A TNT gas sensor based on carbon nanotube heterostructure and a preparation method thereof

Abstract

This invention provides a TNT gas sensor based on a carbon nanotube heterostructure and its preparation method, including interdigitated electrodes and a sensitive material coated on the surface of the interdigitated electrodes. The sensitive material is composed of an aminophenyl bay-substituted perylene diimide derivative and carbon nanotubes through non-covalent interactions. The carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes. The mass ratio of the aminophenyl bay-substituted perylene diimide derivative to the carbon nanotubes is (1-10):1. The TNT gas sensor of this invention has high sensitivity and low detection limit: the strong electron-donating properties of the amino group and the strong electron-withdrawing properties of TNT produce a synergistic effect, realizing efficient charge transfer; the carbon nanotube heterostructure amplifies the change in electrical signal, enabling the sensor to still have a significant response to TNT vapor at a concentration of 7.2 ppb.

Description

Technical Field

[0001] This invention belongs to the field of carbon nanotube technology, and relates to TNT gas sensors, specifically to a TNT gas sensor based on a carbon nanotube heterostructure and its preparation method. Background Technology

[0002] Nitroaromatic compounds, such as 2,4,6-trinitrotoluene (TNT), are major components of military and civilian explosives, and their vapors pose a serious threat to public safety even at extremely low concentrations. Therefore, developing technologies for real-time, on-site detection of trace amounts of TNT gas is of great significance. Currently, TNT detection methods mainly include chromatography-mass spectrometry, fluorescence sensing, and ion mobility spectrometry. However, these methods often rely on large instruments, are complex to operate, and are costly, making them difficult to meet the needs for rapid, portable, and on-site detection.

[0003] Chemielectric resistivity (CRT) gas sensors have shown great potential due to their simple structure, low cost, ease of integration, and miniaturization. Their core lies in the sensing material; when target gas molecules adsorb onto the surface of the sensing material and interact with it, a significant change in the material's conductivity occurs. For electron-deficient nitroaromatic molecules like TNT, the ideal sensing material should possess electron-rich properties to achieve efficient sensing through charge transfer.

[0004] In the prior art, Chinese invention patent application CN108489953A discloses an in-situ modified paper-based fluorescent sensing material, but its stability and portability need improvement due to its reliance on fluorescence quenching. While Chinese invention patent CN113960120B uses a perylene diimide-carbon nanotube composite, its target molecule is methamphetamine, and its sensing mechanism and molecular design (especially the selection of functional groups) are fundamentally different from TNT detection. TNT molecules are rich in nitro groups and are strong electron acceptors, thus requiring a sensitive material to provide a strong electron donor for effective charge transfer. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a TNT gas sensor based on a carbon nanotube heterostructure and its preparation method, thereby solving the technical problem that the sensitivity and selectivity of existing TNT gas sensors need to be further improved.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A TNT gas sensor based on a carbon nanotube heterostructure includes interdigitated electrodes and a sensitive material coated on the surface of the interdigitated electrodes; the sensitive material is composed of a perylene diimide derivative substituted with aminophenyl bay region and carbon nanotubes through non-covalent interactions.

[0007] The present invention also has the following technical features: The structural formula of the aminophenyl bay-substituted perylene diimide derivative is: or ; In the formula: R is a primary amine group, a secondary amine group, or a tertiary amine group.

[0008] The carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes.

[0009] The mass ratio of the aminophenyl bay-substituted perylene diimide derivative to carbon nanotubes is (1-10):1.

[0010] The TNT gas sensor operates at room temperature, with a detection limit of no more than 10 ppb for TNT gas and a response time of less than 30 seconds.

[0011] TNT gas sensors are chemical resistance sensors; by monitoring the decrease in resistance value of the TNT gas sensor before and after contact with TNT gas, qualitative and quantitative detection of TNT gas can be achieved.

[0012] This invention also protects a method for fabricating a TNT gas sensor based on a carbon nanotube heterostructure, the method comprising the following steps: Step 1: The aminophenyl bay-substituted perylene diimide derivative and carbon nanotubes are co-dispersed in an organic solvent and ultrasonically treated to form a uniform composite suspension.

