Bismuth tantalum oxyhalide modified by synergistic modification of Bi element and oxygen defect, preparation method and application thereof

Abstract

This invention discloses a bismuth tantalum halide oxide synergistically modified with elemental Bi and oxygen vacancies, its preparation method, and its application, belonging to the field of photocatalysis technology. This invention synthesizes a Bi4TaO8Cl photocatalyst synergistically modified with elemental Bi and oxygen vacancies. By utilizing the SPR effect of bismuth metal, the absorption of visible light by Bi4TaO8Cl is enhanced, forming more active free radicals. At the same time, the synergistic modification of the photocatalyst by oxygen vacancies is effectively utilized to improve the carrier separation efficiency, further enhancing the photocatalytic degradation of NO by pure Bi4TaO8Cl.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis technology, specifically to a bismuth tantalum halide oxide synergistically modified with elemental Bi and oxygen vacancies, and also to a method for preparing the bismuth tantalum halide oxide and its application in photocatalytic removal of nitrogen oxides. Background Technology

[0002] Large amounts of sulfides (SO₄) are emitted from various sectors, including chemical combustion and automobile exhaust. X ), nitrogen oxides (NO) X Toxic substances such as volatile organic compounds (VOCs), including NO. X This mainly includes nitrous oxide (N₂O), nitric oxide (NO), nitrogen dioxide (NO₂), dinitrogen trioxide (N₂O₃), and dinitrogen tetroxide (N₂O₄). Low concentrations of NO... X Not only does it trigger a series of environmental problems such as photochemical smog and ozone layer depletion, causing immense damage to the environment, it also poses a significant threat to human health, leading to respiratory diseases, affecting cardiopulmonary function, and even causing cancer. Traditional NO... x There are various control technologies, such as catalytic combustion, absorption, condensation, and physical adsorption, but they generally suffer from high energy consumption, poor versatility, and strong susceptibility to environmental factors. In contrast, solar photocatalysis technology, as a new type of economical, efficient, and low-energy degradation technology, can convert renewable light energy into chemical energy. It has mild reaction conditions, high nitrogen oxide degradation efficiency, and no secondary pollution, showing great application prospects in environmental purification.

[0003] Currently, common semiconductor photocatalysts can be classified into the following types: (1) Metal oxide semiconductor photocatalysts, such as TiO2, which is abundant in nature and has a unique electronic structure, excellent light absorption performance and carrier lifetime. However, its band gap is about 3.2 eV, corresponding to a light absorption wavelength of 387.5 nm. The light absorption is limited to the ultraviolet region, and this wavelength accounts for 5% of the sunlight that reaches the ground. Therefore, the utilization efficiency of solar energy is not high. (2) Metal sulfide semiconductor photocatalysts, such as CdS, are inexpensive to prepare and have a simple manufacturing process. The band gap is about 2.42 eV, and it has excellent visible light activity. However, its stability is poor and it is prone to photocorrosion, which leads to a decrease in catalytic efficiency. (3) Non-metallic semiconductor photocatalysts, such as g-C3N4, are a new type of non-metallic semiconductor photocatalyst. It has a unique two-dimensional layered structure, good stability, and is easy to control. The band gap of g-C3N4 is about 2.7 eV, and it has good visible light response. However, the commonly used bulk g-C3N4 has drawbacks such as high recombination rate of photogenerated carriers, low quantum efficiency, and small specific surface area, which makes its photocatalytic performance still insufficient.

