Polymeric core-shell microspheres, methods for their preparation and use

Abstract

The application provides a polymer core-shell structure microsphere, a preparation method and application thereof, wherein the polymer core-shell structure microsphere comprises a polydivinylbenzene inner core and an outer shell loaded with pyridine groups on the surface of the polydivinylbenzene inner core. The microsphere core particle has high crosslinking degree, low water swelling rate and large structural strength, the shell layer has low crosslinking degree and large functional group density, the capture of hexavalent chromium ions is shell adsorption, and the adsorption response speed is fast.

Description

Technical Field

[0001] This application relates to the field of heavy metal ion adsorption materials, and in particular to a polymer core-shell structured microsphere, its preparation method, and its application. Background Technology

[0002] The electroplating and surface treatment industries frequently require chromium plating to increase the surface hardness and oxidation resistance of materials. However, this process results in the presence of hexavalent chromium ions in the associated wastewater. Hexavalent chromium can cause irreversible damage to humans, animals, plants, and aquatic life, and is classified as a Class I pollutant under strict national control. Therefore, it is essential to completely remove it from wastewater. Currently, the main technical solutions for the removal, separation, or enrichment and recovery of hexavalent chromium ions in water bodies are as follows:

[0003] Chemical purification treatment. A common method is the reduction-precipitation method, which first reduces hexavalent chromium to trivalent chromium with a reducing agent, and then precipitates it with alkali. However, this method is incomplete in both the reduction and precipitation processes, especially when treating low-concentration hexavalent chromium wastewater, where complete reduction is difficult.

[0004] Porous material adsorption method. This method mainly utilizes porous materials with a large specific surface area to physically adsorb hexavalent chromium ions in water, such as activated carbon and molecular sieves. However, it has a small adsorption capacity and poor selectivity.

[0005] This invention aims to overcome the drawbacks of the above methods and provide new methods, materials and technologies for removing hexavalent chromium ions from water. Summary of the Invention

[0006] This application aims to at least partially address one of the technical problems in the related art.

[0007] Therefore, the purpose of this application is to propose a polymer core-shell structured microsphere with high cross-linking degree, low water swelling rate, and high structural strength of the core particles, and low cross-linking degree and high functional group density of the shell. The capture of hexavalent chromium ions is shell adsorption, and the adsorption response speed is fast.

[0008] To achieve the above objectives, this application proposes a polymer core-shell structured microsphere comprising a polyvinylbenzene core and a shell with pyridine groups loaded on its surface covering the polyvinylbenzene core.

[0009] The structure of the polyvinylbenzene core is shown in formula (I):

[0010]

[0011] The structure of the polymer core-shell structured microspheres is shown in formula (II) or formula (III):

[0012]

[0013] The surface of the polymer core-shell structured microspheres in formulas (II) and (III) above is loaded with pyridine groups.

[0014] This application also proposes a method for preparing polymer core-shell structured microspheres, the specific preparation process of which is as follows:

[0015] Step 1: Prepare PDVB microspheres by free radical polymerization of divinylbenzene;

[0016] Step 2: After swelling the PDVB microspheres with 4-vinylpyridine or 2-vinylpyridine shells, add them to an aqueous solution of gum arabic to carry out a coating reaction, and obtain polymer core-shell structured microspheres with pyridine groups loaded on the surface.

[0017] Furthermore, the specific process for preparing PDVB microspheres by divinylbenzene via free radical polymerization is as follows:

[0018] A certain concentration of polyvinyl alcohol aqueous solution, methylene blue aqueous solution, and distilled water are added to a reaction vessel and heated to a certain temperature.

[0019] A mixture of benzoyl peroxide and divinylbenzene was added to the reaction vessel and stirred until the oil droplets were of a suitable size. The reaction was then carried out with a programmed temperature increase, followed by cooling, washing, and drying to obtain PDVB microspheres.

