A highly efficient photocatalytic material for the reduction of carbon dioxide, its preparation method and application

Abstract

This invention belongs to the field of metal-organic framework materials, specifically relating to a highly efficient photocatalytic material for the photoreduction of carbon dioxide, its preparation method, and its application. The molecular formula of the single-crystal structure of the complex material is: [Fe(bidpe)2(SCN)2]; where bidpe is 4,4'-bis(imidazolium-1-yl)diphenyl ether. The complex material of this invention is a non-covalent metal-organic layer (MOL) formed by the self-assembly of a one-dimensional chain containing a bisimidazole ligand. This invention constructs a photocatalytic reaction system using Fe-MOL as a catalyst, RuPS as a photosensitizer, and BIH as a sacrificial agent. This system can reduce CO2 to CO under visible light irradiation greater than 400 nm, exhibiting extremely high CO yield and selectivity, demonstrating the application potential of non-covalent MOL catalysts with single-metal catalytic active sites in the field of "artificial photosynthesis".

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework materials, specifically relating to a highly efficient photocatalytic material for the photoreduction of carbon dioxide, its preparation method, and its application. Background Technology

[0002] Molecular-based crystal materials, such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have been widely synthesized and used as potential catalysts for artificial photosynthesis and photocatalysis, including the hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), water oxidation, and organic photocatalysis. The structural modification and synthesis of these catalytic materials are tunable, and multiple structural units can be functionally optimized, including photosensitizers (PSs) and catalytic centers, to promote efficient electron transfer in photocatalytic systems. However, most previously reported examples involve noble metal elements such as Re, Ir, and Pd. Furthermore, in some cases, the selectivity of CO2RR is often poor due to competition from HER in the aqueous medium. Catalysts without noble metals are not only limited, but their catalytic activity is also much lower than that of those containing noble metals. Therefore, developing molecular-based crystal materials without noble metal ions for the efficient photoreduction of carbon dioxide is of great importance.

[0003] Metal-organic layers (MOLs) are a novel type of two-dimensional functional material in the field of artificial photosynthesis in recent years; iron is an abundant and non-toxic transition metal on Earth. MOLs utilize iron as the catalytic center, and due to their ultrathin thickness, they can overcome most of the weaknesses of bulk MOFs. Because most photosensitizers have high absorption rates, the active centers exposed on the thin MOL layers readily participate in the photoreaction; the nanoscale MOF particles also minimize light scattering and increase photon utilization. The catalytic activity of CO2RR or HER in this system depends on the metal center, and its activity is superior to most crystalline catalysts, including some noble metals, exhibiting good performance in terms of CO2 selectivity and structural stability. Furthermore, with the increase of the number of substrates exposed on the surface of MOLs, the photocatalytic efficiency may continue to improve.

[0004] The key to catalytic performance lies in introducing single catalytic active sites of specific metal atoms, which possess tunable catalytic selectivity. However, most metal-organic frameworks (MOLs) have covalently extended two-dimensional topologies, while MOLs with novel linkage types remain rare. Supramolecular metal-organic framework catalysts can exert single-metal catalytic site-dependent catalytic activity. Therefore, it is essential to introduce supramolecular frameworks to immobilize self-assembled one-dimensional metal-organic chains into two-dimensional MOLs. Summary of the Invention

[0005] This invention provides a catalytic material with highly efficient and selective photoreduction of carbon dioxide, its preparation method, and its applications. Using this material as a catalyst yields excellent structural stability. The supramolecular interactions between the self-assembled one-dimensional metal-organic chains can maximize the monocoordinate atom-dependent catalytic effect.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0007] The first aspect of this invention is to provide a catalytic material with highly efficient and selective photoreduction of carbon dioxide. The single-crystal molecular formula of the material is: [Fe(bidpe)2(SCN)2] (hereinafter referred to as bidpe-Fe); wherein bidpe is 4,4'-bis(imidazol-1-yl)diphenyl ether. The complex material of this invention is a non-covalent metal-organic layer (MOL) formed by the self-assembly of a one-dimensional chain containing a bisimidazole ligand. π-π stacking introduces a supramolecular framework, giving the MOL good structural stability. The photosensitizer has a high absorption rate; the thinner the MOL, the lower the light scattering, the easier it is for the active center to participate in the photoreaction, the higher the photon utilization rate, and the easier it is to exert a single metal coordination atom-dependent catalytic effect.

[0008] Furthermore, the material belongs to the triclinic crystal system, with space group [missing information]. Crystal parameters are α=87.638(2)°, β=88.487(2)°, γ=83.507(2)°, Z=1, Specifically, the crystallographic data for the single-crystal structure are as follows:

[0009]

[0010] a GOF=[∑[w(F0 2 -F c 2 ) 2 ] / (Nobs-N params )] 1 / 2 ,based on the data with I>2σ(I).

