Carbon quantum dot leak detection agent for pipeline gas leakage detection and preparation method and application thereof

Abstract

The invention belongs to the technical field of integrity management of oil and gas safety pipelines, and particularly relates to a carbon quantum dot leak detection agent for pipeline gas leakage detection and a preparation method and application thereof. By introducing C12H25 long-chain alkyl and adopting a targeted purification process, the problems that an existing quantum dot leak detection agent is prone to agglomeration due to interfacial tension difference in a non-polar leakage medium due to the fact that traditional carbon quantum dots are high in hydrophilicity, the nitrogen doping rate is low, the detection sensitivity is low due to the fact that the carbon quantum dots are prone to degradation and agglomeration in a traditional purification process, and the like are solved. And the core requirements of high fluorescence, easy detection and high stability of the leakage detection agent in pipeline gas leakage detection are met.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas pipeline integrity management technology, specifically relating to a carbon quantum dot leak detector for pipeline gas leak detection, its preparation method and application. Background Technology

[0002] Pipeline transportation, as one of the main methods of gas transport, is crucial for industrial production and environmental protection due to its safety and stability. However, pipelines are prone to leaks due to corrosion, aging, and third-party damage, leading not only to economic losses but also potential safety accidents such as explosions and poisoning. Therefore, efficient and sensitive leak detection technology is urgently needed. Leak detection using leak detectors is an important method for detecting pipeline gas leaks. Leak detectors are generally classified into chemical leak detectors, radioactive leak detectors, and physical leak detectors. Chemical leak detectors pose problems such as potential environmental pollution with long-term use and potential toxicity at high concentrations. Radioactive leak detectors pose environmental diffusion risks and require complex detection equipment. Physical leak detectors, on the other hand, are expensive and have limitations in their application environment. Therefore, a leak detector that is highly sensitive, low-risk, safe, environmentally friendly, and low-cost is needed based on actual engineering requirements.

[0003] In recent years, the emergence of nanomaterials has brought new breakthroughs to this field. Among them, carbon quantum dots, as a novel carbon nanomaterial, have become a research hotspot due to their unique optical properties, good biocompatibility, and other chemical properties. Carbon quantum dots are a type of carbon nanomaterial with good fluorescence properties and chemical stability. By introducing various functional groups onto the surface of carbon quantum dots, their chemical and physical properties can be significantly altered. Research is being conducted on the preparation of new carbon quantum dots or heteroatom-doped carbon quantum dots using different raw materials, and exploring their new applications. For example, Chinese patent document CN120505101A discloses a method for hydrothermal synthesis of carbon quantum dots based on tartaric acid and organic amines. This method uses tartaric acid and organic amines to hydrothermally synthesize carbon quantum dots with good controllability and uniform particle size. However, the ethanolamine, diethanolamine, and triethanolamine used in the synthesis of carbon quantum dots all contain polar hydroxyl groups, resulting in low nitrogen doping rates, weak fluorescence intensity, and poor stability, which cannot meet the needs of pipeline gas leak detection. Therefore, it is of great significance to develop a carbon quantum dot with high fluorescence intensity and high stability as a pipeline gas leak detection agent to achieve high sensitivity, low risk, safety, environmental protection and low cost, and to solve the performance shortcomings or application limitations of traditional leak detection agents. Summary of the Invention

[0004] In view of this, the present invention aims to provide a carbon quantum dot leak detector for pipeline gas leak detection and its preparation method, by introducing C 12 H 25Long-chain alkyl groups and targeted purification processes are used to address the problems of existing quantum dot leak detectors, such as the strong hydrophilicity of traditional carbon quantum dots, which easily leads to agglomeration due to interfacial tension differences in non-polar leak media, low nitrogen doping rate, and low detection sensitivity and insufficient stability caused by carbon quantum dot degradation and agglomeration in traditional purification processes. This approach meets the core requirements of leak detectors in pipeline gas leak detection, which need to be highly fluorescent, easy to detect, and highly stable.

[0005] To achieve the above objectives, the first objective of this invention is to provide a carbon quantum dot leak detector for detecting pipeline gas leaks, employing the following technical solution: A carbon quantum dot leak detector for detecting gas leaks in pipelines, comprising carbon quantum dots with the chemical formula C x H y N z O w The core carbon-nitrogen-oxygen skeleton and m chemical formulas are C 12 H 25 The dodecylamine molecules of NH2 are linked by covalent or hydrogen bonds to form a composite nanostructure, wherein x≥50, y≥20, 1≤z≤15, 5≤w≤20, and 1≤m≤3.

[0006] Furthermore, the carbon quantum dot leak detector comprises nanoscale carbon-based particles CQDs-NC 12 H 25 The CQDs-NC 12 H 25 The core carbon-nitrogen-oxygen framework is a graphene-like sp. 2 Hybrid carbon nanostructures with surface-modified functional groups such as amino, long-chain alkyl, hydroxyl, and carboxyl groups.

[0007] It is worth noting that the carbon quantum dot leak detector includes carbon quantum dots (CQDs-NC). 12 H 25 These carbon quantum dots are nanoscale carbon-based particles with a core of sp²-hybridized amorphous or graphitized carbon. The surface is modified with functional groups such as amino, long-chain alkyl, hydroxyl, and carboxyl groups, and nitrogen atoms are doped into the carbon framework in the form of graphitic nitrogen. These carbon quantum dots are prepared via a solvothermal reaction using tartaric acid as the carbon source, ethylenediamine as the nitrogen source, and dodecylamine as the surface modifier. Their elemental composition mainly includes carbon, hydrogen, nitrogen, and oxygen. They do not have a fixed single molecular formula but possess the following structural characteristics: The core carbon-nitrogen-oxygen framework: This framework is formed by the solvothermal polymerization of tartaric acid and ethylenediamine, and is a graphene-like sp. 2Hybrid carbon nanostructures; in which carbon is the core of the framework, forming a basic topological structure of six-membered rings or six-membered rings; nitrogen comes from the amino group of ethylenediamine and is doped into the carbon framework in the form of graphite nitrogen; oxygen comes from the carboxyl and hydroxyl groups of tartaric acid, part of which is retained on the surface of the core framework in the form of hydroxyl and carboxyl functional groups, and part of which is embedded in the edge of the carbon framework in the form of C=O bonds. Surface functional groups: include amino groups derived from ethylenediamine, long-chain alkyl groups from dodecylamine, hydroxyl groups from tartaric acid, and carboxyl groups. The proportions of each functional group vary slightly depending on the reaction conditions. Among them, the amino group in the dodecylamine molecule undergoes an amidation reaction with the carboxyl group on the surface of the core framework to form a -CONH- covalent bond, introducing a long-chain alkyl group. The amino group in the dodecylamine molecule forms a hydrogen bond with the hydroxyl group on the surface of the core framework.

