Mn-MOF material and preparation method and application thereof

Abstract

The invention belongs to the technical field of adsorption materials, and particularly relates to a Mn-MOF material and a preparation method and application thereof. According to the invention, biphenyl-3, 3 ', 5, 5'-tetracarboxylic acid and 1, 4-bis [(1H-imidazole-1-yl) methyl] benzene are used as organic ligands, and the organic ligands are self-assembled with manganese ions by adopting a solvothermal process, so that the crystalline MOF material {C110H97Mn8N14O40)} n with good adsorption performance is constructed. The Mn-MOF material disclosed by the invention is also applied to methylene blue adsorption in a sewage system. The preparation method is simple and easy to implement, a new choice is provided for adsorption of methylene blue molecules in wastewater, meanwhile, the application value of organic ligands is expanded, and the prepared Mn-MOF material adsorbent is good in stability and shows excellent adsorption performance in an adsorption experiment of dye methylene blue, so that the Mn-MOF material adsorbent has very high removal rate and environmental friendliness.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials, and specifically relates to an Mn-MOF material, a preparation method thereof, and an application thereof. Background Art

[0002] Organic dyes are one of the dyes widely used in current industrial production and consumption. With the rapid development of the textile, paper, plastic, food, and cosmetics industries in China, a large amount of organic dyes are applied to industrial production. The wastewater generated during the production process will seriously pollute the environment, posing a great threat to human health and the ecological environment. A certain amount of harmful substances, such as heavy metal ions, aromatic compounds, and nitrites, will be produced during the production and use of organic dyes. If not properly treated, it will cause water pollution. Moreover, the dye molecules themselves have small pore sizes, high toxicity, strong colors, and are difficult to degrade. Direct discharge will damage the aquatic ecosystem and further damage the ecological environment. Therefore, there is an urgent need to develop a class of environmentally friendly materials that can effectively adsorb dye molecules.

[0003] At present, the treatment methods for removing organic dyes from wastewater are divided into three categories according to the degradation principle: physical methods, chemical methods, and biological methods. Physical methods include adsorption, membrane separation technology, and magnetic separation technology; chemical methods include electrochemistry, redox, and photocatalytic oxidation; biological methods use bacteria and fungi to degrade organic dyes. Since chemical methods and biological methods are relatively cumbersome to operate, have high treatment costs, and may also cause new pollution, while the adsorption method in physical methods has a simple principle, is easy to operate, has good treatment effects, can remove multiple pollutants simultaneously, and can also treat high-concentration organic wastewater. When the adsorbent reaches saturation, it can be regenerated and reused. Therefore, it is widely used in the treatment of organic dye wastewater.

[0004] However, the existing adsorbents for removing organic dyes from wastewater have technical defects such as poor adsorption performance, structural stability, and thermal stability, which affect the use of the adsorbents. Summary of the Invention

[0005] Aiming at the above deficiencies of the existing technologies, the purpose of the present invention is to provide an Mn-MOF material, a preparation method thereof, and an application thereof. The present invention uses biphenyl-3,3',5,5'-tetracarboxylic acid and 1,4-bis[(1H-imidazol-1-yl)methyl]benzene as organic ligands, and through the solvothermal method, self-assembles with manganese ions to construct a crystalline MOF material {C 110 H 97 Mn8N 14 O 40)}n, namely the Mn-MOF material. The preparation method of the present invention is simple and easy to implement, providing a new option for adsorbing methylene blue molecules in wastewater, and the prepared Mn-MOF material adsorbent has excellent structural stability and thermal stability. The Mn-MOF material of the present invention was also used for the application of methylene blue adsorption in a sewage system, showing excellent adsorption performance in the methylene blue adsorption experiment, indicating a high methylene blue removal rate and environmental friendliness.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention protects a preparation method of a Mn-MOF material, which includes the following steps:

[0008] Mix the main ligand auxiliary ligand and MnSO4·H2O in a solvent to obtain a suspension, and then carry out a solvothermal reaction on the suspension. At this time, the main ligand and the auxiliary ligand jointly perform self-assembly with manganese ions to obtain the Mn-MOF material.

[0009] Preferably, the molar ratio of the main ligand auxiliary ligand to MnSO4·H2O is 30 - 35:25 - 30:55 - 60. Compared with the main ligand, the amount of the auxiliary ligand is less. In terms of structure, it ensures the coordination of the main ligand with manganese ions.

