阅读说明：本技术 一种荧光碳量子点在检测环烷酸中的应用及环烷酸的检测方法 (Application of fluorescent carbon quantum dots in naphthenic acid detection and naphthenic acid detection method ) 是由 任红威 刘翼泽 李美玉 赵腾达 张若瑶 齐雷敏 周世龙 韩静 段二红 于 2021-08-10 设计创作，主要内容包括：本发明涉及有机污染物检测技术领域,具体公开一种荧光碳量子点在检测环烷酸中的应用及环烷酸的检测方法。所述荧光碳量子点由有机胺类化合物与聚乙二醇与水合锡盐组成的低共熔溶剂通过水热反应制得。将制备的荧光碳量子点加入含有环烷酸的废水中,混合均匀后进行荧光强度检测,确定废水中环烷酸的含量。本发明提供的基于荧光碳量子点检测环烷酸的方法,通过荧光碳量子点与环烷酸的荧光猝灭效应对环烷酸进行定性定量检测,检出限可达0.432μmol/L,具有快速、简便、检出限低、高效等优点,具有很好的经济、环境和社会效益,具有较高的推广应用价值。(The invention relates to the technical field of organic pollutant detection, and particularly discloses application of fluorescent carbon quantum dots in naphthenic acid detection and a naphthenic acid detection method. The fluorescent carbon quantum dot is prepared by a hydrothermal reaction of an organic amine compound, a eutectic solvent consisting of polyethylene glycol and hydrated tin salt. Adding the prepared fluorescent carbon quantum dots into wastewater containing naphthenic acid, uniformly mixing, and then carrying out fluorescence intensity detection to determine the naphthenic acid content in the wastewater. The method for detecting the naphthenic acid based on the fluorescent carbon quantum dots, provided by the invention, can be used for qualitatively and quantitatively detecting the naphthenic acid through the fluorescence quenching effect of the fluorescent carbon quantum dots and the naphthenic acid, the detection limit can reach 0.432 mu mol/L, and the method has the advantages of rapidness, simplicity, convenience, low detection limit, high efficiency and the like, has good economic, environmental and social benefits, and has higher popularization and application values.)

1. The application of the fluorescent carbon quantum dot in detecting naphthenic acid is characterized in that the fluorescent carbon quantum dot is prepared from a eutectic solvent consisting of an organic amine compound, polyethylene glycol and a tin hydrate salt.

2. The application of the fluorescent carbon quantum dot in detecting naphthenic acid according to claim 1, wherein the organic amine compound is at least one of p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, ethylenediamine, n-butylamine, n-pentylamine, or p-nitrophenylamine.

3. The application of the fluorescent carbon quantum dot in detecting naphthenic acid according to claim 2, wherein the organic amine compound is at least one of p-phenylenediamine, o-phenylenediamine or m-phenylenediamine.

4. The use of the fluorescent carbon quantum dot in detecting naphthenic acid according to claim 1, wherein the polyethylene glycol is at least one of PEG200, PEG300, PEG400 or PEG 600.

5. The use of fluorescent carbon quantum dots to detect naphthenic acids according to claim 1, wherein the hydrated tin salt is tin tetrachloride pentahydrate.

6. The application of the fluorescent carbon quantum dot in detecting naphthenic acid according to claim 1, wherein the mass ratio of the organic amine compound, the polyethylene glycol and the hydrated tin salt is 1: 130-160: 16-18.

7. The application of the fluorescent carbon quantum dot in detecting naphthenic acid according to any one of claims 1 to 6, wherein the preparation method of the fluorescent carbon quantum dot comprises the following steps:

step a, uniformly mixing an organic amine compound, polyethylene glycol and hydrated tin salt, heating to 90-110 ℃, and keeping the temperature constant until the system is uniform and transparent to obtain an organic amine-polyethylene glycol-tin salt eutectic solvent;

and b, adding the organic amine-polyethylene glycol-tin salt eutectic solvent into absolute ethyl alcohol, and carrying out hydrothermal reaction to obtain the fluorescent carbon quantum dot.

