Enhanced removal of oxytetracycline from aquatic solution using MnOx@Fe3O4 bimetallic nanoparticle coated powdered activated carbon: synergism of adsorption and chemical autocatalytic oxidation processes

Abstract

MnO_x@Fe₃O₄ bimetallic nanoparticle coated powdered activated carbon (MnO_x@Fe₃O₄-PAC) was successfully synthesized by a two-step chemical co-precipitation method. A comprehensive analysis of MnO_x@Fe₃O₄-PAC's surface profile, crystal structure, and element composition was conducted to investigate its structural characteristics and oxytetracycline (OTC) removal mechanism. It was observed that MnO_x@Fe₃O₄ bimetallic nanoparticles were distributed on surfaces, pores, and channels of PAC. The removal efficiency of OTC reached its optimum (76.8%, OTC₀ = 100 mg L⁻¹) at pH 3. Inorganic ions and humic acid (HA) had a limited impact on the adsorption process of OTC on MnO_x@Fe₃O₄-PAC. The Freundlich isotherm and Elovich kinetic models could accurately describe the adsorption process of OTC on MnO_x@Fe₃O₄-PAC. According to thermodynamic analysis, the adsorption process was dominated by chemisorption/surface complexation, which was a spontaneous endothermic reaction (ΔH = 51.62 kJ mol⁻¹). The magnetically separable MnO_x@Fe₃O₄-PAC had superior adsorption and oxidation capabilities for OTC removal from aqueous solution, and provided an alternative to PAC in the treatment of antibiotic wastewater. Furthermore, the self-catalytic reaction extended the service life of MnO_x@Fe₃O₄-PAC without the additional use of oxidants, which made MnO_x@Fe₃O₄-PAC a green, efficient, and recyclable composite for potentially practical applications.