A monodisperse nano-tin dioxide quantum dot in aqueous solution and its preparation method

Abstract

This invention discloses a monodisperse nano-tin dioxide quantum dot in aqueous solution and its preparation method. The preparation method includes the following steps: (1) adding an organic weak acid to an aqueous solution containing stannate, producing a white precipitate, and stirring; the organic weak acid includes at least one of acetic acid, benzoic acid, citric acid, lactic acid, oxalic acid, and propionic acid; (2) subjecting the mixed aqueous solution obtained in step (1) to a hydrothermal reaction at 120-240℃, separating the solid and liquid phases after the reaction, and dissolving the solid phase in an aqueous solvent to obtain a tin dioxide-aqueous dispersion; (3) adding a quaternary ammonium salt and dimethyl sulfoxide to the tin dioxide-aqueous dispersion, and stirring to obtain monodisperse nano-tin dioxide quantum dots in aqueous solution. The nano-tin dioxide quantum dots of this invention are extremely small and controllable in size, have a significant quantum dielectric confinement effect, and are simple and inexpensive to prepare, thus broadening the application field of SnO2 and having important application value.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, specifically to a monodisperse nano-tin dioxide quantum dot in aqueous solution and its preparation method. Background Technology

[0002] Wide-bandgap metal oxide nanomaterials have shown broad application prospects in many fields. Tin dioxide nanocrystals (SnO2 NPs) are a typical wide-bandgap n-type semiconductor. Due to their unique size and surface characteristics, they exhibit excellent optical, electrical and interfacial properties and are widely used in transparent conductive electrodes, perovskite solar cells, OLED quantum dot light-emitting diodes, gas sensors, photocatalysis, lithium-ion batteries and other fields.

[0003] The electrical and optical properties of tin dioxide nanocrystals generally increase with decreasing size. When the size of tin dioxide nanocrystals approaches or decreases to below their Bohr radius, they exhibit unique physical and chemical properties due to the quantum confinement effect. Optically, this manifests as tunable band gaps and optical absorption characteristics; electrically, it manifests as enhanced conductivity and carrier concentration. Simultaneously, the increased specific surface area leads to increased surface activity, providing numerous reaction sites, and thus, they are widely used in the decomposition of environmental pollutants and high-efficiency catalytic reactions. However, reducing the nanoscale size increases the surface energy of the particles, leading to adsorption and aggregation, which can render them unusable. According to the principle of particle dispersion, tin dioxide nanocrystals require appropriate dispersion methods to reduce the attractive forces between particles in practical applications. For example, surfactants, polymers, or other small molecules can be used. A stable dispersion system is a prerequisite for the application of tin dioxide nanocrystals.

[0004] Aqueous solvents are environmentally friendly, non-toxic, and inexpensive, exhibiting good stability and dispersibility. They are suitable for commercial production and environmentally friendly applications, and are the dispersant used in the vast majority of tin dioxide nanocrystals currently on the market. To ensure the uniformity of tin dioxide nanocrystals during preparation, storage, and application, potassium hydroxide (KOH) is typically added as a stabilizer. The hydroxide ions (OH-) generated by the ionization of potassium hydroxide... - Potassium hydroxide adsorbs onto the surface of tin dioxide nanocrystals and disperses them through electrostatic repulsion. However, the strong alkalinity of potassium hydroxide produces significant side effects in certain chemical environments. Therefore, finding a method for the stable dispersion of tin dioxide nanocrystals in aqueous solvents is crucial for expanding their application range.

[0005] Quaternary ammonium salts containing hydroxyl groups have unique applications in the field of water-soluble cationic surfactants, where the introduction of hydroxyl groups usually enhances the adsorption of tin dioxide nanocrystals and the water solubility of solvents. Literature (Mengyu Chen, Xingtong Chen, Wenchen Ma, et al. Highly Stable SnO2-Based Quantum-Dot Light-Emitting Diodes with the Conventional Device Structure[J].ACS Nano,2022,16(6):9631-9639.) and Chinese patent application CN114314645A use tin chloride (SnCl4) as the tin source. A tin dioxide-alcohol dispersion is obtained through hydrothermal reaction, followed by the addition of a quaternary ammonium base, resulting in well-dispersed tin dioxide nanoparticles. However, compared to aqueous solvents, alcohol solvents may have potential problems such as volatility and toxicity, interference or participation in chemical reactions, and high cost, which are not conducive to large-scale industrial applications. Furthermore, the dispersion effect of quaternary ammonium bases on tin dioxide nanoparticles in aqueous solvents is relatively limited.

