Claims:We Claim:
1. An absorbent comprising reduced graphene oxide (rGO) coated substrate.
2. The absorbent as claimed in claim 1, wherein the substrate is selected from a group comprising microfiber composed of polyester and/or polyamide and melamine foam.
3. The absorbent as claimed in claim 1, wherein the absorbent has capacity to absorb component selected from a group comprising oil and organic solvent.
4. The absorbent as claimed in claim 3, wherein the solvent is selected from a group comprising dimethyl formamide and acetone.
5. The absorbent as claimed in claim 3, wherein the absorbent has oil absorbing capacity ranging from about 7 gm/ gm of absorbent to 9 gm/ gm of absorbent.
6. The absorbent as claimed in claim 3, wherein the absorbent has organic solvent absorbing capacity ranging from about 4 gm/ gm of absorbent to 6.5 gm/ gm of absorbent
7. The absorbent as claimed in claim 1, wherein the absorbent is hydrophobic.
8. A method of preparing the absorbent as claimed in claim 1, said method comprises coating of the reduced graphene oxide on the substrate.
9. The method as claimed in claim 8, wherein the coating of the reduced graphene oxide on the substrate selected from a group comprising microfiber composed of polyester and/or polyamide comprises-
- soaking the substrate in graphene oxide dispersion, followed by drying; and
- contacting the dried substrate with vapors of hydroiodic acid to obtain the substrate coated with reduced graphene oxide.
10. The method as claimed in claim 9, wherein the graphene oxide dispersion is prepared by dispersing graphene oxide in water, followed by sonicating for a duration ranging from about 2 hours to 3 hours to obtain the graphene oxide dispersion having concentration ranging from about 1 mg/ml to 2mg/ml.
11. The method as claimed in claim 9, wherein the soaking the substrate in the graphene oxide dispersion is carried out for a duration ranging from about 2 hours to 3 hours.
12. The method as claimed in 9, wherein the drying is carried out for a duration ranging from about 18 hours to 24 hours at a temperature ranging from about 40 ºC to 50 ºC.
13. The method as claimed in claim 9, wherein contacting the dried substrate with vapors of hydroiodic acid comprises- heating the hydroiodic acid solution to a temperature ranging from about 70 ºC to 80 ºC to generate vapors, followed by contacting the vapors with the substrate.
14. The method as claimed in claim 8, wherein the coating of the reduced graphene oxide on the substrate selected from a group comprising melamine porous foam comprises- soaking the substrate with reduced graphene oxide (rGO) dispersion, followed by drying the substrate to obtain reduced graphene oxide coated substrate.
15. The method as claimed in claim 14, wherein the soaking is carried out for a duration ranging from about 1 hour to 2 hours.
16. The method as claimed in claimed 14, wherein the drying is carried out for a duration ranging from about 1 hour to 2 hours at a temperature ranging from about 70 ºC to 80 ºC
17. The method as claimed in 14, wherein the reduced graphene oxide dispersion is at a concentration ranging from about 5 mg/ml to 7mg/ml.
18. A method of separating oil and/or solvent from a mixture, said method comprises:
- contacting the mixture with the absorbent as claimed in claim 1, whereby the absorbent absorbs the oil or the solvent; and
- separating the oil or the solvent from the absorbent.
19. The method as claimed in claim 18, wherein the separation is carried out by technique selected from a group comprising centrifugation, vacuum filtration and mechanical squeezing.
20. The method as claimed in claim 19, wherein the centrifugation is carried out by placing the absorbent comprising the oil or the solvent in a porous container and subjecting the container to a rotation at a speed ranging from about 3000 RPM to 4000 RPM, whereby the oil or the solvent is collected through the porous container.
21. The method as claimed in claim 19, wherein the vacuum filtration is carried out by subjecting the absorbent comprising the oil or the solvent to suction pressure ranging from about 10 PSI to 20 PSI.
22. The method as claimed in claim 18, wherein the mixture is selected from a group comprising oil-water mixture and mixture of water, acetone-water mixture, and DMF-water mixture.

