Preparation method and application of ZIF-8 magnetic double-ion cross-linked double-network gel ball

Abstract

The invention discloses a preparation method and application of ZIF-8 magnetic double-ion cross-linked double-network gel beads, and relates to the technical field of adsorption material preparation. According to the method, natural macromolecular polysaccharide is used as a gel skeleton, successfully synthesized ZIF-8 is introduced, a magnetic material is added, a double-ion cross-linking agent is used for reaction, and finally vacuum drying is performed to prepare the ZIF-8 gel. The ZIF-8 magnetic dual-ion cross-linked dual-network gel ball not only keeps a complete ZIF-8 crystal structure, but also obviously enlarges the specific surface area of the adsorbent. In addition, the composite adsorbent further has the advantages of magnetism, good mechanical performance, efficient adsorption effect and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adsorbent material preparation, in particular to a preparation method of ZIF-8 magnetic bi-ion cross-linked double network gel spheres and application thereof. BACKGROUND

[0002] ZIF-8 is a kind of imidazole-based zeolite metal-organic framework with 2-methylimidazole (2-MIM) as the main component, and its structure is derived from the self-assembly of coordination bonds between zinc ions and 2-methylimidazole. Due to its excellent thermal stability and chemical stability, as well as its high porosity and large specific surface area, it has a significant effect in the field of adsorption. According to various preparation techniques, the particle size of ZIF-8 can be extended from nanoscale to microscale, generally in the form of white powder. However, the powder form of ZIF-8 has difficulties in collection and exhibits unstable properties in acidic environments, which to some extent hinders its practical use. In recent years, in order to overcome these shortcomings and expand the application range of ZIF-8, researchers have begun to focus on how to prepare ZIF-8 powder into a certain shape of composite material while maintaining its crystal integrity. Natural high molecular materials such as cellulose, sodium alginate, and soybean protein are widely present in nature as natural polymers, and their cost is relatively low. In addition, their surfaces are rich in various oxygen-containing functional groups, which endows them with excellent hydrophilicity and biocompatibility. For example, sodium alginate is considered as an adhesive for shaping ZIF-8 due to its good gel-forming ability and biological activity, and it exhibits high stability in acidic environments. When ZIF-8 is combined with natural high molecular materials to form a composite adsorbent, it not only maintains good biocompatibility, but also has significant regeneration ability, so that this material can maintain high adsorption performance in multiple cycles. Using sodium alginate as an adhesive can not only protect ZIF-8 from low-pH environments, but also enhance the adsorption performance by adding a double gel network structure formed by carboxymethyl cellulose. After the adsorbent adsorbs pollutants, it must be separated from water, and the addition of magnetic Fe3O4 in the composite adsorbent can achieve separation and recovery without generating secondary pollutants.

[0003] At present, ZIF-8 / organic composite adsorbents have made some progress in water treatment applications, but there is still a lack of corresponding attention in the following important aspects.

[0004] 1. Optimize the composite ratio of organic matter and ZIF-8

[0005] The ratio of organic matter to ZIF-8 in the composite adsorbent has a significant impact on its performance and cost. In this system, ZIF-8 is mainly responsible for providing high adsorption capacity. However, when the proportion of ZIF-8 exceeds a certain limit, its effect on improving adsorption performance may no longer be significant, and it may even lead to a decrease in adsorption efficiency, resulting in uneconomical use of materials. In addition, the proportion of organic components plays a key role in the structural stability, hydrophilicity, and biocompatibility of the adsorbent.

[0006] 2. Enhanced adsorption capacity of the material for different types of dyes

[0007] The composite adsorbent formed by ZIF-8 combined with organic matter exhibits multifunctionality beyond other types of composite adsorbents, capable of efficiently treating multiple types of dyes simultaneously. In contrast, many existing composite adsorbents are functionally single, often only effective against a specific type or class of dye, greatly limiting their application breadth and flexibility in complex wastewater treatment. To enhance the adsorption efficiency of composite adsorbents for various pollutants in water, thereby improving their actual treatment capacity, the focus of the study is on optimizing the structural design and functional group modification of the adsorbent. Through these improvements, the adsorption selectivity and capacity of organic composite adsorbents for different types of pollutants can be significantly improved, thereby broadening their application prospects in environmental remediation and water treatment.

[0008] 3. Key pain points not addressed by existing technology

[0009] The existing ZIF-8 / polymer composite adsorbent still has three unbroken technical bottlenecks: ① Poor selectivity for different structural anionic dyes (such as direct violet 51 (DV51) and direct black 19 (DB19)) coexisting in complex wastewater, making it difficult to achieve targeted removal of anionic dyes; ② Desorption process relies on strong acid / strong base elution, which can easily damage the material structure and produce secondary acid / alkali wastewater, not meeting the green treatment requirements; ③ The gel ball has a single pore size and the pore channel is easily blocked, resulting in slow diffusion rate of anionic dye molecules and long adsorption equilibrium time (usually 2-4 hours), which cannot meet the requirements of industrial wastewater rapid treatment. Therefore, developing ZIF-8-based adsorbent materials with high selectivity, intelligent desorption, and fast mass transfer characteristics has become a core problem that needs to be solved in this field. SUMMARY

[0010] The present application aims to overcome the deficiencies of the prior art, and provides a preparation method of ZIF-8 magnetic double-ion crosslinking double-network gel balls and application thereof. The method uses natural high-molecular polysaccharide as a gel skeleton, introduces successfully synthesized ZIF-8, and adds magnetic materials, and finally is prepared by vacuum drying through double-ion crosslinking agent reaction. The ZIF-8 magnetic double-ion crosslinking double-network gel balls not only maintain the complete ZIF-8 crystal structure, but also significantly expand the specific surface area of the adsorbent. In addition, the composite adsorbent also has many advantages such as magnetism, good mechanical properties and high adsorption efficiency.

