A flexible quantum dot composite material, its preparation method and application

Abstract

This invention discloses a flexible quantum dot composite material, its preparation method, and its applications. The flexible quantum dot composite material includes a flexible substrate, a polymer substrate, and aerogel particles loaded with quantum dots. The polymer substrate is disposed on the flexible substrate. The polymer substrate has micropores. The aerogel particles loaded with quantum dots are disposed within the micropores. The quantum dots in the flexible quantum dot composite material of this invention are uniformly distributed and do not agglomerate. Furthermore, the composite material is flexible. Applying this composite material to flexible sensors can give the sensors advantages such as good flexibility, resistance to breakage, and light weight. It can also achieve the detection of sulfite ions in sulfur dioxide gas or liquid with high detection accuracy and good selectivity, unaffected by interference from other detection gases or impurities. In addition, the composite material can be stably stored for more than 90 days without a significant decrease in detection accuracy.

Description

Technical Field

[0001] This invention relates to the field of materials, specifically to a flexible quantum dot composite material, its preparation method, and its applications. Background Technology

[0002] With the continuous development and progress of science and technology, various miniaturized and portable sensors have been applied in various fields. However, most traditional sensors are based on rigid materials and lack ductility and flexibility, which limits their integration, micro-nano fabrication, and specific application scenarios, greatly restricting the application scope of sensors.

[0003] Currently, the main methods for detecting SO2 include spectrophotometry, ultraviolet fluorescence, ion chromatography, and titration. However, most of these methods suffer from drawbacks such as complex detection procedures and high instrument and maintenance costs. Electrochemical methods, while maintaining detection sensitivity, avoid the use of large, precision instruments, thus further reducing detection costs and shortening detection time. However, these methods are susceptible to electromagnetic interference and have complex preparation processes, which to some extent limits their application in SO2 detection. Quantum dots possess superior optical properties such as good stability, tunable fluorescence spectra, long fluorescence lifetime, and broad excitation and narrow emission spectra. They are widely used in mechanics, electricity, thermodynamics, optics, and chemical activity, and have gradually become one of the hot research topics both domestically and internationally. However, there are also many challenges in the production and application of quantum dot materials. Among them, the aggregation of quantum dots is a significant factor affecting their luminescence and sensing performance. Because quantum dot materials reach the nanoscale, their specific surface area is large and their surface energy is high, placing them in a thermodynamically unstable state. To achieve stability, particles often aggregate through electrostatic Coulomb forces and van der Waals forces. Therefore, varying degrees of aggregation occur during the preparation and application of quantum dots. Due to the quantum confinement effect, quantum dots can only maintain stable luminescence properties when the particle size is relatively small. Agglomeration increases the particle size of quantum dots, leading to a decrease in their fluorescence emission intensity and thus a loss of quantum properties. Therefore, maintaining the stability of the optical properties of quantum dot materials during applications is an urgent problem to be solved. Thus, to address the shortcomings of the existing technologies, there is a pressing need to develop a flexible sulfur dioxide gas detection sensor based on uniformly dispersed and non-agglomerated quantum dots. Summary of the Invention

[0004] In order to overcome the problems existing in the prior art, one of the objectives of the present invention is to provide a flexible quantum dot composite material.

[0005] The second objective of this invention is to provide a method for preparing flexible quantum dot composite materials.

[0006] The third objective of this invention is to provide a sensor.

[0007] The fourth objective of this invention is to provide a sulfur dioxide gas detection system.

[0008] The fifth objective of this invention is to provide an application of flexible quantum dot composite materials in gas detection or liquid detection.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A first aspect of the present invention provides a flexible quantum dot composite material, comprising a flexible substrate, a polymer substrate, and quantum dot-loaded aerogel particles; the flexible substrate is provided with the polymer substrate; the polymer substrate has micropores; and the quantum dot-loaded aerogel particles are provided within the polymer substrate.

[0011] Preferably, the thickness of the flexible substrate is 250–350 μm; more preferably, the thickness of the flexible substrate is 280–330 μm; and even more preferably, the thickness of the flexible substrate is 290–320 μm.

[0012] Preferably, the thickness of the polymer substrate is 250–350 μm; more preferably, the thickness of the polymer substrate is 280–330 μm; and even more preferably, the thickness of the polymer substrate is 290–320 μm.

[0013] Preferably, the quantum dot-loaded aerogel particles are located within micropores in the polymer substrate.

[0014] Preferably, the quantum dots are CdTe quantum dots modified with mercaptoethylamine groups.

[0015] Preferably, the aerogel is selected from silica aerogel, carbide aerogel, or graphene aerogel. SiO2 aerogel has the characteristics of good thermal insulation, light weight, chemical inertness, and reusability.

[0016] Preferably, the aerogel has pores with a diameter of 10–50 nm. Quantum dots are loaded within the pores of the aerogel.

[0017] Preferably, the flexible substrate is made of at least one material selected from polydimethylsiloxane, polyvinyl alcohol, polyester, polyimide, and polyethylene naphthalate. More preferably, the flexible substrate is made of polydimethylsiloxane.

[0018] Preferably, the polymer substrate material is selected from at least one of polydimethylsiloxane, polyvinyl alcohol, polyester, polyimide, and polyethylene naphthalate. More preferably, the polymer substrate material is selected from polydimethylsiloxane. PDMS in this invention is a high molecular weight polymer material with a large number of microporous structures distributed in its molecular structure, which is conducive to the permeation and diffusion of gas molecules and can play a good role in enriching low concentrations of sulfur dioxide gas molecules. Using PDMS as a flexible substrate for gas sensors can effectively improve the sensitivity of the sensor to gas detection. In addition, the PDMS in this invention has excellent properties such as good light transmittance, low surface energy, good biocompatibility, pollution resistance, corrosion resistance, low and high temperature resistance, light weight, good stability, and low density. Moreover, its structure is simple to prepare and low in cost, making it suitable for large-area production.

[0019] Preferably, the diameter of the micropores is 50–90 μm.

[0020] Preferably, the diameter of the quantum dot-loaded aerogel particles is 50–90 μm.

