Desalination can help to alleviate the fresh-water crisis facing the world. Thermally driven membrane distillation is a promising way to purify water from a variety of saline and polluted sources by utilizing low-grade heat. However, membrane distillation membranes suffer from limited permeance and wetting owing to the lack of precise structural control. Here, we report a strategy to fabricate membrane distillation membranes composed of vertically aligned channels with a hydrophilicity gradient by engineering defects in covalent organic framework films by the removal of imine bonds. Such functional variation in individual channels enables a selective water transport pathway and a precise liquid–vapour phase change interface. In addition to having anti-fouling and anti-wetting capability, the covalent organic framework membrane on a supporting layer shows a flux of 600 l m^–2 h^–1 with 85 °C feed at 16 kPa absolute pressure, which is nearly triple that of the state-of-the-art membrane distillation membrane for desalination. Our results may promote the development of gradient membranes for molecular sieving.

海水淡化有助于缓解世界面临的淡水危机。热驱动膜蒸馏是一种很有前途的方法，可以利用低热量从各种盐水和污染源中净化水。然而，由于缺乏精确的结构控制，膜蒸馏膜的渗透性和润湿性有限。在这里，我们报告了一种策略，通过去除亚胺键，通过共价有机框架膜中的工程缺陷来制造由具有亲水性梯度的垂直排列通道组成的膜蒸馏膜。单个通道中的这种功能变化可以实现选择性的水传输路径和精确的液-气相变界面。除了具备防污防湿能力外，^–2  h ^–1在 85 °C 进料和 16 kPa 绝对压力下，这几乎是用于脱盐的最先进的膜蒸馏膜的三倍。我们的结果可能会促进用于分子筛分的梯度膜的发展。