Fe-ca co-crosslinked bimetallic zifs microsphere composite adsorbent and preparation method and application thereof

Abstract

The application belongs to the field of functional adsorption materials, and specifically discloses a Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent, a preparation method and application thereof. The composite adsorbent is synthesized by a ball method through co-dropping of Fe-Ca multi-metal ions, and the dropping liquid containing bimetallic ZIFs is dropped into a solidification liquid containing Fe and Ca, and is quickly solidified and formed under the synergistic effect of ions, wherein Fe-Ca acts as a co-component to participate in the network construction of the microspheres, so as to promote the adsorbent to form a dense and multi-stage pore and enhance the stability of the skeleton. Finally, a Fe-Ca@bimetallic ZIFs microsphere composite material with stable structure is obtained. The preparation cost is low, the process conditions are mild, the problems of easy suspension, difficult settlement, high risk of secondary pollution and difficult recovery of the powder adsorbent are effectively overcome, the microsphere composite adsorbent has the characteristics of good formability, large specific surface area, easy separation and recovery, high adsorption capacity and good selectivity, can be used for efficient removal of organic pollutants in water bodies, and has good prospects for engineering and large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, and relates to composite adsorbents for water treatment, specifically to a Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent, its preparation method, and its application. Background Technology

[0002] Antibiotics are highly effective drugs for treating infection-related diseases in humans and animals, and their global usage is surging. The large amounts of residues generated during their production and use enter the aquatic and terrestrial environments through various pathways, becoming a pressing environmental pollutant. Antibiotic pollutants are characterized by complex molecular structures, low biodegradability, and strong environmental persistence. Long-term exposure to low concentrations can easily induce the development of antibiotic resistance genes (ARGs) in microorganisms, which, after accumulation through the food chain, pose a significant and potentially long-term threat to ecosystem balance and human health. More importantly, the solubility and stability of antibiotics make them difficult to remove effectively by traditional wastewater treatment processes, leading to a year-on-year increase in environmental pollution levels. Therefore, the development of efficient and environmentally friendly antibiotic pollutant removal technologies and functional materials has become a key research focus in the field of water environment management.

[0003] Currently, methods used to treat antibiotic-contaminated wastewater include advanced oxidation, membrane technology, adsorption, and coagulation-flocculation. Studies have shown that adsorption is simple to operate, does not produce secondary pollution, and has high treatment efficiency, making it significantly superior to other methods. However, existing commercially available and laboratory-developed adsorbents, such as activated carbon, biochar, and traditional molecular sieves, generally suffer from drawbacks such as cumbersome preparation processes, long adsorption equilibrium times, low adsorption capacity, and poor selectivity. These limitations make it difficult to meet the advanced treatment requirements of high-concentration, complex-component antibiotic wastewater. Therefore, developing high-performance adsorbent materials has become the core breakthrough for the application of adsorption methods.

[0004] Metal-organic framework materials (ZIFs) have become a research hotspot in the field of water pollution control due to their ultra-high specific surface area and porosity, open metal active sites, strong structural designability, excellent chemical stability and simple synthesis process. Among them, ZIF-8 has been widely used in the adsorption and separation of water pollutants. However, traditional ZIFs-based adsorbent materials still face many technical bottlenecks: First, pure-phase ZIF-8 is mainly composed of microporous structures with a single active site, which creates steric hindrance for the diffusion and mass transfer of macromolecular antibiotic pollutants, significantly reducing adsorption efficiency; Second, ZIFs are originally in powder form, which is easily suspended and difficult to settle in aqueous solutions, making solid-liquid separation difficult. In practical applications, problems such as particle aggregation and deactivation, pore blockage, and high pressure drop exist, making recycling and regeneration difficult, increasing usage costs and easily causing secondary pollution; Third, existing ZIFs molding and modification processes are still insufficient. The binder added by the granulation method easily blocks the material pores and reduces porosity. When the phase inversion method is used to combine ZIFs powder with polymers, the polymer chains easily coat the ZIFs active sites and destroy their pore structure, resulting in a significant decrease in the material's specific surface area and adsorption performance.

[0005] Although some studies have attempted to prepare microsphere adsorbents by combining MOF materials with polymer substrates, it is difficult to balance the integrity of the pore structure and the stability of the forming process, and thus it is impossible to achieve synergistic optimization of high specific surface area and good solid-liquid separation performance. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent, its preparation method, and its application. This adsorbent combines the advantages of high specific surface area, hierarchical pore structure, and abundant active sites for adsorption performance. It also possesses engineering application characteristics such as good formability, easy separation and recovery, strong structural stability, and recyclability. It can efficiently remove antibiotic-like organic pollutants from water bodies and is suitable for engineering and large-scale water treatment needs.

