CN104492367B - Super high sensitivity precious metal-modified ZnO micro-nano hierarchical structure and preparation method thereof - Google Patents

Abstract

The invention provides a preparation method of a super high sensitivity precious metal-modified ZnO micro-nano hierarchical structure, and the method is as follows: 1, synthesis of a micro-nano hierarchical structure comprising ultrathin porous nano single crystal ZnO nanosheets; 2, modification of the ZnO micro-nano hierarchical structure; and 3, preparation of the precious metal-modified ZnO micro-nano hierarchical structure. The super high sensitivity precious metal-modified ZnO micro-nano hierarchical structure prepared by the method has the characteristics of single crystal, ultrathin thin, porous and hierarchical structure and assistant precious metal nanoparticle modification, the points are beneficial to improvement of the sensitivity of ZnO to organic gaseous pollutants, compared with the ZnO materials in the prior art, the super high sensitivity precious metal-modified ZnO micro-nano hierarchical structure has super high gas sensitivity, and the detection limit is less than 1ppb.

Description

An ultra-high-sensitivity noble metal-modified ZnO micro-nano hierarchical structure and its preparation method

technical field

The invention relates to a detection instrument for organic gas pollutants, in particular to a noble metal-modified ultra-thin single-crystal porous ZnO micro-nano hierarchical structure with ultra-high sensitivity to organic pollutants and a preparation method thereof.

Background technique

Organic gas pollutants such as ethanol, formaldehyde, benzene, and toluene brought by decoration materials have great damage to human health, and are likely to cause respiratory diseases, pneumonia, bronchitis and other diseases, and even have the risk of cancer. Therefore, the detection and real-time monitoring of organic gas pollutants have been widely concerned. At present, the traditional detection techniques of organic gas pollutants are chemical analysis methods, such as gas chromatography and mass spectrometry. This detection method has a large workload, complicated procedures, expensive equipment, and cannot realize real-time detection. Electrical gas sensors based on semiconductor oxides have broad application prospects in the detection and real-time monitoring of organic pollutants due to their advantages such as low power consumption, fast response, simple structure, and mature technology.

As a semiconductor with a wide bandgap (3.37eV), ZnO has the characteristics of high electron mobility and good chemical stability, and it has good gas-sensing properties for indoor air pollutants. However, traditional sensors are often based on bulk ZnO sensitive materials, so their sensitivity is not high. Studies have shown that ZnO materials with ultra-thin, single-crystal, porous, hierarchical structures and supplemented with noble metal nanoparticles can improve the sensitivity of ZnO to indoor air pollutants, because: (1) when the size of ZnO is smaller than the width of the depletion layer At 2 times (that is, 22nm), the entire particle becomes a depletion layer, and almost all the mobile charges of the semiconductor material are bound to the adsorbed oxygen molecules. Molecules are released, causing a huge change in the response current, thereby improving the sensitivity of the sensor; (2) the single crystal structure has no grain boundary, and there is no loss when electrons are transported in the body, which can not only improve the sensitivity, but also ensure the stability of the sensor; ( 3) The porous structure is conducive to increasing the specific surface area of the material, thereby increasing the active adsorption sites of the analyte; (4) The hierarchical structure can not only provide the channels required for the diffusion of the analyte gas, but also ensure that the ultra-thin material is free from Agglomeration; (5) Noble metal nanoparticles can increase the reactivity of sensitive materials due to their high catalytic activity.

Existing ZnO-based sensors often use one or several of the five items mentioned above to improve sensitivity, but there are no reports that can achieve these five items at the same time. Therefore, how to prepare a hierarchical structure with ultrathin porous single-crystal ZnO and how to achieve nano-modification of noble metal materials has become a great challenge to improve the sensitivity of sensors.

Contents of the invention

Aiming at the shortcomings of insufficient sensitivity based on traditional ZnO materials, the invention proposes a ZnO micro-nano hierarchical structure composed of ultra-thin single-crystal porous ZnO nanosheets modified by precious metal particles.

