Preparation method, product and application of an amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial

Abstract

The present invention discloses a preparation method, product and application of an amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial, belonging to the field of energy materials and electrochemistry. The present invention prepares amorphous ZIF-67 (a s -ZIF-67) through a simple and rapid solid-phase reaction, and an amorphous ZIF-67 solid solution can be obtained without adding any solvent. Using the amorphous ZIF-67 solid solution as a precursor, cobalt-doped porous carbon nanomaterials (a s -Co@NC) can be obtained through high-temperature pyrolysis. During the pyrolysis process, the morphology of the Co-doped carbon-based material regulated by amorphous coordination turns into a three-dimensional cross-linked porous structure. Most importantly, not only is the agglomeration of Co significantly weakened, thereby improving the catalytic activity of the catalyst in water electrolysis and electrochemical sensing, but also the yield of the catalyst is increased.

Description

Technical Field

[0001] The present invention relates to the fields of energy materials and electrochemistry, and particularly to a preparation method, product and application of an amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial. Background Art

[0002] Cobalt-doped carbon nanocomposites generally exhibit good electrocatalytic activity. There are many precursors for preparing cobalt-doped carbon nanocomposites. Among them, zeolitic imidazolate framework material ZIF-67 has advantages such as rich cobalt and nitrogen sources and large specific surface area, and is widely used in the preparation of nanocatalysts. However, ZIF-67 usually requires high-temperature pyrolysis to obtain the required catalyst. In this case, cobalt atoms will spontaneously aggregate to form large-sized cobalt particles, resulting in a reduction in the electrochemically active area and active sites. The methods to overcome the serious aggregation of metal atoms mainly include "metal-doping isolation", "heteroatom-doping anchoring" and "spatial isolation". However, these methods are cumbersome and have complex processes, increasing the preparation cost and improving the quality assurance, which is not conducive to the scalability of mass production and greatly hinders their wide application. Therefore, it is highly desirable to explore new strategies to simply and low-costly regulate the uniform distribution of metal atoms without significant aggregation. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a preparation method of an amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial; the second purpose of the present invention is to provide an electrochemical sensor prepared from the cobalt-doped porous carbon nanomaterial prepared by the above method; the third purpose of the present invention is to provide the application of the electrochemical sensor in detecting O 2 · in one aspect.

[0004] To achieve the above purposes, the present invention provides the following technical solutions:

[0005] 1. A preparation method of an amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial, comprising the following steps:

[0006] (1) Weigh a certain amount of cobalt nitrate hexahydrate and dimethylimidazole, directly mix them and stir vigorously for a solid-phase reaction to obtain a solid solution, namely amorphous ZIF-67;

[0007] (2) Place the obtained amorphous ZIF-67 in a quartz tube furnace and carbonize it under a nitrogen atmosphere to obtain a porous aerogel material;

[0008] (3) Grind the obtained porous aerogel material into powder to obtain a cobalt-doped porous carbon material.

[0009] Preferably, in step (1), the molar ratio of cobalt nitrate hexahydrate to dimethylimidazole is 1:4 to 1:32.

[0010] Preferably, in step (1), the stirring time is 10 s to 30 s.

[0011] Preferably, in step (2), the carbonization is carried out by heating to 900 °C and carbonizing for 1 h.

[0012] Preferably, the heating rate is 2 °C / min to 10 °C / min.

[0013] 2. The electrochemical sensor prepared from the cobalt-doped porous carbon nanomaterial prepared by the method is prepared as follows: After configuring the cobalt-doped porous carbon nanomaterial into a suspension slurry of 1.0 mg / mL with water, ultrasonically mixing evenly, dropping 5.0 μL of this slurry on the surface of a polished glassy carbon electrode, and naturally drying, then dropping 3.0 μL of 0.5% Nafion ethanol solution on the surface of the modified electrode, and naturally drying to obtain the electrochemical sensor.

[0014] The particle size of the cobalt-doped porous carbon nanomaterial is 7 - 16 nm.

[0015] 3. The application of the electrochemical sensor in detecting O 2 ·−.

