High-stability nano cerium oxide dispersion liquid, preparation method thereof and sunscreen cream

Abstract

The invention discloses a high-stability nano cerium oxide dispersion liquid, a preparation method thereof and sunscreen cream, and belongs to the technical field of nano materials. The preparation method of the high-stability nano cerium oxide dispersion liquid comprises the following steps: mixing cerium salt, an alkali solution and a plant extract, controlling the pH value to be greater than or equal to 12, and reacting at 2-10 DEG C under ultrasonic and stirring conditions to form a reaction liquid A; mixing the reaction solution A with a surfactant, and carrying out hydrothermal treatment to form a reaction solution B; and mixing the reaction liquid B with an oxidizing agent, naturally settling, adding water, grinding, and centrifuging to form the high-stability nano cerium oxide dispersion liquid. The high-stability nano cerium oxide dispersion liquid prepared by the invention is good in stability, uniform in nano cerium oxide particle size and easy to mix with other solvent systems, and can meet the use requirements of sunscreen cream. According to the method, calcination treatment is not adopted, and the situation that nano cerium oxide is sintered in the calcination process, large particles are formed and are difficult to disperse again subsequently can be avoided.

Description

Technical Field

[0001] The present application relates to the technical field of nanomaterials, and particularly to a highly stable nano-ceria dispersion liquid, a preparation method thereof, and a sunscreen. Background Art

[0002] Sunscreens can be divided into chemical sunscreens and physical sunscreens, and both have their own advantages and disadvantages. Chemical sunscreens have a good skin feel and little impact on skin color after application. However, the effective time of chemical sunscreens is short, and they need to be reapplied continuously. It takes a certain amount of time to take effect after application, and the products decomposed by chemical sunscreens under ultraviolet light are likely to have adverse effects on the skin. If only chemical sunscreens are used to achieve a high SPF value, a large amount of sunscreens need to be added, which not only affects the skin feel of the sunscreen, making it sticky and heavy, but also increases the risk of skin allergies. Physical sunscreen uses zinc oxide and titanium dioxide as sunscreens, and its mechanism is to achieve sun protection by reflecting, scattering, and absorbing ultraviolet light. Due to its special sun protection mechanism, physical sunscreen can provide rapid, long-lasting, and high-efficiency sun protection with little irritation to the skin. However, their high refractive index makes the skin look unnaturally white, resulting in a "plastered wall feeling". Ultrafine cerium oxide (CeO 2 ) has ideal properties as a broad-spectrum inorganic sunscreen in personal care products. It is relatively transparent to visible light but has good ultraviolet radiation absorption performance. It looks natural on the skin and does not give a feeling of excessive paleness, and has excellent dispersibility and transparency.

[0003] If physical sunscreen powders such as zinc oxide, titanium dioxide, and cerium oxide are directly added to sunscreen products, they are likely to be unevenly dispersed, affecting the effect after application. Dispersing these inorganic powder bodies in water first and then adding them to sunscreen products can solve the above problems. To prepare a stable aqueous dispersion of inorganic nanoparticles, it is necessary to keep the nanoparticles stable in the aqueous solution without agglomeration and sedimentation through various methods. Adding surfactants is the most common method. Surfactants can form steric hindrance or electrostatic repulsion on the surface of nanoparticles to keep the nanoparticles stably dispersed. However, agglomerates may have formed before the addition of surfactants to the nanoparticles. Therefore, some physicochemical methods have to be used to depolymerize the agglomerated nanoparticles into monodisperse particles to be more uniformly coated with surfactants. These commonly used depolymerization methods include ball milling, ultrasonic treatment, acid dissolution, etc. Ball milling can only be used for powders with larger particle sizes and cannot work continuously with complex operations. Ultrasonic treatment generates high noise and requires controlling the water temperature during operation, thus consuming high energy. Acid dissolution is only suitable for a small part of agglomerated nanoparticles.

[0004] In traditional methods for synthesizing cerium oxide, methods include co-precipitation method, hydrothermal method, microemulsion method, sol-gel method, etc. Although the hydrothermal method can stably synthesize nanoparticles with uniform morphology, it requires high-temperature and high-pressure equipment, has complex operations, harsh experimental conditions and low yield, which all limit its application. The microemulsion method and sol-gel method both have problems such as harsh reaction conditions, low yield, and difficult sample separation, restricting their industrial applications. The co-precipitation method has high yield, simple synthesis steps, and low cost, being suitable for industrial applications, but there are problems in controlling the synthesized morphology and particle size. Moreover, the nano-ceria prepared by current methods has poor dispersibility and stability in water and cannot be stored for a long time. Summary of the Invention

[0005] Based on this, the main object of this application is to provide a method for preparing a highly stable nano-ceria dispersion, which can form a nano-ceria dispersion with good stability and uniform nano-ceria particle size, and is used to solve the problems of poor dispersibility, poor stability, and easy agglomeration of nano-ceria aqueous solution in the prior art.

