Plasma-ferroelectric WO3-x / K4Nb6O17 heterojunction as well as preparation method and application thereof

Abstract

The invention relates to the technical field of energy environment science and engineering, in particular to a plasma-ferroelectric WO3-x / K4Nb6O17 heterojunction and a preparation method and application thereof. According to the plasma-ferroelectric WO3-x / K4Nb6O17 heterojunction, a ferroelectric K4Nb6O17 nanosheet serves as a substrate, oxalic acid dihydrate and sodium borohydride serve as composite reducing agents, in-situ synthesis of WO3-x nanoparticles with oxygen vacancies and in-situ loading and growth of the WO3-x nanoparticles on the surface of the K4Nb6O17 nanosheet are achieved in the solvent heat treatment process, and the plasma-ferroelectric WO3-x / K4Nb6O17 heterojunction is obtained. Therefore, the plasma-ferroelectric WO3-x / K4Nb6O17 heterojunction is obtained. The WO3-x / K4Nb6O17 heterojunction can be used as a photocatalyst, and the coupling reaction efficiency of preparing CO through photocatalytic CO2 reduction and preparing hydrogenated benzoin through benzyl alcohol oxidation is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy environment science and engineering, and in particular to a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, a preparation method thereof, and an application thereof. Background Art

[0002] Photocatalytic technology can convert low-density solar energy into high-density chemical energy, which is crucial for the sustainable development of humanity. However, due to the severe recombination of photoexcited charges in a wide spatio-temporal range, the current efficiency of the photocatalytic process is insufficient to meet the commercialization requirements. Therefore, improving the charge separation efficiency has always been a key issue for realizing efficient solar energy conversion. Currently, a large number of studies expect to adjust the charge transfer pathway in the catalyst to regulate the separation efficiency of photogenerated carriers, such as doping heteroatoms, introducing vacancy defects, and constructing heterojunctions. Although these strategies can inhibit the surface recombination of charge carriers to a certain extent or promote the interfacial separation of electron-hole pairs, they cannot avoid the rapid bulk recombination of photoexcited charge carriers, which has also become the main obstacle to the development of current photocatalytic applications.

[0003] The key to accelerating the separation of bulk charges is to establish a polarization field along the direction of photogenerated charge migration. In other words, an internal electric field is introduced as a driving force to hinder charge recombination. The spontaneous polarization of ferroelectric materials, caused by the asymmetric displacement of positive and negative dipoles, makes them widely used in flexible electronics, sensors, and semiconductor devices. In addition, the spontaneous dipole moment inside ferroelectric semiconductors can generate a permanently polarized electric field, which is expected to be used as a direct driving force to achieve the spatial separation of photogenerated carriers from the catalyst body to the surface, thereby greatly improving the photocatalytic performance. Therefore, based on the above advantages, a large number of ferroelectric materials have been developed and applied to photocatalysis, including perovskite-type semiconductors such as BaTiO3, Bi3TiNbO9, KNbO3, and BiFeO3. However, the strength of the spontaneous polarization field in a single ferroelectric semiconductor is still not satisfactory. For example, the weak ferroelectric polarization field in the new two-dimensional layered K4Nb6O 17 The weak ferroelectric polarization field in ferroelectric semiconductors provides limited help in separating electrons and holes, making it not an ideal photocatalyst. Moreover, the existing methods for improving the ferroelectric polarization of ferroelectric materials are complex in operation and relatively costly, such as gradient doping or corona polarization. Obviously, developing a simple strategy to increase the polarization field strength of ferroelectric semiconductors and achieve higher photocatalytic performance remains a major challenge.

[0004] Meanwhile, in the context of the depletion of fossil resources and the deterioration of environmental problems, there is an urgent need to convert renewable energy into chemical fuels to meet current demands. Therefore, it is desired to integrate CO2 conversion with selective organic oxidation in a photocatalytic system to allow for the co-production of gaseous and liquid-phase value-added chemicals, which follows the scientific concept of sustainable development and circular economy. Benzyl alcohol is a renewable biomass derivative that can be selectively oxidized to produce high-value-added chemicals. However, to date, most reports in the field of photocatalysis have mainly focused on the oxidation of benzyl alcohol to benzaldehyde, and the production of higher-value-added C-C coupling chemicals remains a major challenge. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, its preparation method and application, and the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction can be used as a photocatalyst in the photocatalytic carbon dioxide reduction synergistic benzyl alcohol C-C coupling reaction to improve the coupling reaction efficiency of photocatalytic CO2 reduction to prepare CO and benzyl alcohol oxidation to prepare hydrobenzoin.

[0006] The present invention provides a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, which is characterized in that ferroelectric K4Nb6O 17 nanosheets are used as a substrate, and oxalic acid dihydrate and sodium borohydride are used as a composite reducing agent to achieve in-situ synthesis of WO 3-x nanoparticles with oxygen vacancies and in-situ loading and growth of WO 3-x nanoparticles on the surface of K4Nb6O 17 nanosheets during the solvothermal treatment process, thereby obtaining a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

[0007] The present invention also provides a preparation method of a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, comprising the following steps:

[0008] S1) Under stirring conditions, the solution B is added dropwise to the dispersion A, and after continuous stirring for a period of time, an ethanol solution of sodium borohydride is added dropwise to the stirred mixture, and then ultrasonic treatment is carried out in an ice-water bath;

[0009] The dispersion A is obtained by uniformly dispersing ferroelectric K4Nb6O 17 nanosheets in absolute ethanol;

[0010] Solution B is obtained by mixing WCl6, oxalic acid dihydrate and absolute ethanol;

[0011] S2) Subject the mixed solution obtained in step S1) to a solvothermal reaction to obtain a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

[0012] Preferably, in solution B, the molar ratio of WCl6 to oxalic acid dihydrate is 5-20:1586.

