A time-sequential logic type gas sensor

Abstract

This invention provides a sequential logic gas sensor, relating to the field of sensor technology. The sequential logic gas sensor provided by this invention includes a substrate electrode and a sensitive material layer coated on the surface of the substrate electrode; the specific surface area of ​​the sensitive material is ≥20 m² / g. 2 / g; the sensitive material includes semiconductor metal oxides; the absolute value of the theoretical adsorption energy between at least one semiconductor metal oxide in the sensitive material and the gas molecules to be measured is ≥2.0eV. The time-series logic gas sensor composed of the present invention has both gas response and response signal memory functions, enabling effective monitoring of intermittent low-concentration pollutant gases.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a time-sequential logic gas sensor. Background Technology

[0002] Semiconductor metal oxide (SMO) gas sensors are widely used in the field of pollutant gas monitoring due to their advantages such as low cost, small size, and ease of integration. Traditional SMO-based gas sensors are designed for real-time gas monitoring; therefore, they exhibit fast response / recovery speeds, as gas adsorption / desorption on the SMO surface is rapid and reversible. In this case, if the pollutant gas in the environment disappears briefly, the SMO gas sensor quickly returns to its initial state. Therefore, traditional gas sensors can only achieve immediate detection of single instances of high-concentration pollution and cannot detect the potential hazards of intermittently occurring pollutants based on their frequency and concentration.

[0003] Low concentrations of pollutants are generally considered to be less harmful and are often overlooked. However, prolonged and frequent exposure to these low concentrations can cause irreversible damage to the environment and organisms. Therefore, it is crucial to assess the potential hazards of pollutants by monitoring their frequency and concentration over a long period to provide early warnings. Summary of the Invention

[0004] The purpose of this invention is to provide a time-sequence logic gas sensor that can effectively monitor intermittent low-concentration pollutant gases.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a time-series logic gas sensor, comprising a base electrode and a sensitive material layer coated on the surface of the base electrode; the specific surface area of ​​the sensitive material is ≥20 m². 2 / g; the sensitive material includes a composite semiconductor metal oxide; the absolute value of the theoretical adsorption energy between at least one semiconductor metal oxide in the sensitive material and the gas molecules to be measured is ≥2.0eV.

[0007] Preferably, the sensitive material includes a semiconductor metal oxide nanofiber heterojunction material.

[0008] Preferably, the semiconductor metal oxide nanofiber heterojunction material includes a nanofiber backbone and nanowire branches loaded on the surface of the nanofiber backbone; the nanofiber backbone is a first semiconductor metal oxide; and the nanowire branches are a second semiconductor metal oxide containing oxygen vacancies.

[0009] Preferably, the first semiconductor metal oxide includes ZnO, WO3, or SnO2.

[0010] Preferably, the second semiconductor metal oxide containing oxygen vacancies includes MoO. 3-x BiO 2-x or WO 3-x .

[0011] The present invention provides a time-series logic gas sensor as described above, wherein the diameter of the nanofiber backbone is 50-200 nm and the diameter of the nanowire branches is 5-10 nm.

[0012] Preferably, the thickness of the sensitive material layer is 0.3 to 0.8 mm.

[0013] Preferably, the substrate electrode is made of a noble metal or copper.

[0014] Preferably, the precious metal includes gold or silver / palladium.

[0015] Preferably, the base electrode is an interdigital electrode.

[0016] This invention provides a time-series logic gas sensor, comprising a base electrode and a sensitive material layer coated on the surface of the base electrode; the specific surface area of ​​the sensitive material is ≥20 m². 2 / g; the sensitive material includes a composite semiconductor metal oxide; the absolute value of the theoretical adsorption energy between at least one semiconductor metal oxide in the sensitive material and the gas molecules to be measured is ≥2.0eV.

