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In this work we demonstrate the preparation of highly catalytically active Pt formed by the galvanic replacement of the copper adlayer on Au substrates, modified by the self-assembly of fourth generation amine terminated PAMAM dendrimer (G4NH2). The copper adlayer was formed on the dendrimer-modified gold substrate by chemical preconcentration of copper ions followed by electrochemical reduction. The Pt overlayer was characterized by SEM, XPS and by cyclic voltammetry. The catalytic efficiency of the modified film thus prepared through soft route was evaluated by the electro catalytic oxidation of methanol using cyclic voltammetry, chronoamperometry and AC impedance techniques. This work also demonstrates that the copper adlayer formed on the dendrimer-modified electrode can undergo galvanic replacement by nobler metals like Au and Ag, besides Pt. An elegant soft route involving a new three-step protocol to build the concentration of active Pt on the Au surface has been developed. Concentration of the same metal (Pt) or two different metals (Pt–Au) can be built at the interface in a stepwise manner at ambient temperature.

Indium tin oxide (ITO) glass substrates are widely used in electrochemical devices and as substrates for in situ spectro-electrochemical experiments owing to their interesting optical, electrical and electrochemical properties. In this work, we found ITO surfaces to undergo substantial changes in their properties on potentiodynamic stresses in the acidic pH range. The surface changes occurring during cathodic cycling of ITO were characterized by redox couples in cyclic voltammetry, and the resultant surfaces examined by scanning electron microscopy (SEM), atomic force microscopy (AFM), optical transmittance measurements, X-ray diffraction (XRD) and the compositional changes by X-ray fluorescence spectroscopy (XRF). The studies of electrical, optical and structural properties of ITO during cathodic cycling in the acidic pH range clearly point to a set of conditions that help retaining the stability of ITO substrates intact for electrochemical applications.

Polyanisidine films doped with two different anions, viz., perchlorate and paratoluene sulphonate anions are prepared electrochemically on a gold substrate. Polyanisidine films doped with the anions aid in retaining the redox conductivity of the polyanisidine films. This behaviour is similar to that of polyaniline films. Unlike polyaniline films, even smaller ions like perchlorate and paratoluene sulphonate are sufficient for retaining the redox conductivity of the film, which may be primarily due to the compact, non-permeant films formed during electropolymerization. The films are found to be suitable for the immobilization of glucose oxidase enzyme and are found to be an efficient sensing matrix for glucose. The films also exhibited catalytic activity towards the oxidation of NADH. These studies indicate the usefulness of polyanisidine–anion films as sensing platform for biomolecules.

The direct electron transfer exhibited by the yeast cells, Hansenula anomala has been demonstrated using the electrochemical technique cyclic voltammetry by immobilizing the microorganisms by two different methods viz., physical adsorption and covalent linkage. The analysis of redox enzymes present in the outer membrane of the microorganisms has been carried out in this work. This paper demonstrates that yeast cells with redox enzymes present in their outer membrane are capable of communicating directly with the electrode surface and contribute to current generation in a mediatorless biofuel cells. The efficiency of current generation has been evaluated using three anode materials.

The layer-by-layer assembly of silver nanoclusters with 3,3'-dithiodipropionic acid (DTDPA) as spacers was prepared through self-assembly on a gold foil and has been characterized by cyclic voltammetric and AFM techniques. The DTDPA molecules acting as spacers between the layers of silver serve as molecular interconnects for the four layers prepared in this work. The organization of layers was found to decrease with an increase in the number of layers. The layer-by-layer assembly of silver clusters motivated us to prepare silver nanowires stabilized by the bifunctional molecules DTDPA through template synthesis using cellulose nitrate membranes. The nanostructures formed by this method were characterized by SEM, TEM, AFM, FTIR, CV, and photoluminescence studies. It is observed that the DTDPA molecules, instead of forming molecular interconnects, protect the structures by self-assembling themselves along the edges of the nanostructures. The concept of self-assembly protecting the nanostructures is demonstrated in this work.

Investigations are carried out with Clostridium sp. which is isolated from sugar industry effluents, as a biocatalyst for current generation in a microbial fuel cell. Two different configurations of the cell are evaluated. In both cells, the anode compartment consists of suspended cells of Clostridium sp. in a nutrient broth in a phosphate buffer. In the first configuration, the cathode compartment consisted of ferricyanide solution (0.05 M). In the second configuration, the cathode compartment consisted of cells of Thiobacillus ferrooxidans suspended in a nutrient broth. The second configuration represents a complete microbial cell with the anodic and cathodic reactions driven by micro-organisms. The performance characteristics of the two configurations are evaluated with two different anode materials, graphite and graphite felt.

