Sea urchin-shaped oxygen-rich vacancy O vac CuO@ZIF-8 core-shell structured photothermal catalyst, its preparation method and application

Abstract

This invention discloses a sea urchin-shaped oxygen-rich vacancy O vac This paper describes a CuO@ZIF-8 core-shell structured photothermal catalyst, its preparation method, and its application, belonging to the fields of photocatalytic materials and artificial nitrogen fixation technology. The technical solution is as follows: the catalyst has a core-shell structure, with the core being urchin-shaped copper oxide (CuO) microspheres. These microspheres are assembled from radially arranged one-dimensional nanoneedles or nanospikes, and the surface of the core contains oxygen vacancies (O). vac The shell is an in-situ grown ultrathin zeolite imidazole ester framework material, ZIF-8, which possesses hydrophobic and molecular diffusion channel properties. This invention also constructs a matching biomimetic three-phase interface photothermal reaction system. Through the synergy of a hydrophilic substrate supplying water and a hydrophobic, permeable shell, it achieves a balance between gas diffusion and proton supply, reducing the submersion of active sites by liquid water and the occurrence of side reactions. This invention has significant advantages such as high photothermal conversion efficiency, mild preparation conditions, and high gas-liquid interface mass transfer efficiency.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials and artificial nitrogen fixation technology, specifically relating to a sea urchin-shaped oxygen-rich vacancy O vac -CuO@ZIF-8 core-shell structured photothermal catalyst, its preparation method and application. Background Technology

[0002] Ammonia (NH3) is an indispensable basic chemical raw material for modern industry and agriculture. The traditional Haber-Bosch process for ammonia synthesis requires high temperature and pressure (300-500℃, 150-200 atm), resulting in enormous energy consumption and large CO2 emissions. Photothermal catalytic nitrogen reduction for ammonia synthesis using solar energy is a green alternative to the energy-intensive Haber-Bosch process. However, existing photothermal catalytic systems face significant challenges:

[0003] Morphology limits light absorption: Existing CuO-based catalysts (such as patent CN116493014A) are mostly synthesized with the assistance of CTAB, tending to form a "flower-like" structure assembled from two-dimensional nanosheets. Although the specific surface area is acceptable, their reflectivity to incident light is high, making it difficult to achieve deep light trapping and photothermal conversion.

[0004] The methods for regulating active sites are limited and energy-intensive: Existing technologies mostly regulate electronic structure by doping with heterogeneous metals (such as Co, Ni, Zr, etc.), which usually requires high-temperature calcination (such as above 350℃) and the process is complex.

[0005] Lack of microscopic gas-liquid interface construction: Traditional ZIF-8 coating technology mainly focuses on the adsorption and enrichment of acidic gases such as CO2, neglecting the crucial "water management" issue in photothermal catalysis. In all-liquid phase reactions, N2 has low solubility, hindering mass transfer; while in pure gas phase reactions, there is a lack of proton sources. Existing catalyst shells are often too thick and fail to effectively construct a "hydrophobic, liquid-blocking, porous, and permeable" microenvironment, leading to liquid water easily submerging active sites and triggering the hydrogen evolution reaction (HER).

[0006] Therefore, developing a new type of catalyst is key to breaking through the bottleneck of photothermal nitrogen fixation efficiency. Summary of the Invention

[0007] This invention provides a sea urchin-shaped oxygen-rich vacancy O vac The -CuO@ZIF-8 core-shell structured photothermal catalyst, its preparation method, and its application aim to solve the technical problems of low photothermal conversion efficiency, liquid water hindering gas diffusion, and the difficulty of conventional catalysts to efficiently drive the reaction under normal pressure in existing photothermal catalysis.

[0008] The technical solution of this invention is as follows:

[0009] Firstly, the oxygen-rich vacancy O in sea urchin-like structures was disclosed. vac -CuO@ZIF-8 core-shell structured photothermal catalyst, wherein the catalyst has a core-shell structure, the core being urchin-shaped copper oxide CuO microspheres, the microspheres being assembled from radially arranged one-dimensional nanoneedles or nanospikes, and the surface of the core containing oxygen vacancies O. vac The shell is an in-situ grown zeolite imidazole ester framework material ZIF-8. The shell forms a continuous or quasi-continuous porous covering layer on the surface of the core, thereby providing molecular diffusion channels for nitrogen and water vapor. At the same time, the shell has hydrophobic properties, which can reduce the probability of liquid water wetting and covering the surface of the core.

[0010] Preferably, the shell layer has a thickness of 10nm to 50nm and strong hydrophobic properties, with a contact angle greater than 125°; the core body has a diameter of 1 to 5μm.

[0011] Secondly, the aforementioned sea urchin-shaped oxygen-rich vacancy O is disclosed. vac The preparation method of CuO@ZIF-8 core-shell structured photothermal catalyst includes the following steps:

[0012] 1) Preparation of core-body sea urchin-shaped copper oxide microspheres: Copper source and polyethylene glycol are dissolved in a mixture of water and ethanol and subjected to hydrothermal reaction. The molecular guiding effect of polyethylene glycol is used to make copper oxide crystals grow and assemble along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres.

[0013] 2) Construction of surface defects on the nucleus: The urchin-shaped copper oxide microspheres prepared in step 1 are dispersed in solvent one, and a reducing agent solution is added to carry out a liquid-phase etching reaction, introducing oxygen vacancies in situ to obtain oxygen-vacancy-rich copper oxide O. vac -CuO;

[0014] 3) Growth of ultrathin hydrophobic shell: The oxygen-rich vacancy copper oxide O obtained in step 2) vac -CuO was dispersed in solvent two to adsorb the zinc source, and then 2-methylimidazole solution was added for in-situ growth. After the reaction was completed, the catalyst was obtained by centrifugation, washing and drying.

