2,4,6-Triphenylthiapyrylium cation as homogeneous solar photocatalyst

Triphenylthiapyrylium cation (TPTP+) has been studied as solar photocatalyst and compared with other organic dyes (triphenylpyrylium, acridine yellow, methylene blue, rosolic acid and alcian blue) using ferulic acid as model pollutant. The best results were obtained with TPTP+ (ca. 85% elimination), although important photodegradation was also achieved with acridine yellow and triphenylpyrylium. Concentrations of TPTP+ in the range 10–30 mg/l had only a moderate effect on the reaction rate; on the other hand, the concentration of ferulic acid had a remarkable influence on the pseudo-first order rate constant, for which higher values were measured in diluted solutions of the substrate. The results from photophysical studies based on fluorescence quenching and laser flash photolysis were compatible with an electron transfer mechanism. Although the process is thermodynamically feasible from the first singlet excited state, triplet involvement cannot be ruled out at the present stage. The studies were extended to detoxification of Sevnol, a commercial pesticide, based on carbaryl as active ingredient. Total removal of carbaryl was accomplished, although mineralization was only 30%. However, activated sludge respirometry showed that elimination of carbaryl resulted in a complete detoxification of the solution and a significant enhancement of the biodegradability.