# Granular Activated Carbon from Grape Seeds Hydrothermal Char
## 3 Results and Discussion
### Chemistry Characterization by FTIR  
The chars produced from HTC, as well as the raw grape seeds, were analyzed by means of FTIR. Figure 5 reports the relevant results.  
The HTC chars retained some characteristic functional groups of the starting material. The peak around 3000 cm\({}^{-1}\) represents hydrogen bounded to the unsaturated carbon chain (C-H), while slightly lower wavelength peaks indicate the group that is attached to the saturated carbon chain. The unsaturated carbon-carbon bond, possibly in the form of aromatic, is confirmed by dense  
Figure 4: Scanning electron micrographs (SEM) of selected activated carbon samples: (**a**) H180K050; (**b**) H220K050; and, (**c**) H250K050.  
peaks at about 1600 cm\({}^{-1}\). The moderate peak around 2800 cm\({}^{-1}\) is associated with aldehyde C-H. The existence of carbonyl (C=O), possibly in the form of aldehyde, is confirmed by the peak at 1740 cm\({}^{-1}\).  
It is interesting to notice that the signal corresponding to alkenes C-H attached to the unsaturated carbons is more pronounced at 220 \({}^{\circ}\)C than at 180 \({}^{\circ}\)C. This result is in agreement with other research studies, and can be due to aromatization reactions [45]. However, at the highest temperature, such as peak diminishes, which is likely due to high temperature decomposition of aromatic species. Interestingly, the peak testifying the existence of carbonyl functional groups is less pronounced at the highest HTC temperature. In general, the hydrochar obtained at the highest HTC temperature shows a lower intensity for all of the peaks, suggesting that severe HTC conditions may strip the oxygen functional groups off the char surface. This is in agreement with the results of [PERSON] et al. [24], who found that the lower the HTC temperature, the higher = the carbon-oxygen complexes availability on the hydrochar surface.  
Figure 6 shows the results of FTIR analysis of a selection of GSAC samples and the relevant hydrochar precursor.  
Figure 5: Fourier Transform Infrared Spectroscopy (FTIR) spectra of hydrothermal carbonization (HTC) chars and raw material.  
Figure 6: FTIR spectra of hydrochar before activation (H220) and GSAC samples.  
Figure 6 testifies that most of the oxygen functional groups that are present in the parent hydrochar were removed from the surface after activation. Moreover, KOH activation did not promote the development of any new functional group. According to [PERSON] et al. [2], functional groups might be preserved and still appear on the FTIR spectra when the activation temperature does not exceed 500 \({}^{\circ}\)C: higher temperatures degrade most functional groups, including oxygen-containing groups, and this is confirmed in Figure 6. Actually, [PERSON] et al. [46] showed that KOH activated chars retain all of their initial surface functional groups if the activation is performed at room temperature.  
The band at 3000-2850 cm\({}^{-1}\) corresponding to C-H stretch of alkanes practically disappeared: KOH removed a considerable amount of hydrogen from the surface.  
As a whole, the procedure that is described in the present paper allows for obtaining an activated carbon that is relatively free of oxygen functional groups. This opens very interesting possibilities for commercial exploitation: the GSAC surface could be functionalized for specific technological applications.