[0004] To address the shortcomings of existing catalysts, a novel photocatalyst is urgently needed to effectively remove NO. Among bismuth-based semiconductor photocatalysts, Bi4TaO8Cl is a novel semiconducting photocatalyst with a unique Sillén–Aurivillius perovskite crystal structure. This crystal structure can generate an internal electrostatic field between layers, thereby promoting the separation and transfer of photogenerated carriers. It is also low-cost, non-toxic, and structurally stable. However, its photocatalytic NO degradation efficiency remains low. Therefore, we modified it to achieve highly efficient NO degradation under visible light. Summary of the Invention

[0005] In view of this, one objective of the present invention is to provide a method for preparing bismuth tantalum halide oxides synergistically modified with elemental Bi and oxygen vacancies, wherein the raw materials are readily available and the preparation method is simple; a second objective of the present invention is to provide bismuth tantalum halide oxides synergistically modified with elemental Bi and oxygen vacancies prepared by the method, which exhibit stable catalytic performance and high catalytic efficiency under visible light; a third objective of the present invention is to provide the application of the bismuth tantalum halide oxides synergistically modified with elemental Bi and oxygen vacancies in photocatalytic removal of nitrogen oxides.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] 1. A method for preparing a bismuth tantalum halide oxide synergistically modified with elemental Bi and oxygen vacancies, comprising the following preparation steps:

[0008] 1) BiOCl halooxides were synthesized using a one-step synthesis method;

[0009] 2) The BiOCl halide compound prepared in step 1) is calcined with a mixture of Ta2O5, Bi2O3, NaCl and KCl to form a perovskite-type Bi4TaO8Cl bismuth tantalum halide compound with a thick nanosheet structure.

[0010] 3) The Bi₄TaO₈Cl bismuth-tantalum halide compound prepared in step 2) is reduced under the action of NaBH₄ to reduce the Bi₄TaO₈Cl bismuth-tantalum halide compound. 3+ While reducing to elemental Bi, oxygen vacancies are generated, resulting in a Bi4TaO8Cl catalyst that is synergistically modified by elemental Bi and oxygen vacancies.

[0011] In a preferred embodiment of the present invention, the specific method for synthesizing BiOCl halooxides in step 1) is as follows: Bi(NO3)3·5H2O is added to a certain amount of ethylene glycol and ultrasonically stirred until dissolved. Then, KCl aqueous solution is added dropwise to the mixed solution of Bi(NO3)3·5H2O and ethylene glycol and stirred at room temperature for 2 hours.

[0012] In a further preferred embodiment of the present invention, the mass ratio of Bi(NO3)3·5H2O to KCl is 10:1.

[0013] Preferably, in step 2), the molar ratio of the mixture composed of BiOCl, Ta2O5, Bi2O3, NaCl, and KCl is 1:2:3:10:10.

[0014] Preferably, the calcination is performed at 700°C for 3 hours.

[0015] Preferably, in step 3), the mass ratio of NaBH4 to Bi4TaO8Cl is 1:10.

[0016] 2. The Bi4TaO8Cl catalyst prepared by the method is synergistically modified with elemental Bi and oxygen defects.

[0017] 3. Application of the Bi4TaO8Cl catalyst synergistically modified with elemental Bi and oxygen defects in photocatalytic removal of nitrogen oxides.

[0018] Combining the above technical solutions and applications, the advantages and positive effects of the technical solution to be protected by this invention are as follows: This invention synthesizes a bismuth tantalum halide photocatalyst synergistically modified with elemental Bi and oxygen vacancies. Using BiOCl synthesized in a one-step method as a precursor, a mixture of BiOCl, Ta2O5, Bi2O3, NaCl, and KCl is calcined with molten salt to form Bi4TaO8Cl, which has a unique lamellar structure. Furthermore, a bismuth tantalum halide photocatalyst simultaneously modified with elemental Bi and oxygen vacancies is prepared in situ using sodium borohydride as a reducing agent. Elemental Bi, oxygen vacancies, and Bi4TaO8Cl coexist, forming a synergistic modification effect.

