A dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst, its preparation method and application

Abstract

The present invention belongs to the technical field of photocatalytic CO₂ reduction, and specifically relates to a dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst, its preparation method and application. In the present invention, ZIF-8 and Bi-MOF are first prepared by a solvothermal method. After halogenating Bi-MOF with ammonium bromide, ZIF-8 is in-situ grown, and a composite photocatalyst with a dual-MOFs structure composed of zinc oxide particles with a dodecahedral structure derived from ZIF-8 and bismuth oxybromide derived from Bi-MOF is prepared by a one-step calcination method. Under room temperature, xenon lamp illumination, and without a sacrificial agent, this catalyst can effectively catalyze the reduction of carbon dioxide into carbon monoxide and methane, and has good photocatalytic CO₂ reduction performance, stability and repeatability. This preparation method has low cost, high reproducibility, and mild and controllable preparation conditions, and has broad application prospects in the field of photocatalytic CO₂ reduction.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic nanomaterials, and relates to a preparation method of a zinc oxide / bismuth oxybromide composite photocatalyst derived from dual MOFs. Background Art

[0002] The environmental pollution and energy crisis brought about by the rapid development of the world economy are becoming increasingly serious. Solving these problems is a major challenge faced globally. Since Fujishima and Honda first demonstrated the photoelectrocatalytic decomposition of water on a photoactive semiconductor catalyst in 1972, people have been committed to developing efficient photocatalysts that can collect solar energy and convert it into chemical energy. In the past few decades, various photocatalysts have been developed, including metal oxides, metal sulfides, and organic polymers. Bismuth (Bi)-based catalysts have the application prospect of photocatalytic carbon dioxide reduction due to their rich reserves, non-toxicity, and special electronic structure. Among them, bismuth halides (BiOX; X = Cl, Br, and I) have attracted extensive attention in the photocatalytic reduction of carbon dioxide due to their unique layered structure and optical properties.

[0003] However, the narrow bandgap and low carrier mobility of the BiOBr photocatalyst limit its practical applications. In addition, during the preparation process of BiOBr nanosheets, severe aggregation leads to a decrease in active sites, resulting in lower photocatalytic activity. Metal-organic frameworks (MOFs) are fascinating porous crystalline materials due to their inherent porosity, tunable pore size, and rich surface chemistry. BiOBr derived from bismuth-based metal-organic frameworks (MOFs) can maintain the high specific surface area and ultra-high porosity structure of MOFs, and provide rich active sites and a stable porous structure, but insufficient light response ability and low charge separation efficiency are the main obstacles to its photocatalytic CO2 reduction. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: Based on the above problems, the present invention provides a preparation method of a zinc oxide / bismuth oxybromide composite photocatalyst derived from dual MOFs.

[0005] One technical solution adopted by the present invention to solve its technical problems is: A preparation method of a zinc oxide / bismuth oxybromide composite photocatalyst derived from dual MOFs, comprising the following steps:

[0006] (1) Preparation of Bi-MOF: Dissolve trimesic acid and bismuth nitrate pentahydrate in methanol, stir evenly, and then transfer the solution to a reaction kettle and react at 120 - 160 °C for 8 - 12 h. After the reaction is completed, cool the solution to room temperature, collect the product by centrifugation, then wash it with deionized water and absolute ethanol, and freeze-dry to obtain Bi-MOF;

[0007] (2) Preparation of ZIF-8: Zinc nitrate hexahydrate and 2-methylimidazole were separately dissolved in anhydrous methanol and stirred evenly to obtain a zinc nitrate hexahydrate solution and a 2-methylimidazole solution. Subsequently, the 2-methylimidazole solution was quickly poured into the zinc nitrate hexahydrate solution and stirred evenly. Then, the solution was transferred to a reaction kettle and heated at 100 °C for 12 h. After the reaction ended, the solution was cooled to room temperature, and the product was collected by centrifugation, washed with methanol, and dried to obtain ZIF-8.

