An S-type WO3 / FeWO4 heterojunction photocatalyst, its synthesis method and application method

Abstract

The present invention relates to the field of photocatalysis technology, and discloses an S-type WO3 / FeWO4 heterojunction photocatalyst, a synthesis method thereof and an application method; FeWO4 nanoneedles are loaded on the surface of WO3 nanorods to form an S-type heterojunction with an interlaced energy band structure, and its built-in electric field and 1D / 1D structure synergistically promote the separation of photo-generated carriers; the synthesis method is as follows: using ammonium metatungstate as a tungsten source, WO3 nanomaterials are prepared by a hydrothermal method; WO3 is ultrasonically dispersed in an ammonium ferrous sulfate solution to form a suspension system, and a sodium tungstate solution is dropped into the above suspension under continuous stirring, and an S-type WO3 / FeWO4 heterojunction photocatalyst with strong interfacial coupling effect is obtained through secondary hydrothermal crystallization; the S-type WO3 / FeWO4 heterojunction photocatalyst prepared by the present invention has excellent hydrogen production activity and good stability in photocatalytic water splitting, and has good application prospects in the field of photocatalytic water splitting for hydrogen production.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysis, and particularly to an S-type WO3 / FeWO4 heterojunction photocatalyst, a synthesis method thereof, and an application method thereof. Background Art

[0002] Photocatalytic water splitting for hydrogen production is a technology that converts solar energy into hydrogen energy, which is of great significance for solving energy crises and environmental problems. The core of this technology lies in the development of highly efficient and stable photocatalysts to achieve efficient conversion of solar energy into chemical energy. As a visible-light-responsive n-type semiconductor material, tungsten trioxide (WO3) has been widely used in the field of photocatalysis due to its suitable optical bandgap, relatively high valence band position, and good chemical stability. However, single WO3 has problems such as a high recombination rate of photo-generated carriers and slow kinetics of water oxidation reaction, resulting in a low photocatalytic water splitting hydrogen production efficiency.

[0003] In the prior art, strategies such as constructing heterojunctions (such as WO3 / g-C3N4, WO3 / CdS) are mostly adopted to improve the carrier separation efficiency of WO3. However, insufficient energy band matching at the interface of traditional heterojunctions will lead to disordered charge transport paths. Especially in traditional type-II heterojunction systems, although the spatial separation of photo-generated carriers is achieved, the redox potential is inevitably reduced, resulting in a decrease in the driving force of the photocatalytic system. In addition, the heterojunction interface will have interface defects due to lattice mismatch, and these defects will become centers of charge recombination, reducing the charge transport efficiency.

[0004] Recent studies have found that S-type (Step-scheme) heterojunctions can achieve the directional migration of photo-generated carriers through the synergistic effect of built-in electric fields and energy band bending at the interface, while maintaining strong redox ability and improving charge separation efficiency. Therefore, developing S-type heterojunction photocatalysts with precise energy band matching and stable interface structures has become an effective way to improve the photocatalytic water splitting hydrogen production efficiency. Summary of the Invention

[0005] In order to solve the above problems, the purpose of the present invention is to provide an S-type WO3 / FeWO4 heterojunction photocatalyst, which can improve the photocatalytic water splitting hydrogen production performance.

[0006] The S-type WO3 / FeWO4 heterojunction photocatalyst provided by the present invention has a 1D / 1D structure, that is, a nanorod / nanoneedle structure; the FeWO4 nanoneedles are loaded on the surface of WO3 nanorods to form an S-type heterojunction with an interleaved energy band structure, which can reduce the defect state recombination centers.

[0007] The WO3 / FeWO4 heterojunction photocatalyst provided by the present invention can promote the separation of photo-generated electron-hole pairs, enhance the utilization rate of visible light, and exhibit excellent hydrogen production activity in the photocatalytic water splitting system.

