A PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor and its preparation method

Abstract

The application discloses a kind of PdO-SnO2-SiO2 / SiO2 Self-supporting flexible gas-permeable nanofiber membrane gas sensor and preparation method thereof.Si electrospinning fiber is prepared by single needle head electrospinning method first, then Si electrospinning fiber and Pd-Sn electrospinning fiber interwoven fiber membrane is prepared on it by double needle head electrospinning method, then PdO-SnO2-SiO2 / SiO2 Flexible gas-permeable nanofiber membrane is obtained by heat treatment, finally electrode is prepared on its surface to obtain gas sensor.SiO2 Nanofiber in the sensor of the application has good flexibility, as a framework material to ensure the flexibility of the fiber membrane;Interwoven fiber membrane can effectively prevent SiO2 Nanofiber and PdO-SnO2 Nanofiber from separating, and has good gas permeability;At the same time, the fiber membrane is all inorganic material, which can maintain the original shape at high temperature, has good high temperature resistance and gas sensitivity.The sensor of the application has simple preparation process, stable performance, wide range of use, low cost, and has broad application prospect.

Description

Technical Field

[0001] This invention belongs to the field of flexible gas sensor technology, specifically relating to a fiber membrane with SiO2 nanofibers as the skeleton. First, Si sol is subjected to single-needle electrospinning, then Pd-Sn sol and Si sol are subjected to double-needle mixed electrospinning to obtain a fiber membrane in which Pd-Sn electrospun fibers and Si electrospun fibers are interwoven. After calcination, a PdO-SnO2-SiO2 / SiO2 flexible nanofiber membrane is obtained with a PdO-SnO2-SiO2 mixed nanofiber layer on the surface and a SiO2 nanofiber layer on the base. Electrodes are deposited on the flexible nanofiber membrane using ion sputtering or direct spraying to prepare a PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor. Background Technology

[0002] With technological advancements, researchers have developed numerous high-performance gas sensors, which are widely used in daily life and production. Gas sensors provide timely and reliable early warning signals, helping to eliminate potential hazards. In recent years, the rapid development of wearable flexible devices has provided new application areas for gas sensors, thus placing higher demands on their mechanical properties, especially their flexibility.

[0003] According to literature reports, current technologies for fabricating flexible gas sensors can be categorized into coating, printing, in-situ growth, in-situ polymerization, and vapor deposition. The essence of these technologies is to cover the sensitive material onto a flexible substrate. Existing flexible substrates mainly utilize materials such as organic plastics, textiles, and paper. Organic plastic substrates primarily include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polystyrene (PS), polyimide (PI), and silicone rubber (PDMS); textiles are mainly composed of organic fibers (such as nylon and cotton fibers). However, these technical solutions have the following shortcomings: (1) The substrate material has poor resistance to high temperature. For example, organic plastic substrates will undergo permanent deformation and fail when the temperature is higher than 300℃; (2) The adhesion between the sensitive material and the substrate is poor. During use, the sensitive material is prone to gaps with the substrate, or even separation from the substrate, which will lead to the failure of the flexible sensor; (3) The organic plastic substrate has poor air permeability, which will reduce the exchange of air and moisture and reduce comfort when applied to wearable fields. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor and its preparation method. The preparation process is simple, stable, and low in cost, and it has good sensitivity to NO2, ethanol, methanol, acetone and acetic acid.

[0005] To achieve the above objectives, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor used in this invention is prepared by the following method:

[0006] Step 1: Mix tetraethyl orthosilicate, distilled water and phosphoric acid evenly, then add 10% polyvinyl alcohol aqueous solution and stir evenly to obtain Si sol; stir stannous chloride dihydrate, palladium chloride, N,N-dimethylformamide and polyacrylonitrile evenly to obtain Pd-Sn sol.

[0007] Step 2: First, the Si sol from Step 1 is subjected to single-needle electrospinning to obtain a Si electrospinned fiber layer; then, the Pd-Sn sol from Step 1 is introduced and subjected to double-needle mixed electrospinning with the Si sol to form a fiber film on the surface of the Si electrospinned fiber layer in which Pd-Sn electrospinned fibers and Si electrospinned fibers are interwoven, resulting in a fiber film with Si electrospinned fibers as the bottom layer and Pd-Sn electrospinned fibers and Si electrospinned fibers as the top layer.

[0008] Step 3: Collect the fiber membrane from Step 2 and calcine the collected fiber membrane to obtain a PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with gas-sensitive properties.

[0009] Step 4: Cover the surface of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with a mask, and prepare interdigitated electrodes by depositing electrode material using ion sputtering, or prepare non-interdigitated electrodes by directly depositing electrode material on the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane using spray coating. After cutting the prepared interdigitated or non-interdigitated electrodes, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor is obtained.

