## 4 Discussion  
In this study, the synthesis of CeO\({}_{2}\) NPs was successfully performed via the sol-gel method. The interaction between the oxygen atoms in gelatin and the cerium cations allowed the gelatin molecules to first adsorb on the solvated Ce\({}^{3+}\) ions in water. Due to the oxygen in the air, Ce\({}^{3+}\) simultaneously switched to Ce\({}^{4+}\), changing the original solution's color from colorless to light yellow. Following the sol-gel method with gelatin as a stabilizer and subsequent heat treatment, highly crystallized CeO\({}_{2}\) NPs were developed. The results are encouraging as it was observed that, as the Ce precursor/gelatin ratio increases, the crystallinity raises (Figure 2), as well as the hemocompatibility and the antioxidant activity improve (Figures 5 and 6). According to [PERSON] et al., the introduction of gelatin in the sol-gel served as a stabilizing agent for both the initial ions and the final products. In particular, gelatin significantly prevented agglomeration by stabilizing the Ce(OH)\({}_{4}\) nuclei and CeO\({}_{2}\) NPs as they were produced by bonding between the carbonyl groups and surface hydroxyls [51]. The use of gelatin has been proposed in many studies for the synthesis of different types of NPs (Table 2). [PERSON] and his team synthesized LiFePO\({}_{4}\)/C nanocomposites via sol-gel with and without gelatin [64]. Their results showed that, when LiFePO\({}_{4}\) was produced using gelatin, the XRD patterns revealed a pure, highly crystalline phase of LiFePO\({}_{4}\). However, LiFePO\({}_{4}\) produced without gelatin had high levels of impurities (FeP, LiCO\({}_{3}\), and Fe\({}_{2}\)P), demonstrating that gelatin promotes the production of LiFePO\({}_{4}\). In their SEM micrographs, the average particle size of NPs generated with gelatin was around 183 nm. In contrast, the particle size of powders synthesized without gelatin was greater (1-2 um). This outcome demonstrates that the gelatin-based sol-gel method may successfully adjust particle size as in our study. In another study, [PERSON] and his team prepared Ag-NPs in gelatin solutions under UV light irradiation [65]. Gelatin concentrations had a clear impact on the SPR (surface plasmon resonance) bands of silver nanostructures. Also, as the ratio of AgNO/gelatin raised, greater yields of Ag-NPs were produced. Finally, the surface morphology of the finely distributed Ag-NPs was shown by the AFM result to have a dense and evenly packed structure as also revealed in the present study by SEM and TEM. In a previous study, different ratios of gelatin to precursor at different temperatures were examined. It was concluded that the amount of gelatin has an impact on several structural characteristics, such as the uniformity of the size distribution and the size of the particles, including the temperature at which the structures develop. The results showed that with the smallest ratio of gelatin to the precursor (1:1 and 2:1), the formation of a crystalline phase was observed to occur at 550 degrees, while with the largest ratio (3:1), crystallization initiated at 350 degrees. From these data, it can be concluded that gelatin concentration is crucial for the development of crystalline structure as well as for regulating the size of the NPs [66]. These findings agree with our results since with the applied calcination temperature (550 \({}^{\circ}\)C), high crystallinity was present in all samples and as the ratio of precursor/gelatin increased, crystallinity slightly increased. This is verified by the presence of more sharp peaks in the XRD diffractogram with the increase of Ce precursor/gelatin ratio (Figure 2). In the XRD pattern of CeO1g, although pure crystalline material was observed, a broadening of the peaks is evidenced. The broadened peaks may be due to the presence of smaller-sized particles [67; 68], as was also observed in the present study, where CeO1g samples presented NPs in the range of 4.5-9.5 nm (Figure 4). Similar were the results of [PERSON] et al.