Title of Invention	A PROCESS FOR THE MANUFACTURE OF NANO-SIZE PURE AND DOPED BIVALENT METAL SULPHIDE POWDER
Abstract	the present invention provides a process for the manufacture of pure bivalent nanosize metal sulphide powder, such as Zn, Cd, Pb. The present invention particularly provides a process for manufacturing doped bivalent metal sulphide nanopowder with substances such as rare earth and transition metal. The powder exhibits minimum mean particle size of 10 nm. The gel powder after heating at 80 ° C produces cubic ZnS, CdS and PbS phases. Yield of powder were up to 95%.

Title of Invention

A PROCESS FOR THE MANUFACTURE OF NANO-SIZE PURE AND DOPED BIVALENT METAL SULPHIDE POWDER

Abstract

the present invention provides a process for the manufacture of pure bivalent nanosize metal sulphide powder, such as Zn, Cd, Pb. The present invention particularly provides a process for manufacturing doped bivalent metal sulphide nanopowder with substances such as rare earth and transition metal. The powder exhibits minimum mean particle size of 10 nm. The gel powder after heating at 80 ° C produces cubic ZnS, CdS and PbS phases. Yield of powder were up to 95%.

Full Text	The present invention relates to a process for the manufacture of nano-size pure and doped bivalent metal sulphide powder. This invention particularly relates to a novel method for the manufacture of bivalent metal sulphide nanopowder and doped bivalent metal sulphide nanopowder, such as pure Zn, Cd, Pb sulphide nano-size powder and Zn, Cd, Pb sulphide nano-size powder doped with rare earth and transition metals. These powders are used in various fields, such as electroluminescent materials (phosphors), infrared (ir) windows, solar cells, pigments and such other related fields. With a dispersion in a suitable matrix, they also find applications in thin film eletroluminescent (TFEL) devices. Because of the high surface area and surface energy, the physical and chemical properties of these nanometer sized particles markedly differ from those of bulk materials. The present day methods of preparing ZnS nanopowders mainly consists of solution phase reaction. Reference may be made to "Comprehensive Inorganic Chemistry Vol. 3, First edition, eds., J. C. Bailar Jr., H. J. Emeleus, Sir Ronald Nyholm, A. F. Trotman-Dickenson, (Pergamon Press Ltd., Headington HillHall, Oxford, 1973) p. 227" wherein ZnS is prepared by passing hydrogen sulphide (H2S) to a solution of Zn2+ ions buffered to pH 3, zinc sulphide is quantitatively precipitated. The product is heated in a nitrogen stream at 650°C to give the cubic zinc blende form and at 1150°C to give hexagonal wurzite. Single crystals of the cubic form may be grown hydrothermally from polycrystalline ZnS and aqueous Na2S and NaOH. The main drawbacks of the above process are: (i) Uncontrolled nucleation and subsequent growth of the precipitated particles in a bulk aqueous medium generates large particles with a wide size disribution. (ii) It requires high temperature for the preparation of ZnS particles (iii) The product of this proces contain cationic impurities Reference may also be made to Edward J. Donahue, Arlette Roxburg and Michael Yurchenko in "Materials Research Bulletin, Vol. 33, No. 2 (1998) pp 323-329" wherein ZnS is prepared through sol-gel route using organic dithiols. In this process fifty millilitres of a 10 mol% solution of zinc chloride (Fluka) in ethanedithiol (Aldrich) was prepared in an inert atmosphere glove box (Tek-Vac Model 323); the dithiol was transferred via syringe to minimize exposure. The mixture was then gently heated overnight under flowing dry argon at 65°C. All chemicals were used without purification, and the effluent from the reflux was bubbled through 0.1 M silver nitrate (Aesar) solution in order to test for the evolution of HCI. The reflux was allowed to cool, and the resultant clear sol was collected. The bubblers containing the silver nitrate were emptied, and the solution removed from them was filtered. The recovered precipitate was dried in a vacuum oven and weighed. The sol was then analyzed by TGA (Perkin-Elmer Model TGA-7) under flowing nitrogen to determine the appropriate processing temperature. Samples of the sol were then fired at 600°C under flowing argon, producing highly crystalline ZnS, as determined by X-ray. However, these samples were found by TGA to be highly contaminated with carbon. A three-step process was developed in which the samples were heated under flowing air for 10 min at 300°C to remove excess dithiol, fired at 550°C under argon for crystallization, and heated under air again at 400°C to remove any excess carbon. The effluent was bubled through nitric acid and then water while the sols were heated, effectively eliminating all unpleasant odours and allowing the work to be conducted in a fume hood. Main drawbacks of the above processes may be summarized as: (i) It requires high processing temperature for the preparation of ZnS particles; and thus giving rise to the possibility of agglomerate formation, (ii) It needs many processing steps, (iii) This process is very costly. Reference may further be made to A. R. Kortan, R. Hull, R. L. Opila, M. G. Bawendi, M. L. Steigerwald, P. J. Carroll and L. E. Brus in "J. Am. Chem. Soc. 112 (1990) pp 1327-1332" wherein a sulphide solution of zinc was made by dissolving 150 µmol of Na2S in 40 mL micellar solution (heptane solution of bis(2-ethylhexyl) sulfosuccinate, disodium salt (0.12 M) and water (0.96 M)). This solution was injected with stirring into 255 mL of "micellar solution containing 160 µL of 1 M aqueous Zn(ClO4)2. To this was added, dropwise, 70 µL of 1 M Zn(ClO4)2- Finally thiophenol (70 µL in 10 mL of heptane) was injected with stirring, immediately followed by 1 mL of pyridine. The solution became turbid at this point. A white powder obtained by filtering on a fine frit was washed three times with petrolium ether. The main drawback of the above process is the contamination of cation impurities with the generated ZnS particles. Reference may also be made to Ahmet Celikkaya and Mufit Akinc in " J. Am. Ceram. Soc. 73 (1990) pp 2360- 2365" wherein a stock solution of zinc ions was prepared by dissolving Zn(NO3)2.6H20 in deionized water and then filtering through 0.1 um cellulose nitrate membrane filters to give a final zinc ion concentration of 1.56 M. An 8.3 mL aliquot of this stock was transferred into a beaker, and nitric acid solution (0.1 N or 0.01 N) was added to bring the total volume to slightly less than 250 mL. The solution was heated to reaction temperature, the desired amount of thioacetamide (TAA) was added and the final volume was brought to 250 mL. The beaker was then immersed in a water bath at the set reaction temperature. After a certain period of aging, a bluish tint in the solution was judged to indicate the onset of precipitation. The time interval necessary to induce the change in the solution colour was recorded. Aliquot (30 mL) were collected and quenched to 15°C periodically after precipitation had started. A number of combination of experimental variables were investigated. Ageing temperature of 60°, 70° and 80°C were employed. Initial thioacetamide concentrations were varied to give [TAA]o/[Zn]0 ratios of 4, 8 and 16 for pH 1 and pH 2. Initial zinc ion concentration [Zn]0 was held constant at 0.05 M in all experiment. The main drawbacks of the above process are: (i) The particle size distribution was controlled by two competing processes, rate of sulphide ion generation and rate of growth of agglomerates, (ii) The particle size of this process is in the submicron range. Reference may further be made to G. Counio, S. Esnouf, T. Gacoin and J. P. Boilot in "J. Phys. Chem. 100 (1996) pp 20021-20026" wherein CdS:Mn nanocrystals were prepared in inverted micelles from water/AOT (sodium salt of bis(2-ethylhexyl) sulfosuccinate)/heptane microemulsions. In the experiment, the AOT and water concentrations were taken as 0.5 and 2.5 mol.L"1 respectively. A solution was prepared containing the cadmium and manganese salts dissolved in water droplets. This solution was then added to the same volume of a similar solution containing sodium sulfide. In all experiments, the initial concentrations of Cd2+, Mn2+ and S2" dissolved in the water pools were taken respectively equal to 0.2, 0.12 and 0.38 mol.L"1. After a few seconds, Cds: Mn colloids were formed in inverted micelles. The addition of pyridine to the solution (1.4X10"2 mol.L'1) was found to improve the sulfide precipitation yield through a mechanism which was not well understood. At the same time, the pyridine molecule complexes the surface of the nanoparticles which were thus no more stable in the inverted micelles. This allows the separation of the sulfides as a powder of pyridine-capped nanoparticles. This powder was washed with large amounts of petroleum ether to eliminate residual AOT, and the nanocrystals were finally dispersed in pure pyridine, giving a transparent yellow-orange colloid solution of CdS:Mn. The average size of the nanoclusters was found to fluctuate between 1.2 and 2.4 nm. The main drawbacks of the above process are: (i) The generated CdS:Mn particles are contaminated with cation impurities, (ii) The mechanism of using pyridine as surface capping agent which allows the separation of the particles from the microemulsion was not established. Reference may also be made to Minati Chatterjee and Amitava Patra in " J. Am. Ceram. Soc. 84 (2001) pp 1439-44" wherein cadmium sulphide nanoparticles were prepared by microemulsion method using sorbitan monooleate and thioacetamide. The starting materials for cadmium sulphide (CdS) was cadmium acetate (AR Grade, Glaxo, India) and thioacetamide (GR Grade, Loba Chemie, India). Aqueous solutions of cadmium acetate (of varying concentrations) and thioacetamide were prepared by dissolving the respective salts in deionized water. The cadmium acetate and thioacetamide solutions were mixed under stirring in the desired proportions so as to obtain homogeneous solutions (called "CT") of varying Cd2+/thioacetamide mole ratios. The support solvent containing 5 vol% of sorbitan monooleate in cyclohexane was used for emulsification, i.e. for the preparation of water-in-oil (w/o) type emulsion in the present study. The volume ratio of the CT:cyclohexane was 1:4 in all the experiments. A measured volume of the support solvent was taken in a closed glass container. The solution CT was then dispersed in the support solvent under mechanical agitation of 500 rpm to obtain a w/o emulsion. The stabilized emulsion was then subjected to an ultrasonic treatment (26 kHz) for 10 min at ambient temperature and was then placed in an oil bath kept at a temperature of 80° ± 1°C. The emulsion was aged at 80° ± 1°C for 10 min under stirring and then removed from the bath. Following the above procedure, altogether four experiments with varying concentrations of Cd2+ were performed. Another set of experiments were performed with increasing ageing time, i.e. 20 and 30 min., at the above temperature using a fixed Cd2+ concentration of 0.05M keeping other parameters unaltered. The CdS particles were collected from the reverse micellar solutions by adding a known volume of methanol (GR grade). Immediate separation of particles occurred which were collected by centrifugation at 6000 rpm. To remove the last traces of adhered impurities, the particles were first washed twice with methanol followed by acetone (GR grade), each time collecting the particles centrifugually as described above followed by its dispersion in the washing solvents. The washed particles were dried at 60°C. Particle size distribution was in the range 10-50 nm. Using the above said process, yield of the product was 40wt%. The main drawback of the above process is the low yield of the product and therefore is industrially unviable. The main object of the present invention is to provide a process for the manufacture of nanosize pure and doped bivalent metal sulphide powder which obviates the drawbacks of the hitherto known processes. Another object of the present invention is to provide a process for the manufacture of pure bivalent nanosize metal sulphide powder, such as Zn, Cd, Pb. Yet another object of the present invention is to provide a process for manufacturing doped bivalent metal sulphide nanopowder with substances such as rare earth and transition metal. Still another object of the present invention is to provide a process for manufacturing nanopowder of varying particle size and size distribution. Accordingly, the present invention provides a process for the manufacture of nano-size pure and doped,bivalent metal sulphide powder characterized in that (i) preparing an aqueous solution of bivalent metal salt selected from nitrate, acetate of Zn, Cd, or Pb; (ii) adding under stirring 0 to 10 mol % of a water soluble dopant salt selected from rare earth or transition metal to the said metal salt solution; (iii) mixing the obtained metal salt solution, with or without dopant, under stirring with an aqueous solution of sulphide source selected from thioacetamide in a proportion in the range of 1:1 to 1:3 (v/v); (iv) mixing the solution so obtained in a proportion in the range of 1:1 to 1:5 (v/v) under stirring to a solution of a water-immiscible organic solvent and a non-ionic surfactant to obtain water-in oil (w/o) type emulsion; (v) subjecting the emulsion to sonication with a frequency of 26 kHz for 10 minutes; (vi) refluxing the resultant emulsion at a temperature in the range of 80 - 90°C to obtain sulphide particles; (vii)adding an organic solvent to obtain a water-organic mixed solution; (viii) collecting the particles so formed by adding under stirring an organic amine compound to attain a pH in the range of 8 - 9 to bring about flocculation, separating the flocculated particles by conventional methods, followed by washing with organic solvent and drying to get the nano sized metal sulphide powder. In an embodiment of the present invention, concentration of the water soluble bivalent metal salt is in the range of 0.025 - 6 M. In another embodiment of the present invention, concentration of sulphide source such as thioacetamide taken in the solution is in the range of 0.025-6 M. In yet another embodiment of the present invention surfactant solution is prepared by mixing water immiscible organic solvent such as cyclohexane, n-hexane, n-heptane with a non -ionic surfactant such as sorbitan monooleate, sorbitan monopalmitate, sorbitan monolaurate, polyethoxyetylene sorbitan monooleate, polyethoxyetylene sorbitan monoostearate with a concentration in the range of 0.25-5 vol% with respect to the volume of the water immiscible organic solvent under stirring. In still another embodiment of the present invention the organic solution of non-ionic surfactant has hydrophilic-lipophilic (HLB) value in the range of 4 to 15, In another embodiment of the present