State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, 200240, People's Republic of China.
College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018, People's Republic of China.
Nanoscale. 2023 May 4;15(17):7703-7709. doi: 10.1039/d3nr00702b.
Understanding the growth and coarsening mechanisms of metal-organic framework (MOF) nanoparticles is crucially important for the design and fabrication of MOF materials with diverse functionalities and controllable stability. Oriented attachment (OA) growth is a common manner of MOF nanocrystal coarsening and agglomeration, but the underlying molecular mechanisms have not been well understood to date. Here we report the molecular-scale characterization of the OA interfaces of zeolitic imidazolate framework (ZIF) crystals by state-of-the-art low-dose aberration-corrected transmission electron microscopy. A series of OA interfaces with different molecular structures are captured, implying that multiple kinetic steps are involved in the OA growth of ZIF crystals from non-directional physical attractions between primary nanocrystals, lattice-aligned attachment of the ligand-capped nanocrystals, to coherent interfaces with perfect lattice alignment or stacking faults. It was found that the surface-capping organic ligands not only play an essential role in crystal lattice alignment by near-field directional interactions, but also dominate the interfacial reaction kinetics by interfacial diffusion-controlled elimination of excess surface-capping ligands. These observations provide molecular-scale insights into the OA growth mechanisms of ZIF crystals, which is important for engineering MOF crystal growth pathways by designing surface-capping ligands.
了解金属-有机骨架（MOF）纳米粒子的生长和粗化机制对于设计和制备具有多种功能和可控稳定性的 MOF 材料至关重要。定向附着（OA）生长是 MOF 纳米晶体粗化和聚集的常见方式，但迄今为止，其潜在的分子机制尚未得到很好的理解。在这里，我们通过最先进的低剂量像差校正透射电子显微镜报告了沸石咪唑酯骨架（ZIF）晶体 OA 界面的分子尺度特征。捕获了一系列具有不同分子结构的 OA 界面，这意味着 ZIF 晶体的 OA 生长涉及多个动力学步骤，包括初级纳米晶体之间的非定向物理吸引力、配体封端纳米晶体的晶格对准附着，以及具有完美晶格对准或堆叠缺陷的相干界面。研究发现，表面封端的有机配体不仅通过近场定向相互作用在晶格对准中起至关重要的作用，而且通过界面扩散控制消除多余的表面封端配体来控制界面反应动力学。这些观察结果为 ZIF 晶体的 OA 生长机制提供了分子尺度的见解，这对于通过设计表面封端配体来工程化 MOF 晶体生长途径非常重要。
