FIELD OF INVENTION
[001] The present invention relates in general to a method for 5 preparation of graphene oxide from sugarcane bagasse. The present work has opened up a new aspect for use of bagasse as a by-product of sugar industry, by converting it into value-added graphene oxide and offering new opportunities for cost-effective production of graphene-based materials for various applications including biology, 10 medicine and organic synthesis.
BACKGROUND/PRIOR ART
[002] Carbon, the sixth-most abundant element, shows the unique 15 property of forming a broad range of structures and allotropes with varying dimensions from zero-dimensional to three-dimensional. Graphite is a well-known allotropic form of carbon. It consists of stacks of parallel two-dimensional graphene sheets. Each graphene sheet has a two-dimensional hexagonal lattice of sp2-hydridized 20 carbon atoms. Graphene is the world’s thinnest, strongest, and stiffest material and exhibits very unusual properties such as high electron mobility (2 X 105 cm2 V-1 S-1) at room temperature, thermal conductivity (5 x 105 Wm-1K-1) and high Young’s modulus (~ITPa) [Science, 306, 666, 2004; Nature, 438, 197, 2005: Phys. Rev. Lett., 25 100, 016602, 2008; Science, 321, 385, 2008] and high theoretical surface area of 2630 m2g-1. The graphene sheet also provides
3
resistance to the penetration of the most of the chemical ions. Considering these extraordinary properties of graphene, it is envisaged that graphene and its derivaties are the futuristic material for the application in electronics, photonics, optoelectronic devices, as a corrosion prevention materials for metals and catalysis. 5
[003] In a graphite crystal the individual graphene sheets are held together by weak van der Waals-forces, while within each graphene sheet the carbon atoms are covalently bound. It is considered that, it is this anisotropy that provides individual graphene sheets (single-10 layer graphene) and stacks of only a few graphene sheets (multilayer graphene) with their unique mechanical, thermal and electrical properties. These properties are similar and sometimes even superior to those of carbon nanotubes. Thus, there is a keen interest in finding ways to mass produce single-layer and multi-layer graphene 15 in order to exploit its properties on an industrial scale.
[004] In K.S. Novoselov et al., “Electric field effect in atomically thin carbon films” (Science, 306, 666, 2004), and the corresponding online supplement, it is disclosed that individual graphene sheets are 20 thermodynamically stable and can be exfoliated and placed on a silicon dioxide substrate by means of an adhesive film. The requirement of an adhesive film may render it difficult, however, to scale the method up to mass production, another mechanical method of graphene production is disclosed in the patent application 25 EP 2 275 385 A1, where graphene is exfoliated from graphite particles by means of grinding. Other methods for separating the sheets that make up graphite involve chemical exfoliation by means
4
of the oxidation of graphite yielding graphite oxide as an intermediate product. As compared to graphite, graphite oxide can more easily be exfoliated into single sheets or stacks of only a few sheets, which material is referred to as “graphene oxide”.
5
[005] Different from graphene, which is almost not soluble and cannot be dispersed in water or any organic solvent, graphene oxide contains high-density oxygen functional groups, like hydroxyl and epoxy group on its basal plane, and carboxyl at its edge. They afford graphene oxide with excellent water solubility, ease of 10 functionalization and convenience in processing etc, making it the most popular precursor of graphene. Undoubtedly, it is of great significance to devise economical, eco-friendly and scalable procedure to produce graphene oxide.
15
[006] Methods for oxidizing graphite are known in the art. The synthesis of graphite oxide was first published by Brodie in 1859 (see B.C. Brodie, “On the Atomic Weight of Graphite”, Philosophical Transactions of the Royal Society of London 1859, 149, page 249). Graphite was mixed with potassium chlorate and fuming nitric acid 20 to yield graphite oxide. W.S. Hummers in mixed with potassium chlorate and fuming nitric acid to yield graphite oxide. W.S. Hummers in the patent US 2 798 878 A discloses a process for the production of graphitic oxide from graphite implementing an oxidizing liquid comprising sulphuric acid, anhydrous nitrate and 25 anhydrous permanganate. Most of the commercially available graphene oxide or its derivatives are synthesized by Hummers’ method or a modified version utilizing flake graphite.
