Cerium-modified iron oxides applied as catalysts in the heterogeneous Fenton system for degradation of cephalexin

Abstract

The effect of incorporation of different amounts of cerium on iron oxides and different heat treatment temperatures was evaluated for the degradation of cephalexin (CEX) using heterogeneous Fenton and photo-Fenton processes. The materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), specific area (BET), and zeta potential (ZP). The conversion of magnetite to maghemite was observed when a 140 °C thermal treatment was applied. The insertion of cerium resulted in a loss of the uniform spherical shape of the particles. The material containing the lowest amount of cerium (0.5% w/w) presented an increase in the specific area from 91.2 to 171.6 m2 g−1 relative to the pure iron oxide, while with 2% (w/w) a decrease to 99.2 m2 g−1 was observed for the materials treated at 70 °C. The same behavior was observed for materials treated at 140 °C, however, with smaller areas. At pH 6.0, a low catalytic activity was observed contrasting to the high consumption of H2O2, suggesting its catalytic decomposition into water and oxygen. This was confirmed by the very low production of HO• in the degradation system. On the other hand, the high production of HO• was observed at pH 3.5, which was chosen as a working pH. The material treated at 140 °C and containing 1% Ce (w/w) was the highlight, promoting degradation of 0.052 mg of CEX per m2 area of the catalyst after 150 min using 1.0 mmol L−1 of H2O2. The CEX intermediates identified indicated hydroxylation as the major route of degradation.