[0021] A second aspect of the present invention provides a method for preparing the flexible quantum dot composite material provided in the first aspect of the present invention, comprising the following steps:

[0022] S1: Mix aerogel with quantum dot solution to obtain quantum dot-loaded aerogel particles;

[0023] S2: A flexible substrate and a polymer substrate are formed sequentially on a substrate, the substrate is removed, and then aerogel particles loaded with quantum dots are dispersed in the polymer substrate to obtain the flexible quantum dot composite material.

[0024] Preferably, the quantum dot solution is prepared by mixing and reacting a cadmium source, mercaptoethylamine or its hydrochloride, a tellurium source, and an alkali metal borohydride at 85–95°C for 8–10 hours. In the quantum dot solution, the quantum dots are uniformly dispersed and do not agglomerate under the action of the solvent. However, in the detection of SO2 gas, to achieve portability and real-time detection, the quantum dots need to be dried to form a film. During the drying process of the quantum dot solution, as water molecules continuously evaporate, their interaction force with the quantum dot particles gradually disappears. Combined with the surface tension of the liquid, this easily leads to quantum dot agglomeration. Agglomeration between quantum dots can change the size of the nanoparticles, thereby disrupting the quantum confinement effect and weakening or even quenching the fluorescence intensity of the quantum dots. Furthermore, contact between quantum dots can cause the ligands specifically modified on their surfaces to detach, increasing surface defects and causing carrier recombination via non-radiative means, resulting in a significant decrease in the luminescence efficiency of the quantum dots. This invention avoids the aggregation of quantum dots by loading a quantum dot solution into aerogel particles and then distributing the aerogel particles in a porous polymer substrate.

[0025] Preferably, the cadmium source is a cadmium salt; more preferably, the cadmium salt is selected from cadmium chloride.

[0026] Preferably, the tellurium source is tellurite; more preferably, the tellurite is selected from at least one of sodium tellurite and potassium tellurite.

[0027] Preferably, the alkali metal borohydride is selected from at least one of sodium borohydride and potassium borohydride.

[0028] Preferably, the aerogel is prepared by: hydrolyzing a silicon source, then performing a polymerization reaction, then aging it in a plastic bag, and finally drying it.

[0029] Preferably, the hydrolysis reaction is carried out under acidic conditions.

[0030] Preferably, the polymerization reaction is carried out under acidic conditions.

[0031] Under acidic catalysis, silicon sources can form porous wet gels through hydrolysis-condensation reactions. A subsequent aging process of several hours prepares the gel for further condensation reactions, thereby improving the overall mechanical strength of the aerogel. Finally, drying removes the solvent from the wet gel, yielding a SiO2 aerogel with a nanostructure.

[0032] Preferably, the silicon source is selected from at least one of methyl orthosilicate, tetraethoxysilane, sodium silicate, and polysilane.

[0033] Preferably, the aging time is 20 to 30 hours.

[0034] Preferably, the drying process is selected from at least one of supercritical drying, atmospheric pressure drying, and freeze-drying. Supercritical drying can effectively avoid structural shrinkage or collapse caused by capillary forces generated during the drying of wet gels. Freeze-drying is less expensive than supercritical drying and is suitable for large-scale industrial preparation. Atmospheric pressure drying can dry wet gels under normal environmental pressure. This method has low energy consumption, mild conditions, simple equipment, low risk, and low cost, and therefore has broad application prospects in the production of aerogels.

[0035] Preferably, the mixing in step S1 is ultrasonic mixing.

[0036] Preferably, step S2 includes the following steps:

[0037] Step a: Mix polydimethylsiloxane with a curing agent, degas to obtain a polymer mixture; then coat the polymer mixture onto a substrate and dry it at 55-70°C to form a film, thus obtaining a flexible substrate;

[0038] Step b: After mixing the polymer mixture with the pore-forming agent, the mixture is coated onto the flexible substrate, then the substrate is removed, and the substrate is washed with water to obtain the polymer substrate;

[0039] Step c: Prepare a solution of quantum dot-loaded aerogel particles, then coat it onto the surface of the polymer substrate, and dry it at 15-25°C and 0.05-0.07 MPa for 5-8 hours to obtain the flexible quantum dot composite material.

[0040] A third aspect of the present invention provides a sensor comprising the flexible quantum dot composite material provided in the first aspect of the present invention; the sensor is used to detect sulfur dioxide gas or sulfite ions in water. The sensor of the present invention is mainly used for sensing sulfur dioxide (SO2), which exists primarily as sulfite ions in water and as sulfur dioxide gas in air.

[0041] A fourth aspect of the present invention provides a sulfur dioxide gas detection system, comprising a gas supply system, a sensing device, a waste collection device, and a fluorescence detection system; the sensing device is connected to the gas supply system and the waste collection device respectively via pipelines; the sensing device is connected to the fluorescence detection system; the sensing device includes a sensor.

[0042] Preferably, the sensing device further includes a detection chamber, a mounting frame, an optical filter A, and an optical filter B; the detection chamber is equipped with the mounting frame; the mounting frame is equipped with the optical filter A, a sensor, and the optical filter B; the sensor is located between the optical filter A and the optical filter B.

[0043] Preferably, the bandpass of optical filter A is <400nm.

[0044] Preferably, the bandpass of optical filter A is >400nm.

[0045] Preferably, the gas supply system includes a sulfur dioxide gas supply device, a nitrogen gas supply device, and a gas mixer, wherein the gas mixer is connected to a sensing device via a pipeline; the gas mixer is connected to the sulfur dioxide gas supply device via a pipeline; and the gas mixer is connected to the nitrogen gas supply device via a pipeline.

[0046] Preferably, the pipeline is equipped with a gas flow controller.

[0047] Preferably, the pipeline is equipped with a control valve.

[0048] Preferably, the waste collection device includes an alkali solution tank.

[0049] Preferably, the alkaline solution tank contains a sodium hydroxide solution.

