1. A preparation method of a novel ZIF-8 material is characterized by comprising the following steps:

and slowly adding a zinc ion aqueous solution into the 2-methylimidazole aqueous solution, sealing and stirring for 12-13 h, separating out solids, washing and drying to obtain the zinc ion aqueous solution.

2. The method according to claim 1, wherein the zinc ion is derived from zinc nitrate or zinc acetate.

3. The method according to claim 1, wherein the aqueous solution of zinc ions further contains cobalt ions.

4. The method according to claim 3, wherein the molar ratio of the cobalt ions to the zinc ions is 5 to 5.5: 1.

5. The method according to claim 3, wherein the cobalt ion is derived from cobalt nitrate or cobalt acetate.

6. The method according to claim 1, wherein the concentration of zinc ions in the aqueous solution of zinc ions is 0.45 to 0.55 mol/L.

7. The method according to claim 1, wherein the concentration of the 2-methylimidazole aqueous solution is 0.9 to 1.1 mol/L.

8. The method according to claim 1, wherein the volume ratio of the 2-methylimidazole aqueous solution to the zinc ion aqueous solution is 8-9: 1.

9. A novel ZIF-8 material prepared by the process of any one of claims 1 to 8.

10. Use of the novel ZIF-8 material prepared by the preparation method of any one of claims 1 to 8 for removing organic dyes.

Background

ZIF-8 is called as zeolite imidazole framework-like material-8, is the most typical material in ZIF in MOFs family, and has excellent chemical properties such as high specific surface area, porosity, catalysis and the like. Has been a key research target of a great number of researchers, and has wide application in the aspects of electrochemistry, gas (ion) adsorption, photocatalysis and the like. The complex porous structure and the positively charged surface characteristics of the porous material make the porous material have strong adsorption performance on many substances. As a metal organic framework compound, active sites formed on the surface by zinc ions have certain catalytic performance.

However, the existing ZIF-8 can not meet the application requirements, and a new material with higher adsorption capacity and photodegradation capacity to organic matters needs to be developed.

Disclosure of Invention

Aiming at the problems of the prior art, the invention provides a novel ZIF-8 material, a preparation method and application thereof, and the material has better adsorption and photodegradation capability to organic matters. The novel ZIF-8 material prepared by the invention changes the structure and the form of ZIF-8 and further improves the adsorption and catalysis performances of the ZIF-8.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a novel ZIF-8 material comprises the following steps:

and slowly adding a zinc ion aqueous solution into the 2-methylimidazole aqueous solution, sealing and stirring for 12-13 h, separating out solids, washing and drying to obtain the zinc ion aqueous solution. The solid obtained was white.

Preferably, the method for slowly adding the zinc ion aqueous solution comprises the following steps: continuously stirring the 2-methylimidazole aqueous solution under the action of a magnetic stirrer, and slowly dripping the zinc ion aqueous solution at the same time.

Preferably, the method for separating out solids is centrifugation. Preferably, the centrifugation is carried out for 9-10 min at a speed of 8000-10000 rpm.

Preferably, the concentration of the 2-methylimidazole aqueous solution is 0.9-1.1 mol/L.

Preferably, the washing method comprises the following steps: washed first with water and then with methanol. And after each washing, the washing liquid and the solid are separated in a centrifugal mode.

Preferably, the drying is performed at the temperature of 60-65 ℃.

Preferably, the zinc ion is derived from zinc nitrate or zinc acetate.

Preferably, the water is ultrapure water.

Preferably, the preparation method is carried out at room temperature.

Preferably, the aqueous solution of zinc ions further contains cobalt ions.

Preferably, the cobalt ions are derived from cobalt nitrate or cobalt acetate.

Preferably, the concentration of zinc ions in the zinc ion aqueous solution is 0.45-0.55 mol/L.

Preferably, the molar ratio of the cobalt ions to the zinc ions is 5-5.5: 1.

Preferably, the volume ratio of the 2-methylimidazole aqueous solution to the zinc ion aqueous solution is 8-9: 1.

The second purpose of the invention is to provide a novel ZIF-8 material prepared by the method.

The third purpose of the invention is to provide the application of the novel ZIF-8 material prepared by the method in removing organic dyes. The organic dye is preferably methylene blue, methylene orange or Congo red.

