Spherical nano titanium dioxide and preparation method thereof

Abstract

The invention relates to spherical nano titanium dioxide and a preparation method thereof, and the preparation method comprises the following steps: introducing a carrier gas carrying titanium tetrachloride gas into an aqueous solution containing a stabilizer, and hydrolyzing to obtain metatitanic acid; and mixing metatitanic acid and a pyrolysis auxiliary agent, and carrying out pyrolysis to obtain the spherical nano titanium dioxide. The spherical nano titanium dioxide is prepared by adopting a bubble template method, and the reaction temperature is reduced and the hydrolysis rate is accelerated by changing the titanium tetrachloride introduction mode and introducing the aqueous solution in a titanium tetrachloride gas mode. By adding the stabilizer, the viscosity of the solution is improved, the bubble stability is improved, spherical hollow metatitanic acid is finally formed, and hollow spherical titanium dioxide is formed after pyrolysis.

Description

Technical Field

[0001] This invention relates to the field of inorganic nanomaterials technology, and in particular to a spherical nano-titanium dioxide and its preparation method. Background Art

[0002] Nano-titanium dioxide, due to its unique physicochemical properties and excellent optical performance, has become an indispensable multifunctional material in modern industry. Because of its high refractive index, strong chemical stability, and non-toxicity, it is widely used in traditional fields such as coatings, plastics, papermaking, rubber, and food additives. At the same time, due to its high dielectric constant and resistivity, it also possesses semiconductor properties, playing an important role in high-tech industries such as electronic ceramics, semiconductor capacitors, thermistors, and specialty glasses.

[0003] Nano-spherical titanium dioxide, due to its excellent flowability and dispersibility, large specific surface area, and high packing density, shows great promise for applications in high-tech fields such as photocatalysts, photonic crystals, high-performance ceramics, and electronics. Furthermore, metal 3D printing technology (additive manufacturing) is developing at an astonishing pace, and titanium and titanium alloy powders, with their superior properties, have become the most important alloying raw materials in this technology. Therefore, spherical titanium dioxide precursors also have very broad application prospects in the field of metal 3D printing technology.

[0004] Currently, the main methods for preparing spherical titanium dioxide are gas-phase and liquid-phase methods. The gas-phase method is costly and requires sophisticated equipment, therefore the liquid-phase method is mostly used. CN107285377A discloses a method for preparing mesoporous hollow spherical titanium dioxide, including precursor preparation and the preparation of mesoporous hollow spherical titanium dioxide. Although this method produces hollow titanium dioxide particles, it still suffers from drawbacks such as complex process flow, high cost, and relatively large particle size of the spherical titanium dioxide.

[0005] CN106904651A discloses a method for preparing spherical titanium dioxide nanoparticles. This method includes preparing spherical titanium dioxide nanoparticles in one step using a titanium-containing precursor solution based on an aerosol. The specific steps of this method are as follows: (1) Using ethanol as a solvent and tetrabutyl titanate as a raw material, 1-5 mL of tetrabutyl titanate is added dropwise to 5-50 mL of anhydrous ethanol under stirring, and the mixture is stirred thoroughly to obtain a Ti-source precursor solution; (2) The precursor solution prepared in (1) is introduced into a tube furnace using an atomizer. The temperature of the tube furnace is 400℃-800℃. The powder at the tail end of the tube furnace is collected to obtain spherical titanium dioxide nanoparticles. This method has disadvantages such as high raw material cost, low reaction efficiency, uncontrollable reaction, solid spherical particles, and small specific surface area.

[0006] Therefore, how to develop a novel preparation process to achieve controllable reaction temperature and rate, good product dispersibility, adjustable crystal ratio, and titanium dioxide with a spherical hollow structure, and its preparation method, is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a method for preparing spherical nano-titanium dioxide. This method, using a bubble template approach, achieves controllable reaction temperature and rate by altering the introduction of titanium tetrachloride, thereby shortening the process flow, improving reaction efficiency, and reducing production costs. Furthermore, the addition of stabilizers and pyrolysis aids enables the preparation of highly dispersed titanium dioxide with adjustable crystal structure ratios.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0010] A carrier gas carrying titanium tetrachloride gas is passed into an aqueous solution containing a stabilizer, and after hydrolysis, metatitanic acid is obtained.

[0011] By mixing metatitanic acid with a pyrolysis aid and then pyrolyzing, spherical nano-titanium dioxide is obtained.

[0012] This invention employs a bubble template method to prepare spherical nano-titanium dioxide. On one hand, by changing the way titanium tetrachloride is introduced—using titanium tetrachloride gas to introduce it into the aqueous solution—the reaction temperature is lowered, and the hydrolysis rate is accelerated. Furthermore, the reaction rate can be controlled by adjusting the amount of titanium tetrachloride introduced, thus controlling the amount introduced. Using bubbles as templates and adding stabilizers, hollow spherical metatitanic acid can be prepared. The addition of pyrolysis aids inhibits particle agglomeration and lowers the crystal transformation temperature, thereby reducing production costs. This method shows promising application prospects and economic benefits.