[0011] To achieve the above object, the present application provides the following scheme:

[0012] The preparation method of the ZIF-8 magnetic double-ion crosslinking double-network gel balls comprises the following steps:

[0013] Step 1: preparation of ZIF-8 powder with crystal face regulation and cationic functional group modification:

[0014] The dimethyl imidazole solution is mixed with the solution containing zinc ions, and at the same time, crystal face regulating and cationic functional group modifying ZIF-8 5% to 15% of the mass of the crystal face regulating agent (one or both of the optional polyvinylpyrrolidone PVP and sodium dodecyl benzene sulfonate SDBS) is added for stirring reaction. After the reaction is completed, the precipitate is obtained by stirring and centrifugation, and then washed with alcohol and repeated centrifugation three times to remove impurities. After the product is collected by suction filtration, it is soaked in 0.1 to 0.5 mol / L of a cationic functional group modifier (optionally 3-aminopropyl triethoxysilane APTES, which enhances the electrostatic adsorption and specific binding to anionic dyes by introducing -NH2) for surface modification at 30 to 40 DEG C for 2 to 4 h, and finally dried to obtain the ZIF-8 powder with crystal face regulation and cationic functional group modification for standby use;

[0015] Step 2: an appropriate amount of the ZIF-8 powder with crystal face regulation and cationic functional group modification prepared above is uniformly dispersed in deionized water, and mechanical stirring is combined with ultrasonic treatment for 2 to 3 h to ensure that the ZIF-8 powder can be fully dispersed in the solvent to form a stable suspension.

[0016] Step 3: nano-sized Fe3O4 particles are dispersed into the above suspension, and continuous stirring is performed for 1 to 2 h to ensure uniform distribution of the particles and avoid aggregation, forming a dispersion liquid;

[0017] Step 4: gel ball preparation:

[0018] ZIF-8 powder with mass ratio of crystal face regulation and cationic functional group modification: sodium alginate: sodium carboxymethyl cellulose = 1-5: 10: 5-10, sodium alginate, sodium carboxymethyl cellulose, and 10%-20% of the total mass of sodium alginate and sodium carboxymethyl cellulose of the pore-forming agent ammonium bicarbonate are added to the prepared dispersion. Ultrasonic is used to promote the complete dissolution of the three substances and fully mix with the ZIF-8 powder for 1-2 h. Then, the dispersed nano-Fe3O4 solution is added, and the stirring is continued until the ingredients are evenly mixed. To eliminate possible bubbles, the mixed solution is subjected to ultrasonic debubbling treatment for 15-30 min. The above-mentioned mixed solution is dropped into a bimetallic ion cross-linking solution with a total mass concentration of 30 g / L using a peristaltic pump (flow rate 0.0003-50 mL / min), and the cross-linking solution is a mixture of Fe(III) (ferric chloride hexahydrate), Y(III) (yttrium nitrate hexahydrate), and a temperature-sensitive cross-linking aid (N-isopropyl acrylamide NIPAM), wherein the mass ratio of iron ions to yttrium ions is 1:1-2:1, and the temperature-sensitive cross-linking aid accounts for 5%-15% of the total mass of the cross-linking solution; after standing for 30-50 min, the droplets dropped are cross-linked to form gel balls. After cross-linking is completed, the gel balls are washed with water to remove unreacted ingredients, and then further treated by vacuum freeze-drying technology, finally obtaining ZIF-8 magnetic bionic cross-linked double network gel balls.

[0019] Preferably, in steps 1, 2, 3 and 4, the stirring speed is 100-400 rpm.

[0020] Preferably, in step 1, the molar ratio of the dimethyl imidazole solution and the zinc ion solution is (7-11):1. The zinc ion solution can be selected from one or more of zinc sulfate heptahydrate, zinc nitrate hexahydrate, zinc acetate dihydrate, zinc chloride hexahydrate, zinc phosphate, zinc borate, zinc chlorate, or zinc chlorate hexahydrate.

[0021] Preferably, in step 1, the stirring reaction time is 7-11 h, and the stirring and centrifugation conditions are 4400 rpm for 15-30 min.

[0022] Preferably, in step 4, the mass ratio of ZIF-8, sodium alginate and sodium carboxymethyl cellulose is 2:10:6.

[0023] The application also provides ZIF-8 magnetic bionic cross-linked double network gel balls prepared by the above preparation method.

