Efficient and Environmentally Friendly Adsorbent Based on β‑Ketoenol-Pyrazole-Thiophene for Heavy-Metal Ion Removal from Aquatic Medium: A Combined Experimental and Theoretical Study

A new sustainable and environmentally friendly adsorbent based on a β-ketoenol-pyrazole-thiophene receptor grafted onto a silica surface was developed and applied to the removal of heavy metal ions (Pb(II), Cu(II), Zn(II) and Cd(II)) from aquatic medium. The new material SiNPz-Th was well characterized and confirms the success of the covalent binding of the receptor on the silica surface. The effect of environmental parameters on adsorption including pH, contact time, temperature and the initial concentration were investigated. The maximum adsorption capacities of SiNPz-Th for Pb(II), Cu(II), Zn(II) and Cd(II) ions were 102.20, 76.42, 68.95 and 32.68 mg/g, respectively, at 30 min and pH = 6. The adsorption isotherms, kinetics and thermodynamic process were investigated and showed efficiency and selectivity towards Pb(II) and good regeneration performance. Density functional theory (DFT), non-covalent-interaction (NCI) and quantum theory of atoms in molecules (QTAIM) calculations were used to study and to gain a deeper understanding of both adsorption mechanism and selectivity of metal ions onto adsorbent. Accordingly, the metal ions such as Pb(II), Cu(II) and Zn(II) are bidentate coordinated with the adsorbent by nitrogen and oxygen atoms of Schiff base C=N and hydroxyl group –OH, respectively, to form stable complexes. While the Cd(II) is coordinated in a monodentate fashion with oxygen atom of hydroxyl group. Furthermore, the affinity of SiNPz-Th towards the metal ions was decreased in the order of Pb(II) ˃ Cu(II) ˃ Zn(II) ˃ Cd(II), in good agreement with experimental results. All these results highlight that the SiNPz-Th has a good potential to be an advanced adsorbent for the removal of lead ions from real water.