[0013] On the other hand, the present invention uses a bubble template method to prepare metatitanic acid. Its formation mechanism mainly includes the following stages: First, the carrier gas carries titanium tetrachloride gas into the water to form bubbles. The titanium tetrachloride on the outside of the bubbles hydrolyzes with water to generate nanoparticles. The addition of a stabilizer increases the viscosity of the solution and increases the stability of the bubbles. During the slow rise of the bubbles, due to the low energy of the gas-liquid interface, the nanoparticles aggregate to establish a spherical framework. Subsequently, the bubbles inside the framework burst, and some of the internal titanium tetrachloride overflows and hydrolyzes with water. Water enters the interior of the framework and hydrolyzes with the internal titanium tetrachloride. The internal nanoparticles aggregate along the inner wall, and the external nanoparticles aggregate and grow along the outer surface, eventually forming spherical hollow metatitanic acid, which is then pyrolyzed to form hollow spherical titanium dioxide.

[0014] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0015] Preferably, the stabilizer comprises glycerol and / or polyvinyl alcohol.

[0016] This invention uses glycerol and / or polyvinyl alcohol as stabilizers to increase solution viscosity and bubble stability. During the slow rise of bubbles, due to the low energy at the gas-liquid interface, nanoparticles aggregate to form a spherical framework. Subsequently, the bubbles inside the framework rupture, and some of the internal titanium tetrachloride overflows and hydrolyzes with water. Water enters the framework and hydrolyzes with the internal titanium tetrachloride, causing internal nanoparticles to aggregate along the inner wall and external nanoparticles to aggregate and grow along the outer surface, ultimately forming spherical hollow metatitanic acid. Simultaneously, glycerol and polyvinyl alcohol possess strong coordination capabilities and suitable steric hindrance effects, resulting in well-dispersible spherical particles.

[0017] Monohydroxy alcohols, due to their weak coordination ability and low viscosity, cannot effectively "grasp" and "control" the particle surface, thus failing to guide spherical growth. Reactant diffusion is too rapid, hydrolysis is violent and uneven, nucleation occurs at different times, and growth rates vary, ultimately resulting in poorly dispersed, irregularly shaped particles. Other high-molecular-weight organic compounds, lacking strong coordination ability, steric hindrance, and high viscosity, cannot be synergistically used to prepare monodisperse hollow spherical particles.

[0018] Preferably, the mass percentage of the stabilizer in the aqueous solution containing the stabilizer is 5%-50%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] This invention further controls the mass percentage of stabilizer to 5%-50%. The stabilizer content affects the morphology and crystal form of the product. If the stabilizer content is too low, some spherical particles will be produced, while most will have no fixed morphology. Due to the influence of the stabilizer content, the hydrolysis rate will be too fast, and the anatase phase will transform into the rutile phase. If the stabilizer content is too high, the hydrolysis rate will be too slow, the gas absorption efficiency will be reduced, and the raw materials and stabilizer resources will be wasted.

[0020] Preferably, the viscosity of the aqueous solution containing the stabilizer is 0.5 mPa·s to 6 mPa·s, for example, it can be 0.5 mPa·s, 1 mPa·s, 1.5 mPa·s, 2 mPa·s, 2.5 mPa·s, 3 mPa·s, 3.5 mPa·s, 4 mPa·s, 4.5 mPa·s, 5 mPa·s, 5.5 mPa·s or 6 mPa·s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the carrier gas includes any one or a combination of at least two of air, nitrogen, or oxygen. Typical but non-limiting combinations include combinations of air and nitrogen, nitrogen and oxygen, air and oxygen, and air, nitrogen, and oxygen.

[0022] Preferably, the water content of the carrier gas is ≤0.002 g / m³. 3 For example, it could be 0g / m 3 0.0005g / m 3 0.001g / m 3 0.0015g / m 3 Or 0.002g / m 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0023] This invention further controls the water content of the carrier gas to ≤0.002 g / m³. 3 If the carrier gas contains too much water, it will cause the titanium tetrachloride gas to hydrolyze with the gas in the gas tube during the introduction process and slowly accumulate, leading to blockage of the gas tube.

[0024] Preferably, the inlet flow rate of the carrier gas is 0.1L / min-2L / min, for example, it can be 0.1L / min, 0.15L / min, 0.5L / min, 0.8L / min, 1L / min, 1.5L / min, 1.8L / min or 2L / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] This invention further controls the carrier gas flow rate to 0.1L / min-2L / min. If the carrier gas flow rate is too high, a large amount of titanium tetrachloride gas will escape without participating in the reaction, resulting in waste of raw materials. If the carrier gas flow rate is too low, the reaction efficiency will be slow, and primary particles of metatitanic acid will continuously accumulate on the surface of metatitanic acid, resulting in an increase in particle size.

