阅读说明：本技术 一种含光控氧空位BiOBr光催化剂的合成及应用方法 (Synthesis and application method of BiOBr photocatalyst containing optically controlled oxygen vacancies ) 是由 张璐璐 李�瑞 樊彩梅 刘建新 张小超 张长明 王雅文 王韵芳 于 2020-12-14 设计创作，主要内容包括：一种含光控氧空位BiOBr光催化剂的合成及应用方法,属于纳米材料技术领域,可解决现有含氧空位(OVs)BiOBr光催化剂的稳定性差的缺点,本发明以五水硝酸铋和溴酸钠为原料,调节反应温度,利用一步水解法制得含光控氧空位的BiOBr材料。即在光照条件下,催化剂可脱除氧原子产生氧空位,而当光源移除后,催化剂会吸附水或空气中的氧原子,使得氧空位复原,当再次光照时,氧空位再次产生,以解决氧空位易失活及反应效率不高的问题,为设计高效稳定的合成氨光催化剂提供了新的研究思路。(A method for synthesizing and applying a BiOBr photocatalyst containing optically controlled oxygen vacancies belongs to the technical field of nano materials, and can solve the defect of poor stability of the existing Oxygen Vacancy (OVs) BiOBr photocatalyst. Under the illumination condition, the catalyst can remove oxygen atoms to generate oxygen vacancies, and after a light source is removed, the catalyst can adsorb the oxygen atoms in water or air to recover the oxygen vacancies, and when the light source is illuminated again, the oxygen vacancies are generated again so as to solve the problems that the oxygen vacancies are easy to inactivate and the reaction efficiency is not high, thereby providing a new research idea for designing a high-efficiency and stable synthetic ammonia photocatalyst.)

1. A synthetic method of a BiOBr photocatalyst containing optically controlled oxygen vacancies is characterized by comprising the following steps: the method comprises the following steps:

firstly, weighing bismuth nitrate pentahydrate, placing the bismuth nitrate pentahydrate into diethylene glycol, stirring for 0.5-2.5 hours at room temperature until the bismuth nitrate pentahydrate is completely dissolved, and marking as a solution A;

secondly, weighing sodium bromate, placing the sodium bromate in distilled water, and stirring at room temperature for 0.5-2.5 hours until the solution becomes clear, and marking as a solution B;

thirdly, adding the solution B into the solution A, stirring to uniformly mix the solution B and the solution A, and then stirring to react for 2-5 hours at the reaction temperature of 2-20 ℃ to obtain a precipitate;

and fourthly, separating the precipitate obtained in the third step by using a suction filter, washing the precipitate for 2-3 times by using distilled water and absolute ethyl alcohol respectively, and drying the precipitate at 50-70 ℃ to obtain the BiOBr nano material containing the light-controlled oxygen vacancy, which can be used for artificial photocatalysis nitrogen fixation.

2. The method for synthesizing the BiOBr photocatalyst containing the optically controlled oxygen vacancies as claimed in claim 1, wherein the method comprises the following steps: in the first step, the ratio of the bismuth nitrate pentahydrate to the diethylene glycol is 0.080-0.138 g/mL.

3. The method for synthesizing the BiOBr photocatalyst containing the optically controlled oxygen vacancies as claimed in claim 1, wherein the method comprises the following steps: in the second step, the ratio of the sodium bromate to the distilled water is 0.025-0.043 g/mL.

4. The method for synthesizing the BiOBr photocatalyst containing the optically controlled oxygen vacancies as claimed in claim 1, wherein the method comprises the following steps: the molar ratio of the bismuth nitrate pentahydrate to the sodium bromate is 0.975-1.025.

5. The BiOBr photocatalyst containing optically controlled oxygen vacancies prepared by the synthesis method of claim 1 is applied to aqueous phase photocatalytic nitrogen fixation reaction.

