A z-type heterojunction composite material and a preparation method and application thereof

Abstract

The application provides a Z-type heterojunction composite material and a preparation method and application thereof, and belongs to the field of photocatalytic material preparation. WCl6 is used as a tungsten source, and hexamethylenetetramine is used as a reducing agent to facilitate the formation of a product with good crystallinity, and a sheet structure WO3 is obtained; then, the WO3 is mixed with urea and calcined to in-situ synthesize g-C3N4 on the surface of the WO3 to obtain the Z-type heterojunction composite material, the microstructure of which is controllable, and the g-C3N4 in the Z-type heterojunction is in close contact with the WO3, and the Z-type heterojunction exhibits excellent visible light absorption capacity and high efficient photogenerated carrier separation efficiency.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic material preparation, and in particular to a Z-type heterojunction composite material, its preparation method, and its application. Background Technology

[0002] Hydrogen energy is considered a highly promising future energy carrier. Photocatalytic hydrogen production technology utilizes catalysts to decompose hydrogen storage carriers under light conditions to generate hydrogen, representing a highly efficient and environmentally friendly method. Ammonia borane (NH3BH3), a compound with a high hydrogen storage capacity (19.6 wt%), can be hydrolyzed by metal nanocatalysts under light to release hydrogen, offering a highly efficient and mild hydrogen release method. Noble metals (Ru, Pt, and Au, etc.) possess high catalytic activity and are often used as traditional metal nanocatalysts, but their high cost and low reserves make them unsuitable for large-scale applications. Abundant non-noble metals (Fe, Co, and Ni) are gradually replacing noble metals as the more suitable active components for hydrogen production via NH3BH3 hydrolysis.

[0003] Photoactive semiconductors with photoresponsive properties are excellent supports for non-noble metal catalysts, such as inexpensive and chemically stable graphitic carbon nitride (g-C3N4) and tungsten trioxide (WO3). However, the visible light absorption range of g-C3N4 is mainly concentrated in the λ < 460 nm range, limiting its light utilization efficiency; while WO3 can absorb visible light, photogenerated carriers are prone to recombination. Neither is suitable as a standalone photoactive support for the preparation of non-noble metal-based hydrogen production catalysts. Due to the band structure matching of the two materials, the heterojunction prepared by combining g-C3N4 and WO3 is beneficial for promoting the separation and transfer of photogenerated electrons and holes, thereby improving photocatalytic performance.

[0004] Currently, the main methods for preparing g-C3N4@WO3 heterojunctions include physical mixing, sol-gel, and in-situ growth. The physical mixing method first prepares g-C3N4 and WO3 separately, then mixes them thoroughly in a certain proportion using grinding or ultrasonic dispersion, and finally dries to obtain the composite material. This method is simple to operate, but the composite has poor uniformity, insufficient interfacial contact, and reduced separation and transport efficiency of photogenerated carriers. It also forms interfacial defects that trap photogenerated electrons and holes, and the material has poor stability and a reduced lifespan. The sol-gel method disperses g-C3N4 in a sol containing a WO3 precursor, and then disperses it uniformly by stirring or ultrasonic treatment. Finally, the solvent is evaporated or the sol is converted into a gel through a gelation process, followed by drying and calcination to obtain the g-C3N4@WO3 composite material. This method can precisely control the composition and structure of composite materials, but the surface of g-C3N4 lacks sufficient active functional groups, making it difficult to form effective chemical bonds with precursors or intermediates in WO3 sol. It has poor compatibility and is prone to phase separation. Similarly, it is difficult to form a tight and continuous heterojunction interface between g-C3N4 and WO3.

[0005] The in-situ growth method disperses g-C3N4 in a solution containing a WO3 precursor, and by controlling the reaction conditions, WO3 is uniformly grown on the g-C3N4 surface. Although this method can achieve close contact between the two materials and form a good interface, the reaction conditions are quite harsh, and uneven growth or the generation of by-products is very likely to occur. This will severely inhibit the separation of photogenerated carriers, reduce light absorption and utilization efficiency, and lead to a decline in the photocatalytic performance of the material. Summary of the Invention

[0006] The purpose of this invention is to provide a Z-type heterojunction composite material, its preparation method and application. In the Z-type heterojunction composite material prepared by the preparation method provided by this invention, WO3 is tightly attached to the surface of g-C3N4, and the Z-type heterojunction composite material has excellent visible light absorption capacity and high efficiency of photogenerated carrier separation.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a Z-type heterojunction composite material, comprising the following steps: (1) WCl6, hexamethylenetetramine and alcohol were mixed and crystallized, and then the resulting solid product was calcined to obtain WO3; (2) After mixing the WO3 and urea obtained in step (1), the mixture is sealed and subjected to a second calcination to obtain a Z-type heterojunction composite material; In step (2), the mass ratio of WO3 to urea is 1:(0.25~2.5).

[0008] Preferably, in step (1), the mass ratio of WCl6 to hexamethylenetetramine is 1:(0.1~0.3).

[0009] Preferably, in step (1), the mass ratio of WCl6 to the volume of alcohol is 1 g: (20~40) mL.

[0010] Preferably, the temperature of the crystallization reaction in step (1) is 140~180℃ and the time of the crystallization reaction is 16~36h.

[0011] Preferably, the temperature of the first calcination in step (1) is 400~600℃ and the time of the first calcination is 1~5h.

[0012] Preferably, the mass ratio of WO3 to urea in step (2) is 1:2.25.

[0013] Preferably, the temperature of the second calcination in step (2) is 400~600℃, and the time of the second calcination is 0.5~3h.

[0014] The present invention provides a Z-type heterojunction composite material prepared by the preparation method described above, wherein the Z-type heterojunction composite material is a g-C3N4@WO3 Z-type heterojunction; and the microstructure of the Z-type heterojunction composite material is a layered structure.

[0015] This invention provides a non-precious metal catalyst, comprising the Z-type heterojunction composite material described above and active metal nanoparticles supported on the Z-type heterojunction composite material.

