A metal-organic framework / bismuth oxybromide composite photocatalyst and its preparation and application

Abstract

The present invention provides a metal-organic framework / bismuth oxybromide composite photocatalyst and its preparation and application, which relates to the technical field of water pollution detection and environmental catalysis. The metal-organic framework is Ce-MOF. Through hydrothermal reaction, the present invention combines the metal-organic framework with bismuth tetraoxide bromide to form a heterojunction, which modifies the photocatalyst. The structure of the heterojunction endows it with excellent charge mobility and light absorption coefficient in the visible light range, improves the absorption ability of the metal-organic framework / bismuth oxybromide in the visible light range, enhances the separation efficiency of photo-generated electron-hole pairs, increases the distribution of active sites and specific surface area on the surface of the composite photocatalyst, effectively improves the adsorption and photocatalytic performance of the photocatalyst, and thus shows good degradation effect when degrading organic phosphorus pollutants in water.

Description

Technical Field

[0001] The present invention relates to the technical fields of water pollution detection and environmental catalysis, and particularly relates to a metal-organic framework / bismuth oxybromide composite photocatalyst and its preparation and application. Background Art

[0002] Organophosphorus pollutants are a class of compounds containing C-P bonds or phosphate derivatives containing organic groups, which have been widely used in processes such as agriculture, pharmaceuticals, and the materials industry. Inevitably, organophosphorus compounds will enter water environments and soils through various channels, posing non-negligible ecological risks to the environment and causing varying degrees of harm to human health. However, due to their water solubility, recalcitrance, and persistence, the removal of organophosphorus pollutants remains a challenge for researchers at home and abroad.

[0003] Photocatalytic oxidation technology is an effective method for removing organophosphorus pollutants from wastewater, with advantages such as high efficiency, high stability, and low cost-effectiveness. However, a key challenge in this field is that bismuth-based photocatalysts still have problems such as low removal efficiency and low oxidation efficiency for treating organophosphorus pollutants in water. Therefore, a metal-organic framework / bismuth oxybromide composite photocatalytic system has been developed, which has good removal ability for organophosphorus pollutants in water.

[0004] In recent years, bismuth-based photocatalysts have attracted attention due to their stable chemical properties, non-toxicity, good antibacterial properties, and narrow band gaps. Among them, BiOBr has excellent visible light response under visible light due to its narrow band gap, unique electronic structure, and good stability, and is a Bi-based photocatalyst that can effectively improve catalytic activity.

[0005] In the field of photocatalytic degradation, as an important class of photocatalysts, the photocatalytic mechanism of MOFs is due to the transfer of photo-induced electrons from the excited-state linker to the metal node, forming charge-separated transient species participating in the redox process. The complexes in MOFs are regularly arranged in the porous lattice in space, and this structural feature enables the internal charge-separated transients to enter the substrate through the pores, thus having the possibility of charge carrier delocalized migration. Although MOFs have a certain photoexcitation response, their photocatalytic efficiency still needs to be further improved, especially in aspects such as light absorption ability, the matching degree of the energy band position and the reaction redox potential, and efficient charge separation efficiency, where there is still a large room for improvement. Therefore, how to construct a simple and efficient metal-organic framework / bismuth-based composite photocatalyst is an urgent problem to be solved in this field. Summary of the Invention

[0006] The object of the present invention is to provide a metal-organic framework / bismuth oxybromide composite photocatalyst and its preparation and application, and to provide a simple and efficient method for removing organic phosphorus pollutants in water, overcoming the problems of low charge separation efficiency, poor light absorption ability, low efficiency in removing organic phosphorus pollutants in water and low oxidation efficiency in the above-mentioned prior art.

[0007] Another object of the present invention is to provide a metal-organic framework / bismuth-based composite photocatalyst, namely cerium-based metal-organic framework / bismuth oxybromide photocatalyst (Ce-MOF / Bi3O4Br).

[0008] Another object of the present invention is to provide a preparation method of the above-mentioned metal-organic framework / bismuth oxybromide photocatalyst. The preparation method of the present invention can simply and efficiently prepare the above-mentioned metal-organic framework / bismuth-based composite photocatalyst, and the prepared material has excellent photocatalytic performance and accurate selective oxidation performance.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] The present invention provides a metal-organic framework / bismuth oxybromide composite photocatalyst, and the metal-organic framework is Ce-MOF.

[0011] The present invention also provides a preparation method of the above-mentioned metal-organic framework / bismuth oxybromide composite photocatalyst, including the following steps:

[0012] S1: Place bismuth salt in a solvent for the first stirring, then add H2BTC for the second stirring, further add cerium salt solution for the third stirring, and adjust the pH value to obtain a mixed solution;

[0013] S2: Place the mixed solution in a reaction kettle for hydrothermal reaction, and obtain a metal-organic framework / bismuth oxybromide composite photocatalyst after treatment.

[0014] Further, on the basis of the above technical solution, the bismuth salt is bismuth tetroxide bromide;

[0015] and / or, the cerium salt solution is ammonium cerium nitrate solution or cerium chloride solution;

[0016] Preferably, the molar concentration of the cerium salt solution is 0.45 - 0.55M, preferably 0.533M.

[0017] Further, on the basis of the above technical solution, the solvent is dimethylformamide.