[0026] Preferably, the titanium tetrachloride gas is obtained by heating a titanium tetrachloride solution.

[0027] Preferably, the heating temperature is 135℃-200℃, for example, it can be 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃ or 200℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0028] Preferably, the molar concentration of the titanium tetrachloride solution is 0.05M-2M, for example, it can be 0.05M, 0.08M, 0.1M, 0.4M, 0.5M, 0.9M, 1.0M, 1.2M, 1.5M, 1.8M or 2M, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the process after hydrolysis and before obtaining metatitanic acid further includes solid-liquid separation, washing, and drying;

[0030] Preferably, the washing process includes sequentially washing with water and washing with alcohol.

[0031] Preferably, the number of water washes is 2 to 5 times, for example, 2, 3, 4 or 5 times, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the washing solution after alcohol washing contains Cl - The mass ratio of the metatitanic acid to the metatitanic acid is (0.1-5):100, for example, it can be 0.1:100, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100 or 5:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] This invention further controls the Cl content in the metatitanic acid solid after alcohol washing. - The mass ratio of Cl to metatitanic acid is (0.1-5):100. - As a mineralizing agent, Cl can effectively reduce the crystal transformation temperature during pyrolysis. - If the content is too high, it will result in residual Cl in the product. - This results in poor product purity; if the Cl- content is too low, the crystal transformation temperature will decrease less, leading to increased production costs.

[0034] Preferably, the pyrolysis aid includes citric acid and / or oxalic acid.

[0035] This invention selects citric acid and oxalic acid as pyrolysis aids. By complexing with titanium ions, they decompose during pyrolysis, inhibiting particle agglomeration. Moreover, they decompose completely at high temperatures, leaving little residue.

[0036] Preferably, the mass ratio of the pyrolysis aid to metatitanic acid is (5-15):100, for example, it can be 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100, 12:100, 13:100, 14:100 or 15:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the pyrolysis temperature is 400℃-800℃, for example, it can be 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0038] This invention achieves complete decomposition of the pyrolysis aid by further controlling the pyrolysis temperature to 400℃-800℃, resulting in no impurities remaining in titanium dioxide. Furthermore, the crystal form (anatase phase and rutile phase) can be continuously adjusted by regulating the pyrolysis temperature.

[0039] Preferably, the pyrolysis time is 0.5h-5h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 1h-4h.

[0040] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0041] (1) Heating a titanium tetrachloride solution with a molar concentration of 0.05M-2M at 135℃-200℃ yields titanium tetrachloride gas with a water content ≤0.002g / m³. 3 Using any one or a combination of at least two of air, nitrogen, or oxygen as the carrier gas, the carrier gas carrying titanium tetrachloride gas is passed into an aqueous solution containing a stabilizer at a flow rate of 0.1 L / min to 2 L / min, and hydrolysis is carried out by bubble template method at 25℃ to 100℃ to obtain metatitanic acid slurry.

[0042] The stabilizer includes glycerol and / or polyvinyl alcohol; the aqueous solution containing the stabilizer has a stabilizer content of 5%-50% by mass.

[0043] (2) The metatitanic acid slurry obtained in step (1) is subjected to solid-liquid separation, water washing 2-5 times, and alcohol washing until Cl is added to the washing solution. - The mass ratio of metatitanic acid to metatitanic acid is (0.1-5):100, and after drying, metatitanic acid is obtained.

[0044] (3) The metatitanic acid obtained in step (2) is mixed with the pyrolysis aid and pyrolyzed at 400℃-800℃ for 1h-4h to obtain spherical nano-titanium dioxide; the pyrolysis aid includes citric acid and / or oxalic acid; the mass ratio of the pyrolysis aid to metatitanic acid is (5-15):100.

[0045] In a second aspect, the present invention provides a spherical nano-titanium dioxide, which is prepared by the preparation method described in the first aspect.

[0046] The spherical nano-titanium dioxide prepared by this invention has high dispersibility, uniform particle size, and controllable crystal form.

[0047] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has at least the following beneficial effects:

[0049] (1) This invention uses a bubble template method to prepare spherical nano-titanium dioxide. By changing the way titanium tetrachloride is introduced, titanium tetrachloride gas is introduced into the aqueous solution to lower the reaction temperature and accelerate the hydrolysis rate. The reaction rate can be controlled by controlling the amount of titanium tetrachloride introduced. The addition of a stabilizer increases the viscosity of the solution and increases the stability of the bubbles. During the slow rise of the bubbles, due to the low energy of the gas-liquid interface, the nanoparticles aggregate to form a spherical framework. Subsequently, the bubbles inside the framework burst, and some of the internal titanium tetrachloride overflows and hydrolyzes with water. Water enters the interior of the framework and hydrolyzes with the internal titanium tetrachloride. The internal nanoparticles aggregate along the inner wall, and the external nanoparticles aggregate and grow along the outer surface, eventually forming spherical hollow metatitanic acid, which is then pyrolyzed to form hollow spherical titanium dioxide.

