A kind of Bi 2-x Eu x WO6 / Nb2C MXene photothermal material and its preparation method and application

Abstract

The present invention provides a Bi 2‑x Eu x WO6 / Nb2C MXene photothermal material and its preparation method and application, the preparation method comprises: dissolving Bi(NO3)3, Eu(NO3)3 and Na2WO4 in ethylene glycol to obtain a reaction precursor solution, performing a hydrothermal reaction to obtain Bi 2‑ x Eu x WO6; Nb2C MXene powder was dispersed in ethanol to obtain suspension A; Bi 2‑x Eu x WO6 was dispersed in ethanol to obtain suspension B; suspension A and suspension B were irradiated with ultraviolet light respectively, then suspension A was slowly added to suspension B, and the obtained mixed suspension was irradiated with ultraviolet light to obtain Bi 2‑x Eu x WO6 / Nb2C MXene photothermal material. 2‑x Eu x WO6 / Nb2C MXene photothermal material improves the photothermal catalytic CO2 reduction activity and methane selectivity.

Description

Technical Field

[0001] The present invention belongs to the field of composite materials for environmental protection and solar energy utilization, and is specifically a Bi 2-x Eu x WO6 / Nb2C MXene photothermal material, preparation method and application thereof. Background Art

[0002] The resource utilization of CO2 is an effective approach to developing clean energy. Currently, there are many commercial carbon sequestration methods, such as biological carbon sequestration and thermal catalytic CO2 methanation. Among them, photothermal catalytic CO2 reduction offers significant advantages, converting CO2 into clean energy or high-value chemicals such as CO, CH4, CH3OH, and C2H4.

[0003] Bi2WO6 is composed of perovskite (Bi2O2) 2+ and fluorite (WO4) 2- The alternating layers not only provide a large number of low-coordinate atoms as catalytic sites but also shorten the carrier transport distance. In addition, the redox potential of Bi2WO6 is suitable for all CO2 photoreduction reactions. However, due to its low photoelectron separation efficiency and poor surface activation energy, the photocatalytic performance of pure Bi2WO6 is relatively low. Summary of the Invention

[0004] In order to solve the above-mentioned problems of the prior art, the present invention provides a Bi 2-x Eu x WO6 / Nb2C MXene photothermal materials, their preparation methods, and applications promote the activity and selectivity of Bi2WO6 photothermal catalytic CO2 reduction.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present invention provides a Bi 2-x Eu x The preparation method of WO6 / Nb2C MXene photothermal material comprises the following steps:

[0007] Step 1: dissolve Bi(NO3)3, Eu(NO3)3 and Na2WO4 in ethylene glycol and stir to obtain a reaction precursor solution; subject the reaction precursor solution to a hydrothermal reaction to obtain Bi 2-x Eu x WO6;

[0008] Step 2: Add Nb2C MXene powder to ethanol and disperse it ultrasonically to obtain suspension A; 2-x Eu x WO6 was added to ethanol and ultrasonically dispersed to obtain suspension B;

[0009] Step 3: Suspension A and suspension B are irradiated with ultraviolet light respectively, and then suspension A is slowly added to suspension B, and the resulting mixed suspension is irradiated with ultraviolet light. The product is washed and dried to obtain Bi 2-x Eu x WO6 / Nb2C MXene photothermal material.

[0010] Preferably, in step 1, the molar ratio of Eu(NO3)3 to Bi(NO3)3 is (0.002-0.010):1.

[0011] Preferably, in step 1, the hydrothermal reaction temperature is 150-180° C. and the time is 9-12 h.

[0012] Preferably, in step 2, Bi 2-x Eu x The molar ratio of WO6 and Nb2C MXene is (0.5-1):1.

[0013] Preferably, in step 2, the preparation method of Nb2C MXene powder is: adding Nb2AlC precursor powder to HF solution, and then stirring the resulting mixture solution in a water bath to react. After the reaction is completed, the resulting product is washed and dried to obtain Nb2C MXene.

[0014] Preferably, in step 3, the suspension A and the suspension B are respectively irradiated with ultraviolet light for 30-60 minutes.

[0015] Preferably, in step 3, the mixed suspension is irradiated with ultraviolet light for 3-6 hours.

[0016] The present invention provides Bi obtained by the preparation method as described above 2-x Eu x WO6 / Nb2C MXene photothermal material.