[0010] Further preferably, in step 1 above, the mass ratio of tetraethyl orthosilicate, distilled water, phosphoric acid, and a 10% polyvinyl alcohol aqueous solution in the Si sol is 150:100-200:1-2.5:200-400.

[0011] Further preferably, in step 1 above, the mass ratio of stannous chloride dihydrate, palladium chloride, N,N-dimethylformamide, and polyacrylonitrile in the Pd-Sn sol is 1000:0.5-1.5:8000-120000:500-1250.

[0012] Further preferably, in step 2 above, the propulsion rate of the Si sol is 0.4 to 2 mL / h, the positive high voltage is 14 to 25 kV, the negative high voltage is -1 to 3 kV, and the spinning time is 1 to 8 h.

[0013] Further preferably, in step 2 above, when the Si sol and Pd-Sn sol are electrospun in a double-needle mixture, the feed rate of the Pd-Sn sol is 0.4 to 2 mL / h, the ratio of the feed rates of the Si sol to the Pd-Sn sol is 1:1 to 5, the positive high voltage is 14 to 25 kV, the negative high voltage is -1 to 3 kV, and the spinning time is 1 to 4 hours.

[0014] In a further preferred embodiment, in step 3 above, the heating rate of calcination is 1-20℃ / min, the calcination temperature is 500-800℃, and the time is 1-10h.

[0015] In a further preferred embodiment, in step 4 above, the width of the interdigitated electrode prepared by the ion sputtering method is 0.5–2 mm, and the gap between the interdigitated fingers is 0.5–2 mm.

[0016] In a further preferred embodiment, in step 4 above, the non-interdigitated electrode prepared by the spraying method has an electrode width of 3-8 mm and an electrode gap of 3-10 mm.

[0017] In a further preferred embodiment, in step 4 above, the electrode material is Au, Ag, or Pd.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention employs a hybrid electrospinning process combining single-needle and double-needle techniques. First, Si sol is electrospinned using a single needle to obtain a Si electrospun fiber substrate. Then, Si sol and Pd-Sn sol are electrospinned using a double-needle hybrid technique to form an interwoven electrospun layer of Si and Pd-Sn electrospun fibers on the surface of the Si electrospun fiber substrate. A calcination process is then used to prepare the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane. Finally, electrodes are fabricated on the surface of the fiber membrane to obtain the gas sensor. The preparation method of this invention is simple, low-cost, and highly stable.

[0020] 2. The PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane of the present invention is paper-like, not easily torn, and has an intact structure. Traditional commercial flexible gas sensors coat gas-sensitive materials on a flexible substrate, which requires additional substrate materials. The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane of the present invention can be used to prepare gas sensors without adding an additional substrate and has a self-supporting function.

[0021] 3. The PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane of the present invention is an all-inorganic material with excellent stability at 800℃. The sensor made from it is structurally stable at 500℃. Compared with the traditional commercial PET-based PdO-SnO2 flexible gas sensor which fails at 300℃, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention has better heat resistance.

[0022] 4. In the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention, the SiO2 nanofiber skeleton material and the PdO-SnO2 nanofiber gas-sensitive material are interwoven, which can effectively prevent the separation of the sensitive material and the skeleton material. Compared with the traditional commercial PET-based PdO-SnO2 flexible gas sensor, the gas-sensitive material on the surface falls off after 50 bends, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention maintains its complete morphology after 3200 bends, and has better mechanical stability.

[0023] 5. The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention is composed of interwoven nanofibers, exhibiting excellent breathability. For example, the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane has a much higher permeability to HCl molecules than filter paper. This excellent breathability facilitates the diffusion of gas molecules within the fiber membrane, promoting the exchange of air and moisture, and enhancing comfort when applied in wearable devices.

[0024] 6. The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention exhibits excellent gas-sensing performance for NO2, ethanol, methanol, acetone, and acetic acid. For example, compared with traditional commercial PET-based PdO-SnO2 flexible gas sensors, it has better gas-sensing response, with a response of 1.4 to NO2 at a concentration of 1000 ppb at room temperature; it has better gas-sensing stability, maintaining a stable response to NO2 at different bending angles and showing no attenuation in its gas-sensing response to NO2 after 3200 bends; and it has a wider operating temperature range, maintaining good gas-sensing performance even at 300°C.

[0025] 7. The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention utilizes the excellent flexibility of SiO2 nanofibers and the skeletal effect of SiO2 nanofibers, enabling the fiber membrane to exhibit excellent flexibility. Compared with traditional commercial PET-based PdO-SnO2 flexible gas sensors, the stress applied during bending is smaller, resulting in better flexibility. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the electrospinning process using a combination of Si sol and Pd-Sn sol in this invention.

[0027] Figure 2 The X-ray diffraction patterns (a) of the pure SiO2 fiber membrane and the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane prepared in Examples 1 and 2, and the X-ray photoelectron spectrum (b) of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane prepared in Example 1 are shown.

[0028] Figure 3 SEM images of pure SiO2 fiber membrane (a) and PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane prepared in Example 1 (b).

[0029] Figure 4 The image shows a photograph of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane (a) prepared in Example 1 and its bending at 180° (b).

[0030] Figure 5 These are photographs of the interdigitated Au electrode (a) of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 and the non-interdigitated Ag electrode (b) of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 3.

[0031] Figure 6 These are photographs of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1, bent at different angles.

[0032] Figure 7 The gas sensors prepared in Example 1 and Comparative Example 1, as well as the gas sensor prepared with a flexible SiO2 fiber membrane, show the gas-sensitive response of different concentrations of NO2 at 25°C.

[0033] Figure 8 The response of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 to NO2 concentrations of 50–1000 ppb at 25°C and different bending degrees is shown.

[0034] Figure 9 The response of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 to a concentration of 1000 ppb NO2 after being bent at 25°C and at different numbers of times.

[0035] Figure 10The response of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 to NO2 at different temperatures (a) and to ethanol, acetone, methanol and acetic acid at a concentration of 500 ppm at 300 °C (b).

[0036] Figure 11 This is a comparison diagram of the air permeability performance of filter paper (a) and the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane (b) prepared in Example 1.

[0037] Figure 12 This is the PdO-SnO2-SiO2 nanofiber membrane prepared in Comparative Example 2.

[0038] Figure 13 This is the PdO-SnO2 / SiO2 nanofiber membrane prepared in Comparative Example 3.

[0039] Figure 14 The images show (a) of the commercial PET-based PdO-SnO2 flexible gas sensor prepared in Comparative Example 4 and its results after being bent 50 times (b) and kept at 300℃ for 0.5 h (c).

[0040] Figure 15 This is a schematic diagram (d) of the stress applied during cyclic bending of the commercial PET-based PdO-SnO2 flexible gas sensor prepared in Comparative Example 4 and the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1, and the response (e) of the commercial PET-based PdO-SnO2 flexible gas sensor prepared in Comparative Example 4 to a concentration of 1000 ppb NO2 after bending at 25°C and different numbers of times. Detailed Implementation

[0041] The preparation method of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention is carried out according to the following steps:

[0042] Step 1: Mix tetraethyl orthosilicate, distilled water, and phosphoric acid until homogeneous, then add a 10% (w / w) polyvinyl alcohol aqueous solution and stir until homogeneous to obtain Si sol; stir stannous chloride dihydrate, palladium chloride, N,N-dimethylformamide, and polyacrylonitrile in an 80°C water bath until homogeneous to obtain Pd-Sn sol; the mass ratio of tetraethyl orthosilicate, distilled water, phosphoric acid, and 10% (w / w) polyvinyl alcohol aqueous solution in the Si sol is 150:100-200:1-2.5:200-400. The mass ratio of stannous chloride dihydrate, palladium chloride, N,N-dimethylformamide, and polyacrylonitrile in the Pd-Sn sol is 1000:0.5-1.5:8000-120000:500-1250.

[0043] Step 2: First, perform single-needle electrospinning on the Si sol from Step 1, with a feed rate of 0.4–2 mL / h, a positive voltage of 14–25 kV, and a negative voltage of -1–3 kV, for 1–8 hours to obtain a Si electrospun fiber layer as the substrate. Then, introduce the Pd-Sn sol from Step 1 and perform double-needle mixed electrospinning with the Si sol (e.g., ...). Figure 1 As shown, the propulsion rate of Pd-Sn sol is 0.4-2 mL / h, the ratio of the propulsion rate of Si sol to Pd-Sn sol is 1:1-5, the positive voltage is 14-25 kV, the negative voltage is -1-3 kV, and the spinning time is 1-4 h. A fiber membrane in which Pd-Sn electrospun fibers and Si electrospun fibers interweave is formed on the surface of the Si electrospun fiber layer, that is, a fiber membrane with Si electrospun fibers as the bottom layer and Pd-Sn electrospun fibers and SiO2 electrospun fibers interweaving on the surface layer is obtained.

[0044] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 1-20℃ / min, the calcination temperature to be 500-800℃, and the calcination time to be 1-10h to obtain a PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with gas-sensitive properties.

[0045] Step 4: Cover the surface of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with a mask. Prepare interdigitated electrodes by ion sputtering, or directly prepare non-interdigitated electrodes by spray coating. After cutting the prepared interdigitated or non-interdigitated electrodes, obtain the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor. The width of the interdigitated electrodes prepared by ion sputtering is 0.5–3 mm, and the gap between the interdigitated electrodes is 0.5–3 mm; the width of the non-interdigitated electrodes prepared by spray coating is 3–8 mm, and the gap between the electrodes is 3–10 mm; the electrode material is Au, Ag, or Pd.

[0046] Example 1

[0047] Step 1: Mix 5.0g tetraethyl orthosilicate, 5.0g distilled water and 60mg phosphoric acid until homogeneous, then add 10.0g of 10% polyvinyl alcohol aqueous solution and stir until homogeneous to obtain Si sol; mix 1.0g stannous chloride dihydrate, 1mg palladium chloride, 9.5g N,N-dimethylformamide and 0.7g polyacrylonitrile and stir in a water bath at 80℃ until homogeneous to obtain Pd-Sn sol.

[0048] Step 2: First, the Si sol from Step 1 is subjected to single-needle electrospinning at a feed rate of 1.2 mL / h, a positive voltage of 19 kV and a negative voltage of -2.5 kV, and a distance of 15 cm between the syringe needle tip and the aluminum foil collector. Spinning is performed for 4 hours to obtain a Si electrospun fiber layer. Then, the Pd-Sn sol from Step 1 is introduced and subjected to double-needle mixed electrospinning with the Si sol. The feed rate of the Pd-Sn sol is 0.8 mL / h, the feed rate of the Si sol is 0.2 mL / h, the positive voltage is 19 kV and the negative voltage is -2.5 kV, and the spinning time is 2.5 hours. A fiber membrane of interwoven Pd-Sn and Si electrospun fibers is formed on the surface of the Si electrospun fiber layer, resulting in a fiber membrane with a bottom layer of Si electrospun fibers and a top layer of interwoven Pd-Sn and Si electrospun fibers.

[0049] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 5℃ / min, the calcination temperature to be 650℃, and the calcination time to be 4h to obtain a PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with gas-sensitive properties.

[0050] Step 4: Cover the surface of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with a mask, and deposit Au to prepare interdigitated electrodes using ion sputtering. The width of the interdigitated electrodes is 0.8 mm, and the gap between the interdigitated electrodes is 0.8 mm. After cutting the prepared interdigitated electrodes, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor is obtained.

[0051] Example 2

[0052] Step 1: Mix 5.0g tetraethyl orthosilicate, 5.0g distilled water and 40mg phosphoric acid until homogeneous, then add 10.0g of 10% polyvinyl alcohol aqueous solution and stir until homogeneous to obtain Si sol; mix 1.0g stannous chloride dihydrate, 0.5mg palladium chloride, 9.5g N,N-dimethylformamide and 1.0g polyacrylonitrile and stir in a water bath at 80℃ until homogeneous to obtain Pd-Sn sol.

[0053] Step 2: First, the Si sol from Step 1 is subjected to single-needle electrospinning at a feed rate of 2 mL / h, a positive voltage of 25 kV and a negative voltage of -3 kV, and a distance of 15 cm between the syringe needle tip and the aluminum foil collector. Spinning is performed for 1 hour to obtain a Si electrospun fiber layer. Then, the Pd-Sn sol from Step 1 is introduced and subjected to double-needle mixed electrospinning with the Si sol. The feed rates of both the Pd-Sn sol and Si sol are 1 mL / h, with a positive voltage of 25 kV and a negative voltage of -3 kV. The spinning time is 1 hour. A fiber membrane of interwoven Pd-Sn and Si electrospun fibers is formed on the surface of the Si electrospun fiber layer, resulting in a fiber membrane with a bottom layer of Si electrospun fibers and a top layer of interwoven Pd-Sn and Si electrospun fibers.

[0054] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 20℃ / min, the calcination temperature to be 500℃, and the calcination time to be 10h to obtain a PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane.

[0055] Step 4: Cover the surface of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with a mask, and deposit Pd to prepare interdigitated electrodes using ion sputtering. The width of the interdigitated electrodes is 2 mm and the gap between the interdigitated electrodes is 1 mm. After cutting the prepared interdigitated electrodes, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor is obtained.

[0056] Example 3

[0057] Step 1: Mix 5.0g tetraethyl orthosilicate, 5.0g distilled water and 60mg phosphoric acid until homogeneous, then add 10.0g of 10% polyvinyl alcohol aqueous solution and stir until homogeneous to obtain Si sol; mix 1.0g stannous chloride dihydrate, 1mg palladium chloride, 9.5g N,N-dimethylformamide and 0.8g polyacrylonitrile and stir in a water bath at 80℃ until homogeneous to obtain Pd-Sn sol.

[0058] Step 2: First, the Si sol from Step 1 is subjected to single-needle electrospinning at a feed rate of 0.4 mL / h, a positive voltage of 14 kV and a negative voltage of -1 kV, and a distance of 15 cm between the syringe needle tip and the aluminum foil collector. Spinning is performed for 8 hours to obtain a Si electrospun fiber layer. Then, the Pd-Sn sol from Step 1 is introduced and subjected to double-needle mixed electrospinning with the Si sol. The feed rates of both the Pd-Sn and Si sols are 0.4 mL / h, with a positive voltage of 14 kV and a negative voltage of -1 kV. The spinning time is 4 hours. A fiber membrane of interwoven Pd-Sn and Si electrospun fibers is formed on the surface of the Si electrospun fiber layer, resulting in a fiber membrane with a bottom layer of Si electrospun fibers and a top layer of interwoven Pd-Sn and Si electrospun fibers.

[0059] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 1℃ / min, the calcination temperature to be 800℃, and the calcination time to be 1h to obtain a PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane.

[0060] Step 4: Spray Ag onto the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane to prepare non-interdigitated electrodes with an electrode width of 5 mm and an electrode gap of 5 mm; cut the prepared non-interdigitated electrodes to obtain the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor.

[0061] Comparative Example 1 (without PdCl2 involvement)

[0062] Step 1: Mix 5.0g tetraethyl orthosilicate, 5.0g distilled water and 60mg phosphoric acid until homogeneous, add 10.0g of 10% polyvinyl alcohol aqueous solution and stir until homogeneous to obtain Si sol; mix 1.0g stannous chloride dihydrate, 9.5g N,N-dimethylformamide and 0.7g polyacrylonitrile and stir in a water bath at 80℃ until homogeneous to obtain Sn sol.

[0063] Step 2: First, the Si sol from Step 1 is subjected to single-needle electrospinning at a feed rate of 1.2 mL / h, a positive voltage of 19 kV and a negative voltage of -2.5 kV, and a distance of 15 cm between the syringe needle tip and the aluminum foil collector. The spinning is carried out for 4 hours to obtain Si electrospun fibers. Then, the Sn sol from Step 1 is introduced and subjected to double-needle mixed electrospinning with the Si sol. The feed rate of the Sn sol is 0.8 mL / h, the feed rate of the Si sol is 0.2 mL / h, the positive voltage is 18 kV and the negative voltage is -1 kV, and the spinning time is 4 hours to obtain a fiber membrane with Si electrospun fibers as the bottom layer and Sn electrospun fibers interwoven with Si electrospun fibers as the surface layer.

[0064] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 5℃ / min, the calcination temperature to be 650℃, and the calcination time to be 4h to obtain the SnO2-SiO2 / SiO2 flexible fiber membrane.

[0065] Step 4: Cover the SnO2-SiO2 / SiO2 flexible fiber membrane with a mask, and deposit Au to prepare interdigitated electrodes using ion sputtering. The width of the interdigitated electrodes is 0.8 mm, and the gap between the interdigitated electrodes is 0.8 mm. After cutting the prepared interdigitated electrodes, the SnO2-SiO2 / SiO2 self-supporting flexible fiber membrane gas sensor is obtained.

[0066] Comparative Example 2 (without SiO2 substrate)

[0067] Step 1: Mix 5.0g tetraethyl orthosilicate, 5.0g distilled water and 60mg phosphoric acid until homogeneous, then add 10.0g of 10% polyvinyl alcohol aqueous solution and stir until homogeneous to obtain Si sol; mix 1.0g stannous chloride dihydrate, 1mg palladium chloride, 9.5g N,N-dimethylformamide and 0.7g polyacrylonitrile and stir in a water bath at 80℃ until homogeneous to obtain Pd-Sn sol.

[0068] Step 2: The Pd-Sn sol and Si sol from Step 1 are electrospun using a double-needle mixing method. The distance between the syringe needle tip and the aluminum foil collector is 15 cm. The feed rate of the Pd-Sn sol is 0.8 mL / h, the feed rate of the Si sol is 0.8 mL / h, the positive voltage is 19 kV, the negative voltage is -2.5 kV, and the spinning time is 4 h, resulting in a fiber membrane in which Pd-Sn electrospun fibers and Si electrospun fibers are interwoven.

[0069] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 5℃ / min, the calcination temperature to be 650℃, and the calcination time to be 2h to obtain PdO-SnO2-SiO2 nanofiber membrane.

[0070] Comparative Example 3 (Pd-Sn sol not blended with Si sol)

[0071] Step 1: Mix 5.0g tetraethyl orthosilicate, 5.0g distilled water and 60mg phosphoric acid until homogeneous, then add 10.0g of 10% polyvinyl alcohol aqueous solution and stir until homogeneous to obtain Si sol; mix 1.0g stannous chloride dihydrate, 1mg palladium chloride, 9.5g N,N-dimethylformamide and 0.7g polyacrylonitrile and stir in a water bath at 80℃ until homogeneous to obtain Pd-Sn sol.

[0072] Step 2: First, the Si sol from Step 1 is subjected to single-needle electrospinning at a feed rate of 1.2 mL / h, a positive voltage of 19 kV and a negative voltage of -2.5 kV, with the distance between the syringe needle tip and the aluminum foil collector being 15 cm. The spinning is carried out for 4 hours to obtain a Si electrospun fiber layer. Then, the Pd-Sn sol from Step 1 is subjected to single-needle electrospinning at a feed rate of 0.8 mL / h, a positive voltage of 19 kV and a negative voltage of -2.5 kV, and a spinning time of 2.5 hours to obtain a fiber membrane with Si electrospun fibers as the bottom layer and Pd-Sn electrospun fibers as the surface layer.

[0073] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 5℃ / min, the calcination temperature to be 650℃, and the calcination time to be 4h to obtain PdO-SnO2 / SiO2 nanofiber membrane.

[0074] Comparative Example 4 (Commercial PET Flexible Gas Sensor)

[0075] Step 1: Mix 1.0g stannous chloride dihydrate, 1.0mg palladium chloride, 9.5g N,N-dimethylformamide and 0.7g polyacrylonitrile and stir evenly in a water bath at 80℃ to obtain Pd-Sn sol.

[0076] Step 2: The Pd-Sn sol from Step 1 was subjected to single-needle electrospinning at a feed rate of 0.8 mL / h, a positive voltage of 14 kV and a negative voltage of -1 kV, with the distance between the syringe needle tip and the aluminum foil collector being 15 cm. The spinning was carried out for 4 hours to obtain a Pd-Sn electrospun fiber membrane.

[0077] Step 3: Collect the fiber membrane from Step 2, and calcine the collected fiber membrane. Control the heating rate to be 5℃ / min, the calcination temperature to be 650℃, and the calcination time to be 4h to obtain PdO-SnO2 nanofibers.

[0078] Step 4: Add 50 mg of PdO-SnO2 nanofibers to 100 μL of ethanol to make a slurry, and then coat it onto a commercial PET gas sensor substrate to obtain a commercial PET-based PdO-SnO2 flexible gas sensor.

[0079] Various performance characteristics were performed on the fiber membranes and gas sensors prepared in Examples 1-3 and Comparative Examples 1-4, and the results are as follows: Figures 2-15 As shown.

[0080] The X-ray diffraction spectra of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membranes and pure SiO2 fiber membranes prepared in Examples 1 and 2 are as follows: Figure 2As shown in (a), no diffraction peaks of SiO2 were found in the SiO2 fiber membrane, only one broad diffraction peak, indicating that SiO2 is amorphous. The X-ray diffraction peaks of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membranes prepared in Examples 1 and 2 are in good agreement with SnO2 (JCPDS 77-0447), indicating that the prepared fiber membranes contain crystalline SnO2; the absence of SiO2 diffraction peaks is due to the amorphous structure of SiO2; the lack of Pd diffraction peaks in Example 1 is due to the very low Pd content. X-ray photoelectron spectroscopy analysis of the fiber membrane in Example 1 yielded the following results: Figure 2 As shown in (b), it is demonstrated that the Pd in ​​the fiber membrane prepared in Example 1 has a +2 valence and exists in the form of PdO. Therefore, Examples 1 and 2 prepared PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membranes.

[0081] SEM images of the pure SiO2 fiber membrane and the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane prepared in Example 1 are shown below. Figure 3 As shown in (a) and (b), by Figure 3 (a) It can be seen that the prepared SiO2 nanofibers have a diameter of about 200 nm and a very smooth surface; Figure 3 (b) It can be seen that PdO-SnO2-SiO2 / SiO2 is composed of two types of fibers with different structures: smooth-surfaced fibers with a diameter of 200 nm are SiO2 nanofibers; porous fibers with a diameter greater than 400 nm are PdO-SnO2 fibers. The figure clearly shows that SiO2 nanofibers and PdO-SnO2 fibers are interwoven. The PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane prepared in Example 1 has a smooth and intact surface, without material separation or shedding (e.g., Figure 4 (a) shown), fold it in half as follows Figure 4 As shown in (b), the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane has good flexibility.

[0082] Two types of PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensors prepared in Examples 1 and 3 are as follows: Figure 5 As shown, Figure 5 (a) is an interdigitated gold electrode. Figure 5 (b) Non-interdigitated silver electrode.

[0083] Example 1 shows a PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared at different bending angles. Figure 6As shown, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor has good flexibility and bending performance.

[0084] Example 1, Comparative Example 1, and the gas sensors prepared from flexible SiO2 fiber membranes showed the following gas-sensitive responses at 25°C to different concentrations of NO2: Figure 7 As shown, the flexible SiO2 fiber membrane shows almost no response to NO2. The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 exhibits a significantly higher response to NO2 than the SnO2-SiO2 / SiO2 self-supporting flexible nanofiber membrane gas sensor prepared in Comparative Example 1. The response values ​​of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 to NO2 at concentrations of 50 ppb, 100 ppb, 200 ppb, 500 ppb, and 1000 ppb are 1.1, 1.2, 1.4, 2.4, and 3.8, respectively. These results demonstrate that the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in this invention has a good response to NO2.

[0085] The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 responded to NO2 concentrations of 50–1000 ppb at 25°C and different bending angles as follows: Figure 8 As shown in the figure, when the sensor bending angle is 0°, 35°, 70°, 105°, and 140°, the responses to 50ppb, 100ppb, 200ppb, 500ppb, and 1000ppb are 1.1, 1.2, 1.4, 2.4, and 3.8, respectively. The results indicate that the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in this invention exhibits stable responses to NO2 under different bending angles.

[0086] The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 responded to a concentration of 1000 ppb NO2 after being bent at 25°C and for different numbers of times, as follows: Figure 9 As shown in the figure, after the sensor is bent 0, 200, 400, 800, 1600, and 3200 times, the responses to 1000 ppb are 3.8, 3.8, 3.7, 3.7, 3.7, and 3.7, respectively. The results indicate that the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in this invention can maintain a stable response to NO2 even after multiple bends.

[0087] The response of the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 to NO2 at different temperatures is as follows: Figure 10 As shown in (a), the responses to 1000 ppb NO2 at temperatures of 25, 50, 100, and 150 °C are 3.8, 14.4, 110.8, and 1.4, respectively. These results demonstrate that the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in this invention has a wide operating temperature range for NO2.

[0088] The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 responded to ethanol, acetone, methanol, and acetic acid at a concentration of 500 ppm at 300 °C as follows: Figure 10 As shown in (b), the values ​​are 16.9, 12.9, 9.1 and 7.2, respectively, indicating that the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor of the present invention has good gas-sensing response capability and high-temperature resistance at high temperatures.

[0089] To evaluate the air permeability of the PdO-SnO2-SiO2 / SiO2 flexible nanofiber membrane prepared in Example 1, a comparison with filter paper was used. Figure 11 As shown in the figure, PdO-SnO2-SiO2 / SiO2 flexible nanofiber membranes and filter paper were respectively placed over wide-mouth bottles containing 8 mol / L HCl aqueous solution. The color change of pH test paper wetted with distilled water was observed. HCl molecules could pass through the PdO-SnO2-SiO2 / SiO2 flexible nanofiber membrane and cause the pH test paper to begin to change color after 15 s; it took 120 s for HCl molecules to pass through the filter paper and cause the pH test paper to change color. The degree of pH color change caused by the PdO-SnO2-SiO2 / SiO2 flexible nanofiber membrane at 120 s was much higher than that caused by the filter paper at 300 s, indicating that the amount of HCl molecules permeating through the PdO-SnO2-SiO2 / SiO2 flexible nanofiber membrane within 120 s was much higher than that permeating through the filter paper within 300 s, proving that the PdO-SnO2-SiO2 / SiO2 flexible nanofiber membrane has good air permeability.

[0090] The PdO-SnO2-SiO2 flexible fiber membrane prepared in Comparative Example 2 is as follows: Figure 12 As shown, the fiber membrane splits after calcination, indicating that the PdO-SnO2-SiO2 nanofiber membrane lacks a SiO2 substrate. Calcination cannot maintain its complete morphology, making it unsuitable for fabrication into a flexible gas sensor. Therefore, using electrospun Si sol as a substrate followed by Pd-Sn sol and Si sol blending to prepare the sensitive layer is beneficial for improving the stability of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane.

[0091] The PdO-SnO2 / SiO2 nanofiber membrane prepared in Comparative Example 3 is as follows: Figure 13 As shown, the separation of the surface PdO-SnO2 layer from the substrate SiO2 layer after calcination is observed. This is because Sn sol was not introduced during the electrospinning of Pd-Sn sol, and the different shrinkage rates of Pd-Sn and Si electrospun fibers during calcination lead to delamination. When using double-needle blending, the Si electrospun fibers act as a skeleton, inhibiting the shrinkage of Pd-Sn electrospun fibers during calcination, thereby reducing the surface shrinkage rate and ensuring the integrity of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane. Therefore, the process of first electrospinning Si sol as the substrate and then blending Pd-Sn sol and Si sol to prepare the sensitive layer can suppress the delamination phenomenon of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane and improve the stability of the fiber membrane.

[0092] Comparative Example 4 prepared a commercial PET-based PdO-SnO2 flexible gas sensor, such as... Figure 14 As shown in (a), the commercial PET-based PdO-SnO2 flexible gas sensor prepared in Comparative Example 4, after being bent 50 times, exhibits the following properties: Figure 14 As shown in (b), the PdO-SnO2 nanofibers on the surface begin to detach, indicating that the commercial PET-based PdO-SnO2 flexible gas sensor has poor stability during bending. The commercial PET-based PdO-SnO2 flexible gas sensor prepared in Comparative Example 4, after being kept at 300℃ for 0.5 h, showed... Figure 14 As shown in (c), the PET substrate deformed and the sensor was destroyed, indicating that the commercial PET-based PdO-SnO2 flexible gas sensor has poor heat resistance.

[0093] The commercial PET-based PdO-SnO2 flexible gas sensor prepared in Comparative Example 4 and the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor prepared in Example 1 exhibit real-time stress during cyclic bending from 0 to 140° as shown in the figure. Figure 15 As shown in (a), the attractive forces applied by the instrument to the commercial PET-based PdO-SnO2 flexible gas sensor and the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor during cyclic bending were -174 to 143 mN and -64 to 40 mN, respectively. This indicates that the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor experiences less force during bending and exhibits better flexibility compared to the commercial PET-based PdO-SnO2 flexible gas sensor. The response of the commercial PET-based PdO-SnO2 flexible gas sensor prepared in Comparative Example 4 to a concentration of 1000 ppb NO2 after bending is as follows: Figure 15As shown in (b), the response to 1000 ppb decreased by 63.8% and 85.6% respectively after the sensor was bent 200 and 800 times. The gas-sensing performance of the commercial PET-based PdO-SnO2 flexible gas sensor decreased sharply after bending, indicating that the commercial PET-based PdO-SnO2 flexible gas sensor has poor stability.

Claims

1. A method for preparing a PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor, characterized in that: The preparation method includes the following steps: Step 1: Mix tetraethyl orthosilicate, distilled water and phosphoric acid evenly, then add 10% polyvinyl alcohol aqueous solution and stir evenly to obtain Si sol; stir stannous chloride dihydrate, palladium chloride, N,N-dimethylformamide and polyacrylonitrile evenly to obtain Pd-Sn sol. Step 2: First, the Si sol from Step 1 is subjected to single-needle electrospinning to obtain a Si electrospinned fiber layer; then, the Pd-Sn sol from Step 1 is introduced and subjected to double-needle mixed electrospinning with the Si sol to form a fiber film on the surface of the Si electrospinned fiber layer in which Pd-Sn electrospinned fibers and Si electrospinned fibers are interwoven, resulting in a fiber film with Si electrospinned fibers as the bottom layer and Pd-Sn electrospinned fibers and Si electrospinned fibers as the top layer. Step 3: Collect the fiber membrane from Step 2 and calcine the collected fiber membrane to obtain a PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with gas-sensitive properties. Step 4: Cover the surface of the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane with a mask, and prepare interdigitated electrodes by depositing electrode material using ion sputtering, or prepare non-interdigitated electrodes by directly depositing electrode material on the PdO-SnO2-SiO2 / SiO2 flexible breathable nanofiber membrane using spray coating. After cutting the prepared interdigitated or non-interdigitated electrodes, the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor is obtained.

2. The method for preparing the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to claim 1, characterized in that: In step 1, the mass ratio of tetraethyl orthosilicate, distilled water, phosphoric acid, and 10% polyvinyl alcohol aqueous solution in the Si sol is 150:100-200:1-2.5:200-400.

3. The method for preparing the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to claim 1, characterized in that: In step 1, the mass ratio of stannous chloride dihydrate, palladium chloride, N,N-dimethylformamide, and polyacrylonitrile in the Pd-Sn sol is 1000:0.5-1.5:8000-120000:500-1250.

4. The method for preparing the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to claim 1, characterized in that: In step 2, the propulsion rate of the Si sol is 0.4–2 mL / h, the positive high voltage is 14–25 kV, the negative high voltage is -1–3 kV, and the spinning time is 1–8 h.

5. The method for preparing the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to claim 1, characterized in that: In step 2, when the Si sol and Pd-Sn sol are electrospun in a double-needle mixture, the feed rate of the Pd-Sn sol is 0.4 to 2 mL / h, the ratio of the feed rates of the Si sol to the Pd-Sn sol is 1:1 to 5, the positive voltage is 14 to 25 kV, the negative voltage is -1 to 3 kV, and the spinning time is 1 to 4 hours.

6. The method for preparing the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to claim 1, characterized in that: In step 3, the heating rate of calcination is 1-20℃ / min, the calcination temperature is 500-800℃, and the time is 1-10h.

7. The method for preparing the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to claim 1, characterized in that: In step 4, the width of the interdigitated electrode prepared by the ion sputtering method is 0.5-2 mm, and the gap between the interdigitated fingers is 0.5-2 mm.

8. The method for preparing the PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to claim 1, characterized in that: In step 4, the non-interdigitated electrode prepared by the spraying method has an electrode width of 3-8 mm and an electrode gap of 3-10 mm.

9. The method for preparing a PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor according to any one of claims 1, 7, and 8, characterized in that: In step 4, the electrode material is Au, Ag, or Pd.

10. The PdO-SnO2-SiO2 / SiO2 self-supporting flexible breathable nanofiber membrane gas sensor obtained by the preparation method of claim 1.

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