[0013] Step 2: Coat the surface of the interdigitated electrode with the composite suspension obtained in Step 1.

[0014] Step 3: Drying, forming a composite thin film of sensitive material on the surface of the interdigitated electrodes, to obtain a TNT gas sensor based on a carbon nanotube heterostructure.

[0015] In step one, the organic solvent is DMF (N,N-dimethylformamide), NMP (N-methylpyrrolidone), toluene, tetrahydrofuran, acetonitrile, acetone, chloroform, or dichloromethane.

[0016] In step one, the ultrasonic treatment time is 30 to 120 minutes.

[0017] Compared with the prior art, the present invention has the following technical effects: (I) The TNT gas sensor of the present invention has high sensitivity and low detection limit: the strong electron-donating properties of amine groups and the strong electron-withdrawing properties of TNT produce a synergistic effect, realizing efficient charge transfer; the heterojunction structure of carbon nanotubes amplifies the changes in electrical signals, so that the sensor still has a significant response to TNT vapor at a concentration of 7.2 ppb.

[0018] (II) The TNT gas sensor of the present invention has high selectivity: the specific interaction between the amine group and the TNT nitro group (such as hydrogen bonding and charge transfer) is much stronger than that with other common volatile organic compounds, so the sensor exhibits excellent selectivity for TNT.

[0019] (III) The TNT gas sensor of the present invention can respond / recover quickly: the good stacking of one-dimensional nanostructured carbon nanotubes and perylene diimide molecules forms a porous network structure, which is conducive to the rapid diffusion and desorption of TNT gas molecules.

[0020] (IV) The TNT gas sensor of the present invention can operate at room temperature: no heating device is required, which reduces power consumption and simplifies the device structure.

[0021] (V) The TNT gas sensor of the present invention has a simple manufacturing process and low cost: the sensitive material is compounded by a simple solution method, the sensor manufacturing process has strong compatibility and is suitable for large-scale production. Attached Figure Description

[0022] Figure 1(a) is the 1H NMR spectrum of the aminophenyl bay-substituted perylene diimide derivative (3-amino-phenyl-PDI) synthesized in Example 1 of the present invention.

[0023] Figure 1(b) is the 1H NMR spectrum of the aminophenyl bay-substituted perylene diimide derivative (4-amino-phenyl-PDI) synthesized in Example 1 of this invention.

[0024] Figure 2 These are scanning electron microscope images; (a) are pure CNTs, (b) are C8-PDI-CNTs, (c) are 4-PDI-CNTs, and (d) are 3-PDI-CNTs.

[0025] Figure 3 The infrared spectra of the heterostructure TNT gas sensor sensitive materials of pure CNTs, C8-PDI-CNTs, 4-PDI-CNTs, and 3-PDI-CNTs prepared in Example 2 of this invention are shown.

[0026] Figure 4 This is the real-time resistance response curve of the sensor prepared in Example 2 of the present invention to TNT vapor of different concentrations.

[0027] Figure 5 This is a bar chart showing the selective response of the sensor prepared in Embodiment 2 of the present invention to TNT and other interfering gases.

[0028] Figure 6This is the response graph of the sensor prepared by unfunctionalized perylene diimide and carbon nanotubes in the Bay Area for transmitting 2.6 ppm TNT gas, as shown in Comparative Example 1.

[0029] The specific content of the present invention will be further explained in detail below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, all raw materials and equipment used in this invention are those known in the prior art.

[0031] Perylene diimide is a class of n-type organic semiconductors with large π-conjugated planes, widely studied for its excellent photoelectric properties and modifiability. By introducing specific functional groups into its bay area, its electronic structure and intermolecular interactions can be tuned. Carbon nanotubes, on the other hand, possess extremely high specific surface area and excellent carrier mobility, making them ideal substrate materials for constructing high-performance sensors. Combining the two allows for the integration of their respective advantages, enabling the creation of high-performance sensing interfaces.

