A method for synthesis of NANO urea and its composites thereof

Abstract

The present invention relates to method of synthesizing nano urea and nano urea- composites thereof. More particularly, the present invention provides nano urea as well as a composite of nano urea and sodium ascorbate with cellulose and carbon black with varying equivalents through a simple, reliable, fast and cost-effective manner. The nano urea is synthesized with a reducing agent and a biodegradable and biocompatible coating material through milder reaction conditions having mechanical properties.

Description

[0001] A METHOD FOR SYNTHESIS OF NANO UREA AND ITS COMPOSITES THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of fertilizers. More particularly, the present invention relates to a cost-effective, reliable, simple and fast method of synthesis of nano urea and its composite, i.e., sodium ascorbate with cellulose and carbon black-nano urea composite.

[0004] BACKGROUND OF THE INVENTION

[0005] Urea is widely known as a nitrogen-rich fertilizer that has been a cornerstone in agricultural practices. Urea, a white crystalline compound, is a concentrated source of nitrogen and provides an essential nutrient for plant growth. This nutrient is crucial for the formation of proteins, enzymes and chlorophyll in plants, promoting robust growth and increased crop yields. However, the effectiveness of urea is hindered by inefficiencies in nutrient utilization contributing to environment concerns and suboptimal crop yields.

[0006] Urea is a highly water soluble solid that is neither basic nor acidic, because of the rich source of nitrogen. Urea metabolizes the nitrogen compounds in animals and is the primary source of nitrogen in mammal urine. Urea is generally applied to the farms at an interval to minimize leaching losses due to volatilization. Presently, about 20-30% of fertilizers reach the soil and then to the plant roots and get fixed at the end. This causes the rest of the fertilizers to be washed away resulting in eutrophication. This problem is mitigated by a better control on the dissolution and release of urea into the soil by the urea miniaturization and / or encapsulation.

[0007] Conventionally, urea fertilization often suffers from issues such as leaching and volatilization leading to the loss of essential nutrients before plants fully absorb them. In addition, rapid hydrolysis of urea leads to uneven nutrient distribution and losses if not managed properly. Other factors that affect urea fertilization are environmental impacts, acidification and nutrient imbalance. IN202121058946A discloses nanostructure composite fertilizers manufacturing process and formulations of the same, where manufacturing nanostructure composite fertilizers by a solution of urea contains 4.22-4.6% nitrogen prepared in water to which the 0.08- 0.15% w / w is a water-soluble cellulosic material, i.e., sodium carboxymethyl cellulose. Nanostructure composite fertilizers are formed as a powder with the use of lyophilization process at -60°C to -78°C. However, in the process of manufacturing nanostructure composite fertilizers, great amount of nutrients are lost.

[0008] IN202122043098A discloses a method of manufacturing nano urea using urea for slow release, enhanced utilization by the plants and application thereof, where forming of urea or ammonia solution from nitrogenous aerosol and carbohydrate polymer made of glucose units hydrolyses to form nano-fiber of oligosaccharide, forming the length of nano oligosaccharide formation depending on the temperature and the rate of hydrolysis. However, the method of manufacturing nano urea utilizes harsh temperature and pressure conditions.

[0009] Tiwary, S. in International Journal of Research and Review Vol. 10; Issue: 3; March 2023 discusses about nano urea as a small solution with a big impact on sustainable agriculture, where nano urea is made by first dissolving urea in water to create a solution. This solution is then subjected to a high-pressure homogenization process that breaks the urea particles down into nanoparticles. The resulting nano urea particles have a high surface area to volume ratio allowing efficient absorption by plants. However, the production costs of nano urea are comparatively higher than traditional urea due to the use of specialized equipments and materials.

[0010] Chaitaly T. et al. in ACS Omega 2020, 5, 23960-23966 discloses a new formulation of a hybrid nanofertilizer (HNF) for slow and sustainable release of nutrients into soil and water. Urea-modified hydroxyapatite was synthesized, that is a rich source of nitrogen, calcium and phosphate. Nanoparticles such as copper, iron and zinc were incorporated into urea-modified hydroxyapatite to increase the efficiency of the fertilizer. Nevertheless, the released nutrients remained constant and were delivered at a slow rate.

[0011] However, the previous methods for the synthesis of nano urea mentioned above, possess some limitations such as significant loss of nutrients, harsh reaction conditions for the synthesis of nano urea, slow delivery of nutrients and competitively higher costs than traditional urea due to the utilization of specialized equipment and materials.

