CN117470919A - ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, and preparation method and application thereof - Google Patents

ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, and preparation method and application thereof Download PDF

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CN117470919A
CN117470919A CN202311345342.2A CN202311345342A CN117470919A CN 117470919 A CN117470919 A CN 117470919A CN 202311345342 A CN202311345342 A CN 202311345342A CN 117470919 A CN117470919 A CN 117470919A
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zinc
hydroxyfluoride
zif
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dimensional matrix
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吴莉莉
金之栋
赵金博
刘久荣
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Shandong University
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Abstract

The invention discloses a ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, a preparation method and application thereof, wherein the ZIF-8/zinc hydroxyfluoride composite gas-sensitive material comprises a zinc hydroxyfluoride three-dimensional matrix and a nano porous ZIF-8 layer growing on the surface of the zinc hydroxyfluoride three-dimensional matrix; the three-dimensional zinc hydroxyfluoride matrix is of a micron level and is assembled by zinc hydroxyfluoride nanorods. The invention adopts a solvothermal synthesis route, has simple process and low cost, and the prepared snowflake ZIF-8/zinc hydroxyfluoride gas-sensitive material has the characteristics of low working temperature, good selectivity, high sensitivity, excellent humidity resistance and stability and the like.

Description

ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, and preparation method and application thereof
Technical Field
The invention relates to the technical field of gas sensing materials, in particular to a ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, and a preparation method and application thereof.
Background
The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.
Nitrogen dioxide (NO) 2 ) Is a brownish red gas with toxic and pungent smell, can cause serious environmental pollution problem and can cause harm to human health, so that the concentration of nitrogen dioxide in the atmosphere needs to be strictly controlled, and the annual average concentration limit value of the nitrogen dioxide in the ambient air is lower than 40 mu g/m 3 。
The resistance type semiconductor gas sensor is widely focused and applied due to the advantages of simple preparation, high detection precision and the like, and the detection principle is that the oxidation-reduction characteristic of the gas to be detected is utilized, and the gas to be detected can generate electron exchange after contacting with a material to change the conductivity of the gas sensor so as to generate gas-sensitive response. Zinc hydroxyfluoride as a novel semiconductor gas-sensitive material, and its unique electronic structure can optimize the NO of the sensing material 2 Is provided. However, the relative humidity of the working environment of the general resistance type semiconductor gas sensor is generally higher, and a large amount of surface hydroxyl groups generated under the high humidity condition occupy effective gas adsorption sites of the resistance type semiconductor gas sensor material to inhibit the gas sensitivity performance of the resistance type semiconductor gas sensor. The poor stability against humidity can severely inhibit the specific application of the resistive semiconductor gas sensitive material.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide the ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, and the preparation method and the application thereof.
In order to achieve the above object, the present invention is realized by the following technical scheme:
in a first aspect, the invention provides a ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, which comprises a zinc hydroxyfluoride three-dimensional matrix and a nano-porous ZIF-8 layer growing on the surface of the zinc hydroxyfluoride three-dimensional matrix;
the diameter of the zinc hydroxyfluoride three-dimensional matrix is 10-100 mu m, the zinc hydroxyfluoride three-dimensional matrix is assembled by zinc hydroxyfluoride nanorods, and the diameter of the zinc hydroxyfluoride nanorods is 100-500nm;
the mass ratio of the nano-porous ZIF-8 to the zinc hydroxyfluoride three-dimensional matrix is 0.03-0.12:1.
ZIF-8 is a zeolite imidazole skeleton, the structure of which has excellent porosity and hydrophobicity, the porous performance of which effectively improves the specific surface area and the porosity of the material, and is beneficial to NO 2 The unique pore structure of the gas diffusion and gas-sensitive response process can selectively permeate different gas molecules, thereby improving NO 2 The probability of the contact of gas molecules and zinc hydroxyfluoride improves the selectivity; the hydrophobic property of the material effectively eliminates signal interference of water molecules in a high humidity environment on gas-sensitive test, and improves the gas-sensitive stability of the material in the high humidity environment.
In some embodiments, the ZIF-8 is a porous regular dodecahedron structure.
In some embodiments, the zinc hydroxyfluoride three-dimensional matrix is radial.
