Core-shell structure In based on adjustable shell thickness 2 O 3 @ZnO composite sensitive material acetone gas sensor and preparation method thereof

Abstract

An acetone gas sensor based on a core-shell structure In2O3@ZnO composite sensitive material with adjustable shell thickness and its preparation method belong to the technical field of semiconductor oxide gas sensors. It consists of a ceramic tube, two parallel annular and discrete gold electrodes wrapped around the outer surface of the ceramic tube, and a core-shell structure In2O3@ZnO composite sensitive material with adjustable shell thickness coated on the outer surface of the ceramic tube and the gold electrodes. The thickness of the ZnO shell layer coated on the In2O3 core is controlled by adjusting the growth time of the ZIF-8 derivative. Compared with the In2O3-based sensor, the sensor based on the core-shell structure In2O3@ZnO composite sensitive material of the present invention exhibits higher sensitivity to acetone, faster response time, better selectivity, and stronger anti-humidity ability at a working temperature of 300 °C, and has broad application prospects in the field of effectively regulating the selective detection of VOCs gases.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor oxide gas sensors, and particularly relates to a core-shell structure In 2 O 3 @Acetone gas sensor based on ZnO composite sensitive material and its preparation method. Background Art

[0002] Metal oxide semiconductor (MOS) gas sensors have been successfully applied in the fields of air pollution monitoring, Internet of Things construction, new energy vehicle safety monitoring, disease breathing detection, etc. However, the inherent low selectivity of metal oxide semiconductor (MOS) gas sensors has not been fundamentally solved. Some researchers pointed out that due to the formation of heterojunctions and the synergistic effect of heterostructures and selective catalytic oxidation, constructing heterostructure composite materials as sensitive materials is the best way to improve selectivity. Among different heterostructures, concentric core-shell heterostructures refer to heterostructures in which one metal oxide semiconductor is used as the core layer and another metal oxide semiconductor is used as the shell layer, which is completely and uniformly covered on the surface of the core. Concentric core-shell heterostructures have attracted extensive attention from researchers due to their excellent stability, superior physicochemical properties, rich active sites, outstanding synergistic effects, easy surface functionalization, controllable design of the core layer and shell layer, and precise regulation of the interaction between the core and shell. At the same time, by changing the core-shell composition and its ratio, the conductivity and free carrier concentration of the core-shell heterostructure can be precisely controlled, thereby achieving selective and sensitive detection. Studies have shown that the shell thickness in the core-shell heterostructure is a key parameter affecting the gas sensing performance. The ALD method can achieve uniform coating of the shell layer on the nanocore, but this method is costly, complex, and not suitable for large-scale industrial production. Therefore, there is an urgent need for a simple and alternative method to prepare concentric core-shell heterostructures and appropriately adjust the shell film thickness.

[0003] In recent years, structures derived from metal organic frameworks (MOFs) have been shown to be able to be uniformly coated on the surface of nanostructures to form good films. Moreover, the structure and morphology of MOF derivatives can be precisely controlled during the growth process. In addition, the unique mesoporous structure, rich active reaction sites, and adjustable components of MOF derivatives can also enhance electron transport, which is beneficial to improving gas sensing performance. MOF derivatives are used as the shell layer of the concentric core-shell heterostructure to achieve uniform coating, and the thickness of the shell layer can be effectively controlled. Summary of the invention

[0004] The purpose of the present invention is to achieve the regulation of the electrical properties, band structure and corresponding gas sensing performance of the core-shell MOS heterostructure by adjusting the shell thickness of ZIF-8 (a highly potential MOF material) derivatives, thereby providing a core-shell structure In based on adjustable shell thickness.2 O 3 @ZnO composite sensitive material acetone gas sensor and its preparation method. The present invention controls the growth time of ZIF-8 derivatives coated on In 2 O 3 The thickness of the ZnO shell on the core is due to the formation of the nn heterojunction at the core-shell interface and the electrons from In 2 O 3 The transfer of the core to the ZnO shell can study the effect of the modulation of the electron accumulation layer and the free carrier concentration on the gas sensing performance. 2 O 3 Different from the intrinsic catalytic oxidation activity of ZnO, the increase of ZnO shell thickness leads to the 2 O 3 The selectivity of the @ZnO heterostructures is changed from ethanol to acetone. 2 O 3 Compared with the sensor based on core-shell structure In 2 O 3 @The sensor made of ZnO composite sensitive material shows higher sensitivity, faster response time and better selectivity to acetone at an operating temperature of 300°C.

