The production of pyrogenic (fumed) silica is increasing worldwide at a 7% annual growth rate, in... more The production of pyrogenic (fumed) silica is increasing worldwide at a 7% annual growth rate, including expanded use in food, pharmaceuticals and other industrial products. Synthetic amorphous silica, including fumed silica, has been generally recognized as safe (GRAS) for use in food products by the Food and Drug Administration (FDA). However, emerging evidence from experimental studies now suggests that fumed silica could be hazardous due to its siloxane ring structure, high silanol density, and "string-of-pearl-like" aggregate structure, which could combine to cause membrane disruption, generation of reactive oxygen species, pro-inflammatory effects, and liver fibrosis. Based on this structure-activity analysis (SAA), we investigated whether calcination and rehydration of fumed silica changes its hazard potential in the lung due to an effect on silanol density display. This analysis demonstrated that the accompanying change in surface reactivity could indeed impact cyt...
Langmuir : the ACS journal of surfaces and colloids, Jan 7, 2012
Fundamental knowledge about the mechanisms of adhesion between oxide particles with diameters of ... more Fundamental knowledge about the mechanisms of adhesion between oxide particles with diameters of few nanometers is impeded by the difficulties associated with direct measurements of contact forces at such a small size scale. Here we develop a strategy based on AFM force spectroscopy combined with all-atom molecular dynamics simulations to quantify and explain the nature of the contact forces between 10 nm small TiO(2) nanoparticles. The method is based on the statistical analysis of the force peaks measured in repeated approaching/retracting loops of an AFM cantilever into a film of nanoparticle agglomerates and relies on the in-situ imaging of the film stretching behavior in an AFM/TEM setup. Sliding and rolling events first lead to local rearrangements in the film structure when subjected to tensile load, prior to its final rupture caused by the reversible detaching of individual nanoparticles. The associated contact force of about 2.5 nN is in quantitative agreement with the resu...
ABSTRACT Oxidation catalysis by gold spurred intensive research efforts over the last two decades... more ABSTRACT Oxidation catalysis by gold spurred intensive research efforts over the last two decades, which is encouraged by the unparalleled activity at temperatures even below 0 °C. Yet, gold nanostructures are inherently prone to coalescence at elevated temperatures, which limits their application. We demonstrate that this impediment can be overcome by reversing the classical order, that is, by depositing oxide nanoparticles on a high-surface area gold support. We used atomic layer deposition and liquid phase deposition, which leads to densely arranged oxide nanoparticles on the surface of a nanoporous gold material. In the case of a titania-coated material, a catalyst with so far unprecedented high catalytic activity already at ambient temperatures and stability up to 600 °C could be obtained. We demonstrate its high catalytic potential for two important reactions in the context of exhaust gas treatment: the oxidation of CO and the reduction of NO already proceeding at ambient temperatures.
ABSTRACT Nanoporous gold is a material with many possible applications e.g. in catalysts, sensors... more ABSTRACT Nanoporous gold is a material with many possible applications e.g. in catalysts, sensors and electrode materials. We studied the functionalization of the nanoporous gold with TiO2 particles. Aiming at the low temperature oxidation of CO, the nanoporous gold can be coated with TiO2 in order to enhance catalytic activity. Structure and distribution of the TiO2 on the gold surface are important structural features, which were investigated by transmission electron microscopy. The preparation of the porous gold was tested with focused ion beam - preparation, conventional Ar+ ion beam preparation of nanoporous gold embedded in epoxy and ultramicrotome preparation of nanoporous gold embedded in epoxy. Considering the beam damage on the structure and the contamination of the surface, ultramicrotome preparation turned out to be the best solution. It was shown, that the gold ligaments are abundantly covered by approximately 5 nm TiO2 particles. The determination of the largest lattice fringe distance in high resolution mode revealed that the crystalline nanoparticles consist of the anatase phase. The spatial Ti distribution was measured with energy filtered transmission electron microscopy. Scanning transmission electron microscopy tomography was applied to reconstruct the three-dimensional structure of the gold coated with TiO2 particles.
