CN111830086A - Preparation method of gas sensor based on polyaniline film surface modification - Google Patents
Preparation method of gas sensor based on polyaniline film surface modification Download PDFInfo
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- C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
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- C08G73/026—Wholly aromatic polyamines
- C08G73/0266—Polyanilines or derivatives thereof
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Abstract
The invention provides a preparation method of a gas sensor based on polyaniline film surface modification, which comprises the steps of firstly preparing polyaniline PANI powder by a chemical oxidation method and dissolving the polyaniline PANI powder in a low-toxicity solvent, secondly carrying out spin coating on a cover glass subjected to plasma treatment to form a film, and then providing a method for separating a PANI film, carrying out floating de-doping and re-doping, thus preparing a substrate-free PANI film. And performing surface chemical modification of fatty acid on the surface of the PANI film in a re-doping process, and finally attaching the PANI film to a flexible substrate with interdigital electrodes to manufacture the gas sensor. The preparation method is effective, low in cost, novel and environment-friendly, the prepared PANI film is controllable in volume, the fatty acids with different carbon chain lengths modified on the surface of the PANI film form hydrophobic layers on the surface of the PANI film, the gas-sensitive performance of the PANI film is obviously improved, the response of high-concentration water vapor can be effectively reduced, and a new idea is improved for the design and application of the gas-sensitive sensor without humidity influence.
Description
Technical Field
The invention belongs to the technical field of preparation of film gas sensors, and particularly relates to a preparation method of a gas sensor based on polyaniline film surface modification.
Technical Field
Gas sensors are sensors used to monitor gas concentration and composition, and play an important role in environmental surveillance, food safety surveillance, and disease detection. The gas sensor is exposed to a simple or complex environment, and due to the fact that factors such as temperature, humidity, oil mist and dust of the monitored environment change greatly, part of interference gas can be attached to the surface of the sensing element, and the sensing performance of the gas sensor is often poor. Therefore, the gas sensor is required to work continuously and stably for a long time, and has the advantages of good repeatability, high response speed, strong selectivity, strong capacity of resisting disturbance gas and the like.
Common gas sensors include resistance change type gas sensors, field effect transistor gas sensors, solid state electrochemical gas sensors, and quartz crystal microbalance gas sensors. The resistance change type gas sensor is a resistance change type detection device caused by the interaction of an analyte and a sensing material, and main sensitive elements are classified into a semiconductor metal oxide type and a high-molecular conductive polymer type. The chemical resistance type gas sensor based on the high polymer material has the characteristics of low cost, simple operation, portability, flexible working conditions, high stability and the like, and can be used for detecting various Volatile Organic Compounds (VOCs) related to atmospheric pollutants or biomarkers of certain diseases. Polyaniline, a high molecular compound, has special electrical and optical properties, and can be processed to obtain sensors with excellent performance and special functions, such as enzyme sensors which can be used as biological or chemical sensors, gas sensors with high selectivity and sensitivity, and the like. In addition, polyaniline has been widely studied due to its easily available raw materials, simple synthesis process, unique doping mechanism, good chemical and environmental stability, and the like.