invention organic solvent is added to sulphide suspension in liquid medium in a proportion in the range of 5:1 to 10:1 (v/v). In a further embodiment of the present invention the organic amine compound used is such as pyridine, monoethylamine , diethylamine, triethyl amine. The novelty of the present invention primarily resides in providing a process which is economical, provides impurity-free nanoparticles and higher yield which makes the process suitable for industrial manufacture. This has been made possible by the inventive steps comprising a novel process for the manufacture of pure and doped bivalent metal sulphide nanopowders which comprises preparing an aqueous solution of bivalent metal salt such as nitrate, acetate of Zn, Cd or Pb. Adding under stirring 0 to 10 mol% of a water soluble dopant salt such as rare earth and transition metal to the said metal salt solution. Mixing the resultant solution with an aqueous solution of a sulphide source such as thioacetamide in the proportion in the range of 1:1 -1:3 (v/v) under stirring, filtering to obtain a aqueous mixed solution. Pouring the said aqueous mixed solution into an organic solution of non-ionic surfactant, having hydrophilic-lipophilic balance (HLB) value in the range 4 - 15, in a proportion in the range of 1:1 - 1:5 (v/v) under constant stirring to obtain an water-in oil (w/o) type emulsion. Optionally subjecting the emulsion to sonication to obtain a modified emulsion. Refluxing the modified emulsion at a raised temperature in the range of 80°-90°C to obtain sulphide particles. Adding to the sulphide suspension an organic solvent in the range of 5 : 1 to 10 : 1 (v/v) to obtain a water-organic mixed solution. Collecting the particles so formed by adding an organic amine compound such as pyridine, monoethylamine, diethylamine, triethylamine under stirring to attain a pH in the range 8 - 9 till solid sulphide particles are flocculated, separating the flocculated particles by conventional methods, followed by washing with organic solvent and drying The invention is described herein in details in the following examples, which are cited by way of illustration only and therefore should not be construed to limit the scope of the invention. Example 1 14.87 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 7.513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monooleate surfactant (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 20 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 93%. Example 2 14.87 g of zinc nitrate hexahydrate (Zn(N03)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 7.513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of n-heptane, a water immiscible organic solvent was taken. To this solvent, 8 mL of sorbitan monooleate surfactant was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing sorbitan monooleate and n-heptane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion (w/o) system was refluxed in an oil bath at 85°±1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Monoethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 90 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 92%. Example 3 7.436 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 3.756 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 6 mL of sorbitan monopalmitate (HLB value 6.7) surfactant was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing sorbitan monopalmitate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:3. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was reflux in an oil bath at 90°±1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 10:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 8. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 15 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 93% Example 4 7.436 g of zinc nitrate hexahydrate (Zn(NO3)2.6H20) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 3.756 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution", hi another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 ml of polyoxyethylene sorbitan monooleate surfactant (HLB value 15) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing polyoxyethylene sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:5. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refiuxed in an oil bath at 80°+1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 5:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 10 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 91%. Example 5 14.87 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 7.513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 200 mL of cyclohexane, a water immiscible organic solvent was taken and stirred magnetically with a speed of 150 rpm for 5 mins to obtain a n"oil phase". The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase", i.e. cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Diethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 150 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 93%. Example 6 4.7345 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) and 0.1619g of terbium nitrate pentahydrate (Tb(NO3)3.5H20) was dissolved in 25 mL of deionized water. To this solution of zinc and terbium nitrate, 25 mL of thioacetamide solution prepared by dissolving 3.7565 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monooleate surfactant (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of zinc nitrate, terbium nitrate and thioacetamide was added to the "oil phase" containing sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain (Zn,Tb)S nanopowders. The powder exhibited mean particle size of 22 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 94%. Example 7 1.3327 g of cadmium acetate dihydrate (Cd(CH3COO)2.2H2O) was dissolved in 25 mL of deionized water. To this solution of cadmium acetate, 25 mL of thioacetamide solution prepared by dissolving 4.6951 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of n-hexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monopalmitate surfactant (HLB value 6.7) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of cadmium acetate and thioacetamide was added to the "oil phase" containing sorbitan monopalmitate and n-hexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°+1°C in an air oven for 1h to obtain CdS nanopowders. The powder exhibited mean particle size of 14 nm. The X-ray diffraction (XRD) indicated the formation of cubic CdS particles. Yield of the powder was 93%. Example 8 1.3327 g of cadmium acetate dihydrate (Cd(CH3COO)2.2H2O) and 0.4947 g of manganous chloride tetrahydrate (MnCl2.4H2O) was dissolved in 25 mL of deionized water. To this solution, 25 mL of thioacetamide solution prepared by dissolving 0.7513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of n-heptane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monolaurate surfactant (HLB value 8.6) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of cadmium acetate, manganous nitrate and thioacetamide was added to the "oil phase" containing sorbitan monolaurate and n-heptane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain (Cd,Mn)S nanopowders. The powder exhibited mean particle size of 10 nm. The X-ray diffraction (XRD) indicated the formation of cubic CdS particles. Yield of the powder was 91%. Example 9 4.14 g of lead nitrate (Pb(NO3)2) was dissolved in 25 mL of deionized water. To this solution of lead nitrate, 25 mL of thioacetamide solution prepared by dissolving 0.9391 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monolaurate surfactant (HLB value 8.6) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase". The "aqueous mixed solution" containing the solution of lead nitrate and thioacetamide was added to the "oil phase" containing sorbitan monolaurate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins. The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain PbS nanopowders. The powder exhibited mean particle size of 11 nm. The X-ray diffraction (XRD) indicated the formation of PbS particles. Yield of the powder was 92%. In the process of the present invention, a novel method has been provided for the manufacture of high yield, impurity-free pure and doped bivalent metal sulphide nanocrystalline particles by non-obvious inventive step of using organic amine compound such as monoethylamine, diethylamine, triethylamine, pyridine. Because of high basicity of triethylamine, TEA (KB = 9.6X10-4 at 25°C) compared to that of pyridine (KB = 1.7X10-9 at 25°C), the former is more advantageous for accelerating the process of particle separation from the emulsion system. The mechanism of particles separation using TEA may be represented as the following steps: (i) Triethylamine (TEA) in presence of H2O forms triethylammoniurn hydroxide: (C2H5)3N + H20 (C2H5)3N+HOH- (ii) Triethylammonium hydroxide increases pH of the system by liberating hydroxide (OH-) ions. (iii) The OH- ion attacks C- atom of the ester carbonyl (>C=O) group in the surfactant molecule (sorbitan monooleate), causing hydrolysis as follows: (Formula Removed) (iv) Hydrolysis of the sorbitan monooleate destabilizes the emulsion system followed by the agglomeration and flocculation of the generated particles Thus the novelty of the process lies in the manufacture of impurity free pure and also doped bivalent metal sulphide nanopowders with high yield of product formation and the non-obvious inventive step lies in the use of the organic amine compound to increase the yield of impurity free nanoproduct. The main advantages of the present invention are: (i) The process for the preparation of pure and doped bivalent metal sulphide nanopowders does not require any sophisticated instruments. (ii) The process provides nanoparticles of high purity level. (iii) The process of the present invention directly provides the end product and does not require any post-processing steps like high energy ball-milling, screening, thus avoiding possibility of contamination. (iv) The process requires low (~80°C) crystallization temperature, thus the process is energy efficient. (v) The process involves minimum agglomeration, thus resulting in exhibiting improve characteristics. (vi) It is a tailor-made process, as the particle size and size distribution can be varied according to the necessity. (vii) The method is cost-effective. We Claim: 1. A process for the manufacture of nano-size pure and doped bivalent metal sulphide powder characterized in that (i) preparing an aqueous solution of bivalent metal salt selected from nitrate, acetate of Zn, Cd, or Pb; (ii) adding under stirring 0 to 10 mol % of a water soluble dopant salt selected from rare earth or transition metal to the said metal salt solution; (iii) mixing the obtained metal salt solution, with or without dopant, under stirring with an aqueous solution of a sulphide source thioacetamide in a proportion in the range of 1:1 to 1:3 (v/v); (iv) mixing the solution so obtained in a proportion in the range of 1:1 to 1:5 (v/v) under stirring to a solution of a water-immiscible organic solvent and a non-ionic surfactant to obtain water-in oil (w/o) type emulsion; (v) subjecting the emulsion to sonication with a frequency of 26 kHz for 10 minutes; (vi) refluxing the resultant emulsion at a temperature in the range of 80 - 90°C to obtain sulphide particles; (vii)adding an organic solvent to obtain a water-organic mixed solution; (viii) collecting the particles so formed by adding under stirring an organic amine compound to attain a pH in the range of 8 - 9 to bring about flocculation, separating the flocculated particles by conventional methods, followed by washing with organic solvent and drying to get the nano-sized metal sulphide powder. 2. A process as claimed in claim 1 wherein concentration of water soluble bivalent metal salt in the solution is in the range of 0.025 - 6 M. 3. A process as claimed in claim 1 wherein concentration of sulphide source thioacetamide in the solution is in the range of 0.025-6 M. 4. A process as claimed in claim 1 wherein water immiscible organic solvent used is selected from cyclohexane, n-hexane, n-heptane non - ionic surfactant used is selected from sorbitan monooleate, sorbitan monopalmitate, sorbitan monopalmitate, sorbitan monolaurate, polyethoxyetylene sorbitan monooleate, polyethoxyetylene sorbitan monoostearate at a concentration in the range of 0.25 - 5 vol% with respect to the volume of the water immiscible organic solvent. 5. A process as claimed in claim 1 - 4 wherein the organic solution of non-ionic surfactant has hydrophilic-lipophilic balance (HLB) value in the range of 4 to 15. 6. A process as claimed in claim 1 wherein organic solvent is added to the sulphide suspension in liquid medium in a proportion in the range of 5:1 to 10:1 (v/v). 7. A process as claimed in claim 1 wherein the organic amine compound used is selected from pyridine, monoethylamine, diethylamine, triethylamine. 8. A process for the manufacture of nano-size pure and doped bivalent metal sulphide powders substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for the manufacture of nano-size pure and doped bivalent metal sulphide powder. This invention particularly relates to a novel method for the manufacture of bivalent metal sulphide nanopowder and doped bivalent metal sulphide nanopowder, such as pure Zn, Cd, Pb sulphide nano-size powder and Zn, Cd, Pb sulphide nano-size powder doped with rare earth and transition metals.
These powders are used in various fields, such as electroluminescent materials (phosphors), infrared (ir) windows, solar cells, pigments and such other related fields. With a dispersion in a suitable matrix, they also find applications in thin film eletroluminescent (TFEL) devices. Because of the high surface area and surface energy, the physical and chemical properties of these nanometer sized particles markedly differ from those of bulk materials.
The present day methods of preparing ZnS nanopowders mainly consists of solution phase reaction. Reference may be made to "Comprehensive Inorganic Chemistry Vol. 3, First edition, eds., J. C. Bailar Jr., H. J. Emeleus, Sir Ronald Nyholm, A. F. Trotman-Dickenson, (Pergamon Press Ltd., Headington HillHall, Oxford, 1973) p. 227" wherein ZnS is prepared by passing hydrogen sulphide (H2S) to a solution of Zn2+ ions buffered to pH 3, zinc sulphide is quantitatively precipitated. The product is heated in a nitrogen stream at 650°C to give the cubic zinc blende form and at 1150°C to give hexagonal wurzite. Single crystals of the cubic form may be grown hydrothermally from polycrystalline ZnS and aqueous Na2S and NaOH.
The main drawbacks of the above process are:
(i) Uncontrolled nucleation and subsequent growth of the precipitated particles in a bulk aqueous medium generates large particles with a wide size disribution. (ii) It requires high temperature for the preparation of ZnS particles (iii) The product of this proces contain cationic impurities

