CN112763548A

CN112763548A - Carbon monoxide detection method and system based on polymer composite film

Info

Publication number: CN112763548A
Application number: CN202011484802.6A
Authority: CN
Inventors: 张广迪; 杨帆; 刘伟; 倪娜
Original assignee: Beijing Institute of Radio Metrology and Measurement
Current assignee: Beijing Institute of Radio Metrology and Measurement
Priority date: 2020-12-16
Filing date: 2020-12-16
Publication date: 2021-05-07

Abstract

The invention discloses a carbon monoxide detection method and a carbon monoxide detection system based on a polymer composite film, which comprise the following steps: firstly, preparing a carbon nano tube/polymer composite film as a sensitive film of a gas sensor, uniformly coating the composite film on a resistance type gas sensor by adopting a gas spraying process, and putting the resistance type gas sensor coated with the composite film into a vacuum drying oven for drying until a solvent evaporation film is stable to obtain the carbon nano tube/polymer composite film; then, providing a gas distribution system and a data acquisition system, fixing the resistance type gas sensor coated with the composite film in a gas distribution system test cavity, and then distributing the concentration of the gas to be measured; and finally, introducing the gas to be detected with the concentration into the test cavity to fully contact with the composite membrane to react to obtain resistance change data of the composite membrane, and analyzing by a data acquisition system to detect the gas to be detected. The method has the advantages of high sensitivity, good selectivity and strong anti-interference capability.

Description

Carbon monoxide detection method and system based on polymer composite film

Technical Field

The invention belongs to the technical field of gas sensors, and relates to a carbon monoxide detection method and system based on a polymer composite film.

Background

In recent years, air pollution gradually receives wide attention of people, and the normal life of people is endangered by the influence of haze weather; underground pipeline accidents frequently occur, and the problems of effective utilization of underground space and safe space operation are more and more concerned by people. Therefore, the control of air pollution and the real-time monitoring of various harmful gases are not slow, and people put higher demands on the prevention of pollutants in the air. This also presents greater opportunities and challenges for the study and development of gas sensors. Much research has been focused on the sensitive materials of gas sensors, especially on toxic and harmful gases such as carbon monoxide (CO), hydrogen sulfide (H2S), ammonia (NH3), etc. Carbon monoxide is a colorless, odorless gas, and has a very serious impact on human health once inhaled into a human body. It combines with hemoglobin to produce carboxyhemoglobin, thereby failing to provide oxygen to the body tissues and causing hypoxia. When the concentration of carbon monoxide is 667ppm, about half of hemoglobin in a human body is converted into carboxyhemoglobin, which seriously endangers human life. Therefore, monitoring of carbon monoxide is particularly important, and the development of a carbon monoxide sensor which is miniaturized, intelligent, low in cost, reliable in selectivity and stability and high in sensitivity is imperative.

The carbon monoxide sensor has a variety of types, and generally, after receiving a corresponding signal through a sensor conduction system, the signal is converted into a change form of voltage (resistance), light intensity or frequency through an electrode, an optical fiber or a mass sensitive element, and the change form is transmitted to a subsequent system for amplification or output, so that a physical quantity to be measured is detected. Currently, the types of CO sensors that have been put into production and used are mainly: metal oxide semiconductor type, electrochemical solid electrolyte type, and electrochemical polymer electrolyte type.

The working principle of the resistance type gas sensor is as follows: when gas passes through the surface of the sensitive material of the sensor, the resistance value of the material is changed, so that the concentration of the gas to be detected is detected; the non-resistance type gas sensor is detected using other physical quantities or device characteristics. Of the two, the resistive sensor is the most widely used and most commonly studied gas sensor. The resistance type sensor is simple to manufacture, simple in structure, convenient to operate, high in sensitivity, short in response time and low in cost, but has some problems at the same time: poor selectivity and repeatability, short service life, poor corrosion resistance, complex sensitive mechanism and the like.

Therefore, it is necessary to design a carbon monoxide sensor with high sensitivity, good stability and good selectivity.