[0016] Preferably, the active metal nanoparticles include one or more of nano-Co, nano-Fe, and nano-Ni.

[0017] This invention provides a method for preparing a Z-type heterojunction composite material, comprising the following steps: (1) mixing WCl6, hexamethylenetetramine, and an alcohol, and then performing a crystallization reaction and a first calcination to obtain WO3; (2) mixing the WO3 obtained in step (1) with urea and then performing a second calcination to obtain a Z-type heterojunction composite material; the mass ratio of WO3 to urea in step (2) is 1:(0.25~2.5). This invention uses WCl6 as a tungsten source and hexamethylenetetramine as a reducing agent to facilitate the formation of a well-crystallized product, obtaining a layered WO3; then mixing it with urea and calcining it, and synthesizing g-C3N4 in situ on the surface of WO3 to obtain a Z-type heterojunction composite material. The microstructure is controllable, and g-C3N4 in the Z-type heterojunction is in close contact with WO3, exhibiting excellent visible light absorption capacity and high efficiency of photogenerated carrier separation. The results of the examples show that the non-noble metal catalyst supported on the Z-type heterojunction composite material prepared in this invention has higher NH3BH3 room temperature hydrolysis dehydrogenation activity and 100% H2 selectivity, with a maximum dehydrogenation turnover rate (TOF) of 100 min. -1 Even after five cycles of use, the hydrogen production efficiency of the non-precious metal catalyst did not decrease significantly, and it was still able to maintain high catalytic activity, demonstrating excellent stability and reusability. Attached Figure Description

[0018] Figure 1 High-resolution transmission electron microscopy image of g-C3N4@WO3-0.25 prepared in Example 6; Figure 2 for Figure 1 High-resolution transmission electron microscope image of the marked portion; Figure 3 XPS images of g-C3N4@WO3-0.25 prepared in Example 6 and Co / g-C3N4@WO3-0.25 prepared in Application Example 1; Figure 4 High-resolution C 1s spectra of g-C3N4@WO3-0.25 prepared in Example 6 and g-C3N4 prepared in Comparative Example 2; Figure 5 The high-resolution N 1s spectrum of g-C3N4@WO3-0.25 prepared in Example 6 and g-C3N4 prepared in Comparative Example 2; Figure 6 The W 4f spectra of g-C3N4@WO3-0.25 prepared in Example 6 and WO3 prepared in Comparative Example 1; Figure 7 The O 1s spectra of g-C3N4@WO3-0.25 prepared in Example 6 and WO3 prepared in Comparative Example 1.

[0019] Figure 8Mott-Schottky curve of WO3 prepared for Comparative Example 1; Figure 9 Mott-Schottky curve of g-C3N4 prepared for Comparative Example 2; Figure 10 (Ahν) of WO3 prepared for Comparative Example 1 and g-C3N4 prepared for Comparative Example 2. 1 / 2 - Photon energy relationship curve; Figure 11 A schematic diagram of the band structure of g-C3N4@WO3 obtained from the conduction band potential and band gap of g-C3N4 and WO3; Figure 12 Graphs showing the change in hydrogen volume over time obtained by the methods provided in Application Examples 1-7 and Comparative Application Examples 1-3; Figure 13 TOF plots obtained by applying the methods provided in Examples 1-7 and comparing them with those provided in Examples 1-3; Figure 14 Cyclic stability curves of the non-noble metal catalyst (Co / g-C3N4@WO3-2.25) prepared in Example 6; Figure 15 High-resolution transmission electron microscopy image of the non-noble metal catalyst (Co / g-C3N4@WO3-2.25) prepared in Example 6; Figure 16 EDS plot of the non-noble metal catalyst (Co / g-C3N4@WO3-2.25) prepared in Example 6. Detailed Implementation

[0020] This invention provides a method for preparing a Z-type heterojunction composite material, comprising the following steps: (1) WCl6, hexamethylenetetramine and alcohol were mixed and subjected to crystallization reaction and first calcination in sequence to obtain WO3; (2) After mixing the WO3 and urea obtained in step (1), the mixture is sealed and subjected to a second calcination to obtain a Z-type heterojunction composite material; In step (2), the mass ratio of WO3 to urea is 1:(0.25~2.5).

[0021] In this invention, unless otherwise specified, all raw materials used are commercially available products well known to those skilled in the art or products prepared by known methods.

[0022] In this invention, WCl6, hexamethylenetetramine and alcohol are mixed and then subjected to a crystallization reaction and a first calcination to obtain WO3.

[0023] In this invention, the alcohol is preferably n-butanol, methanol, ethanol, n-propanol, or benzyl alcohol, more preferably n-butanol; the mass ratio of WCl6 to hexamethylenetetramine is preferably 1:(0.1~0.3); the mass ratio of WCl6 to the volume ratio of the alcohol is preferably 1g:(20~40)mL. In this invention, WCl6, as a tungsten source, first reacts with the alcohol, where chlorine atoms are gradually replaced by alkoxy groups to generate soluble tungsten alkoxy chlorides. This process avoids the uneven precipitation caused by violent hydrolysis in direct hydrothermal systems. Hexamethylenetetramine, as a reducing agent, can selectively adsorb onto certain specific crystal faces of WO3 crystal nuclei, changing the surface energy of these crystal faces and forcing the crystals to preferentially grow along the uncovered direction, thereby forming a nanosheet morphology. On the other hand, the hexamethylenetetramine molecules adsorbed on the surface of the nanoparticles form a physical barrier, utilizing the steric hindrance effect generated by its molecular size to prevent adjacent nanosheets from precipitating. During growth, the crystal nuclei move closer together and adhere to each other, thus reducing agglomeration. At the same time, hexamethylenetetramine can decompose and slowly release alkali (NH3) at temperatures above 120°C, thereby regulating the pH. Since the alcohol contains only trace amounts of water or produces a small amount of water through alcoholysis, the release of NH3 is slow and controllable. This slow decomposition characteristic can control the release rate and supersaturation of tungstate ions in the solution, allowing the crystal nuclei to grow under milder conditions and avoiding severe agglomeration caused by explosive nucleation, which is conducive to the formation of well-crystallized products. By controlling the ratio of WCl6, hexamethylenetetramine, and alcohol, it is beneficial to ensure that the raw materials react fully and reduce waste of raw materials.

