Incorporating two-dimensional (2D) nanomaterials into polymer matrices can be an effective strategy to increase the performance of membranes, overcoming the permeability/selectivity trade-off. So far, MXene-based gas separation mixed matrix membranes (MMMs) have been limited to Ti3C2 and they demonstrated high gas separation performance. However, information about the influence of composition and structure of MXene on the performance of MMM is still lacking. Herein, a systematic investigation of the effect of the chemical composition and number of layers of MXenes on the CO2 transport properties of MMMs is reported. Mo2TiC2, Ti2C and V2C MXenes were incorporated into a Pebax-1657 matrix. The results revealed that the number of MXene layers considerably affects the dispersion of MXenes in the polymer matrix that contain crystalline and amorphous domains, M3C2 MXenes (Mo2TiC2 and Ti3C2) improve membrane separation more than M2C MXenes (Ti2C and V2C). In addition, in the case of M3C2 MXenes (Mo2TiC2 and Ti3C2), composition strongly affect the dispersion of nanosheets in the polymer, as confirmed by X-ray diffraction and mechanical properties analysis. Molecular dynamics (MD) simulation combined with gas permeation models further confirmed the excellent compatibility of MXenes with the polymer chains. Significant improvement in CO2 permeability (up to 70%) and CO2/N2 separation selectivity (up to 137%) was achieved, placing MXene MMMs above the 2008 Robeson upper bound, implying defect-free interfaces and excellent matrix dispersion. Finally, the impact of feed composition, temperature, and pressure on gas separation performance of the MMMs was fully investigated. Our findings indicate the tremendous potential that tuning MXene properties can have for the development of high-performance gas separation membranes.
