Reversible fire warning composite aerogel and preparation method thereof

Abstract

The present application relates to a kind of reversible fire warning composite aerogel and its preparation method, reversible fire warning composite aerogel is magnetic graphene oxide / expanding graphite / biomass matrix composite aerogel, by the function of composite aerogel evenly dispersed in biomass aqueous solution matrix, utilize intermolecular hydrogen bond crosslinking to build three-dimensional network structure;Make full use of Fe3O4 Nanoparticle reversible resistance-temperature response characteristics and with graphene oxide synergistic fire warning semiconductor behavior, expanding graphite high-temperature expansion is adiabatic layer and the carbonization characteristics of biomass matrix, prepared with excellent flame retardant performance, can break through single temperature monitoring limit reversible fire warning composite aerogel, it can also be used as positive electrode friction material structure friction nanogenerator, realize the self-power supply of early warning process, can further improve its fire safety performance, broaden in high-rise building, chemical, electrical, fire and other fields of application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional nanocomposites, in particular to a reversible fire warning composite aerogel and a preparation method thereof. BACKGROUND

[0002] In recent years, fire accidents caused by organic combustible materials in the fields of lithium batteries, high-rise building insulation, electricity, etc. occur frequently, causing huge life and property losses, so more stringent requirements are put forward for the fire safety performance of application materials. Aerogels have become an ideal substitute for traditional combustible materials due to their ultra-lightness, high porosity and excellent thermal insulation performance, and have wide application potential in the fields of petrochemical industry, military industry, aerospace, chemical engineering, construction, batteries, environmental protection and transportation, etc. However, organic aerogels have a certain degree of fire hazard, which seriously limits their practical application in the above-mentioned fields, so it is imperative to improve their fire safety performance. Studies have shown that the addition of inorganic fillers such as layered montmorillonite, sodium bicarbonate, expanded graphite and graphene can significantly improve the flame retardant performance of organic aerogels, so preparing flame-retardant aerogels is a basic strategy to improve their fire safety performance. In addition, by monitoring the changes of resistance, temperature, smoke concentration or infrared intensity, a warning signal can be triggered by a specific functional material before a fire occurs, which can realize the advance of the fire prevention pass, and endowing aerogels with sensitive fire warning capability is an effective way to further improve the fire safety performance.

[0003] At present, the study of flame-retardant aerogel systems is relatively systematic and perfect, and the study of early warning aerogel with higher fire safety performance is in the initial stage. Since 2020, "An ultrasensitive fire-warning chitosan / montmorillonite / carbon nanotube composite aerogel with high fire-resistance". Chem. Eng. J., 399 (2020) 125729 and "Flame-retardant cellulose nanofiber aerogel modified with graphene oxide and sodium montmorillonite and its fire-alarm application". Polym. Adv. Technol., 32 (2021) 1877-1887. respectively reported that researchers based on the thermal reduction of carbon-based nanomaterials such as carbon nanotubes and graphene oxide, first prepared carbon-based composite aerogels that can achieve rapid temperature response in high temperature / fire early stage. However, once the type of aerogel undergoes thermal reduction at high temperature, its resistance no longer changes, and it lacks repeatable temperature monitoring capability. Secondly, when used as a temperature sensor, it generally needs to be powered by an external power supply, which is easy to be damaged at high temperature, which may cause the fire alarm material to fail due to power interruption. Preparing reversible fire warning aerogel for building self-powered sensors still faces great challenges.

[0004] Chinese invention patent publication CN114210276A discloses a magnetic carbon-based composite aerogel with fire warning and flame retardancy and a preparation method. By reasonable setting, the prepared magnetic carbon-based composite aerogel has the characteristics of fire warning and flame retardancy, but it does not have reversible fire warning. SUMMARY

[0005] In view of the fact that the existing carbon-based composite aerogel can only achieve single high temperature / fire early stage rapid response, and building a repeatable temperature monitoring and self-powered sensor still faces challenges, the purpose of the present application is to provide a reversible fire warning composite aerogel and a preparation method thereof.

[0006] In order to achieve the purpose of the present application, the technical scheme of the present application is as follows:

[0007] A reversible fire warning composite aerogel, which is prepared by self-assembling magnetic graphene oxide nanosheets, expanded graphite nanosheets and biomass matrix through intermolecular hydrogen bond crosslinking, and then freeze-drying.