With the improvement of quality of life, people pay more and more attention to health, and wearable medical equipment is used for monitoring the health state of a human body in real time, which becomes a hotspot and a difficulty of research. Research shows that the human body can produce biological markers VOCs related to diseases when being metabolized. However, the actually collected breath sample always contains humidity of different concentrations. Specifically, the relative humidity of a human breath sample exceeds 90%, water is a polar molecule, the sensing material always causes a change in conductivity once contacting the polar molecule, and the sensing signal of the VOCs is disturbed by the humidity response. In order to reduce the interference of water vapor on the gas to be detected, one method is to dry the gas to be detected, but the concentration of the gas to be detected changes after drying; the other is to detect specific gas by a pattern recognition method using a cross-reaction sensor array, but the whole process is too complicated. The Yaoming water and the like are coated on the sensitive material by a hydrophobic Metal Organic Framework (MOF), and the influence of water vapor on the gas to be detected is inhibited by utilizing the screening effect of the MOF, so that the gas selectivity is improved. See: yao plain water, Yao, M. -S., Tang, W. -X., Wang, G. -E., etc. the MOF Thin Film-Coated Metal Oxide nanowire array, Significantly Improved chemical resistance Sensor Performance [ J ]. advanced materials, Jul 13, 2016, 28 (26): 5229 Deng Yunfeng et al, used to selectively suppress water vapor by modifying the oil hydrophobic layer on the PANI membrane, while also maintaining the sensing signal of VOCs. See: dunn cloud, ding, y, Sun, J, Jin, h, etc. chemical ly Modified polymers for the Detection of volateile biomarkers of minor Sensitivity to Humidity and bundling [ J ] advanced health Materials, Aug 8, 2018, 7 (15). however, the regulation of process conditions to prepare a gas sensor that selectively suppresses water vapor remains a key and difficult point of the current technology to optimize the sensing performance.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of a gas sensor based on polyaniline film surface modification aiming at the defects in the prior art.
The technical scheme is as follows for solving the technical problem of the invention:
a preparation method of a gas sensor based on polyaniline film surface modification comprises the following specific processes:
(1) preparation of polyaniline powder
Aniline, hydrochloric acid and deionized water form a solution A after purification treatment; mixing ammonium persulfate and deionized water to form a solution B; adding the solution B into the solution A at 0 ℃ for reaction, after the reaction is finished, washing the prepared polyaniline PANI powder, soaking the polyaniline PANI powder in concentrated ammonia water, washing the polyaniline PANI powder after soaking, exchanging the washed polyaniline PANI powder with a mixed solution of toluene, ethanol and water under the protection of nitrogen to remove oligomers, filtering and collecting a product, and performing vacuum drying to obtain polyaniline powder;
(2) preparation of substrate-free PANI film
Dissolving the polyaniline powder obtained in the step (1) in N-methylpyrrolidone (NMP), stirring until the polyaniline powder is completely dissolved, spin-coating on a cover glass to obtain a PANI film, storing the PANI film on the cover glass in vacuum at normal temperature overnight, exposing the cover glass with the PANI film in an environment with hydrochloric acid steam, taking out the cover glass to obtain a substrate-free PANI film, and standing for later use;
(3) surface modification of non-substrate PANI film
Soaking the substrate-free PANI film prepared in the step (2) in a container in deionized water, replacing the deionized water with a phosphoric acid solution after the color of the substrate-free PANI film is changed from semitransparent green to semitransparent blue, replacing one half of the phosphoric acid solution with a fatty acid methylbenzene solution, adding the remaining half of the fatty acid methylbenzene solution to modify the surface of the substrate-free PANI film, and standing for later use;
(4) manufacture of interdigital electrode
Coating the middle part of polyethylene glycol terephthalate (PET) with a preservative film, performing magnetron sputtering, plating a layer of Ti film and a layer of Ag film, taking down the coated preservative film after film plating is finished, and finishing the manufacture of the interdigital electrode;
(5) and (4) taking out the PANI film subjected to surface modification in the step (3), placing the PANI film on an interdigital electrode, removing water vapor and solvent in vacuum to obtain the PANI film gas-sensitive sensor, fixing a lead and the electrode together at two ends of the electrode of the PANI film gas-sensitive sensor by silver paste, and leading out an electrode wire.
The concentration of the phosphoric acid solution in the step (3) is 0.01 mol/L.
In the step (4), the time for sputtering Ti is 30s, the thickness is 30nm, the time for sputtering Ag is 5min, and the thickness is 100 nm.
The parameters of the spin coating in the step (2) are as follows: 500-700 r/min: 300- & lt600 & gt, high speed: 3000-5000r/min time: 8-15S.
The fatty acid methylbenzene solution in the step (3) is one of caprylic acid C8, capric acid C9, pelargonic acid C10, undecanoic acid C11, lauric acid C12, heptadecanoic acid C17 and behenic acid C22 methylbenzene solution, wherein the concentration of the fatty acid methylbenzene solution is 0.01 mol/L.
