A hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor based on MOF derivation

Abstract

The application discloses a hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor based on MOF derivation, and relates to the technical field of semiconductor oxide gas sensors. The application adopts room temperature aging treatment and two-stage calcination treatment process to prepare a well-crystallized hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material based on the MOF derivation strategy, and uses the material to prepare a triethylamine gas sensor. The heterojunction sensitive material fully plays the synergistic effect of a perovskite structure and a metal organic framework, has a fast response speed and high sensitivity to triethylamine, and solves the bottleneck problems of a high working temperature, poor selectivity and insufficient sensitivity of a traditional triethylamine sensor. The application not only provides a new material system for efficient detection of triethylamine, but also opens up a new direction for developing a low-power-consumption and high-stability TEA sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor oxide gas sensors, in particular to a MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor. BACKGROUND

[0002] Triethylamine (TEA) is an organic compound with a strong fishy smell, widely used as an industrial solvent, catalyst, preservative and organic synthesis intermediate. However, triethylamine is volatile and toxic, long-term exposure to its vapor can cause irritation to the respiratory system, eyes and skin of the human body, and can even cause central nervous system inhibition. In chemical production, food processing and laboratory environment, it is very important to monitor the leakage of triethylamine, and it is urgent to develop efficient and sensitive gas sensors to realize real-time early warning and protect personnel health and production safety.

[0003] In recent years, due to the relatively simple preparation, very stable structure, excellent thermal stability and other excellent characteristics, the application range of new metal oxide semiconductor (MOS) sensitive material perovskite LaFeO3 is very wide, covering sensing, ferroelectric, catalysis, multiferroic, superconducting and other fields. Research results show that LaFeO3 sensitive material exhibits good gas sensitive properties to triethylamine. However, the limited response of LaFeO3 sensitive material limits its practicality. How to improve the response of LaFeO3 sensitive material to triethylamine is the focus of research by those skilled in the art. SUMMARY

[0004] The purpose of the present application is to provide a MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine (TEA) gas sensor, in order to solve the problems of high working temperature, poor selectivity and insufficient sensitivity of the sensor in the prior art.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] One of the technical solutions of the present application: a preparation method of a MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material, comprising the following steps: mixing a lanthanum source, an iron source, a solvent and an organic ligand, and aging to obtain a precipitate; the precipitate is subjected to two-stage calcination treatment to obtain the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material;

[0007] The two-stage calcination treatment includes: the temperature of the first-stage calcination treatment is 800-900 DEG C, and the temperature of the second-stage calcination treatment is 700-750 DEG C.

[0008] Metal-organic frameworks (MOFs) are a class of porous multifunctional materials, which are formed by bridging metal center clusters with functional organic ligands. The use of MOFs as precursors to prepare perovskite LaFeO3-based sensing materials in the present application helps to obtain sensing materials with more abundant pore structures. In addition, the present application also constructs a multi-metal oxide heterojunction structure, which can utilize the synergistic effect of various MOS to enhance the gas sensing ability of the material by adjusting the interface properties, microstructure and carrier transfer process of the material.

[0009] Specifically, the LaFeO3 / La2O3 heterojunction sensing material prepared by the MOF derivation strategy of the present application has a hollow mesoporous structure and a heterojunction structure. The hollow mesoporous structure is beneficial to the diffusion of gas, significantly improving the gas adsorption and surface reaction efficiency (i.e. promoting the chemical interaction between triethylamine gas molecules and the surface adsorbed oxygen of the sensing material). The heterojunction structure can improve the carrier mobility of the sensor and accelerate the surface re-oxidation reaction, thereby improving the sensing ability and speeding up the response / recovery speed. The hollow mesoporous structure and the heterojunction structure work together to make the LaFeO3 / La2O3 heterojunction sensing material of the present application have a fast response speed and high sensitivity to triethylamine, and can realize sensitive detection of triethylamine gas.

[0010] Further, the lanthanum source includes lanthanum nitrate.

[0011] Further, the iron source includes iron nitrate.

[0012] Further, the organic ligand includes terephthalic acid.

[0013] Further, the molar ratio of the lanthanum source, the iron source and the organic ligand is 10-12:10-12:10-12.

[0014] Further, the solvent includes a mixed solution of ethanol and N,N-dimethylformamide.

[0015] Further, the volume ratio of the ethanol and the N,N-dimethylformamide is 3-4:1-2.

[0016] Further, the amount ratio of the lanthanum source and the solvent is 10-12 mmol:40-60 mL.

[0017] Further, the temperature of the aging treatment is 20-25℃ (i.e. room temperature), and the time of the aging treatment is 4-6h.

[0018] Further, the first stage calcination treatment is carried out in an argon environment, and the time of the calcination treatment is 2-3h.

[0019] Further, the second stage calcination treatment is performed in an oxygen environment, and the time of the calcination treatment is 2-3h.

[0020] Further, the oxygen environment is an air environment.