Dated this 01st day of March 2022
Signature:
Name: Sridhar R
To: Of K&S Partners, Bangalore
The Controller of Patents Agent for the Applicant
The Patent Office, at Kolkata IN/PA No. 2598

, Description:TECHNICAL FIELD
The present disclosure relates to field of material sciences. The disclosure particularly relates to an absorbent comprising reduced graphene oxide (rGO) coated substrate for separating oil and solvent from a mixture. The disclosure further relates to method of preparing said absorbent. The disclosure also relates to simple and cost-effective method for separating oil and solvent from a mixture.

BACKGROUND OF THE DISCLOSURE
Crude oil is a vital natural source of energy and chemicals which significantly improve the living quality of humans. Therefore, in order to meet the large demand, production and transport of crude oil from oil reservoirs have become much more frequent. Consequently, it increases the chances of different environmental disasters, such as oil spillage and leakage which have catastrophic effect on the marine and aquatic ecosystems. In 2010, the oil spillage accident at Gulf of Mexico is considered as largest accidental oil spill in history and it was estimated that around 4.9 million barrels of crude oil has been released and to mitigate the damage around 2.1 million gallons of dispersants were used. Thus, oil spillage not only impact the environment, but also significantly affect the economy due to the loss of large amount of oil and massive remediation tasks for the clean-up process. Unlike an organic solvent, crude oil is a mixture of hydrocarbons. Mostly, crude oils are composed of naphthalene or cycloalkane (50%), paraffins or alkanes (30%), different aromatic compounds (15%), polar compounds which contain nitrogen, sulfur, oxygen and trace amount of metals. Beside the oil-spillage accidents, the leakages of different water insoluble organic solvents and industrially used oil also threaten the ecosystem.

Because of the strong cohesive forces between oil and water, oil spill remediation is an expensive task, and the process can be categorized into four parts: (a) in-situ burning of oil, (b) use of dispersants and sorbent materials, (iii) bioremediation process and (iv) mechanical recovery using booms and skimmers where oil is contained by booms and skimmed by pumps. However, each method has its own disadvantages. The recovery process should be cost-effective, efficient and should not harm the environment and marine life. Among these separation processes, sorbent materials are much more attractive because it does not bring any adverse effect to the environment and can separate and recover oil efficiently from the water surface. Absorbent material should have good hydrophobic and oleophilic properties and it should be cost effective. Different microporous materials, such as activated carbon, wool-fiber, zeolites have been used as absorbent materials, but these materials have demonstrated low oil uptake capacity. Further, different microporous polymers have also been studied because of their large surface area and hydrophobicity. However, the manufacture cost of these polymers is very high and environmental and ecological impact of the application of these materials is still not clear.

Thus, there is need for development of improved absorbent material for separating oil and solvent, respectively from mixture. In the present disclosure, an improved absorbent material is described which is scalable and cost effective for separation and recovery of oil from oil-water mixture and separation of solvent from solvent-water mixture.

STATEMENT OF THE DISCLOSURE
The present disclosure describes an absorbent comprising reduced graphene oxide coated substrate, which is simple, cost effective and economically friendly in separating and/or recovering oil and solvent, respectively from a mixture. Moreover, the absorbent is scalable and reusable for separating and/or recovering oil and solvent, respectively.

The disclosure further describes a method of preparing the absorbent, said method comprises coating the reduced graphene oxide on the substrate.

The disclosure further describes a method for separating oil and/or solvent from a mixture, said method comprises- contacting the mixture with the absorbent, whereby the absorbent absorbs the oil or the solvent; and separating the oil or the solvent from the absorbent.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the present disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, where:

Figure 1 depicts schematic representation of the preparation of the absorbent (reduced graphene oxide (rGO) coated microfiber (MF). The figure also depicts the uncoated microfiber and rGO coated microfiber.
Figure 2 depicts schematic representation of the preparation of the absorbent (reduced rGO coated foam).

Figure 3 illustrates Scanning electron microscope (SEM) images of- a) and b) uncoated microfiber; c) and d) reduced graphene oxide (rGO) coated microfiber. Inset of figure 3d) shows magnified image of the fiber. Scale bar of the images under a) to d) are 1 mm and 400 µm respectively.

