Unsymmetrical dimethylhydrazine sensor based on Pt cluster loaded WO3 nanosheet sensitive material prepared by atomic layer deposition and preparation method of unsymmetrical dimethylhydrazine sensor

Abstract

The invention discloses an unsymmetrical dimethylhydrazine sensor of a Pt cluster loaded WO3 nanosheet sensitive material prepared based on atomic layer deposition and a preparation method of the unsymmetrical dimethylhydrazine sensor, and belongs to the technical field of semiconductor metal oxide gas sensors. The preparation method comprises the following steps: performing hydro-thermal synthesis on a WO3 nanosheet sensitive material by using sodium tungstate dihydrate, concentrated hydrochloric acid and citric acid monohydrate, and then preparing the Pt cluster-loaded WO3 nanosheet sensitive material by using trimethyl (methyl cyclopentadienyl) platinum (IV) as a Pt precursor and tert-butylhydrazine as a reducing agent and using an atomic layer deposition method. The material has high response (96.6-50ppm) and fast response recovery time (2 / 118s) to low-concentration UDMH gas under the working condition of 200 DEG C. The commercially available indirectly-heated structure sensor is simple in manufacturing process, small in size and beneficial to industrial batch production, has important application value and has wide application prospects in the aspect of UDMH detection in a specific environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor metal oxide gas sensors, and in particular relates to an unsymmetrical dimethylhydrazine sensor based on a Pt cluster-loaded WO3 nanosheet sensitive material prepared by atomic layer deposition and a preparation method thereof. Background Art

[0002] Unsymmetrical dimethylhydrazine (UDMH), also known as 1,1-dimethylhydrazine and 1,1-dimethylhydrazine, has the chemical formula C2H8N2 and is a primary fuel for missiles, satellites, spacecraft, and launch vehicles. However, UDMH is a volatile liquid that is flammable, explosive, and highly toxic, and is classified as a Class 2B carcinogen by the International Agency for Research on Cancer. As a strong reducing agent, UDMH is easily oxidized in air to produce a variety of toxic nitrogen-containing products. Therefore, to protect the environment and human health, real-time monitoring and detection of UDMH leaks during storage and transportation is necessary.

[0003] In recent years, there have been many studies on the detection of UDMH in water and soil, but there are not many studies on the monitoring and detection of UDMH in the air. Most of the methods reported in recent years for detecting UDMH in the air are gas chromatography / mass spectrometry. These methods require complex and bulky equipment and are time-consuming, and cannot achieve real-time monitoring of UDMH gas concentration. On the contrary, gas sensors can achieve real-time monitoring and detection of specific gases due to their advantages such as small size, simple manufacturing methods and easy integration. Among the many types of gas sensors, resistive gas sensors with semiconductor metal oxides as sensitive materials have the advantages of high response value, high stability, good selectivity, fast response and recovery speed, and low cost. They are currently one of the most widely used gas sensors.

[0004] Tungsten oxide (WO3) is a common wide-bandgap n-type semiconductor with a bandgap of 2.5 to 2.8 eV. Due to its low cost, green and non-toxic properties, and excellent thermal and environmental stability, it is a hot material in the fields of photocatalysis and water splitting. In the field of gas sensing, it is also commonly used by researchers to detect reducing gases such as hydrogen (H2), ammonia (NH3), and acetone. There are many studies on improving the gas-sensing properties of WO3 nanomaterials by loading them with precious metals (such as Au, Ag, Pt, and Pd). Therefore, the preparation of Pt-loaded WO3 nanomaterials has the potential to be used as a sensing material for high-performance UDMH detection equipment. Summary of the Invention

[0005] The present invention aims to provide a UDMH sensor based on Pt cluster-loaded WO3 nanosheet sensitive material prepared by atomic layer deposition and a preparation method thereof.

