Bi8(CrO4)O 11 Preparation and application of photocatalysts

Abstract

This invention relates to the field of photocatalysts, and more particularly to a Bi8(CrO4)O 11 Preparation and application of photocatalysts. In this invention, a yellow transparent potassium chromate solution is added dropwise to a white emulsion of bismuth nitrate pentahydrate, and the mixture is continuously stirred to obtain an orange-yellow emulsion. This emulsion is then transferred to a reaction vessel and reacted at 160–190 °C for 6–12 h. After natural cooling to room temperature, an orange-red precipitate is obtained. The precipitate is filtered, collected, thoroughly washed with deionized water, and then freeze-dried to obtain orange-red Bi8(CrO4)O. 11 Photocatalyst. The Bi8(CrO4)O prepared in this invention... 11 Photocatalysts, with suitable band positions, can efficiently generate ·OOH with moderate oxidizing power as the main active species, and have excellent performance in inhibiting the over-oxidation of intermediate products in continuous reactions.

Description

Technical Field

[0001] This invention relates to the field of photocatalysts, and more particularly to a Bi8(CrO4)O 11 Preparation and application of photocatalysts. Background Technology

[0002] Methane, a short-lived and potent greenhouse gas, has a greenhouse effect more than 20 times that of carbon dioxide. It is the second largest greenhouse gas contributing to global warming since the Industrial Revolution, with emissions increasing dramatically due to the extensive use of fossil fuels such as coal and oil. Therefore, effectively utilizing methane and reducing its emissions has become an urgent problem to be solved.

[0003] Photocatalytic oxidation of methane to produce liquid products utilizes solar energy instead of thermal energy, using H2O, O2, or H2O2 as the oxidant. This achieves methane activation at room temperature and pressure, avoiding the traditional high-temperature and high-pressure conditions, making it a highly promising methane utilization technology that has attracted widespread attention in recent years. However, current photocatalytic oxidation of methane to produce liquid products mainly utilizes photogenerated holes (h2O2) at the oxidation end. + The activation of CH4 generates ·CH3, which then undergoes coupling oxidation with reactive oxygen species (ROS) produced during the process to generate liquid products. The ROS mainly include hydroxyl radicals (·OH) and peroxidized hydroxyl radicals (·OOH). ·OH has a higher oxidizing activity than h. + The higher oxidizing power of methanol, a liquid product obtained from methane oxidation, makes it highly susceptible to peroxidation in the presence of ·OH, thus preventing the selective "targeting" synthesis of high-value-added liquid fuel products without the need for CO and CO2 peroxidation products. Compared to ·OH, ·OOH has a milder oxidizing property and can inhibit the formation of peroxidation products such as CO and CO2. Therefore, from a practical application perspective, developing photocatalysts with high selectivity for generating the required active free radicals and good stability to promote the generation of ·OOH, thereby avoiding methane peroxidation and improving its selectivity, has become a key challenge in the application of photocatalytic oxidation of methane to liquid products. Summary of the Invention

[0004] This invention provides a Bi8(CrO4)O photocatalyst to develop a photocatalyst with high selectivity for generating desired active free radicals and good stability. 11 Preparation and application of photocatalysts.

[0005] This invention is achieved through the following technical solution: a Bi8(CrO4)O 11 The preparation method of photocatalyst includes the following steps:

[0006] (1) At room temperature, bismuth nitrate pentahydrate and potassium chromate were dissolved in an aqueous solvent and stirred continuously to obtain a white emulsion and a yellow transparent solution, respectively.

[0007] (2) The yellow transparent potassium chromate solution from step (1) above is added dropwise to the white emulsion of bismuth nitrate pentahydrate, and the mixture is stirred continuously to obtain an orange-yellow emulsion;

[0008] (3) Transfer the emulsion from step (2) above to a reaction vessel and react at 160-190°C for 6-12 hours. After naturally cooling to room temperature, an orange-red precipitate is obtained.

[0009] (4) Filter the precipitate from step (3) above, collect the solid, wash the precipitate thoroughly with deionized water, and freeze-dry the solid to obtain orange-red Bi8(CrO4)O. 11 Photocatalyst.

[0010] As a further improvement to the preparation method of the present invention, the concentration of bismuth nitrate pentahydrate in step (1) is 50-80 mol / L and the concentration of potassium chromate is 25-40 mol / L.

[0011] As a further improvement to the preparation method of the present invention, the molar ratio of bismuth nitrate pentahydrate and potassium chromate in the orange-yellow emulsion of step (2) is 2:1.

