Bromine-doped and bismuth-modified defective bismuth tungstate nanosheet as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a bromine-doped and bismuth-modified defective bismuth tungstate nanosheet, which comprises the following steps: 1) sequentially dispersing precursors of bismuth, tungsten and bromine in deionized water to obtain a suspension; (2) adjusting the pH value of the turbid liquid to 11 by using high-concentration alkali liquor, and carrying out constant-temperature reaction in a drying oven to obtain the bromine-doped defect type bismuth tungstate nanosheet; and (3) respectively dispersing a reducing agent and the bromine-doped defect type bismuth tungstate nanosheet in deionized water, mixing and magnetically stirring at room temperature, and obtaining the bromine-doped and bismuth-modified defect type bismuth tungstate nanosheet through a wet chemical method. The preparation method has the advantages of simple steps, easily available raw materials and excellent performance; according to the obtained defect type bismuth tungstate nanosheet doped with the bromide ions and modified with the bismuth simple substance on the surface, the photoelectric property of the material can be greatly improved through the bromide ions modified on the surface, the bismuth simple substance and oxygen vacancies, and the capacity of photocatalytic purification of nitric oxide is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalysis, and particularly relates to a bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet catalyst and a preparation method thereof, and application of the catalyst in photocatalytic removal of nitrogen oxides. BACKGROUND

[0002] As a typical atmospheric pollutant, nitrogen oxides (NO X ) are difficult to be removed by traditional methods due to high energy consumption and secondary pollution. Photocatalysis is a green technology, but it is limited by high recombination rate of carriers and insufficient oxidation ability, resulting in excessive release of nitrogen dioxide (NO2) in practical application. Among many photocatalytic materials, bismuth tungstate (Bi2WO6) is of great concern due to its unique layered structure and easily controllable electronic properties.

[0003] Bi2WO6 belongs to Aurivillius-type bismuth-based oxides, and its crystal structure is composed of alternately stacked [Bi2O2] 2+ layers and [WO4] 2- octahedral layers. This layered heterostructure can form an internal electric field, which is theoretically beneficial to the spatial separation of photo-generated carriers. The band gap width is about 2.7-2.8 eV, which has better visible light response ability than traditional TiO2 (3.2 eV). However, the original Bi2WO6 still has defects such as poor photoelectric performance and insufficient surface active sites, making it difficult to achieve efficient deep oxidation of nitrogen monoxide (NO).

[0004] Recent studies have shown that the exposure of high surface energy crystal faces can effectively promote the generation of active oxygen free radicals through crystal face regulation; the construction of intermediate energy levels by element doping (such as Fe 3+ ) or introduction of defect sites can extend the light response range to visible light; the construction of Z-type heterojunction (such as Bi2WO6 / g-C3N4) can simultaneously improve the carrier separation efficiency and redox potential. However, the existing modification methods still have problems such as complex preparation process and poor stability, for example, lattice distortion caused by metal doping and accelerated carrier recombination caused by heterojunction interface defects.

[0005] It is particularly noteworthy that Bi2WO6 has the problem of selective oxidation in the process of photocatalytic removal of NO. Studies have shown that the removal rate of NO is only about 30% under full-spectrum irradiation, and the generation rate of NO2 is higher than 20%. This is due to the fact that the surface and interface properties and the valence band position of Bi2WO6 are not conducive to the sufficient generation of active oxygen free radicals, resulting in that the deep oxidation path of NO is blocked by nitrite intermediates. Therefore, how to realize the efficient directional conversion of NO to nitrate through the synergistic effect of surface and interface modification and energy band regulation is still a key bottleneck for the practical application of the material. SUMMARY

[0006] The present application aims to solve at least one of the technical problems in the related art. To this end, the main object of the present application is to provide a bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet catalyst, The present application aims to solve the problem of low efficiency of existing Bi2WO6-based catalysts in removing NO.

[0007] The second object of the present application is to also provide a preparation method of the bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet catalyst.

[0008] The third object of the present application is to provide an application of the bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet catalyst in photocatalytic removal of nitrogen oxides, which has stable catalytic performance and high catalytic efficiency under visible light irradiation.

