A Eu-MOF / BiOBr hybrid material and its preparation method and application in photocatalytic reduction of CO2

Abstract

This application relates to a Eu-MOF / BiOBr hybrid material, its preparation method and application in photocatalytic reduction of CO2, belonging to the field of photocatalysis technology. This application proposes a hybrid material with a heterostructure formed by nanoflower-like BiOBr and rod-like Eu-MOF. The internal resistance of electron transfer at the heterostructure interface is significantly reduced, which is conducive to the directional migration of photo-generated electrons, increasing the electron-hole separation efficiency and having good catalytic effect. This hybrid material can be used as a catalyst for photocatalytic reduction of CO2.

Description

Technical Field

[0001] The present invention relates to the field of photocatalytic technology, and in particular to a Eu-MOF / BiOBr hybrid material and a preparation method thereof and a method for photocatalytic reduction of CO 2 Application in. Background Art

[0002] Greenhouse gas CO 2 Conversion into carbon-based fuels is one of the most effective solutions to the greenhouse effect. 2 The typical process of CO reduction involves capturing sunlight, separating photogenerated carriers, and adsorbing and activating CO 2 As with the short-board effect, the synergistic effect of these processes determines the overall efficiency. However, current inorganic materials generally exhibit weak CO 2 Electron-hole adsorption and rapid recombination. Meanwhile, organic metal frameworks exhibit thermal aggregation and low electron-hole separation efficiency. How to design organic metal frameworks with high CO 2 The adsorption and rapid separation of photogenerated carriers from materials is a major challenge.

[0003] Bismuth-based materials have attracted extensive attention in the field of photocatalysis due to their stable physicochemical properties and unique structures. In particular, ternary metal oxides BiOX (X = Cl, Br, I) have good photocatalytic performance due to their suitable band gap and band position. However, due to the weak built-in electric field on its surface, the internal electron-hole separation efficiency of BiOBr is low. In addition, the specific surface area of ​​BiOBr mainly comes from the interlayer stacking between sheets, and the small specific surface area limits its CO 2 Currently, most reports only involve the separation of photogenerated BiOBr carriers by doping components or constructing heterojunctions.

[0004] Metal-organic frameworks (MOFs) have attracted much attention due to their flexible coordination environment, tunable electronic structure and strong adsorption capacity for gas molecules. But in fact, the photogenerated carrier separation efficiency of MOF materials is actually much lower than that of traditional inorganic photocatalysts. Whether better photocatalytic performance can be obtained by surface hybridization of MOF materials with traditional inorganic photocatalysts, which not only obtains two advantages but also makes up for their shortcomings.

[0005] Based on this, the present invention proposes a Eu-MOF / BiOBr hybrid material. Summary of the invention

[0006] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a Eu-MOF / BiOBr hybrid material and a preparation method thereof and a method for photocatalytic reduction of CO 2In the application of BiOBr nanoflowers, the photocatalytic performance is improved by hybridizing Eu-MOF materials.

[0007] The technical solution of the present invention is as follows:

[0008] A Eu-MOF / BiOBr hybrid material, wherein nano-flower-like BiOBr and rod-like Eu-MOF form a heterogeneous structure.

[0009] The preparation method of the above-mentioned Eu-MOF / BiOBr hybrid material comprises the following steps:

[0010] S1. Preparation of BiOBr nanoflowers

[0011] Dissolve bismuth nitrate in water to obtain solution A, and dissolve bromide in water to obtain solution B; slowly add solution A to solution B and stir evenly; adjust the pH to neutral with ammonia water, and add PVP to obtain a mixed solution; place the mixed solution in a high-pressure reactor, and perform a hydrothermal reaction at 170-190° C. for 20-28 hours; cool to room temperature, filter, wash, and dry to obtain;

[0012] Wherein, the dosage ratio of bismuth nitrate, bromide salt and PVP is 2-3mmol:2-3mmol:500mg;

[0013] S2. Preparation of rod-shaped Eu-MOF

[0014] It is prepared by hydrothermal method using europium nitrate and trimesic acid as raw materials;

[0015] S3. Preparation of Eu-MOF / BiOBr

[0016] The nano-flower-like BiOBr prepared in step S1 is dissolved in anhydrous ethanol, and the rod-like Eu-MOF prepared in step S2 is added, and the mixture is stirred for 20-28 hours by an electrostatic self-assembly method at room temperature and pressure, and then filtered, washed, and dried to obtain the product;

[0017] Among them, the usage of rod-shaped Eu-MOF is 14-17% of nanoflower-shaped BiOBr.

