SI23219A - Anatase nanoparticles and process of synthesis for obtaining anatase nanoparticles - Google Patents

Abstract

The subject of the invention are anatase nanoparticles and a process of synthesis for obtaining anatase nanoparticles from metatitanium acid which is a semifinished product in the production of TiO2 pigments. The synthesis of anatase nanoparticles from metatitanium acid is based on the so called gel-sol process. Anatase nanoparticles according to the invention are very fine particles in the form of an acid/neutral suspension, where anatase nanoparticles are polycrystalline and the crystallites exhibit isothropic morphology and have a diameter of about 4-5 nm, while anatase nanoparticles themselves have a diameter between 30 and 80 nm and a specific surface of 200 m2/g or more.

Description

Anatase nanoparticles and synthesis procedure for the production of anatase nanoparticles

The subject matter of the invention is anatase nanoparticles and a synthesis process for the production of anatase nanoparticles from metatitanoic acid, which is a by-product of the production of TiO ₂ pigment. The synthesis of metatitanoic acid anatase nanoparticles according to the invention is based on the so-called sol-gel method of preparing metatitanoic acid and its further treatment with barium chloride solution.

The invention contemplates a synthesis process whereby well dispersed, uniformly sized and well crystalline TiO ₂ nanoparticles of the anatase crystal structure can be obtained from metatitanic acid. The invention also addresses the material itself, i.e. the anatase nanoparticles and its characteristics. The invention also relates to a method of producing metatitanoic acid of various forms. Namely, metatitanoic acid, TiO ₂ gel, is an agglomerate of smaller polycrystalline anatase nanoparticles whose basic size is determined by the hydrolysis parameters of the so-called black solution. Depending on the form of metatitanoic acid, suspensions of anatase nanoparticles, which vary in size, can be obtained in the process of its further treatment with barium chloride solution.

The synthesis process describes a method of preparing various forms of metatitanoic acid, which is an agglomerate of smaller polycrystalline anatase nanoparticles, the size of which is determined by the method of hydrolysis, e.g. black solution, and further describes the process of obtaining stable suspensions of anatase nanoparticles from the starting metatitanic acid by treatment with a solution of barium chloride. Synthesis of anatase nanoparticles in suspension form is very important, as no synthesis step produces an intermediate, potentially harmful, dusty phase, as well as the formation of well crystalline nanoparticles as a final product, which eliminates the need for a calcination process which is energy wasteful and burdens the environment with greenhouse gas emissions.

Titanium dioxide in the form of pigment is a material with a wide range of applications, and is useful for coatings, paints, as an additive to plastics, paper, cosmetics, the pharmaceutical industry and many other applications. Today, two processes for the production of pigment titanium dioxide, i.e. sulfate and chloride process. Both the sulfate and chloride process are based on the high-temperature conversion of the corresponding components into pigment titanium dioxide. In the sulfate process, the pigment is formed in the process of calcination in the reactions

-2 hydrolysis of the obtained anatase gel, while in the chloride process the pigment forms in the high-temperature combustion of titanium tetrachloride with oxygen. The high-temperature calcination process present in the sulfate and chloride process also prevents the production of nano-sized anatase particles. however, it is typical that high calcination temperatures always lead to the conversion of anatase to the thermodynamically more stable TiO ₂ phase, rutile. The calcination process is also heavily laden with high energy consumption and a correspondingly high amount of greenhouse gas emissions. In addition, the resulting product is present in the form of dust that can be potentially harmful to health and the environment.

This is why many different processes for the production of anatase nanoparticles have been developed in recent years.

US 20060254461 discloses a process for the preparation of anatase nanoparticles by a sol-gel process, from starting organic alkoxides, which under specific reaction conditions hydrolyze and form the corresponding salt. The salt then undergoes an aging process at a temperature of 120-140 ° C, which triggers the nucleation and growth of well crystalline anatase nanoparticles.

US 4954476 discloses a process for the production of anatase nanoparticles by the hydrothermal method. The starting material is meta- or orthotitanoic acid, which is then subjected to a hydrothermal reaction under specific conditions. Typically, a hydrothermal reaction takes place for several hours at a temperature of about 180 ° C and an elevated pressure of the aqueous suspension. At lower temperature, hydrothermal synthesis takes a long time, even for several days.

