A spin regulation induced co2 reduction catalytic material and a method for preparing and applying the same

Abstract

The present invention belongs to the field of high-efficiency catalytic materials for photoreduction of carbon dioxide, and relates to a spin-regulated CO2 reduction catalytic material and its preparation and application methods. The molecular formula of the single crystal structure of the material is: [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O or [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O; wherein, dopz is 2,2'-bipyrazine carbonate hydrazine; dspz is 2,2'-bipyrazine thiohydrazine. By adjusting the coordination environment of the Fe site to precisely control its spin state, the spin state of the catalytic center is changed from Fe to 3+ The low spin was converted to high spin, which significantly improved the activity of the cluster in the CO2 photoreduction reaction. After 4 hours of light irradiation, the CO yield reached 9.53 mmol g ‑1 , indicating that the photocatalytic performance can be effectively tuned by regulating the spin state of the metal center.

Description

Technical Field

[0001] The present invention belongs to the field of high-efficiency catalytic materials for photoreduction of carbon dioxide reaction, and relates to a spin-regulated CO2 reduction catalytic material and a preparation and application method thereof. Background Art

[0002] With the deterioration of the environment and the depletion of fossil fuels, new clean, renewable and sustainable resources are urgently needed to replace fossil fuels. Photocatalysis has been widely explored in water splitting, CO2 reduction, N2 fixation and pollutant degradation, and is considered to be one of the important ways to achieve sustainable energy supply and environmental remediation. Unfortunately, the photocatalytic efficiency of photocatalysts used in large-scale practical applications is still relatively low. The catalytic efficiency of photocatalysts is affected by several key factors, such as: (1) light harvesting ability; (2) substrate adsorption and activation energy; (3) separation and transportation of photocarriers. It is worth noting that the development of suitable photocatalysts is crucial for the efficient execution of this catalytic process. It is well known that the performance of photocatalysts depends largely on the intrinsic properties of their electronic states, such as the spin states of transition metal sites. In the past few years, efforts have been made to develop various strategies to regulate the spin states of metal centers to further improve their catalytic performance.

[0003] The electronic structure determines the properties of the material, among which spin is an important inherent characteristic of electrons. It can reflect the electronic structure of the catalyst and dominate the chemical behavior of the catalyst.

[0004] However, there are very limited examples of spin regulation in photocatalysis, especially photocatalytic CO2 reduction, which may be due to the huge challenges in regulating the spin state in common photocatalysts. Currently, the spin state regulation of heterogeneous photocatalysts is mainly limited to the generation of structural vacancies and elemental doping. Unfortunately, vacancies and dopants are not necessarily catalytically active for CO2 reduction, and sometimes vacancies are even recombination centers for electrons and holes. At the same time, the distribution of vacancies and dopants in the catalyst is not uniform, and only local spin states change. Therefore, the generation of vacancies and elemental doping in photocatalysts remains a challenge, not only in terms of precise fabrication, but also in establishing the relationship between spin regulation and photocatalysis. Summary of the Invention

[0005] The present invention provides a spin-modulated CO2 reduction catalytic material, its preparation, and application methods, involving a tetranuclear cation cluster. This material modulates the spin state by altering the coordination microenvironment of the Fe site, without necessarily changing the Fe oxidation state. This manipulation results in differences in charge separation efficiency and changes in CO2 adsorption and activation abilities.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] The first aspect of the present invention provides a spin-regulated CO2 reduction catalytic material, the single crystal structure molecular formula of the material is: [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O or [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O; wherein, dopz is 2,2'-bipyrazine carbonate hydrazine; dspz is 2,2'-bipyrazine thiohydrazine.

[0008] A second aspect of the present invention provides a method for preparing a spin-regulated CO2 reduction catalytic material, the method comprising:

[0009] S1. Preparation of organic ligand dopz: Place dihydrazide carbonate in a reaction flask, add ethanol, stir to dissolve, then add 2-acetylpyrazine, then dropwise add glacial acetic acid, heat and stir. After the reaction is complete, cool to room temperature, filter, and vacuum dry to obtain a white powder product;

[0010] The reaction formula is as follows:

[0011]

[0012] Under the catalysis of glacial acetic acid, the nitrogen atom of the hydrazine group (nucleophilic center) attacks the carbonyl carbon to form an unstable addition intermediate: the addition intermediate undergoes a dehydration reaction under acidic conditions, and the hydroxyl group (-OH) and the adjacent proton (H + ) is removed to form a bipyrazine-connected carbon-nitrogen double bond structure, which is then dehydrated to generate the target product dopz.

