CN113390959B - Composite sensitive film and preparation method thereof, gas sensor and preparation method thereof - Google Patents

Abstract

The invention discloses a composite sensitive film and a preparation method thereof, a gas sensor and a preparation method thereof.A toxic gas sensitive material is dispersed into a solvent and then is coated on the surface of a two-dimensional material prepared by taking metal as a substrate through chemical vapor deposition, so that the composite sensitive film with a stacked structure is obtained; cutting the composite sensitive film into a proper size, and placing the composite sensitive film on the liquid level of etching liquid to etch the metal substrate of the composite sensitive film so as to obtain a self-supporting composite sensitive film; and rinsing the self-supporting composite sensitive film on the liquid level of the deionized water, and transferring the self-supporting composite sensitive film to the surface of a measuring element of the gas sensor by using a dipping and pulling method. The two-dimensional material layer in the composite sensitive film has good hydrophobicity and mechanical strength, and the integrity of the composite sensitive film on the liquid level is ensured. In addition, the two-dimensional material layer also has very high surface energy, so that the adhesiveness of the composite sensitive film and the surface of the piezoelectric substrate can be improved, the coupling effect of the toxic gas sensitive material and the surface acoustic wave device can be enhanced, and the response sensitivity and response speed of the sensor to sarin toxic gas and a simulator thereof can be improved.

Description

A composite sensitive film and preparation method, gas sensor and preparation method

technical field

The invention belongs to the field of sensing technology, relates to a surface acoustic wave gas sensor manufacturing technology, and in particular relates to a composite sensitive film and a preparation method, a gas sensor and a preparation method for detecting sarin poison gas and its simulant.

Background technique

Sarin (isopropyl mefludronate) is a typical nerve agent, colorless, odorless, and lethal by overstimulating muscles and vital organs and affecting the nervous system. Sarin can penetrate the human body through the respiratory tract or skin and mucous membranes, and is extremely lethal. Due to the high risk of sarin, laboratories usually use a simulant of sarin, dimethyl methylphosphonate (DMMP), to test the performance of sarin sensors.

A surface acoustic wave device is a solid-state electronic device composed of a piezoelectric crystal and a metal interdigital transducer prepared on the polished surface of the crystal. When a high-frequency electrical signal is applied to both ends of the metal interdigital transducer electrodes, the surface of the piezoelectric crystal will generate mechanical vibration through the inverse piezoelectric effect, and at the same time excite a kind of frequency that is the same as the electrical signal and propagates along the surface of the crystal. Elastic waves are surface acoustic waves. The frequency and energy of surface acoustic waves drift as the environment changes. Based on this characteristic, the surface of the crystal in the transmission direction of the surface acoustic wave is coated with a gas-sensitive film that selectively adsorbs a certain gas, which can be made into a surface acoustic wave gas sensor. The working principle of this sensor is to use the sensitive membrane to absorb gas, causing the material properties (mass, viscoelasticity, conductivity, etc.) of the membrane layer to change, thereby causing the oscillation frequency and insertion loss of the device to change, and finally realizing the gas detection function.

The hexafluoroisopropanol aniline functionalized sensitive material is integrated into the surface acoustic wave device, and the changes in parameters such as mass, viscoelasticity, and electrical conductivity caused by the adsorption of DMMP gas can cause the oscillation frequency and insertion loss of the device. Therefore, this type of device is more responsive to DMMP than resistive type sensors. However, to fabricate a surface acoustic wave gas sensor with high sensitivity, fast response, and low detection limit, the preparation method of the gas-sensitive thin film is particularly critical.

At present, the preparation method of the sensitive film in the surface acoustic wave gas sensor is mainly to dissolve the sensitive material in a solvent, and then prepare it on the surface of the piezoelectric crystal by methods such as drop coating and spraying. When the solvent evaporates, the sensitive material solidifies to form a thin film on the crystal surface. However, these methods cannot precisely control the area and shape of the sensitive film, and when the solvent evaporates, the sensitive material tends to gather at the edge of the film, resulting in a "coffee ring effect", resulting in a thicker edge and poor overall uniformity after the film is cured. The coupling between the membrane and the surface acoustic wave device is weak, and the gas sensing performance decreases.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the existing sensitive film preparation methods, the present invention provides a composite sensitive film, a preparation method, a gas sensor and a preparation method, which can accurately control the use of a hexafluoroisopropanol aniline functionalized sensitive material in a gas sensor The area and shape of the sensitive film formed on the measuring element can improve the overall uniformity of the film, improve the coupling between the sensitive material and the measuring element, and enhance the gas sensing performance of the sensor.

