Preparation and test method of In2O3-rGO-PPy aerogel for rapidly detecting hydrogen at room temperature

Abstract

The invention discloses a preparation method and a test method of In2O3-rGO-PPy aerogel for rapidly detecting hydrogen at room temperature. The preparation method comprises the following specific steps: mixing CO (NH2) 2, In (NO3) 3.4. 5H2O and NH4F, reacting in a reaction kettle, washing and purifying after the reaction is completed, and annealing at 400 DEG C for 1-2 hours to prepare indium oxide (In2O3) nanoparticles; the preparation method comprises the following steps: preparing methyl orange, FeCl3. 6H2O and pyrrole into a mixed solution, standing to obtain a product, washing and purifying, and finally freeze-drying to obtain a polypyrrole (PPy) tube; the preparation method comprises the following steps: dissolving graphene oxide, polypyrrole and indium oxide in deionized water, carrying out ultrasonic treatment in an ice bath, carrying out a hydrothermal reaction to obtain composite hydrogel, washing and purifying the composite hydrogel, and finally carrying out freeze drying to obtain the three-dimensional In2O3-rGO-PPy aerogel. The innovative overall testing method is used for testing the sensor, a metal sheet and a wire are connected to the two ends of aerogel, the aerogel is integrally placed in a gas chamber, the introduction amount of hydrogen and air is controlled, a hydrogen environment with a certain concentration is kept, and the sensor is tested under the condition.

Description

Technical Field

[0001] The invention belongs to the field of gas sensing materials, and specifically relates to a preparation and testing method of an In2O3-rGO-PPy aerogel for rapid detection of hydrogen at room temperature. Background Art

[0002] As an ideal green energy, hydrogen energy is considered to be one of the most promising new energy carriers in the 21st century. It is also an important part of the emerging energy system and an important tool to promote the new energy security strategy. The importance of hydrogen (H2) is becoming more and more prominent in the context of modern energy demand. However, the flammable and explosive properties of hydrogen bring great safety hazards to the use, transportation and storage of hydrogen. Hydrogen has the characteristics of low explosion limit (4.1%), wide explosion range (4.1%-74.1%) and high explosion energy. Once it reaches the explosion condition, it is very easy to cause combustion and explosion accidents, causing loss of life and property to the people. Therefore, it is necessary to develop a gas sensor for real-time detection of hydrogen. In recent years, metal oxide semiconductor (MOS) sensors with the advantages of high electron mobility, wide band gap, low resistivity and low cost have been widely used and studied. Many metal oxides such as CeO2, In2O3, ZnO, MnO2 and WO3 are used as gas-sensitive materials in the research of gas sensors. Some studies have proposed the use of Cr@In2O3 materials for H2 detection, with a response of about 83.3% to 1000ppm H2 at 240°C. However, the operating temperature of metal oxides is usually as high as hundreds of degrees, and their sensing performance will be greatly reduced at room temperature.

[0003] To solve this problem, methods such as precious metal modification, material morphology control, or the introduction of other materials to construct heterojunctions are often used. For example, by compounding two-dimensional graphene oxide (GO) materials with metal oxides, a composite material of reduced graphene oxide (rGO) and metal oxides is formed by a hydrothermal method to reduce the operating temperature of the sensor. Some researchers have prepared rGO / In2O3 composite aerogel materials by a one-step hydrothermal method, which has a response of 13.04 to 10000ppm H2 at room temperature. However, this aerogel material still faces problems such as insufficient mechanical properties, difficulty in direct molding, long response time, and gas-sensitive performance that needs to be improved, which limits the application prospects of aerogel sensors. Summary of the invention

[0004] In order to solve the technical problems faced by existing graphene-based hydrogen sensors, the present invention provides a method for preparing and testing a macroscopic three-dimensional In2O3-rGO-PPy aerogel that quickly responds to hydrogen at room temperature, comprising the following steps:

[0005] Weigh CO(NH2)2 and In(NO3)3·4.5H2O according to the molar ratio of 5:(1 - 3), and mix them in 50 mL of deionized water to form a mixed solution 1. Stir rapidly until the solution is clear and transparent. Weigh the corresponding amount of NH4F according to the molar ratio of NH4F and In(NO3)3·4.5H2O (1 - 3):1. Mix NH4F with solution 1 and stir for 20 minutes to obtain a mixed solution 2. Put the well-stirred mixed solution 2 into a high-pressure reaction kettle lined with polytetrafluoroethylene, place it in an oven and react at 150 °C for 10 hours. After the reaction is completed and cooled to room temperature, collect the product, wash it repeatedly with deionized water, and dry it. Finally, place it in a muffle furnace and heat it to 400 °C at a rate of 3 - 5 °C / min and then anneal for 1 - 2 hours to prepare nano-In2O3;

