-
[show abstract]
[hide abstract]
ABSTRACT: Excitation of the weak electron donor decamethylosmocene on illumination with white light produces an excited-state species capable of reducing organically solubilized protons under biphasic conditions. Insight into the mechanism and kinetics of light-driven biphasic hydrogen evolution are obtained by analysis with gas chromatography, cyclic voltammetry, and UV/Vis and (1) H NMR spectroscopy. Formation of decamethylosmocenium hydride, which occurs prior to hydrogen evolution, is a rapid step relative to hydrogen release and takes place independently of light activation. Remarkably, hydride formation occurs with greater efficiency (ca. 90 % conversion) under biphasic conditions than when the reaction is carried out in an acidified single organic phase (ca. 20 % conversion). Cyclic voltammetry studies reveal that decamethylosmocene has a higher proton affinity than either decamethylferrocene or osmocene.
ChemPhysChem 05/2013; · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Rarely reported low-cost molybdenum boride and carbide microparticles, both of which are available in abundant quantities due to their widespread use in industry, adsorb at aqueous acid-1,2-dichloroethane interfaces and efficiently catalyse the hydrogen evolution reaction in the presence of the organic electron donor - decamethylferrocene. Kinetic studies monitoring biphasic reactions by UV/vis spectroscopy, and further evidence provided by gas chromatography, highlight (a) their superior rates of catalysis relative to other industrially significant transition metal carbides and silicides, as well as a main group refractory compound, and (b) their highly comparable rates of catalysis to Pt microparticles of similar dimensions. Insight into the catalytic processes occurring for each adsorbed microparticle was obtained by voltammetry at the liquid-liquid interface.
Physical Chemistry Chemical Physics 01/2013; · 3.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nanoporous and planar gold electrodes were utilised as supports for the redox enzymes Aspergillus niger glucose oxidase (GOx) and Corynascus thermophilus cellobiose dehydrogenase (CtCDH). Electrodes modified with hydrogels containing enzyme, Os-redox polymers and the cross-linking agent poly(ethylene glycol)diglycidyl ether were used as biosensors for the determination of glucose and lactose. Limits of detection of 6.0 (±0.4), 16.0 (±0.1) and 2.0 (±0.1) μM were obtained for CtCDH-modified lactose and glucose biosensors and GOx-modified glucose biosensors, respectively, at nanoporous gold electrodes. Biofuel cells composed of GOx- and CtCDH-modified gold electrodes were utilised as anodes, together with Myrothecium verrucaria bilirubin oxidase (MvBOD) or Melanocarpus albomyces laccase as cathodes, in biofuel cells. A maximum power density of 41 μW/cm(2) was obtained for a CtCDH/MvBOD biofuel cell in 5 mM lactose and O(2)-saturated buffer (pH 7.4, 0.1 M phosphate, 150 mM NaCl).
Analytical and Bioanalytical Chemistry 12/2012; · 3.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: An efficient electrocatalyst for hydrogen evolution has been developed based upon in situ reduction of MoS2 on ordered mesoporous carbon nanospheres (MoS2/MCNs). The properties of MoS2/MCNs were characterised by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Polarisation curves and electrochemical impedance measurements were obtained for MoS2/MCNs modified glassy carbon electrodes. The MoS2/MCNs exhibit high catalytic activity for hydrogen evolution with a low overpotential and a very high current density. A theory outlining the origins of the Tafel slope for a Volmer-Heyrovsky (rate determining step) mechanism of hydrogen evolution at MoS2 catalytic edge sites is presented.
Electrochemistry Communications 06/2012; 22:128-132. · 4.86 Impact Factor
-
Peiyu Ge, Micheál D Scanlon,
Pekka Peljo,
Xiaojun Bian,
Heron Vubrel,
Arlene O'Neill,
Jonathan N Coleman,
Marco Cantoni,
Xile Hu,
Kyösti Kontturi,
Baohong Liu,
Hubert H Girault
[show abstract]
[hide abstract]
ABSTRACT: The activities of a series of MoS(2)-based hydrogen evolution catalysts were studied by biphasic reactions monitored by UV/Vis spectroscopy. Carbon supported MoS(2) catalysts performed best due to an abundance of catalytic edge sites and strong electronic coupling of catalyst to support.
