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.
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This research was supported by the analysis and testing centre of the Beijing Institute of Technology for basic characterization. We acknowledge D. Lu and J. Li from Tsinghua University for their suggestions on mechanism discussion. C.J. appreciates the help from M. Wu. B.W. acknowledges financially support from the National Natural Science Foundation of China (grant nos 21625102 and 21971017), National Key Research and Development Program of China (2020YFB1506300), Beijing Municipal Science and Technology Project (Z181100004418001) and Beijing Institute of Technology Research Fund Program. X.F. acknowledges support from the National Natural Science Foundation of China (grant nos 21922502 and 21674012). R.Y. acknowledges support from the 1331 Project of Shanxi Province. F.W. acknowledges support from the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB22040402) and the CAS Youth Innovation Promotion Association.
The authors declare no competing interests.
Peer review information Nature Materials thanks Zhiping Lai, Huanting Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Zhao, S., Jiang, C., Fan, J. et al. Hydrophilicity gradient in covalent organic frameworks for membrane distillation. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-01052-w