Photocatalyst for degrading pollutants and preparation method thereof

Abstract

The invention discloses a photocatalyst for degrading pollutants and a preparation method thereof, and belongs to the technical field of catalysts, the photocatalyst comprises graphite phase carbon nitride and nitrogen-doped titanium dioxide; graphite-phase carbon nitride is a polymer semiconductor of a graphene-like layered structure formed by sp2 hybridization of carbon and nitrogen atoms, and the basic structural unit is a tri-s-triazine ring or a triazine ring; the nitrogen-doped titanium dioxide is in crystal lattices of TiO2, and part of oxygen atoms are replaced by nitrogen atoms to form a doped structure; the mass ratio of the graphite-phase carbon nitride to the nitrogen-doped titanium dioxide is (2: 8)-(7: 3). A compact Z-type heterojunction between nitrogen-doped titanium dioxide and graphite-phase carbon nitride is successfully constructed through a hydrothermal-calcination two-step method; the structure can drive photo-induced electrons to be transferred from a conduction band of nitrogen-doped titanium dioxide to a valence band of graphite-phase carbon nitride and compounded with holes, so that efficient spatial separation of carriers is realized, and meanwhile, the strongest oxidation-reduction capability of a catalyst system is maintained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a photocatalyst for degrading pollutants and a preparation method thereof. BACKGROUND

[0002] The photocatalytic degradation process generally involves a series of redox reactions initiated by a photocatalyst (titanium dioxide) under light irradiation, and the core steps can be summarized as the following key stages:

[0003] 1. Light excitation generates electron-hole pairs; 2. Holes oxidize water molecules to generate hydroxyl radicals; 3. Electrons reduce oxygen to generate superoxide anion radicals; 4. Protonation of superoxide anion generates hydrogen peroxide; 5. Chain reaction of active oxygen species; 6. Oxidative degradation of organic pollutants; 7. Final mineralization into harmless products.

[0004] The main preparation methods of titanium dioxide photocatalysts can be divided into the following ways:

[0005] Sol-gel method: by mixing titanium ester (such as tetrapropyl titanate, tetrabutyl titanate) with solvent, adding catalyst under stirring to form sol, and generating uniform titanium matrix through gelation reaction, finally drying and calcining to obtain titanium dioxide. This method has low cost and simple process, but the material structure is relatively simple.

[0006] Hydrothermal method: under high temperature and high pressure (usually 100-200℃), titanium source is mixed with solvent, acid and base adjuster to generate nanoparticles. This method can prepare titanium dioxide with high dispersity, high purity and high crystal quality, but has high energy consumption.

[0007] Physical vapor deposition method: including sputtering method, evaporation method, etc., by high temperature treatment in vacuum environment to deposit titanium or titanium source gas on the substrate to form a thin film. This method has the advantages of fast deposition rate, uniform film layer and high purity, and is suitable for large-scale industrial production.

[0008] Solid phase reaction method: by solid phase reaction, titanium salt precursor is converted into titanium dioxide, which needs high temperature calcination and multiple washing to remove impurities. This method can prepare titanium dioxide with special morphology, but the process is complex and has high energy consumption.

[0009] Composite doping method: by physical or chemical methods, metal ions (such as Ag, Ti), carbon sources (such as graphene oxide), and sulfur molybdate nanoclusters are doped into titanium dioxide to optimize its photocatalytic performance. For example, silver linear titanium dioxide combined with graphene oxide can expand the light response range and improve the catalytic efficiency.

[0010] According to the patent with the authorized publication number CN109772283B, a kind of titanium dioxide photocatalyst and its preparation method can be known, the patent is known prior art, and the patent although the prepared titanium dioxide photocatalyst has superior catalytic performance, the patent and the titanium dioxide photocatalyst in prior art still have the following defects: limited light absorption range: the band gap of titanium dioxide is about 3.2eV, only ultraviolet light (wavelength>387nm) can be absorbed, and the ultraviolet light in sunlight only accounts for 4%, resulting in very low light energy utilization rate; High recombination rate of photo-generated carriers: the electrons and holes generated by ultraviolet light excitation are easy to quickly recombine on the surface of the catalyst, which significantly reduces the photocatalytic efficiency. Although methods such as noble metal doping and semiconductor compounding can partially alleviate the problem, the recombination rate is still high. SUMMARY

[0011] The purpose of the present application is to provide a photocatalyst for degrading pollutants and a preparation method thereof to solve the problems raised in the above background.

[0012] To achieve the above-mentioned purpose, the present application provides the following technical solution: a photocatalyst for degrading pollutants, comprising graphite phase carbon nitride and nitrogen-doped titanium dioxide; the graphite phase carbon nitride is a polymer semiconductor with a graphite-like layered structure formed by sp2 hybridization of carbon and nitrogen atoms, and the basic structural unit is a triazine ring or a triazine ring; the nitrogen-doped titanium dioxide has a doping structure in which part of the oxygen atoms in the TiO2 lattice are replaced by nitrogen atoms.

[0013] The mass ratio of graphite phase carbon nitride and nitrogen-doped titanium dioxide is 2:8-7:3, and the atomic doping amount of nitrogen in the nitrogen-doped titanium dioxide is 0.3%-4%; the nitrogen-doped titanium dioxide and the graphite phase carbon nitride form a Z-type heterojunction material.

[0014] A preparation method of a photocatalyst for degrading pollutants, comprising the photocatalyst for degrading pollutants, comprising the following steps:

[0015] S1, preparation of graphite phase carbon nitride g-C3N4: place a nitrogen-rich precursor in a covered crucible and process it in a muffle furnace to obtain a light yellow g-C3N4 powder;

[0016] S2, preparation of nitrogen-doped titanium dioxide N-TiO2 precursor solution: dissolve a titanium source in anhydrous ethanol and stir to form a uniform solution A; dissolve a nitrogen source in deionized water to form solution B; under vigorous stirring, slowly add solution B to solution A and continue stirring for 1-3 hours to form a stable sol;

[0017] S3, hydrothermal reaction and compounding: disperse the g-C3N4 powder prepared in step S1 into the sol obtained in step S2 and mix;

[0018] S4, post-processing: after the reaction of S3 is finished, the obtained product is naturally cooled to room temperature, centrifuged, washed with deionized water and anhydrous ethanol alternately for several times, and dried, calcined and ground to obtain the final nitrogen-doped titanium dioxide / graphitic carbon nitride N-TiO2 / g-C3N4 composite photocatalyst.

[0019] As a preferred embodiment, the nitrogen-rich precursor is one of urea, melamine, thiourea, carbohydrazide and a sodium silicate composite system.

[0020] As a preferred embodiment, the treatment in the muffle furnace in S1 is heating at a rate of 2-5℃ / min to 500-600℃, and holding for 2-4 hours, naturally cooling and then grinding.

[0021] As a preferred embodiment, the titanium source is one of tetrabutyl titanate and titanium tetrachloride, and the nitrogen source is one of urea, melamine and carbohydrazide.

[0022] As a preferred embodiment, in S3, the mixed treatment is ultrasonic treatment for 0.5-1 hour to make it uniformly dispersed, and then the mixed solution is transferred to a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene liner, and reacted at 120-180℃ for 12-24 hours.

[0023] As a preferred embodiment, in S4, the drying treatment is vacuum drying at 60-80℃ for 6-12 hours.

[0024] As a preferred embodiment, in S4, the dried powder is calcined in a muffle furnace at 300-450℃ for 2-3 hours.

[0025] As a preferred embodiment, in S4, the powder after calcination is ground by a ball mill for 10-30 minutes, and the particle size is controlled to 1-5nm.

[0026] The photocatalyst is used for degrading organic pollutants in water or air, and the organic pollutants include one or a mixture of more than one of dyes, phenolic compounds, petroleum chemical waste gas and wastewater, pesticides, detergents and oils.

[0027] Compared with the prior art, the photocatalyst has the following advantages:

[0028] The photocatalyst for degrading pollutants and the preparation method thereof, the present application successfully constructs the close Z-type heterojunction between nitrogen-doped titanium dioxide and graphite phase carbon nitride through the hydrothermal-calcination two-step method; the structure can drive the photo-generated electrons to transfer from the conduction band of the nitrogen-doped titanium dioxide to the valence band of the graphite phase carbon nitride and recombine with holes, so that the strong reductive electrons are retained in the conduction band of the graphite phase carbon nitride, the strong oxidizing holes are retained in the valence band of the nitrogen-doped titanium dioxide, the efficient spatial separation of the carriers is realized, and the strongest redox ability of the catalyst system is maintained;

[0029] The photocatalyst for degrading pollutants and the preparation method thereof, the introduction of the graphite phase carbon nitride widens the absorption range of the composite material to visible light; the doping of N elements further improves the utilization efficiency of titanium dioxide to visible light; the synergistic effect of the two significantly improves the utilization rate of sunlight; the composite photocatalyst shows much higher degradation efficiency on various organic pollutants than single-component titanium dioxide or graphite phase carbon nitride under visible light or simulated sunlight irradiation, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is the preparation flow chart of the photocatalyst in the present application;

[0031] Figure 2 It is the performance test table of the photocatalyst in the present application. DETAILED DESCRIPTION

[0032] The present application will be further described below in combination with examples.

[0033] The following examples are used to illustrate the present application, but cannot be used to limit the protection scope of the present application. The conditions in the examples can be further adjusted according to specific conditions, and the simple improvement of the method of the present application under the concept of the present application belongs to the scope of protection of the present application.

[0034] Please refer to Figure 1 The present application provides a photocatalyst for degrading pollutants, which comprises graphite phase carbon nitride and nitrogen-doped titanium dioxide; the graphite phase carbon nitride is a polymer semiconductor with a graphite-like layered structure formed by sp2 hybridization of carbon and nitrogen atoms, sp 2 Hybridization is three orbitals with the same energy formed by mixing one s orbital and two p orbitals, the spatial configuration is a planar triangle with an angle of 120°, and the basic structural unit is a triazine ring or a triazine ring; the nitrogen-doped titanium dioxide is partially substituted by nitrogen atoms in the crystal lattice of TiO2, forming a doped structure;

[0035] The mass ratio of the graphite phase carbon nitride and the nitrogen-doped titanium dioxide is 2:8-7:3, and in the nitrogen-doped titanium dioxide, the atomic doping amount of nitrogen element is 0.3%-4%; the nitrogen-doped titanium dioxide and the graphite phase carbon nitride are compounded to form a Z-type heterojunction material.

[0036] A preparation method of a photocatalyst for degrading pollutants, comprising a photocatalyst for degrading pollutants, comprising the following steps:

[0037] S1, preparation of graphite phase carbon nitride g-C3N4: place a nitrogen-rich precursor in a covered crucible and process it in a muffle furnace to obtain light yellow g-C3N4 powder; the nitrogen-rich precursor is one of urea, melamine, thiourea, carbohydrazide and sodium metasilicate composite system. The processing method in the muffle furnace is to heat it to 500-600℃ at a rate of 2-5℃ / min and keep it for 2-4 hours, then cool it naturally and grind it.

[0038] S2, preparation of nitrogen-doped titanium dioxide N-TiO2 precursor solution: dissolve a titanium source in anhydrous ethanol to form a uniform solution A; dissolve a nitrogen source in deionized water to form solution B; slowly add solution B to solution A under vigorous stirring, continue stirring for 1-3 hours to form a stable sol; the titanium source is one of tetrabutyl titanate and titanium tetrachloride, and the nitrogen source is one of urea, melamine and carbohydrazide.

[0039] S3, hydrothermal reaction and compounding: disperse the g-C3N4 powder prepared in step S1 into the sol obtained in step S2 and mix them; after ultrasonic treatment for 0.5-1 hour to make them uniformly dispersed, transfer the mixed solution to a stainless steel high-pressure reaction kettle with a polytetrafluoroethylene liner, and react it at 120-180℃ for 12-24 hours.

[0040] S4, post-treatment: after the reaction of S3 is completed, cool it to room temperature naturally, centrifuge the obtained product, wash it with deionized water and anhydrous ethanol alternately for several times, and dry, calcine and grind it to obtain the final nitrogen-doped titanium dioxide / graphite phase carbon nitride N-TiO2 / g-C3N4 composite photocatalyst. The drying treatment is vacuum drying at 60-80℃ for 6-12 hours, and in S4, the dried powder is calcined in a muffle furnace at 300-450℃ for 2-3 hours. Low-temperature drying (60℃) + medium-temperature calcination (300-400℃) to preserve porosity, and grind the powder after calcination by a ball mill for 10-30 minutes to control the particle size to 1-5nm.

[0041] The application of the photocatalyst in degrading organic pollutants in water or air, including one or more mixtures of dyes, phenolic compounds, petroleum chemical waste gas and wastewater, pesticide production, detergents, oils and fats, etc.

[0042] Example 1:

[0043] S1: Take 10 g of carbohydrazide and place it in an alumina crucible, cover it, and put it in a muffle furnace. Increase the temperature to 550°C at a rate of 3°C / min, and keep it at this temperature for 3 hours. After natural cooling, grind it to obtain a light yellow g-C3N4 powder;

[0044] S2: Dissolve 5 mL of tetrabutyl titanate in 40 mL of anhydrous ethanol, and magnetically stir for 30 minutes, denoted as solution A. Dissolve 0.5 g of urea (as a nitrogen source) in 10 mL of deionized water, denoted as solution B. Under vigorous stirring, slowly add solution B to solution A, and continue stirring for 2 hours after the addition is complete to obtain a clear transparent sol.

[0045] S3: Take 0.15 g of the g-C3N4 powder prepared in step 1 (the target composite mass ratio is N-TiO2:g-C3N4 = 7:3), and add it to the above sol, and ultrasonically disperse for 40 minutes.

[0046] S4: Transfer the mixed solution into a 100 mL polytetrafluoroethylene-lined high-pressure reaction kettle, and react at 150°C for 18 hours. After the reaction is completed, centrifugally collect the product, wash it with deionized water and ethanol three times respectively, and dry it in a 70°C oven for 10 hours. After the drying, calcine the powder in a 400°C muffle furnace for 2 hours, and grind it after natural cooling to obtain the final product, denoted as N-TiO2 / g-C3N4 (7:3).

[0047] Example 2:

[0048] The difference between this example and Example 1 is that the amount of g-C3N4 added in step S3 is 0.25 g (the target composite mass ratio is N-TiO2:g-C3N4 = 5:5); and the obtained product is denoted as N-TiO2 / g-C3N4 (5:5).

[0049] Example 3:

[0050] The difference between this example and Example 1 is that the amount of g-C3N4 added in step S3 is 0.35 g (the target composite mass ratio is N-TiO2:g-C3N4 = 3:7); and the obtained product is denoted as N-TiO2 / g-C3N4 (3:7).

[0051] Comparative Example 1 (pure TiO2):

[0052] Without adding g-C3N4 and carbohydrazide nitrogen source, only tetrabutyl titanate is used as the raw material, and the same hydrothermal and calcination process is used to prepare pure TiO2.

[0053] Comparative Example 2 (pure g-C3N4):

[0054] Directly use the pure g-C3N4 powder prepared in step S1 of Example 1.

[0055] Performance test:

[0056] Take 50 mg of the photocatalyst prepared in each of the above examples and comparative examples, and add to 100 mL of methylene blue aqueous solution with a concentration of 10 mg / L, and the reaction time is 60 min. Stir for 30 min in the dark room by magnetic stirring to achieve adsorption-desorption equilibrium. Then, turn on the 300 W xenon lamp (equipped with 420 nm cutoff filter to filter out ultraviolet light) as a visible light source for irradiation. Sample every certain time, take the supernatant after centrifugation, and measure the absorbance at 664 nm by ultraviolet-visible spectrophotometer to calculate the degradation rate of methylene blue.

[0057] See Figure 2 It can be seen that the degradation efficiency of Comparative Example 1 (pure TiO2) is extremely low due to poor visible light response; Comparative Example 2 (pure g-C3N5) has certain visible light catalytic activity, but the efficiency is limited. The degradation rates of the composite photocatalysts prepared in Examples 1-3 of the present application are all much higher than those of the two single components, and the sample of Example 1 (mass ratio 7:3) shows the highest photocatalytic activity, with a methylene blue degradation rate of more than 95% under 60 min visible light irradiation, which proves the successful construction of Z-type heterojunction and its significant synergistic catalytic effect.

[0058] Although the embodiments of the present application have been shown and described, it can be understood by those of ordinary skill in the art that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A photocatalyst for degrading pollutants, characterized in that: This includes graphitic carbon nitride and nitrogen-doped titanium dioxide; graphitic carbon nitride is composed of carbon and nitrogen atoms separated by sp... 2 The basic structural unit of the graphene-like layered polymer semiconductor formed by hybridization is a triazine ring or a triazine ring; in the TiO2 lattice, nitrogen-doped titanium dioxide has some oxygen atoms replaced by nitrogen atoms to form a doped structure. The mass ratio of graphitic carbon nitride to nitrogen-doped titanium dioxide is 2:8-7:3, and the atomic doping amount of nitrogen in nitrogen-doped titanium dioxide is 0.3%-4%; the Z-type heterojunction material is formed by the composite of nitrogen-doped titanium dioxide and graphitic carbon nitride.

2. A method for preparing a photocatalyst for degrading pollutants, comprising the photocatalyst for degrading pollutants as described in claim 1, characterized in that: Includes the following steps: S1. Preparation of graphitic carbon nitride g-C3N4: A nitrogen-rich precursor was placed in a covered crucible and treated in a muffle furnace to obtain pale yellow g-C3N4 powder. S2. Preparation of nitrogen-doped titanium dioxide (N-TiO2) precursor solution: Dissolve the titanium source in anhydrous ethanol and stir to form a homogeneous solution A; dissolve the nitrogen source in deionized water to form solution B; under vigorous stirring, slowly add solution B to solution A and continue stirring for 1-3 hours to form a stable sol. S3. Hydrothermal reaction and composite: The g-C3N4 powder prepared in step S1 is dispersed into the sol obtained in step S2 and mixed. S4. Post-processing: After the reaction in S3 is completed, the product is naturally cooled to room temperature. The product is then centrifuged, washed several times with deionized water and anhydrous ethanol, and dried, calcined, and ground to obtain the final nitrogen-doped titanium dioxide / graphite phase carbon nitride N-TiO2 / g-C3N4 composite photocatalyst.

3. The method for preparing a photocatalyst for degrading pollutants according to claim 2, characterized in that: Nitrogen-rich precursors include one of the following: urea, melamine, thiourea, carbazide, and sodium hydroxylite complex.

4. The method for preparing a photocatalyst for degrading pollutants according to claim 1, characterized in that: The processing method in the muffle furnace in S1 is as follows: heat to 500-600℃ at a rate of 2-5℃ / min, hold for 2-4 hours, cool naturally, and then grind.

5. The method for preparing a photocatalyst for degrading pollutants according to claim 1, characterized in that: The titanium source is one of tetrabutyl titanate and titanium tetrachloride, and the nitrogen source is one of urea, melamine, and carbazide.

6. The method for preparing a photocatalyst for degrading pollutants according to claim 1, characterized in that: In S3, the mixing process involves ultrasonic treatment for 0.5-1 hours to ensure uniform dispersion, followed by transfer of the mixed solution to a PTFE-lined stainless steel high-pressure reactor, where it is reacted at 120-180°C for 12-24 hours.

7. The method for preparing a photocatalyst for degrading pollutants according to claim 1, characterized in that: In S4, the drying process is vacuum drying, which is carried out at 60-80℃ for 6-12 hours.

8. The method for preparing a photocatalyst for degrading pollutants according to claim 7, characterized in that: In S4, the dried powder is calcined in a muffle furnace at 300-450°C for 2-3 hours.

9. The method for preparing a photocatalyst for degrading pollutants according to claim 8, characterized in that: In S4, the calcined powder is milled for 10–30 minutes using a ball mill to control the particle size to 1–5 nm.

10. The application of the photocatalyst according to any one of claims 1-9 in the degradation of organic pollutants in water or the atmosphere, wherein the organic pollutants include one or more mixtures of dyes, phenolic compounds, petrochemical waste gas and wastewater, pesticide production, detergents, greases, etc.

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