[0007] This invention is achieved through the following technical solution: A method for preparing an Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent includes the following steps: Step 1: Place 9-15 g of 2-methylimidazole in 90-150 mL of ultrapure water and stir until homogeneous. Then add 0.3-0.5 g of alkyl surfactant and stir to form a homogeneous solution A. Add 2.4-4 g of zinc acetate dihydrate to 10-15 mL of ultrapure water and stir until completely dissolved. Then add 0.094-0.157 g of ferrous sulfate hexahydrate and sonicate to form a homogeneous solution B. Under stirring conditions, add solution B dropwise to solution A. After the addition is complete, continue stirring for 24 h to form a light orange suspension. After the reaction is complete, wash and dry to obtain bimetallic ZIFs powder. Step 2: Add 150-300 mg of the bimetallic ZIFs powder prepared in Step 1 to 3-5 mL of sodium alginate solution with a concentration of 15-30 mg / mL. Stir and mix thoroughly to obtain a suspension, which is the bimetallic ZIFs powder drop solution, for later use. Step 3: Add 0.1~1.4 g of polyacrylic acid to a mixture of 90~100 mL of anhydrous ethanol and ultrapure water, and stir until completely dissolved. Then add 300~500 mg of anhydrous calcium chloride and ferric chloride hexahydrate powder to the mixture, and stir to form a uniform solidified liquid for later use. The mass ratio of anhydrous calcium chloride to ferric chloride hexahydrate is (0.3-1):1. Step 4: Add the bimetallic ZIFs powder prepared in Step 2 dropwise to the curing solution prepared in Step 3 according to a volume ratio of (0.8~1.5):30. Curing is carried out for 25 min~1 h. After the microspheres are formed, the mixture is filtered through a sieve, washed with deionized water, and finally freeze-dried to obtain Fe-Ca co-crosslinked bimetallic ZIFs microspheres, namely Fe-Ca@bimetallic ZIFs microspheres.

[0008] The present invention also has the following technical features: Preferably, the alkyl surfactant mentioned in step one is anionic alkyl surfactant, including any one of sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium dodecyl sulfonate, sodium hexadecyl sulfonate, sodium dodecyl sulfate, sodium hexadecyl sulfate, and sodium lauryl polyoxyethylene ether sulfate.

[0009] Preferably, the ultrasound in step one is performed at room temperature with a power of 200-300 W for 10-20 minutes.

[0010] Preferably, in step one, the washing is performed by alternating centrifugal washing with anhydrous ethanol and ultrapure water 3 to 5 times, and the drying is performed by placing the washed solid in a vacuum drying oven and drying it at 60 to 80 ℃ for 12 to 24 hours.

[0011] Preferably, the bimetallic ZIFs powder described in step two is added to the sodium alginate solution in 3 to 5 portions, with a stirring time of 1 to 2 hours.

[0012] Preferably, in step three, the volume ratio of ultrapure water to anhydrous ethanol in the mixture of anhydrous ethanol and ultrapure water is (5~7):1.

[0013] Preferably, the dropwise addition method described in step four is to use a syringe of 2.5 mL to 10 mL or a peristaltic pump to drip the solution, with the flow rate of the peristaltic pump being 1 mL / min.

[0014] Preferably, in step four, the deionized water washing method is to rinse with flowing deionized water for 5 to 10 minutes, and the freeze drying is to freeze dry at -40 ℃ to -60 ℃ for 24 to 30 hours.

[0015] This invention also protects a Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent prepared according to the above method and its application in the adsorption of antibiotics: ciprofloxacin, tetracycline hydrochloride and oxytetracycline hydrochloride. The adsorption method includes the following steps: S1. Fe-Ca@bimetallic ZIFs microspheres were added to an aqueous solution with a pH of 4-8 and an antibiotic concentration of 5-80 mg / L for adsorption under stirring. The amount of Fe-Ca@bimetallic ZIFs microsphere composite adsorbent added was 0.1-0.5 g / L, the adsorption time was 12-24 h, and the stirring speed was 200 rpm-350 rpm. S2. After the adsorption is complete, the Fe-Ca@bimetallic ZIFs microspheres containing the drug are filtered through a sieve.