Disclosure of Invention

The invention aims to provide a carbon monoxide detection method and system based on a polymer composite film, and solves the problems of low sensitivity, poor selectivity and poor repeatability of the existing carbon monoxide sensor based on the traditional gas-sensitive film.

In view of the above, the present invention provides a method for detecting carbon monoxide based on a polymer composite film, comprising:

firstly, preparing a carbon nano tube/polymer composite film as a sensitive film of a gas sensor, uniformly coating the composite film on a resistance type gas sensor by adopting a gas spraying process, and putting the resistance type gas sensor coated with the composite film into a vacuum drying oven for drying treatment until a solvent evaporation film is stable to obtain the carbon nano tube/polymer composite film;

then, providing a gas distribution system and a data acquisition system, fixing the resistance type gas sensor coated with the composite film in a gas distribution system test cavity, and then distributing the concentration of the gas to be measured;

and finally, introducing the gas to be detected with the concentration into the test cavity to fully contact with the composite membrane to react to obtain resistance change data of the composite membrane, and acquiring the resistance change data by a data acquisition system for analysis so as to detect the concentration of the gas to be detected.

Further, the method for uniformly coating the resistor type gas sensor by adopting a gas spraying process comprises the following steps:

taking 1ml of single-walled carbon nanotube aqueous dispersion liquid into a 10ml measuring cylinder, adding ultrapure water for diluting by 10 times, pouring the solution into a beaker, and putting the beaker into ultrasonic cleaning equipment for ultrasonic dispersion for 30 minutes;

20mg of polyaniline powder was weighed with an electronic balance and dissolved in 10ml of tetrahydrofuran solution while being sonicated for 30 minutes. Mixing the two solutions after the ultrasonic treatment into a beaker, and continuing the ultrasonic treatment for 30 minutes;

after the ultrasonic cleaning is finished, 0.2ml of the dispersion liquid is taken out by a micro-injection meter, and the dispersion liquid is uniformly coated on the resistance type gas sensor by adopting a spraying process.

Further, the gas distribution system includes: the gas cylinder, the gas distribution device and the gas-sensitive testing cavity are connected through a gas guide pipe.

Further, the data acquisition system comprises: keithley2700 and a back end computer, wherein the Keithley2700 is used for acquiring the resistance change data in real time and transmitting the resistance change data to the back end computer.

Further, the mass fraction of the carbon nanotubes in the carbon nanotube/polymer composite film is smaller than the mass fraction of the polymer in the carbon nanotube/polymer composite film.

Further, the resistance type gas sensor is an interdigital electrode.

Another object of the present invention is to provide a carbon monoxide detecting system based on a polymer composite film, comprising:

the preparation device of the composite membrane comprises a resistance type gas sensor and a vacuum drying oven, and is used for preparing the composite membrane of the carbon nano tube/polymer as a sensitive membrane of the gas sensor, wherein the composite membrane is uniformly coated on the resistance type gas sensor by adopting a gas spraying process, and the resistance type gas sensor coated with the composite membrane is placed into the vacuum drying oven for drying treatment until the solvent evaporation membrane is stable, so that the composite membrane of the carbon nano tube/polymer is obtained;

the detection equipment comprises a gas distribution system and a data acquisition system, and is used for fixing the resistance type gas sensor coated with the composite film in a gas distribution system test cavity and then distributing the concentration of the gas to be detected; and introducing the gas to be detected with the concentration into the test cavity to fully contact with the composite membrane to react to obtain resistance change data of the composite membrane, and acquiring the resistance change data by a data acquisition system for analysis so as to detect the concentration of the gas to be detected.

