Co-b / zif-67 / dt-cof composite material and preparation method and application thereof

Abstract

This invention discloses a Co-B / ZIF-67 / DT-COF composite material. First, a metal-organic framework compound, ZIF-67, is prepared using a methanol method. Then, Co-B particles are loaded onto ZIF-67 as a support via chemical reduction to obtain Co-B / ZIF-67. Finally, DT-COF is grown on the surface of Co-B / ZIF-67 using a solvothermal method to obtain a magnetic Co-B / ZIF-67 / DT-COF. ZIF-67, as the support, has a rhombic dodecahedral structure with a size of 1.2 μm. Co-B, as the active material, has a nanoparticle structure and is loaded onto the ZIF-67 surface. DT-COF is used as a coating material to coat the surface of Co-B / ZIF-67. The preparation method includes the following steps: 1. Preparation of ZIF-67; 2. Preparation of Co-B / ZIF-67; 3. Preparation of Co-B / ZIF-67 / DT-COF. When used as a catalyst for hydrogen production by the hydrolysis of sodium borohydride, the maximum hydrogen production rate is 7000–10000 mL / min at 303 K. ‑1 ·g ‑1 The hydrogen release reaches 100% of the theoretical value; after 10 recycling / reuse cycles, it retains 85.4-90.1% of the initial catalytic activity; the activation energy is E. a =29.4-30.9kJ·mol ‑1 .

Description

Technical Field

[0001] This invention relates to the technical field of catalytic sodium borohydride hydrolysis for hydrogen production, specifically to Co-B / ZIF-67 / DT-COF composite materials, their preparation methods, and applications. Background Technology

[0002] Among chemical hydrogen storage materials, NaBH4 exhibits high hydrogen storage density and conversion efficiency, reaching 10.8 wt.%. Furthermore, solid NaBH4 is convenient to store and transport, and its borate reserves are abundant. Additionally, NaBH4 hydrolysis for hydrogen production offers advantages such as high hydrogen purity, easy reaction control, clean and recyclable products, and mild operating conditions. However, a technical challenge with NaBH4 is the extremely low rate and yield of its spontaneous hydrolysis reaction, which cannot meet the energy demands of most mobile applications.

[0003] The conventional approach to solving these problems is to add highly efficient catalysts to improve hydrogen production efficiency and control the hydrogen release rate. Common types of highly efficient catalysts are noble metal catalysts, such as those containing elemental platinum, ruthenium, palladium, and rhodium, or compounds. However, these noble metal-based catalysts inevitably suffer from high costs, limiting their large-scale application in industry.

[0004] Therefore, non-precious metal catalysts, such as elements or compounds of cobalt, copper, iron, aluminum, manganese, and zinc, can be used to improve catalytic performance. For example, existing literature 1 (Jeong SU, Kim RK, Cho EA, et al. A study on hydrogen generation from NaBH4 solution using the high-performance Co-B catalyst[J]. Journal of Power Sources, 2005, 144(1):129-134.) synthesized a Co-B catalyst by chemical reduction, with a maximum hydrogen production rate of only 1100 mL·min. -1 ·g -1 The fundamental reason for the poor catalytic activity of this technology is that the Co-B particles aggregate, resulting in a small contact area with the NaBH4 solution during the reaction, which leads to a low maximum hydrogen production rate.

[0005] Currently, the main approach to addressing aggregation is to introduce suitable support materials and protective layers to enhance the hydrogen production performance and cycle stability of the materials. Common support materials include carbon materials, metal-organic frameworks, graphene, and TiO2. For example, existing literature 2 (Q.Li,W.Yang,F.Li,A.Cui,J.Hong,Preparation of CoB / ZIF-8 supported catalyst by single step reduction and its activity in hydrogen production,Int.J.Hydrog.Energy vol.43(1)(2018)271-282.) prepared a CoB / ZIF-8 catalyst by loading CoB particles onto ZIF-8 via chemical reduction, achieving a maximum hydrogen production rate of 453.6 mL·min. -1 ·g -1 The activation energy is 57.72 kJ·mol⁻¹. -1 This technical solution uses ZIF-8 as a support to reduce the aggregation of Co-B particles and increase the specific surface area of ​​Co-B, thereby improving the hydrogen production performance of the material. However, a technical problem with this solution is that Co-B particles easily detach from the support, directly leading to poor catalytic activity and cycle performance. The main reason why Co-B particles easily detach from ZIF-8 is that the method used in this solution is a chemical reduction method—the interaction between the Co-B particles prepared by this method and ZIF-8 is mainly physical adsorption or electrostatic interaction, that is, no strong chemical bonds are formed. This directly results in a weak interfacial interaction between Co-B particles and ZIF-8. Therefore, when Co-B particles are subjected to external forces, they easily detach from the ZIF-8 surface.

[0006] Therefore, the existing technology currently has the following technical problems:

[0007] 1. Sodium borohydride hydrolysis hydrogen production catalyst has poor stability, and is prone to agglomeration, oxidation, and shedding, which directly leads to poor catalytic activity and cycle performance;

[0008] 2. The catalyst support material has poor stability and its structure is prone to collapse, resulting in poor catalyst recyclability. Summary of the Invention

[0009] The purpose of this invention is to provide a Co-B / ZIF-67 / DT-COF composite material, its preparation method, and its application.

