Application of a metal-organic framework microsphere material with both microporous and mesoporous properties in organic dye and heavy metal wastewater

Abstract

This invention discloses the application of a metal-organic framework (MOF) microsphere material possessing both microporous and mesoporous properties in organic dye and heavy metal wastewater. The invention focuses on mesoporous spheres formed by the self-assembly of block copolymers. Using regular and highly dense mesoporous micron-sized particles of a self-assembled amphiphilic block copolymer (PS-b-PAA) in a selective solvent mixture as templates, UiO-66-NH2 and ZIF-67 micron-sized microspheres with both microporous and mesoporous pore sizes, formed by the mutual growth of MOF nanocrystals, are produced, achieving higher loading capacity and thus more efficient adsorption and separation. These microspheres are used for dye adsorption and heavy metal ion adsorption, respectively, and their adsorption performance and mechanism are investigated. This combination of microporous and mesoporous MOF microspheres as adsorbents provides a simpler, more convenient, and novel method for adsorption.

Description

Technical Field

[0001] This invention relates to the preparation of UiO-66-NH2 and ZIF-67 micron-sized microsphere nanomaterials with both microporous and mesoporous pore sizes, and their application in the adsorption of organic dyes and heavy metal wastewater. Background Technology

[0002] Organic dyes and heavy metal ions pollute water, causing serious environmental problems. Methylene blue (MB), in particular, is toxic, carcinogenic, and non-biodegradable. Its decomposition produces harmful compounds (such as sulfur oxides, nitrogen oxides, and carbon monoxide) closely linked to serious diseases such as cancer, gastritis, and hypertension. Chromium (Cr) is a common pollutant in surface and groundwater, widely used in industries such as electroplating, leather making, printing, pigments, and polishing. Cr(VI) contamination of aquatic systems and drinking water sources can increase the risk of severe diarrhea and bladder, liver, kidney, and skin cancer, posing a serious threat to the environment and human health. Even at low concentrations, Cr(VI) remains harmful to humans due to its high toxicity, carcinogenicity, and bioaccumulation through the food chain.

[0003] Research indicates that adsorption is the optimal technology for removing dyes and heavy metals from wastewater. Compared to traditional adsorbents such as activated carbon and nanoparticles, MOFs (Metal-Organic Frameworks) have higher specific surface area and porosity. Furthermore, the structure of MOFs is tunable, allowing for modification and alteration based on specific adsorption targets, thereby enhancing the adsorption force between the material and the target molecules. This invention utilizes self-assembled amphiphilic block copolymer (PS-b-PAA) microspheres in a selective solvent. These microspheres possess regular and highly dense mesoporous micron-sized particles. Using these microspheres as soft templates, UiO-66-NH2 and ZIF-67 micron-sized microspheres, formed by the mutual growth of metal-organic framework nanocrystals, are produced, exhibiting both microporous and mesoporous pore sizes. These microspheres are then used for dye adsorption and heavy metal ion adsorption, respectively, and their adsorption performance and mechanism are investigated. Summary of the Invention

[0004] This invention provides a metal-organic framework microsphere material with both microporous and mesoporous properties and a synthesis method. It has a larger specific surface area, providing more active sites. The metal-organic framework microsphere particle material has a high adsorption capacity for methylene blue aqueous solution and Cr(VI) solution, while also having good chemical and thermal stability.

[0005] To solve the aforementioned technical problems, this invention adopts the following technical solution: a method for synthesizing metal-organic framework microspheres that possess both microporous and mesoporous properties. The preparation route of the metal-organic framework microspheres with both microporous and mesoporous properties is as follows:

[0006] (1) The amphiphilic block copolymer polystyrene-block-polyacrylic acid was dissolved in a mixed solvent of toluene / methanol and stirred for a certain time under magnetic stirring. Then, a large amount of methanol was added to fix the mesoporous spheres. The mesoporous spheres were collected by centrifugation and dispersed evenly in the alcohol solution to form solution 1.

[0007] (2) Add the 2-aminoterephthalic acid / 2-methylimidazolol solution to solution 1 above, and stir the two solutions in an oil bath at 70°C / room temperature to obtain solution 2. Add zirconium tetrachloride / cobalt nitrate hexahydrate solution and formic acid catalyst to solution 2 and continue stirring. Cool to room temperature and record as solution 3. Wash the product several times with ultrapure water, ethanol, and DMF.

[0008] (3) After centrifuging solution 3, the product was placed in DMF and stirred at room temperature. Finally, it was washed with DMF, ultrapure water and ethanol to remove the polymer soft template, and then dried in a vacuum oven for 12-24 h. The obtained substance is metal-organic framework microsphere particles.

