Preparation method and application of metal-free photocatalyst TCP / g-c3n4

Abstract

The application discloses a preparation method and application of a metal-free photocatalyst TCP / g-C3N4 and belongs to the technical field of nanometer material preparation and application. Triangulene is used as raw material, nitro substitution, amino substitution and bromine substitution are carried out to obtain tribromotriangulene, tribromotriangulene is used as raw material, g-C3N4 is added, and in-situ synthesis of triangulene porous polymer (TCP) on the surface of g-C3N4 (CN) is carried out through Suzuki coupling reaction, so that the metal-free photocatalyst TCP / g-C3N4 is obtained. The composite photocatalyst is prepared from raw materials which are easy to obtain, the process is simple, and the conditions are easy to control. The prepared metal-free photocatalyst TCP / g-C3N4 is a porous metal-free photocatalyst, has the advantages of stable chemical property, high catalytic efficiency and the like, and has excellent hydrogen production activity in a seawater system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterial preparation and application, and particularly relates to a preparation method and application of a metal-free photocatalyst TCP / g-C3N4. BACKGROUND

[0002] Photocatalytic hydrogen production addresses the clean energy conversion problem by developing green and sustainable solar energy. So far, most of the photocatalytic hydrogen evolution studies have been carried out in deionized water or freshwater systems. It is worth noting that only about 2.5% of the water on earth is freshwater, and more than 97.5% of the water is saltwater. The population growth and rapid industrial development exacerbate the freshwater shortage. Therefore, it is a valuable proposal to use seawater and readily available solar energy to obtain renewable hydrogen gas. Many reports show that the abundant ions in seawater can significantly affect the photocatalytic performance. The average salinity of natural seawater is about 3.5%, in which NaCl is the main species. Na + Ions can help TiO2 absorb sacrificial agents (ethanol) under alkaline or neutral conditions, which is beneficial to the hydrogen evolution process. Other cations (such as K + , Mg 2+ , and Ca 2+ ) can promote the electron well effect of carbon dots, thereby improving the photocatalytic activity. In view of this, it is very desirable to develop an efficient and salt-tolerant photocatalyst for hydrogen production in seawater.

[0003] TCP is a new type of visible light driven semiconductor with very attractive optical properties and excellent chemical stability, and is considered as a candidate for photocatalytic applications. Triphenylene with an extended π plane is composed of three benzene units and exhibits excellent electron transport capability. POPs with similar characteristics to metal-organic frameworks (MOFs) are applied to photocatalysis due to their large surface area, good chemical stability and excellent physical and chemical properties. However, the photocatalytic hydrogen evolution efficiency of TCP is still very low. Therefore, it is still a challenging task to improve the photocatalytic activity by precisely modifying the nanostructure of TCP. In our previous studies (CN107876094A, CN108906125A), triphenylene polymer TCP can significantly improve the hydrogen production efficiency of metal sulfides. However, metal catalysts can be corroded by seawater and have certain biological toxicity when they are used to produce hydrogen in seawater.

[0004] A large number of studies have shown that graphite phase carbon nitride (g-C3N4), as a very promising material, has been widely studied due to its low cost, rich functional groups, non-toxicity, high structural stability and other advantages. In g-C3N4, C and N atoms are both sp 2They are hybridized. They are connected by σ bonds, forming a hexagonal structure. This six-atom ring is called a triazine ring. Each triazine ring is connected to a small unit via a CN bond. However, due to the small surface area and limited carrier mobility of bulk g-C3N4, its hydrogen production performance is very limited. This invention combines the advantages of g-C3N4 and TCP to construct a porous metal-free catalyst with low biotoxicity, stability in seawater, and multiple active sites. Summary of the Invention

[0005] Based on the above problems, the purpose of this invention is to provide a method for preparing and applying a metal-free photocatalyst TCP / g-C3N4, in which a tripterene porous polymer (TCP) is supported on graphitic carbon nitride (g-C3N4, abbreviated as CN). This catalyst is metal-free and is used for photocatalytic stable hydrogen production in seawater.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a metal-free photocatalyst TCP / g-C3N4 includes the following steps:

[0008] (1) Preparation of CN: Melamine is heated from room temperature to 550°C in a muffle furnace at a heating rate of 2°C / min, calcined at 550°C for 2 hours, naturally cooled to room temperature, and then ground into powder to obtain the product.

