Nickel-doped metal organic framework material as well as preparation method and application thereof

Abstract

The invention relates to a nickel-doped metal organic framework material as well as a preparation method and application thereof, and belongs to the technical field of wastewater treatment. The metal organic framework is ZIF-8, the molar percentage of the nickel element in the material to the total amount of metal elements is x, and x is more than 0 and less than or equal to 15%. The nickel-doped metal organic framework material prepared by the invention has excellent catalytic activity and adsorption capacity, and can keep stable performance in a reutilization process. The prepared nickel-doped metal organic framework material can activate peroxymonosulfate to remove As (III) in a water body, has excellent degradation capacity and adsorption capacity, and can also be used in cooperation with MNBs to improve the As removal effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and in particular relates to a nickel-doped metal organic framework material and a preparation method and application thereof. Background Art

[0002] Arsenic (As) is a toxic metalloid element with a metallic luster. Its soluble compounds are highly toxic and pose a serious threat to humans and the environment. Arsenic exists mainly in inorganic forms in natural water bodies, including two oxidation states, As(III) and As(V). Among them, As(III) is the main form of arsenic in groundwater and surface water due to its higher mobility and toxicity. Studies have shown that As(III) is highly mobile in water bodies and is difficult to remove.

[0003] In existing arsenic treatment technologies, traditional adsorption methods usually require As(III) to be pre-oxidized to As(V), and then the arsenic is separated by adsorption. Its removal rate is limited by the oxidation reaction rate of As(III). At present, advanced oxidation techniques (AOPs) of persulfate systems are considered to be highly promising water pollution control technologies due to their strong oxidizing properties and wide applicability. Persulfate (PMS) can be used as an effective As(III) oxidant in water environments, but its oxidation efficiency is low and it takes a long time to completely oxidize As(III), which limits its effectiveness in practical applications. The oxidative activity of PMS depends on the generation of reactive oxygen species (ROSs), especially sulfate radicals (SO4 •⁻ ), but its direct oxidation effect on pollutants at room temperature is limited, and it needs to rely on efficient MOFs materials to achieve an efficient activation process.

[0004] The introduction of heterogeneous MOFs materials is considered to be an effective way to improve the activity of PMS. Transition metal-doped heterogeneous catalytic systems have wide applicability and economy. Among them, transition metals such as Ni and Co with variable valence and unoccupied three-dimensional orbitals have been proven to be the most effective PMS activators. Metal-organic framework (MOFs) materials have great application potential in the fields of adsorption and catalysis due to their high specific surface area, porosity and excellent chemical stability. ZIFs, as a typical class of MOFs materials, have a topological structure similar to zeolites. Among them, ZIF-8 (formed by zinc ions and imidazole ester ligands) is one of the most widely studied materials and has been applied in the field of arsenic removal. Studies have found that the research on Ni-doped metal framework materials in the field of PMS activation and degradation of pollutants has made certain progress, but its application in the efficient removal of As(Ⅲ) in water bodies still needs further exploration.

[0005] Based on this, the present invention proposes a nickel-doped metal-organic framework material (Ni-ZIF-8), and through its synergistic effect with persulfate (PMS), it realizes the efficient removal of As(Ⅲ) in the water environment. The Ni-ZIF-8 material can not only activate PMS to generate reactive oxygen species and rapidly oxidize As(Ⅲ) to As(V), but also has excellent capture ability, thus significantly improving the removal efficiency of As(Ⅲ) in water. This innovative integrated treatment technology has important application value in the field of water body arsenic pollution remediation. Summary of the Invention

[0006] In order to improve the removal effect of metal-organic framework materials on As(Ⅲ) in water bodies, the purpose of the present invention is to provide a nickel-doped metal-organic framework material Ni-ZIF-8, its preparation method and application. This material has excellent catalytic activity and adsorption capacity, and can maintain stable performance during the reuse process. Applying the nickel-doped metal-organic framework material prepared by the present invention to the efficient removal of As(Ⅲ) in the water environment has excellent degradation ability.

[0007] To achieve the above technical purposes and reach the above technical effects, the present invention is realized through the following technical solutions: A nickel-doped metal-organic framework material, wherein the metal-organic framework is ZIF-8, and the molar percentage of nickel element in the total amount of metal elements in the material is x, 0 < x ≤ 15%.

[0008] Preferably, x = 5%.

