Enhanced catalytic degradation of aqueous doxycycline (DOX) in Mg-Fe-LDH@biochar composite-activated peroxymonosulfate system: Performances, degradation pathways, mechanisms and environmental implications

In this study, the Mg-Fe-LDH@biochar composite was firstly fabricated and applied for effectively activation peroxymonosulfate (PMS) for aqueous doxycycline (DOX) degradation. The physiochemical properties of the as-synthesized composite were thoroughly characterized. In the developed Mg-Fe-LDH@biochar/PMS system, the catalytic DOX degradations were evaluated under different conditions. Under the optimal condition (0.75 g/L catalyst loading, 0.75 g/L PMS dosage, pH = 7.0), about 88.76% DOX (35 mg/L) was removed within 120 mins. The results of quenching test and electron paramagnetic resonance (EPR) illustrated that the •OH, SO₄•^- and •O₂^– radicals all contributed to the DOX degradation in the Mg-Fe-LDH@biochar/PMS system, whereas the ¹O₂-based non-radical degradation played the dominant role in DOX removal. The developed system was almost not adversely affected by the high-strength anions and exhibited high DOX decomposition rates in a wide pH range from 3.0 to 9.0, indicating the great potential in the practical application. The satisfactory reusability of the composite catalyst was demonstrated in the recycling test, with the DOX removal efficiency slightly declined from 90.08 to 84.42% after five runs. Based on the generation of reactive oxidative species and the transformation intermediates identified by HPLC-MS, the possible degradation pathways and reaction mechanism of DOX degradation in Mg-Fe-LDH@biochar/PMS system were proposed.