[0032] This invention designs a novel derivative by introducing an aminophenyl group into the bay region of perylene diimide. The amino group is a strong electron donor, significantly increasing the electron cloud density of perylene diimide and thus enhancing its charge transfer interaction with TNT molecules. By constructing a heterojunction with carbon nanotubes, the high conductivity of the carbon nanotubes can be utilized to achieve rapid signal transmission and amplification, thereby enabling highly sensitive, selective, and rapid detection of TNT vapor.

[0033] The synthetic route in this invention is as follows: ; .

[0034] In this invention, the structural formula of C8-PDI is: .

[0035] In this invention, 3-PDI-CNTs refers to a sensitive material formed by the non-covalent interaction of 3-amino-phenyl-PDI and a single-walled tube; 4-PDI-CNTs refers to a sensitive material formed by the non-covalent interaction of 4-amino-phenyl-PDI and a single-walled tube.

[0036] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0037] Example 1: This embodiment provides a method for synthesizing an aminophenyl bay-region substituted perylene diimide derivative, which includes the following steps: Under a nitrogen atmosphere, 4Cl-PDA and n-octylamine were dissolved in toluene solution and placed in a double-necked flask. The mixture was reacted at 110°C for 24 hours. After cooling, the solution was added dropwise to methanol solution, resulting in an orange-red precipitate. The precipitate was collected by filtration and dried. The orange-red solid product 4Cl-PDI was obtained by column chromatography (dichloromethane: petroleum ether = 1:1, volume ratio).

[0038] Under nitrogen protection, 4Cl-PDI powder was placed in a double-necked flask with 3-aminophenol or p-aminophenol and potassium carbonate, and NMP was added to dissolve it. The mixture was reacted at 120°C for 72 hours under nitrogen atmosphere. After cooling to room temperature, the solution was added dropwise to 20% hydrochloric acid solution, which produced a purple precipitate. The precipitate was filtered, washed with deionized water until the filtrate was neutral, dried, and then subjected to column chromatography (dichloromethane: petroleum ether = 2:1, volume ratio) to obtain a dark purple solid product.

[0039] The structure of the dark purple solid product was confirmed by the 1H NMR spectra shown in Figures 1(a) and 1(b) to be an aminophenyl bay-substituted perylene diimide derivative (i.e., 3-amino-phenyl-PDI and 4-amino-phenyl-PDI).

[0040] Example 2: This embodiment provides a TNT gas sensor based on a carbon nanotube heterostructure, including interdigitated electrodes and a sensitive material coated on the surface of the interdigitated electrodes; the sensitive material is composed of a perylene diimide derivative substituted with aminophenyl bay region and carbon nanotubes through non-covalent interactions.

[0041] The aminophenyl bay-substituted perylene diimide derivatives are the aminophenyl bay-substituted perylene diimide derivatives prepared in Example 1 (i.e., 3-amino-phenyl-PDI and 4-amino-phenyl-PDI, also known as aminophenyl PDI derivatives).

[0042] The carbon nanotubes are single-walled carbon nanotubes.

[0043] The mass ratio of aminophenyl bay-substituted perylene diimide derivatives to carbon nanotubes is 1:1.

[0044] This embodiment also provides a method for fabricating a TNT gas sensor based on a carbon nanotube heterostructure, which includes the following steps: Step 1: Accurately weigh 1 mg of the aminophenyl PDI derivative synthesized in Example 1 and 1 mg of single-walled carbon nanotubes, and add them together to 10 mL of DMF solvent. Sonicate the mixture in an ice-water bath for 30 minutes, avoiding overheating. A uniform and stable black suspension is obtained after treatment; this is the aminophenyl PDI / carbon nanotube composite sensitive material suspension.

[0045] Step two: Select a silica substrate with gold interdigitated electrodes. First, ultrasonically clean the interdigitated electrodes sequentially in acetone, ethanol, and deionized water for 10 minutes each, then dry them with nitrogen gas. Next, use a micropipette to take 2 μL of the composite suspension prepared in step one and evenly drop it onto the sensitive area of ​​the interdigitated electrodes.

