Magnetic-fluorescent dual-function nano-particles as well as preparation method and application of magnetic-fluorescent dual-function nano-particles

Abstract

The invention relates to the technical field of nondestructive testing, in particular to magnetic-fluorescent difunctional nanoparticles as well as a preparation method and application thereof. The preparation method provided by the invention comprises the following steps: dissolving ferric chloride hexahydrate and sodium salt in ethylene glycol, adding an amine compound and an emulsifier, uniformly mixing, heating for reaction, and cleaning and drying after the reaction is finished to obtain amino-modified magnetic iron oxide nanoparticles; the preparation method comprises the following steps: dispersing magnetic iron oxide nanoparticles in absolute ethyl alcohol, adding a polymer monomer, stirring, carrying out heating reaction, and carrying out magnetic separation, cleaning and drying after the reaction is ended, so as to obtain aminated magnetic iron oxide nanoparticles with an intermediate layer; dispersing the prepared nano-particles in absolute ethyl alcohol, adding a rare earth compound, a rare earth fluorescent complex and an amine compound, performing stirring reaction at room temperature, performing magnetic separation, cleaning and drying after the reaction, and performing post-treatment on the nano-particles to obtain the magnetic-fluorescent dual-function nano-particles.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a magnetic-fluorescent bifunctional nanoparticle, its preparation method, and its application. Background Technology

[0002] Currently, magnetic particle testing is a widely used non-destructive testing method, mainly used to detect cracks and defects on or near the surface of metallic materials and equipment. The basic principle of magnetic particle testing is to create a magnetic field by spraying magnetic powder onto the surface to be tested. During the testing process, when the magnetic field passes through the metal containing cracks or defects, these defective areas cause localized leakage of magnetic flux, and the magnetic powder accumulates around the defects, thus presenting the morphology of a crack. To enhance the visibility of crack detection, some studies in recent years have introduced fluorescent materials. These fluorescent magnetic powders emit visible light signals under ultraviolet light irradiation, making cracks clearer, and are particularly suitable for detection in low-light environments. For example, patent CN1296268A discloses a manufacturing process for fluorescent magnetic powder for flaw detection, which involves mixing black magnetic powder and fluorescent powder, and then encapsulating the black magnetic powder and fluorescent powder in the form of microcapsules. Traditional fluorescent magnetic powders typically use physical mixing methods, simply coating the fluorescent material onto the surface of magnetic powder, or combining magnetic and fluorescent properties through electrostatic adsorption. This type of magnetic particle inspection material can enhance the visual contrast of cracks and defects under ultraviolet light, thereby improving the sensitivity of detection.

[0003] Although fluorescent magnetic particle detection offers some improvements, existing technologies still have several significant shortcomings, specifically: 1. Poor stability of the fluorescent and magnetic bonding: Traditional fluorescent magnetic particles mostly combine fluorescent materials and magnetic particles through physical mixing or electrostatic adsorption. This bonding method has poor stability in practical applications; fluorescent materials are prone to detachment or migration during detection, leading to uneven fluorescence signals or reduced detection sensitivity. Especially in complex detection environments, the detachment of fluorescent materials significantly affects detection results and reduces the visibility of cracks. 2. Poor fluorescence lifetime and photostability: The fluorescent materials used in traditional fluorescent magnetic particles are mostly organic dyes or ordinary phosphors. Although these materials can provide visible light signals for a short time, they typically suffer from poor photostability and short fluorescence lifetimes. These fluorescent materials are prone to light decay under prolonged ultraviolet light irradiation, causing the visibility of cracks or defects to weaken over time, affecting the durability of detection. 3. Lack of efficient dual-function bonding: Traditional fluorescent magnetic particles struggle to achieve efficient bonding of magnetic and fluorescent properties, lacking a close correlation between the two. Because magnetic and fluorescent materials often employ different chemical structures and lack suitable bonding methods, it is difficult to achieve sensitive detection of cracks and defects. In practice, the magnetic powder aggregation effect at cracks does not always match the fluorescence signal, reducing the accuracy of crack and defect identification. 4. Insufficient applicability in magnetic microcapsule detection: Traditional magnetic particle detection methods are mainly applied to metallic materials, while their application in detecting magnetic leakage in magnetic microcapsules is limited. Magnetic microcapsules are capsule structures containing magnetic materials, and their magnetic and fluorescent properties require higher bonding and stability to reveal magnetic leakage in small cracks or structural discontinuities. However, traditional magnetic particles cannot meet this detailed detection requirement, and their detection accuracy and clarity are low.

