Pod-like TA-ZIF-8/TCOH composite filler for the preparation of mixed matrix membrane for efficient CO2 separation

Rapid industrialization poses a serious threat to the balance of ecosystems and environmental sustainability, and the application of membrane technology is an effective way to alleviate this situation. Two-dimensional (2D) MXene nanosheets are superior materials for constructing high-performance separation membranes, but their biggest drawback is that they are prone to agglomeration. After alkalizing them, the obtained alkaline MXene (TCOH) nanosheets have hydroxyl-rich surfaces, stabilized structure and great affinity for CO2. Based on this, a self-supported TA-ZIF-8/TCOH@Pebax mixed matrix membranes (MMMs) with block polymer Pebax-1657 as matrix and TA-ZIF-8/TCOH as composite filler were prepared in this work. ZIF-8 was modified with tannic acid (TA) to enrich the surface with hydroxyl groups, yielding TA-ZIF-8 that is both pro-CO2 and well interfacially compatible. The using of TA-ZIF-8 not only improves the selectivity of the separation membrane, but also its mutually repulsive electrostatic force with TCOH can expand the layer spacing of TCOH nanosheets as much as possible, which leads to a rich gas transportation channel of the membrane. Experiments have shown that the prepared TA-ZIF-8/TCOH@Pebax MMM had outstanding separation performance beyond the 2019 Robinson upper bound when the content of TA-ZIF-8 was appropriate. Also, the TA-ZIF-8/TCOH@Pebax MMM showed superior thermal stability, durability and mechanical properties. In summary, the strategy of combining nanoparticles and nanosheets as composite fillers in this study provides an effective way to regulate the low permeance of MMMs. In the meantime, the application of TCOH provides a novel idea for further research on gas separation membranes.