[0018] Further, on the basis of the above technical solution, the mass ratio of the cerium salt solution to the solvent is (0.088 - 0.1075):1, preferably 0.1042:1;

[0019] and / or, the mass ratio of the bismuth salt to the cerium salt solution is (0.0254 - 0.5085):1;

[0020] Preferably, the mass ratio of the bismuth salt to the cerium salt solution is 0.05085:1;

[0021] and / or, the mass ratio of the bismuth salt to H2BTC is (0.0847 - 1.695):1, preferably 0.1695:1.

[0022] Further, on the basis of the above technical solution, in step S1, the first stirring is ultrasonic stirring;

[0023] Preferably, the ultrasonic stirring time is 15 - 25 min, preferably 20 min;

[0024] and / or, the second stirring includes:

[0025] The temperature is 22 - 30 °C, the stirring speed is 120 - 140 r / min, and the stirring time is 25 - 35 min, preferably 30 min;

[0026] and / or, the third stirring includes:

[0027] The temperature is 22 - 30 °C, the stirring speed is 120 - 140 r / min, and the stirring time is 25 - 35 min, preferably 30 min;

[0028] and / or, the pH value adjustment includes: using 4.0 mol / L and 0.2 mol / L NaOH solutions to jointly adjust the pH value of the solution to 11.5.

[0029] Further, on the basis of the above technical solution, the hydrothermal reaction includes:

[0030] The temperature is 90 - 100 °C, preferably 100 °C, and the reaction time is 15 - 25 min, preferably 20 min.

[0031] Further, on the basis of the above technical solution, the treatment includes ultrasonic stirring, centrifugation, washing, and drying;

[0032] Preferably, the time of the ultrasonic stirring is 5 - 10 min;

[0033] Preferably, the centrifugation rate is 7000 - 8000 r / min, and the time is 3 - 5 min;

[0034] Preferably, the detergent for washing is anhydrous ethanol and water;

[0035] Preferably, the drying conditions include:

[0036] The drying temperature is 50 - 70 °C, preferably 60 °C, and the drying time is 4 - 8 h.

[0037] The present invention also provides an application of the metal-organic framework / bismuth oxybromide composite photocatalyst as described above or the metal-organic framework / bismuth oxybromide composite photocatalyst prepared by the preparation method of the metal-organic framework / bismuth oxybromide composite photocatalyst as described above.

[0038] Furthermore, on the basis of the above technical solution, the metal-organic framework / bismuth oxybromide composite photocatalyst can be used to remove organic phosphorus pollutants in water.

[0039] A metal-organic framework / bismuth oxybromide composite photocatalyst provided by the present invention and its preparation and application have the following beneficial effects:

[0040] 1. Through hydrothermal reaction, the present invention combines the metal-organic framework with bismuth bromotetroxide to form a heterojunction, modifies the photocatalyst, increases the distribution of active sites and specific surface area on the surface of the composite photocatalyst, effectively improves the adsorption property of the photocatalyst, and thus provides more favorable conditions for the subsequent photocatalytic reaction. In the metal-organic framework / bismuth oxybromide photocatalytic system, the structure of the heterojunction endows it with excellent charge mobility and light absorption coefficient in the visible light range, enhances the absorption ability of the metal-organic framework / bismuth oxybromide in the visible light range, improves the separation efficiency of photo-generated electron-hole pairs, and enhances the photocatalytic performance.

[0041] 2. By regulating the mass ratio of the bismuth-based and metal-organic framework and through hydrothermal reaction, the present invention prepares a metal-organic framework / bismuth oxybromide composite photocatalyst, constructs a heterojunction composed of a Ce-MOF metal-organic framework and a Bi3O4Br inorganic semiconductor, modifies the prepared metal-organic framework / bismuth oxybromide, improves the adsorption property of the photocatalyst, and enhances its photocatalytic performance. And due to the strong interaction between Ce(III) and phosphate, this leads to the formation of CePO4 precipitation, thereby realizing an efficient adsorption process. This strong interaction mainly stems from the strong inner-sphere complexation ability of Ce(III), which shows extremely high affinity for phosphate ions, thus promoting the formation of CePO4 precipitation.

[0042] 3. The metal-organic framework / bismuth oxybromide photocatalysis prepared by the present invention has good photocatalytic performance and has good photocatalytic performance in degrading organic phosphorus pollutants in water. The preparation method has the advantages of simple operation and high efficiency. Description of the Drawings

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings required for the description of the specific embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0044] Figure 1 X-ray diffraction images of the metal-organic framework / bismuth oxybromide composite photocatalysts prepared in Examples 1-4 of the present invention for BTC, and the Bi3O4Br photocatalyst prepared in Comparative Example 1.

[0045] Figure 2 Scanning electron microscope image of the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Example 1 of the present invention at a characteristic size of 500 nm.

[0046] Figure 3 Scanning electron microscope image of the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Example 1 of the present invention at a characteristic size of 5 nm.

[0047] Figure 4 XPS spectra of Bi 4f of the metal-organic framework / bismuth oxybromide composite photocatalyst BBTC-10 prepared in Example 4 of the present invention and the Bi3O4Br photocatalyst prepared in Comparative Example 1.

[0048] Figure 5 XPS spectra of Br 3d of the metal-organic framework / bismuth oxybromide composite photocatalyst BBTC-10 prepared in Example 4 of the present invention and the Bi3O4Br photocatalyst prepared in Comparative Example 1.

