Preparation method of MXene / PANI coated SnO2 sensor and application of MXene / PANI coated SnO2 sensor in food freshness detection

Abstract

The invention discloses a preparation method of an MXene / PANI (at) SnO2 sensor and application of the MXene / PANI (at) SnO2 sensor in the aspect of food freshness detection, and relates to a preparation method of an MXene / PANI (at) SnO2 composite material and application of the MXene / PANI (at) SnO2 sensor in the aspect of food freshness detection. The objective of the invention is to solve the problems of low intelligence, lack of quantitative monitoring and the like of existing freshness indication. The experimental method comprises the following steps: etching to prepare multiple layers of MXene; polymerizing polyaniline on the surface to form an MXene / PANI composite material; and loading SnO2 nanoparticles on the surface through a hydrothermal reaction to obtain the MXene / PANI (at) SnO2 ternary composite material. An interdigital electrode is coated with an MXene / PANI (at) SnO2 ternary composite material, the MXene / PANI (at) SnO2 ternary composite material is integrated with a wireless communication module, a microprocessor and a multi-stage warning module, a portable intelligent sensing system is constructed, the food freshness is judged in real time by monitoring the concentration of ammonia gas released in the food spoilage process, and safety state visual alarm is achieved according to a preset threshold value. The method effectively solves the problems of complex process, high cost and difficulty in real-time monitoring of a traditional detection method, has high sensitivity and excellent stability to ammonia gas at room temperature, and is suitable for intelligent monitoring of food quality.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor fabrication technology, specifically relating to a method for fabricating a room temperature ammonia smart sensor based on MXene / PANI@SnO2 ternary composite material and its application. Background Technology

[0002] In recent years, with the development of the fresh food supply chain, the need for real-time, accurate, and convenient monitoring of its freshness has become increasingly urgent. Traditional freshness indication methods, such as colorimetric films or fluorescent indicators, have limitations such as high cost, difficulty in integration, non-real-time operation, and non-reusability. Intelligent gas sensor technology, especially the intelligent electronic nose system formed by combining with modified atmosphere packaging, demonstrates significant advantages such as low cost, easy integration, intelligence, real-time visualization, and reusability, providing broad application prospects for quality monitoring and shelf-life extension throughout the entire fresh food supply chain.

[0003] During the spoilage process of protein-rich fresh foods (such as meat and fish), microorganisms such as Pseudomonas decompose amino acids, producing ammonia. As a key volatile product, its concentration directly reflects the degree of protein degradation. Therefore, ammonia has been established by the National Food Safety Standard (GB 5009.228-2016) as an important basis for determining the spoilage of such foods. This standard assesses the degree of spoilage by detecting the total volatile basic nitrogen (TVB-N) value (ammonia is one of its core components). When the TVB-N value exceeds a specific limit (30 mg / 100 g), it is considered spoiled. Based on this, the development of a portable, highly sensitive ammonia sensor capable of room temperature detection is of great practical significance for achieving rapid on-site detection of food safety and protecting consumer health.

[0004] To meet the urgent need for room temperature, high-performance gas sensors, two-dimensional transition metal carbides / nitrides (MXene, general formula M...) are being developed. n+1 X n T x MXene-based ethanol sensor materials have attracted widespread attention due to their abundant surface functional groups, tunable interlayer spacing, high Fermi level, and excellent room-temperature sensing capabilities. For example, the invention patent "A Method for Preparing Room-Temperature MXene-Based Ethanol Sensor Materials Using Supercritical Carbon Dioxide" (Publication No.: CN120195236A) discloses a method for preparing MXene-based ethanol sensor materials. This method uses supercritical carbon dioxide as a medium, and the MXene / TiO2 composite material prepared with the assistance of ethanol adsorption and reaction sites achieves a specific response to ethanol. However, this sensor also suffers from key defects such as severe cross-response, low sensitivity, and poor long-term stability, which seriously restricts the improvement of its practical application performance.