The present invention is achieved through the following technical solutions:

A composite sensitive film includes a two-dimensional material layer, and a hexafluoroisopropanol aniline functionalized poison gas sensitive material layer supported on the film.

Preferably, the material of the poison gas sensitive material layer is hexafluoroisopropanol aniline functionalized carbon nanotube, graphene, graphene oxide or carbon nanosphere.

Preferably, the two-dimensional material is multilayer hexagonal boron nitride or graphene prepared on a metal substrate by chemical vapor deposition.

Preferably, the thickness of the two-dimensional material layer is 5-15 nm; the thickness of the poison gas sensitive material layer is 200-1000 nm.

A preparation method of a composite sensitive film, comprising the following steps:

Step 1. Prepare a dispersion liquid of poison gas sensitive material, and the molar ratio of the sensitive material to the solvent is 1:50.

Step 2, drop the poison gas sensitive material dispersion prepared in step 1 on the surface of the two-dimensional material with the metal as the substrate, and then spin-coat, and then dry the obtained metal substrate, and form the metal substrate after drying. A composite film stacked with gas-sensitive materials and two-dimensional materials;

Step 3, performing solution etching on the metal substrate obtained in step 2, and removing the metal substrate to obtain a composite sensitive film.

The rotational speed of the spin coating in step 3 and step 2 is 100-500 rpm.

In step 3 and step 2, the drying temperature is 50-80° C., and the thermal drying time is 10-30 minutes.

The metal substrate in step 3 and step 2 is copper foil or nickel foil.

A gas sensor, the surface of the measuring element of the gas sensor is loaded with a composite sensitive film.

A preparation method of a gas sensor, comprising the following steps:

Step 11, according to the size of the measuring element, cut the composite sensitive film with the metal substrate as a whole;

Step 12, performing solution etching on the metal substrate obtained in step 11, and removing the metal substrate to obtain a composite sensitive film;

Step 13: Transfer the composite sensitive film to the surface of the measuring element of the sensor by dipping and pulling method.

Compared with the prior art, the present invention has the following beneficial technical effects:

The invention provides a composite sensitive film, comprising a two-dimensional material layer and a hexafluoroisopropanol aniline-functionalized sensitive material layer formed on the surface thereof, which has an adsorption effect on DMMP vapor, and the two-dimensional material layer is formed on the sensitive material layer. The support body makes the sensitive material layer have sufficient mechanical strength to avoid the damage of the composite sensitive film due to the liquid surface tension and liquid level fluctuation during the transfer process. Secondly, the two-dimensional material has a large specific surface area and a large surface energy. The stronger adhesion on the measuring element of the sensor helps to promote the coupling between the hexafluoroisopropanol aniline-functionalized sensitive material film layer and the measuring element, thereby improving the sensitivity and gas-sensing response of the device.

The invention provides a preparation method of a composite sensitive film. The sensitive material is coated on a two-dimensional material by spin coating, the shape and area of the composite sensitive film are precisely controlled, and the overall uniform performance of the formed sensitive material layer can be ensured. It can eliminate the problem of sensitive materials agglomerating at the edge of the film, and obtain a sensitive film with better uniformity; by controlling the concentration of the hexafluoroisopropanol aniline-functionalized sensitive material in the dispersion and the speed of spin-coating the dispersion, it can be effectively controlled Thickness of the sensitive film. The optimization of the thickness of the sensitive film can make the device have the best gas response sensitivity.