[0017] This invention selects a semiconductor metal oxide with a high adsorption energy for the gas molecules to be measured as the sensitive material and controls the specific surface area of ​​the sensitive material to ensure that when the gas molecules to be measured are present, they are strongly adsorbed on the surface of the sensitive material. This strong adsorption allows the gas molecules to remain in an adsorbed state for a long time, and the sensor's response signal does not disappear immediately after the gas to be measured disappears (under the condition that the concentration of the gas to be measured at room temperature is 1 ppm, the sensor response recovery time is ≥500s after the gas to be measured disappears). The sensor exhibits a certain memory function for the response signal. This characteristic means that the sensor's response signal at a certain moment depends not only on the real-time gas concentration, but also on the remaining memory (instantaneous state) affected by previous gas pollution. Therefore, it can record the history of intermittent gas pollution and realize the effective monitoring of intermittent low-concentration polluting gases.

[0018] Since the gas sensor provided by this invention has both gas response and response signal memory functions, the response signal output at a certain moment depends not only on the real-time gas concentration, but also on the sensor's response memory of past gas pollution. Its signal output characteristics are similar to those of a sequential logic circuit. Therefore, this invention refers to this gas sensor as a sequential logic gas sensor (SLC).

[0019] The results of the embodiments show that the sequential logic gas sensor provided by the present invention can achieve effective memory-type detection of intermittent low-concentration gases. Even a NO2 pulse with a concentration of only 25 ppb can trigger a significant output signal from the device. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the working principle of the sequential logic gas sensor of the present invention;

[0021] Figure 2 This is a schematic diagram of the process for preparing nanofiber heterostructure materials in Example 1 of the present invention;

[0022] Figure 3 This is a SEM image of the nanofiber heterojunction material prepared in Example 1 of the present invention;

[0023] Figure 4 These are TEM images and partial HRTEM images of the nanofiber heterojunction material prepared in Example 1 of this invention;

[0024] Figure 5 WO prepared in Example 1 of this invention 3-x The theoretical adsorption energy of WO3 material for NO2 molecules;

[0025] Figure 6 The nitrogen adsorption-desorption curve and pore size distribution of the nanofiber heterojunction material prepared in Example 1 of this invention are shown.

[0026] Figure 7 This is a schematic diagram of the structure of the sequential logic gas sensor prepared in Embodiment 1 of the present invention;

[0027] Figure 8 This is a structural diagram of the device for gas detection using a timing logic type gas sensor according to Embodiment 2 of the present invention;

[0028] Figure 9 The response recovery curve of the device prepared in Example 2 of this invention to 1 ppm NO2;

[0029] Figure 10 This is a graph showing the sensitivity characteristics of the device prepared in Example 2 of the present invention to NO2 gas with complex and irregular spacing.

[0030] Figure 11This is a graph showing the sensitivity characteristics of the device prepared in Example 2 of the present invention to NO2 gas of complex and irregular concentrations.

[0031] Figure 12 The response recovery curves and response values ​​of the devices prepared in Comparative Examples 1 and 2 of this invention to NO2 are shown. Detailed Implementation

[0032] This invention provides a time-series logic gas sensor, comprising a base electrode and a sensitive material layer coated on the surface of the base electrode; the specific surface area of ​​the sensitive material is ≥20 m². 2 / g; the sensitive material includes a composite semiconductor metal oxide; the absolute value of the theoretical adsorption energy between at least one semiconductor metal oxide in the sensitive material and the gas molecules to be measured is ≥2.0eV.

[0033] The timing logic gas sensor provided by this invention includes a base electrode.

[0034] In this invention, the substrate electrode is preferably made of a noble metal or copper; the noble metal preferably includes gold or silver / palladium. In this invention, the substrate electrode is preferably an interdigitated electrode; the width of the interdigitated electrode is preferably 0.5–2 mm, more preferably 0.5–1 mm. The use of interdigitated electrodes in this invention helps to reduce the resistance of the device, thereby ensuring that the resistance or current is within the detection limit of the multimeter during testing. In this invention, the smaller the gap between adjacent interdigitated electrodes, the lower the resistance of the device; using interdigitated electrodes with excessively large gaps may cause the device resistance to reach the MΩ or even GΩ level, which may exceed the detection limit of the multimeter used for testing. This invention does not have special requirements for the gap distance between adjacent interdigitated electrodes, as long as the generated current or resistance is within the detection limit of the multimeter. This invention does not have special requirements for the thickness of the interdigitated electrodes; thicknesses well known in the art can be used.

