β-Cyclodextrin conjugated graphene oxide: A regenerative adsorbent for cadmium and methylene blue

Abstract

This study describes an eco-friendly approach for the synthesis of β-cyclodextrin functionalized graphene oxide (βCD-GO) and its evaluation as adsorbent for removal of cadmium (Cd2+) and methylene blue (MB) from aqueous medium. Owing to a βCD mass loading of ~15.3% on GO sheets, the as-prepared nanocomposite displayed superior thermal stability. Moreover, in spite of its fairly low Brunauer–Emmett–Teller specific surface area of 14.24 m2 g−1, the βCD-GO composite demonstrated significantly high adsorption capacity toward both Cd2+ (117.07 mg g−1) and MB (323.98 mg g−1). The equilibrium data presented excellent fit to the Langmuir isotherm, implying monolayer adsorption of Cd2+ and MB onto βCD-GO. The molecular mechanisms involved in the uptake of these pollutants were ion-exchange, electrostatic, hydrophobic and π-π interactions. Further, the uptake of Cd2+ and MB on βCD-GO followed the pseudo-second order kinetics, and the rate of Cd2+ removal was faster than that of MB. Additionally, thermodynamic analysis revealed a spontaneous and endothermic nature of the adsorption process. Most importantly, the βCD-GO composite did not show any significant drop in adsorption efficiency even after three adsorption-desorption cycles. Overall, our preliminary findings suggest that βCD-GO merits further consideration for removal of dyes and heavy metals from wastewaters.