[0006] The present invention firstly uses sodium tungstate dihydrate (Na2WO4·2H2O), concentrated hydrochloric acid (HCl) and citric acid monohydrate (C6H8O7·H2O) to hydrothermally synthesize WO3 nanosheet sensitive material, and then uses trimethyl (methylcyclopentadienyl) platinum (IV) (MeCpPtMe3) as Pt precursor, tert-butyl hydrazine (C4H 12 Using nitrogen (N2) as a reducing agent, a Pt cluster-loaded WO3 nanosheet sensor was prepared via atomic layer deposition (ALD). This material exhibits a high response (96.6-50 ppm) to low-concentration UDMH gas at 200°C and a fast response recovery time (2 / 118s). The commercially available indirectly heated sensor employed in this invention boasts a simple fabrication process and a compact size, making it suitable for industrial mass production. It possesses significant application value and holds broad promise for detecting UDMH in specific environments.

[0007] The present invention discloses a Pt cluster-loaded WO3 UDMH sensor prepared based on atomic layer deposition, which comprises an Al2O3 ceramic substrate with a pair of interdigitated gold electrodes on the upper surface and a RuO2 heating electrode on the lower surface, and a Pt cluster-loaded WO3 nanosheet sensitive material coated on the upper surface of the Al2O3 flat ceramic substrate and the interdigitated gold electrodes.

[0008] The method for preparing a UDMH sensor based on atomic layer deposition of Pt clusters loaded with WO3 nano-sensitive materials described in the present invention comprises the following steps:

[0009] (1) Add 0.6-0.7 g of Na2WO4·2H2O and 0.3-0.5 g of C6H8O7·H2O to 30-40 mL of deionized water and stir continuously at room temperature for 15-25 minutes;

[0010] (2) adding 2-4 mL of 36-38% HCl to the solution obtained in step (1) and stirring thoroughly for 25-35 minutes;

[0011] (3) The solution obtained in step (2) was transferred to a hydrothermal reactor, maintained at 130-150° C. for 10-14 hours, taken out, naturally cooled to room temperature, and filtered. The obtained precipitate was washed by centrifugation with deionized water and anhydrous ethanol several times, and then dried at room temperature; the obtained powder was calcined in air at 350-450° C. for 1.5-2.5 hours, and cooled to room temperature to obtain 0.3-0.5 g of WO3 nanosheet sensitive material;

[0012] (4) taking 40-60 mg of the WO3 nanosheet sensitive material obtained in step (3) and adding it to 200-300 μL of anhydrous ethanol solution and stirring at room temperature for 6-10 hours;

[0013] (5) The mixed solution obtained in step (4) was spin-coated on the upper surface of an Al2O3 ceramic substrate having a pair of interdigitated gold electrodes on the upper surface and a RuO2 heating electrode on the lower surface, dried at room temperature, and placed in a heat-sealed ALD chamber; Pt was loaded using the ALD method, wherein the Pt precursor was MeCpPtMe3 and the reducing agent was C4H 12 N2, high-purity N2 is used as carrier gas and purge gas; during this process, the temperature of the reaction chamber is 180-220°C, the preheat temperature of the Pt precursor and the reducing agent is 60-80°C, and the chamber is in a vacuum state; each ALD cycle includes 'MeCpPtMe3 pulse 0.5-1.5s'-'exposure 15-25s'-'N2 purge 20-30s'-'tert-butylhydrazine pulse 0.5-1.5s'-'exposure 15-25s'-'N2 purge 20-30s', and a total of 4-6 cycles are performed, and the obtained sensitive layer thickness is 4-8μm;

[0014] (6) The Al2O3 ceramic substrate is taken out, and then welded and packaged according to the indirect heating gas sensor, thereby obtaining the Pt cluster-loaded WO3 nano-sensitive material prepared based on atomic layer deposition.

[0015] The Al2O3 flat ceramic sheet is square, with a side length of 2 to 5 mm and a thickness of 0.2 to 0.5 mm; the width of the interdigitated gold electrode is 0.3 to 0.6 mm, the interdigital spacing is 0.5 to 2.0 mm, and the gap distance between adjacent interdigits is 0.2 to 0.4 mm; platinum wires are led out from the interdigitated gold electrodes and the heating electrodes, and their length is 3 to 6 mm.