[0016] The beneficial effects of the present invention are as follows:

[0017] In order to weaken the adverse effects brought by the agglomeration of Co atoms during the carbonization process, the present invention prepares amorphous ZIF-67 (a s -ZIF-67) through a simple and rapid solid-phase reaction, and an amorphous ZIF-67 solid solution can be obtained without adding any solvents. Using the amorphous ZIF-67 solid solution as a precursor, cobalt-doped porous carbon nanomaterials (a s -Co@NC) can be obtained through high-temperature pyrolysis. During the pyrolysis process, the morphology of the Co-doped carbon-based material regulated by amorphous coordination becomes a three-dimensional cross-linked porous structure. Most importantly, not only the agglomeration of Co is significantly weakened, thereby improving the catalytic activity of the catalyst in water electrolysis and electrochemical sensing, but also the yield of the catalyst is improved. Description of the Drawings

[0018] In order to make the objectives, technical solutions, and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0019] Figure 1 It is the technical flow chart of the present invention;

[0020] Figure 2 It is the a prepared in Example 1 sPhoto of -Co@NC;

[0021] Figure 3 c prepared for the comparative example r Photo of -Co@NC;

[0022] Figure 4 a prepared for Example 1 s SEM image of -Co@NC;

[0023] Figure 5 c prepared for the comparative example r SEM image of -Co@NC;

[0024] Figure 6 a prepared for Example 1 s TEM image of -Co@NC;

[0025] Figure 7 a prepared for Example 1 s Aberration-corrected HAADF-STEM image of -Co@NC;

[0026] Figure 8 c prepared for the comparative example r TEM image of -Co@NC;

[0027] Figure 9 a prepared for Example 1 s -ZIF-67 and c prepared for the comparative example r XRD pattern of -ZIF-67;

[0028] Figure 10 a prepared for Example 1 s -ZIF-67 and c prepared for the comparative example r Infrared spectrum of -ZIF-67;

[0029] Figure 11 a prepared for Example 1 s -Co@NC and c prepared for the comparative example r XRD pattern of -Co@NC;

[0030] Figure 12 a prepared for Example 1 s DSC curve of -ZIF-67, heating rate 5 °C / min;

[0031] Figure 13 a prepared for Example 1 s -Co@NC and c prepared for the comparative example r Nitrogen adsorption-desorption isotherm of -Co@NC;

[0032] Figure 14a prepared in Example 1 s -Co@NC prepared in the comparative example, c r -Co@NC and the commercial catalyst RuO 2 Linear sweep voltammetry (LSV) curves of the OER reaction of the modified electrode;

[0033] Figure 15 a prepared in Example 1 s -Co@NC prepared in the comparative example, c r -Co@NC and the commercial catalyst RuO 2 OER reaction of the modified electrode, overpotential histogram at a current density of 10 mA·cm -2 ;

[0034] Figure 16 a prepared in Example 1 s -Co@NC and c prepared in the comparative example r Cyclic voltammogram of -Co@NC modified electrode for detecting O 2 ·－ ;

[0035] Figure 17 a prepared in Example 1 s -Co@NC and c prepared in the comparative example r Current density and half-wave potential histogram of -Co@NC modified electrode for detecting O 2 ·－ ;

[0036] Figure 18 Linear relationship between current density and scan rate of catalysts prepared at different temperatures at different scan rates;

[0037] Figure 19 Nernst plot of the modified electrode of catalysts prepared at different temperatures;

[0038] Figure 20 CV response of the modified electrode of catalysts prepared at different temperatures to 25.0 μM O 2 ·- ; Detailed implementation mode

[0039] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0040] The technical flow chart of the present invention is as shown in Figure 1Shown as follows: 1. By directly mixing cobalt nitrate hexahydrate and 2-methylimidazole, a solid-phase reaction is carried out. After stirring for 20 s, a purple solid solution, namely amorphous ZIF-67, is formed and named a s -ZIF-67; 2. The solid solution a s -ZIF-67 is directly placed in a quartz tube furnace and pyrolyzed under a nitrogen atmosphere at 900 °C. During the pyrolysis process, amorphous ZIF-67 transforms from a glassy state to a highly elastic state, and a large amount of gas is decomposed from the unsaturated coordinated 2-methylimidazole. These gases serve as templates, and the coordination polymer of amorphous ZIF-67 rearranges to form a three-dimensional structure with a rich hollow sphere closely arranged. After grinding, a cobalt-doped porous carbon material is obtained and named a s -Co@NC; 3. The a s -Co@NC is modified on a glassy carbon electrode to investigate the oxygen evolution reaction (OER) performance of water electrolysis, and an electrochemical sensor is constructed to investigate the catalytic performance for superoxide anion (O 2 ·- ).

