MOF-driven one-dimensional metal oxide hollow nanofiber material, preparation method thereof and application of MOF-driven one-dimensional metal oxide hollow nanofiber material in gas sensitive sensor

Abstract

The invention discloses an MOF-driven one-dimensional metal oxide hollow nanofiber material, a preparation method thereof and application of the MOF-driven one-dimensional metal oxide hollow nanofiber material in a gas sensor. A unique one-dimensional hollow nanotube is prepared by adopting an in-situ self-assembly strategy. The unique one-dimensional hollow structure has a larger specific surface area, and provides a channel for rapid diffusion of gas; more adsorption sites are provided; an efficient electron transmission path is provided, scattering and loss in the electron transmission process are reduced, and therefore the electron transmission efficiency is improved. Besides, the small-size precious metal is packaged in the cavity of the MOF by using the unique microporous structure of the MOF, so that the agglomeration and aggregation of the precious metal are prevented, and the dispersity and stability of the precious metal are improved. The sensor has the advantages of high sensitivity and selectivity, low detection limit, quick response and good long-term stability, and is very suitable for detection of low-concentration industrial acetone and diagnosis and monitoring of diabetes mellitus.

Description

Technical Field

[0001] The present invention belongs to the field of gas sensors, and particularly relates to a MOF-driven one-dimensional metal oxide hollow nanofiber material, a preparation method thereof, and an application thereof in a gas sensor. Background Art

[0002] In recent years, the accurate detection of volatile organic compounds (VOCs) has attracted more and more attention and research in industrial safety control, environmental monitoring, and human health management. Acetone (CH 3 COCH 3 )), as a typical representative of VOCs, is generally considered an important biomarker for detecting diabetes. Under normal circumstances, the acetone content in the exhaled gas of healthy people is maintained within the range of 0.3 - 0.9 ppm, while this value in diabetic patients significantly rises to 1.25 - 2.5 ppm. However, the components of human exhaled gas are complex and diverse, and the relative concentration of acetone in it is relatively low, making precise detection particularly difficult. Therefore, it is particularly important to develop a chemical gas sensor with high responsiveness and reliability to acetone. Currently, chemiresistive gas sensors, due to their advantages such as high sensitivity, fast response and recovery capabilities, simple structure, and cost-effectiveness, show broad application potential in the field of gas monitoring. Among them, ZnO, with its excellent electron mobility and diverse physicochemical properties, is regarded as one of the most promising MOS sensing materials and performs well in gas detection. Nevertheless, traditional metal oxide semiconductor (MOS) sensors still face challenges such as poor selectivity, high operating temperature, and insufficient long-term stability. In recent years, metal-organic framework (MOF) materials, with their high specific surface area, adjustable pore size structure, and abundant chemical functional sites, have shown great potential in the fields of gas adsorption and separation, catalysis, and sensing. MOF-derived MOS sensors, in particular, have advantages such as high sensitivity, high selectivity, excellent thermal stability, and chemical stability, and have become a research hotspot in the field of gas sensing. However, MOF particles are prone to agglomeration during the preparation process, which will cover the exposed active sites and greatly limit the improvement of sensor performance. On the other hand, noble metal catalysts are also prone to agglomeration at high temperatures, resulting in a decline in catalytic performance. Therefore, an effective synthesis strategy needs to be designed to avoid this situation. Summary of the Invention

[0003] The object of the present invention is to provide a MOF-driven one-dimensional metal oxide hollow nanofiber material, its preparation method and application in gas sensors. The doped Pt-ZnO nanotubes (Pt-ZnO NTs) created by the in-situ self-assembly strategy used in the present invention not only ensure the uniform growth and monodisperse distribution of nanocrystals on the substrate surface, but also confine the noble metal Pt in the cavities of the MOF, preventing the agglomeration and aggregation of the noble metal. The acetone sensor based on the Pt-ZnO NTs material has high sensitivity and selectivity, a low detection limit, a fast response, and good long-term stability, and is expected to be applied to the detection of low-concentration industrial acetone and the diagnosis and monitoring of diabetes.

