UIO-66 (at) Hf-MOF micro-nano hypersensitive material and preparation method and application thereof, gas sensor and preparation method and application thereof

Abstract

The invention relates to the field of gas sensing, and discloses a UIO-66 (at) Hf-MOF micro-nano hypersensitive material and a preparation method and application thereof, a gas sensor and a preparation method and application thereof, the UIO-66 (at) Hf-MOF micro-nano hypersensitive material comprises an Hf-MOF material, and the surface of the Hf-MOF material is loaded with a UIO-66 material. The UIO-66 (at) Hf-MOF micro-nano hypersensitive material shows excellent gas sensitivity, including high sensitivity to gas H2 and CO dissolved in oil of electrical equipment at low temperature.

Description

Technical Field

[0001] The present invention relates to the field of gas sensing, and particularly to UIO-66@Hf-MOF micro-nano hypersensitive materials and their preparation methods and applications, gas sensors and their preparation methods and applications. Background Art

[0002] Power transformers are the core equipment of the power grid, and their internal defects are difficult to directly monitor by external means. However, internal faults will cause chemical reactions in transformer oil and insulating materials, generating and dissolving fault characteristic gases such as hydrogen and carbon monoxide. Therefore, the detection of dissolved gases in transformer oil is of great significance for timely discovering potential hazards and defects inside transformers and ensuring the safe and stable operation of the power grid.

[0003] Although traditional methods such as gas chromatography can play a certain role, they have deficiencies in terms of real-time performance, operation convenience, and cost-effectiveness. In addition, with the development of power equipment condition monitoring technology, the requirements for gas-sensitive materials are also increasing. However, existing gas-sensitive materials generally have problems such as insufficient sensitivity, poor stability, and high operating temperature when detecting dissolved gases in power equipment oil. Summary of the Invention

[0004] The purpose of the present invention is to overcome a series of problems existing in existing gas-sensitive materials when detecting low-concentration gases such as H2 and CO dissolved in power equipment oil, such as insufficient sensitivity, poor stability, and high operating temperature, and to provide UIO-66@Hf-MOF micro-nano hypersensitive materials and their preparation methods and applications, gas sensors and their preparation methods and applications. The UIO-66@Hf-MOF micro-nano hypersensitive material exhibits excellent gas-sensing performance, including high sensitivity to H2 and CO dissolved in power equipment oil at low temperatures.

[0005] To achieve the above purpose, on the one hand, the present invention provides a UIO-66@Hf-MOF micro-nano hypersensitive material, and the UIO-66@Hf-MOF micro-nano hypersensitive material includes an Hf-MOF material, and the UIO-66 material is loaded on the surface of the Hf-MOF material.

[0006] The UIO-66@Hf-MOF micro-nano hypersensitive material of the present invention is a two-dimensional porous nano-bimetallic organic hybrid material, belonging to nano-porous materials; the specific surface area of the UIO-66@Hf-MOF micro-nano hypersensitive material is 800 - 1200m 2 / g.

[0007] On the second aspect, the present invention provides a preparation method of the above UIO-66@Hf-MOF micro-nano hypersensitive material, and the preparation method includes the following steps:

[0008] Mix hafnium salt, aromatic polycarboxylic acid A, organic solvent A and organic acid to obtain a mixed material. React the mixed material, cool it after the reaction ends to obtain material A. Perform solid-liquid separation on material A to obtain solid product A. Wash and dry solid product A to obtain the Hf-MOF material;

[0009] Mix the Hf-MOF material, zirconium salt and organic solvent B, and stir to obtain solution A;

[0010] Mix aromatic polycarboxylic acid B and organic solvent C, and stir to obtain solution B;

[0011] Mix solution A and solution B to obtain a reaction solution, then carry out a hydrothermal reaction on the reaction solution. Cool it after the hydrothermal reaction ends to obtain material B. Perform solid-liquid separation on material B to obtain solid product B. Wash and dry solid product B to obtain the UIO-66@Hf-MOF micro-nano hypersensitive material.

[0012] Furthermore, the hafnium salt is selected from one or more of hafnium tetrachloride, hafnium oxychloride and hafnium oxynitrate; in a specific embodiment, the hafnium salt is selected from hafnium tetrachloride.

[0013] Among them, the organic solvent A is methanol and / or N,N-dimethylformamide; in a specific embodiment, the organic solvent A is N,N-dimethylformamide (DMF).

[0014] Preferably, the dosage ratio of the hafnium salt, aromatic polycarboxylic acid A and organic solvent A is 1 g: 1-2 g: 50-100 mL.

[0015] Furthermore, the solid-liquid ratio of the hafnium salt and the organic acid is 1 g: 50-100 mL.

[0016] In the present invention, controlling the dosages of the above-mentioned hafnium salt, aromatic polycarboxylic acid A, organic solvent A and organic acid within the corresponding ranges helps to ensure the smooth progress of the reaction and the quality and performance of the final product.

[0017] Preferably, the aromatic polycarboxylic acid A is selected from one or more of 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB), benzene-1,3,5-tricarboxylic acid (BTC) and biphenyldicarboxylic acid (BPDC); among them, the aromatic polycarboxylic acid A reacts with the hafnium salt as a ligand to form the framework structure of Hf-MOF; in a specific embodiment, the aromatic polycarboxylic acid A is selected from 1,3,5-tris(4-carboxyphenyl)benzene.

[0018] Preferably, the organic acid is selected from one or more of formic acid, acetic acid, and propionic acid; the organic acid is used as a regulator in the present invention, which helps to adjust the pH value of the reaction, promote the coordination of the ligand with the metal ion, and affect the porosity and crystal morphology of the MOF material; in a specific embodiment, the organic acid is selected from formic acid.

[0019] Further, the specific operation of mixing the hafnium salt, aromatic polycarboxylic acid A, organic solvent A, and organic acid to obtain a mixed material includes: mixing the hafnium salt, aromatic polycarboxylic acid A, and organic solvent A and then performing a first stirring to obtain a mixed solution, and then mixing the mixed solution with the organic acid, followed by a second stirring to obtain a mixed material.

[0020] In a specific embodiment, the operation of mixing the hafnium salt, aromatic polycarboxylic acid A, organic solvent A, and organic acid to obtain a mixed material is carried out at room temperature.

