Kinetics of oxytetracycline sorption on magnetite nanoparticles

Iron oxide nanoparticles (nano-Fe) have been widely used in environmental remediation, including that of emerging contaminants, such as antibiotics. Magnetite nanoparticles (nano-Fe₃O₄) have been reported to form on the outer surface of nano-Fe and have the potential to be a good sorbent for certain antibiotics. This study reports, for the first time, the kinetics and thermodynamics of adsorption of a common tetracycline group antibiotic, oxytetracycline (OTC), on nano-Fe₃O₄. Batch sorption kinetics were evaluated by varying initial OTC concentration (0.25-2 mM), nano-Fe₃O₄ concentration (2.5-20 g L^-1), pH (3.8-7.6), temperature (5, 15, 35 °C), and ionic strength (0.01-0.5 M KCl) to derive thermodynamic and kinetic constants. Results show that OTC sorption kinetics is rapid and increases with increasing temperature. The derived thermodynamic constants suggest a surface chemical-controlled reaction that proceeds via an associative mechanism. Results indicate the potential of developing a nano-magnetite-based remediation system for tetracycline group of antibiotics.