Tin dioxide nanoparticle water-phase dispersion liquid as well as preparation method and application thereof

Abstract

The invention provides a tin dioxide nanoparticle water-phase dispersion liquid as well as a preparation method and application thereof. Trimethylamine is adsorbed on the surfaces of tin dioxide nanoparticles in the tin dioxide nanoparticle water-phase dispersion liquid. According to the method, the mixed alkali containing ammonium bicarbonate and tetramethylammonium hydroxide reacts with the tin precursor, so that smooth production of the tin dioxide hydrate can be ensured, agglomeration can be avoided through the steric effect provided by a small amount of tetramethylammonium hydroxide, and the final tin dioxide solid content of the system can be increased to 15 wt%. The nanoparticle suspension prepared by the method is easy to store at normal temperature, high in solid content, good in dispersity and controllable in impurity component; impurity components can be recycled and reused.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tin dioxide preparation, and particularly relates to a tin dioxide nanoparticle aqueous dispersion, a tin dioxide nanoparticle and a preparation method and application thereof. BACKGROUND

[0002] Tin dioxide has excellent optical properties, electrical properties and chemical stability, and is thus widely used in the fields of optoelectronic devices, gas sensors, photocatalysts, transparent conductive films / electron transport layers and lithium battery electrode modification. Reducing the size of tin dioxide particles to the nanometer level can further improve product performance. In the fields of gas sensors / catalysts, the smaller the size of tin dioxide crystal grains, the higher the surface activity, and the better the performance of sensors / photocatalysts; in the fields of conductive films / electron transport layers, the smaller the size of nanoparticles that constitute the film, the better the uniformity and conductivity of the film, and the more controllable the thickness; in the field of lithium battery electrodes, reducing the particle size can well alleviate the volume change of the negative tin dioxide during the charging and discharging process, and promote the transmission speed of lithium ions in the electrode. As can be seen, the smaller the size of tin dioxide nanoparticles, the higher the added value.

[0003] There are many ways to synthesize tin dioxide nanoparticles, but the methods that can control the particle size of nanoparticles to be below 6 nm and monodisperse are very limited, and there are few existing commercial products. According to existing literature and patents, the related preparation methods only include hydrothermal / solvothermal synthesis and homogeneous precipitation. In the hydrothermal / solvothermal synthesis method, a tin precursor (stannous chloride or tin tetrachloride) aqueous or hydroalcoholic solution is directly mixed with an alkaline solution, and after repeated washing to remove chloride ions, the tin dioxide nanoparticle suspension is directly formed in a high-temperature high-pressure system; in the homogeneous precipitation method, a tin precursor aqueous / hydroalcoholic solution is mixed with a precipitant (such as urea, thiourea, hydrazine hydrate, etc.), and the precipitant gradually hydrolyzes or decomposes to generate an alkaline substance in the reaction, which reacts with the precursor to generate a tin dioxide nanoparticle suspension.

[0004] The main problems existing in the prior art, which limit the industrial application of the above methods, mainly have two points.

[0005] First, the solid content of tin dioxide obtained by the final reaction system of homogeneous precipitation method is too low, resulting in low production efficiency. The concentration of tin precursor in the reaction solution determines the solid content of tin dioxide in the final solution. The increase of precursor concentration will lead to the growth of particle size and particle agglomeration (Ribeiro, C., etc. Study of synthesis variables in the nanocrystal growth behavior of tin oxide processed by controlled hydrolysis. The Journal of Physical Chemistry B, 2004, 108(40), 15612-15617), which leads to the solid content of tin dioxide suspension (particle size <6 nm) obtained by homogeneous precipitation method not more than 4wt%; the solid content of tin dioxide obtained by hydrothermal / solvothermal synthesis method with inorganic base as reactant is not more than 3wt%. Some literatures (Aziz, M., etc. Size-controlled synthesis of SnO2 nanoparticles by sol-gel method. Materials Letters, 2013, 91, 31-34.) try to add surfactants (such as polyethylene glycol) to inhibit the growth and aggregation of particles, but the residual organic matter such as surfactants in the final suspension will affect the electrical properties of the product.

