Modified cobalt-based ZIF material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalyst materials, in particular to a modified cobalt-based ZIF material and a preparation method and application thereof. The preparation method comprises the following steps: A) uniformly mixing a nitrate solution with a 2-methylimidazole solution, and reacting to obtain a crystal; the nitrate comprises cobalt nitrate and copper nitrate; and B) carrying out suction filtration, washing and drying on the crystal to obtain the modified cobalt-based ZIF material. The modified cobalt-based ZIF material prepared by the method is rhombic regular dodecahedron particles with regular morphology and uniform size, and efficient dechlorination can be realized; meanwhile, the preparation method is simple to operate, low in cost, mild in condition, good in controllability, green, efficient, low in cost, suitable for large-scale preparation and suitable for commercial popularization and application, and large-scale preparation can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst materials, and in particular to a modified cobalt-based ZIF material, a preparation method and application thereof. Background Art

[0002] Chlorinated organic compounds have unique properties due to their carbon-chlorine bonds and are widely used in the chemical, pharmaceutical and printing industries. With the large-scale consumption and discharge of chlorinated organic compounds, chlorinated pollutants such as flame retardants, antibiotics and fuels are frequently detected in wastewater. Most of the molecules in the list of persistent organic pollutants specified in the Stockholm Convention are chlorinated organic compounds, which cause mutagenicity by inducing DNA damage and exhibit environmental persistence, bioaccumulation and toxicity due to their inert, lipophilic carbon-chlorine bonds.

[0003] For refractory chlorinated organic pollutants, efficient activation and breaking of carbon-chlorine bonds is a key step in the removal process. However, carbon-chlorine bonds have a large bond energy (327 kJ mol -1 ) and there is a problem of high difficulty in activation. Studies have shown that under oxidative conditions, chlorinated organic pollutants are difficult to degrade due to their high oxidation state and are prone to generate by-products, while selective dechlorination can be achieved under reducing conditions. Therefore, reduction dechlorination provides a highly feasible solution. Among them, the chemical reduction method requires the addition of a reducing agent, such as sodium pyrosulfite and nano zero-valent iron. Although the reaction rate is fast, it has the disadvantage of poor sustainability. The catalytic reduction method usually uses the precious metal palladium (Pd) as a catalyst and uses hydrogen (H 2 ) as an electron donor has the advantages of being clean and efficient, but it is also limited by high material costs and great safety risks. Electrocatalytic reduction technology uses electric current as a safe and controllable reducing agent, bringing new opportunities for the treatment of chlorinated organic pollutants.

[0004] The ZIF-67 / C composite material disclosed in the application document with publication number CN110106518A is prepared by simply mixing ZIF-67 and conductive carbon black, and its function is positioned to improve the electrocatalytic hydrogen evolution performance and stability under alkaline conditions. The preparation method of the ZIF-67 / C composite material is mainly to form a composite electrocatalyst by mixing ZIF-67 nanomaterials with conductive carbon black and Nafion solution and ultrasonically. This method does not modify or optimize the crystal structure, surface chemical properties or functionality of the metal center of ZIF-67. The properties of the prepared composite material mainly come from the addition of conductive carbon black and the simple combination of the two. When used as a dechlorination electrocatalyst, the chlorine removal rate is low.

[0005] Therefore, how to establish a simple, efficient and economical method to study high-performance, low-cost reduction dechlorination electrocatalysts has become an urgent problem to be solved in this field. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a modified cobalt-based ZIF material, a preparation method and application thereof. The modified cobalt-based ZIF material prepared by the present invention is a rhombic regular dodecahedron particle with regular morphology and uniform size, which can efficiently dechlorinate.

[0007] The present invention provides a method for preparing a modified cobalt-based ZIF material, comprising the following steps:

[0008] A) mixing a nitrate solution and a 2-methylimidazole solution, and reacting the mixture to obtain a crystal;

[0009] The nitrates include cobalt nitrate and copper nitrate;

[0010] B) After filtering, washing and drying the crystals, a modified cobalt-based ZIF material is obtained.

[0011] Preferably, the molar ratio of copper nitrate to cobalt nitrate is 0.45-0.75:1.

[0012] Preferably, the solvent of the nitrate solution is methanol; and the concentration of the nitrate solution is 0.1-0.5 mol / L.

[0013] Preferably, the solvent of the 2-methylimidazole solution is methanol; and the concentration of the 2-methylimidazole solution is 1.2 to 1.6 mol / L.

[0014] Preferably, the mixing time is 25 to 35 minutes;

[0015] The reaction is carried out under static conditions; after the mixing, the reaction time is 10 to 14 hours.