[0013] Preferably, the temperature of the solvothermal reaction is 80-120 °C and the time is 22-26 h.

[0014] Preferably, the preparation method of the ferroelectric K4Nb6O 17 nanosheets includes the following steps:

[0015] Disperse niobium pentoxide powder into a potassium hydroxide solution, and carry out a hydrothermal reaction at 200-240 °C to obtain ferroelectric K4Nb6O 17 nanosheets.

[0016] Preferably, the molar ratio of niobium pentoxide powder to potassium hydroxide is 0.5-1.5:9-11.

[0017] Preferably, after the solvothermal reaction, it further includes: cooling, collecting the precipitate, washing, and drying to obtain a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

[0018] The present invention also provides a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction as described above, or a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction prepared by the preparation method described above as an application of a photocatalyst.

[0019] Preferably, the photocatalyst is a photocatalyst for photocatalytic carbon dioxide reduction and synergistic benzene methanol C-C coupling reaction.

[0020] The present invention also provides a method for photocatalytic carbon dioxide reduction and synergistic benzene methanol C-C coupling reaction, including the following steps:

[0021] Under the irradiation of xenon lamp light, under normal temperature and pressure and carbon dioxide atmosphere conditions, under the action of a photocatalyst, photocatalytic reduction of CO2 synthesizes carbon monoxide, methane and hydrogen, and synergistically oxidizes benzene methanol to prepare hydrobenzoin and benzaldehyde;

[0022] The photocatalyst is the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction described above, or the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction prepared by the preparation method described above.

[0023] The present invention provides a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction. Using ferroelectric K4Nb6O 17 nanosheets as a substrate, oxalic acid dihydrate and sodium borohydride (NaBH4) as a composite reducing agent, realizing the in-situ synthesis of WO 3-x nanoparticles with oxygen vacancies during the solvothermal treatment process, and the in-situ loading and growth of WO 3-x nanoparticles on the surface of K4Nb6O 17 nanosheets, thereby obtaining the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction. The present invention proposes to use two-dimensional layered K4Nb6O 17 ferroelectric semiconductor as the reduction-end catalyst, and the plasma defect semiconductor WO 3-x with adjustable light response range as the oxidation-end catalyst. And solvothermal treatment is adopted to make the two establish close contact to form WO 3-x / K4Nb6O 17 heterojunction, and then realize the coupling of the LSPR effect and ferroelectric polarization, so as to enhance the intensity of the local electromagnetic field enhancement and ferroelectric polarization field, provide a driving force for the efficient spatial separation and directional extraction of photoexcited charges, and finally improve the performance of the photocatalytic CO2 reduction and the coupling reaction of benzyl alcohol C-C coupling, and improve the coupling reaction efficiency of photocatalytic CO2 reduction to prepare CO and benzyl alcohol oxidation to prepare hydrobenzoin. Description of the Drawings

[0024] Figure 1 XRD patterns of WO 3-x nanoparticles, ferroelectric K4Nb6O5] 17 nanosheets, and plasma-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunction photocatalysts;

[0025] Figure 2 Scanning electron microscope images of ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles, and plasma-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunction photocatalysts;

[0026] Figure 3 For ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmon-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunction photocatalyst transmission electron microscope images;

[0027] Figure 4 For ferroelectric K4Nb6O 17 Atomic force microscopy image of nanosheets and the height curve corresponding to the black dotted line marker;

[0028] Figure 5 For ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmon-ferroelectric WO 3-x / K4Nb6O 17 -3 heterojunction high-resolution transmission electron microscope image; WO 3-x / K4Nb6O 17 -3 heterojunction high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) image and corresponding energy-dispersive X-ray spectroscopy (EDS) mapping image;

[0029] Figure 6 For ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmon-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunction ultraviolet-visible-near-infrared diffuse reflectance spectra;

[0030] Figure 7 For ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmon-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunction surface-enhanced Raman spectroscopy test results with different probe molecules;

[0031] Figure 8 For ferroelectric K4Nb6O 17 Nanosheet plasmon-ferroelectric WO 3-x / K4Nb6O 17 -3 heterojunction piezoresponse force microscopy (PFM) test results;

[0032] Figure 9 For ferroelectric K4Nb6O 17 nanosheets, WO 3-xNanoparticles and plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunctions, curves of the yields of different gas-phase products versus time in the photocatalytic CO2 reduction coupled with the C-C coupling reaction of benzyl alcohol;

[0033] Figure 10 For ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunctions, curves of the yields of different liquid-phase products versus time in the photocatalytic CO2 reduction coupled with the C-C coupling reaction of benzyl alcohol;

[0034] Figure 11 For the plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -3 heterojunction photocatalytic CO2 reduction coupled with the C-C coupling reaction of benzyl alcohol, cyclic stability test curve. Detailed implementation manners

[0035] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0036] The present invention provides a plasmonic-ferroelectric WO 3-x / K4Nb6O 17 heterojunction. Using ferroelectric K4Nb6O 17 nanosheets as the substrate, oxalic acid dihydrate and sodium borohydride (NaBH4) as the composite reducing agent, in-situ synthesis of WO 3-x nanoparticles with oxygen vacancies is achieved during the solvothermal treatment process, and the in-situ loading and growth of WO 3-x nanoparticles on the surface of K4Nb6O 17 nanosheets, thereby obtaining the plasmonic-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

[0037] The plasmonic-ferroelectric WO 3-x / K4Nb6O 17 heterojunction provided by the present invention has a nanosheet-like structure, wherein the WO 3-x nanoparticles are uniformly distributed on the surface of K4Nb6O 17 nanosheets.

