Green method of synthesis of carbon dots based NANO formulation from garden tea waste and NANO formulation thereof

Abstract

GREEN METHOD OF SYNTHESIS OF CARBON DOTS BASED NANO FORMULATION FROM GARDEN TEA WASTE AND NANO FORMULATION THEREOF A green method of synthesis of carbon dots (CDs) from garden tea waste (GTW) and developing a stable nano emulsion using the synthesized carbon dots is disclosed in the present invention. The carbon dots are synthesized by combining pyrolysis and ultra-sonication from garden tea waste without the use of chemical precursors or reducing agents while simultaneously increasing the recovery and enhancing the biocompatibility and optical properties of carbon dots. The synthesized carbon dots are formulated into a nano emulsion for prolonged stability and enhanced wettability, which in turn is used as a biostimulant for tea plantation to achieve environmental and economical sustainability.

Description

FIELD OF THE INVENTION

[002] The present invention relates to Carbon Dots (CDs / C-Dots), particularly to the green method of synthesis of carbon dots from garden tea waste, more particularly an oil-in-water carbon dots based nano emulsion for prolonged stability and enhanced wettability, which in turn is used as a biostimulant for tea plantation to achieve environmental and economical sustainability.BACKGROUND OF THE INVENTION

[003] Synthesis of carbon dots from bio mass waste has been widely reported (Kang et al., 2020). Gunjal et al., 2018 has reported the conversion of kitchen derived spent tea waste into carbon dots using one step carbonization process named pyrolysis followed by overnight magnetic stirring and syringe filtration. The overnight magnetic stirring used by (Gunjal et al., 2018) to disperse the carbonized tea waste into distilled water is a time consuming (10-12 hours) and low yielding method (16-17%). In the present invention, Garden tea waste is used as bio mass raw material and followed a two-step carbon dots method of synthesis by combining pyrolysis and ultra-sonication leading to the reduction in carbon dots dispersion time and simultaneously enhancing the carbon dots recovery (22-23%).

[004] Carbon Dots are unique nano particles that exhibit excitation by absorption of ultra violet rays and emission at visible light range. When carbon dots are applied to plants, the phenomenon of UV absorption and Visible light emission is known to escalate the electron transportation in the chloroplasts and in turn increases the photosynthetic rate. In many of the prior arts or earlier researches, applications of carbon dots were reported using freshly synthesized carbon dots, whereas none of them discussed about the storage or stability of carbon dots for a prolonged time. In the present invention, the target crop is tea and tea leaves are covered by tea cuticular waxes which are hydrophobic in nature. The water dispersed carbon dots will have very less probability in getting absorbed into the leaf after foliar application. Carbon dots exhibit instability for an extended period of time and have poor wettability in tea leaves.

[005] Hence, it is essential to develop a green method for synthesizing carbon-dots from tea waste and to prepare a suitable formulation that keeps the carbon-dots stable for a prolonged duration (4-5 months) without aggregation to sustain the functionality. The aforementioned limitations of the prior art are therefore eliminated by the present invention. The outcome of the present invention bestows a sustainable solution to the issues of both carbon-dots production and effective C-Dots based oil in water biostimulant formulation for tea plantations.OBJECT OF THE INVENTION

[006] The main object of the invention is to develop carbon dots based nano formulation utilizing the carbon dots synthesized from garden tea waste.

[007] It is another object of the invention to develop carbon dots based nano emulsion with prolonged stability and enhanced wettability and use it as a biostimulant for tea plantations.

[008] It is yet another object of the invention to develop a simple cost-effective less time consuming ecofriendly method of synthesis of carbon dots based nano formulation with enhanced recovery of carbon dots.

[009] Other objects of the inventions will be apparent from the description of the invention herein below.SUMMARY OF THE INVENTION

[0010] The aspects of the present invention can overcome the problems mentioned above and other problems in the prior art by providing an oil-in-water nano emulsion based on garden tea waste derived carbon dots with prolonged stability and enhanced wettability.

