CN114624290B - Preparation and application of a sensing membrane for alkaline gas sensor - Google Patents

Abstract

The present invention provides a preparation and application of a sensing film for an alkaline gas sensor, belonging to the technical field of gas sensors. The sensing film material is a polypyrrole aerogel microporous material; polypyrrole can be grown in situ to form an aerogel skeleton without a template. The triethylamine sensing film based on the polypyrrole aerogel material prepared by the present invention has high sensitivity, high selectivity, strong repeatability and good stability. Room temperature sensing greatly reduces the power consumption of the sensor during use and improves the portability of the sensor. It has important practical and research value in this technical field.

Description

Preparation and application of a sensing membrane for alkaline gas sensor

Technical Field

The invention belongs to the technical field of gas sensors, and in particular relates to a nano composite material that can be used as an alkaline gas sensing membrane.

Background Art

As people's quality of life improves, the requirements for industrial production and living conditions are getting higher and higher, and people's demand for gas sensors is also increasing. The research and development of gas sensors, especially the research on toxic and harmful gas sensors, has developed rapidly. Among alkaline gases, triethylamine is flammable, explosive, toxic, and has a strong ammonia odor. It is a common solvent, catalyst and raw material in the organic synthesis industry. Triethylamine is flammable, and its vapor can form an explosive mixture with air. It can cause combustion and explosion when it encounters open flames and high heat; it can react strongly with oxidants; its vapor is heavier than air and can spread to a considerable distance at a lower level. It will catch fire and burn back when it encounters a fire source; it is highly corrosive. At present, gas sensors for detecting triethylamine have been widely used in municipal, fire protection, gas, telecommunications, petroleum, chemical, coal, electricity, pharmaceutical, metallurgy, coking, storage and transportation and other industries. Commonly used metal oxide materials (such as tungsten oxide, molybdenum oxide, tin oxide, etc.), but the detection limit is high, which is far from the detection limit of 10ppm for triethylamine in air specified by the Occupational Safety and Health Administration of the United States. How to improve the sensitivity of triethylamine detector and reduce the detection limit is the key to the research of triethylamine gas sensor.

In recent years, research on organic conductive polymer materials has been very active, and their research on the preparation and performance improvement of sensors has also received attention. Before and after gas circulation, the conductive polymer material undergoes proton acid doping and dedoping processes, and its resistance will change significantly, thereby realizing the function of gas sensing. Since the sensitivity and selectivity of alkaline gas sensors are somewhat different from the specified detection limit, designing the morphology and performance of polymer conductive materials to improve the sensitivity and selectivity of sensors has become one of the important directions of sensor research and has developed very rapidly. Yang Wei and his team used In ₂ O ₃ nanotubes and nanowires with surface defects as sensing materials, which can achieve 0.1ppm ammonia detection, but it needs to be carried out at a high temperature of 300℃; Cao Bingqiang's team used Au/ZnO/SnO ₂ nanorods as materials to achieve 2ppm triethylamine detection at 40℃, but the cost is expensive and not suitable for actual production. Wu Zhongshuai's team prepared porous polypyrrole materials, but added templates in the middle, so it needs to be burned out later, and the residual carbon deposits have a great influence on the sensing effect. The present invention uses polypyrrole conductive aerogel as a sensing material, has simple preparation steps, low cost, and does not use any template agent, so it does not need to be burned and removed, and no other components remain. Aerogel has a high specific surface area due to its typical three-dimensional structure; in addition, the presence of a macroporous structure in the gel is conducive to the adsorption and desorption of gas, greatly improving the sensitivity of the sensor and reducing the sensing and recovery time, thereby achieving high selectivity, high stability, and high sensitivity detection of triethylamine.

Summary of the invention

In order to solve the above problems, the purpose of the present invention is to prepare an alkaline gas sensor that can eliminate the interference of volatile organic compounds, has high selectivity and high sensitivity even at room temperature, and has good response recovery and repeatability, and can meet the detection needs of trace triethylamine at room temperature and in the presence of multiple interfering gases.

The technical solution of the present invention is: a sensing membrane for an alkaline gas sensor, wherein the sensing membrane adopts a polypyrrole aerogel macroporous material that is in-situ polymerized at room temperature; the thickness of the sensing membrane is 10-1000nm; the sensing membrane is characterized in that: the polypyrrole aerogel structure is a macroporous aerogel structure, the diameter of the pores is 0.02-100μm, the porosity is 10-80%, and the aerogel skeleton is a naturally grown polypyrrole skeleton, with a diameter of 0.005-20μm.

