Room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure and preparation method thereof

Abstract

The invention discloses a room-temperature NO2 gas sensor based on a ZnSe-ZnS heterostructure and a preparation method thereof, and relates to the technical field of gas sensing, the room-temperature NO2 gas sensor comprises an Al2O3 substrate electrode and the ZnSe-ZnS heterostructure, and the ZnSe-ZnS heterostructure is coated on the Al2O3 substrate electrode to form the NO2 gas sensor; the ZnSe-ZnS heterostructure comprises a zinc selenide nanosheet substrate and zinc sulfide nanoparticles modified on the surface of the zinc selenide nanosheet substrate; according to the invention, ZnS nanoparticles are creatively adopted to modify ZnSe nanosheets to construct a heterostructure, and the design has the following advantages: firstly, the ZnS nanoparticles can effectively regulate and control electron distribution on the surface of ZnSe to form more active sites; secondly, energy band matching at a heterogeneous interface is beneficial to charge transfer, and the response sensitivity of the material to target gas is improved; and finally, the common agglomeration problem of the monatomic catalyst can be avoided through nano-particle modification, and the stability of the material is ensured.

Description

Technical Field

[0001] This invention relates to the field of gas sensing technology, specifically to a room temperature NO2 gas sensor based on a ZnSe-ZnS heterostructure and its preparation method. Background Technology

[0002] With the rapid development of modern industry, air pollution has become increasingly serious, especially the emission of toxic gases such as nitrogen dioxide (NO2), which has posed a serious threat to the environment and human health. NO2 not only causes acid rain and photochemical smog, but long-term exposure can also lead to respiratory diseases. Currently, the U.S. Environmental Protection Agency (EPA) and the European Union have set annual average concentration limits for NO2 at 53 ppb and 40 ppb, respectively, which places higher demands on gas detection technologies.

[0003] Traditional semiconductor metal-oxide (MOS) gas sensors, while offering advantages such as low cost and fast response, still face two major technical bottlenecks: firstly, their operating temperature is too high (200-600℃), leading to high energy consumption and safety hazards; secondly, their selectivity is poor, making them susceptible to cross-interference from other gases. These problems severely limit their application in portable detection devices. Therefore, this invention designs a room-temperature NO2 gas sensor based on a ZnSe-ZnS heterostructure and its fabrication method to solve the aforementioned problems. Summary of the Invention

[0004] The purpose of this invention is to provide a room temperature NO2 gas sensor based on a ZnSe-ZnS heterostructure and its preparation method, so as to solve the problems existing in the prior art mentioned in the background.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A room temperature NO2 gas sensor based on a ZnSe-ZnS heterostructure includes an Al2O3 substrate electrode and a ZnSe-ZnS heterostructure, wherein the ZnSe-ZnS heterostructure is coated on the Al2O3 substrate electrode to form the NO2 gas sensor. The ZnSe-ZnS heterostructure comprises a zinc selenide nanosheet substrate and zinc sulfide nanoparticles modified on the surface of the zinc selenide nanosheet substrate.

[0006] Preferably, the loading of the zinc sulfide nanoparticles is 1-10 wt%.

[0007] Preferably, the mass ratio of ZnSe to ZnS is in the range of 1:2 to 1:10.

[0008] Preferably, the room temperature NO2 gas sensor has a response value R of 10 ppm NO2 gas at room temperature. a / Rg ≥8, the response time to NO2 gas does not exceed 24 seconds, and the recovery time does not exceed 78 seconds.

[0009] This invention also provides a method for preparing a room temperature NO2 gas sensor based on a ZnSe-ZnS heterostructure, comprising the following steps: S1: Preparation of precursor solution: Na2S·9H2O and Zn(CH3COO)2·2H2O were dissolved in deionized water, and ZnS precursor solution was generated by ultrasonic dispersion and magnetic stirring. S2: ZnSe-ZnS heterostructure construction: ZnSe nanosheets were ultrasonically dispersed in deionized water and then a ZnS precursor solution was added for in-situ deposition reaction. S3: Annealing treatment, low-temperature annealing treatment, to obtain ZnSe-ZnS heterostructure; S4: Gas sensor fabrication: Annealed ZnSe-ZnS heterojunction material is coated onto an Al2O3 substrate electrode and dried to prepare a gas sensor.

