Multiwall carbon nanotubes decorated on calcined eggshell waste as a novel nano-sorbent: Application for anionic dye Congo red removal

In this study multiwall carbon nanotubes (MWCNTs) was decorated on calcined eggshell (CES) to obtain a novel and low cost nano-sorbent for removal purposes. The MWCNTs/CES was prepared by a simple hydrothermal method and was characterized by X-ray powder diffraction, scanning electron microscopy and zeta potential measurements. Removal efficiency of the nano-sorbent was evaluated using anionic Congo red dye as a sample pollutant. The experiments were carried out in a batch system to optimize operation variables such as adsorbent dosage, Congo red concentration, solution pH and contact time. Langmuir, Freundlich, Tempkin and Dubinin-Raduskovich adsorption isotherm models were studied and the experimental results were addressed by Langmuir isotherm model. The maximum adsorption capacity was 136.99 mg g−1, indicating high potential of MWCNTs/CES in the adsorption of Congo red. The adsorption kinetics was studied with the pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models. The thermodynamic parameters indicated that the adsorption of Congo red on the MWCNTs/CES was an exothermic and spontaneous process. Based on experimental results, MWCNTs/CES exhibit improved adsorption performance in comparison with non-treated eggshell (NES) and CES.