Preparation of molybdenum-doped bismuth trioxide and application thereof in photocatalytic nitrogen fixation

Abstract

The application discloses a preparation method of Mo-doped Bi2O3 and application of the Mo-doped Bi2O3 in photocatalytic nitrogen fixation, and is characterized in that: in the synthesis process of Bi2O3, molybdenum salt is added to obtain brownish yellow Mo-doped Bi2O3 through a solvothermal method. The preparation method is simple, raw materials are cheap and easy to obtain, the environment is less polluted, and the Mo-doped Bi2O3 is harmless to human bodies, has good photocatalytic nitrogen reduction performance, and has a good application prospect in the field of photocatalytic nitrogen fixation.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic nitrogen reduction material technology, specifically relating to a method for preparing Mo-doped Bi2O3 and its application in photocatalytic nitrogen fixation. Background Technology

[0002] Ammonia is a key raw material for the production of fertilizers, refrigerants, and cleaning agents, playing a vital role in human societal development. Its high hydrogen content and energy density also make it a promising green fuel. The Haber-Bosch process is the primary method for ammonia synthesis, directly synthesizing ammonia from N2 and H2 under high temperature and pressure conditions (400-500 ℃, 150-250 atm). However, this method is energy-intensive and highly polluting, consuming 1% of the world's annual energy. The high-purity hydrogen used is derived from the reforming of fossil fuels like natural gas, resulting in annual CO2 emissions of up to 450 million tons. Therefore, with increasing environmental awareness, finding a green, environmentally friendly, and low-energy-consumption method for ammonia synthesis is of great significance.

[0003] Since the 1970s, when researchers discovered that TiO2 could be used to photocatalyze water splitting under sunlight, photocatalysis technology has gradually come into focus. Photocatalysis provides a method for ammonia synthesis under mild conditions, namely, reducing N2 using N2 and H2O as raw materials on a semiconductor catalyst under light irradiation. Currently, researchers have developed inorganic semiconductor catalysts such as TiO2, InVO4, Bi2WO6, Bi2O3, and BiOBr for photocatalytic nitrogen reduction reactions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing Mo-doped Bi2O3 and its application in the field of photocatalytic nitrogen fixation. The catalyst raw materials are inexpensive and readily available, the preparation process is simple, and its photocatalytic nitrogen reduction performance is significantly improved compared with pure Bi2O3.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing Mo-doped Bi₂O₃ involves adding molybdenum salt during the synthesis of Bi₂O₃ to achieve Mo doping of Bi₂O₃; the method includes the following steps:

[0007] (1) Add Bi(NO3)3·5H2O and Na2MoO4·2H2O to a mixed solution of tert-butanol and ethylene glycol, sonicate for 30 min to disperse evenly, and then stir for 1 h to obtain a transparent solution.

[0008] (2) The transparent solution obtained in step (1) is transferred to a polytetrafluoroethylene reactor for solvothermal reaction. The resulting precipitate is centrifuged, washed and dried to obtain brownish-yellow Mo-doped Bi2O3.

[0009] Further, the volume ratio of tert-butanol to ethylene glycol in the mixed solution in step (1) is 4:1.

[0010] Furthermore, in the transparent solution obtained in step (1), the concentration of Bi(NO3)3·5H2O is 0.4850 g / 40 mL, and the concentration of Na2MoO4·2H2O is 0.0353-0.0823 g / 40 mL.

[0011] Furthermore, the temperature of the solvothermal reaction in step (2) is 160 °C and the time is 8 h.

[0012] Furthermore, the amount of Mo doping in the obtained Mo-doped Bi2O3 is 6~14 wt%.

[0013] The prepared Mo-doped Bi2O3 has good photocatalytic nitrogen reduction performance, and therefore can be used as a photocatalyst to reduce N2 to ammonia in the presence of H2O, thereby achieving photocatalytic nitrogen fixation.

[0014] The significant advantages of this invention are:

[0015] (1) The present invention has low requirements, readily available raw materials, simple operation, low energy consumption, and low toxicity;

[0016] (2) The material obtained by the present invention has good light absorption capacity and good photogenerated carrier separation efficiency;

[0017] (3) The material obtained by the present invention exhibits good photocatalytic nitrogen fixation performance in an environment with N2 and H2O as raw materials, and has good application prospects. Attached Figure Description

[0018] Figure 1 The image shows a SEM image of the 10 wt% Mo-doped Bi2O3 prepared in the example.