[0010] Preferably, in S1, the weight ratio of Na2S·9H2O and Zn(CH3COO)2·2H2O is 0.8:1 to 1.2:1, and the reaction time is 2 hours.

[0011] Preferably, the low-temperature annealing temperature in S3 is set to 100℃-150℃.

[0012] Preferably, in step S4, the drying parameters are set to 60°C for 5 hours.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention innovatively uses ZnS nanoparticles to modify ZnSe nanosheets to construct a heterostructure. This design has the following advantages: First, ZnS nanoparticles can effectively regulate the electron distribution on the ZnSe surface, forming more active sites; second, the band matching at the heterostructure interface is conducive to charge transfer, improving the material's response sensitivity to the target gas; finally, nanoparticle modification can avoid the agglomeration problem common in single-atom catalysts, ensuring the stability of the material.

[0014] 2. The band gap difference between the two materials in the ZnSe-ZnS heterostructure of this invention (ZnSe approximately 2.7 eV, ZnS approximately 3.7 eV) forms a type II band arrangement. This structure is beneficial for the separation and transport of photogenerated carriers. Experiments show that by precisely controlling the loading of ZnS nanoparticles (1-10 wt%), the best NO2 sensing performance can be obtained, exhibiting high sensitivity and fast response characteristics at room temperature. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the gas sensor fabrication method based on the ZnSe-ZnS heterostructure of the present invention.

[0016] Figure 2 The images show the Raman spectra of the ZnSe-ZnS heterostructure of this invention: (a) ZnSe nanosheets; (b) ZnS nanoparticles; and (c) ZnSe-ZnS heterostructure.

[0017] Figure 3 The X-ray diffraction analysis diagrams of the ZnSe-ZnS heterostructure of the present invention are shown in (a) ZnSe-ZnS heterostructure and (b) ZnS nanoparticles.

[0018] Figure 4 The X-ray photoelectron spectrum of the ZnSe-ZnS heterostructure of this invention is shown in (a) Zn element; (b) Se element; (c) S element.

[0019] Figure 5 The following are the gas-sensing performance of the sensitive layer in Example 1 at room temperature for different concentrations of NO2, including: (a) dynamic response of 0.5-10 ppm NO2 gas; (b) response vs concentration fitting graph; (c) response and recovery time graph of 10 ppm NO2 gas; and (d) repeatability graph of 10 ppm NO2 gas. Detailed Implementation

[0020] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0021] Please see Figure 1-5 The present invention provides the following technical solutions: Example 1 like Figure 1 As shown in the figure, this embodiment provides a method for fabricating a room temperature NO2 gas sensor based on a ZnSe-ZnS heterostructure. The specific steps are as follows: S1: Preparation of ZnS precursor solution S11: Under room temperature conditions, accurately weigh 246 mg Na2S·9H2O (analytical grade, ≥99%) and 225 mg Zn(CH3COO)2·2H2O (analytical grade, ≥99%) powders using an electronic balance, dissolve them separately in 25 mL of deionized water, and ultrasonically disperse (power 100 W, frequency 40 kHz) for 1 h until completely dissolved; S12: Mix the two solutions in a 50 mL beaker and stir magnetically (500 r / min) for 2 hours to obtain a colorless and transparent ZnS precursor solution.

[0022] S2: Preparation of ZnSe / ZnS heterostructure S21: Weigh 100 mg of ZnSe nanosheets (purity 99.99%) at room temperature, disperse them in 20 mL of deionized water, and sonicate (150 W, 30 minutes) to form a uniform ZnSe dispersion. S22: Under magnetic stirring (500 r / min), 10 mL of ZnS precursor solution was added dropwise to ZnSe dispersion. After the addition was complete, stirring was continued for 2 hours. S23: After the reaction is complete, let the solution stand until it is clearly separated into layers, then centrifuge at 7000 r / min for 3 minutes, remove the supernatant, and wash it three times alternately with ultrapure water and anhydrous ethanol (analytical grade, ≥99.7%) to obtain ZnSe / ZnS precipitate.

