Super-macroporous PGMA (at) ZIF-8 (at) Au composite microsphere with micro-nano two-stage confinement structure and preparation method of super-macroporous PGMA (at) ZIF-8 (at) Au composite microsphere

Abstract

The invention belongs to the technical field of functional composite materials, and particularly relates to a super-macroporous composite microsphere with a micron-nano two-stage confinement structure and a preparation method of the super-macroporous composite microsphere. The preparation method comprises the following steps: firstly, preparing super-macroporous polyglycidyl methacrylate (PGMA) microspheres by adopting a composite pore-foaming agent, then performing imidazole functional modification on pore channels and surfaces of the microspheres, and growing ZIF-8 crystals in situ in a heterogeneous nucleation manner to obtain super-macroporous PGMA-ZIF-8 microspheres, and finally, etching the ZIF-8 pore channels by utilizing a sulfydryl-containing etching agent, and loading nanogold in the ZIF-8 pore channels through Au-S bonds. According to the technology, by designing a micro-nano two-stage confinement structure, spatial orientation anchoring of gold nanoparticles (AuNPs) is achieved, and the problems that a noble metal catalyst is poor in dispersity, prone to falling off, limited in mass transfer and the like are effectively solved. The PGMA (at) ZIF-8 (at) Au composite microspheres prepared by the method have wide application value in the fields of industrial catalysis, environmental governance, biosensing and surface enhanced Raman scattering detection.

Description

Technical Field

[0001] The present invention belongs to the field of functional composite materials technology, specifically relating to ultra-macroporous composite microspheres with a micron-nano dual-level confinement structure and their preparation method. The composite microspheres utilize poly(glycidyl methacrylate) (PGMA) as a micron-sized carrier. A zeolite imidazolate framework (ZIF-8) is grown in situ on the surface and selectively etched to form nanoscale confinement cavities, enabling spatially oriented anchoring of gold nanoparticles (AuNPs). This addresses the issues of poor dispersion, easy shedding, and limited mass transfer associated with noble metal catalysts. Background Art

[0002] In recent years, the acceleration of industrialization and modernization has led to a surge in the discharge of phenol-containing wastewater. Phenolic compounds are widely used as the main components of synthetic pesticides, organic dyes, and pharmaceuticals and have been identified as environmental pollutants. Among them, p-nitrophenol (PNP), as a typical toxic phenolic pollutant, poses a serious threat to the ecological environment and human health due to its strong chemical stability, difficulty in biodegradation, and easy accumulation in organisms. Studies have shown that PNP can cause blood system diseases, liver damage, and skin irritation in humans. Its efficient removal in water bodies has become an urgent need for environmental governance (Ecotoxicology and Environmental Safety, 2024, 281, 116611).

[0003] Among the many pollutant treatment technologies, catalytic reduction is considered to be an ideal method for degrading PNPs due to its mild reaction conditions and high efficiency. AuNPs have shown great potential in the 4-NP reduction reaction due to their unique surface plasmon resonance effect and excellent catalytic activity. However, the high surface energy of AuNPs makes them very easy to agglomerate, resulting in a decrease in catalytic activity, and the difficulty in recovering nanoparticles seriously limits their practical application. Therefore, the development of carrier materials that can stably load AuNPs and are easy to separate and recover has become a key challenge in current research. Organic polymer microspheres and metal-organic frameworks (MOFs) are often used as excellent carriers of metal nanoparticles. For example, poly(glycidyl methacrylate) (PGMA) microspheres have a micron-sized size (10-50 μm) that is easy to separate and recover, and the rich epoxy groups on the surface can provide a large number of modification sites. However, the specific surface area of ​​this type of carrier is limited (usually <100 m 2 / g), resulting in low AuNPs loading and particles easily aggregated in the pores. ZIF-8 is a typical MOF material with a high specific surface area (>1000m 2 / g) and tunable nanopores, and AuNPs are generally loaded by in situ synthesis and post-impregnation reduction method (Electrochem. Commun., 2020, 114, 106715). However, the direct use of ZIF-8 to load AuNPs is easily restricted by its pores, resulting in low accessibility of active sites, AuNPs easily aggregate and leak on the surface of ZIF-8, and nano-scale ZIF-8 itself is difficult to recycle. In summary, although PGMA microspheres and ZIF-8 materials each show unique advantages in loading Au NPs, there are still obvious limitations when the two are used independently. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this paper proposes a novel "micro-nano dual-level confinement" strategy: PGMA microspheres with ultra-large pores serve as the matrix. Imidazoline functional groups are modified on the surface to provide high-density sites for heterogeneous nucleation of ZIF-8, enabling in situ growth of ZIF-8. Furthermore, ligand competitive etching is used to create precise defects in the ZIF-8 layer, ultimately achieving high-dispersion fixation of AuNPs within nano-confined cavities on the easily recyclable ZIF-8-loaded micronized carrier. This design overcomes the performance bottleneck of traditional carrier materials and provides a new approach for the construction of efficient catalytic systems.

