## 3 Results and Discussions
### Fourier Transform Infrared Spectrometry (FT-IR)  
FT-IR spectroscopy was used to confirm the synthesis of GO, GO-Ag and GO-ZnO powders by identifying the molecular groups structures of these compounds, before and after the silanization process, respectively. The FT-IR spectrum of the APTES recorded in the wavenumber range of 4000-500 cm\({}^{-1}\) is shown in Figure 1.  
The APTES silane has amine and silane groups that are able to react with the functional groups on the surface of graphene oxide sheets. The attachment of the silane to the GO sheets leads to the formation of ethers and silica esters. Thus, the amine from APTES can bind to the carboxylic and epoxy groups of GO, while the silica can bind the oxygen containing functional groups from the surface of GO sheets [14]. In the APTES spectrum (Figure 1), the absorption bands observed at 2973 cm\({}^{-1}\) and from 2925 cm\({}^{-1}\) are attributed to the asymmetric vibrations of the CH\({}_{3}\) and CH\({}_{2}\) groups, respectively. The band from 2882 cm\({}^{-1}\) corresponds to the vibration of the C-H functional group, while the absorption bands from 1390 cm\({}^{-1}\) and 1442 cm\({}^{-1}\) are assigned to the symmetrical bending vibrations of the C-CH\({}_{3}\) group and to the shear vibrations of the C-CH\({}_{2}\) group, respectively. The band from 1295 cm\({}^{-1}\) is attributed to the stretching vibrations of the C-N group [15]. It could be also noticed in Figure 1, the presence of three intense absorption bands with peaks at 1072 cm\({}^{-1}\) corresponding to the stretching vibrations Si-O, at 763 cm\({}^{-1}\) assigned to the bending vibrations of the C-H bond [16] and at 952 cm\({}^{-1}\) due to the vibrations of Si-C, C-O and Si-O bonds [17]. The FT-IR spectra of the graphene oxide (GO) and of the silanized graphene oxide (GO-APTES), ranging between 4000-500 cm\({}^{-1}\) are shown in Figure 2.  
In the GO spectrum, one could observe a large absorption band with three peaks at 3338 cm\({}^{-1}\) and 3197 cm\({}^{-1}\) assigned to the stretching vibration of the C-H and O-H bnd [18]  
Figure 1: FT-IR spectra of silane (APTES). Figure 2: FT-IR spectra of graphene oxide (GO) and silanized graphene oxide (GO-APTES). and at 2854 cm\({}^{-1}\) corresponding to the C-H stretching vibrations [19]. In the GO-APTES spectrum there is also a large absorption band with one peak at 2933 cm\({}^{-1}\) that can be assigned to the C-H bond vibration from the CH\({}_{2}\) or CH\({}_{3}\) group [20] The smaller peak at 2360 cm\({}^{-1}\) can be attributed to the stretching vibration of the C-H bond [21]. Moreover, in the GO spectrum, several peaks of higher intensity could be observed at 1718 cm\({}^{-1}\) corresponding to the stretching vibrations of carbonyl groups [22], and at 1619 cm\({}^{-1}\) assigned to the C=O stretching vibrations from carbonyl or carboxyl groups [23], but also to the physically adsorbed water molecules on or between the graphene sheets [24]. The peak at 1361 cm\({}^{-1}\) corresponds to the stretching vibration of C=O group, while the one observed at 1222 cm\({}^{-1}\) can be assigned to the stretching vibration of the C-O bond; the last was found in the GO-ATPES spectrum at 1220 cm\({}^{-1}\)[25]. In the GO-APTES spectrum, the small peaks around 1500 cm\({}^{-1}\) can be ascribed to the asymmetrically stretch of the C=C bonds in the aromatic ring [24] or to the skeletal vibration of graphene sheet [26] while the peak at 1386 cm\({}^{-1}\) can be assigned to the stretching vibration of C-N bond [27]. In the GO spectrum, the peak at 1049 cm\({}^{-1}\) corresponds to the alkoxy group [15; 28] and the one at 981 cm\({}^{-1}\) is assigned to the ring out-of-plane deformation [29]. In the GO-APTES spectrum, the peaks are found at lower wavelengths, respectively at 1029 cm\({}^{-1}\) due to the valence vibrations of the Si-O-Si bond [15; 30] and at 910 cm\({}^{-1}\) assigned to the Si-O-C bond [17]. The peak at 692 cm\({}^{-1}\) corresponds to the Si-phenyl compounds [31].