[0021] Among them, the purpose of mixing the hafnium salt, aromatic polycarboxylic acid A, organic solvent A, and organic acid by stepwise feeding and mixing stirring is to ensure that the reactants are fully dissolved and evenly mixed, act together in the reaction process, and help to prepare a final product with excellent performance.

[0022] In the present invention, the room temperature refers to 20 - 30 °C.

[0023] Among them, in order to ensure that the solute can be fully dissolved and evenly mixed, the conditions for the first stirring include: the stirring speed is 300 - 800 revolutions per minute, and the stirring time is 15 - 20 min; the conditions for the second stirring include: the stirring speed is 300 - 800 revolutions per minute, and the stirring time is 15 - 20 min.

[0024] In a preferred case, the conditions for the reaction include: the temperature is 120 - 180 °C, and the time is 24 - 48 hours; controlling the reaction conditions within this range can ensure that the reaction proceeds fully.

[0025] Among them, after the above reaction is completed, it is cooled to room temperature to obtain material A, and then the material A is subjected to solid-liquid separation by centrifugation (the conditions for centrifugation here include: the rotation speed is 8000 - 12000 r / min, and the time is 10 - 20 min) to obtain a solid product A, and the solid product A is washed and dried to obtain the Hf-MOF material.

[0026] Further preferably, in order to remove unreacted raw materials, solvent residues, and possible impurities generated, the specific operations for washing and drying the solid product A include: centrifugally washing the solid product A 3 to 5 times with one of methanol, N,N-dimethylformamide, or ethanol (the rotation speed for each centrifugal washing of the solid product A is 10,000 to 12,000 revolutions per minute, and the time is 10 to 20 minutes. After each centrifugal washing, the precipitated part after centrifugation is retained, and the supernatant is discarded), and then drying the centrifugally washed solid product A to ensure that the solvent in the centrifugally washed solid product A is completely volatilized, obtaining a pure Hf-MOF material, where the drying conditions include: the temperature is 50 to 80 °C, and the time is 12 to 24 hours.

[0027] Further, the dosage ratio of the Hf-MOF material, zirconium salt, and organic solvent B is 1 g: 1 g: 50 to 100 mL;

[0028] Wherein the zirconium salt is selected from one or more of zirconyl chloride, zirconium tetrachloride, and zirconium nitrate; in a specific embodiment, the zirconium salt is selected from zirconium tetrachloride.

[0029] Wherein the organic solvent B is methanol and / or N,N-dimethylformamide; in a specific embodiment, the organic solvent B is N,N-dimethylformamide.

[0030] In the present invention, the Hf-MOF material, zirconium salt, and organic solvent B are mixed. In order to further ensure that all solutes can be fully dissolved and mixed evenly, it is therefore also necessary to stir for a certain time at an appropriate stirring speed. Therefore, it is preferably stirred at a stirring speed of 300 to 500 revolutions per minute for 15 to 30 minutes to obtain solution A.

[0031] In the present invention, the solid-liquid ratio of the aromatic polycarboxylic acid B and the organic solvent C is 1 g: 50 to 100 mL. Controlling the solid-liquid ratio of the aromatic polycarboxylic acid B and the organic solvent C within this range can ensure that the reactants are fully dissolved and mixed evenly, jointly acting on the reaction process, which helps to prepare a final product with excellent performance.

[0032] Wherein the organic solvent C is methanol and / or N,N-dimethylformamide; in a specific embodiment, the organic solvent C is N,N-dimethylformamide.

[0033] Preferably, the aromatic polycarboxylic acid B is selected from one or more of terephthalic acid, trimesic acid, and biphenyl dicarboxylic acid; in a specific embodiment, the aromatic polycarboxylic acid B is selected from terephthalic acid.

[0034] In the present invention, the selection of organic solvent A, organic solvent B, and organic solvent C is independent of each other, and organic solvent A, organic solvent B, and organic solvent C can be the same or different.

[0035] In the present invention, aromatic polycarboxylic acid B is mixed with organic solvent C. Similarly, to ensure that the solute can be fully dissolved and mixed evenly, stirring is also required under appropriate conditions. Preferably, it is stirred at a stirring speed of 300 - 800 revolutions per minute for 15 - 20 minutes to obtain solution B.

[0036] Furthermore, to avoid precipitation caused by too high local concentration when solution A and solution B are mixed, preferably, solution B is slowly and continuously poured into solution A while gently stirring to obtain a uniformly mixed reaction solution, and then the reaction solution is subjected to a hydrothermal reaction.

[0037] In the preferred case, the volume ratio of solution A to solution B is 1:1 - 2.

[0038] Furthermore, the conditions of the hydrothermal reaction include: the temperature is 120 - 180 °C, and the time is 12 - 18 h; controlling the amounts of solution A and solution B and the conditions of the hydrothermal reaction within the above ranges helps to form a stable and uniformly structured micro - nano hypersensitive material.

[0039] In the present invention, after the hydrothermal reaction, it is preferably naturally cooled to room temperature to obtain material B, so as to avoid damage to the material structure caused by a sudden drop in temperature.

[0040] In the present invention, when performing solid - liquid separation on material B, the operation of solid - liquid separation here can be filtration or centrifugation, and further preferably filtration.

[0041] Furthermore, in order to remove unreacted raw materials, solvent residues, and possible impurities generated, the specific operations of washing and drying the solid product B include: centrifugally washing the solid product B three times with absolute ethanol (the rotation speed for each centrifugal washing of the solid product B is 10000 - 12000 revolutions per minute, and the time is 10 - 20 minutes. After each centrifugal washing, the precipitated part after centrifugation is retained and the supernatant is discarded), and then drying the centrifugally washed solid product B to ensure that the solvent in the centrifugally washed solid product B is completely volatilized to obtain a pure UIO - 66@Hf - MOF micro - nano hypersensitive material, where the conditions of the drying include: the temperature is 60 - 80 °C, and the time is 12 - 24 h.

[0042] MOF (Metal-Organic Framework)-based micro-nano hypersensitive materials combine the characteristics of high specific surface area and structural tunability of MOF materials themselves. These materials have an extremely high specific surface area, which can provide a large number of active sites, enhancing adsorption and catalytic performance. At the same time, their structures can be finely designed and adjusted according to needs, thereby optimizing physical and chemical properties to meet different application requirements. These advantages make MOF-based micro-nano hypersensitive materials show great potential in the field of dissolved gas detection in power equipment oil.

