A composite magnetic nanoparticle Fe3O4@SiO2-C 18 / NH2 / COOH, a preparation method thereof and application thereof

Abstract

The application belongs to the technical field of nanomaterials, and particularly relates to a composite magnetic nanoparticle Fe3O4@SiO2-C 18 / NH2 / COOH, which is a core-shell structure, and comprises an inner core, an intermediate layer and an outer shell; the inner core is a Fe3O4 magnetic nanoparticle, the intermediate layer is a SiO2 coating layer, and the outer shell is an organic modification layer, which comprises three functional groups of octadecyl, amino and carboxyl. 18 By simultaneously grafting three functional groups of octadecyl (C 18 ), amino (-NH2) and carboxyl (-COOH) on the surface of Fe3O4@SiO2, the application can realize synchronous and efficient adsorption of target objects with weak polarity, medium polarity and strong polarity, and overcome the problems of narrow adsorption spectrum and the need for multi-step extraction of existing single or double functional group materials.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, and specifically relates to a composite magnetic nanoparticle Fe3O4@SiO2-C 18 / NH2 / COOH, its preparation methods, and its applications. Background Technology

[0002] Magnetic nanoparticles, especially iron(III) oxide (Fe3O4) nanoparticles, have shown great application potential in fields such as biomedicine, environmental remediation, and analytical chemistry due to their unique superparamagnetism and high specific surface area. However, exposed Fe3O4 nanoparticles are prone to aggregation, have poor chemical stability, and have limited surface functional groups, which restricts their direct application.

[0003] To address the aforementioned issues, existing technologies typically employ silicon dioxide (SiO2) to coat the Fe3O4 magnetic core, forming an Fe3O4@SiO2 core-shell structure. This enhances its stability and provides an easily modifiable silanol (Si-OH) surface. Furthermore, by grafting specific functional groups using methods such as silane coupling agents, the material can acquire selective adsorption capabilities for specific target analytes.

[0004] However, in the pretreatment of complex samples (such as serum, agricultural products, and environmental water samples), it is often necessary to simultaneously detect multiple analytes with significantly different properties (e.g., pesticides of different polarities). Most existing magnetic nanoparticles are designed for single-type or single-polarity targets, lacking the ability to simultaneously and efficiently capture multiple molecules of different polarities. To achieve simultaneous enrichment of multiple target analytes, it is usually necessary to use a mixture of multiple adsorbents or perform multi-step extraction operations, which increases the complexity and time cost of pretreatment.

[0005] Therefore, developing a composite magnetic nanomaterial that is simple to prepare, can simultaneously introduce multiple synergistic functional groups, and has excellent adsorption performance for analytes of different polarities is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to propose a composite magnetic nanoparticle Fe3O4@SiO2-C 18 / NH2 / COOH, its preparation method, and its application are proposed to solve the technical problem that existing magnetic nano-adsorbents are unable to achieve simultaneous and efficient separation and enrichment of multiple targets with different polarities, especially pesticides with different polarities, in complex samples.

[0007] On the one hand, the present invention provides a composite magnetic nanoparticle Fe3O4@SiO2-C 18The composite magnetic nanoparticles of / NH2 / COOH have a core-shell structure, which includes a core, an intermediate layer, and an outer shell. The core is Fe3O4 magnetic nanoparticles, the intermediate layer is a SiO2 coating layer, and the outer shell is an organic modification layer, which includes three functional groups: octadecyl, amino, and carboxyl.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned composite magnetic nanoparticles, comprising the following steps: (1) Fe3O4 magnetic nanoparticles were prepared by chemical coprecipitation method; (2) The Fe3O4 magnetic nanoparticles obtained in step (1) were coated with SiO2 using the sol-gel method to obtain Fe3O4@SiO2 magnetic nanoparticles; (3) Using a simultaneous modification method, (3-aminopropyl)triethoxysilane, octadecyltrimethylsilane, and maleic anhydride were grafted onto the surface of the Fe3O4@SiO2 magnetic nanoparticles obtained in step (2) to obtain the composite magnetic nanoparticles Fe3O4@SiO2-C. 18 / NH2 / COOH.

[0009] Furthermore, step (1) includes the following steps: Heat deionized water to 70-90℃, and add Fe under nitrogen protection and stirring. 3+ with Fe 2+ A 2:1 molar ratio of iron salt mixed solution was used to adjust the pH of the system to ≥9.2 for precipitation reaction. Then, sodium citrate was added for surface modification. After magnetic separation, washing, and vacuum freeze-drying, Fe3O4 magnetic nanoparticles were obtained. Preferably, the iron salt mixed solution is a ferric chloride hexahydrate solution and a ferrous chloride tetrahydrate solution, wherein the concentrations of the ferric chloride hexahydrate solution and the ferrous chloride tetrahydrate solution are 0.5-1.5 mol / L, respectively; more preferably, the concentration of the ferric chloride hexahydrate solution is 1.12 mol / L, and the concentration of the ferrous chloride tetrahydrate solution is 0.56 mol / L. Preferably, the pH value of the system is adjusted using 25% ammonia water, with an addition amount of 5.8-6.8 mL; more preferably, the addition amount is 6.3 mL.

[0010] Preferably, the concentration of sodium citrate is 0.033 mol / L, and the amount added is 4-6 mL; more preferably, the amount added is 5 mL.

[0011] Furthermore, step (2) includes the following steps: The Fe3O4 magnetic nanoparticles obtained in step (1) were ultrasonically dispersed in a dispersion system composed of anhydrous ethanol and deionized water. Sodium hydroxide solution was added under nitrogen protection, and the temperature was maintained at 38-42℃. Anhydrous ethanol solution of tetraethyl orthosilicate was added, and the reaction was carried out at a constant temperature for 10-14 h. After the reaction was completed, the Fe3O4@SiO2 magnetic nanoparticles were obtained by washing and drying.

[0012] Preferably, the amount of Fe3O4 nanoparticles added is 60 mg; the volume ratio of anhydrous ethanol to deionized water is 48.5:1.5; the amount of tetraethyl orthosilicate added is 0.22 mg dissolved in 1 mL of anhydrous ethanol solution; the concentration of sodium hydroxide solution is 1 mol / L, and the amount added is 0.57 mL. Preferably, the temperature is maintained at 40 °C for 10 min, and the isothermal reaction time is 12 h.

[0013] Furthermore, step (3) includes the following steps: a. Add an organic reaction solvent into the inner cavity of the high-pressure reactor; b. Add (3-aminopropyl)triethoxysilane, octadecyltrimethylsilane and maleic anhydride to the system in step a simultaneously, and dissolve and mix well; c. Add Fe3O4@SiO2 magnetic nanoparticles to the system in step b; d. Seal the high-pressure reactor, introduce inert gas, and react at a constant temperature with stirring. After the reaction is complete, wash and dry the product to obtain the composite magnetic nanoparticles Fe3O4@SiO2-C. 18 / NH2 / COOH.

