CN109100397B - Flexible planar ammonia gas sensor based on nano sensitive material and application thereof - Google Patents

Abstract

A flexible planar ammonia gas sensor based on PANI@WO ₃ hollow sphere nano-sensitive material and its application in detecting ammonia gas at room temperature in an atmospheric environment belong to the technical field of gas sensors. The sensor is composed of a flexible PET substrate and PANI@WO ₃ hollow sphere nano-sensitive materials grown on the surface of the PET substrate in situ. In addition to high sensitivity, the sensor developed in the present invention also has a low detection limit, can detect NH ₃ as low as 500 ppb, the sensitivity to 100 ppm NH ₃ can reach 25.02, and exhibits very good selectivity. The flexible and bendable planar structure sensor of the invention has the advantages of simple manufacturing process, small volume, safety and harmlessness, and has important application value.

Description

A flexible planar ammonia gas sensor based on nano-sensitive materials and its application

technical field

The invention belongs to the technical field of gas sensors, and in particular relates to a flexible planar ammonia sensor based on PANI@WO ₃ hollow sphere nano-sensitive materials and its application in detecting ammonia at room temperature in an atmospheric environment.

Background technique

Ammonia (NH ₃ ) is a colorless but pungent odor gas that is highly corrosive to eyes and respiratory organs. According to the national standard "Occupational Exposure Limits for Hazardous Factors in the Workplace GBZ2-2002", the maximum allowable concentration of NH ₃ in the workshop is 40ppm. Therefore, it is of great practical significance to develop a low-cost _NH3 gas sensor with high sensitivity, low detection limit, detectable at room temperature and low price.

In fact, in the past few years, research around NH ₃ sensors has been deepening, and various types of NH ₃ sensors have been developed, such as traditional oxide semiconductor gas sensors (SnO ₂ , In ₂ O ₃ , Fe ₂ O ₃ , WO ₃ , etc.) and mixed-potential gas sensors (zirconia and Ni ₃ V ₂ O ₈ , TiO ₂ @WO ₃ ). However, the biggest disadvantage of these materials is that the fabricated sensors usually respond to ammonia gas at very high temperatures, which greatly increases energy consumption and limits the practical application of the developed materials. NH sensors based _on organic conductive polymers and semiconductor oxide composite materials not only retain the advantages of high sensitivity of semiconductor oxides, but also have the characteristics of low detection temperature and good selectivity of conductive polymers, so they are of great interest. As a typical n-type semiconductor oxide, WO ₃ has the characteristics of relatively low resistance, easy synthesis, low cost and environmental protection, and is widely used in gas sensor materials. Conductive polyaniline (PANI) has attracted extensive attention due to its high conductivity, easy synthesis, low cost, and good environmental stability, and is considered as the best candidate material for flexible gas sensors. PANI is a special p-type sensitive material that conducts through hydrogen ions. By contacting with _NH3 , the free hydrogen ions are reduced and the resistance is increased, and the change of gas concentration is converted into a detectable electrical signal. And the formation of pn heterojunction greatly improves the sensitivity of the material. Based on this, the design and fabrication of organic _- inorganic composite NH sensors are of great scientific significance for expanding the application of gas sensors. The present invention uses the WO ₃ hollow sphere and the polyaniline composite material as the nano-sensitive material to develop a flexible sensor, which can show high sensitivity to NH ₃ at room temperature.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a flexible planar NH ₃ sensor based on the PANI@WO ₃ hollow sphere nano-sensitive material, a preparation method and its application in detecting NH ₃ at room temperature in an atmospheric environment. The invention improves the sensitivity of the sensor, improves the response recovery rate of the sensor by preparing the WO ₃ hollow sphere nano-sensitive material and in-situ polymerization with the organic polymer PANI, so that the sensor can be detected at room temperature, and promotes the sensor in the field of gas sensing detection. utilisation.

The sensor developed by the invention has higher sensitivity, the sensitivity to 100ppm NH ₃ can reach 25.02, and also has a lower detection limit, which can detect NH ₃ as low as 500ppb, and exhibits very good selectivity and repeatability. The flexible and bendable planar structure sensor of the invention has the advantages of simple manufacturing process, small volume, safety and harmlessness, and has important application value.

