Nano-silver-loaded porous cyclodextrin microspheres as well as preparation method and application thereof

Abstract

The invention discloses porous cyclodextrin microspheres loaded with nano-silver as well as a preparation method and application of the porous cyclodextrin microspheres. The porous cyclodextrin microspheres are obtained by loading nano-silver on oligomeric cyclodextrin with the molecular weight of 8000-14000, then blending the oligomeric cyclodextrin with poly (methyl vinyl ether-alt-maleic acid) to obtain microspheres and then cross-linking the microspheres. The porous cyclodextrin microspheres are selected as the carrier of AgNP, and cyclodextrin has a hydrophobic cavity, so that specific hydrophobic molecules and pollutants can be included in the cavity, and contact and catalysis processes of reactants and silver particles are promoted synergistically. Moreover, the cyclodextrin microspheres have micron-scale and even millimeter-scale porous structures, the abundant porous structures can ensure that reactants quickly enter the microspheres to be in full contact with silver, the catalytic reaction is efficiently carried out, and meanwhile, the larger size of the microspheres ensures that fluid can pass through the microspheres at a high speed in a fixed bed reactor, so that the catalytic efficiency is improved. And the contradiction between the catalyst efficiency and the large particle size in practical application is solved.

Description

Technical Field

[0001] The invention relates to a nano-silver loaded microsphere, in particular to a nano-silver loaded porous cyclodextrin microsphere and a preparation method and application thereof. Background Art

[0002] With the rapid development of industrialization and the continuous growth of population, a large amount of untreated sewage is discharged into natural water bodies, causing serious deterioration of water quality and making water resources extremely scarce. Among them, the pollution caused by untreated industrial toxic dyes and nitrophenol compound wastewater is the most serious (Chemical Engineering Journal 2024, 487,150516). The discharge of untreated dye wastewater not only causes discoloration of the receiving water body and hinders the photosynthesis of aquatic plants (Regional Studies in Marine Science 2021, 45, 101802), but also poses a serious threat to organisms due to its carcinogenicity, teratogenicity, mutagenicity and non-biodegradability. Sewage containing nitrophenols can also induce a variety of diseases and even cancer in the human body (Environmental Pollution 2022, 307, 119570). Therefore, the conversion of nitrophenols and dyes in water bodies is the key to controlling water pollution.

[0003] In recent years, silver nanoparticles (AgNP) have attracted more and more attention in the field of dye and nitrophenol catalysis due to their excellent catalytic ability and environmental friendliness. However, AgNP is easy to agglomerate during the catalytic process, resulting in a decrease in the catalytic rate and a small particle size that is difficult to recycle and reuse in the catalytic system. Therefore, in recent years, many studies have chosen to use a carrier to load AgNP to solve its agglomeration problem. For example, AgNP is fixed on iron oxide (Fe3O4) (Colloids and Surfaces A: Physicochemical and Engineering Aspects 2023, 668, 131402), graphene oxide (Chemical Engineering Journal 2012, 211-212, 412-420) and mesoporous silica (Catalysis Communications 2011, 12, 1104-1108) for catalysis and pollutant degradation. However, it is worth noting that these carriers can only play the role of physically carrying silver particles, and they themselves cannot participate in the catalytic process and play a synergistic role. In addition, to ensure that the catalyst is in full contact with the reactants, silver particles and carriers often need to be prepared into nano-scale microparticles to obtain a sufficiently large contact area and improve catalytic efficiency. However, too small a size often causes the particles to be difficult to separate when recycled, making them difficult to apply in practice. In particular, for reactors such as fixed beds that are easy to control and can be continuously produced, the use of nanoparticles easily causes excessive pressure drop in the fluid flow rate and slow reaction speed. To ensure that the fluid passes quickly, fixed-bed catalyst particles often need to be prepared into larger micron or even millimeter-scale particles, which inevitably leads to a decrease in the contact ability of the catalyst with the reactants, and thus causes the catalytic performance to be limited. At present, there is an urgent need to design and prepare a carrier that can play a synergistic catalytic role with silver nanoparticles, and to solve the contradiction between catalyst efficiency and large particle size in practical applications of fixed-bed reactors.

[0004] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0005] The purpose of the present invention is to provide a porous cyclodextrin microsphere loaded with nanosilver and a preparation method and application thereof. The porous cyclodextrin microsphere loaded with nanosilver not only has the excellent catalytic ability of the silver particles themselves, but also can synergistically promote the catalysis by encapsulating the catalytic substrate through the cyclodextrin cavity. At the same time, the porous structure is conducive to the rapid diffusion of the catalytic substrate, so that it exhibits excellent catalytic performance.

[0006] In order to achieve the above-mentioned object, the present invention provides a porous cyclodextrin microsphere loaded with nanosilver. The porous cyclodextrin microsphere is prepared by loading nanosilver on oligomeric cyclodextrin with a molecular weight of 8000 to 14000, blending the microsphere with poly (methyl vinyl ether-alt-maleic acid) and then cross-linking.