[0006] Weigh methyl orange and FeCl3·6H2O according to the molar ratio of 1:(10 - 20), dissolve them in 100 ml of deionized water and use a probe ultrasonic instrument to ultrasonic for 5 minutes to obtain a mixed solution 3. Weigh pyrrole according to the molar ratio of methyl orange and pyrrole of 1:(10 - 30) and add it to the mixed solution 3 while stirring to form a mixed solution 4. After stirring for 2 minutes, cover the mouth of the beaker of the mixed solution 4 with a sealing film, and let it stand and react at 4 °C for 18 hours to obtain a black solid product. Wash it alternately with deionized water, ethanol, and n-butanol until the filtrate is clear and transparent. Pre-freeze the filtered product at -10 °C for 10 hours. Place the pre-frozen solid in a vacuum freeze dryer and freeze-dry it at -50 °C for 24 hours to obtain polypyrrole (PPy) tube monomers;

[0007] Prepare graphene oxide by the Hummers method. Weigh graphene oxide, polypyrrole tubes, and nano-indium oxide according to the mass ratio of 1:(1 - 5):(1 - 3). First, dissolve graphene oxide in 20 mL of deionized water and ultrasonic for 5 minutes to make the solution uniform. Dissolve indium oxide in 5 ml of deionized water and ultrasonic for 2 minutes. Mix the graphene oxide solution, indium oxide solution, and polypyrrole, and ultrasonic for 10 minutes under ice bath conditions to obtain a mixed solution 5. Transfer the mixed solution 5 to a 50 mL high-pressure reaction kettle lined with polytetrafluoroethylene and carry out hydrothermal reaction at (120 - 180) °C for (10 - 18) h. After the reaction is completed and cooled to room temperature, obtain a composite hydrogel. Alternately replace the solvent of the hydrogel with deionized water and ethanol for 2 days. Filter dry the excess water of the hydrogel and put it into the freezer, pre-freeze it at -10 °C for 10 hours. Place the pre-frozen solid in a vacuum freeze dryer and freeze-dry it at -50 °C for 48 hours to finally prepare a three-dimensional In2O3-rGO-PPy aerogel.

[0008] To better demonstrate the response potential of the aerogel sensor, the present invention proposes an overall testing method that maintains the dual three-dimensional structure of the aerogel sensor at the macroscopic and microscopic levels, including the following steps:

[0009] Connect wires to two conductive metal sheets (gold (Au), silver (Ag), copper (Cu)) with a length-to-width ratio of 2:1 and fabricate them into two gold electrodes. Then attach the two electrodes to both ends of the prepared three-dimensional In2O3-rGO-PPy aerogel. Use a three-necked sealed container as the testing gas chamber, closely attach a thermometer and a hygrometer to the outside of the gas chamber, place the entire aerogel sensor in the gas chamber, and connect the wires to an electrochemical workstation and a computer. Adjust the input amounts of air and hydrogen at the gas inlet respectively to expose the sensor to a hydrogen environment with a certain ratio, and conduct a response test on hydrogen while maintaining the macroscopic three-dimensional structure of the aerogel.

[0010] Preferably, weigh CO(NH2)2 and In(NO3)3·4.5H2O according to a mass ratio of 5:1.

[0011] Preferably, weigh the corresponding amount of NH4F according to a molar ratio of NH4F to In(NO3)3·4.5H2O of 2:1.

[0012] Preferably, transfer the mixed solution 2 to a reaction kettle lined with polytetrafluoroethylene and heat it at 150 °C for 10 h.

[0013] Preferably, heat the dried product in a muffle furnace at a rate of 3 - 5 °C / min to 400 °C and then anneal it for 1 - 2 hours.

[0014] Preferably, weigh methyl orange and FeCl3·6H2O according to a molar ratio of 1:10 and dissolve them in 100 mL of deionized water.

[0015] Preferably, weigh pyrrole according to a molar ratio of methyl orange to pyrrole of 1:15 and stir to make the ratio of pyrrole:methyl orange:FeCl3 = 15:1:10 in the mixed system.

[0016] Preferably, let the mixed solution 4 stand and react at 4 °C for 18 h.

[0017] Preferably, use the improved Hummers method to synthesize graphene oxide from natural graphite powder.

[0018] Preferably, weigh graphene oxide, polypyrrole tubes, and indium oxide nanoparticles according to a mass ratio of 1:2:4 respectively and mix them to prepare solution 5.

[0019] Preferably, ultrasonically treat the mixed solution 5 under ice bath conditions.

[0020] Preferably, the In2O3-rGO-PPy hydrogel is obtained through a hydrothermal reaction of the mixed solution 5 at 160 °C for 14 hours.

