Metal covalent organic framework material for regulating and controlling charge transfer path as well as preparation method and application of metal covalent organic framework material

Abstract

The invention discloses a metal covalent organic framework material for regulating and controlling a charge transfer path as well as a preparation method and application of the metal covalent organic framework material. The chemical structural formula of the metal covalent organic framework material is as shown in a formula I which is described in the specification. According to the invention, a molecular-level ordered crystal skeleton is constructed, a donor-acceptor structural unit is introduced, and the directed migration of photo-generated charges from a donor to an acceptor in the skeleton is realized by utilizing an electron push-pull effect, so that the transfer path of photo-generated electrons is effectively regulated and controlled, and the electron density and reaction activity of a catalytic activity center are further influenced. According to the prepared TN-Cu3L3-COF material, by means of fine regulation and control on an electronic structure, efficient separation and transfer of photo-generated charges are achieved, and the hydrogen production efficiency of the TN-Cu3L3-COF material in the photocatalytic hydrolysis hydrogen production process is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a metal covalent organic framework material, in particular to a metal covalent organic framework material for regulating charge transfer paths, and a preparation method and application thereof. Background Art

[0002] Hydrogen production has been explored in numerous research projects as an environmentally friendly and clean energy conversion method. Researchers have developed a variety of photocatalysts, including inorganic semiconductors, organic semiconductors such as carbon nitride, and metal-organic frameworks. However, their applications in photocatalytic water splitting for hydrogen production are limited by uncontrollable band gaps, structural disorder, and poor stability.

[0003] As a promising class of porous crystalline polymers, metal covalent organic frameworks have shown considerable advantages and application potential in the field of photocatalytic water splitting to produce hydrogen due to their designable structure, tunable function and metal active sites.

[0004] Currently, research on metal covalent organic frameworks (MOFs) for photocatalytic hydrogen production from water splitting primarily focuses on constructing strong donor-acceptor structures, enhancing dipole polarization, and performing post-modification of the framework. However, a systematic exploration of the relationship between charge transfer pathways within the framework and photocatalytic efficiency remains a research gap. Therefore, studying MOFs with different charge transfer pathways and exploring their impact on photocatalytic hydrogen production from water splitting is of great scientific value and practical significance.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the Invention

[0006] The purpose of the present invention is to provide a metal covalent organic framework material for regulating the charge transfer path, as well as its preparation method and application. By finely regulating the electronic structure, the present invention realizes the efficient separation and transfer of photogenerated charges, significantly improving its hydrogen production efficiency in the process of photocatalytic hydrolysis to produce hydrogen.

[0007] In order to achieve the above objectives, the present invention provides a metal covalent organic framework material for regulating charge transfer pathways, the chemical structure of the metal covalent organic framework material is shown in Formula I:

[0008] In the formula, the wavy line represents the repetition of the structure shown in Formula I.

[0009] A second object of the present invention is to provide a method for preparing the metal covalent organic framework material for regulating charge transfer pathways, the method comprising: Trinuclear copper Cu3L3, 2,2′,2′′-(benzene-1,3,5-triyl)triacetonitrile, and 1,8-diazacyclo[5,4,0]undecene-7 were reacted in an organic reagent under vacuum sealing conditions at 150-170°C to prepare a metal covalent organic framework material TN-Cu3L3-COF with a regulated charge transfer path. .

[0010] Preferably, the organic reagent is selected from o-dichlorobenzene or n-butanol.

[0011] Preferably, the molar ratio of the trinuclear copper Cu3L3 and 2,2′,2′′-(benzene-1,3,5-triyl)triacetonitrile is 1:1; or / and, the amount relationship of the trinuclear copper Cu3L3 and 1,8-diazacyclo[5,4,0]undecene-7 is 0.05-0.15 mmol:0.1-0.3 mL; or / and, the amount relationship of the trinuclear copper Cu3L3 and the organic reagent is 0.05-0.15 mmol:0.7-1.3 mL.