[0005] The present invention firstly prepares In by ultrasonic spray pyrolysis 2 O 3 The microspheres were successfully prepared by ultrasonic spray pyrolysis using a certain amount of hydrated indium nitrate as raw material and a mixture of dilute hydrochloric acid and hydrogen peroxide as solvent. 2 O 3 microspheres; then ultrasonically treated with a certain amount of PVP-K30 2 O 3 The microspheres were then washed alternately with deionized water and ethanol; then, a certain proportion of hydrated zinc nitrate, dimethylimidazole and In 2 O 3 Microspheres were used as raw materials, methanol solution was used as solvent, and the mixture was left to stand at room temperature for different periods of time to generate In 2 O 3 @ZIF-8 microspheres were washed alternately with deionized water and ethanol, dried and calcined in air to obtain the core-shell heterostructured In 2 O 3 @ZnO composite sensitive material.

[0006] The present invention discloses an In core-shell structure with adjustable shell thickness. 2 O 3The acetone gas sensor made of ZnO composite sensitive material adopts a side-heated structure, which consists of a ceramic tube, two parallel ring-shaped and discrete gold electrodes surrounding the outer surface of the ceramic tube, and a core-shell structure In with adjustable shell thickness coated on the outer surface of the ceramic tube and the gold electrode. 2 O 3 @ZnO composite sensitive material composition; among them, the core-shell structure In with adjustable shell thickness 2 O 3 The ZnO composite sensitive material is prepared by the following steps:

[0007] (1) 0.30 to 0.80 g of In(NO 3 ) 3 4.5H 2 O, 0.10-0.20 mL of 1-2% dilute hydrochloric acid solution, and 0.10-0.20 mL of 28-30% hydrogen peroxide solution are sequentially added into 10-20 mL of deionized water, and stirred at room temperature for 30-90 minutes until they are completely dissolved;

[0008] (2) using helium as carrier gas (helium flow rate: 400-500 sccm) to subject the solution obtained in step (1) to ultrasonic spray pyrolysis at a pyrolysis temperature of 500-800° C. for a pyrolysis time of 1-2 h; washing the product obtained by the reaction with deionized water and ethanol alternately for 5-7 times, drying at 70-90° C., and calcining at 500-700° C. for 2-4 h to obtain In 2 O 3 Microsphere powder;

[0009] (3) 0.3 to 0.8 g of In obtained in step (2) 2 O 3 The microsphere powder and 0.5-2 g PVP-K30 were sequentially added into 10-20 mL deionized water and stirred for 30-90 min until they were completely dissolved; the reaction product was washed alternately with deionized water and ethanol for 5-7 times;

[0010] (4) Add the product obtained in step (3) to a solution containing 0.05 to 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.05-0.5g of dimethylimidazole in 10-20mL of methanol solution, let stand at room temperature for 1-6h; 2 O 3 @ZIF-8 was washed with deionized water and ethanol alternately for 5 to 7 times, then dried at 70 to 90°C, and then calcined at 500 to 700°C for 2 to 4 hours, thereby obtaining the In core-shell structure with adjustable shell thickness described in the present invention. 2 O 3@ZnO composite sensitive material.

[0011] The core-shell structure In based on adjustable shell thickness involved in the present invention 2 O 3 The acetone gas sensor made of ZnO composite sensitive material adopts a side-heating structure, and its preparation steps are as follows:

[0012] (1) Core-shell structure with adjustable shell thickness In 2 O 3 @ZnO composite sensitive material and isopropanol are uniformly mixed in a mass ratio of 0.3 to 0.5:1 to form a slurry. The slurry is applied with a brush to the Al2O3 electrode with two parallel, annular and separate gold electrodes on the outer surface. 2 O 3 The outer surface of the ceramic tube is completely covered with gold electrodes; the outer surface of the ceramic tube is 2 O 3 @The thickness of ZnO composite sensitive material is 10~20μm; Al 2 O 3 The inner diameter of the ceramic tube is 0.6-0.8 mm, the outer diameter is 1.0-1.5 mm, and the length is 4-5 mm; the width of a single gold electrode is 0.4-0.5 mm, the thickness is 0.12-0.15 μm, the distance between two gold electrodes is 0.5-0.6 mm, and the length of the platinum wire lead from the gold electrode is 4-6 mm;

[0013] (2) The ceramic tube coated with the composite sensitive material is sintered at 200-300°C for 2-4h, and then a nickel-chromium alloy heating wire with a resistance value of 30-40Ω is passed through the ceramic tube to provide a suitable working temperature for the sensor. Then, the gold electrode and the nickel-chromium alloy heating wire are welded to a universal indirect heating hexagonal tube socket through a platinum wire conductor, thereby obtaining the core-shell structure In based on adjustable shell thickness according to the present invention. 2 O 3 @Acetone gas sensor based on ZnO composite sensitive material.

