Adsorption of anionic dye Direct Red 23 onto magnetic multi-walled carbon nanotubes-Fe3C nanocomposite: Kinetics, equilibrium and thermodynamics

Magnetic multi-walled carbon nanotubes-Fe3C nanocomposite (MMWCNTs-ICN) was synthesized by chemical vapor deposition (CVD) process and was used as an adsorbent for the removal of anionic dye Direct Red 23 (DR23) from aqueous solution. The effects of various parameters such as initial DR23 concentration (9–54 mg L−1), pH solution (3.7–11.1) and temperature (20–60 °C) were investigated. The adsorbent was characterized with using several methods such as XRD, HRTEM, EDX, FTIR, BET and particle size distribution by laser diffraction. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with the Freundlich model. Kinetic adsorption data were analysed using the Lagergren pseudo-first-order kinetic model, the pseudo-second-order model and the intraparticle diffusion model. The regression results showed that the adsorption kinetics was more accurately represented by pseudo-second-order model. Thermodynamics parameters, ΔG°, ΔH° and ΔS°, were calculated. All ΔG° values were negative. The values of enthalpy (ΔH°) and entropy (ΔS°) were 12.6 kJ mol−1 and 61.7 J mol−1 K−1, respectively, indicating that adsorption of DR23 onto MMWCNTs-ICN was spontaneous and endothermic in nature.

► Magnetic nanocomposite was used as an adsorbent for the removal of Direct Red 23.
► Nanocomposite can be easily separated from the water by external magnetic field.
► Adsorption of Direct Red 23 onto nanocomposite was favored at low pH.
► Adsorption of Direct Red 23 onto nanocomposite was endothermic in nature.