Method for preparing carbon-doped zinc oxide by using soybean stalk biological template and application thereof

Abstract

A method for preparing carbon-doped zinc oxide using soybean straw as a biotemplate and its application are disclosed. This method aims to address the technical problems of existing zinc oxide gas sensors, including poor selectivity for NO2 and H2S, high power consumption, poor response speed and long-term stability, and high detection limits. The method comprises: 1. Soybean straw pretreatment; 2. Precursor preparation; 3. Calcination treatment. The resulting carbon-doped zinc oxide material retains the natural multi-level tubular structure of soybean straw, has a rough surface, is assembled from nanoparticles, and is rich in oxygen vacancy defects. The detection limits for NO2 and H2S are 0.1 ppm and 0.05 ppm, respectively, making it suitable for automotive exhaust and food emission detection.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation and gas sensing technology, specifically relating to a method for preparing carbon-doped zinc oxide using biological templates and its application. Background Technology

[0002] Nitrogen dioxide (NO2) and hydrogen sulfide (H2S), both globally recognized as highly toxic and corrosive inorganic gases, pose serious threats to the environment and health. NO2 primarily originates from the combustion of fossil fuels, especially from vehicle exhaust, and is a key component of urban air pollution. Hydrogen sulfide (H2S), a "nerve gas," is widely found in industrial, agricultural, and daily waste disposal sites and livestock farms, posing a serious threat to the ecological environment and human health. Furthermore, H2S is associated with various respiratory diseases and can be used as a standard for assessing halitosis, gastrointestinal diseases, and food freshness. Both gases readily react with atmospheric water vapor to form nitrate and sulfate particulate matter, important precursors to acid rain and PM2.5 smog. Studies have shown that long-term exposure to low concentrations (such as 100 ppb NO2 and 83 ppb H2S) significantly increases the risk of respiratory and cardiovascular diseases, thus causing sustained and profound harm to environmental safety and public health. Therefore, rapid and effective monitoring of NO2 and H2S gases in the environment and food is of significant practical importance.

[0003] Metal-oxide-semiconductor (MOS) gas sensors have become a research hotspot in the field of gas detection due to their advantages such as high sensitivity, fast response, low cost, and ease of miniaturization. Among them, zinc oxide (ZnO), as a typical wide-bandgap n-type semiconductor, has advantages such as stable physicochemical properties and simple fabrication process, and is widely used in gas sensing. The detection mechanism of MOS sensors is usually based on the change in carrier concentration caused by the redox reaction between the target gas and the oxygen adsorbed on the material surface, which leads to a change in resistance. However, traditional single-component ZnO gas sensors still face many challenges in practical applications: First, their selectivity for NO2 and H2S is poor, and they are easily interfered with in complex gas environments; second, they usually require a high operating temperature (200~400 ℃) to activate the surface reaction, resulting in high power consumption; third, the response recovery speed and long-term stability still need to be improved, and the detection capability for low concentrations is insufficient. Summary of the Invention

[0004] This invention aims to address the technical problems of existing zinc oxide gas sensors, such as poor selectivity for NO2 and H2S detection, high power consumption, poor response speed and long-term stability, and high detection limits. It provides a method for preparing carbon-doped zinc oxide using soybean straw as a biological template and its application. This invention utilizes soybean straw as a biological template to prepare oxygen-vacancy-rich carbon-doped zinc oxide, enabling efficient detection of NO2 and H2S gases released from automobile exhaust and food samples at low temperatures.

[0005] The method for preparing carbon-doped zinc oxide using soybean straw biotemplate of the present invention is carried out according to the following steps:

[0006] I. Soybean straw pretreatment: Cut soybean straw (SS) into pieces, wash with water and dry; then put the straw into an ammonia solution, heat to boiling and maintain reflux for 6-8 hours. After reflux, wash until neutral and dry again to obtain pretreated straw template (t-SS).

[0007] II. Precursor preparation: The pretreated straw template was immersed in zinc nitrate hexahydrate solution, ultrasonically treated, and then allowed to stand and soak to allow zinc ions to be fully adsorbed onto the template; the straw template was filtered out and then dried to obtain zinc-straw precursor (Zn-SS).

[0008] III. Calcination Treatment: The zinc-straw precursor was placed in a muffle furnace and heated to 400-430℃ at a heating rate of 2-5℃ / min, and held for 2-3 hours for calcination. This removed the biological template and caused in-situ decomposition of the zinc salt, yielding carbon-doped zinc oxide prepared using soybean straw as a biological template. This carbon-doped zinc oxide material retains the natural multi-level tubular structure of soybean straw, has a rough surface, is assembled from nanoparticles, and is rich in oxygen vacancy defects.