[0017] Preferably, the Bi 2-x Eu x Bi in WO6 / Nb2C MXene photothermal materials 2-x Eu x The morphology of WO6 is nano-flower-shaped, Bi 2-x Eu x WO6 is distributed on the surface of Nb2C MXene.

[0018] The present invention also provides the Bi 2-x Eu x Application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention successfully uses ultraviolet irradiation to dope Bi with rare earth element Eu. 2-x Eu x WO6 was composited with Nb2C MXene to successfully prepare Bi 2-x Eu x WO6 / Nb2C MXene heterojunction photothermal materials. Nb2C MXene and Bi 2-x Eu x The electron concentration difference of WO6 causes electrons to move from Bi 2-x Eu x WO6 transferred to Nb2C MXene, accompanied by Bi 2-x Eu x Bi in WO6 / Nb2C MXene 5+ The reduction of Bi 2-x Eu x WO6 points to the built-in electric field of Nb2C MXene.

[0021] The Bi prepared by the present invention 2-x Eu x When WO6 / Nb2C MXene heterojunction photothermal materials are used in the process of photothermal reduction of CO2, the structure of Bi2WO6 is adjusted by doping with rare earth elements to generate more electrons to participate in the CO2 reduction reaction; 2- x Eu x Under the combined effects of the built-in electric field of the WO6 / Nb2C MXene heterojunction, the LSPR effect of Nb2C MXene, and the upconversion effect of the rare earth element Eu, the electrons required for the photothermal reduction of CO2 reaction are continuously replenished, thereby improving the photothermal catalytic CO2 reduction activity and selectivity, significantly enhancing the degree of product methanation, and achieving a methane selectivity of 100%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 The XRD pattern of the photothermal material prepared in the present invention;

[0024] Figure 2 This is the SEM image of the Nb2C MXene photothermal material prepared in Comparative Example 1 of the present invention;

[0025] Figure 3 This is the SEM image of the Bi2WO6 / Nb2C MXene photothermal material prepared in Comparative Example 2 of the present invention;

[0026] Figure 4 This is an SEM image of the photothermal material prepared in Example 2 of the present invention;

[0027] Figure 5 TEM image of the photothermal material prepared in Example 2 of the present invention;

[0028] Figure 6 This is a HRTEM image of the photothermal material prepared in Example 2 of the present invention;

[0029] Figure 7 MB absorbance curve of Nb2C MXene prepared in comparative example 1 of the present invention under dark conditions;

[0030] Figure 8 MB absorbance curve of Bi2WO6 / Nb2C MXene prepared in comparative example 2 of the present invention under dark conditions;

[0031] Figure 9 MB absorbance curve of the photothermal material prepared in Example 2 of the present invention under dark conditions;

[0032] Figure 10 This is the hole EPR spectrum of the photothermal material prepared in Example 2 of the present invention under dark conditions;

[0033] Figure 11 Bi of the present invention 2-x Eu x WO6 / Nb2C MXene formation process;

[0034] Figure 12 UV-Vis-NIR DRS spectra of the photothermal materials of Comparative Example 3 and Examples 1-4 prepared in the present invention;

[0035] Figure 13 Bi prepared by the present invention 2-x Eu x WO6 / Nb2C MXene photothermal catalytic reduction of CO2 conversion rate diagram;

[0036] Figure 14 Bi prepared by the present invention 2-x Eu x WO6 / Nb2C MXene photothermal catalytic reduction of CO2 cycle diagram;

[0037] Figure 15 This is a graph showing the change in surface temperature of the photothermal material prepared in Example 2 of the present invention over time;

[0038] Figure 16 This is a graph of the CO2 photocatalytic conversion rate of the photothermal materials prepared in Comparative Example 3 and Example 2 of the present invention under a single wavelength light source. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0041] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise specified, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the present invention.

[0042] In the following embodiments, Bi 2-x Eu x WO6 was prepared according to the method of Comparative Example 3, except that the amount of Eu(NO3)3 was adjusted according to the value of x.

[0043] Comparative Example 1

[0044] Step 1: Add Nb2AlC powder to a HF solution with a concentration of >40% to form a mixed solution; wherein the concentration of Nb2AlC is 0.05 g / mL.

[0045] Step 2: Place the mixed solution in a water bath, heat to 55°C, and stir at a stirring rate of 600 r / min for 96 h.