[0009] The present invention also provides a preparation method of the above nickel-doped metal-organic framework material, which includes the following steps: S1. Dissolve zinc nitrate hexahydrate and nickel nitrate hexahydrate in anhydrous methanol according to the molar ratio to obtain a mixed solution A; S2. Dissolve 2-methylimidazole in anhydrous methanol to obtain a mixed solution B; S3. Slowly pour the mixed solution A obtained in S1 into the mixed solution B obtained in S2, mix evenly to obtain a mixed solution C; S4. Stir the mixed solution C obtained in S3 at room temperature, collect the product by centrifugation, wash it thoroughly with anhydrous methanol, and vacuum dry to obtain the nickel-doped metal-organic framework material.

[0010] Preferably, in step S4, the stirring time is 8 - 12 h, and the stirring speed is 300 - 400 rpm.

[0011] Preferably, in step S4, the centrifuge speed is 8000 - 12000 rpm, and the centrifugation time is 4 - 6 min.

[0012] Preferably, in step S4, the drying is specifically: vacuum drying at 60 °C for 24 h.

[0013] The present invention also provides an application of the above nickel-doped metal-organic framework material in activating peroxymonosulfate to remove As(III) in water. This application includes the following steps: Add the above nickel-doped metal-organic framework material into the As(III) contaminated solution, then add PMS, react at room temperature, and perform solid-liquid separation to obtain arsenic-removed wastewater.

[0014] Preferably, the solid-liquid ratio of the nickel-doped metal-organic framework material to the As(III) solution is 0.02 - 0.15 g / L.

[0015] Micro-nano bubbles (MNBs) can rapidly supplement dissolved oxygen in water. Compared with ordinary aeration, micro-nano bubbles can efficiently supplement dissolved oxygen in water because of their higher mass transfer rate, realizing the change of the environment from anaerobic to oxygen-rich state, which helps the oxidation of pollutants. Micro-nano bubbles act as an O2 reservoir to achieve sustainable supply of molecular oxygen. Micro-nano bubbles have a longer existence time in water. The high gas density state inside makes the diffusion of gas inside slow and can last for a long time, which enables micro-nano bubbles to continuously provide molecular oxygen for MOFs materials and achieve long-term catalytic effects. Based on this, the present invention constructs a "MOFs / MNBs / PMS" synergistic system.

[0016] Furthermore, the application further includes: the As(III) contaminated solution contains MNBs.

[0017] Preferably, the MNBs are generated by a micro-nano bubble generator, with a flow rate of 0.8 - 1.2 m 3 / h and a time of 5 - 30 min.

[0018] The present invention has the following advantages compared with the prior art: (1) The nickel-doped metal-organic framework material provided by the present invention can greatly improve the activation efficiency of peroxymonosulfate PMS. The material is prepared by a solvent synthesis method at room temperature, with simple operation, energy saving and safety.

[0019] (2) The nickel-doped metal-organic framework material provided by the present invention has good adsorption effect while catalyzing degradation, and has high reusability and stability.

[0020] (3) By constructing a "MOFs / MNBs / PMS" synergistic system, the present invention significantly improves the removal efficiency of trivalent arsenic (As(III)). The coupling of micro-nano bubbles and PMS can enhance the oxidation ability of the system, which can not only effectively remove pollutants, but also avoid additional pollution to water bodies, reduce treatment costs, and can be reused repeatedly. The treatment effect is sustainable, providing a new green and clean method for effectively treating pollutants. This method of combining MOFs materials and MNBs to improve the oxidation ability of the PMS system provides new ideas for future advanced oxidation research. Description of the Drawings

[0021] Figure 1 It is a graph showing the removal ability of metal-organic framework materials with different Ni doping amounts in Example 1 of the present invention for As(III) in solution; Figure 2 It is a graph showing the removal ability of different dosages of 5% Ni-ZIF-8 materials in Example 2 of the present invention for As(III) in solution; Figure 3 It is a graph showing the removal ability of different dosages of PMS in Example 3 of the present invention for As(III) in solution; Figure 4 It is a graph showing the removal ability of different initial pH values in Example 4 of the present invention for As(III) in solution; Figure 5 It is a graph showing the removal ability of different coexisting anions in water in Example 5 of the present invention for As(III) in solution; Figure 6 It is a cyclic experiment graph of the 5% Ni-ZIF-8 / PMS system for removing As(III) in Example 6 of the present invention; Figure 7 It is a graph showing the removal ability of different reaction systems for As in solution in Example 6 of the present invention; Figure 8 It is a graph showing the removal ability of different initial pH for As(III) in solution in Example 7 of the present invention; Figure 9 It is a graph showing the removal ability of different PMS addition amounts for As(III) in solution in Example 8 of the present invention; Figure 10 It is a graph showing the removal ability of different MNBs preparation times for As(III) in solution in Example 9 of the present invention. Detailed Embodiments

[0022] The technical solutions of the present invention will be further explained below in conjunction with specific embodiments.