8. The application of the fluorescent carbon quantum dot in detecting naphthenic acid according to claim 7, wherein in the step b, the mass ratio of the organic amine-polyethylene glycol-tin salt eutectic solvent to absolute ethyl alcohol is 1: 20-25; and/or

In the step b, the temperature of the hydrothermal reaction is 190-220 ℃, and the reaction time is 10-14 h.

9. The application of the fluorescent carbon quantum dots in the detection of naphthenic acid according to claim 7, wherein in the step b, after the hydrothermal reaction is finished, the obtained fluorescent carbon quantum dot solution is purified by centrifugation, filtration and dialysis in a dialysis bag with molecular weight cutoff of 3500Da in sequence.

10. A method for detecting naphthenic acid based on fluorescent carbon quantum dots is characterized by comprising the following steps:

the fluorescent carbon quantum dot as claimed in any one of claims 1 to 9 is added into wastewater containing naphthenic acid, and fluorescence intensity detection is performed after uniform mixing.

Technical Field

The invention relates to the technical field of organic pollutant detection, in particular to application of fluorescent carbon quantum dots in naphthenic acid detection and a naphthenic acid detection method.

Background

With the rapid development of petrochemical industry, naphthenic acid pollution is an important and irremediable environmental problem, and has attracted people's extensive attention and research in recent years. Naphthenic acid is a general name of various organic compounds, is a viscous liquid which is difficult to volatilize at normal temperature, and has strong ecological toxicity. According to the records of related data, when the concentration of naphthenic acid reaches 300mg/Kg, the rats can obviously suffer from cardiovascular diseases, hepatopathy and other diseases. If the naphthenic acid content in the produced water or industrial wastewater does not reach the standard, serious harm is generated to the ecological environment and human health.

At present, the naphthenic acid is mainly analyzed and detected by ion chromatography, spectrometry, mass spectrometry, nuclear magnetic resonance and other analytical and detection methods at home and abroad. However, these detection methods mostly use precise large-scale instruments, and require pretreatment of the sample, such as derivatization of the sample, which results in complicated operation process, long detection period, and the need for professional operation and detection. In addition, the error caused in the pretreatment process of the sample may be further amplified in the detection process, which affects the accuracy of the final detection result. Therefore, the research and development of a material and a method for accurately detecting naphthenic acid quickly, conveniently, economically and efficiently has very important significance for the detection of naphthenic acid in the environment.

Disclosure of Invention

Aiming at the problems that most methods for detecting naphthenic acid in the prior art need precise detection instruments, are complex to operate, high in cost and the like, the invention provides the application of the fluorescent carbon quantum dots in the detection of naphthenic acid and the detection method of naphthenic acid.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

the application of the fluorescent carbon quantum dot in detecting naphthenic acid is characterized in that the fluorescent carbon quantum dot is prepared from a eutectic solvent consisting of an organic amine compound, polyethylene glycol and a hydrated tin salt.

Preferably, the fluorescent carbon quantum dot is prepared by a eutectic solvent consisting of an organic amine compound, polyethylene glycol and a hydrated tin salt through a hydrothermal reaction.

The naphthenic acid has a molecular formula of C_nH_2n-2O₂N represents the number of carbon atoms, and n is more than or equal to 7 and less than or equal to 11.

The fluorescent carbon quantum dot is prepared by taking an eutectic solvent consisting of an organic amine compound, polyethylene glycol and a tin hydrate salt as a raw material, wherein the polyethylene glycol is used as a carbon source and a modification group of the carbon quantum dot, and can carry out in-situ modification on the surface of the carbon quantum dot by an oxygen-containing functional group, so that the distribution form of the oxygen-containing functional group on the surface of the carbon quantum dot is optimized, and the photoinduced charge transfer property, the chemical stability and the fluorescence property of the carbon quantum dot are further improved; the hydrated tin salt is used as a neutral ligand for preparing the eutectic solvent, plays a role in catalysis in the reaction process of preparing the fluorescent carbon quantum dots, and improves the reaction efficiency; and then organic amine is used as nitrogen for doping, so that carbon quantum dots with rich surface functional groups are obtained, and the aim of quickly identifying naphthenic acid in wastewater is fulfilled through the functional groups on the surfaces of the carbon quantum dots. The carbon quantum dot provided by the invention has high fluorescence quantum yield and good fluorescence stability, can realize qualitative and quantitative detection of naphthenic acid in wastewater by using the quenching effect of the naphthenic acid on the fluorescence thereof, has high accuracy and sensitivity, can realize qualitative and quantitative detection of the naphthenic acid only by detecting the fluorescence intensity without a precise detection instrument, has low requirements on instruments, operators and operation environment, has extremely high detection efficiency, greatly reduces the test cost, and has wide application prospect in the field of naphthenic acid detection.