[0012] As a further improvement to the preparation method of the present invention, the freeze-drying time is 10-24 hours.

[0013] The present invention further provides the Bi8(CrO4)O prepared by the above preparation method. 11 Photocatalyst.

[0014] The present invention also provides Bi8(CrO4)O prepared by the above preparation method. 11 Application of photocatalysts in the photocatalytic oxidation of methane to produce liquid fuel products.

[0015] As a further improvement to the application technology solution of the present invention, the specific method of the application is as follows: adding Bi8(CrO4)O to water. 11 The photocatalyst is placed in a high-pressure reactor. The air is replaced multiple times with a mixture of methane and oxygen and the reactor is filled to the reaction pressure. The reactor is then irradiated with a light source with a wavelength of 300–850 nm to produce liquid fuel products.

[0016] As a further improvement to the application technology solution of the present invention, the volume ratio of methane to oxygen is 0.5-0.95:0.05-0.5.

[0017] As a further improvement to the application technology of the present invention, the reaction pressure is 0.1 to 3 MPa.

[0018] The present invention also provides Bi8(CrO4)O prepared by the above preparation method. 11 Application of photocatalysts in photocatalytically promoting the generation of ·OOH to improve the selectivity of methane oxidation.

[0019] This invention provides a Bi8(CrO4)O 11 The preparation and application of photocatalysts have the following advantages compared with existing technologies:

[0020] 1. Bi8(CrO4)O prepared by the method of the present invention 11 Compared to commercially available P25 photocatalysts, this photocatalyst has a very wide light absorption range, which can broaden the absorption band edge to 700nm and has a high light utilization efficiency.

[0021] 2. The method of this invention prepares Bi8(CrO4)O with a broad spectral response via a simple one-step hydrothermal method. 11 Photocatalysts have simple and reproducible preparation methods, providing a good technical foundation and material guarantee for commercial applications;

[0022] 3. The Bi8(CrO4)O prepared by this invention 11 Photocatalysts, with suitable band positions, can efficiently generate ·OOH with moderate oxidizing power as the main active species, and have excellent performance in inhibiting the over-oxidation of intermediate products in continuous reactions. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 Bi8(CrO4)O prepared in Example 1 11 Powder X-ray diffraction pattern of photocatalyst.

[0026] Figure 2 Bi8(CrO4)O prepared in Example 1 11 Scanning electron microscope image of the photocatalyst.

[0027] Figure 3 Bi8(CrO4)O prepared in Example 1 11 UV-Vis diffuse reflectance spectrum of photocatalyst.

[0028] Figure 4 Bi8(CrO4)O prepared in Example 1 11 Comparison of the distribution of photocatalysts, Bi2MoO6 prepared in Comparative Example 1, and Bi2WO6 prepared in Comparative Example 2 in the photocatalytic production of liquid methane.

[0029] Figure 5 Bi8(CrO4)O prepared in Example 1 11 Schematic diagram of the photocatalytic production of ·OOH by the photocatalyst, Bi2MoO6 prepared in Comparative Example 1, and Bi2WO6 photocatalyst prepared in Comparative Example 2. Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0032] This invention provides a Bi8(CrO4)O 11 A specific embodiment of the preparation method of the photocatalyst includes the following steps:

[0033] (1) At room temperature, bismuth nitrate pentahydrate and potassium chromate were dissolved in an aqueous solvent and stirred continuously to obtain a white emulsion and a yellow transparent solution, respectively.

[0034] (2) The yellow transparent potassium chromate solution from step (1) above is added dropwise to the white emulsion of bismuth nitrate pentahydrate, and the mixture is stirred continuously to obtain an orange-yellow emulsion;

[0035] (3) Transfer the emulsion from step (2) above to a reaction vessel and react at 160-190°C for 6-12 hours. After naturally cooling to room temperature, an orange-red precipitate is obtained.

[0036] (4) Filter the precipitate from step (3) above, collect the solid, wash the precipitate thoroughly with deionized water, and freeze-dry the solid to obtain orange-red Bi8(CrO4)O. 11 Photocatalyst.

[0037] In different embodiments, the reaction temperature in step (3) can be 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, or any two of the defined ranges.

[0038] In different embodiments, the reaction time in step (3) can be 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, or within any two defined ranges.

[0039] In one embodiment of the present invention, the concentration of bismuth nitrate pentahydrate in step (1) is 50-80 mol / L and the concentration of potassium chromate is 25-40 mol / L.

