Fourier transform infrared characterization was carried out to
determine functional groups within the bulk silica matrix using
ATR cell (FTIR 680 Plus JASCO). The absorption spectra were recorded
in the 500–1500 cm1 range. The spectrum of each sample
represents an average of 32 scans. With the aim of comparison, all
FTIR spectra were normalized with respect to the maximum absorbance
value for each sample.