## 3 Results and Discussions
### Fourier Transform Infrared Spectrometry (FT-IR)
The presence of the silane peaks in the GO spectrum confirms its presence on the GO sheets. The FT-IR spectra of the GO, GO-Ag and GO-Ag-APTES powder are shown in Figure 3.  
In the GO-Ag spectrum, the peaks at 3850 cm\({}^{-1}\) and at 3733 cm\({}^{-1}\) can be assigned to the absorbed water due the stretching vibration of O-H group of carboxyl, alcohol and absorbed water molecules (some also noticed in the GO-Ag-APTES spectrum) [32]. The broadband between 3000-3700 cm\({}^{-1}\) from the GO-Ag and GO-Ag-APTES spectra can  
Figure 3: FT-IR spectra of graphene oxide (GO), graphene oxide with silver (GO-Ag) and silanized graphene oxide with silver (GO-Ag-APTES). be attributed to the oxygen groups, mainly to the hydroxyl groups located both on the surface and at the edge of GO sheets [24]. The peak at 1621 cm\({}^{-1}\) can be assigned to the stretching vibrations of C=O [33], while the one at 1373 cm\({}^{-1}\) can be due to the O-H bending vibration [34]. The peak at 1288 cm\({}^{-1}\) corresponds to the \(-\)C-N bond (characteristic of PVP used in the synthesis of Ag nanoparticles) and the one at 1051 cm\({}^{-1}\) can be due to the C-O-C stretching vibration of alkoxy group [35]. The peak noticed at 1718 cm\({}^{-1}\) in the GO spectrum almost disappeared in the GO-Ag spectrum and the peak at 981 cm\({}^{-1}\) decreased to 973 cm\({}^{-1}\), which indicates the interaction of the Ag nanoparticles with the functional groups that give absorption peak in those areas. Moreover, the intense peak at 1051 cm\({}^{-1}\) in the GO-Ag spectrum may indicate a strong interaction between the Ag\({}^{+}\) ions and the functional groups on the GO sheets. In the GO-Ag-APTES spectrum, the peak at 2886 cm\({}^{-1}\) can be attributed to the vibrations of the alkyl groups, of the silane fraction on the graphene sheets [9,15]. The peak at 1635 cm\({}^{-1}\) can be assigned to the C=C stretching vibration [9], and the one at 1396 cm\({}^{-1}\) might be due to the C-OH stretching vibrations [36], but also to the C-N stretching vibration [37]. The peak at 1292 cm\({}^{-1}\) is assigned to the C-N bending vibration [37], while the ones at 1037 cm\({}^{-1}\) and 694 cm\({}^{-1}\) correspond to the presence of Si-O-Si and Si-O-C on the graphene sheets surface [9]. The peak at 910 cm\({}^{-1}\) can be assigned to the epoxy group stretch [38]. The FT-IR spectra of the GO, GO-ZnO and GO-ZnO-APTES powder are presented in Figure 4.  
In the GO-ZnO powder, the amount of graphene oxide is about 20 times lower than the amount of ZnO. Therefore, the spectrum of GO-ZnO powder is significantly different from the spectrum of GO. Comparing the three spectra from Figure 4, a series of smaller peaks appearing between 3500 cm\({}^{-1}\) and 4000 cm\({}^{-1}\) could be observed. They are more prominent in the GO-ZnO powder spectrum and can be associated with the OH group, indicating the hydrophilic character of this powder. The prom  
Figure 4: FT-IR spectra of graphene oxide (GO), graphene oxide with zinc oxide (GO-ZnO) and silanized graphene oxide with zinc oxide (GO-ZnO-APTES). 3365 cm\({}^{-1}\) in the GO-Zn spectrum, and at 3363 cm\({}^{-1}\) in the GO-ZnO-APTES spectrum can be attributed to the stretching vibrations specific to the OH group and to the N-H stretching vibration, respectively [15; 33; 39]. The small peaks at 2987 cm\({}^{-1}\) and 2900 cm\({}^{-1}\) in the GO-ZnO spectrum, which could be also noticed at 2932 cm\({}^{-1}\) and 2885 cm\({}^{-1}\) in the GO-ZnO-APTES spectrum can be ascribed to the C-H stretching vibration of the alkane group [40]. In the GO-ZnO and GO-ZnO-APTES spectra, a series of small peaks appeared in the range of 1980 cm\({}^{-1}\) and 1610 cm\({}^{-1}\) which could be assigned to the stretching vibration of the C=O bond within esters, amides, carboxylic, ketones groups [15]. The peaks at 1718 cm\({}^{-1}\) (carbonyl groups), and at 1619 cm\({}^{-1}\) (C=O bond) from the GO spectrum were reduced in both, GO-ZnO and GO-ZnO-APTES spectra, during the preparation process of the GO-ZnO powders.