[0008] (3) Preparation of the dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst: The Bi-MOF prepared in step (1) was added to deionized water containing ammonium bromide, stirred for 10 - 20 min, then ZIF-8 prepared in step (2) was added, and after stirring evenly, it was stirred in an oil bath at 90 °C for 1 h. The product was collected by centrifugation, washed, vacuum dried, then placed in a muffle furnace and calcined at 350 - 550 °C for 2 h to obtain the dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst.

[0009] Furthermore, the molar ratio of trimesic acid and bismuth nitrate pentahydrate described in step (1) is 36:3.1.

[0010] Furthermore, the molar ratio of zinc nitrate hexahydrate and 2-methylimidazole described in step (2) is 27:64. Furthermore, the mass ratio of ammonium bromide, Bi-MOF, and ZIF-8 described in step (3) is 1.9588:1:0.2856 - 0.8672.

[0011] Application of the dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst prepared by the described method in photocatalytic reduction of carbon dioxide to produce CO and CH4 under visible light.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] The present invention first prepares ZIF-8 and Bi-MOF by a solvothermal method. After halogenating Bi-MOF with ammonium bromide, ZIF-8 is in-situ grown, and then through a one-step calcination method, a dual-MOF photocatalyst composed of dodecahedron-structured zinc oxide particles (ZnO) derived from ZIF-8 and bismuth oxybromide (BiOBr) derived from Bi-MOF is prepared.

[0014] First of all, the in-situ halogenation of the bismuth-based MOF (Bi-MOF) in the present invention to prepare BiOBr with a MOF structure can improve the dispersion of nanosheet-structured BiOBr, and at the same time provide more active sites and a stable porous structure.

[0015] Secondly, a heterojunction is formed between ZnO and BiOBr, which significantly extends the lifetime of photo-generated electrons, improves the light capture ability, obtains higher quantum efficiency, and enhances the separation of photo-generated carriers. Calcination enables the formation of a tight chemical bond of Zn-O-Bi between MOF-derived ZnO and BiOBr, making the resulting composite photocatalyst have a well-matched bandgap and sufficient contact area, which can provide a strong driving force for promoting the transfer of photo-induced charges, contribute to improving the transport and transfer of photo-excited charges, increase the active sites, and broaden the application of such novel composite materials in the field of photocatalysis.

[0016] Finally, the preparation method has low cost, high reproducibility, and mild and controllable preparation conditions. The prepared double-MOF-derived zinc oxide / bismuth oxybromide composite photocatalyst is a green and environmentally friendly photocatalyst, with high photocatalytic reduction activity and stability of CO2. The CO production rate reaches 21.13 μmol·h -1 ·g -1 , which are 6.3 and 4.2 times that of pure bismuth oxybromide and pure zinc oxide respectively, and still maintain good catalytic activity after 4 cycles, showing good stability. Description of the Drawings

[0017] The present invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 It is the preparation flow chart of the double-MOF-derived zinc oxide / bismuth oxybromide composite photocatalyst;

[0019] Figure 2 It is the X-ray diffraction pattern of the photocatalysts prepared in Examples 1-5 and Comparative Examples 1-2 of the present invention;

[0020] Figure 3 It is the scanning electron microscopy image of bismuth oxybromide prepared in Comparative Example 1;

[0021] Figure 4 It is the scanning electron microscopy image of zinc oxide prepared in Comparative Example 2;

[0022] Figure 5 It is the scanning electron microscopy image of the composite photocatalyst prepared in Example 2;

[0023] Figure 6 It is the photocatalytic CO2 reduction effect diagram of the photocatalysts prepared in Examples 1-3 and 5 and Comparative Examples 1-2 of the present invention;

[0024] Figure 7 It is the photocatalytic carbon dioxide reduction experimental cycle diagram of the 20-zinc oxide / bismuth oxybromide composite photocatalyst prepared in Example 2 of the present invention. Detailed Embodiments

[0025] The present invention will now be further described in conjunction with specific embodiments. The following embodiments are intended to illustrate the present invention rather than further limit the present invention.