[0049] Figure 6 XPS spectra of O1s of BTC, the metal-organic framework / bismuth oxybromide composite photocatalyst BBTC-10 prepared in Example 4 of the present invention, and the Bi3O4Br photocatalyst prepared in Comparative Example 1.

[0050] Figure 7 XPS spectra of Ce 3d of the metal-organic framework / bismuth oxybromide composite photocatalyst BBTC-10 prepared in Example 4 of the present invention.

[0051] Figure 8 XPS spectra of N1s of the metal-organic framework / bismuth oxybromide composite photocatalyst BBTC-10 prepared in Example 4 of the present invention.

[0052] Figure 9The first-order kinetic constant diagram of BTC, the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Examples 1-4 of the present invention, and the Bi3O4Br photocatalyst prepared in Comparative Example 1 for the adsorption and degradation of chloroquine phosphate (CQP).

[0053] Figure 10 The photocatalytic degradation curve diagram of BTC, the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Examples 1-4 of the present invention, and the Bi3O4Br photocatalyst prepared in Comparative Example 1 for CQP under visible light irradiation.

[0054] Figure 11 The comparison diagram of the adsorption capacity and specific surface area of the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Examples 1-4 of the present invention for CQP. Detailed implementation manners

[0055] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention. The process parameters without specific conditions noted in the following embodiments are usually in accordance with conventional conditions.

[0056] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0057] According to the first aspect of the present invention, a metal-organic framework / bismuth oxybromide composite photocatalyst is provided, and the metal-organic framework is Ce-MOF.

[0058] Specifically, in the present invention, Ce-MOF is abbreviated as BTC.

[0059] Through a hydrothermal reaction, the present invention combines a metal-organic framework with bismuth bromide tetraoxide to form a heterojunction, modifying the photocatalyst, increasing the distribution of active sites and specific surface area on the surface of the composite photocatalyst, effectively improving the adsorption property of the photocatalyst, and thus providing more favorable conditions for subsequent photocatalytic reactions. In the metal-organic framework / bismuth oxybromide photocatalytic system described above, the structure of the heterojunction endows it with excellent charge mobility and light absorption coefficient in the visible light range, enhancing the absorption ability of the metal-organic framework / bismuth oxybromide in the visible light range, improving the separation efficiency of photo-generated electron-hole pairs, and enhancing the photocatalytic performance.

[0060] According to the second aspect of the present invention, there is provided a method for preparing the above-mentioned metal-organic framework / bismuth oxybromide composite photocatalyst, comprising the following steps:

[0061] S1: Place a bismuth salt in a solvent for the first stirring, then add H2BTC for the second stirring, further add a cerium salt solution for the third stirring, and after adjusting the pH value, obtain a mixed solution;

[0062] S2: Place the mixed solution in a reaction kettle for hydrothermal reaction, and obtain a metal-organic framework / bismuth oxybromide composite photocatalyst after treatment.

[0063] Specifically, the present invention prepares a metal-organic framework / bismuth oxybromide composite photocatalyst by regulating the mass ratio of the bismuth-based material and the metal-organic framework and through a hydrothermal reaction, constructs a heterojunction composed of a Ce-MOF metal-organic framework and a Bi3O4Br inorganic semiconductor, modifies the obtained metal-organic framework / bismuth oxybromide, improves the adsorption property of the photocatalyst, and enhances its photocatalytic performance. And due to the strong interaction between Ce(III) and phosphate, this leads to the formation of CePO4 precipitation, thus realizing an efficient adsorption process. This strong interaction mainly stems from the strong inner-sphere complexation ability of Ce(III), which shows a very high affinity for phosphate ions, thereby promoting the formation of CePO4 precipitation.

[0064] As an optional implementation manner of the present invention, the bismuth salt is bismuth bromide tetraoxide.

[0065] As an optional implementation manner of the present invention, the cerium salt solution is ammonium cerium nitrate solution or cerium chloride solution;

[0066] Preferably, the molar concentration of the cerium salt solution is 0.45 - 0.55 M, preferably 0.533 M.

[0067] As an optional implementation manner of the present invention, the solvent is dimethylformamide.

[0068] As an alternative embodiment of the present invention, the mass ratio of the cerium salt solution to the solvent is (0.088 - 0.1075):1, preferably 0.1042:1;

[0069] and / or, the mass ratio of the bismuth salt to the cerium salt solution is (0.0254 - 0.5085):1;

[0070] Preferably, the mass ratio of the bismuth salt to the cerium salt solution is 0.05085:1;

[0071] Specifically, the present invention defines the mass ratio of the bismuth salt to the cerium salt solution as (0.0254 - 0.5085):1 because as the mass ratio of Bi3O4Br increases, the photocurrent shows a trend of increasing first and then decreasing. Within the range of the mass ratio of the bismuth salt to the cerium salt solution being (0.0254 - 0.5085):1, the combination of BTC and Bi3O4Br effectively enhances the charge transfer efficiency at the interface, thereby reducing the recombination rate of photo-generated electrons and holes; further, as the mass fraction of Bi3O4Br increases, both the specific surface area and adsorption performance of the composite material show a trend of increasing first and then decreasing. However, too high a content of Bi3O4Br may lead to a reduction in the reaction sites with phosphate ions, thereby affecting the adsorption and reducing the synergistic effect on photocatalysis; and the strong attraction between Ce(III) and phosphate will form CePO4 precipitation. Therefore, only by ensuring that the mass of the cerium salt is higher than that of the bismuth salt solution can a greater adsorption be achieved for the combination between Ce(III) and phosphate.

