Method for improving photocatalytic nitrogen reduction reaction and application

Abstract

The invention provides a method for improving photocatalytic nitrogen reduction reaction and application, and belongs to the technical field of ammonia production through nitrogen reduction. The method comprises the following steps: providing a solution containing micro-nano bubbles, adding a photocatalytic material to construct a reaction system, and illuminating the reaction system by adopting a xenon lamp light source; the micro-nano bubbles are nitrogen micro-nano bubbles, the photocatalytic material comprises a transition metal oxide treated by sodium borohydride, the surface of the photocatalytic material has an oxygen vacancy structure, the surface oxygen defect signal based on XPS characterization accounts for 20-40%, and the oxygen vacancy of the photocatalytic material accounts for 20-40%. Nitrogen is filled into the micro-nano bubbles, so that the amount of gas which is in contact with and reacts with a catalytic material in a reaction system can be effectively increased; due to the high-speed mass transfer characteristic, the reaction is promoted, the coupling effect of a three-phase interface is improved, and a complete catalytic environment is induced to be formed among three phases of a catalytic material, bubbles and a solution, so that the reaction rate is increased, and the method has a very good practical application prospect.

Description

Technical Field

[0001] This invention relates to the field of nitrogen reduction ammonia production technology, and in particular to a method and application for improving photocatalytic nitrogen reduction reaction. Background Technology

[0002] Currently, the primary industrial method for ammonia production is the Haber process. This process requires high temperatures (500 °C) and high pressures (200-300 atmospheres), resulting in high energy consumption and correspondingly high costs. This contradicts the current concept of green and sustainable development and also generates massive carbon emissions. In the stage of achieving high-quality development with peak carbon emissions and carbon neutrality, reducing carbon emissions from the Haber process is imperative. Therefore, under the current circumstances, there is an urgent need for technologies with milder reaction conditions and lower energy consumption for ammonia synthesis.

[0003] Photocatalytic ammonia production technology is based on the redox capabilities of photocatalysts under light irradiation, enabling the reduction of nitrogen to ammonia in an aqueous environment. This light-driven technology can operate at room temperature and pressure, and is considered a promising alternative to the Haber process in industrial ammonia production. The photocatalytic ammonia production reaction involves three phases: solid, liquid, and gas, and the coupling at the three-phase interface significantly impacts the catalytic reaction. Currently, photocatalytic nitrogen reduction involves directly introducing nitrogen into the reaction system, where it is reduced at the three-phase interface formed by the catalytic material and solution during the bubble rise phase. However, the low solubility of nitrogen in water severely limits the reaction efficiency, hindering the large-scale application of this technology. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned shortcomings of the prior art by providing a method and application for improving the photocatalytic nitrogen reduction reaction. By introducing micro-nano bubbles into the photocatalytic nitrogen reduction reaction system, the high-speed mass transfer characteristics of the bubbles promote the reaction, enhance the coupling effect of the three-phase interface, and induce the formation of a complete catalytic environment among the three phases of catalytic material, bubbles, and solution.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a method for improving the photocatalytic nitrogen reduction reaction, which involves providing a solution containing micro-nano bubbles, adding a photocatalytic material to construct a reaction system, and irradiating the reaction system with a xenon lamp light source; wherein the micro-nano bubbles are nitrogen micro-nano bubbles, and the photocatalytic material includes a transition metal oxide treated with sodium borohydride, and the surface of the photocatalytic material has an oxygen vacancy structure, wherein the surface oxygen defect signal characterized by XPS accounts for 20% to 40%.

[0006] Furthermore, the transition metal oxide is selected from TiO2. 2-x MoO 3-x and / or WO3-x .

[0007] Furthermore, the solution containing micro-nano bubbles is obtained by compressing high-purity nitrogen gas using an ultrafine bubble generator and then introducing it into a methanol aqueous solution.

[0008] Furthermore, the pressure range during the compression process is 0.2~0.5 MPa.

[0009] Furthermore, the flow rate of the nitrogen gas is controlled at 10~30 mL / min.

[0010] Furthermore, the nitrogen gas is introduced during the compression process for 10 to 40 minutes.

[0011] Furthermore, the concentration of the micro-nano bubbles is 1×10⁻⁶. 6 ~1×10 8 per mL.

