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ABSTRACT: Polyaniline of low molecular weight (ca. 10 kDa) is combined with cellulose nano-fibrils (sisal, 4-5 nm average cross-sectional edge length, with surface sulphate ester groups) in an electrostatic layer-by-layer deposition process to form thin nano-composite films on tin-doped indium oxide (ITO) substrates. AFM analysis suggests a growth in thickness of ca. 4 nm per layer. Stable and strongly adhering films are formed with thickness dependent coloration. Electrochemical measurements in aqueous H2SO4 confirm the presence of two prominent redox waves consistent with polaron and bipolaron formation processes in the polyaniline – nanocellulose composite. Measurements with a polyaniline - nanocellulose film applied across an ITO junction (a 700 nm gap produced by ion beam milling) suggest a jump in electrical conductivity at ca. 0.2 V vs. SCE and a propagation rate (or percolation speed) two orders of magnitude slower compared to that observed in pure polyaniline This effect allows tuning of the propagation rate based on the nanostructure architecture. Film thickness dependent electrocatalysis is observed for the oxidation of hydroquinone.
Journal of Solid State Electrochemistry. 01/2011;
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ABSTRACT: The formation of variable-thickness CeO2 nanoparticle mesoporous films from a colloidal nanoparticle solution (approximately 1–3-nm-diameter CeO2) is demonstrated using a layer-by-layer deposition process with small organic binder molecules such as cyclohexanehexacarboxylate
and phytate. Film growth is characterised by scanning and transmission electron microscopies, X-ray scattering and quartz
crystal microbalance techniques. The surface electrochemistry of CeO2 films before and after calcination at 500 °C in air is investigated. A well-defined Ce(IV/III) redox process confined to
the oxide surface is observed. Beyond a threshold potential, a new phosphate phase, presumably CePO4, is formed during electrochemical reduction of CeO2 in aqueous phosphate buffer solution. The voltammetric signal is sensitive to (1) thermal pre-treatment, (2) film thickness,
(3) phosphate concentration and (4) pH. The reversible ‘underpotential reduction’ of CeO2 is demonstrated at potentials positive of the threshold. A transition occurs from the reversible ‘underpotential region’
in which no phosphate phase is formed to the irreversible ‘overpotential region’ in which the formation of the cerium(III)
phosphate phase is observed. The experimental results are rationalised based on surface reactivity and nucleation effects.
Journal of Solid State Electrochemistry 11/2008; 12(12):1541-1548. · 2.13 Impact Factor
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ABSTRACT: Glassy carbon electrodes are modified with a thin film of a cellulose-chitosan nanocomposite. Cellulose nanofibrils (of ca. 4 nm diameter and 250 nm length) are employed as an inert backbone and chitosan (poly-D-glucosamine, low molecular weight, 75–85% deacetylated) is introduced as a structural binder and “receptor” or molecular binding site. The composite films are formed in a solvent evaporation method and prepared in approximately 0.8 μm thickness. The adsorption of three molecular systems into the cellulose-chitosan films is investigated and approximate Langmuirian binding constants are evaluated: i) Fe(CN)64− (KFerrocyanide=2.2×103 mol−1 dm3 in 0.1 M phosphate buffer at pH 6) is observed to bind to ammonium chitosan functionalities (present at pH<7), ii) triclosan (KTriclosan=2.6×103 mol−1 dm3 in 0.1 M phosphate buffer pH 9.5) is shown to bind only weakly and under alkaline conditions, and iii) the anionic surfactant dodecylsulfate (KSDS=3.3×104 mol−1 dm3 in 0.1 M phosphate buffer pH 6) is shown to bind relatively more strongly in acidic media. The competitive binding of Fe(CN)64− and dodecylsulfate anions is proposed as a way to accumulate and indirectly determine the anionic surfactant.
