Preparation and application of a covalent organic framework anchoring metal atoms

Abstract

The present invention relates to the field of covalent organic framework technology, specifically disclosing the preparation and application of a covalent organic framework for anchoring metal atoms. The invention involves vacuum-activating PCCo-TFPN, placing it in a metal salt solution, reacting it at high temperature, cooling it, centrifuging it, filtering it, washing it, and drying it to obtain the covalent organic framework. The covalent organic framework is then added to a solvent as a photocatalyst and exposed to light for 1-2 hours to produce hydrogen peroxide.

Description

Technical Field

[0001] The present invention relates to the technical field of covalent organic frameworks, and in particular to the preparation and application of a covalent organic framework for anchoring metal atoms. Background Art

[0002] Hydrogen peroxide (H2O2), a versatile and environmentally friendly oxidant, plays a key role in a wide range of applications, including environmental protection, healthcare, and organic synthesis. However, the currently dominant, energy-intensive anthraquinone process for producing hydrogen peroxide presents safety and environmental challenges. Consequently, significant efforts have been made to identify alternative methods to address these challenges.

[0003] In recent years, the electrochemical synthesis of H2O2 via the two-electron oxygen reduction reaction (ORR) has attracted widespread attention. This method is considered to be both environmentally friendly, safe, and energy-efficient. However, the two-electron oxygen reduction reaction faces competition from the four-electron oxygen reduction process, which requires efficient electrocatalysts to achieve the selective conversion of O2 to H2O2.

[0004] To date, a variety of photocatalysts and electrocatalysts have been developed, including precious metals, non-metallic materials, transition metal single-site catalysts, metal complexes, and metal oxides, to selectively accelerate the two-electron oxygen reduction reaction. Among them, covalent organic frameworks (COFs) are a new type of crystalline porous material constructed by covalent bonds from organic building blocks. Due to their pre-designable structural flexibility and easy modification, they are widely used in gas adsorption and separation, sensing, catalysis, and energy storage. Studies have found that two-dimensional covalent organic frameworks with fully conjugated structures, high stability, high intrinsic conductivity, and excellent visible light absorption capacity can be prepared by aromatic connection using planar conjugated building blocks (porphyrin, phthalocyanine (Pc), and hexabenzocoronene, etc.); metal Pc building blocks with M-N4 coordination configuration have been proven to be effective active sites for catalyzing various reactions.

[0005] However, by incorporating different organic building blocks, the tunable band structures of covalent organic frameworks (COFs) at the molecular level give them designable light harvesting and charge transport properties, making them potential photocatalytic activities for various reactions, such as hydrogen evolution reaction, carbon dioxide reduction reaction and nitrogen reduction reaction. It is worth noting that despite the versatility of covalent organic frameworks (COFs), they are rarely used as catalysts for hydrogen peroxide synthesis. In addition, the covalent organic framework photocatalysts synthesized in recent years have limited electronic absorption regions associated with small conjugated building blocks (such as biphenyl, triphenylamine, triazine and pyrene) below 600nm, which significantly hinders the further improvement of their overall photosynthetic performance because they cannot effectively utilize visible light and near-infrared light. At the same time, single atoms have also become catalyst materials that have attracted widespread attention in recent years. They have played a role in the field of photocatalysis, especially in the photocatalytic production of hydrogen peroxide and reduction of carbon dioxide.

[0006] In summary, considering the defects of covalent organic frameworks (COFs) in catalyzing hydrogen peroxide synthesis and the problems of photosynthetic performance, the present invention explores and develops a phthalocyanine covalent organic framework anchoring metal single atoms to expand the visible light absorption range and improve its overall photosynthetic performance. This research has opened up a new way to rationally regulate the electrons of the catalytic active center and the electrons inside the covalent organic framework (COFs) to form a neighboring electron effect, and provides guidance for the design of efficient photocatalysts. It has certain implications for the development of new covalent organic frameworks (COFs) anchoring single atoms for photocatalytic redox production of hydrogen peroxide and gas production. Summary of the Invention

[0007] The purpose of the present invention is to provide a preparation and application of a covalent organic framework for anchoring metal atoms to solve the problems raised in the above background technology.

[0008] A method for preparing a covalent organic framework for anchoring metal atoms comprises the following steps:

[0009] The PcCo-TFPN is vacuum activated and then placed in a metal salt solution for high temperature reaction, followed by cooling, centrifugation, filtration, washing, and drying to obtain a covalent organic framework.

