Synthesis of BiOBr / WO3 heterojunction photochromic ultrathin nanosheet and research on photocatalytic activation of C-H bond

Abstract

According to the preparation method disclosed by the invention, ammonium tungstate, Bi (NO3) 35H2O and NaBr are used as precursors, and the oxygen-enriched BiOBr / WO3 heterojunction photocatalyst with the photochromic effect is prepared by adopting a one-step hydrothermal method. The preparation method comprises the following steps: firstly, dissolving mannitol and hexadecyl trimethyl ammonium bromide in water, and then sequentially adding Bi (NO3) 3.5 H2O, a certain amount of ammonium tungstate ((NH4) 10H (W2O7) 6.xH2O) and an aqueous solution containing a bromine source; and carrying out hydrothermal reaction on the obtained mixed solution, and then washing and drying to prepare the BiOBr / WO3 ultrathin nanosheet. The prepared BiOBr / WO3 heterojunction ultrathin nanosheet with the photochromic effect can be used for photocatalytic oxidation reaction of ethylbenzene at normal temperature and pressure under visible light irradiation, and the excellent photocatalytic performance of the BiOBr / WO3 heterojunction ultrathin nanosheet is derived from the synergistic effect of a heterojunction structure and photochromism. On one hand, due to the construction of the heterojunction, the visible light absorption range is widened, the transportation distance of charges is shortened, and favorable conditions are provided for photocatalytic reaction; on the other hand, the photochromic effect induced W < 6 + > / W < 5 + > species can be used as an electron capture center to capture and store photogenerated electrons, so that the separation and transfer efficiency of photogenerated charges is effectively improved.

Description

Technical Field

[0001] This invention utilizes photochromic and oxygen-rich BiOBr / WO3 heterojunction ultrathin nanosheets for the oxidation of CH bonds, achieving the generation of high-value-added acetophenone under visible light irradiation, which belongs to the research field of semiconductor photocatalysis. Background Technology

[0002] In recent years, BiOBr materials have been widely used in photocatalysis for CO2 reduction, nitrogen fixation, and organic matter degradation. BiOBr typically has a narrow band gap between 2.7 and 2.9 eV, indicating a wide visible light absorption range. Theoretically, this should lead to superior catalytic performance in visible light-driven photocatalytic oxidation reactions. However, BiOBr suffers from weak redox capabilities and low photogenerated carrier separation efficiency, resulting in less than ideal efficiency in the photocatalytic oxidation of CH bonds. To overcome this challenge, common methods include ion doping, heterojunction construction, and morphology manipulation. Among them, it has been reported that by combining BiOBr with other semiconductor materials to form a heterojunction, the band structure of BiOBr can be effectively adjusted, the visible light absorption range can be broadened, and the separation and transfer efficiency of photogenerated charges can be improved, thereby improving the photocatalytic performance of the composite material (Long YN, Yu GL, Yang K. Efficient removal of tetracycline hydrochloride undervisible-light irradiation with novel Fe / BiOBr / BiOI photocatalyst prepared by dual modification strategy[J]. Journal of Environmental Chemical Engineering,2024, 12(5): 114045.)(Sun YL, Wang XL, Lee HL. Enhanced photodegradation of ceftazidime by BiOBr(110) / BiOCl(110) composite: Its synthesis, mechanism, and degradation pathways[J]. Journal of Environmental Chemical Engineering,2024, 12(5): 113332.). At the same time, some researchers have applied photochromic semiconductor nanomaterials to C(sp 3The selective oxidation of ethylbenzene (H) has attracted widespread attention. For example, Li et al. (Cao X, Huang AJ, Liang C, et al. Engineering lattice disorder on a photocatalyst: Photochromic BiOBrnanosheets enhance activation of aromatic CH bonds via water oxidation[J]. Journal of the American Chemical Society, 2022, 144(8): 3386-3397.) reported that BiOBr nanosheets efficiently separate photogenerated carriers by capturing photogenerated holes under visible light during photochromism, thereby realizing the photocatalytic oxidation of ethylbenzene in water.