[0026] Example 1

[0027] (1) Preparation of Bi-MOF powder: 0.75 g of trimesic acid and 0.15 g of bismuth nitrate pentahydrate were dissolved in 60 mL of methanol solution and stirred evenly. Subsequently, the obtained mixture was transferred to a stainless-steel autoclave lined with polytetrafluoroethylene, sealed, and heated at 160 °C for 8 h. After natural cooling, the product was centrifuged, washed with deionized water and ethanol, and freeze-dried overnight to finally obtain Bi-MOF powder.

[0028] (2) Preparation of ZIF-8 powder: 0.81 g of zinc nitrate hexahydrate and 0.526 g of 2-methylimidazole were respectively dissolved in 10 mL of anhydrous methanol solution and 40 mL of anhydrous methanol solution, and stirred evenly to obtain a zinc nitrate hexahydrate solution and a 2-methylimidazole solution. Subsequently, the obtained mixture was transferred to a stainless-steel autoclave lined with polytetrafluoroethylene, sealed, and heated at 100 °C for 12 h. After natural cooling, the product was centrifuged, washed with methanol, and dried at 60 °C overnight. After the reaction, the solution was cooled to room temperature to obtain ZIF-8.

[0029] (3) Preparation of a dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst: 0.25 g of Bi-MOF and 0.4897 g of ammonium bromide were added to 25 mL of deionized water. After stirring for 10 min, 0.0714 g of ZIF-8 was added. After stirring evenly again, it was stirred in an oil bath at 90 °C for 1 h. The product was collected by centrifugation, washed with water and ethanol, vacuum-dried overnight, and then calcined in a muffle furnace at 450 °C at a rate of 1 °C / min for 2 h to obtain a dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst (ZnO / BiOBr-1) with a mass ratio of ZIF-8 to Bi-MOF of 0.2856:1.

[0030] Example 2

[0031] The difference between Example 2 and Example 1 is that: in step (3), the addition amount of ZIF-8 is 0.1429 g, and the others are the same as in Example 1, to obtain a dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst (ZnO / BiOBr-2) with a mass ratio of ZIF-8 to Bi-MOF of 0.5716:1.

[0032] Example 3

[0033] Example 3 is different from Example 2 in that: in step (1), "heating at 160 °C for 8 h" is changed to "heating at 120 °C for 12 h", and the others are the same as in Example 2, to obtain a double-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst (ZnO / BiOBr-3).

[0034] Example 4

[0035] Example 4 is different from Example 2 in that: in step (3), the calcination temperature is changed to 350 °C, and the others are the same as in Example 2, to obtain a double-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst (ZnO / BiOBr-4).

[0036] Example 5

[0037] Example 5 is different from Example 2 in that: in step (3), the calcination temperature is changed to 550 °C, and the others are the same as in Example 2, to obtain a double-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst (ZnO / BiOBr-5).

[0038] Example 6

[0039] Example 6 is different from Example 1 in that: in step (3), the addition amount of ZIF-8 is 0.2143 g, and the others are the same as in Example 1, to obtain a double-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst (ZnO / BiOBr-6) with a mass ratio of ZIF-8 to Bi-MOF of 0.8572:1.

[0040] Comparative Example 1

[0041] Preparation of bismuth oxybromide: Dissolve 0.75 g of trimesic acid and 0.15 g of bismuth nitrate pentahydrate in 60 mL of methanol solution, stir evenly, and then transfer the obtained mixture to a stainless-steel autoclave lined with polytetrafluoroethylene, seal it, and heat it at 160 °C for 8 h. After natural cooling, centrifuge the product, wash it with deionized water and ethanol, and freeze-dry it overnight to finally obtain Bi-MOF powder.