[0024] Further, the application provides the use of the above-mentioned ZIF-8 magnetic bionic cross-linked double network gel balls in dye molecule adsorption, and the wastewater is wastewater containing anionic pollutants (direct violet 51 (DV51), direct black 19 (DB19)).

[0025] The beneficial effects of the present application are:

[0026] (1) The ZIF-8 magnetic double-ion crosslinked double-network gel ball has less pH influence in the adsorption process;

[0027] (2) The ultrasonic bubble removal in the preparation process makes the internal structure of the gel ball uniform, and the mass of the loaded Fe3O4 and ZIF-8 is stable;

[0028] (3) The internal product of pure sodium alginate and trivalent iron ion crosslinking is prone to collapse, and the adsorption efficiency is low. The present application introduces carboxymethyl cellulose sodium to interact with sodium alginate, so that it is fully crosslinked with trivalent iron and trivalent yttrium ions, which significantly improves the stability and adsorption efficiency of the gel ball;

[0029] (4) The ZIF-8 magnetic double-ion crosslinked double-network gel ball makes the loaded Fe3O4 and ZIF-8 more stable through multiple internal microscopic intermolecular interactions, and is not easy to lose, avoiding the degradation of ZIF-8 and the weakening or disappearance of the magnetic separation effect;

[0030] (5) The ZIF-8 magnetic double-ion crosslinked double-network gel ball can use the magnetic force of the external magnetic field to quickly and efficiently separate the magnetic material from the solution, avoiding the loss of adsorbent and secondary pollution;

[0031] (6) The ZIF-8 magnetic double-ion crosslinked double-network gel ball can realize efficient adsorption of different structures of anionic dyes through multiple physical and chemical actions (such as electrostatic adsorption of cationic functional groups and anionic dyes, complexation of ZIF-8 active sites and dyes), and has high adsorption efficiency for anionic dyes direct violet 51 (DV51) and direct black 19 (DB19);

[0032] (7) The ZIF-8 magnetic double-ion crosslinked double-network gel ball can be reused, and the adsorption effect is good after repeated use, effectively reducing the application cost;

[0033] (8) The preparation process of the ZIF-8 magnetic double-ion crosslinked double-network gel ball is simple, and is convenient for industrial application;

[0034] (9) The ZIF-8 magnetic double-ion crosslinked double-network gel ball uses natural polymers as the substrate, which has the advantages of abundant source and renewable resources;

[0035] (10) The ZIF-8 magnetic double-ion crosslinked double-network gel ball controls the ZIF-8 crystal face (exposes the {110} active crystal face in a certain direction, enriches Zn 2+Modification with cationic functional groups (introducing -NH2) significantly improves the adsorption selectivity of the material for two anionic dyes (DV51 and DB19) with different structures.

[0036] (11) The introduction of thermosensitive crosslinking aid (NIPAM) enables the gel spheres to have temperature responsiveness: at 25-30℃, the gel spheres maintain a stable crosslinking structure, and the positive charge on their surface forms a strong interaction with the anionic dyes for efficient adsorption; at 40-50℃, the crosslinking network swells reversibly, and the positive charge density temporarily decreases, achieving gentle desorption of the anionic dyes without the need for strong acid / base elution. After 5 adsorption-desorption cycles, the adsorption rate of DV51 and DB19 is still ≥88%, the desorption rate is ≥90%, and there is no secondary pollution.

[0037] (12) The 50-200nm mesoporous-macroporous hierarchical pore structure constructed by the pore-forming agent significantly reduces the diffusion resistance of anionic dye molecules inside the gel spheres. The adsorption equilibrium time is shortened from the traditional 2-4 hours to 30-60 minutes, and the specific surface area is increased by more than 40% compared with gel spheres without pore-forming agents, meeting the needs of rapid treatment of industrial anionic dye wastewater. Attached Figure Description

[0038] Appendix Figure 1 The images show the infrared spectra of sodium alginate (SA), sodium carboxymethyl cellulose (CMC-Na), ZIF-8, Fe3O4, and ZIF-8 magnetic double-ion cross-linked double-network gel spheres.

[0039] Appendix Figure 2 Scanning electron microscope image (top left), surface image (top right), internal image (bottom left), and photograph (bottom right) of the ZIF-8 magnetic dual-ion cross-linked dual-network gel spheres prepared for this invention.

[0040] Appendix Figure 3 The adsorption capacity, cycle number, and adsorption kinetics of DV51 and DB19 on the ZIF-8 magnetic dual-ion cross-linked dual-network gel spheres prepared in this invention at different temperatures were investigated. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0042] Comparative Example 1

[0043] (1) Preparation of ordinary ZIF-8 powder (without regulation and modification of crystal face): 25 mL of deionized water was added to beaker A, then 1.5 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added and stirred until completely dissolved. 25 mL of deionized water was added to beaker B, then 5.6 g of 2-methylimidazole (2-MIM) was added and stirred until completely dissolved. The solution in beaker A was added to beaker B, and after stirring at room temperature for 10 hours, centrifugation was performed at 4500 rpm for 10 minutes, and the supernatant was discarded. 100% ethanol was added for washing, and centrifugation was performed again, which was repeated three times, and finally dried at 25°C to obtain ordinary ZIF-8 powder.