[0008] A second objective of this invention is to provide a method for preparing the carbon quantum dot leak detector as described above.

[0009] A method for preparing a carbon quantum dot leak detector, using tartaric acid as a carbon source, ethylenediamine as a nitrogen source, and dodecylamine as a surface modifier, is prepared by a solvothermal reaction.

[0010] It is worth noting that, considering the strong hydrophilicity of traditional carbon quantum dots, their tendency to agglomerate due to interfacial tension differences in non-polar leakage media, and their low nitrogen doping rate, as well as the technical difficulties of carbon quantum dot degradation and agglomeration in traditional purification processes, resulting in the disadvantages of low detection sensitivity and insufficient stability of existing quantum dot leak detectors, the preparation method of carbon quantum dot leak detectors disclosed in this invention introduces C 12 H 25 Long-chain alkyl groups can solve the above problems.

[0011] First, C 12 H 25 Long-chain alkyl groups are typical nonpolar hydrophobic segments. By chemically bonding with the carbon quantum dot framework, their compatibility bottleneck with nonpolar media is overcome. While the inherent polar groups such as hydroxyl and amino groups on the surface of carbon quantum dots endow them with excellent dispersibility in polar media, their strong hydrophilicity and lack of hydrophobic interaction when exposed alone lead to agglomeration due to interfacial tension differences in nonpolar leakage media. Secondly, C... 12 H 25 Long-chain alkyl groups are covalently anchored to the surface of carbon quantum dots. Their hydrophobic properties form a dense steric hindrance layer around the carbon core, which on the one hand inhibits the aggregation of carbon quantum dot particles due to van der Waals forces, and on the other hand reduces the damage to the luminescent centers of carbon quantum dots by active substances such as moisture and oxygen in the external environment, thereby improving their chemical and optical stability. Also, C 12 H 25The introduction of long-chain alkyl groups can precisely match the usage requirements of leak detection scenarios: through the amphiphilic design of the carbon quantum dot surface, two-phase adaptive dispersion is achieved in methanol-hydrocarbon mixed media, which maintains dispersion stability and enhances the affinity for hydrocarbon leaks; during the leak detection process, the hydrophobic segments can reduce the non-specific adsorption of carbon quantum dots to leak gaps, reduce their movement resistance in the gaps, and combined with the rapid volatilization characteristics of methanol, promote the directional migration of carbon quantum dots along the gas escape channel, and finally enrich and stably retain them at the leak point.

[0012] Furthermore, the specific steps of the preparation method include: (1) Dissolve tartaric acid and ethylenediamine in dimethylformamide at a certain mass-volume ratio, heat to 50-80 °C, and stir magnetically at 200-300 rpm for 20-30 min until completely dissolved to form a transparent mixed solution; (2) Add a certain mass-volume ratio of dodecylamine to the transparent mixed solution in step (1), and continue to stir magnetically for 10-15 minutes to form a precursor solution; (3) Transfer the precursor solution obtained in step (2) to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 20-30 min. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 180-200 °C at a rate of 5-10 °C / min and keep it at a constant temperature for 8-12 h. (4) After the reaction is complete, the suspension is naturally cooled to room temperature. The suspension is then filtered through a filter membrane with a pore size of 0.22~0.45μm to remove large particulate impurities and obtain the supernatant precursor solution. (5) Transfer the supernatant precursor solution obtained in step (4) to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 3~5 ℃, centrifuge at 7000~10000 rpm for 30~45 min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. (6) Slowly drop the supernatant obtained in step (5) into anhydrous ethanol, sonicate for 15-20 min, then centrifuge at 10000-15000 rpm for 10-15 min and collect the precipitate; (7) The precipitate collected in step (6) is redispersed in deionized water to prepare a deionized water dispersion mixture. The pH value of the mixture is measured and the pH is adjusted according to the measurement results. (8) Transfer the deionized water dispersion mixture obtained in step (7) to a regenerated cellulose dialysis bag with a molecular weight cutoff of 500~3500 Da, seal both ends with dialysis clamps, completely immerse the dialysis bag in a beaker containing deionized water, place a stir bar, and perform low-speed magnetic stirring at a stirring speed of 200~300 rpm. Replace the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. (9) Dispense the carbon quantum dot solution after dialysis in step (8) into lyophilization bottles, place the lyophilization bottles in a freezer at -60~80℃ for 2 hours, quickly transfer the pre-frozen sample to the cold trap of a freeze dryer pre-cooled to -30~50℃, immediately start the vacuum pump, set the vacuum degree to 0.1~1mbar, and maintain it for 12~24 hours to obtain light yellow powdered carbon quantum dots CQDs-NC 12 H 25 Store in a nitrogen atmosphere; (10) The carbon quantum dots CQDs-NC obtained in step (9) 12 H 25 Carbon quantum dot leak detectors can be obtained by dispersing them in sufficient methanol at room temperature and pressure until they are completely dissolved.

[0013] It is worth noting that this invention utilizes ethylenediamine as a highly active nitrogen source for the diamino group and dodecylamine as a composite nitrogen source for synergistic doping. Under nitrogen protection at 200°C, the mixture is pyrolyzed at a heating rate of 10°C / min for 12 hours. This allows the highly active nitrogen atoms in ethylenediamine to efficiently embed into the carbon framework through cyclization, condensation, and carbon-nitrogen co-doping reactions, forming a stable doped structure dominated by pyridine nitrogen. Simultaneously, the C atoms in dodecylamine... 12 H 25 Long-chain alkyl groups are embedded in the surface of carbon quantum dots. On the one hand, pyridine nitrogen introduces lone pairs of electrons into the carbon framework, changing the local electron cloud density and band structure. As an electron donor, it effectively passivates the dangling bonds and nonradiative recombination centers on the carbon quantum dot surface, reducing fluorescence quenching and optimizing the crystallinity and size distribution of the carbon core to form a more uniform quantum confinement effect, significantly improving luminescence intensity and solving the problems of low nitrogen doping rate and weak fluorescence in traditional carbon quantum dots. On the other hand, C 12 H 25 The long chain endows carbon quantum dots with moderate hydrophobicity, enhancing their adsorption at the interface of leaked gas media and inhibiting the aggregation of carbon quantum dots due to polarity differences. At the same time, the purification process uses a combination of filtration and centrifugation to achieve efficient separation of the reaction mixture, avoiding interference from impurities. Dialysis is used to remove salts and small molecule impurities, and precise control of the solution environment pH can achieve the effect of stabilizing the dispersion of carbon quantum dots and preventing their aggregation or degradation. Finally, freeze-drying technology is used to achieve high-stability preservation of carbon quantum dots, solving the problem of thermal decomposition or aggregation caused by drying in traditional methods.

