CN115124077A

CN115124077A - Bi 5 O 7 Preparation method of Br nanosheet

Info

Publication number: CN115124077A
Application number: CN202210805915.4A
Authority: CN
Inventors: 米艳; 王运静; 廖桂慧
Original assignee: Guangxi University for Nationalities
Current assignee: Guangxi University for Nationalities
Priority date: 2022-07-08
Filing date: 2022-07-08
Publication date: 2022-09-30

Abstract

The invention discloses a Bi ₅ O ₇ A method of preparing Br nanoplates, comprising: putting bismuth nitrate pentahydrate, mannitol and polyvinylpyrrolidone K23-27 into water, and stirring to obtain transparent clear liquid; adding a potassium bromide saturated solution and triethylamine into the obtained transparent clear liquid to obtain a mixed solution; and carrying out hydrothermal reaction on the obtained mixed solution, washing the obtained product and drying the product to obtain the catalyst. Wherein the addition amount of triethylamine is 1.15-1.73 times of the amount of mannitol substances, and the addition amount of the saturated solution of potassium bromide is calculated by taking 2-2.5 mL of the added solution as a reference when the amount of bismuth nitrate pentahydrate substances is 1 mmol. In the method, the triethylamine and the mannitol are used as structure control agents to generate mutual competition induction to form Bi ₅ O ₇ Br, by adjusting the ratio of the two, the group of samples obtained by synthesis is regulated and controlledFormation, crystal structure and surface morphology to obtain two-dimensional Bi ₅ O ₇ And (4) Br ultrathin nanosheets.

Description

Bi 5 O 7 Preparation method of Br nanosheet

Technical Field

The invention relates to preparation of a photocatalytic nano material, in particular to Bi ₅ O ₇ A preparation method of Br nano-sheets.

Background

Bismuth oxyhalide BiOX (X ═ Cl, Br)And I) a class of layered materials with suitable band structures, have been applied for photocatalytic energy conversion and environmental remediation. It has high chemical and optical stability, no toxicity, low cost and high corrosion resistance. BiOX is composed of [ Bi ₂ O ₂ ]Layer and atomic layer of dihalide crossed therein along [001 ]]Directionally formed, the special structure endows the photocatalyst with self-built internal electrostatic field, thereby ensuring the excellent photocatalytic performance of the photocatalyst. Wherein, bismuth oxybromide (BiOBr) is a novel photocatalytic material and takes a square layered crystal structure; the special crystal structure makes the photoproduction electron hole pair not easy to be compounded, thereby promoting the application of photocatalytic degradation. The bismuth oxybromide can decompose organic dye into carbon dioxide and water molecules under the action of visible light, and the catalytic efficiency of the bismuth oxybromide is higher than that of commercial photocatalyst titanium dioxide, so that the bismuth oxybromide can be used for purifying sewage and the like. In addition, bismuth oxybromide has important applications in the fields of gas sensing, cosmetics, selective oxidation catalysts, ion conductors, ferroelectric materials and the like.

