High-entropy oxide supported lanthanum ferrite gas sensing material, preparation method and application thereof

Abstract

The application discloses a high-entropy oxide loaded lanthanum ferrite gas-sensitive material and a preparation method and application thereof, and comprises the following steps: preparing lanthanum ferrite powder; dispersing the lanthanum ferrite powder in water, adding citric acid, and then performing ultrasonic treatment under ice water bath conditions to obtain a surface-modified base suspension liquid; under ice water bath and stirring conditions, dropping a high-entropy complex mother liquor into the base suspension liquid, then adding urea, and performing hydrothermal reaction to obtain a precipitate; washing and drying the precipitate, and then performing stepwise temperature increasing calcination in air. The sensor prepared from the gas-sensitive material has a low baseline resistance of 11 MΩ at an optimal working temperature of 180 DEG C, a response degree of 45.24 to 50 ppm of acetone, and an optimal working temperature which is reduced by 75 DEG C than that of a pure LaFeO3 sensor; the response and recovery times are shortened to 23.38 seconds and 8 seconds respectively, and the sensor exhibits excellent kinetic characteristics.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor gas-sensitive materials technology, and particularly relates to a high-entropy oxide-supported lanthanum ferrite gas-sensitive material, its preparation method, and its application. Background Technology

[0002] Acetone (C3H6O), a typical volatile organic compound (VOC), is widely used in various industrial fields such as chemical and pharmaceutical industries. However, long-term or high-concentration exposure to acetone vapor can damage the human central nervous system, seriously threatening occupational health and public safety. Furthermore, acetone is also a component of human exhaled breath. Detecting acetone levels in exhaled breath can help determine if someone has diabetes. The concentration of acetone in the exhaled breath of healthy individuals ranges from 300 to 900 ppb, while the concentration in diabetic patients can exceed 1800 ppb. This means that an acetone concentration exceeding 1.8 ppm in exhaled breath may indicate diabetic ketoacidosis. Therefore, developing highly sensitive, selective, and stable acetone detection technologies and sensors has significant social and economic value.

[0003] Currently, gas sensors based on metal-oxide-semiconductor (MOS) have become a research hotspot due to their low cost and fast response. Lanthanum ferrite (LaFeO3), as a typical p-type perovskite semiconductor, has great potential in the field of gas sensing. However, pure LaFeO3 prepared by conventional methods faces two major technical bottlenecks: first, the baseline resistance is extremely high (often reaching the GΩ level), resulting in a very low signal-to-noise ratio and causing its optimal operating temperature to be too high (>250℃); second, the response recovery speed is slow, both of which limit its practical application.

[0004] To improve sensing performance, researchers often employ modification methods such as noble metal modification, heterostructure building, and element doping. CN109019696A discloses an Au-LaFeO3 nanocomposite material, which exhibits high sensitivity and rapid response recovery to acetone. Although noble metal modification can improve catalytic activity and lower operating temperature to some extent, noble metals are expensive and prone to agglomeration and deactivation under long-term heating conditions, making it difficult to meet the needs of large-scale commercial applications. CN121426179A discloses the preparation of a LaFeO3-ZnO composite material, which shows a significantly higher response to acetone than its comparative LaFeO3 material, and its response recovery time is reduced from 96s to 79s. Although this patent greatly improves the problem of uncontrollable nucleation rate in conventional hydrothermal preparation processes by using a "solvent ratio-ligand size" synergistic control strategy, it still suffers from a slow recovery time. CN121428700A discloses a method for preparing Sm-doped LaFeO3 nanofibers. Although sensors prepared with this material exhibit increased acetone response, their operating temperature reaches as high as 250°C, and their recovery time is as long as 20 seconds. Furthermore, their baseline resistance is in the GΩ range at a heating voltage of 180°C. While this patent employs Sm doping to generate oxygen vacancies through lattice distortion, it does not address the issues of excessively high baseline resistance, high operating temperature, and long recovery time. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a high-entropy oxide-supported lanthanum ferrite gas-sensitive material, its preparation method and application, so as to improve sensing performance.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for preparing a high-entropy oxide-supported lanthanum ferrite gas-sensitive material includes the following steps:

[0008] S1. Preparation of lanthanum ferrite powder;

[0009] S2. Lanthanum ferrite powder was dispersed in water, citric acid was added, and then ultrasonic treatment was performed under ice-water bath conditions to obtain a surface-modified substrate suspension.

[0010] S3. Under ice-water bath and stirring conditions, the high-entropy complexing mother liquor was dripped into the base suspension, and then urea was added to carry out a hydrothermal reaction to obtain the precipitate;

[0011] The high-entropy complexing mother liquor is an aqueous solution containing soluble iron salt, soluble cobalt salt, soluble nickel salt, soluble zinc salt, soluble manganese salt, and citric acid; wherein the molar ratio of iron in the high-entropy complexing mother liquor to lanthanum ferrate in the base suspension is 1:(190~220); the dropping rate of the high-entropy complexing mother liquor is controlled at 1 drop / 2~3 seconds;

[0012] S4. The precipitate is washed and dried, and then calcined in air by step heating to load Fe-Co-Ni-Zn-Mn high-entropy oxides on LaFeO3 to obtain the lanthanum ferrite gas-sensitive material.

