A high-stability cerium-aluminum bimetallic MOF, a preparation method thereof and application thereof in phosphorus-containing wastewater

Abstract

This invention relates to the field of water treatment and adsorption materials, and particularly to a highly stable cerium-aluminum bimetallic MOF, its preparation method, and its application in phosphorus-containing wastewater. The preparation method of this highly stable cerium-aluminum bimetallic MOF includes the following steps: mixing cerium salt, aluminum salt, organic ligand, and solvent, reacting the mixture, cooling and separating the resulting product after the reaction to obtain a solid product; and then freeze-drying the solid product under vacuum to obtain the highly stable cerium-aluminum bimetallic MOF. This invention significantly enhances the stability of the MOF by introducing cerium and aluminum to construct dual active centers, and achieves high adsorption capacity and rapid adsorption kinetics by using 2-aminoterephthalic acid containing an amino functional group as the organic ligand.

Description

Technical Field

[0001] This invention relates to the field of water treatment and adsorption materials, and particularly to a highly stable cerium-aluminum bimetallic MOF, its preparation method, and its application in phosphorus-containing wastewater. Background Technology

[0002] Phosphorus is a key limiting element causing eutrophication in water bodies. Excessive phosphorus discharge leads to explosive algal blooms, depletion of dissolved oxygen, and severe disruption of aquatic ecological balance. With industrial, agricultural, and urban development, the discharge of phosphorus-containing wastewater continues to increase, posing a serious threat to water environmental safety. To control eutrophication, strict phosphorus discharge standards have been established (e.g., the Class A standard in the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" GB 18918-2002 stipulates total phosphorus ≤ 0.5 mg / L). Therefore, developing efficient and economical deep phosphorus removal technologies is crucial.

[0003] Currently, common phosphorus removal technologies include biological methods, chemical precipitation, ion exchange, and adsorption. Biological methods have long treatment cycles and are unstable in removing low concentrations of phosphorus; chemical precipitation produces large amounts of sludge and may introduce secondary pollution; ion exchange is costly and the resin is easily contaminated. In contrast, adsorption is widely studied due to its operational flexibility, high efficiency, and potential applicability to resource recovery. The core of adsorption technology lies in the performance of the adsorbent, with metal-based materials being a key research focus due to their specific and strong affinity for phosphate ions.

[0004] Metal-organic frameworks (MOFs), as a novel class of porous crystalline materials, have shown great promise in the field of adsorption due to their ultra-high specific surface area, tunable pore structure, and abundant metal sites. Constructing bimetallic MOFs to utilize the synergistic effect between metals can further enhance their adsorption performance for specific pollutants. However, existing MOF adsorbents still face significant challenges in practical water treatment applications: First, many high-performance MOFs (such as cerium-based MOFs) exhibit insufficient structural stability in the aqueous phase, especially under the acid / alkali conditions required for the adsorption-desorption cycle, making them prone to hydrolysis or collapse; second, nano- or micron-sized powder materials face difficulties in solid-liquid separation and low recovery rates in practical operations, limiting their large-scale application; third, in complex wastewater, competing ions (such as Cl-) coexist... - SO4 2- F - (etc.) can significantly interfere with the selective adsorption efficiency of adsorbents for phosphates; finally, most studies focus on batch static adsorption, lacking system performance evaluation and material design for continuous flow dynamic adsorption processes, which is the key to engineering applications.

[0005] Therefore, developing an easily recyclable bimetallic MOF adsorbent that combines high adsorption capacity, excellent structural stability, good resistance to ion interference, and suitability for dynamic adsorption processes is a crucial technical problem that needs to be solved to achieve efficient removal and resource recovery of phosphates. Summary of the Invention

[0006] This invention provides a highly stable cerium-aluminum bimetallic MOF, its preparation method, and its application in phosphorus-containing wastewater, aiming to solve the problems of limited adsorption capacity, low selectivity, and poor performance of existing adsorbents in complex aquatic environments.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for preparing a highly stable cerium-aluminum bimetallic MOF, comprising the following steps: Cerium salt, aluminum salt, organic ligand and solvent are mixed and reacted. After the reaction is completed, the product is cooled and separated into solid and liquid components to obtain a solid product. The solid product was freeze-dried under vacuum to obtain a highly stable cerium-aluminum bimetallic MOF.

