Claims:WE CLAIM:
1. A crop protection formulation comprising porous silica nanoparticles and at least one pesticide, wherein the pesticide is entrapped within pores of the silica nanoparticles and the formulation has pesticide loading of at least 0.5% (w/w).

2. The crop protection formulation as claimed in claim 1 is a nanocomposite.

3. The crop protection formulation as claimed in claim 1, wherein the pesticide loading is in a range of 0.5% to 63% (w/w).

4. The crop protection formulation as claimed in claim 1, wherein silica nanoparticles have particle size in a range of 10 nm to 1000 nm.

5. The crop protection formulation as claimed in claim 1, wherein the pesticide is selected from one or more fungicide, insecticide, herbicide or a combination thereof.

6. A method of preparing a crop protection formulation comprising:
dispersing at least one pesticide in an aqueous solution of sodium silicate to obtain a precursor solution;
adding sulfuric acid-surfactant mixture to the precursor solution to obtain porous silica nanoparticles entrapping at least one pesticide within its pores; and
separating porous silica nanoparticles entrapping at least one pesticide within its pores, from the solution obtained in the previous step.

7. The method as claimed in claim 6, wherein the aqueous solution of sodium silicate is in a concentration range of 7-14% (w/v).

8. The method as claimed in claim 6, wherein the sulfuric acid-surfactant mixture comprises a surfactant selected from lignin, gelatin, octylamine, chitosan, dioctyl sulfosuccinate sodium salt (AOT) and combinations thereof.

9. The method as claimed in claim 6, wherein the sulfuric acid-surfactant mixture comprises surfactant in a concentration range of 1-5% (w/w).

10. The method as claimed in claim 6, wherein the sulfuric acid-surfactant mixture comprises sulfuric acid in a concentration range of 1.0 M – 5 M.

11. The method as claimed in claim 6, wherein addition of sulfuric acid-surfactant mixture to the precursor solution is carried out to facilitate gel formation followed by addition of water to liquefy the gel and subsequent addition of sulfuric acid-surfactant mixture to the liquefied gel till neutralization.

12. The method as claimed in claim 6, wherein addition of sulfuric acid-surfactant mixture to the precursor solution is carried out at a rate of 5 mL/min to 100 mL/min.

13. The method as claimed in claim 6, wherein the separation of porous silica nanoparticles entrapping at least one pesticide within its pores is carried out by centrifugation or filtration.

14. The method as claimed in claim 6, further comprising drying the separated porous silica nanoparticles entrapping at least one pesticide within its pores at a temperature of 60 ºC – 90 ºC.

15. The method as claimed in claim 14, further comprising grinding or milling to obtain a fine powder of porous silica nanoparticles entrapping at least one pesticide within its pores.

