Controlling ZIF-8 nano- and microcrystal formation and reactivity through zinc salt variations

What is it about?

We demonstrated that phase pure ZIF-8 crystals can be produced from Hmim and various zinc sources in methanol at room temperature. The reactivity of the zinc salt in the growth solution was found to markedly affect the size and morphology of ZIF-8 particles produced after 1 h reaction and at the same concentration of the zinc salt. Small ZIF-8 nanocrystals with diameters varying between ca. 50 and 200 nm were obtained with reactive zinc salts like Zn(acac)2, Zn(NO3)2, ZnSO4 or Zn(ClO4)2. The use of ZnCl2, Zn(OAc)2 or ZnI2 afforded crystals with sizes varying between ca. 350 and 650 nm. Finally, the use of the low reactive ZnBr2 was found to generate microsized crystals. These significant changes in particle size induced distinctive changes in the adsorption properties as demonstrated by BET measurements but also in the catalytic performance of ZIF-8 crystals in Knoevenagel and Friedländer condensation reactions used as models. The small sized crystals produced from Zn(NO3)2 exhibited the highest surface area and the best catalytic activity.

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Why is it important?

Particle size and morphology were found to be dependent on the reactivity of the Zn(+2) salt. The size of ZIF-8 crystals allows to tune their reactivity.

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