Abstract:

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·L⁻¹, c(PAA) = 200 μmol·L⁻¹, c(SMX) = 10 μmol·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•, 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•) 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).

Key words: Spinel cobalt ferrite, Copper oxide, Advanced oxidation, Sulfamethoxazole, Peracetic acid, Organic radical