[0007] The porous cyclodextrin microspheres loaded with nanosilver particles (Ag@PCM) of the present invention not only have the excellent catalytic ability of the silver particles themselves, but also can promote the catalysis by inclusion of the catalytic substrate in the cyclodextrin cavity. At the same time, the porous structure helps the rapid diffusion of the catalytic substrate, so that Ag@PCM exhibits excellent catalytic performance. The excellent catalytic ability enables Ag@PCM to be used as a catalyst in a fixed bed reactor for the reduction and decomposition of various substances, or for the rapid removal of pollutants in water.

[0008] Preferably, the molecular weight of the poly(methyl vinyl ether-alt-maleic acid) is 80,000; or / and, the oligomeric cyclodextrin is prepared by using cyclodextrin, and the cyclodextrin is selected from α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, or small molecule derivatives of these three cyclodextrins.

[0009] Preferably, the three small molecule derivatives of cyclodextrin include: hydroxypropyl β-cyclodextrin and aldehyde α-cyclodextrin.

[0010] The second object of the present invention is to provide a method for preparing the porous cyclodextrin microspheres loaded with nanosilver, the method comprising: loading nanosilver on oligomeric cyclodextrin with a molecular weight of 8000 to 14000, dissolving the loaded nanosilver in water and blending with a poly(methyl vinyl ether-alt-maleic acid) aqueous solution, spraying the loaded nanosilver on an organic solvent supercooled at -84 to -93°C by a spray gun to obtain microspheres, filtering and freeze-drying, and cross-linking at 80 to 120°C to obtain porous cyclodextrin microspheres loaded with nanosilver; wherein the organic solvent does not solidify at -84 to -93°C and has low solubility for oligomeric cyclodextrin.

[0011] Preferably, the blending comprises mixing a 10 wt% aqueous solution of loaded nanosilver oligomeric cyclodextrin with a 5-20 wt% aqueous solution of poly(methyl vinyl ether-alt-maleic acid), and the mass ratio of loaded nanosilver oligomeric cyclodextrin to poly(methyl vinyl ether-alt-maleic acid) is 3:1.

[0012] Preferably, the spray gun is a gun-type spray gun with a caliber of 0.3-0.9 mm, and the muzzle is 2-20 cm away from the receiving container; or / and, the organic solvent is n-hexane, and the amount of n-hexane used is 5-20 times that of water. The reason for selecting n-hexane as the coagulation bath solvent is that it has a lower solidification point (n-hexane is -95°C), can remain liquid at low temperatures, and has very low solubility in cyclodextrin; or / and, the cross-linking time is 6-11 h.

[0013] Preferably, the preparation of the oligomeric cyclodextrin-loaded nanosilver comprises: (1) Synthesis of oligomeric cyclodextrin Add epichlorohydrin to a NaOH aqueous solution of β-CD, and heat the solution at 30-45°C for 1-6 hours to obtain an oligomeric cyclodextrin solution; wherein the mass fraction of NaOH in the NaOH aqueous solution of β-CD is 10-25 wt%, and the concentration of β-CD is 0.4-0.8 M; the volume of epichlorohydrin is 20-30% of the volume of the NaOH aqueous solution; The oligomeric cyclodextrin solution is poured into an isopropanol solution to stop the reaction, the pH of the mixed solution is adjusted to 7, and then the mixed solution is transferred into a dialysis bag with a molecular weight of 8000-14000 for dialysis, and after the dialysis is completed, the solvent is removed to obtain oligomeric cyclodextrin; (2) Synthesis of oligomeric cyclodextrin loaded with nanosilver The oligomeric cyclodextrin is dissolved in a NaOH aqueous solution, wherein the mass fraction of the oligomeric cyclodextrin in the mixed solution is 3-10 wt%, and the concentration of NaOH in the mixed solution is 0.001-0.003 M. Then, a 0.001-0.005 M AgNO3 aqueous solution is added, and the volume ratio of the AgNO3 aqueous solution to the NaOH aqueous solution is (3-9): (30-60). The mixture is heated at 40-70°C for 2-6 h. After the reaction is completed, the solvent is removed to obtain oligomeric cyclodextrin loaded with nanosilver.

[0014] Preferably, the amount of the isopropanol solution is 10 to 20 times that of the NaOH aqueous solution; and 6 M hydrochloric acid is used to adjust the pH of the mixed solution to 7.

[0015] The third object of the present invention is to provide the use of the porous cyclodextrin microspheres loaded with nano-silver in reducing and decomposing pollutants.

[0016] Preferably, the pollutants include any one or more of methylene blue, rhodamine b and p-nitrophenol.