[0021] The first calcination in an argon atmosphere is to form an amorphous precursor, and the second calcination in air is to obtain an oxide. If the whole process is performed in an argon atmosphere, LaFeO3 can be formed, but the crystal structure is not good, and it is more difficult to form La2O3. If the whole process is performed in air, the metal organic framework structure is easy to collapse seriously.

[0022] Further, the aging treatment is performed in an air environment.

[0023] Further, the two-stage calcination treatment further comprises a washing and drying step for the precipitate.

[0024] Further, the temperature of the drying is 60-70℃.

[0025] Further preferably, the preparation method of the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material further comprises the following more specific steps:

[0026] (1) 10-12 mmol of lanthanum nitrate and 10-12 mmol of iron nitrate are dissolved in a mixed solution of 30-40 mL of anhydrous ethanol and 10-20 mL of N,N-dimethylformamide, and stirred for 30-40 min to obtain solution A;

[0027] (2) 10-12 mmol of terephthalic acid is added to solution A, stirred for 30-40 min, and then placed in an air environment for room temperature (20-25℃) aging treatment for 4-6h to obtain a red precipitate;

[0028] (3) The red precipitate obtained in step (2) is washed with anhydrous ethanol for 3-4 times, and then dried at 60-70℃ in an air atmosphere;

[0029] (4) The dried material in step (3) is calcined at 800-900℃ for 2-3h in an argon environment to obtain a preliminary calcined material;

[0030] (5) The preliminary calcined material obtained in step (4) is calcined at 700-750℃ for 2-3h in an air environment to obtain a MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material.

[0031] The second technical solution of the present application is a MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material prepared by the above preparation method.

[0032] The third technical solution of the present application is application of the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material in preparation of a triethylamine gas sensor.

[0033] The fourth technical solution of the present application is a MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor, which comprises a ceramic tube substrate provided with a pair of annular gold electrodes on the outer surface, a sensitive material coated on the outer surface of the ceramic tube substrate and the surface of the annular gold electrodes, and a heating wire arranged inside the ceramic tube substrate.

[0034] The sensitive material is the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material.

[0035] The MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor of the present application comprises a ceramic tube substrate provided with a pair of annular gold electrodes on the outer surface, a LaFeO3 / La2O3 sensitive material coated on the outer surface of the ceramic tube substrate and the gold electrodes, and a nickel-cadmium alloy heating wire arranged inside the ceramic tube substrate. When the sensor is working, the heating wire is supplied with direct current to provide the working temperature of the sensor, and the function of measuring the concentration of triethylamine is realized by measuring the direct current resistance value between the two gold electrodes in different atmospheres.

[0036] Further, the thickness of the sensitive material is 20-30 μm.

[0037] Further, the pair of (two) annular gold electrodes are arranged in parallel and separately from each other.

[0038] Optionally, the ceramic tube substrate is an Al2O3 ceramic tube substrate.

[0039] Optionally, the heating wire is a nickel-cadmium alloy heating wire, and the resistance value of the nickel-cadmium alloy heating wire is 30-40 Ω.

[0040] Optionally, the MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor is of a side heating type structure.

[0041] The fifth technical solution of the present application: the preparation method of the MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor, comprising the following steps: mixing the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material with a solvent to obtain a slurry; coating the slurry on the surface of the ceramic tube substrate provided with a pair of annular gold electrodes, so that the slurry completely covers the outer surface of the ceramic tube and the annular gold electrodes, and after drying treatment, passing a heating wire through the inside of the ceramic tube substrate, welding the ceramic tube substrate to the base through a wire, and then aging treatment to obtain the MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor.

[0042] Further, the drying treatment temperature is 20-25℃ (i.e. room temperature), and the time is 2-3h.

[0043] Further, the aging treatment temperature is 300-350℃, and the time is 2-5 days.

[0044] Further, the mass ratio of the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material to the solvent is 1-2:1, and the solvent is anhydrous ethanol.

[0045] Optionally, the wire is a platinum wire.

[0046] Optionally, the platinum wire is led out from the gold electrode.

[0047] Optionally, the inner diameter of the ceramic tube substrate is 0.6-0.8mm, the outer diameter is 1.0-1.3mm, and the length is 4-5mm; the width of a single gold electrode is 0.4-0.5mm, and the distance between the two annular gold electrodes is 0.5-0.6mm; the length of the platinum wire led out from the gold electrode is 4-5mm.

[0048] Preferably, the preparation method of the MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor further comprises the following steps:

[0049] (1) uniformly mix MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material powder and anhydrous ethanol in a mass ratio of 1-2:1 to form a slurry; use a micro pipette gun to coat the slurry on the outer surface of an Al2O3 ceramic tube provided with two parallel, annular and separate gold electrodes, so that the slurry completely covers the outer surface of the Al2O3 ceramic tube and the annular gold electrodes on the outer surface;

[0050] (2) The coated Al2O3 ceramic tube is dried in an air environment at room temperature (20-25℃) for 2-3 hours, and then a nickel-cadmium alloy heating wire with a resistance of 30-40Ω is passed through the inside of the Al2O3 ceramic tube, and the heating wire is used to provide working temperature for the sensor by passing direct current;

[0051] (3) The Al2O3 ceramic tube is welded on a side-heating hexagonal tube base through a platinum wire lead-out from the gold electrode; finally, the sensor is aged in an air environment at 300-350℃ for 2-5 days, thereby obtaining a MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor.

