Liquid-like CNT/SiO₂ nanoparticle organic hybrid materials as fillers in mixed matrix composite membranes for enhanced CO₂-selective separation

Nanoparticle organic hybrid materials (NOHMs) have shown great potential as absorbents for CO₂ capture owing to their attractive properties, including macroscopic liquid-like behavior, good dispersion properties, and tunable structures. However, only a few NOHMs are used as fillers to prepare mixed-matrix composite membranes (MMMs) for CO₂ capture. Here, we demonstrated novel MMMs comprising a Pebax-1657 polymer matrix and NOHM fillers for separating a CO₂/N₂ mixture. Various types of NOHMs with a core/corona/canopy structure based on a CNT/SiO₂ composite core were prepared and incorporated into the Pebax-1657 matrix. In particular, the effect of the composite core composition on CO₂/N₂ mixture permeation was systematically investigated. Benefiting from the dispersion properties of liquid-like NOHMs, excellent interfacial compatibility was obtained. Furthermore, functional groups on the canopy of NOHMs were confirmed to enhance the CO₂-philic properties for separation. Specifically, the as-prepared membrane presented optimal performance regarding CO₂ permeability (148.3 Barrer) and the separation factor (66.5 for CO₂/N₂), while also showing improvements in CO₂ permeability by 142.3% and the CO₂/N₂ separation factor by 62.5% compared with neat Pebax membrane, overcoming the Robeson upper bound. Finally, the influence of the composite core composition (CNT/SiO₂ weight ratio) in NOHMs on CO₂ selective separation was investigated. A possible CO₂ selective separation mechanism was also proposed.