[0006] In the first aspect of this application, there is provided a method for preparing a highly stable nano-ceria dispersion, including the following steps:

[0007] Mix a cerium salt, an alkali solution, and a plant extract, control pH≥12, and react at 2-10°C under the conditions of first ultrasonic and stirring to form reaction solution A;

[0008] Mix reaction solution A with a surfactant and perform hydrothermal treatment to form reaction solution B;

[0009] Mix reaction solution B with an oxidant, perform natural sedimentation, add water for grinding, and centrifuge to form the highly stable nano-ceria dispersion.

[0010] In some embodiments, the cerium salt includes at least one of cerium nitrate, cerium sulfate, and cerium chloride; and / or the alkali solution includes sodium hydroxide solution and / or potassium hydroxide solution;

[0011] and / or the plant extract includes green tea extract;

[0012] and / or the surfactant includes at least one of sodium hexametaphosphate, polyvinylpyrrolidone, sodium citrate, dextran, and Tween 80;

[0013] and / or the oxidant includes peroxide.

[0014] In some embodiments, the peroxide includes at least one of hydrogen peroxide, sodium peroxide, and potassium peroxide.

[0015] In some embodiments, the molar ratio of the cerium salt to the alkali in the alkali solution is 1:3-8;

[0016] and / or the molar mass ratio of the cerium salt to the plant extract is 0.1 mol: 10 - 100 g;

[0017] and / or the mass ratio of the cerium salt to the surfactant is 200: (0.5 - 20);

[0018] and / or the addition amount of the oxidant is based on controlling the pH of the reaction solution B to neutral;

[0019] and / or the concentration of the alkali solution is based on adjusting the pH of the reaction system ≥ 12;

[0020] and / or the concentration of the highly stable nano - cerium oxide dispersion is 1 - 5 wt%.

[0021] In some embodiments, the first ultrasonic conditions include: ultrasonic power 1000 - 3000 W, ultrasonic frequency 20 - 400 kHz;

[0022] and / or the conditions of the stirring include: stirring rate 300 - 1000 rpm;

[0023] and / or the reaction time ≥ 1 h.

[0024] In some embodiments, the conditions of the hydrothermal treatment include: heating rate 3 - 20 °C / min, heat preservation temperature 100 - 300 °C, reaction time 2 - 48 h.

[0025] In some embodiments, the hydrothermal treatment is carried out under the conditions of the second ultrasonic; the conditions of the second ultrasonic include: ultrasonic power 1000 - 3000 W, ultrasonic frequency 20 - 400 kHz.

[0026] In some embodiments, the conditions of the natural sedimentation include: standing for 12 - 72 h;

[0027] and / or the centrifugation conditions include: centrifugal force 1000 - 10000 g, centrifugation time 10 - 30 min;

[0028] and / or the grinding includes ball milling and / or sand milling.

[0029] In some embodiments, the grinding is sand milling; the conditions of the sand milling include: sand milling speed 500 - 3000 rpm, sand milling time 2 - 24 h.

[0030] In the second aspect of the present application, there is provided a highly stable nano - cerium oxide dispersion prepared by the foregoing preparation method.

[0031] In the third aspect of the present application, there is provided an application of the foregoing highly stable nano - cerium oxide dispersion in sunscreen.

[0032] In the fourth aspect of the present application, a sunscreen is provided, the raw materials of which include the aforementioned highly stable nano-ceria dispersion.

[0033] Advantages of the present application:

[0034] 1. In the present application, a cerium salt, an alkali solution and a plant extract are first subjected to a low-temperature reaction under ultrasonic and stirring conditions, then a surfactant is added for hydrothermal treatment, and then an oxidant is added. After natural sedimentation, grinding and centrifugation, a highly stable nano-ceria dispersion is prepared. This highly stable nano-ceria dispersion has good stability, uniform particle size of nano-ceria, and is easy to mix with other solvent systems, meeting the usage requirements of sunscreens.

[0035] 2. In the method for preparing nano-ceria in the present application, calcination treatment is not adopted, which can avoid sintering of nano-ceria during calcination, forming large particles that are difficult to redisperse subsequently, and affecting the stability of the subsequent ceria dispersion.

[0036] 3. In the present application, hydrothermal treatment is adopted, which increases the crystallinity of nano-ceria, makes it more mature, improves the stability of the nano-ceria dispersion, and does not change color after long-term storage. The nano-ceria prepared by the method of the present application has uniform and controllable particle size and good dispersibility in water.