[0020] Furthermore, the concentration of the polyvinyl alcohol aqueous solution is 1%-10%, and the addition ratio of polyvinyl alcohol, benzoyl peroxide and divinylbenzene is in the range of 1:1 to 5:1000.

[0021] Furthermore, the size of the oil droplets is 0.2–1.0 mm.

[0022] Furthermore, the process of swelling PDVB microspheres with shell 4-vinylpyridine or 2-vinylpyridine is as follows: PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene are added to a reaction vessel and swollen for a period of time.

[0023] Furthermore, the addition ratio of the PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene ranges from 100:50 to 100:1 to 5:100 to 150.

[0024] Furthermore, the concentration of the gum arabic aqueous solution is 1%-10%, and the amount of gum arabic aqueous solution added is 10 to 20 times the amount of 4-vinylpyridine or 2-vinylpyridine added.

[0025] Furthermore, it also includes: repeating the process in step 2 with the prepared polymer core-shell structured microspheres and using the shell layer 4-vinylpyridine or 2-vinylpyridine to carry out the coating reaction again to obtain multilayer coated polymer core-shell structured microspheres.

[0026] This application also proposes an application of polymer core-shell structured microspheres, which are used for the directional capture of hexavalent chromium ions. The specific application process is as follows:

[0027] Take electrolytic copper foil wastewater containing hexavalent chromium or other industrial wastewater containing hexavalent chromium, and add polymer core-shell structured microspheres to it for adsorption;

[0028] The adsorbed polymer core-shell structured microspheres were eluted with 5% sodium hydroxide solution.

[0029] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0030] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 This is a reaction mechanism diagram of the PDVB microsphere preparation process in this application;

[0032] Figure 2 This is a schematic diagram of the PDVB-P4VP reaction mechanism of this application;

[0033] Figure 3 This is a schematic diagram of the PDVB-P2VP reaction mechanism of this application;

[0034] Figure 4 This is an adsorption diagram of hexavalent chromium ions, copper ions, zinc ions and trivalent iron in the hexavalent chromium-containing wastewater from electrolytic copper foil enterprises using PDVB-P2VP as described in this application;

[0035] Figure 5a This is a photograph of the PDVB microspheres used in this application;

[0036] Figure 5b This is a photo of the PDVB-P4VP file in this application;

[0037] Figure 5c This is a photo of the PDVB-P2VP in this application;

[0038] Figure 6a This is the overall surface morphology of the PDVB microspheres in this application;

[0039] Figure 6b This is a local surface morphology of the PDVB microspheres in this application;

[0040] Figure 6c This is the surface morphology of PDVB-P2VP in this application;

[0041] Figure 6d This is the kernel-shell interface of the PDVB-P2VP in this application;

[0042] Figure 6e This is a cross-sectional view of the PDVB-P2VP core-shell structured microspheres of this application;

[0043] Figure 6f This is the core-shell interface of the PDVB-P2VP microspheres in this application;

[0044] Figure 6g This is a cross-sectional view of the PDVB-P4VP core-shell structured microspheres of this application;

[0045] Figure 6h This is the core-shell interface of the PDVB-P4VP microspheres in this application;

[0046] Figure 7 These are the infrared spectra of the PDVB microspheres and PDVB-P2VP core-shell structured microspheres of this application;

[0047] Figure 8a This application involves EDX analysis of the nitrogen content on the surface of PDVB microspheres.

[0048] Figure 8b This application relates to the EDX analysis of nitrogen content on the surface of PDVB-P4VP core-shell microspheres. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other technical solutions obtained by those skilled in the art based on the embodiments of this invention are within the scope of protection of this invention.

[0050] The first aspect of the present invention provides a polymeric core-shell structured microsphere comprising a polyvinylbenzene core and a shell coated with pyridine groups on the surface of the polyvinylbenzene core.

[0051] The structure of the polyvinylbenzene core is shown in formula (I):

[0052]

[0053] It is understandable that the polyvinylbenzene core can be prepared by polymerizing divinylbenzene, and the surface of the prepared polyvinylbenzene core has a large number of unreacted double bonds.