[0014] Working principle:

[0015] When the core-shell structure In 2 O 3 When the gas sensor made of ZnO composite sensitive material is placed in the air, the surface of the semiconductor material forms adsorbed oxygen O through physical adsorption and chemical adsorption. 2 - , a depletion layer is formed on the surface of the material. When the sensor is exposed to VOCs gas at a certain suitable operating temperature, the gas molecules will be adsorbed on the surface of the sensor and react with the chemically adsorbed oxygen on the surface of the sensitive material, causing the captured electrons to be released to the sensitive material. The increase in electron concentration is manifested as a decrease in the resistance value of the gas sensor. Define the sensitivity S of the sensor: S = R gas / R air , where R air is the resistance between the two gold electrodes of the sensor in the air, R gas It is the resistance between the two gold electrodes of the sensor after it contacts the gas to be measured.

[0016] Advantages of the present invention:

[0017] (1) The present invention controls the growth time of the ZIF-8 derivative coated on In 2 O 3 The thickness of the ZnO shell on the core is controlled to achieve the preparation of a concentric core-shell structure with controllable shell thickness.

[0018] (2) The core-shell structure In of the present invention with controllable shell thickness 2 O 3 @ZnO composite sensitive materials realize the directional regulation of carriers, and at the same time realize the regulation of the electrical properties, band structure and corresponding gas-sensing performance of sensitive materials, providing an effective idea for the development of VOCs gas sensors.

[0019] (3) The present invention is based on In 2 O 3 Different from the inherent catalytic oxidation activity of ZnO, the selectivity can be improved by adjusting the thickness of the ZnO shell. 2 O 3 @The selectivity of ZnO heterostructures is changed from ethanol to acetone.

[0020] (4) The core-shell structure In prepared by the present invention 2 O 3 The production process of acetone gas sensor based on ZnO composite sensitive material is simple, the method is controllable and the preparation steps are simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The core-shell structures In with different shell thicknesses obtained in Comparative Example 1 and Examples 1 to 6 of the present invention are 2 O 3 @SEM image of ZnO composite sensitive material.

[0022] Figure 2 The core-shell structures In with different shell thicknesses obtained in Examples 1 to 6 of the present invention are 2 O 3 @TEM image of ZnO composite sensitive material.

[0023] Figure 3 The core-shell structures In with different shell thicknesses obtained in Comparative Example 1 and Examples 1 to 6 of the present invention are 2 O 3 @XRD pattern of ZnO composite sensitive material.

[0024] Figure 4 In before calcination prepared in Example 5 of the present invention 2 O 3 @FT-IR spectra of ZIF-8 and ZIF-8 prepared in Comparative Example 2 before calcination.

[0025] Figure 5 The selectivity of the sensors of Comparative Examples 1 to 2 and Examples 1 to 6 of the present invention to different VOCs gases at 100 ppm at different operating temperatures (200° C. to 325° C.) is shown.

[0026] Figure 6 The sensitivity-concentration gradient characteristic curves of the sensors of Example 5 of the present invention and Comparative Examples 1 and 2 to acetone gas at the corresponding optimal operating temperatures.

[0027] Figure 7 This is the response-recovery characteristic curve of the sensor prepared in Example 5 of the present invention to 100 ppm acetone gas at the optimal working temperature.

[0028] Figure 8 The stability curve of the sensor device at the optimal operating temperature in Example 5 of the present invention, the sensitivity curve of the gas sensor to 100 ppm acetone (Figure a) and the stable resistance in the air, i.e., the baseline resistance curve (Figure b).

[0029] like Figure 1 As shown, it can be seen that all samples have the morphology of wrinkled microspheres. 2 O 3 The microspheres have finer wrinkles. As the MOF growth time increases, In 2 O 3 ZnO nanoparticles were grown on the surface of wrinkled microspheres. 2 O 3 @ZnO-1, due to the short growth time of zinc oxide, the ZnO layer cannot achieve full loading of the shell structure. As the loading time increases, the shell thickness gradually becomes complete, and as the growth time increases, In 2 O 3 The morphology of ZnO microspheres has changed from finer wrinkles to coarser wrinkles.

[0030] like Figure 2 As shown, it can be seen that In is formed at the core-shell heterointerface 2 O 3 The nn heterostructure of ZnO was successfully controlled by adjusting the ZIF-8 growth time. 2 O 3The average thickness of the ZnO shell of the heterostructures @ZnO-1, 2, 3, 4, 5, and 6 are 12.6, 23.3, 32.2, 42.1, 55.3, and 72.4 nm, respectively. This indicates that the growth time of the ZIF-8 derivatives can be controlled to control the coating on the In 2 O 3 The thickness of the ZnO shell on the core is controlled to achieve the preparation of a concentric core-shell structure with controllable shell thickness.

[0031] like Figure 3 As shown, the X-ray powder (XRD) characterization of Comparative Example 1 and Examples 1-6 shows that only In 2 O 3 The XRD peaks of the ZnO-4, 5, and 6 composite materials have characteristic peaks of hexagonal zinc oxide and cubic indium oxide. At the same time, the characteristic peaks of the other sensitive materials are consistent with those of cubic indium oxide. This is probably because the loading amount of zinc oxide is relatively small.