[0013] Preferably, the molar ratio of carbonate dihydrazide to 2-acetylpyrazine is 1:2, and the volume ratio of ethanol to glacial acetic acid is: 49.9 mL to 50.1 mL: 0.15 mL to 0.25 mL. During the reaction, the hydrazide group (-NH-NH2) of carbonate dihydrazide provides two active sites per molecule, while the carbonyl group of 2-acetylpyrazine serves as the electrophilic center of the reaction. The 1:2 molar ratio ensures that each hydrazide group fully reacts, eliminating excess reactive sites and reducing the occurrence of side reactions.

[0014] As a solvent, ethanol can well dissolve reactants and intermediates, provide a uniform reaction environment, and avoid reactant aggregation or excessive local concentration. The amount of glacial acetic acid (0.15 mL to 0.25 mL) is sufficient to protonate the carbonyl group in 2-acetylpyrazine, increase its electrophilicity, and thus accelerate the nucleophilic addition reaction.

[0015] Furthermore, the reaction time under heating reflux and stirring is 5 to 6 hours at a temperature of 78°C to 82°C. 78°C to 82°C is close to the boiling point of ethanol (approximately 78.5°C), ensuring that the solvent is in a reflux state and providing a constant high-temperature environment for the reaction. This temperature can effectively stimulate the reaction energy barrier between dihydrazide carbonate and 2-acetylpyrazine, promoting the smooth progress of nucleophilic addition and dehydration condensation reactions. The reaction time of 5 to 6 hours can ensure that all reactants are fully reacted, reduce the residual unreacted raw materials, and increase the yield of the target product dopz.

[0016] S2. Preparation of organic ligand dspz: Place thiomethylhydrazine in a reaction flask, add ethanol, stir to dissolve, then add 2-acetylpyrazine, followed by dropwise addition of glacial acetic acid, heat and stir. After the reaction is complete, cool to room temperature, filter, and vacuum dry to obtain a light green powder product;

[0017] The reaction formula is as follows:

[0018]

[0019] The nitrogen atom of the hydrazine group (-NH-NH2) in thiomethylhydrazine attacks the carbonyl carbon (C=O) of 2-acetylpyrazine. Glacial acetic acid protonates the carbonyl oxygen, which enhances the electrophilicity of the carbonyl carbon. After nucleophilic addition, an intermediate containing a hydroxyl group (-OH) and a thiocarbonyl group (C=S) is formed. The addition intermediate undergoes a dehydration reaction, and the hydroxyl group (-OH) reacts with the proton (H + ) combines, removes a molecule of water, and simultaneously generates a C=N double bond: the reaction continues, and another molecule of 2-acetylpyrazine undergoes a second nucleophilic addition reaction with the hydrazine group (-NH-NH2) in the product to form a bipyrazine structure, and finally generates the target product dspz, in which two molecules of 2-acetylpyrazine are connected by the hydrazine group to form the core structure of 2,2'-bipyrazinethiohydrazine.

[0020] Preferably, the molar ratio of thiomethylhydrazine to 2-acetylpyrazine is 1:2. The thiomethylhydrazine molecule contains two active sites (-NH-NH- and -C=S). Each active site requires one molecule of 2-acetylpyrazine to participate in the reaction. The molar ratio of 1:2 can ensure that each thiomethylhydrazine molecule fully reacts with two molecules of 2-acetylpyrazine to form a bipyrazine structure.

[0021] The volume ratio of ethanol to glacial acetic acid is: 49.9 mL to 50.1 mL: 0.15 mL to 0.25 mL. Ethanol, as a solvent, can dissolve thiomethylhydrazine and 2-acetylpyrazine, improving the uniformity of the reactants in the solution. The amount of glacial acetic acid has been optimized to effectively degrade the carbonyl group in 2-acetylpyrazine, increasing its electrophilicity and accelerating the nucleophilic addition reaction. The amount of glacial acetic acid is moderate to avoid excessive acidity that may cause degradation of thiomethylhydrazine or intermediates.

[0022] Furthermore, the reaction time under heating reflux and stirring is 5 to 6 hours, and the temperature is 78° C. to 82° C.

[0023] S3. Preparation of complex: Add the ligand dopz prepared in step S1 or the ligand dspz prepared in step S2 into a beaker containing acetonitrile / acetonitrile and ethanol, stir to dissolve, add metal salt Fe(CF3SO3)2, mix and stir evenly at room temperature, filter, and let stand for one week to obtain complex crystals.