The bismuth oxybromide has a one-dimensional nanowire structure, a two-dimensional nanosheet structure, a three-dimensional flower-like structure and the like. At present, hydrothermal method is mainly adopted for synthesizing bismuth oxybromide nano material, such as literature (First hydrothermal synthesis of Bi) ₅ O ₇ Br and its photocatalytic properties for molecular oxygen activation and RhB degradation. appl.Surf. Sci.2015,346,311-316.DOI 10.1016/j. apsusc.2015.04.021) reported a preparation of Bi ₅ O ₇ Br nanowire method, firstly 4mmol of Bi (NO) ₃ ) ₃ ·5H ₂ Dissolving O and 4mmol KBr in 20mL distilled water, and stirring to form a transparent solution; then, the mixed solution was adjusted to pH 13 with NaOH solution of appropriate concentration, stirred for 10min, and then transferred to a teflon-lined stainless steel autoclave, sealed and maintained at 160 ℃ for 16 h; then, the prepared product is centrifuged, washed with distilled water and ethanol for several times, and finally dried in the air at 60 ℃ overnight to obtain the product. Obtained by the method is Bi ₅ O ₇ Br nano-wire, and the hydrothermal reaction time is longer. Also as described in the literature (Enhanced animal ammonium photosynthesis by Mo-doped Bi) ₅ O ₇ Br nanosheets with light-switchable oxygen catalysts, Chinese Journal of Catalysis 2021,42,2020-2026 DOI 10.1016/s1872-2067(21)63837-8) reported a hydrothermal synthesis of Bi ₅ O ₇ A method of preparing Br nano-sheet, in particular to a method of preparing 1mmol of Bi (NO) ₃ ) ₃ ·5H ₂ O (0.486g) and 0.4g polyvinylpyrrolidone (PVP) were mixed in 20mL deionized water and vigorously stirred for 1 h; then 10mL of saturated KBr solution is dripped, after stirring for 30 minutes, the pH value of the solution is adjusted to 10.5 by using 6mol/L NaOH solution, and the obtained solution mixture is placed in a stainless steel autoclave with a Teflon lining and heated for 3 hours at 435K; after this time, the mixture was centrifuged, washed 3 times with deionized water and ethanol, and finally dried at 335K for 4 hours. Although Bi is obtained by the method ₅ O ₇ Br nanosheets, but like the hydrothermal method described above for obtaining nanowires, were obtained with the addition of NaOH solution. The application provides a new solution, and the two-dimensional Bi with less atomic layers is synthesized by controlling the proportion of triethylamine and mannitol in the reaction process ₅ O ₇ And (4) Br ultrathin nanosheets.

Disclosure of Invention

The technical problem to be solved by the invention is to provide Bi ₅ O ₇ The preparation method of the Br nanosheet is used for accurately regulating and controlling the composition, crystal structure and surface morphology of a synthetic sample by regulating and controlling the proportion of triethylamine and mannitol in the reaction process to obtain Bi ₅ O ₇ An ultrathin Br nanosheet.

In order to solve the technical problems, the invention adopts the following technical scheme:

bi ₅ O ₇ The preparation method of the Br nanosheet comprises the following steps:

1) taking bismuth nitrate pentahydrate (Bi (NO) ₃ ) ₃ ·5H ₂ O), mannitol and polyvinylpyrrolidone K23-27 are put in water and stirred until a transparent clear liquid is obtained; wherein the dosage of mannitol is 2.45-2.55 times of that of the bismuth nitrate pentahydrate substance;

2) adding a saturated potassium bromide solution into the obtained transparent clear liquid under the stirring condition, stirring for a certain time, then adding triethylamine, and continuing stirring to obtain a mixed solution; the adding amount of the saturated potassium bromide solution is determined according to the amount of a bismuth nitrate pentahydrate substance in the transparent clear liquid, and is specifically calculated by taking 2-2.5 mL of the saturated potassium bromide solution added when the amount of the bismuth nitrate pentahydrate substance is 1mmol as a reference; the addition amount of the triethylamine is 1.15-1.73 times of the amount of a mannitol substance in the transparent clear liquid;

3) placing the obtained mixed solution into a hydrothermal reaction kettle for hydrothermal reaction, naturally cooling after the reaction is finished, collecting a product in the hydrothermal reaction kettle, washing and drying to obtain the Bi ₅ O ₇ Br nanosheet.

In the step 1) of the preparation method, the average molecular weight of the polyvinylpyrrolidone K23-27 is 24000, and the dosage of the polyvinylpyrrolidone K23-27 is preferably 0.016-0.017 times of that of the bismuth nitrate pentahydrate substance. In the step, the dosage of the mannitol is more preferably 2.49-2.52 times of that of the bismuth nitrate pentahydrate substance. The test results of the Applicant have shown that, under otherwise unchanged conditions, when other surfactants such as cetyltrimethylammonium bromide, polyvinylpyrrolidone K15, polyvinylpyrrolidone K30 or polyvinylpyrrolidone K90, etc., are used instead of polyvinylpyrrolidone K23-27, there is no Bi target product ₅ O ₇ And generating Br nano sheets.

