A graphene-based composite material, a preparation method and application thereof

Abstract

The application provides a graphene-based composite material and a preparation method and application thereof, the graphene-based composite material comprising reduced graphene, a first functional material and a second functional material; the first functional material comprising at least one of 1,3,5-benzenetricarboxylic acid, m-dihydroxybenzene, p-dihydroxybenzene, o-dihydroxybenzene, 2,5-dihydroxybenzoic acid, 1,5-naphthalene disulfonic acid, 2,6-naphthalene disulfonic acid sodium and anthraquinone-2-sulfonic acid sodium; and the second functional material comprising at least one of a metal, a metal oxide and a conductive polymer. The sensing element or sensor prepared from the graphene-based composite material can realize the integration of humidity and gas (such as formaldehyde and NO2) detection functions under light assistance, greatly saving space and improving detection efficiency. Meanwhile, the sensing element or sensor prepared from the graphene-based composite material has higher sensitivity and faster response speed, thereby laying a foundation for preparing commercialized humidity and gas sensitive cooperative detection sensors.

Description

Technical Field

[0001] This invention belongs to the field of composite materials and sensing technology, specifically relating to a graphene-based composite material, its preparation method, and its application. Background Technology

[0002] Humidity measurement and control are crucial in precision instruments, semiconductor integrated circuits, and component manufacturing plants. Furthermore, humidity sensors are widely used in weather forecasting, medicine, food processing, and other fields. When people breathe (inhale and exhale), the humidity of the air changes. It can reflect the body's activity level and serve as one of the most important health indicators. Because humidity sensors are vital to human production and daily life, there is an urgent need to develop reliable humidity sensors.

[0003] Depending on the output voltage, humidity sensors are classified into resistive, capacitive, and frequency-based types. Resistive humidity sensors offer advantages such as reusability, low cost, ease of mass production, and miniaturization, making them one of the most widely researched humidity sensors. Various materials, such as ceramics, organic polymers, semiconductors, and electrolytes, have been extensively studied as humidity sensing materials. Graphene, due to its large specific surface area, strong adsorption capacity, and inherent flexibility, has been widely researched and applied in resistive humidity sensors. However, graphene exhibits poor hydrophilicity during water absorption and poor repeatability after water absorption, limiting its applications.

[0004] In practical applications, accurate and efficient humidity detection is required, as well as the ability to identify the levels of other harmful gases under high humidity conditions. Furthermore, in addition to the importance of humidity detection, the detection of harmful gases such as formaldehyde and NO2 is also crucial in daily life.

[0005] However, traditional humidity sensors and gas sensors (such as formaldehyde and NO2) often operate independently (i.e., humidity-sensitive elements and gas-sensitive elements are fabricated separately and tested separately), which not only occupies a large space but also has low detection efficiency. At the same time, some existing detection methods cannot guarantee detection accuracy in complex environments, especially under high humidity, which can interfere with the sensor's monitoring of other target gases, failing to meet the growing demand for high-precision detection. Summary of the Invention

[0006] To address the problems and shortcomings of existing technologies, this invention provides a graphene-based composite material, its preparation method, and its applications. Sensing elements or sensors prepared using this graphene-based composite material can integrate humidity and gas (such as formaldehyde and NO2) detection functions under light assistance, significantly saving space and improving detection efficiency. Furthermore, the sensing elements or sensors prepared using this graphene-based composite material exhibit higher sensitivity and faster response speed, laying the foundation for the preparation of commercially available humidity and gas-sensing co-detection sensors.

[0007] According to a first aspect of the present invention, a graphene-based composite material is provided, comprising reduced graphene, a first functional material, and a second functional material; the first functional material comprises at least one selected from 1,3,5-benzenetricarboxylic acid, resorcinol, catechol, 2,5-dihydroxybenzoic acid, 1,5-naphthalenedisulfonic acid, sodium 2,6-naphthalenedisulfonic acid, and sodium anthraquinone-2-sulfonate; the second functional material comprises at least one selected from metal, metal oxide, and conductive polymer.

[0008] As mentioned in the background section, graphene has been widely studied and applied in resistive humidity sensors due to its large specific surface area, strong adsorption capacity, and inherent flexibility. Furthermore, graphene has also been extensively studied and applied in gas sensors for harmful gases such as formaldehyde and NO2. However, graphene exhibits poor hydrophilicity during water absorption and poor repeatability after water absorption, limiting its applications. Therefore, improving the hydrophilicity and stability of graphene after water absorption is of great significance for obtaining humidity and gas sensors with high sensitivity and accuracy.

[0009] The graphene-based composite material designed in this invention comprises reduced graphene, a first functional material (organic molecule), and a second functional material (metal, metal oxide, or conductive polymer). Reduced graphene exhibits higher chemical stability and conductivity compared to graphene oxide, while retaining the original graphene's large specific surface area, strong adsorption capacity, and inherent flexibility. This makes it more advantageous as a sensor material, ensuring sensor stability, detection accuracy, and sensitivity. However, the reactivity of pure reduced graphene is not ideal under certain conditions, particularly in humid (high humidity) environments, affecting its detection performance for specific gases such as formaldehyde and NO2. Furthermore, the sensitivity of pure reduced graphene for detecting certain trace substances may not meet requirements.

[0010] Therefore, this invention provides a graphene-based composite material, which modifies the surface of reduced graphene with the aforementioned first functional material (organic molecule) and second functional material (metal, metal oxide, or conductive polymer). Firstly, the first functional material contains an aromatic cyclic conjugated structure, which can interact with graphene via π-π interactions. Therefore, the first functional material can effectively modify graphene, improving its dispersibility and electron transport properties. Furthermore, in addition to the conjugated structure, some of the organic molecules provided by this invention also contain carboxyl or hydroxyl groups or charged functional groups. Since reduced graphene is usually derived from the reduction of graphene oxide, the final reduced graphene still carries some active groups such as hydroxyl and carboxyl groups. Therefore, the organic molecules can also combine with the reduced graphene via non-covalent bonds such as hydrogen bonds or electrostatic bonds, thus further optimizing the dispersibility and electron transport properties of graphene. Moreover, the organic molecules have specific responses, thus enabling stable sensing in humidity sensing. In particular, organic molecules with aromatic benzene rings or conjugated structures can further optimize the electronic transport stability and sensitivity of the sensing process, thus improving the sensitivity and accuracy of the material sensing. Secondly, the secondary functional material further improves the resistive stability of graphene-based composite materials, giving them a more stable and sensitive resistive response, i.e., higher sensitivity in humidity detection and gas (such as formaldehyde and NO2) detection.