5
[007] Further, reference may be made to US 20130079552, which claims that halo acids are efficient reducing agents for the production of good quality graphene oxide. Reference may be made to US 20110052813, which makes a disclosure regarding the preparation of funcationalized graphene oxide by chemical method. Again, reference 5 may be made to US 0044890, which recites a chemical method for the production of magnetic-graphene based nanocomposite.
[008] However, most of these processes are tedious and involve vigorous reaction that often result in, for example, spontanoues 10 ignition or explosion of potassium chlorate, including toxic gas generation (NO2, N2O4), residual nitrate high cost and poor scalability in practical applications. The most common carbon source to access graphene oxide till date is flake graphite, a naturally occurring mineral, as is purified to remove heteroatomic 15 contamination. In recent years, with the increasing awareness of environmental protection, it is a need and indeed a desire to explore various other carbon sources or precursors especially more sustainable and renewable materials that can be readily tailored to graphene oxide. 20
[009] In current scenario of Sugar Industry, co-products of the sugarcane provide an alternative to increase the productivity of the factories, to improve the development of new areas of interest, and to promote parallel businesses and make greater profits. The effective 25 utilization of the co-products and waste-products of sugar manufacture, as well as the sugar itself, to produce new and useful products and chemicals is gaining popularity as it not only fetches
6
them additional revenue but also pavestheway for survival. Indian sugar factories are crushing approximately 250 million tons cane per year, which generates about 37.5 million tons of bagasse on dry weight basis. It is commonly used as a primary fuel source for sugar mills and the production of pulp, paper, and boar in substitution of 5 wood. However, there is a potential to make better use of the renewable resource by producing novel functional biobased materials.
[0010] Thus, keeping in view the current scenario of Indian Sugar 10 Industry and the drawbacks of the hitherto reported prior art to access graphene oxide, there exists a dire need to provide a method for the preparation of graphene oxide from a readily available, renewable carbon precursor that is easy, industrially viable and cost-effective. Hence, the present invention has been introduced. 15
OBJECTS OF THE INVENTION
[0011] An object of the present invention is to provide a method for preparation of graphene oxide from sugarcane bagasse which 20 obviates shortcomings of the prior arts.
[0012] Another object of the invention is to provide a method for the preparation of graphene oxide from sugarcane bagasse by graphitizing easily accessible, inexpensive, sustainable and renewable 25 carbon precursor in the form of the sugarcane bagasse.
7
[0013] Yet another object of the present invention is to provide a method for the preparation of graphene oxide avoiding high cost and poor scalability in practical application with facilitation for adaptation by Industry.
5
[0014] Further object of this invention is to propose a method for the preparation of graphene oxide from sugarcane bagasse which in turn its derivatives without using flake graphite, hazardous and toxic oxidizing agents.
10
[0015] Still further object of the invention is to provide a method for the preparation of value added materials chiefly from abundantly available carbon precursor.
SUMMARY OF THE INVENTION 15
[0016] In today’s social and political enviornment, sugar industry is striving to be environmentally sustainable and “green”, while maintaining profitability through value addition by better co-product utilization. Thus, the effective utilization of the co-20 products and waste-products of sugar manufacture, as well as the sugar itself, to produce new and useful products and chemicals is gaining popularity as it not only fetches them additional revenue but also paves way for survival in current scenario. Graphene oxide, as the derivative of graphene, plays a vital role in many areas including 25 biology, medicine and organic synthesis.
8
[0017] The conventional methods for the graphene oxide synthesis utilize highly pure graphite as the main input material and are not completely efficient from economic and ecological viewpoints. As such, a sustainable approach that enables the efficient access to graphene oxide is of broader importance. 5
[0018] The present invention is pertinent to a simple and eco-friendly process capable for the large scale production of graphene oxide. The method involves heating the sugarcane bagasse as a renewable natural carbon precursor in controlled atmosphere at the 10 temperature ranging between 450 to 800 degree C for a time period of 30 to 180 minutes. The obtained graphitic raw carbon is oxidized by means of nitric acid to produce graphene oxide. As per the end product is concerned, a valuable graphene oxide powder can be prepared using cheaply available carbon source. 15
[0019] The present invention discloses a process capable of producing graphene oxide in a few simple steps that is easy, industrially viable and cost-effective and at the same time avoids the usage of flake graphite, hazardous and toxic oxidizing agents such as potassium 20 chlorate, NaNo3, KMnO4, K2FeO4, K2S2O8 and P2O5.