[0035] The timing logic gas sensor provided by the present invention includes a sensitive material layer coated on the surface of the substrate electrode.

[0036] In this invention, the specific surface area of ​​the sensitive material is ≥20m². 2 / g, preferably ≥40m 2 / g; In an embodiment of the present invention, the specific surface area of ​​the sensitive material is 88.0 m². 2 / g. In this invention, the absolute value of the theoretical adsorption energy between at least one semiconductor metal oxide in the sensitive material and the gas molecules to be tested is ≥2.0 eV, preferably ≥2.2 eV; this invention does not have special requirements for the type of gas to be tested, and can be selected according to actual needs, specifically it can be NO2 or NO, and in the embodiments of this invention, it is specifically NO2.

[0037] This invention selects a semiconductor metal oxide with a high adsorption energy for the target gas molecules as the sensing material and controls the specific surface area of ​​the sensing material to ensure strong adsorption of the gas molecules on the surface of the sensing material when they are present. At this time, the adsorption rate of the gas molecules is much greater than the desorption rate, so the gas molecules continuously accumulate on the surface of the sensing material, and the sensor's response signal continuously increases. After the target gas molecules disappear, the gas molecules on the surface of the sensing material desorb at an extremely slow rate, and the sensor response gradually fades. Under the condition of a target gas concentration of 1 ppm at room temperature, the response recovery time of the device after the target gas disappears is ≥500 s. Since the sensor's response signal does not disappear immediately after the target gas disappears, the sensor exhibits a certain memory function for the response signal. Therefore, the sensor composed of electrodes modified according to this invention can effectively monitor intermittent low-concentration pollutant gases.

[0038] In this invention, the sensitive material comprises a composite semiconductor metal oxide. This invention uses a semiconductor metal oxide as the sensitive material to ensure that the sensitive material has the ability to generate electron-hole pairs, thereby possessing sensing performance; by combining different semiconductor metal oxides, the sensor has a high electron-hole separation capability, thus ensuring that the sensor has a good response capability to the gas being measured.

[0039] In this invention, the sensitive material preferably comprises a semiconductor metal oxide nanofiber heterojunction material; the semiconductor metal oxide nanofiber heterojunction material preferably comprises a nanofiber backbone and nanowire branches loaded on the surface of the nanofiber backbone; the nanofiber backbone is a first semiconductor metal oxide; the nanowire branches are a second semiconductor metal oxide containing oxygen vacancies. In this invention, the first semiconductor metal oxide preferably comprises ZnO, WO3, or SnO2, more preferably WO3; the second semiconductor metal oxide containing oxygen vacancies preferably comprises MoO. 3-x BiO 2-x or WO 3-x WO is preferred. 3-x In this invention, when the second semiconductor metal oxide containing oxygen vacancies is MoO... 3-x When 0 < x < 3; when the second semiconductor metal oxide containing oxygen vacancies is BiO 2-x When 0 < x < 2; when the second semiconductor metal oxide containing oxygen vacancies is WO 3-x When x < 3, 0 < x < 3. In this invention, the diameter of the nanofiber backbone is preferably 50–200 nm; the diameter of the nanowire branches is preferably 5–10 nm, and the length is preferably 20–50 nm.

[0040] In this invention, the thickness of the sensitive material layer is preferably 0.3 to 0.8 mm, more preferably 0.4 to 0.7 mm, and even more preferably 0.5 to 0.6 mm.

[0041] The present invention does not have any special requirements for the preparation method of the time-sequential logic gas sensor. The sensitive material is directly coated onto the surface of the substrate electrode and then vacuum dried to obtain the sensor.

[0042] In this invention, when the sensitive material is the semiconductor metal oxide nanofiber heterojunction material described above, a schematic diagram of the preparation method of the semiconductor metal oxide nanofiber heterojunction material is shown below. Figure 2 As shown, the preferred method includes the following steps:

[0043] A spinning solution is obtained by mixing a first semiconductor metal oxide precursor, a viscosity modifier, and a solvent.

