Innovative hollow fiber membranes decorated with cobalt-doped Mn3O4: Sustainable solution for effective tetracycline removal from wastewater

Tetracycline (TC) contamination in aquatic environments poses ecological and public health risks due to its persistence and role in antibiotic resistance. Although manganese oxides can oxidatively degrade TC, their instability due to Mn loss limits practical application. In this study, we developed an innovative oxygen-based membrane reactor decorated with cobalt-doped Mn3O4 to enhance TC degradation efficiency and material stability. Comprehensive characterization confirmed uniform cobalt doping and structural modifications of Mn3O4. Under optimal conditions (pH 7.0 and 0.06 MPa oxygen pressure), the cobalt-doped reactor achieved a TC removal efficiency of 92.9 % at a concentration of 15 mg/L, following pseudo-first-order kinetics (kobs = 0.1962 h-1), outperforming the undoped reactor. Multi-cycle stability tests showed the manganese loss rate of the cobaltdoped system was one-sixth that of the undoped system and retained > 85 % TC degradation efficiency over 10 cycles. Mechanistic studies identified superoxide radicals (center dot O2-) as the important reactive species, confirmed by electron paramagnetic resonance and quenching experiments. Mass spectrometry analysis further showed that cobalt doping redirects TC degradation pathways, reducing toxicity of transformation products and increasing mineralization to 25 % (vs. 12 % in the control). We propose that cobalt mitigates manganese loss during the reaction, enhancing the stability and reactivity of Mn3O4 on hollow fibers. This study offers an effective and sustainable approach for antibiotic degradation from wastewater.