[0072] and / or, the mass ratio of the bismuth salt to H2BTC is (0.0847 - 1.695):1, preferably 0.1695:1.

[0073] As an alternative embodiment of the present invention, in step S1, the first stirring is ultrasonic stirring;

[0074] Preferably, the ultrasonic stirring time is 15 - 25 min, preferably 20 min;

[0075] and / or, the second stirring includes:

[0076] The temperature is 22 - 30 °C, the stirring speed is 120 - 140 r / min, and the stirring time is 25 - 35 min, preferably 30 min;

[0077] and / or, the third stirring includes:

[0078] The temperature is 22 - 30 °C, the stirring speed is 120 - 140 r / min, and the stirring time is 25 - 35 min, preferably 30 min;

[0079] And / or, adjusting the pH value includes: using 4.0 mol / L and 0.2 mol / L NaOH solutions to synergistically adjust the pH value of the solution to 11.5.

[0080] As an alternative embodiment of the present invention, the hydrothermal reaction includes:

[0081] The temperature is 90 - 100 °C, preferably 100 °C, and the reaction time is 15 - 25 min, preferably 20 min.

[0082] As an alternative embodiment of the present invention, the treatment includes ultrasonic stirring, centrifugation, washing, and drying;

[0083] Preferably, the time for ultrasonic stirring is 5 - 10 min;

[0084] Preferably, the centrifugation rate is 7000 - 8000 r / min, and the time is 3 - 5 min;

[0085] Preferably, the detergent for washing is anhydrous ethanol and water;

[0086] Preferably, the drying conditions include:

[0087] The drying temperature is 50 - 70 °C, preferably 60 °C, and the drying time is 4 - 8 h.

[0088] Specifically, after the hydrothermal reaction, the obtained mixed solution is cooled to room temperature, ultrasonic stirring is carried out for 5 - 10 min, then centrifugation is carried out at a rate of 7000 - 8000 r / min for 3 - 5 min. The supernatant is poured off, and the lower-layer powder is washed alternately with anhydrous ethanol and deionized water several times, placed in an oven, and dried at 50 - 70 °C for 4 - 8 h to obtain the metal-organic framework / bismuth oxybromide composite photocatalyst.

[0089] According to the third aspect of the present invention, there is provided an application of the metal-organic framework / bismuth oxybromide composite photocatalyst as described above or the metal-organic framework / bismuth oxybromide composite photocatalyst prepared by the preparation method as described above.

[0090] Specifically, due to the introduction of the Bi3O4Br component into the Ce-MOF metal-organic framework, the formation of Ce 3+ is promoted. And the increase of Ce 3+ further enhances the adsorption capacity of the Ce-MOF / Bi3O4Br nanosheets for phosphorus-containing organic compounds, showing high specific adsorption performance for phosphorus-containing organic compounds, and providing a new effective strategy for phosphate removal and eutrophication control.

[0091] As an alternative embodiment of the present invention, the metal-organic framework / bismuth oxybromide composite photocatalyst can be used to remove organic phosphorus pollutants in water bodies.

[0092] Specifically, under the excitation of visible light, due to the Z-scheme heterojunction mechanism of Ce-MOF / Bi3O4Br, in the CB of Ce-MOF, e - rapidly migrates to the valence band of / , and at the same time combines with the generated h + This process reduces the recombination rate of photogenerated electrons and holes, effectively inhibits the rapid recombination of photogenerated carriers, enabling a large number of carriers to effectively migrate to the catalyst surface; on the other hand, due to the specific adsorption of Ce-MOF / Bi3O4Br to phosphate, the photogenerated carriers migrating to the catalyst surface more efficiently oxidize the phosphate adsorbed on the catalyst surface. Under the synergistic effect of adsorption and photocatalysis, the phosphate is effectively mineralized into small molecule organic substances, water, and carbon dioxide, with high oxidation efficiency.

[0093] The present invention will be further described in detail below with specific examples and comparative examples.

[0094] Example 1

[0095] This example provides a preparation method of the above-mentioned metal-organic framework / bismuth oxybromide (Ce-MOF / Bi3O4Br) photocatalyst, and the specific steps are as follows:

[0096] The Ce-MOF / Bi3O4Br composite catalyst is synthesized by a one-step hydrothermal method, and the specific steps are as follows:

[0097] Weigh 0.06 g of Bi3O4Br and dissolve it in 12 ml of DMF solution, ultrasonic for 20 min, then add 0.354 g of H2BTC to the mixed solution. Under the condition of a temperature of 25 °C, stir at a stirring speed of 140 r / min for 30 min. Further add 4 ml of (NH4)2Ce(NO3)6 solution with a molar concentration of 0.533 M, and under the condition of a temperature of 25 °C, stir at a stirring speed of 140 r / min for 30 min to obtain a mixed solution;

[0098] Pour the mixed solution into a 100 ml reaction kettle and heat it at 100 °C for 20 min; after the reaction kettle cools to room temperature, perform ultrasonic stirring for 10 min, then perform centrifugation at a centrifugation rate of 7000 r / min for 3 min. Pour off the supernatant, wash the yellow powder at the bottom with anhydrous ethanol and deionized water alternately for several times, place it in a drying oven, and dry it at 60 °C for 8 h to obtain the metal-organic framework / bismuth oxybromide composite photocatalyst, named BBTC-10.