[0006] Water has significant advantages as a solvent in terms of environmental protection, cost, and application fields. In Chinese patent application CN105417575A, an aqueous solution of inorganic tin salt is added to an aqueous solution of inorganic alkali and then separated to precipitate. The precipitate is then mixed with water and stirred before being separated again to remove the precipitate, thus obtaining tin dioxide quantum dot hydrosol. However, the hydrosol obtained by simple centrifugation cannot accurately control the actual content of tin dioxide, which presents many difficulties in practical applications.

[0007] How to quantitatively and controllably obtain monodisperse nano-tin dioxide quantum dots in aqueous solution is an important technical problem that urgently needs to be solved. Summary of the Invention

[0008] To address the aforementioned technical problems and shortcomings in this field, the present invention provides a method for preparing monodisperse tin dioxide nanoparticles in aqueous solution. The tin dioxide nanoparticles prepared by this invention have extremely small and controllable sizes, exhibit significant quantum dielectric confinement effects, and the preparation method is simple and low-cost, thus broadening the application fields of SnO2 and possessing significant application value.

[0009] A method for preparing nano-tin dioxide quantum dots monodisperse in aqueous solution includes the following steps:

[0010] (1) Add an organic weak acid to an aqueous solution containing stannate, a white precipitate is produced, and the solution is stirred; the organic weak acid includes at least one of acetic acid, benzoic acid, citric acid, lactic acid, oxalic acid, and propionic acid;

[0011] (2) The mixed aqueous solution obtained in step (1) is subjected to hydrothermal reaction at 120-240℃ (e.g., 120℃, 140℃, 180℃, 200℃, 240℃, etc.). After the reaction is completed, the solid and liquid phases are separated, and the solid phase is dissolved in an aqueous solvent to obtain tin dioxide-water dispersion.

[0012] (3) Add quaternary ammonium salt and dimethyl sulfoxide to the tin dioxide-water dispersion and stir to obtain nano-tin dioxide quantum dots that are monodispersed in the aqueous solution.

[0013] The preparation method provided by this invention is a method for preparing nano-tin dioxide quantum dots that are monodisperse in aqueous solution, which is low in cost, mild in reaction conditions, and industrially applicable. The resulting quantum dot aqueous solution is transparent, clear, and colorless, and has good dispersibility. The average particle size of the tin dioxide particles is less than 5 nm (measured by transmission electron microscopy), exhibiting a significant quantum dielectric confinement effect.

[0014] This invention uses stannate as the tin source, which avoids the problems of tin dioxide made from tin tetrachloride and other tin sources having difficulty forming a tin dioxide-water dispersion with a high concentration of tin dioxide in an aqueous solvent and having difficulty obtaining high concentrations of monodisperse nano-tin dioxide quantum dots in an aqueous solution. Moreover, stannate is less expensive than tin tetrachloride.

[0015] In step (1), the stannate may include at least one of sodium stannate, potassium stannate, lithium stannate, magnesium stannate, and calcium stannate.

[0016] In step (1), the concentration of the stannate in the aqueous solution containing stannate can be 16 to 100 g / L.

[0017] In step (1), the volume ratio of the organic weak acid to the aqueous solution containing stannate is preferably no more than 5:1.

[0018] In step (2), the hydrothermal reaction time can be 2 to 24 hours.

[0019] In step (2), the mass fraction of tin dioxide in the tin dioxide-water dispersion may not exceed 30%, for example, it may be 1% to 30%. The preparation method of the present invention can obtain nano-tin dioxide quantum dots with a mass concentration of up to 30% in aqueous solution.

[0020] In step (3), the quaternary ammonium salt can be added in the form of an aqueous solution of quaternary ammonium salt.

[0021] In step (3), the volume ratio of the quaternary ammonium salt aqueous solution to the tin dioxide-water dispersion can be 1:3 to 20.

[0022] In step (3), the mass fraction of the quaternary ammonium salt in the aqueous solution of the quaternary ammonium salt can be 20% to 40%.

[0023] In step (3), the volume ratio of the quaternary ammonium salt aqueous solution to the dimethyl sulfoxide can be 0.15 to 0.65:1.

[0024] In step (3), the quaternary ammonium salt may include at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide.

[0025] In step (3), the stirring reaction time can be 5 to 4500 min.