[0032] like Figure 4 As shown in the Fourier transform infrared (FT-IR) spectrum, the uncalcined Example 5 and the uncalcined Comparative Example 2 both have a peak at 480 cm -1 There are Zn-N vibration peaks at 1306, 1145 and 759 cm -1 The vibration peak of the imidazole ring of ZIF-8 is found at 2 O 3 Successful preparation of ZIF-8 shell with @ZnO.

[0033] like Figure 5 As shown, the sensitivity change curves of the sensors of Comparative Example 1 and Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6 to 100 ppm of VOCs (ethanol, acetone, formaldehyde, methanol, toluene) gas at different operating temperatures. It can be seen from the figure that Comparative Example 1 has the highest sensitivity to 100 ppm of ethanol at 325°C, S=5.1, and Comparative Example 2 has the highest sensitivity to 100 ppm of acetone at 300°C, S=6.5. Example 1 of the core-shell structure has the highest sensitivity to 100 ppm of ethanol at 300°C and the best selectivity, S=12.0. As the shell growth time increases, the VOCs selectivity of the embodiments changes. Example 5 of the core-shell structure has good gas-sensitive characteristics to 100 ppm of acetone at 300°C, S=23.3. The gas-sensitive test results show that the increase in the thickness of the ZnO shell leads to the increase in In 2 O 3 @ZnO heterostructures switch from ethanol to acetone. Adjustment of shell thickness leads to radial modulation of the electron accumulation region in the nn heterostructures, and the core-shell heterostructure In 2 O 3@The shell thickness control of ZnO not only improves the selectivity but also the sensitivity of acetone.

[0034] like Figure 6 As shown in the figure, when all devices are at their optimal operating temperature, the sensitivity of the sensor to 0.1-100 ppm acetone and the gas concentration function curve can be seen to increase with the increase of acetone concentration. When the working temperature of Example 5 is 300°C, the lower limit of acetone concentration that can be detected is 0.1 ppm, and the corresponding sensitivity is 1.6. Compared with Comparative Examples 1 and 2, the sensor in Example 5 has a lower detection limit and a higher sensitivity.

[0035] like Figure 7 As shown, the response recovery curve of the sensor prepared in Example 5 at an operating temperature of 300° C. The sensor in Example 5 exhibits the best gas-sensing properties and has a faster response time of 2 s.

[0036] like Figure 8 As shown in the figure, the sensitivity of Example 5 to 100 ppm acetone at an operating temperature of 300°C was tested over a period of 30 days. Over a period of 30 days, the fluctuation range of the sensitivity (Figure a) and baseline resistance value (Figure b) of the gas sensor was basically maintained within a stable range. It can be seen that the sensor exhibits good stability. DETAILED DESCRIPTION

[0037] Comparative Example 1: In 2 O 3 The specific production process of the gas sensor made of microsphere nano-sensitive materials is as follows:

[0038] (1) First, 0.50 g of In(NO 3 ) 3 4.5H 2 O, 0.10 mL of 2% dilute hydrochloric acid solution, and 0.10 mL of 30% hydrogen peroxide solution were added into 20 mL of deionized water in sequence and stirred at room temperature for 90 min until they were completely dissolved.

[0039] (2) The solution obtained in step (1) was subjected to ultrasonic spray pyrolysis using helium as carrier gas (helium flow rate: 500 sccm), the pyrolysis temperature was 700°C, and the pyrolysis time was 2 hours. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70°C. After drying, the product was calcined at 600°C for 4 hours to obtain In 2 O 3 Microsphere powder;

[0040] (3) Take In 2 O 3The microsphere powder and isopropanol are uniformly mixed at a mass ratio of 0.5mg:1mg to form a coating slurry. A small amount of slurry is applied to the outer surface of the ceramic tube with a brush to form a nanomaterial sensitive layer with a thickness of 20μm, and the layer completely covers the gold electrode;

[0041] (4) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 The heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire ceramic tube are welded to the universal indirect heating hexagonal tube socket through the platinum wire conductor; thus, In 2 O 3 Gas sensor made of microsphere nano-sensitive materials; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between two gold electrodes is 0.55mm; the length of the platinum wire led out from the gold electrode is 5mm.