[0006] Second, it is difficult to remove impurities. Impurities such as chloride ions, metal ions in inorganic bases, and decomposition products of precipitants / additives in tin dioxide suspension may affect the performance of the final product. In existing literature and patents, repeated centrifugal washing, dialysis method, and high-temperature annealing method are generally used to remove impurities. The repeated centrifugal washing method takes a long time, is complicated to operate, and has poor repeatability of cleaning effect, and multiple centrifugation can easily damage the internal structure of the particles, making the particles more prone to agglomeration; the dialysis method also has the problems of long time consumption, poor repeatability and large amount of ammonium chloride waste liquid; high-temperature annealing can remove residual organic matter but will damage the particle morphology.

[0007] In addition, due to the surface effect, small size effect and quantum effect of nanomaterials, they are in an unstable energy state. In order to reach a stable state, particles will spontaneously agglomerate and settle, resulting in a short shelf life of the produced tin dioxide nanoparticle dispersion and the need for low-temperature storage. SUMMARY

[0008] In view of the problems existing in the prior art, one of the purposes of the present application is to provide a tin dioxide nanoparticle aqueous dispersion with high solid content and not easy to aggregate at room temperature, and the second purpose of the present application is to provide a method for producing a high solid content tin dioxide nanoparticle (<6 nm) aqueous suspension, and a method for removing impurities from a tin dioxide nanoparticle suspension with strong controllability. The nanoparticle suspension prepared by the method of the present application is easy to store at room temperature, has high solid content, good dispersibility and controllable impurity components; the impurity components can be recycled and reused.

[0009] One of the purposes of the present application is to provide a tin dioxide nanoparticle aqueous dispersion, wherein the tin dioxide nanoparticles contained therein have trimethylamine adsorbed on the surface thereof.

[0010] According to the present application, the tin dioxide nanoparticle aqueous dispersion comprises:

[0011] The particle size of the tin dioxide is less than 10 nm, preferably less than 6 nm;

[0012] The content of tin dioxide in the tin dioxide nanoparticle aqueous dispersion is 2-15 wt%.

[0013] The tin dioxide nanoparticle aqueous dispersion provided by the present application is obtained by reacting a tin-containing compound aqueous solution in an alkaline solution containing at least ammonium bicarbonate and tetramethylammonium hydroxide, adjusting the pH and heating the reaction. Since trimethylamine is adsorbed on the surface of the tin dioxide nanoparticles, the tin dioxide nanoparticle aqueous dispersion is not easy to aggregate at room temperature. This is because the tetramethylammonium group in tetramethylammonium hydroxide is adsorbed on the surface of the tin dioxide precursor during the reaction, and a demethylation reaction occurs at high temperature, leaving tin dioxide nanoparticles with trimethylamine adsorbed thereon, as shown below.

[0014]

[0015] The adsorption of trimethylamine on the tin dioxide nanoparticles is dynamic adsorption, which can inhibit the aggregation of tin dioxide nanoparticles at room temperature. Since trimethylamine is volatile, it can be easily removed at high temperature, which is beneficial for applications requiring high purity tin dioxide.

[0016] The second purpose of the present application is to provide a method for preparing the above-mentioned tin dioxide nanoparticle aqueous dispersion, comprising: reacting a tin-containing compound aqueous solution in an alkaline mixed solution, adjusting the pH of the solution and heating the reaction to obtain the tin dioxide nanoparticle aqueous dispersion; preferably, the alkaline mixed solution comprises at least ammonium bicarbonate and tetramethylammonium hydroxide; further preferably, the preparation method further comprises the step of electrolytic impurity removal.

[0017] According to the present application, the preparation method of the tin dioxide nanoparticle aqueous dispersion specifically comprises the following steps:

[0018] (1) weigh the tin-containing compound and dissolve it in water to prepare a tin-containing aqueous solution;

[0019] (2) prepare a basic mixed solution of ammonium bicarbonate and tetramethylammonium hydroxide;

[0020] (3) mix the tin-containing aqueous solution obtained in step (1) with the basic mixed solution obtained in step (2), stir and then stand to obtain a mixed solution;

[0021] (4) add a pH adjusting agent dropwise to the mixed solution to adjust the pH of the solution;

[0022] (5) heat the solution obtained in step (4) to react, cool and then obtain the tin dioxide nanoparticle aqueous dispersion.