[0099] Example 2

[0100] This embodiment provides a preparation method of the above-mentioned metal-organic framework / bismuth oxybromide (Ce-MOF / Bi3O4Br) photocatalyst, and the specific steps are as follows:

[0101] The Ce-MOF / Bi3O4Br composite catalyst is synthesized by a one-step hydrothermal method, and the specific steps are as follows:

[0102] Weigh 0.03 g of Bi3O4Br and dissolve it in 12 ml of DMF solution, ultrasonicate for 20 min, then add 0.354 g of H2BTC to the mixed solution, and under the condition of a temperature of 25 °C, stir at a stirring speed of 140 r / min for 30 min. Further add 4 ml of a (NH4)2Ce(NO3)6 solution with a molar concentration of 0.533 M, and under the condition of a temperature of 25 °C, stir at a stirring speed of 140 r / min for 30 min to obtain a mixed solution;

[0103] Pour the mixed solution into a 100 ml autoclave and heat it at 100 °C for 20 min; after the autoclave is cooled to room temperature, perform ultrasonic stirring for 10 min, then perform centrifugation at a centrifugation rate of 7000 r / min for 3 min, pour off the supernatant, wash the yellow powder in the lower layer with anhydrous ethanol and deionized water alternately several times, place it in an oven, and dry it at 60 °C for 8 h to obtain a metal-organic framework / bismuth oxybromide composite photocatalyst, named BBTC-5.

[0104] Example 3

[0105] This embodiment provides a preparation method of the above-mentioned metal-organic framework / bismuth oxybromide (Ce-MOF / Bi3O4Br) photocatalyst, and the specific steps are as follows:

[0106] The Ce-MOF / Bi3O4Br composite catalyst is synthesized by a one-step hydrothermal method, and the specific steps are as follows:

[0107] Weigh 0.102 g of Bi3O4Br and dissolve it in 12 ml of DMF solution, ultrasonicate for 20 min, then add 0.354 g of H2BTC to the mixed solution, and under the condition of a temperature of 25 °C, stir at a stirring speed of 140 r / min for 30 min. Further add 4 ml of a (NH4)2Ce(NO3)6 solution with a molar concentration of 0.533 M, and under the condition of a temperature of 25 °C, stir at a stirring speed of 140 r / min for 30 min to obtain a mixed solution;

[0108] Pour the mixed solution into a 100 ml reaction kettle and heat it at 100 °C for 20 min. After the reaction kettle is cooled to room temperature, perform ultrasonic stirring for 10 min, then perform centrifugation at a centrifugation rate of 7000 r / min for 3 min. Pour off the supernatant, wash the yellow powder in the lower layer with anhydrous ethanol and deionized water alternately for several times, place it in a drying oven, and dry it at 60 °C for 8 h to obtain a metal-organic framework / bismuth oxybromide composite photocatalyst named BBTC-17.

[0109] Example 4

[0110] This example provides a preparation method of the above-mentioned metal-organic framework / bismuth oxybromide (Ce-MOF / Bi3O4Br) photocatalyst, and the specific steps are as follows:

[0111] Synthesize the Ce-MOF / Bi3O4Br composite catalyst by a one-step hydrothermal method, and the specific steps are as follows:

[0112] Weigh 0.6 g of Bi3O4Br and dissolve it in 12 ml of DMF solution, ultrasonicate for 20 min, then add 0.354 g of H2BTC to the mixed solution, and stir at a stirring speed of 140 r / min at a temperature of 25 °C for 30 min. Further add 4 ml of (NH4)2Ce(NO3)6 solution with a molar concentration of 0.533 M, and stir at a stirring speed of 140 r / min at a temperature of 25 °C for 30 min to obtain a mixed solution;

[0113] Pour the mixed solution into a 100 ml reaction kettle and heat it at 100 °C for 20 min. After the reaction kettle is cooled to room temperature, perform ultrasonic stirring for 10 min, then perform centrifugation at a centrifugation rate of 7000 r / min for 3 min. Pour off the supernatant, wash the yellow powder in the lower layer with anhydrous ethanol and deionized water alternately for several times, place it in a drying oven, and dry it at 60 °C for 8 h to obtain a metal-organic framework / bismuth oxybromide composite photocatalyst named BBTC-100.

[0114] Comparative Example 1

[0115] This comparative example provides a preparation method of a bismuth oxybromide Bi3O4Br photocatalyst, and the specific steps are as follows:

[0116] Bi3O4Br nanosheets were synthesized by a simple hydrothermal method. The specific steps are as follows. First, 2.910 g of Bi(NO3)3·5H2O and 2.4 g of PVP were dissolved in 200 mL of a 3.643 g mannitol solution (0.1 mol / L), and stirred for 30 min. The solution obtained after stirring was named A, and the 40 mL NaBr (1 mM) solution was named B. Subsequently, solution B was added dropwise to solution A using an acid burette. After vigorous stirring for 30 min, 4 mol / L and 0.2 mol / L NaOH solutions were used to adjust the pH value of the above AB mixed solution to 11.5. The mixed solution with the adjusted pH was poured into a reaction kettle and heated at 160 °C for 24 hours. Finally, Bi3O4Br nanosheets were collected by centrifugation, rinsed three times with deionized water, and dried at 60 °C for 8 hours.

