Adsorption of aqueous cadmium (II) onto modified multi-walled carbon nanotubes following microwave/chemical treatment

This study evaluates the aqueous cadmium (II) adsorption efficiency of as-grown carbon nanotubes (CNTs) and of those modified by microwave (MW)/H2SO4 and MW/H2SO4/KMnO4 processes. The surface area, pHiep, and FTIR spectra of CNTs were, before and after modification, compared. Aromatic groups, carbonyl groups and hydroxyl groups were herein detected on the surfaces of MW/H2SO4 and MW/H2SO4/KMnO4-modified CNTs. At a particular pH, the adsorption capacity of Cd2+ of the MW/H2SO4/KMnO4-modified CNTs exceeded that of MW/H2SO4-modified CNTs and as-grown CNTs. The kinetic analyses of adsorption were performed and a pseudo second-order model accurately captured the adsorption kinetics. This study suggests that MW/H2SO4 and MW/H2SO4/KMnO4 modification not only increased the area of active adsorption sites of CNTs but also reduced the modification period by microwave heating.