[0054] The structure of the polymer core-shell structured microspheres is shown in formula (II) or formula (III):

[0055]

[0056] The surface of the polymer core-shell structured microspheres in formulas (II) and (III) above is loaded with pyridine groups.

[0057] It is understandable that, since the surface of the polydivinylbenzene core contains a large number of unreacted double bonds, the polydivinylbenzene core can react with substances containing double bonds and pyridine groups to coat the surface of the polydivinylbenzene core with a shell loaded with pyridine groups, so that the surface of the prepared polymer core-shell structure microspheres is loaded with a large number of pyridine groups.

[0058] The second aspect of this invention provides a method for preparing polymer core-shell structured microspheres, the preparation process of which is as follows:

[0059] Step 1: PDVB microspheres were prepared by free radical polymerization of divinylbenzene. The surface of the microspheres was loaded with a large number of unreacted double bonds; the reaction mechanism is as follows. Figure 1 As shown;

[0060] Step 2: After swelling PDVB microspheres with 4-vinylpyridine or 2-vinylpyridine shells, add them to an aqueous solution of gum arabic. The unreacted double bonds on the microsphere surface then react with 4-vinylpyridine or 2-vinylpyridine to obtain polymer core-shell structured microspheres with pyridine groups on their surface. The reaction mechanism is as follows: Figure 2 and Figure 3 As shown, free radical polymerization using divinylbenzene as a raw material results in PDVB microspheres with high crosslinking degree, low water swelling rate, and high structural strength. Furthermore, the surface of the PDVB microspheres is uniformly covered with a large number of unreacted double bonds, which can undergo crosslinking reactions with 4-vinylpyridine or 2-vinylpyridine. This introduces a large number of pyridine groups onto the surface of the PDVB microspheres, thereby increasing the density of functional groups on the shell surface of the prepared polymer core-shell structure microspheres, providing more adsorption sites, and thus improving the material's adsorption capacity for hexavalent chromium ions.

[0061] For example, a method for preparing PDVB microspheres using divinylbenzene as a raw material includes, but is not limited to, free radical polymerization. PDVB microspheres are prepared via free radical polymerization. Furthermore, since the surface of the PDVB microspheres contains unreacted vinyl groups, using the PDVB microspheres as seed cores, the PDVB microspheres are first moderately swollen using a second monomer, 4-vinylpyridine or 2-vinylpyridine. Then, the unreacted C=C double bonds on the surface of the PDVB microspheres are used to capture the swollen monomer 4-vinylpyridine or 2-vinylpyridine on the microsphere surface for free radical polymerization. This results in the prepared polymeric core-shell structure microspheres having a large amount of 4-vinylpyridine or 2-vinylpyridine in the shell layer. Both 4-vinylpyridine and 2-vinylpyridine groups have tertiary amino nitrogen atoms, which can directionally capture hexavalent chromium ions under acidic conditions. The capture process is shell adsorption, and its outstanding advantage is a fast adsorption response.

[0062] In some embodiments, the specific process for preparing PDVB microspheres by divinylbenzene via free radical polymerization is as follows:

[0063] A certain concentration of polyvinyl alcohol aqueous solution, methylene blue aqueous solution, and distilled water are added to a reaction vessel and heated to a certain temperature.

[0064] A mixture of benzoyl peroxide and divinylbenzene was added to the reaction vessel and stirred until the oil droplets were of appropriate size. The reaction was then carried out with a programmed temperature increase. After cooling, washing and drying, PDVB microspheres were obtained. A free radical polymerization reaction was carried out between polyvinyl alcohol solution and divinylbenzene. The main raw material was divinylbenzene, and polyvinyl alcohol was only used as a dispersant to ensure that the obtained microspheres would not stick together but would separate into independent microspheres.