[0012] Furthermore, the size of the micro-nano bubbles is between 150 nm and 250 nm.

[0013] Furthermore, the rated power of the xenon lamp light source is 200~500W.

[0014] Another object of the present invention is to provide the application of the above-described method in nitrogen reduction for ammonia production.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention introduces micro- and nano-bubbles into a photocatalytic nitrogen reduction reaction system. The introduction of nitrogen into the micro- and nano-bubbles can effectively increase the amount of gas in the reaction system that contacts and reacts with the catalytic material. Its high-speed mass transfer characteristics promote the reaction, enhance the coupling effect of the three-phase interface, and induce the formation of a complete catalytic environment between the catalytic material, bubble, and solution phases, thereby increasing the reaction rate and showing great promise for practical applications. Attached Figure Description

[0016] Figure 1 (a) Bubble size distribution and (b) morphology of the micro / nano bubble generator; Figure 2a This is a schematic diagram of a photocatalytic nitrogen fixation system containing micro-nano bubbles; Figure 2b A schematic diagram of a conventional photocatalytic nitrogen fixation system with nitrogen gas introduced. Figure 3a This is a schematic diagram showing the positional relationship between bubbles and photocatalytic materials in a micro / nano bubble photocatalytic system. Figure 3b This is a schematic diagram showing the positional relationship between bubbles and photocatalytic materials in a conventional photocatalytic system. Figure 4A comparison of ammonia production rates for different photocatalytic materials catalyzed by micro-nano bubbles and nitrogen inflatation; Figure 5a TiO2 with different oxygen vacancy concentrations 2-x Comparison of photocatalytic ammonia production rates under micro-nano bubbles and nitrogen blowing conditions; Figure 5b MoO with different oxygen vacancy concentrations 3-x Comparison of photocatalytic ammonia production rates under micro-nano bubbles and nitrogen blowing conditions; Figure 5c For different oxygen vacancy concentrations (WO) 3-x Comparison of photocatalytic ammonia production rates under micro-nano bubbles and nitrogen blowing conditions; Figure 6 TiO 2-x Photocatalytic ammonia production rate at different micro / nano bubble concentrations; Figure 7 Mechanism analysis for enhancing catalytic rate using micro / nano bubbles; (a) for MoO 3-x Transient photocurrent curves of photoelectrodes of photocatalytic materials under different environments; (b) MoO 3-x Electron paramagnetic resonance (EPR) detection curves of photocatalytic materials under different nitrogen injection pathways under illumination (DMPO is the trapping agent). Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0018] In this invention, "XPS" refers to X-ray photoelectron spectroscopy, a commonly used material characterization technique in the field, which can be used to analyze the elemental composition and chemical state of material surfaces. In this invention, XPS is used to characterize the surface oxygen vacancy structure of the prepared photocatalytic material to confirm the formation of oxygen vacancies.

[0019] In this invention, the "ammonia production rate of the photocatalyst" is calculated by taking out the reaction solution after 1 hour of photocatalytic reaction, determining the concentration of ammonium ions in the solution using Nessler's reagent method, repeating the process three times for each sample, calculating the amount of ammonia produced based on the concentration of ammonia generated and the volume of the reaction solution, and then calculating the ammonia production rate of the photocatalyst.

[0020] The sodium borohydride (NaBH4, 99.5 wt.%, Shanghai Aladdin Biochemical Technology Co., Ltd.), molybdenum trioxide (MoO3, ≥99.95%, Shanghai Aladdin Biochemical Technology Co., Ltd.), titanium dioxide (TiO2, ≥99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.), and tungsten trioxide (WO3, ≥99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.) used in this invention.

[0021] This invention utilizes the NANOscientific research-grade bubble generator from Shanghai Xingheng Technology Co., Ltd. to prepare nitrogen micro / nano bubbles. High-purity nitrogen gas is compressed using an ultrafine bubble generator and then introduced into a background solution (water:methanol = 9:1). By controlling the device pressure at 0.2–0.5 MPa, the nitrogen gas flow rate at 10–30 mL / min, and the gas introduction time at 10–40 min, micro / nano bubbles of different concentrations are obtained. The bubble concentration is controlled at 1 × 10⁻⁶. 6 ~1×10 8 The number of micro- and nano-bubbles per mL is stable at 150 nm to 250 nm (D1). 50 ), where the bubble particle size and morphology are as follows Figure 1 As shown.