[0014] Furthermore, in step a, the inner cavity of the high-pressure reactor is lined with polytetrafluoroethylene.

[0015] Furthermore, in step a, the organic reaction solvent is a mixed solvent of N,N-dimethylacetamide and toluene, and the volume ratio of the mixed solvent of N,N-dimethylacetamide and toluene is (3-5):1, preferably 4:1.

[0016] Furthermore, in step b, the amount of Fe3O4@SiO2 magnetic nanoparticles added is 20 mg, the amount of (3-aminopropyl)triethoxysilane is 250-350 µL, the amount of octadecyltrimethylsilane is 40-60 µL, and the amount of maleic anhydride is 0.060-0.070 g.

[0017] Preferably, the amount of (3-aminopropyl)triethoxysilane is 300 µL, the amount of octadecyltrimethylsilane is 50 µL, and the amount of maleic anhydride is 0.066 g.

[0018] Furthermore, in step d, the stirring speed is 400-600 rpm, preferably 500 rpm; Furthermore, the reaction temperature in step d is 70-90℃, preferably 80℃; Furthermore, the reaction time in step d is 50-70 min, preferably 60 min.

[0019] Thirdly, the present invention provides the application of the above-mentioned composite magnetic nanoparticles as magnetic solid-phase extraction adsorbents.

[0020] Furthermore, the application is in the simultaneous adsorption, separation, or enrichment of pesticides of different polarities.

[0021] Compared with the prior art, the present invention has the following advantages: (1) In this invention, octadecyl (C) groups are simultaneously grafted onto the surface of Fe3O4@SiO2. 18 It has three functional groups: amino (-NH2) and carboxyl (-COOH). These three functional groups have synergistic effects in terms of hydrophobic interaction, hydrogen bonding and electrostatic attraction, which can achieve simultaneous and efficient adsorption of weakly polar, moderately polar and strongly polar target substances, overcoming the problems of narrow adsorption spectrum and multi-step extraction required by existing single or bifunctional group materials.

[0022] (2) The composite magnetic nanoparticles prepared by this invention still maintain good superparamagnetism and can be rapidly separated under an external magnetic field. The operation is simple and fast, meeting the requirements of efficient separation for complex sample pretreatment. This method has the advantages of uniform particle synthesis, simple operation, low cost, high yield, good product purity, and environmental friendliness.

[0023] (3) The composite magnetic nanoparticles prepared by this invention have high precision, high accuracy and broad-spectrum adsorption capacity for typical pesticides of different polarities (chlorpyrifos, tebuconazole and imidacloprid), and are suitable for the simultaneous enrichment and detection of multiple polarity risk factors in the fields of food safety, environmental monitoring and agricultural product testing.

[0024] (4) The present invention optimizes the material input parameters (APTES 300µL, OTS 50µL, MA 0.066g), so that the three functional groups are grafted to the surface of the nanoparticles with high density and uniform distribution, and the total infrared characteristic peak area integral value reaches 300, which is significantly better than other ratio schemes. The preparation method has good controllability and high reproducibility. Attached Figure Description

[0025] Figure 1The image shows the transmission electron microscope (TEM) test results of Fe3O4 magnetic nanoparticles in Example 1; where a is the TEM image of Fe3O4 magnetic nanoparticles and b is the particle size distribution statistics of Fe3O4 magnetic nanoparticles. Figure 2 The results of the vibration sample magnetometer (VSM) test on the Fe3O4 magnetic nanoparticles in Example 1 are shown. Figure 3 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the Fe3O4 magnetic nanoparticles in Example 1; where a is the Fe 2p spectrum and b is the O 1s spectrum. Figure 4 The Zeta potential diagram of the Fe3O4 magnetic nanoparticles in Example 1; Figure 5 The image shows the transmission electron microscope (TEM) test results of the Fe3O4@SiO2 magnetic nanoparticles in Example 1; where a is the TEM image of the Fe3O4@SiO2 magnetic nanoparticles and b is the particle size distribution statistics of the Fe3O4@SiO2 magnetic nanoparticles. Figure 6 The images show the magnetometer test results and Fourier transform infrared (FTIR) test results of the vibrating sample of Fe3O4@SiO2 magnetic nanoparticles in Example 1; where a is the VSM image and b is the FTIR image. Figure 7 The image shows the X-ray photoelectron spectroscopy (XPS) spectra of the Fe3O4@SiO2 magnetic nanoparticles in Example 1; where a is the Fe 2p spectrum; b is the O 1s spectrum; and c is the Si 2p spectrum. Figure 8 Fe3O4@SiO2-C in Example 1 18 Transmission electron microscopy (TEM) results of / NH2 / COOH composite magnetic nanoparticles; where a is the TEM image and b is the particle size distribution graph. Figure 9 Fe3O4@SiO2-C in Example 1 18 Elemental distribution map of / NH2 / COOH composite magnetic nanoparticles by transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS); Figure 10 Fe3O4@SiO2-C in Example 1 18 X-ray photoelectron spectroscopy (XPS) measurements of / NH2 / COOH composite magnetic nanoparticles, where a is the full spectrum; b is the Fe 2p spectrum; c is the Si 2p spectrum; d is the O 1s spectrum; e is the C 1s spectrum; and f is the N 1s spectrum. Figure 11The results of the single-factor experiment based on FTIR characteristic peak analysis are shown in Figure a, where a represents the effect of APTES dosage on the NH peak; and b represents the change in peak area due to APTES dosage. Figure 12 The results of the single-factor experiment based on FTIR characteristic peak analysis are shown, where c represents the effect of OTS dosage on the CH peak; d represents the change in peak area due to OTS dosage. Figure 13 The results of the single-factor experiment are analyzed based on FTIR characteristic peak analysis, where e represents the effect of MA dosage on the C=O peak; f represents the change in peak area due to MA dosage. Figure 14 The results of the single-factor experiment are analyzed based on FTIR characteristic peak analysis, where g represents the effect of reaction time on the C=O peak, and h represents the change in peak area over reaction time. Figure 15 The results of the single-factor experiment based on FTIR characteristic peak analysis are shown, where i represents the effect of the DMAC / toluene volume ratio on the peaks of the three functional groups; j represents the change in peak area of ​​the DMAC / toluene volume ratio. Figure 16 The results of the single-factor experiment are analyzed based on FTIR characteristic peak analysis, where k represents the effect of reaction temperature on the peaks of the three functional groups; and l represents the change in peak area at reaction temperature. Figure 17 Fe3O4@SiO2-C based on FTIR characteristic peak analysis 18 Ranking of F-values ​​in single-factor experiments for optimizing the functional groups of / NH2 / COOH surface; Figure 18 Fe3O4@SiO2-C based on FTIR characteristic peak analysis 18 FTIR results of orthogonal experimental grouping for optimization of functional groups on the / NH2 / COOH surface; Figure 19 Fe3O4@SiO2-C prepared under optimal combination conditions 18 FTIR spectrum of / NH2 / COOH nanoparticles; Figure 20 Fe3O4 magnetic nanoparticles, Fe3O4@SiO2 magnetic nanoparticles, and Fe3O4@SiO2-C 18 Vibrating sample magnetometer (VSM) test results and magnetic response time diagram of / NH2 / COOH composite magnetic nanoparticles; Figure 21 Fe3O4 magnetic nanoparticles, Fe3O4@SiO2 magnetic nanoparticles, and Fe3O4@SiO2-C 18 Nitrogen adsorption-desorption isotherms of / NH2 / COOH composite magnetic nanoparticles; Figure 22 Fe3O4 magnetic nanoparticles, Fe3O4@SiO2 magnetic nanoparticles, and Fe3O4@SiO2-C 18 Thermogravimetric analysis (TGA) curves of / NH2 / COOH composite magnetic nanoparticles; Figure 23 This is a conformation diagram of the binding of functional groups with pesticide molecules in a molecular docking simulation test. Detailed Implementation