[0013] The stepped heating calcination includes two stages: heating to 220~280℃ and holding at that temperature, and heating to 500~600℃ and holding at that temperature.

[0014] Furthermore, the process of preparing lanthanum ferrite powder by S1 includes: dissolving soluble lanthanum salt, soluble iron salt and citric acid in water, adjusting the pH value to alkaline, and heating the reaction to obtain precursor sol;

[0015] The precursor sol was subjected to hydrothermal treatment, followed by centrifugation, washing, drying, calcination in air, and grinding to obtain lanthanum ferrite powder; the hydrothermal treatment temperature was 160~180℃, and the calcination temperature was 600~680℃.

[0016] Furthermore, the molar ratio of lanthanum ferrite powder to citric acid in S2 is (2~3):1.

[0017] Furthermore, the molar ratio of iron, cobalt, nickel, zinc, manganese and citric acid in the high-entropy complexing mother liquor described in S3 is 1:1:1:1:1:(1.2~1.8).

[0018] Furthermore, the stirring speed in S3 is not less than 800 rpm.

[0019] Furthermore, the hydrothermal reaction described in S3 includes: first, a pre-reaction is carried out at 80~90℃, and then the reaction is carried out in a high-pressure reactor at a temperature of 110~130℃.

[0020] Furthermore, the washing described in S4 includes: centrifuging the precipitate with a mixture of water and anhydrous ethanol, wherein the volume ratio of water to anhydrous ethanol in the mixture is (0.8~1.2):1, and the centrifugation speed is not less than 8000 rpm.

[0021] The present invention also provides a high-entropy oxide-supported lanthanum ferrite gas-sensitive material, which is prepared by the preparation method described above.

[0022] The present invention also provides an application of the high-entropy oxide-supported lanthanum ferrite gas-sensitive material, wherein the lanthanum ferrite gas-sensitive material is used to make a gas sensor for detecting volatile organic compounds containing acetone.

[0023] To address the problems in the background technology, this invention employs a method of loading high-entropy oxides (HEO) onto the surface of LaFeO3, utilizing their multi-metal synergistic catalytic ability to achieve rapid recovery of the LaFeO3 response to acetone and a significant reduction in its operating temperature. Theoretically, loading trace amounts of HEO nanoislands onto the LaFeO3 surface can provide abundant catalytic active centers without obscuring the porous network of the substrate. However, this concept suffers from fatal technical flaws in practical processing: First, with extremely low loading, conventional impregnation or hydrothermal methods easily induce explosive nucleation within the high-entropy system itself, leading to extremely uneven distribution of nanoislands; second, when the loading is extremely low and the nanoparticles are extremely small, severe "colloidal dissolution" (pseudo-dissolution) easily occurs during subsequent centrifugation, washing, and purification, causing a large amount of carefully synthesized trace amounts of high-entropy active components to be lost with the supernatant; finally, conventional one-step high-temperature calcination directly destroys the fragile mesoporous structure under extremely low loading. In summary, how to reduce the baseline resistance of LaFeO3 by controlling its intrinsic morphology and successfully overcome the problems of nucleation aggregation and colloidal loss during the loading process of micro-multimetal systems is a key technical challenge that urgently needs to be addressed in this field.

[0024] This invention proposes a two-stage synergistic preparation method: First, an intrinsically low-resistivity LaFeO3 substrate with a large number of surface oxygen vacancies is prepared by using sol-gel-hydrothermal coupling and a relatively mild calcination process; then, through innovative processing techniques of "ice bath fine activation" and "step-by-step pore-forming calcination", trace amounts of Fe-Co-Ni-Zn-Mn high-entropy oxides are successfully and uniformly anchored on the LaFeO3 substrate, overcoming the above-mentioned technical difficulties and preparing an acetone sensor with lower operating temperature and shorter recovery time.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention overcomes the challenge of rapid nucleation and aggregation of trace heterogeneous phases through a "crystal bath fine activation and micro-droplet" process, achieving stable anchoring and extreme dispersion of ultra-small, high-entropy nano-islands on the LaFeO3 surface. Stepwise calcination induces the favorable reconstruction of surface oxygen species (lattice oxygen O). L With adsorbed oxygen O C (Significantly increased), and introduced a highly efficient Mars-vanKrevelen (MvK) catalytic mechanism, thereby achieving excellent acetone sensing properties.

