A method for preparing spherical zinc-tin composite metal oxides and its application as a gas-sensitive sensing material.

Abstract

This invention discloses a method for preparing a spherical zinc-tin composite metal oxide and its application as a gas-sensitive sensing material. The invention prepares a spherical ZnSn-LDHs precursor, which, after calcination, yields porous spherical ZnO / SnO2. Macroscopically, the spherical structure has a large specific surface area and porosity, increasing the reaction area. The formation of mesopores increases gas permeability, effectively enhancing the reaction between the analyte gas and the gas-sensitive material. Microscopically, it possesses a large number of oxygen vacancies, activating the surface, increasing surface energy and activity, and enhancing oxygen adsorption. This results in a thicker depletion layer, increasing the initial resistance and leading to higher sensitivity and response values. The porous spherical zinc-tin composite metal oxide, as an H2S gas-sensitive sensing material, exhibits a fast response recovery time and excellent H2S selectivity. Furthermore, it has a simple structure, a simple working principle, low cost, and can be mass-produced.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor gas sensing technology, specifically relating to a method for preparing a spherical zinc-tin composite metal oxide and its application as a gas sensing material. Background Technology

[0002] With economic development and the continuous improvement of living standards, household waste is becoming more diversified, with a more balanced composition of various nutrients. This leads to the generation of more types and quantities of malodorous gases under suitable conditions. Typical malodorous gases include: CS2, H2S, CH4S, C2H6S, and NH3. Among them, H2S is the gas that contributes the most to the odor, and it is a colorless, flammable gas with a typical toxic odor resembling rotten eggs. It is usually a product of some chemical reactions and the natural decomposition of proteins, and is widely present in various production processes, such as the extraction and refining of sulfur-containing oils and gases, petroleum processing, low-temperature coking of coal, rubber processing, sewage treatment, garbage disposal, and fertilizer manufacturing. Hydrogen sulfide is a potent neurotoxin with a strong irritant effect on mucous membranes. Even low concentrations of hydrogen sulfide can damage a person's sense of smell. High concentrations of hydrogen sulfide can directly paralyze the olfactory nerve even without a sense of smell. Although the human sense of smell is very sensitive to H2S, using the nose to detect hydrogen sulfide gas is fatal and unacceptable. In addition, in medicine, the type and concentration of a patient's exhaled gases are often detected to determine the type and severity of a disease. Smoke detectors, breathalyzers, and other devices are used to detect gases to ensure safety in production and daily life. Therefore, gas detection has practical applications.

[0003] Common methods for detecting H2S gas include spectrophotometry, electrochemistry, and mass spectrometry, but these methods all require expensive analytical instruments and are complex to operate. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a spherical zinc-tin composite metal oxide, and to apply it as a gas-sensitive sensing material for H2S detection, so as to achieve early warning of the surrounding environment and thus ensure the safety of the human living environment.

[0005] The preparation method of the spherical zinc-tin composite metal oxide is as follows: calcining zinc-tin hydrotalcite at 400-600℃ for 0.5-5h yields the spherical zinc-tin composite metal oxide.

[0006] The aforementioned spherical zinc-tin composite metal oxide is a porous spherical shape, consisting of porous spherical multi-level structures of 8-10 μm composed of porous thin sheets of 50-400 nm.

[0007] The preparation method of the zinc-tin hydrotalcite is as follows: soluble divalent zinc salt, soluble tetravalent tin salt, and urea are mixed and dissolved in deionized water, wherein the molar ratio of zinc, tin, and urea is 2-4:1:9-18. Then, the mixture is placed in a reaction vessel and reacted at 90-120℃ for 20-36 hours. After natural cooling, the mixture is centrifuged, washed, and dried to obtain spherical zinc-tin hydrotalcite.

[0008] The above-prepared spherical zinc-tin composite metal oxide is used as a semiconductor gas-sensitive material.

[0009] The above-prepared spherical zinc-tin composite metal oxide is used in the preparation of H2S gas sensors.

[0010] The method for preparing the H2S gas sensor is as follows: A spherical zinc-tin composite metal oxide is ground and mixed with ethanol to form a paste, which is then uniformly coated onto the outside of a ceramic tube based on Al2O3. The paste is then aged at 150-300℃ for 1-7 days. Finally, the ceramic tube is welded onto a hexagonal base to obtain the H2S gas sensor. The stable resistance value of the H2S gas sensor in air is R. a The stable resistance value in H2S gas is R. g Sensitivity S is expressed as R a / R g .

