Synthesis and characterization of a polystyrenic resin functionalized by catechol: Application to retention of metal ions

Chelating solid phase extraction is a preconcentration method adapted for metal ions extraction in water and requires functionalization of a solid sorbent by an organic ligand. A new chelating resin has been prepared by grafting catechol on Amberlite^® XAD-4 with an imine bridge and reducing it to enhance stability of the modified resin. Synthesis was first carried out at molecular level to validate experimental conditions, optimize yields and facilitate characterization of solid sorbent (particularly by FTIR). Each synthesis step of grafting on Amberlite^® XAD-4 was characterized by FTIR, Py-GC–MS and TGA-DSC. BET measurements showed a decrease in specific area after grafting from 865 to 425 m² g⁻¹ and in total pore volume from 1.19 to 0.66 cm³ g⁻¹. The grafting rate of 33% was determined by back titration of –OH (0.31 ± 0.03 mmol g⁻¹ of resin) and –NH-functions (0.93 ± 0.02 mmol g⁻¹ of resin). The increase in the sorbent hydrophilicity was confirmed by evaluating the water regain. Finally the retention properties of Cd(II), Cu(II), Ni(II) and Pb(II) were determined by ICP-AES at a pH range from 2 to 9. Retention rates of 94% and 98% were found at pH 8 for Cu(II) and Pb(II), respectively. Sorption capacities of 25.8 ± 2.5 μmol g⁻¹ for Cd(II), 89.7 ± 8.4 μmol g⁻¹ for Cu(II), 49.0 ± 10.5 μmol g⁻¹ for Ni(II) and 31.5 ± 1.6 μmol g⁻¹ for Pb(II) were measured.