[0009] UiO-66-NH2 is a type of zirconium metal MOF with extremely strong water stability, enabling more efficient adsorption of pollutants. ZIF-67, due to its hydrophobic surface, high chemical and thermal stability, and simple synthesis operation (it can be synthesized at room temperature), was chosen as the basis for loading these two MOFs onto polymer microspheres and conducting subsequent adsorption experiments.

[0010] Preferably, 2 ml of 10 mg / ml ethanol solution of 2-aminoterephthalic acid is added to 4 ml of PS-b-PAA microsphere alcohol solution and stirred thoroughly for 60 minutes. Then, 2 ml of 20 mg / ml ethanol solution of zirconium tetrachloride and 2 ml of 3M formic acid aqueous solution are added. The resulting mixture is placed in an oil bath at 70°C for 12 hours. The PS-b-PAA@UiO-66-NH2 reaction mixture is then cooled to room temperature, and the precipitate is collected by centrifugation. The precipitate is washed several times with ethanol and ultrapure water to obtain PS-b-PAA@UiO-66-NH2 microspheres. The prepared composite material PS-b-PAA@UiO-66-NH2 microspheres are immersed in N,N'-dimethylformamide (DMF) to dissolve the PS-b-PAA portion of the block copolymer. The product is collected by centrifugation and washed several times with DMF and methanol. Finally, the mixture is dried under vacuum at 60°C for 12 hours to produce UiO-66-NH2 microspheres with both micropores and mesopores.

[0011] 2 ml of 40 mg / ml 2-methylimidazole methanol solution was added to 4 ml of PS-b-PAA microsphere methanol solution and stirred thoroughly for 60 minutes. Then, 2 ml of 35 mg / ml Co(NO3)2·6H2O methanol solution was added. The resulting mixture was then stirred at room temperature for 24 hours. The PS-b-PAA@ZIF-67 reaction mixture was cooled to room temperature, and the precipitate was collected by centrifugation and washed several times with methanol to obtain PS-b-PAA@ZIF-67 microspheres. The prepared composite material PS-b-PAA@ZIF-67 microspheres were immersed in N,N'-dimethylformamide (DMF) to dissolve the block copolymer PS-b-PAA portion. The product was collected by centrifugation and then washed several times with DMF and methanol. Finally, the microspheres were dried under vacuum at 60 °C for 12 hours to produce ZIF-67 microspheres with both micropores and mesopores.

[0012] Preferably, adding 5 mg of aminated metal-organic framework UiO-66-NH2 microspheres to a 20-80 mol / L methylene blue solution and stirring at 20-50 °C for 5-60 min results in the highest adsorption capacity at 80 mg / L and 50 °C, reaching 696.59 mg / g; adding 5 mg of metal-organic framework ZIF-67 microspheres to a 5-40 mol / L Cr(VI) solution and stirring at 20-50 °C for 5-180 min results in the highest adsorption capacity at 40 mg / L and 50 °C, reaching 148.11 mg / g.

[0013] Preferably, the maximum adsorption rate can reach 93.85% when 5 mg of aminated metal-organic framework UiO-66-NH2 microspheres are added to a 20 mol / L methylene blue solution and stirred at room temperature for 30 min; and the maximum adsorption rate can reach 90.18% when 5 mg of metal-organic framework ZIF-67 microspheres are added to a 5 mol / L Cr(VI) solution and stirred at room temperature for 90 min.

[0014] Preferably, in step (2), the solvent used for the UiO-66-NH2 microspheres is ethanol, and the catalyst is formic acid. Ethanol will not damage the morphology of the microspheres compared with DMF and ultrapure water. Formic acid is more acidic than acetic acid, and adding a small amount of formic acid can achieve a good catalytic effect.

[0015] Preferably, in step (2), after adding the zirconium tetrachloride alcohol solution, the stirring temperature should be 70°C and the time should be 12 hours. If the temperature is higher than 100°C, the microsphere template will be destroyed. If the temperature is too low or the reaction time is too short, the MOF cannot grow completely.

[0016] Preferably, in step (2), after adding the cobalt nitrate hexahydrate solution, the mixture is stirred at room temperature for 24 hours. The molar ratio of the organic ligand 2-methylimidazole to the metal cobalt nitrate hexahydrate is 4:1, and the concentrations of the organic ligand 2-methylimidazole and the metal cobalt nitrate hexahydrate methanol are 40 mg / L and 35 mg / L, respectively.

[0017] Preferably, in step (3), the stirring time for removing the soft template using the polymeric good solvent DMF should be greater than 24 h. If the time is less than 24 h, the template cannot be completely removed.