[0012] Therefore, there is a need for an improved method for synthesizing nano urea and its composites thereof to overcome the above-mentioned shortcomings of the cited prior methodologies.

[0013] OBJECT OF THE INVENTION

[0014] The main object of the present invention is to provide a cost-effective, fast and simple method for synthesizing nano urea.

[0015] Another object of the present invention is to provide a method for synthesizing nano urea with a reducing agent and a biocompatible and biodegradable coating material.

[0016] Yet another object of the present invention is to provide a method for synthesizing nano urea through milder temperature and pressure conditions.

[0017] Yet another object of the present invention is to provide a method for synthesizing composites of nano urea.

[0018] Yet another object of the present invention is to provide nano urea that is in the shape of nano-fringes with good crystallinity.

[0019] Still another object of the present invention is to provide nano urea with a value addition to carbon dioxide.

[0020] SUMMARY OF THE INVENTION

[0021] The present invention relates to a method of synthesizing nano urea and its composites thereof under mild temperature and pressure conditions and in a simple, reliable and cost- effective manner.

[0022] In an embodiment, the present invention provides a method of synthesis of nano urea and a nano urea-composite comprising the steps of: (i) reacting 236-250 kg of ammonia (NH3) with 152-167 kg of carbon dioxide in a molar ratio at a predefined temperature and a predefined pressure in an autoclave for 20-30 minutes to form ammonium carbamate (NH4COONH2); (ii) dehydrating NH4COONH2formed in step (i) by heating to obtain urea and water; (iii) mixing 208-224 kg of urea obtained in step (ii) with 458-512 kg of an inhibitor in a nanourea-reactor under an optimum condition with constant stirring at 800- 1000 rpm to form an ash colored nano urea; and (iv) reacting the ash colored nano urea obtained in step (iii) with a reducing agent to obtain neat nano urea; and (v) reacting the ash colored nano urea obtained in step (iii) with the reducing agent and a biopolymer to obtain a nano urea composite.

[0023] The present invention provides a nano urea composite possessing mechanical properties that is employed as a fertilizer owing to the rich content of nitrogen in the composite-based fertilizer. Moreover, the present invention provides a simple, fast and cost-effective method of synthesizing nano urea having mechanical properties and its composites thereof.

[0024] The above objects and advantages of the present invention will become apparent from the hereinafter set forth brief description of the drawings, detailed description of the invention, and claims appended herewith.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] An understanding of the method of synthesizing nano urea and composites thereof of the present invention may be obtained by reference to the following drawings:

[0027] Figure 1 is a graphical representation for p-XRD plots of varied amount of CD-IITG capping agent 1 (sodium ascorbate with carbon black) taken as a reducing agent for the synthesis of neat nano urea, according to an embodiment of the present invention.

[0028] Figure 2 is a graphical representation for p-XRD plots of varied amounts of CD-IITG capping agent 2 (trisodium citrate with carbon black) taken as a reducing agent for the synthesis of neat nano urea, according to the present invention.

[0029] Figure 3 is a graphical representation for p-XRD plots of varied amounts for the synthesis of sodium ascorbate with cellulose and carbon black-nano urea composite, according to the present invention. Figure 4 is a graphical representation for p-XRD plots of ash coloured nano urea having nano urea with 0.25 equivalents of trisodium citrate with carbon black (NU-TSC0.25_Bulk) prepared on 200 g scale, according to the present invention.

[0030] Figure 5 is pictorial representation of FESEM of nano urea with 0.5 equivalents of sodium ascorbate with carbon black (NU_SA0.5), according to the present invention.

[0031] Figure 6 is a pictorial representation of FESEM of varied amounts of trisodium citrate with carbon black as a reducing agent for the synthesis of ash coloured nano urea illustrating samples: nano urea with 1.0 equivalents of trisodium citrate with carbon black (NU_TSCi.o) in part (a); nano urea with 0.5 equivalents of trisodium citrate with carbon black (NU_TSCO.5) in part (b); nano urea with 0.25 equivalents of trisodium citrate with carbon black (NU_TSC0.25) in part (c); and nano urea with 0.125 equivalents of trisodium citrate with carbon black (NU_TSC0.I25) in part (d); according to the present invention.