[0027] The LaFeO3-HEO sensor prepared in this invention exhibits a baseline resistance as low as 11 MΩ at its optimal operating temperature of 180 °C and a responsivity of 45.24 for 50 ppm acetone, several times higher than that of pure LaFeO3 sensors processed using other methods. Furthermore, its optimal operating temperature is 75 °C lower than that of pure LaFeO3 sensors. The response and recovery times are shortened to 23.38 seconds and 8 seconds, respectively, demonstrating superior kinetic characteristics. This invention overcomes the dual technical bottlenecks of extremely high baseline resistance and high operating temperature associated with LaFeO3, filling the gap in the application of high-entropy oxide-modified LaFeO3 materials in gas sensing. It shows broad application prospects in the field of high-performance volatile organic compound (VOCs) detection. Attached Figure Description

[0028] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a scanning electron microscope (SEM) image of the LaFeO3-HEO nanospheres prepared in Example 1 of the present invention;

[0030] Figure 2 The X-ray diffraction (XRD) patterns of the materials prepared in Example 1 and the comparative example of this invention are shown.

[0031] Figure 3 X-ray photoelectron spectroscopy (XPS) prepared in Example 1 and the comparative example of the present invention.

[0032] Figure 4 The response-operating temperature relationship curves of the sensors prepared in Example 1 and the comparative example of the present invention are shown.

[0033] Figure 5 The dynamic response-recovery curve of the sensor prepared in Example 1 of the present invention to 50 ppm acetone at 180°C;

[0034] Figure 6 The curve showing the change in resistance of acetone to acetone over time at a heating temperature of 180℃ is shown for Comparative Example 4.

[0035] Figure 7 The resistance-time curve of the sensor prepared in Example 1 of the present invention at 180°C to 50 ppm acetone. Detailed Implementation

[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0039] This invention provides a method for preparing a gas-sensitive material loaded with high-entropy oxides (Fe-Co-Ni-Zn-Mn) by using a sol-gel-hydrothermal coupling process to prepare a lanthanum ferrite substrate, and by using ice bath fine activation, anti-solubilization and stepped calcination processes.

[0040] In some specific embodiments, the preparation method of the high-entropy oxide-supported lanthanum ferrite gas-sensitive material of the present invention includes the following steps:

[0041] (I) First stage: Preparation of lanthanum ferrite substrate

[0042] In some embodiments, the method for preparing the lanthanum ferrite substrate includes:

[0043] (a) Dissolve soluble lanthanum salt, soluble iron salt and citric acid in water, add ammonia to adjust the pH to 8.5~9.5, and heat in a water bath to obtain precursor sol.

[0044] Preferably, the soluble lanthanum salt is lanthanum acetate hydrate, the soluble iron salt is ferric nitrate nonahydrate, and the citric acid is citric acid monohydrate.

[0045] In some embodiments, the molar ratio of soluble lanthanum salt, soluble iron salt, and citric acid is 1:1:(2~4), preferably 1:1:3. The water bath heating temperature is 55~65℃, and the time is 1~2 hours.

[0046] (b) The precursor sol is subjected to hydrothermal treatment, centrifuged, washed and dried, and then calcined and ground in air to obtain lanthanum ferrite powder, which is a lanthanum ferrite LaFeO3 nanosphere substrate material with high surface activity.

[0047] In some embodiments, the hydrothermal treatment temperature is 160~180℃, and the time is 10~15 hours. The calcination temperature is 600~680℃ (preferably 650℃), and the calcination holding time is 1.5~3 hours.

[0048] (ii) Second stage: Loading of high-entropy oxides

[0049] In some embodiments, the loading of the high-entropy oxide includes:

[0050] (1) Dissolve soluble iron salts (e.g., ferric nitrate), soluble cobalt salts (e.g., cobalt nitrate), soluble nickel salts (e.g., nickel nitrate), soluble zinc salts (e.g., zinc acetate), and soluble manganese salts (e.g., manganese nitrate) in deionized water and stir to form a high-entropy complex mother liquor. Citric acid is an extremely strong multidentate chelating agent (containing 3 carboxyl groups and 1 hydroxyl group). After adding citric acid, it will form complexes with these five metal ions with different properties, ensuring the absolute homogeneous mixing of the five high-entropy components in the liquid phase from the source.

[0051] In some embodiments, the molar ratio of iron, cobalt, nickel, zinc, manganese and citric acid is 1:1:1:1:1:(1.2~1.8), preferably 1:1:1:1:1:1.5, and the concentration of iron in the high-entropy complexing mother liquor is 0.0015~0.0025 mol / L, preferably 0.002 mol / L.

[0052] (2) Disperse the lanthanum ferrite powder obtained in (a) in deionized water, add citric acid monohydrate, and sonicate under ice-water bath conditions to obtain a surface-modified substrate suspension.

[0053] In some embodiments, the molar ratio of lanthanum ferrite powder to citric acid monohydrate is (2~3):1, preferably 2.5:1.