[0021] Preferably, the hydrothermally treated hydrogel is subjected to solvent replacement with deionized water, ethanol, and n-butanol for 48 h.

[0022] Preferably, it is pre-frozen at -10 °C for 10 hours and then freeze-dried at -50 °C for 48 hours to obtain the In2O3-rGO-PPy aerogel.

[0023] Preferably, the electrode sheet of the overall test device is a gold sheet with a width of 1 cm and a length of 2 cm.

[0024] Preferably, the gas chamber of the overall test device is a sealed three-necked container.

[0025] Preferably, a thermometer and a hygrometer are attached closely to the outer wall of the gas chamber of the overall test device.

[0026] The present invention successfully prepares a macroscopic three-dimensional In2O3-rGO-PPy nanocomposite through in-situ polymerization, hydrothermal method, and freeze-drying method. The prepared polypyrrole is significantly hollow tubular. After the one-dimensional PPy tubes are combined with two-dimensional reduced graphene oxide, a three-dimensional network structure is constructed in the composite material, shortening the ion diffusion path and improving the electrical conductivity of the material. Moreover, the introduction of PPy tubes effectively prevents the stacking and agglomeration between graphene sheets, significantly increasing the specific surface area of the composite material, enabling the material to expose more active sites and improving the gas adsorption performance. In addition, after the nano-hollow tubular PPy is combined with graphene oxide, the mechanical properties of the composite material are greatly improved. It not only presents a three-dimensionally interconnected porous network structure microscopically but also can maintain its three-dimensional structure macroscopically relying on strong mechanical strength.

[0027] Meanwhile, by directly device-izing the aerogel sensor and then testing it as a whole in the gas chamber, the method avoids the damage to the integrity of the three-dimensional network structure of the material by the traditional interdigital electrode method. Through the innovative overall testing method, as well as the P-N heterojunction between In2O3 and rGO and the π-π interaction between PPy and rGO, this three-dimensional composite aerogel sensor has excellent response performance and mechanical properties to hydrogen at room temperature. Under the conditions of not adding noble metals and at room temperature, the In2O3-rGO-PPy sensor has a response value of up to 11.6 to 1000 ppm hydrogen, which is twice that of the In2O3-rGO sensor; the response / recovery time is as low as 13 / 29 s, which is 2.9 times shorter than that of the In2O3-rGO sensor. The mechanical properties of the sensor have also been significantly improved. The compressive strength of the In2O3-rGO-PPy aerogel reaches 109.5 Kpa, which is 13.3 times higher than that of the In2O3-rGO sensor at 8.23 Kpa. Brief Description of the Drawings

[0028] Figure 1 It is a schematic diagram for testing using the innovative overall testing method of the present invention;

[0029] Figure 2 It is the XRD images of In2O3, 3D In2O3-rGO and 3D In2O3-rGO-PPy nanocomposites;

[0030] Figure 3 It is the Raman spectra of 3D In2O3-rGO, 3D In2O3-rGO-PPy nanocomposites and GO;

[0031] Figure 4 It is the XPS spectrum of 3D In2O3-rGO-PPy nanocomposite: (a) Total XPS spectrum of 3D In2O3-rGO-PPy aerogel; (b) In 3d spectrum; (c) C1s spectrum; (d) N1s spectrum; (e) O1s spectrum of In2O3-rGO aerogel; (f) O1s spectrum of In2O3-rGO-PPy aerogel;

[0032] Figure 5 It is the SEM images: (a, b) PPy nanotubes; (c) In4-rGO; (d, f) In4-rGO-PPy2; (e) Ground In4-rGO-PPy2;

[0033] Figure 6 It is the TEM image of 3D In2O3-rGO-PPy aerogel;

[0034] Figure 7Nitrogen adsorption - desorption isotherm and pore size distribution curve of 3D In2O3 - rGO - PPy nanocomposite;

[0035] Figure 8 Mechanical property test diagrams: (a) In2O3 - rGO; (b) In2O3 - rGO - PPy1; (c) In2O3 - rGO - PPy2; (d) In2O3 - rGO - PPy3; (e) Strength comparison diagram of all materials; (f) Elastic modulus comparison diagram of all materials;

[0036] Figure 9 Room - temperature gas - sensing test diagrams of In2O3 - rGO aerogels with different In2O3 contents: (a) Response and recovery curves of In x -rGO; (b) Bar chart of response / recovery time and response value of In x -rGO;

[0037] Figure 10 Room - temperature gas - sensing test diagrams of In2O3 - rGO - PPy aerogels with different PPy contents: (a) Response and recovery curves of In4 - rGO - PPy x ; (b) Bar chart of response / recovery time and response value of In4 - rGO - PPy x ;