[0009] The object of the present application is achieved by the following technical solutions: A preparation method of a bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet, comprising the following steps: 1) dispersing bismuth, tungsten and bromine precursors in deionized water in turn to obtain a suspension; 2) adjusting the suspension to a pH value of 9-12 with an alkali solution, and performing constant temperature reaction in an oven to obtain bromine-doped defect-type bismuth tungstate nanosheets; 3) dispersing a reducing agent and the bromine-doped defect-type bismuth tungstate nanosheets in deionized water respectively, and mixing and magnetically stirring at room temperature, collecting the precipitate after standing, washing and drying to obtain bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheets.

[0010] In some embodiments, the bismuth precursor is bismuth nitrate.

[0011] In some embodiments, the tungsten precursor is sodium tungstate.

[0012] In some embodiments, the bromine precursor is sodium bromide.

[0013] In some embodiments, the alkali solution is a 1-3M sodium hydroxide solution.

[0014] In some embodiments, the process conditions for the constant temperature reaction in the oven in step 2) are: a reaction temperature of 120-180℃ and a reaction time of 15-25h.

[0015] In some embodiments, the molar ratio of the bismuth precursor, the tungsten precursor and the bromine precursor in step 1) is (1-3):(0.5-1.5):(0.5-1.5).

[0016] In some specific embodiments, the mass ratio of the reducing agent to the bromine-doped defect-type bismuth tungstate nanosheet in step 3) is (0.001-0.1):1; and the reducing agent is sodium borohydride.

[0017] A bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet prepared by the aforementioned preparation method.

[0018] A bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet prepared by the aforementioned preparation method.

[0019] Compared with the prior art, the present application has at least the following advantages: The preparation method provided by the present application has simple steps, readily available raw materials, and excellent performance; and the bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheet obtained has bromide ions, bismuth elements and oxygen defects on the surface, which can greatly improve the light absorption of the material and promote the separation of photo-generated electron-hole pairs.

[0020] 2) The defect-type bismuth tungstate nanosheet of the present application is applied to photocatalytic removal of nitrogen oxides; the successful construction of the bromine ion and bismuth element modified defect-type bismuth tungstate nanosheet photocatalyst effectively utilizes the LSPR effect of bismuth elements, enhances the light absorption of the defect-type Bi2WO6, and the doped bromide ions and constructed oxygen defects have electron localization ability, which can improve the carrier separation efficiency, promote the generation of active free radicals, and further improve the photocatalytic purification NO capacity of the modified defect-type Bi2WO6. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the specific embodiments of the present application, the drawings required to be used in the specific embodiments or prior art description will be briefly introduced below.

[0022] Figure 1 XRD patterns of the BWO, Br / BWO, Br / BWOR3 and BWOR3 catalysts prepared in Examples 1, 2, 3 and 4; Figure 2 XRD patterns of the BWO, Br / BWO, Br / BWOR3 and BWOR3 catalysts prepared in Examples 1, 2, 3 and 4; Figure 3 TEM and HRTEM patterns of the BWO catalyst prepared in Example 1; Figure 4 TEM and HRTEM patterns of the Br / BWO catalyst prepared in Example 2; Figure 5 Br element corresponding TEM-Mapping pattern of the Br / BWO catalyst prepared in Example 2; Figure 6 TEM and HRTEM images of Br / BWOR3 catalyst prepared in Example 3; Figure 7 TEM-Mapping image of Br element of Br / BWOR3 catalyst prepared in Example 3; Figure 8 TEM and HRTEM images of BWOR3 catalyst prepared in Example 4; Figure 9 UV-Vis DRS images of BWO, Br / BWO, Br / BWOR3 and BWOR3 catalysts prepared in Examples 1, 2, 3 and 4; Figure 10 Photoluminescence spectra of BWO, Br / BWO, Br / BWOR3 and BWOR3 catalysts prepared in Examples 1, 2, 3 and 4; Figure 11 NO concentration change within 30 min of photocatalytic removal of NO by BWO, Br / BWO, Br / BWOR1, Br / BWOR2, Br / BWOR3, Br / BWOR4 and BWOR3 catalysts prepared in Examples 1, 2, 3 and 4; Figure 12 NO2 concentration change within 30 min of photocatalytic degradation of NO by BWO, Br / BWO, Br / BWOR1, Br / BWOR2, Br / BWOR3, Br / BWOR4 and BWOR3 catalysts prepared in Examples 1, 2, 3 and 4; Figure 13 Reaction cycle test of photocatalytic degradation of NO by Br / BWOR3 catalyst prepared in Example 3. DETAILED DESCRIPTION

[0023] The application will be further described in the following detailed description with reference to the drawings and examples, which are described for illustrative purposes only and are not intended to limit the scope of the application.

