Aqueous two-phase system features with ultralow interfacial tension and thick interfacial region, affording unique confined space for membrane assembly. Here, for the first time, an aqueous two-phase interfacial assembly method is proposed to fabricate covalent organic framework (COF) membranes. The aqueous solution containing polyethylene glycol and dextran undergoes segregated phase separation into two water-rich phases. By respectively distributing aldehyde and amine monomers into two aqueous phases, a series of COF membranes are fabricated at water–water interface. The resultant membranes exhibit high NaCl rejection of 93.0–93.6% and water permeance reaching 1.7–3.7 L m⁻² h⁻¹ bar⁻¹, superior to most water desalination membranes. Interestingly, the interfacial tension is found to have pronounced effect on membrane structures. The appropriate interfacial tension range (0.1–1.0 mN m⁻¹) leads to the tight and intact COF membranes. Furthermore, the method is extended to the fabrication of other COF and metal–organic polymer membranes. This work is the first exploitation of fabricating membranes in all-aqueous system, confering a green and generic method for advanced membrane manufacturing.

水性两相系统具有超低界面张力和厚界面区域的特点，为膜组装提供了独特的密闭空间。在这里，首次提出了一种水性两相界面组装方法来制造共价有机骨架（COF）膜。含有聚乙二醇和葡聚糖的水溶液经历分离的相分离成两个富含水的相。通过将醛和胺单体分别分配到两个水相中，在水-水界面制备了一系列 COF 膜。所得膜表现出 93.0–93.6% 的高 NaCl 排斥率和水渗透率达到 1.7–3.7 L m ⁻²  h ⁻¹  bar ⁻¹，优于大多数海水淡化膜。有趣的是，发现界面张力对膜结构有显着影响。适当的界面张力范围 (0.1–1.0 mN m ^-1 ) 会产生紧密且完整的 COF 膜。此外，该方法还扩展到其他 COF 和金属有机聚合物膜的制造。这项工作是在全水体系中制造膜的首次开发，为先进的膜制造提供了一种绿色和通用的方法。