Synthesis and characterization of the magnetic chitosan/zinc oxide nanocomposite: an efficient magnetic adsorbent for removal of harmful aromatic micropollutants from wastewater

Abstract

In this work, a magnetic chitosan/zinc oxide nanocomposite (CS/ZnO-Fe3O4) was fabricated for efficient adsorptive removal of harmful aromatic micropollutants, including Cephalexin (CFX) antibiotic and Eosin B (EB) dye from wastewater samples. To maximize the adsorption efficiency of the CS/ZnO-Fe3O4, the adsorption process was first modeled and statistically optimized by using the response surface methodology based on central composite design (RSM-CCD). The results demonstrated that the maximum removal efficiency of the adsorbent for CFX and EB was 98.87% and 99.08%, respectively. Also, the adsorption isotherms, kinetics, and thermodynamics were also studied in detail under the optimum conditions. The results indicated that the adsorption equilibrium data was fit well with the Langmuir isotherm model, which indicated monolayer adsorption via chemisorption process. The Langmuir maximum adsorption capacity (Qmax) was 81.38 mg g−1 and 144.4 mg g−1 for CFX and EB, respectively. The adsorption kinetic was followed by the pseudo-second-order kinetic model, and the thermodynamic studies showed that the adsorption process was endothermic and spontaneous, as well as that adsorption entropy was also increased during the process. Also, the main adsorption mechanism was considered to be based on H-bonding, n-π, and electrostatic interactions. The regeneration experiments indicated that the spent adsorbent was easily regenerated by NaOH solution (0.1 mol L−1) and reused for subsequent cycles without a significant decrease in its performance, so that removal efficiency remained about 90% at the fourth cycle. Overall, the results indicated that CS/ZnO-Fe3O4 could be used as a promising adsorbent for the efficient removal of aromatic micropollutants from wastewater.