[0041] Example 1

[0042] A preparation method of an amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial, which specifically includes the following steps:

[0043] 1. Weigh 2.91 g of cobalt nitrate hexahydrate and 6.56 g of 2-methylimidazole (i.e., the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:7). After direct mixing, vigorous stirring is carried out for 20 s for a solid-phase reaction to obtain a dark purple solid solution, namely amorphous ZIF-67, named a s -ZIF-67.

[0044] 2. Pour the obtained a s -ZIF-67 into a porcelain boat, and in a quartz tube furnace under a nitrogen atmosphere, heat it to 900 °C at a rate of 2 °C / min for carbonization for 1 h, and naturally cool to room temperature to obtain a porous aerogel material.

[0045] 3. Grind the obtained porous aerogel material into a black powder to obtain a cobalt-doped porous carbon material a s -Co@NC.

[0046] 4. Use the obtained a s -Co@NC for the OER test: The prepared a s-Co@NC (4.0 mg) was directly dispersed in 1.0 mL of ethanol solution containing 20 μL of 5.0 wt% Nafion (the volumes of water and ethanol were 680 μL and 300 μL respectively), and ultrasonicated for 30 minutes to obtain a suspension slurry. Then, 5 μL was accurately pipetted and drop-coated on the surface of a polished glassy carbon electrode (GCE), and dried in air for 2 h to obtain a working electrode for the OER reaction.

[0047] 5. The obtained a above s -Co@NC was used to construct an electrochemical sensor: 1.0 mg / mL of a s -Co@NC ink was ultrasonicated for 30 minutes, then 5.0 μL of this ink was drop-coated on the surface of a polished GCE. After natural drying, 3.0 μL of 0.5% Nafion ethanol solution was drop-coated on the surface of the modified electrode, and after natural drying, the electrochemical sensor a s -Co@NC / GCE was obtained for the electrochemical detection of O 2 ·－

[0048] Comparative Example: According to the method of a crystalline ZIF-67-derived cobalt-doped porous carbon nanocatalyst reported in the literature (Mn-Etched Zeolitic Imidazolate Framework-67 Nanostructures for Biomimetic Superoxide Anion Sensing, DOI: 10.1021 / acsanm.2c00295), the preparation method specifically includes the following steps:

[0049] 1. 0.1 mol of Co(NO 3 ) 2 ·6H 2 O and 0.8 mol of 2-methylimidazole were respectively dissolved in 75 mL of methanol. After mixing the two, they were stirred at room temperature for 2 h to obtain a mixture.

[0050] 2. The obtained mixture was centrifuged at a speed of 800 r / min in a centrifuge for 5 min. The obtained precipitate was washed 5 - 7 times with ultrapure water and ethanol, and freeze-dried to obtain crystalline ZIF-67 denoted as c r -ZIF-67.

[0051] 3. The obtained c r -ZIF-67 was poured into a porcelain boat and carbonized in a quartz tube furnace under a nitrogen atmosphere at a rate of 2 °C / min to 900 °C for 1 h, and then naturally cooled to room temperature to obtain a black powder.

[0052] 4. The obtained black powder was ground to obtain a cobalt-doped porous carbon material c​r -Co@NC.

[0053] 5. Disperse the obtained c r -Co@NC prepared above for OER testing: Disperse the prepared catalyst (4.0 mg) directly in 1.0 ml of ethanol solution containing 20 μL of 5.0 wt% Nafion (the volumes of water and ethanol are 680 μL and 300 μL respectively), and ultrasonically treat for 30 minutes to obtain a suspension slurry. Then accurately measure 5 μL with a pipette and drop-coat it on the surface of a polished glassy carbon electrode (GCE), and dry it in air for 2 h to obtain a working electrode for the OER reaction. A commercial RuO 2 The performance of the catalyst-modified electrode was compared.

[0054] 6. Disperse the obtained c r -Co@NC for constructing an electrochemical sensor: After ultrasonically treating the c r -Co@NC ink with a concentration of 1.0 mg / mL for 30 min, drop-coat 5.0 μL of this ink on the surface of a polished glassy carbon electrode (GCE). After natural drying, drop-coat 3.0 μL of 0.5% Nafion ethanol solution on the surface of the modified electrode, and after natural drying, obtain the electrochemical sensor c r -Co@NC / GCE for electrochemical detection of superoxide anions.

[0055] Figure 2 The a s -Co@NC prepared in Example 1. As can be seen from the figure, it is powdery and the yield is very low.

