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

Abstract

Based on PANI @ WO₃A flexible planar ammonia sensor made of hollow sphere nano sensitive materials and application thereof in detecting ammonia gas at room temperature in atmospheric environment belong to the technical field of gas sensors. The sensor is formed by a flexible PET substrate and PANI @ WO which is grown on the surface of the PET substrate in situ₃The hollow sphere nano sensitive material. The sensor developed by the invention has higher sensitivity, lower detection lower limit and capability of detecting NH as low as 500ppb₃For 100ppm NH₃The sensitivity of (2) can reach 25.02 and the selectivity is very good. The flexible and bendable sensor with the planar structure has the advantages of simple manufacturing process, small volume, safety, harmlessness and important application value.

Description

Flexible planar ammonia gas sensor based on nano sensitive material and application thereof

Technical Field

The invention belongs to the technical field of gas sensors, and particularly relates to a PANI @ WO-based gas sensor₃A flexible planar ammonia sensor made of a hollow sphere nano sensitive material and application thereof in detecting ammonia at room temperature in an atmospheric environment.

Background

Ammonia gas (NH)₃) Is a colorless but pungent odor, and is strongly corrosive to the eyes and respiratory organs. According to the regulation of national standard 'workplace harmful factor occupational contact limit GBZ 2-2002', workshop NH₃Highest point of the designThe allowable concentration was 40 ppm. Therefore, NH has been developed which has high sensitivity, low detection limit, can be detected at room temperature and is inexpensive₃The gas sensor has important practical significance.

In fact, in the past years, NH has been surrounded₃The research of sensors has been deepened, and various types of NH have been developed₃Sensors, e.g. conventional oxide semiconductor gas sensors (SnO)₂、In₂O₃、Fe₂O₃、WO₃Etc.) and mixed potential type gas sensors (zirconia and Ni)₃V₂O₈、TiO₂@WO₃). However, the biggest disadvantage of these materials is that the sensors produced are generally responsive to ammonia at very high temperatures, which greatly increases the energy consumption and limits the practical applications of the materials that have been developed. NH based on organic conductive polymer and semiconductor oxide composite material₃The sensor not only retains the advantage of high sensitivity of the semiconductor oxide, but also has the characteristics of low detection temperature and good selectivity of the conductive polymer, and thus is focused on. WO₃As a typical n-type semiconductor oxide, the material has the characteristics of relatively low resistance, easiness in synthesis, low cost and environmental friendliness, and is widely used as a gas sensor material. Conductive Polyaniline (PANI) has received much attention due to its high electrical conductivity, easy synthesis, low cost and good environmental stability, and is considered to be the best candidate material for flexible gas sensors. PANI is a special p-type sensitive material that conducts by hydrogen ions, by reaction with NH₃The contact causes the free hydrogen ions to decrease and the resistance to increase, converting the change in gas concentration into a detectable electrical signal. And the formation of the p-n heterojunction greatly improves the sensitivity of the material. Based on this, organic-inorganic composite NH is developed₃The design and preparation of the sensor have very important scientific significance for expanding the application of the gas sensor. The present invention uses WO₃The flexible sensor developed by using the hollow sphere and polyaniline composite material as a nano sensitive material can be used for NH at room temperature₃And the sensitivity is higher.

Disclosure of Invention

The invention aims to provide a PANI @ WO-based food₃Flexible planar NH of hollow sphere nano sensitive material₃Sensor, preparation method and NH room temperature detection in atmospheric environment₃Application of the aspect. The invention is realized by preparing WO₃The hollow sphere nano sensitive material is polymerized with organic polymer PANI in situ, so that the sensitivity of the sensor is improved, the response recovery rate of the sensor is improved, the sensor can detect at room temperature, and the practicability of the sensor in the field of gas sensitive detection is promoted.

The sensor developed by the invention has higher sensitivity to 100ppm NH₃The sensitivity of (A) can reach 25.02, and the detection has lower limit, can detect NH as low as 500ppb₃And exhibits very good selectivity and repeatability. The flexible and bendable sensor with the planar structure has the advantages of simple manufacturing process, small volume, safety and harmlessness and important application value.

