S-type WO3 / FeWO4 heterojunction photocatalyst as well as synthesis method and application method thereof

Abstract

The invention relates to the technical field of photocatalysis, and discloses an S-type WO3 / FeWO4 heterojunction photocatalyst as well as a synthesis method and an application method thereof. The FeWO4 nanoneedle is loaded on the surface of the WO3 nanorod to form an S-type heterojunction with a staggered energy band structure, and a built-in electric field and a 1D / 1D structure synergistically promote separation of photon-generated carriers; the synthesis method comprises the following steps: preparing a WO3 nano material by taking ammonium metatungstate as a tungsten source through a hydrothermal method; the preparation method comprises the following steps: ultrasonically dispersing WO3 in an ammonium ferrous sulfate solution to form a suspension system, dropwise adding a sodium tungstate solution into the suspension under continuous stirring, and carrying out secondary hydrothermal crystallization to obtain the S-type WO3 / FeWO4 heterojunction photocatalyst with a strong interface coupling effect. The S-type WO3 / FeWO4 heterojunction photocatalyst prepared by the invention has excellent hydrogen production activity and good stability in photocatalytic decomposition of water, and has a better application prospect in the field of hydrogen production by photocatalytic decomposition of water.

Description

Technical Field

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

[0002] Photocatalytic water decomposition to produce hydrogen is a technology that converts solar energy into hydrogen energy, which is of great significance to solving energy crises and environmental problems. The core of this technology lies in the development of 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 a suitable optical band gap, a high valence band position and good chemical stability and is widely used in the field of photocatalysis. However, single WO3 has problems such as high recombination rate of photogenerated carriers and slow kinetics of water oxidation reaction, resulting in low efficiency of photocatalytic water decomposition to produce hydrogen.

[0003] In the existing technology, the strategy of constructing heterojunction (such as WO3 / g-C3N4, WO3 / CdS) is often used to improve the carrier separation efficiency of WO3. However, the insufficient band matching of the traditional heterojunction interface will lead to the disorder of the charge transfer path. Especially in the traditional type II heterojunction system, although the spatial separation of photogenerated 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 cause interface defects due to lattice mismatch, and these defects will become the center of charge recombination, reducing the charge transfer efficiency.

[0004] Recent studies have found that the S-type (Step-scheme) heterojunction can achieve directional migration of photogenerated carriers through the synergistic effect of built-in electric field and interface band bending, while maintaining strong redox ability and improving charge separation efficiency. Therefore, the development of S-type heterojunction photocatalysts with precise band matching and stable interface structure has become an effective way to improve the efficiency of photocatalytic water decomposition to produce hydrogen. Summary of the invention

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

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

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

[0008] A method for synthesizing an S-type WO3 / FeWO4 heterojunction photocatalyst: Step 1: ammonium metatungstate hydrate ((NH4)6H2W 12 O 40 ·xH2O) is dissolved in deionized water, and then concentrated hydrochloric acid (containing 36-38% HCl) is added dropwise under magnetic stirring to obtain solution A; then hydrogen peroxide solution (containing 30% H2O2) is added to solution A, and magnetic stirring is performed for 1 hour to obtain a precursor solution, and the precursor solution is subjected to hydrothermal reaction. After the reaction is completed, it is centrifuged, washed, dried, and finally annealed in a muffle furnace in an air atmosphere to obtain WO3 nanomaterials; Step 2: Sodium tungstate and ammonium ferrous sulfate are dissolved in water to obtain an aqueous solution respectively, and the WO3 obtained in the above step 1 is added to the ammonium ferrous sulfate solution to obtain a uniformly dispersed suspension under the action of ultrasound; then the sodium tungstate solution is dropped into the above suspension under continuous stirring, and a hydrothermal reaction is carried out after stirring. After the reaction is completed, centrifugal washing and drying are performed to obtain a WO3 / FeWO4 heterojunction photocatalyst material.

[0009] In step 1, the amount of ammonium metatungstate hydrate is 1.0 g, and the amount of deionized water added is 95 mL; In step 1, the volume of the HCl solution added is 2-3 mL, and the volume of the H2O2 solution added is 2-3 mL.

[0010] In step 1, the hydrothermal reaction temperature is 160-180° C., and the hydrothermal time is 4-5 h.

[0011] In step 1, the annealing temperature is 500-550°C, the heating rate is 5°C / min, and the annealing time is 1-2h.