[0005] To address the aforementioned problems, this invention provides a method for fabricating a room-temperature ammonia smart sensor based on an MXene / PANI@SnO2 ternary composite material and its application. The material consists of an MXene-based framework, an intermediate tin dioxide (SnO2) functional layer, and a surface-modified polyaniline (PANI) layer. This composite structure enables precise ammonia detection at the ppb level under high humidity conditions at room temperature. The p-type polyaniline facilitates the formation of a Schottky heterojunction with the high work function MXene and a PN junction with the n-type tin oxide. The synergistic effect of these three components significantly improves the ammonia adsorption capacity and reduces the adsorption of ammonia by chemically adsorbed oxygen (O2). - The reaction barrier between the gas and the ammonia gas was investigated. These effects collectively improved charge transfer efficiency and gas response performance, and a smart portable ammonia gas sensing device was also designed. This system integrates a gas sensor, a mobile terminal for data processing, and an alarm module, demonstrating its practicality in monitoring the freshness of fresh produce such as pork, fish, and shrimp. This method provides a new approach for intelligent quality supervision in the fresh food sector. Summary of the Invention

[0006] This invention provides a method for preparing MXene / PANI@SnO2 ternary composite material and its application in food freshness detection, aiming to solve the key problems of existing gas-sensitive materials having high operating temperatures and being unable to perform real-time dynamic detection.

[0007] A method for preparing an MXene / PANI@SnO2 ternary composite material, specifically comprising the following steps:

[0008] I. Preparation of Multilayer MXene: First, 1–2 g of lithium fluoride was dissolved in 40–50 mL of 8 mol / L hydrochloric acid under ice bath conditions. Then, 1–2 g of Ti3AlC2 powder was added to the solution and stirred thoroughly. Next, the mixture was transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and sealed. The reaction was carried out at 40–50 °C for 36–48 h. After the reaction, the resulting suspension was repeatedly washed with deionized water until neutral, centrifuged at 4000–5000 r / min for 8–10 min each time, repeating this washing process 5–6 times. Finally, the solid product was separated to obtain a slurry, which was then vacuum dried at 60 °C for 10–12 h to obtain multilayer MXene powder.

[0009] II. Preparation of MXene / PANI@SnO2 ternary composite material: Dissolve 0.2 mmol to 0.3 mmol of ammonium persulfate in 10 to 20 mL of 1 mol / L hydrochloric acid, prepare a certain amount of distilled aniline and add it to the above solution, add 90 to 100 mg of MXene powder obtained in step one, then perform ultrasonic treatment for 20 to 30 min and react in an ice-water bath for 1 to 2 h. Subsequently, 180–200 mg of tin tetrachloride pentahydrate and 40–50 mL of a mixed solution of ethanol and water were added and stirred until transparent. Then, a small amount of hydrochloric acid was added to adjust the pH to 4, and the mixture was sonicated for 30 min to form a uniform suspension. Under nitrogen atmosphere, the suspension was slowly added dropwise to 10–20 mL of 1 mol / L sodium hydroxide solution. After stirring for 30 min, the resulting mixture was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and reacted at 80 °C for 24–36 h. After the reaction, the mixture was cooled to room temperature, and the product was washed three times with deionized water and three times with anhydrous ethanol to remove residual alkali and impurities. Finally, it was vacuum dried at 50–60 °C for 12–18 h to obtain the MXene / PANI@SnO2 ternary composite material.

[0010] The fabrication of an MXene / PANI@SnO2 gas sensor and its application in food freshness detection are carried out according to the following steps:

[0011] I. Preparation of the Ammonia Smart Sensor: 8–10 mg of powder sample was ultrasonically dispersed in 0.5–1 mL of ethanol for 5–10 min. The solution was then pipetted onto the silver cross-shaped electrodes. The electrodes were dried in a vacuum drying oven for 12–18 h, and subsequently welded to form a gas-sensitive sensor module. The system uses an external power supply with an appropriate voltage, which is then reduced to a level suitable for microcontroller operation via a voltage regulator. The system integrates a Bluetooth communication module, using level signals to indicate the connection status. A general-purpose microcontroller is selected for sensor signal acquisition and communication transmission. Based on the correlation between total volatile basic nitrogen and ammonia concentration in relevant standards, two concentration thresholds are set to trigger multi-level alarms. The system is equipped with a three-color warning light: a green light illuminates when the gas concentration is below the first threshold, indicating a safe state; an orange light illuminates when the concentration is between the two thresholds, indicating a risk of spoilage; and a red light illuminates when the concentration exceeds the second threshold, indicating a high degree of spoilage. Simultaneously, the monitoring results are displayed in real-time on an LED display, providing a visual output of the gas concentration.