[0018] Furthermore, in step S1, the usage ratio of bismuth nitrate, bromide salt and PVP is 2.5mmol:2.5mmol:500mg.

[0019] Furthermore, in step S1, a hydrothermal reaction is carried out at 180° C. for 24 hours.

[0020] Furthermore, in step S2, the specific process of the hydrothermal preparation is:

[0021] Completely dissolve europium nitrate and trimesic acid in a molar ratio of 1:1 in DMF; transfer to a stainless steel autoclave lined with polytetrafluoroethylene, heat at 120-140°C for 10-14 h, collect the product, wash and dry.

[0022] Furthermore, in step S2, heating is performed at 130° C. for 12 h.

[0023] Furthermore, in step S3, the amount of the rod-shaped Eu-MOF is 17% of the nanoflower-shaped BiOBr.

[0024] The above Eu-MOF / BiOBr hybrid material was used as a catalyst in the photocatalytic reduction of CO 2 Application in.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The Eu-MOF / BiOBr hybrid material provided by the present invention has a simple preparation method, utilizes Eu-MOF material to improve the photogenerated carrier separation efficiency and adsorption capacity of BiOBr, has high photocatalytic activity, and can greatly improve the photocatalytic reduction of CO 2 efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 XRD spectra of BiOBr, Eu-MOF and 17% Eu-MOF / BiOBr prepared in the examples of the present invention;

[0029] Figure 2 This is the transmission electron microscopy image of 17%Eu-MOF / BiOBr;

[0030] Among them, (a) is a transmission electron microscope image, (b) is a HRTEM image, (c) is a HADDF image, and (d)-(h) are different element mapping images;

[0031] Figure 3 This is the XPS test fitting result of 17%Eu-MOF / BiOBr;

[0032] Figure 4 This is the EPR test result of 17%Eu-MOF / BiOBr;

[0033] Figure 5 Characterization of the electrochemical performance of BiOBr, Eu-MOF, 14%Eu-MOF / BiOBr, 17%Eu-MOF / BiOBr and 20%Eu-MOF / BiOBr;

[0034] Among them, (a) is the AC impedance spectrum; (b) is the transient photocurrent spectrum; (c) is the steady-state fluorescence spectrum;

[0035] Figure 6 Photocatalytic reduction of CO by BiOBr, Eu-MOF, 14%Eu-MOF / BiOBr, 17%Eu-MOF / BiOBr, and 20%Eu-MOF / BiOBr 2 performance. DETAILED DESCRIPTION

[0036] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. The following content is only an example and explanation of the concept of the present invention. The technicians in the relevant technical field make various modifications or supplements to the specific implementation cases described or replace them with similar methods. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0037] Unless otherwise specified, the raw materials, equipment, etc. involved in the present invention are common commercially available products.

[0038] Example 1: A method for preparing a Eu-MOF / BiOBr hybrid material, the steps are as follows:

[0039] S1. Preparation of BiOBr nanoflowers

[0040] 1.2125 g (2.5 mmol) Bi(NO 3 ) 3 ·5H 2 O was added to 25 mL of deionized water and fully dissolved, and the solution was labeled A. Then 0.2575 g (2.5 mmol) NaBr was added to 25 mL of deionized water and fully dissolved, and the solution was labeled B. Solution A was slowly added to solution B, and the mixture was stirred for 30 min. The mixed solution was adjusted to pH 7 with 5% ammonia solution, and 500 mg PVP was added. The above solution was slowly poured into a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and hydrothermal at 180 ° C for 24 h. After the sample was cooled to room temperature, it was filtered, washed three times with deionized water and anhydrous ethanol respectively, and dried in a vacuum oven for 10 h to obtain white solid BiOBr.

