TWI701217B - Preparation method of magnesium oxide/tin dioxide nano composite material - Google Patents

Abstract

A method for preparing a magnesium oxide/tin dioxide nanocomposite material, comprising: (1) preparing a precursor liquid, which contains magnesium alkoxide, tin alkoxide and a solvent; (2) adding urea to the precursor liquid and performing Hydrolysis reaction to obtain a transparent sol, wherein the molar ratio of urea to tin alkoxide is not greater than 5; (3) subjecting the transparent sol to a condensation polymerization reaction to obtain a transparent gel; (4) drying the transparent gel And annealing at a temperature not higher than 600°C to obtain the magnesium oxide/tin dioxide nanocomposite.

Description

Preparation method of magnesium oxide/tin dioxide nano composite material

The present invention relates to a preparation method of magnesium oxide/tin dioxide nanocomposite materials, in particular to a magnesium oxide/tin dioxide (MgO/SnO ₂ ) nanocomposite material using sol-gel (sol-gel) method Preparation method of composite material.

Azo dyes such as acid orange 7 (AO7 for short) have an azo group (-N=N-) connected to both ends of the aromatic ring in their structure, which is a kind of chromophore. ), which has become a common synthetic dye on the market, widely used in dyeing and finishing textile industry, leather industry and food processing industry.

When the azo dyes in industrial wastewater enter rivers or soils, they can be reduced and decomposed into aromatic amine compounds by microorganisms in the environment. Aromatic amine compounds are not easy to decompose and are easily retained in rivers or soil as pollutants. , And then affect the ecological environment. However, because aromatic amine compounds are still carcinogenic to the human body, methods such as activated carbon adsorption, sludge pumping, precipitation or microbial metabolism are generally used to remove azo dyes in wastewater. However, these methods have limited removal results. , And the waste it produces may also cause secondary pollution. Therefore, in order to avoid the shortcomings of the above methods, there are currently methods that use photocatalysts to degrade and remove azo dyes in wastewater.

Among the current photocatalysts that degrade azo dyes, TiO ₂ is the most widely used, such as commercial TiO ₂ (P25) photocatalysts. However, since the electron-hole pairs are easy to recombine, the photocatalytic activity gradually decays or even fails.

In order to improve the photocatalytic efficiency of single-component photocatalysts (such as TiO ₂ ), in recent years, the world has been committed to using modification treatment to prepare photocatalysts. The main methods are: (1) Synthesis of heterogeneous materials with nanostructures (such as TiO ₂₎ /ZnO and ZnO/CuO, etc.), and (2) plated with precious metal elements (such as Au, Pt, Ag, etc.) or non-metal elements (such as nitrogen, carbon, sulfur, etc.) to reduce the recombination of photo-generated electron-hole pairs Rate [see Journal of Renewable and Sustainable Energy , vol.5(2013), p.033118-1-033118-13; Journal of the American Chemical Society , vol.132(2010), p.5858-5868 and Journal of Materials Chemistry , vol. 20 (2010), p. 5301-5309].

Synthesizing heterogeneous phase materials can use the potential energy difference of the heterogeneous interface to increase the separation efficiency of photogenerated electron-hole pairs (reduce the recombination rate), while plating with precious metals or non-metal elements can reduce the charge due to the absorption of photogenerated electrons or changing the energy gap Rejoin. However, the preparation costs of the above methods are quite high and difficult to popularize. In addition, in addition to increasing the separation efficiency of electron-hole pairs, the photocatalytic activity can also be improved by changing the powder properties of the photocatalyst. For example, the photocatalyst can have a nano-sized particle size, narrow particle size distribution, low agglomeration state, and high Specific surface area, good crystalline phase, etc.

Magnesium oxide/tin dioxide (MgO/SnO ₂ ) nanocomposites are known to be used as photocatalysts to degrade chlorophenol and methylene blue (MB) azo dyes. The existing preparation of magnesium oxide/tin dioxide (MgO/SnO ₂ ) The method of nanocomposite materials is mainly the solution mixing method [see Applied Catalysis A: General , vol.319(2007), p.58-63 and the sol-gel method [see Materials Research Bulletin , vol.48(2013), p.3790-3799].

But the solution mixing method has the problem of low degradation efficiency. It is to prepare SnO ₂ powder coated with MgO after mixing SnO ₂ and MgO (3~4wt%) powder in a solution and then heating to 450℃. Due to the coarsening of the powder particles, it can only be photocatalyzed for 3 hours. Degrade 50% of chlorophenol.