[0046] Step 3: The mixed solution obtained in step 2 was centrifuged, and the obtained product was washed with deionized water until the pH of the supernatant reached about 6-7, and then vacuum dried at 60 °C for 12 h to obtain Nb2C MXene.

[0047] Comparative Example 2

[0048] Step 1: Dissolve 1 mmol of Bi(NO3)3 and 0.5 mmol of Na2WO4 in 30 ml of ethylene glycol, stir magnetically for 30 minutes to obtain a reaction precursor solution, and then transfer the reaction precursor solution to a 50 ml hydrothermal reactor for hydrothermal reaction at 160°C for 12 hours. After cooling to room temperature with the furnace, the resulting precipitate is washed three times with deionized water and anhydrous ethanol respectively, and dried at 70°C for 12 hours to obtain Bi2WO6.

[0049] Step 2: Add 1 mmol of Nb2C MXene powder to 20 ml of ethanol and ultrasonically disperse it for 30 minutes to obtain suspension A.

[0050] Step 3: Add 1 mmol of Bi2WO6 to 20 ml of ethanol and disperse by ultrasonic for 30 min to obtain suspension B.

[0051] Step 4: Suspension A and suspension B were irradiated with ultraviolet light for 30 minutes under magnetic stirring conditions, and then suspension A was slowly added to suspension B. The molar ratio of Bi2WO6 and Nb2C MXene was 1:1. The resulting mixed suspension was irradiated with ultraviolet light for 3 hours. The product was first washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70°C for 12 hours to obtain a Bi2WO6 / Nb2C MXene heterojunction photocatalyst.

[0052] Comparative Example 3

[0053] Step 1: Dissolve 1 mmol of Bi(NO3)3, 0.005 mmol of Eu(NO3)3 and 0.5 mmol of Na2WO4 in 30 ml of ethylene glycol and stir magnetically for 30 min to obtain a reaction precursor solution.

[0054] Step 2: Transfer the reaction precursor solution to a 50ml hydrothermal reactor and react at 160℃ for 12h. After cooling to room temperature, the resulting precipitate was washed with deionized water and anhydrous ethanol three times respectively, and dried at 70℃ for 12h to obtain Bi 1.995 Eu 0.005 WO6.

[0055] Example 1:

[0056] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0057] Step 2, 1mmol Bi 1.998 Eu 0.002 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0058] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.998 Eu 0.002 The molar ratio of WO6 and Nb2C MXene was 1:1, and the obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.998 Eu 0.002 WO6 / Nb2C MXene heterojunction photocatalyst.

[0059] Example 2:

[0060] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0061] Step 2, 1mmolBi 1.995 Eu 0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0062] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 1:1, and the obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005 WO6 / Nb2C MXene heterojunction photocatalyst.

[0063] Example 3:

[0064] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0065] Step 2, 1mmolBi 1.9925 Eu 0.0075 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0066] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.9925 Eu 0.0075The molar ratio of WO6 and Nb2C MXene was 1:1, and the obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.9925 Eu 0.0075 WO6 / Nb2C MXene heterojunction photocatalyst.

[0067] Example 4:

[0068] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0069] Step 2, 1mmolBi 1.990 Eu 0.010 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0070] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.990 Eu 0.010 The molar ratio of WO6 and Nb2C MXene was 1:1, and the obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.990 Eu 0.010 WO6 / Nb2C MXene heterojunction photocatalyst.

[0071] Example 5:

[0072] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0073] Step 2, 1mmol Bi 1.995 Eu 0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0074] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 1:1, and the obtained mixed suspension was irradiated with UV light for 4 h. The product was washed 3 times with deionized water, 3 times with anhydrous ethanol, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005WO6 / Nb2C MXene heterojunction photocatalyst.

[0075] Example 6:

[0076] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0077] Step 2, 1mmol Bi 1.995 Eu 0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0078] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 1:1, and the obtained mixed suspension was irradiated with UV light for 5 h. The product was washed 3 times with deionized water, 3 times with anhydrous ethanol, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005 WO6 / Nb2C MXene heterojunction photocatalyst.

[0079] Example 7:

[0080] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0081] Step 2, 1mmol Bi 1.995 Eu 0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0082] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 1:1, and the obtained mixed suspension was irradiated with UV light for 6 h. The product was washed 3 times with deionized water, 3 times with anhydrous ethanol, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005 WO6 / Nb2C MXene heterojunction photocatalyst.