[0014] Furthermore, in step (1), the mass-to-volume ratio of tartaric acid and ethylenediamine is 5:(4~6), and the volume ratio of dimethylformamide to the tartaric acid-ethylenediamine mixed solution is (23~30):1.

[0015] Furthermore, in step (2), the mass ratio of dodecylamine to tartaric acid added in step (1) is (2~5):1.

[0016] Furthermore, in step (6), the volume ratio of anhydrous ethanol to supernatant is 3:1.

[0017] Furthermore, in step (7), when pH < 7, dilute ethylenediamine solution is added dropwise and stirred continuously until the solution pH ≈ 7; when pH > 7, dilute tartaric acid solution is added dropwise and stirred continuously until the solution pH ≈ 7.

[0018] Furthermore, in step (10), carbon quantum dots (CQDs-NC) 12 H 25 The mass-to-volume ratio of methanol to methanol is 1:(10~100).

[0019] It is worth noting that this invention achieves efficient nitrogen doping in the form of pyridine nitrogen through the synergistic and mild pyrolysis of ethylenediamine and dodecylamine. Pyridine nitrogen modulates the electronic structure by introducing lone pairs of electrons into the carbon framework, passivates surface dangling bonds and nonradiative recombination centers, and combines with the C introduced by dodecylamine. 12 H 25 Hydrophobic long chains reduce water and oxygen erosion and surface aggregation, improving the material's resistance to photo / oxidative degradation from a structural perspective. At the same time, a multi-stage purification process is adopted to systematically remove unreacted precursors, soluble byproducts, and unstable surface components, avoiding fluorescence quenching induced by photo-oxidation, acid and alkali corrosion, and aggregation. Through the synergistic improvement of stability through "high-efficiency nitrogen doping - structural modification - purification guarantee", the long-term stability of carbon quantum dot fluorescence signal is finally achieved.

[0020] A third objective of this invention is to provide an application of the carbon quantum dot leak detector as described above.

[0021] An application of a carbon quantum dot leak detector, which is suitable for detecting leaks in pipelines containing hydrocarbon gases and inert gases. The leak is detected by mixing the leaked gas with the gas in the pipeline after atomization and by using a fluorescence spectrometer. The detection sensitivity is ≤1 ppm.

[0022] It is worth noting that this invention addresses the problems of low nitrogen doping rate, weak fluorescence intensity, and insufficient stability in traditional carbon quantum dots. It achieves efficient embedding of nitrogen into the carbon framework in the form of pyridine nitrogen through the synergistic and mild pyrolysis of ethylenediamine and dodecylamine, combined with the C introduced by dodecylamine. 12 H 25By using hydrophobic long chains to modulate the electronic structure of carbon quantum dots, passivating surface dangling bonds and nonradiative recombination centers, enhancing the conjugation stability of carbon nuclei, and improving surface hydrophobicity, the adsorption capacity at the interface with leaked gases is significantly improved, promoting the enrichment of carbon quantum dots and signal response near the leak point. At the same time, a multi-stage purification process is used to systematically remove unstable components and avoid the influence of photo-oxidation, agglomeration, and quenching sources. Finally, nitrogen-doped carbon quantum dots with high fluorescence intensity, strong interfacial affinity, long-term stability, and low water activity are obtained. In practical applications such as gas leak detection, the sensitivity, response speed, and stability are comprehensively improved, highlighting the technological advancement of the synergistic regulation of "efficient nitrogen doping-structural modification-purification assurance".

[0023] Compared with existing technologies, this invention discloses a method for preparing highly stable nitrogen-doped carbon quantum dots through pyridine nitrogen doping and a multi-stage purification process, achieving the following beneficial effects: 1. This invention utilizes a synergistic and mild pyrolysis technique involving ethylenediamine and dodecylamine to efficiently embed nitrogen into the carbon framework in the form of pyridine nitrogen. This combines the regulation of carbon electronic structure by pyridine nitrogen with the carbon-based electron configuration introduced by dodecylamine. 12 H 25 The hydrophobic long chain solves the problems of nitrogen doping rate and surface properties from the essence of material structure, and solves the problems of weak fluorescence signal and insufficient detection sensitivity caused by low nitrogen doping rate and many defects in traditional carbon quantum dots.

[0024] 2. This invention creatively adopts a "hydrophobic-hydrophilic balance" design concept, introducing C through dodecylamine. 12 H 25 Long-chain modulation of carbon quantum dot surface properties not only enhances the stability of carbon nuclei but also imparts appropriate hydrophobicity to the material. This not only improves the dispersion ability of carbon quantum dots in nonpolar media and solves the problem of poor interfacial affinity and difficulty in enriching response at gas leak sites for traditional carbon quantum dots, but also significantly enhances the detection adaptability to nonpolar leaking gas media. Furthermore, surface state optimization further suppresses nonradiative recombination centers, providing a dual guarantee for improving fluorescence intensity.

[0025] 3. This invention designs a multi-stage purification process that systematically removes unreacted precursors, soluble impurities, and unstable surface components, avoiding fluorescence quenching induced by photo-oxidation, structural defects, and aggregation. This process works synergistically with the structural stabilizing effect of pyridine nitrogen to ultimately produce nitrogen-doped carbon quantum dots with high fluorescence intensity, excellent interfacial dispersibility, and long-term stability. In practical leak detection applications, these dots exhibit significant technical advantages such as high detection sensitivity, fast response speed, and stable performance. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0027] Figure 1 The carbon quantum dots (CQDs-NC) prepared in Example 1 of this invention 12 H 25 Fourier transform infrared spectrum.

[0028] Figure 2 The carbon quantum dots (CQDs-NC) prepared in Example 1 of this invention 12 H 25 The fluorescence spectrum.