[0043] Based on this, the present invention uses two-dimensional Hf-MOF nanosheets as the substrate, and constructs UIO-66@Hf-MOF micro-nano hypersensitive materials by in-situ loading of UIO-66 nanoparticles. The UIO-66@Hf-MOF micro-nano hypersensitive materials of the present invention have a high specific surface area and a hierarchical pore structure. Through the specific interaction between Hf 4+ / Zr 4+ Lewis acid sites and gas molecules, combined with the enhanced electron transport effect of the Schottky junction, can significantly improve the adsorption and signal response to H2 and CO.

[0044] The third aspect of the present invention provides an application of the above UIO-66@Hf-MOF micro-nano hypersensitive material in a gas sensor.

[0045] The fourth aspect of the present invention provides a gas sensor, which includes a conductive melamine sponge. The conductive melamine sponge includes a melamine sponge, and the surface and pores of the melamine sponge are loaded with the above UIO-66@Hf-MOF micro-nano hypersensitive material.

[0046] The fifth aspect of the present invention provides a preparation method of the above gas sensor, including the following steps:

[0047] Mix the UIO-66@Hf-MOF micro-nano hypersensitive material with methanol, and stir to obtain a conductive solution;

[0048] Treat the melamine sponge with the UIO-66@Hf-MOF micro-nano hypersensitive material to obtain a conductive melamine sponge; the operation of treating the melamine sponge with the UIO-66@Hf-MOF micro-nano hypersensitive material includes: immersing the melamine sponge in the conductive solution, and then drying;

[0049] Assemble electrode materials on both sides of the conductive melamine sponge, and then weld conductive copper wires on the electrode materials to obtain a gas sensor.

[0050] In the present invention, the content of the UIO-66@Hf-MOF micro-nano hypersensitive material in the conductive solution is 5-10 wt%, so as to ensure good conductivity and gas-sensing performance. If the content of the UIO-66@Hf-MOF micro-nano hypersensitive material is too low, the conductivity of the sensor will be insufficient, affecting signal transmission and detection sensitivity; if the content is too high, the solution viscosity will increase, affecting the uniformity and consistency of the sensor.

[0051] Among them, in order to ensure sufficient mixing of the materials, the UIO-66@Hf-MOF micro-nano hypersensitive material is mixed with methanol, preferably stirred at a stirring speed of 300-800 revolutions per minute for 15-20 min to obtain a conductive solution.

[0052] Melamine sponge has become an ideal substrate material for preparing conductive melamine sponge due to its excellent flexibility and processability, good liquid absorption and permeability, chemical stability and high temperature resistance, as well as low cost and easy availability. These characteristics jointly affect the performance of the sensor, making the gas-sensing sensor based on melamine sponge show great application potential in the field of dissolved gas detection in power equipment oil; therefore, in the present invention, melamine sponge is selected as the flexible substrate to prepare conductive melamine sponge. The melamine sponge used is a commercially available melamine sponge, in the shape of a cuboid, and can be cut into cuboid blocks of appropriate size according to the size of the gas-sensing sensor required by the actual working conditions, and then the UIO-66@Hf-MOF micro-nano hypersensitive material is loaded, or the UIO-66@Hf-MOF micro-nano hypersensitive material is loaded directly without shearing.

[0053] In the present invention, preferably, the melamine sponge can be first soaked in methanol for 5-10 min for cleaning to remove surface impurities and oil stains, and then dried at 50-80 °C for 4-8 hours, and then the dried melamine sponge is subjected to the treatment of loading the UIO-66@Hf-MOF micro-nano hypersensitive material.

[0054] Among them, in the operation of the treatment of loading the UIO-66@Hf-MOF micro-nano hypersensitive material, in order to ensure that the melamine sponge is fully impregnated with the conductive solution, long-term impregnation or continuous extrusion of the melamine sponge can be selected (the operation of continuous extrusion can shorten the impregnation time; there is no requirement for the number of extrusion times, as long as it can be fully extruded to ensure that the melamine sponge is fully impregnated), so that the UIO-66@Hf-MOF micro-nano hypersensitive material in the conductive solution can be more fully immersed into the melamine sponge.

[0055] In the specific operation, when the melamine sponge is immersed in the conductive solution, the amount of the conductive solution only needs to completely submerge the melamine sponge.

[0056] In order to ensure that the melamine sponge can fully load the UIO-66@Hf-MOF micro-nano hypersensitive material and reach the maximum loading amount, preferably, the melamine sponge is subjected to 4 to 6 treatments of loading the UIO-66@Hf-MOF micro-nano hypersensitive material, and finally a conductive melamine sponge is obtained.

[0057] Among them, the drying conditions include: the temperature is 50 to 80 °C, and the time is 4 to 8 hours.

[0058] In the present invention, the electrode material is preferably a conductive metal tape, which can be conveniently assembled on both sides of the conductive melamine sponge to achieve conductive contact between the two; in the specific implementation manner, the electrode material is a conductive copper foil tape.

[0059] Preferably, the electrode material is assembled on the upper and lower surfaces of the conductive melamine sponge, and the shape and size of the electrode material assembled on the upper and lower surfaces are adapted to the shape and size of the corresponding upper and lower surfaces, that is, the shape and size of the electrode material assembled on the upper surface of the conductive melamine sponge are the same as those of the upper surface, and the shape and size of the electrode material assembled on the lower surface are the same as those of the lower surface. Because if the electrode material is too large, there will be a risk of contact short circuit between the electrode materials on the upper and lower surfaces; if the electrode material is too small, the uncoated part of the conductive melamine sponge will not be able to exert its performance, resulting in waste.

[0060] Further, when welding the conductive copper wire, first remove a small part of the outer skin at both ends of the conductive copper wire to expose the copper wire at both ends directly, and then weld one end of the exposed copper wire to the electrode material with an electric welding gun (a conductive copper wire is welded to each electrode material in the above manner, so that the conductive melamine sponge can be connected to an external circuit (such as a resistance tester). When the gas sensor responds to a specific substance, the response value is detected by measuring changes in electrical parameters such as resistance), and the encapsulation is completed to obtain a gas sensor.

[0061] The sixth aspect of the present invention provides an application of the above gas sensor in the detection of H2 and CO.