[0008] The magnetic graphene oxide nanosheet is a graphene oxide nanosheet modified by magnetic Fe3O4 nanoparticles.

[0009] The expanded graphite nanosheet can expand by 100-250 times in volume instantaneously at high temperature, and change from a sheet shape to a worm shape to form a good thermal insulation layer.

[0010] The biomass matrix is one or more of carboxymethyl chitosan, hydroxypropyl chitosan, hydroxypropyl methyl cellulose, cellulose nanofiber, and sodium alginate.

[0011] Preferably, the mass ratio of the magnetized graphene oxide nanosheet in the reversible fire warning composite aerogel is 10-60 wt%, wherein the content of the magnetic Fe3O4 nanoparticles is the upper limit of the graphene oxide sheet capable of growing and / or grafting magnetic Fe3O4 nanoparticles; the mass ratio of the expanded graphite nanosheet in the reversible fire warning composite aerogel is 0.5-6 wt%.

[0012] Preferably, the magnetic Fe3O4 nanoparticles and the expanded graphite nanosheet are flame-retardant functional bodies in the reversible fire warning composite aerogel, and respectively play the roles of catalyzing carbonization and expanding physical barrier; the expanded graphite nanosheet and the biomass matrix serve as a carbon source to form a stable and dense carbon layer.

[0013] Preferably, the preparation method of the reversible fire warning composite aerogel comprises the following steps:

[0014] (1) Magnetic modification of graphene oxide nanosheet:

[0015] The magnetic graphene oxide nanosheet is obtained by one of the following two methods: grafting magnetic Fe3O4 nanoparticles by using interfunctional group reaction or in-situ growing magnetic Fe3O4 nanoparticles by coprecipitation.

[0016] The method of grafting magnetic Fe3O4 nanoparticles by using interfunctional group reaction is as follows: the amino group of the surface of the existing magnetic Fe3O4 nanoparticles is modified by silane ligand exchange, and the magnetic modification is realized by interreaction between the magnetic Fe3O4 nanoparticles and the carboxyl functional group on the surface of the graphene oxide nanosheet to obtain the magnetic graphene oxide nanosheet; the size of the magnetic Fe3O4 nanoparticles is 10-200 nm.

[0017] The method of in-situ growing magnetic Fe3O4 nanoparticles by coprecipitation is as follows: the precursors of Fe 2+ and Fe 3+ are added to the graphene oxide dispersion, and the magnetic graphene oxide nanosheet is generated in-situ by coprecipitation under the condition of heating and alkaline catalysis.

[0018] (2) Preparation of reversible fire warning composite aerogel: in the biomass matrix aqueous solution, under the condition of ultrasonic frequency of 38-42 KHz (preferably 40 KHz) and temperature of 22-28℃ (preferably 25℃), add expanded graphite nanosheets of mass (1.12-17.65) wt% and magnetic graphene oxide nanosheets prepared in step (1) of mass (11.2-176.5) wt% to the biomass matrix aqueous solution, and the mass ratio of the magnetic graphene oxide nanosheets and the expanded graphite nanosheets is (20-5):1; carry out ultrasonic dispersion, the ultrasonic dispersion time is 0.5-1h, and then realize three-dimensional network structure construction through intermolecular hydrogen bond induction self-assembly, then carry out aging treatment, the aging treatment time is 2-6h, then carry out freeze-drying treatment, the freeze-drying temperature is-20-(-80)℃, and the freeze-drying time is 12-24h, to prepare the reversible fire warning composite aerogel.

[0019] As preferred, the method for grafting magnetic Fe3O4 nanoparticles by reaction between functional groups is as follows:

[0020] I, 0.18-0.22M sodium oleate aqueous solution and 0.18-0.22M anhydrous ferric chloride aqueous solution are mixed in a volume ratio of 1:(0.9-1.1), the red-brown precipitate is generated after sufficient stirring, then the precipitate is dried in a vacuum oven after filtration and deionized water washing, the wax-like substance is obtained after drying, the wax-like substance is dissolved in ethanol, the volume of ethanol is 55-65% of the volume of the sodium oleate aqueous solution, then oleic acid is added to the ethanol and mixed uniformly, the volume of the oleic acid is 8-12% of the volume of the ethanol, then the mixture is transferred to a polytetrafluoroethylene high-pressure reaction kettle, and the mixture is reacted at a temperature of 175-185℃ for 4-6h, then the mixture is washed with anhydrous ethanol, and then the mixture is separated by a magnet, and the separated substance is dispersed in toluene to obtain a Fe3O4 nanoparticle toluene dispersion.

