A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material, its preparation method, and a n-butanol gas sensor

Abstract

The application provides a Sn-MOF@SnO2 / Fe2O3 multistage structure nanocomposite material and a preparation method and n-butanol gas sensor thereof, and belongs to the technical field of material synthesis, and aims to solve the technical problem of poor gas sensing performance of a Sn-MOF induced metal oxide nanocomposite material. The preparation method of the Sn-MOF@SnO2 / Fe2O3 multistage structure nanocomposite material comprises the following steps: tin source, ligand and alkali are added into a solvent I to prepare a mixed solution I, and then Sn-MOF is prepared through reaction; Sn-MOF, iron source and alkali precipitant are added into a solvent II to prepare a mixed solution II, and then Sn-MOF@SnO2 / Fe2O3 precursors are prepared through reaction under the condition of microwave assistance; and the Sn-MOF@SnO2 / Fe2O3 precursors are calcined to prepare the Sn-MOF@SnO2 / Fe2O3 multistage structure nanocomposite material. The n-butanol gas sensor prepared by using the Sn-MOF@SnO2 / Fe2O3 multistage structure nanocomposites as a sensitive layer has good gas sensing performance. The optimal detection working temperature of the sensor for n-butanol gas is 200 DEG C, and the sensor also has the advantages of fast response speed, large response value and good long-term stability.

Description

Technical Field

[0001] This invention belongs to the technical field of materials synthesis, and particularly relates to a gas-sensitive material. Background Technology

[0002] With the acceleration of industrialization, industrial production, transportation, and other sectors continuously emit harmful gases such as volatile organic compounds (VOCs), which not only seriously pollute the atmospheric environment but also directly threaten human health and ecological security. Against this backdrop, achieving accurate and real-time monitoring of low concentrations of harmful VOCs in the air has become a core requirement for environmental governance and public safety assurance, making gas sensor technology a research hotspot both domestically and internationally.

[0003] Among various gas sensors, those based on metal oxide semiconductor materials occupy an important research position due to their advantages such as environmental friendliness, portability, and low cost. Metal oxides such as SnO2, TiO2, ZnO, and Fe2O3 are commonly used gas-sensitive materials, and sensors fabricated from them exhibit characteristics such as high sensitivity, low power consumption, and short response recovery time. They can effectively detect a variety of harmful gases and have been widely used in daily life, medical diagnosis, agricultural production, and industrial safety.

[0004] Although metal oxide semiconductor gas-sensitive materials have broad application prospects, existing technologies still face several bottlenecks: First, they exhibit poor selectivity, with single metal oxides (such as n-type semiconductor SnO2 and Fe2O3 with unique electrical and catalytic properties) struggling to accurately identify target gases in complex gas environments. Second, they suffer from poor stability, easily affected by external environmental factors such as temperature and humidity, leading to drift in detection performance. Third, their operating temperature is relatively high, increasing energy consumption and limiting their application in room-temperature scenarios. Fourth, their detection sensitivity for low-concentration gases at room temperature is insufficient, and the short lifespan of the devices severely restricts their effectiveness in practical, complex scenarios.

[0005] Currently, relevant research has focused on optimizing the gas-sensing performance of multi-metal-based oxide semiconductor materials. For example, patent publication number CN115385372A discloses a moisture-resistant, highly selective, and responsive triethylamine gas-sensing material constructed based on a bimetallic MOF route, along with its preparation method and applications. The preparation method includes the preparation of a Sn / Zn bimetallic MOF precursor, followed by calcination in a muffle furnace under air atmosphere to obtain the moisture-resistant, highly selective, and responsive triethylamine gas-sensing material. This gas-sensing material can be fabricated into a side-heated sensor for the practical determination of triethylamine. Patent publication number CN117607219A discloses a flower-like MoS2-induced Fe2O3 / Fe2(MoO4)3 nanocomposite material, its preparation method, and its application. The preparation method of Fe2O3 / Fe2(MoO4)3 nanomaterial includes the following steps: dissolving and mixing a molybdenum source and a sulfur source in solvent I, adjusting the pH, and obtaining molybdenum disulfide through a hydrothermal reaction; dispersing and dissolving molybdenum disulfide and an iron source in solvent II, adding a precipitant, reacting under microwave-assisted conditions, and washing and drying the product; calcining the dried product to obtain the Fe2O3 / Fe2(MoO4)3 nanocomposite material using a two-step method. The obtained Fe2O3 / Fe2(MoO4)3 nanocomposite material exhibits good selectivity and stability response to ethanol gas.