[0044] (2) Preparation of ZIF-8 magnetic bi-ion crosslinking double network gel balls (without porogen, without temperature-sensitive crosslinking auxiliary agent): 1 g of ordinary ZIF-8 powder was taken and added to a beaker containing 100 mL of ultrapure water, and ultrasonic dispersion was performed for 2 hours. 0.4 g of nano Fe3O4 was taken and added to the uniformly dispersed suspension, and ultrasonic dispersion was continued for 2 hours. 0.5 g of sodium alginate (SA) and 0.5 g of sodium carboxymethyl cellulose (CMC-Na) were added to the uniformly dispersed suspension, and uniform stirring was performed for 1 hour. The mixed solution was dropped into a 30 g / L bi-metal ion crosslinking solution (solvent: water, solute: iron chloride hexahydrate, yttrium nitrate hexahydrate, mass ratio of iron ions to yttrium ions: 2:1, mass concentration of bi-metal ions: 30 g / L), and soaked for 24 hours. Washed with deionized water for 3 times, and freeze-dried.

[0045] (3) Adsorption of ZIF-8 magnetic bi-ion crosslinking double network gel balls to anionic dyes: 0.025 g of the above gel balls was added to 25 mL of anionic dyes direct black 19 (DB19) and direct violet 51 (DV51) with a concentration of 40 mg / L at 25°C, and stirred for 2 hours. The concentration of dyes in the solution after adsorption was detected by ultraviolet-visible spectrophotometer, and the adsorption rate of the composite adsorbent to the dyes was calculated. The results showed that the adsorption rate of the gel balls to anionic dyes DB19 was 72%, and the adsorption rate to DV51 was 62%; the adsorption equilibrium time was 120 minutes; after 3 cycles, the adsorption rate decreased to 58% (DB19) and 50% (DV51).

[0046] Comparative Example 2

[0047] (1) Preparation of ordinary ZIF-8 powder (without crystal face regulation and modification): 25 mL of deionized water was added to beaker A, and then 1.5 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added and stirred until completely dissolved. 25 mL of deionized water was added to beaker B, and then 5.6 g of 2-methylimidazole (2-MIM) was added and stirred until completely dissolved. The solution in beaker A was added to beaker B, and after stirring at room temperature for 12 hours, centrifugation was performed at 4500 rpm for 15 minutes, and the supernatant was discarded. 100% ethanol was added for washing, and centrifugation was performed again, repeated three times, and finally dried at 25°C to obtain ordinary ZIF-8 powder.

[0048] (2) Preparation of ZIF-8 magnetic bi-ion crosslinking double network gel balls (without porogen, without temperature-sensitive crosslinking auxiliary agent): 0.1 g of ordinary ZIF-8 powder was taken and added to a beaker containing 100 mL of ultrapure water, and ultrasonic dispersion was performed for 2 hours. 0.4 g of nano Fe3O4 was taken and added to the uniformly dispersed suspension, and ultrasonic dispersion was continued for 2 hours. 1 g of sodium alginate (SA) and 1 g of sodium carboxymethyl cellulose (CMC-Na) were added to the uniformly dispersed suspension, and uniform stirring was performed for 1 hour. The mixed solution was dropped into a 30 g / L bi-metal ion crosslinking solution (solvent: water, solute: iron chloride hexahydrate, yttrium nitrate hexahydrate, mass ratio of iron ions to yttrium ions: 2:1, mass concentration of bi-metal ions: 30 g / L), and soaked for 24 hours. Deionized water was used for washing 3 times, and freeze-drying was performed.

[0049] (3) Adsorption of ZIF-8 magnetic bi-ion crosslinking double network gel balls to anionic dyes: 0.025 g of the above gel balls was added to 25 mL of anionic dyes direct black 19 (DB19) and direct violet 51 (DV51) with a concentration of 40 mg / L at 25°C, and stirring adsorption was performed for 2 hours. The test results showed that the adsorption rate of anionic dyes DB19 was 78%, and the adsorption rate of DV51 was 72%; the adsorption equilibrium time was 110 minutes; after 3 cycles, the adsorption rate decreased to 63% (DB19) and 55% (DV51).

[0050] Comparative Example 3

[0051] (1) Preparation of ordinary ZIF-8 powder (without crystal face regulation and modification): 25 mL of deionized water was added to beaker A, and then 1.5 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added and stirred until completely dissolved. 25 mL of deionized water was added to beaker B, and then 5.6 g of 2-methylimidazole (2-MIM) was added and stirred until completely dissolved. The solution in beaker A was added to beaker B, and after stirring at room temperature for 12 hours, centrifugation was performed at 4500 rpm for 15 minutes, and the supernatant was discarded. 100% ethanol was added for washing, and centrifugation was performed again, repeated three times, and finally dried at 25°C to obtain ordinary ZIF-8 powder.

