A method for preparing a lanthanum ferrite / biochar composite material and its application in gas detection.

Abstract

The application discloses a preparation method of a lanthanum ferrite / biochar composite material and application thereof in detection of gas, and belongs to the technical field of gas-sensitive sensor materials. The application first adopts a NaOH solution to treat rice husks, and prepares biochar with a porous structure after calcination, then combines the high specific surface area, porous structure and surface functional groups of the biochar with the P-type semiconductor characteristics and high catalytic activity of LaFeO3, and significantly improves the adsorption capacity and electron transmission efficiency of the composite material to ethanol. Moreover, the LaFeO3 in the composite material obtained by the preparation method of the application is uniformly loaded on the surface of the biochar in the form of regular spherical nanoparticles, and forms a porous interconnected structure, meanwhile, the surface of the biochar still retains rich functional groups such as hydroxyl groups and carboxyl groups, high-sensitivity, low-energy-consumption and high-selectivity detection of ethanol are realized, and the response speed and stability are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of gas-sensitive sensor material technology, and particularly relates to a method for preparing a lanthanum ferrite / biochar composite material and its application in gas detection. Background Technology

[0002] Ethanol is a common pollutant among volatile organic compounds (VOCs), and excessive exposure can harm human health and pose safety hazards. Traditional gas detection methods are costly and have low automation levels, while metal-oxide-semiconductor (MODS) sensors are widely studied due to their advantages such as low cost and simple structure.

[0003] LaFeO3, as a p-type semiconductor, possesses high catalytic activity and redox properties, but as a single material, it suffers from insufficient sensitivity, high optimal operating temperature (e.g., the optimal temperature for detecting ethanol with pure LaFeO3 is 240℃), and limited selectivity. Biochar, a porous carbon material, features high specific surface area, abundant surface functional groups, and low cost. Its porous structure increases gas diffusion pathways, and its surface functional groups enhance the chemisorption of target gases. However, research on the composite of biochar and perovskite oxides for gas sensors is currently limited. Therefore, there is an urgent need to develop a composite material that synergistically enhances the gas-sensing performance of LaFeO3 using biochar. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for preparing a lanthanum ferrite / biochar composite material and its application in gas detection.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a lanthanum ferrite / biochar composite material, comprising the following steps:

[0007] (1) Rice husks were pretreated with NaOH solution, dried and then calcined for the first time to obtain porous rice husk char.

[0008] (2) Citric acid, lanthanum nitrate and ferric nitrate were mixed and dissolved in water, and the lanthanum ferrate precursor was obtained by hydrothermal reaction.

[0009] (3) The porous rice husk char obtained in step (1) and the lanthanum ferrite precursor obtained in step (2) are mixed and then subjected to a second calcination to obtain the lanthanum ferrite / biochar composite material.

[0010] Steps (1) and (2) are not in any particular order.

[0011] Technical Principle: This invention first treats rice husks with NaOH solution, then calcines them to prepare biochar with a porous structure. Combining the high specific surface area, porous structure, and surface functional groups of biochar with the p-type semiconductor properties and high catalytic activity of LaFeO3, the adsorption capacity and electron transport efficiency of the composite material for ethanol are significantly improved. Furthermore, in the composite material prepared by this invention, LaFeO3 is uniformly loaded as regular spherical nanoparticles on the surface of the biochar, forming a porous interconnected structure. Simultaneously, the biochar surface retains abundant hydroxyl and carboxyl functional groups, achieving high sensitivity, low energy consumption, and high selectivity for ethanol detection, with significantly improved response speed and stability.

[0012] Further, in step (1), the concentration of the NaOH solution is 1 mol / L; the pretreatment time is 36 h; and / or,

[0013] The first calcination temperature is 750℃, the first calcination time is 2h, and the rate of heating to the first calcination temperature is 1℃ / min.

[0014] Furthermore, in step (2), the molar ratio of lanthanum nitrate and ferric nitrate is 1:1.

[0015] Furthermore, in step (2), the molar ratio of citric acid to lanthanum nitrate is 2:1.

[0016] Furthermore, in step (2), the temperature of the hydrothermal reaction is 180°C and the time of the hydrothermal reaction is 9 hours.