[0011] b R1=∑||F0|-|F c || / ∑|F0|;wR2=[∑[w(F0 2 -F c 2 ) 2 ] / ∑[w(F0 2 ) 2 ]] 1 / 2 .

[0012] Crystallographic data were obtained using a Bruker APEX-IICCD single-crystal diffractometer (graphite monochromatic radiation Mo-Kα, incident radiation). Diffraction data of the prepared bidpe-Fe were collected at room temperature. Data collection, data reduction, and cell refinement were performed using Bruker InstrumentService v4.2.2 and SAINT v8.34A software. The structure was optimized using a direct method in SHELXS software. The SADABS program was used for absorption correction, employing an F-based method. 2 The full matrix least squares method is used to optimize the anisotropy of all non-hydrogen atoms, and after geometrically generating hydrogen atoms in the running mode, it is refined to obtain specific crystallographic data.

[0013] Furthermore, the smallest asymmetric unit of the material consists of one metal ion and two SCNs. - It consists of two ligands, bidpe; the coordination mode is all-nitrogen six-coordinate, and the spatial structure is a twisted octahedral structure; the nitrogen atoms on the terminal imidazoles of the main organic ligand bidpe coordinate with metal atoms, forming a one-dimensional chain structure through extension. Due to the metal nodes and SCN... - The weak coordination bonds between the metals leave abundant metal sites in the supramolecular layer to satisfy the six-coordinate relationship of the metals.

[0014] Furthermore, adjacent metal ions are interconnected through two bide ligands, and the crystal structure exhibits a chain-like structure with channels. The Fe-N bond length of the material is [missing information]. The bond angle around the Fe center is 89.55(7)-180(12)°, and the distance between Fe...Fe reaches... The distance between the two nearest benzene ring centers between layers The shortest atomic distance on the benzene ring is Adjacent chains are tightly stacked, with a distance of [missing information]. This demonstrates that the material is an ultrathin MOF constructed from metal-organic layers through π-π supramolecular interactions between benzene ring surfaces.

[0015] A second aspect of the present invention is to provide a method for preparing a photocatalytic material with highly efficient and selective photoreduction of carbon dioxide, the method comprising:

[0016] S1. Preparation of organic ligand bidpe: A mixture of cuprous oxide, 4,4'-dibromodiphenyl ether, imidazole and anhydrous potassium carbonate was placed in a round-bottom flask, DMF was added, and the mixture was reacted under N2 atmosphere. After cooling and filtration, distilled water was poured into the filtrate, and a white flocculent solid was generated. The solid was collected by filtration and vacuum dried to obtain the organic ligand bidpe.

[0017] S2. Preparation of the complex [Fe(bidpe)2(SCN)2]: Prepare an aqueous solution of ferrous chloride, a mixed solution of methanol and water, and a methanol solution of ligand bidpe and potassium thiocyanate. Place the three solutions in a test tube in descending order of density, seal the tube, and let it stand at room temperature for two weeks to obtain the complex [Fe(bidpe)2(SCN)2], which is a light yellow blocky crystal suitable for single-crystal X-ray diffraction testing. This preparation method uses readily available raw materials, is simple to synthesize, has a high yield, and achieves the same technical advantages.

[0018] Furthermore, in step S1, the molar ratio of cuprous oxide, 4,4'-dibromodiphenyl ether, imidazole, and anhydrous potassium carbonate is 0.49–0.51: 9.9–10.1: 39.9–40.1: 39.9–40.1;

[0019] The volume ratio of DMF to distilled water is 29.9–30.1:299.7–300.3.

[0020] Furthermore, in step S1, the synthesis of the ligand bidpe is carried out under a N2 atmosphere, with a required temperature of 155℃~165℃ and a reflux reaction time of 46~50h.

[0021] Furthermore, in step S1, the synthesis of the organic ligand bidpe was carried out under an N2 atmosphere with a flow rate of 1.25 × 10⁻⁶. -4 ~1.5×10 -4 m 3 / h, after which the reaction is completed, cool to room temperature.

[0022] Furthermore, in step S1, cuprous oxide acts as a catalyst, lowering the activation energy of the chemical reaction, promoting the reaction rate, and increasing the reaction selectivity; anhydrous potassium carbonate can not only act as a catalyst to accelerate the reaction rate, but also provide an alkaline environment and keep the reaction system dry; excess imidazole can ensure complete reaction with 4,4'-dibromodiphenyl ether, increasing the reaction yield; the volume ratio of DMF to water maximizes the production of white flocculent solids.

[0023] Furthermore, in step S2, the molar ratio of ferrous chloride, ligand bidpe, and potassium thiocyanate is 0.007–0.009: 0.015–0.017: 0.015–0.017;

[0024] The volume ratio of an aqueous solution of ferrous chloride, a mixed solution of methanol and water, and a methanol solution of ligand bidpe and potassium thiocyanate is 3.9–4.1:4.9–5.1:3.9–4.1.

