Sulfur Dioxide Sensor and Its Applications

Abstract

The present invention provides a sulfur dioxide sensor and its application, relating to the technical field of sensors. The sulfur dioxide sensor provided by the present invention includes a substrate, a polyaniline microfiber array, and electrodes. Among them, the substrate mainly serves to carry the responsive material; the polyaniline microfiber array is composed of microfibers arranged in parallel, with a high specific surface area, and serves as the responsive center for detecting sulfur dioxide in air samples; the electrodes are connected to both ends of the microfibers and are fixed to the substrate together with the microfibers, serving to connect to the outside. The sensor provided by the present invention can detect sulfur dioxide in ambient air, with a fast detection speed, high sensitivity, and fast response speed. It does not require cumbersome operations by staff, avoiding the problem of unstable detection accuracy in manual detection.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to a sulfur dioxide sensor and its application. Background Art

[0002] Sulfur dioxide (SO2) is widely used as a preservative in the food and beverage industries due to its excellent antibacterial properties without causing discoloration of bacterial growth and oxidation. However, there is much evidence showing that the health risks of sulfur dioxide exposure are significant, including skin and mucosal inflammation of the eyes, nose, throat, and lungs. Given the potential risks of sulfur dioxide to human health, it is necessary to measure the sulfur dioxide content in the ambient gas atmosphere.

[0003] Currently, the determination of sulfur dioxide in ambient air is generally carried out by the formaldehyde absorption pararosaniline spectrophotometry method. However, when the existing equipment processes chemical reactions, the operation is complex, and the users need to conduct cumbersome experiments. Due to the high requirement for personnel experience in the operation, the problem of unstable detection accuracy often occurs.

[0004] In view of the disadvantages of the existing sulfur dioxide liquid-phase detection device, such as large volume, difficult to carry, slow response, and low sensitivity, it is very necessary to develop a miniaturized sulfur dioxide solid-phase sensor.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a sulfur dioxide sensor, which can detect sulfur dioxide in ambient air, does not require cumbersome operations by staff, and avoids the problem of unstable detection accuracy in manual detection. Moreover, the response center has a large specific surface area, and sulfur dioxide can fully contact with the response center to achieve the purpose of faster response speed and lower detection limit in gas sensing, so as to solve at least one of the above problems.

[0007] The second object of the present invention is to provide the application of the above sulfur dioxide sensor in air quality detection.

[0008] In the first aspect, the present invention provides a sulfur dioxide sensor, including a substrate, a polyaniline microfiber array, and electrodes;

[0009] The polyaniline microfiber array is composed of microfibers mainly prepared from protonic acid-doped polyaniline arranged in parallel;

[0010] There are at least 2 electrodes, which are respectively connected to both ends of the microfibers;

[0011] The polyaniline microfiber array and the electrodes are fixed on the substrate.

[0012] As a further technical solution, the width of the microfilaments on the substrate is 1-2 μm;

[0013] Preferably, the height of the microfilaments on the substrate is 0.1-1 μm;

[0014] Preferably, the length of the microfilaments is 50-10,000 μm;

[0015] Preferably, the spacing between adjacent microfilaments is 2-15 μm.

[0016] As a further technical solution, by mass parts, the raw materials of the polyaniline microfilament array include: 20-100 parts of protonic acid-doped polyaniline, 0-5 parts of conductive carbon black, 0-5 parts of single-walled carbon nanotubes, and 0-5 parts of graphene.

[0017] As a further technical solution, the particle size of the conductive carbon black is 30-50 nm;

[0018] The diameter of the single-walled carbon nanotubes is 3-15 nm, and the length is 10-20 μm;

[0019] The thickness of the graphene is 0.3-1 nm, and the diameter is 1-10 μm.

[0020] As a further technical solution, the polyaniline microfilament array is prepared by the self-assembled liquid film directional contraction method.

[0021] As a further technical solution, the material of the substrate is selected from silicon or quartz.