The sol-gel method has the problems of poor crystallinity and high agglomeration of the powder, and low photodegradation efficiency of methylene blue (<83%). It is made by mixing magnesium methoxide and tin tetrachloride, and adding a lot of ammonia water to form a precipitated colloid because it is not easy to gel. The powder is prepared by sintering at 500 and 700°C. The product is SnO ₂ crystalline phase and MgO amorphous. Phase, and the powder is prone to severe agglomeration, which affects the stability and reproducibility of the detection catalytic efficiency.

Therefore, how to improve the existing preparation method of magnesium oxide/tin dioxide (MgO/SnO ₂ ) nanocomposite materials without adding a large amount of ammonia to avoid the formation of precipitates, and can be prepared with nano-particle size and narrow particle size MgO/SnO ₂ nanocomposites with good distribution, good crystallinity, low agglomeration and high specific surface area, and the prepared MgO/SnO ₂ nanocomposites have high near-ultraviolet or visible light catalytic activity. Committed to the direction of research.

Therefore, the purpose of the present invention is to provide a method for preparing a magnesium oxide/tin dioxide (MgO/SnO ₂ ) nanocomposite material. The preparation method of the present invention does not need to add a large amount of ammonia water as a precipitant, can naturally form gelation, can reduce the state of powder agglomeration, and the prepared magnesium oxide/tin dioxide nanocomposite material will have nanometer particle size and narrow particle size. The diameter distribution, good crystallinity, low agglomeration, high specific surface area and high photocatalytic activity can overcome the above-mentioned shortcomings of the prior art.

Therefore, the preparation method of the magnesium oxide/tin dioxide nanocomposite of the present invention includes the following steps: (1) Prepare a precursor liquid, which contains magnesium alkoxide, tin alkoxide and a solvent; (2) Add urea to the precursor liquid and perform a hydrolysis reaction to obtain a transparent sol, wherein the urea and tin alkoxide The ear number ratio is not more than 5; (3) subjecting the transparent sol to a condensation polymerization reaction to obtain a transparent gel; and (4) drying the transparent gel and annealing at a temperature not higher than 600°C to obtain The magnesium oxide/tin dioxide nanocomposite material.

The effect of the present invention is that: the preparation method of the present invention uses the magnesium alkoxide as the magnesium source, and the tin alkoxide as the tin source. The gelation can be formed naturally by the polycondensation reaction, and the tight and uniform distribution of the constituent molecules can be maintained. Improve the crystallinity of magnesium oxide/tin dioxide nanocomposites, and add a specific amount of urea as a hydrolysis aid in the process (the molar ratio of urea to tin alkoxide is not higher than 5), which can promote the hydrolysis reaction In order to greatly improve the dispersibility and homogeneity of the generated sol, the preparation method of the present invention does not need to use a large amount of ammonia as a precipitating agent, and the prepared magnesium oxide/tin dioxide nanocomposite has less agglomeration and average particle size It is smaller, and can increase the specific surface area of the magnesium oxide/tin dioxide nanocomposite, and improve its near ultraviolet and visible light catalytic activity. In addition, step (2) of the present invention can further carry out the hydrolysis reaction in the presence of a common metal agent, which can further increase the specific surface area of the prepared magnesium oxide/tin dioxide nanocomposite and improve its photocatalytic activity .

The content of the present invention will be described in detail below:

The step (1) of the preparation method of the present invention is to prepare a precursor liquid, which contains magnesium alkoxide, tin alkoxide and a solvent.

The magnesium alkoxide can be used alone or in combination of multiple types, and it can be, but not limited to, magnesium methoxide [Mg(OCH ₃ ) ₂ ] or magnesium ethoxide [Mg(OC ₂ H ₅ ) ₂ ]. In a specific embodiment of the present invention, the magnesium alkoxide is magnesium methoxide.

The tin alkoxide can be used alone or in combination of multiple types, and it can be, but not limited to, tetramethoxide tin [Sn(OCH ₃ ) ₄ ] or tetraethoxy tin [Sn(OC ₂ H ₅ ) ₄ ]. In a specific embodiment of the present invention, the tin alkoxide is tin tetramethoxide.

The solvent can be used alone or in a mixture of multiple types, and it can be an alcohol solvent, specifically but not limited to methanol or ethanol. In a specific embodiment of the present invention, the solvent is ethanol.