Dated this 20th day of November, 2015

Aparna Kareer
Of Obhan & Associates
Agent for the Applicant
Patent Agent No. 1359
, Description:The present disclosure provides a crop protection formulation and a method of preparing the same.
BACKGROUND
Crop protection products or pesticides, are compositions based on natural product(s), chemical(s) or biological agent(s) intended to provide protection against the damaging influence of insects, weeds, and microbes. The use of pesticides in the agricultural practice has become unavoidable on account of the considerable damage caused by the pests, often leading to destruction of the entire produce. However, the use of pesticides also has serious implications on the health of humans, animals and the environment and requires careful control. Uncontrolled use of pesticides not only adds to the cost of farming but also calls for heavy investments in the research and development of new pesticide formulations in order to cope with cases of resistance development among pests to known pesticides.
Pesticides are categorized on the basis of their target pests, for example, insecticides (imidacloprid, flubendiamide etc), fungicide (hexaconazole, kresoxim methyl etc) and herbicide (metribuzin).
Imidacloprid and flubendiamide are systemic insecticide and act on termites, sucking pests and caterpillars. Due to its high water solubility and rapid hydrolysis, imidacloprid readily leaches out in soil and therefore has a short duration of action. Multiple applications are therefore required to maintain the pesticidal activity. Use of flubendiamide also suffers from serious toxicity concerns. Herbicides such as metribuzin are used both pre- and post-emergence in crops and are very effective in controlling annual grasses and certain broadleaf weeds. They work by inhibiting photosynthetic system, but unfortunately are also found to contaminate ground water. Hexaconazole is a systemic fungicide, effective in the treatment of a number of phyto-fungal diseases. Its mode of action is the inhibition of ergosterol biosynthesis. Kresoxim-methyl is another important quasi-systemic fungicide. It is also used over a range of phyto-fungal diseases. Both these fungicides pose danger in aquatic environment and need to be restricted to lower doses.
Given the spectrum of pesticides and hazards associated with their use, there is a pressing need to reduce the amount of their usage. It is also desirable to improve the rate and extent of their absorption by plants.
Nanotechnology provides an interesting agricultural tool to increase the absorption ability of plants. Nanotechnology based delivery systems will ensure a better crop protection from pests (insects, fungus, weeds etc.) without multiple pesticide applications and reduced environmental and financial burden. There is therefore a need to develop a nanotechnology based formulation which uses bio-friendly agents to enhance the uptake of pesticides.
SUMMARY
A crop protection formulation is disclosed. The crop protection formulation comprises porous silica nanoparticles and at least one pesticide, wherein the pesticide is entrapped within pores of the silica nanoparticles and the formulation has pesticide loading of at least 0.5% (w/w).
A method of preparing a crop protection formulation is also disclosed. The method comprises dispersing at least one pesticide in an aqueous solution of sodium silicate to obtain a precursor solution; adding sulfuric acid-surfactant mixture to the precursor solution to obtain porous silica nanoparticles entrapping at least one pesticide within its pores; and separating porous silica nanoparticles entrapping at least one pesticide within its pores, from the solution obtained in the previous step.