[0024] In one embodiment of the present invention, the mass ratio of WCl6 to hexamethylenetetramine can be 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19, 1:0.2, 1:0.21, 1:0.22, 1:0.23, 1:0.24, 1:0.25, 1:0.26, 1:0.27, 1:0.28, or 1:0.29; the WCl6... The mass ratio of Cl6 to the volume of alcohol can be 1g:21mL, 1g:22mL, 1g:23mL, 1g:24mL, 1g:25mL, 1g:26mL, 1g:27mL, 1g:28mL, 1g:29mL, 1g:30mL, 1g:31mL, 1g:32mL, 1g:33mL, 1g:34mL, 1g:35mL, 1g:36mL, 1g:37mL, 1g:38mL, or 1g:39mL.

[0025] This invention does not impose any particular limitation on the specific method of mixing WCl6, hexamethylenetetramine, and the alcohol; any conventional method that ensures uniform mixing is acceptable. As one embodiment of this invention, the mixing method may involve adding WCl6 and hexamethylenetetramine to the alcohol and stirring to dissolve for 10-30 minutes.

[0026] In this invention, the preferred temperature for the crystallization reaction is 140-180°C; the preferred time for the crystallization reaction is 16-36 hours; and the preferred method for the crystallization reaction is to carry out the reaction in a reactor lined with polytetrafluoroethylene. As one embodiment of this invention, the temperature for the crystallization reaction can be 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, or 175°C; and the preferred time for the crystallization reaction can be 18 hours, 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours, or 34 hours. In this invention, WCl6, as a tungsten source, first reacts with an alcohol, where chlorine atoms are gradually replaced by alkoxy groups to generate a soluble mixture of tungsten alkoxy chlorides. Hexamethylenetetramine, as a reducing agent, decomposes at temperatures above 120°C, slowly releasing alkali (NH3), thereby regulating pH, accelerating the conversion process of the tungsten source, and promoting the hydrolysis and condensation of tungsten. The tungsten source gradually hydrolyzes and condenses to form an amorphous tungsten-oxygen-hydrogen network. After washing to remove soluble substances, an amorphous precursor powder is obtained. By controlling the parameters of the crystallization reaction, the reaction efficiency can be further improved.

[0027] After the crystallization reaction is completed, the present invention preferably further includes washing and drying the crystallization product sequentially. In this invention, the washing is preferably performed using high-purity water and anhydrous ethanol followed by filtration. The present invention does not have a specific limitation on the number of washing cycles, as long as impurities in the product are completely removed. The present invention does not have a specific limitation on the drying temperature and time, as long as drying to constant weight is achieved. Through washing and drying, the present invention can remove impurities from the product to obtain high-purity WO3.

[0028] In this invention, the preferred temperature for the first calcination is 400-600℃; the preferred calcination time is 1-5 hours; the preferred atmosphere for the first calcination is air; the preferred cooling method after the first calcination is natural cooling or furnace cooling; and the first calcination is preferably carried out in a muffle furnace. As one embodiment of this invention, the temperature for the first calcination can be 420℃, 450℃, 500℃, 520℃, or 550℃; and the preferred calcination time can be 2 hours, 3 hours, or 4 hours. This invention transforms the precursor powder obtained from the crystallization reaction into tungsten oxide through the first calcination; by controlling the parameters of the first calcination, the conversion efficiency of the precursor powder can be improved.

[0029] After obtaining WO3, the present invention mixes the WO3 with urea, seals the mixture, and performs a second calcination to obtain a Z-type heterojunction composite material.

[0030] In this invention, the mass ratio of WO3 to urea is 1:(0.25~2.5). As one embodiment of this invention, the mass ratio of WO3 to urea is 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.75, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.25, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.75, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.25, 1:2.3, or 1:2.4. In this invention, urea is used as a precursor to generate g-C3N4; by controlling the ratio of WO3 to urea, the interaction between g-C3N4 and WO3 in the g-C3N4@WO3Z heterojunction can be regulated.

[0031] The present invention does not impose any particular limitation on the mixing method of WO3 and urea; any method known to those skilled in the art that can ensure uniform mixing is acceptable. As one embodiment of the present invention, the mixing method of WO3 and urea may be grinding.

[0032] This invention does not impose any special limitations on the specific operation of the capping and sealing; conventional sealing methods are sufficient. The second calcination performed after capping and sealing helps to slow down the volatilization of the urea precursor, promotes the condensation reaction, and increases the yield of g-C3N4.

[0033] In this invention, the preferred temperature for the second calcination is 400-600℃; the preferred calcination time is 0.5-3 hours; the preferred cooling method after the second calcination is natural cooling or furnace cooling; and the second calcination is preferably carried out in a muffle furnace. As one embodiment of this invention, the temperature for the second calcination can be 420℃, 450℃, 500℃, 520℃, or 550℃; and the preferred calcination time can be 1 hour, 1.5 hours, 2 hours, or 2.5 hours. This invention does not have a specific limitation on the atmosphere for the second calcination; the raw material is placed in the muffle furnace and sealed to carry out the second calcination. Through the second calcination, this invention allows urea to be transformed into g-C3N4, which combines with WO3 and forms a good heterojunction interface. This close contact enables efficient electron transfer and separation between the two. Under illumination, photogenerated electrons generated by g-C3N4 can rapidly transfer to the WO3 surface, while photogenerated holes generated by WO3 remain on the g-C3N4 surface. This Z-shaped heterojunction significantly improves the separation efficiency of photogenerated carriers and reduces electron-hole recombination, thereby significantly enhancing the photocatalytic performance of the material. Furthermore, this structure endows the material with a wider light absorption range and higher stability, and non-noble metal catalysts prepared using it as a support exhibit excellent catalytic activity in the photocatalytic decomposition of NH3BH3 to produce hydrogen.