[0010] The more optimized specific preparation method of the covalent organic framework is as follows: the activated PcCo-TFPN is placed in a 5 mL DMA solution of 49.5 mg nickel acetate tetrahydrate, and then placed in an electric blast drying oven, the reaction temperature is set to 100 ° C, the reaction time is set to 48 hours, and after the reaction is completed, centrifugation is performed to obtain a phthalocyanine covalent organic framework anchored with Ni metal atoms, which is then washed with DMF, H2O, and acetone in sequence, and finally dried in a drying oven at 60 ° C for 24 hours to obtain a covalent organic framework.

[0011] More optimally, the covalent organic framework is formed by reacting octahydroxyphthalocyanine cobalt powder with tetrafluoroterephthalonitrile in a high-temperature sealed vacuum environment to generate PcCO-TFPN, and then anchoring Ni atoms inside the framework at high temperature after activation.

[0012] More optimally, the covalent organic framework includes 98.3 wt% to 98.4 wt% of PcCo-TFPN and 1.6 wt% to 1.7 wt% of metal atoms.

[0013] More optimally, the PcCo-TFPN includes 6 wt % to 7 wt % of Co atoms.

[0014] More optimally, in the metal salt solution, the metal salt is a nickel salt, including nickel acetate tetrahydrate.

[0015] More optimally, the vacuum activation temperature is 170-180° C., and the vacuum activation time is 22-26 hours; the high-temperature reaction temperature is 95-110° C., and the high-temperature reaction time is 45-50 hours.

[0016] More optimally, the vacuum activation temperature is typically but not limited to 170°C, 171°C, 172°C, 173°C, 174°C, 175°C, 176°C, 177°C, 178°C, 179°C, and 180°C, and the vacuum activation time is typically but not limited to 22 hours, 23 hours, 24 hours, 25 hours, and 26 hours.

[0017] The optimized specific preparation method of PcCo-TFPN is as follows: dissolving cobalt octahydroxyphthalocyanine and tetrafluoroterephthalonitrile in a mixed solvent of N,N-dimethylacetamide-1,3,5-trimethylbenzene, ultrasonically treating, adding triethylamine, and continuing ultrasonication to obtain a raw material liquid; degassing through a cyclic freezing-vacuuming-thawing process, heating at 150-155°C for 3 days under sealing, cooling, centrifuging, washing, and drying to obtain PcCo-TFPN.

[0018] The optimized method for preparing PcCo-TFPN is as follows: 7.64 mg of PcCo-(OH)8 powder and 4 mg of TFPN powder were mixed and dissolved in a Pyrex tube containing 1 mL of DMA and 1 mL of 1,3,5-trimethylbenzene. After 3 minutes of sonication, 0.1 mL of triethylamine was added to the solution, and sonication was repeated for another 3 minutes. The tube was degassed by three cycles of freeze-evacuation and thawing with liquid nitrogen, then sealed in a vacuum drying oven and heated at 150°C for 3 days. After cooling to room temperature, the mixture was filtered and washed sequentially with DMA, HO, and ethanol to obtain PcCo-TFPN.

[0019] A more optimized covalent organic framework is prepared by the method for preparing a covalent organic framework for anchoring metal atoms.

[0020] The invention discloses an application of a covalent organic framework for anchoring metal atoms, which is more optimized. The covalent organic framework is used as a catalyst to produce hydrogen peroxide.

[0021] The more optimized specific application process of producing hydrogen peroxide is: adding the covalent organic framework to a solvent, irradiating with light for 1 to 2 hours, and producing hydrogen peroxide; the solvent includes one or both of deionized water and ethanol.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) Planar conjugated building blocks, through aromatic connection, prepared two-dimensional COFs (PcCo-TFPN) with fully conjugated structure, high stability, high intrinsic conductivity and excellent visible light absorption ability. The cobalt phthalocyanine (PcCo) contained in it is highly selective and active for the two-electron oxygen reduction reaction. It is a two-dimensional PcCo-based COFs with a fully conjugated structure and is expected to become a promising photocatalyst for hydrogen peroxide photosynthesis.