[0011] Secondly, the aforementioned first functional material (organic molecules) can modulate the photothermal effect under light source assistance, effectively enabling high-performance sensors for complete gas detection. Experience shows that light sources can damage materials and even cause them to burn under excessive light intensity. Adding organic molecules helps improve the overall stability and thermal conductivity of graphene materials, thus protecting them and ensuring stable response to target substances in complex environments, achieving highly stable and sensitive sensing of gases such as formaldehyde and NO2. Simultaneously, the second functional material can assist the first functional material in further optimizing and modulating the photothermal effect under light source assistance. For example, metals have surface plasmon resonance effects, absorbing light energy of specific wavelengths and converting it into heat energy, thereby affecting the photothermal effect; metal oxides and conductive polymers also absorb light energy and produce photothermal effects, thus modulating the overall photothermal effect. Furthermore, the second functional material, besides modulating the photothermal effect, also plays other important roles. For example, metals or metal oxides can act as active sites, undergoing specific chemical reactions with target gases (such as formaldehyde and NO2), thereby improving the sensor's sensitivity to the target gas.

[0012] Furthermore, it is important to emphasize that the graphene-based composite material provided by this invention enables the synergistic detection of humidity and gas, effectively overcoming the limitations of traditional humidity and gas sensors operating independently, as well as the significant humidity-dependent nature of gas sensors. This provides a novel solution for detection work in related fields. Specifically, the sensor provided by this invention can achieve sensitive detection not only of humidity but also of target gases (such as formaldehyde and NO2) that are significantly affected by humidity. In other words, it can maintain high sensitivity for detecting target gases (such as formaldehyde and NO2) even under high humidity conditions, avoiding the influence of humidity on the detection of these gases.

[0013] Preferably, the mass ratio of reduced graphene, the first functional material, and the second functional material is (0.1~7):(10~300):(1~1000). At this ratio, the three materials exhibit better synergistic effects, meaning they can more fully utilize their beneficial properties, resulting in a better balance of overall stability, thermal conductivity, and other comprehensive properties of the graphene-based composite material. This leads to higher sensing performance for humidity and gas in the graphene-based composite material.

[0014] Preferably, the mass ratio of reduced graphene, the first functional material, and the second functional material is (0.1~5):(10~200):(1~500). Preferably, the mass ratio of reduced graphene, the first functional material, and the second functional material is (0.1~5):(10~200):(1~200). Preferably, the mass ratio of reduced graphene, the first functional material, and the second functional material is (0.1~5):(10~200):(1~100). Preferably, the mass ratio of reduced graphene, the first functional material, and the second functional material is (0.1~5):(10~200):(1~50).

[0015] Preferably, the metal includes at least one of Au, Ag, Cu, Fe, and Pt; the metal oxide includes at least one of titanium dioxide, zinc oxide, tin oxide, indium oxide, tungsten trioxide, copper oxide, ferric oxide, ferric oxide, molybdenum trioxide, cobalt trioxide, and cerium oxide; and the conductive polymer includes at least one of polyaniline, polypyrrole, and polythiophene.

[0016] Preferably, the first functional material includes at least one of 1,3,5-benzenetriformic acid and resorcinol.

[0017] Preferably, the second functional material includes at least one of Ag, zinc oxide, and polyaniline.

[0018] Preferably, the graphene-based composite material comprises reduced graphene, 1,3,5-benzenetricarboxylic acid, and Ag; or the graphene-based composite material comprises reduced graphene, 1,3,5-benzenetricarboxylic acid, and zinc oxide; or the graphene-based composite material comprises reduced graphene, resorcinol, and polyaniline. Further optimization of the combination of various materials is more conducive to leveraging the interactions between materials, thereby improving the sensitivity and accuracy of the graphene-based composite material in detecting humidity and gases.

[0019] According to a second aspect of the present invention, a method for preparing the above-mentioned graphene-based composite material is provided. When the second functional material includes a metal, the preparation method includes the following steps: S11. Preparing a graphene oxide dispersion using graphene oxide and water; S12. Mixing the first functional material with water, then adjusting the pH of the resulting solution to 6.8-7.2, then adding the graphene oxide dispersion and a metal salt solution containing the metal, mixing evenly, then adding a reducing agent solution, and reacting at 85-95°C for 0.5-2 hours; S13. Filtering and washing the mixture after the reaction in S12 to obtain the graphene-based composite material. Through the above steps, a graphene-based composite material with good composite properties of reduced graphene, the first functional material (organic molecule), and the metal can be obtained. Furthermore, the obtained graphene-based composite material can achieve synergistic detection of humidity and gas, with high detection sensitivity and accuracy.

[0020] Preferably, in step S11, the concentration of the graphene oxide dispersion is 0.5~5 mg / L. More preferably, in step S11, the concentration of the graphene oxide dispersion is 0.5~2 mg / L.

[0021] Preferably, in step S12, the mass-to-volume ratio of the first functional material to water is 80-300 mg:40 mL. More preferably, in step S12, the mass-to-volume ratio of the first functional material to water is 100-250 mg:40 mL.

[0022] Preferably, in step S12, the pH is adjusted to 6.8-7.2 using an alkaline solution; the alkaline solution includes at least one of sodium hydroxide solution and potassium hydroxide solution. Preferably, the mass concentration of the alkaline solution is 7-15 wt%.

[0023] Preferably, in S12, the metal salt solution contains at least one of the following: chloroauric acid, silver chloride, silver nitrate, chloroplatinic acid, copper nitrate, and ferric chloride. Preferably, in S12, the concentration of the metal salt solution is 0.05~0.2 mol / L.

[0024] Preferably, in S12, the reducing agent in the reducing agent solution includes at least one of hydrazine hydrate, sodium borohydride, ascorbic acid, and glucose.

[0025] Preferably, in step S12, the mass ratio of graphene oxide, the first functional material, the metal salt, and the reducing agent is (1~10):(100~500):(10~100):(1~100). Preferably, in step S12, the mass ratio of graphene oxide, the first functional material, the metal salt, and the reducing agent is (1~10):(100~500):(10~100):(1~50). Preferably, in step S12, the mass ratio of graphene oxide, the first functional material, the metal salt, and the reducing agent is (1~10):(100~500):(10~100):(1~20). Preferably, in step S12, the mass ratio of graphene oxide, the first functional material, the metal salt, and the reducing agent is (1~10):(100~500):(10~100):(1~10).

