Method for synthesizing nitric acid by utilizing hole polarons in rich-ordered hole nanosheet for photocatalysis of nitrogen
By using KTaO3 nanosheet photocatalysts with rich disordered pores to directly convert nitrogen into nitric acid in a photocatalytic reaction, the problems of low efficiency and high energy consumption in the synthesis of nitric acid from nitrogen in existing technologies have been solved, and efficient and sustainable nitric acid production has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- UNIV OF SCI & TECH OF CHINA
- Filing Date
- 2024-04-26
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies are insufficient for efficiently synthesizing nitric acid from nitrogen, especially under mild conditions. Furthermore, current industrial production processes for nitric acid are energy-intensive and emit large amounts of pollutants. There is a lack of green and sustainable photocatalytic technologies that can be combined with chemical products.
Using KTaO3 nanosheets with rich disordered pores as a catalyst, nitrogen gas is directly converted into nitric acid through photocatalytic reaction. The active polarons generated by the KTaO3 nanosheets with rich disordered pores are used for catalysis, and the nanosheet material is synthesized by one-pot hydrothermal method.
The efficient catalytic synthesis of nitric acid under sunlight has been achieved. The catalyst has high photocatalytic activity, the reaction conditions are mild and easy to control, and it can be reused, showing good prospects for industrial application.
Smart Images
Figure FT_1 
Figure FT_2 
Figure FT_3
Abstract
Description
Technical Field
[0001] This invention relates to the field of photocatalytic reaction technology, and in particular to a method for photocatalytic synthesis of nitric acid from nitrogen gas using hole polarons in disordered porous nanosheets. Background Technology
[0002] Nitrogen is one of the fundamental elements constituting living organisms and a core element upon which all organic matter depends for survival. Furthermore, nitrogen derivatives such as nitrates, nitrogen-based fertilizers, and nitrogen-based explosives are closely related to national production, industry, agriculture, and military defense, thus attracting significant research attention. However, nitrogen in nature exists primarily as nitrogen gas and cannot be directly utilized. The bond energy of nitrogen molecules is as high as 942 kJ / mol, making it extremely difficult to chemically break the nitrogen-nitrogen triple bond to convert free nitrogen gas into combined nitrogen (such as nitrate or ammonium). Therefore, how to break the strong chemical bonds of nitrogen molecules and recombine them into combined nitrogen has become a highly challenging issue for materials chemists.
[0003] In recent years, semiconductor photocatalysis technology has attracted widespread attention from scientists as a novel technique for artificial nitrogen fixation. This technology utilizes the energy of sunlight to excite electrons in the conduction band of clean, non-toxic semiconductors, forming photogenerated electron-hole pairs. The redox potential of these electrons and holes is then used to oxidize or reduce N₂ to nitrogen or nitrate. Because this process is clean, sustainable, and mild, it is considered a very attractive technology for achieving artificial nitrogen fixation.
[0004] Nitric acid is a high-value-added nitrogen-containing compound and an indispensable raw material in fertilizers, gunpowder, dyes, explosives, emulsifiers, and other fields. Large-scale industrial production of nitric acid involves multiple chemical reactions, including methane steam reforming, the Haber-Bosch process for ammonia production, and the Ostwald process for catalytic oxidation of ammonia to nitric acid. Each step requires high temperature and pressure (673-873 K, 15-25 MPa), resulting in enormous energy consumption and greenhouse gas emissions. Currently, combining green and sustainable photocatalytic technology with the production of nitric acid, a crucial chemical product, is a highly attractive yet challenging topic that requires further exploration and practical application by researchers. Summary of the Invention
[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for photocatalytic synthesis of nitric acid from nitrogen gas using hole polarons in nanosheets rich in disordered pores, which has high photocatalytic efficiency.
[0006] To achieve the above objectives, this invention provides a method for photocatalytic synthesis of nitric acid from nitrogen gas using hole polarons in disordered porous nanosheets. The method uses disordered porous KTaO3 nanosheets as a catalyst and nitrogen-containing gas as a nitrogen source to carry out a photocatalytic reaction to prepare nitric acid.