[0040] In another embodiment of the present invention, the molar ratio of bismuth nitrate pentahydrate and potassium chromate in the orange-yellow emulsion of step (2) is 2:1.

[0041] In one embodiment of the present invention, the freeze-drying time is 10 to 24 hours.

[0042] The present invention further provides the Bi8(CrO4)O prepared by the above preparation method. 11 Photocatalyst.

[0043] The present invention also provides Bi8(CrO4)O prepared by the above preparation method. 11 Application of photocatalysts in the photocatalytic oxidation of methane to produce liquid fuel products.

[0044] Furthermore, the specific method of application is as follows: adding Bi8(CrO4)O to water. 11 A photocatalyst is placed in a high-pressure reactor. The air is repeatedly replaced with a mixture of methane and oxygen until the reaction pressure is reached. The reactor is then irradiated with a light source with a wavelength of 300–850 nm to produce liquid fuel products. Among these products is Bi8(CrO4)O. 11 The concentration of the photocatalyst in water is 0.1–5 g / L; the volume ratio of methane to oxygen is 0.5–0.95:0.05–0.5. The reaction pressure is 0.1–3 MPa.

[0045] The present invention also provides Bi8(CrO4)O prepared by the above preparation method. 11 Application of photocatalysts in photocatalytically promoting the generation of ·OOH to improve the selectivity of methane oxidation.

[0046] To further demonstrate the Bi8(CrO4)O of the present invention 11Photocatalysts can promote the generation of ·OOH under photocatalytic conditions. This invention also provides a method for detecting ·OOH as follows:

[0047] (1) Add Bi8(CrO4)O to methanol 11 Photocatalyst, Bi8(CrO4)O 11 The concentration of the photocatalyst in methanol is 5–30 mg / mL;

[0048] (2) Add DMPO as a ·OOH scavenger to the solution in step (1) above, maintain the concentration of DMPO at 3-5 mmol / L, and purge with oxygen for 10-30 min;

[0049] (3) Place the solution from step (2) above into a capillary tube and then into a special tube for EPR testing. Install it onto the EPR detection instrument, irradiate the reaction system with a light source of wavelength 300-850nm, and collect the EPR signal for a certain period of time.

[0050] The specific embodiments of the present invention will be described in detail below.

[0051] Example 1

[0052] At room temperature, 4 mmol of bismuth nitrate pentahydrate and 2 mmol of potassium chromate were dissolved in 30 mL of aqueous solution, respectively, and stirred continuously to obtain a white emulsion and a yellow transparent solution, respectively. The yellow transparent potassium chromate solution was then added dropwise to the white bismuth nitrate pentahydrate emulsion, and stirred continuously to obtain an orange-yellow emulsion. This emulsion was then transferred to a stainless steel reactor with a polytetrafluoroethylene liner and reacted at 180°C for 10 h. After naturally cooling to room temperature, the emulsion was filtered, washed three times thoroughly with deionized water, and freeze-dried for 12 h to obtain orange-red Bi8(CrO4)O. 11 Photocatalysts, such as Figure 1 , 2 And as shown in 3.

[0053] The obtained Bi8(CrO4)O 11 Photocatalysts are used for the photocatalytic oxidation of methane. The reaction conditions are: Bi8(CrO4)O... 11 The photocatalyst was mixed with water at a mass-to-volume ratio of 4 g / L and then added to a micro high-pressure reactor. The air was repeatedly replaced with a mixture of methane and oxygen until the required reaction pressure was reached (methane to oxygen volume ratio of 1, reaction pressure 2 MPa). Finally, the reactor was irradiated with a light source with a wavelength of 300–850 nm to produce liquid fuel products, such as… Figure 4 As shown.

[0054] The obtained Bi8(CrO4)O 11The detection of reactive oxygen species in the photocatalytic process was performed under the following conditions: 5 mg of Bi8(CrO4)O was added to 200 μL of methanol under light-protected conditions. 11 The photocatalyst was ultrasonically dispersed to obtain a suspension. Then, 2 μL of DMPO was added as a ·OOH scavenger, and the mixture was purged with oxygen for 10–30 min. Finally, the solution was placed in a capillary tube and then into a dedicated EPR testing tube, which was then mounted on an EPR detection instrument. The capillary tube was irradiated with a light source of 300–850 nm wavelength, and the corresponding EPR signal was acquired after 3 minutes of illumination. Specific results are as follows: Figure 5 As shown.