[0044] The spinning solution is electrospun to obtain a first semiconductor metal oxide precursor fiber.

[0045] The first semiconductor metal oxide precursor fiber was calcined to obtain the first semiconductor metal oxide nanofiber.

[0046] The second semiconductor metal oxide precursor is dissolved in an alcohol solvent, and the resulting solution is mixed with the first semiconductor metal oxide nanofibers and subjected to a solvothermal reaction to obtain a semiconductor metal oxide nanofiber heterojunction material.

[0047] This invention involves mixing a first semiconductor metal oxide precursor, a viscosity modifier, and a solvent to obtain a spinning solution. In this invention, when the first semiconductor metal oxide is ZnO, the first semiconductor metal oxide precursor preferably includes zinc acetate; when the first semiconductor metal oxide is SnO2, the first semiconductor metal oxide precursor preferably includes tin tetrachloride; when the first semiconductor metal oxide is WO3, the first semiconductor metal oxide precursor preferably includes phosphotungstic acid, ammonium paratungstate, or ammonium metatungstate.

[0048] In this invention, the viscosity modifier preferably includes polyvinylpyrrolidone, polyvinyl alcohol, or polyacrylonitrile; when the viscosity modifier is polyvinylpyrrolidone or polyvinyl alcohol, the solvent is preferably water; when the viscosity modifier is polyacrylonitrile, the solvent is preferably N,N-dimethylformamide.

[0049] In this invention, the preferred mass ratio of the first semiconductor metal oxide precursor, viscosity modifier, and solvent is (1-3):(1-3):(20-50), more preferably (1.0-1.5):(2-2.5):(20-40). By controlling the mass ratio of the first semiconductor metal oxide precursor, viscosity modifier, and solvent within the above range, this invention can obtain first semiconductor metal oxide nanofibers with superior morphology.

[0050] After obtaining the spinning solution, the present invention performs electrospinning on the spinning solution to obtain a first semiconductor metal oxide precursor fiber.

[0051] In this invention, the electrospinning voltage is preferably 8–15 kV, more preferably 9–12 kV; the electrospinning receiving distance is preferably 15–20 cm, more preferably 16–18 cm; the fluid velocity is preferably 5–10 μL / min, more preferably 7–8 μL / min; and the nozzle inner diameter is preferably 0.3–0.5 mm, more preferably 0.35–0.45 mm. Controlling the spinning voltage within the above range in this invention is more conducive to obtaining nanofibers of uniform thickness. In this invention, the nanofibers obtained by electrospinning have a layered network structure.

[0052] After obtaining the first semiconductor metal oxide precursor fiber, the present invention calcines the first semiconductor metal oxide precursor fiber to obtain the first semiconductor metal oxide nanofiber.

[0053] In this invention, the calcination temperature is preferably 400–800°C, more preferably 450–750°C, and most preferably 500–650°C; the calcination time is preferably 2–10 h, more preferably 2–6 h. The rate of temperature increase from room temperature to the calcination temperature is preferably 2–10°C / min, more preferably 4–8°C / min. The calcination is preferably carried out in an air atmosphere. During the calcination process, the first semiconductor metal oxide precursor reacts with oxygen in the air to generate the corresponding first semiconductor metal oxide, while simultaneously removing polyvinylpyrrolidone, polyacrylonitrile, or polyvinyl alcohol from the nanofiber precursor during the calcination process.

[0054] After obtaining the first semiconductor metal oxide nanofiber, the present invention dissolves the second semiconductor metal oxide precursor in an alcohol solvent, mixes the resulting solution with the first semiconductor metal oxide nanofiber, and performs a solvothermal reaction to obtain a semiconductor metal oxide nanofiber heterojunction material.

[0055] In this invention, when the second semiconductor metal oxide containing oxygen vacancies is WO3... 3-xIn this case, the second semiconductor metal oxide precursor is preferably tungsten hexacarbonyl or tungsten hexachloride; when the semiconductor metal oxide containing oxygen vacancies is MoO 3-x In this case, the precursor of the second semiconductor metal oxide is preferably molybdenum pentachloride; when the semiconductor metal oxide containing oxygen vacancies is BiO 2-x In this case, the precursor of the second semiconductor metal oxide is preferably bismuth nitrate.