[0023] As a preferred embodiment, the step of adjusting the pH of the solution optionally comprises a step of removing the impurity NH4Cl, preferably by electrolysis.

[0024] Specifically, the electrolysis is carried out in a double-chamber electrolytic cell with a diaphragm, and the electrolysis is preferably constant-current electrolysis.

[0025] More preferably, the electrolysis is carried out as follows: the mixed solution obtained in step (3) is introduced into the cathode chamber, and an aqueous sodium chloride solution is introduced into the anode chamber, and constant-current electrolysis is carried out by applying electricity, and the chlorine gas generated by the anode and the mixture of hydrogen gas and ammonia gas generated by the cathode are optionally collected and recycled.

[0026] Further, the total discharge amount of chlorine gas is recorded by a flow meter to determine whether to stop the electrolysis, or the chlorine ion content in the solution in the cathode chamber is determined by a residual chlorine meter to determine whether to stop the electrolysis, or the voltage change is monitored to determine whether to stop the electrolysis.

[0027] According to a specific embodiment of the present application, in the electrolysis:

[0028] The cathode and the anode in the double-chamber electrolytic cell are inert electrodes, preferably titanium coated with ruthenium oxide.

[0029] The volume of the solution in the cathode chamber is the same as the volume of the solution in the anode chamber.

[0030] The concentration of the aqueous sodium chloride solution is 4 g / L to 25 g / L.

[0031] A heater is provided outside the electrolytic cell, and the electrolysis conditions are as follows: temperature 40-70°C, electrolysis time 1-4 hours.

[0032] The current density in the electrolysis process is 15-50 mA / cm 3 .

[0033] According to the present application, the preparation method of the tin dioxide nanoparticle aqueous dispersion comprises the following steps:

[0034] The tin-containing compound is tin tetrachloride;

[0035] The molar concentration of the tin-containing compound in the tin-containing aqueous solution is 0.2-4 mol / L, preferably 1.2-3 mol / L;

[0036] In the basic solution, the molar ratio of ammonium bicarbonate to tetramethylammonium hydroxide is (3-50):1, preferably (10-30):1;

[0037] In the basic solution, the molar concentration of ammonium bicarbonate is 1-5 mol / L, preferably 1-3 mol / L;

[0038] The molar ratio of the tin-containing compound to ammonium bicarbonate is 1:(1-6), preferably 1:(3-5), wherein the tin-containing compound is calculated based on the tin element contained therein;

[0039] The pH regulator is selected from at least one of tetramethylammonium hydroxide, ammonia, potassium hydroxide, and sodium hydroxide, and the pH regulator can be prepared into a solution for use, and the concentration of the solution is not particularly limited, as long as the solution pH value can be adjusted.

[0040] According to the present application, the preparation method of the tin dioxide nanoparticle aqueous dispersion comprises the following steps:

[0041] The stirring in step (3) is performed for at least 1 hour, preferably 1-3 hours;

[0042] The standing in step (3) is performed for at least 2 hours, preferably 2-8 hours;

[0043] The pH of the solution is adjusted to 10-11.5, preferably 10.3-11.3, in step (4);

[0044] The heating reaction in step (5) is performed at a temperature of 150-200°C for 2-24 hours;

[0045] After step (5), step (6) of blowing off the residual gas in the solution by introducing a protective gas is optionally included, and the protective gas can be nitrogen or other protective gas.

