A ZIF-67-derived hierarchical porous Co3O4 / C composite material, its preparation method and application

Abstract

This invention discloses a ZIF-67-derived hierarchical porous Co3O4 / C composite material, its preparation method, and its application, belonging to the field of environmental catalytic materials technology. Cobalt salt and 2-methylimidazole are dissolved in solvents to obtain solution A and solution B, respectively. Solution A and solution B are mixed and stirred to obtain solution C. Solution C is centrifuged, washed, and dried to obtain a ZIF-67 precursor. The ZIF-67 precursor is placed in a tube furnace and heated to a preset holding temperature at a preset heating rate under an inert atmosphere. After holding at this temperature for a preset time, it is naturally cooled to room temperature to obtain the ZIF-67-derived hierarchical porous Co3O4 / C composite material. The mesoporous pore volume of the ZIF-67-derived hierarchical porous Co3O4 / C composite material accounts for more than 40% of the total pore volume, significantly improving the material's room-temperature catalytic oxidation performance for formaldehyde.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalytic materials technology, specifically relating to a ZIF-67 derived hierarchical porous Co3O4 / C composite material, its preparation method, and its application. Background Technology

[0002] Indoor air pollution, especially formaldehyde pollution, has become a significant environmental problem threatening human health. Formaldehyde mainly originates from building materials, furniture, and paints. Long-term exposure to low concentrations of formaldehyde increases the risk of diseases such as leukemia and nasopharyngeal carcinoma. Therefore, developing efficient and stable formaldehyde removal technologies is of great practical importance.

[0003] Catalytic oxidation is considered one of the most promising formaldehyde removal technologies because it can completely oxidize formaldehyde into non-toxic carbon dioxide and water without secondary pollution. Among these technologies, transition metal oxides have attracted considerable attention due to their low cost and good thermal stability. Co3O4, as a typical p-type semiconductor, has Co on its surface... 3+ The active sites have excellent activation ability for formaldehyde molecules, making them ideal materials for catalytic oxidation of formaldehyde.

[0004] Metal-organic framework (MOF)-derived materials have shown great potential in the field of catalysis in recent years. ZIF-67 (zeolite imidazolium ester framework structure material), as a typical MOF material, has become an ideal precursor for the preparation of Co3O4 / C composite materials due to its high specific surface area, regular pore structure and abundant cobalt source. By heat-treating ZIF-67, composite materials in which cobalt oxide is uniformly embedded in a carbon framework can be obtained.

[0005] However, the existing ZIF-67-derived Co3O4 / C materials mainly have the following technical bottlenecks: (1) The pore structure is mainly micropores, which is not conducive to the rapid diffusion of reactants and products and limits the utilization rate of active sites; (2) There is a lack of precise control methods for mesoporous structures, making it difficult to optimize the structure-activity relationship between pore parameters and catalytic performance; (3) There is insufficient targeted design for formaldehyde catalytic oxidation, and the room temperature activity needs to be improved.

[0006] Therefore, there is an urgent need for a ZIF-67 derived Co3O4 / C composite material to solve the problems of the existing ZIF-67 derived Co3O4 / C composite material, such as simple pore structure, low mesoporous ratio and insufficient mass transfer efficiency. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of simple pore structure, low mesopore ratio and insufficient mass transfer efficiency of existing ZIF-67 derived Co3O4 / C composite materials, and to propose a ZIF-67 derived multi-level porous Co3O4 / C composite material, its preparation method and application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a ZIF-67-derived hierarchical porous Co3O4 / C composite material, the composite material having a hierarchical porous structure composed of micropores and mesopores, wherein the pore size distribution of the mesopores is 2~10nm, and the pore volume of the mesopores accounts for more than 40% of the total pore volume.

[0009] Furthermore, mesoporous pores account for 40%-60% of the total pore volume.

[0010] Furthermore, the specific surface area of ​​the composite material is 100-300 m². 2 / g, total pore volume is 0.3~0.7cm³ 3 / g.

