Title of Invention

A LOW TEMPERATURE PROCESS FOR THE SYNTHESIS OF RUTILE TITANIUM DIOXIDE NANOPARTICLES

Abstract

A low temperature process for the preparation of rutile TiO2 nanoparticles, optionally coated with zinc oxide, said process comprises: a) treating of Titanium source in a organic solvent with a suitable surfactant/oil phase mixture to get the micro emulsion; b) treating of the said microemulsion with ammonium hydroxide; c) optional treatment of the said microemulsion with another microemulsion containing zinc salt; d) separation of the rutile TiO2 nano particle precipitate from the bulk; e) washing and drying the said precipitate.

Full Text

FORM 2 THE PATENTS ACT, 1970 [39 OF 1970] COMPLETE SPECIFICATION [See section 10, Rule 13 ;] A Low temperature process for the synthesis of rutile titanium dioxide nanoparticles ICI INDIA R & T CENTRE, P.O. Box No. 155, Thane Belapur Road, Thane-400 601, ICI INDIA LIMITED, ICI House, 34 Chowringhee Road, Calcutta-700 071 and INDIAN INSTITUTE OF TECHNOLOGY, Powal, Mumbai-400 076, India ORIGINAL 265/MUMNP/2000 GRANTED 18-5-2005 The present invention relates to a low temperature process for the preparation of rutile TiO2 nanoparticles. Titanium dioxide (T1O2) is an important non-toxic pigment used in the manufacture of many everyday substances, such as paints and cosmetics. They are also used as catalysts and sensors and also in dielectric ceramics. TiOb is unique in that it combines high refractive index with a high degree of transparency in the visible region of the spectrum. This unique combination of properties affords the coating formulators a convenient route to highly opaque and bright whites or tints at minimum film thickness, TiO2 is commercially available in two crystal structures viz. anatase and rutile. Usually, rutile TiO2 pigments are preferred over the anatase because the former scatter light about 30% more efficiently than the latter. This is because larger the difference between refractive index of the pigment and the medium in which it is dispersed greater the refractive light scattering. Further, the rutile pigments are durable, stable and more weather resistant than the anatase pigments. Traditionally, titanium dioxide pigments are prepared from the ores of titanite viz,, rutile and ilmeniteby a complex wet process involving, (a) digestion in sulfuric acid, (b) removal of Fe as FeS04 (c) concentration in vacuum evaporators, (d) precipitation of titanium hydrate, and (e) calcination, grinding and bagging. Subsequently, a flame process has also been developed. The pigment obtained by the flame process is found to be of superior quality. Also the flame process is more cost effective than the traditional wet process. In the flame process, the ore is chlorinated and the volatile is separated from if iron impurity is present in the ore. Then, the which is liquid at room temperature, is fed to a burner along with oxygen where the following reaction occurs: However, the main disadvantage of the said flame process is that the reaction takes place at about 1500°C and, therefore, special refractory lined furnaces with special designs are found to be necessary for carrying out the process. Various other methods are also known for the preparation of rutile type TiO2 nanoparticles. In most of these known methods, the precursor materials used are the costly organotitanium compounds, and the particles are formed using the sol-gel process. Usually, in most of the cases, amorphous particles of TiOh are initially formed which are then subjected to suitable heat treatment (calcination) to produce the anatase and then the rutile particles. The temperature at which this phase transition occurs is found to be dependent on the precursor material used as well as the methodology employed. According to the present invention there is provided a low temperature process for the preparation of rutile TiO2 nanoparticles, optionally coated with zinc oxide, said process comprises: a) treating of Titanium source in a organic solvent with a suitable surfactant/oil phase mixture to get the micro emulsion; b) treating of the said microemulsion with ammonium hydroxide; c) optional treatment of the said microemulsion with another microemulsion containing zinc salt; d) separation of the rutile TiO2 nano particle precipitate from the bulk; e) washing and drying the said precipitate. An object of the present invention is to directly prepare rutile TiC>2 nanoparticles at a low temperature, preferably at or near room temperature, and we have been able to achieve this by employing a microemulsion route. Previous attempts at room temperature to directly synthesis titanium dioxide nanoparticles via microemulsion route were not successful, and they resulted in the formation of only amorphous particles of TiO2 which then had to be subjected to heat treatment (calcination) to undergo phase changes from amorphous to anatase and then to rutile form. Therefore, another object of the present invention is to directly obtain the rutile form at or near room temperature via microemulsion route. With these and other objects in view, the present invention provides a low temperature process for the preparation of rutile TiO2 nanoparticles, optionally coated