[0020] The produced graphene oxide was characterized using UV-visible absorption spectroscopy. FTIR spectroscopy, Raman spectroscopy, XRD and SEM. 25
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
9
[0021] Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings of the exemplary embodiments and wherein:
5
Fig.1 shows: The UV-Vis in absorption spectra of graphene oxide according to the invention.
Fig.2 shows: The FT IR spectra of graphene oxide in accordance with the invention. 10
Fig.3 shows: The Raman spectrum of graphene oxide of the present invention.
Fig.4 shows: The XRD pattern of graphene oxide according to 15 the invention.
Fig.5 shows: SEM micrograph of graphene oxide prepared according to the invention.
20
DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[0022] The present invention makes a disclosure regarding a 25 technology pertaining to a method for the preparation of graphene oxide from sugarcane bagasse.
10
[0023] The renewable carbon precursor utilized for the purposes of the present invention consists of sugarcane bagasse which is obtained from a commercial sugar factory. It is a typical lignocellulosic waste residue produced by sugar industry. It comprises of fibers, water and 5 relatively small quantities of soluble solids- mostly sugar. The average composition of mill-run bagasse is: fiber (including ash) 48%; moisture 50%; soluble solids 2.0%. The fiber consists mainly of cellulose (27%), pentosans (30%), lignin (20%) and ash (3.0%).
10
[0024] Keeping in view its abundant availability, the present invention utilizes the sugarcane bagasse to prepare graphene oxide under optimized conditions.
[0025] The method for preparation of graphene oxide from sugarcane 15 bagasse is discussed hereinunder.
[0026] The ground sugarcane bagasse is dried by heating at temperature of 60 to 100 degree C for a time period of 60 to 300 minutes in air. 20
[0027] The dried sugarcane bagasse thus obtained is mixed with the iron salt/compound used as graphitizing agent.
[0028] The mixture of sugarcane bagasse and iron salt powder thus 25 obtained is heated at temperature ranging between 450 to 800 degree C for a time period of 30 to 180 minutes in a controlled atmosphere to obtain raw carbon. Thereafter, the raw carbon is washed with
11
aqueous solution of hydrochloric acid, sodium hydroxide and finally with distilled water. This results in black solid, which is subjected to purification with the help of soxhlet extractor using organic solvent. Thereafter, the resultant black solid undergoes drying by heating at a temperature in the range of 90 to 100 degree C for a time period of 30 5 to 180 miuutes in air.
[0029] The resultant dried black solid thus obtained is oxidized by treating with concentrated nitric acid at room temperature for a time period of 600 to 1200 minutes. 10
[0030] This is followed by decantation of the acid from the mixture as obtained and washing of the residue with distilled water to obtain the brown mass. Eventually, the resultant brown mass as obtained is heated at temperature range of 70 to 110 degree C for a time period 15 of 60 to 240 minutes in air so as to obtain graphene oxide powder.
[0031] The heating source for the drying of sugarcane bagasse is selected from electro heating oven, hot plate or muffle furnace.
20
[0032] The iron salt/compound used as graphitizing agent may be selected from nitrate, chloride, oxide or a combination thereof.
[0033] The amount of the graphitizing agent with respect to dried sugarcane bagasse is 5 to 15% (w/w). 25
[0034] The concentration of aqueous hydrochloric acid and sodium hydroxide is in the range of 2 to 10% (v/v).
12
[0035] The organic solvent used as purifying agent may be selected from acetone, ethanol, petroleum ether or a combination thereof.
[0036] The method overcomes the problems associated with the use of 5 flake graphite, hazardous chemicals, cost and the large scale production of grapheme oxide that are encountered in the prior arts used for the preparation of graphene oxide till date. All other reagents were of analytical grade and used without further purification. UV-Vis spectra of graphene oxide in water were performed by Double 10 beam UV-Visible spectrometer (EI 2375 spectrophotometer). FT-IR spectra were recorded using Perkin Elmer-Spectrum RX-I FT IR spectrophotometer using KBr disc. Raman spectra were recorded with Witec model Raman spectrometer using Ar+ laser (λe= 532 nm) as an excitation source. X-ray diffraction (XRD) analysis was carried 15 out using a Rigaku X-ray diffractometer with monochromated Cu
K radiation (λ=1.5406Å). The morphologies of the graphene oxide were observed under scanning electron microscope (SEM, Quanta 200 FEG).