[0007] This invention utilizes active polarons generated by KTaO3 nanosheets with rich disordered pores for the direct catalytic synthesis of nitric acid using nitrogen as the nitrogen source.
[0008] The present invention preferably employs a one-pot hydrothermal synthesis method to synthesize the above-mentioned disordered porous KTaO3 nanosheets.
[0009] Specifically, this invention provides a method for preparing disordered porous KTaO3 nanosheets, comprising the following steps:
[0010] Tantalum pentoxide and potassium hydroxide were mixed in hexane, then water was added, and the mixture was mixed twice. The mixture was then reacted under high temperature and high pressure to obtain KTaO3 nanosheets with disordered pores.
[0011] The volume ratio of water to n-hexane is 1:(29~299).
[0012] The equation for the above reaction is as follows:
[0013] Ta2O5 + KOH → KTaO3 + H2O.
[0014] In some specific embodiments of the present invention, the amount of water added is 0.1 to 1.0 ml, and the total volume of water and n-hexane is 30 ml.
[0015] In some specific embodiments of the present invention, the amount of water added is 0.05~1.0 ml, and the total volume of water and n-hexane is 30 ml.
[0016] The amounts of water and n-hexane mentioned above are proportional. Those skilled in the art can adjust the amounts of water and n-hexane according to the reaction scale.
[0017] The mass ratio of tantalum pentoxide to potassium hydroxide is preferably 1:1 to 1:10, and more preferably 13:50.
[0018] The amount of n-hexane added is 29 to 29.9 ml, more preferably 29 ml, 29.5 ml or 29.9 ml.
[0019] The preferred temperature for the secondary mixing is room temperature, more preferably 28 degrees Celsius; the preferred time for the secondary mixing is 30 minutes to 1 hour, more preferably 1 hour.
[0020] The temperature of the high-temperature and high-pressure reaction is preferably 120-200 degrees Celsius, more preferably 160 degrees Celsius; the reaction time is preferably 6 hours to 48 hours, more preferably 24 hours; and the pressure is preferably 0.1 MPa to 10 MPa.
[0021] Preferably, after the reaction is complete, the resulting white suspension is centrifuged, and the supernatant is discarded to obtain the product.
[0022] Preferably, the product undergoes a post-processing step of washing and drying.
[0023] The present invention does not impose any special limitations on the specific parameters of centrifugation, washing, and drying.
[0024] Preferably, the centrifugation speed is 12000 rpm and the centrifugation time is 3 minutes.
[0025] The washing process preferably involves washing with distilled water and ethanol in sequence.
[0026] The drying temperature is preferably 30-80 degrees Celsius, more preferably 60 degrees Celsius; the drying time is preferably 2-48 hours, and more preferably 8 hours.
[0027] This invention synthesizes very thin KTaO3 nanosheets by controlling the amount of water added during the preparation of KTaO3 nanomaterials. Using KTaO3 nanosheets as a substrate, disordered pores are introduced on the surface of the material. Polarons can be induced near the disordered pores, resulting in an increase in carrier separation lifetime, which in turn participates more actively in the reaction and improves the reaction efficiency.
[0028] The above-mentioned method for preparing KTaO3 nanosheet photocatalysts with disordered pores has many advantages, such as low synthesis cost, strong catalyst practicality and recyclability, mild synthesis method and easy large-scale production, and has a good prospect for industrial application.
[0029] The present invention also provides a KTaO3 nanosheet material with disordered pores.
[0030] The material has surface pores with a radius of 4 nm ± 2 nm.
[0031] The thickness of the nanosheet material is preferably 4 nm ± 2 nm.
[0032] The KTaO3 nanosheet material with disordered pores prepared by this invention has low raw material and equipment costs, simple process, and strong reusability as a catalyst. It is a new type of broad-spectrum multifunctional nanomaterial.
[0033] This invention provides the application of the above-mentioned disordered porous KTaO3 nanosheet material as a photocatalytic reaction catalyst.
[0034] Preferably, before the photocatalytic reaction, the disordered porous KTaO3 nanosheet material is dispersed in deionized water and then stirred in the dark to reach adsorption equilibrium. This operation helps to adsorb nitrogen and oxygen molecules.
[0035] The preferred stirring time in the dark is 30-60 minutes.
