FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICA TION
(See section 10, rule 13)
1. Title of the invention
A PROCESS FOR SYNTHESIS OF MESOPOROUS NANO SILICON DIOXIDE PARTICLES
2. Applicant(s)
Name Nationality Address
TATA CHEM ECALS LTD. INDIA BOMBAY HOUS E, 24 MODI STREET, MUMBAI- 400001
3. Preamble to the description
COMPLETE SPECIFICA TION
The following specification particularly describes the invention and the manner in which it is
to be performed.

The disclosure relates a process for the manufacture of mesoporous nano silicon dioxide (Si02). More particularly the disclosure relates to a process for the manufacture of mesoporous nano silicon dioxide from rice husk.
BACKGROUND
Nano silicon dioxide has a potential of extensive use in a wide range of commercial applications. Nano silicon dioxide is a multi-functional ceramic material that is being used in rubber, food, health care, paper, paints, batteries, ceramics and refractories, coatings, chemical mechanical planarization, automobiles and electronics industries. It is used as a scratch-resistance, abrasion resistance, hydrophobic and self-cleaning coating. It is also used as a flame retardant material in paints, flame retardant material for polymer (PET, PBT, PP etc) and as polymer nancomposites.
A material containing pores with diameters in the range of 2 and 50 nanometers are known as mesoporoes material. Mesoporous nano silicon dioxide particles find use in a number of applications. They are used as catalysts, for drug delivery and in imaging.
Mesoporous nano silicon dioxide particles may be synthesized by reacting tetraethyl orthosilicate with a template made of micellar rods. This results in nano-sized spheres or rods of silicon dioxide that are filled with a regular arrangement of pores. The template is then removed by washing with a solvent adjusted to the proper pH.
Another method for synthesis of mesoporous nano silicon dioxide particles involves the simultaneous hydrolytic condensation of tetraorthosilicate to form silica and polymerization of styrene into polystyrene. An amino acid catalyst, octane hydrophobic-supporting reaction component, and cetyltrimethylammonium bromide surfactant are used in the preparation process. The final step in the method involves removal of the organic components by calcinations, yielding the mesoporous silica particles.