The preparation method of the gas sensor based on polyaniline film surface modification comprises the following specific steps:
(1) preparation of polyaniline powder
Distilling aniline under reduced pressure, and then taking 11.4mL of aniline, 12.5mL of 1mol/L hydrochloric acid and 125mL of deionized water to form a solution A; dissolving 14.25g of ammonium persulfate in 125mL of deionized water to form a solution B; gradually and slowly adding the solution B into the solution A at the speed of 250 ml/h, stirring and reacting for 8-10h at the temperature of 0 ℃, observing that the solution is changed from colorless transparency to dark green, filtering and washing the solution with water, dispersing the collected product into concentrated ammonia water, stirring for 12-14h, filtering and washing with water to obtain dedoped polyaniline, sequentially carrying out solvent exchange by using a mixed solution of toluene, ethanol and water under the protection of nitrogen to remove oligomers, filtering and collecting the product, and carrying out vacuum drying overnight to obtain polyaniline powder;
(2) preparation of substrate-free PANI film
Dissolving 0.2g of polyaniline powder in 15 mLN-methylpyrrolidone NMP, stirring until the polyaniline powder is completely dissolved to form uniform dark blue ink solution, treating 22 x 0.16m cover glass with plasma, uniformly dropping 70 mu L of polyaniline solution on the cover glass, and adjusting the spin-coating parameters to be low speed: 500-700 r/min: 300S, high speed: 3000-5000r/min time: 10S, spin-coating, drying overnight in vacuum, exposing the dried cover glass to hydrochloric acid vapor for 5-10S, changing the PANI film from dark blue to light green, transferring the PANI film to a weighing bottle filled with deionized water, enabling water to enter between the film and the cover glass, peeling off the PANI film, floating the PANI film doped with hydrochloric acid on the water surface, changing water every 20-28h, and standing for 3 days;
(3) surface modification of non-substrate PANI film
Preparing 0.01mol/L phosphoric acid solution, replacing deionized water in the weighing bottle, injecting slowly by using an injector to prevent the membrane from being damaged, standing for 3 days, preparing 0.01mol/L fatty acid methylbenzene solution, replacing half of the phosphoric acid solution in the weighing bottle, adding the remaining half of the fatty acid methylbenzene solution into the weighing bottle along the bottle wall, and standing the replaced weighing bottle for 22-28 hours for later use;
(4) manufacture of interdigital electrode
Taking a 10 x 1.5mm polyethylene terephthalate (PET) substrate, coating the middle of PET with a preservative film, wherein the coated area is 10 x 1mm, the coated PET substrate is used for magnetron sputtering, firstly plating a Ti film and then plating an Ag film, the time for sputtering Ti is 30s, the thickness is 30nm, the time for sputtering Ag is 5min, the thickness is 100nm, the coated preservative film is taken down after sputtering, and the manufacture of the interdigital electrode is finished;
(5) and finally, fixing the lead and the electrode together at two ends of the electrode of the PANI film sensor by silver paste, and leading out an electrode wire.
And (5) the method for fishing out the surface-modified PANI film comprises the steps of sucking out the upper toluene solution, lifting the liquid level by using 0.01mol/L phosphoric acid solution, and fishing out the PANI film and placing the PANI film on the interdigital electrode.
The mixed solution of ethanol and water in the step (1) is prepared by mixing neutral ethanol and water, wherein the volume ratio of the ethanol to the water is 9: 1.
The time for treating the cover glass by the plasma is 25-35min, and the power is 45-55W.
The polyaniline powder is dissolved in N-methylpyrrolidone NMP and stirred for 7 days at the rotating speed of 800-.