[0011] Furthermore, the Co3O4 nanoparticles in the composite material are uniformly dispersed in the carbon skeleton, and the particle size of the Co3O4 nanoparticles is 10~30nm.

[0012] Secondly, the present invention provides a method for preparing ZIF-67-derived hierarchical porous Co3O4 / C composite material, comprising the following steps: Cobalt salt and 2-methylimidazole were dissolved in solvents to obtain solution A and solution B. Solution A and solution B were mixed and stirred to obtain solution C. Solution C was centrifuged, washed and dried to obtain ZIF-67 precursor. The ZIF-67 precursor was placed in a tube furnace and heated to a preset holding temperature at a preset heating rate under an inert atmosphere. After holding for a preset time, it was naturally cooled to room temperature to obtain the ZIF-67-derived hierarchical porous Co3O4 / C composite material. The mesoporous pore volume of the ZIF-67-derived hierarchical Co3O4 / C composite material accounts for more than 40% of the total pore volume.

[0013] Furthermore, the preset heating rate is 5~10℃ / min, the preset holding temperature is 600~800℃, and the preset holding time is 2~4 h.

[0014] Furthermore, the inert atmosphere is nitrogen or argon, and the gas flow rate is 50~100 mL / min.

[0015] Further, the cobalt salt is at least one of cobalt nitrate, cobalt acetate, or cobalt chloride; the solvent is methanol or ethanol; and the molar ratio of the cobalt salt to 2-methylimidazole is 1:4.

[0016] Thirdly, the present invention provides an application of ZIF-67-derived hierarchical porous Co3O4 / C composite material in the catalytic oxidation of formaldehyde.

[0017] Furthermore, it is applied to the catalytic oxidation of gaseous formaldehyde at room temperature.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: This invention proposes a ZIF-67-derived hierarchical porous Co3O4 / C composite material with a hierarchical pore structure composed of micropores and mesopores. The mesopores have a pore size distribution of 2–10 nm, and their pore volume accounts for more than 40% of the total pore volume, significantly improving the material's room-temperature catalytic oxidation performance for formaldehyde. When the mesopore size is controlled within the range of 2–10 nm and the mesopore volume accounts for more than 40%, the material simultaneously possesses the high specific surface area provided by micropores and the rapid mass transfer channels provided by mesopores, forming an ideal "micropore-mesopore" hierarchical pore system.

[0019] Furthermore, the composite material obtained in this invention exhibits excellent catalytic oxidation activity for formaldehyde at room temperature. Experiments show that when the mesoporous pore volume ratio is less than 40%, the formaldehyde degradation efficiency is less than 80%; while when the mesoporous pore volume ratio reaches more than 40%, the degradation efficiency can be increased to more than 95%. This dramatic improvement in performance proves that 40% mesoporous pore volume ratio is the critical value for exerting the synergistic effect of multi-level pores.

[0020] This invention proposes a method for preparing ZIF-67-derived hierarchical porous Co3O4 / C composite material. Through systematic optimization of the ZIF-67 heat treatment process, the method achieves precise control of the mesoporous structure of the Co3O4 / C composite material, resulting in a hierarchical porous structure with mesopore diameters concentrated in the range of 2-10 nm and mesopore volume accounting for more than 40% of the total pore volume.

[0021] Furthermore, this invention achieves directional control of the mesoporous structure of ZIF-67 derived Co3O4 / C composite materials by optimizing heat treatment process parameters (heating rate, holding temperature, and holding time).