[0042] Add 0.25 g of the prepared Bi-MOF and 0.4897 g of ammonium bromide to 25 mL of deionized water, stir in an oil bath at 90 °C for 1 h, collect the product by centrifugation, wash it with water and ethanol, dry it under vacuum overnight, and then calcine it in a muffle furnace at 450 °C at a rate of 1 °C / min for 2 h to obtain bismuth oxybromide powder after drying and calcination.

[0043] Comparative Example 2

[0044] Preparation of zinc oxide: 0.81 g of zinc nitrate hexahydrate and 0.526 g of 2-methylimidazole were separately dissolved in 10 mL of anhydrous methanol solution and 40 mL of anhydrous methanol solution, and stirred evenly to obtain a zinc nitrate hexahydrate solution and a 2-methylimidazole solution; Subsequently, the obtained mixture was transferred to a stainless steel autoclave lined with polytetrafluoroethylene, sealed and heated at 100 °C for 12 h. After natural cooling, the product was centrifuged, washed with methanol and dried at 60 °C overnight. After the reaction, the solution was cooled to room temperature to obtain ZIF-8 powder. The prepared ZIF-8 powder was calcined in a muffle furnace at a heating rate of 1 °C / min to 450 °C for 2 h to obtain zinc oxide powder.

[0045] The crystal phase structures of the bismuth oxybromide, zinc oxide, and zinc oxide / bismuth oxybromide composite photocatalysts prepared in Examples 1-6 and Comparative Examples 1-2 were analyzed by a Rigaku D / max2500PC X-ray diffractometer. Among them, the X-ray was Cu target Kα The voltage was 40 kV, the current was 100 mA, the step size was 0.02°, and the scanning range was 5-80°. The X-ray diffraction pattern is as Figure 1 shown. Both bismuth oxybromide and zinc oxide had strong diffraction peaks, which matched well with the standard cards, indicating the successful synthesis of bismuth oxybromide and zinc oxide. At the same time, it can be seen that as the content of zinc oxide increased, the diffraction peak of zinc oxide gradually increased.

[0046] If in the preparation of step (3) of Example 2, the calcination temperature was 350 °C or 550 °C and other operations were the same, the crystallinity of the zinc oxide / bismuth oxybromide composite photocatalyst synthesized at this calcination temperature decreased and impurity peaks appeared, which would reduce the photocatalytic carbon dioxide reduction activity.

[0047] [[ID=IS]]The morphologies of the photocatalysts prepared in Example 2 and Comparative Examples 1-2 were observed by a Japanese JSM-6360A scanning electron microscope. From Figures 2 - 4 the scanning electron micrograph, it can be seen that the composite visible light photocatalyst zinc oxide prepared in this embodiment was loaded on the surface of rod-shaped bismuth oxybromide.

[0048] The zinc oxide / bismuth oxybromide composites prepared in Examples 1-6 and Comparative Examples 1-2 were used for photocatalytic carbon dioxide reduction. The specific steps were as follows: Weigh 10 mg of different catalysts and dissolve them in 50 mL of deionized water by ultrasonic treatment. Then, pour the solution into a 370 mL glass reactor and stir continuously. Before illumination, it is necessary to introduce CO2 (99.95%) to evacuate the gas in the reactor. The exhaust process takes about 30 min, and all experiments are carried out at room temperature. In this test, a 300 W xenon lamp was used as the light source. 500 μL of gas was taken with a gas-phase sampling needle every 30 min, and the total illumination time was 3 h. CO and CH4 were detected by the FID signal of gas chromatography. The contents of CO and CH4 were calculated according to the fitting equations obtained from the calibration curve and the external standard method. The experimental results are as Figure 5 shown. The CO production rates of pure bismuth oxybromide and zinc oxide were 3.33 and 5.11 μmol / g / h, respectively, and the CH4 production rates of pure bismuth oxybromide and zinc oxide were 0.54 and 1.11 μmol / g / h, respectively. The CO production rate of ZnO / BiOBr-2 was 21.13 μmol / g / h, which was about 6.3 and 4.1 times that of pure bismuth oxybromide and zinc oxide. The CH4 production rate of ZnO / BiOBr-2 was 2.2 μmol / g / h, which was about 4.1 and 2 times that of pure bismuth oxybromide and zinc oxide. It can be seen that loading zinc oxide can effectively improve the photocatalytic carbon dioxide reduction activity of the composite photocatalyst, and the prepared dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst has high photocatalytic activity.