The invention relates to a product based on PANI @ WO₃NH of hollow sphere nano sensitive material₃The gas sensor is of a planar structure and is formed by a flexible PET substrate and PANI @ WO which is grown on the upper surface of the flexible PET substrate in situ₃The hollow sphere nano sensitive material is composed of PET (polyethylene terephthalate); the sensor is prepared by the following steps:

(1) dissolving 0.5-2 g of sodium tungstate and 0.5-2 g of citric acid in 11-50 mL of a mixed solution of deionized water and glycerol, wherein the amount of the deionized water and the amount of the glycerol are respectively 10-30 mL and 1-20 mL, and uniformly stirring;

(2) adding 1-5 mL of 1-5M hydrochloric acid into the solution, and stirring for 10-30 min;

(3) transferring the solution obtained in the step (2) into a hydrothermal reaction kettle, and carrying out hydrothermal reaction for 20-30 h at the temperature of 100-200 ℃;

(4) cooling the product obtained in the step (3) to room temperature, then alternately carrying out centrifugal washing by using water and ethanol, and drying the obtained centrifugal product at 50-100 ℃;

(5) drying the centrifugal product in the step (4)Then calcining the mixture for 1 to 5 hours at the temperature of between 400 and 600 ℃ to obtain WO₃Hollow sphere nano sensitive material;

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

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

(8) mixing the two solutions obtained in the steps (6) and (7), then putting the mixture into a flexible PET substrate, and reacting for 1-3 h in an ice-water mixed bath;

(9) taking out the flexible PET substrate obtained in the step (8), and drying at room temperature, thereby preparing PANI @ WO on the upper surface of the flexible PET substrate₃A hollow sphere nano sensitive material film;

(10) placing the device obtained in the step (9) at room temperature for 1-2 days to obtain the PANI @ WO-based device₃NH of hollow sphere nano sensitive material₃A sensor.

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

(1) cutting the flexible PET with the thickness of 100-200 mu m into a flexible PET substrate with the length of 5-15 mm and the width of 5-10 mm;

(2) and (3) putting the flexible PET substrate into 10-30 g/L NaOH aqueous solution, stirring for 60-100 min at 50-80 ℃, then washing with deionized water and ethanol in sequence, and drying to obtain the flexible PET substrate.

The working principle is as follows:

polyaniline, a commonly used conductive polymer, is itself conductive, and when it is based on PANI @ WO₃Flexible NH of hollow sphere nano sensitive material₃The sensor is connected to a Rigol signal tester to detect the resistance. When based on PANI @ WO₃NH of hollow sphere nano sensitive material₃When the sensor is placed in the air, a large amount of free hydrogen ions exist in the acidified polyaniline, and PANI and WO simultaneously₃The heterogeneous p-n junction between them forms a very narrow depletion layer, where the resistance is very low. When the sensor is exposed to NH at room temperature₃When is NH₃The method can deprive free hydrogen ions in the polyaniline, so that the polyaniline is changed from conductive imine salt to intrinsic imine alkali, and meanwhile, a depletion layer is obviously widened, so that the resistance is increased. The sensitivity of the sensor is defined herein as S: r ═ S_g/R_aWherein R is_aIs the resistance of the sensor in air, R_gFor contacting the sensor with NH₃The latter resistance.

Prepared by the invention based on PANI @ WO₃NH of hollow sphere₃The sensor has the following advantages:

1. by mixing PANI @ WO₃The hollow sphere nano sensitive material is polymerized on the flexible PET substrate in situ, the method is simple, and the NH content is greatly improved₃Has a rapid response recovery speed, and can detect NH at room temperature₃The method has wide application prospect in the aspect of content detection;

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

3. PANI @ WO prepared by the invention₃Hollow ball NH₃The sensor has simple preparation process, the used PET substrate and low cost. Has good application prospect in the aspect of environmental monitoring.