[0062] The above-mentioned gas sensor of the present invention uses UIO-66@Hf-MOF micro-nano hypersensitive material as the core sensitive element, showing significant advantages in the detection of H2 and CO: The UIO-66@Hf-MOF material combines the characteristics of high specific surface area and Hf and Zr bimetallic active sites. On the one hand, the high specific surface area enables the UIO-66@Hf-MOF material to expose more active sites, thus increasing the contact opportunities with H2 and CO gas molecules and improving the adsorption efficiency. On the other hand, the presence of Hf and Zr bimetallic active sites endows the UIO-66@Hf-MOF material with stronger adsorption ability and specific interaction with H2 and CO gas molecules; this synergistic effect not only improves the adsorption efficiency but also enhances the stability of the gas sensor to the target gas.

[0063] In addition, the melamine sponge, as the flexible substrate of the gas sensor, not only provides good mechanical support and conductivity but also further enhances the portability and applicability of the sensor. Therefore, the prepared gas sensor exhibits high sensitivity, fast response, and good stability in the detection of H2 and CO, and is particularly suitable for the real-time monitoring of dissolved gases in transformer oil of power equipment, providing a strong guarantee for the safe and stable operation of the power grid.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] Improve detection sensitivity: The UIO-66@Hf-MOF micro-nano hypersensitive material shows high sensitivity to dissolved gases H2 and CO in transformer oil at low temperatures. Applying it to the gas sensor overcomes the problem of insufficient sensitivity of existing gas-sensitive materials in detecting low-concentration gases.

[0066] Improve stability: The porous structure and chemical stability of the UIO-66@Hf-MOF micro-nano hypersensitive material contribute to improving the adsorption stability to the target gas, and using it in the gas sensor can improve the stability of the gas sensor.

[0067] Reduce the operating temperature: Compared with traditional gas-sensitive materials, the UIO-66@Hf-MOF micro-nano hypersensitive material can exhibit excellent gas-sensitive performance at a lower operating temperature. Preparing it into a gas sensor helps reduce the energy consumption and cost of the gas sensor.

[0068] Achieve flexibility and portability: The gas sensor based on the UIO-66@Hf-MOF micro-nano hypersensitive material on the conductive melamine sponge has the characteristics of flexibility and portability, facilitating real-time monitoring and detection at the site of power equipment. Brief Description of the Drawings

[0069] Figure 1 is a schematic diagram of the preparation of the UIO-66@Hf-MOF micro-nano hypersensitive material of the present invention;

[0070] Figure 2 It is the SEM image of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4;

[0071] Figure 3 It is the XRD pattern of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 and the Hf-MOF material of Comparative Example 1;

[0072] Figure 4 It is the N2 adsorption isotherm of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4;

[0073] Figure 5 It is the response curve of the gas sensor of Example 8 to 5 ppm H2 at different operating temperatures;

[0074] Figure 6 It is the response curve of the gas sensor of Example 8 to 5 ppm CO at different operating temperatures;

[0075] Figure 7 It is the long-term stability test chart of the gas sensor of Example 8 to 5 ppm H2 at 90 °C. Detailed implementation manners

[0076] The following describes in detail the specific implementation manners of the present invention in conjunction with the accompanying drawings and examples. It should be understood that the specific implementation manners described herein are only for explaining and understanding the present invention, and are not used to limit the present invention.

[0077] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0078] In addition, the technical solutions between the various embodiments provided by the present invention can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions conflicts or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0079] The preparation schematic diagram of the UIO-66@Hf-MOF micro-nano hypersensitive material of the present invention is as Figure 1 shown.

[0080] The room temperature in the following examples all refers to 25 °C.

[0081] The experimental materials used in the following examples and comparative examples are all commercially available unless otherwise specified.

[0082] Example 1

[0083] (1) At room temperature, add 50 mL of organic solvent A (N,N-dimethylformamide) to a beaker. Weigh 1 g of hafnium salt (hafnium tetrachloride) and 1 g of aromatic polycarboxylic acid A (1,3,5-tris(4-carboxyphenyl)benzene) and add them thereto and mix. Then perform the first stirring. The conditions of the first stirring include: the stirring speed is 300 revolutions per minute and the stirring time is 15 min to obtain a clear mixed solution. Then add 50 mL of organic acid (anhydrous formic acid) to the clear mixed solution and mix. Then perform the second stirring. The conditions of the second stirring include: the stirring speed is 300 revolutions per minute and the stirring time is 15 min to obtain a mixed material. Transfer the mixed material to a polytetrafluoroethylene reaction kettle and place it in a forced-air drying oven. Set the heating temperature to 120 °C for reaction. The reaction conditions include: the temperature is 120 °C and the time is 24 hours. After the reaction, cool to room temperature to obtain material A. Use a centrifuge to perform solid-liquid separation on material A by centrifugation (the centrifugation conditions here include: the rotation speed is 8000 r / min and the time is 10 min), remove the supernatant to obtain solid product A. Use methanol to wash solid product A by centrifugation 3 times (the rotation speed for each centrifugation washing of solid product A is 10000 revolutions per minute and the time is 10 min). Then transfer the centrifugation-washed solid product A to a forced-air drying oven. Set the heating temperature to 80 °C for drying. The drying conditions include: the temperature is 80 °C and the time is 12 h to obtain a pure Hf-MOF material;

[0084] (2) Weigh 1 g of the Hf-MOF material obtained in step (1) and 1 g of zirconium salt (zirconium tetrachloride) and add them to a beaker containing 50 mL of organic solvent B (N,N-dimethylformamide). Mix the Hf-MOF material, zirconium salt obtained in step (1) with organic solvent B and stir at a stirring speed of 300 revolutions per minute for 15 min to obtain solution A;

[0085] (3) Weigh 1 g of aromatic polycarboxylic acid B (terephthalic acid) and add it to a beaker containing 50 mL of organic solvent C (N,N-dimethylformamide). Mix aromatic polycarboxylic acid B with organic solvent C and stir at a stirring speed of 300 revolutions per minute for 15 min to obtain solution B;

[0086] (4) Slowly and continuously pour Solution B into Solution A while gently stirring to obtain a uniformly mixed reaction solution (the volume ratio of Solution A to Solution B is 1:1). Then transfer the reaction solution to a 200 mL polytetrafluoroethylene-lined reaction kettle, seal it, and place it in an oven preheated to 120 °C for hydrothermal reaction. The conditions of the hydrothermal reaction include: temperature of 120 °C, time of 12 h, and keep the oven temperature constant during this period. After the hydrothermal reaction, let the reaction kettle cool naturally to room temperature to obtain Material B. Filter Material B to obtain solid product B, and wash the solid product B by centrifugation with absolute ethanol three times (the rotation speed for each centrifugal washing of the solid product B is 10,000 revolutions per minute, and the time is 10 min). Then place the centrifugally washed solid product B in a vacuum drying oven for drying. The drying conditions include: temperature of 60 °C, time of 24 h, to obtain pure UIO-66@Hf-MOF micro-nano hypersensitive material.