[0024] When expressing a range, a preferred range, or a range of preferred upper and lower limits for a particular quantity, concentration, or other values or parameters, unless otherwise stated, it is intended to literally incorporate all range values, and all individual values falling within the range, even if the range or individual values are not explicitly stated. The recitation of a range of values or parameters is intended to serve as a shorthand method of referring individually to each numerical value or sub-range falling within the range. Unless otherwise indicated, the numerical values listed in this specification are not intended to be precise.

[0025] All percentages, parts, ratios, etc. are by weight unless otherwise indicated.

[0026] The materials, methods, and examples herein are exemplary only and, unless otherwise specified, should not be construed as limiting.

[0027] In the following examples, the bismuth nitrate raw material is analytically pure, specifically purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.; the sodium tungstate raw material is analytically pure, specifically purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.; the sodium bromide raw material is analytically pure, specifically purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.; and the sodium hydroxide raw material is analytically pure, specifically purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0028] The test methods used in the following examples include: By testing the physicochemical properties of each test sample, the photoelectric performance and surface redox performance of the material are exhibited. The main properties tested in this application include phase structure, relative concentration of oxygen defect phase, micro-morphological structure, light absorption capacity, light carrier separation capacity, and photocatalytic NO oxidation performance.

[0029] 1) X-ray diffraction spectrum test (XRD) An X-ray diffraction device is used to test the crystal structure of the sample according to the national standard or laboratory specified X-ray diffraction analysis method. 2) Electron paramagnetic resonance test (EPR) An electron paramagnetic resonance device is used to magnetically test unpaired electrons in the sample according to the EPR standard method to analyze its electronic structure and defect characteristics. 3) Transmission electron microscope test (TEM) A transmission electron microscope device is used to perform high-resolution testing of the nanostructure and morphology of the sample according to the relevant operation specifications. 4) Elemental analysis test (TEM-Mapping) A transmission electron microscope device is used to perform surface elemental analysis testing of the sample according to the elemental analysis test operation specification. 5) Ultraviolet-visible diffuse reflectance absorption spectrum test (UV-Vis DRS) An ultraviolet-visible diffuse reflectance absorption spectrum device is used to perform ultraviolet-visible diffuse reflectance absorption spectrum testing of the sample according to the absorption spectrum measurement standard method to evaluate its light response characteristics. 6) Photoluminescence spectrum test (PL) A photoluminescence spectrometer is used to measure the photoluminescence spectrum of the sample according to the photoluminescence spectrum measurement standard method to obtain its photoluminescence characteristics. 7) Photocatalytic NO oxidation test The photocatalytic reactor and nitrogen oxide analyzer are adopted, the sample is tested according to the experimental standard of photocatalytic NO oxidation, and the efficiency of oxidizing NO and the amount of NO2 generated in the process are evaluated.

[0030] Example 1: Preparation of defective Bi2WO6 catalyst The defective Bi2WO6 is prepared, and the specific method is as follows: 1) 2 mmol of Bi(NO3)3·5H2O and 1 mmol of Na2WO4·2H2O are weighed and poured into 60 mL of deionized water in sequence, and continuously ultrasonic magnetic stirring is performed for dispersion for 30 min to obtain a uniform suspension; the pH value of the suspension is adjusted to 11 by using a 2 M NaOH solution, and ultrasonic magnetic stirring is performed again for 30 min to obtain a precursor liquid; 2) The precursor liquid is transferred to an oven, and continuously reacted at 160℃ for 20 h; the precipitate obtained after the reaction is washed with deionized water and ethanol to remove soluble impurities, and dried at 60℃ for 12 h to obtain defective Bi2WO6 nanosheets (BWO).

[0031] The XRD result of the BWO provided in the example is shown in Figure 1 , the EPR result is shown in Figure 2 , the TEM and HRTEM are shown in Figure 3 ; it can be known from Figure 1 , Figure 2 and Figure 3 that the diffraction peaks of the BWO correspond to the corresponding crystal face diffraction peaks of the Bi2WO6 standard card one by one, the BWO catalyst has oxygen defect sites and is in the form of nanosheets, and the preparation method of the application successfully obtains the defective Bi2WO6 nanosheet.

