Engineering Ultra-Small Ag Nanoparticles with Enhanced Activity in Microporous Polymer Membranes for C₂H₄/C₂H₆...

The separation of C₂H₄ and C₂H₆ is a critical yet energy-intensive operation in the petrochemical industry. Gas separation membranes offer energy-efficient alternatives, but their effectiveness is hindered by the similar physical properties of C₂H₄ and C₂H₆. Here, a metallic nanocomposite membrane (MNM) comprising ultra-small Ag nanoparticles embedded in an amidoxime-modified polymer of intrinsic microporosity (AOPIM-1) is reported for highly efficient C₂H₄/C₂H₆ separation. The microporous structure of AOPIM-1, combined with anchoring groups (amidoxime groups) inside the microcavities, enables size-controlled growth of Ag nanoparticles with ‒≈3 nm diameter, which maximizes the contact with ethylene molecules. The amidoxime groups as electron acceptors effectively enrich the positive charge on the surface of Ag nanoparticles. The activated Ag form reversible complexes with ethylene molecules endowing them with preferential affinity over ethane. The resulting Ag nanocomposite membrane demonstrates a ≈10-fold increase in C₂H₄ permeability, reaching 322.1 barrer, and a ≈3-fold increase in C₂H₄/C₂H₆ selectivity, reaching 8.8. The comprehensive separation performance is superior over all the polymer membranes and mixed matrix membranes reported so far. The MNMs also demonstrate stable mixed gas separation performance under elevated feed gas pressures. This study provides valuable insights into designing and fabricating polymer membranes with high C₂H₄/C₂H₆ separation performance.