Deep eutectic solvent- and nanocellulose-tuned MXene membranes for efficient gas separation

Abstract

MXene-based membranes exhibit significant potential for gas separation. However, two major challenges persist: regulating the interlayer spacing of 2D MXenes and mitigating non-selective voids within the membrane structure. In this work, composite membranes comprising cellulose nanocrystals (CNCs), MXenes, and choline chloride/urea deep eutectic solvent (DES) were fabricated, and they contained carbon dioxide (CO₂)-selective nanochannels. The incorporation of DES effectively modulates the interlayer spacing of MXene nanosheets to match CO₂ molecules. Moreover, CNCs act as a continuous polymer skeleton, forming hydrogen bonds with adjacent MXenes to increase the inorganic‒organic interface affinity. This design facilitates CO₂ transport through multiple mechanisms: (i) the solution-diffusion properties of the CNC-based polymer phase; (ii) optimized 2D MXene channels with an appropriate interlayer spacing to accelerate CO₂ permeation; and (iii) the amine groups in the alkaline DES as CO₂ carriers. The membrane demonstrated exceptional gas separation capabilities, attaining a maximum CO₂ permeability of 496.7 Barrer, along with ideal selectivities for CO₂/N₂ and CO₂/CH₄ of 78.8 and 90.3, respectively. This research proposes a novel strategy for regulating the interlayer spacing of MXenes and designing nanocellulose-based separation membranes.