Preferably, the organic amine compound is at least one of p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, ethylenediamine, n-butylamine, n-pentylamine, and p-nitrophenylamine.

More preferably, the organic amine compound is at least one of p-phenylenediamine, o-phenylenediamine and m-phenylenediamine.

Preferably, the polyethylene glycol is at least one of PEG200, PEG300, PEG400 or PEG 600.

Preferably, the hydrated tin salt is tin tetrachloride pentahydrate.

Preferably, the mass ratio of the organic amine compound to the polyethylene glycol to the hydrated tin salt is 1: 130-160: 16-18.

Preferably, the organic amine, the polyethylene glycol and the tin salt hydrate can form a eutectic solvent with good uniformity, so that reactants are in full contact, the preparation of the eutectic solvent is facilitated, the dispersibility of the carbon quantum dot is improved, meanwhile, the eutectic solvent is used for modifying various groups such as amino, phenyl, oxygen-containing functional groups and nitro on the surface of the carbon quantum dot, the fluorescence active sites on the surface of the carbon quantum dot are enriched, the fluorescence quantum yield is improved, and particularly when the organic amine is a phenylenediamine substance, the phenyl, diamino and the oxygen-containing functional groups of the polyethylene glycol on the surface of the carbon quantum dot are more beneficial to quickly capturing naphthenic acid, and the quick detection of the naphthenic acid is realized. On the other hand, the hydrated tin salt as an intermediate ligand in the eutectic solvent can be hydrolyzed to generate SnO in the hydrothermal reaction process₂Nanoparticles, SnO₂The nano particles can be used as a catalyst to effectively shorten the time of pyrolysis reaction and improve the preparation efficiency of the carbon quantum dots.

Preferably, the preparation method of the fluorescent carbon quantum dot comprises the following steps:

step a, uniformly mixing an organic amine compound, polyethylene glycol and hydrated tin salt, heating to 90-110 ℃, and keeping the temperature constant until the system is uniform and transparent to obtain an organic amine-polyethylene glycol-tin salt eutectic solvent;

and b, adding the organic amine-polyethylene glycol-tin salt eutectic solvent into absolute ethyl alcohol, and carrying out hydrothermal reaction to obtain the fluorescent carbon quantum dot.

Preferably, in the step a, the constant temperature time is 20min to 50 min.

The preparation method of the fluorescent carbon quantum dot provided by the invention has the advantages of simple process, convenience in operation, low cost, low toxicity and environmental protection, is a low-cost and eco-friendly preparation method, and is convenient for realizing industrial production and application.

Preferably, in the step b, the mass ratio of the organic amine-polyethylene glycol-tin salt eutectic solvent to the absolute ethyl alcohol is 1: 20-25.

Preferably, in the step b, the temperature of the hydrothermal reaction is 190-220 ℃, and the reaction time is 10-14 h.

More preferably, in step b, after the hydrothermal reaction is finished, the obtained fluorescent carbon quantum dot solution is purified by sequentially centrifuging, filtering and dialyzing by a dialysis bag with the molecular weight cutoff of 3500 Da.

Further preferably, the fluorescent carbon quantum dots are obtained by centrifuging for 5min at 10000rpm, filtering through a 0.22-micron microporous membrane, and dialyzing filtrate through a dialysis bag with the molecular weight cutoff of 3500 Da.

Preferably, the fluorescent carbon quantum dots are stored in the form of ethanol solution of the fluorescent carbon quantum dots obtained by hydrothermal reaction, so that the fluorescent carbon quantum dots are convenient to take and use, and the dispersibility of the fluorescent carbon quantum dots is good in the storage process.