[0008] Preferably, the molar ratio of cerium ions in the cerium salt to aluminum ions in the aluminum salt is (1~3):(3~1).

[0009] Preferably, the cerium salt comprises cerium nitrate.

[0010] Preferably, the aluminum salt includes aluminum chloride.

[0011] Preferably, the organic ligand comprises 2-aminoterephthalic acid.

[0012] Preferably, the solvent includes N,N-dimethylformamide.

[0013] Preferably, the mass ratio of the cerium salt to the organic ligand is (0.1~0.5):(0.7~0.9).

[0014] Preferably, the ratio of the amount of cerium salt to the amount of solvent is (0.1~0.5) g : (50~80) mL.

[0015] Preferably, the reaction conditions are: heating rate of 1~2℃ / min, final temperature of 130~180℃, and holding time of 24~28h.

[0016] Preferably, the freeze-drying temperature is -50~0℃, and the freeze-drying time is 12~24h.

[0017] A second aspect of the present invention also provides a highly stable cerium-aluminum bimetallic MOF prepared by the above-mentioned method.

[0018] A third aspect of the present invention also provides the application of the above-mentioned highly stable cerium-aluminum bimetallic MOF in phosphorus-containing wastewater.

[0019] Preferably, the application includes: Highly stable cerium-aluminum bimetallic MOFs were dispersed in phosphorus-containing wastewater for adsorption. After adsorption, solid-liquid separation was performed, and the phosphorus concentration in the water was measured.

[0020] Preferably, the phosphorus-containing wastewater includes phosphate-containing wastewater.

[0021] Preferably, the initial phosphate concentration in the phosphate-containing wastewater is 10-300 mg P / L, and the pH is 1-12.

[0022] Preferably, the dosage of the highly stable cerium-aluminum bimetallic MOF is 0.1~2 g / L.

[0023] Preferably, the adsorption temperature is 15~35℃, and the adsorption equilibrium time is 30~300min.

[0024] Compared with the prior art, the present invention has the following beneficial effects: This invention significantly enhances the stability of a bimetallic MOF by introducing cerium (Ce) and aluminum (Al) to construct a dual active center. Furthermore, it utilizes 2-aminoterephthalic acid, containing an amino functional group, as an organic ligand, achieving high adsorption capacity (e.g., over 300 mg P / g when Ce:Al = 1:1) and rapid adsorption kinetics. The resulting bimetallic MOF adsorbent exhibits excellent chemical stability, functioning effectively across a wide pH range (pH = 1-12) and demonstrating strong environmental adaptability. This material exhibits high selectivity for phosphates, maintaining excellent phosphorus removal performance even in water bodies with high concentrations of competing cations and anions, and demonstrates strong resistance to interference. The material is suitable not only for batch static adsorption but also performs exceptionally well in dynamic packed column experiments, exhibiting high throughput and a late breakthrough point. It provides a highly efficient, stable, and promising novel adsorbent solution for addressing the challenge of deep phosphorus removal in practical wastewater. Moreover, the preparation method is simple, the conditions are mild, and the raw materials used are all commercially available products, facilitating large-scale preparation. Attached Figure Description

[0025] The above and other objects, features, and advantages of the invention will be apparent from the following description of preferred embodiments illustrating the gist of the invention and its use, and the accompanying drawings, in which: Figure 1The images show the SEM and EDS elemental spectra of Ce-BDC-NH2 in Example 1 and Al / Ce-BDC-NH2 in Example 3; where (a) is the SEM image of Ce-BDC-NH2, (b) is a magnified view of (a), (c) is the SEM image of Al / Ce-BDC-NH2, (d) is a magnified view of (c), (e)~(i) are the EDS elemental spectra of Ce-BDC-NH2, and (j)~(O) are the EDS elemental spectra of Al / Ce-BDC-NH2.