[0021] II, the modification is performed by using a silane ligand exchange method, that is, under the condition of ultrasonic frequency of 38-43 KHz (preferably 40 KHz) and temperature of 21-28℃ (preferably 25℃), 0.4-0.6% of amino silane and 0.008-0.015% of acetic acid are added to the Fe3O4 nanoparticle toluene dispersion obtained in step I, and the mixture is ultrasonically dispersed for 15-30min; then the mixture is stirred at room temperature for 22-48h; then the mixture is washed with toluene, and then the mixture is separated by a magnet, and the separated substance is subjected to freeze-drying treatment to obtain amino-modified magnetic Fe3O4 nanoparticles; and the surface of the magnetic Fe3O4 nanoparticles is modified with amino groups through silane ligand exchange.

[0022] III, then the reaction between the amino-modified magnetic Fe3O4 nanoparticles and the carboxyl functional groups on the surface of the graphene oxide nanosheets is used to achieve magnetization modification, to obtain magnetic graphene oxide nanosheets.

[0023] The reaction between the amino-modified magnetic Fe3O4 nanoparticles and the carboxyl functional groups on the surface of the graphene oxide nanosheets is preferably: the graphene oxide nanosheets are uniformly dispersed in water (preferably, for example, 1 g of graphene oxide nanosheets is dispersed in 50 mL of water), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) are added thereto (preferably, the ratio of the two is 1.5-2.5:1), after activation at room temperature for 10-18 min, the amino-modified magnetic Fe3O4 nanoparticles prepared in step II are added thereto (preferably, the addition ratio is 8-12 wt% of the graphene oxide nanosheets), and ultrasonic reaction is performed for 10-15 h, to prepare magnetic carbon nanotubes (i.e., magnetic graphene oxide nanosheets).

[0024] As a preference, the amino silane is one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 4-aminobutyldimethylmethoxysilane, 4-aminobutyltriethoxysilane, 3-[(2-aminoethylamino)propyl]dimethoxysilane, and (3-aminopropyl)dimethylethoxysilane.

[0025] As a preference, the method for co-precipitation in-situ growth of magnetic Fe3O4 nanoparticles is: under magnetic stirring at a rotation speed of 500-800 rpm, graphene oxide nanosheets are ultrasonically dispersed in deionized water to obtain a graphene oxide dispersion, wherein the graphene oxide nanosheets: deionized water is (1.5-2.5) g: (48-52) mL; then, deoxygenation is performed by passing in an inert gas for 1.8-2.2 h, then a deionized water volume of 0.8-1.5% of a molar ratio of (1.5-2.5):1 of Fe 3+ and Fe 2+ solutions is added, stirring is continued at room temperature under the protection of the inert gas for 2-5 h, then the temperature is raised to 70-90°C, then ammonia water is added to adjust the pH value of the solution to 9-12, and the reaction is continued at a temperature of 70-90°C for 1-2 h, to obtain magnetic graphene oxide nanosheets.

[0026] As a preference, the inert gas is N2.

[0027] As a preference, the mass ratio of the magnetic graphene oxide nanosheets and the expanded graphite nanosheets is 10:1.

[0028] The application of a reversible fire warning composite aerogel, the application is in the field of high-rise building fire alarm and fire retardant, heat insulation, fire fighting; the reversible fire warning composite aerogel is the reversible fire warning composite aerogel or the reversible fire warning composite aerogel prepared by the preparation method.

[0029] As preferred, the application is to use magnetic Fe3O4 nanoparticles with reversible resistance-temperature response as fire warning functional body, graphene oxide nanosheet with single thermal reduction and multiple thermal conduction characteristics as carrier of Fe3O4, and to realize the synergistic effect of breaking through the limitation of single temperature monitoring. In normal state, the reversible fire warning composite aerogel does not trigger fire warning and light the warning light; when encountering fire or high temperature for the first time, the resistance of magnetic Fe3O4 nanoparticles decreases, and at the same time, the resistance of graphene oxide nanosheet sharply decreases due to the removal of functional groups by thermal reduction, so that the resistance and current change significantly in the closed circuit, triggering the warning and / or lighting the warning light; when encountering fire or high temperature for the Nth time (N≥2), the resistance of magnetic Fe3O4 nanoparticles still reversibly decreases, while the graphene sheet only provides a continuous electron conduction path, thereby assisting the magnetic Fe3O4 nanoparticles to realize repeated fire warning and / or lighting the warning light.