[0038] Figure 11 Dynamic response curves and repeatability tests for 1000 ppm H2 at room temperature: (a, d) In4 - rGO; (b, e) In4 - rGO - PPy2 - F; (c, f) In4 - rGO - PPy2 - H;

[0039] Figure 12 Dynamic response curves of In4 - rGO - PPy2 sensor exposed to different concentrations of H2 at room temperature: (a) In4 - rGO - PPy2 - H; (b) In4 - rGO - PPy2 - F; Line chart of response to different concentrations of H2 at room temperature: (c) In4 - rGO - PPy2; Long - term stability of the sensor to 1000 ppm H2 at room temperature: (d) In4 - rGO - PPy2; Selectivity of the sensor to various interfering gases at room temperature: (e) In4 - rGO - PPy2; Detailed implementation manners

[0040] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific implementation manners and drawings. However, the present invention is not limited thereto.

[0041] Graphene oxide was synthesized using the improved Hummers method with natural graphite powder as the raw material. This is prior art and will not be elaborated here.

[0042] First, the preparation of nano-In2O3: 1.5 g of CO(NH2)2, 0.3 g of In(NO3)3·4.5H2O, and 0.6 g of NH4F were added to deionized water and stirred to form a mixed solution, which was then placed in a high-pressure reactor and heated. After the reaction was completed, the hydrogel was washed and purified with deionized water and ethanol, and finally placed in a muffle furnace and heated to 400 °C and annealed for 1 - 2 hours to obtain indium oxide (In2O3) nanoparticles. Then, the preparation of hollow PPy tubes: 0.2 g of methyl orange and 1.6 g of FeCl3·6H2O were dissolved in deionized water to form a mixed solution. 430 μL of pyrrole was transferred to the mixed solution under stirring, and the solution was left standing at 4 °C for 18 h to obtain a black product. The product was washed and purified with deionized water, ethanol, and n-butanol, and then freeze-dried at -50 °C for 24 hours to obtain polypyrrole (PPy) tubes. Finally, the preparation of In2O3-rGO-PPy aerogel: 40 mg of graphene oxide, 80 mg of polypyrrole, and 160 mg of indium oxide were dissolved in deionized water, and ultrasonically treated for 10 minutes in an ice bath. The mixed solution was transferred to a high-pressure reactor and heated to obtain a composite hydrogel. The hydrogel was washed and purified with deionized water and ethanol, pre-frozen for 10 h, and then freeze-dried at -50 °C for 48 hours to finally obtain three-dimensional In2O3-rGO-PPy aerogel. In addition, the innovative overall testing method of the present invention is as follows: two gold sheets were connected with wires and then connected to both ends of the aerogel. The aerogel was placed as a whole in three closed gas chambers, and the amounts of hydrogen and air introduced into the gas chambers were controlled so that the sensor was in a hydrogen environment with a certain concentration. The sensor was tested under this condition.

[0043] For comparison, five In2O3-rGO composites (In1-rGO, In2-rGO, In3-rGO, In4-rGO, In5-rGO) with mass ratios of In2O3 to rGO of 1:1, 2:1, 3:1, 4:1, and 5:1 were first prepared. After In4-rGO was selected as the best, three In2O3-rGO-PPy aerogels (In4-rGO-PPy1, In4-rGO-PPy2, In4-rGO-PPy3) with mass ratios of rGO to PPy of 1:1, 1:2, and 1:3 were prepared. The best three-dimensional In2O3-rGO-PPy aerogel (In4-rGO-PPy2) was selected through a series of characterizations and tests.

[0044] As Figure 1As shown, using the innovative holistic testing method (HTM), two gold (Au) sheets with a length-width ratio of 2:1 are used as electrode sheets. An aerogel monolith is sandwiched between the two electrode sheets, and the connected aerogel monolith is placed into three gas chambers. A thermometer and a hygrometer are closely attached to the gas chambers. During the test, the wire connecting the aerogel is connected to an electrochemical workstation, and the inflow rates of hydrogen and air are controlled to maintain the hydrogen concentration in the gas chambers. HTM maintains the macroscopic integrity of the sample. Meanwhile, since there is no mechanical grinding process, the damage to the three-dimensional network structure of the aerogel is relatively small.

[0045] To study the crystal structure and phase composition of each material, X-ray diffraction (XRD) characterization was performed on the samples. As Figure 2 shown, the main diffraction peaks of all samples are in complete agreement with the standard card (JCPDS: 71-2195) of cubic-phase In2O3, and the corresponding crystallization indices are (211), (222), (400), (411), (332), (431), (440), (611), (622), indicating that the synthesized In2O3 has a relatively high crystallinity.

