Bismuth-based superlattice material and application thereof in photocatalytic carbon-nitrogen coupling reaction

Abstract

The invention discloses a bismuth-based superlattice material and application thereof in photocatalytic carbon-nitrogen coupling reaction, in the material, Bi4TaO8Cl crystal structure layers and Bi2YO4Cl crystal structure layers are periodically arranged to form a superlattice structure, generation of a series polarization interface can be induced, and the carrier separation life is prolonged, so that the obtained catalyst has higher photocatalytic reaction activity, and the photocatalytic performance of the material is improved. The efficient C-N cross-coupling reaction is realized. The preparation method provided by the invention has the advantages of low synthesis cost, mild reaction conditions, easy control of the reaction conditions and the like, and is easy for large-scale production.

Description

Technical Field

[0001] The invention relates to the fields of nanomaterials and energy and environmental science and engineering, and specifically relates to a bismuth-based superlattice material and its application in photocatalytic carbon-nitrogen coupling reactions. Background Art

[0002] As a core method for integrating nitrogen in organic synthesis, CN-type cross-coupling reactions have attracted considerable research attention due to their widespread applications in pharmaceuticals, materials, and agricultural chemistry. However, existing technologies face significant bottlenecks. Traditional nickel-based catalysts are susceptible to reductive elimination, leading to deactivation of active sites and requiring external reducing agents to maintain the reaction cycle, which severely impacts reaction reproducibility. Therefore, to further improve the performance of CN cross-coupling reactions, solutions to address the issue of metal catalyst deactivation are urgently needed.

[0003] Photogenerated charge carriers in semiconductors can not only drive redox catalytic reactions in inorganic systems, but also provide the required external energy for organic reactions, thereby effectively alleviating the deactivation of metal catalysts. However, the efficiency of photogenerated charge carriers is often hindered by their rapid recombination, which significantly reduces the overall driving force of the reaction. In photocatalytic materials, light excites semiconductors to generate electron-hole pairs as excitons. Exciton dissociation is crucial because it can separate electrons and holes to form free charge carriers necessary to drive catalytic reactions. To solve the problem of low charge separation efficiency, it is necessary to develop highly controllable carrier strategies to enhance the separation ability of charge carriers, which is crucial to improving photocatalytic conversion efficiency. Many scientists have conducted a lot of research work. Among them, patent CN117712205A discloses a heterojunction solar cell that enhances photogenerated carriers, describing the process of enhancing photogenerated excitons and exciton dissociation. In addition, patent CN116078418A discloses a dual P-site doped carbon nitride photocatalyst, its preparation method and application, which utilizes a rich porous structure, high exciton dissociation efficiency, and exhibits efficient photocatalytic performance. In addition, some scientists have studied semiconductor photocatalytic carbon-nitrogen coupling from different angles in an attempt to find a more effective method. For example, Pieber et al. explored the cause of heterogeneous photocatalytic deactivation caused by the deposition of catalytically inert and low-valent nickel species in the article "Overcoming limitations in dual photoredox / nickel-catalysed C–N cross-couplings due to catalyst deactivation" (Nat Catal., 2020, 3, 611–620). In their article, “Acridine-Functionalized Covalent Organic Frameworks (COFs) as Photocatalysts for Metallaphotocatalytic CN Cross-Coupling,” Thomas et al. investigated novel covalent organic frameworks to evaluate their effectiveness in metallaphotocatalytic cyanamide cross-coupling reactions (Angew. Chem. Int. Ed. 2022, 61, e202117738). Currently, combining green and sustainable photocatalytic technology with organic carbon-nitrogen coupling, a key chemical process, is a highly attractive and challenging topic, requiring further research and practice.