The working temperature of the sensor is 0-100° C. The principle is that before and after the flow of triethylamine, the polypyrrole aerogel material undergoes proton acid doping and dedoping processes, and its resistance changes significantly.

The preparation method of the sensing film is as follows:

(1) Preparation of polypyrrole aerogel by in-situ polymerization: Pyrrole is added to ethanol (preferably the volume ratio of pyrrole to ethanol is 1:1-5000) and stirred without adding any template to form a uniform mixed solution, referred to as solution A;

An oxidant (preferably ferric chloride hexahydrate, ammonium persulfate, benzoyl peroxide, etc.) and an acidifying agent (preferably hydrochloric acid, sulfuric acid, sulfosalicylic acid, etc.) are successively added to ionized water (preferably the molar ratio of pyrrole monomer, oxidant, and acidifying agent is 1:0.01-3:0.05-500, and the molar concentration of pyrrole monomer in the final mixed solution is 0.05-5M) to obtain solution B.

(2) adding solution A to solution B and mixing them evenly by ultrasonication (the volume ratio of solution A to solution B is 1:10), and allowing the polymerization to grow for 2-24 hours at a low temperature of -10 to 80°C, so that pyrrole polymerizes to form polypyrrole hydrogel;

(3) Soak and wash with deionized water several times to remove excess impurities;

(4) sucking out the liquid, freeze-drying it using a freeze dryer, and taking it out after 72 hours to obtain polypyrrole aerogel;

The invention uses polypyrrole aerogel material as a sensitive element, and coats the sensitive element on a ceramic tube substrate with interdigitated gold electrodes on the surface to form a sensing film, thereby preparing a resistive thin film triethylamine sensor; the sensor signal is a change in the resistance value of the polypyrrole aerogel material film under air and triethylamine gas atmosphere with air as the background.

The polypyrrole aerogel material has a macroporous structure, which is similar to a three-dimensional nanostructure and has a high specific surface area. In addition, the polypyrrole aerogel material is doped with concentrated hydrochloric acid during synthesis, and the acidified polypyrrole has an excellent response effect to amines. When the gas to be measured flows, it is converted into an eigenstate, thereby increasing the resistance. The macroporous aerogel network structure, as a structure that can greatly improve the gas adsorption performance of the material, also plays an important role in improving the sensing performance of the material. The polypyrrole aerogel material of the present invention can be conveniently fixed on an electrode pair and a substrate, such as by coating, lamination, etc. to construct a sensor.

The present invention has the following advantages:

(1) The prepared polypyrrole aerogel material has a macroporous three-dimensional network structure and a large specific surface area, which enables the sensor to have high sensitivity, rapid response and good response reversibility at room temperature, solving the problem that semiconductor gas sensor membranes usually require high temperature working conditions.

(2) Compared with traditional macroporous materials, the sensing membrane material of the present invention does not add any template agent during the preparation process, thereby eliminating the influence of carbon deposits on the sensing effect and achieving low-temperature preparation.

(3) Compared with the traditional semiconductor gas sensor membrane, the sensor membrane material of the present invention can be fixed on the electrode pair and the substrate by a simple method (such as drop coating, spin coating, etc.). The film forming method is simple and the processability is good, which is conducive to processing on electrodes of different shapes, thus solving the problem that the traditional gas sensor membrane requires high temperature sintering and complex processing.

(4) Compared with the synthesis process of traditional semiconductor materials, this synthesis process basically does not involve high-temperature operation, is simple to operate, and is convenient for large-scale preparation.

(5) Compared with the existing triethylamine sensor membrane, the sensor of the present invention can eliminate the interference of volatile organic compounds and amine similar substances, has high selectivity and high sensitivity both at room temperature and high temperature, and has good response recovery and repeatability, and can meet the detection requirements of triethylamine at room temperature and in the presence of multiple interfering gases.

(6) The sensor membrane of the present invention has a wide operating temperature range and can work at room temperature, which greatly reduces power consumption and does not require additional heating equipment. It has the advantages of energy saving and portability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the microstructure of the skeleton of the sensing membrane material prepared in Example 1.

FIG. 2 is a response recovery curve of the sensing film prepared in Example 1 to 20 ppm triethylamine at room temperature

FIG3 is a dynamic response curve of the sensing membrane prepared in Example 1 to different concentrations of triethylamine at room temperature.

FIG. 4 is a curve showing the response sensitivity of the sensing film prepared in Example 1 to triethylamine at room temperature as a function of gas concentration.