6. The use of a photo-catalyst comprising optically controlled oxygen vacancies bibbr as claimed in claim 5, wherein: the reaction conditions are as follows: the method is characterized by comprising the steps of (1) normal temperature and pressure, the dosage of a catalyst is 0.05 g, the dosage of distilled water is 100 mL, a used light source is a xenon lamp, the power is 300W, the illumination is 120klx, the distance from a reaction interface is 20 cm, and the emitted light is simulated sunlight with the wavelength of 200-800 nm.

Technical Field

The invention belongs to the technical field of nano materials, and particularly relates to a synthesis and application method of a BiOBr photocatalyst containing optically controlled oxygen vacancies, which can be used for synthesizing ammonia by photocatalytic reduction of nitrogen.

Background

Ammonia is a chemical substance and energy carrier necessary for human production and life, and is in great demand. The ammonia synthesis reaction currently used in industry is the traditional Haber-Bosch process, i.e. ammonia synthesis using nitrogen and hydrogen, but this technology requires conditions of high temperature and pressure (15-25 MPa, 300-. In the times of global fossil fuel shortage and climate warming becoming serious, it is of great significance to find cheap, efficient, green and energy-saving synthetic ammonia technology.

Reacting the hydrogen source for synthesizing ammonia with H₂Is changed to H₂O, with N at normal temperature and pressure₂By direct reaction to form NH₃Is a new way for synthesizing ammonia. So far, research directions such as biological nitrogen fixation, electrocatalysis, photoelectrocatalysis, photocatalysis and the like have appeared, wherein the photocatalysis with the sunlight as the driving force synthesizes ammonia, and the consumption of organic solvent, electric energy and heat energy is not needed, so that the method is a sustainable green process and has good development prospect.

Among a plurality of representative photocatalysts, the BiOBr photocatalyst containing Oxygen Vacancies (OVs) is widely applied to the field of photocatalytic nitrogen fixation due to the unique open layered structure, indirect transition mode, excellent photoresponse capability, adsorption and activation of self oxygen vacancies on nitrogen molecules and inhibition of carrier recombination. For example, BiOBr-OVs photocatalysis is synthesized by Zhang Production team by using hydrothermal methodThe presence of oxidant, oxygen vacancies, allows ammonia synthesis rates as high as 223.3 [ mu ] mol.h^-1·g^-1（J. Am. Chem. Soc. 2015, 137, 6393−6399) (ii) a Xue et al synthesized BiOBr containing oxygen vacancies with an ammonia synthesis rate of 54.7 μmol. h under simulated solar irradiation^-1·g^-1Up to ten times higher than BiOBr without oxygen vacancies (Nano Lett. 2018, 18, 7372−7377）。

However, since oxygen vacancies are easily oxidized when exposed to air, such catalysts generally have the problems of easy deactivation and poor stability (Environ. Sci.: Nano.2014, 1, 90) It is important to create abundant and stable sustainable oxygen vacancies on semiconductor materials: (Adv. Mater. 2017, 29, 1701774). It is reported that oxygen-containing catalysts remove oxygen atoms and form oxygen vacancies under UV irradiation (Nanoscale. 2014, 6, 8473) And simultaneously, the formed oxygen vacancy can absorb oxygen atoms in water or air after the light source is removed, and the original composition is recovered, so that the recycling of the oxygen vacancy and high-efficiency nitrogen fixation are realized.

Disclosure of Invention

The invention provides a synthesis and application method of a BiOBr material containing optically controlled oxygen vacancies aiming at the defect of poor stability of the existing Oxygen Vacancy (OVs) BiOBr photocatalyst, and aims to provide a simple, economic and environment-friendly hydrolysis method for preparing a novel photocatalyst with stronger performance and single composition, thereby achieving the effects of fully and effectively utilizing solar energy and synthesizing ammonia by artificially and photocatalytically reducing nitrogen.

