Sub‐Nanoporous Engineered Fibrous Aerogel Molecular Sieves with Nanogating Channels for Reversible Molecular Separation

Abstract

mainly relies on the energy-intense method involving repeated cryogenic distillation and extraction cycles, while the associated energy penalty urgently promotes interest in alternative energy-saving separation methods. [3] Adsorption separation using the nanoporous molecular sieves is considered to be an appealing alternative due to the integrated advantages of mild energy consumption, ease of operation, and tiny carbon footprints. [4] Traditional porous molecular sieves, such as porous carbon and resin microspheres, are plagued by intractable obstacles to achieving the precise separation toward molecules with sub-nanoscale size (<1 nm) due to the larger inherent pore window size. [5] Intuitively, sub-nanoporous architecture is the critical prerequisite to fulfill impressive separation selectivity, because sub-1 nm pores could synergistically enhance the surface area and amplify the size-exclusion effect. [6] Therefore, developing a new class of sub-nanoporous engineered molecular sieves is necessary yet an emerging challenge to the chemistry community. Recently, the state-of-the-art sub-nanoporous structured metal-organic frameworks (MOFs), porous organic cages (POCs), and covalent-organic frameworks (COFs) have been synthesized through bottom-up strategies via molecular engineering. [7] The intrinsic rigid molecular-level channels and abundant sub-nanoscale pores derived from highly delicate molecular engineering can discriminate complicated guests with different shapes, sub-nanoscale size, and polarity. However, the abovementioned molecular sieves are confronted with two limiting issues when it comes to the practical chemical separations: i) the onefold and nonreversible surface polarity of nanoporous channels is a hindrance to achieving the on-demand separation of polar/nonpolar molecule mixtures; and ii) the object materials are normally in the form of discrete powders rather than 3D macroscopic monolith, practical applications for employing powders as sieving layers require integrating them on continuous bulk substrates. [8] In sharp contrast, nanofibers, with the integration of excellent structural continuity and self-supporting characteristics, hold great promise in real-world molecular separation applications. Whereas, it has remained a challenging issue of nanofibers to achieve precise sieving for sub-nanoscale molecule mixtures due to the innate deficiency that they are usually nonporous or just contain a combination of pores of larger size Gating molecular separation using artificial sub-nanoporous molecular sieves is highly desirable in large-scale chemical and energy processing, such as gas separation, hydrogen recovery, carbon dioxide capture, seawater desalination, etc. However, it has remained an insurmountable challenge to create such materials. Herein, a binary meso-reconstruction strategy to develop biomimetic sub-nanoporous engineered aerogel molecular sieves (NAMSs) with reversible nanogating channels is demonstrated, in which sub-1 nm pores (≈7 Å) provide coupling size-thermodynamic gat...

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