In a second aspect, the invention provides a preparation method of the ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, which comprises the following steps:
mixing divalent inorganic zinc salt, fluorine-containing compound and alkali in proportion, and performing primary solvothermal reaction to prepare a zinc hydroxyfluoride three-dimensional matrix material;
uniformly dispersing the prepared zinc hydroxyfluoride three-dimensional matrix material and 2-methylimidazole salt in a solvent according to the mass ratio of 1:0.4-6, and then performing a secondary solvothermal reaction to prepare the ZIF-8 in-situ composite zinc hydroxyfluoride material.
The preparation principle of the gas-sensitive material in the invention is as follows: in the first step of synthesis of zinc hydroxyfluoride precursor, zn in divalent inorganic zinc salt 2+ F produced by hydrolysis with fluorine-containing compounds - OH generated by alkali source - The ions react in the solvent process to generate zinc hydroxyfluoride white precipitate, and the morphology is snowflake-shaped three-dimensional matrix structure with the particle diameter of about 11 mu m and composed of nano rods;
in the second step of in-situ composite ZIF-8 synthesis, because ZIF-8 is a material containing Zn 2+ The zeolite imidazole salt structure as a framework, so that no extra zinc source is needed to be introduced into the solution in the synthesis, the first stepDispersing the one-step synthesized zinc hydroxyfluoride precursor into a solvent, adding 2-methylimidazole salt as an organic ligand for synthesizing ZIF-8, wherein in solvothermal synthesis, the 2-methylimidazole can be combined with Zn on the surface of the zinc hydroxyfluoride structure 2+ And the ZIF-8 is formed by combination, so that the ZIF-8 is in-situ compounded on the surface of the zinc hydroxyfluoride.
In some embodiments, the molar ratio of divalent inorganic zinc salt, fluorine-containing compound, and base is 1:0.3-0.8:0.5-1.5.
In some embodiments, the divalent inorganic zinc salt is selected from Zn (CH 3 COO)·2H 2 O、Zn 3 (C 6 H 5 O 7 ) 2 Or ZnSO 4 One or a combination thereof;
or, the fluorine-containing compound is selected from NH 4 F、Na 2 SiF 6 Or NaBF 4 One or a combination thereof;
or, the base is selected from (CH) 2 NH 2 ) 2 、NH 3 ·H 2 O or C 6 H 12 N 4 One or a combination thereof.
In some embodiments, the temperature of the primary solvothermal reaction is 70-180 ℃ and the reaction time is 1-24 hours;
preferably, the temperature of the primary solvothermal reaction is 80-120 ℃ and the reaction time is 1-6h.
In some embodiments, the primary solvothermal solvent is water;
or, the solvent of the secondary solvothermal is anhydrous methanol.
In some embodiments, the temperature of the secondary solvothermal reaction is 50-120 ℃ and the reaction time is 2-40 hours;
preferably, the temperature of the secondary solvothermal reaction is 60-90 ℃ and the reaction time is 5-24h.
In some embodiments, the zinc hydroxyfluoride three-dimensional matrix material and the 2-methylimidazole salt are present in a mass ratio of 1:0.4-4.
In a third aspect, the invention provides the ZIF-8/zinc hydroxyfluoride composite gas-sensitive material for preparing NO 2 Gas sensor or NO 2 Application in concentration detection.
The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:
(1) The gas-sensitive material prepared by the invention has rich pore diameter structure and larger specific surface area (277.9 m) 2 Per g), which may promote NO 2 Diffusion of gas and provision of more gas adsorption sites, helping to enhance the material's resistance to NO 2 Molecular recognition and response capabilities.
(2) The ZIF-8 porous structure used by the gas-sensitive material prepared by the invention is deposited on the surface of the zinc hydroxyfluoride material, and the ZIF-8 serving as a porous structure can selectively permeate different gases to be detected, such as NO 2 At the same time, part of gas is isolated, thereby further improving the NO detection of the material 2 Is used for optimizing the gas-sensitive performance.