The invention provides a gas sensor for detecting sarin poison gas and its simulant. By precisely controlling the area and shape of the sensitive film formed on the measuring element of the gas sensor by the sensitive material functionalized with hexafluoroisopropanol aniline, the introduced two-dimensional material has a high surface energy, which improves the performance of the composite sensitive film and the gas sensor. The adhesion on the surface of the measuring element improves the overall uniformity of the film and improves the coupling between the sensitive material and the measuring element of the gas sensor, and enhances the gas sensing performance of the sensor. The gas sensor prepared by this method has high sensitivity to sarin poison gas and its simulant, fast response speed and low detection limit.

Description of drawings

Fig. 1 is the composite sensitive film preparation and transfer flow chart of the present invention based on hexafluoroisopropanol aniline functionalized sensitive material/two-dimensional material stack structure;

2 is a schematic diagram of preparation and transfer of a gas-sensitive thin composite sensitive film based on a carbon nanotube/hexagonal boron nitride nanofilm stack structure functionalized with hexafluoroisopropanol aniline in the present invention;

3 is a schematic diagram of the shape, area and coverage area of the composite sensitive film on the surface acoustic wave device of the present invention;

4 is an optical picture of the gas-sensitive composite film of the hexafluoroisopropanol aniline-functionalized carbon nanotubes and the hexagonal boron nitride nanofilm stacked in the present invention after being transferred to a surface acoustic wave device;

Fig. 5 is the scanning electron microscope picture of hexafluoroisopropanol aniline functionalized carbon nanotubes of the present invention

6 is the gas-sensing response to different concentrations of DMMP vapor measured by the gas-sensing composite film of the carbon nanotubes and hexagonal boron nitride nano-films stacked on the surface acoustic wave device of the present invention. Graph.

2. Metal substrate; 3. Poison gas sensitive material layer; 4. Metal interdigital transducer; 5. Composite sensitive film; 6. Piezoelectric substrate; 7. Encapsulation shell.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings, which are to explain rather than limit the present invention.

A composite sensitive film comprises a two-dimensional material layer 1, and a hexafluoroisopropanol aniline functionalized poison gas sensitive material layer 3 supported thereon.

The poisonous gas sensitive material is hexafluoroisopropanol aniline functionalized carbon nanotube, graphene, graphene oxide or carbon nanosphere.

The two-dimensional material is multi-layer hexagonal boron nitride or graphene prepared on a metal substrate by chemical vapor deposition.

The thickness of the two-dimensional material layer is 5-15 nm; the thickness of the poison gas sensitive material layer is 200-1000 nm.

In the composite sensitive film, the upper layer of the sensitive material film functionalized with hexafluoroisopropanol aniline group has an adsorption effect on DMMP vapor, and the lower two-dimensional material makes the sensitive material film layer hydrophobic and still has sufficient mechanical strength as a whole, Prevent the composite membrane from sinking into water or being damaged by liquid surface tension and liquid level fluctuation during the transfer process. In addition, the ultra-high specific surface area of the two-dimensional material makes it have a large surface energy, which can have a stronger adhesion on the measuring element of the gas sensor, which is helpful to promote the sensitive material functionalized by the hexafluoroisopropanol aniline group. The coupling between the film layer and the measuring element of the gas sensor improves the sensitivity and gas-sensing response of the device.

The preparation method of the above-mentioned composite sensitive film, as shown in Figure 1, comprises the following steps:

Step 1. Prepare a dispersion liquid of poison gas sensitive material, and the molar ratio of the sensitive material to the solvent is 1:50.

Specifically, the poison gas-sensitive material is added to the solvent, first shaken for 10-30 minutes, and then sonicated for 8-12 hours to obtain a uniform poison gas-sensitive material dispersion.

Solvents are N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP).

Step 2, drop the poison gas sensitive material dispersion prepared in step 1 on the surface of the two-dimensional material with the metal as the substrate, and form a composite film stacked with the poison gas sensitive material and the two-dimensional material on the metal substrate after drying.