[0026] The present invention also provides nano-tin dioxide quantum dots prepared by the above preparation method in an aqueous solution.

[0027] Compared with the prior art, the beneficial effects of this invention are as follows:

[0028] 1. This invention preferably uses inexpensive stannate as the tin source to controllably prepare tin dioxide nanocrystals via a one-step hydrothermal method. This allows for the production of monodisperse tin dioxide quantum dots even in high-concentration aqueous solutions of tin dioxide nanocrystals by adding quaternary ammonium salts and dimethyl sulfoxide (DMSO). On one hand, the large steric hindrance effect of quaternary ammonium salts and the adsorption of tin dioxide nanocrystals by hydroxyl groups solve the dispersion problem of SnO2 in aqueous solvents. On the other hand, the miscibility of DMSO with aqueous solvents and quaternary ammonium salts further improves the stability of the SnO2 aqueous dispersion. The resulting tin dioxide quantum dots are colorless, transparent, and clear in aqueous solvents, exhibiting good stability. In this invention, DMSO has a synergistic effect with quaternary ammonium salts and water. The introduction of DMSO reduces the amount of quaternary ammonium salt required, resulting in superior dispersion of tin dioxide quantum dots with less quaternary ammonium salt.

[0029] 2. The nano-tin dioxide quantum dots prepared by this invention have extremely small and controllable size, with an average particle size of 2.88–4.65 nm (measured by transmission electron microscopy). They exhibit a significant quantum dielectric confinement effect and have potential application potential.

[0030] 3. The nano-tin dioxide quantum dots prepared by this invention use inexpensive stannate as the tin source and water as the dispersant. The preparation method is simple, requires low equipment, is safe and environmentally friendly, and the product is easy to promote on a large scale. Attached Figure Description

[0031] Figure 1 The image shows the X-ray diffraction pattern of the tin dioxide nanocrystals prepared in Example 1 of this invention.

[0032] Figure 2 The X-ray diffraction patterns are those of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention.

[0033] Figure 3 Transmission electron microscope images of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention.

[0034] Figure 4 These are high-resolution transmission electron microscope images of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention.

[0035] Figure 5 The image shows the dynamic light scattering particle size results of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention.

[0036] Figure 6 Digital photographs of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention under natural light.

[0037] Figure 7 The Fourier transform infrared spectra of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention are shown.

[0038] Figure 8 The UV-Vis-NIR absorption spectrum and optical bandgap diagram of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Example 1 of this invention. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0040] Example 1

[0041] (1) Weigh 0.57g of sodium stannate trihydrate and add it to 30mL of deionized water. Slowly add 6mL of acetic acid while stirring. A white precipitate is produced. After stirring for 15min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 180℃, 12h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles (i.e., tin dioxide nanocrystals) are obtained.

[0042] (2) The nano-SnO2 quantum dot particles prepared in step (1) were dissolved in 15 mL of deionized water to obtain a 3% tin dioxide-water dispersion. 0.75 mL of a 25% tetramethylammonium hydroxide solution and 2.25 mL of dimethyl sulfoxide were added under stirring. The mixture was stirred for 120 min to obtain a monodisperse nano-tin dioxide quantum dot aqueous solution (TMAH-DMSO-SnO2-water dispersion). The solution was spin-coated onto ITO and FTO substrates. The electrical properties measured using a Hall effect testing system are shown in Table 1 below.

[0043] Table 1

[0044]

[0045] Comparative Example 1

[0046] (1) Weigh 0.57g of sodium stannate trihydrate and add it to 30mL of deionized water. Slowly add 6mL of acetic acid while stirring. A white precipitate is produced. After stirring for 15min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 180℃, 12h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0047] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 15 mL of deionized water to obtain a 3% tin dioxide-water dispersion. Stir continuously for 120 min to obtain an agglomerated nano tin dioxide quantum dot aqueous solution (SnO2-water dispersion).

[0048] Comparative Example 2

[0049] (1) Weigh 0.57g of sodium stannate trihydrate and add it to 30mL of deionized water. Slowly add 6mL of acetic acid while stirring. A white precipitate is produced. After stirring for 15min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 180℃, 12h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0050] (2) The nano-SnO2 quantum dot particles prepared in step (1) were dissolved in 15 mL of deionized water to obtain a 3% tin dioxide-water dispersion. 3 mL of a 25% tetramethylammonium hydroxide solution was added while stirring, and stirring was continued for 120 min to obtain a monodisperse nano-tin dioxide quantum dot aqueous solution (TMAH-SnO2-water dispersion). This solution was spin-coated onto ITO and FTO substrates. The electrical properties measured by the Hall effect testing system are shown in Table 2 below.

