Synthesis of Iron and Cobalt Oxide Nanocatalysts with Various Molar Ratios and Their Application for Antibiotic Removal from Aqueous Solutions

With the growing concern over the environmental and health risks posed by antibiotic contamination in water systems, this study evaluates the potential of iron and cobalt oxide nanocatalysts with varying molar ratios, synthesized using the co-precipitation method, for the efficient removal of antibiotics from aqueous solutions. The optimal nanocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM), revealing high surface area and well-defined crystalline structures, enhancing catalytic activity. Kinetic analysis showed that Co_0.5Fe_0.5Fe₂O₄ exhibited the best performance, with a Michaelis–Menten constant (K_m) of 0.0366 mM and maximum reaction velocity (V_max) of 1.10 × 10⁻⁴ µM.min⁻¹. The reaction rate constants, k₁ = 6.12 × 10³ M⁻¹ S⁻¹ and k₃ = 3.64 × 10² M⁻¹ S⁻¹) and turnover number (kcat = 5.213 × 10⁻¹ S⁻¹) confirmed its superior catalytic properties. Antibiotic removal was further evaluated through batch adsorption experiments, with adsorption kinetics and isotherms studied to determine optimal conditions for antibiotic removal. The Co_0.5Fe_0.5Fe₂O₄ nanocatalyst exhibited superior peroxidase-like activity compared to the other nanocatalysts when tested with the common chromogenic substrate 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) diammonium salt. Based on this enzymatic activity, a colorimetric sensing platform was designed for H₂O₂ detection. Additionally, the Co_0.5Fe_0.5Fe₂O₄ nanocatalyst exhibited excellent adsorption capacity for various antibiotics, including ciprofloxacin, azithromycin, levofloxacin, moxifloxacin, amoxicillin, and metronidazole, with 100% removal efficiency under optimal conditions. This study highlights the potential of enzyme-mimicking nanostructures as efficient adsorbents for the removal of antibiotics from aqueous solutions, addressing significant environmental challenges posed by antibiotic contamination.