[0032] Figure 7 is a pictorial representation of FESEM of varied amounts of sodium ascorbate with cellulose and carbon black for the synthesis of nano urea composites illustrating image for nano urea with 0.5 equivalents of sodium ascorbate with cellulose and carbon black (NU_SA0 5_Co.5) in part (a); and image for nano urea with 1.2 equivalents of sodium ascorbate with cellulose and carbon black (NU_SA0 5_Ci.2) in part (b), according to the present invention.

[0033] Figure 8 is a pictorial representation of FESEM of bulk ash coloured nano urea illustrating: an image for NU-TSC0.25_Bulkl in powdered form in part (a); and image for NU-TSCo.25_Bulkl dispersed in water followed by drop-casted on a glass slide in part (b), according to the present invention.

[0034] Figure 9 is a graphical representation of Fourier transform infrared (FTIR) spectroscopy of varied amounts of CD-IITG capping agent 1 (sodium ascorbate and carbon black) as reducing agent for the synthesis of neat nano-urea, according to the present invention.

[0035] Figure 10 is a graphical representation of FTIR of varied amounts of CD-IITG capping agent 2 (trisodium citrate and carbon black) as reducing agent for the synthesis of ash colored nano urea, according to the present invention. Figure 11 is a graphical representation of FTIR of varied amounts of sodium ascorbate with cellulose and carbon black as a capping agent with 0.5 equivalent of sodium ascorbate and carbon black as reducing agent for the synthesis of the sodium ascorbate with cellulose and carbon black-nano urea composite, according to the present invention.

[0036] Figure 12 is a graphical representation of EDX of NU_SA0 5, according to the present invention.

[0037] Figure 13 is a graphical representation of EDX of varied amounts of tris odium citrate with carbon black as reducing agent for the synthesis of neat nano urea, according to the present invention.

[0038] Figure 14 is a graphical representation of EDX of NU_SA0 5_C0.5, according to the present invention.

[0039] Figure 15 is a graphical representation of EDX of NU-TSC0.25_Bulkl dispersed in water followed by dropcasted on a glass slide, according to the present invention.

[0040] Figure 16 is a graphical representation of zeta potential of NU_SA0.5taken in water as solvent, according to the present invention.

[0041] Figure 17 is a graphical representation of zeta potential of NU_SA025taken in water as solvent, according to the present invention.

[0042] Figure 18 is a graphical representation of zeta potential of NU_SA0.I25taken in water as solvent, according to the present invention.

[0043] Figure 19 is a graphical representation of zeta potential of NU_TSCi.otaken in water as solvent, according to the present invention.

[0044] Figure 20 is a graphical representation of zeta potential of NU_TSC0.5taken in water as solvent, according to the present invention.

[0045] Figure 21 is a graphical representation of zeta potential of NU_TSC0.25taken in water as solvent, according to the present invention.

[0046] Figure 22 is a graphical representation of zeta potential of NU_TSC0.I25taken in water as solvent, according to the present invention. Figure 23 is a graphical representation of zeta potential of NU_SA0.5C0.5taken in water as solvent, according to the present invention.

[0047] Figure 24 is a graphical representation of zeta potential of NU_SA0.5Ci.2taken in water as solvent, according to the present invention.

[0048] Figure 25 is a graphical representation of zeta potential of NU_TSC0.25Bulk 1 taken in water as solvent, according to the present invention.

[0049] DETAILED DESCRIPTION OF THE INVENTION

[0050] The present invention will now be described hereinafter with reference to the accompanying drawings in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough, and will fully convey the scope of the invention to those skilled in the art.

[0051] The present invention now will be described hereinafter with reference to the detailed description, in which some, but not all embodiments of the invention are indicated. Indeed, the invention may be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. The present invention is described fully herein with nonlimiting embodiments and exemplary experimentation.

[0052] The present invention provides a cost-effective, simple and fast method of synthesizing nano urea through milder conditions wherein said nano urea possesses mechanical properties and a nano-fringe like shape, and its composites thereof.