[0018] UiO-66-NH2 and ZIF-67 micron-sized microspheres, possessing both microporous and mesoporous pore sizes, were used to adsorb methylene blue aqueous solution and Cr(VI) solution. Specific adsorption experiments were conducted as follows: 20 and 40 mol / L methylene blue aqueous solution, and 5 and 10 mol / L Cr(VI) solutions were prepared. 5 mg of UiO-66-NH2 and ZIF-67 micron-sized microspheres were added to the 20 and 40 mol / L methylene blue aqueous solution and the 5 and 10 mol / L Cr(VI) solutions, and stirred at room temperature for 5–180 min. The absorbance at the maximum absorption wavelength was observed using a UV spectrophotometer. The adsorption capacity at 20–50 °C was calculated, and the adsorption rates at different temperatures and concentrations were studied. A control group was set up to study the adsorption capacity of UiO-66-NH2 and ZIF-67 nanoparticles alone under the same conditions.

[0019] Beneficial effects:

[0020] This invention utilizes a simple hydrothermal method to grow thin layers of MOF seeds on the pore walls and surfaces of block copolymer mesoporous microspheres through carboxyl complexation between metal and polymer microspheres, forming a PS-b-PAA@MOF composite material. Finally, the soft template is dissolved using a good polymer solvent to obtain UiO-66-NH2 and ZIF-67 microspheres with both mesoporous and microporous structures. The prepared microspheres are used for the adsorption of the organic dye methylene blue and the heavy metal hexavalent chromium solution. These MOF microspheres can rapidly and efficiently adsorb these substances in a short time, increasing the adsorption capacity by 13.6-14.7% compared to pure MOF nanoparticles, while exhibiting excellent intrinsic stability.

[0021] Comparative Example 1 shows that, through Figure 2Observation of SEM images under different preparation conditions revealed that when ultrapure water was used as the solvent, PS-b-PAA microspheres agglomerated into spherical shapes. When DMF was used as the solvent, it dissolved the PS-b-PAA microspheres, causing them to rupture. When ethanol was used as the solvent, good growth of UIO-66-NH2 nanoparticles on the surface of the microspheres was observed. Incomplete MOF particle growth was observed at a reaction temperature of 30℃ and a reaction time of 5 h. At a reaction temperature of 100℃, the excessive temperature damaged the polymer soft template morphology, leading to microsphere rupture. Therefore, through screening, the optimal conditions for synthesizing UIO-66-NH2 microspheres were determined to be ethanol as the reaction solvent and a reaction in an oil bath at 70℃ for 12 h.

[0022] Comparative Example 2 shows that, through Figure 4 SEM images of PS-b-PAA@ZIF-67 microspheres under different reaction conditions revealed that the ZIF-67 particle size decreased with increasing molar ratio. When the molar ratio of organic ligand to metal was 4:1, ZIF-67 nanoparticles grew well on the PS-b-PAA microspheres. When the concentrations of 2-methylimidazole and cobalt nitrate hexahydrate in methanol were 20 mg / L and 17.5 mg / L, respectively, fewer ZIF-67 nanoparticles formed on the surface of the PS-b-PAA microspheres. When the reaction time was 5 h and 12 h, the ZIF-67 precursor solution did not react sufficiently with the PS-b-PAA microspheres. Therefore, through screening, the optimal conditions for synthesizing ZIF-67 microspheres were a molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate of 4:1, concentrations of 2-methylimidazole and cobalt nitrate hexahydrate in methanol of 40 mg / L and 35 mg / L, respectively, and a reaction time of 24 h at room temperature. Attached Figure Description

[0023] Figure 1 SEM image of PS-b-PAA microspheres;

[0024] Figure 2 SEM images of PS-b-PAA@UiO-66-NH2 microspheres under different reaction conditions;

[0025] Figure 3 SEM image of UiO-66-NH2 microspheres obtained after optimizing experimental conditions;

[0026] Figure 4 SEM images of PS-b-PAA@ZIF-67 microspheres under different reaction conditions;

[0027] Figure 5 SEM images of ZIF-67 microspheres obtained after optimizing experimental conditions;

[0028] Figure 6 BET plot of UiO-66-NH2 microspheres;

[0029] Figure 7 BET plot of ZIF-67 microspheres;

[0030] Figure 8 XRD patterns of UiO-66-NH2 microspheres immersed in different organic solvents

[0031] Figure 9 XRD patterns of ZIF-67 microspheres immersed in different organic solvents

[0032] Figure 10 The adsorption effect of UiO-66-NH2 microspheres and UiO-66-NH2 nanoparticles on methylene blue aqueous solution is shown in the figure.

