Rita Patakfalvi

Synthesis and characterization of silver nanoparticle/kaolinite composites

Abstract Ag nanoparticles were synthetized in the interlamellar space of a layered kaolinite clay mineral. Disaggregation of the lamellae of non-swelling kaolinite was achieved by intercalation of dimethyl sulfoxide. The kaolinite was suspended in aqueous AgNO 3 solution and, after adsorption of Ag + , the ions were reduced with NaBH 4 . The interlamellar space limits particle growth ( d ave =3.8–4.2 nm); however, larger silver particles may be formed on the exterior surface of kaolinite with d ave =5.6–10.5 nm diameter. The diameter of the particles prepared in this way is depending on the initial AgNO 3 concentration. The silver nanoparticles prepared were characterized by UV–vis spectroscopy, X-ray diffraction (XRD), Small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM).

Growing and stability of gold nanoparticles and their functionalization by cysteine

Gold nanoparticles in aqueous dispersion were prepared using the trisodium citrate reduction method to control the size of particles by changing the concentration of HAuCl4. The average particle size measured by DLS is higher than that obtained by TEM at a zeta potential of -40 mV. When trisodium citrate concentration is kept constant, the particle size increases with gold concentration. The kinetics of growth was studied and apparent kinetic rate constants were determined at various gold/citrate ratios. Gold nanoparticles were attached to silanized glass surfaces; Au rods were grown (ca. 200 nm) by adding more precursors and the rods’ growth rate was monitored by UV-Vis spectroscopy as well as by AFM. Surface functionalization of gold surface was influenced by cysteine. The surface modification by cysteine at pH=6.0 results in aggregation and the red shift of absorption maximum is nearly 200 nm. When glutathione molecules are bound onto the cysteinelinked Au rods on the glass surface, the spectral shift reaches only an amount of 5–10 nm, because the surface attachment hinders the tendency to aggregate.

Structural properties of cationic surfactant/pentanol/water systems and their interaction with negatively charged layer silicates

Abstract Hexadecyltrimethylammonium bromide/pentanol/water and hexadecylpyridinium chloride/pentanol/water liquid crystalline systems were investigated. We studied the influence of water and pentanol on the swelling and rheological properties of lamellar liquid crystalline systems. We studied the possibility of inserting negatively charged layer silicates in these cationic surfactant/pentanol/water systems. Combining the adsorption data from X-ray diffraction, the composition of adsorption layer was calculated. After addition of Na-montmorillonite to the liquid crystalline system, the silicate lamellae were built up into the ordered liquid crystalline structure. Therefore, in the case of adsorption from aqueous solution, ordered liquid crystalline structure appears in the adsorption space between the silicate layers, and this structure determines the degree of swelling and the adsorption layer composition on the solid silicate surface.

Synthesis and characterization of noble metal nanoparticles/kaolinite composites

Silver, palladium, and rhodium nanoparticles were prepared by heterogeneous nucleation in the interlamellar space of a layered kaolinite support. Disaggregation of the lamellae of nonswelling kaolinite was achieved by intercalation of dimethyl sulfoxide. The kaolinite was suspended in various metal precursor solutions and the adsorbed metal cations were reduced with NaBH4.The diameter of the silver particles (4–10 nm) prepared in this way depends on the initial Ag+> concentration. Palladium and rhodium particles were stabilized by polymers and by the lamellae of kaolinite. The effect of the molecular mass and the concentration of the polymers on the size of the particles formed was studied using neutral poly(vinylpyrrolidone). The effect of the concentration of the precursor was also examined. The average particle size fell in the range 1–3 nm, depending on the stabilization method used and the concentration of precursor ions. Interlamellar incorporation of nanoparticles was monitored by X-ray diffraction, and was verified by transmission electron microscopy and small-angle X-ray scattering.

Incorporation of silver nanoparticles in kaolinite clays

Silver nanoparticles were synthesized in the interlamellar space of alayered kaolinite clay m ineral. Disaggregation of the lamellae of non-swelling kaolinite was achieved by intercalation of dimethylsulfoxide. The Ag+ ions after adsorption in the interlamellar space were reduced by NaBH4 or by UV irradation. The changing of the structure of kaolinite and the intercalation of silver nanoparticles were monitored by x-ray diffraction. We compared the effects of the two reduciont methods on the size and the size distribution of Ag nanoparticles by TEM investigation and SAXS experiments how clay mineral structure is altered as a consequence of particle formation. It was established that the size of Ag nanoparticles depends on both silver content and the reduction method. The chemical reduction showed Ag nanoparticles with 7.1-10.5 nm and photoreduciont of silver led to the formation of relatively large Ag nanoparticles with 8.3-11.2 nm.

Some Colloidal Routes to Synthesize Metal Nanoparticle-Based Catalysts

Inorganic colloids and especially metal nanoparticles (NPs) have been in the focus of interest for a long time. Their valuable characteristics due to their small size, such as their unique electron structure and extremely large specific surface area, open the way for their practical utilization. By virtue of their high activity and selectivity, they have become widely known as novel type catalysts. Various methods are developed for their preparation, from which colloidal chemical routes became more and more widespread. In this study, some colloidal methods for preparation of metal (Pd, Rh, Au, Ag) NPs and NP-based catalysts are presented. The effects of various polymer molecules, clay lamellae, and reducing agents on the kinetic of NPs formation were investigated. The formation of NPs was followed by transmission electron microscopy (TEM), UV–Vis spectroscopy, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS). NPs were also prepared on clay mineral surface. Interlamellar space of clay minerals is capable of stabilizing colloid particles. Influence of the NPs into the original lamellar structures was examined by X-ray diffraction and small-angle X-ray scattering. The surface oxidation state of the particles sitting on the support in the metal-containing catalysts was determined by XPS.