US 7510694 discloses a process for the preparation of anatase nanoparticles from a solution of titanium tetrachloride to which an appropriate amount of hydrazine monohydrate is added. The reaction is carried out at room temperature at a pH of about 8, yielding a product of high specific surface area with very small basic anatase crystallites.

The above examples of synthesis of anatase nanoparticles lead to the desired product, but are unsuitable or less suitable for industrial production, since the processes described are either based on the use of expensive and / or toxic organic substances, or it takes a long and energy-consuming process to obtain the desired shape of the nanoparticles. A major disadvantage of the processes described is that the end product is a highly agglomerated powder of anatase nanoparticles, which reduces the possibility of application of the end product.

Anatase nanoparticles and synthesis process for the production of metatitanic acid anatase nanoparticles according to the invention eliminates the aforementioned disadvantages as they allow the production of uniformly • · • ·

-3 large, well crystalline and well-dispersed anatase nanoparticles in stable suspension, which greatly facilitates their use in high-tech applications.

The present invention describes anatase nanoparticles and anatase nanoparticle production process suitable for industrial application based on the synthesis of anatase nanoparticles from raw materials used in the production of T1O2 pigment in the form of final suspensions, the synthesis process being not based on the use of organic components, it does not include the calcination process and the associated potentially harmful dry phase of the product, and consequently does not pollute the environment with greenhouse gas emissions and discharges.

The present invention is a process for the production of anatase nanoparticles in the form of a stable suspension, starting from a T1O2 gel, that is metatitanic acid. The present invention describes a process for the preparation of metatitanoic acid in a manner that allows the size of anatase nanoparticles formed during hydrolysis to be controlled, e.g. black solutions and which combine into a strongly agglomerated gel1Ο2 gel, methattanoic acid. The process of treating metatitanoic acid with barium chloride solution is also described, breaking down methattanic acid agglomerates and subsequently releasing the anatase nanoparticles, which are then present in a stable suspension.

The present invention is therefore based on two processes, namely, obtaining the desired form of metatitanic acid and subsequently treating it with a solution of barium chloride, thereby releasing entrained anatase nanoparticles into the methattanic acid agglomerate. The present invention is characterized by the fact that the process is carried out at low temperatures of 105 ° C, which is the boiling point of the solution from which methattanoic acid is obtained, while the treatment of the methattanic acid itself is carried out at room temperature. It is characteristic of the present invention to obtain high yield anatase nanoparticles in excess of 90% in the form of polycrystalline isotropic spherical nanoparticles. The basic properties of anatase nanoparticles are controlled by the method of preparation of the desired form of metatitanoic acid. Usually nanoparticles are between 30 and 40 nanometers in size and have a specific surface area of over 200 m / g.

The main object of the present invention is to provide a process suitable for the industrial production of anatase nanoparticles. The main advantages of the present invention are:

- that the process is carried out at a relatively low temperature of about 105 ° C, during which only the process of obtaining the desired form of metatitanoic acid is carried out, whereas its treatment with barium chloride solution can be carried out at room temperature, • ·

-4- that the nanoparticles form in the form of final suspensions, which excludes the product into the dry phase forms and therefore does not present a potential risk of dusting,

- that the nanoparticles are well crystalline and therefore do not require calcination of the product, which means energy savings and consequently that the process does not burden the environment with greenhouse gas emissions

- that the nanoparticles are well dispersed in the final suspension, which facilitates their use,

- that the nanoparticles are uniformly large,

- the size of anatase nanoparticles can be affected by controlling the reaction parameters of the production of metatitanoic acid,

- yields very high and usually above 90%.

Description of the invention

The invention will hereinafter be described with a description of the synthesis, figures and embodiments that adequately illustrate the synthesis process itself and the anatase nanoparticles themselves.

Pictures show:

Figure 1: Anatase nanoparticles obtained according to the invention, recorded using a scanning electron microscope,

Figure 2: X-ray powder diffraction pattern showing that the particles have the crystal structure of anatase.

