A room temperature NO2 catalyst based on BiOI / ZnO nanorod heterostructure composite 2 Sensor, preparation method and application

Abstract

A room-temperature NO2 sensor based on a BiOI / ZnO nanorod heterostructure composite material, a preparation method thereof, and an application thereof in the rapid detection of NO2 with a concentration in the ppb order of magnitude at room temperature, belonging to the technical field of semiconductor oxide gas sensors. It consists of a ceramic chip substrate with metal interdigital electrodes and a sensitive layer of a BiOI / ZnO nanorod heterostructure composite material coated on the metal interdigital electrodes. The zinc oxide has a rod-like morphology, with a large specific surface area, which can provide more attachment sites and is in full contact with the relatively small-sized BiOI, thereby obtaining a gas-sensitive element with good gas-sensing response and fast response and recovery speeds. In addition, as an excellent optoelectronic material, BiOI can absorb visible light, thereby providing more photo-generated carriers. The sensor of the present invention adopts a planar structure, with a simple process and a short production cycle, and is suitable for mass production.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor oxide gas sensors, and in particular relates to a room temperature NO2 sensor based on a BiOI / ZnO nanorod heterostructure composite material. 2 Sensors, preparation methods and applications. Background Art

[0002] Nitrogen oxides (NO x ) mainly comes from industrial emissions, automobile exhaust and natural gas combustion, and has become one of the main air pollutants. Nitrogen oxides can cause chronic respiratory diseases, asthma attacks and even lung cancer in children and adults. Recently, researchers have also found that ppb levels of NO in urban air pollution 2 It is positively correlated with the mortality rate of COVID-19 (DH Liang, et al., Urban Air Pollution May Enhance COVID-19 Case-Fatality and Mortality Rates in the United States [J], Innovation-Amsterdam, 1 (2020) 100047). 2 Monitoring is of great significance.

[0003] In the past decade, metal oxide semiconductor gas sensors that work at room temperature have the advantages of low energy consumption, long-term stability, safety and reliability, which has aroused great interest among researchers. At present, the operating temperature of the sensor can be reduced by three common methods: surface morphology modification, addition of precious metals or transition metals, and photo-assistance. In comparison, photo-assistance is a very promising method to achieve gas sensors working at room temperature and obtaining good performance. It can provide the energy required for electrons to transition from the valence band of the semiconductor to the conduction band, generating a large number of photogenerated carriers. BiOX (X = F, Cl, Br, I), as a ternary oxide semiconductor, is a promising photocatalyst due to its non-toxicity, low cost, environmental protection and excellent photocatalytic performance under visible light. BiOX is mainly composed of Bi 2 O 2 2+ Layer composition, with halide atomic layers interwoven between its layered structure. The electrostatic field formed between this layered structure can greatly accelerate the migration of photogenerated carriers. Among BiOX, BiOI has the narrowest band gap and exhibits high photocatalytic activity. However, due to the rapid recombination of photon-generated carriers, the catalytic performance of BiOI is still not very satisfactory, so it is often used to form a heterojunction with other semiconductor materials such as ZnO to obtain better photocatalytic performance. Summary of the invention

[0004] The present invention aims to provide a room temperature NO based on BiOI / ZnO nanorod heterostructure composite material. 2 Sensor, preparation method and NO sensor with ppb concentration at room temperature 2 Application in rapid testing.

[0005] The present invention modifies the surface of conventional gas sensing metal semiconductor oxides to obtain a BiOI / ZnO nanorod heterostructure composite material, in which the narrow-bandgap BiOI as a photosensitive material can absorb visible light and generate a large number of photogenerated carriers, while the metal oxide as a gas-sensitive material completes the gas-sensing process, realizing the detection of NO under visible light excitation at room temperature. 2 Efficient detection.

