阅读说明：本技术 一种以金属有机框架为前驱体配体可回收制备不同形貌四氧化三钴的方法与应用 (Method for preparing cobaltosic oxide with different morphologies in recoverable mode by taking metal organic framework as precursor ligand and application of method ) 是由 钟金平 叶代启 曾译葵 付名利 吴军良 黄皓旻 于 2020-06-29 设计创作，主要内容包括：一种以金属有机框架为前驱体配体可回收制备不同形貌四氧化三钴的方法与应用。本发明采用溶剂热法,将预先制备好的Co-MOF-74与尿素或六次甲基胺混合,后离心分离得到不同形貌碳酸钴和反应母液,随后将反应母液化学提纯,有效回收得到纯净的有机桥连配体以及通过两段式煅烧不同形貌的碳酸钴得到用于高效降解挥发性有机物的四氧化三钴催化剂。本发明制备方法简单易行、不需要额外增加表面活性剂或软硬模板、能够大规模制备具有不同形貌四氧化三钴,所制四氧化三钴催化剂具有较大的比表面积,形貌可控、尺寸均一；最为重要的是所添加的有机桥连配体完全可以回收,实现了资源的可重复利用,极大的降低了催化剂的制备成本。(A method for preparing cobaltosic oxide with different morphologies in a recoverable way by taking a metal organic framework as a precursor ligand and application thereof. According to the invention, a solvothermal method is adopted, Co-MOF-74 prepared in advance is mixed with urea or hexamethylene amine, then the mixture is centrifugally separated to obtain cobalt carbonate and reaction mother liquor with different morphologies, then the reaction mother liquor is chemically purified, pure organic bridging ligands are effectively recovered, and the cobaltosic oxide catalyst for efficiently degrading volatile organic compounds is obtained by calcining cobalt carbonate with different morphologies in a two-stage mode. The preparation method is simple and easy to implement, does not need to additionally increase a surfactant or a soft and hard template, can prepare the cobaltosic oxide with different shapes in a large scale, and the prepared cobaltosic oxide catalyst has larger specific surface area, controllable shape and uniform size; most importantly, the added organic bridging ligand can be completely recycled, so that the resource can be recycled, and the preparation cost of the catalyst is greatly reduced.)

1. A method for preparing cobaltosic oxide with different morphologies in a recoverable way by taking a metal organic framework as a precursor ligand is characterized in that cobalt salt and an organic bridging ligand are respectively dissolved in a methanol solvent, then the cobalt salt and the organic bridging ligand are mixed and uniformly stirred at room temperature, subjected to ultrasonic treatment, and centrifugally washed to obtain a Co-MOFs-74 precipitate; then dispersing and dissolving the Co-MOFs-74 precipitate in deionized water, adding a precipitator, mixing and stirring uniformly, and obtaining cobaltosic oxide catalysts with different shapes for efficiently catalyzing and degrading VOCs through solvothermal reaction, centrifugal washing, vacuum drying and two-stage calcination; the cobalt salt is cobalt acetate, the organic bridging ligand is 2, 5-dihydroxy terephthalic acid, and the precipitator is urea or hexamethylenetetramine.

2. The method for preparing cobaltosic oxide with different morphologies in a recoverable way by using the metal-organic framework as the precursor ligand according to claim 1, wherein the preparation method comprises the following steps:

(1) preparation of Co-MOFs-74:

under stirring at room temperature, weighing cobalt acetate and 2, 5-dihydroxy terephthalic acid, and respectively dissolving in methanol to form a solution A and a solution B; slowly adding the solution B into the solution A, mixing and stirring to obtain a mixed solution C, ultrasonically treating the mixed solution C at room temperature, centrifuging, washing with methanol for several times to remove unreacted cobalt salt and organic ligand, washing with deionized water for several times to remove methanol, and vacuum-drying to obtain Co-MOFs-74 for later use;

