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Figure 7.14 Mechanosynthesis of porous ZIFs investigated by time-resolved in situ
powder X-ray diffractiony:
17
(a) quantitative synthesis of ZIF-8 by LAG or
ILAG reaction of ZnO and 2-methylimidazole; (b) kinetic curves for the
LAG and ILAG syntheses of ZIF-8, based on monitoring changes in
intensity of the characteristic ZIF-8 (211) X-ray reflection during milling
(adapted from ref. 17); (c) time-resolved X-ray powder diffractogram
(left) and reaction scheme (right) for the mechanochemical reaction of
ZnO and imidazole with a small amount of DMF, which first gives rise
to the open ZIF-4 structure, which subsequently transforms into the
low-porosity ZIF-6 (adapted from ref. 17). (d) Field emission scanning
electron microscopy (FESEM) images of product particles after 240 h
milling of ZnO and 2-methylimidazole, demonstrating the formation of
core-shell structures composed of ZnO and ZIF-8.
103
Reproduced from ref. 103.
considerable amount (ca. 30% of the reaction mixture) of an amorphous
phase during mechanochemical LAG and ILAG reactions. While in situ and
real time quantification of amorphous content is of particular importance
for understanding mechanochemical reactions, the presence of large
amounts of amorphous material during LAG reactions is in contrast to
conclusions of previous ex situ studies, which suggested LAG processes in-
volved very little amorphous phase or none at all. The most recent addition
to the new toolkit of techniques of in situ and real time monitoring of
mechanochemical reactions is Raman spectroscopy, enabled through the
introduction of optically transparent poly(methyl methacrylate) (PMMA) re-
action vessels. The first results of this new and readily accessible laboratory
technique, obtained on the reaction system of CdCl
2
and cnge, confirm that
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