Application of ZnO-Fe3O4 nanocomposite on the removal of azo dye from aqueous solutions: Kinetics and equilibrium studies

In this study, zinc oxide was immobilized on magnetite nanoparticles by chemical method and it was used as an adsorbent to remove reactive black 5 (RB5) dye from aqueous solution. The removal efficiency of RB5 was studied as the function of adsorbent dosage, pH, initial RB5 concentration, H2O 2, and ionic strength (sodium carbonate, sodium bicarbonate, sodium sulfate, and sodium chloride). Removal efficiency of RB5 by ZnO-Fe 3O4 was greater than that by ZnO and Fe3O 4 in similar conditions. Maximum adsorption of ZnO-Fe 3O4 was obtained at neutral pH, and adsorption capacity was estimated to be 22.1 mg/g. Adsorption kinetic study revealed that the pseudo-second-order model better described the removal rate than the pseudo-first-order model. Adsorption isotherm was analyzed by both Langmuir and Freundlich equations, and results showed that it was better described by the Langmuir equation. The removal efficiency of RB5 was increased with increasing initial H2O2 concentrations from 2 to 5 mM but was decreased above 5 mM. The adsorption capacities of RB5 was increased in the presence of NaCl but was greatly decreased in the presence of bicarbonate, carbonate, and sulfate ion. Adsorption activity of RB5 by ZnO-Fe 3O4 composite was maintained even after five successive cycles, suggesting a promising adsorbent for wastewater-contaminated organic dyes. © Springer International Publishing Switzerland 2014