In the step 2) of the preparation method, the addition amount of the saturated potassium bromide solution is further preferably calculated based on 2 to 2.3mL of the added bismuth nitrate pentahydrate substance when the amount of the bismuth nitrate pentahydrate substance is 1mmol, and the stirring time after the saturated potassium bromide solution is added is usually 10 to 20 min. The addition amount of the triethylamine is preferably 1.4-1.5 times of the amount of mannitol substances in the transparent clear liquid, and the stirring time after the triethylamine is added is usually controlled to be 10-20 min. In this step, the saturated potassium bromide solution and triethylamine are preferably added in a dropwise manner.

In the step 3) of the preparation method, the operation of the hydrothermal reaction and the subsequent washing and drying is the same as that of the prior art, specifically, the temperature of the hydrothermal reaction is controlled to be 150-180 ℃, but the time of the hydrothermal reaction is controlled to be 150-200 min; washing is carried out by using absolute ethyl alcohol and water, and drying is preferably freeze drying.

Compared with the prior art, the invention is characterized in that:

1. the reductive organic micromolecule triethylamine and mannitol are used as structure control agents to be mutually competitive and induced to form Bi ₅ O ₇ Br, the composition, the crystal structure and the surface appearance of a synthesized sample are accurately regulated and controlled by regulating the proportion of triethylamine and mannitol which participate in synthesis, and two-dimensional Bi is obtained ₅ O ₇ And (4) Br ultrathin nanosheets.

2. The method is carried out at room temperature, has mild and easily-controlled conditions, no energy consumption and low cost.

Drawings

Fig. 1 is an XRD pattern of samples prepared in example 1 of the present invention, comparative example 1 and comparative example 2.

FIG. 2 is a TEM image of a sample prepared in example 1 of the present invention.

FIG. 3 is a TEM image of a sample prepared in comparative example 1 of the present invention.

FIG. 4 is a TEM image of a sample prepared in comparative example 2 of the present invention.

FIG. 5 is a graph showing the relationship between the residual MO concentration and time in the experiments of photocatalytic degradation MO for the samples prepared in example 1, comparative example 1 and comparative example 2 of the present invention.

FIG. 6 is a graph of residual BPA concentration versus time for experiments involving photocatalytic degradation of BPA for samples made according to the present invention from example 1, comparative example 1 and comparative example 2.

FIG. 7 is a graph showing the residual ENR concentration with respect to time in the ENR photocatalytic degradation experiment for the samples obtained in example 1, comparative example 1 and comparative example 2 of the present invention.

FIG. 8 is a graph of the concentration of CIP remaining in the photocatalytic degradation CIP test of the samples prepared in example 1, comparative example 1 and comparative example 2 of the present invention as a function of time.

FIG. 9 is a bar graph showing the degradation rates of ENR and CIP in photocatalytic degradation ENR and CIP experiments for the samples prepared in example 1, comparative example 1 and comparative example 2 of the present invention.

FIG. 10 is a TEM side view of a sample prepared in example 1 of the present invention.

FIG. 11 is a TEM side view of a sample prepared in comparative example 1 of the present invention.

FIG. 12 is a TEM side view of a sample prepared in comparative example 2 of the present invention.

Fig. 13 is an XRD pattern of a sample prepared in comparative example 3 of the present invention.

FIG. 14 is an SEM photograph of a sample prepared in comparative example 3 of the present invention.

Fig. 15 is an XRD pattern of a sample prepared in comparative example 4 of the present invention.