[0037] 4. The reaction of the cerium salt, the alkali solution and the plant extract in the present application needs to be carried out under ultrasonic, stirring and low-temperature conditions. The temperature condition, stirring and ultrasonic jointly affect the morphology and particle size of the nanoparticles. When the ultrasonic power is too low, the uniformity of the reaction system cannot be guaranteed, and heterogeneous nucleation is likely to occur in the area with too high cerium salt concentration, and the originally spherical nanoparticles grow radially to form rod-shaped particles; when the stirring rate is too low, insufficient stirring will also cause heterogeneous nucleation. Too high ultrasonic power or stirring rate cannot further affect the morphology and particle size, but cause waste; too high reaction temperature leads to too fast reaction rate, which is not conducive to ensuring uniform precipitation subsequently.

[0038] 5. The present application adds a plant extract, which contains bioactive substances such as polyphenols and can be used as a reducing agent to reduce cerium ions, thereby forming nano-ceria. In addition, it can not only reduce metal ions, but also stabilize the newly formed nanoparticles to a certain extent, prevent their aggregation, and help maintain the dispersibility and stability of the nanoparticles; and the plant extract has natural antibacterial and antioxidant properties, increasing the biocompatibility of nano-ceria.

[0039] 6. In the present application, a surfactant is added to the reaction solution A, which can modify the surface of nano-ceria and make the material have excellent dispersibility in aqueous solution.

[0040] 7. After natural sedimentation in this application, grinding treatment can be adopted to improve the stability of nano-ceria in aqueous solution. And natural sedimentation cannot be replaced by centrifugation or pressure filtration, etc., as the latter will cause excessive aggregation and caking of nano-particles, affecting the stability of the nano-ceria dispersion. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for description in the embodiments or the prior art. The drawings are only for the purpose of showing the preferred embodiments and are not considered as a limitation to the present application. Throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0042] Figure 1 TEM image of the highly stable nano-ceria dispersion prepared in Example 1;

[0043] Figure 2 Ultraviolet absorption spectrum of the highly stable nano-ceria dispersion prepared in Example 1;

[0044] Figure 3 Picture of the highly stable nano-ceria dispersion prepared in Example 1 after being placed for one month;

[0045] Figure 4 Picture of the highly stable nano-ceria dispersion prepared in Comparative Example 1 after being placed for one month. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] To make the objectives, technical solutions and advantages of the present application clearer and the understanding of the disclosed content of the present application more thorough and comprehensive, the following will clearly and completely describe the technical solutions of the present application in combination with specific embodiments and corresponding drawings of the present application. The described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0047] The following will make a detailed description of the implementation of the present application in combination with the drawings. This embodiment is implemented on the premise of the technical solution of the present application, and gives detailed implementation manners and specific operation processes, but the protection scope of the present application is not limited to the following embodiments.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0049] TERMS

[0050] Unless otherwise stated or there are contradictions, the terms or phrases used herein have the following meanings:

[0051] In this application, terms such as "multiple" and "multiple types", without special limitation, refer to a quantity greater than or equal to 2. For example, "one or more types" and "at least one type" mean one type or two or more types.

[0052] In this application, terms such as "further" and "especially" are used for descriptive purposes, indicating differences in content, but should not be construed as limiting the scope of protection of this application.

[0053] In the technical features described in an open-ended manner in this application, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0054] In this application, regarding numerical intervals (i.e., numerical ranges), without special instructions, the distribution of the selectable numerical values within this numerical interval is regarded as continuous, and includes the two numerical endpoints of this numerical interval (i.e., the minimum value and the maximum value), as well as each numerical value between these two numerical endpoints. Without special instructions, when the numerical interval only refers to integers within this numerical interval, it includes the two endpoint integers of this numerical range, as well as each integer between the two endpoints, which is equivalent to directly listing each integer. When providing multiple numerical ranges to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein. The "numerical values" in this numerical interval can be any quantitative values, such as numbers, percentages, ratios, etc. The "numerical interval" allows for a broad inclusion of numerical interval types such as percentage intervals, ratio intervals, and ratio value intervals.

[0055] In this application, the term "room temperature" generally refers to 4 - 35°C, preferably 20 ± 5°C. In the embodiments of this application, room temperature refers to 20 - 30°C.

[0056] In this application, without special limitation, the temperature parameter allows both constant temperature treatment and variation within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0057] In this application, regarding the unit of the data range, if there is only a unit after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 2 - 5h means that the units of the left endpoint "2" and the right endpoint "5" are both h (hours).

[0058] In the first aspect of this application, a method for preparing a highly stable nano-ceria dispersion is provided, including the following steps:

[0059] Mix a cerium salt, an alkali solution, and a plant extract, control the pH≥12, and react at 2-10°C under the conditions of first ultrasound and stirring to form reaction solution A;

[0060] Mix reaction solution A with a surfactant, perform hydrothermal treatment to form reaction solution B;

[0061] Mix reaction solution B with an oxidant, perform natural sedimentation, add water for grinding, and centrifuge to form the high-stability nano-ceria dispersion.

