Diamond electrodes have shown outstanding properties such as high stability, high charge transport and surface conductivity for H-terminated surfaces. These properties have been obtained from a number of electrochemical studies on diamond films. Diamond-particle electrodes could have all those properties with the advantage of a high surface area, which would make good materials for electrocatalysis applications. Chemically reduced graphene oxide (CR-GO) has shown promising properties to be used as electrode materials. However, their electrochemistry is still not fully understood. In this study, electrochemical properties of HPHT diamond-particle and graphene-DNA (G-DNA) composite assemblies are investigated. The studies of diamond particles involve electrostatic self-assembly, electrochemistry, and lateral and vertical charge transport. All properties were probed as a function of particle surface termination. Diamond particles (DP) were treated in a hot acid bath and a H2 plasma reactor to obtain 0- (ODP) and H-terminated (HDP) particles, respectively. In aqueous media, all diamond samples showed negative surface charge at pH ≥7. The negative surface charge allowed the electrostatic adsorption of the particles on ITO electrodes. The diamond assemblies were used as working electrodes for electrochemical studies. sp2 surface states are responsible for the electrochemical response of DP. The response of HDP is associated with the accumulation of surface holes due to electrochemical surface doping. Electrochemical analysis provided an estimated sur- face hole density, as well as the valence band edge of HDP. Vertical charge-transport of diamond particles is obtained from charge-transfer mediation across a blocking layer. Lateral conductivity is obtained from an electrochemical field-effect transistor. HDP shows higher lateral and vertical charge transport than DP and ODP. The high charge transport of HDP is linked to the accumulation of surface holes due to the surface doping of hydrogenated diamonds. The studies of G-DNA involve characterisation, electrochemistry and charge-transfer mediation across a blocking layer. Comparisons with graphene oxide (GO) were made in all cases. Spectroscopic characterisation demonstrates that G-DNA is partially re- duced GO and it contains a high defect density. The electrochemical behaviour of G-DNA assemblies is similar to other conventional sp2 carbon electrodes. The enhancement of electron-transfer mediation by G-DNA is due to the high density of states near the Fermi level. High surface-area electrodes of discrete materials can be prepared by electrostatic self-assembly. Electrochemical studies showed that the electrochemical behaviour is surface-termination dependent for diamond particles. Partially hydrogenated particles of diamond can have high charge transport due to the surface doping. The high defect density G-DNA shows higher electrochemical reactivity than GO.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:551304 |
| Date | January 2011 |
| Creators | Hongthani, Wiphada |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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