[0016] Compared with the prior art, the present invention has the following technical effects: This invention employs a Fe-Ca multimetallic ion co-drop method to form spheres. Through the synergistic co-crosslinking effect of multivalent metal ions and polymers, efficient molding of bimetallic ZIFs is achieved under mild conditions while preserving their pore structure and adsorption activity. Using Fe-Ca multimetallic ions as the co-crosslinking core, a composite crosslinking network is formed with polyacrylic acid (PAA) and sodium alginate. Bimetallic ZIF powder, acting as the adsorption active core, is uniformly coated within this network. The entire molding process is a room-temperature liquid-phase reaction, without harsh conditions such as high temperature or high pressure, thus preserving the crystal structure of the bimetallic ZIFs themselves. When Fe-Ca participates in the construction of the microsphere network, it promotes the formation of a dense, multi-level porous structure. This porous structure serves as both... This process serves as a mass transfer channel for pollutants, allowing pollutants such as antibiotics in the water to quickly contact the internal active sites of bimetallic ZIFs. It also avoids the problem of polymer chains clogging the ZIFs pores in traditional molding processes, ensuring that the high specific surface area is not reduced and that the adsorption active sites are fully exposed. The bimetallic ZIFs powder is gradually added to the sodium alginate solution in 3-5 batches with thorough stirring, achieving uniform dispersion in the droplet solution. After being added to the curing liquid, the Fe-Ca crosslinking network quickly fixes the dispersed ZIFs powder, preventing particle aggregation during molding and use. This prevents deactivation problems such as active site encapsulation and pore blockage caused by agglomeration, ensuring that the adsorption activity of each ZIFs particle can be effectively exerted. This invention utilizes Fe-Ca co-crosslinking to create microspheres, transforming a powder state into a regular spherical solid structure. The synergistic crosslinking effect of Fe-Ca multi-metal ions allows the droplet to rapidly solidify into a monolithic spherical structure in the curing liquid, agglomerating nano / micron-sized bimetallic ZIF powders into millimeter-sized microspheres. These microspheres have a density and particle size far greater than the powder state, preventing suspension and diffusion in water and enabling rapid solid-liquid stratification. This completely overcomes the problems of easy suspension and difficult sedimentation of powder adsorbents. Fe-Ca, as a co-component, participates in the microsphere network construction, significantly enhancing the microsphere's... The microspheres exhibit excellent skeletal stability and mechanical properties. During conventional separation operations using sieve filtration, the microspheres do not break or swell, and secondary powder contamination is avoided. The structural integrity of the microspheres is effectively maintained after separation. The formed microspheres are regular solid spheres that are insoluble in aqueous systems. Complex separation methods such as centrifugation and ultrafiltration are unnecessary. Solid-liquid separation from water can be quickly achieved using only the simple conventional method of sieve filtration. The separation operation is simple and efficient, and the separated microspheres can be directly collected for subsequent regeneration and recycling. In summary, the Fe-Ca co-crosslinking molding mechanism achieves complete preservation of the bimetallic ZIFs adsorption active core through mild crosslinking, pore protection, and uniform dispersion. Furthermore, it achieves a fundamental transformation of the adsorbent from a "difficult-to-separate powder" to an "easily-separable spherical solid phase" through microsphere solid-phase molding and mechanical structural reinforcement, ultimately optimizing both adsorption activity and separation and recovery. The process is simple, requires minimal equipment, offers highly controllable structure and composition, boasts large adsorption capacity and high recovery rate, and can be scalable. Simple filtration enables rapid separation from the solution, demonstrating excellent solid-liquid separation performance and operational stability. It maintains stable performance under long-term operating conditions and exhibits high adsorption efficiency, structural stability, separation performance, and recyclability when used for antibiotic adsorption and removal, resulting in significant economic and environmental benefits. Attached Figure Description

[0017] Figure 1 The image shows the XRD pattern of the Fe-Ca@bimetallic ZIFs microspheres prepared in Example 1. Figure 2 SEM image of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 1; Figure 3 This is a photograph of the Fe-Ca@bimetallic ZIFs microspheres prepared in Example 1. Figure 4 SEM image of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 2; Figure 5 SEM image of Fe-Ca@bimetallic ZIFs microspheres without PAA added, prepared as Comparative Example 1; Figure 6 The removal efficiency diagrams are for the Fe-Ca@bimetallic ZIFs microspheres prepared in Example 2 and Comparative Example 1. Figure 7 The graph shows the relationship between adsorption time and adsorption amount of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 2. Figure 8 Nitrogen adsorption-desorption isotherms of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 3 and Comparative Example 2; Figure 9 The nitrogen adsorption-desorption isotherms of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 4 and Comparative Example 3 are shown. Figure 10 EDS-mapping image of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 4; Figure 11 The graph shows the effect of different pH values ​​on the adsorption performance of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 4. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0019] The preferred molecular weight range of the polyacrylic acid used in the following examples is 1000~50000 Da.