[0026] Preferably, in S12, when the reducing agent is hydrazine hydrate, the concentration of the reducing agent solution is 0.1~1μL / mL.

[0027] Preferably, in step S13, the filtration process employs vacuum filtration. Preferably, the water washing process is performed 2-5 times. Water washing is to completely remove free primary functional materials (organic molecules) and metal ions such as Na+ from the alkaline solution. + or K + Ag + NO3 - To avoid these materials affecting the sensing performance of the final graphene-based composite material, including its response to humidity or other gases, we use hydrazine hydrate.

[0028] Preferably, in step S13, the water-washed product can be redispersed in water and freeze-dried for characterization using electron microscopy, XRD, etc. The freeze-drying temperature is -60 to -50°C, and the pressure is 1 to 10 Pa.

[0029] Preferably, the water used in the above steps is deionized water.

[0030] According to a third aspect of the present invention, a method for preparing the above-mentioned graphene-based composite material is provided. When the second functional material includes a metal oxide, the preparation method includes the following steps: S21. Preparing a graphene oxide dispersion using graphene oxide and water; S22. Mixing the first functional material with water, then adjusting the pH of the resulting solution to 6.8-7.2, then adding the graphene oxide dispersion, mixing evenly, adding a reducing agent solution, reacting at 85-95°C for 0.5-2 hours, filtering and washing the resulting mixture with water, and redispersing the resulting solid in water; S23. Continuing to add the oxide to the dispersion obtained in S22, mixing for 0.5-2 hours, centrifuging and washing the resulting product with water to obtain the graphene-based composite material. Through the above steps, a graphene-based composite material with good composite properties of reduced graphene, the first functional material (organic molecule), and the metal oxide can be obtained. Furthermore, the obtained graphene-based composite material can achieve synergistic detection of humidity and gas, with high detection sensitivity and accuracy.

[0031] Preferably, in step S21, the concentration of the graphene oxide dispersion is 0.5~5 mg / L. More preferably, in step S21, the concentration of the graphene oxide dispersion is 0.5~2 mg / L.

[0032] Preferably, in step S22, the mass-to-volume ratio of the first functional material to water is 80-300 mg:40 mL. More preferably, in step S22, the mass-to-volume ratio of the first functional material to water is 100-250 mg:40 mL.

[0033] Preferably, in step S22, the pH is adjusted to 6.8-7.2 using an alkaline solution; the alkaline solution includes at least one of sodium hydroxide solution and potassium hydroxide solution. Preferably, the mass concentration of the alkaline solution is 7-15 wt%.

[0034] Preferably, in S22, the reducing agent in the reducing agent solution includes at least one of hydrazine hydrate, sodium borohydride, ascorbic acid, and glucose.

[0035] Preferably, in step S22, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~500):(0.001~20). Preferably, in step S22, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~500):(0.01~10). Preferably, in step S22, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~500):(0.1~10). Preferably, in step S22, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~300):(1~10). Preferably, in step S22, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~200):(1~10).

[0036] Preferably, in S22, when the reducing agent is hydrazine hydrate, the concentration of the reducing agent solution is 0.1~1μL / mL.

[0037] Preferably, in step S22, the filtration process employs vacuum filtration. Preferably, the water rinsing process is performed 2 to 5 times.

[0038] Preferably, in step S23, the amount of oxide added is calculated using a mass ratio of graphene oxide, the first functional material, the reducing agent, and the oxide of (1~10):(10~500):(0.001~20):(1~1000). Preferably, in step S23, the amount of oxide added is calculated using a mass ratio of graphene oxide, the first functional material, the reducing agent, and the oxide of (1~10):(10~500):(0.01~10):(1~500). Preferably, in step S23, the amount of oxide added is calculated using a mass ratio of graphene oxide, the first functional material, the reducing agent, and the oxide of (1~10):(10~500):(0.1~10):(1~500). Preferably, in step S23, the amount of oxide added is calculated using a mass ratio of graphene oxide, the first functional material, the reducing agent, and the oxide of (1~10):(10~300):(1~10):(1~300). Preferably, in S23, the amount of oxide added is calculated with the mass ratio of graphene oxide, the first functional material, the reducing agent, and the oxide being (1~10):(10~300):(1~10):(1~200).

[0039] Preferably, in step S23, the centrifugation speed is 6000~9000 rpm and the centrifugation time is 3~10 minutes. Preferably, the water washing process is performed 2~5 times.

[0040] Preferably, the water used in the above steps is deionized water.

[0041] According to a fourth aspect of the present invention, a method for preparing the above-mentioned graphene-based composite material is provided. When the second functional material includes a conductive polymer, the preparation method includes the following steps: S31. Preparing a graphene oxide dispersion using graphene oxide and water; S32. Mixing the first functional material with water, then adding the graphene oxide dispersion, mixing evenly, adding a reducing agent solution, reacting at 85~95℃ for 0.5~2h, filtering and washing the resulting mixture with water, and drying to obtain a solid; S33. Dispersing the solid in S32 in an acidic solution, then adding a monomer, mixing for 0.5~2h, adding an initiator, and reacting the resulting mixture at -5~6℃ for 3~6h, then centrifuging and washing the obtained product with water to obtain the graphene-based composite material. Through the above steps, a graphene-based composite material with good composite properties of reduced graphene, the first functional material (organic molecule), and the conductive polymer can be obtained. Furthermore, the obtained graphene-based composite material can achieve synergistic detection of humidity and gas, with high detection sensitivity and accuracy.

[0042] Preferably, in step S31, the concentration of the graphene oxide dispersion is 0.5~5 mg / L. More preferably, in step S31, the concentration of the graphene oxide dispersion is 0.5~2 mg / L.

[0043] Preferably, in step S32, the mass-to-volume ratio of the first functional material to water is 80-300 mg:40 mL. More preferably, in step S32, the mass-to-volume ratio of the first functional material to water is 100-250 mg:40 mL.

[0044] Preferably, in step S32, the pH is adjusted to 6.8-7.2 using an alkaline solution; the alkaline solution includes at least one of sodium hydroxide solution and potassium hydroxide solution. Preferably, the mass concentration of the alkaline solution is 7-15 wt%.

[0045] Preferably, in S32, the reducing agent in the reducing agent solution includes at least one of hydrazine hydrate, sodium borohydride, ascorbic acid, and glucose.

