Photocatalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of photocatalysts, and discloses a photocatalyst and a preparation method and application thereof.The preparation method comprises the following steps that 1, melamine, boric acid and water are mixed and then subjected to a hydrothermal reaction, and a hydrothermal product is obtained; (2) mixing the hydrothermal product with mixed salt, and then calcining at the temperature of 500-600 DEG C; wherein the mixed salt comprises lithium chloride and potassium chloride. The photocatalytic activity of g-C3N4 is greatly improved through crystallization degree optimization and boron doping synergistic effect, so that the obtained boron-crystalline carbon nitride photocatalyst has excellent photocatalytic activity, can be widely applied to various application scenes of photocatalysis, and particularly can be applied to photocatalytic degradation of NOx and photocatalytic production of hydrogen peroxide.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and particularly relates to a photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Graphitic carbon nitride (g-C 3 N 4 ) as a typical non-metallic polymer semiconductor has been widely used in the fields of photocatalytic hydrogen production, photocatalytic degradation of nitrogen oxides (NO x ), and photocatalytic hydrogen peroxide production due to its unique advantages such as visible light response performance, simple composition elements, good stability, and rich precursors.

[0003] g-C 3 N 4 The traditional preparation method of g-C 3 N 4 is the thermal polycondensation method, that is, precursors such as cyanamide, dicyandiamide, melamine, ammonium thiocyanate, urea, or thiourea are calcined at a temperature of 550-600 °C; during this process, the precursor molecules are gradually condensed and polymerized by removing small molecules, and finally bulk g-C 3 N 4 is generated. This preparation method is simple to operate. However, during the traditional thermal polymerization method, it is controlled by reaction kinetics, and the synthesized original g-C 3 N 4 has problems such as poor crystallinity, narrow light absorption range, and serious recombination of photo-generated carriers, resulting in poor photocatalytic performance, which greatly restricts its application in the field of photocatalysis. Summary of the Invention

[0004] The object of the present invention is to overcome the problems existing in the prior art that the original g-C 3 N 4 has problems such as poor crystallinity, narrow light absorption range, and serious recombination of photo-generated carriers, resulting in poor photocatalytic performance, and to provide a photocatalyst, a preparation method thereof, and an application thereof, and the photocatalyst has excellent photocatalytic performance.

[0005] To achieve the above object, on the one hand, the present invention provides a preparation method of a photocatalyst, and the method includes: (1) Mixing melamine, boric acid, and water, and then performing a hydrothermal reaction to obtain a hydrothermal product; (2) Mixing the hydrothermal product with a mixed salt, and then calcining at a temperature of 500-600 °C; wherein, the mixed salt includes lithium chloride and potassium chloride.

[0006] Preferably, in step (1), the dosage ratio of melamine to boric acid is 4 g: 0.5-3 mmol.

[0007] Preferably, in step (1), the dosage ratio of melamine to water is 4 g: 50-100 mL.

[0008] Preferably, in step (1), the conditions of the hydrothermal reaction include: the temperature is 150-200 °C and the time is 5-15 h.

[0009] Preferably, in step (2), the weight ratio of the hydrothermal product to the mixed salt is 1:8-12.

[0010] Preferably, in the mixed salt of step (2), the mass fraction of lithium chloride is 55-65% and the mass fraction of potassium chloride is 35-45%.

[0011] Preferably, step (2) further includes: washing and drying the product obtained by calcination.

[0012] In a second aspect of the present invention, a photocatalyst is provided, and the photocatalyst is prepared by the method described above.

[0013] In a third aspect of the present invention, the above-mentioned photocatalyst is provided for photocatalytic degradation of NO x in it.

[0014] In a fourth aspect of the present invention, the above-mentioned photocatalyst is provided for the application in photocatalytic production of hydrogen peroxide.

[0015] In the technical solution provided by the present invention, melamine is selected as the precursor and boric acid is used as the doping agent for boron element. Based on the induction of boric acid under hydrothermal conditions, part of the melamine is hydrolyzed in-situ into cyanuric acid. Then, melamine, cyanuric acid and boric acid achieve self-assembly of the supramolecular precursor through hydrogen bond interaction. Then, the melt salt method is used to optimize the crystallinity, and boron-doped g-C 3 N 4 , that is, the photocatalyst, is obtained. Through the synergistic effect of crystallinity optimization and boron doping, the present invention greatly improves the photocatalytic activity of g-C 3 N 4 , so that the obtained boron-doped carbon nitride photocatalyst has excellent photocatalytic activity and can be widely applied to various application scenarios of photocatalysis, especially for photocatalytic degradation of NO x and photocatalytic production of hydrogen peroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the XRD pattern of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 of the present invention; Figure 2 is the photocatalytic degradation of NO of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 of the present invention x effect picture; Figure 3It is the photocatalytic hydrogen peroxide production effect diagram of the photocatalysts prepared in Example 1 and Comparative Examples 1-3 of the present invention. Detailed Embodiments