(2) preparing cobalt carbonate with different shapes:

weighing the Co-MOF-74 prepared in the step (1) and dispersing in deionized water, then weighing a precipitator, mixing and stirring uniformly at room temperature, transferring to an inner container of a polytetrafluoroethylene reaction kettle, then putting the reaction kettle into a high-pressure reaction kettle for hydrothermal reaction, naturally cooling to room temperature, carrying out centrifugal separation to obtain a precipitate and dark brown reaction mother liquor for later use, washing the precipitate for several times by using deionized water and adjusting the pH, then carrying out centrifugal washing by using ethanol, and carrying out vacuum drying to obtain dark purplish red cobalt carbonate for later use; the precipitant is urea or hexamethylenetetramine;

(3) recovery of 2, 5-dihydroxyterephthalic acid organic bridged ligand:

transferring the reaction mother liquor obtained by centrifugation in the step (2) to a beaker, adding dilute hydrochloric acid, continuously stirring at room temperature, adjusting the pH until the pH generates a tawny precipitate, stopping adding the dilute hydrochloric acid, carrying out suction filtration on the dilute hydrochloric acid to obtain a tawny precipitate, then dispersing the tawny precipitate in deionized water again, adding concentrated ammonia water, adjusting the pH to completely dissolve the tawny precipitate, carrying out suction filtration to remove undissolved impurities to obtain a dark brown filtrate for later use, transferring the filtrate obtained by suction filtration to the beaker, adding the dilute hydrochloric acid, adjusting the pH until the pH generates a light yellow precipitate, carrying out suction filtration to obtain the tawny precipitate, repeatedly washing and adjusting the yellow precipitate with deionized water until the pH is weakly acidic, and carrying out vacuum drying to obtain a light yellow 2, 5-dihydroxyterephthalic acid ligand;

(4) preparing cobaltosic oxide with different shapes:

and (3) carrying out two-stage calcination on the cobalt carbonate with different morphologies prepared in the step (2) to obtain cobaltosic oxide catalysts with different morphologies, tabletting the cobaltosic oxide catalysts under the set pressure of a tabletting machine, and sieving to obtain the catalysts with the particle size of 40-60 meshes.

3. The method for preparing cobaltosic oxide with different morphologies in a recoverable way by using a metal-organic framework as a precursor ligand according to claim 2, wherein in the step (1), the mass of the cobalt acetate is 0.44-1.32 g, and the mass of the 2, 5-dihydroxyterephthalic acid is 0.12-0.36 g; the volume of the methanol in the solution A and the volume of the methanol in the solution B are 10-30 mL, and the volume of the mixed solution C is 20-60 mL; the stirring temperature is 25-35 ℃; the stirring time is 0.5-1 h; the stirring speed is 100-200 r/min; the ultrasonic time is 0.5-1 h, and the ultrasonic temperature is 25-35 ℃; the ultrasonic frequency is 35-40 kHz, and the ultrasonic power is 520-560W; the centrifugal rotating speed is 3500-4000 r/min; the vacuum drying temperature is 60-80 ℃, and the drying time is 8-12 h.

4. The method for preparing cobaltosic oxide with different morphologies in a recoverable way by taking the metal-organic framework as the precursor ligand according to claim 2, wherein in the step (2), the mass of the Co-MOF-74 is 1.05-1.55 g; the volume of the deionized water is 40-60 mL; the precipitant is urea or hexamethylenetetramine; the mass of the precipitator is 0.25-0.75 g; the stirring temperature is 25-35 ℃; the stirring time is 0.5-1 h; the stirring speed is 100-200 r/min; the volume specification of the reaction kettle is 60-100 mL; the reaction temperature is 120-140 ℃, the reaction pressure is 0.1-0.3 MPa, the reaction time is 12-24 h, and the centrifugal rotation speed is 3500-4000 r/min; the pH is adjusted to be 6-7; the vacuum drying temperature is 60-80 ℃, and the drying time is 8-12 h; the calcination temperature is 300-400 ℃, and the calcination time is 6-10 h.

5. The method for preparing cobaltosic oxide with different morphologies in a recoverable way by using the metal organic framework as the precursor ligand according to claim 2, wherein in the step (3), the stirring temperature is 25-35 ℃; the stirring time is 0.5-1 h; the stirring speed is 100-200 r/min; the concentration of the dilute hydrochloric acid is 6 mol/L; the volume is 10-20 mL; adjusting the pH value to 4-6 until a tawny precipitate and a yellowish precipitate are generated; the mass percentage concentration of the ammonia water is 25%; the volume is 20-25 mL; adjusting the pH value to make the completely dissolved value be 8-9; the washing is adjusted to a pH value of 6-7 when the pH value is weak acid; the vacuum drying temperature is 60-80 ℃; the vacuum drying time is 6-12 h.

