CN114989821B - Eutectic solvent, fluorescent carbon quantum dot, preparation method and application - Google Patents

Eutectic solvent, fluorescent carbon quantum dot, preparation method and application Download PDF

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CN114989821B
CN114989821B CN202210664177.6A CN202210664177A CN114989821B CN 114989821 B CN114989821 B CN 114989821B CN 202210664177 A CN202210664177 A CN 202210664177A CN 114989821 B CN114989821 B CN 114989821B
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polyvinylidene fluoride
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张金锋
董红雨
任红威
闫忠清
赵腾达
贾本真
毛艳丽
纪晨龙
王梦雪
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Hebei University of Science and Technology
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Abstract

The invention relates to the technical field of VOCs detection, and particularly discloses a eutectic solvent, fluorescent carbon quantum dots, a preparation method and application thereof. The eutectic solvent is prepared from an amide compound and hydrophobic amino acid. The preparation method of the fluorescent carbon quantum dot comprises the following steps: adding the eutectic solvent into absolute ethyl alcohol, uniformly mixing, performing hydrothermal reaction at 200-220 ℃ for 10-14 h, centrifuging, and filtering to obtain a fluorescent carbon quantum dot solution. And compounding the fluorescent carbon quantum dots and the polyvinylidene fluoride film to obtain the polyvinylidene fluoride composite film. According to the invention, after the fluorescent carbon quantum dots containing the hydrophobic functional groups, amino groups, hydroxyl groups, carboxyl groups and other functional groups are compounded with the polyvinylidene fluoride film, on the premise that the hydrophobicity of the polyvinylidene fluoride is unchanged, the polyvinylidene fluoride film is provided with more binding reaction sites for VOCs gas such as toluene, so that the detection capability of the polyvinylidene fluoride on the VOCs is obviously improved, and the high-efficiency detection of the VOCs gas is realized.

Description

Eutectic solvent, fluorescent carbon quantum dot, preparation method and application
Technical Field
The invention relates to the technical field of VOCs detection, in particular to a eutectic solvent, fluorescent carbon quantum dots, a preparation method and application.
Background
Volatile organic compounds (Volatile Organic Compounds), VOCs for short, are defined by the world health organization, compounds having boiling points between 50 ℃ and 260 ℃ and saturated vapor pressures exceeding 133.32Pa at room temperature, and a class of organic compounds that exist in the air as vapors at room temperature are collectively referred to as Volatile Organic Compounds (VOCs). Common VOCs are benzene, toluene, xylene, paradichlorobenzene, ethylbenzene, styrene, and the like. In recent years, with rapid development of urban and industrialized production, the discharge amount of VOCs in the industries of chemical industry, pharmacy and the like is gradually increased. VOCs pollutes and threatens ecological environment and human health greatly, when the VOCs in the environment reach a certain concentration, people feel headache, nausea, vomit, hypodynamia and the like in a short time, and when serious, convulsions and coma occur, and liver, kidney, brain and nervous system of people are injured, so that serious consequences such as hypomnesis and the like are caused. Toluene is one of the most representative gases in VOCs, 200ppm-570ppm toluene can severely stimulate human respiratory tract and eye mucosa, and 1000ppm toluene gas can cause human body function attenuation and even death. Therefore, development of a highly sensitive technology for detecting VOCs is desired.
At present, the detection method of the domestic traditional VOCs mainly comprises gas chromatography, high performance liquid chromatography, ion chromatography and the like. These analysis and detection methods need to rely on large and expensive precision equipment, and have the defects of complex detection procedures, long detection period, need to be operated by professional technicians, and the like, so that none of the detection methods can be applied to rapid field detection. The fluorescence spectrometry can quantitatively detect the detected object through the fluorescence intensity change after the interaction of the fluorescent probe and the detected object. The fluorescent carbon quantum dots are widely applied to the fields of environmental monitoring and the like with the advantages of low cost, easy surface modification, visualization, high stability and the like. The carbon quantum dot solution has stronger fluorescence intensity, and the fluorescence intensity of the carbon quantum dot solid is obviously reduced or even quenched due to aggregation-induced fluorescence quenching effect. Therefore, the research and development of the solid fluorescent carbon quantum dot material with high sensitivity response to VOCs has great significance for realizing quick and efficient on-site detection of VOCs.
Disclosure of Invention
Aiming at the problems that the method for detecting VOCs in the prior art needs to rely on large-scale expensive precise equipment, has complex detection procedures, long detection period, needs to be operated by professional technicians and the like, the invention provides a eutectic solvent, fluorescent carbon quantum dots, a preparation method and application.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a eutectic solvent is prepared from amide compound and hydrophobic amino acid;
wherein the amide compound is at least one of benzamide, acetamide, caprolactam or acetanilide; the hydrophobic amino acid is at least one of alanine, proline, phenylalanine, valine or leucine.