Figure 3: High resolution image of anatase nanoparticles taken with a transmission electron microscope obtained according to embodiment 1,

Figure 4: Plot size distribution of nanoparticles obtained according to Embodiment 1, showing that the average nanoparticle diameter is 40 nm,

Figure 5: X-ray powder diffractogram of the by-product of the reaction, barium sulphate, showing that the barium sulphate which has been ejected has good crystallinity,

Figure 6: Anatase nanoparticles obtained from Embodiment 2, taken with a scanning electron microscope,

Figure 7: Plot size distribution of nanoparticles obtained according to embodiment 2, which shows that the average nanoparticle diameter is 80 nm,

Figure 8: Anatase nanoparticles obtained according to embodiment 3, taken with a scanning electron microscope,

Figure 9: Plot size distribution of nanoparticles obtained according to the 3rd embodiment, which shows that the average nanoparticle diameter is 60 nm,

Figure 10: Anatase nanoparticles obtained from Embodiment 4, taken with a scanning electron microscope,

Figure 11: Plot size distribution of nanoparticles obtained according to Embodiment 4, which shows that the average nanoparticle diameter is 30 nm,

Figure 12: Anatase nanoparticles obtained according to the 5th embodiment, recorded with a scanning electron microscope,

Figure 13: Plot size distribution of nanoparticles obtained according to Embodiment 4, which shows that the average nanoparticle diameter is 20 nm.

The synthesis process of anatase nanoparticles is based on the use of e.g. black solution, which is a by-product of the production of T1O2 pigment and is a strongly acidic solution of titanyl sulfate, which is the water-soluble component of Ti (IV). From the black solution, metatitanoic acid of a specific form can be directly obtained, i.e. hydrolysis process. In the process of hydrolysis of the black solution at the boiling point of the black solution, i.e., about 105 ° C, polycondensation, nucleation, and particle growth reactions take place in which the final polycrystalline anatase nanoparticles are formed, in the form of a strongly agglomerated T1O2 gel, i.e. metatitanic acid of the chemical formula TiCLKhO. The size of the metatitanic acid-forming anatase polycrystalline nanoparticles is influenced directly by the specific reaction parameters of the hydrolysis implementation, and the amount of hydrolysis tin added is particularly important, which controls the hydrolysis reaction appropriately while increasing the final yield of the reaction. Hydrolysis pads are specially prepared nano crystals of anatase, which are approximately 5 nm in size and are highly agglomerated. They are an important raw material that is produced by hydrolysis of a solution of titanyl sulfate and is used mainly to control the hydrolysis reactions of the black solution and to increase the yield of these reactions.

The amount of hydrolysis kale added is very important because they direct the hydrolysis reaction of the black solution through a process of t.i. secondary nucleation, which assumes that a single crystallite of anatase present in the hydrolysis pellets may represent the nucleation and growth center of the anatase nanoparticles in the final reaction product, i.e. metatitanoic acid. This means that the amount of hydrolysis tin added can directly affect the degree of supersaturation and, consequently, the size of the basic anatase polycrystals present in methattanic acid. This gives the possibility to control and obtain differently sized polycrystalline anatase nanoparticles by varying the amount of hydrolysis kale added during hydrolysis of the black solution.

• ·

-6Metatitanic acid obtained from the hydrolysis of the black solution is filtered and washed after the end of the reaction to remove the sulfuric acid present. The final metatitanoic acid is a high-viscosity TiO ₂ gel, which is suitable for the direct production of anatase nanoparticles. They are obtained by adding an appropriate volume of barium chloride aqueous solution with a molar concentration of 0.5 M to a given volume of methattanic acid with a high concentration of TiO ₂ above 350 g / L and stirring under normal conditions (room temperature, atmospheric pressure) for 15 minutes. . When stirring is stopped, a very stable suspension of anatase nanoparticles released from metatitanoic acid is obtained by reaction with barium chloride. The barium cation has a very high tendency to bind the sulfate ion, which is the binding element between the polycrystalline anatase nanoparticles within the methattanic acid agglomerate. When barium ion binds with sulfate ions within the methattanic acid agglomerate, the anatase nanoparticles are released and present only as well-dispersed nanoparticles within a very stable suspension. Barium sulfate, which is a by-product of the reaction between barium cation and the sulfate ion, is removed to the bottom of the reaction vessel and can be removed by centrifugation / decantation or filtration. It is also possible to remove any interfering ions from the suspension by agglomeration of the anatase nanoparticles by raising the pH of the suspension, thereby reaching the so-called isoelectric point. Agglomerated anatase nanoparticles can be filtered on coarse filters and the resulting cake filters are washed off, eliminating any disturbing ions present. The purified product can then be resuspended in water to obtain a stable suspension in which only anatase nanoparticles are present.

