# Fractionation of Lignocellulosic Biomass by Selective Precipitation from Ionic Liquid Dissolution
## 3 Results and Discussion
### FTIR Analysis  
FTIR spectroscopy has been extensively employed to study the functional groups of cellulose, xylan-like hemicellulose and lignin in the literature. Changes in the composition of Solid I and Solid II were monitored using FTIR. The spectra of Solid I and Solid II are very different. Figure 2 demonstrates that the IR spectra of the raw barley straw, Solid I and Solid II show a broad and intense band in the region of 3800-2600 cm\({}^{-1}\), which is associated with OH groups and their interactions with water molecules via H-bridging bonds [59]. In addition, a set of overlapping peaks appears between 3000 and 2800 cm\({}^{-1}\) due to the stretching vibration modes of C-H bonds. The relative intensity of these peaks increases in Solid II with respect to the spectra of raw barley straw and Solid I, indicating an enrichment of lignin, the component containing a greater proportion of C-H bonds than O-H groups.  
The spectra of Solid I, Solid II and references of commercial cellulose, xylan and lignin are displayed in the region between 1800 and 800 cm\({}^{-1}\) in Figures 3 and 4, respectively. The bands are assigned to the characteristic bending or stretching modes of different specific groups of lignocellulosic biomass in the \"fingerprint\" region. The peak structure of this region is quite complicated, but the peaks can be assigned  
Figure 2: FTIR spectra of Solid I, Solid II and raw barley straw.  
as follows [60; 61; 62; 63]: 1735 cm\({}^{-1}\) indicates unconjugated C=O in xylans (hemicellulose); 1653 cm\({}^{-1}\) indicates absorbed O-H and conjugated C-O in lignin; 1593 cm\({}^{-1}\) and 1508 cm\({}^{-1}\) indicate C=C skeletal vibrations (aromatic ring) in lignin; 1457 cm\({}^{-1}\) and 1420 cm\({}^{-1}\) indicate C-H deformation in lignin and carbohydrates; 1375 cm\({}^{-1}\) indicates C-H deformation in cellulose and hemicellulose; 1336 cm\({}^{-1}\) and 1318 cm\({}^{-1}\) indicate C-H vibration in cellulose and C-O vibration in syringl derivatives; 1264 cm\({}^{-1}\) indicates guaiacyl ring breathing, C-O stretching in lignin and C-O linkages in guaiacyl aromatic methoxyl groups; 1157 cm\({}^{-1}\) indicates C-O-C vibration in cellulose and hemicellulose; 1118 cm\({}^{-1}\) indicates aromatic skeletal vibration; 1085 and 1035 cm\({}^{-1}\) indicate C-O deformation in aliphatic ether and guaiacyl aromatic methoxyl groups, respectively; 1048 cm\({}^{-1}\) indicates C-O stretching in cellulose and hemicellulose; and 896 cm\({}^{-1}\) indicates C-H deformation in cellulose [60; 61; 62; 63].  
The presence of a peak at 1508 cm\({}^{-1}\) is usually taken as an indication of the presence of lignin, especially when a weak band at 1520 cm\({}^{-1}\) is present [63] (Figure 4), whereas the 1735, 1157, 1048 and 897 cm\({}^{-1}\) peaks are characteristic of polysaccharides [60; 63]. There are some weak bands typical of lignin in Figure 4, confirming that low amounts of lignin are retained in Solid I, as can be deduced from the mass balance data (Table 2). However, no peaks attributed to polysaccharides are evident in  
Figure 4: FTIR spectra of Solid II and commercial lignin.  
Figure 3: FTIR spectra of Solid I, commercial cellulose and xylan.  
the spectrum of Solid II (Figure 4). In summary, the spectrum of Solid I is similar to that corresponding to the pure cellulose reference, whereas the spectrum of Solid II is similar to that corresponding to lignin. These data indicate that selective precipitation occurred, except for small amounts of lignin incorporated into Solid I.