Drawings

FIG. 1: prepared by the invention based on PANI @ WO₃NH of hollow sphere nano sensitive material₃Schematic plane structure of sensor (left figure), prepared by the invention based on PANI @ WO₃The shape of the hollow sphere nano sensitive material (right picture), wherein the middle picture in the right picture shows a single PANI @ WO₃The shape of the hollow sphere;

FIG. 2: FESEM image (a) of PANI according to the present invention, WO according to the present invention₃FESEM image of hollow sphere, wherein the inset is single WO₃FESEM image of hollow ball (b), FESEM image of PAWHs10 nano-sensitive material of the invention, wherein the inset is FESEM image of single PAWHs10 nano-sensitive material (c), TEM image of PAWHs10 nano-sensitive material of the invention, wherein the inset is local magnified TEM image of PAWHs10 nano-sensitive material (d), HRTEM image of PAWHs10 nano-sensitive material of the invention (e), PAWHs10 nano-sensitive material of the invention (d)EDS plot (f) of W, N, O for rice sensitive material.

FIG. 3: comparative example 1, comparative example 2, example 1, example 2, example 3, example 4 and example 5 to 10ppm NH₃Sensitivity response plot of gas.

FIG. 4: comparative examples 1, 2 and 3 at room temperature at 0.5 to 100ppm NH₃Graph (a) of sensitivity change in atmosphere, comparative example 2 and example 3 at room temperature, 0.5-100 ppm NH₃Fitted graph (b) of sensitivity change in atmosphere.

FIG. 5: comparative example 2 and example 3 response to 10ppm of 8 different gases at room temperature (a), example 3 at room temperature to 10ppm NH₃Graph (b) shows the response recovery time curve and the repeatability curve (inset in graph (b)).

As shown in fig. 1, the names of the respective components are: PET substrate 1, PANI @ WO₃And (3) hollow sphere sensitive electrode material 2.

As shown in fig. 2(a), the PANI is a uniform one-dimensional nanofiber, and as can be seen from a partial enlarged view of the PANI nanofiber, the PANI has a diameter of about 30 to 40nm, and a network structure is formed between the fibers. WO obtained as shown in FIG. 2(b)₃In the form of hollow spheres, from WO₃From a close-up view of the hollow spheres, WO₃The diameter of the hollow sphere is 1.2 um. FIG. 2(c) FESEM image of PAWHs10 nano-sensitive material, it can be seen that the prepared PAWHs10 is formed by coating polyaniline and growing in WO₃The surface of the hollow sphere. FIGS. 2(d) and 2(e) are TEM and HRTEM images of PAWHs10 nano-sensitive material, from which WO can be seen₃The shell of the hollow sphere is about 300nm in thickness and is wrapped in WO₃The PANI thickness of the surface layer of the hollow sphere is 15.7 nm. FIG. 2(f) is EDS diagram of PAWHs10 nano-sensitive material, from which WO can be seen₃Is of hollow structure, and N element is distributed in WO₃Of (2) is provided.

As can be seen from FIG. 3, with WO₃Increase of adding amount of hollow sphere nano sensitive material, sensor to NH₃Example 3 improvement and decrease of sensitivity to NH at room temperature₃Has the greatest sensitivity to 10ppm NH₃The sensitivity of (2) can reach 6.25.

FIG. 4(a) shows comparative example 1, comparative example 2 and example 3 at room temperature for different NH concentrations₃(0.5 to 100ppm) response curve of gas. The sensitivity test method comprises the following steps: firstly, putting the sensor into a gas bottle, measuring the resistance through a meter connected with the sensor, and obtaining the resistance value of the sensor in the air, namely R_a(ii) a Then, injecting 0.5-100 ppm NH into the gas bottle by using an injector₃By measuring the concentration of NH in the sensor₃Resistance value of (1) R_gAccording to the definition of sensitivity S, formula S ═ R_g/R_aThe sensitivity of the sensor under different concentrations is obtained through calculation, and NH is finally obtained₃Standard working curve of concentration-sensitivity. It can be seen from the figure that the sensitivity of the sensor is a function of NH₃The concentration increases. FIG. 4(b) shows comparative example 2 and example 3 for different NH₃The response of the gas fits a curve that conforms to an exponential model.

