Preparation, structural characterization and photocatalytic activity of mesoporous Ti-silicates

Abstract

This paper focuses on structural and photocatalytic properties of ordered mesoporous Ti-silicates, prepared by both impregnation (IMP) and coprecipitation (CP) methods. Catalyst characterization was carried out by inductively coupled plasma analysis, nitrogen adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). Photocatalytic activity was evaluated for gaseous trichloroethylene (TCE) decomposition in a batch reactor under near-UV irradiation.Both the Ti incorporation method (IMP or CP) and TiO2 content (4.7–35.0wt.%) had large effects on structural characteristics and photocatalytic activity of Ti-silicates, whereas no important effects were observed with respect to calcination temperature (200–600°C). At all conditions, TiO2 was present as pure anatase crystallites with particle diameters in IMP catalysts of 4.4–7.0nm, being clearly smaller than those in CP ones (12.0–19.6nm). The ordered structure of the silica was at least partially preserved up to a TiO2 content of 25wt.% (CP) and 33wt.% (IMP). With increasing TiO2 content, specific surface area (SSA 376–805m2g−1) of both CP and IMP catalysts decreased. Similar trends were observed for pore volumes (0.6–1.2mLg−1) and pore diameters (4.5–7.5nm) in IMP catalysts. Initial photocatalytic TCE degradation rate constants (0.014–0.202min−1) obtained with CP catalysts increased systematically with TiO2 contents up to 35wt.%, while in IMP ones, they levelled off at TiO2 contents above 17wt.%. TCE degradation rates obtained with CP catalysts were up to a factor of six higher than those measured applying the IMP method. This may be explained by a different TiO2 localization in the silica structure. During IMP preparation, TiO2 is mostly incorporated within the silica mesopores, whereas during CP synthesis, it is mainly localized on the external silica surface.