[0083] Example 8:

[0084] In step 1, 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0085] Step 2, 1mmol Bi 1.995 Eu 0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0086] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 0.5:1. The obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005 WO6 / Nb2C MXene heterojunction photocatalyst.

[0087] Example 9:

[0088] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0089] Step 2, 1mmol Bi 1.995 Eu 0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0090] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 0.7:1. The obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005 WO6 / Nb2C MXene heterojunction photocatalyst.

[0091] Example 10:

[0092] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0093] Step 2, 1mmol Bi 1.995 Eu0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0094] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 0.8:1. The obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005 WO6 / Nb2C MXene heterojunction photocatalyst.

[0095] Example 11:

[0096] Step 1: 1 mmol of Nb2C MXene powder was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension A.

[0097] Step 2, 1mmol Bi 1.995 Eu 0.005 WO6 was added to 20 ml of ethanol and ultrasonically dispersed for 30 min to obtain suspension B.

[0098] Step 3: Suspension A and suspension B were irradiated with UV light for 30 min under magnetic stirring conditions, and then suspension A was slowly added to suspension B. 1.995 Eu 0.005 The molar ratio of WO6 and Nb2C MXene was 0.9:1. The obtained mixed suspension was irradiated with UV light for 3 h. The product was washed with deionized water 3 times, then washed with anhydrous ethanol 3 times, and dried at 70 ° C for 12 h to obtain Bi 1.995 Eu 0.005 WO6 / Nb2C MXene heterojunction photocatalyst.

[0099] Photothermal catalytic carbon dioxide reduction reaction test:

[0100] 60 mg of the material prepared by the present invention was added to a culture dish, water was added and stirred, and then the culture dish was placed in a vacuum oven and vacuum dried at 65 ° C. The culture dish was placed in a normal pressure photothermal catalytic device at 250 ° C, and an inert gas was continuously passed at a flow rate of 2 mL / min for 10 minutes. The inlet and outlet valves were closed, and 20 mL of carbon dioxide gas and 60 mL of hydrogen were filled into the normal pressure photothermal catalytic device. The pressure after filling was 0.12 MPa, and the reaction was carried out for 3 hours. 1 mL was sampled every hour for gas chromatography analysis to detect the carbon monoxide and methane content. The light source used was a 300W xenon lamp, and the auxiliary heating temperature was 250 ° C.

[0101] Figure 1 for Bi 2-x Eu x XRD pattern of WO6 / Nb2C MXene heterojunction. For the Nb2C MXene nanosheets in Comparative Example 1, a clear characteristic diffraction peak can be found at 9.8°, which is attributed to the layered stacking structure of Nb2C MXene. 1.995 Eu 0.005 The XRD spectrum of WO6 shows obvious diffraction peaks at 28.4°, 32.8°, 47.2°, 56.0° and 59.6°, corresponding to the (131), (200), (260), (331) and (262) crystal planes of Bi2WO6 (PDFNo.79-2381). In the XRD spectra of Example 1, Example 2, Example 3 and Example 4 compared with Comparative Example 2, it can be observed that the (131) and (260) crystal planes are broadened and shifted by 0.3° and 0.2° respectively, which proves that the Eu element is successfully doped into the Bi2WO6 lattice. In addition, the samples of Comparative Example 2, Example 1 to Example 4 have characteristic peaks of both Nb2C MXene and Bi2WO6, indicating the formation of Bi 2-x Eu x WO6 / Nb2CMXene photothermal material. In addition, it can be observed that the characteristic peak at 9.8° in Comparative Example 2 and Examples 1-4 weakens after compounding, which is presumably due to Bi2WO6 or Bi 2-x Eu x WO6 grows on the surface of Nb2C MXene, which weakens the diffraction peak.

[0102] Figure 2 The SEM image of Nb2C MXene in Comparative Example 1 shows a layered structure with uniform thickness and interlayer spacing. Figure 3 In the SEM image of Comparative Example 2Bi2WO6 / Nb2C MXene, it can be seen that flake Bi2WO6 grows on the surface of layered Nb2C MXene. Figure 4 In the SEM image of the heterojunction of Example 2, Bi 1.995 Eu 0.005 WO6 (Eu-Bi2WO6) grows on the surface of Nb2C MXene in the form of nanoflower balls. Figure 5 In the TEM of the heterojunction of Example 2, nano-flower balls are present between the Nb2C MXene layers. Figure 6 The interplanar spacing in the HRTEM image of the heterojunction of Example 2 is 0.32 nm, corresponding to the (014) plane of Bi2WO6, and the lattice fringes with an interplanar spacing of 0.28 nm correspond to Nb2C MXene, confirming the preparation of Bi 2-xEu x WO6 / Nb2C MXene heterojunction.