[0012] 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.

[0013] In step 2, the amount of WO3 added is 0.25~0.5g.

[0014] In step 2, the hydrothermal reaction temperature is 180-200° C., and the hydrothermal time is 12-16 h.

[0015] The present invention also provides an application method of the above WO3 / FeWO4 heterojunction photocatalyst in photocatalytic decomposition of water to produce hydrogen: The WO3 / FeWO4 heterojunction photocatalyst was dispersed in a mixed solution of deionized water and 15% methanol under magnetic stirring, added into a quartz reaction cell, introduced with argon gas, and reacted under irradiation with a 300W xenon lamp. The mass volume ratio of the photocatalyst to the mixed solution was 50mg:100mL.

[0016] In this application method, methanol, as a hole sacrificial agent, preferentially reacts with photogenerated holes, effectively inhibiting the recombination of electron-hole pairs and improving the reduction ability of photogenerated electrons. The construction of an argon environment can eliminate the competitive consumption of photogenerated electrons by dissolved oxygen, avoid the generation of byproducts such as superoxide radicals, and ensure that electrons participate in the proton reduction hydrogen production process in a directional manner.

[0017] 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, promoting the diffusion of water molecules to the catalyst surface and the desorption of hydrogen.

[0018] The present invention uses ammonium metatungstate as a tungsten source through a step-by-step hydrothermal method and combines the secondary hydrothermal crystallization of ammonium ferrous sulfate and sodium tungstate to successfully construct an S-type WO3 / FeWO41D / 1D heterojunction photocatalyst with strong interface coupling.

[0019] The hydrogen production mechanism of the S-type WO3 / FeWO4 heterojunction photocatalyst in the present invention is as follows: under light excitation, WO3 and FeWO4 form a built-in electric field due to the Fermi level difference, inducing band bending at the interface. Driven by the interface electric field, WO3 conduction band electrons recombine with FeWO4 valence band holes, while FeWO4 conduction band electrons (-0.45eVvs.NHE) migrate to the surface under the action of the band bending gradient and directly participate in H + Reduction produces H2, and the WO3 valence band holes are quickly captured by methanol molecules, effectively inhibiting charge recombination.

[0020] The one-dimensional nanowire heterogeneous interface forms an efficient charge transfer channel through the interfacial chemical bonds, accelerating the carrier transport. The active sites exposed on the WO3 surface reduce the adsorption barrier of H2O molecules and promote proton supply.

[0021] The heterojunction forms a stepped band structure through the precise combination of nanoneedle-shaped FeWO4 and nanorod WO3. The synergistic effect of the interface electric field and band bending promotes the directional migration of photogenerated carriers, effectively inhibiting recombination and improving the kinetics of redox reactions.

[0022] Compared with the traditional type II heterojunction, 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, and no precious metal co-catalyst is required, which has important application value in the field of solar energy-hydrogen energy conversion.

[0023] Compared with the prior art, the present invention has the following beneficial effects: By constructing an S-type WO3 / FeWO4 heterojunction, 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 photogenerated carriers is achieved. Compared with the disordered charge transfer path caused by energy level dislocation in the traditional II-type heterojunction, 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 of the traditional heterojunction sacrificing the redox potential due to the spatial separation of carriers.

[0024] The preparation method proposed in the present invention uses a step-by-step hydrothermal method combined with an annealing process, and utilizes the controllable reaction of ammonium metatungstate and ammonium ferrous sulfate to successfully construct an S-type WO3 / FeWO4 heterojunction photocatalyst with strong interface coupling. This method precisely controls the heterojunction morphology and interface characteristics through two hydrothermal crystallizations, without the need for precious metal co-catalysts. The prepared material has a tight interface, stable structure and good repeatability, providing a new idea for the rational design of efficient photocatalysts.

[0025] The present invention uses low-cost tungsten and iron sources, and realizes controllable growth of heterojunctions through gentle regulation of hydrothermal conditions. The entire process does not require complex equipment or harsh conditions, the reaction temperature and time are highly controllable, the raw material utilization rate is high, and it is environmentally friendly, which significantly reduces production costs.

[0026] The S-type WO3 / FeWO4 heterojunction prepared by the present invention enhances light absorption efficiency and active site exposure through the nanorod / nanoneedle structure, and the synergistic effect of the step-type energy band matching and the built-in electric field of the interface realizes the efficient separation and directional migration of photogenerated carriers, while maintaining high redox ability and improving the photocatalytic performance.

