## 3 Results and Discussions
### Thermogravimetric Analysis (TG/DTA)  
Thermal degradation of GO, GO-Ag, GO-Ag-APTES, GO-ZnO and GO-ZnO-APTES powders was investigated by TG/DTA. From Figure 5, it can be seen that the total mass loss of GO is 39.38%. The GO powder was thermally decomposed in two steps. In the first step, up to 140 \({}^{\circ}\)C, a weight loss of 10.21% occurs, being accompanied by an endothermic effect noticed on the DTA curve at 73 \({}^{\circ}\)C. Since GO has a hydrophilic nature, this loss may be due to the vapor removal of the physically adsorbed water, but also to some functional groups with oxygen on the surface of graphene (hydroxyl type) [46]. The weight loss occurring in the second step, of 29.17%, was accompanied by an exothermic maximum at 229 \({}^{\circ}\)C and may be due to the decomposition of more stable oxygen functional groups, with the CO and CO\({}_{2}\) release [46]. [PERSON] and co showed that the temperature range between 200-300 \({}^{\circ}\)C is often neglected in the literature, and the weight loss is also due to the release of SO\({}_{2}\), in addition to the water and CO\({}_{2}\)[47]. The total mass loss of GO-Ag is 34.52%, lower than that of GO, which allows us to assume that a series of functional groups on the surface of GO sheets reacted with Ag nanoparticles. The GO-Ag powder is thermally decomposed in four steps. The mass loss of 5.84%, recorded up to 130 \({}^{\circ}\)C, which occurs in the first step, may be due, as previously explained, to the removal of the physically adsorbed water. In the second step, between 130-300 \({}^{\circ}\)C, there is a higher mass loss (16.35%), accompanied by a strong exothermic effect at 218 \({}^{\circ}\)C, which could be due to the removal of some functional groups with oxygen from the graphene surface. The weight losses occurring in the third step (3.92%) between 300-420 \({}^{\circ}\)C and in the fourth step (8.41%) between 420-600 \({}^{\circ}\)C might be due to the removal of GO. They are indicated on the DTA curve by the slight exothermic effects at 390 \({}^{\circ}\)C and 550 \({}^{\circ}\)C [48,49]. The thermal maxima at which the mass losses of the GO-Ag powder occurred are lower than those recorded for GO powder indicating the role of the silver nanoparticles as catalysts, ensuring the reduction at the decomposition temperatures, when they are present on the GO sheets [50]. The total mass loss of GO-Ag-ATPES is 31.06%, lower than the loss suffered in the case of GO-Ag, which allows us to assume that some of the functional groups on the GO surface which remained unreacted after the interaction with Ag nanoparticles reacted with the silane (APTES). As for GO-Ag, the weight loss was achieved in four steps. The mass losses suffered in the first two steps, between 25-120 \({}^{\circ}\)C and 120-270 \({}^{\circ}\)C, accompanied by a strong exothermic effect at 198 \({}^{\circ}\)C are 4.70% and 15.39%, respectively. They are lower for the GO-Ag-APTES sample as compared to the GO-Ag sample. Therefore, in addition to the losses of CO, CO\({}_{2}\) and moisture, some of the functional groups on the GO-Ag surface (especially the epoxy group) can be assumed to be functionalized with silane. In the steps three and four, the total mass losses (10.97%) are also lower than those of GO-Ag (12.33%) confirming the previous assumption regarding the interaction of GO-Ag with the silane. Thus, APTES decompositions take place in a large temperature domain. It starts at 390 \({}^{\circ}\)C with removal of nitrogenous fragments and continue with decomposition of oxyethyl groups, between 450-600 \({}^{\circ}\)C [51]. From the TG curve corresponding to the GO-ZnO powder, a total mass loss of 4.50% can be observed, which is much lower than that of GO. Recall that the ratio of GO: ZnO is 1:20. As in the previous case, the mass losses were realized in four steps. In the first two steps, between 25-140 \({}^{\circ}\)C and 140-230 \({}^{\circ}\)C, the mass losses have the same value (0.72%).