The removal of lead ions from aqueous solutions by modified multi-walled carbon nanotubes with 1-isatin-3-thiosemicarbazone

Carboxylated multiwalled carbon nanotubes (MWCNT-COOH) were functionalized with 1-isatin-3-thiosemicarbazone (MWCNT-f) and used for the removal of lead ions from aqueous solutions. The resulting materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscope and thermogravimetric analysis. Effects of pH, concentration of the lead, amount of adsorbents and contact time were investigated by the batch method. An orthogonal array design with four factors was applied to assign the significant factors affecting the Pb+ 2 uptakes. The chosen experimental parameters and their ranges were the following: adsorbents, MWCNT-COOH and MWCNT-f; pH, 3.5-6.5; dosage of adsorbents, 0.010-0.060 g; and Pb+ 2 concentration, 20-80 mg/L. L18 orthogonal array for experimental design was used to determine the optimum conditions, which were found to be MWCNT-f as adsorbent, pH = 5.5, 0.06 g dosage of adsorbent, and 50 mg/L Pb+ 2 concentration. The kinetic data were fitted with pseudo-first order, pseudo-second-order, and intra-particle diffusion models. Sorption kinetics were well described by pseudo-second-order kinetic model for both adsorbents. In addition, the adsorption isotherms of lead ions from aqueous solutions onto MWCNTs were studied. The three isotherm models: Langmuir (four linear forms), Freundlich and Temkin were applied to determine the characteristic parameters of adsorption process. The results showed that the Langmuir isotherm for MWCNT-COOH and Freundlich model for MWCNT-f were found to best represent the measured sorption data.