[0038] In some embodiments of the present invention, hydrothermal method at high temperature is used to prepare ferroelectric K4Nb6O 17 nanosheets. Specifically, the preparation method of the ferroelectric K4Nb6O 17 nanosheets comprises the following steps:

[0039] Disperse niobium pentoxide (Nb2O5) powder into potassium hydroxide (KOH) solution, and carry out hydrothermal reaction at 200 - 240 °C to obtain ferroelectric K4Nb6O 17 nanosheets.

[0040] The molar ratio of the niobium pentoxide powder to potassium hydroxide is 0.5 - 1.5:9 - 11, such as 1:10.

[0041] The concentration of the potassium hydroxide (KOH) solution is 0.8 - 1.2 mol / L, such as 1 mol / L.

[0042] The dispersion is carried out under stirring conditions, specifically magnetic stirring, the stirring speed is 1400 - 1800 rpm, such as 1600 rpm; the time is 0.5 - 1.5 h, such as 1 h.

[0043] The temperature of the hydrothermal reaction is 220 °C; the time is 16 - 20 h, such as 18 h. The hydrothermal reaction is carried out in a stainless steel autoclave.

[0044] After the hydrothermal reaction, it further includes: cooling, filtering and collecting the white solid, washing and then drying to obtain ferroelectric K4Nb6O 17 nanosheets.

[0045] The cooling is natural cooling to room temperature. The washing uses deionized water, specifically: washing several times with deionized water until the supernatant is neutral, specifically, until the pH value of the supernatant is 7. The drying is vacuum drying; the temperature is 50 - 70 °C, such as 60 °C; the time is 10 - 14 h, such as 12 h. After drying, it further includes: grinding evenly at room temperature. The grinding time is 30 - 40 min, such as 30 min.

[0046] The present invention also provides a preparation method of a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, comprising the following steps:

[0047] S1) Under stirring conditions, drop the solution B into the dispersion A, continue stirring for a period of time, then drop the ethanol solution of sodium borohydride into the stirred mixture, and then carry out ultrasonic treatment in an ice-water bath;

[0048] The dispersion A is composed of ferroelectric K4Nb6O 17obtained by uniformly dispersing nanosheets in absolute ethanol;

[0049] The solution B is obtained by mixing WCl6, oxalic acid dihydrate and absolute ethanol;

[0050] S2) Subject the mixed solution obtained in step S1) to a solvothermal reaction to obtain a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

[0051] Regarding step S1):

[0052] The dispersion A is obtained by uniformly dispersing ferroelectric K4Nb6O 17 nanosheets in absolute ethanol.

[0053] In some embodiments of the present invention, the uniform dispersion is carried out under ultrasonic conditions, and the temperature of the uniform dispersion is room temperature. The power of the ultrasonic wave is 380 - 420 W, such as 400 W. The present invention has no special limitation on the dosage ratio of the K4Nb6O 17 nanosheets to absolute ethanol, as long as it can satisfy the uniform dispersion of the K4Nb6O 17 nanosheets. Specifically, the dosage ratio of the ferroelectric K4Nb6O 17 nanosheets to absolute ethanol can be 200 mg: 30 mL.

[0054] The solution B is obtained by mixing WCl6, oxalic acid dihydrate and absolute ethanol.

[0055] In some embodiments of the present invention, the molar ratio of WCl6 to oxalic acid dihydrate is 5 - 20: 1586, such as 5: 1586. The volume ratio of the total mass of WCl6 and oxalic acid dihydrate to absolute ethanol is 2.02 - 2.08 g: 20 mL, such as 2.02 g: 20 mL, 2.04 g: 20 mL, 2.06 g: 20 mL, 2.08 g: 20 mL.

[0056] In the present invention, under stirring conditions, the solution B is added dropwise to the dispersion A, and after continuous stirring for a period of time, an ethanol solution of sodium borohydride is added dropwise to the stirred mixture, and then ultrasonic treatment is carried out in an ice-water bath. The ice-water bath is used to prevent the heating effect caused by ultrasonic action from driving the reaction of WCl6 with oxygen to generate tungsten oxychloride by-products. The power of the ultrasonic wave is 380 - 420 W, such as 400 W.

[0057] In some embodiments of the present invention, the stirring is magnetic stirring, the rotation speed of the stirring is 1400 - 1800 rpm, such as 1600 rpm. The dropping rate of solution B is 4 - 6 mL / min, such as 5 mL / min. The time for continuous stirring is 15 - 25 min, such as 20 min. The concentration of the sodium borohydride ethanol solution is 3 - 7 mg / mL, such as 5 mg / mL. The sodium borohydride ethanol solution is added dropwise. The volume ratio of the sodium borohydride ethanol solution to the mixed solution is 0.8 - 1.2:4 - 6, such as 1:5. The power of ultrasonic treatment in the ice-water bath is 350 - 450 W, such as 400 W, and the time is 30 - 60 min, such as 40 min.

