An ammonia gas sensor and its preparation method

Abstract

The present invention discloses an ammonia gas sensor, which includes electrodes, and a sensitive layer formed by covering a PEDOT:PSS / CNF composite material on the surface of the electrodes. The ammonia gas sensor disclosed by the present invention still has high sensitivity to trace (sub-ppm level concentration) ammonia in a medium-high humidity environment, while pure PEDOT:PSS devices do not have this phenomenon; at the same time, the detection limit of ammonia for the ammonia gas sensor disclosed by the present invention can reach 200 ppb; compared with the currently reported NH3 detection work based on conductive polymers, the ammonia gas sensor disclosed by the present invention has shorter response and recovery times, and both the response time and the recovery time are controlled below 6 s, achieving ultra-fast response and recovery of the device, and overcoming the deficiencies in sensitivity and response recovery speed when a single conductive polymer detects NH3; in addition, the ammonia gas sensor disclosed by the present invention has the characteristic of high selectivity for ammonia, and the resistance value of the device does not show obvious fluctuations in the presence of gas interference, and the performance is stable.

Description

Technical Field

[0001] The present invention relates to the technical field of ammonia detection, and particularly relates to an ammonia gas sensor and a preparation method thereof. Background Art

[0002] Ammonia (NH 3 ) as a toxic gas can cause serious damage to human skin, eyes and respiratory system. Due to the wide application of ammonia in the fields of semiconductors, industrial safety, agricultural production, biomedicine, etc., the real-time detection of ammonia, especially the detection of low-concentration ammonia, has great practical significance.

[0003] Current resistive NH 3 sensors are mainly based on metal oxide sensitive materials and mostly require high-temperature heating, which will increase power consumption and is not conducive to device miniaturization; at the same time, NH 3 sensors based on conductive polymers, although they can work at room temperature without heating, most of them have very slow response and recovery speeds and low sensitivity.

[0004] Currently, gas sensors based on conductive polymers / two-dimensional modification materials have attracted people's attention due to their excellent environmental stability and significantly improved sensitivity. For example, the invention patent with the application number 201910849934.5 discloses a high-efficiency ammonia sensor based on a polystyrene sulfonic acid-doped polyaniline composite flexible film and a preparation method thereof, which realizes highly selective detection of ammonia at room temperature by using the ammonia-sensitive characteristics of polyaniline and the high conductivity of polystyrene sulfonic acid. For example, the invention patent with the application number 201910445405.9 discloses a Ti 3 C 2 Tx / polyaniline composite film ammonia sensor and its preparation method and application. This invention uses the sufficient ammonia-sensitive functional groups and large specific surface area on the surface of Ti 3 C 2 T x / polyaniline material to prepare a highly sensitive and highly selective ammonia sensor.

[0005] However, existing ammonia detection methods are difficult to achieve highly sensitive detection, fast response and recovery of low-concentration (sub-ppm level concentration) ammonia gas at room temperature, and are generally greatly affected by humidity. Therefore, designing an ammonia sensor that can adapt to medium and high humidity, achieve ultra-fast response and recovery to low-concentration ammonia, and at the same time have high selectivity and high sensitivity has great practical application value. Summary of the Invention

[0006] The object of the present invention is to provide an ammonia gas sensor and a preparation method thereof, so as to solve the technical problems that the existing ammonia detection methods are difficult to achieve highly sensitive detection, rapid response and recovery of ammonia gas at sub-ppm levels at room temperature.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] An ammonia gas sensor includes electrodes, and a sensitive layer formed by covering the surface of the electrodes with a PEDOT:PSS / CNF composite material; the PEDOT:PSS / CNF composite material is obtained by preparing a PEDOT:PSS / CNF composite material solution in which the polymer PEDOT:PSS and carbon nanofibers CNF are uniformly dispersed in deionized water.

[0009] Preferably, in the PEDOT:PSS / CNF composite material, the weight ratio range of the polymer PEDOT:PSS to the carbon nanofibers CNF is 0.5:1 to 5:200.

[0010] Preferably, in the PEDOT:PSS / CNF composite material, the weight ratio of the polymer PEDOT:PSS to the carbon nanofibers CNF is 1:1.

[0011] Preferably, the calculation formula for the response value of the ammonia sensor to a specific ammonia concentration is: (R - R 0 ) / R 0 ;

[0012] In the formula: R is the stable resistance value at a specific ammonia concentration, and R 0 is the initial resistance value of the device.

[0013] Preferably, the electrodes are planar interdigital electrodes.