Reference may also be made to Edward J. Donahue, Arlette Roxburg and Michael Yurchenko in "Materials Research Bulletin, Vol. 33, No. 2 (1998) pp 323-329" wherein ZnS is prepared through sol-gel route using organic dithiols. In this process fifty millilitres of a 10 mol% solution of zinc chloride (Fluka) in ethanedithiol (Aldrich) was prepared in an inert atmosphere glove box (Tek-Vac Model 323); the dithiol was transferred via syringe to minimize exposure. The mixture was then gently heated overnight under flowing dry argon at 65°C. All chemicals were used without purification, and the effluent from the reflux was bubbled through 0.1 M silver nitrate (Aesar) solution in order to test for the evolution of HCI. The reflux was allowed to cool, and the resultant clear sol was collected. The bubblers containing the silver nitrate were emptied, and the solution removed from them was filtered. The recovered precipitate was dried in a vacuum oven and weighed. The sol was then analyzed by TGA (Perkin-Elmer Model TGA-7) under flowing nitrogen to determine the appropriate processing temperature. Samples of the sol were then fired at 600°C under flowing argon, producing highly crystalline ZnS, as determined by X-ray. However, these samples were found by TGA to be highly contaminated with carbon. A three-step process was developed in which the samples were heated under flowing air for 10 min at 300°C to remove excess dithiol, fired at 550°C under argon for crystallization, and heated under air again at 400°C to remove any excess carbon. The effluent was bubled through nitric acid and then water while the sols were heated, effectively eliminating all unpleasant odours and allowing the work to be conducted in a fume hood.
Main drawbacks of the above processes may be summarized as:
(i) It requires high processing temperature for the preparation of ZnS particles; and thus giving rise to the possibility of agglomerate formation, (ii) It needs many processing steps, (iii) This process is very costly.
Reference may further be made to A. R. Kortan, R. Hull, R. L. Opila, M. G. Bawendi, M. L. Steigerwald, P. J. Carroll and L. E. Brus in "J. Am. Chem. Soc. 112