[0052] The working principle of the MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor of the application is as follows:

[0053] The sensing mechanism of the triethylamine gas sensor is based on the redox reaction between triethylamine molecules and the chemisorbed oxygen on the surface of the hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material. When the sensor is working, oxygen molecules (O2) in the air are adsorbed on the surface of the hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material, and form chemisorbed oxygen species (such as O - or O 2- , the specific form is related to the working temperature) by capturing electrons in the conduction band of the material. When triethylamine molecules contact the surface of the heterojunction sensitive material, they react with the chemisorbed oxygen as a reducing gas to generate CO2 and H2O, etc., while releasing electrons back to the conduction band, resulting in a decrease in the resistance of the heterojunction sensitive material. The reaction process can be simplified as:

[0054] (C2H5)3N+O - →NO2+H2O+CO2+e - ;

[0055] The sensitivity (S) of the sensor is defined as:

[0056] S=R g / R a ;

[0057] Wherein, R a is the resistance of the sensor in air, and R g is the resistance after exposure to triethylamine gas.

[0058] Traditional TEA gas sensors mostly use metal oxide materials such as SnO2, ZnO, Fe2O3, etc. as sensitive materials, and usually need to work at high temperature of 250-350℃ to realize effective detection of TEA. This not only leads to high energy consumption, but also limits its application in low-power scenarios such as wearable devices and portable terminals.

[0059] To break through the above technical bottleneck, the application is based on metal organic framework (MOF) derivation strategy, adopts room temperature aging treatment combined with two-stage calcination process, constructs well-crystallized hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material, and is used for preparing high-performance TEA gas sensor. The constructed heterojunction sensitive material forms a heterojunction structure with good energy band matching between perovskite LaFeO3 and La2O3, effectively promotes the separation and transfer of carriers at the interface, thereby enhancing the gas response behavior. At the same time, the MOF derivation process endows the material with hollow mesoporous structure and high specific surface area, which is beneficial to the rapid diffusion and adsorption of TEA molecules, and thus improves the response speed and sensitivity. In addition, the perovskite LaFeO3 has excellent redox activity and adjustable electronic structure, and is suitable for detecting amine reducing gas; and La2O3 has strong alkalinity, which can improve the selective recognition ability to TEA molecules. The application not only provides a new sensitive material system for efficient and low-temperature detection of TEA, but also opens up a new research direction and technical path for developing low-power and high-stability TEA gas sensor.

[0060] The application discloses the following technical effects:

[0061] (1) The LaFeO3 / La2O3 heterojunction sensitive material is prepared by the MOF derivation strategy, and the hollow mesoporous structure is beneficial to the diffusion of the gas, and significantly improves the gas adsorption and surface reaction efficiency.

[0062] (2) In the LaFeO3 / La2O3 heterojunction sensitive material, the LaFeO3 / La2O3 heterojunction structure improves the carrier mobility of the sensor, accelerates the surface reoxidation reaction, thereby improving the sensing ability and speeding up the response / recovery speed.

[0063] (3) The gas sensing test results show that the triethylamine gas sensing performance of the hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor based on the MOF derivation is effectively improved. At the optimal working temperature of 240 DEG C, the response of the hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor based on the MOF derivation to 100 ppm triethylamine is as high as 150, which is 10 times that of the pure LaFeO3 sensor, and the theoretical detection limit is as low as 83 ppb, and good detection selectivity and stability are maintained. Therefore, it can be known that the gas sensor has wide application prospects in detecting the content of triethylamine in a microenvironment.

[0064] (4) The hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material is prepared by using a metal organic framework as a precursor, through room temperature aging treatment and subsequent calcination treatment process, and the process is simple, has high repeatability, is suitable for industrialized batch production, and provides a reliable technical path for practical application of the triethylamine gas sensor. BRIEF DESCRIPTION OF DRAWINGS

[0065] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0066] Figure 1 It is a structural schematic diagram of the triethylamine gas sensor in the present application.

[0067] Figure 2 It is an XRD diffraction pattern of the sensitive material prepared in Comparative Example 1, Example 1 and Comparative Example 2.

[0068] Figure 3 It is an SEM image ((a)-(c)) of the sensitive material prepared in Comparative Example 1, Example 1 and Comparative Example 2, and an HRTEM image ((d)-(f)) and an element distribution diagram ((g)-(i)) of the sensitive material prepared in Example 1.

