Multifunctional magnetic carbon quantum dot sensor, preparation method and application

Abstract

The invention discloses a multifunctional magnetic carbon quantum dot sensor, a preparation method and application, and aims to solve the technical problems of detection and synchronous separation and recovery of Al < 3 + > in a water body. The sensor is formed by carrying out electrostatic self-assembly loading on aminated ZnFe2O4 (at) SiO2 nanoparticles and carbon quantum dots with carboxyl and hydroxyl on the surfaces, and has a core-shell structure and superparamagnetism. The preparation process comprises three steps of carbon quantum dot hydrothermal synthesis, ZnFe2O4 coated SiO2 nanoparticle coating and amino modification, and electrostatic self-assembly compounding, and the process is simple and easy to control. The sensor has specific recognition capability on Al, is excellent in anti-interference performance, can realize rapid magnetic separation by virtue of self magnetism, does not need centrifugation or filtration assistance, can be recycled after elution, and can avoid secondary pollution. Detection and adsorption separation of Al < 3 + > are synchronously achieved, the green chemistry concept is met, and the method has important application value in the fields of wastewater treatment and aluminum resource recovery.

Description

Technical Field

[0001] This invention relates to a multifunctional magnetic carbon quantum dot sensor, its preparation method, and its application. Background Technology

[0002] Aluminum ions (Al) 3+ Aluminum is a typical heavy metal pollutant in aquatic environments. Long-term excessive intake of aluminum can lead to neurodegenerative diseases such as Alzheimer's and Parkinson's. 3+ Excessive aluminum concentration can cause damage to fish gill tissue, respiratory problems, and even death, posing a serious threat to the ecosystem. Meanwhile, aluminum, a crucial strategic resource in modern industry, is known as the "vitamin of modern industry." If it were possible to achieve aluminum concentration levels in water... 3+ The detection and simultaneous separation and recycling can both prevent pollution and create social and economic benefits.

[0003] Currently, the main methods for detecting aluminum ions include stripping voltammetry, atomic absorption spectrometry, and inductively coupled plasma atomic absorption spectrometry. These methods suffer from drawbacks such as complex operation, reliance on expensive instruments, and difficulty in rapid on-site detection, thus limiting their widespread application.

[0004] Fluorescent probe technology has become a research hotspot due to its advantages such as ease of operation, no need for expensive equipment, and high sensitivity. Although various aluminum ion fluorescent probes have been developed, existing technologies still have the following shortcomings: complex preparation processes, high detection limits, and poor practical application results; probes are difficult to recycle and reuse, and the detection process requires repeated centrifugation or filtration separation, which can easily cause secondary pollution. Summary of the Invention

[0005] The present invention provides a multifunctional magnetic carbon quantum dot sensor, its preparation method, and its application in order to solve the problems existing in the prior art.

[0006] The technical solutions adopted in this invention are as follows:

[0007] A multifunctional magnetic carbon quantum dot sensor includes aminated ZnFe2O4@SiO2 nanoparticles and carbon quantum dots, wherein the carbon quantum dots are loaded onto the surface of the aminated ZnFe2O4@SiO2 nanoparticles via electrostatic self-assembly.

[0008] Furthermore, the carbon quantum dots are carbon quantum dots with carboxyl and hydroxyl functional groups on the surface; the aminated ZnFe2O4@SiO2 nanoparticles have a core-shell structure, with the core being ZnFe2O4 nanoparticles and the shell being a SiO2 layer with amino groups on the surface.

[0009] Furthermore, the mass ratio of the carbon quantum dots to the aminated ZnFe2O4@SiO2 nanoparticles is (20~40):20 (i.e. 1~2:1).

[0010] This invention also discloses a method for fabricating a multifunctional magnetic carbon quantum dot sensor, comprising the following steps:

[0011] (1) Carbon powder, water and hydrogen peroxide solution are mixed and subjected to hydrothermal reaction, and carbon quantum dots are obtained by separation and freeze drying;

[0012] (2) ZnFe2O4 nanoparticles, silicon source, alcohol, water and ammonia were mixed and coated on the surface. An amino reagent was added to the obtained ZnFe2O4@SiO2 nanoparticles for amino modification to obtain aminated ZnFe2O4@SiO2 nanoparticles.

[0013] (3) Add the carbon quantum dots obtained in step (1) and the aminated ZnFe2O4@SiO2 nanoparticles obtained in step (2) to 20 mL of deionized water, disperse them evenly by ultrasonication, add 2 mL of Tris-HCl buffer to adjust the pH of the system to 6.0~7.0, and electrostatically self-assemble for 20~50 min under room temperature and light-protected conditions. After separation, washing and drying, a multifunctional magnetic carbon quantum dot sensor is obtained.

[0014] Further, in step (1), the mass ratio of carbon powder to water is (3~5):500; the volume ratio of hydrogen peroxide solution to water is (1~2):10; and the mass concentration of hydrogen peroxide solution is 30%.

[0015] Furthermore, in step (1), the temperature of the hydrothermal reaction is 160~200 ℃ and the time is 2~6 h.

[0016] Further, in step (2), the silicon source is tetraethyl orthosilicate, methyl orthosilicate or methyltriethoxysilane; the mass ratio of ZnFe2O4 nanoparticles to silicon source is 50:(84~177.5).

[0017] Further, in step (2), the amino reagent is 3-aminopropyltriethoxysilane or trihydroxymethylaminomethane hydrochloride; the mass ratio of ZnFe2O4 nanoparticles to amino reagent is 100:(367~734).

[0018] Further, in step (3), the electrostatic self-assembly temperature is room temperature and the time is 20~50 min; the pH of the Tris-HCl buffer is 6.0~7.0; the ratio of carbon quantum dots, aminated ZnFe2O4@SiO2 nanoparticles, and deionized water is (20~40) mg:20mg:20mL; and the amount of Tris-HCl buffer used is 2 mL.

[0019] This invention also discloses a multifunctional magnetic carbon quantum dot sensor for detecting Al in wastewater. 3+ Applications.

[0020] In this magnetic carbon quantum dot sensor, the role of CQDs is to interact with Al. 3+ Fluorescence is excited upon contact, Al 3+ The selective fluorescence excitation of the nanocomposite material may be due to the interaction between CQDs and Al on the sensor surface. 3+ The formation of complexes through coordination and electrostatic interactions leads to the aggregation of CQDs, resulting in fluorescence excitation. The fluorescence enhancement is attributed to the AIEE effect, given the aggregation of CQDs. While other metal ions can form physical adsorption on the CQD surface, their binding strength and selectivity are significantly weaker than those of Al. 3 + Therefore, this magnetic carbon quantum dot sensor has the characteristics of high selectivity and high sensitivity.

[0021] In this magnetic carbon quantum dot sensor, ZnFe2O4@SiO2 nanoparticles, after amino modification, can load CQDs through electrostatic self-assembly. Furthermore, the presence of these magnetic nanoparticles allows the sensor to rapidly accumulate and separate Al from water under an external magnetic field, utilizing their own magnetism. 3+ Furthermore, it can be quickly, easily, and efficiently separated from the solution, facilitating sensor recovery. It can both control pollution and be recycled, effectively avoiding secondary pollution. It is environmentally friendly, renewable, and can be described as "three benefits in one".