[0009] (2) Preparation of tribromotriptene:

[0010] Preparation of trinitrotriptene: Triptene was weighed and dissolved in nitric acid, stirred and heated at 75°C for 24 h, cooled and washed with deionized water, dried at 60°C and then separated and purified by column chromatography using petroleum ether:ethyl acetate.

[0011] Preparation of triaminotriptene: The above-mentioned trinitrotriptene was added to a round-bottom flask and Raney nickel was added. After vacuuming, tetrahydrofuran and hydrazine hydrate were injected and heated at 60°C for 6 hours. Then, the sample was washed multiple times on diatomaceous earth using dichloromethane and tetrahydrofuran as detergents and then dried by rotary evaporation.

[0012] Preparation of tribromotriptene: The above-mentioned triaminotriptene was added to a round-bottom flask, along with deionized water and hydrobromic acid. The mixture was then rapidly cooled with ice. A sodium nitrite aqueous solution was added, and after 20 minutes, a solution of cuprous bromide in hydrobromic acid was added. The mixture was then heated at 120°C for 2 hours. After separation and drying, the mixture was purified by column chromatography with petroleum ether.

[0013] (3) Preparation of metal-free photocatalyst TCP / g-C3N4: Tribromotriphenylene prepared in step (2) was added to carbon nitride CN, 1,4-phenyldiboronic acid, palladium acetate and triphenylphosphine obtained in step (1). After vacuuming, tetrahydrofuran and potassium carbonate aqueous solution were injected. The mixed solution was reacted at 65°C for 12 h. After the reaction was completed, it was repeatedly washed with tetrahydrofuran, anhydrous ethanol and deionized water and filtered. It was dried at 60°C to obtain metal-free photocatalyst TCP / g-C3N4 (TCP-CN).

[0014] Furthermore, in step (2), the volume ratio of petroleum ether to ethyl acetate is 10:1.

[0015] Furthermore, in step (2), the mass ratio of trinitrotriptene to Raney nickel is 1:1.

[0016] Furthermore, in step (2), the solution of cuprous bromide in hydrobromic acid is made by dispersing cuprous bromide in hydrobromic acid solution, with a concentration of 440 mg / mL.

[0017] Furthermore, in step (3), the mass ratio of tribromotriphenylene, carbon nitride, 1,4-phenylenediboric acid, palladium acetate, and triphenylphosphine is 100:50 to 300:54:1.5:3.95.

[0018] Furthermore, the concentration of the potassium carbonate aqueous solution in step (3) is 43.84 mg / mL.

[0019] The above-mentioned metal-free photocatalyst TCP / g-C3N4 is used in photocatalytic hydrogen production from seawater.

[0020] Compared with existing technologies, the beneficial effects of this invention are: the microporous polymer based on tripterene possesses ultra-high surface area, strong covalent bonds, and unique physicochemical properties, which can significantly promote hydrogen diffusion and stabilize charge. By compositing g-C3N4 with porous semiconductors to prepare porous metal-free catalysts, the composite photocatalyst prepared by this method exhibits good stability, no secondary pollution, and can achieve a seawater hydrogen evolution rate of 4317 μmol g within 180 min using TCP-CN-1 photocatalysis. -1 h -1 The yield in pure water can reach 2404 μmol g. -1 h -1 Furthermore, the preparation method of this composite photocatalyst has the advantages of being simple, having easily controllable preparation conditions, and producing no secondary pollution. Therefore, combining g-C3N4 with porous semiconductors is a promising method to improve surface area and charge transfer. Attached Figure Description

[0021] The invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 These are X-ray diffraction patterns of pure CN prepared in Examples 1-3 of this invention and pure TCP prepared in Comparative Example 1 (metal-free photocatalyst TCP-CN).

[0023] Figure 2 These are the infrared spectra of pure CN and metal-free photocatalyst TCP-CN prepared in Examples 1-3 of this invention, and pure TCP prepared in Comparative Example 1.

[0024] Figure 3 These are scanning electron microscope (SEM) images of pure TCP (a) prepared in Comparative Example 1 of this invention, pure CN (b) prepared in Example 1, and the metal-free photocatalyst TCP-CN (b).