[0030] The reversible fire warning composite aerogel has excellent fire retardant performance, wherein: the inorganic Fe3O4 nanoparticles and expanded graphite nanosheet act as fire retardant functional bodies, respectively playing the roles of catalyzing carbonization and physical barrier of sheet layer; the biomass matrix such as cellulose is beneficial to carbon formation and forms a stable and dense carbon layer; and the synergistic effect of each component improves the fire retardant performance. Excellent fire retardant performance is the basis for the material to realize fire warning. In order to realize rapid flame detection and fire warning alarm response, the material should have thermal stability and fire retardancy during detection, otherwise it cannot realize timely and reliable alarm.

[0031] The reversible fire warning composite aerogel has repeatable temperature monitoring performance. Fe3O4 nanoparticles with reversible resistance-temperature response act as fire warning functional body, and graphene oxide nanosheet with single thermal reduction and multiple thermal conduction characteristics act as carrier of Fe3O4, and the synergistic effect breaks through the limitation of single temperature monitoring. In normal state, the composite aerogel does not trigger fire warning and light the warning light; when encountering fire / high temperature for the first time, the resistance of Fe3O4 nanoparticles decreases, and at the same time, the resistance of graphene oxide sharply decreases due to the removal of functional groups by thermal reduction, so that the resistance / current changes significantly in the closed circuit, triggering the warning and lighting the warning light; in the Nth (N≥2) fire / high temperature state, the resistance of Fe3O4 nanoparticles still reversibly decreases, and at this time, the graphene sheet only provides a continuous electron conduction path, thereby assisting the Fe3O4 nanoparticles to realize repeated fire warning and lighting the warning light.

[0032] A reversible fire warning performance test scheme of the reversible fire warning composite aerogel is influenced by the non-constant resistance change rule of graphene oxide, a reasonable test method needs to be designed, a "three-step" test scheme is selected, specifically including: first, the resistance-temperature response curve of three aerogel samples (GO-Fe3O4, GO only and Fe3O4 only) in the range of 30-400 DEG C is determined by using a four-probe resistivity meter; second, the sample is placed on a heating plate for alternating heating (300 DEG C) and cooling (room temperature) treatment, and the output current curve is determined by using a digital multimeter to characterize the reversibility of the resistance-temperature response, and a reasonable trigger warning resistance value is set; finally, a complete circuit containing the aerogel sample, the alarm indicator lamp and the power supply is designed, the sample is exposed to the alcohol lamp flame with a period of 20s or 40s, and the current change and the lighting of the alarm lamp are recorded.

[0033] The technical effect of the present application is that:

[0034] The present application produces a series of composite aerogels by reasonably and specifically setting the composition of each component of the reversible fire warning and the production parameters of each step in the preparation method, establishes the internal relationship between material composition-structure-performance, and realizes the optimization design of the preparation parameters and process of the aerogel in a performance-oriented manner.

[0035] The present application sets the composition of the specific product by exploring the fire retardant and reversible fire warning mechanism and revealing the mechanism of the above performance from the molecular level, and further improves the fire safety performance of the aerogel material, which can be applied in the fields of high-rise building fire alarm, fire retardant, heat insulation, fire fighting and the like. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of the reversible fire warning composite aerogel (magnetic graphene oxide / expanding graphite / biomass matrix).

[0037] Figure 2 It is a fire warning schematic diagram of the reversible fire warning composite aerogel.

[0038] Figure 3 It is a repeatable temperature monitoring schematic diagram of the reversible fire warning composite aerogel. DETAILED DESCRIPTION

[0039] The preferred embodiments of the present application will be described in detail below with reference to the embodiments. It should be understood that the following embodiments are given only for the purpose of illustration, and are not intended to limit the scope of the present application. Those skilled in the art can make various modifications and replacements to the present application without departing from the purpose and spirit of the present application.

[0040] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available unless otherwise specified.