[0017] The porous cyclodextrin microspheres loaded with nanosilver and the preparation method and application thereof of the present invention have the following advantages: (1) The present invention selects porous cyclodextrin microspheres as carriers of AgNPs. First, cyclodextrin itself has hydrophobic cavities, which can enclose specific hydrophobic molecules and pollutants in its cavities, thereby synergistically promoting the contact between reactants and silver particles and the catalytic process. Second, cyclodextrin microspheres are prepared into micron-level or even millimeter-level porous structures by spray freeze drying. The rich pore structure can ensure that the reactants quickly enter the microspheres and fully contact the silver, so that the catalytic reaction is carried out efficiently. At the same time, the large size of the microspheres ensures that the fluid can pass through at high speed in the fixed bed reactor, solving the contradiction between catalyst efficiency and large particle size in practical applications. (2) The present invention uses porous cyclodextrin microsphere carriers, which have synergistic catalytic ability that other carriers do not have, and show higher catalytic ability, that is, the catalyst of the present invention has an extremely high apparent rate for pollutants; (3) The present invention obtains a polycyclodextrin solution loaded with silver nanoparticles by in-situ reduction of oligomeric cyclodextrin, and then forms porous microspheres of the polycyclodextrin / nanosilver by spraying and freeze drying to obtain porous cyclodextrin microspheres loaded with nanosilver, and finally performs secondary crosslinking on the porous microspheres to increase stability. The present invention can quickly, simply and efficiently synthesize porous cyclodextrin microspheres loaded with nanosilver, and is convenient for large-scale synthesis of catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The electron microscope images of the porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 1 of the present invention; (a) to (c) are SEM images of Ag@PCM, and (d) is a particle size distribution diagram of Ag@PCM.

[0019] Figure 2 XRD patterns (a) of silver nanoparticle-loaded oligomeric cyclodextrin (Ag@P-β-CD) and Ag@PCM prepared in Example 1 of the present invention, and XPS curves (b) to (c) of Ag@PCM.

[0020] Figure 3 The catalytic degradation effect diagram of methylene blue by porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 1 of the present invention; (a) is the ultraviolet absorption spectrum of MB, (b) is the apparent rate of MB catalyzed by Ag@PCM, (c) is the ultraviolet absorption spectrum of MB after 5 cycles of catalysis, and (d) is the removal rate of MB after 5 cycles of catalysis.

[0021] Figure 4 The catalytic degradation effect diagram of Rhodamine b by the porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 3 of the present invention; (a) is the UV absorption spectrum of RhB, (b) is the apparent rate of RhB catalyzed by Ag@PCM, (c) is the UV absorption spectrum of RhB after 5 cycles of catalysis, and (d) is the removal rate of RhB after 5 cycles of catalysis.

[0022] Figure 5 The catalytic degradation effect diagram of the porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 4 of the present invention on p-nitrophenol, wherein (a) is the ultraviolet absorption spectrum of 4-NP, (b) is the apparent rate of 4-NP catalyzed by Ag@PCM, (c) is the ultraviolet absorption spectrum of 4-NP after 5 cycles of catalysis, and (d) is the removal rate of 4-NP after 5 cycles of catalysis.

[0023] Figure 6 The catalytic comparison results of Ag@PCM and sodium adamantanecarboxylate-treated microspheres (Ag@PCM-T) on RhB (a), MB (b) and 4-NP (c) in Experimental Example 2 of the present invention.

[0024] Figure 7 The fluidized bed experiment diagram of porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 1 of the present invention; (a) schematic diagram of MB passing through the column, (b) ultraviolet absorption spectrum of MB after passing through the column.

[0025] Figure 8 Schematic diagram of the fluidized bed experiment of porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 2 of the present invention; (a) schematic diagram of MB passing through the column, (b) ultraviolet absorption spectrum of MB after passing through the column. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] It should be noted that: if the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the instruments is not specified, they are all conventional products that can be purchased commercially. If the manufacturer of the raw materials and reagents is not specified, they are all commercially available products or can be prepared by known methods.

[0028] In the present invention, all features defined in the form of numerical ranges or percentage ranges, such as values, quantities, contents and concentrations, are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0029] The features mentioned in the present invention can be combined arbitrarily, as long as there is no contradiction in the combination of these features, all possible combinations should be considered as the scope of this specification. Each feature disclosed in the specification can be replaced by any alternative feature that can provide the same, equal or similar purpose. Therefore, unless otherwise specified, the disclosed features are only general examples of equal or similar features.

[0030] Example 1 A porous cyclodextrin microsphere loaded with nanosilver (Ag@PCM), the preparation method of which comprises the following steps: (1) Synthesis of oligomeric cyclodextrin Take 20 g of β-CD and dissolve it in 30 mL of NaOH solution, where the mass fraction of NaOH in the mixed solution is 15wt%, and the concentration of β-CD in the mixed solution is 0.6 M. Then, add 8 mL of epichlorohydrin (the volume is 27% of the volume of the NaOH aqueous solution) to the β-CD NaOH aqueous solution, heat and react at 35 °C for 3 h to obtain an oligomeric cyclodextrin solution.