[0023] Example 1: A preparation method of a nickel-doped metal-organic framework material, the preparation includes the following steps: (1) Dissolve zinc nitrate hexahydrate and nickel nitrate hexahydrate in anhydrous methanol to obtain a mixed solution A; dissolve 2-methylimidazole in anhydrous methanol to obtain a mixed solution B; slowly pour the mixed solution A into the mixed solution B and mix evenly to obtain a mixed solution C; (2) Stir the mixed solution C at room temperature, collect the product by centrifugation, wash it thoroughly with anhydrous methanol, and dry it under vacuum to obtain a nickel-doped metal-organic framework composite material.

[0024] In the mixed solution A, the molar concentration of the metal elements (Zn + Ni) in the obtained solution is maintained at 0.1 M, and the molar percentage of Ni element in the metal elements is x% (in this experiment, x = 0, 5, 10, 15). Test the removal ability of metal-organic framework materials with different Ni doping amounts for As(III) in the solution.

[0025] The results are as Figure 1 shown. In the x% Ni-ZIF-8 / PMS system with an initial arsenic concentration of 1 mg / L within 30 min (C catalyst = 0.12 g·L -1 , C PMS = 0.03 mM), 0% Ni-ZIF-8 without Ni doping can only remove 85.8% of arsenic. After Ni doping, the removal efficiency of x% Ni-ZIF-8 for As(III) is significantly improved. Among them, 5% Ni-ZIF-8 has the strongest arsenic removal efficiency, and it can almost completely remove As(III) in the water environment within 10 min.

[0026] Example 2: Prepare an As(III) solution with a concentration of 1 mg / L using deionized water, add 5% Ni-ZIF-8 materials at dosages of 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, and 0.15 g / L respectively, and then add 0.03 mM PMS. Test the removal ability of different dosages of 5% Ni-ZIF-8 materials for As(III) in the solution.

[0027] The results are as Figure 2 shown. When the dosage of 5% Ni-ZIF-8 increases (0.02 g·L -1 -0.12 g·L -1 ), the arsenic removal efficiency in the system also gradually increases. Increasing the concentration of MOFs materials can provide more active sites, thereby promoting the activation of PMS to improve the removal efficiency of As(III). However, when the dosage increases to 0.15 g·L -1 , the arsenic removal rate of the 5% Ni-ZIF-8 / PMS system decreases. This may be due to the aggregation of the adsorbent caused by the increase in the adsorbent dosage, thus reducing the arsenic adsorption amount.

[0028] Example 3: An As(III) solution with a concentration of 1 mg / L was prepared using deionized water. 5% Ni-ZIF-8 material was added at a solid-liquid ratio of 0.12 g / L, and then 0.01, 0.03, 0.05, 0.07, 0.09, and 0.1 mM PMS were added respectively to test the removal ability of different PMS dosages on As(III) in the solution.

[0029] The results are as Figure 3 shown. When the dosage of PMS was not excessive ( C PMS = 0.03 mM), 5% Ni-ZIF-8 could completely remove As(III) within 30 min. However, the arsenic removal efficiency did not increase with the continuous increase of PMS concentration (0.03 mM - 0.1 mM). This may be because a large number of free radicals are generated in the MOFs material by high-concentration PMS, and the excess free radicals generated by excessive PMS produce a self-quenching effect, resulting in a slowdown of the As(III) oxidation rate and thus a decrease in the arsenic removal efficiency. Generally speaking, 5% Ni-ZIF-8 coupled with PMS can effectively promote the removal of As(III).

[0030] Example 4: Using 1 M HCl or NaOH solution, the initial pH value of an As(III) solution with a concentration of 1 mg / L prepared using deionized water was adjusted to 3, 5, 7, 9, 11, and then 5% Ni-ZIF-8 material and 0.03 mM PMS were added at a solid-liquid ratio of 0.12 g·L -1 to test the removal ability of different initial pH values on As(III) in the solution.

[0031] The results are as Figure 4 shown. When pH = 3, the arsenic removal rate was only 80.2% within 30 min. The removal rate was the fastest at pH = 5, and arsenic could be almost completely removed within 8 min. It can be seen that 5% Ni-ZIF-8 has a very strong removal effect on As(Ⅲ) under weak acid and neutral conditions.