Specifically, the two-dimensional material grown on the metal substrate 2 with a thickness of 25-50 microns is placed in the center of the turntable of the glue spinner, and the poison gas-sensitive material is drawn with a dropper to disperse droplets on the surface of the two-dimensional material, and the entire surface is spread. Full. Set the speed of the glue dispenser between 100-500 r/min and the time in the range of 10-60 seconds, start the glue dispenser, and after the spin coating is completed, a wet film is formed on the surface of the two-dimensional material. Then, the temperature of the hot plate is set to 50-80 °C, and the heat drying time is set to 10-30 minutes, and the solvent in the wet film is evaporated by the hot plate, thereby forming a stack of gas-sensitive materials and two-dimensional materials on the metal substrate. composite membrane.

The metal substrate is copper foil or nickel foil.

Step 3, performing solution etching on the metal substrate obtained in step 2, and removing the metal substrate to obtain a composite sensitive film.

Specifically, the metal substrate is placed on the liquid surface of the etching solution, the time required for etching is 4 hours, and after the etching is completed, a composite sensitive film without the support of the metal substrate is obtained.

The etching solution is an ammonium sulfate solution or a ferric trichloride solution. The ammonium persulfate or ferric trichloride is dissolved in deionized water, stirred evenly, and an etching solution with a concentration of 0.1 mol/L is prepared.

A gas sensor includes a measuring element on which the above-mentioned composite sensitive film 5 is attached.

The measuring elements are interdigitated electrodes, ceramic tubes or surface acoustic wave devices.

A preparation method of a gas sensor, which adopts the dipping and pulling method to transfer the composite sensitive film to the surface of the measuring element of the gas sensor, and specifically includes the following steps:

Step 11, according to the size of the measuring element, cut the composite sensitive film with the metal substrate as a whole;

Step 12, performing solution etching on the metal substrate obtained in step 11, and removing the metal substrate to obtain a composite sensitive film;

Step 13: Transfer the composite sensitive film to the surface of the measuring element of the gas sensor by dipping and pulling.

The composite sensitive membrane floating on the surface of the etching solution was transferred to the surface of deionized water by dipping and pulling method, and rinsed for 10 minutes. Then, the rinsed composite sensitive membrane was transferred to the surface of the measuring element of the gas sensor by the same dip-pulling method. After the transfer was completed, it was dried at room temperature for 30 minutes, and then placed on a hot plate for further drying. The temperature of the hot plate was set at 50°C, and the heat-baking time was 30 minutes.

Example 1

A preparation method of a surface acoustic wave gas sensor, as shown in Figure 2, includes the following steps:

1) Preparation of hexafluoroisopropanol aniline functionalized carbon nanotube dispersion.

10 mg of hexafluoroisopropanol aniline functionalized carbon nanotubes were added to 50 ml of solvent, first shaken for 10 minutes, and then sonicated for 8 hours to obtain a uniform hexafluoroisopropanol aniline functionalized carbon nanotube dispersion.

2) Spin-coating the hexafluoroisopropanol aniline functionalized carbon nanotube dispersion on the surface of the two-dimensional material.

Place the multi-layer hexagonal boron nitride nanofilm grown on copper foil 2 with a thickness of 25 microns in the center of the turntable of the glue dispenser, and suck the prepared hexafluoroisopropanol aniline functionalized carbon nanotube dispersion with a dropper. , drop on the surface of the hexagonal boron nitride nanofilm 1, and cover the entire surface. Set the speed of the dispenser to 100 rpm for 10 seconds, then start the dispenser. After the spin coating is completed, a wet film is formed on the surface of the hexagonal boron nitride nanofilm 1 . Then, the temperature of the hot plate is set to 50° C., and the heat-baking time is set to 10 minutes, and the solvent in the wet film is evaporated by the hot plate to obtain the sensitive material layer 3 . At this time, a composite film 5 in which the hexafluoroisopropanol aniline functionalized carbon nanotube thin film and the multi-layer hexagonal boron nitride nanofilm are stacked is formed on the metal substrate.

3) Cut the composite film

The composite film is cut according to the area between the metal interdigital transducers in the surface acoustic wave device to obtain the cut composite film. In principle, the shape of the composite membrane is required to be consistent with the shape of the area between the metal interdigital transducers, and the area is slightly smaller than the area between the metal interdigital transducers. As shown in FIG. 3 , the length L2 and the width W2 of the composite film B respectively account for 70%-90% of the length L1 and the width W1 of the region between the metal interdigital transducers.

