Defective metal organic framework MIL-125 core-shell material as well as preparation method and application thereof

Abstract

The invention discloses a defective metal organic framework MIL-125 core-shell material as well as a preparation method and application thereof, and belongs to the technical field of semiconductor materials and sensing. The material has the characteristics of an ultra-thin nanosheet assembled shell, a crystal / amorphous coexistence region, a rich mesoporous structure, an ultra-large specific surface area and the like. The preparation method adopts a two-step solvothermal method, and the process comprises the following steps: adding tetrabutyl titanate into a mixed solution of N, N-dimethylformamide dissolved with terephthalic acid and methanol, uniformly stirring, transferring the mixed solution into a hydrothermal reaction kettle, and preserving heat for a certain time. And adding the solution obtained in the above process into a mixed solution containing N, N-dimethylformamide and methanol again, and carrying out a hydrothermal reaction at 200 DEG C for a certain time to finally obtain the defective metal organic framework core-shell material. A gas sensor based on the material has excellent gas sensitivity to ethanol gas at room temperature (-25 DEG C), and especially, the detection limit is as low as 0.83 ppm. In addition, the preparation method of the material is simple, convenient, short in period, low in cost and suitable for mass production.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor materials and sensor technology, and in particular relates to a defective metal organic framework MIL-125 core-shell material and a preparation method and application thereof. Background Art

[0002] Ethanol plays a vital role in daily life and industrial production. In medicine, ethanol gas effectively kills a wide range of pathogens and is widely used for surface disinfection of medical devices and cleaning of medical facilities. It also serves as a good solvent for skincare products and cosmetics. In the food industry, ethanol is a food additive used to brew a variety of alcoholic beverages. Because ethanol combustion produces air-friendly H₂O and CO₂, it can replace fossil fuels as an efficient and environmentally friendly biofuel, widely used in the automotive, aerospace, and other fields. However, ethanol is highly volatile and has a low flash point (13°C). Exposure to high-temperature objects such as open flames or sparks can cause combustion or even explosion. Therefore, improper storage of ethanol at room temperature (~25°C) poses a potential risk. Furthermore, ethanol gas is irritating and toxic. Long-term inhalation of this gas can cause severe respiratory irritation, leading to numerous adverse reactions and threats to human health. Therefore, the development of efficient room-temperature ethanol sensing materials is essential, as they will play an indispensable role in fire prevention, confined space safety, food and pharmaceutical production process monitoring, equipment fault detection, and public transportation safety monitoring.

[0003] Among numerous gas-sensing materials, metal-organic frameworks (MOFs) are crystalline porous materials formed by the self-assembly of metal ions and organic ligands. They possess advantages such as a large surface area far exceeding that of traditional oxides, a regular pore size distribution, adjustable pores, and significantly exposed active sites, making them widely used in catalysis, adsorption, gas sensing, and other fields. While the gas-sensing properties of MOFs and their derivatives have been reported (e.g., a metal-organic framework-derived CuO / ZnO nanomaterial and its preparation and application), most studies focus on high-temperature gas sensing (e.g., one-step preparation of a La2O3-modified MOF-SnO2 gas sensor for ethanol detection). Prolonged exposure to high temperatures often leads to structural collapse and a sharp decrease in surface area of ​​gas-sensing materials. Therefore, mild modification of MOF materials can improve their room-temperature gas sensing performance.

[0004] In summary, there is an urgent need for a room-temperature ethanol gas-sensitive material based on MOF materials to fill the gap in room-temperature ethanol sensors. Summary of the Invention

[0005] In view of this, the present invention aims to propose a defective metal-organic framework MIL-125 core-shell material and its preparation method and application, so as to solve the problem that MOF materials are currently less used in the gas sensing field and their comprehensive performance needs to be improved.

[0006] In order to solve the above technical problems, the purpose of the first aspect of the present invention is to provide a defective metal organic framework MIL-125 core-shell material, comprising an ultrathin nanosheet assembled shell, a large specific surface area and a crystalline / amorphous coexistence structure.