(3) The zinc hydroxyfluoride material used for the gas-sensitive material prepared by the invention has a unique electronic structure, and the energy band structure thereof inhibits the formation of chemisorbed oxygen and promotes NO 2 The chemical adsorption of water molecules on the surface of the material is effectively eliminated during sensing, the formation of surface hydroxyl is avoided, and the water molecules in the environment mainly act on the material in a physical adsorption mode. In addition, ZIF-8 is used as a material with hydrophobicity, and the deposition of the material on the surface of the zinc hydroxyfluoride material can also improve the hydrophobicity of the material and reduce the physical adsorption of water, so that the high humidity stability of the material is simultaneously improved from the action modes of physical and chemical adsorption of water molecules, and the serious interference of humidity on gas-sensitive detection signals is avoided.
(4) The sensor prepared from the gas-sensitive material prepared by the invention is characterized in that NO 2 The assay showed excellent selectivity, lower optimum operating temperature (200 ℃) and higher response value (12.5 vs. 10ppmNO 2 ) Low NO 2 Detection limit (500 ppb) and excellent stability against humidity (response value up to 88% at 80% RH) under 20% RH conditions.
(5) The synthesis process for preparing the gas-sensitive material is simple and feasible, environment-friendly, pollution-free and low in manufacturing cost.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is an XRD diffraction pattern of snowflake-shaped zinc hydroxyfluoride precursor (a), pure ZIF-8 crystals (b) and in situ composite zinc hydroxyfluoride (c) of ZIF-8 prepared in examples 1-6 of the present invention.
FIG. 2 is an SEM image of a snowflake-shaped zinc hydroxyfluoride precursor and an in situ composite zinc hydroxyfluoride of ZIF-8 prepared according to examples 1-5 of the present invention; wherein a1, a2 are SEM images of the sample prepared in example 1; b1 B2 is an SEM image of the sample prepared in example 2; c1 C2 is an SEM image of the sample prepared in example 3; d1 D2 is an SEM image of the sample prepared in example 4; e1 E2 is an SEM image of the sample prepared in example 5.
FIG. 3 is TEM (a and b) and HRTEM (c and d) graphs of in-situ composite zinc hydroxyfluoride gas sensitive materials of ZIF-8 prepared in example 4 of the present invention.
FIG. 4 is a TG pattern of an in-situ composite ZIF-8 zinc hydroxyfluoride gas-sensitive material prepared in example 4 of the present invention.
FIG. 5 is an XPS plot of snowflake-shaped zinc hydroxyfluoride precursors prepared in examples 1 and 4 of the present invention and zinc hydroxyfluoride of in situ composite ZIF-8.
FIG. 6 is BET and BJH plots of the snowflake zinc hydroxyfluoride precursors prepared in examples 1 and 4 and the in situ composite zinc hydroxyfluoride of ZIF-8 of the present invention, where a is the BET plot of the snowflake zinc hydroxyfluoride precursor prepared in example 1; b is a BJH diagram of the snowflake zinc hydroxyfluoride precursor prepared in example 1; c is the BET plot of the zinc hydroxyfluoride of in situ composite ZIF-8 prepared in example 4; d is a BJH diagram of the in-situ composite zinc hydroxyfluoride of ZIF-8 prepared in example 4.
FIG. 7 is a graph of UV-DRs (a) and band gap-absorbance of snowflake-shaped zinc hydroxyfluoride precursors and zinc hydroxyfluoride of in situ-complexed ZIF-8 prepared in examples 1-5 of the present invention.
FIG. 8 is a VB-XPS plot of a snowflake-shaped zinc hydroxyfluoride precursor and an in situ composite zinc hydroxyfluoride of ZIF-8 prepared in examples 1-5 of the present invention, where b is a partial magnified view of a.
FIG. 9 shows the present inventionSnowflake-like zinc hydroxyfluoride precursor prepared in examples 1-5 and in situ composite zinc hydroxyfluoride to 10ppmNO of ZIF-8 2 A response value versus operating temperature plot.
FIG. 10 shows the snowflake-like zinc hydroxyfluoride precursor and the in situ composite zinc hydroxyfluoride of ZIF-8 prepared in examples 1 and 4 of the present invention at 200deg.C for different concentrations of NO 2 Response value curves of (a).
