CN101704505B - Method for preparing high-thermostability tin oxide nano-powder on Ca-doped basis - Google Patents

Abstract

The invention discloses a preparation method of calcium-doped high thermal stability tin oxide nanopowder, which mainly uses inorganic tin salt, inorganic calcium salt and alkali source as raw materials, and the experimental process mainly includes precursor preparation, hydrothermal reaction , precipitate washing and drying steps, and analyzed the thermal stability of Ca-doped tin oxide nanopowders by high-temperature heat treatment, the main advantages of which are: the uniform doping of Ca in _SnO2 was realized by low-temperature hydrothermal method, and the obtained Ca-doped tin oxide nano-powder has small particle size and large specific surface area; compared with undoped tin oxide, the thermal stability of Ca-doped tin oxide nano-powder prepared by this method is obviously improved, and its thermal stability It can reach 900°C and has broad application prospects in the fields of gas sensing and catalysis. The method of the present invention does not add any surfactant, the raw materials are simple and easy to obtain, the process is simple and pollution-free, the preparation cycle is short, the conditions are mild, and the cost is low. Large-scale production is an environmentally friendly synthesis method.

Description

Preparation method of high thermal stability tin oxide nanopowder based on calcium doping

technical field

The invention relates to a preparation method of nanomaterials, in particular to a preparation method based on calcium-doped tin oxide nano-powder with high thermal stability.

Background technique

The existing tin oxide (SnO ₂ ) has excellent photoelectric characteristics and sensitivity to reducing gases, and has been widely used in the fields of gas sensor materials, conductive powders and photocatalytic materials. When the grain size of SnO ₂ material _enters the nanometer level, due to the unique small size effect, surface effect and quantum size effect of nanomaterials, it shows many special physical and chemical properties. Applications such as photocatalysis have shown great advantages, but due to the high specific surface energy of SnO ₂ nanoparticles, they are thermodynamically unstable systems. In order to achieve a stable state, the particles will spontaneously agglomerate; in addition, undoped SnO ₂ nanoparticles are thermally stable The property is poor, and the crystal grains will grow up with the increase of temperature; particle agglomeration or grain growth will weaken the advantages of _SnO2 nanomaterials due to the increase in size. Therefore, a key problem to be solved for SnO ₂ nanomaterials in the actual high-temperature application environment is how to improve their thermal stability, which is very important for improving the performance and cycle life of the material. Numerous studies have shown that doping different elements into pure _SnO2 nanomaterials is an effective way to solve this problem. Element Ca is an effective grain growth inhibitor of SnO ₂ nanomaterials. CaO present at the SnO ₂ grain boundary can significantly inhibit the growth of SnO ₂ grains, thereby controlling the growth of SnO ₂ grains. size, improving its thermal stability (Bong-Ki Min, Soon-Don Choi, Sensors and Actuators B, 2004, 99, 288-296).

There are few research reports on the preparation of Ca-doped SnO ₂ nanopowders. Among them, Choi's research group reported a wet chemical method for preparing Ca-doped SnO ₂ nanomaterials. They used stannous chloride as the tin source, first obtained Precipitation of aqueous SnO ₂ , and then the precipitation is dried, calcined, ball milled to obtain pure SnO ₂ nanomaterials, and then Ca-doped SnO ₂ nanomaterials are finally obtained by immersion in Ca acetate solution (Soon -Don Choi, Duk-Dong Lee, Sensors and Actuators B, 2001, 77, 335-338; Bong-Ki Min, Soon-Don Choi, Sensors and Actuators B, 2004, 99, 288-296; Bong-Ki Min, Soon -Don Choi, Sensors and Actuators B, 2005, 108, 119-124). Liu Wei and others used stannous chloride and calcium nitrate as the main raw materials to prepare Ca-doped SnO ₂ nanomaterials by sol-gel method (LIU Wei, CAO Lili, SCIENCE IN CHINA (Series B), 2001, 44 , 63-67).

However, the above-mentioned preparation method of Ca-doped _SnO nanopowder has the following disadvantages:

1), the heat treatment temperature in the above-mentioned preparation method is high, and the high-temperature calcination process is easy to introduce impurities, leading to the growth and agglomeration of nano-powder particles, and causing the migration or segregation of the doped calcium element, resulting in uneven doping of calcium, affect the final performance of the powder.