[0024] Furthermore, the stirring temperature is room temperature (25±2°C).

[0025] Among them, in step S3, two complexes were prepared due to different raw materials. When the ligand dopz was used to prepare the complex, the ligand dopz was added to a beaker filled with acetonitrile and stirred to dissolve. The metal salt Fe(CF3SO3)2 was added and mixed and stirred evenly at room temperature to obtain a wine-red clear liquid. After filtering, the filtrate was evenly divided into test tubes, placed in a wide-mouth bottle filled with isopropyl ether, and allowed to stand for one week to obtain black square crystals, which were the complex [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O;

[0026] Specifically, the ligand dopz was completely dissolved in acetonitrile and mixed with the iron salt Fe(CF3SO3)2. 2+ ions gradually formed coordination bonds with the pyrazine ring nitrogen atom (N) in the dopz molecule. Under stirring conditions at room temperature, the four Fe 2+ ions and four dopz ligands form a [2×2] metal framework structure through self-assembly; the dopz ligand connects Fe 2+ ions, each Fe forms a N4O2 coordination environment: the coordination solution (wine red clear solution) is filtered and divided into test tubes, which are placed in a wide-mouth bottle filled with isopropyl ether. The miscibility between isopropyl ether and acetonitrile is limited, resulting in slow evaporation of acetonitrile, and the solution gradually reaches a supersaturated state. In the supersaturated state, the [Fe4(dopz)4] core and CF3SO 3- Anions, acetonitrile (MeCN) molecules and water molecules together form a crystal structure, and after a week, black square crystals are generated.

[0027] Preferably, the molar ratio of dopz to Fe(CF3SO3)2 is 1:1; the usage ratio of acetonitrile to dopz is: 39mL~41mL: 0.19mmol~0.21mmol. The molar ratio of 1:1 means that each Fe 2+The ion and a dopz ligand can be fully matched to avoid excess or insufficient reactants. The amount of acetonitrile used as a solvent has been optimized. 39mL~41mL of acetonitrile provides sufficient dissolution space for 0.19mmol~0.21mmol of dopz, ensuring that the reactants are evenly distributed in the solution. A sufficient amount of solvent can avoid excessive concentration of local reactants, thereby reducing the occurrence of side reactions.

[0028] When the ligand dspz is used to prepare the complex, the ligand dspz is added to a beaker containing ethanol and acetonitrile, stirred to dissolve, and the metal salt Fe(CF3SO3)2 is added. The mixture is mixed and stirred evenly at room temperature to obtain a dark brown clear liquid. The solution is filtered and allowed to stand in a beaker for one week to obtain black rhombus crystals, which are the complex [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O.

[0029] The ligand dspz was fully dissolved in the mixed solvent of ethanol and acetonitrile to form a solution with uniform molecular distribution. The two nitrogen atoms (N) on the pyrazine ring first reacted with Fe 2+ Coordination occurs, and the sulfur atom (S) and nitrogen atom (N) in the thiohydrazine group then react with Fe 2+ Further coordination occurs, and as the reaction proceeds, the four Fe 2+ The ion and the four dspz ligands gradually form a [2×2] node-like framework structure through multidentate coordination. Each dspz ligand bridges the adjacent Fe through a pyrazine ring and a thiohydrazine group. 2+ ions, forming a highly stable structure. After the coordination framework is formed, CF3SO 3- Anions, ethanol and water molecules further combine with the metal framework to form a crystal structure. By leaving the solution to stand for a week, ethanol and acetonitrile slowly evaporate, and the solution gradually reaches a supersaturated state, promoting the nucleation and growth of crystals, and eventually forming black rhombus crystals.

[0030] Preferably, the molar ratio of dspz to Fe(CF3SO3)2 is 1:1; the usage ratio of dspz, ethanol and acetonitrile is: 0.19mmol~0.21mmol:19mL~21mL:19mL~21mL. The 1:1 molar ratio ensures that each dspz ligand can react with one Fe 2+ The ions are fully coordinated to avoid excess or deficiency of reactants. Ethanol and acetonitrile ensure that dspz and Fe(CF3SO3)2 are evenly distributed in the mixed solvent, promoting the complete reaction.

