A modified zif-8 material and applications thereof

Abstract

The application discloses a modified ZIF-8 material, wherein the ZIF-8 material is modified under a plasma discharge gas atmosphere for 10-60 seconds under the condition of a 40W-60W plasma discharge power to obtain the modified ZIF-8 material. The ZIF-8 is modified by low-temperature plasma, the photocatalytic efficiency of the ZIF-8 material is improved, and the modified ZIF-8 still retains good adsorption capacity for hexavalent chromium. The modified ZIF-8 material has the advantages of simple preparation, environmental protection and high efficiency. The modified ZIF-8 is added into chromium-containing wastewater, and is subjected to photocatalysis through light irradiation, so that the chromium-containing wastewater can be efficiently degraded. The method is simple, easy and environmental protection, and only needs light irradiation. The modified ZIF-8 can be recycled and reused, and can be used for further functionalization or industrial processing.

Description

Technical Field

[0001] This application relates to the fields of catalysis science and materials science, and more specifically, to a modified ZIF-8 material and its applications. Background Technology

[0002] Metal-organic frameworks (MOFs) possess many excellent properties. The pore size of MOFs is similar to that of some organic molecules, enabling selective adsorption and degradation of organic molecules in chromium-containing wastewater. ZIF-8 (2-methylimidazolium zinc MOF) is one of the most representative MOF materials. Because ZIF-8 is mostly synthesized at room temperature, the conditions are mild, the preparation is simple, and it has broad application prospects. Photocatalysis technology has advantages such as not producing secondary pollution and directly utilizing solar energy without consuming additional energy, making it one of the effective means to solve environmental pollution and energy shortages. ZIF-8, as a photocatalyst, has good thermal stability, but its photocatalytic efficiency is not high.

[0003] In the field of materials modification, low-temperature plasma surface modification is a common method to improve the surface properties of materials and enhance their usability. Low-temperature plasma surface treatment technology has attracted considerable attention from researchers due to its wide applicability. Existing technologies also include research on modifying ZIF-8 materials using low-temperature plasma. For example, patent applications CN113019329A and CN112657558A both utilize low-temperature plasma to modify ZIF-8 materials. However, the modified ZIF-8 materials obtained in these patent applications only show improved adsorption efficiency; the photocatalytic ability of the prepared materials is not improved. Therefore, it is necessary to provide a modified material that can improve photocatalytic efficiency while maintaining adsorption capacity. Summary of the Invention

[0004] This invention provides a modified ZIF-8 material, which is obtained by modifying the ZIF-8 material for 10-60 seconds under a plasma discharge power of 40W to 60W in a plasma discharge gas atmosphere.

[0005] Specifically, the discharge power is 40W; and / or the modification treatment time is 45 seconds.

[0006] The plasma discharge gas is selected from any one of air, nitrogen, argon, and ammonia; and / or, the flow rate of the plasma discharge gas is 30ccm to 50ccm.

[0007] The modification process was carried out in a low-temperature plasma reactor.

[0008] The preparation method of the ZIF-8 material is as follows:

[0009] Zinc nitrate hexahydrate and 2-methylimidazole were dissolved in deionized water, respectively. The resulting zinc nitrate solution and 2-methylimidazole solution were then stirred and mixed until a milky white color was obtained. After centrifugation, the precipitate was washed several times with deionized water, centrifuged again, and dried. Specifically, (1) the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole was 1:60-80; (2) centrifugation was performed at 5000-8000 rpm for 10-20 min; and (3) the drying temperature was 60℃-100℃, and the drying time was 6h-12h. Preferably, the molar ratio of zinc nitrate hexahydrate to 2-methylimidazole was 1:70; and / or centrifugation was performed at 6000 rpm for 15 min.

[0010] The present invention also provides an application of the aforementioned modified ZIF-8 material in the treatment of chromium-containing wastewater.

[0011] Specifically, the aforementioned modified ZIF-8 material is added to chromium-containing wastewater and reacted in the dark for 6-12 hours, then placed under light conditions for more than 8 hours.