20
[0037] Now, reference may be made to the accompanying figures.
[0038] From Figure 1, it is observed that bagasse derived GO shows maximum absorption peak at ~230 nm attributable to λ-λ* transition of C-C and C=C bonds in sp2 hybrid regions and shoulder 25 peak at ~303 nm due to n-λ* transitions of C=O bond in sp3 hybrid regions. In addition, there is no obvious band edge absorption feature
13
found up to 800 nm. The absorption spectrum pattern of graphene oxide suggests the successful graphitization and oxidation of raw carbon obtained from bagasse.
[0039] FT-IR spectroscopy was performed to study the presence of 5 different functional groups. FT-IR spectra of garphene oxide in Figure 2, indicates the presence of the different type of oxygen functionalities in graphene oxide. An intense and broad peak centred at 3392 cm-1 attributes the stretching mode of O-H bond. The O-H groups in graphene oxide bonded to the various sites of carbon 10 skeleton varying from sheets centre to its border, which may causes shifts in frequency of O-H vibration, resultant peak broadening. The presence of intercalated water molecules between grapheme oxide sheets also participate in broadening of O-H band. The strong band at 1724 cm-1 attributes to stretching vibration of C=O in carboxylic 15 acid and carbonyl groups. The peak at 1620 cm-1 was assigned to the vibrations of the adsorbed water molecules and also due to sp2 hybridized carbon atom. The band at 1225 cm-1 usually attributed to the C-OH stretching vibrations and band at 1060 cm-1 assigned to C-O (epoxy) groups. 20
[0040] To verify the structure of graphene oxide as well as to ensure its complete synthesis, Raman sepectroscopy was performed, which showed the present of Sp2 and Sp3 hybridized forms of carbon in the graphene oxide (Figure 3). The Raman spectrum of graphene oxide 25 exhibited two characteristics bands at 1597 and 1354 Cm-1 corresponding to G (graphitic band) and D (defects band) modes, respectively. A shift in the G towards higher wave number is mainly
14
attributed to overlap of the G band with the D band owing to presence of various structural defects created by efficient oxidation by nitric acid that results: the incorporation of the oxygen-containing functional groups, separation of the discrete sp
2 domains and limited number of layers in the graphene oxide. 5
[0041] The XRD pattern of graphene oxide in Figure 4 illustrates a broad diffraction peak at 2θ = 11.5° with a corresponding d spacing of 0.77 nm according to Bragg’s law: 2d sinθ = nλ, where n is an integer determined by the given order, and λ is the wavelength. The value of 10 the d-spacing is consistent with the literature value. The ample oxygen functionalities in the basal plane of graphene oxide along with absorbed water molecules increased the interlayer distance. This XRD pattern suggests that the bagasse derived raw carbon is well graphitized and oxidized two-dimensional structures made of 15 graphene oxide sheets.
[0042] The SEM micrographs of bagasse derived graphene oxide with different scale bars are given in Figure 5, where it can be observed that graphene oxide has layered structure, which affords ultrathin 20 and homogenous graphene films. Such films are folded or continuous at times and it is possible to distinguish the edges of individual sheets, including kinked and wrinkled areas.
Working Example: 25
15
[0043] The following example for synthesis of graphene oxide is given by way of illustration and therefore should not be construed to limit the scope of the present invention in any manner.
[0044] The 2.0 g of dried and ground sugarcane bagasse was mixed with 0.3 g of Ferric oxide (Fe2O3) powder, which was pyrolysed in a 5 muffle furnace at 800 0C for 1.5 h in controlled atmosphere. This resulted in the formation of black solid which was collected at room temperature and then washed with 5 (v/v) % HCI aqueous solution followed by aqueous solution of NaOH 3 (v/v) % and finally with distilled water. The obtained raw carbon was taken in a thimble made 10 of Whatman filter paper. Then, this raw carbonized bagasse was subjected to soxhlet purification. Thereafter, continuous washing of raw carbon powder was carried out by petroleum ether followed by acetone and ethanol. Then, the raw carbonized bagasse was oxidized by treating with concentrated nitric acid (HNO3) for 18 hours. The 15 acid was decanted off and the brown mass was thoroughly washed with distilled water until it was free from acid and became neutral. The brown residue was finally dried at 80oC in vacuum and subjected to further analysis.
