A core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, a preparation method and application thereof

Abstract

The application provides a kind of core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent and its preparation method and application, the adsorbent includes Fe3O4 magnetic inner core, SiO2 isolation shell layer coated on the outer surface of Fe3O4 magnetic inner core, polypyrrole functional shell layer coated on the outer surface of SiO2 isolation shell layer, and cetyltrimethylammonium bromide modification layer combined on the surface of polypyrrole functional shell layer by hydrophobic interaction and π-cation interaction.Cetyltrimethylammonium bromide modification layer provides electrostatic interaction site, polypyrrole functional shell layer provides π-π stacking interaction site and hydrogen bond interaction site, three kinds of interaction sites form ternary coupling adsorption interface synergistically, so that the adsorbent realizes electrostatic interaction, π-π stacking interaction and hydrogen bond interaction synergistically when treating anionic azo dye wastewater.The adsorption capacity of the adsorbent to anionic azo dye reaches 425.3mg / g, and the adsorption capacity retention rate is greater than 90% after 5 cycles.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, its preparation method, and its application. Background Technology

[0002] As a major textile and dyeing country globally, my country generates approximately 4.2 billion tons of wastewater annually from its dyeing and printing industry, with benzidine-based anionic azo dyes accounting for over 50% of the total. Due to their high toxicity and carcinogenicity, these dyes are widely discharged into water systems during production and use, posing a significant threat to ecosystems and public health. Currently, methods for treating benzidine-based anionic azo dyes mainly include adsorption, biological treatment, and electrochemical processes. Adsorption has become an important method for treating this type of wastewater due to its low cost, simple operation, high performance, and recyclability.

[0003] Iron oxide magnetic nanoparticles possess advantages such as superparamagnetism, high specific surface area, high magnetic susceptibility, and easy recovery through the application of an external magnetic field, making them suitable as adsorbents for wastewater treatment. However, due to their nanoscale size and strong dipole-dipole interactions, they are prone to aggregation and exhibit limited colloidal stability in suspensions, reducing recyclability and thus limiting practical applications. Chinese patent CN103143305B discloses the preparation of core-shell structured silica-modified iron oxide magnetic nanoparticles via a coating method; Chinese patent CN110767437B also discloses similar core-shell structured magnetic nanoparticles. However, while these methods have solved the aggregation problem of nano-iron oxide, practical applications have revealed low adsorption capacity and poor selectivity for benzidine-based anionic azo dye wastewater, resulting in unsatisfactory treatment effects.

[0004] Therefore, there is a need to develop a modified magnetic microsphere adsorbent that is not prone to aggregation, is easy to recycle, and has high adsorption capacity and rapid adsorption kinetics for benzidine-based anionic azo dyes. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, its preparation method, and its application, to solve the problems of easy aggregation, low adsorption capacity, poor selectivity, and difficult recovery of existing magnetic adsorbents when treating benzidine anionic azo dye wastewater.

[0006] To achieve the above and other related objectives, the present invention provides the following technical solutions: In a first aspect, the present invention provides a core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, comprising a Fe3O4 magnetic core, a SiO2 isolation shell coating the outer surface of the Fe3O4 magnetic core, a polypyrrole (PPy) functional shell coating the outer surface of the SiO2 isolation shell, and a hexadecyltrimethylammonium bromide (CTAB) modified layer bonded to the surface of the polypyrrole functional shell.

[0007] The polypyrrole functional shell contains a conjugated aromatic ring framework and NH groups. The hexadecyltrimethylammonium bromide modified layer is bonded to the surface of the polypyrrole functional shell through hydrophobic interactions and π-cation interactions. The quaternary ammonium groups in the hexadecyltrimethylammonium bromide modified layer provide electrostatic interaction sites, the conjugated aromatic ring structure in the polypyrrole functional shell provides π-π stacking interaction sites, and the NH groups in the polypyrrole functional shell provide hydrogen bonding interaction sites. These three interaction sites synergistically form a ternary coupled adsorption interface, enabling the adsorbent to achieve synergistic effects of electrostatic interactions, π-π stacking interactions, and hydrogen bonding interactions when treating anionic azo dye wastewater.

[0008] The ternary coupling adsorption mechanism is specifically manifested as follows: (1) Electrostatic effect: CTAB on the surface of the modified magnetic microspheres provides a large number of quaternary ammonium groups ( N + (CH3)3) generates a strong electrostatic attraction between itself and the sulfonate anion group in the anionic azo dye molecule, which acts as a long-range driving force to attract the dye molecule to the surface of the adsorbent. (2) Hydrogen bonding: The NH group on the PPy chain in the modified magnetic microsphere structure acts as a hydrogen bond donor, bonding with the amino group present in the anionic azo dye molecule. NH2) or azo group ( N=N The N atoms of the N atoms form a hydrogen bond network, achieving short-range specific binding and further enhancing the adsorption process; (3) π π-stacking: The PPy framework in the modified magnetic microsphere structure contains a conjugated aromatic ring structure, while the anionic azo dye molecule contains naphthalene and benzene ring structures. The overlap of the π electron clouds between the two enables π-stacking. π-stacking interactions form stable complexes, which promote the adsorption of anionic azo dyes on modified magnetic microspheres; (4) Ternary coupling effect: The above three forces exhibit a coupling effect. The electrostatic interaction distance provided by CTAB is the longest, which can be used as the initial driving force to attract anionic azo dye molecules to the adsorbent surface; PPy provides π π stacking and hydrogen bonding enable short-range and specific binding, with the three effects working synergistically and enhancing each other, exhibiting a coupling effect.

