Mixed-Matrix Membranes Containing Carbon Nanotubes Composite with Hydrogel for Efficient CO₂ Separation

In this study, a carbon nanotubes composite coated with N-isopropylacrylamide hydrogel (NIPAM-CNTs) was synthesized. Mixed-matrix membranes (MMMs) were fabricated by incorporating NIPAM-CNTs composite filler into poly(ether-block-amide) (Pebax MH 1657) matrix for efficient CO₂ separation. The as-prepared NIPAM-CNTs composite filler mainly plays two roles: (i) The extraordinary smooth one-dimensional nanochannels of CNTs act as the highways to accelerate CO₂ transport through membranes, increasing CO₂ permeability; (ii) The NIPAM hydrogel layer coated on the outer walls of CNTs acts as the super water absorbent to increase water content of membranes, appealing both CO₂ permeability and CO₂/gas selectivity. MMM containing 5 wt % NIPAM-CNTs exhibited the highest CO₂ permeability of 567 barrer, CO₂/CH₄ selectivity of 35, and CO₂/N₂ selectivity of 70, transcending 2008 Robeson upper bound line. The improved CO₂ separation performance of MMMs is mainly attributed to the construction of the efficient CO₂ transport pathways by NIPAM-CNTs. Thus, MMMs incorporated with NIPAM-CNTs composite filler can be used as an excellent membrane material for efficient CO₂ separation.