[0006] Although the aforementioned patents have disclosed the application of multi-metal oxides in gas detection and confirmed the effectiveness of multi-component synergistic modification in improving gas sensing performance, there are significant differences in the detection performance and the types of target gases that metal oxide gas sensing materials with different structures can be adapted to. There are no existing technologies that disclose dedicated sensors for n-butanol gas, which cannot meet the actual needs for accurate and efficient monitoring of harmful gases such as n-butanol. Therefore, the development of high-performance gas sensing materials and sensors adapted for n-butanol detection still has important practical significance and research value. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a Sn-MOF@SnO2 / Fe2O3 hierarchical structure nanocomposite material, its preparation method, and its application. A n-butanol gas sensor made using the Sn-MOF@SnO2 / Fe2O3 hierarchical structure composite material exhibits excellent gas sensing performance.

[0008] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A method for preparing Sn-MOF@SnO2 / Fe2O3 hierarchical structured nanocomposite material includes the following steps: (1) Add tin source, ligand and base to solvent I to prepare mixture I, and then carry out reaction to prepare Sn-MOF; (2) Sn-MOF, iron source and alkaline precipitant were added to solvent II to prepare mixed solution II, and the reaction was carried out under microwave-assisted conditions to obtain Sn-MOF@SnO2 / Fe2O3 precursor; (3) The Sn-MOF@SnO2 / Fe2O3 precursor was collected by centrifugation, washed, freeze-dried and then calcined to obtain the Sn-MOF@SnO2 / Fe2O3 multi-level structured nanocomposite material.

[0009] The tin source is one or two of stannous sulfate, stannous chloride, or stannous acetate; the ligand is terephthalic acid or phthalic acid; the base is one or two of sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia, or urea; and the solvent I is one or two of water, ethanol, or N,N-dimethylformamide.

[0010] The concentration of the tin source in the mixture I is 0.001-0.02 mol / L; the molar ratio of the tin source to the ligand is 1:(0.8-1.5), and the molar ratio of the ligand to the base is 1:(2-4).

[0011] The reaction in step (1) is carried out under stirring, at a temperature of room temperature to 100°C, for a time of 2 to 12 hours.

[0012] The iron source is one or more of ferric nitrate, ferric chloride, or ferric sulfate; the alkaline precipitant is one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia, or urea; and the solvent II is one or two of water, ethanol, or N,N-dimethylformamide.

[0013] In step (2), the molar ratio of the iron source to the tin source in step (1) for Sn-MOF preparation is 1:(0.8-19), and the molar ratio of the iron source to the alkaline precipitant is 1:(3-6); the concentration of the iron source in the mixed solution II is 0.002-0.01 mol / L.

[0014] The microwave-assisted conditions are: reaction temperature of 100℃, microwave power of 100-1000W, and time of 1-20min.

[0015] The washing solvent is water and ethanol, and the drying is carried out by freeze drying at -40 to 80°C for 12 to 24 hours; the calcination temperature is 500 to 600°C and the time is 1 to 6 hours.

[0016] A n-butanol gas sensor includes a sensor substrate and a gas-sensitive layer coated on the surface of the substrate, wherein the raw material of the gas-sensitive layer includes Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material.

