Room temperature synthesis of olefin-linked single atom modified covalent organic frameworks without electron-withdrawing substituents, and preparation method and application thereof

Abstract

The application discloses a room-temperature-synthesized olefin-connection-type single-atom-modified covalent organic framework material without an electron-withdrawing substituent, a preparation method and application thereof, and belongs to the technical field of photocatalysis. The application first synthesizes the olefin-connection-type covalent organic framework (COF) without the electron-withdrawing substituent through a Horner-Wadsworth-Emmons reaction (HWE reaction) under room-temperature conditions, and introduces a cobalt single atom through post-modification, so that the prepared COF material has excellent light absorption performance, rich cobalt single-atom active sites, and high carrier separation capacity promoted by the full conjugated olefin connection and single-atom modification, and can simultaneously drive the photocatalytic CO2 reduction and H2O oxidation reaction. The COF material provided by the application can realize efficient visible light-driven artificial photosynthesis without adding a sacrificial agent or a photosensitizer, and has high catalytic activity and good stability.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, and specifically relates to a room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework material, its preparation method, and its application. Background Technology

[0002] The excessive consumption of fossil fuels has led to a continuous rise in atmospheric carbon dioxide concentration. Photocatalytic carbon dioxide reduction technology, mimicking the natural process of photosynthesis, utilizes solar energy to convert carbon dioxide into high-value-added chemical feedstocks. Currently, researchers have made significant progress in the field of photocatalytic carbon dioxide reduction, utilizing traditional inorganic semiconductors such as TiO2 and ZnO, as well as novel photocatalysts such as MOFs and g-C3N4. However, these photocatalysts still face many key challenges in practical application and large-scale production, such as the easy recombination of photogenerated electron-hole pairs, insufficient stability, or uneven active sites. Therefore, the core challenge of this technology lies in developing photocatalysts that combine high activity, excellent stability, and high selectivity.

[0003] In recent years, covalent organic frameworks (COFs) have shown great potential in the field of photocatalysis due to their highly designable crystal structures, tunable porosity, excellent stability, and functionalizable organic skeletons. Among them, imine-bonded COFs have been studied extensively, but the localization effect of π electrons in imine-bonded COFs leads to low photogenerated carrier mobility, which limits their efficiency in practical photocatalytic applications. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a room-temperature synthesized, electron-withdrawing substituent-free olefin-linked, single-atom modified covalent organic framework material, its preparation method, and its applications. This covalent organic framework material exhibits excellent light absorption performance, abundant cobalt metal active sites, fully conjugated COFs linked by olefins, and single-atom modification promoting carrier separation. It simultaneously achieves photocatalytic CO2 reduction and H2O oxidation reactions in pure water without the addition of sacrificial agents or photosensitizers, demonstrating high catalytic activity and good stability.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified COF material, the chemical structural formula of which is shown in Formula I: Formula I, Where, in the formula This indicates an omitted repeating structural unit.

[0006] Constructing COFs with fully conjugated structures is crucial for promoting the generation, separation, and migration of photogenerated carriers, and is key to improving their photocatalytic performance. At the same time, introducing single-atom active sites can enhance carbon dioxide adsorption and promote the separation and transport of photogenerated carriers, thereby further improving photocatalytic efficiency.

[0007] Secondly, the present invention provides a method for preparing a room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified COF material, comprising the following steps: S1. Under a nitrogen atmosphere, tris(4-formylphenyl)amine, 5,5′-bis(diethylphosphomethyl)-2,2′-bipyridine and potassium tert-butoxide were placed in an organic solvent and reacted with stirring. After the reaction was completed, the mixture was filtered, washed and dried to obtain an olefin-linked COF without electron-withdrawing substituents. S2. The olefin-linked COF without electron-withdrawing substituents is placed in an organic solvent and reacted with cobalt chloride hexahydrate under stirring. After the reaction is completed, the mixture is filtered, washed, and dried to obtain a room-temperature synthesized, olefin-linked single-atom modified COF material without electron-withdrawing substituents.