[0022] This invention prepares magnetic carbon quantum dot nanofluorescent sensors (ZnFe2O4@SiO2-CQDs) by electrostatically self-assembling carbon quantum dots (CQDs) onto aminated magnetic composite particles (ZnFe2O4@SiO2-NH2). The method is simple and easy to implement.

[0023] The resulting effective effect is:

[0024] (1) High detection sensitivity and strong selectivity: The sensor has high sensitivity to Al 3+ It exhibits specific recognition capabilities, with a detection limit as low as 0.71 μM, and demonstrates good linearity within the concentration range of 0-40 μM, with a response time of only 2 minutes; it can still achieve Al under conditions where 15 competing ions coexist. 3+ Its specificity detection and anti-interference ability are significant.

[0025] (2) Convenient magnetic separation and recyclable: ZnFe2O4@SiO2 nanoparticles in the sensor endow the material with superparamagnetism, which can achieve rapid enrichment and separation under the action of an external magnetic field without the need for centrifugation or filtration; after elution with EDTA, it can be recycled, reducing the cost of use.

[0026] (3) Avoiding secondary pollution and environmentally friendly: After the detection is completed, the sensor can be completely removed from the water body through magnetic separation, and Al can be realized simultaneously. 3+The adsorption and separation processes are efficient; the entire detection process does not generate secondary pollutants, which aligns with the principles of green chemistry.

[0027] (4) Simple preparation process and stable structure: It is prepared by electrostatic self-assembly method, which is simple and easy to control; the core-shell structure effectively protects the ZnFe2O4 magnetic core, prevents agglomeration, and ensures that the sensor remains stable in aqueous solution with pH 3.0-7.0. Attached Figure Description

[0028] Figure 1 TEM images of CQDs(a), ZnFe2O4(b), and ZnFe2O4@SiO2-CQDs(c) prepared in Example 3;

[0029] Figure 2 VSM diagrams of ZnFe2O4, ZnFe2O4@SiO2 and ZnFe2O4@SiO2-CQDs prepared in Example 3 are shown in the inset, which is a physical image of the magnetic response of ZnFe2O4@SiO2-CQDs.

[0030] Figure 3 XRD patterns of CQDs, ZnFe2O4 and ZnFe2O4@SiO2-CQDs prepared in Example 3;

[0031] Figure 4 FT-IR images of CQDs, ZnFe2O4, and ZnFe2O4@SiO2-CQDs prepared in Example 3;

[0032] Figure 5 The ZnFe2O4@SiO2-CQDs prepared in Example 3 were tested under different pH conditions with or without the addition of Al. 3+ Fluorescence intensity under ionic conditions (a) and stability of ZnFe2O4@SiO2-CQDs at different times (b);

[0033] Figure 6 The ZnFe2O4@SiO2-CQDs sensor prepared in Example 3 exhibits resistance to Al under competitive ion coexistence. 3+ The selectivity and specificity of ions;

[0034] Figure 7 The image shows the sensitivity results of the ZnFe2O4@SiO2-CQDs sensor prepared in Example 3. In this image, (a) shows the fluorescence intensity at 425 nm as a function of Al. 3+ The change in ion concentration with increasing concentration, (b) represents the sensor response rate and Al 3+ The relationship between ion concentrations;

[0035] Figure 8The graph shows the cycling results of the ZnFe2O4@SiO2-CQDs sensor prepared in Example 3;

[0036] Figure 9 For Al 3+ Concentration-absorbance standard curve;

[0037] Figure 10 The ZnFe2O4@SiO2-CQDs sensor prepared in Example 3 was tested with varying adsorbent dosage (a) and Al content. 3+ The effect of different initial ion concentrations (b) on adsorption performance;

[0038] Figure 11 The image shows the fluorescence changes of ZnFe2O4 nanoparticles under 365 nm ultraviolet light irradiation in Comparative Example 1. (a1) shows a ZnFe2O4 aqueous suspension, and (a2) shows the ZnFe2O4 aqueous suspension with 100 µmol / L Al added. 3+ Solution;

[0039] Figure 12 The images show the fluorescence changes of ZnFe2O4@SiO2-NH2 nanoparticles under 365 nm UV irradiation in Comparative Example 2. (b1) shows the ZnFe2O4@SiO2-NH2 aqueous suspension, and (b2) shows the Fe3O4@SiO2-NH2 aqueous suspension with 100 µmol / L Al added. 3+ Solution;

[0040] Figure 13 The image shows the fluorescence changes of GQDs under 365 nm UV light irradiation in Comparative Example 3. (c1) is a 3 mg / L aqueous suspension of GQDs, and (c2) is a 3 mg / L aqueous suspension of GQDs with 100 µmol / L Al added. 3+ Solution. Detailed Implementation

[0041] The invention will now be further described with reference to the accompanying drawings.

[0042] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0043] This invention provides a multifunctional magnetic carbon quantum dot sensor, comprising aminated ZnFe2O4@SiO2 nanoparticles and carbon quantum dots, wherein the carbon quantum dots are loaded onto the surface of the aminated ZnFe2O4@SiO2 nanoparticles via electrostatic self-assembly.

[0044] In this invention, carbon quantum dots (CQDs) are loaded onto the surface of ZnFe2O4@SiO2-NH2 nanoparticles via electrostatic self-assembly.

[0045] This invention provides a method for fabricating the multifunctional magnetic carbon quantum dot sensor described above, comprising the following steps:

[0046] Carbon powder, water and hydrogen peroxide solution are mixed and subjected to hydrothermal reaction. The resulting carbon quantum dot mixture is then separated and freeze-dried to obtain carbon quantum dots.

[0047] ZnFe2O4 nanoparticles, silicon source, alcohol, water and ammonia were mixed and surface coated. An amino reagent was added to the obtained ZnFe2O4@SiO2 product for amino modification to obtain ZnFe2O4@SiO2-NH2.

[0048] The carbon quantum dots, ZnFe2O4@SiO2-NH2, and Tris-HCl buffer solution were mixed in deionized water and electrostatically self-assembled to obtain a multifunctional magnetic carbon quantum dot sensor.

[0049] This invention involves mixing carbon powder, water, and hydrogen peroxide solution, conducting a hydrothermal reaction, and then sequentially separating and freeze-drying the resulting carbon quantum dot mixture to obtain carbon quantum dots.

[0050] In this invention, the mass ratio of the carbon powder to water is preferably (3~5):500, more preferably (4~5):2000, and even more preferably 1:100; the volume ratio of the hydrogen peroxide solution to water is preferably (1~2):10, more preferably 1:5; and the mass concentration of the hydrogen peroxide solution is preferably 30%.

[0051] The present invention preferably involves adding water and hydrogen peroxide solution to toner, followed by sonication and then pouring the solution into a polytetrafluoroethylene reactor for hydrothermal reaction to obtain a CQDs solution that emits blue fluorescence.

[0052] In this invention, the temperature of the hydrothermal reaction is preferably 160~200 ℃, more preferably 170~180 ℃, and the time is preferably 2~6 h, more preferably 3~5 h.

