Cavity engineering of amorphous zeolitic imidazolate framework colloids and their core-shell architectures

Metal-organic frameworks (MOFs), as a class of typical crystalline porous solids, have been extensively studied and applied in various fields, including gas adsorption and separation, catalysis, and chemical sensing. Recently, compared to their crystalline counterparts, the amorphous states of MOFs have attracted growing interest because they possess unique properties such as mechanical robustness, stability, molecular selectivity, and processability. However, the direct synthesis of amorphous MOF colloids remains a significant challenge, particularly for fabricating complex micro- and nanostructures such as hollow or yolk-shell architectures. Herein, we develop a simple strategy to synthesize hollow structures in amorphous zeolitic imidazolate framework (ZIF) colloids through controlled post-synthetic etching. Tannic acid, functioning as a proton etching agent, was utilized to achieve selective dissolution of the inner region in pre-formed monodisperse amorphous ZIF colloids, forming a uniform hollow structure. This etching process has been successfully demonstrated across various ZIFs, providing strong evidence of the method’s universality for ZIF systems. Furthermore, this method can also be applied to the synthesis of conformal yolk-shell structures by precisely etching the core-shell structure. The synthesized hollow ZIF nanoparticles hold great potential for applications across diverse fields, including catalysis and drug delivery. More importantly, this method pioneers a new pathway for cavity engineering of amorphous MOF colloids.