[0046] Preferably, in step S32, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~100):(1~100). Preferably, in step S32, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~100):(1~50). Preferably, in step S32, the mass ratio of graphene oxide, the first functional material, and the reducing agent is (1~10):(10~100):(1~10).

[0047] Preferably, in step S32, when the reducing agent is hydrazine hydrate, the concentration of the reducing agent solution is 0.1~1 μL / mL.

[0048] Preferably, in step S32, the filtration process employs vacuum filtration. Preferably, the water rinsing process is performed 2 to 5 times.

[0049] Preferably, in S33, the solid-liquid ratio of the solid to the acidic solution is 90-100 mg:10 mL. Preferably, the H+ in the acidic solution... + The concentration is 0.5~2 mol / L. Preferably, the acidic solution includes hydrochloric acid solution.

[0050] Preferably, in step S33, the amount of monomer and initiator is calculated using a mass ratio of graphene oxide, the first functional material, the reducing agent, the monomer, and the initiator of (1~10):(10~100):(1~100):(10~100):(1~50). Preferably, in step S33, the amount of monomer and initiator is calculated using a mass ratio of graphene oxide, the first functional material, the reducing agent, the monomer, and the initiator of (1~10):(10~100):(1~50):(10~70):(1~50). Preferably, in step S33, the amount of monomer and initiator is calculated using a mass ratio of graphene oxide, the first functional material, the reducing agent, the monomer, and the initiator of (1~10):(10~100):(1~20):(10~50):(1~20). Preferably, in S33, the amount of monomer and initiator is calculated by the mass ratio of graphene oxide, first functional material, reducing agent, monomer, and initiator as (1~10):(10~100):(1~10):(10~50):(1~10).

[0051] Preferably, in S33, the initiator includes at least one of ammonium persulfate and potassium persulfate.

[0052] Preferably, in step S33, the centrifugation speed is 1000~10000 rpm and the centrifugation time is 5~20 minutes. Preferably, the water washing process is performed 2~5 times.

[0053] Preferably, the water used in the above steps is deionized water.

[0054] According to a fifth aspect of the present invention, a sensing element is provided, comprising an electrode and the above-described graphene-based composite material or a graphene-based composite material prepared by the method described above for preparing the graphene-based composite material.

[0055] Preferably, the process of laminating graphene-based composite materials onto the electrode surface includes at least one of sputtering, spraying, screen printing, and vapor deposition.

[0056] Preferably, the electrodes include interdigitated electrodes.

[0057] According to a sixth aspect of the present invention, an application of the above-described sensing element in the detection of humidity and gases, wherein the gases include at least one of formaldehyde and NO2.

[0058] According to a seventh aspect of the present invention, a sensor is provided, comprising a light source and the aforementioned sensing element.

[0059] According to an eighth aspect of the present invention, an application of the above-described sensing element in humidity and gas detection is provided, wherein the gas includes at least one of formaldehyde and NO2; the light source includes at least one of infrared light and near-infrared light; and the intensity of the light source is 1~1000 mW / cm². 2 By using infrared or near-infrared light as a light source, the simultaneous detection of humidity and gases (such as formaldehyde and NO2) can be achieved. That is, a single sensor device can detect both humidity and gases (such as formaldehyde and NO2). For example, humidity can be detected without a light source, but when a light source is applied, the presence of gases (such as formaldehyde and NO2) will cause a significant change in response (such as a change in resistance in a resistive sensor). This allows for the differentiation between the responses to humidity and gases (such as formaldehyde and NO2). Therefore, the sensing element provided by this invention can achieve the simultaneous detection of humidity and gases (such as formaldehyde and NO2). Furthermore, the intensity of the light source used needs to be within a specific range. Insufficient intensity will not provide enough stimulation to effectively differentiate between the responses to humidity and gases, while excessive intensity will damage the sensitive materials in the sensing element, affecting the accuracy and sensitivity of the detection results, and may even severely damage the sensitive materials, rendering them incapable of sensing.

[0060] It is also important to emphasize that the sensing elements or sensors prepared from the graphene-based composite materials provided in this invention can still achieve good detection of gases (such as formaldehyde and NO2) under light stimulation and high humidity conditions. In other words, they are unaffected by humidity and can achieve accurate and stable gas testing. High humidity environments refer to conditions such as ≥60% humidity, meaning that even under complex environments with 60% humidity, the target gas can still be detected with high precision and high sensitivity.

[0061] Preferably, the wavelength of the light source is 800~2500 nm.

[0062] In summary, compared with the prior art, the present invention has the following technical effects: (1) The graphene composite material modified by the first functional material (organic molecule) and the second functional material (metal or metal oxide or conductive polymer) can not only ensure the large specific surface area, strong adsorption capacity and inherent flexibility of graphene, but also highlight the specific response of organic molecules, so that it can be stably sensed in humidity or gas (such as formaldehyde, NO2). At the same time, the first functional material and the second functional material can further improve the stability and specific responsiveness of the graphene-based composite material, and optimize its detection sensitivity and accuracy for humidity and gas.

[0063] (2) A high-performance sensor that utilizes the photothermal effect assisted by organic molecules to regulate the light source and combines it with light assistance to effectively realize complete gas detection.

[0064] (3) It adopts graphene-based composite sensing material with both high conductivity and high thermal conductivity and a unique light-assisted structure design, which can realize the coordinated detection of humidity and gas in complex environments. It effectively overcomes the limitations of traditional humidity sensors and gas sensors working independently, as well as the defect of gas sensors being greatly affected by humidity, and brings a brand-new solution to the detection work in related fields. Attached Figure Description

[0065] Figure 1 SEM images of the TMA-rGO / Ag-2.5 sample in Example 1 and the TMA-rGO-100, TMA-rGO-150, TMA-rGO-200 and TMA-rGO-250 samples in Comparative Example 1;

[0066] Figure 2 The infrared spectra of TMA-rGO-150 and TMA-rGO-200 samples in Comparative Example 1, the rGO sample in Comparative Example 4, and TMA are shown.

[0067] Figure 3 The images show the XRD patterns of the TMA-rGO / Ag-2.5 sample from Example 1, the TMA-rGO-200 sample from Comparative Example 1, and Ag.

[0068] Figure 4 This is a microscope image of the TMA-rGO / Ag sample on the electrode in Example 1;

[0069] Figure 5 The response curves of TMA-rGO / Ag and TMA-rGO samples in Example 1 and Comparative Example 1 to different humidity levels are shown.