[0004] The technical solution of the present invention is as follows:

[0005] A preparation method of a MOF-driven one-dimensional metal oxide hollow nanofiber material, comprising the following steps:

[0006] (1) Dissolve styrene and methacrylic acid in water, heat and stir until boiling, add potassium persulfate, stir and react at 70-90 °C for 1-5 h, and then wash and dry the precipitate after the reaction to obtain PS-COOH;

[0007] (2) Dissolve polystyrene in organic solvent A, add PS-COOH and zinc acetate and stir to obtain a uniform and transparent spinning precursor solution A; dissolve polyacrylonitrile in organic solvent B and form a uniform and transparent spinning precursor solution B after stirring, and use the spinning precursor solutions A and B to prepare nanofibers with a core-shell structure by coaxial electrospinning;

[0008] (3) Immerse the nanofibers with a core-shell structure in a 2-methylimidazole solution at room temperature, and dry to obtain nanofibers with uniform growth of ZIF-8;

[0009] (4) Immerse the nanofibers with uniform growth of ZIF-8 in a chloroplatinic acid solution, and then reduce it in a sodium borohydride solution and dry;

[0010] (5) Calcinate the nanofibers in step (4) in a protective atmosphere and in air respectively to obtain a MOF-driven one-dimensional hollow metal oxide nanofiber material.

[0011] Further, in step (1), the volume ratio of styrene to methacrylic acid is (35-45):1, the mass-volume ratio of styrene to potassium disulfate is (70-90) mL:1 g, the heating method is a water bath method, the heating temperature is 70-80 °C, and the time is 2-4 h.

[0012] Further, in step (1), the washing is to perform centrifugal washing with water two to five times, and this process can remove unnecessary organic and inorganic impurity ions.

[0013] Further, in step (2), organic solvent A and organic solvent B are one or a mixture of two of ethanol, dichloromethane, ethyl acetate, and DMF in any proportion; the concentration of polystyrene in organic solvent A in the spinning precursor solution A is 0.2 - 0.3 g / mL; the concentration of zinc acetate in organic solvent A is 0.6 - 0.75 mmol / mL; the mass ratio of PS-COOH to zinc acetate is 1:(1.2 - 1.6); the concentration of polyacrylonitrile in organic solvent B in the spinning precursor solution B is 0.08 - 0.1 g / mL; this ratio can ensure the evaporation rate of electrospinning, prevent needle clogging, enable continuous spinning, and ensure the uniformity of the spun fibers. The stirring time during the preparation of the spinning precursor solution is 8 - 10 h.

[0014] Further, in step (2), the specific steps of the electrospinning method include:

[0015] Inject the spinning precursor solution A into syringe 1 as the outer spinning solution, and inject the spinning precursor solution B into syringe 2 as the inner spinning solution; control the distance between the receiving device and the syringe needle to be 13 - 17 cm, set the electrospinning voltage to 15 - 20 kV, and the feeding rate to be 0.1 - 0.5 mL / h -1 , and perform electrospinning to collect nanofibers.

[0016] Further, in step (3), the 2-methylimidazole solution refers to a methanol solution of 2-methylimidazole, and the concentration of 2-methylimidazole in methanol is 20 - 30 g / L; the soaking time is 5 - 8 h. This concentration can ensure that ZIF-8 grows uniformly on the nanofibers.

[0017] Further, in step (4), the mass percentage of Pt in the chloroplatinic acid solution is 0.5% - 3%; the concentration of the sodium borohydride solution is 1 - 2 mg / mL; the reduction time is 0.5 - 2 h; the drying temperature is 50 - 80 °C, and the time is 0.5 - 2 h. This concentration can ensure that metallic platinum is confined within the framework of the MOF without forming agglomeration.

[0018] Further, in step (5), the calcination parameters in the protective atmosphere are: heating rate 1 - 5 °C / min, calcination time 2 - 3 h, calcination temperature 500 - 600 °C, and the protective atmosphere is at least one of N 2 and Ar; the calcination parameters in the air atmosphere are: heating rate 1 - 5 °C / min, calcination time 2 - 3 h, calcination temperature 600 - 650 °C. This temperature can remove the core-layer polymer and nitride and fix the shell structure, thus ensuring the integrity of the nanofiber structure.

[0019] A MOF-driven one-dimensional metal oxide hollow nanofiber material is prepared by the above method. The hollow nanofibers are composed of a large number of zinc oxide nanocrystals. The MOF is uniformly grown on the nanofibers by in-situ self-assembly, and the noble metal Pt is confined in the MOF framework without forming agglomerates.