[0003] Chinese patent document CN118908797A discloses a method for photo-initiated preparation of acetophenone from ethylbenzene. The material is prepared by dissolving the compound in a solvent under oxygen- or air-containing conditions, adding ferric chloride as a catalyst, and subjecting the reaction to light at room temperature to obtain the oxidation product. Wherein, R-1-R-4 are hydrogen, alkyl, alkoxy, cyano, aryl, or halogen; R-5 is alkyl, aryl, haloaryl, or aromatic heterocyclic. While ferric chloride exhibits good catalytic performance in certain reactions, its strong corrosiveness, potential for product discoloration, difficulty in handling, and potential harm to human health warrant careful consideration in practical applications.

[0004] Therefore, developing visible light-responsive BiOBr / WO3 heterojunction photochromic ultrathin nanosheets for efficient photocatalytic oxidation of CH bonds has high practical application value. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to develop a photochromic material exhibiting blue light response for the efficient photocatalytic oxidation of the CH bond in ethylbenzene to prepare acetophenone. When the sample (BW-2) with a theoretical ammonium tungstate / bismuth nitrate molar ratio of 0.05 is excited by blue light, electrons jump from the valence band to the conduction band, forming photogenerated electrons, while photogenerated holes are formed in the conduction band. In the conduction band, the photogenerated electrons will... +6 Species reduced to W 5+ The species, thus producing a photochromic effect. Photogenerated holes in the valence band have an oxidizing effect, oxidizing ethylbenzene to generate benzyl radicals and H+. + Simultaneously, O2 adsorbed on oxygen vacancies in BW-2 reacts with photogenerated electrons to generate O2. •- Subsequently, the benzyl radical reacts with O2.•- Further reactions generate peroxide free radicals, which then react with H+. + Together, they undergo dehydration to form the final product, acetophenone. During this process, the doping of W ions significantly improves the separation and transfer efficiency of photogenerated charges, primarily due to the W ions induced by photochromism. 6⁺ / W 5⁺ The species can act as an electron-capturing center to capture photogenerated electrons. Additionally, oxygen vacancies on BW-2 facilitate the adsorption and activation of O2, promoting O2 production. •- The formation of [a substance] further enhances the oxidation capacity of the material.

[0006] The technical solution of the present invention is as follows:

[0007] A BiOBr / WO3 heterojunction ultrathin nanosheet photochromic material rich in oxygen vacancies, wherein the surface of the ultrathin nanosheet photochromic material rich in oxygen vacancies is modified with hexadecyltrimethylammonium bromide (CTAB) and mannitol; the size of the bismuth oxybromide ultrathin nanosheet photochromic material is 13-25 nm and the thickness is 1.5-2.9 nm.

[0008] To achieve the above-mentioned invention and solve the problems existing in the prior art, the technical solution adopted by the present invention is as follows: using mannitol and CTAB as surfactants, and ammonium tungstate, Bi(NO3)3·5H2O and NaBr as precursors, a series of oxygen-rich BiOBr / WO3 composite photocatalysts with different molar ratios are prepared by a one-step hydrothermal method. According to the present invention, the preparation method of the above-mentioned oxygen-vacancy-rich BiOBr / WO3 heterojunction ultrathin nanosheet photochromic material includes the following steps:

[0009] First, weigh 0.6 g of mannitol and 0.1 g of hexadecyltrimethylammonium bromide (CTAB) and dissolve them in 30 mL of H2O. Then, add 0.485 g of Bi(NO3)3·5H2O and a certain amount of ammonium tungstate ((NH4)2) in sequence. 10 BiOBr / WO3 ultrathin nanosheets were prepared by stirring 5 mL of NaBr aqueous solution (0.2 M) with H(W2O7)6·xH2O at room temperature for 30 min until homogeneous. The mixture was then transferred to a 50 mL polytetrafluoroethylene (PTFE) reactor and reacted at 160 °C for 6 h. After the reaction, the mixture was allowed to cool naturally to room temperature, centrifuged to collect the precipitate, washed twice with anhydrous ethanol, and then dried in a 60 °C oven for 6 h to obtain the BiOBr / WO3 sample. Samples with theoretical ammonium tungstate / bismuth nitrate molar ratios of 0.03, 0.05, and 0.10 are designated as BW-1, BW-2, and BW-3, respectively, with BW-2 being labeled as the typical sample. BiOBr ultrathin nanosheets were also prepared using the same procedure but without the addition of ammonium tungstate.

[0010] According to a preferred embodiment of the present invention, the average molecular weight of the hexadecyltrimethylammonium bromide is 50,000-110,000; and the mass ratio of the hexadecyltrimethylammonium bromide to the bismuth source is 1-3:1.

[0011] According to a preferred embodiment of the present invention, the mass ratio of mannitol to bismuth source is 1-5:1.

[0012] According to a preferred embodiment of the present invention, the bismuth source is bismuth nitrate pentahydrate, bismuth chloride, bismuth carbonate, bismuth sulfate, or bismuth phosphate.

[0013] According to a preferred embodiment of the present invention, the mass ratio of the bismuth source to the volume of water is 1 g: 40-100 mL.

[0014] According to a preferred embodiment of the present invention, the bromine source is sodium bromide, potassium bromide, or hydrogen bromide; and the concentration of the bromine source in the aqueous solution containing the bromine source is 0.1-0.6 mol / L.

[0015] According to a preferred embodiment of the present invention, the molar ratio of bromine in the bromine source to bismuth in the bismuth source is 1-4:1.

[0016] According to a preferred embodiment of the present invention, the hydrothermal reaction temperature is 130-170 °C and the hydrothermal reaction time is 4-7 h.

[0017] According to a preferred embodiment of the present invention, the washing is performed by centrifugal washing using a mixed solvent of anhydrous ethanol or acetone and deionized water; the volume ratio of anhydrous ethanol or acetone to deionized water in the mixed solvent is 4-5:1.

[0018] According to the present invention, the above-mentioned oxygen-vacancy-rich bismuth oxybromoacetate ultrathin nanosheet photochromic material is used in photochromic materials;

[0019] Furthermore, the oxygen-vacancy-rich bismuth oxybromophosphate ultrathin nanosheet photochromic material has important application prospects in photocatalysis and carbon dioxide reduction.

[0020] The technical features and beneficial effects of this invention are as follows:

[0021] (1) A BiOBr / WO3 composite photocatalyst with a unique photochromic effect was developed, and the visible light catalytic oxidation of ethylbenzene was realized at room temperature and pressure. Among them, BW-2 showed the highest catalytic activity, with an ethylbenzene conversion rate of up to 98%. Its excellent catalytic performance is mainly due to the presence of oxygen vacancies, which enhances the activation ability of the composite material for O2. The synergistic effect between the heterojunction and the photochromic effect greatly improves the separation and transfer efficiency of photogenerated carriers.

[0022] Furthermore, the BW-2 composite material also exhibited high catalytic activity in the photocatalytic selective activation of isoquinoline coupling reaction. This work provides a feasible approach to improving the catalytic activity of photocatalysts by constructing a synergistic system of photochromic effect and heterojunction.

[0023] (2) The activation and oxidation of hydrocarbons into high-value-added chemical or pharmaceutical intermediates, including aldehydes, ketones, and epoxides, are very important in the chemical industry and organic synthesis. In particular, acetophenone, produced by the oxidation of ethylbenzene, is an important raw material for the production of pharmaceuticals, fragrances, cellulose ethers, resins, and other products, and has significant commercial value. Attached Figure Description

[0024] Figure 1 The XRD patterns are of pure BiOBr in Comparative Example 1 and BiOBr / WO3 heterojunction photochromic ultrathin nanosheets with different molar ratios in Examples BW-2, Comparative Example 2, and Comparative Example 3.

