Hollow zinc oxide composite material loaded with nanogold as well as preparation method and application of hollow zinc oxide composite material

Abstract

The invention belongs to the technical field of electronic devices, and relates to a nanogold-loaded hollow zinc oxide composite material as well as a preparation method and application thereof. According to the preparation method, chloroauric acid and trisodium citrate are adopted as raw materials, monodisperse gold nanoparticles are synthesized through a hydrothermal method, then the gold nanoparticles are added into a sodium zincate solution, the composite material with the gold nanoparticles evenly dispersed on zinc oxide is manufactured through the hydrothermal method again, and the composite material has the unique hollow structure characteristic and can be used for preparing the composite material. The structure not only is beneficial to diffusion of gas molecules, but also can remarkably increase the contact area between the material and the gas.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic devices, and relates to a hollow zinc oxide composite material loaded with nano-gold, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the increasing attention of society to environmental safety, life and health, and industrial production processes, the demand for the monitoring of various volatile organic compounds (VOCs) has been growing day by day, which has directly promoted the research and development of sensors for different types of VOCs. Among many concerns, formic acid, as an important organic chemical raw material, is not only widely used in many fields such as medicine, chemical industry, and agriculture, but also is a part of human sweat and certain insect secretions. Its characteristics of irritation and corrosion require accurate monitoring in the fields of production safety and biological tracking. Although there have been various sensor technologies for formic acid detection reported, including electrochemistry-based, optical-based, and resistive sensors, etc., these existing technologies can only reach the lowest detection limit of the ppm level, that is, the volume concentration is 10 -6 level, far from meeting the accurate detection requirements for formic acid at a concentration as low as the ppb level (10 -9 ). Therefore, the research and development of formic acid gas sensors with high sensitivity and high selectivity has become an important direction of current research.

[0003] Gas sensors based on metal oxides have become a widely used choice due to their high cost-effectiveness, easy manufacturability, good integration ability, and high sensitivity to volatile organic compounds. For example, materials such as tin dioxide (SnO2), zinc oxide (ZnO), etc., can effectively respond to the presence of specific VOCs after appropriate treatment. It is worth mentioning that gold, as a typical noble metal, has shown great potential in improving the performance of metal oxide-based sensors by virtue of its high electron density and spillover effect. By loading gold particles on the surface of metal oxides, the sensitivity of the composite material to volatile organic compounds can be significantly enhanced. However, to reduce the lowest detection concentration of formic acid to the ppb level and at the same time improve the selectivity of the sensor, innovative methods and technical paths still need to be explored. This means that not only the interaction mechanism between formic acid and other VOCs needs to be deeply understood, but also new functional materials need to be developed to overcome the bottlenecks of existing technologies, and finally achieve a more accurate and reliable formic acid detection goal.

[0004] The Chinese patent application document (Publication No.: CN105215347A) discloses a composite material of zinc oxide and gold nanoparticles and a preparation method thereof. The preparation method requires calcination treatment at a high temperature of 300 °C. Although high-temperature calcination helps to form a stable composite material structure, it may also cause an increase in the size of gold nanoparticles. The large particle size may reduce the specific surface area of the material, thereby affecting the gas-sensing performance of the material. In addition, high-temperature treatment may also cause internal stress changes or crystal defects in the material, and these factors may further affect the stability and reusability of the material. Summary of the Invention

[0005] The object of the present invention is to propose a hollow zinc oxide composite material loaded with nano-gold in view of the above problems existing in the prior art, further improving the sensitivity of the material and realizing highly sensitive and ultra-low concentration detection of formic acid gas.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A hollow zinc oxide composite material loaded with nano-gold, wherein the composite material is obtained by loading nano-gold on zinc oxide with a hollow structure. The particle size of the nano-gold particles is 5-10 nm, and the size of the zinc oxide with a hollow structure is 500-1200 nm. The molar ratio of gold to zinc in the composite material is 1:0.1-3.0.

[0008] Preferably, the molar ratio of gold to zinc in the composite material is 1:0.8-1.2.

[0009] The present invention also provides a preparation method of the above-mentioned hollow zinc oxide composite material loaded with nano-gold. The method comprises the following steps:

[0010] S1. Add a colloidal Au nanoparticle solution to a sodium zincate solution and mix and ultrasonicate.

[0011] S2. Then perform high-temperature treatment, followed by solid-liquid separation, and finally perform drying treatment to obtain a nano-gold loaded hollow zinc oxide composite material.

