# Granular Activated Carbon from Grape Seeds Hydrothermal Char
## 3 Results and Discussion
### Pore Volumes and Textural Characterization by Nitrogen Physisorption at 77 K
However, such a general trend was not respected by the results that were obtained with sample H250K050, at the highest HTC temperature (250 \({}^{\circ}\)C). In this case, the surface area obtained after activation at intermediate KOH:hydrochar ratio (0.50) was higher than that obtained at the highest ratio. It is evident that the activation treatment was able to develop micro-pores. If hydrochars are taken into account, very low values of pore volume were obtained: never higher than 0.028 cc/g. Moreover, such volume was almost entirely (-90%) represented by meso- and macro-pores. The activation treatment enormously increased pore volume, up to around 0.5 cc/g. For GSACs, micro-pores were clearly preponderant, as they represented 60-90% of the total pore volume. Figure 1: Nitrogen adsorption isotherms at 77 K of selected samples. In general, higher amounts of activator resulted in higher micro-pore volume. However, especially for the samples that were derived from the HTC treatment at higher temperatures, a very high amount of activator induced the development of large pores. This is especially evident for the samples obtained at a HTC temperature of 250 \({}^{\circ}\)C. Here, with the highest amount of activator, meso- and macro-pores increased from 10.4% (H250K050) to 29.5% (H250K100) of the total pore volume that, notably, was approximately constant (\(\sim\)0.48 cc/g). Such result is in perfect agreement with the clear diminution in specific surface area occurred when passing from H250K050 sample to H250K100 sample. The evolution of the pore size can be observed in Figure 2. Here, the pore size distribution (PSD) of the hydrochar and GSAC samples obtained at a HTC temperature of 220 \({}^{\circ}\)C is represented. A comparable situation was observed for the samples obtained at a HTC temperature of 180 \({}^{\circ}\)C and 250 \({}^{\circ}\)C, hence, the corresponding PSDs were omitted. It is confirmed that the raw char has a very low pore volume (Figure 2a). The pores of hydrochar are in the range of meso-pores and larger. Meanwhile, the GSAC samples have a narrow micro-pore distribution, peaked at 6 A, with a significant pore improvement in the meso-pore region in comparison to the parent hydrochar. By increasing the concentration of the activating agent, further meso-pores in the 20-50 A range were developed. Another effect of increasing KOH concentration was the enlargement of narrow micro-pores (10 A) \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Sample ID** & \begin{tabular}{c} **Y\({}_{\text{act}}\)** \\ **(wt \%)** \\ \end{tabular} & \begin{tabular}{c} **Y\({}_{\text{ovr}}\)** \\ **(wt \%)** \\ \end{tabular} & \begin{tabular}{c} **S\({}_{\text{BET}}\)** \\ **(m\({}^{2}\)/g)** \\ \end{tabular} & \begin{tabular}{c} **S\({}_{\text{micro}}\)** \\ **(m\({}^{2}\)/g)** \\ \end{tabular} & \begin{tabular}{c} **V\({}_{\text{tot}}\)** \\ **(m\({}^{2}\)/g)** \\ \end{tabular} & \begin{tabular}{c} **V\({}_{\text{micro}}\)** \\ **(cc/g)** \\ \end{tabular} & \
\begin{tabular}{c} **V\({}_{\text{micro}}\)** \\ **(vol \%)** \\ \end{tabular} &
\begin{tabular}{c} **PH\({}_{\text{PZC}}\)** \\ **(-)** \\ \end{tabular} \\ \hline H180 & - & 80.5 & 4.8 & 1.5 & 0.0256 & 0.0020 & 7.8 & 6.41 \\ H180K025 & 45.8 & 36.9 & 132 & 75 & 0.0761 & 0.0485 & 63.7 & 9.86 \\ H180K050 & 44.9 & 36.1 & 618 & 385 & 0.3196 & 0.2616 & 81.9 & 9.29 \\ H180K100 & 44.1 & 35.7 & 692 & 407 & 0.4619 & 0.3723 & 80.4 & 7.92 \\ H220 & - & 75.3 & 8.2 & 3.2 & 0.0270 & 0.0031 & 11.5 & 5.62 \\ H220K025 & 40.8 & 30.7 & 370 & 253 & 0.1779 & 0.1428 & 80.3 & 9.49 \\ H220K050 & 44.9 & 33.8 & 661 & 376 & 0.323 & 0.2714 & 84.0 & 8.31 \\ H220K100 & 40.4 & 30.4 & 770 & 484 & 0.4716 & 0.3325 & 70.5 & 7.76 \\ H250 & - & 66.5 & 7.7 & 1.3 & 0.0277 & 0.0028 & 10.1 & 6.36 \\ H250K025 & 61.7 & 41.0 & 432 & 302 & 0.2340 & 0.1563 & 66.8 & 10.74 \\ H250K050 & 52.3 & 34.8 & 1018 & 832 & 0.4857 & 0.4354 & 89.6 & 9.00 \\ H250K100 & 53.3 & 35.4 & 765 & 621 & 0.4716 & 0.3325 & 70.5 & 8.10 \\ \hline \hline \end{tabular}
\end{table}