FIG. 5(a) is a graph comparing the response values of comparative example 2 and example 3 to 10ppm of 8 different gases at room temperature. As can be seen from the figure, example 3 is for NH₃Has better selectivity. FIG. 5(b) is a graph of example 3 at room temperature versus 10ppm NH₃The response recovery time curve and the repeatability curve of (c). As can be seen from the figure, example 3 is on 10ppm NH₃The method has the advantages that the response recovery rate is high, the response time is 136s, and the recovery time is 130 s; as can be seen from the inset repeatability curve, example 3 is on 10ppm NH at room temperature₃The sensitivity of (a) is relatively stable at the value, demonstrating that example 3 achieves acceptable reproducibility.

Detailed Description

Comparative example 1:

preparation of WO by hydrothermal method₃Hollow sphere nano-sensitive material, WO₃Method for preparing plane NH by hollow ball nano sensitive material₃The sensor comprises the following specific manufacturing processes:

1. preparing a PET substrate: cutting the PET with the thickness of 125 μm into a rectangular substrate with the length of 10mm and the width of 8mm, then placing the PET substrate in 20g/L NaOH solution, stirring for 90min at 60 ℃, then washing with deionized water and ethanol in sequence, and drying.

2. Preparation of WO₃The hollow sphere nano sensitive material comprises: dissolving 1g of sodium tungstate and 1.2g of citric acid in a mixed solution of 25mL of deionized water and 10mL of glycerol, and uniformly stirring; then adding 3mL of 4M hydrochloric acid, stirring for 20min, then putting the solution into a 50mL hydrothermal reaction kettle, and then putting the hydrothermal reaction kettle into an oven, wherein the oven parameters are set to be 180 ℃ and 24 h; after the reaction is finished, cooling the obtained product to room temperature, then alternately carrying out centrifugal washing by using water and ethanol, and drying the obtained product at 80 ℃; sintering the dried product in a muffle furnace at 500 ℃ for 3 hours at a heating rate of 2 ℃/min to obtain WO₃Hollow sphere nano sensitive material;

3. the preparation is based on WO₃Plane type NH of hollow ball sensitive material₃A sensor: coating WO on PET substrate surface by using spin coating method₃(WO₃Ultrasonically dispersing the powder into an ethanol solution), and drying at room temperature; finally, the device is placed for 24 hours at room temperature, thereby obtaining the WO-based device₃Plane NH of hollow sphere nano sensitive material₃A sensor.

Comparative example 2:

preparing PANI nano-sensitive material by in-situ oxidation polymerization method, and preparing planar NH by using PANI as nano-sensitive material₃The sensor comprises the following specific manufacturing processes:

1. preparing a PET substrate: same as in comparative example 1.

2. Preparation of planar NH based on PANI sensitive Material₃A sensor: dissolving 0.2mmol aniline in 15mL 1M hydrochloric acid, and performing ultrasonic treatment for 30 min; dissolving 0.2mmol of ammonium persulfate in 15mL of 1M hydrochloric acid, and stirring for 30min in an ice-water bath; mixing the two solutions, adding a PET substrate, and reacting for 2 hours in an ice-water mixed bath; after the reaction is finished, taking out the PET with the PANI growing in situ, and drying at room temperature; the device is placed at room temperature for 24h, so that planar NH based on PANI sensitive material is obtained₃A sensor.

Example 1:

preparation of WO by hydrothermal method₃Hollow sphere nano sensitive material as PANI @ WO₃Hollow sphere nano-sensingMaterial making of planar NH₃Sensor, in which WO₃The addition amount of the hollow spheres is (WO)₃2 mol% of/Ani), and the specific preparation process comprises the following steps:

2.32mg of WO₃Dissolving the hollow sphere nano sensitive material and 0.2mmol of aniline in 15mL of 1M hydrochloric acid, and carrying out ultrasonic treatment for 30 min; the manufacturing process of the rest of the devices is the same as that of comparative example 2, and the obtained NH₃The sensor is labeled as sensor PAWHs 2.

