Rapid removal of toxic metals Cu²⁺ and Pb²⁺ by amino trimethylene phosphonic acid intercalated layered double hydroxide: A combined experimental and DFT study

Phosphonates are environmental friendly materials, and can be potentially employed to improve the removal efficiency of the clay materials. In the present work, Zn-Al layered double hydroxide (LDH) intercalated with amino trimethylene phosphonic acid (ATMP) by a facile technique and employed as an adsorbent for Cu²⁺ and Pb²⁺ from wastewater. The adsorption characteristics and microscopic mechanism of ATMP in the interlayer space were explored by a combination of experimental and density functional theory (DFT). The adsorption capacity for Cu²⁺ and Pb²⁺ could reach 42.02 mg.g⁻¹ and 84.06 mg.g⁻¹, respectively. The adsorption kinetics curves were matched well with the pseudo-second-order model, indicating chemical adsorption via electrostatic interaction mechanism. Based on Multiwfn and VMD program calculation, the ways of electrostatic potential and average local ionization energy were firstly applied to predict reactive sites of ATMP molecule and corresponding anion, suggesting that anion state was more easily to provide lone pair electrons for electrophilic reaction. The weak interaction analysis indicated that interactions among ATMP and LDH are mainly dominated by H-bond. These results recommended that modified LDH can be a promising adsorbent for the adsorption of toxic metal ions in practical applications.