(353c) Highly Selective Polymer Membranes Containing Poly(amic-acid) Stabilized Silver Nanoparticles

Facilitated Transport Membranes (FTMs) have proved to be a viable approach to overcome the perm-selectivity trade-off experienced by conventional polymer membranes. However, despite their high performance on the short time-frame, facilitated transport carriers experience photo/chemical aging, which causes, in turn, a rapid decay of their performance. Moreover, when embedded in polymer materials to form mixed matrix membranes, structural defects may form at the metal-polymer interface, which have a detrimental effect on selectivity.

To address the issues mentioned above, we fabricated silver nanoparticles (NPs) stabilized by chelating them with a poly(amic acid) (PAA) derived from 4,4-oxydiphthalic anhydride and a polyetheramine. In conjunction with the metal core, polymer agents may be used to not only provide stability against aggregation to the NP, but also evoke Janus transport properties through the simultaneous targeting of the diffusivity- and solubility-selectivity, by means of the actions of silver ions, which promotes CO₂ facilitated transport, and that of the Jeffamine ether groups, which promotes CO₂ solubility. Additionally, these polymer agents can mediate an interphase between silver and the bulk polymer, to avoid the formation of non-selective defects while offering carrier sites protection from photo/chemical degradation.

The synthesized silver-PAA nanoparticles, which were thoroughly characterized via TEM/EDS analysis, showed near spherical morphology (~5 nm) and lack of aggregation. The occurrence of the chelating reaction between silver and the PAA showed that favorable carbonyl-silver coordination interactions were achieved. The effect of the PAA length and ether functional group concentration on the structure and transport properties of nanoparticles were systematically investigated.

The silver-PAA Janus nanoparticles were then incorporated into a commercial polymer, Pebax, to fabricate defect-free mixed matrix membranes for CO₂/CH₄ separation, whose structure and transport properties were examined at various NP loadings. Remarkably, inclusion of only 1% wt nanoparticles in Pebax enhances CO₂ permeability by about 50% and CO₂ selectivity by about 100% relative to neat polymer. The molecular origin of the observed permeability behavior was elucidated by measuring separately the solubility and diffusion coefficients, which were systematically correlated to the structure of the mixed matrix membrane and NPs.

Remarkably, these materials also exhibit enhanced stability relative to previously reported facilitated transport membranes.