[0007] The defective metal-organic framework MIL-125 core-shell material has the following morphological characteristics: the material is a disc-shaped core-shell structure, the shell is assembled from nanosheets, the nanosheets are about 1.5nm thick, and the shell is about 75nm thick. The core-shell structure has an overall diameter of about 1.5μm, the diameter of the internal core structure is about 750nm, and the cavity extends from the core to the inside of the shell. Mesopores are formed in the material with an average pore diameter of 3.9nm and a specific surface area of ​​719.7m 2 g -1 .

[0008] The second aspect of the present invention aims to provide a method for preparing the above-mentioned defective metal organic framework MIL-125 core-shell material.

[0009] The method for preparing the defective metal organic framework MIL-125 core-shell material of the present invention comprises the following steps:

[0010] Step 1: Measure 20-30 mL of N,N-dimethylformamide and 3-5 mL of anhydrous methanol in a beaker, add 1.0-1.5 g of terephthalic acid to the mixed solution, and stir for 30 minutes to obtain a uniform solution.

[0011] Step 2: Add 0.5-1.2 mL of tetrabutyl titanate to the solution obtained in step 1, and continue stirring the solution for 30 minutes until the solution is uniformly mixed.

[0012] Step 3: Ultrasonicate the mixed solution from step 2 for 10 minutes, then transfer it to a 50 mL polytetrafluoroethylene-lined hydrothermal autoclave, seal it, and incubate it at 120-160°C for 10-18 hours. Allow it to cool naturally to room temperature to obtain a white precipitate, which is then washed three times with anhydrous ethanol, centrifuged, and finally dried in an oven at 50-70°C for 12 hours to obtain Material A.

[0013] In step 4, mix 15-20 mL of N,N-dimethylformamide and 5-10 mL of anhydrous methanol in a beaker. Add 0.05-0.1 g of Material A obtained in step 3 to the beaker and stir for 30 minutes. Transfer the mixed solution to a polytetrafluoroethylene-lined hydrothermal autoclave, seal it, and incubate it at 170-210°C for 2-10 hours. Allow it to cool naturally to room temperature to obtain a white precipitate. Wash it three times with anhydrous ethanol, centrifuge it, and finally dry it in an oven at 50-70°C for 12 hours.

[0014] The third aspect of the present invention aims to provide the use of the defective metal organic framework MIL-125 core-shell material as a gas-sensitive material in a room temperature ethanol gas sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0016] Figure 1 (a) X-ray diffraction pattern, (bc) field emission scanning electron microscopy images, (de) high-resolution transmission electron microscopy images, and (f) nitrogen adsorption-desorption analysis (the inset shows the pore size distribution) of the defective metal-organic framework MIL-125 core-shell material described in Example 1 of the present invention;

[0017] Figure 2 Figure 1 shows the selectivity diagram of the defective metal-organic framework MIL-125 core-shell material gas sensor for different gases at room temperature, (a) the response-recovery curve for 100 ppm ethanol, (b) the response-recovery curve for 5-300 ppm ethanol at room temperature, and (d) a schematic diagram of the sensitivity-concentration fitting curve of the sensor at room temperature.

[0018] Figure 3 (a) X-ray diffraction pattern, (b) nitrogen adsorption-desorption analysis (the inset shows the pore size distribution) of the defective metal-organic framework MIL-125 core-shell material described in Example 2 of the present invention, and (c) schematic diagram of the response-recovery curve to 100 ppm ethanol at room temperature.

[0019] Figure 4 (a) X-ray diffraction pattern of the defective metal-organic framework MIL-125 core-shell material described in Example 3 of the present invention, (b) nitrogen adsorption-desorption analysis (the inset shows the pore size distribution), and (c) schematic diagram of the response-recovery curve to 100 ppm ethanol at room temperature. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with examples of the present invention.