[0034] This invention uses WCl6 as a tungsten source and hexamethylenetetramine as a reducing agent to facilitate the formation of a well-crystallized product, resulting in a layered WO3. Then, it is mixed with urea and calcined to synthesize g-C3N4 in situ on the surface of WO3, thus obtaining a Z-type heterojunction composite material with controllable microstructure. In the Z-type heterojunction, g-C3N4 and WO3 are in close contact, exhibiting excellent visible light absorption and high efficiency in photogenerated carrier separation.

[0035] The present invention also provides a Z-type heterojunction composite material prepared by the preparation method described above; the Z-type heterojunction composite material is a g-C3N4@WO3 Z-type heterojunction; the microstructure of the Z-type heterojunction composite material is a layered structure.

[0036] In this invention, the Z-type heterojunction composite material is preferably composed of g-C3N4 and WO3 nanosheets attached to the surface of the g-C3N4; the mass ratio of WO3 to g-C3N4 in the Z-type heterojunction composite material is preferably 1:(0.015~0.375). As one embodiment, the mass ratio of WO3 to g-C3N4 in the Z-type heterojunction composite material can be 1:0.05, 1:0.075, 1:0.1, 1:0.125, 1:0.15, 1:0.175, 1:0.2, 1:0.225, 1:0.25, 1:0.275, 1:0.3, 1:0.325, or 1:0.35.

[0037] The Z-type heterojunction composite material provided by this invention forms a heterojunction by close contact between g-C3N4 and WO3, exhibiting excellent visible light absorption capability and high efficiency in photogenerated carrier separation.

[0038] The present invention also provides a non-precious metal catalyst, comprising the Z-type heterojunction composite material described in the above technical solution and active metal nanoparticles supported on the Z-type heterojunction composite material.

[0039] In this invention, the active metal nanoparticles preferably include one or more of nano-Co, nano-Fe, and nano-Ni; the mass ratio of the active metal nanoparticles to the Z-type heterojunction composite material is preferably (0.5~4):16. As one embodiment of this invention, the mass ratio of the active metal nanoparticles to the Z-type heterojunction composite material can be 0.6:16, 0.8:16, 1:16, 1.2:16, 1.4:16, 1.5:16, 1.6:16, 1.8:16, 2:16, 2.5:16, 3:16, 3.5:16, or 3.8:16. This invention, by loading highly active metal nanoparticles onto the Z-type heterojunction composite material, can further improve the catalytic performance of the composite material.

[0040] In this invention, the preferred method for preparing the non-precious metal catalyst includes: mixing a non-precious metal precursor, a Z-type heterojunction composite material, a solvent, and a reducing agent to carry out an in-situ reduction reaction to obtain the non-precious metal catalyst.

[0041] In this invention, the non-precious metal precursor is preferably one or more of Co-based, Fe-based, and Ni-based precursors; the Co-based precursor is preferably cobalt chloride hexahydrate (CoCl2·6H2O), cobalt sulfate hexahydrate (CoSO4·6H2O), or cobalt acetate tetrahydrate ((CH3COO)2Co·4H2O); the Fe-based precursor is preferably ferric chloride hexahydrate (FeCl3·6H2O), ferrous chloride tetrahydrate (FeCl2·4H2O), ferrous sulfate (FeSO4·7H2O), or ferric nitrate (Fe(NO3)3·9H2O); the Ni-based precursor is preferably nickel sulfate hexahydrate (NiSO4·6H2O), nickel nitrate hexahydrate (Ni(NO3)2·6H2O), nickel chloride hexahydrate (NiCl2·6H2O), or nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O). By employing the aforementioned non-precious metal precursor, this invention allows for the introduction of desired active metal nanoparticles into Z-type heterojunction composite materials as needed.

[0042] In this invention, the preferred mass ratio of the Z-type heterojunction composite material to the non-precious metal precursor is (10~25):8. As one embodiment of this invention, the mass ratio of the Z-type heterojunction composite material to the non-precious metal precursor can be 11:8, 12:8, 13:8, 14:8, 15:8, 16:8, 17:8, 18:8, 19:8, 20:8, 21:8, 22:8, 23:8, or 24:8.

[0043] In this invention, the solvent is preferably water, more preferably distilled water. In this invention, the mass ratio of the Z-shaped heterojunction composite material to the volume ratio of water is preferably (10~25) mg:(0.5~5) mL. In one embodiment of the present invention, the mass ratio of the Z-type heterojunction composite material to the volume ratio of water can be 11 mg: (1~2.5) mL, 12 mg: (1~2.5) mL, 13 mg: (1~2.5) mL, 14 mg: (1~2.5) mL, 15 mg: (1~2.5) mL, 16 mg: (1~2.5) mL, 17 mg: (1~2.5) mL, 18 mg: (1~2.5) mL, 19 mg: (1~2.5) mL, 20 mg: (1~2.5) mL, 21 mg: (1~2.5) mL, 22 mg: (1~2.5) mL, 23 mg: (1~2.5) mL, or 24 mg: (1~2.5) mL.

[0044] In this invention, the reducing agent is preferably sodium borohydride (NaBH4) or potassium borohydride (KBH4). In this invention, the mass ratio of the Z-type heterojunction composite material to the reducing agent is preferably (10~25):2.6. As one embodiment of this invention, the mass ratio of the Z-type heterojunction composite material to the reducing agent can be 11:2.6, 12:2.6, 13:2.6, 14:2.6, 15:2.6, 16:2.6, 17:2.6, 18:2.6, 19:2.6, 20:2.6, 21:2.6, 22:2.6, 23:2.6, or 24:2.6.

[0045] In this invention, the preferred method for mixing the non-precious metal precursor, Z-type heterojunction composite material, solvent, and reducing agent is to stir and mix the non-precious metal precursor, Z-type heterojunction composite material, and solvent, then turn on the xenon lamp light source, and then add the reducing agent. This invention does not impose specific limitations on the stirring rate and stirring time, as long as the non-precious metal precursor, Z-type heterojunction composite material, and solvent are mixed uniformly. As one embodiment of this invention, the stirring time can be 0.5~2 hours, or 1~1.5 hours.