[0070] Figure 6 The fitted curves of the sensitivity of the TMA-rGO / Ag and TMA-rGO samples in Example 1 and Comparative Example 1 as a function of relative humidity are shown.

[0071] Figure 7 The graph shows the response of the TMA-rGO / ZnO composite material in Example 2 to 65% RH humidity under near-infrared light assistance.

[0072] Figure 8 The graph shows the response of the TMA-rGO / ZnO composite material in Example 2 to 10 ppm NO2 under near-infrared light and 65% RH humidity.

[0073] Figure 9 The graph shows the response curves of the rGO / ZnO composite material in Comparative Example 2 to 10 ppm NO2 under light and 65% RH humidity.

[0074] Figure 10 The response curves of the resorcinol-rGO / polyaniline material in Example 3 to humid environments and formaldehyde under light irradiation are shown.

[0075] Figure 11 The response curves of the polyaniline material in Comparative Example 3 to humid environments and formaldehyde under light illumination are shown.

[0076] Figure 12 The response curves of the TMA-rGO / Ag sample in Example 1 to humid environments and formaldehyde under both light and no light conditions are shown. Detailed Implementation

[0077] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0078] Example 1

[0079] The graphene-based composite material (1,3,5-benzenetricarboxylic acid (TMA) modified graphene / Ag composite material) of this embodiment was synthesized according to the following steps.

[0080] S11. Prepare a graphene oxide dispersion (1 mg / mL) using graphene oxide and deionized water.

[0081] S12. Dissolve 200 mg TMA in 40 mL of deionized water and stir. Add NaOH solution (10 wt%) to adjust the pH to 7. Then add 5 mL of graphene oxide dispersion (1 mg / mL) and 2.56 mL of silver nitrate (0.1 mol / L) and stir for 1 h. Add 10 mL of hydrazine hydrate solution (0.5 μL / mL water) and stir for another 1 h at 90 °C. The mass ratio of graphene oxide, TMA, silver nitrate, and hydrazine hydrate is 5:200:43.52:5.15.

[0082] S13. Finally, the sample is vacuum filtered, rinsed three times with deionized water, and redispersed in 10 ml of deionized water. The dried sample is the graphene-based composite material, labeled TMA-rGO / Ag (TMA-rGO / Ag-2.5 in the attached figure is also this substance). In this embodiment, the mass ratio of rGO, TMA, and Ag in TMA-rGO / Ag is 4.5:150:20.

[0083] Example 2

[0084] The graphene-based composite material (1,3,5-benzenetricarboxylic acid (TMA) modified graphene / zinc oxide composite material) of this embodiment is synthesized according to the following steps.

[0085] S21. Prepare a graphene oxide dispersion (1 mg / mL) using graphene oxide and water.

[0086] S22. Dissolve 200 mg TMA in 40 mL of deionized water and stir. Add 10 wt% NaOH solution to adjust the pH to 7. Then add 5 mL of graphene oxide dispersion (1 mg / mL) and stir for 1 hour. Add 10 mL of hydrazine hydrate solution (0.5 µL / mL water) and stir at 90 °C for another hour. Vacuum filter, wash three times with deionized water, and redisperse the resulting sample (denoted as TMA-rGO) in 10 mL of deionized water.

[0087] S23. Continue adding 100 mg of zinc oxide to the dispersion obtained in S22 (the mass ratio of graphene oxide, TMA, hydrazine hydrate, and zinc oxide is 5:200:5.15:100), stir for 1 hour, centrifuge the product at 8000 rpm for 8 minutes, wash it three times with deionized water, and dry it to obtain the graphene-based composite material, denoted as TMA-rGO / ZnO. In this example, the mass ratio of rGO, TMA, and ZnO in TMA-rGO / ZnO is 4.5:150:90.

[0088] Example 3

[0089] The graphene-based composite material (resorcinol-modified graphene / polyaniline composite material) of this embodiment is synthesized according to the following steps.

[0090] S31. Prepare a graphene oxide dispersion (1 mg / mL) using graphene oxide and water.

[0091] S32. Dissolve 50 mg of resorcinol in 40 mL of deionized water and stir until dissolved. Then add 5 mL of graphene oxide dispersion (1 mg / mL) and stir for 1 hour. Add 10 mL of hydrazine hydrate solution (0.5 µL / mL water) and stir at 90 °C for another hour. Vacuum filter, wash three times with deionized water, and dry to obtain resorcinol-modified reduced graphene, labeled as resorcinol-rGO.

[0092] S33. The dispersion from S32 was placed in 10 mL of hydrochloric acid solution (1 mol / L), and then 20 µL of aniline monomer was introduced into the dispersion. After stirring for 1 h, a certain amount of ammonium persulfate (APS) initiator was added (the mass ratio of graphene oxide, resorcinol, hydrazine hydrate, aniline monomer, and initiator was 5:50:5.15:20:5). The mixture was transferred to a refrigerator at 4°C and polymerized for 3-6 hours. Finally, the product was washed three times with deionized water by centrifugation and then freeze-dried to obtain a graphene-based composite material, denoted as resorcinol-rGO / polyaniline. In this embodiment, the mass ratio of rGO, resorcinol, and polyaniline in resorcinol-rGO / polyaniline was 4.5:38:18.

[0093] Comparative Example 1

[0094] The specific steps for synthesizing the TMA-rGO composite material in this comparative example are as follows:

[0095] 100, 150, 200, and 250 mg of TMA were dissolved in 40 mL of deionized water and stirred. 10 wt% NaOH solution was added to adjust the pH of these solutions to 7. Then, 5 mL of graphene oxide dispersion (1 mg / mL) was added to each of these solutions. After stirring for 1 hour, 10 mL of hydrazine hydrate solution (0.5 µL / mL water) was added to each solution. The mixture was stirred at 90 °C for another hour. After vacuum filtration and rinsing three times with deionized water, the resulting samples were redispersed in 10 mL of deionized water and labeled as TMA-rGO-100, TMA-rGO-150, TMA-rGO-200, and TMA-rGO-250, respectively.