Preferably, the step (1) is to stir at 25-30°C to form the precursor liquid. In a specific embodiment of the present invention, the step (1) is to stir at 25°C to form the precursor liquid.

In a specific embodiment of the present invention, the step (1) is to dissolve the magnesium alkoxide and the tin alkoxide in the solvent.

The step (2) of the preparation method of the present invention is to add urea to the precursor liquid and conduct a hydrolysis reaction to obtain a transparent sol.

In a specific embodiment of the present invention, the molar ratio of urea to tin alkoxide is not more than 5. If the molar ratio of urea to tin alkoxide is greater than 5, the resulting sol or gel has a lower appearance and transparency, and the required gelation time is longer.

Preferably, the molar ratio of urea to the tin alkoxide ranges from 0.5 to 5. More preferably, the molar ratio of urea to the tin alkoxide ranges from 1 to 3. In some specific embodiments of the present invention, the molar ratio of urea to the tin alkoxide is 3.

Preferably, the precursor liquid in this step (2) is added with a common metal agent before the hydrolysis reaction is carried out. The common metal agent is titanium (IV) salt, manganese (II) salt, europium (III) salt, copper (II) Salt, aluminum salt or a combination thereof.

In a specific embodiment of the present invention, the titanium (IV) salt is titanium (IV) isopropoxide, the manganese (II) salt is manganese (II) chloride, and the europium (III) salt is europium (III) chloride. ), the aluminum salt is aluminum chloride.

Preferably, the molar ratio of the common metal agent to the tin alkoxide ranges from 0.01 to 0.05. More preferably, the molar ratio of the common metal agent to the tin alkoxide ranges from 0.01 to 0.03. In this range, the powder products prepared in some specific embodiments of the present invention have a larger BET specific surface area. , And has high photocatalytic activity.

When the step (2) is to carry out the hydrolysis reaction in the presence of a common metal agent, in the powder product obtained after the subsequent annealing step, the common metal ions in the common metal agent will be solid-dissolved in the magnesium oxide/two In the crystal lattice of tin oxide nanocomposites, ordinary metal ions can reduce the recombination rate of photogenerated electron-hole pairs, and increase the BET specific surface area of the powder product, thereby increasing the magnesium oxide/tin dioxide nanocomposite Photocatalytic activity of composite materials.

Preferably, the step (2) is to perform a hydrolysis reaction at 25-30°C to obtain the transparent sol. In a specific embodiment of the present invention, the step (2) is to conduct a hydrolysis reaction at 25° C. to obtain the transparent sol.

Step (3) of the preparation method of the present invention is to subject the transparent sol to a condensation polymerization reaction to obtain a transparent gel.

Preferably, the step (3) is to perform a condensation polymerization reaction at 25-30°C to obtain the transparent gel. In a specific embodiment of the present invention, the step (3) is to perform a condensation polymerization reaction at 25°C to obtain the transparent gel.

Preferably, this step (3) is to carry out the condensation polymerization reaction at a relative humidity of 55-85%. In a specific embodiment of the present invention, this step (3) is to carry out the condensation polymerization reaction at a relative humidity of 85%.

In the specific embodiment of the present invention, the step (3) is to carry out the condensation polymerization reaction for 36 hours.

The step (4) of the preparation method of the present invention is to dry the transparent gel and perform annealing at a temperature not higher than 600° C. to obtain the magnesium oxide/tin dioxide nanocomposite material.

In a specific embodiment of the present invention, the step (4) is to dry the transparent gel at 150°C.

Preferably, this step (4) is annealing at a temperature of 400-600°C. More preferably, this step (4) is to perform annealing at a temperature of 400 to 500°C.

In the specific embodiment of the present invention, under the condition of irradiating visible light for 1.5 hours, the degradation rate of the acid orange 7 azo dye of the magnesium oxide/tin dioxide nanocomposite is above 95.5%, and the degradation rate constant is 0.0350 min ^-1 or more.

In some specific embodiments of the present invention, under the condition of irradiating near ultraviolet light for 1.5 hours, the degradation rate of the acid orange 7 azo dye of the magnesium oxide/tin dioxide nanocomposite is above 97.1%, and the degradation rate The constant is above 0.0389min ^-1 .

