Multifunctional magnetic graphene quantum dot sensor, preparation method thereof and application of multifunctional magnetic graphene quantum dot sensor in detection of Cu < 2 + > in wastewater

Abstract

The invention provides a multifunctional magnetic graphene quantum dot sensor as well as a preparation method and application thereof in detection of Cu < 2 + > in wastewater, and belongs to the technical field of water pollution control and treatment. The multifunctional magnetic graphene quantum dot sensor disclosed by the invention comprises aminated Fe3O4 (at) SiO2 nanoparticles and graphene quantum dots, wherein the graphene quantum dots are grafted on the surfaces of the aminated Fe3O4 (at) SiO2 nanoparticles. The magnetic graphene sensor shows excellent recognition capability on Cu < 2 + >, can quickly qualitatively and quantitatively analyze copper ions in a solution, realizes detection and treatment of Cu < 2 + > ions in wastewater, is high in selectivity and sensitivity, and can quickly enrich Cu < 2 + > under the action of an external magnetic field by utilizing the magnetism of the sensor, adsorb and separate Cu < 2 + > from a water body. The method not only can treat pollution, but also can be recycled, effectively avoids secondary pollution, is environment-friendly and renewable, and has three effects in one.

Description

Technical Field

[0001] The present invention relates to the field of water pollution control and treatment technology, and in particular to a multifunctional magnetic graphene quantum dot sensor and a preparation method thereof and a method for detecting Cu in wastewater. 2+ application. Background Art

[0002] Copper ions (Cu 2+ ) is a typical heavy metal pollutant in water environment, and its excessive concentrations can cause health hazards and ecological risks with significant multiple characteristics. 2+ It can cause gastrointestinal disorders, kidney damage and abnormal nerve conduction. Pregnant women and infants are more susceptible to toxic accumulation due to their fragile metabolic systems. Intake of copper salts can cause acute poisoning (vomiting, diarrhea) and chronic liver and kidney damage. When the concentration reaches 0.1-0.2 mg / L, Cu 2+ By inhibiting the activity of cellular respiratory enzymes, copper can cause damage to fish gill tissue and deformities in shellfish larvae. Its bioaccumulation effects can be amplified along the food chain, ultimately leading to imbalances in population structure. Given the bioaccumulation and environmental persistence of copper pollution, the development of highly sensitive detection technologies has become a core focus in environmental toxicology research, water quality monitoring, and clinical diagnosis.

[0003] Currently, there are many publicly reported methods for detecting copper ions, such as stripping voltammetry, atomic absorption spectroscopy, and inductively coupled plasma spectroscopy. However, these methods are generally complex to operate and require expensive detection equipment, which greatly limits their promotion and application. Therefore, the development of new copper ion detection methods is of great significance.

[0004] Copper ion fluorescent probes have attracted considerable attention due to their ease of use, lack of expensive instrumentation, excellent detection results, and high sensitivity. These include Chinese patents CN119555653A, CN119470292A, and CN114563384B. While these reported probes exhibit high sensitivity and selectivity, they still face numerous challenges, including complex preparation processes, high detection limits, and poor practical application. Furthermore, these probes are difficult to recycle, require repeated separation aids during preparation and use, and are prone to secondary contamination during the detection process. Summary of the Invention

[0005] The purpose of the present invention is to provide a multifunctional magnetic graphene quantum dot sensor and its preparation method and its application in detecting Cu in wastewater. 2+ This multifunctional magnetic graphene quantum dot sensor can realize Cu 2+ Detection and treatment of ions, with strong selectivity and high sensitivity, can use its own magnetism to quickly enrich and adsorb and separate Cu from water under the action of an external magnetic field 2+, which can not only control pollution but also recycle and reuse, effectively avoiding secondary pollution.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a multifunctional magnetic graphene quantum dot sensor, comprising amination Fe3O4@SiO2 nanoparticles and graphene quantum dots, wherein the graphene quantum dots are grafted onto the surface of the amination Fe3O4@SiO2 nanoparticles.

[0008] The present invention provides a method for preparing the multifunctional magnetic graphene quantum dot sensor described in the above technical solution, comprising the following steps:

[0009] Mixing graphite oxide powder, water and hydrogen peroxide solution to perform a hydrothermal reaction, and sequentially separating, dialyzing and freeze-drying the resulting graphene quantum dot mixture to obtain graphene quantum dots;

[0010] Fe3O4 nanoparticles, silicon source, alcohol, water and ammonia are mixed for surface coating, and an amino reagent is added to the obtained Fe3O4@SiO2 product for amino modification to obtain Fe3O4@SiO2-NH2;

[0011] The graphene quantum dots, Fe3O4@SiO2-NH2, Tris-HCl buffer, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride are mixed and grafted to obtain a multifunctional magnetic graphene quantum dot sensor.

[0012] Preferably, the mass ratio of the graphite oxide powder to water is (1-3):2000; the volume ratio of the hydrogen peroxide solution to water is (1-2.5):20; and the mass concentration of the hydrogen peroxide solution is 30%.

[0013] Preferably, the temperature of the hydrothermal reaction is 160-200° C., and the time is 30-90 minutes.

[0014] Preferably, the silicon source includes tetraethyl orthosilicate, methyl orthosilicate or methyltriethoxysilane; the mass ratio of the Fe3O4 nanoparticles to the silicon source is 100:(46.5-93); the surface coating temperature is room temperature, and the time is 8-16 hours.

[0015] Preferably, the amino reagent includes 3-aminopropyltriethoxysilane, trishydroxymethylaminomethane hydrochloride, and sodium diethyldithiocarbamate trihydrate; and the mass ratio of the Fe3O4 nanoparticles to the amino reagent is 100:(71-142).

[0016] Preferably, the temperature for amino modification is 80-100° C., and the time is 8-16 h.

[0017] Preferably, the mass ratio of the graphene quantum dots, Fe3O4@SiO2-NH2, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 30:100:(82.6~102.6):(82.6~102.6).

[0018] Preferably, the grafting temperature is room temperature and the grafting time is 12 to 36 hours.

[0019] The present invention provides a multifunctional magnetic graphene quantum dot sensor according to the above technical solution or a multifunctional magnetic graphene quantum dot sensor prepared by the preparation method according to the above technical solution for detecting Cu in wastewater. 2+ application.

[0020] The present invention provides a multifunctional magnetic graphene quantum dot sensor, comprising amination Fe3O4@SiO2 nanoparticles and graphene quantum dots, wherein the graphene quantum dots are grafted onto the surface of amination Fe3O4@SiO2 nanoparticles. The hydroxyl and carboxyl functional groups on the surface of GQDs in the magnetic graphene sensor interact with Cu 2+ Has a strong affinity for Cu 2+ It shows excellent recognition ability and can quickly perform qualitative and quantitative analysis of copper ions in the solution, realizing the identification of Cu ions in wastewater. 2+ Detection and treatment of ions.

