Preparation of Schiff base-intercalated layered double hydroxides for selective copper(II) ion capture

This paper demonstrates a new interlayer synthesis method for producing a metal adsorbent composed of a layered double hydroxide (LDH) and a Schiff base. LDH are appropriate adsorbents for many kinds of toxic waste, especially heavy metals, in terms of preparation, handling, cost, and toxicity. Metal ions present in LDH form complexes with ligands; therefore, preparing a ligand-intercalated LDH is difficult. The specific LDH synthesized in the present study consists of magnesium, aluminum, and a Schiff base prepared in the interlayer from an aliphatic amine and salicylaldehyde. A precursor aliphatic amine-intercalated LDH was first prepared by coprecipitation and then converted into a Schiff base-intercalated LDH by reaction with salicylaldehyde in an alcoholic medium. The Schiff base-intercalated LDH obtained was characterized by X-ray diffractometry, Fourier-transform infrared spectroscopy, thermogravimetric-differential thermal analysis, elemental analysis, and scanning electron microscopy. The characterization data show that the Schiff base exists in the LDH interlayer and that the Schiff base-intercalated LDH adsorbs Cu(II) ions from an aqueous solution within 2 h under mild pH, and temperature. However, Ni(II), Zn(II), Cd(II), Pb(II), and Na(I) ions were not adsorbed by the LDH. The adsorption of Cu(II) ions onto the Schiff base-intercalated LDH conforms to the Redlich-Peterson equation, suggesting the existence of multiple kinds of Cu(II) adsorption sites in the interlayer of the Schiff base-intercalated LDH.