[0031] The synthesized oligomeric cyclodextrin solution was poured into 400 mL of isopropanol solution (13 times the volume of NaOH aqueous solution) to terminate the reaction. The pH of the mixture was adjusted to 7 using hydrochloric acid solution (6 M), and then the mixture was transferred into a dialysis bag with a molecular weight of 8000-14000 for dialysis. After the dialysis was completed, the oligomeric cyclodextrin was dried by rotary evaporation at 90 °C to obtain the oligomeric cyclodextrin.

[0032] (2) Synthesis of Ag@P-β-CD loaded with nanosilver oligomeric cyclodextrin Take 3 g of the synthesized oligomeric cyclodextrin (P-β-CD) and dissolve it in 50 mL of NaOH solution, wherein the mass fraction of oligomeric cyclodextrin in the mixed solution is 6 wt%, and the concentration of NaOH in the mixed solution is 0.001 M. Then add 6 mL of 0.002 M AgNO3 aqueous solution, heat and react at 50 °C for 5 h until the reaction mixture becomes brown-yellow, and remove the solvent by rotary evaporation at 90 °C to obtain a brown-yellow solid, which is the loaded nanosilver oligomeric cyclodextrin.

[0033] (3) Preparation of porous cyclodextrin microspheres loaded with nanosilver 6 g of the above-synthesized loaded nanosilver oligomeric cyclodextrin was dispersed in 60 mL of deionized water, the mass fraction of loaded nanosilver oligomeric cyclodextrin in the aqueous solution was 10 wt%, 2 g of poly(methyl vinyl ether-alt-maleic acid) (as a cross-linking agent, molecular weight of 80000) was completely dissolved in 20 mL of deionized water, the mass fraction of poly(methyl vinyl ether-alt-maleic acid) in the aqueous solution was 10 wt%, and then mixed in the loaded nanosilver oligomeric cyclodextrin aqueous solution. The mixed solution was loaded into a high-pressure spray gun (Taiwan Blue Brand 116 gun-type spray gun, caliber selected as 0.3 mm), the muzzle was 15 cm away from the receiving beaker, and it was sprayed into 500 mL of supercooled n-hexane (temperature of -93 ° C), and the cyclodextrin mixed aqueous solution was sprayed from the spray gun in the form of droplets, and after entering the supercooled n-hexane, the droplets were quickly frozen into microspheres. The n-hexane solution was filtered and freeze-dried at -70 °C for 48 h to obtain porous cyclodextrin microspheres loaded with nanosilver.

[0034] (4) Cross-linking of porous cyclodextrin microspheres loaded with silver nanoparticles The freeze-dried microspheres were placed in an oven and cross-linked at 95 °C for 8 h. The hydroxyl groups on the hexagonal ring of cyclodextrin reacted with the carboxyl groups in poly(methyl vinyl ether-alt-maleic acid) to obtain porous cyclodextrin microspheres (Ag@PCM) loaded with nanosilver.

[0035] Example 2 A porous cyclodextrin microsphere loaded with nanosilver (Ag@PCM), the preparation method of which is basically the same as that of Example 1, except that: In step (1), 25 g of γ-CD was used to replace 20 g of β-CD; the mass fraction of NaOH in the mixed solution was 20 wt%; the amount of epichlorohydrin used was 7 mL (23% of the volume of the NaOH aqueous solution); the reaction was heated at 40 °C for 2 h; the amount of isopropanol solution used was 450 mL (15 times the volume of the NaOH aqueous solution) In step (2), the amount of oligomeric cyclodextrin is 2 g, the mass fraction of oligomeric cyclodextrin in the mixed solution is 4 wt%, and the concentration of NaOH in the mixed solution is 0.002 M; the concentration of the AgNO3 aqueous solution is 0.003 M, and the amount is 8 mL; the reaction is heated at 55 °C for 4 h; and the solvent is removed by rotary evaporation at 85 °C; In step (3), the amount of loaded nanosilver oligomeric cyclodextrin is 7 g, which is dispersed in 80 mL of deionized water, and the mass fraction of loaded nanosilver oligomeric cyclodextrin in the aqueous solution is 9 wt%; the amount of poly(methyl vinyl ether-alt-maleic acid) is 1 g, which is dissolved in 14 mL of deionized water, and the mass fraction of poly(methyl vinyl ether-alt-maleic acid) in the aqueous solution is 7 wt%; the caliber of the high-pressure spray gun is 0.5 mm, and the muzzle is 8 cm away from the receiving beaker.