[0004] In the BiOX (X = Cl, Br and I) photocatalyst group, the most common photocatalytic semiconductor material, the separation efficiency of photogenerated electrons is significantly improved, mainly due to the lattice effect of the (001) plane in the [X-Bi-O-Bi-X] structure, in which the lattice-induced perpendicular polarization field plays a key role in promoting this effect. A key challenge is how to fully utilize the advantages of this polarization field in a single-phase photocatalyst to provide a strong driving force for efficient charge separation. The present invention notes that these layered compounds have the characteristics of strong covalent bonding within the two-dimensional (2D) layer and weaker interlayer van der Waals interactions perpendicular to the layer. They have similar lattice constants, making them promising candidate materials for forming superlattice structures. Bi x MO y X materials belong to the BiOX family, which is characterized by the insertion of MOy layers within the Bi2O2 layer while retaining the halide ion characteristics. Depending on the choice of M cations, the bond breakage of the Bi-O layer will lead to changes in the local symmetry at the Bi site and provide an adjustable superlattice structural unit. By inserting a YO2 layer into a conventional Bi2O2 layer, a 3-shaped chain structure is formed in Bi2YO4Cl, resulting in high photoconductivity, however, the low conduction band minimum limits the effective transmission and transfer of photogenerated electrons. Bi4TaO8Cl has a layered structure consisting of (Bi2O2) 2+ The structure of these two layered compounds is similar to that of TaO6 perovskite blocks, but more stable. These two layered compounds have similar lattice constants. The strong covalent bonding within the layers and the weaker van der Waals interactions between them enable the formation of a superlattice-like structure through stacking. The unique alternating layered structure of superlattice-like materials provides a promising platform for tandem polarization interfaces, potentially providing stable and sustained driving force for charge separation in photocatalysis. Summary of the Invention

[0005] In order to overcome the bottlenecks of easy deactivation of transition metal catalysts and low traditional photocatalytic efficiency in existing photocatalytic CN coupling reaction systems, the present invention proposes a bismuth-based superlattice material and its application in photocatalytic carbon-nitrogen coupling reactions. The purpose is to induce the generation of series polarization interfaces by constructing a superlattice structure, increase the carrier separation lifetime, so that the obtained catalyst has higher photocatalytic reaction activity and realize efficient CN cross-coupling reaction.

[0006] To achieve the purpose, the present invention adopts the following technical solutions:

[0007] The present invention first provides a bismuth-based superlattice material, in which Bi4TaO8Cl crystal structure layers and Bi2YO4Cl crystal structure layers are periodically arranged to form a superlattice structure.

[0008] Furthermore, when the molar ratio of Bi4TaO8Cl to Bi2YO4Cl in the material is 1:1, the bismuth-based superlattice material is a Bi4TaO8Cl-Bi2YO4Cl nanosheet having a superlattice structure, and the periodic arrangement of the Bi4TaO8Cl crystal structure layer and the Bi2YO4Cl crystal structure layer is: five atomic sublayers [Bi4TaO8] stacked vertically 1+ , [Cl] layer 1 -, three atomic sublayers [Bi2YO4] 1+ 、[Cl] 1- The layers form a period. Multiple complete periods in the middle and a complete or incomplete period on the upper and lower sides form a superlattice structure (that is, the superlattice structure can start and end from any layer in the period).

[0009] The present invention also provides a method for preparing the bismuth-based superlattice material, comprising the following steps:

[0010] Step 1: Weigh Bi2O3, BiOCl, Ta2O5 and Y2O3 and mix them to obtain a mixed salt; add CsCl and NaCl as flux to the mixed salt and grind until uniformly dispersed to obtain a mixed powder.

[0011] Step 2: Transfer the mixed powder to an alumina crucible, heat it to 600-900° C. at a rate of 5-20° C. / min under a nitrogen atmosphere (purity ≥ 99.999%), and keep it at that temperature for 600-1000 minutes; and cool it naturally to room temperature to obtain a sintered product;

[0012] Step 3: Immerse the sintered product in 60-100° C. hot deionized water and stir and wash for multiple times until the conductivity of the filtrate is less than 50 μS / cm; collect the precipitate by suction filtration and dry it in a vacuum drying oven at 40-80° C. for 6-20 hours to obtain a bismuth-based superlattice material.

[0013] Furthermore, the molar ratio of the raw materials in the mixed salt in step 1 is Bi2O3:BiOCl:Ta2O5:Y2O3=4:4:1:1, and the obtained bismuth-based superlattice material is Bi4TaO8Cl-Bi2YO4Cl nanosheets with a superlattice structure.

[0014] Furthermore, in step 1, the mass ratio of CsCl to NaCl is 1 to 3:1.

[0015] Furthermore, in step 1, the mixed salt accounts for 3% to 10% of the total molar amount of the mixed salt and the flux.

[0016] The bismuth-based superlattice material obtained by the present invention can be used as a photocatalyst in a photocatalytic carbon-nitrogen coupling reaction, and can specifically be used to catalyze the carbon-nitrogen coupling reaction of tetrahydropyrrole and aryl bromide to synthesize a coupling product.