Figure 4 illustrate Raman spectra plot of uncoated microfiber (MF) and rGO coated microfiber.

Figure 5(a) illustrates Thermogravimetric analysis (TGA) plot of uncoated microfiber and rGO coated microfiber.

Figure 5(b) illustrates differential thermal gravimetry (DTG) plot of uncoated microfiber and rGO coated microfiber.

Figure 6 illustrates Fourier transform infrared spectroscopy (FTIR) plot of uncoated microfiber and rGO coated microfiber.

Figure 7 illustrates separation/recovery of oil from oil-water mixture employing rGO coated microfiber, wherein- a) jute batching oil (JBO) oil-water mixture; b) depicts addition of rGO coated microfiber to the oil-water mixture; c) depicts complete absorption of oil by the rGO coated microfiber; and d) depicts recovery of the oil by squeezing of the rGO coated microfiber.

Figure 8 illustrates position of uncoated microfiber and rGo coated microfiber in oil-water mixture, wherein- a) depicts position of rGO coated microfiber in oil medium in the mixture; and b) depicts position of uncoated microfiber in water medium.

Figure 9 illustrates absorption of oil and not water by the rGO coated microfiber, wherein- a), b) and c) depicts formation of water droplet (stained with CuSO4) on surface of the rGO coated microfiber; and d) and e) depicts no formation of oil droplet on the rGO coated microfiber, implying absorption of the oil by the rGO coated microfiber.

Figure 10(a) illustrates absorption of oils (JBO, mustard oil and soyabean oil) and solvent (acetone and dimethylformamide (DMF)) by the rGO coated microfiber.
Figure 10(b) illustrates a plot depicting recyclability capacity of rGO coated microfiber, tested for jute batching oil (JBO).

Figures 11(a) and 11(b) illustrates scanning electron microscope (SEM) images of uncoated melamine foam.

Figures 11(c) and 11(d) illustrates scanning electron microscope (SEM) images of rGO coated melamine foam.

Figure 11(e) illustrates reduced graphene oxide (rGO) assembled on the melamine foam.

Figures 12 (a) and 12 (b) illustrates hydrophobic behaviour of reduced graphene oxide (rGO) coated melamine foam, wherein the blue droplet (water mixed with blue dye) is not absorbed by the foam.

Figure 13(a) illustrates absorption of oils (JBO, mustard oil and soyabean oil) and solvent (acetone and dimethylformamide (DMF)) by the rGO coated melamine foam.

Figure 13(b) illustrates a plot depicting recyclability capacity of rGO coated melamine foam, tested for jute batching oil (JBO).

Figure 14 depicts schematic representation of separation/recovery of oil from rGO coated microfiber by centrifugation technique.

Figure 15 depicts schematic representation of separation/recovery of oil rGO coated melamine foam by vacuum filtration technique.

Figure 16a) depicts image of oil-water mixture in a beaker.

Figure 16 b) depicts image of oil free water after separation in a funnel from oil-water mixture by rGO coated melamine foam.

Figure 16 c) depicts image of separated oil in a funnel after separation from oil-water mixture by rGO coated melamine foam.

DETAILED DESCRIPTION OF THE DISCLOSURE
Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. By means of further guidance, term definitions are included for better understanding of the present disclosure.

As used herein, the singular forms ‘a’, ‘an’ and ‘the’ include both singular and plural referents unless the context clearly dictates otherwise.

The term ‘comprising’, ‘comprises’ or ‘comprised of’ as used herein are synonymous with ‘including’, ‘includes’, ‘containing’ or ‘contains’ and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

The term ‘about’ as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of ±10% or less, preferably ±5% or less, more preferably ±1% or less and still more preferably ±0.1% or less of and from the specified value, insofar such variations are appropriate to perform the present disclosure. It is to be understood that the value to which the modifier ‘about’ refers is itself also specifically, and preferably disclosed.

Reference throughout this specification to ‘some embodiments’, ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. thus, the appearances of the phrases ‘in some embodiments’, ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The present disclosure relates to simple, cost effective and environmentally friendly absorbent material for separation of oil and/or solvent from the mixtures containing oil and solvent, respectively.