[0021] Several commercial Al2O3 ceramic tubes (4 mm long, 1.2 mm outer diameter, 0.6 mm inner diameter, 0.7 mm gold ring width, 0.8 mm spacing) with four Pt wires attached were placed in a beaker. A 75% ethanol solution was added to the beaker to cover the tubes and ultrasonically cleaned. The tubes were then rinsed with deionized water and dried in a 50°C oven for 0.5 h. An appropriate amount of material was placed in a mortar and pestle. Anhydrous ethanol was added dropwise as a binder (approximately 4:1 weight ratio) according to the sample weight. Grind the mixture until it formed a paste. The slurry was applied to a clean ceramic tube to form a uniform film (approximately 0.2 mm thick) and dried in a 50°C oven for 15 min. Solder paste was applied to four diagonal solder joints on the base and the four Pt wires on the ceramic tube were spot-welded to the corresponding locations. To ensure test accuracy, at least three devices were prepared for each sample for gas sensing testing. Resistance measurements were taken for each device to ensure proper soldering.

[0022] Gas sensing experiments were conducted using the "Nanodog" (NS-4000 sensor analyzer) produced by Beijing Zhongke Micro-Nano Internet of Things Co., Ltd. One end of the device is a monitor with PC functions, capable of real-time monitoring of the electrical signals of the gas-sensing device. Connected to the other end is a test rod that can be inserted into the sensor base. The test rod consists of 12 channels, with the sensor device and the element connected in series and the elements connected in parallel. During the gas sensing test, the test rod with the base inserted was placed in a 30L gas hood equipped with two circulating fans and a heated evaporation table for gas evaporation and diffusion. The gas sensing experiments were conducted at room temperature using the static gas distribution method (solvent evaporation method).

[0023] The response value is defined as S r =(|R a -R g | / R a )×100%, where R a is the base resistance of the material in air, R g is the stable resistance of the material in the target gas. Response time (τ res ) is the time required for the sensor to switch from air to target gas and the resistance change is 90%. Recovery time (τ rec ) is the time required for the sensor to recover 90% resistance after switching from the target gas to air. The limit of detection is defined as LOD = 3σ / k, where σ is the standard deviation of the baseline resistance and k is the slope of the sensitivity-concentration curve.

[0024] The material structure was obtained by a SmartLab 9kW X-ray diffractometer from Rigaku, Japan. The operating voltage and current were 40 kV and 150 mA, respectively. The CuKα1 radiation wavelength was λ = 0.15406 nm and the scanning rate was 10° / min.

[0025] Sample morphology and dimensions were obtained using a JEOL JSM-6700F field emission scanning electron microscope (FESEM) operating at 10 kV. A small amount of powder sample was attached to a conductive adhesive for observation. Morphology and microstructure were characterized using a JEOL JEM-2010 transmission electron microscope (TEM) operating at an accelerating voltage of 200 kV. The microscope was equipped with an energy dispersive X-ray spectrometer (EDS). Solid sample preparation was as follows: a small amount of sample was placed in anhydrous ethanol, ultrasonically dispersed for 10 minutes, and then spotted onto a carbon-coated copper grid. The sample was allowed to dry at room temperature before measurement.

[0026] The specific surface area and pore size distribution were measured by nitrogen adsorption method using a BELSORP-max adsorption instrument from MicrotracBEL (Japan) at a temperature of 77 K. Before the test, the samples were heated at 100 °C and 10 -4 The samples were dried and degassed for 4 to 6 h under Pa conditions. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) method, and the pore size distribution was calculated using the BJH (Barrett-Joyner-Halenda) method.

[0027] In the following examples, all reagents were commercially available analytical grade and required no pretreatment. Terephthalic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and other reagents, including tetrabutyl titanate, N,N-dimethylformamide, methanol, ethanol, benzene, toluene, xylene, ammonia, methylamine, dimethylamine, and trimethylamine, were purchased from Tianjin Damao Chemical Reagent Factory.

