Effectiveness of carbon nanotube–cobalt ferrite nanocomposites for the adsorption of rhodamine B from aqueous solutions

Abstract

The efficiency of adsorption of rhodamine B (RhB) from aqueous solution was investigated through a series of batch experiments by using cobalt ferrite nanoparticles (CoFe₂O₄), acid-functionalized multiwalled carbon nanotubes (MWCNT–COOH) and carbon nanotube–cobalt ferrite nanocomposites. The adsorption capacity was evaluated as a function of pH, contact time, adsorbent dose, dye concentration and temperature. The effect of increasing the percentage of MWCNT–COOH in the nanocomposites was also studied. The adsorption capacity was lowest in CoFe₂O₄ (5.165 mg g⁻¹) and highest with MWCNT–COOH (42.68 mg g⁻¹). For the nanocomposites, the adsorption capacity was enhanced with an increase in the amount of MWCNT–COOH. The optimum pH for adsorption was observed at 7 at which equilibrium was reached after 360 min. The kinetics of adsorption was fitted to the pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion models. The results showed that the pseudo-second order model best described the data as reflected in the lowest value for the sum of squared residuals. Among the various adsorption isotherms tested, the Langmuir isotherm provided the best fit to the equilibrium data. The thermodynamic parameters, ΔH°, ΔS° and ΔG°, were obtained over a temperature range of 20–45 °C. Adsorption was spontaneous, endothermic and entropy-driven, except for one of the doped nanocomposites for which adsorption was exothermic. A good desorption of RhB from the loaded adsorbents was obtained by using either acetone or ethanol with a desorption efficiency in the range of 62–95%.