[0058] Regarding step S2):

[0059] Perform a solvothermal reaction on the mixed solution obtained in step S1) to obtain a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

[0060] In some embodiments of the present invention, the temperature of the solvothermal reaction is 80 - 120 °C, such as 100 °C; the time is 22 - 26 h, such as 24 h. The solvothermal reaction is carried out in a stainless steel autoclave.

[0061] After the solvothermal reaction, it further includes: cooling, collecting the precipitate, washing, and then drying to obtain a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

[0062] The cooling is natural cooling to room temperature. The washing is carried out with anhydrous ethanol and deionized water respectively. The drying is vacuum drying; the temperature is 50 - 70 °C, such as 60 °C; the time is 10 - 14 h, such as 12 h. After drying, it further includes: grinding evenly at room temperature. The grinding time is 30 - 40 min, such as 30 min.

[0063] The present invention also provides an application of the above-mentioned plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, or the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction prepared by the above-mentioned preparation method as a photocatalyst. Specifically, it is used as a photocatalyst in the photocatalytic reduction of carbon dioxide (CO2) and the C-C coupling reaction of benzyl alcohol.

[0064] The present invention also provides a method for photocatalytic reduction of carbon dioxide and C-C coupling reaction of benzyl alcohol, which includes the following steps:

[0065] Under xenon lamp irradiation, under normal temperature and pressure and in a carbon dioxide atmosphere, with the assistance of a photocatalyst, photocatalytic reduction of CO2 is carried out to synthesize carbon monoxide, methane and hydrogen, and simultaneously, benzyl alcohol is oxidized to prepare hydrobenzoin and benzaldehyde;

[0066] The photocatalyst is the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction described above, or the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction prepared by the preparation method described above.

[0067] The carbon dioxide atmosphere is preferably a high-purity carbon dioxide atmosphere, and the purity of carbon dioxide is 99.999%.

[0068] The power of the xenon lamp irradiation is 300 W.

[0069] In the present invention, the preparation method of the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction photocatalyst is low-temperature solvothermal in-situ growth. The synthesis method, process conditions and operation process of the present invention are simple, the reaction conditions are mild and easy to control, and the repeatability is strong; the chemical reagents used are non-toxic, harmless and easy to obtain, with strong applicability, high industrial application value and easy to promote and utilize.

[0070] The plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction obtained in the present invention is formed by two-dimensional nanosheets supporting nanoparticles, has a uniform morphological structure, and the synergistic effect of its exhibited LSPR effect coupling ferroelectric polarization can greatly enhance the amplitude of the local electromagnetic field enhancement and the intensity of the ferroelectric polarization field, thereby accelerating the bulk separation and interfacial transfer of photo-generated charge carriers, and ultimately promoting the photocatalytic CO2 conversion and the benzyl alcohol C-C coupling reaction.

[0071] At room temperature and atmospheric pressure, the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction realizes efficient photocatalytic CO2 reduction coupling benzyl alcohol C-C coupling. Among them, the yields of CO and hydrobenzoin are up to 294.76 μmol g -1 h -1 and 311.81 μmol g -1 h -1 respectively; no additional cocatalyst and sacrificial agent need to be added during the photocatalytic reaction process, the system is simple, the conditions are mild, the repeatability is good, and it has good industrial application prospects.

[0072] The present invention has no special restrictions on the raw material sources used above, and they can be commercially available in general.

[0073] To further illustrate the present invention, a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, its preparation method and applications will be described in detail below with reference to embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0074] Example 1

[0075] 1) Preparation of ferroelectric K4Nb6O 17 nanosheets:

[0076] Weigh 0.8 g of niobium pentoxide (Nb2O5) powder and disperse it in 30 mL of 1 mol / L potassium hydroxide (KOH) solution under magnetic stirring at 1600 rpm (stirring time 1 h). Then transfer it to a 50 mL stainless steel autoclave with a polytetrafluoroethylene liner and carry out a hydrothermal reaction at 220 °C for 18 h. After the autoclave is naturally cooled to room temperature, filter and collect the white solid, and wash it several times with deionized water until the pH value of the supernatant is 7. Finally, dry the product under vacuum at 60 °C for 12 h, and grind the dried sample at room temperature for 30 min to make the particle size uniform. The obtained white sample is the ferroelectric K4Nb6O 17 nanosheets.

[0077] 2) Preparation of plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction:

[0078] Under room temperature and ultrasonic conditions (power 400 W), uniformly disperse 200 mg of the ferroelectric K4Nb6O 17 nanosheets in 30 mL of absolute ethanol to form dispersion A.

[0079] Weigh 0.0198 g (0.05 mmol) of anhydrous tungsten hexachloride (WCl6) and 2 g (15.86 mmol) of oxalic acid dihydrate, dissolve them in 20 mL of absolute ethanol, and stir to form a uniform yellow solution B;

[0080] Under the condition of magnetic stirring at 1600 rpm, solution B was slowly added dropwise (at a dropping rate of 5 mL / min) to dispersion A, and stirring was continued for 20 min to obtain a mixed solution; subsequently, 10 mL of an ethanol solution of NaBH4 (5 mg / mL) was added dropwise to the mixed solution, and the volume ratio of the ethanol solution of NaBH4 to the mixed solution was 1:5. The obtained mixed dispersion was ultrasonically treated (at a power of 400 W) in an ice-water bath for 40 min. Then, it was transferred to a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner and subjected to a solvothermal reaction at 100 °C for 24 h. After the autoclave was naturally cooled to room temperature, the precipitate was collected, washed with absolute ethanol and deionized water respectively, and dried under vacuum at 60 °C for 12 h. The dried sample was ground at room temperature for 30 min to make the particle size uniform, and finally the light blue target product, the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction photocatalyst, and named WO 3-x / K4Nb6O 17 -1.