[0022] Furthermore, the method of the present invention is based on a one-step heat treatment of ZIF-67, which does not require the addition of additional template agents or complex post-treatment. The process is simple, low-cost, and easy to scale up for production. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] The present invention will now be described in further detail: A ZIF-67-derived hierarchical Co3O4 / C composite material possesses a hierarchical pore structure composed of micropores and mesopores. The mesopores have a pore size distribution of 2–10 nm, and their pore volume accounts for more than 40% of the total pore volume. This hierarchical Co3O4 / C composite material combines the high adsorption capacity of micropores for formaldehyde with the efficient diffusion and mass transfer advantages of mesopores for gaseous formaldehyde. The high proportion of mesopores significantly improves the formaldehyde gas transport rate and catalyst structural stability. Combined with the high adsorption capacity of the carbon framework and the high room-temperature catalytic activity of Co3O4, the material exhibits advantages such as high degradation efficiency, fast purification speed, long service life, and good stability in the catalytic oxidation of gaseous formaldehyde at room temperature.

[0025] A method for preparing a ZIF-67-derived hierarchical porous Co3O4 / C composite material includes: Prepare the ZIF-67 precursor, then heat it to 600-800℃ at a heating rate of 5-10℃ / min under an inert atmosphere and hold for 2-4 h, then allow it to cool naturally to obtain the final product.

[0026] This invention achieves precise control of the mesoporous structure by regulating the heat treatment process. The resulting material combines the high specific surface area of ​​micropores with the rapid mass transfer channels of mesopores. It exhibits excellent catalytic oxidation performance of formaldehyde at room temperature (degradation efficiency ≥95%), good stability, strong moisture resistance, and a simple and controllable preparation process. It has broad application prospects in the field of indoor air purification.

[0027] The process of calcining in an inert atmosphere with moderate heating and appropriate temperature and time is simple and easy to control. It can efficiently prepare multi-level porous Co3O4 / C composite materials with complete structure, well-developed channels, uniform dispersion and good conductivity, which is beneficial to improving its electrochemical performance and stability and is suitable for large-scale production.

[0028] Mesoporous pores account for 40%-60% of the total pore volume. The specific surface area of ​​the composite material is 100~300m². 2 / g, total pore volume is 0.3~0.7cm³ 3 / g. In the composite material, Co3O4 nanoparticles are uniformly dispersed in the carbon skeleton, and the particle size of the Co3O4 nanoparticles is 10-30nm.

[0029] The present invention proposes a ZIF-67-derived hierarchical porous Co3O4 / C composite material that combines high specific surface area and high pore volume, enabling rapid adsorption, diffusion and full contact of gaseous formaldehyde molecules; at the same time, the Co3O4 nanoparticles are uniform in size and uniformly dispersed, and can efficiently catalyze the oxidation of formaldehyde at room temperature, with advantages such as high catalytic activity, good stability and long service life, and is suitable for the field of room temperature gaseous formaldehyde purification.

[0030] Specifically, a method for preparing ZIF-67-derived hierarchical porous Co3O4 / C composite materials includes the following steps: (1) Preparation of ZIF-67 precursor: Cobalt salt and 2-methylimidazole were dissolved in solvents respectively, mixed and stirred to react, and then centrifuged, washed and dried to obtain ZIF-67 precursor; (2) Heat treatment: The ZIF-67 precursor obtained in step (1) is placed in a tube furnace and heated to a specific temperature at a specific heating rate under an inert atmosphere. The temperature is held for a specific time and then naturally cooled to room temperature to obtain the ZIF-67 derived multi-level porous Co3O4 / C composite material. The selection of the heating rate, holding temperature, and holding time ensures that the mesoporous pore volume of the resulting composite material accounts for more than 40% of the total pore volume.

[0031] In step (2), the heating rate is 5~10℃ / min, the holding temperature is 600~800℃, and the holding time is 2~4h.

[0032] In step (2), the inert atmosphere is nitrogen or argon, and the gas flow rate is 50~100mL / min.

[0033] In step (1), the cobalt salt is at least one of cobalt nitrate, cobalt acetate, or cobalt chloride; the solvent is methanol or ethanol; and the molar ratio of the cobalt salt to 2-methylimidazole is 1:4.

[0034] Application of ZIF-67-derived hierarchical porous Co3O4 / C composite materials or ZIF-67-derived hierarchical porous Co3O4 / C composite materials prepared by the same method in the catalytic oxidation of formaldehyde.