[0020] A gas sensor uses the above MOF-driven one-dimensional metal oxide hollow nanofiber material as the sensitive layer material.

[0021] Specifically, the MOF-driven one-dimensional metal oxide hollow nanofiber material is mixed with ethanol to form a slurry, which is coated on a ceramic tube (the coating thickness is 100 - 500 μm). The ceramic tube is heated to 250 - 350 °C at a heating rate of 1 - 5 °C / min and calcined for 1 - 3 h. After calcination, a Ni-Cr heating wire is inserted into the ceramic tube as a heating electrode, and the leads are welded to the test base. Finally, the gas sensor element is placed on an aging device and aged at 350 - 350 °C for 6 - 8 days. The gas sensor is tested on a WS-30B (Zhengzhou, China) gas sensing system equipped with a heating voltage (V -1 ) and a loop power (V h ). The gas sensing characteristics of the sensor are observed by measuring the voltage (V c ) at the load resistor (R L ). out )

[0022] The above gas sensor is used for industrial acetone detection or for diabetes monitoring. At 240 °C, it shows an ultra-high response of R a / R g = 46.67 for 10 ppm of acetone.

[0023] The beneficial effects of the present invention are as follows:

[0024] (1) The MOF-driven metal oxide hollow nanofiber material proposed by the present invention is a one-dimensional hollow nanotube prepared by an in-situ self-assembly strategy, which has a larger specific surface area, provides a channel for rapid gas diffusion and more adsorption sites. Its unique nanostructure provides an efficient electron transport path, improving the electron transport efficiency. Moreover, the microporous structure of the MOF can effectively prevent the agglomeration and aggregation of noble metals, improving their dispersion and stability.

[0025] (2) The preparation method of the present invention is simple and controllable, with mild process conditions, low energy consumption, short production cycle, low requirements for equipment, no environmental pollution, and is simple and low-cost, suitable for large-scale preparation.

[0026] (3) The gas sensor made of the MOF-driven metal oxide hollow nanofiber material provided by the present invention shows an Ra / R g With an ultra-high response of 46.67, it is 4.68 times the response value of the original ZnO NTs (9.97). In addition, the sensor based on Pt-ZnO NTs has good selectivity and long-term stability performance of more than 30 days, maintaining more than 90% of the initial response, with a high response value and a low detection limit (68 ppb) at low concentrations, and can be used for the diagnosis and monitoring of diabetes.

[0027] (4) The one-dimensional metal oxide hollow nanofibers driven by MOF provided by the present invention are expected to be applied to the detection of low-concentration industrial acetone and the diagnosis and monitoring of diabetes. Brief Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the preparation process of the Pt-ZnO NTs material in the embodiment of the present invention.

[0029] Figure 2 It is the scanning electron microscope image (a) and transmission electron microscope image (b) of the original ZnO NTs material in the embodiment of the present invention, the electron microscope image (c) and transmission electron microscope image (d) of the 1% Pt-ZnO NTs material, and the high-resolution transmission microscope image (e) and energy dispersive spectrum element image (f) of the 1% Pt-ZnO NTs material.

[0030] Figure 3 It is the X-ray diffraction pattern (a) of the original ZnO NTs and Pt-ZnO NTs materials in the embodiment of the present invention and the X-ray photoelectron spectroscopy images on the Zn 2p (b), O 1s (c), and Pt 4f (d) orbits.

[0031] Figure 4 It is the image (a) of the response of the original ZnO NTs and Pt-ZnO NTs sensors to 10 ppm acetone varying with the working temperature in the embodiment of the present invention, the dynamic response-recovery curves (b) of the original ZnO NTs and Pt-ZnO NTs sensors to 1–5 ppm and (c) 5–50 ppm acetone at 240 °C, the linear relationship (d) between the original ZnO NTs and Pt-ZnO NTs sensors and 1–50 ppm acetone at 240 °C, the dynamic response curve (e) of the original ZnO NTs and Pt-ZnO NTs sensors to 10 ppm acetone at 240 °C, and the response time and response-recovery time of the original ZnO NTs and Pt-ZnO NTs sensors to 10 ppm acetone at 240 °C.