[0027] The photocatalyst of the present invention exhibits excellent cycle stability and practicality in the water decomposition hydrogen production system. Its unique interfacial chemical bonding effectively inhibits photocorrosion, maintains high catalytic activity under long-term illumination, and can stably produce hydrogen without relying on high-concentration sacrificial agents. The material has both high activity and high durability, providing a reliable material basis for the practical application of solar-driven hydrogen production technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the SEM image of WO3 / FeWO4 prepared in Example 2.

[0029] Figure 2 It is the XRD diagram of WO3 and WO3 / FeWO4 prepared in Example 2.

[0030] Figure 3These are the TEM and HRTEM images of WO3 / FeWO4 prepared in Example 2.

[0031] Figure 4 It is the BET diagram of WO3 and WO3 / FeWO4 prepared in Example 2.

[0032] Figure 5 It is the UV-vis spectra of WO3, WO3 / FeWO4 prepared in Example 2 and FeWO4 prepared in Comparative Example 3.

[0033] Figure 6 It is the XPS spectrum of WO3 and WO3 / FeWO4 prepared in Example 2.

[0034] Figure 7 It is the IT curve of WO3 and WO3 / FeWO4 prepared in Example 2 under 0.5V bias voltage.

[0035] Figure 8 It is the Nyquist spectra of WO3 and WO3 / FeWO4 prepared in Example 2.

[0036] Fig. 9 It is the Mott-Schottky curve of WO3 prepared in Example 2 and FeWO4 prepared in Comparative Example 3.

[0037] Fig.10 It is a graph of the photocatalytic hydrogen production rate of WO3 prepared in Examples 1-4.

[0038] Fig.11 It is a photocatalytic hydrogen production rate diagram of WO3 / FeWO4 prepared in Example 1-4 and WO3 / FeWO4 prepared in Comparative Example 1-2.

[0039] Fig.12 This is the photocatalytic hydrogen production cycle diagram of WO3 / FeWO4 prepared in Example 2. DETAILED DESCRIPTION

[0040] In order to better understand the content of the present invention, the present invention is further described below in conjunction with embodiments and drawings, but the protection scope of the present invention is not limited to the following embodiments.

[0041] Example 1

[0042] Step 1: 1.0g (NH4)6H2W 12 O 40xH2O was dissolved in 95 mL of deionized water, and 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 anhydrous ethanol, and dried at 60 ° C for 4 h. Finally, the dried powder was placed in a muffle furnace, heated to 500 ° C at a rate of 5 ° C / min, and annealed for 1.5 h to obtain WO3 nanomaterials, WO3-1.

[0043] Step 2: Dissolve 3mmolNa2WO4∙2H2O and 3mmol(NH4)2SO4Fe(SO4)∙6H2O in 40mL water respectively, add 0.25gWO3 to the (NH4)2SO4Fe(SO4) solution and ultrasonicate for 10min. Drop Na2WO4 into the above suspension under continuous stirring and stir for 30min. Transfer the obtained suspension to a 100mL polytetrafluoroethylene-lined stainless steel autoclave and heat at 180°C for 16h. After cooling naturally to room temperature, the sample was centrifuged, washed with deionized water and anhydrous ethanol, and then dried at 80°C for 6h to obtain a WO3 / FeWO4 heterojunction photocatalyst, recorded as WO3 / FeWO4-1.

[0044] Example 2

[0045] Step 1: 1.0g (NH4)6H2W 12 O 40 xH2O was dissolved in 95 mL of deionized water, and 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 anhydrous ethanol, and dried at 60 ° C for 4 h. Finally, the dried powder was placed in a muffle furnace, heated to 500 ° C at a rate of 5 ° C / min, and annealed for 1 h to obtain WO3 nanomaterials, WO3-2.

[0046] Step 2: Dissolve 2mmolNa2WO4∙2H2O and 2mmol(NH4)2SO4Fe(SO4)∙6H2O in 40mL water respectively. Add 0.27gWO3 to the (NH4)2SO4Fe(SO4) solution and ultrasonicate for 10min. Drop Na2WO4 into the above suspension under continuous stirring and stir for 30min. Transfer the obtained suspension to a 100mL polytetrafluoroethylene-lined stainless steel autoclave and heat at 180°C for 12h. After cooling naturally to room temperature, the sample was centrifuged, washed with deionized water and anhydrous ethanol, and then dried at 80°C for 6h to obtain a WO3 / FeWO4 heterojunction photocatalyst, recorded as WO3 / FeWO4-2.

