Preparation method and application of samarium-doped lanthanum ferrite nanofiber

Abstract

The invention discloses a preparation method and application of samarium-doped lanthanum ferrite nanofibers, and the preparation method is a design thought based on synergistic interaction of'defect engineering 'and'morphology control': samarium (Sm) ions with a specific proportion are creatively introduced to the A site of LaFeO3, and lattice distortion is induced by utilizing radius mismatch between the samarium (Sm) ions and lanthanum (La) ions; therefore, high-concentration gas-sensitive active sites (oxygen vacancies) are generated in the intrinsic structure of the material; and the material is constructed into a one-dimensional nanofiber network with a high specific surface area through an electrostatic spinning technology, so that the exposure efficiency of active sites is maximized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor gas sensitive materials, and particularly relates to a gas sensitive material based on a perovskite structure metal oxide, in particular to a preparation method and application of samarium-doped lanthanum ferrite nanofibers. BACKGROUND

[0002] Acetone (C3H6O) as a typical volatile organic compound (VOCs) is widely used in chemical industry, pharmaceutical industry and other industrial fields. However, long-term or high-concentration exposure to acetone vapor can cause damage to the central nervous system of the human body, seriously threatening occupational health and public safety. In addition, acetone is also an important precursor of photochemical reactions in the atmosphere. Therefore, it has great social and economic value to develop acetone detection technology and sensors with high sensitivity, high selectivity and high stability.

[0003] At present, gas sensors based on metal oxide semiconductors (MOS) have become a research hotspot due to their low cost and fast response. As a typical ABO3 type perovskite structure metal oxide, lanthanum ferrite (LaFeO3) has a unique crystal structure and excellent electrical properties, and shows great potential in the field of gas sensing. However, pure LaFeO3 material still has problems such as insufficient sensitivity, high working temperature, slow response and recovery speed, and poor selectivity to different gases when used for acetone detection, which limits its practical application.

[0004] In order to improve its sensing performance, researchers often use modification methods such as noble metal loading, heterostructure building and element doping. However, noble metal loading (such as Pt, Pd) is costly and easy to agglomerate and deactivate; heterostructure building (such as complexing with ZnO, SnO2) is complex in process and the interface compatibility is difficult to control. In terms of element doping, by doping alkaline earth metal ions such as strontium (Sr) or calcium (Ca) at A site, oxygen vacancies can be effectively generated, which to some extent improves the response of the material to gases such as acetone and ethanol. This kind of non-equivalent substitution is often accompanied by complex changes in carrier concentration, sometimes it is difficult to improve sensitivity while ensuring the fast response / recovery dynamics of the material. By doping transition metal ions such as cobalt (Co) with high catalytic activity at B site, the catalytic oxidation ability to target gases can be directly enhanced. This modification sometimes reduces the selectivity of the material to specific gases, and the stability of the catalytic center also faces challenges. In addition, for A-site doping of LaFeO3, how to choose the appropriate doping ions and accurately control the doping amount to maximize the oxygen vacancy concentration without destroying the main crystal phase of the perovskite is still a challenge in this field.

[0005] Therefore, developing a preparation method capable of simultaneously realizing morphology optimization and high-efficiency doping, and preparing a LaFeO3-based gas-sensitive material with high sensitivity, high selectivity and fast response to acetone is a technical problem to be solved in the field. SUMMARY

[0006] The present application aims to overcome the deficiencies of the prior art, and provides a samarium-doped lanthanum ferrite nanofiber material with a simple preparation method and excellent performance, and applies the material to the construction of a high-performance acetone gas sensor.

[0007] To achieve the above object, the present application provides the following technical solutions.

[0008] A preparation method of a samarium-doped lanthanum ferrite nanofiber, comprising the following steps:

[0009] (a) dissolving a soluble lanthanum salt, a soluble samarium salt, a soluble iron salt and a polymer spinning template in a polar aprotic solvent to form a uniform and transparent precursor solution.

[0010] (b) electrospinning the precursor solution under a high-voltage electrostatic field to obtain a precursor nanofiber membrane.

[0011] (c) calcining the precursor nanofiber membrane to obtain a samarium-doped lanthanum ferrite (La x Sm (1-x) FeO3) nanofiber.