[0008] Synthesis method of an S-type WO3 / FeWO4 heterojunction photocatalyst:

[0009] Step 1: Dissolve ammonium metatungstate hydrate ((NH4)6H2W 12 O 40 ·xH2O) in deionized water, and then dropwise add concentrated hydrochloric acid (containing 36 - 38% HCl) under magnetic stirring to obtain solution A; subsequently, add hydrogen peroxide solution (containing 30% H2O2) to solution A, stir magnetically for 1 h to obtain a precursor solution, perform hydrothermal reaction on the precursor solution, after the reaction ends, centrifuge, wash, dry, and finally anneal in a muffle furnace with an annealing atmosphere of air to obtain WO3 nanomaterials;

[0010] Step 2: Dissolve sodium tungstate and ammonium ferrous sulfate in water respectively to obtain aqueous solutions, add the WO3 obtained in Step 1 above to the ammonium ferrous sulfate solution, and obtain a uniformly dispersed suspension under ultrasonic action; then dropwise add the sodium tungstate solution into the above suspension under continuous stirring, stir and then perform hydrothermal reaction, after the reaction ends, centrifuge, wash, dry to obtain the WO3 / FeWO4 heterojunction photocatalyst material.

[0011] Among them, in Step 1, the amount of ammonium metatungstate hydrate is 1.0 g, and the added deionized water is 95 mL;

[0012] Among them, in Step 1, the volume of the added HCl solution is 2 - 3 mL, and the volume of the added H2O2 solution is 2 - 3 mL.

[0013] Among them, in Step 1, the hydrothermal reaction temperature is 160 - 180 °C, and the hydrothermal time is 4 - 5 h.

[0014] Among them, in Step 1, the annealing temperature is 500 - 550 °C, the heating rate is 5 °C / min, and the annealing time is 1 - 2 h.

[0015] Among them, in Step 2, the concentration of sodium tungstate is 0.05 - 0.08 mol / L, the concentration of ammonium ferrous sulfate is 0.05 - 0.08 mol / L, and the concentrations of sodium tungstate and ammonium ferrous sulfate are equal.

[0016] Among them, in Step 2, the added amount of WO3 is 0.25 - 0.5 g.

[0017] Among them, in Step 2, the hydrothermal reaction temperature is 180 - 200 °C, and the hydrothermal time is 12 - 16 h.

[0018] The present invention also provides an application method of the above WO3 / FeWO4 heterojunction photocatalyst in photocatalytic water splitting for hydrogen production:

[0019] Under magnetic stirring, this WO3 / FeWO4 heterojunction photocatalyst was dispersed in a mixed solution of deionized water and 15% methanol, added to a quartz reaction cell, argon was introduced, and the reaction was carried out under irradiation of a 300 W xenon lamp. The mass-volume ratio of the photocatalyst to the mixed solution was 50 mg:100 mL.

[0020] In this application method, methanol, as a hole sacrificial agent, preferentially reacts with photo-generated holes, effectively inhibiting the recombination of electron-hole pairs and enhancing the reduction ability of photo-generated electrons. The construction of an argon environment can exclude the competitive consumption of photo-generated electrons by dissolved oxygen, avoid the generation of by-products such as superoxide radicals, and ensure the directional participation of electrons in the proton reduction to produce hydrogen process.

[0021] By simulating the solar spectrum with a xenon lamp, the practical application potential of the catalyst in a wide spectral range was verified, while magnetic stirring enhanced the mass transfer efficiency at the solid-liquid interface, promoted the diffusion of water molecules to the catalyst surface and the desorption of hydrogen.

[0022] In this invention, an S-type WO3 / FeWO4 1D / 1D heterojunction photocatalyst with strong interfacial coupling was successfully constructed by a stepwise hydrothermal method using ammonium metatungstate as the tungsten source and combining the secondary hydrothermal crystallization of ammonium ferrous sulfate and sodium tungstate.

[0023] The hydrogen production mechanism of the S-type WO3 / FeWO4 heterojunction photocatalyst in this invention is as follows: under light excitation, an internal electric field is formed between WO3 and FeWO4 due to the Fermi level difference, inducing band bending at the interface. Driven by the interfacial electric field, the conduction band electrons of WO3 recombine with the valence band holes of FeWO4, while the conduction band electrons of FeWO4 (-0.45 eV vs. NHE) migrate to the surface under the action of the band bending gradient and directly participate in the H + reduction to produce H2, and the valence band holes of WO3 are quickly captured by methanol molecules, effectively inhibiting charge recombination.

[0024] The one-dimensional nanowire heterojunction forms an efficient charge transport channel through interfacial chemical bonds, accelerating the carrier transport. The exposed active sites on the surface of WO3 reduce the adsorption energy barrier of H2O molecules and promote proton supply.

[0025] This heterojunction forms a stepped energy band structure through the precise combination of nanoneedle-like FeWO4 and nanorod-like WO3. The synergistic effect of the interfacial electric field and band bending promotes the directional migration of photo-generated carriers, effectively inhibiting recombination and enhancing the kinetics of redox reactions.