[0010] The technical problems existing in the current technical solution can be improved through the following principles and methods:

[0011] 1. Using ZIF-67 support to load Co-B particles improves the microstructure of the material, increases the specific surface area of ​​Co-B, increases active sites, inhibits the aggregation of Co-B particles, thereby increasing the contact area between Co-B and NaBH4 and improving catalytic performance.

[0012] 2. By using DT-COF coating, a suitable protective layer is generated on the catalyst surface, which effectively inhibits the shedding of active Co-B particles. At the same time, it reduces the collapse of the material structure during the hydrolysis reaction, thereby significantly improving the cycle stability of the material.

[0013] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0014] A Co-B / ZIF-67 / DT-COF composite material is described. First, a metal-organic framework compound ZIF-67 is prepared using a methanol method. Then, Co-B particles are loaded onto ZIF-67 using a chemical reduction method to obtain Co-B / ZIF-67. Finally, DT-COF is grown on the surface of Co-B / ZIF-67 using a solvothermal method to obtain a covalent organic framework DT-COF-coated Co-B composite material supported on a metal-organic framework ZIF-67 carrier, referred to simply as Co-B / ZIF-67 / DT-COF.

[0015] The raw materials for preparing ZIF-67 are cobalt nitrate hexahydrate and 2-methylimidazole;

[0016] The raw materials for preparing the Co-B are citric acid monohydrate, cobalt sulfate heptahydrate, and sodium borohydride;

[0017] The raw materials for preparing the DT-COF are dimethylformamide (DMF), trifluoropropylene (TFP), diaminoanthraquinone (DAAQ), and acetic acid;

[0018] The Co-B / ZIF-67 / DT-COF is obtained by combining Co-B, ZIF-67 and DT-COF.

[0019] The ZIF-67 used as a carrier has a rhombic dodecahedral structure with a size of 1.2 μm.

[0020] The Co-B, as the active material, has a microstructure of nanoparticles and is loaded on the surface of ZIF-67.

[0021] The DT-COF is used as a coating material to coat the surface of Co-B / ZIF-67;

[0022] The Co-B / ZIF-67 / DT-COF is magnetic.

[0023] A method for preparing a Co-B / ZIF-67 / DT-COF composite material includes the following steps:

[0024] Step 1, Preparation of ZIF-67: First, cobalt nitrate hexahydrate is placed in methanol and sonicated to obtain mixture A. At the same time, 2-methylimidazole is placed in methanol to obtain mixture B. Then, mixture B and mixture A are stirred under certain conditions. After stirring, they are allowed to stand under certain conditions. Finally, the obtained product is centrifuged and vacuum dried under certain conditions to obtain ZIF-67.

[0025] In step 1, the mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:2;

[0026] In step 1, the stirring conditions are: mixture B is quickly added to mixture A, and the stirring time is 1 hour.

[0027] In step 1, the standing conditions are: standing time is 18 hours; the drying conditions are: drying temperature is 80°C and drying time is 12 hours.

[0028] Step 2, Preparation of Co-B / ZIF-67: First, ZIF-67 is placed in deionized water to obtain solution C. Then, citric acid monohydrate and cobalt sulfate heptahydrate are placed in solution C and sonicated under certain conditions. After sonication, the mixture is allowed to stand under certain conditions to obtain mixture D. At the same time, sodium borohydride is placed in deionized water to obtain solution E. Then, under stirring conditions, solution E is slowly added dropwise to mixture D under certain conditions. After the addition is complete, the mixture is allowed to stand under certain conditions. Finally, the obtained product is filtered and washed with ethanol and then vacuum dried under certain conditions to obtain Co-B / ZIF-67.

[0029] In step 2, the mass ratio of ZIF-67, citric acid monohydrate, sulfuric acid heptahydrate, and sodium borohydride is (8-8.8):1:(10-12):(14-16);

[0030] In step 2, the ultrasound conditions are that the ultrasound time is 1 hour;

[0031] In step 2, the conditions for preparing mixture D to stand are: standing time of 24 hours; the conditions for adding the mixture are: dropping rate of 0.02 mL / s; and the conditions for standing after adding the mixture are: standing time of 3 hours.

[0032] In step 2, the drying conditions are: drying temperature of 80℃ and drying time of 12h.

[0033] Step 3, Preparation of Co-B / ZIF-67 / DT-COF: First, the Co-B / ZIF-67 obtained in Step 2 is placed in ethanol and sonicated under certain conditions to obtain mixed solution F. The TFP monomer is placed in DMF to obtain TFP solution, and the DAAQ monomer is placed in DMF to obtain DAAQ solution. Then, the TFP solution is placed in mixed solution F and stirred under certain conditions to obtain mixed solution G. Next, the DAAQ solution and acetic acid are placed in mixed solution G and stirred under certain conditions to obtain mixed solution H. Finally, mixed solution H is reacted under certain conditions. After the reaction is complete, it is cooled to room temperature. The obtained product is washed by centrifugation with DMF and ethanol, and then vacuum dried under certain conditions to obtain the covalent organic framework DT-COF-coated Co-B composite material supported by metal-organic framework ZIF-67, abbreviated as Co-B / ZIF-67 / DT-COF.

