TDI coupling chemistry as an efficient alternative to silane-based methods for the synthesis of silica-based metal chelators

This study used toluene 2,4-diisocyanate (TDI) as a flexible linker to attach functional ligands onto silica through stable urethane bonds. Four chelating sorbents were prepared by coupling 8-hydroxyquinoline (HQ), 2,3-dihydroxypyridine (DHP), 1-nitroso-2-naphthol (NN) and alizarin (AZ) to activated silica via TDI. Its two reactive isocyanate groups allowed stepwise bonding with silica hydroxyls and ligands, improving structural stability and functionality. The resulting materials were characterized by Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), N₂ adsorption-desorption and elemental analysis. All sorbents showed strong Zn(II) adsorption, with capacities of 8.42–8.96 mg g−1 at pH 8 and retained mesoporous structures with surface areas of 319–381 m2 g−1. The prepared sorbents were successfully applied to preconcentrate Zn(II) ions from groundwater samples, achieving recoveries of 88.66%–100.46% and detection limits of 0.0073–0.0105 μg L−1 using inductively coupled plasma mass spectrometry (ICP-MS). High reproducibility (RSD < 3%) and excellent linearity (R 2 > 0.995) confirmed their suitability for trace zinc analysis in environmental water.