FIG. 11 is a graph showing the response of snowflake-shaped zinc hydroxyfluoride precursors and in situ composite zinc hydroxyfluoride of ZIF-8 prepared in examples 1-5 of the present invention to 10ppm of different gases at 200deg.C.
FIG. 12 shows the snowflake-like zinc hydroxyfluoride precursor and the in situ composite zinc hydroxyfluoride of ZIF-8 prepared in examples 1 and 4 of the present invention at 200℃against 10ppmNO under different relative humidity conditions 2 Response value curves of (a).
FIG. 13 is a schematic view of a gas sensor prepared in example 9 of the present invention.
Detailed Description
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
As described in the background, existing NO 2 The invention provides an in-situ composite ZIF-8/zinc hydroxyfluoride snowflake-shaped gas-sensitive material and a preparation method thereof, and further describes the invention by combining specific embodiments.
Example 1
A preparation method of zinc hydroxyl fluoride snowflake-shaped gas-sensitive material comprises the following steps:
1) Zn (CH) 3 COO) 2 ·2H 2 O、NH 4 F and C 6 H 12 N 4 Adding the mixture into 75mL of deionized water solvent according to the molar mass ratio of 1:0.5:1, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction for 2h at 95 ℃, and performing centrifugal washing on the product after the reaction is finished,Drying to obtain snowflake zinc hydroxyfluoride.
Example 2
The preparation method of the in-situ composite ZIF-8/zinc hydroxyfluoride snowflake-shaped gas-sensitive material comprises the following steps:
1) Zn is added 3 (C 6 H 5 O 7 ) 2 、NaBF 4 And NH 3 ·H 2 Adding O into 80mL deionized water solvent according to the molar mass ratio of 1:0.3:1.5, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction at 70 ℃ for 24 hours, and centrifugally washing and drying the product after the reaction is finished to obtain snowflake zinc hydroxyfluoride precursor.
2) And (2) adding the snowflake-shaped zinc hydroxyfluoride precursor prepared in the step (1) and 2-methylimidazole into 40mL of anhydrous methanol solvent according to a molar mass ratio of 1:0.4, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction at 70 ℃ for 24 hours, and performing centrifugal washing and drying on the product after the reaction is finished to obtain the zinc hydroxyfluoride snowflake-shaped material of the in-situ composite ZIF-8.
Example 3
The preparation method of the in-situ composite ZIF-8/zinc hydroxyfluoride snowflake-shaped gas-sensitive material comprises the following steps:
1) Zn (CH) 3 COO) 2 ·2H 2 O、Na 2 SiF 6 And (CH) 2 NH 2 ) 2 Adding the mixture into 60mL of deionized water solvent according to the molar mass ratio of 1:0.8:0.5, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction for 1h at 180 ℃, and centrifugally washing and drying the product after the reaction is finished to obtain snowflake-shaped zinc hydroxyfluoride precursor.
2) And (2) adding the snowflake-shaped zinc hydroxyfluoride precursor prepared in the step (1) and 2-methylimidazole into 80mL of anhydrous methanol solvent according to a molar mass ratio of 1:0.8, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction at 50 ℃ for 40h, and performing centrifugal washing and drying on the product after the reaction is finished to obtain the zinc hydroxyfluoride snowflake-shaped material of the in-situ composite ZIF-8.
Example 4
The preparation method of the in-situ composite ZIF-8/zinc hydroxyfluoride snowflake-shaped gas-sensitive material comprises the following steps:
1) Zn is added 3 (C 6 H 5 O 7 ) 2 、NH 4 F and C 6 H 12 N 4 Adding the mixture into 70mL of deionized water solvent according to the molar mass ratio of 1:0.5:1.5, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction for 6 hours at 80 ℃, and centrifugally washing and drying the product after the reaction is finished to obtain snowflake-shaped zinc hydroxyfluoride precursor.
2) And (2) adding the snowflake-shaped zinc hydroxyfluoride precursor prepared in the step (1) and 2-methylimidazole into 30mL of anhydrous methanol solvent according to a molar mass ratio of 1:1.2, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction at 60 ℃ for 5 hours, and performing centrifugal washing and drying on the product after the reaction is finished to obtain the zinc hydroxyfluoride snowflake-shaped material of the in-situ composite ZIF-8.