[0062] In this application, a cerium salt, an alkali solution, and a plant extract are first reacted at low temperature under the conditions of ultrasound and stirring, then a surfactant is added for hydrothermal treatment, and then an oxidant is added. The high-stability nano-ceria dispersion is prepared through natural sedimentation, grinding, and centrifugation. This high-stability nano-ceria dispersion has good stability, uniform particle size of nano-ceria, and is easy to mix with other solvent systems, meeting the usage requirements of sunscreen.

[0063] In the method for preparing nano-ceria in this application, calcination treatment is not adopted, which can avoid sintering of nano-ceria during calcination, forming large particles that are difficult to redisperse subsequently, affecting the stability of the subsequent ceria dispersion.

[0064] Hydrothermal treatment is adopted in this application, which increases the crystallinity of nano-ceria, makes it more mature, improves the stability of the nano-ceria dispersion, does not change color after long-term storage. The nano-ceria prepared by the method of this application has uniform and controllable particle size and good dispersibility in water.

[0065] In the reaction of this application, it is necessary to control the pH≥12. Too low pH will affect the morphology and particle size of nano-ceria. During the reaction, the alkali solution is in an excessive state, which can react the cerium salt completely. Due to strong stirring and ultrasound, cerous hydroxide formed by the cerium salt and the alkali solution is rapidly oxidized by oxygen in the air and turns light yellow to hydrated ceria, that is, reaction solution A contains a large amount of hydrated ceria.

[0066] The plant extract contains bioactive substances, such as polyphenols, which can act as a reducing agent to reduce cerium ions, thereby forming nano-ceria. In addition, it can not only reduce metal ions, but also stabilize the newly formed nano-particles to a certain extent, preventing their aggregation, contributing to maintaining the dispersibility and stability of the nano-particles; and the plant extract has natural antibacterial and antioxidant properties, increasing the biocompatibility of nano-ceria.

[0067] In some embodiments, in the high-stability nano-ceria dispersion, the particle size of nano-ceria is 5-20nm.

[0068] Specifically, the reaction temperature can be 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, etc. It should be noted that since ultrasound will increase the temperature of the solution and affect the morphology of the material and the uniformity of the particle size, it is necessary to control the reaction temperature to be maintained at 2 - 10°C. In this application, under the above-defined ultrasound, stirring, and temperature conditions, it is necessary to control the temperature and pH value for a reaction of ≥1 h to ensure complete reaction of the materials.

[0069] Specifically, the cerium salt includes at least one of cerium nitrate, cerium sulfate, and cerium chloride; and / or the alkali solution includes sodium hydroxide solution and / or potassium hydroxide solution.

[0070] Specifically, the plant extract includes green tea extract.

[0071] Specifically, the preparation process of the green tea extract includes: mixing green tea with water, extracting at 70 - 100°C for 1 - 4 h, and taking the filtrate, which is the green tea extract. For example: Take 10.0 g of dried and pulverized green tea powder, add it to 100 mL of deionized water, and place it in a round-bottom flask. In an oil bath at 80°C, use a magnetic stirrer to stir and reflux at a speed of 400 r / min for 2 hours. After the reaction, filter it with filter paper to obtain the plant extract solution, and store it in a 4°C refrigerator for later use.

[0072] Specifically, the surfactant includes at least one of sodium hexametaphosphate, polyvinylpyrrolidone, sodium citrate, dextran, and Tween 80.

[0073] It should be noted that the function of the surfactant is, on the one hand, to prevent the agglomeration of nanoparticles during the hydrothermal process, and on the other hand, to form a molecular layer on the surface of the material to improve the dispersibility of the material in aqueous solution.

[0074] In some embodiments, the oxidant includes peroxide. Specifically, the peroxide includes at least one of hydrogen peroxide, sodium peroxide, and potassium peroxide.

[0075] It should be noted that hydrogen peroxide plays an oxidizing role, oxidizing all the low-valent cerium to +4 valence to form cerium oxide.

[0076] Specifically, the molar ratio of the cerium salt to the alkali in the alkali solution is 1:3 - 8, such as 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, etc. The concentration of the alkali solution is adjusted so that the pH of the reaction system ≥12.

[0077] Specifically, the molar mass ratio of the cerium salt to the plant extract is 0.1 mol: 10 - 100 g, such as 0.1 mol: 10 g, 0.1 mol: 20 g, 0.1 mol: 30 g, 0.1 mol: 40 g, 0.1 mol: 50 g, 0.1 mol: 60 g, 0.1 mol: 70 g, 0.1 mol: 80 g, 0.1 mol: 90 g, 0.1 mol: 100 g, etc.

