ABSTRACT
We synthesize platinum nanoparticles with controlled average sizes of 2, 4, 6, and 8 nm and use them as model catalysts to study isopropanol oxidation to acetone in both the liquid and gas phases at 60 °C. The reaction at the solid/liquid interface is 2 orders of magnitude slower than that at the solid/gas interface, while catalytic activity increases with the size of platinum nanoparticles for both the liquid-phase and gas-phase reactions. The activation energy of the gas-phase reaction decreases with the platinum nanoparticle size and is in general much higher than that of the liquid-phase reaction which is largely insensitive to the size of catalyst nanoparticles. Water substantially promotes isopropanol oxidation in the liquid phase. However, it inhibits the reaction in the gas phase. The kinetic results suggest different mechanisms between the liquid-phase and gas-phase reactions, correlating well with different orientations of IPA species at the solid/liquid interface vs the solid/gas interface as probed by sum frequency generation vibrational spectroscopy under reaction conditions and simulated by computational calculations.
ABSTRACT
As a result of their characteristic physical and optical properties, including their size, intense fluorescence, broad excitation, narrow emission and resistance to photobleaching, semiconductor nanocrystals are potentially useful for a variety of biological applications including molecular imaging, live-cell labeling, photodynamic therapy and targeted drug delivery. In this study, zinc sulfide (ZnS) semiconductor nanocrystals were synthesized in the 3 to 4 nm size range with selected capping agents intended to protect the nanocrystal core and increase its biological compatibility. We show that the biocompatibility of ZnS nanocrystals with primary murine splenocytes is influenced by the chemical structure of the outer capping agent on the nanocrystal. Additionally, the cytotoxicity of ZnS nanocrystals increases markedly as a function of time spent in suspension in phosphate-buffered saline (PBS). These data suggest that the potential therapeutic and/or biological use of ZnS nanocrystals is inherently dependent upon the proper choice of capping agent, as well as the conditions of nanocrystal preparation and storage.
Subject(s)
Cell Survival/drug effects , Metal Nanoparticles/toxicity , Spleen/drug effects , Sulfides/toxicity , Zinc Compounds/toxicity , Animals , Biomarkers/metabolism , Cells, Cultured , Female , Metal Nanoparticles/chemistry , Mice , Mice, Inbred C57BL , Pulp Capping and Pulpectomy Agents/chemistry , Spleen/metabolism , Spleen/pathology , Sulfides/chemistry , Suspensions , Time Factors , Zinc Compounds/chemistryABSTRACT
An immobilized platinum nanocatalyst was prepared by first functionalizing the surface of activated silica with poly(vinylpyrrolidone) (PVP) and then reducing encapsulated platinum ions in the presence of these functionalized supports to form nanoparticles. Surface functionalization was monitored by infrared spectroscopy and surface area measurements, and the resulting nanocatalyst was characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Platinum nanoparticle size was determined to be approximately 5 nm based on TEM and XRD measurements. Catalytic activity of this material for the hydrogenation of cyclohexanone was found to be greater than that of unsupported colloidal PVP-capped platinum nanocatalysts. In addition, the immobilized nanocatalyst displayed no change in activity after being recycled. Taken together, these results clearly indicate advantages in the design of catalytic materials with desired properties.