[0020] Example 1 This embodiment provides a Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent, the preparation method of which includes the following steps: 1) Preparation of bimetallic ZIFs: 9.2 g of 2-methylimidazole was placed in 90 mL of ultrapure water and stirred until homogeneous. Then, 0.35 g of sodium dodecylbenzenesulfonate was added and stirred to form a homogeneous solution A. 2.45 g of zinc acetate dihydrate was added to 11 mL of ultrapure water and stirred until completely dissolved. Then, 0.1 g of ferrous sulfate hexahydrate was added and sonicated at 220 W for 15 min at room temperature to form a homogeneous solution B. Under stirring conditions, solution B was added dropwise to solution A. After the addition was complete, stirring was continued for 24 h to form a light orange suspension. After the reaction was completed, the solid was washed three times by alternating centrifugation with anhydrous ethanol and ultrapure water. The washed solid was placed in a vacuum drying oven and dried at 60 ℃ for 24 h to obtain bimetallic ZIFs powder. 2) Preparation of the dropping solution: 225 mg of bimetallic ZIFs powder prepared in 1) was added to 3.5 mL of 22 mg / L sodium alginate solution in 4 portions under stirring. The mixture was stirred for 1.5 h to obtain a suspension as the bimetallic ZIFs powder dropping solution, which was then set aside for use. 3) Preparation of curing solution: Add 0.3 g of polyacrylic acid (PAA) to a mixture of 90 mL of anhydrous ethanol and ultrapure water, with a volume ratio of ultrapure water to anhydrous ethanol of 6:1. Stir until completely dissolved. Then add 310 mg of anhydrous calcium chloride and ferric chloride hexahydrate to the mixture, with a mass ratio of anhydrous calcium chloride to ferric chloride hexahydrate of 0.5:1. Finally, stir to form a uniform curing solution for later use. 4) The bimetallic ZIFs powder prepared in 2) was added dropwise to the curing solution prepared in 3) using a 10 mL syringe at a volume ratio of 0.8:30. The curing time was 1 h. After the microspheres were formed, they were filtered through a sieve and then rinsed with flowing deionized water for 5 min. Finally, the prepared microspheres were freeze-dried at -45 ℃ for 24 h to obtain Fe-Ca co-crosslinked bimetallic ZIFs microspheres, namely Fe-Ca@bimetallic ZIFs microspheres.

[0021] The Fe-Ca@bimetallic ZIFs microsphere composite adsorbent prepared above is used for ciprofloxacin, specifically including the following steps: 20 mg of Fe-Ca@bimetallic ZIFs microsphere composite adsorbent was added to 150 mL of 10 mg / L ciprofloxacin solution. The mixture was stirred at 25 °C and 200 rpm for 24 h. After adsorption saturation, the mixture was separated by sieve. 5 mL of the supernatant was then filtered through a membrane, and the concentration of ciprofloxacin in the filtrate was determined using a UV spectrophotometer. The remaining ciprofloxacin concentration was calculated based on the ciprofloxacin standard curve. Finally, the adsorption efficiency of ciprofloxacin was calculated, which was 80%.

[0022] The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results of the Fe-Ca co-crosslinked bimetallic ZIFs microspheres prepared in this embodiment are as follows: Figure 1 and Figure 2 As shown, from Figure 1 and Figure 2 As can be seen from the XRD pattern, the Fe-Ca@bimetallic ZIFs microspheres exhibit characteristic diffraction peaks typical of ZIFs in the low-angle region, indicating that the material successfully encapsulates bimetallic ZIFs, and the introduction of iron and calcium does not disrupt their main crystal structure. The SEM image shows that the prepared Fe-Ca@bimetallic ZIFs microspheres have an overall spherical structure, with the surface formed by the accumulation of fine particles. The structure is relatively dense and has a certain degree of roughness, which is beneficial for providing abundant adsorption active sites and mass transfer channels. Figure 3 A photograph of the prepared Fe-Ca@bimetallic ZIFs microspheres.

