Removal of lead from water by amino modified multi-walled carbon nanotubes

Pristine, oxidized, ethylenediamine, diethylenetriamine and triethylenetetramine modified multi-walled carbon nanotubes (raw-MWCNT, o-MWCNT, e-MWCNT, d-MWCNT and t-MWCNT, respectively) were employed as adsorbents in order to study individual and competitive adsorption characteristics of Pb2+ and Cd2+ ions. In batch tests, the influence of functionalization, pH, contact time, initial metal ion concentration and temperature, on the ion adsorption on MWCNTs was studied. Adsorption of Pb2+ and Cd2+ on MWCNTs strongly depends on pH. Time dependent Pb2+ adsorption and adsorption data can be described by pseudo-second-order kinetic model and by Langmuir isotherm, respectively. The maximum adsorption capacities of Pb2+ and Cd2+ on d-MWCNT were 58.26 and 31.45 mg g−1 at 45 °C, respectively. The competitive adsorption studies showed that the metal order affinity with respect to d-MWCNT and e-MWCNT is Pb2+ > Cd2+. Thermodynamic parameters showed that the adsorption of Pb2+ on appropriate nanotubes was spontaneous and endothermic. According to desorption studies, regenerated MWCNT can be reused over five times with minimal loss of adsorption capacity. Comparison of obtained results with capacities and affinities of other adsorbents indicates suitability of amino-functionalized MWCNT application for removal of Pb2+ and Cd2+ from aqueous solution.

► The sorption of Pb2+ on oxidized and amino-functionalized MWCNTs follow the Langmuir sorption isotherm.
► Pb2+ adsorption by MWCNTs is dependent on the number of amino groups in alkyl chains, pH and temperature.
► The sorption of Pb2+ on MWCNTs is a rather complex and spontaneous process.
► Mechanism of sorption includes both physisorption and chemisorption mechanisms.
► MWCNTs can be reused over five times with minimal loss of adsorption capacity.