[0041] S2. Preparation of Eu-MOF

[0042] 4.0 mmol Eu(NO 3 ) 3 .6·H 2 O and 4.0 mmol H 3 BTC (tricresyl ether) was completely dissolved in 60 ml DMF at room temperature. The mixture was then transferred to a 100 ml polytetrafluoroethylene-lined stainless steel autoclave and heated at 130 °C for 12 h to synthesize white Eu-MOF crystals. Finally, the product was collected, washed with DMF and water, and then dried at 60 °C for 12 h to obtain white solid Eu-MOF.

[0043] S3. Preparation of Eu-MOF / BiOBr

[0044] 100 mg of the prepared BiOBr was placed in a beaker containing 20 ml of anhydrous ethanol, and Eu-MOF with a BiOBr dosage of 17% was added. It was fully fused by electrostatic self-assembly method at room temperature and pressure (continuous stirring for 24 hours). After the sample was cooled to room temperature, it was filtered, washed three times with deionized water and anhydrous ethanol respectively, and dried in a vacuum oven for 10 hours.

[0045] Embodiment 2: The remaining steps are the same as those of Embodiment 1. The difference is:

[0046] S3. Preparation of Eu-MOF / BiOBr

[0047] 100 mg of the prepared BiOBr was placed in a beaker containing 20 ml of anhydrous ethanol, and 14% of Eu-MOF was added to the BiOBr. The mixture was fully fused by electrostatic self-assembly at room temperature and pressure (stirring was continued for 20 h). After the sample was cooled to room temperature, it was filtered, washed three times with deionized water and anhydrous ethanol respectively, and dried in a vacuum oven for 10 h.

[0048] Embodiment 3: The remaining steps are the same as those in Embodiment 1. The difference is that,

[0049] S3. Preparation of Eu-MOF / BiOBr

[0050] 100 mg of the prepared BiOBr was placed in a beaker containing 20 ml of anhydrous ethanol, and 20% of the Eu-MOF used for BiOBr was added. The mixture was fully fused by electrostatic self-assembly at room temperature and pressure (stirring was continued for 28 h). After the sample was cooled to room temperature, it was filtered, washed three times with deionized water and anhydrous ethanol respectively, and dried in a vacuum oven for 10 h.

[0051] Performance Testing

[0052] X-ray diffraction (Cu Kα-ray) is used to study the crystal structure and phase composition of the catalyst. Figure 1 As shown in the figure, the BiOBr sample shows diffraction peaks at different angles, including 2θ = 10.9°, 21.9°, 25.2°, 31.7°, 32.2°, 32.2°, 39.4°, 46.2°, 46.8°, 50.7°, 56.1°, and 57.1°. These diffraction peaks can be corresponded to different crystal planes of tetragonal BiOBr (PDF#09-0393), namely (001), (002), (101), (102), (110), (112), (200), (113), (104), (114), and (212). Eu-MOF has a wider peak due to its poor crystallinity. The Eu-MOF / BiOBr hybrid material shows the characteristic peaks of Eu-MOF on the basis of the BiOBr diffraction peaks, which preliminarily indicates the successful preparation of organic-inorganic hybrid materials.

[0053] Scanning electron microscopy (SEM, Nova NaNoSEM 450) and transmission electron microscopy (TEM, FEI TalosF200 X) were used to analyze the microscopic information of the catalyst surface and determine the formation of the heterojunction. Figure 2 (a) shows a transmission electron micrograph of 17% Eu-MOF / BiOBr. In the field of view of this photograph, close contact between the flower-shaped BiOBr and the rod-shaped Eu-MOF can still be observed, indicating that a heterogeneous structure has been formed. Figure 2 (b) shows the HRTEM image of the contact edge of BiOBr and Eu-MOF in 17% Eu-MOF / BiOBr. It is not difficult to see that the crystalline surfaces of the two different substances are in close contact; the lattice spacing on the left is 0.197 nm, which is the (200) crystal plane of BiOBr / , and the lattice on the right is fuzzy, which is the bad crystal plane of Eu-MOF. Figure 2 The HADDF image shown in (c) shows Figure 2 From the different element mapping diagrams shown in (d)-(h), it can be seen that the characteristic Bi and Br elements belonging to BiOBr are mainly concentrated on the left side of 17%Eu-MOF / BiOBr, while other elements are cross-linked with each other, and the Eu element belonging to Eu-MOF is mainly distributed on the right side of 17%Eu-MOF / BiOBr.

