Hierarchically-structured Co–CuBi₂O₄ and Cu–CuBi₂O₄ for sulfanilamide removal via peroxymonosulfate activation

Herein, we report the syntheses of Co–CuBi₂O₄ and Cu–CuBi₂O₄ composites using a facile hydrothermal synthesis method for sulfanilamide (SA) removal via peroxymonosulfate (PMS) activation. The composites were characterized using FESEM, XRD and porosimeter and the results indicated that they were hierarchically-structured with several phases. The performance of the composites as catalysts for PMS activation was evaluated with respect to different initial pHs (4.5–9.5), catalyst loadings (L, 0.10–0.60 g L⁻¹) and Oxone^® dosages (D, 0.03–0.30 g L⁻¹) and the empirical relationship between the k_app, L and D were obtained. The results also indicated that Cl⁻ and humic acid exerted negative effect on SA degradation due to the intrinsic competition between Cl⁻ and humic acid with SA for SO₄[rad]⁻ oxidation. The principal reactive radical in the Co–CuBi₂O₄/PMS and Cu–CuBi₂O₄/PMS systems was identified to be SO₄[rad]⁻. A simple method to calculate the normalized steady-state concentrations of SO₄[rad]⁻ ([SO₄[rad]⁻]_Nss) and [rad]OH ([[rad]OH]_Nss) in the heterogeneous catalyst/PMS system is proposed. The results indicated that the generated SO₄[rad]⁻ and [rad]OH in the Co–CuBi₂O₄/PMS system were utilized at least five times more efficiently than the Cu–CuBi₂O₄/PMS system. The proposed method for calculating [SO₄[rad]⁻]_Nss and [[rad]OH]_Nss can be potentially employed to characterize and compare the intrinsic catalytic activity of various heterogeneous catalyst/PMS systems in future studies.