[0046] In this invention, the in-situ reduction reaction is preferably carried out under illumination; the light source is preferably a xenon lamp, more preferably a xenon lamp with a cutoff filter; the light intensity is preferably 400~600mW / cm². 2 More preferably, it is 450~550mW / cm 2 Further optimized to 500mW / cm 2 The spectral range of the illumination is preferably 420~780nm; the temperature of the in-situ reduction reaction is preferably room temperature; and the time of the in-situ reduction reaction is preferably 1.5~2.0min.

[0047] In this invention, a non-noble metal precursor forms metal elemental nanoparticles under the action of a reducing agent. After the active metal nanoparticles are loaded in situ, the resulting electron-rich active centers are beneficial to optimizing the electronic structure of the catalyst. The active metal nanoparticles coordinate with the nitrogen atoms of g-C3N4 and form a strong metal-support interaction with the WO3 surface. g-C3N4 provides electron transport channels, WO3 provides oxygen vacancies and acid sites, and the active metal nanoparticles provide catalytic active centers.

[0048] In one embodiment of the present invention, the application of the non-precious metal catalyst in hydrolysis for hydrogen production preferably includes: mixing the non-precious metal catalyst, water, and NH3BH3 and then performing hydrolysis to produce hydrogen gas.

[0049] In another technical solution of the present invention, the application of the non-precious metal catalyst in hydrolysis for hydrogen production preferably includes: mixing a non-precious metal precursor, a Z-type heterojunction composite material and a solvent, then turning on a xenon lamp light source, and then adding a reducing agent and an aqueous solution of NH3BH3 to simultaneously carry out an in-situ reduction reaction and hydrolysis for hydrogen production, thereby obtaining a non-precious metal catalyst and hydrogen.

[0050] In this invention, the preferred mass ratio of the Z-type heterojunction composite material to NH3BH3 in the non-precious metal catalyst is (10~25):52.8; the preferred mass ratio of NH3BH3 to water is 52.8 mg:(1~2) mL, more preferably 52.8 mg:1.5 mL. As one embodiment of this invention, the mass ratio of the Z-type heterojunction composite material to NH3BH3 can be 11:52.8, 12:52.8, 13:52.8, 14:52.8, 15:52.8, 16:52.8, 17:52.8, 18:52.8, 19:52.8, 20:52.8, 21:52.8, 22:52.8, 23:52.8, or 24:52.8.

[0051] In this invention, the temperature for hydrogen production via hydrolysis is preferably room temperature, more preferably 20-30°C, and even more preferably 24-25°C. This invention does not impose a specific time limit on the hydrogen production via hydrolysis, as long as no hydrogen gas is produced.

[0052] The non-precious metal catalyst prepared by this invention is used for hydrogen production by NH3BH3 water splitting. The required temperature is room temperature, the reaction conditions are mild, and it can be used in fuel cells. This not only provides new ideas and methods for the application of non-precious metal catalysts in the field of photocatalytic hydrogen production, but also lays a solid foundation for the practical application of NH3BH3 water splitting hydrogen production in fuel cells, and is expected to promote the further development of green and sustainable hydrogen energy production.

[0053] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] Example 1 A method for preparing a Z-type heterojunction composite material is as follows: (1) 1g WCl6 and 0.17g hexamethylenetetramine were added to 30mL n-butanol and dissolved. After stirring for 20min, the mixture was transferred to a 50mL polytetrafluoroethylene liner and crystallized at 160℃ for 24h. After washing with high-purity water and anhydrous ethanol, the mixture was filtered, dried at 70℃, and then calcined at 500℃ for 2h in a muffle furnace to obtain WO3. (2) The WO3 and urea obtained in step (1) are ground and mixed evenly at a mass ratio of 1:0.25. The mixture is then calcined for 1 hour at 500°C in a muffle furnace with the furnace covered and sealed. The mixture is then cooled to room temperature to obtain a Z-type heterojunction composite material, denoted as g-C3N4@WO3-0.25.

[0055] Example 2 The mass ratio of WO3 to urea was adjusted to 1:1.25, and other conditions were the same as in Example 1. The resulting Z-type heterojunction composite material was denoted as g-C3N4@WO3-1.25.

[0056] Example 3 The mass ratio of WO3 to urea was adjusted to 1:1.5, and other conditions were the same as in Example 1. The resulting Z-type heterojunction composite material was denoted as g-C3N4@WO3-1.5.

[0057] Example 4 The mass ratio of WO3 to urea was adjusted to 1:1.75, and other conditions were the same as in Example 1. The resulting Z-type heterojunction composite material was denoted as g-C3N4@WO3-1.75.

[0058] Example 5 The mass ratio of WO3 to urea was adjusted to 1:2, and other conditions were the same as in Example 1. The resulting Z-type heterojunction composite material was denoted as g-C3N4@WO3-2.

[0059] Example 6 The mass ratio of WO3 to urea was adjusted to 1:2.25, and other conditions were the same as in Example 1. The resulting Z-type heterojunction composite material was denoted as g-C3N4@WO3-2.25.

[0060] Example 7 The mass ratio of WO3 to urea was adjusted to 1:2.5, and other conditions were the same as in Example 1. The resulting Z-type heterojunction composite material was denoted as g-C3N4@WO3-2.5.

[0061] Comparative Example 1 1 g of WCl6 and 0.17 g of hexamethylenetetramine were dissolved in 30 mL of n-butanol and stirred for 20 min. The mixture was then transferred to a 50 mL polytetrafluoroethylene liner and crystallized at 160 °C for 24 h. After washing with high-purity water and anhydrous ethanol, the mixture was filtered, dried at 70 °C, and calcined in a muffle furnace at 500 °C for 2 h to obtain WO3.

[0062] Comparative Example 2 After grinding the urea evenly, it was placed in a muffle furnace and calcined at 500℃ for 1 hour. The urea was then cooled to room temperature with the furnace to obtain g-C3N4.

