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 nanoframelike 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.

Controllable Synthesis of Metal-Organic Frameworks and Their Hierarchical Assemblies

“…39 Likewise, in 2018, Sun and coworkers sequentially tuned the shapes of a ZIF from fiber to sphere by tuning ratio of zinc and nickel salt. 40 These two works shed light on the emerging prospect of designing multivariate MOFs with tunable geometries.…”

Metal-organic Framework-based Materials: Synthesis, Stability and Applications in Food Safety and Preservation

“…[163] Zhang et al found that microwave-assisted method can synthesize various morphologies of ZIF-8 with spherical, fibrous, hollow butterfly, and ring shapes driven by the change of surface energy with the stimuli of Ni ions. [166] These synthesized ZIF-8 crystals showed different catalytic activities in the Knoevenagel reaction.…”

“…[73] The advantages of microwaveassisted method for MOF synthesis are summarized as less period of reaction time, [163][164][165] high yield, [163] high reaction efficiency, [73] and flexible control of morphology and size. [166] Smaller sized MOF particles with nanoscale and polymorphs are always obtained by the microwave-assisted method, which is likely due to the accelerated nucleation and crystal growth caused by direct heating from microwave. [73] Microwaveassisted synthesis of UiO-66(Zr) in a continuous-flow microwave system was completed for only 10 min with the yield of ~90%, which took typically 24 h for completion in the solvothermal method with a very low synthetic ratio.…”

Entropy‐Driven Mechanochemical Synthesis of Polymetallic Zeolitic Imidazolate Frameworks for CO2 Fixation

“…Divalent metal ions including Mg II , Mn II , Fe II , Cd II , Ni II , Cu II with similar atomic diameters to Zn II or Co II were mainly considered. Among these, particular attention was paid to Mg II , Mn II , Cd II , Ni II and Cu II because of their successful individual synthesis or dope in ZIF‐8 or ZIF‐67 lattices to partially substitute Zn II or Co II . However, the formation of Mg II or Mn II ZIFs needs to perform under inert gas atmosphere, which is too difficult to achieve in a mechanochemical procedure .…”