[0004] In summary, existing applications of fluorescent magnetic particles in crack and defect detection have many shortcomings, including deficiencies in bonding stability, photostability, and detection accuracy. These problems mainly stem from the lack of a strong and stable chemical bond between the fluorescent and magnetic materials, and the limited variety and lifetime of fluorescent materials, thus restricting the detection effectiveness.

[0005] Based on the above analysis, it is essential to provide a nanoparticle with strong stability in combining magnetic particles with fluorescent materials. Summary of the Invention

[0006] This invention provides a magnetic-fluorescent bifunctional nanoparticle, its preparation method, and its application, in order to solve the problem of poor stability of the binding between magnetic particles and fluorescent materials in existing related technologies.

[0007] In a first aspect, the present invention provides a method for preparing magnetic-fluorescent bifunctional nanoparticles, comprising the following steps:

[0008] Step S1, Preparation of amino-modified magnetic iron oxide nanoparticles: Iron chloride hexahydrate and sodium salt are dissolved in ethylene glycol, amine compounds and emulsifiers are added, mixed evenly, heated to react, and after the reaction is completed, washed and dried to obtain amino-modified magnetic iron oxide nanoparticles.

[0009] Step S2, introducing the intermediate layer: Disperse the amino-modified magnetic iron oxide nanoparticles in anhydrous ethanol, add the polymer monomer, stir, heat and react, after the reaction is completed, magnetically separate, wash and dry to obtain amino-modified magnetic iron oxide nanoparticles with an intermediate layer.

[0010] Step S3, coating with rare earth fluorescent complex: The prepared aminated magnetic iron oxide nanoparticles with intermediate layer are dispersed in anhydrous ethanol, and rare earth compounds, rare earth fluorescent complexes and amine compounds are added. The mixture is stirred and reacted at room temperature. After the reaction, the nanoparticles are magnetically separated, washed and dried, and then post-treated to obtain magnetic-fluorescent bifunctional nanoparticles.

[0011] In some embodiments, the mass ratio of ferric chloride hexahydrate, sodium salt, and amine compound is 3.0–4.0:2.5–3.5:2.0–3.0. The amount of emulsifier added is 1%–3% of the total mass of the amino-modified magnetic iron oxide nanoparticles, used to adjust interfacial tension, promote particle size uniformity, and control the magnetic core particle size between 200–500 nm.

[0012] In some embodiments, the mass ratio of amino-modified magnetic iron oxide nanoparticles to polymer monomers is 0.5:0.32 to 0.64.

[0013] In some embodiments, the mass ratio of the aminated magnetic iron oxide nanoparticles with an intermediate layer, the rare earth compound, the rare earth fluorescent complex, and the amine compound is 0.4–0.6:0.35–0.5:0.4–0.6:0.18–0.26.

[0014] In some embodiments, the sodium salt is anhydrous sodium acetate or sodium citrate.

[0015] In some embodiments, the emulsifier is any one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or polyethylene glycol.

[0016] In some embodiments, the amine compound is any one of hexamethylenediamine, ethylenediamine, triethylenetetramine, or polyethyleneimine.

[0017] In some embodiments, the magnetic-fluorescent bifunctional nanoparticles have a particle size of 200–500 nm.

[0018] In some embodiments, in step S1, the temperature of the heating reaction is 180–200°C, and the reaction time is 6–10 h.

[0019] In some embodiments, in step S2, the temperature of the heating reaction is 50–70°C, and the reaction time is 10–14 h.

[0020] In some embodiments, the polymer monomer is any one or a mixture of polyethylene glycol diacid, polyethyleneimine, 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane.

[0021] In some embodiments, the rare earth compound is any one of europium chloride hexahydrate, europium nitrate hexahydrate, terbium chloride hexahydrate, and europium acetylacetonate.