Preferably, the molar ratio of the amide compound to the hydrophobic amino acid is 1-5:5-1.
Preferably, the preparation method of the eutectic solvent comprises the following steps: and uniformly mixing the amide compound and the hydrophobic amino acid, heating to 90-120 ℃, and keeping the temperature until the system is uniform and transparent, thus obtaining the eutectic solvent.
The eutectic solvent in the application takes amide compounds as hydrogen bond donors, hydrophobic compounds as hydrogen bond acceptors and amino-NH of the hydrogen bond acceptors 2 And the carboxyl-COOH of the hydrogen bond donor are combined in a hydrogen bond mode to obtain the eutectic solvent.
The invention also provides application of the eutectic solvent in preparation of fluorescent carbon quantum dots.
The invention also provides a fluorescent carbon quantum dot prepared by the reaction of any one of the eutectic solvents.
The carbon quantum dot prepared by taking the specific amide compound/hydrophobic amino acid eutectic solvent as the precursor has rich hydrophobic groups and amino groups, has functional groups such as hydroxyl groups and carboxyl groups with stable structures, can selectively identify the VOCs molecules by utilizing Van der Waals bonding force, hydrophobic interaction force and the like of the amino groups, the hydroxyl groups, the carboxyl groups and the like with the VOCs molecules through hydrophobic bonding sites, has strong fluorescence characteristics, generates good fluorescence response on the VOCs molecules, and improves the sensitivity of the detection of the VOCs.
The invention also provides a preparation method of the fluorescent carbon quantum dot, which comprises the following steps: adding the eutectic solvent into absolute ethyl alcohol, uniformly mixing, performing hydrothermal reaction at 200-220 ℃ for 10-14 h, centrifuging, and filtering to obtain a fluorescent carbon quantum dot solution.
Preferably, the mass-volume ratio of the eutectic solvent to the absolute ethanol is 1:25-35, wherein the mass unit is gram and the volume unit is milliliter.
Optionally, the rotation speed of the centrifugation is 8000r/min-12000r/min, and the organic filter membrane with the thickness of 0.22 μm is adopted for filtration after the centrifugation.
The preparation method of the carbon quantum dot provided by the invention is simple and easy to implement, wide in raw material sources, environment-friendly in preparation process, good in dispersibility of the prepared carbon quantum dot in a solution, small in diameter and uniform (2-5 nm), high in fluorescence characteristic, high in fluorescence quantum yield, capable of rapidly and sensitively detecting VOCs in the environment, and wide in application prospect in the field of VOCs detection.
The invention also provides a polyvinylidene fluoride composite film which comprises the fluorescent carbon quantum dots and the polyvinylidene fluoride film.
The polyvinylidene fluoride film is a hydrophobic film and is widely applied to detection, separation and treatment of polluted gas, but the polyvinylidene fluoride film has the problems of poor functionality, poor detection and treatment efficiency, low sensitivity and the like. According to the invention, after the fluorescent carbon quantum dots containing the hydrophobic functional groups, amino groups, hydroxyl groups, carboxyl groups and other functional groups are compounded with the polyvinylidene fluoride film, on the premise that the hydrophobicity of the polyvinylidene fluoride is unchanged, the polyvinylidene fluoride film is provided with more binding reaction sites for VOCs gas such as toluene, so that the detection capability of the polyvinylidene fluoride on the VOCs is obviously improved, and the high-efficiency detection of the VOCs gas is realized.
The invention also provides a preparation method of the polyvinylidene fluoride composite film, which comprises the following steps:
step a, uniformly mixing polyvinylidene fluoride powder, a casting solution solvent and the fluorescent carbon quantum dots to obtain a casting solution;
and b, defoaming, film scraping, solidifying and airing the film casting liquid to obtain the polyvinylidene fluoride composite film.
Preferably, the ratio of polyvinylidene fluoride powder, casting solution solvent and fluorescent carbon quantum dots is 1g:40mL-55mL:5mL-10mL.
Preferably, the casting solution solvent is at least one of N, N-dimethylacetamide, N-dimethylbenzamide, N-methylpyrrolidone or dimethyl sulfoxide.
The preferred casting solution solvents allow for uniform loading onto polyvinylidene fluoride films without agglomeration.
Optionally, in the step a, heating polyvinylidene fluoride powder, a casting solution solvent and the fluorescent carbon quantum dots to 50-70 ℃ and stirring for 30-60 min, and uniformly mixing.
Optionally, in the step b, the casting solution is defoamed in a water bath at 50-80 ℃ for 40-72 h in vacuum.
