Preparation method of reduced graphene oxide and tin oxide nano composite material and preparation method of carbon monoxide gas sensor

Abstract

The invention discloses a preparation method of a reduced graphene oxide and stannic oxide nano composite material, which comprises the following steps: dispersing graphene oxide and stannic oxide powder in 10-80 v% ethanol to obtain a dispersion liquid, adding a hydrazine hydrate solution into the dispersion liquid, uniformly stirring, transferring into an ultrasonic device, performing ultrasonic treatment, transferring into a supercritical device, and drying to obtain the reduced graphene oxide and stannic oxide nano composite material. Injecting carbon dioxide into the supercritical device, stirring and reacting for 3-6 hours under the supercritical condition, naturally cooling to room temperature, and releasing the pressure; and separating the solution after supercritical treatment, collecting and separating a substrate, and drying to obtain the reduced graphene oxide and tin oxide composite material. According to the method, firstly, the graphene oxide is reduced under the ultrasonic condition, then the reduced graphene oxide and tin oxide heterojunction is formed through the supercritical carbon dioxide means, compared with a reduced graphene oxide and tin oxide composite material obtained through a traditional hydrothermal method, the cost is lower, and raw materials are easier to obtain.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material preparation, and in particular relates to a method for preparing a reduced graphene oxide and tin oxide nanocomposite material and a method for preparing a carbon monoxide gas sensor. Background Art

[0002] Transformers are crucial hubs of power transmission, transformation, and distribution in ultra-high voltage (UHV) power grids. Their operational status directly impacts the safety and reliability of the grid's power supply. Effectively monitoring faults within power transformers and identifying defects within them is crucial for preventing sudden insulation or aging failures, ensuring the safe operation of power transformers, and ensuring the normal transmission of electricity. During operation, oil-immersed power transformers, under the influence of heat and electricity, generate small amounts of CO, CO₂, and hydrocarbon gases. Therefore, utilizing appropriate gas detection sensors to detect the concentration and composition of characteristic gases dissolved in transformer insulating oil and provide safety warnings is feasible. This helps guide maintenance personnel in proactively eliminating potential safety hazards and preventing major accidents.

[0003] Gas sensors, devices used to detect and measure gas concentrations in the environment, can perform qualitative and quantitative analysis of fault gases generated during the operation of oil-immersed transformers. They offer simple operation, convenient detection, and real-time detection. However, current gas sensors still suffer from limited detection range, limited sensitivity and accuracy, and a need for improved service life and stability. The development and design of new gas sensors with higher accuracy and a wider detection range are highly desirable for transformer oil gas detection in power grids.

[0004] Tin oxide (SnO2) is a typical n-type semiconductor with a wide bandgap (Eg = 3.6 eV). Due to its high conductivity, excellent stability, and ease of synthesis, it is a highly sought-after gas-sensing material. Reduced graphene oxide (rGO) is a p-type semiconductor with a narrower bandgap. While it possesses excellent properties such as excellent conductivity and a high specific surface area, it also possesses abundant surface functional groups, high catalytic activity, and numerous active sites, which facilitate gas adsorption. Studies have shown that the commonly used rGO-SnO2 nanocomposite gas sensors prepared via hydrothermal methods still suffer from shortcomings such as low sensitivity, poor stability, long response / recovery times, and difficulty in recovery. Summary of the Invention

[0005] In view of the defects and shortcomings of the above-mentioned prior art, the object of the present invention is to provide a method for preparing a reduced graphene oxide and tin oxide nanocomposite material and a method for preparing a carbon monoxide gas sensor.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: The method for preparing a reduced graphene oxide and tin oxide nanocomposite material comprises the following steps: S1: dispersing graphene oxide and tin oxide powder in 10-80 vol% ethanol to obtain a dispersion, adding a hydrazine hydrate solution to the dispersion, stirring evenly, and then transferring to an ultrasonic device for ultrasonication; S2: transferring the dispersion after ultrasonic treatment in step S1 to a supercritical device, injecting carbon dioxide into the supercritical device, stirring the reaction under supercritical conditions for 3 to 6 hours, and releasing the pressure after natural cooling to room temperature; separating the solution after supercritical treatment, collecting and drying the separated substrate to obtain a reduced graphene oxide and tin oxide composite material.

[0007] Preferably, in step (1), the mass ratio of graphene oxide to tin oxide is 1:4-4:1, the ratio of the mass of graphene oxide to the volume of the ethanol solution is 0.5-2 mg / ml, and the volume ratio of the ethanol solution to the hydrazine hydrate solution is 2000-1000.

[0008] Preferably, the ultrasonication time in step S1 is 30 to 120 minutes.

[0009] Preferably, the supercritical conditions in step S2 are as follows: temperature 40-100° C., pressure 10-20 MPa.

[0010] Preferably, the separation in step S2 is performed by centrifuge separation, and the separation steps are specifically as follows: the supercritically treated solution is subjected to a first separation, the centrifuge speed for the first separation is 4000~10000 r / min, the centrifugation time is 15 min, the supernatant is taken and centrifuged and washed 2~3 times with 10~80v% ethanol, and then a second separation is performed, the centrifuge speed for the second separation is 8000~12000 r / min, the centrifugation time is 15 min, and after aspirating part of the supernatant, a separated substrate is obtained.

[0011] Preferably, the drying temperature in step S2 is 60-80° C., and the drying time is 12-24 h.

[0012] Preferably, the reduced graphene oxide and tin oxide composite material is obtained according to the method.

[0013] The preparation method of the carbon monoxide gas sensor comprises mixing the reduced graphene oxide and tin oxide composite material with anhydrous ethanol and grinding them to form a paste slurry, which is then applied to the surface of an interdigital electrode with a gold electrode to form a sensitive material film, so that the sensitive material film completely covers the gold electrode, and then aging the interdigital electrode covered with the sensitive material in a muffle furnace.

[0014] Preferably, the volume ratio of the reduced graphene oxide and tin oxide nanocomposite material to anhydrous ethanol is 1-5 mg / ml.

[0015] Preferably, the aging temperature in the muffle furnace is 200-400° C., and the aging time is 4-6 h.

[0016] In the present invention, molybdenum oxide and graphene oxide are commercially available without any modification treatment.

[0017] The present invention has the following beneficial effects: The present invention prepares a composite material of reduced graphene oxide and tin oxide under supercritical carbon dioxide. Since tin oxide is an n-type semiconductor and reduced graphene oxide is a p-type semiconductor, a pn-type heterojunction structure can be formed. This structure has a more excellent carrier transport capability, can provide more active sites, and can achieve rapid adsorption and desorption, thereby improving the sensitivity and reaction speed to reducing gases.

[0018] This method uses raw, unmodified commercially available graphene oxide and tin oxide to prepare a reduced graphene oxide and tin oxide nanocomposite using supercritical carbon dioxide. Compared to reduced graphene oxide and tin oxide nanocomposites prepared using a hydrothermal method, this method offers a simpler process, lower costs, and more readily available raw materials. This composite material is used to fabricate a gas sensor using commercially available planar interdigitated electrodes, resulting in a simple device process and suitability for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the XRD pattern of reduced graphene oxide and tin oxide nanocomposite; Figure 2 C 1s spectrum of XPS graph of reduced graphene oxide and tin oxide nanocomposite; Figure 3 Sn 3d spectrum of XPS graph of reduced graphene oxide and tin oxide nanocomposite; Figure 4 The CO response and recovery curve of the gas sensor at an operating temperature of 125°C is shown in FIG. Figure 5 The response and recovery curves of CO for the materials of Example 2-4 at a working temperature of 125°C are shown below. Figure 5 (a) is a graph of Example 2, Figure 5 (b) is a graph of Example 3, Figure 5 (c) is a graph of Example 4. DETAILED DESCRIPTION

[0020] To make the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Example

[0021] The preparation method of reduced graphene oxide and tin oxide nanocomposite material and the preparation method of carbon monoxide gas sensor are as follows: (1) Disperse 10 mg of graphene oxide and 40 mg of tin oxide powder in 20 mL of 45 v% ethanol and stir to obtain a dispersion. Add 10 μL of hydrazine hydrate solution to the dispersion, stir evenly, and transfer to an ultrasonic device for 30 min. (2) The dispersion after ultrasonication in step (1) is transferred to a supercritical device, and carbon dioxide is injected into the supercritical device to make it reach a supercritical state (20 MPa, 80 ° C). After reacting for 3 hours under magnetic stirring, the carbon dioxide is released to relieve the pressure; then, the dispersion is centrifuged at a speed of 4000 r / min for 15 minutes, the supernatant is taken, and the dispersion is washed 2 to 3 times with 45 v% ethanol by centrifugation at a speed of 10000 r / min for 15 minutes, and part of the supernatant is sucked away, the precipitate is transferred, and the separated substrate is dried in an oven at a temperature of 60 ° C for 24 hours to obtain a reduced graphene oxide and tin oxide nanocomposite material.

[0022] (3) The above-mentioned reduced graphene oxide and tin oxide nanocomposite material was used as raw materials, mixed with anhydrous ethanol and ground into a paste slurry. The mass of the reduced graphene oxide and tin oxide nanocomposite material was 1 mg, and the volume of anhydrous ethanol was 1 ml. The paste slurry was then coated on the surface of the interdigital electrode with a gold electrode to form a sensitive material film. The sensitive material film completely covered the gold electrode. The interdigital electrode covered with the sensitive material was then aged in a muffle furnace at 200°C for 4 h.

[0023] The crystal structure of the reduced graphene oxide and tin oxide nanocomposite material obtained in the experiment was characterized by using an X-ray diffractometer. Figure 1 It shows that the diffraction peaks in the rGO-SnO2 nanocomposite material include the diffraction peak of SnO2, and the peak of rGO cannot be observed due to its low intensity. SnO2 has a tetragonal cassiterite structure and has no diffraction peaks of other impurities.

[0024] The surface element composition and corresponding chemical bonding state of the reduced graphene oxide and tin oxide composite material obtained by XPS analysis experiment, Figure 2 The C 1s spectrum can be subdivided into three different peaks at 284.8, 286.26, and 288.93 eV, corresponding to the C=C, CO, and COC components, respectively.

[0025] Figure 3 The two peaks at 487.41 and 495.82 eV represent the binding energies of Sn 3d5 / 2 and 3d3 / 2 orbitals. The above results prove that Sn exists in the +4 valence state in the gas-sensitive material.

[0026] Figure 4 The gas sensor prepared using the experimentally prepared graphene oxide and tin oxide composite material with a mass ratio of 0.4 shows a resistance change rate ((Rg-Ra) / Ra) response signal to 75 ppm, 85 ppm, and 95 ppm CO concentrations at 125 °C, where R g Indicates the resistance of the sensor after adding the gas to be measured in dry air, R a is the initial resistance of the sensor in dry air. Example

[0027] The difference between this embodiment and embodiment 1 is that no hydrazine hydrate solution is added in step (1). Example

[0028] The difference between this embodiment and embodiment 1 is that the supercritical treatment in step (2) is not performed, but centrifugal separation and drying treatment are directly performed, and the obtained composite material is processed in step (3). Example

[0029] The difference between this embodiment and embodiment 1 is that the aging treatment in the muffle furnace at 200° C. in step (3) is not performed, and the electrode completely covered with the material film is directly subjected to the gas sensitivity test.

[0030] The gas sensor performance of the sensor materials prepared in Examples 2-4 was characterized. Figure 5 Comparing the rapid response and recovery capabilities to different concentrations of carbon monoxide, it was found that the response and recovery time and resistance change rate index parameters of all comparative examples were worse than those of Example 1.

[0031] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a reduced graphene oxide and tin oxide nanocomposite material, characterized in that: The following steps are involved: S1: dispersing graphene oxide and tin oxide powder in 10-80 vol% ethanol to obtain a dispersion, adding a hydrazine hydrate solution to the dispersion, stirring evenly, and then transferring to an ultrasonic device for ultrasonication; S2: transferring the dispersion after ultrasonic treatment in step S1 to a supercritical device, injecting carbon dioxide into the supercritical device, stirring the reaction under supercritical conditions for 3 to 6 hours, and releasing the pressure after natural cooling to room temperature; separating the solution after supercritical treatment, collecting and drying the separated substrate to obtain a reduced graphene oxide and tin oxide composite material.

2. The method according to claim 1, characterized in that In the step (1), the mass ratio of graphene oxide to tin oxide is 1:4-4:1, the ratio of the mass of graphene oxide to the volume of the ethanol solution is 0.5-2 mg / ml, and the volume ratio of the ethanol solution to the hydrazine hydrate solution is 2000-1000.

3. The method according to claim 1, characterized in that The ultrasonic time in step S1 is 30 to 120 minutes.

4. The method according to claim 1, wherein The supercritical conditions in step S2 are as follows: temperature 40-100° C., and pressure 10-20 MPa.

5. The method according to claim 1, wherein The separation in step S2 is performed by centrifuge separation, and the separation steps are specifically as follows: the supercritical solution is subjected to a first separation, the centrifuge speed for the first separation is 4000~10000 r / min, the centrifugation time is 15 min, the supernatant is taken and centrifuged and washed 2~3 times with 10~80v% ethanol, and then a second separation is performed, the centrifuge speed for the second separation is 8000~12000 r / min, the centrifugation time is 15 min, and after aspirating part of the supernatant, a separated substrate is obtained.

6. The method according to claim 1, characterized in that The drying temperature in step S2 is 60-80° C., and the drying time is 12-24 h.

7. The reduced graphene oxide and tin oxide composite material obtained according to the method according to any one of claims 1 to 6.

8. A method for preparing a carbon monoxide gas sensor, characterized in that: The reduced graphene oxide and tin oxide composite material as described in claim 7 is mixed with anhydrous ethanol and ground into a paste slurry, which is then applied to the surface of an interdigitated electrode with a gold electrode to form a sensitive material film, so that the sensitive material film completely covers the gold electrode, and then the interdigitated electrode covered with the sensitive material is aged in a muffle furnace.

9. The method according to claim 8, characterized in that The volume ratio of the reduced graphene oxide and tin oxide nanocomposite material to anhydrous ethanol is 1-5 mg / ml.

10. The method according to claim 8, characterized in that The aging temperature in the muffle furnace is 200-400° C., and the aging time is 4-6 h.

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