[0022] In some embodiments, the rare-earth fluorescent complex is any one or a mixture of benzoylmethane, trifluoroacetylacetone, 1,10-phenanthroline, 2-thiophenecarboxylic acid trifluoroacetylacetone, and acetylacetone. The rare-earth fluorescent complex is bonded to the intermediate layer of the magnetic iron oxide nanoparticles through hexamethylenediamine, thereby stably coating the surface of the nanoparticles with the rare-earth fluorescent complex.

[0023] In some embodiments, the post-treatment process for the nanoparticles involves placing them in a solution of a multifunctional organic small molecule with a mass concentration of 0.1%-0.5%, wherein the multifunctional small molecule is any one or a mixture of citric acid, acrylic acid, succinic acid, malic acid, and ethylenediaminetetraacetic acid. Post-treatment of the nanoparticles can further improve their environmental stability and prevent quenching of the fluorescent layer during use.

[0024] Secondly, the present invention also provides magnetic-fluorescent bifunctional nanoparticles prepared using the above-described preparation method.

[0025] Thirdly, the present invention provides the application of magnetic-fluorescent bifunctional nanoparticles prepared by the above preparation method in crack detection of metallic materials and magnetic leakage detection of magnetic microcapsules.

[0026] The nanoparticles prepared in this invention use Fe3O4 nanoparticles as the core material, endowing the particles with superparamagnetism, enabling them to respond rapidly and aggregate at cracks and defects under an applied magnetic field, thus achieving magnetic marking of defect sites. This invention introduces functional groups such as amino (-NH2) and carboxyl (-COOH) groups onto the Fe3O4 surface through chemical modification, providing stable attachment sites for the binding of fluorescent complexes, ensuring the uniform distribution and stable binding of fluorescent complexes on the particle surface. This invention also incorporates rare earth ions (such as Eu...) 3+ 、Tb 3The fluorescent complex formed by the rare earth element (+) and organic ligands (such as trifluoroacetylacetone) is fixed on the surface of Fe3O4 particles through amide bonds or coordination bonds. When irradiated with ultraviolet light, the rare earth complex emits strong fluorescence, enhancing the visibility of defects and cracks. This magnetic-fluorescent bifunctional nanoparticle material achieves the synergistic effect of magnetic aggregation and fluorescent labeling at defects, making it suitable for high-sensitivity crack and defect detection and magnetic field leakage detection.

[0027] This invention combines magnetic responsiveness and fluorescence imaging capabilities, enabling cracks, defects, and minute magnetic leaks to exhibit high-contrast fluorescence signals under ultraviolet light irradiation, significantly improving the sensitivity and accuracy of detection.

[0028] The beneficial effects of the technical solution provided by this invention include:

[0029] This invention introduces rare-earth fluorescent complexes into Fe3O4 magnetic nanoparticles via chemical bonding, ensuring the uniform distribution and stable binding of the fluorescent complexes on the particle surface. This achieves a dual-functional detection material combining magnetic response and fluorescent labeling, offering significant technical advantages and economic benefits. Specifically:

[0030] 1. This invention utilizes the superparamagnetism of Fe3O4 to achieve magnetic aggregation at cracks and defects. Combined with the strong fluorescence characteristics of rare earth fluorescent complexes, it exhibits a high-contrast fluorescence signal under ultraviolet light irradiation, making micro-cracks, defects, and magnetic leakage more clearly visible. Compared with the prior art, this invention has significantly improved detection sensitivity and accuracy, and is suitable for high-requirement non-destructive testing and quality control.

[0031] 2. The magnetic-fluorescent bifunctional nanoparticles of the present invention have wide applicability and are easy to use. They are suitable for various detection environments and can achieve high-sensitivity crack and defect detection and magnetic field leakage detection through simple magnetic field and ultraviolet light operation. Users do not need complicated instruments and equipment to quickly complete the detection on site, which greatly improves the ease of operation and efficiency of use. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is an electron microscope image of the magnetic-fluorescent bifunctional nanoparticles prepared in Example 1.

[0034] Figure 2 This is an electron microscope image of the magnetic-fluorescent bifunctional nanoparticles prepared in Example 2.

[0035] Figure 3 This is an electron microscope image of the magnetic-fluorescent bifunctional nanoparticles prepared in Comparative Example 1. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention provides a method for preparing magnetic-fluorescent bifunctional nanoparticles, which can solve the problem of poor stability of the binding between existing magnetic particles and fluorescent materials in the prior art.