[0065] For example, there are no restrictions on the specific order in which the polyvinyl alcohol aqueous solution, methylene blue aqueous solution, and distilled water are added to the reaction vessel. Furthermore, the temperature can be raised to a range of 40-45°C, meaning it can be raised to 40°C, 43°C, 45°C, or any range in between. Since a heating process is involved, the reaction vessel can be a four-necked flask. After adding the reactants, a reflux condenser and thermometer are installed on the four-necked flask. The reaction vessel can be heated via a water bath or an oil bath. A stirrer is installed in the four-necked flask to stir the reaction. After the reaction vessel reaches a certain temperature, a mixture of benzoyl peroxide and divinylbenzene is added, and stirring continues until the oil droplets are of suitable size. Then, a programmed temperature increase reaction is carried out to obtain PDVB microspheres.

[0066] In some embodiments, the concentration of the polyvinyl alcohol aqueous solution is 1% to 10%, and the addition ratio of polyvinyl alcohol, benzoyl peroxide, and divinylbenzene ranges from 1:1 to 5:1000.

[0067] For example, the concentration of the polyvinyl alcohol aqueous solution can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range thereto, and the addition ratio between polyvinyl alcohol, benzoyl peroxide and divinylbenzene can be any range from 1:1 to 5:1000.

[0068] In some embodiments, the size of the oil droplets is 0.2 to 1.0 mm, by controlling the size of the oil droplets within the range of 0.2 to 1.0 mm.

[0069] For example, the size of the oil droplets is 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm or any range therein.

[0070] In some embodiments, the specific process of the programmed temperature rise reaction is as follows: first, slowly raise the temperature to 80-83°C and hold the reaction for 1 hour; then raise the temperature to 83-85°C and continue the reaction for 2 hours, while maintaining the stirring speed; then raise the temperature to 95°C and continue the reaction for 1 hour; then remove the water bath. Through three-stage programmed temperature rise, the reaction is difficult to control due to the initial high temperature; the subsequent temperature increase is necessary to ensure complete monomer reaction. After removing the water bath, the temperature can be naturally cooled to below 40°C, stirring is stopped, and then the microspheres are poured into a nylon bag, washed twice with tap water, spun dry, and then placed in a 60°C oven to dry for 3 hours.

[0071] For example, in the three-stage heating process, the first stage of heating is to slowly raise the temperature to 80-83℃, which can be 80℃, 83℃ or any range in between. Similarly, in the second stage of heating, the temperature is raised to 83-85℃, which can be 83℃, 85℃ or any range in between. The third stage of heating is to raise the temperature to 95℃, thus realizing the three-stage heating process.

[0072] In some embodiments, the process of swelling PDVB microspheres with shell 4-vinylpyridine or 2-vinylpyridine is as follows: PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene are added to a reaction vessel and swollen for a period of time. The PDVB microspheres are swollen with 4-vinylpyridine or 2-vinylpyridine so that the monomer diffuses into the surface of the seed sphere and reacts on the surface to truly form a core-shell structure.

[0073] For example, PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene are added to a four-necked flask and swollen for 6-12 hours.

[0074] In some embodiments, the addition ratio of PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene ranges from 100:50 to 100:1 to 5:100 to 150.

[0075] For example, the ratio of PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene can be any range from 100:50 to 100:1 to 5:100 to 150.

[0076] In some embodiments, the concentration of the gum arabic aqueous solution is 1% to 10%, and the amount of gum arabic aqueous solution added is 10 to 20 times the amount of 4-vinylpyridine or 2-vinylpyridine added.

[0077] For example, the concentration of the gum arabic aqueous solution can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range therein.

[0078] In some embodiments, the method further includes: repeating the process in step 2 with a shell layer of 4-vinylpyridine or 2-vinylpyridine to re-coat the prepared polymeric core-shell microspheres, thereby obtaining multi-layered coated polymeric core-shell microspheres. The number of coating layers and the thickness of the shell layer can be flexibly controlled based on the seed microspheres. For example, a shell layer monomer can be added dropwise after the first coating to perform a second coating, increasing the shell layer thickness.