[0042] Comparative Example 2: A gas sensor using ZIF-8 derivative ZnO sensitive material, the specific manufacturing process is as follows:

[0043] (1) First, 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.5 g of dimethylimidazole was added to 20 mL of methanol solution and allowed to stand at room temperature for 6 h. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70 ° C. After drying, the product was calcined at 600 ° C for 4 h to obtain ZIF-8 derivative ZnO sensitive material;

[0044] (2) Take an appropriate amount of ZIF-8 derivative ZnO sensitive material and isopropanol at a mass ratio of 0.5mg:1mg and mix them evenly to form a coating slurry. Use a brush to apply a small amount of slurry on the outer surface of the ceramic tube to form a nanomaterial sensitive layer with a thickness of 20μm, and make it completely cover the gold electrode;

[0045] (3) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 A heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire are welded to a universal indirectly heated hexagonal tube socket through a platinum wire conductor; thereby, a gas sensor of a ZIF-8 derivative ZnO sensitive material is obtained; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between the two gold electrodes is 0.55mm; the length of the platinum wire conductor led out from the gold electrode is 5mm.

[0046] Example 1: In core-shell structure 2 O 3 The specific production process of the gas sensor made of ZnO-1 composite nano-sensitive material is as follows:

[0047] (1) First, 0.50 g of In(NO 3 ) 3 4.5H 2 O, 0.10 mL of 2% dilute hydrochloric acid and 0.10 mL of 30% hydrogen peroxide solution were added into 20 mL of deionized water in sequence and stirred at room temperature for 90 min until they were completely dissolved.

[0048] (2) The solution obtained in step (1) was subjected to ultrasonic spray pyrolysis using helium as carrier gas (helium flow rate: 500 sccm), the pyrolysis temperature was 700°C, and the pyrolysis time was 2 hours. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70°C. After drying, the product was calcined at 600°C for 4 hours to obtain In 2 O 3 Microsphere powder;

[0049] (3) Then 0.5 g of In obtained in step (2) 2 O 3 The microsphere powder and 2 g PVP-K30 were added to 20 mL of deionized water and stirred for 90 min until they were completely dissolved. The obtained product was washed alternately with deionized water and ethanol for 5 times;

[0050] (4) The product obtained in step (3) was added to a solution containing 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.5g of dimethylimidazole in 20mL of methanol solution, and let stand at room temperature for 1h. 2 O 3 @ZIF-8 was washed with deionized water and ethanol alternately for 5 times and then dried at 70 °C. After drying, the product was calcined at 600 °C for 4 h to obtain In core-shell structure with adjustable shell thickness. 2 O 3 @ZnO composite sensitive material, denoted as In 2 O 3 @ZnO-1;

[0051] (5) Take an appropriate amount of core-shell structure In 2 O 3@ZnO-1 composite nano-sensitive material and isopropanol are uniformly mixed at a mass ratio of 0.5mg:1mg to form a coating slurry. Use a brush to apply a small amount of slurry on the outer surface of the ceramic tube to form a 20μm thick nano-material sensitive layer that completely covers the gold electrode;

[0052] (6) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 The heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire are welded to the universal indirect heating hexagonal tube seat through the platinum wire conductor; thus, the core-shell structure In 2 O 3 @Gas sensor made of ZnO-1 composite nano-sensitive material; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between two gold electrodes is 0.55mm; the length of the platinum wire led out from the gold electrode is 5mm.

[0053] Example 2: In core-shell structure 2 O 3 The specific production process of the gas sensor made of ZnO-2 composite nano-sensitive material is as follows:

[0054] (1) First, 0.50 g of In(NO 3 ) 3 4.5H 2 O, 0.10 mL of 2% dilute hydrochloric acid and 0.10 mL of 30% hydrogen peroxide solution were added into 20 mL of deionized water in sequence and stirred at room temperature for 90 min until they were completely dissolved.

[0055] (2) The solution obtained in step (1) was subjected to ultrasonic spray pyrolysis using helium as carrier gas (helium flow rate: 500 sccm), the pyrolysis temperature was 700°C, and the pyrolysis time was 2 hours. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70°C. After drying, the product was calcined at 600°C for 4 hours to obtain In 2 O 3 Microsphere powder;

[0056] (3) Then 0.5 g of In obtained in step (2) 2 O 3 The microsphere powder and 2 g PVP-K30 were added to 20 mL of deionized water and stirred for 90 min until they were completely dissolved. The obtained product was washed alternately with deionized water and ethanol for 5 times;

[0057] (4) The product obtained in step (3) was added to a solution containing 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.5g of dimethylimidazole in 20mL of methanol solution, and let stand at room temperature for 2h. 2 O 3 @ZIF-8 was washed with deionized water and ethanol alternately for 5 times and then dried at 70 °C. After drying, the product was calcined at 600 °C for 4 h to obtain In core-shell structure with adjustable shell thickness. 2 O 3 @ZnO composite sensitive material, denoted as In 2 O 3 @ZnO-2;

[0058] (5) Take an appropriate amount of core-shell structure In 2 O 3 @ZnO-2 composite nano-sensitive material and isopropanol are uniformly mixed at a mass ratio of 0.5mg:1mg to form a coating slurry. Use a brush to apply a small amount of slurry on the outer surface of the ceramic tube to form a 20μm thick nano-material sensitive layer that completely covers the gold electrode;

[0059] (6) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 The heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire are welded to the universal indirect heating hexagonal tube seat through the platinum wire conductor; thus, the core-shell structure In 2 O 3 @Gas sensor made of ZnO-2 composite nano-sensitive material; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between two gold electrodes is 0.55mm; the length of the platinum wire led out from the gold electrode is 5mm.