[0078] Specifically, the mass ratio of the cerium salt to the surfactant is 200: (0.5 - 20), for example, 200: 0.5, 200: 1, 200: 2, 200: 3, 200: 4, 200: 5, 200: 6, 200: 7, 200: 8, 200: 9, 200: 10, 200: 15, and 200: 20.

[0079] Specifically, the addition amount of the oxidant is based on controlling the pH of the reaction solution B to neutral.

[0080] Specifically, the concentration of the highly stable nano - cerium oxide dispersion is 1 - 5 wt%, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, etc.

[0081] Specifically, the conditions of the first ultrasonic treatment include: the ultrasonic power is 1000 - 3000 W, such as 1000 W, 1200 W, 1400 W, 1600 W, 1800 W, 2000 W, 2200 W, 2400 W, 2600 W, 2800 W, 3000 W; the ultrasonic frequency is 20 - 400 kHz, such as 20 kHz, 50 kHz, 100 kHz, 150 kHz, 200 kHz, 250 kHz, 300 kHz, 350 kHz, 400 kHz; the stirring rate is 300 - 1000 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, 950 rpm, 1000 rpm; the reaction time ≥ 1 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc.

[0082] It should be noted that the reaction of the cerium salt, alkali solution and green tea extract at 2-10°C in this application needs to be carried out under the simultaneous presence of ultrasonic and stirring, and specific ultrasonic and stirring conditions are selected. Stirring and ultrasonic jointly affect the morphology and particle size of the nanoparticles. When the ultrasonic power is too low, it is impossible to ensure the uniformity of the reaction system, and heterogeneous nucleation is likely to occur in the area with too high cerium salt concentration. The originally spherical nanoparticles grow radially to form rod-shaped particles. At the same time, when the stirring rate is too low and the stirring is insufficient, heterogeneous nucleation will also occur. Too high ultrasonic power or stirring rate cannot further affect the morphology and particle size, but instead causes waste. Too high reaction temperature leads to too fast reaction speed, which is not conducive to ensuring the uniform precipitation subsequently. Under the ultrasonic and stirring conditions of this application, it is more conducive to preparing a stable nano-ceria dispersion.

[0083] Specifically, the conditions of the hydrothermal treatment include: a heating rate of 3-20°C / min, for example, the heating rate is 3°C / min, 5°C / min, 7°C / min, 9°C / min, 11°C / min, 13°C / min, 15°C / min, 17°C / min, 19°C / min, 20°C / min; a holding temperature of 100-300°C, for example, the temperature is 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C; a reaction time of 2-48 h, for example, the reaction time is 2 h, 6 h, 10 h, 14 h, 18 h, 22 h, 26 h, 30 h, 34 h, 38 h, 42 h, 48 h.

[0084] Specifically, the hydrothermal treatment is carried out under the conditions of the second ultrasonic; the conditions of the second ultrasonic include: an ultrasonic power of 1000-3000 W, for example, 1000 W, 1200 W, 1400 W, 1600 W, 1800 W, 2000 W, 2200 W, 2400 W, 2600 W, 2800 W, 3000 W; an ultrasonic frequency of 20-400 kHz, for example, 20 kHz, 50 kHz, 100 kHz, 150 kHz, 200 kHz, 250 kHz, 300 kHz, 350 kHz, 400 kHz.

[0085] It should be noted that carrying out the hydrothermal treatment under ultrasonic conditions can effectively reduce the agglomeration of the nanomaterials during the reaction and affect their dispersibility. The hydrothermal treatment is a process of recrystallization and growth of nano-ceria, which can improve the stability of the nanoparticles. If the hydrothermal treatment is not carried out, there will be many amorphous nanoparticles in the material, which will affect the ultraviolet shielding effect of the final product and the stability of the dispersion.

[0086] Specifically, the conditions for natural sedimentation include: standing still for 12 - 72 h, for example, standing still for 24 h, 48 h or 72 h; the centrifugation conditions include: a centrifugal force of 1000 - 10000 g, for example, 1000 g, 2000 g, 3000 g, 4000 g, 5000 g, 6000 g, 7000 g, 8000 g, 9000 g, 10000 g; and a centrifugation time of 10 - 30 min, for example, 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min, 30 min.

[0087] Specifically, the grinding includes ball milling and / or sand milling. Preferably, the grinding is sand milling. The conditions for sand milling include: a rotation speed of 500 - 3000 rpm for sand milling, for example, 500 rpm, 700 rpm, 900 rpm, 1100 rpm, 1300 rpm, 1500 rpm, 1700 rpm, 1900 rpm, 2100 rpm, 2300 rpm, 2500 rpm, 2700 rpm, 2900 rpm, 3000 rpm; and a sand milling time of 2 - 24 h, for example, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h.