[0047] Example 3

[0048] Step 1: 1.0g (NH4)6H2W 12 O 40 xH2O was dissolved in 95 mL of deionized water, and 2 mL of concentrated hydrochloric acid (HCl, 36-38%) was added dropwise and stirred for 5 min. Then 3 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 165 ° C for 5 h. After the reaction, it was cooled to room temperature, centrifuged, washed with deionized water and anhydrous ethanol, and dried at 60 ° C for 4 h. Finally, the dried powder was placed in a muffle furnace, heated to 550 ° C at a rate of 5 ° C / min, and annealed for 1.5 h to obtain WO3 nanomaterials, WO3-3.

[0049] Step 2: Dissolve 3mmolNa2WO4∙2H2O and 3mmol(NH4)2SO4Fe(SO4)∙6H2O in 50mL water respectively. Add 0.35gWO3 to the (NH4)2SO4Fe(SO4) solution and ultrasonicate for 10min. Drop Na2WO4 into the above suspension under continuous stirring and stir for 30min. Transfer the obtained suspension to a 100mL polytetrafluoroethylene-lined stainless steel autoclave and heat at 190°C for 12h. After cooling naturally to room temperature, the sample was centrifuged, washed with deionized water and anhydrous ethanol, and then dried at 80°C for 6h to obtain a WO3 / FeWO4 heterojunction photocatalyst, recorded as WO3 / FeWO4-3.

[0050] Example 4

[0051] Step 1: 1.0g (NH4)6H2W 12 O 40xH2O was dissolved in 95 mL of deionized water, and 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 anhydrous ethanol, and dried at 60 ° C for 4 h. Finally, the dried powder was placed in a muffle furnace, heated to 550 ° C at a rate of 5 ° C / min, and annealed for 2 h to obtain WO3 nanomaterials, WO3-4.

[0052] Step 2: Dissolve 3.2mmolNa2WO4∙2H2O and 3.2mmol(NH4)2SO4Fe(SO4)∙6H2O in 40mL water respectively. Add 0.5gWO3 to the (NH4)2SO4Fe(SO4) solution and ultrasonicate for 10min. Drop Na2WO4 into the above suspension under continuous stirring and stir for 30min. Transfer the obtained suspension to a 100mL polytetrafluoroethylene-lined stainless steel autoclave and heat at 180°C for 12h. After cooling naturally to room temperature, the sample was centrifuged, washed with deionized water and anhydrous ethanol, and then dried at 80°C for 6h to obtain a WO3 / FeWO4 heterojunction photocatalyst, recorded as WO3 / FeWO4-4.

[0053] Comparative Example 1: This comparative example discloses a method for synthesizing a WO3 / FeWO4 composite photocatalyst prepared by mechanical mixing, which is characterized in that a hydrothermal interface coupling process is not used, and specifically comprises the following steps: (1) Obtain WO3 nanomaterial according to step 1 in Example 2.

[0054] (2) 2mmol of ammonium ferrous sulfate and 2mmol of sodium tungstate were dissolved in 40mL of water, mixed and ultrasonicated for 10min, and then transferred to an autoclave for hydrothermal treatment at 180℃ for 16h to obtain FeWO4 nanomaterials. WO3 and FeWO4 were mixed in a mass ratio of 1:1, added with ethanol for ultrasonic dispersion for 30min, magnetically stirred for 12h, and then centrifuged and dried to obtain a mechanically mixed WO3 / FeWO4 composite material, which was recorded as WO3 / FeWO4-5.

[0055] Comparative Example 2: This comparative example discloses a method for synthesizing a WO3 / FeWO4 composite photocatalyst prepared by a ball milling method, which is characterized in that the composite is forced to be formed by high-energy mechanical action, and specifically comprises the following steps: WO3 and FeWO4 nanomaterials were prepared according to the method of Comparative Example 1. The two were added into a ball mill at a mass ratio of 1:1, and the materials were fully mixed at 300 rpm using zirconium oxide balls as the medium. The powder was collected by centrifugation and dried at 80°C for 6 hours to obtain a ball-milled composite WO3 / FeWO4 material, which was recorded as WO3 / FeWO4-6.

