A cerium-based metal-organic framework material containing defect sites, preparation method thereof, and application thereof

Abstract

The present invention discloses a cerium-based metal-organic framework material containing defective sites, its preparation method, and application, and belongs to the field of phosphorus adsorption materials. The preparation method of the cerium-based metal-organic framework material containing defective sites of the present invention comprises the following steps: dissolving ammonium cerium nitrate and terephthalic acid in water and an organic solvent, respectively, and then mixing them, then mixing them with a monocarboxylic acid, and performing a solvothermal reaction to obtain the cerium-based metal-organic framework material containing defective sites. The preparation method of the present invention is simple and low-cost; the prepared cerium-based metal-organic framework material containing defective sites has the advantages of large phosphorus adsorption capacity, fast adsorption rate, high selectivity, and a wide pH range of application.

Description

Technical Field

[0001] The present invention relates to the field of phosphorus adsorption materials in water, and in particular to a cerium-based metal organic framework material containing defect sites, a preparation method thereof, and an application thereof. Background Art

[0002] Phosphorus is an essential element for the survival of living things and plays a vital role in ecosystems, particularly in the cellular metabolism of organisms. However, excessive phosphorus levels in water bodies can lead to eutrophication, which can result in reduced biodiversity, simplified community structure, and even ecosystem instability. Furthermore, phosphate minerals are non-renewable, unidirectional, and limited resources, and with the rapid development of industry and agriculture, they will become depleted in the future. Currently, methods for phosphorus recovery include chemical precipitation, biological treatment, and electrolysis, but these methods all have limitations, such as low removal rates, high equipment costs, and the generation of secondary pollution. Adsorption has attracted widespread attention due to its advantages, such as simple process, convenient management, and low installation and maintenance costs for treatment equipment.

[0003] In recent years, metal-organic frameworks (MOFs) have been widely used in gas storage, catalysis, and adsorption due to their large surface area, tunable pore size, and simple preparation methods. Defective MOFs, with their abundant exposed adsorption sites and tunable pore structure, can enhance the transport of phosphate molecules within the pores, allowing them to fully contact the active sites within the pores, thereby increasing the MOFs' adsorption capacity and rate of phosphate. Summary of the Invention

[0004] The present invention aims to provide a cerium-based metal organic framework material containing defect sites, a preparation method thereof, and an application thereof. The preparation method of the present invention is simple and low-cost; the prepared cerium-based metal organic framework material containing defect sites has the advantages of large adsorption capacity, fast adsorption rate, high selectivity, and a wide pH range of application for phosphorus.

[0005] The present invention first provides a preparation method of a cerium-based metal-organic framework material containing defect sites, comprising the following steps: dissolving ammonium cerium nitrate and terephthalic acid in water and an organic solvent respectively, mixing the mixture, then mixing the mixture with a monocarboxylic acid, and performing a solvothermal reaction to obtain the cerium-based metal-organic framework material containing defect sites.

[0006] In the above preparation method, the monocarboxylic acid is at least one of acetic acid, propionic acid, butyric acid and octanoic acid;

[0007] The molar ratio of the cerium ammonium nitrate to the monocarboxylic acid is 1:20 to 1:50; specifically 1:20, 1:30, 1:40 or 1:50;

[0008] The organic solvent is N-N dimethylformamide.

[0009] In the above preparation method, the temperature of the solvent thermal reaction is 80-120°C, specifically 100-110°C, more specifically 100°C; and the time is 6-48 h, specifically 12 h.

[0010] In the above preparation method, the solvent thermal reaction is carried out in a polytetrafluoroethylene reactor.

[0011] In the above preparation method, the molar ratio of the ammonium cerium nitrate to terephthalic acid is 1:0.5 to 1:3, specifically 1:1;

[0012] The mass volume ratio of the ammonium cerium nitrate and water is 0.3-0.8 g / mL, specifically 0.548 g / mL;

[0013] The mass volume ratio of the terephthalic acid to the organic solvent is 0.018-0.108 g / mL, specifically 0.036 g / mL.