[0051] Table 2

[0052]

[0053] Example 2

[0054] (1) Weigh 0.57g of sodium stannate trihydrate and add it to 24mL of deionized water. Slowly add 12mL of acetic acid while stirring. A white precipitate is produced. After stirring for 30min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 200℃, 24h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0055] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 50 mL of deionized water to obtain a 4% tin dioxide-water dispersion. Add 8.5 mL of 25% tetramethylammonium hydroxide solution and 16 mL of dimethyl sulfoxide under stirring. Continue stirring for 4320 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0056] Example 3

[0057] (1) Weigh 0.57g of sodium stannate trihydrate and add it to 18mL of deionized water. Slowly add 18mL of acetic acid while stirring. A white precipitate is produced. After stirring for 5min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 120℃, 2h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0058] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 30 mL of deionized water to obtain a 5% tin dioxide-water dispersion. Add 3.5 mL of 25% tetramethylammonium hydroxide solution and 6 mL of dimethyl sulfoxide under stirring. Continue stirring for 10 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0059] Example 4

[0060] (1) Weigh 0.57g of sodium stannate trihydrate and add it to 12mL of deionized water. Slowly add 24mL of acetic acid while stirring. A white precipitate is produced. After stirring for 20min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 240℃, 6h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0061] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 100 mL of deionized water to obtain a 30% tin dioxide-water dispersion. Add 6 mL of 25% tetramethylammonium hydroxide solution and 35 mL of dimethyl sulfoxide under stirring. Continue stirring for 2880 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0062] Example 5

[0063] (1) Weigh 0.57g of potassium stannate trihydrate and add it to 30mL of deionized water. Slowly add 6mL of oxalic acid while stirring. A white precipitate is produced. After stirring for 15min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 180℃, 12h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0064] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 20 mL of deionized water to obtain a 1% tin dioxide-water dispersion. Add 2 mL of 25% tetraethylammonium hydroxide solution and 3.5 mL of dimethyl sulfoxide under stirring. Continue stirring for 60 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0065] Example 6

[0066] (1) Weigh 1.4g of potassium stannate trihydrate and add it to 50mL of deionized water. Slowly add 30mL of benzoic acid while stirring. A white precipitate is produced. After stirring for 45min, add the mixture to a 100mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 200℃, 18h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0067] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 45 mL of deionized water to obtain a 3% tin dioxide-water dispersion. Add 12.25 mL of 40% tetrapropylammonium hydroxide solution and 20 mL of dimethyl sulfoxide under stirring. Continue stirring for 360 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0068] Example 7

[0069] (1) Weigh 0.7g of zinc stannate and add it to 30mL of deionized water. Slowly add 6mL of lactic acid while stirring. A white precipitate is produced. After stirring for 15min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 200℃, 6h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0070] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 30 mL of deionized water to obtain a 10% tin dioxide-water dispersion. Add 4.5 mL of 25% tetramethylammonium hydroxide solution and 9 mL of dimethyl sulfoxide under stirring. Continue stirring for 1200 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0071] Example 8

[0072] (1) Weigh 0.57g magnesium stannate and add it to 16mL of deionized water. Slowly add 20mL of benzoic acid while stirring. A white precipitate is produced. After stirring for 5min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 140℃, 18h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0073] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 80 mL of deionized water to obtain a 20% tin dioxide-water dispersion. Add 5.5 mL of 20% tetramethylammonium hydroxide solution and 12 mL of dimethyl sulfoxide under stirring. Continue stirring for 720 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0074] Example 9

[0075] (1) Weigh 1.1g of calcium stannate and add it to 48mL of deionized water. Slowly add 24mL of propionic acid while stirring. A white precipitate is produced. After stirring for 15min, add the mixture to a 100mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 180℃, 24h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0076] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 50 mL of deionized water to obtain a 30% tin dioxide-water dispersion. Add 4.25 mL of a 35% tetraethylammonium hydroxide solution and 7.5 mL of dimethyl sulfoxide under stirring. Continue stirring for 1440 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0077] Example 10

[0078] (1) Weigh 0.57g of calcium stannate and add it to 6mL of deionized water. Slowly add 30mL of acetic acid while stirring. A white precipitate is produced. After stirring for 15min, add the mixture to a 50mL high-pressure reactor lined with polytetrafluoroethylene to carry out a hydrothermal reaction. The hydrothermal reaction conditions are: 200℃, 6h. After centrifugation, washing and drying of the reaction product with deionized water, agglomerated nano SnO2 quantum dot particles are obtained.