[0021] The role of GQDs in the magnetic graphene sensor is to 2+ After contact, quenching occurs, Cu 2+ The selective fluorescence quenching of the nanocomposite may be due to the transfer of GQDs to Cu 2+ The efficient electron transfer promotes the transfer of non-radiative electrons, i.e., excited electrons, from the GQDs on the sensor surface to the Cu 2+ The electrons then return to the GQDs ground state in a radiation-free transfer. Although other metal ions can form physical adsorption on the surface of GQDs, their binding strength and selectivity are significantly weaker than those of Cu. 2+ Therefore, the magnetic graphene sensor has the characteristics of strong selectivity and high sensitivity.

[0022] The Fe3O4@SiO2 nanoparticles in the magnetic graphene sensor can be modified with amino groups and then grafted with carboxylated GQDs through an amidation reaction. Moreover, the presence of magnetic nanoparticles enables the sensor to rapidly enrich and adsorb Cu from water under the action of an external magnetic field by utilizing its own magnetism. 2+, and can be separated from the solution quickly, simply and efficiently, making it easy to recycle the sensor. It can both control pollution and be recycled, effectively avoiding secondary pollution. It is environmentally friendly and renewable, which can be said to be "three effects in one".

[0023] The present invention prepares a magnetic graphene quantum dot nanofluorescence sensor (Fe3O4@SiO2-GQDs) by grafting graphene quantum dots (GQDs) onto amino-modified magnetic composite particles (Fe3O4@SiO2-NH2) through an amidation reaction. The method is simple and easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 TEM images of GQDs (a), Fe3O4 (b) and Fe3O4@SiO2-GQDs (c) prepared in Example 3;

[0025] Figure 2 VSM images of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-GQDs prepared in Example 3. The inset is a physical image of the magnetic response of Fe3O4@SiO2-GQDs.

[0026] Figure 3 XRD patterns of GQDs, Fe3O4 and Fe3O4@SiO2-GQDs prepared in Example 3;

[0027] Figure 4 FT-IR images of GQDs, Fe3O4 and Fe3O4@SiO2-GQDs prepared in Example 3;

[0028] Figure 5 Fe3O4@SiO2-GQDs prepared in Example 3 with or without Cu added in different pH environments 2+ Fluorescence intensity under ionic conditions (a) and the stability of Fe3O4@SiO2-GQDs themselves at different times (b);

[0029] Figure 6 The Fe3O4@SiO2-GQDs sensor prepared in Example 3 reacts with Cu in the presence of competing ions. 2+ Ion selectivity and specificity;

[0030] Figure 7 The sensitivity results of the Fe3O4@SiO2-GQDs sensor prepared in Example 3, where (a) is the fluorescence intensity at 425nm as Cu 2+ (b) shows the changes in sensor response rate and Cu 2+ The relationship between ion concentration;

[0031] Figure 8This is a graph showing the cyclic performance of the Fe3O4@SiO2-GQDs sensor prepared in Example 3;

[0032] Figure 9 Cu 2+ Concentration-absorbance standard curve;

[0033] Figure 10 The Fe3O4@SiO2-GQDs sensor prepared in Example 3 under pH (a), adsorbent dosage (b) and Cu 2+ Effect of different initial ion concentrations (c) on adsorption performance;

[0034] Figure 11 The fluorescence changes of Fe3O4 nanoparticles under 365nm ultraviolet light in comparative example 1 are shown in Figure 1, where a is Fe3O4 water suspension, and b is Fe3O4 water suspension with 100μmol / L Cu 2+ solution;

[0035] Figure 12 The fluorescence change of Fe3O4@SiO2-NH2 nanoparticles under 365nm ultraviolet light in comparative example 2 is shown in Figure 2, where a is Fe3O4@SiO2-NH2 aqueous suspension, and b is Fe3O4@SiO2-NH2 aqueous suspension with 100μmol / L of Cu 2 + solution;

[0036] Figure 13 The fluorescence changes of GQDs under 365nm ultraviolet light in comparative example 3 are shown in Figure 3, where a is a 3mg / L GQDs aqueous suspension, and b is a 3mg / L GQDs aqueous suspension in which 100μmol / L Cu is added. 2+ solution. DETAILED DESCRIPTION

[0037] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0038] The present invention provides a multifunctional magnetic graphene quantum dot sensor, comprising amination Fe3O4@SiO2 nanoparticles and graphene quantum dots, wherein the graphene quantum dots are grafted onto the surface of the amination Fe3O4@SiO2 nanoparticles.

[0039] In the present invention, graphene quantum dots GQDs are grafted onto the surface of Fe3O4@SiO2-NH2 nanoparticles through -COOH-NH2- bonds.

[0040] The present invention provides a method for preparing the multifunctional magnetic graphene quantum dot sensor described in the above technical solution, comprising the following steps:

[0041] Mixing graphite oxide powder, water and hydrogen peroxide solution to perform a hydrothermal reaction, and sequentially separating, dialyzing and freeze-drying the resulting graphene quantum dot mixture to obtain graphene quantum dots;

[0042] Fe3O4 nanoparticles, silicon source, alcohol, water and ammonia are mixed for surface coating, and an amino reagent is added to the obtained Fe3O4@SiO2 product for amino modification to obtain Fe3O4@SiO2-NH2;

[0043] The graphene quantum dots, Fe3O4@SiO2-NH2, Tris-HCl buffer, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride are mixed and grafted to obtain a multifunctional magnetic graphene quantum dot sensor.

[0044] The invention mixes graphite oxide powder, water and hydrogen peroxide solution, performs hydrothermal reaction, and sequentially separates, dialyzes and freeze-dries the obtained graphene quantum dot mixed liquid to obtain graphene quantum dots.

[0045] In the present invention, the mass ratio of the graphite oxide powder to water is preferably (1-3):2000, more preferably (1.5-2.5):2000, and further preferably 2:2000; the volume ratio of the hydrogen peroxide solution to water is preferably (1-2.5):20, more preferably (1.5-2):20; and the mass concentration of the hydrogen peroxide solution is preferably 30%.

[0046] The present invention preferably adds water to the graphite oxide powder, ultrasonically treats it, and then adds a hydrogen peroxide solution for ultrasonic treatment. The solution is poured into a polytetrafluoroethylene reactor for hydrothermal reaction to obtain a GQDs solution that emits blue fluorescence.

[0047] In the present invention, the temperature of the hydrothermal reaction is preferably 160-200° C., more preferably 170-180° C., and the time is preferably 30-90 min, more preferably 50-70 min.