[0053] After the hydrothermal reaction is completed, the present invention preferably filters the obtained carbon quantum dot mixture to remove larger impurities using filter paper, and then filters it through a 0.22 µm microporous membrane to obtain a CQDs solution. After freeze-drying, CQDs powder is obtained. The present invention does not have any special limitations on the freeze-drying process, and it can be carried out according to a process well known in the art.

[0054] This invention involves mixing ZnFe2O4 nanoparticles, a silicon source, an alcohol, water, and ammonia to perform surface coating, and then adding an amino reagent to the resulting ZnFe2O4@SiO2 product for amino modification to obtain ZnFe2O4@SiO2-NH2.

[0055] The present invention preferably uses a solvothermal method to prepare monodisperse ZnFe2O4 nanoparticles:

[0056] Glycerol, deionized water, ZnCl2, FeCl3·6H2O, and anhydrous sodium acetate were mixed in a mass ratio of 25.2:20:(0.2~0.27):0.4 (more preferably 25.2:20:(0.25~0.27):0.4), mechanically stirred for 30 min, and reacted at 180~220 °C for 16~24 h (more preferably 200 °C for 12 h). After magnetic adsorption, the mixture was washed three times with deionized water and ethanol, respectively, to obtain ZnFe2O4 nanoparticles. Anhydrous sodium acetate provided an alkaline environment for the reaction, promoting the formation of ZnFe2O4; glycerol, as a high-boiling-point organic solvent, served as the reaction carrier.

[0057] In this invention, the silicon source preferably includes tetraethyl orthosilicate, methyl orthosilicate, or methyltriethoxysilane; the solvent is preferably glycerol; the mass fraction of the ammonia is preferably 25-28%, and the ratio of ammonia to ZnFe2O4 nanoparticles is preferably 1 mL:0.1 g; this invention does not have a special limitation on the amount of glycerol and water, and can be adjusted according to actual needs to ensure uniform mixing of materials.

[0058] In this invention, the mass ratio of the ZnFe2O4 nanoparticles to the silicon source is preferably 100:(168~355), more preferably 100:(168~262); the silicon source is used in the form of an ethanol solution.

[0059] In this invention, the surface coating temperature is preferably 60 °C, and the time is preferably 16~24 h, more preferably 18~22 h.

[0060] In this invention, alcohol, water, and ammonia are mixed, and ZnFe2O4 nanoparticles are dispersed in the mixture by ultrasonication. After the mixture is homogeneous, it is mechanically stirred at 60 °C under N2 protection. At the same time, an ethanol solution of tetraethyl orthosilicate is added dropwise at a uniform rate using a dropper. After the addition is completed, the mixture is stirred to achieve surface coating.

[0061] In this invention, the amino reagent preferably includes 3-aminopropyltriethoxysilane and trihydroxymethylaminomethane hydrochloride; the mass ratio of the ZnFe2O4 nanoparticles to the amino reagent is preferably 100:(367~734), more preferably 100:(551~734).

[0062] In this invention, the temperature for amino modification is preferably 60~100 ℃, more preferably 70~90 ℃, and the time is preferably 20~28 h, more preferably 22~26 h.

[0063] After surface coating is completed, the present invention preferably adds an amino reagent to the obtained product under N2 protection to perform amino modification. After the reaction is completed, the product is separated by an external magnetic field, washed several times with anhydrous ethanol and deionized water until the supernatant is transparent, and dried under vacuum at 60 °C to obtain ZnFe2O4@SiO2-NH2 nanoparticles.

[0064] This invention mixes the carbon quantum dots, ZnFe2O4@SiO2-NH2 with Tris-HCl buffer and deionized water, and then deprotonates the carboxyl-COO groups of the carbon quantum dots through electrostatic self-assembly. - The protonated amino-NH3 group of ZnFe2O4@SiO2-NH2 + Electrostatic interactions yielded a multifunctional magnetic carbon quantum dot sensor.

[0065] In this invention, the pH of the Tris-HCl buffer solution is preferably 6.0 to 7.0, more preferably 6.5. This invention does not impose any special limitation on the amount of Tris-HCl buffer solution used, as long as the materials are mixed evenly and the reaction proceeds smoothly.

[0066] In this invention, ZnFe2O4@SiO2-NH2 and carbon quantum dots are added to 20 mL of deionized water, and after being sonicated for 10 min to mix evenly, 2 mL of Tris-HCl buffer is added to adjust the pH to 6.0~7.0, and the mixture is stirred for 30 min in a dark environment at room temperature.

[0067] In this invention, the electrostatic self-assembly temperature is preferably room temperature, and the time is preferably 20-50 min, more preferably 30 min; the reaction is preferably carried out under light-protected conditions.

[0068] After the reaction is completed, the present invention preferably separates, washes and dries the obtained product in sequence. Specifically, it is preferred to use a magnet to separate and collect the product, wash it with deionized water, and dry it in a vacuum drying oven at 50 °C for 6 h to obtain a multifunctional magnetic carbon quantum dot sensor.

[0069] In this invention, using excess carbon powder can improve the yield of CQDs, but it may lead to an increase in quantum dot size and a wider particle size distribution, thereby affecting the fluorescence quantum yield. The carboxyl group (-COOH) of CQDs is the excitation factor for its fluorescence (related to Al). 3+The key functional groups in this invention are controlled within a certain range to balance the functional group density and quantum dot dispersion. Insufficient dosage leads to insufficient functional groups, while excessive dosage increases the size and reduces the specific surface area, both ultimately affecting fluorescence intensity. Ferric chloride is a precursor for synthesizing ZnFe2O4 nanoparticles, and its dosage determines the yield and particle size of ZnFe2O4. Excessive ferric chloride leads to increased particle size and reduced magnetic responsiveness. After SiO2 coating and amination modification, the amino groups (-NH2) on the ZnFe2O4 surface combine with the carboxyl groups (-COOH) of CQDs through electrostatic self-assembly. Insufficient ferric chloride leads to insufficient amino group density on the ZnFe2O4 surface, while excessive dosage reduces the grafting site density due to excessively large particle size. Furthermore, the carbon powder requires a higher ferric chloride dosage to maintain the loading capacity of the magnetic carrier. Insufficient or excessive ferric chloride dosage will cause CQDs to aggregate after sensor synthesis, thus affecting fluorescence intensity. Similarly, too little ferric chloride will also directly affect fluorescence intensity. Therefore, the multifunctional magnetic carbon quantum dot sensor prepared by the above method and conditions has high fluorescence intensity.

[0070] This invention provides a multifunctional magnetic carbon quantum dot sensor as described in the above technical solution, or a multifunctional magnetic carbon quantum dot sensor prepared by the preparation method described in the above technical solution, for detecting Al in wastewater. 3+ Applications. This invention does not specifically limit the methods for application; any method well-known in the art can be used.

[0071] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0072] Unless otherwise specified, the experimental and testing methods described below are conventional methods; unless otherwise specified, the reagents and raw materials described below are commercially available.