[0026] Figure 2 The XRD patterns are for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7.

[0027] Figure 3 The FTIR spectra are for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7.

[0028] Figure 4 The BET and pore size distribution diagrams are shown for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7; where (a) is the BET and (b) is the pore size distribution diagram.

[0029] Figure 5 The figures show the adsorption performance of the metal MOFs in Examples 1-7; where (a) is the adsorption efficiency of the metal MOFs in Examples 1-5, (b) is the Langmuir and Freundlich model fitting diagrams for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7, (c) is the kinetic curve fitting diagram for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7, and (d) is the internal diffusion model fitting diagram for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7.

[0030] Figure 6This diagram illustrates the effect of the initial pH value of the solution on the adsorption of phosphate by Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7; where (a) represents Ce-BDC-NH2, (b) represents Al / Ce-BDC-NH2, (c) represents Fe / Ce-BDC-NH2, and (d) represents Ni / Ce-BDC-NH2.

[0031] Figure 7 Common coexisting ions (Cl) - NO3 - SO4 2- , F - Fe 3+ Al 3+ Ca 2+ The effect of different concentrations on the adsorption of phosphate by Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7 is shown in the figure. Among them, (a) is Ce-BDC-NH2, (b) is Al / Ce-BDC-NH2, (c) is Fe / Ce-BDC-NH2, and (d) is Ni / Ce-BDC-NH2.

[0032] Figure 8 The stability tests of Ce-BDC-NH2 in Example 1 and Al / Ce-BDC-NH2 in Example 3 are shown below. (a) shows the XRD patterns of Ce-BDC-NH2 in Example 1 after soaking in solutions with different pH values. (b) shows the XRD patterns of Al / Ce-BDC-NH2 in Example 3 after soaking in solutions with different pH values. (c) shows the cyclic flow chart of phosphate adsorption in Al / Ce-BDC-NH2 in Example 3. (d) shows the results of five cycles of phosphate adsorption in Al / Ce-BDC-NH2 in Example 3.

[0033] Figure 9 The images show the FT-IR and high-resolution XPS spectra of Al / Ce-BDC-NH2 before and after phosphate adsorption in Example 3; where (a) is the total XPS spectrum, (b) is the FT-IR spectrum, (c) is P 2p, (d) is O 1s, (e) is N 1s, (f) is Ce 3d, and (g) is Al 2p.

[0034] Figure 10 This is a schematic diagram of the mechanism of phosphate adsorption by Al / Ce-BDC-NH2 in this invention. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1 0.434 g of cerium nitrate hexahydrate, 0.725 g of 2-aminoterephthalic acid and 60 mL of N,N-dimethylformamide were mixed and sonicated at room temperature (25°C) for 5 min to obtain a homogeneous and transparent mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in an oven and heated to 180°C at a rate of 1.5°C / min, and kept at that temperature for a solvothermal reaction for 24 hours. After the reaction is complete, the reaction vessel is allowed to cool naturally to room temperature. The reaction product is then centrifuged (8000 rpm, 5 min), the supernatant is discarded, and the solid product is washed three times with N,N-dimethylformamide and anhydrous ethanol in sequence to remove unreacted substances. The washed solid product was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for 24 hours to obtain a highly stable cerium metal MOF, denoted as Ce-BDC-NH2.

[0037] Example 2 0.326 g of cerium nitrate hexahydrate, aluminum chloride hexahydrate (molar ratio of aluminum chloride hexahydrate to cerium nitrate hexahydrate is 1:3), 0.725 g of 2-aminoterephthalic acid and 60 mL of N,N-dimethylformamide were mixed and ultrasonically treated at room temperature (25 °C) for 5 min to obtain a homogeneous and transparent mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in an oven and heated to 180°C at a rate of 1.5°C / min, and kept at that temperature for a solvothermal reaction for 24 hours. After the reaction is complete, the reaction vessel is allowed to cool naturally to room temperature. The reaction product is then centrifuged (8000 rpm, 5 min), the supernatant is discarded, and the solid product is washed three times with N,N-dimethylformamide and anhydrous ethanol in sequence to remove unreacted substances. The washed solid product was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for 24 hours to obtain a highly stable cerium-aluminum bimetallic MOF.