[0079] For example, the prepared polymer core-shell structure microspheres are added to an aqueous solution of gum arabic with 4-vinylpyridine or 2-vinylpyridine as the shell layer, and after a coating reaction, multilayer polymer core-shell structure microspheres with pyridine groups loaded on the surface are obtained.

[0080] The third aspect of this invention proposes the application of polymer core-shell structured microspheres in the directional capture of hexavalent chromium ions. The specific application process is as follows: Electrolytic copper foil wastewater containing hexavalent chromium or other industrial wastewater containing hexavalent chromium is taken, and polymer core-shell structured microspheres are added for adsorption. The adsorbed polymer core-shell structured microspheres are then eluted with a 5% sodium hydroxide solution. The prepared polymer core-shell structured microspheres can adsorb hexavalent chromium ions in the electrolytic copper foil wastewater. After adsorption, elution with 5% sodium hydroxide removes the hexavalent chromium, which can then be used to process chrome yellow or prepare chrome green. The eluted polymer core-shell structured microspheres are then washed with water, and the resin is regenerated with sulfuric acid. Finally, the microspheres are washed until the pH reaches 1-3, at which point regeneration is complete.

[0081] For example, an electrolytic copper foil company produces wastewater containing hexavalent chromium. The original wastewater has a pH of 1.0-3.0 and a hexavalent chromium content of approximately 10 mg / L, along with other impurities such as copper, zinc, trivalent chromium, and trivalent iron. High-molecular-weight core-shell microspheres are then added. After adsorption, the hexavalent chromium concentration is reduced to 0. Following adsorption, the microspheres are washed with water and then eluted with 5% sodium hydroxide to remove the adsorbed hexavalent chromium ions. The regenerated solution is yellowish-brown, with a peak hexavalent chromium concentration of approximately 20 g / L. The high concentration of sodium chromate in the regenerated solution can be processed into chrome yellow for use in the coatings industry. Alternatively, quantitative reduction followed by neutralization and precipitation can yield chrome green. After washing with water, the resin is converted using sulfuric acid. Finally, it is washed until the pH reaches 1-3, ending the regeneration process. This resin selectively adsorbs only hexavalent chromium ions, without adsorbing other impurity ions. Furthermore, it exhibits a large adsorption capacity and stable, thorough adsorption effect.

[0082] The embodiments and comparative examples will be provided below to illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards. Specific embodiments and comparative examples are as follows:

[0083] Example 1:

[0084] The specific preparation process for preparing polymer core-shell structured microspheres using 4-vinylpyridine (4VP) as a raw material is as follows:

[0085] (1) Preparation of PDVB microspheres: ① In a 250mL four-necked flask, add 4mL of 5% polyvinyl alcohol (PVA) aqueous solution, 160mL of distilled water, and 3 drops of methylene blue aqueous solution in sequence. Attach a reflux condenser and thermometer, start the stirrer, and slowly heat in a water bath until the temperature reaches 40℃, then stop stirring. ② Pour the pre-prepared mixture containing 0.3g benzoyl peroxide and 50g divinylbenzene (DVB) into the four-necked flask, start the stirrer, and control the oil droplet size to 0.2-0.6mm. ③ After the oil droplet size is within acceptable limits, slowly raise the temperature to 80-83℃, maintain the temperature for 1h, then raise the temperature to 83-85℃ and continue the reaction for 2h, maintaining the stirring speed to prevent the microspheres from becoming uneven or agglomerated. ④ Raise the temperature to 95℃ and continue the reaction for 1h, then remove the water bath, allow it to cool naturally to below 40℃, and stop stirring. ⑤ Pour the microspheres into a nylon bag, wash them twice with tap water, spin dry, and then dry them in a 60℃ oven for 3 hours.

