Preparation method and application of flame-retardant conductive hydrogel sensor

Abstract

The invention discloses a preparation method of a flame-retardant conductive hydrogel sensor, the hydrogel sensor is prepared by a method of adding phytic acid twice, and the concentrations of the phytic acid added twice are the same, so that the phytic acid is uniformly distributed in the flame-retardant conductive hydrogel sensor. Uniformly dispersed polyaniline grows on a hydrogel interface by using a gas phase polymerization method, so that the conductivity of the polyaniline hydrogel is effectively improved, the prepared sensor has excellent sensitivity, and more accurate monitoring is provided in the aspects of harmful gas detection and fire early warning.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly to a preparation method and application of a flame-retardant conductive hydrogel sensor. Background Art

[0002] The polyaniline conductive hydrogel gas sensor is a technology for monitoring trace harmful gases indoors. By adsorbing the target gas or reacting specifically with it through the hydrogel, the sensor can detect and measure the concentration of the target gas, thereby realizing the monitoring and control of indoor air quality, and is widely used in industrial, commercial, and household environments.

[0003] However, there are still some deficiencies in the current preparation process of polyaniline hydrogels. The polyaniline hydrogel does not have flame-retardant properties and has poor fire resistance. Its sensing performance is severely affected at high temperatures, which limits its application in the field of fire warning. Chinese patent document with publication number CN108376618A discloses a preparation method of a polyaniline / phytic acid conductive hydrogel, including: preparing a metal current collector electrode on a flexible substrate; preparing an aniline / phytic acid mixed solution; assembling the metal current collector electrode into a three-electrode structure, immersing the metal current collector electrode in the aniline / phytic acid mixed solution, applying a voltage to the metal current collector electrode, and depositing a polyaniline / phytic acid conductive hydrogel on the metal current collector electrode.

[0004] However, in the prior art, the in-situ polymerization method is mostly used to prepare polyaniline, and agglomeration occurs during the synthesis process, resulting in poor dispersion and uniformity of polyaniline. The agglomeration of polyaniline particles hinders the full utilization of the active material, resulting in a significant decrease in the conductivity of polyaniline. Therefore, it is crucial to optimize the synthesis method of polyaniline. Chinese patent document with publication number CN115852696A discloses a preparation method of a wearable flexible sensing material. Using a flexible cotton gauze as a carrier, a polyvinyl alcohol hydrogel is coated on the flexible cotton gauze, and polyaniline is synthesized on the fabric-based flexible substrate by gas-phase polymerization to prepare a multifunctional flexible sensing material. Although the present invention uses the gas-phase polymerization method to prepare polyaniline, due to the use of a polyvinyl alcohol-boric acid cross-linking system, the alkaline environment provided makes polyaniline undergo partial deprotonation, and the conductive performance of the hydrogel is severely affected.

[0005] Therefore, there is an urgent need to find a preparation method for hydrogels that has excellent flame-retardant and conductive properties and can be applied to gas detection and fire warning. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for preparing a flame-retardant conductive hydrogel sensor. By growing uniformly dispersed polyaniline at the hydrogel interface using gas-phase polymerization, the conductivity of the polyaniline hydrogel is effectively improved, enabling the prepared sensor to have excellent sensitivity and providing more accurate monitoring in the detection of harmful gases and fire warning.

[0007] A method for preparing a flame-retardant conductive hydrogel sensor, comprising the following steps:

[0008] (1) Add polyvinyl alcohol to an aqueous solution of phytic acid, stir evenly, and perform degassing treatment to obtain a homogeneous gel solution of polyvinyl alcohol / phytic acid;

[0009] (2) Pour the homogeneous gel solution prepared in step (1) into a mold, perform freeze-thaw treatment, and thaw at room temperature to obtain a polyvinyl alcohol / phytic acid hydrogel;

[0010] (3) Prepare a mixed solution of ammonium persulfate and phytic acid, and rinse the polyvinyl alcohol / phytic acid hydrogel obtained in step (2) with the above mixed solution to obtain a polyvinyl alcohol / phytic acid hydrogel covered with an ammonium persulfate-phytic acid liquid film. Among them, the concentration of phytic acid in the mixed solution is the same as the concentration of the aqueous phytic acid solution in step (1);

[0011] (4) Add an aniline solution to a container to cover the bottom of the container. Fix the polyvinyl alcohol / phytic acid hydrogel covered with the ammonium persulfate-phytic acid liquid film prepared in step (3) above the aniline liquid surface, seal the container with a sealing film, and grow polyaniline at the hydrogel interface by gas-phase polymerization in an ice bath to obtain a flame-retardant conductive hydrogel sensor.

