Adsorption of Reactive Red 2 from aqueous solutions using Fe₃O₄ nanoparticles prepared by co-precipitation in a rotating packed bed

A rotating packed bed (RPB) that was operated at a rotating speed of 1800 rpm with liquid flow rates of 0.5 L/min was used to prepare Fe₃O₄ nanoparticles (RPB-Fe₃O₄). The RPB-Fe₃O₄ had a smaller average size and a narrower size distribution than the Fe₃O₄ that was obtained from Aldrich, and so had a greater capacity to adsorb RR2. The effects of pH, Fe₃O₄ dosage, initial RR2 concentration, and temperature on the adsorption of RR2 were examined experimentally using RPB-Fe₃O₄. A thermodynamic study revealed that the adsorption process was spontaneous and exothermic. The adsorption behavior was more consistent with the Langmuir model than with the Freundlich model, and the maximum adsorption capacity was 97.8 mg/g. At pH 3, 25 °C, an Fe₃O₄ dosage of 0.30 g/L, and an initial RR2 concentration of 10 mg/L, RPB-Fe₃O₄ effectively adsorbed RR2 with a removal efficiency of approximately 95% in 10 min. These promising results clearly reveal the potential of RPB-Fe₃O₄ for use in the effective removal of dyes from aqueous solutions.