[0017] Furthermore, in step (3), the mass ratio of the porous rice husk char to the lanthanum ferrite precursor is (1-5):1.

[0018] Furthermore, in step (3), the second calcination temperature is 750°C, the second calcination time is 2 hours, and the rate of heating to the second calcination temperature is 1°C / min.

[0019] The present invention provides a lanthanum ferrite / biochar composite material prepared by the preparation method described above, wherein the lanthanum ferrite / biochar composite material comprises porous rice husk char and lanthanum ferrite nanoparticles loaded on the surface of the porous rice husk char, and the lanthanum ferrite / biochar composite material has a porous structure.

[0020] Furthermore, the lanthanum ferrite nanoparticles are spherical in shape; the diameter of the lanthanum ferrite nanoparticles is 160-200 nm.

[0021] The present invention also provides the application of the lanthanum ferrite / biochar composite material described in the above technical solution in the detection of ethanol.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] This invention removes impurities and optimizes surface polarity by treating rice husks with NaOH solution, thereby enhancing the interfacial bonding between rice husk char and LaFeO3. By controlling the hydrothermal reaction and calcination conditions, uniform loading of LaFeO3 nanospheres on the surface of rice husk char is achieved, forming a porous structure. By controlling the mass ratio of porous rice husk char to lanthanum ferrite precursor, a high specific surface area and a pore size distribution dominated by mesopores are ensured in the composite material. Finally, by controlling the above process conditions, a composite material with high sensitivity and selectivity to ethanol gas, as well as short response time and good stability, is obtained.

[0024] The lanthanum ferrite / biochar composite material prepared by this invention has a high response value to ethanol (S≥10, 50ppm) and a low optimal operating temperature (≤220℃). Its response to ethanol is significantly higher than that of other VOCs gases (such as acetone, formaldehyde, n-butanol, etc.), with a response ratio ≥3:1. The short-term repeatability error is <1%, and the response value remains above 90% of the initial value in the long-term stability test.

[0025] For the detection of low concentrations of ethanol gas (starting from 10 ppm) and industrial safety monitoring, this invention solves the problems of high cost, high power consumption and slow response of traditional sensors. The lanthanum ferrite / biochar composite material provided by this invention is suitable for leak detection in the fields of food, medical and motor vehicle fuel. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 The images show SEM and TEM images of LFO / C 3# prepared in Example 3 and lanthanum ferrite prepared in Comparative Example 1. (a) is a TEM image of lanthanum ferrite, (b) is a TEM image of LFO / C 3# (200 nm), (c) is an HRTEM image of LFO / C 3# (5 μm), (d) is a SAED image of LFO / C 3#, (e) is a SEM image of lanthanum ferrite, (f) is a SEM image of porous rice husk charcoal from step (1) of Example 3, (g) is a SEM image of LFO / C 3# (2 μm), (h) is a SEM image of LFO / C 3# (1 μm), (i) is a distribution map of La in LFO / C 3#, (j) is a distribution map of Fe in LFO / C 3#, (k) is a distribution map of C in LFO / C 3#, and (l) is a distribution map of LFO / C 3#. Distribution diagram of element O in #3;

[0028] Figure 2The response curves of LFO / C composite materials prepared in Examples 1-5 and lanthanum ferrite prepared in Comparative Example 1 to 50 ppm methanol gas at different temperatures are shown.

[0029] Figure 3 The reaction relationship between different methanol concentrations and optimal temperatures for the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1;

[0030] Figure 4 The linear relationship between the response values ​​of the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1 and the methanol concentration is shown.

[0031] Figure 5 The stability test results are for the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1.

[0032] Figure 6 The repeatability test results are for the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1.

[0033] Figure 7 The results show the test results of the selectivity of the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1 for ethanol. Detailed Implementation

[0034] 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.

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] This invention provides a method for preparing a lanthanum ferrite / biochar composite material, comprising the following steps:

[0037] (1) Rice husks were pretreated with NaOH solution, dried and then calcined for the first time to obtain porous rice husk char.

[0038] (2) Citric acid, lanthanum nitrate and ferric nitrate were mixed and dissolved in water, and the lanthanum ferrate precursor was obtained by hydrothermal reaction.

[0039] (3) The porous rice husk char obtained in step (1) and the lanthanum ferrite precursor obtained in step (2) are mixed and then subjected to a second calcination to obtain the lanthanum ferrite / biochar composite material.