[0014] The present invention also discloses a preparation method of an ammonia gas sensor. Using the above-mentioned ammonia gas sensor, it is characterized by including the following steps:

[0015] Step 1: Uniformly disperse the polymer PEDOT:PSS and carbon nanofibers CNF in deionized water to prepare a PEDOT:PSS / CNF composite material solution;

[0016] Step 2: Cover the surface of the electrode device with the obtained PEDOT:PSS / CNF composite material solution to prepare an electrode device covered with a PEDOT:PSS / CNF composite material thin film;

[0017] Step 3: Dry the electrode device with the PEDOT:PSS / CNF composite film, and finally fabricate a PEDOT:PSS / CNF ammonia gas sensor.

[0018] Preferably, ultrasonic waves are applied to uniformly disperse the polymer PEDOT:PSS and carbon nanofibers CNF in deionized water. The ultrasonic frequency is 20 kHz - 23 kHz, and the ultrasonic time is 60 - 180 min.

[0019] Preferably, in Step 1, in the PEDOT:PSS / CNF composite solution, the weight ratio range of the polymer PEDOT:PSS to the carbon nanofibers CNF is 0.2:1 - 5:200.

[0020] Preferably, the electrode device described in Steps 2 and 3 is a planar interdigital electrode device.

[0021] The present invention has the following beneficial effects:

[0022] 1. The ammonia gas sensor based on the composite material PEDOT:PSS / CNF disclosed in the present invention still has high sensitivity to trace (sub-ppm level concentration) ammonia in a medium to high humidity environment, while the pure PEDOT:PSS device does not have this phenomenon; and the detection limit of the ammonia gas sensor based on the composite material PEDOT:PSS / CNF for ammonia can reach 200 ppb.

[0023] 2. Compared with the current reported detection work based on conductive polymers for NH 3 detection, the response and recovery times of the ammonia gas sensor based on the composite material PEDOT:PSS / CNF disclosed in the present invention are shorter. Both the response time and the recovery time are controlled below 6 s, achieving ultra-fast response and recovery of the device, and overcoming the deficiencies in sensitivity and response recovery speed when a single conductive polymer detects NH 3 ;

[0024] 3. The ammonia gas sensor based on the composite material PEDOT:PSS / CNF disclosed in the present invention has the characteristic of high selectivity to ammonia. When there is gas interference, the resistance value of the device does not show obvious fluctuations, and the performance is stable.

[0025] 4. The device preparation process is simple, and the detection process does not require heating and can be carried out at room temperature, which can greatly reduce power consumption. Description of the Drawings

[0026] In order to make the objectives, technical solutions, and advantages of the invention clearer, the present invention will be further described in detail below with reference to the drawings, where:

[0027] Figure 1SEM surface morphology diagram of the PEDOT:PSS / CNF composite material of the present invention;

[0028] Figure 2 SEM surface morphology diagram of the pure PEDOT:PSS device of the embodiment of the present invention;

[0029] Figure 3 Response and recovery times of the pure PEDOT:PSS device and the PEDOT:PSS / CNF composite material device of the embodiment of the present invention to 1 ppm ammonia;

[0030] Figure 4 Real-time response change diagram and gas selectivity of the ammonia gas sensor based on the composite material PEDOT:PSS / CNF of the embodiment of the present invention at different humidities;

[0031] Figure 5 Detection range of ammonia by the ammonia gas sensor based on the composite material PEDOT:PSS / CNF of the embodiment of the present invention. Specific implementation manners

[0032] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0033] It should be noted that like reference numerals and letters denote like items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship in which the inventive product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance. In addition, terms such as "horizontal" and "vertical" do not mean that the components are required to be absolutely horizontal or hanging, but can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined. In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "arranged", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] The technical problem to be solved by the present invention is the technical problem that the existing ammonia detection methods are difficult to achieve highly sensitive detection, rapid response and recovery of low-concentration (sub-ppm level concentration) ammonia gas at room temperature.

[0035] Based on the above technical problems to be solved, the present invention discloses an ammonia gas sensor, including electrodes, and a sensitive layer formed by covering the surface of the electrodes with a PEDOT:PSS / CNF composite material. The PEDOT:PSS / CNF composite material is obtained by preparing a PEDOT:PSS / CNF composite material solution in which the polymer PEDOT:PSS and carbon nanofibers CNF are uniformly dispersed in deionized water.

