Title of Invention

"PROCESS FOR SIMULTANEOUS PREPARATION OF NANOCRYSTALLINE TITANIUM DIOXIDE AND HYDRAZINE MONOHYDROCHLORIDE"

Abstract The present invention relates to an environmentally benign process for the simultaneous preparation of nanocrystalline anatase titanium dioxide and hydrazine monohydrochloride. The process involves reacting an aqueous solution of titanium tetrachloride taken in concentrated hydrochloric acid with hydrazine monohydrate under constant stirring at ambient temperature and pressure. The reaction is carried out at ambient reaction conditions under nitrogen atmosphere in a single step without any subsequent heat treatment. The reaction condition is 20-40°C and pressure around 1 atmosphere. The byproduct hydrazine monohydrochloride was recovered by freeze drying the filtrate and washings at -40°C. The nanocrystalline anatase titanium dioxide powder is having particle size in the range of 1 to 5 nm
Full Text FIELD OF THE INVENTION
The present invention relates to an environmentally benign process for the simultaneous preparation of nanocrystalline anatase titanium dioxide and hydrazine monohydrochloride. In particular, the present invention relates to a process for the preparation of nanocrystalline anatase titanium dioxide and hydrazine monohydrochloride by reacting an aqueous solution of titanium tetrachloride taken in concentrated hydrochloric acid with hydrazine monohydrate under constant stirring at ambient temperature and pressure.
BACKGROUND OF THE INVENTION
Anatase titanium dioxide which is usually used as a photocatalyst removing environmental pollutants, as pigment material, additives for plastic product or for optical multi-coating reagent. Titanium dioxide has mainly three polymorphic forms of crystalline structure, that is anatase, brookite and rutile. The performance of titanium dioxide in various applications depends on its crystalline phase state, dimensions and morphology. Titanium dioxide with anatase phase has been used as a photocatalyst in different organic reactions. It is also used in photovolatics because of its high photoactivity. Titanium dioxide shows different electrical characteristics according to the oxygen partial pressure since it has wide chemical stability and non-stoichiometric phase region. Because of this it can also be used as a humidity sensor. Impact of nanostructure on the properties of high surface area materials is an area of increasing importance for understanding, creating and improving materials for diverse applications. The synthesis of nanoparticles with controlled size and composition is of technological interest. Reference may be made to the chloride process commercialized by Du Pont in USA in 1956 for preparation of titanium dioxide powders by the chloride process wherein titanium tetrachloride vigorously reacted with air undergoing hydrolysis at 1000°C. The inherent disadvantage of the process is the use of high temperature and costly equipments to control the reactant mixing ratios and less control on the particle shape and size. Reference may be made to the sulfate process which was industrialized Titan company in Norway in 1916 wherein titanium sulfate is conventionally hydrolyzed at temperatures higher than 95°C. The disadvantage is the post calcination at 800-1000°C to obtain the titanium dioxide powder.
The other chemical methods to obtain titanium dioxide powders include (a) hydrolysis with ammonium hydroxide solution (b) sol-gel method (c) hydrothermal synthesis (d)hydrodynamic cavitation etc.
The hydrolysis method suffers from the limitation that it necessitates a post-calcination of the precipitates of hydroxides to obtain the respective oxides. Reference may be made to U.S. Pat. No. 5,030,439 wherein a method is described to prepare particulate anatase titanium dioxide by reacting titanium tetrahalide with sulfuric acid at 65-100°C to first form titanyl sulfate which is subsequently crystallized then re-dissolved in water and hydrolyzed at 85-100°C to form titanium dioxide. The inherent disadvantage is that it is a two step process requiring subsequent heat treatment. The conventional sol-gel method involves metal alkoxides which requires tight control of reaction conditions since alkoxides are intensely hydrolyzed in air. Furthermore, the high price of alkoxides limits the commercialization of this process. Reference may be made to JP 9-124, 320 wherein the gel was formed by adding water to titanium tetrachloride dissolved in alcohol together with various kinds of acetates, oxalates and citrates containing alkali metals or alkaline earth metals. The inherent disadvantage is the use of expensive additives such as organic acids and needs a high temperature treatment after gel formation.
The hydrothermal synthesis needs high temperature and pressure conditions and hence requires the use of an autoclave. All the above wet chemical routes however involve a heat treatment either during the processing or as a post-calcination step. Reference may be made to the work of Bruno (USP 5973175, 1999) wherein titanium dioxide is prepared from amino titanium oxalate precursor by hydrothermal process. Reference may be made to U.S. Pat. No. 4,954,476 wherein a method to prepare a catalyst containing titanium dioxide as a primary ingredient in a hydrothermal process with meta- or ortho-titanic acid as starting material has been described. The inherent disadvantage of all the processes is the high temperature and pressure requirement. Reference may also be made to U.S. Pat. No. 3,242,557 wherein a process is described to prepare pigmentary titanium dioxide by hydrothermal precipitation. The inherent disadvantage is that during the reaction, the reaction mixture is subjected to ultrasonic vibrations.
Attempts to synthesize nano-particles of oxides in particular include the above said chemical routes. But the inherent disadvantages are in controlling the agglomeration
and particle growth, which is mainly caused because of the involved heat treatment. Attempts to use hydrazine hydrate are concentrated in obtaining metal nano-particles like Silver where hydrazine hydrate is used as a strong reducing agent. Reference may be made to the work ofPileni et al J. Phys. Chem. 1993, 97, 12974, wherein silver nano-particles were prepared by reducing silver sulfosuccinate solution by hydrazine hydrate.