[0005] The technical solution adopted in the present invention is:

[0006] A PGMA@ZIF-8@Au composite microsphere with a micro-nano dual-level confined structure and a preparation method thereof, comprising the following steps:

[0007] (1) Mixing monomer glycidyl methacrylate (GMA), a crosslinking agent, a composite porogen, and an initiator to form an oil phase, and stirring to dissolve; dissolving a stabilizer and a salt in deionized water to form an aqueous phase; dispersing the oil phase in the aqueous phase under stirring to form an O / W emulsion, stirring and passing nitrogen for 30 minutes, heating to start polymerization, and obtaining polymer microspheres after a period of reaction; washing the obtained polymer microspheres with water and ethanol several times, respectively, and then extracting with acetone or ethanol for 24 hours, and drying under vacuum at room temperature to obtain ultra-large-porous PGMA microspheres;

[0008] (2) surface-modifying the ultra-macroporous PGMA microspheres obtained in step (2) with an imidazole functionalizing agent, washing with methanol after the reaction, and vacuum drying to obtain ultra-macroporous PGMA microspheres coupled with imidazole groups;

[0009] (3) Imidazole-functionalized ultra-macroporous PGMA microspheres were added to a methanol solution of zinc nitrate hexahydrate and 2-methylimidazole at a certain temperature, so that ZIF-8 crystals were heterogeneously nucleated and grown in situ in the pores and on the surface of the ultra-macroporous PGMA microspheres under the initiation of imidazole groups. After a period of reaction, the ultra-macroporous PGMA@ZIF-8 composite microspheres were washed with methanol and vacuum dried to obtain;

[0010] (4) At room temperature, PGMA@ZIF-8 composite microspheres were added to a methanol solution containing an etchant. The etchant caused the ZIF-8 skeleton to partially dissociate through competitive coordination, and the pores were enlarged. After a period of reaction, the microspheres were washed with methanol and vacuum dried to obtain ultra-macroporous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface.

[0011] (5) The ultra-large-porous PGMA@ZIF-8-SH microspheres were added to a chloroauric acid aqueous solution containing a stabilizer, and AuNPs were in situ generated under the action of a reducing agent. The AuNPs were then loaded onto the PGMA@ZIF-8-SH microspheres through Au-S bonds to obtain ultra-large-porous PGMA@ZIF-8@Au composite microspheres.

[0012] Preferably, the cross-linking agent described in step (1) is selected from at least one of ethylene glycol dimethacrylate (EGDMA), ethylene glycol diacrylate (EGDA), 1,6-hexanediol diacrylate (HDDA), polyethylene glycol dimethacrylate (PEGDMA), polyethylene glycol diacrylate (PEGDA), and divinylbenzene (DVB), and the cross-linking degree is 10-50%.

[0013] Preferably, the porogen in step (1) is selected from at least two of toluene, xylene, chloroform, isopropanol, cyclohexanol, and n-hexanol, and the added amount is 10-150% of the amount of the polymerizable monomer.

[0014] The initiator described in step (1) is an oil-soluble initiator, which can be an azo initiator such as azobisisobutyronitrile (AIBN) and azobisisoheptanenitrile (ABVN); it can be a peroxide initiator such as benzoyl peroxide (BPO) and alkyl hydroperoxide; or it can be a mixture thereof; the amount of the initiator used is 1%-10% by weight of all polymerizable monomers.

[0015] The aqueous phase stabilizer described in step (1) is a water-soluble polymer, such as polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), gelatin, polyethylene glycol (PEG), carboxymethyl cellulose (CMC), etc., with a content of 0.1%-6% of the mass of the aqueous phase; the salt is an inorganic salt such as sodium chloride, sodium sulfate or magnesium sulfate, with a content of 0.02%-3% of the mass of the aqueous phase; the volume ratio of the aqueous phase to the oil phase is in the range of 3:1-30:1.

[0016] Preferably, the reaction time in step (1) is 12-24 h, and the reaction temperature is 65-90° C.

[0017] Preferably, the imidazole functionalizing agent described in step (2) is selected from one of 1-(3-aminopropyl)imidazole, 1-(2-hydroxyethyl)imidazole, 3-(1-imidazolyl)propionic acid, 4-(1-imidazolyl)propionic acid, 4-(1-imidazolyl)benzoic acid, and hydroxybutylimidazole.

[0018] In step (2), the molar concentration range of the imidazole functionalizing reagent in the reaction system is 0.1-3.0M, and the reaction conditions of different imidazole functionalizing reagents and PGMA microspheres are different: for reagents containing amino groups, they can be directly reacted in a buffer solution with a pH of 9-11, at a temperature of 25-60°C, and for 3-12 hours; for reagents containing carboxyl groups, it is necessary to first activate the carboxyl group using a conventional method (such as 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC·HCl) + N-hydroxysuccinimide (NHS)), and then react with the epoxy group under weak alkaline conditions (pH 8-9), at a reaction temperature of 4-25°C, and for 1-24 hours; for reagents containing hydroxyl groups, it is necessary to use a strong base (NaOH, KOH, NaH, etc.) to catalyze the epoxy group ring opening reaction with the hydroxyl group in an anhydrous solvent, at a reaction temperature of 50-80°C, and for 6-48 hours.

[0019] In step (3), the concentration range of zinc nitrate hexahydrate is 25-100 mM, the concentration range of 2-methylimidazole is 50-200 mM, and the reaction temperature is 20-80°C.

[0020] Preferably, the etchant described in step (4) is selected from at least one of 2-mercaptoimidazole, 4-mercaptoimidazole, 1-(2-mercaptoethyl)imidazole, and 2-mercaptobenzimidazole; the mass ratio of ZIF-8 to the etchant is in the range of 1:1-1:10, the etching time is 1-12h, and the etching temperature is room temperature.