The other features and effects of the present invention will be clearly presented in the embodiments with reference to the drawings, in which: [Figure 1] is the X- of the powder products prepared in Examples 1 to 3 and Comparative Examples 3 to 7 Light diffraction pattern; [Figures 2 to 6] are the X-ray diffraction diagrams of the powder products prepared in Examples 19 to 21, 22 to 24, 25 to 27, 28 to 30, and 31 to 33, respectively; [Figures 7 and 8] These are the TEM photographs of the powder products prepared in Example 1 and Comparative Example 3; [Figures 9 to 12] are the powder products prepared in Example 1, Example 2, Example 3, and Comparative Example 5, respectively [Figures 13 and 14] are the photocatalytic activity curves and linear kinetic simulation regression diagrams of comparative examples 1, 2, 4, 5, and 9 respectively for the degradation of AO7 azo dyes exposed to near ultraviolet light; [Figure 15 and 16] are the photocatalytic activity graphs and linear kinetic simulation regression graphs of the degradation of AO7 azo dyes by exposure to near ultraviolet light in Examples 1 to 3, Comparative Example 5, and Comparative Example 6, respectively; and [Figures 17 and 18] are implementation respectively Examples 1 to 4, Comparative Example 5, the photocatalytic activity curve and linear kinetic simulation regression line graph of AO7 azo dyes degraded by visible light exposure.

The present invention will be further described with reference to the following examples, but it should be understood that these examples are for illustrative purposes only and should not be construed as limiting the implementation of the present invention.

<Comparative Example 1>

After the magnesium oxide was annealed at 500° C., the powder product of Comparative Example 1 was obtained.

<Comparative Example 2>

After the tin dioxide was annealed at 500° C., the powder product of Comparative Example 2 was obtained.

<Examples 1 to 3 and Comparative Examples 3 to 7>

The powder products of Examples 1 to 3 and Comparative Examples 3 to 7 were prepared according to the following steps. Among them, the molar ratio of urea to tetramethoxytin in Examples 1 to 3 and Comparative Examples 3 to 7 ( U/Sn) and annealing temperature are shown in Table 1 below.

Step (1) : Dissolve 0.4 mol magnesium methoxide and 0.2 mol tetramethoxide tin in ethanol (solvent), and stir at 25° C. for 1 hour to form a precursor solution.

Step (2) : Add 0.6 mol of urea to the precursor solution, and conduct a hydrolysis reaction at 25° C. for 1 to 2 hours to obtain a sol.

Step (3): the transparent sol is subjected to a condensation polymerization reaction at 25° C. and a relative humidity of 85% for 36 hours to obtain a gel.

Step (4): Dry the transparent gel at 150°C and refine it into colloidal powder. Then, the colloidal powder is annealed for 1 to 2 hours and then cooled to room temperature to obtain the powder products of Examples 1 to 3 and Comparative Examples 3 to 7.

<Examples 4 to 18 and Comparative Example 8>

The preparation methods of Examples 4 to 18 and Comparative Example 8 are similar to those of Example 1. The difference is that the step (2) of Examples 4 to 18 and Comparative Example 8 is to add a common metal agent to the precursor solution and then add 0.6 mol of urea (Comparative Example 8 did not add urea), and the hydrolysis reaction was carried out at 25° C. for 1 to 2 hours to obtain a sol. Step (4) of Examples 4 to 18 and Comparative Example 8 is to perform annealing at a temperature of 400°C. Among them, the types and addition amounts of common metal agents of Examples 4 to 18 and Comparative Example 8 (the molar ratio of common metal agent to tetramethoxide tin) are shown in Table 1 below.

<Examples 19~33>

The preparation methods of Examples 19 to 33 are respectively similar to those of Examples 4 to 18, with the difference that the step (4) of Examples 19 to 33 is an annealing at a temperature of 500°C.

<Comparative Example 9>

The powder product of Comparative Example 9 is commercial titanium dioxide (P25) (brand: UniRegion Bio-Tech).

「-」表示無添加。

"-" means no addition.

[Comparison of polycondensation reaction (gelation) time with the appearance of sol and gel]

The sol and gel were prepared according to the steps (1) to (3) of the above embodiment 1 and the molar ratio (U/Sn) of urea and tetramethoxytin listed in Table 2 below. Next, observe the appearance of the sol and gel prepared under different conditions, and record the polycondensation reaction time (ie gelation time) required in step (3). The results are summarized in Table 2 below.