[0016] Preferably, the detergent used for washing is methanol, and the number of washing times is not less than 3 times.

[0017] Preferably, the drying method includes drying in air, drying in an oven or drying in a vacuum drying oven;

[0018] The drying temperature is 10-200° C. and the drying time is 3-12 hours.

[0019] The present invention also provides a modified cobalt-based ZIF material prepared by the preparation method described above.

[0020] The present invention also provides a use of the modified cobalt-based ZIF material as a dechlorination electrocatalyst.

[0021] The present invention also provides a method for electrochemical dehalogenation, comprising the following steps:

[0022] The modified cobalt-based ZIF material, ethanol, water and Nafion solution described above are mixed and uniformly dispersed by ultrasonication; the obtained dispersion is then drop-coated on carbon paper to obtain a cobalt-based ZIF high-efficiency dechlorination electrocatalyst material electrode, which is a working electrode;

[0023] Electrolysis was carried out at constant potential using a silver / silver chloride electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a phosphate buffer solution containing chloramphenicol as an electrolyte.

[0024] The present invention provides a method for preparing a modified cobalt-based ZIF material, comprising the following steps: A) mixing a nitrate solution with a 2-methylimidazole solution, reacting to obtain crystals; the nitrate comprises cobalt nitrate and copper nitrate; B) filtering, washing and drying the crystals to obtain a modified cobalt-based ZIF material. The present invention introduces other transition metal elements into the cobalt-based ZIF material by a coprecipitation method, and the prepared modified cobalt-based ZIF material is a rhombic regular dodecahedron particle with a regular morphology and uniform size, and at the same time utilizes the synergistic effect between the copper element and the cobalt element to achieve efficient reduction and dechlorination performance. The preparation method of the modified cobalt-based ZIF material provided by the present invention is simple to operate, low in cost, mild in conditions, simple in operation, good in controllability, green and efficient, low in cost, can be prepared on a large scale, is suitable for commercial promotion and application, and provides a potential solution for preparing cobalt-based ZIF materials with high electrocatalytic activity.

[0025] The experimental results show that the modified cobalt-based ZIF material prepared by the method provided by the present invention has high electrocatalytic activity. The modified cobalt-based ZIF material prepared by the method provided by the present invention is used to prepare a working electrode, which is applied to the electrocatalytic reduction degradation of chloramphenicol, with a silver / silver chloride electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a phosphate buffer solution containing 50 mg / L chloramphenicol as an electrolyte. Constant potential reduction is performed at a potential of -1.2 V, which can efficiently disconnect the carbon chlorine bond and achieve the removal of chlorine atoms in chloramphenicol, with a relatively good chlorine removal rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Scanning electron microscope images of the CuCo-MOF material prepared in Example 1 of the present invention and the Co-MOF material prepared in Comparative Example 1;

[0027] Figure 2 The dechlorination of the CuCo-MOF material prepared in Example 1 of the present invention and the Co-MOF material prepared in Comparative Example 1 to a phosphate buffer solution containing 50 mg / L of chloramphenicol at a potential of -1.2 V;

[0028] Figure 3 Cyclic voltammetry curves of the CuCo-MOF material prepared in Example 1 of the present invention and the Co-MOF material prepared in Comparative Example 1 before and after the dechlorination reaction. DETAILED DESCRIPTION

[0029] The technical solution 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 part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The present invention provides a method for preparing a modified cobalt-based ZIF material, comprising the following steps:

[0031] A) mixing a nitrate solution and a 2-methylimidazole solution, and reacting the mixture to obtain a crystal;

[0032] The nitrates include cobalt nitrate and copper nitrate;

[0033] B) After filtering, washing and drying the crystals, a modified cobalt-based ZIF material is obtained.

[0034] Regarding step A):

[0035] The nitrate solution and the 2-methylimidazole solution are mixed and reacted to obtain crystals;

[0036] The nitrates include cobalt nitrate and copper nitrate.

[0037] In some embodiments of the present invention, the solvent of the nitrate solution is methanol. The concentration of the nitrate solution is 0.1-0.5 mol / L, such as 0.46 mol / L.

[0038] In some embodiments of the present invention, the molar ratio of copper nitrate to cobalt nitrate is 0.45-0.75:1, preferably 0.45:1, 0.6:1, or 0.75:1.

[0039] In some embodiments of the present invention, the solvent of the 2-methylimidazole solution is methanol. The concentration of the 2-methylimidazole solution is 1.2-1.6 mol / L, such as 1.4 mol / L.

