Method for preparing doped barium titanate nanocrystals by Pickering reverse miniemulsion

Abstract

The present invention relates to the fields of Pickering miniemulsions, solvent thermal treatment, photocatalysis, and battery electrodes, and particularly to a method for preparing doped barium titanate nanocrystals using a Pickering inverse miniemulsion. The method utilizes the solubility differences of barium hydroxide to prepare a Pickering inverse miniemulsion using solid barium hydroxide as an emulsifier. This liquid droplet serves as a nanoreactor to obtain a Pickering inverse miniemulsion containing a doped barium titanate precursor. Finally, the Pickering inverse miniemulsion is subjected to solvent thermal treatment to form the doped nanocrystals. The doped nanocrystals prepared by this method have potential applications in the fields of photoelectric conversion, battery materials, and catalysis.

Description

Technical Field

[0001] The invention relates to the fields of Pickering miniemulsion, solvent thermal treatment, photocatalysis and battery electrodes, and in particular to a method for preparing doped barium titanate nanocrystals using a Pickering reverse miniemulsion. Background Art

[0002] Pickering emulsions, also known as Pickering emulsions, are emulsions formed using ultrafine solid particles as emulsifiers. Miniemulsions are obtained by shearing a mixture containing two immiscible liquid phases (e.g., oil and water), one or more emulsifiers, and possibly one or more co-emulsifiers (typical examples are hexadecane or cetyl alcohol). Miniemulsions are oil-in-water (O / W) miniemulsions formed using water-soluble salts as co-emulsifiers.

[0003] Pickering inverse miniemulsions combine the characteristics of both inverse miniemulsions and Pickering emulsions, offering advantages such as low cost, environmental friendliness, and strong emulsion stability. The stability of Pickering inverse miniemulsions depends primarily on the adsorption capacity of solid particles at the interface. Solid particles adsorb at the oil / water interface to form a dense film, reducing the likelihood of coalescence between droplets. The electrostatic repulsion between particles also inhibits stratification or sedimentation of the emulsion. Pickering inverse miniemulsions can easily self-assemble into nanomaterials.

[0004] Barium titanate, a white perovskite powder with the chemical formula BaTiO3, possesses excellent electrical properties and is a hot topic in ferroelectric research. Barium titanate has a typical ABO3-type polymorphic crystal structure. Common methods for synthesizing barium titanate crystals include sintering a mixture of titanium tetrachloride, barium chloride, and alkali, or hydrothermally or solvothermally preparing a mixture of n-butyl titanate and barium hydroxide. Synthesis of barium titanate generally requires strong base or acid conditions, which are intolerant to the emulsifiers typically required in miniemulsion methods. Consequently, suitable methods are needed to maintain the stability of the miniemulsion dispersion. Summary of the Invention

[0005] The present invention aims to use a special emulsifier to preliminarily stabilize an inverse miniemulsion and to form a Pickering inverse miniemulsion with doped barium titanate nanocrystals as a solid emulsifier by solvent thermal treatment.

[0006] The above method is carried out according to the following steps:

[0007] (1) Preparation of Pickering reverse miniemulsion with barium hydroxide solid as emulsifier:

[0008] At room temperature, a quantitative saturated barium hydroxide solution, a quantitative alcoholamine, and a quantitative organic solvent are mixed and transferred to an ultrasonic biopulverizer. The mixed system is cooled by salt ice and maintained in an ultrasonic state. After a certain period of ultrasonication, a Pickering reverse miniemulsion with barium hydroxide solid as an emulsifier is obtained, and the system is maintained in a low-temperature state.

[0009] In step (1), the barium hydroxide is barium hydroxide monohydrate or barium hydroxide octahydrate;

[0010] Alcoholamines include monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, dimethylethanolamine, methyldiethanolamine and diglycolamine;

[0011] The organic solvent was a mixture of n-pentane and cyclohexane.