[0009] Furthermore, the mass percentage concentration of the ammonia solution described in step one is 7% to 8%.

[0010] Furthermore, the drying temperature described in step one is 60~70 ℃.

[0011] Furthermore, the zinc salt solution mentioned in step two is a zinc nitrate hexahydrate [Zn(NO3)2·6H2O] solution, and the concentration of the zinc salt solution is 0.8~1 mol / L.

[0012] Furthermore, the ultrasonic treatment in step two lasts for 2 to 3 hours.

[0013] Furthermore, the soaking time described in step two is 2 to 3 days.

[0014] Furthermore, the drying temperature described in step two is 60~70 ℃.

[0015] The aforementioned application of preparing carbon-doped zinc oxide using soybean straw as a biotemplate involves using this carbon-doped zinc oxide as a gas-sensitive material to prepare NO2 and H2S gas sensors. These gas sensors can detect NO2 released from vehicle exhaust, as well as H2S gas released during the spoilage process of food samples, especially protein-rich foods.

[0016] This invention uses soybean straw as a biological template to synthesize multi-level carbon-doped zinc oxide. Soybean straw, as a widely available and renewable agricultural byproduct, possesses unique advantages unmatched by other templates: First, its naturally occurring multi-level tubular structure is highly ordered and uniformly distributed, providing excellent diffusion channels and numerous adsorption sites for gas molecules. Second, straw itself is rich in carbon, allowing for the simultaneous introduction of in-situ carbon doping and oxygen vacancies during controlled calcination, achieving integrated synergy of "structure replication-carbon doping-defect engineering." Finally, as an agricultural waste, straw has virtually zero raw material cost and is produced in huge quantities, fully aligning with the principles of green chemistry and sustainable development.

[0017] This invention successfully replicates the microscopic multi-level tubular structure of soybean straw as a template, preparing a GC / ZnO composite material with excellent gas-sensing properties. The calcination temperature has a decisive influence on the material's structure and properties. Using a relatively low calcination temperature of 400-430℃ not only perfectly preserves the multi-level tubular structure of the straw but also retains more biomass carbon while simultaneously introducing a large number of oxygen vacancy defects. This unique structure-component synergy is manifested in the following ways: the multi-level tubular structure provides rapid gas diffusion channels and abundant reaction interfaces; the appropriate amount of retained biomass carbon not only enhances the material's conductivity but also constructs a ZnO / C heterogeneous interface, further promoting carrier separation; and the high concentration of oxygen vacancies acts as active centers, significantly reducing the adsorption and activation energy of gas molecules. This unique structure and composition derived from soybean straw endows carbon-doped zinc oxide with excellent detection capabilities for H2S gas released during the spoilage of protein-rich foods. This is mainly attributed to the following synergistic mechanisms: First, the multi-level tubular structure derived from soybean straw provides an efficient channel for the rapid diffusion of H2S molecules; second, the abundant oxygen vacancies and biomass carbon residues in the material have a stronger adsorption affinity for H2S molecules; more importantly, this biological morphological structure derived from agricultural straw and the "biological homology recognition effect" generated by H2S gas—that is, the carbon skeleton and structural features derived from natural biological templates have a unique recognition affinity for H2S molecules, which also originate from the biological decay process, significantly enhancing the selective adsorption and response of the material to this target gas.

[0018] The sensor of this invention shows excellent application potential in monitoring the freshness of high-protein foods such as eggs and seafood, and can be used to detect NO2 and H2S gases released from automobile exhaust and food samples. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of the method for preparing carbon-doped zinc oxide using soybean straw biotemplates in Example 1.

[0020] Figure 2 Thermogravimetric (TG) analysis curves of the pretreated straw template (t-SS) in step 1 and the zinc-straw precursor (Zn-SS) in step 2 of Example 1 are shown.

[0021] Figure 3 A scanning electron microscope image of carbon-doped zinc oxide prepared in Example 1;

[0022] Figure 4 The fluorescence spectrum of carbon-doped zinc oxide prepared in Example 1;

[0023] Figure 5 The graphs show the response values ​​of the GC / ZnO-4 and ZnO-5 sensors prepared in Example 1 and Comparative Example 1 to 10 ppm NO2 at different operating temperatures.

[0024] Figure 6 The graphs show the response values ​​of the GC / ZnO-4 and ZnO-5 sensors prepared in Example 1 and Comparative Example 1 to 10 ppm H2S at different operating temperatures.