[0056] Figure 3 The c r -Co@NC prepared in the comparative example. As can be seen from the figure, it is fluffy and porous, and the yield is very high.

[0057] Figure 4 The a s -Co@NC SEM image prepared in Example 1. As can be seen from the figure, a s -Co@NC has a three-dimensional porous structure with closely arranged hollow spheres.

[0058] Figure 5 The c r -Co@NC SEM image prepared in the comparative example. As can be seen from the figure, c r -Co@NC has a dodecahedral structure, and the morphology after carbonization of crystalline ZIF-67 has not changed significantly, only with slight wrinkles and shrinkage on the surface.

[0059] Figure 6 The a sTEM image of -Co@NC. As can be seen from the figure, a s The Co nanoparticles in -Co@NC are evenly dispersed and have small particle sizes. From the particle size distribution diagram in the figure, it can be seen that the diameter of the normally distributed nanoparticles is about 7 - 16 nm.

[0060] Figure 7 For a prepared in Example 1 s Aberration-corrected HAADF-STEM image of -Co@NC. As can be seen from the figure, a s The Co nanoparticles in -Co@NC not only have small sizes but also have a single-atom-dispersed Co structure, indicating that it has successfully overcome the agglomeration of Co nanoparticles during the pyrolysis process and achieved good dispersion of the active substances.

[0061] Figure 8 For c -Co@NC prepared in the comparative example r TEM image of -Co@NC. As can be seen from the figure, c r The Co nanoparticles in -Co@NC are severely agglomerated and have large particle sizes. From the particle size distribution diagram in the inset, it can be seen that the diameter of the non-normally distributed nanoparticles is in the range of 20 - 160 nm.

[0062] Figure 9 For a prepared in Example 1 s -ZIF-67 and c -ZIF-67 prepared in the comparative example r XRD patterns of -ZIF-67. c r The characteristic peaks in -ZIF-67 correspond exactly to the fitted ones, indicating that it has good crystallinity. There are no characteristic peaks in a -ZIF-67 below 10°, indicating that it has very weak crystallinity. s

[0063] Figure 10 For a prepared in Example 1 s -ZIF-67 and c -ZIF-67 prepared in the comparative example r Infrared spectra of -ZIF-67. The spectra show that a s -ZIF-67 has a broad peak at 3555 cm -1 representing O-H stretching. There is a stretching peak of N-H at 3404 cm -1 , stretching peaks of C-H of the methyl group on the imidazole ring at 3128 cm -1 and 2907 cm -1 , a stretching peak of C=N at 1572 cm -1 , and stretching peaks of the imidazole ring at 1428 - 667 cm -1 . There is a vibration peak of Co-N at 414 cm -1 , which confirms the bonding between Co and the ligand. These results indicate that a s ​-ZIF-67 maintains the same structural unit as c within a short range. r -ZIF-67.

[0064] Figure 11 a-Co@NC prepared in Example 1 s and c-Co@NC prepared in the comparative example r XRD patterns. It can be seen that both are Co elemental and graphite carbon phases. From the full width at half maximum of the Co(200) crystal plane, a-Co@NC s has smaller grains, which is consistent with the TEM results.

[0065] Figure 12 a-ZIF-67 prepared in Example 1 s DSC curve with a heating rate of 5 °C / minute. At 61 °C, 211 °C, and 306 °C are the glass transition temperatures of a-ZIF-67. Multiple phase transitions indicate its characteristic of having disordered amorphous and crystalline structures. And there is an exothermic phenomenon before 250 °C, indicating that a large amount of gas escapes. The high elastic state after the glass transition temperature has plasticity, resulting in the formation of a porous three-dimensional structure with a hollow sphere arrangement using gas as a template. s

[0066] Figure 13 a-Co@NC prepared in Example 1 s and c-Co@NC prepared in the comparative example r nitrogen adsorption-desorption isotherms. It can be seen from the figure that a-Co@NC s has a specific surface area 1.5 times larger than that of c-Co@NC. r

[0067] Figure 14 a-Co@NC prepared in Example 1 s , c-Co@NC prepared in the comparative example r and commercial catalyst RuO 2 LSV curves of the OER reaction of the modified electrode (linear sweep voltammetry). It can be seen from the figure that the overpotential of a-Co@NC s is less than that of c-Co@NC r and commercial RuO2, indicating that a-Co@NC s has the lowest overpotential and the highest activity.