Chemical Communications 05/2012; 48(52):6484-6. · 6.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The high surface areas of nanostructured electrodes can provide for significantly enhanced surface loadings of electroactive materials. The fabrication and characterization of nanoporous gold (np-Au) substrates as electrodes for bioelectrochemical applications is described. Robust np-Au electrodes were prepared by sputtering a gold-silver alloy onto a glass support and subsequent dealloying of the silver component. Alloy layers were prepared with either a uniform or nonuniform distribution of silver and, post dealloying, showed clear differences in morphology on characterization with scanning electron microscopy. Redox reactions under kinetic control, in particular measurement of the charge required to strip a gold oxide layer, provided the most accurate measurements of the total electrochemically addressable electrode surface area, A(real). Values of A(real) up to 28 times that of the geometric electrode surface area, A(geo), were obtained. For diffusion-controlled reactions, overlapping diffusion zones between adjacent nanopores established limiting semi-infinite linear diffusion fields where the maximum current density was dependent on A(geo). The importance of measuring the surface area available for the immobilization was determined using the redox protein, cyt c. The area accessible to modification by a biological macromolecule, A(macro), such as cyt c was reduced by up to 40% compared to A(real), demonstrating that the confines of some nanopores were inaccessible to large macromolecules due to steric hindrances. Preliminary studies on the preparation of np-Au electrodes modified with osmium redox polymer hydrogels and Myrothecium verrucaria bilirubin oxidase (MvBOD) as a biocathode were performed; current densities of 500 μA cm(-2) were obtained in unstirred solutions.
Langmuir 01/2012; 28(4):2251-61. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Well defined mediatorless bioelectrocatalytic reduction of oxygen with high current densities of 0.8 mA cm− 2 was obtained on nanoporous gold electrodes modified with Myrothecium verrucaria bilirubin oxidase. A stable faradaic response was observed when the enzyme modified electrode was coated with a specifically designed electrodeposition polymer layer. The response of the enzyme electrode was only slightly inhibited by the addition of F−
Electrochemistry Communications 12/2011; 16:92-95. · 4.86 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The benefit of miniaturization towards the nanoscale of electroanalytical systems was evaluated by assessment of the sensitivity of the response. Ion transfer voltammetry across the interface between two immiscible electrolyte solutions (ITIES) was employed as the basis for detection of nonredoxactive ions. The analytical sensitivity increased on miniaturisation of the interface from millimetre-, to micrometre-, to nanometre-scale, with an improvement in sensitivity of more than three orders of magnitude. This is due to the enhanced mass transport via convergent diffusion as the size of the ITIES is minimised. These results illustrate the benefit of miniaturisation of electrochemical detection methods to the nanoscale.
Electroanalysis 03/2011; 23(4):1023 - 1028. · 2.87 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The behaviour of two biological macromolecules, bovine pancreatic insulin and hen-egg-white lysozyme (HEWL), at aqueous-organogel interfaces confined within an array of solid-state membrane micropores was investigated via cyclic voltammetry (CV). The behaviour observed is discussed in terms of possible charge transferring species and mass transport in the interfacial reaction. Comparison of CV results for HEWL, insulin, and the well-characterised model ion tetraethylammonium cation (TEA(+)) revealed that the biomacromolecules undergo an interfacial reaction comprising biomacromolecular adsorption and facilitated transfer of electrolyte anions from the organic phase to a protein layer on the aqueous side of the interface, whereas TEA(+) undergoes a simple ion transfer process. Evidence for biomacromolecular adsorption on the aqueous side of the micro-interfaces is provided by comparison of the CVs for TEA(+) ion transfer in the presence and absence of the biomacromolecules. Similar experiments in the presence of the low generation polypropylenimine tetraamine dendrimer, (DAB-AM-4), a smaller synthetic molecule, revealed it to be non-adsorbing. The behaviour of biological macromolecules at miniaturised aqueous-organogel interfaces involves adsorption on the aqueous side of the interface and transfer of organic phase electrolyte anions across the interface to associate with the adsorbed biomacromolecule. The data presented support the previously suggested mechanism for biomacromolecular voltammetry at liquid-liquid interfaces, involving adsorption and facilitated ion-transfer of organic electrolyte anions.