[0012] The present invention requires strict control of the addition amounts of sodium zincate solution and colloidal Au nanoparticle solution. When the addition amount of colloidal Au nanoparticles exceeds the optimal value, it may lead to an aggravation of the nanoparticle aggregation phenomenon. This aggregation will reduce the surface area to volume ratio, thereby reducing the number of accessible active sites. In addition, excessive aggregation may also change the electronic structure of the material, affecting its electrical properties. The combined action of these factors will result in a decrease in the gas-sensing sensitivity of the sensor. If the addition of Au nanoparticles is insufficient, the advantages of using them as a catalyst or enhancing the conductivity of the material cannot be fully demonstrated, which is also not conducive to improving the efficiency of detecting gas molecules. A small amount of Au nanoparticles cannot provide enough catalytic active sites to promote the adsorption and reaction of target gas molecules, so it will also lead to a decrease in the overall sensitivity.

[0013] Excessive addition of sodium zincate may lead to uneven distribution of zinc oxide components in the composite material or the formation of unnecessary by-products, which will affect the microstructure and surface characteristics of the material. If the addition amount of sodium zincate is insufficient, it is not sufficient to form an ideal hollow structure, which will directly affect the physical and chemical properties of the material such as specific surface area and porosity. These factors are the key to determining the gas-sensing sensitivity performance of the sensor.

[0014] In the above preparation method of a hollow zinc oxide composite material loaded with nano-gold, the colloidal Au nanoparticle solution is prepared by heating chloroauric acid at 80 - 120 °C for 1 - 5 min and adding trisodium citrate for reaction.

[0015] In the above preparation method of a hollow zinc oxide composite material loaded with nano-gold, the mass ratio of chloroauric acid to trisodium citrate is 2.5 - 5:1.

[0016] In the above preparation method of a hollow zinc oxide composite material loaded with nano-gold, the concentration of the sodium zincate solution is 2 - 6 wt%, and the concentration of the colloidal Au nanoparticle solution is 8 - 16 wt%.

[0017] In the above preparation method of a hollow zinc oxide composite material loaded with nano-gold, the volume ratio of the sodium zincate solution to the colloidal Au nanoparticle solution in step S1 is 3 - 15:1.

[0018] In the above preparation method of a hollow zinc oxide composite material loaded with nano-gold, the temperature of the high-temperature treatment in step S2 is 80 - 100 °C, and the time is 3 - 8 min. The precise control of the temperature range and time of the high-temperature treatment in the present invention helps to ensure the formation of a stable and efficient composite structure between sodium zincate and colloidal Au nanoparticles, thereby obtaining excellent gas-sensing performance. Whether it is incomplete reaction and structural defects caused by too low temperature, or particle aggregation and grain growth caused by too high temperature, it will have an adverse impact on the sensitivity of the final product.

[0019] The present invention also provides a sensitive material for a sensor, and the sensitive material comprises the above-mentioned hollow zinc oxide composite material loaded with nano-gold.

[0020] The present invention also provides a sensor highly sensitive to formic acid, and the sensor comprises the above-mentioned sensitive material.

[0021] In the above-mentioned sensor highly sensitive to formic acid, the sensor comprises a honeycomb-shaped ceramic, an alumina substrate, gold interdigitated electrodes and a sensitive material layer on the surface of the gold interdigitated electrodes. The sensitive material layer is a hollow zinc oxide composite material loaded with nano-gold. Among them, the honeycomb-shaped ceramic is loaded with iron oxide particles, and the iron oxide particles cover the upstream of the air flow of the sensor sensitive layer to form a catalytic layer.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention uses chloroauric acid and trisodium citrate as raw materials, and synthesizes monodisperse gold nanoparticles by a hydrothermal method. Subsequently, these gold nanoparticles are added to a sodium zincate solution, and the hydrothermal method is used again to manufacture a composite material in which the gold nanoparticles are uniformly dispersed on zinc oxide. This composite material presents a unique hollow structure feature. This structure not only facilitates the diffusion of gas molecules, but also significantly increases the contact area between the material and the gas.

[0024] 2. The sensor prepared by the hollow zinc oxide composite material loaded with nano-gold of the present invention shows extremely high sensitivity to formic acid at a working temperature of 250 °C. For formic acid with a concentration of 1 ppm, the gas-sensitive response value reaches 2015.52. However, in order to overcome the problem of poor selectivity of the sensor, the present invention installs a catalytic layer at the front end of the sensor. This improvement effectively improves the selective response of the sensor to formic acid, reduces the interference of other gas components, and does not affect the performance of the sensitive material itself.