[0017] Preferably, the sensor substrate is a hollow ceramic tube, the outer wall of the ceramic tube is provided with a platinum electrode, and a nickel-chromium alloy heating wire is built inside; the gas-sensitive layer is coated on the surface of the ceramic tube.

[0018] The beneficial effects of this invention are as follows: A rod-shaped Sn-MOF matrix rich in micro- and nano-pores is prepared through a chemical reaction. Under microwave assistance, using Sn-MOF as the matrix and precursor, Fe(OH)3 nanoparticles are uniformly coated on the surface of the micro- and nano-pores. Finally, calcination in air generates a Sn-MOF@SnO2 / Fe2O3 hierarchical nanotube composite material. During calcination, Fe2O3 and SnO2 rely on the nodes of the metal-organic framework to form a tubular porous main morphology. This means that, per unit mass, more Fe2O3 / SnO2 heterojunction interfaces with large specific surface areas are provided as active sites and adsorption sites for gas adsorption, electron transport, and reaction, which is extremely beneficial to improving the interaction between the gas and the composite material, thereby improving the gas-sensing performance. Calcination in air can retain the Sn-MOF matrix framework while simultaneously converting the solvent molecules and their organic ligands in its pores into gaseous CO2 and H2O, which then evaporate, thus forming a porous structure on its surface. Simultaneously, under microwave irradiation, Fe(OH)3 uniformly adheres to the inner and outer surfaces of the Sn-MOF-based micro-nanopores. During calcination in air, Fe(OH)3 and Sn-MOF react with oxygen in the air at high temperatures to generate Fe2O3 / SnO2, releasing heat. The escaped gas during the reaction creates numerous pores, and combined with the Kirkendall effect, forms a porous Sn-MOF@SnO2 / Fe2O3 hierarchical nanotube composite material with a large specific surface area. The Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material obtained using the above green preparation method exhibits good selectivity and long-term stability response to n-butanol gas, with an optimal detection operating temperature of 200℃. The sensor also boasts advantages such as fast response speed and high response value. This is of great significance for effectively solving the problems of poor detection selectivity, excessively long response time, and poor stability of gas sensors in previous gas-sensitive detection methods. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The image shows an SEM image of Sn-MOF@SnO2 prepared in Comparative Example 1; in the image, (a) is a low-magnification SEM image; and (b) is a high-magnification SEM image.

[0021] Figure 2 The images show SEM images of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1; in the images, (a) is a low-magnification SEM image and (b) is a high-magnification SEM image.

[0022] Figure 3 The XRD pattern of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1.

[0023] Figure 4 The gas-sensitive response-time dynamic curves for n-butanol are shown in (a) Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite materials prepared in Example 1; and (b) Sn-MOF@SnO2 hierarchical nanocomposite materials prepared in Comparative Example 1.

[0024] Figure 5 The image shows the sensitivity of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1 to different concentrations of n-butanol as a function of temperature.

[0025] Figure 6 The response recovery time images of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1 at various temperatures are shown.

[0026] Figure 7 Selectivity images of different gases for the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (0.1 mmol) and NaOH (0.2 mmol) were dissolved and neutralized. The mixture was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 0.1 mmol of stannous sulfate was added and the mixture was stirred on a magnetic stirrer for 6 hours to carry out coordination polymerization and form a uniform suspension.

[0029] (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then dried in air at 60°C for 12 hours to obtain a white powder product Sn-MOF.

[0030] (3) Disperse all Sn-MOF obtained in step (2) in 50 mL of deionized water. After it is completely dissolved, add 0.1 mmol of ferric nitrate and stir it on a magnetic stirrer for 1 h until it is completely dissolved. Then add 0.45 mmol of urea to form a uniform suspension.

[0031] (4) Place the suspension in a 450 W microwave oven and set the boiling temperature to 100°C. Irradiate the reaction for about 2 minutes until boiling, then continue boiling for 3 minutes. After naturally cooling to about 25°C, centrifuge to collect the precipitate, wash it multiple times with water and anhydrous ethanol, and then freeze dry at -40°C for 12 hours.