20
[0045] The produced grapheme oxide was characterized using UV-Vis absorption spectroscopy, FTIR spectroscopy, Raman spectroscopy, XRD and SEM (Fig. 1-5.)
ADVANTAGES OF THE INVENTION 25
[0046] The current method for the production of graphene oxide powder is associated with several advantageous features. The method
16
uses the sugarcane bagasse as a natural carbon source and avoids the use of flake graphite, hazardous and toxic oxidizing agents such as potassium chlorate, NaNO
3, KMnO4, K2 FeO4, K2 S2 O8 and P2 O5 for the production of graphene oxide. The method is simple and cost effective based on the use of easily accessible, inexpensive 5 sustainable carbon precursor (bagasse), reduced production activities endowed with environmental benignity.
[0047] The preparation of graphene oxide from sugarcane bagasse biomaterial described in this invention can be considered as a 10 reference. The concept of the invention can be extended to other environment-friendly carbon materials to exploit more renewable natural carbon precursor for graphene oxide.
[0048] Although exemplary embodiments of the present invention 15 have been described in detail herein above, it should be clearly understood that many variations and modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.

WE CLAIM:
1. A method for preparation of graphene oxide from sugarcane bagasse comprising steps of heating the mixture of 5 sugarcane bagasse and graphitizing agent in a controlled atmosphere to obtain raw carbon, washing the raw carbon to obtain black solid followed by purification, drying, oxidation and decantation to obtain brown mass, which is subjected to drying to obtain graphene oxide powder. 10
2. A method for preparation of graphene oxide from sugarcane bagasse as claimed in claim 1, wherein the ground sugarcane bagasse is dried by heating at 60-100°C for 60 to 300 minutes in air, which is mixed with the graphitizing 15 agent such as iron salt, in which the amount of the graphitizing agent with respect to dried sugarcane bagasse is 5 to 15% (w/w).
3. A method for preparation of graphene oxide from sugarcane 20 bagasse as claimed in any of the preceding claims wherein the iron salt/compound used as graphitizing agent may be selected from nitrate, chloride, oxide or a combination thereof.
25
18
4. A method for preparation of graphene oxide from sugarcane bagasse as claimed in any of the preceding claims, wherein said heating is carried out at 450-800°C for 30-180 minutes to obtain raw carbon.
5
5. A method for preparation of graphene oxide from sugarcane bagasse as claimed in any of the preceding claims wherein said washing is conducted with aqueous solutions of Hydrocholric acid, Sodium hydroxide and distilled water, in which the concentration of aqueous hydrochloric acid and 10 sodium hydroxide is in the range of 2 to 10% (v/v).
6. A method for preparation of graphene oxide from sugarcane bagasse as claimed in any of the preceding claims wherein the purification of black solid is carried out with the help of 15 soxhlet extractor using organic solvent.
7. A method for preparation of graphene oxide from sugarcane bagasse as claimed in any of the preceding claims wherein the organic solvent used as purifying agent may be selected 20 from acetone, ethanol, petroleum ether or a combination thereof.
8. A method for preparation of graphene oxide from sugarcane bagasse as claimed in any of the preceding claims wherein 25 said drying of black solid is done by heating at 90-100°C for 30-180 minutes in air followed by oxidation by treating with
19
concentrated Nitric acid at room temperature for 600 to
1200 minutes.
9. A method for preparation of graphene oxide from sugarcane
bagasse as claimed in any of the preceding 5 ing claims wherein
said decantation of the acid from the mixture is followed by
washing of the residue with distilled water to obtain the
brown mass.
10 10. A method for preparation of graphene oxide from sugarcane
bagasse as claimed in any of the preceding claims wherein
said drying of brown mass is carried out by heating at 70-
110°C for 60 to 240 minutes in air to obtain graphene oxide
powder.