Ion-selective polymer-supported reagents: the principle of bifunctionality

Abstract

Phosphonic acid ion exchange resins have been synthesized from polystyrene beads and sorption studies with Eu(III) and Fe(III) from acid solutions are reported. The effect of increasing matrix rigidity by crosslinking with 5, 12, and 20% divinylbenzene (DVB) on the extent of complexation is quantified. In a representative example, complexation decreases from 97.7% to 3.60% Eu(III) at a 0.5 h contact time from 10−4 N Eu(NO3)3/0.10 N HNO3 solution as the crosslink level in microporous (i.e., gel) resins changes from 5 to 20% DVB. Complexation at the two crosslink levels decreases to 31.7% and 0.61%, respectively, from 1.00 N HNO3 solution. Macroporosity can increase the level of complexation, but the effect under the present conditions is minimal for 5 and 20% DVB macroporous resins (98.3% and 31.2% Eu(III) from 0.10 N HNO3; 28.8% and 1.26% Eu(III) from 1.00 N HNO3). It is now reported that immobilizing sulfonic acid ligands on to the aromatic rings bearing the phosphonic groups allows the latter to rapidly complex metal ions to levels exceeding 90% from highly acidic solutions. Under the conditions noted above, bifunctional 5 and 20% DVB gel resins complex >99% Eu(III) from 0.10 N HNO3 and 94% Eu(III) from 1.00 N HNO3 solutions. The principle of bifunctionality is thus proposed as an alternative to macroporosity: polymer-supported reagents with enhanced metal ion complexation kinetics require the presence of an access ligand along with a recognition ligand for the targeted selectivity.