Regardless of changing the reaction parameters of the synthesis of anatase nanoparticles, there are common characteristics for the nanoparticles themselves:

• Anatase nanoparticles are polycrystalline, which means they are made up of individual smaller anatase crystallites. The crystallites exhibit isotropic morphology and are about 4-5 nm in size.

• Anatase nanoparticles exhibit characteristic spherical morphology as a result of aggregation of isotropic anatase crystallites.

The synthesis process for the production of anatase nanoparticles with a high specific surface area and spherical morphology according to the invention is based on a sol-gel reaction using a soluble titanium sulphate solution as a starting material and a by-product of producing TiO ₂ pigment. to subject the solution to a hydrolysis reaction in which the titanyl sulfate is converted into polycondensation reactions in the polycondensation reactions, which is nanocrystalline • ·

- Anatase agglomerate to hydrolyze the black solution in the presence of hydrolysis tin, the reaction of which directs and defines the form of metatitanic acid and the anatase polycrystals present therein, so that the resulting form of metatitanic acid is appropriately converted into anatase nanoparticles by the different addition of barium chloride solution that the reaction is carried out between barium chloride and meth-titanium acid-present sulfate at room temperature to form barium sulfate, which is a by-product of the reaction, with the addition of barium chloride, and is formed as a product of precipitation between the meth-titanium acid sulfate ions and barium cations present, the resulting barium sulfate is quantitatively separated from the suspension of anatase nanoparticles by sedimentation and / or centrifugation / decantation, making the resulting acidic suspension of the anatase nanoparticles very stable so that the resulting acid suspension of the anatase nanoparticles contains between 200 and 300 g / L TiO ₂ . Anatase nanoparticles can be purified from the acidic suspension by raising the pH to achieve the nanoparticle agglomeration and washing the resulting product upon filtration. Purified anatase nanoparticles can be resuspended to adjust the suspension with the desired pH and TiO ₂ mass concentration.

By varying the amount of hydrolysis pellets involved in the black solution hydrolysis reaction, the size of the nanoparticles is controlled. Anatase nanoparticle sizes may be adjusted between 30 and 80 nm or more. The anatase nanoparticles obtained are in acidic suspension with an approximate mass concentration of between 200 and 300 g / L and can be isolated and purified. Acid is removed from the initial suspension and the pH is adjusted to the desired value as desired. The process is constantly carried out in the wet, ie in the form of a suspension, which prevents the occurrence of potentially harmful dusting. The nanoparticles obtained are polycrystalline and therefore there is no need for energy-consuming calcination of the product.

The atanas nanoparticles of the invention are polycrystalline, with the crystallites exhibiting isotropic morphology and about 4-5 nm in size and exhibiting characteristic spherical morphology resulting from the aggregation of isotropic anatase crystallites.

Embodiment 1: Synthesis of anatase nanoparticles with high specific surface area and spherical morphology with an average particle diameter of 40 nm.

For the synthesis of anatase nanoparticles, the so-called black solution is used, in which titanyl sulfate is present with a mass concentration between 210 and 230 g / L. The black solution contains sulfuric (VI) acid with a high mass concentration of between 400 and 450 g / L and a lower mass concentration of Ti ³⁺ ion and

-8 otherwise 1-2 g / L. The black solution was heated to 85 [deg.] C. and poured into a batch hydrolyzer, where the sessions were added so-called. hydrolysis tin in the form of a suspension with a mass concentration of 40 g / L and a pH value of approximately 4.3. The addition of hydrolysis potassium is usually up to a final content of 0.6%.