[0009] Furthermore, the specific surface area of ​​the core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent was determined to be 45-80 m² by the BET method. 2 / g, pore volume determined by the BJH method is 0.05-0.10 cm³. 3 / g, pore size was determined to be 4-6nm by the BJH method.

[0010] Specifically, the anionic azo dye is a benzidine-based anionic azo dye, which contains a sulfonate anionic group, an aromatic ring structure, and an azo group.

[0011] In some embodiments, the core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, under conditions of pH=5, temperature 25℃, and adsorbent dosage of 0.4 g / L, achieves a maximum adsorption capacity of 425.3 mg / g for anionic azo dyes, and the adsorption capacity reaches more than 95% of the equilibrium adsorption capacity within 10 min, thereby realizing the rapid adsorption and separation of anionic azo dyes.

[0012] Furthermore, the core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent retains ≥90% of its adsorption capacity after 5 cycles of use.

[0013] A second aspect of the present invention provides a method for preparing a core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, comprising the following steps: (1) Preparation of Fe3O4 magnetic microspheres by solvothermal method: iron salts were dissolved in ethylene glycol, sodium acetate and polyethylene glycol were added, and after dispersion, a solvothermal reaction was carried out. After magnetic separation, washing and drying, Fe3O4 magnetic microspheres were obtained. (2) Coating SiO2 isolation shell by sol-gel method: The Fe3O4 magnetic microspheres were dispersed in a mixed system of water, ethanol and 25% ammonia water, tetraethyl orthosilicate was added and sol-gel reaction was carried out. After magnetic separation, washing and drying, Fe3O4@SiO2 magnetic microspheres were obtained. (3) Preparation of polypyrrole functional shell by in-situ polymerization: The Fe3O4@SiO2 magnetic microspheres were dispersed in water, pyrrole monomer was added, and then an aqueous solution containing hydrochloric acid and ammonium persulfate was added for in-situ polymerization. After magnetic separation, washing and drying, Fe3O4@SiO2@PPy magnetic microspheres were obtained. (4) Introducing a hexadecyltrimethylammonium bromide modified layer by surface modification: The Fe3O4@SiO2@PPy magnetic microspheres were dispersed in water, and a hexadecyltrimethylammonium bromide aqueous solution was added for surface modification. After magnetic separation, washing and drying, a core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent was obtained.

[0014] Further, in step (1), the iron-containing salt is FeCl3·6H2O; wherein the ratio of FeCl3·6H2O, ethylene glycol, sodium acetate and polyethylene glycol is 1.0-2.0g: 50-70mL: 1.5-2.5g: 0.5-1.0g; the solvothermal reaction temperature is 180-220℃, and the reaction time is 8-16h.

[0015] Further, in step (2), the ratio of Fe3O4 magnetic microspheres, water, ethanol, 25% ammonia and tetraethyl orthosilicate is 0.3-0.7g: 30-50mL: 120-160mL: 1.0-3.0mL: 1.5-3.0mL; the sol-gel reaction is carried out at room temperature for 8-12 hours.

[0016] Further, in step (3), the ratio of Fe3O4@SiO2 magnetic microspheres, pyrrole monomer, hydrochloric acid and ammonium persulfate is 0.2-0.5g: 0.05-0.15mL: 3-8mL: 0.15-0.25g; the in-situ polymerization is carried out at room temperature for 10-15h.

[0017] Further, in step (4), the ratio of Fe3O4@SiO2@PPy magnetic microspheres to hexadecyltrimethylammonium bromide is 0.05-0.15g:0.10-0.20g; the surface modification is carried out at room temperature for 10-15h.

[0018] Furthermore, in each step, the applied magnetic field strength for magnetic separation is 0.1-0.5 T, and the magnetic separation time is 3-10 min.

[0019] Furthermore, in each step, the washing process involves alternating between ethanol and deionized water three times.

[0020] Furthermore, in each step, the drying temperature is 40-80℃ and the drying time is 6-18h.

[0021] As a preferred embodiment of step (1), 1.0-2.0 g of FeCl3·6H2O is completely dissolved in 50-70 mL of ethylene glycol, 1.5-2.5 g of sodium acetate and 0.5-1.0 g of polyethylene glycol are added, and the mixture is ultrasonically dispersed at room temperature for 20-40 min. The resulting homogeneous mixture is transferred to a stainless steel autoclave lined with polytetrafluoroethylene, sealed, and reacted at 180-220℃ for 8-16 h. After natural cooling to room temperature, the black product is collected by magnetic separation by applying an external magnetic field, washed three times alternately with deionized water and ethanol, and vacuum dried at 40-80℃ for 6-18 h.

[0022] As a preferred embodiment of step (2), 0.3-0.7 g of Fe3O4 magnetic microspheres are ultrasonically dispersed in a mixture of deionized water (30-50 mL), ethanol (120-160 mL), and 25% ammonia (1.0-3.0 mL) for 20-40 min. 1.5-3.0 mL of tetraethyl orthosilicate is added dropwise, and the mixture is stirred continuously at room temperature for 8-12 h. The black product is collected by magnetic separation by applying an external magnetic field, washed three times alternately with deionized water and ethanol, and vacuum dried at 40-80 °C for 6-18 h.

