New insight into electrochemical-induced synthesis of NiAl2O4/Al2O3: Synergistic effect of surface hydroxyl groups and magnetism for enhanced adsorptivity of Pd(II)

A new promising adsorbent, Ni supported on gamma-Al2O3 was prepared in a simple electrolysis system (Ni/Al2O3-E) in minutes and was compared with the sample prepared by a physical mixing method (Ni/Al2O3-PM). The adsorbents were characterized by XRD, TEM, FTIR, Al-27 MAS NMR, XPS, and VSM. The results showed that besides NiO nanoparticles, a NiAl2O4 spinel was also formed in Ni/Al2O3-E during the electrolysis via the dealumination and isomorphous substitution of Ni2+ ions. In contrast, only agglomerated NiO was found in the Ni/Al2O3-PM. Adsorption test on removal of Pd2+ ions from aqueous solution showed that the Pd2+ ions were exchanged with the hydrogen atoms of the surface-OH groups of both adsorbents. Significantly, the Ni/Al2O3-E demonstrated a higher adsorption towards Pd2+ ions than Ni/Al2O3-PM due to its remarkably higher degree of magnetism, which came from the NiAl2O4. The use of 0.1 g L-1 Ni/Al2O3-E gave the maximum monolayer adsorption capacity (q(m)) of 40.3 mg g(-1) at 303 K and pH 5. The Ni/Al2O3-E showed high potential for simultaneous removal of various noble and transition metal ions and could be also used repetitively without affecting the high adsorptivity for Pd2+ ions. This work may provide promising adsorbents for recovery of various metals as well as other materials for such related applications. (C) 2015 Elsevier B.V. All rights reserved.