Removal of reactive red-120 and 4-(2-pyridylazo) resorcinol from aqueous samples by Fe3O4 magnetic nanoparticles using ionic liquid as modifier

The nanoparticles of Fe₃O₄ as well as the binary nanoparticles of ionic liquid and Fe₃O₄ (IL-Fe₃O₄) were synthesized for removal of reactive red 120 (RR-120) and 4-(2-pyridylazo) resorcinol (PAR) as model azo dyes from aqueous solutions. The mean size and the surface morphology of the nanoparticles were characterized by TEM, DLS, XRD, FTIR and TGA techniques. Adsorption of RR-120 and PAR was studied in a batch reactor at different experimental conditions such as nanoparticle dosage, dye concentration, pH of the solution, ionic strength, and contact time. Experimental results indicated that the IL-Fe₃O₄ nanoparticles had removed more than 98% of both dyes under the optimum operational conditions of a dosage of 60 mg, a pH of 2.5, and a contact time of 2 min when initial dyes concentrations of 10-200 mg L⁻¹ were used. The maximum adsorption capacity of IL-Fe₃O₄ was 166.67 and 49.26 mg g⁻¹ for RR-120 and PAR, respectively. The isotherm experiments revealed that the Langmuir model attained better fits to the equilibrium data than the Freundlich model. The Langmuir adsorption constants were 5.99 and 3.62 L mg⁻¹ for adsorptions of RR-120 and PAR, respectively. Both adsorption processes were endothermic and dyes could be desorbed from IL-Fe₃O₄ by using a mixed NaCl-acetone solution and adsorbent was reusable.