[0032] Figure 5Figure (a) shows the 5-cycle response and recovery curves of the pristine ZnO NTs and Pt-ZnO NTs sensors to 10 ppm acetone at 240 °C. Figure (b) shows the long-term stability test of the pristine ZnO NTs and Pt-ZnO NTs sensors in response to 10 ppm acetone at 240 °C. Figure (c) shows the selectivity test of the pristine ZnO NTs and Pt-ZnO NTs sensors to 10 ppm acetone and 50 ppm other interfering gases (ethanol, methanol, formaldehyde, isopropanol, and ammonia) at 240 °C. Figure (d) shows the dynamic response curves of the pristine ZnO NTs and Pt-ZnO NTs sensors to 10 ppm acetone under different humidity conditions. Specific implementation

[0033] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0034] Example 1

[0035] A preparation method of MOF-driven one-dimensional metal oxide hollow nanofiber materials is as Figure 1 shown, and the process is as follows:

[0036] (1) Dissolve 20 mL (0.174 mol) of styrene and 0.5 mL (0.006 mol) of methacrylic acid in 250 mL of distilled water, heat and stir until boiling, then add 0.25 g of potassium persulfate to the solution, and heat in a water bath at 80 °C for 3 h. After the reaction is completed, cool naturally, wash three times with distilled water, centrifuge to collect the white precipitate, and dry in an oven at 70 °C for 10 h to obtain PS-COOH.

[0037] (2) Dissolve 1.04 g of polystyrene (molecular weight 192000) in 4 mL of DMF under stirring, and then add 0.33 g of PS-COOH and 0.5 g of Zn(Ac) 2 (zinc acetate), and vigorously stir the solution at room temperature for 8 h to obtain the spinning solution precursor A.

[0038] (3) Dissolve 1 g of polyacrylonitrile (molecular weight 150,000) in 10.5 mL of DMF and stir at room temperature for 8 h to obtain the spinning solution precursor B.

[0039] (4) Add the spun liquid precursor A obtained in (2) into a 3 mL plastic syringe 1 as the outer liquid for coaxial electrospinning; add the spun liquid precursor B obtained in (3) into a 3 mL plastic syringe 2 as the inner liquid for coaxial electrospinning. Set the parameters of coaxial electrospinning as follows: a coaxial steel needle with an inner diameter of 17G (inner diameter 1.12 mm) and an outer diameter of 22G (1.48 mm), a layer of aluminum foil wrapped on the steel plate as the receiver for the electrospun membrane, the distance between the aluminum foil and the steel needle is about 15 cm, the electrospinning voltage is 17 kV, and the feeding rate is 0.3 mL h -1 . After 10 hours, an electrospun membrane with a thickness of 100 mm and a size of 15 cm × 10 cm is obtained.

[0040] (5) Add 5 g of 2-methylimidazole into 200 mL of methanol, and then immerse the electrospun membrane obtained in (4) in the imidazole solution at room temperature for 6 h and dry it at 60 °C for 1 h to obtain nanofibers with uniform growth of ZIF-8;

[0041] (6) Place the nanofibers with uniform growth of ZIF-8 dried in step (5) in a tube furnace and calcine them at a temperature of 600 °C for 2 h at a heating rate of 2 °C / min under a nitrogen atmosphere.

[0042] (7) Calcinate the sample obtained in (6) at a temperature of 650 °C for 2 h at a heating rate of 2 °C / min under an air atmosphere. Obtain the original ZnO NTs.

[0043] (8) Immerse the nanofibers with uniform growth of ZIF-8 in (5) in solutions of chloroplatinic acid with different concentrations (the mass percentages of Pt are 0.5%, 1%, 2%, and 3%) for 6 h until the chloroplatinic acid solution is completely adsorbed to obtain Pt-ZnO NTs with different Pt doping amounts.

[0044] (9) Reduce the sample obtained after immersion in (8) in a NaBH 4 solution (1.5 mg mL -1 ) for 1 h and dry it at 60 °C for 1 h to obtain Pt-ZnO NTs with different Pt doping amounts.

[0045] (10) Place the sample obtained in (9) after drying in a tube furnace and calcine it at a temperature of 600 °C for 2 h at a heating rate of 2 °C / min under a nitrogen atmosphere.