[0033] Figure 11 The adsorption effect of ZIF-67 microspheres and ZIF-67 nanoparticles on Cr(VI) solution is shown in the figure. Detailed Implementation

[0034] The following examples further illustrate the above-mentioned content of the present invention in detail, but it should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following examples. All technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention.

[0035] Example 1

[0036] Preparation of block copolymer microspheres

[0037] 10 mg of the block copolymer polystyrene-block-polyacrylic acid (PS-b-PAA) was dissolved in a 1:3 volume ratio of toluene and methanol (1.5 ml). The mixture was stirred at 800 rpm for 10 h with magnetic stirring. Then, five times the volume of methanol was added to quench the structure and fix the morphology of the resulting mesoporous spheres. The solid was collected by centrifugation. The solid was then redispersed in 5 ml of methanol. Figure 1 The PS-b-PAA microspheres were obtained as shown.

[0038] Example 2

[0039] Preparation of UiO-66-NH2 microspheres with both micropores and mesopores

[0040] 2 ml of 2-aminoterephthalic acid (10 mg / ml) ethanol solution was added to 4 ml of PS-b-PAA microsphere ethanol solution, and stirred thoroughly for 60 minutes. Then, 2 ml of zirconium tetrachloride (ZrCl4, 20 mg / ml) ethanol solution and 2 ml of (3M) formic acid aqueous solution were added. The resulting mixture was placed in an oil bath (70°C) for 12 hours. The PS-b-PAA@UiO-66-NH2 reaction mixture was then cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed several times with ethanol and ultrapure water. Figure 2 The reaction was carried out at 70℃ for 12 h in ethanol, and PS-b-PAA@UiO-66-NH2 microspheres were obtained as shown.

[0041] The prepared composite material PS-b-PAA@UiO-66-NH2 microspheres were immersed in N,N'-dimethylformamide (DMF) to dissolve the PS-b-PAA portion of the block copolymer. The resulting product was collected by centrifugation and washed several times with DMF and methanol. Finally, it was dried under vacuum at 60℃ for 12 h. Figure 3 The diagram shows the generation of UiO-66-NH2 microspheres that possess both micropores and mesopores.

[0042] Example 3

[0043] Preparation of ZIF-67 microspheres with both micropores and mesopores

[0044] 2 ml of 2-methylimidazole (HMeIM, 40 mg / ml) methanol solution was added to 4 ml of PS-b-PAA microsphere methanol solution, and the mixture was stirred thoroughly for 60 minutes. Then, 2 ml of Co(NO3)2·6H2O (35 mg / ml) methanol solution was added. The resulting mixture was then stirred at room temperature for 24 hours. The PS-b-PAA@ZIF-67 reaction mixture was cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed several times with methanol. Figure 4 Organic ligand: metal molar ratio 4=1, reaction time 24h, PS-b-PAA@ZIF-67 microspheres were obtained as shown.

[0045] The prepared composite material PS-b-PAA@ZIF-67 microspheres were immersed in N,N'-dimethylformamide (DMF) to dissolve the PS-b-PAA portion of the block copolymer. The product was collected by centrifugation and then washed several times with DMF and methanol. It was then dried under vacuum at 60°C for 12 h. Figure 5 The diagram shows the production of ZIF-67 microspheres that possess both micropores and mesopores.

[0046] Example 4

[0047] 100 mg of the UiO-66-NH2 microspheres synthesized in Example 2 were analyzed by Brunauer-emmet-teller (BET). Figure 6 The specific surface area can be observed to be 882.86 m². 2 / g, the pore size distribution of the N2 adsorption isotherm was determined by DFT method, and the average pore size was 1.7 nm. Figure 6 It can be observed that UiO-66-NH2 microspheres not only have micropores, but also mesopores.

[0048] Example 5

[0049] 100 mg of the ZIF-67 microspheres synthesized in Example 3 were subjected to Brunauer-emmet-teller (BET) analysis. Figure 6 The specific surface area can be observed to be 999.10 m². 2 / g, the pore size distribution of the N2 adsorption isotherm was determined by DFT method, and the average pore size was 1.15 nm. Figure 7 It can be observed that ZIF-67 microspheres not only have micropores, but also mesopores.

[0050] Example 6

[0051] 5 mg of the UiO-66-NH2 microspheres synthesized in Example 2 were immersed in different organic solvents (DCM, DMF, THF, DMSO) and allowed to stand for 12 h. After centrifugation and washing with ethanol, they were placed in a vacuum drying oven at 60 °C overnight. The microspheres were then analyzed by powder X-ray diffraction (PXRD). Figure 8 It can be observed at 7.42 0 8.59 0 25.78 0 30.78 0 The characteristic peaks did not shift, indicating that the structure of the UiO-66-NH2 microspheres did not change under different organic solvent soaking conditions, proving that the microspheres have good chemical stability.