The invention also provides a method for detecting naphthenic acid based on the fluorescent carbon quantum dots, which comprises the following steps:

adding the fluorescent carbon quantum dot into wastewater containing naphthenic acid, and performing fluorescence intensity detection after uniformly mixing.

In combination with the above, the addition amount of the fluorescent carbon quantum dots can be changed or adjusted within a wide range, and is obtained by performing routine adjustment according to the concentration of naphthenic acid in the wastewater, specific components of the wastewater and other conditions.

Preferably, when the prepared fluorescent carbon quantum dot solution is used as a material for detecting naphthenic acid, the volume ratio of the fluorescent carbon quantum dot solution to the naphthenic acid-containing wastewater is 0.5-2: 1.

Specifically, the method for detecting naphthenic acid based on fluorescent carbon quantum dots specifically comprises the following steps:

adding naphthenic acid standard solutions with different concentrations into the prepared fluorescent carbon quantum dot solution respectively, measuring the fluorescence spectrum of the naphthenic acid standard solution by taking 498nm as an excitation wavelength, and obtaining the linear relation between the fluorescence intensity and the concentration of the naphthenic acid. And then adding a sample to be detected into the fluorescent carbon quantum dot solution, and quantitatively calculating the concentration of naphthenic acid in the sample to be detected according to a linear relation through the change of fluorescence intensity.

Compared with the traditional naphthenic acid detection method, the method for detecting the naphthenic acid based on the fluorescent carbon quantum dots provided by the invention can be used for qualitatively and quantitatively detecting the naphthenic acid through the fluorescence quenching effect of the fluorescent carbon quantum dots and the naphthenic acid, the detection limit can reach 0.432 mu mol/L, and the method has the advantages of rapidness, simplicity, convenience, low detection limit, high efficiency and the like, has good economic, environmental and social benefits, and has higher popularization and application values.

Drawings

FIG. 1 is a TEM image of a fluorescent carbon quantum dot prepared in example 5 of the present invention;

FIG. 2 is a particle size distribution diagram of fluorescent carbon quantum dots prepared in example 5 of the present invention;

FIG. 3 is a fluorescent photograph of fluorescent carbon quantum dot solution with different concentrations of naphthenic acid added under the irradiation of an ultraviolet lamp in example 5 of the present invention, wherein the illustrated cuvette is a mixed solution of the fluorescent carbon quantum dot solution and naphthenic acid solutions with concentrations of 0mol/L, 1mol/L, 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L, and 0.001mol/L, respectively, from left to right;

fig. 4 is a fluorescence emission spectrogram of the fluorescent carbon quantum dot solution of example 5 at 498nm excitation wavelength after adding naphthenic acid of different concentrations, and the concentration of the naphthenic acid solution added from bottom to top according to the direction indicated by the arrow is as follows: 1mol/L, 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L, 0.001mol/L, 0 mol/L;

FIG. 5 shows (F) of fluorescent carbon quantum dot solution of example 5₀Linear relationship between/F-1) and naphthenic acid concentration.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to better illustrate the invention, the following examples are given by way of further illustration.

Example 1

The embodiment of the invention provides a fluorescent carbon quantum dot, and the preparation method specifically comprises the following steps:

step a, mixing 1.65g SnCl₄·5H₂O, 0.10g of n-butylamine and 14.20g of polyethylene glycol 200 are uniformly mixed, heated to 100 ℃, stirred at constant temperature for 20min until the system is uniform and transparent, and a n-butylamine-polyethylene glycol-stannic chloride pentahydrate eutectic solvent is obtained;

and b, adding 1g of n-butylamine-polyethylene glycol-pentahydrate stannic chloride eutectic solvent into 20g of absolute ethyl alcohol, carrying out hydrothermal reaction for 14h at 190 ℃, centrifuging the reaction solution for 5min at 10000rpm, filtering through a 0.22-micron filter membrane, and dialyzing the obtained filtrate through a dialysis bag with the molecular weight cutoff of 3500Da to obtain the fluorescent carbon quantum dot solution.