[0025] Figure 2 This is a high-resolution transmission electron microscope (HRTEM) image of the sample with a theoretical ammonium tungstate / bismuth nitrate molar ratio of 0.05 in the example.

[0026] Figure 3 Raman spectra of the theoretical ammonium tungstate / bismuth nitrate molar ratio of 0.05 in the example and in Comparative Example 1, pure BiOBr ultrathin nanosheets.

[0027] Figure 4 Example: The theoretical molar ratio of ammonium tungstate / bismuth nitrate is 0.05. Fourier transform infrared (FT-IR) spectra of the sample before and after blue light irradiation.

[0028] Figure 5 The following are X-ray photoelectron spectroscopy (XPS) spectra of the sample with a theoretical ammonium tungstate / bismuth nitrate molar ratio of 0.05 before and after blue light irradiation: (a) W 4f, (b) Bi 4f and (c) O 1s.

[0029] Figure 6 a represents the electrochemical impedance spectroscopy of BiOBr / WO3 heterojunction ultrathin nanosheets with different molar ratios in Comparative Example 1 and Examples BW-2, Comparative Example 2, and Comparative Example 3. Figure 6 b shows the transient photocurrent spectra of BiOBr / WO3 heterojunction ultrathin nanosheets with different molar ratios in Comparative Example 1 and Examples BW-2, Comparative Example 2, and Comparative Example 3.

[0030] Figure 7 These are schematic diagrams of the electronic band structure of WO3, Comparative Example 1, and Example BW-2.

[0031] Figure 8This study compares the photocatalytic rates of ethylbenzene to acetophenone produced from BiOBr / WO3 heterojunction ultrathin nanosheets with different molar ratios in Comparative Example 1 and Examples BW-2, 2, and 3.

[0032] Figure 9 a is a control experiment of photocatalytic oxidation of ethylbenzene in Example BW-2 under normal conditions or with different scavengers; Figure 9 b is a radical capture experiment of 2,2,6,6-tetramethylpiperidine oxide (TEMPO) under standard conditions, MSI-ES: C 17 H 27 The theoretical value for NO is 261.2090; the experimental value is [M+H]. + 262.2167.

[0033] Figure 10 The ESR spectra of Comparative Example 1 and Example BW-2 in the presence of O2 and dimethylpyridine N-oxide (DMPO) are shown.

[0034] Figure 11 This is a free radical capture experiment of TEMPO under standard conditions, MSI-ES: C 13 H 25 The experimental value for NO2 was 228.1959; the theoretical value was [M+H]. + 228.1964. Detailed Implementation

[0035] The present invention will be further described below with reference to the embodiments.

[0036] In addition, unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; and unless otherwise specified, the reagents and materials are commercially available.

[0037] Example

[0038] (1) Weigh 0.6 g mannitol and 0.1 g cetyltrimethylammonium bromide (CTAB) and dissolve them in 30 mL H2O. Then add 0.485 g Bi(NO3)3·5H2O and a certain amount of ammonium tungstate ((NH4) 10 Add H(W₂O₇)₆·xH₂O and 5 mL of NaBr aqueous solution (0.2 M). Mix thoroughly by stirring continuously for 30 min at room temperature.

[0039] (2) The mixture was transferred to a 50 mL polytetrafluoroethylene reactor and reacted at 160 °C for 6 h to prepare BiOBr / WO3 ultrathin nanosheets.

[0040] (3) After the reaction was completed, the sample was naturally cooled to room temperature, centrifuged to collect the precipitate, washed twice with anhydrous ethanol, and placed in a drying oven at 60℃ for 6 h to obtain the BiOBr / WO3 sample. The sample with a theoretical ammonium tungstate / bismuth nitrate molar ratio of 0.05 is referred to as BW-2 in this paper and is denoted as the typical sample.

