WO2023142668A1

WO2023142668A1 - Method for preparing nitrogen-doped carbon dot-reduced graphene oxide composite material and use thereof

Info

Publication number: WO2023142668A1
Application number: PCT/CN2022/135783
Authority: WO
Inventors: 杨剑波; 王梦豪; 曹凯峰; 刘勇奇; 巩勤学; 李长东
Original assignee: 湖南邦普循环科技有限公司; 广东邦普循环科技有限公司; 湖南邦普汽车循环有限公司
Priority date: 2022-01-28
Filing date: 2022-12-01
Publication date: 2023-08-03
Also published as: CN114538409A

Abstract

Disclosed are a method for preparing a nitrogen-doped carbon dot-graphene oxide composite material and use thereof. The method comprises the following steps: mixing a carbon source and a nitrogen source, performing a hydrothermal reaction, and performing solid-liquid separation to give a nitrogen-doped carbon dot solution; mixing graphene oxide and a reducing agent, stirring, performing solid-liquid separation, and dissolving the solid phase to give a pre-reduced graphene oxide solution; and mixing the nitrogen-doped carbon dot solution and the pre-reduced graphene oxide solution by sonication, dropwise adding the mixture on an electrode, and performing cyclic voltammetry for reduction to give the nitrogen-doped carbon dot-graphene oxide composite material.

Description

Preparation method and application of nitrogen-doped carbon dots-reduced graphene oxide composite material

technical field

The invention belongs to the technical field of composite materials, and in particular relates to a preparation method and application of a nitrogen-doped carbon dot-reduced graphene oxide composite material.

Background technique

Carbon quantum dots (CQDs) are zero-dimensional carbon nanomaterials with fluorescent properties, which are mainly used in fluorescence imaging, fluorescence sensing, and LED device research and development. In 2004, carbon quantum dots were reported for the first time, which have the characteristics of complex structure, various types and various preparation methods, and the chemical composition and lattice characteristics of different carbon quantum dots are also different.

In the field of electrochemical sensing, carbon quantum dots are an ideal material with excellent performance. Its good chemical stability, strong light stability and water solubility endow carbon quantum dots with excellent sensing properties in different systems. performance. In addition, the surface structure of carbon quantum dots can also be adjusted by introducing different functional groups and surface passivation treatment, so as to make them have specific responses to some specific substances. In recent years, with more and more studies on doped CDs, heavily doped modified CDs have gradually become known and gradually become a mainstream method to adjust the fluorescence parameters of traditional CDs. Common dopants for doping traditional CDs mainly include non-metal elements and some metal elements, among which non-metal elements include nitrogen, boron, sulfur, phosphorus, silicon, etc. Studies have shown that the atomic radius of nitrogen is relatively similar to that of carbon, and it is an element that is easier to incorporate into the carbon skeleton of CDs. choose.

Although CQDs have a large specific surface area and strong adsorption capacity, and are rich in functional groups, CQDs have a wide range of applications in the adsorption of various heavy metal ions, organic pollutants and biological macromolecules. However, due to the electrical conductivity of carbon quantum dots Poor performance limits its application in the field of electrochemical sensing, and the sensitivity and detection limit of electrochemical sensing in the prior art are poor.

Contents of the invention

The present invention aims to solve at least one of the technical problems in the above-mentioned prior art. For this reason, the present invention proposes a preparation method and application thereof of a nitrogen-doped carbon dot-graphene oxide composite material. The composite material prepared by the preparation method has the advantages of nitrogen-doped carbon dots and graphene oxide at the same time, and can Effectively improve the sensitivity and detection limit of the electrochemical sensor prepared by the composite material.

To achieve the above object, the present invention adopts the following technical solutions:

A preparation method of nitrogen-doped carbon dots-graphene oxide composite material, comprising the following steps:

(1) Mix carbon source and nitrogen source, carry out hydrothermal reaction, solid-liquid separation, obtain nitrogen-doped carbon dot solution;

(2) Graphene oxide and reducing agent are mixed and stirred, reacted, and solid-liquid separation is taken for solid phase dissolution to obtain a pre-reduced graphene oxide solution;

(3) The nitrogen-doped carbon dot solution and the pre-reduced graphene oxide solution are ultrasonically mixed, added dropwise on the electrode, and subjected to cyclic voltammetry reduction to obtain the nitrogen-doped carbon dot-graphene oxide composite material.