[0012] The mass ratio of the saturated barium hydroxide solution, the alcoholamine and the organic solvent is 10:0.5-1.0:100. The mass ratio of n-pentane to cyclohexane in the organic solvent is 20:80.

[0013] The power of the ultrasonic bio-crusher is 200W, the salt ice is controlled at -5-0°C, the system low temperature is 0-5°C, and the ultrasonic time is 5 minutes.

[0014] (2) Preparation of Pickering inverse miniemulsion containing doped barium titanate precursor:

[0015] At room temperature, a quantitative titanium compound and a quantitative concentration of a water-soluble doping metal salt solution are added dropwise to a Pickering miniemulsion prepared in step (1) and containing a quantitative barium hydroxide solid as an emulsifier, and the mixed system is cooled by salt ice and maintained in an ultrasonic state; after ultrasonication for a certain period of time, a Pickering inverse miniemulsion containing a doped barium titanate precursor is obtained, and the system is maintained in a low-temperature state.

[0016] The titanium compound in step (2) is n-butyl titanate or isobutyl titanate;

[0017] The water-soluble doping metal salt is a functional nitro salt, such as yttrium nitrate, and the mass concentration of the water-soluble doping metal salt solution is 0.1%. The mass ratio of the titanium compound to the water-soluble doping metal salt solution and the Pickering miniemulsion containing the barium hydroxide solid as an emulsifier in step (1) is 1-2:0.1:100.

[0018] The power of the ultrasonic bio-disintegrator is 200W, the salt and ice are controlled at 0-5°C, the system low temperature is 5-10°C, and the ultrasonic time is 1 minute.

[0019] (3) Preparation of Pickering inverse miniemulsion containing doped barium titanate nanocrystals:

[0020] At room temperature, the Pickering miniemulsion containing the doped barium titanate precursor prepared in the quantitative step (2) is transferred to a high-pressure reactor equipped with an ultrasonic device; then the temperature is kept for a predetermined time, and the reaction liquid is taken out after solvent thermal treatment to obtain a Pickering inverse miniemulsion containing doped nanocrystals.

[0021] In step (3), the mass volume ratio of the Pickering inverse miniemulsion containing the doped barium titanate precursor prepared in step (2) to the high-pressure reactor is 50:100 (g / ml); the hydrothermal treatment is set to a holding temperature of 80-120°C, an ultrasonic power of 200W, and a holding time of 12-48 hours.

[0022] The invention utilizes the difference in solubility of barium hydroxide to prepare a Pickering inverse miniemulsion with barium hydroxide solid as an emulsifier; uses the liquid droplets as nanoreactors to obtain a Pickering inverse miniemulsion containing a doped barium titanate precursor; and finally forms a Pickering inverse miniemulsion containing doped nanocrystals through solvent thermal treatment.

[0023] The present invention has the following advantages:

[0024] 1. The Pickering inverse miniemulsion droplet size formed by barium hydroxide as a solid emulsifier can be maintained at 50-200 nanometers, and the solid particle size of barium hydroxide is only about 5 nanometers;

[0025] 2. Using barium hydroxide as a solid emulsifier to form Pickering inverse miniemulsion droplets as a reactor can form a stable Pickering inverse miniemulsion containing doped nanocrystal precursors;

[0026] 3. Solvent thermal treatment of a Pickering inverse miniemulsion containing a doped barium titanate precursor can form a Pickering inverse miniemulsion with doped barium titanate below 10 nanometers as a nano solid stabilizer, and the droplet size can be maintained at 100-200 nanometers.

[0027] 4. Doping barium titanate nanocrystals can improve the performance of the material by modulating its band gap size, conductivity, magnetism, photocatalytic properties, etc. to meet new application needs; it can also improve the photoelectric conversion efficiency and has good stability, and is widely used in the fields of photocatalysis, photovoltaics and sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an electron microscope image of the Pickering inverse emulsion droplets in step (1) of Example 1.