The absorbent described in the present disclosure has improved oil absorption capacity and has improved recyclability efficiency, thus, making them highly suitable for large scale separation of oil from oil-water mixture.

In some embodiments of the present disclosure, the absorbent comprises reduced graphene oxide (rGO) coated substrate.

In some embodiments of the present disclosure, the substrate is selected from a group comprising microfiber composed of polyester and/or polyamide and melamine foam.

In some embodiments of the present disclosure, the absorbent comprises reduced graphene oxide coated microfiber composed of polyester and/or polyamide.

In some embodiments of the present disclosure, the absorbent comprises reduced graphene oxide coated melamine foam.

In some embodiments of the present disclosure, the reduced graphene oxide (rGO) on a substrate can be in an amount ranging from about 20 mg/g to 50 mg/g of the substrate, including all the values in the range, for instance, 20.1mg/g, 20.2 mg/g, 20.3 mg/g, 20.4 mg/g of the substrate and so on and so forth.

In some embodiments of the present disclosure, the reduced graphene oxide (rGO) on a microfiber is in an amount ranging from about 10 mg/g to 20 mg/g of microfiber, including all the values in the range, for instance, 10.1 mg/g, 10.2 mg/g, 10.3 mg/g, 10.4 mg/g and so on and so forth.

In some embodiments of the present disclosure, the reduced graphene oxide (rGO) on a melamine foam is in an amount ranging from about 40 mg/g to 60 mg/g of foam, including all the values in the range, for instance, 40.1 mg/g, 40.2 mg/g, 40.3 mg/g, 40.4 mg/g and so on and so forth.
In some embodiments of the present disclosure, absorbent has capacity to absorb component selected from a group comprising oil and organic solvent.

In some embodiments of the present disclosure, the absorbent has capacity to absorb oil including but not limited to crude oil, jute batching oil (JBO), mustard oil and soyabean oil

In some embodiments of the present disclosure, the absorbent has capacity to absorb oil having viscosity ranging from about 12 cSt to 16 cSt at 37 ºC, including all the values in the range, for instance, 12.1 cSt, 12.2 cSt, 12.3 cSt, 12.4 cSt and so on and so forth.

In some embodiments of the present disclosure, the absorbent has oil absorbing capacity ranging from about 7g/g of absorbent to 150 g/g of absorbent, including all the values in the range, for instance, 7.1g/g, 7.2 g/g, ,7.3 g/g, 7.4 g/g and so on and so forth.

In some embodiments of the present disclosure, the absorbent has capacity to absorb solvent, such as organic solvent including but not limited to dimethyl formamide and acetone.

In some embodiments of the present disclosure, the absorbent has solvent absorbing capacity ranging from about 4 g/g of absorbent to 6.5 g/g of absorbent, including all the values in the range, for instance, 4.1 g/g, 4.2 g/g, 4.3 g/g, 4.4 g/g of absorbent and so on and so forth.

In an embodiment, the Figures 10 and 13 of the present disclosure illustrates oil and solvent absorbing capacity of the absorbent, respectively and recyclability capacity of the absorbent.
The Figure 10a illustrates oil (JBO, mustard oil and soyabean oil) and solvent (acetone and DMF) absorbing capacity of rGO coated microfiber. Further, Figure 10b illustrates recyclability capacity of the rGO coated microfiber for separating oil (for e.g., JBO) from oil-water mixture. The recyclability test indicates that the rGO coated microfiber retains about 70% oil absorbing capacity for at least 25 cycles. The inventors have identified that, after first cycle of oil absorption and squeezing (to recover oil), the oil absorption capacity of the rGO coated microfiber increases due to the squeezing of the coated microfiber. It is noted that, free spaces in the fibers can uptake more oils in the subsequent cycle. Further, no change in the mechanical stability of the rGO coated microfiber is observed from 0th cycle and 30th cycle. Thus, indicating that, the rGO coated microfiber is highly durable for separating oil from oil-water mixture.
Similarly, Figure 13 a illustrates oil (JBO, mustard oil and soyabean oil) and solvent (acetone and DMF) absorbing capacity of rGO coated melamine foam. Further, Figure 13b illustrates recyclability capacity of the rGO coated melamine foam for separating oil (for e.g., JBO) from oil-water mixture. The recyclability test indicates that the rGO coated melamine foam retains about 95% oil absorbing capacity for at least 25cycles. The inventors particularly noted that, high porous nature of the melamine foam contributed to improved oil uptake by the rGO coated melamine foam.