TiO2 and Pt/TiO2 nanoparticles were made by a one-step flame spray pyrolysis (FSP) process that r... more TiO2 and Pt/TiO2 nanoparticles were made by a one-step flame spray pyrolysis (FSP) process that resulted in mostly anatase (69–85wt%) powders with controlled specific surface area and crystallite size. These particles resulted in shorter half-lives for sucrose photomineralisation, up to 50% lower than Degussa P25. Co-precipitation of Pt on TiO2 during FSP increased the rutile content and slightly increased the
The production of pyrogenic (fumed) silica is increasing worldwide at a 7% annual growth rate, in... more The production of pyrogenic (fumed) silica is increasing worldwide at a 7% annual growth rate, including expanded use in food, pharmaceuticals and other industrial products. Synthetic amorphous silica, including fumed silica, has been generally recognized as safe (GRAS) for use in food products by the Food and Drug Administration (FDA). However, emerging evidence from experimental studies now suggests that fumed silica could be hazardous due to its siloxane ring structure, high silanol density, and "string-of-pearl-like" aggregate structure, which could combine to cause membrane disruption, generation of reactive oxygen species, pro-inflammatory effects, and liver fibrosis. Based on this structure-activity analysis (SAA), we investigated whether calcination and rehydration of fumed silica changes its hazard potential in the lung due to an effect on silanol density display. This analysis demonstrated that the accompanying change in surface reactivity could indeed impact cyt...
Langmuir : the ACS journal of surfaces and colloids, Jan 7, 2012
Fundamental knowledge about the mechanisms of adhesion between oxide particles with diameters of ... more Fundamental knowledge about the mechanisms of adhesion between oxide particles with diameters of few nanometers is impeded by the difficulties associated with direct measurements of contact forces at such a small size scale. Here we develop a strategy based on AFM force spectroscopy combined with all-atom molecular dynamics simulations to quantify and explain the nature of the contact forces between 10 nm small TiO(2) nanoparticles. The method is based on the statistical analysis of the force peaks measured in repeated approaching/retracting loops of an AFM cantilever into a film of nanoparticle agglomerates and relies on the in-situ imaging of the film stretching behavior in an AFM/TEM setup. Sliding and rolling events first lead to local rearrangements in the film structure when subjected to tensile load, prior to its final rupture caused by the reversible detaching of individual nanoparticles. The associated contact force of about 2.5 nN is in quantitative agreement with the resu...
ABSTRACT Oxidation catalysis by gold spurred intensive research efforts over the last two decades... more ABSTRACT Oxidation catalysis by gold spurred intensive research efforts over the last two decades, which is encouraged by the unparalleled activity at temperatures even below 0 °C. Yet, gold nanostructures are inherently prone to coalescence at elevated temperatures, which limits their application. We demonstrate that this impediment can be overcome by reversing the classical order, that is, by depositing oxide nanoparticles on a high-surface area gold support. We used atomic layer deposition and liquid phase deposition, which leads to densely arranged oxide nanoparticles on the surface of a nanoporous gold material. In the case of a titania-coated material, a catalyst with so far unprecedented high catalytic activity already at ambient temperatures and stability up to 600 °C could be obtained. We demonstrate its high catalytic potential for two important reactions in the context of exhaust gas treatment: the oxidation of CO and the reduction of NO already proceeding at ambient temperatures.
ABSTRACT Nanoporous gold is a material with many possible applications e.g. in catalysts, sensors... more ABSTRACT Nanoporous gold is a material with many possible applications e.g. in catalysts, sensors and electrode materials. We studied the functionalization of the nanoporous gold with TiO2 particles. Aiming at the low temperature oxidation of CO, the nanoporous gold can be coated with TiO2 in order to enhance catalytic activity. Structure and distribution of the TiO2 on the gold surface are important structural features, which were investigated by transmission electron microscopy. The preparation of the porous gold was tested with focused ion beam - preparation, conventional Ar+ ion beam preparation of nanoporous gold embedded in epoxy and ultramicrotome preparation of nanoporous gold embedded in epoxy. Considering the beam damage on the structure and the contamination of the surface, ultramicrotome preparation turned out to be the best solution. It was shown, that the gold ligaments are abundantly covered by approximately 5 nm TiO2 particles. The determination of the largest lattice fringe distance in high resolution mode revealed that the crystalline nanoparticles consist of the anatase phase. The spatial Ti distribution was measured with energy filtered transmission electron microscopy. Scanning transmission electron microscopy tomography was applied to reconstruct the three-dimensional structure of the gold coated with TiO2 particles.
TiO2 and Pt/TiO2 nanoparticles were made by a one-step flame spray pyrolysis (FSP) process that r... more TiO2 and Pt/TiO2 nanoparticles were made by a one-step flame spray pyrolysis (FSP) process that resulted in mostly anatase (69–85wt%) powders with controlled specific surface area and crystallite size. These particles resulted in shorter half-lives for sucrose photomineralisation, up to 50% lower than Degussa P25. Co-precipitation of Pt on TiO2 during FSP increased the rutile content and slightly increased the
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