[0034] In step 3, the mass ratio of Co-B / ZIF-67, TFP monomer, DAAQ monomer, and acetic acid is (2-2.6):1:(1.5-2):(1.08-1.5).

[0035] In step 3, the conditions for ultrasound are: ultrasound time is 30 min; the conditions for stirring the mixed solution G and mixed solution H are: stirring time is 30 min.

[0036] In step 3, the reaction conditions are: reaction temperature of 100℃ and reaction time of 24h.

[0037] In step 3, the conditions for centrifugal washing are: the number of centrifugal washing cycles is 5; the conditions for drying are: drying temperature is 60℃ and drying time is 12h.

[0038] A Co-B / ZIF-67 / DT-COF composite material, when used as a catalyst for hydrogen production via sodium borohydride hydrolysis, exhibits a maximum hydrogen production rate of 7000-10000 mL·min at 303 K. -1 ·g -1 The hydrogen release reaches 100% of the theoretical value; after 10 recycling / reuse cycles, it retains 85.4-90.1% of the initial catalytic activity.

[0039] The activation energy for catalytic hydrogen desorption is E a =29.4-30.9kJ·mol -1 .

[0040] The technical effectiveness of this invention can be seen from the following tests:

[0041] XRD analysis revealed that the characteristic peaks of Co-B / ZIF-67 / DT-COF simultaneously contain the standard peaks of both ZIF-67 and DT-COF. The test results indicate that Co-B / ZIF-67 / DT-COF was successfully synthesized.

[0042] SEM analysis revealed that the basic microstructure of Co-B / ZIF-67 / DT-COF remained the same as that of Co-B / ZIF-67, consisting of a rhombic dodecahedral structure. The difference lay in the surface roughness of Co-B / ZIF-67 / DT-COF, indicating that DT-COF was deposited on the surface of Co-B / ZIF-67. The test results demonstrate that DT-COF coats the surface of Co-B / ZIF-67, forming a protective layer that helps prevent the shedding of Co-B particles.

[0043] EDS analysis revealed that Co-B / ZIF-67 / DT-COF contains C, O, N, and Co elements, as well as B element, in addition to those found in ZIF-67 and DT-COF. Combined with XRD and EDS results, this demonstrates successful loading of Co-B particles, and that Co-B is amorphous. Furthermore, loading Co-B particles does not affect the crystal structure of ZIF-67 and DT-COF.

[0044] Magnetic testing revealed that Co-B / ZIF-67 / DT-COF is a magnetic material, which facilitates recycling and improves cycle performance.

[0045] Hydrogen production tests via hydrolysis showed that the maximum hydrogen production rate of sodium borohydride at 303 K was 7000-10000 mL·min. -1 ·g -1 The hydrogen release reached 100% of the theoretical value;

[0046] Reaction kinetics tests revealed that the apparent activation energy E of the reaction... a =29.4-30.9kJ·mol -1 ;

[0047] Cyclic performance testing showed that after 10 cycles at 303K, it still retained 85.4-90.1% of its initial catalytic activity for the hydrolysis of NaBH4.

[0048] Therefore, the present invention has the following advantages:

[0049] 1. This invention uses ZIF-67 support to load Co-B particles, which improves the microstructure of the material, enhances uniformity, avoids agglomeration, and thus increases the contact area between Co-B and NaBH4, thereby improving catalytic performance.

[0050] 2. This invention uses ZIF-67 support to load Co-B particles, which increases the specific surface area of ​​Co-B, exposes more active sites, and thus improves the hydrogen production rate of the catalyst.

[0051] 3. Using DT-COF coating, a suitable protective layer is generated on the catalyst surface, which effectively inhibits the shedding of active Co-B particles. At the same time, it reduces the collapse of the material structure during the hydrolysis reaction, thereby significantly improving the cycle stability of the material.

[0052] 4. This invention uses non-precious metal Co instead of precious metal as a catalyst. By supporting it on ZIF-67 and coating it with DT-COF, the cost of catalysis is reduced while improving the hydrogen production rate and cycle performance.

[0053] 5. This invention is magnetic, and magnetic recovery replaces the traditional filtration recovery method, which can effectively improve the problems of oxidation and shedding during use, greatly reduce the process difficulty of recovery and damage to the microstructure of materials, and improve the stability of catalysts. Attached image description:

[0054] Figure 1 The XRD patterns are of the Co-B, ZIF-67, DT-COF, Co-B / ZIF-67 and Co-B / ZIF-67 / DT-COF composite materials in Example 1.

[0055] Figure 2 Here is a SEM image of ZIF-67 in Example 1;

[0056] Figure 3 This is a diagram showing the catalytic hydrolysis of sodium borohydride to produce hydrogen using ZIF-67 and Co-B / ZIF-67 at 303K in Example 1.

[0057] Figure 4 EDS diagram of Co-B / ZIF-67 in Example 1;

[0058] Figure 5 The image shows the SEM image of Co-B / ZIF-67 in Example 1.

