Remarkable simultaneous degradation of cephalexin and amoxicillin employing magnetic nano-catalyst supported on bentonite by heterogeneous photo-Fenton

Abstract

In the present study, the heterogeneous catalysts were synthesized using a facile, economical and environmentally friendly method supported on the natural mineral bentonite to degrade amoxicillin (AMX) and cephalexin (CLX) in the aqueous solutions by employing the photo-Fenton process. The characterization tests including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDAX), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS) and vibrating sample magnetometer (VSM) were evaluated to distinguish the physical and chemical properties of the nanocomposites. The adsorption capacity and catalytic performance of the prepared samples for the removal of AMX were investigated in order to compare the presented catalysts, in addition to the structural analysis. Among the fabricated samples, the magnetic nano-catalyst derived from two different sources of iron (ferrous sulfate and ferric nitrate) named FSF-Be was selected as the appropriate catalyst due to its high efficiency for the simultaneous degradation of CLX and AMX. Response surface method (RSM-central composite design (CCD)) was also applied to determine the effect of the operating conditions encompassing pH, initial concentration of contaminants, dosage of catalyst and hydrogen peroxide concentration for the degradation of CLX and AMX, simultaneously. The quadratic mathematical models were developed with high correlation coefficient (0.9454 and 0.9564) for the removal efficiency of AMX and CLX, respectively. Therefore, the maximum degradation efficiency of CLX and AMX was obtained to be about 96.36% and 81.61%, respectively, at the optimal conditions (pH of 3, H₂O₂ concentration of 12 mM, catalyst dosage of 0.24 g/L and initial concentration of 23 mg/L) in half hour. The ozonation and the combined photo-Fenton/ozone process were investigated. The mineralization analysis illustrated that the photo-Fenton process was able to remove TOC by 73.35%, while only 2.44% of TOC removal was reached by ozonation. The degradation efficiency of CLX and AMX in the photo-Fenton/ozone system within 15 min of reaction was measured as 87.69% and 70.02%, respectively, and 61.9% mineralization was achieved in this system. However, the results showed that the photo-Fenton using FSF-Be was more efficient. The regeneration and reusability of the prepared nanocomposite was also carried out by five consecutive cycles which showed an acceptable performance in the industrial applications. The achievements demonstrated that the removal efficiency of CLX and AMX decreased about 24 and 18% after fifth cycle.