Further, the compound film adopts the gas-blast technology even coating on resistance type gas sensor, includes:

The invention achieves the following significant beneficial effects:

the realization is simple, include: firstly, preparing a carbon nano tube/polymer composite film as a sensitive film of a gas sensor, uniformly coating the composite film on a resistance type gas sensor by adopting a gas spraying process, and putting the resistance type gas sensor coated with the composite film into a vacuum drying oven for drying treatment until a solvent evaporation film is stable to obtain the carbon nano tube/polymer composite film; then, providing a gas distribution system and a data acquisition system, fixing the resistance type gas sensor coated with the composite film in a gas distribution system test cavity, and then distributing the concentration of the gas to be measured; and finally, introducing the gas to be detected with the concentration into the test cavity to fully contact with the composite membrane to react to obtain resistance change data of the composite membrane, and acquiring the resistance change data by a data acquisition system for analysis so as to detect the concentration of the gas to be detected. The method has the advantages of high sensitivity, good selectivity and strong anti-interference capability.

Drawings

FIG. 1 is a schematic diagram of a carbon monoxide detection system based on a polymer composite film according to the present invention;

FIG. 2 is a graph of resistance versus time of a composite membrane for carbon monoxide;

FIG. 3 is a graph of the response of a composite membrane to carbon monoxide versus time;

FIG. 4 is a response-time curve of PANI/SWCNT composite films with different SWCNT contents to CO;

FIG. 5 is a response-concentration curve of PANI/SWCNT composite films with different SWCNT contents to CO;

FIG. 6 is a schematic representation of the reproducibility of PANI/SWCNT (3:1) composite membrane to CO;

FIG. 7 is a schematic diagram of the selectivity of a PANI/SWCNT composite membrane;

FIG. 8 is a SEM surface topography of the PANI/SWCNT composite membrane.

Detailed Description

The advantages and features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings and detailed description of specific embodiments of the invention. It is to be noted that the drawings are in a very simplified form and are not to scale, which is intended merely for convenience and clarity in describing embodiments of the invention.

It should be noted that, for clarity of description of the present invention, various embodiments are specifically described to further illustrate different implementations of the present invention, wherein the embodiments are illustrative and not exhaustive. In addition, for simplicity of description, the contents mentioned in the previous embodiments are often omitted in the following embodiments, and therefore, the contents not mentioned in the following embodiments may be referred to the previous embodiments accordingly.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood that the inventors do not intend to limit the invention to the particular embodiments described, but intend to protect all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. The same meta-module part number may be used throughout the drawings to represent the same or similar parts.

Referring to fig. 1 to 8, the present invention provides a method for detecting carbon monoxide based on a polymer composite film, including:

In one embodiment, the gas-spray process is uniformly coated on the resistance type gas sensor, and comprises the following steps:

In one embodiment, the gas distribution system comprises: the gas cylinder, the gas distribution device and the gas-sensitive testing cavity are connected through a gas guide pipe.

In one embodiment, the data acquisition system comprises: keithley2700 and a back end computer, wherein the Keithley2700 is used for acquiring the resistance change data in real time and transmitting the resistance change data to the back end computer.

In one embodiment, the mass fraction of the carbon nanotubes in the carbon nanotube/polymer composite film is less than the mass fraction of the polymer in the carbon nanotube/polymer composite film.

In one embodiment, the resistive gas sensor is an interdigitated electrode.

In one embodiment, the composite film is uniformly coated on the resistive gas sensor by using a gas spraying process, and comprises the following steps:

The technical principle of the invention is as follows: the carbon nano tube has strong adsorption capacity to a plurality of gases, when the gases are adsorbed on the surface of the carbon nano tube, the gases can interact with the carbon nano tube presenting semiconductor properties, so that the resistance of the material is changed, and the concentration of the gases is detected by measuring the change of the resistance, so that the carbon nano tube is very suitable for manufacturing a sensitive film of a gas sensor. However, since a single carbon nanotube has very poor adsorption selectivity to a gas and often shows very strong adsorption to many gases, the carbon nanotube is often modified to improve the selectivity of the gas sensitive film for different detection gases. The composite material of carbon nano tube and polymer is a novel gas sensitive material in recent years. The composite film is beneficial to improving the gas-sensitive characteristic of the sensor.