[0038] Example 3 0.217 g of cerium nitrate hexahydrate, aluminum chloride hexahydrate (molar ratio of aluminum chloride hexahydrate to cerium nitrate hexahydrate is 1:1), 0.725 g of 2-aminoterephthalic acid and 60 mL of N,N-dimethylformamide were mixed and ultrasonically treated at room temperature (25 °C) for 5 min to obtain a homogeneous and transparent mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in an oven and heated to 180°C at a rate of 1.5°C / min, and kept at that temperature for a solvothermal reaction for 24 hours. After the reaction is complete, the reaction vessel is allowed to cool naturally to room temperature. The reaction product is then centrifuged (8000 rpm, 5 min), the supernatant is discarded, and the solid product is washed three times with N,N-dimethylformamide and anhydrous ethanol in sequence to remove unreacted substances. The washed solid product was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for 24 hours to obtain a highly stable cerium-aluminum bimetallic MOF, denoted as Al / Ce-BDC-NH2.

[0039] Example 4 0.109 g of cerium nitrate hexahydrate, aluminum chloride hexahydrate (molar ratio of aluminum chloride hexahydrate to cerium nitrate hexahydrate is 3:1), 0.725 g of 2-aminoterephthalic acid and 60 mL of N,N-dimethylformamide were mixed and ultrasonically treated at room temperature (25 °C) for 5 min to obtain a homogeneous and transparent mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in an oven and heated to 180°C at a rate of 1.5°C / min, and kept at that temperature for a solvothermal reaction for 24 hours. After the reaction is complete, the reaction vessel is allowed to cool naturally to room temperature. The reaction product is then centrifuged (8000 rpm, 5 min), the supernatant is discarded, and the solid product is washed three times with N,N-dimethylformamide and anhydrous ethanol in sequence to remove unreacted substances. The washed solid product was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for 24 hours to obtain a highly stable cerium-aluminum bimetallic MOF.

[0040] Example 5 0.241 g aluminum chloride hexahydrate, 0.725 g 2-aminoterephthalic acid and 60 mL N,N-dimethylformamide were mixed and ultrasonicated at room temperature (25 °C) for 5 min to obtain a homogeneous and transparent mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in an oven and heated to 180°C at a rate of 1.5°C / min, and kept at that temperature for a solvothermal reaction for 24 hours. After the reaction is complete, the reaction vessel is allowed to cool naturally to room temperature. The reaction product is then centrifuged (8000 rpm, 5 min), the supernatant is discarded, and the solid product is washed three times with N,N-dimethylformamide and anhydrous ethanol in sequence to remove unreacted substances. The washed solid product was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for 24 hours to obtain a highly stable aluminum metal MOF.

[0041] Example 6 0.217 g cerium nitrate hexahydrate, 0.135 g ferric chloride hexahydrate, 0.725 g 2-aminoterephthalic acid and 60 mL N,N-dimethylformamide were mixed and ultrasonically treated at room temperature (25 °C) for 5 min to obtain a homogeneous and transparent mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in an oven and heated to 180°C at a rate of 1.5°C / min, and kept at that temperature for a solvothermal reaction for 24 hours. After the reaction is complete, the reaction vessel is allowed to cool naturally to room temperature. The reaction product is then centrifuged (8000 rpm, 5 min), the supernatant is discarded, and the solid product is washed three times with N,N-dimethylformamide and anhydrous ethanol in sequence to remove unreacted substances. The washed solid product was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for 24 hours to obtain a highly stable cerium-iron bimetallic MOF, denoted as Fe / Ce-BDC-NH2.