[0035] Its application is the catalytic oxidation of gaseous formaldehyde at room temperature.

[0036] Applications include placing the composite material in a fixed-bed reactor, introducing formaldehyde-containing gas, and carrying out a catalytic oxidation reaction at room temperature to convert formaldehyde into carbon dioxide and water.

[0037] The present invention will be further described in detail below with reference to the embodiments: Example 1 (1) 1.455 g (5 mmol) of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was dissolved in 50 mL of methanol to obtain solution A; 1.64 g (20 mmol) of 2-methylimidazole was dissolved in 50 mL of methanol to obtain solution B. Solution B was quickly poured into solution A, stirred and mixed, and allowed to stand at room temperature for 24 h. The resulting purple precipitate was separated by centrifugation, washed three times with methanol, and dried under vacuum at 60 °C for 12 h to obtain the ZIF-67 precursor.

[0038] (2) Take 0.5 g of the above ZIF-67 precursor and place it in a tube furnace. Under nitrogen atmosphere protection (gas flow rate 100 mL / min), heat it to 600℃ at a heating rate of 5℃ / min, keep it at the temperature for 3 h, and then cool it naturally to room temperature to obtain ZIF-67 derived multi-level porous Co3O4 / C composite material, which is denoted as sample C1.

[0039] The mesoporous pore volume of C1 accounts for 40% of the total pore volume, and the specific surface area of ​​the C1 composite material is 100 m². 2 / g, total pore volume is 0.3cm³ 3 / g. The particle size of the Co3O4 nanoparticles is 10nm.

[0040] Example 2 The preparation method was basically the same as in Example 1, except that the heating rate of the heat treatment was adjusted to 8℃ / min, the holding temperature was adjusted to 700℃, and the holding time was adjusted to 3 h. The resulting sample was designated C2.

[0041] The mesoporous pore volume of C2 accounts for 50% of the total pore volume. The specific surface area of ​​the C2 composite material is 200 m². 2 / g, total pore volume is 0.5cm³ 3 / g. In the C2 composite material, Co3O4 nanoparticles are uniformly dispersed in the carbon framework, and the particle size of the Co3O4 nanoparticles is 20nm.

[0042] Example 3 The preparation method was basically the same as in Example 1, except that the heating rate of the heat treatment was adjusted to 10℃ / min, the holding temperature was adjusted to 800℃, and the holding time was adjusted to 3 h. The resulting sample was designated C3.

[0043] The mesoporous pore volume of C3 accounts for 60% of the total pore volume. The specific surface area of ​​the C3 composite material is 300 m². 2 / g, total pore volume is 0.7cm³ 3 / g. In the C3 composite material, Co3O4 nanoparticles are uniformly dispersed in the carbon skeleton, and the particle size of the Co3O4 nanoparticles is 30nm.

[0044] Example 4 The preparation method was basically the same as in Example 2, except that the heat treatment time was adjusted to 2 hours. The resulting sample was designated C4.

[0045] Example 5 The preparation method was basically the same as in Example 2, except that the heat treatment time was adjusted to 4 hours. The resulting sample was designated C5.

[0046] Comparative Example 1 The preparation method was basically the same as in Example 1, except that the heating rate of the heat treatment was adjusted to 2℃ / min, the holding temperature was 600℃, and the holding time was 3h. The resulting sample was designated as D1.

[0047] Comparative Example 2 The preparation method was basically the same as in Example 1, except that the heating rate of the heat treatment was adjusted to 20℃ / min, the holding temperature was 600℃, and the holding time was 3h. The resulting sample was designated as D2.

[0048] Comparative Example 3 The preparation method was basically the same as in Example 2, except that the heat treatment atmosphere was changed to air, the heating rate was 8℃ / min, the holding temperature was 700℃, and the holding time was 3 h. The resulting sample was designated as D3.

