# Conductivity Enhancement of Graphene and Graphene Derivatives by Silver Nanoparticles
## 3 Results and Discussion
TEM image in Figure 4b shows that in the case of the lowest Ag percentage, spherical-shaped AgNPs with an average size of 12 nm have been formed, and most of them are finely dispersed on the _f_-rGO surface. A few aggregates were also observed (see yellow circles in Figure 4b). In the case of the hybrid with the highest Ag percentage, as shown in Figure 4a, many more and larger aggregates have been formed. In both cases, AgNPs not deposited on the graphene substrate were not observed. SEM images show better the morphology of the hybrids, revealing the phylomorphous character of the graphene derivatives and the decoration of the nanosheets with Ag nanoparticles. The amount of AgNPs and their aggregates was obviously higher in the hybrids with a high percentage of Ag. Figure 4: _Cont._  
Figure 3: Dispersion of _f_-rGO/AgNPs hybrids (6 g L\({}^{-1}\), with different AgNPs percentages) in water (from left to right: 15, 18, 30, 49, and 57%). The UV-Vis spectrum of FLG/ AgNPsNPs showed a characteristic absorption curve with a maximum at 284 nm due to the \(\pi\),\(\pi^{\star}\) transitions of the pristine graphene nanosheets (see Figure 5). The same band in the spectrum of _f_-rGO/ AgNPsNPs was recorded at 266 nm, showing a blue shift that is attributed to the partly oxidized character of _f_-rGO. After the AgNPs development onto the graphene surfaces, a characteristic broad absorption appeared due to the plasmon resonance of AgNPs around 400 nm. This band is very broad for both hybrids, and a second maximum appears at 600 nm at the higher Ag percentage in the case of _f_-rGO/AgNPs. This type of absorption band indicates the formation of large Ag nanospheres, aggregates or anisotropic nanoparticles like rods or wires. The intensity of the absorption is proportional to the amount of AgNPs deposited, as estimated before. The XRD patterns of the hybrids also indicate the formation of AgNPs. The analysis of the XRD pattern of the sample _f_-rGO/AgNPs (57% _w_/_w_ Ag) showed a weak and broad peak located around 23\({}^{\circ}\), which corresponds to an interlayered spacing of 3.3 A between 002 atomic planes due to the partly graphitic character of the product, _f_-rGO/AgNPs (see Figure 6). The sharp peaks at 38.18\({}^{\circ}\), 44.3\({}^{\circ}\), 64.4\({}^{\circ}\), and 77.4\({}^{\circ}\) were assigned to the (111), (200), (220), and (311) planes of face-centered cubic (fcc) Ag crystals (4-0783 JCPDS card). The crystallized size of the Ag nanoparticles was calculated using the Scherrer equation (average value from all peaks) to 11 \(\pm\) 2.4 nm, in accordance with the size of the nanoparticles as estimated by the TEM images. To examine the electric conductivity of the _f_-rGO/AgNPs and FLG/AgNPs hybrids, circular spots were formed by drop casting on paper and air-dried. To have comparable results, spots of similar size were formed with the same amount of hybrid (400 \(\upmu\)g dispersed in 50 \(\upmu\)L of water) under certain conditions. The values of the sheet resistance (R\({}_{\rm s}\)) are presented in Table 1.  
Figure 5: UV-Vis spectra of (**a**) f-rGO/AgNPs and (**b**) FLG/AgNPs hybrids in water dispersion. Figure 6: XRD pattern of the sample, _f_-rGO/AgNPs and FLG/AgNPs hybrids,  
The two hybrids contain AgNPs at several percentages between 13 and 57%. The _f_-rGO/AgNPs hybrid showed mildly increased conductivity that ranged between 11 and 20 kS m\({}^{-1}\), starting from 10 kS m\({}^{-1}\) for the pure _f_-rGO. Specifically, as depicted in Figure 7, the electrical conductivity of the _f_-rGO/AgNPs hybrid showed a linear increase versus Ag percentage with a slope of 0.2 and a threshold around 10% (_w_/_w_). Below this percentage, the conductivity seems to be stable, close to 10 kS m\({}^{-1}\), and it represents the conductive network of graphene nanosheets (see Figure 7). The FLG/AgNPs hybrid also showed mild conductivity at low Ag percentages, which increased remarkably at higher Ag percentages.