[0052] Example 7

[0053] Five mg of the ZIF-67 microspheres synthesized in Example 3 were immersed in different organic solvents (DCM, DMF, THF, DMSO) and allowed to stand for 12 hours. After washing by centrifugation with ethanol, they were placed in a vacuum drying oven at 60°C overnight. The microspheres were then analyzed by powder X-ray diffraction (PXRD). Figure 9 It can be observed at 7.1 0 The characteristic peaks did not shift, indicating that the structure of ZIF-67 microspheres did not change under different organic solvent soaking conditions, proving that the microspheres have good chemical stability.

[0054] Example 8

[0055] Methylene blue (MB) aqueous solution was used as a pollutant, and UiO-66-NH2 microspheres were used as adsorbents. 5 mg of the adsorbent was immersed in organic dye aqueous solutions with initial concentrations of 20 and 40 mg / L. Adsorption experiments were conducted at given time points. After adsorption, the adsorbent was removed by filtration through a 0.22 μm microporous PES membrane, and the filtrate was collected. Ultraviolet spectrophotometry showed that the maximum adsorption wavelength of MB was 664 nm. The adsorption capacity of UiO-66-NH2 microspheres for methylene blue was calculated according to Formula 1, and the adsorption capacity at different concentrations and time points was investigated. Figure 10 It was observed that methylene blue (MB) aqueous solution was rapidly adsorbed within 30 min. The initial concentration of methylene blue aqueous solution was 20-80 mg / L, and simulated adsorption was carried out at 20℃, 30℃, 40℃, and 50℃, respectively. The higher the temperature, the greater the adsorption capacity.

[0056] At room temperature, the adsorption capacity of UiO-66-NH2 microspheres for 20 mg / L methylene blue for 30 min was 108.16 mg / g, with a removal rate of 93.85%, and the adsorption capacity for 40 mg / L methylene blue for 30 min was 182.38 mg / g, with a removal rate of 85.83%. Figure 10 It can be observed that, at the same concentration and adsorption time, the adsorption capacity is 1.31 to 1.36 times greater than that of UiO-66-NH2 nanoparticles alone. The adsorption rate is higher, and the removal rate is also greater.

[0057]

[0058] Where q e C is the adsorption capacity (mg / g) at equilibrium time t (min), C0 is the initial concentration of methylene blue (mg / L), and C e V is the concentration of methylene blue at adsorption equilibrium (mg / L), V is the volume of the adsorption solution (mL), m is the mass of the adsorbent (g), and E is the dye removal rate (%).

[0059] Example 9

[0060] Using Cr(VI) solution as a simulated pollutant, ZIF-67 microspheres were used for the adsorption of hexavalent chromium ions. 5 mg of adsorbent was immersed in potassium dichromate solutions with initial concentrations of 5 and 10 mg / L, and adsorption experiments were conducted at given times. After the adsorption experiments, the adsorbent was removed by filtration through a 0.22 μm microporous PES membrane, and the filtrate was collected. Using diphenylcarbazide as a colorimetric reagent and a UV-Vis spectrophotometer, the maximum adsorption wavelength of Cr(VI) was observed to be 540 nm. The adsorption capacity of ZIF-67 microspheres for methylene blue was calculated according to Formula 1, and the adsorption capacity at different concentrations and times was studied. Figure 11 It can be observed that Cr(VI) solution can be rapidly adsorbed within 90 min. The initial concentration of Cr(VI) aqueous solution is 5-40 mg / L, and the adsorption is simulated at 20℃, 30℃, 40℃ and 50℃ respectively. The higher the temperature, the greater the adsorption capacity.

[0061] At room temperature, the ZIF-67 microspheres adsorbed 19.9 mg / g of a 5 mg / L Cr(VI) solution for 90 min, achieving a removal rate of 91.18%. In a 10 mg / L Cr(VI) solution, the adsorption capacity for 90 min was 26.25 mg / g, with a removal rate of 84.51%. Figure 11 It can be observed that, at the same concentration and adsorption time, the adsorption capacity is 1.47 to 1.49 times greater than that of ZIF-67 nanoparticles alone, the adsorption rate is higher, and the removal rate is also higher.