[0025] Figure 4 The graphs show the photocatalytic reduction hydrogen production rates of pure CN and metal-free photocatalyst TCP-CN prepared in Examples 1-3 of this invention, and pure TCP prepared in Comparative Example 1.

[0026] Figure 5 This is a hydrogen production cycle diagram of the metal-free photocatalyst TCP-CN prepared in Example 1 of this invention. Detailed Implementation

[0027] The present invention will now be further described with reference to specific embodiments. The following embodiments are intended to illustrate the present invention and not to further limit the present invention.

[0028] Example 1

[0029] (1) Preparation of carbon nitride (CN): First, weigh 10g of melamine and grind it for 30min. Then put it into a crucible and heat it from room temperature to 550℃ in a muffle furnace at a heating rate of 2℃ / min. Then calcine it at 550℃ for about 2h. Then cool it naturally to room temperature and grind it into powder, which is graphitic carbon nitride (g-C3N4).

[0030] (2) Preparation of tribromotriptene:

[0031] Preparation of trinitrotriptene: 2.5 g of triptene was weighed and dissolved in 100 mL of nitric acid. The mixture was stirred and heated in an oil bath at 75 °C for 24 h. After cooling, it was washed with 4 L of deionized water, dried at 60 °C, and then purified by column chromatography using petroleum ether:ethyl acetate (10:1).

[0032] Preparation of triaminotriptene: 1g of the above-mentioned trinitrotriptene was added to a round-bottom flask and 1g of Raney nickel was added. After vacuuming, 20mL of tetrahydrofuran and 1.5mL of hydrazine hydrate were injected and heated at 60℃ for 6h. Then, the sample was washed multiple times on diatomaceous earth with dichloromethane and tetrahydrofuran as detergents and then dried by rotary evaporation.

[0033] Preparation of tribromotriptene: 1g of the above-mentioned triaminotriptene was added to a round-bottom flask, followed by 10mL of deionized water and 3mL of hydrobromic acid. The mixture was then rapidly cooled with ice. 0.8g of sodium nitrite aqueous solution (5mL) was added and the mixture was allowed to stand for 20 minutes. Then, a solution of 2.2g of cuprous bromide in hydrobromic acid (5mL) was added and the mixture was heated at 120℃ for 2 hours. The mixture was then separated, evaporated to dryness, and purified by column chromatography with petroleum ether.

[0034] (3) Preparation of the metal-free photocatalyst TCP-CN-1: 0.1 g of tribromotriptene prepared in step (2) was added to 0.05 g of carbon nitride, 0.054 g of 1,4-phenylenediboric acid, 0.0015 g of palladium acetate and 0.00395 g of triphenylphosphine. After vacuuming, 20 mL of tetrahydrofuran and potassium carbonate aqueous solution (0.2192 g dissolved in 5 mL of distilled water) were injected. The mixed solution was reacted at 65 °C for 12 h. After the reaction was completed, the solution was repeatedly washed with tetrahydrofuran, anhydrous ethanol and deionized water and filtered. The solution was dried at 60 °C for 12 h to obtain TCP-CN-1 (the mass ratio of carbon nitride to tribromotriptene was 1:0.5).

[0035] Example 2

[0036] (1) Preparation of carbon nitride (CN): Same as in Example 1;

[0037] (2) Preparation of tribromotriptene: Same as in Example 1;

[0038] (3) Preparation of the metal-free photocatalyst TCP-CN-2: 0.1 g of tribromotriptene prepared in step (2) was added to 0.1 g of carbon nitride, 0.054 g of 1,4-phenylenediboric acid, 0.0015 g of palladium acetate and 0.00395 g of triphenylphosphine. After vacuuming, 20 mL of tetrahydrofuran and potassium carbonate aqueous solution (0.2192 g dissolved in 5 mL of distilled water) were injected. The mixed solution was reacted at 65 °C for 12 h. After the reaction was completed, the solution was repeatedly washed with tetrahydrofuran, anhydrous ethanol and deionized water and filtered. The solution was dried at 60 °C for 12 h to obtain TCP-CN-2 (the mass ratio of carbon nitride to tribromotriptene was 1:1).