[0019] The catalyst of this invention is applied to the photocatalytic removal of nitrogen oxides. The successful construction of the Bi@Bi4TaO8Cl-OVs visible light catalyst effectively utilizes the SPR effect of Bi metal to enhance the absorption of visible light by Bi4TaO8Cl, forming more active free radicals. Simultaneously, it effectively utilizes oxygen vacancies to synergistically modify the photocatalyst, improving carrier separation efficiency and further enhancing the photocatalytic degradation of NO by pure Bi4TaO8Cl. Compared with photocatalysts reported in other patents, the photocatalyst provided by this invention has a simple reaction and excellent performance. This invention proposes a novel photocatalyst, Bi@Bi4TaO8Cl-OVs, which is simple to synthesize and efficiently degrades harmful NO gases. Attached Figure Description

[0020] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration:

[0021] Figure 1The XRD pattern of the Bi4TaO8Cl catalyst prepared in Example 1;

[0022] Figure 2 SEM image of the Bi4TaO8Cl catalyst prepared in Example 1;

[0023] Figure 3 TEM and HRTEM images of the Bi4TaO8Cl catalyst prepared in Example 1;

[0024] Figure 4 The image shows a SEM image of the Bi@Bi4TaO8Cl-OVs catalyst prepared in Example 2.

[0025] Figure 5 TEM and HRTEM images of the Bi@Bi4TaO8Cl-OVs catalyst prepared in Example 2;

[0026] Figure 6 The XRD pattern of the Bi@Bi4TaO8Cl-OVs catalyst prepared in Example 2 is shown below.

[0027] Figure 7 XPS images of Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs catalysts;

[0028] Figure 8 EPR diagrams of Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs catalysts;

[0029] Figure 9 Photocurrent plots of Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs catalysts;

[0030] Figure 10 Photocatalytic activity of Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs catalysts for NO degradation after 30 min;

[0031] Figure 11 The activity cycle diagram of photocatalytic degradation of NO by Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs catalysts is shown.

[0032] Figure 12 The photocatalytic activity of Bi@Bi4TaO8Cl-OVs catalysts with different bismuth loadings in the degradation of NO is shown in the figure. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0034] Example 1: Preparation of pure Bi₄TaO₈Cl catalyst

[0035] The specific method for preparing pure Bi₄TaO₈Cl is as follows:

[0036] Weigh 2g Bi(NO3)3·5H2O and 0.2g KCl and add them to 100ml ethylene glycol and 30ml deionized water respectively. Stir with sonication until dissolved. Then add KCl aqueous solution dropwise to the mixed solution of Bi(NO3)3·5H2O and ethylene glycol. Stir at room temperature for 2h and centrifuge to dry to obtain BiOCl.

[0037] The obtained BiOCl was added to an agate mortar and ground thoroughly with Ta2O5, Bi2O3, NaCl and KCl in a molar ratio of 1:2:3:10:10. After thorough grinding and mixing, the mixture was placed in a muffle furnace and calcined at a temperature of about 700℃ with a heating rate of 5℃ / min and a holding time of 3h. The resulting bright yellow Bi4TaO8Cl precursor was obtained by vacuum filtration.

[0038] The XRD pattern of the bright yellow precursor Bi4TaO8Cl provided in this embodiment is shown in the figure. Figure 1 As shown, the SEM image is as follows: Figure 2 As shown, TEM and HRTEM images are as follows. Figure 3 As shown.

[0039] Example 2: Preparation of Bi4TaO8Cl catalyst synergistically modified with elemental Bi and oxygen vacancies

[0040] The preparation method of Bi@Bi4TaO8Cl-OVs is as follows:

[0041] Weigh 2g Bi(NO3)3·5H2O and 0.2g KCl and add them to 100ml ethylene glycol and 30ml deionized water respectively. Stir with sonication until dissolved. Then add KCl aqueous solution dropwise to the mixed solution of Bi(NO3)3·5H2O and ethylene glycol. Stir at room temperature for 2h and centrifuge to dry to obtain BiOCl.

[0042] The obtained BiOCl was added to an agate mortar and ground thoroughly with Ta2O5, Bi2O3, NaCl and KCl in a molar ratio of 1:2:3:10:10. After thorough grinding and mixing, the mixture was placed in a muffle furnace and calcined at a temperature of about 700℃ with a heating rate of 5℃ / min and a holding time of 3h. The resulting bright yellow Bi4TaO8Cl precursor was obtained by vacuum filtration.