[0053] In a preferred embodiment, the present invention provides a method of synthesis of nano urea and a nano urea-composite comprising the steps of: (i) reacting 236-250 kg of ammonia (NH3) with 152-167 kg of carbon dioxide in a molar ratio at a predefined temperature and a predefined pressure in an autoclave for 20-30 minutes to form ammonium carbamate (NH4COONH2); (ii) dehydrating NH4COONH2formed in step (i) by heating to obtain urea and water; (iii) mixing 208-224 kg of urea obtained in step (ii) with 458-512 kg of an inhibitor in a nanourea-reactor under an optimum condition with constant stirring at 800-1000 rpm to form ash colored nano urea; and (iv) reacting the ash colored nano urea obtained in step (iii) with a reducing agent to obtain neat nano urea; and (v) reacting the ash colored nano urea obtained in step (iii) with the reducing agent and a biopolymer to obtain a nano urea composite.

[0054] Here, said molar ratio of ammonia and carbon dioxide in step (i) is in a range of 3: 1 to 4: 1 ; said predefined temperature and said predefined pressure in step (i) is 180-200°C and 100- 250 bar; said inhibitor in step (iii) is trisodium citrate with carbon black and said optimum condition includes a temperature range of 80-90°C and a time-period of 6-12 hours; said reducing agent in steps (iv-v) is sodium ascorbate with carbon black and said biopolymer in step (v) is sodium ascorbate with cellulose and carbon black; and said nano urea composite obtained in step (v) is selected from 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite or 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite.

[0055] Further, said method yields 8.216-8.3 g of neat nano urea and 6.297-12.77 g of said nano urea composite. Additionally, neat nano urea is formed in the form of nanoparticles of size ranging from 100 to 200 nm and exhibits zeta potential in a range of 2.27 to 9.34 mV. Moreover, said nano urea composite exhibits size ranging from 20 to 30 nm and zeta potential in a range of -7.04 to 7.01 mV.

[0056] In another preferred embodiment, the present invention provides a method of preparation of neat nano urea comprising the steps of: (a) taking 6.006-6.01 g of the ash colored nano urea and 9.5-10.0 g of sodium ascorbate with carbon black in 50-55 mL of ethanol and heating at a temperature of 70-80°C for 6-6.5 hours under continuous stirring to obtain a reaction mixture; and (b) washing the reaction mixture obtained in step (a) twice in 10 mL of ethanol at 12000 rpm for 10 minutes followed by vacuum drying at 60°C overnight to obtain a yellowish powder of neat nano urea.

[0057] In yet another preferred embodiment, the present invention provides a method of preparation of 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite comprising the steps of: (a) mixing 3.003 g of the ash colored nano urea and 4.053 g of sodium ascorbate with cellulose and carbon black in 50 mL of ethanol under continuous stirring to obtain a homogenous mixture; (b) adding slowly 4.75 g of sodium ascorbate with carbon black in the homogenous mixture obtained in step (a) and heating at 70°C for 6 hours to obtain an orange colored solution; (c) washing the orange colored solution obtained in step (b) thrice with 10 mL of ethanol at 12000 rpm for 10 minutes to obtain a residue; and (d) subjecting the residue obtained in step (c) to vacuum drying at 60°C overnight followed by grounding with a mortar and pestle to obtain a yellowish powder of 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite.

[0058] In still another preferred embodiment, the present invention provides a method of preparation of 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite comprising the steps of: (a) mixing 3.003 g of the ash colored nano urea and 10 g of sodium ascorbate with cellulose and carbon black in 80 mL of ethanol under continuous stirring to obtain a homogenous mixture; (b) adding slowly 4.75 g of sodium ascorbate with carbon black in the homogenous mixture obtained in step (a) and heating at 70°C for 6 hours to obtain an orange colored solution; (c) washing the orange colored solution obtained in step (b) thrice with 10 mL of ethanol at 12000 rpm for 10 minutes to obtain a residue; and (d) subjecting the residue obtained in step (c) to vacuum drying at 60°C overnight followed by grounding with a mortar and pestle to obtain a yellowish powder of 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite.

[0059] The present invention provides nano urea having nano-fringes like shape and a fibre like surface morphology with good crystallinity.

[0060] Referring to Figure 1 , a graphical representation for p-XRD plots of varied amount of CD- IITG capping agent 1 (sodium ascorbate with carbon black) taken as a reducing agent for the synthesis of neat nano urea, is depicted.