FIG5 is a repeatability curve of the sensing film prepared in Example 1 in response to 20 ppm triethylamine at room temperature.

FIG6 is a comparison diagram of the sensing signals of the sensing membrane prepared in Example 1 to triethylamine and various interfering gases at room temperature.

FIG. 7 is a curve showing the change in the sensing signal of triethylamine of the sensing film prepared in Example 1 at room temperature and different humidity conditions.

DETAILED DESCRIPTION

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

Example 1

The preparation of the polypyrrole aerogel material sensing film includes the following steps:

0.75 mL of pyrrole was added to 1.5 mL of ethanol and ultrasonically mixed for 30 minutes to form a uniform mixed solution, which is solution A; 1.0 g of ferric chloride hexahydrate and 0.025 mL of concentrated hydrochloric acid were added to 15 mL of deionized water, and ultrasonically mixed to form solution B. Solution A was slowly added to solution B for ultrasonic dispersion for 10 minutes, and the solution was allowed to stand at room temperature for polymerization for 8 hours to obtain a polypyrrole hydrogel. It was soaked and washed three times with deionized water, each time for 3 hours, to remove excess impurities. The liquid was then sucked out and freeze-dried with a freeze dryer. After 72 hours, it was taken out to obtain a polypyrrole aerogel. The skeleton structure of the obtained material is shown in Figure 1.

Example 2

Construction of triethylamine sensor

In order to test the performance of the sensing membrane, a triethylamine sensor was built, which consists of a sensing membrane, an electrode pair, and an insulating substrate. Among them, the insulating substrate material is ceramic, the shape is a hollow cylinder, and the dimensions are: outer diameter 1.2mm, inner diameter 1.0mm, length 4.0mm; the electrodes at both ends are interdigitated gold electrodes; the sensing membrane is the sensing membrane described in Example 1; two interdigitated gold electrodes are fixed on the outer surface of the ceramic substrate at an interval (about 3.0mm), the sensing membrane is coated on the ceramic substrate between the interdigitated gold electrodes and the interdigitated gold electrodes, and the interdigitated gold electrodes have leads for transmitting electrical signals.

The polypyrrole aerogel material described in Example 1 was drop-coated on the surface of the interdigitated gold electrode with a ceramic substrate, and the sensing film thickness was 200 nm. The material was air-dried at room temperature to obtain a room temperature triethylamine sensor based on the polypyrrole aerogel material.

Sensor testing: A digital multimeter was used to measure the change in resistance of the sensor in air and in an atmosphere of triethylamine with different concentrations of air as the background, which was taken as the sensor signal.

The polypyrrole aerogel-based sensor has an obvious response to 50 ppm triethylamine, and the response recovery time is extremely fast, as shown in FIG. 2 .

The dynamic response curves of the triethylamine sensor to different concentrations of triethylamine at room temperature are shown in Figure 3. It can be seen that the sensor has a rapid response to different concentrations of triethylamine and is extremely sensitive, the signal variation amplitude is large, and the response has good reversibility, which proves that the sensor has excellent application prospects in triethylamine detection and early warning.

The response sensitivity curve of the triethylamine sensor to different concentrations of triethylamine at room temperature is shown in Figure 4. It can be seen that the sensor has good linearity to a certain concentration of triethylamine at room temperature and can perform rough quantitative detection. The response value for 100ppm triethylamine reaches 0.26.

The response repeatability curve of the prepared triethylamine sensor based on polypyrrole aerogel material to 70 ppm triethylamine at room temperature is shown in Figure 5. It can be seen that after multiple cycle tests at room temperature, the shape of its response curve remains almost unchanged, indicating that the sensor has good response repeatability.

The comparison of the sensing signals of triethylamine and various interfering gases of the prepared triethylamine sensor based on polypyrrole aerogel material at room temperature is shown in Figure 6. It can be seen that the developed sensor exhibits good triethylamine sensing performance and excellent selectivity at room temperature.

The response sensitivity change curve of the triethylamine sensor to 100 ppm triethylamine at room temperature and different humidity is shown in Figure 7. It can be seen that the developed sensor has a better response effect when the humidity is higher, but it also has an obvious response at low humidity, and can be applied to complex environment detection.

Example 3

The preparation method described in Example 1, wherein the synthesis time is 6h, 8h, and 12h, respectively, and the porosity of the prepared polypyrrole composite material is 68%, 57%, and 55%, respectively. According to the method in Example 2, a sensor is prepared, and the change of the resistance value of the sensor in air and in a 100ppm triethylamine atmosphere with air as the background is measured by a digital multimeter as the sensor signal. The sensor responses of the three sensors to triethylamine are 0.24, 0.28, and 0.30, respectively, and the response times are 54s, 67s, and 78s, respectively. The developed sensors all show good sensing performance to triethylamine at room temperature.