[0025] Furthermore, in step S2, the volume ratio of methanol to water in the mixed solution of methanol and water is 0.9–1.1:0.9–1.1.

[0026] Furthermore, in step S2, ferrous chloride preferentially reacts with potassium thiocyanate to form Fe(SCN)₂. Therefore, the concentration ratio of ferrous chloride to potassium thiocyanate is determined to be 1:2. Secondly, bidpe contains two coordination sites—nitrogen atoms on the imidazole groups. Therefore, the coordination ratio of Fe(SCN)₂ to bidpe is 1:2. However, the specific coordination process involves competition for coordination sites and difficulties in coordination. Therefore, the concentration of ferrous chloride is 2 μmol / mL, and the concentrations of KSCN and the ligand bidpe are 4 μmol / mL. This is the optimal solution concentration, resulting in crystals with a high single-crystal yield, suitable size, regular shape, and obvious luster. Lower concentrations may lead to fewer single crystals, microcrystals, or even a clear liquid; higher concentrations may lead to poor crystal quality, polycrystalline clusters, or even precipitation.

[0027] A third aspect of this invention provides the application potential of a highly efficient photocatalytic material for the reduction of carbon dioxide, as described above, in the field of artificial photosynthesis. Bispe-Fe, as a non-covalent MOL single-metal site catalyst, offers the possibility of lowering the activation barriers of the two transition states in the CO2RR process. Its application potential in the field of artificial photosynthesis includes, but is not limited to: the construction of structural units, the rational optimization of catalytic activity, and the improvement of the catalytic selectivity of CO2-CO.

[0028] Specifically, a photocatalytic reaction system was constructed using bidpe-Fe material as a non-covalent MOL single-metal site catalyst, [Ru(bpy)3]Cl2·6H2O (RuPS) as a photosensitizer, and BIH as a sacrificial agent. In an acetonitrile aqueous solution saturated with carbon dioxide, CO2 was selectively reduced to CO and H2O was reduced to H2 by irradiation with visible light greater than 400 nm.

[0029] Furthermore, in the above reaction system, using the material as a catalyst in an aqueous solution of acetonitrile saturated with carbon dioxide, an extremely high CO yield (4 mmol g) can be obtained. -1 h -1 Both the selectivity (91.6%) and the selectivity are superior to most crystalline catalysts, including some precious metals.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The bidpe-Fe provided by this invention, as a molecular-based crystal material, exhibits good selectivity for CO2RR without the presence of noble metals (such as Re, Ir and Pd), with a CO selectivity of 91.6%, proving that the MOL molecular-based photocatalyst has high selectivity for CO2RR.

[0032] (2) The bidpe-Fe provided by this invention uses iron as the catalytic center and has an ultra-thin thickness, overcoming the defects of bulk MOFs. Because most photosensitizers have high absorption rates, the active centers exposed on the MOF thin layer can easily participate in the photoreaction; the nanoscale MOF particles also minimize light scattering and increase photon utilization. The catalytic activity of this system for CO2RR or HER depends on the metal center, and its activity is superior to most crystalline catalysts, including some noble metals. A high CO yield of up to 4 mmol g was obtained in a saturated aqueous solution of carbon dioxide and acetonitrile. -1 h -1 This demonstrates that the MOL molecular-based photocatalyst has high activity for CO2RR.

[0033] (3) The bidpe-Fe provided by this invention introduces a supramolecular framework, exhibiting good structural stability. Most MOLs have a two-dimensional topological structure extended by covalent bonds, while bidpe-Fe forms two-dimensional MOLs through the supramolecular interactions between self-assembled one-dimensional metal-organic chains. The key to the catalytic performance of bidpe-Fe is the presence of single catalytic active sites with specific atoms, which have tunable catalytic selectivity. The supramolecular metal-organic framework can exert a greater degree of single-metal coordination atom-dependent catalytic effect. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 (a) is the design concept of a two-dimensional MOL; Figure 1 (b) and (c) are transmission electron microscope images of bidpe-Fe under normal and high resolution, respectively; Figure 1 (d) shows the morphology and height profile of bidpe-Fe under an atomic force microscope in the selected area; Figure 1 (e) shows the theoretical and calculated values ​​of powder X-ray diffraction for MOLs; Figure 1 (f) shows the crystal structure of two-dimensional MOLs with supramolecular non-covalent linkages.

[0036] Figure 2 Fourier transform infrared spectra of the complex bidpe-Fe and its ligand bidpe.

[0037] Figure 3 The thermogravimetric curve of bidpe-Fe.