[0059] Figure 6 EDS diagram of Co-B / ZIF-67 / DT-COF in Example 1;

[0060] Figure 7 SEM image of Co-B / ZIF-67 / DT-COF in Example 1

[0061] Figure 8 The graph shows the hydrogen production process catalyzed by the hydrolysis of sodium borohydride using Co-B / ZIF-67 / DT-COF at different temperatures in Example 1.

[0062] Figure 9 The activation energy diagram of Co-B / ZIF-67 / DT-COF in Example 1;

[0063] Figure 10 This is a diagram showing the adsorption of Co-B / ZIF-67 / DT-COF on the surface of a magnetic stir bar during the cyclic test in Example 1.

[0064] Figure 11 The graph shows the cycling performance of Co-B / ZIF-67 / DT-COF in Example 1, which catalyzes the hydrolysis of sodium borohydride and hydrogen release after 10 cycles at 303K.

[0065] Figure 12 This is a comparison diagram of the hydrogen release from sodium borohydride hydrolysis catalyzed at 303K for Example 1, Comparative Example 1, and Comparative Example 2.

[0066] Figure 13 The image shows the SEM image of Co-B in Comparative Example 2. Detailed Implementation

[0067] The present invention will be further described in detail through embodiments and with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0068] Example 1

[0069] A method for preparing a Co-B / ZIF-67 / DT-COF composite material, the specific steps of which are as follows:

[0070] Step 1, Preparation of ZIF-67: First, 1.5g of cobalt nitrate hexahydrate was placed in 40mL of methanol and sonicated for 25min to obtain mixture A. At the same time, 3g of 2-methylimidazole was placed in 40mL of methanol to obtain mixture B. Then, mixture B was quickly added to mixture A and stirred for 1h. After stirring, it was allowed to stand for 18h. Finally, the obtained product was centrifuged and vacuum dried at 80℃ for 12h to obtain ZIF-67.

[0071] To verify the crystal structure of ZIF-67 obtained in step 1, XRD tests were performed. The test results are as follows: Figure 1 As shown, the characteristic peaks of ZIF-67 are consistent with the standard peaks of ZIF-67. The test results indicate that ZIF-67 was successfully synthesized.

[0072] To verify the microstructure of ZIF-67 obtained in step 1, SEM testing was performed. The test results are as follows: Figure 2 As shown, ZIF-67 is a rhombic dodecahedron with a size of 1.2 μm.

[0073] To demonstrate the hydrogen production performance of ZIF-67 obtained in step 1 as a sodium borohydride hydrolysis catalyst, a hydrogen production test was conducted. The specific method for the hydrogen production test was as follows: Under the experimentally set temperature conditions, a solution containing 1.5 wt.% NaBH4 and 5 wt.% NaOH was placed in a constant-temperature water bath. After reaching equilibrium at the aforementioned set temperature, 10 mL was added to a wide-mouth bottle containing the catalyst. The volume of hydrogen produced per unit time was collected and recorded by water displacement to obtain the hydrogen release rate. Unless otherwise specified, the temperature condition was 303 K.

[0074] The test results of hydrogen production by hydrolysis of ZIF-67 are as follows: Figure 3 As shown, at 303 K, the hydrogen production rate is 0 mL / min. -1 ·g -1 This indicates that ZIF-67 does not possess catalytic activity.

[0075] Step 2, Preparation of Co-B / ZIF-67: First, 200 mg of ZIF-67 was placed in deionized water to obtain solution C. Then, 25 mg of citric acid monohydrate and 281.1 mg of cobalt sulfate heptahydrate were placed in solution C and sonicated for 1 hour. After sonication, the mixture was allowed to stand for 24 hours to obtain mixture D. Simultaneously, 378.3 mg of sodium borohydride was placed in deionized water to obtain solution E. Then, under stirring conditions, solution E was slowly added dropwise to mixture D at a dropping rate of 0.02 mL / s. After the addition was complete, the mixture was allowed to stand for 3 hours. Finally, the obtained product was washed with ethanol by vacuum filtration and dried at 80°C for 12 hours to obtain Co-B / ZIF-67.

[0076] To verify the composition of Co-B / ZIF-67 obtained in step 2, XRD testing was performed. The test results are as follows: Figure 1 As shown, the characteristic peak of Co-B / ZIF-67 is the same as the standard peak of ZIF-67, with no shift; meanwhile, no Co-B characteristic peak was detected.

[0077] Since no characteristic peak of Co-B was detected, the composition of Co-B / ZIF-67 was further confirmed by EDS testing. The EDS test results are as follows: Figure 4 As shown, Co-B / ZIF-67 contains not only the C, O, N, and Co elements of ZIF-67, but also the B element.

[0078] The combined XRD and EDS test results prove that Co-B particles were successfully loaded, and that Co-B is amorphous; at the same time, loading Co-B particles has no effect on the crystal structure of ZIF-67.

[0079] To verify the microstructure of Co-B / ZIF-67 obtained in step 2, SEM testing was performed. The SEM test results are as follows: Figure 5 As shown, the basic microstructure of Co-B / ZIF-67 remains the same as that of ZIF-67, which is a rhombic dodecahedral structure. The difference is that Co-B spherical particles are attached to the surface of ZIF-67 in step 2, and the size of the Co-B spherical particles is 50 nm.