The NH ₃ gas sensor based on the PANI@WO ₃ hollow sphere nano-sensitive material described in the present invention is a planar structure, and consists of a flexible PET substrate and a PANI@WO ₃ hollow core grown on the upper surface of the flexible PET substrate in situ. The ball is composed of nano-sensitive materials, and PET is polyethylene terephthalate; and the sensor is prepared by the following steps:

(1) Dissolve 0.5-2 g sodium tungstate and 0.5-2 g citric acid in a mixed solution of 11-50 mL deionized water and glycerol, wherein the amounts of deionized water and glycerin are 10-30 mL and 1-20 mL, respectively, and stir uniform;

(2) 1～5mL, 1～5M hydrochloric acid was added to the above solution, and stirred for 10～30min;

(3) transferring the solution obtained in step (2) into a hydrothermal reaction kettle, and performing a hydrothermal reaction at 100～200° C. for 20～30h;

(4) cooling the product obtained in step (3) to room temperature, then alternately performing centrifugal washing with water and ethanol, and drying the obtained centrifugal product at 50 to 100° C.;

(5) drying the centrifuged product in step (4) and calcining at 400-600° C. for 1-5 h to obtain WO ₃ hollow sphere nano-sensitive material;

(6) Dissolving 1-120 mg of the WO ₃ hollow spherical nano-sensitive material and 0.1-0.5 mmol of aniline obtained in step (5) in 10-30 mL of 1-3 M hydrochloric acid, and ultrasonicating for 20-40 min;

(7) Dissolve 0.1-0.5 mmol of ammonium persulfate in 10-30 mL of 1-3 M hydrochloric acid, and stir in an ice-water bath for 20-60 min;

(8) mixing the two solutions obtained in step (6) and step (7), then placing it into a flexible PET substrate, and reacting in an ice-water mixed bath for 1-3 hours;

(9) taking out the flexible PET substrate obtained in step (8) and drying at room temperature, thereby preparing a PANI@WO ₃ hollow sphere nano-sensitive material film on the upper surface of the flexible PET substrate;

(10) The device obtained in step (9) is placed at room temperature for 1-2 days, thereby obtaining an NH ₃ sensor based on the PANI@WO ₃ hollow sphere nano-sensitive material.

In the gas sensor of the present invention, the flexible PET substrate is prepared by the following steps:

(1) Cut flexible PET with a thickness of 100 to 200 μm into a flexible PET substrate with a length of 5 to 15 mm and a width of 5 to 10 mm;

(2) The above flexible PET substrate was placed in a 10-30 g/L NaOH aqueous solution, stirred at 50-80° C. for 60-100 min, washed with deionized water and ethanol in sequence, and dried to obtain a flexible PET substrate.

working principle:

As a commonly used conductive polymer, polyaniline itself has conductivity. When the flexible NH ₃ sensor based on the PANI@WO ₃ hollow sphere nano-sensitive material is connected to the Rigol signal tester, its resistance can be detected. When the NH sensor based _on the PANI@WO hollow sphere nano _- sensitive material was placed in air, a large amount _of free hydrogen ions existed in the acidified polyaniline, while the hetero pn junction between PANI and WO formed a narrow depletion layer, the resistance is very low at this time. When the sensor is exposed to _NH3 at room temperature, _NH3 abstracts the free hydrogen ions in the polyaniline, making the polyaniline change from a conductive imide salt to an intrinsic imine base, and at the same time, the depletion layer is significantly widened, resulting in a resistance Increase. The sensitivity of the sensor is defined here as S: S=R _g /R _a , where R _a is the resistance of the sensor in the air, and R _g is the resistance of the sensor after the sensor is in contact with NH ₃ .

The NH ₃ sensor based on the PANI@WO ₃ hollow sphere prepared by the present invention has the following advantages:

1. By in-situ polymerization of PANI@WO hollow sphere nano _- sensitive materials onto flexible PET substrates, the method is simple, greatly improves the sensitivity to _NH3 , has a fast response recovery speed, and can be detected at room temperature NH ₃ , which has broad application prospects in detecting content;

2. The developed sensor has good stability and reliability, and the detection limit of the sensor can reach 500ppb;

3. The PANI@WO ₃ hollow sphere NH ₃ sensor prepared by the present invention has a simple preparation process, and uses a PET substrate with low cost. It has good application prospects in environmental monitoring.