[0046] Raman spectroscopy was used to characterize the carbon skeleton structure and defect evolution law of each material. As Figure 3 shown, all three materials exhibit obvious D and G bands in the range of 1300 - 1600 cm -1 , which proves the existence of graphene. Compared with the ID D / IG G value (0.89) of GO, the ID D / IG G ratio (1.09) of In-rGO increases. After adding PPy, the D peak (1346.12 cm -1 ) of In2O3-rGO-PPy remains unchanged, but the G peak (1577.54 cm -1 ) shows an obvious red shift, which may be due to the strong interaction between the π-π conjugate structure of PPy and the sp 2 carbon domain of rGO, which also proves the tight combination between PPy and rGO.

[0047] XPS was used to characterize the elemental composition and valence states. Figure 4 Figure a shows the full XPS spectrum of rGO-In2O3-PPy, which clearly shows the characteristic peaks of C, N, In, and O, proving the existence of the corresponding elements. Figure 4 Figure b shows the high-resolution spectrum of In 3d, which shows the characteristic peaks of spin-orbit splitting (445.02 eV) related to In 3d 5 / 2 and In 3d 3 / 2The doublet corresponding to the spin-orbit splitting characteristic peak (452.01 eV) has a peak spacing of 6.99 eV, which is in good agreement with the binding energy data of the standard In 3+ oxidation state.

[0048] Figure 4 The C1s peak in c is the sp 2 hybridized C-C / C═C at 284.75 eV, and the binding energies at 286.56 eV and 290.66 eV correspond to C-O and C═O, respectively. Figure 4 d shows the N1s peak at 399.17 eV, corresponding to unprotonated pyrrole nitrogen (-NH-), and 400.08 eV and 401.8 eV are related to protonated nitrogen (-NH + -) and nitrogen oxide (N-O), respectively. Figure 4 e and Figure 4 f show the high-resolution spectra of the O1s peaks of rGO-In2O3 and rGO-In2O3-PPy, where their binding energies to lattice oxygen (O L ), oxygen vacancy (O V ), and adsorbed oxygen (O C ) are marked. The percentages of O V and O C in rGO-In2O3-PPy are 37.92% and 26.8% respectively, showing a significant increase compared with 27.27% and 21.87% of rGO-In2O3.

[0049] The micro-morphologies of PPy-NTs, In4-rGO, and In4-rGO-PPy2 were observed by scanning electron microscopy. Figure 5 a and Figure 5 b show the morphology and structure of the synthesized PPy nanotubes. They are slender tubular and evenly distributed without obvious agglomeration. As can be clearly seen from the Figure 5 red circle in b, the PPy-NTs are hollow tubular with an inner diameter of about 60 nm, an outer diameter of about 140 nm, and a length of about 800 nm, which proves that the hollow tubular PPy nanotubes are successfully obtained.

[0050] The morphological structures of In4-rGO and In4-rGO-PPy2 are shown in Figure 5 c and Figure 5 d, respectively. As can be seen from Figure 5 c, the rGO sheets are severely stacked and the three-dimensional structure is not prominent. As can be seen from Figure 5 d, the one-dimensional tubular structure of PPy-NTs and the hydrogen bonds of rGO are combined into a three-dimensional porous network structure through π-π interactions. As shown in Figure 5As shown in e, In2O3 nanoparticles are uniformly embedded in the three-dimensional network structure, and the one-dimensional tubular structure of PPy-NTs is not damaged. The traditional testing method is to grind the aerogel material for fabricating sensors. Figure 5 Figure f shows the In4-rGO-PPy2 material after grinding, and it can be seen that the integrity of the three-dimensional network structure has been significantly damaged. Obviously, when using the traditional gas-sensing testing method, the integrity of the three-dimensional network structure of the material will be damaged, making it difficult for the sensor to fully utilize the advantages of the three-dimensional structure in gas-sensing response.

[0051] To observe the nanostructure and morphology of the material in more detail, we characterized the three-dimensional In2O3-rGO-PPy composite using transmission electron microscopy (TEM). As Figure 6 shown in Figure a, PPy nanotubes and rGO construct a three-dimensional network structure, and In2O3 is uniformly distributed in the three-dimensional network. In addition, the rGO sheets are well-organized, forming macropores at the micron scale. From Figure 6 Figure b and Figure 6 c, it can be clearly observed that the PPy tubes are hollow and transparent, which is consistent with the conclusion of scanning electron microscopy. At the same time, it can also be seen that In2O3 is distributed in a cubic shape and embedded in the PPy tubes. In addition, from Figure 6 Figure d, the lattice bands of In2O3 can also be observed, with a spacing of 0.286 nm, which is consistent with the crystal plane (222), and this is consistent with the results of XRD.