[0079] (2) Dissolve the nano SnO2 quantum dot particles prepared in step (1) in 10 mL of deionized water to obtain a 1% tin dioxide-water dispersion. Add 0.7 mL of 25% tetrapropylammonium hydroxide solution and 1.5 mL of dimethyl sulfoxide under stirring. Continue stirring for 2320 min to obtain a monodisperse nano tin dioxide quantum dot aqueous solution.

[0080] Sample analysis:

[0081] Figure 1 This is the X-ray diffraction pattern of the tin dioxide nanocrystals prepared in Example 1 of this invention. The high intensity of the diffraction peaks indicates good crystallinity, and the wide peak width indicates very small crystal size. The grain size of the SnO2 nanocrystals was estimated based on the full width at half maximum (FWHM) using the Scherrer formula. The calculation was performed, where K was 0.89, λ was 0.15406, and β was the half-width at half-maximum of the (110), (101), and (211) crystal planes. The average grain size of the sample was found to be 3.46 nm, and the peak position in the figure corresponds to the pure tetragonal SnO2 crystal structure (PDF#99-0024).

[0082] Figure 2 The images show the X-ray diffraction patterns of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention. Example 1 shows better crystallinity, with peak intensities and positions corresponding to pure tetragonal SnO2. Due to the aggregation of SnO2 nanocrystals, the diffraction peak intensity of Comparative Example 1 is lower than that of Example 1. Meanwhile, the diffraction peaks of Examples 1 and 2 are wider, indicating smaller crystallite sizes.

[0083] Figure 3These are transmission electron microscope (TEM) images of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention. Figure 3 A is a transmission electron microscope image of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Comparative Example 1. Figure 3 B is a transmission electron microscope image of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Comparative Example 2. Figure 3 C is a transmission electron microscope image of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Example 1. It can be seen that when SnO2 is directly dispersed in water, it tightly aggregates and clusters due to the high energy on the crystal surface. Although the size of the SnO2 nanocrystals is small, the agglomeration cannot be dispersed. The addition of tetramethylammonium hydroxide (TMAH) allows the hydroxyl groups to combine with the surface of the SnO2 nanocrystals. Simultaneously, the presence of organic groups increases steric hindrance, promoting the dispersion of the SnO2 nanocrystals. Dimethyl sulfoxide (DMSO) is miscible with TMAH and the aqueous solution, further dispersing the SnO2 nanocrystals, thus forming a monodisperse nano-tin dioxide quantum dot aqueous solution.

[0084] Figure 4 These are high-resolution transmission electron microscope images of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention. Figure 4 A is a high-resolution transmission electron microscope image of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Comparative Example 1. Figure 4 B is a high-resolution transmission electron microscope image of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Comparative Example 2. Figure 4 C is a high-resolution transmission electron microscope image of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Example 1. It can be seen that the addition of TMAH disperses the aggregated SnO2 nanocrystals, and there are large gaps between the grains. All three samples show obvious lattice fringes. The interplanar spacing of Comparative Example 1, Comparative Example 2 and Example 1 samples are 0.337 nm, 0.353 nm and 0.347 nm, respectively, all corresponding to the (110) crystal plane.

[0085] Figure 5 The results show the dynamic light scattering particle size of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention. It can be seen that the volume-weighted average particle size of the SnO2 aqueous dispersion with added TMAH is mainly concentrated around 9.655 nm, indicating that the particle size of these two samples is relatively small and uniform. The addition of DMSO increases the volume percentage of small-sized SnO2. In contrast, the SnO2 aqueous dispersion without added TMAH and DMSO shows a significant increase in the peak average particle size due to agglomeration, with the volume-weighted average particle size concentrated around 768.5 nm.