[0010] Preferably, the conditions of the solvothermal reaction are: keep warm at 85°C - 95°C for 70h - 75h.

[0011] Preferably, the volume ratio of N,N-dimethylformamide to water is 5 - 6:3 - 4. The polarity and alkalinity of the solvent of the present invention are suitable for the formation of the Mn-MOF material.

[0012] Preferably, in the suspension, the mass percentage of the solvent is 95% - 98%.

[0013] The present invention also protects the Mn-MOF material prepared by the above preparation method. The unit cell structure of the Mn-MOF material is monoclinic.

[0014] The present invention also protects the application of the above Mn-MOF material in the preparation of a methylene blue adsorbent.

[0015] Preferably, mix the wastewater containing methylene blue with the Mn-MOF material, and under light conditions, use the Mn-MOF material to adsorb methylene blue in the wastewater. Illumination during the adsorption process helps the Mn-MOF material to bind with methylene blue molecules; without illumination, the adsorption effect will decrease.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. In the present invention, biphenyl-3,3',5,5'-tetracarboxylic acid and 1,4-bis[(1H-imidazol-1-yl)methyl]benzene are used as organic ligands, and through a solvothermal method with manganese sulfate, the self-assembly of the organic ligands and manganese ions is achieved. At this time, the metal ions and the organic ligands undergo a coordination reaction to construct a crystalline Mn-MOF material with good adsorption performance. In the present invention, biphenyl-3,3',5,5'-tetracarboxylic acid and 1,4-bis[(1H-imidazol-1-yl)methyl]benzene containing imidazole are used as double organic ligands. By using two different ligands as mixed ligands for application, the mixed ligands are used to prepare the Mn-MOF material. And because there are two manganese ions with different coordination environments in each unit cell molecule of MnSO4·H2O, different structural vacancies are formed, which is more conducive to the formation of Mn-MOF materials with different pore sizes, and thus conducive to the adsorption performance of methylene blue.

[0018] 2. The methylene blue adsorption experiment was carried out using the Mn-MOF material of the present invention. The results show that the adsorption effect on the dye methylene blue is the best under white light irradiation conditions, the adsorption efficiency can reach 97.97%, and the adsorption capacity is 19.59 mg·g -1 . The preparation method of the present invention is simple and feasible, providing a new choice for adsorbing methylene blue molecules in wastewater. At the same time, it expands the application value of organic ligands. The prepared Mn-MOF material adsorbent has good stability and shows excellent adsorption performance in the adsorption experiment of the dye methylene blue, indicating a high removal rate and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the morphology diagram of the Mn-MOF material of Example 1 of the present invention.

[0020] Figure 2 It is the single crystal structure diagram of the Mn-MOF material of Example 1 of the present invention.

[0021] Figure 3 It is the metal environment coordination diagram of the Mn-MOF material of Example 1 of the present invention. Among them, (a) is the metal environment coordination diagram of Mn1, (b) is the metal environment coordination diagram of Mn2, and (c) is the metal environment coordination diagram of Mn1 and Mn2.

[0022] Figure 4 It is the three-dimensional framework structure stacking diagram of the Mn-MOF material of Example 1 of the present invention in the a-axis direction.

[0023] Figure 5 It is the three-dimensional framework structure stacking diagram of the Mn-MOF material of Example 1 of the present invention in the b-axis direction.

[0024] Figure 6Stacking diagram of the three-dimensional framework structure of the Mn-MOF material in the c-axis direction of Example 1 of the present invention.

[0025] Figure 7 Adsorption effect diagram of methylene blue by the Mn-MOF material of Example 1 of the present invention under blue light; wherein, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram at different adsorption times.

[0026] Figure 8 Adsorption effect diagram of methylene blue by the Mn-MOF material of Example 1 of the present invention under ultraviolet light; wherein, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram at different adsorption times.

[0027] Figure 9 Adsorption effect diagram of methylene blue by the Mn-MOF material of Example 1 of the present invention under white light; wherein, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram at different adsorption times.

[0028] Figure 10 X-ray powder diffraction patterns of Mn-MOF (upper) and single crystal analysis simulation (lower).

[0029] Figure 11 Thermogravimetric analysis curve diagram of the Mn-MOF material of Example 1.