[0050] Preferably, the fluorescence detection system includes a fluorescence excitation device, a fluorescence detection device, and a control system. The fluorescence excitation device is connected to the fluorescence detection device, the fluorescence detection device is connected to the sensing device, and the fluorescence detection device is connected to the control system.

[0051] Preferably, the control system is a computer.

[0052] The fifth aspect of the present invention provides the application of the flexible quantum dot composite material provided in the first aspect of the present invention in gas detection or liquid detection.

[0053] The beneficial effects of this invention are: the quantum dots in the flexible quantum dot composite material of this invention are uniformly distributed and do not agglomerate, and the composite material is flexible. When applied to flexible sensors, the flexible sensors can have advantages such as good flexibility, not easy to break, and light weight. Moreover, the sensors using this composite material can detect sulfite ions in sulfur dioxide gas or liquid with high detection accuracy, good selectivity, and are not affected by other detection gases or impurities. In addition, the composite material can be stably stored for more than 90 days without significant reduction in detection accuracy. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the preparation process of the flexible quantum dot composite material in Example 1.

[0055] Figure 2 This is a transmission electron microscope (TEM) image of the SiO2 aerogel from Example 1.

[0056] Figure 3The image shows the EDS spectrum of the MEA-CdTe quantum dot-functionalized SiO2 aerogel in Example 1.

[0057] Figure 4 The image shows the SEM images of the ground NaCl particles and MEA-CdTe QDs@AGs from Example 1.

[0058] Figure 5 This is a SEM image of the porous flexible PDMS substrate in Example 1.

[0059] Figure 6 The image shows the SEM images of the flexible quantum dot composite material and the QDs@AGs / blank PDMS composite film in Example 1.

[0060] Figure 7 This is a schematic diagram of the sulfur dioxide gas detection system in Example 2.

[0061] Figure 8 The images show the fluorescence spectrum and linear curve of SO2 gas tested using the flexible quantum dot composite material in Example 1.

[0062] Figure 9 The images show the fluorescence spectrum and linear curve of sulfite ions tested by MEA-CdTe QDs in Example 1.

[0063] Figure 10 This is a selective test diagram of the flexible quantum dot composite material in Example 1.

[0064] Figure 11 This is a stability test diagram of the flexible quantum dot composite material in Example 1.

[0065] Figure 12 These are initial fluorescence intensity test images of four different composite films in this invention.

[0066] Figure 13 The images show the fluorescence emission patterns of four different composite films in this invention.

[0067] Figure 14 The UV-Vis absorption spectra of MEA-CdTe QDs before and after the reaction are shown.

[0068] Figure 15 The image shows the fluorescence decay characteristics of the MEA-CdTe QDs@AGs / porous PDMS composite film in Example 1. Detailed Implementation

[0069] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0070] The information on the raw materials and instruments used in this invention is as follows:

[0071] SYLGARD 184 curing agent and polydimethylsiloxane were both purchased from Shanghai Deji Trading Co., Ltd.

[0072] The spin coater, model EZ4, was purchased from Jiangsu Leibo Scientific Instruments Co., Ltd.

[0073] The fluorescence spectrometer was an AvaSpec-ULS2048L (Avantes, Netherlands) spectrometer.

[0074] The gas flow controller, model D08-1F&1FP, was purchased from Beijing Qixing Huachuang Flowmeter Co., Ltd.

[0075] The phenanthrene imidazole fluorophore, also known as the phenanthrene imidazole fluorophore, is described in Venkatachalam K, Asaithambi G, Rajasekaran D, et al. A novel ratiometric fluorescent probe for “naked-eye” detection of sulfite ion: Applications in detection of biological SO3. 2- ions in food and live cells[J]. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2020, 228: 117788.

[0076] The cation ratiometric sensor, also known as the cationic ratiometric sensor, is described in Yuan G, Zhou L, Yang Q, et al. Rational development of a new reaction-based ratiometric fluorescent probe with a large stokesshift for selective detection of bisulfite in tap water, real food samples, onion tissues, and zebrafish[J]. Journal of Agricultural and Food Chemistry, 2021, 69(16):4894-902.

[0077] Conjugated microporous polymers, also known as CMPs, are described in Wu K, Guo J, Wang C. Dispersible and discrete metalloporphyrin-based CMP nanoparticles enabling colorimetric detection and quantitation of gaseous SO2[J]. Chemical Communications, 2014, 50(6):695-7).

[0078] 4-Hydroxy-1,8-naphthalimide fluorescent probe, also known as Probe 1, is described in Wang C, Feng S, Wu L, et al. A new fluorescent turn-on probe for highly sensitive and selective detection of sulfite and bisulfite[J]. Sensors and Actuators B: Chemical, 2014, 190: 792-9).

[0079] In the following text, MEA-CdTe QDs@AGs / porous PDMS composite film, QDs@AGs / porous PDMS, and composite film all refer to the flexible quantum dot composite material in Example 1.

[0080] Example 1

[0081] Reference Figure 1 The schematic diagram in the image shows the preparation process. The flexible quantum dot composite material in this example was prepared using the following method, with the specific steps as follows:

[0082] (1) Preparation of SiO2 aerogel

[0083] Blank SiO2 aerogels (AGs) were prepared via a hydrolysis-condensation reaction using tetraethoxysilane (TEOS) as the silicon source. The specific steps are as follows:

[0084] First, 22.4 mL of TEOS, 14.2 mL of ethanol, and 1.8 mL of deionized water were mixed in a beaker and stirred vigorously for 20 minutes to obtain a homogeneous solution. Since hydrolysis is favored under acidic conditions, the pH of the solution was adjusted to 2–3 using hydrochloric acid, and the mixture was stirred continuously at 40°C for 2 hours. Under the catalysis of hydrochloric acid, TEOS reacted with water, and the alkoxy groups (-OR) in the reactants were replaced by hydroxyl groups (-OH), forming Si-OH groups. The reaction equation is as follows:

[0085] Si(OR)₄ + 4H₂O → Si(OH)₄ + 4ROH

[0086] The subsequent polycondensation reaction can be carried out in both acidic and alkaline environments, but the rate of polycondensation is faster under alkaline conditions. In this example, 61.8 mL of ethanol, 5.4 mL of deionized water, and 48 μL of ammonia solution were thoroughly mixed and added to the mixed solution prepared by the above hydrolysis reaction. The ammonia solution was used to adjust the pH value. After rapid stirring for 10 minutes, the Si(OH)4 groups crosslinked with each other, and polymerization occurred. The dispersed phase began to form a gel. The reaction equation is as follows:

[0087] Si(OH)₄ + (OH)Si → Si-O-Si + H₂O

[0088] When the condensation reaction reaches the polymerization point, stirring is stopped. Because the unreacted groups inside the gel continue to polymerize, the wet gel at this stage cannot be dried directly. It needs to be aged for several hours to provide conditions for further condensation reactions, thereby improving the overall mechanical strength of the aerogel. The resulting wet gel is placed in a plastic bag and aged for 24 hours. Finally, the aged wet gel is removed from the plastic bag and dried to obtain a white, blocky silica aerogel solid.

[0089] (2) Preparation of MEA-CdTe QDs quantum dot solution

[0090] 36.7 mg of CdCl2 and 68.2 mg of mercaptoethylamine hydrochloride (MEA) were weighed using an electronic balance and dissolved in 30 mL of deionized water. The pH of the mixture was adjusted to 5.6 with hydrochloric acid, and the solution was magnetically stirred for 30 minutes at room temperature to ensure thorough mixing. Next, 8.9 mg of Na2TeO3 and 11.3 mg of NaBH4 were added to the mixture, and the solution was heated to 90 °C in an oil bath using a thermostatic magnetic stirrer with continuous stirring. After reflux with continuous magnetic stirring for 9 hours, stirring was stopped, and the temperature was lowered to 25 °C. An appropriate amount of anhydrous ethanol was then added to allow for complete precipitation. The suspension was centrifuged at 10,000 rpm for 15 minutes. The resulting precipitate was washed repeatedly with ethanol and deionized water to remove excess reactants and impurities. Finally, the obtained quantum dots were dispersed in 1 mL of deionized water to obtain a MEA-CdTe quantum dot solution.

[0091] This invention utilizes sodium tellurite as the Te source and employs a hydrothermal method to prepare mercaptoethylamine-modified quantum dots, exhibiting good monodispersity and fluorescence stability. During the preparation process, the emission wavelength and fluorescence intensity of the quantum dots can be controlled by adjusting the reflux time and the Cd:Te ratio. Through multiple trials, this invention discovered that the optimal ratio for preparing MEA-CdTe quantum dots is Cd:Te = 1:0.20, the optimal reflux time is 9 hours, and the optimal fluorescence emission wavelength is 620 nm.

[0092] (3) Preparation of MEA-CdTe quantum dot-functionalized SiO2 aerogel

[0093] The prepared blank SiO2 aerogel was ground into a fine powder beforehand. 10 mg of AGs powder was weighed using an electronic balance and added to 1 mL of the previously prepared MEA-CdTe quantum dot solution. The resulting suspension was then placed in an ultrasonic machine to fully disperse the MEA-CdTe quantum dots, allowing them to be saturated and adsorbed into the porous SiO2 aerogel, thus obtaining MEA-CdTe quantum dot-functionalized SiO2 aerogel, denoted as MEA-CdTe QDs@AGs.

[0094] (4) Preparation of flexible quantum dot composite materials

[0095] First, take an appropriate amount of PDMS main agent and curing agent (mass ratio 10:1) and place them in a beaker. Stir continuously until dense and uniform bubbles are generated in the colloid, indicating that the PDMS main agent and curing agent have been mixed evenly, thus obtaining a PDMS precursor mixture. Place the PDMS precursor mixture in a vacuum drying oven and evacuate it at room temperature for 1 hour until all bubbles in the PDMS precursor mixture disappear. Then, take an appropriate amount of bubble-free PDMS precursor mixture and spin-coat it onto a quartz glass substrate with a diameter of 1 cm and a thickness of 1 mm at a speed of 500 r / s. Cure it in a constant temperature drying oven at 60℃ for 1 hour to obtain a primary flexible substrate.

[0096] Uniformly ground NaCl particles were ultrasonically dispersed into a pre-prepared PDMS precursor mixture and uniformly spin-coated onto a primary flexible substrate at 600 r / s. After thorough curing in an oven, the prepared composite film substrate was peeled off from a quartz glass slide and ultrasonically cleaned in deionized water for 30 mins to remove NaCl particles, resulting in a porous flexible PDMS substrate. Finally, 20 μL of MEA-CdTe QDs@AGs solution was added to the porous flexible PDMS substrate, and spin-coated to ensure uniform distribution of the solution on the composite film. The substrate was then placed in a vacuum drying oven and dried at 20 °C and 0.06 MPa for 6 hours to prepare the flexible quantum dot composite material in this example, denoted as: MEA-CdTe QDs@AGs / porous PDMS composite film.

[0097] The SiO2 aerogel prepared in step (1) was tested using transmission electron microscopy. The specific test results are as follows: Figure 2 As shown, where Figure 2 (A) and Figure 2 (B) Transmission electron microscopy (TEM) images of SiO2 aerogel at scale bars of 100 nm and 50 nm, respectively. Figure 2 It is known that the surface microstructure of SiO2 aerogel is a loose and porous sponge-like structure with abundant nanopores, the pore size of which is about 10-50 nm and the specific surface area is relatively large. This not only facilitates the adsorption of MEA-CdTe QDs quantum dots on SiO2 aerogel, reducing the aggregation of quantum dots and greatly enhancing the initial fluorescence intensity of the composite film, but also increases the contact area between the gas to be measured and the sensing film, thereby improving the detection sensitivity of the sensor made of this material.

[0098] The elemental composition and content of MEA-CdTe quantum dot functionalized SiO2 aerogel were analyzed using energy dispersive X-ray spectroscopy (EDS). Specific test results are as follows: Figure 3 As shown in Table 1.