[0056] In this invention, the alcohol solvent preferably includes ethanol, ethylene glycol, or isopropanol, more preferably ethanol. In this invention, the mass ratio of the second semiconductor metal oxide precursor to the alcohol solvent is preferably (0.1–0.2):15.8, more preferably (0.15–0.2):15.8. In this invention, the mass ratio of the first semiconductor metal oxide nanofibers to the alcohol solvent is preferably (0.01–0.03):15.8, more preferably 0.02:15.8.

[0057] In this invention, the temperature of the solvothermal reaction is preferably 150–220°C, more preferably 160–210°C, and even more preferably 180–200°C; the time of the solvothermal reaction is preferably 12–24 h, more preferably 12–20 h, and even more preferably 12–18 h. During the solvothermal reaction, the second semiconductor metal oxide precursor grows as a branch of the second semiconductor metal oxide nanofiber on the surface of the first semiconductor metal oxide nanofiber. Because the alcohol solvent has reducing properties, it can promote the formation of oxygen vacancies in the second semiconductor metal oxide during the solvothermal reaction.

[0058] In this invention, when the temperature of the solvothermal reaction is within the above-mentioned range, it is more conducive to improving the branching growth effect of nanowires.

[0059] In this invention, when the second semiconductor metal oxide precursor is WCl6 and the alcohol solvent is ethanol, the following reaction occurs when the second semiconductor metal oxide precursor is dissolved in the alcohol solvent: WCl6 + xC2H5OH → WCl n (OC2H5) x +xHCl; the following reaction occurs during the solvothermal process: WCl n (OC2H5) x +HO2→WO 3-x +C2H5OH+HCl.

[0060] After the solvothermal reaction is completed, the present invention preferably performs solid-liquid separation on the obtained reaction product liquid, and vacuum dries the obtained solid to obtain semiconductor metal oxide nanofiber heterojunction material.

[0061] This invention does not have special requirements for the solid-liquid separation method; any solid-liquid separation method well-known in the art, such as filtration, can be used. In this invention, the vacuum drying temperature is preferably 50–80°C, more preferably 50–60°C; the vacuum drying time is preferably 6–24 hours, more preferably 10–12 hours. This invention does not have special requirements for the vacuum degree of the vacuum drying; any vacuum degree well-known in the art can be used.

[0062] The present invention does not have any special requirements for the method of using the time-sequential logic gas sensor, that is, the gas sensitivity test method, and any test method well known in the art can be used.

[0063] In an embodiment of the present invention, a substrate electrode coated with a sensitive material is used as a sequential logic gas sensor, and it is assembled into a gas-sensitivity testing device to evaluate the performance of the sequential logic gas sensor. In the present invention, the specific structure of the gas-sensitivity testing device is as follows: Figure 8 As shown, the device includes a benchtop multimeter, computer testing hardware and software, a visible light source, a dynamic gas mixing system, a test chamber, and a time-series logic gas sensor. The benchtop multimeter is connected to the computer testing hardware and software to record the real-time output signal of the sensor; the visible light source is used to excite the time-series logic gas sensor; the visible light source is connected to the test chamber via an optical fiber, with the fiber optic cable 1 cm away from the time-series logic gas sensor; the dynamic gas mixing system provides the gas pulses required for the test and is connected to the test chamber via a gas path. In practical application, the time-series logic gas sensor is placed in the test chamber and connected to the benchtop multimeter via wires. In this invention, the wavelength of the visible light source is preferably 400–700 nm; the test light intensity is preferably 10³ mW / cm². 2 .

