posted on 2024-03-15, 11:55authored byTristan
K. Jongert, Ian A. Slowinski, Benjamin Dao, Victor H. Cortez, Thomas Gredig, Nestor D. Plascencia, Fangyuan Tian
The crystal nucleation and growth mechanism of monodispersed
metal–organic
framework nanoparticles were studied using time-resolved light dynamic,
electrokinetic, and powder X-ray diffraction methods. We confirmed
that zeolitic imidazolate framework-8 (ZIF-8) nanocrystals follow
a nonclassical crystal growth pathway, where a fast nucleation occurs
with dense liquid clusters or nanocrystals forming spontaneously when
two precursors are mixed. We also explored the zeta potential and
solvodynamic size changes of ZIF-8 prepared by a surfactant-assisted
synthesis. Three modulators, including 1-methylimidazole (1-mIm),
tris(hydroxymethyl)aminomethane (THAM), and (1-hexadecyl)trimethylammonium
bromide (CTAB), were studied. We found that 1-mIm dramatically increases
the rate of nucleation of ZIF-8. With an increasing amount of 1-mIm,
which functions as a coordination modulator, the size increases, and
the zeta potential of ZIF-8 decreases. Whereas THAM, as both a coordination
and a deprotonation modulator, increases the size and zeta potential
of ZIF-8 simultaneously, CTAB, as a long alkyl cationic surfactant,
mainly adsorbs on the surface of ZIF-8, and the zeta potential of
the formed ZIF-8 is controlled by the amount of CTAB in solution compared
with its critical micelle concentration. Overall, we reveal that the
modulator type and concentration can be used to control the size and
zeta potential of the dispersed ZIF-8 nanocrystals in a colloid system.
The experiments also enable identification of the nucleation and crystal
growth processes of ZIF-8. The findings will be applicable to other
nanocrystals in colloid systems, which are used for heterogeneous
catalysis and guest molecular loadings.