[0041] (4) Weigh 10 mg of catalyst and place it into a 10 mL quartz glass reactor containing a mixed solution (3 mL acetonitrile, 0.1 mmol ethylbenzene). Sonicate the solution to ensure uniform dispersion of the catalyst. Then, cover with a rubber stopper, replace the gas with oxygen, seal the reactor, and attach an oxygen ball approximately 15 cm in diameter to the stopper. Use a 405 nm LED lamp (100 mW / cm²). 2 The reaction solution is subjected to light irradiation.

[0042] The XRD pattern of the BiOBr / WO3 heterostructure ultrathin nanosheets with photochromic effect prepared in this embodiment is shown below. Figure 1 As shown, the positions of the diffraction peaks of pure BiOBr correspond to the crystal planes (001), (002), (011), (012), (110), (112), (020), (113), and (212), and the positions of the diffraction peaks correspond to the pure BiOBr standard card (JCPDS card No. 73-2061). Furthermore, no other impurity peaks appeared in the spectrum, indicating that the synthesized pure BiOBr material has high purity. By comparing the number and shape of characteristic peaks in the XRD patterns of pure BiOBr and a series of BiOBr / WO3 heterojunction ultrathin nanosheets, it was found that the number of characteristic peaks in the BiOBr / WO3 heterojunction ultrathin nanosheets decreased, and the full width at half maximum (FWHM) of some characteristic peaks increased. Furthermore, as the mass of ammonium tungstate increases, the intensity of the pure BiOBr characteristic peak of the BiOBr / WO3 heterojunction ultrathin nanosheets gradually decreases, and the characteristic peak of WO3 clearly appears in the XRD pattern of the BW-2 composite material, which proves the successful construction of the BiOBr / WO3 heterojunction.

[0043] The HRTEM characterization results of a typical sample in this embodiment are as follows: Figure 2 a and b are shown. From Figure 2 As can be seen from a, there are crystal planes with different lattice spacings in the composite material. Among them, the lattice fringes arranged in two different directions have a spacing of 0.275 nm and an included angle of 90°. o Corresponding to the (110) and (020) planes of the tetragonal phase BiOBr, the fringe with a lattice spacing of 0.315 nm corresponds to the WO3 (200) crystal plane. Furthermore, in Figure 2 In b, a lattice spacing of 2.290 nm was also observed, corresponding to the BiOBr (112) crystal plane. The above results further prove that the BiOBr / WO3 heterojunction was successfully constructed.

[0044] Figure 3 Raman spectra of pure BiOBr (Comparative Example 1) and typical sample BW-2 (Example Example). Figure 3 As shown, the Raman spectrum of pure BiOBr exhibits four distinct peaks: 60 cm⁻¹ -1 Peak corresponding to External Bi-Br stretching mode; 91cm -1 The peak belongs to External Bi-Br stretching mode; 112 cm -1 The peak at that location is Internal Bi-Br stretching mode; 162 cm -1 The peak at that location represents Internal Bi-Br stretching mode. Compared to pure BiOBr, the reduction in nanosheet thickness in typical BW-2 samples leads to... External Bi-Br stretching mode from approximately 58 cm -1 It shifts to higher wavenumbers to approximately 60 cm. -1 In a typical BW-2 sample, 91 cm -1 Place The strength of the external Bi-Br tensile mode almost disappears. Due to oxygen vacancies, typical BW-2 samples at 111 cm⁻¹... -1 place The internal Bi-Br stretching mode shifted to 106 cm. -1 At the same time, compared to pure BiOBr, typical BW-2 samples... and The number of vibrational peaks increased, and varying degrees of broadening were observed. This is mainly attributed to the increased oxygen vacancies, which caused a certain degree of distortion in the structure of the typical BW-2 sample. Furthermore, at 969 cm⁻¹... -1 The presence of a characteristic peak of WO3 (W=O) indicates that pure BiOBr and WO3 coexist in the typical BW-2 sample.