According to the invention, polyaniline is doped, and then H & lt + & gt decomposed by doped protonic acid enters a main chain, so that the polyaniline has high conductivity, the number of electrons in the doping process is not changed, and the doping and the de-doping of the polyaniline are completely reversible by a unique mechanism; the cover glass treated by the oxygen plasma is hydrophilic, the PANI film on the cover glass is hydrophobic, and water in a weighing bottle enters between the film and the glass to separately prepare the PANI film without the substrate; water is a polar molecule, the PANI thin film is a P-type semiconductor, and when water vapor contacts the surface of the PANI thin film, electron transfer occurs, causing a change in resistance reduction. The PANI film surface is modified with fatty acids with different carbon chain lengths, which can play the role of a hydrophobic layer, thereby reducing the response of water vapor.
The gas sensor based on the PANI film surface modification, which is obtained by the invention, can play a role in inhibiting water vapor response along with the increase of the modified fatty acid carbon chain, and the error of the same sensor is small.
The invention has the following beneficial effects: the polyaniline powder prepared by the invention has low cost and simple process. The preparation method of the substrate-free PANI film provided by the invention is novel, the size and the thickness of the film are controllable, the environment is protected, and the preparation process requirement is not high. According to the invention, the response to water vapor can be obviously reduced by modifying the fatty acid with different carbon chain lengths on the basis of the PANI film surface, the sensor device has good stability, small baseline drift and small error, and a new thought and direction are hopefully provided for preparing the gas sensor for selectively inhibiting water vapor.
Drawings
FIG. 1 is a drawing of a PANI thin film spin coating apparatus of the present invention, in FIG. 1, 1 is a polyaniline solution, 2 is a cover glass, and 3 is a spin coating apparatus;
FIG. 2 is a flow chart of the process for preparing the non-substrate PANI thin film of the present invention, wherein 1 in FIG. 2 is the PANI thin film after spin coating, which is blue; 2 is a PANI film after exposure to hydrochloric acid vapor, which is green; 3 is a water separation diagram, water passes through the middle of the membrane and the glass sheet to separate the membrane and floats on the surface of deionized water;
FIG. 3 is a schematic view of the preparation method of the PANI film surface modification of the present invention. Fig. 3, 1 is the PANI film after three days of standing, when it has been removed as a dedoped PANI film; 2 is a PANI film doped by 0.01mol/L phosphoric acid; 3 is a schematic diagram after injecting the fatty acid toluene solution; 3, in the two-phase interface diagram, the upper layer is fatty acid methyl benzene solution, the lower layer is phosphoric acid solution, and the PANI film exists at the two-phase interface; 4, a film fishing schematic diagram, namely sucking out the upper toluene solution, then lifting the liquid level, and fishing out the PANI film;
FIG. 4 is a schematic diagram of the interdigital electrode of the present invention, in FIG. 4, 1 is PET,2 is Ti film, and 3 is Ag film;
FIG. 5 is a schematic diagram of the PANI thin film gas sensor of the present invention, wherein 1 is a device diagram in FIG. 5, and 2 is a diagram of volatilizing water vapor and solvent in vacuum and bringing sensitive materials and electrodes into close contact;
FIG. 6 is a performance test chart of the gas sensor with the PANI film surface modified according to the present invention.
Detailed Description
The invention is further described in detail below with reference to the figures and examples.
Example 1
A preparation method of a gas sensor based on polyaniline film surface modification comprises the following specific steps:
1.1 preparation of sensitive Material for gas sensor
Aniline is used after reduced pressure distillation, 11.4mL of aniline, 12.5mL of 1mol/L hydrochloric acid and 125mL of deionized water are taken to form a solution A; dissolving 14.25g of ammonium persulfate in 125mL of deionized water to form a solution B; the solution B is slowly and dropwise added into the solution A at the rate of 250 ml/h, and the reaction is carried out for 8h at the temperature of 0 ℃. The solution was observed to change from colorless and transparent to greenish black, filtered and rinsed with copious amounts of water. And dispersing the collected product in concentrated ammonia water, stirring for 14h, filtering, and washing with a large amount of water to obtain the dedoping polyaniline. And under the protection of nitrogen, sequentially performing solvent exchange by using toluene, ethanol and water (v/v =9:1), removing oligomers, filtering and collecting a product, and performing vacuum drying overnight to obtain polyaniline powder.