[0081] Example 2

[0082] 1) Preparation of ferroelectric K4Nb6O 17 nanosheets:

[0083] Same as Example 1.

[0084] 2) Preparation of plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction:

[0085] The difference from Example 1 is that:

[0086] The preparation method of yellow solution B is:

[0087] Weigh 0.0397 g (0.10 mmol) of anhydrous tungsten hexachloride (WCl6) and 2 g (15.86 mmol) of oxalic acid dihydrate, dissolve them in 20 mL of absolute ethanol, and stir to form a uniform yellow solution B.

[0088] The remaining steps are the same as those in Example 1, and finally the light blue target product, the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction photocatalyst, and named WO 3-x / K4Nb6O 17 -2.

[0089] Example 3

[0090] 1) Preparation of ferroelectric K4Nb6O 17 nanosheets:

[0091] Same as Example 1.

[0092] 2) Plasma - ferroelectric WO 3-x / K4Nb6O 17 Preparation of the heterojunction:

[0093] The difference from Example 1 is:

[0094] The preparation method of yellow solution B is:

[0095] Weigh 0.0595 g (0.15 mmol) of anhydrous tungsten hexachloride (WCl6) and 2 g (15.86 mmol) of oxalic acid dihydrate, dissolve them in 20 mL of anhydrous ethanol, and stir to form a homogeneous yellow solution B.

[0096] All the remaining steps are the same as those in Example 1, and finally, the light blue target product, plasma - ferroelectric WO 3-x / K4Nb6O 17 heterojunction photocatalyst, is named WO 3-x / K4Nb6O 17 -3.

[0097] Example 4

[0098] 1) Preparation of ferroelectric K4Nb6O 17 nanosheets:

[0099] Same as Example 1.

[0100] 2) Plasma - ferroelectric WO 3-x / K4Nb6O 17 Preparation of the heterojunction:

[0101] The difference from Example 1 is:

[0102] The preparation method of yellow solution B is:

[0103] Weigh 0.0793 g (0.20 mmol) of anhydrous tungsten hexachloride (WCl6) and 2 g (15.86 mmol) of oxalic acid dihydrate, dissolve them in 20 mL of anhydrous ethanol, and stir to form a homogeneous yellow solution B.

[0104] All the remaining steps are the same as those in Example 1, and finally, the light blue target product, plasma - ferroelectric WO 3-x / K4Nb6O 17 heterojunction photocatalyst, is named WO 3-x / K4Nb6O 17 -4.

[0105] Comparative Example 1

[0106] The photocatalyst is WO3-x Nanoparticles, WO 3-x The preparation method of nanoparticles is:

[0107] Weigh 0.5mmol of anhydrous tungsten hexachloride (WCl6) and 2g of dihydrated oxalic acid and dissolve them in 30mL of anhydrous ethanol. After stirring for 30min, a uniform yellow solution is obtained. Subsequently, 10mL of an ethanol solution of sodium borohydride (NaBH4) (5mg / mL) is added dropwise to the above solution under magnetic stirring at 1400rpm. The resulting mixed solution is magnetically stirred for 30min and then transferred to a 50mL stainless steel autoclave lined with polytetrafluoroethylene and subjected to solvent thermal reaction at 100℃ for 24h. After the reactor is cooled to room temperature naturally, the dark blue precipitate is collected, washed with anhydrous ethanol and deionized water respectively, and dried under vacuum at 60℃ for 12h to obtain a dark blue sample, which is WO 3-x Nanoparticles.

[0108] Comparative Example 2

[0109] The photocatalyst is ferroelectric K4Nb6O 17 Nanosheets, ferroelectric K4Nb6O 17 Preparation of nanosheets:

[0110] Same as Example 1.

[0111] Figure 1 For WO 3-x Nanoparticles, ferroelectric K4Nb6O 17 Nanosheets, Plasmonic-Ferroelectric WO 3-x / K4Nb6O 17 -1~4 heterojunction photocatalyst XRD pattern. Figure 1 It can be seen that the ferroelectric K4Nb6O prepared in the embodiment of the present invention 17 The phase of the nanosheet corresponds to orthorhombic K4Nb6O 17 (Standard card is JCPDS No.76-0977), the WO 3-x The phase of the nanoparticles corresponds to tetragonal WO 3-x (The standard card is JCPDS No.53-0434). 3-x / K4Nb6O 17 The characteristic diffraction peaks of the heterojunction are also consistent with those of orthorhombic K4Nb6O 17 and SifangWO 3-x This shows that the present invention can successfully prepare phase-pure WO 3-x / K4Nb6O 17 Heterojunction.

[0112] Figure 2 Ferroelectric K4Nb6O17 Nanosheets, WO 3-x Nanoparticles and Plasmon-Ferroelectric WO 3-x / K4Nb6O 17 -1~4 scanning electron microscope images of heterojunction photocatalysts. Figure 2 Figure a is ferroelectric K4Nb6O 17 SEM images of nanosheets. Figure 2 Figure b in the figure is WO 3-x SEM images of nanoparticles. Figure 2 Figure c is a plasma-ferroelectric WO 3-x / K4Nb6O 17 -1 SEM image of heterojunction, Figure 2 Figure d in the figure is plasma-ferroelectric WO 3-x / K4Nb6O 17 -2 SEM image of heterojunction, Figure 2 Figure e in the figure is plasma-ferroelectric WO 3-x / K4Nb6O 17 -3 SEM image of heterojunction, Figure 2 Figure f is a plasma-ferroelectric WO 3-x / K4Nb6O 17 -4 SEM image of heterojunction.