[0032] Example 2: Preparation of bromine-doped defective Bi2WO6 catalyst The bromine-doped defective Bi2WO6 is prepared, and the specific method is as follows: 1) 2 mmol of Bi(NO3)3·5H2O, 1 mmol of Na2WO4·2H2O and 1 mmol of NaBr are weighed and poured into 60 mL of deionized water in sequence, and continuously ultrasonic magnetic stirring is performed for dispersion for 30 min to obtain a uniform suspension; the pH value of the suspension is adjusted to 11 by using a 2 M NaOH solution, and ultrasonic magnetic stirring is performed again for 30 min to obtain a precursor liquid; 2) The precursor liquid is transferred to an oven, and continuously reacted at 160℃ for 20 h; the precipitate obtained after the reaction is washed with deionized water and ethanol to remove soluble impurities, and dried at 60℃ for 12 h to obtain bromine-doped defective Bi2WO6 nanosheets (Br / BWO).

[0033] The phase analysis XRD results of the Br / BWO provided by the embodiment are shown in Figure 1 The EPR results are shown in Figure 2 The TEM and HRTEM are shown in Figure 4 The TEM-Mapping results corresponding to the Br element are shown in Figure 5 From Figure 1 , Figure 2 , Figure 4 and Figure 5 , it can be seen from the figures that the diffraction peaks of the Br / BWO correspond to the diffraction peaks of the corresponding crystal face of the Bi2WO6 standard card one by one, the Br / BWO catalyst has oxygen defect sites, the Br element is uniformly distributed on the surface, and the Br / BWO catalyst has a nanosheet morphology, and the preparation method of the application successfully obtains the Br-doped defect-type Bi2WO6 nanosheet. The EPR comparative analysis of the Br / BWO and the BWO catalyst is shown in Figure 2 It is found that the Br / BWO has more abundant oxygen defects than the BWO.

[0034] The UV-Vis DRS (as shown in Figure 9 ) and the PL (as shown in Figure 10 ) comparative analysis of the Br / BWO and the BWO catalyst shows that the photoelectric properties of the Br / BWO and the BWO catalyst are not much different.

[0035] Example 3: Preparation of a bromine-doped and bismuth-modified defect-type Bi2WO6 catalyst The preparation of the bromine-doped and bismuth-modified defect-type Bi2WO6 is as follows: 1) 2 mmol of Bi(NO3)3·5H2O, 1 mmol of Na2WO4·2H2O and 1 mmol of NaBr were weighed and poured into 60 mL of deionized water in sequence, and continuously ultrasonically and magnetically stirred and dispersed for 30 min to obtain a uniform suspension; the pH value of the suspension was adjusted to 11 with a 2 M NaOH solution, and the suspension was again ultrasonically and magnetically stirred for 30 min to obtain a precursor solution; 2) The precursor solution was transferred to an oven and continuously reacted at 160°C for 20 h; the precipitate obtained after the reaction was washed with deionized water and ethanol to remove soluble impurities, and dried at 60°C for 12 h to obtain bromine-doped defect-type Bi2WO6 nanosheets (Br / BWO).

[0036] 3) Br / BWO nanosheets 1 g was weighed and dispersed in 20 mL deionized water, different mass (0.0043 g, 0.0170 g, 0.0511 g, 0.0851 g) of NaBH4 was weighed and dissolved in 20 mL deionized water, the NaBH4 solution was added dropwise into the Br / BWO suspension, and the mixture was mixed and magnetically stirred at room temperature for 30 min, and then the precipitate was collected after standing, and the soluble impurities were removed by repeated washing with deionized water and ethanol; finally, dried in a vacuum oven at 60°C for 12 hours to obtain bromine-doped and bismuth-modified defect-type Bi2WO6 nanosheets (Br / BWOR), according to different mass ratios of NaBH4 to Br / BWO, the prepared bromine-doped and bismuth-modified defect-type Bi2WO6 nanosheets are marked as Br / BWOR1, Br / BWOR2, Br / BWOR3 and Br / BWOR4 (wherein different mass 0.0043 g, 0.0170 g, 0.0511 g, 0.0851 g NaBH4, the corresponding catalysts are Br / BWOR1, Br / BWOR2, Br / BWOR3 and Br / BWOR4, respectively).