[0026] Compared with traditional type II heterojunctions, the S-type structure significantly enhances the charge separation efficiency while maintaining a high redox potential. The prepared WO3 / FeWO4 heterojunction exhibits excellent hydrogen production activity and cycle stability in the photocatalytic water splitting system. Its preparation process is simple and controllable, without the need for noble metal co-catalysts, and has important application value in the field of solar energy-hydrogen energy conversion.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] By constructing an S-type WO3 / FeWO4 heterojunction and utilizing the precise energy band matching characteristics between WO3 and FeWO4, combined with the strong built-in electric field formed by interfacial chemical bonding, the directional migration of photo-generated carriers is achieved. Compared with the disordered charge transport paths caused by energy level misalignment in traditional type-II heterojunctions, the stepped energy band structure of the present invention not only drives the efficient separation of electrons and holes through the built-in electric field but also retains the strong reduction characteristics of FeWO4 electrons, fundamentally solving the contradiction problem of sacrificing redox potential due to the spatial separation of carriers in traditional heterojunctions.

[0029] The preparation method proposed by the present invention successfully constructs an S-type WO3 / FeWO4 heterojunction photocatalyst with strong interfacial coupling through a hydrothermal method combined with an annealing process and by using the controllable reaction of ammonium metatungstate and ammonium ferrous sulfate. This method precisely regulates the morphology and interfacial characteristics of the heterojunction through two hydrothermal crystallizations, without the need for noble metal co-catalysts. The prepared material has a tightly bonded interface, a stable structure, and good repeatability, providing a new idea for the rational design of efficient photocatalysts.

[0030] The present invention uses low-cost tungsten and iron sources to achieve the controllable growth of the heterojunction through mild regulation of hydrothermal conditions. The whole process does not require complex equipment or harsh conditions, has strong controllability of reaction temperature and time, high raw material utilization rate, and is environmentally friendly, significantly reducing production costs.

[0031] The S-type WO3 / FeWO4 heterojunction prepared by the present invention enhances the light absorption efficiency and the exposure of active sites through a nanorod / nanoneedle structure. Meanwhile, the synergistic effect of the stepped energy band matching and the interfacial built-in electric field realizes the efficient separation and directional migration of photo-generated carriers, while maintaining high redox ability and improving photocatalytic performance.

[0032] The photocatalyst of the present invention exhibits excellent cyclic stability and practicability in the water splitting hydrogen production system. Its unique interfacial chemical bonding effectively inhibits photocorrosion, maintains high catalytic activity under long-term light irradiation, and can stably produce hydrogen without relying on high-concentration sacrificial agents. This material combines high activity and high durability, providing a reliable material basis for the practical application of solar-driven hydrogen production technology. Description of the Drawings

[0033] Figure 1 It is the SEM image of WO3 / FeWO4 prepared in Example 2.

[0034] Figure 2 It is the XRD pattern of WO3 and WO3 / FeWO4 prepared in Example 2.

[0035] Figure 3 These are the TEM and HRTEM images of WO3 / FeWO4 prepared in Example 2.

[0036] Figure 4 These are the BET diagrams of WO3 and WO3 / FeWO4 prepared in Example 2.

[0037] Figure 5 These are the UV-vis spectra of WO3 prepared in Example 2, WO3 / FeWO4 prepared in Example 2, and FeWO4 prepared in Comparative Example 3.

[0038] Figure 6 These are the XPS spectra of WO3 and WO3 / FeWO4 prepared in Example 2.

[0039] Figure 7 These are the I-T curves of WO3 and WO3 / FeWO4 prepared in Example 2 under a bias voltage of 0.5 V.

[0040] Figure 8 These are the Nyquist plots of WO3 and WO3 / FeWO4 prepared in Example 2.

[0041] Figure 9 These are the Mott-Schottky curves of WO3 prepared in Example 2 and FeWO4 prepared in Comparative Example 3.

[0042] Figure 10 These are the photocatalytic hydrogen production rate diagrams of WO3 prepared in Examples 1-4.

[0043] Figure 11 These are the photocatalytic hydrogen production rate diagrams of WO3 / FeWO4 prepared in Examples 1-4 and WO3 / FeWO4 prepared in Comparative Examples 1-2.