[0036] Then, nitrogen-containing gas is introduced into the aqueous phase to carry out a photocatalytic reaction.
[0037] The present invention does not impose any special limitation on the method of introducing the nitrogen-containing gas, including but not limited to introducing it using a bubbler.
[0038] Preferably, in the photocatalytic reaction, the amount of the disordered porous KTaO3 nanosheets is 15 mg.
[0039] Preferably, the light source for the photocatalytic reaction is a xenon lamp.
[0040] Preferably, the temperature of the photocatalytic reaction is room temperature, specifically 25 degrees Celsius.
[0041] Preferably, the nitrogen-containing gas has a nitrogen volume content of 20% to 90%.
[0042] In some specific embodiments of the present invention, the nitrogen-containing gas may be air or a gas containing nitrogen and oxygen.
[0043] Experimental results show that the catalyst prepared in this invention exhibits strong photoactivity under the solar spectrum. The average rate of nitrate synthesis per gram of catalyst is 2.1 mg g. -1 h -1 Meanwhile, analysis of the apparent quantum efficiency of the prepared catalyst revealed that it exhibits strong absorption in the ultraviolet region, indicating that the catalyst has high quantum efficiency under sunlight.
[0044] Compared with the prior art, the present invention provides a method for photocatalytic synthesis of nitric acid from nitrogen gas using hole polarons in disordered porous nanosheets. The method uses disordered porous KTaO3 nanosheets as catalysts and nitrogen-containing gas as nitrogen source to carry out photocatalytic reaction and prepare nitric acid.
[0045] The present invention achieves the following beneficial effects:
[0046] 1. The reaction conditions in this preparation method are relatively mild and easy to control;
[0047] 2. Using KTaO3 nanosheets with disordered pores as a photocatalytic reaction catalyst, it has high photocatalytic reaction activity under sunlight. No other additives or sacrificial agents need to be added during the photocatalytic reaction, and nitrogen gas can be directly converted into nitric acid in one step.
[0048] 3. This reaction exhibits high activity, with an average rate of 2.1 mg g / g catalyst for the synthesis of nitrate. -1 h -1 It has great potential for industrial applications. Attached Figure Description
[0049] Figure 1 Images showing the surface adsorption and pore structure analysis of the disordered porous KTaO3 nanosheet catalyst prepared in this invention.
[0050] Figure 2 An atomic force microscope image of the disordered porous KTaO3 nanosheet catalyst prepared in this invention;
[0051] Figure 3 High-angle circular dark-field scanning transmission electron microscope image of the disordered porous KTaO3 nanosheet catalyst prepared for this invention.
[0052] Figure 4 X-ray powder diffraction pattern of the disordered porous KTaO3 nanosheet catalyst prepared in this invention.
[0053] Figure 5 Electron paramagnetic resonance spectrum of the disordered porous KTaO3 nanosheet catalyst prepared in this invention;
[0054] Figure 6 Ultrafast spectra of the disordered porous KTaO3 nanosheet catalyst prepared in this invention;
[0055] Figure 7 Concentration-time spectrum of nitrate synthesis catalyzed by the disordered porous KTaO3 nanosheet catalyst prepared in this invention;
[0056] Figure 8 Experimental spectrum of apparent quantum efficiency for photocatalytic nitric acid production using the disordered porous KTaO3 nanosheet catalyst prepared in this invention. Detailed Implementation
[0057] To further illustrate the present invention, the method for photocatalytic synthesis of nitric acid from nitrogen using hole polarons in disordered porous nanosheets, provided by the present invention, is described in detail below with reference to embodiments. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims.
[0058] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.
[0059] Example 1
[0060] Accurately weigh 0.442 g of analytical grade tantalum pentoxide and 1.68 g of potassium hydroxide, add them to 29.9 ml of n-hexane, then add 0.1 ml of water, and stir at 20 °C for 0.5 h. Transfer the solution to a 45 ml high-pressure reactor, place it in a forced-air drying oven, and react at 160 °C for 24 h. After the reaction is complete, remove the reactor after it has cooled naturally. Centrifuge the white suspension at 12000 rpm for 5 min, and discard the supernatant. Wash the precipitate five times each with distilled water and ethanol. Dry the obtained white product overnight at 60 °C. After cooling, the target photocatalytic nanomaterials are obtained and labeled as disordered–pore nanosheets.