[0060] Example 3: In core-shell structure 2 O 3 The specific production process of the gas sensor made of ZnO-3 composite nano-sensitive material is as follows:

[0061] (1) First, 0.50 g of In(NO 3 ) 3 4.5H 2 O, 0.10 mL of 2% dilute hydrochloric acid and 0.10 mL of 30% hydrogen peroxide solution were added into 20 mL of deionized water in sequence and stirred at room temperature for 90 min until they were completely dissolved.

[0062] (2) The solution obtained in step (1) was subjected to ultrasonic spray pyrolysis using helium as carrier gas (helium flow rate: 500 sccm), the pyrolysis temperature was 700°C, and the pyrolysis time was 2 hours. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70°C. After drying, the product was calcined at 600°C for 4 hours to obtain In 2 O 3 Microsphere powder;

[0063] (3) Then 0.5 g of In obtained in step (2) 2 O 3 The microsphere powder and 2 g PVP-K30 were added to 20 mL of deionized water and stirred for 90 min until they were completely dissolved. The obtained product was washed alternately with deionized water and ethanol for 5 times;

[0064] (4) The product obtained in step (3) was added to a solution containing 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.5g of dimethylimidazole in 20mL of methanol solution, and let stand at room temperature for 3h. 2 O 3 @ZIF-8 was washed with deionized water and ethanol alternately for 5 times and then dried at 70 °C. After drying, the product was calcined at 600 °C for 4 h to obtain In core-shell structure with adjustable shell thickness. 2 O 3 @ZnO composite sensitive material, denoted as In 2 O 3 @ZnO-3;

[0065] (5) Take an appropriate amount of core-shell structure In 2 O 3 @ZnO-3 composite nano-sensitive material and isopropanol are uniformly mixed at a mass ratio of 0.5mg:1mg to form a coating slurry. Use a brush to apply a small amount of slurry on the outer surface of the ceramic tube to form a 20μm thick nano-material sensitive layer that completely covers the gold electrode;

[0066] (6) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 The heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire are welded to the universal indirect heating hexagonal tube seat through the platinum wire conductor; thus, the core-shell structure In 2 O 3@Gas sensor made of ZnO-3 composite nano-sensitive material; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between two gold electrodes is 0.55mm; the length of the platinum wire led out from the gold electrode is 5mm.

[0067] Example 4: In core-shell structure 2 O 3 The specific production process of the gas sensor made of ZnO-4 composite nano-sensitive material is as follows:

[0068] (1) First, 0.50 g of In(NO 3 ) 3 4.5H 2 O, 0.10 mL of 2% dilute hydrochloric acid and 0.10 mL of 30% hydrogen peroxide solution were added into 20 mL of deionized water in sequence and stirred at room temperature for 90 min until they were completely dissolved.

[0069] (2) The solution obtained in step (1) was subjected to ultrasonic spray pyrolysis using helium as carrier gas (helium flow rate: 500 sccm), the pyrolysis temperature was 700°C, and the pyrolysis time was 2 hours. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70°C. After drying, the product was calcined at 600°C for 4 hours to obtain In 2 O 3 Microsphere powder;

[0070] (3) Then 0.5 g of In obtained in step (2) 2 O 3 The microsphere powder and 2 g PVP-K30 were added to 20 mL of deionized water and stirred for 90 min until they were completely dissolved. The obtained product was washed alternately with deionized water and ethanol for 5 times;

[0071] (4) The product obtained in step (3) was added to a solution containing 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.5g of dimethylimidazole in 20mL of methanol solution, and let stand at room temperature for 4h. 2 O 3 @ZIF-8 was washed with deionized water and ethanol alternately for 5 times and then dried at 70 °C. After drying, the product was calcined at 600 °C for 4 h to obtain In core-shell structure with adjustable shell thickness. 2 O 3 @ZnO composite sensitive material, denoted as In 2 O 3 @ZnO-4;

[0072] (5) Take an appropriate amount of core-shell structure In 2 O 3 @ZnO-4 composite nano-sensitive material and isopropanol are uniformly mixed at a mass ratio of 0.5mg:1mg to form a coating slurry. Use a brush to apply a small amount of slurry on the outer surface of the ceramic tube to form a 20μm thick nano-material sensitive layer that completely covers the gold electrode;

[0073] (6) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 The heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire are welded to the universal indirect heating hexagonal tube seat through the platinum wire conductor; thus, the core-shell structure In 2 O 3 @Gas sensor made of ZnO-4 composite nano-sensitive material; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between two gold electrodes is 0.55mm; the length of the platinum wire led out from the gold electrode is 5mm.