[0103] Figure 7 、 Figure 8 、 Figure 9 Comparative Example 1 Nb2C MXene, Comparative Example 2 Bi2WO6 / Nb2C MXene and Example 2 Bi 1.995 Eu 0.005 The electron concentration of WO6 is 31.9 μmol·g -1 , 26.8 μmol·g -1 and 42.8 μmol·g -1 . Explain the Bi of the present invention 2-x Eu x The electron concentration of the WO6 / Nb2C MXene heterojunction is higher than that of Nb2C MXene and Bi2WO6 / Nb2C MXene. The hole concentration stored in the heterojunction of Example 2 was estimated to be 173 μmol·g by EPR quantum spin number measurement under dark conditions. -1 ( Figure 10 ).

[0104] from Figure 11 It can be seen that UV light irradiation forms Bi 2-x Eu x During the WO6 / Nb2C MXene process, the electrons of Bi2WO6 tend to move from E fWO E flowing to Nb2C MXene crystals fNC ( Figure 11 (a) green and blue dotted lines), which makes electrons accumulate in the Nb2C MXene crystal. Such electron flow trend will make the E fBWO until the Fermi levels of the two reach equilibrium ( Figure 11 The red dashed line E in (b) f(E-BWO-NC) ), Bi 2-x Eu x The work function of WO6 / Nb2CMXene is 4.73eV ( Figure 11 (c)), at the interface where Nb2C MXene and Bi2WO6 contact, Bi2WO6 is positively charged and Nb2C MXene is negatively charged, forming a built-in electric field at the interface between Nb2C MXene and Bi2WO6, with the direction pointing from Bi2WO6 to the Nb2C MXene interface. At the same time, the conduction band and valence band of Nb2C MXene at the heterojunction interface are bent upward to -0.43 / 0.69eV respectively. Therefore, Bi2WO6 is formed by UV irradiation. 2-x Eu xWO6 / Nb2C MXene heterojunction.

[0105] Figure 12 These are UV-vis-NIR DRS diagrams of the catalysts of Comparative Example 1, Comparative Example 3, and Examples 1 to 4. All materials have light absorption in the ultraviolet-visible-near infrared spectrum range of 200 to 2200 nm. Figure 12 The illustration in FIG. 3 shows that comparative example 3 has absorption peaks at 762 nm and 795 nm due to the upconversion effect after Eu doping.

[0106] Figure 13 Figure 3 shows the photothermal reduction CO2 conversion rate of the catalysts in Comparative Example 3 and Examples 1-4. Under simulated sunlight for 3 hours, the catalyst in Comparative Example 3 enhanced light absorption, resulting in the presence of free electrons. After illumination, these electrons were excited to generate hot electrons that participated in the CO2 reduction reaction, resulting in a CH4 yield of 155.6 μmol·g. -1 ·h -1 After UV irradiation and recombination, the CH4 yields of the catalysts of Examples 1 to 4 reached 218.8 μmol·g -1 ·h -1 、304.7μmol·g -1 ·h -1 、183.7μmol·g -1 ·h -1 、157.7μmol·g -1 ·h -1 It shows that after introducing different proportions of Eu into Bi2WO6, 2-x Eu x The WO6 upconversion effect enhances light absorption, generates more electrons to participate in the CO2 reduction reaction, and makes Bi 2-x Eu x The degree of methanation of CO2 products reduced by WO6 / Nb2C MXene heterojunction is significantly enhanced, and the methane selectivity reaches 100%. For the Nb2C MXene in Comparative Example 1, the photothermal catalytic reduction product of CO2 is only CO, while the selectivity of the catalyst in Comparative Example 3 for the reduction of CO2 products to CH4 can reach 100%. Moreover, the selectivity of the catalysts in Examples 1-4 for the reduction of CO2 products to CH4 all reaches 100%, and the yield of CO2 product methane is significantly enhanced compared with Comparative Example 2. This shows that in Bi 2-x Eu x The built-in electric field of the WO6 / Nb2C MXene heterojunction, the LSPR effect of Nb2C MXene, and the upconversion effect of the rare earth element Eu jointly replenish the electrons required for the photothermal reduction of CO2 reaction, thereby improving the photothermal catalytic CO2 reduction activity and selectivity. Figure 14After 6 complete cycles of photocatalytic reduction of CO2, the activity of the catalyst in Example 2 was still 296.3 μmol·g -1 ·h -1 , which proves that the prepared Bi 2-x Eu x WO6 / Nb2C MXene photothermal material has good cycle stability.