[0044] Figure 12 These are the photocatalytic hydrogen production cycle diagrams of WO3 / FeWO4 prepared in Example 2. Detailed implementation manners

[0045] To better understand the content of the present invention, the present invention will be further described below in conjunction with examples and drawings. However, the protection scope of the present invention is not limited to the following examples.

[0046] Example 1

[0047] Step 1: Weigh 1.0 g of (NH4)6H2W 12 O 40·xH2O was dissolved in 95 mL of deionized water, 2.5 mL of concentrated hydrochloric acid (HCl, 36 - 38%) was added dropwise and stirred for 5 min. Then 2.5 mL of hydrogen peroxide solution (H2O2, 30%) was added and stirred for 1 h to obtain a precursor solution. The precursor solution was transferred to a polytetrafluoroethylene-lined autoclave and reacted at 160 °C for 4 h. After the reaction, it was cooled to room temperature, centrifuged, washed with deionized water and absolute ethanol, dried at 60 °C for 4 h. Finally, the dried powder was placed in a muffle furnace and heated to 500 °C at a heating rate of 5 °C / min and annealed for 1.5 h to obtain WO3 nanomaterial, WO3-1.

[0048] Step 2: 3 mmol of Na2WO4∙2H2O and 3 mmol of (NH4)2SO4Fe(SO4)∙6H2O were respectively dissolved in 40 mL of water. 0.25 g of WO3 was added to the (NH4)2SO4Fe(SO4) solution and sonicated for 10 min. Under continuous stirring, Na2WO4 was dropped into the above suspension and stirred for 30 min. The obtained suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 180 °C for 16 h. After naturally cooling to room temperature, the sample was centrifuged, washed with deionized water and absolute ethanol, and then dried at 80 °C for 6 h to obtain a WO3 / FeWO4 heterojunction photocatalyst, denoted as WO3 / FeWO4-1.

[0049] Example 2

[0050] Step 1: 1.0 g of (NH4)6H2W 12 O 40 ·xH2O was dissolved in 95 mL of deionized water, 3 mL of concentrated hydrochloric acid (HCl, 36 - 38%) was added dropwise and stirred for 5 min. Then 2 mL of hydrogen peroxide solution (H2O2, 30%) was added and stirred for 1 h to obtain a precursor solution. The precursor solution was transferred to a polytetrafluoroethylene-lined autoclave and reacted at 160 °C for 4 h. After the reaction, it was cooled to room temperature, centrifuged, washed with deionized water and absolute ethanol, dried at 60 °C for 4 h. Finally, the dried powder was placed in a muffle furnace and heated to 500 °C at a heating rate of 5 °C / min and annealed for 1 h to obtain WO3 nanomaterial, WO3-2.

[0051] Step 2: Dissolve 2 mmol of Na2WO4∙2H2O and 2 mmol of (NH4)2SO4Fe(SO4)∙6H2O separately in 40 mL of water. Add 0.27 g of WO3 to the (NH4)2SO4Fe(SO4) solution and sonicate for 10 min. While continuously stirring, dropwise add Na2WO4 into the above suspension and stir for 30 min. Transfer the obtained suspension to a 100 mL stainless-steel autoclave lined with polytetrafluoroethylene and heat at 180 °C for 12 h. After naturally cooling to room temperature, centrifuge the sample, wash it with deionized water and anhydrous ethanol, and then dry it at 80 °C for 6 h to obtain the WO3 / FeWO4 heterojunction photocatalyst, denoted as WO3 / FeWO4-2.

[0052] Example 3

[0053] Step 1: Dissolve 1.0 g of (NH4)6H2W 12 O 40 ·xH2O in 95 mL of deionized water, add 2 mL of concentrated hydrochloric acid (HCl, 36 - 38%) dropwise and stir for 5 min. Then add 3 mL of hydrogen peroxide solution (H2O2, 30%) and stir for 1 h to obtain the precursor solution. Transfer the precursor solution to a polytetrafluoroethylene-lined autoclave and react at 165 °C for 5 h. After the reaction is completed, cool to room temperature, centrifuge, wash with deionized water and anhydrous ethanol, dry at 60 °C for 4 h, and finally place the dried powder in a muffle furnace and heat it to 550 °C at a heating rate of 5 °C / min and anneal for 1.5 h to obtain the WO3 nanomaterial, WO3-3.