[0023] Example 2 This embodiment provides a Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent, the preparation method of which includes the following steps: 1) Preparation of bimetallic ZIFs: 15 g of 2-methylimidazole was placed in 150 mL of ultrapure water and stirred until homogeneous. Then, 0.5 g of sodium cetylbenzenesulfonate was added and stirred to form a homogeneous solution A. 4 g of zinc acetate dihydrate was added to 15 mL of ultrapure water and stirred until completely dissolved. Then, 0.157 g of ferrous sulfate hexahydrate was added and sonicated at 300 W for 10 min at room temperature to form a homogeneous solution B. Under stirring conditions, solution B was added dropwise to solution A. After the addition was complete, stirring was continued for 24 h to form a light orange suspension. After the reaction was complete, the solid was washed 5 times by alternating centrifugation with anhydrous ethanol and ultrapure water. The washed solid was placed in a vacuum drying oven and dried at 80 ℃ for 12 h to obtain bimetallic ZIFs powder. 2) Preparation of the drop solution: 250 mg of bimetallic ZIFs powder prepared in 1) was added to 4 mL of 22 mg / mL sodium alginate solution in 4 portions under stirring. The mixture was stirred for 1.5 h to obtain a suspension as the bimetallic ZIFs powder drop solution, which was then set aside for use. 3) Preparation of curing solution: Add 0.3 g of polyacrylic acid (PAA) to a mixture of 90 mL of anhydrous ethanol and ultrapure water, with a volume ratio of ultrapure water to anhydrous ethanol of 5:1. Stir until completely dissolved. Then add 310 mg of anhydrous calcium chloride and ferric chloride hexahydrate to the mixture, with a mass ratio of anhydrous calcium chloride to ferric chloride hexahydrate of 0.5:1. Finally, stir to form a uniform curing solution for later use. 4) The bimetallic ZIFs powder prepared in 2) was added dropwise to the curing solution prepared in 3) using a 7.5 mL syringe at a volume ratio of 1:30. The curing time was 40 min. After the microspheres were formed, they were filtered through a sieve and then rinsed with flowing deionized water for 10 min. Finally, the prepared microspheres were freeze-dried at -40 ℃ for 30 h to obtain Fe-Ca co-crosslinked bimetallic ZIFs microspheres, namely Fe-Ca@bimetallic ZIFs microspheres.

[0024] Comparative Example 1 Comparative Example 1 is basically the same as Example 2, except that PAA was not added during the preparation of the curing liquid in step 3).

[0025] The two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents prepared in Example 2 and Comparative Example 1 were analyzed by scanning electron microscopy. Figure 4 and Figure 5 As shown, compared with the Fe-Ca@bimetallic ZIFs microsphere composite adsorbent prepared without PAA, the Fe-Ca@bimetallic ZIFs microsphere composite adsorbent has more bimetallic ZIFs powder on the surface of the microspheres, indicating that the addition of PAA is beneficial to coating more bimetallic ZIFs powder.

[0026] The two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents prepared in Example 2 and Comparative Example 1 were used for tetracycline hydrochloride, specifically including the following steps: 20 mg of two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents were added to 150 mL of a 10 mg / L tetracycline hydrochloride solution. The mixture was stirred at 25℃ and 250 rpm for 24 h until adsorption saturation. Afterward, the mixture was separated using a sieve. 5 mL of the supernatant was then filtered through a membrane, and the concentration of tetracycline hydrochloride in the filtrate was determined using a UV spectrophotometer. The remaining tetracycline hydrochloride concentration was calculated based on the tetracycline hydrochloride standard curve, and the adsorption efficiency of tetracycline hydrochloride was finally calculated. Figure 6 It can be seen that the adsorption capacity of Fe-Ca@bimetallic ZIFs microspheres prepared with the addition of PAA is significantly higher than that of microsphere composite adsorbents prepared without the addition of PAA. The adsorption efficiency of Fe-Ca@bimetallic ZIFs microspheres for tetracycline hydrochloride is 90%.

[0027] The adsorption performance of the Fe-Ca@bimetallic ZIFs microsphere composite adsorbent prepared in Example 2 for tetracycline hydrochloride at different adsorption times is shown in the figure below. Figure 7 As shown, by Figure 7 As can be seen from the data, within the range of 0 to 24 h, the adsorption capacity of Fe-Ca@bimetallic ZIFs microsphere composite adsorbent for tetracycline hydrochloride first increases and then tends to level off over time. This is mainly because there are more active sites in the initial stage of adsorption, and as time goes on, the sites are occupied and the adsorption capacity tends to reach equilibrium.

