Electrochemical sensing of sulphur dioxide: a comparison using dodecanethiol and citrate capped gold nanoclusters

A comparison of cyclic voltammograms of dodecanethiol (DDT) capped Au nanoclusters (5.0 0.5 nm) and trisodium citrate (Cit) capped Au nanoclusters (approximately 10-15 nm) modified glassy carbon electrode shows a dramatic variation in the current when exposed to a small amount of sulphur dioxide. This is explained using the electrocatalytic properties of Au nanoclusters towards the oxidation of SO2, thus facilitating the fabrication of electrochemical sensors for the detection of SO2. The intrinsic redox changes observed for gold nanocluster-modified glassy carbon electrodes disappear on passing SO2, despite a dramatic current increase, which indeed scales up with the amount of dissolved SO2. Interestingly, a complete rejuvenation of the redox behavior of gold is also observed on subsequent removal of SO2 from the solution by passing pure nitrogen for 15 minutes. Further, these nanoclusters when characterized with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) after SO2 passage reveal a variety of SO2 adsorption modes on gold surface. XP spectra also show a shift of 1.03 eV towards higher binding energy indicating a strong adsorption of SO2 gas, while FTIR gives conclusive evidence for the interaction of SO2 with gold nanoparticles.     

TiO2–Au plasmonic nanocomposite for enhanced dye-sensitized solar cell (DSSC) performance

Anatase TiO₂ nanoparticles dressed with gold nanoparticles were synthesized by hydrothermal process by using mixed precursor and controlled conditions. Diffused Reflectance Spectra (DRS) reveal that in addition to the expected TiO₂ interband absorption below 360 nm gold surface plasmon feature occurs near 564 nm. It is shown that the dye sensitized solar cells made using TiO₂–Au plasmonic nanocomposite yield superior performance with conversion efficiency (CE) of ～6% (no light harvesting), current density (J_SC) of ～13.2 mA/cm², open circuit voltage (V_oc) of ～0.74 V and fill factor (FF) 0.61; considerably better than that with only TiO₂ nanoparticles (CE ～ 5%, J_SC ～ 12.6 mA/cm², V_oc ～ 0.70 V, FF ～ 0.56).     

Electrochemical organization of monolayer protected gold nanoclusters on single-walled carbon nanotubes: significantly enhanced double layer capacitance

This paper reports a novel electrochemical route for anchoring monolayer protected gold nanoclusters (size 8 +/- 0.2 nm) on single-walled carbon nanotube bundles, resulting in the formation of hybrid materials. Monolayer protected gold nanoclusters prepared by modified Brust synthesis route were organized on SWNT bundles by cycling the potential in dichloromethane between -1 to +1 V at a scan rate of 50 mV/s. Monolayer protected nanoclusters in electrolyte solutions possess ionic space charge around them (double layer charging), making them suitable for organization on nanotube bundles, by tuning the electrostatic interactions. More significantly, analysis of the double layer capacitance of these hybrid materials shows almost ten times increase in capacitance compared to that of bare SWNT bundles. We believe that these hybrid materials are potentially useful in nanoelectronics.     

Electron transfer behavior of monolayer protected nanoclusters and nanowires of silver and gold

Understanding the electron transfer behavior of nanometer sized, both metallic and semiconducting particles and wires is important due to the fundamental interest in size and shape dependent electronic properties and also because of its applications in nano-electronic devices like single electron transistors and molecular switches. Monolayer protected nanoclusters enable one simple and elegant method of synthesis of these types of metallic and semiconducting materials using interfacial chemistry as has been successfully used in several applications ranging from catalysis to molecular electronics. The success of this type of nanostructured materials is due in part to the well known protecting/stabilizing action of the ligands (also known as surface passivating/capping agents), which facilitate the synthesis and processing of these hydrophobic colloids in solution form. The present article discusses the electron transfer behavior of silver nanowires and nanoparticles with varied sizes. In particular, we have investigated the electrochemical properties of silver nanowires (diameter 70 nm, length several micrometers) and compared with the behavior of similar relatively larger sized nanoparticles (size 40 nm). A critical analysis of the redox behavior of silver nanowires and nanoparticles is presented in aqueous medium under various electrolytic conditions along with a comparison of analogous properties of smaller sized (2-7 nm) silver and gold nanoclusters.     

