Harnessing nanoscale spatial effects in inner-modified zeolitic imidazolate framework-8 for enhanced Knoevenagel condensation reaction

Abstract

Metal–organic frameworks (MOFs) have played a pivotal role in catalysis, driven by their remarkable surface areas and structural versatility. The structural manipulation of zeolitic imidazolate frameworks (ZIFs) has shed light on the impact of size, facet orientation, and functional groups in enhancing their catalytic performance. However, these strategies possess inherent limitations, necessitating the pursuit of novel avenues. This study introduces an innovative methodology to elucidate the intricate interplay between the ZIF structure and catalytic activity. This involves externally modifying existing ZIF nanocrystals through precise carving, resulting in the creation of heterogeneous porous architectures. Through the chemical etching of core metal nanoparticles within ZIF-8 nanocrystals, the introduction of heterogeneous internal mesoporosity within ZIF-8 emerges, providing effective mass transport and uncoordinated active sites for enhanced heterogeneous catalysis. The effectiveness of this porous inner space is demonstrated through the Knoevenagel condensation reaction. Four different types of ZIF-8 crystal structures undergo evaluation for catalytic activity: pristine ZIF nanocubes, etched ZIF nanocubes, ZIFs with gold nanorod cores, and ZIFs with inner etched spaces. This innovative approach, centered on introducing heterogeneous porosity within ZIF-8, offers promising prospects for the design of ZIF-based catalysts boasting exceptional catalytic efficiency in various organic transformations.