Functionalized track-etched PVDF membrane-electrodes for toxic metal detection in water

Present work reports on radiation grafting of poly(acrylic acid) (PAA), poly(4-vinyl pyridine) (P4VP) and poly(bis[2-(methacryloyloxy)ethyl] phosphate) (PB2MP) functional polymers inside nanoporous structure of track-etched poly(vinylidene fluoride) (PVDF) membranes for selective preconcentration of Pb(II), Hg(II) and U(VI) from aqueous solutions. Track-etched PVDF membranes were made by swift heavy ion (SHI) irradiation followed by ion track revealing. The resulting nanoporous PVDF membranes were then functionalized through remained radicals trapped in the nanopore walls. EPR spectroscopy was used to examine the amount and reactivity of radical species, notably towards a novel functional PB2MP polymer. It was found out that these radicals, alkyl and peroxy ones, were sufficient to initiate free-radical polymerization in presence of three studied monomers. FESEM, FTIR and a less conventional zeta potential measurements were utilized for examination of functional group presence. In case of P4VP grafting, the measured nanopore surface charge versus pH demonstrated relatively dense grafting all along the nanopore channels. As the objective of this work is to develop innovative electrochemical sensors for toxic metal detection in water, sorption experiments were performed to investigate adsorption characteristics. The results confirmed that efficient uptakes of the grafted track-etched PVDF membranes are due to the presence of functional groups that facilitate complex formation through either inherent to PAA electrostatic interaction or metal coordination with P4VP, and PB2MP complexation character in between. The moderate interaction effect in case of U(VI) adsorption by PB2MP is due to co-existence of ion exchange and chelating groups. For electrochemical detection, membranes functionalized with abovementioned functional polymers were converted into electrodes. Toxic metal preconcentration inside the nanoporous structure permitted to below stripping voltammetry sensitivity limits to sub-ppb (g/L) level. Time-resolved photoluminescence (TRPL) measurements accompanied with XPS were performed on uranyl adsorbed PB2MP-g-PVDF membranes in order to understand deeper the U(VI)PB2MP mechanism. (author)