[0024] (2) The cyanide group of cobalt phthalocyanine easily acts as a free radical for the photocatalytic production of hydrogen peroxide, significantly enhancing the two-electron oxygen reduction process. The cyanide group in cobalt phthalocyanine (PcCo) can also serve as an anchoring site (N4), anchoring the single-atom Ni in the covalent organic framework through the cyanide group, forming a neighboring electron effect with the Co atom in the phthalocyanine organic framework, thereby synergistically promoting the two-electron oxygen reduction reaction (ORR) to produce hydrogen peroxide.

[0025] (3) Co anchored by four nitrogen atoms (Co-N4) is the main active site for O2 adsorption and activation, promoting the formation of key intermediates *OOH and the desorption of *OH, thereby accelerating the multi-electron reaction kinetics; Ni anchored by four nitrogen atoms (Ni-N4) acts as a regulator, which can effectively adjust the electron localization of adjacent Co-N4 sites, promote the desorption of *OH and the adsorption of *H at the Co-N4 sites, and significantly enhance the two-electron oxygen reduction reaction to produce hydrogen peroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0027] In the attached figure:

[0028] Figure 1 is a scanning electron micrograph of the covalent organic framework (PcCo-TFPN) in Example 1;

[0029] Figure 2 is a scanning electron microscope image of the covalent organic framework anchoring single atoms in Example 2;

[0030] Figure 3 This is a schematic diagram of the process of producing hydrogen peroxide using a covalent organic framework anchored with single atoms as a photocatalyst in Experimental Example 4. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] It should be noted that the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions and illustratively include: PcCo-(OH)8 (98%) powder was purchased from Zhengzhou Huiju Chemical Co., Ltd.; TFPN (99%), DMA (AR = 99%), 1,3,5-trimethylbenzene (AR = 97%), and triethylamine were purchased from Shanghai Aladdin Sublimation Technology Co., Ltd.; nickel acetate tetrahydrate (99.5%) was purchased from Shanghai Aladdin Sublimation Technology Co., Ltd.

[0033] The specific embodiments of the present invention are as follows:

[0034] Example 1: A method for preparing PcCo-TFPN, comprising the following steps:

[0035] 7.64 mg of PcCo-(OH)8 powder and 4 mg of TFPN powder were mixed and dissolved in a Pyrex test tube containing 1 mL of N,N-dimethylacetamide and 1 mL of 1,3,5-trimethylbenzene. After 3 minutes of ultrasonic treatment, 0.1 mL of triethylamine was added to the solution, and ultrasonic treatment was performed for another 3 minutes. The test tube was degassed through three liquid nitrogen freeze-vacuum-thaw cycles, then sealed in a vacuum drying oven and heated at 150°C for 3 days. After cooling to room temperature, the mixture was filtered and washed with N,N-dimethylacetamide, deionized water, and ethanol in sequence to obtain PcCo-TFPN.

[0036] Example 2: A method for preparing a covalent organic framework anchoring metal atoms, comprising the following steps:

[0037] PcCo-TFPN was placed in a vacuum drying oven, the vacuum activation temperature was set to 170°C, and the vacuum activation time was 24 hours; the activated PcCo-TFPN was placed in a 5 mL N,N-dimethylacetamide solution of 49.5 mg nickel acetate tetrahydrate, and then placed in an electric blast drying oven, the reaction temperature was set to 100°C, and the reaction time was set to 48 hours. After the reaction was completed, centrifugation was performed to obtain a phthalocyanine covalent organic framework anchoring Ni metal atoms, which was washed with N,N-dimethylacetamide, deionized water, and ethanol in sequence, and finally dried in a drying oven at 60°C for 24 hours to obtain Ni@PcCo-TFPN (covalent organic framework).

[0038] Performance Experiment 1: 5 mg of the PcCo-TFPN from Example 1 was added to a mixture of 50 mL of deionized water, 45 mL of deionized water, and 5 mL of ethanol. The mixture was then exposed to light under a mercury lamp at 300 W for 1 hour. The hydrogen peroxide generation rate was measured. The data obtained are the average of three degradation experiments, as shown in Table 1.

[0039]

[0040] Table 1

[0041] Conclusion: By comparison, it is known that in a mixed solution with sacrificial agent ethanol, the rate of hydrogen peroxide generation per unit time by the catalyst phthalocyanine covalent organic framework PcCo-TFPN is twice the rate of deionized water generation.