[0046] (11) The samples obtained in (10) were calcined at a temperature of 650 °C for 2 h in an air atmosphere at a heating rate of 2 °C / min. Pt-ZnO NTs with different Pt doping amounts were obtained, namely 0.5% Pt-ZnO NTs, 1% Pt-ZnO NTs, 2% Pt-ZnO NTs, and 3% Pt-ZnO NTs.

[0047] The morphologies, compositions, and elemental species of the ZnO NTs obtained in step (7) and the Pt-ZnO NTs obtained in step (11) were analyzed. As Figure 2 a and Figure 2 b are the SEM and TEM images of ZnO NTs, respectively. The SEM image results show that ZnO grows uniformly on the fibers, and the hollow structure increases the specific surface area of the material, accelerating the gas adsorption and desorption processes, which is beneficial to gas diffusion and gas detection. Subsequently, Pt was introduced into ZnO NTs by the soaking method. During the soaking process, Pt 4+ ions diffuse into the cavities of ZIF-8. After calcination, ZIF-8 is thermally decomposed and oxidized into a ZnO skeleton, and Pt 4+ is reduced to Pt NPs and remains in the ZnO framework. The ZIF-8-driven ZnO skeleton structure can effectively prevent the aggregation of noble metal Pt ( Figure 2 c). In the TEM image of Pt-ZnO NTs ( Figure 2 d), the strong contrast between the dark edge and the bright center indicates the hollow structure, which is consistent with the SEM characterization results. In the high-resolution transmission electron microscope (HRTEM) image of Pt-ZnO NTs ( Figure 2 e), distinct lattice fringes can be clearly identified, and the interplanar spacings are 0.246 nm and 0.226 nm, corresponding to the (101) crystal plane of wurtzite-phase ZnO and the (111) crystal plane of cubic-phase Pt, respectively. The EDX mapping image results of Pt-ZnO NTs show ( Figure 2 f) that Zn, O, and Pt are uniformly distributed on the entire hollow fiber, which also demonstrates the uniform dispersion of noble metal Pt in the ZIF-8-driven ZnO framework.

[0048] The XRD images of ZnO NTs and Pt-ZnO NTs are as Figure 3 shown in a. The main peaks in the five samples conform to the hexagonal wurtzite structure of ZnO (PDF#79-0205). There are two typical peaks of metallic Pt at 39.8° and 46.2°, indicating that ZnO NTs have been successfully functionalized with metallic Pt. As the Pt doping amount increases, the diffraction peaks shift to higher angles, which can be attributed to Zn being replaced by Pt with a smaller atomic radius is replaced. In the XPS results, the elements Zn, O, and Pt were observed. Figure 3 The Zn 2p spectrum of the original ZnO NTs in b shows that the Zn 2p1 / 2 peak is at 1044.7 eV and the Zn 2p3 / 2 peak is at 1021.7 eV. After the addition of Pt, the peak positions of Pt-ZnO NTs show an obvious red shift relative to those of the original ZnO NTs, which is due to the transfer of electrons from ZnO to Pt after contact. Figure 3 In the XPS spectrum of O1s in c, three peaks with different binding energies are generated by peak fitting, which are 530.28, 531.38, and 532.24 eV respectively, corresponding to lattice oxygen (OL), defective oxygen (Ov), and adsorbed oxygen (Oads). The defective oxygen ratio is determined according to the ratio of the integral area of the defective oxygen peak to the entire area of the O1s peak, and the corresponding defective oxygen ratios are calculated to be 24.05%, 27.90%, 42.67%, 30.90%, and 36.27%. From the results, 1% Pt-ZnO NTs have the largest oxygen vacancies. The increase in oxygen vacancies may be due to the substitution of Pt ions for Zn ions. Pt ions have higher metallic activity than Zn, capture oxygen ions from the ZnO lattice, resulting in an increase in the number of oxygen vacancies in the ZnO lattice, and at the same time promoting oxygen adsorption. And due to the addition of the Pt catalyst, a spillover effect occurs. Due to the catalytic effect of Pt, the oxygen vacancies increase, providing more catalytically active sites for gas diffusion and adsorption. Figure 3 d shows the Pt 4f XPS spectra of 0.5% Pt-Zn NTs, 1% Pt-Zn NTs, 2% Pt-Zn NTs, and 3% Pt-Zn NTs respectively. The XPS spectrum of Pt 4f can be fitted into four peaks, which are Pt 4f 5 / 2 (73.73 eV) and Pt 4f 7 / 2 (70.14 eV) of the Pt elemental state and Pt 4f 5 / 2 (75.31 eV) and Pt 4f 7 / 2 (72.17 eV) of the Pt 2+ state. As the Pt doping amount increases, the XPS of Pt 4f gradually shifts to lower binding energies, which corresponds to the red shift of the Zn2p peak position. The shift of the binding energy in the XPS spectrum is due to the fact that the electronegativity of Pt atoms is greater than that of Zn 2+ ions (1.65). Pt atoms can attract electrons from Zn 2+ ions, resulting in a decrease in the number of electrons of Zn 2+ ions, but an increase in the number of Pt atoms due to the shielding effect. This leads to the shift of the Pt 4f peak to a lower binding energy and the shift of the Zn 2p peak to a higher binding energy, thus increasing the surface activity of ZnO.