[0011] Accordingly in one aspect, the invention provides an oil-in-water nano emulsion comprising oil phase of essential oil, surfactant and aqueous phase of carbon dots derived from garden tea waste dispersed in water in the ratio of 1-2:4-6:20-22.

[0012] In another aspect, the invention provides the method of preparation of oil-in-water nano emulsion based on garden tea waste derived carbon dots comprising the steps of a)collecting garden tea waste, solar drying and pulverizing into fine powder; b) pyrolysis of the fine powder to obtain carbonized powder; c) ultrasonicating the carbonized powder dispersed in double distilled water; d) centrifuging the sonicated solution to collect the supernatant; e) filtering the supernatant to obtain carbon dots; f) emulsifying an oil phase of essential oil and the aqueous phase of water dispersed carbon dots with a surfactant and homogenizing the mixture to obtain coarse emulsion and g) sonicating the coarse emulsion to obtain carbon dots based nano emulsion. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a better understanding of the invention, few embodiments are described below with reference to the accompanying figures, purely by way of example and non-limiting in which:Figure 1 is a flow chart illustrating the green method of synthesis of carbon dots based nano formulation / emulsion in accordance with one or more embodiments of the present invention;Figure 2 is the pictorial representation of the green method of synthesis of carbon dots based nano emulsion in accordance with one or more embodiments of the present invention wherein A - Pulverized Garden tea waste; B - Pyrolysis; C - Carbonized GTW powder; D - Ultra sonication ; E - Sonicated carbonized GTW solution; F - Centrifuging; G - Whatman filtration of supernatant; H - Membrane filtration to obtain carbon dots; I - Organic phase: essential oil; J - Surfactant; K - Aqueous phase :Carbon dots dispersed in water; L 4 - Magnetic stirring; M - Coarse emulsion; N - Ultra sonication and O - Carbon dots nano formulation / emulsion;Figure 3 is the pictorial representation of molecular docked components of the nano formulation / emulsion;Figure 4 is a High-Resolution Transmission Electron Microscopy image which illustrates the particle size of Carbon Dots derived from garden tea waste;Figure 5 is a Transmission Electron Microscopy image which illustrates the particle size of Carbon Dots nano formulation / emulsion;Figure 6 is a Fourier Transmitted Infrared Spectroscopy based spectra to identify the functional groups in Tween 80, Clove oil, C-Dots and C-Dots nano formulation / emulsion;Figure 7 is a UV-Vis and Fluorescence Spectroscopy based absorption and emission spectra for Carbon dots;Figure 8 is a UV-Vis and Fluorescence Spectroscopy based absorption and emission spectra for Carbon dots nano formulation / emulsion;Figure 9 illustrates the X-ray diffraction peaks for Carbon dots to determine its crystallinity;Figure 10 illustrates the X-ray diffraction peaks for Carbon dots nano formulation / emulsion to determine its crystallinity;Figure 11 illustrates the 4 months before and after zeta potential values for carbon dots and carbon dots nano formulation / emulsion, which demonstrates their stability;Figure 12 illustrates the UV-Vis absorption spectra of 4 months stored carbon dots and carbon dots nano formulation / emulsion, which confirms their functionality due to extended stability;Figure 13 illustrates the contact angle of carbon dots droplet placed on a fresh tea leaf surface; andFigure 14 illustrates the contact angle of carbon dots nano formulation / emulsion droplet placed on a fresh tea leaf surface.DESCRIPTION OF THE INVENTION

[0014] For the better understanding of the objects, technology and advantages of the present invention, the instant invention will be further explained in detail with respect to embodiments. It should be understood that the specific embodiments described herein are only to be used for explaining the present invention but not used to limit the present invention.

[0015] Garden tea waste is approximately being generated to the tune of 1.05 kg of dry matter annually per bush. The thermal process like pyrolysis can transform tea wastes into carbonaceous materials that can be used in many ways. The use of inexpensive, renewable, and environmentally friendly biomass not only facilitates large-scale production of CDs but also fosters sustainable applications. Conversion of waste to wealth is need of the hour and transformation of garden tea waste into carbon nano materials especially carbon dots opens up a new area of research.

[0016] The present invention, in an aspect discloses the Carbon dots Nano formulation with prolonged stability and enhanced wettability of carbon dots and utilizing it as a biostimulant in tea plantations.

[0017] In an embodiment, the nano formulation is a nano emulsion.

[0018] In an embodiment, the nano emulsion is an oil-in water emulsion comprising an oil phase, aqueous phase and a surfactant.

[0019] In an embodiment the oil phase comprises 3 - 5% v / v of essential oil selected from clove oil, neem oil, citronella oil or eucalyptus oil.

[0020] In an embodiment, the aqueous phase comprises carbon dots synthesized from garden tea waste dispersed in double distilled water.

[0021] In an embodiment, aqueous phase comprises 0.20-.0.25 % w / v of carbon dots.

[0022] In an embodiment, the surfactant comprises 5-18% v / v selected from tween 80, tween 20, span 80 or span 20.

[0023] In an embodiment, the oil phase, surfactant and aqueous phase are mixed in the ratio of 1-2:4-6:20-22

[0024] In an embodiment, the mean particle size of the nano emulsion is 5-9 nm.

[0025] In an embodiment, the zeta potential of nano emulsion based on garden tea waste derived carbon dots is - 39 to -54 mV showing enhanced stability for a prolonged duration of 4-5 months without aggregation to sustain the functionality.

[0026] In an embodiment, the contact angle of nano emulsion based on garden tea waste derived carbon dots is 20º to 21º exhibiting greater wettability and improved foliar adhesion of the carbon dots of the formulation in tea leaves.

[0027] In an embodiment, the carbon dots are synthesized using eco-friendly techniques such as pyrolytic carbonization and ultrasonication followed by membrane filtration from Garden Tea Waste (GTW).

[0028] The present invention, in another aspect, discloses the method of preparation of oil-in-water nano emulsion based on garden tea waste derived carbon dots comprising the steps of:a) collecting garden tea waste, solar drying and pulverizing into fine powder;b) pyrolysis of the fine powder to obtain carbonized powder;c) ultrasonicating the carbonized powder dispersed in double distilled water;d) centrifuging the sonicated solution to collect the supernatant;e) filtering the supernatant to obtain carbon dots;f) emulsifying an oil phase of essential oil and the aqueous phase of water dispersed carbon dots with a surfactant and homogenizing the mixture to obtain coarse emulsion andg) sonicating the coarse emulsion to obtain oil in water oil-in-water nano emulsion based on garden tea waste derived carbon dots.

[0029] In an embodiment, in step (b) the pyrolysis is done at 250 - 350 °C for 4 -5 hours.

[0030] In an embodiment, in step (c), the ultrasonication is done at 70 - 80% amplitude for 15-25 mins.

[0031] In an embodiment, in step (d), the centrifuging is done at 10000 - 12000 rpm for 20 - 30 mins.

[0032] In an embodiment, in step (e), the particle size of the carbon dots is 4 to 5nm.

[0033] In an embodiment, in step (f), the oil phase comprises 3 - 5% v / v of the total nano emulsion.

[0034] In an embodiment, in step (f), the essential oil is selected from clove oil, neem oil, citronella oil or eucalyptus oil.

[0035] In an embodiment, in step (f), the aqueous phase comprises 0.20-.0.25 % w / v of carbon dots synthesized from garden tea waste of the total nano emulsion.

[0036] In an embodiment, the surfactant comprises 15-18% v / v of the total nano emulsion.

[0037] In an embodiment, the surfactant is selected from tween 80, tween 20, span 80 or span 20.

[0038] In an embodiment, in step (f) the oil phase, surfactant and aqueous phase are mixed in the ratio of 1-2:4-6:20-22

[0039] In an embodiment, in step (f), homogenizing is done at 1000 - 1200 rpm using magnetic stirrer.

[0040] In an embodiment, in step (g), the sonication is done at 20-30% amplitude for 10-15 mins.