The resulting suspension was heated directly with steam to a boiling point between 105-110 ° C (20 minutes) and then boiled at this temperature for a further 45 minutes. Water was added to a suitable dilution over a period of 120 minutes, depending on the concentration of TiO ₂ inlet solution. This is followed by the discharge from the hydrolyzer and the suspension being cooled to 60 ° C.

The product obtained is then filtered on special candle filters and washed intensively with water, thus eliminating sulfuric acid and other water-soluble ions. This produces a TiO ₂ gel, ie methattanoic acid, which can be directly used to obtain polycrystalline anatase nanoparticles.

A typical lab experiment was as follows. It captured 400 mL of metatitanoic acid (TiO ₂ concentration between 370 and 410 g / L), to which 150 mL of aqueous barium chloride solution with a bulk concentration of 0.5 M was added while stirring. The stirring was continued for a further 15 min at 200 rpm. The reaction is started immediately after the addition of barium chloride to the methattanoic acid suspension. Barium cation binds to the sulfate ions present within the methattanic acid agglomerates, releasing the anatase nanoparticles, and as a by-product barium sulfate is formed, which settles to the bottom of the reaction vessel. The precipitated barium sulfate can be easily removed by centrifugation / decantation of the resulting suspension of anatase nanoparticles or by filtration. In the case of filtration, the anatase nanoparticles pass through the filter, and barium sulfate remains on the filter surface and can be quantitatively removed.

At the end of the separation, two products are thus obtained, namely a very stable suspension of anatase nanoparticles and barium sulfate, which is formed in the reaction between sulfate ions and the barium cations present in metatitanic acid.

Anatase nanoparticles can be used in suspension or can be isolated if necessary. Isolation is carried out by adding an appropriate amount of base to the acid suspension of the anatase nanoparticles, e.g. NaOH, which causes agglomeration of the nanoparticles because they have reached the isoelectric point. The agglomerated nanoparticles can then be washed and dried or resuspended in the selected medium to obtain a suspension having the desired characteristics, that is, with a certain pH value and a certain mass concentration of TiO ₂ .

Anatase nanoparticles were analyzed by XRD, scanning electron microscopy (SEM) and screening electron microscopy (TEM).

-9The anatase nanoparticles shown in Figure 1 were recorded on a scanning electron microscope. The image shows that the nanoparticles measure approximately 40 nm and exhibit spherical morphology. The crystal structure of anatase nanoparticles was determined by XRD analysis (Figure 2). The X-ray powder diffractogram shows characteristic anatase deflections, which, however, are wide due to the small size of the crystallites.

Figure 3 shows a high-resolution image of the anatase nanoparticle, showing its specific morphology and the nature of the crystallites that make up it. As can be seen from the figure, the anatase nanoparticle consists of very small crystals aggregated into a single polycrystalline nanoparticle.

Figure 4 shows the nanoparticle size distribution showing that the largest fraction of nanoparticles has a diameter of about 40 nm.

Figure 5 is an X-ray powder diffraction pattern of the reaction product, barium sulfate.

The diffractogram clearly shows that the peaks are very well defined, indicating good crystallinity of barium sulfate. Likewise, diffractograms do not show any anatase deviations, which proves that we were able to quantitatively separate anatas from barium sulfate during separation.

Embodiment 2: Synthesis of anatase nanoparticles with a high specific surface area and spherical morphology with an average particle diameter of 70 nm.

Synthesis of anatase nanoparticles was carried out according to the same procedure as in embodiment 1, except that 0.1% hydrolysis kale was added during the hydrolysis phase of the black solution. As a result, the hydrolysis of the anatase nanoparticles formed is shown in Figure 6. Figure 7 shows the nanoparticle size distribution showing that the largest proportion of nanoparticles has a diameter of about 70 nm.

Embodiment 3: Synthesis of anatase nanoparticles with a high specific surface area and spherical morphology with an average particle diameter of 50-55 nm.

