# Deep Eutectic Solvent Pretreatment and Green Separation of Lignocellulose
## 5 Effect of DES Treatment on the Chemical Structure of Lignocellulosic Separation Products  
FT-IR spectroscopy can be used to study the effect of DES pretreatment on the internal chemical structure of lignocellulosic by comparing the characteristic absorption peaks of chemical bonds such as CH, C-C, and CO [135]. This technique allows for the identification and quantification of functional groups present in the lignocellulosic material, providing insights into the chemical changes induced by the pretreatment process [63]. [PERSON] et al. [136] pretreated Moso bamboo with ChCl/zinc acetate DES under microwave-assisted conditions and performed FT-IR characterization of the samples before and after treatment. The FT-IR results showed changes in lignocellulosic characteristic peaks associated with OH, CH, CO, and CO bond stretching. After DES pretreatment, the characteristic peak at 3331 cm\({}^{-1}\) almost disappeared. This suggested that bands of intramolecular and intermolecular hydrogen bonds between 3500 and 3100 cm\({}^{-1}\) were destroyed by DES. In addition, the absorbance of DES pretreated biomass decreased at 1734 cm\({}^{-1}\). These peaks indicate removal of hemicellulose because they suggest stretching vibrations of acetyl groups in hemicellulose [137]. [PERSON] et al. [138] pretreated rape straw with ChCl/oxalate acid DES and performed FT-IR characterization of the samples before and after treatment. It was found that peaks near 3420 cm\({}^{-1}\) were associated with tensile vibrations of OH in biomass lignin, and -CH\({}_{2}\) vibration was detected near 2930 cm\({}^{-1}\). The ester bond stretching vibration between hemicellulose and lignin was close to 1732 cm\({}^{-1}\). After pretreatment, the characteristic peaks at 3420 cm\({}^{-1}\) and 2930 cm\({}^{-1}\) were significantly reduced, indicating that the hydrogen bond within lignocellulosic was broken. Additionally, the tensile vibration of aromatic ring-associated CO near 1625 cm\({}^{-1}\) was significantly reduced, indicating the degradation of lignin in the raw material [139]. The peak near 1420 cm\({}^{-1}\) was associated with the bending of -CH\({}_{2}\) in cellulose. Peaks near 1050 cm\({}^{-1}\) corresponded to CO stretching in the hemicellulose-cellulose-lipgin polymers. The peak near 896 cm\({}^{-1}\) was associated with the \(\beta\)-glucoside bond. These FT-IR data indicated that DES pretreatment can effectively remove hemicellulose and lignin from biomass [140]. Table 3 clearly summarizes the chemical bond changes in the biomass after DES treatment of lignocellulosic. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**Substrate** & **DES** & **Condition** & **Untreated Glucose Yield (\%)** & **DES-Treated Glucose Yield (\%)** & **Increase Rate (100\(\times\)\%)** & **Ref.** \\ \hline Industrial xylose & ChCl: & & & & & \\ residue & monoethanolamine & 10 FPU/g CTec2 & 34.95 & 95.89 & 1.74 & [16] \\ \hline \multirow{3}{*}{Sugarcane} & ChCl: lactic acid & Solid loading, 10 wt\%, & & & & \\  & 1:2 & 15 mg protein/g solid, & & & & \\  & 1:2 & cellulase enzymes & & & & \\  & NS22257 & & & & & \\ \hline \multirow{3}{*}{Corn stover} & FeCl\({}_{3}\)/ChCl: & & & & & \\  & \(N\)-(2-hydroxyethyl) & Solid loading, 5 wt\%, & & & \\  & Ethylenediamine & 30 FPU/g CTec2 & 16.54 & 98.6 & 4.96 & [134] \\  & 1:4 & & & & & \\ \hline \multirow{3}{*}{Soybean straw} & P-ToCH/BTEAC: & & & & & \\  & glycerol & 10 FPU/g, CTec2 & 9.17 & 90.18 & 8.83 & [131] \\  & 1:12 & & & & & \\ \hline \multirow{3}{*}{Eucalyptus wood chips} & AlCl\({}_{3}\)/Betaine: lactic acid & & & & & \\  & 1:2 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._DES pretreatment can significantly affect the types and contents of functional groups in lignocellulosic biomass, playing a crucial role in disrupting the interactions between lignocellulosic components and lignin structure [142]. The structural differences of regenerated lignin are usually analyzed by 2D-HSQC NMR [143].