Covalent organic framework membrane reconstructed through intra-pore reaction having tunable performance for molecular separation

An amine-rich covalent organic framework (COF) membrane was firstly designed and fabricated through the interfacial polymerization (IP) of 3,3′-diaminobenzidine (DAB) and 1,3,5-triformylphloroglucinol (Tp) reactive monomers on polysulfone (PSf) substrate. The as-prepared TpDAB/PSf membrane displayed an ultra-high water permeability of ∼ 61 L⋅m−2⋅h−1⋅bar−1 and excellent dye/salt separation performance with 97.7% rejection of congo red and no rejection of MgCl2 or Na2SO4. And then, small molecules with acyl chloride groups including sebacyl-chloride (SBC) or 1,3,5-trimellityl-chloride (TMC) were introduced to reconstruct the nanoporous structure of COF through intra-pore reaction with amine groups of the TpDAB separation layer. Although the TpDAB-SBC/PSf and TpDAB-TMC/PSf membranes exhibited reduced water permeability of ∼ 15 L⋅m−2⋅h−1⋅bar−1, both showed high rejection or desalination performance toward small molecules, such as ≥ 95% dye rejection (Mw > 461.4 Da), ∼10% Na2SO4 rejection and nearly no rejection of MgCl2. Therefore, a facile and rapid intra-pore reaction was feasible for reconstructing the nanoporous structure of amine-rich COF membranes to achieve tunable performance for the removal, purification and desalination of small molecules.