[0086] (2) Preparation of polymer core-shell structured microspheres: ① The PDVB seed spheres were swollen with shell 4VP monomer to allow the monomer to diffuse into the surface of the seed spheres. In a four-necked flask equipped with a reflux condenser, thermometer, and stirrer, the following ingredients were added: 5g seed spheres, 7.5mL 4VP, 0.75mL DVB (DVB:4VP = 1:10), 0.05g BPO, and 10mL toluene. Swelling was allowed for 6-12 hours. ② In the same four-necked flask, 100mL of a 2% gum arabic aqueous solution was slowly added. The mixture was heated in a water bath to 85℃ and reacted with stirring for 10 hours. The stirring speed was adjusted to allow the microspheres to remain suspended in the solution. ③ After the reaction, the reaction solution was filtered off, and the microspheres were extracted with anhydrous methanol under reflux in a Soxhlet extractor for 6 hours, followed by washing with tap water. After washing, the microspheres were dried in an oven at 323K to constant weight to obtain polymer core-shell structured microspheres (PDVB-P4VP).

[0087] The application of polymer core-shell structured microspheres in the directional capture of hexavalent chromium ions is as follows:

[0088] Wastewater containing hexavalent chromium from an electrolytic copper foil manufacturer was collected. The original wastewater had a pH of 1.0-3.0 and a hexavalent chromium content of approximately 10 mg / L, along with other impurities such as copper, zinc, hexavalent chromium, and ferric iron. High-molecular-weight core-shell microspheres were then added to the wastewater, and the mixture was shaken at room temperature for 3-6 hours. After filtration, the concentrations of hexavalent chromium ions, copper ions, zinc ions, and ferric iron in the filtered solution were measured. The adsorption curves of the high-molecular-weight core-shell microspheres for hexavalent chromium ions, copper ions, zinc ions, and ferric iron were obtained as shown in the figure. Figure 4 As shown, the polymer core-shell structured microspheres exhibit a significant adsorption effect on hexavalent chromium, adsorbing it to undetectable levels. The volume of the adsorbed hexavalent chromium solution is 1000 times the volume of the polymer core-shell structured microspheres. They do not adsorb copper ions, zinc ions, or ferric ions. The principle of directional adsorption is that the pyridine groups all possess tertiary amino nitrogen atoms, which can selectively bind to hexavalent chromium ions under acidic conditions.

[0089] After filtration, the polymer core-shell structured microspheres are washed with water, and then the hexavalent chromium ions adsorbed by the resin are eluted with 5% sodium hydroxide. During the washing process, 4–8 grams of 5% sodium hydroxide are added per gram of polymer core-shell structured microspheres. The resulting regenerated solution is yellowish-brown, with a peak hexavalent chromium concentration of approximately 20 g / L. The high concentration of sodium chromate in the regenerated solution can be processed into chrome yellow for use in the coatings industry. Alternatively, quantitative reduction followed by neutralization and precipitation can yield chrome green.

[0090] After elution, the polymer core-shell structured microspheres are washed with water and then transformed with 2% to 10% sulfuric acid. The volume ratio of sulfuric acid to the volume of polymer core-shell structured microspheres is 2 to 5:1. Finally, the microspheres are washed with water until the pH reaches 1 to 3, and the regeneration is completed.

[0091] Example 2

[0092] The specific preparation process for preparing polymer core-shell structured microspheres using 2-vinylpyridine (2VP) as a raw material is as follows:

[0093] ① In a four-necked flask equipped with a reflux condenser, thermometer, and stirrer, add the following ingredients: 5g of PDVB microspheres prepared in Example 1, 7.5mL of 2VP, 0.75mL of DVB (DVB:2VP = 1:10), 0.05g of BPO, and 10mL of toluene. Allow to swell for 6-12 hours. ② In the same four-necked flask, slowly add 100mL of a 2% gum arabic aqueous solution. Heat in a water bath to 85°C and react with stirring for 10 hours. The stirring speed should be such that the microspheres remain suspended in the solution. ③ After the reaction is complete, filter out the reaction solution and extract with anhydrous methanol in a Soxhlet extractor under reflux for 6 hours. Then wash with tap water. After washing, dry the microspheres in an oven at 323K to constant weight to obtain polymeric core-shell structured microspheres (PDVB-P2VP).