[0074] Example 5: In core-shell structure 2 O 3 The specific production process of the gas sensor made of ZnO-5 composite nano-sensitive material is as follows:

[0075] (1) First, 0.50 g of In(NO 3 ) 3 4.5H 2 O, 0.10 mL of 2% dilute hydrochloric acid and 0.10 mL of 30% hydrogen peroxide solution were added into 20 mL of deionized water in sequence and stirred at room temperature for 90 min until they were completely dissolved.

[0076] (2) The solution obtained in step (1) was subjected to ultrasonic spray pyrolysis using helium as carrier gas (helium flow rate: 500 sccm), the pyrolysis temperature was 700°C, and the pyrolysis time was 2 hours. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70°C. After drying, the product was calcined at 600°C for 4 hours to obtain In 2 O 3 Microsphere powder;

[0077] (3) Then 0.5 g of In obtained in step (2) 2 O 3 The microsphere powder and 2 g PVP-K30 were added to 20 mL of deionized water and stirred for 90 min until they were completely dissolved. The obtained product was washed alternately with deionized water and ethanol for 5 times;

[0078] (4) The product obtained in step (3) was added to a solution containing 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.5g of dimethylimidazole in 20mL of methanol solution, and let stand at room temperature for 5h. 2 O 3 @ZIF-8 was washed with deionized water and ethanol alternately for 5 times and then dried at 70 °C. After drying, the product was calcined at 600 °C for 4 h to obtain In core-shell structure with adjustable shell thickness. 2 O 3 @ZnO composite sensitive material, denoted as In 2 O 3 @ZnO-5;

[0079] (5) Take an appropriate amount of core-shell structure In 2 O 3 @ZnO-5 composite nano-sensitive material and isopropanol are uniformly mixed at a mass ratio of 0.5mg:1mg to form a coating slurry. Use a brush to apply a small amount of slurry on the outer surface of the ceramic tube to form a 20μm thick nano-material sensitive layer that completely covers the gold electrode;

[0080] (6) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 The heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire are welded to the universal indirect heating hexagonal tube seat through the platinum wire conductor; thus, the core-shell structure In 2 O 3 @Gas sensor made of ZnO-5 composite nano-sensitive material; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between two gold electrodes is 0.55mm; the length of the platinum wire led out from the gold electrode is 5mm.

[0081] Example 6: In core-shell structure 2 O 3 The specific production process of the gas sensor made of ZnO-6 composite nano-sensitive material is as follows:

[0082] (1) First, 0.50 g of In(NO 3 ) 3 4.5H 2O, 0.10 mL of 2% dilute hydrochloric acid and 0.10 mL of 30% hydrogen peroxide solution were added into 20 mL of deionized water in sequence and stirred at room temperature for 90 min until they were completely dissolved.

[0083] (2) The solution obtained in step (1) was subjected to ultrasonic spray pyrolysis using helium as carrier gas (helium flow rate: 500 sccm), the pyrolysis temperature was 700°C, and the pyrolysis time was 2 hours. The obtained product was washed with deionized water and ethanol alternately for 5 times, and then dried at 70°C. After drying, the product was calcined at 600°C for 4 hours to obtain In 2 O 3 Microsphere powder;

[0084] (3) Then 0.5 g of In obtained in step (2) 2 O 3 The microsphere powder and 2 g PVP-K30 were added to 20 mL of deionized water and stirred for 90 min until they were completely dissolved. The obtained product was washed alternately with deionized water and ethanol for 5 times;

[0085] (4) The product obtained in step (3) was added to a solution containing 0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.5g of dimethylimidazole in 20mL of methanol solution, and let stand at room temperature for 6h. 2 O 3 @ZIF-8 was washed with deionized water and ethanol alternately for 5 times and then dried at 70 °C. After drying, the product was calcined at 600 °C for 4 h to obtain In core-shell structure with adjustable shell thickness. 2 O 3 @ZnO composite sensitive material, denoted as In 2 O 3 @ZnO-6;

[0086] (5) Take an appropriate amount of core-shell structure In 2 O 3 @ZnO-6 composite nano-sensitive material and isopropanol are uniformly mixed at a mass ratio of 0.5mg:1mg to form a coating slurry. Use a brush to apply a small amount of slurry on the outer surface of the ceramic tube to form a 20μm thick nano-material sensitive layer that completely covers the gold electrode;

[0087] (6) The coated ceramic tube was sintered at 250°C for 2 h, and a nickel-chromium alloy heating wire with a resistance value of 35 Ω was passed through the Al 2 O 3 The heat source is provided inside the ceramic tube, and then the gold electrode and the nickel-chromium alloy heating wire are welded to the universal indirect heating hexagonal tube seat through the platinum wire conductor; thus, the core-shell structure In2 O 3 @Gas sensor made of ZnO-6 composite nano-sensitive material; the inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, the thickness is 0.13μm, and the distance between two gold electrodes is 0.55mm; the length of the platinum wire led out from the gold electrode is 5mm.