Optionally, in the step b, the specific steps of film scraping, solidification, water bath soaking and airing are as follows:
heating a clean glass plate to 60-80 ℃, scraping a liquid film with the thickness of 0.05-0.10 mm on the glass plate by a film scraping knife, soaking in a water bath at 20-30 ℃ for 5-10 h, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again for 24-48 h, removing residual solvent, taking out the polyvinylidene fluoride film, putting the polyvinylidene fluoride film on a foam plate, and naturally airing at room temperature.
The invention also provides application of the polyvinylidene fluoride composite film in fluorescence detection of VOCs.
According to some embodiments of the invention, the application comprises: and (3) putting the fluorescent carbon quantum dot/polyvinylidene fluoride composite film into toluene gas with different concentrations, taking out after a period of time, and detecting the linear relation between the fluorescent intensity and the toluene gas with different concentrations by taking 330nm as an excitation wavelength through a fluorescence spectrophotometer. And then placing the fluorescent carbon quantum dot/polyvinylidene fluoride composite film into the gas to be detected, and calculating the concentration of toluene gas in the gas to be detected according to the linear relation through the change of the fluorescent intensity.
The preparation of the gas to be tested comprises the following steps: toluene standard gas and nitrogen are used for preparing toluene gas to be tested with different concentrations.
The detection process comprises the following steps: and (3) putting the fluorescent carbon quantum dot/polyvinylidene fluoride composite film into gas to be detected, taking out after a period of time, and measuring a fluorescent emission spectrum graph by using a fluorescent spectrophotometer.
Drawings
FIG. 1 is a transmission electron microscope image of a fluorescent carbon quantum dot prepared in example 5 of the present invention;
FIG. 2 is a scanning electron microscope image of the polyvinylidene fluoride film used in example 5 of the present invention;
FIG. 3 is a scanning electron microscope image of the fluorescent carbon quantum dot/polyvinylidene fluoride film prepared in example 5 of the present invention;
FIG. 4 is a graph showing fluorescence emission spectra of the fluorescent carbon quantum dot/polyvinylidene fluoride film prepared in example 5 of the present invention for detecting toluene gas with different concentrations at an excitation wavelength of 330 nm;
FIG. 5 shows the fluorescence intensity (F) of the fluorescent carbon quantum dot/polyvinylidene fluoride film prepared in example 5 of the present invention 0 -F)/F 0 A linear relationship graph between different toluene gas concentrations;
FIG. 6 is a graph showing fluorescence emission spectra of the fluorescent carbon quantum dot/polyvinylidene fluoride film prepared in comparative example 1 of the present invention for detection of toluene gas of different concentrations at an excitation wavelength of 330nm, wherein the inset is a partial enlarged view of a box portion;
FIG. 7 is a graph showing fluorescence emission spectra of the fluorescent carbon quantum dot/polyvinylidene fluoride film prepared in comparative example 3 according to the present invention for detection of toluene gas of different concentrations at an excitation wavelength of 330nm, wherein the inset is a partial enlarged view of a box portion;
FIG. 8 is a graph showing fluorescence emission spectra of the fluorescent carbon quantum dot/polyvinylidene fluoride film prepared in comparative example 4 according to the present invention for detecting toluene gas of different concentrations at an excitation wavelength of 330nm, wherein the inset is a partial enlarged view of a box portion;
FIG. 9 is a graph showing fluorescence emission spectra of the fluorescent carbon quantum dot/polyvinylidene fluoride film prepared in comparative example 5 of the present invention for detection of toluene gas of different concentrations at an excitation wavelength of 330nm, wherein the inset is a partial enlarged view of a box portion;
FIG. 10 is a graph showing fluorescence emission spectra of the fluorescent carbon quantum dot/polyvinyl alcohol film prepared in comparative example 6 according to the present invention for detecting toluene gas of different concentrations at an excitation wavelength of 330nm, wherein the inset is a partial enlarged view of a box portion.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
In order to better illustrate the present invention, the following examples are provided for further illustration.
Example 1
The embodiment of the invention provides a eutectic solvent, fluorescent carbon quantum dots and polyvinylidene fluoride composite film,
the eutectic solvent is prepared from acetamide and alanine in a molar ratio of 1:5, and specifically comprises the following steps:
after 0.017mol (1 g) of acetamide and 0.085mol (7.54 g) of alanine were mixed, the mixture was heated to 90℃and stirred at constant temperature for 3 hours to obtain an acetamide/alanine eutectic solvent.
