A photocatalyst, a preparation method thereof and an application thereof

Abstract

The present invention discloses a photocatalyst, a preparation method thereof and an application thereof, belonging to the technical field of photocatalysts. The catalyst is prepared by the following method: S1. Prepare Bi₄O₇ material; S2. Mix deionized water, glacial acetic acid and absolute ethanol uniformly to form solution A; S3. Add tetrabutyl titanate and Bi₄O₇ material into absolute ethanol to form solution B, wherein the mass ratio of Bi₄O₇ material to tetrabutyl titanate is 0-0.004:1; S4. Drop solution B into solution A, stir for 1-4 h and age for 12-48 h, then raise the temperature to 120-200 °C under a closed condition and react for 3-12 h, and finally carry out separation, washing and drying to obtain the product. The visible light catalyst of the present invention has abundant oxygen vacancies and has a high removal efficiency for tetracycline under visible light catalysis.

Description

Technical Field

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

[0002] Photocatalytic technology can utilize light sources to achieve the degradation of pollutants. When the photon energy is greater than or equal to the semiconductor bandgap energy (Eg), electrons in the valence band (VB) are excited to jump to the conduction band (CB), and at the same time, photo-generated holes are left on the VB. The photo-generated electrons and holes then move to the surface of the catalyst and react with the substances adsorbed on the surface. The photo-generated holes have strong oxidizing properties and can oxidize donor molecules and react with H2O to generate hydroxyl radicals (·OH). At the same time, the photo-generated electrons on the CB can reduce O2 in water to generate superoxide radicals (·O2 - ). Finally, the reactants are reduced and oxidized by electrons, holes, or the generated active species, and the products are desorbed from the surface of the photocatalyst. After this reaction is completed, the photo-generated electrons generated by light are eliminated, and the stored energy is ultimately converted into the chemical energy stored in the products. The photocatalyst returns to its initial state and is ready for another reaction cycle. Titanium dioxide (TiO2) is the most widely studied semiconductor catalyst, with characteristics such as stable chemical properties and high photocatalytic efficiency. Bismuth-based semiconductors have a relatively narrow bandgap and have good responsiveness to visible light. Traditional photocatalysts have the defects of poor visible light responsiveness and easy recombination of electron-hole pairs. They only respond to ultraviolet light, and ultraviolet light only accounts for 5% of sunlight. The recombination rate of photo-generated electron-hole pairs in a single photocatalyst is high. Forming heterojunctions using the differences in the energy band structures between multiple materials can significantly improve photocatalytic performance.

[0003] Chinese Patent CN103551138B discloses a preparation method of a bismuth oxide-sensitized titanium dioxide nanotube photocatalyst. Through the screen printing method and the calcination method, the operation of the screen printing method is difficult to control. Although a Z-type structure is constructed, the improvement of visible light activity is still limited, and the pollutant degradation effect still needs to be improved. Chinese Patent CN114433107A discloses a preparation method of a Co3O4 / Bi4O7 / Bi2O3 heterojunction photocatalyst. The photocatalytic effect of the catalyst prepared by this method is relatively weak, and the TC removal rate under visible light is about 47.7%. Summary of the Invention

[0004] In view of this, in order to solve the above problems, an object of the present invention is to provide a photocatalyst, a preparation method thereof, and an application thereof. The photocatalyst of the present invention has a high degradation efficiency.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A preparation method of a photocatalyst, comprising the following steps:

[0007] S1. Prepare Bi4O7 material;

[0008] As a specific embodiment of the present invention, the Bi4O7 material is prepared by a method comprising the following steps:

[0009] S11. Disperse sodium bismuthate dihydrate in an NaOH solution; the specific dispersion method can be stirring, ultrasonic dispersion, etc.

[0010] S12. Heat the solution of S11 to 120 - 200 °C and maintain for 4 - 12 h;

[0011] S13. Cool, centrifuge, and dry the product of S12 to obtain the Bi4O7 material.

[0012] S2. Mix deionized water, glacial acetic acid (anhydrous acetic acid), and absolute ethanol uniformly to form solution A, wherein the volume ratio of deionized water to glacial acetic acid is preferably 1:1 - 4, more preferably 1:2.

[0013] S3. Add tetrabutyl titanate and the Bi4O7 material to absolute ethanol to form solution B, wherein the mass ratio of the Bi4O7 material to tetrabutyl titanate is 0 - 0.004:1, preferably 0.002:1.

