POLYMER PENDANT LIGAND CHEMISTRY .3. A BIOMIMETIC APPROACH TO SELECTIVE METAL-ION REMOVAL AND RECOVERY FROM AQUEOUS-SOLUTION WITH POLYMER-SUPPORTED SULFONATED CATECHOL AND LINEAR CATECHOL AMIDE LIGANDS

The design of organic Ligands to selectively remove and recover metal ions from aqueous solution is a new and important area of environmenta l inorganic chemistry. One approach to designing organic ligands for t hese purposes is to use biological systems as examples for selective m etal ion complexation. Thus, we report on our results on the synthesis of several biomimetically important polymer-supported, sulfonated cat echol (PS-CATS), sulfonated bis(catechol) linear amide (PS-2-6-LICAMS) , and sulfonated 3,3-linear tris(catechol) amide (PS-3,3-LICAMS) ligan ds that are chemically bonded to modified 6% cross-linked macroporous polystyrene-divinylbenzene beads (PS-DVB) for selective removal and re covery of environmentally and economically important metal ions from a queous solution, as a function of pH. The Fe3+ ion selectivity was dra matically shown for PS-CATS, PS-2-6-LICAMS and PS-3,3-LICAMS polymer b eads in competition with a similar concentration of Cu2+, Zn2+, Mn2+, Ni2+, Mg2+, Al3+, and Cr3+ ions at pH 1-3, while metal ion selectivity could be changed at higher pH values in the absence of Fe3+ (for exam ple, Hg2+ at pH 3). Rates of removal and recovery of the Fe3+ ion with the PS-CATS, PS-2-6-LICAMS and PS-3,3-LICAMS polymer beads were also studied as well as relative equilibrium selectivity coefficient (K-m) values for all metal competition studies. The chelate effect for the o ctahedrally predisposed PS-3,3-LICAMS polymer pendant ligand, as shown for the homogeneous ligand, appears to be the reason that this polyme r pendant ligand has a more pronounced selectivity for Fe3+ ion in com parison to the PS-CATS polymer beads, while the square planar predispo sed PS-2-6-LICAMS series of polymer pendant ligands were more selectiv e to divalent metal ions, CU2+, Zn2+, Mn2+, Ni2+, and Mg2+, than eithe r PS-CATS or PS-3,3-LICAMS, although Fe3+ ion still dominated in compe tition with other divalent and trivalent metal ions. It is interesting to note that changing the cavity size from two CH2 groups to six CH2 groups in the PS-2-6-LICAMS polymer pendant ligand series did not affe ct the order of metal ion selectivity.