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

Abstract

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.