Adsorption of ciprofloxacin in water using Fe₃O₄ nanoparticles formed at low temperature and high reactant concentrations in a rotating packed bed with co-precipitation

A rotating packed bed was used to form Fe₃O₄ nanoparticles at 25 °C with a rotational speed of 1800 rpm, flow rates of 0.5 L/min, and FeCl₂, FeCl₃, and NaOH concentrations of 0.15 mol/L, 0.3 mol/L, and 1.2 mol/L, respectively. The as-formed Fe₃O₄ nanoparticles had an average diameter of 9 nm, a BET specific surface area of 140 m²/g, and a saturation magnetization of 68 emu/g. The effectiveness of the as-formed Fe₃O₄ nanoparticles in adsorbing ciprofloxacin in water was evaluated. Increasing the Fe₃O₄ dosage from 1 to 2.5 g/L reduced the equilibrium adsorption capacity of the as-formed Fe₃O₄ nanoparticles but increased the efficiency of removal of ciprofloxacin. The equilibrium adsorption capacity of the as-formed Fe₃O₄ nanoparticles increased with the initial concentration of ciprofloxacin at all pH values. The equilibrium adsorption capacity of the as-formed Fe₃O₄ nanoparticles was highest at pH 7 with low initial concentrations of ciprofloxacin (10–30 mg/L). However, with high initial concentrations of ciprofloxacin (40–100 mg/L), the equilibrium adsorption capacity of the as-formed Fe₃O₄ nanoparticles was highest at pH 8. The adsorption of ciprofloxacin onto the as-formed Fe₃O₄ nanoparticles was more consistent with the Freundlich model than with the Langmuir model at all pH values. At pH 8, an initial concentration of ciprofloxacin of 100 mg/L, and an Fe₃O₄ dosage of 2.5 g/L, the equilibrium adsorption capacity of the as-formed Fe₃O₄ nanoparticles was around 24 mg/g. The results demonstrate that the as-formed Fe₃O₄ nanoparticles are an efficient adsorbent of ciprofloxacin from water.