[0006] The room temperature NO based on BiOI / ZnO nanorod heterostructure composite material of the present invention 2 The sensor is characterized in that it is composed of a ceramic substrate with Au metal interdigital electrodes on the upper surface and a sensitive material coated on the Au metal interdigital electrodes and the upper surface of the ceramic substrate, and characterized in that the sensitive material is a BiOI / ZnO nanorod heterostructure composite material, and is prepared by the following steps:

[0007] (1) 0.073 g of hexadecyltrimethylammonium bromide and 1.92 g of sodium hydroxide were mixed in 10-20 mL of deionized water, 2.32 g of zinc nitrate hexahydrate was added, and then stirred for 0.5-1.5 h; the obtained solution was poured into a polytetrafluoroethylene inner liner in a stainless steel autoclave, heated to 85-95° C. and reacted for 14-16 h; the obtained precipitate was washed alternately by centrifugation with ethanol and deionized water for 3-5 times, dried at 75-85° C., and then calcined at 350-450° C. for 1.5-2.5 h, thereby obtaining ZnO nanorods;

[0008] (2) adding 0.081 g of the ZnO nanorods prepared in step (1) into 25-35 mL of deionized water and stirring to obtain a solution A; dissolving bismuth nitrate pentahydrate and potassium iodide in 15-25 mL and 9-11 mL of ethylene glycol, respectively, and then adding the bismuth nitrate solution dropwise into the solution A and stirring for 15-25 min; then adding the potassium iodide solution dropwise into the solution A and stirring for 0.5-1.5 h; wherein the atomic ratio of Bi to I is 1:1, and the atomic ratio of Bi or I to Zn is 1:1. 3:100; finally, the obtained solution is centrifuged and the centrifugal product is dried at 50-70°C for 11-13h to obtain a BiOI / ZnO nanorod heterostructure composite material; the composite materials in which the atomic ratio of Bi (or I) to Zn is 1:100, 1.5:100, 2:100, and 3:100 are named 1.0at%BiOI-ZnO, 1.5at%BiOI-ZnO, 2.0at%BiOI-ZnO, and 3.0at%BiOI-ZnO, respectively.

[0009] The morphology of the ZnO material obtained by the above method is a nanoflower assembled into a rod-like structure, and the BiOI nanoparticles are modified on the surface of the ZnO nanorods, and the diameter of the ZnO nanorods is 50-100nm; the Bi element in BiOI is positive, similar to a positive charge potential field, and the surface of zinc oxide has oxygen hanging bonds, which makes the two attract each other by electrostatic interaction. The inconsistency of the Fermi level between BiOI and ZnO leads to the formation of a pn heterojunction at the interface through charge transfer, further strengthening the interface contact.

[0010] The room temperature NO based on BiOI / ZnO nanorod heterostructure composite material of the present invention 2 The preparation method of the sensor comprises the following steps:

[0011] (1) placing a ceramic substrate with Au metal interdigital electrodes on the upper surface in acetone, ethanol, and deionized water, respectively, ultrasonically cleaning for 15 to 30 minutes, and then drying at 50 to 70° C.;

[0012] (2) dissolving 10-20 mg of the BiOI / ZnO nanorod heterostructure composite material in 2-5 mL of ethanol, mixing well, and applying the mixture on the ceramic substrate obtained in step (1) with a fine brush, so that the composite material completely covers the Au metal interdigital electrode and the upper surface of the ceramic substrate; then heat treating the mixture at 70-90° C. for 10-20 min to evaporate all the ethanol; finally, calcining the ceramic substrate at 260-330° C. for 1.5-2.5 h, and introducing argon as a protective gas, thereby obtaining a room temperature NO based on the BiOI / ZnO nanorod heterostructure composite material. 2 sensor.

[0013] Room temperature NO based on BiOI / ZnO nanorod heterostructure composite material prepared by the present invention 2 The sensor has the following advantages:

[0014] 1. BiOI / ZnO nanorod heterostructure composite materials can be prepared by simple hydrothermal method and co-precipitation method, the synthesis method is simple and the cost is low;

[0015] 2. The zinc oxide morphology is a rod-like structure assembled into nanoflowers, which has a large specific surface area and can provide more attachment sites, fully contacting with the smaller BiOI material, thereby obtaining a gas sensor with better gas-sensitive response and faster response recovery speed. In addition, BiOI, as an excellent optoelectronic material, can absorb visible light, thereby providing more photogenerated carriers.