A method for preparing an ultrahigh-sensitivity noble metal-modified ZnO micro-nano hierarchical structure, comprising the steps of:

(1) Synthesis of ZnO micro-nano hierarchical structure:

Dissolve zinc acetate (Zn(CH ₃ COO) ₂ ) and urea (CO(NH ₂ ) ₂ ) in a solvent to form a transparent solution; then seal the transparent solution and keep it warm for 3-24 hours, then centrifuge and wash it , drying to obtain an ultra-thin nano-ZnO precursor; finally, the ultra-thin nano-ZnO precursor is annealed to obtain a ZnO micro-nano hierarchical structure composed of ultra-thin single-crystal porous ZnO nanosheets;

(2) Modification of ZnO micro-nano hierarchical structure:

The ZnO micro-nano hierarchical structure prepared by (1) is ultrasonically dispersed in a polymer coupling agent solution with a pH value of 7.5-9. After stirring evenly, the ZnO micro-nano hierarchical structure is separated by centrifugation and dried. Obtain the modified ZnO micro-nano hierarchical structure;

(3) Preparation of noble metal nanoparticle sol:

First, add the soluble precious metal solution with a mass concentration of 0.1%-4% into deionized water and boil, add a reducing agent during the boiling process, then continue heating for 5-10 minutes, and cool naturally to obtain a precious metal with a certain size and good dispersion Nanoparticle sol;

(4) Preparation of noble metal-modified ZnO micro-nano hierarchical structure:

Mix the modified ZnO micro-nano hierarchical structure with the noble metal nano-particle sol, stir for 0.5-4 hours, modify the noble metal particles on the ZnO micro-nano hierarchical structure through electrostatic interaction, centrifuge, and dry to obtain the precious metal-modified ZnO micro-nano fraction structure.

Further, the mass ratio of zinc acetate to urea in the step (1) is 0.5-2:1-8;

The solvent is composed of deionized water and ethylene glycol in a volume ratio of 0.5-5:1.

Further, in the step (1), heat preservation for 3-24 hours refers to heat preservation for 3-24 hours in an oven at a temperature of 70-110°C;

The annealing treatment refers to annealing treatment in a muffle furnace or a tube furnace at a temperature of 250-500°C.

Further, the ultra-thin single crystal porous ZnO nanosheets in the step (1) refer to ZnO nanosheets with a length of 1-20µm, a width of 50nm-10µm, a thickness of no more than 22nm, and a wurtzite phase;

The ZnO micro-nano hierarchical structure refers to a flower-shaped or spherical hierarchical structure composed of ZnO nanosheets with a particle size of 1-100 μm.

Further, the polymer coupling agent in the step (2) refers to aminosilane coupling agent, mercaptosilane coupling agent or polyethyleneimine.

Further, in the step (2), the stirring time after ultrasonic dispersion is 2-24 hours; the drying refers to drying in an oven with a temperature lower than 80°C.

Further, the soluble noble metal in the step (3) refers to gold, silver, platinum or palladium with a particle size of 5-100 nm; the soluble noble metal solution includes chloroauric acid solution, silver nitrate solution, chloroplatinic acid solution and chlorine Palladium acid solution, etc.

Further, the reducing agent in the step (3) is a citric acid solution or trisodium citrate solution with a mass concentration of 0.1%-4%, and the mass ratio of the soluble precious metal solution to the reducing agent is 0.5:1-1:5 .

Further, in the step (4), the weight ratio of the modified ZnO micro-nano hierarchical structure to the noble metal nanoparticles is 1:0.005-0.05.

Another object of the present invention is to provide a ZnO micro-nano hierarchical structure modified by noble metals prepared by the above preparation method, the shape of the ZnO micro-nano hierarchical structure modified by noble metals is spherical or flower-like, and the particle size is 1-100 μm , which has ultrahigh sensitivity to low concentrations of organic gas pollutants.

Since ZnO is an amphoteric metal oxide, if the pH of the polymer dispersion is too high, too strong alkalinity will cause the dissolution of the ZnO hierarchical structure in the polymer solution, so its pH must be controlled in the range of 7.5-9 Inside.

The present invention is a ZnO precursor with a spherical or flower-like hierarchical structure composed of flat ZnO nanosheet stacks with a size of 100nm-10μm by a hydrothermal method; ZnO micro-nano hierarchical structure composed of flakes; then it was modified. Finally, the modified ZnO micro-nano hierarchical structure is mixed with the noble metal nanoparticle sol, and modified by electrostatic interaction to obtain the noble metal-modified ZnO micro-nano hierarchical structure. That is, the noble metal-modified ZnO micro-nano hierarchical structure prepared by the present invention utilizes its porous and hierarchical structure characteristics to improve the adsorption capacity of molecules to be detected on the surface of ZnO; utilizes the advantages of ultra-thin, single crystal and noble metal modification to increase the sensitivity and stability of the sensor , so as to achieve ultra-high sensitivity detection of low-concentration organic gas pollutants.