[0048] After completing the hydrothermal reaction, the present invention preferably filters and separates the obtained graphene quantum dot mixture through a 0.22 μm microporous filter membrane, transfers it to a dialysis bag (molecular weight cutoff: 3500da), and simultaneously dissolves the MnO2 powder in deionized water by ultrasound as a dialysis solution (catalytic decomposition of excess H2O2, H2O2+MnO2→H2O+O2↑) and adds it to another identical dialysis bag. The two dialysis bags are dialyzed until no more bubbles are generated in the solution, that is, the excess H2O2 is completely decomposed, and then the manganese dioxide suspension is replaced with deionized water, and further dialyzed to remove any trace dissolved manganese dioxide molecules that may exist to obtain a GQDs solution. After freeze-drying, GQDs powder is obtained. The present invention has no special limitation on the freeze-drying, and it can be carried out according to the process well known in the art.

[0049] The present invention mixes Fe3O4 nanoparticles, a silicon source, alcohol, water and ammonia water for surface coating, and adds an amino reagent to the obtained Fe3O4@SiO2 product for amino modification to obtain Fe3O4@SiO2-NH2.

[0050] The present invention preferably adopts a solvent thermal method to prepare monodisperse Fe3O4 nanoparticles:

[0051] Ethylene glycol, diethylene glycol, FeCl3·6H2O and anhydrous sodium acetate were dissolved by ultrasonication for 20 minutes in a mass ratio of 41.74:41.93:(0.16-0.21):3.75 (more preferably 41.74:41.93:(0.16-0.18):3.75), and reacted at 180-200°C for 8-16 hours (more preferably 180°C for 8 hours), and after magnetic absorption, washed with deionized water and ethanol three times respectively, and dried in a 35°C oven for 6 hours to obtain Fe3O4 nanoparticles. Among them, anhydrous sodium acetate was used as a reducing agent to reduce part of Fe 3+ Reduction to Fe 2+ ; Ethylene glycol and diethylene glycol are high-boiling point organic solvents used as carriers for the reaction.

[0052] In the present invention, the silicon source preferably includes tetraethyl orthosilicate, methyl orthosilicate or methyltriethoxysilane; the alcohol is preferably ethanol; the mass fraction of the ammonia water is preferably 25-28%, and the dosage ratio of the ammonia water to the Fe3O4 nanoparticles is preferably 1mL:0.1g; the present invention has no special limitation on the dosage of the alcohol and water, and can be adjusted according to actual needs to ensure uniform mixing of the materials.

[0053] In the present invention, the mass ratio of the Fe3O4 nanoparticles to the silicon source is preferably 100:(46.5-93), more preferably 100:(74.4-85); the silicon source is used in the form of an ethanol solution.

[0054] In the present invention, the surface coating temperature is preferably room temperature, and the coating time is preferably 8 to 16 hours, more preferably 10 to 12 hours.

[0055] The present invention preferably mixes alcohol, water and ammonia water, disperses Fe3O4 nanoparticles in the mixture by ultrasonication, and after the mixture is evenly mixed, mechanically stirs at room temperature, and simultaneously drips an ethanol solution of tetraethyl orthosilicate at a uniform speed using a rubber-tipped dropper. After the dripping is completed, the mixture is stirred for surface coating.

[0056] In the present invention, the amino reagent preferably includes 3-aminopropyltriethoxysilane, trishydroxymethylaminomethane hydrochloride or sodium diethyldithiocarbamate trihydrate; the mass ratio of the Fe3O4 nanoparticles to the amino reagent is preferably 100:(71-142), more preferably 100:(71-113.6).

[0057] In the present invention, the temperature for amino modification is preferably 80-100° C., more preferably 90-100° C., and the time is preferably 8-16 h, more preferably 10-12 h.

[0058] After the surface coating is completed, the present invention preferably adds an amino reagent to the obtained product under N2 protection to carry out amino modification. After the reaction is completed, it is separated using an external magnetic field, washed several times with anhydrous ethanol and deionized water until the supernatant is transparent, and dried at 60°C in vacuum to obtain Fe3O4@SiO2-NH2 nanoparticles.

[0059] The present invention mixes the graphene quantum dots, Fe3O4@SiO2-NH2 with Tris-HCl buffer, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and performs grafting to obtain a multifunctional magnetic graphene quantum dot sensor.

[0060] In the present invention, the pH of the Tris-HCl buffer is preferably 6.0 to 7.0, more preferably 6.5. The present invention has no particular limitation on the amount of the Tris-HCl buffer, as long as the materials are mixed evenly and the reaction proceeds smoothly.

[0061] In the present invention, the mass ratio of the graphene quantum dots, Fe3O4@SiO2-NH2, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is preferably 30:100:(82.6~102.6):(82.6~102.6), and more preferably 30:100:92.6:92.6.

[0062] The present invention preferably adds 9N-hydroxysuccinimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and graphene quantum dots to Tris-HCl buffer, stirs at room temperature for 30 minutes, and then adds Fe3O4@SiO2-NH2 and stirs in the dark for grafting.

[0063] In the present invention, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride are used to activate the carboxyl groups on GQDs and the amino groups on the aminated ferrosoferric oxide nanoparticles, facilitating an amidation reaction between the two and thus successfully grafting GQDs.

[0064] In the present invention, the grafting temperature is preferably room temperature, the grafting time is preferably 12 to 36 hours, more preferably 24 hours; and the grafting is preferably carried out in the dark.

[0065] After the grafting 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 three times with deionized water, and dry it in a vacuum drying oven at 50°C for 6 hours to obtain a multifunctional magnetic graphene quantum dot sensor.

[0066] In the present invention, the use of excess graphite oxide can increase the yield of GQDs, but it may lead to an increase in quantum dot size and a broadening of the particle size distribution, thereby affecting the fluorescence quantum yield. The hydroxyl (-OH) and carboxyl (-COOH) groups of GQDs are the fluorescence quenchers (for Cu 2+ ), the present invention controls the amount of graphite oxide within a certain range to balance the functional group density and quantum dot dispersibility. Too little dosage will lead to insufficient functional groups, while excessive dosage will reduce the specific surface area due to increased size, which will ultimately affect the fluorescence intensity. Ferric chloride is a precursor for synthesizing Fe3O4 nanoparticles. Its dosage determines the yield and particle size of Fe3O4. Excessive ferric chloride will cause the particle size to increase and reduce the magnetic responsiveness. After the Fe3O4 surface is coated with SiO2 and amino-modified, its surface amino group (-NH2) is grafted with the carboxyl group (-COOH) of GQDs through an amidation reaction. Insufficient ferric chloride dosage will lead to insufficient amino group density on the Fe3O4 surface, while excessive dosage will reduce the grafting site density due to excessive particle size. In addition, excessive graphite oxide requires a higher ferric chloride dosage to maintain the loading capacity of the magnetic carrier. If the amount of ferric chloride is insufficient or excessive, it will cause GQDs to agglomerate after the sensor is synthesized, thereby affecting the fluorescence intensity. Similarly, too little ferric chloride dosage will also directly affect the fluorescence intensity. Therefore, the multifunctional magnetic graphene quantum dot sensor prepared by the present invention using the above method and conditions has high fluorescence intensity.