[0049] (12)Disperse the ZnO NTs obtained in step (7) and the Pt-ZnO NTs powder obtained in step (11) in a small amount of absolute ethanol, ultrasonicate for 1 min at 50 W, put them in a mortar and grind for 3 min until the materials become slurry, and coat them on a ceramic tube (the coating thickness is 300 μm). Heat the ceramic tube at a heating rate of 2 °C min -1 to 300 °C and calcine for 2 h.

[0050] (13)Insert a Ni-Cr heating wire into the ceramic tube as a heating electrode, and weld the lead wires to the test base.

[0051] (14)Finally, place the gas sensor element on an aging device and age it for one week at an aging temperature of 300 °C.

[0052] Gas sensing test:

[0053] The test is carried out on a WS-30B (Zhengzhou, China) gas sensing system equipped with a heating voltage (V h ) and a loop power (V c ). Observe the gas sensing characteristics of the sensor by measuring the voltage (V L ) at the load resistor (R out ). The static method is adopted to control the gas concentration during the test. The resistance response is calculated by the following formula (1).

[0054]

[0055] The static method is adopted to control the gas concentration during the test. Inject the target gas into the closed chamber (18 L) and mix it fully with air. For liquids, heat them on a hot plate until they are completely evaporated and mixed. For gases, adjust the gas concentration by changing the gas volume. The corresponding gas test concentrations are obtained from the following formulas (2) and (3).

[0056]

[0057] where Q (mL) is the volume of the injected liquid or gas, V (mL) is the volume of the test chamber, C (mL m -3 ) is the target gas concentration, M (g mol -1 ) is the relative molecular weight of the liquid, T R (°C) and T C (°C) are the ambient temperature and the temperature in the test chamber respectively, d (g cm -3 ) is the liquid density, and p is the purity of the selected solution. During the test, use a sampler to extract the required volume of the target gas and inject it into the closed chamber. The target gas quickly evaporates into vapor by heating, contacts the sensor and reacts for testing. After the test, open the closed chamber to expose the sensor to air. The response value is detected using the formula to detect the response R a / Rg , where R a and R g are the resistances in air and the test gas, respectively.

[0058] Gas sensing performance:

[0059] Figure 4 a The gas sensing characteristics of five sensors to 10 ppm acetone between 160 °C and 300 °C were tested. The response of each sensor initially increased with the increase in temperature, reached a peak at the ideal operating temperature, and then decreased with further increase in temperature. Compared with other samples, the 1% Pt-ZnO NTs sensor showed the highest response (10 ppm, R a / R g = 46.67). Compared with the original ZnO NTs sensor, the introduction of Pt reduced the optimal operating temperature of the sensor from 260 °C to 240 °C. Since the noble metal catalyst reduced the activation energy of gas chemisorption and increased the adsorbed oxygen species, the addition of Pt nanoparticles reduced the optimal operating temperature of the original ZnO NTs. Due to the low Pt doping amount in 0.5% Pt, the adsorbed oxygen content of the sample was low and the catalytic effect was not obvious. When the Pt loading exceeded 1% and reached 2% and 3%, the response value showed a downward trend. This phenomenon can be explained as that the excessive doping of Pt led to the coverage of the active sites on the surface of ZnO NTs, resulting in an adsorbed oxygen content lower than that of the 1% Pt sample. Figure 4 b shows the dynamic response-recovery curves of five samples to different concentrations (1 - 5 ppm) of acetone at an operating temperature of 240 °C. The response value of the 1% Pt-ZnO NTs sensor to 5 ppm acetone was 25.42, which was 4.79 times higher than that of the original ZnO NTs (R a / R g = 5.3), 3.21 times higher than that of the 0.5% Pt-ZnO NTs sensor (R a / R g = 7.9), 1.29 times higher than that of the 2% Pt-ZnO NTs sensor (R a / R g = 19.66), and 1.39 times higher than that of the 3% Pt-ZnO NTs sensor (R a / R g = 18.2). To show the wider detection range and sensitivity of the sensor, the dynamic response-recovery curves of the five sensors to 5 - 50 ppm acetone at 240 °C are shown in Figure 4 c. The response value of the 1% Pt-ZnO NTs sensor reached 136.5 at 50 ppm, demonstrating an extremely wide detection range. Figure 4d is the linear fit between the acetone concentration (1–50 ppm) and the responses of five sensors on a logarithmic scale. According to the fitted linear curve Y = 0.73X + 0.87, the theoretical detection limit is 68 ppb (R a / R g > 1.2). Figure 4 e shows the dynamic response curves of different sensors when exposed to 10 ppm acetone. Compared with other sensors, the 1% Pt-ZnONTs sensor shows the highest response (Ra / Rg = 48.16), which is consistent with the results shown in Figure 4 c. And Figure 4 e also demonstrates the high sensitivity of the sensor, namely the response time and response recovery time when exposed to acetone and air. In Figure 4 f, the response time and response recovery time of the five sensors in 1-5 ppm acetone are summarized. The 1% Pt-ZnONTs sensor exhibits the shortest response (response time is 3 s) and recovery time (recovery time is 12 s).

[0060] Sensing stability and repeatability are also important parameters for evaluating sensor performance. The cyclic dynamic response curves of the five sensors are shown in Figure 5 a. All sensors can recover and drop to the baseline when exposed to air, showing good reversibility, and excellent repeatability in five cycles. And the long-term stability test of the sensor was carried out, as shown in Figure 5 b. A long-term stability test for up to one month was carried out on it. The results show that the 1% Pt-ZnO NTs sensor exhibits excellent repeatability, and in the long-term stability test, it can maintain more than 90% of the initial response, confirming its excellent stability. To test the selectivity of the sensor, the responses of the five sensors to 10 ppm acetone and other different interfering gases (including C 2 H 5 OH, CH 3 OH, HCHO, C 3 H 8 O and NH 3 ) at the optimal temperature are shown in Figure 5 c. Among them, the response of the 1% Pt-ZnO NTs sensor to 10 ppm acetone is 48.16 (R a / R g ), which is at least 4.08 times higher than that of other different interfering gases (R a / R g < 11.8). For other sensors, they also have excellent selectivity for acetone. In addition, the sensing test of the sensor at different humidities (25-70% RH) was carried out, as shown in Figure 5As shown in d, the response value of the 1% Pt-ZnO NTs sensor in a humidity environment of 25% RH is 48.16, and the response value in a humidity environment of 70% RH is 20.33. The response value is only 43% of the response value at 25% RH. In a high-humidity environment, H 2 O molecules will adsorb on the sensor surface to form OH - , which hinders the chemical absorption of oxygen and the migration of target gases on the surface, resulting in a decrease in sensor performance.

[0061] This application innovatively uses the chemical sites of PS-COOH to enable ZIF-8 to be combined with the electrospinning method in a point-to-point in-situ growth manner. The advantage is that this ordered arrangement of nanoparticles can increase the contact area between acetone gas and the material, as well as fully expose the active sites, thereby improving the sensitivity of the device. Moreover, this ordered arrangement of nanoparticles has a lower potential barrier, enabling a faster response to acetone gas. The way of doping noble metal Pt is not direct doping, but by taking advantage of the cavity of the ZIF-8 structure, making each Pt nanoparticle independent of each other. On the one hand, it has an economic advantage and avoids the waste of noble metals. On the other hand, this method can effectively avoid the agglomeration of noble metal nanoparticles during calcination, thereby ensuring higher catalytic activity of the noble metal, generating more reactive oxygen species, and further improving the sensitivity of the device. The prepared gas-sensitive element can reach a detection limit of 68 ppb for acetone, and the response time can be as fast as 3 s and the recovery time can be as fast as 10 s, which is a very advanced performance among the same series of materials and device structures.

