Pore segmentation and shielding: a dual strategy to prepare sub-nanometer covalent-organic-framework based membranes for selective metal ion sieving

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 (PK = 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 (SK/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.