[0099] Table 1. Compositional Elements of MEA-CdTe Quantum Dot Functionalized SiO2 Aerogel

[0100]

[0101] Depend on Figure 3As shown in Table 1, Cd, Te, C, O, Si, and S elements were successfully detected on the SiO2 aerogel, corresponding to the CdTe quantum dots modified with mercaptoethylamine. The S element originates from the thiol group (-SH), while the Si and O elements mainly originate from SiO2. Furthermore, because the substrate for sample placement during EDS testing was an ultrathin copper mesh, a high content of Cu element was observed in the energy dispersive spectroscopy (EDS) spectrum. These results demonstrate that MEA-CdTe quantum dot materials were successfully loaded into SiO2 aerogel. This invention attaches MEA-CdTe quantum dots to the nanopores and surface of SiO2 aerogel, effectively reducing the weakening or quenching of fluorescence emission caused by quantum dot aggregation during the drying and film formation process.

[0102] The surface morphology of the NaCl particles and MEA-CdTe QDs@AGs after grinding in step (4) was tested using scanning electron microscopy, as shown in the figure below. Figure 4 As shown, where, Figure 4 Figure (A) and Figure (B) are SEM images of NaCl particles and MEA-CdTe QDs@AGs, respectively. Figure 4 It can be seen that the NaCl particle template and the SiO2 aerogel particles are basically the same size, both distributed at around 50 μm. Then, scanning electron microscopy was used to test the surface morphology of the porous flexible PDMS substrate, and the test results are as follows: Figure 5 As shown, where, Figure 5 (A) and Figure 5 (B) SEM images of porous flexible PDMS substrates with scale bars of 100 μm and 2 μm, respectively. Figure 5 It is known that after removing the NaCl template, the pore size of the micropores on the porous flexible PDMS substrate is approximately 50–90 μm, the micropores are uniformly distributed, and the shape and size of the micropores are similar to those of the NaCl template. Therefore, the size of the micropores can be changed by altering the size of the NaCl particles, and the number density of micropores in the porous flexible PDMS substrate can also be controlled by changing the number of NaCl particles. Furthermore, the porous structure provides a rough adhesion surface for the SiO2 aerogel functionalized with MEA-CdTe QDs, which can improve the film formation effect by enhancing the surface hydrophobicity of the PDMS film.

[0103] In this invention, MEA-CdTe QDs@AGs were spin-coated onto a blank PDMS flexible substrate (without NaCl pore creation) and dried to obtain a MEA-CdTe QDs@AGs / blank PDMS composite film, denoted as QDs@AGs / blank PDMS composite film. The surface morphology of the flexible quantum dot composite material and the QDs@AGs / blank PDMS composite film in this invention was tested using scanning electron microscopy. Specific test results are as follows: Figure 6 As shown, where, Figure 6 (A) and Figure 6 (B) SEM images of flexible quantum dot composite materials with scale bars of 2 μm and 200 nm, respectively; Figure 6 (C) is a SEM image of the QDs@AGs / blank PDMS composite film. Figure 6 It is evident that the MEA-CdTe QDs@AGs / porous PDMS composite film has a loose and porous surface with a large specific surface area, which is beneficial for the effective adsorption of analyte gases, thereby improving the detection efficiency of SO2 gas. Furthermore, the MEA-CdTe QDs@AGs are tightly bonded to the porous PDMS flexible substrate, and the MEA-CdTe QDs@AGs are uniformly distributed without agglomeration or uneven dispersion, exhibiting superior film-forming properties. In addition, both the PDMS film and SiO2 aerogel material used in the preparation process have good light transmittance, which can significantly reduce the reflection of excitation light and the loss of light intensity during transmission. This is beneficial for the excitation of MEA-CdTe quantum dots in the MEA-CdTe QDs@AGs / porous PDMS composite film by the ultraviolet LED light source, effectively improving the initial fluorescence intensity and detection sensitivity of the composite film. In contrast, the QDs@AGs on the surface of the QDs@AGs / blank PDMS composite film are prone to agglomeration and uneven distribution during the drying process.

[0104] The flexible quantum dot composite material in Example 1 can be directly used as a gas detection membrane in a sulfur dioxide gas detection sensor, where SO2 gas can be adsorbed on the surface of the MEA-CdTe QDs@AGs / porous PDMS composite film.

[0105] Example 2

[0106] like Figure 7As shown, this example provides a sulfur dioxide gas detection system, including a nitrogen source, a sulfur dioxide gas source, a gas flow controller, a gas mixer, a gas detection sensor, an alkaline solution tank, and a fluorescence detection system. The fluorescence detection system includes a computer, a fluorescence spectrometer, and an optical device. The fluorescence detection system is connected to the gas detection sensor. The inlet of the gas detection sensor is connected to the gas mixer via a pipe. The gas mixer is connected to both the nitrogen source and the sulfur dioxide gas source via pipes. A gas flow controller is installed on the pipe connecting the gas mixer to the nitrogen source and the pipe connecting the gas mixer to the sulfur dioxide gas source. The outlet of the gas detection sensor is connected to the alkaline solution tank, which is filled with sodium hydroxide solution. The gas detection sensor includes a sensing chamber, a cage-type optical frame, a light-shielding cloth, a high-pass optical filter, a low-pass optical filter, and the MEA-CdTe QDs@AGs / porous PDMS composite film as described in Example 1. The MEA-CdTe QDs@AGs / porous PDMS composite film is disposed between the high-pass optical filter and the low-pass optical filter. The high-pass optical filter, the low-pass optical filter, and the MEA-CdTe QDs@AGs / porous PDMS composite film are all fixed by the cage-type optical frame. The light-shielding cloth is used to block light on the cage-type optical frame. The cage-type optical frame, the light-shielding cloth, the high-pass optical filter, the low-pass optical filter, and the MEA-CdTe QDs@AGs / porous PDMS composite film are all located in the sensing chamber.

