TWI767833B - Ternary polymer composite with n-doped gqd intermediate layer for ammonia gas detection and production method thereof - Google Patents

Abstract

The present study is related to a ternary polymer composite with N-doped GQD intermediate layer for ammonia gas detection. The Indium oxide fibers were fabricated by electrospinning and an optical ratio of indium oxide fibers and polyaniline for detecting ammonia gas was found. By introducing N-doped GQD as an intermediate layer, the present study can improve the electronic conduction of p-n interface of the original type semiconductor polyaniline and n-type semiconductor indium oxide fiber. The N-doped GQD intermediate layer as a modified layer between polyaniline and indium oxide fiber is able to improve the sensibility and response of the ammonia gas detection.

Description

Ternary composite material for ammonia gas sensing using nitrogen-doped graphene quantum dots and its manufacturing method

A composite material for ammonia gas sensing, particularly a ternary composite material for ammonia gas sensing with nitrogen-doped graphene quantum dots and a manufacturing method thereof.

In addition to a large amount of nitrogen, oxygen, water vapor and carbon dioxide, normal human breath also contains more than 400 kinds of trace organic volatile compounds (Volatile Organic Compounds, VOCs). According to research, the increase in the concentration of VOCs in exhaled breath is closely related to diseases. By analyzing the phenomenon of abnormal VOCs concentration in human exhalation, it can be used as a reference for non-invasive diagnosis. If the general invasive diagnostic methods such as blood drawing are replaced by the breath test, the discomfort of the patient can be reduced, and the information in the breath can also be used to increase the understanding of the basic functions of the body.

In today's technology, the analysis methods for exhaled gas are mainly based on gas chromatography (GC) and related technologies or infrared spectroscopy (IR) and other technologies, but such analysis technology requires the construction of instruments and equipment. The threshold for professional training and result analysis also requires a certain amount of time. The general public's willingness to choose and convenience are very low, so it cannot be widely used by the general public. If a real-time gas sensor can be developed, which can measure the concentration of respiratory ammonia in time and can detect the concentration of respiratory ammonia with a fast enough response time, as a screening and diagnosis tool for kidney disease, it can be judged in advance whether there may be liver-related diseases. Disease patients, and advance treatment to achieve preventive medicine.

In order to improve the high-threshold equipment construction and personnel training standards of existing exhaled gas analysis methods, as well as the demand for rapid response to sensing results, the present invention provides a ternary complex for ammonia gas sensing with nitrogen-doped graphene quantum dots The material is fibrous and comprises from the inner layer to the outer layer of the fiber: a hollow nano-indium oxide fiber; a nitrogen-doped graphene quantum dot intermediate layer discontinuously coated on the surface of the hollow nano-fiber surface; and a continuous coating A polyaniline polymer layer covering the middle layer of the hollow nano-indium oxide fiber and the nitrogen-doped graphene quantum dots.

Wherein, the nitrogen-doped graphene quantum dot intermediate layer accounts for less than 10wt% of the overall fiber; the polyaniline polymer layer accounts for 30-40wt% of the overall fiber; and the hollow nano-indium oxide fiber accounts for less than 10wt% of the overall fiber 50wt%.

A method for manufacturing a ternary composite material for ammonia gas sensing with nitrogen-doped graphene quantum dots, the steps comprising: step 1: spinning a solution containing indium nitrate and polyvinylpyrrolidone into an electrospinning process by an electrospinning process silk fiber, heating the electrospinning fiber to sinter the polyvinylpyrrolidone to obtain a hollow nano indium oxide fiber; step 2: soaking the hollow nano indium oxide fiber in a solution containing nitrogen-doped graphene quantum dots, The negatively charged nitrogen-doped graphene quantum dots are adsorbed on the positively charged surface of the hollow indium oxide nanofibers by electrostatic adsorption; and step 3: the outermost layer is coated with polyaniline polymer by in-situ polymerization to obtain the Ternary composite material for ammonia gas sensing with nitrogen-doped graphene quantum dots.

