Recently there have been considerable interests in nanometerial study. In this work, we have used carbon nanotubes (CNTs) and polypyrrole (PPy) conducting polymers (CPs) as models to make a nanotube and conducting polymer composite material. Under electro-oxidation condition, the PPy/CNT films can be grown on conventional substrates such as a glassy carbon electrode in aqueous and non-aqueous media. These nano-conjugated materials are based on the doping of CNTs particles into conducting polymer network while oxidatively polymerizing. CNTs serve as dopants and solely supporting electrolytes in the preparation. The CP/CNT new composite materials have showed promise not only in a potential environmental remedy such as conversion of highly toxic Cr(VI) into less harmful Cr(III), but also in electrocatalysis of the quinone/hydroquinone redox reaction. Voltammetry, bulk electrolysis with coulometry, AC impedance, and EQCM techniques have been used to elucidate the preparation, ion transport, and intermolecular interaction processes within these composites.

The service life and electrocatalytic activity of tantalum oxide/iridium oxide coated titanium plate and mesh anodes used in the electrolytic production of chromic acid were investigated by performing accelerated life tests, voltammetric and chronoamperometric measurements in chrome (VI) solutions. Experimental results showed that the service life for the coated mesh anode was 1059 hours, compared to 828 hours for the plate anode at a current density of 1.2 A cm-2. In addition, the coating failed earlier in higher chromic acid concentration. Physical analysis by SEM and EDS before and after accelerated life test confirmed that the deactivation was a result of corrosion of IrO2 followed by titanium substrate passivation. A simple and rapid method for assessing the electrocatalytic activity of iridium–tantalum oxide coating based on a chronoamperometric technique was developed.

The main purpose of this work is study of electrochemical hydrogen peroxide and ascorbate reactions on electrodes modified by Prussian blue (PB), with the aim to apply these electrodes in creation of sensors and biosensors. For this purpose, a detailed study of electrochemical reduction of hydrogen peroxide, as well as of oxidation of ascorbate at Prussian blue modified rotating disk electrode. In view of the results obtained, a mechanism for hydrogen peroxide reduction at PB modified electrode has been proposed. In accordance with this mechanism, electron transfer appears to be rate-limiting step. The kinetics of decomposition of PB modified electrode in the course of a cathodic reduction of hydrogen peroxide has been studied, and the influence of different factors to this process has been determined. Prototypes of sensors and biosensors, for different analytes have been elaborated and tested. / Darbo tikslas yra elektrocheminių vandenilio peroksido ir askorbato reakcijų tyrimas ant Berlyno mėlynuoju (BM) modifikuotų elektrodų, siekiant pritaikyti šiuos elektrodus jutiklių ir biojutiklių kūrimui. Ištirta vandenilio peroksido redukciją ir askorbato oksidaciją naudojant sukamojo disko elektrodą. Gauti rezultatai galimai įrodo stadijinį vandenilio peroksido katodinės redukcijos mechanizmą vykstantį ant BM modifikuoto elektrodo. Detaliai ištirta BM sluoksnio irimo kinetika vandenilio peroksido elektroredukcijos metu, ir nustatyti faktoriai, įtakojantys irimo proceso greitį. Sukurti jutiklių ir biojutiklių prototipai, kurie galėtų būti panaudoti biologiškai aktyvių medžiagų (vandenilio peroksido, askorbato, gliukozės) nustatymui.

Darbo tikslas yra elektrocheminių vandenilio peroksido ir askorbato reakcijų tyrimas ant Berlyno mėlynuoju (BM) modifikuotų elektrodų, siekiant pritaikyti šiuos elektrodus jutiklių ir biojutiklių kūrimui. Ištirta vandenilio peroksido redukciją ir askorbato oksidaciją naudojant sukamojo disko elektrodą. Gauti rezultatai galimai įrodo stadijinį vandenilio peroksido katodinės redukcijos mechanizmą vykstantį ant BM modifikuoto elektrodo. Detaliai ištirta BM sluoksnio irimo kinetika vandenilio peroksido elektroredukcijos metu, ir nustatyti faktoriai, įtakojantys irimo proceso greitį. Sukurti jutiklių ir biojutiklių prototipai, kurie galėtų būti panaudoti biologiškai aktyvių medžiagų (vandenilio peroksido, askorbato, gliukozės) nustatymui. / The main purpose of this work is study of electrochemical hydrogen peroxide and ascorbate reactions on electrodes modified by Prussian blue (PB), with the aim to apply these electrodes in creation of sensors and biosensors. For this purpose, a detailed study of electrochemical reduction of hydrogen peroxide, as well as of oxidation of ascorbate at Prussian blue modified rotating disk electrode. In view of the results obtained, a mechanism for hydrogen peroxide reduction at PB modified electrode has been proposed. In accordance with this mechanism, electron transfer appears to be rate-limiting step. The kinetics of decomposition of PB modified electrode in the course of a cathodic reduction of hydrogen peroxide has been studied, and the influence of different factors to this process has been determined. Prototypes of sensors and biosensors, for different analytes have been elaborated and tested.

