# Conductivity Enhancement of Graphene and Graphene Derivatives by Silver Nanoparticles
## 3 Results and Discussion  
Two graphene substrates were used in this study: pristine FLG and _f_-rGO. FLG nanosheets were produced by LPE of graphite [25], while _f_-rGO was produced by the subsequent functionalization and reduction of GO with 2,4 diaminobenzenesulfonic acid [19]. The two substrates have a common basic graphene structure; however, they are quite different. FLG, consisting of a few graphene layers (usually 1-5), is highly aromatic and mostly hydrophobic since only a few oxygen groups are formed on the surface during the preparation treatment from graphite. On the other hand, _f_-rGO consists mostly of one layer; it is less aromatic due to the defects that have been created in the preparation step of GO and highly hydrophilic due to the functional groups that have been added during the treatment of GO with 2,4 diamino benzene sulfonic acid. Both substrates, pristine FLG and _f_-rGO, are well dispersed in DMF. Ag\({}^{+}\) ions were slowly added to the dispersion of the graphene substrate and the reducing agent--NaBH\({}_{4}\)--in DMF. The reduction of Ag\({}^{+}\) ions led to the development of Ag nanoparticles, preferably on graphene surfaces (see Figure 1). By altering the amount of Ag\({}^{+}\) ions added, _f_-rGO/AgNP and FLG/AgNP hybrids with different Ag percentages were produced. In the next step, the structure and properties of the nanohybrids were studied in detail. Due to the thermal stability of AgNPs, TG analysis was the preferred way to verify the Ag percentage of the as-produced nanohybrids. The thermal profiles of the \(f\)-GO/AgNPs and FLG/ AgNPs were recorded as shown in Figure 2. Under air, the \(f\)-GO/ AgNPs samples exhibited an overall weight loss that ranged between 43% and 85% up to 700 \({}^{\circ}\)C, reflecting the residue of AgNPs after the combustion of the \(f\)-GO content of the hybrids. The percentage of AgNPs in the hybrid was in good agreement with the starting amount of Ag\({}^{+}\) ions (see the theoretical Ag percentage in the inset of Figure 2), indicating that the deposition of AgNPs onto \(f\)-rGO surfaces was strongly favored. Similar weight loss and good agreement with the theoretical Ag percentage were also recorded for the FLG/ AgNPs between 500 and 600 \({}^{\circ}\)C. A 10% weight loss between 200 and 400 \({}^{\circ}\)C of the \(f\)-rGO/ AgNPs samples was due to the removal of the functional groups of \(f\)-rGO, while in the same temperature region, FLG/ AgNPs samples have lost less than 3% of their weight. The \(f\)-rGO samples have a strong hydrophilic character due to the amino denzenesulfonic groups [19], and this is reasonably affecting the final hybrids, inducing high dispersibility of the hybrid \(f\)-rGO/ AgNPs in water, a fact that further enhances the rheological properties and the stability of the related conductive inks. In Figure 3, certain amounts of the different Ag percentages of the \(f\)-rGO/ AgNPs hybrids were suspended in water, affording stable dispersions. The FLG/AgNPs hybrid samples are based on FLG nanosheets, which have, like pristine graphene, much fewer functional groups--usually few carboxy or hydroxy groups--that formed during the preparation procedure. Therefore,  
Figure 1: The formation and subsequent deposition of Ag nanoparticles onto FLG and \(f\)-rGO surfaces. Figure 2: TGA diagrams of \(f\)-rGO/AgNPs and FLG/AgNPs hybrids. FLG/AgNPs hybrids showed much less stability in water due to the hydrophobic character of FLG nanosheets. The morphological characteristics of the hybrids were elucidated through the TEM and SEM microscopy images (see Figure 4). TEM images in Figure 4a,b and SEM images in Figure 4c,d correspond to _f_-rGO/AgNPs hybrids with the highest and lowest Ag percentages, respectively. Similarly, SEM images in Figure 4g,h are from FLG/AgNPs hybrids with the lowest and highest Ag percentages, respectively. EDS analysis confirmed the Ag percentage for both hybrids.