Preferably, in step (1), the carbon source is mung bean.

Preferably, in step (1), the nitrogen source is melamine.

Melamine not only acts as a nitrogen source but also has an effective synergistic catalytic effect during the reaction.

Preferably, in step (1), the mass ratio of the carbon source to the nitrogen source is (8-12):1.

Preferably, in step (1), the temperature of the hydrothermal reaction is 180-200° C., and the time of the hydrothermal reaction is 6-8 hours.

Preferably, in step (1), the inner lining of the reactor for hydrothermal reaction is polytetrafluoroethylene.

Preferably, in step (1), the specific step of solid-liquid separation is: filter and centrifuge the mixed solution after the hydrothermal reaction, collect the supernatant, and then filter and dialyze to obtain a nitrogen-doped carbon dot solution .

Preferably, in step (2), the mass ratio of the graphene oxide to the reducing agent is (0.05-0.2):1.

Preferably, in step (2), the solid phase dissolution uses absolute ethanol to dissolve the solid phase.

Preferably, in step (2), the reducing agent is ascorbic acid.

Preferably, in step (3), the volume ratio of the nitrogen-doped carbon dot solution to the pre-reduced graphene oxide solution is (1-4):1.

Preferably, in step (3), the electrode is a glassy carbon electrode, which is prepared by the following method: wet polishing the glassy carbon electrode, then ultrasonically cleaning, scanning, drying with nitrogen, and sequentially heating the electrode in K ₃ [ Fe(CN) ₆ ], K ₄ [Fe(CN) ₆ ] and KCl electrolyte solution are scanned to obtain a glassy carbon electrode with a potential difference between the oxidation peak and the reduction peak below 100mV.

Further preferably, the wet polishing treatment is to polish the glassy carbon electrode on a suede covered with alumina suspension.

Preferably, in step (3), the specific steps of the scanning are: the glassy carbon electrode is placed in 0.5 mol/L dilute sulfuric acid with a voltage range of -0.5V to 1V to perform repeated sweep cyclic voltammetry scanning until a stable cyclic voltammograms.

Preferably, in step (3), the specific step of the cyclic voltammetry reduction is: the glassy carbon electrode which is dripped with the mixed solution of nitrogen-doped carbon dots/reduced graphene oxide is dried under an infrared lamp to form a film , and then placed in the electrochemical workstation CHI 660E, the electrolyte solution is a phosphate buffer solution, and the cyclic voltammetry reduction is carried out to obtain it.

Further preferably, the scanning potential of the cyclic voltammetry reduction is -1.5-0V, the scanning rate is 0.05-0.1V/s, and the number of scanning is 30-40 cycles.

The present invention also provides the application of the nitrogen-doped carbon dot-graphene oxide composite material prepared by the above preparation method in detecting heavy metal ions.

Preferably, the heavy metal ions are lead ions and cadmium ions.

An electrochemical sensor, comprising the nitrogen-doped carbon dot-graphene oxide composite material prepared by the preparation method.

Principle: Graphene oxide has good electrochemical performance and large specific surface area, and can form coordination compounds with different metal ions through coordination bonds, but the active sites and oxygen-containing functional groups on its surface limit its Applications in the field of electrochemical sensing. Then, chemical modification can be used to increase the active sites. On the one hand, a variety of functional groups can be introduced on the surface of graphene oxide through covalent or non-covalent interactions, so as to modify graphene oxide to make it functional and improve Graphene oxide has the ability to adsorb and enrich analytes. On the other hand, doping other atoms in graphene oxide can adjust the energy band structure of electrons and improve the physical and chemical properties and electrochemical activity of graphene oxide. Therefore, this method first prepares nitrogen-doped carbon dots. The nitrogen-doped carbon dots have nitrogen-containing and oxygen-containing groups, and the oxygen-containing functional groups can provide a large number of active sites through electrostatic interaction and complexation. Improve the sensitivity and detection limit of electrochemical sensors. Using graphene oxide as a carrier of nitrogen-doped carbon dots improves the electrical conductivity and electron transport rate of the composite.