Description of drawings

Figure 1: Schematic diagram of the planar structure of the NH ₃ sensor based on the PANI@WO ₃ hollow sphere nano-sensitive material prepared by the present invention (left of the figure), and the morphology of the nano-sensitive material based on the PANI@WO ₃ hollow sphere prepared by the present invention (right of the figure) , where the inset on the right shows the morphology of a single PANI@WO ₃ hollow sphere;

Figure 2: FESEM image (a) of the PANI of the present invention, FESEM image of the WO ₃ hollow spheres of the present invention, wherein the inset is the FESEM image of a single WO ₃ hollow sphere (b), the PAWHs of the present invention are 10 nanometer sensitive FESEM image of the material, wherein the inset is the FESEM image of a single PAWHs10 nano-sensitive material (c), the TEM image of the PAWHs10 nano-sensitive material of the present invention, wherein the inset is a partially enlarged TEM image of the PAWHs10 nano-sensitive material (d), the present invention HRTEM image (e) of the PAWHs10 nano-sensitive material, and EDS image (f) of W, N and O of the PAWHs10 nano-sensitive material of the present invention.

Figure 3: Sensitivity response graph of Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3, Example 4 and Example 5 to 10 ppm NH ₃ gas.

Figure 4: Sensitivity change curve (a) of Comparative Example 1, Comparative Example 2 and Example ₃ at room temperature in an atmosphere of 0.5-100 ppm NH ₃ Fitted graph (b) of sensitivity change in atmosphere.

Fig. 5: Comparison diagram (a) of the response values of Comparative Example 2 and Example 3 to 10 ppm of 8 different gases at room temperature, and the response recovery time curve and repeatability curve of Example ₃ to 10 ppm NH at room temperature ( Inset in panel b) panel (b).

As shown in Figure 1, the names of the components are: PET substrate 1, PANI@WO ₃ hollow ball sensitive electrode material 2.

As shown in Figure 2(a), the prepared PANI is in the form of uniform one-dimensional nanofibers. It can be seen from the partial enlarged view of the PANI nanofibers that the diameter of the PANI is about 30-40 nm, and a network structure is formed between the fibers. As shown in Figure 2(b), the prepared WO ₃ is in the shape of a hollow sphere, and it can be seen from the partial enlarged view of the WO ₃ hollow sphere that the diameter of the WO ₃ hollow sphere is 1.2um. Figure 2(c) FESEM image of PAWHs10 nano-sensitive material, it can be seen that the prepared PAWHs10 is polyaniline-coated and grown on the surface of WO ₃ hollow spheres. Figure 2(d) and Figure 2(e) are the TEM and HRTEM images of the PAWHs10 nano-sensitive material. It can be seen from the figures that the thickness of the outer shell of the WO ₃ hollow sphere is about 300 nm, and the thickness of the PANI wrapped on the surface of the WO ₃ hollow sphere is 15.7 nm. nm. Figure 2(f) is the EDS image of the PAWHs10 nano-sensitive material. It can be seen from the figure that WO ₃ is a hollow structure, and N element is distributed on the surface of WO ₃ .

It can be seen from Figure _{3 that with the increase of the amount of nano-sensitive material added in the WO hollow spheres, the sensitivity of the sensor to NH 3 first increases and} then decreases. The sensitivity can reach 6.25.

Figure 4(a) shows the response curves of Comparative Example 1, Comparative Example 2 and Example 3 to gases with different concentrations of NH ₃ (0.5-100 ppm) at room temperature. Sensitivity test method: first put the sensor into the gas bottle, measure the resistance at this time through the meter connected to the sensor, and obtain the resistance value of the sensor in the air, namely _Ra ; then use a syringe to inject 0.5-100ppm NH into the gas bottle _3. The resistance value of the sensor in different concentrations of NH ₃ , namely R _g , is obtained by measurement. According to the definition formula of sensitivity S, S=R _g /R _a , the sensitivity of the sensor under different concentrations is obtained by calculation, and finally the NH ₃ concentration-sensitivity is obtained. standard working curve. It can be seen from the figure that the sensitivity of the sensor increases with the increase of NH ₃ concentration. Figure 4(b) shows that the response fitting curves of Comparative Example 2 and Example 3 to different NH ₃ gases fit an exponential model.