[0014] In the above-mentioned preparation method, the method further comprises the step of mixing ammonium cerium nitrate, terephthalic acid and monocarboxylic acid and then dissolving them by ultrasonication;

[0015] Specifically, the ultrasonic time is 3 to 5 minutes.

[0016] In the above-mentioned preparation method, the method further comprises the steps of washing, activating and drying the product after the solvent thermal reaction;

[0017] Specifically, the washing can be carried out using N-dimethylformamide, ethanol and water in sequence;

[0018] The activating agent is methanol;

[0019] The activation temperature may be 60-80°C, specifically 60°C; the activation time may be 24-72 h, specifically 72 h;

[0020] The drying can be carried out in a vacuum oven;

[0021] The drying temperature may be 60-80° C., specifically 60° C.; the drying time may be 12-24 h, specifically 12 h.

[0022] The specific operation of the activation step is as follows: the washed material is added to methanol and heated for activation; the amount of methanol is not particularly limited and can be in excess.

[0023] The present invention further provides a cerium-based metal organic framework material containing defect sites prepared by the above preparation method.

[0024] The application of the above-mentioned cerium-based metal organic framework material containing defect sites to recover phosphorus in water also falls within the scope of protection of the present invention.

[0025] In the above application, the pH value of the water is 2-12; specifically, it can be 2-11; more specifically, it can be 3-10.

[0026] In the above application, the water contains Cl - 、NO3 - 、HCO3 - 、CO3 2- 、SO4 2- and at least one of FA.

[0027] More specifically, the water contains Cl - 、NO3 - 、SO4 2- or FA.

[0028] The present invention has the following beneficial effects:

[0029] (1) The preparation method of the present invention is simple and does not require high-end equipment, which can reduce the preparation cost; (2) Compared with existing adsorbents, the present invention has the advantages of large adsorption capacity, fast adsorption rate, high selectivity, and a wide pH range; (3) The present invention can synthesize materials with different pore structures; (4) The defective cerium-based metal organic framework material of the present invention is used for the adsorption of phosphorus in water, has strong anti-interference ability against coexisting anions, and can be regenerated and reused multiple times. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The Ce-MOF prepared in Example 1 of the present invention ( a Figure 2. The adsorption effect of monocarboxylic acid on phosphorus.

[0031] Figure 2 This is the XRD pattern of Ce-MOF (40 monocarboxylic acid) prepared in Example 1.

[0032] Figure 3 This is the SEM image of Ce-MOF (40 monocarboxylic acid) prepared in Example 1.

[0033] Figure 4 This is a diagram of cerium dissolution from Ce-MOF (40 monocarboxylic acid) in Example 2 of the present invention.

[0034] Figure 5 This is the adsorption isotherm of Ce-MOF (40 monocarboxylic acid) for phosphorus.

[0035] Figure 6 This is the adsorption kinetics diagram of phosphorus on Ce-MOF (40 monocarboxylic acid).

[0036] Figure 7 This is a diagram showing the adsorption effect of Ce-MOF (40-butyric acid) on phosphorus under the coexistence of different anions.

[0037] Figure 8 This is a diagram showing the adsorption effect of Ce-MOF (40 butyric acid) on phosphorus at different initial pH values.

[0038] Figure 9 Figure 3. Effect of adsorption-desorption cycles on phosphorus adsorption by Ce-MOF (40-butyric acid).

[0039] Figure 10 Thermogravimetric analysis (TGA) diagram of Ce-MOF (40 butyric acid).

[0040] Figure 11 For Ce-MOF ( a Butyric acid) pore size distribution diagram.

[0041] Figure 12 SEM-EDS image of Ce-MOF (40 butyric acid).

[0042] Figure 13 This is the SEM-EDS image of Ce-MOF (40 butyrate) after phosphorus adsorption.

[0043] Figure 14 This is a comparison chart of the adsorption effects of UiO-66 and Ce-MOF (40 butyric acid) on phosphorus. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below in conjunction with specific embodiments. The examples given are only for illustrating the present invention, not for limiting the scope of the present invention.

[0045] The experimental methods in the following examples are conventional methods unless otherwise specified.