[0012] In the present invention, polyaniline not only polymerizes on the surface of the hydrogel to form a polyaniline film on the surface of the hydrogel, but also polymerizes and grows inside the hydrogel to form a three-dimensional conductive network. The hydrogel sensor is prepared by adding phytic acid twice, and the concentrations of phytic acid added twice are the same, so that phytic acid is uniformly distributed in the flame-retardant conductive hydrogel sensor. Phytic acid, as a bifunctional "bridge" molecule, acts as both a cross-linking agent for polyvinyl alcohol and a dopant to provide a stable protonation environment for polyaniline. At the same time, the introduction of phytic acid overcomes the defect of polyaniline in flame retardancy and broadens the working temperature range of the sensor. The preparation of polyaniline by gas-phase polymerization can overcome the problem of polyaniline agglomeration in the hydrogel matrix during the polymerization process, effectively improve the conductivity of polyaniline, enable the prepared sensor to have excellent sensitivity, and provide more accurate monitoring in the detection of harmful gases and fire warning.

[0013] Preferably, the concentration of phytic acid is 7.00 - 35.00 wt%. In the present invention, phytic acid can replace the existing boric acid as a crosslinking agent for polyvinyl alcohol (PVA) hydrogel. Phytic acid molecules contain a large number of oxygen-containing groups, which can form a large number of hydrogen bonds with PVA molecular chains to form a three-dimensional conductive network. Phytic acid can also replace the existing hydrochloric acid as a dopant for polyaniline conductive polymer. As a green organic acid derived from plant seeds, phytic acid can not only provide a proton source for the doping of polyaniline, but also endow the hydrogel material with excellent flame retardancy, and has better biocompatibility than the doping acid boric acid. When the concentration of phytic acid is within the above range, the prepared flame-retardant conductive hydrogel sensor has excellent flame retardancy, and the limiting oxygen index is greater than 30%.

[0014] Preferably, in step (1), the mass ratio of phytic acid to polyvinyl alcohol is 1 - 7:1.

[0015] In the present invention, the homogeneous gel solution of polyvinyl alcohol / phytic acid is processed by freeze-thaw cycling to obtain a hydrogel electrode. The hydroxyl groups on phytic acid molecules can form hydrogen bonds with the hydroxyl groups on polyvinyl alcohol, providing physical crosslinking points for the formation of the hydrogel, thereby regulating the formation conditions of the hydrogel. Under freeze-thaw conditions, the hydrogen bond interaction between phytic acid and polyvinyl alcohol weakens the hydrogen bond interaction between polyvinyl alcohols, thereby reducing the crystallinity of polyvinyl alcohol. By controlling the ratio of polyvinyl alcohol and phytic acid, the crosslinking degree of the hydrogel can be regulated, and when the ratio is within the above range, the crosslinking degree is relatively optimal.

[0016] Preferably, the temperature of freeze-thaw is -20 - -10 °C, the time is more than 12 h, and the thawing time is equal to the freeze-thaw time.

[0017] Preferably, in step (3), the concentration of ammonium persulfate is 0.5 mol / L.

[0018] The conductive polymer polyaniline has electrochemical properties similar to those of inorganic materials such as semiconductors and metals. The electrochemical properties of the conductive polymer depend on its structure, and this structure largely depends on the synthesis method and doping conditions.

[0019] The electrochemical activity of polyaniline stems from the π-electron conjugated structure in the molecular chain. In the present invention, the hydrogen ions and counter anions generated by the decomposition of phytic acid enter the main chain and combine with the N atoms in the amino / imine groups on the polyaniline chain to form polarons and bipolarons delocalized into the conjugated structure of the entire molecular chain, thereby rendering polyaniline highly conductive. When phytic acid is used as a dopant, it can not only play the role of acid doping but also act as a small molecule cross-linking agent, making the structure of the conductive polymer more compact and the mechanical and electrochemical properties more stable. An ammonium persulfate-phytic acid liquid film uniformly covers the surface of the polyvinyl alcohol hydrogel. When the ratio of ammonium persulfate to phytic acid is within the above range, polyaniline uniformly dispersed and doped with phytic acid can be grown at the hydrogel interface by gas phase polymerization.

