Halloysite Nanotubes-based Co-Mn Composite Oxides for Efficient Degradation of Tetracycline Hydrochloride via Peroxymonosulfate Activation

A facile deposition-precipitation method was adopted to fabricate a series of Co-Mn bimetallic composite oxides supported on reconstructed halloysite nanotubes (CMO/rHNTs), which were used for the efficient degradation of tetracycline hydrochloride (TCH) through peroxymonosulfate (PMS) activation. The metal loading capacity of rHNTs was found to be 1.8-fold higher than that of pristine HNTs. Benefitting from enhanced PMS activation facilitated by accelerated electron transfer between Co²⁺/Co³⁺ and Mn²⁺/Mn³⁺/Mn⁴⁺ redox couples, the C₁M₁O/rHNTs catalyst (with a Co/Mn molar ratio of 1: 1 and theoretical metal loads of 10 wt%) afforded the highest TCH degradation efficiency of 98% (rate constant k=0.152 min^-1) within 25 min at initial pH 4.47, 0.6 mg⸱mL^-1 PMS and 0.2 mg⸱mL^-1 catalyst. Mechanistic studies identified synergistic contributions from SO₄^•− and ¹O₂ pathways to TCH degradation. Based on the degradation intermediates detected by LC-MS, the major degradation pathways of TCH mediated by C₁M₁O/rHNTs were proposed. Moreover, the C₁M₁O/rHNTs nanocomposites exhibited excellent reusability, maintaining >90% TCH removal efficiency after five consecutive cycles. Of note, the catalyst demonstrated exceptional adaptability across a broad pH range (4.47-10.51) and strong resistance toward common interfering anions (NO₃⁻ Cl⁻, SO₄²⁻, H₂PO₄⁻).