[0017] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0018] 1. The present invention synthesizes bismuth-based materials with superlattice structures, such as Bi4TaO8Cl-Bi2YO4Cl nanosheets. The Bi4TaO8Cl and Bi2YO4Cl crystal structures are periodically arranged, with a long-period period of 2.3 nm. The preparation method of the present invention has the advantages of low synthesis cost, relatively mild reaction conditions, and easy control of reaction conditions, and is suitable for large-scale production.

[0019] 2. A photocatalytic carbon-nitrogen coupling reaction was conducted using a xenon lamp as a simulated light source (the emission spectrum is very similar to visible sunlight). The results showed that the bismuth-based superlattice material obtained by the present invention has high photocatalytic activity under visible light, achieving an efficient coupling reaction of pyrrolidine and 4-bromobenzonitrile (99% conversion, 99% selectivity) within 2 hours. No auxiliary or sacrificial agents are required during the photoreaction process, and the catalyst is recyclable and reusable, showing strong practicality. Furthermore, the catalyst of the present invention can be applied to a variety of reactions with aryl bromide substrates, representing a broad-spectrum, multifunctional novel nanomaterial with promising prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a high-angle circular dark field scanning transmission electron microscope image of the Bi4TaO8Cl-Bi2YO4Cl nanosheet with a superlattice structure prepared in Example 1 of the present invention ( Figure 1 (a)) and crystal structure diagram ( Figure 1 (b)).

[0021] Figure 2 Atomic resolution X-ray energy dispersion spectrum of the Bi4TaO8Cl-Bi2YO4Cl nanosheets with superlattice structure prepared in Example 1 of the present invention

[0022] Figure 3 This is the X-ray diffraction pattern of the Bi4TaO8Cl-Bi2YO4Cl nanosheets with a superlattice structure prepared in Example 1 of the present invention. Figure 3 (b) is an enlarged view of a portion of (a).

[0023] Figure 4 This is the small-angle X-ray diffraction pattern of the Bi4TaO8Cl-Bi2YO4Cl nanosheets with a superlattice structure prepared in Example 1 of the present invention. The figure uses a physical mixture of pure Bi4TaO8Cl nanosheets and Bi2YO4Cl nanosheets prepared in the comparative example as a comparison.

[0024] Figure 5This is the photovoltage spectrum of the Bi4TaO8Cl-Bi2YO4Cl nanosheets with a superlattice structure prepared in Example 1 of the present invention. The figure uses pure Bi4TaO8Cl nanosheets and Bi2YO4Cl nanosheets prepared in the comparative example as comparison.

[0025] Figure 6 This is the ultrafast spectrum of the Bi4TaO8Cl-Bi2YO4Cl nanosheet catalyst with a superlattice structure prepared in Example 1 of the present invention. In the figure, τ1 mainly represents the rapid relaxation of carriers or the initial charge separation process, τ2 mainly represents the slower recombination or charge capture process, and τ ave It reflects the overall relaxation behavior of charge carriers during the photocatalytic process. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the present invention more clear, the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0027] Example 1

[0028] In this embodiment, Bi4TaO8Cl-Bi2YO4Cl nanosheets with a superlattice structure are synthesized according to the following steps:

[0029] Step 1. Accurately weigh 6.26 g (13.44 mmol) of analytically pure Bi2O3, 3.06 g (13.44 mmol) of analytically pure BiOCl, 1.48 g (3.36 mmol) of electronically pure Ta2O5, and 0.76 g (3.36 mmol) of electronically pure Y2O3 and mix them to obtain a mixed salt; add 8.44 g of analytically pure CsCl (50.11 mmol) and 4.54 g of analytically pure NaCl (77.74 mmol) as flux to the mixed salt; place the above raw materials in an agate mortar and manually grind them for 30 minutes until they are evenly dispersed to obtain a mixed powder.

[0030] Step 2: Transfer the mixed powder to an alumina crucible, heat to 750°C at a rate of 10°C / min under a nitrogen atmosphere (purity ≥99.999%), and keep warm for 720 minutes; cool naturally to room temperature to obtain a bulk sintered product.

[0031] Step 3: Immerse the sintered product in 80°C hot deionized water with stirring and washing for 6 hours, and repeat the water washing until the filtrate conductivity is less than 10 μS / cm; collect the precipitate by filtration, and dry it in a vacuum drying oven at 60°C for 12 hours to obtain Bi4TaO8Cl-Bi2YO4Cl nanosheet material with a superlattice structure.