[0107] Figure 15 The graph of the catalyst surface temperature of Example 2 changing with time when the internal temperature of the reactor is room temperature and 250°C. After 15 minutes of simulated sunlight irradiation, the catalyst surface temperature increases to 196°C and 329°C respectively compared with the ambient temperature, indicating that Bi 2-x Eu x WO6 / Nb2C MXene heterojunction has good photothermal conversion performance.

[0108] Figure 16 After irradiation with light of 740, 800, 940 and 1100 nm wavelengths, the photocatalytic reduction CO2 activity of Comparative Example 3 was 2.3 μmol·g -1 ·h -1 , 3.2 μmol·g -1 ·h -1 , 3.2 μmol·g -1 ·h -1 , 5.3 μmol·g -1 ·h -1 , the photocatalytic reduction CO2 activity of Example 2 was 5.2 μmol·g -1 ·h -1 , 6.1 μmol·g -1 ·h -1 , 7.3 μmol·g -1 ·h -1 , 1.2 μmol·g -1 ·h -1 The photocatalytic reduction of CO2 in Example 2 is most active after irradiation with light of 940nm wavelength. 2-x Eu x The upconversion effect of Eu in WO6 / Nb2C MXene is mainly to convert 940nm to 762nm and 795nm to enhance light absorption, which further proves that the upconversion effect produces more photogenerated electrons and promotes the catalytic conversion of CO2.

[0109] The above is only one embodiment of the present invention, not all or the only embodiment. Any equivalent transformation of the technical solution of the present invention made by ordinary technicians in this field after reading the specification of the present invention is covered by the claims of the present invention.

Claims

1. A Bi 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: The Bi 2-x Eu x The preparation method of WO6 / Nb2C MXene photothermal material includes the following steps: Step 1: dissolve Bi(NO3)3, Eu(NO3)3 and Na2WO4 in ethylene glycol and stir to obtain a reaction precursor solution; subject the reaction precursor solution to a hydrothermal reaction to obtain Bi 2-x Eu x WO6; Step 2: Add Nb2C MXene powder to ethanol and disperse it ultrasonically to obtain suspension A; 2-x Eu x WO6 was added to ethanol and ultrasonically dispersed to obtain suspension B; Step 3: Suspension A and suspension B are irradiated with ultraviolet light respectively, and then suspension A is slowly added to suspension B, and the resulting mixed suspension is irradiated with ultraviolet light. The product is washed and dried to obtain Bi 2-x Eu x WO6 / Nb2C MXene photothermal material.

2. Bi according to claim 1 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: In step 1, the molar ratio of Eu(NO3)3 to Bi(NO3)3 is (0.002-0.010):

1.

3. Bi according to claim 1 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: In step 1, the hydrothermal reaction temperature is 150-180° C. and the time is 9-12 h.

4. Bi according to claim 1 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: In step 2, Bi 2-x Eu x The molar ratio of WO6 and Nb2C MXene is (0.5-1):

1.

5. Bi according to claim 1 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: In step 2, the preparation method of Nb2C MXene powder is as follows: Nb2AlC precursor powder is added to HF solution, and then the resulting mixture solution is stirred and reacted in a water bath. After the reaction is completed, the resulting product is washed and dried to obtain Nb2C MXene.

6. Bi according to claim 1 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: In step 3, the suspension A and the suspension B are respectively irradiated with ultraviolet light for 30-60 minutes.

7. Bi according to claim 1 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: In step 3, the mixed suspension is irradiated with ultraviolet light for 3-6 hours.

8. Bi according to claim 1 2-x Eu x The application of WO6 / Nb2C MXene photothermal material in photothermal catalytic reduction of CO2 to produce methane is characterized by: The Bi 2-x Eu x Bi in WO6 / Nb2C MXene photothermal materials 2-x Eu x The morphology of WO6 is nano-flower-shaped, Bi 2-x Eu x WO6 is distributed on the surface of Nb2C MXene.

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