[0014] S4. Drop solution B into solution A, stir for 1 - 4 h (preferably 3 h), age for 12 - 48 h (preferably 24 h), then raise the temperature to 120 - 200 °C (preferably 150 °C) under a closed condition and react for 3 - 12 h (preferably 5 h), and finally carry out separation, washing, and drying to obtain the Bi4O7 / TiO 2-x photocatalyst; the carboxyl group in acetic acid has a strong coordination effect with Ti ions, inhibiting the crystallization process of the titanium precursor and resulting in smaller nanocrystal sizes.

[0015] Another object of the present invention is to provide a photocatalyst prepared by the above method.

[0016] Another object of the present invention is to provide an application of the above photocatalyst as a visible light photocatalyst for degrading tetracycline.

[0017] The beneficial effects of the present invention are as follows:

[0018] (1) The visible light photocatalyst of the present invention has abundant oxygen vacancies and has a high removal efficiency for tetracycline under visible light catalysis.

[0019] (2) The visible light photocatalyst of the present invention has characteristics such as a large specific surface area, good adsorption performance, and high photocatalytic oxidation efficiency, and can effectively improve the applicability of the system.

[0020] (3) The photocatalyst of the present invention can achieve a high degradation efficiency of tetracycline at a low dosage. Description of the Drawings

[0021] Figure 1 It is a comparison chart of the degradation efficiency of TC by composite catalysts with different ratios.

[0022] Figure 2 It is a first-order kinetic fitting curve chart of TC by composite catalysts with different ratios.

[0023] Figure 3 It is TiO 2-x , Bi4O7 and XRD pattern of 0.2BT;

[0024] Figure 4 It is TiO 2-x , BiO 2-x and EPR spectrum of 0.2BT;

[0025] Figure 5 It is the effect diagram of different dosages of 0.2BT on the degradation of TC;

[0026] Figure 6 It is a comparison chart of the degradation efficiency of TC by TiO2, TiO 2-x , Bi4O7 and 0.2BT photocatalytic degradation.

[0027] Figure 7 It is a first-order kinetic fitting curve chart of TC by TiO2, TiO 2-x , Bi4O7 and 0.2BT photocatalytic degradation.

[0028] Figure 8 It is a comparison chart of the degradation of MO and TC by 0.2BT. Detailed Embodiments

[0029] The present invention will be further described below by specific examples, but not limited thereto. All raw materials used in the examples are conventional raw materials and can be obtained commercially; the methods are all prior arts unless otherwise specified.

[0030] Example 1 (Preparation of Bi4O7 / TiO 2-x catalysts with different Bi / Ti ratios)

[0031] Preparation of Bi4O7: Dissolve 2.4 g of NaOH in 60 mL of distilled water, add 2.8 g of NaBiO3·2H2O, stir for 1 h, transfer it into a 100 mL autoclave, keep it at 180 °C for 6 h, cool it, wash it with distilled water until neutral, and dry it at 60 °C to obtain Bi4O7.

[0032] Bi4O7 / TiO 2-xPreparation of catalyst: Mix 20 mL of absolute ethanol, 10 mL of glacial acetic acid and 5 mL of distilled water to form solution A; add Bi4O7 to 20 mL of absolute ethanol, and then add 10 mL of tetrabutyl titanate to form solution B; slowly drop solution B into solution A, stir for 3 h and age for 24 h, then transfer to a 100 mL high-pressure reactor and maintain at 150 °C for 5 h; after cooling, wash with absolute ethanol and distilled water multiple times respectively, and dry at 60 °C to obtain Bi4O7 / TiO 2-x catalyst.

[0033] In this example, with the amount of tetrabutyl titanate fixed, the addition amounts of Bi4O7 were adjusted to 0, 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.4 wt.% (based on the amount of tetrabutyl titanate as the mass measurement benchmark), and the prepared composite catalysts were respectively denoted as TiO 2-x , 0.05BT, 0.1BT, 0.2BT and 0.4BT.

[0034] Test Example 1 (Bi4O7 / TiO 2-x catalyst for determining the optimal Bi / Ti ratio)

[0035] To clarify the Bi4O7 / TiO 2-x catalyst with the optimal Bi / Ti ratio, the performance of different Bi4O7 / TiO 2-x catalysts in the degradation of tetracycline (TC) under visible light was investigated respectively.

[0036] The specific experimental process is as follows: Take the same mass of the five catalysts prepared in Example 1 and add them to 100 mL of tetracycline solution with an initial concentration of 50 mg / L respectively, place them in the dark and stir for 20 min until adsorption equilibrium, then turn on a 300 W xenon lamp light source (410 nm - 780 nm) and continue to stir for 60 min. Regularly suck the reaction solution with a syringe, and then filter it through a 0.22 μm filter membrane and immediately measure the tetracycline concentration at a wavelength of 357 nm under an ultraviolet-visible spectrophotometer. The experimental results are as Figure 1 , Figure 2 shown.

[0037] As Figure 1 can be seen, the removal rate of tetracycline after 20 min of dark reaction adsorption by TiO 2-x is about 16.0%. After 60 min of photocatalytic degradation, the removal rate of tetracycline reaches 53.9%. As the Bi / Ti ratio increases, the adsorption capacity of the composite catalyst for tetracycline first increases continuously, and the adsorption capacity of 0.2BT reaches the maximum value, about 31.4%. As the Bi / Ti ratio further increases, the adsorption capacity of 0.4BT for tetracycline decreases to 27.8%. After turning on the light source, Bi4O7 / TiO with different Bi / Ti ratios 2-xThe change trend of the photocatalytic degradation effect of the catalyst on tetracycline is consistent with the change in adsorption capacity. The removal rate of tetracycline by 0.2BT reaches the maximum, about 71.6%. However, with the further increase of the Bi / Ti ratio, the degradation efficiency of 0.4BT for tetracycline decreases to 56.7%, which may be due to the structural change caused by the addition of excessive Bi4O7, and the excessive Bi element will form an electron-hole recombination center.

[0038] It can be seen from Figure 2 that with the increase of the Bi / Ti ratio, the reaction rate of the composite catalyst first increases and then decreases, and too high Bi / Ti ratio will inhibit the photocatalytic activity. To sum up, 0.2BT has the best adsorption performance and photocatalytic degradation performance.

[0039] Test Example 2 (Characterization of the catalyst)

[0040] For Bi4O7 and TiO prepared in Example 1 2-x and 0.2BT, the crystal structure of the catalyst was analyzed by XRD, the specific surface area and pore structure of the catalyst were analyzed by BET, the reactive substances in the reaction system were analyzed by EPR, and the oxygen vacancies in the photocatalyst were analyzed.

[0041] It can be seen from Figure 3 that the diffraction peaks of TiO 2-x correspond to the standard card of anatase TiO2 (JCPDS No. 99-0008). Among them, at 2θ = 25.3°, 37.8°, 48.0°, 53.9°, 55.1°, 62.7°, 68.7°, 70.3°, 75.0°, they correspond to the (101), (004), (200), (105), (211), (204), (116), (220), (215) crystal planes of anatase TiO2 respectively. The diffraction peaks are narrow and sharp, and no other peaks appear, indicating that the synthesized TiO 2-x has high purity. In addition, the diffraction peaks of Bi4O7 correspond to its standard card (JCPDS 47-1058), proving its successful synthesis. It should be noted that the diffraction pattern of 0.2BT is basically the same as that of TiO 2-x , and no diffraction peak of Bi4O7 is observed, which may be due to the low content and high dispersion of the added Bi4O7, not reaching the detection limit. At the same time, the rich oxygen vacancies on the surface of 0.2BT will lead to the disorder of the surface structure. Therefore, the peak intensity of the XRD pattern of 0.2BT is weaker than that of TiO 2-x .

[0042] Table 1 Pore structure parameters of TiO2, TiO 2-x , Bi4O7 and 0.2BT

[0043] Sample <![CDATA[BET specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Pore size (nm) <![CDATA[TiO2]]> 11.40 0.02 7.16 <![CDATA[TiO 2-x > 203.13 0.27 5.38 <![CDATA[Bi4O7]]> 4.36 0.01 9.24 0.2BT 175.53 0.49 11.25

[0044] Note: TiO2 is a commercially available product from Chengdu Kelong Chemical Co., Ltd., with analytical purity (AR).

[0045] As can be seen from Table 1, compared with TiO2, the prepared oxygen vacancy TiO 2-x has a higher specific surface area (203.13 m 2 / g) and pore volume (0.27 cm 3 / g), and the average pore diameter is approximately distributed at 5.38 nm, indicating that oxygen vacancies can increase the specific surface and pore volume of TiO2, which is beneficial to the occurrence of the adsorption process. The specific surface area and pore volume of 0.2BT are 175.53 m 2 / g and 0.49 cm 3 / g respectively, and the pore diameter is about 11.25 nm. The addition of Bi4O7 increases the pore diameter and pore volume, which can increase the adsorption performance of 0.2BT and thus improve the photocatalytic activity.

[0046] From Figure 4 it can be seen that the symmetric resonance peak at g = 2.003 is caused by oxygen vacancies. Among them, the symmetric resonance peaks of TiO 2-x and Bi4O7 are not obvious, but for the double-defect composite catalyst 0.2BT, it can be seen that the resonance peak intensity increases significantly, indicating an increase in the number of its oxygen vacancies. Oxygen vacancies construct a new photoexcitation process, which is beneficial to improving the photocatalytic performance of 0.2BT. Electrons are excited to the defect state of VB under visible light irradiation. In addition, since oxygen vacancies are used as electron traps, the photoexcited electrons in the defect state are not easily recombined with photoexcited holes, and the lifetime of the photoexcited electrons in the traps is longer. The electrons in the defect state can react with O2 adsorbed by oxygen vacancies to generate ·O2 - , thereby realizing the degradation of pollutants.

[0047] Test Example 3 (Determination of the optimal dosage of the catalyst)

[0048] To reduce costs and achieve practical applications, the effect of the catalyst dosage on the photocatalytic process was studied.

[0049] The specific process is as follows: Weigh different masses of 0.2BT and disperse them in 100 mL of TC solution with an initial concentration of 50 mg / L respectively. Place them in the dark and stir for 20 min until adsorption equilibrium is reached. Then turn on a 300 W xenon lamp source (410 nm - 780 nm) and continue stirring for 60 min. Regularly draw the reaction solution with a syringe, and then filter it through a 0.22 μm filter membrane and immediately measure the TC concentration at a wavelength of 357 nm under an ultraviolet-visible spectrophotometer. In this test, the catalyst concentrations in the TC solution are 0.1 g / L, 0.2 g / L, 0.3 g / L, and 0.4 g / L respectively. The experimental results are shown in Figure 5 .

[0050] FromFigure 5 It can be seen that the adsorption performance for tetracycline also increases after the catalyst concentration increases. After 20 min of dark adsorption, the removal rates of tetracycline are 17.8%, 31.4%, 46.0% and 59.1% respectively. Obviously, the higher the catalyst concentration, the more the corresponding active site number increases, resulting in the increase of the adsorption removal rate. With the increase of the catalyst, the photocatalytic degradation efficiency for tetracycline also increases in turn, and the degradation efficiencies of tetracycline correspond to 48.5%, 71.6%, 86.7% and 92.2% in turn. However, excessive catalyst dosage will accumulate the turbidity of the solution and reduce the light penetration through the tetracycline solution. Therefore, considering the low cost and the excellent photocatalytic performance of the catalyst comprehensively, the dosage is selected as 0.3 g / L.

[0051] Test Example 4 (Comparative experiment on degradation of tetracycline by different photocatalysts)

[0052] To clarify the photocatalytic performance of 0.2BT, TiO2, TiO 2-x and Bi4O7 were used as control catalysts to catalytically degrade tetracycline under visible light under the same conditions.

[0053] The specific experimental process is as follows: Weigh 20 mg of the catalyst, disperse it in 100 mL of a TC solution with an initial concentration of 50 mg / L, place it in the dark and stir for 20 min until adsorption equilibrium is reached. Then turn on a 300 W xenon lamp (410 nm - 780 nm) and continue to stir for 60 min. Regularly draw the reaction solution with a syringe, then filter it through a 0.22 μm filter membrane and immediately measure the TC concentration at a wavelength of 357 nm under an ultraviolet-visible spectrophotometer. The experimental results are shown in Figure 6 .

[0054] From Figure 6 and Figure 7 it can be seen that the adsorption capacities of TiO2 and Bi4O7 for tetracycline are 1.3% and 2.7% respectively, which are almost negligible. After 60 min of light irradiation, the photocatalytic degradation efficiency of Bi4O7 for tetracycline (10.5%, k = 0.0014 min -1 ) is slightly higher than that of TiO2 for tetracycline (7.2%, k = 0.0011 min -1 ). The ability of TiO2 and Bi4O7 to photocatalytically degrade tetracycline is limited. The main reason is that the large band gap of TiO2 leads to poor visible light response performance, while the photogenerated electrons and holes generated by Bi4O7 are prone to recombination. However, the adsorption capacity of the modified TiO 2-x for tetracycline is significantly improved. After 20 min of dark adsorption, the removal rate of tetracycline rises to 16.0%. Under 60 min of light irradiation, the photocatalytic degradation efficiency for tetracycline reaches 53.9%, and the apparent reaction rate constant reaches 0.0089 min -1, which is 8.2 times that of TiO2. The adsorption capacity of the 0.2BT composite catalyst for TC further increased to 31.4%, and the photocatalytic degradation efficiency for tetracycline also increased to 71.6%, with the apparent reaction rate constant (k = 0.0128 min -1 ) being 11.9 times and 9.0 times that of TiO2 and Bi4O7 respectively, and also 1.5 times that of TiO 2-x . Therefore, it is concluded that the modification of TiO2 and the addition of Bi4O7 significantly improve the ability of the 0.2BT composite catalyst to photocatalytically degrade tetracycline. The improvement in photocatalytic performance can be attributed to two aspects. One is that the adsorption performance of the catalyst is improved, and adsorption can make pollutants more concentrated, which is beneficial to the subsequent photocatalytic reaction. The other is that the formation of heterojunctions improves the photocatalytic performance of the composite catalyst.

[0055] Test Example 5 (Comparative experiment on the degradation of different pollutants by the optimal Bi4O7 / TiO 2-x catalyst)

[0056] Weigh 87 mg of 0.2BT and disperse it in 100 mL of methyl orange (MO) solution with an initial concentration of 20 mg / L; weigh 20 mg of 0.2BT and disperse it in 100 mL of TC solution with an initial concentration of 20 mg / L. Then, stir both solutions in the dark for 20 min until adsorption equilibrium is reached. Immediately turn on a 300 W xenon lamp (410 nm - 780 nm) and continue stirring for 20 min. Regularly draw the reaction solution with a syringe, filter it through a 0.22 μm filter membrane, and then immediately measure the concentration of MO at a wavelength of 484 nm and the concentration of TC at a wavelength of 357 nm under an ultraviolet-visible spectrophotometer. It can be Figure 8 seen that the 0.2BT achieves a 98% MO removal rate under 20 min of light irradiation, and the 0.2BT achieves an 88% TC removal rate under 20 min of light irradiation.

[0057] As described above, the above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing a photocatalyst, characterized in that, It includes the following steps: S1. Prepare Bi4O7 material; S2. Mix deionized water, glacial acetic acid, and absolute ethanol evenly to form solution A; S3. Add tetrabutyl titanate and Bi4O7 material into absolute ethanol to form solution B, wherein the mass ratio of Bi4O7 material to tetrabutyl titanate is 0.0005 - 0.004:1; S4. Add solution B dropwise to solution A, stir for 1 - 4 h and age for 12 - 48 h, then raise the temperature to 120 - 200 °C under a closed condition and react for 3 - 12 h. Finally, carry out separation, washing and drying to obtain Bi4O7 / TiO 2-x photocatalyst.

2. The preparation method of the photocatalyst according to claim 1, characterized in that, The mass ratio of Bi4O7 material to tetrabutyl titanate is 0.002:

1.

3. The preparation method of the photocatalyst according to claim 1, wherein, The Bi4O7 material is prepared by a method including the following steps: S11. Disperse sodium bismuthate dihydrate in NaOH solution; S12. Heat the solution of S11 to 120 - 200 °C and keep it for 4 - 12 h; S13. Cool, centrifuge, and dry the product of S12 to obtain Bi4O7 material.

4. The preparation method of the photocatalyst according to claim 1, wherein, In step S2, the volume ratio of deionized water to glacial acetic acid is 1:1 - 4.

5. A photocatalyst, characterized in that, It is prepared by the method described in any one of claims 1 - 4.

6. An application of a photocatalyst, characterized in that, Use the photocatalyst described in claim 5 as a visible light photocatalyst for degrading tetracycline.

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