# Characterization of Grape Extract-Colored SiO2 Synthesized via the Sol-Gel Method
## 3 Results and Discussion
### Thermal Analysis  
Hybrid materials were tested using thermal analysis to evaluate the thermal stability of the grape extract (GRE) encapsulated within the silica matrix. The thermal degradation of GRE under a nitrogen (N\({}_{2}\)) atmosphere was studied using TGA, with the DTG derived from the curve. The thermal profile, shown in Figure 8A, reveals that the GRE extract underwent three distinct thermal events. In the TGA curve, two primary thermal events were recorded, with DTG peaks at 50 \({}^{\circ}\)C and 70.4 \({}^{\circ}\)C (red curve), corresponding to mass losses of 33% and 43.7%, respectively (black curve). These losses are attributed to the evaporation of volatile substances and the removal of surface-bound water. After dehydration, the decomposition of the organic components of the extract occurred, with a DTG minimum observed at 213 \({}^{\circ}\)C, associated with a mass loss of 17.7%. These results are consistent with those observed in the TGA analysis of the anthocyanin-rich extract of _Euterepe olerae_ Mart., for which the decomposition of the sample organic components was recorded at temperatures between 119-216 \({}^{\circ}\)C [42].  
Figure 8B shows the mass loss curves for S (SiO\({}_{2}\) without extract), S5 GRE, and S15 GRE, while Figure 8C presents the corresponding DTG curves from the TGA analysis. The S sample exhibits three main mass loss events. The first occurs between 30 \({}^{\circ}\)C and 200 \({}^{\circ}\)C, with two DTG minima at 44 \({}^{\circ}\)C and 163 \({}^{\circ}\)C, which are attributed to the evaporation of the residual ethanol trapped in the SiO\({}_{2}\) matrix and the loss of absorbed water. The loss due to solvent evaporation is also observed in the curves of S5 GRE and S15 GRE, but with a DTG minimum shifted to 60 \({}^{\circ}\)C. The percentage loss increases with the amount of encapsulated extract in the SiO\({}_{2}\), as the extract was dissolved in ethanol in proportions corresponding to the amount added during sol-gel synthesis. The mass loss observed between 200 \({}^{\circ}\)C and 600 \({}^{\circ}\)C, with a DTG peak at 547 \({}^{\circ}\)C in the S system, is attributed to the decomposition of the silanol groups [43]. This mass loss is absent in the hybrid materials, as the -OH groups from the silanols interact with the -OH groups released from the thermally degraded grape extract molecules, thereby enhancing stability within this temperature range. The hybrids, in addition to the mass loss associated with the evaporation of solvents, show a mass loss due to degradation after 200 \({}^{\circ}\)C, which is greater in S15 GRE. The higher mass loss of S15 GRE compared to that of S5 GRE is attributed to the larger amount of extract incorporated into the silica matrix. In particular, the DTG curves for S5 GRE and S15 GRE display minima at 262 \({}^{\circ}\)C and 209 \({}^{\circ}\)C, respectively. These results indicate that the S matrix provides thermal stabilization to the GRE extract, with degradation observed at around 262 \({}^{\circ}\)C, compared to the results for the pure GRE extract, which exhibits a DTG minimum  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Theoretical GRE Loaded (\%)** & **Effective GRE Loaded (\%)** \\ \hline
**S5 GRE** & 5 & 4.93 \(\pm\) 0.16 \\ \hline
**S15 GRE** & 15 & 8.19 \(\pm\) 0.32 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Theoretical and effective GRE amount in percentage added to hybrid system synthesized via sol–gel route.  
Figure 7: Loading rate efficiency of S5 GRE and S15 GRE.  
at 213 \({}^{\circ}\)C. This stabilization is attributed to the SiO\({}_{2}\) network encapsulating the extract. Conversely, the S15 GRE system shows a broader DTG band with a minimum of 209 \({}^{\circ}\)C, consistent with extract degradation. In this case, the SiO\({}_{2}\) matrix does not fully encapsulate the extract, leaving a portion on the surface, as confirmed by the encapsulation efficiency.