(1990) pp 1327-1332" wherein a sulphide solution of zinc was made by dissolving 150 µmol of Na2S in 40 mL micellar solution (heptane solution of bis(2-ethylhexyl) sulfosuccinate, disodium salt (0.12 M) and water (0.96 M)). This solution was injected with stirring into 255 mL of "micellar solution containing 160 µL of 1 M aqueous Zn(ClO4)2. To this was added, dropwise, 70 µL of 1 M Zn(ClO4)2- Finally thiophenol (70 µL in 10 mL of heptane) was injected with stirring, immediately followed by 1 mL of pyridine. The solution became turbid at this point. A white powder obtained by filtering on a fine frit was washed three times with petrolium ether.
The main drawback of the above process is the contamination of cation impurities with the generated ZnS particles.
Reference may also be made to Ahmet Celikkaya and Mufit Akinc in " J. Am. Ceram. Soc. 73 (1990) pp 2360- 2365" wherein a stock solution of zinc ions was prepared by dissolving Zn(NO3)2.6H20 in deionized water and then filtering through 0.1 um cellulose nitrate membrane filters to give a final zinc ion concentration of 1.56 M. An 8.3 mL aliquot of this stock was transferred into a beaker, and nitric acid solution (0.1 N or 0.01 N) was added to bring the total volume to slightly less than 250 mL. The solution was heated to reaction temperature, the desired amount of thioacetamide (TAA) was added and the final volume was brought to 250 mL. The beaker was then immersed in a water bath at the set reaction temperature. After a certain period of aging, a bluish tint in the solution was judged to indicate the onset of precipitation. The time interval necessary to induce the change in the solution colour was recorded. Aliquot (30 mL) were collected and quenched to 15°C periodically after precipitation had started. A number of combination of experimental variables were investigated. Ageing temperature of 60°, 70° and 80°C were employed. Initial thioacetamide concentrations were varied to give [TAA]o/[Zn]0 ratios of 4, 8 and 16 for pH 1 and pH 2. Initial zinc ion concentration [Zn]0 was held constant at 0.05 M in all experiment.
The main drawbacks of the above process are:

(i) The particle size distribution was controlled by two competing processes, rate of sulphide ion generation and rate of growth of agglomerates, (ii) The particle size of this process is in the submicron range.
Reference may further be made to G. Counio, S. Esnouf, T. Gacoin and J. P. Boilot in "J. Phys. Chem. 100 (1996) pp 20021-20026" wherein CdS:Mn nanocrystals were prepared in inverted micelles from water/AOT (sodium salt of bis(2-ethylhexyl) sulfosuccinate)/heptane microemulsions. In the experiment, the AOT and water concentrations were taken as 0.5 and 2.5 mol.L"1 respectively. A solution was prepared containing the cadmium and manganese salts dissolved in water droplets. This solution was then added to the same volume of a similar solution containing sodium sulfide. In all experiments, the initial concentrations of Cd2+, Mn2+ and S2" dissolved in the water pools were taken respectively equal to 0.2, 0.12 and 0.38 mol.L"1. After a few seconds, Cds: Mn colloids were formed in inverted micelles. The addition of pyridine to the solution (1.4X10"2 mol.L'1) was found to improve the sulfide precipitation yield through a mechanism which was not well understood. At the same time, the pyridine molecule complexes the surface of the nanoparticles which were thus no more stable in the inverted micelles. This allows the separation of the sulfides as a powder of pyridine-capped nanoparticles. This powder was washed with large amounts of petroleum ether to eliminate residual AOT, and the nanocrystals were finally dispersed in pure pyridine, giving a transparent yellow-orange colloid solution of CdS:Mn. The average size of the nanoclusters was found to fluctuate between 1.2 and 2.4 nm.
The main drawbacks of the above process are:
(i) The generated CdS:Mn particles are contaminated with cation impurities, (ii) The mechanism of using pyridine as surface capping agent which allows the separation of the particles from the microemulsion was not established.
Reference may also be made to Minati Chatterjee and Amitava Patra in " J. Am. Ceram. Soc. 84 (2001) pp 1439-44" wherein cadmium sulphide nanoparticles were prepared by microemulsion method using sorbitan monooleate and thioacetamide. The