[0067] The present invention provides a multifunctional magnetic graphene quantum dot sensor according to the above technical solution or a multifunctional magnetic graphene quantum dot sensor prepared by the preparation method according to the above technical solution for detecting Cu in wastewater. 2+ The present invention has no particular limitation on the method of application, and the application can be carried out according to methods well known in the art.

[0068] 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 by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0069] The following experimental methods and detection methods, unless otherwise specified, are conventional methods; the following reagents and raw materials, unless otherwise specified, are commercially available.

[0070] Example 1

[0071] 1) Weigh 10 mg of graphite oxide powder and put it into a round-bottom flask, add 20 mL of deionized water, ultrasonicate for 2 minutes, then add 1 mL of 30% hydrogen peroxide solution, ultrasonicate for 1 minute, pour it into a polytetrafluoroethylene reactor, react at 170 ° C for 70 minutes, and then take it out to obtain a GQDs solution emitting blue fluorescence; the above solution is filtered through a 0.22 μm microporous filter membrane and transferred to a dialysis bag (molecular weight cutoff: 3500 Da), and at the same time, weigh 0.1 g of MnO2 powder and dissolve it in 20 mL of deionized water as a dialysate, add it to another identical dialysis bag, place the above two dialysis bags in a beaker and dialyze until no bubbles are generated in the solution, then replace the manganese dioxide suspension in the beaker with deionized water, further dialyze to obtain a pure GQDs solution, and freeze-dry to obtain GQDs powder;

[0072] 2) Weigh 0.16 g of ferric chloride hexahydrate and add it to a beaker, then weigh 3.75 g of anhydrous sodium acetate, and use a graduated cylinder to measure 37.5 mL of ethylene glycol and 37.5 mL of diethylene glycol, respectively, and add them to the beaker. Stir and sonicate for 20 minutes to obtain an orange solvent, which is then evenly added to two polytetrafluoroethylene reactors. The mixture is reacted at 200°C for 8 hours, removed from the reactor, cooled to room temperature, and the resulting black precipitate is collected using a magnet. The precipitate is washed three times with ethanol and three times with deionized water, respectively, and dried in a vacuum drying oven at 35°C for 6 hours to obtain Fe3O4 nanoparticles.

[0073] 3) Adoption Method, coating SiO2 on the surface of Fe3O4 nanoparticles: use a measuring cylinder to measure 80mL of ethanol, 20mL of deionized water and 1mL of ammonia water with a mass fraction of 25-28% in a beaker to obtain a mixed solution, weigh 0.1g of the Fe3O4 nanoparticles prepared above and ultrasonically disperse them in the mixed solution. After mixing evenly, transfer them to a three-necked round-bottom flask and mechanically stir them at room temperature. At the same time, use a rubber-tipped dropper to uniformly add 20mL of ethanol solution mixed with 0.1mL of tetraethyl orthosilicate (93mg). After the addition is completed, continue stirring for 12h; after the reaction is completed, heat the water bath to 100℃, add 0.15mL (142mg) of 3-aminopropyltriethoxysilane under N2 protection, and continue the reaction for 12h. After the reaction is completed, separate with an external magnetic field, wash with anhydrous ethanol and deionized water several times until the supernatant is transparent, and dry in a vacuum at 60℃ to obtain Fe3O4@SiO2-NH2 nanoparticles;

[0074] 4) To a pH 6.5 Tris-HCl buffer, 92.6 mg of N-hydroxysuccinimide and 92.6 mg of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 10 mL of the above-mentioned GQDs aqueous suspension (3.0 mg / mL) were added and stirred at room temperature for 30 min. Then, 100 mg of Fe3O4@SiO2-NH2 nanoparticles dispersed in 40 mL of methanol solution were added and stirred in the dark for 24 h. The product was collected with a magnet, washed three times with deionized water, and dried in a vacuum drying oven at 50°C for 6 h to obtain a multifunctional magnetic graphene quantum dot sensor, which was recorded as Fe3O4@SiO2-GQDs.

[0075] Example 2

[0076] The only difference from Example 1 is:

[0077] In step 1), 20 mg of graphite oxide powder was weighed to obtain GQDs powder;

[0078] In step 2), 0.21 g of ferric chloride hexahydrate was weighed to obtain Fe3O4 nanoparticle powder;

[0079] In step 3), the volume of tetraethyl orthosilicate was 0.08 mL (74.4 mg) and the volume of 3-aminopropyltriethoxysilane was 0.12 mL (113.6 mg) to obtain Fe3O4@SiO2-NH2 nanoparticles;

[0080] In step 4), 82.6 mg of N-hydroxysuccinimide and 82.6 mg of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride were weighed to obtain Fe3O4@SiO2-GQDs.

[0081] Example 3

[0082] The only difference from Example 1 is:

[0083] In step 1), 30 mg of graphite oxide powder was weighed and 1.5 mL of 30% hydrogen peroxide solution was added to obtain GQDs powder;

[0084] In step 2), 0.18 g of ferric chloride hexahydrate was weighed to obtain Fe3O4 nanoparticle powder;

[0085] Step 3) The same as in Example 1, to obtain Fe3O4@SiO2-NH2 nanoparticles;

[0086] Step 4) is the same as in Example 1 to obtain Fe3O4@SiO2-GQDs.

[0087] Example 4

[0088] The only difference from Example 1 is:

[0089] In step 1), 25 mg of graphite oxide powder was weighed and 1.5 mL of 30% hydrogen peroxide solution was added to obtain GQDs powder;

[0090] In step 2), 0.21 g of ferric chloride hexahydrate was weighed to obtain Fe3O4 nanoparticle powder;

[0091] In step 3), the volume of tetraethyl orthosilicate is 0.05 mL (46.5 mg), and the volume of 3-aminopropyltriethoxysilane is 0.075 mL (71 mg) to obtain Fe3O4@SiO2-NH2 nanoparticles;

[0092] Step 4) is the same as in Example 1 to obtain Fe3O4@SiO2-GQDs.

[0093] Example 5

[0094] The only difference from Example 1 is:

[0095] In step 1), 15 mg of graphite oxide powder was weighed to obtain GQDs powder;

[0096] Step 2) The same as in Example 1, obtaining Fe3O4 nanoparticle powder;

[0097] In step 3), the volume of tetraethyl orthosilicate was 0.08 mL (74.4 mg) and the volume of 3-aminopropyltriethoxysilane was 0.12 mL (113.6 mg) to obtain Fe3O4@SiO2-NH2 nanoparticles;

[0098] In step 4), 102.6 mg of N-hydroxysuccinimide and 102.6 mg of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride were weighed to obtain Fe3O4@SiO2-GQDs.