[0041] Example 1

[0042] This example provides a preparation method of a graphene oxide in-situ magnetization modified composite aerogel with high fire safety performance and reversible fire warning of the present application, and the preparation structure is as shown in Figure 1 The specific steps include the following:

[0043] (1) Preparation of magnetic graphene oxide nanosheet

[0044] Synthesized by coprecipitation method, specifically, 2 g of graphene oxide nanosheet was ultrasonically dispersed in 50 mL of deionized water, deoxygenated by N2 for 2 h, then 0.5 mL of Fe 3+ / Fe 2+ (1.6 g of FeCl3·6H2O and 0.93 g of FeSO4·7H2O) with a molar ratio of 2:1 was added, stirred at room temperature under N2 protection for 5 h, then heated to 80°C, ammonia was added to adjust the solution pH to 12, reacted for 1 h, then collected by a magnet and washed with deionized water for 3 times to obtain magnetic graphene oxide nanosheet, marked as GO@Fe3O4.

[0045] (2) Preparation of reversible fire warning composite aerogel

[0046] 3 g of cellulose nanofiber was dispersed in 6 mL of deionized water, ultrasonically dispersed. 0.5 g of GO@Fe3O4 and 0.25 g of expanded graphite nanosheet were added respectively, and ultrasonic reaction was carried out for 2 h. Subsequently, the obtained cross-linked hydrogel was aged at room temperature for 3 h, and then freeze-dried (-45°C, 260 Pa) for 18 h to prepare the reversible fire warning composite aerogel.

[0047] Example 2

[0048] This example provides a preparation method of graphene oxide grafted magnetic particle modified composite aerogel with high fire safety performance and reversible fire warning of the present application, and the preparation process is as follows:

[0049] (1) Preparation of Fe3O4 nanoparticles

[0050] 100 mL of aqueous sodium oleate solution (0.2 M) was mixed with 100 mL of aqueous anhydrous ferric chloride solution (0.2 M), and a red-brown precipitate was generated by stirring, filtered, washed with deionized water, and then dried in a vacuum oven. The dried wax was dissolved in 60 mL of ethanol, 6 mL of oleic acid was added and mixed uniformly, and then transferred to a polytetrafluoroethylene high-pressure reaction kettle, and reacted at 180°C for 5 h. After washing with anhydrous ethanol and magnetic separation, it was dispersed in toluene for standby.

[0051] (2) Amino-modification of Fe3O4 nanoparticles

[0052] The modification was performed by silane ligand exchange method, i.e. 100 mL Fe3O4 nanoparticles (0.1 g) toluene dispersion was added with 0.5% (v / v) 3-aminopropyltriethoxysilane and 0.01% (v / v) acetic acid, and stirred at room temperature for 24 h. After washing with toluene, magnetic separation and freeze-drying, the prepared Fe3O4@NH2 was ready for use.

[0053] (3) Preparation of magnetic graphene oxide nanoplatelets

[0054] 1 g graphene oxide nanoplatelets were uniformly dispersed in 50 mL water, and 0.62 g 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 0.31 g N-hydroxysuccinimide (NHS) were added thereto. After activation reaction at room temperature for 15 min, 0.1 g Fe3O4@NH2 nanoparticles were added thereto, and ultrasonic reaction was performed for 12 h to prepare magnetic carbon nanotubes, which were marked as GO@Fe3O4.

[0055] (4) Preparation of reversible fire warning composite aerogel

[0056] 3 g cellulose nanofibers were dispersed in 6 mL deionized water, and ultrasonic dispersion was performed. 0.75 g GO@Fe3O4 and 0.375 g expanded graphite nanoplatelets were added thereto, and ultrasonic reaction was performed for 2 h. Subsequently, the obtained crosslinked hydrogel was aged at room temperature for 3 h, and freeze-drying (-45℃, 260 Pa) was performed for 18 h to prepare a composite aerogel.