FIG. 16 is an SEM photograph of a sample prepared in comparative example 4 of the present invention.

FIG. 17 is an SEM photograph of a sample obtained in comparative example 5 in which cetyltrimethylammonium bromide was used in place of polyvinylpyrrolidone K23-27.

FIG. 18 is an SEM photograph of a sample obtained in comparative example 5 in which polyvinylpyrrolidone K15 was used in place of polyvinylpyrrolidone K23-27.

FIG. 19 is an SEM photograph of a sample obtained in comparative example 5 in which polyvinylpyrrolidone K30 was used in place of polyvinylpyrrolidone K23-27.

FIG. 20 is an SEM photograph of a sample obtained in comparative example 5 in which polyvinylpyrrolidone K90 was used in place of polyvinylpyrrolidone K23-27.

Detailed Description

In order to better explain the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and examples, but the embodiments of the present invention are not limited thereto.

Example 1

1) Weighing 0.4850g (1mmol) of bismuth nitrate pentahydrate, 0.4550g (2.50mmol) of mannitol and 0.4000g (0.0167mmol) of polyvinylpyrrolidone K23-27 (average molecular weight 24000) into a beaker, adding 25mL of deionized water into the beaker to dissolve the components, and continuously stirring at room temperature until a transparent and clear liquid is obtained;

2) dropwise adding 2mL of KBr saturated solution into the obtained transparent and clear liquid under stirring, and then continuing stirring for 10 min; then 0.5mL (3.60mmol) of triethylamine is added into the solution dropwise, and the solution is stirred for 10min to obtain a mixed solution;

3) transferring 20mL of the mixed solution obtained in the step 2) by using a liquid transfer gun, placing the mixed solution into a hydrothermal reaction kettle, placing the hydrothermal reaction kettle into an oven, reacting for 180min at 160 ℃, and naturally cooling after the reaction is finished; when the temperature of the reaction kettle naturally drops to the environmental temperature, collecting a yellow sample in the reaction kettle, firstly washing the sample with absolute ethyl alcohol for 3 times (centrifuging for 5min by using an ultra-high speed refrigerated centrifuge with the rotating speed of 9000 rmp/min), and then washing the sample with deionized water for 3 times; after the washing, the sample was collected in a sample bottle with water, and the precipitate obtained in the sample bottle was frozen with liquid nitrogen and then dried in a freeze dryer, and the obtained sample was referred to as the sample of example 1.

The sample of example 1 was subjected to X-ray diffraction (XRD) analysis, and its XRD pattern is shown in FIG. 1. from FIG. 1, it can be seen that the sample prepared in this example has characteristic peaks and Bi ₅ O ₇ Br Standard card was identical, and therefore, it was determined that the sample obtained in this example was Bi ₅ O ₇ A Br material.

The TEM analysis of the sample of example 1 is shown in FIG. 2, and it can be seen from FIG. 2 that Bi is obtained ₅ O ₇ The Br material is a thin-layer nanosheet and is uniform in appearance.

The side surface of the sample of example 1 was analyzed by transmission electron microscopy, the TEM image is shown in FIG. 10, and Bi is shown in FIG. 10 ₅ O ₇ The Br nano-sheet has a thickness of 3 to 4 atomic layers, considering Bi ₅ O ₇ Average height of Br monolayer (c: 1.1497nm), Bi prepared in this example ₅ O ₇ The thickness of Br is 3-4 nm.

Comparative example 1

Example 1 was repeated, except that triethylamine was not added dropwise in step 2).

The sample obtained after drying is referred to as comparative example 1.

The sample of comparative example 1 was subjected to X-ray diffraction (XRD) analysis, and its XRD pattern is shown in fig. 1, and it can be seen from fig. 1 that the characteristic peaks of the sample prepared in this comparative example are consistent with those of the BiOBr standard card, thus determining that the sample obtained in this comparative example is a BiOBr material.

