Mg/Al layered double hydroxides intercalated with ethylenediamine-tetramethylene phosphonic acid for efficient removal of Pb2+ and Cd2+ ions and the intercalation mechanism study

Abstract

Mg/Al layered double hydroxides (LDH) intercalated by Ethylenediamine-tetramethylene phosphonic acid (EDTMP) was synthesized to remove Pb2+ and Cd2+ from aqueous solutions, and the intercalation of EDTMP enhanced the adsorption capacity of LDH for both of the heavy metal ions. At a pH of 6.5 and with an optimal intercalation amount of 20% EDTMP, the 20EDT-LDH composite demonstrated an adsorption capacity of 249.82 mg/g for Pb2+ and 160.85 mg/g for Cd2+, resulting in a removal rate of 64.34% for Pb2+ and 99.93% for Cd2+. 20EDT-LDH showed great resistance to interference ions, as it maintained satisfying adsorption performance when a much higher concentration of K+ and Ca2+ than that of Pb2+ and Cd2+ were present, with the adsorption capacity of Pb2+ and Cd2+ being greater than 83.4% and 66.3% of the maximum adsorption capacity, respectively. This was due to the strong chelation ability of EDTMP with Pb2+ and Cd2+, as confirmed by characterizations after adsorption of 20EDT-LDH with Pb2+ and Cd2+. Moreover, the affinity between EDTMP and LDH was revealed via Independent Gradient Model based on the Hirshfeld partition of molecular density (IGMH) and Hirshfeld surface analysis.