[0022] As a further technical solution, the surface of the substrate is hydrophilically modified.

[0023] As a further technical solution, the material of the electrode is selected from metals.

[0024] As a further technical solution, the metal electrode is fixed on the substrate by vacuum evaporation.

[0025] In a second aspect, the present invention provides the application of the above sulfur dioxide sensor in air quality detection.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The sulfur dioxide sensor provided by the present invention includes a substrate, a polyaniline microfiber array, and electrodes. Among them, the substrate mainly serves to carry the responsive material; the polyaniline microfiber array is composed of microfibers arranged in parallel, with a high specific surface area, and serves as the responsive center for detecting sulfur dioxide in air samples; the electrodes are connected to both ends of the microfibers and fixed to the substrate together with the microfibers, serving to connect to the outside. The sensor provided by the present invention can detect sulfur dioxide in ambient air, with fast detection speed, high sensitivity, and fast response speed. It does not require cumbersome operations by staff, avoiding the problem of unstable detection accuracy in manual detection. Description of the Drawings

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 is the preparation process of the polyaniline microfiber array;

[0030] Figure 2 is the silicon column template with a microgroove structure;

[0031] Figure 3 is the sulfur dioxide sensing device provided in Example 1;

[0032] Figure 4 is the volt-ampere characteristic curve of the sulfur dioxide sensor in Test Example 1;

[0033] Figure 5 is the single-response curve of the sulfur dioxide sensor in Test Example 2;

[0034] Figure 6 is the cyclic response curve of the sulfur dioxide sensor in Test Example 2;

[0035] Figure 7 is the response curve of the sulfur dioxide sensor in Test Example 3.

[0036] Icon: 1 - Substrate; 2 - Polyaniline microfiber array; 3 - Electrode; 4 - Probe. Detailed Embodiments

[0037] The embodiments of the present invention will be described in detail below in conjunction with the implementation manners and examples. However, those skilled in the art will understand that the following implementation manners and examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the examples in the present invention, all other examples obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Those not specifying specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0038] After research by the inventor, it was found that the conductivity of polyaniline changes after binding with sulfur dioxide, and based on this, the present invention was proposed.

[0039] In a first aspect, the present invention provides a sulfur dioxide sensor, comprising a substrate, a polyaniline microfiber array, and electrodes;

[0040] The polyaniline microfiber array is composed of microfibers arranged in parallel and mainly prepared from protonic acid-doped polyaniline;

[0041] There are at least two electrodes, which are respectively connected to both ends of the microfibers;

[0042] The polyaniline microfiber array and the electrodes are fixed on the substrate.

[0043] The sulfur dioxide sensor provided by the present invention comprises a substrate, a polyaniline microfiber array, and electrodes. Among them, the substrate mainly serves to carry the response material; the polyaniline microfiber array is composed of microfibers arranged in parallel, with a high specific surface area, and serves as the response center for detecting sulfur dioxide in air samples; the electrodes are connected to both ends of the microfibers and are fixed on the substrate together with the microfibers, serving to connect to the outside. The sensor provided by the present invention can detect sulfur dioxide in ambient air, with a fast detection speed, high sensitivity, and fast response speed, without the need for cumbersome operations by staff, avoiding the problem of unstable detection accuracy in manual detection.

[0044] The measurement principle of the sulfur dioxide sensor of the present invention is as follows:

[0045] When the polyaniline microfibers come into contact with sulfur dioxide in the atmosphere, the conductivity of the polyaniline material will change. The micron fiber array structure with a high specific surface area can improve the sensor sensitivity and response speed by increasing the contact area between the polyaniline material and the gas atmosphere. At the same time, the unidirectional current conduction ability of the one-dimensional structure of the micron fiber array can further improve the signal stability. The generated current signal is conducted to the electrical signal receiving instrument through the electrodes, thereby realizing the detection of sulfur dioxide in the air.