BRIEF DESCRIPTION OF DRAWINGS
Figure 1: FTIR analysis of plain silica (curve 1), hexaconazole-silica nanocomposite with 11% loading (curve 2) and hexaconazole-silica nanocomposite with 16% loading (curve 3), in accordance with an embodiment of the present invention.
Figure 2A and 2B: FTIR spectra of pure silica (curve 1), hexaconazole-silica nanocomposite with 38% loading (curve 2) and pure technical grade hexaconazole (curve 3) recorded in two different regions of the infrared region, in accordance with an embodiment of the present invention.
Figure 3: Orientation of hexaconazole on silica surface (not to scale), in accordance with an embodiment of the present invention.
Figure 4: Structure of the crop protection formulation in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the disclosed process and the disclosed composition, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The present disclosure provides a crop protection formulation and a method of preparing the same. The crop protection formulation comprises porous silica nanoparticles and at least one pesticide, wherein the pesticide is entrapped within pores of the silica nanoparticles and the formulation has a pesticide loading of at least 0.5% (w/w).
In accordance with an embodiment, the crop protection formulation is a nanocomposite of pesticide and silica nanoparticles.
In accordance with an embodiment, the crop protection formulation has a pesticide loading in the range of 0.5% to 63% (w/w). In accordance with a specific embodiment, the crop protection formulation has a pesticide loading of 5% (w/w). By way of an example, the crop protection formulation for application to fungal or insecticidal attack on paddy, groundnut or sugarcane comprises up to 5% (w/w) of either hexaconazole or imidacloprid.
Entrapment of the pesticide within the pores of silica nanoparticles is a one-pot procedure wherein nano-silica synthesis and pesticide entrapment occur simultaneously. The one-pot procedure comprises addition of a sulfuric acid-surfactant mixture to a sodium silicate solution comprising at least one pesticide. Crop protection formulation having high pesticide loading such as 63% (w/w) is obtained.
A comparison of surface area of silica nanoparticles with increasing pesticide loading showed that the surface area of silica nanoparticles was reduced. A high surface area is a measure of a high porosity of the silica nanoparticles. Therefore, a reduction in surface area with increasing pesticide loading indicates that the porosity is reduced as a result of the pesticides occupying the pores. Further, an increase in porosity which led to an increase in surface area was observed following removal of pesticide by sonication in dichloromethane. This further indicates that the pesticide is entrapped within the porous matrix of silica nanoparticles. This substantiates that in the crop protection formulation pesticide and the silica nanoparticles do not have a core-shell relationship neither the pesticide is encapsulated by the silica nanoparticles.
In accordance with an embodiment, the crop protection formulation comprises silica nanoparticles in a particle size range of 10 nm to 1000 nm.
In accordance with an embodiment, the pesticide is any pesticide not limited to fungicides, insecticides and herbicides. By way of an example, the pesticide is a fungicide such as hexaconazole or kresoxim methyl, insecticide such as imidacloprid or flubendiamide, herbicide such as metribuzin.
In accordance with an embodiment, the crop protection formulation of the present disclosure is absorbed by the plant tissue directly and the pesticides are released within the plant cells.
In accordance with an embodiment, the crop protection formulation of the present disclosure as designed is not intended to provide slow release, sustained release, delayed release or controlled release effect of pesticides from silica nanoparticles.
The present disclosure also provides a method of preparing a crop protection formulation. The method comprises dispersing at least one pesticide in an aqueous solution of sodium silicate to obtain a precursor solution; adding sulfuric acid-surfactant mixture to the precursor solution to obtain porous silica nanoparticles entrapping at least one pesticide within its pores; and separating said porous silica nanoparticles entrapping at least one pesticide within its pores from the solution obtained in the previous step.