Example 5
The preparation method of the in-situ composite ZIF-8/zinc hydroxyfluoride snowflake-shaped gas-sensitive material comprises the following steps:
1) Zn (CH) 3 COO) 2 ·2H 2 O、NaBF 4 And (CH) 2 NH 2 ) 2 Adding the mixture into 70mL of deionized water solvent according to the molar mass ratio of 1:0.3:1, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction for 6h at 120 ℃, and centrifugally washing and drying the product after the reaction is finished to obtain snowflake-shaped zinc hydroxyfluoride precursor.
2) And (2) adding the snowflake-shaped zinc hydroxyfluoride precursor prepared in the step (1) and 2-methylimidazole into 30mL of anhydrous methanol solvent according to a molar mass ratio of 1:4, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction at 60 ℃ for 5 hours, and performing centrifugal washing and drying on the product after the reaction is finished to obtain the zinc hydroxyfluoride snowflake-shaped material of the in-situ composite ZIF-8.
Example 6
A preparation method of a regular dodecahedron ZIF-8 material comprises the following steps:
1) Zn (CH) 3 COO) 2 ·2H 2 Adding O and 2-methylimidazole into 75mL deionized water solvent according to a molar mass ratio of 1:4, performing ultrasonic treatment for 10min, stirring to be uniform, and mixing the mixtureTransferring the solution into a 100mL reaction kettle, performing solvothermal reaction for 24 hours at 70 ℃, and centrifugally washing and drying the product after the reaction is finished to obtain the regular dodecahedron ZIF-8 material.
Example 7
The preparation method of the in-situ composite ZIF-8/zinc hydroxyfluoride snowflake-shaped gas-sensitive material comprises the following steps:
1) ZnSO is added to 4 、NH 4 F and C 6 H 12 N 4 Adding the mixture into 75mL of deionized water solvent according to the molar mass ratio of 1:0.5:1.5, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction for 1h at 140 ℃, and centrifugally washing and drying the product after the reaction is finished to obtain snowflake-shaped zinc hydroxyfluoride precursor.
2) And (2) adding the snowflake-shaped zinc hydroxyfluoride precursor prepared in the step (1) and 2-methylimidazole into 65mL of anhydrous methanol solvent according to a molar mass ratio of 1:2, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction at 90 ℃ for 5 hours, and performing centrifugal washing and drying on the product after the reaction is finished to obtain the zinc hydroxyfluoride snowflake-shaped material of the in-situ composite ZIF-8.
Example 8
The preparation method of the in-situ composite ZIF-8/zinc hydroxyfluoride snowflake-shaped gas-sensitive material comprises the following steps:
1) Zn is added 3 (C 6 H 5 O 7 ) 2 、NH 4 F and C 6 H 12 N 4 Adding the mixture into 65mL of deionized water solvent according to the molar mass ratio of 1:0.3:0.8, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction for 12h at 90 ℃, and centrifugally washing and drying the product after the reaction is finished to obtain snowflake-shaped zinc hydroxyfluoride precursor.
2) And (3) adding the snowflake-shaped zinc hydroxyfluoride precursor prepared in the step (1) and 2-methylimidazole into 70mL of anhydrous methanol solvent according to a molar mass ratio of 1:3, transferring the solution into a 100mL reaction kettle, performing solvothermal reaction at 90 ℃ for 40h, and performing centrifugal washing and drying on the product after the reaction is finished to obtain the zinc hydroxyfluoride snowflake-shaped material of the in-situ composite ZIF-8.
Example 9
The preparation method of the gas sensor specifically comprises the following steps:
the gas-sensitive materials prepared in the above examples 1 to 8 were prepared according to the mass ratio of the materials to anhydrous methanol of 1:3 mixing and grinding uniformly to obtain slurry, uniformly coating the obtained slurry on a gas sensor substrate, then placing the coated substrate in a 100 ℃ oven for drying for 5min, taking out, repeating the coating and drying operation for 5 times, placing the substrate in 100 ℃ for 24h until the substrate is thoroughly dried, and taking out to obtain the gas sensor.
