Carbon-coated nitrogen-doped TiO2 photocatalyst for NH3 removal and its preparation method

Abstract

The application discloses a carbon-coated nitrogen-doped titanium dioxide photocatalyst for removing ammonia and a preparation method thereof. In the synthesis process, TiO2 is first subjected to crystal modification, nitrogen-containing substances such as ethylenediamine and urea are used as nitrogen sources, and nitrogen-doped TiO2 is first synthesized through a one-step solvothermal method. Then, the surface of the nitrogen-doped TiO2 is coated on the basis of the nitrogen-doped TiO2, organic substances are used as carbon sources, the organic substances and the N-doped TiO2 powder are fully mixed in an ethanol solution through mechanical stirring, and then the mixture is dried and finally calcined in a tube furnace under an inert gas atmosphere to obtain the photocatalyst. The photocatalyst can maintain a high NH3 removal rate for a long time, can obtain high N2 selectivity, can remove pollutants, and can reduce secondary pollution to the environment. The catalyst has low preparation and application costs, and can be applied to the photocatalytic oxidation removal of NH3 under room temperature conditions.

Description

Technical Field

[0001] This invention relates to a photocatalyst, specifically, to a photocatalyst for removing ammonia and its preparation method. Background Technology

[0002] Ammonia-containing waste gas has significant applications in fertilizer synthesis and industrial fields. Direct emission of NH3 not only affects the ecological environment, causing soil acidification and eutrophication of water bodies, but also seriously harms human health. Medium- and high-concentration NH3 can be recovered and utilized using absorption, membrane separation, and adsorption methods, as well as selective catalytic oxidation. However, how to remove low-concentration ammonia-containing waste gas remains a major challenge.

[0003] Photocatalytic oxidation is an effective method for removing low-concentration ammonia-containing waste gas. It is convenient to operate, has mild reaction conditions, high pollutant removal efficiency, and low cost. The core of photocatalytic oxidation for NH3 removal lies in the catalyst. TiO2, as a novel functional material, is widely used due to its advantages such as stable chemical properties, high activity, good stability, high efficiency, low price, and no pollution. However, some problems still need to be solved: TiO2 has a band gap energy of 3.2 eV, and can only absorb ultraviolet light with wavelengths less than 380 nm (accounting for only 4-5% of the solar spectrum), resulting in low utilization of visible light; the recombination rate of photogenerated electron-hole pairs in the photocatalytic process is relatively fast, leading to poor stability; and NO reduction is needed during the NH3 removal process. x The generation of N2 improves N2 selectivity.

[0004] Therefore, developing a novel TiO2 photocatalyst can reduce the cost of photocatalyst preparation and solve the harm caused by NH3 emissions, which is of great significance. Summary of the Invention

[0005] The first objective of this invention is to provide a photocatalyst for removing NH3, which can photocatalytically oxidize and remove NH3 from a mixed gas at room temperature.

[0006] Another objective of this invention is to provide a photocatalyst for the efficient removal of NH3, which can maintain a high NH3 removal rate for a long period of time and also achieve high N2 selectivity, thereby reducing secondary pollution to the environment while removing pollutants.

[0007] Another objective of this invention is to provide a method for preparing a photocatalyst for removing NH3. In this method, TiO2 is modified by crystal modification and surface coating to reduce its band gap, thereby improving light utilization and reaction stability, and thus solving the aforementioned technical problems.

[0008] A photocatalyst for removing NH3, wherein nitrogen is doped into the TiO2 lattice system in the form of O-Ti-N and carbon is dispersed and coated on the surface.

[0009] By modifying TiO2 with nitrogen elements and coating its surface, its band gap can be reduced, which can improve its light utilization and reaction stability.

[0010] A method for preparing a photocatalyst for removing NH3, comprising:

[0011] The N source solution and the titanium source solution are mixed to obtain a first mixture, and the first mixture undergoes a hydrothermal reaction to precipitate a solid.

[0012] After solid-liquid separation, a first solid substance is obtained. The first solid substance is mixed with a solution containing carbon organic matter to obtain a mixture. The mixture is dried and calcined to obtain a photocatalyst for removing NH3.