[0039] Example 3

[0040] (1) Preparation of carbon nitride (CN): Same as in Example 1;

[0041] (2) Preparation of tribromotriptene: Same as in Example 1;

[0042] (3) Preparation of the metal-free photocatalyst TCP-CN-0.6: 0.1 g of tribromotriptene prepared in step (2) was added to 0.3 g of carbon nitride, 0.054 g of 1,4-phenylenediboric acid, 0.0015 g of palladium acetate and 0.00395 g of triphenylphosphine. After vacuuming, 20 mL of tetrahydrofuran and potassium carbonate aqueous solution (0.2192 g dissolved in 5 mL of distilled water) were injected. The mixed solution was reacted at 65 °C for 12 h. After the reaction was completed, it was repeatedly washed with tetrahydrofuran, anhydrous ethanol and deionized water and filtered. It was then dried at 60 °C for 12 h to obtain TCP-CN-0.6 (the mass ratio of carbon nitride to tribromotriptene was 1:0.3).

[0043] Comparative Example 1

[0044] Preparation of Tribromotriptene Porous Polymer (TCP): 0.1 g of tribromotriptene, 0.054 g of 1,4-phenylenediboric acid, 0.0015 g of palladium acetate and 0.00395 g of triphenylphosphine were injected into a vacuum solution of 20 mL of tetrahydrofuran and potassium carbonate aqueous solution (0.2192 g dissolved in 5 mL of distilled water). The mixture was reacted at 65 °C for 12 h. After the reaction was completed, the mixture was repeatedly washed with tetrahydrofuran, anhydrous ethanol and deionized water and filtered. The solution was then dried at 60 °C for 12 h to obtain TCP.

[0045] 1. Component determination of the metal-free photocatalyst TCP-CN-1.

[0046] The pure CN and TCP-CN composite photocatalysts prepared in Examples 1-3, as well as the pure TCP structure prepared in Comparative Example 1, were analyzed using an X-ray diffractometer (D / MAX2500, Japan), where the X-ray target was Cu. Voltage 40kV, current 100mA, step size 0.02°, scanning range 5°~80°. X-ray diffraction pattern as follows. Figure 1 As shown in the figure, the XRD diffraction pattern of the prepared TCP-CN composite photocatalyst shows characteristic diffraction peaks of CN at 12.9° and 27.5°, corresponding to the (110) and (002) crystal planes of CN, respectively. However, no TCP peaks are observed in the TCP-CN composite material in the X-ray diffraction pattern. This is because TCP is amorphous and amorphous. Therefore, the composite photocatalyst contains only CN peaks, and the chemical structure and crystal form of both materials were not altered during the composite process.

[0047] Using a Thermo Fisher IS50 infrared spectrometer, all catalysts showed a wavelength of 3000-3600 cm⁻¹. -1 The broadband width is due to the NH or OH extension peaks. 810 cm⁻¹ -1 The signal belongs to the typical triazine unit of CN, while the 1100-1680cm -1Some vibrational peaks at this location are attributed to the skeletal vibrations of the CN heterocycle. Additionally, at 1463 cm⁻¹... -1 The characteristic peak at 2856-3090 cm⁻¹ belongs to the carbon-carbon double bond skeletal vibration of the benzene ring in the tripterene unit. -1 Several characteristic peaks at this point belong to the CH bonds of TCP. The infrared spectrum of TCP-CN shows peaks at 810 and 1463 cm⁻¹. -1 The peaks at all locations are present in the composite material, indicating the coexistence of TCP and CN. Among them, the TCP-CN0.6 composite material exhibits an infrared spectrum similar to that of pure TCP at a low TCP loading ratio, while as the TCP loading ratio increases, the characteristic TCP infrared peaks in TCP-CN-1 and TCP-CN-2 become more prominent.

[0048] The morphology of the pure CN and TCP-CN composite photocatalysts prepared in Example 1 and the pure TCP prepared in Comparative Example 1 was observed using a Quanta 200F field emission scanning electron microscope. The scanning electron microscope images are shown below. Figure 3 As shown in the figure, TCP has the morphology of spherical nanoparticles, CN has the morphology of a simple block structure, and the TCP-CN composite photocatalyst has the morphology of TCP nanospheres uniformly loaded on the surface of the block CN.