[0015] Preferably, in step 1), the copper source is copper acetate, the volume ratio of water to ethanol in the water and ethanol mixture is 1:3, the number average molecular weight of polyethylene glycol is 2000~6000 (g / mol), the mass ratio of copper source to polyethylene glycol is 1:(8~15), the hydrothermal reaction temperature is 100-130℃, and the reaction time is 10~18h.

[0016] Preferably, in step 2), solvent one is a mixture of water and ethanol in a volume ratio of 1:1, reducing agent is a NaBH4 solution with a concentration of 0.01~0.1mol / L, and reaction time is 20~60s.

[0017] Preferably, in step 3), solvent 2 is one of methanol and N,N-dimethylformamide, zinc source is one of zinc nitrate, zinc acetate and zinc chloride, and in-situ growth time is 10~60 min.

[0018] Preferably, in step 3), oxygen-rich vacancy copper oxide O vac The mass ratio of CuO, zinc source and 2-methylimidazole solution is 1:(0.5~1):(1~2).

[0019] Thirdly, the application of the aforementioned photothermal catalyst in the photothermal catalytic reduction of N2 to ammonia at the gas-liquid interface is disclosed, constructing a biomimetic reaction system of "gas-liquid-solid" three-phase interface for the photothermal catalytic reduction of N2 to ammonia. Specific steps include:

[0020] 1) The photothermal catalyst was loaded onto a porous hydrophilic substrate;

[0021] 2) Place the substrate with the catalyst supported on the support platform inside the reactor. The bottom of the reactor is filled with water. Water is drawn to the substrate through a water-absorbing medium to keep the substrate wet.

[0022] 3) Introduce a nitrogen gas flow to carry out a photothermal catalytic reaction under simulated sunlight conditions;

[0023] 4) After the reaction is complete, the substrate with the supported catalyst is subjected to ultrasonic extraction using dilute sulfuric acid solution, and the ammonia yield is detected by colorimetric method.

[0024] Preferably, the nitrogen flow rate is 20-50 mL / min, and the solar irradiance is 1 solar irradiance (1000 W / m²). 2 The reaction time is 1-4 hours.

[0025] This invention utilizes a unique "sea urchin-like" structure to construct light traps: long-chain molecules of PEG (polyethylene glycol) are used as soft templates and guiding agents to induce CuO crystals to grow into one-dimensional nanoneedles along a specific axis, which are then further radially assembled into three-dimensional sea urchin-shaped microspheres. Compared with the existing "flower-like / sheet-like" structures, the sea urchin-like structure has deep pores, causing multiple reflections and scattering of incident light between the nanoneedles, significantly enhancing light absorption (light trapping effect) and thus greatly improving photothermal conversion efficiency.

[0026] This invention utilizes NaBH4 liquid-phase etching to construct oxygen-rich vacancies: abandoning the traditional modification approaches of high-temperature calcination or metal doping, it innovatively employs NaBH4 solution for rapid and controlled liquid-phase reduction etching of sea urchin-like precursors. This process strips surface lattice oxygen under mild conditions (room temperature), creating a high concentration of surface oxygen vacancies (O2) in situ. vacThese oxygen vacancies not only act as Lewis acid sites to efficiently activate the N≡N triple bond of the N₂ molecule, but also change the catalyst color to deep black, enabling efficient absorption across the entire solar spectrum.

[0027] To address the mass transfer challenge, this invention employs a "seed crystal adsorption-in-situ growth" strategy to grow an ultrathin (10-50 nm) ZIF-8 shell on the CuO surface. Unlike conventional long-term hydrothermal coating, this method controls nucleation through pre-adsorption of a zinc source, resulting in a short reaction time. This shell exhibits macroscopic hydrophobicity, preventing direct contact between liquid water and the CuO core, thus preventing "flooding." Simultaneously, it possesses microporous permeability, allowing N2 molecules and high-temperature water vapor generated by photothermal processes to pass through, thereby constructing a unique artificial "gas-liquid-solid" three-phase microreactor.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The CuO prepared by this invention exhibits a three-dimensional sea urchin-like microsphere structure assembled from one-dimensional nanoneedles. Compared with the two-dimensional sheet-like stacking (flower-like) in the prior art, this sea urchin-like structure can produce multiple reflections and scattering under light, which significantly enhances the light absorption capacity and photothermal conversion efficiency. Experiments show that the surface temperature increases more significantly under the same light irradiation.

[0030] 2. This invention abandons the traditional approach of controlling activity through heterogeneous metal doping (such as Co, Ni, etc.), and instead employs NaBH4 liquid-phase controlled etching technology to create high-concentration oxygen vacancies in situ on the CuO surface under mild conditions. These surface defects not only serve as reactive centers but also significantly enhance the material's color, achieving efficient absorption across the entire solar spectrum.

[0031] 3. Unlike existing technologies that utilize ZIF-8 for simple CO2 adsorption and enrichment, this invention constructs an ultrathin hydrophobic and permeable shell on the CuO surface by precisely controlling the growth kinetics of ZIF-8. This shell creates a unique artificial gas-liquid-solid three-phase interface, effectively preventing liquid water from directly contacting the catalyst core and avoiding the "flooding" effect, while allowing efficient transport of gaseous water and reactant gases, making it specifically designed for high-efficiency gas-liquid interface photothermal catalytic systems.