[0088] It should be noted that natural sedimentation is to remove the excess reaction solution to make the finally prepared dispersion neutral. During the sedimentation process, the centrifugal effect can be avoided to prevent serious agglomeration of the material. If the centrifuged material is directly put into water for redispersion, an aqueous solution with good dispersibility cannot be obtained. In addition, sand milling treatment needs to be carried out again. The material is accurately quantified before sand milling treatment to ensure that the final aqueous solution reaches the required concentration. After measuring the absorbance values of different concentration standard samples of the material at 301 nm by an ultraviolet spectrophotometer, a standard curve is plotted, and based on this standard curve, the ratio of the material to water during sand milling is determined. Centrifugation treatment is to remove some still agglomerated particles, and the centrifuged solution is the high-stability nano-ceria dispersion.

[0089] In addition, for nano-particle aqueous dispersions with lower requirements for conditions such as dispersibility and transparency, corresponding products can be prepared only through ordinary stirring or homogenization. However, inorganic nano-particles such as hydrophilic ceria are naturally prone to agglomeration in aqueous solutions. If only stirred, the surface modifier cannot uniformly coat the nano-particles, so the properties such as the dispersibility and transparency of the prepared aqueous dispersion are not good enough.

[0090] Therefore, in this application, sanding treatment is adopted. If the sanding time is too short or the sanding speed is too low, it will affect the dispersibility of the aqueous solution. During the sanding process, a stabilizer that can maintain the stability of the dispersion can also be added to the aqueous solution. For example, the stabilizer is one or more of sodium hexametaphosphate, polyvinylpyrrolidone, sodium citrate, dextran, or Tween 80.

[0091] In the second aspect of this application, a highly stable nano-ceria dispersion prepared by the aforementioned preparation method is provided.

[0092] In the third aspect of this application, the application of the aforementioned highly stable nano-ceria dispersion in sunscreen is provided.

[0093] In the fourth aspect of this application, a sunscreen is provided, which includes the aforementioned highly stable nano-ceria dispersion.

[0094] It should be noted that the raw materials used in the embodiments of this application are all ordinary commercially available products, and no specific limitation is imposed on their sources.

[0095] Preparation Example 1

[0096] Preparation of green tea extract: Take 10.0 g of dried and pulverized green tea powder, add it to 100 mL of deionized water, and place it in a round-bottom flask. In an oil bath at 80 °C, use a magnetic stirrer to stir and reflux at a speed of 400 r / min for 2 hours. After the reaction is completed, filter the plant extract solution with filter paper and store it in a refrigerator at 4 °C for later use.

[0097] Example 1

[0098] A preparation method of a highly stable nano-ceria dispersion is as follows:

[0099] (1) React cerium sulfate at 4 °C with potassium hydroxide solution and green tea extract (Preparation Example 1) under ultrasonic and stirring conditions. The ultrasonic power is 1000 W, the ultrasonic frequency is 400 kHz, the stirring rate is 300 rpm, the reaction temperature is 8 °C, and the reaction time is ≥1 h to obtain reaction solution A; among them, the molar ratio of cerium sulfate to potassium hydroxide is 1:6, and the molar mass ratio of cerium sulfate to green tea extract is 0.1 mol:50 mL; the concentration of the potassium hydroxide solution is controlled to make the pH of the reaction system 12.

[0100] (2) Add polyvinylpyrrolidone to the reaction solution A. The mass ratio of cerium sulfate to polyvinylpyrrolidone is 200:1, transfer it to a reaction kettle, and carry out hydrothermal treatment under ultrasonic conditions. The ultrasonic power is 1000 W, the ultrasonic frequency is 400 kHz, and the hydrothermal treatment conditions are: the heating rate is 3 °C / min, the holding temperature is 100 °C, and the reaction time is 48 h to obtain reaction solution B.

[0101] (3) Add hydrogen peroxide to the reaction solution B until it is neutral, and conduct natural sedimentation treatment for 48 h. Add water to the sediment after natural sedimentation for sand grinding treatment. The rotation speed of sand grinding is 500 rpm, and the sand grinding time is 24 h. Then conduct centrifugation treatment. The centrifugation conditions are: the centrifugal force is 1000 g, and the centrifugation time is 30 min to obtain the high-stability nano-ceria dispersion (1 wt%).

[0102] The high-stability nano-ceria dispersion prepared in this example was respectively tested for TEM images and ultraviolet absorption spectra, as shown in Figure 1 and 2 respectively. The nano-ceria prepared in this example is spherical, and the particle size is 5 - 20 nm.