[0012] The beneficial effects of this invention include:

[0013] This invention improves the photocatalytic efficiency of ZIF-8 material by modifying it with low-temperature plasma, while retaining its good adsorption capacity for hexavalent chromium. The method for preparing the modified ZIF-8 material in this invention is simple, environmentally friendly, and efficient.

[0014] Modified ZIF-8, when added to chromium-containing wastewater, can efficiently degrade chromium-containing wastewater through photocatalysis under light irradiation. This method is simple, easy to implement, and environmentally friendly, requiring only light exposure. Furthermore, the modified ZIF-8 can be repeatedly recycled and reused for further functionalization or industrial processing. Attached Figure Description

[0015] Figure 1 The flowchart for the synthesis of modified ZIF-8;

[0016] Figure 2 The images shown are of the zinc nitrate solution and 2-methylimidazole solution before and after mixing in Example 1. The left image shows the 2-methylimidazole solution before mixing, and the right image shows the solution after mixing.

[0017] Figure 3 The image shows a SEM image of ZIF-8 prepared in step a of Example 1.

[0018] Figure 4 The XRD pattern of ZIF-8 prepared in step a of Example 1;

[0019] Figure 5 The images show SEM images of the modified ZIF-8 prepared in Example 1, with the left image being ZIF-8-10 and the right image being ZIF-8-20.

[0020] Figure 6 This is a graph showing the photocatalytic concentration ratio of ZIF-8 material in different concentrations of chromium-containing wastewater over time in Example 2.

[0021] Figure 7 This is a graph showing the concentration ratio of hexavalent chromium in chromium-containing wastewater in chromium-containing wastewater over time for different modified ZIF-8 materials in Example 2.

[0022] Figure 8 The adsorption capacity of different modified ZIF-8 materials for hexavalent chromium in chromium-containing wastewater in Example 2;

[0023] Figure 9 XRD patterns of different modified ZIF-8 materials in Example 3;

[0024] Figure 10 The graph shows the concentration ratio of hexavalent chromium in chromium-containing wastewater under photocatalysis over time using different modified ZIF-8 materials in step (1) of Example 4.

[0025] Figure 11 This is a graph showing the concentration ratio of hexavalent chromium in chromium-containing wastewater under photocatalysis over time using different modified ZIF-8 materials in step (2) of Example 4.

[0026] Figure 12 The graph shows the time-dependent photocatalytic degradation rate of hexavalent chromium in chromium-containing wastewater by the modified ZIF-8 material obtained under different flow rate conditions in Example 5.

[0027] Figure 13 The graph shows the time-dependent photocatalytic degradation rate of hexavalent chromium in chromium-containing wastewater by the modified ZIF-8 material obtained under different discharge power conditions in Example 6. Detailed Implementation

[0028] The present invention will be further described and illustrated below with reference to embodiments. However, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the present invention and the embodiments, all other inventions and embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0030] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0031] Example 1: Preparation of modified ZIF-8 material

[0032] According to such Figure 1 The process is shown below, and the specific operations are as follows:

[0033] a. Dissolve 1.17g of zinc nitrate hexahydrate in 8g of deionized water, and dissolve 22.7g of 2-methylimidazole in 80g of deionized water. Then, mix the zinc nitrate solution and the 2-methylimidazole solution under stirring. The mixed solution quickly turns milky white (as shown in the image). Figure 2 As shown in the right figure, the solution was stirred at room temperature for about five minutes, then centrifuged at 6000 rpm for 15 minutes. The resulting sample was washed 2 to 3 times with deionized water and then dried in a vacuum drying oven at 65°C for 10 hours. The final yield of ZIF-8 product was 0.78 g, with a yield of approximately 56%.

[0034] The SEM image of ZIF-8 prepared in this embodiment is shown below. Figure 3 As shown.

[0035] The XPS table of the ZIF-8 prepared in this embodiment is shown in Table 1 below.

[0036] Table 1. XPS table of ZIF-8 prepared in this embodiment.

