CN107282077A - A kind of preparation method and applications of photocatalysis fixed nitrogen catalyst - Google Patents

Abstract

The invention discloses a preparation method and application of a photocatalytic nitrogen fixation catalyst. The preparation method is as follows: 1) Dissolving Na ₂ WO ₄ ·2H ₂ O in deionized water, fully stirring to dissolve completely, and obtaining solution A ; 2) Add NaI into the above solution A under stirring condition, continue to stir to dissolve it completely, and obtain solution B; 3) Add Bi(NO ₃ ) ₃ ·5H ₂ O to solution B according to the stoichiometric ratio, and then Stir for 0.5-1 h to obtain solution C; 4) Transfer the above-mentioned solution C to a reaction kettle and conduct a hydrothermal reaction at 120-130°C for 24 h. The obtained precipitate is centrifuged, washed, and dried to obtain BiOI/Bi ₂ WO ₆ composite material, that is, the photocatalytic nitrogen fixation catalyst. The preparation process of the present invention is simple, the conditions are easy to control, the process parameters are adjustable, and the energy consumption and cost are low. The obtained BiOI/Bi ₂ WO ₆ material has good photocatalytic activity and can be applied to the field of photocatalytic nitrogen fixation. Its photocatalytic activity characterization system It is novel and easy to operate, and provides a practical activity evaluation method for the evaluation of photocatalytic materials.

Description

A kind of preparation method and application of photocatalytic nitrogen fixation catalyst

technical field

The invention relates to the technical field of photocatalytic application, in particular to a preparation method and application of a photocatalytic nitrogen fixation catalyst.

technical background

Ammonia is a bulk product of modern chemical industry and a basic guarantee for agricultural development. Its source mainly depends on biological nitrogen fixation and synthetic ammonia chemical production, among which industrial synthetic ammonia is the most important source of agricultural nitrogen fertilizer ammonia. However, the industrial preparation process is relatively complicated, and researchers are still looking for a simpler chemical nitrogen fixation method. We can get inspiration from the known nitrogen fixation methods: organisms reduce molecular nitrogen to ammonia under the action of iron-molybdenum nitrogenase, and reduce nitrogen to ammonia under the action of industrial iron catalysts, that is, to seek a suitable catalyst, in a mild and convenient way. Catalytic reduction of nitrogen to ammonia under certain reaction conditions.

Photocatalytic technology has attracted people's attention because of its own advantages, and countries all over the world have invested a lot of energy in the research and development of photocatalytic materials. Traditional semiconductor photocatalytic materials represented by TiO ₂ have a wide band gap and narrow solar light response, so it is necessary to modify them or develop new photocatalytic materials. Applying photocatalytic technology to nitrogen fixation will be an ideal way to realize nitrogen fixation under mild and simple conditions.

Among the new photocatalysts, bismuth-based photocatalysts have become a research hotspot in visible light catalyst materials due to their unique crystal structure and electronic structure, and a series of significant achievements have been made. Among them, Bi ₂ WO ₆ is an Aurivillius phase compound, which is composed of Bi ₂ O ₂ layers and WO ₆ layers alternately along the c-axis. Its forbidden band width is narrower than that of TiO ₂ (3.2ev), about 2.7eV. It can be excited by visible light, has high photocatalytic activity under visible light, and has good photostability. It is a potential Visible light-responsive photocatalytic materials. Most of the modification studies on Bi ₂ WO ₆ are morphology control, doping and compounding. For example, Yu Hongwen et al. (Chinese patent application CN103877971A) prepared raw materials Na ₂ WO ₆ 2H ₂ O and Bi(NO ₃ ) ₃ 5H ₂ O by adjusting the ratio of Bi ₂ WO ₆ to solvent water and ethylene glycol respectively. Bi ₂ WO ₆ microspheres were thermally prepared. Wu Qiang et al. (Chinese patent application CN103342389A) solidified a layer of Bi ₂ WO ₆ on the base material SiO ₂ to prepare a macroscopically ordered Bi ₂ WO ₆ . But this shape-based control method can no longer change its inertial response range and electron transport mechanism to the maximum extent. For this reason, Duan Fang et al. (Chinese patent application CN102489298A) loaded Bi ₂ WO ₆ on noble metals, and Wu Mingzai et al. (Chinese patent CN103349982A) loaded Bi ₂ WO ₆ on TiO ₂ , in addition to element doping, etc., so that Bi ₂ WO ₆ has been greatly modified, and the photocatalytic performance of the obtained material has been greatly improved.