From the results in Table 2, it can be seen that although the appearance of the sol obtained without adding urea during the process is clear, the appearance of the gel is translucent. In addition, sols and gels obtained by adding urea and the molar ratio (U/Sn) of urea to tetramethoxytin not greater than 5 during the manufacturing process are all clear and transparent in appearance. However, although urea is added in the process, the appearance of the sol obtained with U/Sn greater than 5 is turbid, and the gel appearance is translucent (U/Sn=7) or white and opaque (U/Sn=10).

In addition, it needs to be supplemented that there is a preparation method that adds urea and U/Sn is not greater than 5 in the process of the present invention. The addition of ordinary metal agents only slightly prolongs the gelation time, and the appearance of the sol and gel is clear. And transparency.

It can be seen from the above description that there is a preparation method in which urea is added and U/Sn is not greater than 5 in the process of the present invention, which can be made into sol and gel with a clear and transparent appearance. Uniform hydrolysis), and then a clear sol and transparent gel can be obtained later.

[X-ray diffraction (XRD) analysis]

The powder products prepared in Examples 1 to 3 and Comparative Examples 3 to 7 were subjected to X-ray diffraction analysis with an X-ray diffractometer (manufacturer: Bruker; model: D8 Advance). The obtained X-ray The diffraction pattern is shown in Figure 1. The powder products prepared in Examples 19-21, 22-24, 25-27, 28-30, 31-33 were subjected to X-ray diffraction analysis, and the obtained X-ray diffraction diagrams are shown in Figure 2. ~6 shown.

It can be seen from Figure 1 that the colloidal powder obtained without adding urea in the process has only the crystalline phase of SnO ₂ (JCPDS Card no.41-1445) after annealing at 400℃ (Comparative Example 3) until the annealing temperature is 500~600℃ (Comparative Examples 4~5), the _two -phase structure of MgO (JCPDS Card no.45-0946) and SnO ₂ has only begun. The colloidal powder obtained by adding urea in the process, after annealing at 400~600℃ (Examples 1~3), it is mainly a _two -phase structure of MgO and SnO ₂ , but after annealing at 700~800℃ (Comparative Examples 6~7 ) Will begin to produce crystalline phases of MgSnO ₃ (magnesium metastannate; JCPDS Card no.30-0798) and Mg ₂ SnO ₄ (magnesium stannate; JCPDS Card no.24-0723), and will increase with the annealing temperature High, the crystalline phase diffraction peaks of MgSnO ₃ and Mg ₂ SnO ₄ will also be significantly enhanced.

Therefore, it can be known from the above description that the powder product prepared by the preparation method with the annealing temperature not higher than 600° C. of the present invention has a dual-phase structure of MgO and SnO ₂ . When the annealing temperature is increased to 700~800℃, the powder product obtained will also contain magnesium metastannate and magnesium stannate, which will produce a mixed phase of MgO/SnO ₂ and MgSnO ₃ , Mg ₂ SnO ₄ , and It is not possible to obtain pure magnesium oxide/tin dioxide (MgO/SnO ₂ ) nanocomposites.

In addition, the results of adding urea in the process (Examples 1 to 3) can be calculated according to the Scherrer equation, and the average grain size of MgO is 20.8~30.5nm, and the average grain size of SnO ₂ is 3.8~7.0nm; The results of no addition of urea in the process (comparative examples 4~5) can be calculated according to Scherrer equation. The average grain size of MgO is 28.6~32.2nm, and the average grain size of SnO ₂ is 6.7~7.9nm, indicating that there is addition in the process The powder product of urea has a finer grain size.

It can be found from Figures 2 to 5 that the examples 19-21, 22-24, 25-27, 28-30, 31-33 annealed at 500 ℃ are mainly the _two -phase structure of MgO and SnO ₂ , indicating doping A small amount of common metal ions has no obvious effect on the crystallization behavior of the powder product, indicating that the common metal ions can be dissolved in the lattice of MgO and SnO ₂ . It should be added that similar results will be obtained when the annealing temperature is 400°C or 600°C.