So the beneficial effects of the present invention have:

1. The noble metal-modified ZnO micro-nano hierarchical structure prepared by the present invention has the characteristics of ultra-thin, single crystal, porous, and hierarchical structure, and the modification with noble metal nanoparticles can improve the sensitivity of ZnO to indoor air pollutants. Compared with existing Some ZnO materials have ultra-high gas sensitivity to organic gas pollutants such as ethanol, formaldehyde, and acetone, and the detection limit can reach 1ppb, which is three orders of magnitude higher than the sensitivity of existing ZnO bulk and powder materials, and is also much higher than conventional nano Material.

2. The noble metal-modified ZnO micro-nano hierarchical structure prepared by the present invention utilizes the characteristics of porous and hierarchical structures to improve the adsorption capacity of the molecules to be detected on the surface of ZnO, and utilizes the advantages of ultra-thin, single crystal and noble metal modification to increase the sensitivity and stability of the sensor , so as to achieve ultra-high sensitivity detection of low-concentration organic gas pollutants.

3. The preparation method of the present invention can accurately control the size and morphology of the ZnO micro-nano hierarchical structure and the porous structure, size and thickness of the porous ultra-thin single crystal ZnO nanosheets that make up it, which is beneficial to the sensitivity of the ZnO micro-nano hierarchical structure Improvement, specifically: by controlling the size and shape of the ZnO micro-nano hierarchical structure, the pore structure in the hierarchical structure can be effectively regulated, and the molecules to be tested can be effectively diffused inside the ZnO material; by controlling the composition of its porous and ultra-thin single The pore structure of the crystalline ZnO nanosheets can increase the adsorption active sites on the ZnO material, thereby effectively capturing the molecules to be measured; by controlling the size and thickness of the nanosheets, the proportion of the depletion layer on the ZnO nanosheets can be controlled to reduce the electron loss. internal loss.

4. The present invention adjusts the concentration of the polymer coupling agent solution by controlling the pH value of the polymer coupling agent solution to 7.5-9, and can effectively prevent the formation of the polymer coupling agent while realizing the modification of the ZnO micro-nano hierarchical structure. The ZnO dissolution caused by the alkaline solution of the agent is too strong.

5. The present invention provides a novel method for modifying noble metal particles on the ZnO micro-nano hierarchical structure, which can accurately control the modification amount of the noble metal particles to be modified, and effectively increase the gas sensitivity of the ZnO micro-nano hierarchical structure. At the same time, the investment in preparation equipment is small, the synthesis process is simple, and the operation is easy.

6. The design idea and preparation method of the ZnO sensitive material provided by the present invention provide a new design idea and preparation method for the practical application of sensor sensitive materials with ultra-high sensitivity performance.

Description of drawings

Fig. 1 is a scanning electron microscope image of the ZnO micro-nano hierarchical structure prepared by the present invention.

Fig. 2 is a scanning electron microscope image and an electron diffraction image of an ultra-thin single crystal porous ZnO nanosheet constituting a ZnO micro-nano hierarchical structure.

Fig. 3 is a scanning electron microscope image and a transmission image of the ZnO micro-nano hierarchical structure modified by silver particles.

Fig. 4 is a comparison of the XRD spectra of the ZnO micro-nano hierarchical structure before and after silver particle modification.

Fig. 5 is the gas sensitive detection diagram of the ZnO micro-nano hierarchical structure to ethanol before and after silver particle modification.

detailed description

Example 1

(1) Synthesis of ZnO micro-nano hierarchical structure: Dissolve 1g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 4g of urea (CO(NH ₂ ) ₂ ) in 40ml of deionized water and ethylene glycol by volume In a mixed solvent composed of 3:1, stir to form a transparent solution; then transfer it to a sealed Erlenmeyer flask, and place it in an oven at a temperature of 90°C for 10 hours; then centrifuge to separate the white precipitate and use it to After washing it with ion water for 2-3 times, put it into a 60ºC vacuum drying oven to dry to obtain the ZnO precursor; finally, anneal the dried ZnO precursor in a muffle furnace or tube furnace at 400ºC to obtain an ultra-thin ZnO micro-nano hierarchical structure composed of single crystal porous ZnO nanosheets.

