Dye photodegradation employing mesoporous organosilicas functionalized with 1,8-naphthalimides as heterogeneous catalysts

Mesoporous organosilicas containing covalently bound 1,8-naphthalimides (NI) were shown to be efficient heterogeneous catalysts for the photodegradation of methylene blue (MB), a typical textile pollutant. The NI-containing mesoporous silicas (SBANI materials) were prepared by a co-condensation reaction, in conditions similar to those used for inorganic SBA-15. For the photocatalytic tests, the SBANI materials were suspended in aqueous MB solutions, and the suspensions were irradiated with a 100 W Hg lamp (bandpass filter: 320-480 nm). The activity of the SBANI catalysts was proportional to the NI content in the sample. When MB was irradiated in the presence of a sample with high NI content, total bleaching of MB was observed after 300 min irradiation. In addition, blue shifts in the visible MB band were observed during irradiation. The results can be explained by concomitant mineralization and N-demethylation of MB. N-demethylation led to the formation of azure dyes, which were detected in the reaction mixtures after irradiation. The photocatalytic activity can be attributed to the formation of NI triplets, which can react with MB by both Type (II) (via oxygen reactive species) and Type I (via electron transfer) mechanisms.