[0012] Further, the soluble lanthanum salt is lanthanum nitrate hexahydrate, the soluble samarium salt is samarium nitrate hexahydrate, and the soluble iron salt is iron acetylacetonate.

[0013] Further, the polymer spinning template is polyvinylpyrrolidone (PVP), and the solvent is N,N-dimethylformamide (DMF).

[0014] Further, the molar ratio of lanthanum, samarium and iron in the precursor solution is x:(1-x):1, wherein 0

[0015] Further, the value of x in the molar ratio is 0.4, and the La 0.4 Sm 0.6 FeO3 nanofiber prepared by using the raw materials in the ratio has the highest sensitivity to acetone.

[0016] Further, the electrospinning is performed by loading the precursor solution into a syringe with a metal needle, applying a high-voltage electrostatic field on an electrospinning device to perform spinning, and collecting the precursor nanofiber membrane on a receiving plate, wherein the high voltage is 12-13 kV, the solution advancing flow rate is 0.3-0.6 mL / h, and the distance between the needle and the receiving plate is 15 cm.

[0017] Furthermore, the calcination process is carried out in an air atmosphere, where the temperature is raised to the target temperature at a certain rate and then held at that temperature. The heating rate is 1-3℃ / min, the target temperature is 600-750℃, and the holding time is 1-3 hours.

[0018] The present invention also provides an application of samarium-doped lanthanum ferrite nanofiber material prepared by the above method in an acetone gas sensor.

[0019] This invention proposes a design approach based on the synergistic effect of "defect engineering" and "morphology control": First, by creatively introducing a specific proportion of samarium (Sm) ions into the A-site of LaFeO3, the radius mismatch between samarium (Sm) and lanthanum (La) ions is used to induce lattice distortion, thereby generating a high concentration of gas-sensitive active sites (oxygen vacancies) in the intrinsic structure of the material; Second, the material is constructed into a one-dimensional nanofiber network with a high specific surface area through electrospinning technology to maximize the exposure efficiency of the active sites.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) The preparation method is simple and the cost is low: the electrospinning combined with high temperature calcination method has a short process flow, low equipment requirements, and is easy to achieve large-scale preparation.

[0022] (2) Significantly improved performance: By doping Sm at the A sites of LaFeO3, lattice distortion was successfully introduced, increasing the oxygen vacancy concentration and specific surface area of ​​the material. This provides more active sites for gas adsorption and reaction, and optimizes the electron transport channels.

[0023] (3) Excellent acetone sensing properties: the prepared La 0.4 Sm 0.6 At its optimal operating temperature of 250℃, the FeO3 nanofiber sensor exhibits a response of up to 40.2 to 50ppm acetone, several times that of a pure LaFeO3 sensor. The response and recovery times are shortened to 24 seconds and 20 seconds, respectively, demonstrating excellent kinetic characteristics. Meanwhile, its selectivity for acetone is far superior to that for common interfering gases such as methanol, ethanol, and formaldehyde. Attached Figure Description

[0024] Figure 1 La prepared in Example 1 of this invention 0.4 Sm 0.6 Scanning electron microscope (SEM) image of FeO3 nanofibers.

[0025] Figure 2 The X-ray diffraction (XRD) patterns of the materials prepared in Example 1 and Comparative Examples 1, 2, 3, and 4 of this invention are shown.

[0026] Figure 3 The images show the N2 adsorption / desorption isotherms and pore size distribution of the materials prepared in Example 1 and Comparative Example 1 of this invention.

[0027] Figure 4 The response-operating temperature relationship curves of the sensors prepared for Embodiment 1 and Comparative Examples 1, 2, 3, and 4 of this invention.

[0028] Figure 5 The dynamic response-recovery curve of the sensor prepared in Example 1 of the present invention to 50 ppm acetone at 250 °C. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but these embodiments do not constitute any limitation on the scope of protection of the present invention.

[0030] Example 1

[0031] a) Dissolve soluble lanthanum salt, soluble samarium salt, soluble iron salt and polymer spinning template in a polar aprotic solvent and stir to form a homogeneous, transparent precursor solution.

[0032] (1) In a clean beaker, add 6 mL of N,N-dimethylformamide (DMF) as a solvent.