[0049] 2. Study on the photocatalytic performance and potential applications of the metal-free photocatalyst TCP-CN-1

[0050] The composite photocatalysts prepared in Examples 1-3 and Comparative Example 1 were subjected to photocatalytic hydrogen evolution from pure water or seawater. 10 mg of the catalyst was weighed and dispersed in a mixed solution of 5 mL triethanolamine and 45 mL deionized water or seawater, and sonicated for 30 min. The mixed solution was then placed in a Pyrex glass reactor and bubbled under an argon gas system to ensure anaerobic conditions for 30 minutes. A 300W xenon lamp was used for the photocatalytic experiment. Samples were taken four hours after the reaction and analyzed by gas chromatography (GC-7860Plus, TCD detector).

[0051] The composite photocatalysts prepared in Examples 1-3 and Comparative Example 1 exhibit the following photocatalytic hydrogen evolution performance: Figure 4 As shown. By Figure 4 It can be seen that the TCP-CN photocatalytic hydrogen evolution rate in seawater can reach 4317 μmol g within 180 min. -1 h -1 The photocatalytic hydrogen evolution rate of pure water can reach 2404 μmol g. -1 h -1 Therefore, the prepared metal-free photocatalyst TCP-CN exhibits high photocatalytic activity. Figure 5The performance of the metal-free photocatalyst TCP-CN after four cycles is shown, indicating that the catalyst is relatively stable in seawater.

Claims

1. A method for preparing a metal-free photocatalyst TCP / g-C3N4, characterized in that, Includes the following steps: (1) Preparation of tribromotriptene: Preparation of trinitrotriptene: Triptene was dissolved in concentrated nitric acid, stirred and heated in an oil bath at 75°C for 24 hours. After the reaction was completed, it was cooled, washed and purified to obtain trinitrotriptene. Preparation of triaminotriptene: The above-mentioned trinitrotriptene was added to a round-bottom flask and Raney nickel was added. After vacuuming, tetrahydrofuran and hydrazine hydrate were injected and heated at 60℃~70℃ for 6h-8h. Then, dichloromethane and tetrahydrofuran were used as detergents to wash the sample multiple times on diatomaceous earth and then evaporated. Preparation of tribromotriptene: The above-mentioned triaminotriptene was added to a round-bottom flask, along with deionized water and hydrobromic acid. The mixture was then rapidly cooled with ice. Sodium nitrite aqueous solution was added and waited for 20 minutes. Then, a hydrobromic acid solution of cuprous bromide was added and the mixture was heated at 120°C for 2 hours. The mixture was then separated, evaporated to dryness, and purified by column chromatography with petroleum ether. (2) Preparation of metal-free photocatalyst TCP / g-C3N4: Tribromotriphenylene, g-C3N4, 1,4-phenyldiboronic acid, palladium acetate and triphenylphosphine obtained in step (1) were added to a reaction sealing tube, and after vacuuming, tetrahydrofuran and potassium carbonate aqueous solution were injected to obtain a mixed solution; the mixed solution was reacted at 55℃~65°C for 10h~12h. After the reaction was completed, it was repeatedly washed with tetrahydrofuran, anhydrous ethanol and deionized water and filtered and dried to obtain metal-free photocatalyst TCP / g-C3N4; The mass ratio of tribromotriphenylene, g-C3N4, 1,4-phenylenediboric acid, palladium acetate, and triphenylphosphine is 100:50~100:54:1.5:3.

95.

2. The method for preparing the metal-free photocatalyst TCP / g-C3N according to claim 1, characterized in that: In step (1) of the preparation of triaminotriptene, the mass ratio of trinitrotriptene to Raney nickel is 1:

1.

3. The method for preparing the metal-free photocatalyst TCP / g-C3N4 according to claim 1, characterized in that: In step (1) of the preparation of tribromotriphenylene, the volume ratio of deionized water to hydrobromic acid is 10:

3.

4. The method for preparing the metal-free photocatalyst TCP / g-C3N4 according to claim 1, characterized in that, In step (1) of the preparation of tribromotriphenylene, the hydrobromic acid solution of cuprous bromide is made by dispersing cuprous bromide in hydrobromic acid solution, and the concentration is 440 mg / mL.

5. The method for preparing the metal-free photocatalyst TCP / g-C3N4 according to claim 1, characterized in that, The concentration of the potassium carbonate aqueous solution in step (2) is 43.84 mg / mL.

6. An application of the metal-free photocatalyst TCP / g-C3N4 prepared by the method according to any one of claims 1-5, characterized in that, Application of the metal-free photocatalyst TCP / g-C3N4 in photocatalytic seawater hydrogen production.

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