Internally Extended Growth of Hierarchical MOF-on-MOF Nanostructures for Adsorption

The fabrication of metal–organic frameworks with hierarchical porosity (HP-MOFs) is one of the most efficient ways to solve the mass transfer problems of most MOFs caused by micropores. This study develops a facile and efficient strategy for nanoconstructing HP-MOFs using polyvinylpyrrolidone (PVP) coated γ-cyclodextrin-MOF (γ-CD-MOF) as a template. The PVP on the surface of the γ-CD-MOF acts as an attachment site for metal ions and provides nucleation sites for the subsequent growth of other MOFs with different crystallographic parameters since the polar groups of PVP have a strong affinity for metallic ions. The γ-CD-MOF/PVP templates are easily removed by an alcohol/water solution, resulting in the formation of HP-MOF. This general strategy has been successfully used to prepare ZIF-67 and ZIF-8. The hierarchical porosity can be adjusted by tuning the size of the γ-CD-MOF/PVP templates. In potential applications, such as the catalytic degradation of tetracycline and adsorption of malachite green, HP-ZIF-67 demonstrates significantly higher catalytic and adsorption efficiencies compared to ZIF-67 due to its nanoconstructing enhanced mass transfer capabilities.