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 environmental inorganic chemistry. One approach to designing organic ligands for these purposes is to use biological systems as examples for selective metal ion complexation. Thus, we report on our results on the synthesis of several biomimetically important polymer-supported, sulfonated catechol (PS-CATS), sulfonated bis(catechol) linear amide (PS-2-6-LICAMS), and sulfonated 3,3-linear tris(catechol) amide (PS-3,3-LICAMS) ligands that are chemically bonded to modified 6% cross-linked macroporous polystyrene-divinylbenzene beads (PS-DVB) for selective removal and recovery of environmentally and economically important metal ions from aqueous solution, as a function of pH. The Fe3+ ion selectivity was dramatically shown for PS-CATS, PS-2- 6-LICAMS and PS-3,3-LICAMS polymer beads 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 example, 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 (Km) values for all metal competition studies. The chelate effect for the octahedrally predisposed PS-3,3-LICAMS polymer pendant ligand, as shown for the homogeneous ligand, appears to be the reason that this polymer pendant ligand has a more pronounced selectivity for Fe3+ ion in comparison to the PS-CATS polymer beads, while the square planar predisposed PS-2-6-LICAMS series of polymer pendant ligands were more selective to divalent metal ions, Cu2+, Zn2+, Mn2+, Ni2+, and Mg2+, than either PS-CATS or PS-3,3-LICAMS, although Fe3+ ion still dominated in competition 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 affect the order of metal ion selectivity. © 1995, American Chemical Society. All rights reserved.

Duke Scholars

Author Katherine J. Franz Chemistry