[0036] Example 3 A porous cyclodextrin microsphere loaded with nanosilver (Ag@PCM), the preparation method of which is basically the same as that of Example 1, except that: In step (1), 12 g of α-CD was used to replace 20 g of β-CD; the mass fraction of NaOH in the mixed solution was 10 wt%, and the concentration of α-CD in the mixed solution was 0.4 M; the amount of epichlorohydrin used was 6 mL (20% of the volume of the NaOH aqueous solution); the reaction was heated at 30 ° C for 1 h; the amount of isopropanol solution used was 300 mL (10 times the volume of the NaOH aqueous solution); In step (2), the amount of oligomeric cyclodextrin is 1 g, the amount of NaOH aqueous solution is 30 mL, and the mass fraction of oligomeric cyclodextrin in the mixed solution is 3 wt%; the concentration of AgNO3 aqueous solution is 0.001 M, and the amount is 3 mL; the reaction is heated at 40 °C for 2 h; the solvent is removed by rotary evaporation at 80 °C; In step (3), the amount of deionized water used to disperse the loaded nanosilver oligomeric cyclodextrin is 120 mL, and the mass fraction of the loaded nanosilver oligomeric cyclodextrin in the aqueous solution is 5 wt%; the amount of polymethyl vinyl ether-alt-maleic acid is 1 g, and the mass fraction of poly(methyl vinyl ether-alt-maleic acid) in the aqueous solution is 5 wt%; the caliber of the high-pressure spray gun is 0.3 mm, and the distance between the gun muzzle and the receiving beaker is 5 cm; the temperature of the supercooled n-hexane is -89 °C, and the amount of supercooled n-hexane used is 600 mL; In step (4), cross-linking is carried out at a high temperature of 80°C for 6 h.

[0037] Example 4 A porous cyclodextrin microsphere loaded with nanosilver (Ag@PCM), the preparation method of which is basically the same as that of Example 1, except that: In step (1), 37 g of hydroxypropyl β-CD is used to replace 20 g of β-CD, the mass fraction of NaOH in the mixed solution is 25 wt%, and the concentration of hydroxypropyl β-CD in the mixed solution is 0.8 M; the amount of epichlorohydrin used is 9 mL (30% of the volume of the NaOH aqueous solution); the reaction is heated at 45 ° C for 6 h; the amount of isopropanol solution used is 600 mL (20 times the volume of the NaOH aqueous solution); In step (2), the amount of oligomeric cyclodextrin is 6 g, the amount of NaOH aqueous solution is 60 mL, the mass fraction of oligomeric cyclodextrin in the mixed solution is 10 wt%, and the concentration of NaOH in the mixed solution is 0.003 M; the concentration of AgNO3 aqueous solution is 0.005 M, and the amount is 9 mL; the reaction is heated at 70 °C for 6 h; In step (3), the amount of deionized water used to disperse the loaded nanosilver oligomeric cyclodextrin is 40 mL, and the mass fraction of the loaded nanosilver oligomeric cyclodextrin in the aqueous solution is 15 wt%; the amount of deionized water used to dissolve poly(methyl vinyl ether-alt-maleic acid) is 10 mL, and the mass fraction of poly(methyl vinyl ether-alt-maleic acid) in the aqueous solution is 20 wt%; the caliber of the high-pressure spray gun is 0.8 mm, and the distance between the gun muzzle and the receiving beaker is 20 cm; the temperature of the supercooled n-hexane is -84 °C, and the amount of supercooled n-hexane used is 800 mL; In step (4), cross-linking is carried out at a high temperature of 120°C for 11 h.

[0038] Experimental Example 1 Characterization of microsphere structure like Figure 1 As shown in the figure, it is an electron microscope image of the porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 1 of the present invention, wherein (a) to (c) are SEM images of Ag@PCM, and (d) is a particle size distribution diagram of Ag@PCM. It can be seen from the SEM electron microscope image that Ag@PCM has an obvious pore structure of 100~250 μm. It can be seen from the particle size distribution diagram that Ag@PCM is mainly distributed in 5~20 μm, with an average particle size of 11 μm.

[0039] In addition, according to electron microscopy, the particle size of the porous cyclodextrin microspheres loaded with nanosilver particles prepared in Example 2 of the present invention is mainly distributed in 10-30 μm, and the average particle size is 15 μm. The particle size of the porous cyclodextrin microspheres loaded with nanosilver particles prepared in Example 3 of the present invention is mainly distributed in 15-40 μm, and the average particle size is 20 μm. The particle size of the porous cyclodextrin microspheres loaded with nanosilver particles prepared in Example 4 of the present invention is mainly distributed in 20-50 μm, and the average particle size is 30 μm.

[0040] like Figure 2As shown, (a) is the XRD pattern of loaded nanosilver oligomeric cyclodextrin (Ag@P-β-CD) and Ag@PCM, which show characteristic peaks at 2θ=38.1°, 44.4°, 64.4° and 77.5°, respectively, corresponding to the (111), (200), (220) and (311) lattice planes of the AgNP face-centered cubic crystal structure, indicating the successful loading of AgNP on the microspheres. (b)~(c) are the XPS curves of Ag@PCM, which effectively verify the presence of the Ag element. The high-resolution scan of Ag 3d reveals two fitting peaks, located at 367.71 and 373.64 eV, respectively, which are attributed to Ag 3d 5 / 2 and Ag 3d 3 / 2 The three-dimensional double-peak spin-orbit separation of Ag is 6.0 eV, which confirms that the valence state of metallic silver is in the zero-valence state.