[0008] Further, in step S1, the molar ratio of tris(4-formylphenyl)amine, 5,5′-bis(diethylmethylphospho)-2,2′-bipyridine and potassium tert-butoxide is 0.02∶0.03∶0.12.

[0009] In the above formula I As structural units, the chemical structure of the room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified COF material prepared in this invention is determined by the geometric symmetry of the reactant monomers, the number of functional groups, the linkage mode, and the single-atom introduction strategy. The combination of the geometric symmetry of the monomers and the number of functional groups predetermines the possible topological type. This invention constructs a C3-symmetric tris(4-formylphenyl)amine containing three aldehyde groups. As an aldehyde monomer, 5,5′-bis(diethylphosphomethyl)-2,2′-bipyridine contains two active methylene groups at C2. As a nucleophilic group, it forms C=C double bonds through nucleophilic addition reactions. The C=C double bonds are connected to form periodically repeating structural units. The COFs prepared in this invention are hcb topological structures constructed with the symmetry of [C3+C2] monomers. The COFs extend infinitely in a two-dimensional plane, and the repeating unit is a six-membered ring, i.e. Formula I.

[0010] Furthermore, in step S1, the organic solvent is selected from tetrahydrofuran.

[0011] Furthermore, in step S1, the reaction is carried out at room temperature for 72 hours.

[0012] Furthermore, in step S2, the mass ratio of the olefin-linked COF without electron-withdrawing substituents to cobalt chloride hexahydrate is 1:0.08.

[0013] Furthermore, in step S2, the organic solvent is selected from methanol.

[0014] Furthermore, in step S2, the reaction is carried out at room temperature for 18 hours.

[0015] Thirdly, this invention provides an application of room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified COF material in the simultaneous photocatalytic reduction of CO2 and oxidation of H2O.

[0016] The room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified COF material uses CO2 and H2O as reactants, and simultaneously photocatalyzes the reduction of CO2 and the oxidation of H2O to generate CO and O2.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: (1) This invention is the first to synthesize olefin-linked single-atom modified COFs without electron-withdrawing substituents by the Horner-Wozworth-Emmons reaction (HWE reaction) at room temperature, and introduces cobalt single atoms through post-modification, so that the prepared COF material has excellent light absorption performance, abundant cobalt single-atom active sites, olefin-linked fully conjugated COFs and single-atom modification promote carrier separation, and can simultaneously achieve photocatalytic CO2 reduction and H2O oxidation.

[0018] (2) The room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified COF material provided by the present invention can directly carry out photocatalytic reaction in pure water without the addition of sacrificial agents and photosensitizers, exhibiting high catalytic activity and good stability.

[0019] (3) The method for preparing room temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified COF material provided by the present invention is relatively simple and the post-processing is relatively easy. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of UJN-COF-8 prepared in Example 1; Figure 2SEM image of UJN-COF-8 prepared in Example 1; Figure 3 Infrared spectra of UJN-COF-8, precursor UJN-COF-7, and raw materials tris(4-formylphenyl)amine (TFPA) and 5,5′-bis(diethylphosphomethyl)-2,2′-bipyridine (PA) prepared in Example 1; Figure 4 The X-ray diffraction pattern of UJN-COF-8 prepared in Example 1; Figure 5 Synchrotron radiation diagram of cobalt atoms in UJN-COF-8 prepared in Example 1; where a is the k-side X-ray near-side structure (XANES) spectrum of cobalt atoms, b is the Fourier transform Co R space EXAFS spectrum of UJN-COF-8, and c is the R space EXAFS data and fitting curve of UJN-COF-8. Figure 6 The solid-state UV-Vis absorption spectrum of UJN-COF-8 prepared in Example 1; Figure 7 Tauc curve of UJN-COF-8 prepared in Example 1; Figure 8 The Mott-Schottky spectrum of UJN-COF-8 prepared in Example 1; Figure 9 Electrochemical impedance spectroscopy of UJN-COF-8 prepared in Example 1; Figure 10 The results show the photocatalytic performance of UJN-COF-8 prepared in Example 1. Figure 11 The UJN-COF-8 prepared in Example 1 18 Results of O isotope labeling test; Figure 12 The photocatalytic stability test results are for UJN-COF-8 prepared in Example 1. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] The room temperature in this invention refers to 25±2℃.