Compared with the prior art, the beneficial effects of the present invention are as follows:

1. The present invention utilizes mung bean as a carbon source, melamine as a nitrogen source, and utilizes hydrothermal method to form nitrogen-doped carbon dots. Since mung bean has nitrogen-containing and oxygen-containing groups, it also has good water solubility, and the formed The surface of nitrogen-doped carbon dots also has abundant nitrogen-containing and oxygen-containing groups, and the oxygen-containing functional groups can provide a large number of active sites through electrostatic interaction and complexation to improve the sensitivity and detection limit of electrochemical sensors; Graphene oxide was pre-reduced and then ultrasonically mixed with nitrogen-doped carbon dot solution, and then reduced by cyclic voltammetry. Reducing graphene oxide as a carrier of nitrogen-doped carbon dots improved the electrical conductivity and electron transport rate of the composite.

2. The nitrogen-doped carbon dots-graphene oxide composite material prepared by the present invention has the advantages of nitrogen-doped carbon dots and graphene oxide at the same time, and has a high specific surface area, excellent electrical conductivity and electron transport rate and rich activity site.

3. The electrochemical sensor prepared by using the nitrogen-doped carbon dots-reduced graphene oxide composite material of the present invention can be applied to the detection of lead ions and cadmium ions in farmland soil, and has a satisfactory recovery rate.

4. The present invention adopts an electrochemical preparation method to prepare nitrogen-doped carbon dots-graphene oxide composite material, and this method is applicable to the composite of various carbon nanomaterials.

Description of drawings

Fig. 1 is the synthetic schematic diagram of nitrogen-doped carbon dots-reduced graphite oxide composite material of the present invention;

Fig. 2 is the transmission electron microscope picture of the nitrogen-doped carbon dot of embodiment 1 of the present invention;

Fig. 3 is the transmission electron micrograph of the nitrogen-doped carbon dot-reduced graphite oxide composite material of embodiment 1 of the present invention;

Fig. 4 is the scanning electron micrograph of the nitrogen-doped carbon dot-reduced graphite oxide composite material of embodiment 1 of the present invention;

Fig. 5 is the Fourier transform infrared spectrogram of nitrogen-doped carbon dot-reduced graphite oxide composite material, reduced graphite oxide and nitrogen-doped carbon dot of embodiment 1;

Fig. 6 is (bare electrode) Bare GCE of embodiment 1 of the present invention, (electroreduction carbon point/reduction graphene oxide electrode) Er-NCQD/rGO-GCE, (reduction graphene oxide electrode) rGO-GCE and (carbon Point electrode) cyclic voltammetry spectrum of NCQDs-GCE modified electrode;

Fig. 7 is (bare electrode) Bare GCE of embodiment 1 of the present invention, (electroreduction carbon point/reduction graphene oxide electrode) Er-NCQD/rGO-GCE, reduction graphene oxide electrode) rGO-GCE and (carbon point Electrode) Electrochemical impedance spectroscopy of NCQDs-GCE modified electrode.

Detailed ways

The conception and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments, so as to fully understand the purpose, features and effects of the present invention. Apparently, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts belong to The protection scope of the present invention.

Example 1

The preparation method of the nitrogen-doped carbon dots-reduced graphene oxide composite material (Er-NCQD/rGO) of the present embodiment comprises the following steps:

(1) Grinding the glassy carbon electrode on the suede covered with alumina suspension, and testing it through the electrochemical workstation to obtain a qualified glassy carbon electrode for standby;

(2) First weigh 100mg of mung bean powder and 10mg of melamine in a beaker, add 50mL of distilled water and stir evenly, transfer to a polytetrafluoroethylene liner, put it into an autoclave, and put it into a blast drying oven to heat to 180°C React for 8 hours, after cooling to room temperature, filter the liquid in it to obtain a brownish-yellow liquid, then centrifuge (8000r/min) for 5 minutes, collect the supernatant, filter and dialyze to obtain a nitrogen-doped carbon dot solution;