[0021] Preferably, the concentration range of the aqueous chloroauric acid solution in step (5) is 0.5-10 mM, the reaction temperature is room temperature, and the reaction time is 1-12 h.

[0022] The stabilizer in step (5) is the same as that in step (1), with a concentration range of 0.01%-1%.

[0023] The reducing agent in step (5) is selected from one of sodium borohydride, sodium cyanoborohydride, sodium citrate, and ascorbic acid, and the molar ratio of the reducing agent to chloroauric acid is 2:1-10:1.

[0024] The mass concentration of PGMA microspheres in the reaction system in steps (2)-(5) ranges from 1 to 10 g / 100 mL.

[0025] The ultra-large-pore PGMA@ZIF-8@Au composite microspheres with a micro-nano dual-level confined structure were obtained through the above steps. The particle size was 20-300 μm, the pore size was 100-1000 nm, and the specific surface area was 50-200 m 2 / g, ZIF-8 loading capacity was 500-1000 mg / g microspheres, and AuNPs loading capacity was 20-100 mg / g microspheres.

[0026] The present invention is beneficial in that:

[0027] The present invention effectively resolves the contradiction between the loading capacity, dispersibility, and recyclability of traditional carrier materials by designing a "micro-nano dual-level confinement" structure. First, the PGMA microspheres with ultra-large pores not only ensure the in-situ growth and loading capacity of ZIF-8 crystals within the pores, but also improve the mass transfer efficiency during the catalytic process. Secondly, a thiol-containing etchant is used to construct thiol-containing nano-gaps in the ZIF-8 layer, achieving nano-confinement and fixation of AuNPs, avoiding the leakage and aggregation problems of AuNPs. The PGMA@ZIF-8@Au composite microspheres prepared by the present invention have broad application value in the fields of industrial catalysis, environmental governance, biosensing, and surface-enhanced Raman scattering detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Scanning electron microscope images of the ultra-macroporous PGMA microspheres prepared in Example 1 of the present invention at (a) ×600 and (b) ×5000 magnifications;

[0029] Figure 2 : is the pore size distribution diagram of the ultra-macroporous PGMA microspheres prepared in Example 1 of the present invention;

[0030] Figure 3 : is the particle size distribution diagram of the ultra-macroporous PGMA microspheres prepared in Example 1 of the present invention;

[0031] Figure 4 The ultra-macroporous PGMA@ZIF-8 composite microspheres prepared in Example 1 of the present invention are (a) × 170 and (b) ×

[0032] Scanning electron microscope photo at 30,000x magnification;

[0033] Figure 5 The ultra-large porous PGMA@ZIF-8-SH composite microspheres after etching in Example 1 of the present invention are (a) × 170 and (b)

[0034] Scanning electron microscope photo at ×30000 magnification;

[0035] Figure 6 This is the EDS element mapping of the PGMA@ZIF-8@Au composite microspheres prepared in Example 1 of the present invention;

[0036] Figure 7 Optical photographs of the ultra-macroporous PGMA@Au microspheres (a) in the comparative example and the ultra-macroporous PGMA@ZIF-8@Au microspheres (b) in Example 1;

[0037] Figure 8 The PGMA@ZIF-8@Au composite microspheres prepared in Example 1 of the present invention and the PGMA@ZIF-8@Au composite microspheres prepared in the comparative example

[0038] Graph of the degradation rate of PNP catalyzed by PGMA@Au microspheres. Specific implementation methods

[0039] The specific implementation method of the present invention is as follows:

[0040] Example 1:

[0041] (1) The monomer GMA (3g), crosslinker EGDMA (1g), toluene (5g), isopropanol (1g) and initiator BPO (0.16g) were mixed evenly as the oil phase; 100g of the aqueous phase (PVA content of 1.5%, NaCl content of 0.1%); under stirring conditions, the oil phase was dispersed in the aqueous phase to form an O / W emulsion, stirred at 120rpm and nitrogen was passed through for 30min, and then reacted at 75℃ for 20h. The obtained microspheres were washed with water and ethanol several times, then extracted with ethanol for 24h, and dried in vacuum at room temperature to obtain ultra-large porous PGMA microspheres. The obtained microspheres had an average particle size of 98μm, an average pore size of 630nm, a porosity of 65.7%, and a specific surface area of ​​78.3m 2 / g, SEM images are shown in Figure 1 , particle size distribution see Figure 2 , pore size distribution see Figure 3 .

[0042] (2) 100 mL of carbonate buffer solution (pH 10) containing 1-(3-aminopropyl)imidazole (1 M) and 1 g of the ultra-large porous PGMA microspheres prepared in step (1) were added to a 250 mL three-necked flask in sequence, and the mixture was stirred at 50°C and 120 rpm using a constant temperature water bath and an overhead mechanical stirrer for 3 h. The remaining liquid was then filtered using a Buchner funnel, and the microspheres were repeatedly washed five times with methanol solution. The washed microspheres were placed in a vacuum drying oven and dried for 6 h to obtain imidazole-modified ultra-large porous PGMA microspheres.