[0087] Example 2

[0088] Implemented according to the method of Example 1, except that in step (1), 1 g of hafnium salt (hafnium tetrachloride) and 2 g of aromatic polycarboxylic acid A (1,3,5-tris(4-carboxyphenyl)benzene) are weighed and added to a beaker containing 50 mL of organic solvent A, that is, the dosage ratio of hafnium salt, aromatic polycarboxylic acid A, and organic solvent A is 1 g:2 g:50 mL, to prepare UIO-66@Hf-MOF micro-nano hypersensitive material.

[0089] Example 3

[0090] Implemented according to the method of Example 1, except that in step (2), 1 g of the Hf-MOF material obtained in step (1) and 1 g of zirconium salt (zirconium tetrachloride) are weighed and added to a beaker containing 100 mL of organic solvent B (N,N-dimethylformamide), that is, the dosage ratio of the Hf-MOF material, zirconium salt, and organic solvent B is 1 g:1 g:100 mL, to prepare UIO-66@Hf-MOF micro-nano hypersensitive material.

[0091] Example 4

[0092] A UIO-66@Hf-MOF micro-nano hypersensitive material, which includes an Hf-MOF material with UIO-66 material loaded on the surface of the Hf-MOF material; this UIO-66@Hf-MOF micro-nano hypersensitive material is prepared by the method of Example 1.

[0093] Example 5

[0094] A UIO-66@Hf-MOF micro-nano hypersensitive material, the UIO-66@Hf-MOF micro-nano hypersensitive material includes Hf-MOF material, and the surface of the Hf-MOF material is loaded with UIO-66 material; the UIO-66@Hf-MOF micro-nano hypersensitive material is prepared by the method of Example 2.

[0095] Example 6

[0096] A UIO-66@Hf-MOF micro-nano hypersensitive material, the UIO-66@Hf-MOF micro-nano hypersensitive material includes Hf-MOF material, and the surface of the Hf-MOF material is loaded with UIO-66 material; the UIO-66@Hf-MOF micro-nano hypersensitive material is prepared by the method of Example 3.

[0097] Example 7

[0098] The UIO-66@Hf-MOF micro-nano hypersensitive materials in Examples 4 to 6 all have a high specific surface area and a hierarchical pore structure, and can pass through Hf 4+ / Zr 4+ The specific interaction between the Lewis acid sites and gas molecules, combined with the enhanced electron transport effect of the Schottky junction, can significantly improve the adsorption and signal response to H2 and CO, and can all be applied to gas sensors to further improve the sensitivity of gas sensors.

[0099] Example 8

[0100] A gas sensor, the gas sensor includes a conductive melamine sponge, the conductive melamine sponge includes a melamine sponge, and the surface and pores of the melamine sponge are loaded with the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4.

[0101] Example 9

[0102] A gas sensor, the gas sensor includes a conductive melamine sponge, the conductive melamine sponge includes a melamine sponge, and the surface and pores of the melamine sponge are loaded with the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 5.

[0103] Example 10

[0104] A gas sensor, the gas sensor includes a conductive melamine sponge, the conductive melamine sponge includes a melamine sponge, and the surface and pores of the melamine sponge are loaded with the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 6.

[0105] Example 11

[0106] The method for preparing the gas sensor of Example 8 specifically comprises the following steps:

[0107] S1. Weigh 50 mg of the UIO-66@Hf-MOF micro-nano supersensitive material of Example 4, add it to 100 mL of methanol, and stir it at a stirring speed of 300 rpm for 15 min to obtain a uniform conductive solution. The content of the UIO-66@Hf-MOF micro-nano supersensitive material in the conductive solution is 5 wt %;

[0108] S2, cutting the melamine sponge into small rectangular pieces to obtain a block melamine sponge, soaking the block melamine sponge in methanol for 5 minutes to clean it to remove impurities and oil stains on the surface, putting it in an oven after cleaning, and drying it at 50°C for 8 hours to obtain a dried melamine sponge, and loading the dried melamine sponge with UIO-66@Hf-MOF micro-nano supersensitive material for 4 times to obtain a conductive melamine sponge; wherein the specific operation of loading the UIO-66@Hf-MOF micro-nano supersensitive material each time includes: placing the melamine sponge in the conductive solution obtained in step S1, and fully impregnating the melamine sponge with the conductive solution by continuously squeezing the melamine sponge, and then taking out the melamine sponge fully impregnated with the conductive solution with tweezers, placing it in a glass culture dish, and then placing the glass culture dish in a blast drying oven set at a temperature of 50°C for drying, and the drying conditions include: temperature of 50°C and time of 4 hours;

[0109] S3, cutting the conductive copper foil tape into a suitable shape and size, and then pasting conductive copper foil tapes of suitable shape and size on the upper and lower surfaces of the conductive melamine sponge obtained in step S2, so that the shape and size of the conductive copper foil tape pasted on the upper surface of the conductive melamine sponge are the same as those of the upper surface, and the shape and size of the conductive copper foil tape pasted on the lower surface are the same as those of the upper surface, then taking two conductive copper wires, removing a small part of the outer skin at both ends of the two conductive copper wires, so that the copper wires at both ends are directly exposed, and then using an electric welding gun to weld the two conductive copper wires to the conductive copper foil tapes pasted on the upper and lower surfaces respectively (both copper wires with one end exposed are welded to the conductive copper foil tape with an electric welding gun), completing the packaging, and obtaining a gas sensor.

[0110] Example 12

[0111] The preparation method of the gas sensor of Example 9 is specifically implemented according to the method of Example 11, except that the UIO-66@Hf-MOF micro-nano ultrasensitive material of Example 5 is used in step S1 to prepare the gas sensor.