[0103] Example 2

[0104] A preparation method of a high-stability nano-ceria dispersion is as follows:

[0105] (1) React cerium nitrate at 4 °C with sodium hydroxide solution and green tea extract (Preparation Example 1) under the conditions of ultrasonic and stirring. The ultrasonic power is 2000 W, the ultrasonic frequency is 210 kHz, the stirring rate is 650 rpm, the reaction temperature is 8 °C, and the reaction time is ≥1 h to obtain reaction solution A; wherein, the molar ratio of cerium nitrate to sodium hydroxide is 1:6, and the molar mass ratio of cerium nitrate to green tea extract is 0.1 mol:50 mL; the concentration of the sodium hydroxide solution is controlled to make the pH of the reaction system 12.

[0106] (2) Add sodium hexametaphosphate to the reaction solution A. The mass ratio of cerium nitrate to sodium hexametaphosphate is 200:6. Transfer it to a reaction kettle for hydrothermal treatment under ultrasonic conditions. The ultrasonic power is 2000 W, the ultrasonic frequency is 210 kHz. The hydrothermal treatment conditions are: the heating rate is 11 °C / min, the holding temperature is 200 °C, and the reaction time is 25 h to obtain reaction solution B.

[0107] (3) Add hydrogen peroxide to the reaction solution B until it is neutral, conduct the first natural sedimentation treatment for 48 h. Add water to the sediment after natural sedimentation for sand grinding treatment. The rotation speed of sand grinding is 1700 rpm, and the sand grinding time is 425 h. Then conduct the second centrifugation treatment. The second centrifugation conditions are: the centrifugal force is 550 g, and the centrifugation time is 20 min to obtain the high-stability nano-ceria dispersion (1 wt%).

[0108] The TEM image of the high-stability nano-ceria dispersion prepared in this example is basically the same as that of Example 1.

[0109] Example 3

[0110] A method for preparing a highly stable nano-ceria dispersion, the steps are as follows:

[0111] (1) React cerium chloride at 4 °C with sodium hydroxide solution and green tea extract (Preparation Example 1) under the conditions of ultrasonic and stirring. The ultrasonic power is 3000 W, the ultrasonic frequency is 20 kHz, the stirring rate is 1000 rpm, the reaction temperature is 8 °C, and the reaction time is ≥1 h to obtain reaction solution A; wherein, the molar ratio of cerium chloride to sodium hydroxide is 1:6, and the molar mass ratio of cerium chloride to green tea extract is 0.1 mol:50 mL; the concentration of the sodium hydroxide solution is controlled so that the pH of the reaction system is 12.5;

[0112] (2) Add sodium citrate to the reaction solution A. The mass ratio of cerium chloride to sodium citrate is 200:10, transfer it to a reaction kettle and perform hydrothermal treatment under ultrasonic conditions. The ultrasonic power is 3000 W, the ultrasonic frequency is 20 kHz, and the hydrothermal treatment conditions are: the heating rate is 20 °C / min, the holding temperature is 300 °C, and the reaction time is 2 h to obtain reaction solution B;

[0113] (3) Add hydrogen peroxide to the reaction solution B, perform natural sedimentation treatment for 48 h, add water to the sediment after natural sedimentation and perform sand grinding treatment. The sand grinding speed is 3000 rpm, the sand grinding time is 2 h, and then perform centrifugation treatment. The centrifugation conditions are: the centrifugal force is 10000 g, and the centrifugation time is 10 min to obtain the highly stable nano-ceria dispersion (1 wt%).

[0114] The TEM image of the highly stable nano-ceria dispersion prepared in this example is basically the same as that of Example 1.

[0115] Comparative Example 1

[0116] The preparation method of the nano-ceria dispersion in this comparative example is basically the same as that of Example 1, except that the reaction in step (1) is only carried out under ultrasonic conditions without stirring.

[0117] Comparative Example 2

[0118] The preparation method of the nano-ceria dispersion in this comparative example is basically the same as that of Example 1, except that the reaction in step (1) is only carried out under stirring without ultrasonic.

[0119] Comparative Example 3

[0120] The preparation method of the nano-ceria dispersion in this comparative example is basically the same as that of Example 1, except that no surfactant is added in step (2).

[0121] Comparative Example 4

[0122] The preparation method of the nano-ceria dispersion liquid in this comparative example is basically the same as that in Example 1, except that after adding a surfactant to the reaction liquid A in step (2), hydrothermal treatment is not carried out, and step (3) is directly carried out.

[0123] Comparative Example 5

[0124] The preparation method of the nano-ceria dispersion liquid in this comparative example is basically the same as that in Example 1, except that in step (3), sanding treatment is not carried out.

[0125] Comparative Example 6

[0126] The preparation method of the nano-ceria dispersion liquid in this comparative example is basically the same as that in Example 1, except that in step (1), the pH value needs to be controlled at 9 during the reaction.

[0127] Comparative Example 7

[0128] Prepare a cerium oxide nanosphere solution according to the method of Example 3 in Patent CN108017081A.