[0046] It should be noted that polyaniline itself is not conductive. In order to realize the detection of sulfur dioxide by polyaniline, the inventor doped polyaniline with a protonic acid. The protonic acid-doped polyaniline belongs to a p-type semiconductor and has certain conductivity.

[0047] In the present invention, there is no specific limitation on the type of protonic acid. For example, it can be an acid that can provide hydrogen ions such as hydrochloric acid, sulfuric acid, acetic acid, etc. There is no specific limitation on the way of doping polyaniline with the protonic acid in the present invention. For example, the protonic acid can be added during the synthesis of polyaniline.

[0048] In some preferred embodiments, the width of the microfilaments on the substrate can be, for example, but not limited to, 1 μm, 1.5 μm, or 2 μm;

[0049] Preferably, the height of the microfilaments on the substrate can be, for example, but not limited to, 0.1 μm, 0.5 μm, or 1 μm;

[0050] Preferably, the length of the microfilaments can be, for example, but not limited to, 50 μm, 100 μm, 500 μm, 1000 μm, 5000 μm, or 10000 μm;

[0051] Preferably, the spacing between adjacent microfilaments can be, for example, but not limited to, 2 μm, 5 μm, 10 μm, or 15 μm.

[0052] It should be noted that in the present invention, the "width of the microfilaments on the substrate" refers to the width of the microfilaments after being fixed on the substrate, and the "height of the microfilaments on the substrate" refers to the height of the microfilaments relative to the substrate after being fixed on the substrate.

[0053] In some preferred embodiments, the polyaniline microfilament array of the present invention is mainly prepared from protonic acid-doped polyaniline. Since the conductivity of the protonic acid-doped polyaniline is general, in order to further improve the conductivity and adsorption of the polyaniline microfilament array, conductive carbon black, single-walled carbon nanotubes, or graphene can also be added. Among them, the mass fraction of the protonic acid-doped polyaniline can be, for example, but not limited to, 20 parts, 40 parts, 60 parts, 80 parts, or 100 parts; the mass fraction of the conductive carbon black can be, for example, but not limited to, 0 parts, 1 part, 2 parts, 3 parts, 4 parts, or 5 parts; the mass fraction of the single-walled carbon nanotubes can be, for example, but not limited to, 0 parts, 1 part, 2 parts, 3 parts, 4 parts, or 5 parts; the mass fraction of the graphene can be, for example, but not limited to, 0 parts, 1 part, 2 parts, 3 parts, 4 parts, or 5 parts. When the above component is 0 part, that is, this component is not added.

[0054] The particle size of the conductive carbon black can be, for example, but not limited to, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm;

[0055] The diameter of the single-walled carbon nanotubes can be, for example, but not limited to, 3 nm, 6 nm, 9 nm, 12 nm, 3 - 15 nm or 15 nm, and the length can be, for example, but not limited to, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm;

[0056] The thickness of the graphene can be, for example, but not limited to, 0.3 nm, 0.5 nm, 0.7 nm, 0.9 nm or 1 nm, and the diameter can be, for example, but not limited to, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm.

[0057] In some preferred embodiments, the polyaniline microfiber array is prepared by the self-assembled liquid film directional contraction method, as Figure 1 shown, and the preparation process is as follows:

[0058] I. Prepare a conductive PANI (polyaniline) concentrate. The specific method is to first dissolve a certain mass of conductive PANI (i.e., protonic acid-doped polyaniline) in NMP (N-methylpyrrolidone) to obtain a conductive PANI solution, and use a centrifuge to ultrasonically centrifuge at a speed of 8000 r / min to remove a very small number of undissolved conductive PANI particles. After centrifugation, use a magnetic stirring hot plate to heat, and prepare conductive PANI solutions with different concentrations by controlling the amount of volatile solvent.