[0028] All raw materials required in the embodiments of this invention were purchased commercially.

[0029] Example 1: A method for preparing a room-temperature synthesized, electron-withdrawing, olefin-linked single-atom modified COF material. (1) Under a nitrogen atmosphere, a mixture of 5,5′-bis(diethylphosphomethyl)-2,2′-bipyridine dispersion (82.2 mg, 0.18 mmol) and tris(4-formylphenyl)amine (40.2 mg, 0.12 mmol) was placed in a round-bottom flask containing anhydrous tetrahydrofuran (30 mL), and potassium tert-butoxide (81.0 mg, 0.72 mmol) was added. The reaction was carried out at room temperature for 72 h. After the reaction was completed, the solid product was separated by filtration and washed with DMF, acetone, water and ethanol in sequence. The obtained solid product was dried under vacuum at 60 °C for 12 h to obtain an olefin-linked COF without electron-withdrawing substituents, which was an orange-yellow powder and was designated as precursor UJN-COF-7. (2) At room temperature, the precursor UJN-COF-7 (40.0 mg) and cobalt chloride hexahydrate (3.2 mg) obtained in step (1) were added to 10 mL of methanol and stirred at room temperature for 18 h to obtain a dispersion solution. The dispersion solution was washed with methanol and dried under vacuum at 60 °C for 12 h to obtain a room temperature synthesized olefin-linked single-atom modified COF material without electron-withdrawing substituents, denoted as UJN-COF-8. Figure 1 This is a schematic diagram of the structure of UJN-COF-8 prepared in Example 1.

[0030] Performance testing The structure of UJN-COF-8 prepared in Example 1 was characterized by scanning electron microscopy. Figure 2 The image shows a SEM image of UJN-COF-8 prepared in Example 1. Figure 2 As can be seen from the above, the UJN-COF-8 prepared in Example 1 has a porous network structure composed of tiny particles.

[0031] Figure 3 The infrared spectra of UJN-COF-8, the precursor UJN-COF-7, and the raw materials tris(4-formylphenyl)amine (TFPA) and 5,5′-bis(diethylphosphomethyl)-2,2′-bipyridine (PA) prepared in Example 1 are shown, with the aldehyde group (1690 cm⁻¹) being the most prominent. -1 ) and phosphorus-oxygen double bond (1250 cm) -1 The disappearance of ) and the C=C bond (1630 cm) -1 The presence of ) indicates the successful preparation of UJN-COF-8, and after the insertion of metal Co, there is no significant change in the FT-IR of UJN-COF-8 compared with UJN-COF-7, revealing the preservation of the framework during the post-modification process.

[0032] Figure 4 The X-ray diffraction pattern of UJN-COF-8 prepared in Example 1 shows distinct diffraction peaks at 2θ = 2.6° and 4.3°, which are attributed to the reflections of the (100) and (110) crystal planes, respectively, indicating that the COF material has good crystallinity.

[0033] Figure 5 Synchrotron radiation diagram of cobalt atoms in UJN-COF-8 prepared in Example 1; where a is the k-edge X-ray near-edge structure (XANES) spectrum of cobalt atoms, b is the Fourier transform Co R space EXAFS spectrum of UJN-COF-8, and c is the R space EXAFS data and fitting curve of UJN-COF-8, indicating that cobalt exists in the form of single atoms in UJN-COF-8 prepared in Example 1.

[0034] Figure 6The solid-state UV-Vis absorption spectrum of UJN-COF-8 prepared in Example 1 is shown below. Figure 6 As can be seen from the above, the light absorption range of UJN-COF-8 prepared in Example 1 is the entire visible light region.

