Microwave-Assisted, Ni-Induced Fabrication of Hollow ZIF-8 Nanoframes for the Knoevenagel Reaction

Abstract

Morphology-controlled synthesis of metal–organic frameworks (MOFs) is of tremendous importance to understand the morphology–structure–property relationships. Although great emphasis has been placed on the controllable synthesis of MOFs, the preparation of hollow and nanoframe-like MOFs, especially using the microwave irradiation method, remains a great challenge. In the present work, we report microwave-assisted synthesis of hollow butterfly and ring zeolitic imidazolate framework-8 (ZIF-8) with the stimuli of Ni ions. Interestingly, the sphere, butterfly, and fiber ZIF-8 catalysts were also fabricated when adjusting the weight ratio of Zn and Ni resources. Specifically, sphere, butterfly, hollow butterfly, and ring particles have maintained the ZIF-8 structure. On the basis of the time sequential experiments, we inferred that the formation of hollow butterfly and ring particles is driven by the change of surface energy. The Knoevenagel reaction was carried out to explore the catalytic activity of these ZIF materials. The ring particles with ZIF-8 structure showed the highest catalytic activity. The open structure, thin walls, and the amount of basicity have been extensively discussed to shed light on the superior catalytic performance of ring particles.