[0107] SO2 and N2 standard gases are connected to gas flow controllers, and the SO2 concentration is adjusted by mixing SO2 and N2. SO2 gas samples of different concentrations are uniformly mixed in a gas mixer and then injected into the sensing chamber, where they immediately interact with the MEA-CdTe QDs@AGs / porous PDMS composite film at the center of the chamber. The fluorescence emitted by the composite film changes with the SO2 gas concentration. During detection, a 365nm ultraviolet LED light source is used to excite the MEA-CdTeQDs@AGs / porous PDMS composite film, with the excitation light passing through a low-pass optical filter (400nm bandpass) to eliminate ambient light interference. The fluorescence signal after the composite film contacts the SO2 gas sample is filtered through a high-pass optical filter (800nm ​​bandpass) to eliminate excitation light interference, and then transmitted via an optical fiber at the top of the chamber to a fluorescence spectrometer for analysis. Subsequent analysis and processing are performed using computer software.

[0108] The fluorescence spectra of MEA-CdTe QDs@AGs / porous PDMS composite films under different SO2 gas concentrations were detected using the above detection system. Five measurements were taken for each concentration, and the average value was calculated. Specific test results are shown below. Figure 8 As shown in (A), a linear curve was then plotted based on the SO2 gas concentration and fluorescence intensity, as detailed below. Figure 8 As shown in (B). From Figure 8 It can be seen that within the range of 0–10 ppm, the fluorescence intensity of the MEA-CdTe QDs@AGs / porous PDMS composite film increases with increasing SO2 concentration. When the SO2 concentration increases from 0 to 10 ppm, the measured peak fluorescence intensity of the MEA-CdTe QDs@AGs / porous PDMS composite film increases from 10 kJ to 16 kJ, representing a 60% increase in fluorescence intensity, while also exhibiting a good linear relationship (R0). 2 =0.9919), the linear fitting formula is:

[0109] (I-I0) / I0 = 0.05062C - 0.00761#

[0110] Where I and I0 represent the composite film at 620 nm (λ) with and without SO2, respectively. ex The fluorescence intensity at 365 nm was measured. The limit of detection (LoD) was calculated using the formula LoD = 3σ / K, where σ is the standard deviation of the blank group and K is the slope of the calibration line, yielding a detection limit of 0.12 ppm. The above experimental results demonstrate that the fluorescence intensity of the MEA-CdTeQDs@AGs / porous PDMS composite film of this invention exhibits a good linear relationship with the SO2 concentration, and can be applied to the quantitative detection of SO2 gas concentration.

[0111] The fluorescence spectra of MEA-CdTe QDs at different concentrations of sulfite ions (0 μmol / L, 1 μmol / L, 2 μmol / L, 3 μmol / L, 5 μmol / L, 7 μmol / L, 10 μmol / L, 15 μmol / L, 20 μmol / L, 25 μmol / L, 30 μmol / L, 40 μmol / L, and 50 μmol / L) were detected using the above detection system. Five measurements were taken for each concentration, and the average value was calculated. Specific test results are shown below. Figure 9 As shown in (A), a linear curve was then plotted based on the sulfite ion concentration and fluorescence intensity, as detailed below. Figure 9 As shown in (B). From Figure 9 It can be seen that MEA-CdTe QDs can selectively detect SO3. 2- (The ions formed by SO2 dissolving in water) are not affected by other common anions. When SO3 2- As the concentration increased from 0 μM to 50 μM, the fluorescence intensity of the solution increased by 50%, while exhibiting a good linear relationship (R0). 2 =0.9909), the linear fitting formula is:

[0112] (I-I0) / I0 = 0.01064C + 0.01286#

[0113] Where I and I0 represent the composite film at 620 nm (λ) with and without a solution containing sulfite ions, respectively. ex Fluorescence intensity at 365 nm.

[0114] The gas detection system of this invention is equipped with a dynamically detectable sensing chamber and a waste gas treatment device (i.e., an alkaline solution tank), enabling real-time acquisition and analysis of the fluorescence signal of the composite thin film, while also preventing SO2 leakage and environmental pollution during testing. Using a 365nm ultraviolet LED instead of a bulky laser as the excitation source improves the system's portability. Low-pass and high-pass optical filters eliminate interference from excitation light and ambient light, thereby reducing experimental errors and ensuring the accuracy and reliability of the detection results. This system provides a technical approach for in-situ detection of SO2 gas and the miniaturization and integration of sensor devices.

[0115] (1) Selectivity test

[0116] Using the gas detection system in Embodiment 2 of this invention, some interfering gases were tested under the same experimental conditions. Gases such as CO2, N2, Ar, NO2, and O2, which may be present when detecting SO2 in the atmosphere, were selected as references. Five samples were tested for each gas. Specific test results are as follows: Figure 10 As shown. By Figure 10 It can be seen that when gases such as CO2, N2, Ar, NO2, and O2 are introduced, the fluorescence intensity of the MEA-CdTe QDs@AGs / porous PDMS composite film does not change significantly compared to the initial fluorescence intensity; however, when SO2 is introduced, the fluorescence intensity of the composite film is significantly enhanced. Therefore, the MEA-CdTe QDs@AGs / porous PDMS composite film of this invention exhibits good selectivity for SO2 and is unaffected by interference from gases such as CO2, N2, Ar, NO2, and O2 during detection.

[0117] (2) Stability test

[0118] The MEA-CdTe QDs@AGs / porous PDMS composite film from Example 1 was placed at room temperature for 90 days, and the fluorescence spectrum of the composite film was measured every 5 days. The specific test results are as follows: Figure 11 As shown in (A). Figure 11It can be seen that the fluorescence intensity and wavelength of the composite film did not change significantly over 90 days, remaining in a stable state. After 90 days of storage, six samples of the MEA-CdTe QDs@AGs / porous PDMS composite film were tested with SO2 gas at a concentration of 10 ppm. The results are as follows. Figure 11 As shown in (B), when SO2 gas was introduced, the fluorescence intensity of all six composite films was significantly enhanced, and the enhancement ratio was consistent with that of the composite films. Figure 8 The test results in (A) are basically consistent. The above results indicate that after placing the MEA-CdTeQDs@AGs / porous PDMS composite film at room temperature for 90 days, the optical properties and SO2 gas sensing performance of the composite film are highly stable.