The method for preparing the fluorescent carbon quantum dots by using the acetamide/alanine eutectic solvent specifically comprises the following steps:
1g of acetamide/alanine eutectic solvent is mixed with 30mL of absolute ethyl alcohol, the mixture is subjected to hydrothermal reaction at 200 ℃ for 14h, and then is centrifuged at 8000r/min for 25min, and the mixture is filtered by adopting a 0.22 mu m organic filter membrane, so that a yellowish fluorescent carbon quantum dot solution is obtained.
The preparation method of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film comprises the following steps:
step a, taking 1g of polyvinylidene fluoride powder, 45mLN, N-dimethylacetamide and 7mL of the prepared fluorescent carbon quantum dot solution, mixing, and stirring at 60 ℃ for 45min to obtain uniform casting solution;
and b, sealing the casting film liquid in a water bath at 70 ℃ for defoaming for 60 hours, taking a dried glass plate heated to 77 ℃, scraping a liquid film with the thickness of 0.07mm on the glass plate by a film scraping knife, soaking in the water bath at 25 ℃ for 6 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again, immersing for 32 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent spectrophotometers are used for detecting the fluorescent intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and are respectively filled with different toluene gases.
As a result, the fluorescence intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film is gradually enhanced along with the increase of the toluene concentration, which indicates that the fluorescent carbon quantum dot/polyvinylidene fluoride composite film prepared by the embodiment has good detectability to toluene.
Example 2
The embodiment of the invention provides a eutectic solvent, fluorescent carbon quantum dots and polyvinylidene fluoride composite film,
the eutectic solvent is prepared from caprolactam and valine with a molar ratio of 3:1, and specifically comprises the following steps:
after 0.009mol (1 g) of caprolactam and 0.003mol (0.35 g) of valine were mixed, the mixture was heated to 100℃and stirred at constant temperature for 3 hours to obtain a caprolactam/valine eutectic solvent.
The method for preparing the fluorescent carbon quantum dots by using the caprolactam/valine eutectic solvent specifically comprises the following steps:
1g of caprolactam/valine eutectic solvent is mixed with 25mL of absolute ethyl alcohol, the mixture is subjected to hydrothermal reaction at 210 ℃ for 13h, and then is centrifuged at 10000r/min for 15min, and the mixture is filtered by adopting a 0.22 mu m organic filter membrane, so that a yellowish fluorescent carbon quantum dot solution is obtained.
The preparation method of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film comprises the following steps:
step a, taking 1g of polyvinylidene fluoride powder, mixing 40mL of N-methyl pyrrolidone and 5mL of the prepared fluorescent carbon quantum dot solution, and stirring for 58min at 50 ℃ to obtain uniform casting film liquid;
and b, sealing the casting film liquid in a water bath at 60 ℃ for defoaming for 65 hours, taking a dried glass plate heated to 80 ℃, scraping a liquid film with the thickness of 0.05mm on the glass plate by a film scraping knife, soaking in the water bath at 20 ℃ for 6 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again for 36 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent spectrophotometers are used for detecting the fluorescent intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and are respectively filled with different toluene gases.
As a result, the fluorescence intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film is gradually enhanced along with the increase of the toluene concentration, which indicates that the fluorescent carbon quantum dot/polyvinylidene fluoride composite film prepared by the embodiment has good detectability to toluene.
Example 3
The embodiment of the invention provides a eutectic solvent, fluorescent carbon quantum dots and polyvinylidene fluoride composite film,
the eutectic solvent is prepared from benzamide and leucine in a molar ratio of 1:1, and specifically comprises the following steps:
after 0.008mol (1 g) of benzamide and 0.008mol (1.08 g) of leucine were mixed, they were heated to 120℃and stirred at constant temperature for 2 hours to obtain a benzamide/leucine eutectic solvent.
The method for preparing the fluorescent carbon quantum dots by using the benzamide/leucine eutectic solvent specifically comprises the following steps:
1g of benzamide/leucine eutectic solvent is mixed with 25mL of absolute ethyl alcohol, the mixture is subjected to hydrothermal reaction at 220 ℃ for 12 hours, and then the mixture is centrifuged at 9000r/min for 20 minutes and filtered by adopting a 0.22 mu m organic filter membrane, so that a pale yellow fluorescent carbon quantum dot solution is obtained.
The preparation method of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film comprises the following steps:
step a, taking 1g of polyvinylidene fluoride powder, mixing 50mL of dimethyl sulfoxide and 10mL of the prepared fluorescent carbon quantum dot solution, and stirring at 80 ℃ for 30min to obtain uniform casting solution;
and b, sealing the casting film liquid in a water bath at 55 ℃ for defoaming for 68 hours, taking a dry glass plate heated to 60 ℃, scraping a liquid film with the thickness of 0.06mm on the glass plate by a film scraping knife, soaking in the water bath at 24 ℃ for 7 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again, immersing for 40 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent spectrophotometers are used for detecting the fluorescent intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and are respectively filled with different toluene gases.
