Threshold silver concentration for facilitated olefin transport in polymer/silver salt membranes

Abstract

The existence of a threshold concentration for silver ions has been observed in solid-state facilitated transport membranes comprising silver salt and a polymer matrix. The threshold silver concentration for facilitated olefin transport through the membranes was systematically investigated, with particular attention paid to the relative interactions of polymer/silver ions and of silver ions/counteranions. This behavior was assessed for membranes consisting of silver salt and polymer matrix with and without various ligands, specifically, phthalate, amide, ether, ketone, ester, or C = C bonds. The threshold concentration of silver salt for facilitated olefin transport was found to be strongly dependent on the polymeric ligand. With respect to the polymer, the determined order of highest threshold concentration capacity to lowest capacity is listed in the following order: phthalate > amide > ether >ketone ≈ C = C bond > ester > no ligand. This dependence of the threshold concentration on the polymeric ligand is correlated with both the interaction strength of silver ions with the different ligands and that with their counteranions. It has been concluded that when the former interaction is weak and, consequently, the latter interaction is strong, the threshold concentration for facilitated olefin transport is low, and vice versa. These interactions were characterized using X-ray photoelectron spectroscopy (XPS), FT-Raman spectroscopy, and theoretical ab initio calculation.