[0069] Figure 4 It is a nitrogen adsorption-desorption curve and a pore size distribution curve of the sensitive material prepared in Comparative Example 1, Example 1 and Comparative Example 2, wherein (a) is the nitrogen adsorption-desorption curve, and (b) is the pore size distribution curve.

[0070] Figure 5 It is an XPS O 1s analysis result of the sensitive material prepared in Comparative Example 1 and Example 1, wherein (a) is Comparative Example 1, and (b) is Example 1.

[0071] Figure 6 It is a response of the sensor prepared in Comparative Example 1, Example 1 and Comparative Example 2 to 100 ppm triethylamine at different working temperatures.

[0072] Figure 7 It is a selective response of the sensor prepared in the present application, Example 1 and Comparative Example 2 to 100 ppm various volatile gases at the optimal working temperature of 240 DEG C.

[0073] Figure 8 It is a sensitivity of the sensor prepared in Example 1 of the present application to triethylamine with different concentrations at the optimal working temperature of 240 DEG C.

[0074] Figure 9 Fitting curve of the sensor prepared in Example 1 of the present application for different concentrations of triethylamine at the optimum working temperature of 240 °C.

[0075] Figure 10 Continuous measurement curve of the sensor prepared in Example 1 of the present application for 100 ppm triethylamine at the optimum working temperature of 240 °C.

[0076] Figure 11 Dynamic response-recovery curve of the sensor prepared in Example 1 of the present application for 100 ppm triethylamine at the optimum working temperature of 240 °C. DETAILED DESCRIPTION

[0077] Various exemplary embodiments of the present application will now be described in detail, with reference to the figures. The detailed description is not to be regarded as limiting the present application, but rather as exemplifying some aspects, features and embodiments of the present application.

[0078] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of a parameter, unless otherwise stated, each intervening value of the parameter is also specifically included within the scope of the present application. The intervening values of the parameter are combined with a stated value of the parameter in range form. These are only examples of the various embodiments of the present application, which are not limited to particular examples described. The above description is intended to be illustrative, and not restrictive. Many other possible embodiments can be apparent to those of skill in the art from the description herein.

[0079] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict, the content of the specification will control.

[0080] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples herein. The description and examples are illustrative of the application and are not intended to limit the scope of the application.

[0081] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0082] It should be noted that the invention is not detailed, which is the conventional means of operation in the art, and is not the focus of the invention.

[0083] In the following examples, comparative examples and test examples of the present application, if referring to room temperature or normal temperature, it specifically refers to 20-25℃.

[0084] In the following examples, comparative examples and test examples of the present application, if no special instructions are given, all raw materials are ordinary commercially available products, among which the inner diameter of the Al2O3 ceramic tube is 0.6mm, the outer diameter is 1.0mm, and the length is 4mm; the width of the single gold electrode on the surface of the Al2O3 ceramic tube is 0.4mm, and the distance between the two ring-shaped gold electrodes is 0.5mm.

[0085] The structure diagram of the triethylamine gas sensor involved in the following examples and comparative examples of the present application is shown in Figure 1 , wherein the components include: Al2O3 insulating ceramic tube, nickel-cadmium alloy heating wire, ring-shaped gold electrode, platinum wire as electrode lead and sensitive material layer.

[0086] Example 1

[0087] A MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material is prepared by the following steps:

[0088] (1) First, 10mmol of lanthanum nitrate and 10mmol of iron nitrate are dissolved in a mixed solution of 30mL of anhydrous ethanol and 10mL of N,N-dimethylformamide, and stirred thoroughly for 30min to obtain solution A;

[0089] (2) 10mmol of terephthalic acid is added to solution A, stirred thoroughly for 30min, and then placed in an air environment for natural aging treatment at room temperature for 4h to obtain a red precipitate;

[0090] (3) The red precipitate obtained in step (2) is washed with anhydrous ethanol for 3 times, and then dried at 60℃ in an air atmosphere;

[0091] (4) The dried material in step (3) is calcined at 800℃ for 2h in an argon environment to obtain a preliminary calcined material;

[0092] (5) The preliminary calcined material obtained in step (4) is calcined at 700℃ for 2h in an air environment to obtain a MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material.

[0093] The preparation of a MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor is as follows:

[0094] (1) MOF derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material powder and anhydrous ethanol were mixed uniformly in a mass ratio of 1:2 to form a slurry; the slurry was taken with a micro pipette gun to coat the outer surface of an Al2O3 ceramic tube with two parallel, ring-shaped and separate gold electrodes on the outer surface, so that the slurry completely covers the outer surface of the Al2O3 ceramic tube and the ring-shaped gold electrodes on the outer surface; the thickness of the sensitive material layer is about 20 μm;

[0095] (2) The coated Al2O3 ceramic tube was dried at room temperature in air for 2 h, and then a nickel-cadmium alloy heating wire with a resistance of 30 Ω was inserted into the Al2O3 ceramic tube; the heating wire was used to pass a direct current to provide a working temperature for the sensor;

[0096] (3) The Al2O3 ceramic tube was welded to a side-heated hexagonal tube base through a platinum wire lead (the platinum wire lead was drawn from the gold electrode, and the length of the platinum wire lead drawn from the gold electrode was 4 mm); finally, the sensor was aged at 300°C in air for 2 days, thereby obtaining a MOF derived hollow mesoporous LaFeO3 / La2O3 based triethylamine gas sensor, ready for use.