[0032] (5) Place the dried product in a crucible and calcine it in air at 500°C for 2 hours to obtain the Sn-MOF@SnO2 / Fe2O3 composite material.

[0033] Example 2 A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (1 mmol) and NaOH (2 mmol) were dissolved to neutralize the solution. The solution was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 0.9 mmol of stannous sulfate was added and the solution was stirred on a magnetic stirrer for 6 hours to carry out coordination polymerization reaction and form a uniform suspension.

[0034] (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then dried in air at 60°C for 12 hours to obtain a white powder product Sn-MOF.

[0035] (3) Disperse all Sn-MOF obtained in step (2) in 50 mL of deionized water. After it is completely dissolved, add 0.2 mmol of ferric nitrate and stir it on a magnetic stirrer for 1 h until it is completely dissolved. Then add 1.2 mmol of urea to form a uniform suspension. (4) Place the suspension in a 300 W microwave oven and set the boiling temperature to 100℃. Irradiate the reaction for about 5 minutes until boiling, then continue boiling for another 5 minutes. Cool naturally to room temperature and centrifuge to collect the precipitate. Wash it multiple times with water and anhydrous ethanol, and then freeze dry at -60℃ for 15 hours.

[0036] (5) The dried product was placed in a crucible and calcined in air at 500°C for 3 hours to obtain Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material.

[0037] Example 3 A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (0.5 mmol) and NaOH (1.5 mmol) were dissolved and neutralized. The mixture was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 0.4 mmol of stannous chloride was added and the mixture was stirred on a magnetic stirrer for 3 hours to carry out coordination polymerization and form a uniform suspension. (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then dried in air at 60°C for 12 h to obtain a white powder product Sn-MOF. (3) Disperse all Sn-MOF obtained in step (2) in 50 mL of deionized water. After it is completely dissolved, add 0.5 mmol of ferric chloride and stir it on a magnetic stirrer for 1 h until it is completely dissolved. Then add 1 mL of ammonia water (1 mol / L) to form a uniform suspension. (4) Place the suspension in an 800 W microwave oven and irradiate it for about 2 minutes until it boils, then continue boiling for 6 minutes. After naturally cooling to about 25°C, centrifuge to collect the precipitate, wash it several times with water and anhydrous ethanol, and then freeze dry it at -40°C for 16 hours.

[0038] (5) The dried product was placed in a crucible and calcined in air at 550°C for 2 hours to obtain Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material.

[0039] Example 4 A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (0.3 mmol) and ammonia (0.9 mL, concentration 1 mol / L) were dissolved and neutralized. The mixture was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 0.2 mmol of stannous chloride was added and the mixture was stirred on a magnetic stirrer for 6 hours to carry out coordination polymerization and form a uniform suspension. (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then dried in air at 70°C for 12 h to obtain a white powder product Sn-MOF; (3) Disperse all Sn-MOF obtained in step (2) in 50 mL of deionized water. After it is completely dissolved, add 0.2 mmol of ferric nitrate and stir it on a magnetic stirrer for 1 h until it is completely dissolved. Then add 0.9 mmol of urea to form a uniform suspension. (4) Place the suspension in a 900 W microwave oven and irradiate it for about 2 minutes until it boils, then continue boiling for 4 minutes. After naturally cooling to about 25°C, centrifuge to collect the precipitate, wash it several times with water and anhydrous ethanol, and then freeze dry for 12 hours.

[0040] (5) The dried product was placed in a crucible and calcined in air at 600°C for 2 hours to obtain Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material.

