Ru / WO3-MWCNTs photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a Ru / WO3-MWCNTs photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of nano photocatalysis. The photocatalyst comprises the following components in percentage by mass: 0.4%-3% of an active component Ru; ru can catalyze H2 to be dissociated into H atoms, and a hydrogen overflow starting site is provided; 5%-25% of a conductive and dispersing auxiliary agent MWCNTs; the MWCNTs can promote the separation and transmission of photo-generated charges and inhibit the agglomeration of WO3; the balance of a hydrogen storage carrier WO3; wO3 stores H atoms through bulk phase lattice gaps, and spatial separation of WO3 and O2 is achieved; the sum of the three components is 100%. The H2 dissociation activity of Ru, the charge transfer capacity of MWCNTs and the bulk phase hydrogen storage capacity of WO3 are combined for the first time, in-situ separation of H * and O2 in the photocatalytic process is achieved through hydrogen overflow-bulk phase hydrogen storage cooperation, no extra separation equipment is needed, and the hydrogen-oxygen mixing problem of traditional photocatalytic hydrogen production is solved; the preparation process is green and efficient; the obtained photocatalyst is excellent and stable in performance and wide in application prospect.

Description

Technical Field

[0001] This invention relates to a Ru / WO3-MWCNTs photocatalyst based on a hydrogen overflow mechanism for hydrogen storage and in-situ hydrogen-oxygen separation, its preparation method, and its application. It is particularly suitable for the simultaneous production, storage, and separation of hydrogen and oxygen during photocatalytic water splitting; it belongs to the field of nanophotocatalysis technology. Background Technology

[0002] With the goal of developing clean and sustainable energy, photocatalytic water splitting technology has attracted much attention from academia and industry because it can directly convert solar energy into hydrogen energy (H2). This technology uses a photocatalyst to absorb sunlight to generate high-energy charge carriers, which drive water molecules to split into H2 and O2. However, the explosion risk of the hydrogen-oxygen mixture and the high separation cost have seriously restricted the large-scale application of hydrogen energy.

[0003] Existing hydrogen-oxygen separation methods are divided into physical separation (such as low-temperature distillation and adsorption separation, which rely on the differences in the physical properties of hydrogen and oxygen) and chemical separation (which selectively fixes H2 or O2 through chemical reactions and then desorbs, resulting in higher selectivity). Li Y et al. (Li Y, Xiyu L, Guozhen Z, et al. Combining photocatalytic hydrogen generation and capsule storage in graphene based sandwich structures.[J]. Nature Communications, 2017, 8(1): 16049.DOI: 10.1038 / ncomms16049.) proposed a GO-CN-GO sandwich structure that achieves synergistic hydrogen production and storage, but does not involve in-situ separation during the photocatalytic process; Li et al. (Li H, Abdelgaid M, Paudel RJ, et al. Operando Unveiling of Hydrogen Spillover Mechanisms on Tungsten Oxide Surfaces.[J]. Journal of the American Chemical Society, 2025,DOI: 10.1021 / JACS.4C13711.) discovered that H2 forms H after the dissociation of Pt clusters. Atoms can diffuse to the WO3 surface through hydrogen spillover and trigger WO3 reduction, confirming the bulk spillover potential of WO3, but it was not separated and combined with hydrogen and oxygen, and Pt-based catalysts are expensive.

[0004] To address the aforementioned shortcomings, this invention innovatively constructs a Ru / WO3-MWCNTs ternary composite system: using low-cost Ru to replace Pt as the active site for H2 dissociation, leveraging the high conductivity of MWCNTs to promote charge transport, and relying on the bulk hydrogen spillover effect of WO3, H atoms are stored in MWCNTs in situ during photocatalytic water splitting, while O2 is generated at the oxidation end, fundamentally solving the problem of hydrogen-oxygen mixing, reducing catalyst costs, and providing key technical support for the practical application of photocatalytic hydrogen production. Summary of the Invention

[0005] The present invention aims to provide a Ru / WO3-MWCNTs photocatalyst and its preparation method. The preparation method is simple, economical and environmentally friendly, and is especially suitable for photocatalytic water splitting. It can also efficiently utilize solar energy and simultaneously complete photocatalytic water splitting, hydrogen storage and hydrogen-oxygen separation.