[0113] Figure 3 Ferroelectric K4Nb6O 17 Nanosheets, WO 3-x Nanoparticles and Plasmon-Ferroelectric WO 3-x / K4Nb6O 17 -1~4 Transmission electron microscope images of heterojunction photocatalysts. Figure 3 Figure a is ferroelectric K4Nb6O 17 TEM image of nanosheets. Figure 3 Figure b in the figure is WO 3-x TEM images of nanoparticles. Figure 3 Figure c is a plasma-ferroelectric WO 3-x / K4Nb6O 17 -1TEM image of heterojunction, Figure 3 Figure d in the figure is plasma-ferroelectric WO 3-x / K4Nb6O 17 -2TEM image of heterojunction, Figure 3 Figure e in the figure is plasma-ferroelectric WO 3-x / K4Nb6O 17 -3 TEM image of heterojunction, Figure 3 Figure f is a plasma-ferroelectric WO 3-x / K4Nb6O 17TEM image of the -4 heterojunction.

[0114] Figure 4 is ferroelectric K4Nb6O 17 Atomic force microscopy image of the nanosheets and the height curve marked by the corresponding black dotted line. Among them, Figure 4 Figure a in 17 is the atomic force microscopy image of the ferroelectric K4Nb6O Figure 4 Figure b in

[0115] Figure 5 is ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmon-ferroelectric WO 3-x / K4Nb6O 17 -3 heterojunction high-resolution transmission electron microscopy image; WO 3-x / K4Nb6O 17 -3 heterojunction high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and corresponding energy-dispersive X-ray spectroscopy (EDS) mapping image. Among them, Figure 5 Figure a in 17 is the high-resolution transmission electron microscopy image of the ferroelectric K4Nb6O Figure 5 Figure b in 3-x is the high-resolution transmission electron microscopy image of the WO Figure 5 Figure c in 3-x / K4Nb6O 17 -3 heterojunction high-resolution transmission electron microscopy image, Figure 5 Figure d in 3-x / K4Nb6O 17 -3 heterojunction high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and corresponding energy-dispersive X-ray spectroscopy (EDS) mapping image.

[0116] From Figures 1 - 5 it can be seen that the morphology of the ferroelectric K4Nb6O 17 nanosheets prepared in this invention is mainly two-dimensional ultra-thin nanosheets, with the lateral size extending up to several micrometers and the average thickness of about 4.7 nm. And the said WO 3-x nanoparticles are irregular nanoparticle shapes, with sizes all less than 100 nm. WO 3-x / K4Nb6O 17 -3 heterojunction as a whole still presents a nanosheet structure, and at the same time, the clearly visible WO 3-x nanoparticles are evenly distributed on the surface of the K4Nb6O 17 nanosheets, and the two-component morphology is compared with that of the single K4Nb6O17 and WO 3-x No obvious change occurred.

[0117] Figure 6 is ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunction UV-visible-near-infrared diffuse reflectance spectra. From Figure 6 it can be seen that WO 3-x / K4Nb6O 17 -1 to 4 heterojunctions have a full spectral range and stronger light response and absorption compared to the single-component K4Nb6O 17 This benefits from the LSPR effect of WO 3-x .

[0118] Figure 7 is ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -1 to 4 heterojunction surface-enhanced Raman spectroscopy test results for different probe molecules. Among them, Figure 7 Figure a in -5 is the Raman spectrum of 10 Figure 7 Figure b in -5 is the Raman spectrum of 10

[0119] Figure 8 is ferroelectric K4Nb6O 17 nanosheet plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -3 heterojunction piezoresponse force microscopy (PFM) test results. Among them, Figure 8 Figure a in 17 is the PFM topography image of K4Nb6O Figure 8 Figure b in 17 is the amplitude of K4Nb6O Figure 8 Figure c in 17 is the phase mapping image of K4Nb6O Figure 8 Figure d in 17 is the butterfly amplitude loop and phase curve of K4Nb6O Figure 8 Figure e in 3-x is the PFM topography image of WO 17 / K4Nb6O Figure 8 Figure f in 3-x / K4Nb6O 17 -3 heterojunction amplitude, Figure 8 Figure g in the figure is WO 3-x / K4Nb6O 17 -3 Phase mapping image of heterojunction, Figure 8 Figure h in the figure is WO 3-x / K4Nb6O 17 Butterfly-shaped amplitude loop and phase curve of the -3 heterojunction.

[0120] from Figures 7 - 8 It can be seen that the surface enhanced Raman spectroscopy and piezoresponse force microscopy test results confirm that in the heterojunction prepared by the present invention, WO 3-x LSPR effect and K4Nb6O 17 The ferroelectric polarizations are coupled and reinforced with each other, which not only promotes the surge of the local electromagnetic field but also greatly enhances the intensity of the ferroelectric polarization field, which is expected to accelerate the bulk and surface separation of photogenerated charge carriers and thus promote the photocatalytic reaction.