[0063] Comparative Example 3 A method for preparing a Z-type heterojunction composite material (physical mixing method) is as follows: (1) 1g WCl6 and 0.17g hexamethylenetetramine were added to 30mL n-butanol and dissolved. After stirring for 20min, the mixture was transferred to a 50mL polytetrafluoroethylene liner and crystallized at 160℃ for 24h. After washing with high-purity water and anhydrous ethanol, the mixture was filtered, dried at 70℃, and then calcined at 500℃ for 2h in a muffle furnace to obtain WO3. (2) After grinding the urea evenly, it was placed in a muffle furnace and calcined at 500℃ for 1 hour. After cooling to room temperature with the furnace, g-C3N4 was obtained. (3) Mix the WO3 obtained in step (1) and the g-C3N4 obtained in step (2) in a mortar and grind for 10 minutes to ensure thorough mixing. Then dry the mixture to obtain a Z-type heterojunction composite material. The mass ratio of WO3 to urea is 1:2.25.

[0064] Application Example 1 The method for preparing a non-noble metal catalyst for simultaneous hydrolysis to produce hydrogen using g-C3N4@WO3-0.25 prepared in Example 1 is as follows: Cobalt chloride hexahydrate (8 mg), g-C3N4@WO3-0.25 (16 mg), and distilled water (1 mL) were mixed and stirred for 1 hour. Then, a xenon lamp with a cutoff filter was turned on, and the light intensity was controlled at 500 mW / cm². 2 The spectral range of the illumination is 420~780nm. Then, a mixture of sodium borohydride (2.6mg) and NH3BH3 (52.8mg) (the solvent of the mixture is 1.5mL of distilled water) is added dropwise to carry out an in-situ reduction reaction, and a non-precious metal catalyst (denoted as Co / g-C3N4@WO3-0.25) and hydrogen are obtained.

[0065] Application Example 2 Replacing g-C3N4@WO3-0.25 with g-C3N4@WO3-1.25 prepared in Example 2, and using the same conditions as in Application Example 1, yielded a non-noble metal catalyst (denoted as Co / g-C3N4@WO3-1.25) and hydrogen.

[0066] Application Example 3 Replacing g-C3N4@WO3-0.25 with g-C3N4@WO3-1.5 prepared in Example 3, and using the same conditions as in Application Example 1, yielded a non-precious metal catalyst (denoted as Co / g-C3N4@WO3-1.5) and hydrogen.

[0067] Application Example 4 Replacing g-C3N4@WO3-0.25 with g-C3N4@WO3-1.75 prepared in Example 4, and using the same conditions as in Application Example 1, yielded a non-noble metal catalyst (denoted as Co / g-C3N4@WO3-1.75) and hydrogen.

[0068] Application Example 5 Replacing g-C3N4@WO3-0.25 with g-C3N4@WO3-2 prepared in Example 5, and using the same conditions as in Application Example 1, yielded a non-precious metal catalyst (denoted as Co / g-C3N4@WO3-2) and hydrogen.

[0069] Application Example 6 Replacing g-C3N4@WO3-0.25 with g-C3N4@WO3-2.25 prepared in Example 6, and using the same conditions as in Application Example 1, yielded a non-precious metal catalyst (denoted as Co / g-C3N4@WO3-2.25) and hydrogen.

[0070] Application Example 7 Replacing g-C3N4@WO3-0.25 with g-C3N4@WO3-2.5 prepared in Example 7, and using the same conditions as in Application Example 1, yielded a non-precious metal catalyst (denoted as Co / g-C3N4@WO3-2.5) and hydrogen.

[0071] Comparative Application Example 1 By replacing g-C3N4@WO3-0.25 with WO3 prepared in Comparative Example 1, and keeping other conditions the same as in Application Example 1, a non-noble metal catalyst (denoted as Co / WO3) and hydrogen were obtained.

[0072] Comparative Application Example 2 By replacing g-C3N4@WO3-0.25 with g-C3N4 prepared in Comparative Example 2, and keeping other conditions the same as in Application Example 1, a non-noble metal catalyst (denoted as Co / g-C3N4) and hydrogen were obtained.

[0073] Comparative Application Example 3 By replacing g-C3N4@WO3-0.25 with g-C3N4@WO3-2.25 prepared in Comparative Example 3, and keeping other conditions the same as in Application Example 1, a non-noble metal catalyst (denoted as Co / g-C3N4@WO3-2.25-w) and hydrogen were obtained.

[0074] The g-C3N4@WO3-2.25 prepared in Example 6 was observed using a high-resolution transmission electron microscope. The resulting high-resolution transmission electron microscope image is shown below. Figure 1 As shown; high-resolution transmission electron microscopy was used to examine... Figure 1 The marked portion was magnified for observation, and the resulting high-resolution transmission electron microscope image is shown below. Figure 2 As shown. By Figure 1 It can be seen that the g-C3N4@WO3-2.25 prepared in this invention is a nanoscale heterojunction, composed of... Figure 2 It can be seen that in g-C3N4@WO3-2.25, WO3 is tightly adhered to the surface of g-C3N4.

[0075] The g-C3N4@WO3-2.25 prepared in Example 6 and the Co / g-C3N4@WO3-2.25 prepared in Example 6 were tested using X-ray photoelectron spectroscopy, and the obtained XPS spectra are shown below. Figure 3 As shown. By Figure 3 It can be seen that C, N, W, and O elements were detected in the XPS full spectrum of g-C3N4@WO3-2.25, indicating that the prepared material contains the above elements, suggesting that a g-C3N4@WO3 heterojunction composite material has been formed. This result is consistent with high-resolution transmission electron microscopy (HRTEM)... Figure 1 and Figure 2 The characterization results are consistent.