[0031] A third aspect of the present invention provides the use of the aforementioned spin-induced CO2 reduction catalytic material in the field of artificial photosynthesis. This material serves as a core catalyst, combined with a photosensitive semiconductor (such as TiO2 or CdS) to construct an artificial photosynthesis photocatalytic reactor suitable for indoor or outdoor CO2 conversion plants, converting CO2 from industrial waste gas or air into fuel.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention provides two complexes. The single crystal structure of complex 1 is [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O. It crystallizes in the triclinic Pī space group and presents a [2×2] grid structure. The complex is assembled by four ligands dopz and four Fe ions, and each Fe forms a N4O2 coordination environment. The average Fe-N bond length of Fe1 in complex 1 is Average Fe-N bond length of Fe2 Average Fe-N bond length of Fe3 Average Fe-N bond length of Fe4 Therefore, the coordination bond length analysis shows that the complex may have mixed valence, where Fe1 and Fe4 are Fe Ⅱ , Fe2, Fe3 are Fe Ⅲ , presenting a cis mixed valence structure.

[0034] (2) The single crystal structure of complex 2 is [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O. It crystallizes in the single crystal orthorhombic C2 / c space group. Four neutral ligands dspz are connected with four Fe to form a [2×2] node structure. Each Fe forms a coordination environment for N4S2. Complex 2 has four CF3SO 3– And one molecule of ethanol and three molecules of water participate in the crystallization. Complex 2 has only one coordination environment of Fe ions, and the average bond length of Fe-N bond of Fe ions is

[0035] (3) The present invention successfully synthesized an iron metal tetranuclear cation cluster with a high spin state electronic structure through self-assembly technology. This cluster achieves the change of spin state by finely regulating the coordination microenvironment of the iron (Fe) site. This change of spin state has a significant effect on catalytic activity. The spin state of the catalytic center changes from Fe to 3+ When the low spin is changed to high spin, complex 1 shows more active CO2 photoreduction performance. After 4 hours of light irradiation, the CO yield of complex 1 reaches 9.53 mmol g -1This significant improvement in activity demonstrates that photocatalytic performance can be effectively tuned by manipulating the spin state of the metal center, which has important guiding significance for the design of new and efficient photocatalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 The X-ray crystal structures of complex 1 (a) and complex 2 (b);

[0038] Figure 2 Infrared spectra of complex 1 (a) and complex 2 (b);

[0039] Figure 3 Powder X-ray diffraction patterns of complex 1 (a) and complex 2 (b);

[0040] Figure 4 Thermogravimetric images of complex 1 (a) and complex 2 (b);

[0041] Figure 5 Magnetic susceptibility curves of complex 1 (a) and complex 2 (b);

[0042] Figure 6 Screening of photocatalytic solvent ratios for complexes 1(a) and 2(b);

[0043] Figure 7 The photocatalytic gas production of complex 1 (a) and complex 2 (b) changes with time;

[0044] Figure 8 This is the experimental diagram for controlling the photocatalytic performance of the complex;

[0045] Figure 9 Cyclic voltammetry curves of complex 1 (a) and complex 2 (b) under different atmospheres;

[0046] Figure 10 Electrochemical impedance spectroscopy (EIS) of complex 1 (red) and complex 2 (blue). DETAILED DESCRIPTION

[0047] To further illustrate the technical means and effectiveness of the present invention in achieving its intended objectives, a method for preparing a spin-induced CO2 reduction catalytic material according to the present invention, along with its specific implementation, features, and effectiveness, is described below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0048] The reagents involved in the experiment were produced by manufacturers such as Anaiji Chemical and Shanghai Lingfeng, and the details are shown in Table 1. The reagents involved were used directly without further purification.

[0049] Table 1 Reagents

[0050]

[0051] The equipment and instruments used in the experiment are shown in Table 2:

[0052] Table 2 Main instruments

[0053]

[0054]

[0055] Example 1

[0056] Preparation of the ligand dopz: Place dihydrazide carbonate (0.45 g, 5 mmol) in a reaction flask, add 30 mL of ethanol, and stir to dissolve. Then, add 2-acetylpyrazine (1.22 g, 10 mmol), followed by 3-5 drops of glacial acetic acid. Heat and stir at 80°C for 5 h. After the reaction is complete, cool to room temperature, filter, and vacuum dry to obtain 2,2'-dipyrazine carbonate hydrazine as a white powder.

