Preparation method of Cu-doped BiOBr petal-shaped material applied to photocatalytic nitrogen fixation

Abstract

The invention discloses a preparation method of a Cu-doped BiOBr petal-shaped material applied to photocatalytic nitrogen fixation. Copper-doped BiOBr is synthesized by adopting a hydrothermal method. In the first hour of photocatalysis, the ammonia generation rate of the photocatalyst reaches 466.3 [mu] mol.gcat <-1 >. H <-1 >, and the photocatalyst shows excellent photocatalytic performance. X-ray photoelectron spectroscopy (XPS) proves that the Cu element is successfully doped with BiOBr. According to the catalyst prepared by the invention, ultrahigh synthetic ammonia yield is realized, the economic benefit of photocatalytic nitrogen fixation is improved, and the catalyst has positive influence on agricultural production and environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalytic nitrogen fixation and relates to a Cu-doped BiOBr petal-shaped photocatalyst and a preparation method thereof. Background Art

[0002] Ammonia (NH3) is an important inorganic chemical raw material for the synthesis of various nitrogen-containing compounds and plays an important role in modern agriculture, medicine, energy, military, metallurgy, chemical industry and other industries. Although the proportion of nitrogen in the atmosphere is about 78%, due to its high bond energy (941 kJ·mol -1 ) and weak polarization ability, converting it into NH3 remains challenging. Since the successful synthesis of NH3 by the Haber-Bosch method in 1913, it has been the main method for artificial nitrogen fixation. However, this method requires high temperature (400-500℃), high pressure (150-250 atm), and consumes non-renewable resources. Photocatalysis is an artificial catalytic nitrogen fixation method that uses sunlight as its energy source and is green, environmentally friendly and pollution-free.

[0003] Recently, bismuth-based semiconductors with excellent photocatalytic properties have been widely explored in the field of photocatalysis. Bismuth oxyhalide materials have a special layered structure and are considered to be promising nitrogen fixation materials due to their low toxicity, suitable intrinsic band gap and high chemical stability. However, the weak interaction between BiOX and N2 is far from the condition for activation of the N≡N bond. Its catalytic activity is largely limited by the rapid complexation of photogenerated electrons and holes and the scarcity of reaction sites. In order to overcome these difficulties, some scientists have proposed strategies to overcome obstacles such as metal doping and structural defects to effectively enhance the photocatalytic ability of BiOX. In 2023, Ren et al. used a photodeposition method to fabricate BiOBr with fine-tunable Pt-doped by controlling the synthesis conditions for photocatalytic nitrogen fixation, NH4 + The generation rates were 23.8 μmol g cat −1 Subsequently, in 2024, Xia et al. reported an in situ photoreduction method to anchor Ru on BiOBr with oxygen vacancies, and its NH4 + The generation rates were 121.97 μmol·g cat -1 However, these studies have the disadvantages of low N2 conversion efficiency and the use of precious metals. Therefore, it is imperative to develop new photocatalysts that can achieve efficient photocatalytic nitrogen fixation while avoiding the use of precious metals, thereby improving the economic value of photocatalytic nitrogen fixation catalysts. Summary of the invention

[0004] The invention discloses a method for preparing a Cu-doped BiOBr petal-shaped material for photocatalytic nitrogen fixation. The photocatalyst makes up for the deficiencies of the prior art, has the advantages of simple preparation and easy operation, realizes the reaction path of N2→NH3, improves the economic benefits of photocatalytic nitrogen fixation, and has a positive impact on agricultural production and environmental protection.

[0005] 1. Preparation of Cu-doped BiOBr photocatalyst Take Bi(NO3)3·5H2O, Cu(NO3)2·3H2O and KBr as raw materials and ethylene glycol as solvent, stir and mix them evenly, then transfer them to a polytetrafluoroethylene reactor, heat to 170~180℃ for hydrothermal reaction for 10~12 hours, wash the product with deionized water and ethanol, and then vacuum dry at 80℃ for 6~8 hours to obtain Cu-doped BiOBr petal-shaped material.

[0006] The molar ratio of Bi(NO3)3·5H2O to Cu(NO3)2·3H2O is 100:1-100:5, and the molar ratio of Cu(NO3)2·3H2O to KBr is 1:100-5:100.