[0036] The PEDOT:PSS is an aqueous solution of a polymer, and its aqueous solution has a very high conductivity. The PEDOT:PSS is composed of two substances, PEDOT and PSS. PEDOT is a polymer of EDOT (3,4-ethylenedioxythiophene monomer), and PSS is polystyrene sulfonate. The combination of these two substances greatly improves the solubility of PEDOT. The aqueous solution conductor is mainly used in the hole transport layer of organic light-emitting diodes (OLEDs), organic solar cells, organic thin-film transistors, supercapacitors, etc.

[0037] The CNF mentioned refers to carbon nanofiber, which is a synthetic fiber. Its component is nylon. However, after nylon is made into ultrafine fibers with a diameter of dozens of nanometers (1 nanometer is one billionth of a meter), it has almost the same moisture absorption performance as cotton fibers.

[0038] The working principle of the present invention is as follows: For the ammonia sensor of the present invention, the SEM surface morphology diagram of the PEDOT:PSS / CNF composite material device is as Figure 1 shown. By covering the sensitive layer formed by the PEDOT:PSS / CNF composite material on the electrode surface, the detection limit of ammonia concentration can be greatly reduced. The principle is as follows: When one-dimensional CNF is added to PEDOT:PSS, it not only weakens the agglomeration phenomenon of a single polymer material, but also promotes the formation of a networked porous composite film structure, which is beneficial to the transfer and diffusion of gas molecules and improves the response recovery speed; the rich adsorption sites of CNF itself increase the adsorption capacity of NH 3 molecules, realizing highly sensitive detection at low concentrations.

[0039] In addition, for the ammonia sensor of this solution, the response value of the PEDOT:PSS / CNF composite material device to ammonia is significantly higher under medium and high humidity than that under dry air. The medium and high humidity refers to the humidity range between 42%RH and 69%RH. This is because as the humidity in the gas environment rises, water molecules with the same reducibility will also provide electrons to the sensitive layer of the sensor. At the same time, it will also enhance the adsorption effect of ammonia, thereby greatly enhancing the response of the sensor to ammonia.

[0040] As a preferred solution, in the PEDOT:PSS / CNF composite material, the weight ratio range of PEDOT:PSS to CNF is 0.2:1 to 5:200.

[0041] In this way, when the weight ratio range of PEDOT:PSS to CNF is 0.5:1 to 5:200, the manufactured ammonia sensor has high sensitivity to trace (sub-ppm level concentration) ammonia and can effectively detect it.

[0042] As a preferred embodiment, the weight ratio of PEDOT:PSS / CNF is 1:1, and the relative mass fraction of PEDOT:PSS is 0.05 wt% - 2.5 wt%.

[0043] As a preferred embodiment, the calculation formula for the response value of the ammonia sensor to a specific ammonia concentration is: (R - R 0 ) / R 0 ;

[0044] In the formula: R is the stable resistance value at a specific ammonia concentration, and R 0 is the initial resistance value of the device.

[0045] As a preferred embodiment, the electrode is a planar interdigital electrode.

[0046] The present invention also discloses a preparation method of an ammonia gas sensor. Using the above-mentioned ammonia gas sensor, it is characterized by including the following steps:

[0047] Step 1: Uniformly disperse PEDOT:PSS and CNF in deionized water to prepare a PEDOT:PSS / CNF composite material solution;

[0048] Step 2: Cover the surface of the electrode device with the obtained PEDOT:PSS / CNF composite material solution to prepare an electrode device covered with a PEDOT:PSS / CNF composite material thin film;

[0049] Step 3: Dry the electrode device with a PEDOT:PSS / CNF composite material thin film to finally prepare a PEDOT:PSS / CNF ammonia gas sensor.

[0050] As a preferred embodiment, in Step 1, use ultrasonic waves to uniformly disperse PEDOT:PSS and CNF in deionized water. The ultrasonic frequency is 20 kHz - 23 kHz, and the ultrasonic time is 120 min.

[0051] As a preferred embodiment, in Step 1, in the PEDOT:PSS / CNF composite material solution, the weight ratio range of PEDOT:PSS to CNF is 0.2:1 - 5:200.

[0052] As a preferred embodiment, in Step 2, use the drop coating method to cover the surface of the electrode device with the obtained PEDOT:PSS / CNF composite material solution. This can simply and effectively cover the PEDOT:PSS / CNF composite material on the surface of the electrode device.

[0053] As a preferred embodiment, in Step 3, dry the electrode device with a PEDOT:PSS / CNF composite material thin film by vacuum drying and heating (60 °C) for 2 hours.