[0045] Figure 4 These are the FT-IR spectra of a typical BW-2 sample before and after illumination. The spectra show no new absorption peaks or disappearances of existing absorption peaks. The characteristic peaks of BiOBr, WO3, and mannitol also remain unchanged, and the intensity of all absorption peaks is also unchanged, demonstrating that the material has high stability.

[0046] Figure 5 XPS tests were performed on typical BW-2 samples before and after blue light irradiation, and the results are shown in the figure. Figure 5 As can be seen from a, after blue light irradiation, W 4f 5 / 2The binding energy of the peak shifted from 36.42 eV to 36.37 eV, W 4f 7 / 2 The binding energy of the peak shifted from 34.30 eV to 34.25 eV. After blue light irradiation, the W in the composite material... 6+ The relative intensity of the signal peaks weakens, while W 5+ The increase in the relative intensity of the signal peak indicates that under blue light irradiation, W 6+ The species was reduced to W by photogenerated electrons. 5+ The species, on a macroscopic scale, changed from white to blue. From Figure 5 The Bi 4f XPS spectrum of b shows that after blue light irradiation, Bi 4f... 7 / 2 and Bi 4f 5 / 2 The peak shifted to a lower binding energy by 0.5 eV, indicating that a small amount of Bi... 3+ It was reduced to Bi by photogenerated electrons. (3-x)+ . Figure 5 The c O1s XPS spectrum shows that the peak area of ​​the O 1s atom, which represents oxygen vacancies in the composite material, increases and the peak position shifts to the direction of lower binding energy by 0.15 eV. This indicates that blue light irradiation promotes the generation of oxygen vacancies on the surface of the composite material.

[0047] To investigate the separation efficiency of photogenerated carriers in photocatalysts, transient photocurrent and electrochemical impedance spectroscopy were performed on pure BiOBr and a series of BiOBr / WO3 heterojunction ultrathin nanosheets with different molar ratios. Figure 6 Figure a shows the electrochemical impedance spectroscopy (EIS) spectra of pure BiOBr and a series of BiOBr / WO3 heterojunction ultrathin nanosheets with different molar ratios. Generally, the smaller the radius of the Nyquist semicircle in the impedance spectrum, the lower the electron transfer resistance and the higher the photogenerated carrier transfer efficiency. As can be seen from the figure, the pure BiOBr sample has the largest Nyquist semicircle radius, while the typical BW-2 sample has the smallest. This indicates that this catalyst has the lowest resistance to photogenerated charge transport, which is beneficial for the transfer of photogenerated charges. Photocurrent density reflects the separation and migration ability of photogenerated charges. Under the same test conditions, a higher photocurrent density indicates that the material can generate more photogenerated charges and has a higher charge carrier transfer efficiency. Figure 6 As shown in b, the pure BiOBr sample has the lowest photocurrent density, while the typical BW-2 sample has the highest photocurrent density. This indicates that the composite material has the highest photogenerated electron-hole separation and transfer efficiency, which is consistent with the test results of the electrochemical impedance spectroscopy.

[0048] Figure 7 The diagram shows the electronic band structure of typical samples WO3, pure BiOBr, and BW-2. The Et values ​​of these typical samples were calculated. VBThe values ​​are 2.18, 2.44, and 2.27 V, respectively. Compared to pure BiOBr, the typical BW-2 sample exhibits a higher conduction band position, enhanced photoreduction activity, and a lower valence band position (+2.27 V, vs. NHE), which is higher than the potential required for ethylbenzene oxidation (+2.14 V, vs. NHE), thus driving the oxidation of ethylbenzene (+2.14 V, vs. NHE). In summary, the reduced band gap of the typical BW-2 sample enhances its absorption in the visible light range, and the photochromic effect induces W in BW-2. 6+ / W 5+ The species become electron-capturing centers, thus significantly improving the efficiency of photogenerated charge separation and transfer. Therefore, the BW-2 photochromic composite material exhibits excellent catalytic activity in the photocatalytic oxidation of ethylbenzene.

