A general strategy for fabricating polymer/nanofiller composite membranes with enhanced CO2/N2 separation performance

Abstract

Aggregation of nanofillers, one of the critical challenges for developing high-performance composite membranes, induces non-selective gas transport paths, and thus reduces the gas separation selectivity. Here, we propose a facile and general filtration-spray strategy for fabricating polymer/nanofiller composite membranes to inhibit nanofiller aggregation. In this way, the nanofiller scaffold is first deposited on the surface of the porous substrate through filtration. Then, the polymer covers the scaffold via a spray method. Finally, a defect-free membrane is formed after penetration of polymer and thus filling of the inter-filler gaps during the solvent evaporation process. This strategy avoids redispersion and aggregation of nanofillers in polymer matrix, thus diminishing the non-selective defects of interparticles caused by nanofiller aggregation and forming dense polymer/nanofiller composite membranes with well-dispersed nanofillers. The as-prepared Pebax/PEI-ZIF-62 (polyethyleneimine functionalized ZIF-62) membrane exhibits an enhanced gas separation performance with a CO2 permeance of 58 GPU and a CO2/N2 selectivity of 83, which are 45% and 51% higher than those of the pure Pebax membrane, respectively, surpassing Robeson 2008 upper bound. However, the CO2 separation selectivity of PEI-ZIF-62@Pebax membrane prepared via spraying the mixed solution of Pebax and PEI-ZIF-62 decreases to 38, probably due to the formation of non-selective voids. To demonstrate the versatility of this facile strategy, various nanofillers, such as SiO2, ZIF-8, zeolite, and porous polymer sphere, have been used to prepare the composite membranes by this strategy, showing improved CO2 separation performance. Overall, these results demonstrate that the filtration-spray fabrication strategy is effective in preventing nanofiller aggregation in composite membranes.