Measuring 3mL of 1mol/L naphthenic acid solution and 2mL of the prepared fluorescent carbon quantum dot solution according to the volume ratio of 1.5:1, putting the solutions into a 10mL centrifugal tube for mixing, respectively measuring 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions according to the same volume ratio, putting the solutions into an ultrasonic cleaner for ultrasonic oscillation for 30min, and observing the fluorescence intensity of the mixed solution under the irradiation of ultraviolet light, wherein the fluorescence quenching phenomenon of the fluorescent carbon quantum dot solution is gradually enhanced along with the increase of the concentration of the naphthenic acid solution. It is demonstrated that the fluorescent carbon quantum dots prepared in this example have good detectability for naphthenic acids.

Example 2

The embodiment of the invention provides a fluorescent carbon quantum dot, and the preparation method specifically comprises the following steps:

step a, mixing 1.77g SnCl₄·5H₂Mixing 0.10g of n-pentylamine and 15.80g of polyethylene glycol 600 uniformly, heating to 105 ℃, stirring at constant temperature for 30min until the system is uniform and transparent, and obtaining the n-pentylamine-polyethylene glycol-stannic chloride pentahydrate eutectic solvent;

and b, adding 1g of n-pentylamine-polyethylene glycol-stannic chloride pentahydrate eutectic solvent into 21g of absolute ethyl alcohol, carrying out hydrothermal reaction for 13h at 200 ℃, centrifuging the reaction solution for 5min at 10000rpm, filtering by using a 0.22 mu m filter membrane, and dialyzing the obtained filtrate by using a dialysis bag with the molecular weight cutoff of 3500Da to obtain the fluorescent carbon quantum dot solution.

Measuring 3mL of 1mol/L naphthenic acid solution and 5mL of the prepared fluorescent carbon quantum dot solution according to the volume ratio of 0.6:1, putting the solutions into a 10mL centrifugal tube for mixing, respectively measuring 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions according to the same volume ratio, putting the solutions into an ultrasonic cleaner for ultrasonic oscillation for 30min, and observing the fluorescence intensity of the mixed solution under the irradiation of ultraviolet light, wherein the fluorescence quenching phenomenon of the fluorescent carbon quantum dot solution is gradually enhanced along with the increase of the concentration of the naphthenic acid solution. It is demonstrated that the fluorescent carbon quantum dots prepared in this example have good detectability for naphthenic acids.

Example 3

The embodiment of the invention provides a fluorescent carbon quantum dot, and the preparation method specifically comprises the following steps:

step a, mixing 1.60g SnCl₄·5H₂O, 0.10g of m-phenylenediamine and 13.80g of polyethylene glycol 400 are uniformly mixed, heated to 90 ℃, stirred at constant temperature for 45min until the system is uniform and transparent, and the m-phenylenediamine-polyethylene glycol-pentahydrate stannic chloride eutectic solvent is obtained;

and b, adding 1g of m-phenylenediamine-polyethylene glycol-stannic chloride pentahydrate eutectic solvent into 23g of absolute ethyl alcohol, carrying out hydrothermal reaction for 13h at 205 ℃, centrifuging the reaction solution for 5min at 10000rpm, filtering the reaction solution through a 0.22-micron filter membrane, and dialyzing the obtained filtrate through a dialysis bag with the molecular weight cutoff of 3500Da to obtain the fluorescent carbon quantum dot solution.

Measuring 4mL of 1mol/L naphthenic acid solution and 2mL of the prepared fluorescent carbon quantum dot solution according to the volume ratio of 2:1, putting the solutions into a 10mL centrifugal tube for mixing, respectively measuring 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions according to the same volume ratio, putting the solutions into an ultrasonic cleaner for ultrasonic oscillation for 35min, observing the fluorescence intensity of the mixed solution under the irradiation of ultraviolet light, and finding that the fluorescence quenching phenomenon of the fluorescent carbon quantum dot solution is gradually enhanced along with the increase of the concentration of the naphthenic acid solution. It is demonstrated that the fluorescent carbon quantum dots prepared in this example have good detectability for naphthenic acids.