As shown in fig. 1: the carbon monoxide detection system based on the polymer composite film is composed of a spray gun 1, an iron stand 2, an air inlet 3 and an interdigital electrode 4. When the air spraying film is formed, air is introduced into the spray gun 1 through the air inlet hole 3 and is uniformly sprayed on the interdigital electrode 4 to finish the coating of the film. The preparation method of the Polyaniline (PANI)/single-walled carbon nanotube (SWCNT) composite membrane comprises the following steps: and (3) putting 1ml of the single-walled carbon nanotube aqueous dispersion into a 10ml measuring cylinder, adding ultrapure water for diluting by 10 times, pouring the solution into a beaker, and putting the beaker into ultrasonic cleaning equipment for ultrasonic dispersion for 30 minutes. PANI powder 20mg was weighed out on an electronic balance and dissolved in 10ml tetrahydrofuran solution while sonicating for 30 minutes. The sonicated solutions were mixed into a beaker and sonication continued for 30 minutes. After the ultrasonic cleaning is finished, 0.2ml of the dispersion liquid is taken out by a micro-injection meter, and the dispersion liquid is uniformly coated on the interdigital electrode by adopting a spraying process. And finally, putting the device into a vacuum drying oven for drying treatment, and obtaining the needed PANI/SWCNT composite film after the solvent evaporation film is stable.

FIG. 2 is a graph of the resistance versus time of the PANI/SWCNT composite film with respect to carbon monoxide. When CO is introduced into the gas-sensitive test cavity, the resistance of the composite membrane can rapidly rise. With the continuous introduction of CO, the tendency of the resistance rise gradually becomes slower and more stable. When CO is stopped being introduced and nitrogen is introduced into the gas-sensitive test cavity again for desorption, the resistance of the composite membrane is sharply reduced. It can be seen that the response of the gas sensitive detection system increases as the concentration of CO introduced increases. At 100ppm CO, the gas detection system had a response value of 175 ohms.

FIG. 3 is a graph showing the response-concentration of PANI/SWCNT composite membrane to carbon monoxide. Within the five tested concentrations, the response of the gas sensitive detection system exhibited a certain linearity, with a linearity R2 reaching 0.99. At 100ppm, the gas sensitive detection system had a response of 0.28 and a response value of 175 ohms. The response was 0.19 even at 20ppm and the response was 120 ohms. The method has important significance for the back-end data processing of the gas-sensitive detection system, and has a certain prediction effect on the concentration of the gas measured by the gas-sensitive detection system.

FIG. 4 is a graph of response versus time of PANI/SWCNT composite films with different SWCNT content to CO. In order to explore the influence of the content of the carbon nano tube on the gas-sensitive characteristic of the polymer/carbon nano tube composite material, 3 composite film gas-sensitive detection systems with different proportions are manufactured and the response to CO is tested under the same condition. Wherein the mass fraction ratio of the sensor1 polymer to the single-walled carbon nanotube is 3: 1; the mass fraction ratio of the sensor2 polymer to the single-walled carbon nanotube is 3: 2; the mass fraction ratio of the sensor3 polymer to the single-walled carbon nanotubes was 3: 3. In the test process, the 3 gas-sensitive detection systems are simultaneously placed in a gas-sensitive test chamber, and the response of the gas-sensitive detection systems to CO under the five concentrations of 20ppm, 40ppm, 60ppm, 80ppm and 100ppm is sequentially tested by adopting the same test method. The response-time curves of the gas-sensitive detection systems for different mass fraction ratios of the three polymers and the single-walled carbon nanotube to CO are shown in fig. 4-6. Experimental results show that after CO is introduced into the gas-sensitive test cavity, the resistances of the three gas-sensitive detection systems can rapidly rise, and with the continuous introduction of CO, the CO molecules adsorbed and desorbed on the surface of the material in unit time reach dynamic balance, and the resistance change of the gas-sensitive detection systems tends to be gentle and saturated. And when the response of the gas-sensitive detection system is stable, stopping introducing CO, and introducing nitrogen into the gas-sensitive test cavity for desorption. The gas sensitive detection system can increase the conductivity and rapidly decrease the resistance because gas molecules are desorbed from the sensitive material. It can be seen that the response curves of the three gas-sensitive detection systems are basically consistent, and the baseline shift phenomenon exists more or less. The response of the Sensor1 is larger than that of the Sensor2 and Sensor3, and the response of the gas sensing system increases with the increase of the introduced CO concentration. Sensor3, although exhibiting good recovery, responded slightly lower than both of the other two gas sensitive detection systems at the 5 concentrations tested and the magnitude of the response at each concentration differed little. The mass fraction ratio of polyaniline to single-walled carbon nanotubes in the sensitive material of Sensor1 is 3:1, and the mass fraction ratio in Sensor3 is 3: 3. Therefore, we believe that the lower the mass fraction of carbon nanotubes in the PANI/SWCNT composite film, the greater the response exhibited by the gas sensitive detection system.