[0061] EXAMPLE 1

[0062] Materials and method

[0063] Materials

[0064] Urea, sodium ascorbate, carbon black were procured from FINAR, Sigma-Aldrich and MERCK respectively. An analytical reagent based absolute ethanol was purchased from CSS. The chemicals were taken of high purity without any further purification. Method

[0065] The present invention synthesises nano sized urea through a simple and cost effective mode with and without a capping agent. The nano urea was synthesized with (a) sodium ascorbate with carbon black without a capping agent, (b) trisodium citrate with carbon black and without a capping agent and (c) sodium ascorbate with cellulose and carbon black

[0066] Cost-effective method for producing nano urea

[0067] The production of urea was performed at mild conditions (at a temperature of 180°C and a pressure of 100 bar) by the method mentioned below:

[0068] An amount of 236 kg of ammonia (NH3) and 152 kg of carbon dioxide (CO2) was taken and reacted at a pressure ranging from 140-250 bar and at a temperature range of 180- 200°C in an autoclave to form ammonium carbamate (NH4COONH2). The molar ratios ofNH3:CO2was in a range from 3: 1 to 4: 1 and retention time in a range of 20 to 30 minutes were the reaction conditions that were employed to obtain 208 kg of nano urea, as shown in Equation (1):

[0069] NH3+ C02- > NH4COONH2AH = -117kJ / mol(1)

[0070] The obtained NH4COONH2was subsequently dehydrated by heating to form urea and water, as shown in Equation (2):

[0071] The aqueous urea solution was concentrated to 95-99.7 wt% in a vacuum evaporator.

[0072] 208 kg of urea was then mixed with 458 kg of trisodium citrate with carbon black in a nano urea reactor under optimum conditions (90°C, 1 hour) with constant stirring that resulted in the formation of nano urea (ash colour). The obtained ash coloured nano urea by said method resulted in an effective cost close to Rs. 60 / kg for the nano urea synthesized. Here, trisodium citrate with carbon black served as a nitrification inhibitor for nano urea synthesis. The urea molecules were then mixed with a variety of alternative agglomerating agents (biocompatible derivatives of nanomaterials including graphene, carbon NTs) to bring down the overall cost (Rs.15 / kg) to achieve the desired ratio of nitrogen (N), phosphorous (P) and potassium (K) for employing the synthesized nano urea as a fertilizer.

[0073] Water was not required in the method of producing nano urea. Nevertheless, approximately 3 temperature-programmed desorption (TPD) water was synthesized and stripped off.

[0074] Synthesis of neat nano urea

[0075] The synthesis of neat nano urea was carried out by heating a solution of urea [0.1 M, 6.006 g] and sodium ascorbate with carbon black in 50 mL ethanol at 70°C for 6 hours under continuous stirring. The sodium ascorbate (C6H7O6Na) with carbon black acted as a reducing agent. The addition of the reducing agent was followed by washing of the obtained reaction mixture twice with 10 mL of ethanol at 12,000 rpm for 10 minutes and vacuum drying the sample at 60°C overnight. A yellowish orange powder (8.216 g) was obtained as the final product.

[0076] Synthesis of 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite

[0077] The synthesis of 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite was carried out with slight modifications to the above-mentioned method. Briefly, 0.05 M (3.003 g) of urea, and 0.025 M (4.053 g) of sodium ascorbate with cellulose and carbon black were taken in 50 mL of ethanol under continuous stirring (600-1000 rpm) and after obtaining a complete homogeneous solution, 0.025 M (4.75 g) of sodium ascorbate with carbon black was added slowly. The mixture was left for heating at 70°C for 6 hours to obtain an orange colored solution. The solution was then washed thrice with 10 mL of ethanol at 12,000 rpm for 10 minutes and the residue was kept for vacuum drying at 60°C overnight. A yellowish powder of 6.297 g was obtained as the final product after grounding with a clean mortar and pestle.

[0078] Synthesis of 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite

[0079] The synthesis of 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite was carried out by with slight modifications to the above-mentioned method. Briefly, 0.05 M (3.003 g) of urea, and 0.061 M (10.0 g) of sodium ascorbate with cellulose and carbon black were taken in 80 mL of ethanol under continuous stirring on a magnetic stirrer with 600-1000 rpm and after obtaining a complete homogeneous solution, 0.025 M (4.75 g) of sodium ascorbate and carbon black was added slowly. The mixture was left for heating at 70°C for 6 hours to obtain an orange colored solution. The solution was then washed thrice with 10 mL of ethanol at 12,000 rpm for 10 minutes and the residue was kept for vacuum drying at 60°C overnight. A yellowish powder of 12.77 g was obtained as the final product after grounding with a clean mortar and pestle.