[0038] Figure 4 These are ordinary resolution transmission electron microscope (TEM) images of bidpe-Fe at different scales.

[0039] Figure 5 High-resolution transmission electron microscopy images of bidpe-Fe at different scales.

[0040] Figure 6 Nanolayer height analysis of bidpe-Fe using atomic force microscopy.

[0041] Figure 7 This is the X-ray photoelectron spectrum of bidpe-Fe.

[0042] Figure 8 (a) is a graph of the temperature-dependent magnetic susceptibility of bidpe-Fe; Figure 8 (b) Electron paramagnetic resonance (EPR) of bidpe-Fe at 2K in the X-band; Figure 8 (c) is the X-ray photoelectron spectrum of bidpe-Fe in the Fe 2p orbital.

[0043] Figure 9 Cyclic voltammetry curves of the bidpe-Fe nanolayer after introducing N2 (black) and 0.23M CO2 (red) gases (scan rate: 0.1 V s) -1 Electrolyte: 0.1M sodium sulfate aqueous solution).

[0044] Figure 10 The cyclic voltammetry curves of RuPS with ferrocene as an internal standard are shown.

[0045] Figure 11 The amounts of CO and H2 produced after 5 hours of light irradiation in three parallel experiments using bidpe-Fe as a catalyst.

[0046] Figure 12 The amount of CO and H2 produced by bidpe-Fe under light irradiation changes over time.

[0047] Figure 13 Cyclic tests were conducted for bidpe-Fe, with each cycle lasting 5 hours.

[0048] Figure 14 The image shows the PXRD pattern after the bide-Fe photocatalytic reaction.

[0049] Figure 15 (a) is the UV-Vis diffuse reflectance spectrum of bidpe-Fe; Figure 15 (b) is the Tauc diagram obtained from this.

[0050] Figure 16 X-ray photoelectron spectrum of the valence band (VB) of bide-Fe.

[0051] Figure 17 This is the band structure diagram of the MOL catalyst.

[0052] Figure 18 (a) and (b) are the photoluminescence spectra of BIH and bidpe-Fe after adding different amounts of RuPS, respectively.

[0053] Figure 19 [Ru(bpy)3] 2+ I0 / I is a function of BIH concentration.

[0054] Figure 20 This describes the mechanism of CO2 photocatalytic reduction to CO and H2O reduction to H2 in the bidpe-Fe / RuPS / BIH system. Detailed Implementation

[0055] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the specific implementation methods, features, and effects of a highly efficient photocatalytic material for the reduction of carbon dioxide, its preparation method, and its application, based on the present invention, are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0056] All chemical reagents used in the experiment were purchased from retailers without purification, and came from manufacturers such as Anaiji Chemical, Alfa Reagents, and Sinopharm Group. Details are shown in Table 1.

[0057] Table 1 Reagent List

[0058]

[0059] The equipment and instruments used in the experiment are shown in Table 2:

[0060] Table 2 Main Instruments

[0061]

[0062]

[0063] Example 1

[0064] This invention proposes a single-crystal structure of a photocatalytic material with highly efficient selective photoreduction of carbon dioxide. The molecular formula of the single-crystal structure of the complex material is: [Fe(bidpe)2(SCN)2]; wherein, bidpe is 4,4'-bis(imidazol-1-yl)diphenyl ether.

[0065] Using a Bruker APEX-IICCD single-crystal diffractometer (graphite monochromatic radiation Mo-Kα, incident radiation...) Diffraction data of the prepared bidpe-Fe were collected at room temperature. Bruker Instrument Service v4.2.2 and SAINT v8.34A software were used for data collection, data reduction, and cell refinement. The structure was optimized using a direct method in SHELXS software. The SADABS program was used for absorption correction, employing an F-based method. 2 The full matrix least squares method was used to optimize the anisotropy of all non-hydrogen atoms, and after geometrically generating hydrogen atoms in the running mode, the crystallographic data were refined, thus obtaining specific crystallographic data, as shown in Table 3.

[0066] Table 3 Summary of Crystal Data (T = 100K)

[0067]

[0068] a GOF=[∑[w(F0 2 -F c 2 ) 2 ] / (Nobs-N params )] 1 / 2 ,based on the data with I>2σ(I).

[0069] b R1=∑||F0|-|F c || / ∑|F0|;wR2=[∑[w(F0 2 -F c 2 ) 2 ] / ∑[w(F0 2 ) 2 ]] 1 / 2 .