[0041] Experimental Example 2 Analysis of microsphere degradation performance 1. Catalytic experiments of Ag@PCM on various pollutants The specific process of the catalytic experiment is as follows: 7 mg of Ag@PCM prepared in the above example was added to 20 mL 4-NP (20 mg / L), 20 mL MB (40 mg / L) and 20 mL RhB (160 mg / L). Subsequently, NaBH4 solution (5 mL, 0.02 M) was added to the above mixture. The catalytic hydrogenation process was determined at different time points using a UV-visible spectrophotometer.

[0042] (1) Catalytic degradation of methylene blue (MB) like Figure 3 As shown, the catalytic degradation effect diagram of the porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 1 of the present invention on methylene blue, wherein (a) is the ultraviolet absorption spectrum of MB, (b) is the apparent rate of MB catalyzed by Ag@PCM, (c) is the ultraviolet absorption spectrum of MB catalyzed by 5 cycles, and (d) is the removal rate of MB catalyzed by 5 cycles. Since cyclodextrin has a synergistic catalytic ability to pollutants, in the presence of sodium borohydride (NaBH4), the Ag@PCM prepared in Example 1 exhibits excellent catalytic degradation ability to methylene blue (MB), and can quickly eliminate the ultraviolet absorption peak of the reaction substrate MB.

[0043] The apparent reaction rate (k) was calculated using formula (1). app ), as follows: (1) In formula (1), A t and A0 represent the absorbance values ​​of the substrate (MB in this experiment) at time t and 0, respectively; C tand C0 are the concentrations of the substrate at time t and 0, respectively.

[0044] like Figure 3 As shown in (b), the apparent reaction rate k of MB app Reached 28×10 -3 s -1 .like Figure 3 As shown in (c) and (d), after the catalyst was recycled 5 times, the MB removal rate of Ag@PCM prepared in Example 1 was still close to 99%.

[0045] The Ag@PCM prepared in Example 2 of the present invention also exhibited excellent catalytic ability for MB in the presence of NaBH4. The apparent reaction rate k of MB was app Reached 17×10 -3 s -1 After the catalyst was recycled for 5 times, the MB removal rate still reached 89%.

[0046] (2) Catalytic degradation of rhodamine b (RhB) like Figure 4 As shown, the catalytic degradation effect diagram of Rhodamine b by the porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 3 of the present invention, wherein (a) is the UV absorption spectrum of RhB, (b) is the apparent rate of RhB catalyzed by Ag@PCM, (c) is the UV absorption spectrum of RhB catalyzed for 5 times, and (d) is the removal rate of RhB catalyzed for 5 times. Since cyclodextrin has a synergistic catalytic ability to pollutants, in the presence of sodium borohydride (NaBH4), Ag@PCM exhibits excellent catalytic degradation ability to RhB, and can quickly eliminate the UV absorption peak of the reaction substrate RhB.

[0047] The apparent reaction rate (k app ) is calculated in the same way as in the above formula (1).

[0048] like Figure 4 As shown in (b), the apparent reaction rate k of MB app Reached 20×10 -3 s -1 .like Figure 4 As shown in (c) and (d), after the catalyst was recycled 5 times, the Ag@PCM prepared in Example 3 still had a RhB removal rate of up to 97%.

[0049] (3) Catalytic degradation of p-nitrophenol (4-NP) like Figure 5As shown, the catalytic degradation effect diagram of the porous cyclodextrin microspheres Ag@PCM loaded with nanosilver prepared in Example 4 of the present invention on p-nitrophenol, wherein (a) is the UV absorption spectrum of 4-NP, (b) is the apparent rate of 4-NP catalyzed by Ag@PCM, (c) is the UV absorption spectrum of 4-NP catalyzed for 5 times, and (d) is the removal rate of 4-NP catalyzed for 5 times. Since cyclodextrin has a synergistic catalytic ability to pollutants, in the presence of sodium borohydride (NaBH4), Ag@PCM exhibits excellent catalytic degradation ability to 4-NP, and can quickly eliminate the UV absorption peak of the reaction substrate 4-NP.

[0050] The apparent reaction rate (k app ) is calculated in the same way as in the above formula (1).

[0051] like Figure 5 As shown in (b), the apparent reaction rate k of 4-NP app Reached 6×10 -3 s -1 .like Figure 5 As shown in (c) and (d), after the catalyst was recycled for 5 times, the removal efficiency of 4-NP by Ag@PCM was still as high as 91%.