starting materials for cadmium sulphide (CdS) was cadmium acetate (AR Grade, Glaxo, India) and thioacetamide (GR Grade, Loba Chemie, India). Aqueous solutions of cadmium acetate (of varying concentrations) and thioacetamide were prepared by dissolving the respective salts in deionized water. The cadmium acetate and thioacetamide solutions were mixed under stirring in the desired proportions so as to obtain homogeneous solutions (called "CT") of varying Cd2+/thioacetamide mole ratios. The support solvent containing 5 vol% of sorbitan monooleate in cyclohexane was used for emulsification, i.e. for the preparation of water-in-oil (w/o) type emulsion in the present study. The volume ratio of the CT:cyclohexane was 1:4 in all the experiments. A measured volume of the support solvent was taken in a closed glass container. The solution CT was then dispersed in the support solvent under mechanical agitation of 500 rpm to obtain a w/o emulsion. The stabilized emulsion was then subjected to an ultrasonic treatment (26 kHz) for 10 min at ambient temperature and was then placed in an oil bath kept at a temperature of 80° ± 1°C. The emulsion was aged at 80° ± 1°C for 10 min under stirring and then removed from the bath. Following the above procedure, altogether four experiments with varying concentrations of Cd2+ were performed. Another set of experiments were performed with increasing ageing time, i.e. 20 and 30 min., at the above temperature using a fixed Cd2+ concentration of 0.05M keeping other parameters unaltered.
The CdS particles were collected from the reverse micellar solutions by adding a known volume of methanol (GR grade). Immediate separation of particles occurred which were collected by centrifugation at 6000 rpm. To remove the last traces of adhered impurities, the particles were first washed twice with methanol followed by acetone (GR grade), each time collecting the particles centrifugually as described above followed by its dispersion in the washing solvents. The washed particles were dried at 60°C. Particle size distribution was in the range 10-50 nm.
Using the above said process, yield of the product was 40wt%.
The main drawback of the above process is the low yield of the product and therefore is industrially unviable.

The main object of the present invention is to provide a process for the manufacture of nanosize pure and doped bivalent metal sulphide powder which obviates the drawbacks of the hitherto known processes.
Another object of the present invention is to provide a process for the manufacture of pure bivalent nanosize metal sulphide powder, such as Zn, Cd, Pb.
Yet another object of the present invention is to provide a process for manufacturing doped bivalent metal sulphide nanopowder with substances such as rare earth and transition metal. Still another object of the present invention is to provide a process for manufacturing nanopowder of varying particle size and size distribution.
Accordingly, the present invention provides a process for the manufacture of nano-size pure and doped,bivalent metal sulphide powder characterized in that (i) preparing an aqueous solution of bivalent metal salt selected from nitrate, acetate of Zn, Cd, or Pb; (ii) adding under stirring 0 to 10 mol % of a water soluble dopant salt selected from rare earth or transition metal to the said metal salt solution; (iii) mixing the obtained metal salt solution, with or without dopant, under stirring with an aqueous solution of sulphide source selected from thioacetamide in a proportion in the range of 1:1 to 1:3 (v/v); (iv) mixing the solution so obtained in a proportion in the range of 1:1 to 1:5 (v/v) under stirring to a solution of a water-immiscible organic solvent and a non-ionic surfactant to obtain water-in oil (w/o) type emulsion; (v) subjecting the emulsion to sonication with a frequency of 26 kHz for 10 minutes; (vi) refluxing the resultant emulsion at a temperature in the range of 80 - 90°C to obtain sulphide particles; (vii)adding an organic solvent to obtain a water-organic mixed solution; (viii) collecting the particles so formed by adding under stirring an organic amine compound to attain a pH in the range of 8 - 9 to bring about flocculation, separating the flocculated particles by conventional methods, followed by washing with organic solvent and drying to get the nano sized metal sulphide powder.
In an embodiment of the present invention, concentration of the water soluble bivalent metal salt is in the range of 0.025 - 6 M.

In another embodiment of the present invention, concentration of sulphide source such as thioacetamide taken in the solution is in the range of 0.025-6 M.
In yet another embodiment of the present invention surfactant solution is prepared by mixing water immiscible organic solvent such as cyclohexane, n-hexane, n-heptane with a non -ionic surfactant such as sorbitan monooleate, sorbitan monopalmitate, sorbitan monolaurate, polyethoxyetylene sorbitan monooleate, polyethoxyetylene sorbitan monoostearate with a concentration in the range of 0.25-5 vol% with respect to the volume of the water immiscible organic solvent under stirring.
In still another embodiment of the present invention the organic solution of non-ionic surfactant has hydrophilic-lipophilic (HLB) value in the range of 4 to 15,
In another embodiment of the present invention organic solvent is added to sulphide suspension in liquid medium in a proportion in the range of 5:1 to 10:1 (v/v).
In a further embodiment of the present invention the organic amine compound used is such as pyridine, monoethylamine , diethylamine, triethyl amine. The novelty of the present invention primarily resides in providing a process which is economical, provides impurity-free nanoparticles and higher yield which makes the process suitable for industrial manufacture. This has been made possible by the inventive steps comprising a novel process for the manufacture of pure and doped bivalent metal sulphide nanopowders which comprises preparing an aqueous solution of bivalent metal salt such as nitrate, acetate of Zn, Cd or Pb. Adding under stirring 0 to 10 mol% of a water soluble dopant salt such as rare earth and transition metal to the said metal salt solution. Mixing the resultant solution with an aqueous solution of a sulphide source such as thioacetamide in the proportion in the range of 1:1 -1:3 (v/v) under stirring, filtering to obtain a aqueous mixed solution. Pouring the said aqueous mixed solution into an organic solution of non-ionic surfactant, having hydrophilic-lipophilic balance (HLB) value in the range 4 - 15, in a proportion in the range of 1:1 - 1:5 (v/v) under constant stirring to obtain an water-in oil (w/o) type emulsion. Optionally subjecting the emulsion to sonication to obtain a modified emulsion. Refluxing the modified emulsion at a raised temperature in the range of 80°-90°C to obtain sulphide particles. Adding to the sulphide suspension an organic solvent in the range of 5 : 1 to 10 : 1 (v/v) to obtain a water-organic

