**2. Synthesis of graphene oxide from biomass waste**

Natural graphite and synthetic graphite have several constraints as the precursors in the production of GO, where the natural sources of graphite are limited in some countries and the production process of synthetic graphite requires extremely high temperatures (≥2500°C) and demands utmostly high cost [13]. Meanwhile, biomass waste has been widely recommended as a potential precursor material for carbon-based synthesis due to its environmental-friendly characteristic, lower temperature process, abundant availability, geographically wide spreading, and lower cost requirements compared to conventional graphite. Several recent studies have suggested biomass as a very appropriate alternative starting material for preparing valuable carbonaceous materials [14–16].

The following section describes the synthesis of GO conducted by the authors by modifying Hummer's method with activated carbon precursors from oil palm empty fruit bunches (OPEFB), rice husks, and coconut shells.

#### **2.1 The synthesis of GO from oil palm empty fruit bunches (OPEFB)**

Graphene oxide synthesis from OPEFB was started out by drying the collected empty fruit bunches for 2 days under the sunlight to reduce the water content.

*Graphene Oxide Based on Biomass Waste: Synthesis and Applications DOI: http://dx.doi.org/10.5772/intechopen.107488*

Subsequently, the raw material is then chopped into small pieces and put into various 50, 60, 100, and 125 ml evaporating dishes and let dry in the oven for 60 min at 100°C to completely remove water content existing in empty fruit bunches. The raw material the heated in the furnace for 30 min at various temperature of 250, 300, 350, and 400°C, to convert the empty bunches into charcoal. Furthermore, the charcoal is crushed using a mortar and pestle to produce charcoal powder and sieved with a 270 mesh filter.

The carbon activation was carried out by adding the charcoal powder into 50 ml NaOH solution and left the mixture for 24 h. The solution was dried using oven at 105°C for 3 h to obtain the activated carbon sample. **Figure 1** shows XRD pattern of the sample where the diffraction peaks (002) and (100) presents at 2θ = 29 degree and 2θ = 46 degree indicate the sample could be considered as graphite. The obtained sample was used as a graphene oxide precursor using the modified Hummer's method.

The synthesis of graphene oxide was carried out by mixing 1.5 g of activated charcoal from OPEFB, 0.75 g of NaNO3, and 34.5 ml of H2SO4 in an Erlenmeyer and stirring the mixture using a magnetic stirrer with 250 rpm at a temperature of 0–5°C for 20 min. The Erlenmeyer was subsequently put into an ice bath to reduce the temperature and keep stirring for 2 h. KMnO4 powder was slowly added to the mixture to avoid rapid increase in temperature and explosion. Since 4.5 g of KMnO4 was successfully added, Erlenmeyer was removed from ice bath and stirring temperature was set into 35°C for 30 min. The process was carried out until the mixture shows a milk chocolate color. Furthermore, 69 ml of distilled water was slowly poured into the mixture using a dropper and kept stirring for 20 min until the solution color turned dark brown with the appearance of bubbles. The oxidation process was terminated by adding 100 ml of distilled water followed by 1.5 ml of H2O2 which was indicated by yellow color of the solution. Finally, the solution was diluted by adding 50 ml of distilled water and the graphite oxide sample was gathered. Then, the sample GO was sonicated to peel the graphite oxide into layered graphene oxide. The sample was neutralized by distilled water and centrifuged to separate the precipitate and solvent. The separated precipitate was graphene oxide sample that subsequently dried in the oven to completely remove the water content. The GO sample was confirmed by the characterization instrument. **Figure 2** shows

**Figure 1.** *XRD pattern of activated carbon from (OPEFB).*

#### **Figure 2.**

*XRD diffraction pattern of graphene oxide from oil palm empty fruit bunches for carbonization temperature (a) 300* °*C, (b) 350* °*C, and (c) 400* °*C.*

XRD pattern of OPEFB-based GO. Diffraction peak of the sample appears at angle 2θ = 26–29° that indicates the structure of graphene oxide.