[0052] In order to compare the superiority of the Ag@PCM of the present invention with other nanosilver, the catalytic performance of nanosilver particles in the literature in recent years is listed in Table 1 below. It can be seen that when the Ag@PCM of the present invention catalyzes the degradation reactions of 4-NP, RhB and MB, both the reaction rate and the degradation conversion amount per unit time are at the leading level.

[0053] Table 1 The degradation effects of Ag@PCM of the present invention and existing different nanocatalysts on pollutants

[0054] 2. Verify the synergistic catalytic performance of cyclodextrin The Ag@PCM prepared by the method of Example 1 was selected to carry out the following catalytic experiment, and the specific process is as follows: 20 mg of Ag@PCM and 60 mg of sodium adamantanecarboxylate were dissolved in 20 mL of deionized water. The control group consisted of only 20 mg of Ag@PCM dissolved in 20 mL of deionized water. Both were stirred for 12 h to ensure that sodium adamantanecarboxylate could fully enter the cyclodextrin cavity. Subsequently, 200 mL of RhB (100 mg / L) and 40 mL of NaBH4 (0.02 M) were added for catalytic reaction.

[0055] 10 mg of Ag@PCM and 60 mg of sodium adamantanecarboxylate were dissolved in 10 mL of deionized water. The control group consisted of only 10 mg of Ag@PCM dissolved in 10 mL of deionized water. Both were stirred for 12 h to ensure that sodium adamantanecarboxylate could fully enter the cyclodextrin cavity. Subsequently, 60 mL of MB (40 mg / L) and 30 mL of NaBH4 (0.02 M) were added for catalytic reaction.

[0056] 7 mg of Ag@PCM and 21 mg of sodium adamantanecarboxylate were dissolved in 20 mL of deionized water. The control group consisted of only 7 mg of Ag@PCM in 20 mL of deionized water. Both solutions were stirred for 12 h to ensure that sodium adamantanecarboxylate completely entered the cyclodextrin cavity. Subsequently, 20 mL of 4-NP (40 mg / L) and 5 mL of NaBH4 (0.02 M) were added under the same conditions to initiate the catalytic reaction.

[0057] exist Figure 6 In the figure, (a) to (c) are the catalytic comparison results of Ag@PCM and microspheres treated with sodium adamantane carboxylate (Ag@PCM-T) on RhB, MB and 4-NP. The k of RhB catalyzed by Ag@PCM-T is app The value is 4.90×10 -3 s -1 , while the value of Ag@PCM is 10.39×10 -3 s -1 ; Ag@PCM-T catalyzes the k app The value is 14.91×10 -3 s -1 , while the value of Ag@PCM is 17.06×10 -3 s -1 ;Ag@PCM-T catalyzes the k app The value is 3.45×10 -3 s -1 , while the value of Ag@PCM is 3.58×10 -3 s -1 Three sets of comparative experiments verified that after sodium adamantanecarboxylate occupied the cavity of cyclodextrin in Ag@PCM, the catalytic rate of the polluted substrate was reduced, thus verifying that the cyclodextrin in Ag@PCM played a synergistic catalytic role in pollutants.

[0058] Experimental Example 3 Microsphere fluidized bed experiment like Figure 7As shown in (a), the Ag@PCM microspheres prepared in Example 1 were filled into the column, and a MB-catalyzed fluidized bed experiment was conducted. The process was briefly summarized as follows: 25 mL of NaBH4 solution (0.02 M) and 100 mL of MB solution (40 mg / L) were mixed under the push of an automatic liquid feeder and flowed through the catalytic column at a propulsion rate of 400 mL / h (the catalytic column consisted of a catalyst and a filter layer, and the filter layer was composed of a combination of absorbent cotton and a hydrophobic sieve plate with a pore size of 10 um, and its function was to intercept the Ag@PCM) and was catalytically reduced to a colorless aqueous solution. Figure 7 As shown in (b), in the absence of catalyst and only with filter layer, the ultraviolet absorption peak of the mixed solution of MB and NaBH4 decreased slightly, which was attributed to the adsorption of MB by the filter layer. After adding the catalyst, the mixed solution flowed through the column at a rate of 400 mL / h, and the ultraviolet absorption peak of MB completely disappeared, proving that the Ag@PCM prepared in Example 1 has excellent performance when used in a fixed bed.

[0059] like Figure 8 As shown in (a), the Ag@PCM microspheres prepared in Example 2 were filled into the column, and a MB-catalyzed fluidized bed experiment was conducted. The process was briefly summarized as follows: under the push of an automatic liquid feeder, 25 mL of NaBH4 solution (0.02 M) and 100 mL of MB solution (40 mg / L) were mixed and flowed through the catalytic column (the catalytic column consisted of a catalyst and a filter layer) at a propulsion rate of 400 mL / h to be catalytically reduced to a colorless aqueous solution. Figure 8 As shown in (b), in the absence of catalyst and only with filter layer, the ultraviolet absorption peak of the mixed solution of MB and NaBH4 decreased slightly, which was attributed to the adsorption of MB by the filter layer. After adding the catalyst, the mixed solution flowed through the column at a rate of 400 mL / h, and the ultraviolet absorption peak of MB completely disappeared, proving that the Ag@PCM prepared in Example 2 also has excellent performance when used in a fixed bed.