[0112] Embodiment 13

[0113] The preparation method of the gas sensor of Example 10 is specifically carried out according to the method of Example 11. The difference is that in step S1, the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 6 is used to prepare the gas sensor.

[0114] Example 14

[0115] The gas sensors in Examples 8 to 10 all have good sensitivity and can be used to detect H2 and CO.

[0116] Comparative Example 1

[0117] The Hf-MOF material was prepared by the method of step (1) of Example 1.

[0118] Comparative Example 2

[0119] It was carried out according to the method of Example 11. The difference is that in step S1, the Hf-MOF material in Comparative Example 1 was used to replace the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 to obtain the gas sensor.

[0120] Comparative Example 3

[0121] It was carried out according to the method of Example 1. The difference is that the Hf-MOF material was not prepared, and the zirconium salt and N,N-dimethylformamide were directly mixed to prepare the micro-nano hypersensitive material. The specific preparation method is as follows:

[0122] a. Weigh 1 g of zirconium salt (zirconium tetrachloride) and add it to a beaker containing 50 mL of N,N-dimethylformamide. Mix the zirconium salt and N,N-dimethylformamide, and stir at a stirring speed of 300 revolutions per minute for 15 min to obtain solution A;

[0123] b. Weigh 1 g of terephthalic acid and add it to a beaker containing 50 mL of N,N-dimethylformamide. Mix the terephthalic acid and N,N-dimethylformamide, and stir at a stirring speed of 300 revolutions per minute for 15 min to obtain solution B;

[0124] c. Slowly and continuously pour Solution B into Solution A while gently stirring to obtain a uniformly mixed reaction solution (the volume ratio of Solution A to Solution B is 1:1). Then transfer the reaction solution to a 200 mL polytetrafluoroethylene-lined reaction kettle, seal it, and place it in an oven preheated to 120 °C for hydrothermal reaction. The conditions of the hydrothermal reaction include: temperature of 120 °C, time of 12 h, and keep the oven temperature constant during this period. After the hydrothermal reaction, let the reaction kettle cool naturally to room temperature to obtain the material. Filter the material to obtain the solid product, and wash the solid product by centrifugation three times with absolute ethanol (the rotation speed for each centrifugal washing of the solid product is 10,000 revolutions per minute, and the time is 10 min). Then place the centrifugally washed solid product in a vacuum drying oven for drying. The drying conditions include: temperature of 60 °C, time of 24 h, to obtain a pure micro-nano hypersensitive material.

[0125] Comparative Example 4

[0126] Implemented according to the method of Example 11, except that in step S1, the micro-nano hypersensitive material of Comparative Example 3 is used to replace the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 to obtain a gas sensor.

[0127] Test Example 1

[0128] Perform scanning electron microscopy (SEM) observation on the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4. The SEM image is as Figure 2 shown. It can be seen from Figure 2 that the prepared UIO-66@Hf-MOF micro-nano hypersensitive material is a two-dimensional sheet structure. This two-dimensional structure provides more adsorption and reaction surfaces for gas molecules, which may enhance the gas-sensing performance of the material. At the same time, it can be clearly seen that UIO-66 nanoparticles are loaded on the surface of the Hf-MOF nanosheets, and these particles are evenly distributed on the Hf-MOF nanosheets, forming a composite material. This composite structure combines the advantages of UIO-66 and Hf-MOF, further improving the gas-sensing performance of the material, especially the detection sensitivity for dissolved gases in the oil of power equipment. Perform scanning electron microscopy (SEM) observation on the UIO-66@Hf-MOF micro-nano hypersensitive materials of Examples 5 and 6 in the same way. The results are similar to the SEM image of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4. The UIO-66@Hf-MOF micro-nano hypersensitive materials of Examples 5 and 6 are both two-dimensional sheet structures, and UIO-66 nanoparticles are loaded on the surface of the Hf-MOF nanosheets.

[0129] Test Example 2

[0130] XRD tests were respectively carried out on the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 and the Hf-MOF material of Comparative Example 1. The XRD patterns are as shown in Figure 3 . It can be seen from Figure 3 that compared with the Hf-MOF material, new diffraction peaks appeared in the UIO-66@Hf-MOF micro-nano hypersensitive material. This is because due to the loading of UIO-66 nanoparticles, new diffraction peaks appeared in the crystal structure of the prepared micro-nano hypersensitive material, which represents new crystal structure characteristics and optimizes the performance of the micro-nano hypersensitive material, especially improving its gas-sensing performance. The UIO-66@Hf-MOF micro-nano hypersensitive materials of Examples 5 and 6 were respectively subjected to XRD tests in the same way, and the results were similar to the XRD patterns of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4.

[0131] Test Example 3

[0132] The N2 adsorption isotherm of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 was detected. The specific operation is as follows: First, the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 was placed in a specific surface area and porosity analyzer test device. Subsequently, the UIO-66@Hf-MOF micro-nano hypersensitive material was degassed at 120 °C to remove the impurity gases adsorbed on the surface of the UIO-66@Hf-MOF micro-nano hypersensitive material. Then, nitrogen was introduced into the test system as the adsorbate. By precisely controlling the partial pressure of nitrogen, the nitrogen concentration was gradually increased, and the adsorption amount of nitrogen by the UIO-66@Hf-MOF micro-nano hypersensitive material at different nitrogen concentrations was recorded. By plotting the relationship curve between the adsorption amount and the partial pressure of nitrogen, the N2 adsorption isotherm of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 was obtained.

[0133] The N2 adsorption isotherm of the UIO-66@Hf-MOF micro-nano hypersensitive material of Example 4 is as shown in Figure 4 . It can be seen from Figure 4 that the specific surface area of this UIO-66@Hf-MOF micro-nano hypersensitive material is as high as 954 m 2 / g, which far exceeds the specific surface area of conventional metal oxide materials. And the N2 adsorption isotherm shows that this material has micropores and mesopores. The existence of micropores provides a large number of adsorption sites for gas molecules, enabling the material to efficiently capture and fix gas molecules; while the mesopores serve as channels for the diffusion and transmission of gas molecules inside the material, helping gas molecules quickly reach the adsorption sites and promoting the adsorption and desorption processes.