[0017] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0018] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0019] The present invention provides a method for preparing a photocatalyst, which method comprises the following steps: (1) Mix melamine, boric acid and water, and then carry out a hydrothermal reaction to obtain a hydrothermal product; (2) Mix the hydrothermal product with a mixed salt, and then calcine it under the condition of 500-600 °C to obtain a boron-doped carbon nitride photocatalyst; Wherein, the mixed salt comprises lithium chloride and potassium chloride.

[0020] In the method of the present invention, the highly crystalline g-C 3 N 4 prepared by the molten salt method has few bulk phase defects, has a more ordered structure, a higher degree of polymerization and a more extended conjugated plane, which is thus conducive to promoting the transfer of photo-generated carriers, reducing the recombination of electron-hole pairs, and finally enhancing the photocatalytic activity of highly crystalline g-C 3 N 4 ; meanwhile, by doping boron into g-C 3 N 4 , the visible light spectral response range of g-C 3 N 4 can be broadened. The present invention simultaneously solves many disadvantages of the original g-C 3 N 4 , such as poor crystallinity, narrow visible light absorption range, serious carrier recombination, small specific surface area, etc., through a synergistic modification strategy of crystallinity optimization and boron doping, and greatly enhances the photocatalytic activity of g-C 3 N 4 .

[0021] In the method of the present invention, in step (2), the calcination temperature can be 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, 560 °C, 580 °C or 600 °C.

[0022] In a preferred embodiment, in step (2), the calcination temperature is 540 - 560 °C.

[0023] In order to make the photocatalytic activity of the photocatalyst better, in a preferred embodiment, in step (1), the dosage ratio of melamine to boric acid is 4 g : 0.5 - 3 mmol. Specifically, for example, it can be 4 g:0.5 mmol, 4 g:0.6 mmol, 4 g:0.8 mmol, 4 g:1 mmol, 4 g:1.5 mmol, 4 g:2 mmol or 4 g:3 mmol.

[0024] In the method of the present invention, in step (1), the water is distilled water.

[0025] In some embodiments, in step (1), the dosage ratio of melamine to water is 4 g : 50 - 100 mL. Specifically, for example, it can be 4 g:50 mL, 4 g:60 mL, 4 g:70 mL, 4 g:80 mL or 4 g:100 mL.

[0026] In some embodiments, in step (1), the mixing is carried out under a stirring state, so that the mixing efficiency is higher. In some embodiments, the mixing time is 20 - 40 min.

[0027] In a specific embodiment, step (1) includes: adding melamine and water into a reactor, and then adding boric acid, and stirring for 20 - 40 min.

[0028] In order to make the degree of self-assembly of the supramolecular precursor induced by the hydrothermal reaction appropriate, in a preferred embodiment, in step (2), the hydrothermal reaction temperature is 150 - 200 °C. Specifically, for example, it can be 150 °C, 160 °C, 170 °C, 180 °C, 190 °C or 200 °C, and preferably 170 - 190 °C.

[0029] In a preferred embodiment, in step (2), the hydrothermal reaction time is 5 - 15 h. Specifically, for example, it can be 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h or 15 h, and preferably 8 - 12 h.

[0030] In some embodiments, step (1) specifically includes: mixing melamine, boric acid and water, and then carrying out hydrothermal reaction and drying to obtain a hydrothermal product. The present invention does not make a special limitation on the drying temperature. In a specific embodiment, the drying temperature is 40 - 60 °C. The present invention also does not limit the specific drying time, as long as the water is evaporated completely. Specifically, during implementation, the drying time is 24 - 36 h.

[0031] The molten salt method refers to preparing a reaction mixture by mixing a mixed salt and raw materials in a certain proportion. After mixing evenly, the salt is heated to melt, and the reactants undergo a chemical reaction in the molten salt. In the method described in the present invention, the mixed salt package is lithium chloride and potassium chloride. In a preferred embodiment, in step (2), in the mixed salt, the mass fraction of lithium chloride is 55 - 65%, and the mass fraction of potassium chloride is 35 - 45%. By selecting the mixed salt with the above composition ratio, the crystallinity of the boron-doped carbon nitride photocatalyst prepared is higher.