[0052] (2) Preparation of ZIF-8 magnetic bi-ion crosslinking double network gel balls (without porogen, without temperature-sensitive crosslinking assistant): 0.3 g of ordinary ZIF-8 powder was added to a beaker containing 100 mL of ultrapure water and ultrasonically dispersed for 2 hours. 0.4 g of nano Fe3O4 was added to the uniformly dispersed suspension and ultrasonically dispersed for another 2 hours. 1 g of sodium alginate (SA) and 0.1 g of sodium carboxymethyl cellulose (CMC-Na) were added to the uniformly dispersed suspension, and stirred at a uniform speed for 1 hour. The mixed solution was dropped into a 30 g / L bi-metal ion crosslinking solution (solvent: water, solute: ferric chloride hexahydrate and yttrium nitrate hexahydrate, mass ratio of iron ions to yttrium ions: 2:1, mass concentration of bi-metal ions: 30 g / L) and soaked for 24 hours. Then, it was washed with deionized water for 3 times and freeze-dried.

[0053] (3) Adsorption of ZIF-8 magnetic bi-ion crosslinking double network gel balls to anionic dyes: 0.025 g of the above gel balls was added to 25 mL of anionic dyes direct black 19 (DB19) and direct violet 51 (DV51) with a concentration of 40 mg / L at 25°C, and stirred for 2 hours for adsorption. The test results showed that the adsorption rate of DB19 was 65%, and the adsorption rate of DV51 was 53%; the adsorption equilibrium time was 130 minutes; and the adsorption rate decreased to 50% (DB19) and 42% (DV51) after 3 cycles.

[0054] Comparative Example 4

[0055] (1) Preparation of ordinary ZIF-8 powder (without crystal face regulation and modification): The same as step (1) of Comparative Example 3, ordinary ZIF-8 powder was obtained.

[0056] (2) Preparation of ZIF-8 magnetic bi-ion crosslinking double network gel balls (without porogen, without temperature-sensitive crosslinking assistant): 0.3 g of ordinary ZIF-8 powder was added to a beaker containing 100 mL of ultrapure water and ultrasonically dispersed for 2 hours. 0.4 g of nano Fe3O4 was added to the uniformly dispersed suspension and ultrasonically dispersed for another 2 hours. 1 g of sodium alginate (SA) and 0.5 g of sodium carboxymethyl cellulose (CMC-Na) were added to the uniformly dispersed suspension, and stirred at a uniform speed for 1 hour. The mixed solution was dropped into a 30 g / L bi-metal ion crosslinking solution (solvent: water, solute: ferric chloride hexahydrate and yttrium nitrate hexahydrate, mass ratio of iron ions to yttrium ions: 2:1, mass concentration of bi-metal ions: 30 g / L) and soaked for 24 hours. Then, it was washed with deionized water for 3 times and freeze-dried.

[0057] (3) Adsorption of anionic dyes by ZIF-8 magnetic bi-ion cross-linked double network gel balls: 0.025 g of the above gel balls were added to 25 mL of anionic dyes Direct Black 19 (DB19) and Direct Violet 51 (DV51) with a concentration of 40 mg / L at 25°C, and stirred for 2 hours for adsorption. The test results showed that the adsorption rate of anionic dyes DB19 was 76%, and the adsorption rate of DV51 was 52%; the adsorption equilibrium time was 125 minutes; and the adsorption rate decreased to 60% (DB19) and 45% (DV51) after 3 cycles.

[0058] Example 1

[0059] (1) Preparation of ZIF-8 powder with amino modification and crystal face regulation (amino modification + crystal face regulation): 25 mL of deionized water was added to beaker A, 1.1 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added and stirred to dissolve, and 0.1 g of crystal face regulator polyvinylpyrrolidone (PVP) was added. 25 mL of deionized water was added to beaker B, and 5.6 g of 2-methylimidazole (2-MIM) was added and stirred to dissolve. The solution in beaker A was added to beaker B, stirred at 200 rpm for 10 hours, then centrifuged at 4500 rpm for 15 minutes, and the supernatant was discarded; the centrifugation was repeated 3 times with ethanol, and the product was soaked in a 0.2 mol / L 3-aminopropyltriethoxysilane (APTES) solution, stirred at 35°C for 3 hours for modification, and finally dried at 25°C to obtain ZIF-8 powder with amino modification and crystal face regulation.

[0060] (2) Preparation of ZIF-8 magnetic bi-ion cross-linked double network gel balls (containing porogen): 0.1 g of the above ZIF-8 powder with crystal face regulation and cationic functional group modification was added to 100 mL of ultrapure water and ultrasonically dispersed for 2 hours; 0.4 g of nano Fe3O4 was added and ultrasonically dispersed for another 2 hours. 1 g of sodium alginate (SA), 0.5 g of sodium carboxymethyl cellulose (CMC-Na), and 0.15 g of porogen ammonium bicarbonate (NH4HCO3) were added, and stirred at 200 rpm for 1 hour; after ultrasonic defoaming for 20 minutes, the mixed solution was dropped into a 30 g / L bi-metal ion cross-linking solution (solvent: water, solute: ferric chloride hexahydrate and yttrium nitrate hexahydrate, mass ratio of iron ions to yttrium ions: 2:1, mass concentration of bi-metal ions: 30 g / L) using a peristaltic pump (flow rate: 0.001 mL / min), and left to stand for 40 minutes. After washing with water for 3 times, freeze-drying was performed to obtain the target gel balls.

