FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention
A PROCESS FOR PREPARATION OF NANO ZINC OXIDE PARTICLES

2. Applicant(s)
Name Nationality Address
TATA CHEMICALS LIMITED INDIA BOMBAY HOUSE, 24 HOMI MODI STRELT. MUMBAI-400001


3. Preamble to the description

COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it is
to be performed.

The invention relates to a process for preparing nano particles. More particularly the invention relates to a process for the preparation of capped nano zinc oxide particles.
BACKGROUND
Zinc Oxide is used for various purposes including as a white pigment, as a catalyst, as a constituent of anti-bacterial skin protection ointment, sunscreens and wood varnishes. Zinc oxide is also known as wide band gap semiconductor and is well suited for emissive devices. Materials used for blocking UV radiation are required to be transparent to the visible part of the solar radiation while blocking the harmful UV radiation and nano zinc oxide is considered favorable in this regard. The term 'nano' or 'nano particle' is generally used to refer to particles having a diameter of less than about lOOnm.
Though numerous processes are known for the synthesis of nano zinc oxide particles, such processes are not scalable in an efficient manner and do not produce free flowing nano zinc oxide particle powders.
The applicants earlier filed Indian patent application no 480/MUM/2008 dated March 10th, 2008 describes a process for production of nano zinc oxide particles on a large scale. The process includes a molar reaction in which the zinc metal precursor is dissolved in a solvent to obtain a zinc metal precursor solution, a base is dissolved in an alcohol to obtain an alkali solution and the alkali solution is added to the zinc metal precursor solution for a predetermined period of time to obtain nano zinc oxide particles. Figure 1 illustrates one method of determining reaction completion. An analysis of the reaction mixture indicates that the transmittance is below 20% after approximately 360 nm. This is assumed as a 100% reaction completion.

Capped nano zinc oxide particles can also be obtained by the process by adding a capping agent to the zinc metal precursor solution prior to the addition of the alkali solution to the first solution to obtain capped nano zinc oxide particles. However, in this case it is observed that a 100% complete reaction is not achieved, as illustrated in figure 2 where it is observed that the transmittance at certain wavelengths below 360 nm is above 20% and reaches almost 50% at certain wavelengths. This indicates a partially competed reaction.
SUMMARY
The invention relates to a process for the preparation of capped nano zinc oxide particles including dissolving a zinc precursor in a solvent to obtain a first solution, adding a capping agent to the first solution, dissolving a base in an alcohol to obtain an alkali solution, and adding the alkali solution to the first solution over a predetermined period of time to obtain capped nano zinc oxide particles, wherein the quantity of the alkali solution added is at least 5% in excess to the quantity of the alkali solution required for a molar reaction.
In accordance with an aspect the quantity of the alkali solution added is between 5% to 40% in excess to the quantity of the alkali solution required for a molar reaction.
DESCRIPTION OF ACCOMPANYING DRAWINGS The accompanying drawings illustrate the preferred embodiments of the invention and together with the following detailed description serve to explain the principles of the invention.
Figure 1 illustrates the transmittance at different wavelengths of the solar spectrum for a sample of nano zinc oxide particles formed by addition of alkali solution required for a molar reaction.

Figure 2 illustrates the transmittance at different wavelengths of the solar spectrum for a sample of octylamine capped nano zinc oxide particles formed by addition of alkali solution required for a molar reaction.
Figure 3 illustrates the transmittance at different wavelengths of the solar spectrum for a sample of octylamine capped nano zinc oxide particles formed by addition of 5% excess alkali solution than that is required for a molar reaction.
Figure 4 illustrates the transmittance at different wavelengths of the solar spectrum for a sample of octylamine capped nano zinc oxide particles formed by addition of 10% excess alkali solution than that is required for a molar reaction.
DETAILED DESCRIPTION
The invention as described herein is an improvement over the applicant's earlier filed patent application no 480/MUM/2008 dated March 10th, 2008.
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment described 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 process, 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.
A method to synthesize capped nano zinc oxide particles in a single-phase organic medium is disclosed. The process in accordance with the principles of the invention involves dissolving the zinc metal precursor in a solvent to obtain a zinc