[0046] As a preferred embodiment of the present application, the tin dioxide nanoparticle aqueous dispersion can be prepared by the following steps: (i) weighing anhydrous tin tetrachloride or tin tetrachloride hydrate solid, dissolving in deionized water to prepare a tin tetrachloride aqueous solution; (ii) preparing a mixed solution containing at least ammonium bicarbonate and tetramethylammonium hydroxide; (iii) mixing the tin tetrachloride aqueous solution obtained in step (i) with the mixed alkali solution obtained in step (ii), stirring at room temperature for at least 1 hour and standing for at least 2 hours; the reaction formula of ammonium bicarbonate and tin tetrachloride in this step is as follows: SnCl4+4NH4HCO3→SnO2·nH2O+4NH4Cl+(2-n)H2O; (iv) passing the solution obtained in step (iii) into the cathode chamber of a double-chamber electrolytic cell with a diaphragm, passing the same volume of sodium chloride aqueous solution into the anode chamber of the electrolytic cell, and performing constant current electrolysis, collecting and processing the mixed gas of hydrogen, ammonia and chlorine gas generated by the anode; (v) adding a pH adjuster to the solution after electrolysis in step (iv) to adjust the pH value of the solution to 10-11.5; (vi) adding the solution obtained in step (v) into a pressure reaction vessel, heating at 150-200°C for 2-24 hours, and then naturally cooling to room temperature; (vii) taking out the solution obtained in step (vi), passing a protective gas to strip the residual gas in the solution, and obtaining a tin dioxide nanoparticle suspension. In step (iv), the gas generated by the anode passes through a pipeline containing a flow meter, and the total discharge amount of chlorine gas recorded by the flow meter during the process can be used to determine whether to stop electrolysis, or the chlorine ion content in the solution in the cathode chamber can be determined by a residual chlorine instrument to determine whether to stop electrolysis, or the voltage change can be monitored to determine whether to stop electrolysis; the chlorine gas generated by the anode can be passed into a sodium hydroxide solution for collection and utilization, or can be passed into an industrial device for producing sodium hypochlorite, such as a spraying reaction tower with a conductivity meter and an automatic alkali supplementing device; the mixed gas generated by the cathode passes through a gas washing device containing water to absorb NH3 gas, and the remaining gas is stored in a hydrogen tank after purification and drying.

[0047] The third object of the present application is to provide the application of the preparation method of the above-mentioned tin dioxide nanoparticle aqueous dispersion in the industrial production of tin dioxide nanoparticle dispersion.

[0048] The innovation of the present application not only lies in the innovation of the reaction system formula, but also is the first time to apply electrolysis technology to the chlorine removal process of tin dioxide nanoparticle suspension, thereby realizing highly controllable chlorine removal.

[0049] Advantages:

[0050] (1) Mixing two kinds of alkali liquor (ammonium bicarbonate and tetramethylammonium hydroxide) with tin precursor can not only ensure the smooth production of tin dioxide hydrate, but also avoid agglomeration by the steric effect provided by a small amount of tetramethylammonium hydroxide, so as to improve the final tin dioxide solid content of the system to 10wt%. In addition, compared with using tetramethylammonium hydroxide as the only alkali liquor, the method provided by the application greatly reduces the amount of organic alkali added, and is more green and environmentally friendly.

[0051] (2) The tetramethylammonium in tetramethylammonium hydroxide can be adsorbed on the surface of tin dioxide, and under high temperature conditions (> 150℃), demethylation occurs to form trimethylamine adsorbed on the surface of tin dioxide nanoparticles, thereby avoiding the agglomeration of nanoparticles.

[0052] (3) In the prior art, tetramethylammonium hydroxide is added to the prepared nanoparticle suspension as a dispersant to achieve particle dispersion. However, the addition of tetramethylammonium hydroxide at the later stage of preparation can only improve the dispersity of the already shaped nanoparticles, and cannot control the particle size. In addition, the addition of organic alkali at the later stage of preparation means the introduction of additional impurities, which affects the performance of the end product. In the application, tetramethylammonium hydroxide is added before the high pressure and high temperature reaction of the system, and decomposes into trimethylamine gas and methanol under high temperature conditions; this means that after the reaction is completed, only the dissolved trimethylamine gas and methanol in the solution need to be removed by nitrogen blowing or low temperature heating, and the purity of the tin dioxide nanoparticle suspension obtained in the application is higher.

[0053] (4) The use of electrolysis to remove ammonium chloride in the solution can achieve a chlorine removal rate of more than 90%, and connecting the anode gas outlet pipe of the electrolytic cell to an industrial sodium hypochlorite production device or an accident chlorine device can achieve economic utilization of the byproduct chlorine.

[0054] (5) The water-containing gas washing bottle connected to the cathode of the electrolytic cell absorbs ammonia gas to become ammonia water, and subsequent introduction of carbon dioxide into the ammonia water can generate ammonium bicarbonate, achieving raw material regeneration. The hydrogen gas generated by the cathode can be used as fuel for storage.