[0032] In the most preferred embodiment, in step (2), in the mixed salt, the mass fraction of lithium chloride is 57 - 62%, and the mass fraction of potassium chloride is 38 - 43%.

[0033] In a preferred embodiment, in step (3), the weight ratio of the hydrothermal product to the mixed salt is 1:8 - 12. Specifically, for example, it can be 1:8, 1:9, 1:10, 1:11, or 1:12, and the most preferred is 1:10.

[0034] In some embodiments, in step (2), the calcination time can be 3 - 5 h, preferably 3.5 - 4.5 h.

[0035] In some embodiments, step (2) further includes: washing and drying the product obtained by calcination.

[0036] The present invention also provides a photocatalyst, which is prepared by the method as described above. The preparation method of the photocatalyst adopts a strategy of synergistic modification of crystallinity optimization and non-metal doping. Therefore, the boron-doped carbon nitride photocatalyst prepared by this method has excellent photocatalytic activity.

[0037] The present invention also provides the application of the photocatalyst as described above in photocatalytic degradation of NO x in which, and the efficiency of this photocatalyst in degrading NO x is high.

[0038] In addition, the present invention also provides the application of the photocatalyst as described above in photocatalytic production of hydrogen peroxide.

[0039] The present invention will be described in detail below through examples, but the protection scope of the present invention is not limited thereto. The experimental methods in the following examples are all conventional methods in the art unless otherwise specified. The experimental materials used in the following examples are all commercially available products unless otherwise specified.

[0040] Example 1 This example is used to illustrate the photocatalyst and its preparation method described in the present invention.

[0041] (1) Add 4 g of melamine and 60 ml of water to the reactor, then add 1 mmol of boric acid, stir for 30 min, subject the resulting mixed solution to hydrothermal reaction at 180 °C for 10 h, and then dry at 50 °C for 24 h to obtain a hydrothermal product; (2) Mix the hydrothermal product obtained by drying in step (1) with the mixed salt (LiCl:KCl = 59:41) in a mass ratio of 1:10, calcine in a muffle furnace at 550 °C for 4 h, then wash and dry the resulting product to obtain a boron-doped carbon nitride photocatalyst, denoted as "B-PTI".

[0042] Example 2 (1) Add 4 g of melamine and 60 ml of water to the reactor, then add 1.5 mmol of boric acid, stir for 30 min, subject the resulting mixed solution to hydrothermal reaction at 180 °C for 12 h, and then dry at 50 °C for 24 h to obtain a hydrothermal product; (2) Mix the hydrothermal product in step (1) with the mixed salt (LiCl:KCl = 59:41) in a mass ratio of 1:10, calcine in a muffle furnace at 550 °C for 5 h, then wash and dry the resulting product to obtain a boron-doped carbon nitride photocatalyst.

[0043] Example 3 (1) Add 4 g of melamine and 60 ml of water to the reactor, then add 1 mmol of boric acid, stir for 30 min, subject the resulting mixed solution to hydrothermal reaction at 180 °C for 10 h, and then dry at 50 °C for 24 h to obtain a hydrothermal product; (2) Mix the hydrothermal product in step (1) with the mixed salt (LiCl:KCl = 60:40) in a mass ratio of 1:9, calcine in a muffle furnace at 550 °C for 4 h, then wash and dry the resulting product to obtain a boron-doped carbon nitride photocatalyst.

[0044] Comparative Example 1 Raw carbon nitride: Calcinate melamine in a muffle furnace at 550 °C for 4 h to obtain a raw carbon nitride product, denoted as "CN".

[0045] Comparative Example 2 Mix 4 g of melamine with the mixed salt (LiCl:KCl = 59:41) in a mass ratio of 1:10, calcine in a muffle furnace at 550 °C for 4 h to obtain a product, denoted as "PTI".

[0046] Comparative Example 3 (1) Add 4 g of melamine and 60 ml of water to the reactor, then add 1 mmol of boric acid, stir for 30 min, subject the resulting mixed solution to hydrothermal reaction at 180 °C for 10 h, and then dry at 50 °C for 24 h to obtain a hydrothermal product; (2) The hydrothermal product obtained by drying in step (1) is calcined in a muffle furnace at 550 °C for 4 h, and then the obtained product is washed with water and dried to obtain a product, denoted as "B-CN".

[0047] Test Example 1 The boron-doped carbon nitride photocatalyst prepared in Example 1 and the products prepared in Comparative Examples 1-3 were subjected to X-ray diffraction (XRD), and the test results are as Figure 1 shown.

