## 3 Results
### ATR-FTIR and Raman Spectra Analysis  
The ATR-FTIR spectra of the blue shark and commercial chondroit sulfate-based carbons, and the blue shark gelatine-based carbon (as well as their precursors) were studied in the range of 4000-600 cm\({}^{-1}\), and are presented in Figure 7.  
The spectra of raw blue shark chondroit sulfate exhibit a clear and notable band between 3500 and 3250 cm\({}^{-1}\), which can be assigned to the stretching vibrations of the hydroxyl (-OH) groups [12]. However, this band is absent after the carbonization process. Additionally, the intensity of this peak is less prominent in commercial chondroit sulfate and blue shark gelatine. A prominent peak at approximately 1000 cm\({}^{-1}\) in the raw blue shark chondroit sulfate corresponds to the stretching vibration of the C-O group. This indicates the presence of oxygen-containing functional groups. These functional groups' existence contributes to the surface's hydrophilic nature. The spectrum of the raw materials reveals a double band between 1089 and 1043 cm\({}^{-1}\), with a more noticeable presence in the blue shark chondroit sulfate. This double band  
Figure 7: FTIR-ATR spectra of gelatine and chondroit sulfate-based carbons (dashed line) and raw gelatine and chondroit sulfate (solid line). is attributed to the vibration of the =C-O-C bond in the aromatic ether [32]. This same band is also visible in both carbonized samples, albeit with reduced intensity. With low intensity, the C-H bands of aliphatic hydrocarbons can be assigned to the band noted between 2900 and 2800 cm\({}^{-1}\) in all three biocarbon samples [33; 34]. The peak detected at around 2350 cm\({}^{-1}\) arises from the C=C stretching vibrations [35]. The Raman spectra measured for the three biocarbons are presented in Figure 8. [PERSON] et al. [36] developed nitrogen-rich carbon materials from gelatine precursors showing similar D and G peaks in the first Raman region. The same comparison could not be presented for the chondro sulfate-based carbons due to the lack of information in the literature. An assessment of the first and second Raman regions for the blue shark chondro sulfate-based carbon is presented in Figure 9a,b. The first and second Raman regions for the blue shark gelatine and commercial chondro sulfate-based carbons are shown in Figure S5 in Supplementary Materials. After the deconvolution analysis, different peaks are presented in the first Raman region [37; 38; 39]. The D\({}_{1}\), D\({}_{2}\), D\({}_{3}\) and D\({}_{4}\) (D peaks) correspond to the breathing mode of carbon atoms in graphene or carbon-based materials, and it is associated with defects and disorders in the crystal lattice. The G peak is a prominent feature in the Raman spectrum of carbon-based materials, particularly graphene. It arises from the stretching mode of the carbon-carbon (C-C) bonds in the hexagonal lattice of graphene. The G peak is sensitive to the sp\({}^{2}\) hybridization of carbon atoms and is used to determine the number of graphene layers and the level of graphitic carbon in a sample. In the second Raman region [37; 38; 39], the D\({}_{1}\)+G peak combines the D\({}_{1}\) peak (related to defects and disorder in carbon-based materials) and the G peak (associated with the stretching mode of carbon-carbon bonds in the hexagonal lattice of graphene). The 2D\({}_{1}\) peak provides information about the number of layers and the stacking order of graphene sheets. The D\({}_{2}\)+G peak results from the D\({}_{2}\) peak (related to defects and disorder) and the G peak. It also indicates the coexistence of disorder and graphitic carbon in the material. The G\({}^{*}\) peak is a variation of the G peak that arises when graphene is under strain or in a highly doped state. Figure 8: Raman spectra of (black) blue shark chondro sulfate-based carbon (1000 \({}^{\circ}\)C, 1 h), (red) blue shark gelatine-based carbon (1000 \({}^{\circ}\)C, 1 h), and (blue) commercial chondroi sulfate-based carbon (1000 \({}^{\circ}\)C, 1 h).