Performance testing
FIG. 1 shows XRD diffraction patterns of snowflake-shaped zinc hydroxyfluoride precursors, pure ZIF-8 crystals and in-situ composite zinc hydroxyfluoride of ZIF-8 prepared in examples 1-6 of the invention, and in FIG. 1a, the material phase obtained in example 1 shows pure ZnOHF and has good crystallinity. The material host phases obtained in examples 2-5 still exhibited ZnOHF, while peaks belonging to other phases appeared at the low angle diffraction peak positions. In FIG. 1b, it can be seen that the phase structure of the pure ZIF-8 crystals prepared in comparative example 6, peaks of other phases are assigned to ZIF-8, and the intensity of diffraction peaks of ZIF-8 increases as the content of 2-methylimidazole salt increases in the synthesis. Analysis of the diffraction peaks of ZnOHF in the range of 20.0-21.5 deg. in XRD in FIG. 1c shows that with in situ recombination of surface ZIF-8, the diffraction peaks of ZnOHF move to low diffraction angles, indicating that the ZnOHF surface Zn 2+ After being captured by 2-methylimidazole salt to form ZIF-8 crystal, partial Zn 2+ Precipitation causes the interplanar spacing of ZnOHF to become large.
FIG. 2 is an SEM image of a snowflake-shaped zinc hydroxyfluoride precursor and an in-situ composite ZIF-8 zinc hydroxyfluoride prepared in examples 1-5 of the present invention, the morphology of the prepared material is a hexagonal snowflake-shaped morphology, the snowflake diameter is about 11 μm, the snowflake-shaped structure is composed of a plurality of ZnOHF nanorods, and the diameter of the nanorods is about 200nm. After the ZIF-8 crystal is compounded on the surface of the ZnOHF in situ, the main morphology of the snowflake-shaped ZnOHF is not damaged, but the nanorods forming the morphology structure tend to be agglomerated, and ZIF-8 materials are separated out on the surface.
FIG. 3 is a TEM and HRTEM image of the in situ composite ZIF-8 hydroxyzinc fluoride gas-sensitive material prepared in example 4 of the present invention, and it can be seen that the obtained material has a snowflake shape, and the diameter size is about 11 μm, which is the same as the result shown by SEM. Meanwhile, ZIF-8 crystals are observed on the surface of the nanorod, and the lattice fringes in the HRTEM figure have a measured interplanar spacing of 0.237nm, which corresponds to a (020) crystal plane of the ZnOHF, so that the obtained material is further proved to be the ZnOHF material with the ZIF-8 in-situ composite surface.
FIG. 4 is a TG pattern of an in-situ composite ZIF-8 ZnOHF gas-sensitive material prepared in example 4 of the present invention. It can be seen that the material maintains good thermal stability below 300 ℃, starts to decompose at 300 ℃, is stable at 700 ℃, and has a mass loss of about 26.0% in a thermogravimetric test, which corresponds to the mass loss in the process of decomposing the two-part structure of ZnOHF and ZIF-8 into ZnO. In addition, the thermal stability of the material indicates that the gas sensor prepared from the material can be operated at an operating temperature of less than 300 ℃.
FIG. 5 is an XPS plot of snowflake-shaped zinc hydroxyfluoride precursors prepared in examples 1 and 4 of the present invention and zinc hydroxyfluoride of in situ composite ZIF-8. The results show that the snowflake-shaped zinc hydroxyfluoride precursor shows peaks of Zn, O and F ion signals, the figure 5a shows peak positions of divalent zinc ions only, the figures 5b-c show single-peak signals of O and F only, the single-peak signals correspond to lattice oxygen and lattice fluorine in ZnOHF respectively, other chemisorbed oxygen is not existed, the precursor in figure 5d has no signal of N, and the signal of N element appears after ZIF-8 in-situ recombination. In addition, after in-situ composite ZIF-8, the binding energy of Zn, O and F is increased, which indicates that Zn 2+ The chemical state of each element of the ZnOHF is changed after the ZIF-8 is precipitated.
