Pore segmentation and shielding: A dual strategy to prepare sub-nanometer covalent-organic-framework based membranes...

The extensive use of nuclear energy has led to an urgent need for effective management of radioactive waste. Membrane separation of radionuclides is considered to be a promising method for nuclear waste treatment and resource recovery. However, most reported membranes have difficulties achieving a balance between permeability and selectivity. In this work, we propose a dual strategy to produce sub-nanometer COF-based membranes, which includes constructing covalent organic frameworks (COFs) from smaller building blocks ('pore segmentation') and introducing a graphene oxide (GO) nanosheet by weak interaction to shield pores ('pore shielding') during the preparation of COF membranes. The as-prepared TpDAH@GO membrane shows two times higher permeability (P _K = 4.5 mmol m^-2 h^-1) than that of pure GO membrane due to the retention of unique 'pore transport' of COFs. In addition, the selectivity of TpDAH@GO membrane for metal ion sieving (S _K/Th = 3.93) nearly doubles when compared with that of the original COF membrane, due to the additional introduction of 'interlayer transport'. The dual strategy proposed in this study successfully constructed a sub-nanometer COF-based membrane and achieved a valuable balance between permeability and selectivity on the membrane, which provides new possibilities for the pore regulation of COF membranes as well as the preparation of high-performance sub-nanometer membranes for efficient metal ion sieving.