[0062] Comparative Example 1

[0063] The preparation of PS-b-PAA@UiO-66-NH2 microspheres is basically the same as in Example 2, with other conditions remaining unchanged. The only difference is that the solvent, reaction temperature, and reaction time are changed to conduct the following screening experiments:

[0064] In Example 3, ethanol was used as the reaction solvent, and the reaction was carried out in an oil bath at 70°C for 12 hours.

[0065] (1) Disperse 2-aminoterephthalic acid (10 mg / ml) in 2 ml of different solvents (ultrapure water, DMF) and record it as solution a. Disperse zirconium tetrachloride (ZrCl4, 20 mg / ml) in 2 ml of ultrapure water, DMF and record it as solution b.

[0066] (2) Mix solution a with 4 ml of PS-b-PAA microsphere alcohol solution, add 3 M formic acid aqueous solution and stir thoroughly for 60 minutes, then add solution b, and place the resulting mixture at different temperatures (30℃, 100℃).

[0067] (3) The reaction time is 5 hours.

[0068] The PS-b-PAA@UiO-66-NH2 reaction mixture was cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was then washed several times with ethanol and ultrapure water.

[0069] pass Figure 2 Observing SEM images under different preparation conditions, it can be found that when ultrapure water is used as the solvent, PS-b-PAA microspheres aggregate into spherical shapes on the surface. When DMF is used as the solvent, DMF dissolves PS-b-PAA microspheres, causing the microspheres to rupture. When ethanol is used as the solvent, UIO-66-NH2 nanoparticles can be observed to grow well on the surface of the microspheres.

[0070] When the reaction temperature was 30℃ and the reaction time was 5h, incomplete growth of MOF particles could be observed. When the reaction temperature was 100℃, the excessive temperature damaged the morphology of the polymer soft template, and the microspheres ruptured. Therefore, through screening, the optimal conditions for synthesizing UIO-66-NH2 microspheres were to use ethanol as the reaction solvent and react at 70℃ in an oil bath for 12h.

[0071] Comparative Example 2

[0072] The preparation of PS-b-PAA@ZIF-67 microspheres was basically the same as in Example 3, with other conditions remaining unchanged. The only difference was that the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate, the concentration of 2-methylimidazole to cobalt nitrate hexahydrate methanol solution, and the reaction time were changed to conduct the following screening experiments:

[0073] In Example 3, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate was 4:1, and the concentrations of 2-methylimidazole and cobalt nitrate hexahydrate methanol solution were 40 mg / L and 35 mg / L, respectively, and the reaction time was 24 h.

[0074] (1) Add the 2-methylimidazole (HMeIM) alcohol solution to the PS-b-PAA microsphere alcohol solution and stir thoroughly for 60 minutes, then add the cobalt nitrate hexahydrate (Co(NO3)2·6H2O) alcohol solution. The molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 1:1 and 2:1, respectively.

[0075] (2) Add 2 ml (20 mg / L) 2-methylimidazolium (HMeIM) methanol solution to 4 ml PS-b-PAA microsphere alcohol solution and stir thoroughly for 60 minutes. Then add 2 ml (17.5 mg / L) cobalt nitrate hexahydrate (Co(NO3)2·6H2O) alcohol solution.

[0076] (3) The resulting mixture was stirred at room temperature for 5 h and 12 h respectively.

[0077] The PS-b-PAA@ZIF-67 reaction mixture was cooled to room temperature, the precipitate was collected by centrifugation, and the precipitate was washed several times with methanol.

[0078] pass Figure 4SEM images of PS-b-PAA@ZIF-67 microspheres under different reaction conditions revealed that the ZIF-67 particle size decreased with increasing molar ratio. When the molar ratio of organic ligand to metal was 4:1, ZIF-67 nanoparticles grew well on the PS-b-PAA microspheres. When the concentrations of 2-methylimidazole and cobalt nitrate hexahydrate in ethanol were 20 mg / L and 17.5 mg / L, respectively, fewer ZIF-67 nanoparticles formed on the surface of the PS-b-PAA microspheres. When the reaction time was 5 h and 12 h, the ZIF-67 precursor solution did not react sufficiently with the PS-b-PAA microspheres. Therefore, through screening, the optimal conditions for synthesizing ZIF-67 microspheres were a molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate of 4:1, concentrations of 2-methylimidazole and cobalt nitrate hexahydrate in ethanol solution of 40 mg / L and 35 mg / L, respectively, and a reaction time of 24 h at room temperature.