[0020] Preferably, in step (4), the polyvinyl alcohol / phytic acid hydrogel covered with the ammonium persulfate-phytic acid liquid film is fixed about 5 cm above the liquid surface of aniline.

[0021] Preferably, in step (4), the reaction temperature of the gas phase polymerization method is 0-5 °C, and the reaction time is 12-48 h.

[0022] When preparing polyaniline by in-situ polymerization and doping it into the hydrogel alone, it is usually easy to form aggregated domains and difficult to form a continuous and uniformly dispersed polyaniline conductive network. The present invention uses the gas phase polymerization method to prepare polyaniline, which can overcome the problem of polyaniline agglomeration in the hydrogel matrix during the polymerization process. The grown polyaniline is uniformly dispersed, effectively improving the conductivity of the polyaniline hydrogel and making the sensor have higher sensitivity.

[0023] The present invention also provides a flame-retardant conductive hydrogel sensor prepared by the above preparation method, and the limiting oxygen index of the sensor > 30%.

[0024] The present invention also provides the application of the above flame-retardant conductive hydrogel sensor in gas monitoring and fire warning. The hydrogel sensor has excellent flame-retardant and conductive effects, high sensitivity of the sensor, and can be used for detecting formaldehyde gas. Due to the excellent flame-retardant effect of the sensor, the working temperature range of the sensor is broadened, enabling the sensor to still be used at higher temperatures, and it is particularly suitable for harmful gas monitoring and fire warning.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The flame-retardant and conductive hydrogel sensor in the present invention is prepared by adding phytic acid twice, and the concentrations of phytic acid added twice are the same, so that phytic acid is evenly distributed in the flame-retardant and conductive hydrogel sensor. As a bifunctional "bridge" molecule, phytic acid not only acts as a cross-linking agent for polyvinyl alcohol but also acts as a dopant to provide a stable protonation environment for polyaniline. At the same time, the introduction of phytic acid overcomes the defects of polyaniline in terms of flame retardancy and broadens the working temperature range of the sensor.

[0027] (2) The hydrogel sensor prepared in the present invention has excellent flame-retardant and conductive properties, high sensitivity of the sensor, and can be used for detecting formaldehyde gas. Due to the excellent flame-retardant effect of the sensor, the working temperature range of the sensor is broadened, so that the sensor can still be used at a higher temperature, and it is particularly suitable for harmful gas monitoring and fire warning. Description of the Drawings

[0028] Figure 1 It is the preparation flow chart of Examples 1-4 of the present invention.

[0029] Figure 2 It is the electron microscope images of the hydrogel sensor prepared in Comparative Example 1 and the flame-retardant and conductive hydrogel sensors prepared in Examples 1-4.

[0030] Figure 3 It is the thermogravimetric analysis curves of the hydrogel sensor prepared in Comparative Example 1 and the flame-retardant and conductive hydrogel sensors prepared in Examples 1-4.

[0031] Figure 4 It is the vertical burning comparison diagram of Example 3 and Comparative Example 1, where A and B are the vertical burning diagrams of the hydrogel sensors of Comparative Example 1 and Example 3 respectively.

[0032] Figure 5 It is the sensitivity response diagram of the flame-retardant and conductive hydrogel sensor prepared in Example 3 to formaldehyde. Detailed Embodiments

[0033] The following combines examples to further describe the present invention in detail, but the embodiments of the present invention are not limited to the following examples.

[0034] All raw materials used in the present invention are commercially available, and the preparation process is as Figure 1 shown.

[0035] Example 1

[0036] (1) Add 4.3 g of an aqueous phytic acid solution (50 wt%) to 22.7 mL of water to obtain 30 g of a 7.16 wt% aqueous phytic acid solution. Place the solution in a water bath and heat it to 95 °C. Then, slowly add 3 g of polyvinyl alcohol (type n = 124) to the aqueous phytic acid solution multiple times, stir for 2 h, and perform degassing treatment under ultrasonic waves for 20 min to obtain a homogeneous gel solution of polyvinyl alcohol / phytic acid;

[0037] (2) Pour the homogeneous gel solution of polyvinyl alcohol / phytic acid obtained in step (1) into a pre-cooled mold, freeze it at -20 °C for 12 h, and thaw it at room temperature (20 °C) for 12 h to obtain a polyvinyl alcohol / phytic acid hydrogel;