[0030] Figure 12 Adsorption effect diagram of methyl orange by the Mn-MOF material of Example 1 of the present invention under ultraviolet light; wherein, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram at different adsorption times.

[0031] Figure 13 Adsorption effect diagram of methyl orange by the Mn-MOF material of Example 1 of the present invention under blue light; wherein, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram at different adsorption times.

[0032] Figure 14 Adsorption effect diagram of methyl orange by the Mn-MOF material of Example 1 of the present invention under white light; wherein, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram at different adsorption times.

[0033] Figure 15 Adsorption effect diagram of rhodamine B by the Mn-MOF material of Example 1 of the present invention under ultraviolet light; wherein, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram at different adsorption times.

[0034] Figure 16Adsorption effect diagram of the Mn-MOF material of Example 1 of the present invention on Rhodamine B under blue light; among them, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram under different adsorption times.

[0035] Figure 17 Adsorption effect diagram of the Mn-MOF material of Example 1 of the present invention on Rhodamine B under white light; among them, (a) is the spectrogram of absorbance changing with wavelength, and (b) is the adsorption amount diagram under different adsorption times.

[0036] Figure 18 Reuse diagram of the Mn-MOF material of Example 1. Detailed implementation manners

[0037] The following will describe in detail the specific implementation manners of the present invention, but it should be understood that the protection scope of the present invention is not limited by the specific implementation manners. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0038] Considering the technical defects of poor adsorption performance, structural stability and thermal stability of the adsorbents for removing organic dyes in wastewater in the prior art, the present invention starts from organic ligands and coordinates biphenyl-3,3',5,5'-tetracarboxylic acid and 1,4-bis[(1H-imidazol-1-yl)methyl]benzene with MnSO4·H2O to obtain Mn-MOF materials with different structural vacancies. The diversity of structures and pores facilitates the adsorption of methylene blue molecules. Compared with the methylene blue adsorbents in the prior art, the adsorption performance is effectively improved. In addition, the present invention also conducts XRD comparison and TGA detection on the Mn-MOF materials. The results show that the obtained Mn-MOF materials have excellent structural stability and thermal stability, improving the service life of the adsorbent.

[0039] The following will further explain and illustrate the technical solutions of the present invention by means of examples, as specifically shown below:

[0040] Example 1

[0041] A preparation method of a Mn-MOF material, comprising the following steps:

[0042] Weigh the main ligand Biphenyl-3,3',5,5'-tetracarboxylic acid (11.6 mg, 0.035 mmol), auxiliary ligand 1,4-Bis[(1H-imidazol-1-yl)methyl]benzene (7.2 mg, 0.03 mmol) and MnSO4·H2O (10.2 mg, 0.06 mmol).

[0043] The main ligand, auxiliary ligand and MnSO4·H2O were added together to a mixed solvent of N,N-dimethylformamide (5 mL) and water (3 mL) to obtain a suspension. The suspension was placed in a programmable temperature oven, and the oven temperature program was set. The temperature was raised from room temperature to 90 °C in 10 h, kept warm for 72 h, and then cooled to room temperature within 10 h. The crystals were filtered and washed with clean mother liquor (the mother liquor is a mixture of N,N-dimethylformamide and water with a volume ratio of 5:3) to obtain colorless block crystals, which were the Mn-MOF material.

[0044] Example 2

[0045] A preparation method of an Mn-MOF material, comprising the following steps:

[0046] Weigh the main ligand Biphenyl-3,3',5,5'-tetracarboxylic acid (9.94 mg, 0.03 mmol), auxiliary ligand 1,4-Bis[(1H-imidazol-1-yl)methyl]benzene (6 mg, 0.025 mmol) and MnSO4·H2O (9.35 mg, 0.055 mmol).

[0047] The main ligand, auxiliary ligand and MnSO4·H2O were added together to a mixed solvent of N,N-dimethylformamide (6 mL) and water (4 mL) to obtain a suspension. The suspension was placed in a programmable temperature oven, and the oven temperature program was set. The temperature was raised from room temperature to 85 °C in 10 h, kept warm for 75 h, and then cooled to room temperature within 10 h. The crystals were filtered and washed with clean mother liquor (the mother liquor is a mixture of N,N-dimethylformamide and water with a volume ratio of 6:4) to obtain colorless block crystals, which were the Mn-MOF material.