[0037] The XRD results of Br / BWOR1, Br / BWOR2, Br / BWOR3 and Br / BWOR4 provided by the embodiment are shown in Figure 1 , the EPR results are shown in Figure 2 , the TEM and HRTEM are shown in Figure 6 , and the TEM-Mapping results corresponding to Br element are shown in Figure 7 ; it can be seen from Figure 1 , Figure 2 , Figure 6 and Figure 7 that most of the diffraction peaks of Br / BWOR1, Br / BWOR2, Br / BWOR3 and Br / BWOR4 correspond to the corresponding crystal face diffraction peaks of the Bi2WO6 standard card, and in addition, Br / BWOR3 and Br / BWOR4 have two diffraction peaks near 2θ = 40°, which correspond to the (104) and (110) crystal face diffraction peaks of the elemental Bi standard card; the Br / BWOR3 catalyst has oxygen defect sites, uniformly distributed Br element on the surface and nanosheet morphology, and the preparation method of the application successfully obtains Br-doped and Bi-modified defect-type Bi2WO6 nanosheets; The EPR comparative analysis of Br / BWOR3, Br / BWO and BWO catalysts is shown in Figure 2 , and it is found that Br / BWOR3 has more abundant oxygen defects than Br / BWO and BWO.

[0038] The UV-Vis DRS of Br / BWO3, Br / BWO and BWO catalysts is shown inFigure 9 (as shown) and PL (as shown) Figure 10 Comparative analysis (as shown) revealed that the Br / BWO3 catalyst exhibits excellent photoelectric properties, with significantly enhanced absorption of visible light and a markedly increased separation efficiency of photogenerated carriers.

[0039] Example 4: Preparation of bismuth-modified defective Bi2WO6 catalyst The specific method for preparing bismuth-modified defective Bi2WO6 is as follows: 1) Weigh 2 mmol Bi(NO3)3·5H2O and 1 mmol Na2WO4·2H2O and pour them into 60 mL of deionized water. Disperse the suspension by continuous ultrasonic magnetic stirring for 30 min to obtain a uniform suspension. Adjust the pH of the suspension to 11 with 2 M NaOH solution and stir by ultrasonic magnetic stirring again for 30 min to obtain the precursor fluid. 2) The precursor liquid was transferred to an oven and reacted continuously at 160°C for 20 h. The precipitate obtained after the reaction was washed with deionized water and ethanol to remove soluble impurities, and then dried at 60°C for 12 h to obtain defective Bi2WO6 nanosheets (BWO).

[0040] 3) Weigh 1 g of BWO nanosheets and disperse them in 20 mL of deionized water. Weigh 0.511 g of NaBH4 and dissolve it in 20 mL of deionized water. Add the NaBH4 solution dropwise to the BWO suspension. Mix and stir magnetically for 30 min at room temperature. After standing, collect the precipitate and wash it repeatedly with deionized water and ethanol to remove soluble impurities. Finally, dry it in a vacuum oven at 60 °C for 12 hours to obtain bismuth-modified defective Bi2WO6 nanosheets (BWOR3).

[0041] The phase analysis XRD results of BWOR3 provided in this embodiment are as follows: Figure 1 As shown, the EPR results are as follows: Figure 2 As shown, TEM and HRTEM are as follows Figure 8 As shown; from Figure 1 , Figure 2 and Figure 8 As can be seen from the figure, most of the diffraction peaks of BWOR3 correspond one-to-one with the corresponding crystal plane diffraction peaks of the Bi2WO6 standard card. In addition, BWOR3 has two diffraction peaks near 2θ = 40° that correspond one-to-one with the (104) and (110) crystal plane diffraction peaks of the elemental Bi standard card. The BWOR3 catalyst has oxygen defect sites, uniform Br element distribution on the surface and nanosheet morphology. The preparation method of this application successfully obtained Bi modified defective Bi2WO6 nanosheets. The EPR comparison analysis of the BWOR3 and Br / BWOR3 catalysts yielded the following results: Figure 2As shown, it is found that BWOR3 has less oxygen defects than Br / BWOR3.

[0042] As shown in the UV-Vis DRS (as shown in Figure 9 As shown in the UV-Vis DRS (as shown in Figure 10 As shown in the UV-Vis DRS (as shown in

[0043] Example 5: Explore the application of the catalyst in purifying NO pollutants 1) Defect-type Bi2WO6 nanosheet catalytic performance test: 0.2 g of defect-type Bi2WO6 nanosheet powder prepared in Example 1 was weighed into a 12 cm diameter culture dish, an appropriate amount of ethanol was added, ultrasonic treatment was performed for 5 min, and then the mixture was uniformly dispersed and placed in an oven at 60°C for drying for 30 min.

