catalysis of the oxygen reduction reaction (ORR) at (DNA linked) platinum nanoparticles. The ORR can be replaced with other reduction reactions to detect other species such as anthraquinones. The possibility of using this device for quantitative sensing of both DNA and other species is discussed