The invention aims to design a simple, economic and environment-friendly method for preparing the BiOBr nano material containing the light-controlled oxygen vacancy for the photocatalytic nitrogen fixation reaction, namely, under the illumination condition, the catalyst can remove the oxygen atom to generate the oxygen vacancy, when a light source is removed, the catalyst can adsorb the oxygen atom in water or air to recover the oxygen vacancy, when the light source is illuminated again, the oxygen vacancy is generated again, so that the problems that the oxygen vacancy is easy to inactivate and the reaction efficiency is low are solved, and a new research idea is provided for designing a high-efficiency and stable synthetic ammonia photocatalyst.

The invention relates to a synthesis and application method of a BiOBr material containing a light-controlled oxygen vacancy, which takes bismuth nitrate pentahydrate and sodium bromate as raw materials, precisely adjusts the reaction temperature, and prepares the BiOBr material containing the light-controlled oxygen vacancy by utilizing a simple, economic and environment-friendly one-step hydrolysis method.

The invention adopts the following technical scheme:

a synthesis and application method of a BiOBr photocatalyst containing optically controlled oxygen vacancies comprises the following steps:

firstly, weighing bismuth nitrate pentahydrate, placing the bismuth nitrate pentahydrate into diethylene glycol, stirring for 0.5-2.5 hours at room temperature until the bismuth nitrate pentahydrate is completely dissolved, and marking as a solution A;

secondly, weighing sodium bromate, placing the sodium bromate in distilled water, and stirring at room temperature for 0.5-2.5 hours until the solution becomes clear, and marking as a solution B;

thirdly, adding the solution B into the solution A, stirring to uniformly mix the solution B and the solution A, and then stirring to react for 2-5 hours at the reaction temperature of 2-20 ℃ to obtain a precipitate;

and fourthly, separating the precipitate obtained in the third step by using a suction filter, washing the precipitate for 2-3 times by using distilled water and absolute ethyl alcohol respectively, and drying the precipitate at 50-70 ℃ to obtain the BiOBr nano material containing the light-controlled oxygen vacancy, which can be used for artificial photocatalysis nitrogen fixation.

In the first step, the ratio of the bismuth nitrate pentahydrate to the diethylene glycol is 0.080-0.138 g/mL.

In the second step, the ratio of the sodium bromate to the distilled water is 0.025-0.043 g/mL.

The molar ratio of the bismuth nitrate pentahydrate to the sodium bromate is 0.975-1.025.

A BiOBr photocatalyst containing light-controlled oxygen vacancies is applied to water-phase photocatalytic nitrogen fixation reaction.

A BiOBr photocatalyst containing optically controlled oxygen vacancies is applied to aqueous phase photocatalytic nitrogen fixation reaction, and the reaction conditions are as follows: the method is characterized by comprising the steps of (1) normal temperature and pressure, the dosage of a catalyst is 0.05 g, the dosage of distilled water is 100 mL, a used light source is a xenon lamp, the power is 300W, the illumination is 120klx, the distance from a reaction interface is 20 cm, and the emitted light is simulated sunlight with the wavelength of 200-800 nm.

The invention has the following beneficial effects:

1. the preparation method of the existing oxygen vacancy-containing BiOBr photocatalyst is mainly a solvothermal method, the reaction temperature is up to 160 ℃, or a surfactant such as polyvinyl pyrrolidone (PVP) and the like is added for synthesis, or a BiOBr nano material containing oxygen vacancies is obtained through high-temperature heat treatment. The method is simple, feasible, economical and environment-friendly, does not generate toxic and harmful byproducts, uses conditions of normal temperature and pressure, is simple and safe, has cheap and easily-obtained raw materials, and is easy to realize industrial production;

2. the catalyst prepared by the invention has a single composition and has a photo-controlled oxygen vacancy, namely under the illumination condition, the catalyst can remove oxygen atoms to generate the oxygen vacancy, and when a light source is removed, the catalyst can absorb the oxygen atoms in water or air, so that the oxygen vacancy is recovered. Optically controlled oxygen vacancy materials exhibit the advantage of being more consistently stable than materials containing naturally occurring synthetic oxygen vacancies ((Adv. Mater. 2017, 29, 1701774）；

3. Compared with the conventional TiO₂(P25) and a BiOBr photocatalyst, wherein the BiOBr catalyst containing the optically controlled oxygen vacancy shows good photocatalytic nitrogen fixation activity, has stable performance and can be repeatedly used.