[0099] Characterization and testing

[0100] 1) Morphology characterization

[0101] The morphologies of GQDs, Fe3O4 and Fe3O4@SiO2-GQDs prepared in Example 3 were characterized by transmission electron microscopy (TEM). Figure 1 shown. Figure 1 TEM images of GQDs (a), Fe3O4 (b) and Fe3O4@SiO2-GQDs (c) prepared in Example 3; Figure 1 As shown in (a), the prepared GQDs quantum dots are spherical, uniform in size, and well dispersed. According to statistics, the particle size distribution of GQDs is 1.05 to 3.35 nm, with an average particle size of 2.18 nm. Figure 1 As shown in (b), the Fe3O4 nanoparticles have regular shapes, an average particle size of 163.67nm, and good dispersibility. Figure 1 As shown in (c), the surface of the Fe3O4 nanoparticles is coated with a gray region corresponding to an amorphous SiO2 shell, confirming the presence of a core-shell structure. This is due to the GQDs being coated onto the surface of the nanospheres via amide bonds. Furthermore, the prepared Fe3O4@SiO2-GQDs are spherical nanoparticles with a diameter of approximately 188.25 nm, with the GQDs loaded around the surface of the nanospheres.

[0102] 2) Magnetic performance test

[0103] At room temperature, the magnetic properties of the samples Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-GQDs prepared in Example 3 were analyzed using VSM technology. The results are shown in Figure 2 . Figure 2 The VSM diagrams of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-GQDs prepared in Example 3 are shown in the inset, which is the actual magnetic response diagram of Fe3O4@SiO2-GQDs. Figure 2 As shown, no significant remanence was detected in any of the samples. The saturation magnetizations of Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2-GQDs were 69.79 emu / g, 51.34 emu / g, and 35.72 emu / g, respectively. Their remanence and coercivity approached zero, indicating superparamagnetism. The reduction in saturation magnetization is likely due to the formation of a continuous antimagnetic layer (aminosilicon layer and GQDs) on the surface of the Fe3O4 nanoparticles, indicating that the Fe3O4 nanoparticles are successfully coated with SiO2.

[0104] When a magnet is placed on the right side of the cuvette ( Figure 2(middle inset), Fe3O4@SiO2-GQDs aggregate on the right side of the cuvette, while the solution on the left gradually turns colorless. These results indicate that this property facilitates the rapid separation of the Fe3O4@SiO2-GQDs sensor from the measured water sample, thus avoiding secondary contamination.

[0105] 3) Crystal form analysis

[0106] Figure 3 The XRD patterns of GQDs, Fe3O4 and Fe3O4@SiO2-GQDs prepared in Example 3 are shown in FIG. Figure 3 As shown, a new characteristic peak (002) appears at 2θ = 26.23°, which is consistent with the inter-graphene distance, indicating that the prepared GQDs have good crystallinity. The six characteristic diffraction peaks of Fe3O4 and Fe3O4@SiO2-GQDs at 30.13°, 35.48°, 43.22°, 53.58°, 57.16°, and 62.65° are completely consistent with the XRD standard PDF card (JCPDS no. 19-0629) of spinel Fe3O4 crystals, indicating that the surface coating and modification process did not significantly change the crystal form of Fe3O4. Due to the amorphous nature of the prepared SiO2, no diffraction peaks corresponding to SiO2 were observed. In addition, due to the low content, high dispersion, and low crystallinity of the GQDs in Fe3O4@SiO2-GQDs, the stronger peaks of Fe3O4 partially obscure the weaker peaks of the GQDs. Therefore, no obvious diffraction peak of GQDs appears.

[0107] 4) Surface structure analysis

[0108] Figure 4 FT-IR images of GQDs, Fe3O4 and Fe3O4@SiO2-GQDs prepared in Example 3. Figure 4 As shown, Fe3O4 particles are at 585cm -1 The strong absorption peak at 1602cm corresponds to the characteristic stretching absorption peak of Fe-O. This peak has a complete shape. -1 and 3422cm -1 The peaks at 1619cm correspond to the bending vibration and stretching vibration characteristic peaks of -OH, indicating the successful synthesis of Fe3O4 magnetic nanoparticles. -1 The strong peak at 3418 cm is mainly attributed to the C=C stretching vibration of polycyclic aromatic hydrocarbons, indicating that GQDs retain the structure of graphene. -1 The characteristic peak at 1725 cm is caused by the stretching vibration of OH. -1 、1401cm -1 and 1049cm -1The peaks at 3417 cm-1 are attributed to C=O, CO (carboxyl) and CO (alkoxy) functional groups, indicating that after hydrothermal oxidation, the surface of GQDs has a large number of oxygen-containing functional groups, which gives GQDs excellent water solubility. -1 The broad and strong peak at 2970cm is attributed to the stretching vibration peaks of -OH and -NH groups. -1 The peaks at 1573 cm represent the asymmetric stretching vibration and symmetric vibration peaks of CH. -1 The clear peak at 1070 cm is associated with the bending vibration of the C=C group. -1 The characteristic peak at 584 cm corresponds to the stretching vibration of Si-O. -1 The peak at is caused by the vibration of Fe-O. The spectrum of the nanocomposite contains the main characteristic peaks of GQDs (except the peak of Fe3O4@SiO2-NH2), which indicates that GQDs are successfully grafted on the surface of Fe3O4@SiO2-NH2.

[0109] Application Example 1

[0110] The Fe3O4@SiO2-GQDs sensor prepared in Example 3 was used to perform a divalent copper ion sensing test, which included the following steps:

[0111] The Fe3O4@SiO2-GQDs sensor was weighed and dispersed in ultrapure water by ultrasonication to obtain a sensor suspension (concentration of 1 mg / mL).

[0112] Weigh CuSO4·5H2O, Mg(NO3)2·6H2O, CaCl2, CdCl2·2.5H2O, ZnCl2, MnCl2, Ag2SO4, KCl, NaCl, and NH4Cl and dissolve them in ultrapure water to prepare competing ion stock solutions at a concentration of 100 μmol / L. Dilute the pre-prepared 500 μmol / L CuSO4·5H2O stock solution to prepare a 100 μmol / L CuSO4·5H2O stock solution.

[0113] First, the stability of Fe3O4@SiO2-GQDs in different pH environments was studied. Then, the sensor stock solution was mixed with the competitive ion stock solution according to the concentration and ratio designed in the experiment. After ultrasonic vibration for 30 seconds, it was allowed to stand for 15 minutes, and then the fluorescence spectrum test was performed. 2+ Competition experiments between Cu and other ions were conducted. The obtained spectra were analyzed and studied to evaluate the sensor's performance on Cu 2+ ion selectivity. Then, Cu 2+After the ion mother solution was diluted in proportion (0-140 μM), the same volume of sensor stock solution was added to the same volume of Cu 2+ In the ion solution, ultrasonic vibration was performed for 30 seconds and then the fluorescence intensity was tested after 10 minutes of standing. The fluorescence intensity of the sensor was analyzed. 2+ Response sensitivity of ions.