[0016] The present invention has the following advantages:

[0017] 1. The Pt cluster-loaded WO3 nanosheet sensitive material was successfully prepared using a simple hydrothermal method and atomic layer deposition method. The synthesis method is simple;

[0018] 2. By loading a small amount of Pt clusters on the surface of the WO3 material, the WO3-based sensor's response to UDMH was significantly improved (96.6-50 ppm) and the response time was reduced (2 s). The sensor also exhibited excellent selectivity and long-term stability, and has broad application prospects in detecting low-concentration UDMH gas in specific environments.

[0019] 3. Using commercially available planar chip sensors, the device process is simple, the size is small, and it is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the upper and lower surface structures of the sensor according to the present invention;

[0021] Figure 2XRD patterns of pure WO3 and Pt-WO3 sensitive materials prepared in Comparative Example 1 and Example 1;

[0022] Figure 3 (a), (b) and (c) are SEM morphologies of pure WO3 sensitive materials; (d) is the SEM morphology of Pt-WO3 sensitive materials;

[0023] Figure 4 (a), (b) and (c) are low-magnification TEM, high-magnification TEM and HRTEM images of Pt-WO3 sensitive materials, respectively;

[0024] Figure 5 (a), (b), (c) and (d) are the XPS total spectra, W 4f XPS spectra, O1s XPS spectra and Pt 4f XPS spectra of pure WO3 and Pt-WO3 sensitive materials, respectively;

[0025] Figure 6 : Response curves of the sensors in Comparative Example 1 and Example 1 to 50 ppm UDMH gas at different operating temperatures;

[0026] Figure 7 : A bar graph showing the response values ​​of the sensor to 8 gases to be tested in Example 1;

[0027] Figure 8 (a) and (b) are the dynamic resistance curves of the sensor in comparative example 1 and example 1 at the optimal operating temperature (200°C) in 50ppm UDMH gas over time;

[0028] Figure 9 The dynamic response curve of the sensor in Example 1 at the optimal operating temperature (200°C) in 50 ppb to 100 ppm UDMH gas changes with time;

[0029] Figure 10 (a) and (b) are the response value-UDMH concentration characteristic curves of the sensor in Example 1 at the optimal working temperature (200°C);

[0030] Figure 11 : Six-time repeatability curve of the sensor in Example 1 at 200°C for 50 ppm UDMH;

[0031] Figure 12 : Response value-humidity and baseline resistance-humidity characteristic curves of the sensor in Example 1 at different humidity levels to 50 ppm UDMH at 200° C.;

[0032] Figure 13 : The long-term stability curve of the resistance value in air and the response value to 50 ppm UDMH gas in Example 1 when the sensor is operated at 200°C;

[0033] like Figure 1 As shown, the side length of the Al2O3 square flat ceramic plate is 3mm and the thickness is 0.25mm; the width of the gold electrode is 0.45mm, the interdigital spacing is 1mm, and the gap distance between adjacent interdigits is 0.3mm; the length of the platinum wire led out from the gold electrode is 5mm; there is a heating electrode at the bottom;

[0034] like Figure 2 As shown, the XRD spectra of pure WO3 and Pt-WO3 are consistent with the WO3 standard card 43-1035;

[0035] like Figure 3 As shown, the SEM image shows that the morphology of the pure WO3 sensitive material is a rectangular nanosheet with a length and width of approximately 214 and 256 nm and a thickness of approximately 40 nm. In addition, there is almost no difference in morphology between Pt-WO3 and pure WO3, indicating that the supported precious metal Pt is small in size and is not obvious in the SEM image.

[0036] like Figure 4 The TEM image of the Pt-WO3 nanomaterial shows that the morphology of the main body of the material is consistent with the SEM image. The high-magnification TEM image shows the presence of Pt clusters, the size of which is 1 to 2 nm. The HRTEM image shows a lattice spacing of 0.262 nm, which is consistent with the (202) crystal plane of WO3.