[0013] The carbon-containing organic compounds include one or more of glucose, sucrose, acetic acid, and citric acid.

[0014] The carbon-coated, nitrogen-doped TiO2 catalyst prepared by this method maintains a high NH3 removal rate for a longer period of time and also achieves high N2 selectivity.

[0015] The term "coating" as used in this application refers to the dispersed loading of carbon (C) onto the surface of N-doped TiO2. The combined effect of N, C, and Ti elements provides a beneficial result.

[0016] The temperature referred to as "room temperature" in this application is between 10 and 35°C. Attached Figure Description

[0017] Figure 1 Raman characterization diagram of the catalyst prepared in Example 2

[0018] Figure 2 This is a view of the reaction stability of the catalyst in Example 2. Detailed Implementation

[0019] To make the technical problems, technical solutions and advantages of this application clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments.

[0020] The solvothermal (hydrothermal) method refers to a synthesis method in which the original mixture reacts in a closed system, such as an autoclave, using water as a solvent, at a certain temperature and under the autogenous pressure of the solution.

[0021] Among various TiO2 modification techniques, non-metallic element doping can effectively reduce the band gap energy of TiO2, broaden the photoresponse range, enhance light absorption, and suppress carrier recombination. In non-metallic element modification, C and N element doping can generate hybrid orbitals near the valence band of TiO2, thereby reducing the TiO2 band gap energy. However, there are no reports on the photocatalytic oxidation of NH3 removal by non-metallic element C and N-doped TiO2. The inventors used nitrogen-containing substances such as urea, ethylenediamine, NH4Cl, and triethylamine, as well as carbon-containing organic substances such as glucose, sucrose, acetic acid, and citric acid to modify TiO2 with C and N elements to improve its NH3 removal performance.

[0022] A photocatalyst for removing NH3, wherein nitrogen is doped into TiO2 and the surface of TiO2 is coated with carbon.

[0023] First, nitrogen (N) is doped into the TiO2 crystal system via a solvothermal method, forming impurity energy levels that lower the band gap energy of TiO2 and broaden its photoresponse range. Second, N doping increases the acidic sites in TiO2, enhancing its NH3 adsorption capacity. Furthermore, because N successfully replaces O to form O-Ti-N bonds, the Ti-O bond energy is weakened, further facilitating NH3 adsorption and desorption.

[0024] Based on this, carbon coating is applied, and the resulting catalyst, after calcination, is grayish-black. It is bonded to nitrogen-doped TiO2 material via a specific bond energy (C / N-TiO2), further reducing the band gap and causing a redshift in its absorption range, while still exhibiting strong absorption capacity under visible light. Secondly, the carbon-coated catalyst has a higher oxygen vacancy ratio, which can suppress electron-hole pair recombination and improve reaction stability. The catalyst maintains relatively high photocatalytic activity even after prolonged use.

[0025] In the photocatalyst, the molar ratio of N to Ti is (0.5–2):1.

[0026] Preferably, in the photocatalyst, the molar ratio of N to Ti is (0.5-1):1.

[0027] In the photocatalyst, the molar ratio of C to Ti is (0.03–0.3):1.

[0028] When the amount of N doping is controlled within the above range, a relatively high photocatalytic effect can be achieved. However, the photocatalytic effect will decrease as the amount of C coating increases.

[0029] The above-mentioned method for preparing the photocatalyst for removing NH3 includes:

[0030] A nitrogen source solution and a titanium source solution are mixed to obtain a first mixture, and the first mixture undergoes a hydrothermal reaction to precipitate a solid.

[0031] After solid-liquid separation, a first solid substance is obtained. The first solid substance is mixed with a solution containing carbon organic matter to obtain a mixture. The mixture is dried and calcined to obtain a photocatalyst for removing NH3.

[0032] The carbon-containing organic compounds include one or more of glucose, sucrose, acetic acid, and citric acid.

[0033] A solution containing carbonaceous organic matter refers to a carbonaceous organic matter dissolved in an organic solvent, including alcohol solvents such as ethanol.