[0096] Comparative Example 2

[0097] The specific steps for synthesizing the reduced graphene / zinc oxide (rGO / zinc oxide) composite material in this comparative example are as follows:

[0098] A graphene oxide dispersion (1 mg / mL) was prepared using graphene oxide and water. 5 mL of the graphene oxide dispersion (1 mg / mL) was taken and stirred for 1 hour. Then, 10 mL of hydrazine hydrate solution (0.5 µL / mL water) was added, and the mixture was stirred at 90 °C for another hour. The mixture was then vacuum filtered and washed three times with deionized water. The resulting sample (denoted as rGO) was redispersed in 10 mL of deionized water. 100 mg of zinc oxide was added to 10 mL of the rGO dispersion (0.5 mg / mL), and the mixture was stirred for 1 hour. The product was centrifuged at 8000 rpm for 8 minutes and washed three times with deionized water. After drying, the rGO / ZnO composite material was obtained.

[0099] Comparative Example 3

[0100] The specific steps for synthesizing polyaniline material in this comparative example are as follows:

[0101] 20 µL of aniline monomer was introduced into 10 mL of hydrochloric acid solution (1 mol / L), stirred for 1 h, and then a certain amount of ammonium persulfate (APS) initiator was added (the mass ratio of aniline monomer to initiator was 20:5). The mixture solution was transferred to a refrigerator at 4 °C and polymerized for 3-6 hours. Finally, the product was washed three times by centrifugation with deionized water and then freeze-dried to obtain polyaniline material.

[0102] Comparative Example 4

[0103] The specific steps for synthesizing reduced graphene in this comparative example are as follows:

[0104] A graphene oxide dispersion (1 mg / mL) was prepared using graphene oxide and water. 5 mL of the graphene oxide dispersion (1 mg / mL) was taken and stirred for 1 hour. Then, 10 mL of hydrazine hydrate solution (0.5 µL / mL water) was added and stirred at 90 °C for another hour. The mixture was then vacuum filtered and washed three times with deionized water. The resulting sample (denoted as rGO) was then redispersed in 10 mL of deionized water.

[0105] Test Analysis

[0106] 1. Morphological analysis

[0107] The materials prepared in Example 1 and Comparative Example 1 were analyzed by SEM, such as... Figure 1 As shown, from Figure 1 (a~d) It can be seen that the morphology of TMA-rGO-100 and TMA-rGO-250 samples exhibits aggregation and stacking, meaning that the organic TMA molecules aggregate and stack under both small and excessive amounts, while the morphology of TMA-rGO-150 and TMA-rGO-200 samples is well-distributed. Furthermore, from... Figure 1As can be seen in (e), the Ag nanoparticles are uniformly distributed in the TMA-rGO / Ag material. That is, the three can achieve a good uniform distribution in the TMA-rGO / Ag material, which is more conducive to improving the overall performance of the composite material and its sensing performance of humidity, gaseous formaldehyde, and NO2, thereby improving sensitivity and accuracy.

[0108] 2. Infrared analysis

[0109] Infrared spectroscopy was performed on the TMA-rGO-150 and TMA-rGO-200 samples in Comparative Example 1, the rGO sample in Comparative Example 4, and the TMA. The results are as follows: Figure 2 As shown, from Figure 2 As can be seen, compared with rGO, the TMA-rGO-150 and TMA-rGO-200 samples show the characteristic peaks of TMA, reflecting the successful modification of graphene by the organic molecule TMA.

[0110] 3. XRD Analysis

[0111] The TMA-rGO-200 sample from Comparative Example 1, the TMA-rGO / Ag-2.5 sample from the examples, and Ag were subjected to XRD tests, and the results are as follows: Figure 3 As shown, from Figure 3 As can be seen, compared with TMA-rGO-200, the diffraction peaks of the TMA-rGO / Ag-2.5 composite material match the diffraction peaks of Ag, indicating good crystallinity.

[0112] 4. Electrode Microscopy Analysis

[0113] The TMA-rGO / Ag-2.5 sample (undried dispersion) from Example 1 was coated onto an interdigitated electrode and dried at 55°C to obtain an electrode containing the sensing material, i.e., a sensing element. Microscopic analysis was performed on the electrode, and the results are as follows: Figure 4 As shown, from Figure 4 It can be seen that TMA-rGO / Ag-2.5 is spread evenly on the electrode, with a small amount required, allowing for large-scale preparation. The uniform distribution also helps to ensure that the sensing material has better sensing stability and sensitivity.

[0114] 5. Humidity and / or gas (formaldehyde, NO2) testing

[0115] (1) The TMA-rGO / Ag-2.5 sample in Example 1 and the TMA-rGO-200 sample in Comparative Example 1 (both were 10 μL of undried dispersion) were coated on the interdigital electrode and dried at 55°C to obtain the electrode containing the sensing material, i.e. the sensing element.

[0116] Humidity responsiveness tests were conducted on the TMA-rGO / Ag-2.5 and TMA-rGO-200 sensors, respectively. The specific test methods are as follows: The sensors were installed in a sealed test chamber and connected to the matching detection circuit and data acquisition equipment. Dry nitrogen gas was first introduced, and the initial electrical signal of the sensor was recorded. The flow rates of dry nitrogen and standard humid gas were adjusted proportionally to obtain mixed gases with different relative humidity levels of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%. These mixtures were then introduced into the test chamber at specific flow rates, and the data was recorded. After each humidity point test, dry nitrogen gas was introduced to restore the sensor to its initial state. Finally, the sensor response parameters, such as sensitivity, i.e., the rate of change of resistance (ΔR / R), were calculated. a *100%= R g -R a / R a *100%), plot the humidity-response curve.

[0117] The result is as follows Figure 5 As shown, comparison Figure 5 (a) and Figure 5 (b) When the relative humidity is between 10% and 90% RH, the TMA-rGO / Ag sample exhibits superior humidity response performance compared to the TMA-rGO sample. The resistance variation range of the TMA-rGO sample is between 12 and 145 MΩ (resistance change of the electrode from dry (0%) to the most humid (90%) state. For example, the resistance of TMA-rGO at 0% RH is 145 MΩ, and at 90% RH it is 12 MΩ.), while the resistance variation range of the TMA-rGO / Ag sample is between 21 and 1500 MΩ. The TMA-rGO / Ag sample offers higher resistance variation resolution, thus providing greater sensitivity and accuracy for humidity detection.

[0118] Furthermore, the sensitivity was analyzed, and the results are as follows: Figure 6 As shown, from Figure 6 (a) and Figure 6 (b) It can be seen that the sensitivity of both TMA-rGO and TMA-rGO / Ag samples increases with increasing relative humidity, and the overall curves show a high degree of fit, indicating good sample sensitivity. In particular, TMA-rGO / Ag has a wider humidity response range, which is more conducive to practical detection applications.