[0037]

[0038] The XRD pattern of ZIF-8 prepared in this embodiment is as follows: Figure 4 As shown.

[0039] b. Place the above product ZIF-8 into a low-temperature plasma reactor, evacuate the plasma reactor, and then purge with ammonia gas at a flow rate of 30ccm and a discharge power of 40W. Discharge with ammonia gas at low-temperature plasma for 10s and 20s respectively to obtain ammonia plasma modified ZIF-8 materials, which are respectively denoted as ZIF-8-10 and ZIF-8-20.

[0040] The SEM images of ZIF-8-10 (left) and ZIF-8-20 (right) prepared in this embodiment are as follows: Figure 5 As shown in Table 2, the BET values ​​of ZIF-8 before and after modification prepared in this embodiment are shown in Table 2. It can be seen from the table that the low-temperature plasma discharge treatment has little effect on the specific surface area of ​​the material. Figure 3 and Figure 5 The SEM images show that the particle size and porosity of ZIF-8 before and after modification are not significantly different.

[0041] Table 2. BET table of ZIF-8 before and after modification prepared in this embodiment.

[0042]

[0043] Analysis of the application effects of ZIF-8 materials prepared in Example 2 and Example 1 and modified ZIF-8 materials

[0044] (1) Using hexavalent chromium solutions with different initial concentrations as variables, the effect of the initial concentration of hexavalent chromium on the photocatalytic reduction rate of ZIF-8 was discussed.

[0045] In this experiment, hexavalent chromium solutions with initial concentrations of 100 mg / L, 40 mg / L, and 20 mg / L were selected. The ZIF-8 material prepared in Example 1 was added to chromium-containing wastewater of different concentrations and reacted in the dark for 6 hours. Samples were taken and filtered to determine the initial concentrations at adsorption equilibrium, which were 98 mg / L, 38 mg / L, and 18 mg / L, respectively. The hexavalent chromium wastewater solutions with different initial concentrations were irradiated under a xenon gas constant current power supply, and samples were taken every 2 hours and filtered through a microporous filter to measure the absorbance. Based on the absorbance of the above solutions, a concentration ratio of ZIF-8 material photocatalysis over time in chromium-containing wastewater of different concentrations was obtained, as shown in the figure. Figure 6 As shown.

[0046] Depend on Figure 6 It can be seen that the photocatalytic reduction rate decreases with increasing initial concentration of the photoreaction. When the initial concentration of the photoreaction is 98 mg / L, the photocatalytic reduction rate is about 20% after 10 hours of reaction; when the initial concentration of the photoreaction is 38 mg / L, the photocatalytic reduction rate is about 26% after 10 hours of reaction; and when the initial concentration of the photoreaction is 18 mg / L, the photocatalytic reduction rate is about 38% after 10 hours of reaction.

[0047] (2) Using ZIF-8 with different modification parameters as variables, we discussed the effects of different modification time conditions on the catalytic performance of modified ZIF-8.

[0048] The experiment used unmodified ZIF-8 prepared in Example 1, ZIF-8-10 modified with ammonia plasma for 10 s, and ZIF-8-20 modified with ammonia plasma for 20 s. The material dosage was 20 mg / 50 mL, and the initial concentration of hexavalent chromium solution was 20 mg / L. The reaction was carried out in the dark at 25 °C with stirring for 6 h. The concentration of hexavalent chromium at adsorption equilibrium was measured by filtration through a microporous filter. The solution was then reacted under xenon gas constant current illumination, and samples were taken every 2 h and filtered through a microporous filter to measure the absorbance. Based on the absorbance of the above solutions, a graph showing the photocatalytic concentration ratio of hexavalent chromium in chromium-containing wastewater treated with different modified ZIF-8 materials over time was obtained, as shown in the figure. Figure 7 As shown.