[0057] Preparation of complex (1) [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O: Add the ligand dopz (0.2 mmol, 0.0396 g) to a beaker containing 40 mL of acetonitrile and stir to dissolve. Add the metal salt Fe(CF3SO3)2 (0.2 mol, 0.0728 g) and mix thoroughly to obtain a wine-red clear solution. Filter and divide the filtrate equally into test tubes, place them in a wide-mouth bottle containing isopropyl ether, and let it stand for about a week to obtain black square crystals.

[0058] Example 2

[0059] Preparation of ligand dspz: Thiosemicarbazide (0.53 g, 5 mmol) was put into a reaction bottle, 30 mL of ethanol was added, stirred and dissolved, then 2-acetylpyrazine (1.22 g, 10 mmol) was added, followed by 3-5 drops of glacial acetic acid, and heated and stirred at 80°C for 5 h. After the reaction was completed, it was cooled to room temperature, suction filtered, and vacuum dried to obtain light green powder product 2,2'-dipyrazyl thiosemicarbazide.

[0060] Preparation of complex (2) [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O: The ligand dspz (0.2 mmol, 0.0396 g) was added to a beaker containing 20 mL of ethanol and 20 mL of acetonitrile, stirred and dissolved, and the metal salt Fe(CF3SO3)2 (0.2 mmol, 0.0728 g) was added, mixed and stirred to obtain a dark brown clear solution. The solution was filtered and left to stand in a beaker for about a week to obtain black rhombic crystals.

[0061] Crystallographic data of complex (1), complex (2) were collected on a Bruker APEX-II CCD instrument with graphite monochromatic radiation Mo Kα at the corresponding temperature. Data collection, data reduction and unit optimization were performed using two program packages, Bruker Instrument Service v4.2.2 and SAINT V8.34A. The complex structure was resolved using the SHELXS program package, and the crystal data were optimized by full-matrix least squares method using the SHELXL program package. Absorption correction was performed using the multi-scan program package SADABS. The hydrogen atoms of the organic ligand were optimized on F2 by riding mode on the SHELXTL program package. The crystallographic data of the complex are shown in Table 3.

[0062] Table 3 Crystallographic parameters of the complex

[0063]

[0064] a R1=∑(||F0|-|Fc||) / ∑|F0|; b wR2=[∑w(|F0 2 |-|Fc 2 ) 2 / ∑w|F0 2 | 2 ] 1 / 2 ; c GOF=

[0065] [∑[w(F0 2 -Fc 2 ) 2] / (Nobs-Nparams)] 1 / 2 ,based on the dataI>2σ(I).

[0066] The single crystal structure of complex 1 is [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O, crystallized in the triclinic Pī space group, showing a [2×2] grid structure, and the unit cell parameters of the complex are α=87.315(2)°, β=82.628(2)°, γ=87.616(2)°, Z=2, The complex is composed of four ligands dopz and four Fe ions, each of which forms a coordination environment for N4O2. The average Fe-N bond length of Fe1 in complex 1 is Average Fe-N bond length of Fe2 Average Fe-N bond length of Fe3 Average Fe-N bond length of Fe4 Therefore, the coordination bond length analysis shows that the complex may have mixed valence, where Fe1 and Fe4 are Fe Ⅱ , Fe2, Fe3 are Fe Ⅲ , presenting a cis mixed valence structure.

[0067] The single crystal structure of complex 2 is [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O, crystallized in single crystal orthorhombic C2 / c space group, and the unit cell parameters of the complex are α=90°, β=107.039(3)°, γ=90°, Z=4, The complex is composed of four neutral ligands dspz connected to four Fe to form a [2×2] node structure, and each Fe forms a coordination environment for N4S2. Complex 2 has four CF3SO 3– And one molecule of ethanol and three molecules of water participate in the crystallization. Complex 2 has only one coordination environment of Fe ions, and the average bond length of Fe-N bond of Fe ions is

[0068] Infrared absorption spectroscopy analysis: Figure 2 As shown, complexes 1 and 2 have the highest peaks at 1068 cm -1 The medium-strong peak at the bottom is the anion CF3SO 3- The absorption peak is at 1605~1615cm -1 The absorption peak appearing at is the stretching vibration peak of the Schiff base C=N bond.

[0069] Powder X-ray diffraction analysis: Figure 3As shown in (a), there is good consistency between the crystalline powder X-ray diffraction pattern of complex 1 (represented by the red spectrum) and the simulated diffraction pattern calculated based on the single crystal structure (represented by the black spectrum), which confirms that complex 1 is a pure crystalline phase. Figure 3 (b) shows the agreement between the powder X-ray diffraction data (red spectrum) and the simulated diffraction pattern (black spectrum) of complex 2, further confirming the purity and crystal structure of complex 2. Although there are differences in the intensity of the diffraction peaks, which may be due to the preferred orientation effect of the powder sample, the consistency of the peak positions still shows a high degree of consistency between the experimental data and the theoretical model.