mixed solution. Collecting the particles so formed by adding an organic amine compound such as pyridine, monoethylamine, diethylamine, triethylamine under stirring to attain a pH in the range 8 - 9 till solid sulphide particles are flocculated, separating the flocculated particles by conventional methods, followed by washing with organic solvent and drying
The invention is described herein in details in the following examples, which are cited by way of illustration only and therefore should not be construed to limit the scope of the invention.
Example 1
14.87 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 7.513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monooleate surfactant (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".
The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a

volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 20 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 93%.
Example 2
14.87 g of zinc nitrate hexahydrate (Zn(N03)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 7.513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of n-heptane, a water immiscible organic solvent was taken. To this solvent, 8 mL of sorbitan monooleate surfactant was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".
The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing sorbitan monooleate and n-heptane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion (w/o) system was refluxed in an oil bath at 85°±1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The

entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Monoethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 90 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 92%.
Example 3
7.436 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 3.756 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 6 mL of sorbitan monopalmitate (HLB value 6.7) surfactant was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".
The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing sorbitan monopalmitate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:3. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion

(w/o) system was reflux in an oil bath at 90°±1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 10:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 8. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 15 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 93%
Example 4
7.436 g of zinc nitrate hexahydrate (Zn(NO3)2.6H20) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 3.756 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution", hi another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 ml of polyoxyethylene sorbitan monooleate surfactant (HLB value 15) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".
The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase" containing polyoxyethylene sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic

phase in the emulsion was 1:5. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refiuxed in an oil bath at 80°+1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 5:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 10 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 91%.
Example 5
14.87 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was dissolved in 25 mL of deionized water. To this solution of zinc nitrate, 25 mL of thioacetamide solution prepared by dissolving 7.513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 200 mL of cyclohexane, a water immiscible organic solvent was taken and stirred magnetically with a speed of 150 rpm for 5 mins to obtain a n"oil phase".
The "aqueous mixed solution" containing the solution of zinc nitrate and thioacetamide was added to the "oil phase", i.e. cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The

volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Diethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain ZnS nanopowders. The powder exhibited mean particle size of 150 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 93%.
Example 6
4.7345 g of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) and 0.1619g of terbium nitrate pentahydrate (Tb(NO3)3.5H20) was dissolved in 25 mL of deionized water. To this solution of zinc and terbium nitrate, 25 mL of thioacetamide solution prepared by dissolving 3.7565 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monooleate surfactant (HLB value 4.3) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".

The "aqueous mixed solution" containing the solution of zinc nitrate, terbium nitrate and thioacetamide was added to the "oil phase" containing sorbitan monooleate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain (Zn,Tb)S nanopowders. The powder exhibited mean particle size of 22 nm. The X-ray diffraction (XRD) indicated the formation of cubic ZnS particles. Yield of the powder was 94%.
Example 7
1.3327 g of cadmium acetate dihydrate (Cd(CH3COO)2.2H2O) was dissolved in 25 mL of deionized water. To this solution of cadmium acetate, 25 mL of thioacetamide solution prepared by dissolving 4.6951 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of n-hexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monopalmitate

surfactant (HLB value 6.7) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".
The "aqueous mixed solution" containing the solution of cadmium acetate and thioacetamide was added to the "oil phase" containing sorbitan monopalmitate and n-hexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°+1°C in an air oven for 1h to obtain CdS nanopowders. The powder exhibited mean particle size of 14 nm. The X-ray diffraction (XRD) indicated the formation of cubic CdS particles. Yield of the powder was 93%.
Example 8
1.3327 g of cadmium acetate dihydrate (Cd(CH3COO)2.2H2O) and 0.4947 g of manganous chloride tetrahydrate (MnCl2.4H2O) was dissolved in 25 mL of deionized water. To this solution, 25 mL of thioacetamide solution prepared by dissolving 0.7513 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove

impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of n-heptane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monolaurate surfactant (HLB value 8.6) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".
The "aqueous mixed solution" containing the solution of cadmium acetate, manganous nitrate and thioacetamide was added to the "oil phase" containing sorbitan monolaurate and n-heptane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain (Cd,Mn)S nanopowders. The powder exhibited mean particle size of 10 nm. The X-ray diffraction (XRD) indicated the formation of cubic CdS particles. Yield of the powder was 91%.
Example 9
4.14 g of lead nitrate (Pb(NO3)2) was dissolved in 25 mL of deionized water. To this solution of lead nitrate, 25 mL of thioacetamide solution prepared by dissolving

0.9391 g of thioacetamide (CH3CSNH2) in 25 mL of deionized water was added under stirring magnetically to dissolve it followed by filtering the resulting solution to remove impurities. This water soluble solution is called "aqueous mixed solution". In another container (conical flask), 190 mL of cyclohexane, a water immiscible organic solvent was taken. To this solvent, 10 mL of sorbitan monolaurate surfactant (HLB value 8.6) was added and stirred magnetically with a speed of 150 rpm for 5 mins to obtain an "oil phase".
The "aqueous mixed solution" containing the solution of lead nitrate and thioacetamide was added to the "oil phase" containing sorbitan monolaurate and cyclohexane under stirring magnetically with a speed of 150 rpm when a water in oil (w/o) type emulsion was formed. The volume ratio of water phase: organic phase in the emulsion was 1:4. Stirring was continued for 10 mins. The emulsion was subjected to sonication with a frequency of 26 kHz for 10 mins at room temperature. The emulsion (w/o) system was refluxed in an oil bath at 80° ± 1°C for 10 mins under constant magnetic stirring with a speed of 150 rpm. After this the container was removed from the oil bath and allowed to cool. The entire mass was poured in a container containing acetone in a volume ratio of 8:1 to that of the emulsion followed by stirring at the speed of 300 rpm. Triethylamine was added to the acetone containing mixture under magnetic stirring at a speed of 300 rpm until the pH of the resulting mixture reached a value up to 9. The precipitated particles were separated and floculated at the bottom of the container when it was allowed to stand for 10 mins.
The particles obtained were collected by centrifugation at 6000 rpm for 10 mins and again dispersed in acetone under stirring. The process was repeated four times to remove the soluble impurities, i.e. electrolytes. The washed particles were then dried at 100°±1°C in an air oven for Ih to obtain PbS nanopowders. The powder exhibited mean particle size of 11 nm. The X-ray diffraction (XRD) indicated the formation of PbS particles. Yield of the powder was 92%.
In the process of the present invention, a novel method has been provided for the manufacture of high yield, impurity-free pure and doped bivalent metal sulphide