[0049] Depend on Figure 7It can be seen that the modified ZIF-8 differs from the unmodified ZIF-8 in its ability to photocatalytically degrade hexavalent chromium. Ammonia plasma modification improves the ability of ZIF-8 to photocatalytically degrade hexavalent chromium. Plasma modification increases the active sites of ZIF-8, thereby enhancing its ability to photocatalytically degrade hexavalent chromium. After 10 hours of photocatalysis, the reduction rate of hexavalent chromium photocatalytically degraded by unmodified ZIF-8 is approximately 38%, while the reduction rate of hexavalent chromium photocatalytically degraded by ZIF-8 after 20 seconds of ammonia modification can reach 45%.

[0050] (3) Using ZIF-8 with different modification parameters as variables, we discussed the effects of different modification time conditions on the adsorption performance of modified ZIF-8.

[0051] The experiment used unmodified ZIF-8 prepared in Example 1, ZIF-8-10 modified by ammonia plasma for 10 s, and ZIF-8-20 modified by ammonia plasma for 20 s. A hexavalent chromium solution with an initial concentration of 20 mg / L was used. The material dosage was 10 mg / 50 mL. The mixture was stirred at 25 °C and reacted in the dark for 12 h. The mixture was filtered through a 0.45 μm microporous filter. The initial concentration of the solution and the concentration of the filtrate at adsorption equilibrium were measured, and the equilibrium adsorption capacity qe was calculated. The results are as follows: Figure 8 As shown.

[0052] After obtaining the absorbance of the colorimetric hexavalent chromium solution using a UV spectrophotometer, the adsorption capacity q was then balanced. e This indicates the content of hexavalent chromium adsorbed by the composite and modified materials in the solution. The calculation formula is as follows:

[0053] q e =(C0-C e )·V / m

[0054] In the formula: C0 (unit: mg / L) is the initial concentration; C e (Unit: mg / L) is the concentration at adsorption equilibrium; V (unit: L) is the solution volume; m (unit: g) is the amount of adsorbent used; q e (Unit: mg / g) represents the equilibrium adsorption capacity.

[0055] Depend on Figure 8 It can be seen that different modification conditions do not significantly alter the adsorption performance of ZIF-8, and there is no obvious pattern. Therefore, plasma modification of ZIF-8 has no significant impact on the adsorption performance of hexavalent chromium; the modified ZIF-8 still retains good adsorption properties for hexavalent chromium.

[0056] Example 3: Preparation of modified ZIF-8 material

[0057] a. Following the same steps as in Example 1, ZIF-8 is obtained.

[0058] b. Place 1g of the ZIF-8 sample to be modified obtained in step 1 into the plasma reactor. First, purge with ammonia gas for 15s at a flow rate of 30ccm and a discharge power of 40W. Then, discharge under the ammonia atmosphere for 15s, 30s, and 45s respectively to obtain ZIF-8 modified samples for 15s, 30s, and 45s, which are denoted as ZIF-8-15, ZIF-8-30, and ZIF-8-45 respectively.

[0059] The XRD patterns of ZIF-8, ZIF-8-15, ZIF-8-30, and ZIF-8-45 prepared in this embodiment are shown below. Figure 9 As shown.

[0060] The BET values ​​of ZIF-8 before and after modification prepared in this embodiment are shown in Table 3.

[0061] Table 3. BET table of ZIF-8 before and after modification prepared in this embodiment.

[0062]

[0063] This data shows that the surface area of ​​ZIF-8, both before and after modification, is 1600 m². 2 The specific surface area is around 1 / g, which is consistent with the characteristics of ZIF-8 material. At the same time, since the specific surface area does not change much before and after modification, it can be considered that the modification has little impact on ZIF-8.

[0064] Analysis of the application effects of ZIF-8 materials prepared in Examples 4 and 3 and modified ZIF-8 materials

[0065] (1) Using ZIF-8 with different modification parameters as variables, we discussed the effects of different modification time conditions on the catalytic performance of modified ZIF-8.