[0034] Nitrogen sources include one or more N-containing substances such as urea, ethylenediamine, and triethylamine; titanium sources include tetrabutyl titanate, titanium isopropoxide, anhydrous TiCl4, titanium sulfate, and TiCl3.

[0035] Preferably, the nitrogen source is urea and the titanium source is tetrabutyl titanate.

[0036] Urea and triethylamine are preferred nitrogen sources, especially urea, which, when doped into titanium dioxide, forms anatase nano-titanium dioxide and exhibits better catalytic performance.

[0037] In some embodiments, the hydrothermal reaction temperature is 120–200°C.

[0038] The nitrogen source doping process employs a hydrothermal method because the TiO2 synthesized by this method exhibits anatase form, possessing a superior crystal structure. In nature, TiO2 exists in three types: anatase, rutile, and brookite. Anatase TiO2 is an indirect bandgap semiconductor, where electron recombination in the conduction band requires a certain displacement, thus suppressing electron-hole recombination and resulting in higher photocatalytic activity. Therefore, this application selects a solvothermal (hydrothermal) method to synthesize the photocatalyst. The catalyst surface exhibits good adsorption performance for water molecules and possesses hydroxyl radicals, which is one of the reasons for its excellent photocatalytic activity.

[0039] Preferably, the hydrothermal reaction temperature is 120–180°C.

[0040] More preferably, the hydrothermal reaction temperature is 160–180°C.

[0041] The hydrothermal reaction time is preferably 6 to 12 hours.

[0042] Preferably, the hydrothermal reaction time is 8 to 12 hours; more preferably, the thermal reaction time is 8 to 11 hours.

[0043] During the hydrothermal reaction, the optimal preparation temperature for the solvothermal method is between 120℃ and 180℃, resulting in better photocatalytic oxidation and deamination activity. However, the activity decreases when the preparation temperature of the solvothermal method is further increased.

[0044] In some implementations, the molar ratio of N to Ti is (0.1 to 8):1.

[0045] Preferably, the molar ratio of N to Ti is (0.1 to 6):1.

[0046] A more preferred scheme is that the molar ratio of N to Ti is (0.2 to 2):1.

[0047] The mass ratio of carbon-containing organic matter to the first solid substance is (0.01 to 0.5):1.

[0048] The first solid substance only needs to have a water content of less than 10%.

[0049] Preferably, the first solid substance is dried at 110°C under normal pressure.

[0050] In some embodiments, the mass ratio of carbon-containing organic matter to the first solid substance is (0.01 to 0.3):1.

[0051] Preferably, the mass ratio of carbon-containing organic matter to the first solid substance is (0.01 to 0.2):1.

[0052] In some embodiments, the mass ratio of carbon-containing organic matter to the first solid substance is (0.01 to 0.1):1.

[0053] Preferably, the mass ratio of carbon-containing organic matter to the first solid substance is (0.01–0.05):1.

[0054] By incorporating an appropriate amount of nitrogen (N) into the TiO2 crystal system, N replaces oxygen atoms to create an intermediate energy level near the valence band of TiO2, thereby lowering the band gap energy and increasing the photoresponse range. Carbon (C) coating the surface of the N-doped TiO2 increases its surface acidity and forms active sites for the photocatalytic oxidation of NH3. Furthermore, in conjunction with N, it enhances the photosensitivity of the catalyst. Therefore, under visible light, it exhibits strong catalytic oxidation capability for ammonia and maintains high catalytic performance over a long period.

[0055] In some embodiments, the calcination temperature is controlled at 200–600°C; preferably, the calcination temperature is controlled at 300–550°C.

[0056] A more preferred calcination temperature is controlled at 300–450°C.

[0057] During the calcination process of this application, the preferred temperature is 300-450℃, and more preferably the reaction temperature is controlled at 400℃, so that the crystal structure of the N-doped TiO2 is kept as anatase, resulting in the best photocatalytic effect.

[0058] The calcination time is 2 to 8 hours; preferably, the calcination time is 2 to 5 hours.

[0059] The calcination process includes: calcination in an inert gas atmosphere (such as N2 or Ar), with the calcination temperature gradually increasing at a rate of 2–5 °C / min.

