Browsing by Author "Bhargava, SK"

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    Investigations on gold nanoparticles supported on rare earth oxide catalytic materials.
    (Elsevier, 2007-04-18) Bhargava, SK; Akolekar, DB; Foran, GJ
    Supported gold nanoparticles rare earth (europium, dysprosium, samarium oxide, neodymium, gadolinium oxide and lanthanum oxide) materials were prepared using precipitation–deposition/co-precipitation methods. The techniques employed for the characterization of these materials were ICP-MS, TEM, XRD, BET, and XAS. Au L3-edge X-ray absorption spectroscopic measurements were carried out over a series of rare earth materials containing gold nanoparticles. The size of gold nanoparticles varied in the range of 2 to 6nm in the Eu/Dy/Sm/Nd/Gd/La materials. These materials possess surface areas ranging from 29 to 41m2/g with the high phase purity and crystallinity of the support (Eu/Dy/Sm/Nd/Gd/La) materials. An X-ray absorption fine structure (XANES, EXAFS) technique was used in obtaining critical information about the atomic distances, bonding and neighbouring environment for gold atoms in the rare earth Eu/Dy/Sm/Nd/Gd/La oxide materials for understanding the typical characteristics and structure of gold nanoparticles in these materials. © 2007, Elsevier Ltd.
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    Mercury diffusion in gold and silver thin film electrodes on quartz crystal microbalance sensors.
    (Elsevier, 2009-03-28) Sabri, YM; Ippolito, SJ; Tardio, J; Atanacio, AJ; Sood, DK; Bhargava, SK
    Diffusion behavior of mercury into both gold and silver electrodes of polished and roughened quartz crystal microbalances (QCMs) is presented. Several QCM devices were exposed to mercury vapor for 8 h and allowed to desorb for 5 h under controlled nitrogen atmosphere. The process was repeated for different Hg concentrations of 1.02, 1.87 and 3.65mg/m3 at an elevated temperature of 40 °C. The chemical composition and surface morphology of each QCM surface was characterized by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), Secondary Ion Mass Spectroscopy (SIMS), Atomic Force Microscope (AFM) and Field Emission Secondary Electron Microscope (FE-SEM). The Ag electrodeswere found to contain up to 16% more adsorbed/amalgamated Hg by mass than the Au samples. It was found that the ratio of amalgamated to adsorbed Hg is less for Au than Ag. SIMS analysis confirmed high Hg diffusion through rough substrates, 40 days after Hg exposure. In situ sticking probability of the tested mercury vapor concentrations to Au and Ag surfaces at 40 °C was found to drop at quicker rates than the reported Hg–Au and Hg–Ag room temperature values. Overall, in the context of Hg vapor phase gas sensing applications, the rougher gold substrate was found to outperform the other samples due to its superior adsorption/desorption properties. © 2008, Elsevier Ltd.
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    Mercury vapor sensor enhancement by nanostructured gold deposited on nickel surfaces using galvanic replacement reactions
    (Royal Society of Chemistry, 2012-07-16) Sabri, YM; Ippolito, SJ; Atanacio, AJ; Bansal, V; Bhargava, SK
    Anthropogenic mercury emission is a serious global environmental problem because of its toxicity to humans, plants and wildlife. In order to control these emissions, accurate and reliable online continuous mercury monitoring systems (CMMs) are critical. Such systems can notify appropriate authorities or provide feedback signals to a process control system in time, thus making them an integral part of monitoring and controlling Hg emissions. We demonstrate how nanostructured gold can easily be deposited in small quantities on nickel electrode based QCMs using galvanic replacement (GR) reactions with the resultant surface having excellent Hg monitoring properties. The developed GR surfaces were observed to have higher sensitivity and selectivity in the presence of interfering gas species (NH3 and H2O), as well as to have ∼80% higher mercury sorption capacity than the most efficient mercury sorbents reported to date. Investigations towards the Hg-sensing capabilities of the resultant Ni–Au surface based Hg sensors showed ∼50% better sensitivity and detection limit over control Au films. Furthermore, the GR based QCMs were found to self-regenerate without changing the operating temperature of the sensor, undergoing Hg desorption with sensor recoveries of 93.7–99.3% following Hg exposure at an operating temperature of 90 °C. Surface depth profile analysis of the Ni–Au electrode surfaces showed that the high recovery rate of the sensors was primarily due to the Ni–Au structures, which unlike continuous Au thin-films more commonly used for Hg sensing applications, do not accumulate Hg at the sensitive-layer–substrate interface. Furthermore, the GR Ni–Au surfaces were found to be highly selective towards Hg vapor in the presence of NH3 and H2O interfering gas species which makes them potentially suitable for operating in harsh industrial effluent environments.© The Royal Society of Chemistry 2012