Preconcentration and separation of toxic metal ions using modified multiwalled carbon nanotubes

Abstract

Heavy metals (HMs) are considered as serious inorganic pollutants which cannot be destroyed. The environmental exposure to the heavy metals is a well known risk factor for human health, animals, plants and life in aquatic system. In the present work, the analytical potential of multiwalled carbon nanotubes (MWCNTs) as an adsorbent for the preconcentration and separation of trace metals such as Cr3+ and Cr6+, Ni2+, Zn2+, Cd2+, Cu2+ and Pb2+ was evaluated. The adsorption of heavy metal ions was carried out in the present study includes copper, nickel and zinc. Heavy metals are one of the essential elements not only for mammals but also for plants and lower forms of organisms. It has various and many biological effects as an essential and as a toxic element. The adsorption of Cd2+ and Pb2+ from its aqueous solution through a MWCNTs impregnated with D2EHPA and bis-(2,4,4-trimethyl pentyl)phosphonic acid (Cyanex 272) carrier was investigated separately. The adsorption was found to be mainly due to the chemical interactions between the metal ions and functional group (P=O and C=O) presented in the impregnated MWCNTs. The present study reveals that maximum adsorption of cadmium and lead occurs at pH 4.5 with 500 mg of MWCNTs. The enrichment factor of Cd and Pb was found to be 40 and 30 for MWCNTs impregnated with D2EHPA and Cyanex272 separately. To study the effect of temperature on adsorption of mixed metals such as copper, nickel, lead, zinc and cadmium ions experiments were carried out in a themostat with mechanical shaking for 120 min. Experiments were performed at different temperature such as 298, 308 and 318 K. The results showed that, the quantitative adsorption of mixed metal ions, i.e., copper (II) and chromium (III) are 98% gt nickel (II) 97% gt lead (II) 96.5% gt cadmium (II) 96.2% gt zinc (II) 95 % was obtained at pH 5.0 ± 0.1. The negative values of and#916;G° for all the mixed metal ions are indicating the feasibility as well as the spontaneity of the adsorption process. newline newline newline