[0049] To verify the stability of the dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst prepared in the present invention, a photocatalytic carbon dioxide reduction cycle experiment was carried out on the zinc oxide / bismuth oxybromide composite catalyst prepared in Example 2. The experimental results are as Figure 6 shown, indicating that the prepared dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst has good stability.

[0050] Taking the above ideal embodiments based on the present invention as an inspiration, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A preparation method of a dual-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst, characterized in that, It includes the following steps: Add Bi-MOF to deionized water containing ammonium bromide. After stirring for 10 - 20 min, add ZIF-8, stir and react, then centrifuge to collect the product. After washing and drying, calcine it in a muffle furnace to obtain a double-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst.

2. The preparation method of the zinc oxide / bismuth oxybromide composite photocatalyst derived from dual MOFs according to claim 1, characterized in that, The mass ratio of ammonium bromide, Bi-MOF, and ZIF-8 is 1.9588:1:0.2856 - 0.8672.

3. The preparation method of the zinc oxide / bismuth oxybromide composite photocatalyst derived from double MOFs according to claim 1, characterized in that, The stirring reaction temperature is 90 °C and the time is 1 h.

4. The preparation method of the zinc oxide / bismuth oxybromide composite photocatalyst derived from double MOFs according to claim 1, characterized in that, The calcination temperature is 350 - 550 °C and the time is 2 h.

5. The preparation method of the zinc oxide / bismuth oxybromide composite photocatalyst derived from double MOFs according to claim 1, characterized in that, The specific preparation steps of the Bi-MOF are as follows: Dissolve trimesic acid and bismuth nitrate pentahydrate in methanol at a molar ratio of 36:3.

1. Subsequently, transfer this solution to a reaction kettle for hydrothermal reaction. After the reaction is completed, cool the solution to room temperature, collect the product by centrifugation, then wash it with deionized water and absolute ethanol, and obtain Bi-MOF after freeze-drying.

6. The preparation method of the zinc oxide / bismuth oxybromide composite photocatalyst derived from dual MOFs according to claim 5, characterized in that The temperature of the hydrothermal reaction is 120 - 160 °C and the hydrothermal reaction time is 8 - 12 h.

7. The preparation method of the zinc oxide / bismuth oxybromide composite photocatalyst derived from dual MOFs according to claim 1, characterized in that, The specific preparation steps of the ZIF-8 are as follows: Dissolve zinc nitrate hexahydrate and 2-methylimidazole in absolute methanol respectively to obtain a zinc nitrate hexahydrate solution and a 2-methylimidazole solution; quickly pour the 2-methylimidazole solution into the zinc nitrate hexahydrate solution, stir evenly, then transfer this solution to a reaction kettle, react at 100 °C for 12 h. After the reaction is completed, cool the solution to room temperature, collect the product by centrifugation, wash it with methanol, and obtain ZIF-8 after drying.

8. According to the method for preparing a double-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst according to claim 7, the molar ratio of zinc nitrate hexahydrate and 2-methylimidazole is 27:

64.

9. Application of a double-MOFs-derived zinc oxide / bismuth oxybromide composite photocatalyst prepared by the method according to any one of claims 1 - 8 in visible-light catalytic reduction of carbon dioxide to produce CO and CH4.

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