Hydrazine monohydrate has been used earlier to synthesize oxides like ferrites where hydrazine is used to form an intermediate which decomposes by self-ignition or self propagating high temperature synthesis to obtain the ultra fine powders of ferrites. In this context, reference may be made to the publications of Ravindranathan et. al J. Mat, Sci., 1986, 5, 221, wherein v-ferric oxide was prepared by thermal decomposition of hydrazine precursors in air around 200°C. Also reference may be made to the work by Suresh et. al. J. Thermal Anal., 1989, 35, 1137 wherein Magnesium ferrite has been prepared by the thermal decomposition of a metal oxalate hydrazinate precursor. Reference may also be made to the work of Madhusudan Reddy et al, (J. Solid Slate Chem., 2001, 158, 180 & Mater. Chem. Phys., 2002, 78, 239) wherein hydrazine monohydrate is used with titanium tetrachloride to obtain anatase titanium dioxide nano-particles with 5-15nm. The inherent disadvantage is that the precipitate was air dried at 80-100°C followed by heat treatment at 300-400°C.
The main difference in the procedure adopted by Madhusudan Reddy et al. (J. Solid State Chem., 2001,158,180 and Mater. Chem Phys., 2002, 78, 239) and the present invention for the synthesis of nano-particles of anatase titanium dioxide are the following.
1. Madhusudan Reddy et al obtained the crystalline nano-particles only after air
drying the samples at 80-100 °C and then calcining at 300-400 °C.
2. The Applicants' present conditions of temperature i.e., 20-40 °C and pressure
around 1 atmosphere, and carrying out the reaction under nitrogen
atmosphere; all of them result in nano-particles of anatase titanium dioxide
unambiguously less than 5 nm; crystalline in nature with no heat treatment and
calcinations.
Hydrazine monohydrochloride is a salt, which is obtained dissolved in the reaction
medium, i.e., water. Freeze drying of the solution gives the salt in powder form. It is a deliquescent material hence the particle size cannot be obtained. However from XRD, the crystallite size can be estimated to be in the range of 15-20 nm. The present invention discloses the preparation of nano-crystalline anatase titanium dioxide powder of particle size less than 5nm reacting acidic aqueous titanium
i
tetrachloride solution with hydrazine monohydrate at ambient reaction conditions in a
single step without any subsequent heat treatment.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a convenient process for the
preparation of nano-crystalline anatase titanium dioxide of particle size less than 1 to
5nm in a single step process, which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a process for the preparation of
nano-crystalline anatase titanium dioxide powder at ambient conditions.
Yet another object of the present invention is to provide a process for the preparation
of nano-crystalline anatase titanium dioxide powder without subjecting the reaction
mixture to any heat treatment so as to prevent agglomeration.
SUMMARY OF THE INVENTION
The present invention relates to a process for the simultaneous preparation of the
nanocrystalline anatase titanium dioxide powder having particle size in the range of 1
to 5 nm and hydrazine monohydrochloride, said process comprising the steps of:
a) adding hydrazine monohydrate solution drop wise to acidic aqueous solution of
titanium tetra chloride at temperature in the range of 20 to 45 °C with constant stirring
to form precipitate,
b) filtering the precipitate of step (a) to obtain titanium dioxide having particle size in
the range of 1 to 5 nm and optionally freeze drying and washing the filtrate to obtain
hydrazine monohydrochloride.
The novelty in the present invention is highlighted by the mechanism proposed for the
formation of anatase titanium dioxide nanoparticles at room temperature from acidic
aqueous titanium tetrachloride and hydrazine monohydrate. Hydrazine is a high
energy compound having a positive heat of formation implying a high activity. The
complete chemical equation for the process is formulated as:
TiCl4 + HC1 +5N2H4.H2O-> TiO2 + 5N2H4HC1 + 3H2O
Thermodynamic calculations for the Gibb's free energy (AG°) and heat of reaction
(AH°) for the above equation have been found to be negative. The former indicates that the reaction is thermodynamically favorable and the latter suggesting the reaction is exothermic. It is this exothermicity which is responsible for the formation of anatase titanium dioxide nanoparticles at room temperature via a hydrazine complex formation. Since the reaction is instantaneous there is no noticeable increase in temperature of the reaction mixture. On the basis of the above equation, gravimetric analysis of the reactants and products gives a complete material balance with the mismatch of theoretical and practical yield less than 5% which justifies the technique to be termed as a 'green route'.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows Electron Diffraction Pattern of anatase titanium dioxide nanoparticles of size less than 3 nm.
Figure 2 depicts Transmission Electron Microscope (TEM) patterns of anatase titanium dioxide nano-particles.
Figure 3 depicts FT-IR of anatase titanium dioxide nano-particles.
Figure 4 shows Transmission Electron Microscope (TEM) patterns of anatase titanium dioxide nano-particles of size less than 5 nm.
Figure 5 shows Transmission Electron Microscope (TEM) patterns of anatase titanium dioxide nano-particles of size less than 6 nm.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, the present invention provides an environmentally benign process for the simultaneous preparation of the nanocrystalline anatase titanium dioxide powder and hydrazine monohydrochloride, said process comprising the steps of:
a) adding hydrazine monohydrate solution containing hydrazine monohydrate in the
range of 10 to 99% v/v drop wise to acidic aqueous solution of titanium tetra
chloride containing TiCl4 in the range of 5 to 40% v/v at temperature in the range
of 20 to 45 °C with constant stirring to form precipitate,