Physical Chemistry Chemical Physics 09/2010; 12(34):10040-7. · 3.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Ion transfer across interfaces between immiscible liquids provides a means for the nonredox electrochemical detection of ions. Miniaturization of such interfaces brings the benefits of enhanced mass transport. Here, the electrochemical behavior of geometrically regular arrays of nanoscale interfaces between two immiscible electrolyte solutions (nanoITIES arrays) is presented. These were prepared by supporting the two electrolyte phases within silicon nitride membranes containing engineered arrays of nanopores. The nanoITIES arrays were characterized by cyclic voltammetry of the interfacial transfer of tetraethylammonium cation (TEA(+)) between the aqueous phase and the gelled organic phase. Effects of pore radius, pore center-to-center separation, and number of pores in the array were examined. The ion transfer produced apparent steady-state voltammetry on the forward and reverse sweeps at all experimentally accessible scan rates and at all nanopore array designs. However, background-subtraction of the voltammograms revealed the evolution of a peak-shaped response on the reverse sweep with increasing scan rate, indicative of pores filled with the organic phase to a certain extent. The steady-state voltammetric behavior at the nanoITIES arrays on the forward sweep for arrays with significant diffusion zone overlap between adjacent nanoITIES is indicative of the dominance of radial diffusion to interfaces at the edge of the arrays over linear diffusion to interfaces within the arrays. This implies that nanoITIES arrays, which occupy an overall area of micrometer dimensions, behave like a single microITIES of corresponding area to the nanoITIES array.
Analytical Chemistry 07/2010; 82(14):6115-23. · 5.86 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Microporous silicon membranes were recently introduced to create hexagonally-patterned arrays of micro-scale interfaces between two immiscible electrolyte solutions (μITIES). In this report we present a simulation study of the application of differential pulse stripping voltammetry (DPSV) using these μITIES arrays for ion sensing. Simulations showed that the stripping current for ion detection was enhanced by use of relatively deep pores (i.e. a low pore aspect ratio) and a viscous organic phase. These factors decrease the speed of escape of the pre-concentrated ion from the organic side of the ITIES. The stripping current initially increased steeply with pre-concentration time but eventually reached a plateau. Experiments performed using a μITIES array with micropores of radius 26 μm, depth of 100 μm and with a gelified organic phase demonstrated the saturation of the stripping peak with increasing pre-concentration time for the DPSV detection of tetraethylammonium ion. The reasons for the saturations are discussed in terms of diffusion coefficients and depth of the micropores.
Journal of Electroanalytical Chemistry 01/2010; 641:7-13. · 2.58 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The electrochemical behaviour of hen-egg-white lysozyme (HEWL) was studied at the polarized water/1,2-dichloroethane interface. The voltammetric ion-transfer response was found to be dependent on the pH and ionic strength of the aqueous phase solution and also on the nature of the organic phase electrolyte anion. The current-pH behaviour of HEWL was dominated by the charge of the biomolecule at each pH, as indicated by the close relationship between the experimental peak currents and the theoretical curve for HEWL based on its known acid-base chemistry. Three organic electrolyte anions of differing hydrophobicities were investigated (TFPB-, TPBCl- and TPB-) and it was found that the ion transfer voltammetric peaks occurred at successively higher potentials in the order of increasing hydrophobicity, Deltaphi(TPB) < Deltaphi(TPBCl) < Deltaphi(TPBF). The voltammetric response was time dependent during multi-cyclic voltammetry experiments, with the formation of a white film of precipitate at the interface. A pre-peak consistent with adsorption of the HEWL ion transfer product at the liquid/liquid interface was also observed. The results suggest that an adsorption or re-arrangement of HEWL molecules with time at the interface is taking place. A mechanism for the response on application of a triangular potential waveform with cyclic voltammetry is proposed based on an i-C-i mechanism. Our results indicate that HEWL is electroactive at the polarized liquid/liquid interface and that such electrochemical methods may provide an approach to the label-free detection and characterization of protein molecules.