[0042] Example 7 0.217 g cerium nitrate hexahydrate, 0.145 g nickel nitrate hexahydrate, 0.725 g 2-aminoterephthalic acid and 60 mL N,N-dimethylformamide were mixed and ultrasonicated at room temperature (25 °C) for 5 min to obtain a homogeneous and transparent mixed solution. The mixed solution was transferred to a polytetrafluoroethylene-lined high-pressure reactor and sealed. The reactor was then placed in an oven and heated to 180°C at a rate of 1.5°C / min, and kept at that temperature for a solvothermal reaction for 24 hours. After the reaction is complete, the reaction vessel is allowed to cool naturally to room temperature. The reaction product is then centrifuged (8000 rpm, 5 min), the supernatant is discarded, and the solid product is washed three times with N,N-dimethylformamide and anhydrous ethanol in sequence to remove unreacted substances. The washed solid product was transferred to a freeze dryer and freeze-dried under vacuum at -40°C for 24 hours to obtain a highly stable cerium-nickel bimetallic MOF, denoted as Ni / Ce-BDC-NH2.

[0043] Characterization and performance testing 1. Characterization Figure 1 The images show the SEM and EDS elemental spectra of Ce-BDC-NH2 in Example 1 and Al / Ce-BDC-NH2 in Example 3. In the images, (a) is the SEM image of Ce-BDC-NH2, (b) is a magnified view of (a), (c) is the SEM image of Al / Ce-BDC-NH2, (d) is a magnified view of (c), (e) to (i) are the EDS elemental spectra of Ce-BDC-NH2, and (j) to (O) are the EDS elemental spectra of Al / Ce-BDC-NH2.

[0044] Depend on Figure 1 It can be seen that the sample of Example 1 has a microsphere morphology, and the microspheres are composed of smooth bipyramidal particles. In Example 3, longer bipyramidal particles were obtained, and the aggregation into spheres was greatly reduced. In Example 1, it was observed that the four elements C, O, N, and Ce were all uniformly distributed. In Example 3, it was observed that C, O, N, Ce, and Al were uniformly distributed.

[0045] Figure 2 The XRD patterns are for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7.

[0046] Figure 3 The FTIR spectra are for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7.

[0047] Depend on Figure 2 and Figure 3 As shown, the XRD characteristic peaks and FT-IR characteristic peaks of Examples 1, 3, 6 and 7 are almost identical, indicating that their crystal structures are basically the same.

[0048] Figure 4 The BET and pore size distribution diagrams are shown for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6 and Ni / Ce-BDC-NH2 in Example 7, where (a) is the BET and (b) is the pore size distribution diagram.

[0049] Depend on Figure 4The structural parameters of Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7 are shown in Table 1.

[0050] Table 1

[0051] like Figure 4 As shown, the specific surface area and total pore volume of Example 1 are 10.45 m². 2 / g and 0.0578cm 3 / g. The specific surface area of ​​Example 3 increased to 169.90 m². 2 / g and 0.3615cm 3 / g, and the pore size distribution is still mainly mesoporous.

[0052] 2. Performance Testing (1) Performance testing method: 5 mg of the metal MOF adsorbent prepared in Examples 1-7 was added to 20 mL of known initial concentration (except for...). Figure 5 (b) A phosphate solution prepared with sodium dihydrogen phosphate (except for 10-300 mg P / L, the rest are 50 mg P / L) was placed in a constant temperature shaker (25℃, 300 rpm) and shaken for a certain period of time (usually 60-300 min to reach equilibrium). The mixture was then sampled, filtered, and the residual phosphate concentration in the filtrate was determined.

[0053] (2) Performance test results: Figure 5 The figures show the adsorption performance of the metal MOFs in Examples 1-7; where (a) is the adsorption efficiency of the metal MOFs in Examples 1-5, (b) is the Langmuir and Freundlich model fitting diagrams for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7, (c) is the kinetic curve fitting diagram for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7, and (d) is the internal diffusion model fitting diagram for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7.

[0054] according to Figure 5 The adsorption effects of the metal MOF adsorbents prepared in Examples 1 to 5 (a) are shown in Table 2.