[0026] The following detailed embodiments further illustrate the concept and technical effects of the present invention to fully understand its purpose, features, and effects. Unless otherwise specified, all methods described are conventional methods. Unless otherwise specified, all materials are available from publicly available commercial sources. The illustrative embodiments and descriptions of the present invention are used to explain the invention and do not constitute an undue limitation thereof. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] Example 1: Composite magnetic nanoparticles Fe3O4@SiO2-C 18 Preparation of / NH2 / COOH Composite magnetic nanoparticles Fe3O4@SiO2-C 18 The preparation method of / NH2 / COOH is as follows: 1. Fe3O4 magnetic nanoparticles were prepared by chemical coprecipitation. The specific steps are as follows: First, 75 mL of deionized water was heated to 80 °C, and nitrogen gas was introduced for deoxygenation for 5 min under mechanical stirring at 700 ± 5 rpm. Then, 5 mL of 1.12 mol / L ferric chloride hexahydrate solution and 5 mL of 0.56 mol / L ferrous chloride tetrahydrate solution were added simultaneously to allow Fe... 3+ with Fe 2+ The molar ratio reached 2:1. Under nitrogen protection and constant temperature, the orange-red mixture was stirred for 20 minutes, and then 6.3 mL of 25% ammonia solution was rapidly added within 5 seconds. At this point, the pH of the system was not lower than 9.2, and the solution color rapidly changed from orange-red to black. After maintaining the reaction at 80℃ for 35 minutes, 5 mL of a 0.033 mol / L sodium citrate solution was added, and the temperature was raised to 90 ± 1℃ to continue the reaction for 60 minutes. Stirring was stopped, and the nitrogen atmosphere was removed. The sample was immediately transferred to a beaker for magnetic separation, washed three times with deionized water (5 mL each time), and finally dried in a vacuum freeze dryer for 48 hours for characterization.

[0028] Overall reaction equation: Decomposition reaction equation: 2. Fe3O4@SiO2 magnetic nanoparticles were prepared using the sol-gel method. The specific steps are as follows: 60 mg of the Fe3O4 magnetic nanoparticles prepared in step 1 were placed in a mixture of 48.5 mL anhydrous ethanol and 1.5 mL deionized water. The mixture was sonicated for 60 min to ensure thorough dispersion of the Fe3O4 magnetic nanoparticles, guaranteeing a homogeneous system without precipitation. Subsequently, the mixture was stirred at 700 rpm for 10 min under nitrogen protection, and 0.57 mL of 1 mol / L sodium hydroxide solution was added. The mixture was then maintained at 40 °C for 10 min. Next, 1 mL of anhydrous ethanol solution containing 0.22 mL of tetraethyl orthosilicate (TEOS) was added to the system, and the reaction was carried out at a constant temperature and rate for 12 h. When the system color changed from black to dark brown, the reaction was complete. The product was washed three times each with anhydrous ethanol and deionized water (10 mL each time), and finally dried in a vacuum freeze dryer for 24 h. The resulting dried Fe3O4@SiO2 nanoparticles were used for subsequent characterization. This process facilitates the protection of the Fe3O4 magnetic nanoparticles and makes them easier to modify with functional groups.

[0029] 3. Preparation of Fe3O4@SiO2-C using a simultaneous modification method 18 The specific steps for producing / NH2 / COOH composite magnetic nanoparticles are as follows: First, 50 mL of a 4:1 (volume ratio) mixture of N,N-dimethylacetamide (DMAC) and toluene was added to a 75 mL polytetrafluoroethylene liner as a reaction solvent. Then, 300 µL of (3-aminopropyl)triethoxysilane (APTES), 50 µL of octadecyltrimethylsilane (OTS), and 0.066 g of maleic anhydride (MA) were added sequentially to the solvent. The mixture was sonicated at 100% power for 5 min to ensure complete dissolution and homogenization. 20 mg of Fe3O4@SiO2 magnetic nanoparticles were added to the above system, and the liner was placed in a small laboratory high-pressure reactor. An oxygen-free environment was created by purging with nitrogen, and the stirring speed was set to 500 rpm. The reaction was carried out at 80 °C for 60 min. After the reaction, the product was washed three times with 10 mL of methanol. Finally, the sample was dried in a vacuum drying oven for 48 hours to obtain Fe3O4@SiO2-C. 18 / NH2 / COOH composite magnetic nanoparticles.

[0030] Fe3O4@SiO2 magnetic nanoparticles formed a SiO2 shell via a sol-gel method, providing abundant Si-O groups and active sites for subsequent chemical modification. Then, the amino groups (-NH2) of APTES covalently bonded to the Si-O groups, introducing amino functionality; OTS, through its alkyl chain (C... 18 The reaction between the nanoparticles and Si-O groups endows them with hydrophobicity; the reaction of MA with surface amino groups via its carboxyl groups (-COOH) further enhances the multifunctionality of the nanomaterials. Using this method, Fe3O4@SiO2-C was successfully prepared. 18 The / NH2 / COOH composite magnetic nanoparticle material not only possesses magnetism but also incorporates three functional groups: amino, carboxyl, and hydrophobic groups, demonstrating its enrichment potential.

