# Conductivity Enhancement of Graphene and Graphene Derivatives by Silver Nanoparticles
## 2 Materials and Methods
### Method Section  
Graphene preparation. A total of 300 mg of graphite was dispersed in 300 mL of DMF and sonicated for 1 h in bath sonicator. The unexfoliated graphite that precipitates after 1 h of standing was separated from the liquid phase. The dispersed material, a few layers of graphene nanosheets (FLG), was isolated from the solvent by filtration using hydrophobic nylon membrane filters (0.45 \(\upmu\)m) [26].  
Graphite oxide preparation [27]. A total of 5 g of graphite was added to a cold mixture of concentrated sulfuric acid (80 mL) and nitric acid (40 mL). Then 40 g of potassium chlorate was slowly added by stirring and continuously cooling. The reaction was stopped 18 h later by pouring the mixture into water, and GO was isolated by centrifugation and washed several times with water until neutral. The product was air-dried.  
Functionalization and reduction of graphene oxide (_f_-rGO). The functionalized reduced graphene oxide was prepared according to ref. [19]. A total of 100 mg of GO were dispersed in deionized water under sonication for 30 min (110 W, 40 kHz). A total of 300 mg of 2,4 diaminobenzzenesulfonic acid was then added, and the mixture was heated under reflux for 5 h. The product was isolated by centrifugation (9000 rpm) and washed extensively with water, alkaline water, ethanol, and acetone, then air-dried.  
Deposition of Ag nanoparticles on _f_-rGO (_f_-rGO/AgNPs). A total of 4 mg of _f_-rGO was dispersed in 20 mL of DMF, followed by the addition of 60 mg of NaBH\({}_{4}\). A certain amount of AgNO\({}_{3}\) (0.25 M) was diluted in 3 mL H\({}_{2}\)O and added dropwise into the reaction mixture for 30 min. The mixture was then centrifuged (10,000 rpm, 20 min), and the precipitate was washed twice with water. This procedure was used to produce _f_-rGO/AgNPs nanocomposites with the following theoretical Ag percentages and the added volume of AgNO\({}_{3}\) in parenthesis: 15% (28 \(\upmu\)L), 25% (52 \(\upmu\)L), 30% (68 \(\upmu\)L), 40% (108 \(\upmu\)L), and 57% (216 \(\upmu\)L).  
Deposition of Ag nanoparticles on FLG (FLG/AgNPs). A total of 6 mg of FLG nanosheets was dispersed in 20 mL of DMF, followed by the addition of 60 mg of NaBH\({}_{4}\). A certain amount of AgNO\({}_{3}\) (0.25 M) was diluted in 3 mL of H\({}_{2}\)O and added dropwise into the reaction mixture for 30 min. Then, 200 mg of sodium citrate diluted in 3 mL of water was added dropwise into the reaction mixture. The aggregate that formed was isolated by centrifugation (10,000 rpm, 20 min) and washed by redispersion in 20 mL of water and centrifugation (10,000 rpm, 20 min). Finally, the solid composite was dispersed in 1 mL of water. This procedure was used to produce FLG/AgNPs nanocomposites with the following Ag percentages and the volume of AgNO\({}_{3}\) in parenthesis: 15% (40 \(\upmu\)L), 20% (56 \(\upmu\)L), 30% (96 \(\upmu\)L), 45% (183 \(\upmu\)L), and 60% (336 \(\upmu\)L).  
Preparation of the _f_-rGO/AgNPs ink formulation. An appropriate amount of the sample f-rGO/AgNP\({}_{2}\) was mixed with the underproduction system of resins R-UDP (solid content approx. 42%) and water to produce an ink with a ratio of pigment solids/resinsolids of 50/50. The mixing of ink components is made using a homogenizer (Witeg Labortechnik GmbH, Wertheim, Germany) and a vortex mixer (LLG-uniTEXER, LabLogistics Group GmbH, Meckenheim, Germany).