Polyol mediated synthesis for the preparation of tungsten trioxide and titanium doped tungsten trioxide has been reported. The reaction was carried out using chlorides of tungsten and titanium in diethylene glycol medium and water as the reagent for hydrolysis at 190 deg. C. Formation of a blue coloured dimensionally stable suspension of the precursor materials was observed during the course of the reaction. The particle sizes of the precursor materials were observed to be around 100 nm. The precursor materials were annealed to give tungsten trioxide and titanium doped tungsten trioxide. The precursor materials were characterised using TGA/DTA, FT-IR, optical spectra, SEM, TEM and powder XRD methods. It was observed that the doping of titanium could be effected at least up to 10% of Ti in WO{sub 3}. The TGA/DTA studies indicated that WO{sub 3-x}.H{sub 2}O is the dominant material that formed during the polyol mediated synthesis. The XRD data of the annealed samples revealed that the crystalline phase could be manipulated by varying the extent of titanium doping in the tungsten trioxide matrix.

The effect of surfactant matrices on the voltammetry of an antimicrobial agent, triclosan (TCN) and its release into the aqueous continuous phase for voltammetric detection have been studied in this paper. As the surfactant concentration (wt%) was increased, the peak current was found to decrease in the order: Tween-80 > Tween-60 >>> sodium laurylsulphate. The results of these experiments are found to correlate with the published data obtained using microcalorimetry. Attempts have been made to overcome the trapping effect of surfactant matrices by designing a solution composition based on hydrotrope-driven disruption of micellar encapsulants for complete release of TCN into the analyte solution for voltammetric detection. The hydrotropes employed in this study are sodium p -toluenesulphonate and sodium benzenesulphonate. The experiments intended to show the effect of hydrotropes on the ‘pre-adsorbed’ triclosan-surfactant “pseudo-complex” proved that hydrotrope-driven disruption of micelles takes place even on the electrode surface. Thus, immersion of the surfactant-covered electrode into a hydrotrope solution can “strip” the antimicrobial agent off the surfactant. The results of these proof-of-concept experiments were applied to the analysis of low concentrations (0.1–0.8 mM) in product formulations containing TCN. A linear relationship was found between TCN concentration and current magnitude with a correlation coefficient of 0.97, the sensitivity of the measurement towards the TCN oxidation being 12.8 μA mM −1 .

Mixed self-assembled monolayer of thiols were formed on the electrode surface using aromatic and aliphatic thiols and the modified interface were used to demonstrate charge trapping behavior at the modified interface. The electrode surface was modified by two schemes. In Scheme 1, electrode surface modified with methylene blue (MB) shows charge trapping behavior when contacts the electrolyte containing potassium ferricyanide. In Scheme 2, a redox-active bilayer is constructed using hexamineruthenium (II) chloride and methylene blue. This redox-active bilayer assembly exhibits unidirectional flow of current.

Electrochemical sensing of glucose on a gold electrode modified by the sequential incorporation of the mediator, 1,4-diaminoanthraquinone (DAAQ) and the enzyme, glucose oxidase (GOD), through covalent linkage onto a self-assembled monolayer configuration is described in this paper. It has been shown that two alternate layers of enzyme and mediator could be formed on the surface. The modified electrode is catalytic towards glucose oxidation. The catalytic response becomes more well behaved with the two-layer configuration and it is demonstrated by the amperometric experiments. The results also indicated that the mediator catalyzes the oxidation of H2O2, and also it establishes a weak electrical communication between the enzyme and the electrode surface. The results present the scope for the fabrication of membrane-free biosensors of ultra-thin dimensions.

In a new process for the production of synthetic rutile, aeration rusting is the major step where metallic iron is converted to iron oxide in the presence of catalysts such as NH 4 Cl and air. An electrochemical investigation to understand the anodic dissolution of reduced ilmenite (RI) has been carried out using a reduced ilmenite carbon paste (CP) electrode at 30 °C. Intermediate products with different iron contents were formed during the rusting reaction. Synthetic rutile with a negligible iron content was used for the investigations. The reaction mechanism and the influence of TiO 2 matrix were studied.