[0060] Preferably, the heating rate during the calcination stage is 2℃ / min.

[0061] The airflow rate is 50-100 ml / min.

[0062] Controlling the heating rate to 2–5 °C / min makes it easier to maintain the crystal structure and improve the catalytic activity of the catalyst.

[0063] In some embodiments, a method for preparing a photocatalyst for removing NH3 includes the following steps:

[0064] S1. Add titanium source solution to nitrogen source solution, mix and stir until the solution is completely homogeneous, and carry out hydrothermal reaction of the resulting mixture;

[0065] S2. Separate the mixture after the hydrothermal reaction into solid and liquid components, collect the solid components, and dry them.

[0066] S3. Dissolve the carbon-containing organic matter in an ethanol solution, and grind the first solid component obtained in S2 into powder and place it in the carbon-containing organic matter solution for stirring until it is evenly mixed and then dry it.

[0067] S4. Grind the solid obtained in S3 and then calcine it to obtain a photocatalyst for removing NH3.

[0068] In this application, the drying conditions refer to drying at a temperature of 60-110°C. The drying time is controlled according to the desired final moisture content. For example, the drying time is not less than 6 hours.

[0069] In some embodiments, the nitrogen source solution and the titanium source solution are stirred during mixing, with the stirring rate controlled at 350-700 r / min, and the stirring is carried out for ≥1 h until the mixture is homogeneous.

[0070] When mixing the carbon-containing organic solution with the first solid, stirring is performed at a rate of 200–500 r / min. Stirring continues for 24 hours.

[0071] In some embodiments, the solid-liquid separation method after the hydrothermal reaction includes: filtration with medium- or slow-speed filter paper, or centrifugation using a centrifuge with a speed of 1200–5000 rpm or higher. During this process, the liquid is washed with ethanol and H2O until neutral.

[0072] The catalyst prepared using the method of this invention can maintain a high NH3 removal rate for a relatively long period of time and also achieve high N2 selectivity, reducing secondary pollution to the environment while removing pollutants. Furthermore, the catalyst has low preparation and application costs and can be used for photocatalytic oxidation removal of NH3 at room temperature. The preparation method of this invention uses readily available raw materials, is simple to operate, and has good reproducibility, achieving the goal of efficient removal of low-concentration NH3 over a long period of time while reducing the cost of photocatalysts.

[0073] The photocatalyst for removing NH3 in this application is applied to a reaction system that catalyzes the oxidation of NH3 to N2.

[0074] During the reaction, light with a wavelength range of 200-800nm ​​is used, and the reaction temperature is 10-50℃.

[0075] In some implementations, a 300W xenon lamp light source is used to simulate natural light.

[0076] Preferably, the reaction temperature is between 20-40℃.

[0077] Preferably, the light is irradiated with visible light with a wavelength between 400 and 780 nm.

[0078] Using the above-mentioned photocatalyst to oxidize ammonia, a good conversion rate and nitrogen selectivity are still maintained after 72 hours.

[0079] The efficacy of the catalyst in this application will be further explained below with specific examples.

[0080] Example 1

[0081] (a) Weigh 1.8g of urea and dissolve it in 60ml of ethanol solution. Add 20.4g of tetrabutyl titanate and 0.6ml of 37% hydrochloric acid. Then quickly add 160ml of deionized water and stir evenly.

[0082] (b) Stir the solution in (a) at 700 r / min until homogeneous, then transfer it to a 150 ml reactor and hydrothermally react at 180 °C for 10 h.

[0083] (c) After the reaction is complete, the resulting mixture is subjected to solid-liquid separation. The solid is washed with ethanol and water until neutral. The mixture is centrifuged at 1200 r / min during the washing process. The solid components are collected and placed in an oven to dry at 110°C to obtain a milky white solid.

[0084] (d) Weigh a certain amount of glucose and dissolve it in 30 ml of ethanol solution. Then add 1.6 g of (c) dried milky white solid (mass ratio of glucose to milky white solid = 0.01:1) to the glucose solution. Stir and mix on a magnetic stirrer at 300 r / min at room temperature for 24 h. Then dry in an oven at 60 ℃ to obtain a pale yellow solid.