[0061] (3) Anionic dye adsorption performance test: ① Selectivity test: 0.025 g of the gel balls was added to 25 mL of anionic dyes DB19 (40 mg / L), DV51 (40 mg / L) and interfering anion SO4 2-(100mg / L, simulating the actual wastewater composition) mixed solution for 2 hours; ②mass transfer efficiency test: record the adsorption rate of DB19 and DV51 at 15, 30, 60 minutes. The results show that: ①DB19 adsorption rate 92%, DV51 adsorption rate 90%, SO4 2- The influence on adsorption rate is only 3% (excellent selectivity for anionic dyes); ②DB19 adsorption rate 70% at 15 minutes, DV51 adsorption rate 68%, 30 minutes to adsorption equilibrium.

[0062] Example 2

[0063] (1) Preparation of {110} crystal face regulated ZIF-8 powder ({110} crystal face regulation): In beaker A, add 25 mL of deionized water, add 1.7 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and stir to dissolve, then add 0.15 g of crystal face regulator sodium dodecyl benzene sulfonate (SDBS); In beaker B, add 25 mL of deionized water, add 5.6 g of 2-methyl imidazole (2-MIM) and stir to dissolve. Add the solution in beaker A to beaker B, stir at 300 rpm for 10 hours, then centrifuge at 4500 rpm for 20 minutes, discard the supernatant; ethanol wash and centrifuge 3 times, dry at room temperature to obtain {110} crystal face regulated ZIF-8 powder.

[0064] (2) Preparation of ZIF-8 magnetic bionic ion cross-linked double network gel balls (containing temperature-sensitive cross-linking auxiliary agent): Take 1 g of the above {110} crystal face exposed ZIF-8 powder and add 100 mL of ultrapure water, ultrasonic dispersion for 2 hours; add 0.4 g of nano Fe3O4 and continue to ultrasonic dispersion for 2 hours. Add 1 g of sodium alginate (SA) and 0.5 g of carboxymethyl cellulose sodium (CMC-Na), stir at 200 rpm for 1 hour; after ultrasonic defoaming for 20 minutes, drop the mixed solution into 30 g / L bimetallic ion cross-linking solution (solvent is water, solute is ferric chloride hexahydrate, yttrium nitrate hexahydrate, N-isopropyl acrylamide (NIPAM), the mass ratio of iron ion to yttrium ion is 2:1, NIPAM accounts for 10% of the total solute mass, the mass concentration of bimetallic ions is 30 g / L) at a flow rate of 0.002 mL / min and a hose inner diameter of 1 mm, and stand for 40 minutes. Wash with water 3 times, freeze-dry to obtain the target gel balls.

[0065] (3) Anion dye adsorption-desorption cycle test: ① Adsorption: 0.025 g of gel balls were added to 25 mL of an anion dye DB19 (40 mg / L) and DV51 (40 mg / L) mixed solution at 25°C, and adsorbed for 2 hours to measure the adsorption rate; ② Desorption: the adsorbed gel balls were placed in 45°C deionized water and stirred for 30 minutes for desorption; ③ The above steps were repeated 5 times. The results showed that the first adsorption rate was DB19 89%, DV51 82%; after 5 cycles, the adsorption rate was DB19 87%, DV51 80%, and the desorption rate was ≥90%.

[0066] Example 3

[0067] (1) Preparation of ZIF-8 powder with carboxyl modification and crystal face regulation (carboxyl modification + crystal face regulation): 25 mL of deionized water was added to beaker A, 1.4 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was added and stirred to dissolve, and 0.12 g of polyvinylpyrrolidone (PVP) was added; 25 mL of deionized water was added to beaker B, and 5.6 g of 2-methylimidazole (2-MIM) was added and stirred to dissolve. The solution in beaker A was added to beaker B, and after stirring at 250 rpm for 10 hours, centrifugation was performed at 4500 rpm for 18 minutes, and the supernatant was discarded; the product was washed with ethanol and centrifuged 3 times, and after suction filtration, the product was soaked in a 0.3 mol / L succinic anhydride solution, stirred at 35°C for 3.5 hours for carboxyl modification, and dried at 25°C to obtain ZIF-8 powder with carboxyl modification and crystal face regulation.

[0068] (2) Preparation of ZIF-8 magnetic bi-ion cross-linked double network gel balls (porogenic + temperature sensitive): 0.5 g of the above carboxyl modified ZIF-8 powder was added to 100 mL of ultrapure water and ultrasonically dispersed for 2 hours; 0.4 g of nano Fe3O4 was added and ultrasonically dispersed for another 2 hours. 1 g of sodium alginate (SA), 0.6 g of carboxymethyl cellulose sodium (CMC-Na), and 0.2 g of porogen polyethylene glycol-4000 (PEG-4000) were added, and stirred at 250 rpm for 1 hour; after ultrasonic defoaming for 25 minutes, the mixed solution was dropped into a 30 g / L bi-metal ion cross-linking solution (solvent: water, solute: ferric chloride hexahydrate, yttrium nitrate hexahydrate, N-isopropyl acrylamide (NIPAM), iron ion to yttrium ion mass ratio of 2:1, NIPAM accounting for 8% of the total solute mass, bi-metal ion mass concentration of 30 g / L) using a peristaltic pump (flow rate 0.0015 mL / min, inner diameter of hose 0.9 mm), and left to stand for 45 minutes. Washed with water 3 times, freeze-dried to obtain the target gel balls.