[0035] Figure 7 The Tauc curve of UJN-COF-8 prepared in Example 1 is shown below. Figure 7 As can be seen from the data, the band gap (E) of UJN-COF-8 prepared in Example 1 is... g The value is 2.01 eV.

[0036] Figure 8 The Mott-Schottky spectrum of UJN-COF-8 prepared in Example 1 is shown. It can be seen that the conduction band (CB) of UJN-COF-8 is -1.03 eV (relative to Ag / AgCl), and therefore -0.93 eV relative to the standard hydrogen electrode (NHE). This is determined by formula E. VB =E CB + E g The valence band can be calculated to be 1.08 eV, which can simultaneously achieve photocatalytic CO2 reduction and H2O oxidation.

[0037] Figure 9 Electrochemical impedance spectroscopy of UJN-COF-8 prepared in Example 1. From... Figure 9 As can be seen, the UJN-COF-8 prepared in Example 1 exhibits a low charge transport impedance, which significantly promotes the migration and separation efficiency of photogenerated carriers, thereby effectively enhancing photocatalytic activity.

[0038] Application Example 1: Photocatalysis Experiment 2 mg of UJN-COF-8 prepared in Example 1 was dispersed in 1 mL of water and uniformly coated onto a circular glass surface (38 mm in diameter). The glass surface with UJN-COF-8 on its surface was dried at room temperature for 12 h, and then placed on a glass support in a 150 mL photocatalytic reactor. 5 mL of distilled water was added to the bottom of the photocatalytic reactor as a reducing agent. Before illumination, air was removed from the photocatalytic reactor by gas replacement to ensure that the reactor was ultimately in a CO2 atmosphere. A light intensity of 16.7 mW / cm² was used. -2 A 300 W xenon lamp with a 420 nm filter was used as the light source to simulate sunlight. After a period of irradiation, 1 mL of gas sample was taken and the CO content was determined by gas chromatography (8890 GC System, Agilent, USA). Samples were taken and tested at irradiation times of 0, 1, 2, 3, and 4 hours. Simultaneously, [the following method was used]. 18 O-labeled water (H2) 18O) was used as a reactant, replacing ordinary water (H2) under exactly the same reaction conditions. 16 The photocatalytic reaction was carried out using O), and isotope labeling experiments were conducted. The gaseous products were analyzed using a triple quadrupole gas chromatography-mass spectrometry (Shimadzu 8040) to confirm that the generated O2 originated from the reactant H2O. The photocatalytic performance test results of UJN-COF-8 prepared in Example 1 are as follows: Figure 10 As shown, the CO yield reaches 149.60 μmol g after 4 hours of reaction. -1 (wherein, μmol g) -1 (As of μmol product / g UJN-COF-8). In H2 18 O replaces H2 16 When O is a reactant, such as Figure 11 As shown, it was detected in the generated gas. 18 O2 (m / z = 36) 16 O 18 O (m / z = 34) 18 O (m / z = 18) and H2 18 A signal with m / z = 20. Wherein, 18 The generation of O2 is direct evidence that O2 originates from water molecules.

[0039] Application Example 2: Cyclic Stability Experiment 2 mg of UJN-COF-8 prepared in Example 1 was dispersed in 1 mL of water and uniformly coated onto a circular glass surface (38 mm in diameter). The glass surface with UJN-COF-8 was dried at room temperature for 12 h and then placed on a glass support in a 150 mL photocatalytic reactor. 5 mL of distilled water was added to the bottom of the photocatalytic reactor as a reducing agent. Before illumination, air was removed from the photocatalytic reactor by gas replacement to ensure that the reactor was ultimately in a CO2 atmosphere. A light intensity of 16.7 mW / cm² was used. -2A 300 W xenon lamp with a 420 nm filter was used as the light source to simulate sunlight. After a period of irradiation, 1 mL of gas sample was taken and the CO content was determined by gas chromatography (8890 GC System, Agilent, USA). Samples were taken at 1, 2, 3, and 4 hours of irradiation, and the reaction lasted for 4 hours, constituting the first photocatalytic process. After the first photocatalytic reaction, the light source was turned off, the glass surface with UJN-COF-8 was removed, dried in a 60 °C oven for 6 hours, and then placed back on the glass support in the photocatalytic reactor. 5 mL of distilled water was added to the bottom of the photocatalytic reactor, and air was removed by gas replacement to ensure that the reactor was ultimately in a CO2 atmosphere. The light source was then turned on for the second photocatalytic reaction, which lasted for 4 hours. This process was repeated for a total of 5 photocatalytic reactions. The photocatalytic stability test results of UJN-COF-8 prepared in Example 1 are as follows: Figure 12 As shown, the performance of UJN-COF-8 prepared by this invention did not decrease significantly after 5 cycles, indicating that it has good stability.