The bismuth oxyhalide material in the bismuth series materials has a tetragonal crystal structure, which is alternately arranged with Bi ₂ O ₂ layers and two halide ion layers. BiOI has the strongest visible light response in bismuth oxyhalides, so combining it with Bi ₂ WO ₆ may change the photoresponse and electron transport state of Bi ₂ WO ₆ to the greatest extent. For example, Ju Peng et al. (Chinese patent application CN105289666A) stirred the precursors of BiOI and Bi ₂ WO ₆ in a mixed solution of ethanol and sodium hydroxide to prepare a layered flower-like structure BiOI/Bi ₂ WO ₆ composite photocatalytic insecticide agent; Yu Jianqiang et al. (Chemical Engineering Journal, 2016, 288: 264-275) prepared a series of BiOI/Bi ₂ WO ₆ pn junction composites by chemical etching, and found that it has good catalytic and bactericidal properties; Fang Zhanqiang et al. ( J ChemTechnol Biotechnol, 2015; 90: 947–954) BiOI/Bi ₂ WO ₆ with good visible light response and photocatalytic dye degradation performance was prepared in a 50 ml reactor with dilute nitric acid as solvent and one-step hydrothermal method. The BiOI/Bi ₂ WO ₆ prepared above improves the photoresponse and electron transport properties of Bi ₂ WO ₆ to a certain extent, but the photocatalysis of BiOI/Bi ₂ WO ₆ is applied to conventional sterilization and dye degradation, if the It is even more significant to apply it to a new photocatalytic reaction system.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a preparation method and application of a photocatalytic nitrogen fixation catalyst with mild reaction conditions, simple and easy operation, environment-friendly and low consumption.

In order to achieve the above object, the present invention adopts the above technical solutions:

A preparation method of a photocatalytic nitrogen fixation catalyst, comprising the following steps:

1) Dissolve Na ₂ WO ₄ 2H ₂ O in deionized water, stir well to dissolve completely, and obtain solution A,

2) Add NaI to the above solution A under stirring condition, continue to stir to dissolve it completely, and obtain solution B;

Wherein, the ratio of NaI to Na ₂ WO ₄ ·2H ₂ O is 0.1-1.5:0.35-0.95;

3) According to the stoichiometric ratio, add Bi(NO ₃ ) ₃ ·5H ₂ O to solution B, and then stir for 0.5-1 h to obtain solution C;

Wherein, the ratio of Bi(NO ₃ ) ₃ .5H ₂ O to Na ₂ WO ₄ .2H ₂ O is 1:0.175-0.475;

4) The above solution C was transferred to a reaction kettle, and subjected to hydrothermal reaction at 120-130°C for 24 hours, and the resulting precipitate was centrifuged, washed, and dried to obtain a BiOI/Bi ₂ WO ₆ composite material, which is the photocatalytic nitrogen fixation catalyst.

In step 1), the ratio of Na ₂ WO ₄ ·2H ₂ O to deionized water is 0.35-0.95mmol:80mL.

Further, the sum of twice the amount of Na ₂ WO ₄ ·2H ₂ O and the amount of NaI is 2 mmol.

In step 3) of the present invention, adding Bi(NO ₃ ) ₃ 5H ₂ O to solution B according to the stoichiometric ratio means that the corresponding Bi ₂ WO ₆ is generated according to the total molar amount of Na ₂ WO ₄ and NaI in solution B and the amount of Bi(NO ₃ ) ₃ 5H ₂ O required by BiOI, add the corresponding molar amount of Bi(NO ₃ ) ₃ 5H ₂ O, so as to control the ratio relationship between BiOI and Bi ₂ WO ₆ in the obtained photocatalytic nitrogen fixation catalyst .