[0044] The dried defect-type Bi2WO6 nanosheet powder was subjected to photocatalytic performance test using a continuous flow reactor, and the specific test conditions were as follows: relative humidity was 60%; oxygen content was 21%; NO gas flow rate was 3.3 L / min; completely mixed NO and air to make the initial NO concentration about 550 ppb; the amount of catalyst was 0.2 g; the light source was a 150 W halogen tungsten lamp with an additional cutoff filter (<420 nm); and the performance of removing NO under visible light irradiation was tested. After 30 min of light irradiation, the NO removal rate was 4.6%, and the NO2 concentration was 12 ppb. The results are shown in Table 1.

[0045] 2) Catalytic performance test of bromine-doped defect-type Bi2WO6 nanosheet 0.2 g of bromine-doped defect-type Bi2WO6 nanosheet prepared in Example 2 was weighed into a 12 cm diameter culture dish, an appropriate amount of ethanol was added, ultrasonic treatment was performed for 5 min, and then the mixture was uniformly dispersed and placed in an oven at 60°C for drying for 30 min.

[0046] The dried bromine-doped defect-type Bi2WO6 nanosheet was subjected to photocatalytic performance test using a continuous flow reactor, and the specific test conditions were as follows: relative humidity was 60%; oxygen content was 21%; NO gas flow rate was 3.3 L / min; completely mixed NO and air to make the initial NO concentration about 550 ppb; the amount of catalyst was 0.2 g; the light source was a 150 W halogen tungsten lamp with an additional cutoff filter (<420 nm); and the performance of removing NO under visible light irradiation was tested. After 30 min of light irradiation, the NO removal rate was 25.1%, and the NO2 concentration was 52 ppb. The results are shown in Table 1.

[0047] 3) Catalytic performance test of bromine-doped and bismuth-modified defect-type Bi2WO6 nanosheets 0.2 g of the bromine-doped and bismuth-modified defect-type Bi2WO6 nanosheets prepared in Example 3 was weighed into a petri dish with a diameter of 12 cm, an appropriate amount of ethanol was added, and the mixture was uniformly dispersed by ultrasonic treatment for 5 min and then placed in an oven at 60°C for drying for 30 min.

[0048] The dried bromine-doped and bismuth-modified defect-type Bi2WO6 nanosheets were subjected to photocatalytic performance test using a continuous flow reactor, and the specific test conditions were as follows: the relative humidity was 60%; the oxygen content was 21%; the flow rate of the NO gas stream was 3.3 L / min; the initial NO concentration was about 550 ppb by completely mixing NO and air; the amount of catalyst was 0.2 g; and the light source was a 150 W tungsten halogen lamp with an additional cutoff filter (< 420 nm). The performance of the catalyst in removing NO under visible light irradiation was tested, and the results are shown in Table 1. Under 30 min of light irradiation, the NO removal rates of Br / BWOR1, Br / BWOR2, Br / BWOR3 and Br / BWOR4 were 15.9%, 48.0%, 53.1% and 23.8%, respectively, and the corresponding NO2 concentrations were 41 ppb, 39 ppb, 4 ppb and 3 ppb, respectively.

[0049] 4) Catalytic performance test of bismuth-modified defect-type Bi2WO6 nanosheets 0.2 g of the bismuth-modified defect-type Bi2WO6 nanosheets prepared in Example 2 was weighed into a petri dish with a diameter of 12 cm, an appropriate amount of ethanol was added, and the mixture was uniformly dispersed by ultrasonic treatment for 5 min and then placed in an oven at 60°C for drying for 30 min.

[0050] The dried bismuth-modified defect-type Bi2WO6 nanosheets were subjected to photocatalytic performance test using a continuous flow reactor, and the specific test conditions were as follows: the relative humidity was 60%; the oxygen content was 21%; the flow rate of the NO gas stream was 3.3 L / min; the initial NO concentration was about 550 ppb by completely mixing NO and air; the amount of catalyst was 0.2 g; and the light source was a 150 W tungsten halogen lamp with an additional cutoff filter (< 420 nm). The performance of the catalyst in removing NO under visible light irradiation was tested, and the results are shown in Table 1. Under 30 min of light irradiation, the NO removal rate was 17.2%, and the NO2 concentration was 28 ppb.