[0055] Comparative Example 1

[0056] Using the above preparation method, Bi₂MoO₆ was prepared by replacing an equimolar amount of potassium chromate with sodium molybdate. The resulting photocatalyst was then used to directly photocatalyze the oxidation of methane, and its reactive oxygen species were detected. The reaction conditions and operations were the same as in Example 1 above, and the results are as follows. Figure 4 and Figure 5 As shown.

[0057] Comparative Example 2

[0058] Using the above preparation method, Bi₂WO₆ was prepared by replacing an equimolar amount of potassium chromate with sodium tungstate. The resulting photocatalyst was then used to directly photocatalyze the oxidation of methane, and its active oxygen species were detected. The reaction conditions and operations were the same as in Example 1 above, and the results are as follows. Figure 4 and Figure 5 As shown.

[0059] Depend on Figure 1 Powder X-ray diffraction patterns indicate that the prepared sample belongs to the monoclinic Bi8(CrO4)O type. 11 ,from Figure 2 The scanning electron microscope image shows the synthesized Bi8(CrO4)O 11 The photocatalyst samples exhibit a nanoribbon-like structure with a diameter ranging from 100 to 400 nm and a smooth surface. Figure 3 Bi8(CrO4)O can be seen in the ultraviolet-visible diffuse reflectance spectrum. 11 The photocatalyst exhibits a very wide light absorption range, with the absorption band edge extending to 600 nm and a theoretical light utilization efficiency as high as 44.3%. Its band gap, calculated using the Kubelka-Munk function, is 1.8 eV. This makes Bi8(CrO4)O... 11 Photocatalysts have become a very promising photocatalytic material.

[0060] from Figure 4 The distribution diagram of photocatalytic methane partial oxidation products shows that Bi8(CrO4)O 11There are no deep oxidation products (CO2), and the selectivity for oxygen-containing compounds is close to 100%, including CH3OH (61.87 μmol·g). -1 ), HCHO (59.82 μmol·g) -1 ), CH3CH2OH (12.81 μmol·g) -1 ) and CH3CHO (12.50 μmol·g -1 Conversely, three oxygen-containing compounds, CH3OH, HCHO, and CH3CH2OH, as well as a large amount of worthless CO2 over-oxidation products, were detected on Bi2MoO6 and Bi2WO6. The oxygen-containing compound selectivity of Bi2MoO6 and Bi2WO6 was only 38.8% and 51.0%, respectively. Figure 5 Characterization experiments of DMPO capturing ·OOH show that Bi8(CrO4)O 11 The DMPO-·OOH signal of the photocatalyst was 4.63 times and 14.78 times that of Bi2MoO6 and Bi2WO6, respectively, indicating that it can generate ·OOH reactive oxygen free radicals more efficiently.

[0061] Example 2

[0062] At room temperature, 3 mmol of bismuth nitrate pentahydrate and 1.5 mmol of potassium chromate were dissolved in 20 mL of aqueous solution, respectively, and stirred continuously to obtain a white emulsion and a yellow transparent solution, respectively. The yellow transparent potassium chromate solution was then added dropwise to the white bismuth nitrate pentahydrate emulsion, and stirred continuously to obtain an orange-yellow emulsion. This emulsion was then transferred to a stainless steel reactor with a polytetrafluoroethylene liner and reacted at 160 °C for 12 h. After naturally cooling to room temperature, the emulsion was filtered, washed three times thoroughly with deionized water, and freeze-dried for 20 h to obtain orange-red Bi8(CrO4)O. 11 Photocatalyst.

[0063] The obtained Bi8(CrO4)O 11 Photocatalysts are used for the photocatalytic oxidation of methane. The reaction conditions are: Bi8(CrO4)O... 11 The photocatalyst was mixed with water at a mass-to-volume ratio of 4 g / L and then added to a micro high-pressure reactor. The air was replaced multiple times with a mixture of methane and oxygen and the reactor was filled to the pressure required for the reaction. The volume ratio of methane to oxygen was 1 (0.5:0.5), and the reaction pressure was 2 MPa. Finally, the reactor was irradiated with a light source with a wavelength of 300–850 nm to produce liquid fuel products.