6. The method for preparing cobaltosic oxide with different morphologies in a recoverable way by using the metal-organic framework as the precursor ligand according to claim 2, wherein in the step (4), the two-stage calcination method comprises the following steps: firstly, under the nitrogen atmosphere, heating the temperature from room temperature to 320-450 ℃ at the speed of 3-5 ℃/min by a heating program, and keeping the temperature for 3-5 h; then, closing the nitrogen and switching to air, reducing the temperature of the cooling program from 320-450 ℃ to 300-350 ℃ at the speed of 3-5 ℃/min, keeping the temperature for 3-5 h, and finally reducing the temperature to room temperature at the speed of 1-10 ℃/min;

the pressure of the tablet press is 13-17 MPa, and the stabilization time is 1-3 min.

7. The cobaltosic oxide catalyst with different morphologies can be prepared by recovering the metal organic framework serving as the precursor ligand by the preparation method of any one of claims 1 to 6.

8. The method of claim 7, wherein the cobaltosic oxide catalyst with different morphologies can be prepared by recovering the ligand with the metal organic framework as the precursor, and is applied to the field of air pollution control.

Technical Field

The invention belongs to the technical field of material chemistry and environmental functional materials, and particularly relates to a method for preparing cobaltosic oxide with different shapes in a recyclable manner by taking a metal organic framework as a precursor ligand and application of the method.

Background

In recent years, with the emission of large amounts of Volatile Organic Compounds (VOCs), VOCs are used as O₃And an important precursor of PM2.5, which has very serious influence on the natural environment and human health, is one of the major environmental problems faced by the atmospheric composite pollution in China at present. Among the emissions of numerous VOCs, benzene-based materials, typically represented by benzene, toluene, etc., have received much attention because they are commonly used in industrial solvents for construction, packaging, hard brushing, coating, etc., resulting in a high percentage of pollutants in typical pollution sources.

At present, the conventional technologies for treating VOCs include non-thermal plasma, biomass method, photocatalysis, photothermal catalysis, direct combustion method, catalytic oxidation method and the like. In the reported traditional technologies for treating VOCs, the catalytic oxidation method has the advantages of high treatment efficiency, no secondary pollution, small occupied area, easy operation and the like, and is widely applied. In this technology, the design and preparation of catalysts are one of the key technical problems for the catalytic oxidation of VOCs. Generally speaking, high efficiency catalysts often require large specific surface area, high thermal stability, low commercial cost, water resistance, and reproducible regeneration. Aiming at the defects of small specific surface area, poor water resistance, higher commercial cost, shorter service life, unreusable property and the like of the conventional industrial catalyst, the research and development of a catalyst which is more efficient and can quickly realize the efficient degradation of VOCs is urgently needed. At present, a large number of catalysts are used for degrading VOCs, and the catalysts with different three-dimensional shapes are widely applied due to the fact that the catalysts have large specific surface areas, more exposed active sites, large contact areas and high mass transfer capacity. At present, the preparation process of cobaltosic oxide with different morphologies usually needs to add a soft and hard template method and mainly calcines a metal organic framework compound, however, the preparation methods are complex, a catalyst with a specific morphology cannot be synthesized, a ligand cannot be recycled, the cost is high, and the like.

In view of the above, the invention develops a method for preparing cobaltosic oxide catalysts with different morphologies in a recoverable way by using a metal organic framework as a precursor ligand, and the catalyst has the advantages of large specific surface area, controllable morphology and uniform size; the method can realize the recovery of the organic bridging ligand, greatly saves the preparation cost, can prepare a large amount of cobaltosic oxide with uniform size and different appearances, and has great popularization and application in industry and practical application.

Disclosure of Invention

The invention aims to overcome the defects of high preparation cost, the need of adding a soft and hard template or a surfactant, the unrecoverable and recyclable ligand and the like in the prior art, and provides a brand-new preparation method for preparing the cobaltosic oxide catalyst with different shapes and uniform size in a large scale, wherein the prepared catalyst has high-efficiency adsorption catalytic degradation performance on VOCs.