[0028] Example 3 A method for preparing an Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent includes the following steps: 1) Preparation of bimetallic ZIFs: 9 g of 2-methylimidazole was placed in 90 mL of ultrapure water and stirred until homogeneous. Then, 0.3 g of sodium dodecyl sulfonate was added and stirred to form a homogeneous solution A. 2.4 g of zinc acetate dihydrate was added to 10 mL of ultrapure water and stirred until completely dissolved. Then, 0.094 g of ferrous sulfate hexahydrate was added and sonicated at 200 W for 20 min at room temperature to form a homogeneous solution B. Under stirring conditions, solution B was added dropwise to solution A. After the addition was complete, stirring was continued for 24 h to form a light orange suspension. After the reaction was completed, the solid was washed 4 times by alternating centrifugation with anhydrous ethanol and ultrapure water. The washed solid was placed in a vacuum drying oven and dried at 70 ℃ for 16 h to obtain bimetallic ZIFs powder. 2) Preparation of the dropping solution: 150 mg of bimetallic ZIFs powder prepared in 1) was added to 3 mL of 15 mg / L sodium alginate solution in 3 portions under stirring. The mixture was stirred for 1 h and thoroughly mixed to obtain a suspension, which was then used as the bimetallic ZIFs powder dropping solution. 3) Preparation of curing solution: Add 0.1 g of polyacrylic acid (PAA) to a mixture of 92 mL of anhydrous ethanol and ultrapure water, with a volume ratio of ultrapure water to anhydrous ethanol of 5.5:1. Stir until completely dissolved. Then add 300 mg of anhydrous calcium chloride and ferric chloride hexahydrate to the mixture, with a mass ratio of anhydrous calcium chloride to ferric chloride hexahydrate of 0.3:1. Finally, stir to form a uniform curing solution for later use. 4) The bimetallic ZIFs powder prepared in 2) was added dropwise to the curing solution prepared in 3) using a 2.5 mL syringe at a volume ratio of 1.5:30. The curing time was 25 min. After the microspheres were formed, they were filtered through a sieve and then rinsed with flowing deionized water for 8 min. Finally, the prepared microspheres were freeze-dried at -60 ℃ for 28 h to obtain Fe-Ca co-crosslinked bimetallic ZIFs microspheres, namely Fe-Ca@bimetallic ZIFs microspheres.

[0029] Comparative Example 2 Comparative Example 2 is basically the same as Example 3, except that 92 mL of ultrapure water was used in the preparation of the curing solution in step 3), and no ethanol was added.

[0030] The nitrogen adsorption-desorption isotherm analysis was performed on the two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents prepared in Example 3 and Comparative Example 2. The results are as follows: Figure 8 As shown, the results indicate that the adsorption capacity of Fe-Ca@bimetallic ZIFs microspheres increases rapidly in the low relative pressure region, indicating that the material possesses a relatively rich microporous structure. Compared with Fe-Ca bimetallic ZIFs microspheres prepared without ethanol, the overall adsorption capacity is significantly improved, demonstrating that the addition of ethanol effectively enhances the specific surface area and pore structure characteristics of the material.

[0031] The two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents prepared in Example 3 and Comparative Example 2 were used for oxytetracycline hydrochloride, specifically including the following steps: Two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents were added to 150 mL of a 20 mg / L oxytetracycline hydrochloride solution. The mixture was stirred at 25 °C and 220 rpm for 24 h until adsorption saturation was achieved. Separation was then performed using a sieve, and 5 mL of the supernatant was filtered through a membrane. The concentration of oxytetracycline hydrochloride in the filtrate was measured using a UV spectrophotometer. The remaining concentration of oxytetracycline hydrochloride was calculated based on the plotted oxytetracycline hydrochloride standard curve, and the adsorption efficiency was finally calculated. Experimental results showed that the Fe-Ca@bimetallic ZIFs microspheres prepared with anhydrous ethanol had an adsorption capacity of 131.6 mg / g and an oxytetracycline hydrochloride adsorption efficiency of 88%, significantly higher than the 78.8 mg / g of the microsphere composite adsorbent prepared without anhydrous ethanol.

[0032] The adsorption performance of Fe-Ca@bimetallic ZIFs microspheres composite adsorbent prepared in Example 3 for oxytetracycline hydrochloride under different temperature conditions is shown in Table 1. As can be seen from Table 1, within the range of 25℃ to 35℃, the adsorption capacity of Fe-Ca@bimetallic ZIFs microspheres for oxytetracycline hydrochloride increases with increasing temperature.

[0033] Table 1 Adsorption capacity of oxytetracycline hydrochloride at different temperatures Example 4 This embodiment provides a Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent, the preparation method of which includes the following steps: 1) Preparation of bimetallic ZIFs: 10 g of 2-methylimidazole was placed in 100 mL of ultrapure water and stirred until homogeneous. Then, 0.4 g of sodium hexadecyl sulfonate was added and stirred to form a homogeneous solution A. 3 g of zinc acetate dihydrate was added to 13 mL of ultrapure water and stirred until completely dissolved. Then, 0.12 g of ferrous sulfate hexahydrate was added and sonicated at 200 W for 20 min at room temperature to form a homogeneous solution B. Under stirring conditions, solution B was added dropwise to solution A. After the addition was complete, stirring was continued for 24 h to form a light orange suspension. After the reaction was completed, the solid was washed 4 times by alternating centrifugation with anhydrous ethanol and ultrapure water. The washed solid was placed in a vacuum drying oven and dried at 70 ℃ for 12 h to obtain bimetallic ZIFs powder. 2) Preparation of the drop solution: 300 mg of bimetallic ZIFs powder prepared in 1) was added to 5 mL of 30 mg / L sodium alginate solution in 5 portions under stirring. The mixture was stirred for 2 h and thoroughly mixed to obtain a suspension, which was then used as the bimetallic ZIFs powder drop solution. 3) Preparation of curing solution: Add 1.4 g of polyacrylic acid (PAA) to a mixture of 100 mL of anhydrous ethanol and ultrapure water, with a volume ratio of ultrapure water to anhydrous ethanol of 7:1. Stir until completely dissolved. Then add 500 mg of anhydrous calcium chloride and ferric chloride hexahydrate to the mixture, with a mass ratio of anhydrous calcium chloride to ferric chloride hexahydrate of 1:1. Finally, stir to form a uniform curing solution for later use. 4) The bimetallic ZIFs powder prepared in 2) was added dropwise to the curing solution prepared in 3) at a volume ratio of 1.2:30 using a micro peristaltic pump at a flow rate of 1 mL / min. The curing time was 1 h. After the microspheres were formed, they were filtered through a sieve and then rinsed with flowing deionized water for 5 min. Finally, the prepared microspheres were freeze-dried at -45℃ for 24 h to obtain Fe-Ca co-crosslinked bimetallic ZIFs microspheres, namely Fe-Ca@bimetallic ZIFs microspheres.