FIG. 5 is a graph of the response-concentration of PANI/SWCNT composite films to CO for different SWCNT contents. The PANI/SWCNT composite films with three ratios show good linearity in five tested concentrations within 20ppm-100 ppm. The linearity R2 of the Sensor1 is 0.99, the linearity of the Sensor2 is 0.97, and the linearity of the Sensor3 is 0.98. Table 4-2 shows the response time T1, recovery time T2, and corresponding S for the three gas sensing systems at different CO concentrations. As can be seen from the table, at each concentration tested, sensor1 was greater than sensor2 and sensor 3. At 100ppm CO, the response of sensor1 was 0.28, while sensor2 and sensor3 were 0.21 and 0.101, respectively. The response time T1 of the three gas-sensitive detection systems is very small, but the recovery time T2 is very large, which indicates that the desorption of CO molecules from sensitive materials is difficult, and the main reason for the baseline drift of the gas-sensitive detection systems is also the reason.

FIG. 6 shows the reproducibility of the PANI/SWCNT (3:1) composite membrane to CO. The sensor1 was placed in the gas sensitive test chamber and a section of nitrogen gas was first introduced at a flow rate of 250cm3/min to remove interfering gases from the chamber. And after the resistance of the gas-sensitive detection system is stabilized, introducing 20ppm CO into the test cavity to observe the change of the resistance. And when the response is basically stable, stopping introducing CO, and continuing introducing nitrogen for desorption so as to desorb CO molecules from the sensitive material. The same operation is carried out on the gas-sensitive detection system for 5 times according to the same steps, and the practical result shows that after 20ppm of CO is introduced into the test chamber, the resistance of the gas-sensitive detection system is rapidly increased and gradually approaches to saturation. When the response is stable, nitrogen is introduced for desorption, the resistance value of the gas-sensitive detection system is rapidly reduced, but the resistance value is difficult to reach or approach the initial value of the resistance, and a certain baseline drift phenomenon exists. In the next several periods, the response to CO is basically consistent, but the resistance value of the gas-sensitive detection system can only be reduced to about 680 ohms when nitrogen is introduced for desorption, and the offset from the initial value of the resistance is about 26 ohms. For the latter few cycles of the test, we consider the fluctuations to be small.

FIG. 7 shows the selectivity of the PANI/SWCNT (3:1) composite membrane. It can be seen that the PANI/SWCNT composite film responds to 20ppm hydrogen as: 0.04; the response to 20ppm carbon dioxide was: 0.02; the response to 20ppm methane was: 0.08; the response to 20ppm of sulfur dioxide was: 0.1; the response to 20ppm of carbon monoxide is: 0.19. the response of the PANI/SWCNT composite membrane to CO is the largest under the same concentration, and the response shows obvious difference compared with other interference gases. This indicates that the PANI/SWCNT composite membrane is ideal as a carbon monoxide sensitive film.

FIG. 8 is a SEM surface topography of the PANI/SWCNT composite membrane. It can be seen from the figure that the carbon nanotubes are uniformly dispersed in the matrix of the polymer polyaniline, and play a good role in electrical conduction in the composite film. In the polymer/carbon nanotube composite gas-sensitive material, gas is adsorbed on the surface of a film, and the polymer generates a swelling effect, so that a conductive chain is destroyed, the conductivity of the material is reduced, and the resistance is increased. It can also be seen from the figure that the surface of the film is dispersed with pores, and the formation of the pores is favorable for the adsorption of gas molecules and improves the response of the sensitive film.