[0052] To better study the pore size and specific surface area of the rGO-In2O3-PPy composite, a nitrogen (N2) adsorption / desorption test was conducted on the material. As Figure 7 shown, it can be clearly seen that the adsorption / desorption isotherm is a type-IV curve, and there is an H3-type hysteresis loop at 0.8 to 1.0 (P / P0). The specific surface area (S BET ) of the rGO-In2O3-PPy composite is 82.72 m 2 2 -1 , and the pore size distribution curve shows a sharp peak at 4 nm. In addition, there is a broader peak at 14 nm, indicating the presence of mesopores near 14 nm.

[0053] The mechanical properties of different aerogels were tested using a universal testing machine. Figure 8 Figures a-8e show the stress-strain curves of each material. The In2O3-rGO-PPy2 has the best mechanical properties, with a compressive strength of 109.5 KPa at a compression ratio of 80%, while the In2O3-rGO has the worst mechanical properties, with a compressive strength of 8.23 KPa at a compression ratio of 68%. Figure 8Figure f shows the comparison of the elastic modulus of aerogels with different PPy addition ratios. As the addition amount increases, the elastic modulus first increases and then decreases, and the elastic modulus of In2O3-rGO-PPy2 is the largest (47.5 KPa). After adding PPy, the compressive and elastic properties of the composite material are significantly improved.

[0054] Figure 9 Figure a shows the response-recovery curves of In2O3-rGO sensors with different In2O3 ratios to 1000 ppm H2 at room temperature. The corresponding response value (R g / R a ) and response / recovery time are as Figure 9 shown in Figure b. The response value first increases and then decreases with the increase of the In2O3 ratio, and reaches the maximum value (5.8) when In / rGO = 4. The response / recovery time also shows a trend of first shortening and then increasing, and the time is the shortest (39 s / 69 s) when In / rGO = 4. When the ratio of In2O3 to rGO is higher than 4:1, the reaction performance decreases.

[0055] Figure 10 Figure shows the response-recovery curves of In4-rGO-PPy sensors with different PPy concentrations to 1000 ppm H2 at room temperature. After adding PPy, the initial resistance decreases significantly, which proves that the conductivity of the material is enhanced. Figure 10 Figure b shows the response performance of the In4-rGO-PPy sensor. With the addition of PPy, the response value and response / recovery time first increase and then decrease. The response value of In4-rGO-PPy2 is the largest (11.6), and the response / recovery time is the shortest (13 s / 29 s).

[0056] Comparison Figure 11 Figures a and 11b show that after adding PPy, the response value increases from 5.8 to 6.3, and the response / recovery time shortens from 38 s / 69 s to 35 s / 67 s. Comparing Figure 11 Figures b and 11c, it can be seen that the response performance of the In4-rGO-PPy2-H sensor tested by the integral method is significantly improved compared with that of the In4-rGO-PPy2-F sensor tested by the interdigital electrode method. The response value increases from 6.3 to 11.6, an increase of 1.84 times, and the response recovery decreases from 35 s / 67 s to 13 s / 29 s, which is 37% of the original. The traditional interdigital electrode test method has a step of grinding the material, and the three-dimensional network structure of the material will be partially damaged during the grinding process, which is verified by comparing the scanning electron microscope pictures of the two methods ( Figure 5 Figures e and 5f). Figure 11The repeatability test results of the three sensors are shown in d-11f. During the five-cycle repeatability test, the responses of the three sensors to H2 were basically stable, with a maximum fluctuation of 0.35. The average response values and standard deviations of each sensor were In4-rGO (5.78, 0.14), In4-rGO-PPy2-F (6.21, 0.11), and In4-rGO-PPy2-H (11.5, 0.19), indicating stable sensor performance.

[0057] Figure 12 Figures a and 12b show the transient response / recovery curves of the In4-rGO-PPy2 sensors tested by two different methods to different concentrations of H2 at room temperature. The response values increase with the increase in H2 concentration, with maximum values (11.6, 6.2) and minimum values (1.67, 1.31) at 1000 ppm and 100 ppm, respectively. The variation ranges of the sensor response values of the two test methods are basically close, but the variation range of the response / recovery time of the In4-rGO-PPy2-H sensor is significantly smaller than that of the In4-rGO-PPy2-F sensor.

[0058] As can be seen from Figure 12 Figure c, the response value does not show a linear relationship with the magnitude of the H2 concentration. When the concentration is below 150 - 200 ppm, the response value increases more, while when the concentration is between 200 - 300 ppm, the response value changes slowly. In addition, when the H2 concentration approaches 1000 ppm, the response value of In4-rGO-PPy2-H increases more than that of In4-rGO-PPy2-F. The long-term stability of the sensor was detected, verifying the reliability of the sensor ( Figure 12 Figure d).