(3) Weigh 2.5mg of graphene oxide in a 250mL beaker, add 0.044g of ascorbic acid and 5ml of deionized water and stir at room temperature for 2h, then add 2mL of absolute ethanol solution and keep the ultrasonic environment, and then Sonicate for 30 minutes, then place in a centrifuge tube and then centrifuge at 8000r/min for 5 minutes, and then use absolute ethanol and deionized water to centrifuge, wash three times each time, collect the sediment in the lower layer, and use anhydrous Ethanol was dissolved to 0.5mg/mL to obtain a pre-reduced graphene oxide solution;

(4) The nitrogen-doped carbon dot solution and the reduced graphene oxide solution are ultrasonically mixed according to a volume ratio of 2:1 to obtain a nitrogen-doped carbon dot/reduced graphene oxide mixed solution;

(5) Take 8 μL of the mixed solution of nitrogen-doped carbon dots/reduced graphene oxide and add it dropwise on the glassy carbon electrode in step (1), then dry it under infrared light to form a film, and use the electrochemical workstation CHI 660E (Shanghai Chen Chemical Instrument Co., Ltd.), the electrolytic solution is 0.1mol/L.pH=5 phosphoric acid buffer solution, carry out cyclic voltammetry reduction, the potential range of scanning is between-1.5 to 0V, and scanning rate is 0.05V/s, Sweep 30 times to prepare nitrogen-doped carbon dots-graphene oxide (Er-NCQD/rGO) composites.

Example 2

(2) First weigh 80mg of mung bean powder and 10mg of melamine in a beaker, add 50mL of distilled water and stir evenly, transfer to a polytetrafluoroethylene liner, put it into an autoclave, and put it into a blast drying oven to heat to 180°C After reacting for 8 hours and cooling to room temperature, filter the liquid in it to obtain a brownish-yellow liquid, then centrifuge (8000r/min) for 5 minutes, collect the supernatant, filter and dialyze to obtain a purified nitrogen-doped carbon dot solution ;

(3) Weigh 5mg of graphene oxide in a 250mL beaker, add 0.044g of ascorbic acid and 5ml of deionized water and stir at room temperature for 2h, then add 2mL of absolute ethanol solution and keep the ultrasonic environment, and then ultrasonic at room temperature 30min, then placed in a centrifuge tube and then centrifuged at 8000r/min for 5min, and centrifuged with absolute ethanol and deionized water in turn, each time centrifuged and washed three times, the sediment in the lower layer was collected, and dehydrated with absolute ethanol Dissolved to 0.5mg/mL to obtain a pre-reduced graphene oxide solution;

(4) The nitrogen-doped carbon dot solution and the reduced graphene oxide solution are ultrasonically mixed according to a volume ratio of 1:1 to obtain a nitrogen-doped carbon dot/reduced graphene oxide mixed solution;

(5) Take 8 μL of the mixed solution of nitrogen-doped carbon dots/reduced graphene oxide and add it dropwise on the glassy carbon electrode in step (1), then dry it under infrared light to form a film, and use the electrochemical workstation CHI 660E (Shanghai Chen Chemical Instrument Co., Ltd.), the cyclic voltammetry reduction was carried out in a phosphate buffer solution with an electrolyte solution of 0.1mol/LpH=6, the potential range of the scan was between -1.5 and 0V, and the scan rate was 0.05V/s. The nitrogen-doped carbon dots-graphene oxide (Er-NCQD/rGO) composite was prepared.

Example 3

(2) First weigh 120mg of mung bean powder and 10mg of melamine in a beaker, add 50mL of distilled water and stir evenly, transfer to a polytetrafluoroethylene liner, put it into an autoclave, and put it into a blast drying oven to heat to 180°C After reacting for 8 hours and cooling to room temperature, filter the liquid in it to obtain a brownish-yellow liquid, then centrifuge (8000r/min) for 5 minutes, collect the supernatant, filter and dialyze to obtain a purified nitrogen-doped carbon dot solution ;

(4) The nitrogen-doped carbon dot solution and the reduced graphene oxide solution are ultrasonically mixed according to a volume ratio of 4:1 to obtain a nitrogen-doped carbon dot/reduced graphene oxide mixed solution;

(5) Take 8 μL of the mixed solution of nitrogen-doped carbon dots/reduced graphene oxide and drop it on the glassy carbon electrode in step (1), then dry it under infrared light to form a film, and use the electrochemical workstation CHI 660E (Shanghai Chen Chemical Instrument Co., Ltd.), the cyclic voltammetry reduction was carried out in a phosphate buffer solution with an electrolyte solution of 0.1mol/LpH=6, the potential range of the scan was between -1.5 and 0V, and the scan rate was 0.05V/s. The nitrogen-doped carbon dots-graphene oxide (Er-NCQD/rGO) composite was prepared.