[0012] II. Method for indicating food freshness: The food to be tested is placed in the testing space, and the gas sensor periodically collects gas concentration data within a specific time period to obtain a dynamic curve of gas release. Based on the correlation model between the collected characteristic gas concentration and the spoilage judgment index, the degree of spoilage of the sample can be non-destructively and in real time.

[0013] Advantages of this invention: (1) The material preparation process is relatively simple and the preparation cycle is short, which lays the foundation for large-scale production; (2) The composite material exhibits excellent sensitivity characteristics at room temperature and can achieve high sensitivity and rapid response to low concentration ammonia, thereby ensuring the core performance of the sensing device in accurate quantification and real-time monitoring of food freshness; (3) It does not require the complex experimental environment of the national standard semi-micro nitrogen determination method, and has the characteristics of being portable, reusable and low-cost. It has a high degree of intelligence and provides a new solution suitable for industrial promotion for intelligent quality supervision of fresh products. Attached Figure Description

[0014] Figure 1 This is the XRD pattern of the MXene / PANI@SnO2 ternary composite material. Figure 1 As can be seen from Example 1, the MXene / PANI@SnO2 ternary composite material exhibits diffraction peaks with 2θ values ​​of 6.6°, 26.6°, 33.9°, and 51.8°, which correspond to the original Ti3AlC2MAX and tetragonal rutile SnO2 crystal faces. This demonstrates the successful preparation of the MXene / PANI@SnO2 ternary composite material.

[0015] Figure 2 This is a scanning electron microscope (SEM) image of the MXene / PANI@SnO2 ternary composite material. The SEM image shows that Example 1, the MXene / PANI@SnO2 ternary composite material, exhibits a typical two-dimensional layered structure with uniform single-layer thickness and obvious wrinkles on the sides. PANI forms a network structure on the MXene surface with nanofibers, and the fiber diameter is approximately 50-60 nm. SnO2 nanoparticles are uniformly distributed on the MXene surface after in-situ growth.

[0016] Figure 3 This is the dynamic response-recovery curve of ammonia in Example 1, from... Figure 3 As can be seen from the data, the MXene / PANI@SnO2 ternary composite material in Example 1 achieved a response value of 12.61 at 200 ppm. This indicates that the addition of SnO2 and PANI improved the sensitivity of MXene to ammonia, demonstrating the significant advantages of the MXene / PANI@SnO2 ternary composite material in the field of ammonia detection.

[0017] Figure 4 This is a graph from Example 1 showing the long-term stability test of 5 ppm ammonia. Figure 4It can be seen that after 60 days, the response value of MXene / PANI@SnO2 ternary composite material to 5 ppm ammonia gas decreased from the initial 1.58 to 1.25, and the performance retention rate was still about 80%. The results prove that MXene / PANI@SnO2 ternary composite material has high stability and good practical value.

[0018] Figure 5 This study illustrates the relationship between ammonia concentration and total volatile basic nitrogen (TVB-N) content during the spoilage of fresh shrimp. According to the graph, ammonia production is relatively low in the first 6 hours of spoilage, and changes in TVB-N are mainly influenced by other volatile nitrogenous substances. Between 6 and 12 hours, ammonia levels rise significantly, and changes in TVB-N show a clear correlation with ammonia release. Between 18 and 36 hours, ammonia levels increase sharply, becoming the dominant factor in changes in TVB-N. Furthermore, the data shows that when the TVB-N content is 20 mg / 100 g, the corresponding ammonia concentration is approximately 1 ppm; when the TVB-N content reaches 30 mg / 100 g, the ammonia concentration is approximately 5 ppm. Referring to the national standard GB 5009.228-2016 and related literature on the changes in total volatile basic nitrogen content during food spoilage, and the corresponding relationship with ammonia concentration in this experiment, the ammonia concentration thresholds were set to 1 ppm and 5 ppm, respectively, to trigger multi-level alarms.

