Complexation properties of water-soluble poly(vinyl alcohol) (PVA)-based acidic chelating polymers

Water-soluble polymers are attractive materials for pollutants removal thanks to their ability to easily interact with soluble metal cations. In the present contribution, the chemical modification of biocompatible and non-toxic poly(vinyl alcohol) (PVA) was achieved with ethylene diamine tetraacetic acid (EDTA) groups, thus leading to new water-soluble polymers, named PVA(EDTA). Modification was carried out using Mitsunobu's reaction as an original pathway to obtain statistical copolymers with different EDTA functionalization rates in the PVA chains. Preliminary study about the variation of EDTA rate and chain length permitted determining the optimal polymeric structures. Then, sorption properties of heavy metal (i.e. Co(II), Ni(II), Zn(II), Pb(II), Cd(II), Cu(II)) on structures containing 15% of chelating agent were determined by performing thorough adsorption isotherms or determining removal percentage, at a high or low concentration, respectively. Additionally, the performances of the polymers were tested in a more complex effluent constituted by previous pollutants in the presence of Ca(II) and Mn(II) cations. We demonstrated that water-soluble PVA(EDTA) led to a great improvement of sorption properties in comparison with PVA. Indeed, results obtained showed high sorption capacities for Pb(II), Ni(II), Zn(II), and good selectivity towards some cations, in consistency with EDTA-metal complex formation constants. Isotherm Titration Calorimetry measurements allowed evidencing the complexation stoichiometry, and determining the interaction constant and the enthalpy. This study highlighted the interest of modifying basic commercial polymers with chelating agents for further applications based on Polymer Enhanced Ultrafiltration (PEUF) process.