[0050] (2) The spherical nano-titanium dioxide particles prepared by the present invention have uniform particle size and continuously adjustable crystal form. Attached Figure Description

[0051] Figure 1 These are the XRD patterns of the nano-titanium dioxide prepared in Examples 1-7 of this invention;

[0052] Figure 2 Here is a SEM image of the nano-titanium dioxide prepared in Example 4 of this invention;

[0053] Figure 3 This is a SEM image of the titanium dioxide prepared in Example 8 of this invention;

[0054] Figure 4 This is a SEM image of the titanium dioxide prepared in Example 10 of this invention;

[0055] Figure 5 This is a SEM image of the titanium dioxide prepared in Example 11 of this invention;

[0056] Figure 6 This is a SEM image of the titanium dioxide prepared in Comparative Example 1 of this invention;

[0057] Figure 7 This is a SEM image of the titanium dioxide prepared in Comparative Example 2 of this invention;

[0058] Figure 8 This is a SEM image of the titanium dioxide prepared in Comparative Example 3 of this invention;

[0059] Figure 9 This is a SEM image of the titanium dioxide prepared in Comparative Example 4 of this invention. Detailed Implementation

[0060] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0061] Unless otherwise specified, all reagents and consumables used in the following examples and comparative examples were purchased from conventional reagent manufacturers in the art; unless otherwise specified, the experimental methods and techniques used were conventional methods and techniques in the art.

[0062] Example 1

[0063] This embodiment provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0064] (1) Heating a titanium tetrachloride solution with a molar concentration of 0.05 M at 200 °C yields titanium tetrachloride gas with a water content of 0.0005 g / m³. 3 Using air as the carrier gas, the carrier gas carrying titanium tetrachloride gas was introduced into an aqueous solution containing 30% by mass at a flow rate of 0.1 L / min, and hydrolysis was carried out at 100 °C using a bubble template method to obtain metatitanic acid slurry.

[0065] (2) The obtained metatitanic acid slurry was subjected to solid-liquid separation, washed with water three times, and washed with alcohol until the metatitanic acid solid was dissolved. - The mass ratio of metatitanic acid to metatitanic acid is 0.5:100, and after drying, metatitanic acid is obtained.

[0066] (3) The mixed metatitanic acid and citric acid were pyrolyzed at 400℃ for 2h to obtain spherical nano-titanium dioxide; the mass ratio of citric acid to metatitanic acid was 11:100.

[0067] Example 2

[0068] This embodiment provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0069] (1) Heating a 0.9 M titanium tetrachloride solution at 180 °C yields titanium tetrachloride gas with a water content of 0.0015 g / m³. 3 Nitrogen gas was used as the carrier gas, and the carrier gas carrying titanium tetrachloride gas was introduced into an aqueous solution containing 50% polyvinyl alcohol by mass at a flow rate of 0.3 L / min. Hydrolysis was carried out by bubble template method at 80 °C to obtain metatitanic acid slurry.

[0070] (2) The obtained metatitanic acid slurry was subjected to solid-liquid separation, washed twice with water, and washed with alcohol until the metatitanic acid solid was dissolved. - The mass ratio of metatitanic acid to metatitanic acid is 1:100, and after drying, metatitanic acid is obtained.

[0071] (3) The mixed metatitanic acid and oxalic acid were pyrolyzed at 500℃ for 2h to obtain spherical nano-titanium dioxide; the mass ratio of oxalic acid to metatitanic acid was 9:100.

[0072] Example 3

[0073] This embodiment provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0074] (1) Heating a titanium tetrachloride solution with a molar concentration of 0.08 M at 145 °C yields titanium tetrachloride gas with a water content of 0.0003 g / m³. 3 Using oxygen as the carrier gas, the carrier gas carrying titanium tetrachloride gas was passed into an aqueous solution containing 10% by mass of glycerol at a flow rate of 1.8 L / min. The mixture was then hydrolyzed using a bubble template method at 40 °C to obtain metatitanic acid slurry.

[0075] (2) The obtained metatitanic acid slurry was subjected to solid-liquid separation, water washing five times, and alcohol washing until the metatitanic acid solid was dissolved. - The mass ratio of metatitanic acid to metatitanic acid is 0.1:100, and after drying, metatitanic acid is obtained.

[0076] (3) The mixed metatitanic acid and oxalic acid were pyrolyzed at 600℃ for 3.5h to obtain spherical nano-titanium dioxide; the mass ratio of oxalic acid to metatitanic acid was 7:100.

[0077] Example 4

[0078] This embodiment provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0079] (1) Heating a 1.5 M titanium tetrachloride solution at 135 °C yields titanium tetrachloride gas with a water content of 0.001 g / m³. 3 A mixture of air and nitrogen (volume ratio 1:1) was used as the carrier gas. The carrier gas carrying titanium tetrachloride was introduced into an aqueous solution containing 20% ​​polyvinyl alcohol by mass at a flow rate of 2 L / min. Hydrolysis was carried out at 60 °C using a bubble template method to obtain metatitanic acid slurry.

