Preparation method and application of TiO2 / Bi / X ternary heterostructure photocatalyst

Abstract

The invention provides a preparation method and application of a TiO2 / Bi / X ternary heterostructure photocatalyst, and belongs to the technical field of photocatalytic materials.The preparation method comprises the steps that TiO2 nanorods containing Ti < 3 + > and oxygen vacancies are prepared; the preparation method comprises the following steps: adding the TiO2 nanorod and X into deionized water, stirring, centrifuging, reserving precipitate, drying in vacuum, grinding, and calcining to obtain a TiO2 / Bi / X ternary heterostructure photocatalyst; x is BiOI, Bi2WO6 or BiOBr, and the structural formula is shown in the description. The method for in-situ construction of the Bi metal mediated ternary heterojunction without additionally adding a reducing agent has the advantages that synthesis is simple, conditions are mild, and impurities are not easy to introduce; compared with single TiO2 and BiOI catalysts, the TiO2 / Bi / X prepared by the method has the advantages that the tetracycline degradation effect is obviously improved, and the TiO2 / Bi / X has a very good application prospect in the field of photocatalysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and in particular relates to a preparation method and application of a TiO2 / Bi / X ternary heterogeneous structure photocatalyst. Background Art

[0002] The use of heterojunction and metal modification to improve the performance of TiO2 has attracted more and more attention. The construction of heterojunction can significantly improve the separation ability of photogenerated holes and electrons in photocatalysts, thereby improving the photocatalytic performance. On this basis, the use of metals to modify the catalyst can further optimize the photocatalytic performance of the catalyst.

[0003] TiO2 is a very important photocatalyst material in the field of environment and energy. It has the advantages of stable chemical properties, non-toxicity and relatively low price, so it has attracted widespread attention. However, due to its band gap (3.2eV), it is not conducive to the utilization of large sunlight energy. At the same time, its fast hole-electron recombination rate also limits its application to a certain extent. Therefore, it is necessary to optimize its structure to improve its performance. Currently, the commonly used modification methods include metal doping, non-metal doping, vacancy engineering and heterostructure construction.

[0004] BiOI has a unique layered structure, suitable band gap and photochemical stability. It can form a heterojunction with TiO2 to improve the performance of TiO2. In order to further improve the performance of TiO2 / BiOI, further modification with metals is an effective and feasible strategy. Currently, precious metals (Au, Ag) are commonly used as electron media to improve the performance of heterojunctions. Due to the high price of precious metals, its application has been limited to a certain extent. Bi metal has been proven to be a more economical alternative because it has similar properties to precious metals. In addition, the in-situ generated elemental bismuth nanoparticles have a stronger interface contact and can effectively avoid leaching and agglomeration. However, the in-situ construction method reported in the report usually requires the addition of reducing agents such as NaBH4 and glucose. The process is cumbersome and difficult to control, and there is also a risk of introducing impurities. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method and application of a TiO2 / Bi / X ternary heterostructure photocatalyst. This method does not require the addition of an additional reducing agent to construct a Bi metal-mediated ternary heterojunction in situ, has the advantages of simple synthesis, mild conditions, and is not easy to introduce impurities, and provides a certain reference for the construction of the same type of heterojunction. It is specifically achieved through the following technical solutions:

[0006] The first aspect of the present invention provides a method for preparing a TiO2 / Bi / X ternary heterostructure photocatalyst, comprising the following steps:

[0007] Preparation of Ti3+ and TiO2 nanorods with oxygen vacancies;

[0008] Containing Ti 3+ The TiO2 nanorods with oxygen vacancies and X are added into deionized water and stirred, centrifuged to retain the precipitate, and then vacuum dried, ground, and calcined to obtain a TiO2 / Bi / X ternary heterostructure photocatalyst;

[0009] The X is BiOI, Bi2WO6 or BiOBr.

[0010] Furthermore, the X and the Ti 3+ The mass ratio of TiO2 nanorods to oxygen vacancies is 1:(5-15); for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14 or 1:15.

