Continuous ZIF-8 membranes have showed great potential for gas separation. The prospect is subjected to two pivotal issues: shorten the time to construct the ZIF-8 selective layer and tightly bond ZIF-8 layer onto the substrate. In our previous work, Zn(II)-doped polydopamine (Zn-PDA) linkage layer was proposed and effectual to solve these problems. In this research, the mechanism likely to support the improvements is studied intensively. The dominant factor is that Zn(II) ions can be chelating and depositing sufficiently in the linkage layer. The strongly alkaline condition for dopamine polymerization is also beneficial to Zn(II) chelation and deposition, which has been confirmed by DFT simulation, together with characterization tests, e.g., XPS, FTIR, and Zn(OH)₂ precipitation for Zn(II)–O coordination. Phenolic hydroxyl groups are deprotonated in the strongly alkaline environment with high Mulliken charge (−0.515 & −0.524 e) and become strong chelation sites to Zn(II). Subsequently, Zn(II) clusters extensively filled in the PDA linkage layer are acting as the starting sites for ZIF-8 heterogeneous nucleation and growth. The correspondence between Zn(II) clusters probed by EDX and nascent ZIF-8 crystals visualized by FE-SEM can support this phenomenon clearly. On the whole, the abundant starting sites in Zn-PDA enhanced ZIF-8 growth, and ZIF-8 growth from the rooting-in Zn(II) clusters created an indented and hinged boundary for tightly bonding ZIF-8 layer onto the substrate.

连续的ZIF-8膜已显示出巨大的气体分离潜力。该前景面临两个关键问题：缩短构建ZIF-8选择性层的时间以及将ZIF-8层紧密粘合到基板上的时间。在我们以前的工作中，提出了掺杂Zn（II）的聚多巴胺（Zn-PDA）连接层，对于解决这些问题是有效的。在这项研究中，对可能支持改进的机制进行了深入研究。主导因素是Zn（II）离子可以在连接层中充分螯合和沉积。多巴胺聚合的强碱性条件也有利于Zn（II）的螯合和沉积，这已通过DFT模拟以及表征测试（例如XPS，FTIR和Zn（OH）₂）得到了证实。沉淀的Zn（II）-O配位。苯酚羟基在强碱性环境中具有高Mulliken电荷（-0.515＆-0.524 e）去质子化，并成为Zn（II）的强螯合位点。随后，大量填充在PDA链接层中的Zn（II）簇充当ZIF-8异质成核和生长的起始位点。EDX探测到的Zn（II）团簇与FE-SEM观察到的新生ZIF-8晶体之间的对应关系可以清楚地支持这一现象。总体而言，Zn-PDA中大量的起始位点增强了ZIF-8的生长，而扎根于Zn（II）簇中的ZIF-8的生长则形成了一个锯齿状和铰接的边界，可将ZIF-8层牢固地粘合到基底上。