Investigating molecule transport behaviors in two-dimensional nanochannels with adjusted interlayer spacing

Two-dimensional (2D) lamellar membranes are favored over other membrane materials. However, the molecule transport behaviors in confined 2D nanochannels remain ambiguous, specifically the role of interlayer spacing which determines the confined effect. Herein, vertically-aligned nanochannel membranes with adjusted interlayer spacing (0.6 nm, 2.1 nm, and 3.9 nm) were fabricated by vermiculite lamellar membranes. These robust and long-range 2D nanochannels maintain stable molecule configuration state throughout the transport process, providing ideal platforms for investigating molecule transport behaviors. We demonstrate that molecules with weak molecule-molecule interactions (mainly nonpolar molecules) continuously collide with each other in the nanochannels. The extremely confined nanochannels (0.6 nm) restrict the random molecule collision and permit the oriented flow along transport direction, thus offering the highest transport efficiency. In contrast, molecules in wider nanochannels (3.9 nm) collide randomly, impairing the velocity of molecules or even compelling some of them to move to the adverse flow direction. This consumes cohesive energy and leads to lower permeance. The transport rate of benzene reaches over 130 L m -2 h -1 bar -1 nm -1 for 0.6 nm-nanochannel membrane, which is 8 times higher than that of 3.9 nm-nanochannel membrane. Compared to nonpolar molecules, the strong molecule-molecule and molecule-channel interactions for polar molecules would weaken this collision effect, thus the difference of transport rate is relatively small with nanochannel size.