[0043] Add 0.5g of Bi4TaO8Cl to 50ml of deionized water and sonicate until dissolved. Then, add 20ml of NaBH4 solution prepared with ice water (NaBH4:Bi4TaO8Cl mass ratio is 1:10) dropwise to the Bi4TaO8Cl aqueous solution and stir for 1h. Centrifuge multiple times to obtain Bi@Bi4TaO8Cl-OVs.

[0044] The SEM image of the elemental Bi@Bi4TaO8Cl-OVs catalyst synthesized in this embodiment is shown below. Figure 4 As shown, HRTEM analysis of the Bi@Bi4TaO8Cl-OVs photocatalyst revealed that the 104 crystal plane corresponding to elemental Bi, as shown... Figure 5 As shown, this demonstrates the successful in-situ growth of elemental Bi. The XRD pattern of the phase analysis is shown below. Figure 6 As shown.

[0045] XPS analysis of the Bi4TaO8Cl photocatalyst prepared in Example 1 and the Bi@Bi4TaO8Cl-OVs photocatalyst prepared in Example 2 revealed that Bi@Bi4TaO8Cl-OVs exhibited corresponding elemental Bi peaks. Figure 7 As shown.

[0046] EPR analysis of the Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs photocatalysts revealed that Bi@Bi4TaO8Cl-OVs exhibits more oxygen vacancies, such as... Figure 8 As shown, this demonstrates the existence of oxygen vacancies.

[0047] Photocurrent analysis was performed on the Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs photocatalysts. The results showed that Bi@Bi4TaO8Cl-OVs exhibited better carrier separation performance, such as... Figure 9 As shown.

[0048] Example 3: Investigating the role of catalysts in the treatment of pollutant NO x Applications in purification

[0049] Weigh 0.2 g of Bi₄TaO₈Cl prepared in Example 1 and pour it into a 12 cm diameter petri dish. Add an appropriate amount of ethanol, sonicate for 5 min, disperse evenly, and then place in a 60 °C oven to dry for 30 min. Place the dried sample into the reaction chamber of a nitrogen oxide analyzer and introduce nitrogen oxides at a concentration of ppb level. When the concentration in the nitrogen oxide analyzer stabilizes, turn on a 150 W halogen tungsten lamp, react for 30 min, and then turn off the light source.

[0050] Weigh 0.2 g of Bi@Bi4TaO8Cl-OVs prepared in Example 2 and pour it into a 12 cm diameter petri dish. Add an appropriate amount of ethanol, sonicate for 5 min, disperse evenly, and then place in a 60 °C oven to dry for 30 min. Place the dried sample into the reaction chamber of a nitrogen oxide analyzer and introduce nitrogen oxides at a concentration of ppb level. When the concentration in the nitrogen oxide analyzer stabilizes, turn on a 150 W halogen tungsten lamp, react for 30 min, and then turn off the light source.

[0051] (1) The Bi4TaO8Cl prepared in Example 1 was tested for catalytic performance under visible light conditions using an intermittent flow reactor. The specific test conditions were as follows: the initial NO concentration was 594 ppb, the amount of catalyst was 0.2 g, the light source was a 150 W halogen tungsten lamp, a visible light filter was used, and the flow rate ratio of NO to air was adjusted to 19:2400 by a flow controller to completely mix NO and air. The performance and stability of NO removal under visible light were tested. Under 30 min of light irradiation, it was able to degrade NO harmful gas by 83 ppb, and the removal rate reached 14%. The results are shown in Table 1.

[0052] (2) The Bi@Bi4TaO8Cl-OVs prepared in Example 2 were tested for catalytic performance under visible light conditions using an intermittent flow reactor. The specific test conditions were as follows: the initial NO concentration was 611 ppb, the amount of catalyst was 0.2 g, the light source was a 150 W halogen tungsten lamp, a visible light filter was used, and the flow rate ratio of NO to air was adjusted to 19:2400 by a flow controller to completely mix NO and air. The performance and stability of NO removal under visible light were tested. Under 30 min of light irradiation, it was able to degrade 448 ppb of harmful NO gas, with a removal rate of 73%, showing excellent removal rate and broad spectral response. The results are shown in Table 1.