Claims

1. A core-shell structure with adjustable shell thickness 2 O 3 @Acetone gas sensor made of ZnO composite sensitive material adopts a side-heating structure. Features: The invention comprises a ceramic tube, two parallel annular and separate gold electrodes surrounding the outer surface of the ceramic tube, and an In core-shell structure with adjustable shell thickness coated on the outer surface of the ceramic tube and the gold electrodes. 2 O 3 @ZnO composite sensitive material composition; the adjustment of shell thickness will lead to radial modulation of the electron accumulation area in the nn heterostructure, the core-shell heterostructure In 2 O 3 @ZnO shell thickness control changes the selectivity of VOCs and improves the sensitivity to acetone; among them, the In core-shell structure with adjustable shell thickness 2 O 3 @ZnO composite sensitive material is prepared by the following steps: (1) 0.30~0.80 g of In(NO 3 ) 3 4.5H 2 O, 0.10-0.20 mL of 1-2% dilute hydrochloric acid solution, and 0.10-0.20 mL of 28-30% hydrogen peroxide solution are sequentially added into 10-20 mL of deionized water and stirred at room temperature for 30-90 min until they are completely dissolved; (2) subjecting the solution obtained in step (1) to ultrasonic spray pyrolysis using helium as a carrier gas at a pyrolysis temperature of 500-800°C for a pyrolysis time of 1-2 h; washing the product obtained by the reaction with deionized water and ethanol alternately for 5-7 times, drying at 70-90°C, and calcining at 500-700°C for 2-4 h to obtain In 2 O 3 Microsphere powder; (3) 0.3-0.8 g of In obtained in step (2) 2 O 3 The microsphere powder and 0.5-2 g PVP-K30 were sequentially added into 10-20 mL deionized water and stirred for 30-90 min until they were completely dissolved. The product obtained by the reaction was washed alternately with deionized water and ethanol for 5-7 times. (4) Add the product obtained in step (3) to a solution containing 0.05-0.5 g of Zn(NO 3 ) 2 6H 2 O, 0.05~0.5 g of dimethylimidazole in 10~20 mL of methanol solution, let stand at room temperature for 1~6 h; 2 O 3 @ZIF-8 was washed alternately with deionized water and ethanol for 5 to 7 times, then dried at 70 to 90 °C, and then calcined at 500 to 700 °C for 2 to 4 h, thereby obtaining the In core-shell structure with adjustable shell thickness. 2 O 3 @ZnO composite sensitive material.

2. An In core-shell structure with adjustable shell thickness as claimed in claim 1 2 O 3 @Acetone gas sensor made of ZnO composite sensitive material, Features: Ceramic tube outer surface In 2 O 3 @The thickness of ZnO composite sensitive material is 10~20 μm.

3. The In core-shell structure with adjustable shell thickness as claimed in claim 1 2 O 3 @Acetone gas sensor made of ZnO composite sensitive material, Features: Al 2 O 3 The inner diameter of the ceramic tube is 0.6~0.8 mm, the outer diameter is 1.0~1.5 mm, and the length is 4~5 mm; the width of a single gold electrode is 0.4~0.5 mm, the thickness is 0.12~0.15 μm, the distance between the two gold electrodes is 0.5~0.6 mm, and the length of the platinum wire leading out of the gold electrode is 4~6 mm.

4. The In core-shell structure with adjustable shell thickness as claimed in any one of claims 1 to 3 2 O 3 The preparation method of the acetone gas sensor of the @ZnO composite sensitive material comprises the following steps: (1) In with a core-shell structure with adjustable shell thickness 2 O 3 @ZnO composite sensitive material and isopropanol are uniformly mixed in a mass ratio of 0.3-0.5:1 to form a slurry, and a brush is used to apply the slurry to the outer surface of a ceramic tube with two parallel, annular and separate gold electrodes on the outer surface, so that the gold electrodes are completely covered; (2) The ceramic tube coated with the composite sensitive material is sintered at 200-300 °C for 2-4 h, and then a nickel-chromium alloy heating wire with a resistance value of 30-40 Ω is passed through the ceramic tube to provide a suitable working temperature for the sensor. Then, the gold electrode and the nickel-chromium alloy heating wire are welded to a universal indirect-heated hexagonal tube socket through a platinum wire conductor, thereby obtaining an In-shell core-shell structure with adjustable shell thickness. 2 O 3 @Acetone gas sensor based on ZnO composite sensitive material.

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