[0086] Figure 6 These are digital photographs of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention under natural light. Figure 6 A is a digital photograph of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Comparative Example 1 under natural light. Figure 6 B is a digital photograph of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Comparative Example 2 under natural light. Figure 6 C is a digital photograph of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Example 1 under natural light. It can be seen that when the mass fraction of SnO2 is 3%, Comparative Example 1 appears cloudy and milky white under natural light, indicating that SnO2 aggregates in the aqueous solution. Comparative Example 2 is slightly cloudy but almost completely transparent under natural light, indicating that the vast majority of SnO2 nanoparticles are uniformly dispersed in the aqueous solution, but a very small portion of SnO2 nanoparticles are not completely dispersed and form small aggregates. Example 1 is completely transparent and stable under natural light, indicating that the SnO2 nanoparticles are fully dispersed in the aqueous solution, forming a stable and clear colloidal solution.

[0087] Figure 7 The images show the Fourier transform infrared (FTIR) spectra of the monodisperse nano-tin dioxide quantum dot aqueous solutions prepared in Examples 1, 1, and 2 of this invention. Specifically, the Fourier transform infrared spectra of Examples 1, 1, and 2 are all at 3400 cm⁻¹. -1 A broad absorption peak is generated near 1650 cm⁻¹ due to the stretching vibration of the OH bond. -1 Absorption peaks are generated nearby due to the bending vibrations of water molecules. Examples 1 and 2 show absorption peaks in the range of 1350–1450 cm⁻¹. -1 The characteristic absorption peak near the methyl group is generated due to the vibration of the CH bond in the methyl group. In Example 1, the peak is at 1000 cm⁻¹. -1 The nearby absorption peak is due to the stretching vibration of the S=O double bond in dimethyl sulfoxide.

[0088] Figure 8 The UV-Vis-NIR absorption spectrum and optical bandgap diagram of the monodisperse nano-tin dioxide quantum dot aqueous solution prepared in Example 1 of this invention are shown. The absorbance exhibits a significant absorption peak in the 250–400 nm wavelength range, approaches zero in the 400–1250 nm range, and increases slowly in the 1250–2000 nm range, maintaining a certain level of absorption across the entire wavelength range. The optical bandgap value is calculated using the formula αhv. 2 =A(hv-E) g The calculation is performed, where hv is the photon energy. The intrinsic semiconductor band gap of SnO2 is 0 to 3.6 eV. Due to the quantum interdomain effect and the increase in carrier concentration, the optical band gap of SnO2 in Example 1 is significantly increased to 4.48 eV.

[0089] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing nano-tin dioxide quantum dots monodisperse in an aqueous solution, characterized in that, Including the following steps: (1) An organic weak acid is added to an aqueous solution containing stannate, a white precipitate is produced, and the solution is stirred; the stannate includes at least one of sodium stannate, potassium stannate, lithium stannate, magnesium stannate, and calcium stannate; the concentration of the stannate in the aqueous solution containing stannate is 16~100 g / L; the organic weak acid includes at least one of acetic acid, benzoic acid, citric acid, lactic acid, oxalic acid, and propionic acid; (2) The mixed aqueous solution obtained in step (1) is subjected to hydrothermal reaction at 120~240℃. After the reaction is completed, the solid and liquid phases are separated, and the solid phase is dissolved in an aqueous solvent to obtain tin dioxide-water dispersion. (3) Add quaternary ammonium salt and dimethyl sulfoxide to the tin dioxide-water dispersion and stir to obtain nano-tin dioxide quantum dots monodisperse in aqueous solution; the quaternary ammonium salt includes at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide.

2. The preparation method according to claim 1, characterized in that, In step (1), the volume ratio of the organic weak acid to the aqueous solution containing stannate does not exceed 5:

1.

3. The preparation method according to claim 1, characterized in that, In step (2), the hydrothermal reaction takes 2 to 24 hours.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass fraction of tin dioxide in the tin dioxide-water dispersion does not exceed 30%.

5. The preparation method according to claim 1 or 4, characterized in that, In step (3): The quaternary ammonium salt is added in the form of an aqueous solution of quaternary ammonium salt; The volume ratio of the quaternary ammonium salt aqueous solution to the tin dioxide-water dispersion is 1:3~20; The mass fraction of the quaternary ammonium salt in the aqueous solution is 20% to 40%. The volume ratio of the quaternary ammonium salt aqueous solution to the dimethyl sulfoxide is 0.15~0.65:

1.

6. The preparation method according to claim 1, characterized in that, In step (3), the stirring reaction time is 5 to 4500 min.

7. Monodisperse tin dioxide nanoparticles in aqueous solution prepared by the preparation method according to any one of claims 1 to 6.

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