Electroanalysis 09/2008; 20(22):2395 - 2402. · 2.87 Impact Factor
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ABSTRACT: A strategy for the formation of thin reconstituted cellulose films (pure or modified)) with embedded receptors or embedded ion-selective components is reported. Cellulose nanofibril ribbons from sisal of typically 3-5 nm diameter and 250 nm length are reconstituted into thin films of typically 1.5-2.0 µm thickness (or into thicker free-standing films). Cellulose and cellulose nanocomposite films are obtained in a simple solvent evaporation process. Poly-(diallyldimethylammonium chloride) or PDDAC is readily embedded into the cellulose film and imparts anion permselectivity to allow binding and transport of hydrophobic anions. The number of binding sites is controlled by the amount of PDDAC present in the film. The electrochemical properties of the cellulose films are investigated first for the Fe(CN) 6 3-/4-model redox system and then for the accumulation and detection of triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether, a hydrophobic polychlorinated phenol). Pure nanocellulose thin films essentially block the access to the electrode surface for anions such as Fe(CN) 6 3-and Fe(CN) 6 4-. In contrast, in the presence of cellulose-PDDAC films, accumulation and transport of both Fe(CN) 6 3-and Fe(CN) 6 4-in electrostatic binding sites occurs (Langmuirian binding constants for both are about 1.2 × 10 4 mol -1 dm 3 in aqueous 0.1 M KCl). Facile reduction/oxidation at the electrode surface is observed. Triclosan, a widely used antifungal and antibacterial polychlorinated phenol is similarly accumulated into cationic binding sites (Langmuirian binding constant about 2.1 × 10 4 mol -1 dm 3 in aqueous 0.1 M phosphate buffer pH 9.5) and is shown to give well-defined oxidation responses at glassy carbon electrodes. With a cellulose-PDDAC film electrode (80 wt % cellulose and 20 wt % PDDAC), the analytical range for triclosan in aqueous phosphate buffer at pH 9.5 is about 10 -6 -10 -3 mol dm -3 .
The Journal of Physical Chemistry C 01/2008; 112:2660. · 4.80 Impact Factor
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ABSTRACT: Voltammetric measurements at the surface of cotton fabric were conducted after impregnating the surface of the textile with graphite flakes. The resulting conducting surface contact was connected to a conventional basal plane pyrolytic graphite substrate electrode and employed both in stagnant solution and in rotating disc voltammetry mode. Diffusion through the immobilized cotton sample (inter-fiber) is probed with the aqueous Fe(CN)6(4-/3-) redox system. With a small amount of platinum immobilized at the cotton surface, catalase reactivity toward hydrogen peroxide was observed and used to further quantify the diffusion (intra- and inter-fiber) into the reactive zone at the graphite-cotton interface. A well-known catalase model system, the dinuclear manganese metal complex [Mn(IV)2(micro-O)3L2](PF6)2 (with L=1,4,7-trimethyl-1,4,7-triazacyclononane), is investigated in aqueous 0.1 M carbonate buffer at pH 9.8 in contact with cotton fabric. Absorption of the metal complex is monitored and quantified by voltammetric methods. A Langmurian binding constant of approximately K=2x103 M-1 was determined. Voltammetric measurements of the adsorbed metal complex reveal strong absorption and chemically irreversible reduction characteristics similar to those observed in solution. In the presence of hydrogen peroxide, catalyst coverage dependent anodic catalase activity was observed approximately following the rate law rate=k[catalyst]surface[H2O2]solution and with k=3x104 dm3 s-1 mol-1. The catalyst reactivity was modified by the presence of cotton.
Langmuir 03/2007; 23(4):2239-46. · 4.19 Impact Factor
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ABSTRACT: Voltammetric measurements at the surface of cotton fabric were conducted after impregnating the surface of the textile with graphite flakes. The resulting conducting surface contact was connected to a conventional basal plane pyrolytic graphite substrate electrode and employed both in stagnant solution and in rotating disc voltammetry mode. Diffusion through the immobilized cotton sample (inter-fiber) is probed with the aqueous Fe(CN)64-/3- redox system. With a small amount of platinum immobilized at the cotton surface, catalase reactivity toward hydrogen peroxide was observed and used to further quantify the diffusion (intra- and inter-fiber) into the reactive zone at the graphite−cotton interface. A well-known catalase model system, the dinuclear manganese metal complex [Mn(IV)2(μ-O)3L2](PF6)2 (with L = 1,4,7-trimethyl-1,4,7-triazacyclononane), is investigated in aqueous 0.1 M carbonate buffer at pH 9.8 in contact with cotton fabric. Absorption of the metal complex is monitored and quantified by voltammetric methods. A Langmurian binding constant of approximately K = 2 × 103 M-1 was determined. Voltammetric measurements of the adsorbed metal complex reveal strong absorption and chemically irreversible reduction characteristics similar to those observed in solution. In the presence of hydrogen peroxide, catalyst coverage dependent anodic catalase activity was observed approximately following the rate law rate = k[catalyst]surface[H2O2]solution and with k = 3 × 104 dm3 s-1 mol-1. The catalyst reactivity was modified by the presence of cotton.
12/2006;
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ABSTRACT: Nanoparticle film voltammetry is employed to explore the presence and reactivity of surface-stabilised iron redox centers at the interface of immobilised Fe2O3 nanoparticles of ca. 4 nm diameter and aqueous buffer media. Mesoporous films of Fe2O3 nanoparticles on tin-doped indium oxide (ITO) substrates are formed in a layer-by-layer deposition process from aqueous colloidal Fe2O3 and aqueous cyclohexyl-hexacarboxylate followed by thermal (500 °C) removal of the organic binder content. Both reversible oxidation and reversible reduction responses for Fe(III) are observed in phosphate and carbonate buffer media in the “underpotential” zone. Higher oxidation states of iron formed anodically (here tentatively assigned to Fe(IV)) are shown to be inert in phosphate buffer media but reactive towards the oxidation of glucose in carbonate buffer media.
Electrochemistry Communications 10(11):1773-1776. · 4.86 Impact Factor
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ABSTRACT: Cotton is an excellent cellulose-based absorbent mainly due to amorphous cellulose regions in the nanocrystalline (cellulose-I) natural fiber structure. It is shown here for the case of a woven cotton textile with ca. 20 μm fiber diameter and ca. 270 μm thickness that cation and anion absorption and diffusion processes occur within cotton fibers. An electrochemical approach based on voltammetry is developed to investigate and quantify absorption and leaching processes as well as the chemical reactivity within cotton fibers.The metal complexes , , [Fe(II)(N,N-bis(pyridin-2-yl-methyl)-1,1-bis(pyridin-2-yl)-1-aminoethane)Cl]+ or Fe(BBA)Cl+, and [Fe(III)(protoporphyrinato-IX)(H2O)(OH)]2− or hemin are readily absorbed into cotton in the electrochemically active form. The ability of and to absorb appears to be predominantly due to “entrapment” without specific interaction with the amorphous cellulose. The approximate rate of diffusion of these ions in cellulose is estimated to be a factor 4 slower when compared to the rate of diffusion in solution. In contrast, Fe(BBA)Cl+ and hemin diffuse much slower (by a factor 24 and 70, respectively) within the cotton matrix. The slower diffusion is correlated with “specific” binding of the metal complexes to sites within the amorphous cellulose. In addition, Fe(BBA)Cl+ exhibits a new redox process within the cotton matrix indicating a change in chemical reactivity when compared to that observed in aqueous solution environments.
Journal of Electroanalytical Chemistry. 601:211-219.
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ABSTRACT: Cellulose films of variable thickness are electro-deposited from aqueous alkaline thiourea solution onto polished boron-doped diamond substrates in an anodic process. Films with “net-like” topography are formed and shown to consist of both cellulose-I and cellulose-II components. Properties of these films are investigated.When immersed in aqueous electrolyte solution, ion partitioning into the electro-deposited cellulose films occurs. The accumulation and release of two aqueous redox systems, and methylviologen2+/+, is reported. Relatively slow diffusion of these cations is observed within cellulose (approximately 5 orders of magnitude slower when compared to diffusion in aqueous media). For the methylviologen2+/+ redox system partitioning leads to irreversibility in the voltammetric response and to the preferred formation of aggregates immobilized within the cellulose film.
Electrochemistry Communications 9(1):42-48. · 4.86 Impact Factor
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ABSTRACT: Porous composite films containing cellulose nanofibrils (from sisal) and TiO2 nanoparticles (ca. 6 nm diameter) are obtained in a layer-by-layer assembly process. Each layer consists of ca. 0.18 μg cellulose nanofibrils and ca. 0.72 μg TiO2 (determined by QCMB) and adds a thickness of ca. 16 nm (by AFM) to the uniform deposit. The TiO2 nanophase is creating conducting pathways for electrons in a relatively open cellulose structure (ca. 82% open pores) potentially suitable for the immobilization of large redox proteins such as methemoglobin.Methemoglobin is shown to readily adsorb into the cellulose–TiO2 film. However, electrochemical responses for the immobilized methemoglobin in aqueous 0.1 M phosphate buffer at pH 5.5 suggest that facile demetallation occurs. Experiments with Fe3+ in the absence of protein result in voltammetric responses indistinguishable from those observed for immobilized methemoglobin. In the presence of ethylenediamine tetraacetic acid (EDTA) the voltammetric signals for the Fe3+ immediately disappear. Complementary experiments conducted in 0.1 M acetate buffer at pH 5.5 demonstrate that methemoglobin can indeed be immobilized in electrochemically active form and without demetallation loss of the voltammetric signal in the presence of EDTA. Demetallation appears to occur (i) in the presence of phosphate, (ii) at pH 5.5, (iii) and in the presence of a charged surface.
Electrochemistry Communications.