[0059] II. Prepare a lyophobic silicon wafer template. Use photolithography and deep reactive ion etching (DRIE) techniques to prepare a microgroove-structured silicon pillar template, as Figure 2 shown (there are silicon pillars spaced between the grooves, and the end of the silicon pillar far from the groove is the top of the silicon pillar). After modification, an asymmetric wettability microcolumn template with hydrophobic sidewalls and hydrophilic tops is prepared.

[0060] III. Prepare PANI-MWS (polyaniline microfiber array) by the self-assembled liquid film directional contraction method. The substrate is selected as a quartz glass sheet, and two modified superhydrophobic silicon wafer substrates are placed in the middle, which can better withstand the clamping force. Use a pipette to suck 10 mL of the prepared conductive PANI solution with a certain concentration and drop it onto the silicon wafer respectively, cover the top with another quartz glass sheet, and fix it with a long-tail clip. The solution forms a thin film dispersion between the silicon wafer substrate and the quartz glass sheet, forming a capillary bridge-mediated assembly system structure, similar to a sandwich structure. Due to the Laplace pressure of asymmetric wettability between the striped silicon microcolumns, during the process of heating and volatilizing the solvent, the three-phase contact line is fixed at the top of the silicon microcolumns and guides the vertical dewetting of the liquid meniscus. As the liquid meniscus develops, the continuous liquid film splits into a series of independent capillary bridges at the top of the silicon microcolumns. As the heating time prolongs, the capillary bridges are further dehumidified, leaving uniform striped conductive PANI-MWS on the top quartz glass plate that conforms to the silicon wafer template.

[0061] In some preferred embodiments, the material of the substrate is selected from silicon or quartz, or a substrate well-known to those skilled in the art, for carrying the polyaniline microfiber array and the electrode.

[0062] In some preferred embodiments, the surface of the substrate is hydrophilically modified.

[0063] The hydrophilic substrate helps to improve the adhesion of the polyaniline microfiber array prepared by the self-assembled liquid film directional contraction method on the substrate.

[0064] In some preferred embodiments, the electrode is a hydrophilically modified Si / SiO2 substrate, and the preparation method is as follows:

[0065] Take a flat silicon wafer with a thickness of 200 - 1000 μm (P-doped, <100> orientation), oxidize it in a forced-air oven to obtain a silicon wafer with a SiO2 oxide thin film layer on the surface (Si / SiO2 substrate), and then clean the silicon wafer with a cationic cleaning agent (PLASMA) to obtain a hydrophilically modified Si / SiO2 substrate.

[0066] In some preferred embodiments, the material of the electrode is selected from metals. The present invention does not specifically limit the type of metal, and any metal well-known to those skilled in the art that can be used as an electrode can be used.

[0067] In some preferred embodiments, the metal electrode is fixed on the substrate by vacuum evaporation.

[0068] In some preferred embodiments, the metal electrode is a gold / chromium electrode, and the preparation method is as follows:

[0069] After fixing the polyaniline microfiber array on the substrate, a chromium layer with a side length of 20 - 200 μm and a thickness of 10 - 100 nm is fixed on the substrate by evaporation, and then a gold layer with a thickness of 10 - 100 nm is evaporated on the chromium layer.

[0070] In a second aspect, the present invention provides the application of the above sulfur dioxide sensor in air quality detection.

[0071] The sulfur dioxide sensor provided by the present invention can be used for detecting sulfur dioxide in the air, and therefore, can be used in the detection of air quality.

[0072] The present invention will be further illustrated by specific examples and comparative examples below. However, it should be understood that these examples are only for more detailed illustration and should not be construed as limiting the present invention in any way.

[0073] Example 1

[0074] A sulfur dioxide sensor, as Figure 3 shown, includes a hydrophilic modified Si / SiO2 substrate, a polyaniline microfilament array, and a gold / chromium electrode.