[0029] Figure 3 The carbon quantum dots (CQDs-NC) prepared in Example 1 of this invention 12 H 25 XPS graph. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0032] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0033] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0034] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0035] This invention discloses a carbon quantum dot leak detector for pipeline gas leak detection, its preparation method, and its application, belonging to the field of oil and gas pipeline integrity management technology. This invention introduces C... 12 H 25 Long-chain alkyl groups and targeted purification processes are used to address the problems of existing quantum dot leak detectors, such as the strong hydrophilicity of traditional carbon quantum dots leading to agglomeration due to interfacial tension differences in non-polar leak media, low nitrogen doping rate, and low detection sensitivity and insufficiency caused by carbon quantum dot degradation and agglomeration in traditional purification processes. This approach meets the core requirements of leak detectors in pipeline gas leak detection, which need to be highly fluorescent, easy to detect, and highly stable.

[0036] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0037] Example 1 A carbon quantum dot leak detector for pipeline gas leak detection and its preparation method, specifically including the following steps: Step 1: Dissolve 1.00g tartaric acid and 0.8mL ethylenediamine in 50mL dimethylformamide, heat to 50℃, and magnetically stir at 300rpm for 30min until completely dissolved to form a transparent mixed solution; Step 2: Add 0.16g of dodecylamine to the clear mixed solution from Step 1, and continue magnetic stirring for 15 minutes to form a precursor solution; Step 3: Transfer the precursor solution obtained in Step 2 to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 30 min to remove oxygen. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 200°C at a rate of 10°C / min and keep it at the temperature for 12 h. Step 4: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45μm and 0.22μm pore size filter membranes to remove large particulate impurities, resulting in a supernatant precursor solution. Step 5: Transfer the supernatant precursor solution obtained in Step 4 to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 5℃, centrifuge at 8000rpm for 45min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. Step 6: Slowly drop the supernatant obtained in step 5 into anhydrous ethanol, sonicate for 20 min, then centrifuge at 12000 rpm for 15 min and collect the precipitate; Step 7: Redisperse the precipitate collected in Step 6 in deionized water to prepare a deionized water dispersion mixture. Measure the pH value of the mixture and adjust the pH according to the measurement results: when pH < 7, add dilute ethylenediamine solution dropwise while stirring continuously until the solution pH ≈ 7; when pH > 7, add dilute tartaric acid solution dropwise while stirring continuously until the solution pH ≈ 7. Step 8: Transfer the deionized water dispersion mixture obtained in Step 7 to a regenerated cellulose dialysis bag with a molecular weight cutoff of 1000 Da. Seal both ends with dialysis clamps. Completely immerse the dialysis bag in a beaker containing deionized water. Place a stir bar in the beaker and perform low-speed magnetic stirring at 300 rpm. Replace the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. Step 9: Aliquot the carbon quantum dot solution from Step 8 into lyophilization vials, place the vials in a -80°C freezer for 2 hours, and quickly transfer the pre-frozen sample to a freeze dryer cold trap pre-cooled to -50°C. Immediately start the vacuum pump, set the vacuum level to 0.1 mbar, and maintain this for 24 hours to obtain pale yellow nitrogen-doped carbon quantum dots (CQDs-NC). 12 H 25 Store in a nitrogen atmosphere; Step 10: The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in step 9 are... 12 H 25 Carbon quantum dot leak detectors can be obtained by dispersing them in sufficient methanol at room temperature and pressure until they are completely dissolved.

[0038] Figure 1 The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in this embodiment 12 H 25 The Fourier transform infrared spectrum, in the infrared spectrum, 1626 cm⁻¹ 1 The absorption peaks at 2924 and 2853 cm⁻¹ are caused by the C=C stretching vibration, indicating the formation of carbon nuclei. 1 The absorption peak at C is due to Produced by H stretching vibration, 1626cm 1 The absorption peak at 1580 cm⁻¹ is generated by the stretching vibration of C=O and is the amide I band. 1The absorption peak at 3300~3500 cm⁻¹ is the coupling of the NH bending vibration and CN stretching vibration in the amide bond, which is the amide II band. The coexistence of both amide I and II bands confirms the presence of the amide bond. 1 A broad and strong absorption peak exists due to N. The stretching vibration of H is generated at 1241 cm. 1 The absorption peak at the point is generated by the stretching vibration of aliphatic CN. This indicates that nitrogen has been doped into the carbon skeleton of CQDs through a solvothermal reaction. Dodecylamine participates in the reaction, successfully introducing long-chain alkyl groups, thus exhibiting high vapor pressure and fluorescence performance.

[0039] Figure 2 The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in this embodiment 12 H 25 The fluorescence spectrum of the carbon quantum dots prepared in Example 1 was prepared into a 0.01 mg / mL solution and tested using a fluorescence spectrometer. The results are shown in the figure. As can be seen from the figure, the optimal emission wavelength of this carbon quantum dot leak detector is 509 nm, a characteristic wavelength located in the green region, which is consistent with the typical fluorescence emission range of carbon quantum dots. Furthermore, this emission peak has a narrow half-width, indicating that the prepared carbon quantum dots have good monodispersity and size uniformity. In addition, the strong fluorescence emission at 509 nm indicates that this carbon quantum dot leak detector has good fluorescence performance.

[0040] Figure 3 The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in this embodiment 12 H 25 The XPS spectra are as follows: a) is the full spectrum, showing C1s, N1s, and O1s peaks with no obvious impurity elements; b) is the narrow C1s spectrum, showing a sp²C=C aromatic carbon core structure at 284.8 eV, a CN peak at 285.5 eV, and a CO peak at 286.5 eV, confirming nitrogen doping in the framework; c) is the narrow O1s spectrum, showing a C=O peak at 531.5 eV and a CO / -OH peak at 532.5 eV, indicating the presence of carboxyl and hydroxyl functional groups on the surface; d) is the narrow N1s spectrum, showing only a pyridine nitrogen peak at 398.5 eV, with no free nitrogen peak at 400.0 eV. The consistency between the 286.5 eV CO / CN peak in the C1s spectrum and the Fourier transform infrared spectrum further confirms the successful participation of the long-chain alkyl group of the dodecylamine in the reaction.