1.2 preparation of substrate-free PANI thin films
Dissolving 0.2g of polyaniline powder in 15mL of NMP, stirring at the rotating speed of 1000r/min for 7 days to form uniform dark blue ink solution, wherein the attached drawing 1 is a PANI thin film spin-coating device diagram, treating a cover glass with O2 plasma for 25min, controlling the power to be 55W, controlling the size of the cover glass to be 22 x 0.16mm, taking 70 mu L of polyaniline solution, uniformly dripping the polyaniline solution on the cover glass, and adjusting the spin-coating parameters to be low speed: 700r/min time: 300S, high speed: time 3000 r/min: 10S, spin coating and vacuum drying overnight. FIG. 2 is a flow chart of the preparation of the substrate-free PANI film, the dried cover glass is exposed in hydrochloric acid vapor for 5S, the PANI film changes from dark blue to light green, then the cover glass is transferred to a weighing bottle with deionized water, water enters between the film and the cover glass, the PANI film is peeled off, the hydrochloric acid doped PANI film floats on the water surface, and the cover glass is kept still for 3 days.
1.3 substrate-free PANI film surface modification
FIG. 3 is a schematic diagram of the preparation method of the PANI thin film surface modification. Preparing 0.01mol/L phosphoric acid solution, replacing deionized water in the weighing bottle, injecting slowly by using an injector to prevent the membrane from being damaged, preparing 0.01mol/L octanoic acid C8 toluene solution, replacing the phosphoric acid solution in the weighing bottle by half of the octanoic acid C8 toluene solution, and slowly adding the remaining half of the octanoic acid C8 toluene solution into the weighing bottle along the bottle wall. At this time, in the two-phase interface diagram of FIG. 3, the upper layer is a solution of octanoic acid C8 in toluene, the lower layer is a solution of phosphoric acid, and a PANI film is present at the two-phase interface, and the displaced vial is left to stand for 24 hours.
1.4 fabrication of interdigital electrodes
Figure 4 is a schematic view of an interdigitated electrode. A number of 10X 1.5mm PET substrates were cut and the PET was wrapped with a cling film in the middle to provide a 10X 1mm wrap. The wrapped PET substrate is used for magnetron sputtering, and a layer of Ti is plated first, and then a layer of Ag is plated. The time for sputtering Ti is 30s, the thickness is 30nm, the time for sputtering Ag is 5min, and the thickness is 100 nm. And taking down the wrapped preservative film, and finishing the electrode manufacturing.
1.5 in the attached figure 3, 4 is a schematic diagram of membrane fishing, wherein an upper layer of octanoic acid C8 toluene solution is firstly sucked out, then the liquid level is lifted by 0.01mol/L phosphoric acid solution, and the PANI membrane is fished to the manufactured electrode. The finished device is stored overnight and then is put into a vacuum pot to remove water vapor and solvent, and the PANI film can be tightly attached to the substrate under the negative pressure state. And fixing the lead and the electrode together by silver paste at two ends of the electrode of the PANI film sensor, and leading out an electrode wire. And finishing the manufacturing of the PANI film gas sensor.
Example 2
A preparation method of a gas sensor based on polyaniline film surface modification comprises the following specific steps:
1.1 preparation of sensitive Material for gas sensor
Aniline is used after reduced pressure distillation, 11.4mL of aniline, 12.5mL of 1mol/L hydrochloric acid and 125mL of deionized water are taken to form a solution A; dissolving 14.25g of ammonium persulfate in 125mL of deionized water to form a solution B; the solution B is slowly and dropwise added into the solution A at the rate of 250 ml/h, and the reaction is carried out for 10h at the temperature of 0 ℃. The solution was observed to change from colorless and transparent to greenish black, filtered and rinsed with copious amounts of water. And dispersing the collected product in concentrated ammonia water, stirring for 12 hours, filtering, and washing with a large amount of water to obtain the dedoping polyaniline. And under the protection of nitrogen, sequentially performing solvent exchange by using toluene, ethanol and water (v/v =9:1), removing oligomers, filtering and collecting a product, and performing vacuum drying overnight to obtain polyaniline powder.