[0012] Preferably, the reaction time is 119 to 121 hours.

[0013] Preferably, the preparation method of the trinuclear copper Cu3L3 comprises: Copper nitrate trihydrate and 1H-pyrazole-4-carboxaldehyde are reacted in an inert atmosphere with a mixed solution of DMF, H2O and ethanol as a solvent at 90-110°C under sealed conditions to prepare trinuclear copper Cu3L3.

[0014] More preferably, the molar ratio of the copper nitrate trihydrate to 1H-pyrazole-4-carboxaldehyde is (0.8-1): (0.9-1.1).

[0015] More preferably, the volume ratio of DMF, H2O and ethanol is (5-7): (4-6): (5-7); or / and the amount of copper nitrate trihydrate and solvent is 0.8-1 mmol: 14-20 mL.

[0016] More preferably, the heating reaction time is 20 to 24 hours.

[0017] The third object of the present invention is to provide the use of the metal covalent organic framework material for regulating charge transfer pathways in photocatalytic hydrolysis to produce hydrogen.

[0018] Preferably, the metal covalent organic framework material is used as a catalyst, and sodium ascorbate with a concentration of 0.05 to 3 mol / L in the catalytic reaction solution is used as a sacrificial agent to produce hydrogen by hydrolysis under visible light conditions.

[0019] The metal covalent organic framework material for regulating charge transfer paths of the present invention, and its preparation method and application solve the problem and have the following advantages: (1) The present invention constructs a molecular-level ordered crystal framework, introduces donor-acceptor structural units, and utilizes the electron push-pull effect to achieve directional migration of photogenerated charges from donors to acceptors in the framework, effectively regulating the transfer path of photogenerated electrons, thereby affecting the electron density and reaction activity of the catalytic active center. The TN-Cu3L3-COF material prepared by the present invention achieves efficient separation and transfer of photogenerated charges by finely regulating the electronic structure, significantly improving its hydrogen production efficiency in the process of photocatalytic hydrolysis.

[0020] (2) The present invention can change the charge transfer path within the framework by regulating the electron donor / acceptor properties of the building module (compared to the trinuclear copper (Cu3L3) building module), and then further study its effect on the photocatalytic performance. It was found that TN-Cu3L3-COF with trinuclear copper (Cu3L3) as the electron acceptor and 2,2′,2′′-(benzene-1,3,5-triyl)triacetonitrile (TN) as the electron donor and TMT-Cu3L3-COF with 2,4,6-trimethyl-1,3,5-triazine (TMT) as the electron acceptor and Cu3L3 as the electron donor, the two materials showed completely different photocatalytic activities. TN-Cu3L3-COF showed excellent photocatalytic hydrogen production activity, while TMT-Cu3L3-COF showed no photocatalytic activity. This is because the two metal organic framework materials have different charge transfer pathways. (3) The present invention constructs a metal-organic framework material with a customized charge transfer pathway, which has excellent catalytic activity without the addition of a co-catalyst. This opens up a new perspective for the study of the use of metal covalent organic framework materials for photocatalytic water splitting to produce hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the PXRD spectrum of TN-Cu3L3-COF of the present invention.

[0022] Figure 2 This is the PXRD spectrum of TMT-Cu3L3-COF of the present invention.

[0023] Figure 3 The N2 isothermal adsorption-desorption curve and pore size distribution diagram of TN-Cu3L3-COF of the present invention are shown.

[0024] Figure 4 The N2 isothermal adsorption-desorption curve and pore size distribution diagram of the TMT-Cu3L3-COF of the present invention.

[0025] Figure 5FT-IR spectra of TN-Cu3L3-COF (a) and TMT-Cu3L3-COF (b) of the present invention.

[0026] Figure 6 2 are the photocurrent response diagrams of TN-Cu3L3-COF and TMT-Cu3L3-COF of the present invention.

[0027] Figure 7 In situ EPR images of TN-Cu3L3-COF (a) and TMT-Cu3L3-COF (b) of the present invention.