[0040] Steps (1) and (2) are not in any particular order.

[0041] In a preferred embodiment, in step (1), the rice husks are further subjected to a drying process before being pretreated with NaOH solution; the drying process is carried out at a temperature of 80°C for 24 hours.

[0042] In a preferred embodiment, in step (1), the concentration of the NaOH solution is 1 mol / L; the pretreatment time is 36 h. This invention removes impurities from rice husks and optimizes their surface polarity by treating them with NaOH solution, thereby enhancing the interfacial bonding between the rice husks and LaFeO3.

[0043] In a preferred embodiment, in step (1), the drying temperature is 80°C and the drying time is 24 hours. Excessive drying temperature can cause some hydroxyl groups on the surface of the biochar to detach, affecting the gas-sensitive properties of the composite material.

[0044] In a preferred embodiment, in step (1), the temperature of the first calcination is 750°C, the time of the first calcination is 2 hours, and the rate of heating to the first calcination temperature is 1°C / min.

[0045] In a preferred embodiment, in step (2), the molar ratio of lanthanum nitrate to ferric nitrate is 1:1. This invention ensures the successful synthesis of LaFeO3 by controlling the molar ratio of lanthanum nitrate to ferric nitrate.

[0046] In a preferred embodiment, in step (2), the lanthanum nitrate is preferably La(NO3)3·6H2O; and the ferric nitrate is preferably Fe(NO3)3·9H3O.

[0047] In a preferred embodiment, step (2) further includes dissolving citric acid, lanthanum nitrate and ferric nitrate in water in a 50°C water bath; the dissolution is carried out under stirring conditions; the stirring rate is 1000 r / min and the stirring time is 30 min.

[0048] In a preferred embodiment, in step (2), the molar ratio of citric acid to lanthanum nitrate is 2:1. Citric acid in this invention acts as a complexing agent to prevent metal ions from forming hydroxide precipitates in the solution, ensuring a uniform distribution of La and Fe elements.

[0049] In a preferred embodiment, in step (2), the hydrothermal reaction temperature is 180°C and the hydrothermal reaction time is 9 hours. By conducting the hydrothermal reaction under the above conditions, this invention ensures the uniformity of the LaFeO3 precursor, thereby facilitating the uniform loading of LaFeO3 on the surface of rice husk charcoal.

[0050] In a preferred embodiment, in step (3), the mass ratio of the porous rice husk char to the lanthanum ferrite precursor is (1-5):1, more preferably (1-3):1. The mass of the porous rice husk char and the lanthanum ferrite precursor has a significant impact on the gas-sensing properties of the composite material. Controlling the mass ratio of the porous rice husk char to the lanthanum ferrite precursor within the above range is beneficial for obtaining a composite material with high sensitivity, high selectivity, short response time, and good stability.

[0051] In a preferred embodiment, in step (3), the second calcination temperature is 750°C, the second calcination time is 2 hours, and the rate of heating to the second calcination temperature is 1°C / min. By performing the second calcination under the above conditions, this invention achieves both the successful synthesis of LaFeO3 nanospheres and the uniform loading of LaFeO3 nanospheres onto the surface of rice husk charcoal, thereby forming a composite material with a porous structure.

[0052] The present invention provides a lanthanum ferrite / biochar composite material prepared by the preparation method described above, wherein the lanthanum ferrite / biochar composite material comprises porous rice husk char and lanthanum ferrite nanoparticles loaded on the surface of the porous rice husk char, and the lanthanum ferrite / biochar composite material has a porous structure.

[0053] In a preferred embodiment, the lanthanum ferrite nanoparticles are spherical in shape; the diameter of the lanthanum ferrite nanoparticles is 160-200 nm.

[0054] In a preferred embodiment, the specific surface area of ​​the lanthanum ferrite / biochar composite material is >200 m². 2 / g; the pore size distribution of the lanthanum ferrite / biochar composite material is mainly mesoporous, and more preferably 2-50nm.

[0055] The present invention also provides the application of the lanthanum ferrite / biochar composite material described in the above technical solution in the detection of ethanol.