Wherein, the aforementioned step 1 comprises: weighing 3.52g of polyvinylpyrrolidone and 1.07g of indium nitrate, pouring into 12ml of ethanol and 10.6ml of dimethylformamide, and stirring to make it uniformly dispersed until the solution is clear; The resulting solution was loaded into a needle cylinder, placed in an electrospinning machine and spun at 20kV, 0.3ml/hr, 15cm away from the collection plate, and the collection plate was spun at a collection speed of 50rpm for one day and collected for spinning; and The spinning film on the lower collection plate is clamped with a silicon wafer, and then placed in a high-temperature furnace at a heating rate of 5°C per minute, heated to 800°C and held for 3 hours to obtain the hollow nano-indium oxide fiber. .

Wherein, the aforementioned steps 2 and 3 include: soaking the hollow nano-indium oxide fibers into nitrogen-doped graphene quantum dots and letting them stand for 1 hour; after taking them out, adding an appropriate amount of alcohol, and centrifuging at 5000rpm for 1.5 hours; Dialysis with a 3500Da dialysis belt for one day, then negatively charged nitrogen-doped graphene quantum dots can be adsorbed on the surface of the positively charged hollow indium oxide nanofibers; the above product was added to 20ml of 1M hydrochloric acid solution, and the solution was placed on ice at 4°C In the bath, 0.17ml of aniline monomer was added and stirred for 2 hours; 0.51g of ammonium persulfate was dissolved in 10ml of 1M hydrochloric acid, wherein the molar ratio of ammonium persulfate and aniline monomer was 1.2:1, and slowly dripped In the solution of the previous step, react in an ice bath for 5 hours; pour the above solution into methanol to terminate the reaction; filter the solution with suction, and wash with deionized water and methanol; The ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots can be obtained.

From the above description, the widespread use of high-performance analytical techniques and the development of miniaturized control and processing systems in recent decades have opened up broad prospects for respiratory diagnosis as a non-invasive diagnostic tool for various diseases. The present invention takes the conductive polymer gas sensor as the concept and develops a non-invasive method, which is small, lightweight, easy to carry and popularized, and is applied to a sensing device for measuring the concentration of ammonia gas in human exhalation.

The invention uses electrospinning to produce indium oxide fibers and adds carbon material by nitrogen-doped graphene quantum dot adsorption method to improve the original p-type semiconductor polyaniline and n-type semiconductor indium oxide fibers. Electron conduction at the p-n interface acts as a modifying layer between the two and improves the efficiency and speed of the gas sensing response.

10: Ternary composite for ammonia gas sensing with nitrogen-doped graphene quantum dots

11: Hollow Nano Indium Oxide Fiber

13: Nitrogen-doped graphene quantum dots

15: Polyaniline polymer layer

S1-S3: Steps

The present invention will be further illustrated by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limitative, in these embodiments, the same number represents the same structure, wherein: FIG. 1 is the preferred implementation of the ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots of the present invention Example diagram.

FIG. 2 is a schematic flowchart of the steps of manufacturing the ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots according to the present invention.

3 is an FTIR spectrum diagram of the ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots of the present invention.

4 is an XRD diffraction diagram of a ternary composite material for ammonia gas sensing of nitrogen-doped graphene quantum dots according to the present invention.

5 is the SEM and TEM images of the ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots of the present invention.

6 is a schematic diagram of ammonia gas sensing of the ternary composite material for ammonia gas sensing of nitrogen-doped graphene quantum dots according to the present invention.

7 is a cycle diagram of the ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots of the present invention and the comparative example at a concentration of 1 ppm ammonia gas.

8 is a cycle test of the ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots of the present invention and the 1ppm ammonia gas concentration of the comparative example.

FIG. 9 is a comparison of the dynamic response of the present invention and the comparative example under the ammonia concentration of 0.6-2.0 ppm.

FIG. 10 is the long-term stability test of the present invention and the comparative example.

FIG. 11 is a percentage conversion representation of the response of FIG. 10 .

Figures 12 and 13 are the comparison of the response of different organic volatiles to the present invention and the comparative example under the test environment of 1.0 ppm and 2.0 ppm.

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some examples or embodiments of the present invention. For those of ordinary skill in the art, the present invention can also be applied to the present invention according to these drawings without any creative effort. other similar situations. Unless obvious from the locale or otherwise specified, the same reference numbers in the figures represent the same structure or operation.