[0034] Comparative Example 3 Comparative Example 3 is basically the same as Example 4, except that bimetallic ZIFs were not added during the preparation of the droplet solution in step 2).

[0035] The two microsphere composite adsorbents prepared in Comparative Example 3 and Example 4 were subjected to nitrogen adsorption-desorption isotherm analysis as follows: Figure 9 As shown, the EDS-mapping of Fe-Ca@bimetallic ZIFs microspheres prepared in Example 4 is as follows. Figure 10 As shown. By Figure 9It can be seen that the adsorption capacity of Fe-Ca@bimetallic ZIFs microspheres is significantly higher than that of Fe-Ca@sodium alginate microspheres prepared without the addition of bimetallic ZIFs, indicating that the introduction of bimetallic ZIFs powder effectively improves the pore structure characteristics of the material and increases the specific surface area. The EDS-mapping diagram shows that Ca and Fe elements are uniformly distributed in the microspheres, indicating that iron and calcium elements are successfully introduced and uniformly coated in the bimetallic ZIFs microsphere structure.

[0036] The two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents prepared in Comparative Example 3 and Example 4 were used for ciprofloxacin, specifically including the following steps: 20 mg of each of the two Fe-Ca@bimetallic ZIFs microsphere composite adsorbents were added to 150 mL of a 10 mg / L ciprofloxacin solution. The mixture was stirred at 25℃ and 250 rpm for 24 h until adsorption saturation was achieved. Separation was then performed using a sieve, and 5 mL of the supernatant was filtered through a membrane. The concentration of ciprofloxacin in the filtrate was determined using a UV spectrophotometer. The remaining ciprofloxacin concentration was calculated based on the plotted ciprofloxacin standard curve, and the adsorption efficiency of ciprofloxacin was finally calculated. The experimental results showed that the adsorption capacity of the Fe-Ca@bimetallic ZIFs microspheres prepared with the addition of bimetallic ZIF powder was 68.5 mg / g, significantly higher than the adsorption capacity of the composite adsorbent prepared without the addition of bimetallic ZIF powder (27.6 mg / g).

[0037] The adsorption performance of the Fe-Ca@bimetallic ZIFs microsphere composite adsorbent prepared in Example 4 for ciprofloxacin under different pH conditions is shown in the figure below. Figure 11 As shown, from Figure 11 As can be seen, within the time range of 2.5 to 11, the adsorption capacity of Fe-Ca@bimetallic ZIFs microspheres for ciprofloxacin first increases and then decreases with increasing pH, and remains basically unchanged around 4 to 7.

[0038] This invention utilizes a multi-metal ion co-dropping method to prepare Fe-Ca@bimetallic ZIFs microsphere composite adsorbents. The preparation method is simple, highly controllable, and easily repeatable. Through the synergistic co-crosslinking effect between Fe-Ca multi-metal ions and the bimetallic ZIFs-containing drop solution, rapid and stable microsphere material formation is achieved, facilitating easy recycling and reuse. The prepared Fe-Ca@bimetallic ZIFs microsphere composite adsorbent possesses excellent pore structure, high specific surface area, and abundant active sites. By adjusting the composition and process parameters of the drop solution and solidification solution, effective control over microsphere particle size, structural density, and mechanical properties can be achieved. Compared with traditional powder adsorbents, the microsphere adsorbent prepared by this invention significantly improves recyclability and solid-liquid separation performance while maintaining the adsorption active components. The process is simple, requires minimal equipment, and is suitable for large-scale preparation and engineering applications. It exhibits high adsorption capacity, good structural stability, and recyclability in antibiotic wastewater treatment.

