Marc Schrinner

Single Nanocrystals of Platinum Prepared by Partial Dissolution of Au-Pt Nanoalloys

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 ∼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.

Thermosensitive core-shell microgel as a “nanoreactor” for catalytic active metal nanoparticles

Thermosensitive core-shell microgels can be used as “nanoreactors” for the immobilization of metal nanoparticles. The microgels consist of a polystyrene core and a network made of poly(N-isopropylacrylamide) (PNIPA) cross-linked by N,N′-methylenebisacrylamide. The cross-linked PNIPA shell undergoes a volume transition at around 30 °C in which most of the water is expelled. The microgel particles exhibit a weak positive charge due to the cationic initiator. Metal nanoparticles (such as Au, Rh and Pt) with high catalytic activity can be homogeneously embedded into such a network. The oxidation of alcohols to the corresponding aldehydes or ketones has been chosen as a test reaction to probe the catalytic activity of such metal-microgel nanocomposite particles (metal@T-CoS-MiP). It is demonstrated that the oxidation can be catalyzed by the metal@T-CoS-MiP nanocomposites at room temperature in water using air as oxidant. The Au nanocomposite particles show the highest catalytic activity for the oxidation of benzyl alcohol. Moreover, it has been found that the catalytic activity of the metal nanocomposite can be modulated by the volume transition of microgel particles for the oxidation reaction of benzyl alcohol.

Quantitative analysis of polymer colloids by cryo-transmission electron microscopy.

The structure of colloidal latex particles in dilute suspension at room temperature is investigated by cryogenic transmission electron microscopy (cryo-TEM). Two types of particles are analyzed: (i) core particles made of polystyrene with a thin layer of poly(N-isopropylacrylamide) (PNIPAM) and (ii) core-shell particles consisting of core particles onto which a network of cross-linked PNIPAM is affixed. Both systems are also studied by small-angle X-ray scattering (SAXS). The radial density profile of both types of particles have been derived from the cryo-TEM micrographs by image processing and compared to the results obtained by SAXS. Full agreement is found for the core particles. There is a discrepancy between the two methods in case of the core-shell particles. The discrepancy is due to the buckling of the network affixed to the surface. The buckling is clearly visible in the cryo-TEM pictures. The overall dimensions derived from cryo-TEM agree well with the hydrodynamic radius of the particles. The comparison of these data with the analysis by SAXS shows that SAXS is only sensitive to the average radial structure as expected. All data show that cryo-TEM micrographs can be evaluated to yield quantitative information about the structure of colloidal particles.

Design of multicomponent microgels by selective deposition of nanomaterials.

In the present paper a method for the targeted deposition of different nanomaterials on aqueous microgels is described. In the first stage poly(3,4-ethylenedioxythiophene) (PEDOT) nanorods are introduced into the microgel structure by in situ oxidative polymerization. In the second stage hydrogen tetrachloroaurate is used to transform PEDOT chains to an oxidized state in the microgel structure, leading to the fixation of chloroaurate anions on the surface of the PEDOT nanorods. The reduction of chloroaurate ions induces the formation of gold nanoparticles (AuNPs) predominantly located on the PEDOT surface. Obtained microgel/PEDOT/AuNP hybrid particles with different nanoparticle loadings exhibit superior colloidal stability and temperature sensitivity. The microgel/PEDOT/AuNP hybrid microgels exhibit extraordinary catalytic activity in aqueous media.

Liposomes remain intact when complexed with polycationic brushes

Anionic liposomes adsorb onto the surface of spherical polymer particles bearing grafted linear cationic macromolecules. The size, shape, and encapsulation ability of the liposomes remain unchanged upon adsorption, thus providing immobilized self-organizing containers that have potential applications in the biomedical field.

Hybrid Microgels with Antibacterial Properties

In the present work, we have used aqueous microgels as containers for the deposition of silver nanoparticles (AgNPs). It has been shown that AgNPs can be effectively incorporated in the microgel interior during the in situ reduction of silver ions. Obtained hybrid microgels with variable AgNPs loading (from 1 to 12 wt.-%) have been used as antibacterial agents for two bacteria types. The experimental results indicate that porous microgel structure allows the release of the silver ions from the AgNPs surface into an aqueous phase. This ensures effective reduction in the number of bacterial colonies in test plates and complete bacteria killing. The antibacterial efficiency of the microgel particles increases with AgNPs loading.