[0055] (6) The preparation method provided by the application is green and environmentally friendly, and is suitable for industrial production of tin dioxide nanoparticle dispersion. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 An example of the setting of the electrolytic cell.

[0057] Figure 2 The XRD spectrum of the nanoparticles obtained in Example 1.

[0058] Figure 3 The transmission electron microscope image of the nanoparticles obtained in Example 1.

[0059] Figure 4Transmission electron micrograph of the nanoparticles obtained in Example 2.

[0060] Figure 5 Transmission electron micrograph of the nanoparticles obtained in Example 3. DETAILED DESCRIPTION

[0061] The following specific examples are provided to further illustrate the application. It is to be understood that these examples are not intended to limit the scope of the application. Any changes and modifications that one of ordinary skill in the art would make to the application based on the contents of the application are to be considered as falling within the scope of the application.

[0062] The starting materials used in the examples and comparative examples are, if not otherwise specified, known in the art and are either commercially available or can be prepared according to known methods.

[0063] Example 1

[0064] (1) A tin tetrachloride hydrate solid was dissolved in deionized water to prepare a 1.4 M aqueous tin tetrachloride solution;

[0065] (2) A 1.4 M aqueous ammonium bicarbonate solution was prepared, and 25% aqueous tetramethylammonium hydroxide was added dropwise to the solution to give a molar ratio of ammonium bicarbonate to tetramethylammonium hydroxide of 3:1;

[0066] (3) 30 mL of the aqueous tin tetrachloride solution obtained in step (1) was mixed with the base mixture obtained in step (2) at a volume ratio of 1:4, and stirred at room temperature for 1 hour and then left to stand for 3 hours;

[0067] (4) The solution obtained in step (3) was introduced into the cathode chamber of a double-chamber electrolytic cell with an anion exchange membrane, and 150 mL of a 4 g / L aqueous sodium chloride solution was introduced into the anode chamber of the electrolytic cell. Constant current electrolysis was carried out at a current density of 30 mA / cm 3 after 3 hours of electrolysis, the chlorine removal rate was 89%, and the chlorine gas generated at the anode and the hydrogen gas and ammonia gas generated at the cathode were collected and treated;

[0068] (5) Tetramethylammonium hydroxide solution was added dropwise to the solution obtained after electrolysis in step (4) to give a pH value of 10.4;

[0069] (6) The solution obtained in step (5) was introduced into a pressure reaction vessel, and after being kept at 180°C for 2 hours, it was naturally cooled to room temperature;

[0070] (7) The solution obtained in (6) was taken out and nitrogen was bubbled through the solution for 30 minutes to remove the residual gas, obtaining a tin dioxide nanoparticle suspension with a solid content of 4 wt%. The X-ray diffraction (Xenocs S.A.S, France) spectrum of the obtained nanoparticles is shown in Figure 2 .

[0071] The diffraction peaks of the test sample were consistent with the peak positions of the tin dioxide standard card (JCPDC: 21-1250). The characteristic diffraction peaks at 2θ = 26.58°, 33.99°, 37.95°, 51.75°, 61.89°, 64.73°, and 78.69° corresponded to the crystal faces of (110), (101), (110), (200), (211), (310), (112), and (321), respectively, proving that the synthesized phase composition was rutile crystal tin dioxide. The average grain size calculated according to the Debye-Scherrer formula at the strongest diffraction peak was 3 nm.

[0072] The obtained nanoparticles were characterized by transmission electron microscopy (FEI 300KV), and the spectrum is shown in Figure 3 . The obtained particles were in a monodisperse state, and the particle size distribution was between 2-4 nm.