2) The method Choi adopts has many processes (including precipitation, drying, calcination, ball milling, and impregnation), and the preparation cycle is very long.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing calcium-doped high thermal stability tin oxide nanopowders with simple process and mild conditions

The technical solution adopted by the present invention to solve the above technical problems is: a method for preparing calcium-doped high thermal stability tin oxide nano-powder, the specific steps are as follows:

Step 1, dissolving the tin salt in deionized water or absolute ethanol, stirring to form a tin salt solution with a Sn ion concentration of 0.2 to 1mol/L, dissolving the calcium salt in deionized water, and stirring to form a Ca ion concentration of 0.1～0.5mol/L calcium salt solution, described tin salt is a kind of in stannous chloride, tin chloride or tin nitrate; Described calcium salt is a kind of in calcium chloride or calcium nitrate;

Step 2, according to the molar ratio of Ca ions to Sn ions of 0.5:100~10:100, while stirring, the calcium salt solution prepared in step 1 is added to the tin salt solution, and then continue to stir for 10~30min to form a mixed solution;

Step 3, while stirring, add the alkali source solution dropwise to the mixed solution described in step 2 until the pH value is between 9~13, and then stir for 10~50min to form a precursor solution; the alkali source solution It is an aqueous solution of urea with a concentration of 0.4~1mol/L, an aqueous solution of sodium hydroxide with a concentration of 0.4~1mol/L, an aqueous solution of potassium hydroxide with a concentration of 0.4~1mol/L or ammonia water with a mass concentration of 1~8%. one of

Step 4, transfer the precursor solution obtained in step 3 to a high-pressure reactor, conduct a hydrothermal reaction at 100-200°C for 4-24 hours, then cool naturally to room temperature, and filter out the supernatant to obtain a precipitate;

Step 5, washing the precipitate obtained in step 4 with deionized water and absolute ethanol several times in order to remove soluble ions therein, and then drying the washed precipitate at 60-100°C under vacuum conditions to obtain Ca-doped _SnO2 nanopowders.

The stirring is magnetic stirring, and the stirring intensity is greater when the alkali source solution is added dropwise than in other processes.

The washing method described in step 5 is: the product is washed with deionized water for 3 to 4 times and with absolute ethanol for 1 to 2 times by centrifugation or filtration to remove soluble ions therein.

The soluble ions are one or more of chloride ions, nitrate ions, sodium ions, and potassium ions.

During the washing process, the remaining amount of chloride ions was judged by detecting whether white precipitates were produced in the supernatant or filtrate with the AgNO ₃ solution, the concentration of the AgNO ₃ solution was 0.1 mol/L.

Compared with the prior art, the present invention has the advantages of: the uniform doping of Ca in _SnO2 is realized by the low-temperature hydrothermal method, crystals can be directly generated through the hydrothermal process, and subsequent high-temperature heat treatment is not required, thus avoiding the high-temperature heat treatment process Due to the growth of grains, the introduction of impurities and the migration or segregation of doped calcium elements, the obtained Ca-doped tin oxide nanopowder has a small particle size (about several nanometers) and a large specific surface area (160~190m ² / g); Compared with undoped tin oxide, the thermal stability of the Ca-doped tin oxide nanopowder prepared by this method is significantly improved, and its thermal stability can reach 900°C. In a word, this method does not add any surfactant, the raw materials are simple and easy to obtain, the process is simple and pollution-free, the preparation cycle is short, the conditions are mild, the cost is low, and it is suitable for large-scale production. It is an environmentally friendly synthesis method.

Description of drawings

Fig. 1 is the process flow diagram of preparation method of the present invention;

Fig. 2 is the X-ray diffraction diagram of the product obtained in the specific implementation example 1 of the present invention at different heat treatment temperatures;

Fig. 3 is a comparison chart of the average grain size of the product obtained in Examples 1 and 2 of the specific implementation of the present invention and the undoped tin oxide nanopowder at different heat treatment temperatures.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Specific implementation example 1

Step 1, dissolving 3.506g of SnCl ₄ .5H ₂ O into deionized water, stirring to form a tin chloride solution with a Sn ⁴⁺ concentration of 0.3mol/L; according to the molar ratio of Ca ²⁺ to Sn ⁴⁺ being 10 % take by weighing _0.1109g of CaCl Dissolved in deionized water, then stirred to form Ca ^{Concentration} is 0.5mol/L of CaCl ₂ solution;

Step 2, while stirring, add the _CaCl2 solution prepared in step 1 into the _SnCl4 solution, and then continue to stir for 20min to form a mixed solution;

Step 3, while stirring, add ammonia water with a mass concentration of 7% dropwise to the mixed solution described in step 2 until the pH value is 10, and then stir for 30 minutes to form a precursor solution;

Step 4, transfer the precursor solution obtained in step 3 to an autoclave, perform hydrothermal treatment at 200°C for 4 hours, then cool naturally to room temperature, and filter out the supernatant to obtain a precipitate;

Step 5, the precipitate was washed several times with deionized water and absolute ethanol in order to remove the soluble ions in it, and then the washed precipitate was dried under vacuum at 70°C for 2 h to obtain white Ca-doped SnO ₂ Nanometer powder, the average grain size is about 3.7nm, and the specific surface area is about 176m ² /g.