The purpose of the invention is realized by the following technical scheme:

according to the invention, cobalt carbonate with uniform size and different appearances is prepared by adopting a solvothermal method and taking Co-MOF-74 as a precursor and regulating urea and hexamethylene amine, reaction mother liquor is chemically purified, pure organic bridging ligands are effectively extracted, and then the prepared cobalt carbonate salts with different appearances are subjected to two-stage calcination to obtain the cobaltosic oxide catalyst capable of efficiently degrading volatile organic matters.

A method for preparing cobaltosic oxide with different morphologies in a recoverable way by taking a metal organic framework as a precursor ligand comprises the following steps:

(1) preparation of Co-MOFs-74:

under stirring at room temperature, weighing cobalt acetate and 2, 5-dihydroxy terephthalic acid, and respectively dissolving in methanol to form a solution A and a solution B; slowly adding the solution B into the solution A, mixing and stirring to obtain a mixed solution C, ultrasonically treating the mixed solution C at room temperature, centrifuging, washing with methanol for several times to remove unreacted cobalt salt and organic ligand, washing with deionized water for several times to remove methanol, and vacuum-drying to obtain Co-MOFs-74 for later use;

(2) preparing cobalt carbonate with different shapes:

weighing the Co-MOF-74 prepared in the step (1) and dispersing in deionized water, then weighing a precipitator, mixing and stirring uniformly at room temperature, transferring to an inner container of a polytetrafluoroethylene reaction kettle, then putting the reaction kettle into a high-pressure reaction kettle for hydrothermal reaction, naturally cooling to room temperature, carrying out centrifugal separation to obtain a precipitate and dark brown reaction mother liquor for later use, washing the precipitate for several times by using deionized water and adjusting the pH, then carrying out centrifugal washing by using ethanol, and carrying out vacuum drying to obtain dark purplish red cobalt carbonate for later use; the precipitant is urea or hexamethylenetetramine;

(3) recovery of 2, 5-dihydroxyterephthalic acid organic bridged ligand:

transferring the reaction mother liquor obtained by centrifugation in the step (2) to a beaker, adding dilute hydrochloric acid, continuously stirring at room temperature, adjusting the pH until the pH generates a tawny precipitate, stopping adding the dilute hydrochloric acid, carrying out suction filtration on the dilute hydrochloric acid to obtain a tawny precipitate, then dispersing the tawny precipitate in deionized water again, adding concentrated ammonia water, adjusting the pH to completely dissolve the tawny precipitate, carrying out suction filtration to remove undissolved impurities to obtain a dark brown filtrate for later use, transferring the filtrate obtained by suction filtration to the beaker, adding the dilute hydrochloric acid, adjusting the pH until the pH generates a light yellow precipitate, carrying out suction filtration to obtain the tawny precipitate, repeatedly washing and adjusting the yellow precipitate with deionized water until the pH is weakly acidic, and carrying out vacuum drying to obtain a light yellow 2, 5-dihydroxyterephthalic acid ligand;

(4) preparation of cobaltosic oxide with different shapes

And (3) carrying out two-stage calcination on the cobalt carbonate with different morphologies prepared in the step (2) to obtain cobaltosic oxide catalysts with different morphologies, tabletting the cobaltosic oxide catalysts under the set pressure of a tabletting machine, and sieving to obtain the catalysts with the particle size of 40-60 meshes.

In the method, in the step (1), the mass of the cobalt acetate is 0.44-1.32 g, and the mass of the 2, 5-dihydroxy terephthalic acid is 0.12-0.36 g; the volume of the methanol in the solution A and the volume of the methanol in the solution B are 10-30 mL, and the volume of the mixed solution C is 20-60 mL; the stirring temperature is 25-35 ℃; the stirring time is 0.5-1 h; the stirring speed is 100-200 r/min; the ultrasonic time is 0.5-1 h, and the ultrasonic temperature is 25-35 ℃; the ultrasonic frequency is 35-40 kHz, and the ultrasonic power is 520-560W; the centrifugal rotating speed is 3500-4000 r/min; the vacuum drying temperature is 60-80 ℃, and the drying time is 8-12 h.

