Fabricating Heterostructured Janus Covalent Organic Framework Membranes via Multiphase Interfacial Polymerization

Herein, a multiphase interfacial polymerization strategy has been developed to fabricate A-to-B type Janus covalent organic framework (COF) membranes with asymmetric properties. This approach allows for one-pot construction of COF membranes with opposite wettability on the upper and lower surfaces via simultaneous but independent interfacial polymerizations at two interfaces of a three-phase system. Integrating two distinct two-dimensional COF layers with the same frame structure but differing in side chains, the resulting Janus COF membrane exhibits hydrophilic feature on one side but displays hydrophobic characteristic on the other side, with water contact angle of 0o and 133o, respectively. Additionally, this Janus COF membrane exhibits exceptional anti-pollution performance and exclusively permits unidirectional water transportation. This unique property is not observed in the homogeneous COF membranes fabricated from the same building blocks. This multiphase interfacial polymerization strategy could offer a general way to fabricate Janus membranes with designable, predictable and controllable asymmetric wettability, holding promise for a wide range of materials and diverse applications.