[0011] Furthermore, the X and the Ti 3+ The mass ratio of the total mass of TiO2 nanorods with oxygen vacancies to deionized water is (1-10):1000; for example, 1:1000, 2:1000, 3:1000, 4:1000, 5:1000, 6:1000, 7:1000, 8:1000, 9:1000 or 10:1000.

[0012] Furthermore, the vacuum drying temperature is 60° C., and the vacuum drying time is 6-12 hours.

[0013] Furthermore, the preparation of 3+ and oxygen vacancy TiO2 nanorods, including:

[0014] The titanium dioxide is dissolved in an alkaline solution and reacted at 120-160°C for 12-48 hours to obtain a precipitate A1; the precipitate A1 is washed with ultrapure water until the pH of the washing solution is neutral, and dried for 8-16 hours to obtain a precipitate A2; the precipitate A2 is dissolved in an acid for proton exchange for 20-26 hours, washed with ultrapure water until the pH of the washing solution is neutral, and dried to obtain a precipitate of hydrogen titanate nanotubes; the hydrogen titanate nanotubes are ground and heated to 400-800°C in an air atmosphere at a rate of 2.5°C / min-10°C / min, and then kept at a constant temperature for 2-4 hours to obtain a Ti-containing 3+ and TiO2 nanorods with oxygen vacancies.

[0015] Optionally, the heating rate is 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min or 10℃ / min.

[0016] Optionally, the heating temperature is 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C.

[0017] Furthermore, the mass ratio of the titanium dioxide to the alkaline solution is (15-20):100; for example, 15:100, 16:100, 17:100, 18:100, 19:100 or 20:100.

[0018] Furthermore, the alkaline solution is one of sodium hydroxide and potassium hydroxide.

[0019] Furthermore, the mass ratio of the precipitate A2 to the acid is (2-5):1; for example, 2:1, 3:1, 4:1 or 5:1; the acid includes hydrochloric acid or nitric acid, and the acid is in excess.

[0020] Furthermore, the acid is preferably hydrochloric acid, and the concentration of the hydrochloric acid is 0.1-0.3 mol / L, for example, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L or 0.3 mol / L.

[0021] Among them, the protonation exchange is that the acid provides hydrogen protons to replace the cations provided by the alkaline solution in the titanate nanotubes, such as replacing the sodium ions provided by sodium hydroxide or replacing the potassium ions provided by potassium hydroxide.

[0022] Furthermore, when X is BiOI, it is prepared by the following method:

[0023] Add Bi(NO3)3·5H2O to the first organic solvent and stir, then add I — The ion source is mixed and stirred to obtain a precipitate, the precipitate is washed with deionized water and ethanol, vacuum dried at 60° C.-80° C. for 8-15 h, and then calcined at 300-500° C. for 2-5 h to obtain BiOI;

[0024] The Bi(NO3)3·5H2O, the first organic solvent, I —The mass ratio of the ion source is (1-3):(50-60):1; for example, 1:50:1, 2:50:1, 3:50:1, 1:55:1, 1:60:1, 2:55:1, 3:55:1, 2:60:1, 3:60:1.

[0025] I — Ion sources include: KI, NaI.

[0026] Furthermore, when X is Bi2WO6, it is prepared by the following method:

[0027] Dissolve Bi(NO3)3·5H2O in a second organic solvent, add Na2WO4·2H2O under stirring to obtain a precursor solution, react the obtained precursor solution at 170-220°C for 1-4h, cool and centrifuge to obtain an off-white precipitate, wash with anhydrous ethanol and deionized water several times, and finally vacuum dry at 65-85°C for 5-8h to obtain Bi2WO6;

[0028] The mass ratio of Bi(NO3)3·5H2O, the second organic solvent and Na2WO4·2H2O is (2-3):(40-50):1.