[0080] To demonstrate the hydrogen production performance of Co-B / ZIF-67 obtained in step 2 as a sodium borohydride hydrolysis catalyst, hydrolysis hydrogen production tests were conducted. The results of the Co-B / ZIF-67 hydrolysis hydrogen production tests are as follows: Figure 3 As shown, the maximum hydrogen production rate at 303 K is 5417 mL·min. -1 ·g -1 The hydrogen release reached 100% of the theoretical value. A comparison with the hydrogen production test results obtained from the hydrolysis of ZIF-67 in step 1 shows that the Co-B loaded in step 2 is the active material, directly providing the catalytic effect for the hydrolysis of sodium borohydride, and also proving that ZIF-67 only serves as a support in the technical solution.

[0081] Step 3, Preparation of Co-B / ZIF-67 / DT-COF: First, 100 mg of Co-B / ZIF-67 obtained in Step 2 was placed in 20 mL of ethanol and sonicated for 30 min to obtain mixed solution F. Then, 42 mg of trifluoropropylene (TFP) monomer was placed in 20 mL of DMF to obtain TFP solution. Finally, 71.5 mg of diaminoanthraquinone (DAAQ) monomer was placed in 20 mL of DMF... In DMF, a DAAQ solution was obtained. Then, the TFP solution was placed in mixed solution F and stirred for 30 min to obtain mixed solution G. The DAAQ solution and acetic acid were then placed in mixed solution G and stirred for 30 min to obtain mixed solution H. Finally, mixed solution H was reacted at a reaction temperature of 100℃ for 24 h. After the reaction was completed, it was cooled to room temperature. The obtained product was washed five times by centrifugation with DMF and ethanol, and then vacuum dried at a drying temperature of 60℃ for 12 h to obtain a covalent organic framework DT-COF-coated Co-B composite material supported by a metal-organic framework ZIF-67, abbreviated as Co-B / ZIF-67 / DT-COF.

[0082] To verify the composition of Co-B / ZIF-67 / DT-COF obtained in step 3, XRD analysis was performed. The test results are as follows: Figure 1As shown, the characteristic peaks of Co-B / ZIF-67 / DT-COF simultaneously contain the standard peaks of both ZIF-67 and DT-COF. The test results indicate that DT-COF is successfully coated on the surface of ZIF-67; meanwhile, no characteristic peaks of Co-B were detected.

[0083] Since no characteristic peak of Co-B was detected, the composition of Co-B / ZIF-67 / DT-COF was further confirmed by EDS testing. The EDS test results are as follows: Figure 6 As shown, Co-B / ZIF-67 / DT-COF contains C, O, N, and Co elements, as well as B element, in addition to the C, O, N, and Co elements of ZIF-67 and DT-COF.

[0084] The combined XRD and EDS test results demonstrate the successful loading of Co-B particles, and that Co-B is amorphous; furthermore, the loading of Co-B particles has no effect on the crystal structure of ZIF-67 and DT-COF.

[0085] To verify the microstructure of Co-B / ZIF-67 / DT-COF obtained in step 3, SEM testing was performed. The SEM test results are as follows: Figure 7 As shown, the basic microstructure of Co-B / ZIF-67 / DT-COF remains the same as that of Co-B / ZIF-67, a rhombic dodecahedral structure. The difference lies in the surface roughness of Co-B / ZIF-67 / DT-COF, i.e., DT-COF was attached to the surface of Co-B / ZIF-67 in step 3. Test results show that DT-COF coats the surface of Co-B / ZIF-67, forming a protective layer that helps prevent the detachment of Co-B particles.

[0086] To demonstrate the hydrogen production performance of the Co-B / ZIF-67 / DT-COF obtained in step 3 as a sodium borohydride hydrolysis catalyst, hydrolysis hydrogen production tests were conducted. The results of the hydrolysis hydrogen production tests of Co-B / ZIF-67 / DT-COF are shown in Table 1 and... Figure 8 As shown, the maximum hydrogen production rate at 303 K is 8331 mL / min. -1 ·g -1 The hydrogen release rate was 100% of the theoretical value. A comparison with the hydrogen production test results obtained from the hydrolysis of Co-B / ZIF-67 in step 2 shows that introducing DT-COF to coat Co-B / ZIF-67 in step 3 can significantly improve the maximum hydrogen release rate, with an increase of 153%.

[0087] To demonstrate the reaction kinetics of Co-B / ZIF-67 / DT-COF, hydrogen production via hydrolysis was tested at temperatures of 298 K, 308 K, and 313 K. The test results, fitted by the Arrhenius equation, are shown in Table 1 and [other tables not provided]. Figure 9 As shown, the apparent activation energy of the reaction, Ea, is 30.7 kJ·mol⁻¹. -1 In addition, to compare with existing technologies, the data from the references are summarized in Table 1.

[0088] Table 1. Hydrogen production rate and activation energy of NaBH4 hydrolysis catalyzed by different catalysts.

