Removal of Cd2+ and Hg2+ from aqueous solutions by adsorption onto nitrogen-functionalized carbon nanotubes

The efficiency of nitrogen-functionalized multiwalled carbon nanotubes (MWCNT-ttpy) for the removal of Cd2+ and Hg2+ from aqueous solutions was investigated and compared with their uptake on acid-functionalized multiwalled carbon nanotubes (MWCNT-COOH). Batch adsorption experiments investigating the influence of pH, contact time, adsorbent dose, metal ion concentration and adsorbate temperature were performed to determine the best sorption conditions for their removal. The experimental data obtained for both adsorbates were best described by the pseudo-second-order model, indicating a bimolecular chemical interaction between active sites on the adsorbents and the metal ion species. The Langmuir and Sips isotherm models best described the equilibrium data obtained for both sorbates. For Cd2+, an uptake (q(m)) of 10.41 mg g(-1) for MWCNT-COOH was achieved and 41.51 mg g(-1) for MWCNT-ttpy. An increase in Hg2+ uptake was also obtained for MWCNT-ttpy of 36.13 mg g(-1) compared with 33.89 mg g(-1) for MWCNT-COOH. Hence, MWCNT-ttpy proved to be more effective towards the removal of both adsorbates, relative to MWCNT-COOH. Desorption experiments conducted by using HCl as eluent afforded excellent recovery of sorbates and regeneration of sorbents, thus, increasing the chances of reutilization of sorbents. Hence, the application of MWCNT-ttpy as a potential sorbent for effluent and wastewater treatment is feasible and should be further explored for water pollution control.