Loose nanofiltration membrane constructed via interfacial polymerization using porous organic cage RCC3 for dye/salt separation

Fabricating loose membranes with well-tailored porosity for effective molecular separations remains challenging. Here, we introduce RCC3, a soluble porous organic cage (POC), as an amine monomer to fabricate polyamide (PA) membrane with loose structure via interfacial polymerization and evaluate the membrane performance in dye/salt separation. RCC3 is a [4 + 6] amine molecular cage with ideal stability and sub-nanometer macrocyclic cavity (∼7 Å). The intrinsic porosity and large interchain pores formed by its participation in interfacial polymerization provide extra transport channels in membrane and contribute to realizing precise aperture sieving with high permeation flux. Meanwhile, the unique structure of RCC3 (molecular-level size, organic framework and rich –NH– groups) helps to achieve molecular-level mixing between polymer chains and individual caged molecules in the membrane, thus overcoming the problem of interfacial defects. Under the condition of optimal RCC3/PIP mass ratio, the as-prepared membrane exhibited favorable water permeability of 52.55 LMH/bar (5.2 times of PIP/TMC membrane) with good dye rejection (98.6% for MEB) and salt permeability. Due to the extremely low surface roughness (Ra = 12.5 nm), the membrane exhibited outstanding anti-fouling capacity with high and stable flux recovery rate. Furthermore, the membrane possessed excellent long-term stability, which underlined the promising potential in practical application.