[0040] The mixing is stirring and the mixing time is 25 to 35 minutes, such as 30 minutes.

[0041] The reaction is carried out under static conditions. After the mixing, the reaction time is 10 to 14 hours, such as 12 hours.

[0042] Regarding step B):

[0043] The crystals are filtered, washed and dried to obtain a modified cobalt-based ZIF material.

[0044] In some embodiments of the present invention, the washing agent used in the washing is methanol, and the number of washing times is not less than 3 times, such as 3 times.

[0045] In some embodiments of the present invention, the drying method includes drying in air, drying in an oven or drying in a vacuum drying oven. The drying temperature is 10 to 200° C., such as 60° C., and the drying time is 3 to 12 hours, such as 6 hours.

[0046] After the drying, a purple powder was obtained, which was recorded as a modified cobalt-based ZIF material.

[0047] The present invention also provides a modified cobalt-based ZIF material prepared by the preparation method described above. The modified cobalt-based ZIF material prepared by the present invention is a rhombic regular dodecahedron particle with regular morphology and uniform size.

[0048] The present invention also provides an application of the modified cobalt-based ZIF material as a dechlorination electrocatalyst. The modified cobalt-based ZIF material prepared by the present invention has good dispersibility, structural stability and excellent electrocatalytic reduction dechlorination performance.

[0049] The present invention also provides a method for electrochemical dehalogenation, comprising the following steps:

[0050] The modified cobalt-based ZIF material, ethanol, water and Nafion solution are mixed and uniformly dispersed by ultrasonication; the obtained dispersion is then drop-coated on carbon paper to obtain a cobalt-based ZIF high-efficiency dechlorination electrocatalyst material electrode, which is the working electrode;

[0051] Electrolysis was carried out at constant potential using a silver / silver chloride electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a phosphate buffer solution containing chloramphenicol as an electrolyte.

[0052] The electrochemical dehalogenation is specifically electrocatalytic reduction degradation of chloramphenicol.

[0053] In some embodiments of the present invention, the usage ratio of the modified cobalt-based ZIF material, ethanol, water and Nafion solution is 2-6 mg: 550-650 μL: 350-450 μL: 15-25 μL.

[0054] In some embodiments of the present invention, the drop coating amount is 0.5 to 1.5 mg / cm 2 , for example 1mg / cm 2 .

[0055] In some embodiments of the present invention, the content of chloramphenicol in the phosphate buffer solution containing chloramphenicol is 45-55 mg / L, such as 50 mg / L. The pH value of the phosphate buffer solution containing chloramphenicol is 7.

[0056] The potential of the constant potential electrolysis is -1.2 V; the time is 2 to 4 hours, such as 3 hours.

[0057] The present invention realizes functional modification of ZIF-67 by introducing copper element. This multi-metal synergy significantly improves the stability and electronic structure of the material, greatly improving its activity and selectivity in the dechlorination electrocatalytic reaction.

[0058] The modified cobalt-based ZIF material of the present invention is designed for dechlorination electrocatalytic reaction, and its core lies in optimizing its adsorption and electrocatalytic reduction behavior of organic chlorides by regulating the metal nodes and ligand environment in ZIF-67.

[0059] Through multi-metal doping and functionalization, the catalytic activity, stability and service life of the material of the present invention in the dechlorination reaction are significantly better than those of traditional ZIF-67 and its simple composite materials.

[0060] The preparation method provided by the invention has the advantages of simple operation, low cost, mild conditions, and is suitable for large-scale production and industrial application and promotion.

[0061] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0062] In order to further illustrate the present invention, a cobalt-based ZIF high-efficiency dechlorination electrocatalyst, a preparation method and application thereof provided by the present invention are described in detail below in combination with examples, but it should not be construed as limiting the scope of protection of the present invention.

[0063] Example 1

[0064] 1) Preparation method of cobalt-based ZIF materials with copper introduction:

[0065] 1-1) 9.00 g of 2-methylimidazole was dissolved in 80 mL of methanol to obtain a 2-methylimidazole solution with a concentration of 1.4 mol / L.

[0066] 1.66 g of copper nitrate and 4.00 g of cobalt nitrate were dissolved in 50 mL of methanol, wherein the molar ratio of the copper nitrate to the cobalt nitrate was 0.45:1, to obtain a nitrate solution; the concentration of the nitrate solution was 0.46 mol / L.

[0067] 1-2) The 2-methylimidazole solution and the nitrate solution were stirred and mixed for 30 minutes, and allowed to react for 12 hours to obtain crystals.

