Synthesis and characterization of reduced graphene oxide from pine needles for supercapacitor application

Graphene from Pine needles

1. A Project Report On Synthesis And Characterization of Reduced Graphene Oxide from Pine Needles for Supercapacitor Application Submitted To The Department of Physics M.L.S.M. College Sundernagar For the Partial Fulfillment of The Award of Degree of M aster Science in Physics Supervised By: Submitted by: Dharamender Singh Rana Rahul Sankhyan Amit Kaundal Aaina Thakur

2. INDEX Title Introduction Carbon-Based Nanomaterials Plant Biomass as a Source Research Methodology Characterization Techniques Result And Discussiona Result And Discussion Conclusion References Acknowledgments Thank You

3. Synthesis And Characterization of Reduced Graphene Oxide from Pine Needles for Supercapacitor Application

4. INTRODUCTION One of the most abundant and versatile elements in the universe is carbon. The name "Carbon" is derived from the Latin word "Carbo" which means "coal." It is a chemical element with the atomic number 6 and the letter C. It is nonmetallic and tetravalent in nature, making four electrons available to create covalent chemical connections. The earth's crust contains 0.025 percent carbon. After hydrogen, helium and oxygen, it is the fourth most plentiful element in the universe by mass and the fifteenth most abundant element in the Earth's crust. It is commonly called the "King of the Elements" since it produces more compounds than any other element. Carbon-based nanomaterials (CNMs) are competitive in a variety of business sectors, including coating, packaging, microelectronics, medicine delivery, biotechnology and energy storage because of their extraordinary and distinguishing qualities, which include low density, hardness, corrosion resistance, good mechanical strength, excellent chemical and thermal stability. Synthesis protocols and modification approaches leads to different CNMs like graphene (G), graphene oxides (GOs), reduced graphene oxides (rGOs), carbon nanotubes (CNTs), graphite, fullerene, nanoporous carbons (NPCs) and carbon nanofibers (CNFs)

5. Nature’s way of reusing carbon atoms, which travel from the atmosphere into organisms on the earth and then back into the atmosphere over and over again known as the carbon cycle 1. Structure and Bonding The carbon  atom  is unique in its tendency to form extensive networks of  covalent bonds  with other elements and with itself. Because of its position midway in the second horizontal row of the  periodic table , carbon is neither an electropositive nor an electronegative element. The carbon atom has six electrons; the two electrons are closer to the nucleus and the remaining four act as valence electrons . The four bonds of the carbon atom are directed to the corners of a tetrahedron and make angles of about 109.5° with each other. 2. Allotropy “Allotropy”  comes from the Greek word  allotropia , which means changeableness. Allotropes are elements that exist in two or more different forms in the same physical state but differ in physical properties and may also differ in chemical activity. Carbon is three different crystalline forms: α- (hexagonal), β-(rhombohedral) graphite and diamond. Some other amorphous forms of carbon include coke, coal, charcoal and carbon black. Amorphous carbon is a noncrystalline solid allotropic form of carbon.

6. Carbon-based nanomaterials (a) Graphite Graphite consists of sheets of trigonal planar carbon. Carbon atoms are arranged in a honeycomb lattice in the individual layers known as graphene. Because of the relatively weak van der Waals interactions between layers, the carbon atom uses three electrons to create simple bonds with its three close neighbors. In the bonding level, the fourth and "spare" electrons are dispersed in one layer throughout the full sheet of atoms. They are no longer attached to any atom or pair of atoms. Delocalized electrons no longer have a fixed relationship with a particular carbon atom, they are free to move throughout the sheet.( Fig. 1.2 ) Figure 1.2 Structure of graphite showing the different types of bonding. (b) Graphene The "wonder material" known as graphene is a two-dimensional (2D) one atom thick sheet of   sp 2 hybridized carbon atoms arranged into a honeycomb lattice. The extraction of graphene from graphite has demonstrated great potential in the study of materials science, physics, chemistry, biology, and other disciplines. Following the emergence of other forms of carbon nanostructures such as fullerene (which is formed by wrapping up the 2D graphene layer into a 0D molecule), carbon nanotubes (formed by cylindrically rolling the 2D graphene layer into 1D nanotubes) and graphite (2D graphene layers are stacked into a 3D structure) the invention of graphene has given rise to several new disciplines in science and technology ( Fig. 1.2 ). But, the difficulty of controlled synthesis of graphene with small yields, minimization of folds, limited numbers of layers, etc., still needs to be resolved. Graphene is mostly used as a derivative of graphene oxide (GO) and reduced graphene oxide (rGO) ( Fig. 1.3 ). Figure 1.3 Structure of Graphene, Fullerene, Carbon nanotube and Graphite