[0129] Comparative Example 8

[0130] According to the scheme of Example 1, except that natural sedimentation is replaced by centrifugation at 12000 rpm / min for 30 min, and then centrifuged again after treatment with absolute ethanol.

[0131] Test Example

[0132] Test the stability and water solubility effects of the nano-ceria dispersion liquids prepared in Test Examples 1-3 and Comparative Examples 1-8.

[0133] The specific method is as follows: The concentrations of the nano-ceria dispersion liquids in Examples 1-3 and Comparative Examples 1-8 are the same, both are 1 wt%, and they are left standing at room temperature for one month to observe the stability and water solubility effects. The pictures of the nano-ceria dispersion liquids in Example 1 and Comparative Example 1 after standing for one month are respectively as Figure 3 and 4 shown. Among them, the absorbance values of different concentration standard samples of the material at 301 nm are measured by an ultraviolet spectrophotometer, and then a standard curve is drawn. Based on this standard curve, the ratio of the material to water during sanding is determined. The results are shown in Table 1.

[0134] Table 1 Stability and water solubility of nano-ceria dispersion liquid

[0135]

[0136] From Figure 3-4As can be seen from Table 1, the highly stable nano-ceria dispersion liquids prepared in Examples 1-3 have very good stability. After being placed for one month, they are still uniform dispersion liquids without precipitation or delamination. However, precipitation and delamination occurred in the nano-ceria dispersion liquids of Comparative Examples 1-8, and their stability did not meet the requirements. Only by adopting the preparation process defined in this application can a nano-ceria dispersion liquid with good stability be obtained.

[0137] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0138] The above-described embodiments only represent several implementation manners of this application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several modifications and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of the patent of this application should be subject to the appended claims.

Claims

1. A method for preparing a high-stability nano-cerium oxide dispersion, characterized in that: The steps include: The cerium salt, the alkaline solution and the plant extract are mixed, the pH is controlled to be ≥ 12, and the mixture is reacted at 2-10° C. under the conditions of first ultrasound and stirring to form a reaction solution A; The reaction solution A is mixed with a surfactant and subjected to a hydrothermal treatment to form a reaction solution B; The reaction solution B is mixed with the oxidant, and the mixture is naturally precipitated, ground with water, and centrifuged to form the high-stability nano-cerium oxide dispersion.

2. The preparation method according to claim 1, characterized in that The cerium salt includes at least one of cerium nitrate, cerium sulfate and cerium chloride; and / or the alkaline solution comprises sodium hydroxide solution and / or potassium hydroxide solution; and / or the plant extract comprises green tea extract; and / or the surfactant comprises at least one of sodium hexametaphosphate, polyvinyl pyrrolidone, sodium citrate, dextran and Tween 80; And / or the oxidizing agent comprises a peroxide.

3. The preparation method according to claim 2, characterized in that: The peroxide includes at least one of hydrogen peroxide, sodium peroxide and potassium peroxide.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The molar ratio of the cerium salt to the alkali in the alkali solution is 1:3-8; and / or the molar mass ratio of the cerium salt to the plant extract is 0.1 mol:10-100 g; and / or the mass ratio of the cerium salt to the surfactant is 200:(0.5-20); and / or the amount of the oxidant added is based on controlling the pH of the reaction solution B to be neutral; and / or the concentration of the alkaline solution is based on adjusting the pH of the reaction system to ≥ 12; And / or the concentration of the high-stability nano-cerium oxide dispersion is 1-5wt%.

5. The preparation method according to any one of claims 1 to 3, characterized in that: The first ultrasonic condition includes: ultrasonic power 1000-3000W, ultrasonic frequency 20-400kHz; And / or the stirring conditions include: a stirring rate of 300-1000 rpm; And / or the reaction time is ≥ 1h.

6. The preparation method according to any one of claims 1 to 3, characterized in that: The conditions of the hydrothermal treatment include: a heating rate of 3-20°C / min, a holding temperature of 100-300°C, and a reaction time of 2-48h; And / or the conditions of natural sedimentation include: standing for 12-72 hours; And / or the centrifugal conditions include: centrifugal force 1000-10000g, centrifugal time 10-30min; And / or the grinding comprises ball milling and / or sand milling.

7. The preparation method according to claim 6, characterized in that: The hydrothermal treatment is carried out under the second ultrasonic condition; the second ultrasonic condition includes: ultrasonic power 1000-3000W, ultrasonic frequency 20-400kHz; And / or the grinding is sand grinding; the conditions of the sand grinding include: a sand grinding speed of 500-3000rpm and a sand grinding time of 2-24h.

8. The high-stability nano-cerium oxide dispersion prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the high-stability nano cerium oxide dispersion as claimed in claim 8 in sunscreen.

10. A sunscreen, characterized in that: The raw materials include the high-stability nano-cerium oxide dispersion as described in claim 8.

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