[0061] Example 2
[0062] Accurately weigh 0.442 g of analytical grade tantalum pentoxide and 1.68 g of potassium hydroxide, add them to 29.5 ml of n-hexane, then add 0.5 ml of water, and stir at 20 °C for 0.5 h. Transfer the solution to a 45 ml high-pressure reactor, place it in a forced-air drying oven, and react at 160 °C for 24 h. After the reaction is complete, remove the reactor after it has cooled naturally. Centrifuge the white suspension at 12000 rpm for 5 min, and discard the supernatant. Wash the precipitate five times with distilled water and ethanol, respectively. Dry the obtained white product at 60 °C overnight. After cooling, the target photocatalytic nanomaterials are obtained and labeled as crystalline-pore nanosheets.
[0063] Example 3
[0064] Accurately weigh 0.442 g of analytical grade tantalum pentoxide and 1.68 g of potassium hydroxide, add them to 29.0 ml of n-hexane, then add 1.0 ml of water, and stir at 20 °C for 0.5 h. Transfer the solution to a 45 ml high-pressure reactor, place it in a forced-air drying oven, and react at 160 °C for 24 h. After the reaction is complete, remove the reactor after it has cooled naturally. Centrifuge the white suspension at 12000 rpm for 5 min, and discard the supernatant. Wash the precipitate five times with distilled water and ethanol, respectively. Dry the obtained white product at 60 °C overnight. After cooling, the target photocatalytic nanomaterial is obtained and labeled as bulk.
[0065] The structure of the catalyst material prepared above was characterized, and the results are as follows: Figures 1-6As shown.
[0066] Figure 1 These are surface adsorption images and pore structure analysis images of the KTaO3 nanosheet catalyst with disordered pores prepared above. In the image, a is the surface adsorption image and b is the pore structure analysis image. It can be seen that the pore radius on the material surface is about 4 nm.
[0067] Figure 2 The atomic force microscopy image of the disordered porous KTaO3 nanosheet catalyst prepared above shows that the thickness of the nanosheets is about 4 nm.
[0068] Aberration corrections were performed more intuitively on the surface of KTaO3 nanosheets rich in disordered pores using high-angle circular dark-field scanning transmission electron microscopy (HAADF-STEM). Figure 3 Here are high-angle circular dark-field scanning transmission electron microscope images of the disordered porous KTaO3 nanosheet catalyst prepared above. Figure 3 In the middle, based on the z-contrast difference, it can be clearly seen that disordered structures are introduced near the ordered pores.
[0069] Figure 4 The X-ray powder diffraction pattern of the disordered porous KTaO3 nanosheet catalyst prepared above shows that the crystal phase structure of all synthesized samples is pure KTaO3.
[0070] Figure 5 The electron paramagnetic resonance spectrum of the disordered porous KTaO3 nanosheet catalyst prepared above is shown; the generation of hole polarons after illumination can be clearly observed.
[0071] Figure 6 The ultrafast spectrum of the disordered porous KTaO3 nanosheet catalyst prepared above is shown; the generation of hole polarons after photoexcitation and the improvement of photogenerated carrier separation effect can be clearly observed.
[0072] The air used in Examples 4-6 below is high-purity air, which is obtained by mixing 21% high-purity oxygen and 79% high-purity nitrogen, and the total hydrocarbon content is required to be <2ppm and the moisture content is required to be <5ppm.
[0073] Example 4
[0074] Accurately weigh 0.015 g of disordered porous KTaO3 nanosheets and add them to 120 mL of deionized water. After ultrasonic agitation for 10 min, stir in the dark for 60 min to reach adsorption equilibrium. Air is bubbled into the aqueous phase at a flow rate of 100 mL / min, and then photocatalytic reaction is carried out under xenon lamp irradiation (simulated solar spectrum, 350 W, Zhongjiao Jinyuan CEL–HXF300). Approximately 6 mL of sample is taken periodically and quantitatively. After centrifugation to separate the catalyst, the nitrate concentration is determined by ion chromatography. Concentration is expressed as mg / g of catalyst. -1 h -1 The concentration change curve is as follows: Figure 7 The label in the middle is "disordered–porenanosheets".