[0038] Example 1:

[0039] (1) Preparation of amino-modified magnetic iron oxide nanoparticles:

[0040] 3.5 g of ferric chloride hexahydrate was dissolved in 30 mL of ethylene glycol, 3 g of anhydrous sodium acetate was added, followed by 2.5 g of hexamethylenediamine and 0.08 g of sodium dodecylbenzenesulfonate. After mixing thoroughly, the mixture was transferred to a reaction vessel and reacted at 190 °C for 8 hours. After the reaction was completed, the mixture was cooled, magnetically separated, and washed repeatedly with anhydrous ethanol and deionized water to obtain amino-modified magnetic iron oxide nanoparticles for later use.

[0041] (2) Introducing an intermediate layer:

[0042] 0.5 g of the prepared amino-modified magnetic iron oxide nanoparticles were dispersed in 100 mL of anhydrous ethanol, and 0.32 g of polyethylene glycol diacid (PEG) and 0.32 g of polyethyleneimine (PEI) were added. The mixture was stirred until it was evenly dispersed and reacted at 60 °C for 12 hours. After the reaction was completed, the nanoparticles were obtained by magnetic separation and washing with anhydrous ethanol to obtain amino-modified magnetic iron oxide nanoparticles with an intermediate layer.

[0043] (3) Coated rare earth fluorescent complexes:

[0044] 0.5 g of prepared aminated magnetic iron oxide nanoparticles with an intermediate layer were dispersed in 100 mL of anhydrous ethanol. 0.446 g of europium chloride hexahydrate, 0.25 g of dibenzoylmethane, 0.25 g of trifluoroacetylacetone, and 0.232 g of hexamethylenediamine were added. The mixture was stirred at room temperature for 3 hours. After the reaction was completed, the nanoparticles were magnetically separated, washed with anhydrous ethanol, and dried. The dried nanoparticles were placed in a solution of 0.3% citric acid and succinic acid and stirred gently at room temperature for 2 hours. After washing and drying, magnetic-fluorescent bifunctional nanoparticles with a particle size of about 300 nm were obtained.

[0045] Electron microscopy image of the magnetic-fluorescent bifunctional nanoparticles prepared in Example 1 is shown below. Figure 1 ,from Figure 1 It can be seen that the surface of the nanoparticles is uniformly covered with a rough layer, indicating that an intermediate layer has been successfully formed on the surface of the aminated magnetic iron oxide nanoparticles, and the surface of the nanoparticles is covered with fluorescent material.

[0046] Example 2:

[0047] (1) Preparation of amino-modified magnetic iron oxide nanoparticles:

[0048] 3.3 g of ferric chloride hexahydrate and 3.2 g of sodium citrate were dissolved in 30 mL of ethylene glycol. 2.8 g of triethylenetetramine and 0.08 g of sodium dodecylbenzenesulfonate were added, and the mixture was stirred until homogeneous. The mixture was then transferred to a high-pressure reactor and reacted at 185 °C for 10 hours. After the reaction was completed, the mixture was cooled and magnetically separated. It was then washed repeatedly with anhydrous ethanol and deionized water to obtain amino-modified magnetic iron oxide nanoparticles for later use.

[0049] (2) Introducing an intermediate layer:

[0050] 0.5 g of the prepared amino-modified magnetic iron oxide nanoparticles were dispersed in 100 mL of anhydrous ethanol, and 0.3 g of polyethylene glycol diacid and 0.32 g of polyethyleneimine were added. The mixture was stirred and dispersed evenly, and reacted at 65 °C for 10 hours. After the reaction was completed, magnetic separation was performed, and the nanoparticles were washed with anhydrous ethanol to obtain amino-modified magnetic iron oxide nanoparticles with an intermediate layer.

[0051] (3) Coated rare earth fluorescent complexes:

[0052] 0.45 g of prepared aminated magnetic iron oxide nanoparticles with an intermediate layer were dispersed in 100 mL of anhydrous ethanol. 0.42 g of europium chloride hexahydrate, 0.45 g of trifluoroacetylacetone, and 0.22 g of hexamethylenediamine were added. The mixture was stirred at room temperature for 3 hours. After the reaction was completed, the nanoparticles were separated by magnetic separation, washed with anhydrous ethanol, and dried. The dried nanoparticles were placed in a 0.4% (w / w) solution of acrylic acid and malic acid and stirred gently at room temperature for 2 hours. After washing and drying, magnetic-fluorescent bifunctional nanoparticles with a particle size of approximately 280 nm were obtained.