[0041] Example 5 A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (0.2 mmol) and NaOH (0.4 mmol) were dissolved and neutralized. The mixture was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 0.15 mmol of stannous sulfate was added and the mixture was stirred on a magnetic stirrer for 6 hours to carry out coordination polymerization and form a uniform suspension. (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then dried in air at 60°C for 12 h to obtain a white powder product Sn-MOF. (3) Disperse all Sn-MOF obtained in step (2) in 50 mL of deionized water. After it is completely dissolved, add 0.1 mmol of ferric nitrate and stir it on a magnetic stirrer for 1 h until it is completely dissolved. Then add 0.45 mmol of urea to form a uniform suspension. (4) Place the suspension in a 1000 W microwave oven and irradiate it for about 1 minute until it boils, then continue boiling for 3 minutes. After naturally cooling to about 25°C, centrifuge to collect the precipitate, wash it several times with water and anhydrous ethanol, and then freeze dry it at -40°C for 24 hours.

[0042] (5) The dried product was placed in a crucible and calcined in air at 600°C for 1 h to obtain Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material.

[0043] Example 6 A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (2 mmol) and NaOH (4 mmol) were dissolved to neutralize the solution. The solution was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 1.9 mmol of stannous sulfate was added and the solution was stirred on a magnetic stirrer for 6 hours to carry out coordination polymerization reaction and form a uniform suspension. (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then dried in air at 60°C for 12 h to obtain a white powder product Sn-MOF. (3) Disperse all Sn-MOF obtained in step (2) in 50 mL of deionized water. After it is completely dissolved, add 0.3 mmol of ferric nitrate and stir it on a magnetic stirrer for 1 h until it is completely dissolved. Then add 1.2 mmol of urea to form a uniform suspension. (4) Place the suspension in a 350W microwave oven and irradiate it for about 6 minutes until it boils, then continue boiling for another 10 minutes. After cooling naturally to room temperature, centrifuge to collect the precipitate, wash it several times with water and anhydrous ethanol, and then freeze dry it at -80℃ for 12 hours.

[0044] (5) The dried product was placed in a crucible and calcined in air at 600°C for 1 h to obtain Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material.

[0045] Example 7 A Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (2 mmol) and NaOH (8 mmol) were dissolved and neutralized. The mixture was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 1.9 mmol of stannous acetate was added and the mixture was stirred on a magnetic stirrer for 12 hours to carry out coordination polymerization and form a uniform suspension. (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then dried in air at 60°C for 12 h to obtain a white powder product Sn-MOF. (3) Disperse all Sn-MOF obtained in step (2) in 50 mL of deionized water. After it is completely dissolved, add 0.1 mmol of ferric sulfate and stir it on a magnetic stirrer for 1 h until it is completely dissolved. Then add 0.3 mmol of urea to form a uniform suspension. (4) Place the suspension in a 100W microwave oven and irradiate it for about 10 minutes until it boils, then continue boiling for 20 minutes. After cooling naturally to room temperature, centrifuge to collect the precipitate, wash it several times with water and anhydrous ethanol, and then freeze dry it at -80℃ for 12 hours.

[0046] (5) The dried product was placed in a crucible and calcined in air at 550°C for 6 hours to obtain Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material.

[0047] Comparative Example 1 A Sn-MOF@SnO2 hierarchical nanocomposite material is prepared by the following steps: (1) In 100 ml of deionized water, terephthalic acid (15 mmol) and NaOH (30 mmol) were dissolved to neutralize the solution. The solution was stirred on a magnetic stirrer for 30 minutes until it was completely dissolved. Then, 15 mmol of stannous sulfate solution was added and the solution was stirred on a magnetic stirrer for 6 hours to carry out coordination polymerization reaction and form a uniform suspension. (2) The prepared solution was centrifuged to collect the precipitate, washed repeatedly with water and anhydrous ethanol, and then freeze-dried at -40℃ for 12h to obtain a white powder product Sn-MOF; (3) The dried Sn-MOF product was placed in a crucible and calcined in air at 500°C for 3 hours to obtain Sn-MOF@SnO2 hierarchical nanocomposite material.