In an embodiment, the Figure 7 of the present disclosure illustrates oil absorption capacity of the rGO coated microfiber from oil-water mixture. The figure 7c describes complete absorption of oil, such as JBO from oil-water mixture and Figure 7d describes recovery of oil upon squeezing of the rGO coated microfiber.

In some embodiments of the present disclosure, the absorbent is hydrophobic in nature.

In an embodiment, the Figures 8, 9 and 12 of the present disclosure, illustrates the hydrophobic nature of the absorbent. The Figure 9 (a to c) illustrates formation of water droplet (stained with CuSO4) on the rGO coated microfiber surface and Figure 9 (d to e) describes no formation of droplet on the rGO coated microfiber when oil is added. Similarly, Figure 12 describes formation of water droplet (stained with blue dye) on rGO coated melamine foam.
The Figure 8 exemplifies the position of uncoated microfiber and rGO coated microfiber in oil-water mixture. Figure 8a shows that the rGO coated microfiber is in the oil medium (absorbing oil) due to hydrophobic nature. However, in Figure 8b, the uncoated microfiber can be found in water medium, indicating hydrophilic nature of the uncoated microfiber.

The present disclosure further relates to method of preparing the absorbent described above.

In some embodiments of the present disclosure, the method of preparing the absorbent comprises coating the reduced graphene oxide on the substrate.

In some embodiments of the present disclosure, in the method, coating of the reduced graphene oxide on the substrate, such as microfiber composed of polyester and/or polyamide comprises-
soaking the microfiber in graphene oxide dispersion, followed by drying; and
contacting the dried microfiber with vapours of hydroiodic acid (HI) to obtain the reduced graphene oxide coated microfiber.

In some embodiments of the present disclosure, the graphene oxide dispersion is prepared by dispersing graphene oxide in a solvent including but it is not limited to water, followed by sonicating to obtain homogenise dispersion, for a duration ranging from about 2 hours to 3 hours to obtain the graphene dispersion having concentration ranging from about 1 mg/ml to 2 mg/ml, including all the values range, for instance, 1.1 mg/ml, 1.2 mg/ml, 1.3 mg/ml, 1.4 mg/ml and so on and so forth.

In some embodiments of the present disclosure, the soaking of the microfiber in the graphene dispersion is carried out for a duration ranging from about 2 hours to 3 hours, including all the values in the range, for instance, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours and so on and so forth.

In some embodiments of the present disclosure, the drying is carried out for a duration ranging from about 18 hours to 24 hours, including all the values in the range, for instance, 18.1 hours, 18.2 hours, 18.3 hours, 18.4 hours and so on and so forth, at a temperature ranging from about 40 ºC to 50 ºC, including all the values in the range, for instance, 40.1 ºC, 40.2 ºC, 40.3 ºC, 40.4 ºC and so on and so forth.

In some embodiments of the present disclosure, in the method, contacting the dried substrate with vapours of hydroiodic acid comprises- heating the hydroiodic acid solution to a temperature ranging from about 70 ºC to 80 ºC, including all the values in the range, for instance, 70.1 ºC, 70.2 ºC, 70.3 ºC, 70.4 and so on and so forth, to generate vapours, followed by contacting the vapours with the microfiber.

In an embodiment, Figure 1 of the present disclosure provides a schematic representation of coating reduced graphene oxide on the substrate, such as microfiber composed of polyester and/or polyamide.