[0043] (3) 100 mL of 50 mM methanol solution of zinc nitrate hexahydrate and 1 g of ultra-macroporous PGMA microspheres functionalized with imidazole in step (2) were added to a 250 mL three-necked flask in sequence, and stirred at 40 ° C and 120 rpm for 3 h using a constant temperature water bath and an overhead mechanical stirrer. Then, 2-methylimidazole (1.231 g, 15 mmol) was added and stirred for 3 h. The microspheres were washed with methanol solution and dried in a vacuum drying oven for 6 h to obtain ultra-macroporous PGMA@ZIF-8 composite microspheres. The loading amount of ZIF-8 was 750 mg / g microspheres. The scanning electron micrograph is shown in FIG. Figure 4 .

[0044] (4) The ultra-macroporous PGMA@ZIF-8 composite microspheres (0.1 g), 2-mercaptoimidazole (0.3 g) and 100 mL of methanol solution obtained in step (3) were added to a 100 mL two-necked flask in sequence, and the mixture was stirred at room temperature for 12 h using a mechanical stirrer. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-macroporous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface. The scanning electron micrograph is shown in FIG. Figure 5 .

[0045] (5) In a 250 mL three-necked flask, ultra-large pore PGMA@ZIF-8-SH composite microspheres (0.1 g), chloroauric acid aqueous solution (0.4 mL, 60 mM), and PVA aqueous solution (0.5%, 100 mL) were added in sequence. After mechanical stirring for 10 min, sodium borohydride aqueous solution (0.1 wt%, 20 mL) was added and stirred at room temperature for 12 h. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large pore PGMA@ZIF-8@Au composite microspheres with a nano-gold loading of 67.5 mg / g. The EDS element mapping of the ultra-large pore PGMA@ZIF-8@Au composite microspheres is shown in Figure 2. Figure 6 , it can be seen that in addition to C and O elements, N, Zn, S and Au elements are evenly distributed on the surface of the microspheres, indicating that ZIF-8 and AuNPs have been successfully loaded onto the microspheres.

[0046] Example 2:

[0047] (1) The monomer GMA (3g), crosslinker EGDA (1g), xylene (3g), isopropanol (1g) and initiator BPO (0.16g) were mixed evenly as the oil phase; 100g of the aqueous phase (PVA content of 1.5%, NaCl content of 0.1%); under stirring conditions, the oil phase was dispersed in the aqueous phase to form an O / W emulsion, stirred at 180rpm and nitrogen was passed through for 30min, and then reacted at 75℃ for 20h. The obtained microspheres were washed with water and ethanol several times, then extracted with ethanol for 24h, and vacuum dried at room temperature to obtain ultra-large porous PGMA microspheres. The obtained microspheres had an average particle size of 65μm, an average pore size of 450nm, a porosity of 52.8%, and a specific surface area of ​​95.7m 2 / g.

[0048] (2) 100 mL of carbonate buffer solution (pH 10) containing 1-(3-aminopropyl)imidazole (1 M) and 1 g of the ultra-large porous PGMA microspheres prepared in step (1) were added to a 250 mL three-necked flask in sequence, and the mixture was stirred at 50°C and 120 rpm using a constant temperature water bath and an overhead mechanical stirrer for 3 h. The remaining liquid was then filtered using a Buchner funnel, and the microspheres were repeatedly washed five times with methanol solution. The washed microspheres were placed in a vacuum drying oven and dried for 6 h to obtain imidazole-modified ultra-large porous PGMA microspheres.

[0049] (3) In a 250 mL three-necked flask, 100 mL of 50 mM methanol solution of zinc nitrate hexahydrate and 1 g of the imidazole-functionalized ultra-macroporous PGMA microspheres prepared in step (2) were added in sequence. The mixture was stirred at 40 °C and 120 rpm for 3 h using a constant temperature water bath and an overhead mechanical stirrer. 2-Methylimidazole (1.642 g, 20 mmol) was then added and stirred for another 3 h. The microspheres were washed with methanol solution and dried in a vacuum drying oven for 6 h to obtain ultra-macroporous PGMA@ZIF-8 composite microspheres. The ZIF-8 loading was 516 mg / g microspheres.

[0050] (4) The ultra-large porous PGMA@ZIF-8 composite microspheres (0.1 g), 4-mercaptoimidazole (0.3 g) and 100 mL of methanol solution obtained in step (3) were added to a 100 mL two-necked flask in sequence, and the reaction was stirred at room temperature for 12 h using a mechanical stirrer. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large porous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface.

[0051] (5) Ultra-large pore PGMA@ZIF-8-SH composite microspheres (0.1 g), chloroauric acid aqueous solution (0.4 mL, 60 mM), and PVA aqueous solution (0.5%, 100 mL) were added to a 250 mL three-necked flask in sequence. After mechanical stirring for 10 min, sodium borohydride aqueous solution (0.1 wt%, 20 mL) was added and stirred at room temperature for 12 h. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large pore PGMA@ZIF-8@Au composite microspheres with a nano-gold loading of 59.7 mg / g microspheres.

[0052] Example 3:

[0053] (1) The monomer GMA (3g), cross-linking agent PEGDA (2g), toluene (4g), isopropanol (1g) and initiator BPO (0.2g) were mixed evenly as the oil phase; 100g of the aqueous phase (PVA content of 1.5%, NaCl content of 0.1%); under stirring conditions, the oil phase was dispersed in the aqueous phase to form an O / W emulsion, stirred at 150rpm and nitrogen was passed through for 30min, and then reacted at 75℃ for 20h. The obtained microspheres were washed with water and ethanol several times, then extracted with ethanol for 24h, and vacuum dried at room temperature to obtain ultra-large porous PGMA microspheres. The obtained microspheres had an average particle size of 80μm, an average pore size of 520nm, a porosity of 56.7%, and a specific surface area of ​​87.5m 2 / g.