[0023] As a preferred embodiment of step (3), 0.2-0.5 g of Fe3O4@SiO2 is ultrasonically dispersed in 80-120 mL of deionized water for 20-40 min, 0.05-0.15 mL of pyrrole monomer is added and further ultrasonically treated for 20-40 min, and then 40-60 mL of deionized water containing 3-8 mL of hydrochloric acid and 0.15-0.25 g of ammonium persulfate is added. The mixture is polymerized in situ at room temperature for 10-15 h. The black product is collected by magnetic separation by applying an external magnetic field, washed three times alternately with deionized water and ethanol, and vacuum dried at 40-80 °C for 6-18 h.

[0024] As a preferred embodiment of step (4), 0.05-0.15g of Fe3O4@SiO2@PPy is ultrasonically dispersed in 80-120mL of deionized water for 20-40 min, and then 20-40mL of deionized water containing 0.10-0.20g of hexadecyltrimethylammonium bromide is added. The mixture is reacted at room temperature for 10-15h. After the reaction is completed, the black product is collected by magnetic separation by applying an external magnetic field. The product is washed three times alternately with deionized water and ethanol, and then vacuum dried at 40-80℃ for 6-18h.

[0025] Furthermore, in each step, the ultrasonic power is 100-300w.

[0026] In a third aspect, the present invention provides the application of the above-mentioned core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent in the treatment of anionic azo dye wastewater. The adsorbent is added to the anionic azo dye wastewater for adsorption treatment. After adsorption is completed, the adsorbent is magnetically separated by applying an external magnetic field.

[0027] Specifically, the adsorbent dosage is 0.2-0.6 g / L, the adsorption time is 60-180 min, the pH value is 4-6, and the temperature is 20-30℃.

[0028] Preferably, the adsorbent dosage is 0.4 g / L, the adsorption time is 120 min, the pH value is 5, and the temperature is 25℃.

[0029] In some embodiments, magnetic separation is performed by applying an external magnetic field, with a magnetic field strength of 0.1-0.5T, preferably 0.3T, and a magnetic separation time of 3-10min, preferably 5min.

[0030] As a preferred option, the adsorbent after magnetic separation is desorbed and regenerated with ethanol or 0.1-0.5 mol / L hydrochloric acid solution. The regenerated adsorbent can be recycled up to 5 times, and the adsorption capacity retention rate is ≥90%.

[0031] As described above, the core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent of the present invention, its preparation method, and its application have the following beneficial effects: 1. This invention uses the Fe3O4 magnetic core as the magnetic response unit, enabling the adsorbent to be rapidly separated by an external magnetic field after adsorption, thus avoiding the problem of difficult recovery of powdered adsorbents. At the same time, the SiO2 isolation shell can reduce the aggregation of Fe3O4 nanoparticles due to strong dipole-dipole interactions, improve the colloidal stability of the adsorbent in the suspension, and provide a stable reaction interface for the subsequent in-situ polymerization of the polypyrrole functional shell, thus solving the technical problems of easy aggregation and poor recyclability of magnetic nanoparticles in the prior art.

[0032] 2. A polypyrrole functional shell was prepared by in-situ polymerization on the outer surface of the SiO2 isolation shell, introducing a conjugated aromatic ring framework structure and NH groups. The conjugated aromatic rings of the polypyrrole framework interact with the naphthalene ring and benzene ring structures in the benzidine anionic azo dye molecules to form a stable complex. The NH groups on the polypyrrole chain act as hydrogen bond donors to form a hydrogen bond network with the amino or azo groups in the dye molecules. The two effects work synergistically to enhance the selective adsorption capacity of the adsorbent for benzidine anionic azo dyes, increasing the adsorption capacity by about 7 times compared with pure Fe3O4.

[0033] 3. By utilizing the hydrophobic and π-cation interactions between hexadecyltrimethylammonium bromide and polypyrrole through surface modification, CTAB is stably bound to the surface of the polypyrrole functional shell. The large number of quaternary ammonium groups provided by CTAB increases the positive charge density on the adsorbent surface, generating strong electrostatic attraction between CTAB and the sulfonate anion groups in benzidine-based anionic azo dye molecules. This acts as a long-range driving force to rapidly attract dye molecules to the adsorbent surface. The π-π stacking and hydrogen bonding provided by polypyrrole form a ternary coupling adsorption mechanism, resulting in an adsorption capacity of 425.3 mg / g. Within 10 min, the adsorption capacity reaches more than 95% of the equilibrium adsorption capacity, achieving rapid and efficient adsorption.

[0034] 4. Adsorption kinetics studies revealed that the pseudo-second-order kinetic model fits the adsorption process with a correlation coefficient R. 2 Approaching 1, RMSE and χ 2 The low values ​​indicate that the adsorption process is mainly chemisorption. The electrostatic interaction, π-π stacking interaction, and hydrogen bonding interaction in the ternary coupling adsorption mechanism are all chemisorption properties, ensuring the stability of adsorption. Adsorption thermodynamics studies revealed that the Gibbs free energy change ΔG of the adsorption process is negative, while the enthalpy change ΔH and entropy change ΔS are positive. This indicates that the adsorption process is endothermic, spontaneous, and entropy-driven. Higher temperatures are beneficial to adsorption, and the ternary coupling mechanism is more active at higher temperatures.