[0117] In this comparative example, no metal-organic framework was added, and the prepared photocatalyst was bismuth oxybromide Bi3O4Br.

[0118] Photocatalytic performance test and characterization

[0119] The photocatalytic performance of the metal-organic framework / bismuth oxybromide composite photocatalysts prepared in Examples 1-4 and Bi3O4Br prepared in Comparative Example 1 was tested by degrading chloroquine phosphate (CQP, 1 mg / L) under visible light within 15 min. The photocatalytic performance test is as follows:

[0120] The liquid level distance between the light source and the catalytic reaction system is 12 cm, and the light intensity of the reactor is stabilized at 0.99 W / cm. In a typical photocatalytic degradation experiment, 20 mg of the photocatalyst was dispersed in 100 mL of CQP solution (1 mg / L), and ultrasonic treatment was carried out for 1 min to make the suspension evenly dispersed. Then the above suspension was transferred to a photoreactor. Before illumination, the suspension was stirred in the dark for 30 min to achieve adsorption-desorption equilibrium between the catalyst and the reactants. Then the xenon lamp (500 W) was turned on for photocatalytic reaction. The reactor was maintained at 25 °C using a constant temperature heating magnetic stirrer. At certain time intervals, 2 mL of the suspension was taken and filtered through a 0.22-μm filter to analyze the concentration of residual pollutants. The concentration of CQP was detected by a UPLC system (Waters, ACQUITY UPLC H-CLASS) using a BEH-C18 column and a Waters 486 tunable UV absorption detector. In the experiment to verify the recycling performance, the suspension was centrifuged (11,000 rpm, 3×3 min), the catalyst was collected and dried at 60 °C for 8 hours, and the degradation experiment was carried out by adding 100 mL of CQP solution (1 mg / L) at the end of each cycle. The above experimental steps were repeated to obtain the suspension, and the CQP concentration was detected by a UPLC system (Waters, ACQUITY UPLC H-CLASS) using a BEH-C18 column and a Waters 486 tunable UV absorption detector to explore the recycling performance of the catalyst.

[0121] Photocatalytic performance tests and characterizations were carried out on the metal-organic framework / bismuth oxybromide (Ce-MOF / Bi3O4Br or BTC / Bi3O4Br) composite photocatalysts prepared in Examples 1-4 and the bismuth oxybromide (Bi3O4Br) photocatalyst prepared in Comparative Example 1. The specific tests and characterizations are as follows:

[0122] Through TEM detection, its transmission electron microscopy spectrum was analyzed to obtain its microscopic morphology and particle size distribution; through XPS detection, the chemical state and composition of the sample surface were analyzed, and the concentration information of oxygen vacancies on the sample surface could be obtained. Through the above characterization means, a more in-depth study was carried out on the material structure and physicochemical properties of the above metal-organic framework Ce-MOF / bismuth oxybromide composite catalyst.

[0123] Figure 1 are the X-ray diffraction images of BTC, the metal-organic framework / bismuth oxybromide composite photocatalysts prepared in Examples 1-4 of the present invention, and the Bi3O4Br photocatalyst prepared in Comparative Example 1.

[0124] In the curve of the pure Bi3O4Br sample, the characteristic peaks at 23.9°, 27.8°, 29.0°, 31.4°, 42.7°, 44.9° and 54.3° match the (112), (006), (114), (020), (123) and (206) crystal planes of Bi3O4Br (JCPDS 84-0793) respectively, confirming that the synthesized bismuth-based catalyst is Bi3O4Br. At the same time, characteristic peaks corresponding to the crystal planes of Bi3O4Br and characteristic peaks belonging to BTC can be observed in the composite catalyst samples BBTC-X (BBTC-5, BBTC-10, BBTC-17, BBTC-100), and the higher the proportion of BTC in the composite heterojunction, the stronger the characteristic peaks belonging to BTC in the BBTC-X samples. This result once again proves that the photocatalyst synthesized in this chapter is a BTC / Bi3O4Br composite heterojunction.

[0125] Figure 2 Scanning electron microscope image of the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Example 1 of the present invention at a characteristic size of 500 nm.

[0126] Among them, Bi3O4Br has a two-dimensional nanosheet structure, while Ce-MOF (abbreviated as BTC) has a one-dimensional rod-like structure, and the two grow together relatively closely.

[0127] Figure 3 Scanning electron microscope image of the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Example 1 of the present invention at a characteristic size of 5 nm.

[0128] From Figure 3 it can be observed that obvious lattice fringes appear in some regions, and the measured lattice spacings are 0.285 nm and 0.374 nm respectively, which belong to the (020) and (200) crystal planes of Bi3O4Br; in another part of the region, two shapes are observed in all Ce-MOF / Bi3O4Br composite materials, indicating that a heterostructure between Ce-MOF and Bi3O4Br is expected to form. Especially during the preparation process, with the increase of the Ce-MOF addition amount, more rod-like morphologies corresponding to Ce-MOF are found, indicating that this part belongs to Ce-MOF. At the same time, a tight interface can also be observed between the two parts, indicating that the two are not simply physically mixed, but a heterojunction structure is formed by BTC and Bi3O4Br, which can provide a transmission channel for photo-generated carriers and contribute to the enhancement of photocatalytic activity.