[0054] Step 2: Dissolve 3 mmol of Na2WO4∙2H2O and 3 mmol of (NH4)2SO4Fe(SO4)∙6H2O separately in 50 mL of water. Add 0.35 g of WO3 to the (NH4)2SO4Fe(SO4) solution and sonicate for 10 min. While continuously stirring, dropwise add Na2WO4 into the above suspension and stir for 30 min. Transfer the obtained suspension to a 100 mL stainless-steel autoclave lined with polytetrafluoroethylene and heat at 190 °C for 12 h. After naturally cooling to room temperature, centrifuge the sample, wash it with deionized water and anhydrous ethanol, and then dry it at 80 °C for 6 h to obtain the WO3 / FeWO4 heterojunction photocatalyst, denoted as WO3 / FeWO4-3.

[0055] Example 4

[0056] Step 1: Dissolve 1.0 g of (NH4)6H2W 12 O 40·xH2O was dissolved in 95 mL of deionized water, 3 mL of concentrated hydrochloric acid (HCl, 36 - 38%) was added dropwise and stirred for 5 min. Then 2 mL of hydrogen peroxide solution (H2O2, 30%) was added and stirred for 1 h to obtain a precursor solution. The precursor solution was transferred to a polytetrafluoroethylene-lined autoclave and reacted at 180 °C for 4 h. After the reaction, it was cooled to room temperature, centrifuged, washed with deionized water and absolute ethanol, and dried at 60 °C for 4 h. Finally, the dried powder was placed in a muffle furnace and heated to 550 °C at a heating rate of 5 °C / min and annealed for 2 h to obtain WO3 nanomaterials, WO3-4.

[0057] Step 2: 3.2 mmol of Na2WO4∙2H2O and 3.2 mmol of (NH4)2SO4Fe(SO4)∙6H2O were respectively dissolved in 40 mL of water. 0.5 g of WO3 was added to the (NH4)2SO4Fe(SO4) solution and ultrasonicated for 10 min. Under continuous stirring, Na2WO4 was dropped into the above suspension and stirred for 30 min. The obtained suspension was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heated at 180 °C for 12 h. After naturally cooling to room temperature, the sample was centrifuged, washed with deionized water and absolute ethanol, and then dried at 80 °C for 6 h to obtain a WO3 / FeWO4 heterojunction photocatalyst, denoted as WO3 / FeWO4-4.

[0058] Comparative Example 1:

[0059] This comparative example discloses a synthesis method of a WO3 / FeWO4 composite photocatalyst prepared by mechanical mixing, which is characterized in that the hydrothermal interface coupling process is not adopted, and specifically includes the following steps:

[0060] (1) Obtain WO3 nanomaterials according to Step 1 in Example 2.

[0061] (2) 2 mmol of ammonium ferrous sulfate and 2 mmol of sodium tungstate were respectively dissolved in 40 mL of water, mixed and ultrasonicated for 10 min, transferred to an autoclave and hydrothermally treated at 180 °C for 16 h to obtain FeWO4 nanomaterials. WO3 and FeWO4 were mixed at a mass ratio of 1:1, added with ethanol and ultrasonicated for 30 min, magnetically stirred for 12 h and then centrifuged and dried to obtain a mechanically mixed WO3 / FeWO4 composite material, denoted as WO3 / FeWO4-5.

[0062] Comparative Example 2:

[0063] This comparative example discloses a synthesis method of a WO3 / FeWO4 composite photocatalyst prepared by ball milling, which is characterized in that it is forcibly compounded by high-energy mechanical action, and specifically includes the following steps:

[0064] Prepare WO3 and FeWO4 nanomaterials respectively according to the method of Comparative Example 1. Add the two into a ball milling jar at a mass ratio of 1:1, use zirconia balls as the medium, and ball mill at a speed of 300 rpm for 4 h to fully mix the materials. After centrifugally collecting the powder, dry it at 80 °C for 6 h to obtain the ball milled composite WO3 / FeWO4 material, denoted as WO3 / FeWO4-6.

[0065] Comparative Example 3:

[0066] This comparative example discloses a method for preparing FeWO4 photocatalyst by hydrothermal method, which specifically includes the following steps: Dissolve 2 mmol of Na2WO4∙2H2O and 2 mmol of (NH4)2SO4Fe(SO4)∙6H2O in 40 mL of water respectively. Add the (NH4)2SO4Fe(SO4) solution to the Na2WO4 solution under vigorous stirring, and adjust the pH value of the solution to 8.5 with 1 mol / L NaOH. Transfer the solution to a 100 mL stainless steel autoclave and heat it at 180 °C for 12 h. After cooling to room temperature, centrifuge, wash with ethanol and distilled water, and dry at 80 °C for 6 h to obtain the FeWO4 photocatalyst.