A potentiometric hydrogen peroxide (H2O2) sensing scheme was developed using arylboronic acid as the electrode modifier. It is well-known that both aliphatic and aryl boronic acid undergo electrophilic displacement reaction with H2O2. This reaction involves replacement of boronic acid by the hydroxyl group of peroxide resulting in a change in pKa value that can be exploited for sensing of H2O2. Vinylphenylboronic acid (VPBA) ink was prepared using Nafion as the binder and it was drop cast on an electrode surface. Morphology of the modified electrode was analysed using scanning electron microscopy (SEM). The present modifier exhibited a linear relationship between the difference in electrode potential (∆Ep) vs. [H2O2] with a Nernstian slope of 26 ± 2 mV in the concentration range of 10− 1–10− 5 M. Application of the VPBA modified electrode for hydrogen peroxide sensing was studied in an industrial dye-bleach effluent.

The formation of metal monolayers through underpotential deposition (UPD) depends on the interactions between the electrode surface and the depositing species. Other adsorbable species, if present in the solution, will influence the formation of UPD metal films through their adsorption on the electrode surface, taking place simultaneously. Copper UPD formation on polycrystalline gold surfaces has been investigated in the presence of small amounts of urea, thiourea (TU) and N-substituted thioureas using cyclic voltammetry. The results show that the UPD of copper on gold is significantly influenced by the presence of thiourea in solution. The charge corresponding to the stripping peak obtained in the presence of both Cu2+ and TU in solution is always larger than the sum of the charges resulting when either of them is present alone. Again, the charge observed during stripping in the presence of both Cu2+ and TU is believed to arise from (i) stripping of the UPD Cu, (ii) adsorption–desorption of TU and (iii) oxidation of Cu(TU)n+ complexes. The addition of N-substituted TUs is found to influence the UPD of Cu to different extents. This is tentatively explained in terms of the structure of the organic molecules.

The monolayers of 2-mercaptobenzothiazole (MBT) on polycrystalline Au and Ag films have been studied by surface-enhanced Raman (SERS) and X-ray photoelectron (XPS) spectroscopies. Whereas MBT adsorbs with its molecular plane flat on Ag, its plane is perpendicular on Au. This difference in adsorbate geometry is manifested as differences in the intensities of certain vibrational peaks in the Raman spectra. Ab initio molecular orbital (MO) calculations suggest that MBT adsorbs on Au in the thione form and on Ag in the thiol form. The monolayers are stable up to a temperature of 473 K, much higher than most of the self-assembled monolayers (SAMs) studied so far. The adsorption geometry does not undergo any significant change when the monolayers are heated, although minor changes are observed in the SER spectra of the Ag monolayer. Raman intensities of all the bands increase with heating, and the enhanced intensity is preserved even after cooling. This is attributed to monolayer-induced coalescence of gold islands leading to the formation of an extended self-assembly. XPS studies confirm chemisorption, although structural details are not manifested. Copyright 1999 Academic Press.

In this work, conducting polymer incorporated gold nanoparticles are synthesized through a sequence of chemical and electrochemical routes. These materials are characterized using TEM and FE-SEM techniques. The advantages of these films are demonstrated for sensing biologically important compounds such as dopamine and uric acid in presence of excess ascorbic acid. The PEDOT matrix is recognized to be responsible for the peak separation (selectivity) while also favouring catalytic oxidation of the above compounds and the nanometer-sized gold particles allow nanomolar sensing of DA and UA (sensitivity). Thus, it is possible to detect nanomolar levels of DA and UA in presence of excess of AA.

Modification of electrode surfaces with bilayers of organic/inorganic materials is shown to exhibit a variety of functional characteristics. The use of conducting polymers for bilayer construction has recently been explored by various groups. Gold surface has been modified with bilayers of polyaniline and polypyrrole, and the photoelectrochemical and electrochemical characteristics of such bilayer electrodes have been investigated and are reported in this communication.

The oxidation behaviour of methanol on platinum at room temperature in a low concentration of phosphoric acid (≈ 5%) has been studied. Voltammetric behaviour in phosphoric acid medium is compared with that in perchloric acid. The effect of a bismuth underpotential deposition (upd) layer on the oxidation of methanol is also reported.

The codeposition of lead and thallium UPD's on polycrystalline silver has been investigated. Studies on the effect of deposition time on the formation of the codeposit suggest the codeposit to be a solid solution resulting from underpotentially deposited mono/submono layers of lead and thallium with the stoichiometric ratio of 1 : 2 (Pb : T1).

Simultaneous deposition of lead and thallium UPD s on polycrystalline silver has been investigated under cyclic voltammetric conditions. Voltammetric data, resulting from systematic variation of potential sweep rates and concentration of metal ions, are presented and discussed. The experimental results for composite lead and thallium UPD s, obtained from mixed as well as single metal UPD s, obtained from single salt solutions under comparable conditions, have been analyzed in terms of the empirical models proposed for the growth mechanism based on adsorption/nucleation phenomena.