[0033] (2) Accurately weigh 0.2 mmol (about 0.087 g) of lanthanum nitrate hexahydrate [La(NO3)3·6H2O], 0.3 mmol (about 0.133 g) of samarium nitrate hexahydrate [Sm(NO3)3·6H2O] and 0.5 mmol (about 0.177 g) of ferric acetylacetone [Fe(C5H7O2)3], and add them sequentially to the DMF solvent in (1).

[0034] (3) Dissolve the solution in (2) by initial stirring at room temperature. After the metal salt is completely dissolved, slowly add 0.8 g of polyvinylpyrrolidone (PVP, Mw≈1,300,000) as a template agent for spinning. Seal the beaker and place it on a magnetic stirrer. Stir continuously at room temperature for 12 hours until a clear, homogeneous, and precipitate-free orange-yellow viscous spinning precursor solution is formed.

[0035] b) The precursor solution is electrospun under a high voltage electrostatic field to obtain a precursor nanofiber membrane.

[0036] The precursor solution in (3) was drawn into a 10 mL plastic syringe, a DC high voltage of 13 kV was applied, the injection pump was set to advance speed of 0.6 mL / h, and the vertical distance from the needle tip to the receiving plate was 15 cm for electrospinning.

[0037] c) The precursor nanofiber membrane is calcined to obtain samarium-doped lanthanum ferrite (La). x Sm (1-x) FeO3 nanofibers.

[0038] After spinning, the precursor nanofiber membrane deposited on the aluminum foil was carefully peeled off and placed in a vacuum drying oven at 60°C for 12 hours to fully remove residual DMF solvent.

[0039] The dried fiber membrane was placed in a corundum ark and then placed in a muffle furnace. Under air atmosphere, it was heated to 650°C at a heating rate of 1°C / min and calcined at this temperature for 2 hours. After naturally cooling to room temperature, the resulting pale yellow product was removed; this is La. 0.4 Sm 0.6 FeO3 nanofibers.

[0040] Take an appropriate amount of the above La 0.4 Sm 0.6 FeO3 powder was ground with a small amount of terpineol to form a uniform slurry. The slurry was then evenly coated onto an alumina ceramic tube with gold electrodes using a brush to form a gas-sensitive layer. The coated ceramic tube was dried at 60°C for 6 hours. A nickel-chromium heating wire was then inserted into the ceramic tube, and its pins were soldered to the sensor base. Finally, the manufactured sensor was aged at 200°C for 48 hours to improve its stability.

[0041] The aged sensor was placed in a gas-sensitive testing system, and the operating temperature was controlled by adjusting the heating voltage. The test results are attached. Figures 3-5 As shown, at 250℃, the sensor exhibits a response of 40.2 to 50ppm acetone, a response time of 24s, and a recovery time of 20s, demonstrating excellent overall performance.

[0042] Comparative Example 1: Preparation of pure LaFeO3 nanofibers (undoped)

[0043] Except for the omission of samarium nitrate in step (1) and the adjustment of the amount of lanthanum nitrate to 0.5 mmol, all other preparation and testing steps are exactly the same as in Example 1.

[0044] Comparative Example 2: La 0.8 Sm 0.2 Preparation of FeO3 nanofibers (low doping level)

[0045] Except for adjusting the molar ratio of lanthanum nitrate and samarium nitrate to 0.8:0.2 (i.e., 0.4 mmol of lanthanum nitrate and 0.1 mmol of samarium nitrate) in step (1), all other steps are exactly the same as in Example 1.

[0046] Comparative Example 3: La0.6 Sm 0.4 Preparation of FeO3 nanofibers (medium doping concentration)

[0047] Except for adjusting the molar ratio of lanthanum nitrate and samarium nitrate to 0.6:0.4 (i.e., 0.3 mmol of lanthanum nitrate and 0.2 mmol of samarium nitrate) in step (1), all other steps are exactly the same as in Example 1.

[0048] Comparative Example 4: La 0.2 Sm 0.8 Preparation of FeO3 nanofibers (high doping level)

[0049] Except for adjusting the molar ratio of lanthanum nitrate and samarium nitrate to 0.2:0.8 (i.e., 0.1 mmol of lanthanum nitrate and 0.4 mmol of samarium nitrate) in step (1), all other steps are exactly the same as in Example 1.