[0046] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0047] Example 1, Ce-MOF ( a Preparation of monocarboxylic acid and its phosphorus adsorption performance

[0048] Step 1. Weighing the drugs: Weigh 2.74 g of ammonium cerium nitrate, 0.83 g of terephthalic acid, and monocarboxylic acids with different molar equivalents relative to ammonium cerium nitrate.

[0049] Step 2: Dissolve the drugs: Dissolve terephthalic acid in 23 mL of NN-dimethylformamide (DMF) in a beaker and sonicate for 3 minutes to obtain a solution. Dissolve ammonium cerium nitrate in 5 mL of deionized water in a beaker and sonicate for 3 minutes to obtain a solution. Combine the two solutions and then add varying molar equivalents of monocarboxylic acid.

[0050] Step 3, Solvothermal reaction: Transfer the above solution into a polytetrafluoroethylene reactor and react in an oven at 100°C for 12 h.

[0051] Step 4. Wash and dry the sample: After the reactor is cooled to room temperature, wash the material with DMF, ethanol and water three times, twice and once respectively. After adding methanol (15 g / mL), activate the washed material in a water bath for 72 h at 60°C. Dry the activated material in a vacuum oven for 12 h at 60°C. Grind the dried material in a mortar and store in a desiccator for later use.

[0052] Step 5, adsorption reaction: potassium dihydrogen phosphate (KH2PO4) was used to prepare a phosphorus solution with a concentration of 25 mg P / L for adsorption experiment, and 9 mg of the Ce-MOF prepared above ( a Monocarboxylic acid) in 30 mL of phosphorus solution, and then shaken in a shaker for 12 h (speed 160 rpm, temperature 25 °C).

[0053] Step 6. Determination of phosphorus concentration: A sample was taken from the solution after the above reaction using a disposable syringe, filtered through a 0.45 μm aqueous membrane, and the phosphorus concentration in the filtrate was determined using a Hach spectrophotometer.

[0054] The experiment was repeated three times and the results were averaged.

[0055] The results are as follows Figure 1 As shown in the figure, it can be seen that when 40 molar equivalents of monocarboxylic acid are added, the phosphorus adsorption capacity of the material reaches the maximum. When the amount of monocarboxylic acid added is further increased, the phosphorus adsorption capacity no longer increases.

[0056] Figure 2 This is the XRD pattern of Ce-MOF (40 monocarboxylic acid). From the XRD pattern, it can be seen that the prepared Ce-MOF (40 monocarboxylic acid) matches multiple characteristic peaks of the standard pattern (CCDC 1036904), and the characteristic peaks are sharp, indicating that the material is successfully synthesized and has high crystallinity.

[0057] Figure 3This is the SEM image of Ce-MOF (40 monocarboxylic acid). It can be seen from the figure that the structure of Ce-MOF (40 acetic acid) is a regular octahedral crystal with a size of about 5.5 μm; the size of Ce-MOF (40 propionic acid) is about 2.75 μm; the size of Ce-MOF (40 butyric acid) is about 2.43 μm; the size of Ce-MOF (40 octanoic acid) is about 3.01 μm; the regular octahedral crystals in the figure indicate that the material was successfully synthesized and has good crystallinity.

[0058] Example 2: Dissolution of cerium from Ce-MOF (40 monocarboxylic acid) in aqueous solutions with different pH values

[0059] Step 1: Use 0.1 M hydrochloric acid (HCl) and sodium hydroxide (NaOH) to adjust a series of aqueous solutions with different pH values, namely 2, 3, 5, 7, 9, and 11.

[0060] Step 2: Weigh a certain amount of Ce-MOF (40 monocarboxylic acid) at a dosage of 0.3 g / L and add it to the above-mentioned pH-adjusted aqueous solution. Oscillate at 160 rpm and 25°C for 12 h.

[0061] Step 3: Use a disposable syringe to take samples from the solution after the above reaction, filter through a 0.45 μm aqueous membrane, and determine the amount of cerium dissolved using an inductively coupled plasma-optical emission spectrometer (ICP-OES).

[0062] The experiment was repeated three times and the results were averaged.

