Browsing by Subject "Silver nanoparticles"
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Item LAMA-produced metal-on-oxide nanoparticles and films(2016-05) Gammage, Michael Drew; Kovar, Desiderio; Becker, Michael F; Keto, John W; Henkelman, Graeme; Fan, DongleiThe capability for the Laser Ablation of Microparticle (LAMA) process for producing unique nanostructured particles and films are studied. The processing parameters are adjusted to create nanostructures that have potential for producing superior properties in two distinct technologically important areas – olefin gas separations and plasmonic films. Two extremes in film nanostructure are targeted; 1) Highly porous metallic films for olefin separation and 2) Dense films for plasmonic optical films. For olefin separations, weak chemisorption of ethylene has been shown to be an important characteristic in the use of metals for the separation of ethylene from ethane. Previously, density functional theory (DFT) has been used to predict the binding energies of various metals and alloys, with Ag having the lowest chemisorption energy amongst the metals and alloys studied. Here non-equilibrium Au/Cu alloys are produced using LAMA and investigated by a combination of DFT calculations and experimental measurements. It is inferred from experiments that the binding energy between a Au/Cu alloy and ethylene is lower than to either of the pure metals Au or Cu, and DFT calculations confirm this results from Au segregation to the particle surface. Implications of this work suggest that it may be possible to further tune the binding energy with ethylene by compositional and morphological control of films produced from Au-surface segregated alloys. LAMA-produced metal-on-oxide nanoparticles (NP) are investigated to determine whether the thermal stability of LAMA-produced nanoparticles can be improved without impacting their chemical reactivity. Investigations before and after heating using the transmission electron microscope show that Ag-on-TiO2 nanostructures exhibit excellent resistance to coarsening at elevated temperatures and that there is no change to the binding energy of the ethylene to Ag. For plasmonic film applications, SiO2 and metal-in-SiO2 films were produced using LAMA and studied. Although dense SiO2 films were not produced, it was demonstrated that it was possible to measure the plasmonic absorption peaks of metal NPs embedded in SiO2 films. This opens up a new possibility for the investigation of the plasmonic properties of non-equilibrium metal NPs.Item LAMA-produced metal-on-oxide nanoparticles and films(2016-05) Gammage, Michael Drew; Kovar, Desiderio; Becker, Michael F; Keto, John W; Henkelman, Graeme; Fan, DongleiThe capability for the Laser Ablation of Microparticle (LAMA) process for producing unique nanostructured particles and films are studied. The processing parameters are adjusted to create nanostructures that have potential for producing superior properties in two distinct technologically important areas – olefin gas separations and plasmonic films. Two extremes in film nanostructure are targeted; 1) Highly porous metallic films for olefin separation and 2) Dense films for plasmonic optical films. For olefin separations, weak chemisorption of ethylene has been shown to be an important characteristic in the use of metals for the separation of ethylene from ethane. Previously, density functional theory (DFT) has been used to predict the binding energies of various metals and alloys, with Ag having the lowest chemisorption energy amongst the metals and alloys studied. Here non-equilibrium Au/Cu alloys are produced using LAMA and investigated by a combination of DFT calculations and experimental measurements. It is inferred from experiments that the binding energy between a Au/Cu alloy and ethylene is lower than to either of the pure metals Au or Cu, and DFT calculations confirm this results from Au segregation to the particle surface. Implications of this work suggest that it may be possible to further tune the binding energy with ethylene by compositional and morphological control of films produced from Au-surface segregated alloys. LAMA-produced metal-on-oxide nanoparticles (NP) are investigated to determine whether the thermal stability of LAMA-produced nanoparticles can be improved without impacting their chemical reactivity. Investigations before and after heating using the transmission electron microscope show that Ag-on-TiO2 nanostructures exhibit excellent resistance to coarsening at elevated temperatures and that there is no change to the binding energy of the ethylene to Ag. For plasmonic film applications, SiO2 and metal-in-SiO2 films were produced using LAMA and studied. Although dense SiO2 films were not produced, it was demonstrated that it was possible to measure the plasmonic absorption peaks of metal NPs embedded in SiO2 films. This opens up a new possibility for the investigation of the plasmonic properties of non-equilibrium metal NPs.Item The tolerance of a Rhodococcus drinking water isolate and Zoogloea ramigera to silver nanoparticles in biofilm and planktonic cultures(2011-08) Gao, Qiao Huan; Kirisits, Mary Jo; Katz, Lynn E.Spurred by a host of beneficial uses, the global use of nanoparticles is rapidly growing. Silver nanoparticles (Ag NPs) are used widely in consumer products, medicine, and the semiconductor industry. As