Example 4

The embodiment of the invention provides a fluorescent carbon quantum dot, and the preparation method specifically comprises the following steps:

step a, mixing 1.72g SnCl₄·5H₂O, 0.10g of O-phenylenediamine and 14.50g of polyethylene glycol 600 are uniformly mixed, heated to 95 ℃, stirred at constant temperature for 40min until the system is uniform and transparent, and the O-phenylenediamine-polyethylene glycol-stannic chloride pentahydrate eutectic solvent is obtained;

and b, adding 1g of o-phenylenediamine-polyethylene glycol-stannic chloride pentahydrate eutectic solvent into 25g of absolute ethyl alcohol, carrying out hydrothermal reaction for 11h at 220 ℃, centrifuging the reaction solution at 10000rpm for 5min, filtering the reaction solution through a 0.22-micron filter membrane, and dialyzing the obtained filtrate through a dialysis bag with the molecular weight cutoff of 3500Da to obtain the fluorescent carbon quantum dot solution.

Measuring 4mL of 1mol/L naphthenic acid solution and 5mL of the prepared fluorescent carbon quantum dot solution according to the volume ratio of 0.8:1, putting the solutions into a 10mL centrifugal tube for mixing, respectively measuring 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solution according to the same volume ratio, putting the mixed solution into an ultrasonic cleaner for ultrasonic oscillation for 25min, and observing the fluorescence intensity of the mixed solution under the irradiation of ultraviolet light, wherein the fluorescence quenching phenomenon of the fluorescent carbon quantum dot solution is gradually enhanced along with the increase of the concentration of the naphthenic acid solution. It is demonstrated that the fluorescent carbon quantum dots prepared in this example have good detectability for naphthenic acids.

Example 5

The embodiment of the invention provides a fluorescent carbon quantum dot, and the preparation method specifically comprises the following steps:

step a, mixing 1.75g SnCl₄·5H₂O, 0.10g of p-phenylenediamine and 15.20g of polyethylene glycol 400 are uniformly mixed, heated to 110 ℃, stirred at constant temperature for 30min until the system is uniform and transparent, and the p-phenylenediamine-polyethylene glycol-pentahydrate stannic chloride eutectic solvent is obtained；

And b, adding 1g of p-phenylenediamine-polyethylene glycol-stannic chloride pentahydrate eutectic solvent into 24g of absolute ethyl alcohol, carrying out hydrothermal reaction for 12h at 210 ℃, centrifuging the reaction solution for 5min at 10000rpm, filtering the reaction solution through a 0.22-micron filter membrane, and dialyzing the obtained filtrate through a dialysis bag with the molecular weight cutoff of 3500Da to obtain the fluorescent carbon quantum dot solution.

Fig. 1 is a TEM image of the fluorescent carbon quantum dots prepared in example 5, and fig. 2 is a particle size distribution diagram of the fluorescent carbon quantum dots prepared in example 5, and it can be seen from the diagram that the carbon quantum dots prepared in this example are in a sphere-like shape, have a small particle size, are mainly concentrated in 2nm to 4nm in particle size distribution, and are relatively uniformly distributed.

2mL of 1mol/L naphthenic acid solution and 2mL of the fluorescent carbon quantum dot solution prepared in the example 5 are measured according to the volume ratio of 1:1, the solutions are placed into a 10mL centrifugal tube to be mixed, then 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions are respectively measured according to the same volume ratio, the mixed solution is placed into an ultrasonic cleaner to be ultrasonically vibrated for 30min, the fluorescence intensity of the mixed solution is observed under the irradiation of ultraviolet light, and the fluorescent carbon quantum dot solution without naphthenic acid and only with 2mL of absolute ethyl alcohol is set as a blank control. The detection results are shown in fig. 3-5.

Wherein, fig. 3 is a fluorescent photograph of the fluorescent carbon quantum dot solution of example 5 under the irradiation of an ultraviolet lamp after adding naphthenic acid with different concentrations, fig. 4 is a fluorescent emission spectrogram of the naphthenic acid solution with different concentrations under the excitation wavelength of 498nm, and fig. 5 is (F) of the fluorescent carbon quantum dot₀Linear relationship between/F-1) and naphthenic acid concentration, wherein F₀And F represents the fluorescence intensity of the fluorescent carbon quantum dots when no naphthenic acid is added and naphthenic acid solutions with different concentrations are added, respectively.