Such methods for production of mesoporus nano silicon dioxide particles require complicated steps such as calcinations for removal of surfactants. Moreover, the processes use expensive raw materials for the production of mesoporus nano silicon dioxide particles.
The production of rice, one of the significant food crops in India, generates a major waste, namely, rice husk (RH). Efforts to utilize rice husk has been handicapped by their tough, woody, abrasive nature; low nutritive properties; resistance to degradation; great bulk; and high ash content. Most of the husk obtained from milling is either burnt or dumped as waste in open fields. Only a small amount is used as fuel for boilers, for electricity generation, and as bulking agents for composting of animal manure. Little advantage is taken of the rice husk and pollution is caused in such disposal processes. Rice husk mainly contains lignin, cellulose, and hydrated silica (-20 wt %). It is also to be noted that every tonne of paddy produces about 0.20 tonne of husk and every tonne of husk produces about -0.20 tonne of ash. Rice husk ash (RHA) that is obtained by combustion of rice husk is a silica rich raw material containing approximately 80 percent to 95 percent of silica.
There is a need for a process that would allow for the production of mesoporous nano silicon dioxide from rice husk. The process should be simple and efficient and allow the utilisation of rice husk as a raw material for the production of mesoporous nano silicon dioxide.
SUMMARY
The disclosure relates to a process for the manufacture of mesoporous nano silicon dioxide. The process includes reacting rice husk ash with an alkali metal hydroxide to obtain a silicate solution and precipitating mesoporous nano silicon dioxide particles by adding an acid to the silicate solution in the presence of a stabilizing agent, wherein the stabilizing agent is any one of octyl amine or L.lysine.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
The accompanying drawings illustrate the preferred embodiments of the invention and together with the following detailed description serves to explain the principles of the invention.
Figure 1 illustrates the particle size distribution by intensity from rice husk ash using 7% Octyl amine synthesised in accordance with an aspect.
Figure 2 illustrates the particle size distribution by number from rice husk ash using 7% Octyl amine synthesised in accordance with an aspect.
Figure 3 is a scanning electron microscopy analysis of mesoporous nano silicon dioxide particles synthesized from rice husk ash using 7% Octyl amine
Figure 4 is a transmission electron microscopy analysis of mesoporous nano silicon dioxide particles synthesized from rice husk ash using 7% Octyl amine
DETAILED DISCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the 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 illustrated process, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
Reference throughout this specification to "one embodiment" "an embodiment" or similar language means that a particular feature, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. 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.
A process for the manufacture of mesoporous nano silicon dioxide is disclosed. More particularly a process for the manufacture of mesorporous nano silicon dioxide from rice husk is disclosed.
The process comprises of a preparing a silicate solution by reacting rice husk ash with an alkali metal hydroxide. To the silicate solution thus obtained, acid is added to obtain precipitates of mesoporous nano silicon dioxide. The acid is added to the silicate solution in the presence of a stabilizing agent, wherein the stabilizing agent is any one of octyl amine or lysine.
The process for the manufacture of mesoporous nano silicon dioxide particles comprises of first preparing a silicate solution from rice husk ash by reacting rice husk ash with an alkali metal hydroxide. The rice husk ash used may be any rice husk ash that is produced by burning rice husk. The rice husk ash may be produced by burning rice husk in heaps, in a step grate furnace, fluidized bed furnace or tube-in-basket (TiB) burner. The rice husk ash may also be obtained from boilers and brick kiln, provided it is free of unburned husk and wood tar, grit, stone, and fused lumps of silica.
The rice husk ash is washed prior to reacting it with the alkali metal hydroxide to remove any impurity or unburned matter from the rice husk ash. In accordance with an aspect, the rice husk ash is soaked in water and then boiled. The rice husk ash may be soaked for a period in the range of 15 minutes to 2 hours and boiled for a period in the range of 15 minutes to 2 hours. Water is then separated from the washed rice husk ash. Water may be separated by any known method including but not limited to decanting, filtration or centrifugation.

The washed rice husk ash is reacted with an alkali metal hydroxide to obtain a silicate solution. In accordance with an aspect, to obtain the silicate solution rice husk ash and the alkali metal hydroxide are mixed, the mixture is then heated and the heated mixture is soaked for a predetermined period of time. The mixture may be heated at a temperature of 100°C for a period of 30 minutes to 2 hours. The heated mixture may be soaked for a period preferably in the range of 6 hours to 24 hours. In accordance with an aspect the alkali metal hydroxide that may be added to the rice husk ash includes but is not limited to sodium hydroxide or potassium hydroxide.
To the silicate solution an acid is added in the presence of a stabilizing agent including any one of octyl amine or lysine to obtain mesoporous nano silicon dioxide particles.
The stabilizing agent may be added to the silicate solution to obtain a stabilizing agent silicate mixture. In accordance with an aspect, the stabilizing agent silicate mixture is stirred for a predefined period of time to allow for proper mixing of the stabilizing agent in the silicate solution. The stabilizing agent silicate mixture may be stirred for a period in the range of 15 minutes to 2 hours.
In accordance with an aspect, the stabilizing agent may be dissolved in a suitable solvent before adding it to the silicate solution. By way of a specific example octyl amine is dissolved in ethanol.
The acid is added to the stabilizing agent silicate mixture till the pH of the solution reduces to the range of 6.5 to 7 to precipitate mesoporous nano silicon dioxide particles. In accordance with an aspect, the acid is not added to the stabilizing agent silicate mixture as a dumping action but added in a drop wise manner till the pH of the solution reduces to the range of 6.5 to 7.