[0056] Comparative Example 3: This comparative example discloses a method for preparing a FeWO4 photocatalyst by a hydrothermal method, which specifically comprises the following steps: 2mmolNa2WO4∙2H2O and 2mmol(NH4)2SO4Fe(SO4)∙6H2O are dissolved in 40mL water respectively. The (NH4)2SO4Fe(SO4) solution is added to the Na2WO4 solution under vigorous stirring, and the pH value of the solution is adjusted to 8.5 with 1mol / L NaOH. The solution is transferred to a 100mL stainless steel autoclave and heated at 180°C for 12h. After cooling to room temperature, centrifuge, wash with ethanol and distilled water, and dry at 80°C for 6h to obtain a FeWO4 photocatalyst.

[0057] The comparative examples show that compared with traditional methods such as mechanical mixing and ball milling, the S-type WO3 / FeWO4 heterojunction constructed by hydrothermal interface chemical bonding in the present invention can significantly suppress interface defect states, and at the same time, based on the high reduction potential of the FeWO4 conduction band (verified by comparative example 3), it realizes efficient directional migration of photogenerated electrons, which plays an important role in improving the charge separation efficiency and hydrogen production reaction kinetics.

[0058] The WO3 / FeWO4 photocatalyst obtained in Example 1-4 can be used for photocatalytic decomposition of water to produce hydrogen. The specific operation process is as follows: the prepared WO3 and WO3 / FeWO4 photocatalysts are dispersed in a mixed solution of deionized water and 15% methanol under magnetic stirring, and then added to a quartz reaction cell, argon gas is introduced, and the reaction is carried out under irradiation of a 300W xenon lamp. The mass volume ratio of the photocatalyst to the mixed solution is 50mg:100mL. During the whole process, the reaction temperature is maintained at 25°C, and the generated H2 is detected by gas chromatography every 0.5h.

[0059] Zeiss GeminiSEM300 field emission scanning electron microscope was used to characterize the structure of WO3 / FeWO4 prepared in Example 2. A trace amount of powder sample was glued to the conductive adhesive, and gold was sprayed using QuorumSC7620 sputtering coating instrument to test the surface morphology of the sample, with an acceleration voltage of 3kV.

[0060] Figure 1This is a SEM image of WO3 / FeWO4 prepared in Example 2. As can be seen from the figure, WO3 is a nanorod-like structure with a width of 50-100nm. The surface-loaded FeWO4 is a nanoneedle-like structure with a length of 100-120nm.

[0061] The phase analysis of the samples was carried out using a German Bruker D8 Advance X-ray diffractometer (Cu-Kα radiation, λ=1.5406Å) with a scanning range of 10~80°.

[0062] Figure 2 WO3 and WO3 / FeWO4 prepared in Example 2 are XRD patterns. As shown in the figure, the diffraction pattern of the WO3 sample has 9 obvious diffraction peaks at 2θ of 23.109°, 23.579°, 24.349°, 26.585°, 28.914°, 33.252°, 34.151°, 41.865° and 49.893°, which correspond to the (002), (020), (200), (120), (112), (022), (202), (222) and (400) crystal planes of WO3 (JCPDS No. 72-0677), respectively, indicating that it has 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°, which can be attributed to the FeWO4 phase (JCPDS No. 85-1354). These results show that the WO3 / FeWO4 heterojunction was successfully synthesized and the two substances maintained good crystallinity in the composite. In addition, the intensity and position of the diffraction peaks are consistent with the standard card data, confirming the crystal structure and phase composition of the material.

[0063] The microscopic morphology, crystal structure and crystal plane information of the product were characterized by an American Titan G260-300 transmission electron microscope with an accelerating voltage of 200 kV.

[0064] Figure 3The TEM and HRTEM images of WO3 / FeWO4 prepared in Example 2 are shown in Figure (a). As shown in Figure (a), the TEM image of the sample shows that WO3 / FeWO4 has rod-like and needle-like structures, corresponding to the morphology of WO3 and FeWO4, respectively. From the high-resolution TEM (HRTEM) image in Figure (b), it can be observed that the lattice with a spacing of 0.26nm corresponds to the (202) crystal plane of the monoclinic phase WO3, while the lattice with a spacing of 0.29nm corresponds to the (-111) crystal plane of FeWO4, which is consistent with the XRD results. There is no obvious impurity phase in the interface region between the two phases, indicating that the two phases form a stable heterostructure through interface coupling, which can promote interfacial charge transfer and inhibit the structural degradation of the heterojunction during the photocatalytic reaction, providing microscopic mechanism evidence for the excellent catalytic activity of the material.