[0048] Example 3

[0049] A preparation method of an Mn-MOF material, comprising the following steps:

[0050] Weigh the main ligand Biphenyl-3,3',5,5'-tetracarboxylic acid (10.94 mg, 0.033 mmol), auxiliary ligand 1,4-Bis[(1H-imidazol-1-yl)methyl]benzene (6.48 mg, 0.027 mmol) and MnSO4·H2O (9.69 mg, 0.057 mmol).

[0051] The main ligand, auxiliary ligand and MnSO4·H2O were added to a mixed solvent of N,N-dimethylformamide (5.5 mL) and water (3.5 mL) to obtain a suspension. The suspension was placed in a programmable temperature oven, and the oven temperature program was set. The temperature was raised from room temperature to 95 °C in 10 h, kept at this temperature for 70 h, and then cooled to room temperature within 10 h. The mixture was filtered, and the crystals were washed with clean mother liquor (the mother liquor is a mixture of N,N-dimethylformamide and water with a volume ratio of 5.5:3.5) to obtain colorless block-shaped crystals, which are the Mn-MOF material.

[0052] In Examples 1-3 of the present invention, Mn-MOF materials with excellent adsorption performance for methylene blue were prepared. Taking the Mn-MOF material of Example 1 as an example for research, the specific research methods and results are as follows:

[0053] See Figure 1 , under a stereomicroscope, regular-shaped and transparent crystals were selected, and their single crystal structures were tested by an X-ray single crystal diffractometer. The results showed that the crystallographic parameters of the Mn-MOF material are monoclinic system.

[0054] See Figures 2 to 6 , for the Mn-MOF material obtained in Example 1, both of the two central atoms Mn1 and Mn2 form a six-coordination configuration with the surrounding other atoms, but with different coordination environments: Mn1 coordinates with one N atom and five O atoms respectively. The N atom comes from the imidazole functional group in the organic ligand 1,4-bis[(1H-imidazol-1-yl)methyl]benzene, and among the five O atoms, two come from the solvent N,N-dimethylformamide and water respectively, and the other three O atoms come from three independent biphenyl-3,3',5,5'-tetracarboxylic acid molecules respectively. Mn2 coordinates with six O atoms. Among them, four O atoms are in pairs and coordinate with the carboxylic acid functional groups from two independent biphenyl-3,3',5,5'-tetracarboxylic acid molecules respectively, and the other two O atoms come from two independent biphenyl-3,3',5,5'-tetracarboxylic acid molecules respectively.

[0055] Next, the adsorption experiment of the dye methylene blue was carried out using the Mn-MOF material of Example 1, which is specifically as follows:

[0056] The Mn-MOF material prepared in Example 1 was applied to the adsorption of the dye methylene blue in an aqueous solution. The experimental conditions were: the temperature of the methylene blue aqueous solution was 20 °C, and the concentration of methylene blue was 20 mg·L -1 , and the adsorption was carried out under the irradiation of blue light, purple light and white light respectively. After 6 h of adsorption, the adsorption rates were 45.4%, 63.50% and 97.97% respectively, and the adsorption amounts were 9.08 mg·g -1 , 12.70 mg·g -1 , 19.59 mg·g-1 。 Its adsorption effect is as follows Figures 7 to 9 。

[0057] It can be seen from Figures 7 to 9 that the adsorption capacity of the Mn-MOF material in Example 1 of the present invention for methylene blue gradually increases with the increase of time. Under white light irradiation, the adsorption capacity is the largest at 360 min, reaching 19.59 mg·g -1 。

[0058] The purity of the Mn-MOF material in Example 1 was measured using an X-ray powder diffractometer in the range of 5° ≤ 2θ ≤ 50°. The X-ray powder diffraction pattern of the Mn-MOF material was obtained, and then it was compared with the single crystal analysis simulation pattern to evaluate the sample purity. The results are as follows Figure 10 shown. The comparison results show that the peak pattern of the Mn-MOF material in Example 1 coincides with the peak pattern of the single crystal analysis simulation diagram, indicating that the Mn-MOF material in Example 1 is a pure phase.