[0016] 3. The sensor of the present invention adopts a planar structure, has a simple process, a short production cycle, and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : (a) is the SEM image of pure ZnO under low magnification microscope, and the inset in (a) is the SEM image of pure ZnO under high magnification microscope; (b) is the SEM image of pure BiOI under low magnification microscope, and the inset in (b) is its SEM image under high magnification microscope.

[0018] Figure 2 : (a) is the XRD patterns in the range of 10° to 80° of ZnO, BiOI, 1.0at% BiOI-ZnO, 1.5at% BiOI-ZnO, 2.0at% BiOI-ZnO and 3.0at% BiOI-ZnO composites, and the XRD standard card pattern of ZnO material; (b) is the low-power SEM image of 1.5at% BiOI-ZnO, in which the inset is the SEM image under high-power microscope; (cd) are the TEM and HRTEM images of 1.5at% BiOI-ZnO; (eh) is the EDS image of the elements in 1.5at% BiOI-ZnO.

[0019] like Figure 1 (ab) and Figure 2 As shown in the SEM image (b), the diameter of the ZnO nanorods is 50-100 nm, and the thickness of the BiOI sheet is 10-20 nm. From the enlarged image, it can be seen that the surface morphology of 1.5at% BiOI-ZnO has some more BiOI nanoparticles than the surface of the ZnO nanorods.

[0020] like Figure 2As shown in (a), the ZnO nanorods match well with the standard card of hexagonal wurtzite ZnO (JCPDS File No 36-1451), with 11 main peaks. Compared with the ZnO standard card, the main peak positions of the XRD diffraction spectra of 1.0at% BiOI-ZnO, 1.5at% BiOI-ZnO, 2.0at% BiOI-ZnO and 3.0at% BiOI-ZnO composite materials did not change significantly, indicating that BiOI was not incorporated into the ZnO lattice. And due to the low doping amount, the peak of BiOI did not appear clearly. Figure 2 The TEM results in (cd) show that there is a BiOI lattice structure on the surface of the ZnO rods, and Figure 2 The scanning results in (eh) show that BiOI is uniformly dispersed on the ZnO surface.

[0021] Figure 3 : (a) is the UV-visible spectra of ZnO nanorods, BiOI and 1.0at% BiOI-ZnO, 1.5at% BiOI-ZnO, 2.0at% BiOI-ZnO and 3.0at% BiOI-ZnO composites, and (b) is the converted Tauc plot.

[0022] like Figure 3 As shown, the absorbance of ZnO before and after modification was studied. The UV-visible absorption spectrum shows the absorption band edges of the four materials. It can be seen that ZnO nanorods have an obvious absorption band edge at 380nm, the composite material has absorption at 400-530nm, and the absorption intensity increases with the increase of BiOI mass content. The absorption in the visible light region is caused by the narrow band gap of BiOI. Therefore, we selected four typical LEDs (365nm, 460nm, 490nm and 520nm) as the light source for gas sensing measurement.

[0023] Figure 4 : ZnO, 1.0at% BiOI-ZnO, 1.5at% BiOI-ZnO, 2.0at% BiOI-ZnO and 3.0at% BiOI-ZnO composites for 1 ppm NO under 365nm, 460nm, 490nm, and 520nm illumination. 2 Response curve.

[0024] like Figure 4 As shown, it can be seen that the optimal doping mass content of BiOI is 1.5at%. BiOI, as a photosensitive material, covers the surface of ZnO nanorods. When the doping amount is high, the exposed surface of the gas-sensitive material is reduced and the surface active chemical reaction sites are reduced. More importantly, when the doping amount is low, even if the number of carriers generated by BiOI is sufficient, their lifetime will be short because there is not enough heterojunction to transport and separate electron holes.

[0025] Figure 5 :(a) 520nm wavelength light and 25ppb-1ppm NO 2 Resistance change curves of 1.0at% BiOI-ZnO, 1.5at% BiOI-ZnO composite materials, and Pure ZnO under concentration conditions; (b) is the sensitivity-gas concentration curves of the three composite materials after linear fitting.

