Small metal nanoparticles that are also highly crystalline have the potential for showing enhanced catalytic activity. We describe the preparation of single nanocrystals of platinum that are 2 to 3 nanometers in diameter. These particles were generated and immobilized on spherical polyelectrolyte brushes consisting of a polystyrene core (diameter of approximately 100 nanometers) onto which long chains of a cationic polyelectrolyte were affixed. In a first step, a nanoalloy of gold and platinum (a solid solution) was generated within the layer of cationic polyelectrolyte chains. In a second step, the gold was slowly and selectively dissolved by cyanide ions in the presence of oxygen. Cryogenic transmission electron microscopy, wide-angle x-ray scattering, and high-resolution transmission electron microscopy showed that the resulting platinum nanoparticles are faceted single crystals that remain embedded in the polyelectrolyte-chain layer. The composite systems of the core particles and the platinum single nanocrystals exhibit an excellent colloidal stability, as well as high catalytic activity in hydrogenation reactions in the aqueous phase.

We synthesized well‐defined, crystalline TiO2 nanoparticles at room temperature by using spherical polyelectrolyte brush particles as a template. The template particles consist of a polystyrene core from which long chains of poly(styrene sodium sulfonate) are grafted. Tetraethylorthotitanate is hydrolyzed in the presence of brush particles leading to the formation of well‐dispersed TiO2 nanoparticles (d = 4∼12 nm). Wide‐angle X‐ray scattering demonstrates that anatase nanoparticles with high crystallinity have been generated at room temperature. The as‐prepared TiO2 nanocomposites present high photocatalytic activity for the degradation of Rhodamine B under UV irradiation. Finally, mesoporous TiO2 structures with defined pore size are formed after calcination.magnified image

A polymer-layered silicate nanocomposite coating is prepared by combining a novel synthetic lithium-hectorite and an UV-curable, cationic polyurethane. Oxygen transmission measurements clearly indicate the supremacy of the lithium-hectorite as compared to a standard montmorillonite. In addition, a very high degree of optical transparency of the nanocomposite coating is achieved, rendering this material highly interesting for flexible packaging and encapsulation applications.

No abstract