[0063] Figure 4 The dissolution of cerium from Ce-MOF (40 monocarboxylic acid) in aqueous solutions with different pH values ​​is shown in Figure 2. Figure 4 It can be seen that cerium dissolves significantly at pH = 2, with the maximum value of Ce-MOF (40 octanoic acid) being 62 mg / L and the minimum value of Ce-MOF (40 acetic acid) being 18.7 mg / L. In the pH range of 4~11, the cerium dissolution is less than 0.3 mg / L. The results indicate that Ce-MOF (40 monocarboxylic acid) has low dissolution in a wide pH range and is suitable for phosphate adsorption.

[0064] Example 3. Adsorption Isotherm and Kinetics of Phosphorus on Ce-MOF (40 Monocarboxylic Acid)

[0065] (1) Adsorption isotherm

[0066] Step 1. Use potassium dihydrogen phosphate (KH2PO4) to prepare phosphorus solutions with concentrations of 5, 10, 15, 25, 40, 60, 80, 100, and 200 mg P / L.

[0067] Step 2: Ce-MOF (40 monocarboxylic acid) was added to the above phosphorus solutions with different concentrations at a dosage of 0.3 g / L and shaken at 25°C and 160 rpm for 12 h.

[0068] Step 3: Determination of phosphorus concentration is the same as step 6 in Example 1.

[0069] The experiment was repeated three times and the results were averaged.

[0070] (2) Adsorption kinetics

[0071] Step 1: Prepare 1000 mL of a 25 mg / L phosphorus solution using potassium dihydrogen phosphate (KH2PO4). Transfer 30 mL of this solution to a 100 mL conical flask and add 0.3 g / L of Ce-MOF (40 monocarboxylic acid). Place the conical flask in an oscillating oven for a specified period of time before sampling. Samples were taken at 1, 3, 5, 10, 20, 30, 45, 60, 90, 120, 180, 300, and 500 min, respectively. The oscillating oven parameters were set at 160 rpm and 25°C.

[0072] Step 2: Determination of phosphorus concentration is the same as step 6 in Example 1.

[0073] The experiment was repeated three times and the results were averaged.

[0074] Figure 5 and Figure 6 These are the adsorption isotherm and adsorption kinetics of Ce-MOF (40 monocarboxylic acid) for phosphorus. Figure 5 The fitting results show that the adsorption of phosphorus by Ce-MOF (40 monocarboxylic acid) is more consistent with the Langmuir model, among which the maximum adsorption capacity of Ce-MOF (40 butyric acid) is 117.28 mg P / g. Figure 6 The fitting results show that the adsorption of phosphorus by Ce-MOF (40 monocarboxylic acid) is more consistent with the pseudo-second-order kinetic model, among which the adsorption rate of Ce-MOF (40 butyric acid) is the fastest, and the adsorption capacity can reach more than 93% of the equilibrium adsorption capacity in about 45 minutes.

[0075] Example 4. Phosphorus adsorption performance of Ce-MOF (40-butyric acid) in the presence of different anions

[0076] Step 1: Use potassium dihydrogen phosphate (KH2PO4) to prepare a 25 mg P / L phosphorus solution containing anions Cl - , NO3 - ,HCO3 - , CO3 2- , SO4 2-and organic matter FA, which were prepared by KCl, NaNO3, NaHCO3, Na2CO3, Na2SO4 and FA, respectively, and the concentrations of coexisting ions were set to three gradients: 10 mg / L, 50 mg / L and 100 mg / L.

[0077] Step 2: Add Ce-MOF (40-butyric acid) to the above-mentioned phosphorus solution containing different anions at a dosage of 0.3 g / L and shake at 25°C and 160 rpm for 12 h.

[0078] Step 3: Determination of phosphorus concentration is the same as step 6 in Example 1.

[0079] The experiment was repeated three times and the results were averaged.

[0080] Effect of coexisting anions on phosphorus adsorption Figure 7 , it can be seen that in addition to HCO3 - and CO3 2- Other coexisting anions hardly interfere with the phosphorus adsorption of Ce-MOF (40-butyric acid), indicating that Ce-MOF (40-butyric acid) has a strong anti-interference ability.