Comparative example 1

The preparation method of the nitrogen-doped carbon dot of this comparative example comprises the following steps:

First weigh 100mg of mung bean powder and 10mg of melamine in a beaker, add 50mL of distilled water and stir evenly, transfer it to a polytetrafluoroethylene liner, put it into a high-pressure reactor, and put it in a blast drying oven and heat it to 180°C for 8 hours. After being cooled to room temperature, the liquid therein was filtered to obtain a brownish-yellow liquid, and then centrifuged (8000r/min) for 5 minutes, the supernatant was collected, filtered and dialyzed to obtain a purified nitrogen-doped carbon dot solution.

Comparative example 2

The preparation method of the reduced graphene oxide solution of this comparative example, concrete steps are as follows:

Weigh 2.5mg of graphene oxide into a 250mL beaker, add 0.044g of ascorbic acid and 5ml of deionized water and stir at room temperature for 2h, then add 2mL of absolute ethanol solution and keep the ultrasonic environment, and then ultrasonic at room temperature for 30min, Put it in a centrifuge tube and then centrifuge at 8000r/min for 5min, and then use absolute ethanol and deionized water to centrifuge, wash three times each time, collect the sediment in the lower layer, and use absolute ethanol to dissolve until 0.5mg/mL to obtain a pre-reduced graphene oxide solution.

Comparative example 3

The preparation method of the nitrogen-doped carbon dot-reduced graphene oxide composite material of this comparative example comprises the steps:

(1) First weigh 100mg of mung bean powder and 10mg of melamine in a beaker, add 50mL of distilled water and stir evenly, transfer to a polytetrafluoroethylene liner, put it into an autoclave, and heat it to 180°C in a blast drying oven After reacting for 8 hours and cooling to room temperature, filter the liquid in it to obtain a brownish-yellow liquid, then centrifuge (8000r/min) for 5 minutes, collect the supernatant, filter and dialyze to obtain a purified nitrogen-doped carbon dot solution ;

(2) Weigh 2.5mg of graphene oxide in a 250mL beaker, add 0.044g of ascorbic acid and 5ml of deionized water and stir at room temperature for 2h, then add 2mL of absolute ethanol solution and keep the ultrasonic environment, and then Sonicate for 30 minutes, then place in a centrifuge tube and then centrifuge at 8000r/min for 5 minutes, and then use absolute ethanol and deionized water to centrifuge, wash three times each time, collect the sediment in the lower layer, and use anhydrous Ethanol was dissolved to 0.5mg/mL to obtain a pre-reduced graphene oxide solution;

(3) The nitrogen-doped carbon dot solution and the reduced graphene oxide solution are ultrasonically mixed at a volume ratio of 2:1 to obtain a nitrogen-doped carbon dot/reduced graphene oxide mixed solution.

Embodiment 1-3 and comparative example 1-3 analysis:

Table 1 The detection results of the composite electrochemical sensor prepared in Example 1-3 for Cd ²⁺ and Pb ²⁺ in farmland soil

As shown in Table 1, the nitrogen-doped carbon dot-graphene oxide (Er-NCQD/rGO) composite material prepared by electroreduction using specific implementation 1, specific implementation 2 and specific implementation 3 is prepared into an electrochemical sensor, and then The soil in the experimental farmland is used as a sample to detect heavy metal ions. The amount of Cd ²⁺ added in Example 1 is 100.00 μg/L, and the total detection amount can reach 106.91 μg/L, which reduces the detection limit and improves the recovery rate. . Add an appropriate amount of distilled water into the soil sample, obtain the experimental water sample after vacuum filtration and dialysis, and use the prepared sensor to simultaneously detect Cd ²⁺ and Pb ²⁺ , because the nitrogen-doped carbon dot-reduced graphene oxide composite material of the present invention can A large number of active sites are provided to improve the sensitivity of the electrochemical sensor. The sensor can detect Cd ²⁺ and Pb ²⁺ sensitively, thereby improving the recovery rate of Cd ²⁺ and Pb ²⁺ . The recovery rates of the three examples are respectively: 101.45-106.91%, 89.56-92.34%, 90.33-97.01%.

