A Covalent Organic Framework Membrane with Homo Hierarchical Pores for Confined Reactive Crystallization

Gas-liquid (G-L) reactive crystallization is a major technology for advanced materials construction, which requires a short diffusion path on the interface to ensure the reactant supply and stable crystal nucleation under ultrahigh supersaturation. Herein, a covalent organic framework (COF) membrane with homo hierarchical pore structures was proposed as an effective interfacial material for the regulation of confined reactive crystallization. By combining the ordered nanopores of COFs and micropores of anodic aluminum oxide (AAO), the COF membrane simultaneously provided an excellent nanoscale diffusion-reaction regulation network as the molecular-level confined G-L reactive interface and adjustable submicrometer gas mass transfer channels. The highly selective construction of CaCO₃ superstructures was then achieved. When the submicrometer primary pore size r_p of the constructed COF membrane ranged from 120 to 1.6 nm, the diffusion mechanism of CO₂ varied from viscous flow diffusion to Knudsen diffusion. The growth orientation of CaCO₃ crystals was well confined to obtain spindle-shaped crystals with high selectivity. Meanwhile, the crystal selectivity factor (cube/sphere) increased from 0 to 3.53 under the low interfacial nuclear barrier. Thus, the COF membrane with coupled micro-nanostructures successfully screened the directional preparation conditions for diverse CaCO₃ superstructures, which also paved a meaningful path for the functional application of COFs in accurate mass transfer control and confined chemical reactions.