[0094] The application of polymer core-shell structured microspheres in the directional capture of hexavalent chromium ions follows the same process as in Example 1.

[0095] The following uses PDVB-P4VP and PDVB-P2VP prepared in Examples 1 and 2 as examples for structural characterization. The specific characterization results are as follows:

[0096] (1) Shape analysis of PDVB microspheres, PDVB-P4VP, and PDVB-P2VP:

[0097] Specific ordinary optical photographs, such as Figure 5a , 5b As shown in 5c, Figure 5a Photographs of PDVB microspheres Figure 5b Photos of PDVB-P4VP Figure 5c The images show PDVB-P2VP microspheres, which are colorless and transparent, while PDVB-P4VP or PDVB-P2VP core-shell structure microspheres are amber to dark brown. PDVB microspheres have a smaller particle size, while core-shell structure microspheres have a significantly larger particle size than seed microspheres. PDVB microspheres have extremely high cross-linking and surface hardness, making them less prone to deformation and resulting in a more regular spherical shape. Core-shell structure microspheres, on the other hand, have low shell cross-linking and low surface hardness, making them more easily deformable and thus appearing less spherical.

[0098] (2) Scanning electron microscopy analysis was performed on PDVB microspheres, PDVB-P4VP and PDVB-P2VP. The specific analysis results are as follows:

[0099] Figure 6a , 6b Types 6c, 6d, 6e, 6f, 6g, and 6h are PDVB microspheres with smooth, glossy surfaces. PDVB microspheres have extremely high cross-linking degrees and high hardness, resulting in their smooth surfaces. Core-shell structured microspheres, on the other hand, have low shell cross-linking degrees, low hardness, and softer, relatively rough, and porous surfaces. A clear boundary between the seed core and shell is visible in the core-shell structured microspheres. The shell thickness increases accordingly with the amount of shell monomers added, ranging from approximately 20-50 μm.

[0100] Figure 6a , 6b The PDVB microspheres in the mixture have a smooth and glossy surface. Figure 6c , 6d The surface of the PDVB-P2VP core-shell structured microspheres is relatively porous and rough, and a distinct shell layer can be seen. Figure 6e , 6f The surface of the PDVB-P2VP core-shell structured microspheres is relatively porous and rough, and the thickness of the shell layer in the cross-section can be observed to be about 20 μm. Figure 6g , 6h The surface of the PDVB-P4VP core-shell structured microspheres is relatively porous and rough, and the thickness of the shell layer in the cross section can be seen to be about 50 μm.

[0101] (3) Infrared analysis of the surface of PDVB microspheres and PDVB-P2VP was performed, and the results are as follows:

[0102] like Figure 7 As shown, the characteristic peaks of C=C double bonds on the surface of PDVB microspheres are obvious. For PDVB-P2VP core-shell structure microspheres, a distinct P2VP characteristic peak appears instead of the C=C double bond characteristic peak. ① Due to the large number of unreacted C=C double bonds suspended on the surface of the PDVB microspheres, originating from DVB monomers, a distinct C=C double bond characteristic peak appears near wavenumber 899.81. ② After the PDVB microspheres are covered with a P2VP shell, the C=C double bonds on the PDVB microsphere surface undergo a bonding reaction with the shell monomer 2VP. The C=C double bonds are essentially completely reacted, hence the disappearance of the C=C double bond characteristic peak. Simultaneously, the PDVB microsphere surface is covered by bonded P2VP, therefore, a strong P2VP characteristic peak appears near wavenumber 1601.15.

[0103] (4) The nitrogen content on the surface of PDVB-P2VP microspheres was analyzed by EDX, and the results are as follows:

[0104] like Figure 8a , 8b , Figure 8a EDX analysis of the nitrogen content on the surface of the PDVB microspheres in this application showed that the surface was essentially free of nitrogen. Figure 8b EDX analysis of the nitrogen content on the surface of the PDVB-P4VP core-shell microspheres in this application showed that the surface contained significant nitrogen, as shown in Table 1. The N content on the surface of the PDVB-P2VP microspheres was 16.67%. Normally, PDVB microspheres do not contain nitrogen, but after the PDVB microspheres are coated with a P2VP shell, the presence of nitrogen should be clearly detectable. The nitrogen content data on the surface of the PDVB-P2VP core-shell structure microspheres also fully demonstrates the core-shell structure of the microspheres.