[0025] Figure 7 The response graphs of the GC / ZnO-4 and ZnO-5 sensors to 10 ppm SO2, CO, CO2, O2, H2, Cl2, NO2, NO and H2S gases at a temperature of 92 ℃ are shown.

[0026] Figure 8 The response graphs of the GC / ZnO-4 and ZnO-5 sensors to 10 ppm SO2, CO, CO2, O2, H2, Cl2, NO2, NO and H2S gases at a temperature of 133 ℃ are shown. Detailed Implementation

[0027] To more clearly illustrate the technical solution of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0028] Example 1: The method for preparing carbon-doped zinc oxide using soybean straw biotemplate in this example is carried out according to the following steps:

[0029] I. Soybean Straw Pretreatment: Soybean straw (SS) collected from Zhangbei County, Hebei Province was cut into pieces, washed with ultrapure water, and then dried in an oven at 70 ℃ for 8 hours. Then, the straw was placed in a 7.5% ammonia solution, heated to boiling, and refluxed for 8 hours. After reflux, it was washed with ultrapure water until neutral and then dried in an oven at 70 ℃ for 8 hours to obtain the pretreated straw template (t-SS).

[0030] II. Precursor Preparation: 1 gram of pretreated straw template was immersed in 100 mL of 0.9 mol / L zinc nitrate hexahydrate [Zn(NO3)2·6H2O] aqueous solution, ultrasonically treated for 3 hours, and then allowed to stand for 3 days to allow zinc ions to be fully adsorbed onto the template; the straw template was filtered out and dried in an oven at 70℃ for 8 hours to obtain zinc-straw precursor (Zn-SS).

[0031] III. Calcination treatment: The zinc-straw precursor was placed in a muffle furnace and heated to 410℃ at a heating rate of 2℃ / min and held for 2 hours for calcination to remove the biological template and decompose the zinc salt in situ. After natural cooling, a light yellow final product was obtained. It is carbon-doped zinc oxide prepared using soybean straw biological template, denoted as GC / ZnO-4.

[0032] The flowchart of the preparation and testing of carbon-doped zinc oxide using soybean straw biotemplate in Example 1 is shown below. Figure 1 As shown.

[0033] Thermogravimetric analysis was performed on the pretreated straw template (t-SS) in step 1 of Example 1 and the zinc-straw precursor (Zn-SS) in step 2. The thermogravimetric analysis results are shown in the figure below. Figure 2 As shown. From Figure 2 As can be seen from the TG curves of t-SS and Zn-SS at 410℃, the thermal weight loss of the carbon-doped zinc oxide prepared in Example 1 is 10.4%, which retains more biomass carbon.

[0034] Figure 3 Scanning electron microscope (SEM) images of carbon-doped zinc oxide prepared in Example 1, from... Figure 3 As can be seen, the carbon-doped zinc oxide prepared in Example 1 retains the natural multi-level tubular structure of soybean straw, has a rough surface, and is assembled from nanoparticles.

[0035] Figure 4 The fluorescence spectrum of carbon-doped zinc oxide prepared in Example 1 is shown below. Figure 4 It can be seen that there is a peak at 515 nm, which proves that the carbon-doped zinc oxide prepared in Example 1 introduces a large number of oxygen vacancy defects.

[0036] Comparative Example 1: This comparative example differs from Example 1 in that the calcination temperature in step three is 500 ℃, while the rest is the same as in Example 1. The carbon-doped zinc oxide prepared using soybean straw biotemplate is denoted as ZnO-5.

[0037] The GC / ZnO-4 and ZnO-5 materials prepared in Example 1 and Comparative Example 1, respectively, were coated onto ceramic tube electrodes to fabricate side-heated gas sensors. Their gas-sensing performance for 10 ppm NO2 and 10 ppm H2S was tested at operating temperatures ranging from 50 to 217 °C. The response curves of the sensors to 10 ppm NO2 at different operating temperatures are shown below. Figure 5 As shown, the response curves of the sensor to 10 ppm H2S at different operating temperatures are as follows: Figure 6 As shown. From Figure 5 It can be seen that at the optimal operating temperature of 92 ℃, the GC / ZnO-4 sensor exhibits the highest response value to 10 ppm NO2 gas (S = 205.1), approximately 1.3 times that of ZnO-5 (S = 158.0); from Figure 6 It can be seen that at the optimal operating temperature of 133 ℃, the GC / ZnO-4 sensor exhibits the highest response value to 10 ppm H2S gas (S = 82.3), approximately 2.1 times that of ZnO-5 (S = 38.1). (Comparison) Figure 5 and Figure 6 It can be seen that, compared with ZnO-5, the GC / ZnO-4 sensor exhibits a higher response value to NO2 at a relatively lower operating temperature.