[0065] A 4-station fully automatic specific surface area analyzer of the American Micromeritics APSP2460 model was used to perform nitrogen adsorption and desorption tests on the samples. After the instrument analysis was completed, the isothermal adsorption and desorption curve was obtained, and the total specific surface area of ​​the material was obtained by the BET method.

[0066] Figure 4 The BET diagram of WO3 and WO3 / FeWO4 prepared in Example 2 shows that the specific surface area of ​​single WO3 is 5.0543 m 2 / g, and the specific surface area of ​​WO3 / FeWO4 increased to 30.4915m 2 / g (increased by about 6 times). The loading of FeWO4 increases the exposed area of ​​active sites. The high specific surface area characteristics enable the WO3 / FeWO4 heterojunction to exhibit stronger reactant adsorption capacity and faster mass transfer kinetics in photocatalytic water splitting applications.

[0067] The light absorption properties of the samples were analyzed using a Shimadzu UV-3600iPlus ultraviolet-visible spectrophotometer with a test wavelength of 200-800 nm.

[0068] Figure 5 The UV-vis spectra of WO3 and WO3 / FeWO4 prepared in Example 2 are shown in FIG. As can be seen from the figure, WO3 has an absorption edge at 472nm (band gap is 2.58eV), while the absorption edge of WO3 / FeWO4 is obviously red-shifted. This shows that the introduction of FeWO4 significantly broadens the light response range to the visible light region and improves the visible light absorption capacity. It can also be calculated from the figure that the band gap of FeWO4 is 1.96eV.

[0069] The surface chemical element composition and valence state of the product were characterized by the American ThermoESCALAB250XI photoelectron spectrometer. The working voltage was 14.6 kV, the step size was 0.1 eV, and the charge correction was performed using the C1s binding energy of 284.8 eV as the energy standard.

[0070] Figure 6 The XPS spectra of WO3 and WO3 / FeWO4 prepared in Example 2 show that in the W4f high-resolution spectrum of pure WO3, the peaks at 35.4eV and 37.5eV correspond to W 6+ 4f 7 / 2 and 4f 5 / 2 orbital, while in WO3 / FeWO4, the W4f peak shifts 0.2eV toward the high binding energy direction, indicating that a chemical bond is formed between WO3 and FeWO4. From the O1s spectrum, the characteristic peak at 530.2eV corresponds to the lattice oxygen of WO3 (WO), and the characteristic peak at 530.5eV corresponds to the lattice oxygen of WO and Fe-O. 3 / 2 ) and 723.7eV (Fe2p 1 / 2 ) confirms that Fe in FeWO4 2+ existence.

[0071] The photoelectrochemical properties of the samples were tested using a Chenhua CHI660E electrochemical workstation.

[0072] Figure 7 It is the IT curve of WO3 and WO3 / FeWO4 prepared in Example 2 at 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 suppresses the recombination of photogenerated carriers.

[0073] Figure 8 It is the Nyquist spectra of WO3 and WO3 / FeWO4 prepared in Example 2. The spectra show that the arc radius of WO3 / FeWO4 in the high frequency region is smaller than that of pure WO3, which effectively reduces the transmission barrier of the photogenerated carrier interface and improves the photocatalytic performance.

[0074] Fig. 9 The Mott-Schottky curves of WO3 prepared in Example 2 and FeWO4 prepared in Comparative Example 3 are shown in Table 1. From the figure, it can be calculated that the conduction band (CB) position of WO3 is 0.15 eV, and the CB position of FeWO4 is -0.45 eV. Figure 5The bandgap width values ​​show that the valence band (VB) position of WO3 is 2.73eV, and the VB position of FeWO4 is 1.51eV. Under visible light irradiation, the photogenerated electrons on the CB in WO3 easily recombine with the photogenerated holes on the VB in FeWO4. The photogenerated holes with strong oxidizing ability and the photogenerated electrons with strong reducing ability are retained on the VB of WO3 and the CB of FeWO4, respectively, 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 high reducing ability of photoelectrons to generate H2.