[0105] Table 1: Nitrogen content on the surface of PDVB-P2VP microspheres (EDX analysis)

[0106]

[0107] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0108] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing polymer core-shell structured microspheres, characterized in that, The specific preparation process is as follows: Step 1: Prepare PDVB microspheres by free radical polymerization of divinylbenzene; Step 2: After swelling the PDVB microspheres with 4-vinylpyridine or 2-vinylpyridine shells, add them to an aqueous solution of gum arabic to carry out a coating reaction, and obtain polymer core-shell structured microspheres with pyridine groups loaded on the surface. The addition ratio of the PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene is in the range of 100:50~100:1~5:100~150; The concentration of the gum arabic aqueous solution is 1%-10%, and the amount of gum arabic aqueous solution added is 10-20 times the amount of 4-vinylpyridine or 2-vinylpyridine added.

2. The method for preparing polymer core-shell structured microspheres as described in claim 1, characterized in that, The specific process for preparing PDVB microspheres by divinylbenzene via free radical polymerization is as follows: A certain concentration of polyvinyl alcohol aqueous solution, methylene blue aqueous solution, and distilled water are added to a reaction vessel and heated to a certain temperature. A mixture of benzoyl peroxide and divinylbenzene was added to the reaction vessel and stirred until the oil droplets were of a suitable size. The reaction was then carried out with a programmed temperature increase, followed by cooling, washing, and drying to obtain PDVB microspheres.

3. The method for preparing polymer core-shell structured microspheres as described in claim 2, characterized in that, The concentration of the polyvinyl alcohol aqueous solution is 1%-10%, and the addition ratio of polyvinyl alcohol, benzoyl peroxide and divinylbenzene is in the range of 1:1 to 5:1000.

4. The method for preparing polymer core-shell structured microspheres as described in claim 2, characterized in that, The oil droplets are 0.2 to 1.0 mm in size.

5. The method for preparing polymer core-shell structured microspheres as described in claim 1, characterized in that, The process of swelling PDVB microspheres with shell 4-vinylpyridine or 2-vinylpyridine is as follows: PDVB microspheres, 4-vinylpyridine or 2-vinylpyridine, DVB, BPO and toluene are added to a reaction vessel and swollen for a period of time.

6. The method for preparing polymer core-shell structured microspheres as described in claim 1, characterized in that, Also includes: The prepared polymer core-shell structured microspheres were subjected to the same process as in step 2, with the shell layer being coated again with 4-vinylpyridine or 2-vinylpyridine to obtain multilayer coated polymer core-shell structured microspheres.

7. A polymeric core-shell structured microsphere prepared by the method described in any one of claims 1-6, characterized in that, It includes a polydivinylbenzene core and a shell covering the outside of the polydivinylbenzene core with pyridine groups loaded on its surface; The structure of the polyvinylbenzene core is shown in formula (I): Equation (I) The structure of the polymer core-shell structured microspheres is shown in formula (II) or formula (III): Formula (II) Formula (III) The surface of the polymer core-shell structured microspheres in formulas (II) and (III) is loaded with pyridine groups.

8. The application of the polymer core-shell structured microspheres as described in claim 7, characterized in that, The polymer core-shell structured microspheres are used for the targeted capture of hexavalent chromium ions. The specific application process is as follows: Take electrolytic copper foil wastewater containing hexavalent chromium or other industrial wastewater containing hexavalent chromium, and add polymer core-shell structured microspheres to it for adsorption; The adsorbed polymer core-shell structured microspheres were eluted with 5% sodium hydroxide.

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