[0054] In some embodiments, ultrasonic treatment for 30-60 minutes is performed to fully graft anchor points onto the surface of the lanthanum ferrite particles.

[0055] (3) Ice bath fine activation: Under ice water bath and stirring conditions, the high entropy complex mother liquor is dripped (slowly dripped) into the substrate suspension to obtain a mixture.

[0056] In some embodiments, the amount of high-entropy complexing mother liquor added is based on the molar amount of iron therein, wherein the molar ratio of iron to lanthanum ferrate in the substrate suspension is 1:(190~220), preferably 1:206. The volume ratio of the added high-entropy complexing mother liquor to the volume of the substrate suspension is 1:(15~20).

[0057] In some embodiments, the dropping speed is controlled at 1 drop / 2~3 seconds, and the stirring speed is not less than 800 rpm to prevent explosive nucleation.

[0058] (4) Add urea to the mixture to dissolve it, perform a constant temperature pre-reaction, and then transfer it to a high-pressure reactor for hydrothermal reaction.

[0059] In some embodiments, the amount of urea added is 600 to 650 times the molar amount of iron in the added high-entropy complexing mother liquor, preferably 624 times.

[0060] In some embodiments, the pre-reaction conditions are stirring and heating at 80-90°C for 1-3 hours; the hydrothermal reaction conditions are holding at 110-130°C for 8-12 hours.

[0061] The pre-reaction process involves the gradual hydrolysis of the added urea, creating a uniform and slowly increasing weakly alkaline release field in the solution. This forces the five metal ions in the high-entropy mother liquor to simultaneously transform into amorphous precursors at remarkably similar rates within a completely uniform weakly alkaline environment. The subsequent hydrothermal reaction causes the precursors attached to the substrate to undergo dehydration condensation, resulting in the formation of MOM (metal-oxide-metal) oxygen bridges between the high-entropy metal ions. These MOMs then cross-link with the active hydroxyl groups on the LaFeO3 surface, further strengthening the bond between the precursors and the substrate.

[0062] (5) After cooling, the precipitate is washed by centrifugation with a mixture of water and anhydrous ethanol, and finally washed with pure anhydrous ethanol and concentrated into a slurry.

[0063] In some embodiments, the volume ratio of water to anhydrous ethanol in the mixture is (0.8~1.2):1, and the centrifugation speed is not less than 8000 rpm, in order to demulsify and prevent gelation caused by extremely low loading.

[0064] (6) Stepped pore-forming calcination: The above slurry is dried and then calcined in air with stepped heating to obtain a high-entropy oxide-supported lanthanum ferrite (LaFeO3-HEO) gas-sensitive material.

[0065] In some embodiments, the loading of high-entropy oxide relative to lanthanum ferrite is 2.5 to 3.5 mol, preferably 3 mol.

[0066] In some embodiments, the drying conditions are mild, baking at 55-65°C for 10-15 hours.

[0067] In some embodiments, the step-by-step calcination process is as follows: the temperature is increased from room temperature to 220-280°C at a rate of 1.5-2.5°C / min and held for 1.5-3 hours, then increased to 500-600°C at a rate of 1.5-2.5°C / min and held for 6-10 hours. Upon heating from room temperature to 220-280°C, residual free water molecules on the material surface and within the pores, anhydrous ethanol used for washing, and the water of crystallization in citric acid monohydrate begin to volatilize. Simultaneously, residual urea in the system begins to melt and initiates preliminary decomposition. Heating and holding at 220-280°C induces isothermal pyrolysis. Excess citric acid ligands coated around the high-entropy metal ions, along with urea, undergo slow thermal decarboxylation and incomplete oxidation at 220-280°C, releasing gases such as CO2, H2O, and trace amounts of NH3. The slow, continuous escape of gas molecules "blows" countless micropores into the originally dense organic ligand layer, achieving in-situ nanopore creation and further enriching the specific surface area. During the heating process from 220-280℃ to 500-600℃, as the temperature continues to steadily rise, the remaining amorphous carbon skeleton and stubborn organic functional groups are completely oxidized and burned off by the oxygen in the environment. The high-entropy metal atoms (Fe, Co, Ni, Zn, Mn), stripped of their organic ligand "protective shell," begin to expose extremely high surface energy and, driven by heat, begin localized atomic diffusion and migration. During the isothermal stage at 500-600℃, atoms at the bottom of the HEO nanoislands undergo deep lattice penetration with LaFeO3, forming a stable MO-Fe chemical bond. This not only fills the original surface defects (O in XPS) but also... V (Reduced), and further introduced highly fluid and active high-entropy multimetallic lattice oxygen (O in XPS) L (A sharp increase). This highly active lattice oxygen interface initiates a highly efficient Mars-van Krevelen (MvK) catalytic kinetic mechanism, ultimately achieving an outstanding response of up to 45.24 to acetone at a low temperature of 180℃.