[0054] (2) In a 250 mL three-necked flask, 100 mL of Tris-HCl buffer solution (pH 8) containing 3-(1-imidazolyl)propionic acid (0.1 M), EDC·HCl (3.83 g) and NHS (1.15 g) were added in sequence. After reacting for 3 h, 1 g of the ultra-macroporous PGMA microspheres prepared in step (1) was added. The mixture was stirred at 50°C and 120 rpm using a constant temperature water bath and an overhead mechanical stirrer for 3 h. The remaining liquid was then filtered using a Buchner funnel and washed repeatedly five times with methanol solution. The washed microspheres were placed in a vacuum drying oven and dried for 6 h to obtain imidazole-modified ultra-macroporous PGMA microspheres.

[0055] (3) In a 250 mL three-necked flask, 100 mL of 50 mM methanol solution of zinc nitrate hexahydrate and 1 g of the imidazole-functionalized ultra-macroporous PGMA microspheres prepared in step (2) were added in sequence. The mixture was stirred at 40 °C and 120 rpm for 3 h using a constant temperature water bath and an overhead mechanical stirrer. 2-Methylimidazole (1.231 g, 15 mmol) was then added and stirred for another 3 h. The microspheres were washed with methanol solution and dried in a vacuum drying oven for 6 h to obtain ultra-macroporous PGMA@ZIF-8 composite microspheres. The ZIF-8 loading was 653 mg / g microspheres.

[0056] (4) In a 100 mL two-necked flask, the macroporous PGMA@ZIF-8 composite microspheres obtained in step (3) (0.1 g), 1-(2-mercaptoethyl)imidazole (0.3 g) and 100 mL of methanol solution were sequentially added, and the reaction was stirred at room temperature for 12 h using mechanical stirring, after which the microspheres were washed with methanol and placed in a vacuum drying box for drying for 6 h, to obtain macroporous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface.

[0057] (5) In a 250 mL three-necked flask, macroporous PGMA@ZIF-8-SH composite microspheres (0.1 g), an aqueous chloroauric acid solution (0.4 mL, 60 mM), an aqueous PVA solution (0.5%, 100 mL) were sequentially added, and after mechanical stirring for 10 min, an aqueous sodium citrate solution (0.1 wt%, 20 mL) was added, and the reaction was stirred at room temperature for 12 h, after which the microspheres were washed with methanol and placed in a vacuum drying box for drying for 6 h, to obtain macroporous PGMA@ZIF-8@Au composite microspheres, and the loading of gold nanoparticles was 61.8 mg / g of microspheres.

[0058] Example 4:

[0059] (1) The monomer GMA (3 g), the crosslinking agent DVB (1 g), toluene (4 g), n-hexanol (1 g) and the initiator BPO (0.16 g) were mixed uniformly as an oil phase; the water phase was 100 g (containing 1.5% of PVP and 0.1% of NaCl); under stirring conditions, the oil phase was dispersed in the water phase to prepare an O / W emulsion, and after stirring at 150 rpm and passing nitrogen for 30 min, the reaction was carried out at 75°C for 20 h. The obtained microspheres were washed with water and ethanol several times, respectively, and then extracted with ethanol for 24 h, and after vacuum drying at room temperature, macroporous PGMA microspheres were obtained. The average particle size of the obtained microspheres was 79 μm, the average pore size was 535 nm, the porosity was 54.3%, and the specific surface area was 82.4 m 2 / g.

[0060] (2) In a 250 mL three-necked flask, 100 mL of a carbonate buffer solution (pH 10) containing 1-(3-aminopropyl)imidazole (1 M) and 1 g of the macroporous PGMA microspheres prepared in step (1) were sequentially added, and the reaction was stirred at 50°C and 120 rpm for 3 h using a constant temperature water bath and an overhead mechanical stirrer, after which the remaining liquid was filtered using a Buchner funnel, and the microspheres were washed repeatedly five times using a methanol solution, and the washed microspheres were placed in a vacuum drying box for drying for 6 h, to obtain imidazole group-modified macroporous PGMA microspheres.

[0061] (3) In a 250 mL three-necked flask, 100 mL of 50 mM methanol solution of zinc nitrate hexahydrate and 1 g of the imidazole-functionalized ultra-macroporous PGMA microspheres prepared in step (2) were added in sequence. The mixture was stirred at 40 °C and 120 rpm for 3 h using a constant temperature water bath and an overhead mechanical stirrer. 2-Methylimidazole (1.231 g, 15 mmol) was then added and stirred for another 3 h. The microspheres were washed with methanol solution and dried in a vacuum drying oven for 6 h to obtain ultra-macroporous PGMA@ZIF-8 composite microspheres. The ZIF-8 loading was 692 mg / g microspheres.

[0062] (4) The ultra-large porous PGMA@ZIF-8 composite microspheres (0.1 g), 2-mercaptoimidazole (0.3 g) and 100 mL of methanol solution obtained in step (3) were added to a 100 mL two-necked flask in sequence, and the reaction was stirred at room temperature for 12 h using a mechanical stirrer. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large porous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface.