As can be seen from fig. 3, as the concentration of the naphthenic acid solution increases, a fluorescence quenching phenomenon is clearly observed in the fluorescent carbon quantum dot solution, which indicates that the fluorescent carbon quantum dot prepared in this example has good detectability for naphthenic acid.

As can be seen from FIGS. 4 and 5, the fluorescent carbon quantum dots have (F)₀Solution of/F-1) and naphthenic acidHas a good linear relation in the range of 0.001mol/L to 1mol/L, and the linear relation is (F)₀(iii) F-1) 3.1662x +0.10245, x is the concentration of naphthenic acid solution, R²0.99709. According to fig. 5, the limit of detection is calculated to be 0.432 μmol/L using the formula LOD 3 σ/S, where σ is the standard deviation of the signal (n 5) and S is the slope of the linear calibration plot (σ 0.00045594, S3.1662).

In example 5 of the present invention, other organic amines defined in the present invention can also be used to prepare fluorescent carbon quantum dots, such as ethylenediamine or p-nitroaniline, etc., and the detection limits of the fluorescent carbon quantum dots prepared in examples 1-4, and the detection limits of the fluorescent carbon quantum dots prepared in example 5 from ethylenediamine-polyethylene glycol 400-pentahydrate stannic chloride eutectic solvent and p-nitroaniline-polyethylene glycol 400-pentahydrate stannic chloride eutectic solvent are as follows:

wherein, the detection limits of the carbon quantum dots prepared by the paranitroaniline-polyethylene glycol 400-stannic chloride pentahydrate eutectic solvent in the example 1 and the example 2 are 1.247 mu mol/L, 1.525 mu mol/L and 1.339 mu mol/L. The detection limits of the fluorescent carbon quantum dots prepared in examples 3-4 are 0.441. mu. mol/L and 0.452. mu. mol/L respectively. The detection limit of the carbon quantum dots prepared by the ethylenediamine-polyethylene glycol 400-stannic chloride pentahydrate eutectic solvent is 0.851 mu mol/L.

Comparative example 1

This comparative example provides a fluorescent carbon quantum dot, which was prepared in exactly the same manner as in example 5, except that polyethylene glycol 400 was replaced with an equal amount of glycerol.

Measuring 2mL of 1mol/L naphthenic acid solution and 2mL of the prepared fluorescent carbon quantum dot solution according to the volume ratio of 1:1, putting the solutions into a 10mL centrifugal tube for mixing, respectively measuring 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions according to the same volume ratio, putting the solutions into an ultrasonic cleaner for ultrasonic oscillation for 30min, observing the fluorescence intensity of the mixed solution under the irradiation of ultraviolet light, and finding that the fluorescence quenching phenomenon of the fluorescent carbon quantum dot solution has no obvious change rule after the naphthenic acid solutions with different concentrations are added. Namely, the quantitative detection of naphthenic acid cannot be realized after replacing the polyethylene glycol 400 with the glycerol.

Comparative example 2

This comparative example provides a fluorescent carbon quantum dot, which was prepared in exactly the same manner as in example 5, except that polyethylene glycol 400 was replaced with an equal amount of ethylene glycol.

Measuring 2mL of 1mol/L naphthenic acid solution and 2mL of the prepared fluorescent carbon quantum dot solution according to the volume ratio of 1:1, putting the solutions into a 10mL centrifugal tube for mixing, respectively measuring 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions according to the same volume ratio, putting the solutions into an ultrasonic cleaner for ultrasonic oscillation for 30min, and observing the fluorescence intensity of the mixed solution under the irradiation of ultraviolet light. Namely, the quantitative detection of the naphthenic acid cannot be realized after the polyethylene glycol 400 is replaced by the ethylene glycol.