The product prepared without adding cobalt ions is marked as petal-shaped ZIF-8, the product prepared when doping cobalt is marked as Co @ ZIF-8, the products can be used as adsorbent and catalyst, and the product has good adsorption and catalysis effects on organic matters, especially organic dyes such as methylene blue.

The mechanism that the adsorption and catalytic performance can be improved by doping the cobalt element in the ZIF-8 is as follows:

the doping elements can change the pore structure and the surface morphology of the ZIF-8, complex pores and surfaces are more favorable for adsorbing organic matters, particularly organic dyes such as methylene blue and the like, and doping ions can form more active sites on the surfaces to enhance the catalytic performance of the organic dyes. And cobalt ions are used as a raw material for synthesizing ZIF-67, can form a bond with 2-methylimidazole more easily, and hetero ions and zinc ions compete to form a coordinate bond with 2-methylimidazole, so that more energy level defects and active sites are formed in a material structure, and the adsorption and catalysis capabilities of the material are improved.

The invention has the beneficial effects that:

the petal-shaped ZIF-8 has larger aperture, has certain advantages in the adsorption of organic matters, particularly organic dyes such as methylene blue and the like, and can degrade the organic matters by active sites on the surface of the ZIF-8. The ZIF-8 doped with cobalt ions has certain structural change, can enhance the adsorption of organic matters, is more beneficial to the process of doping ions and simultaneously increasing the number of active sites on the surface, and has the advantage of degrading the organic matters more efficiently due to the multiple active sites.

The invention synthesizes petal-shaped ZIF-8 by a cheap and simple method, introduces cobalt ions to change the structure of the ZIF-8, improves the adsorption and catalysis capability of the ZIF-8, improves the treatment capability of the ZIF-8 on organic pollutants, and has important industrial value in industrial wastewater treatment.

Drawings

FIG. 1 is an X-ray diffraction powder analysis spectrum of petal-shaped ZIF-8 and Co @ ZIF-8;

FIG. 2 is a scanning electron microscope photograph of petal-shaped ZIF-8 and Co @ ZIF-8;

FIG. 3 is a graph of nitrogen adsorption-desorption and BJH calculated pore size distribution for petal-shaped ZIF-8 and Co @ ZIF-8;

FIG. 4 is a graph of adsorption of hexagonal crystal ZIF-8, petal-shaped ZIF-8 and Co @ ZIF-8 to methylene blue at room temperature in the dark;

FIG. 5 is a graph of photodegradation curves of hexagonal crystal ZIF-8, petal-shaped ZIF-8 and Co @ ZIF-8 for methylene blue at room temperature under light.

Detailed Description

Example 1

(1) Dissolving 2-methylimidazole in ultrapure water to obtain a solution A; the concentration is 0.9 mol/L;

(2) dissolving zinc nitrate in ultrapure water to obtain a solution B; the concentration is 0.55 mol/L;

(3) dissolving cobalt nitrate in ultrapure water to obtain a solution C;

(4) and (3) placing the solution A on a magnetic stirrer to be continuously stirred at room temperature, and slowly adding the solution B to be stirred. Wherein the volume ratio of the solution A to the solution B is 8: 1. After the mixed solution was hermetically stirred for 12 hours, it was centrifuged at 8000rpm for 10 minutes to separate a solid and a solution, and then the unreacted reactant on the material was washed with ultrapure water, centrifuged again, washed with methanol and centrifuged, and the material was dried at 60 ℃ to obtain a white powdery solid. Namely, the petal-shaped ZIF-8.

(5) Fully mixing the solution C and the solution B in advance to ensure that the molar ratio of zinc ions to cobalt ions is 5:1 to obtain a mixed solution; thereafter, similarly to step (4), the mixed solution was slowly added to the a solution while stirring the a solution. And then the same washing and drying processes are adopted to obtain the Co @ ZIF-8.

The X-ray diffraction analysis pattern of the materials involved in this example is shown in fig. 1: as can be seen from FIG. 1, the petal-shaped ZIF-8 has a complex diffraction peak shape, and the X-ray diffraction is related to the diffraction angle of the surface of the material, which corresponds to the irregular structure of the petal shape; meanwhile, Co @ ZIF-8 shows a diffraction peak different from that of ZIF-8, which shows that the structure and the form of the ZIF-8 are changed to a certain extent by doping ions.

The morphology of the material involved in this example is shown graphically in scanning electron microscopy in FIG. 2, with the Co @ ZIF-8 being significantly different from the petal ZIF-8 morphology.

