Magnetic activated carbon for improving the removal of antibiotics by heterogeneous solar photo-Fenton at circumneutral pH

Abstract

A pulp and paper industry waste-based powder activated carbon combined with Fe nanoparticles (PAC-Fe) was obtained through a simple one-step synthesis for application in heterogeneous photo-Fenton treatment. PAC-Fe was characterized and applied for the removal of sulfamethoxazole (SMX) and trimethoprim (TMP) from water at circumneutral pH and under simulated solar irradiation. The contribution of the different processes involved in the overall removal of the contaminants (adsorption, Fenton and photo-Fenton) was evaluated. Degradation in both Fenton and photo-Fenton processes were fitted to the pseudo first-order and BMG kinetic models. Photo-Fenton resulted in the complete removal of SMX and TMP from water within 20 min. In contrast, in the absence of the material (H₂O₂ + UV), only 49 % and 59 % of SMX and TMP were removed, respectively, after the same time. The synthesis procedure allowed to obtain a PAC-Fe with a satisfactory saturation magnetization (21.14 emu g^-1) and stability without any detectable leaching of iron during its application. The magnetic properties of PAC-Fe allowed for easy separation from the treated water, with degradation percentage above 50 % and 70 %, for SMX and TMP, respectively, after five consecutive cycles. The removal mechanisms involved a combination of different processes, with heterogeneous photo-Fenton and Fenton proving to be the most significant, followed by adsorption and photo-assisted peroxidation to a smaller extent. Eight transformation products of SMX were identified and fourteen for TMP, which were formed mainly by hydroxylation. The results achieved at pH close to neutral show that the PAC-Fe can be relevant for application in wastewater treatment.