b) filtering the precipitate of step (a) to obtain titanium dioxide having particle size
in the range of 1 to 5 nm and optionally freeze drying and washing the filtrate to
obtain hydrazine monohydrochloride.
Yet another embodiment of the present invention, wherein in step (a) acidic aqueous
solution of titanium tetrachloride contains TiCl4 is in the range of 5 to 40% v/v
Yet another embodiment of the present invention wherein in step (a), hydrazine
monohydrate solution contains hydrazine monohydrate in the range of 10 to 99% v/v.
Yet another embodiment of the present invention wherein in step (a), hydrazine
monohydrate solution contains 99% v/v hydrazine monohydrate. Yet another embodiment of the present invention wherein, the temperature is in the range of 20 to 40 °C. Yet another embodiment of the present invention wherein in step (a), pH of the mixture of hydrazine monohydrate solution and acidic aqueous solution of titanium
tetrachloride is in the range of 7 to 8.
Yet another embodiment of the present invention wherein step (a), is carried out in
nitrogen atmosphere.
Yet another embodiment of the present invention, wherein the anatase titanium
dioxide nano-particles having BET surface area in the range of 200 -250 m2/gm are
obtained.
Yet another embodiment of the present invention wherein hydrazine
monohydrochloride are obtained by freeze drying the filtrate, and washing the filtrate
with water at a temperature in the range of-60 to -40°C.
Yet another embodiment of the present invention, the yield of anatase titanium
dioxide and hydrazine monohydrochloride is above 95%.
Yet another embodiment of the present invention wherein nano-crystalline anatase
titanium dioxide powder obtained by the said process having particle size in the range
of 1 to 5 nm.
Yet another embodiment of the present invention wherein nano-crystalline anatase
titanium dioxide powder obtained by the said process, having BET surface area of in
the range of 200 - 250 m2/gm.
The following examples are given by way of illustration and therefore should not be
construed to limit the scope of the present invention.
EXAMPLE -1 Preparation of anatase titanium dioxide nanoparticles
20% titanium tetrachloride solution was prepared in concentrated hydrochloric acid. Aqueous solution of titanium tetrachloride was then prepared by taking 2ml of the above solution in 100ml distilled water. To the above aqueous acidic solution hydrazine monohydrate (99%) was added in the range of 10 to 99% v/v dropwise under constant stirring at normal temperature 30 °C and about atm. pressure. The pH
of the solution was brought to 7 and stirred further for 30 minutes to obtain the
anatase titanium dioxide as precipitate. The titanium dioxide precipitate was filtered,
washed with distilled water for 15 times and dried at normal temperature in air. The
byproduct hydrazine monohydrochloride was recovered by freeze drying the filtrate
and washing the filtrate with water at a temperature in the range of-60 - 40°C.
The formation of anatase titanium dioxide nanoparticles was confirmed from the
selected area electron diffraction pattern (FIG 1).
The particle size for titanium dioxide was found to be less than 3nm using TEM
(FIG2 2).
The BET surface area of the as prepared anatase titanium dioxide powder was found
to be 245 m2/g.
The byproduct hydrazine monohydrochloride recovered by freeze drying the filtrate
and washings was confirmed by FT-IR[ (FIG 3).
The yield for both the product and byproduct was better than 95%.
EXAMPLE - 2
Preparation of anatase titanium dioxide nanoparticles
50% titanium tetrachloride solution was prepared in concentrated hydrochloric acid. Aqueous solution of titanium tetrachloride was then prepared by taking 2ml of the above solution in 10ml distilled water. To the above aqueous solution hydrazine monohydrate (99%) was added dropwise under constant stirring at 25 °C and about 1 atm. pressure. The pH of the solution was brought to 8 to obtain the anatase titanium dioxide as precipitate. The titanium dioxide precipitate was filtered, washed with distilled water for 10 times and dried at normal temperature in air. The byproduct; hydrazine monohydrochloride was recovered by freeze drying the filtrate and washings at -40°C. The yield for both the product and byproduct was better than 95%.
The particle size for titanium dioxide was found to be less than 5 nm from TEM
image (FIG 4).
The BET surface area of the as prepared anatase titanium dioxide powder was found
tobe210m2/g.
EXAMPLE-3
Preparation of anatase titanium dioxide nanoparticles 20% titanium tetrachloride solution was prepared in concentrated hydrochloric acid.
Aqueous solution of titanium tetrachloride was then prepared by taking 1ml of the
above solution in 10ml distilled water in a round-bottom flask and degassed for 30
minutes by nitrogen purging. To the above aqueous solution hydrazine monohydrate
(99%) was added dropwise under nitrogen atmosphere and constant stirring at 30°C
and about 1 atm pressure. pH of the solution was brought to 7 to obtain the anatase
titanium dioxide as precipitate. The titanium dioxide precipitate was filtered,
washed with distilled water for 10 times and dried at normal temperature in air. The
byproduct hydrazine monohydrochloride was recovered by freeze drying the filtrate
and washings at -40°C.
The formation of anatase titanium dioxide nanoparticles was confirmed from the
selected area electron diffraction pattern.
The yield for both the product and byproduct was better than 95%.
The particle size for titanium dioxide was found to be less than 5nm using TEM
(FIGS)/)
The BET surface area of the anatase titanium dioxide powder was found to be
232 m2/g.
The main advantages of the present invention are:
1. It is an eco-friendly process for the preparation of nanocrystalline titanium dioxide
in substantial amounts using hydrazine monohydrate.
2. It enables preparation of titanium dioxide nanoparticles in pure anatase form.
3. It is a single step process using commercially available titanium tetrachloride and
hydrazine monohydrate without subsequent heating to higher temperatures.
4. It is suitable for large scale preparation of anatase titanium dioxide nanoparticles
for commercial exploitation.