As a result, the fluorescence intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film is gradually enhanced along with the increase of the toluene concentration, which indicates that the fluorescent carbon quantum dot/polyvinylidene fluoride composite film prepared by the embodiment has good detectability to toluene.
Example 4
The embodiment of the invention provides a eutectic solvent, fluorescent carbon quantum dots and polyvinylidene fluoride composite film,
the eutectic solvent is prepared from acetanilide and proline in a molar ratio of 1:2, and specifically comprises the following steps:
after 0.007mol (1 g) of acetanilide and 0.014mol (1.7 g) of proline were mixed, the mixture was heated to 95℃and stirred at constant temperature for 3 hours to obtain an acetanilide/proline eutectic solvent.
The method for preparing the fluorescent carbon quantum dots by using the acetanilide/proline eutectic solvent specifically comprises the following steps:
1g of acetanilide/proline eutectic solvent is mixed with 27mL of absolute ethyl alcohol, the mixture is subjected to hydrothermal reaction at 210 ℃ for 12 hours, and then is centrifuged at 10000r/min, and is filtered by adopting a 0.22 mu m organic filter membrane, so as to obtain a yellowish fluorescent carbon quantum dot solution.
The preparation method of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film comprises the following steps:
step a, taking 1g of polyvinylidene fluoride powder, 45mL of N, N-dimethylacetamide and 10mL of the prepared fluorescent carbon quantum dot solution, mixing, and stirring for 30min at 75 ℃ to obtain uniform casting film liquid;
and b, sealing the casting film liquid in a water bath at 60 ℃ for defoaming for 65 hours, taking a dried glass plate heated to 75 ℃, scraping a liquid film with the thickness of 0.06mm on the glass plate by a film scraping knife, soaking in the water bath at 30 ℃ for 5 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again, immersing for 24 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent spectrophotometers are used for detecting the fluorescent intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and are respectively filled with different toluene gases.
As a result, the fluorescence intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film is gradually enhanced along with the increase of the toluene concentration, which indicates that the fluorescent carbon quantum dot/polyvinylidene fluoride composite film prepared by the embodiment has good detectability to toluene.
Example 5
The embodiment of the invention provides a eutectic solvent, fluorescent carbon quantum dots and polyvinylidene fluoride composite film,
the eutectic solvent is prepared from acetanilide and phenylalanine with a molar ratio of 2:1, and specifically comprises the following steps:
after 0.007mol (1 g) of acetanilide and 0.0035mol (0.61 g) of phenylalanine were mixed, the mixture was heated to 100℃and stirred at constant temperature for 3 hours, to obtain an acetanilide/phenylalanine eutectic solvent.
The method for preparing the fluorescent carbon quantum dots by using the acetanilide/phenylalanine eutectic solvent specifically comprises the following steps:
1g of acetanilide/phenylalanine eutectic solvent is mixed with 30mL of absolute ethyl alcohol, the mixture is subjected to hydrothermal reaction for 12 hours at 220 ℃, and then is centrifuged at 10000r/min, and the mixture is filtered by adopting a 0.22 mu m organic filter membrane, so as to obtain a yellowish fluorescent carbon quantum dot solution.
The preparation method of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film comprises the following steps:
step a, taking 1g of polyvinylidene fluoride powder, 45mL of N, N-dimethylacetamide and 10mL of the prepared fluorescent carbon quantum dot solution, mixing, and stirring at 80 ℃ for 25min to obtain uniform casting film liquid;
and b, sealing the casting film liquid in a water bath at 60 ℃ for defoaming for 70 hours, taking a dried glass plate heated to 80 ℃, scraping a liquid film with the thickness of 0.05mm on the glass plate by a film scraping knife, soaking in the water bath at 28 ℃ for 5 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again for 45 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The TEM image of the fluorescent carbon quantum dot prepared in this embodiment is shown in fig. 1, and it can be seen from the image that the particle size of the fluorescent carbon quantum dot prepared in this embodiment is 2-5nm, and the fluorescent carbon quantum dot has a smaller size and a similar spherical shape, and has a uniform particle size distribution.
An SEM image of the polyvinylidene fluoride film used in this example is shown in fig. 2, and an SEM image of the prepared fluorescent carbon quantum dot/polyvinylidene fluoride composite film is shown in fig. 3. As can be seen from comparing fig. 2 and fig. 3, the fluorescent carbon quantum dots were successfully and uniformly loaded on the polyvinylidene fluoride film without agglomeration.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent spectrophotometers are used for detecting the fluorescent intensity of the fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and are respectively filled with different toluene gases.