[0057] Application example

[0058] The reversible fire warning composite aerogel described in the present application makes full use of the reversible resistance-temperature response characteristics of Fe3O4 nanoparticles, the single thermal reduction and multiple thermal conduction characteristics of Fe3O4 carrier graphene oxide nanoplatelets, and breaks through the limitation of single temperature monitoring. In a normal state, the composite aerogel does not trigger fire warning and light up the warning light (as shown in a of Figure 2 When encountering fire / high temperature for the first time, the resistance of Fe3O4 nanoparticles decreases, and the resistance of graphene oxide sharply decreases due to thermal reduction, which significantly triggers warning and lights up the warning light (as shown in b1 of Figure 2 In the Nth (N≥2) fire / high temperature state, the resistance of Fe3O4 nanoparticles is still reversibly reduced, and at this time, the graphene sheet only provides a continuous electron conduction path to assist Fe3O4 nanoparticles to realize repeated fire warning and light up the warning light (as shown in b2 of Figure 2 ​

[0059] The application example provides a reversible fire warning performance characterization scheme of the composite aerogel with high fire safety performance of the application. Influenced by the non-constant resistance change rule of graphene oxide, a reasonable test method needs to be designed, and a "three-step" test scheme is selected, specifically including: first, the resistance-temperature response curve of three aerogel samples (GO-Fe3O4, only GO and only Fe3O4) in the range of 30-400 DEG C is determined by using a four-probe resistivity meter; second, the sample is placed on a heating plate for alternating heating (300 DEG C) and cooling (room temperature) treatment, and the output current curve is determined by using a digital multimeter to characterize the reversibility of the resistance-temperature response, and a reasonable trigger warning resistance value is set; finally, a complete circuit including the aerogel sample, the alarm indicator lamp and the power supply is designed, the sample is exposed to the alcohol lamp flame with a period of 20 s or 40 s, and the current change and the alarm lamp lighting condition are recorded. Figure 3 The experimental results have significant differences with the current single change and subsequent constant results of the graphene-based aerogel (left figure), and the current appears corresponding periodic change (right figure), which proves the repeatability of temperature monitoring. Figure 3 Figure 3 The left figure is that when the graphene aerogel encounters high temperature for the first time, the resistance decreases and the current increases after the removal of functional groups such as amino and carboxyl groups; but the functional group removal process is irreversible, and there is no functional group to remove when the temperature is encountered for the nth time, the resistance no longer changes, and only single warning can be realized. Figure 3 The right figure is the Fe3O4 semiconductor effect in the application, the resistance changes reversibly with temperature, and repeated monitoring can be realized.

[0060] The reversible fire warning composite aerogel has improved fire safety performance and can be applied to high-rise building fire alarm, flame retardant, heat insulation, fire fighting and other fields.

[0061] Although the application has been described in detail in the foregoing general description and specific embodiments, some modifications or improvements can be made on the basis of the application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the application are within the scope of the application claimed.​

Claims

1. A reversible fire warning composite aerogel, characterized in that, The reversible fire warning composite aerogel is prepared by magnetic graphene oxide nanosheets, expanded graphite nanosheets and biomass matrix through intermolecular hydrogen bond crosslinking, self-assembly into 3D structure, and then freeze-drying; specifically, the reversible fire warning composite aerogel is prepared by the following steps: (1) one of the two methods of grafting magnetic Fe3O4 nanoparticles by using intermolecular reaction or in-situ growth of magnetic Fe3O4 nanoparticles by coprecipitation is used to obtain magnetic graphene oxide nanosheets; The method of grafting magnetic Fe3O4 nanoparticles by using intermolecular reaction is as follows: the surface of the existing magnetic Fe3O4 nanoparticles is modified with amino groups by silane ligand exchange, and the magnetic graphene oxide nanosheets are obtained by magnetization modification using the intermolecular reaction between the surface carboxyl functional groups of the magnetic Fe3O4 nanoparticles and the graphene oxide nanosheets; the size of the magnetic Fe3O4 nanoparticles is 10-200 nm; The method for co-precipitation in-situ growth of magnetic Fe3O4 nanoparticles is: adding Fe 2+ and Fe 3+ precursors in the graphene oxide dispersion, co-precipitating magnetic graphene oxide nanosheets in-situ under heating condition through alkaline catalysis; (2) in the biomass matrix aqueous solution, under the condition of ultrasonic frequency of 38-42 KHz and temperature of 22-28℃, the expanded graphite nanosheets with mass of (1.12-17.65) wt% and the magnetic graphene oxide nanosheets prepared in step (1) with mass of (11.2-176.5) wt% are added to the biomass matrix aqueous solution, and the mass ratio of the magnetic graphene oxide nanosheets and the expanded graphite nanosheets is (20-5):1; ultrasonic dispersion is carried out for 0.5-1 h, three-dimensional network structure is constructed by using intermolecular hydrogen bond induced self-assembly, then aging treatment is carried out for 2-6 h, and then freeze-drying treatment is carried out at a temperature of -20 to (-80) ℃ for 12-24 h to prepare the reversible fire warning composite aerogel; The magnetic graphene oxide nanosheets are magnetic Fe3O4 nanoparticle modified graphene oxide nanosheets; The expanded graphite nanosheets are expanded graphite nanosheets that can instantaneously expand 100-250 times in volume and change from sheet shape to worm shape to form a good thermal insulation layer when high temperature is encountered; the mass ratio of the expanded graphite nanosheets in the reversible fire warning composite aerogel is 0.5-6 wt%; The expanded graphite nanosheets and the biomass matrix serve as carbon sources to form a stable and dense carbon layer; The biomass matrix is one or more of carboxymethyl chitosan, hydroxypropyl chitosan, hydroxypropyl methyl cellulose, cellulose nanofiber and sodium alginate.