Specific implementation example 2

Step 1, dissolve 3.506g of SnCl ₄ .5H ₂ O into deionized water, and stir to form a tin chloride solution with a Sn ⁴⁺ concentration of 0.3mol/L; according to the molar ratio of Ca ²⁺ to Sn ⁴⁺ is 3 % take by weighing _0.0333g of CaCl Dissolve in deionized water, then stir to form Ca ²⁺ concentration is 0.5mol/L CaCl ₂ solution;

Step 2, while stirring, add the _CaCl2 solution prepared in step 1 into the _SnCl4 solution, and then stir for 20min to form a mixed solution;

Step 3, while stirring, add ammonia water with a mass concentration of 7% dropwise to the mixed solution described in step 2 until the pH value is 10, and then stir for 30 minutes to form a precursor solution;

Step 4, transferring the precursor solution described in step 3 into a high-pressure reactor, hydrothermally treating it at 200° C. for 4 hours, then cooling it naturally to room temperature, and filtering off the supernatant to obtain a precipitate;

Step 5, the precipitate was washed several times with deionized water and absolute ethanol in order to remove the soluble ions in it, and then the washed precipitate was dried under vacuum at 70°C for 2 h to obtain white Ca-doped SnO ₂ Nanometer powder, the average grain size is about 3.5nm, and the specific surface area is about 188m ² /g.

Specific implementation example 3

Step 1, dissolve 2.7078g of SnCl ₂ .2H ₂ O in 40ml of absolute ethanol, and stir to form a tin protochloride solution with a Sn ²⁺ concentration of 0.3mol/L; according to the moles of Ca ²⁺ and Sn ²⁺ The ratio is 5%, and the _CaCl of 0.0665g is weighed and dissolved in deionized water, and then stirred to form a _CaCl solution with a Ca concentration of ^0.5mol /L;

Step 2, while stirring, add the _CaCl2 solution prepared in step 1 into the _SnCl2 solution, and then continue to stir for 20min to form a mixed solution;

Step 3, while stirring, add ammonia water with a mass concentration of 7% dropwise to the mixed solution described in step 2 until the pH value is 10, and then stir for 30 minutes to form a precursor solution;

Step 4, transferring the precursor solution described in step 3 into a high-pressure reactor, hydrothermally treating it at 200° C. for 4 hours, then cooling it naturally to room temperature, and filtering off the supernatant to obtain a precipitate;

Step 5, the precipitate was washed several times with deionized water and absolute ethanol in order to remove the soluble ions in it, and then the washed precipitate was dried under vacuum at 70°C for 2 h to obtain white Ca-doped SnO ₂ Nanometer powder, the average grain size is about 3.6nm, and the specific surface area is about 185m ² /g.

Specific implementation example 4

Step 1, dissolve 2.7078g of SnCl ₂ .2H ₂ O in 20ml of absolute ethanol, and stir to form a tin protochloride solution with a Sn ²⁺ concentration of 0.6mol/L; according to the moles of Ca ²⁺ and Sn ²⁺ The ratio is 5%, and 0.0984g of Ca(NO ₃ ) ₂ is weighed and dissolved in deionized water, and then stirred to form a Ca(NO ₃ ) ₂ solution with a Ca ²⁺ concentration of 0.2 mol/L;

Step 2: Add the Ca(NO ₃ ) ₂ solution prepared in Step 1 into the SnCl ₂ solution while stirring, and then continue stirring for 30 minutes to form a mixed solution;

Step 3, while stirring, add an aqueous solution of NaOH with a concentration of 0.5 mol/L dropwise to the mixed solution described in step 2 until the pH value is 12, and then stir for 40 minutes to form a precursor solution;

Step 4, transfer the precursor solution described in step 3 into a high-pressure reactor, hydrothermally treat it at 180° C. for 12 hours, then cool it down to room temperature naturally, and filter out the supernatant to obtain a precipitate;

Step 5, the precipitate was washed several times with deionized water and absolute ethanol in order to remove the soluble ions in it, and then the washed precipitate was dried at 90°C for 1 h under vacuum conditions to obtain white Ca-doped SnO ₂ Nanometer powder, the average grain size is about 3.8nm, and the specific surface area is about 172m ² /g.