[0063] (5) Ultra-large pore PGMA@ZIF-8-SH composite microspheres (0.1 g), chloroauric acid aqueous solution (0.4 mL, 60 mM), and PVP aqueous solution (0.5%, 100 mL) were added to a 250 mL three-necked flask in sequence. After mechanical stirring for 10 min, sodium borohydride aqueous solution (0.1 wt%, 20 mL) was added and stirred at room temperature for 12 h. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large pore PGMA@ZIF-8@Au composite microspheres with a nano-gold loading of 63.7 mg / g microspheres.

[0064] Example 5:

[0065] (1) The monomer GMA (3g), crosslinker PEGDMA (1g), xylene (3g), cyclohexanol (1g) and initiator AIBN (0.16g) were mixed evenly as the oil phase; 100g of the aqueous phase (PVA content of 2.0%, NaCl content of 0.1%); under stirring conditions, the oil phase was dispersed in the aqueous phase to form an O / W emulsion, stirred at 150rpm and nitrogen was passed through for 30min, and then reacted at 75℃ for 20h. The obtained microspheres were washed with water and ethanol several times, then extracted with ethanol for 24h, and vacuum dried at room temperature to obtain ultra-large porous PGMA microspheres. The obtained microspheres had an average particle size of 72μm, an average pore size of 410nm, a porosity of 55.6%, and a specific surface area of ​​86.1m 2 / g.

[0066] (2) 100 mL of carbonate buffer solution (pH 10) containing 1-(3-aminopropyl)imidazole (1 M) and 1 g of the ultra-large porous PGMA microspheres prepared in step (1) were added to a 250 mL three-necked flask in sequence, and the mixture was stirred at 50°C and 120 rpm using a constant temperature water bath and an overhead mechanical stirrer for 3 h. The remaining liquid was then filtered using a Buchner funnel, and the microspheres were repeatedly washed five times with methanol solution. The washed microspheres were placed in a vacuum drying oven and dried for 6 h to obtain imidazole-modified ultra-large porous PGMA microspheres.

[0067] (3) In a 250 mL three-necked flask, 100 mL of 50 mM methanol solution of zinc nitrate hexahydrate and 1 g of the imidazole-functionalized ultra-macroporous PGMA microspheres prepared in step (2) were added in sequence. The mixture was stirred at 40 °C and 120 rpm for 3 h using a constant temperature water bath and an overhead mechanical stirrer. 2-Methylimidazole (1.231 g, 15 mmol) was then added and stirred for another 3 h. The microspheres were washed with methanol solution and dried in a vacuum drying oven for 6 h to obtain ultra-macroporous PGMA@ZIF-8 composite microspheres. The ZIF-8 loading was 537 mg / g microspheres.

[0068] (4) The ultra-large porous PGMA@ZIF-8 composite microspheres (0.1 g), 4-mercaptoimidazole (0.3 g) and 100 mL of methanol solution obtained in step (3) were added to a 100 mL two-necked flask in sequence, and the reaction was stirred at room temperature for 12 h using a mechanical stirrer. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large porous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface.

[0069] (5) Ultra-large pore PGMA@ZIF-8-SH composite microspheres (0.1 g), chloroauric acid aqueous solution (0.2 mL, 60 mM), and CMC aqueous solution (0.5%, 100 mL) were added to a 250 mL three-necked flask in sequence. After mechanical stirring for 10 min, sodium borohydride aqueous solution (0.1 wt%, 20 mL) was added and stirred at room temperature for 12 h. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large pore PGMA@ZIF-8@Au composite microspheres with a nano-gold loading of 30.2 mg / g microspheres.

[0070] Example 6:

[0071] (1) The monomer GMA (3g), crosslinker EGDMA (1g), toluene (3g), isopropanol (2g) and initiator BPO (0.16g) were mixed evenly as the oil phase; 100g of the aqueous phase (PVA content of 1.5%, NaCl content of 0.1%); under stirring conditions, the oil phase was dispersed in the aqueous phase to form an O / W emulsion, stirred at 180rpm and nitrogen was passed through for 30min, and then reacted at 75℃ for 20h. The obtained microspheres were washed with water and ethanol several times, then extracted with ethanol for 24h, and dried in vacuum at room temperature to obtain ultra-large porous PGMA microspheres. The obtained microspheres had an average particle size of 63μm, an average pore size of 607nm, a porosity of 67.2%, and a specific surface area of ​​76.1m 2 / g.

[0072] (2) 100 mL of carbonate buffer solution (pH 10) containing 1-(3-aminopropyl)imidazole (1 M) and 1 g of the ultra-large porous PGMA microspheres prepared in step (1) were added to a 250 mL three-necked flask in sequence, and the mixture was stirred at 50°C and 120 rpm using a constant temperature water bath and an overhead mechanical stirrer for 3 h. The remaining liquid was then filtered using a Buchner funnel, and the microspheres were repeatedly washed five times with methanol solution. The washed microspheres were placed in a vacuum drying oven and dried for 6 h to obtain imidazole-modified ultra-large porous PGMA microspheres.

[0073] (3) In a 250 mL three-necked flask, 100 mL of 50 mM methanol solution of zinc nitrate hexahydrate and 1 g of the imidazole-functionalized ultra-macroporous PGMA microspheres prepared in step (2) were added in sequence. The mixture was stirred at 40 °C and 120 rpm for 3 h using a constant temperature water bath and an overhead mechanical stirrer. 2-Methylimidazole (1.231 g, 15 mmol) was then added and stirred for another 3 h. The microspheres were washed with methanol solution and dried in a vacuum drying oven for 6 h to obtain ultra-macroporous PGMA@ZIF-8 composite microspheres. The ZIF-8 loading was 723 mg / g microspheres.