[0055] Table 2

[0056] Table 2 shows that, comparing Examples 1, 2, 3, 4, and 5, under the same conditions, Example 1 showed the best adsorption effect on phosphate, while Example 5 showed the worst. In the bimetallic MOF, Example 3 showed the best adsorption effect on phosphate, indicating that the optimal molar ratio of cerium in the cerium salt to aluminum in the aluminum salt is 1:1.

[0057] according to Figure 5 The Langmuir and Freundlich isothermal adsorption model parameters for Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7 obtained in (b) are shown in Table 3.

[0058] Table 3

[0059] Comparing Examples 1, 3, 6, and 7, at 25°C, the Langmuir fitting coefficient R is shown in Table 2. 2 All values ​​were higher than those of the Freundlich model, indicating that the Langmuir model is more suitable for describing the adsorption behavior of phosphate on the adsorbent, and that the adsorption process is a homogeneous unimolecular adsorption process. The key parameter 1 / n of the Freundlich adsorption model ranged from 0.1 to 0.5, which, according to the relevant theory of the Freundlich adsorption model, indicates that the adsorbent exhibits a high adsorption capacity. Example 1 showed an adsorption capacity of 327.35 mg P / g for phosphate; among the bimetallic MOFs, Example 3 showed the largest adsorption capacity for phosphate at 313.15 mg P / g, while Examples 6 and 7 showed adsorption capacities of only 236.94 mg / g and 233.72 mg / g, respectively. This indicates that, in terms of adsorption capacity, cerium and aluminum salts are the most effective in bimetallic MOFs.

[0060] according to Figure 5 The kinetic parameters of the phosphate adsorption process of Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6 and Ni / Ce-BDC-NH2 in Example 7 obtained in (c) are shown in Table 4.

[0061] Table 4

[0062] Comparing Examples 1, 3, 6, and 7, it can be seen that the fitting coefficient (R0) of the quasi-second-order kinetic model is... 2 The results were higher than those of the pseudo-first-order model, indicating that chemisorption (involving electron covalent interactions or electron transfer) is the dominant mechanism. Several adsorbents also exhibited extremely rapid kinetics, reaching equilibrium within 80 minutes.

[0063] Changing the initial phosphate concentration and adsorption time in the adsorption system affects the equilibrium adsorption capacity and adsorption rate of the bimetallic MOF adsorbent. When the aluminum-cerium ion feed ratio is 1:1, the initial phosphate concentration is 50 mg P / L, and the adsorption time is 80 min, the equilibrium adsorption capacity is 153 mg / g, and the kinetic process conforms to the pseudo-second-order kinetic model (R2>0.99), indicating that the adsorption process is mainly chemisorption.

[0064] according to Figure 5 The internal diffusion model parameters for the adsorption processes of Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7 obtained in (d) are shown in Table 5.

[0065] Table 5

[0066] As shown in the figure, comparing the internal diffusion models of the phosphate adsorption process in Examples 1, 3, 6, and 7, it can be divided into two stages: the initial stage of the internal diffusion rate constant within the particles (K). P1 The relatively large K value indicates that the adsorption process in this stage is mainly controlled by a rapid liquid film diffusion mechanism; while subsequent stages exhibit a smaller K value. P2 The value indicates a relatively decreased adsorption rate. None of the internal diffusion fitting curves passed through the origin, confirming that the phosphate removal rate is jointly controlled by external diffusion (i.e., boundary layer diffusion) and internal diffusion.

[0067] Figure 6 This is a schematic diagram showing the effect of the initial pH of the solution on the adsorption of phosphate by Ce-BDC-NH2, Al / Ce-BDC-NH2, Fe / Ce-BDC-NH2 and Ni / Ce-BDC-NH2.

[0068] according to Figure 6The pH experiment results (adsorption capacity, mgP.g) are shown in the schematic diagram of the effect of Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7 on phosphate adsorption. -1 As shown in Table 6.