[0007] Synthesis mechanism of Cu-doped BiOBr photocatalyst: Cu-doped BiOBr photocatalyst was synthesized by hydrothermal method. First, Bi(NO3)3·5H2O, Cu(NO3)2·3H2O and KBr were dissolved in solvent as precursors, and then a uniform suspension was formed after stirring and ultrasonic treatment. Then, the mixed suspension was transferred to a polytetrafluoroethylene-lined reactor, heated at a certain temperature for a certain time, and finally dried to obtain Cu-doped BiOBr photocatalyst. Cu ions are doped into the BiOBr lattice, which may replace the position of Bi to form oxygen vacancies. These oxygen vacancies become the enrichment area of ​​photoexcited electrons and the main active sites involved in the nitrogen fixation reaction. The doping of Cu ions can adjust the band structure of BiOBr and achieve better separation and transfer of photogenerated carriers by introducing impurity energy levels. Cu doping can enhance the absorption capacity of BiOBr photocatalyst in the visible light region, improve light utilization efficiency, and increase the number of photogenerated electrons generated per unit time. The interfacial charge transfer mechanism introduced by Cu doping improves the separation efficiency of photogenerated electrons and holes, reduces the photogenerated electron-hole recombination process, and enhances the intensity of photogenerated current, thereby increasing the photocatalytic nitrogen fixation rate.

[0008] 2. Structural Characterization of Cu-doped BiOBr Photocatalyst Figure 1 The Cu 2p spectrum of Cu-doped BiOBr was examined at 932.79 eV (Cu 2p 3 / 2 ) and 952.39 eV (Cu2p1 / 2 ) binding energy peak, indicating the presence of Cu 2+ ions. Despite the limited content of Cu in copper-doped BiOBr, the peak at 941 eV is associated with Bi-4s, which may overlap with the Cu 2p satellite emission. These results confirm that Cu has been effectively doped into the BiOBr structure. Cu-doped BiOBr was successfully synthesized.

[0009] Figure 2 (a) is the SEM image of Cu-doped BiOBr. Figure 2 (a) It can be directly observed that its morphology is microsphere petal-like. Figure 2 (b) TEM further proves that it is a microsphere petal-like structure.

[0010] 3. Performance evaluation and application of Cu-doped BiOBr photocatalyst The catalyst can be used in photocatalytic nitrogen fixation reactions and has good nitrogen fixation performance and distribution of all nitrogen fixation products. After one hour of illumination, the ammonium ion concentration in the photocatalytic reaction system reached 466.3 μmol·g cat -1 ·h -1 , showing good nitrogen fixation efficiency.

[0011] Compared with the prior art, the present invention has the following advantages: 1. The preparation process of Cu-doped BiOBr catalyst is simple, requiring only hydrothermal and simple drying process. The raw materials are cheap and easy to obtain. Compared with the rare precious metals such as ruthenium, platinum and palladium widely used in the current photocatalytic nitrogen fixation research, copper is relatively easy to obtain. Therefore, from the perspective of preparation process and raw material selection, this catalyst has the advantages of being simple, easy to obtain and cheap.

[0012] 2. The photocatalytic nitrogen fixation efficiency of the catalyst is high. No additional sacrificial agent is required during the reaction process. Only water is needed as the reaction medium, which is conducive to the subsequent extraction and utilization of the product and improves the economic benefits of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Cu 2p orbital X-ray photoelectron spectroscopy (XPS) of Cu-doped BiOBr.

[0014] Figure 2 (a) is the SEM image of Cu-doped BiOBr, and (b) is the TEM image of Cu-doped BiOBr.

[0015] Figure 3 The photocatalytic nitrogen fixation performance test results of pure BiOBr and Cu-doped BiOBr.

[0016] Figure 4The photocatalytic nitrogen fixation performance test results of pure BiOBr and optimal Cu-doped BiOBr. DETAILED DESCRIPTION

[0017] The present invention is further explained below with reference to specific embodiments. Example

[0018] 1. Preparation method of pure BiOBr Pure BiOBr was synthesized using a solvothermal method. Typically, 1.213 g Bi(NO3)3•5 H2O (2.5 mmol) and 0.298 g KBr (2.5 mmol) were dissolved in ethylene glycol (50 mL) solution, and the mixture was vigorously stirred for 60 min to obtain a liquid that was fully reacted in a 100 mL polytetrafluoroethylene-lined high-pressure vessel and reacted at 160 °C for 12 h. Subsequently, the autoclave was gradually cooled to ambient temperature. The resulting precipitate was centrifuged and washed several times with ethanol and deionized water to remove impurities. Pure BiOBr was obtained by drying in a vacuum oven at 80 °C for 8 h.