[0019] Figure 2 The XRD patterns of Mo-Bi2O3 with different doping amounts prepared in the examples and pure Bi2O3 prepared in the comparative examples are shown.

[0020] Figure 3 The UV-Vis diffuse reflectance spectra of 10 wt% Mo-doped Bi2O3 prepared in the example and pure Bi2O3 prepared in the comparative example are shown.

[0021] Figure 4Fluorescence spectra of 10 wt% Mo-doped Bi₂O₃ prepared in the example and pure Bi₂O₃ prepared in the comparative example.

[0022] Figure 5 The graph shows the photocatalytic nitrogen fixation performance of Mo-Bi2O3 prepared with different doping amounts in the examples and pure Bi2O3 prepared in the comparative example. Detailed Implementation

[0023] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto. Example

[0024] The preparation steps of Mo-doped Bi2O3 photocatalyst are as follows:

[0025] (1) Add 0.4850 g Bi(NO3)3·5H2O and a certain amount (0.0353 g, 0.047 g, 0.0587 g, 0.0705 g, 0.0823 g) of Na2MoO4·2H2O to a mixed solution of 32 mL tert-butanol and 8 mL ethylene glycol. Sonicate for 30 min to disperse evenly, and then stir for 1 h to obtain a transparent solution.

[0026] (2) The transparent solution obtained in step (1) was transferred to a polytetrafluoroethylene reactor and reacted at 160 °C for 8 h. After the reaction, the precipitate was washed by centrifugation with anhydrous ethanol and deionized water and dried overnight in a vacuum oven at 60 °C to obtain brownish-yellow Mo-doped Bi2O3 photocatalytic material, wherein the doping amounts of Mo were 6%, 8%, 10%, 12%, and 14%, respectively.

[0027] Comparative Example

[0028] The preparation steps of Bi2O3 photocatalyst are as follows:

[0029] (1) Add 0.4850 g Bi(NO3)3·5H2O to a mixed solution of 32 mL tert-butanol and 8 mL ethylene glycol, sonicate for 30 min to disperse Bi(NO3)3 evenly, and then stir for 1 h to obtain a clear and transparent solution.

[0030] (2) The obtained clear and transparent solution was transferred to a polytetrafluoroethylene reactor and reacted at 160 °C for 8 h. After the reaction was completed, the solution was washed by centrifugation with anhydrous ethanol and deionized water, dried overnight in a vacuum oven at 60 °C, and ground to obtain Bi2O3 photocatalytic material.

[0031] Application Examples

[0032] The specific procedures for the gas-solid phase photocatalytic nitrogen reduction experiment are as follows:

[0033] The gas-solid phase photocatalytic nitrogen reduction performance evaluation experiment was conducted in a Schlenk reactor with a volume of approximately 180 mL. The reactor had an exhaust valve at each end and a sampling port at the front, sealed with a rubber stopper. 10 mg of photocatalyst material was dispersed in 1 mL of deionized water, and then the dispersion was evenly dropped onto an 8 cm² plate containing glass fiber filter paper. 2 In a glass dish, the photocatalytic material was spread evenly over a sheet of glass fiber filter paper. The filter paper was then dried in a 60 °C constant-temperature drying oven for 1 hour before being placed in a reactor. The reactor was sealed, and a vacuum pump was used to evacuate it. High-purity nitrogen gas was then injected into the reactor using a balloon (this process was repeated four times to ensure the reactor was filled with high-purity nitrogen). 50 μL of ultrapure water was injected into the reactor through the sampling port. A 300 W xenon lamp was used as the light source to irradiate the glass fiber filter paper containing the photocatalytic material in the reactor for 1 hour. After the reaction, 10 mL of water was injected into the reactor through the sampling port to absorb the ammonia generated during the reaction. After 15 min, the catalytic material in the absorption liquid was filtered through a 0.22 μm pore size filter membrane. The ammonia yield during photocatalysis was determined using the Nessler's reagent method: 5 mL of the absorption liquid was mixed with 200 μL of potassium sodium tartrate solution and 400 μL of Nessler's reagent. After 15 min of color development, the ammonia concentration in the solution was measured at 420 nm using a UV-Vis spectrophotometer.