[0054] As a preferred solution, the electrode device described in Step 2 and Step 3 is a planar interdigital electrode device. Example

[0055] The present invention discloses an example for verifying the effect of an ammonia gas sensor prepared by using the preparation method of the above ammonia gas sensor. The device used in this experiment is a resistive gas sensor based on interdigital electrodes, and the sensitive layer is a PEDOT:PSS / CNF composite material. PEDOT:PSS is used as the sensitive layer of the comparative example for effect verification.

[0056] First, the solution method is adopted. Ultrasonic waves with a frequency of 20 kHz to 23 kHz are used to ultrasonically disperse PEDOT:PSS and CNF evenly in deionized water for 120 min to prepare a PEDOT:PSS / CNF composite material solution. Among them, the weight fraction ratio of PEDOT:PSS / CNF is 1:1, and the relative mass fraction of PEDOT:PSS is 0.05 wt% to 2.5 wt%. The obtained solution is drop-coated on the surface of the planar interdigital electrode device. Then, the film-forming device is vacuum-dried and heated (60 °C) for 2 hours, and finally a PEDOT:PSS / CNF ammonia gas sensor is prepared.

[0057] Next, the performance of the prepared PEDOT:PSS / CNF ammonia gas sensor is tested.

[0058] (1) Performance comparison of ammonia gas sensors made of pure PEDOT:PSS devices and PEDOT:PSS / CNF composite material devices respectively.

[0059] The SEM surface morphology diagrams of the PEDOT:PSS / CNF composite material and the pure PEDOT:PSS device are as Figure 1 and Figure 2 shown.

[0060] Among them, the PEDOT:PSS / CNF composite material adopts two weight fraction ratios, namely, the weight fraction ratio of PEDOT:PSS / CNF is 1:1 and the weight fraction ratio of PEDOT:PSS / CNF is 0.5:1 respectively.

[0061] The response and recovery times of the pure PEDOT:PSS device and the PEDOT:PSS / CNF composite material device to 1 ppm ammonia are as Figure 3As shown, the response time of the pure PEDOT:PSS device to 1 ppm ammonia gas is more than 1 minute. In contrast, the response times of the PEDOT:PSS / CNF composite devices with two weight ratios to 1 ppm ammonia gas are both reduced to within 5 s, achieving an ultra-fast response to the target gas ammonia. This indicates that the PEDOT:PSS / CNF composite device has a good response speed to 1 ppm ammonia gas.

[0062] (2)Effect of humidity on the PEDOT:PSS / CNF ammonia gas sensor.

[0063] As Figure 4 shown in (a), the response value of the PEDOT:PSS / CNF composite device to ammonia gas is significantly higher under medium and high humidity than that under dry air. Under dry air, the device has a low response to NH 3 and long response and recovery times.

[0064] As Figure 4 shown in (b) and Figure 4 (c), under medium and high humidity, which refers to the humidity range between 42%RH and 69%RH, the response of the PEDOT:PSS / CNF composite device increases significantly. After repeated response and recovery tests, it is found that the response time and recovery time of the PEDOT:PSS / CNF composite device under medium and high humidity are both reduced to about 5 s, showing good performance.

[0065] Among them, the calculation formula for the response value of the ammonia sensor to a specific ammonia concentration is: (R - R 0 ) / R 0 ; where: R is the stable resistance value under a specific ammonia concentration, and R 0 is the initial resistance value of the device. The response time is defined as the time when the resistance value rises to 90% * R after contacting the target gas.

[0066] (3)Detection limit detection of the PEDOT:PSS / CNF composite device for ammonia gas.

[0067] As shown in Figure 5 , the PEDOT:PSS / CNF composite device can achieve linear detection of sub-ppm level ammonia gas, and both the response and recovery times maintain excellent indicators.

[0068] (4)Selective detection test of the PEDOT:PSS / CNF ammonia gas sensor.

[0069] The gas sensor covered with the PEDOT:PSS / CNF composite material is placed in an environment with NO, NO 2 , H 2, SO 2 , CO, CO 2 Under the scenarios of gas interferences such as acetone and methanol, the detection values of the PEDOT:PSS / CNF ammonia gas sensor did not show obvious fluctuations, indicating its high selectivity for ammonia. The high selectivity of the PEDOT:PSS / CNF composite device also becomes one of its advantages.