1.2 preparation of substrate-free PANI thin films
Dissolving 0.2g of polyaniline powder in 15mL of NMP, stirring at the rotating speed of 800r/min for 7 days to form uniform dark blue ink solution, treating a cover glass with O2 plasma for 35min, the power being 45W, the size of the cover glass being 22 x 0.16mm, taking 70 muL of polyaniline solution, uniformly dripping the polyaniline solution on the cover glass, and adjusting the spin-coating parameters to be low speed: 500 r/min time: 300S, high speed: 5000 r/min: 10S, spin coating and vacuum drying overnight. Exposing the dried cover glass to hydrochloric acid vapor for 10 seconds, changing the PANI film from dark blue to light green, transferring the cover glass into a weighing bottle with deionized water, enabling the water to enter between the film and the cover glass, peeling off the PANI film, floating the hydrochloric acid-doped PANI film on the water surface, and standing for 3 days.
1.3 substrate-free PANI film surface modification
Preparing 0.01mol/L phosphoric acid solution, replacing deionized water in the weighing bottle, slowly injecting by using an injector to prevent the membrane from being damaged, preparing 0.01mol/L decanoic acid C9 toluene solution, replacing the phosphoric acid solution in the weighing bottle by half of decanoic acid C9 toluene solution, and slowly adding the rest half of decanoic acid C9 toluene solution into the weighing bottle along the bottle wall. At this time, in the two-phase interface diagram of fig. 3, the upper layer is a toluene solution of decanoic acid C9, the lower layer is a phosphoric acid solution, a PANI film is present at the two-phase interface, and the displaced weighing bottle is left to stand for 24 hours.
(4) Manufacture of interdigital electrode
Taking a 10 x 1.5mm polyethylene terephthalate (PET) substrate, coating the middle of PET with a preservative film, wherein the coated area is 10 x 1mm, the coated PET substrate is used for magnetron sputtering, firstly plating a Ti film and then plating an Ag film, the time for sputtering Ti is 30s, the thickness is 30nm, the time for sputtering Ag is 5min, the thickness is 100nm, the coated preservative film is taken down after sputtering, and the manufacture of the interdigital electrode is finished;
(5) and (3) fishing the membrane, namely sucking the toluene solution of the decanoic acid C9 on the upper layer out, then lifting the liquid level by using 0.01mol/L phosphoric acid solution, and fishing the PANI membrane to the manufactured electrode. The finished device is stored overnight and then is put into a vacuum pot to remove water vapor and solvent, and the PANI film can be tightly attached to the substrate under the negative pressure state. And fixing the lead and the electrode together by silver paste at two ends of the electrode of the PANI film sensor, leading out an electrode wire, and finishing the manufacturing of the PANI film gas sensor.
The fatty acid toluene solution of the present invention may be one of toluene solutions of pelargonic acid C10, undecanoic acid C11, lauric acid C12, heptadecanoic acid C17 and behenic acid C22.
The performance test of the gas sensor based on the PANI film surface modified fatty acid layer for inhibiting humidity interference in example 1: the test system of the gas sensor is a dynamic test system, a sensor array test method is adopted, and 10 gas sensors are placed in the chamber each time. The concentrations of water vapor were 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm, 1500ppm, and 2000ppm, respectively, and the response time was set to 5min and the recovery time was set to 15 min. FIG. 6 is a performance test chart of a gas sensor with different types of fatty acid hydrophobic layers modified on the surface of the PANI film. The response of the gas sensor is denoted by R in the figure, with the definition of R = Δ G/G0100%, (Δ G is the change in conductivity of the PANI film when it contacts water vapor, G0Is a PANI film in N2Conductivity under atmosphere). As can be seen from the graph, the response value of each sensor gradually increases as the water vapor concentration increases from 200ppm to 2000 ppm; at the same water vapor concentration, as the chain length of the fatty acid modified by the PANI film increases, the response value of each sensor gradually decreases, for example, at 200ppm, the response value of the sensor without fatty acid modified by the PANI film to water vapor is 28.8%, and the response value of the sensor with behenic acid modified by the PANI film to water vapor is only 1.39%. The experimental results demonstrate that the PANI film plays a hydrophobic role as the chain length of the modified fatty acid increases.