[0031] Comparative Example 1: Composite magnetic nanoparticles Fe3O4@SiO2-C 18 Preparation of / NH2 Fe3O4@SiO2-C 18 The synthesis strategy for / NH2 magnetic nanoparticles involved three steps. All chemical reagents were analytical grade and used directly without further purification, and solutions were prepared using ultrapure water prepared using a Milli-Q system. First, Fe3O4 magnetic nanoparticles were synthesized by coprecipitation and washed multiple times with deionized water. Next, a silica coating was prepared on the Fe3O4 surface using a sol-gel method: 0.10 g of Fe3O4MNPs were ultrasonically activated in 0.1 M HCl solution and then dispersed in a mixture of ethanol (80 mL), deionized water (20 mL), and ammonia (1.0 mL). Subsequently, 0.2 mL of tetraethyl orthosilicate (TEOS) was added, and the mixture was stirred at room temperature for 6 h. After multiple washes with ethanol and water, the resulting Fe3O4@SiO2MNPs were dried at 60 °C. Finally, the Fe3O4@SiO2MNPs were surface functionalized using octadecyltriethoxysilane (ODS) and 3-aminopropyltrimethoxysilane (APTMS). In short, 0.8 g of dry Fe3O4@SiO2MNPs were ultrasonically dispersed in 80 mL of anhydrous toluene, and different proportions of ODS and APTMS (total volume 0.5 mL) were added under vigorous stirring. The mixture was sealed in a reactor and heated at 120 °C for 8 h. The final product was Fe3O4@SiO2-C. 18 / NH2 magnetic nanoparticles.

[0032] Comparative Example 2: Composite magnetic nanoparticles Fe3O4@SiO2-C 18 Preparation of COOH First, magnetic Fe3O4 nanoparticles were prepared using a co-precipitation method. After repeated washing with deionized water, a layer of silica was coated onto the surface of Fe3O4 using a sol-gel method to obtain Fe3O4@SiO2 magnetic nanoparticles. Next, the Fe3O4@SiO2 was modified to be hydrophobic and carboxylated: 0.8 g of dried Fe3O4@SiO2 particles were ultrasonically dispersed in 80 mL of anhydrous toluene. Under vigorous stirring, 0.5 mL of octadecyltriethoxysilane (ODS) and 3-(triethoxysilyl)propylsuccinic anhydride (TESP-SA) were added, and the hydrophobicity and carboxyl content of the material surface were controlled by adjusting the volume ratio of the two. The mixture was sealed in a reaction vessel and reacted at 120 °C for 8 h. After the reaction, the product was collected using magnetic separation technology and washed several times with ethanol and deionized water to remove unreacted residual monomers. Finally, the sample was dried in a vacuum drying oven at 60 ℃ to obtain Fe3O4@SiO2-C. 18 / COOH composite magnetic nanoparticles. This comparative material aims to investigate the differences in enrichment performance for pesticide targets of different polarities when only hydrophobic long chains and carboxyl groups work together in the absence of amino functional groups.

[0033] Performance characterization and testing Performance Test Example 1: Structural and Morphological Characterization 1. Characterization of Fe3O4 magnetic nanoparticles The morphology, particle size, and magnetic properties of Fe3O4 magnetic nanoparticles were characterized using transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), respectively. TEM was used to observe the morphology and statistically analyze the particle size distribution, while VSM was used to determine the magnetization and magnetic response behavior. The surface chemical composition of the Fe3O4 magnetic nanoparticles was determined by X-ray photoelectron spectroscopy (XPS).

[0034] like Figure 1 As shown, the morphology and particle size of Fe3O4 magnetic nanoparticles were determined by TEM. Using Nano Measurer software, the particle size distribution of the Fe3O4 magnetic nanoparticles was statistically analyzed to be approximately 15.9 nm. Gaussian curve fitting confirmed that the particle size distribution conformed to a normal distribution. Figure 2 As shown, the magnetic properties and magnetic response time of Fe3O4 magnetic nanoparticles were determined by VSM. The Fe3O4 magnetic nanoparticles exhibit superparamagnetism, and magnetic separation was achieved in 20 s. The rapid magnetic response time (20 s) indicates that the prepared Fe3O4 magnetic nanoparticles have good magnetic separation performance, which is better than the magnetic separation time of 30 s found in other studies. This is attributed to the suitable particle size and good dispersibility.

[0035] like Figure 3 As shown in Figure a, Fe 2+The binding energy of the characteristic peak is 711.31 eV (Fe 2p). 3 / 2 ); Fe 3+ The binding energy of the characteristic peak is 725.14 eV (Fe 2p). 1 / 2 The positions of these two peaks are highly consistent with the characteristics of the standard XPS spectrum of iron(III) oxide.

[0036] like Figure 3 As shown in Figure b, the OC bond corresponds to the oxygen atom in the iron oxide lattice and is a characteristic oxygen peak of Fe3O4. The O=C bond typically originates from adsorbed hydroxyl groups (-OH), water molecules, or carbon oxides on the surface, reflecting the hydroxylation or adsorbed impurity state on the surface of the magnetic nanoparticles. The dominant peak area of ​​OC indicates that the sample is predominantly Fe3O4, and the presence of adsorbed oxygen on the surface is consistent with the characteristic that Fe3O4 magnetic nanoparticles are easily hydroxylated.

[0037] like Figure 4 As shown, the Fe3O4 magnetic nanoparticles synthesized under the optimal method have a zeta potential of -30.745 mV, which indicates that the synthesized magnetic nanoparticles can be stably and uniformly dispersed in the system.

[0038] 2. Characterization of Fe3O4@SiO2 magnetic nanoparticles To verify the successful coating of SiO2, evaluate the impact of coating on magnetic core performance, and confirm the surface chemical structure, transmission electron microscopy (TEM) was used to observe the morphology and particle size changes after coating. A vibrating sample magnetometer (VSM) was used to test the magnetic properties after coating. Fourier transform infrared spectroscopy (FTIR) was used to characterize the chemical bonds and surface active groups of the SiO2 shell. TEM and VSM were used to confirm the coating thickness and magnetic retention, while FTIR directly demonstrated the presence of the SiO2 shell and the degree of surface hydroxylation through characteristic functional group absorption peaks.

[0039] like Figure 5 As shown, the morphology and particle size of Fe3O4@SiO2 magnetic nanoparticles were determined by TEM. The particle size distribution of Fe3O4@SiO2 magnetic nanoparticles was statistically analyzed using the software NanoMeasurer, and it was found to be around 18 nm. The particle size distribution conformed to a normal distribution after Gaussian curve fitting. Figure 6 -a The magnetic properties and magnetic response time of Fe3O4@SiO2 nanoparticles were determined by VSM. The Fe3O4@SiO2 magnetic nanoparticles exhibited superparamagnetism and achieved magnetic separation in 30 s. Figure 6 -b shows the FTIR spectrum of Fe3O4@SiO2 nanoparticles. (At 1089.2 cm⁻¹) -1The strong absorption peaks observed nearby are attributed to the antisymmetric and symmetric stretching vibrations of Si-O-Si, confirming the successful coating of the SiO2 shell. At 579.2 cm⁻¹ -1 The absorption peak observed at 3400 cm⁻¹ is a characteristic peak of the Fe-O bond, indicating the presence of Fe₃O₄ magnetic nanoparticles. -1 The broad peaks in the vicinity correspond to the OH stretching vibrations of the Si-OH groups on the surface. These abundant hydroxyl groups provide active sites for subsequent functionalization modifications (such as amination, carboxylation, etc.). The Fe3O4@SiO2 nanoparticles prepared in this example exhibit strong Si-OH characteristic peaks, indicating a higher surface hydroxyl density, which is more conducive to further chemical modification.

