Novel photocatalysts containing 2,4,6-triphenylthiapyrylium encapsulated within zeolites. Enhanced photocatalytic activity as compared to the pyrylium analogues

A series of solid photocatalysts containing either 2,4,6-triphenylpyrylium (TP⁺) or 2,4,6-triphenylthiapyrylium (TPTP⁺) encapsulated within zeolite Y or Beta, or deposited on amorphous silica or MCM-41, have been prepared. These photocatalysts have been tested for the degradation of aqueous solutions of phenol (40 ppm) or aniline (40 or 80 ppm, initial pH 3) as model reactions. TPTP⁺ photocatalysts were found to be more active and stable than those containing TP⁺, the initial efficiency order being: TPTP/MCM-41 ≈ TPTP/SiO₂ > TPTP@Beta > TPTP@Y > TiO ₂. In the case of TPTP/SiO₂ and TPTP/MCM-41 the photocatalysts are largely decomposed during the photocatalytic reaction, as compared to TPTP⁺ encapsulated within zeolites Y and Beta; in the latter, although the initial activity is considerably lower the dye persists after the irradiation and can be reused. In this way the final productivity of TPTP@Beta is at least four times higher than when the dye is supported on SiO₂ or MCM-41. Addition of an initial concentration of H ₂O₂ (10^-3 M) accelerates the photodegradation of phenol by a factor of 6 but it does not have much influence in the case of aniline.