The sample of comparative example 1 was analyzed by transmission electron microscopy, the TEM image is shown in fig. 3, and it can be seen from fig. 3 that the obtained BiOBr material exhibits a two-dimensional nano-sheet structure.

The side surface of the sample of comparative example 1 was analyzed by transmission electron microscopy, the TEM image is shown in fig. 11, and as can be seen from fig. 11, the BiOBr nanosheets had a thickness of 4 atomic layers, and the thickness of the BiOBr produced in this example was 3 to 4nm, taking into account the average height of the BiOBr monolayer (c: 0.8103 nm).

Comparative example 2

Example 1 was repeated, except that mannitol was not added dropwise in step 2).

The sample obtained after drying was referred to as comparative example 2 sample.

The XRD pattern of the sample of comparative example 2 was shown in FIG. 1 by X-ray diffraction analysis, and it can be seen from FIG. 1 that the characteristic peak and Bi of the sample of comparative example are shown ₄ O ₅ Br ₂ The standard cards are identical, thus determining that the sample obtained in the comparative example is Bi ₄ O ₅ Br ₂ A material.

The sample of comparative example 2 was subjected to transmission electron microscopy analysis, the TEM image of which is shown in FIG. 4, and it can be seen from FIG. 4 that Bi was obtained ₄ O ₅ Br ₂ The material exhibits a large two-dimensional nano-platelet structure.

The side surface of the obtained sample of comparative example 2 was analyzed by transmission electron microscopy, a TEM image of which is shown in FIG. 12, and Bi is shown in FIG. 12 ₄ O ₅ Br ₂ The nanosheets are 7 atomic layers thick, taking into account Bi ₄ O ₅ Br ₂ Average height of monolayer (c: 1.0830nm), Bi prepared in this example ₄ O ₅ Br ₂ The thickness of (2) is 7-8 nm.

Comparative example 3

Example 1 was repeated, except that the amount of triethylamine to be added dropwise in step 2) was 0.65mL (4.68mmol, corresponding to 1.87 times the amount of mannitol).

The sample obtained after drying is referred to as comparative example 3.

The XRD pattern of the sample of comparative example 3 obtained by the X-ray diffraction analysis is shown in FIG. 13, and it can be seen from FIG. 13 that the characteristic peaks and peaks of the sample prepared by the comparative exampleBi ₅ O ₇ Br Standard card was identical, and thus it was determined that the sample obtained in this comparative example was Bi ₅ O ₇ A Br material.

The sample of comparative example 3 was subjected to transmission electron microscopy analysis, the TEM image of which is shown in FIG. 14, and it can be seen from FIG. 14 that Bi was obtained ₅ O ₇ Br materials exhibit a fine villous, not ultrathin nanosheet structure.

Comparative example 4

Example 1 was repeated, except that the amount of triethylamine added dropwise in step 2) was 0.3mL (2.16mmol, corresponding to 0.86 times the amount of mannitol).

The sample obtained after drying is referred to as comparative example 4.

The XRD pattern of the sample of comparative example 4 was shown in fig. 15, and it can be seen from fig. 15 that the characteristic peaks of the sample prepared in this comparative example were consistent with those of the BiOBr standard card, thereby determining that the sample obtained in this comparative example is a BiOBr material.

The resulting comparative example 4 sample was analyzed by transmission electron microscopy, and its TEM image is shown in fig. 16, and from fig. 16 it can be seen that the resulting BiOBr material exhibited a platelet-like structure.

Comparative example 5

Example 1 was repeated, except that, in step 1), polyvinylpyrrolidone K23-27 was replaced by cetyltrimethylammonium bromide, polyvinylpyrrolidone K15, polyvinylpyrrolidone K30 or polyvinylpyrrolidone K90, and as a result, the desired product Bi was not obtained ₅ O ₇ Br nanosheet. Wherein:

the SEM image of the sample obtained when cetyltrimethylammonium bromide was used in place of polyvinylpyrrolidone K23-27 is shown in FIG. 17, exhibiting a finely divided, small villous structure.