Further, in order to analyze the effect of Ca doping on the thermal stability of tin oxide nanopowders, the _SnO2 nanopowders obtained in the above examples were heat-treated for 3 hours at 400°C, 600°C, 700°C, and 900°C, respectively. The heating rate was 5°C/min. As shown in Figure 2, it is the X-ray diffraction pattern of the 10mol% Ca-doped SnO _nanometer powder annealed for 3h at different heat treatment temperatures in the specific implementation example 1, as can be seen that each diffraction peak in the figure corresponds to the tetragonal rutile type The _SnO2 phase of structure, there is no relevant impurity phase of Ca; As shown in Figure 3, it is undoped _SnO2 nanopowder and the _SnO2 nanopowder of gaining Ca doping in specific implementation example 1 and 2 in different heat treatment The average grain size at temperature, the average grain size here is the average grain size estimated by Scherrer's formula based on the half width of the 110, 101 and 211 diffraction peaks, it can be seen that the Ca-doped SnO ₂ Compared with undoped SnO ₂ , the thermal stability is significantly improved. Ca doping effectively inhibits the growth of SnO ₂ grains at high temperatures, and its thermal stability can reach 900°C (even after 3 hours of heat treatment at 900°C, the grains There is also only a small increase in size, which remains around 10nm).

Obtained from above, the present invention has adopted low-temperature hydrothermal method to realize the uniform doping of Ca in _SnO nanometer material; Stability is significantly improved.

The above is a description but not a limitation of the present invention, and other implementations based on the idea of the present invention are within the protection scope of the present invention.

Claims (5)

1. A preparation method based on calcium-doped high thermal stability tin oxide nano-powder, characterized in that the specific steps are as follows: Step 1, dissolving the tin salt in deionized water or absolute ethanol, stirring to form a tin salt solution with a Sn ion concentration of 0.2 to 1mol/L, dissolving calcium salt in deionized water, and stirring to form a Ca ion concentration of 0.1-0.5mol/L calcium salt solution, the tin salt is one of stannous chloride, tin chloride or tin nitrate; the calcium salt is one of calcium chloride or calcium nitrate; Step 2, according to the molar ratio of Ca ions and Sn ions of 0.5:100 to 10:100, the calcium salt solution prepared in step 1 is added to the tin salt solution while stirring, and then continue to stir for 10 to 30 minutes to form a mixed solution; Step 3, while stirring, add the alkali source solution dropwise to the mixed solution described in step 2 until the pH value is between 9 and 13, and then stir for 10 to 50 minutes to form a precursor solution; the alkali source solution It is an aqueous solution of urea with a concentration of 0.4-1mol/L, an aqueous solution of sodium hydroxide with a concentration of 0.4-1mol/L, an aqueous solution of potassium hydroxide with a concentration of 0.4-1mol/L or ammonia water with a mass concentration of 1-8%. one of Step 4, transfer the precursor solution obtained in step 3 to an autoclave, conduct a hydrothermal reaction at 100-200° C. for 4-24 hours, then naturally cool to room temperature, and filter out the supernatant to obtain a precipitate; Step 5, washing the precipitate obtained in step 4 with deionized water and absolute ethanol several times in order to remove soluble ions therein, and then drying the washed precipitate at 60-100°C under vacuum conditions to obtain Ca-doped _SnO2 nanopowders. 2. the preparation method based on calcium-doped high thermal stability tin oxide nanopowder according to claim 1, is characterized in that: described stirring is magnetic stirring, and the stirring intensity when dripping alkali source solution is stronger than other The process is big. 3. The preparation method of calcium-doped high thermal stability tin oxide nano-powder according to claim 1, characterized in that: the washing method described in step 5 is: adopt centrifugation or filtration to remove the precipitate Wash with deionized water for 3 to 4 times, and wash with absolute ethanol for 1 to 2 times in order to remove soluble ions therein. 4. the preparation method based on calcium-doped high thermal stability tin oxide nanopowder according to claim 1, is characterized in that: described soluble ion is chlorine ion, nitrate ion, sodium ion, potassium ion one or more of. 5. the preparation method based on calcium-doped high thermal stability tin oxide nanopowder according to claim 1, is characterized in that: in washing process, detect whether supernatant liquid or filtrate produces white precipitation by _AgNO solution. Judging the residual amount of chloride ions, the concentration of the _AgNO3 solution is 0.1mol/L.

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