In accordance with an embodiment, the crop protection formulation has a pesticide loading of at least 0.5% (w/w). In accordance with a specific embodiment, the crop protection formulation has a pesticide loading in the range of 0.5% to 63% (w/w). By way of an example, the crop protection formulation for application to fungal or insect attack on paddy, groundnut or sugarcane comprises up to 5% (w/w) of either hexaconazole or imidacloprid. High pressure liquid chromatography (HPLC) and Gas Chromatography (GC) analysis is used for the analysis of the pesticide content of the crop protection formulation.
In accordance with an embodiment, the pesticide(s) is any pesticide not limited to fungicides, insecticides and herbicides. By way of an example, the pesticide is a fungicide such as hexaconazole or kresoxim methyl, insecticide such as imidacloprid or flubendiamide, herbicide such as metribuzin.
In accordance with an embodiment, the silica nanoparticles are in a particle size range of 10 nm to 1000 nm.
In accordance with an embodiment, the aqueous solution of sodium silicate is in a concentration range of 7-14% (w/v).
In accordance with an embodiment, the sodium silicate is synthesized by boiling rice husk ash in an aqueous solution of sodium hydroxide as disclosed in the Indian Patent Application No. 1510/MUM/2010, incorporated herein by reference. In accordance with an alternate embodiment, a commercially available sodium silicate solution is used.
In accordance with an embodiment, addition of sulfuric acid-surfactant mixture to the precursor solution is carried out to facilitate gel formation followed by addition of water to liquefy the gel and further addition of sulfuric acid-surfactant mixture to the liquefied gel is resumed till neutralization.
In accordance with an embodiment, surfactant is selected from lignin, gelatin, octylamine, chitosan, Dioctyl sulfosuccinate sodium salt (AOT), or combinations thereof. In accordance with a specific embodiment, preparation of sulfuric acid-surfactant mixture of gelatin comprises addition of gelatin to sulfuric acid, heating the mixture of gelatin and sulfuric acid to enable complete dissolution of gelatin and cooling to room temperature.
In accordance with an embodiment, preparation of sulfuric acid-surfactant mixture of lignin comprises addition of sodium lignosulfonate to sulfuric acid. Sodium lignosulfonate is a water soluble form of lignin and does not require heating.
In accordance with an embodiment, the sulfuric acid-surfactant mixture comprises sulfuric acid in a concentration of 1.0 M – 5 M.
In accordance with an embodiment, the sulfuric acid-surfactant mixture comprises surfactant in a concentration range of 1-5% (w/w).
In accordance with an embodiment, addition of sulfuric acid-surfactant mixture to the precursor solution is carried out at a rate of 5 mL/min to 100 mL/min.
In accordance with an embodiment, separation of silica nanoparticles entrapping at least one pesticide within its pores from the solution is carried out by centrifugation or filtration.
In accordance with an embodiment, the separation of silica nanoparticles entrapping at least one pesticide within its pores from the solution is carried out by centrifugation at an rpm speed between 4000-8000 for 5-10 minutes.
In accordance with an embodiment, subsequent to separation, the method further comprises drying of silica nanoparticles entrapping at least one pesticide within its pores at a temperature of 60 ºC – 90 ºC.
In accordance with an embodiment, subsequent to drying, the method further comprises grinding or milling of dried silica nanoparticles entrapping at least one pesticide within its pores to obtain a fine powder of silica nanoparticles.
In accordance with an embodiment, the crop protection formulation obtained by the disclosed method is a nanocomposite of pesticide and silica nanoparticles.
EXAMPLES
EXAMPLE 1: Comparison of surface area of Hexaconazole-silica nanocomposite with an increasing pesticide loading.
Hexaconazole-silica nanocomposites were prepared according to the present disclosure and the surface area of the particles determined. Extraction of hexaconazole from 38% Hexaconazole-silica nanocomposite was carried out in dichloromethane by sonication for 1 hour and the surface area was again determined. The surface area data is provided below:

