Advanced technology for photocatalytic degradation of thiophanate-methyl: Degradation pathways, DFT calculations and embryotoxic potential

This study focuses on establishing an efficient two-step technology, which includes: (1) consecutive adsorption-desorption, using cellulose-based membranes, bCells, and (2) photocatalytic degradation of the fungicide thiophanate-methyl (TPM), using synthesized Ag-P25 and Ce-P25 catalysts. The catalysts, obtained by controlled deposition of Ag2O/Ag and CeO2 onto P25 TiO2 carrier (Degussa), were characterized using ATR-FTIR, XRPD, BET, FESEM, HRTEM, HAADF-EDS and UV-DRS techniques. In order to establish a feasible purification technology, preconcentration of TPM was performed by adsorption, achieving 75.5 and 92.9 mg/g of TPM removal using bCell-EpL and bCell-EpL-TA membranes, respectively, followed by efficient desorption (> 95%) that provided acceptable TPM concentration for photodegradation experiments. Under optimal conditions (0.07 g/L of both catalysts), complete degradation of TPM (5 mg/L) occurred within 2 h, compared to 4 h for the base TiO2 P25. Measurements of quantum yield and the results of HPLC-MS analysis, alongside DFT calculation, assisted in understanding the TPM degradation pathways. New degradation products were detected and proposed from HPLC-MS analysis. Embryotoxic assays, performed on zebrafish (Danio rerio), applied to estimate the toxicity evolution of time-dependent generated TPM degradation products, showed low embryotoxic potential. Chemical oxygen demand (26 mg O-2/L) confirmed low ecotoxicological pressure of effluent water.