[0079] Comparative Example 3

[0080] Preparation of UiO-66-NH2 nanoparticles

[0081] 40 mg ZrCl4, 20 mg diaminoterephthalic acid, and 4 mL ethanol were sequentially added to 3 mL of 30% formic acid. The mixture was placed in an ultrasonic system for 10 min until completely dissolved. Then, it was transferred to an oil bath and stirred at 70 °C for 12 h. The mixture was washed 3-5 times with anhydrous ethanol and deionized water. Finally, it was vacuum dried at 60 °C for 12 h to obtain UiO-66-NH2 nanoparticles.

[0082] Methylene blue (MB) aqueous solution was used as a pollutant, and UiO-66-NH2 nanoparticles were used as adsorbents. 5 mg of the adsorbent was immersed in organic dye aqueous solutions with initial concentrations of 20 and 40 mg / L. Adsorption experiments were conducted at given time points. After adsorption, the adsorbent was removed by filtration through a 0.22 μm microporous PES membrane, and the filtrate was collected. Using a UV spectrophotometer, the maximum adsorption wavelength of MB was observed to be 664 nm. The adsorption capacity of UiO-66-NH2 nanoparticles for methylene blue was calculated according to Formula 1. At room temperature, the adsorption capacity of UiO-66-NH2 nanoparticles for 20 mg / L methylene blue solution was 79.529 mg / g. The adsorption capacity at different concentrations and time points was also investigated. The dye removal rate was calculated using Formula 2. The removal rate of methylene blue at 20 mg / L was 87.41%, and the adsorption capacity of UiO-66-NH2 nanoparticles at 40 mg / L was 139.21 mg / g, with a removal rate of 77.36%.

[0083] Comparative Example 4

[0084] Preparation of ZIF-67 nanoparticles

[0085] Dissolve 35 mg of Co(NO3)2 6H2O and 40 mg of 2-methylimidazole in 8 mL of methanol. Add the latter transparent solution to the former pink solution, mix the components, stir for 24 h, centrifuge to collect the purple solid, wash three times with methanol, and dry at 60 °C for 12 h.

[0086] Using Cr(VI) as a simulated pollutant, ZIF-67 nanoparticles were used for the adsorption of hexavalent chromium ions: 5 mg of adsorbent was immersed in potassium dichromate solutions with initial concentrations of 5 and 10 mg / L, and adsorption experiments were conducted at given times. After adsorption, the adsorbent was removed by filtration through a 0.22 μm microporous PES membrane and the filtrate was collected. Using diphenylcarbazide as the colorimetric reagent and a UV-Vis spectrophotometer, the maximum adsorption wavelength of Cr(VI) was observed to be 540 nm. The adsorption capacity of ZIF-67 nanoparticles for Cr(VI) solution was calculated according to Formula 1. At a Cr(VI) solution concentration of 5 mg / L, the adsorption capacity of ZIF-67 nanoparticles was 13.537 mg / g. The adsorption capacity at different concentrations and times was investigated. At room temperature, the adsorption capacity of ZIF-67 microspheres for Cr(VI) solution at 5 mg / L for 30 min was 13.47 mg / g. According to Formula 2, the heavy metal ion removal rate of Cr(VI) solution at 5 mg / L was 82.18%, and the adsorption capacity of Cr(VI) solution at 10 mg / L for 30 min was 17.62 mg / g, resulting in a heavy metal ion removal rate of 76.25% for Cr(VI) solution at 10 mg / L.

Claims

1. An application of a metal-organic framework microsphere material with both microporous and mesoporous properties in organic dye and heavy metal wastewater, characterized in that: MOFs were grown on the surface and in the channels of amphiphilic block polymer mesoporous microspheres using a soft template method. The polymer microspheres were then dissolved in a good polymer solvent to form metal-organic framework MOF microspheres that can have both micropores and mesopores, namely UiO-66-NH2 microspheres or ZIF-67 microspheres. UiO-66-NH2 microspheres were used to adsorb methylene blue solution, and ZIF-67 microspheres were used to adsorb Cr(VI) solution. The preparation method of the metal-organic framework microspheres is as follows: (1) The block copolymer polystyrene-block-polyacrylic acid was dissolved in a mixed solvent of toluene / methanol and stirred for a certain time under magnetic stirring. Then, a large amount of methanol was added to fix the mesoporous spheres. The mesoporous spheres were collected by centrifugation and dispersed evenly in an alcohol solution to form solution 1. (2) Add 2-aminoterephthalic acid or 2-methylimidazol solution to the above solution 1, and stir the two substances to form solution 2; (3) Add zirconium tetrachloride or cobalt nitrate hexahydrate solution to solution 2, stir continuously in an oil bath or at room temperature for 12-24 hours, and then cool to room temperature. This solution is called solution 3. (4) After centrifuging solution 3, the product is obtained. The product is washed with DMF to remove the polymer soft template and then dried in a vacuum oven for 12-24 h. The obtained substance is metal-organic framework microspheres with both micropores and mesopores.