Example 2:

preparation of WO by hydrothermal method₃Hollow sphere nano sensitive material as PANI @ WO₃Method for preparing plane NH by hollow ball nano sensitive material₃Sensor, in which WO₃The addition amount of the hollow spheres is (WO)₃and/Ani is 5 mol%), and the specific preparation process comprises the following steps:

5.8mg of WO₃Dissolving the hollow sphere nano sensitive material and 0.2mmol of aniline in 15mL of 1M hydrochloric acid, and carrying out ultrasonic treatment for 30 min; the manufacturing process of the rest of the devices is the same as that of comparative example 2, and the obtained NH₃The sensor is labeled as sensor PAWHs 5.

Example 3:

preparation of WO by hydrothermal method₃Hollow sphere nano sensitive material as PANI @ WO₃Method for preparing plane NH by hollow ball nano sensitive material₃Sensor, in which WO₃The addition amount of the hollow spheres is (WO)₃10 mol% of/Ani), and the specific preparation process comprises the following steps:

11.6mg of WO₃Dissolving the hollow sphere nano sensitive material and 0.2mmol of aniline in 15mL of 1M hydrochloric acid, and carrying out ultrasonic treatment for 30 min; the manufacturing process of the rest of the devices is the same as that of comparative example 2, and the obtained NH₃The sensor is labeled as sensor PAWHs 10.

Example 4:

preparation of WO by hydrothermal method₃Hollow sphere nano sensitive material as PANI @ WO₃Method for preparing plane NH by hollow ball nano sensitive material₃Sensor, in which WO₃The addition amount of the hollow spheres is (WO)₃20 mol%) and the specific preparation process comprises the following steps:

23.2mg of WO₃The hollow sphere nano sensitive material and 0.2mmol aniline are dissolved in 15mL,Performing ultrasonic treatment in 1M hydrochloric acid for 30 min; the manufacturing process of the rest of the devices is the same as that of comparative example 2, and the obtained NH₃The sensor is labeled as sensor PAWHs 20.

Example 5:

preparation of WO by hydrothermal method₃Hollow sphere nano sensitive material as PANI @ WO₃Method for preparing plane NH by hollow ball nano sensitive material₃Sensor, in which WO₃The addition amount of the hollow spheres is (WO)₃30 mol% of/Ani), and the specific preparation process comprises the following steps:

34.8mg of WO₃Dissolving the hollow sphere nano sensitive material and 0.2mmol of aniline in 15mL of 1M hydrochloric acid, and carrying out ultrasonic treatment for 30 min; the manufacturing process of the rest of the devices is the same as that of comparative example 2, and the obtained NH₃The sensor is labeled as sensor PAWHs 30.

The planar sensors were attached to a Rigol Signal tester by clips, and the sensors prepared in comparative example 1, comparative example 2, example 1, example 2, example 3, example 4, and example 5 were placed in air at 10ppm NH, respectively₃The resistance signal test is performed in the atmosphere of (2).

In Table 1, the amounts of WO in PANI, PANI @2 mol.% are shown₃Hollow sphere, PANI @5 mol.% WO₃Hollow sphere, PANI @10 mol.% WO₃Hollow sphere, PANI @20 mol.% WO₃Hollow sphere, PANI @30 mol.% WO₃Hollow sphere, WO₃Flexible planar sensor PANI, PAWHs2, PAWHs5, PAWHs10, PAWHs20, PAWHs30 and WO₃Hs is 10ppm NH₃The sensitivity of (1). As can be seen from Table 1, device pair NH₃Shows a tendency to increase first and then decrease, with a sensitivity of 1.75 for pure PANI, WO₃The sensitivity of the nano sensitive material is 1 (no signal can be detected at room temperature), compared with a device prepared from pure PANI, the sensitivity of the device prepared from PAWHs10 is improved by 4.5, the maximum sensitivity is reached, and NH is added₃The response value of (a) is the largest, and the highest sensitivity characteristic is shown. It can be seen that by mixing WO in appropriate amounts₃The nano sensitive material can improve the sensitivity of the sensor.

