Modified multiwall carbon nanotubes supported on graphite as a suitable solid nano-sorbent for selective separation and preconcentration of trace amounts of cadmium and lead ions

The present work demonstrates the application of modified multiwall carbon nanotubes (MMWCNTs) as a new selective and stable solid sorbent for the preconcentration of trace amounts of Cd(II) and Pb(II) ions in aqueous solutions. Multiwall carbon nanotubes are oxidized with concentrated HNO3 and modified with cyanuric-SH. Cd(II) and Pb(II) ions are quantitatively retained by the modified multiwall carbon nanotubes. The adsorbed ions are then eluted from the modified MWCNTs with 3.0 mL of 0.050 mol L-1 HNO3 solution and flame atomic absorption spectrometry (FAAS) is used to measure the eluted Cd(II) and Pb(II) ions. The linear range for the determination of Cd(II) is maintained between 0.3 and 2,000 ng mL(-1), while for Pb(II) it remains within 1.0-2,000 ng mL(-1) (in initial solution) with detection limits of 0.1 ng mL(-1) Cd(II) and 0.3 ng mL(-1) Pb(II) in the initial solutions. The enrichment factor of the modified solid phase is determined as 660 for Cd(II) and Pb(II) ions. The sorption capacity of the modified MWCNTs for Cd(II) and Pb(II) are 11.2 and 18.6 mg g(-1), respectively. The relative standard deviations for separation and measurement of the ions in ten 100-mL solutions containing 50 ng mL(-1) Cd(II) and Pb(II) and in 500-mL solutions containing 5.0 ng mL(-1) Cd(II) and Pb(II) were 4.2 and 4.5 % for Cd(II) and 3.4 and 3.5 % for Pb(II), respectively. Finally, the proposed method will be employed for the separation and determination of Cd(II) and Pb(II) in different real samples to confirm its accuracy and validity.