[0053] Electron microscopy images of the magnetic-fluorescent bifunctional nanoparticles prepared in Example 2 are shown below. Figure 2 ,from Figure 2 It can be seen that the surface of the nanoparticles is uniformly covered with a rough layer, indicating that an intermediate layer has been successfully formed on the surface of the aminated magnetic iron oxide nanoparticles, and the surface of the nanoparticles is covered with fluorescent material.

[0054] Example 3:

[0055] (1) Preparation of amino-modified magnetic iron oxide nanoparticles:

[0056] 3.8 g of ferric chloride hexahydrate and 2.6 g of sodium citrate were dissolved in 30 mL of ethylene glycol. 2.5 g of ethylenediamine and 0.08 g of sodium dodecylbenzenesulfonate were added, mixed thoroughly, and then transferred to a high-pressure reactor. The mixture was reacted at 200 °C for 9 hours. After the reaction was completed, the mixture was cooled, magnetically separated, and washed multiple times with anhydrous ethanol and deionized water to obtain amino-modified magnetic iron oxide nanoparticles for later use.

[0057] (2) Introducing an intermediate layer:

[0058] 0.5 g of the prepared amino-modified magnetic iron oxide nanoparticles were dispersed in 100 mL of anhydrous ethanol, and 0.32 g of polyethylene glycol diacid and 0.25 g of polyethyleneimine were added. The mixture was stirred until it was evenly dispersed and reacted at 70 °C for 14 hours to fully coat the nanoparticles. After the reaction was completed, the nanoparticles were separated by magnetic separation, washed with anhydrous ethanol and dried to obtain amino-modified magnetic iron oxide nanoparticles with an intermediate layer.

[0059] (3) Coated rare earth fluorescent complexes:

[0060] 0.46 g of prepared aminated magnetic iron oxide nanoparticles with an intermediate layer were dispersed in 100 mL of anhydrous ethanol. 0.38 g of europium chloride hexahydrate, 0.3 g of 1,10-phenanthroline, 0.25 g of acetylacetone (ACAC), and 0.2 g of hexamethylenediamine were added. The mixture was stirred at room temperature for 4 hours. After the reaction was completed, the nanoparticles were magnetically separated, washed with anhydrous ethanol, and dried. The dried nanoparticles were placed in a solution of 0.5% ethylenediaminetetraacetic acid and citric acid and treated with gentle stirring for 2 hours. After washing and drying, magnetic-fluorescent bifunctional nanoparticles with a particle size of approximately 295 nm were obtained.

[0061] Comparative Example 1:

[0062] (1) Preparation of magnetic nuclei Fe3O4:

[0063] 3.5 g of ferric chloride hexahydrate and 3 g of anhydrous sodium acetate were dissolved in 30 mL of ethylene glycol. 2.5 g of hexamethylenediamine and 0.08 g of sodium dodecylbenzenesulfonate were added and stirred until completely dissolved. The solution was transferred to a high-pressure reactor and heated at 190 °C for 8 hours. After the reaction was completed, the mixture was cooled and magnetically separated. It was washed several times with anhydrous ethanol and deionized water to obtain amino-modified magnetic iron oxide nanoparticles with a particle size of about 200 nm for later use.

[0064] (2) Direct coating of rare earth complexes:

[0065] 0.5 g of the prepared amino-modified magnetic iron oxide nanoparticles were dispersed in 100 mL of anhydrous ethanol, and 0.446 g of europium chloride hexahydrate, 0.5 g of dibenzoylmethane and 0.232 g of hexamethylenediamine were added. The mixture was stirred at room temperature for 3 hours. After the reaction was completed, magnetic separation was performed, and the nanoparticles were washed several times with anhydrous ethanol and dried. The dried nanoparticles were placed in a solution of 0.3% citric acid and succinic acid and stirred gently for 2 hours. After washing with deionized water and drying, magnetic-fluorescent bifunctional nanoparticles were obtained.