[0029] Furthermore, when X is BiOBr, it is prepared by the following method:

[0030] Dissolve Bi(NO3)3·5H2O in the third organic solvent and add Br — Stirring with an ion source, reacting at 100-150°C for 20-28h, washing with deionized water and vacuum drying at 60-80°C for 8-15h to obtain BiOBr;

[0031] The Bi(NO3)3·5H2O, the third organic solvent, Br — The mass ratio of the ion source is (4-7):(10-20):1;

[0032] The Br — Ion sources include: KBr, NaBr.

[0033] Furthermore, the first organic solvent, the second organic solvent and the third organic solvent are all selected from one of ethanol, ethylene glycol and acetic acid.

[0034] Preferably, the first organic solvent is ethanol;

[0035] Preferably, the second organic solvent is ethylene glycol;

[0036] Preferably, the third organic solvent is acetic acid.

[0037] As a preferred embodiment of the present invention, when X is BiOI, it is prepared by the following method: Bi(NO3)3·5H2O is added to ethanol and stirred for 1 hour, and then KI is added and mixed and stirred for 4 hours to obtain a precipitate, and the precipitate is washed with deionized water and ethanol, vacuum dried at 60°C for 12 hours, and then calcined at 350°C for 3 hours to obtain BiOI.

[0038] As a preferred embodiment of the present invention, when X is Bi2WO6, it is prepared by the following method: dissolving Bi(NO3)3·5H2O in ethylene glycol, adding Na2WO4·2H2O under stirring conditions to obtain a precursor solution, placing the obtained precursor solution in a reactor at 190°C for 2h, cooling and centrifuging to obtain an off-white precipitate, washing with anhydrous ethanol and deionized water several times, and finally drying under vacuum at 70°C for 6h to obtain Bi2WO6.

[0039] As a preferred embodiment of the present invention, when X is BiOBr, it is prepared by the following method: dissolving Bi(NO3)3·5H2O in acetic acid, adding KBr and stirring, reacting at 120°C for 24h, washing with deionized water and vacuum drying at 60°C for 12h to obtain BiOBr.

[0040] The second aspect of the present invention provides a TiO2 / Bi / X ternary heterostructure photocatalyst, which is prepared by the above-mentioned preparation method, and the TiO2 / Bi / X ternary heterostructure photocatalyst is TiO2 / Bi / BiOI, TiO2 / Bi / Bi2WO6 or TiO2 / Bi / BiOBr.

[0041] The third aspect of the present invention provides an application of a TiO2 / Bi / X ternary heterostructure photocatalyst in the degradation of tetracycline.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The present invention utilizes modified Ti-containing 3+ A metal Bi-mediated interface is constructed between the TiO2 nanorods with oxygen vacancies and X (X is BiOI, Bi2WO6 or BiOBr), promoting the formation of a metal-mediated ordered structure TiO2 / Bi / X ternary heterojunction. Compared with the metal-mediated ternary heterojunction formed by adding a reducing agent or solvent to heat, this ternary heterojunction synthesis method reduces the impurities introduced by the addition of reducing agents or solvents during the catalyst synthesis process.

[0044] Compared with single TiO2 and BiOI, the first-order kinetic constant of the ordered mediated TiO2 / Bi / BiOI ternary heterojunction photocatalyst of the present invention for photocatalytic degradation of tetracycline is increased by 2.5 times and 8.1 times, and has a good application prospect in the field of photocatalysis. At the same time, the ternary heterojunction synthesis method of the present invention is universal, and the degradation effect of TiO2 / Bi / Bi2WO6 and TiO2 / Bi / BiOBr constructed by the same method in the degradation experiment of tetracycline is also significantly improved compared with a single catalyst.

[0045] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 TEM image and surface element (Bi, O, I and Ti elements) distribution map of the TiO2 / Bi / BiOI sample of Example 2;

[0047] Figure 2 is the X-ray photoelectron spectrum of the TiO2 / Bi / BiOI sample of Example 2;

[0048] Figure 3 TEM images of TiO2, BiOI and TiO2 / Bi / BiOI samples of Example 2;

[0049] Figure 4 This is a high-resolution transmission electron microscopy image of the TiO2 / Bi / BiOI sample of Example 2;

[0050] Figure 5 The electron paramagnetic resonance spectra of TiO2, BiOI and TiO2 / Bi / BiOI samples of Example 2;

[0051] Figure 6 The photocatalytic activity diagram (a) and the photocatalytic degradation first-order reaction kinetic diagram (b) of the TiO2, BiOI, and TiO2 / Bi / BiOI samples of Example 2;

[0052] Figure 7 Graph showing the cycling stability of the TiO2 / Bi / BiOI sample of Example 2;

[0053] Figure 8 TEM image and surface element (Bi, O, I and Ti element) distribution map of the TiO2 / Bi / BiOI sample after illumination in Example 2;

[0054] Fig. 9is the X-ray photoelectron spectrum of the TiO2 / Bi / Bi2WO6 sample of Example 3;

[0055] Fig.10 The photocatalytic activity diagram of TiO2, Bi2WO6, and TiO2 / Bi / Bi2WO6 samples of Example 3;

[0056] Fig.11 is the X-ray photoelectron spectrum of the TiO2 / Bi / BiOBr sample of Example 4;

[0057] Fig.12 This is the photocatalytic activity diagram of TiO2, BiOBr, and TiO2 / Bi / BiOBr samples in Example 4. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical scheme and advantages of the present invention clearer, the embodiments of the present application will be described in detail below in conjunction with specific examples. The technical terms and scientific terms used in the present invention have the meanings generally understood by those of ordinary skill in the art to which the present invention belongs, without other definitions. Without departing from the concept of the present invention, those skilled in the art may make various improvements and changes to the specific embodiments of the present invention specification, which all belong to the protection scope of the present invention. The reagents and raw materials used in the examples can all be obtained commercially.

[0059] The technical solution of the present invention will be further described below in conjunction with embodiments.

[0060] Example 1

[0061] Preparation of TiO2 catalyst raw materials:

[0062] Accurately weigh 6g of commercial titanium dioxide amorphous powder (CAS No. 13463-67-7 of Sinopharm Group), dissolve it in 80mL 10mol / L NaOH solution, ultrasonicate for 30min to fully dissolve it, transfer it to a high-pressure reactor, seal it, put it in an oven, and react it at 150℃ for 48h. After the reaction is completed, cool it to room temperature and take out the white precipitate in the reactor. Wash the precipitate with 1L ultrapure water until the pH of the washing liquid is neutral (pH=7), place it in an oven to dry for 12h, and take out the white precipitate after the oven cools to room temperature. At this time, the obtained white precipitate was protonated and exchanged with 500 mL 0.1 mol / L HCl for 24 h, and then washed with a large amount of ultrapure water until the pH of the washing solution was nearly neutral. The white precipitate was placed in an oven for drying for 12 h to obtain the precipitate hydrogen titanate nanotubes. The precipitate hydrogen titanate nanotubes were ground and placed in a muffle furnace. The temperature was raised to 700 ° C at 2.5 ° C / min in an air atmosphere and then kept at this temperature for 2 h to obtain Ti 3+ and TiO2 nanorods with oxygen vacancies.

[0063] Example 2

[0064] 1. Preparation of TiO2 / Bi / BiOI (titanium dioxide / bismuth / bismuth iodide) ternary heterojunction photocatalyst:

[0065] BiOI nanosheets were synthesized by the following steps. 1.455 g Bi(NO3)3·5H2O was added to 40 mL ethanol and stirred for 1 h, then a KI aqueous solution containing 0.498 g KI and 20 mL deionized water was added, and the two solutions were mixed and stirred for 4 h. The above precipitate was washed with deionized water and ethanol and vacuum dried at 60 °C for 12 h. After drying, the catalyst BiOI was obtained by calcination at 350 °C for 3 h.

[0066] The synthesis of TiO2 / Bi / BiOI is carried out by the following steps: taking 5% by mass of BiOI and 95% by mass of TiO2 / Bi / BiOI prepared in Example 1; 3+ TiO2 nanorods with oxygen vacancies (total mass of the two is 0.3 g) were added to 30 mL of deionized water, ultrasonicated for 10 min and stirred for 30 min. The suspension was centrifuged to retain the precipitate and then vacuum dried at 60 ° C for 12 h. After grinding, it was placed in a muffle furnace and calcined at 200 ° C in air atmosphere for 1 h. The obtained catalyst was recorded as TiO2 / Bi / BiOI.

[0067] 2. Characterization of TiO2 / Bi / BiOI ternary heterojunction photocatalyst:

[0068] Figure 1 The TEM image and surface element (Bi, O, I and Ti elements) distribution map of the TiO2 / Bi / BiOI sample show that the distribution range of Bi and I elements in the sample is completely consistent with that of Ti and O elements, indicating the formation of a highly dispersed ternary heterostructure photocatalyst.

[0069] Figure 2 The X-ray photoelectron spectrum of the TiO2 / Bi / BiOI sample, where: (a) Bi 4f; (b) I 3d; (c) Ti2p; (d) O 1s. The binding energy of the Bi 4f spectrum can be used to determine that the valence state of bismuth is Bi 3+ and Bi 0 The binding energy of the I 3d spectrum can determine that the valence state of iodine is I - , the binding energy corresponding to the peak in the Ti 2p spectrum can be determined to be Ti 4+ , combined with the O1s spectrum, it can be determined that the composite photocatalyst contains three components: BiOI, Bi and TiO2.

[0070] Figure 3Transmission electron microscopy images of TiO, BiOI and TiO2 / Bi / BiOI samples, where a is the TiO2 sample, b is the BiOI sample, and c is the TiO2 / Bi / BiOI sample. It can be seen from the figure that BiOI nanosheets are evenly loaded on the surface of TiO2 nanorods.

[0071] Figure 4 This is a high-resolution transmission electron microscopy image of the TiO2 / Bi / BiOI sample. Lattice fringes of 0.35nm, 0.30nm and 0.23nm can be observed in the image, which can be attributed to the TiO2(101), BiOI(102) and Bi(104) crystal planes, respectively. This shows that the TiO2 / Bi / BiOI ternary heterostructure photocatalyst can be successfully constructed by low-temperature interfacial redox reaction.

[0072] Figure 5 The electron paramagnetic resonance spectra of TiO2, BiOI, and TiO2 / Bi / BiOI samples show that after TiO2 and BiOI form a ternary heterojunction, Ti 3+ The peak at (g = 1.968) disappears, indicating that Ti 3+ The redox reaction occurred with the BiOI surface, and Ti 3+ Transferring electrons to Bi in the BiOI lattice 3+ ,Bi 3+ Elemental Bi is in situ generated at the contact surface of the catalyst, which further proves the existence of the TiO2 / Bi / BiOI ternary heterostructure.

[0073] 3. Test on the degradation performance of TiO2 / Bi / BiOI ternary heterojunction photocatalyst on tetracycline:

[0074] The performance test of TiO2 / Bi / BiOI ternary heterojunction photocatalyst, the method of photocatalytic performance test is: add 100mL of 40mg / L tetracycline hydrochloride solution and 15mg catalyst in the photocatalytic reactor, dark reaction for 1h to reach adsorption and desorption equilibrium; light reaction for 1h, in which 3mL is sampled every 10min, the sample is taken out and centrifuged to take the supernatant, and the absorbance of tetracycline at 356nm is detected by UV-visible spectrophotometer. In addition, the photocatalyst photodegradation behavior of tetracycline hydrochloride under simulated sunlight is kinetically analyzed by fitting the first-order reaction kinetic equation (ln(C0 / C)=kt). Figure 6 (a) is the photodegradation activity diagram of TiO2 / Bi / BiOI, BiOI, and TiO2. Figure 6(b) is the corresponding first-order kinetic degradation rate diagram. After 60 minutes of illumination, the degradation rate of tetracycline by TiO2 nanorods is 55%, and the degradation rate of tetracycline by sheet-like BiOI is 24%. The degradation rate of tetracycline by TiO2 / Bi / BiOI three-phase heterostructure photocatalyst is 86%. It is obvious from the activity diagram that the photodegradation activity of TiO2 / Bi / BiOI three-phase heterostructure photocatalyst is the best, and the first-order reaction kinetic constants are 8.1 times and 2.5 times that of BiOI and TiO2, respectively. This shows that the in-situ constructed metal Bi-mediated ternary heterojunction can significantly improve the photocatalytic activity.

[0075] 4. Stability experiment of TiO2 / Bi / BiOI ternary heterojunction photocatalyst:

[0076] The method of photocatalytic stability test is as follows: after the photocatalytic degradation experiment is completed, the solution is collected and transferred to a centrifuge tube, centrifuged for 5 minutes, and the centrifugal speed is set to 8000r / min. After the centrifugation is completed, the precipitate in the centrifuge tube is collected, repeatedly washed with deionized water and anhydrous ethanol, and then transferred to a drying oven for drying, and the temperature is set to 60°C. The recovered photocatalyst is subjected to the photocatalytic degradation experiment again according to the previous photocatalytic reaction steps.

[0077] Figure 7 This is the cyclic stability diagram of the TiO2 / Bi / BiOI sample. After 4 cycle tests, the degradation rate of tetracycline by TiO2 / Bi / BiOI did not decrease significantly, indicating that the TiO2 / Bi / BiOI ternary heterostructure photocatalyst prepared by in situ interfacial chemical reaction has good stability.

[0078] Figure 8 This is the TEM image of the TiO2 / Bi / BiOI sample after illumination and the distribution map of surface elements (Bi, O, I and Ti elements). By comparison, it is found that the distribution range of Bi and I elements in the sample is still completely consistent with that of Ti and O elements, indicating that the formed ternary heterostructure photocatalyst has good stability.

[0079] The present invention utilizes Ti-rich 3+ The TiO2 nanorods and BiOI nanosheets with oxygen vacancies undergo an in-situ interfacial redox reaction, and metal Bi is generated in-situ at the interface between the two, forming a metal Bi-mediated TiO2 / Bi / BiOI ternary heterojunction. Metal Bi acts as an electron transfer medium, which can significantly improve the separation ability of electrons and holes in the photocatalyst, thereby improving the photocatalytic activity. This method of in-situ construction of a Bi metal-mediated ternary heterojunction does not require the addition of an additional reducing agent, and has the advantages of simple synthesis, mild conditions, and not easy to introduce impurities.

[0080] In order to verify whether the method of redox construction of Bi metal-mediated heterojunction in Example 2 is universal, the present invention replaces BiOI with Bi2WO6 and BiOBr, and conducts experiments to study whether TiO2 / Bi / Bi2WO6 and TiO2 / Bi / BiOBr ternary heterojunctions can be obtained. The following Examples 3 and 4 are universal experiments of the heterostructure construction method:

[0081] Example 3

[0082] 1. Preparation of TiO2 / Bi / Bi2WO6 (titanium dioxide / bismuth / bismuth tungstate) ternary heterojunction photocatalyst:

[0083] First, Bi(NO3)3·5H2O (4.0mmol) was dissolved in 50mL ethylene glycol, and 2mmol Na2WO4·2H2O was added under vigorous stirring at room temperature. Then, the obtained precursor was transferred to a 100mL polytetrafluoroethylene-lined reactor and reacted at 190℃ for 2h. After cooling, the off-white precipitate was centrifuged, washed several times with anhydrous ethanol and deionized water, and finally dried under vacuum at 70℃ for 6h to obtain Bi2WO6.

[0084] Take 5% Bi2WO6 and 95% Ti prepared in Example 1 3+ TiO2 nanorods with oxygen vacancies (total mass of the two is 0.3 g) were added to 30 mL of deionized water, ultrasonicated for 10 min and stirred for 30 min. The suspension was centrifuged to retain the precipitate and then vacuum dried at 60 ° C for 12 h. After grinding, it was placed in a muffle furnace and calcined at 200 ° C in air atmosphere for 1 h. The obtained catalyst was recorded as TiO2 / Bi / Bi2WO6.

