Removal of sudan dyes from aqueous solution by magnetic carbon nanotubes: Equilibrium, kinetic and thermodynamic studies

•Magnetic carbon nanotubes were synthesized and used for removing sudan dyes.•Adsorption equilibrium, kinetic and thermodynamic characteristics were studied.•Nanocomposite can be easily separated from water by external magnetic field.•Magnetic carbon nanotubes can be reused for more than 10 times.

In this study, magnetic carbon nanotubes (MCNTs) have been synthesized by hydrothermal synthesis of Fe3O4 nanoparticles onto carbon nanotubes, and characterized by Fourier transform infrared spectroscopy, transmission electron microscope and physical property measurement system. They were used as adsorbents for the removal of sudan I, sudan II, sudan III, and sudan IV from aqueous solution. The effects of experimental parameters on adsorption were fully studied. The results showed that 5 mg MCNTs can remove sudan dyes sufficiently from 20 mL aqueous solution within 60 min at pH in the range of 4–7. Moreover, the existence of NaCl favored the adsorption. The sorbents can be reused more than ten times with 2% acetic acid ethanol as desorption solution. The equilibrium, kinetic and thermodynamic studies were investigated. The resultant kinetic data were well described by the pseudo-second-order model. The Freundlich model fitted sudan dyes sorption isotherms better than the Langmuir model. The thermodynamic data calculated from the temperature dependent sorption isotherms demonstrated that sudan dyes sorption on the MCNTs was a spontaneous process.