The influence of the interfacial properties of composite catalyst material on the photocatalytic conversion of TiO_2 layer silicates

Solid-gas and solid-liquid interfacial properties of titanium dioxide/layer silicate composite sorbents were studied by sorption experiments and the photocatalytic properties were also investigated. The photocatalyst TiO_2 was prepared by the sol-gel method and the sol obtained was used for heterocoagulation of Na-montmorillonite at several different mass ratios, yielding supported photocatalysts of various compositions. The TiO_2 content of the samples ranged from 20 to 75 wt%. The specific surface areas of the samples, determined by nitrogen adsorption, ranged from 120 to 290 m2/g. The catalytic properties of TiO2/montmorillonite composites were tested by photo-oxidation of dichloro acetic acid (DCA). The specific surface area and the porosity exert a major influence on the photocatalytic efficiency through the interfacial layer properties. The rate of photo-oxidation of DCA depends strongly on the surface accessibility of the intermediates and the specific surface area calculated from gas and liquid mixture adsorption data. The conversion data of DCA presented show that the photocatalytic efficiency of TiO2 can depend significantly on the accessibility of different molecules to the TiO2 nanocrysta ls embedded in the layer silicate support in confined space

Formation and Stabilization of Noble Metal Nanoparticles

The kinetics of homogeneous and heterogeneous nucleation processes of metal (Ag, Pd) nanoparticles was studied by UV-VIS spectrometry. Silver nanoparticles were prepared in aqueous solution by homogeneous nucleation using poly(vinylpyrrolidone) (PVP) and sodium citrate as sterical stabilizers. Reduction was ensured by adding hydroquinone. According to kinetic functions, reduction is an autocatalytic process: a slow, continuous nucleation is followed by a fast, autocatalytic growth. The presence of polymer inhibits nucleation and retards the rate of particle growth. Formation of palladium nanoparticles was investigated in aqueous medium via reduction by hydrazine, using PVP and the clay mineral hectorite as stabilizers. Effects of the polymer and concentration of silicate and palladium ions on the particle formation rate were analyzed. The rate of reduction is decreased by increasing amounts of stabilizing agents and increased by increasing concentrations of precursor ions. The kinetics of heterogeneous nucleation was determined based on the adsorption of the palladium species at the clay mineral particles and the viscosity of the hectorite dispersion