2. The reversible fire warning composite aerogel of claim 1, wherein, The mass ratio of the magnetized graphene oxide nanosheets in the reversible fire warning composite aerogel is 10-60 wt%, and the content of the magnetic Fe3O4 nanoparticles is the upper limit of the amount of magnetic Fe3O4 nanoparticles that can be grown and / or grafted on the graphene oxide sheets.

3. The reversible fire warning composite aerogel according to claim 1 or 2, characterized in that, The magnetic Fe3O4 nanoparticles and the expanded graphite nanosheets are flame retardant functional bodies in the reversible fire warning composite aerogel, and respectively play the roles of catalyzing carbonization and expanding physical barrier.

4. A method of preparing a reversible fire warning composite aerogel, characterized by, The reversible fire warning composite aerogel is the reversible fire warning composite aerogel according to any one of claims 1-3, and the preparation method comprises the following steps: (1) magnetization modification of graphene oxide nanosheets: The magnetic graphene oxide nanosheet is obtained by one of the following two methods: grafting magnetic Fe3O4 nanoparticles by using functional group reaction or in-situ growing magnetic Fe3O4 nanoparticles by co-precipitation; The method for grafting magnetic Fe3O4 nanoparticles by using functional group reaction is as follows: the surface of the existing magnetic Fe3O4 nanoparticles is modified by amino groups through silane ligand exchange, and the magnetic graphene oxide nanosheet is obtained by using the reaction between the magnetic Fe3O4 nanoparticles and the carboxyl functional groups on the surface of the graphene oxide nanosheet; the size of the magnetic Fe3O4 nanoparticles is 10-200 nm; The method for co-precipitation in-situ growth of magnetic Fe3O4 nanoparticles is: adding Fe 2+ and Fe 3+ precursors in the graphene oxide dispersion, co-precipitating in-situ to generate magnetic graphene oxide nanosheets under the condition of alkaline catalysis and heating. (2) reversible fire warning composite aerogel preparation: under the conditions of an ultrasonic frequency of 38-42 KHz and a temperature of 22-28 ℃, expandable graphite nanosheets with a mass of (1.12-17.65) wt% of the biomass matrix aqueous solution and the magnetic graphene oxide nanosheets prepared in step (1) with a mass of (11.2-176.5) wt% of the biomass matrix aqueous solution are added to the biomass matrix aqueous solution, and the mass ratio of the magnetic graphene oxide nanosheets to the expandable graphite nanosheets is (20-5):1; ultrasonic dispersion is performed for 0.5-1 h, a three-dimensional network structure is constructed by using intermolecular hydrogen bond-induced self-assembly, then aging treatment is performed for 2-6 h, and then freeze-drying treatment is performed at a temperature of -20-(-80) ℃ for 12-24 h to prepare the reversible fire warning composite aerogel.