[0028] Figure 8 In situ XPS images of TN-Cu3L3-COF (a) and TMT-Cu3L3-COF (b) of the present invention.

[0029] Figure 9 These are the test results of photocatalytic hydrolysis and hydrogen production of TN-Cu3L3-COF and TMT-Cu3L3-COF of the present invention. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0031] Note: If specific conditions are not specified in the examples, the experiments were conducted under conventional conditions or those recommended by the manufacturer. Instruments used without manufacturer information are commercially available. Raw materials and reagents used without manufacturer information are commercially available or can be prepared by known methods.

[0032] Throughout this disclosure, all features, such as values, amounts, amounts, and concentrations, specified in numerical ranges or percentage ranges are provided for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges (including integers and fractions).

[0033] The features described in this disclosure may be combined in any manner, and as long as there are no conflicts between the combinations of these features, all possible combinations should be considered within the scope of this specification. Each feature disclosed in this specification may be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the features disclosed are merely general examples of equivalent or similar features.

[0034] Example 1 A metal covalent organic framework material for regulating charge transfer pathways, whose structure is shown in Formula Ia, and whose preparation method comprises:

[0035] (1) Preparation of trinuclear copper (Cu3L3) Copper nitrate trihydrate (0.83 mmol, 0.2 g) and 1H-pyrazole-4-carboxaldehyde (1.0 mmol, 0.096 g) were added to a 25 mL reactor and then vacuum-degassed three times. DMF (6.7 mL), H2O (5 mL), and ethanol (6.7 mL) were added under a nitrogen atmosphere. The reactor was sealed and placed in an oven at 100 °C for 12 hours to obtain light yellow crystals. The crystals were collected by filtration and soaked in H2O for 3 days, during which the H2O was changed three times a day. Afterwards, the crystals were quickly washed three times with acetone and then vacuum-dried at 120 °C for 24 hours. 0.2 g of a yellow crystalline solid was obtained with a yield of 73.0%;

[0036] (2) Preparation of TN-Cu3L3-COF A Pyrex tube was charged with 2,2′,2′′-(Benzene-1,3,5-triyl)triacetonitrile (TN) (19.5 mg, 0.1 mmol), Cu₃L₃ (47.6 mg, 0.1 mmol), and o-dichlorobenzene or n-butanol (1 mL). DBU (0.2 mL, 1,8-diazacyclo[5,4,0]undecene-7) was also added. The Pyrex tube was rapidly frozen at 77 K, evacuated and refilled with nitrogen three times, and then sealed under vacuum. The reaction was carried out at 160°C for 120 hours. After completion, the reaction was cooled to room temperature, and the solid was washed with DMF. Finally, the solid was dried at 100°C for 24 hours to obtain 31.2 mg of a dark brown solid powder, designated TN-Cu₃L₃-COF, with a yield of 47.2%.

[0037] Comparative Example 1 A metal covalent organic framework material for regulating charge transfer pathways, whose structure is shown in Formula Ib, and whose preparation method comprises:

[0038] (1) Preparation of trinuclear copper (Cu3L3) The preparation is the same as in Example 1; (2) Preparation of TMT-Cu3L3-COF 2,4,6-Trimethyl-1,3,5-triazine (19.7 mg, 0.16 mmol), Cu3L3 (76.16 mg, 0.16 mmol), and benzoic anhydride (108.8 mg, 0.48 mmol) were added to a Pyrex tube. The tube was rapidly frozen at 77 K, evacuated and refilled with nitrogen three times, and sealed under vacuum. The reaction was then carried out at 180°C for 120 hours. After cooling to room temperature, the solid was washed three times with DMF to obtain the product. Finally, the product was dried at 100°C for 24 hours to obtain 54.5 mg of a brown-black solid powder, designated as TMT-Cu3L3-COF, with a yield of 56.8%.