[0075] Fig.10 The photocatalytic hydrogen production rate of WO3 prepared in Example 1-4 is shown in the figure. It can be seen from the figure that the photocatalytic hydrogen production rate of pure WO3 is stably maintained at 220-241 μmol g -1 h -1 , indicating that the hydrothermal synthesis process of the present invention has good reproducibility in the preparation of different embodiments.

[0076] Fig.11 The photocatalytic hydrogen production rate of WO3 / FeWO4 prepared in Example 1-4 and WO3 / FeWO4 prepared in Comparative Example 1-2 is shown in Figure 1. The hydrogen production rate of WO3 / FeWO4 prepared by hydrothermal method in Example 1-4 is 1358-1602 μmol g -1 h -1 , significantly higher than that of single WO3, indicating that the formation of heterojunction improves the photocatalytic hydrogen production activity. In addition, the hydrothermal induced WO3 and FeWO4 form a strong interface coupling, which is higher than that of the samples prepared by mechanical mixing and ball milling in Comparative Example 1-2, while the physical mixed sample has a loose interface contact between the two phases, resulting in serious recombination of photogenerated carriers. 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 its interface property optimization enables the hydrogen production activity to reach 1.8 times that of the physical mixing method.

[0077] Fig.12 This is a photocatalytic hydrogen production cycle diagram of WO3 / FeWO4 prepared in Example 2. As can be seen from the figure, after five cycle experiments, the hydrogen production rate has almost no decay, indicating that WO3 / FeWO4 has good photocatalytic stability.

[0078] The present invention can have other forms of embodiments according to the above method, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any technician familiar with the profession to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still falls 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 a staggered energy band structure.

2. The method for synthesizing an S-type WO3 / FeWO4 heterojunction photocatalyst according to claim 1, characterized in that: Step 1: ammonium metatungstate hydrate (NH4)6H2W 12 O 40 xH2O is dissolved in deionized water, and then concentrated hydrochloric acid is added dropwise under magnetic stirring, containing 36-38% HCl to obtain solution A; then a hydrogen peroxide solution containing 30% H2O2 is added to solution A, and magnetic stirring is performed for 1 hour to obtain a precursor solution, and the precursor solution is subjected to a hydrothermal reaction. After the reaction is completed, it is centrifuged and washed, dried, and finally annealed in a muffle furnace, and the annealing atmosphere is air to obtain WO3 nanomaterials; step 2, sodium tungstate and ammonium ferrous sulfate are dissolved in water to obtain an aqueous solution, and the WO3 obtained in the above step 1 is added to the ammonium ferrous sulfate solution to obtain a uniformly dispersed suspension under the action of ultrasound; then the sodium tungstate solution is dripped into the above suspension under continuous stirring, and a hydrothermal reaction is performed after stirring. After the reaction is completed, it is centrifuged and washed, and dried to obtain a WO3 / FeWO4 heterojunction photocatalyst material.

3. The method for synthesizing an S-type WO3 / FeWO4 heterojunction photocatalyst according to claim 2, characterized in that: In step 1, the amount of ammonium metatungstate hydrate is 1.0 g, and the amount of deionized water added is 95 mL.

4. The method for synthesizing an S-type WO3 / FeWO4 heterojunction photocatalyst according to claim 2, characterized in that: In step 1, the volume of HCl solution added is 2~3mL, and the volume of H2O2 solution added is 2~3mL.

5. The method for synthesizing an S-type WO3 / FeWO4 heterojunction photocatalyst according to claim 2, characterized in that: 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.

6. The method for synthesizing an S-type WO3 / FeWO4 heterojunction photocatalyst according to claim 2, characterized in that: In step 2, the amount of WO3 added is 0.25~0.5g.

7. The application method of an S-type WO3 / FeWO4 heterojunction photocatalyst according to claim 1, characterized in that: Application method for photocatalytic decomposition of water to produce hydrogen: The WO3 / FeWO4 heterojunction photocatalyst is dispersed in a mixed solution of deionized water and 15% methanol under magnetic stirring, added to a quartz reaction cell, argon gas is introduced, and the reaction is carried out under irradiation of a 300W xenon lamp. The mass volume ratio of the photocatalyst to the mixed solution is 50mg:100mL.

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