[0080] (2) The obtained metatitanic acid slurry was subjected to solid-liquid separation, washed twice with water, and washed with alcohol until the mass ratio of Cl- to metatitanic acid in the metatitanic acid solid was 4:100. After drying, metatitanic acid was obtained.

[0081] (3) The mixed metatitanic acid and citric acid were pyrolyzed at 650℃ for 3h to obtain spherical nano-titanium dioxide; the mass ratio of citric acid to metatitanic acid was 13:100.

[0082] SEM images of spherical nano-titanium dioxide prepared by the bubble template method are shown below. Figure 2 As shown, from Figure 2 As can be seen from the figure, most of the particles are regular monodisperse spherical morphology. Due to compression, stirring, shearing, impact and other reasons, a very small number of particles are broken. After the particles are broken, they can be seen from the figure to be hollow structures with regular and flat inner and outer surfaces. Therefore, it is indicated that the titanium dioxide prepared is a spherical hollow structure.

[0083] Example 5

[0084] This embodiment provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0085] (1) Heating a 0.4 M titanium tetrachloride solution at 165 °C yields titanium tetrachloride gas with a water content of 0.002 g / m³. 3 A mixture of air and oxygen (volume ratio 1:1) was used as the carrier gas. The carrier gas carrying titanium tetrachloride was passed into an aqueous solution containing 5% by mass of glycerol and polyvinyl alcohol (mass ratio of glycerol and polyvinyl alcohol 1:1) at a flow rate of 0.1 L / min. Hydrolysis was carried out at 90 °C using a bubble template method to obtain metatitanic acid slurry.

[0086] (2) The obtained metatitanic acid slurry was subjected to solid-liquid separation, water washing 4 times, and alcohol washing until the mass ratio of Cl- to metatitanic acid in the metatitanic acid solid was 2:100. After drying, metatitanic acid was obtained.

[0087] (3) The mixed metatitanic acid and pyrolysis aid (a mixture of citric acid and oxalic acid in a mass ratio of 1:2) were pyrolyzed at 700℃ for 2.5h to obtain spherical nano-titanium dioxide; the mass ratio of pyrolysis aid to metatitanic acid was 5:100.

[0088] Example 6

[0089] This embodiment provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0090] (1) Heating a 2M titanium tetrachloride solution at 190℃ yields titanium tetrachloride gas with a water content of 0.0018 g / m³. 3 A mixture of nitrogen and oxygen (volume ratio 1:1) was used as the carrier gas. The carrier gas carrying titanium tetrachloride was introduced into an aqueous solution containing 40% by mass at a flow rate of 0.5 L / min. Hydrolysis was carried out at 50 °C using a bubble template method to obtain metatitanic acid slurry.

[0091] (2) The obtained metatitanic acid slurry was subjected to solid-liquid separation, water washing 4 times, and alcohol washing until the mass ratio of Cl- to metatitanic acid in the metatitanic acid solid was 0.8:100. After drying, metatitanic acid was obtained.

[0092] (3) The mixed metatitanic acid and citric acid were pyrolyzed at 750℃ for 1h to obtain spherical nano-titanium dioxide; the mass ratio of citric acid to metatitanic acid was 15:100.

[0093] Example 7

[0094] This embodiment provides a method for preparing spherical nano-titanium dioxide, the method comprising the following steps:

[0095] (1) A titanium tetrachloride solution with a molar concentration of 0.1 M was heated at 150 °C to obtain titanium tetrachloride gas with a water content of 0.0005 g / m³. 3 Air, nitrogen and oxygen (volume ratio of 1:1:1) were used as carrier gas. The carrier gas carrying titanium tetrachloride gas was passed into an aqueous solution containing 35% by mass of glycerol and polyvinyl alcohol (mass ratio of glycerol and polyvinyl alcohol of 1:1) at a flow rate of 1 L / min. The mixture was hydrolyzed by bubble template method at 25 °C to obtain metatitanic acid slurry.

[0096] (2) The obtained metatitanic acid slurry was subjected to solid-liquid separation, washed with water 3 times, and washed with alcohol until the mass ratio of Cl- to metatitanic acid in the metatitanic acid solid was 0.5:100. After drying, metatitanic acid was obtained.

[0097] (3) The mixed metatitanic acid and citric acid were pyrolyzed at 800℃ for 1.5h to obtain spherical nano-titanium dioxide; the mass ratio of citric acid to metatitanic acid was 10:100.

[0098] The XRD patterns of the nano-titanium dioxide prepared in Examples 1-7 are shown below. Figure 1 As shown in the figure, the crystal structure of nano-titanium dioxide can be continuously adjusted by controlling the pyrolysis temperature.