5. The method of claim 4, wherein the reversible fire warning composite aerogel is prepared by the steps of: The method for grafting magnetic Fe3O4 nanoparticles by using functional group reaction is as follows: I, 0.18-0.22 M sodium oleate aqueous solution and 0.18-0.22 M anhydrous ferric chloride aqueous solution are mixed in a volume ratio of 1:(0.9-1.1), and a red-brown precipitate is generated after sufficient stirring, then the precipitate is dried in a vacuum oven after filtration and deionized water washing, a wax-like substance is obtained after drying, the wax-like substance is dissolved in ethanol, the volume of the ethanol is 55-65% of the volume of the sodium oleate aqueous solution, then oleic acid is added to the ethanol and mixed uniformly, the addition amount of the oleic acid is 8-12% of the volume of the ethanol, then the mixture is transferred to a polytetrafluoroethylene high-pressure reaction kettle, and the mixture is reacted at a temperature of 175-185 ℃ for 4-6 h, then the mixture is washed with anhydrous ethanol, and then the mixture is separated by a magnet, and the separated substance is dispersed in toluene to obtain a Fe3O4 nanoparticle toluene dispersion; II, modification by silane ligand exchange method, namely under the condition of ultrasonic frequency of 38-43 KHz and temperature of 21-28℃, adding volume percentage of 0.4-0.6% amino silane and volume percentage of 0.008-0.015 acetic acid to the Fe3O4 nanoparticles toluene dispersion liquid obtained in step I, ultrasonic for 15-30 min; then stirring at room temperature for 22-48 h; then washing with toluene, separating by magnet, and then freezing drying to obtain amino modified magnetic Fe3O4 nanoparticles; realizing amino modification on the surface of magnetic Fe3O4 nanoparticles by silane ligand exchange; III, realizing magnetization modification by the reaction between the amino modified magnetic Fe3O4 nanoparticles of step II and the carboxyl functional groups on the surface of graphene oxide nanosheet, to obtain magnetic graphene oxide nanosheet.

6. The preparation method of the reversible fire warning composite aerogel according to claim 5, wherein the amino silane is one or more of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, 4-aminobutyldimethylmethoxysilane, 4-aminobutyltriethoxysilane, 3-[(2-aminoethylamino)propyl]dimethoxysilane, and (3-aminopropyl)dimethylethoxysilane.

7. The method of claim 4, wherein the reversible fire warning composite aerogel is prepared by the steps of: The method for co-precipitation in-situ growth of magnetic Fe3O4 nanoparticles is as follows: under magnetic stirring at a rotating speed of 500-800 rpm, graphene oxide nanosheets are ultrasonically dispersed in deionized water to obtain a graphene oxide dispersion, wherein the graphene oxide nanosheets:deionized water is (1.5-2.5) g:(48-52) mL; then, inert gas is introduced for oxygen removal for 1.8-2.2 h, then a deionized water volume of 0.8-1.5% of a molar ratio of (1.5-2.5):1 of Fe 3+ and Fe 2+ aqueous solution is added, stirring at room temperature under the protection of inert gas for 2-5 h, then the temperature is increased to 70-90℃, then ammonia water is added to adjust the pH value of the solution to 9-12, the temperature is continuously maintained at 70-90℃, and the reaction is carried out for 1-2 h, to obtain magnetic graphene oxide nanosheets.

8. The method of claim 4, wherein the reversible fire warning composite aerogel is prepared by the steps of: The mass ratio of the magnetic graphene oxide nanosheet and the expanded graphite nanosheet is 10:

1.

9. Use of a reversible fire warning composite aerogel, characterized in that, The application is the application in the field of high-rise building fire alarm and fire retardant, heat insulation and fire fighting; the reversible fire warning composite aerogel is the reversible fire warning composite aerogel of any one of claims 1-3 or the reversible fire warning composite aerogel prepared by the preparation method of any one of claims 4-8.

10. Use of a reversible fire warning composite aerogel according to claim 9, characterized in that, The application is realized by using the magnetic Fe3O4 nanoparticles with reversible resistance-temperature response as the fire warning functional body, the graphene oxide nanosheet with single heat reduction and multiple heat conduction characteristics as the carrier of Fe3O4, and the synergistic effect breaking through the limitation of single temperature monitoring; under normal condition, the reversible fire warning composite aerogel does not trigger the fire warning and light up the warning light; when encountering fire or receiving high temperature for the first time, the resistance of the magnetic Fe3O4 nanoparticles decreases, and the graphene oxide nanosheet sharply reduces the resistance due to the heat reduction effect, so that the resistance and current in the closed circuit change significantly to trigger the warning and / or light up the warning light; when encountering fire or receiving high temperature for the Nth time, wherein N≥2, the resistance of the magnetic Fe3O4 nanoparticles still reversibly decreases, and the graphene sheet only provides a continuous electron conduction path to assist the magnetic Fe3O4 nanoparticles to realize repeated fire warning and / or light up the warning light.

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