[0006] The core innovation of this invention lies in clarifying the synergistic mechanism of "photocatalytic hydrogen production - hydrogen overflow - bulk hydrogen storage - in-situ oxygen release", specifically: (1) Photocatalytic hydrogen production: Under irradiation by a 300W xenon lamp, WO3 absorbs sunlight to generate electron-hole pairs, and MWCNTs rapidly transfer photogenerated electrons to Ru active sites, inhibiting charge recombination; (2) H2 dissociation and hydrogen overflow: H2O is oxidized to O2 under the action of holes (remaining in the reaction system), H + H2 is generated by gaining electrons at Ru sites. H2 then dissociates into H atoms on the Ru surface and migrates from the Ru surface to the WO3 surface through the hydrogen spillover effect. (3) Bulk hydrogen storage and separation: H atoms further diffuse into the interstices of the WO3 bulk lattice and further spill over into MWCNTs. O2, unable to enter the WO3 bulk phase, is released in the reactor headspace, and finally the in-situ separation of H2 and O2 is completed, and H is stored in the catalyst.

[0007] This invention provides a Ru / WO3-MWCNTs photocatalyst, with the following mass percentages of each component: Active component Ru: 0.4%-3%; Core function of Ru: catalyzes the dissociation of H2 into H atoms, providing a hydrogen overflow initiation site; Conductive and dispersing agents MWCNTs: 5%-25%; Core function: Promotes photogenerated charge separation and transport, inhibits WO3 aggregation; Hydrogen storage carrier WO3: Balance; Core function: Stores H atoms through the interstitial lattice gaps to achieve spatial separation from O2; The sum of the above three components is 100%.

[0008] Preferably, the composition of the above photocatalyst is: Ru 0.6%, MWCNTs 15%, and WO3 84.4%. At this ratio, the dissociation activity of Ru, the charge transport efficiency of MWCNTs, and the hydrogen storage capacity of WO3 are optimally matched, and the hydrogen-oxygen separation efficiency (O2 purity ≥ 99.2%) and hydrogen storage capacity (2.23 wt%) are both optimal.

[0009] This invention provides a method for preparing the above-mentioned Ru / WO3-MWCNTs photocatalyst, which adopts a two-step method of "hydrothermal synthesis of WO3-MWCNTs complex + reduction of Ru supported by sodium borohydride". The key process parameters and control procedures are as follows: (1) Preparation of WO3-MWCNTs complex Weigh 0.3-0.5 g of tungsten hexachloride (WCl6) and 20-100 mg of multi-walled carbon nanotubes (MWCNTs), add them to 50-70 mL of ethanol solvent, and ultrasonically disperse for 30-60 min (to ensure uniform dispersion of MWCNTs and avoid agglomeration) to obtain a dark blue suspension. Transfer the suspension to a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner and react at 180-200 °C for 10 h. In this invention, the temperature range of 180-200 °C is selected to generate orthorhombic WO3, whose lattice structure has suitable H atom diffusion channels. Below 180 °C, amorphous WO3 is easily formed, while above 200 °C, MWCNTs are easily oxidized.

[0010] After the reaction was completed, the product was separated by filtration, washed 3-5 times with anhydrous ethanol (to remove unreacted WCl6), and dried in a vacuum drying oven at 50-70℃ for 8-10 h to obtain the WO3-MWCNTs complex.

