Degradation of formetanate hydrochloride by combined advanced oxidation processes

Formetanate hydrochloride (FMT) is an insecticide–acaricide widely used in agriculture. The sonolytic, photocatalytic and sonophotocatalytic degradations of FMT were studied in the presence of homogeneous (Fe3+) and heterogeneous (TiO2) photocatalysts using 213 kHz ultrasound. The degradation rates obtained for sonolysis, photocatalysis and sonophotocatalysis using TiO2 (1 g/L) were about 5.1, 32.6 and 28.1 × 10−7 M min−1, respectively. The combination of sonolysis with TiO2 photocatalysis showed a negative effect of combining two processes with a synergy index of 0.7. The degradation rates obtained for US + Fe3+, UV + Fe3+ and US + UV + Fe3+ are 14.1, 10.1 and 40.9 × 10−7 M min−1, respectively. Unlike TiO2, the Fe3+ addition during the sonophotocatalysis process was found to be beneficial with a synergy index of 1.6. The total organic carbon analysis showed that the mineralization process was synergistic by combining the two processes in the presence of Fe3+. Further studies with electrospray mass spectrometry analysis revealed the formation of mono and dihydroxylated derivatives of FMT during sonolysis.