[0081] Example 5. Phosphorus adsorption performance of Ce-MOF (40-butyric acid) at different pH values

[0082] Step 1: Use 0.1 M hydrochloric acid (HCl) and sodium hydroxide (NaOH) to adjust a series of 25 mg P / L phosphorus solutions (prepared with potassium dihydrogen phosphate) with different pH values ​​of 2, 3, 5, 7, 9, and 11.

[0083] Step 2: Add Ce-MOF (40-butyric acid) to the above-mentioned phosphorus solutions with different pH values ​​at a dosage of 0.3 g / L and shake at 160 rpm and 25°C for 12 h.

[0084] Step 3: Determination of phosphorus concentration is the same as step 6 in Example 1.

[0085] The experiment was repeated three times and the results were averaged.

[0086] See the results Figure 8 , it can be seen that the adsorption capacity of Ce-MOF (40 butyric acid) for phosphorus is very high in the pH range of 2-10, so the adsorbent has a wide pH applicability.

[0087] Example 6. Effect of adsorption-desorption cycles on the phosphorus adsorption performance of Ce-MOF (40-butyric acid)

[0088] Step 1: Add 0.05 g of Ce-MOF (40-butyric acid) to 1000 mL of a 2 mg / L phosphorus solution (prepared with potassium dihydrogen phosphate) and stir at room temperature using a magnetic stirrer. After 12 hours, remove 1 mL of the solution using a disposable syringe, filter through a 0.45 μm aqueous membrane, and measure the phosphorus concentration using a Hach spectrophotometer. Filter the remaining solution to obtain a solid material, which is then dried in a vacuum oven at 60°C for 12 hours.

[0089] Step 2: Place the dried material from Step 1 in 1000 mL of 1 M NaOH solution and shake at 160 rpm and 25°C for 12 hours to desorb phosphorus. The solution is then filtered to obtain a solid material. The resulting material is washed until neutral and dried in a vacuum oven at 60°C for 12 hours. The dried material is ground in a mortar and stored in a desiccator until ready for use. The desorbed material is then stirred at room temperature with a magnetic stirrer at a dosage of 0.05 g / L for phosphorus adsorption. A sample is taken from the reaction solution using a disposable syringe, filtered through a 0.45 μm aqueous membrane, and the phosphorus concentration in the filtrate is measured using a Hach spectrophotometer. The material is then desorbed again using 1 M NaOH solution, and the above steps are repeated.

[0090] The experiment was repeated three times and the results were averaged.

[0091] Figure 9 This figure shows the effect of the number of adsorption-desorption cycles on the adsorption of phosphorus by Ce-MOF (40-butyric acid). It can be seen from the figure that the ratio of the material to the initial adsorption amount decreases slightly with the increase of the number of adsorption and desorption cycles. The adsorption capacity is strong within five cycles and can remain stable.

[0092] Figure 10 This is a thermogravimetric analysis (TGA) graph of Ce-MOF (40-butyric acid). The blue portion represents water and solvent loss, and the gray portion represents ligand loss. It can be clearly seen that after normalization, the actual weight is 162%, which is lower than the theoretical weight of a defect-free MOF of 186%. After subtracting the 100% remaining as CeO2 after combustion from the theoretical weight of a defect-free MOF of 186%, the 86% ligand loss corresponds to six ligands, each accounting for 14.3% of the normalized mass. Since the ligand content of Ce-MOF (40-butyric acid) is 62%, the coordination number of Ce-MOF (40-butyric acid) is 4.3, indicating the presence of defects in Ce-MOF (40-butyric acid), and these defects exist in the form of missing ligands.

[0093] Figure 11 For Ce-MOF ( aThe pore size distribution diagram of the cerium-based metal-organic framework containing defect sites can be clearly seen from the pore size distribution diagram of the monocarboxylic acid. As the molar equivalent of butyric acid increases from 1:20 to 1:40, it can be clearly seen that the proportion of mesopores and macropores also increases. This proves that the pore structure of the defect-containing cerium-based metal-organic framework material can be regulated by adjusting the amount of monocarboxylic acid added.