[0119] (3) Sensor performance test

[0120] Phenanthrene imidazole fluorophore, cationicratiometric sensor, CMP (conjugated microporous polymer), Probe 1 (4-hydrazino-1,8-naphthalimide fluorescent probe), and MEA-CdTe QDs@AGs / porous PDMS composite film from Example 1 were used as sensor materials for sulfur dioxide gas detection. They were installed in the gas detection system of Example 2, and the detection performance for sulfur dioxide gas was then tested. The specific test results are shown in Table 2.

[0121] Table 2. Performance Comparison of Different SO2 Fluorescence Sensors

[0122]

[0123] As shown in Table 2, compared with existing SO2 fluorescence sensors, the MEA-CdTe QDs@AGs / porous PDMS composite film of this invention has a lower detection limit, faster response time, higher stability, simpler operation, stronger anti-interference ability, and lower cost. It can be applied to SO2 detection in both solution and air. Furthermore, the composite film fluorescence sensor of this invention exhibits excellent flexibility and ductility, overcoming the limitations of rigid substrate materials in specific applications. Moreover, the composite film of this invention is loaded onto a porous flexible PDMS substrate with a diameter of only 1 cm, which facilitates the miniaturization and portability of the sensor while enabling its application in a wider range of scenarios.

[0124] (4) Initial fluorescence intensity test

[0125] In accordance with the preparation method described in Example 1, this invention prepared MEA-CdTe QDs@AGs / blank PDMS composite films (denoted as QDs@AGs / blank PDMS, wherein there is no porous structure on the blank PDMS substrate), MEA-CdTe QDs / porous PDMS composite films (denoted as QDs / porous PDMS), and MEA-CdTe QDs / blank PDMS composite films (denoted as QDs / blank PDMS). The initial fluorescence intensity of these composite films and the QDs@AGs / porous PDMS (i.e., MEA-QDs@AGs / porous PDMS) from Example 1 were then measured and compared. Specific test results are as follows: Figure 12 As shown. By Figure 12 It can be seen that, compared with the blank PDMS substrate, the addition of porous PDMS flexible substrate and SiO2 aerogel significantly enhances the initial fluorescence intensity of the composite film. The enhancement effect, from high to low, is QDs@AGs / porous PDMS > QDs@AGs / blank PDMS > QDs / porous PDMS > QDs / blank PDMS. The fluorescence intensity of the QDs@AGs / porous PDMS composite film is nearly 10 times higher than that of the QDs / blank PDMS composite film. Then, the fluorescence emission images of the above different composite films were excited under ultraviolet light, and the specific test results are as follows... Figure 13 As shown, where Figure 13 In the diagram, A, B, C, and D are the fluorescence emission spectra of QDs / blank PDMS, QDs / porous PDMS, QDs@AGs / blank PDMS, and QDs@AGs / porous PDMS, respectively. Figure 13 The test results show that the QDs@AGs / porous PDMS film exhibits more uniform luminescence and no edge aggregation compared to films based on other substrates, and the enhanced fluorescence emission can be observed visually. Furthermore, since both the PDMS substrate and the SiO2 aerogel possess excellent light and gas transmittance, they not only reduce the loss of excitation light and fluorescence but also increase the contact area between the analyte gas and the composite film, thereby improving detection sensitivity.

[0126] The reason why the MEA-CdTe QDs@AGs / porous PDMS composite film in this invention has sensing performance for SO2 and its derivatives is that SO2 can selectively enhance the fluorescence intensity of MEA-CdTe QDs. In the SO2 sensing test experiment, ultraviolet LED light source was mainly used as the excitation light for the quantum dots. To further explore the sensing mechanism of MEA-CdTe QDs for SO2, this invention measured the ultraviolet-visible absorption spectra of MEA-CdTe QDs before and after the reaction. The spectral data were collected using a TU-1810 ultraviolet-visible spectrophotometer. The specific test results are as follows: Figure 14 As shown. By Figure 14 It can be seen that after sufficient reaction with SO2, the absorption of MEA-CdTe QDs in the 200–400 nm ultraviolet band is significantly enhanced compared to before the reaction, meaning that SO2 can enhance the absorption of MEA-CdTe QDs in the ultraviolet band, thus enhancing the fluorescence emission of the quantum dots. After the quantum dots are excited by ultraviolet light, electrons in the ground state or low energy level absorb the excitation light energy and transition to the excited state, and then transition back from the excited state to the ground state, producing fluorescence. After excitation stops, the time required for the fluorescence intensity of the quantum dots to decrease to 1 / e of the maximum fluorescence intensity is the fluorescence lifetime of the quantum dots. The change in fluorescence intensity over time is as follows:

[0127] I t =I0exp(-t / τ)

[0128] Among them I t Let It represent the fluorescence intensity emitted by the quantum dot at time t, I0 be the initial fluorescence intensity of the quantum dot, and τ be the fluorescence lifetime. Fluorescence lifetime is a fundamental characteristic of quantum dots. This invention measures the fluorescence lifetime of the MEA-CdTe QDs@AGs / porous PDMS composite film before and after the reaction to further explore its SO2 sensing mechanism. The fluorescence decay characteristics of the MEA-CdTe QDs@AGs / porous PDMS composite film are as follows: Figure 15 As shown, the fluorescence lifetime of the composite film measured in this experiment can be fitted using a double exponential function, as shown in the following equation:

[0129]

[0130] In the formula, A1 and A2 are undetermined coefficients. Short lifetime τ1 refers to the characteristic time for an electron to directly transition from the excited state back to the ground state, while long lifetime τ2 refers to the characteristic time for an electron to indirectly transition from the excited state back to the ground state via an intermediate state. Figure 15 It can be observed that before the reaction, the short fluorescence lifetime of the MEA-CdTe QDs@AGs / porous PDMS composite film is 1.27 ns and the long fluorescence lifetime is 8.48 ns; after the composite film reacts with SO2 gas, the short fluorescence lifetime decreases to 0.92 ns and the long fluorescence lifetime increases to 9.10 ns.

