Layer-by-Layer Assembled Membranes for Separations and Toxic Metal Capture

Applications of membranes functionalized by layer-by-layer (LBL) assembly with charged poly-amino acids or poly-electrolytes were studied. The first poly-electrolyte layer was covalently attached while subsequent layers were immobilized through electrostatic interaction under convective flow conditions. Possible applications of these LBL-assembled membranes in the areas of bioseparation, toxic metal ion capture, and nanoparticle reactions were explored. In the bioseparations area, avidin that had been electrostatically immobilized demonstrated 63.5% of the active sites as available for binding as compared to 17.7% for a membrane containing avidin covalently-bound to the pore wall. The capture of toxic metals through an ion exchange mechanism was investigated by permeating an aqueous solution of Cupric (II) Sulfate through a membrane containing alternating layers of poly-allylamine and poly-styrene sulfonate. It was shown that these membranes did indeed immobilize toxic metal ions. The expected trend for ion exchange was observed by comparing the mmol Cu²⁺ immobilized by mmol Na⁺ (the counter-ion of the negatively charged poly-electrolyte) exchanged. As a third application of these membranes, the ions immobilized in a membrane layered with poly-electrolytes were reduced into nanoparticles for potential use in environmentally important catalytic reactions. This project was partially supported by NIEHS.