The above are only specific embodiments of the present invention, but the present invention is not limited to these specific embodiments.
Claims (10)
1. A preparation method of a gas sensor based on polyaniline film surface modification is characterized by comprising the following specific processes:
(1) preparation of polyaniline powder
Aniline, hydrochloric acid and deionized water form a solution A after purification treatment; mixing ammonium persulfate and deionized water to form a solution B; adding the solution B into the solution A at 0 ℃ for reaction, after the reaction is finished, washing the prepared polyaniline PANI powder, soaking the polyaniline PANI powder in concentrated ammonia water, washing the polyaniline PANI powder after soaking, exchanging the washed polyaniline PANI powder with a mixed solution of toluene, ethanol and water under the protection of nitrogen to remove oligomers, filtering and collecting a product, and performing vacuum drying to obtain polyaniline powder;
(2) preparation of substrate-free PANI film
Dissolving the polyaniline powder obtained in the step (1) in N-methylpyrrolidone (NMP), stirring until the polyaniline powder is completely dissolved, spin-coating on a cover glass to obtain a PANI film, storing the PANI film on the cover glass in vacuum at normal temperature overnight, exposing the cover glass with the PANI film in an environment with hydrochloric acid steam, taking out the cover glass to obtain a substrate-free PANI film, and standing for later use;
(3) surface modification of non-substrate PANI film
Soaking the substrate-free PANI film prepared in the step (2) in a container in deionized water, replacing the deionized water with a phosphoric acid solution after the color of the substrate-free PANI film is changed from semitransparent green to semitransparent blue, replacing one half of the phosphoric acid solution with a fatty acid methylbenzene solution, adding the remaining half of the fatty acid methylbenzene solution to modify the surface of the substrate-free PANI film, and standing for later use;
(4) manufacture of interdigital electrode
Coating the middle part of polyethylene glycol terephthalate (PET) with a preservative film, performing magnetron sputtering, plating a layer of Ti film and a layer of Ag film, taking down the coated preservative film after film plating is finished, and finishing the manufacture of the interdigital electrode;
(5) and (4) taking out the PANI film subjected to surface modification in the step (3), placing the PANI film on an interdigital electrode, removing water vapor and solvent in vacuum to obtain the PANI film gas-sensitive sensor, fixing a lead and the electrode together at two ends of the electrode of the PANI film gas-sensitive sensor by silver paste, and leading out an electrode wire.
2. The method for preparing a gas sensor based on polyaniline film surface modification according to claim 1, wherein: the concentration of the phosphoric acid solution in the step (3) is 0.01 mol/L.
3. The method for preparing a gas sensor based on polyaniline film surface modification according to claim 1 or 2, wherein: in the step (4), the time for sputtering Ti is 30s, the thickness is 30nm, the time for sputtering Ag is 5min, and the thickness is 100 nm.
4. The method for preparing the gas sensor based on the polyaniline film surface modification as claimed in claim 3, wherein: the parameters of the spin coating in the step (2) are as follows: 500-700 r/min: 300- & lt600 & gt, high speed: 3000-5000r/min time: 8-15S.
5. The method for preparing a gas sensor based on polyaniline film surface modification according to claim 1 or 4, wherein: the fatty acid methylbenzene solution in the step (3) is one of caprylic acid C8, capric acid C9, pelargonic acid C10, undecanoic acid C11, lauric acid C12, heptadecanoic acid C17 and behenic acid C22 methylbenzene solution, wherein the concentration of the fatty acid methylbenzene solution is 0.01 mol/L.