[0032] Example 5: An As(III) solution with a concentration of 1 mg / L was prepared using deionized water, and 100, 200, 400 mg / L of Cl - , SO4 2- , and CO3 2- were added respectively, and a solution without coexisting ions was used as a control; then 5% Ni-ZIF-8 material and 0.03 mM PMS were added at a solid-liquid ratio of 0.12 g·L -1 to test the influence of the coexistence of anions in water on the removal of As(III) in the solution.

[0033] The results are as Figure 5 shown. The inhibitory effects of Cl⁻ and SO4²⁻ on the As removal by 5% Ni-ZIF-8 are weak. When the concentrations of Cl⁻ and SO4²⁻ increase from 0 to 400 mg / L, the As removal rate changes little; CO3²⁻ significantly inhibits the removal of As(III) by 5% Ni-ZIF-8 / PMS. This may be because CO3²⁻ has a similar charge density and tetrahedral structure to AsO4³⁻, and CO3²⁻ may preferentially occupy the metal active sites (such as Zn²⁺) of ZIF-8. In addition, CO3²⁻ also forms complexes with arsenate such as As·CO3 + , As(CO3)²⁻, etc., thus inhibiting the removal of arsenic. Generally speaking, the present invention has good anti-interference ability for the vast majority of anions, and the nickel-doped metal-organic framework material has the potential to be applied to complex water matrices.

[0034] Example 6: A 1 mg / L As(III) solution was prepared with deionized water, and 5% Ni-ZIF-8 material and 0.03 mM PMS were added at a solid-liquid ratio of 0.12 g·L -1 . The reusability and stability of 5% Ni-ZIF-8 were tested.

[0035] Figure 6 Figure for the cyclic experiment of As(III) removal by the 5% Ni-ZIF-8 / PMS system. A total of four cycles were carried out. After each cycle, the arsenic-loaded 5% Ni-ZIF-8 was dispersed in 1 M NaOH solution to desorb arsenic. Subsequently, after shaking for 60 minutes, it was filtered and washed until the supernatant was close to neutral, and then dried overnight in vacuum. Finally, the regenerated 5% Ni-ZIF-8 was used for the next adsorption test. As Figure 6 shown, after four cyclic experiments, the removal efficiency of As(III) remained above 87%, indicating that 5% Ni-ZIF-8 has good reusability.

[0036] Example 7: Solutions of As(III) with a concentration of 1 mg / L were prepared using water containing MNBs and ordinary ultrapure water respectively. Then, 5% Ni-ZIF-8 and 0.03 mM PMS were added at a solid-liquid ratio of 60 mg / L. The reaction system was 100 mL. The experiment was carried out using a magnetic stirrer at 298 K and 350 rpm for 30 minutes. Samples were taken out using a 0.45 μm water pore filter membrane and added to 20 μL of 1 M sodium thiosulfate (Na2S2O3) at t = 0, 1, 2, 4, 6, 8, 10, 15, 20, and 30 minutes as a quenching agent to prevent the reaction from continuing. The experimental group without PMS was set as the control group to evaluate the intrinsic properties of the material. The concentration of As in the treated solution was measured using inductively coupled plasma mass spectrometry to obtain the removal ability of different reaction systems for As in the solution.

[0037] The experiment was carried out in a 100 mL conical flask, and the total volume of the reaction system was 100 mL. The experiment was carried out using a magnetic stirrer at 298 K and 350 rpm for 30 minutes. Samples were taken out using a 0.45 μm water pore filter membrane and added to 20 μL of 1 M sodium thiosulfate (Na2S2O3) at t = 0, 1, 2, 4, 6, 8, 10, 15, 20, and 30 minutes as a quenching agent to prevent the reaction from continuing. The concentration of As in the treated solution was measured using inductively coupled plasma mass spectrometry.

[0038] Water containing MNBs was prepared by a micro-nano bubble generator (Shanghai Jinxiang Environmental Technology Co., Ltd., model JXWNP-AL01S, power: 550), with a flow rate of 0.8 - 1.2 m 3 / h and a time of 5 - 30 min.

[0039] The results are as Figure 7 shown. The MOFs / MNBs / PMS system achieved 100% removal of arsenic within 10 min. The removal efficiency of arsenic by adding 5% Ni-ZIF-8 alone was only 15% within 10 min, and even within 30 min, it only led to 25% arsenic adsorption. As a control, the removal efficiency of arsenic in the MOFs / MNBs system was not effectively improved, but the removal efficiency of arsenic in the MOFs / PMS system was significantly enhanced. Generally speaking, the MOFs / MNBs / PMS system has a significant adsorption and removal effect on arsenic in water, and MNBs play an important role in it.