[0032] 4. The present invention adopts a mild preparation process, which does not require high-temperature calcination throughout the entire process, resulting in low energy consumption and is more conducive to the preservation of surface metastable defects. Attached Figure Description

[0033] Figure 1 This invention features a sea urchin-shaped ZIF-8@O. vac - Schematic diagram of CuO preparation process.

[0034] Figure 2 Contact angle test diagram of the catalyst prepared in Example 1 of this invention.

[0035] Figure 3 SEM images of the catalyst prepared in Example 1 of this invention, wherein (ab) CuO urchin-like structure and (c) thin-layer ZIF-8 coated O vac (d) SEM images of flower-shaped CuO microspheres prepared in Comparative Example 1.

[0036] Figure 4 O prepared in the embodiments of the present invention vac TEM images of the CuO@ZIF-8 catalyst, including (a) a low-magnification TEM image and (b) a high-resolution TEM image.

[0037] Figure 5 Schematic diagram of photothermal catalytic reaction device and three-phase interface mass transfer mechanism.

[0038] Figure 6 Ammonia production rates of the catalysts in Examples 1, 4, and 5 under continuous light irradiation. Detailed Implementation

[0039] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions will be clearly and completely described below in conjunction with the embodiments of this invention.

[0040] This invention relates to sea urchin-like oxygen-rich vacancy O vac A schematic diagram of the preparation process of the CuO@ZIF-8 core-shell structured photothermal catalyst is shown below. Figure 1 As shown, firstly, a precursor solution was constructed using copper as a source and PEG as a structure-directing agent. Under hydrothermal reaction conditions, PEG molecular chains adsorbed and induced copper oxide crystals to grow along a specific direction, self-assembling to form urchin-shaped CuO microspheres composed of numerous radial nanoneedles. Subsequently, the urchin-shaped CuO was chemically reduced at room temperature using sodium borohydride (NaBH4) solution. NaBH4, as a strong reducing agent, extracted lattice oxygen from the CuO surface lattice points without destroying the overall framework structure of the microspheres, thereby introducing abundant oxygen vacancy defects in situ on the nanoneedle surface, obtaining oxygen-vacancy-rich copper oxide (O2O3). vac -CuO). Finally, with O vac -CuO as the core, a metal-organic framework ZIF-8 is grown in situ on its surface using a solvothermal method, with zinc ions (Zn) as the core. 2+ ) with ligand 2-methylimidazole in O vac -CuO surface coordination assembly forms a continuous, uniform porous ZIF-8 shell, resulting in O with hydrophobicity and molecular sieving function. vac -CuO@ZIF-8 core-shell structured photothermal catalyst.

[0041] Example 1

[0042] The sea urchin-shaped oxygen-rich vacancy O vac The preparation method of CuO@ZIF-8 core-shell structured photothermal catalyst includes the following steps:

[0043] 1) Preparation of core-body sea urchin-shaped copper oxide microspheres: 0.15 g of Cu(CH3COO)2·2H2O and 1.2 g of polyethylene glycol PEG-2000 were dissolved in 40 mL of ethanol-water mixture with a volume ratio of 1:3. The mixture was subjected to hydrothermal reaction at 100 °C for 18 h. The molecular guiding effect of polyethylene glycol was used to make copper oxide crystals grow and assemble along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres with a diameter of 1 μm.

[0044] 2) Construction of surface defects on the nucleus: 200 mg of the urchin-shaped copper oxide microspheres prepared in step 1) were dispersed in 40 mL of a 1:1 mixture of water and ethanol. 10 mL of a 0.05 mol / L NaBH4 solution was rapidly added to initiate a liquid-phase etching reaction, with the reaction time strictly controlled to 30 s. Immediately afterwards, a large amount of ice water was added to quench the reaction, introducing oxygen vacancies in situ. After centrifugation and drying, black oxygen-rich copper oxide O was obtained. vac -CuO;

[0045] 3) Growth of an ultrathin hydrophobic shell: 50 mg of the oxygen-rich vacancy copper oxide obtained in step 2) was used... vac CuO was dispersed in 20 mL of methanol, and 20 mL of zinc nitrate solution (1.25 g / L) was added and stirred for 30 min to pre-enrich zinc ions on the surface of CuO nanoneedles through physical adsorption and coordination (seed crystal adsorption). Then, 20 mL of 2-methylimidazole solution (2.5 g / L) was added and the mixture was stirred at room temperature for 10 min to carry out in-situ growth. At this point, O... vac The mass ratio of CuO:zinc source:ligand was 1:0.5:1. After the reaction was completed, the catalyst was obtained by centrifugation, washing, and drying.

[0046] The obtained catalyst was subjected to contact angle testing, specifically as follows: Figure 2 As shown, the water contact angle on the catalyst surface is 129°, indicating that the ZIF-8 shell endows the material with excellent hydrophobic properties. This strong hydrophobicity promotes the formation of a stable gas-liquid-solid three-phase interface on the catalyst surface at the microscopic level. Specifically, the hydrophobic ZIF-8 shell generates strong capillary repulsion due to surface tension, ensuring that liquid water droplets can only remain on the outer surface of the catalyst and cannot penetrate and wet the deep pores inside the microspheres, thus effectively preventing internal O2. vacThe oxygen vacancy active sites in the CuO core are covered by a liquid water layer, preventing the active sites from being deactivated by water molecules or triggering hydrogen evolution side reactions. At the same time, because the liquid water is blocked outside the shell, the micropores of the ZIF-8 shell itself remain dry and unobstructed, acting like a "waterproof and breathable membrane." This specifically allows gaseous water molecules generated by photothermal evaporation and reactive gases (N2) to smoothly penetrate the shell and reach the core to participate in the reaction, solving the problem of liquid water hindering gas mass transfer in traditional systems.