with zinc oxide, said process comprises treating a titanium source/oil mixture with a surfactant/oil mixture followed by treatment with an aqueous ammonia solution, optionally treating the resultant microemulsion with a second microemulsion, the aqueous phase of which contains a zinc salt, and thereafter separating, washing and drying the precipitate formed. The titanium source may be titanium chloride (TiCl4) or an organo titanium compound such as titanium isopropoxide or titanium isobutoxide. The preferred titanium source is TiCl4- The organic solvent may be selected from cyclohexane, decane, octane, heptane, chloroform and aromatic or aliphatic hydrocarbons. Advantageously, anhydrous cyclohexane may be used as the oil. The surfactant may be selected from low or high HLB nonionic or ionic surfactants like nonyl phenol ethoxylates (Triton X-100), Aerosol OT (dioctyl-sulfo-succinate) and Cetyl trimethyl ammonium bromide (CTAB). A preferred surfactant is Triton X-100. The co-surfactant may be selected from the group consisting of butanol, pentanol, hexanol, decanol, dodecanol and aliphatic/aromatic alcohols and acids. A preferred co-surfactant is n-hexanol. The ammonia solution comprises an aqueous solution of NH4OH, preferably 0.2M NH4OH. The treatments may be carried out at or near room temperature. According to a preferred embodiment of the present invention, the process comprises adding a mixture of titanium tetrachloride and cyclohexane to Triton X-100/hexanol/cyclohexane mixture at ambient temperature with stirring . This is followed by addition of aqueous ammonia solution to the resultant mixture. The solution remains clear for around two days after which a white precipitate of rutile TiO2 nanoparticles is observed at the bottom. The precipitate grows with time. The precipitate formed is separated by ultracentrifugation, followed by washing with methanol and/or chloroform and drying. It has also been found that the nanoparticles of titanium dioxide so prepared can, if desired, be coated with zinc oxide particles for use in the preparation of sunscreen formulations, cosmetics, glossy white pigments, etc. This coating may be achieved by treating the microemulsion containing ammonium hydroxide with another microemulsion the acqueous phase of which contains a zinc salt, preferably zinc nitrate. The precipitated particles of TiO2 coated with zinc oxide are separated, washed, and dried. The following Examples are presented to further illustrate, but not in any way to limit, the scope of this invention. EXAMPLE I A microemulsion (ME 1) having a composition shown in following Table 1 was prepared as follows. Table 1 Step 1: 0.5 ml of TiCl4 (S.D. Fine Chemicals) was dissolved in 5ml anhydrous cyclohexane (prepared by refluxing over sodium followed by distillation) in a fuming cupboard with constant stirring. Step 2: 4.3 gms of Triton X-100 surfactant and 3 gms of n-hexanol co-surfactant were dissolved in 25ml of cyclohexane. Step 3: The resultant solution of step 1 was added slowly to the solution obtained from step 2 with constant stirring. Step 4: 2 gms of 0.2 mole aqueous NH4OH (prepared from 25% NH3-Merck) was added to the above solution (step 3). The solution was stirred for further 30 minutes. All these were carried out at room temperature (27°C). The resultant microemulslon was found to be transparent and yellow in colour. The UV-visible absorption spectra was taken for the above solution and it showed the onset of absorption at 400 nm which is characteristic of rutile nanoparticles. After about two days, a white precipitate was observed at the bottom of the glass bottle. The solution was ultracentrifuged at 10,000 r.p.m for about 10 minutes. The precipitate was washed initially with chloroform-methanol (1: 1) mixture followed by methanol and centrifuged again. The precipitate was oven dried at 80- 90°C for 3 to 4 hours before subjecting it to X-ray diffraction and thermal analysis. XRDs were taken after calcination at various temperatures (room temperature to 900°C). The XRD peaks matched with the standard peaks for rutile Ti02 (Fig. 1). Thermal analysis showed two peaks at approx. 300°C and 384°C which correspond to water molecules and organics (e.g. surfactant) present in the system (Fig.2). The XRD clearly showed the formation of a rutile phase while the thermal analysis and XRD both showed no phase changes at higher temperatures. EXAMPLE 2 The coating of zinc oxide over titanium oxide has been described in this Example. The same microemulsion (ME 1) as described in Example 1 was first prepared. Another microemulsion (ME 2) with zinc nitrate as the aqueous phase and having following composition (Table 2) was prepared in a similar manner as described in Example 1. Table 2 The microemulsion ME 1 was added to ME 2 slowly with constrant stirring. The resultant solution was transparent and yellow in colour. After about two days, a white precipitate was observed at the bottom of the glass bottle. The solution was ultracentrifuged at 10,000 r.p.m. for about 10 minutes. The precipitate was washed initially with chloroform-methanol (1:1) mixture followed by methanol and centrifuged again. The precipitate was oven dried at 80-90°C for 3 to 4 hours before subjecting