[0069] Table 6

[0070] Comparing Examples 1, 3, 6, and 7, Examples 1 and 3 exhibited high phosphate adsorption capacity across the entire pH range. Example 1 maintained over 80% adsorption capacity under strongly acidic conditions, while Example 3 maintained over 90% adsorption capacity under strongly acidic conditions; both showed a decrease only under strongly alkaline conditions. Examples 6 and 7 showed relatively weaker acid and alkali resistance, demonstrating that the introduction of aluminum indeed enhanced the stability of the adsorbent.

[0071] Figure 7 Common coexisting ions (Cl) - NO3 - SO4 2- , F - Fe 3+ Al 3+ Ca 2+ The effect of different concentrations on the adsorption of phosphate by Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7.

[0072] according to Figure 7 Interfering ion experiments (adsorption capacity, mg.g) of Ce-BDC-NH2 in Example 1, Al / Ce-BDC-NH2 in Example 3, Fe / Ce-BDC-NH2 in Example 6, and Ni / Ce-BDC-NH2 in Example 7. -1 As shown in Table 7.

[0073] Table 7

[0074] Compared with Examples 1, 3, 6, and 7, anions significantly reduced the material's adsorption capacity for phosphorus, and the inhibition effect increased with increasing concentration. - Concentration up to 50 mg·L -1At that time, the adsorption capacity of Example 1 decreased by 45.39%, while that of Example 3 remained above 80%. The adsorption capacity of the other four anions at the same concentration remained above 75% in Example 1. The inhibitory effect of cations on phosphate adsorption was higher than that of anions.

[0075] By altering the types and concentrations of coexisting competing ions, the bimetallic MOF adsorbent consistently maintains a significant selective adsorption capacity for phosphates. In Example 3, when NO3- at a concentration of 50 mg / L is present in the solution... - At this time, the phosphate removal rate can reach over 90%; when the solution contains 50 mg / L of F... - At that time, the phosphate removal rate remained above 80%; when Fe concentration of 10 mg / L was present... 3+ or Ca 2+ At that time, the phosphate removal rate was not significantly affected, remaining above 99%. This characteristic indicates that the introduction of metallic aluminum enhanced the material's resistance to interference.

[0076] Figure 8 The stability tests of Ce-BDC-NH2 in Example 1 and Al / Ce-BDC-NH2 in Example 3 are shown below. (a) shows the XRD patterns of Ce-BDC-NH2 in Example 1 after soaking in solutions with different pH values. (b) shows the XRD patterns of Al / Ce-BDC-NH2 in Example 3 after soaking in solutions with different pH values. (c) shows the cyclic flow chart of phosphate adsorption in Al / Ce-BDC-NH2 in Example 3. (d) shows the results of five cycles of phosphate adsorption in Al / Ce-BDC-NH2 in Example 3.

[0077] like Figure 8 As shown in (a) and (b), Example 1 completely loses its crystallinity under alkaline conditions, and its poor alkali resistance limits its application in alkaline desorption processes. Example 3 exhibits better structural stability under the same conditions.

[0078] according to Figure 8 The adsorption-desorption results of Al / Ce-BDC-NH2 in Example 3 obtained in (d) are shown in Table 8.

[0079] Table 8

[0080] It can be seen that in Example 3, after Al / Ce-BDC-NH2 has undergone 5 adsorption-desorption cycles, the phosphate removal efficiency can still be maintained at about 70% of that in the first adsorption.

[0081] Figure 9The FT-IR and high-resolution XPS spectra of Al / Ce-BDC-NH2 before and after phosphate adsorption are shown; where (a) is the total XPS spectrum, (b) is the FT-IR spectrum, (c) is P 2p, (d) is O 1s, (e) is N 1s, (f) is Ce 3d, and (g) is Al 2p.