[0035] 5. Through five consecutive Congo red adsorption-desorption cycle experiments, it was verified that the adsorbent's adsorption capacity only decreased by 8.6% after five regeneration cycles, and the adsorption capacity retention rate was ≥90% after five cycles. This indicates that the Fe3O4@SiO2@PPy-CTAB four-layer core-shell structure has high structural stability, the irreversible damage to the ternary coupled adsorption interface during desorption and regeneration is negligible, and magnetic separation and recovery can be quickly achieved by applying an external magnetic field, meeting the recycling requirements of actual wastewater treatment and demonstrating good environmental and economic benefits. Attached Figure Description

[0036] Figure 1 Electron micrographs of the modified magnetic microspheres at different stages in Example 1; wherein: (a) SEM image of Fe3O4, (b) SEM image of Fe3O4@SiO2 (c) SEM image of Fe3O4@SiO2@PPy (d)Fe3O4@SiO2@PPy SEM image of CTAB-modified magnetic microspheres; (e) TEM image of Fe3O4, (f) TEM image of Fe3O4@SiO2 TEM image of (g)Fe3O4@SiO2@PPy (h) TEM image of Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres; (i) Elemental mapping of Fe, Si, O, C and Br in Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres.

[0037] Figure 2 The infrared spectrum of the modified magnetic microspheres prepared in Example 1.

[0038] Figure 3 The XRD pattern of the modified magnetic microspheres prepared in Example 1.

[0039] Figure 4 XPS spectra of the modified magnetic microspheres prepared in Example 1.

[0040] Figure 5 The graphs are XPS adsorption kinetic fitting diagrams of the modified magnetic microspheres in Example 2; where: (a) is the pseudo-first-order (PSO) kinetic model and (b) is the pseudo-second-order (PFO) kinetic model.

[0041] Figure 6 This is a graph showing the adsorption capacity of modified magnetic microspheres at adsorption equilibrium at different temperatures. Detailed Implementation

[0042] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0043] Unless otherwise specified, all raw materials used in the following examples are commercially available. Reagents such as FeCl3·6H2O, sodium acetate, polyethylene glycol, tetraethyl orthosilicate, pyrrole monomer, hydrochloric acid, ammonium persulfate, and hexadecyltrimethylammonium bromide were all analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. Solvents such as ethylene glycol and ethanol were also analytical grade.

[0044] In the following embodiments, scanning electron microscopy was performed using a Hitachi SU8010 field emission scanning electron microscope, transmission electron microscopy was performed using a Hitachi HT7700 transmission electron microscope, infrared spectroscopy was performed using a Nicolet iS50 Fourier transform infrared spectrometer, X-ray diffraction was performed using a Bruker D8 Advance X-ray diffractometer, and X-ray photoelectron spectroscopy was performed using a Thermo Scientific K-Alpha X-ray photoelectron spectrometer. Specific surface area and pore structure were determined using a Micromeritics ASAP 2460 specific surface area and porosity analyzer, with specific surface area determined by the BET method and pore volume and pore size determined by the BJH method. Congo red concentration was measured at a wavelength of 498 nm using a UV-Vis spectrophotometer.

[0045] Example 1 This embodiment provides a method for preparing a core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, comprising the following steps: (1) Preparation of Fe3O4 magnetic microspheres by solvothermal method: 1.5 g of FeCl3·6H2O was completely dissolved in 60 mL of ethylene glycol, and 2.0 g of sodium acetate and 0.7 g of polyethylene glycol were added. The mixture was ultrasonically dispersed at room temperature for 30 min. The resulting homogeneous mixture was transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene. The system was sealed and kept at 200 °C for 12 h. After naturally cooling to room temperature, the black product was collected by magnetic separation using an external magnetic field. The product was washed three times alternately with deionized water and ethanol, and then vacuum dried at 60 °C for 12 h to obtain Fe3O4 magnetic microspheres.

[0046] (2) The SiO2 isolation shell was coated using the sol-gel method: 0.5 g of the Fe3O4 magnetic microspheres prepared above were ultrasonically dispersed in a mixture of 35 mL deionized water, 140 mL ethanol and 2 mL (25% concentration) ammonia for 30 min; then 2 mL tetraethyl orthosilicate was added dropwise, and the resulting mixture was continuously stirred at room temperature for 10 h; the dark brown product was collected by magnetic separation by applying an external magnetic field, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60 °C for 12 h to obtain Fe3O4@SiO2 magnetic microspheres.

[0047] (3) Preparation of polypyrrole functional shells by in-situ polymerization: 0.3 g of the Fe3O4@SiO2 magnetic microspheres prepared above were ultrasonically dispersed in 100 mL of deionized water for 30 min. Then, 0.1 mL of pyrrole monomer was added and the mixture was further ultrasonicated for 30 min to obtain a homogeneous solution. Next, 50 mL of deionized water containing 5 mL of hydrochloric acid and 0.2 g of ammonium persulfate was added, and in-situ polymerization was carried out at room temperature for 12 h. The black product was collected by magnetic separation by applying an external magnetic field, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60 °C for 12 h to obtain Fe3O4@SiO2@PPy magnetic microspheres.

[0048] (4) A cetyltrimethylammonium bromide modified layer was introduced using a surface modification method: 0.1 g of the Fe3O4@SiO2@PPy magnetic microspheres prepared above were ultrasonically dispersed in 100 mL of deionized water for 30 min; then 30 mL of deionized water containing 0.15 g of hexadecyltrimethylammonium bromide was added, and the reaction was carried out at room temperature for 12 h. After the reaction was completed, the product was collected by magnetic separation under an external magnetic field, washed three times alternately with deionized water and ethanol, and dried under vacuum at 60 °C for 12 h to obtain the Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent.