[0073] Example 2

[0074] (1) A tin tetrachloride hydrate solid was weighed and dissolved in deionized water to prepare a 2M tin tetrachloride aqueous solution;

[0075] (2) A 2M ammonium bicarbonate aqueous solution was prepared, and 25% tetramethylammonium hydroxide aqueous solution was added dropwise to the solution to make the molar ratio of ammonium bicarbonate to tetramethylammonium hydroxide 25:1;

[0076] (3) 30 mL of the tin tetrachloride aqueous solution obtained in step (1) was mixed with the base mixture obtained in step (2) at a volume ratio of 1:4, and stirred at room temperature for 1 hour and then stood for 3 hours;

[0077] (4) The solution obtained in step (3) was passed into the cathode chamber of a double-chamber electrolytic cell with an anion exchange membrane, 150 mL of a 6 g / L sodium chloride aqueous solution was passed into the anode chamber of the electrolytic cell, and constant current electrolysis was carried out at a current density of 45 mA / cm 3 for 3 hours at a cell temperature of 45°C, and the chlorine removal rate was 90%. The chlorine gas generated by the anode and the hydrogen gas and ammonia gas generated by the cathode were collected and treated;

[0078] (5) Tetramethylammonium hydroxide solution was added dropwise to the solution after electrolysis in step (4) to make the pH value of the solution 10.6;

[0079] (6) The solution obtained in step (5) is added to a pressure reaction vessel, and after being kept at 170°C for 2 hours, it is naturally cooled to room temperature;

[0080] (7) The solution obtained in step (6) is taken out, and residual gas in the solution is stripped off by blowing nitrogen for 30 minutes to obtain a tin dioxide nanoparticle suspension with a solid content of 6 wt%. The obtained nanoparticles are characterized by transmission electron microscopy (FEI 300KV), and the spectrum is shown in Figure 4 The obtained particles are in a monodisperse state, and the particle size distribution is between 3-5 nm.

[0081] Example 3

[0082] (1) Tin tetrachloride hydrate solid is weighed and dissolved in deionized water to prepare a 3M tin tetrachloride aqueous solution;

[0083] (2) A 2.7M ammonium bicarbonate aqueous solution is prepared, and 25% tetramethylammonium hydroxide aqueous solution is added dropwise to the solution to make the molar ratio of ammonium bicarbonate to tetramethylammonium hydroxide 40:1;

[0084] (3) 30 mL of the tin tetrachloride aqueous solution obtained in step (1) is mixed with the alkali mixture obtained in step (2) at a volume ratio of 1:4.5, and after being stirred at room temperature for 2 hours, it is left to stand for 6 hours;

[0085] (4) The solution obtained in step (3) is introduced into the cathode chamber of a double-chamber electrolytic cell with an anion exchange membrane, 150 mL of 25g / L sodium chloride aqueous solution is introduced into the anode chamber of the electrolytic cell, and constant current electrolysis is carried out at a current density of 50 mA / cm 3 After 4 hours of power-on, the chlorine removal rate is 90%, and the mixed gas of hydrogen, ammonia and chlorine generated by the anode and the cathode is collected and treated;

[0086] (5) Tetramethylammonium hydroxide solution is added dropwise to the solution after electrolysis in step (4) to make the pH value of the solution 11;

[0087] (6) The solution obtained in step (5) is added to a pressure reaction vessel, and after being kept at 150°C for 10 hours, it is naturally cooled to room temperature;

[0088] (7) The solution obtained in step (6) is taken out to obtain a tin dioxide nanoparticle suspension with a solid content of 9 wt%. The obtained nanoparticles are characterized by transmission electron microscopy (FEI 300KV), and the spectrum is shown in Figure 5 The obtained particles are in a monodisperse state, and the particle size distribution is between 4-6 nm. After being left to stand for 3 months, no precipitate or particle agglomeration is observed at the bottom of the bottle.

[0089] Comparative Example 1

[0090] (1) Weigh the solid tin tetrachloride hydrate and dissolve it in deionized water to prepare a 2M tin tetrachloride aqueous solution;

[0091] (2) Prepare a 2M ammonium bicarbonate aqueous solution;

[0092] (3) Mix 30 mL of the tin tetrachloride aqueous solution obtained in step (1) with the base mixture obtained in step (2) at a volume ratio of 1:4, stir at room temperature for 1 hour, and then stand for 3 hours;

[0093] (4) Pass the solution obtained in step (3) into the cathode chamber of a double-chamber electrolytic cell with an anion exchange membrane, pass 150 mL of a 6 g / L sodium chloride aqueous solution into the anode chamber of the electrolytic cell, and perform constant current electrolysis at a current density of 45 mA / cm 3 at a cell temperature of 45°C. After 3 hours of power-on, the chlorine removal rate is 90%, and the chlorine gas generated by the anode, as well as the hydrogen gas and ammonia gas generated by the cathode, are collected;