[0019] Figure 6 This is an example 1, showing the freshness indication of fresh shrimp from a smart sensor prepared using the MXene / PANI@SnO2 ternary composite material. Figure 6 It can be seen that in the first 6 hours, the ammonia concentration released by the fresh shrimp was below 1 ppm, and the green light illuminated, indicating that the shrimp had good freshness and nutritional value. By 12 hours, the ammonia concentration rapidly exceeded 1 ppm, and the warning light turned yellow, indicating that the shrimp should be consumed as soon as possible to prevent spoilage. By 24 hours, the ammonia concentration exceeded 5 ppm, and the red warning light illuminated, indicating that spoilage was accelerated by microbial activity and the shrimp was no longer suitable for consumption. The results show that the smart sensor prepared from the MXene / PANI@SnO2 ternary composite material can quantitatively detect ammonia concentration, demonstrating broad prospects in the field of fresh food quality monitoring and intelligent safety supervision. Detailed Implementation

[0020] Example 1:

[0021] This embodiment describes a method for preparing an MXene / PANI@SnO2 ternary composite material, specifically carried out according to the following steps:

[0022] I. Preparation of Multilayer MXene: First, 2 g of lithium fluoride was dissolved in 40 mL of 8 mol / L hydrochloric acid under ice bath conditions. Then, 2 g of Ti3AlC2 powder was added to the solution and stirred thoroughly. Next, the mixture was transferred to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and sealed, and reacted at 40 °C for 48 h. After the reaction, the resulting suspension was repeatedly washed with deionized water until neutral, centrifuged at 5000 r / min for 10 min each time, and this washing process was repeated 5 times. Finally, the solid product was separated to obtain a slurry, which was then vacuum dried at 60 °C for 12 h to obtain multilayer MXene powder.

[0023] II. Preparation of MXene / PANI@SnO2 ternary composite material: 0.25 mmol / L ammonium persulfate was dissolved in 15 mL of 1 mol / L hydrochloric acid, and 0.5 mmol / L distilled aniline was added to the above solution. 93.1 mg of MXene powder prepared in step one was added to the solution, followed by 30 min of ultrasonic treatment and reaction in an ice-water bath for 2 h. Subsequently, 180 mg of tin tetrachloride pentahydrate was added to a mixed solution of 10 mL of ethanol and 30 mL of water and stirred until transparent. Then, a small amount of hydrochloric acid was added to adjust the pH to 4, and the mixture was sonicated for 30 min to form a uniform suspension. Under nitrogen atmosphere, the suspension was slowly added dropwise to 20 mL of 1 mol / L sodium hydroxide solution. After stirring for 30 min, the resulting mixture was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and reacted at 80 ℃ for 24 h. After the reaction, the mixture was cooled to room temperature, and the product was washed three times with deionized water and three times with anhydrous ethanol to remove residual alkali and impurities. Finally, it was vacuum dried at 60 ℃ for 12 h to obtain the MXene / PANI@SnO2 ternary composite material.

[0024] Example 2:

[0025] This embodiment describes the fabrication of an MXene / PANI@SnO2 gas sensor and its application in food freshness detection, specifically carried out according to the following steps:

[0026] I. Preparation of the Ammonia Intelligent Sensor: 10 mg of powder sample was ultrasonically dispersed in 0.5 mL of ethanol for 5 min. The solution was then pipetted onto the silver cross-shaped electrodes, which were dried in a vacuum drying oven for 12 h. The resulting gas sensor module was then welded together. The system uses a 5 V external power supply, which is reduced to 3.3 V by a voltage regulator. The system integrates a Bluetooth communication module, using level signals to indicate the connection status. A general-purpose microcontroller is used for sensor signal acquisition and communication transmission. Based on the correspondence between total volatile basic nitrogen and ammonia concentration during food spoilage as specified in GB 5009.228-2016, two concentration thresholds of 1 ppm and 5 ppm are set to trigger multi-level alarms. The system is equipped with green, orange, and red warning lights: a green light illuminates when the gas concentration is below the first threshold of 1 ppm, indicating a safe state; an orange light illuminates when the concentration is between the two thresholds of 1 and 5 ppm, indicating a risk of spoilage; and a red light illuminates when the concentration exceeds the second threshold of 5 ppm, indicating a high degree of spoilage. Simultaneously, the monitoring results are displayed in real-time on an LED display, providing a visual output of the gas concentration.

