Tailored design of CO2-selective mixed-matrix membranes using nitrile-functionalized COFs as 2D nanofillers

CO2 capture and separation are indispensable for the supply of energy through a sustainable process. Adaptation of a gas separation technology in the energy production industry is one of the key pathways to achieving net zero energy sources. MMMs are adjudged as propitious membrane systems for industrial-scale gas separation at low cost and environmental footprint, but they require further improvement. Hence, this work reports a pensive selection of COF-316 as a 2D nanofiller with pendant nitrile (-CN) moiety and its effect in elevating CO2 permeability and CO2/N2 selectivity. MMMs containing PEBAX-1657 and COF-316 were created by adding various weight percentages (0.25 to 1.0%) of 2D COF-316 as nanofillers. Several analytical methods such as Fourier transform infrared spectroscopy, X-ray diffraction, Field emission scanning electron microscopy, and Thermo-gravimetric analysis, were used to investigate the structural integrity between PEBAX-1657 and COF-316 nanofiller. The MMMs demonstrated efficient COF-316 nanofiller integration into the PEBAX-1657 matrix resulting increment in free volume within the membrane. Consequently, the addition of COF-316 to the PEBAX-1657 polymeric support increased the gas permeability. However, the presence of dipole-quadrupole interaction between -CN and CO2 enhanced the CO2/N2 selectivity in gas permeation studies. The effect of nanofiller ratio and feed gas pressure were investigated to optimize the overall gas separation process. The 0.5-MMM (with 0.5 wt.% COF-316) demonstrated the highest CO2/N2 selectivity from 29.85 to 73.4 and the largest CO2 permeability augmentation from 89.5 to 330 barrer compared to pure PEBAX-1657 membranes. The 0.5-MMM produced outstanding results that nearly reached Robeson's limit.