In accordance with an embodiment, the stabilizing agent may be added to the acid. In accordance with an aspect, the mixture of the stabilizing agent and acid may be stirred and heated to allow for dissolution of the stabilizing agent in the acid.
To obtain mesoporous nano silicon dioxide particles the mixture of the stabilizing agent and acid is added to the silicate solution till the pH of the solution reduces to the range of 6.5 to 7.
Alternatively, the silicate solution may also be added to the mixture of stabilizing agent and acid. The silicate solution is not added to the mixture of stabilizing agent and acid as a dumping action but added in a drop wise manner. In accordance with an embodiment, where the stabilising agent is dissolved in acid and the silicate solution added to the stabilizing agent acid solution, the pH of the solution may be increased to 6.5 to 7 by adding an alkali. In accordance with an aspect, any alkali including but not limited to ammonia, sodium hydroxide may be added to the stabilizing agent acid solution.
In accordance with an aspect 5% to 10% by volume of stabilising agent is added.
The acid may be any inorganic or organic acid including but not limited to sulphuric acid, hydrochloric acid or formic acid.
In accordance with an aspect, the precipitated nano silicon dioxide particles are separated from the reaction mixture. Precipitated nano silicon dioxide particles may be separated from the reaction mixture by any known method including but not limited to filtration, centrifugation or decanting. The precipitate may be washed to remove any alkali metal salts such as alkali metal sulphate or formate and any uncoordinated stabilizing agent from the precipitated mesoporous nano silicon dioxide powder. In accordance with an aspect, the precipitate is washed at least once with distilled water followed by washing once with hot distilled water. In accordance with an aspect the precipitate may also be washed at least once with distilled water followed by washing with ethanol.

The washed mesoporous nano silicon dioxide particles are dried. The washed mesoporous nano silicon dioxide particles may be dried under vacuum at a temperature of 70°C for 4 hours.
The mesoporous nano silicon dioxide powder thus obtained was characterize by surface area measurement, particle size and zeta potential analyzer, Fourier infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy measurements. Figure 1 illustrates the particle size distribution by intensity from rice husk ash using 7% Octyl amine synthesised in accordance with an aspect. Figure 2 illustrates the particle size distribution by number from rice husk ash using 7% Octyl amine synthesised in accordance with an aspect. Figure 3 is a scanning electron microscopy analysis of mesoporous nano silicon dioxide particles synthesized from rice husk ash using 7% Octyl amine. Figure 4 is a transmission electron microscopy analysis of mesoporous nano silicon dioxide particles synthesized from rice husk ash using 7% Octyl amine. By way of a specific example the size of the mesoporous nano silicon dioxide particles obtained are in range of 40 to 100 nanometers.
Specific Embodiments:
A process for the manufacture of mesoporous nano silicon dioxide comprising reacting rice husk ash with an alkali metal hydroxide to obtain a silicate solution; and precipitating mesoporous nano silicon dioxide particles by adding an acid to the silicate solution in the presence of a stabilizing agent, wherein the stabilizing agent is any one of octyl amine or L.lysine.
Such process(s) wherein the stabilizing agent is added to the silicate solution to obtain a stabilizing agent silicate mixture and acid is added to the stabilizing agent silicate mixture.
Such process(s), wherein the acid is added till the pH of the solution reduces to the range of 6.5 to 7.

Such process(s), wherein the stabilizing agent is added to the acid to obtain a stabilizing agent acid mixture.
Such process(s), wherein the process comprises adding silicate solution to the stabilizing agent acid mixture; and increasing the pH to the range of 6.5 to 7 by adding an alkali to the solution to obtain mesoporous nano silicon dioxide particles.
Such process(s) wherein the amount of stabilising agent is in the range of 5% to 10% by volume.
Such process(s), wherein the stabilizing agent is dissolved in a solvent.
Such process(s), wherein octyl amine is dissolved in ethanol.
Such process(s), wherein the process further comprises of soaking the rice husk ash in water and boiling the soaked rice husk ash prior to reacting it with the alkali metal hydroxide.
Such process(s), wherein reacting the rice husk ash with an alkali metal hydroxide includes mixing the rice husk ash and the alkali metal hydroxide; heating the mixture for a period of 20 minutes to 2 hours; and soaking the heated mixture for a period of 6 hours to 24 hours to obtain silicate solution.
Such process(s), wherein the alkali metal hydroxide is any one of sodium hydroxide or potassium hydroxide.
Such process(s), wherein the acid is any one of sulphuric acid, hydrochloric acid or formic acid.
Such process(s), further comprising washing the precipitated mesoporous nano silicon dioxide to remove alkali metal salts and uncoordinated stabilizer; and drying the precipitate to obtain dried mesoporous nano silicon dioxide powder.
Such process(s) wherein washing includes first washing with water followed by washing with water or ethanol.

