Synthesis and application of magnetic iron oxide nanoparticles on the removal of Reactive Black 5: Reaction mechanism, temperature and pH effects.

The water pollution created by the textiles industry contains a large amount of azo dyes, such as Reactive Black 5 (RB5), which are recalcitrant in the environment. The feasibility and major mechanism of iron oxide nanoparticles (IONPs) in the removal of RB5 were investigated in this study. Our synthesized IONPs (17 nm) had a high surface area of 77.1 m2/g, possessed a magnetite crystal structure, and had a pHzpc of 5.56. The main removal mechanism of RB5 with IONPs was adsorption by electrostatic attraction. The adsorption isotherm of RB5 on IONPs fitted the Langmuir and Freundlich equations well. The removal efficiency of RB5 with IONPs decreased with increasing the initial RB5 concentrations but increased with the increase of NP dosage and temperature. The average adsorption enthalpy was 24 kJ/mol. As the pH increased, the removal efficiency of IONPs decreased due to electrostatic repulsion. The high magnetic property of our iron oxide NPs results in the NPs being easily recyclable from water: the NPs retained a 90% removal efficiency after ten cycles, suggesting their great potential for use in pollution treatments.