Fig. 1 is a schematic diagram of the synthesis of nitrogen-doped carbon dots-reduced graphite oxide composite material of the present invention. As shown in Figure 1, it can be seen that the preparation principle of the present invention is: first prepare nitrogen-doped carbon dots, then pre-reduce graphene oxide and then ultrasonically mix with nitrogen-doped carbon dot solution, and then perform cyclic voltammetry reduction , to obtain nitrogen-doped carbon dots-reduced graphite oxide composites.

Fig. 2 is the transmission electron microscope picture of the nitrogen-doped carbon dot of embodiment 1 of the present invention; , the dispersion is good, and the size is relatively uniform and uniformly dispersed without aggregation.

Figure 3 is a transmission electron microscope image of the nitrogen-doped carbon dot-reduced graphite oxide composite material of Example 1 of the present invention; it can be seen from Figure 3 that NCQDs are disorderly dispersed on the surface of reduced graphene oxide, which may be attributed to reduction oxidation The surface of graphene and nitrogen-doped carbon quantum dots both contain a large number of oxygen-containing groups and defects. When NCQDs/rGO undergoes electrochemical co-reduction, mung bean carbon dots are supported on the surface of pre-reduced graphene oxide.

Fig. 4 is the scanning electron micrograph of the nitrogen-doped carbon dot-reduced graphite oxide composite material of embodiment 1 of the present invention; As can be seen from Fig. 4, the pre-reduced graphene oxide is stacked in sheets and has a certain three-dimensional shape on the surface, which provides a larger specific surface area, while NCQDs cannot be shown in the figure because of their small particle size.

Fig. 5 is the Fourier transform infrared spectrogram of the nitrogen-doped carbon dot-reduced graphite oxide composite material of embodiment 1, reduced graphite oxide and nitrogen-doped carbon dot; Different materials have been carried out Fourier transform infrared spectroscopic characterization, as shown in Fig. 5, showing the infrared spectra of Er-NCQDs-rGO, rGO and NCQDs, respectively. For individual NCQDs, the FT-IR spectrum shows an absorption peak between 3263-3712 cm ^-1 indicating the presence of hydroxyl (-OH), and NCQDs contain various oxygen-containing functional groups, such as hydroxyl, carbonyl, ether or ring Oxygen, these oxygen-containing functional groups provide a large number of lone pairs of electrons, which can provide electron donors when electrochemically detecting heavy metal ions, which is conducive to the enrichment of heavy metal ions to enhance the sensitivity of detection. It can be seen from the curve of NCQDs-rGO that the absorption peaks at 1637cm ^-1 , 1397cm ^-1 , 1119cm ^-1 and 620cm ^-1 originate from NH in-plane vibration, CN stretching vibration and NH out-of-plane vibration. Compared with rGO and NCQDs, the CN absorption peak of NCQDs-rGO decreased around 1397cm ^-1 , while the NH absorption peak appeared at 1119cm ^-1 , indicating that NCQDs-rGO was partially electroreduced ^[93] , and proved that NCQDs successfully loaded onto the rGO surface.

Fig. 6 is (bare electrode) Bare GCE of embodiment 1 of the present invention, (electroreduction carbon dot/reduction graphene oxide electrode) Er-NCQD/rGO-GCE, (reduction graphene oxide electrode) rGO-GCE and (carbon Point electrode) cyclic voltammetry of NCQDs-GCE modified electrodes; Bare/GCE, Er-NCQDs-rGO/GCE, rGO/GCE and NCQDs/GCE modified electrodes were characterized for electrochemical performance. As shown in Fig. 6, it can be found that in [Fe(CN)6] ^3-/4- solution, the electrochemical performance of NCQDs/GCE is slightly worse than Bare/GCE, rGO/GCE and Er-NCQDs/GCE.