[0029] Figure 2 This is an electron microscope image of nano-solids on the surface of Pickering inverse miniemulsion droplets in step (1) of Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to examples.

[0031] Example 1

[0032] (1) Preparation of Pickering reverse miniemulsion with barium hydroxide solid as emulsifier:

[0033] At room temperature, a mixture of 10 grams of a saturated solution of barium hydroxide monohydrate, 0.5 grams of monoethanolamine, and an organic solvent consisting of 20 grams of n-pentane and 80 grams of cyclohexane was transferred to a 200W ultrasonic biopulverizer. The mixture was cooled to -5°C with ice and maintained in an ultrasonic state. After 5 minutes of ultrasonication, a Pickering inverse miniemulsion containing solid barium hydroxide as the emulsifier was obtained, and the system was maintained at a low temperature of 0°C. The Pickering inverse miniemulsion had a Z-average droplet size of 200 nanometers and a dispersion index (PDI) of 0.15. Figure 1 This is a TEM image of Pickering reverse miniemulsion droplets with barium hydroxide solid as emulsifier. Figure 2 This is a morphology image of solid barium hydroxide on the surface of Pickering inverse miniemulsion droplets. The solid barium hydroxide particle size is 5 nanometers.

[0034] (2) Preparation of Pickering inverse miniemulsion containing doped barium titanate precursor:

[0035] At room temperature, 1 gram of n-butyl titanate and 0.1 gram of a 0.1% mass concentration water-soluble yttrium nitrate-doped metal salt are added dropwise to 100 grams of barium hydroxide solid prepared in step (1) as an emulsifier in a Pickering miniemulsion, and the mixed system is cooled to 0°C by salt ice and maintained in an ultrasonic state of a 200W ultrasonic cell crusher; after ultrasonication for 1 minute, a Pickering inverse miniemulsion containing a doped barium titanate precursor is obtained, and the system is maintained at a low temperature of 5°C.

[0036] (3) Preparation of Pickering inverse miniemulsion containing doped barium titanate nanocrystals:

[0037] At room temperature, 50 g of the Pickering miniemulsion containing the doped barium titanate precursor prepared in step (2) was transferred to a 100 ml autoclave equipped with a 200 W ultrasonic device; the mixture was then incubated at 80° C. for 48 hours. After solvent thermal treatment, the reaction solution was removed to obtain a Pickering inverse miniemulsion containing yttrium-doped barium titanate nanocrystals. The Pickering inverse miniemulsion droplets had a Z-average particle size of 150 nm and a dispersion index (PDI) of 0.10. X-ray diffraction analysis showed that the yttrium-doped barium titanate nanomaterials met the characteristic diffraction peaks of the barium titanate PDF standard card, and the spectrum showed a right-shifted secondary diffraction peak of the yttrium-doped barium titanate nanocrystals. The average particle size of the nanocrystals was calculated to be 10 nm based on the half-width at half maximum of the diffraction peak.

[0038] Example 2

[0039] (1) Preparation of Pickering reverse miniemulsion with barium hydroxide solid as emulsifier:

[0040] At room temperature, 10 grams of a saturated solution of barium hydroxide octahydrate, 1.0 grams of diisopropanolamine, and an organic solvent consisting of 20 grams of n-pentane and 80 grams of cyclohexane were mixed and transferred to a 200W ultrasonic biopulverizer. The mixture was cooled to 0°C with ice and maintained in an ultrasonic state. After 5 minutes of ultrasonication, a Pickering inverse miniemulsion containing solid barium hydroxide as the emulsifier was obtained, and the system was maintained at a low temperature of 5°C. The Pickering inverse miniemulsion had a Z-average particle size of 100 nanometers and a dispersion index (PDI) of 0.10.