[0089]

[0090] Note: The reference numbers in Table 1 correspond to the following references:

[0091] [1] Yang F, Zou Y, Xiang C, et al. Synthesis of “needle-cluster” NiCo2O4carbon nanofibers and loading of Co-B nanoparticles for hydrogen production through the hydrolysis of NaBH4. Journal of Alloys and Compounds, 2022,911:165069.

[0092] [2]Peng C, Li T, Zou Y, et al. Bacterial cellulose derived carbon as asupport for catalytically active Co-B alloy for hydrolysis of sodiumborohydride. International Journal of Hydrogen Energy, 2021, 46(1): 666-675.

[0093] [3] Q.Li, W.Yang, F.Li, A.Cui, J.Hong, Preparation of CoB / ZIF-8 supported catalyst by single step reduction and its activity in hydrogen production, Int.J.Hydrog.Energy vol.43(1)(2018)271-282.

[0094] [4]Luyan Shi, Ke Zhu, Yuting Yang, Yi Liu, Shoulei Xu, Tayirjan TaylorIsimjan, Xiulin Yang, Oxygen-vacancy-rich Ru-clusters decorated Co / Ce oxidesmodifying ZIF-67nanocubes as a high-efficient catalyst for NaBH4 hydrolysis, International Journal of Hydrogen Energy, Volume 47, Issue 89, 2022, Pages 37840-37849.

[0095] Based on the above test results and comparative analysis with existing references, the following preliminary conclusions can be drawn:

[0096] 1. References [1], [2] and [3] show that using different supports can also have a significant impact on the maximum generation rate when using the same Co-B loading material;

[0097] This invention is also based on the same loading material Co-B, using ZIF-67 as the carrier. Compared with the cited references [1], [2] and [3], it can not only significantly improve the maximum hydrogen production rate, but also significantly improve the reaction kinetic performance, i.e. the activation energy. This proves that the carrier ZIF-67 of this invention can significantly improve the reaction thermodynamic performance and reaction kinetic performance.

[0098] 2. By comparing references [3] and [4], it can be seen that, based on similar MOFs as supports, different Co and its compounds loaded on the support can have a significant impact on the catalytic performance.

[0099] Based on ZIF-67 as a support, Co-B as a loading material, and DT-COF coating, this invention can further significantly improve the maximum hydrogen production rate, with improvements of 1946.87% and 154.22% compared to references [3] and [4], respectively.

[0100] In summary, compared with existing technologies, the present invention significantly improves catalytic performance. The reasons are as follows:

[0101] 1. This invention uses ZIF-67 as a carrier and introduces DT-COF coating to increase the specific surface area of ​​Co-B particles, obtain more active sites, and thus effectively improve the hydrogen production rate.

[0102] 2. This invention uses ZIF-67 as a support and introduces DT-COF coating to improve the uniformity of Co-B particle loading and inhibit the aggregation of Co-B particles, that is, to improve the dispersion of Co-B particles, so that the catalyst activity changes very little with temperature, thereby effectively reducing the activation energy of the reaction.

[0103] Previous research by the inventor's research group showed that catalyst separation from the reaction liquid can be achieved efficiently through magnetic catalyst recovery. To demonstrate the magnetic properties of the Co-B / ZIF-67 / DT-COF composite material, magnetic testing was conducted. The magnetic test results are as follows: Figure 10 As shown, Co-B / ZIF-67 / DT-COF is attached to the surface of a magnetic stir bar. The test results show that Co-B / ZIF-67 / DT-COF is magnetic, meaning that the catalyst can be recovered through magnetic force.

[0104] To demonstrate the cycling performance of Co-B / ZIF-67 / DT-COF, a cycling performance test was conducted. The specific method for the cycling performance test involved magnetically recovering the Co-B / ZIF-67 / DT-COF that had already undergone hydrogen release testing, and then performing the aforementioned hydrolysis hydrogen production test again. The hydrogen release rate after cycling was then obtained, and the cycling performance of Co-B / ZIF-67 / DT-COF could be calculated using simple methods. The test results are shown in Table 2 and... Figure 11 As shown, after 10 cycles at 303K, 87.6% of the initial catalytic activity was retained. Meanwhile, to compare with existing technologies, data from the references are summarized in Table 2.

[0105] Table 2. Cycle number and cycle performance of different catalysts for NaBH4 hydrolysis

[0106]

[0107] Note: The reference numbers in Table 2 correspond to the following references:

[0108] [4]Luyan Shi,Ke Zhu,Yuting Yang,Yi Liu,Shoulei Xu,Tayirjan TaylorIsimjan,Xiulin Yang,Oxygen-vacancy-rich Ru-clusters decorated Co / Ce oxidesmodifying ZIF-67nanocubes as a high-efficient catalyst for NaBH4 hydrolysis,International Journal of Hydrogen Energy,Volume 47,Issue 89,2022,Pages 37840-37849.

[0109] [5]Maafa I M,Zouli N,Abutaleb A,et al.In Situ Preparation of 2D Co-BNanosheets@1D TiO2 Nanofibers as a Catalyst for Hydrogen Production fromSodium Borohydride[J].Inorganics,2023,11(8):342.

