Competitive adsorption of Pb2+, Cu2+ and Cd2+ ions from aqueous solutions by multiwalled carbon nanotubes Original Research Article

The individual and competitive adsorption capacities of Pb2+, Cu2+ and Cd2+ by nitric acid treated multiwalled carbon nanotubes (CNTs) were studied. The maximum sorption capacities calculated by applying the Langmuir equation to single ion adsorption isotherms were 97.08 mg/g for Pb2+, 24.49 mg/g for Cu2+ and 10.86 mg/g for Cd2+ at an equilibrium concentration of 10 mg/l. The competitive adsorption studies showed that the affinity order of three metal ions adsorbed by CNTs is Pb2+>Cu2+>Cd2+. The Langmuir adsorption model can represent experimental data of Pb2+ and Cu2+ well, but does not provide a good fit for Cd2+ adsorption data. The effects of solution pH, ionic strength and CNT dosage on the competitive adsorption of Pb2+, Cu2+ and Cd2+ ions were investigated. The comparison of CNTs with other adsorbents suggests that CNTs have great potential applications in environmental protection regardless of their higher cost at present.