[0099] Example 8

[0100] This embodiment provides a method for preparing spherical nano-titanium dioxide, which differs from Example 1 only in that the mass percentage of glycerol in the aqueous solution is replaced from 30% to 2%, while the other steps remain unchanged.

[0101] SEM images of the obtained spherical nano-titanium dioxide are shown below. Figure 3 As shown, from Figure 3 As can be seen, there are a large number of small particles and some particles are broken. The main reason is that the morphology cannot be precisely controlled due to the low glycerol content. A small portion forms spherical particles, while most aggregate into small particles. The integrity and uniformity of the particles are far inferior to those in Example 4.

[0102] Example 9

[0103] This embodiment provides a method for preparing spherical nano-titanium dioxide, which differs from Example 1 only in that the mass percentage of glycerol in the aqueous solution is replaced from 30% to 60%, while the other steps remain unchanged.

[0104] Example 10

[0105] This embodiment provides a method for preparing spherical nano-titanium dioxide, which differs from Example 1 only in that glycerol is replaced with an equal mass of ethanol, while the other steps remain unchanged.

[0106] SEM images of the obtained spherical nano-titanium dioxide are shown below. Figure 4 As shown, from Figure 4 As can be seen, some spherical particles appear, but the overall particles are severely aggregated. The main reason is that monohydroxy alcohols, due to their weak coordination ability and low viscosity, cannot effectively "grab" and "control" the particle surface. Therefore, they cannot guide a large number of spherical growths. The reactants diffuse too quickly, the hydrolysis reaction is violent and uneven, nucleation occurs at different times, and the growth rate is different. In the end, the particles are poorly dispersed and have irregular shapes.

[0107] Example 11

[0108] This embodiment provides a method for preparing spherical nano-titanium dioxide, which differs from Example 1 only in that glycerol is replaced with polyethylene oxide, while the other steps remain unchanged.

[0109] SEM images of the prepared spherical nano-titanium dioxide are shown below. Figure 5 As shown, from Figure 5As can be seen, the particle size is in the micrometer range, with severe agglomeration and uneven morphology and particle size. The main reason is that polyethylene oxide does not have strong coordination ability, steric hindrance effect and high viscosity at the same time, so it is impossible to accurately control particle growth, resulting in particle agglomeration, uneven morphology and particle size, and the morphological characteristics are far inferior to those of Example 4.

[0110] Comparative Example 1

[0111] This comparative example provides a method for preparing titanium dioxide, which differs from Example 1 only in that a 0.05M titanium tetrachloride solution is directly added to an aqueous solution containing a stabilizer, followed by liquid-phase hydrolysis to obtain a metatitanic acid slurry. The remaining steps remain unchanged.

[0112] SEM images of the prepared titanium dioxide are shown below. Figure 6 As shown, from Figure 6 As can be seen, the particle size distribution is uneven and the agglomeration is severe. The main reason is that there is no fixed template after the solution is added directly, and titanium tetrachloride hydrolyzes and agglomerates rapidly, so it is impossible to form spherical particles. At the same time, due to the presence of stabilizer, it plays a steric hindrance role, so that the particles are all nano-sized agglomerates, and the morphology is far inferior to that of Example 4.

[0113] Comparative Example 2

[0114] This comparative example provides a method for preparing titanium dioxide, which differs from Example 1 only in that no stabilizer is added, while the other steps remain the same.

[0115] SEM images of the prepared titanium dioxide are shown below. Figure 7 As shown, from Figure 7 As can be seen, the particle size distribution is uneven and the agglomeration is severe. The main reason is that there is no stabilizer. After titanium tetrachloride is introduced, it undergoes rapid hydrolysis. Due to the instability of the system, the nanocrystals tend to aggregate and grow, forming micron-sized agglomerates.

[0116] Comparative Example 3

[0117] This comparative example provides a method for preparing titanium dioxide, which differs from Example 1 only in that no pyrolysis aid is added, while the other steps remain the same.

[0118] SEM images of the prepared titanium dioxide are shown below. Figure 8 As shown, from Figure 8 As can be seen, the product has a large number of broken particles and severe agglomeration. The main reason is that no organic acid molecules were added. In the early stage of roasting, the particles were physically damaged by internal pressure and structural stress. In the later stage of roasting, the particles were fused by surface-driven material migration, which led to agglomeration.

[0119] Comparative Example 4

[0120] This comparative example provides a method for preparing titanium dioxide, which differs from Example 1 in that no stabilizer or pyrolysis aid is added, while the remaining steps remain unchanged.

[0121] SEM images of the prepared titanium dioxide are shown below. Figure 9 As shown, from Figure 9 As can be seen from the data, the particle size distribution is uneven, the agglomeration is severe, and there are no micron-sized large particles with a fixed morphology. The main reason is that no stabilizer was added, which made it impossible to obtain spherical monodisperse metatitanic acid. The absence of pyrolysis aids during the calcination process caused the particles to fuse together, thus resulting in severe agglomeration.