Sr. No. Sample Surface area (m2/g)
1 Plain silica (without pesticide) 400-450
2 8% Hexaconazole-silica nanocomposite 161
3 15% Hexaconazole-silica nanocomposite 159
4 26% Hexaconazole-silica nanocomposite 33
5 38% Hexaconazole-silica nanocomposite Negligible
6 Extraction of hexaconazole from 38% loaded hexaconazole in dichloromethane by sonication for 1 h. 177

A reduction in surface area of silica nanoparticles with increasing Hexaconazole loading indicates that the pesticide particles are occupying the pores of the silica nanoparticles.
Further, an increase in surface area following removal of Hexaconazole from silica nanoparticle formulation further indicates that an entrapment in the porous matrix of silica nanoparticles occurs rather than core-shell formation or encapsulation.
Furthermore, the TEM analysis shows that the formulation has particles as small as 7-10 nm and also bigger geometries in the form of a silica matrix. This is typical for silica wherein the Si-O-Si network forms a matrix. Hexaconazole (pesticide) cannot be imaged by TEM since it is an organic molecule. TEM analysis shows particle and network structures.
Particle size distribution done by dynamic light scattering measurements (DLS) indicates a bigger particle size (~ 100-200 nm) for hexaconazole-silica complex. This is due to the different principles of measurements. DLS uses light scattering and measures the hydrodynamic radii where-as TEM measures the direct size. For the present formulation, DLS would be a better approximation since, silica might also be present in a matrix form and an average particle size can be obtained by DLS.
The following examples 2-14 provide exemplary crop protection formulations and method of their preparation according to the present disclosure.
EXAMPLE 2: 62% Hexaconazole-silica nanocomposite
To a 25 mL solution of 14% sodium silicate, 15 grams of hexaconazole (technical grade; 92% purity) was added under stirring conditions to make a precursor solution. To this, 27 mL of 1.25 M sulfuric acid containing 2% gelatin was added dropwise (The sulfuric acid-gelatin solution was prepared by adding gelatin to sulfuric acid and heating the solution till complete dissolution of gelatin took place). Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 25 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain hexaconazole-silica nanocomposite. The yield was 20 grams. HPLC and GC analysis indicated a loading of 62% Hexaconazole.
EXAMPLE 3: 20% Hexaconazole-silica nanocomposite formulation
To a 25 mL solution of 14% sodium silicate, 2.42 grams of hexaconazole (technical grade; 92% purity) was added under stirring conditions to make a precursor solution. To this, 23 mL of 1.25 M sulfuric acid containing 2% gelatin was added dropwise. (The sulfuric acid-gelatin solution was prepared by adding gelatin to sulfuric acid and heating the solution till complete dissolution of gelatin took place). Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 25 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain hexaconazole-silica nanocomposite. The yield was 7.5 grams. HPLC and GC analysis indicated a loading of 20% Hexaconazole.
EXAMPLE 4: 10% Hexaconazole-silica nanocomposite formulation
To a 25 mL solution of dimethyl formamide (DMF), 8.12 grams of hexaconazole (technical grade; 92% purity) and 25 grams of plain silica nanoparticles were added. This slurry was kept under stirring for a period of 12-18 hours at room temperature. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Hexaconazole-silica nanocomposite. The yield was 26 grams. HPLC and GC analysis indicated a loading of 10% Hexaconazole.
EXAMPLE 5: 20% Hexaconazole-silica nanocomposite formulation
To a 1560 mL solution of 14% sodium silicate, 165 grams of hexaconazole (technical grade; 92% purity) was added under stirring conditions to make a precursor solution. To this, 1250 mL of 1.25 M sulfuric acid containing 2% lignin was added dropwise. (To make a sulfuric acid-lignin solution, sodium lignosulfonate powder was added to sulfuric acid and the solution stirred). Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 1560 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel was converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Hexaconazole-silica nanocomposite. The yield was 560 grams. HPLC and GC analysis indicated a loading of 20% Hexaconazole.
EXAMPLE 6: 30% Hexaconazole-silica nanocomposite formulation
To a 4464 mL solution of 7% sodium silicate, 471.5 grams of hexaconazole (technical grade; 92% purity) was added under stirring conditions to make a precursor solution. To this, 1830 mL of 1.25 M sulfuric acid containing 2% lignin was added dropwise. (To make a sulfuric acid-lignin solution, sodium lignosulfonate powder was added to sulfuric acid and the solution stirred). Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 4464 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Hexaconazole-silica nanocomposite. The yield was 1017 grams. HPLC and GC analysis indicated a loading of 30% Hexaconazole.