[0048] Figure 1 The results show that the boron-doped carbon nitride product with high crystallinity was successfully prepared in the examples of the present invention.

[0049] Test Example 2 This test example is used to illustrate the photocatalytic degradation of NO x performance of the photocatalyst described in the present invention.

[0050] The photocatalysts prepared in Example 1 and Comparative Examples 1-3 were subjected to photocatalytic degradation of NO x performance test. Test method: The prepared catalyst was sprayed onto a clean frosted glass of 70 mm × 40 mm, and then the sample was dried at 60 °C. The steps of spraying and drying were repeated and weighed. Finally, the mass of the photocatalyst coated on the glass sheet was controlled to be 14 mg. The flow rates of the standard NO gas (concentration 50 ppm, balance gas is N 2 ) and high-purity O 2 were controlled by a dynamic gas mixer so that the NO concentration in the gas flowing into the reactor was 1000 ppb, and the gas flow rate was stabilized at 500 mL / min. First, the reactor was placed in a dark environment and the NO concentration at the outlet of the reactor was monitored in real time by a NO analyzer. When the NO concentration was stable, it indicated that the TiO 2 material on the sample surface reached the "adsorption-desorption" equilibrium. At this time, the xenon lamp was turned on, and the current and distance were adjusted so that the light intensity on the sample surface was 30 mw / cm 2 , and then the NO concentration at the outlet was monitored by a NO analyzer. The test results are as Figure 2 shown; among them, the purification efficiency of NO can be calculated according to the following formula (Ⅰ).

[0051] (Ⅰ) In the formula, c 0 is the NO concentration at the inlet, and c is the NO concentration at the outlet.

[0052] It can be seen from Figure 2 that the boron-doped carbon nitride photocatalyst prepared in Example 1 of the present invention can photocatalytically remove NO xThe effect is better, indicating that the boron-doped carbon nitride photocatalyst prepared by the method provided by the present invention has higher catalytic activity.

[0053] Test Example 3 This test example is used to illustrate the photocatalytic hydrogen peroxide production performance of the photocatalyst described in the present invention.

[0054] The photocatalysts prepared in Example 1 and Comparative Examples 1-3 were tested for photocatalytic hydrogen peroxide production performance. The test method was as follows: 50 ml of distilled water was added with 100 mg of the catalyst. After dark treatment, it was decomposed under a xenon lamp. The hydrogen peroxide production effect was measured with a UV-visible spectrophotometer every 10 minutes. The test results are as Figure 3 shown.

[0055] It can be seen from Figure 3 that the boron-doped carbon nitride photocatalyst prepared in the example of the present invention has a better effect on catalytic hydrogen peroxide production, indicating that the boron-doped carbon nitride photocatalyst prepared by the method provided by the present invention has higher catalytic activity.

[0056] It should be noted that the preparation principles of Examples 2-3 are similar to those of Example 1. Therefore, the photocatalysts prepared in Examples 2-3 have high catalytic efficiency when applied to photocatalytic degradation of NO x performance and photocatalytic hydrogen peroxide production.

[0057] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a photocatalyst, characterized in that: The method includes: (1) mixing melamine, boric acid and water, and then performing a hydrothermal reaction to obtain a hydrothermal product; (2) mixing the hydrothermal product with mixed salt, and then calcining at 500-600° C.; Wherein, the mixed salt contains lithium chloride and potassium chloride.

2. The method according to claim 1, characterized in that In step (1), the usage ratio of melamine to boric acid is 4 g: 0.5-3 mmol.

3. The method according to claim 1, characterized in that In step (1), the usage ratio of melamine to water is 4 g:50-100 mL.

4. The method according to any one of claims 1 to 3, characterized in that: In step (1), the conditions of the hydrothermal reaction include: temperature of 150-200° C. and time of 5-15 h.

5. The method according to any one of claims 1 to 4, characterized in that: In step (2), the weight ratio of the hydrothermal product to the mixed salt is 1:8-12.

6. The method according to claim 1 or 5, characterized in that: In step (2), in the mixed salt, the mass fraction of the lithium chloride is 55-65%, and the mass fraction of the potassium chloride is 35-45%.

7. The method according to any one of claims 1 to 6, characterized in that: Step (2) also includes: washing and drying the calcined product.

8. A photocatalyst, characterized in that The photocatalyst is prepared by the method according to any one of claims 1 to 7.

9. The photocatalyst according to claim 8 is used for photocatalytic degradation of NO x Application in.

10. Use of the photocatalyst according to claim 8 in photocatalytic production of hydrogen peroxide.

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