It should be understood that "system", "device", "unit" and/or "module" as used herein is a method used to distinguish different components, elements, parts, parts or assemblies at different levels. However, other words may be replaced by other expressions if they serve the same purpose.

As shown in this specification and the claims, unless the context clearly dictates otherwise, the words "a", "an", "an" and/or "the" are not intended to be specific in the singular and may include the plural. Generally speaking, the terms "comprising" and "comprising" only imply that the clearly identified steps and elements are included, and these steps and elements do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

Referring to FIG. 1, the present invention provides a ternary composite material 10 for ammonia gas sensing with nitrogen-doped graphene quantum dots, which is fibrous and includes a hollow nano-indium oxide fiber 11 from the inner layer to the outer layer of the fiber. A nitrogen-doped graphene quantum dot (N-doped Graphene quantum dot, N-doped GOD) intermediate layer 13 is discontinuously coated on the surface of the hollow nanofiber surface layer 11, and is continuously coated on the hollow nano-indium oxide The fiber 11 and a polyaniline polymer layer 15 of the intermediate layer 13 of the nitrogen-doped graphene quantum dots. Wherein, preferably, the nitrogen-doped graphene quantum dot intermediate layer 13 accounts for less than 10 wt % of the overall fiber content, the polyaniline polymer layer 15 accounts for 30-40 wt % of the overall fiber content, and the hollow nano-indium oxide fibers 11 The total fiber content is less than 50wt%.

Wherein, the aforementioned so-called discontinuous coating state of the nitrogen-doped graphene quantum dot intermediate layer 13 can also be understood as being partially coated on the surface of the hollow nanofiber surface layer 11, so that part of the surface of the hollow nanofiber surface layer 11 is exposed and Directly in contact with the polyaniline polymer layer 15, and covered with the nitrogen-doped graphite The hollow nanofiber surface layer 11 of the ene quantum dot intermediate layer 13 and the outermost polyaniline polymer layer 15 are in contact with the local area to form a three-layer structure.

Next, please refer to FIG. 2 , the present invention also provides a method for manufacturing the ternary composite material 10 for ammonia gas sensing using the nitrogen-doped graphene quantum dots. The solution spinning of (In(NO ₃ ) ₃ ) and polyvinylpyrrolidone (PVP) is electrospun fibers, and the electrospun fibers are heated to sinter the PVP to obtain the hollow nano indium oxide fibers 11; step S2: Immerse the hollow indium nanofiber 11 in a solution containing nitrogen-doped graphene quantum dots, and use electrostatic adsorption to adsorb the negatively charged nitrogen-doped graphene quantum dots to the positively charged hollow indium oxide nanofiber 11 on the surface; and step S3: using the in-situ polymerization method to coat the outermost layer of the polyaniline polymer.

Wherein, a preferred embodiment of the specific steps of the aforementioned step 1 includes: weighing 3.52g of PVP and 1.07g of indium nitrate, pouring them into 12ml of ethanol and 10.6ml of dimethylformamide (DMF), Stir to make it evenly dispersed until the solution is clear; put the obtained solution into the needle cylinder, place it in the electrospinning machine and spin the spinning at 20kV, 0.3ml/hr, 15cm away from the collecting plate, and the collecting plate is at a collecting speed of 50rpm. One day and collect its spinning; and remove the spinning film on the collecting plate, clamp it with a silicon wafer, put it into a high-temperature furnace at a heating rate of 5 °C per minute, heat it to 800 °C and keep the temperature for 3 hours, that is, The hollow nano-indium oxide fiber 11 can be obtained.