[0085] 2. Characterization of TiO2 / Bi / Bi2WO6 ternary heterojunction photocatalyst:

[0086] Fig. 9 X-ray photoelectron spectrum of TiO2 / Bi / Bi2WO6 sample, (a) Bi 4f, (b) W 4f, (c) Ti 2p, (d) O 1s. From the binding energy of (a) Bi 4f spectrum, it can be determined that the valence state of bismuth is Bi 3+ and Bi 0 (b) The binding energy of the W 4f spectrum can be used to determine that the valence state of tungsten is W 4+ , (c) The binding energy corresponding to the peak in the Ti 2p spectrum can be determined to be Ti 4+ , combined with (d) O 1s spectrum, it can be determined that the composite photocatalyst contains three components: Bi2WO6, Bi and TiO2. Fig.10The photocatalytic activity diagram of TiO2, Bi2WO6, and TiO2 / Bi / Bi2WO6 samples. After 60 minutes of illumination, the degradation rate of tetracycline by TiO2 nanorods was 55%, the degradation rate of tetracycline by Bi2WO6 was 60%, and the degradation rate of tetracycline by TiO2 / Bi / Bi2WO6 three-phase heterogeneous structure photocatalyst was 78%. It is obvious from the activity diagram that the photodegradation activity of TiO2 / Bi / Bi2WO6 three-phase heterogeneous structure photocatalyst is the best.

[0087] Example 4

[0088] 1. Preparation of TiO2 / Bi / BiOBr (titanium dioxide / bismuth / bismuth oxybromide) ternary heterojunction photocatalyst:

[0089] 4 mmol Bi(NO3)3·5H2O was dissolved in 7.5 mL acetic acid to form solution 1, and 4 mmol KBr was dissolved in 25 mL deionized water to form solution 2. Then solution 1 was added dropwise to solution 2 to obtain a milky white suspension solution, which was stirred for 30 min. The mixture was transferred to a 100 mL reactor, reacted at 120°C for 24 hours, cooled naturally to room temperature, washed with deionized water, and vacuum dried at 60°C for 12 hours to obtain BiOBr.

[0090] Take 5% BiOBr and 95% Ti prepared in Example 1 3+ TiO2 nanorods with oxygen vacancies (total mass of the two is 0.3 g) were added to 30 mL of deionized water, ultrasonicated for 10 min and stirred for 30 min. The suspension was centrifuged to retain the precipitate and then vacuum dried at 60 ° C for 12 h. After grinding, it was placed in a muffle furnace and calcined at 200 ° C in air atmosphere for 1 h. The obtained catalyst was recorded as TiO2 / Bi / BiOBr.

[0091] 2. Characterization of TiO2 / Bi / BiOBr ternary heterojunction photocatalyst:

[0092] Fig.11 The X-ray photoelectron spectrum of the TiO2 / Bi / BiOBr sample, where (a) Bi 4f, (b) Br 3d, (c) Ti 2p, and (d) O 1s. The binding energy of the (a) Bi 4f spectrum indicates that the valence state of bismuth is Bi 3+ and Bi 0 , (b) The binding energy of the Br 3d spectrum can be used to determine that the valence state of bromine is Br - , (c) The binding energy corresponding to the peak in the Ti 2p spectrum can be determined to be Ti 4+ , combined with the (d)O 1s spectrum, it can be determined that the composite photocatalyst contains three components: BiOBr, Bi and TiO2.

[0093] Fig.12 The photocatalytic activity diagram of TiO2, BiOBr, and TiO2 / Bi / BiOBr samples. After 60 minutes of illumination, the degradation rate of tetracycline by TiO2 nanorods was 55%, the degradation rate of tetracycline by BiOBr was 52%, and the degradation rate of tetracycline by TiO2 / Bi / BiOBr three-phase heterogeneous structure photocatalyst was 69%. It is obvious from the activity diagram that the photodegradation activity of TiO2 / Bi / BiOBr three-phase heterogeneous structure photocatalyst is the best.