[0027] II. Method for Indicating Food Freshness: Place approximately 100 g of fresh shrimp to be tested in a 500 mL gas detection bottle, ensuring a tight seal to prevent interference from external gases. Use a gas sensor to periodically detect ammonia gas release at 6-hour intervals over 36 hours to obtain the ammonia gas release concentration. Based on... Figure 5 The correlation model between the corresponding ammonia concentration and volatile basic nitrogen was used to set freshness thresholds of 1 ppm and 5 ppm to achieve non-destructive, real-time identification of the degree of spoilage of fresh shrimp.

Claims

1. A method for preparing an MXene / PANI@SnO2 ternary composite material, specifically comprising the following steps: I. Preparation of Multilayer MXene: First, 1–2 g of lithium fluoride was dissolved in 40–50 mL of 8 mol / L hydrochloric acid under ice bath conditions. Then, 1–2 g of Ti3AlC2 powder was added to the solution and stirred thoroughly. Next, the mixture was transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene and sealed. The reaction was carried out at 40–50 °C for 36–48 h. After the reaction, the resulting suspension was repeatedly washed with deionized water until neutral, centrifuged at 4000–5000 r / min for 8–10 min each time, repeating this washing process 5–6 times. Finally, the solid product was separated to obtain a slurry, which was then vacuum dried at 60 °C for 10–12 h to obtain multilayer MXene powder. II. Preparation of MXene / PANI@SnO2 ternary composite material: Dissolve 0.2 mmol to 0.3 mmol of ammonium persulfate in 10 to 20 mL of 1 mol / L hydrochloric acid, prepare a certain amount of distilled aniline and add it to the above solution, add 90 to 100 mg of MXene powder obtained in step one, and then perform ultrasonic treatment for 20 to 30 min and react in an ice-water bath for 1 to 2 h. Subsequently, 180–200 mg of tin tetrachloride pentahydrate and 40–50 mL of a mixed solution of ethanol and water were added and stirred until transparent. Then, a small amount of hydrochloric acid was added to adjust the pH to 4, and the mixture was sonicated for 30 min to form a uniform suspension. Under nitrogen atmosphere, the suspension was slowly added dropwise to 10–20 mL of 1 mol / L sodium hydroxide solution. After stirring for 30 min, the resulting mixture was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel high-pressure reactor and reacted at 80 °C for 24–36 h. After the reaction, the mixture was cooled to room temperature, and the product was washed three times with deionized water and three times with anhydrous ethanol to remove residual alkali and impurities. Finally, it was vacuum dried at 50–60 °C for 12–18 h to obtain the MXene / PANI@SnO2 ternary composite material.

2. The fabrication of an MXene / PANI@SnO2 gas sensor and its application in food freshness detection are carried out according to the following steps: I. Preparation of the Ammonia Smart Sensor: 8–10 mg of powder sample was ultrasonically dispersed in 0.5–1 mL of ethanol for 5–10 min. The solution was then pipetted onto the silver cross-shaped electrodes. The electrodes were dried in a vacuum drying oven for 12–18 h, and subsequently welded to form a gas-sensitive sensor module. The system uses an external power supply with an appropriate voltage, which is then reduced to a level suitable for microcontroller operation via a voltage regulator. The system integrates a Bluetooth communication module, using level signals to indicate the connection status. A general-purpose microcontroller is selected for sensor signal acquisition and communication transmission. Based on the correlation between total volatile basic nitrogen and ammonia concentration in relevant standards, two concentration thresholds are set to trigger multi-level alarms. The system is equipped with a three-color warning light: a green light illuminates when the gas concentration is below the first threshold, indicating a safe state; an orange light illuminates when the concentration is between the two thresholds, indicating a risk of spoilage; and a red light illuminates when the concentration exceeds the second threshold, indicating a high degree of spoilage. Simultaneously, the monitoring results are displayed in real-time on an LED display, providing a visual output of the gas concentration. II. Method for indicating food freshness: The food to be tested is placed in the testing space, and the gas sensor periodically collects gas concentration data within a specific time period to obtain a dynamic curve of gas release. Based on the correlation model between the collected characteristic gas concentration and the spoilage judgment index, the degree of spoilage of the sample can be non-destructively and in real time.

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