Raja Ram Pradhananga

Nanoporous carbon materials with enhanced supercapacitance performance and non-aromatic chemical sensing with C1/C2 alcohol discrimination

Abstract We have investigated the textural properties, electrochemical supercapacitances and vapor sensing performances of bamboo-derived nanoporous carbon materials (NCM). Bamboo, an abundant natural biomaterial, was chemically activated with phosphoric acid at 400 °C and the effect of impregnation ratio of phosphoric acid on the textural properties and electrochemical performances was systematically investigated. Fourier transform-infrared (FTIR) spectroscopy confirmed the presence of various oxygen-containing surface functional groups (i.e. carboxyl, carboxylate, carbonyl and phenolic groups) in NCM. The prepared NCM are amorphous in nature and contain hierarchical micropores and mesopores. Surface areas and pore volumes were found in the range 218–1431 m2 g−1 and 0.26–1.26 cm3 g−1, respectively, and could be controlled by adjusting the impregnation ratio of phosphoric acid and bamboo cane powder. NCM exhibited electrical double-layer supercapacitor behavior giving a high specific capacitance of c.256 F g−1 at a scan rate of 5 mV s−1 together with high cyclic stability with capacitance retention of about 92.6% after 1000 cycles. Furthermore, NCM exhibited excellent vapor sensing performance with high sensitivity for non-aromatic chemicals such as acetic acid. The system would be useful to discriminate C1 and C2 alcohol (methanol and ethanol).

Characterization of home-made silver sulphide based iodide selective electrode

Polycrystalline silver sulphide/silver iodide ion selective electrodes (ISEs) with four different compositions, 9:1, 2:1, 1:1, 1:9 Ag(2)S-AgI mole ratios, have been fabricated in the laboratory and characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). X-ray diffraction studies show the presence of Ag(3)SI, Ag(2)S and AgI crystalline phases in the electrode material. The electrode surfaces have been found to become smoother and lustrous with increasing percentage of silver sulphide in silver iodide. ISE 1:1, ISE 2:1 and ISE 9:1 all responded in Nernstian manner with slopes of about 60 mV/decade change in iodide ion concentration in the linear range of 1 x 10(-1) to 1 x 10(-6)M while ISE 1:9 showed sub-Nernstian behavior with slope of about 45 mV up to the concentration 1 x 10(-5)M. Two capacitive loops, one corresponding to the charge transfer process at metal electrode and the back contact and a second loop corresponding to the charge transfer process at membrane-electrolyte interface have been observed at high and low frequency ranges, respectively. Mott-Schottky analysis shows that the materials are n-type semiconductors with donor defect concentrations in the range of 5.1 x 10(14) to 2.4 x 10(19)/cm(3).

Fabrication and Applications of Silver Sulphide Based Ion Sensors

An electrochemical sensor based on the silver sulphide precipitate was fabricated in the laboratory and characterized by x-ray diffraction, SEM equipped with EDAX, and electrochemical techniques. Ion selective electrode (ISE) was found to be sensitive enough to sense the sulphide ion concentration from 10-1 to 10-5 M in alkaline medium. The change in electrode potential per decade change in sulphide ion concentration was found to be 31.5 mV at laboratory temperature indicating adherence of the ion selective electrode to Nernst’s equation. The sensor have been successfully used for the quantitative determination of thiamine in pharmaceutical preparations, hydrogen sulphide in cigarette smoke and determination of solubility products of sparingly soluble silver salts. A trace amount of hydrogen sulphide, a toxic gas, is present in the cigarette smoke. The quantitative estimation of hydrogen sulphide in cigarette smoke is a challenging task to analytical chemist. Hydrogen sulphide in cigarette smoke had been determined by absorbing the cigarette smoke in 0.1 M sodium hydroxide and the resulting solution was analyzed using silver sulphide based ion sensor by standard addition technique using modified Gran plot. The average amounts of hydrogen sulphide produced by a stick of cigarette in 8 different brands of Nepalese cigarette ware found to range from 0.0332 mg to 0.0766 mg. The sensitivity and reliability of these home made ion sensors were excellent and in par with commercial electrodes. For developing countries like Nepal, who can not afford to procure high cost commercial ion selective electrodes, these home made ion sensors are especially appealing since the sensor can be fabricated with ease from the materials that are readily available in the chemistry laboratory and the sensor is quite sensitive and gives reproducible results which are sufficiently accurate for the analysis with ion selective electrodes.

Iodide Ion Sensor for Indirect Determination of As (III) in Water

A simple, low cost and portable iodide sensor for the indirect determination of As(III) has been developed from the polycrystalline material obtained by co-precipitation of silver sulphide and silver iodide from aqueous solution. The Ag2S-AgI sensor was found to behave well up to the iodide concentration of 1×10-6 M with a Nernstian slope 57.5 mV per decade change in concentration. The selectivity coefficient of sensor containing iodide ion in the presence of Br- and Cl- ions was found to be 1.77 × 10-2 and 7.94 × 10-3, respectively indicating that these ions do not interfere in the response of iodide sensor to iodide ion. The electrode was successfully used for the direct determination of iodide and indirect determination of As(III) by titrating with cerric ammonium sulphate at pH 2. The results obtained from this method are comparable to the existing methods for the estimation of As(III).