metal precursor solution, adding to the zinc metal precursor solution a capping agent, followed by the addition of a basic-alcohol solution to obtain capped nano zinc oxide particles, the quantity of basic-alcohol solution added to the metal precursor solution is in excess of the quantity required for a molar reaction.
More specifically, the process involves dissolving the zinc metal precursor in a solvent such as N,N dimethylforrnamide (DMF) to obtain a first solution, adding a capping agent to the first solution, dissolving a base in an alcohol to obtain an alkali solution, and adding the alkali solution to the first solution to obtain capped nano zinc oxide particles; the quantity of the alkali solution added to the first solution is at least 5% in excess of the quantity of the alkali solution required for a molar reaction.
The following description refers to certain specific compounds such as alcohols, bases; solvents and non solvents to explain the principles of the invention. The invention however is not restricted to such compounds as any equivalent chemical compound may be utilized to achieve the desired end result as taught by the invention.
In the following description zinc acetate dihydrate {Zn(oAc)2} has been employed as the source of zinc while the solvent employed is N,N dimethylforrnamide (DMF). The zinc acetate dihydrate is dissolved in N,N dimethylforrnamide (DMF) to obtain a first clear solution. To the first clear solution a capping agent is added. A second solution is prepared independently by dissolving sodium hydroxide (NaOH) in ethanol to get an alkali solution. The alkali solution is added to the zinc acetate solution in a controlled manner and over a predetermined period of time to ensure that only capped nano zinc oxide particles are formed. The quantity of the alkali solution added to the zinc acetate solution is at least 5% in excess of the quantity of the alkali solution required for a molar reaction.

In accordance with an embodiment the capped nano zinc oxide particles that are formed are precipitated out slowly as the reaction proceeds. In such reactions the capping agent acts as a precipitating agent as well as surface modifier.
In accordance with an alternate embodiment to precipitate or cause sedimentation of the capped nano zinc oxide particles a non-solvent such as acetone, hexane, heptane and toluene, or any similar members of their family, or any combination of them is preferably added to the reaction mixture. On the addition of the non-solvent the capped nano zinc oxide particles eventually settle down.
The quantity of alkali solution added to the zinc metal precursor solution is in excess of the quantity of alkali solution that is required for a molar reaction. In accordance with an aspect the quantity of alkali solution that is added in excess is between 5 to 40% of the quantity of alkali solution that is required for a molar reaction.
In accordance with an aspect the manner of addition of the alkali solution to the first solution is not a dumping operation, but spread over a period of time that is appropriate to dehydrate the zinc hydroxide formed after the addition of the alkali solution, such that capped nano zinc oxide particles in dispersion is obtained. In accordance with an aspect the process may be executed by adding the alkali at a rate of approximately 1 % of alkali a minute continuously, or alternatively by adding predetermined amounts of the alkali at specific intervals spread apart by a predetermined period, such as a time interval of 5 to 10 minutes and adding 5% to 10% of the alkali at each interval. Accordingly the process of addition may be spread over 50 to 100 minutes depending on the percentage of reaction completion required to get appropriate particle size and yield.
In accordance with an aspect, it is preferred that on completion of the addition of the alkali solution to the zinc acetate solution, the reaction mixture is stirred to

ensure that the reaction is complete and that all the zinc acetate is converted to capped nano zinc oxide. The formation of capped nano zinc oxide particles may be monitored by doing intermediate UV visible spectroscopy.
The base used for the preparation of the alkali solution may be any OH" or NH" group containing basic compound particularly an alkali metal one like NaOH, KOH, LiOH, tetramethylammonium hydroxide or any other member of the similar family. In accordance with an embodiment the base is sodium hydroxide.
The alcohol may be a monoalcohol or polyalcohol particularly ethanol, methanol, propanol or any other member of the alcohol family. In accordance with an embodiment the alcohol is ethanol.
Any known organic and inorganic molecules including alkylamines like octylamine, dodecylamine, hexadecylamine; polyvinyl pyrrolidone (PVP), alkanethiols, carboxylic acids, phosphines, substituted phosphines, phosphine oxides and substituted phosphine oxides may be employed for capping the nano zinc oxide particles. In accordance with an embodiment octylamine is added as a capping agent. The reactions involved in the process may be summarized as:
Zn(CH3COO)2 + 2NaOH→Zn(OH)2 + 2CH3COONa (1)
Zn(OH)2 → ZnO +H2O (2)
As shown by equation 1, zinc acetate reacts with sodium hydroxide to provide zinc hydroxide and sodium acetate. The zinc hydroxide is dehydrated to provide capped nano zinc oxide and water.

In accordance with an aspect of the invention, a process for the extraction of the capped nano zinc oxide particles at industrial scale is disclosed. The precipitation of the capped nano particles by use of capping agent and the use of non solvent for precipitation of the capped nano particles provides for a simple way to extract particles at high throughput. The process involves sedimentation followed by decantation, centrifugation and finally drying of capped nano particles over phosphorus pentaoxide in a vacuum desiccator.
In accordance with an aspect, the solution containing capped nano zinc oxide particles is transferred to a separating means to allow the capped nano zinc oxide particles to settle; removing the settled capped nano zinc oxide particles from the separating means; decanting excess solution present in the capped nano zinc oxide particles removed from the separating means; and centrifuging the capped nano zinc oxide particles.
The separating means may for example be a separating funnel. The centrifuged capped nano zinc oxide particles may be vacuum dried over phosphorus pentaoxide.
In accordance with an aspect the capped nano zinc oxide particles may also be kept as dispersion in a solvent such as DMF under refrigeration. The refrigeration temperatures may be kept preferably between 0 C to 4 C or even below.
The following examples are provided to explain and illustrate certain preferred embodiments of the process of the invention.
Example 1
219.49 grams of Zn(OAc)2 was dissolved in 2.0 L of DMF to obtain the first solution. 88 grams of NaOH was dissolved in 2.2 L of ethanol, to obtain the alkali solution. 129.25 grams of octylamine (OA) was added to the first solution. 2.1 L of the alkali solution was slowly added to the first solution in order to synthesize capped nano

zinc oxide particles. The solution turned milky white on addition of the base due to
formation and precipitation of OA capped nano zinc oxide particles. After the addition
is complete, the reaction mixture is stirred for some more time. This solution is then
transferred to separating funnels so that particles settle down. The settled particles are
removed from the funnels. The excess solvent from the removed particles is decanted
out and the remaining milky solution is centrifuged. The wet solid obtained is dried
over phosphorus pentaoxide in vacuum desiccators. Figure 3 illustrates the
transmittance at different wavelengths of the solar spectrum for a sample of octylamine
capped nano zinc oxide particles formed by addition of 5% alkali solution in excess of
the quantity of alkali solution required for a molar reaction.
Example 2
219.49 grams of Zn(OAc)2 was dissolved in 2.0 L of DMF to obtain the first
solution. 96 grams of NaOH was dissolved in 2.4 L of ethanol, to obtain the alkali
solution. 129.25 grams of octylamine (OA) was added to the first solution. 2.2 L of the
alkali solution was slowly added to the first solution in order to synthesize capped nano
zinc oxide particles. The solution turned milky white on addition of the base due to
formation and precipitation of OA capped nano zinc oxide particles. After the addition
is complete, the reaction mixture is stirred for some more time. This solution is then
transferred to separating funnels so that particles settle down. The settled particles are
removed from the funnels. The excess solvent from the removed particles is decanted
out and the remaining milky solution is centrifuged. The wet solid obtained is dried
over phosphorus pentaoxide in vacuum desiccators. Figure 4 illustrates the
transmittance at different wavelengths of the solar spectrum for a sample of octylamine
capped nano zinc oxide particles formed by addition of 10% alkali solution in excess
of the quantity of alkali solution required for a molar reaction.

INDUSTRIAL APPLICABILITY
The process as described by the invention provides for large scale production of capped nano zinc oxide particles.
The addition of excess amount of alkali solution allows the reaction to proceed to almost 100% completion and thus allows for the higher yield of capped nano zinc oxide particles.
The dissolving of the zinc metal precursor in DMF provides for significant advantages including no requirement of heating the reaction mixture, easily scalable process for high concentrations, the production of dry capped nano zinc oxide particles at high throughput and a narrow particle distribution.
The high solubility of the zinc metal precursor in DMF at room temperature allows for high production rate of capped nano zinc oxide particles.
The capped nano zinc oxide particles obtained by this process are perfectly dry powder which is a significant advantage of the process. Moreover, the final product is an odorless, white free flowing capped nano zinc oxide particle powder. UV visible spectroscopy on the final product in the dry powder form indicated that all powders are transparent to visible radiation and block the UV radiation. A TEM on the powders indicated that the particle size varies between 5 nm to 50 nm depending upon the concentration and reaction completion done.
The capped nano particles obtained by this process may alternatively be kept as a dispersion that is obtained early on in the process. The dispersion so obtained containing capped nano zinc oxide particles in solvent such as DMF is extremely stable under refrigeration. In accordance with an aspect, the dispersion may be used for applying ultra violet coatings on glass, metals and wood etc. The dispersion may be applied directly as a thin coating on glass. As the dispersion is transparent the films

applied to glass are also transparent. Thus the process of preparing the dispersion is economical and provides significant advantages in subsequent glass coating.
In accordance with an aspect, the dispersion so prepared may be transferred to a glass manufacturing facility under refrigeration or maybe prepared at the glass manufacturing facility.
Thus the simplicity of the process, particularly the absence of any heating requirements and the almost 100% completion reaction rate, allows the process to be easily scaled up to any volume.

We claim:
1. A process for the preparation of capped nano zinc oxide particles comprising
- dissolving a zinc precursor in a solvent to obtain a first solution;
- adding a capping agent to the first solution;
- dissolving a base in an alcohol to obtain an alkali solution; and
- adding the alkali solution to the first solution over a predetermined period of time to obtain capped nano zinc oxide particles; wherein
the quantity of the alkali solution added is at least 5% in excess of the quantity of the alkali solution required for a molar reaction.
2. A process as claimed in claim 1 wherein the quantity of the alkali solution added is between 5% to 40% in excess to the quantity of the alkali solution required for a molar reaction.
3. A process as claimed in claim 1 wherein the capping agent is any of alkylamines like octylamine, dodecylamine, hexadecylamine; polyvinyl pyrrolidone (PVP), alkanethiols, carboxylic acids, phosphines, substituted phosphines, phosphine oxides or substituted phosphine oxides.
4. A process as claimed in claim 1 further comprising adding a non solvent to the reaction mixture of the first solution and the alkali solution to precipitate capped nano zinc oxide particles in solution.

5. A process as claimed in claim 1 comprising transferring the solution containing capped nano zinc oxide particles to a separating means for settling the capped nano zinc oxide particles, removing the settled capped nano zinc oxide particles from the separating means and centrifuging and drying the capped nano zinc oxide particles so removed to obtain dry capped nano zinc oxide particles.
6. A process for the preparation of capped nano zinc oxide particles as claimed in claim 1 comprising

- dissolving zinc acetate dihydrate in N,N dimethyl formamide to obtain a first solution;
- adding a capping agent to the first solution;
- dissolving a base in an alcohol to obtain an alkali solution; and
- adding the alkali solution to the first solution over a predetermined period of time to obtain capped nano zinc oxide particles; wherein
the quantity of the alkali solution added is at least 5% in excess of the quantity of the alkali solution required for a molar reaction.
7. A process for the preparation of capped nano zinc oxide particles as claimed
in claim 1 comprising
- dissolving zinc acetate dihydrate in N,N dimethyl formamide to obtain a first solution;
- adding octylamine to the first solution;
- dissolving sodium hydroxide in ethanol to obtain an alkali solution;

- adding the alkali solution to the first solution over a predetermined period of time to obtain capped nano zinc oxide particles; wherein the quantity of the alkali solution added is at least 5% in excess to the quantity of the alkali solution required for a molar reaction;
- adding acetone to the solution to precipitate capped nano zinc oxide particles;
- transferring solution containing capped nano zinc oxide particles to a separating means to allow the capped nano zinc oxide particles to settle;
- removing the settled capped nano zinc oxide particles from the separating means;
- decanting excess solution present in the capped nano zinc oxide particles removed from the separating means; and
- centrifuging the capped nano zinc oxide particles.
8. A process for the preparation of capped nano zinc oxide particles substantially as herein described with reference to and as illustrated by figures 3 and 4.

Dated this 22nd day of December 2008