[0131] In summary, in this invention, on the one hand, SO2 can enhance the fluorescence emission of MEA-CdTe quantum dots by increasing their absorption in the ultraviolet band. On the other hand, the photoluminescence of quantum dots is caused by the combined radiation of electrons and holes (excitons) during photoexcitation. Due to surface effects, the atoms on the surface of quantum dots are highly active, but this also leads to an increase in surface defects, causing charge carriers to recombine non-radiatively, resulting in a significant decrease in the luminescence efficiency of the quantum dots. Mercaptoethylamine is a common thiol reagent with an amino group at its terminal. In the synthesis process, using mercaptoethylamine as a stabilizer to prepare MEA-CdTe quantum dots allows for amino modification. The amino groups on the surface of MEA-CdTe quantum dots carry a positive charge in solution and can form a stable 1:1 charge transfer complex with SO2. This complex modifies the surface of MEA-CdTe quantum dots, thereby passivating surface defects, reducing the channels for nonradiative transitions in MEA-CdTe quantum dots, increasing the combined radiation of electrons and holes (excitons) within the quantum dots, and thus improving the quantum yield of the quantum dots, resulting in enhanced fluorescence and achieving the purpose of detecting sulfur dioxide.

[0132] The MEA-CdTe QDs@AGs / porous PDMS composite film of this invention is based on the selective detection of SO2 using mercaptoethylamine-modified quantum dots. Combined with a porous PDMS flexible substrate and SiO2 aerogel, it possesses characteristics such as flexibility, stretchability, and compressibility, overcoming the limitations of traditional sensors based on rigid substrates in specific application scenarios. First, a blank SiO2 aerogel was prepared using TEOS as a silicon source via a hydrolysis-condensation reaction, exhibiting high porosity, large specific surface area, good light transmittance, and good heat resistance. Then, using relatively uniform sodium chloride particles as a template, a porous PDMS flexible substrate was prepared via a NaCl removal template method. Combined with MEA-CdTe quantum dot-functionalized SiO2 aerogel, the MEA-CdTe QDs@AGs / porous PDMS composite film was prepared, and its detection capability for SO2 in the air was tested. The study shows that within the range of 0–10 ppm, the fluorescence intensity of the composite film increases with increasing SO2 concentration. When the SO2 gas concentration gradient increased from 0 ppm to 10 ppm, the fluorescence peak intensity of the MEA-CdTe QDs@AGs / porous PDMS composite film increased from 10 kJ to 16 kJ, representing a 60% increase in fluorescence intensity, while exhibiting a good linear relationship. Furthermore, the MEA-CdTe QDs@AGs / porous PDMS composite film possesses advantages such as good selectivity and high stability, simple fabrication, and low cost.

[0133] This invention introduces a porous PDMS flexible substrate and SiO2 aerogel, providing a rough surface and a larger adhesion area for quantum dots. This effectively reduces quantum dot aggregation, maintains stable optical properties and sensing performance, and improves film formation, resulting in a nearly 10-fold increase in the initial fluorescence intensity of the MEA-CdTe QDs@AGs / porous PDMS composite film. To better test the sensing performance of the MEA-CdTe QDs@AGs / porous PDMS composite film, this invention constructs a portable gas sensing and analysis system. This system is a fluorescence sensing system based on a fluorescence spectrometer, combined with optical devices and a gas path system. It can be used for experimental testing and data analysis and acquisition, and can accurately detect the concentration of SO2 gas in the atmosphere in real time.

[0134] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A flexible quantum dot composite material, characterized in that: The invention comprises a flexible substrate, a polymer substrate, and quantum dot-loaded aerogel particles; the flexible substrate has a polymer substrate disposed thereon; the polymer substrate has micropores; and the quantum dot-loaded aerogel particles are disposed within the polymer substrate. The quantum dots are CdTe quantum dots modified with mercaptoethylamine groups; The aerogel is selected from silica aerogel, carbide aerogel or graphene aerogel; The materials of the flexible substrate and the polymer substrate are each independently selected from at least one of polydimethylsiloxane, polyvinyl alcohol, polyester, polyimide, and polyethylene naphthalate.

2. The flexible quantum dot composite material according to claim 1, characterized in that: The diameter of the micropores is 50–90 μm; And / or, the diameter of the quantum dot-loaded aerogel particles is 50–90 μm.

3. The method for preparing the flexible quantum dot composite material according to any one of claims 1 to 2, characterized in that: Includes the following steps: S1: Mix aerogel with quantum dot solution to obtain quantum dot-loaded aerogel particles; S2: A flexible substrate and a polymer substrate are formed sequentially on a substrate, the substrate is removed, and then aerogel particles loaded with quantum dots are dispersed in the polymer substrate to obtain the flexible quantum dot composite material.

4. The method for preparing flexible quantum dot composite materials according to claim 3, characterized in that: The quantum dot solution is prepared by mixing and reacting a cadmium source, mercaptoethylamine or its hydrochloride, a tellurium source, and an alkali metal borohydride at 85–95°C for 8–10 h.

5. A sensor, characterized in that: The sensor comprises the flexible quantum dot composite material according to any one of claims 1 to 2; the sensor is used to detect sulfite ions in sulfur dioxide gas or water.

6. A sulfur dioxide gas detection system, characterized in that: It includes a gas supply system, a sensing device, a waste collection device, and a fluorescence detection system; the sensing device is connected to the gas supply system and the waste collection device respectively through pipelines; the sensing device is connected to the fluorescence detection system; the sensing device includes the sensor as described in claim 5.

7. The sulfur dioxide gas detection system according to claim 6, characterized in that: The sensing device further includes a detection chamber, a mounting frame, an optical filter A, and an optical filter B; the detection chamber is equipped with the mounting frame; the mounting frame is equipped with the optical filter A, a sensor, and the optical filter B; the sensor is located between the optical filter A and the optical filter B.

8. The application of the flexible quantum dot composite material according to any one of claims 1 to 2 in gas detection or liquid detection.

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