[0053] The NO harmful gas degradation activity diagrams of the bright yellow precursor Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs catalyst provided in the embodiments of the present invention are shown in the figure. Figure 10 As shown in the figure, the cyclic activity diagram of the Bi@Bi4TaO8Cl-OVs catalyst for NO degradation is as follows. Figure 11 As shown.

[0054] Table 1. Degradation efficiency of NO harmful gas by Bi4TaO8Cl and Bi@Bi4TaO8Cl-OVs catalysts

[0055]

[0056] Example 4: Investigating the effect of different NaBH4:Bi4TaO8Cl mass ratios on catalytic performance.

[0057] Weigh 0.5 g of Bi₄TaO₈Cl prepared in Example 1 and add it to 50 ml of deionized water. Stir ultrasonically until dissolved. Then, add 20 ml of NaBH₄ solution prepared with ice water (NaBH₄:Bi₄TaO₈Cl mass ratio of 1:20, 1:15, 1:10, and 1:5) dropwise to several groups of Bi₄TaO₈Cl aqueous solutions, stir for 1 h, and centrifuge multiple times to obtain Bi@B with different bismuth loadings. i4 TaO8Cl-OVs were named Bi@Bi4TaO8Cl-OVs-1:20, Bi@Bi4TaO8Cl-OVs-1:15, Bi@Bi4TaO8Cl-OVs-1:10, and Bi@Bi4TaO8Cl-OVs-1:5, respectively.

[0058] Referring to the method in Example 3, the activity of Bi@Bi4TaO8Cl-OVs catalysts with different bismuth loadings prepared in this example for the degradation of NO harmful gas was tested, and the results are as follows: Figure 12 As shown, the catalyst with the best activity was obtained when the mass ratio of NaBH4:Bi4TaO8Cl was 1:10, which is the optimal catalyst for this project.

[0059] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing bismuth tantalum halide oxides synergistically modified with elemental Bi and oxygen vacancies, characterized in that: The preparation steps include the following: 1) BiOCl halooxides were synthesized by a one-step synthesis method. The specific method was as follows: Bi(NO3)3·5H2O was added to a certain amount of ethylene glycol and ultrasonically stirred until dissolved. Then, KCl aqueous solution was added dropwise to the mixed solution of Bi(NO3)3·5H2O and ethylene glycol and stirred at room temperature for 2 h. 2) The BiOCl halide compound prepared in step 1) is calcined with a mixture of Ta2O5, Bi2O3, NaCl, and KCl to form a perovskite-type Bi4TaO8Cl bismuth-tantalum halide compound with a thick nanosheet structure; the molar ratio of the mixture of BiOCl, Ta2O5, Bi2O3, NaCl, and KCl is 1:2:3:10:10; 3) The Bi₄TaO₈Cl bismuth-tantalum halide compound prepared in step 2) is reduced in the presence of NaBH₄ to reduce the Bi₄TaO₈Cl catalyst. 3+ While reducing to elemental Bi, oxygen vacancies are generated, resulting in a Bi4TaO8Cl catalyst synergistically modified with elemental Bi and oxygen vacancies; the mass ratio of NaBH4 to Bi4TaO8Cl is 1:

10.

2. The method for preparing bismuth tantalum halide oxide synergistically modified by elemental Bi and oxygen vacancies according to claim 1, characterized in that: The mass ratio of Bi(NO3)3·5H2O to KCl is 10:

1.

3. The method for preparing bismuth tantalum halide oxide synergistically modified by elemental Bi and oxygen defects according to claim 1, characterized in that: In step 2), the calcination is carried out at 700 °C for 3 h.

4. Bismuth tantalum halide oxides synergistically modified with elemental Bi and oxygen defects, prepared by the method according to any one of claims 1 to 3.

5. The application of the bismuth tantalum halide oxide synergistically modified with elemental Bi and oxygen defects as described in claim 4 in the photocatalytic removal of nitrogen oxides.

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