[0080] EXAMPLE 2

[0081] Characterization

[0082] Characterization of neat nano urea and sodium ascorbate with cellulose and carbon black-nano urea composites

[0083] The synthesis of nano scaled urea fertilizer by employing sodium ascorbate with carbon black as a reducing agent and cellulose as a biocompatible and biodegradable coating material was performed with good yield. Cellulose is a polymer with excellent stiffness, low density and an excellent ability to modify the surface chemistry that makes cellulose a prominent green material. The synthesis of nano urea was carried in three different ways, where the amount of sodium ascorbate with cellulose and carbon black taken was varied and the samples obtained were then characterized through Fourier transform infrared (FTIR), Field emission scanning electron microscopy (FESEM) and Energy dispersive X- Ray spectroscopy (EDS) analysis.

[0084] FTIR analysis

[0085] In FTIR, the standard peaks of urea were typically displayed at 3338 cm1, 2922 cm1, 2864 cm \ 1677 cm11463 cm \ 1577 cm \ 1366 cm ’, 1151cm 1002 cm \ 997cm1and the peaks at 1050 cm1, and 1030 cm1corresponded to standard peaks of cellulose. In contrast to the standard peaks of urea, the peaks observed in nano urea observed a slight deviation due to reduction in size from molecular level to nano level as well as bonding of the nano urea with the reducing / capping agent. A slight shift in peaks was observed for neat urea and 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite sample whereas, for 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea, a couple of peaks were missing. The shift was due to the bonding of urea to biopolymer / reducing agent. Figure 9 shows FTIR plots of varied amounts of sodium ascorbate with carbon black as reducing agent for the synthesis of neat nano-urea. Figure 10 shows FTIR plots of varied amounts of trisodium citrate with carbon black as reducing agent for the synthesis of nano-urea. Figure 11 shows FTIR plots of varied amounts of cellulose as a capping agent with 0.5 equivalent of sodium ascorbate with carbon black as a reducing agent for the synthesis of sodium ascorbate with cellulose and carbon black-nano urea composite.

[0086] X-ray diffraction (XRD) studies

[0087] Typically, urea shows 26 values of 22.4°, 25.1°, 29.4°, 32.65°, 36.9° and 37.4° corresponding to (112), (221), (103), (312), (330) and (420) planes of urea. In all the cases, the diffraction peaks of urea were present. Further, the intensity and broadness of the peaks indicated the size of the particles present in the sample. Most of the peaks corresponding to nano-urea were less intense and broad. Figure 1 shows p-XRD plots of varied amounts of sodium ascorbate with carbon black as reducing agent for the synthesis of neat nano urea. Figure 2 shows p-X RD plots of varied amounts of trisodium citrate with carbon black as reducing agent for the synthesis of ash coloured nano urea. Figure 3 shows p-X RD plots of varied amounts of sodium ascorbate with cellulose and carbon black as a capping agent, sodium ascorbate with carbon black as a reducing agent for the synthesis of sodium ascorbate with cellulose and carbon black-nano urea composite. Figure 4 shows p-X RD plots of nano urea (NU-TSC0.25_Bulkl).

[0088] FESEM analysis

[0089] The morphology of the synthesized nano urea was checked through FESEM analysis, as shown in Figures 5-8 at a scale range of 1 pm and 100 nm and magnification ranging from 25 KX to 175 KX. Agglomerated nano-sized particles were obtained when 0.5 equivalent of sodium ascorbate with carbon black was employed as reducing agent, as depicted in Figure 5. 0.25 equivalent and 0.125 equivalent of sodium ascorbate with carbon black was found as moisture sensitive and thus did not gave a proper FESEM image. Figure 5 shows the FESEM image of NU_SA0.5. On taking varied amounts of trisodium citrate with carbon black as the reducing agent, well defined spherical nanoparticles were obtained. The samples were dissolved in water and then drop-casted on a glass slide and dried before the analysis. The aggregated particles were observed on taking 1.0 equivalent of trisodium citrate with carbon black and on decreasing the amount of reducing agent, the particle size decreased from (69-81 nm) for 0.5 equivalent to (35-43 nm) for 0.25 equivalent. Further decreasing the concentration to 0.125 equivalents did not gave nano-sized particles, as depicted in Figure 6. Figure 6 shows FESEM images of varied amounts of trisodium citrate with carbon black as reducing agent for the synthesis of bulk nano urea samples: NU_TSCi.oin part (a), NU_TSC0.5, in part (b), NU_TSC0.25, in part (c) and NU_TSC0.I25in part (d). On the contrary, on addition of 0.5 equivalent of sodium ascorbate with cellulose and carbon black as the capping agent showed flower like morphology that on higher magnification proved as nano-fringes of 20-30 nm. While in case of 1.2 equivalent of sodium ascorbate with cellulose and carbon black, a rod like structure was obtained that on a higher magnification of 100 KX showed a fibre like surface morphology. Through the analysis, on addition of cellulose, a complete change in morphology of sample was observed, as depicted in Figure 7. Figure 7 shows FESEM images of varied amounts of the cellulose as capping agent for the synthesis of sodium ascorbate with cellulose and carbon black-nano urea composite samples: NU_SAo.5_Co.5in part (a) and NU_SA0.5_CI,2in part (b).