[0085] (e) The pale yellow solid from (d) was placed in a tube furnace and calcined at 400°C for 2 hours under a nitrogen atmosphere at a heating rate of 2°C / min to obtain a gray-black solid (i.e., a photocatalyst for removing NH3).

[0086] The photocatalyst sample obtained in this embodiment for removing low-concentration ammonia-containing waste gas was tested at room temperature under the following conditions: 300W xenon lamp light source, [NH3] = 100 ppm, [O2] = 20 vol.%, N2 as the balance gas, and an illumination area of ​​12.5 cm². 2 The photocatalytic activity was tested under the specified conditions. The conversion rate of NH3 and the N2 selectivity were monitored multiple times at certain intervals within 7 hours of reaction. The results showed that the conversion rate of NH3 was stable at 81.8% to 83.1% and the N2 selectivity was 86.8% to 98.2% within 7 hours.

[0087] The catalyst prepared in this embodiment can maintain a high conversion rate and nitrogen selectivity over a long period of time.

[0088] Example 2

[0089] (a) Weigh 1.8g of urea and dissolve it in 60ml of ethanol solution. Add 20.4g of tetrabutyl titanate and 0.6ml of hydrochloric acid, and then quickly add 160ml of deionized water and stir evenly.

[0090] (b) Stir the solution in (a) at 700 r / min until homogeneous, then transfer it to a 150 ml reactor and hydrothermally react at 180 °C for 10 h.

[0091] (c) After the reaction is complete, the resulting mixture is subjected to solid-liquid separation. The solid is washed with ethanol and water until neutral. The mixture is centrifuged at 1200 r / min during the washing process. The solid components are collected and dried in an oven to obtain a milky white solid.

[0092] (d) Weigh a certain amount of glucose and dissolve it in 30 ml of ethanol solution. Then add 1.6 g of (c) dried milky white solid (mass ratio of glucose to milky white solid = 0.03:1) to the glucose solution. Stir and mix on a magnetic stirrer at 200 r / min at room temperature for 24 h. Then dry in an oven at 60 ℃ to obtain a light yellow solid.

[0093] (e) The pale yellow solid from (d) was placed in a tube furnace and calcined at 400°C for 2 hours under an argon atmosphere at a heating rate of 2°C / min to obtain a gray-black solid.

[0094] The photocatalyst sample obtained in this embodiment for removing low-concentration ammonia-containing waste gas was tested at room temperature under the following conditions: 300W xenon lamp light source, [NH3] = 100 ppm, [O2] = 20 vol.%, N2 as the balance gas, and an illumination area of ​​12.5 cm². 2 The photocatalytic activity was tested under the specified conditions. During the 7-hour reaction, the conversion rate of NH3 and the selectivity of N2 were monitored repeatedly at regular intervals. The results showed that during the 7 hours of reaction, the conversion rate of NH3 remained above 90.1%, reaching a maximum of 94.6%; the selectivity of N2 remained above 93.5%, reaching a maximum of 98%.

[0095] The gray solid (i.e., the photocatalyst for removing NH3) prepared in this embodiment was subjected to Raman spectroscopy analysis. Raman characterization revealed that, compared to pure TiO2, the N-doped catalyst exhibited higher spectral density at 151 cm⁻¹. -1 A peak shift occurred nearby, mainly due to N doping replacing O atoms in the crystal lattice to form O-Ti-N bonds. (1349.9 cm⁻¹) -1 and 1594.5cm -1 The presence of D and G bands at the site proves that element C was successfully loaded onto the surface.

[0096] Under the experimental conditions described above for photocatalytic removal of ammonia waste gas, the catalyst in this embodiment underwent a catalytic reaction within 72 hours, and the results are shown in the appendix. Figure 2 From the appendix Figure 2 The results show that the catalyst still exhibits high photocatalytic activity after 72 hours. It has been reported that other existing catalysts used for the photocatalytic removal of ammonia gas can only be used for a maximum of 13 hours, with the reaction activity decreasing to below 60% or even completely deactivated due to the influence of the byproduct nitrate.

