Nitrogen-doped carbon quantum dot composite film and preparation method thereof

Abstract

The present application relates to the technical field of composite materials, and particularly relates to a nitrogen-doped carbon quantum dot composite film and a preparation method thereof.A specific technical scheme is as follows: a preparation method of a nitrogen-doped carbon quantum dot composite film, comprising the following steps: (1) using polyethylene polyamine as a nitrogen source combined with a carbon source to perform a hydrothermal reaction, and completing preparation of carbon quantum dots; (2) adding 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide and N-hydroxysuccinimide or N-hydroxylthiosuccinimide into a hydrophilic modified polymer composite film to perform a reaction, and after the reaction is completed, a nitrogen-doped carbon dot modified composite film is obtained, and the nitrogen-doped carbon dot modified composite film is stored by being immersed in water.The nitrogen-doping design makes the nitrogen-doped carbon dot composite film have a good effect in capturing and enriching persistent organic pollutants such as perfluorinated compounds, and has good application value for treatment of new pollutants in the environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, in particular to a nitrogen-doped carbon quantum dot composite film based on polyethylene polyamine functionalization regulation and a preparation method thereof. BACKGROUND

[0002] Carbon quantum dots (CQDs) are a new type of nanoscale carbon-based materials with good biocompatibility. According to the different reaction precursors and conditions, they can be divided into graphene quantum dots, carbon nanodots and polymer carbon quantum dots (PCDs). Among them, polymer carbon quantum dots have a core-shell nested structure, and the surface of the carbon core shell is covered with polymer chains and active groups. Therefore, such polymer carbon dots have the integration of nanometer characteristics and polymer functions, not only showing good biocompatibility, environmental friendliness, low toxicity, fluorescence characteristics, but also having the advantages of structural regulation and easy functionalization modification. In actual industrial application, for example, the fluorescence characteristics of PCDs can be used to realize the analysis and detection of heavy metal ions such as cadmium ions, mercury ions, copper ions and ferric ions, and carcinogenic substances such as nitrite. In addition to realizing fluorescence detection and biological imaging by using the fluorescence characteristics of PCDs, the rich active functional groups of PCDs also provide ideas for their use as functional modules of materials.

[0003] The synthesis of carbon quantum dots can be designed and realized by two strategies: top-down and bottom-up. The top-down synthesis strategy peels off small-sized carbon quantum dots from large-sized carbon sources through physical or chemical methods. The top-down strategy usually selects carbon nanotubes, carbon fibers, graphite rods and activated carbon as carbon sources, and peels off the large-sized carbon skeleton to obtain small-sized carbon quantum dots through arc discharge method, laser ablation method, electrochemical synthesis method and other means. The bottom-up synthesis strategy uses small organic molecules or oligomers as carbon sources to synthesize carbon quantum dots. The bottom-up strategy usually selects glucose, polyethylene glycol, biomass, ionic liquid and other carbon sources to realize the synthesis of carbon quantum dots through hydrothermal method, microwave method, solvothermal method, strong acid oxidation method and other means. The bottom-up strategy is the preferred strategy for preparing polymer carbon quantum dots. The bottom-up synthesis strategy has a variety of precursors, so the functional characteristics of the synthesized polymer carbon quantum dots are more abundant.

[0004] With the continuous development and innovation of the functional characteristics of polymer carbon dots, the preparation of new adsorption and separation composite materials based on PCDs has attracted more and more attention. Carbon quantum dot composite membrane material is an important kind of carbon-based functional composite material, especially the research and development of nitrogen-doped polymer carbon quantum dot composite membrane material. This kind of material can realize unique high oxygen nitrogen-rich characteristics and has great potential in adsorption extraction. Using it as a membrane material in membrane extraction process can realize efficient extraction and enrichment of new pollutants such as perfluorinated compounds.

[0005] Membrane extraction technology is a sample processing method that uses polymer membrane materials as carriers to separate, purify, enrich and capture complex matrices. Membrane extraction technology can collect, purify and extract target compounds with only a small amount of solvent or even without solvent, so it has important significance in environmental pollution control and research, and can solve the current urgent problem of new pollutant analysis and detection. Membrane extraction technology has the advantages of low organic solvent consumption, environmental protection, high efficiency, high purification degree, high enrichment factor, small and portable device, easy online analysis instrument connection, etc., so it is widely used in wastewater treatment, environmental harmful organic matter enrichment, drug extraction, heavy metal ion recovery, etc. The key to membrane extraction is the membrane material, and the performance of the membrane material directly determines whether the extraction process is feasible and efficient. In recent years, functional composite membrane materials have become a key area in the new material industry, and there is an urgent need for domestic substitution. Quantum dot composite membrane is a new material that has attracted much attention in the scientific and technological community in recent years. Carbon quantum dot composite membrane has the characteristics of quantum dot material and membrane material, and has excellent performance and application prospect in many fields. The key to the preparation of carbon quantum dot composite membrane material is the synthesis of carbon quantum dots and the modification of membrane materials. Polymer carbon quantum dots can be prepared by a bottom-up synthesis strategy. By selecting suitable carbon source precursors and nitrogen source precursors, high oxygen nitrogen-rich characteristics and other rich functions can be achieved. The selection of precursors is not only diverse and controllable, but also can realize the green and non-toxic raw materials. SUMMARY

[0006] In view of the shortcomings of the prior art, the nitrogen-doped carbon quantum dot composite membrane and the preparation method thereof are provided. Nitrogen-doped carbon quantum dots are prepared by using green, safe and inexpensive carbon sources such as citric acid and multiethylene polyamine nitrogen sources such as diethylene triamine and triethylene tetramine as precursors through a "bottom-up" synthesis strategy. 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide and N-hydroxysuccinimide or N-hydroxylthiosuccinimide are added, and EDC / NHS interfacial cross-linking polymerization is coupled to polyvinylidene fluoride membrane to obtain nitrogen-doped carbon quantum dot functional modified composite membrane material. The application of nitrogen-doped carbon quantum dot composite membrane material in the enrichment and extraction of new pollutants such as perfluorinated compounds is an excellent membrane extraction material.

[0007] To achieve the above purpose, the technical scheme is as follows:

[0008] The application discloses a preparation method of a nitrogen-doped carbon quantum dot composite film.

[0009] (1) using polyethylene polyamine as a nitrogen source and combining with a carbon source to perform a hydrothermal reaction to complete preparation of carbon quantum dots;

[0010] (2) adding 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide and N-hydroxysuccinimide or N-hydroxylthiosuccinimide into a hydrophilic modified polymerization film to perform a reaction, and after the reaction is completed, a nitrogen-doped carbon dot modified composite film is obtained, which is soaked in water for storage.

[0011] Preferably, the polyethylene polyamine is any one of urea, diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, hexaethylene heptamine, polyethylene imine and polyamide-amine dendrimer.

[0012] Preferably, the carbon source is any one of citric acid, vitamin C, glucose and biomass.

[0013] Preferably, in step (1), the reaction medium is deionized water, and the molar ratio of the polyethylene polyamine to the carbon source is greater than or equal to 1.5; during the hydrothermal reaction, the reaction temperature is 160-220 DEG C, and the reaction time is 3-6 hours.

[0014] Preferably, the amount of the polyethylene polyamine is greater than or equal to 1.5 times the equivalent of the carbon source.

[0015] Preferably, in step (1), the prepared carbon quantum dots are dialyzed by using a 3500 equivalent dialysis bag, and after dialysis, the solution is purified by freeze drying for standby use; the particle size of the carbon quantum dots is 3.0-7.2 nm.

[0016] Preferably, in step (2), the preparation process of the hydrophilic modified polymerization film is as follows: after the polymerization film is ultrasonically cleaned, it is soaked in an ethanol solution, then is added into a hydrophilic modification system of an alkaline potassium permanganate oxidant, is transferred into an acrylic acid solution, and is added with azobisisobutyronitrile to perform a polymerization reaction; after the reaction is terminated, the polymerization film is cleaned with deionized water and is dried to obtain the hydrophilic modified polymerization film.

[0017] Preferably, in the alkaline potassium permanganate oxidant hydrophilic modification system, the alkali is potassium hydroxide, the molar concentration of the potassium hydroxide is 2.5 mol / L, and the mass fraction of the potassium permanganate is 5%; during the modification process, the modification temperature is 40-60 DEG C, and the reaction time is 1-2 hours.

[0018] Preferably, in step (2), the reaction is performed under an argon protection environment, the reaction temperature is 0-8 DEG C, the reaction time is 1-2 hours, and the reaction pH is controlled to be 4.0-6.0.

[0019] Accordingly, the preparation method prepared by the above preparation method is a nitrogen-doped carbon dot modified composite film.

[0020] The present application has the following advantages:

[0021] The present application uses ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, polyethyleneimine, polyamide-amine dendrimer, etc. as nitrogen source precursors to prepare nitrogen-doped carbon quantum dots, so that the carbon quantum dot core-shell structure surface has a large number of amine functional groups. The carbon source can be selected from citric acid, vitamin C, glucose, and green leaf biomass, which meets the green, low-toxicity, inexpensive, and easy-to-obtain environmental protection concept. Nitrogen-doped carbon quantum dots are synthesized from bottom to top by one-step hydrothermal method. The size of the quantum dots is uniform, and the particle size is 3.0-7.2nm. By selecting different polyene polyamine molecules such as diethylenetriamine, triethylenetetramine, and tetraethylenepentamine, different nitrogen-doped carbon quantum dot structures can be designed, and the content of amine functional groups of nitrogen-doped carbon quantum dots can be controlled by controlling the ratio of nitrogen source and carbon source. Then, through 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide and N-hydroxysuccinimide or N-hydroxylthiosuccinimide, EDC / NHS reaction is triggered, and specific connection of carboxyl groups on the polymer film and amine groups on the carbon quantum dots is completed, finally obtaining a carbon dot loaded film. The carbon dot loaded film is used as a membrane extraction material, which has good capture and adsorption effect on toxic and harmful molecules such as perfluorinated compounds, and can effectively treat new pollutants in the environment. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Preparation process of nitrogen-doped carbon quantum dot loaded film prepared by nitrogen-doped carbon quantum dots with diethylenetriamine as nitrogen source

[0023] Figure 2 Actual picture and characterization result picture of nitrogen-doped carbon quantum dot loaded film material prepared by nitrogen-doped carbon quantum dots with urea as nitrogen source

[0024] Figure 3 Preparation process of nitrogen-doped carbon quantum dot loaded film prepared by nitrogen-doped carbon quantum dots with polyethyleneimine as nitrogen source

[0025] Figure 4 "Sandwich" type membrane extraction device based on nitrogen-doped carbon quantum dot loaded modified membrane

[0026] Figure 5 Application of membrane extraction device based on nitrogen-doped carbon quantum dot loaded modified membrane in perfluorinated compound analysis and detection. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0028] If not specifically indicated, the technical means used in the examples is the conventional means known to those skilled in the art.

[0029] The application discloses a preparation method of a nitrogen-doped carbon quantum dot composite film, which comprises the following steps: using a multiethylene polyamine such as diethylene triamine and triethylene tetramine as a nitrogen source, using a biomass such as citric acid, vitamin C and green leaf as a carbon source, and using a "bottom-up" synthesis strategy to efficiently and rapidly prepare nitrogen-doped fluorescent carbon quantum dots by one-step hydrothermal method; using a surface chemical modification method to modify a high polymer film by using a potassium permanganate / potassium hydroxide alkaline oxidant hydrophilic system, and then using an EDC / NHS interface cross-linking polymerization to specifically connect the nitrogen-doped carbon quantum dots and the high polymer film, so that a nitrogen-doped carbon quantum dot composite film with adsorption and capture effect on new pollutants such as perfluorinated compounds is obtained, and the adsorption and extraction of the new pollutants such as perfluorinated compounds can be realized by using a membrane separation method.

[0030] Specifically, the method comprises the following steps:

[0031] (1) using a Bottom-up strategy to synthesize functional controllable nanoscale nitrogen-doped carbon quantum dots

[0032] The multiethylene polyamine is used as the nitrogen source in combination with the carbon source, deionized water is used as the medium, a one-step hydrothermal program is set, and the hydrothermal reaction is initiated in a polytetrafluoroethylene autoclave, so that the preparation of the carbon quantum dots is completed from bottom to top by the hydrothermal reaction; the carbon quantum dots are prepared; the carbon quantum dots are dialyzed with a 3500 equivalent dialysis bag, and the solution after dialysis is purified by freeze-drying for standby use.

[0033] The multiethylene polyamine is any one of urea, diethylene triamine, triethylene tetramine, tetraethylene pentaamine, pentaethylene hexamine, hexaethylene heptamine, polyethylene imine and polyamidoamine dendrimer. The carbon source is any one of citric acid, vitamin C, glucose and biomass (such as green leaf). The molar ratio of the multiethylene polyamine to the carbon source is greater than or equal to 1.5, or the amount of the multiethylene polyamine is greater than or equal to 1.5 times the equivalent of the carbon source. During the hydrothermal reaction, the total amount of the reaction solution should not be higher than 2 / 3 of the volume of the inner container of the autoclave, the reaction temperature is 160-220 DEG C, and the reaction time is 3-6 hours.

[0034] (2) using surface chemical modification method to modify the polymerization membrane, make the membrane surface bond with hydrophilic groups, improve the hydrophilic property of the polymerization membrane.

[0035] The polymerization membrane is cleaned with deionized water (taking polyvinylidene fluoride membrane as an example), dried, transferred to ethanol solution for soaking, then added to the basic oxidant (such as basic potassium permanganate) hydrophilic system for phase transfer, to remove the surface hydrophobic bond, make the membrane surface modified with -OH and other hydrophilic groups, then transferred to the acrylic acid solution, added with azobisisobutyronitrile as initiator to initiate polymerization, make the membrane surface modified with -COOH and other hydrophilic groups, then washed with deionized water, dried. The concentration of acrylic acid is 0.2-5 mol / L, and the amount of azobisisobutyronitrile is 0.1%-1% of the weight of the polymerization membrane.

[0036] The polyvinylidene fluoride membrane has a size of 5 cm x 8 cm, the modifier system used is the basic potassium permanganate oxidant system, the basic reagent used is potassium hydroxide solution with a molar concentration of 2.5 mol / L, and the mass fraction of potassium permanganate solution is 5%. The degree of hydrophilic modification of the membrane material can be controlled by the modification time and temperature of the basic potassium permanganate oxidant hydrophilic system, the longer the modification time, the stronger the hydrophilic property. The modification temperature is 40-60℃, and the reaction time is 1-2 hours.

[0037] (3) using surface grafting method to load nitrogen-doped carbon quantum dots onto the modified polymerization membrane, to obtain nitrogen-doped carbon quantum dot composite membrane material that can be used for membrane extraction.

[0038] Under the protection of argon, 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide and N-hydroxysuccinimide or N-hydroxylthiosuccinimide are added to the hydrophilic modified polymer polymeric membrane to trigger the EDC / NHS reaction to form an O-acyl isourea active intermediate, the intermediate is amidated with carboxyl, and the carboxyl and amine on the carbon quantum dots are specifically connected by EDC / NHS interfacial crosslinking polymerization, so that the carbon quantum dots are modified on the polymer polymeric membrane, and finally a nitrogen-doped carbon dot polymer membrane with good adsorption and capture effect on perfluorinated compounds and other pollutants is prepared. The membrane extraction method can realize the adsorption and enrichment of perfluorinated compounds and other pollutants in the environment. After being washed clean, it is soaked in water for storage to obtain a surface amino-functionalized nitrogen-doped carbon dot composite membrane emitting blue fluorescence. The EDC / NHS reaction is selected to be carried out in a buffer system under neutral conditions, N-hydroxysuccinimide can be used as N-hydroxysuccinimide or N-hydroxylthiosuccinimide, the reaction medium is aqueous phase, 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide (EDC) needs to be prepared and used immediately to avoid inactivation, and the reaction pH is controlled at 4.0-6.0. The interfacial polymerization process of the carbon quantum dots loaded and modified on the polymer polymeric membrane can also be realized by using trimesoyl chloride.

[0039] (4) The washed and dried nitrogen-doped carbon dot composite membrane is installed in a membrane extraction device by a sandwich assembly method for the capture and enrichment extraction of perfluorinated compounds and other new pollutants. Double-layer method, solid-phase microextraction fiber membrane type and the like can also be used. The washing is carried out by using 95% ethanol and deionized water, and finally deionized water is used for soaking and storage, and the storage temperature is 4 DEG C to room temperature.

[0040] The amine group loading of the nitrogen-doped carbon dot composite membrane can be controlled by the content of the loaded carbon quantum dots, or can be controlled by the amount or type of nitrogen source in the synthesis process of the carbon quantum dots. The nitrogen source is selected to be a polyethylene polyamine molecule. The nitrogen-doped carbon dot composite membrane adopts a “sandwich” type membrane separation assembly mode for the capture and enrichment of perfluorinated compounds and other harmful substances. The high oxygen and nitrogen characteristics of the nitrogen-doped carbon dot composite membrane can be controlled by controlling the type and proportion of the nitrogen source, and the shell surface active amine group of the nitrogen-doped carbon dot core-shell structure can be realized by controlling the chain length of the nitrogen source molecule. The excess reactants can be removed by dialysis membrane dialysis and the like.

[0041] The application will be further described below in combination with specific examples.

[0042] Example 1

[0043] Reference Figure 1 As shown in the figure, the preparation process of the nitrogen-doped carbon dot composite membrane based on citric acid and diethylene triamine is as follows, and the steps are as follows:

[0044] (1) Functional controllable nanoscale nitrogen-doped carbon quantum dots are synthesized by using a bottom-up strategy.

[0045] Select diethylene triamine molecules as nitrogen source precursor, select anhydrous citric acid as carbon source precursor, set one-step hydrothermal procedure, initiate hydrothermal reaction in polytetrafluoroethylene high-pressure kettle, complete preparation of carbon quantum dots from bottom to top through hydrothermal reaction, the molar ratio of the amount of citric acid and diethylene triamine is set to 1:1.5, the reaction temperature is 180℃, and the reaction time is 3 hours.

[0046] (2) After the reaction is completed, the product solution is placed in a dialysis bag with a molecular weight cut-off of 3500 for dialysis purification and impurity removal. After dialysis, freeze-drying is performed and the product is stored for later use.

[0047] (3) The polyvinylidene fluoride membrane is modified by a hydrophilic system of alkaline potassium permanganate oxidant, then the membrane is transferred to an acrylic acid solution, and azobisisobutyronitrile is added as an initiator to initiate polymerization, so that hydrophilic groups such as -COOH are modified on the surface of the membrane. After the reaction is completed, the membrane is washed with deionized water and dried.

[0048] (4) 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide and N-hydroxysuccinimide are added to trigger the EDC / NHS reaction, and the carboxyl group and amine group on the carbon quantum dots are specifically connected by EDC / NHS interfacial crosslinking polymerization to obtain a carbon dot-loaded membrane.

[0049] Among them, 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide is prepared into a solution of 100 mg / mL with MES buffer solution; N-hydroxysuccinimide is prepared into a solution of 100 mg / mL with MES buffer solution; the amount of 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide and N-hydroxysuccinimide is not less than 1:1, and the upper limit of the amount is until precipitation occurs.

[0050] (5) After cleaning, soak in water for storage to obtain a surface amino-functionalized nitrogen-doped carbon dot composite membrane that emits blue fluorescence.

[0051] Example 2

[0052] The preparation process of the nitrogen-doped carbon dot composite membrane based on citric acid and urea is as follows, and the steps are:

[0053] The steps are the same as steps (1), (2), (3), (4) and (5) of Example 1, and the nitrogen source of step (1) is changed to urea. The actual picture and characterization results of the nitrogen-doped carbon quantum dot composite membrane prepared by using urea as the nitrogen source are shown in Figure 2 .

[0054] Example 3

[0055] Reference Figure 3As shown, the fabrication process of the nitrogen-doped carbon dot composite film based on citric acid and polyethyleneimine is as follows, and the steps are as follows:

[0056] The steps are the same as (1), (2), (3), (4), and (5) of Example 1, except that the nitrogen source in step (1) is changed to polyethyleneimine; the grafting method in step (4) is changed to the interfacial polymerization method of trimesoyl chloride (TMC), that is, N-hydroxysuccinimide is changed to trimesoyl chloride.

[0057] Example 4

[0058] Application of membrane extraction devices based on nitrogen-doped carbon quantum dot-supported modified membranes for the capture, enrichment, and analysis of harmful substances such as perfluorinated compounds.

[0059] like Figure 4 , Figure 5 As shown, using the nitrogen-doped carbon quantum dot composite membranes synthesized in Examples 1, 2, and 3 as membrane materials, a membrane extraction device was constructed using a sandwich model. The device was then coupled with a chromatographic instrument via column switching to finally complete the extraction and analysis of perfluorinated compounds in the sample.

[0060] The results showed that the "sandwich" type membrane extraction device based on nitrogen-doped carbon quantum dot-supported modified membrane provided by this invention can achieve efficient online automated enrichment of perfluorinated compounds in environmental samples. When coupled with a liquid chromatography-mass spectrometry (LC-MS) detector, the device can be used to detect novel perfluorinated pollutants. When applied to environmental water samples from 20 different water bodies, perfluorinated compounds were detected in 14 samples, with concentrations ranging from 12 to 105.4 ng / L.

[0061] The chromatography instrument is equipped with a mass spectrometry detector, and the specific operating conditions are as follows:

[0062] Instrument: Liquid Chromatography = Tandem Mass Spectrometry (LC-MS / MS)

[0063] Mobile phase: 5 mmol / L ammonium acetate aqueous solution + methanol

[0064] Stationary phase: C18 reversed-phase column

[0065] Sample: Environmental water sample (collected independently)

[0066] Flow rate: 0.3 mL / min

[0067] Column temperature: 40℃

[0068] Mode: Negative Ion Mode

[0069] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method for preparing a nitrogen-doped carbon quantum dot composite membrane for the capture and adsorption of perfluorinated compounds, characterized in that: Includes the following steps: (1) Carbon quantum dots are prepared by hydrothermal reaction using polyethylene polyamines as nitrogen source and carbon source; the reaction medium is deionized water, and the molar ratio of the polyethylene polyamines to the carbon source is greater than or equal to 1.5; the reaction temperature is 160-220℃ and the reaction time is 3-6 hours during the hydrothermal reaction; the polyethylene polyamines are any one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, hexaethyleneheptamine, polyethyleneimine, and polyamide-amine dendritic macromolecules. (2) Add 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide or N-hydroxythiosuccinimide to the hydrophilic modified polymer membrane to trigger the EDC / NHS reaction, and complete the specific connection between the carboxyl group on the polymer membrane and the amine group on the carbon quantum dots. The reaction is carried out under argon protection, the reaction temperature is 0-8℃, the reaction time is 1-2 hours, and the reaction pH is controlled at 4.0-6.

0. After the reaction is completed, the nitrogen-doped carbon quantum dot composite membrane is obtained and it is stored by immersing it in water. The preparation process of the hydrophilic modified polymer membrane is as follows: after ultrasonic cleaning, the polymer membrane is soaked in ethanol solution, then added to the alkaline potassium permanganate oxidant hydrophilic modification system, then transferred to acrylic acid solution, azobisisobutyronitrile is added, and a polymerization reaction is carried out. After the reaction is terminated, it is washed with deionized water and dried to obtain the hydrophilic modified polymer membrane. In the alkaline potassium permanganate oxidant hydrophilic modification system, the base is potassium hydroxide, the molar concentration of potassium hydroxide is 2.5 mol / L, and the mass fraction of potassium permanganate is 5%. During the modification process, the modification temperature is 40-60℃ and the reaction time is 1-2 hours.

2. The preparation method according to claim 1, characterized in that: The carbon source is any one of citric acid, vitamin C, glucose, and biomass.

3. The preparation method according to claim 1, characterized in that: The amount of the polyethylene polyamine is greater than or equal to 1.5 times the equivalent of the carbon source.

4. The preparation method according to claim 1, characterized in that: In step (1), the prepared carbon quantum dots are dialyzed using a 3500 equivalent dialysis bag, and the solution is then purified by freeze drying for later use; the particle size of the carbon quantum dots is 3.0-7.2 nm.

5. A nitrogen-doped carbon quantum dot composite membrane for the capture and adsorption of perfluorinated compounds, prepared by the preparation method according to any one of claims 1 to 4.

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