[0056] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0057] Examples 1-5

[0058] A method for preparing a lanthanum ferrite / biochar composite material, the specific steps of which are as follows:

[0059] (1) After drying rice husks at 80℃ for 24h, they were pretreated with 1mol / L NaOH solution for 36h, then dried at 80℃ for 24h, and then placed in a tube furnace and calcined at 750℃ for 2h (heating rate of 1℃ / min) to obtain porous rice husk char (RHB).

[0060] (2) Citric acid, La(NO3)3·6H2O and Fe(NO3)3·9H3O were mixed in deionized water at a molar ratio of 2:1:1 and dissolved in a water bath at 50°C. After stirring at 1000 r / min for 30 min, the mixture was transferred to a reaction vessel and hydrothermally reacted at 180°C for 9 h. The precipitate was collected, washed and dried to obtain the LaFeO3 precursor.

[0061] (3) The porous rice husk char (RHB) obtained in step (1) and the LaFeO3 precursor obtained in step (2) were mixed at mass ratios of 1:1 (Example 1, LFO / C 1#), 1:2 (Example 2, LFO / C 2#), 1:3 (Example 3, LFO / C 3#), 1:4 (Example 4, LFO / C 4#), and 1:5 (Example 5, LFO / C 5#), and calcined in a tube furnace at 750°C for 2 h (heating rate of 1°C / min) to obtain lanthanum ferrite / biochar composite material.

[0062] The specific surface area of ​​the lanthanum ferrite / biochar composite material LFO / C 3# prepared in Example 3 was determined to be 326.91 m² using the biosorption spectroscopy (BET) method. 2 / g, with a pore size of 2.54nm.

[0063] Comparative Example 1

[0064] Citric acid, La(NO3)3·6H2O and Fe(NO3)3·9H3O were mixed in a molar ratio of 2:1:1 and dissolved in deionized water. The mixture was then dissolved in a water bath at 50°C. After stirring at 1000 r / min for 30 min, the solution was transferred to a reaction vessel and hydrothermally reacted at 180°C for 9 h. The precipitate was collected, washed, and dried. The resulting precipitate was then calcined in a tube furnace at 750°C for 2 h (heating rate of 1°C / min) to obtain lanthanum ferrite (LFO).

[0065] The specific surface area of ​​the lanthanum ferrite LFO prepared in Comparative Example 1 was determined to be 47.12 m² using the Biosorption Spectrometry (BET) method. 2 / g.

[0066] Figure 1The images show SEM and TEM images of LFO / C 3# prepared in Example 3 and lanthanum ferrite prepared in Comparative Example 1. (a) is a TEM image of lanthanum ferrite, (b) is a TEM image of LFO / C 3# (200 nm), (c) is an HRTEM image of LFO / C 3# (5 μm), (d) is a SAED image of LFO / C 3#, (e) is a SEM image of lanthanum ferrite, (f) is a SEM image of porous rice husk charcoal from step (1) of Example 3, (g) is a SEM image of LFO / C 3# (2 μm), (h) is a SEM image of LFO / C 3# (1 μm), (i) is a distribution map of La in LFO / C 3#, (j) is a distribution map of Fe in LFO / C 3#, (k) is a distribution map of C in LFO / C 3#, and (l) is a distribution map of LFO / C 3#. Distribution diagram of element O in #3.

[0067] from Figure 1 As can be seen from part (a) of Comparative Example 1, the lanthanum ferrite prepared is spherical. Figure 1 As can be seen in section (b) of the LFO / C 3# composite material, RHB is located in the substrate, and LaFeO3 is a regular spherical shape with a diameter of 160-200 nm. From... Figure 1 As can be seen from part (c), the LFO / C 3# composite material contains two types of crystal plane spacings: 0.20 nm and 0.28 nm. The 0.28 nm crystal plane spacing corresponds to the (121) crystal plane of LaFeO3. Figure 1 The SAED plot in section (d) shows concentric rings, indicating that the LFO / C3# composite material exhibits polycrystalline characteristics. From Figure 1 As can be seen from part (e) in the figure, the LaFeO3 prepared in Comparative Example 1 has a porous and rough surface with an average diameter of 15 μm. Figure 1 As can be seen in section (f), RHB exhibits a layered porous nanostructure. From... Figure 1 As can be seen from the (g)-(h) portion, the LaFeO3 in the LFO / C 3# composite material exhibits a spherical structure with an average diameter of 3 μm. The surface of LaFeO3 has a denser nanoporous structure, and these LaFeO3 spherical particles are tightly attached to the RHB surface. From Figure 1 As can be seen from the (i)-(l) parts, La, Fe, O and C are relatively uniformly distributed in the LFO / C 3# composite material.

