Room-temperature methane sensor based on Pd-doped rGO / SnO2 nano composite material and preparation method of room-temperature methane sensor

Abstract

The invention discloses a room-temperature methane sensor based on a Pd-doped rGO / SnO2 nano composite material and a preparation method of the room-temperature methane sensor, and belongs to the technical field of gas sensors. The Pd-doped rGO / SnO2 nano composite material is synthesized by adopting a hydrothermal method and a liquid phase reduction method, and the Pd-doped rGO / SnO2 nano composite material is dripped and cast on an Al2O3 planar ceramic chip substrate with an Au interdigital electrode. The excellent sensing performance at the room temperature is attributed to doping of rGO and Pd, and rGO plays a role of a conductive network to promote electron transfer, and in addition, the specific surface area of the material can be increased, and methane gas adsorption can be promoted; pd can activate the dissociation of oxygen molecules, so that atomic products are diffused to the surface of metal oxide, the quantity of adsorbed oxygen is increased, the molecule-ion conversion rate is improved, and the activation energy required by sensing reaction is reduced. Therefore, the Pd-doped rGO / SnO2 nano composite material is a promising sensitive material for designing and manufacturing a room-temperature methane gas sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensors, and in particular relates to a room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material and a preparation method thereof. Background Art

[0002] Methane (CH4) is the main component of natural gas, biogas and fuel gas. It is non-toxic, colorless, odorless and highly flammable in the air. At present, in order to achieve sustainable development of energy and environment, the production and consumption of natural gas have ushered in rapid growth, and the use of natural gas in residents' lives has become increasingly popular. However, as a flammable and explosive gas, the explosion limit of methane in the air is 5-15% volume fraction. Once a leak occurs, it will form an explosive mixture with the surrounding air, which may cause an explosion and cause a safety accident. In addition, methane is a potent greenhouse gas. Within a 100-year time frame, its global warming potential is 28 times higher than that of carbon dioxide (CO2). Its leakage and emission will greatly affect the global climate and thus affect normal human social activities. For the above reasons, the development of methane gas sensors is of great significance.

[0003] Sensors based on metal oxide semiconductors such as SnO2, ZnO, Co3O4 and In2O3 are the most widely used sensors for CH4 detection. They tend to have high sensitivity and stability, but usually need to work at high temperatures, which brings certain energy consumption problems and safety hazards, making their application prospects limited. On the other hand, carbon nanomaterials are gradually being used in gas sensing. Reduced graphene oxide (rGO) is a two-dimensional carbon nanomaterial, which is an atomic sheet composed of carbon atoms arranged in a hexagonal array. It has many remarkable properties, such as high mechanical strength, high thermal conductivity, and large surface area. One important point is that it has extremely high charge carrier mobility at room temperature. However, it still has the disadvantages of slow response recovery time and low sensitivity. Therefore, the composite of carbon nanomaterials and metal oxide semiconductors can show good sensing performance at room temperature through synergistic complementary effects, taking advantage of their strengths and avoiding their weaknesses.

[0004] SnO2 is an n-type semiconductor metal oxide with a wide band gap. Due to its high electron mobility, high chemical stability and thermal stability, it has been identified as a promising candidate material for gas sensing applications. In addition, many studies have shown that doping noble metal nanoparticles in gas sensors can reduce operating temperatures and improve gas sensing responses, because noble metal nanoparticles can improve the catalytic activity and electronic conductivity of gas-sensitive materials. Among efficient catalysts, palladium has the advantages of simple synthesis, low cost and high stability, and is a very promising material. Summary of the invention

[0005] The purpose of the present invention is to provide a room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material and a preparation method thereof.

[0006] The present invention synthesizes Pd-doped rGO / SnO2 nanocomposite materials for the first time by two-step hydrothermal method and liquid phase reduction method, and drop-casts them on Al2O3 planar ceramic sheets with Au interdigital electrodes. The results show that Pd-doped rGO / SnO2 nanocomposite materials have high sensitivity, and the sensor has good response and recovery characteristics to methane. Under room temperature conditions, the sensor reaches saturation response to 5% volume concentration of methane, with a response value of 19.7%, and has a fast response speed. There is a good linear relationship between its response value and methane concentration (1-5%). The excellent sensing performance at room temperature is attributed to the doping of rGO and Pd, in which rGO acts as a conductive network to promote electron transfer, and can also increase the specific surface area of ​​the material and promote the adsorption of methane gas; while Pd can activate the dissociation of oxygen molecules, so that the atomic products diffuse to the surface of the metal oxide, increase the number of adsorbed oxygen, improve the molecular-ion conversion rate, and reduce the activation energy required for the sensing reaction. Therefore, Pd-doped rGO / SnO2 nanocomposite materials are a promising sensitive material for designing and manufacturing room temperature methane gas sensors.

[0007] The room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material of the present invention is composed of an Al2O3 planar ceramic substrate with Au interdigital electrodes sputtered on the surface of which a sensitive material is coated. The sensitive material is a Pd-doped rGO / SnO2 nanocomposite material, which is prepared by the following steps:

[0008] (1) Add 20-30 mL of deionized water to 0.1-0.5 mL and 10-50 mg / mL of GO aqueous dispersion, and perform ultrasonic treatment for 10-20 min to make it uniformly dispersed; transfer the obtained solution to a 50 mL polytetrafluoroethylene hydrothermal reactor and perform hydrothermal reaction at 170-190 ° C for 10-20 hours, and then cool it to room temperature to obtain rGO dispersion; add 0.048-0.24 g of SnCl4·5H2O to the rGO dispersion, stir it for 10-20 min, and then perform ultrasonic treatment for 10-20 min, and finally transfer it to a polytetrafluoroethylene hydrothermal reactor and perform hydrothermal reaction at 170-190 ° C for 10-20 hours, centrifuge the obtained precipitate and wash it with deionized water several times to obtain rGO / SnO2 nanocomposite material;

[0009] (2) The rGO / SnO2 composite material obtained in step (1) is dispersed in 30-50 mL of deionized water, and ultrasonicated for 10-20 min to obtain a uniform dispersion; 0.005-0.025 g of PdCl2 is added to the dispersion, and after stirring evenly, 0.004-0.020 g of reducing agent NaBH4 is added, and after stirring for 2-3 h, the obtained precipitate is centrifuged and washed several times with deionized water to obtain the Pd-doped rGO / SnO2 nanocomposite material.

[0010] The method for preparing a room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material of the present invention comprises the following steps:

[0011] (1) Dissolving 10-20 mg of Pd-doped rGO / SnO2 nanocomposite in 10-20 mL of deionized water to prepare a 2 mg / mL suspension;

[0012] (2) Use a micropipette to transfer the suspension obtained in step (1) to the surface of the Al2O3 flat ceramic substrate sputtered with Au interdigital electrodes, with a dosage of 10-20 μL / cm 2 After drying at room temperature, a room-temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material was obtained; the Al2O3 planar ceramic substrate was square with a side length of 3-4 mm and a thickness of 0.2-0.3 mm; the width of a single gold electrode was 0.4-0.5 mm, the interdigital electrode spacing was 1-2 mm, and the gap distance between adjacent interdigits was 0.2-0.3 mm; the number of pairs of Au interdigital electrodes was 5-10 pairs; a platinum wire was led out from the gold electrode, and its length was 4-6 mm.

[0013] The advantages of the present invention are as follows:

[0014] (1) Pd-doped rGO / SnO2 nanocomposites were prepared by hydrothermal reaction and liquid phase reduction method, which has simple preparation process and low cost;

[0015] (2) The conductive network is constructed by compounding rGO to increase the specific surface area of ​​the material, and Pd is doped for efficient catalysis, and the composite effect of the two enhances the sensitivity;

[0016] (3) The room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite prepared in the present invention exhibits excellent sensitivity (19.7%-5%) and repeatability for room temperature methane sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : Morphological characterization of Pd-doped rGO / SnO2 nanocomposite materials, where Figure 1 (a) is the SEM morphology of Pd-doped rGO / SnO2 nanocomposite; Figure 1 (b) TEM of Pd-doped rGO / SnO2 nanocomposite; Figure 1 (c) HRTEM image of Pd-doped rGO / SnO2 nanocomposite;

[0018] Figure 2 : XRD patterns of pure rGO material and Pd-doped rGO / SnO2 nanocomposites;

[0019] Figure 3 : Raman images of pure rGO material and Pd-doped rGO / SnO2 nanocomposites;

[0020] Figure 4 : is a performance result diagram of the sensor described in Example 1 and Comparative Example 1; wherein Figure 4 (a) and Figure 4 (b) are the real-time resistance change curves between the interdigital electrodes of the sensors described in Example 1 and Comparative Example 1 under different CH4 concentrations; Figure 4 (c) is a line graph showing the response value changes of the sensor described in Example 1 and Comparative Example 1 to different concentrations of CH4;

[0021] Figure 5 : Repeatability diagram of the sensor described in Example 1 for 3% volume concentration methane gas at room temperature;

[0022] like Figure 1 As shown, from Figure 1 (a) It can be seen that the Pd-doped rGO / SnO2 nanocomposite material is composed of lamellar rGO and SnO2 thereon; Figure 1 (b) It can be seen that a large number of SnO2 nanospheres with a diameter of about 5 nm are evenly and densely distributed on rGO; Figure 1 Clear lattice fringes can be seen in the Pd-doped rGO / SnO2 nanocomposite in (c), which is attributed to the excellent crystallinity. The measured SnO2 (110) (101) crystal planes can confirm the formation of SnO2 nanospheres.

[0023] like Figure 2 As shown, the XRD spectrum of Pd-doped rGO / SnO2 nanocomposite is consistent with the SnO2 standard card, and no other impurity peaks appear. For pure rGO material, a broad diffraction peak is observed at 26°, which can be attributed to the (002) crystal plane of graphene material. The peak broadening effect is caused by lattice distortion and random stacking of graphene nanosheets.

[0024] like Figure 3 As shown in the figure, compared with the raw material GO, the I D / I GThe ratio increases, which to some extent indicates the degree of reduction of graphene oxide.

[0025] like Figure 4 As shown, the response values ​​of the sensors in Comparative Example 1 and Example 1 to 5% methane are 0.1% and 19.7% respectively. Compared with the sensor in Comparative Example 1, the gas-sensing performance of the sensor in Example 1 is greatly improved.

[0026] like Figure 5 As shown, the sensor described in Example 1 has good repeatability in sensing methane at room temperature.

[0027] Note: The response value is calculated as Where R g is the resistance value between the interdigital electrodes of the sensor exposed to methane, R a is the baseline resistance between the interdigital electrodes when the sensor is placed in air. DETAILED DESCRIPTION

[0028] Comparative Example 1:

[0029] A methane gas sensor based on rGO sensitive material and a preparation method thereof, wherein the steps are as follows:

[0030] (1) Add 0.3 mL of GO aqueous dispersion (concentration of 10 mg / mL) and 20 mL of deionized water into a beaker and disperse evenly by ultrasonication for 10 min. Transfer the solution into a 50 mL polytetrafluoroethylene hydrothermal reactor and heat at 180 °C for 12 h. After cooling naturally to room temperature, the obtained precipitate is centrifuged and washed several times with deionized water to obtain rGO sensitive material with a product mass of 2.5 mg.

[0031] (2) Dissolve 20 mg of rGO sensitive material in 10 mL of deionized water to prepare a 2 mg / mL suspension, which is then transferred to the surface of an Al2O3 flat ceramic substrate sputtered with Au interdigital electrodes using a micropipette at a dosage of 10 μL / cm 2 After drying at room temperature, a room temperature methane sensor based on rGO sensitive material was obtained. The Al2O3 flat ceramic substrate is square, with a side length of 3.5mm and a thickness of 0.25mm; the width of a single gold electrode is 0.45mm, the interdigital electrode spacing is 1.5mm, and the gap distance between adjacent interdigits is 0.25mm; the number of pairs of Au interdigital electrodes is 8; a platinum wire is led out from the gold electrode, and its length is 5mm.

[0032] Embodiment 1:

[0033] A method for preparing a room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material, the steps of which are as follows:

[0034] (1) Add 0.3 mL of GO aqueous dispersion (concentration of 10 mg / mL) and 20 mL of deionized water to a beaker, and ultrasonicate for 10 min to make it evenly dispersed. Transfer the solution to a 50 mL polytetrafluoroethylene hydrothermal reactor, heat at 180 ° C for 12 hours, and naturally cool to room temperature to obtain rGO dispersion. Add 0.144 g of SnCl4·5H2O to the rGO dispersion, stir for 10 min, ultrasonicate for 10 min, transfer to a polytetrafluoroethylene hydrothermal reactor and hydroheat at 180 ° C for 12 hours, centrifuge the obtained precipitate and wash it several times with deionized water to obtain rGO / SnO2 nanocomposite material with a product mass of 62.5 mg;

[0035] (2) The rGO / SnO2 composite material obtained in step 1 was redispersed in 30 mL of deionized water and ultrasonicated for 10 min to obtain a uniform dispersion. 0.015 g of PdCl2 was added to the dispersion, and after stirring evenly, 0.008 g of reducing agent NaBH4 was added. After stirring for 3 hours, the obtained precipitate was centrifuged and washed several times with deionized water to obtain the final product, Pd-doped rGO / SnO2 nanocomposite material, with a product mass of 71.5 mg;

[0036] (3) 20 mg of Pd-doped rGO / SnO2 nanocomposite was dissolved in 10 mL of deionized water to prepare a 2 mg / mL suspension, which was then transferred to the surface of an Al2O3 flat ceramic substrate sputtered with Au interdigital electrodes using a micropipette at a dosage of 10 μL / cm 2 After drying at room temperature, a room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite was obtained. The Al2O3 planar ceramic substrate is square, with a side length of 3.5mm and a thickness of 0.25mm; the width of a single gold electrode is 0.45mm, the interdigital electrode spacing is 1.5mm, and the gap distance between adjacent interdigits is 0.25mm; the number of pairs of Au interdigital electrodes is 8; a platinum wire is led out from the gold electrode, and its length is 5mm.

Claims

1. A room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material, comprising an Al2O3 planar ceramic substrate with Au interdigital electrodes sputtered on the surface of which a sensitive material is coated, characterized in that: The sensitive material is Pd-doped rGO / SnO2 nanocomposite material, which is prepared by the following steps: (1) Add 20-30 mL of deionized water to 0.1-0.5 mL and 10-50 mg / mL of GO aqueous dispersion, and perform ultrasonic treatment for 10-20 min to make it uniformly dispersed; transfer the obtained solution to a 50 mL polytetrafluoroethylene hydrothermal reactor and perform hydrothermal reaction at 170-190 ° C for 10-20 hours, and then cool it to room temperature to obtain rGO dispersion; add 0.048-0.24 g of SnCl4·5H2O to the rGO dispersion, stir it for 10-20 min, and then perform ultrasonic treatment for 10-20 min, and finally transfer it to a polytetrafluoroethylene hydrothermal reactor and perform hydrothermal reaction at 170-190 ° C for 10-20 hours, centrifuge the obtained precipitate and wash it with deionized water several times to obtain rGO / SnO2 nanocomposite material; (2) The rGO / SnO2 composite material obtained in step (1) is dispersed in 30-50 mL of deionized water, and ultrasonicated for 10-20 min to obtain a uniform dispersion; 0.005-0.025 g of PdCl2 is added to the dispersion, and after stirring evenly, 0.004-0.020 g of reducing agent NaBH4 is added, and after stirring for 2-3 h, the obtained precipitate is centrifuged and washed several times with deionized water to obtain the Pd-doped rGO / SnO2 nanocomposite material.

2. A room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material as claimed in claim 1, characterized in that: The Al2O3 flat ceramic substrate is square, with a side length of 3 to 4 mm and a thickness of 0.2 to 0.3 mm; the width of a single gold electrode is 0.4 to 0.5 mm, the spacing between the interdigital electrodes is 1 to 2 mm, and the gap distance between adjacent interdigits is 0.2 to 0.3 mm; the number of pairs of Au interdigital electrodes is 5 to 10 pairs; a platinum wire is led out from the gold electrode, and its length is 4 to 6 mm.

3. A method for preparing a room temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite material according to claim 1 or 2, wherein the steps are as follows: (1) Dissolving 10-20 mg of Pd-doped rGO / SnO2 nanocomposite in 10-20 mL of deionized water to prepare a 2 mg / mL suspension; (2) Use a micropipette to transfer the suspension obtained in step (1) to the surface of the Al2O3 flat ceramic substrate sputtered with Au interdigital electrodes, with a dosage of 10-20 μL / cm 2 After drying at room temperature, a room-temperature methane sensor based on Pd-doped rGO / SnO2 nanocomposite was obtained.

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