Asymmetric structure and enhanced gas separation performance induced by in situ growth of silver nanoparticles in carbon membranes

Ion-exchanged sulfonated poly(aryl ether ketone), SPAEK with different counter-ions (H+, Na+ and Ag+) have been utilized as polymeric precursors to fabricate carbon membranes. The effects of the substituted metal ions in polymeric precursors on the separation properties of resultant carbon membranes were investigated. X-ray diffraction analysis reveals that the polymer chain packing is improved by the substituted metal ions. The silver doped SPAEK membrane demonstrates the smallest d-spacing due to the strong interactions between the silver ions and the polar groups within the polymeric matrix. The carbon membrane derived from Ag-SPAEK exhibits a more porous structure compared to that from ion-exchanged SPAEK membranes. The silver doping enhances the ideal gas permeability of carbonized membranes by 100 fold. On top of this, the H2/N2 selectivity increases from 100 to 220 while the CO2/CH4 selectivity jumps from 25 to 67. An interesting phenomenon was observed, which is the migration of silver nanoparticles and the subsequent accumulation in the bulk of membrane after carbonization. A possible mechanism to explain for this particle relocation is the Ostwald ripening. The special directional dispersion of metal nanoparticles in carbonaceous materials was investigated and discussed.