FIG. 4 is a graph showing fluorescence emission spectra of fluorescent carbon quantum dot/polyvinylidene fluoride composite films without toluene gas and with toluene gas of different concentrations at an excitation wavelength of 330 nm. FIG. 5 shows fluorescence intensity (F-F) of fluorescent carbon quantum dot/polyvinylidene fluoride composite film 0 )/F 0 A linear relationship graph with toluene gas concentration, wherein F 0 And F represents that toluene gas is not introduced and methyl with different concentrations is introducedFluorescent carbon quantum dot of benzene gas/fluorescent intensity of polyvinylidene fluoride composite film.
As can be seen from FIGS. 4 and 5, the fluorescence intensity (F-F 0 )/F 0 The linear relationship with toluene gas concentration is: (F-F) 0 )/F 0 ＝-0.03838+0.00024830x，R 2 = 0.99477, where x is toluene gas concentration.
According to the detection limit formula lod=3δ/S, δ is the standard deviation of a blank sample (δ= 0.00047642), S is the equation (F 0 -F)/F 0 Slope of = -0.03838+0.00024830x, s= 0.00024830, and detection limit of p-toluene gas of fluorescent carbon quantum dot/polyvinylidene fluoride composite film is 5.756ppm.
The detection limits of the fluorescent carbon quantum dots/polyvinylidene fluoride composite films prepared in examples 1 to 4 on toluene gas were calculated according to the above method, and the calculated detection limits of the fluorescent carbon quantum dots/polyvinylidene fluoride composite films prepared in examples 1 to 4 were 7.684ppm, 6.853ppm, 3.547ppm and 6.952ppm, respectively.
Comparative example 1
The comparative example of the present invention provides a fluorescent carbon quantum dot/polyvinylidene fluoride composite film, the preparation method is exactly the same as that of example 5, except that the acetanilide in example 5 is replaced by cyclodextrin with the same amount, and the specific preparation method is as follows:
mixing 1g of cyclodextrin and 0.61g of phenylalanine, heating to 100 ℃ and stirring at constant temperature for 3 hours to obtain a cyclodextrin/phenylalanine eutectic solvent;
1g of cyclodextrin/phenylalanine eutectic solvent is mixed with 30mL of absolute ethyl alcohol, the mixture is subjected to hydrothermal reaction at 220 ℃ for 12h, and then the mixture is centrifuged at 10000r/min and filtered by adopting a 0.22 mu m organic filter membrane, so that a yellowish fluorescent carbon quantum dot solution is obtained.
The fluorescence emission spectra of the prepared fluorescent carbon quantum dot solution under different excitation wavelengths of 310nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm and 400nm are tested, and as shown in figure 6, the fluorescent carbon quantum dot solution has irregular fluorescence emission spectra under different excitation wavelengths and cannot be used for detecting the toluene.
Comparative example 2
The comparative example of the invention provides a fluorescent carbon quantum dot/polyvinylidene fluoride composite film, the preparation method is exactly the same as that of the example 5, and the specific preparation method is as follows, except that the acetanilide in the example 5 is replaced by the equivalent cyclopropanesulfonamide:
1g of cyclopropanesulfonamide and 0.61g of phenylalanine were mixed, heated to 100℃and stirred at constant temperature for 3 hours, and it was found that cyclopropanesulfonamide and phenylalanine failed to synthesize a uniform eutectic solvent.
Comparative example 3
The comparative example of the invention provides a fluorescent carbon quantum dot/polyvinylidene fluoride composite film, the preparation method is completely the same as that of example 5, and the specific preparation method is as follows, except that the acetanilide in example 5 is replaced by the same amount of lactam:
mixing 1g of lactam and 0.61g of phenylalanine, heating to 100 ℃ and stirring at constant temperature for 3 hours to obtain a lactam/phenylalanine eutectic solvent;
mixing 1g of lactam/phenylalanine eutectic solvent with 30mL of absolute ethyl alcohol, performing hydrothermal reaction for 12 hours at 220 ℃, centrifuging at 10000r/min, and filtering by adopting a 0.22 mu m organic filter membrane to obtain a yellowish fluorescent carbon quantum dot solution;
taking 1g of polyvinylidene fluoride powder, 45mL of N, N-dimethylacetamide and 10mL of the prepared fluorescent carbon quantum dot solution, mixing, and stirring at 80 ℃ for 25min to obtain uniform casting solution;
sealing the casting film liquid in a water bath at 60 ℃ for defoaming for 70 hours, taking a dried glass plate heated to 80 ℃, scraping a liquid film with the thickness of 0.05mm on the glass plate by a film scraping knife, soaking in the water bath at 28 ℃ for 5 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again, soaking for 45 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and respectively filled with different toluene gases are detected by a fluorescence spectrophotometer, as shown in figure 7.