[0032] Comparative Example 1

[0033] In this comparative example, pure Bi2YO4Cl nanosheets were synthesized according to the following steps:

[0034] Step 1. Accurately weigh 2.30 g (4.93 mmol) of analytically pure Bi2O3, 2.57 g (9.86 mmol) of analytically pure BiOCl, and 1.11 g (4.93 mmol) of electronically pure Y2O3 and mix them to obtain a mixed salt; add 12.36 g (73.44 mmol) of analytically pure CsCl and 6.66 g (113.97 mmol) of analytically pure NaCl to the mixed salt as a flux; place the above raw materials in an agate mortar and manually grind for 30 minutes until uniformly dispersed to obtain a mixed powder.

[0035] Step 2: Transfer the mixed powder to an alumina crucible, heat to 750°C at a rate of 10°C / min under a nitrogen atmosphere (purity ≥99.999%), and keep warm for 720 minutes; cool naturally to room temperature to obtain a bulk sintered product.

[0036] Step 3: Immerse the sintered product in 80° C. hot deionized water and stir and wash for 6 hours, repeatedly changing the water and washing until the conductivity of the filtrate is less than 10 μS / cm; collect the precipitate by suction filtration, and dry it in a vacuum drying oven at 60° C. for 12 hours to obtain Bi2YO4Cl nanosheet material.

[0037] Comparative Example 2

[0038] In this comparative example, pure Bi4TaO8Cl nanosheets were synthesized according to the following steps:

[0039] Step 1. Accurately weigh 5.62 g (12.06 mmol) of analytically pure Bi2O3, 2.09 g (8.04 mmol) of analytically pure BiOCl, and 1.78 g (4.02 mmol) of electronically pure Ta2O5 and mix them to obtain a mixed salt; add 10.09 g (59.91 mmol) of analytically pure CsCl and 5.43 g (92.94 mmol) of analytically pure NaCl to the mixed salt as a flux; place the above raw materials in an agate mortar and manually grind for 30 minutes until uniformly dispersed to obtain a mixed powder.

[0040] Step 2: Transfer the mixed powder to an alumina crucible, heat to 750°C at a rate of 10°C / min under a nitrogen atmosphere (purity ≥99.999%), and keep warm for 720 minutes; cool naturally to room temperature to obtain a bulk sintered product.

[0041] Step 3: Immerse the sintered product in 80° C. hot deionized water and stir and wash for 6 hours, repeatedly changing the water and washing until the conductivity of the filtrate is less than 10 μS / cm; collect the precipitate by suction filtration, and dry it in a vacuum drying oven at 60° C. for 12 hours to obtain Bi4TaO8Cl nanosheet material.

[0042] High-angle circular dark-field scanning transmission electron microscopy (HAADF-STEM) was used to perform a more intuitive aberration correction on the side of Bi4TaO8Cl-Bi2YO4Cl nanosheets assisted by focused ion beam (FIB). Figure 1 (a) shows that the Bi4TaO8Cl crystal structure layer and the Bi2YO4Cl crystal structure layer are arranged periodically. The crystal structure diagram is shown in Figure 1 (b) Atomic-resolution X-ray energy dispersive spectroscopy (EDS) shows that there are five atomic sublayers [Bi4TaO8] 1+ and three atomic sublayers [Bi2YO4] 1+ are clearly distinguished by the vertical stacking of [Cl] 1- Layer clamped (such as Figure 2 As shown). Figure 3 The X-ray diffraction pattern (XRD) shown in the figure shows that the Bi4TaO8Cl-Bi2YO4Cl nanosheets have characteristic peaks, and the growth of the superlattice leads to the contraction of the Bi4TaO8Cl sublayer and the expansion of the Bi2YO4Cl. Further small-angle XRD results show that the period of the long-period structure is 2.3nm (such as Figure 4 shown). Figure 4 A physical mixture of Bi4TaO8Cl nanosheets and Bi2YO4Cl nanosheets synthesized in the comparative example is used as a comparison.

[0043] like Figure 5 The photovoltage spectrum shown clearly shows that the photovoltage of Bi4TaO8Cl-Bi2YO4Cl nanosheets after superlattice formation is improved compared with Bi4TaO8Cl nanosheets and Bi2YO4Cl nanosheets. Using ultrafast spectroscopy, it can be clearly observed that the photogenerated carrier separation effect of Bi4TaO8Cl-Bi2YO4Cl nanosheets is improved (such as Figure 6 ).

