Abstract
This work reports a comprehensive study of the adsorption characteristics of cadmium(II) on modified structures of carbon nanotubes (CNTs), carbon nanofibres (CNFs), activated carbon (AC), and fly ash (FA). The characterization was performed using field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA) and Brunauer–Emmett–Teller (BET) surface analysis. Several experimental parameters; adsorbent dosage, pH, and agitation speed and contact time, were investigated for their effects on the adsorption of cadmium(II) from water. The optimum conditions of 2h of contact time, pH7, 50mg adsorbent dosage and 150rpm rotational speed were observed. Models of first-order, second-order and pseudo-second-order were fitted to the experimental data, and pseudo-second-order kinetics were observed to describe the adsorption of cadmium(II) on these adsorbents. The adsorption behaviours of cadmium(II) were evaluated using the Freundlich and Langmuir isotherm models. The maximum adsorption capacities of the modified adsorbents were observed to be 2.02mg/g, 1.98mg/g, 1.22mg/g and 1.58mg/g, for CNTs, AC, CNFs and FA, as obtained from Langmuir isotherm models. It was determined that surface modification of the CNTs, CNFs, and AC enhanced their adsorption efficiency. The results obtained are promising for the use of these modified materials with respect to water purification applications.
Chemical modification of carbon nanotubes (CNTs). [Display omitted]
•Oxidation significantly improved the removal efficiencies of carbon nanotubes, carbon nanofibres and activated carbon.•The adsorption capacities of the adsorbents were predicted by the Freundlich and Langmuir isotherm models.•Fly ash (a waste material) can also be used as an adsorbent for the removal of Cd(II).