[0037] like Figure 5 As shown in (a), it can be seen from the XPS total spectrum that there are only signals of W, O and corrected C elements in the spectrum of each sample, and no obvious Pt peak is found in Pt-WO3, indicating that the Pt loading is low; Figure 5 As shown in (b), the two characteristic peaks of W 4f of the two samples correspond to 4f 5 / 2 and 4f 7 / 2 The two characteristic peaks in each sample were deconvoluted into four characteristic peaks by Gaussian fitting. The two fitting peaks at 37.3 and 35.2 eV were derived from W 6+ , and the two fitting peaks at 36.3 and 34.0 eV are derived from W 5+ ;like Figure 5 As shown in (c), the O1s high-resolution spectra in the two samples were Gaussian fitted and deconvoluted into two peaks: lattice oxygen (O lat ) and chemically adsorbed oxygen (O ads ). Compared with pure WO3, the O ads Higher content; such as Figure 5(d) shows the high-resolution spectra of Pt 4f of the two samples. The characteristic peak at 79.0 eV corresponds to W 5s, while the characteristic peak at 74.2 eV in the Pt-WO3 sample comes from the elemental Pt (Pt 0 ), which is consistent with the Pt clusters analyzed in TEM characterization;

[0038] like Figure 6 As shown, the optimal operating temperature of the sensors in Example 1 and Comparative Example 1 is 200°C. At the optimal operating temperature, the response values ​​of the devices in Example 1 and Comparative Example 1 to 50 ppm UDMH are 96.6 and 3.1, respectively; compared with the sensor in Comparative Example 1, the response value of the sensor in Example 1 is 30.2 times higher;

[0039] like Figure 7 As shown, the sensor in Example 1 has the highest response to UDMH, which is much higher than the response to toluene, xylene, methanol, ethanol, isopropanol, formaldehyde and acetone, indicating that the sensor in Example 1 has good selectivity for UDMH gas.

[0040] like Figure 8 As shown in (a), the response recovery curve of the sensor in Comparative Example 1 to 50ppm UDMH gas at an operating temperature of 200°C is relatively smooth, with a response time of 3s and a recovery time of 8s; Figure 8 As shown in (b), the response recovery curve of the sensor in Example 1 to 50 ppm UDMH at an operating temperature of 200°C is relatively smooth, with a response time of 2s, a recovery time of 118s, and a high response value;

[0041] like Figure 9 As shown, the sensor in Example 1 exhibits excellent response and recovery characteristics to UDMH at different concentrations (50 ppb to 100 ppm);

[0042] like Figure 10 As shown, the sensor in Example 1 has a good sensitivity-concentration linear fitting relationship for low concentration (0.05-2ppm) and high concentration (2-100ppm) of UDMH, corresponding to Figure 10 (a) and Figure 10 (b);

[0043] like Figure 11 As shown, the sensor in Example 1 exhibited consistent response recovery characteristics in six 50ppm UDMH gas tests, indicating that the sensor in Example 1 had good repeatability for UDMH gas;

[0044] like Figure 12 As shown in the figure, with the increase of humidity, the sensitivity and baseline resistance of the sensor in Example 1 to UDMH gas decrease. Under the humidity conditions of 18.7%, 43.6%, 54.5%, 69.3% and 85.1%, the sensitivity of the sensor in Example 1 to 50ppm UDMH gas is 104.2, 93.0, 87.2, 85.9 and 80.5 respectively; the baseline resistance of the sensor in Example 1 is 9.8, 6.3, 5.9, 5.4 and 4.9 MΩ respectively;

[0045] like Figure 13 As shown, in the detection for 10 consecutive days, the response and baseline resistance fluctuation of the sensor in Example 1 operating at 200° C. to 50 ppm UDMH gas were small, and the sensor could maintain high sensitivity to UDMH gas for a long time.