[0062] The above-described embodiments have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a one-dimensional metal oxide hollow nanofiber material driven by MOF, characterized in that: The following steps are involved: (1) Dissolve styrene and methacrylic acid in water and heat and stir until boiling, add potassium persulfate, stir and react at 70-90°C for 1-5 hours, then wash and dry the precipitate after the reaction to obtain PS-COOH; (2) dissolving polystyrene in organic solvent A, adding PS-COOH and zinc acetate and stirring to obtain a uniform and transparent spinning precursor solution A; Polyacrylonitrile is dissolved in an organic solvent B and stirred to form a uniform and transparent spinning precursor solution B, and the spinning precursor solutions A and B are used to prepare nanofibers with a core-shell structure by coaxial electrospinning; (3) immersing the nanofibers with a core-shell structure in a 2-methylimidazole solution at room temperature and drying to obtain uniformly grown nanofibers of ZIF-8; (4) soaking the uniformly grown ZIF-8 nanofibers in a chloroplatinic acid solution to allow the chloroplatinic acid solution to be completely adsorbed, and then reducing them in a sodium borohydride solution and drying them; (5) The nanofibers prepared in step (4) are calcined in a protective atmosphere and in air, respectively, to obtain MOF-driven one-dimensional hollow metal oxide nanofiber materials.

2. The preparation method according to claim 1, characterized in that: In step (1), the volume ratio of styrene to methacrylic acid is (35-45):1, and the mass volume ratio of styrene to potassium disulfate is (70-90) mL:1 g; the heating temperature is 70-80°C, and the heating time is 2-4 h.

3. The preparation method according to claim 1, characterized in that: In step (2), the organic solvent A and the organic solvent B are one or a mixture of any two of ethanol, dichloromethane, ethyl acetate, and DMF; the concentration of polystyrene in the spinning precursor solution A in the organic solvent A is 0.2-0.3 g / mL; the concentration of zinc acetate in the organic solvent A is 0.6-0.75 mmol / mL; the mass ratio of PS-COOH to zinc acetate is 1:(1.2-1.6); the concentration of polyacrylonitrile in the spinning precursor solution B in the organic solvent B is 0.08-0.1 g / mL; and the stirring time is 8-10 h.

4. The preparation method according to claim 1, characterized in that: In step (2), the specific steps of the electrospinning method include: injecting the spinning precursor solution A into the syringe 1 as the spinning external solution, and injecting the spinning precursor solution B into the syringe 2 as the spinning internal solution; controlling the distance between the receiving device and the syringe needle to be 13-17 cm, setting the electrospinning voltage to 15-20 kV, and the feed rate to 0.1-0.5 mL h -1 .

5. The preparation method according to claim 1, characterized in that: In step (3), the 2-methylimidazole solution refers to a methanol solution of 2-methylimidazole, and the concentration of the 2-methylimidazole in methanol is 20-30 g / L; the soaking time is 5-8 hours.

6. The preparation method according to claim 1, characterized in that: In step (4), the mass percentage of Pt in the chloroplatinic acid solution is 0.5%~3%; the concentration of the sodium borohydride solution is 1~2 mg / mL; the reduction time is 0.5~2 hh; the drying temperature is 50~80°C, and the time is 0.5~2 h.

7. The preparation method according to claim 1, characterized in that: In step (5), the calcination parameters in the protective atmosphere are: heating rate 1~5°C / min, calcination time 2~3 h, calcination temperature 500~600°C, and the protective atmosphere is at least one of N2 and Ar; the calcination parameters in the air atmosphere are: heating rate 1~5°C / min, calcination time 2~3 h, calcination temperature 600~650°C.

8. A MOF-driven one-dimensional metal oxide hollow nanofiber material, characterized in that: The method as described in any one of claims 1 to 7 is used to prepare the MOF, and the MOF is uniformly grown on the nanofiber by in-situ self-assembly, and the metal platinum is confined in the framework of the MOF without forming agglomerates.

9. A gas sensor, characterized in that: The MOF-driven one-dimensional metal oxide hollow nanofiber material as claimed in claim 8 is used as a sensitive layer material.

10. The gas sensor according to claim 9, characterized in that: The sensor is used for industrial acetone detection or for monitoring diabetes.

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