Abatement of methidathion and carbaryl from aqueous solutions using organic photocatalysts

Degradation of two pesticides, methidathion and carbaryl, has been studied using organic photocatalysts, namely triphenylpyrylium (TPP+), triphenylthiapyrylium (TPTP+) and acridine yellow G (AYG). Experiments carried out using a solar simulator showed that methidathion was more easily photo-oxidised than carbaryl, in all cases. TPP+ and TPTP+ exhibited a better performance than AYG. Detoxification of solutions was related with the primary abatement of the pesticides, as indicated by respirometry studies. Major reaction intermediates were identified by GC–MS, indicating early removal of the carbamate or phosphorated moiety. Photophysical experiments (fluorescence and laser flash photolysis) proved the involvement of an electron-transfer mechanism, most probably from a ground state complex formed between substrate and catalyst.