[0049] Figure 8 The graphs show the photocatalytic oxidation performance of ethylbenzene by pure BiOBr and typical BW-2 samples. It can be seen that under N2, dark, or catalyst-free conditions, the conversion rate of ethylbenzene oxidation by the typical BW-2 sample is negligible, indicating that this reaction is a photocatalytic process. The conversion rate of ethylbenzene oxidation by pure BiOBr sample within 10 h is 44%, while all BW composite materials exhibit better photocatalytic ethylbenzene selective activation than pure BiOBr.

[0050] Figure 9 Figure a shows a control experiment of the photocatalytic oxidation of ethylbenzene by a typical BW-2 sample under normal conditions or with different scavengers. As shown in the figure, without any scavenger, the typical BW-2 sample achieved a 98% conversion rate of ethylbenzene oxidation within 10 h. However, when BQ was added to the reaction system, the ethylbenzene conversion rate dropped sharply to 40%. This significant change indicates that O2... •- It plays a crucial role in photocatalytic oxidation reactions. When AgNO3 and KI were added to the reaction system, respectively, the conversion rates of ethylbenzene oxidized by BW-2 photocatalyst decreased significantly to 8% and 6%, respectively. This indicates that h... + and e - It is the main active species. Figure 9 b shows the radical capture experiment of TEMPO under standard conditions. When TEMPO was added to the reaction system, the oxidation of ethylbenzene to acetophenone was completely inhibited, indicating that the photocatalytic oxidation reaction is a radical reaction. Simultaneously, ESI-MS testing successfully detected the adduct of benzyl radicals with TEMPO, further providing evidence for the potential radical activation process of CH bonds. The main reason for this is the W generated by the photochromic effect. 6⁺ / W 5⁺The species can act as an electron trapping center, effectively suppressing the recombination of photogenerated carriers, thereby enabling the separated photogenerated holes to efficiently activate the CH bonds of ethylbenzene, promoting the generation of benzyl radicals.

[0051] Figure 10 Typical samples of pure BiOBr and BW-2 in methanol solution DMPO-O2 •- ESR spectra of the adducts. The spectra show that DMPO-O2 was detected in both pure BiOBr and typical BW-2 samples after 5 min of light irradiation. •- The signal of the adduct, and the DMPO-O2 of typical BW-2 samples. •- The intensity is higher than that of pure BiOBr. This indicates that oxygen vacancies in typical BW-2 samples can rapidly capture photogenerated electrons and activate the activated O2 adsorbed on the oxygen vacancies to generate O2. •- Meanwhile, the construction of heterojunctions shortens the transport distance of photogenerated charges and improves the separation and transfer efficiency of photogenerated charges, thereby effectively enhancing its photocatalytic activity.

[0052] Furthermore, the complex of TEMPO and THF radicals was detected by ESI-MS, which fully demonstrates the generation of THF radicals in the photocatalytic system. Figure 11 ).

[0053] In summary, the photochromic and oxygen-rich BiOBr / WO3 heterojunction photocatalyst exhibits the highest selective photocatalytic activity for the oxidation of ethylbenzene when the molar ratio of ammonium tungstate to BiOBr is 0.05, achieving a conversion rate of up to 98% after 8 hours of visible light irradiation. Furthermore, the BiOBr / WO3 composite material also demonstrates high activity in the photocatalytic activation of the carbon-nitrogen coupling reaction of isoquinoline and tetrahydrofuran. Its excellent photocatalytic performance stems from the synergistic effect of the heterojunction structure and the photochromic effect, which promotes the separation and transfer efficiency of photogenerated carriers. Simultaneously, the oxygen vacancies in the BiOBr / WO3 composite material promote the adsorption and activation of oxygen, further enhancing its photocatalytic activity.