[0110] [6]Ruan J,Wang S,Yang F,et al.Hydrolysis of NaBH4 using carbonizedmelamine foam-supported cobalt borate composite catalyst for H2 production[J].International Journal of Electrochemical Science,2024,19(2):100461.

[0111] [7] Luo X, Sun L, Xu F, et al. Metal boride-decorated CoNi layered doublehydroxides supported on muti-walled carbon nanotubes as efficient hydrolysiscatalysts for sodium borohydride[J]. Journal of Alloys and Compounds, 2023,930:167339.

[0112] Based on the above test results and comparative analysis with existing references, the following preliminary conclusions can be drawn:

[0113] 1. By comparing references [4] and [5], it can be seen that when an active substance is loaded on a single support, the active substance is easy to fall off the support. At the same time, the single support material has poor stability and its structure is easy to collapse, resulting in poor cyclicity of the catalyst.

[0114] 2. A comparison of references [6] and [7] shows that loading active materials onto composite supports improves the structural stability of the material due to the synergistic effect between the two supports, thus enhancing the catalytic performance compared to single-support catalysts. However, the problem of active materials easily detaching from the support has not been well resolved.

[0115] This invention uses ZIF-67 as a support, Co-B as a loading material, and introduces DT-COF coating to effectively inhibit the shedding of active Co-B particles and significantly improve the cycle performance of the catalyst.

[0116] Based on the above analysis, the significant improvement in the cycle performance of this invention can be attributed to the following reasons:

[0117] 1. The composite structure of Co-B / ZIF-67 / DT-COF provides a robust framework to maintain the stability of catalytic active sites. The overall microstructure is less prone to collapse during the reaction, effectively enhancing the structural stability of the catalyst;

[0118] 2. DT-COF forms a protective layer on the surface of Co-B / ZIF-67, which effectively prevents the aggregation and shedding of Co-B particles during the catalytic process, thereby ensuring the high efficiency and stability of the catalyst during continuous use.

[0119] 3. The Co-B particle catalyst supported on the Co-B / ZIF-67 / DT-COF support is magnetic, which allows it to be quickly recovered using a magnetic stir bar during the cycling test. This reduces the mass loss and morphological damage of Co-B / ZIF-67 / DT-COF during cycling, effectively enhancing the stability of the catalyst during cycling.

[0120] To demonstrate the respective roles of DT-COF and Co-B in the technical solution, Comparative Example 1 and Comparative Example 2 are provided, in which DT-COF and Co-B are prepared separately as catalysts.

[0121] Comparative Example 1

[0122] A method for preparing DT-COF, the steps of which are the same as those in Example 1 unless otherwise specified, are different in that: steps 1 and 2 are not performed, and the Co-B / ZIF-67 obtained in step 2 is not added in step 3, and the material obtained in step 3 is DT-COF.

[0123] The test results of hydrogen production by hydrolysis of DT-COF are as follows: Figure 12 As shown, at 303 K, the hydrogen production rate is 0 mL / min. -1 ·g -1 The test results showed that DT-COF does not have catalytic activity.

[0124] A comparison of Comparative Example 1 and Example 1 shows that DT-COF alone does not exhibit catalytic activity, demonstrating that DT-COF only provides a coating function in the technical solution. Its specific working principle is that DT-COF coating generates a suitable protective layer on the catalyst surface, effectively inhibiting the shedding of active Co-B particles. Simultaneously, it reduces the collapse of the material structure during the hydrolysis reaction, thereby significantly improving the material's cycle stability.

[0125] Comparative Example 2

[0126] A method for preparing Co-B, the steps of which are the same as those in Example 1 unless otherwise specified, except that steps 1 and 3 are not performed, and ZIF-67 obtained in step 1 is not added in step 2, and the material obtained in step 2 is Co-B.

[0127] The SEM test results of Co-B are as follows: Figure 13 As shown, Co-B exists as crystalline aggregates. Combined with the SEM test results of Co-B / ZIF-67, it can be seen that introducing ZIF-67 as a carrier can change and adjust the microstructure of the composite material, achieving the technical effect of avoiding agglomeration, thus proving the role of ZIF-67 in the technical solution.

[0128] The test results for hydrogen production from the hydrolysis of Co-B are as follows: Figure 12 As shown, the maximum hydrogen production rate at 303 K is 2743 mL·min. -1 ·g -1 The hydrogen release rate reached 100% of the theoretical value. Combined with the hydrolysis hydrogen production test results of Co-B / ZIF-67, it can be seen that the introduction of ZIF-67 support can significantly improve the maximum hydrogen release rate, with an increase of 197%, thus proving the role of ZIF-67 in the technical solution.

[0129] A comparison of Comparative Example 2 and Example 1 shows that although Co-B is the active material and can be used directly as a catalyst to achieve basic catalytic hydrolysis of sodium borohydride, its agglomeration occurs when used alone as a catalyst, leading to a decrease in the maximum hydrogen release rate. This demonstrates that using ZIF-67 as a support can directly adjust the microstructure of the composite material, avoid agglomeration, significantly increase the specific surface area, and thus significantly increase the maximum hydrogen release rate, proving the role of ZIF-67 in the technical solution. Furthermore, DT-COF coating forms a protective layer on the catalyst surface, inhibiting the shedding of active Co-B particles and reducing the collapse of the material structure during the hydrolysis reaction.