[0022] refer to Figure 2a The present invention describes a photocatalytic nitrogen fixation system containing micro-nano bubbles. This nitrogen fixation system is connected to a bubble generating device and includes a reaction chamber 1, a stirring assembly 2, and a light source 3. The reaction chamber 1 has a sandwich structure with a circulating medium channel inside the sandwich. This circulating medium channel is connected to a temperature control device, and the temperature of the reaction chamber is controlled by circulating a temperature control medium inside the sandwich. The stirring assembly 2 is located at the bottom of the reaction chamber 1, and a quartz window is provided at the top of the reaction chamber 1. The light source 3 continuously illuminates the reaction chamber through the quartz window.

[0023] The preparation process of the photocatalytic material in this invention is as follows: 6 g of any one of titanium dioxide (TiO2, ≥99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.), molybdenum trioxide (MoO3, ≥99.95%, Shanghai Aladdin Biochemical Technology Co., Ltd.), or tungsten trioxide (WO3, ≥99.99%, Shanghai Aladdin Biochemical Technology Co., Ltd.) is added to 100 mL of pure water to prepare dispersion A; 0.1~0.7 g of sodium borohydride (NaBH4, 99.5 wt.%, Shanghai Aladdin Biochemical Technology Co., Ltd.) is dissolved in 30 mL of pure water to prepare solution B. Under vigorous stirring, solution B is added dropwise to dispersion A, and stirring continues for 5 min. Afterwards, the mixture is centrifuged, washed, and dried at 40~60℃ for 6~8 h to obtain the photocatalytic material, which is labeled as TiO2. 2-x MoO 3-x WO 3-x。XPS was used to characterize the prepared photocatalytic material. After peak separation, the O1s energy level spectrum showed that, in addition to the lattice oxygen peak located at 529.5–530.2 eV, there was also a defect oxygen peak located at 531.0–532.0 eV. This peak is usually related to unsaturated coordinated oxygen associated with oxygen vacancies. By fitting the areas of each characteristic peak, the area of ​​the defect oxygen peak accounted for 20%–40% of the total O1s area.

[0024] This invention provides a method for improving the photocatalytic nitrogen reduction reaction. A solution containing micro / nano bubbles is provided, and the aforementioned photocatalytic material is added to construct a reaction system. The reaction system is irradiated using a xenon lamp source. The micro / nano bubbles are nitrogen micro / nano bubbles. Micro / nano bubbles generated by compressing high-purity nitrogen using an ultrafine bubble generator are introduced into the reaction system to enhance the coupling effect at the three-phase interface, inducing the formation of a complete catalytic environment between the catalytic material, bubbles, and solution phases, thereby increasing the reaction rate.

[0025] In practice, the pressure range during compression is 0.2–0.5 MPa, the nitrogen flow rate is controlled at 10–30 mL / min, and the nitrogen purging time during compression is 10–40 min. Under these conditions, the concentration of generated micro / nano bubbles is 1 × 10⁻⁶. 6 ~1×10 8 The number of micro- and nano-bubbles per mL ranges from 150 nm to 250 nm.

[0026] The method provided by this invention can significantly improve the reaction rate of nitrogen to ammonia, increasing it by 3 to 5 times compared to directly blowing in nitrogen.

[0027] The following is an exemplary description of a method for improving photocatalytic nitrogen reduction reaction provided in this application, with reference to specific embodiments.

[0028] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0029] Example 1 (1) Dispersion A was prepared by adding 6 g of titanium dioxide to 100 mL of pure water; solution B was prepared by dissolving 0.5 g of sodium borohydride in 30 mL of pure water. Solution B was added dropwise to dispersion A under vigorous stirring, and stirring was continued for 5 min. After centrifugation, washing, and drying at 50 °C for 8 h, the photocatalytic material TiO2 was obtained. 2-x The oxygen vacancy concentration was determined to be 27.5% using X-ray photoelectron spectroscopy.