[0042] Performance Experiment 2: 5 mg of Ni@PcCo-TFPN from Example 2 was added as a photocatalyst to 50 mL of deionized water and a mixed solution of 45 mL of deionized water and 5 mL of ethanol, respectively. The samples were then placed under a mercury lamp for illumination. The conditions were set as follows: irradiation power of 300 W, illumination time of 1 hour, and the generation rate of hydrogen peroxide was tested. The obtained data are the average values ​​of three degradation experiments, as shown in Table 2:

[0043]

[0044] Table 2

[0045] Conclusion: The rate of hydrogen peroxide generation by Ni@PcCo-TFPN is almost four times that of the corresponding framework, indicating that the Ni single atom cooperates with the PcCo-TFPN framework to greatly enhance the two-electron oxygen reduction reaction (ORR) under photocatalysis.

[0046] Performance Experiment 3: 5 mg of the PcCo-TFPN prepared in Example 1 was added as a photocatalyst to 50 mL of deionized water saturated with O2, and to a mixed solution of 45 mL of deionized water saturated with oxygen and 5 mL of ethanol. The mixture was then placed under a mercury lamp for illumination. The conditions were set as follows: irradiation power of 300 W, illumination time of 1 hour, and the generation rate of hydrogen peroxide was tested. The obtained data are the average values ​​of three degradation experiments, as shown in Table 3:

[0047]

[0048] Table 3

[0049] Conclusion: Compared with the control group in Table 1, after sufficient O2 was introduced into the solvent, the generation rate of hydrogen peroxide was further improved, almost twice that of the control group.

[0050] Performance Experiment 4: 5 mg of the Ni@PcCo-TFPN from Example 2 was added as a photocatalyst to 50 mL of deionized water saturated with O2, and to a mixture of 45 mL of deionized water saturated with O2 and 5 mL of ethanol. The samples were then exposed to a mercury lamp at 300 W of irradiation power and 1 hour of illumination. The hydrogen peroxide generation rate was measured. The data obtained are the average of three degradation experiments, as shown in Table 4.

[0051]

[0052]

[0053] Table 4

[0054] Conclusion: After sufficient O2 is introduced into the solvent, the rate of hydrogen peroxide generation by Ni@PcCo-TFPN is improved compared with the data in Table 2, but the increase is not large.

[0055] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0056] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a covalent organic framework anchoring metal atoms, characterized in that: The following steps are included: After vacuum activation, PcCo-TFPN is placed in a metal salt solution, reacted at high temperature, cooled, centrifuged, filtered, washed, and dried to obtain a covalent organic framework. In the metal salt solution, the metal salt is a nickel salt, including nickel acetate tetrahydrate; The temperature of vacuum activation is 170~180℃, and the time of vacuum activation is 22~26 hours; the temperature of high temperature reaction is 95~110℃, and the time of high temperature reaction is 45~50 hours; The specific preparation method of the PcCo-TFPN is as follows: dissolving octahydroxyphthalocyanine cobalt and tetrafluoroterephthalonitrile in a mixed solvent of N,N-dimethylacetamide-1,3,5-trimethylbenzene, ultrasonically treating, adding triethylamine, and continuing ultrasonication to obtain a raw material liquid; degassing through a cyclic freezing-vacuuming-thawing process, heating at 150-155°C for 3 days under a sealed state, cooling, centrifuging, washing, and drying to obtain the PcCo-TFPN.

2. The method for preparing a covalent organic framework anchoring metal atoms according to claim 1, characterized in that: The covalent organic framework includes 98.3 wt% to 98.4 wt% of PcCo-TFPN and 1.6 wt% to 1.7 wt% of metal atoms.

3. The method for preparing a covalent organic framework anchoring metal atoms according to claim 1, characterized in that: The PcCo-TFPN includes 6 wt % to 7 wt % of Co atoms.

4. A covalent organic framework prepared according to the method for preparing a covalent organic framework anchoring metal atoms according to any one of claims 1 to 3.

5. Application of a covalent organic framework for anchoring metal atoms, characterized by: The covalent organic framework described in claim 4 is used as a photocatalyst to produce hydrogen peroxide.

6. The use of a covalent organic framework for anchoring metal atoms according to claim 5, characterized in that: The specific application process is: adding the covalent organic framework to a solvent, irradiating with light for 1 to 2 hours, and producing hydrogen peroxide; the solvent includes one or two of deionized water and ethanol.

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