We Claim:
1. An environmentally benign process for the simultaneous preparation of the
nanocrystalline anatase titanium dioxide powder and hydrazine
monohydrochloride, said process comprising the steps of:
a) adding hydrazine monohydrate solution containing hydrazine monohydrate in the range of 10 to 99% v/v drop wise to acidic aqueous solution of titanium tetra chloride containing TiCl4 in the range of 5 to 40% v/v at temperature in the range of 20 to 45 °C with constant stirring to form precipitate,
b) filtering the precipitate of step (a) to obtain titanium dioxide having particle size in the range of 1 to 5 nm and optionally freeze drying and washing the filtrate to obtain hydrazine monohydrochloride.

2. The process as claimed in claim 1, wherein in step (a), hydrazine monohydrate solution contains 99% v/v hydrazine monohydrate.
3. The process as claimed in claim 1, wherein, the temperature is in the range of 20 to 40°C.
4. The process as claimed in claim 1, wherein step (a), pH of the mixture of hydrazine monohydrate solution and acidic aqueous solution of titanium tetrachloride is in the range of 7 to 8.
5. The process as claimed in claim 1„ wherein step (a) is carried out in nitrogen atmosphere.
6. The process as claimed in claim 1, wherein the anatase titanium dioxide nanoparticles having BET surface area in the range of 200 -250 m2/gm are obtained.
7. The process as claimed in claim 1, wherein hydrazine monohydrochloride obtained by freeze drying the filtrate and washing the filtrate with water at a temperature in the range of-60 to -40 °C.
8. The process as claimed in claim 1, the yield of anatase titanium dioxide and hydrazine monohydrochloride is above 95%.
9. An environmentally benign process for the simultaneous preparation of the nanocrystalline anatase titanium dioxide powder and hydrazine monohydrochloride substantially as herein describe with reference to examples accompanying this specification.