[0070] Thermogravimetric analysis: Figure 4 As shown in (a), the thermogravimetric analysis (TGA) of complex 1 revealed that it experienced a significant weight loss stage in the temperature range of 50-330°C, with a total reduction of 4.59%. This is mainly attributed to the gradual removal of solvent molecules, including acetonitrile and water molecules, from the crystal lattice of complex 1. As the temperature further increased to 340°C, the molecular structure of complex 1 began to undergo significant thermal degradation, resulting in a sharp drop in its structural stability. Ultimately, after completing the entire thermal decomposition process, the remaining mass of complex 1 was 22.01%, which may represent its thermally stable skeleton or decomposition product. Similarly, Figure 4 Panel (b) shows the thermogravimetric analysis results of complex 2. At a relatively low temperature of 64°C, the weight of complex 2 begins to slowly decrease, a change attributed to the gradual evaporation and removal of the crystallization solvent, ethanol and water molecules, from its lattice. As the temperature continues to rise, starting at 300°C, the molecular structure of complex 2 begins to undergo thermal degradation. By 450°C, the structure of complex 2 has completely collapsed, marking the limit of its thermal stability.

[0071] Magnetic susceptibility curve analysis: Figure 5 As shown in (a), the temperature-dependent magnetic susceptibility test of complex 1 covers the entire temperature range from 2 to 300 K. At an extremely low temperature of 2 K, the molar magnetic susceptibility of complex 1, χ M T starts at 1.101cm3 / mol K, indicating that it has significant magnetic properties. When the temperature rises to 60K, the magnetic susceptibility enters a plateau period, and χ M The T value reaches 8.014 cm3 / mol K, which may indicate a special spin arrangement or interaction. As the temperature is further increased, the magnetic susceptibility gradually increases until at 300 K, χ M The T value rises to 15.656 cm3 / mol K, and the changes in the entire temperature range show an incomplete spin crossover (SCO) phenomenon, which may be related to the spin state change of the metal center in complex 1. Figure 5(b) describes the magnetic susceptibility behavior of complex 2. At 300K, the χ M The T value is 1.8 cm3 / mol K, which is higher than the theoretical value of four low-spin Fe3+ (s=1 / 2) (1.5 cm3 / mol K), indicating the contribution of orbital magnetic moment. As the temperature decreases, the magnetic susceptibility gradually decreases, which suggests that complex 2 has antiferromagnetic coupling characteristics. At 29K, χ M The T value drops sharply to 0.8 cm³ / mol K, a sudden change that may mark a magnetic phase transition. Combined magnetic susceptibility data confirm that the electronic structure of the Fe ions in complex 2 transforms to low-spin paramagnetic Fe³+ (s=1 / 2) at this temperature, and is in an antiferromagnetic coupling state.

[0072] Photocatalytic solvent ratio screening analysis: A screening experiment was conducted on the solvent ratio. The complex was added as a catalyst (1 mg) in the photocatalytic reaction vessel. The photosensitizer was tris(2,2-bipyridyl)ruthenium(II) chloride hexahydrate (RuPS) (1 mg). The sacrificial agent was 1,3-dimethyl-2-phenylbenzimidazolidine (14 mg). The solvent system was a mixed solution of acetonitrile and water. CO2 was introduced into the photocatalytic system for 15 min. Under a light intensity of 100 mW cm -2 Irradiate for 5 hours, and then perform gas chromatography analysis after the irradiation. Figure 6 As shown, when the solvent ratio is adjusted to a volume ratio of acetonitrile to water of 4.7:0.3, complexes 1 and 2 exhibit the best catalytic effect in the CO2 photocatalytic reduction reaction.

[0073] Analysis of the graph of photocatalytic gas production changing with time: Figure 7 As shown, gaseous products such as CO and H2 were carefully analyzed by gas chromatography, while liquid products were detected by ion chromatography, but only a small amount of HCOOH was found. In the CO2 reduction reaction, as the illumination time increased, the catalytic activity of complex 1 reached a stable state after 4 hours. In contrast, the gas production produced by complex 2 increased more slowly. When complex 1 was used as a photocatalyst, its yield reached 9.53 mmol g after the initial 4 hours of illumination. -1 When complex 2 was used as a catalyst under the same conditions, the CO yield was low, only 2.12 mmol g -1 This comparison highlights the higher efficiency and activity of complex 1 in the photocatalytic CO2 reduction reaction.