[0070] Example 2

[0071] Synthesis of the organic ligand 4,4'-bis(imidazol-1-yl)diphenyl ether (bidpe):

[0072] A mixture of cuprous oxide (0.07 g, 0.5 mmol), 4,4'-dibromodiphenyl ether (3.24 g, 10 mmol), imidazole (2.72 g, 40 mmol), and anhydrous potassium carbonate (5.52 g, 40 mmol) was placed in a 100 mL round-bottom flask. 30 mL of LDM was added, and the mixture was reacted at 160 °C for 2 days under a N2 atmosphere. After cooling, the mixture was filtered, and 300 mL of distilled water was added to the filtrate. A white flocculent solid was formed. The solid was collected by filtration and dried under vacuum to give 4,4'-bis(imidazol-1-yl)diphenyl ether in 75% yield.

[0073] Example 3

[0074] Synthesis of the complex single-crystal material [Fe(bidpe)2(SCN)2](bidpe-Fe):

[0075] Prepare an aqueous solution (4 mL) of ferrous chloride (0.008 mmol, 1.59 mg), a 1:1 mixture of methanol and water (5 mL), and a methanol solution (4 mL) of ligand bidpe (0.016 mmol, 4.83 mg) and potassium thiocyanate (0.016 mmol, 1.56 mg). Place the three solutions in a test tube according to their density from bottom to top, seal the tube, and let it stand at room temperature for two weeks to obtain a light yellow blocky crystal [Fe(bidpe)2(SCN)2] suitable for single-crystal X-ray diffraction testing, with a yield of 60% (calculated as Fe).

[0076] Example 4

[0077] Preparation of metal-organic layer catalysts:

[0078] First, the block catalyst was ground into powder using a mortar and pestle. Then, the ground catalyst was sonicated in 100 mL of ethanol solution for 6-8 hours. Next, the colloidal suspension was collected by centrifugation in air. Finally, it was dried in a nitrogen atmosphere at room temperature for 24 hours, thus successfully preparing the nanolayer catalyst sample.

[0079] Performance testing

[0080] Fourier transform infrared spectroscopy test:

[0081] Recorded at 4000-400 cm⁻¹ on a Bruker EQUINOX-55 Fourier transform infrared spectrometer. -1 Infrared spectrum within the range. Figure 2 To perform Fourier transform infrared spectroscopy (FTIR) measurements on the complex and its ligand, the infrared spectra of bidpe-Fe obtained after the measurements were compared with those of the ligand bidpe. It can be seen that the complex contains the infrared peak of the ligand, and the peak is located at 2066 cm⁻¹. -1 The infrared peak at that location confirms the presence of coordinated SCN in the structure.- This indicates that both the primary and secondary ligands are present and participate in coordination. Specifically, the infrared data for bidpe-Fe (KBr pellet, cm⁻¹) is shown. -1 ): 3423(w),3123(w),2923(w),2853(w),2047(s),1654(w),1514(s),1406(m),1340(w),130 5(m),1246(m),1064(s),962(m),929(m),817(s),733(m),668(m),654(w),541(m),516(w).

[0082] Powder X-ray diffraction (PXRD) test:

[0083] Using Cu Kα (40kV and 100mA) as the X-ray source, PXRD was recorded on a RINT2000 vertical goniometer; the single-crystal CIF file was opened in Crystal Diffract, and the simulation results were obtained as follows. Figure 1 The PXRD pattern shown in (e) leads to the conclusion that the positions of the PXRD diffraction peaks of bidpe-Fe are approximately the same as those of the simulated PXRD diffraction peaks of the crystal structure obtained by single-crystal diffraction, indicating that the complex is a pure phase.

[0084] Thermogravimetric analysis:

[0085] Figure 3 The thermogravimetric analysis (TGA) plot is shown. Under a nitrogen atmosphere, the temperature was increased from 50°C to 800°C at a rate of 10°C per minute to obtain the TGA plot. As shown in the plot, there is almost no weight loss during the initial heating process, and weight loss only begins at 350°C. The first stage of weight loss occurs from 350°C to 510°C, with a weight loss rate of approximately 43.5%; the second stage occurs from 510°C to 670°C, with a weight loss rate of approximately 41.3%; thereafter, the weight of the complex remains at approximately 15.2%. The analysis demonstrates that the complex exhibits excellent thermal stability.

[0086] Elemental analysis test:

[0087] FeC was analyzed using a Vario EL elemental analyzer. 40 H 28 N 10 Elemental analysis of O4S2 (C, H, N): Theoretical values ​​(%): C, 61.30; H, 3.80; N, 18.83; Calculated values ​​(%): C, 61.35; H, 3.77; N, 18.84.

[0088] Transmission electron microscopy (TEM) and atomic force microscopy (AFM):

[0089] Transmission electron microscopy images were taken on a TECNAI F30HRTEM. Figure 1 (b) and Figure 4 The TEM image shows its independent nanolayer morphology. Figure 1 (c) and Figure 5 The high-resolution transmission electron microscope (HRTEM) images confirm that the supramolecular MOL is composed of parallel one-dimensional lattices with a lattice spacing of approximately 0.73 nm, which is close to the interchain distance along the (110) crystal plane. Figure 1 (d) and Figure 6 The AFM image reveals the ultrathin structure of MOL, with an average diameter of 400 nm and an average thickness of 2.78 nm. This thickness is close to the five-layer height (2.84 nm) of bide-Fe determined by single-crystal X-ray diffraction.