Table 1 shows the amounts of PANI and PANI @2mol, respectively.％WO₃Hollow sphere, PANI @5 mol.% WO₃Hollow sphere, PANI @10 mol.% WO₃Hollow sphere, PANI @20 mol.% WO₃Hollow sphere, PANI @30 mol.% WO₃Hollow sphere, WO₃Flexible planar PANI, PAWHs2, PAWHs5, PAWHs10, PAWHs20, PAWHs30 and WO made of sensitive materials₃Hs is 10ppm NH₃At 10ppm NH₃The sensitivity of (1).

In Table 1, PANI, PAWHs2, PAWHs5, PAWHs10, PAWHs20, PAWHs30 and WO are listed respectively₃The flexible planar sensor made of Hs as sensitive material is at 10ppm NH₃The sensitivity of (1). As can be seen from Table 1, with WO₃Increase of addition amount of Hs, device to NH₃Shows a tendency to increase first and then decrease, with a sensitivity of 1.75 for pure PANI. Compared with the device prepared from pure PANI, the sensor device based on PAWHs has improved response. In which the device PAWHs10 reaches maximum sensitivity, NH₃The response value of (a) is the largest, and the highest sensitivity characteristic is shown. It can be seen that by mixing WO in appropriate amounts₃The sensitivity of the sensor can be improved by the hollow sphere nano sensitive material.

Claims (3)

1. Based on PANI @ WO₃The flexible planar ammonia gas sensor of the hollow sphere nano sensitive material is of a planar structure and is formed by a flexible PET substrate and PANI @ WO which is grown on the upper surface of the flexible PET substrate in situ₃The hollow sphere nano sensitive material is composed of PET (polyethylene terephthalate); the sensor is prepared by the following steps:

(1) dissolving 0.5-2 g of sodium tungstate and 0.5-2 g of citric acid in 11-50 mL of a mixed solution of deionized water and glycerol, wherein the amount of the deionized water and the amount of the glycerol are respectively 10-30 mL and 1-20 mL, and uniformly stirring;

(2) adding 1-5 mL of 1-5M hydrochloric acid into the solution, and stirring for 10-30 min;

(3) transferring the solution obtained in the step (2) into a hydrothermal reaction kettle, and carrying out hydrothermal reaction for 20-30 h at the temperature of 100-200 ℃;

(4) cooling the product obtained in the step (3) to room temperature, then alternately carrying out centrifugal washing by using water and ethanol, and drying the obtained centrifugal product at 50-100 ℃;

(5) drying the centrifugal product obtained in the step (4), and calcining at 400-600 ℃ for 1-5 h to obtain WO₃Hollow sphere nano sensitive material;

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

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

(8) mixing the two solutions obtained in the steps (6) and (7), then putting the mixture into a flexible PET substrate, and reacting for 1-3 h in an ice-water mixed bath;

(9) taking out the flexible PET substrate obtained in the step (8), and drying at room temperature, thereby preparing PANI @ WO on the upper surface of the flexible PET substrate₃A hollow sphere nano sensitive material film;

(10) placing the device obtained in the step (9) at room temperature for 1-2 days to obtain the PANI @ WO-based device₃A flexible plane type ammonia sensor made of hollow sphere nano sensitive materials.

2. A method as claimed in claim 1 based on PANI @ WO₃The flexible plane type ammonia gas sensor made of the hollow sphere nano sensitive material is characterized in that: a flexible PET substrate is prepared by the following steps,

(1) cutting PET with the thickness of 100-200 mu m into a flexible PET substrate with the length of 5-15 mm and the width of 5-10 mm;

(2) and (3) putting the flexible PET substrate into 10-30 g/L NaOH aqueous solution, stirring for 60-100 min at 50-80 ℃, then washing with deionized water and ethanol in sequence, and drying to obtain the flexible PET substrate.

3. A process as claimed in any one of claims 1 to 2Based on PANI @ WO₃The flexible plane type ammonia sensor made of the hollow sphere nano sensitive material is applied to the aspect of detecting ammonia under the atmospheric environment room temperature condition.

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