[0046] Note: In the present invention, the response value of the device (N-type semiconductor) in the test reducing gas is defined as the ratio of the resistance (R a / R g ), where R a Indicates the resistance between two gold electrodes in air (R a ), and R g Indicates the resistance value between the two gold electrodes in the gas to be measured (R g During the test, a static test system was used. The device was placed in a 1L gas cylinder, a certain amount of the VOC to be tested was injected, and the resistance change was observed and recorded. The corresponding response value was calculated. DETAILED DESCRIPTION

[0047] Comparative Example 1

[0048] The specific production process of the UDMH gas sensor based on pure WO3 nanosheet sensitive materials is as follows:

[0049] (1) Add 0.66 g of Na2WO4·2H2O and 0.4 g of C6H8O7·H2O to 33 mL of deionized water and stir continuously at room temperature for 20 minutes;

[0050] (2) Add 3 mL of HCl (37% by mass) to the solution obtained in step (1) and stir thoroughly for 30 minutes;

[0051] (3) The solution obtained in step (2) was transferred to a hydrothermal reactor, maintained at 140° C. for 12 hours, taken out, naturally cooled to room temperature, and filtered. The resulting precipitate was washed by centrifugation with deionized water and anhydrous ethanol several times, and then dried at room temperature; the resulting powder was calcined in air at 400° C. for 2 hours, and cooled to room temperature to obtain 0.4 g of WO3 nanosheet sensitive material;

[0052] (4) 50 mg of the WO3 sensitive material obtained in step (3) was added to 250 μL of anhydrous ethanol solution and stirred at room temperature for 8 hours;

[0053] (5) The mixed solution in step (4) is spin-coated on the upper surface of an Al2O3 ceramic substrate having a pair of interdigitated gold electrodes on the upper surface and a layer of RuO2 heating electrodes on the lower surface, and the obtained sensitive layer has a thickness of 6 μm; after drying at room temperature, it is welded and packaged according to the indirect heating gas sensor, thereby obtaining a UDMH gas sensor based on WO3 nanosheet sensitive material.

[0054] The Al2O3 ceramic substrate is square with a side length of 3mm and a thickness of 0.25mm; the width of the interdigitated gold electrode is 0.45mm, the interdigital spacing is 1mm, and the gap distance between adjacent interdigits is 0.3mm; platinum wires are led out from the interdigitated gold electrodes and the heating electrode, and their length is 5mm.

[0055] Example 1

[0056] The specific production process of the UDMH gas sensor based on Pt cluster-loaded WO3 nanosheet sensitive material is as follows:

[0057] (1) Add 0.66 g of Na2WO4·2H2O and 0.4 g of C6H8O7·H2O to 33 mL of deionized water and stir continuously at room temperature for 20 minutes;

[0058] (2) Add 3 mL of HCl (37% by mass) to the solution obtained in step (1) and stir thoroughly for 30 minutes;

[0059] (3) The solution obtained in step (2) was transferred to a hydrothermal reactor, maintained at 140° C. for 12 hours, taken out, naturally cooled to room temperature, and filtered. The resulting precipitate was washed by centrifugation with deionized water and anhydrous ethanol several times, and then dried at room temperature; the resulting powder was calcined in air at 400° C. for 2 hours, and cooled to room temperature to obtain 0.4 g of WO3 nanosheet sensitive material;

[0060] (4) 50 mg of the WO3 nanosheet sensitive material obtained in step (3) was added to 250 μL of anhydrous ethanol solution and stirred at room temperature for 8 hours;

[0061] (5) The mixed solution obtained in step (4) was spin-coated on the upper surface of an Al2O3 ceramic substrate with a pair of interdigitated gold electrodes on the upper surface and a layer of RuO2 heating electrode on the lower surface, and then placed in a heat-sealed ALD chamber after drying at room temperature; the Pt precursor was MeCpPtMe3, and the reducing agent was C4H 12 High-purity N2 was used as the carrier and purge gas. During this process, the reaction chamber temperature was 200°C, the Pt precursor and reducing agent were preheated to 70°C, and the chamber was in a vacuum state. Each ALD cycle consisted of a 1s MeCpPtMe3 pulse, a 20s exposure, a 25s N2 purge, a 1s tert-butylhydrazine pulse, a 20s exposure, and a 25s N2 purge. Five ALD cycles were performed, resulting in a 6μm-thick sensitive layer.

