Szilvia Papp

Preparation of Pd0 nanoparticles stabilized by polymers and layered silicate

Abstract The synthesis of palladium nanoparticles on montmorillonite layer silicates was studied. The solid/liquid interfacial layer was utilized as a nanoreactor for the synthesis of particles in the interlamellar space. Pd2+ ions are first adsorbed from acidic PdCl2 solution in an aqueous suspension of montmorillonite and are next reduced to Pd0 by ethanol within the adsorption layer. Pd0 nanoparticles appear and grow in the internal, interlamellar space as well as on the external surface of the lamellae. Another method for generation of nanoparticles was also carried out using aqueous polymer solutions in the presence of clay; however, the nanoparticles can be bond to the clay mineral lamellae. In the course of clay/polymer aggregation following reduction, the larger clusters formed in the bulk phase may become attached to the silicate layers via macromolecules acting as molecular bridges. The structure, specific surface area, porosity, etc., of montmorillonite are significantly altered by the incorporation of nanoparticles. These alterations were monitored by various techniques (N2 adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM)). TEM is also eminently suitable for the determination of average particle size and size distribution functions.

Colloid synthesis of monodisperse Pd nanoparticles in layered silicates

Abstract Palladium nanoparticles have been generated in the interlamellar space of montmorillonite and kaolinite by different methods in aqueous media. The in situ preparation method was based on the preferential sorption of precursor ions (Pd2+) in the ethanol-rich interlamellar space of montmorillonite in ethanol(1)–water(2) binary liquid mixture and the subsequent reduction of Pd2+ ions to Pd0 at 65°C. A second method for the generation of nanoparticles was also carried out in aqueous suspension. However, nanoparticles were stabilized by polymers, the adsorption of which promoted the adhesion of nanocrystals to the silicate layers. A new method was developed to prepare Pd subcolloids in non-swelling kaolinite. The separation (complete disaggregation) of kaolinite lamellae was achieved by direct intercalation of dimethylsulphoxide (DMSO) at 65°C. Neutral and cationic polymer/kaolinite intercalation complexes were obtained by adsorption from solutions. Characterization of these materials included ICP spectroscopy, XRD and pore-size distribution analysis. TEM measurements, which showed that nearly spherical, nearly monodisperse particles were generated.

Ultrasmall, Ligand-Free Ag Nanoparticles with High Antibacterial Activity Prepared by Pulsed Laser Ablation in Liquid

Since ancient times, silver and its compounds have been known to have a broad spectrum of antimicrobial activities for bacteria, fungi, and viruses. Due to the increasing bacterial resistance to classic antibiotics, the investigations of Ag NPs have increased. Herein, we present the preparation of ligand-free Ag NPs with 3 and 20 nm sizes by applying picosecond laser ablation in liquid at 355 and 1065 nm. Our laser processing system allows a high control on particle sizes. The produced nanoparticles were characterized by means of transmission electron microscopy, UV-Vis spectroscopy, and X-ray diffraction. The size effect on the antibacterial activity of Ag NPs was tested against E. coli and S. aureus. The growth curves of bacteria were monitored at 0–5 mg/L of Ag NPs by a multimode microplate reader. The size effects as well as the concentration of Ag NPs on their antibacterial activity are discussed.

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.

Stabilization of rhodium nanoparticles in an aqueous medium by polymer and layered silicates

The synthesis of rhodium nanoparticles was studied in aqueous polymer solution and on layerd montmorillonite and kaolinite minerals. The effect of the concentration of the rhodium precursor and polymer on the size of the particles formed was studied using neutral polivinylpyrrolidone. Reduction was done by sodium borohydride. Expansion of the interlayer space in kaolinite was effected by intercalation of dimethyl sulfoxide at 65°C. Interlamellar incorporation of nanoparticles was monitored by x-ray diffraction and small angle x-ray scattering, the size and the size distribution function were determined by transmission electron microscopy. Average particle size fell in the range of 1-3 nm, depending on the stabilization method used and the concentration of precursor rhodium ions. The valence of the rhodium particles on the support surface was examined by XPS analysis.

Synthesis, Structure, and Photocatalytic Activity of Titanium Dioxide and Some of Its Surface-Modified Derivatives

Titania-based heterogeneous photocatalysis has been extensively studied at both solid–liquid and solid–gas interfaces. Numerous efforts have been directed to improving the photocatalytic activity of TiO2 in both the UV and the visible wavelength ranges. To enhance the photoactivity, a number of techniques for the doping of TiO2 with various elements have been developed. This chapter presents a brief discussion of three promising materials: phosphate-, nitrogen-, and silver-modified TiO2. Phosphate- and silver-modified TiO2 exhibited very high photocatalytic activity under UV irradiation, while the nitrogen-doped TiO2 had visible light activity. The modified TiO2 derivates were prepared by simple chemical methods and studied by various surface and structural investigation techniques. The effects of the dopant concentration on the structure and photocatalytic activity are discussed.