[0047] The morphology of the obtained catalyst was further characterized. SEM images of the catalyst are shown below. Figure 3 As shown in (ac), the image clearly confirms O. vac -CuO@ZIF-8 exhibits a distinct core-shell structure. Its internal core consists of urchin-like microspheres assembled radially from nanoneedles, while the exterior is uniformly coated with an ultrathin 10nm ZIF-8 shell. High-magnification images reveal that this shell is extremely thin and its surface is covered with nanoscale particles, which assemble to form a rich network of fine pores. This ultrathin, porous shell imparts hydrophobic properties to the catalyst while also serving as a highly efficient molecular diffusion channel, facilitating the smooth passage of reactant gases (N2) and photothermal-generated water vapor, thus avoiding significant gas mass transfer resistance.

[0048] Furthermore, the O prepared in the embodiments of the present invention vac TEM image of CuO@ZIF-8 catalyst as shown Figure 4 As shown. In Figure 4 In the low-magnification TEM image of (a), near-circular particles at the hundreds of nanometer scale are visible, exhibiting low electron transmittance and a dark color, corresponding to a high-density CuO core, while their edges display a continuous, wrinkled, and layered rough structure. Further analysis... Figure 4 (b) High-resolution TEM images clearly show multi-oriented lattice fringes in the internal region, corresponding to well-crystallized CuO nanocrystals, while the outer side is tightly connected to amorphous / weakly crystalline regions, which is the grown ZIF-8 material. This tight interface between the crystalline and amorphous layers, and the continuous growth of the shell at the core edge, fully demonstrate that ZIF-8 is firmly loaded (grown) on the surface of CuO microspheres through a chemical process of "seed adsorption-in-situ growth," rather than simple physical mixing or loose adsorption. This tight core-shell connection provides a stable structural basis for the interfacial transport of photothermal electrons and protons.

[0049] The application of the aforementioned photothermal catalyst in the photothermal catalytic reduction of N2 to ammonia at the gas-liquid interface involves constructing a biomimetic reaction system of a gas-liquid-solid three-phase interface for the photothermal catalytic reduction of N2 to ammonia. Specific steps include:

[0050] 1) The photothermal catalyst was loaded onto a substrate of glass fiber filter paper;

[0051] 2) Place the substrate loaded with catalyst on the support platform (integral three-legged round table) inside the reactor. The bottom of the reactor is filled with water, and the water is guided to the substrate through the water absorption strip (glass fiber water absorption core) to keep the substrate wet.

[0052] 3) Introduce a nitrogen flow at a rate of 20 mL / min, under a solar irradiance of 1 solar intensity (1000 W / m²). 2 The photothermal catalytic reaction was carried out for 2 hours under simulated sunlight conditions.

[0053] 4) After the reaction was complete, the filter paper loaded with the catalyst was placed in a 100 mL beaker, and 10 mL of 0.01 mol / L dilute sulfuric acid was added. The mixture was ultrasonically extracted for 15 min to capture the ammonium ions generated on the catalyst surface. The extract was drawn up using a disposable syringe and filtered through a needle filter to remove solid impurities (both the filter paper and needle filter were pre-cleaned or tested with a blank control to remove background interference). The ammonia yield was determined according to Environmental Protection Standard HJ 536-2009, "Determination of Ammonia Nitrogen in Water - Salicylic Acid Spectrophotometric Method".

[0054] A schematic diagram of the photothermal catalytic reaction device and the three-phase interface mass transfer mechanism is shown below. Figure 5 As shown, this device is constructed based on the principle of interfacial photothermal evaporation: the capillary action of the absorbent strip transports liquid water from the bottom to the hydrophilic substrate (filter paper), while the hydrophobic and breathable ZIF-8@O vac The CuO catalyst, positioned above the moistened filter paper, forms a gas-liquid-solid three-phase interface. At this interface, liquid water is blocked, allowing only high-temperature water vapor generated by photothermal processes to permeate the ZIF-8 shell and react with nitrogen on the oxygen-rich CuO surface. This solves the technical challenges of low N2 solubility in traditional liquid-phase reactions and proton deficiency in pure gas-phase reactions. Specifically, under simulated sunlight, the black oxygen-rich O... vac The CuO core exhibits a significant photothermal effect, causing a local temperature increase in the catalyst. Gaseous water molecules penetrating the ZIF-8 shell and reaching the core surface undergo oxidative decomposition under high temperature and photogenerated holes, generating active protons (H+) in situ. + ) and electrons (e - Meanwhile, nitrogen molecules (N2) adsorb onto oxygen vacancies (O2) on the CuO surface. vac At the defect site, it is activated by photogenerated electron injection, weakening the N≡N triple bond. Subsequently, the in-situ generated active proton (H) + It undergoes a continuous hydrogenation reaction with the activated nitrogen intermediate (N2) (N2 + 6H2O) + +6e -→2NH3), ultimately generating ammonia molecules and desorbing them from the catalyst surface. This in-situ proton-donating mechanism avoids the obstruction of nitrogen diffusion by the liquid water layer, achieving efficient synergistic conversion of nitrogen and water vapor in the gas phase.