Example 4

The preparation method described in Example 1, wherein 15 mL of pyrrole monomer is added to 100 mL of ethanol, the molar ratio of pyrrole monomer, ferric chloride, and hydrochloric acid is 1:0.02:10, and the mixture is stirred at room temperature for 4 hours. The obtained polypyrrole aerogel material has a porosity of 15%. The triethylamine sensor is prepared by the method described in Example 2 to test the performance of the sensing membrane, and the response sensitivity to 100 ppm triethylamine is 0.11.

Example 5

The preparation method described in Example 1, wherein 8 mL of pyrrole monomer is added to 20 mL of ethanol, the molar ratio of pyrrole monomer, ferric chloride, and hydrochloric acid is 1:2:20, and the mixture is stirred at room temperature for 6 hours. The obtained polypyrrole aerogel material has a porosity of 25%. The triethylamine sensor is prepared by the method described in Example 2 to test the performance of the sensing membrane, and the response sensitivity to 100 ppm triethylamine is 0.31.

Example 6

The preparation method described in Example 1, wherein 2 mL of pyrrole monomer is added to 2 mL of ethanol, the molar ratio of pyrrole monomer, ferric chloride, and hydrochloric acid is 1:2:100, and the mixture is stirred at room temperature for 20 hours. The obtained polypyrrole aerogel material has a porosity of 13%. The triethylamine sensor prepared by the method described in Example 2 is used to test the performance of the sensing membrane. The response sensitivity to 100 ppm triethylamine is 0.16, the response sensitivity to 100 ppm diethylamine is 0.26, and the response sensitivity to 100 ppm ammonia is 0.06.

The sensing membrane material of the present invention is a polypyrrole aerogel microporous material; polypyrrole can be grown in situ to form an aerogel skeleton without a template. The triethylamine sensing membrane based on the polypyrrole aerogel material prepared by the present invention has high sensitivity, high selectivity, strong repeatability and good stability. Room temperature sensing greatly reduces the power consumption of the sensor during use and improves the portability of the sensor, which has important practical and research value in the field of this technology.

Claims (5)

1. A method of producing a sensing film for an alkaline gas sensor, comprising at least the steps of:

(1) The polypyrrole aerogel is prepared by adopting an in-situ polymerization method: adding pyrrole into ethanol, stirring, and forming a uniform mixed solution without adding any template agent, namely solution A; sequentially adding an oxidant and an acidifying reagent into ionized water to obtain a solution B;

(2) Adding the solution A into the solution B, and uniformly mixing by ultrasonic, wherein the volume ratio of A, B is 1:10, standing and polymerizing for 2-24h in a low-temperature environment of-10-80 ℃ to polymerize pyrrole to form polypyrrole hydrogel;

(3) Soaking and cleaning for multiple times by using deionized water to remove redundant impurities;

(4) Sucking out the liquid, freeze-drying by a freeze dryer, and taking out after 72 h to obtain polypyrrole aerogel;

The sensing film is made of polypyrrole aerogel macroporous materials; the thickness of the sensing film is 10-1000 nm; the polypyrrole aerogel structure is a macroporous aerogel structure, the diameter of the pores is 0.02-100 mu m, and the porosity is 10-80%;

The prepared sensing film is used for a semiconductor triethylamine gas sensor.

2. The method for preparing a sensing film according to claim 1, wherein the aerogel skeleton is a polypyrrole natural growth skeleton, and the diameter is 0.005-20 μm.

3. The method for producing a sensor film according to claim 1, wherein the operating temperature of the sensor is 0 to 100 ℃.

4. The method according to claim 1, wherein,

Pyrrole to ethanol volume ratio 1:1-5000;

the oxidant is ferric chloride hexahydrate, ammonium persulfate or benzoyl peroxide;

the acidifying reagent is hydrochloric acid, sulfuric acid or sulfosalicylic acid;

The actual molar ratio of pyrrole monomer, oxidant and acidification is as follows: 1:0.01-3:0.05-500, and the molar concentration of pyrrole monomer in the final mixed solution is 0.05-5M.

5. The method of claim 1, wherein the sensor has a triethylamine selectivity of 95% or more relative to common VOCs gas; the stability of six continuous measurements is excellent, and the deviation is less than or equal to 5%.