[0041] Example 2 A carbon quantum dot leak detector for pipeline gas leak detection and its preparation method, specifically including the following steps: Step 1: Dissolve 1.00g tartaric acid and 1.00mL ethylenediamine in 50mL dimethylformamide, heat to 50℃, and magnetically stir at 300rpm for 30min until completely dissolved to form a transparent mixed solution; Step 2: Add 0.16g of dodecylamine to the clear mixed solution from Step 1, and continue magnetic stirring for 15 minutes to form a precursor solution; Step 3: Transfer the precursor solution obtained in Step 2 to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 30 min to remove oxygen. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 200°C at a rate of 10°C / min and keep it at the temperature for 12 h. Step 4: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45μm and 0.22μm pore size filter membranes to remove large particulate impurities, resulting in a supernatant precursor solution. Step 5: Transfer the supernatant precursor solution obtained in Step 4 to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 5℃, centrifuge at 8000rpm for 45min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. Step 6: Slowly drop the supernatant obtained in step 5 into anhydrous ethanol, sonicate for 20 min, then centrifuge at 12000 rpm for 15 min and collect the precipitate; Step 7: Redisperse the precipitate collected in Step 6 in deionized water to prepare a deionized water dispersion mixture. Measure the pH value of the mixture and adjust the pH according to the measurement results: when pH < 7, add dilute ethylenediamine solution dropwise while stirring continuously until the solution pH ≈ 7; when pH > 7, add dilute tartaric acid solution dropwise while stirring continuously until the solution pH ≈ 7. Step 8: Transfer the deionized water dispersion mixture obtained in Step 7 to a regenerated cellulose dialysis bag with a molecular weight cutoff of 1000 Da. Seal both ends with dialysis clamps. Completely immerse the dialysis bag in a beaker containing deionized water. Place a stir bar in the beaker and perform low-speed magnetic stirring at 300 rpm. Replace the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. Step 9: Aliquot the carbon quantum dot solution from Step 8 into lyophilization vials, place the vials in a -80°C freezer for 2 hours, and quickly transfer the pre-frozen sample to a freeze dryer cold trap pre-cooled to -50°C. Immediately start the vacuum pump, set the vacuum level to 0.1 mbar, and maintain this for 24 hours to obtain pale yellow nitrogen-doped carbon quantum dots (CQDs-NC). 12 H 25 Store in a nitrogen atmosphere; Step 10: The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in step 9 are... 12 H 25 Carbon quantum dot leak detectors can be obtained by dispersing them in sufficient methanol at room temperature and pressure until they are completely dissolved.

[0042] Example 3 A carbon quantum dot leak detector for pipeline gas leak detection and its preparation method, specifically including the following steps: Step 1: Dissolve 1.00g tartaric acid and 1.20mL ethylenediamine in 50mL dimethylformamide, heat to 50℃, and magnetically stir at 300rpm for 30min until completely dissolved to form a transparent mixed solution; Step 2: Add 0.16g of dodecylamine to the clear mixed solution from Step 1, and continue magnetic stirring for 15 minutes to form a precursor solution; Step 3: Transfer the precursor solution obtained in Step 2 to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 30 min to remove oxygen. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 200°C at a rate of 10°C / min and keep it at the temperature for 12 h. Step 4: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45μm and 0.22μm pore size filter membranes to remove large particulate impurities, resulting in a supernatant precursor solution. Step 5: Transfer the supernatant precursor solution obtained in Step 4 to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 5℃, centrifuge at 8000rpm for 45min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. Step 6: Slowly drop the supernatant obtained in step 5 into anhydrous ethanol, sonicate for 20 min, then centrifuge at 12000 rpm for 15 min and collect the precipitate; Step 7: Redisperse the precipitate collected in Step 6 in deionized water to prepare a deionized water dispersion mixture. Measure the pH value of the mixture and adjust the pH according to the measurement results: when pH < 7, add dilute ethylenediamine solution dropwise while stirring continuously until the solution pH ≈ 7; when pH > 7, add dilute tartaric acid solution dropwise while stirring continuously until the solution pH ≈ 7. Step 8: Transfer the deionized water dispersion mixture obtained in Step 7 to a regenerated cellulose dialysis bag with a molecular weight cutoff of 1000 Da. Seal both ends with dialysis clamps. Completely immerse the dialysis bag in a beaker containing deionized water. Place a stir bar in the beaker and perform low-speed magnetic stirring at 300 rpm. Replace the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. Step 9: Aliquot the carbon quantum dot solution from Step 8 into lyophilization vials, place the vials in a -80°C freezer for 2 hours, and quickly transfer the pre-frozen sample to a freeze dryer cold trap pre-cooled to -50°C. Immediately start the vacuum pump, set the vacuum level to 0.1 mbar, and maintain this for 24 hours to obtain pale yellow nitrogen-doped carbon quantum dots (CQDs-NC). 12 H 25 Store in a nitrogen atmosphere; Step 10: The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in step 9 are... 12 H 25 Carbon quantum dot leak detectors can be obtained by dispersing them in sufficient methanol at room temperature and pressure until they are completely dissolved.

[0043] Example 4 A carbon quantum dot leak detector for pipeline gas leak detection and its preparation method, specifically including the following steps: Step 1: Dissolve 1.00g tartaric acid and 0.80mL ethylenediamine in 50mL dimethylformamide, heat to 50℃, and magnetically stir at 300rpm for 30min until completely dissolved to form a transparent mixed solution; Step 2: Add 0.24g of dodecylamine to the clear mixed solution from Step 1, and continue magnetic stirring for 15 minutes to form a precursor solution; Step 3: Transfer the precursor solution obtained in Step 2 to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 30 min to remove oxygen. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 200°C at a rate of 10°C / min and keep it at the temperature for 12 h. Step 4: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45μm and 0.22μm pore size filter membranes to remove large particulate impurities, resulting in a supernatant precursor solution. Step 5: Transfer the supernatant precursor solution obtained in Step 4 to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 5℃, centrifuge at 8000rpm for 45min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. Step 6: Slowly drop the supernatant obtained in step 5 into anhydrous ethanol, sonicate for 20 min, then centrifuge at 12000 rpm for 15 min and collect the precipitate; Step 7: Redisperse the precipitate collected in Step 6 in deionized water to prepare a deionized water dispersion mixture. Measure the pH value of the mixture and adjust the pH according to the measurement results: when pH < 7, add dilute ethylenediamine solution dropwise while stirring continuously until the solution pH ≈ 7; when pH > 7, add dilute tartaric acid solution dropwise while stirring continuously until the solution pH ≈ 7. Step 8: Transfer the deionized water dispersion mixture obtained in Step 7 to a regenerated cellulose dialysis bag with a molecular weight cutoff of 1000 Da. Seal both ends with dialysis clamps. Completely immerse the dialysis bag in a beaker containing deionized water. Place a stir bar in the beaker and perform low-speed magnetic stirring at 300 rpm. Replace the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. Step 9: Aliquot the carbon quantum dot solution from Step 8 into lyophilization vials, place the vials in a -80°C freezer for 2 hours, and quickly transfer the pre-frozen sample to a freeze dryer cold trap pre-cooled to -50°C. Immediately start the vacuum pump, set the vacuum level to 0.1 mbar, and maintain this for 24 hours to obtain pale yellow nitrogen-doped carbon quantum dots (CQDs-NC). 12 H 25 Store in a nitrogen atmosphere; Step 10: The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in step 9 are... 12 H 25 Carbon quantum dot leak detectors can be obtained by dispersing them in sufficient methanol at room temperature and pressure until they are completely dissolved.

