Functionalized Halloysite for enhanced removal of toxic metal ions from aqueous solutions

During the last years several nanomaterials have been extensively used in the heavy metal ions removal from aqueous solutions. Among them, clay minerals have gathered particular interest owing to their unique features (e.g., high specific surface area, low toxicity and natural availability at low price). Halloysite nanotubes (Hal) are particular clay minerals with a predominantly hollow tubular structure. In this work Hal and their derivatives, Hal-NH2 and Hal-SH, were used as adsorbent materials of lead(II) and mercury(II) ions from aqueous solutions. The adsorption ability of clay nanomaterials towards toxic metal ions has been studied takeing into account important variables of the metal ion solution (e.g., ionic medium, ionic strength, pH, etc.). The Kinetic and the thermodyamic of the metal adsorption were evaluated by using the Differential Pulse Anodic Stripping Voltammetry (DP-ASV) and the Inductively coupled plasma – optical emission specrtoscopy techniques to check the metal ion concentration in the solutions. Several equilibrium and kinetic equations were used to fit the experimental data. The speciation of metal ion solutions together with the characterization of the adsorbents were considered in order to establish the mechanism of metal ion removal. The collected data showed that the functionalization enhances the adsorption ability of Halloysite and makes the nanoclay mineral a good candidate as adsorbent of toxic metal ion from aqueous solutions.