[0068] This invention first prepares a LaFeO3 substrate with a porous nanosphere morphology using a sol-gel-hydrothermal coupling process. Then, the substrate is finely activated using an ice-water bath and citric acid. A trace amount of Fe-Co-Ni-Zn-Mn high-entropy complex mother liquor is added dropwise under vigorous stirring. After hydrothermal crystallization, the substrate is washed and demulsified by high-speed centrifugation with a water-alcohol mixture to completely prevent the loss of trace amounts of active components. Finally, the target product is obtained by stepwise calcination.

[0069] This invention breaks through the conventional path of modifying traditional metal oxide semiconductor gas-sensitive materials, proposing a synergistic design concept based on "dual pre-regulation of morphology and defects" combined with "interfacial dynamic control of ultra-micro dispersed phases." Firstly, the first stage of this invention employs a process of "sol-gel-hydrothermal coupling + relatively mild calcination at 650℃." The hydrothermal process pre-constructs a one-dimensional / three-dimensional nanoframework with a unique mesoporous network, while the mild calcination at 650℃ ensures the crystallization of the perovskite phase and avoids grain aggregation and excessive escape of lattice oxygen. This morphology has a huge specific surface area, exposing a massive number of surface active sites. In the air, a large number of oxygen molecules are chemically adsorbed on the material surface (forming O2). - Or O - This significantly reduces the baseline resistivity of LaFeO3. Secondly, this invention is the first to introduce monohydrated citric acid into an ice-water bath for ultrasonic activation of the substrate. The low temperature drastically reduces the thermal motion rate of the system molecules, inhibiting free collisions of metal ions. Simultaneously, under ultrasonic action, the carboxyl groups (-COOH) and hydroxyl groups (-OH) in the citric acid molecules are densely and uniformly grafted onto the surface of the LaFeO3 particles, forming numerous "chemical anchoring sites." This allows the Fe-Co-Ni-Zn-Mn multimetallic complex to be rapidly captured after entering the system. After calcination, the high-entropy oxide (HEO) forms a tight heterogeneous interface bond with the substrate. A high proportion of lattice oxygen (O2)... L This introduces a highly efficient Mars-van Krevelen (MvK) catalytic oxidation mechanism to the material. Benefiting from HEO's unique "cocktail effect" and abundant multi-metal valence variation capabilities, the O on the composite material surface... L It is highly activated. Acetone molecules can directly undergo a highly efficient redox reaction with activated lattice oxygen, breaking the bottleneck of traditional gas-sensitive materials that rely excessively on surface chemical adsorption of free oxygen. As a result, it achieves extremely high sensing response at 180℃. Compared with LaFeO3 without HEO loading, its optimal operating temperature is reduced by 75℃ and the recovery time is shortened to 8s.

[0070] The present invention also provides an application of the high-entropy oxide-supported lanthanum ferrite gas-sensitive material prepared by the above method in the preparation of volatile organic compound (VOC) gas sensors, especially acetone gas sensors.

[0071] In some embodiments, a high-entropy oxide-loaded lanthanum ferrite gas-sensitive material is coated onto an alumina ceramic tube with a gold electrode and dried. The sensor is then fabricated using conventional methods and aged at 180–220°C for 40–50 hours.

[0072] Example 1

[0073] (I) Preparation of low-resistivity lanthanum ferrite substrate

[0074] A soluble lanthanum salt (lanthanum acetate hydrate), an iron salt (ferric nitrate nonahydrate), and a citric acid monohydrate were dissolved in water at a molar ratio of 1:1:3. Ammonia was added dropwise to adjust the pH of the solution to 9. The solution was heated in a water bath at 60°C for 1 hour to obtain a sol. The sol was transferred to a reaction vessel and hydrothermally treated at 160°C for 12 hours. After centrifugation, the precipitate was washed, dried, and then calcined in a muffle furnace at 650°C for 2 hours. After natural cooling, it was ground to obtain a highly surface-active, low-resistivity lanthanum ferrite (LaFeO3) powder substrate.

[0075] (ii) Fine loading of trace amounts of high-entropy oxides

[0076] (1) Preparation of standard high entropy complex mother liquor: Dissolve 40.4 mg ferric nitrate, 29.1 mg cobalt nitrate, 29.1 mg nickel nitrate, 22.0 mg zinc acetate, 25.1 mg manganese nitrate and 31.5 mg citric acid in 50 mL deionized water and stir for 15 minutes until clear.

[0077] (2) Fine activation of the substrate: Accurately weigh 200 mg of the lanthanum ferrite powder prepared in (I) above and put it into a 100 mL beaker. Add 33 mL of deionized water, and then add 67 mg of citric acid monohydrate as a substrate activator. Place the beaker in an ice-water bath and sonicate for 30 minutes to fully graft anchoring points onto the surface of the 200 mg particles, thus obtaining a suspension.