In addition, it should be added that urea is added in the process. When the annealing temperature is 500~600℃, the average grain size of Ti ⁴⁺ doped MgO and SnO ₂ are 25.3~30.1nm and 4.6~6.5nm, respectively , And no urea is added in the process, the average grain size of MgO and SnO ₂ doped with Ti ⁴⁺ are 27.4~31.0nm and 5.3~6.5nm, respectively. It can be seen that the magnesium oxide/tin dioxide formed by adding urea ( The crystal grain size of the MgO/SnO ₂ ) composite material is smaller than that of the MgO/SnO ₂ composite material formed without adding urea. Urea is added in the process. When the annealing temperature is 500~600℃, the average grain size of Mn ²⁺ doped MgO and SnO ₂ are 26.8~30.5nm and 5.7~6.8nm, respectively. No urea is added in the process. The average grain size of MgO and SnO _{2 of the} doped Mn ²⁺ is 28.2~31.6nm and 6.3~7.6nm, respectively. It can be seen that the grain size of the MgO/SnO ₂ composite formed by adding urea is smaller than that formed without adding urea The grain size of the MgO/SnO ₂ composite material. Doping with Eu ³⁺ , Cu ²⁺ or Al ³⁺ ions will also get similar results. It can be seen from the above that doping with a small amount of common metal agent does not have much difference in the average grain size of MgO and SnO ₂ , but compared with the method without adding urea in the process, the method of adding urea in the process will make the MgO and SnO ₂ The grain size is more reduced.

[Transmission electron microscopy (TEM) analysis]

The powder products prepared in Example 1 and Comparative Example 3 were photographed with a transmission electron microscope (manufacturer: JOEL; model: JEM-2100F), and the obtained TEM photos are shown in Figs. 7 and 8 respectively.

According to Fig. 7 and Fig. 8, the powder product obtained without adding urea in the process (Fig. 8) is partially agglomerated with an average particle size of about 15nm; the powder product obtained by adding urea in the process (Fig. 7) is uniform and small Dispersed state, and has a narrow particle size distribution, the average particle size is less than 10nm. It should be added that when urea is added and U/Sn is not greater than 5, similar results will be obtained. The above results show that, compared with the method without adding urea in the process, the method of adding urea and having U/Sn not greater than 5 in the process of the present invention can reduce the agglomeration of the powder product and reduce the average particle size.

[Scanning electron microscopy (SEM) analysis]

The powder products prepared in Example 1, Example 2, Example 3 and Comparative Example 5 were photographed with a scanning electron microscope (manufacturer: Hitachi; model: SU3500), and the obtained SEM photos are shown in Figure 9 and Figure 10, respectively. , Figure 11 and Figure 12. The results of the average particle size of the primary particles obtained from Figures 9 to 12 are summarized in Table 3 below.

It can be seen from the results in Table 3 that at the same annealing temperature, compared to the method without adding urea in the process (Comparative Example 5), the method of adding urea in the process (Example 3) has the average primary particle size of the powder product It is smaller, indicating that the method of adding urea and U/Sn not greater than 5 in the process of the present invention can reduce the agglomeration of the powder product and reduce its average particle size. In addition, it can be seen from the results in Table 3 that the average primary particle diameter of the powder products obtained by annealing at 400°C and 500°C in Example 1 and Example 2 is smaller than that in Example 3, that is, at 400°C. Annealing at ~500℃ can reduce the agglomeration of powder products and reduce the average particle size.

[Specific surface area analysis]

The powder products of Examples 1 to 5, 7, 11, 13, 17 and Comparative Examples 3, 5, and 8 were used with a specific surface area analyzer (manufacturer: Micromeritics; model: ASAP 2020), using the BET method at a temperature of 77K, The isothermal nitrogen adsorption and desorption curve was measured, and the BET specific surface area was calculated. The results are shown in Table 4 below.

It can be seen from the results in Table 4 that at the same annealing temperature, compared with the method without adding urea in the process (Comparative Examples 3, 5, 8), the powder obtained by the method of adding urea in the process (Examples 1, 3, 5) The BET specific surface area of the bulk product is relatively large. It should be added that when urea is added and U/Sn is not greater than 5, similar results will be obtained. The above results indicate that the method of adding urea and U/Sn not greater than 5 in the process of the present invention can increase the BET specific surface area of the powder product. In addition, from the results in Table 4, it can be seen that the BET specific surface area of the powder products obtained by annealing at 400°C and 500°C in Example 1 and Example 2 is larger than that in Example 3, that is, at 400~500°C. Annealing can further increase the BET specific surface area of the powder product.

In addition, from the results in Table 4, it can be seen that compared to the powder products (Examples 1 to 3) made without adding common metal agents in the process, the powder products made by adding common metal agents during the process (Examples 4~5, 7, 11, 13, 17) have a larger BET specific surface area, indicating that the addition of common metal agents in the process can further increase the BET specific surface area of the powder product. In addition, it should be supplemented that when the common metal agent is added in the process and the molar ratio of the common metal agent to tetramethoxytin is greater than 0.05, it will reduce the BET specific surface area of the powder product.