A preferred embodiment of the specific steps of the aforementioned steps 2 and 3 includes: soaking the hollow nano-indium oxide fibers 11 into nitrogen-doped graphene quantum dots and letting them stand for 1 hour; after taking them out, adding an appropriate amount of alcohol and centrifuging at 5000 rpm 1.5 hours; dialyze with a dialysis tape with a molecular weight of 3500 Da for one day, and then the negatively charged nitrogen-doped graphene quantum dots can be adsorbed on the positively charged surface of the hollow indium oxide nanofibers 11; The above product was added to 20ml of 1M hydrochloric acid (HCl) solution, the solution was placed in an ice bath at 4°C, and 0.17ml of Aniline monomer was added and stirred for 2 hours; 0.51g of Ammonium persulphate (APS) was added. Dissolve in 10ml 1M HCl (APS/Aniline monomer molar ratio is 1.2:1), slowly drop it into the solution of the previous step, and react in an ice bath for 5 hours; pour the above solution into methanol to terminate the reaction The solution is suction filtered, and washed several times with DI water and methanol; and the product is put into 60 DEG C and dried for 24 hours, to obtain the ternary for ammonia gas sensing of the nitrogen-doped graphene quantum dots of the present invention Composite 10.

<Qualitative Test>

Please refer to Table 1 below, the elemental analysis table 10 of the ternary composite material for ammonia gas sensing of the nitrogen-doped graphene quantum dots provided by the present invention.

Please refer to FIG. 3 , which is the FTIR spectrum of PANI/NGQD-In. The main signal peaks of polyaniline are at (a) 1565cm ^-1 is the quinone ring C=C stretching deformation peak (stretching deformation); (b) 1463cm ^-1 is the C=C stretching deformation peak of the benzene ring; (c) 1294cm ^-1 is the CN stretching vibration peak on the benzene ring (-N-benzene-N-); (d) 1239cm ^-1 is the CN ⁺ on the hydrochloric acid-doped polyaniline Stretching vibration peak (stretching vibration); (e) 1112cm ^-1 is the C=N stretching vibration peak of the quinone ring; (f) 798cm ^-1 is the out-of-plane CH bending vibration peak (bending vibration) of the benzene ring; (g) 591, 567 and 538 are characteristic peaks of indium oxide with cubic structure.

Please refer to Figure 4, which is the XRD diffraction pattern of PANI/NGQD-In. In the same figure, the diffraction signal belonging to polyaniline and the crystalline diffraction signal of indium oxide can be seen, showing the prepared polyaniline It is a semi-crystalline Emeraldine salt form, which means that the addition of NGQD also does not affect the crystalline form of polyaniline.

Observing PANI/NGQD-In with SEM and TEM, it can be found from Figure 5 that there is no difference in the appearance of the binary material and the ternary material polyaniline, and the thickness of the polyaniline layer covered by the fibers of the two is observed in the TEM image. Consistently, it was shown that the addition of NGQDs did not affect the polyaniline polymerization form and the thickness of the polyaniline layer outside the indium oxide fibers.

<Validity Test>

6 is a schematic diagram of PANI/NGQD-In ammonia gas sensing. When the n-type semiconductor metal oxide In ₂ O ₃ and doped polyaniline (p-type semiconductor) form a composite material, a pn junction will be formed between the two (Junction) leads to charge migration at the interface. After ammonia gas is introduced, the ammonia gas will capture the positive charge on the outermost PANI chain of the indium oxide fiber, resulting in a decrease in the density of electron holes, but the amount of charge carried by the metal oxide decreases. Unaffected, the width of the depletion layer increases, so the resistance increases; nitrogen-doped graphene quantum dots are introduced between the pn interface to promote the carrier transfer efficiency, make the effect of the pn interface more significant, and improve the effect of the sensing response and efficiency.

Figure 7 is a cycle diagram of PANI/NGQD-In and P20In at 1 ppm ammonia concentration. It can be found that the PANI/NGQD-In provided by the present invention has the highest response of 15.2, while the responses of P20In and PANI of the comparative example are 11.2 respectively. Compared with 4.5, such a difference in response is mainly because the present invention uses metal oxide to form a semiconductor p-n interface effect, resulting in an increase in the overall material response; it has n-type semiconductor characteristics. The p-n interface is formed after the metal oxide and the PANI with p-type semiconductor characteristics are in contact. At this time, the PANI holes and the metal oxide electrons reach a diffusion equilibrium at the interface. This area is also called the depletion layer. The width of the depletion layer It will be changed by the charge, mobility and the characteristics of charged ions of both p-n materials. Since polyaniline adsorbs ammonia, its own holes will be reduced, but the charge of metal oxides will not be affected, so that The width of the depletion layer increases, which in turn increases the resistance.