[0040] like Figure 7 The XPS spectrum of the Fe3O4@SiO2 magnetic nanoparticles shown is as follows: Figure 7 As shown in -a, the satellite peak intensity of Fe in the 715-735 eV range is relatively weak, consistent with the phase characteristics of Fe3O4, proving that the main structure of Fe3O4 was not destroyed during synthesis. Figure 7 As shown in -b, the OC bond corresponds to the lattice oxygen of Fe3O4, confirming the presence of Fe3O4. The O-Si bond is a characteristic lattice oxygen peak of silicon dioxide, proving the successful coating of the material. H2O comes from surface-adsorbed water molecules, consistent with the easy hydroxylation characteristic of SiO2 surface, further confirming the presence of the SiO2 layer. Compared with the O1s spectrum of Fe3O4, the peak area of ​​the O-Si bond is significantly increased, indicating that SiO2 has become one of the main sources of oxygen species in the sample. The Si-O-Si bond (102.33 eV) is the core characteristic peak of SiO2, corresponding to the bridging oxygen structure of silicon-oxygen tetrahedra, directly proving the presence of the SiO2 layer. Si(-O)2 (100.46 eV) comes from the incompletely condensed silanol groups (Si-OH) on the surface, which is a typical feature of the SiO2 nanoparticle surface. The above demonstrates the successful synthesis of Fe3O4@SiO2 magnetic nanoparticles.

[0041] 3. Fe3O4@SiO2-C 18 Characterization of / NH2 / COOH composite magnetic nanoparticles Fe3O4@SiO2-C was characterized using transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDS). 18 Morphology, size, and elemental distribution of / NH2 / COOH composite magnetic nanoparticles. Figure 8 and Figure 9The results showed that the nanoparticles exhibited a regular spherical morphology with a clear core-shell structure, and the presence of five elements (Fe, Si, O, C, and N) was detected. Statistical analysis using NanoMeasurer software indicated that the average particle size was approximately 19 nm. After chemical modification, Fe3O4@SiO2-C... 18 The particle size of the / NH2 / COOH composite magnetic nanoparticles is about 1 nm larger than that of Fe3O4@SiO2. Gaussian curve fitting confirmed that the particle size distribution conforms to a normal distribution, indicating that the synthesis method has good controllability.

[0042] like Figure 10 The Fe3O4@SiO2-C shown 18 XPS spectra of / NH2 / COOH composite magnetic nanoparticles, from Figure 10 As can be seen from -a, the C 1s spectrum shows four characteristic peaks, corresponding to different carbon bonds: the C C bond (284.28 eV) originates from C 18 The carbon skeleton of a long alkyl chain. The CN bond (285.27 eV) originates from the carbon-nitrogen linkage of an amino group (-NH2). The CO bond (285.98 eV) originates from the carbon-oxygen single bond of a carboxyl group (-COOH) or a hydroxyl group (-OH). The C=O bond (287.80 eV) originates from the carbon-oxygen double bond of a carboxyl group (-COOH). The combination of these peaks corresponds perfectly to the C... 18 The functional group design of -NH2-COOH. For example... Figure 10 As shown in -b, although the satellite peak intensity in the 715-735 eV range is relatively weak, its characteristics are clear and consistent with the phase characteristics of Fe3O4. This indicates that the Fe3O4 magnetic core remains intact after multilayer modification. Figure 10 As shown in -c, the NC bond (399.23 eV) originates from the connection between the amino group (-NH2) and the carbon chain, while the NH bond (400.99 eV) originates from the amino group (-NH2). This demonstrates the successful modification of the amino group. Figure 10 As shown in -d, the OC bond (531.22 eV) originates from the lattice oxygen of SiO2 or the CO bond of an organic group. The O=C bond (531.95 eV) originates from the C=O bond of a carboxyl group (-COOH). This combination of peaks simultaneously confirms the presence of both the SiO2 layer and carboxyl modification. Figure 10 As shown in the -e indicator, the Si-O-Si bond (102.10 eV) is the core characteristic peak of SiO2, indicating that the SiO2 coating layer is intact. Si(-O)2 (100.46 eV): corresponds to the incompletely condensed silanol groups on the SiO2 surface, a typical surface feature of the SiO2 layer. The presence of this peak indicates that the SiO2 layer, as the intermediate structure connecting the magnetic core and the organic modification layer, remains intact. Figure 10As shown in the -f spectrum, the full spectrum clearly displays the signals of the five characteristic elements Fe, O, Si, C, and N, which are consistent with the target product Fe3O4@SiO2-C. 18 The elemental composition of the / NH2 / COOH composite magnetic nanoparticles is consistent.

[0043] 3. Fe3O4@SiO2-C based on FTIR characteristic peak analysis 18 / NH2 / COOH surface functional group optimization In order to obtain abundant and uniformly distributed C on the Fe3O4@SiO2 surface 18 The NH2 and COOH functional groups were used as quantitative evaluation indicators, with the peak area of ​​the wavenumber peaks corresponding to each characteristic functional group in Fourier transform infrared spectroscopy (FT-IR). First, single-factor experiments were conducted on six key factors affecting the surface modification effect (reaction temperature, reaction time, APTES dosage, OTS dosage, MA dosage, and reagent ratio). The experimental design is shown in Table 1. By comparing the influence of each factor on the peak area of ​​the target functional group, the three most significant factors were selected. Subsequently, using these three main factors as the research objects, a three-factor, three-level L9 (3... 3 The orthogonal experiments are shown in Table 2. The optimal combination of levels for each factor was determined through analysis of variance, ultimately yielding the desired Fe3O4@SiO2-C preparation. 18 Optimal synthesis conditions for / NH2 / COOH nanoparticles.