[0041] The above description of the invention, together with the below accompanying examples should not be construed as limiting the invention because those skilled in the art to which this invention pertains will be able to devise other forms thereof within the ambit of the appended claims.EXAMPLESExample 1: Method of preparation of carbon dots based nano emulsion of the present inventionStep 1: Synthesis of Carbon dots from Garden Tea Wastes (GTW)

[0042] The collected tea wastes were pulverized using a blender and stored separately in airtight containers. As illustrated in Fig. 1 and 2, five grams of pulverized tea waste was weighed into a silica crucible and placed inside muffle furnace. The biomass was subjected to pyrolysis at 250ºC for 4 hours to collect the carbonized powder. The carbonized tea waste (1 g) was subjected to ultrasonication at a frequency of 20 kHz, with 70% amplitude for 15minutes. The sonicated mixture was centrifuged at 12,000 rpm for 20 minutes to remove micro sized particles. The supernatant was then filtered through Whatman No. 40 filter paper and a 0.22 μm syringe filter to eliminate coarse particles.Step 2: Development of Nano emulsion formulation

[0043] As illustrated in Fig. 1 and 2, the coarse emulsion (100 ml) was initially prepared by adding pristine carbon dots (8 ml) dispersed in aqueous phase to the oil phase containing essential oil 4% v / v (4 ml) and the nonionic surfactant Tween 80 16% v / v (16 ml) in the ratio (1:4:20 of oil:surfactant:aqueous C-Dots). The proportion of the initial oil phase was of great importance for the spontaneous emulsification process and also influences the physico-chemical properties

[0044] Magnetic stirrer was then used to mix the constituents and create the coarse emulsion, providing efficient dispersion and blending of the phases. Finally remaining aqueous phase of Carbon dots (72 ml) was then added to make up the volume. The coarse emulsion obtained after magnetic stirring was subjected to ultra-sonication at 70% amplitude for 10 minutes to obtain clear translucent emulsion. Emulsifying agent (Tween 80) effectively prevents droplet growth and gravitational separation of the formulation.

[0045] The source and geographical origin of the biological materials used in the present invention are as follows.Table 1: Source and Biological origin of the raw materials used in the present inventionExample 2: Molecular Docking to study the excipients interaction of the present invention

[0046] Molecular docking of the nano emulsion was performed using PyRx software. 3D structures were prepared in PDB format for all the excipients (C-Dots, Clove oil and Tween 80) present in the formulation. The binding energy between C-Dots and clove oil was observed as -16 kcal / mol and the binding energy between C-Dots and tween 80 was -25 kcal / mol, which indicates good interaction values. Figure 3 demonstrates the pictorial representation of docked components, where the grey coloured molecule is tween 80 and the yellow coloured molecule is clove oil with the spherical carbon dot being positioned at the centre. These results indicate good affinity among the components that are used to prepare the final nano emulsion.Example 3: Measurement of size (TEM) of the present invention

[0047] In this invention, HRTEM was utilized to examine the size and structural features of carbon dots. The findings demonstrated that the C-Dots are spherical in nature, with an average particle size distribution of 4-5 nm. The inset of Fig. 4 shows HRTEM image of C-Dots with an indistinct / unclear lattice structure, indicating its poor crystalline or amorphous nature

[0048] The morphology and shape of C-Dots nano emulsion was examined using Transmission electron microscope with accelerating voltage of 120 kV. The morphology of C-Dots nano emulsion showed individual and number of aggregated spherical nanomicelles. The results revealed that these micelle clusters are aggregated during sample preparation. The TEM image also exhibited the existence of spherical particles with the average particle size of 5- 9 nm in C-Dots nano emulsion (Fig. 5).Example 4: Characterization study of the present invention by Fourier Transform- Infrared Spectroscopy (FTIR)

[0049] The functional group present in the C-Dots nano emulsion was analysed using FTIR through ATR mode. The obtained spectra for Tween 80 (Fig. 6) revealed peaks at 3483 cm-1 which denotes the O-H stretching vibrations, 2857 cm-1 represents the C-H bonds in the alkyl chains. The peaks at 1734 cm-1 and 1457 cm-1 confirms the presence of C=O stretch of carbonyl group and C-H bending of aliphatic group. The peaks present at 1093 cm-1 and 722 cm-1 attribute to the C-O stretching of the ester functional group and CH2 groups in the alkyl chains.

[0050] The FTIR spectra collected from clove oil (Fig. 6) revealed the presence of O-H stretching of hydroxyl group and C-H stretch of aromatic group in eugenol at 3310 cm-1 and 2874 cm-1 respectively. The peaks at 1604 cm-1 represents the aromatic C=C group. The peaks positioned at 1267 cm-1 and 1206 cm-1 represents C-O stretch of ether groups in eugenol, which is a key compound in clove oil. The peaks at 1012 cm-1 and 737 cm-1 corresponds to the aromatic C-H bending and phenolic O-H bending.

[0051] The spectral results showed that the C-Dots have numerous oxygenated functional groups, namely carboxyl, hydroxyl, epoxy, alkoxy, and carbonyl, on their surfaces. The emerging peak at 1061 cm-1 is attributed to stretching vibration of C-O alkoxyl groups. The intense peak observed at 1635 cm-1 indicates the stretching of aromatic C=C groups, formed through the carbon oxidation. The peak at 2116 cm-1 represents the presence of C=C stretching vibration due to the internal alkynes in carbon dots. A broad band appeared at 3339 cm-1 is mainly due to the presence of O-H groups (Fig. 6). The hydrophilic nature of the surface functional groups enables C-Dots to readily disperse and form stable solutions in aqueous environments

[0052] The FT-IR spectra of nano formulation (containing CDs, oil and surfactants) spectra exhibit a similar spectrum, with the peak intensities in certain regions having the sole difference, indicating the presence of excess functional groups that are due to additional components in nano emulsion, when compared to the pristine C-Dots. The spectra confirmed the presence of characteristic functional groups of C-Dots in the nano emulsion, including epoxy, alkoxy, carbonyl carboxylic acid and hydroxyl groups.

[0053] These functional groups were representing the synergy of compounds that are present in the nano formulation. The O-H group at 3341 cm-1 in the spectra is due to the surface functional groups on C-Dots and aqueous phase in the formulation. A characteristic peak of C-H stretch at 2928 cm-1 confirms the presence of alkyl chains of tween 80 and aromatic group of eugenols (clove oil) in the nano formulation. The peaks present at 2116 cm-1 and 1638 cm-1 confirms the presence of C=C (alkyne) stretch and C-O alkoxyl groups of C-Dots. The peak at 1457 cm-1 can be attributed to C-H bending of tween 80 in the nano emulsion. Presence of C-O stretch ether groups at 1251 cm-1 is due to the presence of eugenol (Clove oil) in the nano formulation. The peak at 1087 cm-1 and 1045 cm-1 is due to the C-O stretching of the ester functional group and C-H bending belonging to tween 80 and clove oil in the nano emulsion (Fig. 6). Overall functional groups present in the final formulation reveals the combined effect of all the excipients that are incorporated during the synthesis of C-dots nano emulsion.Example 5: Measurement of absorbance (UV-VIS) of the carbon dots and carbon dots nano emulsion of the present invention

[0054] Carbon dots (CDs) are known for exhibiting strong absorption bands in the ultraviolet region, typically in the range of 220-270 nm. In the present study, water dispersed, aqueous C-Dots exhibited absorption shoulder peaks at 230 nm and 306 nm (Fig. 7). This absorbance peak is mainly attributed to the p-p* transition of C=C and C=N bonds in C-Dots.

[0055] As illustrated in Fig. 8, the UV-VIS spectrum of C-Dots nano emulsion has a maximum absorbance peak at 218 nm and 258 nm. These absorption shoulder peak at 258 nm confirms the presence of C-Dots in the formulation. The peak centred at 218 nm confirms the presence of tween 80 in the nano emulsionExample 6: Measurement of fluorescence of the carbon dots and carbon dots nano emulsion of the present invention

[0056] Fluorescence spectroscopy was employed for studying the excitation-dependent photoluminescence (PL) properties of carbon dots. The C-Dots dispersion emits a notable PL spectrum at 430 nm upon excitation at 290nm (Fig. 7). C-Dots emitted PL (Wavelength and intensity) in vivid blue light regime under UV excitation. Therefore, as prepared, C-Dots exhibited excitation-dependent PL behaviour.

[0057] The fluorescence spectrum of C-Dots nano emulsion shows an emission wavelength of 420 nm when subjected to excitation wavelength of 290 nm (Fig. 8). The results confirm that the C-Dots nano emulsion have similar photoluminescence properties as pristine C-Dots, indicating that the optical properties of C-Dots were retained and are not affected during the nano emulsion process.Example 7: Measurement of crystallinity of the carbon dots and carbon dots nano emulsion of the present invention

[0058] The X-ray diffraction (XRD) technique was used to analyze the crystalline nature of C-Dots at the atomic level. In the liquid XRD, C-Dots exhibited a broad diffraction pattern without distinct lattice fringes associated with interlayer spacing. C-Dots showed characteristic peaks at 9.8º and 25.7º, representing the (001) and (002) graphitic plane with 0.32 nm d spacing (Fig. 9). Based on the peak positions, C-Dots are found to exhibit graphitic crystallinity with hexagonal or honeycomb lattice arrangements in the core, but based on the peak intensities, the weak and broad XRD peaks represent an amorphous nature in the outer layer of the carbon dots.

[0059] The X-ray diffraction pattern of C-Dots nano emulsion shows characteristic wide peaks at 2θ angles 8.2º and 28.4º due to (001) and (002) graphene planes (Fig. 10) which corresponds to the lattice spacing of 0.31 nm. C-Dots nano emulsion exhibited the similar peaks as that of pristine C-Dots. This confirms that the integrity of lattice arrangements in the C-Dots was not affected during the process of formulation. Example 8: Measurement of Zeta potential stability of the present invention

[0060] The zeta potential of nanoparticles plays a significant role in determining their stability in a specific medium. The prepared C-Dots showed zeta potential of -60 mV, which demonstrated the highest stability (Fig. 11). This approach offers insights on C-Dots electric double layer characteristics

[0061] C-Dots nano emulsion exhibited a zeta potential value of -54 mV, indicating good stability of formulation due to the presence of a stabilizing agent at the desired concentration. And also, Fig. 11 demonstrates that pristine C-Dots (stored for 4 months) has lost their stability and exhibited a zeta value of -0.2 mV, whereas C-dot nano emulsion (stored for 4 months) exhibited a zeta value of -39 mV, which indicates greater stability for longer period. The results suggested that the C-Dots nano emulsion improves stability for prolonged durations without agglomeration of C-Dots. The interfacial activity of the emulsifiers plays a pivotal role in preserving the characteristics and stability of the synthesised carbon dots. Mainly, it reduces the interfacial tension between particles thereby preventing the Ostwald ripening (agglomeration).Example 9: Measurement of UV-Vis absorption spectra for evaluating functionality and stability of the present invention

[0062] The UV-Vis absorption spectra for 4 months stored carbon dots and 4 months stored carbon dots nano emulsion are measured to observe the presence of their inherent UV absorption property. Absorption spectra collected for both the samples revealed that the 4 months stored carbon dots has lost their ability to absorb UV radiation while the 4 months stored carbon dots nano emulsion still retained their property of UV absorption (Fig. 12) with peaks at 204 nm and 278 nm, which proves their prevailing functionality.Example 10: Measurement of Contact angle (wettability) of the present invention

[0063] The contact angle of C-Dots and C-Dots nano emulsion against tea leaves were measured to relate the affinity of the spray liquid towards the tea leaf surface. The contact angle measurements of pristine carbon dots against fresh tea leaf was 85.7º (Fig. 13), whereas C-Dots nano emulsion has recorded a contact angle value of 20.7º (Fig. 14). With the low contact angle measured, the C-Dots nano emulsion exhibited improved wettability and hydrophilicity on tea leaf surface when compared to pristine carbon dots. Contact angle of C-Dots nano emulsion decreases as a result of decreased interfacial tension by surface active agents, which effectively increases surface wettability on the tea leaves, it also improves the active ingredient (C-Dots) diffusion through stomatal openings.

[0064] The droplet radius and droplet height recorded for the pristine carbon dots and C-Dots nano emulsion completely coincides with the contact angle registered over the fresh tea leaf. Droplet radius and height of pristine carbon dots was 820 μm and 761 μm respectively. While the droplet radius and height for C-Dots emulsion was 2227 μm and 405 μm. Pristine carbon dots with lower droplet radius and higher droplet height indicates poor wettability and the chances of spray fluid rolling as droplets over leaf surface was very high, thus reducing the efficiency of foliar applied carbon dots. On the other hand, Carbon dots nano emulsion with higher droplet radius and lesser droplet height demonstrates good wettability over the fresh tea leaves and thereby increasing the chances of intake of C-Dots through leaf surface, which facilitates absorption, translocation and internalization of C-Dots in plants.

[0065] Additionally, this information concludes that the limitation of spraying agrochemicals on tea plantations with waxy cuticular layer on their leaf surface is resolved through this technique by improving the surface wettability of spray liquids. Hence, the adjuvant (surfactant) plays a crucial role in improving the efficiency of agrochemicals (bio stimultant), which works aptly for plantation crops in hilly regions.

[0066] While the invention has been described in connection with an illustrative embodiment, it is not intended to limit the scope of the present disclosure to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the scope of the present disclosure.

Claims

1. An oil-in-water nano emulsion based on garden tea waste derived carbon dots comprising: an oil phase comprising 3 - 5% v / v of essential oil selected from clove oil, neem oil, citronella oil or eucalyptus oil; an aqueous phase comprising 0.20-.0.25 % w / v of carbon dots synthesized from garden tea waste; a surfactant comprising 15-18% v / v selected from tween 80, tween 20, span 80 or span 20. wherein: the oil phase, surfactant and aqueous phase are mixed in the ratio of 1-2:4-6:20-22 and the mean particle size of the nano emulsion is 5-9 nm.

2. The oil-in water nano emulsion as claimed in claim 1, wherein the zeta potential of nano emulsion based on garden tea waste derived carbon dots is - 39 to -54 mV 3. The oil-in water nano emulsion as claimed in claim 1, wherein the contact angle of nano emulsion based on garden tea waste derived carbon dots is 20º to 21º4. A method of preparation of oil-in-water nano emulsion based on garden tea waste derived carbon dots comprising the steps of: a) collecting garden tea waste, solar drying and pulverizing into fine powder; b) pyrolysis of the fine powder at 250 - 350 °C for 4 -5 hours to obtain carbonized powder; c) ultrasonicating the carbonized powder dispersed in double distilled water at 70 - 80% amplitude for 15-25 mins; d) centrifuging the sonicated solution at 10000 - 12000 rpm for 20 - 30 mins to collect the supernatant; e) filtering the supernatant to obtain carbon dots with a particle size of 4 to 5nm; f) emulsifying an oil phase of essential oil and the aqueous phase of water dispersed carbon dots with a surfactant and homogenizing the mixture at 1000 - 1200 rpm using magnetic stirrer to obtain coarse emulsion and g) sonicating the coarse emulsion at 20-30% amplitude for 10-15 mins to obtain oil in water nano emulsion based on garden tea waste derived carbon dots.

5. The method of preparation of oil-in-water nano emulsion as claimed in claim 4, wherein in step (f), the oil phase comprises 3 - 5% v / v of essential oil selected from clove oil, neem oil, citronella oil or eucalyptus oil.

6. The method of preparation of oil-in-water nano emulsion as claimed in claim 4, wherein in step (f), aqueous phase comprises 0.20-.0.25 % w / v of carbon dots synthesized from garden tea waste.

7. The method of preparation of oil-in-water nano emulsion as claimed in claim 4, wherein in step (f), the surfactant comprises 15-18% v / v selected from tween 80, tween 20, span 80 or span 20.

8. The method of preparation of oil-in-water nano emulsion as claimed in claim 4, wherein in step (f), the oil phase, surfactant and aqueous phase are mixed in the ratio of 1-2:4-6:20-22.