[0097] Comparative Example 1

[0098] A MOF derived LaFeO3 sensitive material, the preparation steps are as follows:

[0099] (1) First, 10 mmol of lanthanum nitrate and 10 mmol of iron nitrate were dissolved in a mixed solution of 30 mL of anhydrous ethanol and 10 mL of N,N-dimethylformamide, and stirred thoroughly for 30 min to obtain solution A;

[0100] (2) 10 mmol of terephthalic acid was added to solution A, stirred thoroughly for 30 min, and then placed in an air environment at room temperature for 4 h to obtain a red precipitate;

[0101] (3) The red precipitate obtained in step (2) was washed with anhydrous ethanol for 3 times, and then dried at 60°C in an air atmosphere;

[0102] (4) The dried material in step (3) was calcined at 800°C for 2 h in an argon atmosphere to obtain a preliminary calcined material;

[0103] (5) The preliminary calcined material obtained in step (4) was treated at 600°C for 2 h in an air environment to obtain a MOF derived LaFeO3 sensitive material.

[0104] Preparation of a MOF derived LaFeO3 based triethylamine gas sensor, the steps are as follows:

[0105] (1) MOF derived LaFeO3 sensitive material powder and anhydrous ethanol were mixed in a mass ratio of 1:2 to form a slurry; the slurry was coated on the outer surface of an Al2O3 ceramic tube with two parallel, ring-shaped and separate gold electrodes on the outer surface by using a micro pipette gun, so that the slurry completely covered the outer surface of the Al2O3 ceramic tube and the ring-shaped gold electrodes on the outer surface; the thickness of the sensitive material layer was about 20 μm;

[0106] (2) The coated Al2O3 ceramic tube was dried at room temperature in air for 2 h, and then a nickel-cadmium alloy heating wire with a resistance of 30 Ω was inserted into the Al2O3 ceramic tube;

[0107] (3) The Al2O3 ceramic tube was welded on a side-heating hexagonal tube base through a platinum wire lead (the platinum wire lead was drawn from the gold electrode, and the length of the platinum wire lead drawn from the gold electrode was 4 mm); finally, the sensor was aged at 300 °C in air for 2 days, thereby obtaining a MOF derived LaFeO3 based triethylamine gas sensor, ready for use.

[0108] Comparative Example 2

[0109] A MOF derived LaFeO3 / La2O3 heterojunction sensitive material, the preparation steps are as follows:

[0110] (1) First, 10 mmol of lanthanum nitrate and 10 mmol of iron nitrate were dissolved in a mixed solution of 30 mL of anhydrous ethanol and 10 mL of N,N-dimethylformamide, and stirred thoroughly for 30 min to obtain solution A;

[0111] (2) 10 mmol of terephthalic acid was added to solution A, stirred thoroughly for 30 min, and then placed in an air environment at room temperature for 4 h to obtain a red precipitate;

[0112] (3) The red precipitate obtained in step (2) was washed with anhydrous ethanol for 3 times, and then dried at 60 °C in air;

[0113] (4) The dried material in step (3) was calcined at 800 °C for 2 h in an argon environment to obtain a preliminary calcined material;

[0114] (5) The preliminary calcined material obtained in step (4) was calcined at 800 °C for 2 h in air to obtain a MOF derived LaFeO3 / La2O3 heterojunction sensitive material.

[0115] Preparation of a MOF derived LaFeO3 / La2O3 based triethylamine gas sensor, the steps are as follows:

[0116] (1) MOF derived LaFeO3 / La2O3 heterojunction sensitive material powder and anhydrous ethanol were mixed uniformly in a mass ratio of 1:2 to form a slurry; the slurry was taken by a micro pipette gun and coated on the outer surface of an Al2O3 ceramic tube with two parallel, ring-shaped and separate gold electrodes on the outer surface, so that the slurry completely covers the outer surface of the Al2O3 ceramic tube and the ring-shaped gold electrodes on the outer surface; the thickness of the sensitive material layer is about 20 μm;

[0117] (2) The coated Al2O3 ceramic tube was dried at room temperature in air for 2 h, and then a nickel-cadmium alloy heating wire with a resistance of 30 Ω was passed through the inside of the Al2O3 ceramic tube;

[0118] (3) The Al2O3 ceramic tube was welded on a side-heating hexagonal tube base through a platinum wire lead (the platinum wire lead was drawn from the gold electrode, and the length of the platinum wire lead drawn from the gold electrode was 4 mm); finally, the sensor was aged at 300 °C in air for 2 days, thereby obtaining a MOF derived LaFeO3 / La2O3 based triethylamine gas sensor, ready for use.