nanoparticles become more commonly used, the transport of nanoparticles into the environment might negatively affect microorganisms in natural and engineered systems. The effects of Ag NPs on microorganisms have primarily been studied in planktonic or free-swimming cultures, but little work has been done to look at biofilm susceptibility to Ag NPs. This thesis describes bacterial tolerance, or the ability of an organism to survive exposure to an insult, to Ag NPs. The tolerance of planktonic and biofilm cells of the common wastewater treatment bacterium Zoogloea ramigera and a Rhodococcus strain isolated from drinking water was tested. These bacteria were exposed to different concentrations of Ag NPs, ranging from 0 to 25 mg/L, for a period of 5 hours. Results showed decreased tolerance with increasing Ag NP concentrations for both bacterial species. Z. ramigera biofilm cells are slightly more tolerant to Ag NPs than are planktonic cells. On the other hand, Rhodococcus planktonic and biofilm cells exhibit similar tolerance. However, in both cases, biofilm cells do not exhibit a striking protective effect against Ag NPs as compared to planktonic cells. This study shows that even short-term insults with Ag NPs can affect bacteria in engineered systems. A preliminary study of the shedding of free silver ions as a possible mechanism of Ag NP toxicity demonstrated that free silver ions were toxic to Escherichia coli in a 0.14M chloride environment. The data suggest that free silver ions can be pulled into solution from Ag NPs in chloride environments via ligand-promoted dissolution. Further work is needed to examine the antibacterial mechanism of Ag NPs against planktonic and biofilm cells to better understand how the release of nanoparticles into the environment can affect microorganisms in natural and engineered water systems.Item Transport and retention of silver nanoparticles in granular media filtration(2014-08) Kim, Ijung; Lawler, Desmond F.The increasing use of engineered nanoparticles such as silver nanoparticles (AgNPs) has focused more attention on the transport of nanoparticles in natural and engineered systems. Despite a substantial number of studies on the transport of nanoparticles in groundwater flow conditions, other conditions such as those in granular media filtration in water treatment plant have not been fully explored. This study was designed to investigate the transport of AgNPs in granular media filtration with a relatively high filtration velocity (~2 m/hr) and a low influent AgNP concentration (~100 [mu]g/L). Effects of several physical and chemical parameters on the transport and attachment of AgNPs were examined, focusing on the colloidal filtration theory and particle-particle interaction, respectively. Regarding the transport of AgNPs, four physical parameters (filter depth, filtration velocity, filter media size, and AgNP size) were varied at a fixed chemical condition. Positively charged branched polyethylenimine (BPEI) capped AgNPs were chosen to examine the transport of AgNPs under electrostatically favorable attachment conditions. The effects of filter depth, filtration velocity, and filter media size on transport of AgNPs were adequately described by the well-known colloidal filtration model. However, deviation from the model prediction was apparent as the AgNP size became smaller, implying a possible variation of nanoparticle properties in the smaller size such as 10 nm. In the AgNP attachment study, negatively charged citrate- and polyvinylpyrrolidone (PVP)-capped AgNPs were employed to examine the chemical effects on particle (AgNP)-particle (filter media) interaction. When the ionic strength and ion type in the background water were varied, the attachment of citrate AgNPs followed the DLVO theory. Ca- or Mg-citrate complexation was found to lead to charge neutralization, resulting in a greater AgNP deposition onto the filter media. However, PVP AgNPs were only marginally affected by the electrostatic effect, demonstrating a stronger stabilizing effect by PVP than citrate. When natural organic matter (NOM) was introduced in the background water, the deviation from the DLVO theory was considered primarily due to the steric interaction by NOM coating onto particles. Different amounts of AgNP deposition for different types of NOM suggest the variation of steric effects according to the molecular weight of NOM. The deposition of humic acid-coated AgNPs was similar regardless of the capping agent, indicating the possible displacement of the capping agent by NOM. The electrostatic and steric interactions affected the detachment of AgNPs as well as the attachment of AgNPs. The amount of detachment depended on the depth and width of the secondary energy minimum. Also, the detachment was enhanced with NOM coating, probably due to a weak attachment by the steric effect. However, the hydrodynamic force employed in this study was insufficient to yield a remarkable detachment. Overall, the retention profile was a relatively vertical line (i.e., equal deposition with depth) when the AgNP aggregation was prevented by the electrostatic or steric repulsion, implying homogeneous AgNP capture throughout the filter bed. On the other hand, ripening (the capture of particles by attraction to previously retained particles) was favored at the top of the filter bed when the AgNP aggregation was allowable.