Intercrystalline Channels at Subnanometer Scale for Precise Molecular Nanofiltration

Membrane-based technologies can provide cost-effectiveand energy-efficientmethods for various separation processes. The key goal is to developmaterials with uniform, tunable, and well-defined subnanometer-scalechannels. Suitable membrane materials should have high selectivityand permeance and can be manufactured in a robust and scalable fashion.Here, we report the construction of sub-1 nm intercrystalline channelswith such characteristics and elucidate their transport properties.These channels are formed by assembling 3D aluminum formate crystalsduring the amorphous-to-crystalline transformation process. By controllingthe transformation time, the channel size can be tuned from the macroscopicscale to nanometer scale. The resulting membranes exhibit tailoredselectivity and permeance, with molecular weight cutoffs ranging fromaround 300 Da to approximately 650 Da, and ethanol permeance rangingfrom 0.8 to 22.0 L m(-2) h(-1) bar(-1). We further show that liquid flow through these channelschanges from viscosity-dominated continuum flow to subcontinuum flow,which can be described by a modified Hagen-Poiseuille model.Our strategy provides a new scalable platform for applications thatcommonly exploit nanoscale mass transport.