Infra-red spectra of the silica and ligninwere recorded using FT-IR spectrometer. The FTIR spectra of silica from paddystraw appeared essentially similar to that of commercially available silica(Fig. 2a).
The predominant Si-O-Si asymmetry stretching at 1071 cm-1,is clearly evident from Fig. 2a and is characteristic of silica. The observed twosharp peaks at 793 cm-1 and 450 cm-1 are assigned to theSi-O symmetric stretching and bending, respectively (Liu et al., 2011; Liou etal.
, 2004). The bands between 3500 cm-1 and 2800 cm-1 areassigned to the asymmetric stretching and bending vibrations of adsorbed waterand silanol OH groups (SiO-H), respectively (Lu and Hsieh, 2012; Ma et al., 2012;Kalapathy et al., 2002), whereas the peak at 1590 cm-1 belong toH-O-H bending (Kamath and Proctor, 1998). Fromthe FTIR analysis of the separated lignin from paddy straw powder, it was foundthat the spectrum contained most of the absorption bands which are specificallyfound in lignin samples (Fig. 2b). The IR spectrum between 3500 cm-1and 2800 cm-1 are assigned to OH stretching vibrations (Minu et al.,2012).
This can be attributed to the fact that these bands have appeared due tothe presence of phenolic and alcoholic groups involved in hydrogen bonds.Absorption bands located around 1600 cm-1 and 1400 cm-1 arerelated to vibrations of aromatic rings present in lignin, whereas, the bandsabove 1300 cm?1 (syringyl) and 1100 cm?1 (guaiacyl)indicate presence of both syringyl and guaiacyl units in lignin’s chemicalstructure. The presence of absorption bands at 824 cm?1 and 616cm?1 are caused by the deformation vibrations of C-H bonds inthe aromatic rings. Fig.
3a clearly reveals the X-ray diffraction pattern of silica showing a major peakbetween 18° and 30°, centered at 22.5° which is typical for amorphous silica.The results of the present studies were also in line with the previous reports (Liuet al., 2011; Kumagai and Sasaki, 2009; Liou et al.
, 1997). The absence of anyordered crystalline structure indicated relatively high disordered structure ofsilica. Further, the absence of peaks of possible impurities such as alkalineearth metals and sodium silicate affirmed the purity of the derived products. Luand Hsieh, (2012) also observed similar trends during extraction of highlyamorphous nano-silica disks from paddy straw. X-ray diffraction pattern oflignin is presented in Fig.
3b, which shows a major diffraction peak centered between23° and 32°, a typical for standard pure lignin isolated from different biomassresidues.