## 2 Materials and Methods  
### Physicochemical Characterization and Thermal Analysis of Chitin and Chitosan  
Commercial chitin and chitosan samples were obtained from Sigma-Aldrich (St. Louis, MO, USA) and used without any pretreatment. Prior to carbonization experiments, the samples were characterized using FT-IR spectroscopy (Perkin Elmer Spectrum 100, USA) and SEM-EDX (ZEISS Supra 40 VP, Germany), with the resulting spectra and micrographs presented in Figure 1 below.  
The analyses revealed that both raw materials exhibit similar morphologies and contain carbon, oxygen, and nitrogen in their structures. Elemental composition analysis showed that chitosan contains 45.60 wt.% carbon, 10.61 wt.% hydrogen, 9.13 wt.% nitrogen, and 34.66 wt.% oxygen, whereas chitin has 49.88 wt.% carbon, 6.56 wt.% hydrogen, 8.69 wt.% nitrogen, and 34.87 wt.% oxygen. These results, further confirmed by an elemental analyzer (LECO CHN628), indicate that chitosan's slightly higher nitrogen content arises from deacetylation during its derivation from chitin. In the FT-IR spectra of both chitin and chitosan, a broad band of around 3200-3400 cm\({}^{-1}\) corresponds to O-H stretching vibrations, and absorption bands at approximately 2850-2950 cm\({}^{-1}\) are attributed to C-H stretching in aliphatic structures. A C-O-C asymmetric stretching band near 1150 cm\({}^{-1}\) confirms the glycosidic linkages characteristic of polysaccharides. Key amide bands--indicative of the polymer's backbone--include amide I (-1650 cm\({}^{-1}\), C=O stretching), amide II (-1550 cm\({}^{-1}\), N-H bending and C-N stretching), and amide III (-1300-1370 cm\({}^{-1}\), C-N stretching and N-H deformation). The relative intensity and position of these amide bands shed light on structural differences between chitin and chitosan, particularly regarding the degree of deacetylation.  
Before performing TGA experiments on a Hitachi STA 7300 thermal analyzer, the crucibles and chamber were thoroughly cleaned with high-purity compressed air. Carbonization experiments were conducted under a nitrogen atmosphere at a constant carrier gas flow rate of 20 mL/min. To establish a baseline and reduce systematic errors, an empty alumina crucible was run under the same conditions before introducing the samples. A sample mass of 10 mg was maintained in each experiment to mitigate both mass and heat transfer limitations. Four different heating rates (5, 10, 20, and 40 \({}^{\circ}\)C/min) were used to investigate how heating rate influences thermochemical behavior in the temperature range of 25 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C. All measurements were conducted in triplicate to ensure reproducibility,  
Figure 1: SEM-EDX analyses and FT-IR spectra of chitin and chitosan.  
and consistent protocols were followed to enhance precision. Following TGA analysis, the samples were carbonized under the same conditions to obtain carbonaceous products at various temperatures. These chars were further characterized using SEM-EDX (ZEISS Supra 40 VP), Raman spectroscopy (Renishaw, Wotton-under-Edge, UK), and FT-IR spectroscopy (Perkin Elmer Spectrum 100) to evaluate morpho-structural changes during carbonization.