6. The preparation method of the gas sensor based on polyaniline film surface modification according to claim 1, characterized by comprising the following steps:
(1) preparation of polyaniline powder
Distilling aniline under reduced pressure, and then taking 11.4mL of aniline, 12.5mL of 1mol/L hydrochloric acid and 125mL of deionized water to form a solution A; dissolving 14.25g of ammonium persulfate in 125mL of deionized water to form a solution B; gradually and slowly adding the solution B into the solution A at the speed of 250 ml/h, stirring and reacting for 8-10h at the temperature of 0 ℃, observing that the solution is changed from colorless transparency to dark green, filtering and washing the solution with water, dispersing the collected product into concentrated ammonia water, stirring for 12-14h, filtering and washing with water to obtain dedoped polyaniline, sequentially carrying out solvent exchange by using a mixed solution of toluene, ethanol and water under the protection of nitrogen to remove oligomers, filtering and collecting the product, and carrying out vacuum drying overnight to obtain polyaniline powder;
(2) preparation of substrate-free PANI film
Dissolving 0.2g of polyaniline powder in 15 mLN-methylpyrrolidone NMP, stirring until the polyaniline powder is completely dissolved to form uniform dark blue ink solution, treating 22 x 0.16m cover glass with plasma, uniformly dropping 70 mu L of polyaniline solution on the cover glass, and adjusting the spin-coating parameters to be low speed: 500-700 r/min: 300S, high speed: 3000-5000r/min time: 10S, spin-coating, drying overnight in vacuum, exposing the dried cover glass to hydrochloric acid vapor for 5-10S, changing the PANI film from dark blue to light green, transferring the PANI film to a weighing bottle filled with deionized water, enabling water to enter between the film and the cover glass, peeling off the PANI film, floating the PANI film doped with hydrochloric acid on the water surface, changing water every 20-28h, and standing for 3 days;
(3) surface modification of non-substrate PANI film
Preparing 0.01mol/L phosphoric acid solution, replacing deionized water in the weighing bottle, injecting slowly by using an injector to prevent the membrane from being damaged, standing for 3 days, preparing 0.01mol/L fatty acid methylbenzene solution, replacing half of the phosphoric acid solution in the weighing bottle, adding the remaining half of the fatty acid methylbenzene solution into the weighing bottle along the bottle wall, and standing the replaced weighing bottle for 22-28 hours for later use;
(4) manufacture of interdigital electrode
Taking a 10 x 1.5mm polyethylene terephthalate (PET) substrate, coating the middle of PET with a preservative film, wherein the coated area is 10 x 1mm, the coated PET substrate is used for magnetron sputtering, firstly plating a Ti film and then plating an Ag film, the time for sputtering Ti is 30s, the thickness is 30nm, the time for sputtering Ag is 5min, the thickness is 100nm, the coated preservative film is taken down after sputtering, and the manufacture of the interdigital electrode is finished;
(5) and finally, fixing the lead and the electrode together at two ends of the electrode of the PANI film sensor by silver paste, and leading out an electrode wire.
7. The method for preparing the gas sensor based on the polyaniline film surface modification as claimed in claim 6, wherein: and (5) the method for fishing out the surface-modified PANI film comprises the steps of sucking out the upper toluene solution, lifting the liquid level by using 0.01mol/L phosphoric acid solution, and fishing out the PANI film and placing the PANI film on the interdigital electrode.
8. The method for preparing the gas sensor based on the polyaniline film surface modification as claimed in claim 6 or 7, wherein: the mixed solution of ethanol and water in the step (1) is prepared by mixing neutral ethanol and water, wherein the volume ratio of the ethanol to the water is 9: 1.
9. The method for preparing a gas sensor based on polyaniline film surface modification according to claim 8, wherein: the time for treating the cover glass by the plasma is 25-35min, and the power is 45-55W.
10. The method for preparing the gas sensor based on the polyaniline film surface modification as claimed in claim 6 or 9, wherein: the polyaniline powder is dissolved in N-methylpyrrolidone NMP and stirred for 7 days at the rotating speed of 800-.
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