The SEM images of the samples obtained when polyvinylpyrrolidone K15 was used instead of polyvinylpyrrolidone K23-27 are shown in fig. 18, showing a more distinct mixed structure of lines and sheets.

The SEM image of the sample obtained when polyvinylpyrrolidone K30 was used in place of polyvinylpyrrolidone K23-27 is shown in FIG. 19, and shows a mixed structure of wires and sheets in which the wires are the main component.

The SEM image of the sample obtained when polyvinylpyrrolidone K90 was used in place of polyvinylpyrrolidone K23-27 is shown in FIG. 20, and shows a mixed structure of lines and sheets in which the lines are the main component.

Example 2

Example 1 was repeated, except that in step 2), the amount of triethylamine was added dropwise in an amount of 0.59mL (4.24mmol, corresponding to 1.7 times that of mannitol).

The sample obtained in this example was analyzed by X-ray diffraction and transmission electron microscopy to determine that the sample obtained in this example was Bi ₅ O ₇ Br material, and Bi obtained ₅ O ₇ The Br material is a thin-layer nanosheet and is uniform in appearance.

Example 3

Example 1 was repeated, except that, in step 2), the amount of mannitol was 2.55mmol and the amount of triethylamine was 0.43mL (3.09mmol, corresponding to 1.2 times the amount of mannitol) added dropwise.

Example 4

Example 1 was repeated, except that, in step 2), mannitol was used in an amount of 2.45mmol and triethylamine was added dropwise in an amount of 0.51mL (3.669mmol, corresponding to 1.5 times the amount of mannitol).

Example 5

Photocatalytic degradation experiments were performed on the samples prepared in example 1, comparative example 1 and comparative example 2, wherein the sample prepared in example 1 was Bi ₅ O ₇ Br, BiOBr for the sample obtained in comparative example 1 and Bi for the sample obtained in comparative example 2 ₄ O ₅ Br ₂ And (4) showing.

Simulated sunlight equipped with 300W Xe lamps was used as the light source. MO (methyl orange) and BPA (bisphenol a) were selected as model contaminants to evaluate the photocatalytic activity of each sample. The experimental details of photocatalytic degradation of MO or BPA are as follows:

dispersion of 20mg of sample into 50mL MO or BPA solution in photoreactor (10) ^-4 mol/L). Before illumination, the mixed solution is magnetically stirred in the dark for 30min to make the adsorption-desorption balance between the photocatalyst and the pollutants. After switching on the lamp, the reactor was illuminated under simulated sunlight, maintaining the distance from the reactor to the lamp at 6cm, and approximately 4mL of suspension were withdrawn every 10 min. The catalyst was removed by centrifugation, and the absorbance of the supernatant was measured by an ultraviolet-visible spectrophotometer. The absorbance intensity of MO and BPA at 464nm and 276nm wavelengths, respectively, was recorded. The whole experimental process adopts a circulating water system to keep the room temperature, so that the thermocatalysis effect is prevented.