[0044] Example 5 A carbon quantum dot leak detector for pipeline gas leak detection and its preparation method, specifically including the following steps: Step 1: Dissolve 1.00g tartaric acid and 0.80mL ethylenediamine in 50mL dimethylformamide, heat to 50℃, and magnetically stir at 300rpm for 30min until completely dissolved to form a transparent mixed solution; Step 2: Add 0.32g of dodecylamine to the clear mixed solution from Step 1, and continue magnetic stirring for 15 minutes to form a precursor solution; Step 3: Transfer the precursor solution obtained in Step 2 to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 30 min to remove oxygen. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 200°C at a rate of 10°C / min and keep it at the temperature for 12 h. Step 4: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45μm and 0.22μm pore size filter membranes to remove large particulate impurities, resulting in a supernatant precursor solution. Step 5: Transfer the supernatant precursor solution obtained in Step 4 to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 5℃, centrifuge at 8000rpm for 45min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. Step 6: Slowly drop the supernatant obtained in step 5 into anhydrous ethanol, sonicate for 20 min, then centrifuge at 12000 rpm for 15 min and collect the precipitate; Step 7: Redisperse the precipitate collected in Step 6 in deionized water to prepare a deionized water dispersion mixture. Measure the pH value of the mixture and adjust the pH according to the measurement results: when pH < 7, add dilute ethylenediamine solution dropwise while stirring continuously until the solution pH ≈ 7; when pH > 7, add dilute tartaric acid solution dropwise while stirring continuously until the solution pH ≈ 7. Step 8: Transfer the deionized water dispersion mixture obtained in Step 7 to a regenerated cellulose dialysis bag with a molecular weight cutoff of 1000 Da. Seal both ends with dialysis clamps. Completely immerse the dialysis bag in a beaker containing deionized water. Place a stir bar in the beaker and perform low-speed magnetic stirring at 300 rpm. Replace the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. Step 9: Aliquot the carbon quantum dot solution from Step 8 into lyophilization vials, place the vials in a -80°C freezer for 2 hours, and quickly transfer the pre-frozen sample to a freeze dryer cold trap pre-cooled to -50°C. Immediately start the vacuum pump, set the vacuum level to 0.1 mbar, and maintain this for 24 hours to obtain pale yellow nitrogen-doped carbon quantum dots (CQDs-NC). 12 H 25 Store in a nitrogen atmosphere; Step 10: The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in step 9 are... 12 H 25 Carbon quantum dot leak detectors can be obtained by dispersing them in sufficient methanol at room temperature and pressure until they are completely dissolved.

[0045] To further demonstrate the beneficial effects of the present invention and to better understand the invention, the following comparative examples and experimental examples further illustrate the properties and application performance of the carbon quantum dot leak detector for pipeline gas leak detection disclosed in the present invention. However, these should not be construed as limiting the present invention. Other methods and applications obtained by those skilled in the art based on the above-described invention and their application based on the above-described properties are also considered to fall within the protection scope of the present invention.

[0046] Comparative Example 1 Step 1: Dissolve 1.00g tartaric acid and 0.80mL ethylenediamine in 50mL dimethylformamide, heat to 50℃, and magnetically stir at 300rpm for 30min until completely dissolved to form a transparent mixed solution; Step 2: Transfer the transparent mixed solution obtained in Step 1 to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 30 minutes to remove oxygen. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 200°C at a rate of 10°C / min and keep it at the temperature for 12 hours. Step 3: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45 μm and 0.22 μm pore size filter membranes to remove large particulate impurities, resulting in a supernatant precursor solution. Step 4: Transfer the supernatant precursor solution obtained in Step 3 to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 5℃, centrifuge at 8000rpm for 45min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. Step 5: Slowly add the supernatant obtained in step 4 into anhydrous ethanol, sonicate for 20 min, then centrifuge at 12000 rpm for 15 min and collect the precipitate; Step 6: Redisperse the precipitate collected in Step 5 in deionized water to prepare a deionized water dispersion mixture. Measure the pH value of the mixture and adjust the pH according to the measurement results: when pH < 7, add dilute ethylenediamine solution dropwise while stirring continuously until the solution pH ≈ 7; when pH > 7, add dilute tartaric acid solution dropwise while stirring continuously until the solution pH ≈ 7. Step 7: Transfer the deionized water dispersion mixture obtained in Step 6 to a regenerated cellulose dialysis bag with a molecular weight cutoff of 1000 Da. Seal both ends with dialysis clamps. Immerse the dialysis bag completely in a beaker containing deionized water. Place a stir bar in the beaker and perform low-speed magnetic stirring at 300 rpm. Change the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. Step 8: Dispense the carbon quantum dot solution after dialysis in Step 7 into lyophilization bottles, place the lyophilization bottles in a -80℃ freezer for 2 hours, quickly transfer the pre-frozen sample to a freeze dryer cold trap that has been pre-cooled to -50℃, immediately start the vacuum pump, set the vacuum degree to 0.1 mbar, and maintain for 24 hours to obtain light yellow powder nitrogen-doped carbon quantum dots (CQDs-N), which are then stored in a nitrogen atmosphere. Step 9: Disperse the nitrogen-doped carbon quantum dots (CQDs-N) obtained in Step 8 into sufficient methanol at room temperature and pressure until completely dissolved to obtain carbon quantum dot leak detector.