O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX) and O-isobutyl-S-2-diethylaminoethyl methylphosphonothioate (R-VX), are considered chemical warfare agents due to their strong acetylcholinesterase-inhibiting properties. Subsequent to terrorist use of these V-type nerve agents in both Japan and the United States of America (the September 11, 2001 attacks) and the limited capability of anti-terrorist groups to detect such weapons, there has been an increased obligation by the Chemical Weapons Convection for specific detection and identification methods for VX and R-VX. Chemical and/or enzymatic hydrolysis yields sulfhydryl mimic products, diethylaminoethanethiol (DEAET) and dimethylaminoethanethiol (DMAET). This thesis investigates the electrocatalytic parameters of DEAET and DMAET using basal plane pyrolytic graphite electrodes (BPPGEs) modified with: (a) single-wall carbon nanotube (BPPGE-SWCNT); (b) SWCNT functionalised with cobalt (II) tetra-aminophthalocyanine by (i) physical (BPPGE-SWCNT-CoTAPc(mix)), (ii) chemical (BPPGE-SWCNT-CoTAPc(cov)) and (iii) electrochemical adsorption (BPPGE-SWCNT-CoTAPc(ads)) processes; (c) nickel powder (BPPGE-Ni); (d) BPPGE-Ni decorated with SWCNT (BPPGE-Ni-SWCNT), and (e) SWCNT functionalised with nickel (II) tetra-aminophthalocyanine (BPPGE-SWCNT-poly-NiTAPc). Electrochemical studies (performed by voltammetric and electrochemical impedance spectroscopic techniques) revealed that the SWCNT and SWCNT-CoTAPc(mix) films showed comparable electrocatalytic responses towards the detection of DEAET and DMAET whereas competitive electrochemical behaviour was seen between SWCNT and SWCNT-NiTAPc modified BPPGEs. Using the BPPGE-SWCNT-CoTAPc(mix), the estimated catalytic rate constants (k) and diffusion coefficients (D) were higher for DEAET than for the DMAET. Also, the detection limits of approximately 8.0 and 3.0µM for DMAET and DEAET were obtained with sensitivities of 5.0×10−2 and 6.0×10−2 AM−1 for DMAET and DEAET, respectively. Unlike BPPGE-SWCNT-CoTAPc(mix) that detected the two sulfhydryls at slightly different potentials, BPPGE-SWCNT did not. The BPPGE-Ni gave enhanced Faradaic response for the redox probe ([Fe(CN)6]3−/4−) and also displayed enhanced electrocatalytic behaviour towards the detection of DMAET and DEAET with high sensitivity (~23x10−3 AM−1) and low detection limits (4.0 – 9.0 µM range). In comparison to other electrodes reported in the literature, BPPGE-Ni exhibits more promising features required for a simple, highly sensitive, fast and less expensive electrode for the detection of the hydrolysis products of V-type nerve agents in aqueous solution. The efficient response of the BPPGE-Ni is attributed to the high microscopic surface area of the nickel powder. The poor response of the BPPGE-Ni-SWCNT suggests that the nickel impurity in SWCNT did not show any detectable impact on the heterogeneous electron transfer kinetics of SWCNT. Unlike the nickel powder, SWCNT and CoTAPc-SWCNT, the NiTAPc-SWCNT hybrid did not show significant electrocatalysis towards the detection of the sulfhydryls. It is interesting, however, to observe for the first time that SWCNT induced crystallinity on the electropolymer of NiTAPc, and that such electropolymer exhibit charge-storage /-transfer properties that greatly enhance the electrochemical response of nitric oxide. / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted

Synthesis and functionalization of large-area graphene and its structural, electrical and electrochemical properties has been investigated. First, the graphene films, grown by thermal chemical vapor deposition (CVD), contain three to five atomic layers of graphene, as confirmed by Raman spectroscopy and high-resolution transmission electron microscopy. Furthermore, the graphene film is treated with CF4 reactive-ion plasma to dope fluorine ions into graphene lattice as confirmed by X-ray photoelectron spectroscopy (XPS) and UV-photoemission spectroscopy (UPS). Electrochemical characterization reveals that the catalytic activity of graphene for iodine reduction enhanced with increasing plasma treatment time, which is attributed to increase in catalytic sites of graphene for charge transfer. The fluorinated graphene is characterized as a counter-electrode (CE) in a dye-sensitized solar cell (DSSC) which shows ~ 2.56% photon to electron conversion efficiency with ~11 mAcm−2 current density. Second, the large scale graphene film is covalently functionalized with HNO3 for high efficiency electro-catalytic electrode for DSSC. The XPS and UPS confirm the covalent attachment of C-OH, C(O)OH and NO3- moieties with carbon atoms through sp2-sp3 hybridization and Fermi level shift of graphene occurs under different doping concentrations, respectively. Finally, CoS-implanted graphene (G-CoS) film was prepared using CVD followed by SILAR method. The G-CoS electro-catalytic electrodes are characterized in a DSSC CE and is found to be highly electro-catalytic towards iodine reduction with low charge transfer resistance (Rct ~5.05 Wcm2) and high exchange current density (J0~2.50 mAcm-2). The improved performance compared to the pristine graphene is attributed to the increased number of active catalytic sites of G-CoS and highly conducting path of graphene. We also studied the synthesis and characterization of graphene-carbon nanotube (CNT) hybrid film consisting of graphene supported by vertical CNTs on a Si substrate. The hybrid film is inverted and transferred to flexible substrates for its application in flexible electronics, demonstrating a distinguishable variation of electrical conductivity for both tension and compression. Furthermore, both turn-on field and total emission current was found to depend strongly on the bending radius of the film and were found to vary in ranges of 0.8 – 3.1 V/μm and 4.2 – 0.4 mA, respectively.

No description available.

Sol-Gel techniques depend on the hydrolysis and condensation reactions of organosilicon precursors in aqueous media and, thus, provide an inclusive environment with bioaffinity. On the other hand, carbon nanotubes (CNTs), which possess unique electric, thermal, mechanical, and chemical properties, including their high surface area:volume ratio, can be further surface-functionalized to address different material or sensing demands. In this work we describe a new composite material that combines the unique sol-gel network with conductive CNTs. Hydrolysis and subsequent condensation of tetramethyloxysilane (TMOS) in the presence of CNTs result in the formation of a dense, homogeneous material. Properties of this composite material on electrode surfaces are discussed and novel sensing applications are described.

No description available.

<p dir="ltr">Nature moves small things by chemical energy. Inspired by this, catalytic reactions driven microswimmers have been designed and believed to be promising to help transport drugs and other cargos at microscales. However, decorating the microswimmers with drugs and cargos would make them heavy and hard to move. An alternative solution to this would be designing self-pumping devices that can pump the fluid and things carried by the fluid all together without external resources. In this work, we have presented the first full numerical model of electrochemically-powered self-pumping in the Pt-Au coated polycarbonate membrane reported by Jun and Hess [1]. The simulations demonstrate that autonomous flow in self-pumping membranes is an electro-osmotic flow driven by a self-generated electric field. The injection and consumption of H⁺ on Pt and Au respectively lead to a charge asymmetry and an associated electric field that acts on the electric double layers (EDL) coating the pore walls driving fluid move, i.e. self-electro-osmosis. Key parameters controlling the performance of self-pumping are pore radius and background pH values, as they affect the EDL overlap and ionic strength. Other parameters such as porosity and pore length can both be tuned to find the local optimum for a membrane design. By tuning these parameters, the trade-off between increased ionic current and increased ionic strength could be balanced, contributing to an optimum self-pumping performance. When inclination or deformation occurs in cylindrical pores, the self-pumping flow does not significantly deviate from the trend. Membranes with complicated shape of contracting/expanding pores and cross-linked connecting pores should follow same pattern as cylindrical pores with similar pore size. In addition, if we replace the Pt/Au catalytic pairs by TiO₂/Au photocatalytic pairs, self-pumping membrane could be driven by light. The geometry of pore enhances the light absorption, enabling self-pumping membrane achieving high flow rate at large porosity with relatively large pores. At the end, we provide experimental evidence of self-pumping flow on TiO₂-Au plates as well as self-pumping membrane driven by light.</p>