[0034] Figure 1 The image shows a SEM image of the 10 wt% Mo-doped Bi₂O₃ prepared in the example. As can be seen from the image, the 10 wt% Mo-doped Bi₂O₃ consists of microspheres assembled from nanosheets, with a diameter of 2-3 μm.

[0035] Figure 2 The XRD patterns of Mo-Bi2O3 prepared with different doping amounts for the examples and pure Bi2O3 prepared for the comparative examples are shown in the figures. As can be seen from the figures, Mo-doped Bi2O3 and pure Bi2O3 have similar XRD patterns, and no diffraction peaks related to Mo were observed. This means that the addition of Mo ions did not produce a new crystal phase, and only trace amounts of Mo were dispersed in the Bi2O3 substrate. Meanwhile, the diffraction peak intensity of Bi2O3 increased after the introduction of Mo, indicating better crystallinity. Furthermore, the diffraction peaks of the (111) and (200) crystal planes of Mo-doped Bi2O3 shifted to lower angles, indicating that Mo doping caused lattice distortion, resulting in a larger interplanar spacing.

[0036] Figure 3The UV-Vis diffuse reflectance spectra of 10 wt% Mo-doped Bi₂O₃ prepared in the example and pure Bi₂O₃ prepared in the comparative example are shown. As can be seen from the figures, the absorption capacity of the 10 wt% Mo-doped Bi₂O₃ for visible light is significantly enhanced, and the band gap is reduced, further demonstrating that Mo doping contributes to improving the photocatalytic performance of Bi₂O₃.

[0037] Figure 4 The photoluminescence spectra of 10 wt% Mo-doped Bi₂O₃ prepared in the example and pure Bi₂O₃ prepared in the comparative example are shown. Generally, a stronger fluorescence emission peak indicates a higher electron-hole recombination efficiency and lower photocatalytic activity. As can be seen from the figures, the fluorescence emission peak intensity of Bi₂O₃ significantly decreases after Mo doping, indicating a lower photogenerated carrier recombination efficiency, which is beneficial for improving photocatalytic performance.

[0038] Figure 5 The figures show the photocatalytic nitrogen fixation activity evaluation of Mo-doped Bi₂O₃ prepared with different doping amounts in the examples and pure Bi₂O₃ prepared in the comparative example. As can be seen from the figures, the photocatalytic nitrogen reduction performance of the catalyst is significantly improved after doping Bi₂O₃ with Mo doping amount of 10 wt%. Among them, Bi₂O₃ with Mo doping amount of 10 wt% exhibits the best nitrogen fixation performance, with an ammonia production rate of 141.93 μmol·g⁻¹. -1 ·h -1 It is pure Bi₂O₃ (45.2 μmol·g⁻¹). -1 ·h -1 3.14 times that of ).

[0039] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. An application of Mo-doped Bi₂O₃ in photocatalytic nitrogen fixation, characterized in that, In the presence of H2O, the Mo-doped Bi2O3 is used as a photocatalyst to reduce N2 to ammonia. The preparation of the Mo-doped Bi2O3 includes the following steps: (1) Add Bi(NO3)3·5H2O and Na2MoO4·2H2O to a mixed solution of tert-butanol and ethylene glycol, sonicate for 30 min to disperse evenly, and then stir for 1 h to obtain a transparent solution. (2) The transparent solution obtained in step (1) is transferred to a polytetrafluoroethylene reactor for solvothermal reaction. The resulting precipitate is centrifuged, washed and dried to obtain brownish-yellow Mo-doped Bi2O3; wherein the doping amount of Mo is 6~14 wt.

2. The application according to claim 1, characterized in that, In step (1), the volume ratio of tert-butanol to ethylene glycol in the mixed solution is 4:

1.

3. The application according to claim 1, characterized in that, In the transparent solution obtained in step (1), the concentration of Bi(NO3)3·5H2O is 0.4850 g / 40 mL, and the concentration of Na2MoO4·2H2O is 0.0353-0.0823 g / 40 mL.

4. The application according to claim 1, characterized in that, The temperature of the solvothermal reaction in step (2) is 160°C and the time is 8 h.

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