[0047] Comparative Example 2 Step 1: Dissolve 1.00g tartaric acid and 0.8mL ethylenediamine in 50mL dimethylformamide, heat to 50℃, and magnetically stir at 300rpm for 30min until completely dissolved to form a transparent mixed solution; Step 2: Add 0.16g of dodecylamine to the clear mixed solution from Step 1, and continue magnetic stirring for 15 minutes to form a precursor solution; Step 3: Transfer the precursor solution obtained in Step 2 to a polytetrafluoroethylene-lined reactor, seal it, and then purge it with nitrogen for 30 min to remove oxygen. Then place the reactor in an oven and continuously purge it with nitrogen. Heat the reactor to 200°C at a rate of 10°C / min and keep it at the temperature for 12 h. Step 4: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45μm and 0.22μm pore size membranes and 0.22~0.45μm pore size membranes to remove large particulate impurities, resulting in a supernatant precursor solution. Step 5: Transfer the supernatant obtained in step 4 to a dialysis bag with a molecular weight cutoff of 1000 Da, seal both ends with dialysis clamps, and completely immerse the dialysis bag in a beaker containing deionized water. Change the deionized water every 8 hours, and the dialysis time is 24 hours. Step 6: Dispense the dialyzed carbon quantum dot solution from Step 5 into desiccants, and place the desiccants in a 50 ℃ drying oven for 6 h to obtain pale yellow nitrogen-doped carbon quantum dots (CQDs-NC). 12 H 25 Store in a nitrogen atmosphere; Step 7: The nitrogen-doped carbon quantum dots (CQDs-NC) prepared in Step 6... 12 H 25 Carbon quantum dot leak detectors can be obtained by dispersing them in sufficient methanol at room temperature and pressure until they are completely dissolved.

[0048] Comparative Example 3 Step 1: Dissolve 1.00 g tartaric acid and 0.72 g urea in 50 mL dimethylformamide, heat to 50 °C, and magnetically stir at 300 rpm for 30 min until completely dissolved to form a transparent mixed solution; Step 2: Add 0.16 g of dodecylamine to the clear mixed solution from Step 1, and continue magnetic stirring for 15 min to form a precursor solution; Step 3: Transfer the precursor solution obtained in Step 2 to a polytetrafluoroethylene-lined reactor, seal it, and purge with nitrogen for 30 min to remove oxygen. Then place the reactor in an oven and continuously purge with nitrogen. Heat the reactor to 200 °C at a rate of 10 °C / min and react at a constant temperature for 12 h. Step 4: After the reaction is complete, the mixture is allowed to cool naturally to room temperature to obtain a suspension. This suspension is then filtered sequentially through 0.45 μm and 0.22 μm pore size filter membranes to remove large particulate impurities and obtain the supernatant precursor solution. Step 5: Transfer the supernatant precursor solution obtained in Step 4 to a polypropylene centrifuge tube, place it symmetrically in the centrifuge rotor, set the centrifuge parameters to 5 ℃, centrifuge at 8000 rpm for 45 min, start the high-speed refrigerated centrifuge to perform centrifugation, remove unreacted solid residue, and take the supernatant. Step 6: Slowly drop the supernatant obtained in step 5 into anhydrous ethanol, sonicate for 20 min, then centrifuge at 12000 rpm for 15 min and collect the precipitate. Step 7: Redisperse the precipitate collected in Step 6 in deionized water to prepare a deionized water dispersion mixture. Measure the pH value of the mixture and adjust the pH according to the measurement results: when pH < 7, add dilute ethylenediamine solution dropwise while stirring continuously until the solution pH ≈ 7; when pH > 7, add dilute tartaric acid solution dropwise while stirring continuously until the solution pH ≈ 7. Step 8: Transfer the deionized water dispersion mixture obtained in Step 7 to a regenerated cellulose dialysis bag with a molecular weight cutoff of 1000 Da. Seal both ends with dialysis clamps. Immerse the dialysis bag completely in a beaker containing deionized water. Place a stir bar in the beaker and perform low-speed magnetic stirring at 300 rpm. Change the deionized water every 8 hours. When the conductivity of the solution in the dialysis bag is close to that of the deionized water and the pH is approximately 7, the dialysis is considered complete. Step 9: Aliquot the carbon quantum dot solution after dialysis in Step 8 into lyophilization bottles, place the lyophilization bottles in a -80 ℃ freezer for 2 h, quickly transfer the pre-frozen sample to a freeze dryer cold trap pre-cooled to -50 ℃, immediately start the vacuum pump, set the vacuum degree to 0.1 mbar, and maintain for 24 h to obtain light yellow powder nitrogen-doped carbon quantum dots (CQDs-N-C12H25), which are stored in a nitrogen atmosphere; Step 10: Disperse the nitrogen-doped carbon quantum dots CQDs-N-C12H25 obtained in step 9 into sufficient methanol at room temperature and pressure until completely dissolved to obtain carbon quantum dot leak detector.

[0049] Experimental Example 1 Fluorescence performance test Carbon quantum dot leak detectors with a concentration of 0.01 mg / mL were prepared according to Examples 1-5 and Comparative Examples 1-3, respectively. A glass simulated pipeline system with a leak point having a preset pore size of 0.5 mm was constructed. After rinsing with deionized water and purging with nitrogen to remove impurities, the leak detector was injected into the pipeline. Nitrogen was used to propel the leak detector to flow within the pipeline and seep out from the leak point to form a stable permeable film. A portable fluorescence detector was then aimed at the leak point, and the probe distance and angle were fixed. The detection was repeated three times, and the average value was taken as the initial light intensity at the leak point. Afterward, the environmental conditions were kept unchanged, and the system was allowed to stand for 24 hours. The same detection parameters were then used to repeat the detection at the same leak point, and the average value was taken as the light intensity at the leak point after 24 hours. During this period, it was necessary to avoid ambient light interference and changes in the pipeline condition to ensure the validity of the data.

[0050] Table 1 shows the fluorescence performance test conditions and results of the carbon quantum dot leak detectors prepared in Examples 1-5 and Comparative Examples 1-3 of this invention.

[0051] Table 1

[0052] As shown in Table 1, by adjusting the ratio of ethylenediamine and dodecylamine in Examples 1-5, the leak detection agents prepared exhibited excellent fluorescence intensity and long-term stability. The initial leakage intensity in Examples 1-5 was significantly higher than that in Comparative Example 1, indicating that the addition of dodecylamine significantly enhances the fluorescence intensity of carbon quantum dots, making the fluorescence signal at the leakage point easier to capture and improving detection sensitivity. Example 1 showed the lowest light intensity decay rate and the best stability, while Comparative Example 1 showed the highest decay rate and the worst stability. This comparison shows that the addition of dodecylamine is the key factor in improving the long-term stability of fluorescence; the lack of dodecylamine leads to rapid decay of the fluorescence signal. The raw material ratio in Example 1 demonstrated outstanding performance in maintaining stability. The initial leakage intensity in Example 1 was significantly higher than that in Comparative Example 2. The light intensity at the initial leakage point was not significantly different, but the attenuation rate of Comparative Example 2 was much higher than that of Example 1. This indicates that the purification process used in this invention, compared with the conventional carbon quantum dot purification process, can accurately remove residual small molecule impurities in the system, avoid such impurities affecting the fluorescence signal detection of carbon quantum dots, reduce non-radiative quenching, and prolong fluorescence lifetime. The dialysis endpoint is judged by the criterion of "conductivity close to deionized water and neutral pH value", which can ensure that the impurity content and ion concentration are consistent in different batches and improve the stability of the leak detection agent performance. The light intensity at the initial leakage point of Example 1 was higher than that of Comparative Example 3, and the light intensity attenuation rate of Example 1 was lower. This indicates that ethylenediamine as a nitrogen source has a higher nitrogen doping rate than the commonly used urea nitrogen source.