[0028] The technical solution of the present invention is further described below with reference to specific embodiments.

[0029] Example 1

[0030] The defective metal-organic framework MIL-125 core-shell material was prepared by a two-step solvothermal method with the following parameters:

[0031] Step 1: Measure 27 mL of N,N-dimethylformamide and 3 mL of anhydrous methanol in a beaker and mix them evenly. Weigh 9 mmol (1.495 g) of terephthalic acid and dissolve it in the mixed solution.

[0032] Step 2: Slowly add 0.9 mL of tetrabutyl titanate to the solution obtained in step 1 and stir for 30 minutes until uniform.

[0033] Step 3: add the mixed solution obtained in step 2 into a hydrothermal autoclave lined with 50 mL of polytetrafluoroethylene, seal it, keep it at 150° C. for 16 h, and cool it naturally to room temperature.

[0034] Step 4: Centrifuge the mixture obtained in step 3 to obtain a white precipitate, wash it with anhydrous ethanol three times, and finally dry it in an oven at 60° C. for 12 h to obtain material A.

[0035] Step 5: Weigh 0.06 g of material A obtained in step 3, dissolve it in a mixed solution containing 18 mL of N,N-dimethylformamide and 6 mL of anhydrous methanol, and stir until uniform.

[0036] Step 6: Add the mixed solution in step 5 into a hydrothermal autoclave lined with 50 mL of polytetrafluoroethylene, seal it, keep it at 200° C. for 5 h, and cool it naturally to room temperature.

[0037] Step 7: centrifuge the precipitate obtained in step 6 to obtain a white precipitate, wash it with anhydrous ethanol three times, and finally dry it in an oven at 60° C. for 12 h to obtain a defective metal organic framework MIL-125 core-shell material.

[0038] The characterization of the defective metal organic framework MIL-125 core-shell material obtained in Example 1 is as follows:

[0039] Figure 1 (a) X-ray diffraction pattern, (bc) field emission scanning electron microscopy images, (de) high-resolution transmission electron microscopy images, and (f) nitrogen adsorption-desorption analysis (the inset shows the pore size distribution) of the defective metal-organic framework MIL-125 core-shell material of Example 1 of the present invention;

[0040] The X-ray diffraction pattern of the obtained defective metal organic framework MIL-125 core-shell material is consistent with the XRD diffraction results of the simulated MIL-125. After the secondary solvent thermal treatment process, no other diffraction peaks appeared in the sample, indicating that the crystal structure did not change and no impurities appeared. Figure 1 (a).

[0041] Scanning electron microscope photos show that the morphology of the sample is a round cake-shaped core-shell structure. The inner core structure has a diameter of about 750nm, and the outer shell is composed of ultra-thin nanosheets with a thickness of about 75nm. There is a cavity structure between the inner core and the outer shell. Figure 1 (bc).

[0042] Transmission electron microscopy photos show that the sample has a clear core-shell structure. The overall diameter of the core-shell structure of the material is about 1.5μm, the diameter of the internal core structure is about 750nm, and the thickness of the nanosheets that make up the shell of the material is about 1.5nm. Figure 1 (de).

[0043] The results of nitrogen adsorption and desorption analysis showed that the material of Example 1 was rich in mesopores, with an average pore diameter of 3.9 nm and a specific surface area of ​​719.7 m 2 g -1 ,See Figure 1 (f).

[0044] Figure 2 The gas-sensing properties of the defective metal-organic framework MIL-125 core-shell material obtained in Example 1: (a) selectivity to different gases at 100 ppm at room temperature, (b) response-recovery curve to 100 ppm ethanol at room temperature, (c) response-recovery curve of the material to 5-300 ppm ethanol at room temperature, and (d) sensitivity-concentration fitting curve of the sensor at room temperature.