[0049] The surface of Fe3O4@SiO2@PPy magnetic microspheres was modified using the hydrophobic and π-cation interactions between hexadecyltrimethylammonium bromide and polypyrrole. The hydrophobic interaction refers to the interaction between the C atoms in hexadecyltrimethylammonium bromide and the surface of Fe3O4@SiO2@PPy magnetic microspheres. 16 The hydrophobic effect between the long alkyl chain and the hydrophobic aromatic backbone of polypyrrole. π-cation interaction refers to the polarization between the ammonium bromide cation in hexadecyltrimethylammonium bromide and the conjugated π-electron cloud of polypyrrole.

[0050] The specific surface area of ​​the adsorbent, determined by the BET method, was 52.96 m². 2 / g, pore volume determined by the BJH method was 0.065 cm³. 3 / g, pore size was determined to be 4.95nm by the BJH method.

[0051] refer to Figure 1 Scanning electron microscopy and transmission electron microscopy revealed that the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres exhibited a distinct core-shell structure. Furthermore, elemental mapping analysis confirmed the distribution of Fe, Si, O, C, and Br elements within the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres, thus verifying the successful construction of the core-shell structure.

[0052] refer to Figure 2Infrared spectroscopy analysis revealed Fe-O bonds, Si-O-Si bonds, polypyrrole characteristic peaks, and hexadecyltrimethylammonium bromide characteristic peaks in the infrared spectrum of Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres, confirming the successful coating and modification of each layer.

[0053] refer to Figure 3 X-ray diffraction analysis revealed characteristic diffraction peaks of Fe3O4 in the XRD patterns of modified magnetic microspheres at different stages, confirming that the crystal structure of the Fe3O4 magnetic core remained intact.

[0054] refer to Figure 4 X-ray photoelectron spectroscopy analysis revealed characteristic peaks of Fe 2p, Si 2p, O 1s, C 1s, N 1s, and Br 3d in the XPS spectrum of Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres, further confirming the successful construction of the core-shell structure.

[0055] Example 2 This embodiment provides a study on the adsorption kinetics and model of Congo red by Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres.

[0056] The adsorption equilibrium rate of Congo red wastewater by Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres prepared in Example 1 was evaluated by adsorption kinetics. Nonlinear fitting of the experimental data was performed based on pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models. The results are summarized in Table 1 and [Table data would be inserted here]. Figure 5 (a and b).

[0057] The experimental conditions were: pH 5, temperature 25℃, adsorbent dosage 0.4 g / L, and initial concentrations of Congo red 100 mg / L, 200 mg / L, and 300 mg / L, respectively.

[0058] Specifically, 0.04 g of adsorbent was added to 100 mL of Congo red solution, and the solution was shaken at 150 rpm in a constant temperature shaker for adsorption. Samples were taken at different time points to determine the concentration of Congo red.

[0059] The pseudo-first-order dynamic model equation is: q t =q e (1-e^(-k1t)), where q t Let q be the adsorption capacity at time t. e To balance the adsorption capacity, k1 is the pseudo-first-order kinetic rate constant.

[0060] The equation of the pseudo-second-order dynamic model is: q t =k2q e ²t / (1+k2q et), where k2 is the pseudo-second-order kinetic rate constant.

[0061] Using the correlation coefficient R 2 Root mean square error (RMSE) and chi-square value (χ²) 2 Evaluate the fitting effect.

[0062] Table 1. Fitting kinetic parameters of Congo red adsorption onto Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres

[0063] from Figure 5 It can be seen that the adsorption of Congo red on the modified magnetic microspheres mainly occurs in the initial stage, because the adsorbent surface provides sufficient active areas, promoting rapid adsorption. As the contact time increases, the concentration of Congo red in the solution decreases significantly, causing the adsorption rate to gradually slow down until equilibrium is reached at 120 min.

[0064] As shown in Table 2, the pseudo-second-order kinetic model exhibits a higher correlation coefficient R0 under different initial concentrations of Congo red. 2 and lower RMSE and χ 2 This indicates that the adsorption process is mainly chemisorption. At an initial Congo red concentration of 200 mg / L, the adsorption capacity reached 404.0 mg / g within 10 min, accounting for 95.0% of the equilibrium adsorption capacity of 425.3 mg / g, indicating that the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres possess rapid adsorption kinetics.

[0065] The fitting results of the pseudo-second-order kinetic model indicate that the electrostatic interaction, π-π stacking interaction, and hydrogen bonding interaction in the ternary coupled adsorption mechanism are mainly chemisorption properties, which ensure the stability of adsorption.

[0066] Example 3 This embodiment provides a thermodynamic study of the adsorption of Congo red on Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres.

[0067] The equilibrium adsorption capacity data of Congo red on Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres obtained in Example 1 were tested at different temperatures. The experimental results are shown in [Figure 1]. Figure 6 .

[0068] The experimental data were fitted using the Van't Hoff relation, and the results are shown in Table 2. The Gibbs free energy change ΔG, enthalpy change ΔH, and entropy change ΔS were calculated.

[0069] The Van't Hoff relation is: ln Kc = -ΔH / (RT) + ΔS / R, where Kc is the equilibrium constant, R is the gas constant, and T is the absolute temperature.

[0070] The Gibbs free energy change ΔG is calculated using the formula ΔG = ΔH - TΔS.