[0066] The experiment selected unmodified ZIF-8 and ammonia plasma-modified samples ZIF-8-15, ZIF-8-30, and ZIF-8-45 for 15s, 30s, and 45s respectively. The material dosage was 20 mg / 50 mL, the hexavalent chromium concentration was 20 mg / L, and the reaction was carried out in the dark at 25℃ with stirring for 10 h. The concentration of hexavalent chromium at adsorption equilibrium was measured by filtration through a microporous filter. The solution was placed under xenon gas constant current illumination for reaction, and samples were taken every 2 h and filtered through a microporous filter to measure the absorbance. Based on the absorbance of the above solutions, the concentration ratio of hexavalent chromium in chromium-containing wastewater under different modified ZIF-8 materials was obtained as a function of photocatalysis over time, as shown in the figure. Figure 10 As shown.

[0067] Depend on Figure 10It can be seen that the modified ZIF-8 differs from the unmodified ZIF-8 in its ability to photocatalytically degrade hexavalent chromium. Ammonia plasma modification improves the ability of ZIF-8 to photocatalytically degrade hexavalent chromium. Plasma modification increases the active sites of ZIF-8, thereby enhancing its ability to photocatalytically degrade hexavalent chromium. After 10 hours of photocatalysis, the reduction rate of hexavalent chromium increases with the modification time. The reduction rate of hexavalent chromium by ZIF-8-45 modified with ammonia for 45 seconds is higher than that of the unmodified ZIF-8, reaching 42%.

[0068] (2) Using ZIF-8 with different modification parameters as variables, we discussed the effects of different modification time conditions on the catalytic performance of modified ZIF-8.

[0069] Using the preparation method of Example 3, a plasma-modified 60s sample ZIF-8-60 was prepared.

[0070] The experiment selected unmodified ZIF-8 and ammonia plasma-modified samples ZIF-8-15, ZIF-8-30, ZIF-8-45, and ZIF-8-60 for 15s, 30s, 45s, and 60s, respectively. The material dosage was 10 mg / 50 mL, and the reaction was carried out in the dark at 25℃ with stirring for 10 h. The solution was then placed under xenon gas constant current illumination, and samples were taken every 2 h and filtered through a microporous filter to measure the absorbance of hexavalent chromium. Based on the absorbance of the above solutions, a graph showing the concentration ratio of hexavalent chromium in chromium-containing wastewater photocatalyzed by different modified ZIF-8 materials over time was obtained, as shown in the figure. Figure 11 As shown.

[0071] Depend on Figure 11 It can be seen that ammonia plasma modification improves the photocatalytic degradation of hexavalent chromium by ZIF-8. Plasma modification increases the active sites of ZIF-8, but after a certain modification time, the performance of ZIF-8 begins to decrease due to excessive energy, thus reducing its photocatalytic degradation ability of hexavalent chromium. After 10 hours of photocatalysis, the photocatalytic degradation ability of ZIF-8-60 modified by ammonia for 60 seconds is lower than that of ZIF-8-45 modified by ammonia for 45 seconds, and has a similar ability to ZIF-8 modified by 30 seconds.

[0072] Example 5: Effect of different flow rates of plasma-modified gas on modified ZIF-8 material

[0073] (1) Preparation of modified ZIF-8 under different flow rates

[0074] a. Following the same steps as in Example 1, ZIF-8 is obtained.

[0075] b. Evacuate the plasma reactor, purge with ammonia gas, discharge power 40W, then discharge with ammonia gas at low temperature plasma flow rates of 30ccm, 40ccm and 50ccm for 15s respectively, to obtain ammonia plasma modified ZIF-8 materials, denoted as ZIF-8-30cc, ZIF-8-40cc and ZIF-8-50cc.

[0076] (2) Using ZIF-8 with different modification parameters as variables, we discussed the effects of different ammonia flow rates on the catalytic performance of modified ZIF-8.

[0077] The material prepared in step (1) was selected for the experiment. The dosage of the material was 10 mg / 50 mL, and the initial concentration of the hexavalent chromium solution was 20 mg / L. The reaction was carried out in the dark at 25°C with stirring for 10 h. The solution was placed under xenon gas constant current power supply illumination for the reaction. Samples were taken every 2 h and filtered through a microporous filter to measure the absorbance of hexavalent chromium. Based on the absorbance of the above solution, the photocatalytic degradation rate of hexavalent chromium in chromium-containing wastewater by different modified ZIF-8 materials over time was obtained, as shown in the figure. Figure 12 As shown.