Such process(s) wherein the washed precipitate is dried at 70°C for 4 hours under vacuum.
The following examples are provided to explain and illustrate certain preferred embodiments of the process of the invention. Example 1
1 kg of rice husk ash (RHA) was washed by soaking and boiling in 10 liter of distilled water for 30 minutes. This was subjected to filtration. After filtration, the washed rice husk ash was added to 13 liter of 2.307 molar sodium hydroxide (NaOH) and boiled for 1 hour at 100 C followed by 12 hours of soaking. The slurry was filtered and the filtrate containing sodium silicate (~7%) was taken as the starting precursor solution for the mesoporous nano silicon dioxide particle synthesis.
To 1 liter of sodium silicate, a mixture of octyl amine (100 milliliter) and ethanol (100 milliliter) was added and stirred for 30 minutes. To the above solution, 1 molar sulfuric acid is added drop wise with stirring till the pH reduces to 6.5 with a visible white precipitation. The reaction mixture was allowed to settle for 1 hour before subjected to washing by centrifugation. The reaction mixture was centrifuged twice with distilled water followed by centrifugation once with absolute ethanol at 4000 rpm. The washing process by centrifugation was followed in order to remove sodium sulfate iand uncoordinated surfactant. The pellet in the centrifuge tube are separated and dried under vacuum at 70 °C for 4 hours to obtain dried mesoporous nano silicon dioxide powder. The mesoporous nano silicon dioxide powder thus obtained was characterize by surface area measurement, particle size and zeta potential analyzer, Fourier infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy measurements. Octyl amine controls the particle size in the nanometer scale, stabilizes the nano-powder and is believed to participate in the formation of mesoporous nano silicon dioxide structures.

Example 2
1 kilogram of rice husk ash (RHA) was washed by soaking and boiling in 10 liter of distilled water for 30 minutes. This was subjected to filtration. After filtration, the washed rice husk ash was added to 10 liter of 2.307 molar sodium hydroxide (NaOH) and boiled for 1 hour at 100 °C followed by 12 hours of soaking. The slurry was filtered and the filtrate containing sodium silicate (~7%) was taken as the starting precursor solution for the mesoporous nano silicon dioxide synthesis. To 1 liter of sodium silicate, 18.26 grams of L-lysine (0.1 molar) was added and stirred for 15 minutes. To the above solution, 1 molar sulfuric acid is added drop wise with stirring till the pH reduces to 6.5 with a visible white precipitation. Allow the reaction mixture for 1 hour to settle before subject it to washing by centrifugation. Centrifuge the reaction mixture three times with distilled water followed by once with absolute ethanol at 4000 rpm and 25 °C. This washing process by centrifugation was followed in order to remove sodium sulfate and uncoordinated surfactant. The pellet in the centrifuge tube is separated and dried under vacuum at 70 °C for 4 hours to obtain dried mesoporous nano silicon dioxide powder. The mesoporous nano silicon dioxide powder thus obtained was characterize by surface area measurement, particle size and zeta potential analyzer, Fourier infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy measurements.
Example 3
1 kilogram of rice husk ash (RHA) was washed by soaking and boiling in 10 liter of distilled water for 30 minutes. This was subjected to filtration. After filtration, the washed rice husk ash was added to 13 liter of 2.307 molar sodium hydroxide (NaOH) and boiled for 1 hour at 100 °C followed by 12 hours of soaking. The slurry was filtered and the filtrate containing sodium silicate (-7%) was taken as the starting precursor solution for the mesoporous nano silicon dioxide synthesis. To 1 liter of sodium silicate, a mixture of octyl