[0114] 1. pH stability and time responsiveness

[0115] The Fe3O4@SiO2-GQDs magnetic nanosensor was used in aqueous solution with a pH range of 3.0 to 11.0 (pH adjusted by sodium hydroxide or hydrochloric acid) to study the pH response by monitoring the relationship between fluorescence intensity and pH value. 2+ The solution was mixed evenly with 1 mL of sensor suspension (concentration of 1 mg / mL), allowed to stand for 2 min, and placed in a cuvette. The fluorescence intensity of the two solutions at 425 nm was recorded, indicating whether Cu was added or not. 2+ ionic Fe3O4@SiO2-GQDs solution.

[0116] Figure 5 Fe3O4@SiO2-GQDs prepared in Example 3 with or without Cu added in different pH environments 2+ Fluorescence intensity under ionic conditions (a) and the stability of Fe3O4@SiO2-GQDs themselves at different times (b); Figure 5 As shown in (a), as the pH value increases from 2 to 7, the intensity of Fe3O4@SiO2-GQDs increases and tends to be stable under alkaline conditions; however, at each pH value, as Cu 2+ The addition of ions causes a sharp drop in fluorescence intensity, and the fluorescence quenching value first increases and then decreases. It reaches its maximum value at pH = 6.0, which is the best quenching effect. Therefore, pH = 6.0 is selected.

[0117] The fluorescence intensity of Fe3O4@SiO2-GQDs and Cu 2+ Kinetic behavior of the reaction between ions. 2+ The solution was mixed evenly with 1 mL of sensor suspension (concentration of 1 mg / mL), allowed to stand for different time periods, and then placed in a cuvette to measure the fluorescence change using a fluorescence spectrophotometer. 2+ The reaction between ions only takes 2 minutes ( Figure 5 As the reaction time increased to 8 min, the fluorescence signal remained essentially unchanged, so 2 min was selected as the reaction time in subsequent experiments.

[0118] Competitive Analysis

[0119] 6) 1 mL of the aqueous suspension of the Fe3O4@SiO2-GQDs magnetic nanosensor prepared in Example 3 was added to 1 mL of a metal ion aqueous solution of the same concentration (100 μmol / L) (a total of 10 metal ions Cu 2+ , Mg 2+ , Ca 2+ , Cd 2+ , Zn 2+ , Mn 2+ , Ag + , K + , Na + and NH4 + ), ultrasonically vibrate for 30 seconds, then let it stand for 2 minutes, put it into a cuvette, observe the fluorescence signal with a fluorescence spectrophotometer, and test the fluorescence intensity. The results are shown in Figure 6 .

[0120] Figure 6 The Fe3O4@SiO2-GQDs sensor prepared in Example 3 reacts with Cu in the presence of competing ions. 2+ Ion selectivity and specificity. Figure 6 The Fe3O4@SiO2-GQDs sensor prepared in Example 3 shows the sensitivity of different metal ions such as Cu 2+ , Mg 2 + , Ca 2+ , Cd 2+ , Zn 2+ , Mn 2+ , Ag + , K + , Na + and NH4 + The fluorescence response of Figure 6 As shown, even at higher concentrations, Mg 2 + , Ca 2+ , Cd 2+ , Zn 2+ , Mn 2+ , Ag + , K + , Na + and NH4 + There is no obvious fluorescence signal change in metal ion solutions, but Cu 2 + ions have a strong fluorescence quenching phenomenon at 425nm, which further confirms that the magnetic nanosensor only interacts with Cu 2+ Ions have a strong quenching effect and can specifically recognize Cu 2+ions, and the complex product has a strong fluorescence quenching effect, indicating that the prepared Fe3O4@SiO2-GQDs sensor has high specific selectivity. 2+ Ion selectivity can be attributed to Cu 2+ The strong affinity between ions and the carboxyl and hydroxyl functional groups on the surface of GQDs leads to the transfer of ions from GQDs to Cu 2+ The effective electron transfer of ions promotes non-radiative electron / hole recombination annihilation. Some other metal ions can also be adsorbed on the surface of quantum dots, but the ion binding force is weaker and the binding affinity is not as good as Cu 2+ ion.

[0121] 7) Sensitivity analysis

[0122] 1 mL of sensor suspension (concentration of 1 mg / mL) + 1 mL of Cu with different concentrations 2+ Solution (concentration as Figure 7 As shown, the concentrations from low to high are 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, 110, 140 μM) were put into a cuvette and mixed evenly. The mixture was allowed to stand for 2 minutes and the fluorescence intensity was observed. The results are shown in the table. Figure 7 .

[0123] Figure 7 The sensitivity results of the Fe3O4@SiO2-GQDs sensor prepared in Example 3, where (a) is the fluorescence intensity at 425nm as Cu 2+ (b) shows the changes in sensor response rate and Cu 2+ The relationship between ion concentration; Figure 7 (a) Fe3O4@SiO2-GQDs prepared in Example 3 at different concentrations of Cu from 0 to 140 μM 2+ Fluorescence spectrum when ions exist. Figure 7 As shown in (a), as Cu 2+ With the increase of ion concentration, the fluorescence intensity of the solution at 425nm gradually decreased. Under ultraviolet light, the color of the solution gradually darkened. In addition, the I0 / I value and Cu 2+ The functional relationship of ion concentration shows that in the concentration range of 0 to 40 μM, Fe3O4@SiO2-GQDs has a strong affinity for Cu 2+ The ion concentration showed a good linear relationship (R 2 =0.9951,y=0.2704x+1.1794, Figure 7 (b)). By calculating the magnetic quantum dots to Cu 2+The detection limit (LOD) of the ion is 0.13 μM, which is much lower than the U.S. Environmental Protection Agency's regulations on Cu 2+ in drinking water. 2+ The upper limit of the ion content (20 μM) indicates that the prepared Fe3O4@SiO2-GQDs has a good 2+ ions have a high sensitivity. In addition, Figure 7 As shown in (b), under the same conditions, Cu 2+ The fluorescence quenching effect of the competitive ion solution containing the sensor was significantly enhanced after the addition of ions, which means that the coexistence of various competitive ions will not affect the fluorescence quenching of Fe3O4@SiO2-GQDs on Cu 2+ Ion selectivity. This shows that the Fe3O4@SiO2-GQDs sensor prepared in the present invention has high specificity.

[0124] The Fe3O4@SiO2-GQDs sensors prepared in other embodiments of the present invention also have excellent performance similar to that of the sensor prepared in Example 3, with high sensitivity and strong specificity, and easy recovery.

