Surfactant-modifications of Na+–beidellite for the preparation of TiO2–Bd supported photocatalysts: II—Physico-chemical characterization and photocatalytic properties

Abstract

This work deals with the study of the effect of the amount of cethyltrimethylammonium bromide (CTAB) surfactant, used in the preparation of starting organobeidellites, on physico-chemical properties and photocatalytic activity of TiO2 supported beidellite (Bd) nanocomposites against the removal of Orange G (OG) dye from aqueous media. A structural study of organobeidellites used as starting materials was reported in a companion paper. Here, physico-chemical characterizations of the nanocomposite photocatalysts show that TiO2 supported on Bd beforehand organomodified with an amount of CTAB equivalent to 3 CEC of smectite (3CTA+–Bd) exhibits thin fine grained (≈10nm) features which remarkably remained stable in the form of photoactive anatase up to 750°C. Comparatively, the TiO2 coating grown on Bd previously rendered organophilic by using an amount of CTAB equivalent to 5 CEC of Clay mineral (5CTA+–Bd) appears thicker and more porous with larger nanoparticles (≈25nm) which is prone to be readily converted into less photoactive rutile as observed near 700°C. This is likely due to its development mainly outside Bd interlayer spaces promoted by outer organophilic environment created by the adsorption of CTA+ excess. In both cases, anatase is still present as minor phase up to 900°C. As a result of these differences a significant improvement of the photocatalytic activity of TiO2 supported Bd nanocomposite prepared starting from 3CTA+–Bd is observed compared to that from 5CTA+–Bd. For instance, the total elimination of the pollutant from the aqueous solution occurs within about 45min when using the 3CTA+–Bd–TiO2 photocatalyst instead of 90min using the 5CTA+–Bd–TiO2 sample. Furthermore, the best TiO2–Bd supported photocatalyst is also found more efficient than a pure TiO2 xerogel sample.