[0074] Analysis of photocatalytic performance control experimental diagram: Figure 8As shown, in the absence of complexes 1 and 2, only trace amounts of CO and H2 were detected in the experiment. This indicates that without the participation of an effective photocatalyst, the efficiency of the CO2 photoreduction reaction is extremely low. In further experiments, no products were detected in the absence of photosensitizers, sacrificial agents or light irradiation. This result highlights the core role of these components in promoting the CO2 photoreduction process. When Ar gas was used instead of CO2, only trace amounts of gas were detected, which further confirmed that the participation of CO2 is crucial for the occurrence of the reaction. In addition, through comparative experiments, only trace amounts of CO were detected using equimolar FeCl2 and FeCl3 as reference catalysts. The results of these control experiments indicate that the detected CO production is mainly achieved through the photocatalytic action of CO2 on the metal grid molecular catalyst, rather than the thermal decomposition or chemical decomposition of organic matter.

[0075] Analysis of cyclic voltammetry curves under different atmospheres: Figure 9 As shown in Figure 2, in order to further explore the electron transfer mechanism in the photocatalytic and CO2 reduction process, we conducted cyclic voltammetry (CV) tests on complexes 1 and 2 under Ar and CO2 atmospheres. In Ar atmosphere, both complexes showed three significant reduction peaks, corresponding to the Fe 3+ / Fe 2+ 、Fe 2+ / Fe +1 and Fe +1 / Fe 0 However, under CO2 atmosphere, the CV curve of complex 2 showed only a slight current change, indicating that its electron transfer activity with CO2 was relatively low. In contrast, the CV curve of complex 1 under CO2 atmosphere showed a significant redox peak shift, especially a higher reduction potential characteristic peak at 0.89 V. This phenomenon indicates that complex 1 has higher activity in catalyzing CO2 reduction.

[0076] Electrochemical impedance spectroscopy (EIS) analysis: Figure 10 As shown, the curved surface radius of complex 1 is smaller than that of complex 2, a property that indicates lower charge transfer impedance in complex 1. In electrochemical and photocatalytic processes, the efficiency of charge separation and transfer is one of the key factors determining catalytic performance. A smaller arc radius is generally associated with faster charge mobility because the charge is transferred along a shorter path, reducing energy consumption and potential recombination opportunities during the transfer process. Therefore, complex 1, due to its lower charge transfer impedance, is able to more effectively separate and transfer photogenerated charge carriers, which contributes to its enhanced photocatalytic activity. This efficient charge separation and transfer capability enables complex 1 to exhibit superior performance in light-driven chemical reactions, especially in applications requiring rapid charge transfer.

[0077] This study successfully synthesized an iron tetranuclear cationic cluster using self-assembly technology. This cluster possesses a high-spin electronic structure, and its spin state can be precisely controlled by adjusting the coordination environment of the iron (Fe) ion sites. This control strategy significantly improved the cluster's activity in the CO2 photoreduction reaction, achieving a CO yield of 9.53 mmol g within a 4-hour reaction time. -1 , which is four times higher than that of the low-spin metal grid. This research result not only demonstrates the possibility of enhancing photocatalytic performance by regulating the spin state of metal centers, but also provides valuable guidance for the design of future photocatalysts.

[0078] With the above-described preferred embodiments of the present invention as inspiration, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A spin-regulated CO2 reduction catalytic material, the single crystal structure of which is: Complex 1: [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O; DOPZ is 2,2'-dipyrazine carbonate hydrazine; its structural formula is: ； Complex 2: [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O; wherein dspz is 2,2'-dipyrazinethiohydrazine; its structural formula is: ； Complex 1 crystallizes in the triclinic system P ī space group, presenting a [2×2] grid structure, the unit cell parameters of complex 1 are a =13.0294(3)Å, b =13.1002(2)Å, c =24.2159(5)Å, α =87.315(2)°, β =82.628(2)°, γ =87.616(2)°, Z =2, V =4092.05(14)Å 3 The complex is composed of four dopz ligands and four Fe ions, each of which forms a N4O2 coordination environment. In complex 1, the average Fe‒N bond length of Fe1 is 2.143Å, the average Fe‒N bond length of Fe2 is 1.971Å, the average Fe‒N bond length of Fe3 is 1.987Å, and the average Fe‒N bond length of Fe4 is 2.118Å. Complex 2 crystallized in single crystal orthorhombic system C2 / c The space group and unit cell parameters of complex 2 are a =27.7668(8)Å, b =18.7840(5)Å, c =14.8225(5)Å, α =90°, β =107.039(3)°, γ =90°, Z =4, V =7391.6(4)Å 3 Four neutral ligands dspz connect with four Fe to form a [2×2] node structure, and each Fe forms a coordination environment for N4S2; complex 2 has four CF3SO3 – One molecule of ethanol and three molecules of water participated in the crystallization, and the average bond length of the Fe‒N bond of Fe ions in complex 2 was 1.952Å.