[0073] Example 1

[0074] 1) Weigh 300 mg of carbon powder into a beaker, add 50 mL of deionized water and 5 mL of 30% hydrogen peroxide solution, sonicate for 2 min, pour into a polytetrafluoroethylene reactor, react at 180 ℃ for 4 h, and then remove to obtain a CQDs solution that emits blue fluorescence; first filter the above solution with filter paper to remove larger impurities, and then filter it through a 0.22 µm microporous membrane to obtain a pure CQDs solution, and then freeze-dry it to obtain CQDs powder;

[0075] 2) Measure 20 mL of deionized water and 20 mL of glycerol into a beaker using a graduated cylinder, stir, and sonicate for 10 min. Then weigh 270 mg of ferric chloride hexahydrate, 70 mg of zinc chloride, and 400 mg of anhydrous sodium acetate into the beaker, stir at room temperature for 30 min to mix thoroughly, and then place the sample in a polytetrafluoroethylene reactor and heat at 200 ℃ for 12 h. After cooling, obtain a black precipitate by magnetic separation, wash three times with deionized water and ethanol respectively to obtain the final precipitate.

[0076] 3) Using the Stöber method, SiO2 was coated onto the surface of ZnFe2O4 nanoparticles: 35 mL of ethanol, 10 mL of deionized water, and 1 mL of 25-28% ammonia solution were measured into a beaker using a graduated cylinder to obtain a mixed solution. 100 mg of the ZnFe2O4 nanoparticles prepared above were ultrasonically dispersed in the mixed solution. After thorough mixing, the solution was transferred to a three-necked round-bottom flask and mechanically stirred at 60 °C under N2 protection. Simultaneously, 20 mL of an ethanol solution containing 0.18 mL of tetraethyl orthosilicate (168 mg) was added dropwise using a dropper. After the addition was complete, stirring was continued for 20 h. After the reaction was complete, a black precipitate was obtained by magnetic separation and washed three times with deionized water and ethanol, respectively. The ZnFe2O4@SiO2 nanoparticles prepared above were then dispersed in 40 mL of anhydrous ethanol using ultrasound. 0.4 mL (367 mg) of 3-aminopropyltriethoxysilane was dispersed in 20 mL of ethanol and then slowly added dropwise to the suspension. The sample was then refluxed at 80 °C under N2 protection for 24 h. The precipitate was separated by an external magnet, washed three times each with deionized water and ethanol, and then dried to obtain ZnFe2O4@SiO2-NH2 nanoparticles.

[0077] 4) Dissolve 20 mg of CQDs powder in 20 mL of deionized water, add 20 mg of aminated ZnFe2O4@SiO2, sonicate for 10 min, add 2 mL of Tris-HCl buffer to adjust the pH of the system to 6.0-7.0, stir for 30 min in the dark and at room temperature, and then allow to settle by gravity for 10 min. Finally, wash once with deionized water and collect with a magnet, place in a vacuum drying oven at 50 ℃ and dry for 6 h to obtain a multifunctional magnetic carbon quantum dot sensor, denoted as ZnFe2O4@SiO2-CQDs.

[0078] Example 2

[0079] The only difference from Example 1 is:

[0080] In step 1), 400 mg of carbon powder is weighed and added to 10 mL of 30% hydrogen peroxide solution to obtain CQDs powder;

[0081] Step 2) Same as in Example 1, to obtain ZnFe2O4 nanoparticle powder;

[0082] In step 3), the volume of tetraethyl orthosilicate was 0.38 mL (355 mg), and the volume of 3-aminopropyltriethoxysilane was 0.6 mL (551 mg), thus obtaining ZnFe2O4@SiO2-NH2 nanoparticles.

[0083] In step 4), 30 mg of CQDs were weighed to obtain ZnFe2O4@SiO2-CQDs.

[0084] Example 3

[0085] The only difference from Example 1 is:

[0086] In step 1), 500 mg of carbon powder is weighed and added to 10 mL of 30% hydrogen peroxide solution to obtain CQDs powder;

[0087] Step 2) Same as in Example 1, to obtain ZnFe2O4 nanoparticle powder;

[0088] In step 3), the volume of tetraethyl orthosilicate was 0.28 mL (262 mg), and the volume of 3-aminopropyltriethoxysilane was 0.8 mL (734 mg), thus obtaining ZnFe2O4@SiO2-NH2 nanoparticles;

[0089] In step 4), 40 mg of CQDs were weighed to finally obtain ZnFe2O4@SiO2-CQDs.

[0090] Example 4

[0091] The only difference from Example 1 is:

[0092] Step 1) Same as in Example 1, to obtain CQDs powder;

[0093] Step 2) Same as in Example 1, to obtain ZnFe2O4 nanoparticle powder;

[0094] In step 3), the volume of tetraethyl orthosilicate was 0.38 mL (355 mg), and the volume of 3-aminopropyltriethoxysilane was 0.8 mL (734 mg), thus obtaining ZnFe2O4@SiO2-NH2 nanoparticles;

[0095] In step 4), 25 mg of CQDs were weighed to finally obtain ZnFe2O4@SiO2-CQDs.

[0096] Example 5

[0097] The only difference from Example 1 is:

[0098] In step 1), 500 mg of carbon powder is weighed and added to 10 mL of 30% hydrogen peroxide solution to obtain CQDs powder;

[0099] Step 2) Same as in Example 1, to obtain ZnFe2O4 nanoparticle powder;

[0100] In step 3), the volume of 3-aminopropyltriethoxysilane was 0.8 mL (734 mg), resulting in ZnFe2O4@SiO2-NH2 nanoparticles;

[0101] In step 4), 35 mg of CQDs were weighed to finally obtain ZnFe2O4@SiO2-CQDs.

[0102] Characterization and testing

[0103] 1) Morphological characteristics

[0104] The morphology of the CQDs, ZnFe2O4, and ZnFe2O4@SiO2-CQDs prepared in Example 3 above was characterized by transmission electron microscopy (TEM), and the results are as follows: Figure 1 As shown. Figure 1 TEM images of CQDs(a), ZnFe2O4(b), and ZnFe2O4@SiO2-CQDs(c) prepared in Example 3; as shown Figure 1 As shown in (a), the prepared GQDs are spherical, uniform in size, and well-dispersed. Statistical analysis shows that the particle size distribution of the GQDs ranges from 1.05 to 3.35 nm, with an average particle size of 2.18 nm. Figure 1 As shown in (b), the ZnFe2O4 nanoparticles have a regular shape, an average particle size of 25.31 nm, and good dispersibility. Figure 1 As shown in (c), a gray coating region is present on the surface of the ZnFe2O4 nanoparticles, corresponding to an amorphous SiO2 shell, confirming the existence of a core-shell structure. This is because the CQDs are attracted to the surface of the nanospheres by charge. Moreover, the prepared ZnFe2O4@SiO2-CQDs are spherical nanoparticles with a particle size of approximately 34.96 nm, with GQDs loaded around the surface of the nanospheres.

[0105] 2) Magnetic property test

[0106] The magnetic properties of the samples ZnFe2O4, ZnFe2O4@SiO2, and Fe3O4@SiO2-CQDs prepared in Example 3 were analyzed at room temperature using VSM technology. The results are shown in [Figure 1]. Figure 2 . Figure 2The image shows the VSM plots of ZnFe2O4, ZnFe2O4@SiO2, and ZnFe2O4@SiO2-CQDs prepared in Example 3. The inset is a physical image of the magnetic response of ZnFe2O4@SiO2-CQDs. Figure 2 As shown, no significant remanence was detected in any of the samples. The saturation magnetization of ZnFe2O4, ZnFe2O4@SiO2, and ZnFe2O4@SiO2-CQDs were 42.68 emu / g, 36.42 emu / g, and 24.19 emu / g, respectively. Their remanence and coercivity approached zero, indicating superparamagnetism. The decrease in saturation magnetization may be due to the formation of a continuous diamagnetic layer (aminosilicon layer and CQDs) on the surface of the ZnFe2O4 nanoparticles, indicating that the ZnFe2O4 nanoparticles successfully coated SiO2.