[0122] test:

[0123] (1) Crystal content test: The content of rutile was calculated using the quantitative analysis formula.

[0124]

[0125] Wherein, Fr represents the rutile phase content; IA and IB are the diffraction intensities of the anatase (101) diffraction plane (2θ = 25.4°) and the rutile (110) diffraction plane (2θ = 27.4°) in the powder XRD curve, respectively.

[0126] The XRD patterns of the nano-titanium dioxide prepared in Examples 1-7 are shown below. Figure 1 As shown in the figure, the crystal structure of nano-titanium dioxide can be continuously adjusted by controlling the pyrolysis temperature.

[0127] (2) Cl- content test: Dissolve the metatitanic acid sample in dilute nitric acid or sodium hydroxide (choose according to the sample properties), filter to remove insoluble matter, adjust the pH to neutral or weakly alkaline (pH=7-9), add 5% potassium chromate indicator (1mL), and titrate with standard silver nitrate solution (e.g. 0.01mol / L) until a brick-red precipitate appears in the solution and does not fade.

[0128]

[0129] V: Volume of silver nitrate consumed (mL); C: Concentration of silver nitrate (mol / L); m: Mass of sample (g).

[0130] The titanium dioxide prepared in the examples and comparative examples was tested, and the test results are shown in Table 1 below.

[0131] Table 1

[0132]

[0133]

[0134] The test results show that:

[0135] (1) As can be seen from Examples 1-7 and Table 1, the present invention uses the bubble template method to prepare spherical nano-titanium dioxide. By changing the way titanium tetrachloride is introduced, the aqueous solution is introduced in the form of titanium tetrachloride gas, the reaction temperature is reduced, the hydrolysis rate is accelerated, and the reaction rate can be controlled by controlling the amount of titanium tetrachloride introduced. The addition of stabilizer increases the viscosity of the solution and increases the stability of the bubbles. During the slow rise of the bubbles, due to the low energy of the gas-liquid interface, the nanoparticles aggregate to form a spherical framework. Subsequently, the bubbles inside the framework break, and part of the internal titanium tetrachloride overflows and hydrolyzes with water. Water enters the interior of the framework and hydrolyzes with the internal titanium tetrachloride. The internal nanoparticles aggregate along the inner wall, and the external nanoparticles aggregate and grow along the outer surface, eventually forming spherical hollow metatitanic acid, which forms hollow spherical titanium dioxide after pyrolysis.

[0136] (2) By comparing Example 1 with Examples 8-9, it can be seen that the present invention further controls the mass percentage of stabilizer to 5%-50%. The stabilizer content affects the morphology and crystal form of the product. If the stabilizer content is too low, some spherical particles will be produced, and most of them will have no fixed morphology. Due to the influence of the stabilizer content, the hydrolysis rate is too fast and the anatase phase will transform into the rutile phase. If the stabilizer content is too high, the hydrolysis rate will be too slow, the gas absorption efficiency will be reduced, and the raw materials and stabilizer resources will be wasted.

[0137] (3) A comparison of Example 1 with Examples 10-11 shows that the present invention uses glycerol and / or polyvinyl alcohol as stabilizers to increase the viscosity of the solution and enhance bubble stability. During the slow rise of the bubbles, due to the low energy of the gas-liquid interface, nanoparticles aggregate to form a spherical framework. Subsequently, the bubbles inside the framework rupture, and some of the internal titanium tetrachloride overflows and hydrolyzes with water. Water enters the interior of the framework and hydrolyzes with the internal titanium tetrachloride. The internal nanoparticles aggregate along the inner wall, and the external nanoparticles aggregate and grow along the outer surface, eventually forming spherical hollow metatitanic acid. However, monohydroxy alcohols, due to their weak coordination ability and low viscosity, cannot effectively "grasp" and "control" the particle surface, thus failing to guide spherical growth. The reactants diffuse too quickly, the hydrolysis reaction is violent and uneven, nucleation occurs at different times, and the growth rate is inconsistent, ultimately resulting in poorly dispersed and irregularly shaped particles. Other high-molecular organic compounds, due to their lack of strong coordination ability, steric hindrance effect, and high viscosity, cannot synergistically prepare monodisperse hollow spherical particles.

[0138] (4) As can be seen from Example 1 and Comparative Example 1, the spherical nano-titanium dioxide prepared by the bubble template method of the present invention, compared with the liquid phase method in the prior art, has lower local reaction temperature and Ti content. 4+The concentration is controllable and uniform, so the prepared metatitanic acid has good dispersibility and small particle size. In contrast, the local high temperature in Comparative Example 1 accelerated the transformation of the anatase phase to the rutile phase, resulting in an increase in the rutile phase content. Therefore, this invention shows that the process has the advantages of uniform and controllable reaction temperature, simple process, high dispersibility of the prepared spherical nano-titanium dioxide, and controllable crystal form.