[0067] The comparative examples show that compared with traditional methods such as mechanical mixing and ball milling composite, the S-type WO3 / FeWO4 heterojunction constructed by hydrothermal interfacial chemical bonding in the present invention can significantly inhibit interfacial defect states, and at the same time realize efficient directional migration of photogenerated electrons based on the high reduction potential of the FeWO4 conduction band (verified by Comparative Example 3), which plays an important role in improving the charge separation efficiency and hydrogen production reaction kinetics.

[0068] The WO3 / FeWO4 photocatalysts obtained in Examples 1-4 can be used for photocatalytic water splitting to produce hydrogen. The specific operation process is as follows: Under magnetic stirring, disperse the prepared WO3 and WO3 / FeWO4 photocatalysts in a mixed solution of deionized water and 15% methanol, then add them to a quartz reaction cell, introduce argon, and carry out the reaction under irradiation of a 300 W xenon lamp. The mass-volume ratio of the photocatalyst to the mixed solution is 50 mg:100 mL. During the whole process, the reaction temperature is kept at 25 °C, and the generated H2 is detected by gas chromatography every 0.5 h.

[0069] Select a Zeiss GeminiSEM300 field emission scanning electron microscope to perform structural characterization on the WO3 / FeWO4 prepared in Example 2. Take a small amount of powder sample and stick it to the conductive adhesive, and use a Quorum SC7620 sputtering coater to spray gold for testing the surface morphology of the sample, with an acceleration voltage of 3 kV.

[0070] Figure 1It is the SEM image of WO3 / FeWO4 prepared in Example 2. As can be seen from the figure, WO3 has a nanorod-like structure with a width of 50 - 100 nm. The surface-loaded FeWO4 has a nanoneedle-like structure with a length of 100 - 120 nm.

[0071] The phase analysis of the sample was carried out using a German Bruker D8 Advance X-ray diffractometer (Cu-Kα radiation, λ = 1.5406 Å), and the scanning range was 10~80°.

[0072] Figure 2 It is the XRD patterns of WO3 and WO3 / FeWO4 prepared in Example 2. As shown in the figure, nine obvious diffraction peaks appeared in the diffraction pattern of the WO3 sample at 2θ of 23.109°, 23.579°, 24.349°, 26.585°, 28.914°, 33.252°, 34.151°, 41.865° and 49.893°, corresponding to the (002), (020), (200), (120), (112), (022), (202), (222) and (400) crystal planes of WO3 (JCPDS No. 72 - 0677), indicating its good crystallinity. For the WO3 / FeWO4 heterojunction, in addition to the diffraction peaks corresponding to WO3, new diffraction peaks appeared at 2θ of 15.525°, 18.745°, 24.429°, 30.449°, 31.344° and 36.325° positions, and these diffraction peaks can be attributed to the FeWO4 phase (JCPDS No. 85 - 1354). These results indicate the successful synthesis of the WO3 / FeWO4 heterojunction, and both substances maintain good crystallinity in the composite. In addition, the intensity and position of the diffraction peaks are in agreement with the standard card data, confirming the crystal structure and phase composition of the material.

[0073] The microscopic morphology, crystal structure and crystal plane information of the product were characterized using a Titan G260 - 300 transmission electron microscope from the United States, and the acceleration voltage was 200 kV.

[0074] Figure 3These are the TEM and HRTEM images of WO3 / FeWO4 prepared in Example 2. As shown in Figure (a), the TEM image of the sample shows that WO3 / FeWO4 has a rod-like and needle-like structure, corresponding to the morphologies of WO3 and FeWO4, respectively. It can be observed from the high-resolution TEM (HRTEM) image in Figure (b) that the lattice with a spacing of 0.26 nm corresponds to the (202) crystal plane of monoclinic WO3, while the lattice with a spacing of 0.29 nm corresponds to the (-111) crystal plane of FeWO4, which is consistent with the XRD results. There is no obvious impurity phase in the two-phase interface region, indicating that the two phases form a stable heterostructure through interface coupling, which can promote interface charge transfer and inhibit the structural degradation of the heterojunction during the photocatalytic reaction process, providing microscopic mechanism evidence for the excellent catalytic activity of the material.