[0078] (3) Micro-drop addition: Transfer the suspension along with the ice bath to a magnetic stirrer and stir at 800 rpm to form a violent vortex. Use a pipette to accurately extract 2.0 mL of the mother liquor prepared in step (1) and drop it into the center of the vortex at an extremely slow rate of 1 drop / 2 seconds.

[0079] (4) Pre-reaction and hydrothermal crystallization: Add 150 mg of urea to the mixture obtained in step (3) and stir for 5 minutes until dissolved. Remove the ice bath, seal the mouth of the beaker with plastic wrap and poke 3-5 small holes to release the air, and place it in an 85℃ water bath and heat at medium speed for 2 hours to obtain a suspension. Then, transfer 35 mL of the suspension into a 50 mL polytetrafluoroethylene autoclave without damage and keep it at 120℃ for 10 hours.

[0080] (5) Anti-colloidal washing and pure alcohol slurry preparation: After the liquid in the reactor cools naturally, centrifuge at 5000 rpm for 5 minutes and discard the supernatant. To prevent severe colloidal phenomena caused by extremely low loading, add 15 mL of deionized water + 15 mL of anhydrous ethanol to the centrifuge tube, vortex to thoroughly break up the slurry, and increase the speed to 8000 rpm for 5 minutes. Repeat this water-alcohol washing step 3 times until neutral. Finally, add 30 mL of pure anhydrous ethanol and wash twice, leaving 1-2 mL of residual liquid to form a thick paste (Slurry), and pour it into the center of the petri dish.

[0081] (6) Gentle drying and stepped pore-forming calcination: After baking at 60℃ for 12 hours, the product was gently ground. It was then placed in a muffle furnace for air calcination, and the temperature was increased to 250℃ at room temperature at 2℃ / min. It was calcined at this temperature for 2 hours, and then increased to 550℃ at 2℃ / min. It was calcined at this temperature for 8 hours. After the product was naturally cooled to room temperature in the furnace, the resulting yellowish-brown product was taken out, which is LaFeO3-HEO.

[0082] Take an appropriate amount of the above LaFeO3-HEO powder, add a small amount of terpineol and grind it to form a uniform slurry. Use a brush to evenly coat the slurry onto an alumina ceramic tube with gold electrodes to form a gas-sensitive layer. Dry the coated ceramic tube at 60°C for 6 hours, then insert a nickel-chromium heating wire into the ceramic tube and weld its pins to the sensor base. Finally, age the manufactured sensor at 200°C for 48 hours to improve its stability.

[0083] Comparative Example 1: Preparation of pure LaFeO3 (unloaded)

[0084] This comparative example is LaFeO3 prepared according to Example 1 (a).

[0085] Comparative Example 2: HEO loaded onto LaFeO3 material prepared by freeze-drying method

[0086] (I) Preparation of Lanthanum Ferrate Substrate by Freeze-drying Method

[0087] The first step is to dissolve lanthanum nitrate hexahydrate, ferric nitrate nonahydrate, and citric acid monohydrate in 40 ml of deionized water in a ratio of 1:1:2, and stir until all the solids are dissolved.

[0088] The second step is to add ammonia water dropwise until the solution changes from clear to turbid and then back to clear, and the pH value of the solution becomes 7. Finally, stir for 2 hours.

[0089] The third step is to freeze the obtained solution in a refrigerator for 12 hours.

[0090] The fourth step is to place the frozen solid into a freeze dryer and dry it for 24 hours. The freeze dryer is set to a vacuum state (35 Pa) and a temperature of -58°C.

[0091] The fifth step involves placing the freeze-dried solid into a tube furnace filled with air for calcination. The temperature is raised to 650°C at a rate of 1°C / min and held for 2 hours to obtain the LaFeO3 substrate.

[0092] (ii) Loading HEO onto the substrate material

[0093] This step is the same as in Example 1.

[0094] Comparative Example 3: HEO loaded onto LaFeO3 substrate using conventional processes

[0095] The preparation of the substrate material was exactly the same as in Example 1(a). The preparation of the standard high-entropy complex mother liquor was exactly the same as in Example 1. The loading process was as follows:

[0096] 1) Eliminate ice bath: Weigh 300 mg of porous LaFeO3 substrate at room temperature (about 25°C) and add 32.0 mL of deionized water (without adding citric acid activator).

[0097] 2) Cancel slow drip addition: Use a pipette to inject 3.0 mL of high entropy mother liquor into the suspension in one go, add 150 mg of urea, and stir for 5 minutes.

[0098] 3) Cancel the pre-reaction: Do not perform the 85℃ pre-reaction. Put the contents into a 50mL autoclave and heat at 120℃ for 10 hours.

[0099] 4) Eliminate stepped calcination: After drying, place it in a muffle furnace and heat it to 550℃ at a conventional rate of 5℃ / min, and hold it for 8 hours.