The nitrogen adsorption-desorption and pore size distribution diagram of the material according to the present example is shown in fig. 3, wherein the left side is the adsorption-desorption curve of the material, and the right side is the pore size distribution of the three materials. The specific surface area and the average pore diameter calculated from the BET equation are shown in table 1:

TABLE 1 Scale for specific surface area and mean pore size of materials

Sample (I)	Petal-shaped ZIF-8	[email protected]
			BET specific surface area (square meter/g STP)	840.884	1072.73
Average pore diameter (nanometer)	8.111	4.7861

As is clear from Table 1, the petal-shaped ZIF-8 has a large pore diameter of 8 nm on average, and the specific surface area of Co @ ZIF-8 is improved as compared with that of ZIF-8, but the average pore diameter is reduced to about 5 nm.

The absorption test of methylene blue of this example was carried out by mixing 10mg of the adsorbent and a methylene blue solution in the dark and stirring them for 6 hours, and the loss of methylene blue was measured by measuring the absorbance of methylene blue at 665 nm every 2 hours. The adsorption capacity at 6 hours is shown in table 2 and figure 4:

TABLE 2 adsorption Capacity of materials for methylene blue

The photocatalytic experiment of methylene blue of the present example was performed by placing methylene blue adsorbed in the dark under visible light to receive a light source, and the degradation of methylene blue was measured by measuring the absorbance of methylene blue at 665 nm every 30 minutes. The photodegradation within 2 hours is shown in figure 5.

The concentration of the methylene blue is 9.5-10.5 mg/L, and the volume of the solution is 99-101 ml.

The present example further tests the adsorption performance and photocatalytic performance of each similar material, and the obtained results are shown in table 3, wherein:

comparative example 1 is conventional hexagonal ZIF-8;

comparative example 2 is conventional ZIF-67

Comparative example 3 copper-doped petaloid ZIF-8

Comparative example 4 was nickel-doped petal-shaped ZIF-8

Experimental example 1-1 is petal-shaped ZIF-8

Examples 1-2 are Co @ ZIF-8

TABLE 3 Performance test Table

The result shows that the adsorption and photocatalysis capabilities of the petal-shaped ZIF-8 are stronger than those of the traditional hexagonal crystal ZIF-8, the adsorption capability of the ZIF-67 is stronger than that of the traditional hexagonal crystal ZIF-8, but the photocatalysis capability is weaker than that of the traditional hexagonal crystal ZIF-8. Among the various ion-doped petal-shaped ZIFs-8, cobalt-doped ZIFs-8 are the most excellent in adsorption and photocatalytic ability, because cobalt ions are a raw material for synthesizing ZIFs-67 and are capable of more easily forming a bond with 2-methylimidazole, and the remaining hetero ions are inferior in the bonding ability with 2-methylimidazole to cobalt ions. The heteroions and the zinc ions compete with 2-methylimidazole to form coordination bonds, so that more energy level defects and active sites are formed in the material structure, and the adsorption and catalysis capabilities of the material can be improved. Therefore, the cobalt-doped petal-shaped ZIF-8 has the best adsorption and catalysis capability and is expected to be applied to the treatment of organic wastes.

Example 2

(1) Dissolving 2-methylimidazole in ultrapure water to obtain a solution A; the concentration is 1.1 mol/L;

(2) dissolving zinc acetate in ultrapure water to obtain a solution B; the concentration is 0.45 mol/L;

(3) dissolving cobalt acetate in ultrapure water to obtain a solution C;

(4) and (3) placing the solution A on a magnetic stirrer to be continuously stirred at room temperature, and slowly adding the solution B to be stirred. Wherein the volume ratio of the solution A to the solution B is 9: 1. And sealing and stirring the mixed solution for 13h, centrifuging at the speed of 10000rpm for 9min, separating out solid and solution, washing unreacted reactants on the material with ultrapure water, centrifuging again, washing with methanol, centrifuging, and drying the material at 65 ℃ to obtain white powder solid. Namely, the petal-shaped ZIF-8.

(5) Fully mixing the solution C and the solution B in advance to ensure that the molar ratio of zinc ions to cobalt ions is 5.5:1 to obtain a mixed solution; thereafter, similarly to step (4), the mixed solution was slowly added to the a solution while stirring the a solution. And then the same washing and drying processes are adopted to obtain the Co @ ZIF-8.