[0049] Performance testing and characterization (1) Structural characterization The specific surface area and pore structure parameters of the samples obtained in Examples 1-5 and Comparative Examples 1-3 were determined by nitrogen adsorption-desorption test, and the results are shown in Table 1.

[0050] Table 1 Pore structure parameters of each sample

[0051] As shown in Table 1, the pore structure of the obtained composite material can be effectively controlled by adjusting the heat treatment process parameters. When the heating rate is controlled at 5~10℃ / min and the holding temperature is 600~800℃ (Examples 1-5), the mesopore volume ratio of C1, C2, C3, C4, and C5 all reach more than 40%, and the mesopore diameter is concentrated in the range of 2-10 nm. Due to the low heating rate (3℃ / min), D1 (Comparative Example 1) has insufficient mesopore development, with a mesopore volume ratio of only 20.0%; due to the high heating rate (15℃ / min), D2 (Comparative Example 2) has a disordered pore structure, with a mesopore volume ratio of 35.0%; D3 (Comparative Example 3) was heat-treated in air, and the ZIF-67 structure collapsed severely, with a significant decrease in specific surface area.

[0052] The application test is as follows: The catalyst was evaluated in a micro fixed-bed reactor. 50 mg of catalyst (40–60 mesh) was weighed and packed into a U-shaped reaction tube (id = 6 mm). Formaldehyde was generated by passing air (21 vol.% O2 / N2) at a flow rate of 30 mL / min through the U-shaped tube containing paraformaldehyde. The reaction conditions were: formaldehyde concentration 50 ppm, relative humidity (RH) 50%, corresponding to a WHSV of 36,000 mL g. cat -1 h -1The reaction temperature was controlled by a temperature programmable generator. Analysis was performed using gas chromatography equipped with a flame ionization detector (FID), a thermal conductivity detector (TCD), and a Ni conversion furnace.

[0053] Formaldehyde conversion rate ( X 甲醛 The calculation method is as shown in formula (1).

[0054]

[0055] Table 2 lists the catalyst preparation conditions and catalyst performance evaluations for Examples 1-5 and Comparative Examples 1-3. Table 2 Formaldehyde conversion rate of different catalysts at different reaction temperatures

[0056] As shown in Table 2, there is a significant positive correlation between the mesoporous pore volume ratio and the formaldehyde degradation efficiency. When the mesoporous pore volume ratio is below 40% (Comparative Examples 1-2), the formaldehyde degradation efficiency is below 80% (D1, D2); while when the mesoporous pore volume ratio reaches above 40% (Examples 1-5), the formaldehyde degradation efficiency reaches above 95% (C1, C2, C3, C4, C5), especially Sample C2 in Example 2, which has a mesoporous pore volume ratio of 47.1% and a steady-state degradation efficiency as high as 97.5%. This result proves that a mesoporous pore volume ratio of 40% is the critical threshold for achieving efficient formaldehyde catalytic oxidation.

[0057] Although D3 (Comparative Example 3) has a relatively high mesoporous pore volume ratio of 15.0%, its specific surface area is too low (76 m²). 2 / g, with insufficient number of active sites, the catalytic performance is the worst, indicating that it is not advisable to simply pursue the proportion of mesopores at the expense of specific surface area. The multi-level channel design of the present invention achieves the best balance between the proportion of mesopores and specific surface area.

[0058] The reason why the ZIF-67-derived hierarchical porous Co3O4 / C composite material proposed in this invention has high catalytic performance is due to the following synergistic effect: (1) The carbon skeleton derived from ZIF-67 retains some microporous structure, providing a high specific surface area carrier for Co3O4 nanoparticles, allowing the active sites to be fully exposed.

[0059] (2) Mesopores with a pore size of 2-10 nm form an efficient mass transfer network. Formaldehyde molecules can diffuse rapidly into the interior of the material through the mesopores, while the reaction products CO2 and H2O can also be desorbed in time, avoiding the blockage of active sites due to diffusion limitation.