EXAMPLE 7: 5% Hexaconazole-silica nanocomposite formulation
To a 570 mL solution of 7% sodium silicate, 5.6 grams of hexaconazole (technical grade; 92% purity) was added under stirring conditions to make a precursor solution. To this, 230 mL of 1.25 M sulfuric acid containing 2% lignin was added dropwise. (To make a sulfuric acid-lignin solution, sodium lignosulfonate powder was added to sulfuric acid and the solution stirred). Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 570 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Hexaconazole-silica nanocomposite. The yield was 77 grams. HPLC and GC analysis indicated a loading of 5% Hexaconazole.
EXAMPLE 8: 63% Imidacloprid-silica nanocomposite formulation
To a 128 mL solution of 14% sodium silicate, 77.12 grams of imidacloprid (technical grade; 95% purity) was added under stirring conditions to make a precursor solution. To this, 100 mL of 1.25 M sulfuric acid containing 2% gelatin was added dropwise. Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 100 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Imidacloprid-silica nanocomposite. The yield was 100 grams. HPLC analysis indicated a loading of 63% Imidacloprid.
EXAMPLE 9: 35% Imidacloprid-silica nanocomposite formulation
To a 265 mL solution of 14% sodium silicate, 53 grams of imidacloprid (technical grade; 95% purity) was added under stirring conditions to make a precursor solution. To this, 230 mL of 1.25 M sulfuric acid containing 2 % gelatin was added dropwise. Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 100 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converts to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Imidacloprid-silica nanocomposite. The yield was 118 grams. HPLC analysis indicated a loading of 35% Imidacloprid.
EXAMPLE 10: 23% Metribuzin-silica nanocomposite formulation
To a 50 mL solution of 14% sodium silicate, 4.84 grams of metribuzin (technical grade; 95% purity) was added under stirring conditions to make a precursor solution. To this, 41 mL of 1.25 M sulfuric acid containing 2 % lignin was added dropwise. Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 50 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Metribuzin-silica nanocomposite. The yield was 14.75 grams. HPLC analysis indicated a loading of 23% metribuzin.
EXAMPLE 11: 23% Flubendimide-silica nanocomposite formulation
To a 50 mL solution of 14% sodium silicate, 4.84 grams of flubendimide (technical grade; 98 % purity) was added under stirring conditions to make a precursor solution. To this, 43 mL of 1.25 M sulfuric acid containing 2 % lignin was added dropwise. Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 50 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Flubendimide-silica nanocomposite. The yield was 16.5 grams. HPLC analysis indicated a loading of 23% flubendimide.
EXAMPLE 12: 10% Kresoxim-methyl-silica nanocomposite formulation
To a 50 mL solution of 14% sodium silicate, 4.84 grams of Kresoxim-methyl (technical grade; 95 % purity) was added under stirring conditions to make a precursor solution. To this, 47 mL of 1.25 M sulfuric acid containing 2 % lignin was added dropwise. Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 50 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Kresoxim-methyl-silica nanocomposite. The yield was 16 grams. HPLC analysis indicated a loading of 10% Kresoxim-methyl.
EXAMPLE 13: 1.2:1 Hexaconazole-Imidacloprid-silica nanocomposite nanoparticle formulation
To a 446 mL solution of 7% sodium silicate, 23.57 grams of hexaconazole (technical grade; 92% purity) and 23.57 grams of imidacloprid (technical grade; 97% purity) were added under stirring conditions to make a precursor solution. To this, 187 mL of 1.25 M sulfuric acid containing 2 % lignin was added dropwise. Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 446 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converts to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder to obtain Hexaconazole-Imidacloprid-silica nanocomposite with 12.4% hexaconazole and 10% imidacloprid loading respectively (as determined by HPLC), to give a 1.2:1 Hexaconazole-Imidacloprid loaded silica nanoparticle formulation. The yield was 130 grams.
EXAMPLE 14: 37:3 Imidacloprid:Hexaconazole-silica nanocomposite formulation