[0094] Figure 12 、 13 These are the SEM-EDS images of Ce-MOF (40-butyric acid) before and after phosphorus adsorption. It can be clearly seen that the structure of the material is not destroyed after adsorption, phosphorus is successfully adsorbed on the material, and the structure and crystallinity of the material do not change much before and after adsorption, indicating that the material structure is stable.

[0095] Comparative Example

[0096] (1) Preparation of UiO-66

[0097] Step 1. Weigh the chemicals: 0.5825 g zirconium chloride (ZrCl4) and 0.415 g terephthalic acid.

[0098] Step 2: Dissolve the drugs: Dissolve terephthalic acid and zirconium chloride in 30 mL of NN dimethylformamide (DMF) using a beaker and ultrasonically dissolve for 3 minutes to obtain a solution.

[0099] Step 3, Solvothermal reaction: Transfer the above solution into a polytetrafluoroethylene reactor and react in an oven at 110°C for 24 h.

[0100] Step 4: Wash and dry the sample: After the reactor is cooled to room temperature, wash the material three times with DMF and ethanol respectively. Dry the washed material in a vacuum oven for 12 h at 80°C. Grind the dried material in a mortar and store in a desiccator for later use.

[0101] (2) Comparison of phosphorus adsorption performance of UiO-66 and Ce-MOF (40-butyric acid)

[0102] Step 1: Use potassium dihydrogen phosphate (KH2PO4) to prepare a phosphorus solution with a concentration of 25 mg P / L for adsorption experiments. Weigh 9 mg of the above-prepared UiO-66 and Ce-MOF (40 butyric acid) in 30 mL of phosphorus solution, and then place them in an shaking box for 12 h at a speed of 160 rpm and a temperature of 25°C.

[0103] Step 2: Determination of phosphorus concentration is the same as step 6 in Example 1.

[0104] The experiment was repeated three times and the results were averaged.

[0105] The results are as follows Figure 14As shown in the figure, it can be seen that the adsorption effect of Ce-MOF (40 butyric acid) on phosphorus is significantly higher than that of UiO-66, indicating that the experimentally prepared cerium-based metal organic framework containing defect sites has excellent adsorption performance.

Claims

1. A method for preparing a cerium-based metal-organic framework material containing defect sites, comprising the following steps: dissolving ammonium cerium nitrate and terephthalic acid in water and an organic solvent, respectively, and then mixing the mixture; then mixing the mixture with butyric acid; and performing a solvothermal reaction to obtain the cerium-based metal-organic framework material containing defect sites; The molar ratio of the ammonium cerium nitrate to butyric acid is 1:20 to 1:

50.

2. The preparation method according to claim 1, wherein: The molar ratio of the ceric ammonium nitrate to butyric acid is 1:40; The organic solvent is NN dimethylformamide.

3. The preparation method according to claim 1 or 2, characterized in that: The temperature of the solvent thermal reaction is 80-120° C., and the time is 6-48 hours.

4. The preparation method according to claim 1 or 2, characterized in that: The solvent thermal reaction is carried out in a polytetrafluoroethylene reactor.

5. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of the ammonium cerium nitrate to terephthalic acid is 1:0.5 to 1:3; The mass volume ratio of the ammonium cerium nitrate and water is 0.3 to 0.8 g / mL; The mass volume ratio of the terephthalic acid and the organic solvent is 0.018 to 0.108 g / mL.

6. The preparation method according to claim 1 or 2, characterized in that: The method further comprises the steps of washing, activating and drying the product after the solvent thermal reaction; The washing is carried out using N-dimethylformamide, ethanol and water in sequence; The activating agent used in the activation is methanol; The activation temperature is 60-80°C and the activation time is 24-72h; The drying is carried out in a vacuum oven; The drying temperature is 60-80° C. and the drying time is 12-24 hours.

7. A cerium-based metal-organic framework material containing defect sites prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the defective cerium-based metal organic framework material according to claim 7 for recovering phosphorus from water.

9. The use according to claim 8, characterized in that: The pH value of the water is 2-12.

10. The use according to claim 8 or 9, characterized in that: The water contains Cl - 、NO3 - 、HCO3 - 、CO3 2- and SO4 2- At least one of .

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