[0068] 1-3) The crystals were filtered, washed with methanol for three times, and dried in an oven at 60° C. for 6 h to obtain a copper-introduced cobalt-based ZIF material (CuCo-MOF, denoted as S1).

[0069] 2) Method for removing chloramphenicol by electrocatalytic reduction:

[0070] 2-1) 4 mg of cobalt-based ZIF material was mixed with 600 μL of ethanol and 400 μL of aqueous solution, and 20 μL of Nafion solution was added for uniform ultrasonic dispersion; the obtained dispersion was then drop-coated on carbon paper with a drop-coating amount of 1 mg / cm 2 The obtained CuCo-MOF electrode was used as the working electrode, the silver / silver chloride electrode was used as the reference electrode, the platinum sheet electrode was used as the counter electrode, and the phosphate buffer solution (pH = 7) containing 50 mg / L chloramphenicol was used as the electrolyte.

[0071] 2-2) Perform constant potential electrolysis at -1.2 V for 3 h.

[0072] Comparative Example 1

[0073] The difference from Example 1 is:

[0074] In step 1-1), only cobalt nitrate is used as the nitrate, and copper nitrate is not added. The amount of cobalt nitrate used is the same as the total amount of copper nitrate and cobalt nitrate in Example 1.

[0075] The remaining steps are the same as those in Example 1; a cobalt-based ZIF material (Co-MOF, denoted as D1) is obtained.

[0076] Comparative Example 2

[0077] The difference from Example 1 is:

[0078] In step 1-1), copper nitrate is replaced by iron nitrate.

[0079] The remaining steps are the same as those in Example 1; a cobalt-based ZIF material (FeCo-MOF, denoted as D2) with iron introduced is obtained.

[0080] Comparative Example 3

[0081] The difference from Example 1 is:

[0082] In step 1-1), copper nitrate is replaced by nickel nitrate.

[0083] The remaining steps are the same as those in Example 1; a cobalt-based ZIF material (NiCo-MOF, denoted as D3) into which nickel is introduced is obtained.

[0084] Comparative Example 4

[0085] The difference from Example 1 is:

[0086] In step 1-1), copper nitrate is replaced by zinc nitrate.

[0087] The remaining steps are the same as those in Example 1; a cobalt-based ZIF material (ZnCo-MOF, denoted as D4) introduced with zinc is obtained.

[0088] Example 2

[0089] The difference from Example 1 is:

[0090] In step 1-1), the molar ratio of copper nitrate to cobalt nitrate is replaced to 0.6:1.

[0091] The remaining steps are the same as those in Example 1; a copper-introduced cobalt-based ZIF material (CuCo-MOF, denoted as S2) is obtained.

[0092] Example 3

[0093] The difference from Example 1 is:

[0094] In step 1-1), the molar ratio of copper nitrate to cobalt nitrate is replaced to 0.75:1.

[0095] The remaining steps are the same as those in Example 1; a copper-introduced cobalt-based ZIF material (CuCo-MOF, denoted as S3) is obtained.

[0096] The copper-introduced cobalt-based ZIF material (CuCo-MOF) prepared in Example 1 introduces Cu by coprecipitation, and its electrocatalytic activity is significantly enhanced, and it can efficiently electrocatalytically reduce the C-Cl bond in chloramphenicol.

[0097] The surface morphology of the CuCo-MOF and Co-MOF materials prepared in Example 1 of the present invention and Comparative Example 1 was tested. The results are as follows Figure 1 shown. Figure 1 Scanning electron microscope images of the CuCo-MOF material prepared in Example 1 of the present invention and the Co-MOF material prepared in Comparative Example 1.

[0098] Depend on Figure 1 It can be seen that both CuCo-MOF materials and Co-MOF materials have rhombic dodecahedral structures with regular morphology and uniform size.

[0099] The surface morphology of the cobalt-based materials prepared in Examples 2 to 3 of the present invention was detected, and the results showed that the cobalt-based materials all had a regular and uniform rhombus dodecahedral structure.

[0100] The electro-reduction removal activity of chloramphenicol by the CuCo-MOF material and the Co-MOF material prepared in Example 1 of the present invention and Comparative Example 1 was detected.

[0101] Specifically, the following steps are included:

[0102] The CuCo-MOF material was used as the working electrode, the silver / silver chloride electrode was used as the reference electrode, the platinum electrode was used as the counter electrode, and the phosphate buffer solution (pH = 7) containing 50 mg / L chloramphenicol was used as the electrolyte, and electrolysis was carried out at constant potential for 3 h.