The BiOI/Bi ₂ WO ₆ composite material of the present invention is used in the field of photocatalytic nitrogen fixation, and its photocatalytic nitrogen fixation activity is tested as follows:

1) Add the BiOI/Bi ₂ WO ₆ composite material of the present invention into the reaction flask, then add ethanol and ethylene glycol, continuously add N ₂ into the reaction system during the whole process, and fully stir for 1-1.5 h, making the surface of the BiOI/Bi ₂ WO ₆ composite reach an adsorption-desorption equilibrium for ethanol, ethylene glycol and N ₂ ;

Wherein, the ratio of BiOI/Bi ₂ WO ₆ composite material, ethanol, and ethylene glycol is 25mg: 8mL: 8mL, and the N ₂ is added to the reaction system at a flow rate of 40ml/min;

2) Under the condition of stirring, Xe lamp is used as the light source for illumination, and a certain amount of reaction solution is taken at regular intervals during the illumination process;

3) The above reaction solution was centrifuged and filtered, and the concentration of NH ₄ ⁺ in the product was determined by ion chromatography.

Further, the illumination time of step 2) is 4 hours, and 2-2.5 mL of reaction solution is taken every 2 hours during the illumination process.

The physical performance characterization method of the photocatalytic nitrogen fixation catalyst of the present invention is as follows: use UV-Vis Diffuse Reflectance Spectroscopy (DRS) to analyze the light absorption changes of the product, and use X-ray diffraction (XRD) spectrum to analyze the material composition and crystal phase structure of the product , The morphology of the obtained product was characterized by field emission scanning electron microscopy (FESEM).

The beneficial effects of the present invention are: the preparation method of the BiOI/Bi ₂ WO ₆ heterojunction composite photocatalytic material described in the present invention is simple and easy, without adding surfactants and adjusting the pH of the reaction solution, the reaction conditions are mild, and the environment is friendly , low consumption, novel activity characterization system, and convenient operation provide a feasible, effective and valuable activity evaluation method for the evaluation of photocatalytic materials.

Description of drawings

Figure 1 shows the amount of ammonium produced by photocatalytic nitrogen fixation of the series BiOI/Bi ₂ WO ₆ -xI, and the ordinate is the amount of NaI added x mmol.

Fig. 2 is a graph showing the change of the amount of ammonium produced by photocatalytic nitrogen fixation of BiOI/Bi ₂ WO ₆ -0.1I and BiOI/Bi ₂ WO ₆ -0.2I with time.

Fig. 3 is the DRS spectrum of the series BiOI/Bi ₂ WO ₆ -xI.

Fig. 4 is the XRD spectrum of the series BiOI/Bi ₂ WO ₆ -xI.

Fig. 5 is a SEM photo of Bi ₂ WO _6, BiOI/Bi ₂ WO ₆ -0.1I, BiOI/Bi ₂ WO ₆ -0.2I, BiOI/Bi ₂ WO ₆ -0.8I.

Fig. 6 is a diagram of a BiOI/Bi ₂ WO ₆ photocatalytic nitrogen fixation device.

detailed description

A preparation method of photocatalytic nitrogen fixation catalyst, comprising the following steps:

1) Dissolve Na ₂ WO ₄ 2H ₂ O in deionized water, stir well to dissolve completely, and obtain solution A,

2) Add NaI to the above solution A under stirring condition, continue to stir to dissolve it completely, and obtain solution B;

3) According to the stoichiometric ratio, add Bi(NO ₃ ) ₃ ·5H ₂ O to solution B, and then stir for 0.5-1 h to obtain solution C;

4) Transfer the above solution C to a 100 mL reactor, and conduct a hydrothermal reaction at 120-130°C for 24 hours. The obtained precipitate is centrifuged, washed, and dried to obtain a BiOI/Bi ₂ WO ₆ composite material, that is, the photocatalytic The nitrogen fixation catalyst is named as BiOI/Bi ₂ WO ₆ -xI , where x represents the mmol amount of NaI added to the reaction system.

Wherein, step 1), the addition amount of Na ₂ WO ₄ ·2H ₂ O is 0.35-0.95mmol, and the addition amount of deionized water is 80mL;

Step 2), the amount of NaI added is 0.1-1.5 mmol, and the sum of twice the amount of Na ₂ WO ₄ ·2H ₂ O and the amount of NaI is 2 mmol;

Step 3), the amount of Bi(NO ₃ ) ₃ ·5H ₂ O added is 2 mmol.

The present invention will be further described below in conjunction with specific examples.