[0038] (3) Prepare a mixed solution of ammonium persulfate (0.5 mol / L) and an aqueous phytic acid solution (7.16 wt%), and quickly rinse the polyvinyl alcohol / phytic acid hydrogel obtained in step (2) with the above mixed solution to obtain a polyvinyl alcohol / phytic acid hydrogel covered with an ammonium persulfate - phytic acid liquid film;

[0039] (4) Add an aniline solution (the liquid layer height is about 1 cm) to the bottom of a sealed container, fix the polyvinyl alcohol / phytic acid hydrogel covered with the ammonium persulfate - phytic acid liquid film obtained in step (3) about 5 cm above the aniline liquid surface, cover the sealed lid, and seal the container with a sealing film. Then, place the reaction container in an environment of 0 - 5 °C for polymerization for 12 h. After polymerization is completed, perform suction filtration and washing with deionized water to obtain a flame-retardant conductive hydrogel sensor, abbreviated as S-3.

[0040] Example 2

[0041] (1) Add 10.02 g of an aqueous phytic acid solution (50 wt%) to 16.8 mL of water to obtain 30 g of a 16.7 wt% aqueous phytic acid solution. Place the solution in a water bath and heat it to 95 °C. Then, slowly add 3 g of polyvinyl alcohol (type n = 124) to the aqueous phytic acid solution multiple times, stir for 2 h, and perform degassing treatment under ultrasonic waves for 20 min to obtain a homogeneous gel solution of polyvinyl alcohol / phytic acid;

[0042] (2) Pour the homogeneous gel solution of polyvinyl alcohol / phytic acid obtained in step (1) into a pre-cooled mold, freeze it at -20 °C for 12 h, and thaw it at room temperature (20 °C) for 12 h to obtain a polyvinyl alcohol / phytic acid hydrogel;

[0043] (3) Prepare a mixed solution of ammonium persulfate (0.5 mol / L) and an aqueous phytic acid solution (16.7 wt%), and quickly rinse the polyvinyl alcohol / phytic acid hydrogel obtained in step (2) with the above mixed solution to obtain a polyvinyl alcohol / phytic acid hydrogel covered with an ammonium persulfate - phytic acid liquid film;

[0044] (4) Add aniline solution (liquid height is about 1 cm) to the bottom of a sealed container. Fix the polyvinyl alcohol / phytic acid hydrogel covered with ammonium persulfate - phytic acid liquid film obtained in step (3) about 5 cm above the aniline liquid surface. Cover the sealed cap and seal the container with sealing film. Then place the reaction container in an environment of 0 - 5 °C for polymerization for 12 h. After polymerization is completed, filter and wash with deionized water to obtain a flame - retardant conductive hydrogel sensor, abbreviated as S - 7.

[0045] Example 3

[0046] (1) Add 14.32 g of phytic acid aqueous solution (50 wt%) to 12.68 mL of water to obtain 30 g of 23.87 wt% phytic acid aqueous solution. Place the solution in a water bath and heat it to 95 °C. Then slowly add 3 g of polyvinyl alcohol (n = 124 type) to the phytic acid aqueous solution multiple times, stir for 2 h, and perform degassing treatment under ultrasonic for 20 min to obtain a homogeneous gel solution of polyvinyl alcohol / phytic acid;

[0047] (2) Pour the homogeneous gel solution of polyvinyl alcohol / phytic acid obtained in step (1) into a pre - cooled mold in advance, freeze it at - 20 °C for 12 h, and thaw it at room temperature (20 °C) for 12 h to obtain polyvinyl alcohol / phytic acid hydrogel;

[0048] (3) Prepare a mixed solution of ammonium persulfate (0.5 mol / L) and phytic acid aqueous solution (23.87 wt%). Use the above - mentioned mixed solution to quickly rinse the polyvinyl alcohol / phytic acid hydrogel obtained in step (2) to obtain a polyvinyl alcohol / phytic acid hydrogel covered with ammonium persulfate - phytic acid liquid film;

[0049] (4) Add aniline solution (liquid height is about 1 cm) to the bottom of a sealed container. Fix the polyvinyl alcohol / phytic acid hydrogel covered with ammonium persulfate - phytic acid liquid film obtained in step (3) about 5 cm above the aniline liquid surface. Cover the sealed cap and seal the container with sealing film. Then place the reaction container in an environment of 0 - 5 °C for polymerization for 12 h. After polymerization is completed, filter and wash with deionized water to obtain a flame - retardant conductive hydrogel sensor, abbreviated as S - 10.