[0041] (2) Preparation of Pickering inverse miniemulsion containing doped barium titanate precursor:

[0042] At room temperature, 2 g of isobutyl titanate and 0.1 g of a 0.1% mass concentration water-soluble yttrium nitrate-doped metal salt are added dropwise to 100 g of a Pickering miniemulsion prepared in step (1) with barium hydroxide solid as an emulsifier. The mixed system is cooled to 5° C. by salt ice and maintained in an ultrasonic state using a 200W ultrasonic cell crusher. After ultrasonication for 1 minute, a Pickering inverse miniemulsion containing a doped barium titanate precursor is obtained, and the system is maintained at a low temperature of 10° C.

[0043] (3) Preparation of Pickering inverse miniemulsion containing doped barium titanate nanocrystals:

[0044] At room temperature, 50 g of the Pickering miniemulsion containing the doped barium titanate precursor prepared in step (2) was transferred to a 100 ml autoclave equipped with a 200 W ultrasonic device; the reaction mixture was then incubated at 120° C. for 12 hours. After solvent thermal treatment, the reaction solution was removed to obtain a Pickering inverse miniemulsion containing yttrium-doped barium titanate nanocrystals. The Pickering inverse miniemulsion droplets had a Z-average particle size of 100 nm and a dispersion index (PDI) of 0.08. X-ray diffraction analysis showed that the yttrium-doped barium titanate nanomaterials met the characteristic diffraction peaks of the barium titanate PDF standard card, and the spectrum showed a right-shifted secondary diffraction peak of the yttrium-doped barium titanate nanocrystals. The average particle size of the nanocrystals was calculated to be 5 nm based on the half-width at half maximum of the diffraction peak.

[0045] Example 3

[0046] (1) Preparation of Pickering reverse miniemulsion with barium hydroxide solid as emulsifier:

[0047] At room temperature, a mixture of 10 grams of a saturated barium hydroxide octahydrate solution, 0.7 grams of diethanolamine, and an organic solvent consisting of 20 grams of n-pentane and 80 grams of cyclohexane was transferred to a 200W ultrasonic biopulverizer. The mixture was cooled to -3°C with ice and maintained in an ultrasonic state. After 5 minutes of ultrasonication, a Pickering inverse miniemulsion containing solid barium hydroxide as the emulsifier was obtained, and the system was maintained at a low temperature of 3°C. The Pickering inverse miniemulsion had a Z-average particle size of 150 nanometers and a particle dispersion index (PDI) of 0.12.

[0048] (2) Preparation of Pickering inverse miniemulsion containing doped barium titanate precursor:

[0049] At room temperature, 1.5 g of isobutyl titanate and 0.1 g of a 0.1% mass concentration water-soluble yttrium nitrate-doped metal salt are added dropwise to 100 g of a Pickering miniemulsion prepared in step (1) with barium hydroxide solid as an emulsifier. The mixed system is cooled to 3° C. by salt ice and maintained in an ultrasonic state using a 200W ultrasonic cell crusher. After ultrasonication for 1 minute, a Pickering inverse miniemulsion containing a doped barium titanate precursor is obtained, and the system is maintained at a low temperature of 8° C.

[0050] (3) Preparation of Pickering inverse miniemulsion containing doped barium titanate nanocrystals:

[0051] At room temperature, 50 g of the Pickering miniemulsion containing the doped barium titanate precursor prepared in step (2) was transferred to a 100 ml autoclave equipped with a 200 W ultrasonic device; the mixture was then incubated at 100° C. for 36 hours. After solvent thermal treatment, the reaction solution was removed to obtain a Pickering inverse miniemulsion containing yttrium-doped barium titanate nanocrystals. The Pickering inverse miniemulsion droplets had a Z-average particle size of 150 nm and a dispersion index (PDI) of 0.12. X-ray diffraction analysis showed that the yttrium-doped barium titanate nanomaterials met the characteristic diffraction peaks of the barium titanate PDF standard card, and the spectrum showed a right-shifted secondary diffraction peak of the yttrium-doped barium titanate nanocrystals. The average particle size of the nanocrystals was calculated to be 7 nm based on the half-width at half maximum of the diffraction peak.