As a result, it was found that the fluorescence intensity of the composite film was slightly and irregularly changed with the increase of the toluene concentration, and it was presumed that the lactam steric structure was excessively large, and the small-molecule toluene gas was not able to contact the detection site, resulting in poor detection effect.
Comparative example 4
The comparative example of the invention provides a fluorescent carbon quantum dot/polyvinylidene fluoride composite film, the preparation method is completely the same as that of example 5, and the specific preparation method is as follows, except that phenylalanine in example 5 is replaced by betaine with the same amount:
mixing 1g of acetanilide and 0.61g of betaine, heating to 100 ℃ and stirring at constant temperature for 3 hours to obtain an acetanilide/betaine eutectic solvent;
mixing 1g of acetanilide/betaine eutectic solvent with 30mL of absolute ethyl alcohol, performing hydrothermal reaction for 12 hours at 220 ℃, centrifuging at 10000r/min, and filtering by adopting a 0.22 mu m organic filter membrane to obtain a yellowish fluorescent carbon quantum dot solution;
taking 1g of polyvinylidene fluoride powder, 45mL of N, N-dimethylacetamide and 10mL of the prepared fluorescent carbon quantum dot solution, mixing, and stirring at 80 ℃ for 25min to obtain uniform casting solution;
sealing the casting film liquid in a water bath at 60 ℃ for defoaming for 70 hours, taking a dried glass plate heated to 80 ℃, scraping a liquid film with the thickness of 0.05mm on the glass plate by a film scraping knife, soaking in the water bath at 28 ℃ for 5 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again, soaking for 45 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and respectively filled with different toluene gases are detected by a fluorescence spectrophotometer, as shown in figure 8.
As a result, the fluorescent intensity of the composite film is slightly and irregularly changed along with the increase of the concentration of toluene, namely the fluorescent carbon quantum dot/polyvinylidene fluoride composite film prepared by replacing phenylalanine with betaine cannot accurately and quantitatively detect toluene.
Comparative example 5
The comparative example of the present invention provides a fluorescent carbon quantum dot/polyvinylidene fluoride composite film, which has the preparation method identical to that of example 5, except that phenylalanine in example 5 is replaced by equivalent methionine, and the specific preparation method is as follows:
mixing 1g of acetanilide and 0.61g of methionine, heating to 100 ℃ and stirring at constant temperature for 3 hours to obtain an acetanilide/methionine eutectic solvent;
mixing 1g of acetanilide/methionine eutectic solvent with 30mL of absolute ethyl alcohol, performing hydrothermal reaction for 12 hours at 220 ℃, centrifuging at 10000r/min, and filtering by adopting a 0.22 mu m organic filter membrane to obtain a yellowish fluorescent carbon quantum dot solution;
taking 1g of polyvinylidene fluoride powder, 45mL of N, N-dimethylacetamide and 10mL of the prepared fluorescent carbon quantum dot solution, mixing, and stirring at 80 ℃ for 25min to obtain uniform casting solution;
sealing the casting film liquid in a water bath at 60 ℃ for defoaming for 70 hours, taking a dried glass plate heated to 80 ℃, scraping a liquid film with the thickness of 0.05mm on the glass plate by a film scraping knife, soaking in the water bath at 28 ℃ for 5 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again, soaking for 45 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinylidene fluoride composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinylidene fluoride composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinylidene fluoride composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and fluorescent carbon quantum dot/polyvinylidene fluoride composite films which are not filled with toluene gas and respectively filled with different toluene gases are detected by a fluorescence spectrophotometer, as shown in figure 9.
As a result, the fact that the fluorescence intensity of the composite film is changed greatly but irregularly along with the increase of the concentration of toluene is found, and presumably because the coupling effect of sulfur and toluene in methionine interferes with the detection of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film on toluene, namely the fluorescent carbon quantum dot/polyvinylidene fluoride composite film prepared after phenylalanine is replaced by methionine cannot accurately and quantitatively detect toluene.