Example 1

Dissolve 0.95 mmol Na ₂ WO ₄ ·2H ₂ O in 80 ml deionized water, stir well to dissolve it. Then add 0.1 mmol NaI into the Na ₂ WO ₄ solution under stirring, stir well to dissolve and mix well. Then add 2 mmol Bi(NO ₃ ) ₃ ·5H ₂ O and stir for 0.5-1 h. The resulting solution was transferred to a 100 mL reactor and hydrothermally reacted at 120 °C for 24 h. After the reaction was completed and cooled to room temperature, the precipitated product was centrifuged, washed, and then completely dried at 60°C to obtain BiOI/Bi ₂ WO ₆ -0.1I.

The amount of each raw material added is different, and the ratio of BiOI to Bi ₂ WO ₆ in the obtained BiOI/Bi ₂ WO ₆ photocatalytic material is different. When the content of BiOI is small, the BiOI/Bi ₂ WO ₆ heterojunction composite has a higher The photocatalytic nitrogen fixation activity, the light absorption of the obtained product, and the crystal phase composition characteristics have certain changes. (As shown in Figure 3 and Figure 4)

Performance test of photocatalytic nitrogen fixation on the BiOI/Bi ₂ WO ₆ heterojunction composite photocatalytic material obtained above:

Add 25 mg of the obtained BiOI/Bi ₂ WO ₆ catalyst into the reaction tube, then add 8 ml of ethanol and 8 ml of ethylene glycol, and continuously blow N ₂ into the closed reaction system. The reaction tube was stirred for 1 h under dark conditions, so that the surface of the catalyst reached adsorption-desorption equilibrium for ethanol, ethylene glycol and _N2 . Then, under stirring at room temperature, irradiate with Xe lamp for 4 h, in which 2 mL of reaction solution was centrifuged and filtered at intervals of 1 h, and the concentration of NH ₄ ⁺ in the product was determined by ion chromatography. The results show that BiOI/Bi ₂ WO ₆ -xI has certain photocatalytic properties (as shown in Figure 1).

Example 2

The procedure of this example is the same as that of Example 1, except that the amount of Na ₂ WO ₄ ·2H ₂ O is 0.9 mmol, and the amount of NaI is 0.2 mmol. It was found that the photocatalytic activity of BiOI/Bi ₂ WO ₆ was greatly affected by the ratio of BiOI:Bi ₂ WO ₆ , and when the added Na ₂ WO ₄ ·2H ₂ O was 0.9mmol and NaI was 0.2mmol, the prepared The activity of BiOI/Bi ₂ WO _6- 0.2I composite photocatalytic material is enhanced (as shown in Figure 2).

Example 3

Change the amount of raw materials added, and prepare a series of photocatalytic nitrogen fixation catalysts (namely, a series of BiOI/Bi ₂ WO ₆ composite materials) according to the method of implementation 1, named BiOI/Bi ₂ WO ₆ -xI, where x represents the amount of NaI added to the reaction system quantity.

Among them, the addition of each raw material satisfies the following relationship:

The amount of Na ₂ WO ₄ ·2H ₂ O added is 0.35-0.95mmol, and the amount of deionized water added is 80mL;

The amount of NaI added is 0.1-1.5 mmol, and the sum of twice the amount of Na ₂ WO ₄ ·2H ₂ O and the amount of NaI is 2 mmol;

The amount of Bi(NO ₃ ) ₃ ·5H ₂ O added was 2 mmol.

The photocatalytic nitrogen fixation performance test of the obtained series of photocatalytic nitrogen fixation catalysts was carried out according to the method in Example 1. When the addition of NaI is less than or equal to 0.2mmol, the photocatalytic nitrogen fixation activity of the BiOI/Bi ₂ WO ₆ catalyst is greatly improved compared with the single Bi ₂ WO ₆ catalyst, and when the addition of NaI is equal to 0.2mmol, the BiOI/Bi ₂ WO ₆ -0.2I catalyst has the highest activity. When the amount of NaI added was greater than 0.2 mmol, the photocatalytic nitrogen fixation activity of the BiOI/Bi ₂ WO ₆ catalyst gradually decreased with the increase of the amount of NaI added (as shown in Figure 1).