[0044] The catalytic activity of the nanomaterials obtained in the above examples and comparative examples was tested as follows:

[0045] Accurately weigh 0.01 g of a superlattice-structured catalyst material (Bi4TaO8Cl-Bi2YO4Cl nanosheets, pure Bi4TaO8Cl nanosheets, or Bi2YO4Cl nanosheets), 72.8 mg of 4-bromobenzonitrile substrate (0.4 mmol, 1 equivalent), 55 mg of NiBr2·3H2O (20 μmol, 5 mol%), and 55 μL of tetrahydropyrrole (1.2 mmol, 3 equivalents) were dispersed in 2 mL of dimethylacetamide and sealed in a quartz tube. All operations were performed in an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm). The photocatalytic CN cross-coupling reaction was carried out using a 300-W xenon lamp (CEL-HXF300, China Education Guanghua Co., Ltd., Beijing) and an optical cutoff filter (λ > 420 nm). After the reaction, the catalyst was separated from the mixture by ultracentrifugation. 300 μL of the liquid product and 200 μL of DMSO-d6 were mixed in an NMR tube, and 1,3,5-trimethoxybenzene was used as an internal standard. 1H-NMR spectra were recorded on a Bruker Avance III 400 MHz NMR spectrometer.

[0046] The test results are shown in the following table:

[0047] Table 1. Summary of CN coupling performance of the prepared catalysts

[0048]

[0049] By analyzing the experimental data, it can be proved that the prepared Bi4TaO8Cl-Bi2YO4Cl nanosheet catalyst with a superlattice structure achieved an efficient coupling reaction of pyrrolidine and 4-bromobenzonitrile (conversion rate 99%, selectivity 99%) within 2 hours under visible light irradiation, has strong photoactivity, and can be extended to various aromatic bromide substrate reactions.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bismuth-based superlattice material, characterized in that: The Bi4TaO8Cl crystal structure layers and the Bi2YO4Cl crystal structure layers in the bismuth-based superlattice material are arranged periodically to form a superlattice structure.

2. The bismuth-based superlattice material according to claim 1, wherein: When the molar ratio of Bi4TaO8Cl to Bi2YO4Cl in the material is 1:1, the bismuth-based superlattice material is a Bi4TaO8Cl-Bi2YO4Cl nanosheet having a superlattice structure.

3. The bismuth-based superlattice material according to claim 2, wherein: In the Bi4TaO8Cl-Bi2YO4Cl nanosheet with a superlattice structure, the periodic arrangement of the Bi4TaO8Cl crystal structure layer and the Bi2YO4Cl crystal structure layer is as follows: five atomic sublayers [Bi4TaO8] stacked vertically 1+ , [Cl] layer 1- , three atomic sublayers [Bi2YO4] 1+ 、[Cl] 1- The layers form a period; multiple complete periods in the middle and one complete or incomplete period on the upper and lower sides form a superlattice structure.

4. A method for preparing the bismuth-based superlattice material according to any one of claims 1 to 3, characterized in that: The steps include: Step 1, weighing Bi2O3, BiOCl, Ta2O5 and Y2O3 and mixing them to obtain a mixed salt; adding CsCl and NaCl as flux to the mixed salt and grinding until uniformly dispersed to obtain a mixed powder; Step 2: Transfer the mixed powder to an alumina crucible, heat it to 600-900°C at a rate of 5-20°C / min under a nitrogen atmosphere, and keep it warm for 600-1000 minutes; cool it naturally to room temperature to obtain a sintered product; Step 3: Immerse the sintered product in 60-100° C. hot deionized water and stir and wash for multiple times until the conductivity of the filtrate is less than 50 μS / cm; collect the precipitate by suction filtration and dry it in a vacuum drying oven at 40-80° C. for 6-20 hours to obtain a bismuth-based superlattice material.

5. The preparation method according to claim 4, characterized in that: The molar ratio of the raw materials in the mixed salt in step 1 is Bi2O3:BiOCl:Ta2O5:Y2O3=4:4:1:1, and the obtained bismuth-based superlattice material is Bi4TaO8Cl-Bi2YO4Cl nanosheets with a superlattice structure.

6. The preparation method according to claim 4, characterized in that: In step 1, the mass ratio of CsCl to NaCl is 1 to 3:

1.

7. The preparation method according to claim 4, characterized in that: In step 1, the mixed salt accounts for 3% to 10% of the total molar amount of the mixed salt and the flux.

8. Use of the bismuth-based superlattice material according to any one of claims 1 to 3 as a photocatalyst in a photocatalytic carbon-nitrogen coupling reaction.

9. The use according to claim 8, characterized in that Used to catalyze the carbon-nitrogen coupling reaction of tetrahydropyrrole and aryl bromide to synthesize coupling products.

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