Comparative example 3

The comparative example provides a fluorescent carbon quantum dot, and the preparation method specifically comprises the following steps:

step a, mixing 1.75g SnCl₄·5H₂O, 1.50g of oxalic acid, 0.10g of p-phenylenediamine and 15.20g of polyethylene glycol 400(1:152) are uniformly mixed, heated to 125 ℃, and stirred for 90min at constant temperature to obtain a solid-liquid mixture, namely a eutectic solvent cannot be obtained;

and step b, adding 1g of the prepared solid-liquid mixture into 24g of absolute ethyl alcohol (1:24), carrying out hydrothermal reaction for 12h at 210 ℃, then centrifuging the reaction solution for 5min at 10000rpm, filtering through a 0.22-micron filter membrane, and dialyzing the obtained filtrate through a dialysis bag with the molecular weight cutoff of 3500Da to obtain the fluorescent carbon quantum dot solution.

2mL of 1mol/L naphthenic acid solution and 2mL of the prepared fluorescent carbon quantum dot solution are measured according to the volume ratio of 1:1, the solutions are placed into a 10mL centrifugal tube to be mixed, then 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions are respectively measured according to the same volume ratio, the mixed solution is placed into an ultrasonic cleaner to be subjected to ultrasonic oscillation for 30min, and the fluorescence intensity of the mixed solution is observed under the irradiation of ultraviolet light, so that a slight fluorescence quenching phenomenon exists after 1mol/L and 0.5mol/L naphthenic acid solutions are added, the quenching degree of 1mol/L concentration is only slightly higher than 0.5mol/L, and when the concentration is lower than 0.5mol/L, the fluorescence quenching phenomenon hardly exists.

Comparative example 4

The comparative example provides a fluorescent carbon quantum dot, and the preparation method specifically comprises the following steps:

step a, mixing 1.75g SnCl₄·5H₂O, 1.50g of citric acid, 0.10g of p-phenylenediamine and 15.20g of polyethylene glycol 400(1:152) are uniformly mixed, heated to 110 ℃, stirred at constant temperature for 30min to be uniform and transparent, and a eutectic solvent is obtained;

and step b, adding 1g of the prepared eutectic solvent into 24g of absolute ethyl alcohol (1:24), carrying out hydrothermal reaction for 12h at 210 ℃, then centrifuging the reaction solution for 5min at 10000rpm, filtering through a 0.22-micron filter membrane, and dialyzing the obtained filtrate through a dialysis bag with the molecular weight cutoff of 3500Da to obtain the fluorescent carbon quantum dot solution.

2mL of 1mol/L naphthenic acid solution and 2mL of the prepared fluorescent carbon quantum dot solution are measured according to the volume ratio of 1:1, the solutions are placed into a 10mL centrifugal tube to be mixed, then 0.5mol/L, 0.1mol/L, 0.05mol/L, 0.01mol/L, 0.005mol/L and 0.001mol/L naphthenic acid solutions are respectively measured according to the same volume ratio, the mixed solution is placed into an ultrasonic cleaner to be subjected to ultrasonic oscillation for 30min, the fluorescence intensity of the mixed solution is observed under the irradiation of ultraviolet light, a slight fluorescence quenching phenomenon is found after 1mol/L naphthenic acid solution is added, and when the concentration is lower than 1mol/L, the fluorescence quenching phenomenon is hardly found.

As can be seen from comparative examples 4 and 5, the quantitative detection of naphthenic acid cannot be realized by adding oxalic acid and citric acid as carbon sources to the prepared fluorescent carbon quantum dots.

The naphthenic acid reagent used in examples 1-5 and comparative examples 1-4 was C₁₀H₁₈O₂2-cyclopentyl-5-ethyl propionic acid, the structure of which is shown below. The preparation process of naphthenic acid solutions with different concentrations comprises the following steps: adding a proper amount of naphthenic acid standard substance into absolute ethyl alcohol, and uniformly dispersing by ultrasonic wave to obtain the naphthenic acid.

In conclusion, the preparation method of the fluorescent carbon quantum dot provided by the invention is simple and environment-friendly, the prepared fluorescent carbon quantum dot has good detection effects on naphthenic acid solutions with different concentrations, a sample does not need to be pretreated in the detection process, a precise detection instrument is not needed, the detection environment requirement is low, the detection effect is greatly improved, the detection cost is reduced, and the popularization and application values are high.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.