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Degree

Doctor of Philosophy, Miami University, Chemistry, 2011.

Abstract

Designing electrocatalytic systems of desired functionality and physico-chemical properties and their application toward detection of species in solution is a main goal of this work. Chemically modified electrodes (CME), when compared to the traditional non-modified ones can offer higher rates of electrode reactions resulting in improved sensitivity. Polyoxometalates (POMs) can readily adsorb on the electrodes and serve as an electroactive mediators to promote electrochemical reductions. Due to their affinity for gold and weak basicity, they are well-suited surface layers that stabilize gold nanoparticles (AuNPs). Here, we demonstrate that phosphomolybdic acid (PMo12) adsorbed onto AuNP centers acts synergistically toward bromate reduction. Further stabilization of the system with aminopropyltriethoxysilane, (APTES), as a linking monolayer between particles and the electrode, allows successful application of resulting electrode to hydrodynamic conditions. We also incorporate the AuNP-PMo₁₂ into layer-by-layer composites that contain an enzyme and the conducting polymers, polyaniline derivatized with poly(styrenesulfonate), PANI/PSS, and poly(3,4-ethylendioxythiophene), PEDOT. In this system we investigate the electrocatalytic reduction of H₂O₂ and test the stability of the composite electrode in flow injection amperometry. Expanding on the earlier work, we explore the suitability of rhodium-substituted polyoxometalates (Rh₂POM) as a protective ligand for AuNP. These species catalyze reductions via the poloxometalate center and oxidations via the Rh (II,III) couple. A procedure for synthesizing AuNP-Rh₂POM is developed. Strong adsorption of POMs on electrodes suggested direct product attachment, but electrodes modified in this manner are not stable. Thus, glassy carbon electrode (GC) is modified with a monolayer of APTES. This electrostatic assembly yields a modified electrode that is stable in quiescent solution. The sensitivity for the determination of bromate and methionine by cyclic voltammetry is greater with the AuNP-containing film; however, the electrode is not stable in hydrodynamic conditions. To prevent loss of the catalyst under flow conditions, we apply electrochemically assisted deposition of a sol-gel film that contains templated nanopores. After removal of the templating agent with oxygen plasma and capping the silica with a silane, layer-by layer assembly within the pores is used to immobilize AuNP-Rh2POM¬. This electrode shows day-to-day stability and permits the determination of bromate and methionine at the nM-level.

Subject Headings

Chemistry

Keywords

electrocatalysis; nanoparticles; polyoxometalates; sol-gel

Committee / Advisors

James Cox, PhD (Advisor)
Andre Sommer, PhD (Committee Chair)
Neil Danielson, PhD (Committee Member)
Richard Taylor, PhD (Committee Member)
Burcin Bayram, PhD (Committee Member)

Pages

159p.

Document number: miami1321469456
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=miami1321469456

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