[0054] XPS technology is used to study the elemental state of the sample surface and analyze the flow direction of electrons in hybrid materials. Figure 3 The fitting results of XPS test show that compared with Eu-MOF, the Eu 3d 5 / 2The electron binding energy of Eu-MOF / BiOBr obviously shifts to the lower binding energy, which once again confirms that the electrons flow from BiOBr to Eu-MOF in 17%Eu-MOF / BiOBr.

[0055] In order to verify the heterojunction type of the hybrid material, EPR tests were performed on BiOBr, Eu-MOF and 17% Eu-MOF / BiOBr. Figure 4 It is obvious that EPR-·O 2- The EPR-·OH results show that the hybrid material does not maintain a high redox potential, indicating that the heterojunction type of the Eu-MOF / BiOBr hybrid material is type II. In addition, the EPR results show that under light conditions, electrons flow from BiOBr to Eu-MOF, which is consistent with the XPS results.

[0056] In order to explore the effect of hybridization strategy on the efficiency of photogenerated carrier separation, a series of characterizations were performed to obtain Figure 5 The larger the radius of the impedance circle in the AC impedance spectrum, the greater the internal resistance of electron transmission, which is less conducive to the separation of photogenerated carriers. Figure 5 (a) shows that Eu-MOF has the largest impedance circle radius. The transfer internal resistance of 17%Eu-MOF / BiOBr hybrid material has no significant change compared with BiOBr. However, compared with Eu-MOF, it has decreased significantly. This shows that the electron transfer internal resistance of 17%Eu-MOF / BiOBr at the interface has decreased significantly, which is conducive to the directional migration of photogenerated electrons. Figure 5 (b) in the figure is the transient photocurrent spectrum of all samples. Three tests were performed alternately under dark-bright conditions. The higher the photocurrent density, the faster the electron-hole separation. Obviously, Eu-MOF has the weakest photocurrent density, which is caused by its own wide band gap and large electron transfer internal resistance. In addition, BiOBr has the second weakest photocurrent density, which is due to its weak built-in electric field on the surface, resulting in its own poor electron-hole separation efficiency. The photocurrent density of the 17% Eu-MOF / BiOBr hybrid material formed by hybridization is significantly enhanced, which indicates that the hybridization of the hybrid material increases the electron-hole separation efficiency. This means that more photogenerated electrons will participate in the photocatalytic reaction, which is beneficial to the improvement of photocatalytic performance. However, with the continuous increase in the mass fraction of Eu-MOF, the BiOBr / Eu-MOF composite separation is improved, and the electron-hole separation efficiency of the material first increases and then decreases. This is due to the thermal agglomeration caused by the excess Eu-MOF and the difficulty of uniform contact with BiOBr. The recombination of electrons and holes in the catalyst will produce fluorescence. Therefore, the higher the fluorescence intensity, the faster the electron-hole recombination. Figure 5(c) in the figure is the steady-state fluorescence spectra of BiOBr, Eu-MOF and 17%Eu-MOF / BiOBr. Among them, the fluorescence intensity of Eu-MOF is the strongest, which indicates that its electron-hole recombination efficiency is the fastest. When BiOBr and Eu-MOF are hybridized, the fluorescence intensity of 17%Eu-MOF / BiOBr decreases significantly, which indicates that the electron-hole separation efficiency of the hybrid material is significantly improved after hybridization.

[0057] The separation efficiency of photogenerated carriers in the heterostructure is higher, which may be because, due to the interfacial interaction between BiOBr and Eu-MOF, the photogenerated electrons migrate from the CB of BiOBr to the CB of Eu-MOF, and the holes migrate from the VB of Eu-MOF to the VB of BiOBr, resulting in rapid separation of electrons and holes and improving the catalytic efficiency. The specific reaction process is as follows: (1) CO2 and water are adsorbed on the surface sites; (2) the photogenerated electrons react with the adsorbed CO2 to generate CO 2 - , then with H + Combination generates a *COOH intermediate; (3) the *COOH intermediate is converted to CO and desorbed from these sites.