[0100] Comparative Example 4: Non-high-entropy oxides supported on LaFeO3 substrate material

[0101] The preparation of the substrate material is exactly the same as that in Example 1(a).

[0102] Loading of non-high-entropy oxides:

[0103] Preparation of non-high-entropy mother liquor: In 50 mL of high-entropy mother liquor, the total concentration of the two metals is 0.5 mmol. Accurately weigh 49.7 mg of zinc nitrate hexahydrate and 134.9 mg of ferric nitrate nonhydrate, add 31.5 mg of citric acid, dissolve in 50 mL of deionized water, and stir until clear (this is recorded as the non-high-entropy mother liquor). Weigh 300 mg of LaFeO3, add 32.0 mL of deionized water and 100 mg of citric acid, and sonicate in an ice bath for 30 minutes. Subsequent steps are the same as in Example 1.

[0104] To further verify the technical effects of the present invention, the performance of the materials prepared in Example 1 was compared with that of Comparative Examples 1, 2, 3, and 4, and the analysis is as follows:

[0105] Figure 1 SEM images of the product from Example 1 are shown. It can be clearly observed that the obtained product exhibits a regular nanosphere morphology, and the nanospheres retain a large number of pore structures between their stacks, perfectly maintaining a three-dimensional void network that is conducive to gas diffusion.

[0106] Figure 2The XRD patterns of each sample were compared. The results showed that all samples exhibited characteristic diffraction peaks of the perovskite phase LaFeO3. In addition, no independent diffraction peaks of HEO were detected in Example 1, which further confirms that the loaded HEO component has an extremely low content and extremely high dispersion (size far below the XRD detection limit), and that the mild calcination process did not destroy the intrinsic crystal structure of the substrate.

[0107] Combination Figure 3 The XPS results showed that, compared to LaFeO3 without HEO loading in Comparative Example 1, Example 1 exhibited significant surface oxygen species reconstruction, demonstrating a higher content of lattice oxygen (O2). L ) and surface hydroxyl / carbonyl groups (O C O C The significant increase in O2 endows the material surface with stronger specific polar adsorption capabilities (such as hydrogen bonding to capture acetone molecules); while the high proportion of O2... L This confirms the in-situ repair of surface defects by the high-entropy lattice, introducing highly catalytically active multi-metallic lattice oxygen into the material. This structural feature successfully transforms the gas-sensitive reaction into a highly efficient Mars-van Krevelen (MvK) mechanism, significantly reducing the reaction activation energy. This is the microscopic essence that enables it to operate normally at lower operating temperatures. Comparative examples 2, 3, and 4 show that they all have a high proportion of O. C As adsorbed oxygen, this high proportion is likely due to competitive adsorption by water molecules in the air. O... V and O L The proportions of these three materials are not high, and they may be more sensitive to water molecules, with their response being extremely sensitive to humidity.

[0108] The aged sensor was placed in a gas-sensitive testing system, and the operating temperature was controlled by adjusting the heating voltage. Acetone gas was pre-filled into the gas cylinder, and the gas sensor was heated in the air atmosphere. After heating for 50 seconds, the sensor was placed in the acetone gas cylinder and left there for 1 minute. The sensor was then removed, and the change in resistance over time was recorded. The data was collected by a gas-sensitive testing MS-4002S and transmitted to a computer for real-time display. The data was then copied and processed using Origin. The test results are attached. Figure 4-6 As shown.

[0109] Figure 4The key impact of HEO on gas-sensing performance is clearly revealed. Comparative Example 1, without HEO loading, exhibits typical high-temperature driving limitations, with its optimal operating temperature reaching 255°C. As can be seen from the figure, the operating temperatures of Comparative Examples 2 and 4 are also significantly higher than those of Example 1. Although the individual operating temperature of Comparative Example 3 is close to that of Example 1, its response is significantly lower. Furthermore, the response of Comparative Example 4 is much greater than that of the other samples. Although its response is higher than other sensors at a heating temperature of 180°C, its recovery curve at this temperature exhibits severe "tailing," meaning it cannot recover to the baseline resistance under the initial air atmosphere. Figure 6 As shown in the figure. In Example 1, which is loaded with HEO, the "volcano-shaped" peak of the operating temperature curve shifted significantly to the left, and the optimal operating temperature dropped dramatically to 180°C. This breakthrough reduction demonstrates the strong synergistic effect between the multi-metal "cocktail" catalytic effect of the high-entropy nanoislands and the LaFeO3 substrate.