Figure 8 is a cycle test at 1ppm ammonia concentration. After 5 cycles, it is observed that the present invention has the same integrity. After multiple cycles, it can recover to more than 90% of the initial response value. response, nor does it affect the repeatability of the material for ammonia sensing.

Figure 9 is a comparison of the dynamic response of different embodiments and the comparative example under the ammonia concentration of 0.6-2.0ppm. PANI, P20In and the embodiment of the present invention all increase with the increase of the ambient ammonia concentration. When the maximum concentration is 2ppm, PANI /NGQD-In and pure polyaniline were 41.2 and 6.23, respectively, showing that the addition of NGQD had the highest response at different concentrations, and had good circulation, and in the environment of kidney disease detection range of 1.1-1.6ppm, both had detective.

Figure 10 is the long-term stability test, the response changes of PANI, P20In, PANI/NGQD-In after 10 days of long-term test, Figure 11 is the percentage conversion of the response of Figure 10, it is observed from the figure that the PANI response after 10 days of test is 1.30, P20In is 6.51, PANI/NGQD-In is 14.6, PANI itself deprotonates itself due to its reaction with water vapor in the air, and autogenous aging reduces the number of sites where its own ammonia can be adsorbed. At 8 days, the response was less than 50% of the original, while the addition of metal oxides in the embodiment of the present invention provided a relatively stable structure, and the formation of the p-n interface made the change of the depletion layer during the adsorption of ammonia gas, resulting in a further increase in resistance and signal amplification. , NGQD-In effectively improves the electron-hole transport between the p-n interface, so that the response of PANI/NGQD-In is 11.7 after 10 days of testing, which is about 64% of the initial value.

Please refer to FIG. 12 and FIG. 13 , add 1.0ppm and 2.0ppm of volatile solutions of methanol, ethanol, acetone and hexane into the preset cavity, and perform ammonia gas detection in the present invention after the solution volatilizes such as sealing. 12 and 13 show that the response of each material to methanol, ethanol, acetone and hexane is relatively low compared with ammonia, which proves that the present invention has significant selectivity to ammonia and is not easily affected at room temperature. Interference with organic volatiles in the environment.

Next, please refer to the following table 3, the present invention tests the ternary composite material formed by different materials, and it clearly shows that the present invention has a significant response value in 0.60ppm ammonia gas concentration at room temperature, which is expressed as excellent Ammonia gas sensor.

Furthermore, unless explicitly stated in the claims, the order of the processing elements and sequences described in the present invention, the use of numbers and letters, or the use of other names are not intended to limit the order of the processes and methods of the present invention. While the foregoing disclosure discusses by way of various examples some embodiments of the invention that are presently believed to be useful, it is to be understood that such details are for purposes of illustration only and that additional claims are not limited to the disclosed embodiments, but rather The intention is to cover all modifications and equivalent combinations falling within the spirit and scope of the embodiments of the present invention.

Similarly, it should be noted that, in order to simplify the expression of the disclosed technology of the present invention and thus help the understanding of one or more embodiments of the present invention, in the foregoing description of the embodiments of the present invention, various features are sometimes combined into one embodiment. examples, drawings or descriptions thereof. However, this disclosure method does not mean that the claimed object of the present invention requires more features than those mentioned in the embodiments. In fact, there may be fewer features in a claim than all features of a single embodiment disclosed above without prejudice to the invention.

Some examples use numbers to describe quantities of ingredients and attributes, it should be understood that such numbers used to describe the examples, in some examples, use the modifiers "about", "approximately" or "substantially" to retouch. Unless stated otherwise, "about", "approximately" or "substantially" means that a variation of ±20% is allowed for the stated number. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximations that may vary depending upon the desired characteristics of individual embodiments. In some embodiments, the numerical parameters should take into account the specified significant digits and use a general digit reservation method. Notwithstanding that the numerical fields and parameters used in some embodiments of the invention to confirm the breadth of their ranges are approximations, in particular embodiments such numerical values are set as precisely as practicable.

Finally, it should be understood that the embodiments described in the present invention are only used to illustrate the principles of the embodiments of the present invention. Other variations are also possible within the scope of the present invention. Accordingly, by way of example and not limitation, alternative configurations of embodiments of the present invention may be considered consistent with the teachings of the present invention. Accordingly, the embodiments of the present invention are not limited to those expressly introduced and described in the present invention.