[0026] The definition of sensitivity is: Sensitivity = Sensitivity of sensitive electrode material in NO 2 Resistance value in medium / Resistance value in air.

[0027] from Figure 5 It can be seen that NO 2 As an oxidizing gas, it can obtain electrons from n-type semiconductors, which will increase the resistance of the sensor. This also shows that the ZnO material is the main gas sensing part. It can be seen that the sensor of the present invention can detect NO with a concentration of ppb at room temperature. 2 .

[0028] Figure 6 :1.5at%BiOI-ZnO for oxidizing gas (NO 2 ) or reducing gases (ammonia, carbon monoxide, triethylamine, ethanolamine and ethanol).

[0029] Due to the low activation energy required at room temperature, NO 2 Molecules are easily adsorbed on the ZnO surface, so the sensor is sensitive to NO 2 There are good options. DETAILED DESCRIPTION

[0030] Embodiment 1:

[0031] 1. First, 0.073 g of hexadecyltrimethylammonium bromide and 1.92 g of sodium hydroxide were mixed in 15 mL of deionized water, and then 2.32 g of zinc nitrate hexahydrate was added to the solution. After stirring for 1.0 h, the solution was poured into a polytetrafluoroethylene liner in a stainless steel autoclave, heated to 90 ° C for 15 h, and the obtained precipitate was washed three times by alternating centrifugation with ethanol-deionized water, dried at 80 ° C, and then calcined at 400 ° C for 2.0 h to obtain ZnO pure phase nanorods.

[0032] 2. Add 0.081g of the prepared ZnO nanorods to 30mL of deionized water and stir to obtain solution A. According to the atomic ratio of Bi:Zn and I:Zn = 1.5:100, dissolve the corresponding mass of bismuth nitrate pentahydrate and potassium iodide in 20mL and 10mL of ethylene glycol respectively. Then, add the bismuth nitrate solution dropwise to solution A, stir for 20min, and then add the potassium iodide solution dropwise to solution A and stir for 1.0h. Finally, centrifuge the obtained solution, and dry the centrifugal product at 60℃ for 12h to obtain BiOI / ZnO nanorod heterostructure composite material, which is named 1.5at%BiOI-ZnO according to the different BiOI contents.

[0033] 3. The ceramic substrate with Au metal interdigital electrodes on the upper surface was placed in acetone, ethanol, and deionized water, respectively, and ultrasonically cleaned for 25 minutes, and then dried at 60°C. The Au metal interdigital electrodes consisted of twelve pairs of interdigits (100 μm in width, 50 μm in spacing, and 10 μm in thickness), and the length and width of the ceramic substrate were both 10 mm, and the thickness was 0.38 mm.

[0034] 4. Dissolve 15 mg of BiOI / ZnO nanorod heterostructure composite material in 4 mL of ethanol, mix well and apply it on the cleaned ceramic substrate with Au metal interdigital electrodes with a fine brush, so that the composite material completely covers the Au metal interdigital electrodes and the ceramic substrate; then heat treat at 80°C for 15 minutes to evaporate all the ethanol. Finally, place the ceramic substrate covered with the sensitive material in a tubular furnace and calcine at 300°C for 2.0 hours, and introduce argon as a protective gas, and finally obtain room temperature NO based on BiOI / ZnO nanorod heterostructure composite material. 2 sensor.

[0035] 6. Connect the two ends of the Au metal interdigital electrode to the test system to test the sensor, and illuminate it with an LED lamp bead at a distance of 1.5 cm from the sensor, and record the room temperature gas sensor based on the BiOI / ZnO nanorod heterostructure composite material for NO 2 Gas sensitive response characteristic data.

[0036] Embodiment 2:

[0037] BiOI / ZnO was prepared according to the method of Example 1, and the atomic ratios of Bi:Zn and I:Zn were changed to 1.0%. The obtained BiOI / ZnO nanorod heterostructure composite material was marked as 1.0at%BiOI-ZnO. The device preparation method and test method were consistent with Example 1.