[0134] The N2 adsorption isotherms of the UIO-66@Hf-MOF micro-nano hypersensitive materials of Examples 5 and 6 were detected respectively according to the same method. After detection, the specific surface areas of the UIO-66@Hf-MOF micro-nano hypersensitive materials of Examples 5 and 6 were 931 m 2 / g and 895 m 2 / g respectively, and both had micropores and mesopores.

[0135] Test Example 4

[0136] With the adsorption of target gas molecules on the surface of the micro-nano hypersensitive sensor, electrons transfer from the sensor material to the target molecules, resulting in a change in the resistance of the micro-nano hypersensitive sensor. This change can be converted into an electrical signal for output, thus realizing the detection of the target gas. This test example is used to evaluate the gas-sensing performance of the micro-nano hypersensitive sensor for dissolved gases H2 and CO in power equipment oil.

[0137] Detect the response curve of the gas-sensing sensor of Example 8 to 5 ppm H2: First, place the gas-sensing sensor of Example 8 in a test chamber with a controllable atmosphere. Subsequently, inject a mixed gas containing 5 ppm hydrogen concentration (usually using nitrogen or air as the balance gas) into the test chamber through an accurate gas flow controller. At the same time, use a high-precision temperature and humidity control system to maintain the stability and consistency of the test environment, and detect the response values of the gas-sensing sensor of Example 8 to 5 ppm H2 at different temperatures respectively, and obtain the response curve, as Figure 5 shown.

[0138] Detect the response curve of the gas-sensing sensor of Example 8 to 5 ppm CO: First, place the gas-sensing sensor of Example 8 in a test chamber with a controllable atmosphere. Subsequently, inject a mixed gas containing 5 ppm CO concentration (usually using nitrogen or air as the balance gas) into the test chamber through an accurate gas flow controller. At the same time, use a high-precision temperature and humidity control system to maintain the stability and consistency of the test environment, and detect the response values of the gas-sensing sensor of Example 8 to 5 ppm CO at different temperatures respectively, and obtain the response curve, as Figure 6 shown.

[0139] From Figure 5 and Figure 6 it can be seen that with the increase of temperature, the response values of the gas-sensing sensor of Example 8 show a trend of first increasing and then decreasing. The response values of the gas-sensing sensor of Example 8 to H2 and CO reach the maximum values of 78 and 52 respectively when the working temperature is 90 °C;

[0140] Among them, the calculation of the response value uses the calculation formula of the n-type semiconductor micro-nano hypersensitive sensor: S = R g / R a , S is the response value, Rg is the resistance value of the micro-nano hypersensitive sensor in air, R a is the resistance value of the micro-nano hypersensitive sensor in the gas to be measured;

[0141] To detect the long-term stability of the gas sensor in Example 8, the long-term stability test method is as follows: Use a gas mixing system to accurately prepare a 5 ppm H2 gas test sample (N2 as the background gas) to ensure the accuracy and stability of the gas concentration. Place the gas sensor in Example 8 in the test environment and continuously expose it to 5 ppm H2 gas at 90 °C for long-term stability testing. During the test, regularly record the response value of the gas sensor in Example 8 every 5 hours for a total of 50 hours.

[0142] Figure 7 For the long-term stability test of the gas sensor in Example 8 to 5 ppm H2 at 90 °C, it can be seen that during the long-term test of the gas sensor in Example 8, the response value fluctuates very little, indicating that the gas sensor in Example 8 has good long-term stability;

[0143] According to the same method, the response curves and long-term stability tests of the gas sensors in Examples 9-10, and the gas sensors in Comparative Examples 2 and 4 to 5 ppm H2 and 5 ppm CO were detected respectively. It was found that the trends of the response curves of the gas sensors in Examples 9-10, and the gas sensors in Comparative Examples 2 and 4 to 5 ppm H2 and 5 ppm CO are similar to those of the gas sensor in Example 8 to 5 ppm H2 and 5 ppm CO. That is, as the temperature increases, the response value of the micro-nano hypersensitive sensor first increases and then decreases, and at the working temperature of 90 °C, the response value reaches the maximum. The specific maximum response values are shown in Table 1; the long-term stability tests of the gas sensors in Examples 9-10, and the gas sensors in Comparative Examples 2 and 4 to 5 ppm H2 are similar to the long-term stability test results of the gas sensor in Example 8 to 5 ppm H2 at 90 °C, that is, during the long-term test, the response value fluctuates very little and has good long-term stability.

[0144] Table 1

[0145]

[0146] From the results in Table 1, it can be seen that the gas sensor in Example 8 uses Hf-MOF as the substrate and in-situ loads UIO-66 nanoparticles, showing the highest response values (78, 52) to hydrogen and carbon monoxide, indicating that the combination of two-dimensional Hf-MOF nanosheets and UIO-66 nanoparticles significantly improves the gas-sensing performance of the material. The gas sensors prepared in the other examples also show good gas-sensing performance.

[0147] The gas sensor of Comparative Example 2 only used Hf-MOF material as the substrate and did not load UIO-66. Compared with the gas sensor of Example 8, the maximum response value to hydrogen decreased to 36, and the maximum response value to carbon monoxide decreased to 28, indicating that the absence of UIO-66 may affect the gas-sensing performance of the material.

[0148] The gas sensor of Comparative Example 4 only used UIO-66 as the substrate, and the maximum response value to hydrogen decreased to 45, and the maximum response value to carbon monoxide decreased to 31, indicating that the absence of Hf-MOF material also has a negative impact on the gas-sensing performance.

[0149] The high response value of the gas sensor of Example 8 indicates that two-dimensional Hf-MOF has layered open channels and abundant exposed active sites, which is conducive to the diffusion and pre-enrichment of gas molecules (such as CO, H2). The in-situ loading of UIO-66 further enhances the capture ability of gas molecules. Hf 4+ and Zr 4+ As Lewis acid sites, they can have different intensities of interaction with CO (dipole moment 0.11 D) and H2 (non-polar). The two-dimensional electron transport channel of Hf-MOF and the nanoparticles of UIO-66 form a Schottky junction, amplifying the resistance change signal. The organic ligands of Hf-MOF (such as terephthalic acid) can enhance the specific adsorption of CO by introducing functional groups such as -NH2 and -OH, while the rigid structure of UIO-66 (Zr6O4(OH)4 cluster) can stabilize the charge transfer process. High-sensitivity detection of CO and H2 is achieved.