[0097] Example 3

[0098] (a) Weigh 1.8g of urea and dissolve it in 60ml of ethanol solution. Add 20.4g of tetrabutyl titanate and 0.6ml of hydrochloric acid, and then quickly add 160ml of deionized water and stir evenly.

[0099] (b) Stir the solution in (a) at 700 r / min until homogeneous, then transfer it to a 150 ml reactor and hydrothermally react at 180 °C for 10 h.

[0100] (c) After the reaction is complete, the resulting mixture is subjected to solid-liquid separation. The solid is washed with ethanol and water until neutral. The mixture is centrifuged at 1200 r / min during the washing process. The solid components are collected and dried in an oven to obtain a milky white solid.

[0101] (d) Weigh a certain amount of glucose and dissolve it in 30 ml of ethanol solution. Then add 1.6 g of (c) dried milky white solid (mass ratio of glucose to solid = 0.05:1) to the glucose solution. Stir and mix on a magnetic stirrer at 200 r / min at room temperature for 24 h. Then dry it in an oven at 60 ℃ to obtain a light yellow solid.

[0102] (e) The pale yellow solid from (d) was placed in a tube furnace and calcined at 400°C for 2 hours under an argon atmosphere at a heating rate of 2°C / min to obtain a gray-black solid.

[0103] The photocatalyst sample obtained in this embodiment for removing low-concentration ammonia-containing waste gas was tested at room temperature under the following conditions: 300W xenon lamp light source, [NH3] = 100 ppm, [O2] = 20 vol.%, N2 as the balance gas, and an illumination area of ​​12.5 cm². 2 The photocatalytic activity was tested under the specified conditions. The conversion rate of NH3 and the selectivity of N2 were monitored repeatedly at regular intervals over a 7-hour reaction period. The results showed that the highest conversion rate of NH3 reached 83%, and the N2 selectivity remained above 80%, reaching a maximum of 94.6%.

[0104] Example 4

[0105] (a) Weigh 1.8g of urea and dissolve it in 60ml of ethanol solution. Add 20.4g of tetrabutyl titanate and 0.6ml of hydrochloric acid, and then quickly add 160ml of deionized water and stir evenly.

[0106] (b) Stir the solution in (a) at 700 r / min until homogeneous, then transfer it to a 150 ml reactor and hydrothermally react at 180 °C for 10 h.

[0107] (c) After the reaction is complete, the resulting mixture is subjected to solid-liquid separation. The solid is washed with ethanol and water until neutral. The mixture is centrifuged at 1200 r / min during the washing process. The solid components are collected and dried in an oven to obtain a milky white solid.

[0108] (d) Weigh a certain amount of glucose and dissolve it in 30 ml of ethanol solution. Then add 1.6 g of (c) dried composite catalyst (mass ratio = 0.2) to the glucose solution. Stir and mix on a magnetic stirrer at 500 r / min at room temperature for 24 h. Then dry in an oven at 60 ℃ to obtain a light yellow solid.

[0109] (e) The pale yellow solid from (d) was placed in a tube furnace and calcined at 400°C for 2 hours under an argon atmosphere at a heating rate of 2°C / min to obtain a gray-black solid.

[0110] The photocatalyst sample obtained in this embodiment for removing low-concentration ammonia-containing waste gas was prepared at room temperature, using a 300W xenon lamp as the light source, with [NH3] = 100 ppm, [O2] = 20 vol.%, N2 as the balance gas, and an illumination area of ​​12.5 cm². 2 The photocatalytic activity was tested under the specified conditions. The conversion rate of NH3 and the selectivity of N2 were monitored repeatedly at regular intervals over a 7-hour reaction period. The results showed that the conversion rate of NH3 was 72.2%–84.5%, and the selectivity of N2 was 77.69%–87.6%.

[0111] Comparative Example 1

[0112] In this comparative example, pure TiO2 was synthesized using a solvothermal method.

[0113] (a) Weigh 20.4g of tetrabutyl titanate solution and add it to 60ml of ethanol. Add 0.6ml of hydrochloric acid and quickly add 160ml of deionized water and stir evenly.

[0114] (b) Stir the solution in (a) at 700 r / min for 1 h, then transfer it to a 100 ml reactor and hydrothermally react at 180 °C for 10 h.