[0129] Figures 4 - 8XPS spectra of Bi 4f, Br 3d, O 1s, Ce 3d, and N 1s of BTC, the metal-organic framework / bismuth oxybromide composite photocatalyst BBTC-10 prepared in Example 4 of the present invention, and the Bi3O4Br photocatalyst prepared in Comparative Example 1, respectively.

[0130] The Bi 4f peaks at 158.6 eV and 164.0 eV in Bi3O4Br also shift to higher binding energies at 159.6 eV and 165.0 eV in the BBTC-10 composite. Similarly, the Br 3d peaks at 67.9 eV and 69.0 eV in Bi3O4Br also shift to higher binding energies at 68.5 eV and 69.6 eV in the BBTC-10 composite. Observing the O 1s spectrogram, compared with the O 1s peaks at 529.3 eV, 530.9 eV, and 532.1 eV in Bi3O4Br, they shift to higher binding energies of 529.9 eV, 531.5 eV, and 532.7 eV. The new characteristic peak at 529.9 eV in BBTC-10 originates from oxygen atoms bonded to metallic Bi. At the same time, the three different peaks at 529.9 eV, 531.5 eV, and 532.7 eV in BBTC-10 indicate that there are three different types of O atoms on the surface of the prepared catalyst, and these O species are attributed to lattice oxygen, surface hydroxyl, and adsorbed oxygen, respectively.

[0131] Compared with pure BTC, the binding energies of Ce and N elements in the BBTC-10 composite shift to lower values after the formation of the composite compared with pure BTC. This result indicates that there is an effective electronic interaction and electron transfer between BTC and Bi3O4Br during the composite process, and electrons flow from Bi3O4Br into BTC, which is consistent with the Z pathway. A total of 10 peaks can be observed from the Ce 3d spectrum. The characteristic peaks near 917.8 eV, 886.3 eV, 883.6 eV, and 881.8 eV belong to Ce 4+ . And the characteristic peak near 889.1 eV belongs to Ce 3+ . Comparing with pure BTC, the proportion of Ce 3+ / Ce 4+ on the surface of the BBTC-10 composite photocatalyst is larger. The results show that in pure BTC and the BBTC-10 composite photocatalyst, Ce coexists in two valence states, and the introduction of the Bi3O4Br component promotes Ce 3+Generation. By observing the N 1s spectrogram, the N 1s peaks at 400.7 eV, 402.6 eV, and 407.4 eV in BTC also shift towards lower binding energies at 400.3 eV, 402.2 eV, and 407.0 eV in the BBTC-10 composite. In summary, the XPS results clearly demonstrate the successful preparation of the BTC / Bi3O4Br heterojunction catalyst.

[0132] Figure 9 It is the first-order kinetic constant graph of BTC, the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Examples 1-4 of the present invention, and the Bi3O4Br photocatalyst prepared in Comparative Example 1 for the adsorption and degradation of chloroquine phosphate (CQP).

[0133] To further explore the strengthening law of the catalytic activity of the BBTC-X heterojunction under light irradiation, we fitted the degradation kinetics, and the data are shown in the figure. The pseudo-first-order kinetic constant K values of BTC, Bi3O4Br, BBTC-5, BBTC-10, BBTC-17, and BBTC-100 for the photocatalytic degradation of chloroquine phosphate (CQP) are 0.0161, 0.0161, 0.0429, 0.0728, and 0.0443, respectively. Compared with pure BTC and Bi3O4Br, the pseudo-first-order kinetic constants of the composite photocatalyst BBTC-X are greater than both of them, indicating that the combination of BTC and Bi3O4Br enhances the degradation of CQP in the photocatalytic reaction system. At the same time, the photocatalyst with 10% BTC loading, BBTC-10, has the optimal composite ratio. In summary, the good adsorption and photocatalytic properties of BBTC-X can be used to further explore the adsorption-catalysis synergistic effect of BBTC-X.

[0134] Figure 10 It is the photocatalytic degradation curve graph of BTC, the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Examples 1-4 of the present invention, and the Bi3O4Br photocatalyst prepared in Comparative Example 1 for CQP under visible light irradiation.