[0066] Electron microscopy images of the magnetic-fluorescent bifunctional nanoparticles prepared in Comparative Example 1 are shown below. Figure 3 ,from Figure 3 It can be seen that the nanoparticles prepared in Comparative Example 1 have a more uniform morphology, a complete surface, and a distinct core-shell structure. This indicates that although the morphology is neat without the introduction of an intermediate layer, the functional performance is reduced, such as low fluorescence intensity and unstable binding, further reflecting the crucial role of the intermediate layer in performance improvement.

[0067] Comparative Example 2:

[0068] Conventional fluorescent magnetic powder was prepared according to the process of Example 1 disclosed in patent CN1296268A.

[0069] The performance of the nanoparticles of Example 1 and the conventional fluorescent magnetic powder of Comparative Example 2 were tested.

[0070] I. Fluorescence Enhancement Effect Test

[0071] Test procedure: Under the same ultraviolet excitation conditions, the fluorescence emission intensity (unit: relative light intensity au) of the nanoparticles prepared in Example 1 of this invention and the fluorescent magnetic powder prepared in Comparative Example 2 were measured respectively. The results are shown in Table 1:

[0072] Table 1: Fluorescence enhancement test results of Example 1 and Comparative Example 2

[0073] Example Fluorescence intensity (au) Fluorescence enhancement ratio (relative to conventional) Example 1 320±20 1.52 Comparative Example 1 225±15 1.07 Comparative Example 2 210±15 1.0

[0074] As shown in Table 1, although Comparative Example 1 has a more regular morphology, its fluorescence intensity is still about 30% lower than that of Example 1, indicating that the lack of an intermediate layer results in weak bonding and easy quenching. The nanoparticles of Example 1 exhibit a fluorescence intensity that is about 50% higher than that of Comparative Example 2 under UV excitation, demonstrating a more uniform and efficient fluorescence coating effect.

[0075] II. Magnetic Response Test

[0076] Test procedure description: The magnetic saturation intensity (Ms) of the two samples and the aggregation efficiency under an applied magnetic field were measured using a vibrating sample magnetometer (VSM). The aggregation region ratio was obtained through image analysis. The results are shown in Table 2.

[0077] Table 2: Magnetic Response Test Results

[0078]

[0079]

[0080] As shown in Table 2, the magnetic responsiveness of Comparative Example 1 is slightly better than that of Comparative Example 2, but still not as good as that of the Example 1, indicating that the intermediate layer helps the fluorescent layer to bind without affecting the response behavior of the magnetic core. The magnetic saturation intensity and aggregation efficiency of the nanoparticles prepared in Example 1 are both higher than those in Comparative Example 2, which means that under the action of an external magnetic field, the magnetic powder of the present invention can aggregate to the defect region more quickly and in a more concentrated manner.

[0081] III. Crack Detection Success Rate Test

[0082] Test procedure description: Artificial cracks of different sizes (50μm, 100μm, 200μm) were created on the metal sample. The magnetic powder of Comparative Example 2 and the nanoparticles of Example 1 of this invention were used for detection. The crack detection success rate (number of successfully detected cracks / total number of cracks) was calculated. The results are shown in Table 3.

[0083] Table 3: Crack Detection Success Rate Test Results

[0084]

[0085] As shown in Table 3, Comparative Example 1 is still inferior to Example 1 in detecting small and medium-sized cracks, indicating that the intermediate layer can enhance the fluorescence aggregation ability in low-signal regions. The nanoparticles of Example 1 of this invention have significant advantages in detecting smaller cracks, and also exhibit higher accuracy in detecting medium and large-sized cracks.

[0086] IV. Environmental Stability Testing

[0087] Test procedure description: The nanoparticles of Example 1 and the fluorescent magnetic powder of Comparative Example 2 were exposed to high temperature (80°C) and high humidity (85% RH) environments for 48 hours, respectively. Their fluorescence intensity and magnetic retention were measured, and the data are shown in Table 4 (the retention rate is the proportion when the initial value is 100%).

[0088] Table 4: Environmental stability test results

[0089]

[0090]

[0091] As shown in Table 4, although Comparative Example 1 has a complete structure, the lack of the intermediate layer makes the fluorescent material more prone to detachment or deactivation, resulting in insufficient long-term stability. The nanoparticles of Example 1 can better maintain their fluorescence and magnetic properties under high temperature and high humidity conditions, exhibiting superior long-term environmental stability.