[0059] As Figure 11 shown, it is the thermogravimetric analysis curve of the Mn-MOF material in Example 1. It can be observed from the figure that before 300 °C, the mass in the curve decreases rapidly, presumably due to the loss of solvents with relatively low boiling points existing in the pores of the Mn-MOF material, such as water molecules and N,N-dimethylformamide molecules. In the temperature range of 300 °C to 400 °C, the mass in the curve decreases relatively slowly, indicating that the framework of the Mn-MOF material has a certain thermal stability. In the temperature range of 400 °C to 560 °C, the mass in the curve decreases greatly, indicating that the framework of the Mn-MOF material begins to collapse. It can be inferred from this that the Mn-MOF material has good thermal stability below 400 °C.

[0060] In order to study the specific adsorption of the Mn-MOF material for methylene blue, the Mn-MOF material in Example 1 was used to conduct adsorption experiments on rhodamine B and methyl orange as follows:

[0061] It can be seen from Figures 12 to 14 that when the temperature is set at 20 °C and after 6 h of adsorption, under the irradiation of ultraviolet light, blue light and white light respectively, the adsorption rates of the Mn-MOF material for methyl orange (MO) are 12.90%, 16.35% and 18.55% respectively, and the adsorption capacities are 2.58 mg·g -1 , 3.27 mg·g -1 and 3.71 mg·g -1 respectively. The adsorption effect on MO is the best under white light irradiation, and the removal effect is close to 20%.

[0062] It can be seen from Figures 15 to 17It can be seen that when the temperature is set at 20 °C and after 6 h of adsorption, the adsorption rates of the Mn-MOF material for rhodamine B (RhB) under the irradiation of ultraviolet light, blue light, and white light are 7.75%, 4.10%, and 4.00% respectively, and the adsorption amounts are 1.55 mg·g -1 , 0.82 mg·g -1 , and 0.80 mg·g -1 . The adsorption effect on RhB is the best under ultraviolet light irradiation, but the overall adsorption efficiency does not exceed 10%.

[0063] The results show that the adsorption performance of the Mn-MOF material for methylene blue is significantly better than that for rhodamine B and methyl orange, and it has specific adsorption performance for methylene blue.

[0064] Reusability of the Mn-MOF material: The Mn-MOF material adsorbed with methylene blue is ultrasonically dispersed in water. After methylene blue dissolves in water, the Mn-MOF material is separated and dried, and then the dried Mn-MOF material is used to adsorb methylene blue, and the above operations are repeated. Figure 18 The results show that the number of times the Mn-MOF material can be reused can reach more than 5 times. When recycled to the 5th time, the utilization rate of the Mn-MOF material can still reach more than 90%, indicating that the recycling effect of the Mn-MOF material is good.

[0065] Obviously, those skilled in the art can make various changes and deformations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and deformations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and deformations. The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the scope of protection 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 scope of protection of the present invention, and the scope of protection of the present invention is subject to the claims.

Claims

1. A preparation method of an Mn-MOF material, characterized in that, It includes the following steps: Mix the main ligand auxiliary ligand with MnSO4·H2O in a solvent to obtain a suspension, and then carry out a solvothermal reaction on the suspension. At this time, the main ligand and the auxiliary ligand jointly perform self-assembly with manganese ions to obtain a Mn-MOF material.

2. The preparation method of the Mn-MOF material according to claim 1, wherein Main ligand Auxiliary ligand The molar ratio to MnSO4·H2O is 30 - 35:25 - 30:55 - 60.

3. The preparation method of the Mn-MOF material according to claim 1, characterized in that, The conditions for the solvothermal reaction are: maintaining the temperature at 85°C to 95°C for 70 h to 75 h.

4. The preparation method of the Mn-MOF material according to claim 1, characterized in that, The solvent consists of N,N-dimethylformamide and water.

5. The preparation method of the Mn-MOF material according to claim 4, characterized in that, In the suspension, the volume ratio of N,N-dimethylformamide to water is 5 - 6:3 - 4.

6. A Mn-MOF material prepared by the preparation method according to any one of claims 1 to 5.

7. The Mn-MOF material according to claim 6, wherein The unit cell structure of the Mn-MOF material is monoclinic system.

8. Use of the Mn-MOF material according to claim 6 in the preparation of a methylene blue adsorbent.

9. The application according to claim 8, characterized in that, Mix the wastewater containing methylene blue with the Mn-MOF material, and under the condition of light, use the Mn-MOF material to adsorb methylene blue in the wastewater.

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