In the surface acoustic wave device used in this embodiment, the shape of the area between the metal interdigital transducers is square, and the side length is 2.5 mm. Then, a composite film with an area of 2.2 mm*2.2 mm was cut out from the composite film.

4) Wet etching to remove the copper substrate of the composite film

Ammonium persulfate was dissolved in deionized water, stirred evenly, and an etching solution with a concentration of 0.1 mol/L was prepared. Then, the copper substrate of the cut composite film was placed on the liquid surface of the etching solution, and the time required for etching was 4 hours. After the etching is completed, a composite sensitive film without metal substrate support is obtained.

5) Wet transfer composite sensitive film

The composite sensitive membrane floating on the surface of the etching solution was transferred to the surface of deionized water by dipping and pulling method, and rinsed for 10 minutes. Then, the rinsed composite sensitive film is transferred to the surface of the piezoelectric substrate 6 between the metal interdigital transducers 4 of the surface acoustic wave device, and the piezoelectric substrate 6 is located in the package casing 7 by the same dip-pulling method.

It should be noted that a pair of sides of the composite sensitive film is kept parallel to the distance direction of the metal interdigital transducer, and at the same time, the composite sensitive film is prevented from covering the metal interdigital transducer. After the transfer is complete, let it dry at room temperature for 30 minutes before placing it on a hot plate for further drying. The temperature of the hot plate was set at 50°C, and the heat-baking time was 30 minutes.

As shown in FIG. 4 , it is an optical image of the gas-sensitive composite film stacked with hexafluoroisopropanol aniline functionalized carbon nanotubes and hexagonal boron nitride nanofilms in this example after being transferred to a surface acoustic wave device. It can be seen that, through the preparation method provided by the present invention, the sensitive film is successfully transferred between the metal interdigital transducers, and the shape and area of the sensitive film are precisely controlled.

As shown in Figure 5, it is the scanning electron microscope picture of the carbon nanotubes functionalized with hexafluoroisopropanol aniline in this example. It can be seen that the use of this sensitive material is a porous structure with an ultra-high ratio The surface area can provide a large number of adsorption sites for gas molecules, and help to improve the response sensitivity and response speed.

As shown in Figure 6, the surface acoustic wave gas sensor prepared in this implementation has high sensitivity and fast response speed to DMMP vapor. Even at a concentration of 1 ppm, the sensor has a high signal-to-noise ratio, and the detection limit is expected to reach the ppb level.

Example 2

A preparation method of a composite sensitive film, comprising the following steps:

1) 10 mg of hexafluoroisopropanol aniline functionalized graphene was added to 50 ml of solvent, first shaken for 20 minutes, and then ultrasonicated for 10 hours to obtain a uniform hexafluoroisopropanol aniline functionalized graphene dispersion.

2) Place the graphene film grown on the thick 35-micron nickel foil on the center of the turntable of the glue dispenser, suck the prepared hexafluoroisopropanol aniline functionalized graphene dispersion with a dropper, and drop it on the graphene. film surface and cover the entire surface. Set the speed of the dispenser to 300 rpm for 30 seconds, and then start the dispenser. After the spin coating is completed, a wet film is formed on the surface of the graphene film. Then, the temperature of the hot plate was set to 60° C., the heating time was set to 20 minutes, and the solvent in the wet film was evaporated by using the hot plate. After the completion, a composite film of the hexafluoroisopropanol aniline functionalized graphene film and the two-dimensional material graphene film is formed on the metal substrate.

Example 3

A preparation method of a composite sensitive film, comprising the following steps:

1) 10mg hexafluoroisopropanol aniline functionalized graphene oxide is added to 50ml solvent, first shake for 30 minutes, then ultrasonic for 12 hours to obtain uniform hexafluoroisopropanol aniline functionalized graphene oxide dispersion liquid.