[0030] (2) High-purity nitrogen gas was compressed using an ultrafine bubble generator and then introduced into the background solution (water:methanol = 9:1). By controlling the device pressure at 0.4 MPa, the nitrogen gas flow rate at 20 mL / min, and the gas introduction time at 15 min, the concentration of micro-nano bubbles obtained was 3.45 × 10⁻⁶. 7 The number of micro- and nano-bubbles per mL remained stable at 197.1 nm (D0.05). 50 ).

[0031] (3) Take 100 mL of background solution and put it into the photocatalytic reaction system, and add 50 mg of photocatalytic material TiO2. 2-x The mixture was ultrasonically stirred to ensure uniform dispersion in the reaction system. Throughout the process, the reaction system was maintained at 20°C using a circulating water system. High-purity nitrogen gas was compressed using an ultrafine bubble generator to prepare micro-nano bubbles, which were then introduced into the photocatalytic reaction system. (Reference) Figure 2a This is a schematic diagram of a photocatalytic nitrogen fixation system containing micro-nano bubbles.

[0032] (4) Irradiate the reaction system continuously with a 300 W xenon lamp. Take out 2 mL of the reaction solution every 30 min from the start of irradiation, measure the concentration of ammonium ions in it using Nessler's reagent method, and plot the rate curve.

[0033] Example 2 Basically the same as Example 1, except that: TiO 2-x During the preparation process, the amount of NaBH4 added was 0.1 g, and the oxygen vacancy concentration was 20.2%. Example 3 Basically the same as Example 1, except that: TiO 2-x During the preparation process, the amount of NaBH4 added was 0.3 g, and the oxygen vacancy concentration was 23.6%.

[0034] Example 4 Basically the same as Example 1, except that: TiO 2-x During the preparation process, the amount of NaBH4 added was 0.7 g, and the oxygen vacancy concentration was 29.7%.

[0035] Example 5 The results are basically the same as in Example 1, except that the photocatalyst material is MoO2. 3-x During the preparation process, the amount of NaBH4 added was 0.1 g, and the oxygen vacancy concentration was 22.3%. Example 6 The results are basically the same as in Example 1, except that the photocatalyst material is MoO2. 3-x During the preparation process, the amount of NaBH4 added was 0.3 g, and the oxygen vacancy concentration was 25.0%.

[0036] Example 7 The results are basically the same as in Example 1, except that the photocatalyst material is MoO2. 3-x During the preparation process, the amount of NaBH4 added was 0.5 g, and the oxygen vacancy concentration was 29.8%.

[0037] Example 8 The results are basically the same as in Example 1, except that the photocatalyst material is MoO2. 3-x During the preparation process, the amount of NaBH4 added was 0.7 g, and the oxygen vacancy concentration was 33.1%.

[0038] Example 9 This is basically the same as Example 1, except that the photocatalyst material is WO3. 3-x During the preparation process, the amount of NaBH4 added was 0.1 g, and the oxygen vacancy concentration was 23.5%. Example 10 This is basically the same as Example 1, except that the photocatalyst material is WO3. 3-x During the preparation process, the amount of NaBH4 added was 0.3 g, and the oxygen vacancy concentration was 27.6%.

[0039] Example 11 This is basically the same as Example 1, except that the photocatalyst material is WO3. 3-x During the preparation process, the amount of NaBH4 added was 0.5 g, and the oxygen vacancy concentration was 33.4%.

[0040] Example 12 This is basically the same as Example 1, except that the photocatalyst material is WO3. 3-x During the preparation process, the amount of NaBH4 added was 0.7 g, and the oxygen vacancy concentration was 37.7%.

[0041] Comparative Example 1 Basically the same as Example 1, except that nitrogen gas is directly bubbled in, as per reference. Figure 2b .

[0042] Comparative Example 2 It is basically the same as Example 2, except that nitrogen gas is directly bubbled in.

[0043] Comparative Example 3 It is basically the same as Example 3, except that nitrogen gas is directly bubbled in.

[0044] refer to Figure 3a The diagram shows the positional relationship between bubbles and photocatalytic materials in a micro / nano bubble photocatalytic system. The micro / nano bubbles are stably adsorbed on the surface of the catalytic material. In contrast, using conventional nitrogen blowing methods, the nitrogen bubbles are relatively large and almost impossible to adsorb onto the catalytic material surface. Figure 3b As shown.