to Transmission Electron Microscopy (TEM) and thermal analysis. XRDs were taken after calcination at various temperatures. The XRD clearly showed the formation of a rutile phase while thermal analysis and XRD both showed no phase changes at higher temperatures (Fig. 3). The presence of coating of ZnO was confirmed with the aid of FT-IR spectroscopy and TEM results. FT-IR showed characteristics of ZnO (431 cm and TiO2 (580 cm') peaks (Fig. 4). For TEM the particles were prepared by dispersing the particles in butanol with the aid of a sonicator. TEM micrograph showed lnm thick coating of ZnO on 200nm dia TiO2 particles (Fig. 5). A few main advantages of the present method over the methods known hitherto are: (1) It is a simple technique and does not require any extreme conditions of temperature, pressure, etc. (2) No special equipment design is needed for the synthesis of nanoparticles and the reaction can be carried out in a simple glass vessel, and (3) The method does not require any expensive chemicals. WE CLAIM: 1. A low temperature process for the preparation of rutile TiO2 nanoparticles, optionally coated with zinc oxide, said process comprises: a) treating of Titanium source in a organic solvent with a suitable surfactant/oil phase mixture to get the micro emulsion; b) treating of the said microemulsion with ammonium hydroxide; c) optional treatment of the said microemulsion with another microemulsion containing zinc salt; d) separation of the rutile TiO2 nano particle precipitate from the bulk; e) washing and drying the said precipitate. 2. A process as claimed in claim 1, wherein said titanium source is titanium chloride (TiCl4). 3. A process as claimed in claim 1, wherein said titanium source is an organo titanium compound such as titanium isopropoxide and titanium isobutoxide. 4. A process as claimed in any of the preceding claims 1 to 3, wherein said organic solvent is selected from cyclohexane, decane, octane, heptane, chloroform, and aromatic or aliphatic hydrocarbons. 5. A process as claimed in any of the preceding claims 1 to 4, wherein said surfactant is selected from low or high HLB nonionic or ionic surfactants like nonyl phenol ethoxylates Triton X-100, Aerosol OT (dioctyl-sulfo-succinate) and Cetyl trimethyl ammonium bromide (CTAB). 6. A process as claimed in any of the preceding claims 1 to 5, wherein said surfactant includes a co-surfactant selected from the group consisting of butanol, pentanol, hexanol, decanol, dodecanol, and aliphatic/aromatic alcohols and acids. 7. A process as claimed in any of the preceding claims 1 to 6, wherein said titanium source/oil mixture comprises TiCl4 dissolved in anhydrons cyclohexane. 8. A process as claimed in claim 7, wherein TiCl4 and cyclohexane are admixed in a ratio from 1:100 to 1:2 by volume. 9. A process as claimed in claim 8, wherein said ratio is 1:10 by volume. 10. A process as claimed in any of the preceding claims 1 to 9, wherein said surfactant/oil mixture comprises Triton X-100 dissolved in cyclohexane. 11. A process as claimed in claim 10, wherein n-hexanol is added as a co-surfactant. 12. A process as claimed in claim 11, wherein Triton X-100, n-hexanol and cyclohexane are admixed in a ratio ranging from 1:1:5 to 2 : 1 :10 by weight. 13. A process as claimed in any of the preceding claims 1 to 12, wherein said titanium source/oil mixture is slowly added to said surfactant/oil mixture with constant stirring. 14. A process as claimed in any of the preceding claims 1 to 13, wherein said ammonia solution comprises an aqueous solution of NH4OH, preferably 0.2M NH4OH. 15. A process as claimed in claim 14, wherein said aqueous NH4OH is added to said mixture of titanium source, surfactant, co-surfactant and oil under stirring and the stirring is continued for about 30 minutes. 16. A process as claimed in any of the preceding claims 1 to 15, wherein said second microemulsion comprises oil, surfactant, co-surfactant and an aqueous phase containing zinc nitrate. 17. A process as claimed in claim 16, wherein said oil, surfactant, co-surfactant and aqueous phase are in the ratio ranging from 0.5 : 1 : 1:2 to 0.5 :1 :1 : 5 by weight. 18. A process as claimed in claim 17, wherein said ratio is 8:19:15:58. 19. A process as claimed in any of the preceding claims 1 to 18, wherein said first microemulsion is added slowly to said second microemulsion with constant stirring. 20. A process as claimed in any of the preceding claims 1 to 19, wherein said washing of the precipitate is carried out with methanol and/or chloroform. 21. A process as claimed in any of the preceding claims 1 to 20, wherein the treatment are carried out at or near room temperature. 22. A process as claimed in any of the preceding claims 1 to 21, wherein said drying of the precipitate is carried out at 80-90°C for 3 to 4 hours. 23. A process as claimed in any of the preceding claims 1 to 22, wherein said washing of the precipitate is carried out with methanol and/or chloroform. 24. A low temperature process for the preparation of rutile TiO2 nanoparticles, optionally coated with zinc oxide, substantially as herein described and exemplified. Dated this 23rd day of March, 2000. [RITUSHKA NEGI] OF REMFRY & SAGAR ATTORNEY FOR THE APPLICANTS.

Documents:

265-MUM-2000-CANCELLED PAGES(1-6-2005).pdf

265-mum-2000-cancelled pages(18-05-2005).pdf

265-MUM-2000-CLAIMS(24-3-2000).pdf

265-MUM-2000-CLAIMS(GRANTED)-(16-5-2007).pdf

265-mum-2000-claims(granted)-(18-05-2005).doc

265-mum-2000-claims(granted)-(18-05-2005).pdf

265-mum-2000-correspondence(31-04-2006).pdf

265-MUM-2000-CORRESPONDENCE(31-4-2006).pdf

265-mum-2000-correspondence(ipo)-(13-02-2007).pdf

265-MUM-2000-CORRESPONDENCE(IPO)-(18-7-2007).pdf

265-MUM-2000-DESCRIPTION(COMPLETE)-(24-3-2000).pdf

265-MUM-2000-DESCRIPTION(GRANTED)-(16-5-2007).pdf

265-mum-2000-drawing(18-05-2005).pdf

265-MUM-2000-DRAWING(24-3-2000).pdf

265-MUM-2000-DRAWING(29-1-2001).pdf

265-MUM-2000-DRAWING(GRANTED)-(16-5-2007).pdf

265-mum-2000-form 1(24-03-2000).pdf

265-mum-2000-form 13(18-05-2005).pdf

265-mum-2000-form 19(20-04-2004).pdf

265-MUM-2000-FORM 2(COMPLETE)-(24-3-2000).pdf

265-MUM-2000-FORM 2(GRANTED)-(16-5-2007).pdf

265-mum-2000-form 2(granted)-(18-05-2005).doc

265-mum-2000-form 2(granted)-(18-05-2005).pdf

265-MUM-2000-FORM 2(TITLE PAGE)-(COMPLETE)-(24-3-2000).pdf

265-MUM-2000-FORM 2(TITLE PAGE)-(GRANTED)-(16-5-2007).pdf

265-mum-2000-form 3(24-03-2000).pdf

265-mum-2000-power of authority(24-03-2000).pdf

265-mum-2000-power of authority(31-05-2005).pdf

265-MUM-2000-SPECIFICATION(AMENDED)-(1-6-2005).pdf

265-MUM-2000-SPECIFICATION(AMENDED)-(18-5-2005).pdf

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