[0011] (2) Preparation of Ru / WO3-MWCNTs Add 0.4-0.6 g of the WO3-MWCNTs complex to 10-30 mL of deionized water and stir for 0.5 h until uniformly dispersed. Based on the Ru loading, add 0.5-3.75 mL of 10 g / L ruthenium chloride (RuCl3·xH2O) solution and stir at room temperature for 3-5 h (ensuring Ru...). 3+ (The ruthenium chloride is uniformly adsorbed onto the surface of WO3-MWCNTs); then 4-6 mL of 0.5 g / L sodium borohydride (NaBH4) solution is added; the molar ratio of NaBH4 to ruthenium chloride is 8:1 to ensure that Ru... 3+ Completely reduce to metallic Ru; continue stirring for 3-5 h to obtain a dark blue suspension.

[0012] The product was separated by vacuum filtration and washed 3-5 times each with deionized water and anhydrous ethanol (to remove residual Cl). - with Na The Ru / WO3-MWCNTs photocatalyst is obtained by drying it in a vacuum drying oven at 60℃ for more than 6 hours.

[0013] This invention provides the application of the above-mentioned Ru / WO3-MWCNTs photocatalyst in photocatalytic water splitting-hydrogen-oxygen separation. The specific application method is as follows: Reaction system setup: Add 100 mL of deionized water and 0.02 g of Ru / WO3-MWCNTs catalyst to a quartz reactor, and purge with argon gas (purity ≥99.99%) for 30-60 min; remove air from the system to prevent O2 from reacting with H atoms to generate H2O, which would affect hydrogen storage efficiency; Photocatalytic reaction: A 300 W xenon lamp (simulating sunlight, wavelength range 300-800 nm) was used as the light source, with the light source 20-30 cm away from the reaction liquid surface to ensure uniform light intensity on the catalyst surface, approximately 80-120 mW / cm². 2 Irradiated with light at room temperature and pressure for 1 hour; Product testing and hydrogen storage validation: The purity (target ≥99.2%) and yield of O2 in the extracted gas were determined by gas chromatography (model: GC-2014, column: 5Å molecular sieve column, carrier gas: Ar). The valence state of W in the catalyst after the reaction (W) was detected by X-ray photoelectron spectroscopy (XPS). 6+ Partially restored to W 5 + / W 4+ This confirmed that H atoms are embedded in the WO3 bulk phase, and the hydrogen storage capacity was calculated by combining temperature programmed desorption (TPD) tests.

[0014] The beneficial effects of this invention are: (1) This invention combines the H2 dissociation activity of Ru, the charge transport capability of MWCNTs and the bulk hydrogen storage capability of WO3 for the first time. Through the synergistic effect of hydrogen overflow and bulk hydrogen storage, the in-situ separation of H* and O2 in the photocatalytic process is achieved without the need for additional separation equipment, thus solving the problem of hydrogen-oxygen mixing in traditional photocatalytic hydrogen production.

[0015] (2) The preparation process of this invention is green and efficient: it adopts hydrothermal method and chemical reduction method, the reaction conditions are mild (mainly at room temperature and pressure, hydrothermal temperature ≤200℃), there are no toxic and harmful by-products, the cost of Ru used is only 1 / 50 of Pt, MWCNTs are readily available, and it is suitable for large-scale industrial production.

[0016] (3) The resulting photocatalyst has excellent and stable performance: After being irradiated, the hydrogen storage-separation efficiency of the preferred catalyst does not decrease significantly after 5 cycles (retention rate ≥95%), and it has high selectivity, high hydrogen storage capacity and long cycle stability.

[0017] (4) Wide range of applications: It can be directly used in photocatalytic water splitting hydrogen production systems, and can also be extended to fields such as photoelectrocatalysis and photocatalytic CO2 reduction, providing key technical support for the large-scale application of clean hydrogen energy and green energy transformation. Attached Figure Description

[0018] Figure 1 shows the XRD pattern of the 0.6% Ru / 15% MWCNTs-WO3 product prepared in Example 2.

