## 3 Results
### BET Analysis  
The N\({}_{2}\) adsorption/desorption isotherms for the blue shark-based carbons (chondroitin sulfate and gelatine) and the commercial chondro sulfate-based carbon are shown in Figure 11. The isotherms of both samples correspond to Type IV classification based on the Brunauer, Deming, and Teller (BDT) classification system [54]. These isotherms display a hysteresis loop attributed to capillary condensation in the mesopores, and a saturation uptake at higher P/P\({}_{0}\) values. Table 4 reviews the BET surface area, microporous and mesoporous volume, total pore volume, and mean pore diameter for the three biocarbons. The investigation reveals that the chondro sulfate-based carbon derived from blue shark exhibits a BET surface area of \(\sim\)135 m\({}^{2}\) g\({}^{-1}\) and a pore diameter of 1.44 nm, compared to the \(\sim\)76 m\({}^{2}\) g\({}^{-1}\) and 1.11 nm from the commercial precursor. On the other side, the blue shark gelatine-based carbon presents the lowest values, \(\sim\)30 m\({}^{2}\) g\({}^{-1}\) and 0.87 nm, respectively. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Carbon Source**} & \multicolumn{2}{c}{**Interplanar Distance (d)**} \\ \cline{2-3}  & **UHR-STEM** & **XRD** \\ \hline Blue shark chondro sulfate & 2.6 \(\pm\) 0.2 Å & 2.8 \\ \hline Commercial chondro sulfate & 2.9 \(\pm\) 0.1 Å & 3.5 \\ \hline Blue shark gelatine & 3.41 \(\pm\) 0.05 Å & 3.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Interplanar distances (d) calculated using UHR-STEM and XRD techniques. The obtained values indicate that the precursors' nature can significantly affect the porosity of the carbon materials, allowing the enhancement of their characteristics. As previously stated, Table S1 presents the effect of time and temperature on the S\({}_{\text{BET}}\) results. For the three studied carbon precursors, optimal parameters were obtained, showing a maximum value of S\({}_{\text{BET}}\). The trend of an increase and then a decrease in specific surface area (S\({}_{\text{BET}}\)) with carbonization time can be attributed to changes in the structure and chemical components of the carbon material during the carbonization process. These effects rely on several facts. During carbonization, the carbon material undergoes a structural transformation as volatile components, such as hydrogen, oxygen, and nitrogen, are progressively removed, forming a more graphitic carbon structure. With shorter carbonization times, the removal of volatile components may not be completed, resulting in a partially carbonized material with more amorphousness. This can increase the specific surface area, as the amorphous carbon structure possesses a more significant number of surface sites and defects that contribute to the higher surface area. As carbonization time increases, the remaining volatile components are further expelled, and the carbon structure becomes more graphitic and ordered [55]. This increased graphitization leads to the growth of larger graphitic domains, which can reduce the overall surface area, causing a decrease in S\({}_{\text{BET}}\). The chemical composition of the carbon material can significantly influence its properties. With shorter carbonization times, a higher content of non-carbon elements, such as oxygen and hydrogen, may be present due to incomplete removal. These elements can introduce functional groups and surface functionalities, increasing the surface area through increased surface roughness and oxygen-containing groups [56]. As the carbonization time increases, these non-carbon