[0040] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A room-temperature synthesized, electron-withdrawing, olefin-linked, single-atom modified covalent organic framework material, characterized in that, The chemical structural formula of the covalent organic framework material is shown in Formula I: Formula I, Where, in the formula Represents omitted repetitive structural units; The preparation method of the covalent organic framework material includes the following steps: S1. Under a nitrogen atmosphere, tris(4-formylphenyl)amine, 5,5′-bis(diethylphosphomethyl)-2,2′-bipyridine and potassium tert-butoxide were placed in the first organic solvent and stirred at room temperature. After the reaction was completed, the mixture was filtered, washed and dried to obtain an olefin-linked covalent organic framework without electron-withdrawing substituents. S2. The olefin-linked covalent organic framework without electron-withdrawing substituents is placed in a second organic solvent and reacted with cobalt chloride hexahydrate under stirring. After the reaction is completed, the mixture is filtered, washed, and dried to obtain a room-temperature synthesized, olefin-linked single-atom modified covalent organic framework material without electron-withdrawing substituents.

2. A method for preparing a room-temperature synthesized, electron-withdrawing, olefin-linked, single-atom modified covalent organic framework material as described in claim 1, characterized in that, Includes the following steps: S1. Under a nitrogen atmosphere, tris(4-formylphenyl)amine, 5,5′-bis(diethylphosphomethyl)-2,2′-bipyridine and potassium tert-butoxide were placed in the first organic solvent and stirred at room temperature. After the reaction was completed, the mixture was filtered, washed and dried to obtain an olefin-linked covalent organic framework without electron-withdrawing substituents. S2. The olefin-linked covalent organic framework without electron-withdrawing substituents is placed in a second organic solvent and reacted with cobalt chloride hexahydrate under stirring. After the reaction is completed, the mixture is filtered, washed, and dried to obtain a room-temperature synthesized, olefin-linked single-atom modified covalent organic framework material without electron-withdrawing substituents.

3. The method for preparing room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework materials according to claim 2, characterized in that, In step S1, the molar ratio of tris(4-formylphenyl)amine, 5,5′-bis(diethylmethylphospho)-2,2′-bipyridine and potassium tert-butoxide is 0.02∶0.03∶0.

12.

4. The method for preparing room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework materials according to claim 2, characterized in that, The first organic solvent is selected from tetrahydrofuran.

5. The method for preparing room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework materials according to claim 2, characterized in that, In step S1, the reaction is carried out at room temperature for 72 hours.

6. The method for preparing room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework materials according to claim 2, characterized in that, In step S2, the mass ratio of the olefin-linked covalent organic framework without electron-withdrawing substituents to cobalt chloride hexahydrate is 1:0.

08.

7. The method for preparing room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework materials according to claim 2, characterized in that, The second organic solvent is selected from methanol.

8. The method for preparing room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework materials according to claim 2, characterized in that, In step S2, the reaction is carried out at room temperature for 18 hours.

9. The application of a room-temperature synthesized, electron-withdrawing substituent-free olefin-linked single-atom modified covalent organic framework material as described in claim 1 in the simultaneous photocatalytic reduction of CO2 and oxidation of H2O.

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