The DRS spectra, XRD spectra, and SEM images of the obtained series of photocatalytic nitrogen fixation catalysts are shown in Figures 3, 4, and 5, respectively. In Fig. 3, with the increase of NaI introduced into the system of BiOI/Bi ₂ WO ₆ -xI series catalysts, the absorption band edge of the obtained product gradually red-shifted, and the maximum absorption wavelength gradually red-shifted from about 400 nm to 650 nm. When NaI is introduced into the hydrothermal system, the crystal phase of the obtained product BiOI/Bi ₂ WO ₆ gradually transitions from a single Bi ₂ WO ₆ (as shown in Figure 4) to a trace amount of BiOI phase, and then with the NaI in the system As the amount increases, the diffraction peak of the BiOI crystal phase in the XRD diffraction peak of the product gradually increases, while the intensity of the crystal phase diffraction peak of Bi ₂ WO ₆ decreases gradually, which indicates that the obtained product is composed of a single pure phase of Bi ₂ WO ₆ gradually changed into a composite containing Bi ₂ WO ₆ and BiOI. In terms of the morphology and structure of the samples (as shown in Figure 5), as the amount of NaI introduced increases, the morphology of BiOI/Bi ₂ WO ₆ -xI changes from nanospheres to nanosheets, and then to irregular nanoparticles.

Claims (7)

1. A preparation method of a photocatalytic nitrogen fixation catalyst, characterized in that: it may further comprise the steps: 1) Dissolve Na ₂ WO ₄ 2H ₂ O in deionized water, stir well to dissolve completely, and obtain solution A, 2) Add NaI to the above solution A under stirring condition, continue to stir to dissolve it completely, and obtain solution B; Wherein, the ratio of NaI to Na ₂ WO ₄ ·2H ₂ O is 0.1-1.5 : 0.35-0.95; 3) According to the stoichiometric ratio, add Bi(NO ₃ ) ₃ ·5H ₂ O to solution B, and then stir for 0.5-1 h to obtain solution C; Wherein, the ratio of Bi(NO ₃ ) ₃ .5H ₂ O to Na ₂ WO ₄ .2H ₂ O is 1: 0.175-0.475; 4) The above solution C was transferred to a reaction kettle, and subjected to hydrothermal reaction at 120-130°C for 24 hours, and the resulting precipitate was centrifuged, washed, and dried to obtain a BiOI/Bi ₂ WO ₆ composite material, which is the photocatalytic nitrogen fixation catalyst. 2. The preparation method of a photocatalytic nitrogen fixation catalyst according to claim 1, characterized in that in step 1), the ratio of Na ₂ WO ₄ ·2H ₂ O to deionized water is 0.35-0.95mmol: 80mL . 3. The preparation method of a photocatalytic nitrogen fixation catalyst according to claim 1, characterized in that: the sum of twice the amount of substance of Na ₂ WO ₄ ·2H ₂ O and the amount of NaI is 2 mmol. 4. The application of the photocatalytic nitrogen fixation catalyst according to claim 1, characterized in that: the photocatalytic nitrogen fixation catalyst is applied in the field of photocatalytic nitrogen fixation. 5. The application of the photocatalytic nitrogen fixation catalyst according to claim 4, characterized in that: the photocatalytic nitrogen fixation activity test of the photocatalytic nitrogen fixation catalyst is as follows: 1) Add the BiOI/Bi ₂ WO ₆ composite material into the reaction flask, then add ethanol and ethylene glycol, continuously add N ₂ into the reaction system during the whole process, and stir well for 1-1.5h under the condition of avoiding light, so that The surface of BiOI/Bi ₂ WO ₆ composite material reaches adsorption-desorption equilibrium for ethanol, ethylene glycol and N ₂ ; 2) Under the condition of stirring, Xe lamp is used as the light source for illumination, and a certain amount of reaction solution is taken at regular intervals during the illumination process; 3) The above reaction solution was centrifuged and filtered, and the concentration of NH ₄ ⁺ in the product was determined by ion chromatography. 6. The application of a photocatalytic nitrogen fixation catalyst according to claim 5, characterized in that in step 1), the ratio of the BiOI/Bi ₂ WO ₆ composite material, ethanol, and ethylene glycol is 25mg: 8mL : 8mL, the _N2 was added to the reaction system at a flow rate of 40ml/min. 7. The application of a photocatalytic nitrogen fixation catalyst according to claim 5, characterized in that: in step 2), the illumination time is 4 hours, and 2-2.5 mL of reaction solution is taken every 2 hours during the illumination process.