Abstract Covalent organic frameworks (COFs) has emerged as a highly promising platform material for the manufacturing of molecule-separating membranes. However, COF membranes are predominantly used in the separation of dyes from water or organic solvents and there are very few reports on COF-enabled membranes for desalination. In this work, the secondary growth approach based on unidirectional diffusion synthesis is developed to grow continuous thin films of a COF with an intrinsic pore size of 0.8 nm on macroporous substrates to prepare COF membranes for desalination. The amino-modified polymer microfiltration substrate is fixed in a diffusion cell to separate the oil phase containing the aldehyde precursor (1,3,5-triformylphloroglucinol, Tp) and the aqueous phase containing both the amino precursor (hydrazine, Hz) and the catalyst. Because of the immiscible bi-phase solutions and the high molar ratio of Hz to Tp, the unidirectional diffusion of Hz molecules in the pore channel of the substrate is achieved and the polycondensation between the two precursors occurs at the phase interface. The unidirectional diffusion synthesis is sequentially performed for two times and the secondary growth is essential to ensure the formation of a defect-free, continuous thin film of COF (TpHz) on the top surface of the substrate. Cladding COF coatings are also formed along the skeleton in the near-surface region of the substrate. Such an asymmetric structure ensures both a good permselectivity and a strong adhesion between the grown COF layers and the substrates. The continuous COF thin film grown on the substrates serves as the selective layer, and the COF membrane prepared under the optimized condition exhibits an appreciable Na2SO4 rejection of 58.3% and a water permeance of 40.5 L∙m−2∙h−1∙MPa−1 which are ~ ten times higher than other membranes with similar rejections. This study not only demonstrates the potential of COFs in desalination but also showcases an efficient strategy to grow continuous thin films of COFs on porous substrates which are desired in diverse applications.

中文翻译：

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用于快速脱盐的多孔基材上共价有机框架 (COF) 的二次生长

摘要 共价有机骨架 (COF) 已成为制造分子分离膜的一种极具前景的平台材料。然而，COF 膜主要用于从水或有机溶剂中分离染料，关于使用 COF 膜进行脱盐的报道很少。在这项工作中，开发了基于单向扩散合成的二次生长方法，以在大孔基材上生长固有孔径为 0.8 nm 的 COF 连续薄膜，以制备用于脱盐的 COF 膜。氨基改性聚合物微滤基材固定在扩散池中，以分离含有醛前体（1,3,5-三甲酰基间苯三酚，Tp）的油相和同时含有氨基前体（肼，Hz）和催化剂的水相. 由于不混溶的双相溶液和Hz与Tp的高摩尔比，实现了Hz分子在基材孔道中的单向扩散，并且两种前驱体之间的缩聚发生在相界面处。单向扩散合成依次进行两次，二次生长对于确保在基板顶面上形成无缺陷、连续的 COF (TpHz) 薄膜至关重要。包层 COF 涂层也沿基体近表面区域的骨架形成。这种不对称结构确保了良好的渗透选择性和生长的 COF 层与衬底之间的强附着力。在衬底上生长的连续 COF 薄膜作为选择层，在优化条件下制备的 COF 膜表现出可观的 58.3% 的 Na2SO4 截留率和 40.5 L∙m-2∙h-1∙MPa-1 的水渗透率，比具有类似截留率的其他膜高约 10 倍。这项研究不仅证明了 COFs 在海水淡化中的潜力，而且展示了一种在多孔基材上生长连续 COFs 薄膜的有效策略，这是各种应用所需要的。