Tailoring filler/gas vs. filler/polymer interactions via optimizing Co/Zn ratio in bimetallic ZIFs and decorating on GO nanosheets for enhanced CO2 separation

Despite numerous efforts devoted to enhancing the gas separation performance of mixed matrix membranes (MMMs), there still remain challenges in effectively embedding nanofillers into the polymer matrix due to the improper interactions between filler and polymer/gas molecules. Concerning that, synthesizing filler with well-structured physical and chemical properties and endowing its synergistic effects with a 2D filler has been considered a promising idea. Herein, five series of bimetallic ZIFs with various Co/Zn ratios were synthesized and embedded within the Pebax-1657 matrix to investigate the exact influence of metal ratio on the separation performance of MMMs. The results revealed that the Co60Zn40ZIF has the highest Co content that does not induce early chain rigidification, and enhances permeability and selectivity by 41.93 % and 93.65 % at 7.5 wt% loading, respectively. Furthermore, by hybridizing the optimized bimetal ZIF with GO, a substantial enhancement in selectivity was achieved, elevated by 250.37 % (compared to neat Pebax-1657) at the 7.5 % loading of GO@ZIF. The integration of the strategies applied to synthesizing bimetal ZIF with fine-tuned pores on the GO nanosheets exceeded the Robeson upper bond and yielded an exemplary separation index, which may offer enormous prospects for future research on multi-metallic composited MOF fillers.