High CO2 adsorption of ultra-small Zr-MOF nanocrystals synthesized by modulation method boosts the CO2/CH4 separation performance of mixed-matrix membranes

The separation performance of mixed matrix membranes (MMMs) is greatly impacted by both the inherent structure of porous fillers and the interfacial compatibility between the filler and matrix. Here, ultra-small Zr-MOFs (UiO-66-mod and NH2-UiO-66-mod) with more defect sites were synthesized through a simple sodium formate modulation strategy. Then, these modulated Zr-MOFs were used as porous fillers in combination with polyetherimide (PEI) to construct a high-quality mixed matrix membrane for efficient CO2 separation. The modulated Zr-MOF not only exposed more defect sites, which significantly enhanced the CO2 adsorption capacity but also exhibited high dispersion in the PEI matrix due to strong interfacial forces, avoiding non-selective voids. The 10-UiO-66-mod-PEI and 10-NH2-UiO-66-mod-PEI membranes developed here showed admirable CO2/CH4 separation performance (CO2 permeability of around 400 and 440 Barrer, CO2/CH4 selectivity of ∼33 and ∼47, respectively) much higher than that of non-modulated UiO-66-PEI membranes, surpassing the 2008 upper bound of MMMs. This work demonstrated that the proposed UiO-66-mod-PEI and NH2-UiO-66-mod-PEI MMMs could be potential candidates for an efficient CO2 capture process.