[Photocatalytic activity analysis]

Add the powder product to be analyzed to 100 mL of AO7 azo dye aqueous solution (with a concentration of 5.0 mg/L), and stir in a dark box with a magnet for 30 minutes to obtain analysis samples. Then, respectively expose the analysis samples to a wavelength of Under 365nm 400W near ultraviolet (NUV) lamp or 400W halogen lamp with wavelength of 400~700nm (maximum emission wavelength of visible light λ _max is 548nm), the distance between the light source and the analysis sample is 20cm. In the process of exposure to near-ultraviolet or visible light, periodically take 10 mL analysis samples and filter them with a filter membrane (filter hole is 0.45μm), and then use the resulting filtrate with an ultraviolet-visible spectrometer (manufacturer: Shimadzu; model: UV- 1800) Measure the maximum absorption of AO7 azo dye at a wavelength of 483nm.

Convert the above measured absorption value to the concentration of AO7 azo dye, and calculate the relative concentration C/C ₀ and its negative natural logarithmic value -ln( C/C ₀ ), where C is after exposure to near ultraviolet light or visible light The concentration of AO7 azo dye, C ₀ is the concentration of AO7 azo dye before exposure to near ultraviolet light or visible light. The closer the relative concentration C/C _{0 is} to 1, the lower the degradation of AO7 azo dye. Finally, draw the photocatalytic activity curve with the calculated relative concentration C/C ₀ and the exposure time, and draw the linear kinetic simulation regression line with -ln( C/C ₀ ) and the exposure time. The results are shown in Figure 13~18 . Among them, Figure 13 and Figure 14 are respectively the photocatalytic activity curve and linear kinetic simulation regression graph of the degradation of AO7 azo dyes in Comparative Examples 1, 2, 4, 5, and 9 exposed to near ultraviolet light; Figure 15 and Figure 16 are respectively Examples 1 to 3, Comparative Example 5, and Comparative Example 6: The photocatalytic activity curve and linear kinetic simulation regression graph of AO7 azo dyes exposed to near ultraviolet light; Figure 17 and Figure 18 are Examples 1 to 4, comparison Example 5: The photocatalytic activity curve and linear kinetic simulation regression curve of AO7 azo dyes degraded by visible light exposure.

From the above linear kinetic simulation regression line graph, it can be determined that the photocatalytic reaction of the powder product obtained in the embodiment or the comparative example to degrade AO7 azo dye belongs to the first-order reaction, which is expressed by the mathematical relationship as -ln( C/ C ₀ )= kt , where t is the exposure time, k is the reaction rate constant, and the degradation rate η(%)=[( C ₀ - C ) /C ₀ ]×100%.

According to the above analysis method, the degradation rate of AO7 azo dyes and the reaction rate for degradation of AO7 azo dyes of Comparative Examples 1, 2, 4~6, 9 and Examples 1-18 after exposure to near ultraviolet light for 1.5 hours The constants are organized in Table 5 below; Comparative Examples 2, 4, 5, The degradation rates of 9 and Examples 1 to 18 for AO7 azo dyes and their reaction rate constants for degradation of AO7 azo dyes after 1.5 hours of visible light exposure are summarized in Table 6 below.

From the results in Table 5, it can be seen that Comparative Example 3 without adding urea in the process, Examples 1 to 3 in which urea was added in the process, and Examples 4 to 8, 10 to 14, and 16 to 18 in which urea and common metal agents were added in the process The prepared powder product has a degradation rate of over 97.1% for AO7 azo dyes after exposure to near ultraviolet light for 1.5 hours, and its reaction rate constant for degradation of AO7 azo dyes can reach over 0.0389 min ^-1 .

From the results in Table 6, it can be seen that the powder products prepared in Examples 1 to 3 in which urea is added in the process and Examples 4 to 18 in which urea and common metal agents are added in the process are compared to AO7 azo after being exposed to visible light for 1.5 hours. The degradation rate of the dye can reach more than 95.5%, and its reaction rate constant for the degradation of AO7 azo dye can reach more than 0.0350 min ^-1 .

In addition, from the results of Examples 1 to 3, it can be seen that compared to the powder product produced by annealing at 600°C, the powder product produced by annealing at 400~500°C has a higher degradation rate and The reaction rate constant means that it has high near-ultraviolet and visible light catalytic activity.