[0090] X-ray photoelectron spectroscopy (XPS) test:

[0091] XPS data were acquired on an ESCALAB 250Xi system using Al Kα X-rays (6 mA 12 kV) as the excitation source. All measurements were performed in CAE mode with reference to C1s (284.6 eV). Background removal was performed using a linear method, with position, full width at half maximum (FWHM), area, and Lorentz-Gaussian ratio (30%) as the default parameters for the deconvolution process. Figure 7 and Figure 8 (c) It can be seen that Fe 2p 3 / 2 The presence of two resonance peaks at 709.6 eV and 712.2 eV indicates that the iron in the complex bidpe-Fe belongs to the trivalent state.

[0092] Temperature-dependent magnetic susceptibility test:

[0093] To determine the electronic structure of the Fe centers in the samples, the magnetic susceptibility of the MOL samples was measured. Magnetic susceptibility measurements were performed using an MPMS-XL7AC microscope at a magnetic field strength of 2500 Oe and a temperature range of 5–300 K, with corrections made for antimagnetic effects using Pascal's constant. Figure 8 (a) shows the temperature-dependent magnetic susceptibility curve of the complex. As can be seen from the graph, the molar magnetic susceptibility of Bispe-Fe is 4.34 cm⁻¹ at 298 K. 3 K mol -1 This value is related to the magnetically isolated high-spin Fe 3+ The calculated result (4.375cm) for (s=5 / 2, g=2.0) 3 K mol -1 The values ​​are very close. This indicates that most of the iron sites in the ground sample are easily oxidized.

[0094] Electron spin resonance (ESR) spectroscopy:

[0095] High-resolution ESR spectroscopy provides information on the electronic valence states captured in photocatalytic reactions. Data was recorded under vacuum conditions on a JEOL JES-FA200 X-band ESR spectrometer, and the experimental temperature environment was controlled using JEOL's heating / temperature control module. Figure 8 As shown in (b), under 2K conditions, the iron element in bidpe-Fe is in the trivalent state, exhibiting a typical rhombic high-spin Fe structure. 3+ ; in g ‖ =4.21 and g ⊥ The presence of strong and weak signals at 1.85 indicates that it has a local electronic structure.

[0096] Cyclic Voltammetry (CV) Test:

[0097] The chemical vapor deposition (CVs) of the catalyst and photosensitizer were measured on a CHI 660E electrochemical workstation. A glassy carbon electrode, AgCl / Ag, and Pt wire were used as the working electrode, reference electrode, and counter electrode, respectively. The scan rate was 0.10 V / s. -1 The scanning direction is positive, and the potential value is expressed relative to the ordinary hydrogen electrode (NHE). Using deoxygenated 1M sodium sulfate as the electrolyte solution, the catalyst suspension was carefully ground in 0.025 g / mL Nafion solution, then transferred to the surface of a 0.5 cm diameter glassy carbon electrode and dried in air, thus completing the preparation of the working electrode. The CV of RuPS was measured in a degassed CH3CN / H2O (v / v, 9 / 1) solution, using 0.5 mM RuPS and 0.10 M Bu4NPF6 as the electrolyte solution, and ferrocene (Fc) as the internal reference.

[0098] like Figure 9 As shown, the bidpe-Fe sample exhibits three distinct reduction peaks under N2 irradiation, corresponding to Fe... +3 / +2 Fe +2 / +1 and Fe +1 / 0 The reduction of RuPS. When CO2 is introduced into the reaction solution, a significant shift in the redox positions is observed, particularly a high reduction potential at the characteristic peak (-0.96 V). The CV of RuPS is as follows: Figure 10 As shown, the comparison shows that bidpe-Fe can drive CO2RR (CO2 / CO, -0.52V vs. NHE) and HER (H2O / H2, -0.41V vs. NHE), further proving the thermodynamic feasibility of redox reactions.

[0099] Photocatalytic performance test:

[0100] The photocatalytic reduction performance of carbon dioxide was investigated by simulating a solar-driven photoreduction reaction. The photocatalytic experiment was conducted in an 11 mL diaphragm-sealed quartz glass bottle. The catalyst (1 mg) was added to a mixture of 4.7 mL acetonitrile and 0.3 mL water, followed by the addition of 1,3-dimethyl-2-phenylbenzimidazole (BIH, 14 mg) and ruthenium tripyridine chloride (RuPS, 1 mg) as sacrificial and photosensitizers, respectively. The bottle was then bubbled with CO2 for 15 min before irradiation. A 300 W xenon lamp (CEL-HXF 300, CEAULICHT) and a 400 nm cutoff filter were used to simulate a radiation irradiance of 100 mW / cm². 2 Sunlight illumination was used. After the photocatalytic reaction was completed, the amounts of CO and H2 produced during the photocatalytic process were quantitatively determined using gas chromatography (GC9790Plus).