[0090] Further, similar to NU_TSC0.25, the morphology of the nano urea sample (NU_TSCo.25_Bulk 1) also characterised of spherical nanoparticles of size (30-100 nm) stacked together. In solid form (powder), the nanoparticles were closely packed to each other and on dispersing in water got separated that resulted into a discrete arrangement of particles with a size ranging from 69-259 nm. Figure 8 shows FESEM images of NU- TSCo.25_Bulkl in powdered form in part (a) and of NU-TSC0.25_Bulkl dispersed in water and then dropcasted on a glass slide in part (b).

[0091] Energy-dispersive X-ray (EDX) analysis

[0092] The nitrogen content present in the samples was measured through EDX analysis. Typically, the nano-urea sample from IFFCO contains 4.96% by weight of nitrogen. Table 1 shows the nitrogen content by weight for various nano-urea samples. Figure 12 shows EDX image of nano urea sample, NU_SA0.5. Figure 13 shows EDX images of varied amounts of trisodium citrate with carbon black as reducing agent for the synthesis of nano urea sample, NU_TSC0.5in part (a) and NU_TSC0.25in part (b). Figure 14 shows FESEM image of nano urea composite sample, NU_SA0 5_C0.5. Figure 15 shows EDX image of urea sample, NU-TSC0.25_Bulkl dispersed in water followed by dropcasted on a glass slide.

[0093] Table 1: Nitrogen content in various nano-urea samples

[0094] Measurement of zeta potential

[0095] The zeta potential measurement of all the nano-urea samples was carried out by dispersing 3 mg of the sample in 9 mL of deionised (DI) water to make a stock solution. The zeta potential of all the samples were measured in a Malvern Zetasizer instrument by taking 50 pT of the stock solution diluted with 600 pT of DI water, added in a DTS1070 capillary cell at 25°C. The potential value of most of the nano-urea samples were found to possess a positive value, as shown in Table 2. Figure 16 shows zeta potential of the nano urea sample, NU_SA0 5taken in water as solvent. Figure 17 shows zeta potential of the nano urea sample, NU_SA0.25taken in water as solvent. Figure 18 shows zeta potential of the nano urea sample, NU_SA0 i25taken in water as solvent. Figure 19 shows zeta potential of the nano urea sample, NU_TSCi.otaken in water as solvent. Figure 20 shows zeta potential of the nano urea sample, NU_TSC0.5taken in water as solvent. Figure 21 shows zeta potential of the nano urea sample, NU_TSC0.25taken in water as solvent. Figure 22 shows zeta potential of the nano urea sample, NU_TSC0.I25taken in water as solvent. Figure 23 shows zeta potential of the nano urea sample, NU_SA0.5C0.5taken in water as solvent. Figure 24 shows zeta potential of the nano urea sample, NU_SA0 5Ci.2taken in water as solvent. Figure 25 shows zeta potential of the nano urea sample, NU_TSC0.25Bulk 1 taken in water as solvent.

[0096] Table 2: Zeta Potential measurement of nano-urea sample at 25°C

[0097] Therefore, the present invention provides a simple, fast and cost-effective method of synthesizing nano urea through milder reaction conditions comprising of a reducing agent and a biodegradable and biocompatible coating material having mechanical properties.