[0076] X-ray photoelectron spectroscopy was used to test the photoelectron spectra of g-C3N4@WO3-2.25 prepared in Example 6, WO3 prepared in Comparative Example 1, and g-C3N4 prepared in Comparative Example 2. The obtained photoelectron spectra are shown below. Figures 4-7 As shown; where, Figure 4 The high-resolution C 1s spectrum of g-C3N4@WO3-2.25 prepared in Example 6 and g-C3N4 prepared in Comparative Example 2; Figure 5 The high-resolution N 1s spectrum of g-C3N4@WO3-2.25 prepared in Example 6 and g-C3N4 prepared in Comparative Example 2; Figure 6 The W 4f spectra of g-C3N4@WO3-2.25 prepared in Example 6 and WO3 prepared in Comparative Example 1; Figure 7 The O1s spectra of g-C3N4@WO3-2.25 prepared in Example 6 and WO3 prepared in Comparative Example 1 are shown.

[0077] Depend on Figure 4 As can be seen, the high-resolution C 1s spectrum of g-C3N4 prepared in Comparative Example 2 can be decomposed into three characteristic peaks, located at 284.8 eV, 286.3 eV, and 288.1 eV, respectively. The peak at 284.8 eV is attributed to the carbon atoms in the C / C bonds of the contaminating carbon, the peak at 286.3 eV to the carbon atoms in the CO bonds, and the peak at 288.1 eV to the sp(NC=N) bonds in the g-C3N4 layer. 2 Hybridized carbon atoms. (By...) Figure 5 It can be seen that the N 1s spectrum of g-C3N4 prepared in Comparative Example 2 can be decomposed into four characteristic peaks, located at 398.5 eV, 399.8 eV, 400.9 eV, and 404.3 eV, respectively. The peak at 398.5 eV is attributed to the spc in C=NC. 2 The hybrid nitrogen atom shows a peak at 399.8 eV attributed to a tricoordinate N-(C)3 group, a peak at 400.9 eV attributed to a surface-based -NH2 group, and a peak at 404.3 eV attributed to the π-electron excitation peak in the CN heterocyclic conjugated structure. Compared to pure g-C3N4, the binding energies of C 1s and N 1s in g-C3N4@WO3-2.25 prepared in Example 6 are shifted towards higher binding energies, indicating electron transfer from g-C3N4 to WO3.

[0078] Depend on Figure 6 It can be seen that the W 4f spectrum of WO3 prepared in Comparative Example 1 can be decomposed into two characteristic peaks with binding energies of 35.5 eV and 37.6 eV, respectively, corresponding to W 6+ W 4f 7 / 2 and W 4f 5 / 2 In addition, a small peak exists at approximately 41.2 eV, which is attributed to W 5p.3 / 2 .Depend on Figure 7 It can be seen that the O 1s spectrum of WO3 prepared in Comparative Example 1 has two characteristic peaks, located at 530.2 eV and 531.0 eV, respectively, which belong to lattice oxygen and physically adsorbed oxygen. Compared with WO3, the W 4f peak and O 1s peak of g-C3N4@WO3-2.25 prepared in Example 6 both show negative shifts, further indicating that electrons are transferred from g-C3N4 to WO3.

[0079] Depend on Figures 4-7 Analysis shows that a heterojunction is formed between g-C3N4 and WO3 in g-C3N4@WO3-2.25 prepared in Example 6, and the heterojunction has a strong built-in electric field.

[0080] The WO3 prepared in Comparative Example 1 and the g-C3N4 prepared in Comparative Example 2 were detected using an electrochemical workstation, with capacitance C. -2 The Mott-Schottky curves obtained by plotting the applied potential V are as follows: Figure 8 and Figure 9 As shown. (Through) Figure 8 and Figure 9 The conduction band potential of WO3 was measured to be -0.53V (vs. NHE) and that of g-C3N4 was -0.45V (vs. NHE) using the Mott-Schottky curve.

[0081] (Ahν) of WO3 prepared in Comparative Example 1 and g-C3N4 prepared in Comparative Example 2 1 / 2 - Photon energy relationship curve as shown Figure 10 As shown. According to Figure 10 The band gaps of g-C3N4 and WO3 were calculated using the absorption versus square root of photon energy curves. The results showed that the band gaps of g-C3N4 and WO3 were 2.67 eV and 2.59 eV, respectively.

[0082] according to Figures 8-10 The conduction band potential and band gap of g-C3N4 and WO3 were obtained. The schematic diagram of the band structure of g-C3N4@WO3 is shown in the figure. Figure 11 As shown. By Figure 11 It can be seen that Z-type heterojunctions are formed in g-C3N4@WO3-0.25.

[0083] The graphs of hydrogen volume change over time and the corresponding TOF values ​​obtained by applying the methods provided in Examples 1-7 and Comparative Examples 1-2 are shown below. Figure 12 and Figure 13 As shown. By Figure 12 and Figure 13It can be seen that, compared with Co / g-C3N4 and Co / WO3 catalysts, the non-noble metal catalysts prepared in Examples 1-7 have higher NH3BH3 room temperature hydrolysis dehydrogenation activity and TOF value. Moreover, the non-noble metal catalyst in Example 6 has the fastest NH3BH3 hydrogen production rate and the highest TOF value. This indicates that the heterojunction of g-C3N4@WO3-2.25 prepared in Example 6 significantly reduces the recombination rate of photogenerated carriers after absorbing visible light, causing more electrons to transfer to Co nanoparticles. The number of active sites of the catalyst increases, which is beneficial to the separation and transfer of photogenerated electrons and holes.

[0084] The cyclic stability of the non-precious metal catalyst (Co / g-C3N4@WO3-2.25) prepared in Example 6 was tested. The test method was as follows: 16 mg of the washed and dried non-precious metal catalyst and 1 mL of distilled water were stirred and mixed for 1 h. Then, a xenon lamp was turned on, and NH3BH3 solution (52.8 mg of NH3BH3 and 1.5 mL of water) was slowly added to catalytically dehydrogenate hydrogen gas. Hydrogen gas was obtained. The process was stopped when 140 mL of hydrogen gas was obtained each time, and the above operation was repeated five times. The time required for each operation was recorded. The results are shown below. Figure 14 As shown. By Figure 14 It can be seen that after five cycles of reaction, the hydrogen release time of the non-precious metal catalyst prepared in Example 6 did not increase significantly, indicating that the non-precious metal catalyst has good cycle stability.