[0101] Figure 11 Three parallel experiments were conducted on photocatalysis, and it can be seen that the products of photocatalysis are CO and H2. Figure 12 A sampling experiment was conducted on photocatalysis, which showed that after 5 hours of light irradiation, the CO production was 19.66 mmol g. -1 H2 production was 1.78 mmol / g. -1 Thus, the selectivity for CO was 91.7%. To verify the role of each component in the photoreaction, a series of blank control experiments were conducted, as shown in Table 4. The results showed that CO could not be detected when the reaction was carried out without sacrificial agents, photosensitizers, carbon dioxide, or under dark conditions; only in the absence of a catalyst could a small amount of CO be detected.

[0102] After completing one photocatalytic reaction, the catalyst was removed, centrifuged, dried, and recovered. The photocatalytic reaction was then repeated five times under the same conditions as the first experiment. Figure 13 As shown, the gas yield did not change significantly after repeated experiments, indicating that the photocatalyst can be reused multiple times and has high stability. Powder X-ray diffraction analysis was performed on the catalyst after the cycling experiment, as shown... Figure 14 As shown, its diffraction peaks are basically consistent with the measured PXRD simulation values ​​of the crystal structure, indicating that the catalytic reaction process did not change the crystal structure of the catalyst.

[0103] Table 4. Photocatalytic control experiments

[0104]

[0105] Photocatalytic performance investigation:

[0106] To investigate the optical properties and bandgap energy of the material, ultraviolet-visible diffuse reflectance (DRS) spectroscopy of bidpe-Fe was performed using a Lambda 750UV-Vis-NIR spectrophotometer (Perkin Elmer). Figure 15 As shown in (a), it exhibits a broad and strong absorption peak in the range of 300–550 nm, with a large visible light absorption range. The band gap energy Eg is generally calculated using the formula: (αhυ) 2 = (hυ – Eg), draw its Tauc curve, as shown. Figure 15 As shown in (b), the band gap energy Eg = 2.78 eV can be obtained. XPS valence band analysis of bidpe-Fe is shown below. Figure 16 As shown, the intersection of the tangent line and the x-axis is 1.28 eV. According to the formula: E VB,NHE =ψ(equipment work function) + E VB,XPS -4.44 yields a valence band position of 1.04 eV relative to the standard hydrogen electrode. Since the relationship between the conduction band, valence band, and band gap of a semiconductor satisfies the formula: E CB =E VB –Eg, thus calculating the conduction band value of the catalyst material to be -1.74 eV. For example... Figure 17 As shown, the conduction band position of the complex is more negative than the standard reduction potentials of CO2 / CO and H2O / H2, i.e., ΔG < 0. This indicates that both CO2RR and HER are thermodynamically feasible, and the photogenerated electrons have sufficient energy to reduce CO2 and H2O to CO and H2, respectively.

[0107] To investigate the electron migration pathway and efficiency, photoluminescence quenching experiments were conducted on the photosensitizer RuPS using BIH as a sacrificial agent and MOF as a catalyst. The sacrificial agent and catalyst were added separately to a solution containing only RuPS, and the process was monitored using an Edinburgh FS5 fluorescence spectrophotometer. Figure 18 As shown, it can be observed that the peak intensity at 610 nm gradually decreases with increasing concentration of the sacrificial agent in the entire system, indicating that the photosensitizer RuPS in the solution can capture electrons provided by the sacrificial agent BIH. However, after adding bidpe-Fe, the peak intensity at 610 nm did not decrease significantly, indicating that no electron transfer occurred in the reaction system containing only the photosensitizer and catalyst under illumination. Figure 19 As shown, the fluorescence quenching of RuPS by BIH fits well with the Stern-Wolmer equation, yielding a quenching constant (Ksv) of 0.8 ± 0.03 mM. -1 The results indicate that photocatalytic CO2RR is initiated by the transfer of electrons from the BIH to the photoexcited state RuPS*, generating the reduced state RuPS. - And transfer electrons to the Fe catalytic sites of the catalyst MOF.

[0108] Based on the characterization tests of catalyst materials and the experimental phenomena of photocatalytic reactions, the mechanism of the entire photocatalytic system can be inferred as follows: Figure 20 As shown, when light greater than 400 nm irradiates the photocatalytic reactor, the photosensitizer RuPS is excited to RuPS*, and the sacrificial agent BIH reduces RuPS* back to RuPS. - Next, RuPS - Electrons are continuously transferred to the Fe catalytic sites of the catalyst, Fe III It is continuously reduced to the active substance Fe. 0 Then, the O atoms of CO2 react with Fe... 0 They combine to form an adduct, Fe-CO2; finally, through protonation, CO and RuPS are generated. - It can be converted into RuPS to complete the redox cycle.