2) The hexagonal boron nitride film grown on the thick 50-micron nickel foil is placed in the center of the turntable of the glue dispenser, and the prepared hexafluoroisopropanol aniline functionalized graphene oxide dispersion is sucked with a dropper, dripping. On the surface of the hexagonal boron nitride film, and spread the entire surface. Set the speed of the dispenser to 500 rpm for 60 seconds, then start the dispenser. After the spin coating is completed, a wet film is formed on the surface of the hexagonal boron nitride film. Then, the temperature of the hot plate was set to 80° C., the heating time was set to 30 minutes, and the solvent in the wet film was evaporated by using the hot plate. After the completion, a composite film of the hexafluoroisopropanol aniline functionalized graphene oxide film and the hexagonal boron nitride film is formed on the metal substrate.

Example 4

A preparation method of a composite sensitive film, comprising the following steps:

1) 10mg hexafluoroisopropanol aniline-functionalized carbon nanospheres were added to 50 ml of solvent, first shaken for 30 minutes, and then ultrasonicated for 12 hours to obtain uniform hexafluoroisopropanol aniline-functionalized carbon nanospheres dispersed liquid.

2) The hexagonal boron nitride film grown on the thick 40-micron nickel foil is placed in the center of the turntable of the glue dispenser, and the prepared hexafluoroisopropanol aniline functionalized graphene oxide dispersion is sucked with a dropper, dripping. On the surface of the hexagonal boron nitride film, and spread the entire surface. Set the speed of the dispenser to 100 rpm for 50 seconds, and then start the dispenser. After the spin coating is completed, a wet film is formed on the surface of the hexagonal boron nitride film. Then, the temperature of the hot plate was set to 70° C., the heating time was set to 50 minutes, and the solvent in the wet film was evaporated by the hot plate. After completion, a composite film of the hexafluoroisopropanol aniline functionalized carbon nanosphere film and the hexagonal boron nitride film is formed on the metal substrate.

The above content is only to illustrate the technical idea of the present invention, and cannot limit the protection scope of the present invention. Any modification made on the basis of the technical solution proposed in accordance with the technical idea of the present invention falls within the scope of the claims of the present invention. within the scope of protection.

Claims (7)

1. The composite sensitive film is characterized by comprising a two-dimensional material layer and a hexafluoroisopropanol anilino functionalized toxic gas sensitive material layer loaded on the two-dimensional material layer;

the toxic gas sensitive material layer is made of hexafluoroisopropanol anilino functionalized carbon nano tubes, graphene oxide or carbon nano spheres;

the two-dimensional material is multilayer hexagonal boron nitride or graphene prepared on a metal substrate by using a chemical vapor deposition method;

the preparation method of the composite sensitive film comprises the following steps:

step 1, preparing toxic gas sensitive material dispersion liquid, wherein the molar ratio of a sensitive material to a solvent is 1:50;

step 2, dropwise adding the toxic gas sensitive material dispersion liquid prepared in the step 1 on the surface of a two-dimensional material taking metal as a substrate, performing spin coating, drying the obtained metal substrate, and forming a composite film formed by stacking the toxic gas sensitive material and the two-dimensional material on the metal substrate after drying;

and 3, carrying out solution etching on the metal substrate obtained in the step 2, and removing the metal substrate to obtain the composite sensitive film.

2. The composite sensitive film according to claim 1, wherein the thickness of the two-dimensional material layer is 5-15nm; the thickness of the toxic gas sensitive material layer is 200-1000nm.

3. The composite sensitive film according to claim 1, wherein the spin coating in step 2 is performed at a speed of 100-500 rpm.

4. The composite sensitive film of claim 1, wherein the drying temperature in step 2 is 50-80 ℃ and the heat drying time is 10-30 minutes.

5. The composite sensitive film according to claim 1, wherein the metal substrate of step 2 is a copper foil or a nickel foil.

6. A gas sensor, characterized in that the surface of the measuring element of the gas sensor is loaded with a composite sensing membrane according to any one of claims 1 to 5.

7. A method for manufacturing the gas sensor according to claim 6, comprising the steps of:

step 11, cutting the composite sensitive film with the metal substrate integrally according to the size of the measuring element;

step 12, performing solution etching on the metal substrate obtained in the step 11, and removing the metal substrate to obtain a composite sensitive film;

and step 13, transferring the composite sensitive film to the surface of a measuring element of the sensor by adopting a dip-coating method.

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