Nanometer sized tridecylamine capped Rhodium dispersed on high surface area support: catalytic investigations

We report a simple procedure for the synthesis of tridecylamine (TDA) capped Rhodium (RhTDA) nanoparticles in the range of 3-10 nm supported on different supports like SBA-15, SiO2, ZrO2, Al2O3, and TiO2. These are characterized by TEM, XRD, and N2 adsorption studies. The catalytic activity of these nanometallic dispersions are tested for the liquid phase selective hydrogenation of geraniol to citronellol at 323 K under H2 pressure. The primary reaction products are citronellol and 3,7-dimethyloctanol. Analysis of the data suggests that two separate reaction paths are operative i.e., consecutive A --> B --> C and parallel A --> B and A --> C. The size of the Rhodium particle does not have a marked effect on the product distribution, however it is very much depended on the nature of support used.     

Effect of gelling on the open circuit potential against time transients of Pb/PbSO4 electrodes at various states of charge

The technique of open-circuit potential relaxation from a prior prepolarized state has been employed to study the kinetics of the Pb/PbSO₄ electrode in 4.81 m sulphuric acid. The significant features governing the relaxation have been quantitatively analysed to obtain a correlation between state-of-charge of the electrode and its potential-recovery time constant. The effect of immobilizing the electrolyte has also been included due to its relevance in making sealed maintenance-free batteries. The study provides a method for estimating the variation of exchange current density of the Pb/ PbSO₄ and hydrogen evolution reactions at various states-of-charge with and without added gelling agents.This paper is dedicated to the memory of the late Professor S. Sathyanarayana.     

Effect of protonation media on chemically and electrochemically synthesized polyaniline

Polyaniline films have been prepared both chemically and electrochemically using formic (‘Pani‐Formic’), boric (‘Pani‐Boric’) or acetic acid (‘Pani‐Acetic’) as protonation media. Among the three, formic acid seems to be a better protonating medium because it selectively yields the conducting phase of polyaniline. The variation of potential with the amount of oxidizing agent suggests one dimensional growth of polymer chain, which proceeds through a PG/EM mechanism as indicated by spectral data. The Pani‐Boric and Pani‐Acetic acid demonstrate three‐ and four‐step decomposition patterns, respectively, with complete decomposition at about 760 °C. Pani‐Formic acid, in contrast, reveals a three‐step decomposition pattern with 90% weight loss at about 900 °C and shows a tendency to react with the Pt sample holder. The films of polyaniline generated electrochemically also suggest formic acid to be a better protonating medium for achieving a relatively greater fraction of conducting emeraldine salt. However, boric acid produces excellent quality adherent films with very high deposition rate. Morphological features give strong support to this observation. The films of Pani‐Formic and Pani‐Acetic acids show a spongy network and globular morphology, respectively, while Pani‐Boric acid yields an extremely uniform surface coating. Furthermore, cyclic voltammetry reveals different patterns depending upon the formation of different oxidation states and the results are in accordance with optical absorption studies. © 2000 Society of Chemical Industry     

Design of an “all solid-state” supercapacitor based on phosphoric acid doped polybenzimidazole (PBI) electrolyte

The effectiveness of phosphoric acid doped polybenzimidazole as a polymer electrolyte membrane to fabricate an all solid-state super capacitor has been explored using hydrous RuO₂/carbon composite electrodes (20 wt.%) of surface area 250 m² g⁻¹ with many intrinsic advantages. The electrochemical evaluation of these super capacitors through cyclic voltammetry, charge/discharge and impedance measurements demonstrate the utility of this type of thin, compact and flexible supercapacitor capable of functioning at 150 °C to yield a maximum capacitance of about 290 F g⁻¹ along with a life of more than 1,000 cycles. A power density of 300 W kg⁻¹ and energy density of 10 Wh kg⁻¹ have been accomplished although the equivalent series resistance (ESR) of about 3.7 Ω needs to be reduced further for high rated applications.