[0103] The Co-MOF material was used as the working electrode, the silver / silver chloride electrode was used as the reference electrode, the platinum electrode was used as the counter electrode, and the phosphate buffer solution (pH = 7) containing 50 mg / L chloramphenicol was used as the electrolyte, and electrolysis was carried out at a constant potential of -1.2 V for 3 h.

[0104] The results of the electroreduction activity test for chloramphenicol removal are as follows: Figure 2 shown.

[0105] Figure 2 Dechlorination of phosphate buffer containing 50 mg / L chloramphenicol at a potential of -1.2 V by the CuCo-MOF material prepared in Example 1 of the present invention and the Co-MOF material prepared in Comparative Example 1.

[0106] Depend on Figure 2 It can be seen that the chlorine removal rate of Co-MOF is only 41%. Compared with Co-MOF, the electrochemical reduction dechlorination ability of CuCo-MOF is significantly improved to 96%, which has excellent electrochemical dechlorination performance.

[0107] According to the above method, the cobalt-based materials prepared in Comparative Examples 2 to 4 and Examples 2 to 3 of the present invention were tested for dechlorination of a phosphate buffer solution containing 50 mg / L of chloramphenicol at a potential of -1.2 V. The results showed that:

[0108] The chlorine removal rate of cobalt-based material D2 was 13.8%;

[0109] The chlorine removal rate of cobalt-based material D3 was 27.9%;

[0110] The chlorine removal rate of cobalt-based material D4 was 32.8%;

[0111] The chlorine removal rate of cobalt-based material S2 was 86.7%;

[0112] The chlorine removal rate of the cobalt-based material S3 was 48.2%.

[0113] Figure 3 Cyclic voltammetry curves of the CuCo-MOF material prepared in Example 1 of the present invention and the Co-MOF material prepared in Comparative Example 1 before and after the dechlorination reaction.

[0114] Depend on Figure 3It can be seen that the reduction characteristic peak of the Co-MOF material is not obvious, but after the introduction of copper, the CuCo-MOF material has an obvious reduction peak at -0.9V, has better electrochemical activity, and shows its excellent reduction and dechlorination performance.

[0115] The cyclic voltammetry curves of the cobalt-based materials prepared in Comparative Examples 2 to 4 and Examples 2 to 3 of the present invention before and after the dechlorination reaction were investigated according to the above method. The results show that:

[0116] Cobalt-based material D2 has no obvious reduction peak;

[0117] Cobalt-based material D3 has no obvious reduction peak;

[0118] Cobalt-based material D4 has no obvious reduction peak;

[0119] The cobalt-based material S2 has an obvious reduction peak at -1.13 V;

[0120] The cobalt-based material S3 has an obvious reduction peak at -1.22V.

[0121] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a modified cobalt-based ZIF material, comprising the following steps: A) mixing a nitrate solution and a 2-methylimidazole solution, and reacting the mixture to obtain a crystal; The nitrates include cobalt nitrate and copper nitrate; B) After filtering, washing and drying the crystals, a modified cobalt-based ZIF material is obtained.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the copper nitrate to the cobalt nitrate is 0.45-0.75:

1.

3. The preparation method according to claim 1, characterized in that: The solvent of the nitrate solution is methanol; the concentration of the nitrate solution is 0.1-0.5 mol / L.

4. The preparation method according to claim 1, characterized in that: The solvent of the 2-methylimidazole solution is methanol; the concentration of the 2-methylimidazole solution is 1.2-1.6 mol / L.

5. The preparation method according to claim 1, characterized in that: The mixing time is 25 to 35 minutes; The reaction is carried out under static conditions; after the mixing, the reaction time is 10 to 14 hours.

6. The preparation method according to claim 1, characterized in that: The washing agent used in the washing is methanol, and the washing times are not less than 3 times.

7. The preparation method according to claim 1, characterized in that: The drying method includes drying in air, drying in an oven or drying in a vacuum drying oven; The drying temperature is 10-200° C. and the drying time is 3-12 hours.

8. A modified cobalt-based ZIF material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the modified cobalt-based ZIF material according to claim 8 as a dechlorination electrocatalyst.

10. A method for electrochemical dehalogenation, comprising the following steps: The modified cobalt-based ZIF material according to claim 8, ethanol, water and Nafion solution are mixed and uniformly dispersed by ultrasonication; and the obtained dispersion is dropwise coated on carbon paper to obtain a cobalt-based ZIF high-efficiency dechlorination electrocatalyst material electrode, which is a working electrode; Electrolysis was carried out at constant potential using a silver / silver chloride electrode as a reference electrode, a platinum sheet electrode as a counter electrode, and a phosphate buffer solution containing chloramphenicol as an electrolyte.

Images