[0094] (5) Add ammonia water to the solution after electrolysis in step (4) to make the pH value of the solution 10.6;

[0095] (6) Put the solution obtained in step (5) into a pressure reaction vessel, heat at 170°C for 2 hours, and then naturally cool to room temperature;

[0096] (7) Take out the solution obtained in (6) to obtain a tin dioxide nanoparticle suspension with a solid content of 6 wt%. After adding 2 mL of a 25% tetramethylammonium hydroxide aqueous solution and standing overnight, the obtained nanoparticles have a particle size distribution of 30-40 nm.

[0097] The difference between Comparative Example 1 and Example 3 is that the tetramethylammonium hydroxide aqueous solution in Comparative Example 1 is added at the later stage of the reaction, while the tetramethylammonium hydroxide aqueous solution in Example 3 is added before the heating reaction. It can be seen that the addition of tetramethylammonium hydroxide before the heating reaction is very important for particle size control.

[0098] Comparative Example 2

[0099] (1) Weigh the solid tin tetrachloride hydrate and dissolve it in deionized water to prepare a 3M tin tetrachloride aqueous solution;

[0100] (2) Prepare a 2.7M ammonium bicarbonate aqueous solution, and add a 25% tetramethylammonium hydroxide aqueous solution dropwise to the solution to make the molar ratio of ammonium bicarbonate to tetramethylammonium hydroxide 40:1;

[0101] (3) Mix 30 mL of the tin tetrachloride aqueous solution obtained in step (1) with the base mixture obtained in step (2) at a volume ratio of 1:4.5, stir at room temperature for 2 hours, and then stand for 6 hours;

[0102] (4) The solution obtained in step (3) is introduced into the cathode chamber of a two-chamber electrolytic cell with an anion exchange membrane, 150 mL of a 25 g / L sodium chloride aqueous solution is introduced into the anode chamber of the electrolytic cell, and constant current electrolysis is carried out at a current density of 50 mA / cm 3 at a temperature of 50°C in the cell. After 4 hours of power supply, the chlorine removal rate is 90%, and the mixed gas of hydrogen, ammonia and chlorine generated by the anode and cathode is collected;

[0103] (5) Tetramethylammonium hydroxide solution is added dropwise to the solution after electrolysis in step (4) to adjust the pH value of the solution to 11;

[0104] (6) The solution obtained in step (5) is introduced into a pressure reaction vessel, and after being kept at 150°C for 10 hours, it is naturally cooled to room temperature;

[0105] (7) The solution obtained in step (6) is taken out, nitrogen is introduced, and the solution is heated to 70°C and kept for 30 minutes to obtain a tin dioxide nanoparticle suspension with a solid content of 9 wt%. The transmission electron microscopy (FEI 300KV) characterization spectrum of the obtained nanoparticles is shown in Figure 5 , and the obtained particles are in a monodisperse state with a particle size distribution of 4-6 nm. After standing for 3 months, there is a little precipitation at the bottom of the bottle.

[0106] The difference between Comparative Example 2 and Example 3 is that in Comparative Example 2, nitrogen is introduced and most of the trimethylamine groups are removed by heating after the reaction is completed, so that the tin dioxide nanoparticles are easy to agglomerate during storage at room temperature.

Claims

1. An aqueous dispersion of tin dioxide nanoparticles, wherein the tin dioxide nanoparticles contained therein have trimethylamine adsorbed on their surface.

2. The tin dioxide nanoparticle aqueous dispersion according to claim 1, characterized in that, The tin dioxide has a particle size of less than 10 nm, preferably less than 6 nm; and / or, The tin dioxide nanoparticle aqueous dispersion contains 2–15 wt% tin dioxide.

3. A method for preparing an aqueous dispersion of tin dioxide nanoparticles according to any one of claims 1 to 2, comprising: After reacting an aqueous solution of a tin-containing compound in an alkaline mixed solution, the pH of the solution is adjusted and the reaction is heated to obtain the aqueous dispersion of tin dioxide nanoparticles; preferably, the alkaline mixed solution contains at least ammonium bicarbonate and tetramethylammonium hydroxide; more preferably, the preparation method further includes a step of electrolytic removal of impurities.

