MXene versus graphene oxide: Investigation on the effects of 2D nanosheets in mixed matrix membranes for CO2 separation

Two-dimensional titanium carbides, known as MXenes, have attracted growing attention in membrane research community. In this study, a typical MXene, Ti3C2Tx, is incorporated Pebax to fabricate mixed matrix membranes, for CO2 separation, with GO-filled membranes as reference. It is found that MXene-filled membranes afford much higher loading (up to 20 wt%) than GO-filled ones (up to 5 wt%) due to the rich polar groups at MXene surface and the resultant better interfacial interactions. More interestingly, dry-state membranes exhibit the optimal CO2 separation performance at quite low loading (at 1 wt%) for both GO and MXene, which is often seen in Pebax-based mixed matrix membranes, while the permeability and CO2/N2 selectivity of wet-state membranes proceed to increase when filler loading reaches 5 wt% or above, which represents an unusual comparison with the results collected under dry conditions. Since GO and MXene are used without any functionalization, such enhancement of CO2 separation performance at high loading under humidification can be only attributed to the hydrated interlayer channels of MXene/GO. These findings show the unique characteristics of 2D fillers, especially MXene, in wet-state mixed matrix membranes for CO2 separation, and also provide new information to better understand the roles of fillers in Pebax at different content or under different conditions.