Electroanalysis in the nanodomain: quinone monolayers and nanometer dimensioned electrodes
Farrell, Mary M. (2003) Electroanalysis in the nanodomain: quinone monolayers and nanometer dimensioned electrodes. PhD thesis, Dublin City University.
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Spontaneously adsorbed monolayers, which are formed by the immersion o f an electrode into a dilute solution o f surface-active molecules have been studied extensively in recent years. The work presented in this thesis deals with the modification o f mercury electrode surfaces with 9,10-anthraquinone and two anthraquinone derivatives, 1-amino,2- sulphonic,4-hydroxyanthraquinone (1,2,4-AQASH), and 1,5-dimethoxyanthraquinone (1,5- DMAQ). These adsorbates form a n interaction with the electrode surface. The thermodynamics o f adsorption has been modeled using the Langmuir and Frumkin adsorption isotherms. Binary monolayers formed by the coadsorption o f 1,2,4-AQASH and 1,5-DMAQ have been investigated to probe the extent o f interaction between adsorbed moieties. The kinetics o f single component 1,5-DMAQ adsorption has been modeled over a wide concentration range to probe the mode o f adsorption o f these molecules. It has been concluded from the CV and kinetic fits o f this data that 1,5-DMAQ molecules undergo a reorientation on the electrode surface as adsorption proceeds.
Quinonoid monolayers form tightly bound adsórbate layers on mercury, which are stable in both redox forms. These monomolecular films undergo coupled proton and electron transfer reactions and are important in areas such as catalysis, molecular electronics and biological applications. The heterogeneous electron transfer rate o f 1,2,4-AQASH has been investigated and was modeled using the Butler-Volmer and Marcus theories o f electron transfer. Platinum electrodes o f micrometer to nanometer dimensions have been fabricated using a laser based micropipette puller. Mercury has been electrodeposited on the platinum surface to produce micrometer sized mercury electrodes o f hemispherical geometry. These electrodes exhibit faster response times than macroelectrodes and thus enable the measurement o f fast heterogeneous electron transfer rates. A mechanism for the sequence o f proton and electron transfer in monomolecular films o f 1,2,4-AQASH in both oxidation and reduction directions was postulated from the experimental data in solutions o f high and low pH.
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