[0045] The prepared defective metal organic framework MIL-125 core-shell material was made into a indirectly heated gas sensor. The selectivity of the gas sensor to different gases at 100 ppm was Figure 2 (a), it can be seen that the prepared material can detect ethanol with high selectivity and avoid the interference of other gases, such as methanol, benzene, toluene, xylene, ammonia, methylamine, dimethylamine and trimethylamine.

[0046] At room temperature, the defective metal organic framework MIL-125 core-shell material gas sensor showed the highest sensitivity (167.1) to 100 ppm ethanol at room temperature, with a response time of 128 s and a recovery time of 271 s. Figure 2 (b).

[0047] At room temperature, the response-recovery curve of the sample to 5-300 ppm ethanol is shown in Figure 2 (c), indicating that the sample has good response-recovery behavior and a short response-recovery time.

[0048] For the ethanol sensor in Example 1, when the baseline resistance is 10.75 MΩ, the resistance of the defective metal organic framework MIL-125 core-shell material in 5 ppm, 10 ppm, 50 ppm, 100 ppm, 200 ppm and 300 ppm ethanol vapor is 13.56 MΩ, 18.71 MΩ, 23.25 MΩ, 30.2 MΩ, 36.41 MΩ and 40.65 MΩ, respectively. Figure 2 (c) shown.

[0049] The response values ​​of the sensor to different concentrations of ethanol were fitted into sensitivity-concentration curves, see Figure 2 (d), its R 2 The linearity is 0.98, indicating good linearity. Calculations show that the sensor has a detection limit of 0.83 ppm for ethanol, which can meet the needs of ethanol detection in industry and daily life.

[0050] These results indicate that the defective metal organic framework MIL-125 core-shell material of the present invention can be used as a room temperature ethanol gas-sensitive material.

[0051] Example 2

[0052] The defective metal-organic framework MIL-125 core-shell material was prepared by a two-step solvothermal method with the following parameters:

[0053] The difference from Example 1 is that in step 6, the holding time at 200° C. is 3 hours.

[0054] Figure 3 (a) X-ray diffraction pattern of the defective metal-organic framework MIL-125 core-shell material obtained in Example 2, (b) nitrogen adsorption-desorption analysis (the inset shows the pore size distribution), and (c) response-recovery curve to 100 ppm ethanol at room temperature.

[0055] The X-ray diffraction pattern of Example 2 is consistent with the X-ray diffraction results of the simulated MIL-125. No other diffraction peaks appear in the sample, indicating that the crystal structure has not changed and no impurities appear. Figure 3 (a).

[0056] The nitrogen adsorption and desorption results show that the specific surface area of ​​Example 2 is 779.7m 2 g -1 The material has a mesoporous structure with an average pore size of 2.73 nm. Figure 3 (b).

[0057] At room temperature, the response-recovery curve of the sample to 100 ppm ethanol is shown in Figure 3 (c) shows that the sample has good response-recovery behavior, with a response value of 71.6 and response and recovery times of 137 s and 454 s, respectively.

[0058] Example 3

[0059] The defective metal-organic framework MIL-125 core-shell material was prepared by a two-step solvothermal method with the following parameters:

[0060] The difference from Example 1 is that in step 6, the holding time at 200° C. is 8 hours.

[0061] Figure 4(a) X-ray diffraction pattern of the defective metal-organic framework MIL-125 core-shell material obtained in Example 3, (b) nitrogen adsorption-desorption analysis (the inset shows the pore size distribution), and (c) response-recovery curve to 100 ppm ethanol at room temperature.

[0062] The diffraction peak intensity of the X-ray diffraction pattern of Example 3 is relatively weak, indicating that the material contains a large amount of amorphous structure. Figure 4 (a).

[0063] The nitrogen adsorption and desorption results show that the specific surface area of ​​Example 3 is 353.8m 2 g -1 The material has a mesoporous structure with an average pore size of 5.9 nm. Figure 4 (b).