[0078] Depend on Figure 12 It can be seen that increasing the atmospheric flow rate of ammonia plasma modification has a certain increase in the ability of ZIF-8 to photocatalytically degrade hexavalent chromium, but the increase is relatively small.

[0079] Example 6: Effect of discharge power on modified ZIF-8 material

[0080] (1) Preparation of modified ZIF-8 under different discharge power conditions

[0081] a. Following the same steps as in Example 1, ZIF-8 is obtained.

[0082] b. Evacuate the plasma reactor, purge with ammonia gas, and then discharge with ammonia gas at a flow rate of 30ccm. Discharge with ammonia gas at low temperature plasma discharge power of 30W, 40W and 50W for 15s to obtain ammonia plasma modified ZIF-8 materials, denoted as ZIF-8-30W, ZIF-8-40W and ZIF-8-50W.

[0083] (2) Using ZIF-8 with different discharge power modification parameters as variables, we discussed the effect of different discharge power conditions on the catalytic performance of modified ZIF-8.

[0084] The material prepared in step (1) was selected for the experiment. The dosage of the material was 10 mg / 50 mL, and the initial concentration of the hexavalent chromium solution was 20 mg / L. The reaction was carried out in the dark at 25°C with stirring for 10 h. The solution was placed under xenon gas constant current power supply illumination for the reaction. Samples were taken every 2 h and filtered through a microporous filter to measure the absorbance of hexavalent chromium. Based on the absorbance of the above solution, the photocatalytic degradation rate of hexavalent chromium in chromium-containing wastewater by different modified ZIF-8 materials over time was obtained, as shown in the figure. Figure 13 As shown.

[0085] Depend on Figure 13 It can be seen that the discharge power of ammonia plasma modification has a significant impact on the photocatalytic degradation of hexavalent chromium by ZIF-8. Plasma modification discharge increases the active sites of ZIF-8, but the performance of ZIF-8 in degrading hexavalent chromium decreases when the discharge power reaches 50W. The degradation rate at a discharge power of 40W is 24% higher than that at 30W, and the degradation rate at 50W also reaches 47%, but it is 5% lower than that at 40W.

Claims

1. A modified ZIF-8 material, characterized in that, The modified ZIF-8 material was prepared by plasma discharge modification. The plasma discharge power was 40W-60W and the discharge time was 10-60 seconds. The plasma discharge gas was ammonia. The gas flow rate of the discharge atmosphere was 30ccm-50ccm. The photodegradation reduction rate of hexavalent chromium in the modified ZIF-8 material was 45%, the equilibrium adsorption capacity of hexavalent chromium remained stable, and the specific surface area was not lower than that of the unmodified ZIF-8 material. The preparation method of the synthesized ZIF-8 material is as follows: Zinc nitrate hexahydrate and 2-methylimidazole are dissolved in deionized water, and then the resulting zinc nitrate solution and 2-methylimidazole solution are stirred and mixed until milky white. After centrifugation, the precipitate is washed several times with deionized water, centrifuged again and dried.

2. The modified ZIF-8 material according to claim 1, characterized in that, Includes one or more of the following (1)-(3): (1) The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:60~80; (2) Centrifuge at 5000~8000 rpm for 10~20 min; (3) The drying temperature is 60℃~100℃ and the drying time is 6h~12h.

3. The material according to claim 2, characterized in that, The molar ratio of zinc nitrate hexahydrate to 2-methylimidazole is 1:70; and / or, centrifuge at 6000 rpm for 15 min.

4. The application of the modified ZIF-8 material according to any one of claims 1-3 in the treatment of chromium-containing wastewater.

5. The application according to claim 4, characterized in that, The modified ZIF-8 material was added to chromium-containing wastewater and reacted in the dark for 6-12 hours, then placed under light conditions for more than 8 hours.

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