[0053] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A carbon quantum dot leak detection agent for pipeline gas leak detection, characterized by, Including those with the chemical formula C x H y N z O w The core carbon-nitrogen-oxygen skeleton and m chemical formulas are C 12 H 25 The dodecylamine molecules of NH2 are linked by covalent or hydrogen bonds to form a composite nanostructure, wherein x≥50, y≥20, 1≤z≤15, 5≤w≤20, and 1≤m≤3. 2.The carbon quantum dots leak detector according to claim 1, characterized in that, Including nanoscale carbon-based particles CQDs-NC 12 H 25 The CQDs-NC 12 H 25 The core carbon-nitrogen-oxygen framework is a graphene-like sp. 2 Hybrid carbon nanostructures with surface-modified functional groups such as amino, long-chain alkyl, hydroxyl, and carboxyl groups.

3. The method for preparing carbon quantum dots leak detector according to any one of claims 1-2, wherein, The preparation is carried out by a solvothermal reaction with tartaric acid as a carbon source, ethylenediamine as a nitrogen source and dodecylamine as a surface modifier.

4. The production method according to claim 3, characterized by, The specific steps include: (1) tartaric acid and ethylenediamine are dissolved in dimethylformamide at a certain mass-volume ratio, heated to 50-80 ℃, and magnetically stirred at 200-300 rpm for 20-30 min until completely dissolved to form a transparent mixed solution; (2) a certain mass-volume ratio of dodecylamine is added to the transparent mixed solution in step (1), and magnetic stirring is continued for 10-15 min to form a precursor solution; (3) the precursor solution obtained in step (2) is transferred to a polytetrafluoroethylene-lined reaction kettle, sealed, and purged with nitrogen for 20-30 min to remove oxygen, then the reaction kettle is placed in an oven, nitrogen is continuously introduced into the reaction kettle, the temperature is raised to 180-200 ℃ at a rate of 5-10 ℃ / min, and constant temperature reaction is carried out for 8-12 h; (4) after the reaction is completed, it is naturally cooled to room temperature to obtain a suspension, which is filtered through a filter membrane with a pore size of 0.22-0.45 μm to remove large particle impurities, and an upper clear liquid precursor solution is obtained; (5) the upper clear liquid precursor solution obtained in step (4) is transferred to a polypropylene centrifuge tube, balanced and symmetrically placed in the rotor of a centrifuge, the centrifuge parameters are set to a temperature of 3-5 ℃, a speed of 7000-10000 rpm, and a centrifugation time of 30-45 min, and a high-speed refrigerated centrifuge is started to centrifuge and remove unreacted solid residues, and the supernatant is taken; (6) the supernatant obtained in step (5) is slowly dropped into anhydrous ethanol, ultrasonically dispersed for 15-20 min, and then centrifuged at 10000-15000 rpm for 10-15 min to collect the precipitate; (7) the precipitate collected in step (6) is dispersed in deionized water to prepare a deionized water dispersion mixed solution, the pH value of the mixed solution is measured, and pH adjustment is performed according to the measurement results; (8) the deionized water dispersion mixed solution obtained in step (7) is transferred to a regenerated cellulose dialysis bag with a molecular weight cut-off of 500-3500 Da, both ends are sealed with dialysis clamps, the dialysis bag is completely immersed in a beaker containing deionized water, a stirring bar is placed, low-speed magnetic stirring is carried out at a stirring speed of 200-300 rpm, deionized water is replaced every 8 h, and when the conductivity of the solution in the dialysis bag is close to that of deionized water and the pH is approximately 7, it is determined that the dialysis is complete. (9) The carbon quantum dot solution after dialysis in step (8) is divided into freeze-drying bottles, the freeze-drying bottles are placed in a refrigerator at -60~80℃ for 2h, the pre-frozen sample is quickly transferred to a cold trap of a freeze dryer pre-cooled to -30~50℃, a vacuum pump is immediately started, the vacuum degree is set to 0.1~1mbar, and the setting is maintained for 12~24h to obtain a light yellow powder carbon quantum dot CQDs-N-C 12 H 25 Stored under nitrogen environment; (10) The carbon quantum dots CQDs-N-C prepared in step (9) are dispersed in a sufficient amount of methanol at room temperature and normal pressure until completely dissolved to obtain the carbon quantum dot leak detector. 12 H 25 The carbon quantum dots leak detector can be obtained by dispersing the carbon quantum dots prepared in step (9) in a sufficient amount of methanol at room temperature and normal pressure until completely dissolved.

5. The preparation method according to claim 4, characterized in that, In step (1), the mass-volume ratio of tartaric acid and ethylenediamine is 5:(4-6), and the volume ratio of dimethylformamide to tartaric acid-ethylenediamine mixed solution is (23-30):

1.

6. The preparation method according to claim 4, characterized in that, In step (2), the mass ratio of dodecylamine to tartaric acid added in step (1) is (2-5):

1.

7. The preparation method according to claim 4, characterized in that, In step (6), the volume ratio of anhydrous ethanol to supernatant is 3:

1.

8. The preparation method according to claim 4, characterized in that, In step (7), when the pH is less than 7, dilute ethylenediamine solution is added dropwise and continuously stirred until the solution pH is approximately 7; when the pH is greater than 7, dilute tartaric acid solution is added dropwise and continuously stirred until the solution pH is approximately 7.

9. The preparation method according to claim 4, characterized in that, The step (10) carbon quantum dots CQDs-N-C 12 H 25 The mass volume ratio of methanol is 1: (10~100).

10. The use of carbon quantum dots leak detector according to any one of claims 1-2, wherein, The leak detection agent is suitable for detecting leakage of hydrocarbon gas and inert gas pipeline, and is mixed with pipeline gas after atomization, and a fluorescence spectrometer is used to detect the leakage point, and the detection sensitivity is less than or equal to 1 ppm.

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