In the method, in the step (2), the mass of the Co-MOF-74 is 1.05-1.55 g; the volume of the deionized water is 40-60 mL; the precipitant is urea or hexamethylenetetramine; the mass of the precipitator is 0.25-0.75 g; the stirring temperature is 25-35 ℃; the stirring time is 0.5-1 h; the stirring speed is 100-200 r/min; the volume specification of the reaction kettle is 60-100 mL; the reaction temperature is 120-140 ℃, the reaction pressure is 0.1-0.3 MPa, the reaction time is 12-24 h, and the centrifugal rotation speed is 3500-4000 r/min; the pH is adjusted to be 6-7; the vacuum drying temperature is 60-80 ℃, and the drying time is 8-12 h; the calcination temperature is 300-400 ℃, and the calcination time is 6-10 h.

In the method, in the step (3), the stirring temperature is 25-35 ℃; the stirring time is 0.5-1 h; the stirring speed is 100-200 r/min; the concentration of the dilute hydrochloric acid is 6 mol/L; the volume is 10-20 mL; adjusting the pH value to 4-6 until a tawny precipitate and a yellowish precipitate are generated; the mass percentage concentration of the ammonia water is 25%; the volume is 20-25 mL; adjusting the pH value to make the completely dissolved value be 8-9; the washing is adjusted to a pH value of 6-7 when the pH value is weak acid; the vacuum drying temperature is 60-80 ℃; the vacuum drying time is 6-12 h.

In the above method, in step (4), the two-stage calcination method comprises: firstly, under the nitrogen atmosphere, heating the temperature from room temperature to 320-450 ℃ at the speed of 3-5 ℃/min by a heating program, and keeping the temperature for 3-5 h; and then closing the nitrogen and switching to air, reducing the temperature of the cooling program from 320-450 ℃ to 300-350 ℃ at the speed of 3-5 ℃/min, keeping the temperature for 3-5 h, and finally reducing the temperature to room temperature at the speed of 1-10 ℃/min. The pressure of the tablet press is 13-17 MPa, and the stabilization time is 1-3 min.

A cobaltosic oxide catalyst with different morphologies, which can be recovered and prepared by taking a metal organic framework as a precursor ligand, is applied to the field of control of atmospheric pollution (VOCs).

According to the invention, Co-MOF-74 is used as a precursor, urea and hexamethylenetetramine with certain mass are added, cobalt carbonate with different morphologies is prepared by a solvothermal method, and then cobaltosic oxide catalyst with different morphologies is obtained by two-stage calcination. The preparation method of the catalyst overcomes the defects of high cost, harsh preparation conditions, unrecoverable ligand and other technologies of the existing preparation method of the catalyst by taking the metal organic template as the sacrificial template ligand, can prepare the cobaltosic oxide catalyst with different shapes and uniform size in a large scale, has the performance of efficiently adsorbing and catalytically degrading VOCs, has stronger water resistance and better stability, and realizes the recovery and the reutilization of the ligand.

Compared with the prior art, the invention has the following advantages:

1. by controlling the reaction time, the method can prepare cobalt carbonate intermediates with different morphologies, and then calcine the cobaltosic oxide catalyst with high activity and different morphologies, thereby improving the specific surface area of the catalyst material and increasing the exposed active sites.

2. The preparation process is simple and easy to implement, the preparation conditions are mild, the preparation can be carried out on a large scale, the efficient recycling efficiency of the ligand can be realized, and any soft and hard template and other surfactants are not required to be added.

Drawings

FIG. 1 is an SEM image of a catalyst of example 1 of the present invention;

FIG. 2 is an SEM image of a catalyst of example 2 of the present invention;

FIG. 3 is an SEM image of a catalyst of example 3 of the present invention;

FIG. 4 is a BET plot of catalysts of examples 1-3 of the present invention;

FIG. 5 is a schematic diagram showing the recovery of the ligand in example 2 of the present invention;

FIG. 6 is an infrared picture of a ligand in example 2 of the present invention;

FIG. 7 is a graph showing the activity evaluation of catalysts of examples 1 to 3 of the present invention in catalytic oxidative degradation of toluene.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto, and may be carried out with reference to conventional techniques for process parameters not particularly noted.