3.6. FT-IR spectroscopy
To compare the FT-IR spectrum of silica fromcogon grasswith those
obtained from other sources, data reported in other articles [20,21]
were extracted and plotted in Fig. 10. The spectrum of bio-silica can
be divided into four major categories, namely:
i. The siloxane (SiOSi) group related to the silica backbone.
Absorption is usually observed at 800 and 1090 cm−1, which correspond
to the symmetric vibration and asymmetric stretching of the
SiOSi bonds [49].
ii. The silanol (SiOH) group on the surface of silica, which is usually
observed at 960 cm−1 [50].
iii. The (HOH) bending modes of absorbed water molecules
observed at approximately 1650 cm−1 [49].
iv. The (OH) stretching of the silanol group and absorbed water with
a broad band at approximately 3500 cm−1 [49].