[0109] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A catalytic material for the photoreduction of carbon dioxide, characterized in that, The material is a non-covalent metal organic layer formed by self-assembly of one-dimensional chains containing a bimidazolyl ligand, and a molecular formula of a single crystal structure of the material is: [Fe(bidpe)2(SCN)2]; wherein bidpe is 4,4'-bis(imidazol-1-yl) diphenyl ether; the material belongs to a triclinic system, and a space group is P , and crystal parameters are a = 9.3515(2) Å, b = 9.4736(2) Å, c = 10.8457(2) Å, α = 87.638(2)°, β =88.487(2)°, gamma =83.507(2)°, Z = 1, V = 953.64(3) Å 3 .

2. The catalytic material for photo-reduction of carbon dioxide according to claim 1, wherein, The minimum asymmetric unit of the material consists of one metal ion, two SCN − and two ligands bidpe; the coordination mode is hexa-coordination of all nitrogen, and the spatial structure is a distorted octahedral structure; wherein the nitrogen atoms on the two edge terminal imidazoles of the organic ligand bidpe are coordinated with the metal atom, and a one-dimensional chain structure is formed by extension, and the other two nitrogen atoms are connected with the metal node through a weak coordination bond of SCN − .

3. The catalytic material for photo-reduction of carbon dioxide according to claim 1, wherein, The Fe-N bond lengths of the material are in the range of 2.1661(17) Å - 2.2124(18) Å, the bond angles around the Fe center are in the range of 89.55(7) - 180(12)°, the Fe ... The distance of the Fe is up to 16.671 Å, the distance between the nearest two centers of benzene rings between layers is 3.905 Å, the shortest atomic distance on the benzene ring is 3.378 Å; the two adjacent chains are tightly packed with a distance of 7.127 Å.

4. The method of claim 1 to 3, wherein the method is characterized by, The method comprises: S1, preparing an organic ligand bidpe: a mixture of cuprous oxide, 4,4'-dibromo diphenyl ether, imidazole and anhydrous potassium carbonate is placed in a round-bottom flask, DMF is added thereto, and the reaction is carried out under an N2 atmosphere, cooled, filtered, distilled water is poured into the filtrate, white flocculent solid is generated, filtered and collected, and vacuum dried to obtain the ligand bidpe; S2, preparing [Fe(bidpe)2(SCN)2]: an aqueous solution of ferrous chloride, a mixed solution of methanol and water, a methanol solution of ligand bidpe and potassium thiocyanate are prepared, the three solutions are placed in a test tube in the order of density from large to small from bottom to top, sealed, and placed at room temperature for two weeks to obtain the [Fe(bidpe)2(SCN)2) in the form of light yellow block crystals suitable for single crystal X-ray diffraction test.

5. The method for preparing a photocatalytic material for carbon dioxide reduction according to claim 4, characterized in that, In step S1, the molar ratio of the cuprous oxide, the 4,4'-dibromo diphenyl ether, the imidazole and the anhydrous potassium carbonate is 0.49~0.51:9.9~10.1:39.9~40.1:39.9~40.1; The volume ratio of the DMF and distilled water is 29.9~30.1:299.7~300.

3.

6. The method for preparing a photocatalytic material for carbon dioxide reduction according to claim 4, characterized in that, In step S2, the molar ratio of the ferrous chloride, the ligand bidpe and the potassium thiocyanate is 0.007~0.009:0.015~0.017:0.015~0.017; The volume ratio of the aqueous solution of ferrous chloride, the mixed solution of methanol and water, and the methanol solution of ligand bidpe and potassium thiocyanate is 3.9~4.1:4.9~5.1:3.9~4.

1.

7. The method for preparing a photocatalytic material for the reduction of carbon dioxide according to claim 4, characterized in that, In the step S1, the temperature required for the synthesis of the ligand bidpe is 155~165℃, and the reflux reaction time is 46~50 h.

8. The application of a catalytic material for the photoreduction of carbon dioxide according to any one of claims 1~3 in the field of artificial photosynthesis.

9. The method of claim 8, wherein the method is characterized by, The catalytic material for the photoreduction of carbon dioxide is used as a non-covalent MOL single metal site catalyst, [Ru(bpy)3]Cl2·6H2O is used as a photosensitizer, and BIH is used as a sacrificial agent to construct a photocatalytic reaction system, and under the irradiation of visible light with a wavelength greater than 400 nm, CO2 is selectively reduced to CO, and H2O is reduced to H2.

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