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

MnOx@Fe3O4 bimetallic nanoparticle coated powdered activated carbon (MnOx@Fe3O4-PAC) was successfully synthesized by a two-step chemical co-precipitation method. A comprehensive analysis of MnOx@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 MnOx@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 MnOx@Fe3O4-PAC. The Freundlich isotherm and Elovich kinetic models could accurately describe the adsorption process of OTC on MnOx@Fe3O4-PAC. According to thermodynamic analysis, the adsorption process was dominated by chemisorption/surface complexation, which was a spontaneous endothermic reaction (Delta H = 51.62 kJ mol(-1)). The magnetically separable MnOx@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 MnOx@Fe3O4-PAC without the additional use of oxidants, which made MnOx@Fe3O4-PAC a green, efficient, and recyclable composite for potentially practical applications.