[0139] (5) As can be seen from Example 1 and Comparative Examples 2-4, the present invention can obtain spherical nano-titanium dioxide materials with high dispersibility, uniform particle size and controllable crystal form by adding a stabilizer during the hydrolysis process to promote high dispersion of metatitanic acid and inhibit its hydrolysis rate to reduce the rutile phase content, and by adding a pyrolysis aid to inhibit particle agglomeration and reduce crystal transformation temperature during the pyrolysis process.

[0140] In summary, this invention uses a bubble template method to prepare spherical nano-titanium dioxide. By changing the way titanium tetrachloride is introduced into the aqueous solution as titanium tetrachloride gas, the reaction temperature is lowered, and the hydrolysis rate is accelerated. The reaction rate can be controlled by adjusting the amount of titanium tetrachloride introduced through the carrier gas flow rate. The addition of a stabilizer increases the solution viscosity, thereby increasing bubble stability. During the slow rise of the bubbles, due to the low energy at the gas-liquid interface, nanoparticles aggregate to form a spherical framework. Subsequently, the bubbles inside the framework burst, and some of the internal titanium tetrachloride overflows and hydrolyzes with water. Water enters the interior of the framework and hydrolyzes with the internal titanium tetrachloride. The internal nanoparticles aggregate along the inner wall, while the external nanoparticles aggregate and grow along the outer surface, ultimately forming spherical hollow metatitanic acid, which, after pyrolysis, forms hollow spherical titanium dioxide.

[0141] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing spherical nano-titanium dioxide, characterized in that, The preparation method includes the following steps: A carrier gas carrying titanium tetrachloride gas is passed into an aqueous solution containing a stabilizer, and after hydrolysis, metatitanic acid is obtained. By mixing metatitanic acid with a pyrolysis aid and then pyrolyzing, spherical nano-titanium dioxide is obtained.

2. The preparation method according to claim 1, characterized in that, The stabilizer includes glycerol and / or polyvinyl alcohol; Preferably, the stabilizer content in the aqueous solution containing the stabilizer is 5%-50% by mass.

3. The preparation method according to claim 1 or 2, characterized in that, The carrier gas includes any one or a combination of at least two of air, nitrogen, or oxygen.

4. The preparation method according to any one of claims 1-3, characterized in that, The water content of the carrier gas is ≤0.002 g / m³. 3 ; Preferably, the flow rate of the carrier gas is 0.1 L / min to 2 L / min.

5. The preparation method according to any one of claims 1-4, characterized in that, The titanium tetrachloride gas is obtained by heating a titanium tetrachloride solution; Preferably, the heating temperature is 135℃-200℃; Preferably, the molar concentration of the titanium tetrachloride solution is 0.05M-2M.

6. The preparation method according to any one of claims 1-5, characterized in that, The process after hydrolysis and before obtaining metatitanic acid also includes solid-liquid separation, washing, and drying. Preferably, the washing process includes sequentially washing with water and washing with alcohol; Preferably, the Cl in the alcohol-washed metatitanic acid solid is... - The mass ratio of the metatitanic acid to the metatitanic acid is (0.1-5):

100.

7. The preparation method according to any one of claims 1-6, characterized in that, The pyrolysis aid includes citric acid and / or oxalic acid; Preferably, the mass ratio of the pyrolysis aid to metatitanic acid is (5-15):

100.

8. The preparation method according to any one of claims 1-7, characterized in that, The pyrolysis temperature is 400℃-800℃; Preferably, the pyrolysis time is 0.5h-5h, and more preferably 1h-4h.

9. The preparation method according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: (1) Heating a titanium tetrachloride solution with a molar concentration of 0.05M-2M at 135℃-200℃ yields titanium tetrachloride gas with a water content ≤0.002g / m³. 3 Using any one or a combination of at least two of air, nitrogen, or oxygen as the carrier gas, the carrier gas carrying titanium tetrachloride gas is passed into an aqueous solution containing a stabilizer at a flow rate of 0.1 L / min to 2 L / min, and hydrolysis is carried out by bubble template method at 25℃ to 100℃ to obtain metatitanic acid slurry. The stabilizer includes glycerol and / or polyvinyl alcohol; the aqueous solution containing the stabilizer has a stabilizer content of 5%-50% by mass. (2) The metatitanic acid slurry obtained in step (1) is subjected to solid-liquid separation, water washing 2-5 times, and alcohol washing until Cl is added to the washing solution. - The mass ratio of metatitanic acid to metatitanic acid is (0.1-5):100, and after drying, metatitanic acid is obtained. (3) Mix the metatitanic acid obtained in step (2) with the pyrolysis aid and pyrolyze at 400℃-800℃ for 1h-4h to obtain spherical nano titanium dioxide. The pyrolysis aid includes citric acid and / or oxalic acid; the mass ratio of the pyrolysis aid to metatitanic acid is (5-15):

100.

10. A spherical nano-titanium dioxide, characterized in that, The spherical nano-titanium dioxide is prepared by the preparation method according to any one of claims 1-9.

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