[0039] Experimental Example 1 Characterization of TN-Cu3L3-COF and TMT-Cu3L3-COF Materials 1. PXRD The powder X-ray diffraction (PXRD) tests of TN-Cu3L3-COF and TMT-Cu3L3-COF prepared above were carried out respectively. The refined PXRD patterns are shown as follows: Figure 1 and Figure 2 shown.

[0040] Figure 1 The main peak in the spectrum shows a sharp diffraction signal, indicating that the sample has good crystallinity. Materials Studio simulation calculation shows that TN-Cu3L3-COF material belongs to the AA stacking model. Figure 2 The main peak in the spectrum shows a sharp diffraction signal, indicating that the sample has good crystallinity. Materials Studio simulation calculation shows that TMT-Cu3L3-COF material also belongs to the AA stacking model.

[0041] 2. N2 isothermal adsorption-desorption curve and pore size distribution diagram To further analyze the pore structure of the metal covalent organic framework material, nitrogen adsorption and desorption characterization was carried out. The material was vacuum dried at 100 °C for 24 hours, and then its nitrogen adsorption and desorption at 77 K was tested.

[0042] like Figure 3 and Figure 4 As shown in the figure, the N2 isothermal adsorption-desorption curves and pore size distribution diagrams of the prepared TN-Cu3L3-COF and TMT-Cu3L3-COF are shown. From the figure, we can know that the specific surface areas of TN-Cu3L3-COF and TMT-Cu3L3-COF are 600 and 527 m 2 / g, and the pore size distributions are 1.47 nm and 1.55 nm, respectively.

[0043] 3. FT-IR images The FT-IR spectra of metal covalent organic framework materials TN-Cu3L3-COF and TMT-Cu3L3-COF were tested by attenuated total reflectance spectroscopy (ATR) method.

[0044] from Figure 5 It can be clearly seen in (a) and (b) that the two samples have a peak at 1667 cm -1 The stretching vibration peaks of the aldehyde group disappeared, indicating a high degree of polymerization.

[0045] Experimental Example 2 Photocurrent response test The photocurrent responses of the metal covalent organic framework materials TN-Cu3L3-COF and TMT-Cu3L3-COF were tested under visible light irradiation. The results are shown in Figure 6 .

[0046] like Figure 6 As shown in the photocurrent response graph, the photocurrent intensity of TN-Cu3L3-COF is higher than that of TMT-Cu3L3-COF, indicating that TN-Cu3L3-COF has a stronger photoresponse ability during illumination. Therefore, it can be preliminarily judged that TN-Cu3L3-COF has better photocatalytic hydrogen production activity by water splitting than TMT-Cu3L3-COF.

[0047] Experimental Example 3 Characterization of Charge Transfer Paths of TN-Cu3L3-COF and TMT-Cu3L3-COF 1. In situ EPR image The Cu in metal covalent organic framework materials TN-Cu3L3-COF and TMT-Cu3L3-COF were tested under visible light irradiation. 2+ In situ EPR.

[0048] like Figure 7 As shown in (a), the TN-Cu3L3-COF material has a Cu 2+ The EPR signal of Figure 7 As shown in (b), the TMT-Cu3L3-COF material has a Cu 2+ The EPR signal of the TN-Cu3L3-COF increases gradually. Therefore, it can be preliminarily judged that TN-Cu3L3-COF and TMT-Cu3L3-COF have opposite charge transfer pathways under light.

[0049] 2. In situ XPS images In situ XPS of Cu in metal covalent organic framework materials TN-Cu3L3-COF and TMT-Cu3L3-COF was tested under visible light irradiation.

[0050] like Figure 8As shown in (a), the TN-Cu3L3-COF material has a Cu 2+ The relative area of ​​Cu is decreasing, while + The relative area of ​​​​is increasing, indicating that electrons are gathering on the Cu surface. Figure 8 As shown in (b), the TMT-Cu3L3-COF material has a Cu 2+ The relative area of ​​Cu is increasing, while + The relative area of ​​​​is decreasing, indicating that electrons are transferred out of the Cu surface. Therefore, it is further determined that TN-Cu3L3-COF and TMT-Cu3L3-COF have opposite charge transfer pathways under light.