[0107] When a magnet is placed to the right of the cuvette ( Figure 2 (Inset) ZnFe2O4@SiO2-CQDs aggregate on the right side of the cuvette, while the solution on the left gradually turns colorless. These results indicate that this characteristic facilitates the rapid separation of ZnFe2O4@SiO2-CQDs sensors from the water sample, thus avoiding secondary contamination.

[0108] 3) Crystal form analysis

[0109] Figure 3 XRD patterns of CQDs, ZnFe2O4, and ZnFe2O4@SiO2-CQDs prepared in Example 3; as shown Figure 3 As shown, a new characteristic peak (002) appears at 2θ = 21.38°, with a relatively broad peak shape, indicating low crystallinity of the sample, consistent with the typical characteristics of CQDs. The eight characteristic diffraction peaks of ZnFe2O4 and ZnFe2O4@SiO2-CQDs at 18.19°, 29.82°, 35.2°, 42.87°, 53.06°, 56.6°, 62.17°, and 73.33° perfectly match the XRD standard PDF card (JCPDS no. 22-1012) of spinel-structured ZnFe2O4 crystals, indicating that the surface coating and modification process did not significantly change the crystal form of ZnFe2O4. Since the prepared SiO2 is amorphous, no diffraction peaks corresponding to SiO2 were observed. Furthermore, due to the low content, high dispersibility, and low crystallinity of CQDs in ZnFe2O4@SiO2-CQDs, the stronger peaks of ZnFe2O4 mask the weaker peaks of CQDs. Therefore, no obvious diffraction peaks of CQDs are observed.

[0110] 4) Surface structure analysis

[0111] Figure 4The images show the FT-IR spectra of CQDs, ZnFe2O4, and ZnFe2O4@SiO2-CQDs prepared in Example 3. Figure 4 As shown, ZnFe2O4 particles at 435 cm⁻¹ -1 and 575 cm -1 The strong absorption peaks at 1631 cm⁻¹ are attributed to the characteristic stretching vibrations of Zn-O and Fe-O, respectively, with complete peak shapes. -1 and 3450 cm -1 The peaks at 1706 cm⁻¹ correspond to the characteristic peaks of the bending and stretching vibrations of -OH, respectively, indicating the successful synthesis of ZnFe₂O₄ magnetic nanoparticles. -1 The strong peak at 1619 cm⁻¹ is mainly attributed to the C=O stretching vibration, indicating that CQDs retain the original carbon skeleton core structure of the carbon powder (graphite). 3410 cm⁻¹ -1 The characteristic peak at 1706 cm⁻¹ is caused by the stretching vibration of OH. -1 1600 cm -1 1395 cm -1 and 1109 cm -1 The peaks at 3434 cm⁻¹ belong to C=O, CH, and CO (alkoxy) functional groups, respectively, indicating that the CQDs surface has a large number of oxygen-containing functional groups after hydrothermal oxidation, which endows CQDs with excellent water solubility. For ZnFe₂O₄@SiO₂-CQDs nanocomposites, the peaks at 3434 cm⁻¹ are attributed to C=O, CH, and CO (alkoxy) functional groups, respectively, indicating that after hydrothermal oxidation, the CQDs surface has a large number of oxygen-containing functional groups, which endows CQDs with excellent water solubility. -1 The broad, intense peak at 2921 cm⁻¹ is attributed to the stretching vibrations of the -OH and -NH groups. -1 The peak at 1573 cm⁻¹ represents the asymmetric stretching and symmetric vibration peaks of CH. -1 The distinct peak is related to the bending vibration of the C=O group. (1076 cm⁻¹) -1 The characteristic peak at 469 cm⁻¹ corresponds to the stretching vibration of Si-O. -1 and 574 cm -1 The peaks at the specified locations are caused by the vibrations of Zn-O and Fe-O, respectively. The spectrum of this nanocomposite material contains the main characteristic peaks of CQDs (except for the peak of ZnFe2O4@SiO2-NH2), indicating that CQDs were successfully loaded onto the surface of ZnFe2O4@SiO2-NH2.

[0112] Application Example 1

[0113] The ZnFe2O4@SiO2-CQDs sensor prepared in Example 3 above was used to conduct a trivalent aluminum ion sensing and detection experiment, including the following steps:

[0114] The ZnFe2O4@SiO2-CQDs sensor was weighed and ultrasonically dispersed in ultrapure water to obtain a sensor suspension (concentration of 1 mg / mL).

[0115] Weigh out Al(NO3)3·9H2O, CuSO4·5H2O, Mg(NO3)2·6H2O, CaCl2, CdCl2·2.5H2O, ZnCl2, MnCl2, Ag2SO4, KCl, NaCl, CrCl3·6H2O, SnCl2·2H2O, FeSO4·7H2O, CoCl2·6H2O, and NH4Cl, and dissolve them in ultrapure water to prepare competing ion stock solutions with a concentration of 100 μmol / L. Dilute the pre-prepared 500 μmol / L Al(NO3)3·9H2O stock solution to prepare a 100 μmol / L Al(NO3)3·9H2O stock solution.

[0116] First, the stability of ZnFe2O4@SiO2-CQDs under different pH conditions was studied. Then, according to the experimental design, the sensor stock solution and the competing ion stock solution were mixed, ultrasonically vibrated for 30 s, and allowed to stand for 15 min before fluorescence spectroscopy was performed. Under the same conditions, Al... 3+ Competition experiments between ions and other ions. The resulting spectra are analyzed and studied to evaluate the sensor's response to Al. 3+ Ion selectivity. Next, Al... 3+ After diluting the ion stock solution proportionally (0~100 μM), transfer the same volume of sensor stock solution and add it to the same volume of Al solutions of different concentrations. 3+ In an ionic solution, the fluorescence intensity was measured after ultrasonic vibration for 30 seconds and followed by standing for 10 minutes to analyze the sensor's response to Al. 3+ Ion response sensitivity.

[0117] 1. pH stability and time responsiveness

[0118] The ZnFe2O4@SiO2-CQDs magnetic nanosensors were used in aqueous solutions with pH values ​​ranging from 3.0 to 11.0 (pH adjusted with sodium hydroxide or hydrochloric acid) to study the pH response by monitoring the relationship between fluorescence intensity and pH. 100 μmol / L Al... 3+ Mix the solution with 1 mL of sensor suspension (concentration 1 mg / mL), let stand for 2 min, place in a cuvette, and record the fluorescence intensity of the two solutions at 425 nm, i.e., with and without Al addition. 3+ ZnFe2O4@SiO2-CQDs solution containing ions.

