Figure 8: FTIR analysis on ZIF-62
and AgZIF-62 particles
FTIR analysis was also performed on the pure ZIF-62-a and ZIF-62-c, as
well as the silver-loaded AgZIF-62-a and AgZIF-62-c and their melted
components (denoted as the mAgZIF-62) (Figure 8). The FTIR analysis
shows peaks for the C-C in-plane and out of plane bending (600-700
cm-1), C-H out of plane bending (700-1000
cm-1), C-H in-plane bending (1100-1300
cm-1), C-N stretching (1300-1370
cm-1), and C=C stretching (1390-1650
cm-1), which are all present in the ligands used for
the formation of ZIF-62. However, no clear FTIR peak changes between the
silver-loaded ZIF-62 (AgZIF-62-a and ZIF-62-c), its melted components
(mAgZIF-62-a and mAgZIF-62-c), and pure ZIF-62 variants (ZIF-62-a and
ZIF-62-c) can be seen. Thus, it is most likely that these interactions
were not impacted by the presence of silver ions/molecules in the
structure. An extra peak for mAgZIF-62-a that is present at
775cm-1 could be attributed to the out-of-plane
deformation of the imidazolate linker contributed by the presence of
ZIF-zni. This extra peak was also present in FTIR data reported in the
literature for the ZIF-zni phase.[32]
An XPS analysis was also performed to understand the bonding occurring
on the surface of the particles. The wide scan XPS analysis, as can be
seen in Figure S 2a, shows no obvious new peaks between all the
crystalline and melted variations, except for the variations containing
Ag. This is consistent with the sample and demonstrates that the Ag has
been successfully embedded within the sample. The intensity of Ag peaks
relative to other peaks was also diminished in the melted sample when
compared to the crystalline sample, which indicated that the Ag species
may be embedded within the ZIF-62 melted structures rather than being on
the surface. This is because XPS is usually a surface-sensitive
analysis, and with the same penetration power, the XPS will not
penetrate as deeply into the denser melted/zni forms when compared to
the crystalline forms, thus reading less Ag that is situated deeper
within the structure. The summary of the XPS peaks found for different
species can be found in Figure S 3. No clear changes can be seen for all
other species except for Ag. A deeper look into the Ag peak shifts can
also be seen in Figure S 2b, in which the non-melted AgZIF-62 variants
indicate that the Ag may exist in an ionic AgNO3 form,
while the melted mAgZIF-62 variants show a possible oxidised Ag. This
may be due to the exposure of Ag on the surface to air, thus resulting
in the formation of AgO on its surface. As explained above, the lower
penetration depth and surface sensitivity of XPS into the denser
heat-treated ZIF-62 may be a reason for the lack of Ag nanoparticle
peaks, as the Ag nanoparticle may be deeper embedded within the
structure. Thus, the actual state of silver within the melted/zni
particles should closely resemble the results seen in previously
collected XRD data which shows the conversion of silver ions into silver
nanoparticles only at higher temperatures (above
150oC).