The influence of bismuth oxybromide materials with different crystal structures on the photocatalytic activity is revealed by photocatalytic degradation of organic dye MO in aqueous solution. The change in the concentration of the MO solution was determined by analyzing the magnitude of the peak of the characteristic MO solution peak. Fig. 5 shows the relationship between the residual MO concentration and time in the MO photocatalytic degradation experiment of the samples prepared in example 1, comparative example 1 and comparative example 2 of the present invention, and it can be seen from fig. 5 that: the blank test results show that in the case of simulated solar irradiation and without the addition of the three materials, almost no MO is degraded, which indicates that the direct photodegradation of MO, which is formed by the oxidation of the photocatalyst added to the photocatalytic system under light, is almost negligible. Furthermore, we see that in the presence of a photocatalyst, the concentration of MO remaining in the solution gradually decreases as the xenon lamp exposure time is extended. After 20min of illumination, in Bi ₅ O ₇ In the system with Br as the photocatalyst, the absorbance of the MO characteristic peak is almost completely 0, which indirectly shows that in Bi ₅ O ₇ Under the action of the Br nano-sheets, the benzene ring structure of MO is destroyed. Subsequently, use (C) ₀ -C/C ₀ ) X 100% calculation of the removal efficiency (%) of MO solutions, where C ₀ Is the initial concentration of MO and C is the residual concentration of MO. The calculation result shows that BiOBr and Bi are obtained after 20min of illumination ₄ O ₅ Br ₂ The degradation rate of the material is only 53.52 percent and 25.83 percent, which is compared with Bi ₅ O ₇ Br is much worse.

The degradation of the dye is realized by direct semiconductor light excitation and indirect dye photosensitization, and in order to eliminate the photosensitization effect of the dye and further evaluate the photocatalytic degradation activity of a synthesized sample, BPA is used as a colorless phenol pollutant with acute toxicity and biological difficult degradation and is selected as an ideal probe for evaluating the photocatalytic activity of a semiconductor photocatalytic material. FIG. 6 shows the residual BPA concentration versus time for the samples prepared in example 1, comparative example 1 and comparative example 2 of the present invention in a photocatalytic BPA degradation experiment, where the blank test results show that BPA is not removed, indicating that BPA is fairly stable under the test conditions and cannot decompose by itself, and that its own photodegradation can be ignored in the photocatalytic experiment. Obviously, the trend of change of removing BPA is similar to that of MO solution, and Bi ₅ O ₇ The photocatalytic activity of Br was best in the three samples.

To prove Bi ₅ O ₇ The Br nano-sheet has broad spectrum of toxic organic compounds in photocatalytic degradation water, and antibiotics CIP and ENR are selected to replace MO and BPA to serve as model pollutants for experiments. The experimental conditions were the same as those described above for the photocatalytic degradation of MO or BPA, i.e., under the same conditions, 30mg of ciprofloxacin (CIP: 0.4X 10) ^-4 mol/L) and enrofloxacin (ENR: 0.4X 10 ^-4 mol/L) and recording the absorbance intensity of CIP and ENR at the wavelength of 277nm and 271nm respectively to investigate the broad spectrum of the photocatalyst in treating organic wastewater.

Fig. 7 to 9 show that the tendency of CIP and ENR degradation is consistent with the tendency of photocatalytic oxidation of MO and BPA, both presenting such results: bi ₅ O ₇ Br＞BiOBr＞Bi ₄ O ₅ Br ₂ 。

Claims

1. Bi ₅ O ₇ The preparation method of the Br nanosheet comprises the following steps:

1) putting bismuth nitrate pentahydrate, mannitol and polyvinylpyrrolidone K23-27 into water, and stirring until a transparent clear liquid is obtained; wherein the dosage of mannitol is 2.45-2.55 times of that of the bismuth nitrate pentahydrate substance;

2. The preparation method according to claim 1, wherein in the step 1), the amount of the polyvinylpyrrolidone K23-27 is 0.016-0.017 times of that of the bismuth nitrate pentahydrate substance.

3. The method according to claim 1, wherein in the step 1), the amount of mannitol is 2.49 to 2.52 times the amount of the bismuth nitrate pentahydrate.

4. The method according to claim 1, wherein the stirring time after the potassium bromide saturated solution is added in the step 2) is 10 to 20 min.

5. The method according to claim 1, wherein the stirring time after the triethylamine is added in the step 2) is 10 to 20 min.

6. The method according to claim 1, wherein the hydrothermal reaction is carried out at a temperature of 150 to 180 ℃ in the step 3).

7. The method according to claim 1, wherein the hydrothermal reaction time in step 3) is 150 to 200 min.