[0098] Many modifications and other embodiments of the invention set forth herein will readily occur to one skilled in the art to which the invention pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

CLAIMSWe claim:

1. A method of synthesis of nano urea and a nano urea-composite comprising the steps of:(i) reacting 236-250 kg of ammonia (NH3) with 152-167 kg of carbon dioxide in a molar ratio at a predefined temperature and a predefined pressure in an autoclave for 20-30 minutes to form ammonium carbamate (NH4COONH2);(ii) dehydrating NH4COONH2formed in step (i) by heating to obtain urea and water;(in) mixing 208-224 kg of urea obtained in step (ii) with 458-512 kg of an inhibitor in a nanourea-reactor under optimum conditions with constant stirring at 800-1000 rpm to form an ash colored nano urea;(iv) reacting the ash colored nano urea obtained in step (iii) with a reducing agent to obtain neat nano urea; and(v) reacting the ash colored nano urea obtained in step (iii) with the reducing agent and a biopolymer to obtain a nano urea composite; wherein, said molar ratio of ammonia and carbon dioxide in step (i) is in a range of 3:1 to 4:1; said predefined temperature and said predefined pressure in step (i) is 180- 200°C and 100-250 bar; said inhibitor in step (iii) is trisodium citrate with carbon black and the optimum conditions include a temperature range of 80-90°C and a timeperiod of 6-12 hours; said reducing agent in steps (iv-v) is sodium ascorbate with carbon black and said biopolymer in step (v) is sodium ascorbate with cellulose and carbon black; and said nano urea composite obtained in step (v) is selected from 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite or 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite.

2. The method as claimed in claim 1, wherein neat nano urea in step (iv) is obtained by the steps of:(a) taking 6.006-6.01 g of the ash colored nano urea and 9.5-10.0 g of sodium ascorbate with carbon black in 50-55 mL of ethanol and heating at a temperature of 70-80°C for 6-6.5 hours under continuous stirring to obtain a reaction mixture; and(b) washing the reaction mixture obtained in step (a) twice in 10 mL of ethanol at 12000 rpm for 10 minutes followed by vacuum drying at 60°C overnight to obtain yellowish powder of neat nano urea.

3. The method as claimed in claim 1, wherein said method yields 8.216-8.3 g of neat nano urea.

4. The method as claimed in claim 1 , wherein neat nano urea is formed in the form of nanoparticles of size ranging from 100 to 200 nm.

5. The method as claimed in claim 1 , wherein neat nano urea exhibits zeta potential in a range of 2.27 to 9.34 mV.

6. The method as claimed in claim 1, wherein said method yields 6.297-12.77 g of said nano urea composite.

7. The method as claimed in claim 1 , wherein said nano urea composite obtained in step (v) exhibits size ranging from 20 to 30 nm.

8. The method as claimed in claim 1 , wherein said nano urea composite obtained in step (v) exhibits zeta potential in a range of -7.04 to 7.01 mV.

9. The method as claimed in claim 1 , wherein 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite is obtained by the steps of:(a) mixing 3.003 g of the ash colored nano urea and 4.053 g of sodium ascorbate with cellulose and carbon black in 50 mL of ethanol under continuous stirring to obtain a homogenous mixture;(b) adding slowly 4.75 g of sodium ascorbate with carbon black in the homogenous mixture obtained in step (a) and heating at 70°C for 6 hours to obtain an orange colored solution;(c) washing the orange colored solution obtained in step (b) thrice with 10 mL of ethanol at 12000 rpm for 10 minutes to obtain a residue; and(d) subjecting the residue obtained in step (c) to vacuum drying at 60°C overnight followed by grounding with a mortar and pestle to obtain a yellowish powder of 0.5 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite.

10. The method as claimed in claim 1 , wherein 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite is obtained by the steps of:(a) mixing 3.003 g of the ash colored nano urea and 10 g of sodium ascorbate with cellulose and carbon black in 80 mL of ethanol under continuous stirring to obtain a homogenous mixture;(b) adding slowly 4.75 g of sodium ascorbate with carbon black in the homogenous mixture obtained in step (a) and heating at 70°C for 6 hours to obtain an orange colored solution;(c) washing the orange colored solution obtained in step (b) thrice with 10 mL of ethanol at 12000 rpm for 10 minutes to obtain a residue; and(d) subjecting the residue obtained in step (c) to vacuum drying at 60°C overnight followed by grounding with a mortar and pestle to obtain a yellowish powder of 1.2 equivalent of sodium ascorbate with cellulose and carbon black-nano urea composite.

Images