To a 265.5 mL solution of 14% sodium silicate, 55.5 grams of imidacloprid (technical grade; 97% purity) and 4.95 grams of hexaconazole (technical grade; 92% purity) were added under stirring conditions to make a precursor solution. To this, 223 mL of 1.25 M sulfuric acid containing 2 % lignin was added dropwise. Thick gel was formed when the pH reached 9.5 to 10.5. Sulfuric acid addition was stopped at this point. To this gel, 265.5 mL of deionized water was added and the slurry was stirred for 10 minutes. After the gel converted to uniform slurry, the sulfuric acid addition was resumed. The reaction was stopped when the slurry pH reached 6.5-7. The slurry was kept under stirring conditions for another 10 minutes to ensure stable pH of 6.5-7. The slurry was then centrifuged and the cake obtained was dried at 900C for a period of 12-18 hours. The resulting dried cake was ground to fine powder. The loading was analyzed by HPLC and was found to be 37% imidacloprid and 3% for hexaconazole respectively. The yield was 117 grams.
Example 15: FTIR Analysis
Figure 1 shows the FTIR spectra of hexaconazole-silica nanocomposite in the range of 1500-500 cm-1. Curve 1 is the spectrum for plain silica nanoparticles. Curve 2, 3 are spectra recorded for hexaconazole-silica samples having different loadings of hexaconazole (11% and 16% respectively). A sharp feature centered at 1095 cm-1 (feature a) is a characteristic feature of Si-O stretching vibrations and can be clearly seen in all the curves. Absence of any other band in this region indicates that there is no interaction between hexaconazole and silica matrix and the hexaconazole is merely entrapped in the pores and the silica network.
Further, increasing the loading beyond 16% leads to an increase in the hexaconazole features and masking of the silica signals. This can be seen in figure 2 A. It is important to note that hexaconazole has a mild feature around 1095 cm-1 (figure 2A, curve 3) which can also be seen for the hexaconazole-silica complex (figure 2A, curve 2). This figure clearly shows that the curve shape adopted by the hexaconazole-silica (curve 2) is a composite of hexaconazole and silica features (hexaconazole features are riding over the silica peaks). Figure 2B shows the characteristic methyl and methylene symmetric and anti-symmetric stretching modes of vibration in the region 2900-2800 cm-1 (curve 3: pure hexaconazole and curve 2: hexaconazole-silica complex). These features are clearly absent in the silica spectrum (curve 1) this further substantiates that hexaconazole is trapped in silica matrix.
FTIR analysis shows the absence of any type of chemical bond formation between silica and hexaconazole (absence of additional feature in the 1095cm-1 region)
Example 16
Theoretical calculations:
Considering spherical silica particles having size of 100 nm, the surface area of one silica nano-particle is: 4pr2 = 4 x 3.14 x (50 nm)2 = 31400 nm2 = 3.14 x 106 Å2.
Knowing the density of silica (2.2 g/cm3), the weight of 1 silica nanoparticle can be calculated:
Density= mass/volume. Volume = 4/3 pr3, where r = 500 Å; hence volume = 5.2 x 108 Å3. Converting this to cm3 (1 Å = 10-8 cm)
Hence M = (2.2 g/cm3) x (5.2 x 10-16 cm3) = 11.44 x 10-16 g.
Surface area of 1 nanoparticle = 3.14 x 106 Å2 = 3.14 x 10-14 m2.
Hence surface area per gram of nanoparticles = (3.14 x 10-14) m2/ 11.44 x 10-16)g = 27 m2/g.
It is important to note that the surface area of silica nanoparticles considering only the surface is 27 m2/g. As per the experimental BET surface area is 450 m2/g which is about 20 times the simple surface area. This clearly indicates that the silica particles are highly porous.
Now knowing the surface area of 1 nanoparticle, it can be calculated that how many hexaconazole molecules can theoretically fit on one nanoparticle surface assuming close packing.
From literature (Jyotsna Chauhan , Ashish Kumar Sharma, Gargi bhattacharya, Comparative X-Ray crystallographic studies of systemic fungicides hexaconazole and tricyclazole, Journal of Physics: Conference Series 2012, 365, 1-3; doi:10.1088/1742-6596/365/1/012012), The unit cell parameters of Hexaconozole are a=10. 9068(7) Å, b=10.9895(7) Å c=13.6124(8) Å, a=90o, ß=106.554(2)o, ?=90.000(5)o. The Crystal system is Monoclinic. As shown in the scheme figure 3, the projected area of the rectangular block can either be a x b or a x c (either the structure can lie flat on the silica surface or vertical on the silica surface as shown in the figure 3)
Hence the projected area is either 118 Å2 or 148 Å2. For maximum packing, consider projected area as 118 Å2.
Total number of hexaconazole molecules per silica particle = 3.14 x 106 Å2 / 118 Å2 = 26610.
Knowing the weight of 1 silica nanoparticle (11.44 x 10-16 g), it can calculated that total number of nanoparticles in 1 gram of silica sample to be = 0.0874 x 1016.
Now, one nanoparticle surface can be occupied by 26610 hexaconazole molecules; hence in 0.0874 x 1016 nanoparticles (i.e. 1 gram of nanoparticles) will have a total of 2327 x 1016 hexaconazole molecules.
Weight of this hexaconazole can be determined by calculations:
Molecular weight of hexaconazole = 213 g which contains Avogadro number of hexaconazole molecules (6.023 x 1023 molecules). Hence the weight of 2327 x 1016 hexaconazole molecules is 0.00822 grams.