[0068] Gas Sensing Performance Test

[0069] 1. Test conditions: Static gas mixing method, ethanol volume concentration of 10-1000ppm, temperature of 160-300℃.

[0070] 2. Response definition: Response value S = Rg / R a , where R g R is the resistance when ethanol is passed through it. a For air ambient resistance.

[0071] 3. Stability test: The test was conducted in four sessions, with a 6-day interval between each session.

[0072] 4. Repeatability test: Perform four consecutive sensitivity response tests on ethanol at a concentration of 50 ppm at the optimal operating temperature.

[0073] 5. Selectivity test: Compare the response values ​​of six gases (50 ppm): acetone, ammonia, ethyl acetate, n-butanol, ethanol, and methanol.

[0074] Figure 2 The response curves of LFO / C composite materials prepared in Examples 1-5 and lanthanum ferrite prepared in Comparative Example 1 to 50 ppm methanol gas at different temperatures are shown. Figure 2 The temperature-response curves of pure LaFeO3 and LFO / C composites with different proportions in the presence of 50 ppm ethanol gas are shown in the temperature range of 160℃ to 300℃. It can be seen that the temperature response curve first increases and then decreases with increasing operating temperature. This is because in the increasing phase of the temperature response curve, the adsorption rate is greater than the desorption rate, increasing the response. At the highest point of the temperature response curve, the adsorption and desorption rates are in equilibrium. In the decreasing phase of the temperature response curve, the desorption rate is higher than its adsorption rate, reducing the response of the gas-sensitive material. Furthermore, the optimal operating temperatures for pure LaFeO3 and the six gas-sensitive materials LFO / C 1#, LFO / C 2#, LFO / C 3#, LFO / C 4#, and LFO / C 5# are 240℃, 240℃, 220℃, 220℃, 260℃, and 240℃, respectively. The response values ​​of the five LFO / C composites prepared in Examples 1-5 are 5.9, 7.9, 10.3, 13.8, 5.3, and 4.7, respectively. It can be seen that the LFO / C 3# composite material has the highest response value, which is about 2.3 times that of pure LaFeO3, and the optimal operating temperature is 20℃ lower than that of pure LaFeO3, indicating that the introduction of RHB effectively improves the response and reduces the operating temperature.

[0075] Figure 3 The reaction relationship between different methanol concentrations and optimal temperatures for the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1. Figure 3It can be seen that the responses of all six gas-sensitive materials increase as the ethanol gas concentration increases from 10 ppm to 1000 ppm. Furthermore, all six gas-sensitive materials exhibit a p-type semiconductor response, likely due to the significantly lower RHB content compared to the p-type semiconductor material, lanthanum ferrite. Among the six gas-sensitive materials, the LFO / C 3# composite material shows the most significant increase in response. However, when the mass ratio of RHB to LaFeO3 exceeds 3:1, the response of the gas-sensitive materials decreases rapidly, indicating that the LFO / C 3# composite material exhibits the best gas response. Even at an ethanol concentration of 1000 ppm, the LFO / C 3# composite material still shows a high response, suggesting that its surface provides more adsorption sites for gas adsorption.

[0076] Figure 4 The linear relationship between the response values ​​and methanol concentration is shown for the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1. From... Figure 4 It can be seen that there is a linear relationship between the response of pure LaFeO3 and the response of LaFeO3 / RHB composites with different ratios to ethanol gas concentrations (50-1000 ppm). The responses of the five materials prepared in Examples 1-5 increase with increasing ethanol gas concentration. When linearly fitting the data points, the obtained linear equations for the materials are y = 0.04x + 1.5, y = 0.07x + 5.78, y = 0.05x + 4.62, y = 0.07x + 5.78, y = 0.04x + 1.62, and y = 0.05x + 3.69, R0 2 The values ​​were 0.98, 0.96, 0.94, 0.96, 0.99, and 0.94, respectively. It is evident that the fitted linear equation for the LFO / C 3# composite material exhibits a large slope. This implies the presence of more unsaturated active sites on the material surface, suggesting its ability to accurately detect higher concentrations of ethanol gas.