[0051] Table 1. Photocatalytic performance of BWO, Br / BWO and series of Br / BWOR catalysts in removing NO The NO concentration change within 30 min of the photocatalytic removal of NO reaction of the BWO, Br / BWO, Br / BWOR1, Br / BWOR2, Br / BWOR3, Br / BWOR4 and BWOR3 catalysts provided by embodiments 1, 2, 3 and 4 of the present application is shown in Figure 11 The corresponding NO2 concentration change is shown in Figure 12 It can be seen from the data in Table 1 that the defect-type Bi2WO6 nanosheet catalyst doped with an appropriate amount of bromine and modified with bismuth (Br / BWOR3) has more excellent photocatalytic performance for deep oxidation of NO than the defect-type Bi2WO6 nanosheet catalyst (BWO), the defect-type Bi2WO6 nanosheet catalyst doped with bromine or modified with bismuth (Br / BWOR or BWOR3). The cycle test of the photocatalytic removal of NO reaction of the Br / BWOR3 catalyst is shown in Figure 13 It can be seen from the data in Table 1 that the defect-type Bi2WO6 nanosheet catalyst doped with an appropriate amount of bromine and modified with bismuth (Br / BWOR3) has more excellent photocatalytic performance for deep oxidation of NO than the defect-type Bi2WO6 nanosheet catalyst (BWO), the defect-type Bi2WO6 nanosheet catalyst doped with bromine or modified with bismuth (Br / BWOR or BWOR3). The cycle test of the photocatalytic removal of NO reaction of the Br / BWOR3 catalyst is shown in Figures 11-13 It can be seen from the data in Table 1 that the defect-type Bi2WO6 nanosheet catalyst doped with an appropriate amount of bromine and modified with bismuth (Br / BWOR3) has more excellent photocatalytic performance for deep oxidation of NO than the defect-type Bi2WO6 nanosheet catalyst (BWO), the defect-type Bi2WO6 nanosheet catalyst doped with bromine or modified with bismuth (Br / BWOR or BWOR3). The cycle test of the photocatalytic removal of NO reaction of the Br / BWOR3 catalyst is shown in

[0052] The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application.

Claims

1. A method for preparing bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheets, characterized in that, The preparation method comprises the following steps: 1) dispersing bismuth, tungsten and bromine precursors in deionized water in sequence to obtain a suspension; 2) adjusting the suspension to a pH value of 9-12 with an alkali solution, and performing constant temperature reaction in an oven to obtain bromine-doped defect-type bismuth tungstate nanosheets; 3) dispersing a reducing agent and the bromine-doped defect-type bismuth tungstate nanosheets in deionized water respectively, mixing and magnetically stirring at room temperature, collecting the precipitate after standing, washing and drying to obtain bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheets.

2. The method for preparing bromine-doped and bismuth-modified defective bismuth tungstate nanosheets according to claim 1, characterized in that, The bismuth precursor is bismuth nitrate.

3. The method for preparing bromine-doped and bismuth-modified defective bismuth tungstate nanosheets according to claim 1, characterized in that, The tungsten precursor is sodium tungstate.

4. The method for preparing bromine-doped and bismuth-modified defective bismuth tungstate nanosheets according to claim 1, characterized in that, The bromine precursor is sodium bromide.

5. The method for preparing bromine-doped and bismuth-modified defective bismuth tungstate nanosheets according to claim 1, characterized in that, The molar ratio of the bismuth precursor, the tungsten precursor and the bromine precursor in step 1) is (1-3):(0.5-1.5):(0.5-1.5).

6. The method for preparing bromine-doped and bismuth-modified defective bismuth tungstate nanosheets according to claim 4, characterized in that, The process conditions of the constant temperature reaction in step 2) are as follows: the reaction temperature is 120-180℃, and the reaction time is 15-25h.

7. The method for preparing bromine-doped and bismuth-modified defective bismuth tungstate nanosheets according to claim 1, characterized in that, The mass ratio of the reducing agent to the bromine-doped defect-type bismuth tungstate nanosheets in step 3) is (0.001-0.1):1, and the reducing agent is sodium borohydride.

8. Bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheets prepared by the preparation method in any one of claims 1-7.

9. Application of the bromine-doped and bismuth-modified defect-type bismuth tungstate nanosheets in claim 8 in photocatalytic removal of nitrogen oxides.

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