Abstract
2D materials' membranes with well-defined nanochannels are promising for precise molecular separation. Herein, the design and engineering of atomically thin 2D MXene flacks into nanofilms with a thickness of 20 nm for gas separation are reported. Well-stacked pristine MXene nanofilms are proven to show outstanding molecular sieving property for H-2 preferential transport. Chemical tuning of the MXene nanochannels is also rationally designed for selective permeating CO2. Borate and polyethylenimine (PEI) molecules are well interlocked into MXene layers, realizing the delicate regulation of stacking behaviors and interlayer spacing of MXene nanosheets. The MXene nanofilms with either H-2- or CO2-selective transport channels exhibit excellent gas separation performance beyond the limits for state-of-the-art membranes. The mechanisms within these nanoconfined MXene layers are discussed, revealing the transformation from "diffusion-controlled" to "solution-controlled" channels after chemical tuning. This work of precisely tailoring the 2D nanostructure may inspire the exploring of nanofluidics in 2D confined space with applications in many other fields like catalysis and energy conversion processes.