[0075] Example 5
[0076] Accurately weigh 0.015 g of ordered porous KTaO3 nanosheets and add them to 120 mL of deionized water. After ultrasonic agitation for 10 min, stir in the dark for 60 min to reach adsorption equilibrium. Air is bubbled into the aqueous phase at a flow rate of 100 mL / min, and then photocatalytic reaction is carried out under xenon lamp irradiation (simulating solar spectrum, 350 W, Zhongjiao Jinyuan CEL–HXF300). Approximately 6 mL of sample is taken periodically and quantitatively. After centrifugation to separate the catalyst, the nitrate concentration is determined by ion chromatography. Concentration is expressed as mg / g of catalyst. -1 h -1 The concentration change curve is as follows: Figure 7 The image is labeled as crystalline–pore nanosheets.
[0077] Example 6
[0078] Accurately weigh 0.015 g of bulk KTaO3 material and add it to 120 mL of deionized water. Sonicate for 10 min, then stir in the dark for 60 min to reach adsorption equilibrium. Introduce air into the aqueous phase using a bubbler at a flow rate of 100 mL / min. Then, conduct the photocatalytic reaction under irradiation with a xenon lamp (simulating solar spectrum, 350W, Zhongjiao Jinyuan CEL–HXF300). Take approximately 6 mL of sample periodically, centrifuge to separate the catalyst, and determine the nitrate concentration using ion chromatography. Concentration is expressed as mg / g per gram of catalyst. -1 h -1 The concentration change curve is as follows: Figure 7 The middle label is marked as bulk.
[0079] Figure 7The concentration-time spectrum of the disordered porous KTaO3 nanosheet catalyst prepared in this invention for the catalytic synthesis of nitrate is shown. It can be seen that the average rate of nitrate synthesis per gram of catalyst is 2.1 mg g. -1 h -1 .
[0080] Figure 8 The experimental spectrum shows the apparent quantum efficiency of the photocatalytic production of nitric acid by the disordered porous KTaO3 nanosheet catalyst prepared in this invention. It shows that the catalyst has strong absorption in the ultraviolet region, indicating that the catalyst has high quantum efficiency under sunlight.
[0081] The above experimental results show that the disordered porous KTaO3 nanosheets prepared by this invention have strong photoactivity under the solar spectrum and can achieve high catalytic efficiency in the photocatalytic synthesis of nitric acid from nitrogen.
[0082] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.
Claims
1. A method for photocatalytic synthesis of nitric acid from nitrogen gas using hole polarons in disordered porous nanosheets, wherein disordered porous KTaO3 nanosheets are used as catalysts and nitrogen-containing gas is used as nitrogen source to carry out photocatalytic reaction to prepare nitric acid; The KTaO3 nanosheets rich in disordered pores were prepared by the following method: tantalum pentoxide and potassium hydroxide were mixed in n-hexane, then water was added, and after a second mixing, the mixture was reacted under high temperature and high pressure to obtain KTaO3 nanosheets rich in disordered pores. The volume ratio of water to n-hexane is 1:(29~299).
2. The method according to claim 1, characterized in that, The mass ratio of tantalum pentoxide to potassium hydroxide is 1:(1~10).
3. The method according to claim 1, characterized in that, The secondary mixing temperature is room temperature, and the secondary mixing time is 30 minutes to 1 hour.
4. The method according to claim 1, characterized in that, The temperature of the high temperature and high pressure is 120~200 degrees Celsius, and the pressure is 0.1 MPa~10 MPa.
5. The method according to claim 1, characterized in that, The amount of the KTaO3 nanosheets with disordered pores is 5-50 mg.
6. The method according to claim 1, characterized in that, The light source for the photocatalytic reaction is a xenon lamp.
7. The method according to claim 1, characterized in that, The temperature of the photocatalytic reaction is 20~50 degrees Celsius.
8. The method according to claim 1, characterized in that, The nitrogen-containing gas has a nitrogen volume content of 20% to 90%.