[0044] Table 1. Synthesis of Fe3O4@SiO2-C 18 Six single-factor experimental designs for / NH2 / COOH Table 2. Three-factor, three-level orthogonal experimental table (L9) To optimize Fe3O4@SiO2-C 18 The surface modification effect of / NH2 / COOH composite magnetic nanoparticles was investigated using the following initial synthesis conditions: 150 µL of 3-aminopropyltriethoxysilane (APTES), 25 µL of octadecyltrimethylsilane (OTS), 0.0165 g of maleic anhydride (MA), a reaction time of 30 min, an N,N-dimethylacetamide (DMAC) / toluene volume ratio of 3:2, and a reaction temperature of 100 °C. The effects of six key factors on the surface functional group modification were systematically examined. Fourier transform infrared spectroscopy (FT-IR) was used to analyze the peak area changes of characteristic functional groups under different conditions, such as... Figure 11 -a、 Figure 11 -b The results of the single-factor experiment indicate that: Figure 11 -a APTES dosage in 1392cm-1 The area of ​​the characteristic peak of NH has a significant impact, after statistical averaging. Figure 11 -b results showed that the optimal dosage of APTES was 300 µL (P<0.01), and the area of ​​the NH characteristic peak no longer increased significantly with increasing dosage; similarly, Figure 12 -c、 Figure 12 -d OTS dosage for 2940cm -1 The area of ​​the CH characteristic peak was significantly affected, and the optimal dosage was 100 µL (P<0.01); Figure 13 -e, Figure 13 -f MA dosage for 1641cm -1 The area of ​​the characteristic C=O peak at that point was significantly affected, with the optimal dosage being 0.066 g (P<0.01). Furthermore, Figure 14 -g, Figure 14 The reaction time only significantly affects the C=O peak area, with the optimal reaction time being 60 min (P<0.01). Figure 15 -i, Figure 15 The DMAC / toluene volume ratio significantly affected the peak areas of the three target functional groups (NH, C=O, CH), with the optimal ratio being 4:1 (P<0.01). Figure 16 -k, Figure 16 The reaction temperature also has a significant effect on the peak area of ​​the three functional groups, with the optimal temperature being 80℃ (P<0.01).

[0045] To identify the factors that most significantly affect the surface modification effect, F-value statistical analysis was performed on the results of single-factor experiments. For example... Figure 17 As shown, a larger F-value indicates a more significant impact of the factor on the response value. Based on the statistical analysis of the F-values ​​of each factor in the single-factor experiment, the results show that OTS, MA, and APTES have the most significant impact on the surface modification effect, while the effects of reaction temperature, DMAC / toluene volume ratio, and reaction time are relatively small. Therefore, this study selected OTS, MA, and APTES as the three key factors for investigation and designed a three-factor, three-level L9 (3 3 Orthogonal experiments were conducted, using the sum of the characteristic peak areas of FT-IR as a comprehensive evaluation index, to assess... Figure 18 We conducted an analysis and determined the optimal combination of synthesis conditions through analysis of variance.

[0046] After systematic analysis of the orthogonal experimental results, the theoretically optimal synthesis conditions were obtained as follows: APTES 300 µL, OTS 50 µL, MA 0.066 g, DMAC / toluene volume ratio 4:1, reaction temperature 80℃, and reaction time 60 min. To verify the reliability of the orthogonal optimization results, three verification experiments were conducted according to the theoretically optimal conditions. The FT-IR characterization results are as follows. Figure 19 As shown, Fe3O4@SiO2-C was prepared under theoretically optimal conditions. 18 The / NH2 / COOH composite magnetic nanoparticles exhibit a distinct characteristic absorption peak at 2940 cm⁻¹. -1 The CH stretching vibration peak at this point proves that C 18 Successful modification of alkyl chains; 1196 cm -1 CN stretching vibration peak at 1392 cm⁻¹ -1 The NH bending vibration peak at 3293 cm⁻¹ and the peak at 3293 cm⁻¹ -1 The NH stretching vibration peaks at 1641 cm⁻¹ jointly confirm the effective introduction of the amino group (-NH₂); -1 The C=O stretching vibration peak at this point indicates that the carboxyl group (-COOH) was successfully introduced into the nanoparticle surface. As shown in Table 3, the sum of the characteristic peak areas of the three target functional groups reached an integral value of 300. This result is consistent with the data from the fourth group of orthogonal experiments, fully demonstrating that the optimized scheme has good accuracy and reproducibility, providing reliable synthesis parameters for the large-scale preparation of this multifunctional magnetic nanomaterial. The optimized synthesis conditions not only achieved C 18 The efficient modification and uniform distribution of three functional groups—NH2 and COOH—on the surface of nanoparticles were achieved, and the preparation technical parameters were provided for the practical application of this multifunctional magnetic nanomaterial in the separation, enrichment, and selective adsorption of complex samples, which has practical guiding significance. To further determine the functional properties of the prepared functional nanoparticles, they were characterized by vibrating sample magnetometer (VSM), specific surface area measurement (BET), and thermogravimetric analysis (TG).

[0047] Table 3. Experimental results of the effect of functional group ratio on total infrared peak area. Performance Test Example 2: Magnetic Property Test The magnitude of superparamagnetism determines the efficiency of pesticide extraction from magnetic nanoparticles; the greater the superparamagnetism, the shorter the extraction time from the matrix. The test results were characterized using a vibrating sample magnetometer (VSM), and the results are as follows: Figure 20 As shown, the prepared Fe3O4@SiO2-C 18 / NH2 / COOH composite magnetic nanoparticles exhibit typical superparamagnetic characteristics, with remanence and coercivity both approaching zero. Compared to the Fe3O4 and Fe3O4@SiO2 nanoparticles synthesized in the previous two steps, the functionalized Fe3O4@SiO2-C... 18Although the saturation magnetization of the / NH2 / COOH composite magnetic nanoparticles decreased (from 50 emu / g to 10 emu / g), this was due to the dilution of the magnetic core content per unit mass caused by the coating of the non-magnetic organic layers (silanized layer and functional group layer). Magnetic separation tests were performed using a timer. After three tests, the average magnetic separation time was 40 s. This material can still achieve rapid magnetic separation within 40 s under an applied magnetic field, indicating that the magnetic response speed meets the requirements for efficient separation in practical applications.

[0048] Performance Test Example 3: Pore Structure and Thermal Stability Test The application performance of magnetic nanomaterials mainly depends on their specific surface area, pore structure, and surface chemical properties. While pure Fe3O4 magnetic nanoparticles exhibit good magnetic responsiveness, they have limited surface active sites and poor chemical stability. Coating with SiO2 can improve material stability and introduce silanol groups for subsequent modification, while C... 18 Modification with functional groups such as NH2 and COOH can endow materials with multimodal adsorption capabilities. However, surface modification alters the pore structure parameters of the material, thus requiring systematic research on Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2-C. 18 The changes in pore structure during the stepwise modification with / NH2 / COOH were investigated. The three materials were characterized using nitrogen adsorption-desorption (BET) technology. Figure 21 As shown, all three types of magnetic nanoparticles conform to a type IV isotherm (H3 hysteresis loop), indicating that they possess a mesoporous structure. Fe3O4 exhibits the highest surface area, reaching 93.6220 m². 2 / g, which is much higher than the previously reported surface area of ​​Fe3O4 (15.9 m²). 2 / g). This high surface area indicates that Fe3O4 provides a large number of active sites that can be used for adsorption or grafting. However, after coating the Fe3O4 surface with SiO2 to form Fe3O4@SiO2, the surface area decreased to 38.0495 m². 2 / g. This reduction is due to the SiO2 layer covering the Fe3O4 surface, partially blocking the pores. Although the specific surface area is reduced, the SiO2 coating introduces additional functional groups, providing grafting sites for further modification, which is crucial for improving the material's adsorption capacity. Further grafting of C... 18 NH2 and COOH groups form Fe3O4@SiO2-C 18 After applying NH2 / COOH, the surface area decreased sharply to 6.0203 m². 2 / g. This can be understood as the magnetic matrix Fe3O4@SiO2 providing numerous grafting sites, enabling the material to maintain its mesoporous structure while uniformly and densely loading C. 18The presence of NH2 and COOH groups enhances the adsorption potential of the material.

[0049] Table 4 shows that Fe3O4 (0.157627 cm⁻¹) 3 / g) to Fe3O4@SiO2 (0.099521 cm 3 / g) then to Fe3O4@SiO2-C 18 / NH2 / COOH (0.015706 cm) 3 / g), the pore volume showed a continuous decreasing trend, with decreases of 36.9% and 84.2%, respectively. This change is mainly attributed to the coating of the SiO2 shell and the subsequent C during the surface modification process. 18 The grafting of functional groups such as alkyl chains, amino groups, and carboxyl groups fills the original pore structure, resulting in a gradual reduction of usable pore space.

[0050] The pore size increased significantly from 6.7346 nm in Fe3O4 to 10.4623 nm in Fe3O4@SiO2, and then decreased slightly to 10.4353 nm after trifunctionalization modification, remaining basically stable. The increase in pore size during SiO2 coating may be due to the formation of a larger mesoporous structure from the formation of a mesoporous silica shell; while the subsequent organic functional group modification, although occupying part of the pore space, had little impact on the average pore size, indicating that the functionalization modification mainly occurred on the inner wall of the pores, rather than completely blocking the pores.

[0051] Table 4. Structural parameters of three types of nanoparticles Thermal stability is a crucial indicator for evaluating the practical application performance of materials, directly affecting their structural integrity and functional retention during high-temperature or heat treatment processes. For magnetic nano-adsorbents, temperature variations may occur during sample pretreatment, regeneration, or waste disposal; therefore, a systematic evaluation of the stability of the Fe3O4 core, SiO2 protective layer, and surface functional groups is necessary across different temperature ranges. This study used a thermogravimetric analyzer under a nitrogen atmosphere, heating from 25°C to 600°C at a rate of 10°C / min, to investigate the stability of Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2-C. 18 The thermal stability of / NH2 / COOH nanoparticles was characterized. For example... Figure 22 As shown, within the temperature range of 0-230 °C, all three samples lost approximately 8% of their weight, mainly due to the desorption of surface-adsorbed moisture, residual solvent, and volatile organic compounds. At 230-400 °C, Fe3O4@SiO2-C 18 / NH2 / COOH and Fe3O4 lost 15%, while Fe3O4@SiO2 lost 12%. The former was due to C... 18The decomposition of NH2 and COOH groups leads to higher losses, while the latter benefits from the excellent thermal stability of the SiO2 shell, resulting in less loss. At 400-600°C, the weight loss of Fe3O4 and Fe3O4@SiO2 almost stops, exhibiting excellent thermal stability, while Fe3O4@SiO2-C... 18 The loss of / NH2 / COOH reached 35%, attributed to further pyrolysis and carbonization of the functionalized layer. Nevertheless, Fe3O4@SiO2-C 18 / NH2 / COOH exhibits good thermal stability below 400°C, with a weight loss of only 15%, indicating that it has heat resistance in the low to medium temperature range, meeting the application requirements such as magnetic separation.

[0052] Performance Test Example 4: Adsorption Performance and Recovery Rate Test Based on the aforementioned optimization of nanomaterial synthesis conditions and surface multifunctional group modification studies, the differences in detection values ​​after adsorption of pesticides with different polarities were further determined. The adsorption efficiency of pesticides by functional groups was investigated by precisely controlling the addition amounts of APTES, OTS, and MA. The composite magnetic nanoparticles synthesized in this invention were used to treat pesticides added to a complex serum matrix through an adsorption-extraction-desorption process. The pesticide recovery rate was analyzed using UHPLC-QTOF-MS, with the method referring to GB 23200.121-2021 and modified appropriately according to experimental conditions. The results are shown in Table 5. In experimental group 4, with APTES, OTS, and MA added at amounts of 300 µL, 50 µL, and 0.066 g respectively, the optimal adsorption responses were observed for the weakly polar chlorpyrifos, the moderately polar tebuconazole, and the strongly polar imidacloprid. Compared with the responses obtained with added pesticide standards, the average recoveries were 94.9% ± 5.0%, 93.3% ± 6.0%, and 96.0% ± 2.5%, respectively. These results indicate that this novel material has broad potential applications in the pretreatment of complex samples. The composite nanoparticles Fe3O4@SiO2-C... 18 / NH2 / COOH can be used as a highly efficient magnetic solid-phase extraction adsorbent, and is widely used in the detection of risk factors in food safety, environmental water bodies and agricultural products, so as to achieve the simultaneous and rapid separation and enrichment of multiple pesticide residues or trace organic pollutants of different polarities in complex matrices.

[0053] Table 5 Experimental design and results showing the effect of different functional group ratios on the response of pesticides with different polarities. Performance Test Example 5: Molecular Docking Simulation Test Using molecular docking technology, the constructed SiO2@C 18 / NH2、SiO2@C 18 / COOH, SiO2@ NH2 / COOH and SiO2@C 18 The / NH2 / COOH material model was used for one-to-one docking simulations (10 times) with three pesticide molecules of different polarities: chlorpyrifos, tebuconazole, and imidacloprid. As shown in Table 6, SiO2@C 18 The average binding energies of / NH2 / COOH to chlorpyrifos, tebuconazole, and imidacloprid were 1.9381, 1.8574, and 1.8805 kcal / mol, respectively, showing significant increases compared to the three control groups. Independent samples t-tests confirmed that the increases in each group were statistically significant, especially compared to SiO2@C. 18 The -NH2 group showed improvements of 56.89%, 71.09%, and 47.12%, respectively, with p-values ​​all less than 0.0001. After introducing the three functional groups, the relative standard deviations (RSDs) of the binding energies of chlorpyrifos, tebuconazole, and imidacloprid were optimized to 3.96%, 5.45%, and 9.10%, respectively. This reduction in data volatility demonstrates, from a microscopic mechanism, the efficacy of octadecyl (C 18 The advantages of the three functional groups—amino (-NH2) and carboxyl (-COOH)—in enhancing broad-spectrum adsorption affinity provide reliable theoretical support for the high efficiency of this material in processing samples from complex environments. For example... Figure 23 As shown, the docking conformation indicates that the simultaneous action of the three functional groups not only enhances the hydrophobic interaction on the material surface, but also forms a multi-dimensional synergistic effect compared with other single or two functional groups. Driven by electrostatic attraction, hydrogen bonding and hydrophobic interaction, a more stable composite adsorption site is constructed, which improves the broad-spectrum adsorption affinity and precision of the material.