[0119] Figure 5The ZnFe2O4@SiO2-CQDs prepared in Example 3 were tested under different pH conditions with or without the addition of Al. 3+ Fluorescence intensity under ionic conditions (a) and the stability of ZnFe2O4@SiO2-CQDs at different times (b); such as Figure 5 As shown in (a), ZnFe2O4@SiO2-CQDs exhibit excellent pH stability, with no significant fluctuations in background fluorescence regardless of pH changes. However, as an Al³⁺ sensor, its performance is significantly affected by pH. In alkaline environments, the hydrolysis and precipitation of Al³⁺ renders the fluorescence "on" effect insignificant, making it unsuitable. In contrast, within the pH range of 3.0-7.0, the addition of Al³⁺ induces a sharp increase in fluorescence intensity, with the most significant enhancement observed at pH=6.0. Considering all factors, pH=6.0 was determined to be the optimal pH value for this fluorescence sensor to detect Al³⁺.

[0120] The interaction between ZnFe2O4@SiO2-CQDs and Al was studied by monitoring the change in fluorescence intensity over time. 3+ The kinetics of reactions between ions. 1 mL of 100 μmol / L Al... 3+ The solution was mixed thoroughly with 1 mL of sensor suspension (concentration 1 mg / mL), allowed to stand for different times, and then placed in a cuvette. Fluorescence changes were measured using a fluorescence spectrophotometer. Clearly, ZnFe2O4@SiO2-CQDs react with Al... 3+ The reaction between ions only takes 2 minutes. Figure 5 (b)). As the reaction time increased to 8 min, the fluorescence signal remained essentially unchanged. Therefore, 2 min was chosen as the reaction time in subsequent experiments.

[0121] Competitive analysis

[0122] 6) Add 1 mL of the aqueous suspension of the ZnFe2O4@SiO2-CQDs magnetic nanosensor prepared in Example 3 to 1 mL of an aqueous solution of a metal ion of the same concentration (100 μmol / L) (a total of 15 metal ions, Al). 3+ Ag + Ca 2+ Cd 2+ Cr 3+ Co 2+ Cu 2+ K + Fe 2+ Mn 2+ Na + NH4 + Sn 2+ Mg 2+and Zn 2+ After ultrasonic vibration for 30 seconds, the sample was allowed to stand for 2 minutes, then placed in a cuvette. The fluorescence signal was observed using a fluorescence spectrophotometer, and the fluorescence intensity was measured. The results are shown in [Figure number missing]. Figure 6 .

[0123] Figure 6 The ZnFe2O4@SiO2-CQDs sensor prepared in Example 3 exhibits resistance to Al under competitive ion coexistence. 3+ Ion selectivity and specificity. Figure 6 The ZnFe2O4@SiO2-CQDs sensor prepared in Example 3 is shown to react to different metal ions such as Al. 3+ Ag + Ca 2+ Cd 2+ Cr 3+ Co 2+ Cu 2+ K + Fe 2+ Mn 2+ Na + NH4 + Sn 2+ Mg 2+ and Zn 2+ The fluorescence response. For example... Figure 6 As shown, even at higher concentrations, Ag + Ca 2+ Cd 2+ Cr 3+ Co 2+ Cu 2+ K + Fe 2+ Mn 2+ Na + NH4 + Sn 2+ Mg 2+ and Zn 2+ The metal ion solution did not show a significant change in fluorescence signal at 425 nm, while Al 3+ The ions underwent a blue shift and exhibited strong fluorescence excitation, further confirming that this magnetic nanosensor interacts only with Al. 3+ The ions exhibit strong fluorescence excitation and can specifically recognize Al. 3+ The presence of ions and the strong fluorescence excitation of the complexed products indicate that the prepared ZnFe2O4@SiO2-CQDs sensor possesses high specificity and selectivity. The prominent Al... 3+ Ion selectivity can be attributed to Al 3+Ions exhibit a blue shift with the carboxyl and hydroxyl functional groups on the surface of CQDs through electrostatic and coordination interactions, forming complexes with strong affinity. Other metal ions can also adsorb onto the quantum dot surface, but their ionic binding forces are weaker and their affinity is not as strong as that of Al. 3+ ion.

[0124] 7) Sensitivity analysis

[0125] Add 1 mL of sensor suspension (concentration 1 mg / mL) to 1 mL of Al at different concentrations. 3+ Solution (concentration such as) Figure 7 As shown, concentrations from low to high (0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.6, 2.3, 3, 4, 5, 7.5, 10, 12.5, 15, 18, 21, 24, 27, 30, 35, 40, 50, 60, 80, 100 μM) were added to cuvettes, mixed thoroughly, and allowed to stand for 2 min. The fluorescence intensity was then observed. The results are shown in the table below. Figure 7 .

[0126] Figure 7 The image shows the sensitivity results of the ZnFe2O4@SiO2-CQDs sensor prepared in Example 3. In this image, (a) shows the fluorescence intensity at 425 nm as a function of Al. 3+ The change in ion concentration with increasing concentration, (b) represents the sensor response rate and Al 3+ The relationship between ion concentrations; Figure 7 In the image, (a) shows ZnFe2O4@SiO2-CQDs prepared in Example 3 at different Al concentrations from 0 to 100 μM. 3+ Fluorescence spectrum in the presence of ions. (Example:) Figure 7 As shown in (a), with Al 3+ With increasing ion concentration, the fluorescence intensity of the solution at 425 nm gradually increases. Under ultraviolet light irradiation, the color of the solution gradually brightens. Furthermore, as... Figure 7 As shown in (b), the I / I0 value is compared with Al. 3+ The functional relationship of ion concentration shows that within the concentration range of 0~40 μM, ZnFe2O4@SiO2-GQDs has a significant effect on Al... 3+ The ion concentrations showed a good linear relationship (R0). 2 =0.99611, y=0.01049x+1.00324, Figure 7 (b)). By calculating the sensor's response to Al 3+The limit of detection (LOD) for the ions was 0.71 μM, which is far below the upper limit of aluminum content in drinking water specified in China's "Standards for Drinking Water Quality" (GB5749-2022) (0.2 mg / L, approximately 7.4 μM). This indicates that the prepared ZnFe2O4@SiO2-CQDs effectively inhibits the aluminum content in drinking water. 3+ Ions exhibit high sensitivity. Furthermore, such as... Figure 7 As shown in (b), Al was added under the same conditions. 3+ The fluorescence excitation effect of the competing ion solution containing the sensor was significantly enhanced after ionization. This result implies that the coexistence of various competing ions does not affect the fluorescence excitation effect of ZnFe2O4@SiO2-CQDs on Al. 3+ Ion selectivity. This indicates that the ZnFe2O4@SiO2-CQDs sensor prepared in this invention has high specificity.

[0127] The ZnFe2O4@SiO2-CQDs sensors prepared in other embodiments of the present invention also have similar excellent performance to the sensors prepared in Example 3, with high sensitivity and specificity, and easy recovery.

[0128] 8) Cyclic Analysis

[0129] To investigate recyclability, the ZnFe2O4@SiO2-CQDs sensor prepared in Example 3 was subjected to Al2O3 reaction at pH 6 and 100 μmol / L. 3+ After ion detection, the ions are recovered using a magnet, and Al is removed from their surface using EDTA solution as a stripping agent. 3+ The ions are recycled, including the following steps: (1) Wash the recovered ZnFe2O4@SiO2-CQDs with EDTA (wash with 3 mL of 0.01 M EDTA per 5 mg sensor) for 2 min; (2) Wash the ZnFe2O4@SiO2-CQDs three times with deionized water and anhydrous ethanol respectively; (3) Detect the effect of ZnFe2O4@SiO2-CQDs on Al 3+ Cyclic performance of fluorescence response of ions.