[0092] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example is included in at least one embodiment / mode or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0093] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified.

[0094] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing magnetic-fluorescent bifunctional nanoparticles, characterized in that, Includes the following steps: S1, ferric chloride hexahydrate and sodium salt are dissolved in ethylene glycol, amine compounds and emulsifiers are added, mixed evenly, heated to react, and after the reaction is completed, washed and dried to obtain amino-modified magnetic iron oxide nanoparticles; S2, amino-modified magnetic iron oxide nanoparticles are dispersed in anhydrous ethanol, polymer monomers are added, the mixture is stirred and heated to react, magnetic separation is performed after the reaction is completed, and the mixture is washed and dried to obtain amino-modified magnetic iron oxide nanoparticles with an intermediate layer. S3. The prepared aminated magnetic iron oxide nanoparticles with an intermediate layer were dispersed in anhydrous ethanol, and rare earth compounds, rare earth fluorescent complexes and amine compounds were added. The mixture was stirred and reacted at room temperature. After the reaction, the nanoparticles were magnetically separated, washed and dried, and then post-treated to obtain magnetic-fluorescent bifunctional nanoparticles.

2. The method for preparing magnetic-fluorescent bifunctional nanoparticles according to claim 1, characterized in that, In step S1, the mass ratio of ferric chloride hexahydrate, sodium salt, and amine compound is 3.0–4.0:2.5–3.5:2.0–3.0; the amount of emulsifier added is 1%–3% of the total mass of amino-modified magnetic iron oxide nanoparticles.

3. The method for preparing magnetic-fluorescent bifunctional nanoparticles according to claim 1, characterized in that, In step S2, the mass ratio of amino-modified magnetic iron oxide nanoparticles to polymer monomers is 0.5:0.32-0.

64.

4. The method for preparing magnetic-fluorescent bifunctional nanoparticles according to claim 1, characterized in that, In step S3, the mass ratio of the aminated magnetic iron oxide nanoparticles with an intermediate layer, the rare earth compound, the rare earth fluorescent complex, and the amine compound is 0.4–0.6:0.35–0.5:0.4–0.6:0.18–0.

26.

5. The method for preparing magnetic-fluorescent bifunctional nanoparticles according to claim 1, characterized in that, In step S1, the temperature of the heating reaction is 180–200°C, and the reaction time is 6–10 h.

6. The method for preparing magnetic-fluorescent bifunctional nanoparticles according to claim 1, characterized in that, In step S2, the temperature of the heating reaction is 50–70°C, and the reaction time is 10–14 h.

7. The method for preparing magnetic-fluorescent bifunctional nanoparticles according to claim 1, characterized in that, The sodium salt is anhydrous sodium acetate or sodium citrate; the emulsifier is any one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or polyethylene glycol; the amine compounds used in steps S1 and S3 are independently selected from any one of hexamethylenediamine, ethylenediamine, triethylenetetramine, or polyethyleneimine; the polymer monomer is any one or a mixture of polyethylene glycol diacid, polyethyleneimine, 3-aminopropyltriethoxysilane, and 3-glycidoxypropyltrimethoxysilane; the rare earth compound is any one of europium chloride hexahydrate, europium nitrate hexahydrate, terbium chloride hexahydrate, and europium acetylacetonate; the rare earth fluorescent complex is any one or a mixture of dibenzoylmethane, trifluoroacetylacetonate, 1,10-phenanthroline, 2-thiophenecarboxyltrifluoroacetone, and acetylacetonate.

8. The method for preparing magnetic-fluorescent bifunctional nanoparticles according to claim 1, characterized in that, The post-treatment process for nanoparticles involves placing the nanoparticles in a solution of multifunctional organic small molecules with a mass concentration of 0.1%-0.5%; the multifunctional small molecules are any one or a mixture of citric acid, acrylic acid, succinic acid, malic acid, and ethylenediaminetetraacetic acid.

9. Magnetic-fluorescent bifunctional nanoparticles prepared by the preparation method according to any one of claims 1-8.

10. The application of the magnetic-fluorescent bifunctional nanoparticles prepared by the preparation method according to any one of claims 1-8 in crack detection of metallic materials and magnetic leakage detection of magnetic microcapsules.

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