[0085] The non-noble metal catalyst (Co / g-C3N4@WO3-2.25) prepared in accordance with Example 6 was subjected to high-resolution transmission electron microscopy (HRTEM) analysis. The HRTEM image obtained is shown below. Figure 15 As shown, Figure 15 In the diagram, a is a high-resolution transmission electron microscope (TEM) image, b is a magnified TEM image of the marked portion in a, and c shows the distribution of N, W, Co, O, and C elements in the non-noble metal catalyst. Energy dispersive X-ray spectroscopy (EDS) was performed on the non-noble metal catalyst (Co / g-C3N4@WO3-2.25) prepared in Example 6, and the resulting EDS image is shown below. Figure 16 As shown. By Figure 15 and Figure 16 It can be seen that in Co / g-C3N4@WO3-2.25, g-C3N4 exhibits a two-dimensional sheet structure with porous and amorphous properties. The g-C3N4@WO3 composite material not only retains the morphology of WO3 nanosheets, but also shows a close contact between g-C3N4 and WO3, confirming the formation of a heterojunction. Energy-dispersive X-ray spectroscopy (EDS) and elemental mapping also indicate that g-C3N4 is uniformly distributed on the WO3 surface, forming a "face-to-face" g-C3N4@WO3 heterojunction. Furthermore, Figure 15 In (b), clear lattice spacings of 0.34 nm and 0.22 nm were observed on the (021) and (422) crystal planes of WO3 and Co, respectively, which further indicates that Co was successfully loaded on the g-C3N4@WO3 surface.

[0086] In summary, the selectivity and activity of the non-noble metal catalyst prepared in this invention for photocatalytic hydrogen production from the hydrolysis of NH3BH3 first increase and then decrease with increasing g-C3N4 content in g-C3N4@WO3. When the g-C3N4 content is very low, both the selectivity and activity of the catalyst are relatively low. This is because the insufficient support leads to an excessively high loading of active metal nanoparticles, which cannot be dispersed, resulting in poor catalytic performance. When the g-C3N4 content is very low, the synergistic effect between it and WO3 is not obvious, and the separation efficiency of photogenerated carriers is low, leading to poor catalyst activity and selectivity. With the increase of g-C3N4 content, the interfacial contact between the two increases, forming more heterojunctions. This is beneficial for the separation and transfer of photogenerated electrons and holes, thereby improving the photocatalytic performance of the catalyst and significantly enhancing the selectivity and activity of hydrogen production from the hydrolysis of NH3BH3. However, when the g-C3N4 content continues to increase to a certain extent, excessive g-C3N4 will cover some of the active sites of WO3, hindering the contact between reactants and catalysts. At the same time, it will increase the recombination probability of photogenerated carriers, resulting in a decrease in selectivity and activity.

[0087] This invention significantly improves the photocatalytic performance of a catalyst by controlling the recombination rate of photogenerated carriers in the synthesized g-C3N4@WO3Z heterojunction composite material, thereby regulating the content of g-C3N4 in the support. When the mass ratio of urea to WO3 is 2.25:1, the recombination rate of photogenerated carriers decreases significantly, and the number of active sites on the catalyst increases, which is beneficial for the separation and transfer of photogenerated electrons and holes. This significantly improves the hydrogen production efficiency of NH3BH3 hydrolysis, exhibiting high room-temperature hydrolysis hydrogenation activity and 100% H2 selectivity, with a maximum dehydrogenation turnover frequency (TOF) of 100 min. -1 After five cycles of use, the catalyst did not show a significant decrease in hydrogen production efficiency and maintained high catalytic activity, demonstrating excellent stability and reusability. This has strongly promoted the practical application of NH3BH3 as a high-efficiency hydrogen supply source for fuel cells.

[0088] This invention presents a non-precious metal catalyst prepared via a simple, green, and low-cost in-situ reduction-supported method. The non-precious metal catalyst requires room temperature for hydrogen production via NH3BH3 water splitting and can be used in fuel cells. This invention not only provides new ideas and methods for the application of non-precious metal catalysts in photocatalytic hydrogen production but also lays a solid foundation for the practical application of NH3BH3 water splitting in fuel cells, and is expected to further promote the development of green and sustainable hydrogen energy production.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a Z-type heterojunction composite material, characterized in that, Includes the following steps: (1) WCl6, hexamethylenetetramine and alcohol were mixed and crystallized, and then the resulting solid product was calcined to obtain WO3; (2) After mixing the WO3 and urea obtained in step (1), the mixture is sealed and subjected to a second calcination to obtain a Z-type heterojunction composite material; In step (2), the mass ratio of WO3 to urea is 1:(0.25~2.5).

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of WCl6 to hexamethylenetetramine is 1:(0.1~0.3).

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the mass ratio of WCl6 to the volume of alcohol is 1 g: (20~40) mL.

4. The preparation method according to claim 1, characterized in that, The temperature of the crystallization reaction in step (1) is 140~180℃, and the time of the crystallization reaction is 16~36h.

5. The preparation method according to claim 1, characterized in that, In step (1), the temperature of the first calcination is 400~600℃ and the time of the first calcination is 1~5h.

6. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of WO3 to urea is 1:2.

25.

7. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the second calcination is 400~600℃ and the time of the second calcination is 0.5~3h.

8. The Z-shaped heterojunction composite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The Z-type heterojunction composite material is a g-C3N4@WO3 Z-type heterojunction; the microstructure of the Z-type heterojunction composite material is a layered structure.

9. A non-precious metal catalyst, characterized in that, It includes the Z-shaped heterojunction composite material as described in claim 8 and active metal nanoparticles loaded on the Z-shaped heterojunction composite material.

10. The non-precious metal catalyst according to claim 9, characterized in that, The active metal nanoparticles include one or more of nano-Co, nano-Fe, and nano-Ni.

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