Synthesis of anatase nanoparticles was performed according to the same procedure as in embodiment 1, except that 0.3% hydrolysis kale was added during the hydrolysis phase of the black solution. As a result, the hydrolysis of the resulting anatase nanoparticles is shown in Figure 8. Figure 9 shows the size distribution of the nanoparticles, which shows that the largest proportion of nanoparticles has a diameter of about 50-55 nm.

-10Example 4: Synthesis of anatase nanoparticles with a high specific surface area and spherical morphology with an average particle diameter of 30-35 nm.

Synthesis of anatase nanoparticles was performed according to the same procedure as in embodiment 1, except that 0.9% of hydrolysis kale was added during the hydrolysis phase of the black solution. As a result, the hydrolysis of the resulting anatase nanoparticles is shown in Figure 10. Figure 11 shows the nanoparticle size distribution showing that the largest proportion of nanoparticles has a diameter of about 30-35 nm.

Embodiment 5: Synthesis of anatase nanoparticles with a high specific surface area and spherical morphology with an average particle diameter of 30 nm.

Synthesis of anatase nanoparticles was performed according to the same procedure as in Example 1, except that 1.8% of the hydrolysis kale was added during the hydrolysis phase of the black solution. As a result, hydrolysis results in the formation of anatase nanoparticles in Figure 12. Figure 13 shows the nanoparticle size distribution showing that the largest proportion of nanoparticles has a diameter of about 30 nm.

Claims (8)

Patent claims 1. Synthesis process for the production of anatase nanoparticles with a high specific surface area and spherical morphology based on a sol-gel reaction, where a black solution containing soluble titanyl sulfate and a by-product of the production of TiO ₂ pigment is used as the starting material , - that the black solution undergoes a hydrolysis reaction in which the titanyl sulfate is converted into metatitanoic acid in the polycondensation reactions, which is the nanocrystalline anatase agglomerate, - hydrolysis of the black solution is carried out in the presence of hydrolysis tin, the reaction of which directs and defines the form of metatitanoic acid and the anatase polycrystals present therein, - that the resulting form of methattanoic acid is properly converted into anatase nanoparticles by the appropriate addition of a solution of barium chloride of different molar concentrations, - the reaction is carried out between barium chloride and the sulphate present in methattanic acid at room temperature, - that, with the addition of barium chloride, barium sulphate is formed, which is a by-product of the reaction and is formed as a product of precipitation between the sulphate ions and barium cations present in the metatitanic acid, - that the barium sulfate formed is quantitatively separated from the suspension of anatase nanoparticles by deposition and / or centrifugation / decantation, - the acidic suspension of the anatase nanoparticles obtained in the end is very stable, - that the resulting acidic suspension of the anatase nanoparticles contains between 200 and 300 g / L TiO ₂ , - it is possible to purify anatase nanoparticles from acidic suspension by raising the pH value, thereby achieving nanoparticle agglomeration and washing the resulting product upon filtration, - it is possible to resuspend the purified anatase nanoparticles in order to adjust the suspension with the desired pH and TiO ₂ mass concentration. 2. The method according to claim 1, characterized in that the size of the nanoparticles is controlled by varying the amount of hydrolysis pellets involved in the hydrolysis reaction of the black solution. Method according to claim 1, characterized in that the size of the anatase nanoparticles can be adjusted between 30 and 80 nm or more. Process according to claim 1, characterized in that the anatase nanoparticles obtained in the form of an acidic suspension have an approximate mass concentration of between 200 and 300 g / L and can be isolated and purified. • · -125. Process according to claim 1, characterized in that the initial suspension is acid removed and the suspension is optionally adjusted to pH to the desired value. Method according to Claims 1 to 5, characterized in that the process itself is constantly carried out in the wet, ie in the form of a suspension, which prevents the occurrence of potentially harmful dusting. Process according to Claims 1 to 6, characterized in that the nanoparticles thus obtained are polycrystalline and therefore there is no need for energy-wasteful calcination of the product. 8. Atanas nanoparticles, characterized in that they are obtained by the process of claims 1 to 7. 9. Athanas nanoparticles, characterized in that the anatase nanoparticles are polycrystalline, the crystallites exhibiting isotropic morphology and about 4-5 nm in size and exhibiting characteristic spherical morphology resulting from the aggregation of isotropic anatase crystallites.