[0094] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a TiO2 / Bi / X ternary heterostructure photocatalyst, characterized in that: The following steps are involved: Preparation of Ti 3+ and oxygen vacancies in TiO2 nanorods; adding TiO2 nanorods and X into deionized water, stirring, centrifuging to retain the precipitate, vacuum drying, grinding, and calcining to obtain a TiO2 / Bi / X ternary heterogeneous structure photocatalyst; The X is BiOI, Bi2WO6 or BiOBr.

2. The preparation method according to claim 1, characterized in that: The X and Ti 3+ The mass ratio of TiO2 nanorods to oxygen vacancies is 1:(5-15).

3. The preparation method according to claim 1, characterized in that: The Ti 3+ The TiO2 nanorods with oxygen vacancies are prepared by the following steps: The titanium dioxide is dissolved in an alkaline solution to react and obtain a precipitate A1; the precipitate A1 is washed until the pH of the washing solution is neutral, and then dried to obtain a precipitate A2; the precipitate A2 is dissolved in an acid, then washed until the pH of the washing solution is neutral, and then dried to obtain a precipitate of hydrogen titanate nanotubes; the hydrogen titanate nanotubes are ground and then heated to 400-800°C in an air atmosphere and calcined and then kept at a constant temperature for 2-4 hours to obtain a Ti-containing 3+ and TiO2 nanorods with oxygen vacancies.

4. The preparation method according to claim 3, characterized in that: The mass ratio of the titanium dioxide to the alkaline solution is (15-20):100; the mass ratio of the precipitate A2 to the acid is (2-5):

1.

5. The preparation method according to claim 1, characterized in that: When X is BiOI, it is prepared by the following method: Add Bi(NO3)3·5H2O to the first organic solvent and stir. — The ion source is mixed and stirred to obtain a precipitate, the precipitate is washed with deionized water and ethanol, and then vacuum dried, and then calcined at 300-500° C. for 2-5 h to obtain BiOI; I — Ion sources include: KI, NaI; The Bi(NO3)3.5H2O, the first organic solvent, — The mass ratio of the ion source is (1-3):(50-60):

1.

6. The preparation method according to claim 1, characterized in that: When X is Bi2WO6, it is prepared by the following method: Dissolve Bi(NO3)3·5H2O in a second organic solvent, add Na2WO4·2H2O with stirring to obtain a precursor solution, react the obtained precursor solution at 170-220°C for 1-4h, cool and centrifuge to obtain an off-white precipitate, wash with anhydrous ethanol and deionized water several times, and finally vacuum dry to obtain Bi2WO6; The mass ratio of Bi(NO3)3·5H2O, the second organic solvent and Na2WO4·2H2O is (2-3):(40-50):

1.

7. The preparation method according to claim 1, characterized in that: When X is BiOBr, it is prepared by the following method: Dissolve Bi(NO3)3·5H2O in the third organic solvent and add Br — Stirring with an ion source, reacting at 100-150° C. for 20-28 hours, washing with deionized water, and vacuum drying at 60-80° C. for 8-15 hours to obtain BiOBr; The Br — Ion sources include: KBr, NaBr; The Bi(NO3)3·5H2O, the third organic solvent, Br — The mass ratio of the ion source is (4-7):(10-20):

1.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The first organic solvent, the second organic solvent or the third organic solvent is selected from one of ethanol, ethylene glycol and acetic acid.

9. A TiO2 / Bi / X ternary heterostructure photocatalyst prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The TiO2 / Bi / X ternary heterogeneous structure photocatalyst is TiO2 / Bi / BiOI, TiO2 / Bi / Bi2WO6 or TiO2 / Bi / BiOBr.

10. Application of a TiO2 / Bi / X ternary heterostructure photocatalyst in tetracycline degradation.

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