Band gap effect on the photocatalytic activity of supramolecular structures obtained by entrapping photosensitizers in different inorganic supports

Abstract

Different metallophthalocyanines and 2,4,6-triphenylpyrylium (TP⁺) ions were entrapped in different inorganic supports such as Y zeolite, mesoporous MCM-41, TiO₂–SiO₂ and SiO₂ following a specific protocol. The resulting supramolecular structures were characterized by chemical analysis and diffuse reflectance UV–Vis measurements. The determination of the band gap on the basis of UV–Vis measurements showed that the host is not a spectator in this process and an electronic interaction occurs that lowers the band gap of the support. The XPS measurements were performed with an in situX-ray photoelectron spectrometer, which can be operated at pressures of up to 1 mbar at the sample. They indicated that the formation of the supramolecular structure generates a stable environment, in which the oxidation state of the metal can still be influenced by reaction of the metal center with gas molecules. The photocatalytic tests carried out in photodecomposition of dipropyl sulfide showed a good correlation between the band gap values and the photocatalytic activity for metallophthalocyanine complexes. It is remarkable that the triphenylpyrylium ion follows the same trend observed for metallophthalocyanines, although it is a different type of photosensitizer.