[0075] The nitrogen adsorption and desorption tests were carried out on the samples using a 4-station fully automatic specific surface area analyzer of the American Micromeritics APSP2460 model. After the instrument analysis was completed, the isothermal adsorption and desorption curves were obtained, and the total specific surface area of the material was obtained by the BET method.

[0076] Figure 4 These are the BET diagrams of WO3 and WO3 / FeWO4 prepared in Example 2. The results show that the specific surface area of single WO3 is 5.0543 m 2 / g, while the specific surface area of WO3 / FeWO4 is increased to 30.4915 m 2 / g (an increase of about 6 times). The loading of FeWO4 increases the exposed area of active sites, and the high specific surface area characteristic enables the WO3 / FeWO4 heterojunction to exhibit strong reactant adsorption ability and faster mass transfer kinetics in the application of photocatalytic water splitting.

[0077] The Shimadzu UV-3600iPlus type ultraviolet-visible spectrophotometer was used to analyze the light absorption performance of the samples, and the test wavelength was 200 - 800 nm.

[0078] Figure 5 These are the UV-vis spectra of WO3 and WO3 / FeWO4 prepared in Example 2. It can be seen from the figure that WO3 shows an absorption edge at 472 nm (the band gap is 2.58 eV), while the absorption edge of WO3 / FeWO4 is significantly red-shifted. This indicates that the introduction of FeWO4 significantly broadens the light response range to the visible light region and improves the visible light absorption ability. It can also be calculated from the figure that the band gap of FeWO4 is 1.96 eV.

[0079] The surface chemical element composition and valence state of the product were characterized using a Thermo ESCALAB250XI photoelectron spectrometer from the United States. The working voltage was 14.6 kV, the step size was 0.1 eV, and the charge correction was carried out with the binding energy of C1s at 284.8 eV as the energy standard.

[0080] Figure 6 are the XPS spectra of WO3 and WO3 / FeWO4 prepared in Example 2. The results show that in the high-resolution spectrum of W4f of pure WO3, the peaks located at 35.4 eV and 37.5 eV correspond to the 4f 6+ of W 7 / 2 and 4f 5 / 2 orbitals, while in WO3 / FeWO4, the W4f peak shifts 0.2 eV towards higher binding energy, indicating the formation of a chemical bond connection between WO3 and FeWO4. It can be seen from the O1s spectrum that the characteristic peak at 530.2 eV corresponds to the lattice oxygen (W-O) of WO3, and the characteristic peak at 530.5 eV corresponds to the lattice oxygen of W-O and Fe-O. In the Fe2p spectrum, the characteristic peaks at 710.6 eV (Fe2p 3 / 2 ) and 723.7 eV (Fe2p 1 / 2 ) confirm the existence of Fe 2+ in FeWO4.

[0081] The photoelectrochemical performance of the samples was tested using a Chenhua CHI660E electrochemical workstation.

[0082] Figure 7 are the I-T curves of WO3 and WO3 / FeWO4 prepared in Example 2 under a bias voltage of 0.5 V. As shown in the figure, WO3 / FeWO4 exhibits a significantly enhanced photocurrent response, which is about 2.7 times higher than that of pure WO3, indicating that the heterojunction interface effectively inhibits the recombination of photo-generated carriers.

[0083] Figure 8 are the Nyquist spectra of WO3 and WO3 / FeWO4 prepared in Example 2. The spectra show that the arc radius presented by WO3 / FeWO4 in the high-frequency region is smaller than that of pure WO3, effectively reducing the transport barrier at the photo-generated carrier interface and improving the photocatalytic performance.

[0084] Figure 9 are the Mott-Schottky curves of WO3 prepared in Example 2 and FeWO4 prepared in Comparative Example 3. It can be calculated from the figure that the conduction band (CB) position of WO3 is 0.15 eV, and the CB position of FeWO4 is -0.45 eV. Combining the appendix Figure 5For the band gap value, the valence band (VB) position of WO3 can be obtained as 2.73 eV, and the VB position of FeWO4 is 1.51 eV. Under visible light irradiation, the photo-generated electrons on the CB of WO3 are easily recombined with the photo-generated holes on the VB of FeWO4. Photo-generated holes with strong oxidation ability and photo-generated electrons with strong reduction ability are respectively retained on the VB of WO3 and the CB of FeWO4 to participate in the photocatalytic reaction, which conforms to the S-type charge transfer mechanism. The S-scheme charge transfer pathway in this heterojunction photocatalyst can simultaneously achieve effective charge collection and a high reduction ability of photoelectrons for H2 generation.