[0119] (2) The TMA-rGO / ZnO sample (10 μL of the undried dispersion) from Example 2 was coated onto the interdigitated electrode and dried at 55°C to obtain the electrode containing the sensing material, i.e., the sensing element.

[0120] The TMA-rGO / ZnO sensing element was tested for its NO2 gas responsiveness, specifically through two different processes.

[0121] The first test procedure is as follows: The sensing element is installed in a sealed test chamber, and the matching detection circuit and data acquisition equipment are connected. The initial electrical signal of the sensing element is recorded under a 20% RH atmosphere. A measured amount of water is injected onto the heating element, and after evaporation, a 35% RH atmosphere is obtained, yielding a response signal (7.8%). The signal is recovered after returning to a 20% RH atmosphere. (The last sentence appears to be incomplete and possibly refers to a test procedure involving 50 mW / cm².) 2 Irradiation with 980nm light generates a photocurrent (1.97 μA). Moisture is then injected to achieve a humidity level of 65% RH. Due to the photo-assisted dehumidification effect, the sensing element is unaffected by humidity. After the light source is turned off, the photocurrent disappears, but due to the high humidity (65% RH), the sensing element current increases to 1.57 μA. Then, 10 ppm NO2 gas is injected; under high humidity, the gas sensitivity is only 1.07. After recovery, the sensing element signal returns to its original state. Finally, the sensing element response parameters, such as sensitivity (R0), are calculated. a / R g = 1.07).

[0122] The result is as follows Figure 7 As shown, the TMA-rGO / ZnO composite material prepared in Example 2 exhibits an increase in sensor current when the humidity changes from 20% to 35%RH, and the signal recovers when the humidity returns to 20%RH. Under near-infrared light assistance, when a high humidity (65% RH) atmosphere is introduced, the sensor current change is almost zero, indicating that it is unaffected by humidity, which is beneficial for achieving complete gas sensing. When the light source is turned off, the photocurrent disappears, and the current increases to 1.57 μA due to the influence of humidity. The sensitivity for 10 ppm NO2 under high humidity is only 1.07. This demonstrates that testing NO2 under high humidity conditions has higher sensitivity with the assistance of a light source.

[0123] The second testing procedure is as follows: The sensing element is installed in a sealed test chamber, and the matching detection circuit and data acquisition equipment are connected. The initial electrical signal of the sensing element is recorded under the original 20% RH atmosphere, followed by a 50 mW / cm² voltage reading. 2 Irradiation with 980nm light generates a photocurrent (2.91 μA). Moisture is then injected to achieve a humidity level of 65% RH. Due to the photo-assisted dehumidification effect, the sensing element is unaffected by humidity. Next, 10 ppm NO2 gas is injected. Under photo-assisted conditions, even at 65% RH, the gas sensitivity reaches 1.12. After the light source is turned off, the sensing element signal returns to its original 20% RH state. In a drier atmosphere, with the injection of 10 ppm NO2 gas, the gas sensitivity is 1.13. The sensitivity calculation formula is: R... a / R g .

[0124] The result is as follows Figure 8 As shown, the TMA-rGO / ZnO composite sensing material prepared in Example 2 exhibits a response value of 1.12 for 10 ppm NO2 under high humidity (65%RH) and 1.13 under indoor conditions (20%RH). This indicates that, with light assistance, the sensor maintains sensitivity comparable to that under drier conditions, even in high humidity. In other words, it can accurately detect NO2 under high humidity and achieve high-performance synergistic detection of humidity and NO2.

[0125] In a resistance sensor, R a and R g They represent the following meanings respectively: R a Static resistance value, i.e., the resistance value under initial conditions. R g : The resistance value of a gas in a gas sample at a specified concentration.

[0126] (3) The rGO / ZnO sample (10 μL of the undried dispersion) from Comparative Example 2 was coated onto the interdigitated electrode and dried at 55°C to obtain the electrode containing the sensing material, i.e. the sensing element.

[0127] The rGO / ZnO sensing element was subjected to NO2 gas responsiveness testing. The specific testing method is as follows: The sensing element was installed in a sealed test chamber, and the matching detection circuit and data acquisition equipment were connected. The initial electrical signal of the sensing element was recorded under the original 20% RH atmosphere, and then after passing through a 50 mW / cm² gas flow rate test chamber... 2 After being irradiated with 980nm light, a photocurrent (~1.17 μA) is generated. Then, water is injected to bring the humidity to 65% RH. The sensing element is not affected by humidity, but the photocurrent gradually decreases due to light damage. After injecting 10ppm NO2 gas, no useful signal is observed.

[0128] The result is as follows Figure 9 As shown, the rGO / ZnO composite material prepared in Comparative Example 2 is prone to electrode damage and signal instability under light irradiation. In a high humidity environment (65%RH), the sensor has almost no response to 10 ppm NO2.

[0129] (4) The resorcinol-rGO / polyaniline sample (10 μL of the undried dispersion) from Example 3 was coated onto the interdigitated electrode and dried at 55°C to obtain the electrode containing the sensing material, i.e., the sensing element.

[0130] The formaldehyde gas responsiveness of the resorcinol-rGO / polyaniline sensing element was tested using the following method (photocurrent-gas-sensitive signal coupling test method): The sensing element was installed in a sealed test chamber, and the matching detection circuit and data acquisition equipment were connected. The initial electrical signal of the sensing element was recorded under a humid atmosphere of 60% RH, followed by a 100 mW / cm² reading. 2 Irradiation with 980nm light generated a photocurrent (2.25 μA), with a sensitivity of 5.8%, and almost no signal attenuation during repeated testing (5.6%). Subsequently, injection of 55ppm formaldehyde gas resulted in no signal generation (i.e., no moisture-resistant sensing signal) without light irradiation. After exposure to 100 mW / cm² light... 2 Irradiation with 980nm light produces a photocurrent (2.23 μA), with a sensitivity of 4.8%, and almost no signal attenuation during repeated testing (4.9%). Sensitivity calculation formula: ΔR / R a *100%= R g -R a / R a *100%.

[0131] The result is as follows Figure 10 As shown, the resorcinol-rGO / polyaniline composite sensing material prepared in Example 3 exhibits a photocurrent of 5.6%~5.8% in humid air and 4.8%~4.9% in 50 ppm formaldehyde, indicating that the sensor can achieve synergistic detection of humidity and formaldehyde. Here, "in humid air" refers to only humid air (60% RH), and "in 55 ppm formaldehyde" means both humid air and formaldehyde are present. The addition of formaldehyde causes a significant change (weakening) in the photocurrent signal, which can be considered as a change in photocurrent signal caused by formaldehyde. Therefore, synergistic detection of humidity and formaldehyde can be achieved on the same sensor device.