[0074] (4) The ultra-large porous PGMA@ZIF-8 composite microspheres (0.1 g), 2-mercaptophenylimidazole (0.3 g) and 100 mL of methanol solution obtained in step (3) were added to a 100 mL two-necked flask in sequence, and the reaction was stirred at room temperature for 12 h using a mechanical stirrer. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large porous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface.

[0075] (5) Ultra-large pore PGMA@ZIF-8-SH composite microspheres (0.1 g), chloroauric acid aqueous solution (0.4 mL, 60 mM), and CMC aqueous solution (0.5%, 100 mL) were added to a 250 mL three-necked flask in sequence. After mechanical stirring for 10 min, sodium borohydride aqueous solution (0.1 wt%, 20 mL) was added and stirred at room temperature for 12 h. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultra-large pore PGMA@ZIF-8@Au composite microspheres with a nano-gold loading of 65.4 mg / g microspheres.

[0076] Comparative Example:

[0077] 1) The monomer GMA (3 g), the crosslinker EGDMA (1 g), toluene (5 g), isopropyl alcohol (1 g), and the initiator BPO (0.16 g) were uniformly mixed to form the oil phase; 100 g of the aqueous phase (containing 1.5% PVA and 0.1% NaCl) was then dispersed in the aqueous phase under stirring to form an O / W emulsion. After stirring at 120 rpm with nitrogen flow for 30 minutes, the mixture was reacted at 75°C for 20 hours. The resulting microspheres were washed several times with water and ethanol, then extracted with ethanol for 24 hours and dried under vacuum at room temperature to obtain ultra-macroporous PGMA microspheres.

[0078] (2) Ultraporous PGMA microspheres (0.1 g), chloroauric acid aqueous solution (0.4 mL, 60 mM), and PVA aqueous solution (0.5%, 100 mL) were added to a 250 mL three-necked flask in sequence. After mechanical stirring for 10 min, sodium borohydride aqueous solution (0.1 wt%, 20 mL) was added and stirred at room temperature for 12 h. The microspheres were then washed with methanol and dried in a vacuum drying oven for 6 h to obtain ultraporous PGMA@Au composite microspheres. However, it was found that AuNPs could not be directly loaded onto the surface of the ultraporous PGMA microspheres, and the color of the microspheres did not change at all. Figure 7 These are optical photographs of ultra-macroporous PGMA@Au microspheres (a) and ultra-macroporous PGMA@ZIF-8@Au microspheres (b). It can be seen that the PGMA@Au microspheres are pure white, while the PGMA@ZIF-8@Au microspheres are purple-black in appearance, further indicating that PGMA microspheres cannot directly load AuNPs.

[0079] Effect experiment:

[0080] To verify the catalytic degradation of p-nitrophenol by the PGMA@ZIF-8@Au composite microspheres of the present invention, the catalytic performance of the PGMA@ZIF-8@Au composite microspheres prepared in Example 1 was compared with that of the PGMA@Au prepared in the comparative example. The catalytic experimental steps were as follows: 10 mg of PGMA@ZIF-8@Au (or PGMA@Au) composite microspheres and 10 mL of p-nitrophenol (PNP) (0.1 mM) phosphate buffer solution were added to a glass test tube, mixed evenly, and then 1 mL of sodium borohydride (4 wt%) solution was added to initiate the reaction. Subsequently, 0.1 mL of the reaction solution was diluted 10-fold with PBS to 1 mL at 5, 10, 20, 35, and 60 minutes, and the absorbance (At) at 400 nm was immediately measured. This was repeated for 60 minutes to complete a single round of testing. After the reaction, the catalyst was recovered by vacuum filtration, washed three times with methanol and PBS (10 mL each), and then directly added to the next round of reaction system in a wet state for cyclic stability testing. The degradation rate of p-nitrophenol catalyzed by composite microspheres at different times is as follows Figure 8 As shown in the figure, the degradation rate of p-nitrophenol by the PGMA@ZIF-8@Au composite microspheres reached 98.1% after 20 minutes, and p-nitrophenol was completely degraded after 35 minutes. After five cycles, the degradation rate of p-nitrophenol by the composite microspheres at 35 minutes was still 95.1%, indicating the excellent catalytic effect of PGMA@ZIF-8@Au. However, since the PGMA@Au prepared in the comparative example was not successfully loaded with AuNPs, the degradation rate of sodium borohydride alone was very slow, with a degradation rate of less than 20% within 60 minutes.

[0081] The experimental results show that the present invention solves the problems of low precious metal catalyst carrier loading, easy aggregation and shedding of precious metals, and difficulty in recycling, breaks through the performance bottleneck of traditional carrier materials, and provides new ideas for the construction of efficient catalytic systems.

