Detoxification of the herbicide propanil by means of Fenton process and TiO2-photocatalysis

An optimization study was carried out from the detoxification of waters contaminated by the herbicide propanil at the maximum concentrations found in different rice-growing cooperatives in Ecuador. Studies included the degradation, mineralization and detoxification of the herbicide through TiO 2 -photocatalysis using two different catalysts, P25 Evonik and ECT1023t (a catalyst prepared by our research group), and through the Fenton reaction. It was determined that pH (studied between 3 and 7) had a determining effect on mineralization, especially with P25, but not on degradation. Adsorption and FTIR studies revealed a strong interaction of propanil with the catalyst surface, which conditioned the effectiveness of each of the studied catalysts. Propanil degradation with TiO 2 -photocatalysis occurred in 2 h, but complete detoxification required 12 h. In the case of the Fenton reaction, degradation was immediate but detoxification was not possible due to the inhibition of mineralization. With these results in mind, a study was made of a combination of the Fenton and TiO 2 -photocatalysis methods using ECT1023t, which resulted in a fourfold increase in the detoxification rate compared to that for heterogeneous photocatalysis. This result may be highly significant for the application of these techniques in processes in which the reaction time is of considerable importance.