[0064] Figure 1 This is a schematic diagram illustrating the working principle of the sequential logic gas sensor of this invention. Figure 1 As shown, the sensitive material of this invention has a strong adsorption capacity for the gas molecules to be measured. This strong adsorption allows the gas molecules to remain in an adsorbed state for a long time, thus giving the sensor excellent "memory" behavior. In this case, the sensor signal does not disappear immediately after gas detection. This characteristic means that the sensor's response signal at a given moment depends not only on the real-time gas concentration but also on the remaining memory (instantaneous state) affected by previous gas pollution. Therefore, it can record the history of intermittent gas pollution, enabling effective monitoring of intermittent low-concentration polluting gases.

[0065] In this invention, the sequential logic gas sensor has a low detection limit and can generate a sensing signal even at a concentration of only 25 ppb.

[0066] The following detailed description of the timing logic gas sensor provided by the present invention, in conjunction with embodiments, should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] Ammonium metatungstate, polyvinylpyrrolidone, and deionized water are mixed to obtain a spinning solution; the mass ratio of ammonium metatungstate, polyvinylpyrrolidone, and deionized water is 1.5:2:20.

[0069] The spinning solution was electrospun at a voltage of 12kV, a receiving distance of 15cm, and a nozzle inner diameter of 0.4mm. The resulting fibers were calcined at 550℃ for 2h, with the temperature rising from room temperature to the calcination temperature at a rate of 5℃ / min, to obtain WO3 nanofibers.

[0070] WCl6 was dissolved in ethanol, and the resulting solution was mixed with the WO3 nanofibers, wherein the mass ratio of WCl6 to ethanol was 0.2:15.8, and the mass ratio of WO3 nanofibers to ethanol was 0.02:15.8. A solvothermal reaction was carried out at 180°C for 12 hours. After the reaction was complete, the mixture was filtered, and the resulting solid was vacuum dried at 60°C for 12 hours to obtain WO3 / WO3 nanofibers. 3-x Nanofiber heterojunction materials.

[0071] The nanofiber heterostructure material prepared in Example 1 was observed using scanning electron microscopy, and the results are as follows: Figure 3 As shown. From Figure 3 As can be seen, the nanofiber heterojunction material prepared by the present invention consists of a nanofiber backbone and nanowire branches uniformly loaded on the nanofiber backbone, wherein the diameter of the nanowire backbone is 50-200 nm.

[0072] The nanofiber heterostructure material prepared in Example 1 was tested using transmission electron microscopy (TEM). The TEM and local HRTEM images of the nanofiber heterostructure material prepared in Example 1 are shown below. Figure 4 As shown. By Figure 4 As can be seen, the nanofiber heterostructure material prepared by this invention consists of nanofibers uniformly loaded with nanowire branches, the diameter of which is 5–10 nm. The nanowire branches and the nanofiber backbone correspond to WO3 metal oxides containing oxygen vacancies, respectively. 3-x Together with the metal oxide WO3, they form a heterojunction material. HRTEM images of the nanowire branches and nanofiber trunks reveal lattice spacings of 0.378 nm and 0.376 nm, respectively, corresponding to monoclinic WO3. 3-x The (010) plane and the (020) plane of the monoclinal WO3.

[0073] The nanofiber heterostructure material prepared in Example 1 was tested using transmission electron microscopy (TEM). The TEM and local HRTEM images of the nanofiber heterostructure material prepared in Example 1 are shown below. Figure 4 As shown. By Figure 4 It can be seen that the nanofiber heterostructure material prepared by this invention is composed of nanofibers uniformly loaded with nanowire branches, and the nanowire branches and nanofiber trunks correspond to metal oxides WO3 containing oxygen vacancies, respectively. 3-x Together with the metal oxide WO3, they form a heterojunction material. HRTEM images of the nanowire branches and nanofiber trunks reveal lattice spacings of 0.378 nm and 0.376 nm, respectively, corresponding to monoclinic WO3. 3-x The (010) plane and the (020) plane of the monoclinal WO3.

[0074] Figure 5 For WO 3-x The theoretical adsorption energies of NO2 molecules for WO3 and WO3 materials are calculated, with absolute values ​​of 2.47 eV and 1.64 eV, respectively. These adsorption energies were obtained using density functional theory (DFT). For this embodiment, the sensitive material model selected in the calculations was the monoclinic WO3 material obtained from the HRTEM plot. 3-x And WO3. Therefore, the adsorption energy obtained is the theoretical adsorption energy between gas molecules and the sensitive material.