[0055] Example 2

[0056] The sea urchin-shaped oxygen-rich vacancy O vac The preparation method of CuO@ZIF-8 core-shell structured photothermal catalyst includes the following steps:

[0057] 1) Preparation of core-body sea urchin-shaped copper oxide microspheres: 0.15 g of Cu(CH3COO)2·2H2O and 1.50 g of polyethylene glycol PEG-3000 were dissolved in 40 mL of ethanol-water mixture with a volume ratio of 1:3. The mixture was subjected to hydrothermal reaction at 120 °C for 10 h. The molecular guiding effect of polyethylene glycol was used to make copper oxide crystals grow and assemble along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres with a diameter of 3 μm.

[0058] 2) Construction of surface defects on the nucleus: 200 mg of the urchin-shaped copper oxide microspheres prepared in step 1) were dispersed in 40 mL of a 1:1 volume ratio ethanol-water mixture. 5 mL of a 0.1 mol / L NaBH4 solution was rapidly added to initiate a liquid-phase etching reaction, with the reaction time strictly controlled to 20 s. Immediately afterwards, a large amount of ice water was added to quench the reaction, introducing oxygen vacancies in situ. After centrifugation and drying, black oxygen-vacancy-rich copper oxide O was obtained. vac -CuO;

[0059] 3) Growth of an ultrathin hydrophobic shell: 50 mg of the oxygen-rich vacancy copper oxide obtained in step 2) was used... vac CuO was dispersed in 20 mL of N,N-dimethylformamide, and 20 mL of zinc acetate solution (1.25 g / L) was added. The mixture was stirred for 30 min to allow zinc ions to be pre-enriched on the surface of CuO nanoneedles through physical adsorption and coordination (seed crystal adsorption). Then, 20 mL of 2-methylimidazole solution (2.5 g / L) was added, and the mixture was stirred at room temperature for 15 min to allow for in-situ growth. At this point, O... vac -CuO:Zinc source:ligand mass ratio 1:0.5:1. After the reaction is completed, the catalyst is obtained by centrifugation, washing and drying, and the thickness of the shell layer is 25nm.

[0060] The application of the aforementioned photothermal catalyst in the photothermal catalytic reduction of N2 to ammonia at the gas-liquid interface involves constructing a biomimetic reaction system of a gas-liquid-solid three-phase interface for the photothermal catalytic reduction of N2 to ammonia. Specific steps include:

[0061] 1) The photothermal catalyst was loaded onto a substrate of glass fiber filter paper;

[0062] 2) Place the substrate loaded with catalyst on the support platform inside the reactor. The bottom of the reactor is filled with water. Water is drawn to the substrate through the water suction strip to keep the substrate wet.

[0063] 3) Introduce a nitrogen flow at a rate of 30 mL / min, under a solar irradiance of 1 solar irradiance (1000 W / m²). 2 The photothermal catalytic reaction was carried out for 4 hours under simulated sunlight conditions.

[0064] 4) After the reaction was complete, the filter paper loaded with the catalyst was placed in a 100 mL beaker, and 10 mL of 0.01 mol / L dilute sulfuric acid was added. The mixture was ultrasonically extracted for 15 min to capture the ammonium ions generated on the catalyst surface. The extract was drawn up using a disposable syringe and filtered through a needle filter to remove solid impurities (both the filter paper and needle filter were pre-cleaned or tested with a blank control to remove background interference). The ammonia yield was determined according to Environmental Protection Standard HJ 536-2009, "Determination of Ammonia Nitrogen in Water - Salicylic Acid Spectrophotometric Method".

[0065] Example 3

[0066] The sea urchin-shaped oxygen-rich vacancy O vac The preparation method of CuO@ZIF-8 core-shell structured photothermal catalyst includes the following steps:

[0067] 1) Preparation of core-body sea urchin-shaped copper oxide microspheres: 0.15 g of Cu(CH3COO)2·2H2O and 2.0 g of polyethylene glycol PEG-6000 were dissolved in 40 mL of ethanol-water mixture with a volume ratio of 1:3. The mixture was subjected to hydrothermal reaction at 130 °C for 14 h. The molecular guiding effect of polyethylene glycol was used to make copper oxide crystals grow and assemble along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres with a diameter of 5 μm.

[0068] 2) Construction of surface defects on the nucleus: 200 mg of the urchin-shaped copper oxide microspheres prepared in step 1) were dispersed in 40 mL of a 1:1 volume ratio ethanol-water mixture. 20 mL of a 0.01 mol / L NaBH4 solution was rapidly added to initiate a liquid-phase etching reaction. The reaction time was strictly controlled to 60 s. Immediately afterwards, a large amount of ice water was added to quench the reaction, introducing oxygen vacancies in situ. After centrifugation and drying, black oxygen-rich copper oxide O was obtained. vac -CuO;

[0069] 3) Growth of an ultrathin hydrophobic shell: 50 mg of the oxygen-rich vacancy copper oxide obtained in step 2) was used... vacCuO was dispersed in 20 mL of methanol, and 20 mL of zinc chloride solution (2.5 g / L) was added. The mixture was stirred for 30 min to allow zinc ions to be pre-enriched on the surface of CuO nanoneedles through physical adsorption and coordination (seed crystal adsorption). Then, 20 mL of 2-methylimidazole solution (5 g / L) was added, and the mixture was stirred at room temperature for 60 min to allow for in-situ growth. At this point, O... vac The mass ratio of CuO, zinc source, and ligand is 1:1:2. After the reaction, the catalyst is obtained by centrifugation, washing, and drying, and the shell thickness is 50 nm.

