V. Lakshminarayanan

Effect of adsorption of some azoles on copper passivation in alkaline medium

Abstract We have studied the adsorption properties and the effect of some azoles such as benzotriazole (BTA), mercaptobenzothiazole (MBT), benzimidazole (BIMD), mercaptobenzimidazole (MBIMD), imidazole (IMD) and tetrazole on the growth of oxide film on copper in 0.1 M NaOH. Cyclic voltammetry and electrochemical impedance spectroscopy are used to characterise the passivation process. The relative inhibition efficiencies of the azoles in controlling the oxide film formation is found to be in the order MBT > BIMD ≈ MBIMD > BTA ≈ IMD. We find that the azoles follow the Langmuir adsorption isotherm. Study of coverage by the measurement of capacitance obtained from the imaginary component of impedance ( Z ′′ ) as a function of time indicates that in about 800 s more than 95% of the coverage is complete in all the cases of inhibitor adsorption.

Novel conducting nanocomposites: synthesis of triphenylene-covered gold nanoparticles and their insertion into a columnar matrix

Gold nanoparticles fully covered with triphenylene-based discotic liquid crystals (DLCs) were synthesized and dispersed in a columnar matrix. The thermophysical properties of these nanocomposites, studied using polarizing optical microscopy, differential scanning calorimetry and small angle X-ray diffraction studies (SAXS), confirm their insertion into the columnar matrix. The presence of the gold nanoparticles in the triphenylene-based DLCs does not disturb the nature of the mesophase other than altering the transition temperatures. We propose that the gold nanoparticles are distributed between the domain gaps of the DLCs in random disordered manner. Interestingly the DC conductivity measurements show an enhancement of the electrical conductivity by more than a million times upon doping of the discotic liquid crystals with the triphenylene-capped nanoparticles under ambient conditions.

A study of kinetics of adsorption of alkanethiols on gold using electrochemical impedance spectroscopy

The growth kinetics of self assembled monolayer of alkanethiols of different chain lengths and concentrations on an evaporated gold surface on mica has been studied in situ and in real time using electrochemical impedance spectroscopy. The interfacial capacitance obtained from the measurement of the imaginary component of impedance is used to calculate the surface coverage as a function of time. From this data, rate constants of adsorption of alkanethiols have been measured in 0.1 M LiClO4 in ethanol solution. The results show that the adsorption follows Langmuir kinetics at higher thiol concentration of 20 μM and partial diffusion controlled kinetics at 5 μM and lower. The adsorption at a concentration of 1 mM is so rapid that ∼40% of the full monolayer is covered within the first 500 ms.

Inclusion of gold nanoparticles into a discotic liquid crystalline matrixElectronic supplementary information (ESI) available: DSC traces and POM pictures. See http://www.rsc.org/suppdata/cc/b4/b403794d/

The thermophysical properties of mixtures of hexanethiolate-capped gold nanoparticles and three types of discotic liquid crystals, investigated using polarizing optical microscopy, differential scanning calorimetry and DC conductivity, indicate inclusion of gold nanoparticles into a matrix of triphenylene-based discotic liquid crystals.

Cyclic voltammetric and electrochemical impedance studies on the structure, adsorption kinetics, and barrier properties of some organic dithiol self-assembled monolayers on gold

We have studied the orientation and barrier properties of self-assembled monolayers (SAMs) of two alkanedithiols, hexanedithiol, octanedithiol, and an aromatic dithiol, 1,4-benzene dimethanethiol (BDMT), on gold in acetonitrile. From our studies, we conclude that BDMT molecules can form more organized monolayers on gold than aliphatic dithiol SAMs due to extremely strong lateral van der Waals interaction among the phenyl rings in the former. A study of the adsorption kinetics of octanedithiol in ethanol indicates that the adsorption rate law is concentration dependent just as for alkanethiols. However, the rate of adsorption is considerably faster than for simple alkanethiols.