[0121] Application Example 1

[0122] Weigh 10 mg of ferroelectric K4Nb6O 17 Nanosheets, WO 3-x Nanoparticles and Plasmon-Ferroelectric WO 3-x / K4Nb6O 17 Heterojunction photocatalyst (WO 3-x / K4Nb6O 17 -1, WO 3-x / K4Nb6O 17 -2, WO 3-x / K4Nb6O 17 -3.WO 3-x / K4Nb6O 17-4) was added to a 50 mL sealed Pyrex reaction flask containing a mixed solution of 10 mL of acetonitrile and 50 μL of benzyl alcohol, and ultrasonic treatment was carried out for 30 min to disperse it evenly. The reactor was sealed and evacuated to completely remove the air in the reaction vessel. Subsequently, under the conditions of avoiding light and continuous magnetic stirring (stirring rate 800 rpm), the mixed liquid was purged with high-purity CO2 gas (99.999%) for 30 min to achieve the adsorption equilibrium of the catalyst. A 300 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) was used as the light source for the photocatalytic reaction. The reaction system was continuously stirred (stirring rate 800 rpm) to ensure uniform irradiation, and the temperature of the reaction system was maintained at 25 °C through a circulating air blowing system. Every 1 h of reaction, 500 μL of gas was taken out from the system, and the types and yields of the gases generated during the reaction were detected by gas chromatography equipped with a thermal conductivity detector. At the same time, 100 μL of liquid was taken out, and after filtering the solid, the liquid-phase organic products and their yields in the solution were analyzed by gas chromatography equipped with a flame ionization detector. The results are as Figure 9 and 10 shown.

[0123] Figure 9 are the photocatalytic CO2 reduction and synergistic benzyl alcohol C-C coupling reactions of ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -1~4 heterojunctions, showing the curves of the yields of different gas-phase products changing with time. Among them, Figure 9 Figure a in it is the curve of the yield of gas-phase product CO changing with time, Figure 9 Figure b in it is the curve of the yield of gas-phase product CH4 changing with time, Figure 9 Figure c in it is the curve of the yield of gas-phase product H2 changing with time; Figure 9 Figure d in it is the average yield of gas-phase products.

[0124] Figure 10 are the photocatalytic CO2 reduction and synergistic benzyl alcohol C-C coupling reactions of ferroelectric K4Nb6O 17 nanosheets, WO 3-x nanoparticles and plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -1~4 heterojunctions, showing the curves of the yields of different liquid-phase products changing with time. Among them, Figure 10 Figure a in it is the curve of the yield of liquid-phase product HB changing with time, Figure 10 Figure b in it is the curve of the yield of liquid-phase product BAD changing with time; Figure 10 Figure c in it is the average yield of liquid-phase products.

[0125] from Figures 9 - 10 It can be seen that for ferroelectric K4Nb6O 17 Nanosheets. The gas phase products and their corresponding production rates measured in this application example are: CO: 29.85 μmol g -1 h -1 、CH4:12.88μmol g -1 h -1 、H2:44.02μmol g -1 h -1 In addition, the liquid products and their corresponding yields are: CC coupling product - hydrogenated benzoin (HB): 0 μmol g -1 h -1 ; Byproduct benzaldehyde (BAD): 128.62 μmol g -1 h -1 .

[0126] For WO 3-x Nanoparticles. The gas phase products and their corresponding generation rates measured in this application example are: CO: 47.02 μmol g -1 h -1 、CH4:5.69μmol g -1 h -1 、H2:0μmol g -1 h -1 In addition, the liquid products and their corresponding yields are: CC coupling product - hydrogenated benzoin (HB): 0 μmol g -1 h -1 ; Byproduct benzaldehyde (BAD): 69.34 μmol g -1 h -1 .

[0127] For plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -1 heterojunction, the gas phase products and corresponding generation rates measured in this application example are: CO: 107.13 μmol g -1 h -1 、CH4:4.66μmol g -1 h -1 、H2:9.19μmol g -1 h -1 In addition, the liquid products and their corresponding yields are: CC coupling product - hydrogenated benzoin (HB): 118.02 μmol g -1 h -1 ; Byproduct benzaldehyde (BAD): 16.65 μmol g -1 h -1 .

[0128] For plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -2 heterojunction, the gas phase products and corresponding generation rates measured in this application example are: CO: 166.29 μmol g -1 h -1 、CH4:6.82μmol g -1 h -1 、H2:18.12μmol g -1 h -1 In addition, the liquid phase products and their corresponding yields are: CC coupling product - hydrogenated benzoin (HB): 180.17 μmol g -1 h -1 ; Byproduct benzaldehyde (BAD): 25.08 μmol g -1 h -1 .

[0129] For plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -3 heterojunction, the gas phase products and corresponding generation rates measured in this application example are: CO: 294.76 μmol g -1 h -1 、CH4:8.48μmol g -1 h -1 、H2:33.39μmol g -1 h -1 In addition, the liquid products and their corresponding yields are: CC coupling product - hydrogenated benzoin (HB): 311.81 μmol g -1 h -1 ; Byproduct benzaldehyde (BAD): 44.43 μmol g -1 h -1 .

[0130] For plasmonic-ferroelectric WO 3-x / K4Nb6O 17 -4 heterojunction, the gas phase products and corresponding generation rates measured in this application example are: CO: 215.08 μmol g -1 h -1 、CH4:7.05μmol g -1 h -1 、H2:24.38μmol g -1 h -1 In addition, the liquid products and their corresponding yields are: CC coupling product - hydrogenated benzoin (HB): 244.66 μmol g -1 h -1; By-product benzaldehyde (BAD): 35.01 μmol g -1 h -1 .