[0048] Application examples Using the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material synthesized in Example 1 as the gas-sensitive functional layer, a corresponding gas-sensitive element was prepared. The specific procedure was as follows: A small amount of sample was placed in a clean agate mortar thoroughly cleaned with deionized water, and initially ground into a fine powder using a similarly clean pestle. Then, an appropriate amount of anhydrous ethanol was added, and grinding continued thoroughly until a uniform paste was formed. Next, the paste was uniformly coated onto the surface of an alumina ceramic tube with a platinum electrode using a clean, fine-bristled brush, ensuring a uniform coating thickness and taking care to avoid covering the internal platinum resistance wire.

[0049] Subsequently, with the aid of fine tweezers, the nickel-chromium alloy resistance wire was carefully threaded into the center of the ceramic tube. Care must be taken to avoid damaging the resistance wire due to stretching during this process. Afterwards, the platinum leads on the ceramic tube and the threaded resistance wire were soldered to the corresponding pins of the six-pin socket, thus completing the component assembly. A system gas sensitivity test was then conducted on the sensing element using n-butanol as the primary gas.

[0050] Following the same process flow, corresponding gas-sensitive elements were prepared for the samples synthesized in Examples 2 to 6 and Comparative Example 1, respectively, for system performance testing.

[0051] Figure 1The image shows an SEM image of Sn-MOF@SnO2 prepared in Comparative Example 1. It can be seen that the tubular structure is very obvious and has the advantages of large specific surface area.

[0052] Figure 2 The images show SEM images of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1; in the image, (a) is a low-magnification SEM image; and (b) is a high-magnification SEM image. The tubular hierarchical structure of most Sn-MOF@SnO2 / Fe2O3 components is clearly observable, compared to... Figure 1 Images (a) and (b) show that Sn-MOF@SnO2 / Fe2O3 inherited the good morphology and large specific surface area of ​​Sn-MOF during the preparation process. In image (b), Fe2O3 / SnO2 particles are clearly loaded on the metal nodes.

[0053] Figure 3 The image shows the XRD pattern of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1.

[0054] Figure 4 The image shows the real-time sensitivity dynamics of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1 to different concentrations of n-butanol gas. The test temperature was 200℃. Figure 4 As can be seen, the sensitivity of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite to n-butanol gas increases with increasing n-butanol concentration. At a n-butanol concentration of 50 ppm, the sensitivity of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite to n-butanol reaches 150 (ppm). Figure 4 a). Meanwhile, at a test temperature of 200℃ and a n-butanol concentration of 50 ppm, the sensitivity of Sn-MOF preparation in Comparative Example 1 was measured to be 6.8 (…). Figure 4 b).

[0055] Gas Sensing Performance Testing: The gas sensing performance was tested using an HW-30A gas sensing element tester. The prepared gas sensing element was inserted into the electronic board of the tester, and quality testing and aging were performed at 300℃. The test temperature could be adjusted to 300℃ by regulating the heating voltage, thus controlling the tester's operating temperature range. The load voltage across the test element could be changed by adjusting the load resistor, achieving the purpose of testing the element at different temperatures. The system was tested for the gas sensing performance of different concentrations of n-butanol gas at different operating temperatures: 160℃, 180℃, 200℃, 240℃, and 260℃. The target liquid concentrations were 0.1ppm, 0.5ppm, 1ppm, 5ppm, 10ppm, 25ppm, and 50ppm.

[0056] Figure 5 The response of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1 to different concentrations of n-butanol gas at different temperatures was observed. The sensitivity increased with increasing n-butanol gas concentration at each temperature. For the same gas concentration, the sensitivity initially increased and then decreased with increasing temperature. The optimal testing temperature was around 200°C, which is significantly lower than the previously reported optimal temperature of over 300°C, demonstrating a clear advantage in low-temperature detection.

[0057] Figure 6 The bar charts showing the response recovery time of n-butanol gas to the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1 at different temperatures reveal that the response recovery time generally decreases with increasing temperature, indicating a faster response rate. At 200℃, the response / recovery times were 18 s and 65 s, respectively.