Physical Chemistry Chemical Physics 05/2009; 11(13):2272-80. · 3.57 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Miniaturised liquid/liquid interfaces provide benefits for bioanalytical detection with electrochemical methods. In this work, microporous silicon membranes which can be used for interface miniaturisation were characterized by simulations and experiments. The microporous membranes possessed hexagonal arrays of pores with radii between 10 and 25 microm, a pore depth of 100 microm and pore centre-to-centre separations between 99 and 986 microm. Cyclic voltammetry was used to monitor ion transfer across arrays of micro-interfaces between two immiscible electrolyte solutions (microITIES) formed at these membranes, with the organic phase present as an organogel. The results were compared to computational simulations taking into account mass transport by diffusion and encompassing diffusion to recessed interfaces and overlapped diffusion zones. The simulation and experimental data were both consistent with the situation where the location of the liquid/liquid (l/l) interface was on the aqueous side of the silicon membrane and the pores were filled with the organic phase. While the current for the forward potential scan (transfer of the ion from the aqueous phase to the organic phase) was strongly dependent on the location of the l/l interface, the current peak during the reverse scan (transfer of the ion from the organic phase to the aqueous phase) was influenced by the ratio of the transferring ion's diffusion coefficients in both phases. The diffusion coefficient of the transferring ion in the gelified organic phase was ca. nine times smaller than in the aqueous phase. Asymmetric cyclic voltammogram shapes were caused by the combined effect of non-symmetrical diffusion (spherical and linear) and by the inequality of the diffusion coefficient in both phases. Overlapping diffusion zones were responsible for the observation of current peaks instead of steady-state currents during the forward scan. The characterisation of the diffusion behaviour is an important requirement for application of these silicon membranes in electroanalytical chemistry.
The Analyst 02/2009; 134(1):148-58. · 4.23 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Geometrically regular silicon membrane-based micropore arrays were employed for defined arrays of micrometer-sized interfaces between two immiscible electrolyte solutions (μITIES). These were incorporated into a poly(tetrafluoroethylene) (PTFE) hydrodynamic cell. Electrochemistry at the μITIES array was undertaken following gellification of the organic phase using polyvinyl chloride (PVC) and flowing an aqueous phase over the array surface. Cyclic voltammetric characterization of asymmetric diffusion profiles on either side of the μITIES was accomplished under flowing conditions using positively and negatively charged (TEA+ and 4-OBSA−, respectively) model analyte species. Incorporation of an ionophore (dibenzo-18-crown-6 ether) into the organogel allowed the ion-transfer detection of two oligopeptides (phenylalanine dipeptide and lysine dipeptide) within the available potential window under stationary and flowing conditions. Flow rate studies with TEA+ indicated that the amperometric peak currents do not obey the Levich equation, due to diffusion dominating the mass transport, as opposed to convection. The influence of the applied potential () on the amperometric response of the oligopeptides was studied and hydrodynamic voltammograms (HDVs) for the individual oligopeptides were subsequently constructed. The data presented provide a basis for the use of silicon membrane-based μITIES arrays in flow analytical methods.
Electrochimica Acta 12/2008; 55:4234-4239. · 3.83 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The electrochemistry of a series of dendrimers was examined at the interface between two immiscible electrolyte solutions (ITIES), enabling study of non-redox-active dendrimers. Different generations of poly(propylenimine) (DAB-AM-n) and poly(amidoamine) (PAMAM) dendrimers were studied. In their protonated states, the dendrimers were transferred across the ITIES, with the electrochemical behavior observed depending on the dendrimer family, the generation number, and the experimental pH. The electrochemistry of the lower generations studied was characterized by well-defined peaks for both dendrimer families and with small peak-peak separations in the case of the PAMAM family. The voltammetry of the higher generations was more complex, showing distorted voltammograms and instability of the interface. The charges of the transferring dendrimers were calculated by convolution of the voltammetric data and were similar to the theoretical charges for DAB-AM-n. For PAMAM, only the lowest generation exhibited reversible behavior, with higher generations having irreversible behavior. Using cyclic voltammetry, low micromolar concentrations of the dendrimers were detected. The results show that electrochemistry at the ITIES can be a useful method for characterization of ionizable dendrimers and that voltammetry can be a simple method for detection of low concentrations of these multicharged species.
Langmuir 07/2007; 23(13):7356-64. · 4.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The voltammetry of hexavalent chromium (ammonium dichromate) at the interface between two immiscible electrolyte solutions is reported. Detection of Cr(VI) by ion transfer voltammetry is possible by use of an organic phase ionophore, which facilitates the transfer of Cr(VI) from the aqueous into the organic phase. The ionophore was the penta protonated form of polyamine macrocycle 2,5,8,11,14-pentaaza[15]-16,29-phenanthrolinophane (NeoTT). Cyclic voltammetry showed an increase of the peak current on increasing the concentration of Cr(VI). Square wave voltammetry with background subtraction was employed for low level concentration detection. The lowest concentration detected was 0.25 parts per million of Cr(VI).
Electrochemistry Communications 08/2005; 7:976-982. · 4.86 Impact Factor
