Silicalite-1 synthesized with geothermal and Ludox colloidal silica and corresponding TiO2/silicalite-1 hybrid photocatalysts for VOC

Abstract

Silicalite-1 samples of uniform sub-micron size with two distinct morphologies were prepared using colloidal

silica extracted from geothermal fluids. The colloidal silica used was provided by a New Zealand Company,

GEO40 Ltd, and was produced by them using their patented process for recovering colloidal silica from

geothermal brine. Spherical crystals with an average size of ca. 250 nm (S1N) as well as typical MFI-type coffinshaped

crystals with a size of ca. 900 nm (S1M) were prepared from clear synthesis solutions made from colloidal

silica and aqueous tetrapropylammonium hydroxide of different concentration. The silicalite-1 samples prepared

showed very similar characteristics to samples prepared using a conventional silica sol, Ludox SM, as a silica

source. Silicalite-1 samples prepared with geothermal and conventional silica sols were used as supports for TiO2

nanoparticles. The hybrid TiO2/silicalite-1 materials were tested as photocatalysts for the photocatalytic

degradation of trichloroethylene for air pollution control. The hybrid samples reduced the formation rates of

non-desirable reaction products, promoting the mineralization process in comparison with a reference TiO2

xerogel and high Si/Al ratio ZSM-5-based hybrid materials