FIG. 6 is BET and BJH plots of snowflake-shaped zinc hydroxyfluoride precursors and zinc hydroxyfluoride of in situ composite ZIF-8 prepared in examples 1 and 4 of the present invention. BET results of snowflake-shaped zinc hydroxyfluoride precursor prepared in example 1 show that adsorption curve H of type IV 3 The hysteresis indicates that the material has a mesoporous structure and the specific surface area is 8.5m 2 And/g. The ZnOHF after in-situ composite ZIF-8 shows an I-type adsorption curve, which proves that the material has a molecular sieve structure (ZIF-8) and the specific surface area is 277.9m 2 Per g, about 33 times of the pure sample, greatly improving the specific surface area of the material and simultaneously the materialThe porosity of the material is correspondingly improved, which proves that ZIF-8 can influence the number of gas diffusion and adsorption sites and optimize the gas sensitivity.
FIG. 7 is a graph of UV-DRs and band gap-absorbance of snowflake-shaped zinc hydroxyfluoride precursors and zinc hydroxyfluoride of in situ composite ZIF-8 prepared in examples 1-5 of the present invention. It can be seen that the band gap of the material is continuously reduced along with the growth of the ZIF-8 structure, the band gap is reduced from 3.47eV to 3.02eV, and the reduction of the band gap is helpful to promote electrons to transit from the valence band to the conduction band and participate in the gas-sensitive reaction process, so that the gas-sensitive performance is optimized.
FIG. 8 is a VB-XPS plot of snowflake-shaped zinc hydroxyfluoride precursor and zinc hydroxyfluoride of in-situ composite ZIF-8 prepared in examples 1-5 of the present invention. After calculation, it can be obtained that the valence band position of the material rises from 3.72eV to 3.00eV after in-situ composite ZIF-8, and the conduction band bottom position of the material can be calculated by combining the result of FIG. 7, which is lower than O at the working temperature 2 /O 2 - The electrode potential of the redox couple indicates that none of the resulting materials is capable of producing chemisorbed oxygen. Chemisorption of oxygen components in a high humidity environment can combine with water molecules to form surface hydroxyl groups to occupy effective gas-sensitive response sites, so that the gas-sensitive performance is deteriorated; adsorption of oxygen on the surface of the material inhibits NO 2 And promote gas-sensitive response of the material to the reducing gas, indicating that the prepared material is reactive to NO 2 Exhibit high sensitivity, response value and maintain gas-sensitive performance at high humidity.
FIG. 9 shows a snowflake-shaped zinc hydroxyfluoride precursor and zinc hydroxyfluoride of in situ composite ZIF-8 prepared in examples 1-5 of the present invention against 10ppm NO 2 A response value versus operating temperature plot. The prepared material detects NO 2 The optimal working temperature of (2) is 200 ℃, and compared with a pure ZnOHF sample, a proper amount of ZIF-8 is subjected to in-situ recombination to obtain NO 2 The response was partially improved with the optimal sample set at 200℃for 10ppmNO 2 The response value of (2) reaches 12.5, and the gas-sensitive performance after the growth of the excessive ZIF-8 is inhibited.
FIG. 10 shows the zinc hydroxyfluoride precursor in snowflake form and in situ composite ZIF-8 prepared in example 1 and example 4 of the present inventionFor NO with different concentration at 200 DEG C 2 Response value curves of (a). It can be seen that the two materials are specific to NO 2 The response value to NO increases with increasing operating temperature 2 The detection limit of (2) is 500ppb. At different NO 2 Under the concentration, the response values of the zinc hydroxyfluoride materials of the optimal group of in-situ composite ZIF-8 are higher than those of pure materials, which indicates that the zinc hydroxyfluoride of the in-situ composite ZIF-8 has good NO 2 Identification capability.
FIG. 11 is a graph showing the response of snowflake-shaped zinc hydroxyfluoride precursors and in situ composite zinc hydroxyfluoride of ZIF-8 prepared in examples 1-5 of the present invention to 10ppm of different gases at 200deg.C. It can be seen that all materials are specific to NO 2 The response values of the material are far higher than those of other gases, and the material is proved to be NO 2 All can show excellent selectivity.