[0046] Step 3: The electrodes are then placed at room temperature to evaporate and dry naturally for 12 hours to form a uniform sensitive film. After that, they are stored in a vacuum for 1 day to form a composite film of sensitive material on the surface of the interdigitated electrodes, thus obtaining a TNT gas sensor based on a carbon nanotube heterostructure.

[0047] Using SEM characterization, such as Figure 2 As shown, determine several heterostructures. Figure 2 Image (a) shows a pure carbon nanotube (CNT) film in which the carbon nanotubes exhibit a significant aggregated state and multiple layers of carbon nanotubes intertwined together, showing a distinct multi-porous bird's nest structure. Figure 2 Images (b) and (c) show the aggregated state of perylene diimide derivatives and carbon nanotubes. The three aggregates exhibit a clear dispersion state, consistent with... Figure 2 Compared to the heterostructure of C8-PDI-CNTs in (b), Figure 2 4-PDI-CNTs in (c) and Figure 2 In (d), the 3-PDI-CNTs film is thinner, and the dispersion of individual carbon nanotubes is higher. Both 4-PDI and 3-PDI probe molecules modified at their bay positions exhibit better dispersion of carbon nanotubes in solution, which is beneficial for forming thin-layer heterostructure films. This reduces electron scattering between carbon nanotubes, leverages the molecular trapping advantages of one-dimensional heterostructures, facilitates electron transfer between carbon nanotubes, and enhances the sensing effect.

[0048] Several heterostructures were characterized using FTIR, among which Figure 3 Infrared images show the heterostructures of sensitive materials, including pure CNTs, C8-PDI-CNTs, 3-PDI-CNTs, and 4-PDI-CNTs. Characteristic perylene diimide groups are clearly detected in the heterostructure films, with the 1260 cm⁻¹ region showing a significant difference. -1 The location is -COC- stretching vibration, 1605cm -1 and 1625cm -1 The CN bending vibration at the amine group manifests as the aggregation of perylene diimide probe molecules on carbon nanotubes, constructing a stable van der Waals heterostructure. The formation of thin films of C8-PDI-CNTs, 3-PDI-CNTs, and 4-PDI-CNTs is beneficial for leveraging the advantages of one-dimensional heterostructures, utilizing the probe molecules to adsorb amine-containing explosive gas molecules and transmit electrical signals to the heterostructure interface.

[0049] Sensor performance testing: The sensor prepared in Example 2 was placed in a commonly used dynamic gas mixing testing system in the art for performance evaluation. Using dry air as both carrier and dilution gas, TNT standard concentrations of gas were prepared at different concentrations using a gradient temperature saturated vapor method. At room temperature, the change in the sensor's resistance before and after exposure to TNT gas was recorded using a Keysight 34461A digital multimeter.

[0050] Test results show that, Figure 4 As shown, the resistance change rate of 3-PDI-CNTs over time during adsorption and desorption of TNT vapors of different concentrations indicates that the resistance of the sensor prepared in Example 2 increases after contact; and the resistance change rate gradually decreases with decreasing concentration. Thanks to its unique active sites, 3-PDI-CNTs exhibit a resistance increase rate as high as 16.4% in 2.6 ppm TNT vapor. Notably, it also demonstrates exceptional responsiveness even in 7.2 ppb TNT vapor, with a detection limit as low as 8 ppt. The sensor's response value shows a good linear relationship with TNT concentration in the range of 7.2 ppb to 2.6 ppm. The sensor prepared with pure CNTs showed no significant response to 2.6 ppm TNT vapor. Therefore, it can be concluded that the aminobenzene-substituted PDI molecules at the bay position interact non-valently with CNTs to form a heterostructure, effectively sensing TNT gas molecules.

[0051] from Figure 4 It is known that the TNT gas sensor has a detection limit of no more than 10 ppb for TNT gas and a response time of less than 30 seconds.