FIG. 5( a ) is a comparison diagram of the response values of Comparative Example 2 and Example 3 to 10 ppm of 8 different gases at room temperature. It can be seen from the figure that Example 3 has better selectivity to NH ₃ . Figure 5(b) shows the response recovery time curve and repeatability curve of Example 3 to 10 ppm NH ₃ at room temperature. It can be seen from the figure that Example ₃ has a faster response recovery rate to 10ppm NH3, with a response time of 136s and a recovery time of 130s; it can be seen from the repeatability curve of the inset that Example 3 has a faster response to 10ppm NH3 at room temperature The sensitivity of _NH3 is relatively stable in value, demonstrating that Example 3 achieves acceptable repeatability.

Detailed ways

Comparative Example 1:

The WO ₃ hollow sphere nano-sensitive material is prepared by hydrothermal method, and the WO ₃ hollow sphere nano-sensitive material is made into a planar NH ₃ sensor. The specific manufacturing process is as follows:

1. Preparation of PET substrate: cut PET with a thickness of 125 μm into a rectangular substrate with a length of 10 mm and a width of 8 mm, and then place the PET substrate in a 20 g/L NaOH solution and stir at 60 ° C for 90 min, and then use deionized Wash with water and ethanol successively and then dry.

2. Preparation of WO ₃ hollow sphere nano-sensitive material: Dissolve 1 g of sodium tungstate and 1.2 g of citric acid in a mixed solution of 25 mL of deionized water and 10 mL of glycerol, and stir well; then add 3 mL of 4M hydrochloric acid, and stir for 20 min. The solution was put into a 50 mL hydrothermal reaction kettle, and then put into an oven, and the oven parameters were set to 180 ° C for 24 h; after the reaction, the obtained product was cooled to room temperature, and then centrifuged and washed alternately with water and ethanol. The obtained product was dried at 80 °C; the dried product was sintered in a muffle furnace at 500 °C for 3 hours, and the heating rate was 2 °C/min to obtain a WO ₃ hollow sphere nano-sensitive material;

3. Preparation of planar NH ₃ sensor based on WO ₃ hollow sphere sensitive material: coating WO ₃ on the surface of PET substrate using spin coating method (WO ₃ powder was ultrasonically dispersed into ethanol solution), and dried at room temperature; finally, the above-mentioned The device was left at room temperature for 24h, resulting in a planar _NH3 sensor based on WO3 hollow sphere nano _- sensitive material.

Comparative Example 2:

The PANI nano-sensitive material was prepared by in-situ oxidative polymerization, and the planar NH ₃ sensor was fabricated by using PANI as the nano-sensitive material. The specific fabrication process was as follows:

1. Preparation of PET substrate: the same as that of Comparative Example 1.

2. Preparation of planar NH ₃ sensor based on PANI sensitive material: 0.2 mmol aniline was dissolved in 15 mL, 1 M hydrochloric acid, and sonicated for 30 min; 0.2 mmol ammonium persulfate was dissolved in 15 mL, 1 M hydrochloric acid, and stirred in an ice-water bath for 30 min; The two solutions were mixed, a piece of PET substrate was added, and the reaction was carried out in an ice-water mixed bath for 2 hours; after the reaction, the PET with in-situ growth of PANI was taken out and dried at room temperature; the above device was placed at room temperature for 24 hours to obtain a PANI-based Planar _NH3 sensor for sensitive materials.

Example 1:

The WO ₃ hollow sphere nano _- sensitive material was prepared by hydrothermal method, and the planar NH ₃ sensor was fabricated with the PANI@WO ₃ hollow sphere nano _- sensitive material. The production process:

Dissolve 2.32 mg of WO ₃ hollow sphere nano-sensitive material and 0.2 mmol of aniline in 15 mL of 1 M hydrochloric acid, and sonicate for 30 min; the rest of the device fabrication process is the same as in Comparative Example 2, and the obtained NH ₃ sensor is labeled as sensor PAWHs2.