In some embodiments of the present disclosure, in the method, coating of the reduced graphene oxide on the substrate, such as melamine foam comprises- soaking the melamine foam with reduced graphene oxide dispersion, followed by drying the substrate to obtain reduced graphene oxide coated melamine foam.
In some embodiments of the present disclosure, soaking the melamine foam with reduced graphene oxide dispersion is carried out for a duration ranging from about 1 hour to 2 hours, including all the values in the range, for instance, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours and so on and so forth.

In some embodiments of the present disclosure, drying the melamine foam is carried out for a duration ranging from about 1 hour to 2 hours, including all the values in the range, for instance, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours and so on and so forth, at a temperature ranging from about 70 ºC to 80 ºC, including all the values in the range, for instance, 70.1 ºC, 70.2 ºC, 70.3 ºC, 70.4 ºC and so on and so forth.

In some embodiments of the present disclosure, the melamine foam is soaked with reduced graphene oxide (rGO) dispersion having concentration ranging from about 5 mg/ml to 7 mg/ml, including all the values in the range, for instance, 5.1 mg/ml, 5.2 mg/ml, 5.3 mg/ml, 5.4 mg/ml and so on and so forth.

In an embodiment, Figure 2 of the present disclosure provides a schematic representation of coating reduced graphene oxide on the substrate, such as melamine foam.

The present disclosure further describes a method for separating or recovering oil and/or solvent from a mixture employing the absorbent described above.

In some embodiments of the present disclosure, the method of separating oil and/or solvent from a mixture comprises-
contacting the mixture with the absorbent, whereby the absorbent absorbs the oil or the solvent; and
separating the oil or the solvent from the absorbent.

In some embodiments of the present disclosure, the separation or recovery of the oil or the solvent from the absorbent is carried out by technique selected from a group comprising centrifugation, vacuum filtration and mechanical squeezing.

In some embodiments of the present disclosure, the separation or recovery of the oil or the solvent from the absorbent is carried out by centrifugation by placing the absorbent comprising the oil or the solvent in a porous container and subjecting the container to a rotation at a speed ranging from about 3000 RPM to 4000 RPM, including all the values in the range, for instance, 3001 RPM, 3002 RPM, 3003 RPM, 3004 RPM and so on and so forth, as a result, the oil or the solvent is collected through the porous container in a collection container.

In an embodiment, the Figure 14 of the present disclosure describes schematic representation of separation of oil from the absorbent, such as rGO coated microfiber employing centrifugation technique.

In some embodiments of the present disclosure, the separation or recovery of the oil or the solvent from the absorbent is carried out by vacuum filtration by placing the absorbent comprising the oil or the solvent to suction pressure ranging from about 10 PSI to 20 PSI, including all the values in the range, for instance, 10.1 PSI, 10.2 PSI, 10.3 PSI, 10.4 PSI and so on and so forth.

In an embodiment, the Figure 15 of the present disclosure describes schematic representation of separation of oil from the absorbent, such as rGO coated melamine foam employing vacuum filtration technique.

In an embodiment, the Figure 16 of the present disclosure describes the clear oil separation from oil-water mixture upon employing absorbent, such as rGO coated melamine foam as the vacuum filtration technique illustrated in Figure 15.

The absorbent and the methods described in the present disclosure provides for following advantages:
The absorbent is cost effective and reusable after many cycles (at least 30 cycles) for separation of oil or solvent from a mixture.
The absorbent is capable of absorbing all types of oils irrespective of their viscosity.
The method of preparing the absorbent is most-simple method and cost effective.
The method of preparing the absorbent is environmentally friendly as it does not employ any toxic and/or harsh chemicals.

It is to be understood that the foregoing description is illustrative not a limitation. While considerable emphasis has been placed herein on particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure, certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments may be practiced and to further enable those of skill in the art to practice the embodiments. Accordingly, following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES

Materials and Method:
Materials
Hydroiodic acid (57%) and hydrazine hydrate were purchased from Merck. Graphene oxide (GO) powder was received from SRL, India. Microfiber cloth with 222 GSM was obtained from Amazon. Melamine foam was purchased from local market . Jute batching oil (JBO) was bought from market. Organic solvents such as acetone and DMF were received from Merck. Mustard oil and soyabean oil were obtained from Saffola.