[0069] (3) Anion dye comprehensive performance test: 0.025 g of the gel ball is added into 25 mL of a mixed solution containing anion dyes DB19 (40 mg / L), DV51 (40 mg / L) and interfering anion Cl- (100 mg / L) at 25°C, and the adsorption equilibrium time, adsorption rate and 5-cycle performance are tested. The results show that the adsorption equilibrium time is 45 minutes (multistage pore effect); the first adsorption rate is 93% for DB19, 91% for DV51, and the Cl- interference is only 4% (selectivity is good); after 5 cycles, the adsorption rate is 90% for DB19 and 88% for DV51 (temperature-sensitive desorption protects the adsorption sites), and the comprehensive performance meets the requirements of anion dye wastewater treatment.

[0070] Results of the attached drawings

[0071] Figure Figure 1 The infrared spectra of sodium alginate (SA), sodium carboxymethyl cellulose (CMC-Na), unmodified ZIF-8, nano Fe3O4 and the ZIF-8 magnetic bi-ion cross-linked double network gel ball of the application are compared, the abscissa is the wave number (cm -1 ), and the ordinate is the transmittance (%). As can be seen from the figure:

[0072] 1. The -OH stretching vibration peak of pure SA at 3441 cm -1 , the -COO- symmetric stretching vibration peak of CMC-Na at 1444 cm -1 , are all shifted to 3375 cm -1 , 1425 cm -1 in the spectrum of the gel ball, indicating that SA / CMC-Na has a coordination reaction with Fe 3+ / Y 3+ , and forms a stable cross-linked network;

[0073] 2. The characteristic peaks of unmodified ZIF-8 at 421 cm -1 (Zn-N bond), 670-760 cm -1 (C-H bending) are retained and the peak shape is complete in the spectrum of the gel ball, confirming that the crystal form of ZIF-8 is not destroyed;

[0074] 3. The Fe-O stretching vibration peak (corresponding to nano Fe3O4) appears at 834 cm -1 , and the -NH2 stretching vibration peak (originating from APTES modification) is newly added at 3300-3400 cm -1 , directly proving that Fe3O4 is successfully loaded and the ZIF-8 cation modification is effective, providing electrostatic action sites for subsequent anion dye adsorption.

[0075] Figure Figure 2The four subgraphs include low-magnification SEM of the gel ball (top left, magnification 200 times, scale 200 μm), high-magnification surface SEM (top right, magnification 80.0k times, scale 500 nm), cross-sectional internal SEM (bottom left, magnification 35 times, scale 1.00 mm), and a real photograph (bottom right), which collectively reflect the microstructure and macroscopic morphology of the gel ball:

[0076] 1. The top left graph (low magnification) shows that the gel ball is regular spherical in shape, and the surface has no obvious cracks, proving that the double-ion crosslinking gives the material good mechanical integrity;

[0077] 2. The top right graph (high-magnification surface) shows that the surface of the gel ball is "cauliflower-like" rough structure, with a large number of 50-200 nm mesopores, which are multi-level pores formed by the sublimation of the porogen NH4HCO3 / PEG-4000 during freeze-drying, and can reduce the diffusion resistance of anionic dyes (DV51, DB19);

[0078] 3. The bottom left graph (cross-sectional internal) shows that the interior of the gel ball is a loose and porous structure, and the white particles (ZIF-8) and black particles (Fe3O4) are uniformly dispersed in the SA / CMC-Na matrix without obvious agglomeration, confirming that the components are uniformly compounded;

[0079] 4. The bottom right graph (real photograph) shows that the gel ball is a milky white opaque sphere with a diameter of about 1-2 mm, which can be stably suspended in an aqueous solution, and can be quickly aggregated under the action of an external magnetic field, verifying its magnetic separation performance.

[0080] Figure 2 Figure 3 The seven subgraphs include adsorption kinetics curves of DV51 / DB19 at different temperatures (a, b), intraparticle diffusion model fitting curves (c, d), adsorption isotherm (e), pH adaptability curve (f), and cyclic adsorption rate curve (g), which comprehensively reflect the adsorption performance of the gel ball for anionic dyes:

[0081] 1. Subgraphs a, b (adsorption kinetics): the horizontal coordinate is time (min), and the vertical coordinate is adsorption capacity (mg / g), 1 / q t (q t is the adsorption capacity at time t, in mg / g). The pseudo-second-order kinetics model fitting shows that the fitting correlation coefficients R 2 of DV51 and DB19 at 298 K are 0.9997 and 0.9988, respectively, and the adsorption capacity within 30 min reaches more than 90% of the equilibrium adsorption capacity, confirming that the adsorption is mainly chemical adsorption, and the multi-level pores significantly accelerate mass transfer;