Hence 1 gram of silica nanoparticles can have a maximum of 0.0082 grams of hexaconazole. In terms of percent, this translates to 0.82%.
Typically, in the present disclosure, the loadings are quite high (more particularly 23%) and hence, the surface adsorption, if any, can have only 0.82% loading and the rest is all entrapped inside the silica particles.
Number of hexaconazole moloecules theoretically fit in silica particles having surface area of 450 m2/g can also be calculated.
Surface area of 1 hexaconazole molecule = 118 Å2 = 118 x 10-20 m2. Hence 3.81 1020 hexaconazole molecules will fit in 450 m2 area, which as per molecular weight and Avogadro number, translates to 0.134 grams of hexaconazole per 1 gram of silica. This means that the loading is 13%. If surface is also taken into consideration, the maximum loading of entrapment + adsorption ~ 14%.
Now, since the total loading that can be achieved is up to 63%, the only possible structure would be a pesticide-silica complex in which the pesticide is linked by Si-O-Si network in the form of pesticide-silicate nanocomposite. The probable structure is shown in figure 4.
Theoretical calculations indicate that the hexaconazole is not merely adsorbed on the silica surface but is entrapped within the silica matrix.
SPECIFIC EMBODIMENTS ARE DISCRIBED BELOW
A crop protection formulation comprising porous silica nanoparticles and at least one pesticide, wherein the pesticide is entrapped within pores of the silica nanoparticles and the formulation has pesticide loading of at least 0.5% (w/w).
Such formulation(s) is a nanocomposite.
Such formulation(s), wherein the pesticide loading is in a range of 0.5% to 63% (w/w).
Such formulation(s), wherein silica nanoparticles have particle size in a range of 10 nm to 1000 nm.
Such formulation(s), wherein the pesticide is selected from one or more fungicide, insecticide, herbicide or a combination thereof.
FURTHER SPECIFIC EMBODIMENTS ARE DISCRIBED BELOW
A method of preparing a crop protection formulation comprising dispersing at least one pesticide in an aqueous solution of sodium silicate to obtain a precursor solution; adding sulfuric acid-surfactant mixture to the precursor solution to obtain porous silica nanoparticles entrapping at least one pesticide within its pores; and separating porous silica nanoparticles entrapping at least one pesticide within its pores, from the solution obtained in the previous step.
Such method(s), wherein the aqueous solution of sodium silicate is in a concentration range of 7-14% (w/v).
Such method(s), wherein the sulfuric acid-surfactant mixture comprises a surfactant selected from lignin, gelatin, octylamine, chitosan, dioctyl sulfosuccinate sodium salt (AOT) and combinations thereof.
Such method(s), wherein the sulfuric acid-surfactant mixture comprises surfactant in a concentration range of 1-5% (w/w).
Such method(s), wherein the sulfuric acid-surfactant mixture comprises sulfuric acid in a concentration range of 1.0 M – 5 M.
Such method(s), wherein addition of sulfuric acid-surfactant mixture to the precursor solution is carried out to facilitate gel formation followed by addition of water to liquefy the gel and subsequent addition of sulfuric acid-surfactant mixture to the liquefied gel till neutralization.
Such method(s), wherein addition of sulfuric acid-surfactant mixture to the precursor solution is carried out at a rate of 5 mL/min to 100 mL/min.
Such method(s), wherein the separation of porous silica nanoparticles entrapping at least one pesticide within its pores is carried out by centrifugation or filtration.
Such method(s), further comprising drying the separated porous silica nanoparticles entrapping at least one pesticide within its pores at a temperature of 60 ºC – 90 ºC.
Such method(s), further comprising grinding or milling to obtain a fine powder of porous silica nanoparticles entrapping at least one pesticide within its pores.
INDUSTRIAL APPLICABILITY
The present disclosure provides a cost effective and an efficient crop protection formulation comprising porous silica nanoparticles and at least one pesticide entrapped within its porous structure. The crop protection formulation is a nanocomposite. Due to its nano-sized dimensions, the crop protection formulation are absorbed better by the plant tissues and thus provide improved crop protection against pests without the need of frequent re-applications. This reduces the environmental pollution and economical load on farmers. The disclosed crop protection formulation includes a combination of pesticides entrapped within the pores of the silica nanoparticles. Such combination of pesticides prevents or delays development of resistance to pesticides among pests.
The present disclosure also provides a method of preparing said crop protection formulation. The method is easy to perform and economical.