Drawings

FIG. 1 is an XRD spectrum of BiOBr-OVs-A nanomaterial prepared in example 1 of the present invention;

FIG. 2 is an SEM topography of a BiOBr-OVs-A nanomaterial prepared in example 1 of the present invention;

FIG. 3 is a diagram showing the photocatalytic nitrogen fixation performance of the BiOBr-OVs-A nanomaterial prepared in example 1 of the present invention;

FIG. 4 is a diagram showing the photocatalytic nitrogen fixation performance of the BiOBr-OVs-B nanomaterial prepared in example 2 of the present invention;

FIG. 5 is a graph showing the cycling stability of BiOBr-OVs-A nanomaterials made in example 1 of the present invention;

FIG. 6 is a graph showing Electron Paramagnetic Resonance (EPR) of BiOBr-OVs-A produced in example 1 of the present invention under different reaction conditions.

Detailed Description

Example 1

Adding 0.01mol Bi (NO)₃)₃·5H₂O was added to 50mL of diethylene glycol and stirred at room temperature for 1.5h, 0.01mol of NaBrO was added₃Adding the mixture into 50mL of distilled water, stirring at room temperature for 1.5h, mixing the two solutions, continuously reacting for 3 h under the condition until a precipitate is generated, and finally separating, washing and drying the obtained precipitate to obtain the BiOBr containing the light-controlled oxygen vacancy, which is marked as BiOBr-OVs-A.

The obtained BiOBr nano material containing the light-controlled oxygen vacancy is used for photocatalysis nitrogen fixation reaction. The reaction conditions are as follows: the method is characterized by comprising the steps of (1) normal temperature and pressure, the dosage of a catalyst is 0.05 g, the dosage of water is 100 mL, the used light source is a xenon lamp, the power is 300W, the illumination is 120klx, the distance from a reaction interface is 20 cm, and the emitted light is simulated sunlight with the wavelength of 200-800 nm. The method comprises the following specific operation steps: firstly, dissolving a photocatalyst in water, performing ultrasonic treatment to fully dissolve the photocatalyst, and then introducing nitrogen for 0.5 h under the condition of keeping out of the sun so as to completely remove air; and then, turning on a light source, carrying out a photocatalytic nitrogen fixation experiment, illuminating for 1 h, taking out 10 mL of filtrate, and analyzing and calculating the yield of ammonia in the solution by using a Nashin reagent method. Meanwhile, in order to verify the activity, the nitrogen fixation performance of the same catalyst under the condition of introducing argon for 0.5 h under the condition of keeping out of the light before the reaction or under the condition of not using a light source in the reaction process is respectively tested, and the result is shown in fig. 3.

Example 2

0.01mol of Bi (NO)₃)₃·5H₂O was added to 50mL of diethylene glycol and stirred at room temperature for 2 hours, 0.01mol of NaBrO was added₃Adding the mixture into 40mL of distilled water, stirring at room temperature for 2h, mixing the two solutions, controlling the temperature by using a water bath kettle at 4 ℃, continuously reacting for 3 h under the condition until a precipitate is generated, and finally separating, washing and drying the obtained precipitate to obtain the BiOBr containing the light-controlled oxygen vacancy, which is marked as BiOBr-OVs-B.