Claims

1. A super-large-porous PGMA@ZIF-8@Au composite microsphere with a micro-nano dual-level confinement structure and a preparation method thereof, characterized in that The following steps are involved: (1) Mixing monomer glycidyl methacrylate (GMA), a crosslinking agent, a composite porogen, and an initiator to form an oil phase, and stirring to dissolve; dissolving a stabilizer and a salt in deionized water to form an aqueous phase; dispersing the oil phase in the aqueous phase under stirring to form an O / W emulsion, stirring and passing nitrogen for 30 minutes, heating to start polymerization, and obtaining polymer microspheres after a period of reaction; washing the obtained polymer microspheres with water and ethanol several times, respectively, and then extracting with acetone or ethanol for 24 hours, and drying under vacuum at room temperature to obtain ultra-large-porous PGMA microspheres; (2) surface-modifying the ultra-macroporous PGMA microspheres obtained in step (2) with an imidazole functionalizing agent, washing with methanol after the reaction, and vacuum drying to obtain ultra-macroporous PGMA microspheres coupled with imidazole groups; (3) Imidazole-functionalized ultra-macroporous PGMA microspheres were added to a methanol solution of zinc nitrate hexahydrate and 2-methylimidazole at a certain temperature, so that ZIF-8 crystals were heterogeneously nucleated and grown in situ on the pore surface of the ultra-macroporous PGMA microspheres under the initiation of imidazole groups. After a period of reaction, the ultra-macroporous PGMA@ZIF-8 composite microspheres were washed with methanol and vacuum dried to obtain ultra-macroporous PGMA@ZIF-8 composite microspheres. (4) At room temperature, PGMA@ZIF-8 composite microspheres were added to a methanol solution containing an etchant. The etchant caused the ZIF-8 skeleton to partially dissociate through competitive coordination, and the pores were enlarged. After a period of reaction, the microspheres were washed with methanol and vacuum dried to obtain ultra-macroporous PGMA@ZIF-8-SH composite microspheres containing thiol functional groups on the surface. (5) The ultra-large-porous PGMA@ZIF-8-SH microspheres were added to a chloroauric acid aqueous solution containing a stabilizer, and AuNPs were in situ generated under the action of a reducing agent. The AuNPs were then loaded onto the PGMA@ZIF-8-SH microspheres through Au-S bonds to obtain ultra-large-porous PGMA@ZIF-8@Au composite microspheres.

2. The preparation method according to claim 1, wherein: The cross-linking agent described in step (1) is selected from at least one of ethylene glycol dimethacrylate (EGDMA), ethylene glycol diacrylate (EGDA), 1,6-hexanediol diacrylate (HDDA), polyethylene glycol dimethacrylate (PEGDMA), polyethylene glycol diacrylate (PEGDA), and divinylbenzene (DVB), and the cross-linking degree is 10-50%.

3. The preparation method according to claim 1, wherein: The composite porogen described in step (1) is selected from at least two of toluene, xylene, chloroform, isopropanol, cyclohexanol, and n-hexanol, and the added amount is 10-150% of the total mass of the polymerizable monomers.

4. The preparation method according to claim 1, wherein: The initiator in step (1) is at least one of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), benzoyl peroxide (BPO) or alkyl hydroperoxide; the concentration of the initiator ranges from 1% to 10%, the reaction temperature is 65-90° C., and the reaction time is 12-24 hours.

5. The preparation method according to claim 1, wherein: The aqueous phase stabilizer described in step (1) is polyvinyl alcohol, polyvinyl pyrrolidone, gelatin, polyethylene glycol or carboxymethyl cellulose, and its content is 0.1%-6% of the mass of the aqueous phase; the salt is sodium chloride, sodium sulfate or magnesium sulfate, and its content is 0.02%-3% of the mass of the aqueous phase; the mass ratio of the oil phase to the aqueous phase is in the range of 1:4-1:

100.

6. The preparation method according to claim 1, wherein: The imidazole functionalizing agent described in step (2) is selected from one of 1-(3-aminopropyl)imidazole, 1-(2-hydroxyethyl)imidazole, 3-(1-imidazolyl)propionic acid, 4-(1-imidazolyl)propionic acid, 4-(1-imidazolyl)benzoic acid, and hydroxybutylimidazole; the concentration of the imidazole functionalizing agent in the reaction system is 0.05-3.0M.

7. The preparation method according to claim 1, wherein: The concentration of zinc nitrate hexahydrate in step (3) is 25-100 mM, the concentration of 2-methylimidazole is 50-200 mM, and the reaction temperature is 20-80°C.

8. The preparation method according to claim 1, wherein: The etchant described in step (4) is selected from at least one of 2-mercaptoimidazole, 4-mercaptoimidazole, 1-(2-mercaptoethyl)imidazole, and 2-mercaptobenzimidazole; the mass ratio of ZIF-8 to the etchant is 1:1-1:10, the etching temperature is room temperature, and the etching time is 1-12 hours.

9. The preparation method according to claim 1, wherein: The stabilizer described in step (5) is the same as that in step (1), with a concentration of 0.01%-1%; the reducing agent is selected from one of sodium borohydride, sodium cyanoborohydride, sodium citrate, and ascorbic acid, and the molar ratio of the reducing agent to chloroauric acid is 2:1-10:

1.

10. An ultra-large-pore PGMA@ZIF-8@Au composite microsphere having a micro-nano dual-level confined structure obtained by the preparation method of claim 1, characterized in that The composite microspheres use ultra-macroporous PGMA microspheres as micron-scale carriers, load ZIF-8 and form nanoscale confined cavities after etching, and AuNPs are anchored in the confined cavities through Au-S bonds; the ultra-macroporous microspheres have a particle size of 20-300 μm, a pore size of 100-1000 nm, and a specific surface area of ​​50-200 m 2 / g, ZIF-8 loading capacity was 500-1000 mg / g microspheres, and AuNPs loading capacity was 20-100 mg / g microspheres.

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