[0068] Figure 15 a-Co@NC prepared in Example 1 s and c-Co@NC prepared in the comparative example r modified electrodes for detecting O 2 ·－Bar graph of current density and half-wave potential. It can be seen from the figure that when the current density is 10 mA·cm -2 , a s -Co@NC has a lower overpotential than c r -Co@NC and commercial RuO 2 , indicating that a s -Co@NC has better OER catalytic performance.

[0069] Figure 16 For the a s -Co@NC prepared in Example 1 and c r -Co@NC modified electrodes prepared in the comparative example for detecting O 2 ·－ Cyclic voltammograms. It can be seen from the figure that the oxidation peak current generated by a s -Co@NC catalyzing O 2 ·－ is higher than that catalyzed by c r -Co@NC, and the half-wave potential is more negative.

[0070] Figure 17 For the a s -Co@NC prepared in Example 1 and c r -Co@NC modified electrodes prepared in the comparative example for detecting O 2 ·－ Bar graph of current density and half-wave potential. It can be known from the bar graph that the oxidation peak current generated by a s -Co@NC catalyzing O 2 ·－ is 3.4 times that catalyzed by c r -Co@NC, and the half-wave potential is 0.08 V smaller. It shows that a s -Co@NC has higher catalytic performance for O 2 ·－ .

[0071] Figure 18 For the catalysts prepared at different temperatures, the linear relationship between the current density and the scan rate at different scan rates, where the slope is the effective electrochemically active surface area, and the catalyst prepared under the condition of 900 °C has the largest effective electrochemically active surface area.

[0072] Figure 19 Nernst plots for the electrodes modified with catalysts prepared at different temperatures. Among them, the semicircle diameter of the electrode modified with the catalyst prepared at 900 °C is the smallest in the high-frequency region, indicating that it has the smallest charge transfer resistance, and has the largest slope in the low-frequency region, indicating that it has the fastest mass transfer rate.

[0073] Figure 20CV responses of the catalyst modified electrodes prepared at different temperatures to 25.0 μM O 2 ·- . Among them, the catalyst modified electrode prepared at 900 °C has the largest oxidation peak current.

[0074] In the technical solution of Example 1 of the present invention, the optional range of the molar ratio of cobalt nitrate hexahydrate to dimethylimidazole is 1:4 to 1:32, the stirring time is 10 s to 30 s, and the heating rate is 2 °C / min to 10 °C / min.

[0075] The above embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. Preparation method of amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial, characterized in that, it comprises the following steps: (1) Weigh a certain amount of cobalt nitrate hexahydrate and dimethylimidazole, directly mix them and vigorously stir for 10 - 30 s for solid-phase reaction to obtain a solid solution, namely amorphous ZIF-67; (2) Place the obtained amorphous ZIF-67 in a quartz tube furnace, heat it to 700 - 1000 °C in a nitrogen atmosphere and carbonize for 1 h to obtain a porous aerogel material; (3) Grind the obtained porous aerogel material into powder to obtain cobalt-doped porous carbon material.

2. The preparation method of amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial according to claim 1, characterized in that, in step (1), the molar ratio of cobalt nitrate hexahydrate to dimethylimidazole is 1:4 - 1:

32.

3. The preparation method of amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial according to claim 1, characterized in that, in step (2), heat it to 900 °C in a nitrogen atmosphere and carbonize for 1 h.

4. The preparation method of amorphous ZIF-67-derived cobalt-doped porous carbon nanomaterial according to claim 1, characterized in that, in step (2), the heating rate is 2 °C / min - 10 °C / min.

5. Electrochemical sensor prepared from the cobalt-doped porous carbon nanomaterial prepared by the method according to any one of claims 1 - 4, characterized in that, the preparation method is as follows: After configuring the cobalt-doped porous carbon nanomaterial into a suspension slurry of 1.0 mg / mL with water, ultrasonically mix it evenly, drop 5.0 μL of this slurry on the surface of a polished glassy carbon electrode, after natural drying, drop 3.0 μL of 0.5% Nafion ethanol solution on the surface of the modified electrode, and obtain the electrochemical sensor after natural drying.

6. The electrochemical sensor according to claim 5, characterized in that, the particle size of the cobalt-doped porous carbon nanomaterial is 7 - 16 nm.

7. Use of the electrochemical sensor according to claim 5 in detecting O 2 ·－ aspect.

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