The ZnO micro-nano hierarchical structure prepared in this example is shown in Figure 1 1d, and its shape is flower-like.

In addition, the scanning electron microscope image and electron diffraction image of the ultra-thin single-crystal porous ZnO nanosheet prepared in this example are shown in Figure 2, which is about 5 µm in length, 1 µm in width, and 10 nm in thickness, and the nanopores are evenly distributed throughout the nanometer sheet. Chip. 2a and 2b in Fig. 2 are the front and side electron microscope scanning images of the ultra-thin single crystal porous ZnO nanosheets prepared in this embodiment, and the porous structure and ultrathin thickness of the single ZnO nanosheets can be seen; 2c, 2d It is a transmission photo of a single ZnO nanosheet, and its porous structure is clearly visible; 2e is an electron diffraction pattern of a single ZnO nanosheet, and its diffraction pattern is a regular point-like structure, which shows that the nanosheet is a single crystal structure; 2f It is the lattice fringe image of ZnO nanosheets. It can be seen that the lattice fringes are arranged very neatly, which also proves the single crystal structure of ZnO nanosheets.

(2) Modification of ZnO micro-nano hierarchical structure: Take 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared by (1) and ultrasonically disperse it in a polyethyleneimine solution with a pH value of 8.5. After stirring for 3 hours, the modified The activated ZnO micro-nano hierarchical structure was separated from the solution and dried in an oven at 75ºC.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 1wt% silver nitrate solution, add silver nitrate solution and 1wt% citric acid solution during boiling, the mass ratio of silver nitrate solution and citric acid solution is 1:3, Continue heating for 10 minutes and then cool naturally to obtain a silver particle sol with a certain size and good dispersion.

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 100 mg of the modified spherical ZnO micro-nano hierarchical structure with silver sol containing 1 mg of silver nanoparticles in proportion, stir for 0.5 h, and form a flower-shaped structure through electrostatic interaction. The ZnO micro-nano hierarchical structure is modified with silver particles, and then centrifuged and dried to obtain a flower-shaped ZnO micro-nano hierarchical structure decorated with silver particles with a loading capacity of 1%.

The scanning electron micrographs of the flower-like ZnO micro-nano hierarchical structure modified by silver particles prepared by the present invention are shown in 3a and 3b in Figure 3, and it can be seen that a large amount of Ag is distributed on the nanosheets of the micro-nano structure; its transmission diagram is shown in Figure 3 As shown in 3c and 3d, it can be seen that the silver particles have a uniform particle size and are evenly distributed on the surface of the ZnO nanosheets.

The XRD spectrum of the modified ZnO micro-nano hierarchical structure is shown in Figure 4a, while the XRD spectrum of the flower-like ZnO micro-nano hierarchical structure modified by silver particles is shown in Figure 4b. The XRD diffraction peaks of the ZnO micro-nano hierarchical structure all belong to the wurtzite ZnO structure, and a diffraction peak belonging to the Ag(200) plane obviously appears after the silver particle modification, which proves the modification of Ag on the ZnO micro-nano hierarchical structure; and In addition to Zn and O in Figure 4b, Ag peaks also appear, which also proves that Ag has been modified on the ZnO micro-nano fraction.

The silver particle-modified ZnO micro-nano hierarchical structure prepared in this example has excellent response sensitivity to organic gas pollutants, and its gas-sensitive detection of ethanol is shown in Figure 5 in 5a, and its detection limit for ethanol can reach 1 ppb; and its response sensitivity and gas concentration linear relationship diagram is shown in 5b in Figure 5. It can be seen that the Ag particle-modified ZnO micro-nano hierarchical structure has a good linear response to ethanol, which is expected to be applied to the actual ethanol sensor detection.

Example 2

(1) Synthesis of ZnO micro-nano hierarchical structure: Dissolve 0.5g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 3g of urea (CO(NH ₂ ) ₂ ) in 50ml of deionized water and ethylene glycol by volume In a mixed solvent with a ratio of 1:1, stir for 3 minutes to form a transparent solution; then transfer it to a sealed Erlenmeyer flask, and place it in an oven at 75°C for 8 hours; then centrifuge the obtained The white precipitate is separated from the solution, washed with deionized water for 2-3 times, and then dried in a 60ºC vacuum oven to obtain a ZnO precursor; finally, the dried ZnO precursor is annealed at 300ºC to obtain The spherical ZnO micro-nano hierarchical structure shown in Figure 1c is composed of ultra-thin single crystal porous ZnO nanosheets with a length of about 2 µm, a width of about 400 nm, and a thickness of about 8 nm, and the nanoholes are evenly distributed throughout the nanosheet.