[0077] Figure 5 The results show the stability test results of the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1. The stability of gas-sensitive materials is one of the key factors determining the performance of gas sensors. Figure 5 It can be seen that the sensitivity response of the six gas-sensitive materials fluctuates slightly with time, indicating that they have good long-term stability.

[0078] Figure 6 The repeatability test results are for the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1. From... Figure 6It can be seen that the average sensitivity response value of pure LFO after four consecutive tests is 5.92, that of LFO / C 1# composite material is 7.92, that of LFO / C 2# composite material is 10.33, and that of LFO / C 3# composite material is 13.82. The average sensitivity response value of LFO / C 4# composite material is 5.32, and that of LFO / C 5# composite material is 4.73. The results indicate that the sensitivity response values ​​of the five materials fluctuate within a small range and exhibit good short-term repeatability.

[0079] Figure 7 The results show the test results of the selectivity of the LFO / C composite materials prepared in Examples 1-5 and the lanthanum ferrite prepared in Comparative Example 1 for ethanol. Figure 7 It can be seen that among the six synthesized materials, the LFO / C 3# composite material exhibits the highest sensitivity response to ethanol, approximately twice that of the other five materials. Furthermore, among the six gases tested, the LFO / C 3# composite material shows the highest sensitivity response to ethanol, 3-9 times that of the other gases, indicating that this composite material, as a gas-sensitive material, possesses excellent selectivity for ethanol.

[0080] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. Use of a lanthanum ferrite / biochar composite material for detecting ethanol, characterized in that, The preparation method of the lanthanum ferrite / biochar composite material comprises the following steps: (1) The rice husk is pretreated with a NaOH solution, dried, and then first calcined to obtain porous rice husk carbon; (2) Citric acid, lanthanum nitrate, and iron nitrate are mixed and dissolved in water, and then a hydrothermal reaction is performed to obtain a lanthanum ferrite precursor; (3) The porous rice husk carbon obtained in step (1) and the lanthanum ferrite precursor obtained in step (2) are mixed and then second calcined to obtain the lanthanum ferrite / biochar composite material; the mass ratio of the porous rice husk carbon to the lanthanum ferrite precursor is 3:1; Steps (1) and (2) have no sequence.

2. Use of lanthanum ferrite / biochar composite material according to claim 1 for detecting ethanol, characterized in that, In step (1), the concentration of the NaOH solution is 1 mol / L; the pretreatment time is 36 h; and / or, The first calcination temperature is 750 DEG C, the first calcination time is 2 h, and the temperature rising rate to the first calcination temperature is 1 DEG C / min.

3. Use of lanthanum ferrite / biochar composite material according to claim 1 for detecting ethanol, characterized in that, In step (2), the molar ratio of the lanthanum nitrate to the iron nitrate is 1:

1.

4. Use of lanthanum ferrite / biochar composite material according to claim 1 for detecting ethanol, characterized in that, In step (2), the molar ratio of the citric acid to the lanthanum nitrate is 2:

1.

5. Use of lanthanum ferrite / biochar composite material according to claim 1 for detecting ethanol, characterized in that, In step (2), the hydrothermal reaction temperature is 180 DEG C, and the hydrothermal reaction time is 9 h.

6. Use of lanthanum ferrite / biochar composite material according to claim 1 for detecting ethanol, characterized in that, In step (3), the second calcination temperature is 750 DEG C, the second calcination time is 2 h, and the temperature rising rate to the second calcination temperature is 1 DEG C / min.

7. Use of lanthanum ferrite / biochar composite material according to claim 1 for detecting ethanol, characterized in that, The lanthanum ferrite / biochar composite material comprises porous rice husk carbon and lanthanum ferrite nanoparticles loaded on the surface of the porous rice husk carbon, and has a porous structure.

8. Use of lanthanum ferrite / biochar composite material according to claim 7 for detecting ethanol, characterized in that, The shape of the lanthanum ferrite nanoparticles is spherical; and the diameter of the lanthanum ferrite nanoparticles is 160-200 nm.

Images