[0050] Example 4

[0051] (1) Add 18.42 g of phytic acid aqueous solution (50 wt%) to 8.38 mL of water to obtain 30 g of 30.70 wt% phytic acid aqueous solution. Place the solution in a water bath and heat it to 95 °C. Then slowly add 3 g of polyvinyl alcohol (n = 124 type) to the phytic acid aqueous solution multiple times, stir for 2 h, and perform degassing treatment under ultrasonic for 20 min to obtain a homogeneous gel solution of polyvinyl alcohol / phytic acid;

[0052] (2) pouring the polyvinyl alcohol / phytic acid homogeneous gel solution obtained in step (1) into a pre-cooled mold, freezing it at -20°C for 12 hours, and thawing it at room temperature (20°C) for 12 hours to obtain a polyvinyl alcohol / phytic acid hydrogel;

[0053] (3) preparing a mixed solution of ammonium persulfate (0.5 mol / L) and phytic acid aqueous solution (30.70 wt%), and using the mixed solution to quickly rinse the polyvinyl alcohol / phytic acid hydrogel obtained in step (2) to obtain a polyvinyl alcohol / phytic acid hydrogel covered with an ammonium persulfate-phytic acid liquid film;

[0054] (4) Add aniline solution (liquid layer height of about 1 cm) to the bottom of the sealed container, fix the polyvinyl alcohol / phytic acid hydrogel covered with the ammonium persulfate-phytic acid liquid film obtained in step (3) at about 5 cm above the aniline liquid surface, cover with a sealing cover, and seal the container with a sealing film, then place the reaction container in an environment of 0 to 5°C for polymerization for 12 hours. After the polymerization is completed, filter and wash with deionized water to obtain a flame retardant conductive hydrogel sensor, referred to as S-15.

[0055] Comparative Example 1

[0056] The preparation method is the same as that in Example 1, except that ammonium persulfate solution (0.5 mol / L) is used in step (3) instead of a mixed solution of ammonium persulfate and phytic acid to prepare a hydrogel sensor, referred to as S-0.

[0057] Sample analysis

[0058] 1. Morphology analysis

[0059] The flame-retardant conductive hydrogel sensors prepared in Examples 1 to 4 and the hydrogel sensor prepared in Comparative Example 1 were analyzed by electron microscopy.

[0060] Figure 2 The electron microscope images of the hydrogel sensor prepared in Comparative Example 1 and the flame-retardant conductive hydrogel sensor prepared in Examples 1 to 4 are shown in the figure. The surface morphology of the flame-retardant conductive hydrogel is characterized by scanning electron microscopy (SEM). Polyaniline (PANI) is spherical and short rod-shaped on the surface of PVA gel, and presents a clustered morphology as the PA concentration increases. The image shows that PANI successfully grows on the PVA surface and is embedded in the hydrogel.

[0061] 2. Thermogravimetric analysis

[0062] The flame retardant conductive hydrogel sensors prepared in Examples 1 to 4 and the hydrogel sensor prepared in Comparative Example 1 were subjected to thermogravimetric analysis. Thermal performance analysis was performed by TGA-DTG, with a test temperature of 30 to 800° C. and a heating rate of 20° C. / min. Figure 3The thermogravimetric analysis curves of the hydrogel sensors prepared in Comparative Example 1 and the flame-retardant conductive hydrogel sensors prepared in Examples 1-4 are shown in the figure. It is found that compared with Comparative Example 1, as the content of phytic acid in the gel increases, the residual carbon content of the flame-retardant gel at 800 °C increases significantly, by about 40%. This is because phytic acid decomposes into phosphoric acid at low temperatures, which combines with the PVA matrix, further leading to the formation of a dehydrated carbon layer. This carbonized layer has heat insulation and endothermic effects and can protect the material at high temperatures.

[0063] III. Flame-retardant performance

[0064] The flame-retardant performance of the flame-retardant conductive hydrogel sensors prepared in Examples 1-4 and the hydrogel sensors prepared in Comparative Example 1 was tested. According to the UL94 vertical burning test standard, two samples, S-0 and S-10, were selected for combustion performance comparison tests.

[0065] Figure 4 Figure A shows the vertical burning comparison of Example 3 and Comparative Example 1. As shown in Figure 4 A, due to the flammability of S-0, it will quickly melt and burn when exposed to the flame. In just 50 seconds, the entire sample is almost completely burned. As shown in Figure 4 B, S-10 shows significant flame retardancy to high temperatures. It can maintain its original length without melting even after 100 seconds of flame attack and has a self-extinguishing property.