FIG. 12 shows the snowflake-like zinc hydroxyfluoride precursor and the in situ composite zinc hydroxyfluoride of ZIF-8 prepared in examples 1 and 4 of the present invention at 200℃against 10ppm NO under different relative humidity conditions 2 Response value curves of (a). It can be seen that for zinc hydroxyfluoride precursors, NO is detected at high humidity 2 When the response value is obviously reduced, the zinc hydroxyfluoride after in-situ ZIF-8 growth has relatively more stable gas-sensitive performance under high humidity and NO under 80% RH 2 The response value of the material is almost the same as that of 20% RH, which shows that the in-situ composite ZIF-8 structure can obviously improve the stability of the material against humidity.
FIG. 13 is a schematic view of a gas sensor prepared in example 9 of the present invention, wherein the gas sensor comprises; gold test electrode, platinum wire, gas sensing material and ceramic substrate.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A ZIF-8/zinc hydroxyfluoride composite gas-sensitive material is characterized in that: comprises a zinc hydroxyfluoride three-dimensional matrix and a nano-porous ZIF-8 layer growing on the surface of the zinc hydroxyfluoride three-dimensional matrix;
the diameter of the zinc hydroxyfluoride three-dimensional matrix is 10-100 mu m, the zinc hydroxyfluoride three-dimensional matrix is assembled by zinc hydroxyfluoride nanorods, and the diameter of the zinc hydroxyfluoride nanorods is 100-500nm;
the mass ratio of the nano-porous ZIF-8 to the zinc hydroxyfluoride three-dimensional matrix is 0.03-0.12:1.
2. the ZIF-8/zinc hydroxyfluoride composite gas sensitive material according to claim 1, wherein: the zinc hydroxyfluoride three-dimensional matrix is radial.
3. The method for preparing the ZIF-8/zinc hydroxyfluoride composite gas-sensitive material according to claim 1 or 2, which is characterized in that: the method comprises the following steps:
mixing divalent inorganic zinc salt, fluorine-containing compound and alkali in proportion, and performing primary solvothermal reaction to prepare a zinc hydroxyfluoride three-dimensional matrix material;
uniformly dispersing the prepared zinc hydroxyfluoride three-dimensional matrix material and 2-methylimidazole salt in a solvent according to the mass ratio of 1:0.4-6, and then performing a secondary solvothermal reaction to prepare the ZIF-8 in-situ composite zinc hydroxyfluoride material.
4. A method of preparation according to claim 3, characterized in that: the molar ratio of the divalent inorganic zinc salt, the fluorine-containing compound and the alkali is 1:0.3-0.8:0.5-1.5.
5. A method of preparation according to claim 3, characterized in that: the divalent inorganic zinc salt is selected from Zn (CH) 3 COO)·2H 2 O、Zn 3 (C 6 H 5 O 7 ) 2 Or ZnSO 4 One or a combination thereof;
or, the fluorine-containing compound is selected from NH 4 F、Na 2 SiF 6 Or NaBF 4 One or a combination thereof;
or, the base is selected from (CH) 2 NH 2 ) 2 、NH 3 ·H 2 O or C 6 H 12 N 4 One or a combination thereof.
6. A method of preparation according to claim 3, characterized in that: the temperature of the primary solvothermal reaction is 70-180 ℃ and the reaction time is 1-24h;
preferably, the temperature of the primary solvothermal reaction is 80-120 ℃ and the reaction time is 1-6h.
7. A method of preparation according to claim 3, characterized in that: the primary solvothermal solvent is water;
or, the solvent of the secondary solvothermal is anhydrous methanol.
8. A method of preparation according to claim 3, characterized in that: the temperature of the secondary solvothermal reaction is 50-120 ℃ and the reaction time is 2-40h;
preferably, the temperature of the secondary solvothermal reaction is 60-90 ℃ and the reaction time is 5-24h.
9. A method of preparation according to claim 3, characterized in that: the mass ratio of the zinc hydroxyfluoride three-dimensional matrix material to the 2-methylimidazole salt is 1:0.4-4.
10. The use of ZIF-8/zinc hydroxyfluoride composite gas-sensitive material according to claim 1 or 2 for preparing NO 2 Gas sensor or NO 2 Application in concentration detection.
CN202311345342.2A 2023-10-17 2023-10-17 ZIF-8/zinc hydroxyfluoride composite gas-sensitive material, and preparation method and application thereof Pending CN117470919A (en)

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