10: Ternary composite for ammonia gas sensing with nitrogen-doped graphene quantum dots

11: Hollow Nano Indium Oxide Fiber

13: Nitrogen-doped graphene quantum dots

15: Polyaniline polymer layer

Claims (5)

A ternary composite material for ammonia gas sensing with nitrogen-doped graphene quantum dots, which is fibrous and includes from the inner layer to the outer layer of the fiber: a hollow nano-indium oxide fiber; A nitrogen-doped graphene quantum dot intermediate layer on the surface of the fiber surface; and a polyaniline polymer layer continuously coated on the hollow nano-indium oxide fiber and the nitrogen-doped graphene quantum dot intermediate layer. The ternary composite material for ammonia gas sensing of nitrogen-doped graphene quantum dots according to claim 1, wherein: the intermediate layer of nitrogen-doped graphene quantum dots accounts for less than 10wt% of the overall fiber content; the polyaniline high The molecular layer accounts for 30-40 wt % of the whole fiber; and the hollow nano-indium oxide fiber accounts for less than 50 wt % of the whole fiber. A method for manufacturing a ternary composite material for ammonia gas sensing with nitrogen-doped graphene quantum dots, the steps comprising: step 1: spinning a solution containing indium nitrate and polyvinylpyrrolidone into an electrospinning process by an electrospinning process silk fiber, heating the electrospinning fiber to sinter the polyvinylpyrrolidone to obtain a hollow nano indium oxide fiber; step 2: soaking the hollow nano indium oxide fiber in a solution containing nitrogen-doped graphene quantum dots, The negatively charged nitrogen-doped graphene quantum dots are adsorbed on the positively charged surface of the hollow indium oxide nanofibers by electrostatic adsorption; and step 3: the outermost layer is coated with polyaniline polymer by in-situ polymerization to obtain the Ternary composite material for ammonia gas sensing with nitrogen-doped graphene quantum dots. The method for manufacturing a ternary composite material for ammonia gas sensing using nitrogen-doped graphene quantum dots as claimed in claim 3, wherein the aforementioned step 1 includes: Weigh 3.52g of polyvinylpyrrolidone and 1.07g of indium nitrate, pour it into 12ml of ethanol and 10.6ml of dimethylformamide, stir to make it evenly dispersed until the solution is clear; put the obtained solution into a syringe , placed in the electrospinning machine and 20kV, 0.3ml/hr, 15cm away from the collection plate, the collection plate was spun at a collection speed of 50rpm for one day and collected for spinning; And remove the spinning film on the collection plate , after being clamped with a silicon wafer, put into a high-temperature furnace at a heating rate of 5°C per minute, heated to 800°C and held for 3 hours, the hollow nano-indium oxide fiber can be obtained. The method for manufacturing a ternary composite material for ammonia gas sensing using nitrogen-doped graphene quantum dots as claimed in claim 3 or 4, wherein the aforementioned steps 2 and 3 include: the hollow nano-indium oxide fibers are soaked in Nitrogen-doped graphene quantum dots were dissolved overnight for 1 hour; after taking out, add an appropriate amount of alcohol, and centrifuge at 5000rpm for 1.5 hours; dialyze with a dialysis tape with a molecular weight of 3500Da for one day, and then negatively charged nitrogen-doped graphene quantum dots can be obtained. The positively charged surface of the hollow nano-indium oxide fiber; the above product was added to 20ml of 1M hydrochloric acid solution, the solution was placed in an ice bath at 4°C, and 0.17ml of aniline monomer was added and stirred for 2 hours; 0.51g of persulfuric acid was added Ammonium was dissolved in 10ml of 1M hydrochloric acid, wherein the molar ratio of ammonium persulfate and aniline monomer was 1.2:1, and slowly dripped into the solution of the previous step, and reacted in an ice bath for 5 hours; pour the above solution into methanol , the reaction was terminated; the solution was suction filtered, washed with deionized water and methanol; and dried at 60° C. for 24 hours, the ternary composite material for ammonia gas sensing with nitrogen-doped graphene quantum dots was obtained. .

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