[0058] 10 ml of deionized water and 5 mg of catalyst were added to a 50 ml quartz tube. Then, CO was continuously injected into the reactor for 30 minutes. 2 to ensure that the air in the reactor is completely replaced by CO 2 Replacement (stirring during aeration to disperse the sample evenly in the mixed solution). The light source is a 300 W xenon lamp with a 380 nm filter (λ ≥ 380nm). After 2 hours of illumination, 500 μL of the product gas after the reaction was taken for detection and analysis to explore the CO yield. Figure 6 It can be seen that the CO yield of 17% Eu-MOF / BiOBr is 24.64 μmol g -1 h -1 , 14% CO yield was 15.78 μmol g -1 h -1 , 20% CO yield was 18.23 μmol g -1 h -1 . They are much higher than those of BiOBr and Eu-MOF alone, and have excellent CO catalytic selectivity. This shows that the Eu-MOF / BiOBr hybrid material provided in the present invention has excellent catalytic performance and selectivity. The CO yield decreased by only 8.1% after 17% Eu-MOF / BiOBr was reused 5 times, indicating that the Eu-MOF / BiOBr hybrid material of the present invention has good stability and can be recycled.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the principle and scope of the technical solution of the present invention.

Claims

1. A Eu-MOF / BiOBr hybrid material, characterized in that: The nano-flower-like BiOBr and the rod-like Eu-MOF form a heterostructure, and the amount of the rod-like Eu-MOF is 14-17% of the nano-flower-like BiOBr. The preparation method thereof comprises the following steps: S1. Preparation of BiOBr nanoflowers Dissolve bismuth nitrate in water to obtain solution A, and dissolve bromide in water to obtain solution B; slowly add solution A to solution B and stir evenly; adjust the pH to neutral with ammonia water, and add PVP to obtain a mixed solution; place the mixed solution in a high-pressure reactor, and perform a hydrothermal reaction at 170-190° C. for 20-28 hours; cool to room temperature, filter, wash, and dry to obtain; Wherein, the dosage ratio of bismuth nitrate, bromide salt and PVP is 2-3mmol:2-3mmol:500mg; S2. Preparation of rod-shaped Eu-MOF It is prepared by hydrothermal method using europium nitrate and trimesic acid as raw materials; S3. Preparation of Eu-MOF / BiOBr The nano-flower-like BiOBr prepared in step S1 is dissolved in anhydrous ethanol, and the rod-like Eu-MOF prepared in step S2 is added, and the mixture is stirred for 20-28 hours by an electrostatic self-assembly method at room temperature and pressure, and then filtered, washed, and dried to obtain the product.

2. The Eu-MOF / BiOBr hybrid material according to claim 1, characterized in that: In step S1, the usage ratio of bismuth nitrate, bromide salt and PVP is 2.5mmol:2.5mmol:500mg.

3. The Eu-MOF / BiOBr hybrid material according to claim 1, characterized in that: In step S1, a hydrothermal reaction is carried out at 180° C. for 24 h.

4. The Eu-MOF / BiOBr hybrid material according to claim 1, characterized in that: In step S2, the specific process of the hydrothermal preparation is: Completely dissolve europium nitrate and trimesic acid in a molar ratio of 1:1 in DMF; transfer to a stainless steel autoclave lined with polytetrafluoroethylene, heat at 120-140°C for 10-14 h, collect the product, wash and dry.

5. The Eu-MOF / BiOBr hybrid material according to claim 4, characterized in that: In step S2, heating is performed at 130°C for 12 hours.

6. The Eu-MOF / BiOBr hybrid material according to claim 1, characterized in that: In step S3, the amount of the rod-shaped Eu-MOF is 17% of the nanoflower-shaped BiOBr.

7. Use of the Eu-MOF / BiOBr hybrid material according to any one of claims 1 to 6 as a catalyst in photocatalytic reduction of CO2.

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