(2) Modification of ZnO micro-nano hierarchical structure: 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared by (1) was ultrasonically dispersed in a polyethyleneimine solution with a pH value of 7.8, and stirred for 2 hours. Then the modified ZnO micro-nano hierarchical structure was separated from the solution by centrifugation and dried in an oven at 70ºC.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 0.5 wt% chloroauric acid solution. Add 0.5% trisodium citrate during the boiling process, the mass ratio of its chloroauric acid solution to trisodium citrate is 1:2, then continue to heat for 10 minutes and cool naturally to obtain a gold sol with a certain size and good dispersion .

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 1000 mg of the modified spherical ZnO micro-nano hierarchical structure with gold sol containing 10 mg of gold nanoparticles in proportion, stir for 1 hour, and realize gold particles through electrostatic interaction Modification on the spherical ZnO micro-nano hierarchical structure, centrifugation, and drying to obtain a spherical ZnO micro-nano hierarchical structure with a loading capacity of 1% gold particles, which has excellent response sensitivity to organic gas pollutants, among which formaldehyde The detection limit can reach 0.05 ppm.

Example 3

(1) Synthesis of ZnO micro-nano hierarchical structure: Dissolve 0.5g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 1g of urea (CO(NH ₂ ) ₂ ) in 40ml of deionized water and ethylene glycol by volume In a mixed solvent with a ratio of 1:1, stir to form a transparent solution, then transfer it to a sealed Erlenmeyer flask, and place it in an oven at a temperature of 75°C for 5 hours; then centrifuge the obtained white The precipitate is separated from the solution, washed with deionized water for 2-3 times, and then dried in a 60ºC vacuum oven to obtain a ZnO precursor; finally, the dried ZnO precursor is annealed at 300ºC to obtain the The spherical ZnO micro-nano hierarchical structure shown in 1b of 1, the ultra-thin single crystal porous ZnO nanosheets are about 4 µm in length, 500 nm in width, and 12 nm in thickness, and the nanoholes are evenly distributed on the entire nanosheet.

(2) Modification of ZnO micro-nano hierarchical structure: 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared by (1) was ultrasonically dispersed in a polyethyleneimine solution with a pH value of 8, and stirred for 5 hours. Then the ZnO micro-nano hierarchical structure was separated from the solution by centrifugation and dried in a 65ºC oven.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 1wt% chloroplatinic acid solution. Add 1% citric acid during the boiling process, and the mass ratio of chloroplatinic acid solution to citric acid is 1:2; then continue heating for 10 minutes and then cool naturally to obtain a platinum particle sol with a certain size and good dispersion.

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 100 mg of the modified spherical ZnO micro-nano hierarchical structure with platinum sol containing 2 mg of platinum nanoparticles in proportion, stir for 1 hour, and realize platinum particles through electrostatic interaction. Modification on the spherical ZnO micro-nano hierarchical structure, centrifugation, and drying to obtain a platinum particle-modified spherical ZnO micro-nano hierarchical structure with a loading capacity of 2%, which has excellent response sensitivity to organic gas pollutants, especially for acetone The detection limit can reach 10 ppb.

Example 4

(1) Synthesis of ZnO micro-nano hierarchical structure: Dissolve 0.8g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 3.5g of urea (CO(NH ₂ ) ₂ ) in 80ml of deionized water and ethylene glycol In a mixed solvent with a volume ratio of 2:1, stir to form a transparent solution, then transfer it to a sealed Erlenmeyer flask, and place it in an oven at 80°C for 8 hours; then use centrifugation to extract the obtained A white precipitate separated out of solution. Wash it with deionized water for 2-3 times and put it into a 60ºC vacuum oven to dry to obtain the ZnO precursor; finally, anneal the dried ZnO precursor at 300ºC to obtain the spherical shape shown in 1c in Figure 1. ZnO micro-nano hierarchical structure, composed of ultra-thin single-crystal porous ZnO nanosheets with a length of about 5 µm, a width of about 800 nm, and a thickness of about 10 nm.

(2) Modification of ZnO micro-nano hierarchical structure: Take 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared by (1), ultrasonically disperse it in 100 ml polyethyleneimine solution with a pH value of 8, and stir for 12 hours. Then the ZnO micro-nano hierarchical structure was separated from the solution by centrifugation and dried in an oven at 70ºC.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 0.1 wt% chloropalladium acid solution. Add 0.1% citric acid solution in the boiling process, the mass ratio of its chloropalladium acid solution and citric acid solution is to add in the ratio of 1:1, then continue to heat for 10 minutes and then cool naturally to obtain a certain size dispersion Good palladium particle sol.

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 100 mg of the modified spherical ZnO micro-nano hierarchical structure with palladium sol containing 2 mg of palladium nanoparticles in proportion, stir for 2 hours, and realize palladium particles through electrostatic interaction Modification on the spherical ZnO micro-nano hierarchical structure, centrifugation, and drying to obtain a spherical ZnO micro-nano hierarchical structure with a loading capacity of 2% palladium particles, which has excellent response sensitivity to organic gas pollutants, especially for acetone The detection limit can reach 5 ppb.

Example 5

(1) Synthesis of ZnO micro-nano hierarchical structure: Dissolve 1g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 1g of urea (CO(NH ₂ ) ₂ ) in 30ml of deionized water and ethylene glycol by volume In a mixed solvent composed of 0.5:1, stir for 5 minutes to form a transparent solution, then transfer it to a sealed Erlenmeyer flask, and place it in an oven at a temperature of 70°C for 8 hours; then centrifuge the obtained A white precipitate separated out of solution. Wash it with deionized water for 2-3 times, put it into a 60ºC vacuum drying oven to dry to obtain the ZnO precursor; finally anneal the dried ZnO precursor at 300ºC, and you can get the spherical shape shown in Figure 1 1a ZnO micro-nano hierarchical structure, composed of ultra-thin single-crystal porous ZnO nanosheets with a length of about 1 µm, a width of about 50 nm, and a thickness of about 8 nm, and the nanoholes are evenly distributed on the entire nanosheet.

(2) Modification of ZnO micro-nano hierarchical structure: take 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared by (1), ultrasonically disperse it in 100 ml of polyethyleneimine solution with a pH value of 8, and stir for 18 hours. Then the ZnO micro-nano hierarchical structure was separated from the solution by centrifugation and dried in an oven at 75ºC.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 0.1 wt% chloroauric acid solution. Add 0.1% citric acid solution during the boiling process, the mass ratio of chloroauric acid solution to citric acid solution is 1:1, then continue heating for 10 minutes and then cool naturally to obtain a gold particle sol with a certain size and good dispersion.

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 1000 mg of the modified spherical ZnO micro-nano hierarchical structure with gold sol containing 5 mg of gold nanoparticles in proportion, stir for 0.5 h, and realize gold through electrostatic interaction. Modification of particles on the spherical ZnO micro-nano hierarchical structure, centrifugation, and drying to obtain a spherical ZnO micro-nano hierarchical structure with a loading of 0.5% gold particles, which has excellent response sensitivity to organic gas pollutants, among which formaldehyde The detection limit can reach 0.05 ppm.

Example 6

(1) Synthesis of ZnO micro-nano hierarchical structure: 1.3g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 5.5g of urea (CO(NH ₂ ) ₂ ) were dissolved in 40ml of deionized water and ethylene glycol In a mixed solvent with a volume ratio of 4:1, stir for a period of time to form a transparent solution, then transfer the transparent solution to a sealed Erlenmeyer flask, and place it in an oven at 100ºC for 12 hours; then use The resulting white precipitate was separated from solution by centrifugation. Wash it with deionized water for 2-3 times, put it into a 60ºC vacuum drying oven to dry to obtain the ZnO precursor; finally, anneal the dried ZnO precursor at 400ºC to obtain a flower-like ZnO micro-nano hierarchical structure. Its ultrathin single-crystal porous ZnO nanosheets are about 10 µm long, 2 µm wide, and 8 nm thick.

(2) Modification of ZnO micro-nano hierarchical structure: take 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared in (1), ultrasonically disperse it in 100 ml of polyethyleneimine solution with a pH value of 9, and stir for 3 hours. Then the ZnO micro-nano hierarchical structure was separated from the solution by centrifugation and dried in an oven at 80ºC.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 1wt% chloroauric acid solution. Add 1% citric acid solution during the boiling process, the mass ratio of the chloroauric acid solution to the citric acid solution is 1:4, then continue heating for 10 minutes and then cool naturally to obtain a gold particle sol with a certain size and good dispersion.