Comparative example 6
The comparative example of the present invention provides a fluorescent carbon quantum dot/polyvinyl alcohol composite film, which has the preparation method identical to that of example 5, except that the polyvinylidene fluoride film of example 5 is replaced by a polyvinyl alcohol film, and the specific preparation method is as follows:
mixing 1g of acetanilide and 0.61g of phenylalanine, heating to 100 ℃ and stirring at constant temperature for 3 hours to obtain an acetanilide/phenylalanine eutectic solvent;
mixing 1g of acetanilide/phenylalanine eutectic solvent with 30mL of absolute ethyl alcohol, performing hydrothermal reaction for 12 hours at 220 ℃, centrifuging at 10000r/min, and filtering by adopting a 0.22 mu m organic filter membrane to obtain a yellowish fluorescent carbon quantum dot solution;
mixing 1g of polyvinyl alcohol resin, 45mL of deionized water and 10mL of the prepared fluorescent carbon quantum dot solution, and stirring at 80 ℃ for 25min to obtain uniform casting solution;
sealing the casting film liquid in a water bath at 60 ℃ for defoaming for 70 hours, taking a dried glass plate heated to 80 ℃, scraping a liquid film with the thickness of 0.05mm on the glass plate by a film scraping knife, soaking in the water bath at 28 ℃ for 5 hours, taking out the film after the film automatically falls off from the glass plate, immersing the film in deionized water again, soaking for 45 hours, and removing residual solvent. And taking out the polyvinylidene fluoride film, placing the polyvinylidene fluoride film on a foam board, and fixing and drying the polyvinylidene fluoride film at room temperature to obtain the fluorescent carbon quantum dot/polyvinyl alcohol composite film.
The method for detecting toluene by using the fluorescent carbon quantum dot/polyvinyl alcohol composite film specifically comprises the following steps:
toluene standard gas and nitrogen are used for preparing toluene gas of 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm and 1200ppm, 6 pieces of fluorescent carbon quantum dot/polyvinyl alcohol composite films with the same size are respectively placed under toluene gas with different concentrations, the films are taken out after 30 seconds, and a fluorescence spectrophotometer is used for detecting the fluorescence intensity of the fluorescent carbon quantum dot/polyvinyl alcohol composite films which are not filled with toluene gas and are respectively filled with different toluene gases, as shown in figure 10.
As a result, the fluorescence intensity of the composite film has no obvious enhancement trend and no change rule along with the increase of the concentration of toluene, namely the prepared fluorescent carbon quantum dot/polyvinyl alcohol composite film cannot realize the accurate quantitative detection of the toluene.
In conclusion, the preparation method of the fluorescent carbon quantum dot/polyvinylidene fluoride composite film provided by the invention is simple, the sources of raw materials are wide, the prepared fluorescent carbon quantum dot/polyvinylidene fluoride composite film has an excellent detection effect on VOCs, the response speed is high, the quick response on the VOCs can be realized only by 30 seconds, the detection time is greatly shortened, the detection cost is reduced, large-scale expensive precise equipment is not needed, and the operation of professional technicians is not needed, so that the aim of quickly and efficiently detecting the VOCs on site is fulfilled, and the practical value is higher.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, or alternatives falling within the spirit and principles of the invention.

Claims (9)

1. The application of the eutectic solvent in preparing the fluorescent carbon quantum dots is characterized in that the eutectic solvent is prepared from an amide compound and hydrophobic amino acid;
wherein the amide compound is at least one of benzamide, acetamide, caprolactam or acetanilide; the hydrophobic amino acid is at least one of alanine, proline, phenylalanine, valine or leucine.
2. The use of the eutectic solvent according to claim 1 for preparing fluorescent carbon quantum dots, wherein the molar ratio of the amide compound to the hydrophobic amino acid is 1-5:5-1.
3. The use of the eutectic solvent according to claim 1 for preparing fluorescent carbon quantum dots, wherein the preparation method of the eutectic solvent comprises the following steps: and uniformly mixing the amide compound and the hydrophobic amino acid, heating to 90-120 ℃, and keeping the temperature until the system is uniform and transparent, thus obtaining the eutectic solvent.
4. The preparation method of the fluorescent carbon quantum dot is characterized by comprising the following steps of: adding the eutectic solvent of any one of claims 1-3 into absolute ethyl alcohol, uniformly mixing, performing hydrothermal reaction at 200-220 ℃ for 10-14 h, centrifuging, and filtering to obtain a fluorescent carbon quantum dot solution.
5. The method of preparing fluorescent carbon quantum dots according to claim 4, wherein the mass-to-volume ratio of the eutectic solvent to the absolute ethanol is 1:25-35, wherein the mass unit is gram and the volume unit is milliliter.
6. A fluorescent carbon quantum dot produced by the method for producing a fluorescent carbon quantum dot according to claim 4 or 5.
7. A polyvinylidene fluoride composite film comprising the fluorescent carbon quantum dot of claim 6 and a polyvinylidene fluoride film.
8. The method for preparing the polyvinylidene fluoride composite film according to claim 7, comprising the steps of:
step a, uniformly mixing polyvinylidene fluoride powder, a casting solution solvent and the fluorescent carbon quantum dots of claim 6 to obtain a casting solution;
and b, defoaming, film scraping, solidifying and airing the film casting liquid to obtain the polyvinylidene fluoride composite film.
9. The use of the polyvinylidene fluoride composite film according to claim 7 for fluorescence detection of volatile organic compounds.
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