[0071] Table 2. Thermodynamic parameters of Congo red adsorbed onto Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres

[0072] Table 2 shows that ΔG values ​​are negative at all test temperatures, indicating that the adsorption is spontaneous. Fitting calculations reveal that ΔH is positive, indicating that the adsorption process is endothermic; ΔS is positive, indicating an increase in disorder at the solid-liquid interface during adsorption. Therefore, the adsorption of Congo red on modified magnetic microspheres is an endothermic, spontaneous, and entropy-driven process. The π-π stacking and hydrogen bonding interactions in the ternary coupling adsorption mechanism are more active at high temperatures, leading to an increase in adsorption capacity with increasing temperature.

[0073] Example 4 This embodiment provides a comparison of the adsorption effects of magnetic microspheres at different modification stages on Congo red.

[0074] The adsorption effects of the four magnetic microspheres prepared in Example 1—Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@PPy, and Fe3O4@SiO2@PPy-CTAB—were compared, and the results are shown in Table 3.

[0075] The adsorption experimental conditions were: pH 5, adsorbent dosage 0.4 g / L, initial Congo red concentration 200 mg / L, and temperature 25℃. After adsorption, magnetic separation was performed by applying an external magnetic field, and the concentration of Congo red in the supernatant was determined.

[0076] The adsorption capacity is calculated based on the initial and equilibrium concentrations of Congo red. The formula is: q = (C0 - C e )×V / m, where q is the adsorption capacity, C0 is the initial concentration, and C e To achieve equilibrium concentration, V is the solution volume and m is the adsorbent mass.

[0077] Table 3. Comparison of the adsorption effect of magnetic microspheres on Congo red before and after modification.

[0078] As shown in Table 3, the adsorption capacity of magnetic microspheres for Congo red was significantly improved through layer-by-layer modification.

[0079] The adsorption capacity of Fe3O4@SiO2 is about 1.9 times higher than that of pure Fe3O4. This is because the SiO2 isolation shell prevents the aggregation of Fe3O4 nanoparticles and increases the specific surface area of ​​the adsorbent.

[0080] The adsorption capacity of Fe3O4@SiO2@PPy is about 0.6 times higher than that of Fe3O4@SiO2. This is because the polypyrrole functional shell provides π-π stacking interaction sites and hydrogen bonding interaction sites, which enhances the adsorption capacity for Congo red.

[0081] The adsorption capacity of Fe3O4@SiO2@PPy-CTAB is about 0.7 times higher than that of Fe3O4@SiO2@PPy and about 7 times higher than that of pure Fe3O4. This is because the hexadecyltrimethylammonium bromide modification layer provides a large number of quaternary ammonium groups, which generate strong electrostatic attraction with the sulfonate anion groups in the Congo red molecule. It forms a ternary coupling adsorption mechanism with the π-π stacking and hydrogen bonding provided by polypyrrole, which significantly improves the adsorption capacity.

[0082] Example 5 This embodiment provides a study on the recyclability of Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres.

[0083] Five consecutive Congo red adsorption-desorption cycles were conducted using the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres prepared in Example 1.

[0084] The adsorption experimental conditions were: pH 5, adsorbent dosage 0.4 g / L, initial Congo red concentration 200 mg / L, temperature 25℃, and adsorption time 120 min. After adsorption, magnetic separation was performed by applying an external magnetic field, and the concentration of Congo red in the supernatant was measured to calculate the adsorption capacity.

[0085] The adsorbent after magnetic separation was regenerated by desorption with ethanol. The adsorbent was added to 50 mL of ethanol, shaken at room temperature for 30 min, and then magnetically separated by applying an external magnetic field. The adsorbent was washed three times with deionized water and dried under vacuum at 60 °C for 6 h to obtain the regenerated adsorbent. The regenerated adsorbent was used in the next adsorption experiment, and the above adsorption-desorption cycle was repeated five times. The experimental results are shown in Table 4.

[0086] Table 4. Recycling performance of Congo red adsorbed onto Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres

[0087] As shown in Table 4, the adsorption capacity of the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres decreased by only 8.6% after 5 regeneration cycles, and the adsorption capacity retention rate after 5 cycles was 92.1%, which is greater than 90%.

[0088] Experimental results show that the Fe3O4@SiO2@PPy-CTAB four-layer core-shell structure exhibits high structural stability, and the irreversible damage to the ternary coupled adsorption interface during desorption and regeneration is negligible. Magnetic separation and recovery can be rapidly achieved by applying an external magnetic field, with a separation time of only 5 minutes, meeting the recycling requirements of practical wastewater treatment and demonstrating good environmental and economic benefits.

[0089] Example 6 This embodiment verifies the effect of reaction temperature and reaction time on the product properties when preparing Fe3O4 magnetic microspheres by the solvothermal method.

[0090] Following the method in step (1) of Example 1, the solvothermal reaction temperature was adjusted to 180℃, 190℃, 210℃, and 220℃, respectively, and the reaction time was adjusted to 8h, 10h, 12h, 14h, and 16h, respectively. Other conditions remained the same as in Example 1.

[0091] Experimental results show that Fe3O4 magnetic microspheres can be prepared within the temperature range of 180-220℃ and the time range of 8-16 h.

[0092] When the temperature is 180℃ and the time is 8h or 10h, the Fe3O4 magnetic microspheres have low crystallinity, uneven particle size distribution, and weak magnetic properties.

[0093] When the temperature is 220℃ and the time is 16 h, the Fe3O4 magnetic microspheres have a large particle size, and some particles agglomerate, affecting the subsequent coating effect.

[0094] The optimal conditions are 200℃ for 12 h, when the Fe3O4 magnetic microspheres have uniform particle size, high crystallinity, and the best magnetic properties.

[0095] Fe3O4 magnetic microspheres prepared under different conditions were used to prepare Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres according to the method in Example 1, and their adsorption capacity for Congo red was tested.

[0096] Experimental results show that Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres prepared by Fe3O4 magnetic microspheres at 200℃ for 12 h have the highest adsorption capacity for Congo red, reaching 425.3 mg / g.

[0097] Example 7 This embodiment verifies the effects of the amount of tetraethyl orthosilicate and the stirring time on the product properties when coating a SiO2 isolation shell using the sol-gel method.

[0098] Following the method in step (2) of Example 1, the amount of tetraethyl orthosilicate was adjusted to 1.5 mL, 2.5 mL, and 3.0 mL, respectively, and the stirring time was adjusted to 8 h, 9 h, 11 h, and 12 h, respectively, while other conditions remained unchanged.

[0099] Experimental results show that Fe3O4@SiO2 magnetic microspheres can be prepared within the range of 1.5-3.0 mL of tetraethyl orthosilicate and 8-12 h of stirring time.

[0100] When the amount of tetraethyl orthosilicate used was 1.5 mL and the stirring time was 8 h, the SiO2 isolation shell was not completely coated, and some of the Fe3O4 magnetic cores were exposed.

[0101] When the amount of tetraethyl orthosilicate is 3.0 mL and the stirring time is 12 h, the SiO2 isolation shell is too thick, which affects the magnetic properties and adsorption kinetics of the adsorbent.

[0102] When the amount of tetraethyl orthosilicate is 2.0 mL and the stirring time is 10 h, the SiO2 isolation shell thickness is moderate and the coating is complete, which is the optimal condition.

[0103] Fe3O4@SiO2 magnetic microspheres prepared under different conditions were used to prepare Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres according to the method in Example 1, and their adsorption capacity for Congo red was tested.

[0104] Experimental results showed that the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres prepared by using 2.0 mL of tetraethyl orthosilicate and stirring for 10 h had the highest adsorption capacity for Congo red, reaching 425.3 mg / g.

[0105] Example 8 This embodiment verifies the effects of pyrrole monomer dosage and polymerization time on product properties when preparing polypyrrole functional shells by in-situ polymerization.

[0106] Following the method in step (3) of Example 1, the amount of pyrrole monomer was adjusted to 0.05 mL, 0.10 mL, and 0.15 mL, respectively, and the polymerization time was adjusted to 10 h, 12 h, and 15 h, respectively, while other conditions remained unchanged.

[0107] Experimental results show that Fe3O4@SiO2@PPy magnetic microspheres can be prepared within the range of pyrrole monomer dosage of 0.05-0.15 mL and polymerization time of 10-15 h.

[0108] When the amount of pyrrole monomer is 0.05 mL and the polymerization time is 10 h, the polypyrrole functional shell is incomplete, with fewer π-π stacking interaction sites and hydrogen bonding interaction sites.

[0109] When the amount of pyrrole monomer is 0.15 mL and the polymerization time is 15 h, the polypyrrole functional shell is too thick, which affects the adsorption kinetics and magnetic separation efficiency.

[0110] When the amount of pyrrole monomer is 0.1 mL and the polymerization time is 12 h, the polypyrrole functional shell thickness is moderate and the polymerization is complete, which is the optimal condition.

[0111] Fe3O4@SiO2@PPy magnetic microspheres prepared under different conditions were used to prepare Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres according to the method in Example 1, and their adsorption capacity for Congo red was tested.

[0112] Experimental results showed that the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres prepared by using Fe3O4@SiO2@PPy magnetic microspheres prepared with 0.1 mL of pyrrole monomer and 12 h of polymerization had the highest adsorption capacity for Congo red, reaching 425.3 mg / g.

[0113] Example 9 This embodiment verifies the effect of the amount of hexadecyltrimethylammonium bromide and the reaction time on the product properties when introducing a hexadecyltrimethylammonium bromide modified layer using the surface modification method.

[0114] Following the method of step (4) in Example 1, the amount of hexadecyltrimethylammonium bromide was adjusted to 0.10 g, 0.12 g, 0.18 g, and 0.20 g, respectively, and the reaction time was adjusted to 10 h, 11 h, 13 h, and 15 h, respectively. Other steps remained unchanged from Example 1.

[0115] Experimental results show that Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres can be prepared within the range of 0.10-0.20 g of hexadecyltrimethylammonium bromide and 10-15 h of reaction time.

[0116] When the amount of hexadecyltrimethylammonium bromide is 0.10 g and the reaction time is 10 h, the modification is incomplete, the density of quaternary ammonium groups is low, and the electrostatic interaction is weak.

[0117] When the amount of hexadecyltrimethylammonium bromide is 0.20 g and the reaction time is 15 h, the aggregation of hexadecyltrimethylammonium bromide affects adsorption and increases cost.

[0118] When the amount of hexadecyltrimethylammonium bromide is 0.15 g and the reaction time is 12 h, the modified layer is completely covered and the density of quaternary ammonium groups is the highest, which is the optimal condition.

[0119] The adsorption capacity of Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres prepared under different conditions for Congo red was tested.