The obtained BiOBr nano material containing the light-controlled oxygen vacancy is used for photocatalysis nitrogen fixation reaction. The reaction conditions are as follows: the method is characterized by comprising the steps of (1) normal temperature and pressure, the dosage of a catalyst is 0.05 g, the dosage of water is 100 mL, the used light source is a xenon lamp, the power is 300W, the illumination is 120klx, the distance from a reaction interface is 20 cm, and the emitted light is simulated sunlight with the wavelength of 200-800 nm. The method comprises the following specific operation steps: firstly, dissolving a photocatalyst in water, performing ultrasonic treatment to fully dissolve the photocatalyst, and then introducing nitrogen for 0.5 h under the condition of keeping out of the sun so as to completely remove air; and then, turning on a light source, carrying out a photocatalytic nitrogen fixation experiment, illuminating for 1 h, taking out 10 mL of filtrate, and analyzing and calculating the yield of ammonia in the solution by using a Nashin reagent method. Meanwhile, in order to verify the activity, the nitrogen fixation performance of the same catalyst under the condition of introducing argon for 0.5 h under the condition of keeping out of the light before the reaction or under the condition of not using a light source in the reaction process is respectively tested, and the result is shown in fig. 4.

Example 3

The BiOBr nano material BiOBr-OVs-A containing the optically controlled oxygen vacancy obtained in the example 1 is used for photocatalytic nitrogen fixation cyclic reaction to test the stability of the BiOBr nano material BiOBr-OVs-A. The reaction conditions are as follows: the method is characterized by comprising the steps of (1) normal temperature and pressure, the dosage of a catalyst is 0.05 g, the dosage of water is 100 mL, the used light source is a xenon lamp, the power is 300W, the illumination is 120klx, the distance from a reaction interface is 20 cm, and the emitted light is simulated sunlight with the wavelength of 200-800 nm. The method comprises the following specific operation steps: firstly, putting the photocatalyst into water, carrying out ultrasonic treatment to fully dissolve the photocatalyst, and then introducing nitrogen for 0.5 h under the condition of keeping out of the sun so as to completely remove air; and then, turning on a light source, carrying out a photocatalytic nitrogen fixation experiment, after illumination is carried out for 1 h, testing the nitrogen fixation activity of the catalyst, then, recovering the catalyst containing oxygen vacancies, continuing to test the activity of the catalyst, and repeating the steps again to test the activity of the catalyst, wherein the result is shown in fig. 5.

From fig. 1, it can be concluded that no impurity peak is found in the diffraction peaks of the prepared sample, the diffraction peaks are sharp, and the relative intensity is large, so that the sample is pure BiOBr and has good crystallinity.

From FIG. 2, it can be obtained that the prepared BiOBr-OVs catalyst has a flower-ball-shaped structure formed by self-assembly of nano-sheets and a single appearance. The self-assembled flower-ball-shaped structure not only can improve the light utilization rate, but also is beneficial to photoproduction electron and hole transfer, reduces the recombination of the photoproduction electron and the hole transfer, and further improves the photocatalysis performance of the photoproduction electron and the hole transfer.

From FIG. 3, it can be seen that the nitrogen fixation activity of the catalyst prepared in example 1 reached 246. mu. mol. g^-1·h^-1Keeping other conditions unchanged, if no catalyst is added, or under dark conditions, or when no nitrogen is introducedAnd the catalyst has no nitrogen fixation activity, and proves that the photocatalytic synthesis of ammonia is realized under the action of the catalyst.

From FIG. 4, it can be seen that the nitrogen fixation activity of the catalyst prepared in example 2 reached 223. mu. mol. g^-1·h^-1。

From fig. 5, it can be concluded that the prepared photocatalyst still shows good nitrogen fixation activity after 4 cycles, indicating that the photocatalyst has good stability.

From FIG. 6, it can be derived that the catalyst prepared has no oxygen vacancy signal under dark conditions; whereas when illuminated for 15min, a stronger signal appeared at g =2.003, indicating oxygen vacancy production; and when the light source is removed, the oxygen vacancy signal slowly disappears. When the catalyst is recovered and then irradiated again, the EPR signal changes in accordance with each other. The experiment shows that the catalyst with controllable oxygen vacancy is successfully prepared.