#### **2.2 The synthesis of GO from rice husk**

Rice husk-based GO synthesis began by cleaning the rice husk waste and followed by drying process under sunlight for 3 days. Further drying process was carried out using oven at 105°C for 2.5 h to remove the water and moisture properly. Carbonization process was performed using the furnace for 15 min to produce biocarbon. Various carbonization temperature (250, 300, and 350°C) were used to analyzed the resulted product. Resulted biocarbon was filtered using 140-mesh and 170-mesh sieves to produce uniform particles with a size of 88–106 μm and prepared as the precursor of synthesis process. Modified Hummers method was applied to fabricate rice husk-based graphene oxide. The process was started by mixing 1 g of as prepared rice husk-based biocarbon, 23 ml sulfuric acid (H2SO4), and various masses of sodium nitrate (NaNO3) in the ice bath and stirred at a speed of 600 rpm for 2.5 h. Various mass of NaNO3 (0, 0.5, 1, and 2 g) were used. Potassium Permanganate (KMnO4) with mass of 3 g was slowly add into the mixture by keeping the temperature under 20°C to prevent explosion and stirred for 30 min. After KMnO4 was completely added, the reaction temperature was raised to 35°C by removing the ice bath and setting the hotplate temperature and stirring process was carried out for 30 min. The mixture was then diluted by slowly adding 46 ml of distilled water and keeping the temperature at 95–99°C and stirring for 30 min. After the oxidation had taken place, diluted Hydrogen peroxide (H2O2) 3% was added to stop the oxidation process and remove the manganese and permanganate residuals. The oxidation process produced rice husk-based graphite oxide and subsequently, the product was exfoliated to produce rice husk-graphene oxide The solution was set in the Ultrasonic device to perform sonication process. Washing process was performed to neutralize the solution using distilled water and centrifuge for several

*Graphene Oxide Based on Biomass Waste: Synthesis and Applications DOI: http://dx.doi.org/10.5772/intechopen.107488*

#### **Figure 3.**

*XRD diffraction pattern of graphene oxide from rice husk waste for carbonization temperature (a) 250* °*C, (b) 300* °*C, and (c) 350* °*C.*

cycles. When the neutral phase was gathered, the precipitate and liquid were separated. As gathered precipitate was dried in the oven at the temperature of 100°C for 15 min and the rice-husk-based graphene oxide sample was obtained.

The XRD pattern of rice husk-based GO is presented in **Figure 3**. All the variations measured have a fairly identical pattern where the diffraction peak appears at the angle of 2θ = 10° with an interplanar distance of 8.8 Å, at the reflection plane (001), and at the angle of 2θ = 44° with an interplanar distance of 2.1 Å, at the reflection plane (100). These characteristics confirmed the formation of graphene oxide. The diffraction peak at about 2θ = 22° indicates the graphene oxide is not completely bound to oxygen atoms. The diffraction peak at 2θ = 10° indicates the distance between the GO layers, while the diffraction peak around 2θ = 44° indicates the short arrangement of the stack layers GO.

The peak between 26° and 44° indicates the presence of an amorphous solid structure that was formed from natural materials. The change in the peak position was influenced by contained oxygen functional groups, which had oxidized graphite to form GO. This result is in accordance with previous researcher's report that the XRD peak of GO nanoparticles from agricultural waste carbonization appears at the angle of 2θ = 26.6° and 2θ = 44°.

#### **2.3 The synthesis of GO from coconut shells**

The synthesis process as began by cleaning the coconut shells and drying under the sunlight for 3 days. Dried coconut shell then was cut into small pieces and heated at 100°C for 60 min to completely remove water and moisture content. Carbonization process of coconut shell was performed using a furnace for 2 h with temperature variations of 250, 300, 350, 400, and 450°C. As gathered coconut shell charcoal was ground and sieved with 125 mesh filter to produce charcoal powder. Subsequently, the charcoal was activated using NaOH solution.

Modified Hummer's method was applied to synthesized coconut shell-based GO. Activated carbon powder from coconut shell with mass of 1.5 g was mixed with 0.75 g Sodium nitrate (NaNO3) and 34.5 ml of Sulfuric acid (H2SO4 98%) an Erlenmeyer and stirred for 20 min at a temperature of 0–5°C at a constant speed of 250 rpm. The Erlenmeyer was then put in an ice bath and 4.5 g KMnO4 powder was slowly added by considering the temperature of mixture was below 20°C. The Erlenmeyer was removed from the ice bath and the temperature was increased into 35°C and stirred for 30 min to let the oxidation process take place. Distilled water was added to dilute the mixture by volume of 69 ml and stirring process was continued for 20 min and kept the temperature below 50°C. The mixture showed dark brown color with bubbles. In order to terminate the oxidation process 100 ml of deionized water was added and followed by 1.5 ml of 30% H2O2. The appearance of the mixture turned into yellowish color. The mixture was sonicated for 2 h to exfoliate the graphite oxide into GO followed by washing process using distilled water. The solution was precipitated for 1 day until a liquid and solid phases were formed. Separation of the solid and liquid was carried out using a centrifuge at 4000 rpm for 15 min and followed by GO neutralization. After neutral pH was obtained, GO was dried in the oven at a temperature of 60°C for 12 h.

The coconut shell-based GO sample was measured by XRD characterization that presented in **Figure 4**. Diffraction peak of the sample appears at angle 2θ = 26 and 2θ = 29 degree that signifies the structure of graphene oxide.

#### **Figure 4.**

*XRD diffraction pattern of graphene oxide from coconut shell for carbonization temperature (a) 250 °C, (b) 300 °C, (c) 350 °C, (d) 400 °C, and (e) 450 °C.*