[0070] The following results can be obtained from the above embodiments: At medium and high humidity, the PEDOT:PSS / CNF composite device realizes ultra-fast detection of trace ammonia. The optimal detection effect can be achieved when the weight fraction ratio distribution of PEDOT:PSS and CNF in the composite solution takes 1 / 1; for example, at 55%RH, the PEDOT:PSS / CNF ammonia gas sensor can accurately detect ammonia with a concentration of 200ppb - 3000ppb, and the long-term stability can reach 33 days. During the validity period, when 1ppm ammonia passes through, the device response value is stable at 5% - 8%. The high selectivity of the PEDOT:PSS / CNF composite device in the face of NO, NO 2 , H 2 , SO 2 , CO, CO 2 , acetone, methanol and other gas interferences, the device resistance did not show obvious fluctuations, indicating its high selectivity for ammonia.

[0071] In summary, although there are already literature reports on detecting ammonia based on PEDOT:PSS composites, the use of CNF and PEDOT:PSS polymers to prepare composite films for detecting ammonia proposed in this invention is still the first time; this invention proposes a composite film device based on the conductive polymer PEDOT:PSS / nanocellulose (CNF). Compared with pure PEDOT:PSS devices, it shows more excellent performance in terms of sensitivity and response recovery time, and its performance is better than that of the vast majority of reported NH 3 sensors based on conductive polymers. The PEDOT:PSS / CNF composite device has a high selectivity for ammonia. When there are gas interferences, the device resistance does not show obvious fluctuations and the performance is stable.

[0072] The PEDOT:PSS / CNF composite device proposed in this invention still has high sensitivity to trace (sub-ppm level concentration) ammonia in a medium and high humidity environment, while pure PEDOT:PSS devices do not have this phenomenon; and the detection limit of the PEDOT:PSS / CNF composite device for ammonia can reach 200ppb; the ppm refers to parts per million, and the sub-ppm level concentration refers to a concentration slightly lower than one part per million.

[0073] Compared with the currently reported NH detection work based on conductive polymers, the PEDOT:PSS / CNF composite device prepared by the present invention has shorter response and recovery times. Both the response time and the recovery time are controlled below 6 s, realizing the ultrafast response and recovery of the device, and overcoming the deficiencies of single conductive polymers in terms of sensitivity and response recovery speed when detecting NH 3 ; The device preparation process is simple, and the detection process does not require heating and can be carried out at room temperature. 3 It can be understood that the present invention is described through some embodiments. As is known to those skilled in the art, without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. The embodiments described in the present invention are some, rather than all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of the present invention.

[0074] ​

Claims

1. An ammonia gas sensor, comprising an electrode, Characterized in that, A sensitive layer formed by covering the surface of the electrode with a PEDOT:PSS / CNF composite material; the PEDOT:PSS / CNF composite material is obtained by preparing a PEDOT:PSS / CNF composite material solution formed by uniformly dispersing the polymer PEDOT:PSS and carbon nanofibers CNF in deionized water.

2. An ammonia gas sensor according to claim 1, Characterized in that, In the PEDOT:PSS / CNF composite material, the weight ratio of the polymer PEDOT:PSS to the carbon nanofibers CNF is 0.5:1 or 1:

1.

3. An ammonia gas sensor according to claim 1, Characterized in that, The electrode is a planar interdigital electrode.

4. A method for preparing an ammonia gas sensor, used for preparing the ammonia gas sensor according to claim 1, Characterized in that, Comprises the following steps: Step 1: Uniformly disperse the polymer PEDOT:PSS and carbon nanofibers CNF in deionized water to prepare a PEDOT:PSS / CNF composite material solution; Step 2: Cover the surface of the electrode device with the obtained PEDOT:PSS / CNF composite material solution to prepare an electrode device covered with a PEDOT:PSS / CNF composite material thin film; Step 3: Dry the electrode device with the PEDOT:PSS / CNF composite material thin film to finally prepare a PEDOT:PSS / CNF ammonia gas sensor.

5. A method for preparing an ammonia gas sensor according to claim 4, Characterized in that, Use ultrasonic waves to uniformly disperse the polymer PEDOT:PSS and carbon nanofibers CNF in deionized water, the ultrasonic wave frequency is 20 kHz - 23 kHz, and the ultrasonic time is 60 - 180 min.

6. A method for preparing an ammonia gas sensor according to claim 4, Characterized in that, In step 1, in the PEDOT:PSS / CNF composite material solution, the weight ratio of the polymer PEDOT:PSS to the carbon nanofibers CNF is 0.5:1 or 1:

1.

7. A method for preparing an ammonia gas sensor according to claim 4, Characterized in that, The electrode device described in steps 2 and 3 is a planar interdigital electrode device.

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