Fig. 7 is (bare electrode) Bare GCE of embodiment 1 of the present invention, (electroreduction carbon point/reduction graphene oxide electrode) Er-NCQD/rGO-GCE, reduction graphene oxide electrode) rGO-GCE and (carbon point Electrode) Electrochemical impedance spectroscopy of NCQDs-GCE modified electrode. And comparing the electrochemical impedance spectroscopy (EIS) in Figure 7, it can also be seen that the electron transfer efficiency of NCQDs is relatively low. Further from the results of electrochemical studies, it can be known that Er-NCQDs-rGO/GCE exhibited better electrochemical performance compared with NCQDs, but compared with rGO, Er-NCQDs-rGO/GCE had poor electrical conductivity, This may be attributed to the fact that while NCQDs may limit the electron transfer, rGO enhanced the electron transport of the modified electrode, making the electron transfer rate of NCQDs-rGo/GCE larger than that of NCQDs/GCE. After NCQDs-rGO is electroreduced, the interior of the carbon dots is in a charged state, with more free electrons, and at the same time, the content of oxygen and nitrogen elements of the oxygen-containing functional groups on the surface of graphene oxide and carbon dots is adjusted, resulting in a complex The conversion to electron-rich groups inside the material increases the specific surface area of the composite, leading to an enhanced electron transfer efficiency of Er-NCQDs-rGO/GCE.

The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiments, and within the scope of knowledge of those of ordinary skill in the art, various modifications can be made without departing from the spirit of the present invention. Variety. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other if there is no conflict.

Claims

A kind of preparation method of nitrogen-doped carbon dots-graphene oxide composite material, it is characterized in that, comprises the following steps:

(1) Mix carbon source and nitrogen source, carry out hydrothermal reaction, solid-liquid separation, obtain nitrogen-doped carbon dot solution;

(2) Graphene oxide and reducing agent are mixed and stirred, reacted, solid-liquid separation is taken, and the solid phase is dissolved to obtain a pre-reduced graphene oxide solution;

(3) The nitrogen-doped carbon dot solution and the pre-reduced graphene oxide solution are ultrasonically mixed, added dropwise on the electrode, and subjected to cyclic voltammetry reduction to obtain the nitrogen-doped carbon dot-graphene oxide composite material.
The preparation method according to claim 1, characterized in that, in step (1), the carbon source is mung bean.
The preparation method according to claim 1, characterized in that, in step (1), the nitrogen source is melamine.
The preparation method according to claim 1, characterized in that, in step (1), the temperature of the hydrothermal reaction is 180-200° C., and the time of the hydrothermal reaction is 6-8 hours.
The preparation method according to claim 1, characterized in that, in step (1), the specific steps of solid-liquid separation are: filtering and centrifuging the mixed solution formed after the hydrothermal reaction, collecting the supernatant, and then Filtration and dialysis were performed to obtain a nitrogen-doped carbon dot solution.
The preparation method according to claim 1, characterized in that, in step (2), the reducing agent is ascorbic acid.
The preparation method according to claim 1, characterized in that, in step (3), the electrode is a glassy carbon electrode, which is prepared by the following method: wet polishing the glassy carbon electrode, then ultrasonic cleaning, scanning, Blow dry with nitrogen, and scan in K 3 [Fe(CN) 6 ], K 4 [Fe(CN) 6 ], and KCl electrolyte solutions in sequence to obtain a glassy carbon electrode with a potential difference between the oxidation peak and the reduction peak below 100mV.
preparation method according to claim 1, is characterized in that, in step (3), the volume ratio of described nitrogen-doped carbon dot solution and described pre-reduced graphene oxide solution is (1-4):1.
Application of the nitrogen-doped carbon dot-graphene oxide composite material prepared by the preparation method described in claims 1-8 in detecting heavy metal ions.
An electrochemical sensor, characterized in that it comprises the nitrogen-doped carbon dot-graphene oxide composite material prepared by the preparation method described in claims 1-8.