Assessment of Liquid Crystal Template Deposited Porous Nickel as a Supercapacitor Electrode Material

The high surface area porous nickel, obtained by template electrodeposition using a hexagonal liquid crystalline phase medium as a template was evaluated as a potential material for electrochemical capacitors using cyclic voltammetry ~CV! and electrochemical impedance spectroscopy ~EIS! studies in 6 M KOH. A single electrode double layer capacitance of 1.4 F/cm2 ~at 2 mV/s scan rate! was obtained using CV, which corresponds to a specific capacitance of 473 F/g. EIS studies show the typical behavior of a porous electrode and the data were analyzed in terms of complex capacitance and complex power from which the relaxation time constant stod has been determined. Nickel oxide electrode, obtained by the electrochemical oxidation of porous Ni, shows a double layer capacitance value of 171 mF/cm2, which corresponds to a specific capacitance of 57 F/g. The relaxation time constants for the template deposited porous nickel and nickel oxide were determined to be 1.35 s and 33 ms, respectively. The values of double layer capacitance and specific capacitance of the porous nickel with fast response time are the highest values reported for nickel in the literature so far.

One step preparation of ‘ready to use’ Au@Pd nanoparticle modified surface using deep eutectic solvents and a study of its electrocatalytic properties in methanol oxidation reaction

Deep eutectic solvents (DES) are being increasingly used in electrodeposition because they are considered to be environmentally benign. We report here a single step method for the preparation of Au–Pd core–shell nanoparticles (Au@Pd NPs) on a graphite rod in a DES medium. These ready-to-use mesoporous substrates were prepared by the simultaneous electrodeposition of the in situ formed Au@Pd nanoparticles via an anodic dissolution technique. The fabrication strategy by anodic dissolution in a DES avoided the addition of external stabilizers, reducing agents and metal salt precursors. The core–shell morphology of the nanoparticles was characterized by SEM, while the elemental composition was confirmed by EDAX and cyclic voltammetry. The catalytic characteristics of the Au@Pd nanoparticle modified graphite were systematically studied in the electrochemical oxidation of methanol by cyclic voltammetry, Tafel analysis and activation energy measurements. The Au@Pd NPs exhibited superior catalytic performance over its corresponding monometallic counterparts, viz., AuNPs and PdNPs, prepared under identical conditions. The activation energy requirements of the Au@Pd NP modified graphite electrodes were low, making them potential anode catalysts in alkaline media based methanol fuel cells at ambient temperatures. The method suggested here for the synthesis of mesoporous electrocatalysts is simple, effective and environmentally friendly.

Cyclic voltammetric behavior of certain copper-azole systems using carbon paste electrodes

Abstract Pure carbon paste electrodes and chemically modified carbon paste electrodes were used to evaluate the relative ability of certain azoles in inhibiting the corrosion of copper. Three different types of experiments were performed: (1) cyclic voltammetric studies of the azole-modified carbon paste electrodes in Cu(I)-containing supporting electrolyte; (2) cyclic voltammetric studies of pure carbon paste electrodes in supporting electrolytes containing both Cu(I) and the particular azole; (3) cyclic voltammetric studies using Cu(I)-modified and Cu(II)-modified carbon paste electrodes after dipping the electrodes in azole-containing solutions. The magnitude of the anodic dissolution of copper under these conditions is correlated to the corrosion inhibition efficiency. The corrosion rates measured for copper in sodium chloride in the presence of these azoles as inhibitors support this correlation.

Effect of bulk structure of some non-aqueous solvents on the barrier properties of alkanethiol monolayer

Abstract We have carried out cyclic voltammetric and electrochemical impedance spectroscopic studies to compare the barrier properties of monolayer on gold formed by two alkanethiols of different chain lengths in solvents like acetonitrile, propylene carbonate, ethanol and formamide. Our results show that the blocking behavior of the alkanethiol monolayer to ferrocene electron transfer reaction varies in the order formamide>ethanol>acetonitrile≅propylene carbonate. The electron transfer through the monolayer is facilitated by the ability of the solvent molecules to interact with the thiol molecules and disorganize the monolayer. We have correlated the internal order of the solvent molecules with their ability to influence the structural integrity and barrier properties of the monolayer.

Electrical conductivity studies on discotic liquid crystal-ferrocenium donor-acceptor systems.

The dispersion of electron-deficient ferrocenium ions was studied in the electron-rich media of two different triphenylene-based columnar hexagonal liquid-crystalline phases. These composites were characterized using polarizing optical micrography (POM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), visible absorption spectroscopy, and dc and ac conductivity measurements. It was found that these composites form donor-acceptor systems that enhance the quasi-one-dimensional conductivity of the discotic system without altering the hexagonal columnar mesophase. The absorbance spectra confirm the formation of a charge-transfer complex between the electron-rich discotic molecules and the electron-deficient ferrocenium ions.