Example 2:

A WO ₃ hollow sphere nano _- sensitive material was prepared by a hydrothermal method, and a planar NH ₃ sensor was fabricated with the PANI@WO ₃ hollow sphere nano _- sensitive material. The production process:

5.8 mg of WO ₃ hollow spherical nano-sensitive material and 0.2 mmol of aniline were dissolved in 15 mL of 1 M hydrochloric acid, and ultrasonicated for 30 min; the rest of the device fabrication process was the same as that of Comparative Example 2, and the obtained NH ₃ sensor was labeled as sensor PAWHs5.

Example 3:

The WO ₃ hollow sphere nano _- sensitive material was prepared by hydrothermal method, and the planar NH ₃ sensor was fabricated with the PANI@WO ₃ hollow sphere nano _- sensitive material. The production process:

11.6 mg of WO ₃ hollow sphere nano-sensitive material and 0.2 mmol of aniline were dissolved in 15 mL of 1 M hydrochloric acid, and sonicated for 30 min; the rest of the device fabrication process was the same as in Comparative Example 2, and the obtained NH ₃ sensor was labeled as sensor PAWHs10.

Example 4:

A WO ₃ hollow sphere nano _- sensitive material was prepared by a hydrothermal method, and a planar NH ₃ sensor was fabricated with the PANI@WO ₃ hollow sphere nano _- sensitive material. The production process:

Dissolve 23.2 mg of WO ₃ hollow sphere nano-sensitive material and 0.2 mmol of aniline in 15 mL of 1 M hydrochloric acid, and sonicate for 30 min; the rest of the device fabrication process is the same as in Comparative Example 2, and the obtained NH ₃ sensor is labeled as sensor PAWHs20.

Example 5:

The WO ₃ hollow sphere nano _- sensitive material was prepared by hydrothermal method, and the planar NH ₃ sensor was fabricated with the PANI@WO ₃ hollow sphere nano _- sensitive material. The production process:

34.8 mg of WO ₃ hollow sphere nano-sensitive material and 0.2 mmol of aniline were dissolved in 15 mL of 1 M hydrochloric acid, and sonicated for 30 min; the rest of the device fabrication process was the same as in Comparative Example 2, and the obtained NH ₃ sensor was labeled as sensor PAWHs30.

Connect the planar sensor to the Rigol signal tester through a clip, and place the sensors prepared in Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3, Example 4, and Example 5 respectively. The resistance signal test was performed in an atmosphere of air, 10ppm _NH3 .

Table 1 lists the spheres with PANI, _{PANI@2mol.%WO3} hollow spheres, _{PANI@5mol.%WO3} hollow spheres, _{PANI@10mol.%WO3} hollow spheres, _{PANI@20mol.%WO3} hollow spheres, Sensitivity of PANI@30mol.%WO ₃ hollow spheres, flexible planar sensors made _of WO ₃ hollow spheres as sensitive materials in 10ppm NH ₃ . It can be seen from Table 1 that the response characteristics of the device to NH ₃ show a trend of increasing first and then decreasing, in which the sensitivity of pure PANI is 1.75, and the sensitivity of WO ₃ nano-sensitive material is 1 (no signal can be detected at room temperature) , compared with the device prepared by pure PANI, the sensitivity of the device prepared by PAWHs10 is increased by 4.5, reaching the maximum sensitivity, and the response value of _NH3 is the largest, showing the highest sensitivity characteristic. It can be seen that the sensitivity of the sensor can be improved by mixing appropriate amount of WO ₃ nano-sensitive materials.

Table 1 uses PANI, _{PANI@2mol.%WO3} hollow spheres, _{PANI@5mol.%WO3} hollow spheres, _{PANI@10mol.%WO3} hollow spheres, _{PANI@20mol.%WO3} hollow spheres, PANI@30mol.%WO3 hollow spheres, respectively. % WO ₃ hollow sphere, WO ₃ is the sensitivity of flexible planar PANI made of sensitive material, PAWHs2, PAWHs5, PAWHs10, PAWHs20, PAWHs30, WO ₃ Hs in 10 ppm NH ₃ in 10 ppm NH ₃ sensitivity.