[0060] (3) The carbon skeleton not only disperses the Co3O4 nanoparticles, but also regulates the electronic structure of Co through the interaction of Co-C bonds, thereby enhancing its adsorption and activation ability for formaldehyde.

[0061] (4) When the mesoporous pore volume ratio is less than 40%, there are insufficient mass transfer channels and diffusion becomes the rate-limiting step; when the mesoporous pore volume ratio exceeds 40%, the mass transfer resistance is significantly reduced and the catalytic reaction is controlled by kinetics, thus achieving a leap in performance.

[0062] Many embodiments and applications beyond the examples provided will be apparent to those skilled in the art upon reading the foregoing description. Therefore, the scope of this teaching should not be determined by reference to the foregoing description, but rather by reference to the foregoing claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the applicant has not considered that subject matter as part of the disclosed inventive subject matter.

[0063] The above content provides a further detailed description of the present invention. It should not be construed that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the defined protection scope of the present invention.

Claims

1. A ZIF-67-derived hierarchical porous Co3O4 / C composite material, characterized in that, The composite material has a multi-level pore structure composed of micropores and mesopores, wherein the pore size distribution of the mesopores is 2~10nm, and the pore volume of the mesopores accounts for more than 40% of the total pore volume. The raw materials for preparing the composite material include ZIF-67 precursor prepared using cobalt salt and 2-methylimidazole.

2. The ZIF-67-derived hierarchical porous Co3O4 / C composite material according to claim 1, characterized in that, The mesopore volume accounts for 40%-60% of the total pore volume.

3. The ZIF-67-derived hierarchical porous Co3O4 / C composite material according to claim 1, characterized in that, The specific surface area of ​​the composite material is 100-300 m². 2 / g, total pore volume is 0.3~0.7cm³ 3 / g.

4. The ZIF-67-derived hierarchical porous Co3O4 / C composite material according to claim 1, characterized in that, In the composite material, Co3O4 nanoparticles are uniformly dispersed in a carbon skeleton, and the particle size of the Co3O4 nanoparticles is 10~30nm.

5. A method for preparing the ZIF-67-derived hierarchical porous Co3O4 / C composite material according to any one of claims 1-4, characterized in that, Includes the following steps: Cobalt salt and 2-methylimidazole were dissolved in solvents to obtain solution A and solution B. Solution A and solution B were mixed and stirred to obtain solution C. Solution C was centrifuged, washed and dried to obtain ZIF-67 precursor. The ZIF-67 precursor was placed in a tube furnace and heated to a preset holding temperature at a preset heating rate under an inert atmosphere. After holding for a preset time, it was naturally cooled to room temperature to obtain the ZIF-67-derived multi-level porous Co3O4 / C composite material. The mesoporous pore volume of the ZIF-67 derived hierarchical Co3O4 / C composite material accounts for more than 40% of the total pore volume.

6. The method for preparing a ZIF-67-derived hierarchical porous Co3O4 / C composite material according to claim 5, characterized in that, The preset heating rate is 5~10℃ / min, the preset holding temperature is 600~800℃, and the preset holding time is 2~4 h.

7. The method for preparing a ZIF-67-derived hierarchical porous Co3O4 / C composite material according to claim 5, characterized in that, The inert atmosphere is nitrogen or argon, and the gas flow rate is 50~100mL / min.

8. The method for preparing a ZIF-67-derived hierarchical porous Co3O4 / C composite material according to claim 5, characterized in that, The cobalt salt is at least one of cobalt nitrate, cobalt acetate, or cobalt chloride; the solvent is methanol or ethanol; and the molar ratio of the cobalt salt to 2-methylimidazole is 1:

4.

9. The application of the ZIF-67-derived hierarchical porous Co3O4 / C composite material as described in claim 1 in the catalytic oxidation of formaldehyde.

10. The application according to claim 9, characterized in that, The application is the catalytic oxidation of gaseous formaldehyde at room temperature.

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