[0060] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A porous cyclodextrin microsphere loaded with nanosilver, characterized in that: The porous cyclodextrin microspheres are obtained by loading nanosilver on oligomeric cyclodextrin with a molecular weight of 8000 to 14000, blending with poly(methyl vinyl ether-alt-maleic acid) to prepare microspheres, and then cross-linking.

2. The porous cyclodextrin microspheres loaded with nanosilver according to claim 1, characterized in that: The molecular weight of the poly(methyl vinyl ether-alt-maleic acid) is 80,000; Or / and, the oligomeric cyclodextrin is prepared by using cyclodextrin, and the cyclodextrin is selected from α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, or small molecule derivatives of these three cyclodextrins.

3. The porous cyclodextrin microspheres loaded with nanosilver according to claim 2, characterized in that: The three small molecule derivatives of cyclodextrin include: hydroxypropyl β-cyclodextrin and aldehyde α-cyclodextrin.

4. The method for preparing porous cyclodextrin microspheres loaded with nanosilver according to any one of claims 1 to 3, characterized in that: The method includes: The oligomeric cyclodextrin with a molecular weight of 8000-14000 is loaded with nanosilver and dissolved in water and mixed with a poly(methyl vinyl ether-alt-maleic acid) aqueous solution, and then sprayed into an organic solvent supercooled at -84-93°C by a spray gun to obtain microspheres, which are then filtered and freeze-dried, and then cross-linked at 80-120°C to obtain porous cyclodextrin microspheres loaded with nanosilver; The organic solvent does not solidify at -84 to -93°C and has low solubility for oligomeric cyclodextrin.

5. The preparation method according to claim 4, characterized in that: The blending comprises mixing a 5-15 wt% aqueous solution of loaded nanosilver oligomeric cyclodextrin with a 5-20 wt% aqueous solution of poly(methyl vinyl ether-alt-maleic acid), and the mass ratio of loaded nanosilver oligomeric cyclodextrin to poly(methyl vinyl ether-alt-maleic acid) is (3-7):

1.

6. The preparation method according to claim 4, characterized in that: The spray gun is a gun-type spray gun with a caliber of 0.3-0.8 mm and a muzzle distance of 5-20 cm from the receiving container; Or / and, the organic solvent is n-hexane, and the amount of n-hexane is 5 to 20 times that of water; Or / and, the cross-linking time is 6 to 11 hours.

7. The preparation method according to claim 4, characterized in that: The preparation of the oligomeric cyclodextrin-loaded nanosilver comprises: (1) Synthesis of oligomeric cyclodextrin Add epichlorohydrin to a NaOH aqueous solution of β-CD, and heat the solution at 30-45°C for 1-6 hours to obtain an oligomeric cyclodextrin solution; wherein the mass fraction of NaOH in the NaOH aqueous solution of β-CD is 10-25 wt%, and the concentration of β-CD is 0.4-0.8 M; the volume of epichlorohydrin is 20-30% of the volume of the NaOH aqueous solution; The oligomeric cyclodextrin solution is poured into an isopropanol solution to stop the reaction, the pH of the mixed solution is adjusted to 7, and then the mixed solution is transferred into a dialysis bag with a molecular weight of 8000-14000 for dialysis, and after the dialysis is completed, the solvent is removed to obtain oligomeric cyclodextrin; (2) Synthesis of oligomeric cyclodextrin loaded with nanosilver The oligomeric cyclodextrin is dissolved in a NaOH aqueous solution, wherein the mass fraction of the oligomeric cyclodextrin in the mixed solution is 3-10 wt%, and the concentration of NaOH in the mixed solution is 0.001-0.003 M, and then a 0.001-0.005 M AgNO3 aqueous solution is added, and the volume ratio of the AgNO3 aqueous solution to the NaOH aqueous solution is (3-9): (30-60). The mixture is heated at 40-70°C for reaction for 2-6 hours. After the reaction is completed, the solvent is removed to obtain the loaded nanosilver oligomeric cyclodextrin.

8. The preparation method according to claim 7, characterized in that: The amount of the isopropanol solution is 10 to 20 times that of the NaOH aqueous solution; 6 M hydrochloric acid is used to adjust the pH of the mixed solution to 7.

9. Use of the porous cyclodextrin microspheres loaded with nanosilver as claimed in any one of claims 1 to 3 in reducing and decomposing pollutants.

10. The use according to claim 9, characterized in that: The pollutants include any one or more of methylene blue, rhodamine b and p-nitrophenol.

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