In-situ crystallization of covalent organic framework fillers in mixed matrix membranes via the reactive surface segregation approach

Covalent organic frameworks (COFs) offer great potential as membrane materials due to their periodic nanopore structure, high porosity, and extensive chemical tunability. However, directly processing crystallized COFs into membranes presents great challenges. To overcome these issues, alternative routes such as polymer blending during membrane formation and their subsequent crystallization offer promising avenues to harness their advantages. In this work, we decoupled the membrane formation and crystallization of COFs processes and introduced a reactive surface segregation method to fabricate COF-based mixed matrix membranes (MMMs). The amine and aldehyde monomers quickly formed an amorphous network at the solvent/non-solvent interface, while polymer matrix separated from the liquid phase to construct membranes during the non-solvent induced phase separation (NIPS) processes. Subsequently, the prepared membranes were heated in acetic acid solution to in-situ crystalize the COF fillers in the MMMs. The peaks at 8.33° and 12.4° assigned to the (110) and (120) reflection planes in the XRD spectrum indicated that the amorphous network was in-situ crystallized. The optimized membrane exhibited a water permeance of 203 L m −2 h −1 bar −1 , over 98.5 % of rejection rates for dyes, and long-term stability for 720 h. This approach creates a new pathway to prepare the advanced COF-based membranes and represents a significant leap forward in the field of membrane technology.