In addition, under the conditions of the same annealing temperature and the same type of common metal agent, compared to Examples 6, 9, 12, 15, and 18 where the common metal agent addition amount is 0.05, the implementation of the common metal agent addition amount of 0.01~0.03 Examples 4~5, 7~8, 10~11, 13~14, 16~17 prepared powder products have higher degradation rate and reaction rate constant, that is, have higher near ultraviolet light and visible light catalytic activity .

In summary, since the preparation method of the present invention uses the magnesium alkoxide and the tin alkoxide as the magnesium source and the tin source, respectively, gelation can be formed naturally by the condensation polymerization reaction, and the composition molecules can be kept tightly and uniformly distributed. Therefore, the crystallinity of the magnesium oxide/tin dioxide nanocomposite can be improved, and a specific amount of urea (the molar ratio of urea to tin alkoxide is not greater than 5) is added as a hydrolysis aid in the process, thereby promoting hydrolysis The reaction greatly improves the dispersibility and homogeneity of the produced sol, so that the preparation method of the present invention does not need to use ammonia water as a precipitant, and the magnesium oxide/tin dioxide nanocomposite material obtained has fewer agglomerations and has an average particle size It is smaller and undergoes the hydrolysis reaction in the presence of common metal agents, which can further increase the specific surface area of the magnesium oxide/tin dioxide nanocomposite and increase its near-ultraviolet and visible light catalytic activity, so it can indeed reach the cost of the invention purpose.

However, the above are only examples of the present invention. When the scope of implementation of the present invention cannot be limited by this, all simple equivalent changes and modifications made in accordance with the scope of the patent application of the present invention and the content of the patent specification still belong to This invention patent covers the scope.

Claims (10)

A method for preparing a magnesium oxide/tin dioxide nanocomposite material, comprising the following steps: (1) preparing a precursor liquid, which contains magnesium alkoxide, tin alkoxide and a solvent; (2) adding urea to the precursor liquid And perform a hydrolysis reaction to obtain a transparent sol, wherein the molar ratio of urea to tin alkoxide is not greater than 5; (3) subject the transparent sol to a condensation polymerization reaction to obtain a transparent gel; and (4) dry the Transparent gel and annealing at a temperature not higher than 600°C to obtain the magnesium oxide/tin dioxide nanocomposite material. The method for preparing a magnesium oxide/tin dioxide nanocomposite material according to claim 1, wherein the magnesium alkoxide is magnesium methoxide, magnesium ethoxide or a combination thereof. The method for preparing a magnesium oxide/tin dioxide nanocomposite material according to claim 1, wherein the tin alkoxide is tin tetramethoxide, tin tetraethoxide or a combination thereof. The method for preparing the magnesium oxide/tin dioxide nanocomposite material according to claim 1, wherein the molar ratio of urea to the tin alkoxide ranges from 1 to 3. The method for preparing a magnesium oxide/tin dioxide nanocomposite material according to claim 1, wherein, in this step (2), the precursor liquid is further added with a common metal agent before the hydrolysis reaction is carried out, and the common metal agent is titanium (IV) Salt, manganese (II) salt, europium (III) salt, copper (II) salt, aluminum salt or a combination thereof. The method for preparing the magnesium oxide/tin dioxide nanocomposite material according to claim 5, wherein the molar ratio of the common metal agent to the tin alkoxide ranges from 0.01 to 0.03. Preparation of magnesium oxide/tin dioxide nanocomposite material as described in claim 1 The method, wherein the step (4) is annealing at a temperature of 400 to 600°C. The method for preparing a magnesium oxide/tin dioxide nanocomposite material according to claim 7, wherein the step (4) is annealing at a temperature of 400 to 500°C. The method for preparing a magnesium oxide/tin dioxide nanocomposite material according to claim 1, wherein, under the condition of irradiating visible light for 1.5 hours, the magnesium oxide/tin dioxide nanocomposite material has an acid orange 7 azo dye The degradation rate is above 95.5%, and the degradation rate constant is above 0.0350min ^-1 . The method for preparing a magnesium oxide/tin dioxide nanocomposite material according to claim 1, wherein, under the condition of irradiating near ultraviolet light for 1.5 hours, the magnesium oxide/tin dioxide nanocomposite material has an acid orange 7 pair The degradation rate of nitrogen dye is above 97.1%, and the degradation rate constant is above 0.0389min ^-1 .

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