[0050] To further verify the technical effects of the present invention, the performance of the materials prepared in Example 1 and Comparative Examples 1-4 was compared, and the analysis is as follows:

[0051] Combination Figure 3 The N2 adsorption-desorption test results showed that, compared with the undoped LaFeO3 in Comparative Example 1, the isothermal hysteresis loop area of ​​the sample in Example 1 was significantly increased. This indicates that the doping of Sm element combined with the electrospinning process not only changed the composition of the material, but also effectively maintained the high porosity and specific surface area of ​​one-dimensional nanofibers by inhibiting excessive agglomeration of grains, thus providing a richer contact interface for gas-solid reactions.

[0052] Figure 4 The key effects of different components on gas-sensing performance were clearly revealed. The undoped Comparative Example 1 showed the lowest responsivity. With increasing Sm doping, the material's responsivity to acetone exhibited a significant "volcano-shaped" trend, first increasing and then decreasing. Example 1 (La:Sm = 0.4:0.6) reached its performance peak, achieving an average responsivity of 40.2 for 50 ppm acetone at 250°C, far exceeding Comparative Example 1. However, when the Sm content deviated from this ratio, the responsivity of both the lower Comparative Example 2 (Sm = 0.2) and the higher Comparative Examples 3 (Sm = 0.4) and 4 (Sm = 0.8) decreased significantly. This demonstrates that the ratio in Example 1 represents a specific component that achieves the optimal balance between lattice distortion and crystal structure stability.

[0053] also, Figure 5The sensor prepared in Example 1 demonstrates excellent kinetic properties under optimal operating conditions. Its response to 50 ppm acetone gas at 250 °C reaches 63, with response and recovery times reduced to 24 s and 20 s, respectively. This rapid response capability is attributed to the unique structure-component synergy of the material: the one-dimensional nanofiber network constructs a rapid transport channel for gas molecules, while the high concentration of oxygen vacancies generated by optimized Sm doping greatly promotes the rate of surface redox reactions.

Claims

1. A method for preparing samarium-doped lanthanum ferrite nanofibers, characterized by: The method comprises the following steps: (a) dissolving a soluble lanthanum salt, a soluble samarium salt, a soluble iron salt and a polymer spinning template in a polar aprotic solvent to form a uniform and transparent precursor solution by stirring. (b) electrospinning the precursor solution under a high-voltage electrostatic field to obtain a precursor nanofiber membrane. (c) calcining the precursor nanofiber membrane to obtain samarium-doped lanthanum ferrite (La x Sm (1-x) FeO3) nanofiber.

2. The method according to claim 1, wherein the method for preparing samarium-doped lanthanum ferrite nanofibers is characterized by: The soluble lanthanum salt is lanthanum nitrate hexahydrate, the soluble samarium salt is samarium nitrate hexahydrate, and the soluble iron salt is acetylacetone iron.

3. The method for preparing samarium-doped lanthanum ferrite nanofibers according to claim 1 or 2, characterized in that: The polymer spinning template is polyvinylpyrrolidone (PVP), and the solvent is N,N-dimethylformamide (DMF). 4.The method of any one of claims 1-3, characterized in that: The molar ratio of lanthanum, samarium and iron in the precursor solution is x:(1-x):1, wherein 0 5. The method according to claim 4, wherein the method is characterized by: The value of x in the molar ratio is 0.4, and the raw materials prepared in this ratio are used to prepare La 0.4 Sm 0.6 FeO3nanofibers. 6.The method of any one of claims 1-5, characterized in that: The electrospinning: the precursor solution is loaded into a syringe with a metal needle, and the electrospinning is performed on an electrospinning device by applying a high-voltage electrostatic field, and the precursor nanofiber membrane is collected on a receiving plate, wherein the high voltage is 12-13 kV, the solution propelling flow rate is 0.3-0.6 mL / h, and the distance between the needle and the receiving plate is 15 cm.

7. The method for preparing samarium-doped lanthanum ferrite nanofibers according to any one of claims 1-6, characterized in that: The calcination process is carried out in an air atmosphere, and the temperature is raised to the target temperature at a certain heating rate, and then the temperature is kept constant, the heating rate is 1-3 ℃ / min, the target temperature is 600-750 ℃, and the holding time is 1-3 hours.

8. The application of the samarium-doped lanthanum ferrite nanofiber material prepared by the method of any one of claims 1-7 in an acetone gas sensor.

Images