Characterization
For SEM (Scanning Electron Microscope) measurements, a layer of gold was sputtered on top and the sample (rGO coated substrate and uncoated substrate) was examined on ZEISS EVO 60 Scanning Electron Microscope (with oxford EDS detector) operating at 10 kV. Raman microscopy was performed with a Renishaw Raman microscope using 532 nm laser excitation at room temperature. Simultaneous thermogravimetry-differential scanning calorimetry instrument, STA 449 F3 Jupiter, from Netzch was used to determine the TGA profile of the coated and uncoated substrate. The samples were dried to a constant weight in a vacuum at 25°C, and then the thermogravimetric diagrams of the samples were measured using a heating rate of 10 K min-1 upto 600 ºC. The presence of different functional groups present in the cloth were analysed by FTIR measurement (Paragon-1000, Perkin-Elmer, USA).

Oil uptake capacity determination
The weight of dry coated substrate was measured (m_0) and the substrate was then dipped into oil/organic solvents until completely soaked. The excess oil was removed by dripping until the drops stopped falling. The substrate was weighed again (m_c). Thus, oil uptake capacity (q) can be determined by the following equation,
q= (m_c-m_0)/m_0 (1)
For the reusability experiment, the coated substrate was soaked in oil, dripped and weighed again. The experiment was repeated for 30 times.

Example 1: Preparation of rGO coated microfiber
Preparation of graphene oxide dispersion
About 10 mg of graphene oxide was dissolved in about 20 ml of water and the dispersion was bath-sonicated for about 2 hours to obtain 2 mg/ml of graphene oxide dispersion.

Coating of the rGO on microfiber
Microfiber was cut into 10.0 x 10.0 cm2 pieces and soaked into about 2 mg/ml graphene oxide dispersion for about 2 hours. The excess graphene oxide solution from microfiber was removed by dripping and microfiber was dried for about 24 hours in oven at about 40 ºC. For reduction of graphene oxide, hydroiodic acid (HI) vapour was used. graphene oxide coated microfiber was placed above HI solution which was obtained in a glass beaker and the solution was heated to about 70 ºC. Graphene oxide quickly turned black within 2 to 3 minutes after exposure to HI vapour which indicates the reduction of graphene oxide to reduced graphene oxide. Once the reaction was completed, the coated microfiber and beaker was left in a fume hood to eliminate the HI vapour. Figure 1 provides a schematic representation of coating of rGO on microfiber.

The method described herein for preparing the rGO coated microfiber employs no harsh condition. This method is completely suitable for mass production of rGO coated microfibers.

Example 2: Preparation of rGO coated melamine foam
About 50 mg of reduced graphene oxide (rGO) was dispersed in about 10 ml of ethanol to obtain concentration of about 5 mg/ml. Foam with the size of about 4 x 4 cm2 was dip coated into the rGO dispersion for about 1 hour. After about 2 hours, foam was found to be completely soaked with rGO dispersion and the foam was dried in oven for about 1 hour at about 70 ºC for complete removal of ethanol.
Figure 2 provides a schematic representation of coating of rGO on melamine foam.

Example 3: Characterization of rGO coated microfiber
Microscopic characterization:
The microscopic properties of uncoated microfiber and rGO coated microfiber were determined by SEM measurements. The densely fiber network is observed in the rGO coated microfiber (illustrated in figure 3). It was noted that coating the microfiber with GO and treatment with HI did not influence the fibrous properties of the microfiber. However, changes have been detected in the wall surface of the microfibers after treating with rGO (see figures 3c and 3d). The surface coating with rGO was observed in the SEM images at the higher magnification which is shown in the inset of Figure 3d.

Raman measurement:
Figure 4 illustrates microscopic characterization of rGO coated microfiber by Raman measurement. The polyester peaks of the uncoated microfiber were observed at 1610 cm-1 and 1723 cm-1. In case of rGO coated microfiber, beside the polyester peaks, two distinct peaks were also observed at 1374 cm-1 and 1590 cm-1 which is attributed to the D and G band of rGO, respectively. The G band of rGO at 1590 cm-1 and the polyester peak at 1610 cm-1 are overlapped together to form a broad peak and the deconvoluted peaks are shown in the inset of Figure 4.

