Monometallic and bimetallic colloids were prepared in micelles of the block copolymer polystyrene-b-poly-4-vinylpyridine in toluene and analyzed by electron microscopy and various techniques of X-ray analysis. These metal colloids were studied in hydrogenation of cyclohexene, 1,3-cyclooctadiene, and 1,3-cyclohexadiene. A strong influence of the synthetic pathway to the colloids and the type of reducing agent on the catalytic activity of the colloids was found. The lowest activity was observed for N2H4·H2O reduction which is related to a morphology where only a small number of noble-metal colloids is embedded in the micelle core. The highest activity was obtained for the super-hydride reduction where the data suggest the existence of many metal clusters per micelle. The bimetallic Au/Pd colloids with metal ratios 1/5, 1/4, and 1/3 show the highest activity in hydrogenation of cyclohexene to cyclohexane. The Pd monometallic and Au/Pd bimetallic colloids are also rather selective catalysts (both in the homogeneous and a heterogeneous modification), as shown by the hydrogenation of 1,3-cyclooctadiene and 1,3-cyclohexadiene to the corresponding cycloalkenes.

The interaction of polyelectrolyte gel/oppositely charged surfactant complexes with AgNO3 and H2PtCl6 was investigated. Three kinds of gel/surfactant complexes were studied:  a complex of the anionic gel of poly(methacrylic acid) with the cationic surfactant cetylpyridinium chloride and complexes of the cationic gel of poly(diallyldimethylammonium chloride) with two anionic surfactants:  sodium dodecyl sulfate and sodium dodecylbenzenesulfonate. After reduction of metal compounds by hydrazine−hydrate, sodium borohydride, or UV-irradiation, Pt and Ag metal particles embedded in the body of the hydrogel were formed. The degree of metal ion exchange was higher for the oppositely charged metal ion and the polyelectrolyte gel; i.e., Ag+ is strongly absorbed by the complex poly(methacrylic acid)/cationic surfactant, while PtCl6 2- ions are mainly consumed by the complex of poly(diallyldimethylammonium chloride) gel with anionic surfactants. Small-angle X-ray scattering data indicated different structural changes in the gel for the complex of an anionic gel with cationic surfactant and for complexes of cationic gel with anionic surfactants. The incorporation of the metal ions in the body of the hydrogel and the growth of metal nanoparticles was found to lead to the loss of order provided by surfactant aggregates if the distance between charged groups in the polyelectrolyte does not provide a strong hydrophobic interaction between surfactant molecules.

No abstract

Small-angle x-ray scattering is used to study size distributions of noble metal nanoparticles embedded in polyelectrolyte hydrogels with oppositely charged surfactants. A procedure is proposed to subtract matrix scattering and to extract pure scattering due to the nanoparticles allowing to evaluate their size distribution functions by means of a regularization technique. Two kinds of collapsed gel-surfactant complexes were studied: a complex of a cationic gel of poly(diallyldimethylammonium chloride) with an anionic surfactant sodium dodecyl sulfate (PDADMACl/SDS), and that of an anionic gel of poly(methacrylic acid) with a cationic surfactant cetylpyridinium chloride (PMA/CPC). Addition of a gold compound (HAuCl4⋅3H2O) to the PDADMACl/SDS system forms the metal compound clusters and leads to a partial distortion of the gel structure. After subsequent reduction of the gold compound with sodium borohydride (NaBH4) ordering in the gel disappears and gold nanoparticles are formed. Their size distribution includes a fraction of small particles with approximately the same size as the compound clusters before reduction and a fraction of larger particles with the radii up to 40 nm. For the collapsed PDADMACl/SDS gels, aging does not change the size distribution profile; for the noncollapsed PDADMACl gels without surfactant, metal particles are found to grow with time. This suggests that the aggregation of metal colloids is prevented by the ordering in the collapsed gel-surfactant complex. The addition of HAuCl4⋅3H2O and the subsequent reduction of the metal ions in the PMA/CPC system does not distort the gel structure as the degree of incorporation of AuCl4− ions is very low. Particle sizes in the PMA/CPC system are found to be somewhat larger than those in the PDADMACl/SDS system. The PDADMACl/SDS gels loaded with the PtCl4 compound were also studied to analyze the influence of the reducing agent type on the particle size distribution distributions. Fast reduction with NaBH4 yielded mostly small particles with the radii around 2 nm grown from the compound clusters similar to those observed for the gold-loaded gels. In contrast, slow reduction with N2H4⋅H2O was found to produce larger nanoparticles and the size distribution function shows a major fraction of the particles with the radii up to 30 nm.

Size distributions of platinum nanoparticles embedded in nanostructured hybrid matrixes and the internal structure of these systems were studied by anomalous and conventional small-angle X-ray scattering. The complexes of polyelectrolyte gels with oppositely charged surfactants were employed as nanostructured matrixes. Two complexes of a cationic gel of poly(diallyldimethylammonium chloride) with anionic surfactants sodium dodecyl sulfate and sodium dodecylbenzene sulfonate were charged with platinum compounds (PtCl 4 , Na 2 PtCl 6 , (NH 4 ) 2 PtCl 4 , and H 2 PtCl 6 ) and reduced with NaBH 4 and N 2 H 4 ×H 2 O. Fast reduction with NaBH 4 yields mostly small Pt nanoparticles with radii about 2 to 3 nm, whereas for N 2 H 4 ×H 2 O, a significant amount of large (up to 40 nm) particles is found. The pH of the reaction medium and the Pt ion geometry were found to influence particle nucleation and growth. The internal ordering in gel/surfactant complexes during the nanoparticle formation was characterized from the Bragg peaks in the scattering patterns. Although the magnitude of the peaks diminishes after metal nanoparticle formation, quantitative peak parameters indicate an increase of the degree of order. This suggests that the highly ordered zones in the hydrogels concentrate around the growing nanoparticles thus stabilizing them. Addition of Na 2 PtCl 6 to another complex, an anionic gel of poly(methacrylic acid) with a cationic surfactant cetylpyridinium chloride, results in drastic structure rearrangements. The order observed in the collapsed gel nearly degrades due to a competitive interaction of the negative PtCl 6 2ions with positively charged pyridinium heads and a new micellar-like structure is formed instead. Further Pt ion reduction restores the initial gel structure and yields very large (radii up to 80 nm) metal particles growing outside the areas of the surfactant ordering.