[0132] (5) Coat the polyaniline sample (10 μL of the undried dispersion) from Comparative Example 3 onto the interdigitated electrode and dry it at 55°C to obtain the electrode containing the sensing material, i.e., the sensing element.

[0133] The formaldehyde gas responsiveness of the polyaniline sensing element was tested using the following method: The sensing element was installed in a sealed test chamber, and the matching detection circuit and data acquisition equipment were connected. The initial electrical signal of the sensing element was recorded under a humid atmosphere of 60% RH, followed by a reading of 100 mW / cm². 2 Irradiation with 980nm light generated a photocurrent (1.37 μA), with a sensitivity of 3.7%, and almost no signal attenuation (3.6%) during repeated testing. Subsequently, 55 ppm formaldehyde gas was injected; without light, no signal was generated (i.e., no moisture-resistant sensing signal). After exposure to 100 mW / cm² light... 2Irradiation with 980nm light produces a photocurrent (1.37 μA), with a sensitivity of 3.6%. Sensitivity is calculated using the formula: ΔR / R a *100%= R g -R a / R a *100%.

[0134] The result is as follows Figure 11 As shown, the polyaniline sample prepared in Comparative Example 3 exhibited a photocurrent of 3.6%–3.7% in humid air and 3.6% in 55 ppm formaldehyde, indicating that the sensor's synergistic detection effect on humidity and formaldehyde was not significant. In other words, the current signal did not change significantly after the addition of formaldehyde, demonstrating an insignificant synergistic detection effect on humidity and formaldehyde.

[0135] (6) The TMA-rGO / Ag sample (10 μL of the undried dispersion) from Example 1 was coated onto the interdigitated electrode and dried at 55°C to obtain the electrode containing the sensing material, i.e., the sensing element.

[0136] The TMA-rGO / Ag sensor element was tested for its formaldehyde gas responsiveness. The specific test method is as follows: The sensor element was installed in a sealed test chamber and connected to the matching detection circuit and data acquisition equipment. The initial electrical signal of the sensor element was recorded under a humid atmosphere of 50% RH. Moisture was injected to reach a humidity of 65% RH, at which point the sensor element's response was 14.3%. The signal recovered after the humidity returned to 50% RH. The test was conducted at 1000 mW / cm². 2 Irradiation with 808nm light generates a photocurrent (0.013 μA). Moisture is then injected to achieve a humidity level of 65% RH. Due to the light-assisted moisture-resistant effect, the sensing element is unaffected by humidity. Next, 80 ppb of formaldehyde gas is injected. Under light assistance, even at a humidity level as high as 65% RH, the gas sensitivity reaches 5.1%. After the light source is turned off, the sensing element signal returns to the 65% RH state. At high humidity, injecting another 80 ppb of formaldehyde results in no signal generation due to the lack of light (i.e., no moisture-resistant sensing signal). At relatively dry humidity, injecting another 80 ppb of formaldehyde also results in no signal generation due to the lack of light (i.e., no moisture-resistant sensing signal). Sensitivity calculation formula: ΔR / R a *100%= R g -R a / R a *100%.

[0137] The result is as follows Figure 12As shown, the TMA-rGO / Ag sample prepared in Example 1 exhibited a sensitivity of 14.3% when the RH changed from 50% to 65%. Under light illumination, it demonstrated anti-humidity properties; even in a high-humidity environment (65% RH) with light assistance, the sensor responded to 80 ppb formaldehyde with a value of 5.1%. Without light assistance, the sensor showed no response to 80 ppb formaldehyde in both indoor environments (50% RH) and high-humidity environments (65% RH). This indicates that the sensor can achieve synergistic detection of humidity and formaldehyde and possesses highly efficient gas sensing capabilities.

[0138] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A sensing element, characterized in that: The invention includes electrodes and a graphene-based composite material, wherein the graphene-based composite material comprises reduced graphene, a first functional material, and a second functional material. The first functional material includes at least one of 1,3,5-benzenetricarboxylic acid, resorcinol, hydroquinone, catechol, 2,5-dihydroxybenzoic acid, 1,5-naphthalenedisulfonic acid, sodium 2,6-naphthalenedisulfonic acid, and sodium anthraquinone-2-sulfonate. The second functional material includes a metal or a conductive polymer; the metal includes at least one of Au, Ag, Cu, Fe, and Pt; the conductive polymer includes at least one of polyaniline, polypyrrole, and polythiophene. The sensing element is used to detect humidity and gas; the gas is formaldehyde. When the second functional material includes the metal, the preparation method of the graphene-based composite material includes the following steps: S11. Prepare a graphene oxide dispersion using graphene oxide and water; S12. Mix the first functional material with water, then adjust the pH of the resulting solution to 6.8-7.2, then add the graphene oxide dispersion and the salt solution containing the metal, mix evenly, then add the reducing agent solution, and react at 85-95°C for 0.5-2 hours. S13. The mixture after the reaction in S12 is filtered and washed with water to obtain the graphene-based composite material; When the second functional material includes the conductive polymer, the preparation method of the graphene-based composite material includes the following steps: S31. Prepare a graphene oxide dispersion using graphene oxide and water; S32. Mix the first functional material with water, then add the graphene oxide dispersion to it, mix evenly, add a reducing agent solution, react at 85-95°C for 0.5-2 hours, filter the resulting mixture, wash with water, and dry to obtain a solid. S33. The solid in S32 is dispersed in an acidic solution, then a monomer is added to it, and after mixing for 0.5 to 2 hours, an initiator is added. The resulting mixture is placed at -5 to 6°C and reacted for 3 to 6 hours. The resulting product is then centrifuged and washed with water to obtain the graphene-based composite material.

2. The sensing element as described in claim 1, characterized in that: In the graphene-based composite material, the mass ratio of the reduced graphene, the first functional material, and the second functional material is (0.1-7):(10-300):(1-1000).

3. A sensor, characterized in that: It includes a light source and a sensing element as described in any one of claims 1 to 2.

4. The application of the sensor as described in claim 3 in humidity and gas detection, characterized in that: The light source includes at least one of infrared light and near-infrared light; The intensity of the light source is 1–1000 mW / cm². 2 .

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