[0019] Figure 2 is a comparison chart of hydrogen storage capacity using different preparation methods in Example 2 and the comparative example.

[0020] Figure 3 is a comparison of the hydrogen storage capacity of different Ru loadings prepared in Examples 1-5.

[0021] Figure 4 shows the O2 production and H2 storage in Example 2. Detailed Implementation

[0022] The present invention is further illustrated by the following examples, but is not limited to the following examples; in all examples, unless otherwise specified, all reagents used are of analytical grade, and the diameter of MWCNTs is 10-20 nm and the length is 5-10 μm.

[0023] Example 1: Preparation and properties of 0.4% Ru / WO3-MWCNTs (1) Preparation of WO3-MWCNTs: Weigh 0.4 g WCl6 and 60 mg MWCNTs (MWCNTs mass percentage 15%), add 60 mL ethanol and ultrasonically disperse for 30 min, transfer to 100 mL autoclave and react at 200℃ for 10 h; after cooling, filter, wash 5 times with anhydrous ethanol, and vacuum dry at 60℃ for 10 h to obtain WO3-MWCNTs complex.

[0024] (2) Ru loading: Take 0.5 g of the above complex and disperse it in 20 mL of water, add 500 μL of 10 g / L RuCl3 solution (Ru loading 0.4%), stir for 3 h; add 5 mL of 0.5 g / L NaBH4 solution, stir for 3 h; filter, wash and dry at 60℃ for 6 h to obtain 0.4% Ru / WO3-MWCNTs.

[0025] The specific process of performance testing is as follows: 30 mL of deionized water and 0.02 g Ru / WO3-MWCNTs catalyst were added to a 50 mL quartz reactor, and argon gas (purity ≥99.99%) was introduced for 30 min; air in the system was removed to avoid the reaction of O2 and H atoms to generate H2O, which would affect the hydrogen storage efficiency; Photocatalytic reaction: A 300 W xenon lamp (simulating sunlight, wavelength range 300-800 nm) was used as the light source, 20 cm away from the reaction liquid surface to ensure uniform light intensity on the catalyst surface, approximately 100 mW / cm². 2 Irradiated with light at room temperature and pressure for 1 hour; Product detection and hydrogen storage validation: Gas chromatography (GC-2014, 5Å molecular sieve column, carrier gas: Ar) was used to detect the purity (target ≥99.2%) and yield of O2 in the extracted gas; X-ray photoelectron spectroscopy (XPS) was used to detect the valence state of W in the catalyst after the reaction (W... 6+ Partially restored to W 5+ / W 4+ This confirms that H atoms are embedded in the bulk WO3 phase. The hydrogen storage capacity was measured to be 1.57 wt% after illumination.

[0026] Example 2: Preparation and properties of 0.6% Ru / WO3-MWCNTs (1) Preparation of WO3-MWCNTs: Same as in Example 1.

[0027] (2) Ru loading: Add 750 μL of 10 g / L RuCl3 solution (Ru loading 0.6%), and follow the same steps as in Example 1 to obtain 0.6% Ru / WO3-MWCNTs.

[0028] (3) Performance test: After light exposure, the hydrogen storage capacity is 2.23 wt%.

[0029] Example 3: Preparation and properties of 1% Ru / WO3-MWCNTs (1) Preparation of WO3-MWCNTs: Same as in Example 1.

[0030] (2) Ru loading: Add 1250 μL of 10 g / L RuCl3 solution (Ru loading 1%), and follow the same steps as in Example 1 to obtain 1% Ru / WO3-MWCNTs.

[0031] (3) Performance test: After light exposure, the hydrogen storage capacity is 1.57 wt% (excess Ru caused partial aggregation and decreased charge transport efficiency).

[0032] Example 4: Preparation and properties of 2% Ru / WO3-MWCNTs (1) Preparation of WO3-MWCNTs: Same as in Example 1.