[0075] The nanofiber heterostructure material prepared in Example 1 was subjected to BET and pore size measurements, and the results are shown in the figure. Figure 6 .Depend on Figure 6 It can be seen that the BET specific surface area of ​​the nanofiber heterostructure material prepared by this invention is 88.0 m². 2 / g. Figure 6 The smaller figures show the pore size of the nanofiber heterostructure material prepared in this invention. The figures demonstrate that the prepared nanofiber heterostructure material possesses a rich microporous structure.

[0076] After obtaining the nanofiber heterojunction material, this invention coats the nanofiber heterojunction material onto a substrate electrode. The substrate electrode is an interdigitated electrode with an interdigitation width of 0.6 mm. The substrate electrode is made of silver-palladium, and the coating thickness is 0.5 mm. After vacuum drying, a timing logic gas sensor is obtained. A schematic diagram of the timing logic gas sensor is shown below. Figure 7 As shown, Figure 7 The instrument used was a commercially available multimeter (Fluke 8846A digital multimeter) to record the real-time output signal of the sensor. The multimeter and the sensor electrodes were connected by wires. Figure 8 Real-time monitoring is also conducted using the same method described above.

[0077] Example 2

[0078] Example 2 presents an intermittent gas detection performance test on the sequential logic gas sensor prepared in Example 1.

[0079] In this embodiment, the apparatus for testing the gas sensitivity of a sequential logic gas sensor is preferably as follows: Figure 8 As shown. By Figure 8 As can be seen, the device for testing the gas sensitivity of a sequential logic gas sensor consists of six parts: a benchtop multimeter, computer testing hardware and software (computer), a visible light source, a dynamic gas mixing system, a test chamber, and a sequential logic gas sensor. The benchtop multimeter, connected to the testing hardware and software (computer), records the sensor's real-time output signal; the visible light source excites the sensor; the dynamic gas mixing system provides the gas pulses required for the test and is connected to the test chamber via a gas path. The sensor is placed in the test chamber and connected to the benchtop multimeter via wires. The visible light source has a wavelength range of 400–700 nm and a test light intensity of 10³ mW / cm². 2 The test chamber is connected via optical fiber, which is 1 cm away from the sensor.

[0080] The sequential logic gas sensor prepared in Example 1 was placed in a test chamber and irradiated with visible light. NO2 gas was then introduced into the test chamber at a concentration of 1 ppm for 120 seconds using a dynamic gas mixing method. The recovery characteristics of the device were first tested, such as… Figure 9 As shown, the recovery time of the device is 900s.

[0081] Figure 10 To test the sensor's sensitivity to intermittent NO2 gas at different intervals, the gas concentration was 250 ppb, the gas pulse duration was 120 s, the interval between the first 5 gas pulses was 600 s, the interval between the 5th to 7th pulses was 300 s, and the interval between pulses after the 7th pulse was 200 s. Figure 10 It can be seen that the device can achieve effective memory-type detection for intermittent gases, meaning that the output signal generated by a new gas pulse is superimposed on the old output signal. Furthermore, for gas pulses of the same duration and concentration, as the pulse interval decreases, the time it takes for the output signal to reach the alarm point increases. Figure 10 The vertical axis response value (%) is obtained through R = (I g -I a ) / I g ×100% yields, where I g I is the output current of the sensor in air. a This is the output current of the sensor in the gas to be measured (NO2).

[0082] Figure 11This describes the sensor's sensitivity to intermittent NO2 gas at different concentrations. From... Figure 11 It can be seen that the device has a low detection limit for NO2 gas. Even a NO2 pulse with a concentration of only 25 ppb can trigger a significant output signal from the device. Furthermore, as the pulse concentration increases, the rate of increase in the device's output signal accelerates, achieving a rapid alarm effect. The specific testing procedure was as follows: gas pulses with a fixed time interval (100s) were introduced into the test chamber, with a pulse duration of 120s. The gas concentration ranged from 25 ppb to 250 ppb, and each concentration of pulse was introduced three times.

