Highly Efficient Degradation of Sulfamethoxazole Using Activating Peracetic Acid with CoFe2O4/CuO

Advanced oxidation processes (AOPs), especially AOPs that use transition metals as catalyst activated oxidants, are extremely effective in removing organic pollutants; they can completely degrade pollutants into CO2 and H2O. Thus, they have been widely studied in the field of water treatment. However, owing to the low catalytic efficiency and metal leakage, their applicability is currently limited. In this paper, the composite catalyst CoFe2O4/CuO containing spinel cobalt ferrite and copper oxide was successfully prepared by the chemical precipitation and sol-gel methods with two steps. The prepared CoFe2O4/CuO was characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), and its ability to remove sulfamethoxazole (SMX) with different AOPs was evaluated. Characterization results show that CoFe2O4 and CuO are well-complexed together, and the catalyst has good crystallinity. The effects of peracetic acid (PAA) concentration, catalyst dosage, common interfering substances (Cl-, HCO3-, SO42-, and HA) in water, and different radical scavengers on SMX removal were also investigated. The results show that CoFe2O4/CuO has the characteristics of both CoFe2O4 and CuO. Compared with CoFe2O4 or CuO alone, CoFe2O4/CuO exhibits an excellent activation performance for PAA. Under the optimal reaction conditions (catalyst dosage = 20 mg center dot L-1, c(PAA) = 200 mu mol center dot L-1, c(SMX) = 10 mu mol center dot L-1), the degradation rate of SMX reaches 92% within 90 s. The existence of Cu+/Cu2+ electron pairs can convert Co from the high valence to low valence state and accelerate the conversion of Co2+/Co3+, thereby improving the catalytic performance. An increase in the PAA concentration increases the removal efficiency of SMX; however, too high a concentration lowers removal efficiency. Compared to acidic or alkaline conditions, the CoFe2O4/CuO reaction system exhibits a better removal rate of SMX under neutral conditions. The common interfering substances in the environment have different effects on the CoFe2O4/CuO reaction system. Cl- promotes the degradation of SMX by producing Cl center dot, HCO3- and HA inhibit the removal of SMX because of their quenching effect on free radicals, and SO42- has no significant effect on the progress of the reaction. The XPS characterization results before and after the reaction show that the valence state of Co changes, indicating that Co is the main element involved in the activation of PAA. Radical quenching experiments demonstrate that the organic radical (R-O center dot) plays a dominant role in the removal of SMX. Further, the removal rate of SMX decreases after the catalyst is subjected to 3 recycle; nevertheless, it achieves a relatively rapid degradation of SMX (85% within 10 min).

Automated summary

The composite catalyst CoFe2O4/CuO was successfully prepared and showed excellent activation performance for peracetic acid (PAA) and removal efficiency of sulfamethoxazole (SMX) under neutral conditions. The valence state of Co played a crucial role in the activation of PAA, and organic radicals (R-O center dot) dominated the removal of SMX. The CoFe2O4/CuO catalyst achieved a relatively rapid degradation of SMX and was more effective than CoFe2O4 or CuO alone.