11-mercaptoundecanoic-acid and titanium-dioxide

A method, based on self assembly, for preparing core-shell nanostructures that are dispersible in organic solvents is demonstrated for Pd and Pt cores with CeO(2), TiO(2), and ZrO(2) shells. Transmission electron microscopy (TEM) of these nanostructures confirmed the formation of distinct metal cores, approximately 2 nm in diameter, surrounded by amorphous oxide shells. Functional catalysts were prepared by dispersing the nanostructures onto an Al(2)O(3) support; and vibrational spectra of adsorbed CO, together with adsorption uptakes, were used to demonstrate the accessibility of the metal core to CO and the porous nature of the oxide shell. Measurements of water-gas-shift (WGS) rates demonstrated that these catalysts exhibit activities similar to that of conventional supported catalysts despite having lower metal dispersions. Pd-based CeO(2) and TiO(2) core-shell catalysts exhibit significant transient deactivation, which is probably caused by a decrease in the exposed metal surface area due to the ease of reduction of the shells. Alternatively, Pt-based analogous core-shell catalysts do not exhibit such a transient decrease. Both Pd- and Pt-based ZrO(2) core-shell catalysts deactivate at a significantly lower rate due to the less reducible nature of the ZrO(2) shell.

Topics: Adsorption; Carbon Monoxide; Catalysis; Fatty Acids; Nanostructures; Nanotechnology; Palladium; Platinum; Sulfhydryl Compounds; Titanium; Zirconium

Separation/preconcentration of copper and cadmium using TiO(2) core-Au shell nanoparticles modified with 11-mercaptoundecanoic acid and their slurry analysis by flame atomic absorption spectrometry were described. For this purpose, at first, titanium dioxide nanoparticles were coated with gold shell by reducing the chloroauric acid with sodium borohydride and then modified with 11-mercaptoundecanoic acid. The characterization of modified nanoparticles was performed using ultra-violet spectroscopy and dynamic light scattering. Copper and cadmium were then collected on the prepared sorbent by batch method. The solid phase loaded with the analytes was separated by centrifugation and the supernatant was removed. Finally, the precipitate was slurried and directly aspirated into the flame for the determination of analytes. Thus, elution step and its all drawbacks were eliminated. The effects of pH, amount of sorbent, slurry volume, sample volume and diverse ions on the recovery were investigated. After optimization of experimental parameters, the analytes in different certified reference materials and spiked water samples were quantitatively recovered with 5% RSD. The analytes were enriched up to 20-fold. Limits of detection (N=10, 3σ) for copper and cadmium were 0.28 and 0.15 ng mL(-1), respectively.

Topics: Cadmium; Chelating Agents; Copper; Fatty Acids; Hydrogen-Ion Concentration; Metal Nanoparticles; Spectrophotometry, Atomic; Sulfhydryl Compounds; Titanium