[0082] like Figure 9 As shown in Figure (a), the characteristic phosphorus peaks appeared after phosphate adsorption in Example 3, indicating successful phosphate loading. The NH and OH absorption peaks shifted to 3479–3508 cm⁻¹, respectively. -1 and 3355–3391 cm -1 The range indicates the protonated amino group (-NH3). + The metal ions (M-OH2) interact electrostatically with phosphate ions, and phosphate ions undergo ligand exchange with surface -OH groups. Furthermore, the metal-related absorption peaks are significantly weakened or disappear, indicating the presence of hydrated groups (M-OH2) at the metal sites. + The phosphate was involved in its immobilization. XPS analysis of the sample revealed a characteristic peak in the P 2p region, confirming phosphate adsorption. The area of ​​the characteristic peak of the metal oxide in the O 1s spectrum increased from 27.86% to 39.63%, indicating the formation of MOP coordination bonds and the presence of metal complexation. Simultaneously, the -NH2 signal weakened while the -NH3 signal increased. + The signal enhancement indicates that the amino group is protonated and has a positive potential point. Figure 10 A schematic diagram illustrating the mechanism of phosphate adsorption by Al / Ce-BDC-NH2. Figure 10 It is evident that metal complexation forms stable coordination bonds between phosphate ions and the active metal sites of the material; electrostatic interactions promote the efficient binding of charged phosphate ions with oppositely charged regions on the adsorbent surface. These mechanisms work together to form the basis for the material's efficient adsorption of phosphate.

[0083] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. A method for preparing a highly stable cerium-aluminum bimetallic MOF, characterized in that, Includes the following steps: Cerium salt, aluminum salt, organic ligand and solvent are mixed and reacted. After the reaction is completed, the product is cooled and separated into solid and liquid components to obtain a solid product. The solid product was freeze-dried under vacuum to obtain a highly stable cerium-aluminum bimetallic MOF.

2. The method for preparing the highly stable cerium-aluminum bimetallic MOF according to claim 1, characterized in that, The molar ratio of cerium ions in the cerium salt to aluminum ions in the aluminum salt is (1~3):(3~1). The cerium salt includes cerium nitrate; The aluminum salt includes aluminum chloride.

3. The method for preparing the highly stable cerium-aluminum bimetallic MOF according to claim 1, characterized in that, The organic ligand includes 2-aminoterephthalic acid; The solvent includes N,N-dimethylformamide.

4. The method for preparing the highly stable cerium-aluminum bimetallic MOF according to claim 1, characterized in that, The mass ratio of the cerium salt to the organic ligand is (0.1~0.5):(0.7~0.9). The ratio of the amount of cerium salt to the amount of solvent is (0.1~0.5) g : (50~80) mL.

5. The method for preparing the highly stable cerium-aluminum bimetallic MOF according to claim 1, characterized in that, The reaction conditions are as follows: heating rate of 1~2℃ / min, final temperature of 130~180℃, and holding time of 24~28h. The freeze-drying temperature is -50~0℃, and the freeze-drying time is 12~24h.

6. A highly stable cerium-aluminum bimetallic MOF prepared by a method according to any one of claims 1 to 5.

7. The application of the highly stable cerium-aluminum bimetallic MOF as described in claim 6 in phosphorus-containing wastewater.

8. The application of the highly stable cerium-aluminum bimetallic MOF according to claim 7 in phosphorus-containing wastewater, characterized in that, The applications include: Highly stable cerium-aluminum bimetallic MOFs were dispersed in phosphorus-containing wastewater for adsorption. After adsorption, solid-liquid separation was performed, and the phosphorus concentration in the water was measured.

9. The application of the highly stable cerium-aluminum bimetallic MOF according to claim 8 in phosphorus-containing wastewater, characterized in that, The phosphorus-containing wastewater includes phosphate-containing wastewater; The phosphate-containing wastewater has an initial phosphate concentration of 10-300 mg P / L and a pH of 1-12. The dosage of the highly stable cerium-aluminum bimetallic MOF is 0.1~2.0 g / L.

10. The application of the highly stable cerium-aluminum bimetallic MOF according to claim 8 in phosphorus-containing wastewater, characterized in that, The adsorption temperature is 15~35℃, and the adsorption equilibrium time is 30~300min.

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