[0085] Figure 10 is the photocatalytic hydrogen production rate diagram of WO3 prepared in Examples 1-4. It can be seen from the figure that the photocatalytic hydrogen production rate of pure WO3 is stably maintained at 220-241 μmolg -1 h -1 , indicating that the hydrothermal synthesis process of the present invention has good reproducibility in the preparation of different examples.

[0086] Figure 11 is the photocatalytic hydrogen production rate diagram of WO3 / FeWO4 prepared in Examples 1-4 and WO3 / FeWO4 prepared in Comparative Examples 1-2. The hydrogen production rate of WO3 / FeWO4 prepared by the hydrothermal method in Examples 1-4 is 1358-1602 μmolg -1 h -1 , which is significantly higher than that of single WO3, indicating that the formation of the heterojunction improves the photocatalytic hydrogen production activity. In addition, it is higher than the samples prepared by mechanical mixing and ball milling in Comparative Examples 1-2. The hydrothermal method induces strong interfacial coupling between WO3 and FeWO4, while the physical mixing samples have serious recombination of photo-generated carriers due to the loose contact at the two-phase interface. This comparative experiment shows that the hydrothermal synthesis strategy of the present invention is the key to constructing an efficient WO3 / FeWO4 heterojunction photocatalyst, and the optimization of its interfacial properties enables the hydrogen production activity to reach 1.8 times that of the physical mixing method.

[0087] Figure 12 is the photocatalytic hydrogen production cycle diagram of WO3 / FeWO4 prepared in Example 2. It can be seen from the figure that the hydrogen production rate hardly decays after five cycle experiments, indicating that WO3 / FeWO4 has good photocatalytic stability.

[0088] The present invention can have other forms of embodiments according to the above methods, which will not be listed one by one. Therefore, any person skilled in the art, without departing from the scope of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An S-type WO3 / FeWO4 heterojunction photocatalyst, characterized in that: It is a 1D / 1D structure, with FeWO4 nanoneedles loaded on the surface of WO3 nanorods, and an S-type heterojunction with an staggered energy band structure; its synthesis method is as follows: Step 1. Dissolve ammonium metatungstate hydrate (NH4)6H2W 12 O 40 ·xH2O in deionized water. The amount of ammonium metatungstate hydrate is 1.0 g, and the added deionized water is 95 mL; then, under magnetic stirring, slowly dropwise add concentrated hydrochloric acid containing 36 - 38% HCl to obtain solution A; subsequently, add hydrogen peroxide solution containing 30% H2O2 to solution A, stir magnetically for 1 h to obtain a precursor solution, subject the precursor solution to hydrothermal reaction, after the reaction ends, centrifuge, wash, dry, and finally anneal in a muffle furnace, with the annealing atmosphere being air, to obtain WO3 nanomaterials; the volume of the added HCl solution is 2 - 3 mL, and the volume of the added H2O2 solution is 2 - 3 mL; Step 2. Dissolve sodium tungstate and ammonium ferrous sulfate in water respectively to obtain aqueous solutions. The concentration of sodium tungstate is 0.05 - 0.08 mol / L, and the concentration of ammonium ferrous sulfate is 0.05 - 0.08 mol / L, and the concentrations of sodium tungstate and ammonium ferrous sulfate are equal; add the WO3 obtained in the above Step 1 to the ammonium ferrous sulfate solution, and the added amount of WO3 is 0.25 - 0.5 g; obtain a uniformly dispersed suspension under ultrasonic action; then, under continuous stirring, dropwise add the sodium tungstate solution into the above suspension, stir and then conduct hydrothermal reaction, after the reaction ends, centrifuge, wash, dry, to obtain a WO3 / FeWO4 heterojunction photocatalyst material.

2. The application method of an S-type WO3 / FeWO4 heterojunction photocatalyst according to claim 1, characterized in that: Application method for photocatalytic water splitting to produce hydrogen: Under magnetic stirring, disperse this WO3 / FeWO4 heterojunction photocatalyst in a mixed solution of deionized water and 15% methanol, add it to a quartz reaction cell, introduce argon, and carry out the reaction under irradiation with a 300 W xenon lamp. The mass-volume ratio of the photocatalyst to the mixed solution is 50 mg: 100 mL.

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