[0070] The application of the aforementioned photothermal catalyst in the photothermal catalytic reduction of N2 to ammonia at the gas-liquid interface involves constructing a biomimetic reaction system of a gas-liquid-solid three-phase interface for the photothermal catalytic reduction of N2 to ammonia. Specific steps include:

[0071] 1) The photothermal catalyst was loaded onto a substrate of glass fiber filter paper;

[0072] 2) Place the substrate loaded with catalyst on the support platform inside the reactor. The bottom of the reactor is filled with water. Water is drawn to the substrate through the water suction strip to keep the substrate wet.

[0073] 3) Introduce a nitrogen flow at a rate of 50 mL / min, under a solar irradiance of 1 solar intensity (1000 W / m²). 2 The photothermal catalytic reaction was carried out for 1 hour under simulated sunlight conditions.

[0074] 4) After the reaction was complete, the filter paper loaded with the catalyst was placed in a 100 mL beaker, and 10 mL of 0.01 mol / L dilute sulfuric acid was added. The mixture was ultrasonically extracted for 15 min to capture the ammonium ions generated on the catalyst surface. The extract was drawn up using a disposable syringe and filtered through a needle filter to remove solid impurities (both the filter paper and needle filter were pre-cleaned or tested with a blank control to remove background interference). The ammonia yield was determined according to Environmental Protection Standard HJ 536-2009, "Determination of Ammonia Nitrogen in Water - Salicylic Acid Spectrophotometric Method".

[0075] Comparative Example 1

[0076] Unlike Example 1, in step 1) of this comparative example, an equal amount of hexadecyltrimethylammonium bromide (CTAB) was used instead of PEG-2000 to prepare "flower-like" CuO. The specific method is as follows: 0.15 g of Cu(CH3COO)2·2H2O and 1.2 g of CTAB were dissolved in 40 mL of deionized water. The mixture was magnetically stirred for 30 min at room temperature to ensure that the CTAB was completely dissolved and a homogeneous solution was formed. The mixed solution was transferred to a stainless steel reactor lined with polytetrafluoroethylene, sealed, and placed in a 100°C oven for hydrothermal reaction for 16 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature, and the bottom precipitate was collected by centrifugation. The precipitate was washed three times with deionized water and anhydrous ethanol, and finally dried overnight in a vacuum drying oven at 60°C to obtain flower-like copper oxide microspheres assembled from two-dimensional nanosheets.

[0077] Steps 2) and 3) are the same as in Example 1, and the SEM images of the catalyst are as follows: Figure 3 As shown in d.

[0078] Comparative Example 2

[0079] Unlike Example 1, this comparative example does not include step 2, that is, the core is not subjected to NaBH4 reduction etching, but is directly coated. The remaining preparation steps and methods are the same as in Example 1.

[0080] Comparative Example 3

[0081] Unlike Example 1, in step 3) of this comparative example, "stirring reaction at room temperature for 10 min for in-situ growth" is replaced with "stirring reaction at room temperature for 8 h for in-situ growth" (simulating the conventional MOF synthesis time). The remaining preparation steps and methods are the same as in Example 1.

[0082] Comparative Example 4

[0083] The specific method for preparing core-body sea urchin-shaped copper oxide microspheres is as follows: 0.15g of Cu(CH3COO)2·2H2O and 1.5g of polyethylene glycol PEG-2000 are dissolved in 40mL of a 1:3 volume ratio ethanol-water mixture and subjected to a hydrothermal reaction at 100℃ for 16h. Utilizing the molecular guiding effect of polyethylene glycol, copper oxide crystals are grown and assembled along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres.

[0084] Comparative Example 5

[0085] Only oxygen-rich vacancy copper oxide O was prepared vac -CuO, the specific method is as follows:

[0086] 1) Preparation of core-body sea urchin-shaped copper oxide microspheres: 0.15 g of Cu(CH3COO)2·2H2O and 1.2 g of polyethylene glycol PEG-2000 were dissolved in 40 mL of ethanol and water mixed solution with a volume ratio of 1:3. The mixture was subjected to hydrothermal reaction at 100 °C for 18 h. The molecular guiding effect of polyethylene glycol was used to make copper oxide crystals grow and assemble along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres.

[0087] 2) Construction of surface defects on the nucleus: 200 mg of the urchin-shaped copper oxide microspheres prepared in step 1) were dispersed in 40 mL of ethanol. 10 mL of a 0.05 mol / L NaBH4 solution was rapidly added to initiate a liquid-phase etching reaction. The reaction time was strictly controlled to 30 s. Immediately afterwards, a large amount of ice water was added to quench the reaction, introducing oxygen vacancies in situ. After centrifugation and drying, black oxygen-vacancy-rich copper oxide O was obtained. vac -CuO.

[0088] Comparative Example 6

[0089] Unlike Example 1, step 2) of this comparative example uses a high-temperature calcination method to introduce oxygen vacancies. Specifically, the dried, urchin-shaped copper oxide microspheres prepared in step 1) are placed in a ceramic boat and then placed in the constant-temperature zone of a tube furnace. High-purity nitrogen (N2) is introduced into the furnace tube at a flow rate of 100 mL / min, and the furnace is purged for 30 minutes to remove all air. Subsequently, under nitrogen protection, the temperature is increased to 400°C at a rate of 5°C / min and calcined for 2 hours. After naturally cooling to room temperature, the sample is removed to obtain a copper oxide sample with oxygen vacancies introduced through heat treatment.