[0038] Embodiment 3:

[0039] BiOI / ZnO was prepared according to the method of Example 1, and the atomic ratios of Bi:Zn and I:Zn were changed to 2.0%. The obtained BiOI / ZnO nanorod heterostructure composite material was marked as 2.0at%BiOI-ZnO. The device preparation method and test method were consistent with Example 1.

[0040] Embodiment 4:

[0041] BiOI / ZnO was prepared according to the method of Example 1, and the atomic ratios of Bi:Zn and I:Zn were changed to 3.0%. The obtained BiOI / ZnO nanorod heterostructure composite material was marked as 3.0at%BiOI-ZnO. The device preparation method and test method were consistent with those of Example 1.

[0042] Comparative Example 1:

[0043] Pure phase ZnO nanorods were prepared according to the method described in Example 1, and then a sensor based on the pure phase ZnO nanorods was prepared. The device preparation method and the test method were consistent with those in Example 1.

Claims

1. A room temperature NO based on BiOI / ZnO nanorod heterostructure composite 2 sensor, Features: The invention is composed of a ceramic substrate with Au metal interdigital electrodes on the upper surface and a sensitive material coated on the Au metal interdigital electrodes and the upper surface of the ceramic substrate, wherein the sensitive material is a BiOI / ZnO nanorod heterostructure composite material, and is prepared by the following steps: (1) 0.073 g of hexadecyltrimethylammonium bromide and 1.92 g of sodium hydroxide were mixed in 10-20 mL of deionized water, 2.32 g of zinc nitrate hexahydrate was added, and then stirred for 0.5-1.5 h; the obtained solution was poured into a polytetrafluoroethylene inner liner in a stainless steel autoclave, heated to 85-95° C. and reacted for 14-16 h; the obtained precipitate was washed alternately by centrifugation with ethanol and deionized water for 3-5 times, dried at 75-85° C., and then calcined at 350-450° C. for 1.5-2.5 h, thereby obtaining ZnO nanorods; (2) adding 0.081 g of the ZnO nanorods prepared in step (1) into 25-35 mL of deionized water and stirring to obtain a solution A; dissolving bismuth nitrate pentahydrate and potassium iodide in 15-25 mL and 9-11 mL of ethylene glycol, respectively, and then adding the bismuth nitrate solution dropwise into the solution A and stirring for 15-25 min; then adding the potassium iodide solution dropwise into the solution A and stirring for 0.5-1.5 h; wherein the atomic ratio of Bi to I is 1:1, and the atomic ratio of Bi or I to Zn is 1-3:100; finally, centrifuging the obtained solution, and drying the centrifuged product at 50-70° C. for 11-13 h, thereby obtaining a BiOI / ZnO nanorod heterostructure composite material.

2. A room temperature NO based on BiOI / ZnO nanorod heterostructure composite material according to claim 1 2 The preparation method of the sensor comprises the following steps: (1) placing a ceramic substrate with Au metal interdigital electrodes on the upper surface in acetone, ethanol, and deionized water, respectively, ultrasonically cleaning for 15 to 30 minutes, and then drying at 50 to 70° C.; (2) dissolving 10-20 mg of the BiOI / ZnO nanorod heterostructure composite material in 2-5 mL of ethanol, mixing well, and applying the mixture on the ceramic substrate obtained in step (1) with a fine brush, so that the composite material completely covers the Au metal interdigital electrode and the upper surface of the ceramic substrate; then heat treating the mixture at 70-90° C. for 10-20 min to evaporate all the ethanol; finally, calcining the ceramic substrate at 260-330° C. for 1.5-2.5 h, and introducing argon as a protective gas, thereby obtaining a room temperature NO based on the BiOI / ZnO nanorod heterostructure composite material. 2 sensor.

3. A room temperature NO based on BiOI / ZnO nanorod heterostructure composite material according to claim 1 2 The sensor can detect NO at ppb concentration at room temperature. 2 Application in rapid testing.

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