2. The application of the metal-organic framework microsphere material with both microporous and mesoporous properties according to claim 1 in organic dye and heavy metal wastewater, characterized in that: Add 2 ml of 10 mg / ml ethanol solution of 2-aminoterephthalic acid to 4 ml of PS- b -The PAA microspheres were added to an alcohol solution and stirred thoroughly for 60 minutes. Then, 2 ml of 20 mg / ml zirconium tetrachloride ethanol solution and 2 ml of 3M formic acid aqueous solution were added. The resulting mixture was placed in an oil bath at 70°C for 12 hours. Subsequently, PS- b The -PAA@UiO-66-NH2 reaction mixture was cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed several times with ethanol and ultrapure water to obtain PS- b -PAA@UiO-66-NH2 microspheres; the prepared composite material PS- b -PAA@UiO-66-NH2 microspheres were immersed in N,N'-dimethylformamide to dissolve the block copolymer PS- b -PAA fraction: the product obtained by centrifugation was washed several times with DMF and methanol; finally, it was dried under vacuum at 60℃ for 12h to produce UiO-66-NH2 microspheres with both micropores and mesopores. Add 2 ml of 40 mg / ml 2-methylimidazole methanol solution to 4 ml of PS- b -The PAA microspheres were added to a methanol solution and stirred thoroughly for 60 minutes, followed by the addition of 2 ml of Co(NO3)2·6H2O 35 mg / ml methanol solution; the resulting mixture was then stirred at room temperature for 24 hours; PS- b The PAA@ZIF-67 reaction mixture was cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed several times with methanol to obtain PS- b -PAA@ZIF-67 microspheres were used to prepare the composite material PS- b -PAA@ZIF-67 microspheres were immersed in N,N'-dimethylformamide to dissolve the block copolymer PS- b The PAA fraction was collected by centrifugation, then washed several times with DMF and methanol; and then dried under vacuum at 60°C for 12 h to produce ZIF-67 microspheres with both micropores and mesopores.

3. The application of the metal-organic framework microsphere material with both microporous and mesoporous properties according to claim 2 in organic dye and heavy metal wastewater, characterized in that: Adding 5 mg of amino-modified metal-organic framework UiO-66-NH2 microspheres to a 20 mol / L methylene blue solution and stirring at room temperature for 30 min yielded a maximum adsorption rate of 93.85%; adding 5 mg of metal-organic framework ZIF-67 microspheres to a 5 mol / L Cr(VI) solution and stirring at room temperature for 90 min yielded a maximum adsorption rate of 90.18%.

4. The application of the metal-organic framework microsphere material with both microporous and mesoporous properties according to claim 1 in organic dye and heavy metal wastewater, characterized in that: Using mesoporous polymer microspheres as soft templates, UiO-66-NH2 and ZIF-67 micron-sized microspheres with both micropore and mesopore sizes were synthesized by a simple hydrothermal method. These microspheres were formed by the mutual growth of metal-organic framework nanocrystals. The synthesis steps were simplified, and green solvents ethanol and methanol were used.

5. The application of the metal-organic framework microsphere material with both microporous and mesoporous properties according to claim 1 in organic dye and heavy metal wastewater, characterized in that: The concentrations of 2-aminoterephthalic acid, dimethylimidazole, zirconium tetrachloride, and cobalt nitrate hexahydrate solutions were all 10-40 mol / L.

6. The application of the aminated metal-organic framework UiO-66-NH2 microspheres according to claim 1 in the treatment of the organic dye methylene blue, characterized in that: The concentration of methylene blue water adsorbed at room temperature is 20-40 mol / L.

7. The application of the aminated metal-organic framework UiO-66-NH2 microspheres according to claim 1 in the treatment of methylene blue aqueous solution, characterized in that: The adsorption process of the amino-organic framework UiO-66-NH2 microspheres after adsorbing methylene blue solution is irreversible at 20-50℃. A control group was set up. Compared with the adsorption of UiO-66-NH2 nanoparticles alone, the MOF microspheres with both micropores and mesopores have a higher adsorption capacity.

8. The application of the metal-organic framework ZIF-67 microspheres according to claim 1 in the treatment of Cr(VI) solution, characterized in that: The adsorption process of ZIF-67 metal-organic framework microspheres after adsorbing Cr(VI) solution is irreversible at 20-50℃, and has a higher adsorption capacity than ZIF-67 nanoparticles alone. The concentration of Cr(VI) solution adsorbed at room temperature is 5-10 mol / L.

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