[0090] The remaining preparation methods and steps are the same as in Example 1.

[0091] Comparative Example 7

[0092] Unlike Example 1, step 3) uses SiO2 for shell coating. Specifically, oxygen-rich vacancy copper oxide is dispersed in an ethanol / water mixture (volume ratio 4:1), ammonia is added to adjust the pH to 9, and then tetraethyl orthosilicate (TEOS) is slowly added dropwise. The reaction is carried out for 4 hours to obtain O2. vac -CuO@SiO2.

[0093] Comparative Example 8

[0094] Unlike Example 1, the hydrothermal reaction temperature in step 1) is controlled at 160°C and the reaction time is 24 hours. The remaining preparation methods and steps are the same as in Example 1.

[0095] The application of the catalyst in the above comparative example in the photothermal catalytic reduction of N2 at the gas-liquid interface to synthesize ammonia follows the same steps and methods as in Example 1.

[0096] The specific yields of ammonia in the above embodiments and comparative examples are shown in Table 1.

[0097] Table 1. Ammonia yield in the examples and comparative examples.

[0098]

[0099] Table 1 shows that the ammonia yields of Examples 1-3 were generally significantly higher than those of all comparative examples (Comparative Examples 1-8). Among them, Example 1 achieved the highest ammonia yield (138.03 μg·g⁻¹). cat -1 ·h -1 This indicates that the catalyst prepared under these specific conditions exhibits optimal photothermal catalytic reduction performance of nitrogen. In contrast, the performance of the comparative examples varies considerably and is inferior to that of the examples.

[0100] In Comparative Example 1, the flower-shaped copper oxide microspheres were prepared to replace the sea urchin-shaped microspheres in this invention. The ammonia yield was reduced mainly because the two-dimensional layered stacking of the flower-shaped structure had a higher light reflectivity and lacked the "light trap" effect brought by the deep pores of the sea urchin-shaped structure, resulting in lower light absorption capacity and photothermal conversion efficiency than in Example 1.

[0101] The catalyst prepared in Comparative Example 2 did not contain oxygen vacancies, and the ammonia yield was significantly reduced. This demonstrates that oxygen vacancies, as Lewis acid sites, play a crucial role in the chemisorption of N2 molecules and the activation of the N≡N triple bond. Furthermore, the absence of oxygen vacancies also limits the absorption of visible-near-infrared light by the material.

[0102] The ZIF-8 catalyst obtained in Comparative Example 3 has a shell thickness exceeding 200 nm. Despite good hydrophobicity, the ammonia yield decreased significantly in photothermal catalysis tests. This is because the excessively thick shell increases the diffusion resistance of the reactant gases and severely scatters the incident light, reducing the photothermal efficiency of the internal CuO core.

[0103] In Comparative Examples 4 and 5, copper oxide microspheres and oxygen-vacancy-rich copper oxide O were prepared, respectively. vac -CuO significantly reduces ammonia yield, highlighting the importance of constructing a "hydrophobic and permeable core-shell structure" in this invention: without the protection of the ZIF-8 shell, liquid water directly contacts and covers the active sites, hindering N2 contact and easily triggering hydrogen evolution side reactions.

[0104] In Comparative Example 6, oxygen vacancies were introduced by calcination, but the ammonia yield was still low. This was mainly because the high-temperature (400℃) treatment caused partial sintering and fusion of the one-dimensional nanospike structure of the sea urchin-like microspheres, resulting in a significant decrease in specific surface area. Furthermore, the oxygen vacancies generated by the heat treatment were mainly concentrated in the bulk phase rather than the surface, and the catalytic activity was not as high as that of the liquid-phase reduction method.

[0105] In Comparative Example 7, SiO2 was used for shell coating. However, because the SiO2 shell is hydrophilic and lacks the microporous structure unique to ZIF-8, liquid water can easily pass through the shell and submerge the active sites, and also hinder the effective transport of nitrogen, resulting in extremely low ammonia synthesis yield.

[0106] In Comparative Example 8, increasing the temperature of the hydrothermal reaction resulted in the formation of large-sized microspheres with a diameter exceeding 15 μm due to excessive crystal growth. Furthermore, the nano-spiky structures on the surface fused and became coarser, leading to a decrease in specific surface area and a weakening of the light trapping effect.

[0107] In addition, the stability comparison of ammonia production rate of the catalysts in Example 1, Comparative Example 4, and Comparative Example 5 under 10 hours of continuous light irradiation is shown in the figure below. Figure 6 As shown in the figure. Example 1 exhibits excellent stability, with a nearly horizontal curve, indicating that the ZIF-8 shell effectively prevents the flooding and poisoning of active sites, maintaining high efficiency during long-term reactions. Although Comparative Example 5 showed acceptable initial activity, the curve exhibited a significant downward trend, indicating that the lack of a hydrophobic protective layer led to competitive adsorption of water molecules and deactivation of active sites. Comparative Example 4, due to the lack of active sites and effective mass transfer channels, consistently maintained an extremely low reaction rate. This data comparison strongly demonstrates the advancement of the technical solution of this invention. While introducing oxygen vacancies alone (Comparative Example 5) can improve initial activity, it cannot solve the problems of long-term stability and gas-liquid interface mass transfer. Only by combining "oxygen-rich vacancies" and "ZIF-8 hydrophobic shell" can the efficient and sustained photothermal catalytic ammonia synthesis shown in Example 1 be achieved.