[0023] S3: Annealing treatment S31: Transfer the obtained precipitate to a crucible, place it in an oven, and heat it to 100°C at 5°C / min in an air atmosphere, and keep it at that temperature for 2 hours; S32: After natural cooling, ZnSe / ZnS heterostructure powder is obtained.

[0024] S4: Fabrication of Gas Sensor Devices S41: Take 5 mg of ZnSe-ZnS powder and grind it with 0.5 mL of anhydrous ethanol in a mortar to form a uniform slurry; S42: The paste is coated onto the surface of a pretreated Al2O3 ceramic substrate (size 10 mm × 5 mm, pre-printed gold interdigitated electrodes, electrode spacing 0.2 mm) using a screen printing process, with a coating thickness of approximately 50 μm. S43: Place the coated substrate in a drying oven and dry at 60°C for 5 hours to obtain a gas sensor.

[0025] Characterization of sensor material structure: like Figure 2 As shown, Raman spectroscopy was used to characterize the properties of ZnSe, ZnS, and ZnSe-ZnS heterostructures. Three distinct characteristic peaks were observed in the ZnSe nanosheet region (…). Figure 2 (a) is located at 137.6 cm. -1 203.5 cm -1 and 251.0 cm -1 This corresponds to the 2TA, TO, and LO phonon modes of ZnSe. In the ZnS nanoparticle region, a phonon mode located at 217.6 cm⁻¹ appears. -1 349.7cm -1 and 659.2cm -1 The three characteristic peaks ( Figure 2(b) corresponds to the 2LA, LO, and 2LO vibrational modes of ZnS, respectively. Further analysis of the Raman spectrum of the ZnSe-ZnS heterojunction region ( Figure 2 (c) The characteristic peaks of ZnSe and ZnS can be observed simultaneously, indicating that the material properties of ZnSe and ZnS did not change significantly after the formation of the heterojunction.

[0026] like Figure 3 As shown in (a), X-ray diffraction (XRD) analysis of the ZnSe-ZnS heterostructure shows that the diffraction peaks at 2θ values ​​of 27.2°, 45.2°, 53.6°, 65.8° and 72.9° correspond to the (111), (220), (311), (400) and (331) crystal planes of ZnSe (JCPDS 37-1463). Figure 3 (b) shows the diffraction peaks of ZnS at 2θ values ​​of 29.4°, 48.2°, and 56.6°, corresponding to the (111), (220), and (311) crystal planes of ZnS (JCPDS 36-1450), respectively. These diffraction peaks are consistent with the diffraction peaks of ZnS in the ZnSe / ZnS heterostructure, further proving the good formation of the ZnSe / ZnS heterostructure.

[0027] like Figure 4 As shown, XPS analysis of the ZnSe-ZnS heterojunction reveals detailed information about the elemental composition, chemical state, and inter-element interactions on the material surface. In the XPS spectrum of the ZnSe-ZnS heterojunction, the characteristic peaks of Zn are located at 1022.2 eV and 1045.2 eV, respectively, and are attributed to Zn 2p2. 3 / 2 and Zn 2p 1 / 2 Two characteristic peaks ( Figure 4 (a)). For the Se element, its characteristic peaks appear at 54.8 eV and 53.9 eV, respectively, corresponding to Se 3d. 3 / 2 and Se 3d 5 / 2 ( Figure 4 (b) Furthermore, the characteristic peaks of the S element are located at 162.2 eV and 163.6 eV, which are attributed to S 2p, respectively. 3 / 2 and S 2p 1 / 2 ( Figure 4 (c) This further indicates that the chemical states of Se and S are Se and S, respectively. 2- and S 2- .

[0028] Gas sensor performance test conditions: a) The CGS-MT optoelectronic integrated test platform was used during the test, the background gas was high-purity dry air, and the humidity was maintained at <1% RH; b) Before testing, the sensor was placed in a sealed chamber with a volume of 100 ml and purged with 300 sccm of high-purity air until the baseline resistance (Ra) stabilized with a fluctuation range not exceeding ±0.5%; c) The target gas NO2 is mixed with high-purity air through a mass flow meter, and the concentration gradient is adjusted to 0.5 ppm, 1 ppm, 3 ppm, 5 ppm and 10 ppm.