nanocrystalline particles by non-obvious inventive step of using organic amine compound such as monoethylamine, diethylamine, triethylamine, pyridine.
Because of high basicity of triethylamine, TEA (KB = 9.6X10-4 at 25°C) compared to that of pyridine (KB = 1.7X10-9 at 25°C), the former is more advantageous for accelerating the process of particle separation from the emulsion system. The mechanism of particles separation using TEA may be represented as the following steps: (i) Triethylamine (TEA) in presence of H2O forms triethylammoniurn hydroxide:
(C2H5)3N + H20 (C2H5)3N+HOH-
(ii) Triethylammonium hydroxide increases pH of the system by liberating hydroxide (OH-) ions.
(iii) The OH- ion attacks C- atom of the ester carbonyl (>C=O) group in the surfactant molecule (sorbitan monooleate), causing hydrolysis as follows:
(Formula Removed)
(iv) Hydrolysis of the sorbitan monooleate destabilizes the emulsion system followed by the agglomeration and flocculation of the generated particles
Thus the novelty of the process lies in the manufacture of impurity free pure and also doped bivalent metal sulphide nanopowders with high yield of product formation and the non-obvious inventive step lies in the use of the organic amine compound to increase the yield of impurity free nanoproduct.
The main advantages of the present invention are:
(i) The process for the preparation of pure and doped bivalent metal sulphide
nanopowders does not require any sophisticated instruments.
(ii) The process provides nanoparticles of high purity level.
(iii) The process of the present invention directly provides the end product and does not
require any post-processing steps like high energy ball-milling, screening, thus avoiding
possibility of contamination.
(iv) The process requires low (~80°C) crystallization temperature, thus the process is
energy efficient.
(v) The process involves minimum agglomeration, thus resulting in exhibiting improve
characteristics.
(vi) It is a tailor-made process, as the particle size and size distribution can be varied
according to the necessity.
(vii) The method is cost-effective.

We Claim:
1. A process for the manufacture of nano-size pure and doped bivalent metal
sulphide powder characterized in that (i) preparing an aqueous solution of
bivalent metal salt selected from nitrate, acetate of Zn, Cd, or Pb; (ii) adding
under stirring 0 to 10 mol % of a water soluble dopant salt selected from rare
earth or transition metal to the said metal salt solution; (iii) mixing the
obtained metal salt solution, with or without dopant, under stirring with an
aqueous solution of a sulphide source thioacetamide in a proportion in the
range of 1:1 to 1:3 (v/v); (iv) mixing the solution so obtained in a proportion in
the range of 1:1 to 1:5 (v/v) under stirring to a solution of a water-immiscible
organic solvent and a non-ionic surfactant to obtain water-in oil (w/o) type
emulsion; (v) subjecting the emulsion to sonication with a frequency of 26 kHz
for 10 minutes; (vi) refluxing the resultant emulsion at a temperature in the
range of 80 - 90°C to obtain sulphide particles; (vii)adding an organic
solvent to obtain a water-organic mixed solution; (viii) collecting the particles
so formed by adding under stirring an organic amine compound to attain a pH
in the range of 8 - 9 to bring about flocculation, separating the flocculated
particles by conventional methods, followed by washing with organic solvent
and drying to get the nano-sized metal sulphide powder.
2. A process as claimed in claim 1 wherein concentration of water soluble
bivalent metal salt in the solution is in the range of 0.025 - 6 M.
3. A process as claimed in claim 1 wherein concentration of sulphide source
thioacetamide in the solution is in the range of 0.025-6 M.
4. A process as claimed in claim 1 wherein water immiscible organic solvent
used is selected from cyclohexane, n-hexane, n-heptane non - ionic

surfactant used is selected from sorbitan monooleate, sorbitan monopalmitate, sorbitan monopalmitate, sorbitan monolaurate, polyethoxyetylene sorbitan monooleate, polyethoxyetylene sorbitan monoostearate at a concentration in the range of 0.25 - 5 vol% with respect to the volume of the water immiscible organic solvent.
5. A process as claimed in claim 1 - 4 wherein the organic solution of non-ionic
surfactant has hydrophilic-lipophilic balance (HLB) value in the range of 4 to
15.
6. A process as claimed in claim 1 wherein organic solvent is added to the
sulphide suspension in liquid medium in a proportion in the range of 5:1 to
10:1 (v/v).
7. A process as claimed in claim 1 wherein the organic amine compound used is
selected from pyridine, monoethylamine, diethylamine, triethylamine.
8. A process for the manufacture of nano-size pure and doped bivalent metal
sulphide powders substantially as herein described with reference to the
examples.

Documents:

1295-del-2001-abstract.pdf

1295-del-2001-claims.pdf

1295-del-2001-correspondence-others.pdf

1295-del-2001-correspondence-po.pdf

1295-del-2001-description (complete).pdf

1295-del-2001-form-1.pdf

1295-del-2001-form-18.pdf

1295-del-2001-form-2.pdf

1295-del-2001-form-3.pdf

« Previous Patent

Next Patent »

Patent Number

220793

Indian Patent Application Number

1295/DEL/2001

PG Journal Number

30/2008

Publication Date

25-Jul-2008

Grant Date

05-Jun-2008

Date of Filing

28-Dec-2001

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

Inventors:

#	Inventor's Name	Inventor's Address
1	MILAN KANTI NASKAR
2	AMITAVA PATRA
3	MINATI CHATTERJEE

PCT International Classification Number

C01G 1/12

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA