Assessment of carbon nanotube-based materials to preconcentrate metals: kinetic and reusability studies

Carbon nanotubes (CNTs), oxidized carbon nanotubes (oxCNTs) and restricted access carbon nanotubes coated with bovine serum albumin (RACNTs-BSA) were synthesized and characterized by TEM, SEM–EDS, TGA, FTIR, Raman scattering, and zeta potential. Structural defects were observed by TEM for the oxidized materials. Higher thermal stability was observed for oxCNTs. FTIR spectra and zeta potential also confirmed the presence of functional groups after the acid oxidation, which are important for the metal adsorption. The maximum Fe(III) adsorption capacities were 43.73 ± 0.29, 43.29 ± 0.11 and 31.55 ± 0.29 mg g −1 , respectively for CNTs, oxCNTs and RACNTs-BSA. Avrami model (fractional model) was the best to adjust the kinetics data for all the materials, suggesting that the interaction mechanism is based on chemisorption and physisorption. Regarding the experimental data on the adsorption mechanism by the Weber-Morris model fitting, it was found that there are two stages in the diffusion process of CNTs and oxCNTs, as well as one stage for RACNTs-BSA were found. Materials could be applied up to five successive adsorption/desorption cycles, with the same performance. Thus, CNTs, oxCNTs can be excellent alternatives to extract iron from aqueous solutions, whereas RACNTs-BSA shows to be efficient in extraction of iron from protein mediums, being promising for biological sample preparation. Graphical abstract