[0059] To verify the anti-interference performance of the sensor, six interfering gases (CO, NH3, C2H5OH, NO2, CH3OH, CH4) were tested with H2. As can be clearly seen from Figure 12 Figure e, the selectivity of the aerogel to H2 is very good, and the response value of H2 is one order of magnitude higher than that of other gases. From the test results, it can be seen that the tested sensor has excellent selectivity, and the response to H2 has a great advantage over the response to each interfering gas.

[0060] As shown in Table 1, to better evaluate the performance of the sensors prepared in this study, we compared the previous reports on H2 sensing materials with the three-dimensional In2O3-rGO-PPy-H and three-dimensional In2O3-rGO-PPy-F sensors prepared in this study. The magnitude of the response value, as well as the response time and recovery time, are the core elements for evaluating the sensor performance. However, under different conditions such as temperature, hydrogen concentration, and whether noble metals are added, the rationality of the sensing performance should be considered as appropriate. Although the response value of the three-dimensional In2O3-rGO sensor in Reference [1] is higher than that of this study, it was tested at a high concentration of 10,000 ppm. According to the general attenuation degree, its response value at 1,000 ppm should be inferior to that of the sensor of the present invention. The 5Au-1Pt-In2O3 sensor with noble metals added in Reference [3] has a high response value at 240 °C, but noble metal materials are expensive and the working temperature is high, which is not suitable for practical use. Considering various indicators comprehensively, the In2O3-rGO-PPy sensor of the present invention still has unique advantages.

[0061] Table 1 Performance comparison of different hydrogen sensing materials

[0062]

[0063] Note: a =R g / R a , b =(R g -R a ) / R a

[0064] Among them, Reference [1] is Chen, C.Y.; Liu, Y.H.; Zhou, J.; He, X.H.; Chen, C.L.; Xiao, G.Q.; Tang, Y.L.; Chen, W.X. A rapid response room temperature hydrogen sensor based on a three-dimensional Pd-In2O3 / rGO aerogel. New J Chem 2024, 48(13), 5866-5876. DOI: 10.1039 / d3nj05894h. Reference [2] is Zhu, Y.; Meng, X.N.; Wang, X.H.; Gao, W. Low detection based on PdPt / In2O3 nanospheres for rapid hydrogen detection. Sensors and Actuators B-Chemical 2024, 410. DOI: 10.1016 / j.snb.2024.135654. Reference [3] is Wang, H.W.; Duan, P.Y.; Tian, J.M.; Duan, Q.L.; Jin, K.Q.; Sun, J.H. Synergistic effect of bimetallic Au-Pt functionalized In2O3 nanoflowers for ppb-level hydrogen detection. Sensors and Actuators B-Chemical 2025, 426. DOI: ARTN 137082 10.1016 / j.snb.2024.137082. Reference [4] is Zheng, Z.Q.; Zhu, L.F.; Wang, B. In2O3 Nanotower Hydrogen Gas Sensors Based on Both Schottky Junction and Thermoelectronic Emission. Nanoscale Res Lett 2015, 10. DOI: ARTN 2931 0.1186 / s11671-015-1002-4.Reference [5] is Lv, Q. J.; Li, R. F.; Qu, Y. H.; Yu, M. Y.; Zhang, L.; Li, H. H. CeO2 nanorods decorated In2O3 nanoparticles for enhanced low temperature detection of hydrogen. Inorganic Chemistry Communications 2023, 158. DOI: 10.1016 / j.inoche.2023.111474. Reference [6] is Li, M. W.; Sun, X. Y.; Wang, Y. H.; Qin, C.; Cao, J. L.; Wang, Y. Preparation and room - temperature hydrogen sensing property of flower - like In2O3 / SnS2 nanocomposite. Physica E 2024, 160. DOI: ARTN 115938 10.1016 / j.physe.2024.115938.

Claims

1. Preparation and testing method of In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature, characterized in that, It includes the following steps: Weigh CO(NH2)2 and In(NO3)3·4.5H2O according to the molar ratio of 5:(1 - 3), mix them in 50 mL of deionized water and stir to form a mixed solution 1. Weigh the corresponding amount of NH4F according to the molar ratio of NH4F and In(NO3)3·4.5H2O of (1 - 3):1, add NH4F to the mixed solution 1 and stir for 20 minutes to obtain a mixed solution 2; put the mixed solution 2 into a high-pressure reactor for reaction. After the reaction is completed, collect the product, wash it repeatedly with deionized water and dry it. Finally, place it in a muffle furnace at 400 °C for annealing for 1 - 2 h to finally prepare nano-In2O3; Weigh methyl orange and FeCl3·6H2O according to the molar ratio of 1:(10 - 20), dissolve them in 100 mL of deionized water and ultrasonicate for 5 minutes to obtain a mixed solution 3. Weigh pyrrole according to the molar ratio of methyl orange and pyrrole of 1:(10 - 30) and transfer it to the mixed solution 3 to obtain a mixed solution 4. After stirring for 2 minutes, let the mixed solution 4 stand and react at 4 °C for 18 hours to obtain a black solid product. Wash and filter it alternately with deionized water, ethanol and n-butanol. Pre-freeze the filtered product at -10 °C and then place it in a vacuum freeze dryer to obtain polypyrrole (PPy) tubes by freeze drying at -50 °C; Prepare graphene oxide by the Hummers method. Weigh graphene oxide, polypyrrole tubes and nano-indium oxide according to the mass ratio of 1:(1 - 5):(1 - 3). Dissolve graphene oxide in 20 mL of deionized water and ultrasonicate, dissolve indium oxide in 20 mL of deionized water and ultrasonicate. Mix the graphene oxide solution, indium oxide solution and polypyrrole to obtain a mixed solution 5, ultrasonicate it under ice bath conditions, transfer the mixed solution 5 to a high-pressure reactor lined with polytetrafluoroethylene and carry out hydrothermal reaction at (120 - 180) °C for (10 - 18) h. After the reaction is over and cooled to room temperature, obtain a composite hydrogel. Alternately replace the solvent of the hydrogel with deionized water and ethanol. Pre-freeze the hydrogel at -10 °C for 10 hours. Put the pre-frozen solid in a vacuum freeze dryer and freeze dry it at -50 °C for 48 hours to finally prepare a three-dimensional In2O3-rGO-PPy aerogel; Connect wires to two conductive metal sheets (gold (Au), silver (Ag), copper (Cu)) with a length-width ratio of 2:1 to make two electrodes, and fix the two electrodes at both ends of the prepared three-dimensional In2O3-rGO-PPy aerogel respectively; use a three-necked closed container as a test gas chamber, fix a thermometer and a hygrometer outside the gas chamber respectively, place the aerogel sensor as a whole in the gas chamber, and connect the wires to an electrochemical workstation and a computer. Adjust the input amounts of air and hydrogen at the gas inlet respectively to make the sensor exposed to a certain proportion of hydrogen environment, and conduct a response test on hydrogen under the condition of maintaining the macroscopic three-dimensional structure of the aerogel.

2. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, Weigh CO(NH2)2 and In(NO3)3·4.5H2O according to the molar ratio of 5:1, and add NH4F to the mixed solution 1 according to the molar ratio of NH4F and In(NO3)3·4.5H2O of 2:1 and stir for 20 minutes.

3. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, Put the mixed solution 2 into a high-pressure reaction kettle, react at 150 °C for 10 hours, then heat to 400 °C at a rate of 3 - 5 °C / min and anneal for 1 - 2 hours to prepare nano In2O3.

4. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, Weigh methyl orange and FeCl3·6H2O according to the molar ratio of 1:10, dissolve them in 100 ml of deionized water and sonicate for 5 minutes to obtain the mixed solution 3, and weigh pyrrole according to the molar ratio of methyl orange and pyrrole of 1:15 and add it to the mixed solution 3 while stirring.

5. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, The mixed solution 4 reacts at 4 °C for 18 hours to obtain a black solid product, which is purified by alternately washing with deionized water, ethanol, and n-butanol.

6. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, The filtered product is pre-frozen at -10 °C for 10 hours and then freeze-dried at -50 °C for 24 hours to obtain polypyrrole (PPy) tubes.

7. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, Weigh graphene oxide, polypyrrole tubes, and nano indium oxide according to the mass ratio of 1:2:4, and ultrasonically mix them for 10 minutes under ice bath conditions to obtain solution 5.

8. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, Transfer the mixed solution 5 to a 50 ml high-pressure reaction kettle lined with polytetrafluoroethylene, carry out hydrothermal reaction at 160 °C for 14 hours, alternately replace the solvent of the hydrogel with deionized water and ethanol to obtain a hydrogel, pre-freeze it at -10 °C for 10 hours and then freeze-dry it at -50 °C for 24 hours to obtain a three-dimensional In2O3-rGO-PPy aerogel.

9. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that, Connect the wires to two gold (Au) sheets with a width of 1 cm and a length of 2 cm respectively and make them into two gold electrodes, and fix the two electrodes at both ends of the prepared three-dimensional In2O3-rGO-PPy aerogel respectively.

10. The preparation and testing method of an In2O3-rGO-PPy aerogel for rapid hydrogen detection at room temperature according to claim 1, characterized in that Use a three-necked closed container as the test gas chamber, and fix the thermometer and hygrometer outside the gas chamber respectively.

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