[0130] Figure 8 The graph shows the cycling results of the ZnFe2O4@SiO2-CQDs sensor prepared in Example 3, illustrating the change in fluorescence intensity of the ZnFe2O4@SiO2-CQDs prepared in Example 3 during five cycles. Figure 8 As shown, the recovered ZnFe2O4@SiO2-CQDs were successfully used for at least four consecutive cycles, and very little loss of sensing capability was observed. They have broad application potential in the field of aluminum wastewater treatment and detection.

[0131] 9) Analysis of the impact on adsorption performance

[0132] Establishing the standard curve:

[0133] Preparation of aluminum standard stock solution (1000 mg / L): Accurately weigh 13.91 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve it in a small amount of deionized water, transfer it to a 1000 mL volumetric flask, dilute to the mark with deionized water, and shake well before use.

[0134] Preparation of aluminum standard solution (50 mg / L): Accurately transfer 5.0 mL of aluminum standard stock solution into a 100 mL volumetric flask, dilute to the mark with deionized water, and shake well before use.

[0135] Alizarin Red S colorimetric reagent (0.5% w / v): Accurately weigh 0.5 g of Alizarin Red S, dissolve it, and transfer it to a 100 mL brown volumetric flask. Dilute to the mark with deionized water and mix well. Store in a brown reagent bottle at 4°C protected from light for later use.

[0136] Preparation of disodium hydrogen phosphate-citric acid buffer: Prepare 0.2 M disodium hydrogen phosphate solution and 0.2 M citric acid solution separately; then mix the two solutions in a preset ratio with continuous stirring, and use a calibrated pH meter to perform fine titration with 0.2 M disodium hydrogen phosphate or citric acid solution until the pH value of the mixed solution reaches 4.6 precisely; finally, make up the volume to the required volume and shake well for later use.

[0137] Take 50 mL colorimetric tubes (numbers 1-8) and add 2.0 mL of the above buffer solution to each. Then, add 0.0 mL, 0.5 mL, 1.0 mL, 1.5 mL, 2.0 mL, 2.5 mL, 3.0 mL, and 3.5 mL of 50 mg / L aluminum standard working solution sequentially. Next, add 1.0 mL of Alizarin Red S colorimetric reagent to each tube, shake well, and allow to stand for 10 minutes for color development. Finally, dilute to the mark with deionized water and shake well. Measure the absorbance of each tube at a wavelength of 490 nm and plot the standard curve as shown below. Figure 9 As shown, its linear equation is y=0.04974x+0.00283, R²=0.9993, indicating a good linear relationship between aluminum ion concentration and absorbance.

[0138] Through systematic research on adsorbent dosage and Al 3 The effect of initial ⁺ ion concentration on the adsorption performance of ZnFe2O4@SiO2-CQDs was investigated, and its adsorption mechanism was speculated to mainly depend on the chelation effect of surface hydroxyl and carboxyl groups and the electrostatic interaction of nanoparticles (NPs).

[0139] Add 5~35 mg (see details for specific adsorbent dosage) Figure 10ZnFe2O4@SiO2-CQDs prepared in Example 3 were dispersed in 50 mL of 25 mg / L Al. 3+ The pH of the solution is 4.6.

[0140] 25 mg of ZnFe2O4@SiO2-CQDs prepared in Example 3 were dispersed in 50 mL of Al2O3 solution at a concentration of 0–60 mg / L. 3+ solution (specific Al 3+ Initial ion concentrations are shown below. Figure 10 The solution had a pH of 4.6. Its absorbance at 490 nm was measured using a UV-Vis spectrophotometer.

[0141] Figure 10 The ZnFe2O4@SiO2-CQDs sensor prepared in Example 3 was tested with varying adsorbent dosage (a) and Al content. 3 The effect of different initial concentrations (b) of ⁺ ions on adsorption performance. From Figure 10 As can be seen in (a), the adsorbent dosage in this experiment was selected in the range of 5-35 mg. At 25 mg, the adsorption rate reached 90.8%. Further increases in dosage led to a stable adsorption rate due to active site saturation and the dynamic equilibrium of adsorption-desorption, indicating that Al... 3 ⁺ ions preferentially occupy surface active sites at a limited concentration (25 mg / L). For Al... 3 The effect of initial concentration of ⁺ ions, such as Figure 10 As shown in (b), when the concentration is ≤25 mg / L, the adsorption rate increases significantly with increasing concentration. Beyond this concentration, the adsorption rate tends to reach equilibrium due to the depletion of active sites and the dynamic desorption effect. In summary, ZnFe2O4@SiO2-CQDs exhibits good adsorption performance at pH 4.6, a dosage of 25 mg, and Al... 3 The optimal adsorption performance was achieved at an initial ⁺ ion concentration of 25 mg / L.

[0142] Adsorption performance analysis

[0143] To further analyze the material's effect on Al 3 The adsorption process of ⁺ ions was analyzed by fitting the adsorption data using the Langmuir (Equation 1) model and the Freundlich (Equation 2) model.

[0144] (1),

[0145] (2),

[0146] Where Q is the Langmuir saturated adsorption capacity, mg / g; K L The value represents the Langmuir adsorption constant, in L / mg; C eTo balance the adsorption concentration, mg / L. K f Let mg be the equilibrium constant of the Freundlich model. (1-n) L n ) / g; n is the Freundlich linear constant.

[0147] Langmuir model fit correlation (R) 2 =0.99925) is greater than the relevance of the Freundlich model (R² = 0.99925). 2 =0.97996), indicating that the adsorption process is more consistent with the Langmuir isotherm model, that is, the adsorption of Al by ZnFe2O4@SiO2-CQDs is more consistent with the Langmuir isotherm model. 3 The adsorption of ⁺ ions is mainly monolayer chemisorption.

[0148] Comparative Example 1

[0149] Measure 20 mL of deionized water and 20 mL of glycerol into a beaker using a graduated cylinder, stir, and sonicate for 10 min. Then weigh 270 mg of ferric chloride hexahydrate, 70 mg of zinc chloride, and 400 mg of anhydrous sodium acetate into the beaker, stir at room temperature for 30 min to mix thoroughly, and then place the sample in a polytetrafluoroethylene reaction vessel and heat at 200 °C for 12 h. After cooling to room temperature, collect the black precipitate using a magnet, wash it three times with ethanol and deionized water respectively, and then dry it in a vacuum drying oven at 35 °C for 6 h to obtain ZnFe2O4 nanoparticles.

[0150] The product of Comparative Example 1 was subjected to Al treatment according to the method in Application Example 1. 3+ The results of the ion sensing experiment are as follows: Figure 11 As shown, (a1) is an aqueous suspension of ZnFe2O4, and (a2) is an aqueous suspension of ZnFe2O4 with 100 µmol / L Al added. 3+ The solution showed no significant fluorescence change before and after sensing, indicating that it lacked sensing and detection capabilities.