7. (c) Graphene oxide Graphene oxide (GO) has shown some unusual physicochemical characteristics, including large surface area, exceptional strength in 2D structure, small size, electronic properties and interesting optical properties, among others. Because GO differs from graphene in that it contains oxygen functional groups such as epoxy and oxygen groups on its basal plane, as well as small amounts of carbonyl and carboxyl groups at its sheet edges. As a result, GO has excellent aqueous processability, fluorescence quenching ability, surface functionalization capability, amphiphilicity and additional beneficial properties for potential biotechnological applications. (c) Reduced graphene oxide [rGO] Reduced graphene oxide (rGO) has been one of the most exciting materials in research fields, particularly in nanotechnology. It can alternatively be referred to as graphene, functionalized graphene, transformed graphene, or simply   graphene.The ability to create graphene from GO is now a very important area of research because using cheap chemical processes and low-cost graphite as a raw material, it is possible to produce it in large quantities. It is also highly hydrophilic and can form stable aqueous colloids, allowing for the assembly of macroscopic structures using simple and inexpensive solution processes. Both characteristics are critical for biomedical applications. The main system for converting GO to graphene is to reduce it using an electrochemical, chemical and thermal treatment, resulting in reduced graphene oxide (rGO), which has much lower oxygen functional groups than GO. Various reducing agents will result in different carbon-to-oxygen ratios and chemical compositions in rGO. Even though reducing the GO structure to get pristine graphene fully is impossible, the oxygen functional groups' cost-effectiveness and controllability make rGO very attractive for biological application. Figure 1.4 Formation of rGO and GO from graphene or graphite

8. Research Methodology Materials and Chemicals Used The pine needles (raw material) were collected from the nearby forest, Sunder Nagar, Himachal Pradesh-175018 India. H 2 SO 4 was bought from sigma Aldrich with 99% purity. All other chemicals and reagents used in the present study were of analytical grade and used as received without further purification Preparation of reduced Graphene Oxide The following steps were taken to prepare the sample (rGO) from pine needles Pine needle pretreatment The pine needle (20 g) was cut into small pieces and thoroughly washed with distilled water to remove the impurities and dust particles on its surface. To reduce the moisture, it was subsequently dried in an oven at 45°C for 12 hours. Impregnation with activator To guarantee the complete mixing of the activator with the raw material, pine needle was soaked in 200 ml of concentrated sulfuric acid (H 2 SO 4 ) and left undisturbed for 24 hours. The impregnated sample underwent vacuum filtration after being diluted with distilled water to neutralize the acid. The sample was kept in oven at a temperature of 70°C until moisture reduced completely. Carbonization of rGO (reduced graphene oxide) The sample powder was then transferred into a tube furnace and treated at 1200 o C for 5 minutes under a nitrogen atmosphere. The final weight of the sample was 10.08 g.

9. Results and Discussion XRD analysis The prepared material was analyzed through XRD technique to determine its crystallinity and crystal structure. The XRD pattern of the material has been shown in Fig. 4.1 . From the XRD spectrum, we can see that the peaks are not much sharp which indicates that the material is not completely crystalline but, it also has some amorphous content. The diffraction pattern consists of two broad peaks at approximately angles 2θ = 24 ° and 44 ° . When the diffraction peaks of the prepared material were compared with the reference, it was identified as rGO. The broader peak at 2 q = 24.6° corresponds to the (002) plane indicates the formation of layered structure of graphitic carbon nanomaterial [59]. Another broad peek at 44.1° corresponds to the (101) planes, confirming the formation of turbostratic carbon in the carbon nanomaterial. Figure 4.1. XRD Pattern of as-synthesized reduced graphene oxide

10. FESEM and HRTEM Characterization Field emission scanning electron microscopy (FESEM) used for study of surface morphology of sample. The reduced graphene sheets shown in Fig. 4.2 (a) emerged as similar thin sheets randomly arranged with distinct edges with wrinkled surfaces and folding. Also, the carbon particles at a high resolution (100 000 X) appear as small irregular-shaped particles. High–resolution transmission electron microscopy (HRTEM) is the imaging mode of a specialized transmission electron microscope that allows for direct imaging of the internal structures of samples. Fig. 4.2 (b) shows an HRTEM image of reduced graphene sheets that looked to be variable thicknesses and exhibit a sheet-like shape with various transparency in the study area. High transparency areas showed significantly thinner films of graphene layers, while dark areas showed thick stacking of several graphene layers. Figure 4.2 (a) FESEM and (b) HRTEM images of as-synthesized reduced graphene oxide.