[0119] Test Example 1

[0120] Performance characterization of the sensitive material

[0121] Figure 2 For the XRD diffraction patterns of the sensitive materials prepared in Comparative Example 1, Example 1 and Comparative Example 2, it can be seen that the sensitive materials prepared in Comparative Example 1, Example 1 and Comparative Example 2 all exhibit an orthorhombic perovskite LaFeO3 structure, and there is also a clear La2O3 crystal phase in Example 1 and Comparative Example 2, indicating the presence of a heterojunction structure.

[0122] Figure 3 For the SEM images of the sensitive materials prepared in Comparative Example 1, Example 1 and Comparative Example 2, and the HRTEM images and element distribution maps of the MOF derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material prepared in Example 1. Among them, (a) is the SEM image of Comparative Example 1, (b) is the SEM image of Example 1, and (c) is the SEM image of Comparative Example 2. It can be seen that all of them exhibit a porous structure of nanoparticle accumulation. It is worth noting that the sensitive material prepared in Example 1 also exhibits a clear hollow structure (as shown in (b) of the figure). Figure 3(b) shows that this facilitates gas diffusion within the sensitive material. (d)-(f) are HRTEM images of the sensitive material prepared in Example 1 at different magnifications, revealing two different lattice distances. The interstitial planes with interstitial distances of 0.27 nm and 0.29 nm correspond to the (121) crystal plane of LaFeO3 and the (101) crystal plane of La2O3, respectively. This confirms the existence of both LaFeO3 and La2O3 crystal phases. Furthermore, (g)-(i) are elemental distribution maps of the sensitive material prepared in Example 1, showing that Fe, La, and O elements are clearly observed in the nanostructure and are well-distributed.

[0123] Figure 4 The figures show the nitrogen adsorption-desorption curves and pore size distribution curves of the sensitive materials prepared in Comparative Example 1, Example 1, and Comparative Example 2 of this invention, where (a) is the nitrogen adsorption-desorption curve and (b) is the pore size distribution curve. The nitrogen adsorption-desorption curves show that all three exhibit type IV isotherms and have type H3 hysteresis loops. The pore size distribution curves show that the average pore size distributions of Comparative Example 1, Example 1, and Comparative Example 2 are 12.80 nm, 19.51 nm, and 13.48 nm, respectively. All three exhibit mesoporous characteristics (mesoporous refers to pores with a diameter of 2-50 nm), which is beneficial for gas diffusion. Among them, Example 1 exhibits the best mesoporous characteristics.

[0124] Figure 5 The figures show the XPS O 1s analysis results of the sensitive materials prepared in Comparative Example 1 and Example 1 of this invention, where (a) is Comparative Example 1 and (b) is Example 1. Figure 5 As can be seen, the deconvolution O1s spectrum shows three different types of oxygen: lattice oxygen (OL) at 529.0 eV, vacancy oxygen (O) at 529.9 eV, and vacancy oxygen (O) at 529.9 eV. V ) and chemisorbed oxygen (O) at 531.3 eV ads Quantitative analysis showed that O in Example 1 ads The content (42.4%) was significantly higher than that in Comparative Example 1. ads Content (32.7%). Types of oxygen chemisorbed on the surface (O2) ads An increase in the number of gases corresponds to a greater likelihood of improved gas detection sensitivity.

[0125] Test Example 2

[0126] Sensor performance testing

[0127] The gas-sensitive performance testing system mainly consists of a programmable linear DC power supply (DP832A), a 1L gas chamber, and a precision source meter (B2912B). The sensor's operating temperature is controlled by adjusting the output voltage of the DP832A, which in turn controls the heating power of the heating wire, thus achieving precise temperature control.

[0128] (1) Optimum working temperature test

[0129] The sensors prepared in Comparative Example 1, Example 1 and Comparative Example 2 of the present application were tested for their sensitivity (or response value) to triethylamine at different temperatures.

[0130] Test method: Before the test, synthetic air (79% nitrogen + 21% oxygen by volume fraction) was first continuously passed into the chamber at a flow rate of 100 mL / min to establish and maintain a stable baseline environment. When the resistance value of the sensor tended to be stable, its initial resistance value (R a ) was recorded as the reference. Subsequently, a predetermined volume of target gas was taken from a sealed chemical reagent bottle using a syringe and injected into the chamber quickly. After the target gas contacted the sensor, it was waited for about 100 s until the resistance change reached stability, and the resistance value at this time was recorded as R g , and the response value was calculated according to R a and R g . After the test, synthetic air was again passed in to disperse the residual target gas in the chamber, and after the resistance of the sensor returned to the initial state, the next round of detection could be carried out.