[0039] In the protection scheme of the present invention, the anionic alkyl surfactant can also be any one of sodium dodecyl sulfate, sodium hexadecyl sulfate, and sodium lauryl ether sulfate.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the present invention.

Claims

1. A method for preparing a Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent, characterized in that, Includes the following steps: Step 1: Place 9-15 g of 2-methylimidazole in 90-150 mL of ultrapure water and stir until homogeneous. Then add 0.3-0.5 g of alkyl surfactant and stir to form a homogeneous solution A. Add 2.4-4 g of zinc acetate dihydrate to 10-15 mL of ultrapure water and stir until completely dissolved. Then add 0.094-0.157 g of ferrous sulfate hexahydrate and sonicate to form a homogeneous solution B. Under stirring conditions, add solution B dropwise to solution A. After the addition is complete, continue stirring for 24 h to form a light orange suspension. After the reaction is complete, wash and dry to obtain bimetallic ZIFs powder. Step 2: Add 150-300 mg of the bimetallic ZIFs powder prepared in Step 1 to 3-5 mL of sodium alginate solution with a concentration of 15-30 mg / mL. Stir and mix thoroughly to obtain a suspension, which is the bimetallic ZIFs powder drop solution, for later use. Step 3: Add 0.1~1.4 g of polyacrylic acid to a mixture of 90~100 mL of anhydrous ethanol and ultrapure water, and stir until completely dissolved. Then add 300~500 mg of anhydrous calcium chloride and ferric chloride hexahydrate powder to the mixture, and stir to form a uniform solidified liquid for later use. The mass ratio of anhydrous calcium chloride to ferric chloride hexahydrate is (0.3-1):

1. Step 4: Add the bimetallic ZIFs powder prepared in Step 2 dropwise to the curing solution prepared in Step 3 according to a volume ratio of (0.8~1.5):

30. Curing is carried out for 25 min~1 h. After the microspheres are formed, the mixture is filtered through a sieve, washed with deionized water, and finally freeze-dried to obtain Fe-Ca co-crosslinked bimetallic ZIFs microspheres, namely Fe-Ca@bimetallic ZIFs microspheres.

2. The method for preparing the Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent according to claim 1, characterized in that, The alkyl surfactant mentioned in step one is anionic alkyl surfactant, including any one of sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium dodecyl sulfonate, sodium hexadecyl sulfonate, sodium dodecyl sulfate, sodium hexadecyl sulfate, and sodium lauryl ether sulfate.

3. The method for preparing the Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent according to claim 1, characterized in that, The ultrasound described in step one is performed at room temperature with a power of 200-300 W for 10-20 minutes.

4. The method for preparing the Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent according to claim 1, characterized in that, In step one, the washing involves alternating centrifugal washing with anhydrous ethanol and ultrapure water 3 to 5 times, and the drying involves placing the washed solid in a vacuum drying oven and drying it at 60 to 80 ℃ for 12 to 24 hours.

5. The method for preparing the Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent according to claim 1, characterized in that, The bimetallic ZIFs powder described in step two is added to the sodium alginate solution in 3 to 5 portions, with a stirring time of 1 to 2 hours.

6. The method for preparing the Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent according to claim 1, characterized in that, In step three, the volume ratio of ultrapure water to anhydrous ethanol in the mixture of anhydrous ethanol is (5~7):

1.

7. The method for preparing the Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent according to claim 1, characterized in that, The dropwise addition method described in step four uses a syringe or peristaltic pump with a flow rate of 1 mL / min.

8. The method for preparing the Fe-Ca co-crosslinked bimetallic ZIFs microsphere composite adsorbent according to claim 1, characterized in that, In step four, the deionized water washing method is to rinse with flowing deionized water for 5 to 10 minutes, and the freeze drying is to freeze dry at -40 ℃ to -60 ℃ for 24 to 30 hours.

9. A Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent prepared by the method according to any one of claims 1 to 8.

10. The application of the Fe-Ca co-crosslinked bimetallic ZIF microsphere composite adsorbent according to claim 9 in the adsorption of antibiotics: ciprofloxacin, tetracycline hydrochloride, and oxytetracycline hydrochloride, characterized in that, The adsorption method includes the following steps: S1. Fe-Ca@bimetallic ZIFs microspheres were added to an aqueous solution with a pH of 4-8 and an antibiotic concentration of 5-80 mg / L for adsorption under stirring. The amount of Fe-Ca@bimetallic ZIFs microsphere composite adsorbent added was 0.1-0.5 g / L, the adsorption time was 12-24 h, and the stirring speed was 200 rpm-350 rpm. S2. After the adsorption is complete, the Fe-Ca@bimetallic ZIFs microspheres containing the drug are filtered through a sieve.

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