[0052] like Figure 5 As shown, the active sites in 3-PDI-CNTs also contribute to excellent selectivity, thanks to the complex host-guest interactions exhibited during dynamic simulation. This invention investigated the selectivity of the 3-PDI-CNTs sensor, selecting common interfering gases such as acetonitrile, ethanol, ethyl acetate, ammonia, and water vapor for comparative testing. The concentration of each gas was 3 ppm. The test results are shown below. Figure 5As shown, at the same concentration, the sensor exhibits a resistivity change rate of over 16% for TNT gas. In contrast, at the same concentration, other gases cause only extremely small resistivity changes or produce opposite resistivity signal changes, thus having no impact on sensor performance. This verifies the selectivity of the sensitive material and this unique one-dimensional van der Waals heterostructure. Therefore, the one-dimensional van der Waals structure formed by the 3-PDI-CNTs designed in this invention can effectively identify TNT and possesses excellent anti-interference capabilities against common environmental volatile gases. Similarly, the 4-PDI-CNTs designed in this invention also possess a one-dimensional van der Waals structure, can effectively identify TNT, and exhibit excellent anti-interference capabilities against common environmental volatile gases.

[0053] Comparative example: In this comparative example, a sensor (C8-PDI-CNTs) was prepared by combining unfunctionalized perylene diimide (C8-PDI) from the Bay Area with single-walled carbon nanotubes at a mass ratio of 1:1. The infrared spectrum is shown below. Figure 3 As shown. The performance test of Example 2 was repeated. The results are as follows. Figure 6 As shown, the response value of this comparative sensor to 2.6 ppm TNT is much lower than that of the sensor prepared by aminophenyl-functionalized perylene diimide and CNT in this invention, which proves the key role of the introduction of aminophenyl in improving the TNT sensing performance.

Claims

1. A TNT gas sensor based on carbon nanotube heterostructure, comprising interdigital electrodes, and a sensitive material coated on the surface of the interdigital electrodes; characterized in that, The sensitive material is composed of a perylene diimide derivative substituted with aminophenyl bay region and carbon nanotubes through non-covalent interactions.

2. The TNT gas sensor based on a carbon nanotube heterostructure as described in claim 1, characterized in that, The structural formula of the aminophenyl bay-substituted perylene diimide derivative is: or ; In the formula: R is a primary amine group, a secondary amine group, or a tertiary amine group.

3. The TNT gas sensor based on a carbon nanotube heterostructure as described in claim 1, characterized in that, The carbon nanotubes mentioned are single-walled carbon nanotubes, multi-walled carbon nanotubes, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes.

4. The TNT gas sensor based on a carbon nanotube heterostructure as described in claim 1, characterized in that, The mass ratio of the aminophenyl bay-substituted perylene diimide derivative to carbon nanotubes is (1-10):

1.

5. The TNT gas sensor based on a carbon nanotube heterostructure as described in claim 1, characterized in that, The TNT gas sensor operates at room temperature, has a detection limit of no more than 10 ppb for TNT gas, and a response time of less than 30 seconds.

6. The TNT gas sensor based on a carbon nanotube heterostructure as described in claim 1, characterized in that, The TNT gas sensor is a chemielectric resistive sensor; by monitoring the decrease in resistance value of the TNT gas sensor before and after contact with TNT gas, qualitative and quantitative detection of TNT gas can be achieved.

7. A method for fabricating a TNT gas sensor based on a carbon nanotube heterostructure as described in any one of claims 1 to 6, characterized in that, The method includes the following steps: Step 1: The aminophenyl bay-substituted perylene diimide derivative and carbon nanotubes are co-dispersed in an organic solvent and ultrasonically treated to form a uniform composite suspension. Step 2: Coat the surface of the interdigitated electrode with the composite suspension obtained in Step 1. Step 3: Drying, forming a composite thin film of sensitive material on the surface of the interdigitated electrodes, to obtain a TNT gas sensor based on a carbon nanotube heterostructure.

8. The method for fabricating a TNT gas sensor based on a carbon nanotube heterostructure as described in claim 7, characterized in that, In step one, the organic solvent is DMF, NMP, toluene, tetrahydrofuran, acetonitrile, acetone, chloroform, or dichloromethane.

9. The method for fabricating a TNT gas sensor based on a carbon nanotube heterostructure as described in claim 7, characterized in that, In step one, the ultrasonic treatment time is 30 to 120 minutes.

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