[0125] 8) Circularity analysis

[0126] In order to study the recyclability, the Fe3O4@SiO2-GQDs sensor prepared in Example 3 was subjected to Cu2+ reaction at pH 7 and 100 μmol / L. 2+ After ion detection, the copper on the surface was removed by magnet recovery and EDT A solution was used as a stripping agent. 2+ Ions are recycled, including the following steps:

[0127] (1) The recovered Fe3O4@SiO2-GQDs were washed with EDTA (3 mL of 0.01 M EDTA was used for each 5 mg sensor) for 2 min; (2) The Fe3O4@SiO2-GQDs were washed three times with deionized water and anhydrous ethanol respectively; (3) The Fe3O4@SiO2-GQDs were tested for Cu 2+ Cyclic performance of the fluorescence responsiveness of ions.

[0128] Figure 8 This is a graph showing the cycling results of the Fe3O4@SiO2-GQDs sensor prepared in Example 3, which shows the changes in the fluorescence intensity of the Fe3O4@SiO2-GQDs sensor prepared in Example 3 during five cycling experiments. Figure 8 As shown, the recycled Fe3O4@SiO2-GQDs were successfully used for at least four consecutive cycles, and very little loss of sensing ability was observed. This has broad application potential in the field of copper wastewater treatment and detection.

[0129] 9) Analysis of adsorption performance

[0130] Establishment of standard curve:

[0131] Preparation of copper standard stock solution (250 mg / L): Weigh 0.977 g of copper sulfate pentahydrate (CuSO4·5H2O) and dissolve it in a 1000 mL volumetric flask, and make up to volume with deionized water.

[0132] Preparation of copper standard solution (25 mg / L): Take 10 mL of copper standard stock solution and dilute to 100 mL volumetric flask for later use.

[0133] Copper reagent standard solution (100 mg / L): Accurately weigh 0.1 g of diethyldithiocarbamic acid (DDTC-Na), dissolve it in a 1000 mL brown volumetric flask, make up to volume with deionized water, and store in a dark place until used.

[0134] Take 0mL, 0.5mL, 1.0mL, 1.5mL, 2.0mL, 2.5mL, 3.0mL, and 3.5mL of copper standard solution in 50mL colorimetric tubes No. 1-8 in sequence, make up to volume with deionized water, add 25mL of copper reagent standard solution respectively, measure the absorbance at a wavelength of 452nm, and draw a standard curve as shown below: Figure 9 As shown, the linear equation is y = 0.1318x + 0.0011, R 2 =0.9996, indicating that there is a good linear relationship between copper ion concentration and absorbance.

[0135] By systematically studying the pH of the solution, the amount of adsorbent added and the Cu 2+ The effect of initial ion concentration on the adsorption performance of Fe3O4@SiO2-GQDs was studied, and its adsorption mechanism was speculated to be mainly dependent on the chelation effect of surface hydroxyl and carboxyl groups and the electrostatic interaction of nanoparticles (NPs).

[0136] 25 mg of Fe3O4@SiO2-GQDs prepared in Example 3 were dispersed in 50 mL of 25 mg / L Cu 2+ In the solution, use sodium hydroxide or hydrochloric acid to adjust the pH to 2-8 (see Figure 10 ).

[0137] 5~35mg (specific adsorbent dosage see Figure 10 ) The Fe3O4@SiO2-GQDs prepared in Example 3 were dispersed in 50 mL of 25 mg / L Cu 2+ In solution, the pH of the solution is 7;

[0138] 25 mg of Fe3O4@SiO2-GQDs prepared in Example 3 were dispersed in 50 mL of 0-60 mg / L Cu 2+ In solution (specifically Cu 2+ Initial ion concentration see Figure 10 ), the pH of the solution was 7. The absorbance at 452 nm was measured using a UV-visible spectrophotometer.

[0139] Figure 10 The Fe3O4@SiO2-GQDs sensor prepared in Example 3 under pH (a), adsorbent dosage (b) and Cu 2+ The effect of different initial ion concentrations (c) on adsorption performance; e.g. Figure 10 As shown in (a), within the pH range of 2 to 8, the adsorption efficiency first increases and then decreases with increasing pH: it reaches a peak value (91.31%) at pH = 6, while when pH > 6, Cu(OH)2 precipitation forms, resulting in a decrease in adsorption efficiency. Figure 10 As can be seen from (b), the adsorbent dosage in this experiment is selected in the range of 5 to 35 mg. When the dosage is 25 mg, the adsorption rate reaches 91.58%. When the dosage is further increased, the adsorption rate tends to be stable due to the saturation of active sites and the dynamic equilibrium of adsorption and desorption, indicating that Cu 2+ Ions preferentially occupy surface active sites at limited concentrations (25 mg / L). 2+ The effect of initial ion concentration, such as Figure 10 As shown in (c), when the concentration is ≤25 mg / L, the adsorption rate increases significantly with the increase of concentration. When the concentration exceeds this limit, the active sites are exhausted and the dynamic desorption effect tends to be balanced. In summary, Fe3O4@SiO2-GQDs has a good adsorption performance at pH=6, dosage of 25 mg, and Cu 2+ The optimal adsorption performance was achieved when the initial ion concentration was 25 mg / L.

[0140] Adsorption performance analysis

[0141] In order to further analyze the Cu 2+ The adsorption process of ions was analyzed by fitting the Langmuir (Formula 1) model and the Freundlich (Formula 2) model.

[0142]

[0143] Where Q is the Langmuir saturation adsorption capacity, mg / g; K L represents the Langmuir adsorption constant, L / mg; C e is the equilibrium adsorption concentration, mg / L. K f is the equilibrium constant of the Freundlich model, (mg (1-n) ·L n ) / g; n is the Freundlich linear constant.

[0144] Langmuir model fitting correlation (R 2=0.99878) is greater than the correlation of the Freundlich model (R 2 =0.98792), indicating that the adsorption process is more consistent with the Langmuir isotherm model, that is, Fe3O4@SiO2-GQDs adsorption of Cu 2+ The adsorption of ions is mainly monolayer chemical adsorption.

[0145] Comparative Example 1

[0146] Weigh 0.18g of ferric chloride hexahydrate and add it to a beaker, then weigh 3.75g of anhydrous sodium acetate, use a measuring cylinder to measure 37.5mL of ethylene glycol and 37.5mL of diethylene glycol respectively and add them to the beaker, stir and ultrasonicate for 20 minutes to obtain an orange solvent and evenly add it to two polytetrafluoroethylene reactors. After reacting at a high temperature of 200°C for 8 hours, take it out and cool to room temperature. Collect the black precipitate with a magnet, wash it three times with ethanol and deionized water respectively, and dry it in a vacuum drying oven at 35°C for 6 hours to obtain Fe3O4 nanoparticles.

[0147] The product of Comparative Example 1 was subjected to Cu 2+ Ion sensing test, the results are as follows Figure 11 As shown in the figure, a is Fe3O4 water suspension, b is Fe3O4 water suspension with 100μmol / L Cu 2+ solution; it was found that there was no obvious fluorescence change before and after sensing, and it did not have the sensing detection function.

[0148] Comparative Example 2

[0149] Weigh 0.18g of ferric chloride hexahydrate and add it to a beaker, then weigh 3.75g of anhydrous sodium acetate, use a graduated cylinder to measure 37.5mL of ethylene glycol and 37.5mL of diethylene glycol, respectively, and add them to the beaker. Stir and ultrasonicate for 20 minutes to obtain an orange solvent, which is evenly added to two polytetrafluoroethylene reactors. After reacting at 200°C for 8 hours, remove it, cool it to room temperature, and collect the resulting black precipitate with a magnet. Wash it three times with ethanol and deionized water respectively, and dry it in a vacuum drying oven at 35°C for 6 hours to obtain Fe3O4 nanoparticles.

[0150] use Method, SiO2 is coated on the surface of Fe3O4 nanoparticles: 80mL of ethanol, 20mL of deionized water and 1mL of 25-28% ammonia water are measured in a measuring cylinder into a beaker to obtain a mixed solution, and then 0.1g of the Fe3O4 nanoparticles prepared above are weighed and dispersed in the mixed solution by ultrasonication. After mixing evenly, they are transferred to a three-necked round-bottom flask and mechanically stirred at room temperature. At the same time, 20mL of ethanol solution mixed with 0.1mL of tetraethyl orthosilicate is slowly added dropwise at a uniform speed using a rubber-tipped dropper. After the addition is completed, stirring is continued for 12h; after the reaction is completed, the water bath is heated to 100℃, and under N2 protection, 0.15mL of 3-aminopropyltriethoxysilane is added and the reaction is continued for 12h. After the reaction is completed, an external magnetic field is used to separate the particles, and the supernatant is washed several times with anhydrous ethanol and deionized water until it is transparent, and then dried in a vacuum at 60℃ to obtain Fe3O4@SiO2-NH2 nanoparticles.

[0151] According to the method of application example 1, the Fe3O4@SiO2-NH2 nanoparticles in comparative example 2 were tested for sensing performance. The results are as follows: Figure 12 As shown in the figure, a is Fe3O4@SiO2-NH2 aqueous suspension, b is Fe3O4@SiO2-NH2 aqueous suspension with 100 μmol / L Cu 2+ Solution, the Fe3O4@SiO2-NH2 in Comparative Example 2 has no obvious fluorescence change before and after sensing compared with the sensor Fe3O4@SiO2-GQDs prepared in Example 3 under the same detection conditions, and does not have the function of sensing detection.

[0152] Comparative Example 3

[0153] Weigh 30 mg of graphite oxide powder and put it into a round-bottom flask, add 20 mL of deionized water, ultrasonicate for 2 minutes, then add 1.5 mL of 30% hydrogen peroxide solution, ultrasonicate for 1 minute, pour it into a polytetrafluoroethylene reactor after the reaction, react at a high temperature of 170 ° C for 70 minutes, and then take it out to obtain a GQDs solution emitting blue fluorescence. The above solution is first filtered through a 0.22 μm microporous filter membrane and then transferred to a dialysis bag (molecular weight cutoff: 3500 Da). At the same time, weigh 0.1 g of MnO2 powder and dissolve it in 20 mL of deionized water by ultrasonication as a dialysate and add it to another identical dialysis bag. The above two dialysis bags are placed in a beaker and dialyzed until no bubbles are generated in the solution. The manganese dioxide suspension in the beaker is replaced with deionized water, and further dialyzed to obtain a pure GQDs solution, which is then freeze-dried to obtain GQDs powder.

[0154] According to the method of application example 1, the GQDs powder in comparative example 3 was tested for sensing performance. The results are as follows: Figure 13As shown in the figure, a is a 3 mg / L GQDs water suspension, b is a 3 mg / L GQDs water suspension with the addition of 100 μmol / L Cu 2+ Solution; Under the same detection environment, the sensor prepared in Comparative Example 3 has obvious fluorescence changes before and after sensing compared to the sensor prepared in Example 3, and GQDs can 2+ The reaction was quenched, but the comparative example 3 did not incorporate magnetic materials, resulting in difficulty in recovery.

[0155] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A multifunctional magnetic graphene quantum dot sensor, characterized in that: The invention comprises amination Fe3O4@SiO2 nanoparticles and graphene quantum dots, wherein the graphene quantum dots are grafted onto the surface of the amination Fe3O4@SiO2 nanoparticles.

2. The method for preparing the multifunctional magnetic graphene quantum dot sensor according to claim 1, characterized in that: The following steps are involved: Mixing graphite oxide powder, water and hydrogen peroxide solution to perform a hydrothermal reaction, and sequentially separating, dialyzing and freeze-drying the resulting graphene quantum dot mixture to obtain graphene quantum dots; Fe3O4 nanoparticles, silicon source, alcohol, water and ammonia are mixed for surface coating, and an amino reagent is added to the obtained Fe3O4@SiO2 product for amino modification to obtain Fe3O4@SiO2-NH2; The graphene quantum dots, Fe3O4@SiO2-NH2, Tris-HCl buffer, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride are mixed and grafted to obtain a multifunctional magnetic graphene quantum dot sensor.

3. The preparation method according to claim 2, characterized in that The mass ratio of the graphite oxide powder to water is (1-3):2000; the volume ratio of the hydrogen peroxide solution to water is (1-2.5):20; and the mass concentration of the hydrogen peroxide solution is 30%.

4. The preparation method according to claim 2 or 3, characterized in that The temperature of the hydrothermal reaction is 160-200° C., and the time is 30-90 minutes.

5. The preparation method according to claim 2, characterized in that The silicon source includes tetraethyl orthosilicate, methyl orthosilicate or methyltriethoxysilane; the mass ratio of the Fe3O4 nanoparticles to the silicon source is 100:(46.5-93); the surface coating temperature is room temperature, and the time is 8-16 hours.

6. The preparation method according to claim 2 or 5, characterized in that The amino reagent includes 3-aminopropyltriethoxysilane, trishydroxymethylaminomethane hydrochloride, and sodium diethyldithiocarbamate trihydrate; and the mass ratio of the Fe3O4 nanoparticles to the amino reagent is 100:(71-142).

7. The preparation method according to claim 6, characterized in that The temperature of the amino modification is 80-100° C., and the time is 8-16 hours.

8. The preparation method according to claim 2, characterized in that The mass ratio of the graphene quantum dots, Fe3O4@SiO2-NH2, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride is 30:100:(82.6-102.6):(82.6-102.6).

9. The preparation method according to claim 2 or 8, characterized in that The grafting temperature is room temperature, and the grafting time is 12 to 36 hours.

10. The multifunctional magnetic graphene quantum dot sensor according to claim 1 or the multifunctional magnetic graphene quantum dot sensor prepared by the preparation method according to any one of claims 2 to 9 is used to detect Cu in wastewater. 2+ application.

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