[0083] Comparative Example 1

[0084] The only difference from Example 1 is that the single WO3 nanofiber prepared in Example 1 is coated onto the substrate electrode as a sensitive material to serve as a gas sensor. The gas sensor of Comparative Example 1 is assembled into a gas-sensitivity testing device according to the method of Example 2 to test its performance.

[0085] The gas sensor from Comparative Example 1 was placed in the test chamber of Example 2, and subjected to the same visible light irradiation as in Example 2. NO2 gas was introduced into the test chamber at a concentration of 1 ppm using a dynamic gas mixing method for 120 seconds. A second gas pulse was introduced when the sensor signal returned to its initial state. The test results are as follows: Figure 12 As shown. By Figure 12 It can be seen that the sensor returns to its initial state in 300 seconds, proving that it does not have the function of memory response signals.

[0086] Comparative Example 2

[0087] The only difference from Example 1 is that the solvothermal conditions in Example 1 are changed, and WO3 nanofibers are prepared in a solvothermal solution without the addition of WO3 nanofibers. 3-x Nanowires with a surface area of ​​186 m² 2 / g. To use a single WO 3-x Nanowires, used as a sensitive material, were coated onto a substrate electrode to serve as a gas sensor. The gas sensor from Comparative Example 2 was assembled into a gas-sensitivity testing device according to the method of Example 2 to test its performance.

[0088] The gas sensor of Comparative Example 2 was placed in the test chamber of Example 2, and the test procedure was the same as that of Comparative Example 1. The test results are as follows. Figure 12 As shown. By Figure 12It can be seen that the sensor in Comparative Example 2 almost cannot recover after 300 seconds, proving that it has a response signal memory function. However, the response value (%, R = (Ig-Ia) / Ig×100%) of the sensor in Comparative Example 2 to 1ppm NO2 is only 0.8, proving that its gas response function is weak, indicating that the sequential logic gas sensor obtained by using a single semiconductor metal oxide has a weak response value to the gas to be measured. Compared with the sensors in Comparative Examples 1 and 2, the sequential logic gas sensor prepared in Example 1 has both gas response function and response signal memory function, and can realize effective monitoring of intermittent low-concentration pollutant gases.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A time-series logic gas sensor, comprising a base electrode and a sensitive material layer coated on the surface of the base electrode; the specific surface area of ​​the sensitive material is ≥20 m². 2 / g; the sensitive material includes a composite semiconductor metal oxide; the absolute value of the theoretical adsorption energy between at least one semiconductor metal oxide in the sensitive material and the gas molecules to be measured is ≥2.0eV; The sensitive material includes a semiconductor metal oxide nanofiber heterojunction material. The semiconductor metal oxide nanofiber heterojunction material includes a nanofiber backbone and nanowire branches loaded on the surface of the nanofiber backbone; the nanofiber backbone is a first semiconductor metal oxide; and the nanowire branches are a second semiconductor metal oxide containing oxygen vacancies.

2. The sequential logic gas sensor according to claim 1, characterized in that, The first semiconductor metal oxide includes ZnO, WO3, or SnO2.

3. The sequential logic gas sensor according to claim 1, characterized in that, The second semiconductor metal oxide containing oxygen vacancies includes MoO. 3-x BiO 2-x or WO 3-x .

4. The sequential logic gas sensor according to any one of claims 1 to 3, characterized in that, The diameter of the nanofiber backbone is 50~200 nm; the diameter of the nanowire branches is 5~10 nm.

5. The sequential logic gas sensor according to claim 1, characterized in that, The thickness of the sensitive material layer is 0.3~0.8 mm.

6. The sequential logic gas sensor according to claim 1, characterized in that, The substrate electrode is made of precious metals or copper.

7. The sequential logic gas sensor according to claim 6, characterized in that, The precious metals include gold or silver / palladium.

8. The sequential logic gas sensor according to claim 6 or 7, characterized in that, The base electrode is an interdigitated electrode.

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