[0033] (2) Ru loading: Add 2500 μL of 10 g / L RuCl3 solution (Ru loading 2%), and follow the same steps as in Example 1 to obtain 2% Ru / WO3-MWCNTs.

[0034] (3) Performance test: After light exposure, the hydrogen storage capacity of the catalyst (Ru) was severely agglomerated, and the utilization rate of active sites was reduced.

[0035] Example 5: Preparation and properties of 3% Ru / WO3-MWCNTs (1) Preparation of WO3-MWCNTs: Same as in Example 1.

[0036] (2) Ru loading: Add 3750 μL of 10 g / L RuCl3 solution (Ru loading 3%), and follow the same steps as in Example 1 to obtain 3% Ru / WO3-MWCNTs.

[0037] (3) Performance test: After light exposure, the hydrogen storage capacity is 1.05 wt% (Ru). Excessive coverage of WO3 significantly reduces the hydrogen storage capacity.

[0038] Comparative Example: Performance of 0.6% Ru / WO3-MWCNTs prepared by wet impregnation method (1) Preparation of WO3: Weigh 1.60 g of WCl6 and disperse it in 80 mL of ethanol. After stirring for 0.5 h, transfer it to a high-pressure reactor and react at 160 °C for 6 h. After washing and drying, WO3 is obtained.

[0039] (2) Preparation of Ru / WO3: Disperse 0.5 g WO3 in 20 mL of water, add 750 μL of 10 g / L RuCl3 solution, stir for 3 h; add 20 mL of 5 g / L NaBH4 solution, stir for 3 h; wash and dry to obtain Ru / WO3.

[0040] (3) Composite MWCNTs: 60 mg MWCNTs were ultrasonically dispersed in 75 mL of water (suspension A), and Ru / WO3 was dispersed in 25 mL of water (suspension B); B was added dropwise to A, stirred and evaporated at 90℃, and dried at 110℃ for 24 h to obtain 0.6% Ru / WO3-MWCNTs.

[0041] (4) Performance test: After 1 h of light exposure, the hydrogen storage capacity was 0.18 wt% (the wet impregnation method resulted in uneven Ru dispersion and weak bonding between MWCNTs and WO3, and the hydrogen overflow efficiency was only 19.3% of that in Example 2).

[0042] The effect is illustrated in the attached diagram as follows: Figure 1 shows the XRD pattern of the 0.6% Ru / 15% MWCNTs-WO3 product prepared in Example 2. 2θ = 23.1°, 23.6°, and 24.4° correspond to the characteristic diffraction peaks of the orthorhombic WO3 phase (PDF#71-2450), and 2θ = 26.5° corresponds to the (002) crystal plane peak of MWCNTs. No obvious diffraction peaks of Ru were observed (indicating that Ru is highly dispersed in nanoparticle form), confirming the successful synthesis of the ternary composite.

[0043] Figure 2 is a comparison of the hydrogen storage capacity of the products obtained in Example 2 and the comparative example (vertical axis: hydrogen storage capacity wt%, horizontal axis: hydrogen release time min). As can be seen from the figure, the hydrogen storage capacity of the catalyst prepared by the hydrothermal method (Example 2) increases linearly with irradiation time, reaching 2.23 wt% after 50 min; while the hydrogen storage capacity of the wet impregnation method (comparative example) increases slowly, reaching only 0.18 wt% after 50 min, clearly demonstrating the advantages of the preparation method of this invention, corresponding to Example 2.

[0044] Figure 3 is a comparison of hydrogen storage capacity with different Ru loadings obtained in Examples 1-5 (vertical axis: hydrogen storage capacity wt%, horizontal axis: hydrogen release time min). As can be seen from the figure, the H2 storage capacity reaches its maximum value (2.23 wt%) when the Ru loading is 0.6%, and the production decreases when the loading is lower or higher than this ratio.

