## 3 Results and Discussion
### Morpho-Structural Changes During Carbonization  
To gain a more comprehensive understanding of the structural changes occurring during the carbonization of chitin and chitosan, carbonized chars at different temperature levels were obtained at the same conditions and the characteristics of the chars were investigated using FT-IR and Raman spectroscopic techniques. Moreover, SEM-EDX analyses were performed to identify the structural and chemical changes occurring during carbonization, with the solid products obtained at different temperatures. Figure 7 shows Raman and FT-IR spectra of the carbonized products of chitin and chitosan at various temperatures. In the Raman spectrum, one can see the G-band (\(\sim\)1580 cm\({}^{-1}\)) and D-band (\(\sim\)1350 cm\({}^{-1}\)), and their intensity ratios (ID/IG) can be used to assess the structural properties and disorder levels in carbonaceous materials. For both chitosan and chitin, the ID/IG ratio was increased with increasing carbonization temperatures. The ratios for chitosan were found to be 0.863, 0.938, and 0.977 at carbonization temperatures of 500 \({}^{\circ}\)C, 700 \({}^{\circ}\)C, and 900 \({}^{\circ}\)C, respectively. On the other hand, for chitin, the ratios were 0.921, 0.923, and 0.948 at the same respective temperatures. At higher carbonization temperatures, chitosan-derived chars exhibit increasing structural disorder, as evidenced by the rising ID/IG ratio. This suggests that thermal treatment induces bond rearrangements, leading to the fragmentation of smaller graphitic domains and an increase in defect density. Consequently, chitosan chars are more prone to forming amorphous or turbostatic carbon structures rather than well-ordered graphitic domains. In contrast, chitin-derived chars demonstrate greater structural stability across different carbonization temperatures, with a relatively stable ID/IG ratio. This indicates a lower degree of structural transformation compared with chitosan. The increased disorder in chitosan chars results from differences in molecular structure and thermal decomposition mechanisms compared with chitin, affecting defect generation during carbonization. This can be attributed to chitin's inherently more rigid and highly ordered structure, reinforced by strong intra- and intermolecular hydrogen bonding, whereas chitosan, with fewer acetyl groups, follows a distinct thermal decomposition pathway that influences its structural evolution during carbonization. Raman spectroscopy further confirms that neither chitosan nor chitin undergoes full graphitization, as indicated by the relatively high intensity ratio values, which suggest the persistence of a predominantly amorphous or turbostatic carbon structure. From the FT-IR spectra, O-H (hydroxyl) and N-H (amine) stretching is observed at 3200-3500 cm\({}^{-1}\), as well as C=O (carbonyl, amide I) stretching. This band decreased with increasing temperature due to dehydration and deamination. Additionally, C=O (carbonyl, amide I) stretching bands around 1650-1700 cm\({}^{-1}\) were found to be strong at 500 \({}^{\circ}\)C, then weakened due to amide degradation. N-H bending (amide II) and C=C stretching in aromatic structures, at around 1550-1600 cm\({}^{-1}\), were shifted to higher temperatures due to aromatization. Meanwhile, the C-H bending stretching around 1400-1450 cm\({}^{-1}\) decreased as aliphatic structures degraded during carbonization, while aromatic C-H bending was observed at around 800-900 cm\({}^{-1}\), indicating the formation of polyaromatic structures. Figure 7: Raman (**a**) and FT-IR (**b**) spectra of carbonized products of chitin and chitosan at various temperatures. SEM-EDX analyses are also shown in Figure S1 to investigate the thermal degradation effects on the chars. Morphologically, and with increasing temperature, localized pulverization, increased surface roughness, and fractures were observed in the structure, while the elemental carbon content rose to 92.2% for chitosan and 89.3% for chitin.