Documents:

1538-DEL-2003-Abstract-(01-06-2010).pdf

1538-del-2003-abstract.pdf

1538-DEL-2003-Claims-(01-06-2010).pdf

1538-DEL-2003-Claims-(11-01-2011).pdf

1538-del-2003-claims.pdf

1538-DEL-2003-Correspondence-Others-(01-06-2010).pdf

1538-DEL-2003-Correspondence-Others-(11-01-2011).pdf

1538-DEL-2003-Correspondence-Others-(17-08-2010).pdf

1538-del-2003-correspondence-others.pdf

1538-del-2003-correspondence-po.pdf

1538-DEL-2003-Description (Complete)-(01-06-2010).pdf

1538-DEL-2003-Description (Complete)-(11-01-2011).pdf

1538-del-2003-description (complete).pdf

1538-del-2003-drawings.pdf

1538-DEL-2003-Form-1-(11-01-2011).pdf

1538-del-2003-form-1.pdf

1538-del-2003-form-18.pdf

1538-del-2003-form-2.pdf

1538-DEL-2003-Form-3-(01-06-2010).pdf

1538-del-2003-form-3.pdf

1538-DEL-2003-Petition 137-(17-08-2010).pdf


Patent Number 245756
Indian Patent Application Number 1538/DEL/2003
PG Journal Number 05/2011
Publication Date 04-Feb-2011
Grant Date 31-Jan-2011
Date of Filing 11-Dec-2003
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 SUNKARA VARDHIREDDY MANORAMA INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD-500 007, ANDHA PRADESH
2 KONGARA MADHUSUDAN REDDY INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD-500 007, ANDHA PRADESH
3 PRATYAY BASAK INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD-500 007, ANDHA PRADESH
4 CHUNDAYIL KALARICKAL NISHA INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD-500 007, ANDHA PRADESH
5 CHADA VENKATA GOPAL REDDY INDIAN INSTITUTE OF CHEMICAL TECHNOLOGY, HYDERABAD-500 007, ANDHA PRADESH
PCT International Classification Number C10B21/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA