Morphological control of covalent organic frameworks (COFs) is particularly interesting to boost their applications; however, it remains a grand challenge to prepare hollow structured COFs (HCOFs) with high crystallinity and uniform morphology. Herein, we report a versatile and efficient strategy of amorphous-to-crystalline transformation for the general and controllable fabrication of highly crystalline HCOFs. These HCOFs exhibited ultrahigh surface areas, radially oriented nanopore channels, quite uniform morphologies, and tunable particle sizes. Mechanistic studies revealed that H₂O, acetic acid, and solvent played a crucial role in manipulating the hollowing process and crystallization process by regulating the dynamic imine exchange reaction. Our approach was demonstrated to be applicable to various amines and aldehydes, producing up to 10 kinds of HCOFs. Importantly, based on this methodology, we even constructed a library of unprecedented HCOFs including HCOFs with different pore structures, bowl-like HCOFs, cross-wrinkled COF nanocapsules, grain-assembled HCOFs, and hydrangea-like HCOFs. This strategy was also successfully applied to the fabrication of COF-based yolk–shell nanostructures with various functional interior cores. Furthermore, catalytically active metal nanoparticles were implanted into the hollow cavities of HCOFs with tunable pore diameters, forming attractive size-selective nanoreactors. The obtained metal@HCOFs catalysts showed enhanced catalytic activity and outstanding size-selectivity in hydrogenation of nitroarenes. This work highlights the significance of nucleation-growth kinetics of COFs in tuning their morphologies, structures, and applications.

中文翻译：

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无定形到晶体的转变：具有高结晶度的中空结构共价有机框架的一般合成

共价有机框架 (COF) 的形态控制对于促进其应用特别有意义；然而，制备具有高结晶度和均匀形态的中空结构 COF（HCOF）仍然是一个巨大的挑战。在此，我们报告了一种通用且有效的非晶向晶体转变策略，用于高结晶 HCOF 的通用和可控制造。这些 HCOF 表现出超高表面积、径向取向的纳米孔通道、非常均匀的形态和可调节的粒径。机理研究表明，H ₂O、乙酸和溶剂通过调节动态亚胺交换反应在操纵空心过程和结晶过程中发挥了至关重要的作用。我们的方法被证明适用于各种胺和醛，产生多达 10 种 HCOF。重要的是，基于这种方法，我们甚至构建了一个前所未有的 HCOF 库，包括具有不同孔结构的 HCOF、碗状 HCOF、交叉皱纹 COF 纳米胶囊、颗粒组装 HCOF 和绣球花状 HCOF。该策略还成功地应用于制造具有各种功能内核的基于 COF 的蛋黄壳纳米结构。此外，将催化活性金属纳米粒子植入孔径可调的 HCOF 的空腔中，形成有吸引力的尺寸选择性纳米反应器。所获得的金属@HCOFs催化剂在硝基芳烃的加氢中表现出更高的催化活性和出色的尺寸选择性。这项工作突出了 COF 的成核生长动力学在调整其形态、结构和应用方面的重要性。