[0115] (c) After the reaction is complete, the resulting mixture is subjected to solid-liquid separation. The solid is washed with ethanol and water until neutral. During the washing process, the mixture is centrifuged at a speed of 1200-5000 r / min. The solid components are collected and dried in an oven to obtain a milky white solid.

[0116] The photocatalyst sample obtained in this embodiment for removing low-concentration ammonia-containing waste gas was tested at room temperature under the following conditions: 300W xenon lamp light source, [NH3] = 100 ppm, [O2] = 20 vol.%, N2 as the balance gas, and an illumination area of ​​12.5 cm². 2 The photocatalytic activity was tested under the specified conditions. Within 7 hours of reaction, the conversion rate of NH3 was approximately 67.4%, while the N2 selectivity was only 31.8%.

[0117] Comparative Example 2

[0118] In this comparative example, only nitrogen element was doped, and nitrogen element was doped only in the in-situ synthesis of TiO2 by the solvothermal method.

[0119] (a) Weigh 3.6g of urea and dissolve it in 60ml of ethanol solution. Add 20.4g of tetrabutyl titanate and 0.6ml of hydrochloric acid, and then quickly add 160ml of deionized water and stir evenly.

[0120] (b) Stir the solution in (a) at 700 r / min for 1 h, then transfer it to a 100 ml reactor and hydrothermally react at 180 °C for 10 h.

[0121] (c) After the reaction is complete, the resulting mixture is subjected to solid-liquid separation. The solid is washed with ethanol and water until neutral. During the washing process, the mixture is centrifuged at a speed of 1200-5000 r / min. The solid components are collected and dried in an oven to obtain a milky white solid.

[0122] The photocatalyst sample obtained in this embodiment for removing low-concentration ammonia-containing waste gas was prepared at room temperature, with [NH3] = 100 ppm, [O2] = 20 vol.%, N2 as the balance gas, and an illumination area of ​​12.5 cm². 2 The photocatalytic activity was tested under the specified conditions. The conversion rate of NH3 remained at approximately 77.47% within 11 hours, with a fluctuation difference of less than 5%, and the N2 selectivity was 45%.

[0123] Comparative Example 3

[0124] In this comparative example, only nitrogen element was doped, and nitrogen element was doped only in the in-situ synthesis of TiO2 by the solvothermal method.

[0125] (a) Weigh 7.2g of urea and dissolve it in 60ml of ethanol solution. Add 20.4g of tetrabutyl titanate and 0.6ml of hydrochloric acid, and then quickly add 160ml of deionized water and stir evenly.

[0126] (b) Stir the solution in (a) at 700 r / min for 2 h, then transfer it to a 150 ml reactor and hydrothermally react at 180 °C for 10 h.

[0127] (c) After the reaction is complete, the resulting mixture is subjected to solid-liquid separation. The solid is washed with ethanol and water until neutral. During the washing process, the mixture is centrifuged at a speed of 1200-5000 r / min. The solid components are collected and dried in an oven to obtain a milky white solid.

[0128] The photocatalyst sample obtained in this embodiment for removing low-concentration ammonia-containing waste gas was prepared at room temperature, with a light intensity of 300 W, [NH3] = 100 ppm, [O2] = 20 vol.%, N2 as the balance gas, and a light-illuminated area of ​​12.5 cm². 2 The photocatalytic activity was tested under the specified conditions. During the 7 hours of reaction, the NH3 removal rate remained above 77.8%, and the N2 selectivity was above 40.5%, reaching a maximum of 52.3%.

Claims

1. A photocatalyst for catalytic oxidation of NH3 to N2, characterized in that, Nitrogen elements are doped into TiO2, and carbon elements are coated on the surface of TiO2. In the photocatalyst, the molar ratio of N to Ti is (0.5~2):1, and the molar ratio of C to Ti is (0.03~0.3):1; The preparation methods of photocatalysts include: A nitrogen source solution and a titanium source solution are mixed to obtain a first mixture, and the first mixture is subjected to a hydrothermal reaction at 120~200℃ to precipitate a solid. After solid-liquid separation, a first solid substance is obtained. The first solid substance is mixed with a solution containing carbon organic matter to obtain a mixture. The mixture is dried and calcined to obtain a photocatalyst for the catalytic oxidation of NH3 to N2. The calcination temperature is controlled at 200~600℃ and the calcination time is 2~8 h. The carbon-containing organic compounds include one or more of glucose, sucrose, acetic acid, and citric acid.