[0131] Application Example 2

[0132] Weigh 10 mg of plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction photocatalyst (WO 3-x / K4Nb6O 17 -3), and add it to a 50 mL sealed Pyrex reaction flask containing a mixed solution of 10 mL of acetonitrile and 50 μL of benzyl alcohol. Sonicate for 30 min to disperse it evenly. Seal the reactor and evacuate to completely remove the air in the reaction vessel. Subsequently, under the conditions of avoiding light and continuous magnetic stirring (stirring rate 800 rpm), purge the mixed liquid with high-purity CO2 gas (99.999%) for 30 min to make the catalyst reach adsorption equilibrium. Use a 300 W xenon lamp (CEL-HXF300, Beijing Zhongjiao Jinyuan Co., Ltd.) as the light source for the photocatalytic reaction. Continuously stir the reaction system (stirring rate 800 rpm) to ensure uniform irradiation, and keep the temperature of the reaction system at 25 °C through a circulating air blowing system. Every 1 h of reaction, take out 500 μL of gas from the system, and detect the types and yields of the gases generated during the reaction by gas chromatography equipped with a thermal conductivity detector. At the same time, take out 100 μL of liquid, filter the solid, and analyze the liquid-phase organic products and their yields in the solution by gas chromatography equipped with a flame ionization detector. After 3 h of reaction, centrifuge and precipitate to recover the solid catalyst in the system, wash it with absolute ethanol and deionized water, and then place it in a vacuum drying oven at 50 °C for 12 h. The dried sample is subjected to a new round of photocatalytic test according to the above test conditions.

[0133] Repeat the above operation for 5 cycles to verify the stability of the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction photocatalyst. As Figure 11 shown. Figure 11 This is the cyclic stability test curve of the plasma-ferroelectric WO 3-x / K4Nb6O 17 -3 heterojunction photocatalytic CO2 reduction and synergistic benzyl alcohol C-C coupling reaction in the examples of the present invention. Among them, Figure 11 Figure a in it is the cyclic stability test curve of the gas-phase product, Figure 11 Figure b in it is the cyclic stability test curve of the liquid-phase product. As can be seen from Figure 11 , the plasma-ferroelectric WO 3-x / K4Nb6O 17The heterojunction photocatalytic CO2 reduction synergistic with the CC coupling activity of benzyl alcohol has good reproducibility.

[0134] The above embodiments are intended only to facilitate understanding of the methods and core concepts of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A plasma - ferroelectric WO 3-x / K4Nb6O 17 heterojunction, characterized in that, Using ferroelectric K4Nb6O 17 nanosheets as the substrate, oxalic acid dihydrate and sodium borohydride as the composite reducing agent, realizing the in-situ synthesis of WO 3-x nanoparticles with oxygen vacancies during the solvothermal treatment process, and the in-situ loading and growth of WO 3-x nanoparticles on the surface of K4Nb6O 17 nanosheets, thereby obtaining the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

2. A method for preparing a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, comprising the following steps: S1) Under stirring conditions, add the solution B dropwise to the dispersion A. After continuing to stir for a period of time, add an ethanol solution of sodium borohydride dropwise to the stirred mixture, and then perform ultrasonic treatment in an ice-water bath; The dispersion liquid A is obtained by uniformly dispersing ferroelectric K4Nb6O 17 nanosheets in absolute ethanol; The solution B is obtained by mixing WCl6, oxalic acid dihydrate and absolute ethanol; S2) Perform a solvothermal reaction on the mixed solution obtained in step S1) to obtain a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

3. The preparation method according to claim 2, wherein In the solution B, the molar ratio of WCl6 to oxalic acid dihydrate is 5-20:1586.

4. The preparation method according to claim 2, characterized in that, The temperature of the solvothermal reaction is 80-120 °C, and the time is 22-26 h.

5. The preparation method according to claim 2, characterized in that, The ferroelectric K4Nb6O 17 The preparation method of the nanosheets comprises the following steps: Disperse niobium pentoxide powder into a potassium hydroxide solution and carry out a hydrothermal reaction at 200-240 °C to obtain ferroelectric K4Nb6O 17 nanosheets.

6. The preparation method according to claim 5, wherein The molar ratio of the niobium pentoxide powder to potassium hydroxide is 0.5-1.5:9-11.

7. The preparation method according to claim 2, characterized in that, After the solvothermal reaction, it further includes: cooling, collecting the precipitate, washing, and then drying to obtain a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction.

8. Use of a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction, or a plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction prepared by the preparation method according to any one of claims 2 to 7 as a photocatalyst.

9. The application according to claim 8, characterized in that, The photocatalyst is a photocatalyst for photocatalytic carbon dioxide reduction and synergistic benzene methanol C-C coupling reaction.

10. A method for photocatalytic carbon dioxide reduction and synergistic benzene methanol C-C coupling reaction, comprising the following steps: Under the irradiation of xenon lamp light, under normal temperature and pressure and carbon dioxide atmosphere conditions, under the action of a photocatalyst, photocatalytic reduction of CO2 synthesizes carbon monoxide, methane and hydrogen, and synergistically oxidizes benzene methanol to prepare hydrobenzoin and benzaldehyde; The photocatalyst is the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction described in claim 1, or the plasma-ferroelectric WO 3-x / K4Nb6O 17 heterojunction prepared by the preparation method described in any one of claims 2 to 7.

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