[0052] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and modifications made by those skilled in the art based on the present disclosure are intended to fall within the scope of protection of the present invention.

Claims

1. A method for preparing doped barium titanate nanocrystals using a Pickering inverse miniemulsion, characterized in that: The method steps are as follows: (1) Preparation of Pickering inverse miniemulsion with barium hydroxide solid as emulsifier: At room temperature, a saturated barium hydroxide solution, an alcoholamine, and an organic solvent are mixed and transferred to an ultrasonic biopulverizer. The mixed system is cooled by salt ice and maintained in an ultrasonic state. A Pickering reverse miniemulsion with barium hydroxide solid as an emulsifier is obtained by ultrasound, and the system is maintained at a low temperature. The organic solvent is a mixture of n-pentane and cyclohexane in a mass ratio of 20:80; The power of the ultrasonic bio-crusher was 200W, the salt and ice were controlled at -5-0°C, the system low temperature was 0-5°C, and the ultrasonic time was 5 minutes; (2) Preparation of Pickering inverse miniemulsion containing doped barium titanate precursor: At room temperature, the titanium compound and the water-soluble doping metal salt solution are added dropwise to the Pickering reverse miniemulsion prepared in step (1) with the barium hydroxide solid as an emulsifier, and the mixed system is cooled by salt ice and maintained in an ultrasonic state; a Pickering reverse miniemulsion containing a doped barium titanate precursor is obtained by ultrasonication, and the system is maintained in a low temperature state; (3) Preparation of Pickering inverse miniemulsion containing doped barium titanate nanocrystals: At room temperature, the Pickering inverse miniemulsion containing the doped barium titanate precursor prepared in step (2) is transferred to a high-pressure reactor equipped with an ultrasonic device; then the temperature is kept for a predetermined time, and the reaction liquid is taken out after solvent thermal treatment to obtain a Pickering inverse miniemulsion containing doped nanocrystals.

2. The method for preparing doped barium titanate nanocrystals using a Pickering inverse miniemulsion according to claim 1, wherein: In step (1), the barium hydroxide is barium hydroxide monohydrate or barium hydroxide octahydrate; and the alcoholamine is monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, dimethylethanolamine, methyldiethanolamine or diglycolamine.

3. The method for preparing doped barium titanate nanocrystals using Pickering inverse miniemulsion according to claim 1, characterized in that: In step (1), the mass ratio of the saturated barium hydroxide solution, the alcoholamine and the organic solvent is 10:0.5-1.0:

100.

4. The method for preparing doped barium titanate nanocrystals using a Pickering inverse miniemulsion according to claim 1, wherein: In step (2), the titanium compound is n-butyl titanate or isobutyl titanate; the water-soluble doping metal salt is a functional nitro salt, and the mass concentration of the water-soluble doping metal salt solution is 0.1%.

5. The method for preparing doped barium titanate nanocrystals using Pickering inverse miniemulsion according to claim 1, wherein: The mass ratio of the titanium compound, the water-soluble doping metal salt solution in step (2) and the Pickering miniemulsion with the barium hydroxide solid as an emulsifier in step (1) is 1-2:0.1:

100.

6. The method for preparing doped barium titanate nanocrystals using a Pickering inverse miniemulsion according to claim 1, wherein: Step (2) The power of the ultrasonic bio-disintegrator is 200W, the salt and ice are controlled at 0-5°C, the system low temperature is 5-10°C, and the ultrasonic time is 1 minute.

7. The method for preparing doped barium titanate nanocrystals using Pickering inverse miniemulsion according to claim 1, characterized in that: In step (3), the mass volume ratio of the Pickering inverse miniemulsion containing the doped barium titanate precursor prepared in step (2) to the high-pressure reactor is 50 g:100 ml; the hydrothermal treatment is set to a holding temperature of 80-120°C, an ultrasonic power of 200 W, and a holding time of 12-48 hours.

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