3D-ordered macropores in SOM-ZIF-8 for bulky-molecule–involved applications. Furthermore,
the reaction time for complete conversion of
benzaldehyde was consistently 2 to 3 hours when
the average particle size was decreased from
4.3 mm for SOM-ZIF-8(3, 0.67) to 1.3 mm for SOM-
Additionally, SOM-ZIF-8 exhibited superior
structural stability and improved recyclability
as compared with PH-ZIF-8 composed of inter-
grown polycrystals. SOM-ZIF-8(3, 0.33) could be
reused at least seven times (Fig. 4B), with benz-
aldehyde conversion only decreasing from 94.6
to 87.0%. Comparably, a ≥5% decrease in catalytic
activity was observed in every subsequent run for
PH-ZIF-8. The TEM image of used PH-ZIF-8 in-
dicates that the recycling operation may cause a
severe collapse in its hollow structure, resulting
in utrasmall ZIF-8 nanocrystals that are lost in
the separation step (fig. S39). In sharp contrast,
SOM-ZIF-8 experienced much less structural dam-
age, with its 3D-ordered macro-microporous struc-
ture being well preserved after seven reaction
cycles. The durability of SOM-ZIF-8 can be attri-
buted to its robust single-crystalline framework
with much lower defect density in comparison
with PH-ZIF-8 (fig. S40).
The reaction of various substituted benzalde-
hydes with malononitrile was also performed
with SOM-ZIF-8(3, 0.33) and C-ZIF-8 (table S2).
For all investigated substrates, SOM-ZIF-8(3, 0.33)
always showed much higher catalytic activities
than C-ZIF-8 under identical reaction conditions.
The activity enhancement was even notable for
benzaldehydes with bulky groups (table S2, entries
Fig. 3. Controlled growth of SOM-ZIF-8 by regulating solvents and PS
sizes. (A to C) SEM images of various samples prepared with different
volume fractions of NH3·H2O: (A) 0, (B) 0.33, and (C) 0.67. (D to K)
HAADF-STEM images of various SOM-ZIF-8 crystals with macropore sizes
ranging from 190 to 470 nm, as determined by carefully controlling the
diameter of the PS templates: (D and H) 190 nm, (E and I) 340 nm, (F and J)
400 nm, and (G and K) 470 nm. The images in (H) to (K) are magnified
views of the areas outlined by the squares in (D) to (G).
Fig. 4. Comparing the catalytic performance of SOM-ZIF-8 with C-ZIF-8, PH-ZIF-8, and
M-ZIF-8. (A) Benzaldehyde conversions over various samples as a function of reaction time.
(B) Recyclability tests of SOM-ZIF-8(3, 0.33) and PH-ZIF-8.