[0019] 2. The Cu-BiOBr photocatalyst was prepared by hydrothermal method. 0.012g Cu(NO3)2•3H2O (0.05mmol) was placed in a 100mL beaker, and then 1.213g Bi(NO3)3•5H2O (2.5mmol) and 0.298g KBr (2.5mmol) were added to the beaker, dissolved in ethylene glycol (50mL), and stirred for 1 hour. Finally, the homogeneous solution was transferred to a 100mL Teflon-lined stainless steel autoclave and kept at 160℃ for 12h. The product was separated by centrifugation, washed several times with ethanol and deionized water, and dried in a vacuum oven at 80°C for 8h. The obtained product was labeled as 2% Cu-BiOBr. A series of samples for experimental optimization were created using molar variations of Cu(NO3)2•3H2O (0.025~0.125mmol), which are referred to as X%Cu-BiOBr (X=1, 2, 3, 4, 5, X represents the molar ratio of Cu(NO3)2•3H2O and BiOBr).

[0020] Photocatalytic nitrogen fixation reaction determination The Cu-BiOBr prepared in the above example was used as a photocatalyst. 50 mg of the catalyst was added to 100 mL of water, followed by ultrasonic treatment to obtain a corresponding suspension, which was then transferred to a quartz reactor equipped with a water cooling system. Before the light source was introduced, the suspension was stirred in the dark for 30 minutes, and high-purity nitrogen was continuously bubbled to fill the catalytic system with a nitrogen atmosphere. Subsequently, a 300W xenon lamp was turned on as a simulated light source, and nitrogen was still bubbling at room temperature of 25°C. During the irradiation process, the mixed solution (5 ml) was taken out every 30 minutes, and the photocatalyst was filtered with a 0.22µm MCE membrane. NH4 + The photocatalytic nitrogen fixation experiment of Cu-BiOBr was carried out for 150 minutes, and samples were taken every 30 minutes to dynamically detect the change of ammonium radical concentration in the catalytic reaction system. The results are as follows: Figure 3 shown.

[0021] Depend on Figure 3 It can be seen that a series of Cu-doped BiOBr photocatalysts with different ratios were prepared, and all Cu-doped BiOBr variants showed higher photoactivity compared with pure BiOBr. With the increase of Cu addition, the photocatalytic nitrogen fixation activity initially increased and then decreased.

[0022] Depend on Figure 4 It can be seen that after one hour of illumination, the concentration of ammonium ions in the photocatalytic reaction system reached 466.3 μmol·g cat -1 ·h -1 , showing good nitrogen fixation efficiency, and with the increase of light exposure time, the concentration of nitrogen fixation products continued to increase.

[0023] The Cu-BiOBr photocatalyst of the present invention has higher nitrogen fixation performance and higher ammonia yield than those in current research, achieves higher economic value, improves the economic benefits of photocatalytic nitrogen fixation, and has a positive impact on agricultural production and environmental protection.

Claims

1. A method for preparing Cu-doped BiOBr petal-shaped materials for photocatalytic nitrogen fixation, characterized in that: Take Bi(NO3)3·5H2O, Cu(NO3)2·3H2O and KBr as raw materials and ethylene glycol as solvent, stir and mix them evenly, then transfer them to a polytetrafluoroethylene reactor, heat to 170~180℃ for hydrothermal reaction for 10~12 hours, wash the product with deionized water and ethanol, and then vacuum dry at 80℃ for 6~8 hours to obtain Cu-doped BiOBr petal-shaped material.

2. A method for preparing a Cu-doped BiOBr petal-shaped material for photocatalytic nitrogen fixation as claimed in claim 1, characterized in that: The molar ratio of Bi(NO3)3·5H2O to Cu(NO3)2·3H2O is 100:1-100:5, and the molar ratio of Cu(NO3)2·3H2O to KBr is 1:100-5:100.

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