[0151] Comparative Example 2

[0152] Measure 20 mL of deionized water and 20 mL of glycerol into a beaker using a graduated cylinder, stir, and sonicate for 10 min. Then weigh 270 mg of ferric chloride hexahydrate, 70 mg of zinc chloride, and 400 mg of anhydrous sodium acetate into the beaker, stir at room temperature for 30 min to mix thoroughly, and then place the sample in a polytetrafluoroethylene reactor and heat at 200 °C for 12 h. After cooling, obtain a black precipitate by magnetic separation, wash three times with deionized water and ethanol respectively, to obtain ZnFe₂O₄ nanoparticles.

[0153] SiO2 was coated onto the surface of ZnFe2O4 nanoparticles using the Stöber method: 35 mL of ethanol, 10 mL of deionized water, and 1 mL of 25-28% ammonia solution were measured into a beaker using a graduated cylinder to obtain a mixed solution. 100 mg of the prepared ZnFe2O4 nanoparticles were ultrasonically dispersed in the mixed solution. After homogeneous mixing, the solution was transferred to a three-necked round-bottom flask and mechanically stirred at 60 °C under N2 protection. Simultaneously, 20 mL of an ethanol solution containing 0.28 mL of tetraethyl orthosilicate (262 mg) was added dropwise using a dropper. After the addition was complete, stirring was continued for 20 h. After the reaction was complete, a black precipitate was obtained by magnetic separation and washed three times with deionized water and ethanol, respectively. The prepared ZnFe2O4@SiO2 nanoparticles were then dispersed in 40 mL of anhydrous ethanol using ultrasound. 0.8 mL (734 mg) of 3-aminopropyltriethoxysilane was dispersed in 20 mL of ethanol and then slowly added dropwise to the suspension. The sample was then refluxed at 80 °C under N2 protection for 24 h. After the reaction was complete, the sample was separated using an external magnetic field, washed several times with anhydrous ethanol and deionized water until the supernatant was clear, and dried under vacuum at 60 °C to obtain ZnFe2O4@SiO2-NH2 nanoparticles.

[0154] Following the method in Application Example 1, the sensing performance of the ZnFe2O4@SiO2-NH2 nanoparticles in Comparative Example 2 was tested, and the results are as follows: Figure 12 As shown, (b1) is a ZnFe2O4@SiO2-NH2 aqueous suspension, and (b2) is a ZnFe2O4@SiO2-NH2 aqueous suspension with 100 µmol / L Al added. 3+ Compared to the sensor ZnFe2O4@SiO2-CQDs prepared in Example 3, the solution ZnFe2O4@SiO2-NH2 in Comparative Example 2 showed no significant fluorescence change before and after sensing under the same detection conditions, and therefore did not have the function of sensing and detection.

[0155] Comparative Example 3

[0156] Weigh 500 mg of carbon powder and place it in a beaker. Add 50 mL of deionized water and 10 mL of 30% hydrogen peroxide solution. Sonicate for 2 min, pour into a polytetrafluoroethylene reactor, and react at 180 °C for 4 h. Remove the reactor to obtain a CQDs solution that emits blue fluorescence. First, filter the above solution with filter paper to remove larger impurities, and then filter it through a 0.22 µm microporous membrane to obtain a pure CQDs solution. After freeze-drying, obtain CQDs powder.

[0157] Following the method in Application Example 1, the sensing performance of the CQDs powder in Comparative Example 3 was tested, and the results are as follows: Figure 13As shown, (c1) is a 3 mg / L CQDs aqueous suspension, and (c2) is a 3 mg / L CQDs aqueous suspension with 100 µmol / L Al added. 3+ Solution; Under the same detection environment, the sensor prepared in Comparative Example 3 showed a significant fluorescence change before and after sensing compared to the sensor prepared in Example 3. CQDs can detect Al 3+ The reaction produces fluorescence excitation, but Comparative Example 3 lacks the binding of magnetic materials, making recovery difficult.

[0158] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A multifunctional magnetic carbon quantum dot sensor, characterized in that: It includes aminated ZnFe2O4@SiO2 nanoparticles and carbon quantum dots, wherein the carbon quantum dots are loaded onto the surface of the aminated ZnFe2O4@SiO2 nanoparticles via electrostatic self-assembly.

2. The multifunctional magnetic carbon quantum dot sensor as described in claim 1, characterized in that: The carbon quantum dots are carbon quantum dots with carboxyl and hydroxyl functional groups on their surface; The aminated ZnFe2O4@SiO2 nanoparticles have a core-shell structure, with the core being ZnFe2O4 nanoparticles and the shell being a SiO2 layer with amino groups on its surface.

3. The multifunctional magnetic carbon quantum dot sensor as described in claim 1, characterized in that: The mass ratio of the carbon quantum dots to the aminated ZnFe2O4@SiO2 nanoparticles is (20~40):

20.

4. A method for preparing a multifunctional magnetic carbon quantum dot sensor as described in any one of claims 1 to 3, characterized in that: Includes the following steps: (1) Carbon powder, water and hydrogen peroxide solution are mixed and subjected to hydrothermal reaction, and carbon quantum dots are obtained by separation and freeze drying; (2) ZnFe2O4 nanoparticles, silicon source, alcohol, water and ammonia were mixed and coated on the surface. An amino reagent was added to the obtained ZnFe2O4@SiO2 nanoparticles for amino modification to obtain aminated ZnFe2O4@SiO2 nanoparticles. (3) The carbon quantum dots obtained in step (1) and the aminated ZnFe2O4@SiO2 nanoparticles obtained in step (2) are mixed in Tris-HCl buffer and deionized water, and a multifunctional magnetic carbon quantum dot sensor is obtained by electrostatic self-assembly.

5. The preparation method according to claim 4, characterized in that: In step (1), the mass ratio of carbon powder to water is (3~5):500; the volume ratio of hydrogen peroxide solution to water is (1~2):10; and the mass concentration of hydrogen peroxide solution is 30%.

6. The preparation method according to claim 4, characterized in that: In step (1), the hydrothermal reaction temperature is 160~200℃ and the time is 2~6 h.

7. The preparation method according to claim 4, characterized in that: In step (2), the silicon source is tetraethyl orthosilicate, methyl orthosilicate or methyltriethoxysilane; the mass ratio of ZnFe2O4 nanoparticles to silicon source is 50:(84~177.5).

8. The preparation method according to claim 4, characterized in that: In step (2), the amino reagent is 3-aminopropyltriethoxysilane or trihydroxymethylaminomethane hydrochloride; the mass ratio of ZnFe2O4 nanoparticles to amino reagent is 100:(367~734).

9. The preparation method according to claim 4, characterized in that: In step (3), the electrostatic self-assembly temperature is room temperature and the time is 20~50 min; the pH of the Tris-HCl buffer is 6.0~7.0; The ratio of carbon quantum dots, aminated ZnFe2O4@SiO2 nanoparticles, and deionized water is (20~40) mg:20 mg:20 mL; the amount of Tris-HCl buffer is 2 mL.

10. A multifunctional magnetic carbon quantum dot sensor as described in any one of claims 1 to 3 for detecting Al in wastewater. 3+ Applications.

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