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 100 mg of the modified spherical ZnO micro-nano hierarchical structure with gold sol containing 3 mg of gold nanoparticles in proportion, stir for 3 hours, and realize gold particles through electrostatic interaction. Modification on the spherical ZnO micro-nano hierarchical structure, centrifugation, and drying to obtain a spherical ZnO micro-nano hierarchical structure with a loading capacity of 3% gold particles, which has excellent response sensitivity to organic gas pollutants, among which formaldehyde The detection limit can reach 0.08 ppm.

Example 7

(1) Synthesis of ZnO micro-nano hierarchical structure: Dissolve 1.5g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 6g of urea (CO(NH ₂ ) ₂ ) in 40ml of deionized water and ethylene glycol by volume In a mixed solvent with a ratio of 5:1, stir for a period of time to form a transparent solution, then transfer it to a sealed Erlenmeyer flask, and place it in an oven at 110ºC for 18 hours; then centrifuge the The resulting white precipitate separated from solution. Wash it with deionized water for 2-3 times, put it into a 60ºC vacuum drying oven to dry to obtain the ZnO precursor; finally, anneal the dried ZnO precursor at 500ºC to obtain a flower-like ZnO micro-nano hierarchical structure. Its ultrathin single-crystal porous ZnO nanosheets are about 15 µm long, 5 µm wide, and 8 nm thick.

(2) Modification of ZnO micro-nano hierarchical structure: Take 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared by (1), ultrasonically disperse it in 100 ml of polyethyleneimine solution with a pH value of 8, and stir for 24 hours. Then the ZnO micro-nano hierarchical structure was separated from the solution by centrifugation and dried in an oven at 75ºC.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 4 wt % chloroauric acid solution. Add 2% citric acid solution during the boiling process, the mass ratio of the chloroauric acid solution to the citric acid solution is 1:5, then continue heating for 10 minutes and then cool naturally to obtain a gold particle sol with a certain size and good dispersion.

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 100 mg of the modified spherical ZnO micro-nano hierarchical structure with gold sol containing 5 mg of gold nanoparticles in proportion, stir for 4 hours, and the gold particles can be realized through electrostatic interaction. After modifying the spherical ZnO micro-nano hierarchical structure, centrifuging and drying, the spherical ZnO micro-nano hierarchical structure modified by gold particles with a loading capacity of 5% has excellent response sensitivity to organic gas pollutants, especially for ethanol. The detection limit can reach 0.01 ppm.

Example 8

(1) Synthesis of ZnO micro-nano hierarchical structure: Dissolve 2g of zinc acetate (Zn(CH ₃ COO) ₂ ) and 8g of urea (CO(NH ₂ ) ₂ ) in 40ml of deionized water and ethylene glycol by volume In a mixed solvent composed of 8:1, stir to form a transparent solution, then transfer it to a sealed Erlenmeyer flask, and place it in an oven at 110ºC for 24 hours; then centrifuge the obtained white precipitate separated from the solution. Wash it with deionized water for 2-3 times, put it into a 60ºC vacuum drying oven to dry to obtain the ZnO precursor; finally, anneal the dried ZnO precursor at 500ºC to obtain a flower-like ZnO micro-nano hierarchical structure. Its ultrathin single-crystal porous ZnO nanosheets are about 20 µm long, 10 µm wide, and 22 nm thick.

(2) Modification of ZnO micro-nano hierarchical structure: Take 50 mg of the flower-like ZnO micro-nano hierarchical structure prepared by (1), ultrasonically disperse it in 100 ml polyethyleneimine solution with a pH value of 7.5, and stir for 4 hours. Then the ZnO micro-nano hierarchical structure was separated from the solution by centrifugation and dried in an oven at 80ºC.

(3) Preparation of noble metal nanoparticle sol: first boil 100ml of 4wt% chloroauric acid solution. Add 2% citric acid solution during the boiling process, the mass ratio of the chloroauric acid solution to the citric acid solution is 1:5, then continue heating for 10 minutes and then cool naturally to obtain a gold particle sol with a certain size and good dispersion.

(4) Preparation of precious metal-modified ZnO micro-nano hierarchical structure: Mix 100 mg of the modified spherical ZnO micro-nano hierarchical structure with 2.5 mg of gold sol containing gold nanoparticles, stir for 4 hours, and the gold particles can be realized through electrostatic interaction. Modification on the spherical ZnO micro-nano hierarchical structure, centrifugation, and drying to obtain a spherical ZnO micro-nano hierarchical structure modified with gold particles with a loading capacity of 2.5%, and the detection limit of formaldehyde can reach 0.01 ppm.

The above embodiments are not limited to the protection scope of the present invention, and all modifications or changes based on the basic idea of the invention belong to the protection scope of the present invention.

Claims (7)

1. a kind of preparation method of the ZnO micro-nano hierarchical structure of the precious metal modification of ultrahigh sensitivity, it is characterized in that: comprise the steps: (1) Synthesis of ZnO micro-nano hierarchical structure: Zinc acetate (Zn(CH ₃ COO) ₂ ) and urea (CO(NH ₂ ) ₂ ) are dissolved in a solvent at a mass ratio of 0.5-2:1-8 to form a transparent solution; then the transparent solution is sealed and placed After being kept in an oven at 70-110°C for 3-24 hours, it is centrifuged, washed, and dried to obtain an ultra-thin nano-ZnO precursor; finally, the ultra-thin nano-ZnO precursor is annealed to obtain an ultra-thin single crystal ZnO micro-nano hierarchical structure composed of porous ZnO nanosheets; the solvent is composed of deionized water and ethylene glycol in a volume ratio of 0.5-5:1; (2) Modification of ZnO micro-nano hierarchical structure: The ZnO micro-nano hierarchical structure prepared by step (1) is ultrasonically dispersed in a polymer coupling agent solution with a pH value of 7.5-9. After stirring evenly, the ZnO micro-nano hierarchical structure is separated by centrifugation and baked. Dry to obtain a modified ZnO micro-nano hierarchical structure; the polymer coupling agent is polyethyleneimine; (3) Preparation of noble metal nanoparticle sol: First, add the soluble precious metal solution with a mass concentration of 0.1%-4% into deionized water and boil, add a reducing agent during the boiling process, then continue heating for 5-10 minutes, and cool naturally to obtain a precious metal with a certain size and good dispersion Nanoparticle sol; (4) Preparation of noble metal-modified ZnO micro-nano hierarchical structure: Mix the modified ZnO micro-nano hierarchical structure with the noble metal nanoparticle sol at a weight ratio of 1:0.005-0.05, stir for 0.5-4h, modify the precious metal particles on the ZnO micro-nano hierarchical structure through electrostatic interaction, centrifuge, and dry. A noble metal-modified ZnO micro-nano hierarchical structure was obtained. 2. The preparation method according to claim 1: characterized in that: the step (1) annealing refers to annealing in a muffle furnace or tube furnace at a temperature of 250-500°C. 3. The preparation method according to claim 1: it is characterized in that: in the step (1), the ultra-thin single-crystal porous ZnO nanosheets are 1-20µm in length, 50nm-10µm in width, and no more than 22nm in thickness, ZnO nanosheets whose crystal phase is wurtzite phase; The ZnO micro-nano hierarchical structure refers to a flower-shaped or spherical hierarchical structure composed of ZnO nanosheets with a particle size of 1-100 μm. 4. The preparation method according to claim 1: characterized in that: in the step (2), the stirring time after ultrasonic dispersion is 2-24 hours; the drying refers to drying in an oven with a temperature lower than 80°C Dry. 5. The preparation method according to claim 1: characterized in that: the soluble precious metal in the step (3) refers to gold, silver, platinum or palladium with a particle size of 5-100 nm; the soluble precious metal solution includes chlorine Gold acid solution, silver nitrate solution, chloroplatinic acid solution and chloropalladium acid solution. 6. The preparation method according to claim 1: characterized in that: in the step (3), the reducing agent is a citric acid solution or trisodium citrate solution with a mass concentration of 0.1%-4%, and the soluble precious metal solution The mass ratio to the reducing agent is 0.5:1-1:5. 7. A noble metal-modified ZnO micro-nano hierarchical structure prepared by the preparation method according to any one of claims 1-6, characterized in that: the shape of the noble metal-modified ZnO micro-nano hierarchical structure is spherical or floral Shape, particle size of 1-100μm, which has ultra-high sensitivity to low concentration of organic gas pollutants.