[0040] Example 8: Using a 1 mol / L sodium hydroxide solution, the initial pH of 100 ml of a 1 mg / L As(III) solution prepared with MNBs-containing water was adjusted to 3, 5, 7, 9, and 11. Then, 5% Ni-ZIF-8 and 0.03 mM PMS were added at a solid-liquid ratio of 60 mg / L to test the As removal ability in the solution.

[0041] The results are as Figure 8 shown. When pH = 11, the arsenic removal rate was only 55% within 30 min. The removal rate was the fastest at pH = 3, and arsenic could be almost completely removed within 8 min. Although the removal rate of arsenic in the wastewater by the MNBs / PMS / MOFs system showed certain fluctuations under different pH conditions, 5% Ni-ZIF-8 had a very strong removal effect on As(III) at pH < 11.

[0042] Example 9: A 1 mg / L As(III) solution was prepared with MNBs-containing water, and 0.01, 0.03, 0.05, 0.07, 0.09, and 0.1 mM PMS were added respectively. Then, 5% Ni-ZIF-8 was added at a solid-liquid ratio of 60 mg / L to test the As removal ability in the solution.

[0043] The results are as Figure 9 shown. At a PMS dosage of 0.03 mM, the As removal rate reached 100% within 8 min. This is because the increase in PMS concentration accelerates the generation of ROS, promotes the oxidation of As, and thus removes As through adsorption. At high PMS dosages, this effect is no longer obvious, and the increase in the arsenic removal rate is relatively small, which may be because the material has reached the maximum oxidation adsorption removal rate.

[0044] Example 10: MNBs-containing water was prepared by operating the micro-nano bubble generator for 5, 15, and 30 minutes. Then, 5% Ni-ZIF-8 and 0.03 mM PMS were added at a solid-liquid ratio of 60 mg / L to test the As removal ability in the solution.

[0045] The results are as Figure 10 shown. When the preparation time was 15 or 30 minutes, the As removal rate in the system was significantly higher than that at only 5 minutes. There was no significant difference in the As removal rate between the 15- and 30-minute preparation times, which may be because the MNBs were saturated.

[0046] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention shall be covered within the scope of the claims of the present invention as long as they do not depart from the principles and scope of the technical solutions of the present invention.

Claims

1. A nickel-doped metal organic framework material, characterized in that: The metal organic framework is ZIF-8, and the molar percentage of nickel element in the material to the total amount of metal elements is x, 0<x≤15%.

2. The method for preparing a nickel-doped metal organic framework material according to claim 1, characterized in that: x=5%。 3. The method for preparing the nickel-doped metal organic framework material according to claim 1, characterized in that: The following steps are involved: S1. Dissolving zinc nitrate hexahydrate and nickel nitrate hexahydrate in anhydrous methanol in a molar ratio to obtain a mixed solution A; S2, dissolving 2-methylimidazole in anhydrous methanol to obtain a mixed solution B; S3, slowly pour the mixed solution A obtained in S1 into the mixed solution B obtained in S2, mix them evenly, and obtain a mixed solution C; S4. Stir the mixed solution C obtained in S3 at room temperature, collect the product by centrifugation, wash it thoroughly with anhydrous methanol, and dry it in vacuum to obtain a nickel-doped metal organic framework material.

4. The preparation method according to claim 3, characterized in that: In step S4, the stirring time is 8-12 h, and the stirring speed is 300-400 rpm.

5. The method according to claim 3, characterized in that: In step S4, the centrifuge speed is 8000-12000 rpm, and the centrifugation time is 4-6 min.

6. The method according to claim 3, characterized in that: In step S4, the drying is specifically: vacuum drying at 60° C. for 24 h.

7. Use of the nickel-doped metal organic framework material according to any one of claims 1 to 2 in activating peroxymonosulfate to remove As(III) from water, characterized in that: The application comprises the following steps: The nickel-doped metal organic framework material is added to the As(III) contaminated liquid, and then PMS is added to react at room temperature, and the arsenic-removed wastewater is obtained by solid-liquid separation.

8. The use according to claim 7, characterized in that: The solid-to-liquid ratio of the nickel-doped metal organic framework material to the As(III) solution is 0.02-0.15 g / L.

9. The use according to claim 7, characterized in that: Also includes: The As(III)-contaminated solution contains MNBs.

10. The use according to claim 9, characterized in that: The MNBs are generated by a micro-nano bubble generator with a flow rate of 0.8-1.2 m 3 / h, time is 5-30min.

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