[0051] Experimental Example 4 Photocatalytic Hydrolysis Hydrogen Production Test The photocatalytic hydrolysis hydrogen production test of metal covalent organic framework materials TN-Cu3L3-COF and TMT-Cu3L3-COF is as follows: S1: Weigh a certain amount of metal covalent organic framework material and grind the metal covalent organic framework powder in a mortar to facilitate dispersion in the aqueous phase; S2: Prepare an aqueous solution of a certain concentration of sacrificial agent SA, add the ground product to the prepared aqueous solution, and ultrasonicate for 60 minutes to disperse it evenly; S3: Transfer the prepared reaction solution to the photocatalytic reactor and evacuate for 30 minutes to eliminate the interference of oxygen in the air. Finally, turn on the xenon lamp light source and the photocatalytic hydrogen production automatic online sampling system to collect data.

[0052] like Figure 9 As shown in Figure 2, the photocatalytic hydrogen production rate of TN-Cu3L3-COF as a catalyst is 13.0 mmol·g –1 ·h –1 However, under the same conditions, TMT-Cu3L3-COF had no hydrogen production activity. Analysis showed that this was because the different charge transfer pathways in the metal covalent organic framework affected the activity of the metal catalytic center, thereby affecting its photocatalytic efficiency.

[0053] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A metal covalent organic framework material for regulating charge transfer pathways, characterized in that: The chemical structure of the metal covalent organic framework material is shown in Formula I: In the formula, the wavy line represents the repetition of the structure shown in Formula I.

2. The method for preparing a metal covalent organic framework material for regulating charge transfer pathways according to claim 1, wherein: The method includes: Trinuclear copper Cu3L3, 2,2′,2′′-(benzene-1,3,5-triyl)triacetonitrile, and 1,8-diazacyclo[5,4,0]undecene-7 were reacted in an organic reagent under vacuum sealing conditions at 150-170°C to prepare a metal covalent organic framework material TN-Cu3L3-COF with a regulated charge transfer path. 。 3. The preparation method according to claim 2, characterized in that The organic reagent is selected from o-dichlorobenzene or n-butanol.

4. The preparation method according to claim 2, characterized in that The molar ratio of the trinuclear copper Cu3L3 and 2,2′,2′′-(benzene-1,3,5-triyl)triacetonitrile is 1:1; Or / and, the usage ratio of the trinuclear copper Cu3L3 and 1,8-diazacyclo[5,4,0]undecene-7 is 0.05-0.15 mmol: 0.1-0.3 mL; Or / and, the usage ratio of the trinuclear copper Cu3L3 and the organic reagent is 0.05-0.15 mmol: 0.7-1.3 mL.

5. The preparation method according to claim 2, characterized in that The reaction time is 119 to 121 hours.

6. The preparation method according to claim 2, characterized in that The preparation method of the trinuclear copper Cu3L3 comprises: Copper nitrate trihydrate and 1H-pyrazole-4-carboxaldehyde are reacted in an inert atmosphere with a mixed solution of DMF, H2O and ethanol as a solvent at 90-110°C under sealed conditions to prepare trinuclear copper Cu3L3.

7. The preparation method according to claim 6, characterized in that The molar ratio of the copper nitrate trihydrate to 1H-pyrazole-4-carboxaldehyde is (0.8-1): (0.9-1.1).

8. The preparation method according to claim 6, characterized in that The volume ratio of DMF, H2O and ethanol is (5-7): (4-6): (5-7); Or / and, the amount of the copper nitrate trihydrate and the solvent is in the ratio of 0.8-1 mmol to 14-20 mL.

9. The preparation method according to claim 6, characterized in that The heating reaction time is 20 to 24 hours.

10. Use of the metal covalent organic framework material for regulating charge transfer pathways as claimed in claim 1 in photocatalytic hydrolysis to produce hydrogen.

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