[0045] Figure 4 shows the O2 production and H2 storage in Example 2 (vertical axis: O2 production μmol·g). -1 (x-axis: time %). O2 production reaches its maximum (360.83 μmol·g⁻¹) at a Ru loading of 0.6%. -1 Excessive Ru will cover the WO3 hydrogen storage sites, significantly reducing the hydrogen storage capacity.

Claims

1. A Ru / WO3-MWCNTs photocatalyst, characterized in that... The mass percentages of each component are as follows: Active component Ru: 0.4%-3%; Ru can catalyze the dissociation of H2 into H atoms, providing a hydrogen overflow initiation site; Conductive and dispersing agents MWCNTs: 5%-25%; MWCNTs can promote the separation and transport of photogenerated charges and inhibit WO3 aggregation; Hydrogen storage carrier WO3: Balance; WO3 stores H atoms through the interstitial lattice gaps, achieving spatial separation from O2; The sum of the above three components is 100%. 2.The Ru / WO 3-MWCNTs photocatalyst according to claim 1, characterized in that The composition of the photocatalyst is: Ru: 0.6%, MWCNTs: 15%, WO3: 84.4%.

3. A method for preparing the Ru / WO3-MWCNTs photocatalyst according to claim 1 or 2, characterized by: A two-step method was adopted: hydrothermal synthesis of WO3-MWCNTs complex + reduction of Ru-loaded Ru with sodium borohydride; the steps are as follows: (1) Preparation of WO3-MWCNTs complex Weigh 0.3-0.5 g of WCl6 and 20-100 mg of multi-walled carbon nanotubes, add them to 50-70 mL of ethanol solvent, and ultrasonically disperse for 30-60 min to ensure uniform dispersion of MWCNTs and avoid agglomeration, to obtain a blackish-blue suspension; transfer the suspension to a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, and react at 180-200℃ for 10 h; after the reaction, filter to separate the product, wash with anhydrous ethanol 3-5 times to remove unreacted WCl6, and dry in a vacuum drying oven at 50-70℃ for 8-10 h to obtain the WO3-MWCNTs complex; (2) Preparation of Ru / WO3-MWCNTs Add 0.4-0.6 g of the WO3-MWCNTs complex to 10-30 mL of deionized water and stir for 0.5 h until uniformly dispersed. Based on the Ru loading, add 0.5-3.75 mL of 10 g / L ruthenium chloride solution and stir at room temperature for 3-5 h to ensure Ru... 3+ Uniformly adsorbed onto the surface of WO3-MWCNTs; then 4-6 mL of 0.5 g / L sodium borohydride solution was added; the molar ratio of NaBH4 to ruthenium chloride was 8:1 to ensure Ru 3+ Completely reduced to metallic Ru; continue stirring for 3-5 h to obtain a dark blue suspension; filter to separate the product, and wash with deionized water and anhydrous ethanol 3-5 times each to remove residual Cl. - with Na + The Ru / WO3-MWCNTs photocatalyst is obtained by drying in a vacuum drying oven at 60℃ for more than 6 hours.

4. The application of the Ru / WO3-MWCNTs photocatalyst according to claim 1 or 2 in photocatalytic water splitting-hydrogen-oxygen separation.

5. Use according to claim 4, characterized in that: Reaction system setup: Add 100 mL of deionized water and 0.02 g of Ru / WO3-MWCNTs catalyst to a quartz reactor, and purge with Ar for 30-60 min; remove air from the system to prevent O2 from reacting with H atoms to generate H2O, which would affect hydrogen storage efficiency; Photocatalytic reaction: A 300 W xenon lamp was used as the light source, positioned 20-30 cm above the reaction liquid surface to ensure uniform light intensity of 80-120 mW / cm² on the catalyst surface. 2 Irradiate with light for 1 hour at room temperature and pressure.

6. Use according to claim 5, characterized in that: The purity of the argon gas is ≥99.99%.

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