[0054] Comparative Example 1

[0055] A method for preparing bismuth oxybromide material, as described in the examples, involves preparing pure BiOBr ultrathin nanosheets by following the same steps but without adding ammonium tungstate, under the same conditions.

[0056] Comparative Example 2

[0057] A method for preparing a bismuth oxybromide material, as described in the examples, under the same conditions, prepares a sample with a molar ratio of ammonium tungstate / bismuth nitrate of 0.03, referred to herein as BW-1.

[0058] Comparative Example 3

[0059] A method for preparing a bismuth oxybromide material, as described in the examples, under the same conditions, prepares a sample with a molar ratio of ammonium tungstate / bismuth nitrate of 0.10, referred to herein as BW-3.

[0060] Compared to pure BiOBr and WO3 materials, the typical BW-2 sample exhibited the highest photocatalytic activity. Its superior photocatalytic performance stems from the synergistic effect generated by the simultaneous presence of the heterojunction structure and the photochromic effect, which promotes the separation and transfer efficiency of photogenerated carriers. Simultaneously, oxygen vacancies in the BiOBr / WO3 composite material promote O2 adsorption and activation, further enhancing its photocatalytic activity.

Claims

1. A BiOBr / WO3 heterojunction ultrathin nanosheet rich in oxygen vacancies and exhibiting photochromic effect, characterized in that, The structure of the bismuth oxybromotrimethylammonium nanosheet photochromic material is BiOBr / WO3. The surface of the oxygen-vacancy-rich bismuth oxybromotrimethylammonium bromide and mannitol are modified. The size of the bismuth oxybromotrimethylammonium nanosheet photochromic material is 13-25 nm and the thickness is 1.5-2.9 nm.

2. The preparation method of the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 1, comprising the following steps: Hexadecyltrimethylammonium bromide, mannitol, and a bromine source were added to water and stirred until well mixed. Then, an aqueous solution containing the bromine source was added to obtain a mixed solution. The resulting mixed solution was subjected to a hydrothermal reaction, followed by washing and drying to obtain a bismuth oxybromophosphate ultrathin nanosheet photochromic material rich in oxygen vacancies.

3. The method for preparing the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 2, characterized in that, The average molecular weight of the hexadecyltrimethylammonium bromide is 50,000-110,000; the mass ratio of the hexadecyltrimethylammonium bromide to the bismuth source is 1-3:

1.

4. The method for preparing the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 2, characterized in that, The mass ratio of mannitol to bismuth source is 1-5:

1.

5. The method for preparing the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 2, characterized in that, The bismuth source is bismuth nitrate pentahydrate, bismuth chloride, bismuth carbonate, bismuth sulfate, or bismuth phosphate; the mass ratio of the bismuth source to the volume of water is 1 g: 40-100 mL.

6. The method for preparing the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 2, characterized in that, The bromine source is sodium bromide, potassium bromide, or hydrogen bromide; the concentration of the bromine source in the aqueous solution containing the bromine source is 0.1-0.6 mol / L.

7. The method for preparing the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 2, characterized in that, The molar ratio of bromine in the bromine source to bismuth in the bismuth source is 1-4:

1.

8. The method for preparing the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 2, characterized in that, The hydrothermal reaction temperature is 130-170 ℃, and the hydrothermal reaction time is 4-7 h.

9. The method for preparing the oxygen-vacancy-rich bismuth oxybromobismuth ultrathin nanosheet photochromic material according to claim 2, characterized in that, The washing process involves centrifugal washing using a mixed solvent of anhydrous ethanol or acetone and deionized water; the volume ratio of anhydrous ethanol or acetone to deionized water in the mixed solvent is 4-5:

1.

10. The application of the oxygen-vacancy-rich bismuth oxybromobismuth nanosheet photochromic material according to claim 1, characterized in that, It has important application prospects in fields such as photocatalysis and carbon dioxide reduction.

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