[0011] This invention prepares a spherical ZnSn-LDHs precursor, which, after calcination in a muffle furnace, yields porous spherical ZnO / SnO2. Macroscopically, the spherical structure provides a large specific surface area and porosity, increasing the reaction area. The formation of mesopores enhances gas permeability, allowing gas to diffuse deeper into the material, effectively strengthening the reaction between the analyte and the gas-sensitive material. Microscopically, the abundance of oxygen vacancies activates the surface, increasing surface energy and activity, enhancing oxygen adsorption, thickening the depletion layer, and increasing the initial resistance. This results in higher sensitivity and response values ​​compared to non-spherical ZnO and SnO2 gas-sensitive materials. The porous spherical zinc-tin composite metal oxide, as an H2S gas-sensitive sensing material, possesses advantages in both macroscopic and microscopic aspects. Therefore, it can improve the H2S response value and response recovery time at room temperature, enhance H2S selectivity, and achieve H2S detection. It exhibits a fast response recovery time and excellent H2S selectivity, and its simple structure, simple working principle, low cost, and large-scale production capability make it feasible. Attached Figure Description

[0012] Figure 1 The XRD patterns are those of spherical ZnSn-LDHs (a), non-spherical ZnSn-LDHs (b), spherical ZnO / SnO2 obtained by calcination at 400℃ (c), 500℃ (d), and 600℃ (e), and non-spherical ZnO / SnO2 obtained by calcination at 500℃ (f).

[0013] Figure 2 These are SEM images of spherical ZnO / SnO2 obtained by calcining spherical ZnSn-LDHs (A), 400℃ (B), 500℃ (C), and 600℃ (D), non-spherical ZnSn-LDHs (E), and non-spherical ZnO / SnO2 obtained by calcining at 500℃ (F).

[0014] Figure 3 These are TEM (A, B, C, D) and HRTEM (a, b, c, d) images of spherical ZnO / SnO2 obtained by calcination at 400℃ (A, a), 500℃ (B, b), and 600℃ (C, c), and non-spherical ZnO / SnO2 obtained by calcination at 500℃ (D, d).

[0015] Figure 4 This is the HRTEM and elemental distribution diagram of the near-spherical ZnO / SnO2 obtained by calcination at 500℃.

[0016] Figure 5 EPR diagrams of spherical ZnSn-LDHs (a), non-spherical ZnSn-LDHs (b), spherical ZnO / SnO2 obtained by calcination at 400℃ (c), 500℃ (d) and 600℃ (e), and non-spherical ZnO / SnO2 obtained by calcination at 500℃ (f).

[0017] Figure 6 The UV plots (A) and band gap width plots (B) of ZnO, SnO2, and ZnO / SnO2 are shown.

[0018] Figure 7 The responses of ZnO (S1), SnO2 (S2), 400℃ (S3), 500℃ (S4), and 600℃ (S5) to 1 ppm H2S at different temperatures, and the responses of ZnO / SnO2 (S6) to H2S concentration at room temperature are shown in Figure (A) and Figure (B) of ZnO / SnO2 (S4) to H2S concentration at room temperature.

[0019] Figure 8 The dynamic response recovery of 1ppm H2S at 180℃ is shown for spherical ZnO / SnO2 calcined at 400℃ (A), 500℃ (B), and 600℃ (C) and non-spherical ZnO / SnO2 calcined at 500℃ (D). Detailed Implementation

[0020] Example 1

[0021] (1) Preparation of ZnSn-LDHs precursors: At room temperature, 3.213 g Zn(NO3)2·6H2O and 1.262 g SnCl4·5H2O were ultrasonically dissolved in 60 ml deionized water with 4 g urea and 1.5 g urea, respectively. The solutions were then placed in a reaction vessel and reacted at 100 °C for 30 h. After natural cooling, the solutions were centrifuged, washed, and dried to obtain ZnSn-LDHs precursor powders with a size of approximately 8-10 μm, consisting of near-spherical (4 g urea) and non-spherical (1.5 g urea) shapes. The XRD and SEM images of the near-spherical and non-spherical ZnSn-LDHs precursors are shown below. Figure 1 , 2 .

