Pebax Mixed-Matrix Membrane with Highly Dispersed ZIF-8@CNTs to Enhance CO₂/N₂ Separation

In this work, zeolitic imidazolate frameworks (ZIF-8) and carboxylated carbon nanotubes (CNTs) were compounded to prepare a kebab-like one-dimensional linear composite, ZIF-8@CNTs. The mixed-matrix membrane (MMM) for separating carbon dioxide is prepared by embedding it into the polymer matrix Pebax-1657. The results indicated the successful synthesis of the ZIF-8@CNT composite. The combination of ZIF-8 and carboxylated CNTs avoided the aggregation of ZIF-8 in the polymer, increased the free volume of the MMM, and enhanced the CO₂ adsorption performance and CO₂/N₂ separation performance. In addition, the interaction between CNTs and ZIF-8 provided a fast transport channel for CO₂ molecules and improved the mechanical properties of the MMM. The 5 wt % ZIF-8@CNT MMM showed the best separation performance with a CO₂ permeability of 225.5 Barrer and a CO₂/N₂ selectivity of 48.9, which exceeded the Robeson upper limit in 2008. The combination of high permeability and selectivity made Pebax/ZIF-8@CNT MMMs promising for industrial CO₂ separation applications.