[0075] 1. The preparation method of the Si / SiO2 substrate is as follows: Take a flat silicon wafer with a thickness of 200 - 1000 μm, oxidize it in a blast drying oven to obtain a silicon wafer with a SiO2 oxide thin film layer on the surface (Si / SiO2 substrate), and then clean the silicon wafer in a cleaning instrument using a cationic cleaning agent (PLASMA) to obtain a Si / SiO2 substrate with a hydrophilic modified surface. The cleaning power is 200 W, and the cleaning duration is 10 s.

[0076] 2. The polyaniline microfilament array is composed of microfilaments arranged in parallel, which is prepared by the self - assembled liquid film directional contraction method using polyaniline and fixed on the substrate. The width of the microfilaments is 2 μm, the height is 0.2 μm, the length is 5 mm, and the spacing between adjacent microfilaments is 5 μm;

[0077] The self - assembled liquid film directional contraction method is as follows:

[0078] First, a silicon wafer with a diameter of 100 mm, p - doped, <100> - oriented, and 400 μm thick is constructed by laser lithography using a direct laser writing device through photolithography and deep reactive ion etching. On this basis, a periodic micro - column structure substrate with an adjacent column spacing of 5 μm, a width of 2 μm, and a height of 15 μm is prepared. Clean it in a plasma cleaning agent for 20 minutes to remove the photoresist.

[0079] Asymmetric wettability modification of the silicon micro - column template: The template is rinsed with deionized water and acetone in sequence, soaked in ethanol for about 5 minutes, and dried with dry nitrogen. At the same time, clean the glass slide. The photoresist is spin - coated on the glass slide using a spin coater (LEBOscience, KW - 4A, China). Press the side with the photoresist on the micro - column template, place a 10 - gram weight on the micro - column template, and let it stand for 20 seconds. After peeling off the silicon template, irradiate it with 365 - nm ultraviolet light for 3 minutes to cure the photoresist. The results show that the top of the silicon column is protected by the photoresist film, while the side walls and micro - structure gaps of the silicon column are exposed to the air. Then, fumigate the silicon template in a FAS atmosphere at 60 °C for 12 hours. During this process, the side walls of the silicon micro - columns and the surface of their gaps are modified by low - surface - energy FAS molecules. Remove the protective film on the top of the silica column to obtain an asymmetric wettability template with a hydrophilic top and a hydrophobic side wall.

[0080] Preparation of microfilament arrays: Dissolve protonic acid-doped polyaniline in NMP to obtain a conductive PANI solution. Then, drop 10 μL of the conductive PANI solution between the Si / SiO2 substrate and the template, and fix it with a bulldog clip to form a sandwich structure. Then place it in a ventilated place. As the solution evaporates, the three-phase contact line (TCL) gradually recedes. Due to the asymmetric wettability of the template, the liquid film moves towards the column top during the contraction process, causing the solute to form a liquid bridge between the column top and the substrate. Further evaporation leads to the precipitation of the solute, which is deposited on the substrate, and finally, a microfilament array of polyaniline is formed on the substrate.

[0081] 3. There are 2 Au / Cr electrodes, which are respectively connected to both ends of the microfilaments and fixed on the substrate. The preparation method is as follows: After fixing the polyaniline microfilament array on the substrate, deposit a chromium layer with a size of 20 - 200 μm square and a thickness of 10 - 100 nm on the substrate by evaporation, and then deposit a gold layer with a thickness of 10 - 100 nm on the chromium layer by evaporation.

[0082] Test Example 1

[0083] On the probe station, connect the two poles of the probe to the Au / Cr electrodes of the sulfur dioxide sensor provided in Example 1. The probe station is connected to a 4200 - SCS semiconductor characterization system. The scanning voltage is -2 to 2 V. During this period, use a Huayi H310(V) dynamic dilution gas distribution device to output sulfur dioxide gas, and maintain the sulfur dioxide concentration at 50 ppm. The results are as Figure 4 shown.

[0084] The results show that the conductivity of the PANI microfilament array is relatively ideal, and the conductivity increases when sulfur dioxide is blown in. At a voltage of 2 V, the current is about 0.27 μA when nitrogen is blown in, and about 0.35 μA when 50 ppm of sulfur dioxide is blown in.

[0085] Test Example 3

[0086] On the probe station, connect the two poles of the probe to the Au / Cr electrodes of the sulfur dioxide sensor provided in Example 1. The probe station is connected to a 4200 - SCS semiconductor characterization system. Set the continuously input voltage to 2 volts and monitor the change of current with time. During this period, use a Huayi H310(V) dynamic dilution gas distribution device to output sulfur dioxide gas, set to stop outputting for 120 s after outputting for 60 s, and repeat this cycle. Record the change value of current with time, plot with time as the horizontal axis and current value as the vertical axis, which is the response curve. The single - time response results are as Figure 5 shown, and the cyclic response results are as Figure 6 shown.

[0087] From Figure 5 and Figure 6It can be seen that the response speed of the PANI microfilament array is 20.82 ± 0.16 s, and the response time and signal stability are good, enabling continuous multiple responses. Therefore, it is obvious that the PANI microline array has a fast response speed to SO2 gas and can be used to develop an SO2 gas sensing device.

[0088] Test Example 4

[0089] On the probe station, connect the two poles of the probe to the Au / Cr electrodes of the sulfur dioxide sensor provided in Example 1. Connect the probe station to a 4200-SCS type semiconductor characteristic analysis system, set the continuous input voltage to 1 volt, and monitor the change in current over time. During this period, use the Huayi H310(V) dynamic dilution gas distribution device to output sulfur dioxide gas, set it to stop outputting for 120 s after outputting for 60 s, and blow in concentrations that decrease successively (50 ppm, 25 ppm, 10 ppm, 2 ppm, and 1 ppm), and record the change values of the current over time. The results are as Figure 7 shown.

[0090] The results show that the amplitude of the current change is proportional to the concentration of sulfur dioxide blown in, and in this experiment, the PANI microfilament array can detect sulfur dioxide gas as low as 1 ppm. The PANI microfilament array shows a very high sensitivity to sulfur dioxide gas.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sulfur dioxide sensor, characterized in that, It includes a substrate, a polyaniline microfiber array, and electrodes; The polyaniline microfiber array is composed of microfibers mainly prepared from protonic acid-doped polyaniline arranged in parallel; There are at least two electrodes, which are respectively connected to both ends of the microfibers; The polyaniline microfiber array and the electrodes are fixed on the substrate; The width of the microfibers on the substrate is 1 - 2 µm; The height of the microfibers on the substrate is 0.1 - 1 µm; The length of the microfibers is 50 - 10,000 µm; The spacing between adjacent microfibers is 2 - 15 µm; By mass fraction, the raw materials of the polyaniline microfiber array include: 20 - 100 parts of protonic acid-doped polyaniline, 0 - 5 parts of conductive carbon black, 0 - 5 parts of single-walled carbon nanotubes, and 0 - 5 parts of graphene; The polyaniline microfiber array is prepared by the self-assembled liquid film directional shrinkage method; The material of the substrate is selected from silicon or quartz; The surface of the substrate is hydrophilically modified.

2. The sulfur dioxide sensor according to claim 1, wherein The particle size of the conductive carbon black is 30 - 50 nm; The diameter of the single-walled carbon nanotubes is 3 - 15 nm, and the length is 10 - 20 µm; The thickness of the graphene is 0.3 - 1 nm, and the diameter is 1 - 10 µm.

3. The sulfur dioxide sensor according to claim 1, wherein The material of the electrodes is selected from metals.

4. The sulfur dioxide sensor according to claim 3, characterized in that, The metal electrodes are fixed on the substrate by vacuum evaporation.

5. Application of the sulfur dioxide sensor according to any one of claims 1 - 4 in air quality detection.

Images