Magnetic chitosan microspheres for the removal of methyl violet 2B from aqueous solutions

Abstract

This work aimed to evaluate the adsorption capacity of magnetic chitosan microspheres for the removal of methyl violet (MV) 2B dye. For this purpose, magnetite was prepared by chemical precipitation of iron salts in alkaline medium and incorporated to chitosan microspheres which were obtained by the suspension cross-linking technique. The influence of the experimental parameters, such as adsorbent dosage (0.05 to 0.25 g), stirring frequency (100 to 800 rpm), pH (2.0 to 12.0), initial dye concentration (30 to 90 mg L⁻¹), and contact time (5 to 480 min), as well as the equilibrium, kinetics and thermodynamics were also evaluated. Furthermore, five isotherm models and three kinetic models were tested to analyze the experimental data. The results evidenced that the equilibrium was better described by the Langmuir isotherm (q_m = 128.84 mg g⁻¹), although the statistical Fisher's test showed that other models could also be applied to describe the experimental results. Kinetics studies showed that the adsorption followed the pseudo-second order model with a significant difference between the tested models and that the adsorption process involves more than one sorption rate. It was also found that the adsorption of MV 2B dye onto magnetic chitosan microspheres was an exothermic (ΔH°_ads = −1.70 kJ mol⁻¹) and spontaneous (ΔG°_ads = −3.96 kJ mol⁻¹) process. Finally, it can be concluded that the magnetic chitosan microspheres constituted an efficient and inexpensive material for the removal of the MV 2B dye from aqueous solutions.

Graphical Abstract

Keywords:

• chitosan
• magnetite
• methyl violet 2B dye
• adsorption
• wastewater treatment

Acknowledgements

The authors would like to express their gratitude to the Infraestrutura Multiusuária do Laboratório de Magnetismo (IM-LAM) do Instituto de Física da Universidade Federal do Rio Grande do Sul (UFRGS) for the contribution with magnetic measurements and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES, Finance Code 001) for the scholarship.