2. A method for preparing the spin-regulated CO2 reduction catalytic material according to claim 1, characterized in that: The steps include: S1. Preparation of organic ligand dopz: Place dihydrazide carbonate in a reaction flask, add ethanol, stir to dissolve, then add 2-acetylpyrazine, then dropwise add glacial acetic acid, heat and stir. After the reaction is complete, cool to room temperature, filter, and vacuum dry to obtain a white powder product; S2. Preparation of organic ligand dspz: Place thiomethylhydrazine in a reaction flask, add ethanol, stir to dissolve, then add 2-acetylpyrazine, followed by dropwise addition of glacial acetic acid, heat and stir. After the reaction is complete, cool to room temperature, filter, and vacuum dry to obtain a light green powder product; S3. Prepare the complex: add the ligand dopz prepared in step S1 or the ligand dspz prepared in step S2 into a beaker containing acetonitrile or acetonitrile and ethanol, stir to dissolve, add metal salt Fe(CF3SO3)2, mix and stir evenly at room temperature, filter, and let stand for one week to obtain complex crystals.

3. A method for preparing a spin-regulated CO2 reduction catalytic material according to claim 2, characterized in that: In step S3, When the ligand dopz is used to prepare the complex, the ligand dopz is added to a beaker filled with acetonitrile and stirred to dissolve, and the metal salt Fe(CF3SO3)2 is added and mixed and stirred evenly at room temperature to obtain a wine-red clear liquid. After filtering, the filtrate is evenly divided into test tubes, placed in a wide-mouth bottle filled with isopropyl ether, and allowed to stand for one week to obtain black square crystals, which are the complex [Fe4(dopz)4](CF3SO3)4·3MeCN·H2O; When the ligand dspz is used to prepare the complex, the ligand dspz is added to a beaker containing ethanol and acetonitrile, stirred to dissolve, and the metal salt Fe(CF3SO3)2 is added. The mixture is mixed and stirred evenly at room temperature to obtain a dark brown clear liquid. The solution is filtered and allowed to stand in a beaker for one week to obtain black rhombus crystals, which are the complex [Fe4(dspz)4(CF3SO3)4]·EtOH·3H2O.

4. The method for preparing a spin-regulated CO2 reduction catalytic material according to claim 2, wherein: In step S1, the molar ratio of the carbonate dihydrazide to the 2-acetylpyrazine is 1:2, and the volume ratio of the ethanol to the glacial acetic acid is: 49.9 mL to 50.1 mL: 0.15 mL to 0.25 mL.

5. The method for preparing the spin-regulated CO2 reduction catalytic material according to claim 2, wherein: In step S2, the molar ratio of the thiomethylhydrazine to the 2-acetylpyrazine is 1:2, and the volume ratio of the ethanol to the glacial acetic acid is: 49.9 mL ~ 50.1 mL: 0.15 mL ~ 0.25 mL.

6. The method for preparing a spin-regulated CO2 reduction catalytic material according to claim 3, wherein: When the ligand dopz is used to prepare the complex, the molar ratio of the dopz and the Fe(CF3SO3)2 is 1:1; the usage ratio of the acetonitrile and the dopz is: 39 mL ~ 41 mL: 0.19 mmol ~ 0.21 mmol.

7. The method for preparing a spin-regulated CO2 reduction catalytic material according to claim 3, wherein: When the ligand dspz is used to prepare the complex, the molar ratio of the dspz and the Fe(CF3SO3)2 is 1:1; the usage ratio of the dspz, the ethanol and the acetonitrile is: 0.19 mmol ~ 0.21 mmol: 19 mL ~ 21 mL: 19 mL ~ 21 mL.

8. Use of the spin-regulated CO2 reduction catalytic material according to claim 1 in the field of artificial photosynthesis.

Images