[0062] (6) The Al2O3 ceramic substrate is taken out, and then welded and packaged according to the indirect heating gas sensor, thereby obtaining the Pt cluster-loaded WO3 nano-sensitive material prepared based on atomic layer deposition.

[0063] The Al2O3 ceramic substrate is square with a side length of 3mm and a thickness of 0.25mm; the width of the interdigitated gold electrode is 0.45mm, the interdigital spacing is 1mm, and the gap distance between adjacent interdigits is 0.3mm; platinum wires are led out from the interdigitated gold electrodes and the heating electrode, and their length is 5mm.

Claims

1. A method for preparing a UDMH sensor based on Pt clusters loaded with WO3 nano-sensitive materials prepared by atomic layer deposition, the steps of which are as follows: (1) Add 0.6-0.7 g of Na2WO4·2H2O and 0.3-0.5 g of C6H8O7·H2O to 30-40 mL of deionized water and stir continuously at room temperature for 15-25 minutes; (2) adding 2-4 mL of 36-38% HCl to the solution obtained in step (1) and stirring thoroughly for 25-35 minutes; (3) The solution obtained in step (2) was transferred to a hydrothermal reactor, maintained at 130-150° C. for 10-14 hours, taken out, naturally cooled to room temperature, and filtered. The obtained precipitate was washed by centrifugation with deionized water and anhydrous ethanol several times, and then dried at room temperature; the obtained powder was calcined in air at 350-450° C. for 1.5-2.5 hours, and cooled to room temperature to obtain 0.3-0.5 g of WO3 nanosheet sensitive material; (4) taking 40-60 mg of the WO3 nanosheet sensitive material obtained in step (3) and adding it to 200-300 μL of anhydrous ethanol solution and stirring at room temperature for 6-10 hours; (5) The mixed solution obtained in step (4) was spin-coated on the upper surface of an Al2O3 ceramic substrate having a pair of interdigitated gold electrodes on the upper surface and a RuO2 heating electrode on the lower surface, dried at room temperature, and placed in a heat-sealed ALD chamber; Pt was loaded using the ALD method, wherein the Pt precursor was MeCpPtMe3 and the reducing agent was C4H 12 N2, with high-purity N2, is used as the carrier gas and purge gas. During this process, the reaction chamber temperature is 180-220°C, the preheat temperature of the Pt precursor and the reducing agent is 60-80°C, and the chamber is in a vacuum state. Each ALD cycle includes 'MeCpPtMe3 pulse 0.5-1.5s'-'exposure 15-25s'-'N2 purge 20-30s'-'tert-butylhydrazine pulse 0.5-1.5s'-'exposure 15-25s'-'N2 purge 20-30s', and a total of 4-6 cycles are performed. (6) The Al2O3 ceramic substrate is taken out, and then welded and packaged according to the indirect heating gas sensor, thereby obtaining the Pt cluster-loaded WO3 nano-sensitive material prepared based on atomic layer deposition.

2. The method for preparing a UDMH sensor based on Pt clusters loaded with WO3 nano-sensitive materials prepared by atomic layer deposition according to claim 1, characterized in that: The Al2O3 flat ceramic sheet in step (5) is square, with a side length of 2 to 5 mm and a thickness of 0.2 to 0.5 mm; the width of the interdigitated gold electrode is 0.3 to 0.6 mm, the interdigital spacing is 0.5 to 2.0 mm, and the gap distance between adjacent interdigits is 0.2 to 0.4 mm; platinum wires are led out from the interdigitated gold electrodes and the heating electrode, and their length is 3 to 6 mm.

3. The method for preparing a UDMH sensor based on Pt clusters loaded with WO3 nano-sensitive materials prepared by atomic layer deposition according to claim 1, characterized in that: The thickness of the sensitive layer obtained in step (5) is 4 to 8 μm.

4. A UDMH sensor based on Pt clusters loaded with WO3 nano-sensitive materials prepared by atomic layer deposition, characterized by: The invention is prepared by the preparation method according to any one of claims 1 to 3.

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