[0131] Figure 6 The responses of the sensors prepared in Comparative Example 1, Example 1 and Comparative Example 2 of the present application to 100 ppm triethylamine at different working temperatures are shown. It can be seen that the sensitivity of the three sensors all first increased and then decreased with temperature, showing strong temperature dependence. The sensors prepared in Comparative Example 1, Example 1 and Comparative Example 2 showed their peak responses at 240°C. At the optimum working temperature of 240°C, the response value of the sensor prepared in Comparative Example 1 was 15 when exposed to triethylamine with a concentration of 100 ppm. In comparison, the response value of the sensor prepared in Example 1 was as high as 150 at a temperature of 240°C, which was 10 times higher. This is attributed to the heterostructure interaction between LaFeO3 and La2O3 on the one hand, and the excellent hollow porous structure and mesopore size (average pore size 19.51 nm) of the sensor prepared in Example 1 on the other hand, which are conducive to the diffusion of gas. However, the response value of the sensor prepared in Comparative Example 2 was lower than that of the sensor prepared in Example 1, which is attributed to the fact that a large amount of La2O3 was generated and enriched on the surface, resulting in smaller mesopore size of the sensitive material, which is not conducive to the diffusion of gas.

[0132] (2) Selectivity test

[0133] The response values of the sensors prepared in Comparative Example 1, Example 1 and Comparative Example 2 of the present application to different volatile gases were tested at the optimum working temperature of 240°C (test method same as the optimum working temperature test, multiple rounds of detection were carried out by changing the gas species at a fixed working temperature).

[0134] Figure 7 The selectivity response of the sensors prepared in Inventive Example 1 and Comparative Examples 1 and 2 to 100 ppm of various volatile gases at the optimal working temperature of 240 °C (where Methanol represents methanol, Acetone represents acetone, Benzene represents benzene, and Formaldehyde represents formaldehyde). It can be seen that the sensor prepared in Inventive Example 1 has better selectivity to triethylamine and the highest sensitivity at the working temperature of 240 °C compared to the sensors prepared in Comparative Examples 1 and 2.

[0135] (3) Sensitivity test

[0136] Test method: Before the test, first continuously pass synthetic air (79% nitrogen + 21% oxygen by volume fraction) into the chamber at a flow rate of 100 mL / min to establish and maintain a stable baseline environment. When the resistance value of the sensor tends to be stable, record its initial resistance value (R a ) as the reference. Then, a predetermined volume of target gas is taken from a sealed chemical reagent bottle using a syringe and injected into the chamber quickly. After the target gas contacts the sensor, the resistance value (R g ) at different times is tested until the resistance change reaches stability, and the response value at different times is calculated according to R a and R g . After the test, synthetic air is passed again to disperse the residual target gas in the chamber, and after the resistance of the sensor returns to the initial state, another volume of target gas can be injected for the next round of detection.

[0137] Figure 8 The sensitivity of the sensor prepared in Inventive Example 1 to different concentrations (0.5-100 ppm) of triethylamine at the optimal working temperature of 240 °C (where the inset is a partial enlarged view). It can be seen that as the concentration of the detected gas triethylamine increases, the sensitivity (i.e. response value) of the sensor gradually increases.

[0138] Figure 9 The fitting curve of the response value of the sensor prepared in Inventive Example 1 to different concentrations of triethylamine at the optimal working temperature of 240 °C. It can be found from the fitting curve that there is a good linear relationship between the sensitivity of the sensor and the concentration of triethylamine, indicating that the sensor has a good test range, and the theoretical detection lower limit is as low as 83 ppb.

[0139] (4) Reproducibility test

[0140] Test method: Before the test, first continuously pass synthetic air (79% nitrogen + 21% oxygen by volume fraction) into the chamber at a flow rate of 100 mL / min to establish and maintain a stable baseline environment. When the resistance value of the sensor tends to be stable, record its initial resistance value (R a ) as a reference. Then, a predetermined volume of TEA gas is taken from a sealed chemical reagent bottle using a syringe (so that the concentration of TEA in the chamber is 100 ppm), and quickly injected into the chamber. After the TEA gas contacts the sensor, test the resistance value (R g ) at different times until the resistance change reaches stability, and calculate the response value at different times according to R a and R g . After the test, pass synthetic air again to disperse the residual TEA gas in the chamber, and after the resistance of the sensor returns to the initial state, continue to pass a predetermined volume of TEA gas (so that the concentration of TEA in the chamber is 100 ppm) for a second round of detection. Repeat the above steps to achieve continuous 4 detections.

[0141] Figure 10 The continuous measurement curve of the sensor prepared in Example 1 of the present application for 100 ppm triethylamine at the optimal working temperature of 240℃. It can be seen that the sensitivity of the sensor is basically maintained during the four continuous measurements, and it can return to the initial state after the test is completed, indicating that the sensor has good repeatability and stability.