[0135] Before delving into the photocatalytic performance of BBTC-X, we first systematically discussed its adsorption performance for CQP under dark conditions. The data in the figure clearly show that within the initial 4 minutes in the dark environment, the adsorption rates of CQP by the BTC, Bi3O4Br, BBTC-5, BBTC-10, BBTC-17, and BBTC-100 samples are 44%, 5%, 39%, 40%, 16%, and 5% respectively. This phenomenon is mainly attributed to the occupation of surface active sites, that is, under dark conditions, the active sites on the material surface are rapidly occupied by CQP molecules, thereby reaching a preliminary adsorption equilibrium. As the dark adsorption time extends to 20 minutes, the adsorption rates of CQP by each sample gradually stabilize at 77%, 10%, 62%, 71%, 40%, and 10% respectively. This stabilization process is due to the dynamic equilibrium reached between the adsorption and desorption processes on the surface. It is worth noting that the BBTC-X material composed of BTC and Bi3O4Br exhibits good adsorption performance. In particular, as the content of BTC increases, the adsorption performance of BBTC-X shows a trend of increasing first and then decreasing, which may be related to the interaction between BTC and Bi3O4Br and the distribution of active sites on the material surface. Subsequently, the catalytic degradation ability of BBTC-X for CQP in the photocatalytic system was investigated. As can be seen from the figure, after 2 minutes of light irradiation, the degradation rates of CQP by BTC, Bi3O4Br, BBTC-5, BBTC-10, BBTC-17, and BBTC-100 further reach 82%, 10%, 80%, 95%, 75%, and 10% on the basis of adsorption equilibrium. After 4 minutes of light irradiation, the degradation rates of CQP by BTC, Bi3O4Br, BBTC-5, BBTC-10, BBTC-17, and BBTC-100 are 80%, 12%, 68%, 95%, 62%, and 13% respectively. Compared with pure BTC and Bi3O4Br, BBTC-10 shows better degradation effect, indicating that the combination of BTC and Bi3O4Br enhances the photocatalytic performance of Bi3O4Br.

[0136] Figure 11 Comparison chart of CQP adsorption capacity and specific surface area of the metal-organic framework / bismuth oxybromide composite photocatalyst prepared in Examples 1-4 of the present invention.

[0137] As the specific surface area of the composite photocatalyst BBTC-X increases, its adsorption capacity for CQP also shows a gradually increasing trend, indicating that the increase in specific surface area helps to improve the adsorption performance of the photocatalyst, thereby providing more favorable conditions for subsequent photocatalytic reactions.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A metal organic framework / bismuth oxybromide composite photocatalyst, characterized in that: The metal organic framework is Ce-MOF; The preparation method of the metal organic framework / bismuth oxybromide composite photocatalyst comprises the following steps: S1: placing the bismuth salt in a solvent and stirring it for the first time, then adding H2BTC and stirring it for the second time, further adding the cerium salt solution and stirring it for the third time, and adjusting the pH value to obtain a mixed solution; S2: placing the mixed solution in a reactor for hydrothermal reaction, and obtaining a metal organic framework / bismuth oxybromide composite photocatalyst after treatment; The bismuth salt is tribismuth bromine tetroxide; The mass ratio of the bismuth salt to the cerium salt solution is (0.0254-0.5085):

1.

2. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 1, characterized in that: The cerium salt solution is ammonium cerium nitrate solution or cerium chloride solution.

3. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 2, characterized in that: The molar concentration of the cerium salt solution is 0.45-0.55M.

4. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 3, characterized in that: The molar concentration of the cerium salt solution is 0.533M.

5. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 1, characterized in that: The solvent is dimethylformamide.

6. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 1, characterized in that: The mass ratio of the cerium salt solution to the solvent is (0.088-0.1075):1; And / or, the mass ratio of the bismuth salt to the H2BTC is (0.0847-1.695):

1.

7. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 6, characterized in that: The mass ratio of the cerium salt solution to the solvent is 0.1042:

1.

8. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 6, characterized in that: The mass ratio of the bismuth salt to the H2BTC is 0.1695:

1.

9. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 1, characterized in that: The mass ratio of the bismuth salt to the cerium salt solution is 0.05085:

1.

10. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 1, characterized in that: In step S1, the first stirring is ultrasonic stirring; And / or, the second stirring comprises: The temperature is 22-30℃, the stirring speed is 120-140r / min, and the stirring time is 25-35min; And / or, the third stirring comprises: The temperature is 22-30℃, the stirring speed is 120-140r / min, and the stirring time is 25-35min; And / or, the adjusting the pH value comprises: using 4.0 mol / L and 0.2 mol / L NaOH solutions to coordinately adjust the pH value of the solution to 11.

5.

11. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 10, characterized in that: The ultrasonic stirring time is 15-25 min.

12. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 11, characterized in that: The ultrasonic stirring time is 20 min.

13. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 10, characterized in that: The stirring time of the second stirring is 30 min.

14. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 10, characterized in that: The stirring time of the third stirring is 30 min.

15. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 1, characterized in that: The hydrothermal reaction comprises: The temperature is 90-100°C and the reaction time is 15-25 minutes.

16. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 15, characterized in that: The temperature of the hydrothermal reaction is 100° C. and the reaction time is 20 min.

17. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 1, characterized in that: The treatment includes ultrasonic agitation, centrifugation, washing and drying.

18. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 17, characterized in that: The ultrasonic stirring time is 5-10 min.

19. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 17, characterized in that: The centrifugal speed is 7000-8000 r / min, and the time is 3-5 min.

20. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 17, characterized in that: The washing detergent is anhydrous ethanol and water.

21. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 17, characterized in that: The drying conditions include: The drying temperature is 50-70℃ and the drying time is 4-8h.

22. The metal organic framework / bismuth oxybromide composite photocatalyst according to claim 21, characterized in that: The drying temperature is 60°C.

23. Use of the metal organic framework / bismuth oxybromide composite photocatalyst as claimed in any one of claims 1 to 22.

24. The use of the metal organic framework / bismuth oxybromide composite photocatalyst according to claim 23, characterized in that: The metal organic framework / bismuth oxybromide composite photocatalyst can be used to remove organic phosphorus pollutants in water bodies.

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