[0064] The obtained Bi8(CrO4)O 11The detection of reactive oxygen species in the photocatalytic process was performed under the following conditions: 5 mg of Bi8(CrO4)O was added to 200 μL of methanol under light-protected conditions. 11 The photocatalyst was ultrasonically dispersed to obtain a suspension. Then, 2 μL of DMPO was added as a ·OOH scavenger, and the mixture was purged with oxygen for 10–30 min. Finally, the solution was loaded into a capillary tube and placed in a dedicated EPR test tube, which was then mounted on an EPR detection instrument. The reaction system was irradiated with a light source with a wavelength of 300–850 nm, and the corresponding EPR signal was acquired after 3 minutes of illumination.

[0065] Example 3

[0066] At room temperature, 2 mmol of bismuth nitrate pentahydrate and 1 mol of potassium chromate were dissolved in 20 mL of aqueous solution, respectively, and stirred continuously to obtain a white emulsion and a yellow transparent solution, respectively. The yellow transparent potassium chromate solution was then added dropwise to the white bismuth nitrate pentahydrate emulsion, and stirred continuously to obtain an orange-yellow emulsion. This emulsion was then transferred to a stainless steel reactor with a polytetrafluoroethylene liner and reacted at 180 °C for 10 h. After naturally cooling to room temperature, the emulsion was filtered, washed three times thoroughly with deionized water, and freeze-dried for 12 h to obtain orange-red Bi8(CrO4)O. 11 Photocatalyst.

[0067] The obtained Bi8(CrO4)O 11 Photocatalysts are used for the photocatalytic oxidation of methane. The reaction conditions are: Bi8(CrO4)O... 11 The photocatalyst was mixed with water at a mass-to-volume ratio of 4 g / L and then added to a micro high-pressure reactor. The air was replaced multiple times with a mixture of methane and oxygen and the reactor was filled to the pressure required for the reaction. The volume ratio of methane to oxygen was 1, and the reaction pressure was 2 MPa. Finally, the reactor was irradiated with a light source with a wavelength of 300–850 nm to produce liquid fuel products.

[0068] The obtained Bi8(CrO4)O 11 The detection of reactive oxygen species in the photocatalytic process was performed under the following conditions: 5 mg of Bi8(CrO4)O was added to 200 μL of methanol under light-protected conditions. 11 The photocatalyst was ultrasonically dispersed to obtain a suspension. Then, 2 μL of DMPO was added as a ·OOH scavenger, and the suspension was purged with oxygen for 10 min. Finally, the solution was loaded into a capillary tube and placed in a dedicated EPR test tube, which was then mounted on an EPR detection instrument. The capillary tube was irradiated with a light source with a wavelength of 300–850 nm, and the corresponding EPR signal was acquired after 3 minutes of illumination.

[0069] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A Bi8(CrO4)O 11 The application of photocatalysts in photocatalytically promoting the generation of ·OOH to improve the selectivity of methane oxidation for the production of liquid fuel products is characterized by, The Bi8(CrO4)O 11 The preparation method of photocatalyst includes the following steps: (1) At room temperature, bismuth nitrate pentahydrate and potassium chromate were dissolved in an aqueous solvent and stirred continuously to obtain a white emulsion and a yellow transparent solution, respectively. (2) The yellow transparent potassium chromate solution from step (1) above is added dropwise to the white emulsion of bismuth nitrate pentahydrate, and the mixture is stirred continuously to obtain an orange-yellow emulsion; (3) Transfer the emulsion from step (2) above to a reaction vessel and react at 160~190℃ for 6~12 h. After naturally cooling to room temperature, an orange-red precipitate is obtained. (4) Filter the precipitate from step (3) above, collect the solid, wash the precipitate thoroughly with deionized water, and freeze-dry the solid to obtain orange-red Bi8(CrO4)O. 11 Photocatalyst.

2. The application as described in claim 1, characterized in that, The molar ratio of bismuth nitrate pentahydrate to potassium chromate in the orange-yellow emulsion of step (2) is 2:

1.

3. The application as described in claim 1, characterized in that, The freeze-drying time is 10-24 hours.

4. The application as described in any one of claims 1 to 3, characterized in that, The specific method of application is as follows: Bi8(CrO4)O is added to water. 11 The photocatalyst is placed in a high-pressure reactor. The air is replaced multiple times with a mixture of methane and oxygen and the reactor is filled to the reaction pressure. The reactor is then irradiated with a light source with a wavelength of 300~850 nm to produce liquid fuel products.

5. The application as described in claim 4, characterized in that, The volume ratio of methane to oxygen is 0.5~0.95:0.05~0.

5.

6. The application as described in claim 4, characterized in that, The reaction pressure is 0.1~3 MPa.

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