TGA and FTIR measurement:
Thermal gravimetry analysis (TGA) was performed to understand the thermal stability of the rGO coated microfiber. TGA curves of uncoated microfiber and rGO coated microfiber are shown in Figures 5a and 5b. The TGA curves of both the samples are similar and rapid weight loss have been observed for both the samples in the temperature range between 300 ºC to 400 ºC. DGT (differential thermal gravimetry) plot of both the samples (uncoated microfiber and rGO coated microfiber) are demonstrated in Figure 5b. The peak temperature (TP) in the DTG plot represent the temperature at which maximum weight loss is occurred. For uncoated microfibre, the peak temperature is 432 ºC. However, for rGO coated microfiber, two peak temperatures have been observed at 374 ºC and 432 ºC, respectively. The later peak temperature indicates that the coating of rGO on the microfiber does not affect the decomposition behaviour of the cloth. TP at 374 ºC is possibly due to the loose binding of the rGO on the surface of the microfiber at this temperature. From the DTG plot, it can also be noted that the rGO coated microfiber is stable up to 285 ºC.
Presence of different functional groups was confirmed by the FT-IR measurements. The FT-IR spectra of both uncoated microfiber and rGO coated microfiber are shown in Figure 6.

Hydrophobicity of rGO coated microfiber
It was noted that after immersing (under force) the rGO coated microfiber in water of the oil-water mixture, the rGO coated microfiber rose back to the oil phase (illustrated in Figure 8). It was noted that rGO coated microfiber was very stable in water environment demonstrating strong adhesion between rGO and microfiber. Further, it was noted that, after putting the rGO coated microfiber into water medium for about 24 hours no significant contribution was observed in UV-V measurement, and it confirms that rGO is strongly adhered on the surface of the microfiber. However, it was noted that uncoated microfiber rapidly absorbed water and lost their buoyancy. Moreover, it was noted that water was put on the surface of the rGO coated microfiber and it formed droplet (see figures 9a to 9d). However, when oil was put on the rGO coated microfiber, it was immediately absorbed (see figures 9d to 9e).

Example 4: Characterization of rGO coated melamine foam
Figure 11 illustrates the SEM images of the rGO coated melamine foam indicating the porous behaviour of the foam. It was noted that porous nature of the melamine foam was not altered upon coating with the rGO. Flakes of rGO sheets were observed in the SEM images which confirms the successful deposition of rGO on the melamine surface.
Hydrophobic behaviour of the rGO coated melamine foam is illustrated in Figure 12. It was noted that the rGO coated melamine does not absorb water, as a result water droplet (stained with blue dye) was observed on the rGO coated melamine foam.

Example 5: Separation/recovery of oil from oil-water mixture
rGO coated microfiber was put into the oil-water mixture. It was noted that oil absorption by the microfiber was very quick. The oil absorbed microfiber was subjected to separation of oil by centrifugation technique employing bucket type centrifuge (illustrated in Figure 14). The oil absorbed microfiber was put into an inner perforated bucket which was connected with DC motor. Because of the centrifugal force, the oil from the microfiber was collected in the outer bucket. The rGO coated microfiber was subjected for reuse for absorbing oil from oil-water mixture.

rGO coated melamine foam was put into the oil-water mixture. It was noted that oil absorption by the melamine foam was very quick. The oil absorbed melamine foam was subjected to separation of oil by vacuum filtration (illustrated in Figure 15). The oil-water mixture was passed through rGO coated melamine foam, the water passes through the coated melamine foam and the oil is absorbed by the foam. The foam containing the oil is recovered from the foam using vacuum pump by applying pressure of about 10 to 20 PSI, whereby the oil is collected (illustrated in Figure 15b).

The foregoing description of the specific embodiments reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments in this disclosure have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Throughout this specification, the term ‘combinations thereof’ or ‘any combination thereof’ or ‘any combinations thereof’ are used interchangeably and are intended to have the same meaning, as regularly known in the field of patents disclosures.

Any discussion of documents, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.