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

Abstract

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.

Tunable Morphosynthesis of Calcium Carbonate in Aqueous Solution Enabled by Janus Membrane

“…In addition, the transfer of CO 3 2− ions was accompanied by the transfer of NH 4 + ions, which were used as buffer ions to maintain the stable conductivity of the “Ca 2+ ‐CO 3 2− ‐H 2 O” system during the formation of CaCO 3 crystals to stable nucleation. [ 16 ] However, the ion transfer rate decreased significantly with the continuous decrease of the hydrophilicity of JMs, resulting in an insufficient supply of CO 3 2− ions at the L–L interface, which was difficult to maintain the stability of the supersaturated state of the interface. The nucleation rate was reduced, which made it difficult for the number of nano units to meet the assembly requirements of hollow sphere CaCO 3 , resulting in a decrease of hollow CaCO 3 crystals.…”