[0038] The responses of the GC / ZnO-4 and ZnO-5 sensors to 10 ppm SO2, CO, CO2, O2, H2, Cl2, NO2, NO, and H2S gases were then tested at 92 ℃. The response histograms are shown below. Figure 7 As shown, from Figure 7 It can be seen that their response values ​​range from 1.03 to 23.9, with an extremely high response to 10 ppm NO2 gas (S = 205.1). The responses of the GC / ZnO-4 and ZnO-5 sensors to 10 ppm SO2, CO, CO2, O2, H2, Cl2, NO2, NO, and H2S gases were tested at 133 ℃. The response histograms are shown below. Figure 8 As shown, from Figure 8 It can be seen that their response values ​​are between 1.01 and 23.7, and they have an extremely high response to 10 ppm H2S gas (S = 82.3).

[0039] At operating temperatures of 92 ℃ and 133 ℃, the GC / ZnO-4 sensor was placed in pre-configured gas cylinders containing 0.1 ppm NO2 and 0.05 ppm H2S. The response values ​​were 1.25 and 1.33, respectively, indicating that the detection limit of the GC / ZnO-4 sensor for NO2 is 0.1 ppm and the detection limit of the GC / ZnO-4 sensor for H2S is 0.05 ppm.

[0040] The response time was calculated based on the time required for the GC / ZnO-4 sensor to achieve a 90% change in device resistance before and after responding to the target gas. The results showed that the response times of the GC / ZnO-4 sensor to 10 ppm NO2 and 10 ppm H2S were 58 s and 0.2 s, respectively.

[0041] The GC / ZnO-4 sensor was used to detect NO2 from automobile exhaust and low-concentration H2S gas released from hard-boiled eggs left for 7 hours. The results showed a response value of 2.6 for NO2 from automobile exhaust and 4.4 for H2S released from hard-boiled eggs left for 7 hours. This indicates that the material has potential application value in the fields of environmental monitoring (automobile exhaust) and food safety (food spoilage detection).

Claims

1. A method for preparing carbon-doped zinc oxide using soybean straw as a biotemplate, characterized in that, This method is performed in the following steps: I. Soybean straw pretreatment: Cut the soybean straw into pieces, wash it with water and dry it; then put the straw into an ammonia solution, heat it to boiling and keep it under reflux for 6-8 hours. After reflux, wash it until neutral and dry it again to obtain the pretreated straw template. II. Precursor preparation: The pretreated straw template was immersed in zinc nitrate hexahydrate solution, ultrasonically treated, and then allowed to stand and soak to allow zinc ions to be fully adsorbed onto the template; the straw template was filtered out and then dried to obtain zinc-straw precursor; III. Calcination treatment: The zinc-straw precursor was placed in a muffle furnace and heated to 400-430 ℃ at a heating rate of 2-5 ℃ / min and held for 2-3 hours for calcination to remove the biological template and decompose the zinc salt in situ, thus obtaining carbon-doped zinc oxide prepared using soybean straw biological template.

2. The method for preparing carbon-doped zinc oxide using soybean straw biotemplate according to claim 1, characterized in that, The mass percentage concentration of the ammonia solution mentioned in step one is 5% to 8%.

3. A method for preparing carbon-doped zinc oxide using soybean straw biotemplate according to claim 1 or 2, characterized in that, The drying temperature described in step one is 60~70 ℃.

4. A method for preparing carbon-doped zinc oxide using soybean straw biotemplates according to claim 1 or 2, characterized in that, The zinc salt solution mentioned in step two is zinc nitrate hexahydrate solution, and the concentration of the zinc salt solution is 0.8~1 mol / L.

5. A method for preparing carbon-doped zinc oxide using soybean straw biotemplates according to claim 1 or 2, characterized in that, The ultrasonic treatment in step two takes 2 to 3 hours.

6. A method for preparing carbon-doped zinc oxide using soybean straw biotemplate according to claim 1 or 2, characterized in that, The soaking time mentioned in step two is 2 to 3 days.

7. A method for preparing carbon-doped zinc oxide using soybean straw biotemplates according to claim 1 or 2, characterized in that, The drying temperature described in step two is 60~70 ℃.

8. The application of the carbon-doped zinc oxide prepared by the method of claim 1, characterized in that, This application uses carbon-doped zinc oxide as a gas-sensitive material to prepare NO2 gas sensors and / or H2S gas sensors.

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