## 3 Results and Discussion
After 115 \({}^{\circ}\)C, the behavior of the curve is linear, and the weight value of the sample is constant. In this case, the concentration of AgNPs-S is 2.23 mg/mL. The efficacy of the TGA method rests on the fact that the organic components are completely volatilized, and the metallic component is left as a residue. The concentration of nanoparticles is of great importance since, based on these values, the evaluation of the catalytic and antibacterial properties was carried out. Figure 7 shows the FTIR spectra of the ethanol-water _Sargassum_ extract and AgNPs-S. As can be seen, both signals are similar. Regardless of the differences, the wavelength bands above 2000 cm\({}^{-1}\) are aligned. However, below this value, the bands of the AgNPs-S synthesis shift to those from the _Sargassum_ extract. The spectra also have variations in intensity, with almost all the bands from _Sargassum_ being more intense than those from AgNPs-S. The bands that remain in the latter spectrum correspond to the stabilizing compounds of the nanoparticles. In a detailed analysis, a very strong, broad band is seen in the region between 3700 and 2500 cm\({}^{-1}\), which is composed of various signals. Centered around 3400 cm\({}^{-1}\), there is a broad band caused by the overtone of the C=O stretching band. In addition, between 3000 to 2840 cm\({}^{-1}\) are the C-H stretching band (centered at 2925 cm\({}^{-1}\)) and the O-H stretching band of carboxylic acid at 3300-2500 cm\({}^{-1}\) (centered around 3000 cm\({}^{-1}\)). At 2350 cm\({}^{-1}\), there is a sharp transmittance oscillation caused by the O=C=O stretching of carbon dioxide. Cyclic amides show bands around 1750 and 1700 cm\({}^{-1}\). Both FTIR present C-H bending bands between 1465 and 1365 cm\({}^{-1}\), and the O-H bending band of carboxylic acid is centered at 1416 cm\({}^{-1}\). They also exhibit C-O stretching bands at 1259 and 1080 cm\({}^{-1}\). Also present at 873 cm\({}^{-1}\) is the one-band product of C-H bending. These results suggest the involvement of phenolic compounds and polysaccharides in the synthesis of nanoparticles, as has been previously reported [30]. The catalytic properties of the silver nanoparticles were evaluated through the degradation of methylene blue. Monitoring was carried out using UV-vis to obtain a spectrum every minute. From the calibration curve, the concentration and percentage of degradation in each spectrum were determined. Figure 8 shows the degradation curves obtained when evaluating methylene blue concentrations from 1 ppm to 5 ppm. Figure 8a corresponds to the AgNPs-S sample. As can be seen, in all cases, a rapid degradation occurs in the first minutes. When methylene blue was used at 1 ppm, a maximum degradation of 99.9% was achieved after 5 min. After this time, there were no changes in the concentration of the dye. The curves obtained for 2 ppm and 3 ppm show very similar behavior. The degradations obtained after 10 min were 99.8% and 98.9% for 2 ppm and 3 ppm, respectively. When methylene blue is used at 4 ppm, rapid degradation of the dye occurs in the first  
Figure 6: TGA analysis of the samples: (**a**) AgNPs-C and (**b**) AgNPs-S.  
4 min. Afterwards, the reaction begins to stabilize and degradation occurs slowly, until an efficiency of 95.7% in 10 min is obtained. Finally, the evolution of the degradation of methylene blue at 5 ppm occurs similarly. However, in this case, the maximum degradation was 95.6%. On the other hand, Figure 8b shows the degradation curves when using the AgNPs-C sample. The curves corresponding to methylene blue at 1 ppm, 2 ppm, and 3 ppm are very similar, obtaining degradations of 99.7%, 97.2%, and 91.7%, respectively. In samples in which the dye was used at 4 ppm and 5 ppm, a rapid degradation is observed in the first 2 min. After this time, the degradation rate becomes slow and the reaction stabilizes. In this way, degradation percentages of 79% and 75% are obtained for methylene blue at 4 ppm and 5 ppm, respectively.