11. BET Analysis Brunauer- Emmett- Teller (BET) analyzes the physical properties of the prepared material such as surface area, pore size etc, by using nitrogen adsorption-desorption process. Fig. 4.3 shows the nitrogen adsorption–desorption isotherm at 30.33 o C for the material prepared at an activation temperature of 1200 o C using concentrated H 2 SO 4 as an activator. The prepared sample exhibited Type-I isotherm according to IUPAC classification. The prepared material's surface area and total pore volume under optimum conditions were 1200.12 m 2 /g and 0.4868 cm 3 /g respectively. The average pore width above the material was 3.270 nm. This result signifies that the material has adsorbed in a mesoporous manner Figure 4.3. Nitrogen adsorption – desorption isotherm of rGO

12. UV-Visible spectroscopy The synthesized material was further analyzed by UV spectroscopy technique to know the absorbance of the material. UV-Visible spectroscopy is a type of absorption spectroscopy in which a molecule absorbs light in the UV-Visible region (200-700 nm), which causes the electrons to be excited from the ground to a higher energy state . The study was carried out by determining the prepared material's response to UV radiation absorption. Firstly, the dispersion of the material was prepared in a 1:1 mixture of ethanol and distilled water by sonication for 30 minutes. Afterward, the response of dispersion was recorded by spectroscopy. It was observed that the dispersion of prepared material exhibits a strong absorption peak at 233 nm. [ Fig. 4.4 ] Figure 4.4 UV absorption analysis of as-synthesized rGO

13. Electrochemical performances The Cyclic voltammetry measurements offer insights into the electrochemical behavior and performance of the nanocomposite as an electrode material. The electrochemical performance of active material for the supercapacitor application, cyclic voltammetry study (CV) Fig. 4.5 and galvanostatic charging-discharging (GCD) measurements were performed in a three-electrode system. In this three electrodes system, one is the working electrode which is modified with the active material and other two are the reference electrode and the auxiliary electrode /counter electrode which consists of Ag-AgCl and platinum respectively. NaOH has been used as an electrolyte. From this study, we calculated the specific capacitance near about 16.434 Fg −1 at a scan rate of 5 mV s −1 . We got the different values of specific capacitance for different scan rates as shown in Table 1 . Also, rGO demonstrates pseudo-capacitance, an electrochemical phenomenon associated with Faradaic processes that involve fast surface redox reactions, leading to additional energy storage beyond the electrical double-layer capacitance. rGO provides a highly conductive pathway, enabling efficient charge transport. This conductivity is advantageous for applications such as energy storage and electronic devices. Additionally, the high surface area and conductivity enhance the supercapacitor property of reduced graphene oxide.

14. Figure 4.5 Graphical representation of CV curves of rGO Figure 4.6. Specific Capacitance curve for different Scan rates (mV s −1 ) S.No. Scan rate (mVs -1 ) Specific Capacitance (Fg -1 ) 1. 5 16.43420463 2. 10 10.44924774 3. 15 7.595402041 4. 20 5.979665987 5. 30 3.963354401 6. 40 2.949529321 7. 60 1.949476976 8. 100 0.973392816 Table 1. Different values of specific capacitance for different Scan rate

15. Table 1 shows the different specific capacitance values for different scan rates. The value of specific capacitance decreases with the increase in scan rates. Fig. 4.6 shows the graph where the value of specific capacitance decreases exponentially but the value of specific capacitance increases at scan rates 100 mV s −1 . This is due to the pseudocapacitance, rapid and reversible redox processes at the electrode surface are the source of pseudocapacitance, which can considerably increase the capacitance. Due to faster electron transfers, these redox processes can happen more easily at high scan rates. Therefore, the role of pseudocapacitance to the total capacitance increases at very high scan rates. This abrupt rise in specific capacitance seen in the plot is most likely the result of increased pseudocapacitance contribution, which is making up for the decline in ion diffusion-limited capacitance. 5. Conclusion In a nutshell, the pine needle was effectively utilized to synthesize carbon nanomaterial. After the characterization through XRD and FESEM, the layered structure of carbon nanomaterial is confirmed. This indicates the successful synthesis of reduced graphene oxide. Afterward, the as-synthesized nanomaterial is explored for its supercapacitor application. The Scan rate study is conducted, where specific capacitance is calculated at individual scan rates. The nanomaterial has shown high conductivity and high specific capacitance. Further, a sustainable approach to obtain reduced graphene oxide through pine needles is adopted successfully.

16. Thank You