[0120] Experimental results show that the Fe3O4@SiO2@PPy-CTAB modified magnetic microspheres prepared using 0.15 g of hexadecyltrimethylammonium bromide and a reaction time of 12 h exhibit the highest adsorption capacity for Congo red, reaching 425.3 mg / g.

[0121] In summary, the adsorbent of this invention comprises a Fe3O4 magnetic core, a SiO2 isolating shell, a polypyrrole functional shell, and a hexadecyltrimethylammonium bromide modified layer. The polypyrrole functional shell contains a conjugated aromatic ring framework structure and NH groups. The hexadecyltrimethylammonium bromide modified layer is bonded to the surface of the polypyrrole functional shell through hydrophobic interactions and π-cation interactions, forming a ternary coupled adsorption interface of electrostatic interactions, π-π stacking interactions, and hydrogen bonding interactions. This adsorbent achieves an adsorption capacity of 425.3 mg / g for anionic azo dyes, reaching over 95% of the equilibrium adsorption capacity within 10 minutes, and retaining over 90% of the adsorption capacity after 5 cycles. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value.

[0122] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, characterized in that, include: Fe3O4 magnetic core; A SiO2 isolation shell covering the outer surface of the Fe3O4 magnetic core; A polypyrrole functional shell layer is coated on the outer surface of the SiO2 isolation shell layer, wherein the polypyrrole functional shell layer contains a conjugated aromatic ring backbone structure and NH groups; A hexadecyltrimethylammonium bromide modified layer is bonded to the surface of the polypyrrole functional shell through hydrophobic interactions and π-cation interactions.

2. The core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent according to claim 1, characterized in that, The core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent exhibits a maximum adsorption capacity of 425.3 mg / g for anionic azo dyes under the conditions of pH=5, temperature 25℃, and adsorbent dosage of 0.4 g / L. The adsorption capacity reaches more than 95% of the equilibrium adsorption capacity within 10 min.

3. A method for preparing a core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent, characterized in that, Includes the following steps: (1) Preparation of Fe3O4 magnetic microspheres by solvothermal method: iron salts were dissolved in ethylene glycol, sodium acetate and polyethylene glycol were added, and after dispersion, a solvothermal reaction was carried out. After magnetic separation, washing and drying, Fe3O4 magnetic microspheres were obtained. (2) Coating SiO2 isolation shell by sol-gel method: The Fe3O4 magnetic microspheres were dispersed in a mixed system of water, ethanol and 25% ammonia water, tetraethyl orthosilicate was added and sol-gel reaction was carried out. After magnetic separation, washing and drying, Fe3O4@SiO2 magnetic microspheres were obtained. (3) Preparation of polypyrrole functional shell by in-situ polymerization: The Fe3O4@SiO2 magnetic microspheres were dispersed in water, pyrrole monomer was added, and then an aqueous solution containing hydrochloric acid and ammonium persulfate was added for in-situ polymerization. After magnetic separation, washing and drying, Fe3O4@SiO2@PPy magnetic microspheres were obtained. (4) Introducing a hexadecyltrimethylammonium bromide modified layer by surface modification: The Fe3O4@SiO2@PPy magnetic microspheres were dispersed in water, and a hexadecyltrimethylammonium bromide aqueous solution was added for surface modification. After magnetic separation, washing and drying, a core-shell structure Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent was obtained.

4. The preparation method according to claim 3, characterized in that, In step (1), the iron salt is FeCl3·6H2O; wherein the ratio of FeCl3·6H2O, ethylene glycol, sodium acetate and polyethylene glycol is 1.0-2.0g: 50-70mL: 1.5-2.5g: 0.5-1.0g; the solvothermal reaction temperature is 180-220℃ and the reaction time is 8-16h.

5. The preparation method according to claim 3, characterized in that, In step (2), the ratio of Fe3O4 magnetic microspheres, water, ethanol, 25% ammonia and tetraethyl orthosilicate is 0.3-0.7g: 30-50mL: 120-160mL: 1.0-3.0mL: 1.5-3.0mL; the sol-gel reaction is carried out at room temperature for 8-12 hours.

6. The preparation method according to claim 3, characterized in that, In step (3), the ratio of Fe3O4@SiO2 magnetic microspheres, pyrrole monomer, hydrochloric acid and ammonium persulfate is 0.2-0.5g: 0.05-0.15mL: 3-8mL: 0.15-0.25g; the in-situ polymerization is carried out at room temperature for 10-15h.

7. The preparation method according to claim 3, characterized in that, In step (4), the ratio of Fe3O4@SiO2@PPy magnetic microspheres to hexadecyltrimethylammonium bromide is 0.05-0.15g:0.10-0.20g; the surface modification is carried out at room temperature for 10-15h.

8. The preparation method according to claim 3, characterized in that, In each step, the applied magnetic field strength for magnetic separation is 0.1-0.5 T, and the magnetic separation time is 3-10 min; washing involves alternating between ethanol and deionized water three times; the drying temperature is 40-80℃, and the drying time is 6-18 h.

9. The application of the core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent according to any one of claims 1-2 or the core-shell structured Fe3O4@SiO2@PPy-CTAB modified magnetic microsphere adsorbent obtained by the preparation method according to any one of claims 3-8 in the treatment of anionic azo dye wastewater, characterized in that, The adsorbent was added to the anionic azo dye wastewater for adsorption treatment. After adsorption was completed, the adsorbent was magnetically separated by applying an external magnetic field.

10. The application according to claim 9, characterized in that, The anionic azo dye is a benzidine-based anionic azo dye.

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