[0054] Table 6 Comparison of Simulated Binding Energy in Molecular Docking Note: Improvement rate = (Experimental group mean - Control group mean) / Control group mean × 100%. Here, the experimental group is uniformly designated as C. 18 / NH2 / COOH; the significance of the difference was assessed by t-test; *** indicates extremely significant (p<0.001), ** indicates extremely significant (p<0.01), * indicates significant (p<0.05).

[0055] It can be seen that by simultaneously grafting octadecyl (C) groups onto the Fe3O4@SiO2 surface... 18The nanoparticles incorporate three functional groups: amino (-NH2) and carboxyl (-COOH). These three functional groups exhibit synergistic effects in hydrophobic interactions, hydrogen bonding, and electrostatic attraction, enabling simultaneous and efficient adsorption of weakly, moderately, and strongly polar analytes. This overcomes the limitations of existing single- or bifunctional group materials, which suffer from narrow adsorption spectra and require multi-step extraction. Optimized material input parameters (APTES 300µL, OTS 50µL, MA 0.066g) resulted in a high and uniform grafting density of the three functional groups on the nanoparticle surface, achieving a total infrared characteristic peak area integral value of 300, significantly superior to other formulations. The preparation method demonstrates good controllability and high reproducibility.

[0056] The composite magnetic nanoparticles prepared in Example 1 retain good superparamagnetism and can be rapidly separated under an external magnetic field. The operation is simple and quick, meeting the demand for efficient separation in complex sample pretreatment. The composite magnetic nanoparticles prepared in Example 1 exhibit high precision, high accuracy, and broad-spectrum adsorption capacity for typical pesticides of different polarities (e.g., weakly polar chlorpyrifos, moderately polar tebuconazole, and strongly polar imidacloprid), making them suitable for the simultaneous enrichment and detection of multiple polar risk factors in fields such as food safety, environmental monitoring, and agricultural product testing.

[0057] It should be understood that the above detailed description of the technical solutions of the present invention with reference to preferred embodiments is illustrative and not restrictive. Those skilled in the art can modify the technical solutions described in the embodiments or make equivalent substitutions for some of the technical features based on reading this specification; however, these modifications or substitutions do not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite magnetic nanoparticle Fe3O4@SiO2-C 18 / NH2 / COOH, characterized in that, The composite magnetic nanoparticles have a core-shell structure, which includes a core, an intermediate layer, and an outer shell. The core is Fe3O4 magnetic nanoparticles, the intermediate layer is a SiO2 coating layer, and the outer shell is an organic modification layer, which includes three functional groups: octadecyl, amino, and carboxyl.

2. A method for preparing composite magnetic nanoparticles according to claim 1, characterized in that, Includes the following steps: (1) Fe3O4 magnetic nanoparticles were prepared by chemical coprecipitation method; (2) The Fe3O4 magnetic nanoparticles obtained in step (1) were coated with SiO2 using the sol-gel method to obtain Fe3O4@SiO2 magnetic nanoparticles; (3) Using a simultaneous modification method, (3-aminopropyl)triethoxysilane, octadecyltrimethylsilane, and maleic anhydride were grafted onto the surface of the Fe3O4@SiO2 magnetic nanoparticles obtained in step (2) to obtain the composite magnetic nanoparticles Fe3O4@SiO2-C. 18 / NH2 / COOH.

3. The preparation method according to claim 2, characterized in that, Step (1) includes the following steps: Heat deionized water to 70-90℃, and add Fe under nitrogen protection and stirring. 3+ with Fe 2+ A 2:1 molar ratio of iron salt mixed solution was used to adjust the pH of the system to ≥9.2 for precipitation reaction. Then, sodium citrate was added for surface modification. After magnetic separation, washing, and vacuum freeze-drying, Fe3O4 magnetic nanoparticles were obtained. Preferably, the iron salt mixed solution is a ferric chloride hexahydrate solution and a ferrous chloride tetrahydrate solution, wherein the concentrations of the ferric chloride hexahydrate solution and the ferrous chloride tetrahydrate solution are 0.5-1.5 mol / L, respectively; Preferably, the pH value of the system is adjusted using 25% ammonia solution, with an addition volume of 5.8-6.8 mL; Preferably, the concentration of sodium citrate is 0.033 mol / L, and the amount added is 4-6 mL.

4. The preparation method according to claim 2, characterized in that, Step (2) is as follows: The Fe3O4 magnetic nanoparticles obtained in step (1) were ultrasonically dispersed in a dispersion system composed of anhydrous ethanol and deionized water. Sodium hydroxide solution was added under nitrogen protection, and the temperature was maintained at 38-42℃. Anhydrous ethanol solution of tetraethyl orthosilicate was added, and the reaction was carried out at a constant temperature for 10-14 h. After the reaction was completed, the Fe3O4@SiO2 magnetic nanoparticles were obtained by washing and drying.

5. The preparation method according to claim 2, characterized in that, Step (3) includes the following steps: a. Add an organic reaction solvent into the inner cavity of the high-pressure reactor; b. Add (3-aminopropyl)triethoxysilane, octadecyltrimethylsilane and maleic anhydride to the system in step a simultaneously, and dissolve and mix well; c. Add Fe3O4@SiO2 magnetic nanoparticles to the system in step b; d. Seal the high-pressure reactor, introduce inert gas, and react at a constant temperature with stirring. After the reaction is complete, wash and dry to obtain the composite magnetic nanoparticles Fe3O4@SiO2-C. 18 / NH2 / COOH.

6. The preparation method according to claim 5, characterized in that, In step a, the organic reaction solvent is a mixture of N,N-dimethylacetamide and toluene, and the volume ratio of the mixture of N,N-dimethylacetamide and toluene is (3-5):

1.

7. The preparation method according to claim 5, characterized in that, In step b, the amount of Fe3O4@SiO2 magnetic nanoparticles added is 20 mg, the amount of (3-aminopropyl)triethoxysilane is 250-350 µL, the amount of octadecyltrimethylsilane is 40-60 µL, and the amount of maleic anhydride is 0.060-0.070 g.

8. The preparation method according to claim 5, characterized in that, In step d, the stirring speed is 400-600 rpm, and / or The reaction temperature is 70-90℃, and / or The reaction time is 50-70 min.

9. The application of the composite magnetic nanoparticles according to claim 1 or the composite magnetic nanoparticles prepared by the method according to any one of claims 2-8 as magnetic solid-phase extraction adsorbents.

10. The application according to claim 9, characterized in that, The application is in the simultaneous adsorption, separation, or enrichment of pesticides of different polarities.

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