Table 1 shows the sensitivity of flexible planar sensors made of PANI, PAWHs2, PAWHs5, PAWHs10, PAWHs20, PAWHs30, and WO ₃ Hs as sensitive materials in 10 ppm NH ₃ . It can be seen from Table 1 that with the increase of WO ₃ Hs addition amount, the response characteristics of the device to NH ₃ showed a trend of increasing first and then decreasing, in which the sensitivity of pure PANI was 1.75. The sensor device responses based on PAWHs are all improved compared to those fabricated from pure PANI. Among them, the device PAWHs10 achieves the maximum sensitivity, and the response value of _NH3 is the largest, showing the highest sensitivity characteristics. It can be seen that the sensitivity of the sensor can be improved by mixing appropriate amount of WO hollow sphere nano _- sensitive materials.

Claims (3)

1. A flexible planar ammonia gas sensor based on PANI@WO ₃ hollow sphere nano-sensitive materials, which is a planar structure and consists of a flexible PET substrate and PANI@WO ₃ hollow spheres grown on the upper surface of the flexible PET substrate in situ It is composed of nano-sensitive materials, PET is polyethylene terephthalate; and the sensor is prepared by the following steps: (1) Dissolve 0.5-2 g sodium tungstate and 0.5-2 g citric acid in a mixed solution of 11-50 mL deionized water and glycerol, wherein the amounts of deionized water and glycerin are 10-30 mL and 1-20 mL, respectively, and stir uniform; (2) 1～5mL, 1～5M hydrochloric acid was added to the above solution, and stirred for 10～30min; (3) transferring the solution obtained in step (2) into a hydrothermal reaction kettle, and performing a hydrothermal reaction at 100～200° C. for 20～30h; (4) cooling the product obtained in step (3) to room temperature, then alternately performing centrifugal washing with water and ethanol, and drying the obtained centrifugal product at 50 to 100° C.; (5) drying the centrifuged product in step (4) and calcining at 400-600° C. for 1-5 h to obtain WO ₃ hollow sphere nano-sensitive material; (6) Dissolving 1-120 mg of the WO ₃ hollow spherical nano-sensitive material and 0.1-0.5 mmol of aniline obtained in step (5) in 10-30 mL of 1-3 M hydrochloric acid, and ultrasonicating for 20-40 min; (7) Dissolve 0.1-0.5 mmol of ammonium persulfate in 10-30 mL of 1-3 M hydrochloric acid, and stir in an ice-water bath for 20-60 min; (8) mixing the two solutions obtained in step (6) and step (7), then placing it into a flexible PET substrate, and reacting in an ice-water mixed bath for 1-3 hours; (9) taking out the flexible PET substrate obtained in step (8) and drying at room temperature, thereby preparing a PANI@WO ₃ hollow sphere nano-sensitive material film on the upper surface of the flexible PET substrate; (10) The device obtained in step (9) is placed at room temperature for 1-2 days, thereby obtaining a flexible planar ammonia gas sensor based on the PANI@WO ₃ hollow sphere nano-sensitive material. 2. A kind of flexible planar ammonia gas sensor based on PANI@WO ₃ hollow sphere nano-sensitive material as claimed in claim 1, it is characterized in that: flexible PET substrate is prepared by following steps, (1) Cut PET with a thickness of 100 to 200 μm into a flexible PET substrate with a length of 5 to 15 mm and a width of 5 to 10 mm; (2) The above flexible PET substrate was placed in a 10-30 g/L NaOH aqueous solution, stirred at 50-80° C. for 60-100 min, washed with deionized water and ethanol in sequence, and dried to obtain a flexible PET substrate. 3. The application of the flexible planar ammonia sensor based on the PANI@WO ₃ hollow sphere nano-sensitive material according to any one of claims 1 to 2 in the detection of ammonia at room temperature in an atmospheric environment.

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