[0066] Table 1: Flame-retardant performance of the hydrogel sensors prepared in Examples 1-4 and Comparative Example 1

[0067]

[0068] As shown in Table 1, as the phytic acid content in the gel sample preparation process increases from 7.16 wt% to 30.70 wt%, the limiting oxygen index (LOI) of the gel sample increases from 18.0 to 32.6. The LOI of the control sample S-0 < 21%, which belongs to a flammable material. The LOI of the 4 samples with added phytic acid > 30% is difficult to burn in air. The above gels prepared by this experimental technique have excellent flame-retardant performance.

[0069] IV. Sensitivity test

[0070] The conductivity of the flame-retardant conductive hydrogel sensor prepared in Example 3, gel sample S-10, was characterized by a digital multimeter (KEYSIGHT 34461A). The size of the sample strip was 5 mm × 10 mm, and the formaldehyde gas concentrations were 10 ppm, 20 ppm, 30 ppm, 40 ppm, and 50 ppm, Figure 5Sensitivity response graph of the flame-retardant conductive hydrogel sensor prepared in Example 3 to formaldehyde. As shown in the figure, the conductivity of S-10 increases proportionally with the formaldehyde concentration, and each concentration is continuously repeated for 6 cycles. The conductive stability and repeatability of S-10 are good.

[0071] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a flame-retardant conductive hydrogel sensor, characterized in that, It includes the following steps: (1) Add polyvinyl alcohol to an aqueous solution of phytic acid, stir evenly, and perform degassing treatment to obtain a homogeneous gel solution of polyvinyl alcohol / phytic acid; (2) Pour the homogeneous gel solution prepared in step (1) into a mold, perform freeze-thaw treatment, and thaw at room temperature to obtain a polyvinyl alcohol / phytic acid hydrogel; (3) Prepare a mixed solution of ammonium persulfate and phytic acid, and rinse the polyvinyl alcohol / phytic acid hydrogel obtained in step (2) with the above-mentioned mixed solution to obtain a polyvinyl alcohol / phytic acid hydrogel covered with an ammonium persulfate-phytic acid liquid film. Among them, the concentration of phytic acid in the mixed solution is the same as the concentration of the aqueous phytic acid solution in step (1); (4) Add an aniline solution to a container to cover the bottom of the container. Fix the polyvinyl alcohol / phytic acid hydrogel covered with the ammonium persulfate-phytic acid liquid film prepared in step (3) above the aniline liquid surface, seal the container with a sealing film, and grow polyaniline at the hydrogel interface by gas-phase polymerization in an ice bath to obtain a flame-retardant conductive hydrogel sensor.

2. The preparation method of the flame-retardant conductive hydrogel sensor according to claim 1, characterized in that, The concentration of the phytic acid is 7.00 - 35.00 wt%.

3. The preparation method of the flame-retardant conductive hydrogel sensor according to claim 1, characterized in that, In step (1), the mass ratio of the phytic acid to the polyvinyl alcohol is 1 - 7:

1.

4. The preparation method of the flame-retardant conductive hydrogel sensor according to claim 1, wherein, The temperature of the freeze-thaw is -20 to -10 °C, the time is more than 12 h, and the thawing time is equal to the freeze-thaw time.

5. The preparation method of the flame-retardant conductive hydrogel sensor according to claim 1, wherein, In step (3), the concentration of the ammonium persulfate is 0.5 mol / L.

6. The preparation method of the flame-retardant conductive hydrogel sensor according to claim 1, characterized in that, In step (4), the polyvinyl alcohol / phytic acid hydrogel covered with the ammonium persulfate-phytic acid liquid film is fixed about 5 cm above the aniline liquid surface.

7. The preparation method of the flame-retardant conductive hydrogel sensor according to claim 1, wherein, In step (4), the reaction temperature of the gas-phase polymerization method is 0 to 5 °C, and the reaction time is 12 to 48 h.

8. A flame-retardant conductive hydrogel sensor prepared by the preparation method according to any one of claims 1 - 7.

9. The flame-retardant conductive hydrogel sensor according to claim 8, wherein, The limiting oxygen index of the flame-retardant conductive hydrogel sensor > 30%.

10. Application of the flame-retardant conductive hydrogel sensor according to claim 8 or 9 in gas monitoring and fire warning.

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