[0029] Analysis of sensor performance test results: like Figure 5 As shown in (a), the sensor based on the ZnSe-ZnS heterostructure exhibits excellent NO2 response characteristics at room temperature. As the NO2 concentration increases from 0.5 ppm to 10 ppm, the sensor resistance (R0) increases. g The response (R0) exhibits a regular decreasing trend. It is noteworthy that at a NO2 concentration of 10 ppm, the sensor (prepared in Example 1) shows a responsivity (R0). a / R g The performance index reached 8.9, a figure significantly higher than that of conventional room temperature gas sensors. Figure 5 As shown in (b), the sensor exhibits a good linear correlation between its responsivity and gas concentration within the NO2 concentration range of 0.5-10 ppm (fitting equation: y=0.83x+1.04, R²=0.963), indicating that the sensor has reliable quantitative detection capabilities. Furthermore, the sensor's theoretical detection limit is as low as 14 ppb, meeting EPA standards. Figure 5 As shown in (c), the sensor's response time to 10 ppm NO2 at room temperature is only 24 seconds, and its recovery time is 78 seconds. Its response and recovery rates are close to those of traditional metal oxide sensors that require high-temperature operation, and far exceed the response levels of similar room-temperature sensitive materials. Furthermore, as... Figure 5 As shown in (d), repeatability tests were performed on the same sensor (prepared in Example 1) with a NO2 gas concentration of 10 ppm and a flow rate of 300 sccm. Each test included a complete response-recovery process (introducing NO2 until the resistance stabilizes → switching to high-purity air until the baseline is restored). After 5 consecutive cycles of testing, the sensor's response value deviation was controlled within ±5%, indicating that the sensor has excellent repeatability.

[0030] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure, characterized in that, The NO2 gas sensor comprises an Al2O3 base electrode and a ZnSe-ZnS heterostructure coated on the Al2O3 base electrode; The ZnSe-ZnS heterostructure comprises a zinc selenide nanosheet substrate and zinc sulfide nanoparticles modified on the surface of the zinc selenide nanosheet substrate.

2. A room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure according to claim 1, characterized in that: The loading amount of the zinc sulfide nanoparticles is 1-10 wt%.

3. The room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure according to claim 1, wherein: The mass ratio of ZnSe and ZnS ranges from 1:2 to 1:

10.

4. The room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure according to claim 1, characterized in that: The room temperature NO2 gas sensor has a response value R to 10 ppm concentration of NO2 gas under room temperature conditions a / R g ≥ 8, a response time to NO2 gas not more than 24 seconds, and a recovery time not more than 78 seconds.

5. A method for preparing a room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure according to any one of claims 1-4, characterized in that, The method comprises the following steps: S1: Preparation of a precursor solution, Na2S·9H2O and Zn(CH3COO)2·2H2O are respectively dissolved in deionized water, and a ZnS precursor solution is generated through ultrasonic dispersion and magnetic stirring reaction; S2: Construction of a ZnSe-ZnS heterostructure, ZnSe nanosheets are ultrasonically dispersed in deionized water, and then a ZnS precursor solution is added for in-situ deposition reaction; S3: Annealing treatment, low-temperature annealing treatment is performed to obtain a ZnSe-ZnS heterostructure; S4: Preparation of a gas sensor, the annealed ZnSe-ZnS heterojunction material is coated on an Al2O3 base electrode, and a gas sensor is prepared after drying treatment.

6. The method for preparing a room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure according to claim 5, characterized in that: In S1, the weight ratio of Na2S·9H2O and Zn(CH3COO)2·2H2O is 0.8:1-1.2:1, and the reaction time is 2 h.

7. The method for preparing a room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure according to claim 5, characterized in that: In S3, the low-temperature annealing treatment temperature is set to 100-150℃.

8. The method for preparing a room temperature NO2 gas sensor based on ZnSe-ZnS heterostructure according to claim 5, characterized in that: In S4, the drying treatment parameters are set to 60℃ drying for 5 h.

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