Claims

1. Sea urchin-like oxygen-rich vacancy O vac -CuO@ZIF-8 core-shell structured photothermal catalyst, characterized in that... The catalyst has a core-shell structure, with the core being urchin-shaped copper oxide microspheres assembled from radially arranged one-dimensional nanoneedles or nanospikes, and the surface of the core containing oxygen vacancies (O). vac The shell is composed of in-situ grown zeolite imidazolium ester framework material ZIF-8; The shell layer has a thickness of 10 nm to 50 nm and strong hydrophobic properties, with a contact angle greater than 125°; the core body has a diameter of 1 to 5 μm. The sea urchin-shaped oxygen-rich vacancy O vac The preparation method of CuO@ZIF-8 core-shell structured photothermal catalyst includes the following steps: 1) Preparation of core-body sea urchin-shaped copper oxide microspheres: Copper source and polyethylene glycol are dissolved in a mixture of water and ethanol and subjected to hydrothermal reaction. The molecular guiding effect of polyethylene glycol is used to make copper oxide crystals grow and assemble along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres. 2) Construction of surface defects on the nucleus: The urchin-shaped copper oxide microspheres prepared in step 1 are dispersed in solvent one, and a reducing agent solution is added to carry out a liquid-phase etching reaction, introducing oxygen vacancies in situ to obtain oxygen-vacancy-rich copper oxide O. vac -CuO; 3) Growth of ultrathin hydrophobic shell: The oxygen-rich vacancy copper oxide O obtained in step 2) vac -CuO was dispersed in solvent two to adsorb the zinc source, and then 2-methylimidazole solution was added for in-situ growth. After the reaction was completed, the catalyst was obtained by centrifugation, washing and drying.

2. The sea urchin-like oxygen-rich vacancy O as described in claim 1 vac The method for preparing CuO@ZIF-8 core-shell structured photothermal catalyst is characterized by, Includes the following steps: 1) Preparation of core-body sea urchin-shaped copper oxide microspheres: Copper source and polyethylene glycol are dissolved in a mixture of water and ethanol and subjected to hydrothermal reaction. The molecular guiding effect of polyethylene glycol is used to make copper oxide crystals grow and assemble along a specific axis to obtain core-body sea urchin-shaped copper oxide microspheres. 2) Construction of surface defects on the nucleus: The urchin-shaped copper oxide microspheres prepared in step 1 are dispersed in solvent one, and a reducing agent solution is added to carry out a liquid-phase etching reaction, introducing oxygen vacancies in situ to obtain oxygen-vacancy-rich copper oxide O. vac -CuO; 3) Growth of ultrathin hydrophobic shell: The oxygen-rich vacancy copper oxide O obtained in step 2) vac -CuO was dispersed in solvent two to adsorb the zinc source, and then 2-methylimidazole solution was added for in-situ growth. After the reaction was completed, the catalyst was obtained by centrifugation, washing and drying.

3. The sea urchin-like oxygen-rich vacancy O as described in claim 2 vac The method for preparing CuO@ZIF-8 core-shell structured photothermal catalyst is characterized by, In step 1), the copper source is copper acetate, the volume ratio of water to ethanol in the water and ethanol mixture is 1:3, the number average molecular weight of polyethylene glycol is 2000~6000 g / mol, the mass ratio of copper source to polyethylene glycol is 1:(8~15), the hydrothermal reaction temperature is 100-130℃, and the reaction time is 10~18h.

4. The sea urchin-like oxygen-rich vacancy O as described in claim 2 vac The method for preparing CuO@ZIF-8 core-shell structured photothermal catalyst is characterized by, In step 2), solvent one is a mixture of water and ethanol in a volume ratio of 1:1, reducing agent is a NaBH4 solution with a concentration of 0.01~0.1mol / L, and reaction time is 20~60s.

5. The sea urchin-like oxygen-rich vacancy O as described in claim 2 vac The method for preparing CuO@ZIF-8 core-shell structured photothermal catalyst is characterized by, In step 3), solvent 2 is one of methanol and N,N-dimethylformamide, zinc source is one of zinc nitrate, zinc acetate and zinc chloride, and the in-situ growth time is 10~60 min.

6. The sea urchin-like oxygen-rich vacancy O as described in claim 2 vac The method for preparing CuO@ZIF-8 core-shell structured photothermal catalyst is characterized by, Step 3) Oxygen-rich vacancy copper oxide O vac The mass ratio of CuO, zinc source and 2-methylimidazole solution is 1:(0.5~1):(1~2).

7. The application of the photothermal catalyst as described in claim 1 in the photothermal catalytic reduction of N2 to ammonia at the gas-liquid interface, characterized in that, The specific steps include: 1) The photothermal catalyst was loaded onto a porous hydrophilic substrate; 2) Place the substrate with the catalyst supported on the support platform inside the reactor. The bottom of the reactor is filled with water. Water is drawn to the substrate through a water-absorbing medium to keep the substrate wet. 3) Introduce a nitrogen gas flow to carry out a photothermal catalytic reaction under simulated sunlight conditions; 4) After the reaction is complete, the substrate with the supported catalyst is subjected to ultrasonic extraction using dilute sulfuric acid solution, and the ammonia yield is detected by colorimetric method.

8. The application of the photothermal catalyst as described in claim 7 in the photothermal catalytic reduction of N2 to ammonia at the gas-liquid interface, characterized in that, The nitrogen flow rate was 20-50 mL / min, the solar irradiance was 1 solar irradiance, and the reaction time was 1-4 h.

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