[0045] refer to Figure 4 The study compared the ammonia production rates of different photocatalytic materials using micro- and nano-bubbles and nitrogen blowing. It was clear that the ammonia production rate using micro- and nano-bubbles was much higher than that using ordinary blowing. Introducing nitrogen into the reaction system in the form of micro- and nano-bubbles strengthened the coupling of the solid-liquid-gas three-phase interface, which greatly increased the nitrogen reduction reaction rate. This same trend was observed in different metal oxide nitrogen reduction catalytic materials.

[0046] refer to Figures 5a-5c TiO₂ with different oxygen vacancy concentrations 2-x MoO 3-x and WO 3-x A comparison of photocatalytic ammonia production rates under micro / nano bubbles and nitrogen induction shows that adjusting the oxygen vacancy concentration can effectively optimize photocatalytic nitrogen fixation efficiency. Oxygen vacancy defects in metal oxides are active sites for nitrogen reduction. Introducing micro / nano bubbles improves the efficiency of photocatalytic nitrogen fixation for TiO₂ with different oxygen vacancy concentrations. 2-x MoO 3-x and WO 3-x Its nitrogen fixation rate exhibits a similar trend to that of ordinary photocatalytic nitrogen fixation systems. Under the influence of micro-nano bubbles, the ammonia production rate can be significantly improved, especially with TiO₂ as the nitrogen fixation rate. 2-x Under photocatalytic conditions, with an oxygen vacancy concentration of 27.5%, the fastest ammonia production rate reached 1.89 mmol / g. -1 h -1 .

[0047] refer to Figure 6 TiO 2-x The ammonia production rate of photocatalytic materials under different nitrogen concentrations in micro-nano bubble water environments was investigated. By controlling the content of micro-nano bubbles, the nitrogen supply level could be altered. A positive correlation was found between the nitrogen micro-nano bubble density and the ammonia reduction rate.

[0048] refer to Figure 7 By detecting photocurrent signals under different atmospheres, the degree of photocatalytic reduction reaction between the catalytic material and nitrogen can be reflected, such as... Figure 7 a. Compared to the nitrogen bubbling mode, the nitrogen photocurrent reduction is more significant when injected via micro / nanobubbles. This is because the micro / nanobubbles have more contact with the catalytic material, promoting nitrogen reduction on the catalytic material surface. Under photocatalytic conditions, active hydrogen can be detected in the three-phase environment of the micro / nanobubbles. Figure 7 (b) This is beneficial for promoting the subsequent hydrogenation reaction of nitrogen, which is one of the reasons why micro-nano bubbles enhance nitrogen fixation efficiency.

[0049] For any points not covered above, existing technologies shall apply.

[0050] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving photocatalytic nitrogen reduction reaction, characterized by, The solution containing micro-nano bubbles is provided, a photocatalytic material is added to construct a reaction system, and the reaction system is irradiated by a xenon lamp light source; the micro-nano bubbles are nitrogen micro-nano bubbles, the photocatalytic material comprises a transition metal oxide treated by sodium borohydride, and the surface of the photocatalytic material has an oxygen vacancy structure, wherein the proportion of surface oxygen defect signals based on XPS characterization is 20% to 40%.

2. The method of claim 1, wherein, The transition metal oxide is selected from TiO 2-x , MoO 3-x , and / or WO 3-x .

3. The method of claim 1, wherein, The solution containing micro-nano bubbles is obtained by compressing nitrogen gas by a superfine bubble generating device and then introducing the nitrogen gas into a methanol aqueous solution.

4. The method of claim 2, wherein, The pressure range in the compression process is 0.2 to 0.5 MPa.

5. The method of claim 3, wherein, The flow rate of the nitrogen gas is controlled at 10 to 30 mL / min.

6. The method of claim 4, wherein, The nitrogen gas is introduced for 10 to 40 min in the compression process.

7. The method of claim 5, wherein, The concentration of the micro-nano bubbles is 1 x 10 6 ~1 x 10 8 per mL.

8. The method of claim 6, wherein, The size of the micro-nano bubbles is 150 nm to 250 nm.

9. The method of claim 7, wherein, The rated power of the xenon lamp light source is 200 to 500 W.

10. Use of the method according to any one of claims 1 to 9 in the reduction of nitrogen to produce ammonia.

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