4. The preparation method according to claim 3, characterized in that, The preparation method of the tin dioxide nanoparticle aqueous dispersion specifically includes the following steps: (1) Weigh out the tin-containing compound and dissolve it in water to prepare a tin-containing aqueous solution; (2) Prepare an alkaline mixed solution of ammonium bicarbonate and tetramethylammonium hydroxide; (3) Mix the tin-containing aqueous solution obtained in step (1) with the alkaline mixed solution obtained in step (2), stir and let stand to obtain a mixed solution; (4) Add pH adjuster to the mixture to adjust the pH of the solution; (5) After heating and reacting the solution obtained in step (4) and cooling it, the aqueous dispersion of tin dioxide nanoparticles is obtained.

5. The preparation method according to claim 4, characterized in that, Optionally, the step of removing the impurity NH4Cl is included before adjusting the pH of the solution; preferably, the impurity is removed by electrolysis.

6. The preparation method according to claim 5, characterized in that, The electrolysis is carried out in a double-chamber electrolytic cell with a diaphragm, and the electrolysis is preferably constant current electrolysis; More preferably, the electrolysis operation is specifically as follows: in the dual-chamber electrolytic cell, the mixed liquid obtained in step (3) is introduced into the cathode chamber, and the sodium chloride aqueous solution is introduced into the anode chamber. Constant current electrolysis is performed by passing electricity. During the electrolysis process, the chlorine gas generated by the anode and the mixed gas of hydrogen and ammonia generated by the cathode are optionally collected and recycled. Furthermore, the total amount of chlorine emitted can be recorded by a flow meter to determine whether electrolysis should be stopped, or the chloride ion content in the solution in the cathode chamber can be measured by a residual chlorine meter to determine whether electrolysis should be stopped, or the voltage change can be monitored to determine whether electrolysis should be stopped.

7. The preparation method according to claim 6, characterized in that, The cathode and anode in the dual-chamber electrolytic cell are inert electrodes, preferably titanium plated with ruthenium oxide; and / or, The volume of the solution in the cathode chamber is the same as the volume of the solution in the anode chamber; and / or, The concentration of the sodium chloride aqueous solution is 4 g / L to 25 g / L; and / or, The electrolysis conditions are: temperature 40–70°C, electrolysis time 1–4 hours; and / or, During the electrolysis process, the current density is 15–50 mA / cm². 3 .

8. The preparation method according to claim 4, characterized in that, The tin-containing compound is tin tetrachloride; and / or, The molar concentration of the tin-containing compound in the tin-containing aqueous solution is 0.2–4 mol / L, preferably 1.2–3 mol / L; and / or, In the alkaline solution, the molar ratio of ammonium bicarbonate to tetramethylammonium hydroxide is (3-50):1, preferably (10-30):1; and / or, In the alkaline solution, the molar concentration of ammonium bicarbonate is 1–5 mol / L, preferably 1–3 mol / L; and / or, The molar ratio of the tin-containing compound to ammonium bicarbonate is 1:(1-6), preferably 1:(3-5), wherein the tin-containing compound is calculated based on the amount of tin contained therein; and / or, The pH adjuster is selected from at least one of tetramethylammonium hydroxide, ammonia, potassium hydroxide, and sodium hydroxide.

9. The preparation method according to claim 4, characterized in that, In step (3), stirring shall be performed for at least 1 hour, preferably 1 to 3 hours; and / or, In step (3), the mixture is left to stand for at least 2 hours, preferably 2 to 8 hours; and / or, In step (4), the pH of the solution is adjusted to 10–11.5, preferably 10.3–11.3; and / or, The conditions for the heating reaction in step (5) are: a temperature of 150–200°C and a reaction time of 2–24 hours; and / or, Step (5) may optionally be followed by step (6) of introducing a protective gas to remove residual gas from the solution.

10. The method for preparing the aqueous dispersion of tin dioxide nanoparticles according to any one of claims 3 to 9, and its application in the industrial production of dispersions containing tin dioxide nanoparticles.

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