[0064] At room temperature, the response-recovery curve of the sample to 100 ppm ethanol is shown in Figure 4 (c) shows that the sample has good response-recovery behavior, with a response value of 90.5 and response and recovery times of 122 s and 582 s, respectively.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A defective metal-organic framework MIL-125 core-shell material: The material has an ultrathin nanosheet assembly shell, crystalline / amorphous coexistence areas, a rich mesoporous structure, and an ultra-large specific surface area; The material has a circular core-shell structure, with the outer shell assembled from ultrathin nanosheets. The nanosheets are about 1.5 nm thick, and the outer shell is about 75 nm thick. The core-shell structure has an overall diameter of about 1.5 μm, and the diameter of the inner core structure is about 750 nm. The cavity extends from the core to the inside of the shell. The material has abundant mesopores with an average pore diameter of 3.9 nm and a specific surface area of ​​719.7 m 2 g -1 .

2. The method for preparing the defective metal organic framework MIL-125 core-shell material according to claim 1, comprising the following steps: Step 1: Measure 20-30 mL of N,N-dimethylformamide and 3-5 mL of anhydrous methanol in a beaker, add 1.0-1.5 g of terephthalic acid to the mixed solution, and stir for 30 minutes to obtain a uniform solution; Step 2: Add 0.5-1.2 mL of tetrabutyl titanate to the solution obtained in step 1, and continue stirring the solution for 30 minutes until the solution is uniformly mixed; Step 3: After ultrasonic treatment of the mixed solution in step 2 for 10 minutes, transfer it to a 50 mL hydrothermal autoclave lined with polytetrafluoroethylene, seal it, and keep it at 120-160° C. for 10-18 hours; allow it to cool naturally to room temperature to obtain a white precipitate, wash it with anhydrous ethanol three times, centrifuge it, and finally dry it in an oven at 50-70° C. for 12 hours to obtain material A; Step 4: Mix 15-20 mL of N,N-dimethylformamide and 5-10 mL of anhydrous methanol in a beaker, take 0.05-0.1 g of material A obtained in step 3 and place it in the beaker, and stir for 30 minutes; transfer the mixed solution to a 50 mL hydrothermal autoclave lined with polytetrafluoroethylene, seal it, and keep it at 170-210° C. for 2-10 hours; let it cool naturally to room temperature to obtain a white precipitate, wash it with anhydrous ethanol three times, centrifuge it, and finally dry it in an oven at 50-70° C. for 12 hours.

3. Application of the defective metal organic framework MIL-125 core-shell material according to claim 1 as a sensitive layer in a room temperature ethanol gas sensor: The method for preparing the gas sensor comprises the following steps: uniformly mixing the material described in claim 1 with anhydrous ethanol (weight ratio of approximately 4:1) to obtain a slurry, uniformly coating the slurry onto the surface of a commercial Al2O3 ceramic tube (4 mm in length, 1.2 mm in outer diameter, 0.6 mm in inner diameter, 0.7 mm in gold ring width, and 0.8 mm in spacing) to form a sensitive layer with a thickness of approximately 0.2 mm; drying the sensitive layer by keeping the ceramic tube in a forced air drying oven at 50°C for 15 minutes; and welding four Pt wires of the ceramic tube to a base to assemble the gas sensor.

4. The use of the gas sensor based on the defective metal organic framework MIL-125 core-shell material according to claim 3 for detecting ethanol gas at room temperature, comprising: The operating temperature of the gas sensor is room temperature (~25°C); The gas sensor is capable of detecting ethanol gas in air containing methanol, acetone, benzene, toluene, xylene, ammonia, methylamine, dimethylamine or trimethylamine gas; The detection limit of the gas sensor for ethanol gas is 0.83 ppm; The gas sensor has a sensitivity of 167.1 for detecting 100 ppm ethanol gas; The response time of the gas sensor for detecting 100 ppm ethanol gas is 128 s, and the recovery time is 271 s.

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