amine (20 milliliter) and ethanol (100 milliliter) was added and stirred for 30 minutes. To the above solution, 26 molar formic acid is added drop wise with stirring till the pH reduces to 6.5 with a visible white precipitation. The reaction mixture was allowed to settle for 1 hour before subjected to washing by centrifugation. The reaction mixture was centrifuged twice with distilled water followed by once with absolute ethanol at 4000 rpm. The washing process by centrifugation was followed in order to remove uncoordinated sodium formate and uncoordinated octyl amines. The pellet in the centrifuge tube is separated and dried under vacuum at 70 °C for 4 hours to obtain dried mesoporous nano silicon dioxide powder. The mesoporous nano silicon dioxide powder thus obtained was characterize by surface area measurement, particle size and zeta potential analyzer, Fourier infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscopy measurements. Octyl amine and sodium formate are responsible for the particle size control in to nanometer scale and acts as stabilizing agents to the nano-powder.
INDUSTRIAL APPLICABILITY
The process as disclosed allows for the production of mesoporous nano silicon dioxide particles from rice husk ash in a simple and efficient manner. The stabilizing agent used allows for the control of particle size of the nano silicon dioxide particles and also allows for the production of mesoporous nano silicon dioxide particles. The process is therefore a simple and continuous process that allows for the production of nano silicon dioxide particles without the need of complicated steps such as calcinations.
Moreover, the process allows for the use of rice husk, a waste product obtained from a natural renewable source for the production of mesoporous nano silicon dioxide particles.

WE CLAIM:
1. A process for the manufacture of mesoporous nano silicon dioxide comprising:
reacting rice husk ash with an alkali metal hydroxide to obtain a silicate solution; and
precipitating mesoporous nano silicon dioxide particles by adding an acid to the silicate solution in the presence of a stabilizing agent, wherein the stabilizing agent is any one of octyl amine or L.lysine.
2. A process as claimed in claim 1, wherein the stabilizing agent is added to the silicate solution to obtain a stabilizing agent silicate mixture and acid is added to the stabilizing agent silicate mixture.
3. A process as claimed in claim 2, wherein the acid is added till the pH of the solution reduces to the range of 6.5 to 7.
4. A process as claimed in claim 1, wherein the stabilizing agent is added to the acid to obtain a stabilizing agent acid mixture.
5. A process as claimed in claim 4, wherein the process comprises
adding silicate solution to the stabilizing agent acid mixture; and increasing the pH to the range of 6.5 to 7 by adding an alkali to the solution to obtain mesoporous nano silicon dioxide particles.

6. A process as claimed in any preceding claim wherein the amount of stabilising agent is in the range of 5% to 10% by volume.
7. A process as claimed in claim 1, wherein the stabilizing agent is dissolved in a solvent.
8. A process as claimed in claim 7, wherein octyl amine is dissolved in ethanol.
9. A process as claimed in claim 1, wherein the process further comprises of soaking the rice husk ash in water and boiling the soaked rice husk ash prior to reacting it with the alkali metal hydroxide.
10. A process as claimed in claim 1, wherein reacting the rice husk ash with an alkali metal hydroxide includes:
mixing the rice husk ash and the alkali metal hydroxide; heating the mixture for a period of 20 minutes to 2 hours; and soaking the heated mixture for a period of 6 hours to 24 hours to obtain silicate solution.
11. A process as claimed in claim 1 or 10, wherein the alkali metal hydroxide is any one of sodium hydroxide or potassium hydroxide.
12. A process as claimed in claim 1, wherein the acid is any one of sulphuric acid, hydrochloric acid or formic acid.

13. A process as claimed in claim 1, further comprising
washing the precipitated mesoporous nano silicon dioxide to remove alkali metal salts and uncoordinated stabilizer; and
drying the precipitate to obtain dried mesoporous nano silicon dioxide powder.
14. A process as claimed in claim 12, wherein washing includes first washing with water followed by washing with water or ethanol.
15. A process as claimed in claim 13 or 14, wherein the washed precipitate is dried at 70°C for 4 hours under vacuum.
16. A process for the manufacture of mesoporous nano silicon dioxide substantially as herein claimed with reference to and as illustrated by the accompanying figures.