[0110] also, Figure 5 The sensor prepared in Example 1 demonstrates excellent kinetic characteristics under optimal operating conditions. Its response to 50 ppm acetone gas at 180°C reaches 45.24, with response and recovery times shortened to 23.38 s and 8 s, respectively, exhibiting superior overall performance. In contrast, the response times of other comparative examples 1, 2, 3, and 4 to 50 ppm acetone at this temperature are 30 s, 50 s, 46 s, and 37 s, respectively, with recovery times of 20 s, 24 s, and 18 s, and failure to recover to baseline resistance. This rapid response capability of Example 1 is attributed to the unique structure-component synergistic advantages of the material: on the one hand, the numerous porous networks formed by the stacked nanospheres act as high-speed channels for Knudsen diffusion of the gas, greatly reducing the steric hindrance of acetone molecules and enabling them to rapidly enter and exit the material; on the other hand, the highly dispersed HEO active islands and the high proportion of activated lattice oxygen (O2)... L It provides extremely dense catalytic sites, completely breaking the slow dynamics of relying solely on surface physical adsorption of oxygen, and realizing efficient oxidation-reduction and desorption of the target gas.

[0111] Figure 6 The curve of the resistance of Comparative Example 4 to acetone over time at a heating temperature of 180°C is shown, indicating the existence of a "tailing" phenomenon, which means that the resistance of Comparative Example 4 after being removed from the acetone gas at this temperature cannot be restored to the baseline resistance under air atmosphere.

[0112] Figure 7 The curve showing the resistance of the sensor prepared in Example 1 as a function of time at 180 degrees Celsius is displayed, indicating that its baseline resistance in an air atmosphere is approximately 11 MΩ.

[0113] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-entropy oxide-supported lanthanum ferrite gas-sensitive material, characterized in that, Includes the following steps: S1. Preparation of lanthanum ferrite powder; the process for preparing lanthanum ferrite powder includes: Soluble lanthanum salt, soluble iron salt, and citric acid are dissolved in water, the pH is adjusted to 8.5-9.5, and the reaction is heated to obtain a precursor sol; the temperature of the heating reaction is 55-65℃. The precursor sol was subjected to hydrothermal treatment, followed by centrifugation, washing, drying, calcination in air, and grinding to obtain lanthanum ferrite powder; the hydrothermal treatment temperature was 160~180℃, and the calcination temperature was 600~680℃. S2. Lanthanum ferrite powder was dispersed in water, citric acid was added, and then ultrasonic treatment was performed under ice-water bath conditions to obtain a surface-modified substrate suspension. S3. Under ice-water bath and stirring conditions, the high-entropy complexing mother liquor was dripped into the base suspension, and then urea was added to carry out a hydrothermal reaction to obtain the precipitate; The high-entropy complexing mother liquor is an aqueous solution containing soluble iron salt, soluble cobalt salt, soluble nickel salt, soluble zinc salt, soluble manganese salt, and citric acid; wherein the molar ratio of iron in the high-entropy complexing mother liquor to lanthanum ferrate in the base suspension is 1:190~220; the dropping rate of the high-entropy complexing mother liquor is controlled at 1 drop / 2~3 seconds; S4. The precipitate is washed and dried, and then calcined in air by step heating to load Fe-Co-Ni-Zn-Mn high-entropy oxides on LaFeO3 to obtain the lanthanum ferrite gas-sensitive material. The stepped heating calcination includes two stages: heating to 220~280℃ and holding at that temperature, and heating to 500~600℃ and holding at that temperature.

2. The method for preparing the high-entropy oxide-supported lanthanum ferrite gas-sensitive material according to claim 1, characterized in that, The molar ratio of lanthanum ferrite powder to citric acid in S2 is 2~3:

1.

3. The method for preparing the high-entropy oxide-supported lanthanum ferrite gas-sensitive material according to claim 1, characterized in that, The molar ratio of iron, cobalt, nickel, zinc, manganese, and citric acid in the high-entropy complexing mother liquor described in S3 is 1:1:1:1:1:1.2~1.

8.

4. The method for preparing the high-entropy oxide-supported lanthanum ferrite gas-sensitive material according to claim 1, characterized in that, The stirring speed in S3 should not be less than 800 rpm.

5. The method for preparing the high-entropy oxide-supported lanthanum ferrite gas-sensitive material according to claim 1, characterized in that, The hydrothermal reaction described in S3 includes: first, a pre-reaction at 80~90℃, and then a transfer to a high-pressure reactor for heat treatment at 110~130℃.

6. The method for preparing the high-entropy oxide-supported lanthanum ferrite gas-sensitive material according to claim 1, characterized in that, The washing described in S4 includes: centrifuging the precipitate with a mixture of water and anhydrous ethanol, wherein the volume ratio of water to anhydrous ethanol in the mixture is 0.8 to 1.2:1, and the centrifugation speed is not less than 8000 rpm.

7. A high-entropy oxide-supported lanthanum ferrite gas-sensitive material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. An application of the high-entropy oxide-supported lanthanum ferrite gas-sensitive material according to claim 7, characterized in that, A gas sensor was fabricated using the aforementioned lanthanum ferrite gas-sensitive material to detect volatile organic compounds containing acetone.

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