[0082] 2. Subgraphs c, d (intraparticle diffusion model): the horizontal coordinate is time 1 / 2 (min1 / 2 ), the ordinate is the adsorption capacity (mg / g). The curve is divided into two stages of "surface adsorption" and "intra-pore diffusion", and no straight line passes through the origin, indicating that intra-particle diffusion is not the only rate-controlling factor, which is consistent with the kinetic conclusion;

[0083] 3. Subgraph e (adsorption isotherm): the abscissa is the equilibrium concentration (mg / L), and the ordinate is the equilibrium adsorption capacity (mg / g). The Langmuir model fitting shows that the maximum adsorption capacity of the gel ball for DV51 and DB19 is 463.7 mg / g and 458.2 mg / g respectively at 298 K, which is significantly higher than that of the comparative sample without pore-forming agent and without modification;

[0084] 4. Subgraph f (cycle performance): the abscissa is the cycle number (1-7 times), and the ordinate is the adsorption rate (%). After 7 cycles of "adsorption (25℃)-desorption (45℃ deionized water)", the adsorption rate of DV51 still remains above 85%, without obvious decrease, proving that the temperature-sensitive crosslinking system realizes green desorption, and the material has excellent cycle stability.

Claims

1. A method for preparing a magnetic bi-ion cross-linked double network gel ball of ZIF-8, characterized in that, The method comprises the following steps: Step 1: Preparation of ZIF-8 powder with crystal face regulation and cationic functional group modification Mix the dimethyl imidazole solution with the solution containing zinc ions, while adding 5-15% of the crystal face regulator of the ZIF-8 powder with crystal face regulation and cationic functional group modification to stir the reaction; the crystal face regulator is selected from one or both of polyvinylpyrrolidone (PVP) and sodium dodecyl benzene sulfonate (SDBS); after the reaction is completed, the precipitate is obtained by stirring and centrifugation, and then washed with alcohol and centrifuged to remove impurities; after the product is collected by suction filtration, it is soaked in a 0.1-0.5 mol / L cationic functional group modifier, and surface modification is performed by stirring at 30-40°C for 2-4 h, and finally dried to obtain the ZIF-8 powder with crystal face regulation and cationic functional group modification for standby; Step 2: Disperse the ZIF-8 powder with crystal face regulation and cationic functional group modification prepared above in deionized water, and mechanically stir and ultrasonically treat for 2-3 h to form a suspension; Step 3: Disperse the nano-sized Fe3O4 particles into the suspension, continuously stir for 1-2 h to ensure uniform distribution of the particles and avoid aggregation, and form a dispersion liquid; Step 4: Preparation of gel balls According to the mass ratio of the ZIF-8 powder with crystal face regulation and cationic functional group modification, sodium alginate and carboxymethyl cellulose sodium, 1-5:10:5-10, add sodium alginate, carboxymethyl cellulose sodium, and 10%-20% of the pore-forming agent ammonium bicarbonate based on the total mass of sodium alginate and carboxymethyl cellulose sodium to the prepared dispersion liquid; use ultrasonic waves to promote complete dissolution and fully mix with the ZIF-8 powder for 1-2 h; then, add the dispersed nano Fe3O4 solution, and continue to stir until the components are uniformly mixed; to eliminate possible air bubbles, ultrasonic debubbling treatment is performed on the mixed solution for 15-30 min; use a peristaltic pump to drop the above mixed solution into a bimetallic ion crosslinking solution with a total mass concentration of 30 g / L; the crosslinking solution is a mixture of Fe(III) and Y(III) and a temperature-sensitive crosslinking aid, wherein the mass ratio of iron ions to yttrium ions is 1:1-2:1, and the temperature-sensitive crosslinking aid accounts for 5%-15% of the total mass of the crosslinking solution; stand for 30-50 min to allow the droplets dropped to undergo crosslinking reaction to form gel balls; after the crosslinking is completed, wash the gel balls with water to remove unreacted components, and then obtain the ZIF-8 magnetic bionic ion crosslinked double network gel balls by vacuum freeze-drying technology.

2. The method of claim 1, wherein, In steps 1, 2, 3 and 4, the stirring speed is 100-400 rpm.

3. The method of claim 1, wherein, In step 1, the molar ratio of the dimethyl imidazole solution to the zinc ion solution is (7-11):1; the zinc ion solution is selected from one or more of zinc sulfate heptahydrate, zinc nitrate hexahydrate, zinc acetate dihydrate, zinc chloride hexahydrate, zinc phosphate, zinc borate, zinc chlorate, or zinc chlorate hexahydrate.

4. The method of claim 1, wherein, In step 1, the stirring reaction time is 7-11 h, and the stirring and centrifugation conditions are 4400 rpm centrifugation for 15-30 min.

5. The method of claim 1, wherein, In step 4, the mass ratio of the ZIF-8, sodium alginate and carboxymethyl cellulose sodium is 2:10:

6.

6. The ZIF-8 magnetic dual-ion crosslinked double network hydrogel spheres prepared by the method of claim 1.

7. The use of the ZIF-8 magnetic dual-ion crosslinked double network hydrogel spheres of claim 6 in the adsorption of dye molecules, wherein the wastewater is wastewater containing anionic pollutants.

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