2. The photocatalyst for catalytic oxidation of NH3 to N2 according to claim 1, characterized in that, In the photocatalyst, the molar ratio of N to Ti is (0.5~1):

1.

3. A method for preparing the photocatalyst for the catalytic oxidation of NH3 to N2 as described in claim 1, comprising: A nitrogen source solution and a titanium source solution are mixed to obtain a first mixture, and the first mixture is subjected to a hydrothermal reaction at 120~200℃ to precipitate a solid. After solid-liquid separation, a first solid substance is obtained. The first solid substance is mixed with a solution containing carbon organic matter to obtain a mixture. The mixture is dried and calcined to obtain a photocatalyst for the catalytic oxidation of NH3 to N2. The calcination temperature is controlled at 200~600℃ and the calcination time is 2~8 h. The carbon-containing organic compounds include one or more of glucose, sucrose, acetic acid, and citric acid.

4. The preparation method according to claim 3, characterized in that, The hydrothermal reaction temperature is 120~180℃.

5. The preparation method according to claim 3, characterized in that, The hydrothermal reaction temperature is 160~180℃.

6. The preparation method according to claim 3, characterized in that, The hydrothermal reaction time is preferably 6 to 12 hours.

7. The preparation method according to claim 3, characterized in that, The hydrothermal reaction time is 8~12 h.

8. The preparation method according to claim 3, characterized in that, The hydrothermal reaction time is 8~11 h.

9. The preparation method according to any one of claims 3-8, characterized in that, The molar ratio of N element in the nitrogen source solution to Ti element in the titanium source solution is (0.1~8):

1.

10. The preparation method according to any one of claims 3-8, characterized in that, The molar ratio of N element in the nitrogen source solution to Ti element in the titanium source solution is (0.1~6):

1.

11. The preparation method according to any one of claims 3-8, characterized in that, The molar ratio of N element in the nitrogen source solution to Ti element in the titanium source solution is (0.2~2):

1.

12. The preparation method according to any one of claims 3-8, characterized in that, The mass ratio of carbon-containing organic matter to the first solid substance is (0.01~0.3):

1.

13. The preparation method according to any one of claims 3-8, characterized in that, The mass ratio of carbon-containing organic matter to the first solid substance is (0.01~0.2):

1.

14. The preparation method according to any one of claims 3-8, characterized in that, The mass ratio of carbon-containing organic matter to the first solid substance is (0.01~0.1):

1.

15. The preparation method according to any one of claims 3-8, characterized in that, The mass ratio of carbon-containing organic matter to the first solid substance is (0.01~0.05):

1.

16. The preparation method according to claim 3, characterized in that, The calcination temperature is controlled between 300 and 550℃.

17. The preparation method according to claim 3, characterized in that, The calcination temperature is controlled at 300~450℃.

18. The preparation method according to claim 3, characterized in that, The calcination process includes: calcination in an inert gas atmosphere, with the calcination temperature gradually increasing at a rate of 2-5 °C / min.

19. The preparation method according to any one of claims 3-8, characterized in that, When mixing the nitrogen source solution and the titanium source solution, stir at a rate of 350-700 r / min for ≥1 h until the mixture is homogeneous.

20. The preparation method according to claim 19, characterized in that, When mixing the carbon-containing organic solution with the first solid, stirring is carried out at a speed of 200-500 r / min.

21. The application of the photocatalyst for the catalytic oxidation of NH3 to N2 as described in claim 1 or 2 in a reaction system for the catalytic oxidation of NH3 to N2. in, During the reaction, visible light is applied, and the reaction temperature is between 10-50℃; the wavelength range of the light used is 200-800nm.

22. The application according to claim 21, characterized in that, The visible light wavelength range used is 400~780nm.

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