Catechol immobilized on crosslinked polystyrene resins by grafting or copolymerization: Incidence on metal ions adsorption

Porous poly(styrene-co-divinylbenzene) resins functionalized with catechol were prepared in two different ways. Catechol was either grafted on commercial Amberlite® XAD-4 resin via a reduced imine and diazo bridges or incorporated by direct copolymerization of divinylbenzene with dimethoxystyrene followed by deprotection of the methoxy groups. The efficiency of functionalization was evidenced by pyrolysis coupled with gas phase chromatography and infra-red spectroscopy. The amount of incorporated catechol inside the different resins was determined by acido-basic back titration and varies between 0.27 and 1.38 mmol/g of resin. Grafting resulted in a decrease of the surface area due to the blocking of some connections between the mesopores. For synthesized copolymers, high contents of divinylbenzene monomer led to high surface areas. Comparing metal retention properties of both kind of materials towards Pb(II), Cu(II), Ni(II) and Cd(II) ions proved the equivalence of these sorbents. At low metal concentration, interactions with the sorbents seem to be non specific whereas at higher concentration catechol is responsible for the retention properties. Since the synthesis of copolymers is easier than the grafting of sorbents, it appears to be a more attractive procedure to obtain chelating sorbents.