Development of Novel Methodologies for the Electrodeposition of Polypyrrole-based Films in Controlled Morphologies with Potential Application in Nitrate Sensing.


McCarthy, Conor P. (2013) Development of Novel Methodologies for the Electrodeposition of Polypyrrole-based Films in Controlled Morphologies with Potential Application in Nitrate Sensing. PhD thesis, National University of Ireland Maynooth.

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Abstract

In this thesis the novel electrochemical deposition of poly[N-(2-cyanoethyl)pyrrole] (PPyEtCN) into nanowire and microtube morphologies is reported. Cyclic and pulsed electrochemical techniques were employed to electrodeposit copper micro and nano particles at PPyEtCN and polypyrrole (PPy) surfaces. A PPy nanowire/copper modified electrode was investigated for its effectiveness as an electrochemical sensor for the detection of the nitrate ion. To produce PPyEtCN in a nanowire morphology a facile, one step, electrochemical method was employed, which did not require the use of any templates or surfactants. Using optimised conditions the nanowires nucleated to give a homogeneous film across the electrode surface, with lengths of approximately 2 μm and diameters of 150 nm. Evidence is presented to support an instantaneous 3-D nucleation and growth mechanism. Structural information on the nanowires was obtained using vibrational spectroscopy which reveals the polaron as the main charge carrier within the polymer matrix. To fabricate novel vertically aligned open and closed-pore microstructures of PPyEtCN, an electrodeposition procedure was developed using an emulsion in a cosolvent mixture. Adsorbed toluene droplets were employed as soft templates to direct polymer growth. The microstructures only grew in the presence of both ClO4 - and H2PO4 - doping ions, due to a slower rate of polymer propagation in this electrolyte. Two sonication methods (probe and bath) were used to form the emulsion, producing significantly different microstructure morphologies. Control over microtube diameter was achieved by simply altering the emulsion sonication time or the amount of toluene added to form the emulsion. Electrochemical characterisation indicated the PPyEtCN microtube morphology had an increased electrochemical response compared to its bulk counterpart. TEM analysis of individual closed-pore microtubes identified a hollow interior at the base within which the toluene droplet was encapsulated. This cavity may be used to entrap other compounds making these materials useful in a range of applications. The methodology was also applied to form microstructures of poly(3,4-ethylenedioxythiophene) and PPy. Electrodeposition of copper crystals at PPy and PPyEtCN was performed using constant potential and cyclic voltammetry techniques. For potentiostatic deposition, the concentration of copper and the magnitude of the overpotential were altered to control the deposited crystal habit. Using a negative potential of -0.200 V, the evolution of a dendrite morphology was followed using microscopy. This morphology had an increased surface area due to the copper branching extending into the electrolyte. PPy nanowire/copper electrodes were developed by altering the speed and cycle number of the cyclic deposition procedure. This was an accurate means of controlling the shape and size of the deposits. Varying the scan rate from 100 to 900 mV/s resulted in the size of the copper deposits changing from m to nm. Sensing experiments revealed that the PPy/copper electrode was not as sensitive as a glassy carbon/copper electrode due to interference from residual carbonate ions remaining within the polymer matrix; however, it was observed to be more stable over repeated cycling due to a charge transfer interaction between the copper and pyrrole nitrogen.

Item Type: Thesis (PhD)
Keywords: Novel Methodologies; Electrodeposition of Polypyrrole-based Films; Controlled Morphologies; Potential Application; Nitrate Sensing;
Academic Unit: Faculty of Science and Engineering > Chemistry
Item ID: 6739
Depositing User: IR eTheses
Date Deposited: 07 Jan 2016 15:12
URI:

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