Figure 5: XRD on the thermal
structural dynamics of a)ZIF-62-a and silver-doped ZIF-62 structures
b)AgZIF-62-a, c)AgZIF-62-b, and d)AgZIF-62-c. Ag peak marked with
asterisk (*), and ZIF-zni peak marked with hash (#).
A dynamic study of the
thermal effects of Ag-doped ZIF-62 crystals was performed using in-situ
thermal XRD in Figure 5 to further understand the structural changes in
Ag-doped ZIF-62. For a lower bIm ratio, Ag nanoparticles start to form
at a temperature of between 150 oC to 200oC. It is also interesting to note that ZIF-zni was
formed for a lower bIm ratio and at a much lower temperature of below
200 oC than that previously reported for ZIF-4 and
ZIF-62 via recrystallization [30,31]. ZIF-zni is a
dense form of the imidazolate (Im) based ZIF and the presence of
benzimidazolate (bIm) ligand usually prevents its formation due to the
bulkier ligands preventing the complete collapse of the frameworks. The
temperature of ZIF-zni formation here is close to the
AgNO3 melting point, which may indicate that the
AgNO3 molecules were mobilized at this temperature and
started to interact with bIm in the structure. This caused the
rearrangement of imidazole parts to form a ZIF-zni structure. However,
at a higher bIm ratio, ZIF-zni formation was not observed, and the glass
was able to be melted fully and become fully amorphous with Ag
nanoparticle present. This shows that the Ag in the structure may have
interacted with bIm in the structure during heating, leading to these
observable changes. As the formation of ZIF-zni is seen in both
AgZIF-62-a and AgZIF-62-b, future analysis will be only focused on
AgZIF-62-a and AgZIF-62-c to compare and understand the interactions and
functionality of ZIF-zni-forming and glass-forming AgZIF-62.