The specific technical scheme of the invention is as follows: the air spraying has the characteristics of simple operation, controllable film thickness, uniform film surface and the like. The coating process of the invention adopts an air-jet process, and the device of the air-jet process is shown in figure 1. The Polyaniline (PANI)/single-walled carbon nanotube (SWCNT) composite film is uniformly coated on the interdigital electrode by adopting an air-jet process. And finally, putting the device into a vacuum drying oven for drying treatment, and obtaining the needed PANI/SWCNT composite film after the solvent evaporation film is stable.

The gas sensitive test platform mainly comprises two parts: gas distribution system and data acquisition system. The gas distribution system consists of a gas cylinder, an MT50-4J gas distribution device and a gas-sensitive test cavity. The data acquisition system comprises Keithley2700, a GPIP card, a back-end computer, corresponding special acquisition software and the like. In the actual test process, firstly, a gas cylinder, a gas distribution device and a test cavity are connected through a gas guide tube, an interdigital electrode is fixed in the test cavity, then the required gas concentration is distributed through the MT50-4J gas distribution device, gas is introduced into the test cavity through the gas guide tube to fully contact with a film to react, and at the moment, the resistance changes. The change of the resistance can be collected into a back-end computer by Keithley2700 in real time, and the concentration of the gas to be detected can be detected by observing the real-time change of the resistance. After the full adsorption reaction, the resistance tends to be stable and unchanged, and then the carbon monoxide is stopped to be introduced and the pure nitrogen is introduced into the gas-sensitive test cavity for desorption. The resistance of the interdigital electrode is then slowly restored or approached to the previous value.

The novel gas-sensitive film prepared by adopting the gas-jet film forming mode shows excellent response to carbon monoxide gas at room temperature. A comparison method is adopted to verify that the gas-sensitive property of the composite film of the single-walled carbon nanotube and the polyaniline is superior to that of the traditional carbon nanotube film. The repeatability of the Polyaniline (PANI)/single-walled carbon nanotube (SWCNT) composite membrane is tested, and the excellent gas-sensitive characteristic of the gas-sensitive film detection system to carbon monoxide is verified.

The invention achieves the following significant beneficial effects:

Any other suitable modifications can be made according to the technical scheme and the conception of the invention. All such alternatives, modifications and improvements as would be obvious to one skilled in the art are intended to be included within the scope of the invention as defined by the appended claims.

Claims

1. A carbon monoxide detection method based on a polymer composite film is characterized by comprising the following steps:

2. The method for detecting carbon monoxide based on a polymer composite film according to claim 1, wherein: adopt even coating of gas spraying technology on resistance type gas sensor, include:

3. The method for detecting carbon monoxide based on a polymer composite film according to claim 2, wherein: the gas distribution system comprises: the gas cylinder, the gas distribution device and the gas-sensitive testing cavity are connected through a gas guide pipe.

4. The method for detecting carbon monoxide based on a polymer composite film according to claim 3, wherein: the data acquisition system includes: keithley2700 and a back end computer, wherein the Keithley2700 is used for acquiring the resistance change data in real time and transmitting the resistance change data to the back end computer.

5. The method for detecting carbon monoxide based on a polymer composite film according to claim 1, wherein: the mass fraction of the carbon nanotubes in the carbon nanotube/polymer composite film is less than the mass fraction of the polymer in the carbon nanotube/polymer composite film.

6. The method for detecting carbon monoxide based on a polymer composite film according to claim 1, wherein: the resistance type gas sensor is an interdigital electrode.

7. A polymer composite film based carbon monoxide detection system, comprising:

8. The polymer composite film based carbon monoxide detection system according to claim 7, wherein: the compound film adopts the even coating of gas spraying technology on resistance type gas sensor, includes: