An In2O3 chlorine gas sensor prepared from amorphous MOF and preparation method thereof

Abstract

The present application relates to the field of gas sensors, and discloses an In2O3 chlorine sensor prepared by amorphous MOF and a preparation method thereof. The chlorine sensor comprises: a gas-sensitive layer, wherein the gas-sensitive layer is an In2O3 material prepared by amorphous MOF; a ceramic tube, wherein the gas-sensitive layer is coated on the ceramic tube; the preparation method of the In2O3 comprises the following steps: S1, dissolving 2-aminoterephthalic acid, benzoic acid and pyridine in N,N-dimethylformamide, and ultrasonicating until completely dissolved; S2, dissolving 4.5 hydrated indium nitrate in N,N-dimethylformamide, and ultrasonicating until completely dissolved, and then adding the solution of step S1, and ultrasonicating; S3, heating the mixture in a container, cooling it naturally, collecting and drying it to obtain NH2-MIL-68(In); S4, dispersing NH2-MIL-68(In) in a dimethylimidazole aqueous solution, collecting, washing and drying it after stirring, and finally calcining it at a high temperature to obtain the In2O3 material. The invention obtains the In2O3 gas-sensitive material by adopting a simple water bath method and amorphization treatment of dimethylimidazole.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to an In2O3 chlorine sensor prepared from amorphous MOF and a preparation method thereof. Background Art

[0002] Chlorine (Cl2) is a common gas around us. It is a yellow-green toxic gas with a strong pungent smell. Plastics, synthetic fibers, bleach, disinfectants, etc. commonly used in our lives all use Cl2 as a raw material. Chlorine is toxic and can damage the respiratory mucosa when inhaled. Inhaling more than 1000ppm of chlorine is life-threatening. In addition, chlorine is one of the main elements that destroy the ozone layer. Therefore, from the perspective of protecting the environment and protecting human health, it is very necessary to develop a chlorine sensor with a low detection limit and high sensitivity. Chlorine sensors can be used in environmental monitoring, safety testing, transportation and other fields.

[0003] There are already some known methods for detecting Cl2, such as optical gas sensors, gas chromatography and impedance gas sensors. Among them, impedance semiconductor gas sensors in impedance gas sensors have attracted much attention because they are more economical and have good stability. Semiconductor metal oxide sensors such as ZnO, SnO2 and WO3 and their derivatives of Cl2 sensors have been widely studied and reported. However, there is still a need for a Cl2 gas sensor with a simpler preparation method, lower detection limit and higher sensitivity.

[0004] Metal organic frameworks (MOFs) are a type of crystalline porous materials that are widely used due to their controllable composition, porous properties and ultra-high specific surface area. They are composed of metal ions or metal elements combined with organic ligands. Metal oxides prepared using metal organic frameworks as templates have porous properties, which is conducive to the escape of gases. In recent years, metal oxides prepared based on MOF template method have been widely reported in the field of gas sensing. Compared with crystalline MOFs, amorphous MOFs have the versatility of MOFs, in addition to other advantages, such as having more defect sites and hierarchical porous structures, which can be used to improve gas sensing performance. However, oxide-based gas-sensitive materials based on amorphous MOFs have not been reported for research and use. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides an In2O3 chlorine gas sensor prepared by amorphous MOF and a preparation method thereof. The In2O3 gas-sensitive material is obtained by a simple water bath method and amorphization treatment with dimethylimidazole. The In2O3 material prepared by amorphous MOF has a porous structure and abundant defect sites, and can adsorb more chlorine molecules. The surface of the material can adsorb more electrons, thereby improving the performance of the gas sensor.

[0006] To achieve the above objectives, the present invention is implemented by the following technical scheme: an In2O3 chlorine sensor prepared by amorphous MOF, comprising:

[0007] A gas-sensitive layer, wherein the gas-sensitive layer is an In2O3 material prepared from an amorphous MOF;

[0008] A ceramic tube, wherein the gas-sensitive layer is coated on the ceramic tube;

[0009] The preparation method of In2O3 comprises the following steps:

[0010] S1. Dissolve 2-aminoterephthalic acid, benzoic acid and pyridine in N,N-dimethylformamide and perform ultrasonication until completely dissolved;

[0011] S2, dissolving 4.5 hydrated indium nitrate in N,N-dimethylformamide, ultrasonically treating until completely dissolved, then adding the solution of step S1, and ultrasonically treating;

[0012] S3, heating the mixture in a container and then cooling it naturally, collecting and drying it to obtain NH2-MIL-68(In);

[0013] S4. Disperse NH2-MIL-68 (In) in a dimethylimidazole aqueous solution, collect, wash, and dry after stirring, and finally calcine at a high temperature to obtain In2O3 material.

[0014] Preferably, the sensor further comprises a base;

[0015] The ceramic tube is provided with two annular electrodes, and both ends of the ceramic tube are provided with four platinum wires, and the platinum wires are welded on the base;

[0016] A nickel-chromium alloy resistance wire for heating is arranged in the middle of the ceramic tube.

[0017] Preferably, the ring electrode is one of an Au electrode, a Pd electrode and an Ag electrode.

[0018] Preferably, the In2O3 material prepared by the amorphous MOF is one of nanoparticles, nanorods and nanosheets.

[0019] Preferably, the container in step S3 is a stainless steel container with a polytetrafluoroethylene lining.

[0020] Preferably, the preparation method of In2O3 further comprises the following steps:

[0021] S10, dissolving 300-600 mg of 2-aminoterephthalic acid, 70-90 mg of benzoic acid and 300-500 μL of pyridine in 10-20 mL of N,N-dimethylformamide, and sonicating until completely dissolved;

[0022] S20, dissolving 900-1200 mg of 4.5 hydrated indium nitrate in 5-15 mL of N,N-dimethylformamide, adding the solution of step S1 after ultrasonic treatment until completely dissolved, and ultrasonic treatment for 3-8 min;

[0023] S30, transferring the mixture to a stainless steel container with a polytetrafluoroethylene liner, heating at 100-150° C. for 2-3 h at a heating rate of 1-3° C. / min, and after natural cooling, collecting the product and washing it by centrifugation with ethanol, and vacuum drying it at 60-90° C. overnight to obtain NH2-MIL-68(In);

[0024] S40. Disperse 5-15 mg of NH2-MIL-68 (In) in a 0.5-0.8 M aqueous solution of dimethylimidazole, stir for one day, collect and wash with ethanol by centrifugation, then vacuum dry at 60-90°C overnight, and finally calcine at 400-600°C for 3-5 hours to obtain In2O3 material.

[0025] The present invention also provides a method for preparing an In2O3 chlorine gas sensor prepared by an amorphous MOF, comprising the following steps:

[0026] a) mixing and grinding the prepared In2O3 material with pineneol;

[0027] b) coating the ground sample onto a ceramic tube;

[0028] c) after drying, calcining at 200-300° C. for 1-2 hours;

[0029] d) fixing the ceramic tube on a base and performing aging to obtain the chlorine gas sensor.

[0030] Preferably, the aging step is performed by using an aging instrument at a temperature of 250 to 350° C. for 4 to 8 days.

[0031] The present invention provides an In2O3 chlorine gas sensor prepared from amorphous MOF and a preparation method thereof. It has the following beneficial effects:

[0032] 1. The present invention obtains In2O3 gas-sensitive material by adopting a simple water bath method and amorphization treatment of dimethylimidazole. This method is low-cost and easy to operate. In addition, the In2O3 material prepared by amorphous MOF has a porous structure and abundant defect sites, which can adsorb more chlorine molecules. The surface of the material can adsorb more electrons, thereby improving the performance of the gas sensor.

[0033] 2. Compared with the In2O3 sensor prepared by MOF, the In2O3 sensor prepared by the amorphous MOF of the present invention has better sensitivity and selectivity to chlorine at a lower temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of SEM morphology characterization of an embodiment of the present invention, wherein (a) In2O3 material, (b) a-In2O3 material;

[0035] Figure 2 XRD spectrum materials of In2O3, a-In2O3, and aNH2-MIL-68(In) in the embodiments of the present invention;

[0036] Figure 3 Schematic diagram of the gas sensing performance of In2O3 material and a-In2O3 material in the embodiment of the present invention;

[0037] Figure 4 Schematic diagram of the dynamic response curve of a-In2O3 material to 2ppm Cl2 at different humidity in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The present invention provides a chlorine gas sensor with high sensitivity, good selectivity and strong stability through an In2O3 chlorine gas sensor prepared from amorphous MOF and a preparation method thereof, which can detect Cl2 gas at a relatively low temperature. The specific embodiments of the present invention are described in detail below.

[0040] 1. Composition of the sensor

[0041] Gas-sensing layer: The gas-sensing layer is In2O3 material prepared from amorphous MOF. In2O3 material prepared from amorphous MOF has more oxygen vacancies and can absorb more electrons, thereby improving the sensitivity of the gas sensor.

[0042] Ceramic tube: The gas-sensitive layer is coated on the ceramic tube. The ceramic tube provides a stable structural support and has good high temperature resistance, which is conducive to the sensor working in a high temperature environment.

[0043] Base and electrode assembly: The ceramic tube has two ring electrodes, each with four platinum wires at both ends, which are welded to the base. A nickel-chromium alloy resistance wire for heating is set in the middle of the ceramic tube to adjust the working temperature. The ring electrode can be one of Au electrode, Pd electrode or Ag electrode.

[0044] The use of ceramic tube and nickel-chromium alloy resistance wire ensures that the sensor has good stability and durability under high temperature conditions.

[0045] 2. Preparation method of In2O3 material

[0046] 1. Dissolving and mixing: Dissolve 300-600 mg of 2-aminoterephthalic acid (NH2-H2BDC), 70-90 mg of benzoic acid and 300-500 μL of pyridine in 10-20 mL of N,N-dimethylformamide (DMF) and sonicate until completely dissolved. Dissolve 900-1200 mg of 4.5 hydrated indium nitrate ((NO3)3·4.5H2O) in 5-15 mL of DMF and sonicate until completely dissolved, then add the above solution and continue sonication for 3-8 minutes.

[0047] 2. Heating and cooling: The mixture was transferred to a stainless steel container with a polytetrafluoroethylene liner and heated at 100-150°C for 2-3 hours at a heating rate of 1-3°C / min. After the heating was completed, the product was collected after natural cooling, washed by centrifugation with ethanol, and vacuum dried at 60-90°C overnight to obtain NH2-MIL-68(In).

[0048] 3. Secondary treatment and calcination: 5-15 mg of NH2-MIL-68(In) was dispersed in a 0.5-0.8 M dimethylimidazole aqueous solution and stirred at room temperature for one day. After collecting the precipitate, it was washed by centrifugation with ethanol and vacuum dried overnight at 60-90°C to obtain aNH2-MIL-68(In). Finally, it was calcined at 400-600°C for 3-5 hours to obtain In2O3 material.

[0049] The In2O3 material prepared by amorphous MOF can adsorb more chlorine molecules due to its unique porous structure and abundant defect sites, and the surface of the material can adsorb more electrons, thereby improving the performance of the gas sensor.

[0050] 3. Preparation method of sensor

[0051] 1. Sample preparation:

[0052] The prepared In2O3 material was mixed with an appropriate amount of pineol and ground to obtain a thin paste sample.

[0053] 2. Coating and firing:

[0054] The ground sample is coated on a ceramic tube with four platinum wires, and a nickel-chromium alloy heating resistance wire is placed in the middle of the ceramic tube. After the sample is coated, it is dried and fired at 200-300°C for 1-2 hours.

[0055] 3. Assembly and aging:

[0056] The fired ceramic tube is fixed on the base by welding wire. In order to ensure the stability of the gas-sensitive test, the sensor is placed on the aging instrument and aged at 250-350℃ for 4-8 days.

[0057] The In2O3 material prepared by amorphous MOF has a high specific surface area, porous structure and abundant oxygen vacancies, which are conducive to the adsorption and reaction of gases. When chlorine (Cl2) is adsorbed on the surface of In2O3 material, it reacts with oxygen vacancies, resulting in resistance changes, thereby realizing the detection of Cl2.

[0058] The present application is further described below through specific examples.

[0059] Embodiment 1:

[0060] In this embodiment, In2O3 material for Cl2 detection is prepared, and its preparation process includes the following steps:

[0061] Step 1: Prepare the precursor solution

[0062] Take 920 mg NH2-H2BDC, 160 mg benzoic acid and 800 μL pyridine and dissolve them in 30 mL N,N-dimethylformamide. Then dissolve 2100 mg In(NO3)3·4.5H2O in 20 mL N,N-dimethylformamide.

[0063] Step (ii): Preparation of In2O3 precursor for amorphous MOF

[0064] The two-step solutions were mixed, ultrasonicated, and then heat treated at 125°C for 2.5 h. The precipitate was collected and dried.

[0065] Step (III): Preparation of In2O3 prepared from amorphous MOF

[0066] The precursor powder was dispersed in dimethylimidazole solution, stirred at room temperature for 12 h, and the precipitate was collected and sintered at 450 °C for 4 h.

[0067] Embodiment 2:

[0068] In this embodiment, an In2O3 semiconductor Cl2 sensor made of amorphous MOF for Cl2 detection is prepared, and the specific steps are as follows:

[0069] Step (i): Grind a small amount of In2O3 prepared from amorphous MOF and an appropriate amount of pineneol in a mortar;

[0070] Step (ii): applying the ground paste sample to the surface of a ceramic tube with a platinum wire;

[0071] Step (three): sinter it at 300°C for 2h, weld the ceramic tube to the black base, and place a heating resistance wire inside the ceramic tube.

[0072] A gas-sensitive test instrument is used to perform a gas-sensitive test on an In2O3 semiconductor Cl2 sensor prepared from an amorphous MOF, the steps comprising:

[0073] (1) Connecting the In2O3 semiconductor Cl2 sensor prepared by amorphous MOF to the working system, with an operating voltage of 5 V and an operating temperature of 160°C;

[0074] (2) Indoor air as background gas;

[0075] (3) Under the current working conditions, after the output signal of the In2O3 semiconductor Cl2 sensor prepared by amorphous MOF is stabilized, a certain amount of Cl2 gas is introduced to observe the change in resistance value;

[0076] (4) Open the air hood and observe that the resistance value recovers until it is close to the initial value;

[0077] (5) Repeat the experiment and repeat steps (2)-(4).

[0078] The test results show that the In2O3 semiconductor Cl2 sensor prepared by amorphous MOF exhibits high sensitivity to Cl2.

[0079] Embodiment 3:

[0080] In this example, In2O3 prepared from amorphous MOF and In2O3 prepared from MOF were prepared respectively to compare the differences in their microstructures.

[0081] The preparation method of In2O3 prepared by amorphous MOF is the same as that in Example 1. For the convenience of comparison, the same batch of precursors was used to prepare In2O3 prepared by MOF. The specific method is as follows:

[0082] Take the In2O3 precursor prepared by the amorphous MOF and directly sinter it at 450℃ for 4h.

[0083] like Figure 1 As shown, (a) is the In2O3 material prepared by MOF, and (b) is the In2O3 prepared by amorphous MOF

[0084] As can be seen from the image, the In2O3 material prepared by MOF has a relatively regular rod-like structure, a relatively smooth surface, and uniform size. The material has a high degree of crystallinity and a complete structure. The In2O3 material prepared by amorphous MOF shows an irregular rod-like structure, with a large number of nanoparticles attached to the surface, showing porous characteristics. The material surface is rough and has more defect sites, which are conducive to the adsorption and reaction of gas molecules.

[0085] Through comparative analysis of SEM images, the microstructural advantages of In2O3 materials prepared by amorphous MOF were verified, further supporting its application prospects in chlorine gas sensors.

[0086] Embodiment 4:

[0087] This example compares the X-ray diffraction (XRD) patterns of In2O3 prepared from amorphous MOF, In2O3 prepared from MOF, and aNH2-MIL-68(In) obtained during the preparation of In2O3 prepared from amorphous MOF.

[0088] In2O3 prepared from amorphous MOF: The preparation method is the same as that in Example 1.

[0089] In2O3 prepared by MOF: Take the In2O3 precursor prepared by amorphous MOF in the same way, and directly sinter it at 450°C for 4 hours to obtain the In2O3 material prepared by MOF.

[0090] aNH2-MIL-68(In): During the preparation of In2O3 prepared from amorphous MOF, the precipitate collected before firing is aNH2-MIL-68(In).

[0091] X-ray diffraction (XRD) analysis was performed on the above three samples to determine their crystal phase structures. Figure 2 shown.

[0092] As can be seen from the figure:

[0093] aNH2-MIL-68(In) lacks obvious crystal diffraction peaks and shows an amorphous structure.

[0094] a-In2O3 shows clear characteristic peaks of In2O3 crystals, indicating that after high-temperature calcination, the amorphous MOF is successfully converted into In2O3 crystalline materials with high specific surface area and oxygen vacancies.

[0095] In2O3 also shows the crystal characteristic peaks of In2O3, but its peak intensity is different from that of a-In2O3, indicating that different preparation methods have a certain influence on the crystal structure.

[0096] XRD analysis shows that the In2O3 material prepared using amorphous MOF as a precursor has unique crystal structure characteristics. Compared with the traditional MOF preparation method, the In2O3 material prepared by amorphous MOF has more oxygen vacancies while maintaining a high specific surface area and porous structure. These characteristics help to improve the sensitivity and selectivity of the chlorine sensor.

[0097] Embodiment 5:

[0098] In this example, In2O3 prepared from amorphous MOF and In2O3 prepared from MOF were prepared respectively.

[0099] The preparation method of In2O3 prepared by amorphous MOF is the same as that in Example 1. For the convenience of comparison, the same batch of precursors is used to prepare In2O3 prepared by MOF. The specific method is:

[0100] Take the In2O3 precursor prepared by the amorphous MOF and directly sinter it at 450℃ for 4h.

[0101] This embodiment adopts the same preparation method as that of embodiment 2 to prepare In2O3 gas sensor prepared by amorphous MOF (a-In2O3) and In2O3 gas sensor prepared by MOF (In2O3). The test method adopted in this embodiment is similar to that of embodiment 2. The working temperature is set at different temperatures and Cl2 gas sensitive test is performed. The concentration of Cl2 is 2ppm. The test results are shown in FIG. Figure 3 The experimental results show that the sensitivity of a-In2O3 sensor is significantly higher than that of In2O3 sensor, and the optimal working temperature of both sensors is 160℃.

[0102] Embodiment 6:

[0103] In this embodiment, an In2O3 semiconductor Cl2 sensor prepared by amorphous MOF is prepared. The preparation steps of the In2O3 material prepared by amorphous MOF are the same as those in Example 1, and the preparation steps of the sensor are the same as those in Example 2.

[0104] In this embodiment, a Cl2 gas-sensing test is performed on the In2O3 semiconductor Cl2 sensor prepared by the prepared amorphous MOF, and the test method is similar to that of Example 5. The Cl2 gas-sensing test is performed at different humidities, 30%, 40%, 45%, 50%, and 65%.

[0105] like Figure 4 As shown, the experimental results show that the sensitivity of the In2O3 semiconductor In2O3 sensor prepared by amorphous MOF decreases with the increase of humidity.

[0106] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An In2O3 chlorine gas sensor prepared from amorphous MOF, characterized in that: include: A gas-sensitive layer, wherein the gas-sensitive layer is an In2O3 material prepared from an amorphous MOF, and the In2O3 material prepared from the amorphous MOF is one of nanoparticles, nanorods, and nanosheets; A ceramic tube, wherein the gas-sensitive layer is coated on the ceramic tube; The preparation method of In2O3 comprises the following steps: S1. Dissolve 300-600 mg of 2-aminoterephthalic acid, 70-90 mg of benzoic acid and 300-500 μL of pyridine in 10-20 mL of N,N-dimethylformamide, and sonicate until completely dissolved; S2, dissolving 900-1200 mg of 4.5 hydrated indium nitrate in 5-15 mL of N,N-dimethylformamide, adding the solution of step S1 after ultrasonic treatment until completely dissolved, and ultrasonic treatment for 3-8 min; S3, transferring the mixture to a stainless steel container with a polytetrafluoroethylene liner, heating at 100-150°C for 2-3h, with a heating rate of 1-3°C / min, and after natural cooling, collecting the product and washing it by centrifugation with ethanol, and vacuum drying it at 60-90°C overnight to obtain NH2-MIL-68(In); S4. Disperse 5-15 mg of NH2-MIL-68 (In) in a 0.5-0.8 M aqueous solution of dimethylimidazole, stir for one day, collect and wash with ethanol by centrifugation, then vacuum dry at 60-90°C overnight, and finally calcine at 400-600°C for 3-5 hours to obtain In2O3 material.

2. An In2O3 chlorine gas sensor prepared from amorphous MOF according to claim 1, characterized in that: The sensor also includes a base; The ceramic tube is provided with two annular electrodes, and both ends of the ceramic tube are provided with four platinum wires, and the platinum wires are welded on the base; A nickel-chromium alloy resistance wire for heating is arranged in the middle of the ceramic tube.

3. An In2O3 chlorine gas sensor prepared from amorphous MOF according to claim 2, characterized in that: The ring electrode is one of an Au electrode, a Pd electrode and an Ag electrode.

4. The In2O3 chlorine gas sensor prepared from amorphous MOF according to claim 1, characterized in that: The container in step S3 is a stainless steel container with a polytetrafluoroethylene lining.

5. A method for preparing an In2O3 chlorine gas sensor prepared from an amorphous MOF, for preparing an In2O3 chlorine gas sensor prepared from an amorphous MOF as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: a) mixing and grinding the prepared In2O3 material with pineneol; b) coating the ground sample onto a ceramic tube; c) after drying, calcining at 200-300° C. for 1-2 hours; d) fixing the ceramic tube on a base and performing aging to obtain the chlorine gas sensor.

6. The preparation method according to claim 5, characterized in that: The aging step is to use an aging instrument at a temperature of 250 to 350° C. for 4 to 8 days.

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