[0142] (5) Response / recovery speed test

[0143] Test method: Before the test, first continuously pass synthetic air (79% nitrogen + 21% oxygen by volume fraction) into the chamber at a flow rate of 100 mL / min to establish and maintain a stable baseline environment. When the resistance value of the sensor tends to be stable, record its initial resistance value (R a ) as a reference. Then, a predetermined volume of TEA gas is taken from a sealed chemical reagent bottle using a syringe (so that the concentration of TEA in the chamber is 100 ppm), and quickly injected into the chamber. After the TEA gas contacts the sensor, start timing, test the resistance value (R g ) at different times until the resistance change reaches stability, and calculate the response value at different times according to R a and R g . After the test, pass synthetic air again to disperse the residual TEA gas in the chamber, and test the resistance value (R g), and the flow of synthetic air is paused when the sensor resistance returns to its initial state, thus completing one dynamic response-recovery test. The response time is defined as the time required for the sensor resistance to reach 90% of the total change after exposure to the TEA gas. Conversely, the recovery time is the duration required for the resistance to recover to 90% of its initial state during the removal of the TEA gas by the flow of synthetic air.

[0144] Figure 11 The dynamic response-recovery curve of the sensor prepared in Example 1 of the present application for 100 ppm triethylamine at the optimal operating temperature of 240 °C is shown in Figure 2. It can be seen that the sensor has fast sensing dynamics, with a response time of 31 seconds and a recovery time of 41 seconds.

[0145] The above-described examples are merely preferred modes of the present application and are not intended to limit the scope of the present application, and various modifications and improvements to the technical solutions of the present application made by those of ordinary skill in the art without departing from the design spirit of the present application shall fall within the scope of protection of the present application as defined by the claims.

Claims

1. Application of a MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material in preparation of a triethylamine gas sensor, characterized in that, The preparation steps of the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material include: mixing a lanthanum source, an iron source, a solvent and an organic ligand to obtain a precipitate through aging treatment; and performing two-stage calcination treatment on the precipitate to obtain the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material. The two-stage calcination treatment includes: the temperature of the first-stage calcination treatment is 800-900 DEG C, and the temperature of the second-stage calcination treatment is 700-750 DEG C. The temperature of the aging treatment is 20-25 DEG C, and the aging treatment time is 4-6 h. The first-stage calcination treatment is performed in an argon environment, and the calcination treatment time is 2-3 h. The second-stage calcination treatment is performed in an oxygen-containing environment, and the calcination treatment time is 2-3 h.

2. Use according to claim 1, wherein The lanthanum source includes lanthanum nitrate. And / or, the iron source includes iron nitrate. And / or, the organic ligand includes terephthalic acid. And / or, the molar ratio of the lanthanum source, the iron source and the organic ligand is 10-12:10-12:10-12.

3. The use according to claim 1, wherein The solvent includes a mixed solution of ethanol and N, N-dimethylformamide.

4. Use according to claim 3, wherein the compound is ###0002### The volume ratio of the ethanol and the N, N-dimethylformamide is 3-4:1-2. And / or, the dosage ratio of the lanthanum source and the solvent is 10-12 mmol:40-60 mL.

5. A hollow mesoporous LaFe03 / La203-based triethylamine gas sensor based on MOF derivatization, characterized by, The MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor includes a ceramic tube substrate provided with a pair of annular gold electrodes on an outer surface, a sensitive material coated on the outer surface of the ceramic tube substrate and the surface of the annular gold electrodes, and a heating wire arranged inside the ceramic tube substrate. The sensitive material is a MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material. The preparation steps of the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material include: mixing a lanthanum source, an iron source, a solvent and an organic ligand to obtain a precipitate through aging treatment; and performing two-stage calcination treatment on the precipitate to obtain the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material; The two-stage calcination treatment includes: the temperature of the first-stage calcination treatment is 800-900 DEG C, and the temperature of the second-stage calcination treatment is 700-750 DEG C. The temperature of the aging treatment is 20-25 DEG C, and the aging treatment time is 4-6 h. The first-stage calcination treatment is performed in an argon environment, and the calcination treatment time is 2-3 h. The second-stage calcination treatment is performed in an oxygen-containing environment, and the calcination treatment time is 2-3 h.

6. A method for preparing a MOF-derived hollow mesoporous LaFe03 / La203-based triethylamine gas sensor according to claim 5, characterized in that, The method comprises the following steps: mixing the MOF-derived hollow mesoporous LaFeO3 / La2O3 heterojunction sensitive material with a solvent to obtain a slurry; coating the slurry on the surface of a ceramic tube substrate provided with a pair of annular gold electrodes, so that the slurry completely covers the outer surface of the ceramic tube and the annular gold electrodes; after drying treatment, threading a heating wire through the inside of the ceramic tube substrate; welding the ceramic tube substrate to a base through a wire; and then aging treatment to obtain the MOF-derived hollow mesoporous LaFeO3 / La2O3-based triethylamine gas sensor.

7. The preparation method of MOF-derived hollow mesoporous LaFe03 / La203-based triethylamine gas sensor according to claim 6, wherein, The drying treatment is performed at a temperature of 20-25 DEG C for 2-3 hours; and / or the aging treatment is performed at a temperature of 300-350 DEG C for 2-5 days.

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