[0058] Figure 7 The selectivity of the Sn-MOF@SnO2 / Fe2O3 hierarchical nanocomposite material prepared in Example 1 for n-butanol gas relative to other gases, where n-butanol and other detection gases are both 10 ppm. As shown in the figure, the composite material exhibits better selectivity for even lower concentrations of n-butanol gas than for other gases with higher concentrations.

[0059] When exposed to n-butanol gas, the resistivity of the Sn-MOF@SnO2 / Fe2O3 hierarchical structure sample decreased rapidly, and after the gas supply was stopped, its resistance recovered to its initial state in a short time, exhibiting a fast recovery speed. This behavior is mainly due to the n-type semiconductor characteristics of the composite material as a whole. In air, oxygen molecules adsorb onto the material surface and capture free electrons from the material's conduction band, forming a relatively thick carrier depletion layer on the surface, leading to an increase in sensor resistance. Furthermore, the n-n heterojunction formed by the Sn-MOF@SnO2 / Fe2O3 hierarchical structure within the material further enhances the depletion effect, further increasing the resistance. However, when the sensor is in a n-butanol atmosphere, the n-butanol molecules adsorbed on the material surface react with the captured electrons, causing the electrons to return to the conduction band, thereby reducing the width of the depletion layer and causing a significant decrease in resistance. This significant change in resistance results in high gas sensitivity for the gas-sensitive element based on the Sn-MOF@SnO2 / Fe2O3 hierarchical composite material.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a multi-level structured nanocomposite material, characterized in that, Includes the following steps: (1) Add tin source, ligand and base to solvent I to prepare mixture I, and then carry out reaction to prepare Sn-MOF; (2) Sn-MOF, iron source and alkaline precipitant were added to solvent II to prepare mixed solution II, and the reaction was carried out under microwave-assisted conditions to obtain Sn-MOF@SnO2 / Fe2O3 precursor; (3) The Sn-MOF@SnO2 / Fe2O3 precursor was washed, dried and then calcined to prepare a multi-level structured nanocomposite material; The tin source is one or more of stannous sulfate, stannous chloride, or stannous acetate; the ligand is terephthalic acid or phthalic acid; the base in step (1) is one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia, or urea; the solvent I is one or two of water, ethanol, or N,N-dimethylformamide. The concentration of the tin source in the mixture I is 0.001-0.02 mol / L; the molar ratio of the tin source to the ligand is 1:(0.8-1.5), and the molar ratio of the ligand to the base is 1:(2-4). The molar ratio of the iron source in step (2) to the tin in the Sn-MOF prepared in step (1) is 1:(0.8-19), and the molar ratio of the iron source to the alkaline precipitant in step (2) is 1:(3-6). The microwave-assisted conditions are: reaction temperature of 100℃, microwave power of 100-1000W, and time of 1-20min; The calcination temperature is 500-600℃ and the calcination time is 1-6h.

2. The method for preparing the multi-level structured nanocomposite material according to claim 1, characterized in that, The reaction in step (1) is carried out under stirring, the reaction temperature is room temperature to 100℃, and the reaction time is 2 to 12 hours.

3. The method for preparing the multi-level structured nanocomposite material according to claim 1, characterized in that, The iron source is one of ferric nitrate, ferric chloride, or ferric sulfate; the alkaline precipitant is one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, ammonia, or urea; and the solvent II is one or two of water, ethanol, or N,N-dimethylformamide.

4. The method for preparing the multi-level structured nanocomposite material according to claim 1, characterized in that, The washing solvent is water and ethanol, and the drying is carried out by freeze drying at -40 to 80°C for 12 to 24 hours.

5. The multi-level structured nanocomposite material prepared by the method according to any one of claims 1-4.

6. A n-butanol gas sensor, comprising a sensor substrate and a gas-sensitive layer coated on the surface of the substrate, characterized in that, The raw material for the gas-sensitive layer includes the multi-level structured nanocomposite material described in claim 5.

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