[0022] (2) Preparation of porous spherical and non-spherical zinc-tin composite metal oxide gas-sensitive materials: The precursor prepared in step (1) was calcined in air at 400℃, 500℃, and 600℃ respectively, with a heating rate of 10℃ / min and a holding time of 3h. Zinc-tin composite metal oxides with different compositions and morphologies were obtained. The XRD, SEM, and HRTEM images after calcination are shown in the figure. Figure 1 , 2 3. The elemental distribution of the calcined sample is shown in Figure 1. Figure 4 The results of oxygen vacancy detection are shown in Figure 5 The bandgap for solid-state ultraviolet calculations is shown in [reference needed]. Figure 6 XRD patterns showed that the amount of urea affected crystallinity, and the same trend was observed after calcination, indicating successful synthesis of ZnSn-LDHs. A ZnO-related peak appeared at 400℃, a weak SnO2 peak appeared at 500℃, and the overall peaks were sharp at 600℃, indicating better crystallinity. Figure 2 SEM revealed that after high-temperature calcination, a porous structure emerged while maintaining a near-spherical shape. At 400℃, the pores were small; at 500℃, both the number and diameter of pores increased; and at 600℃, a plate-like sintering occurred, with a decrease in the number of pores. More detailed morphology and elemental distribution were explained by HRTEM. Lattice analysis confirmed the formation of ZnO / SnO2, with the plate-like structure being ZnO and the granular structure being SnO2. Mapping showed a uniform elemental distribution. EPR indicated that the composite metal oxides formed after calcination at 400℃ and 500℃ had more oxygen vacancies, resulting in greater oxygen adsorption and thus a large number of active sites. Figure 6 Solid-state UV results showed that the band gap of the composite oxide generated after calcination was narrower than that of either of the individual oxides, indicating the formation of a composite and heterojunction between the two.

[0023] Fabrication and performance testing of a spherical zinc-tin composite H2S gas sensor:

[0024] The spherical and non-spherical composite metal oxides, pure ZnO, and pure SnO2, calcined at different temperatures in step (2), were placed in a mortar, mixed with a small amount of ethanol, and ground into a paste. The paste was then evenly applied to the surface of a ceramic tube with a fine brush and aged at 200°C for one day. A heating wire was added to the center of the ceramic tube, which was then welded to a hexagonal base and installed in an intelligent gas-sensitive analysis system. The widely accepted reaction mechanism is that oxygen molecules adsorb onto the surface of an n-type semiconductor material, taking away electrons from the conduction band to become adsorbed oxygen, generating different types of oxygen anions. This thickens the depletion layer and increases the material resistance. Then, H2S reacts with the oxygen anions on the surface to generate SO2, which then releases electrons back to the conduction band, thereby reducing the resistance.

[0025] The response value is obtained by measuring the change in resistance before and after the introduction of H2S gas. Performance testing is described in [link to performance test]. Figure 7 and Figure 8 The specific test data and response recovery time are shown in Table 1. It was found that the sample calcined at 500℃ had the highest response value and response recovery time, and could achieve detection at room temperature. This is mainly attributed to the fact that the designed material has a large specific surface area and transmittance on a macroscopic scale, and the doping of SnO2 on a microscopic scale introduces a large number of oxygen vacancies, which makes ZnO / SnO2 have excellent H2S gas sensing performance.

[0026] Table 1. Response time and recovery time to H2S at 180℃

[0027]

Claims

1. Use of a spheroid-like zinc-tin composite metal oxide in the preparation of a H2S gas sensor, characterized in that, The preparation method of the spheroid-like zinc-tin composite metal oxide is as follows: the zinc-tin hydrotalcite is calcined at 400-500 DEG C for 0.5-5 h to obtain the spheroid-like zinc-tin composite metal oxide; the obtained spheroid-like zinc-tin composite metal oxide is a porous spheroid-like shape, which is a porous spheroid-like multi-level structure of 8-10 µm composed of 50-400 nm porous flake; The preparation method of the zinc-tin hydrotalcite is as follows: a soluble divalent zinc salt, a soluble tetravalent tin salt and urea are mixed and dissolved in deionized water, wherein the molar ratio of zinc, tin and urea is 2-4:1:9-18, then the mixture is placed in a reaction kettle and reacted at 90-120 DEG C for 20-36 h, and after natural cooling, centrifugation, washing and drying, the spheroid-like zinc-tin hydrotalcite is obtained.

2. Use according to claim 1, characterized in that, The preparation method of the H2S gas sensor is as follows: after the spherical zinc-tin composite metal oxide is ground, it is mixed with ethanol to form a paste, which is uniformly coated on the outer surface of a ceramic tube with Al2O3 as the substrate, then the ceramic tube is aged at 150-300 DEG C for 1-7 days, the ceramic tube is welded on a hexagonal base to obtain the H2S gas sensor, the stable resistance value of the H2S gas sensor in air is R a , the stable resistance value in H2S gas is R g , and the sensitivity S is represented as R a / R g .

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