Claims

1. A method for preparing a Co-B / ZIF-67 / DT-COF composite material, characterized in that... Includes the following steps: Step 1, Preparation of ZIF-67: First, cobalt nitrate hexahydrate is placed in methanol and ultrasonically mixed to obtain mixture A. At the same time, 2-methylimidazole is placed in methanol to obtain mixture B. Then, mixture B and mixture A are stirred under certain conditions. After stirring, they are allowed to stand under certain conditions. Finally, the obtained product is centrifuged and vacuum dried under certain conditions to obtain ZIF-67. Step 2, Preparation of Co-B / ZIF-67: First, ZIF-67 is placed in deionized water to obtain solution C. Then, citric acid monohydrate and cobalt sulfate heptahydrate are placed in solution C and sonicated under certain conditions. After sonication, the mixture is allowed to stand under certain conditions to obtain mixture D. At the same time, sodium borohydride is placed in deionized water to obtain solution E. Then, under stirring conditions, solution E is slowly added dropwise to mixture D under certain conditions. After the addition is complete, the mixture is allowed to stand under certain conditions. Finally, the obtained product is filtered and washed with ethanol and then vacuum dried under certain conditions to obtain Co-B / ZIF-67. Step 3, Preparation of Co-B / ZIF-67 / DT-COF: DT-COF is grown on the surface of Co-B / ZIF-67 using a solvothermal method. First, the Co-B / ZIF-67 obtained in Step 2 is placed in ethanol and sonicated under certain conditions to obtain a mixed solution F. The TFP monomer is placed in DMF to obtain a TFP solution, and the DAAQ monomer is placed in DMF to obtain a DAAQ solution. Then, the TFP solution is placed in mixed solution F and stirred under certain conditions to obtain a mixed solution G. Next, the DAAQ solution and acetic acid are placed in mixed solution G and stirred under certain conditions to obtain a mixed solution H. Finally, mixed solution H is reacted under certain conditions. After the reaction is complete, it is cooled to room temperature. The obtained product is washed by centrifugation with DMF and ethanol, and then vacuum dried under certain conditions to obtain the covalent organic framework DT-COF-coated Co-B composite material supported by the metal-organic framework ZIF-67, abbreviated as Co-B / ZIF-67 / DT-COF.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:2; In step 2, the mass ratio of ZIF-67, citric acid monohydrate, cobalt sulfate heptahydrate, and sodium borohydride is (8-8.8):1:(10-12):(14-16); In step 3, the mass ratio of Co-B / ZIF-67, TFP monomer, DAAQ monomer and acetic acid is (2-2.6):1:(1.5-2):(1.08-1.5).

3. The preparation method according to claim 1, characterized in that: In step 1, the stirring conditions are: mixture B is quickly added to mixture A, and the stirring time is 1 hour. In step 1, the standing conditions are: standing time is 18 h; the drying conditions are: drying temperature is 80℃ and drying time is 12 h.

4. The preparation method according to claim 1, characterized in that: In step 2, the ultrasound conditions are as follows: ultrasound time is 1 hour. In step 2, the conditions for preparing mixture D to stand are: standing time of 24 h; the conditions for adding the mixture are: adding at a rate of 0.02 mL / s; and the conditions for standing after adding the mixture are: standing time of 3 h. In step 2, the drying conditions are: drying temperature of 80℃ and drying time of 12 h.

5. The preparation method according to claim 1, characterized in that: In step 3, the conditions for ultrasound are: ultrasound time is 30 min; the conditions for stirring the mixed solution G and mixed solution H are: stirring time is 30 min. In step 3, the reaction conditions are: reaction temperature of 100℃ and reaction time of 24 h. In step 3, the conditions for centrifugal washing are: the number of centrifugal washing cycles is 5; the conditions for drying are: drying temperature is 60℃ and drying time is 12 h.

6. The preparation method according to claim 1, characterized in that: The resulting Co-B / ZIF-67 / DT-COF composite material is obtained by combining Co-B, ZIF-67, and DT-COF. The ZIF-67 used as a carrier has a rhombic dodecahedral structure with a size of 1.2 μm. The Co-B, as the active material, has a microstructure of nanoparticles and is loaded on the surface of ZIF-67. The DT-COF is used as a coating material to coat the surface of Co-B / ZIF-67; The Co-B / ZIF-67 / DT-COF is magnetic.

7. The preparation method according to claim 1, characterized in that: When the obtained Co-B / ZIF-67 / DT-COF composite material was used as a catalyst for hydrogen production by sodium borohydride hydrolysis, the maximum hydrogen production rate was 7000-10000 mL·min at 303 K. -1 ·g -1 The hydrogen release reaches 100% of the theoretical value; after 10 recycling / reuse cycles, it retains 85.4-90.1% of the initial catalytic activity.

8. The preparation method according to claim 1, characterized in that: When the obtained Co-B / ZIF-67 / DT-COF composite material is used as a catalyst for hydrogen production by sodium borohydride hydrolysis, the activation energy for catalytic hydrogen release is E. a = 29.4-30.9 kJ·mol -1 .

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