[0150] It should be understood that the parts not elaborated in detail in this specification all belong to the prior art.

[0151] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A UIO-66@Hf-MOF micro-nano hypersensitive material, characterized in that, The UIO-66@Hf-MOF micro-nano hypersensitive material includes an Hf-MOF material, and the UIO-66 material is loaded on the surface of the Hf-MOF material.

2. The UIO-66@Hf-MOF micro-nano hypersensitive material according to claim 1, characterized in that, The specific surface area of the UIO-66@Hf-MOF micro-nano hypersensitive material is 800-1200 m 2 / g.

3. A preparation method of the UIO-66@Hf-MOF micro-nano hypersensitive material according to claim 1 or 2, characterized in that, The preparation method includes the following steps: Mix hafnium salt, aromatic polycarboxylic acid A, organic solvent A and organic acid to obtain a mixed material, react the mixed material, cool after the reaction ends to obtain material A, perform solid-liquid separation on material A to obtain solid product A, wash and dry the solid product A to obtain the Hf-MOF material; Mix the Hf-MOF material, zirconium salt and organic solvent B, and stir to obtain solution A; Mix aromatic polycarboxylic acid B and organic solvent C, and stir to obtain solution B; Mix solution A and solution B to obtain a reaction solution, then perform a hydrothermal reaction on the reaction solution, cool after the hydrothermal reaction ends to obtain material B, perform solid-liquid separation on material B to obtain solid product B, wash and dry the solid product B to obtain the UIO-66@Hf-MOF micro-nano hypersensitive material.

4. The preparation method according to claim 3, characterized in that, The hafnium salt is selected from one or more of hafnium tetrachloride, hafnium oxychloride and hafnium oxynitrate; and / or The organic solvent A is methanol and / or N,N-dimethylformamide; and / or The dosage ratio of the hafnium salt, aromatic polycarboxylic acid A and organic solvent A is 1 g: 1-2 g: 50-100 mL; and / or The aromatic polycarboxylic acid A is selected from one or more of 1,3,5-tris(4-carboxyphenyl)benzene, trimellitic acid and phthalic acid; and / or The solid-liquid ratio of the hafnium salt and the organic acid is 1 g: 50-100 mL; and / or The organic acid is selected from one or more of formic acid, acetic acid and propionic acid.

5. The preparation method according to claim 3 or 4, characterized in that, The specific operation of mixing the hafnium salt, aromatic polycarboxylic acid A, organic solvent A and organic acid includes: mixing the hafnium salt, aromatic polycarboxylic acid A and organic solvent A and then performing a first stirring to obtain a mixed solution, then mixing the mixed solution with the organic acid, and then performing a second stirring to obtain a mixed material.

6. The preparation method according to claim 5, wherein The conditions of the first stirring include: the stirring speed is 300-800 revolutions per minute, and the stirring time is 15-20 min; and / or The conditions of the second stirring include: the stirring speed is 300-800 revolutions per minute, and the stirring time is 15-20 min.

7. The preparation method according to claim 3 or 4, characterized in that, The conditions of the reaction include: the temperature is 120-180 °C, and the time is 24-48 hours.

8. The preparation method according to claim 3, characterized in that, The dosage ratio of the Hf-MOF material, zirconium salt and organic solvent B is 1 g: 1 g: 50-100 mL; and / or The zirconium salt is selected from one or more of zirconium oxychloride, zirconium tetrachloride and zirconium nitrate; and / or The organic solvent B is methanol and / or N,N-dimethylformamide; and / or Mix the Hf-MOF material, zirconium salt and organic solvent B, and stir at a stirring speed of 300-500 revolutions per minute for 15-30 min to obtain solution A.

9. The preparation method according to claim 3 or 8, characterized in that, The solid-liquid ratio of the aromatic polycarboxylic acid B and the organic solvent C is 1 g: 50-100 mL; and / or The aromatic polycarboxylic acid B is selected from one or more of terephthalic acid, trimellitic acid, and phthalic acid biphenyl; and / or The organic solvent C is methanol and / or N,N-dimethylformamide; and / or The aromatic polycarboxylic acid B and the organic solvent C are mixed and stirred at a stirring speed of 300 - 800 revolutions per minute for 15 - 20 min to obtain solution B.

10. The preparation method according to claim 3, wherein, The volume ratio of solution A to solution B is 1:1 - 2; and / or The conditions of the hydrothermal reaction include: the temperature is 120 - 180 °C and the time is 12 - 18 h.

11. Use of the UIO-66@Hf-MOF micro-nano hypersensitive material according to claim 1 or 2 in a gas sensor.

12. A gas sensor, characterized in that, The gas sensor includes a conductive melamine sponge, and the conductive melamine sponge includes a melamine sponge, and the surface and pores of the melamine sponge are loaded with the UIO-66@Hf-MOF micro-nano hypersensitive material according to claim 1 or 2.

13. A method for preparing the gas sensor according to claim 12, characterized in that, It includes the following steps: The UIO-66@Hf-MOF micro-nano hypersensitive material is mixed with methanol and stirred to obtain a conductive solution; The melamine sponge is subjected to the treatment of loading the UIO-66@Hf-MOF micro-nano hypersensitive material to obtain a conductive melamine sponge; the operation of the treatment of loading the UIO-66@Hf-MOF micro-nano hypersensitive material includes: immersing the melamine sponge in the conductive solution and then drying; Electrode materials are assembled on both sides of the conductive melamine sponge, and then conductive copper wires are welded to the electrode materials to obtain a gas sensor.

14. The preparation method according to claim 13, wherein, The content of the UIO-66@Hf-MOF micro-nano hypersensitive material in the conductive solution is 5 - 10 wt%; and / or The UIO-66@Hf-MOF micro-nano hypersensitive material is mixed with methanol and stirred at a stirring speed of 300 - 800 revolutions per minute for 15 - 20 min to obtain a conductive solution; and / or The melamine sponge is subjected to the treatment of loading the UIO-66@Hf-MOF micro-nano hypersensitive material 4 - 6 times to obtain a conductive melamine sponge; and / or The conditions of the drying include: the temperature is 50 - 80 °C and the time is 4 - 8 hours; and / or The electrode material is a conductive metal tape.

15. Use of the gas sensor according to claim 12 in the detection of H2 and CO.

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