[0025] 3. The hollow zinc oxide composite material loaded with nano-gold of the present invention has the advantages of low cost and easy large-scale production, providing a feasible solution for the development of high-performance gas sensors. On the one hand, the uniform dispersion of the surface gold nanoparticles enhances the catalytic effect; on the other hand, the hollow structure of zinc oxide promotes gas diffusion and increases the reaction interface. Therefore, the gold particle-loaded zinc oxide material prepared by this method achieves ultra-high sensitivity to formic acid detection. In addition, by adding a catalytic layer to improve the selectivity of the sensor, this method is simple and practical, which not only improves the specific recognition ability of the sensor, but also does not damage the basic performance of the sensitive material, opening up a new way for the development of more efficient and selective gas sensors. Description of the Drawings

[0026] Figure 1Schematic diagram of the sensor structure prepared from the composite material according to Example 1; 1. Catalytic layer, 2. Honeycomb ceramic, 3. Gold interdigital electrode.

[0027] Figure 2 TEM images of Au nanoparticles and Au / ZnO with a hollow structure prepared in Example 1: (a) Au, (b) Au / ZnO;

[0028] Figure 3 XPS spectra of pure ZnO and Au / ZnO with a hollow structure prepared in Example 1 and Comparative Example 1: O 1s, Au 4f, and Zn 2p spectra of ZnO (a, b, c) at 25 °C; O 1s, Au 4f, and Zn 2p spectra of Au / ZnO (d, e, f) at 25 °C, (g, h, i) at 200 °C, (j, k, l) at 250 °C, (m, n, o) at 300 °C, (p, q, r) at 350 °C;

[0029] Figure 4 In-situ infrared spectrum of Au / ZnO with a hollow structure prepared in Example 1;

[0030] Figure 5 Response graphs of the Au / ZnO sensor prepared in Example 1 to 1 ppm of different gases from 200 °C to 350 °C;

[0031] Figure 6 Response graphs of the Au / ZnO sensor prepared in Example 1 to inorganic gases and VOC gases at a concentration of 1 ppm under the condition of 250 °C;

[0032] Figure 7 Response graphs of the ZnO sensor prepared in Comparative Example 1 to inorganic gases and VOC gases at a concentration of 1 ppm under the condition of 250 °C;

[0033] Figure 8 Graph of the resistance change of the Au / ZnO sensor prepared in Example 1 in formic acid with a concentration ranging from 0.5 ppb to 1 ppm under the condition of 250 °C;

[0034] Figure 9 Graph of the resistance change of the Au / ZnO sensor prepared in Example 1 at 250 °C in formic acid at 5 ppb under different humidity levels;

[0035] Figure 10 Long-term stability graphs of the Au / ZnO sensor prepared in Example 1 to 100 ppb, 50 ppb, 10 ppb, and 5 ppb of formic acid under the condition of 250 °C;

[0036] Figure 11XRD patterns of the catalytic materials: (a) Fe2O3; (b) V2O5; (c) CeO2; (d) Cr2O3; (e) Pd / Al2O3; (f) nanozeolite;

[0037] Figure 12 The SEM images of the catalytic materials: (a) SEM image of Fe2O3; (b) SEM image of V2O5; (c) SEM image of CeO2; (d) SEM image of Cr2O3; (e) SEM image of Pd / Al2O3; (f) SEM image of nanozeolite;

[0038] Figure 13 The response graphs of the Au / ZnO sensor prepared in Example 1 under the catalytic conditions of Fe2O3, V2O5, CeO2, Cr2O3, Pd / Al2O3 and zeolite at 250 °C in inorganic gases and VOC gases with a concentration of 1 ppm. Detailed implementation manners

[0039] The following are specific examples of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these examples.

[0040] Example 1:

[0041] S1. Put 42 mg of chloroauric acid and 100 ml of ultrapure water into a 200 ml transparent glass beaker, and stir well with a glass rod to obtain a chloroauric acid solution;

[0042] S2. Put the prepared chloroauric acid solution into a thermostatic heating magnetic stirrer with heat collection, then quickly add 2 ml (0.6%) of trisodium citrate solution, heat and stir at 100 °C for 2 minutes to obtain a colloidal Au nanoparticle solution;

[0043] S3. Dissolve 25.2 mg of zinc acetate dihydrate in 10 ml of ultrapure water, add 1 ml (2 mol / L) of NaOH solution to form a white zinc hydroxide Zn(OH)2 precipitate, and add 1 ml (2 mol / L) of NaOH solution to dissolve the white precipitate to form a sodium zincate solution;

[0044] S4. Take out 8 ml of the colloidal Au nanoparticle solution and dilute it to 40 ml with a concentration of 4.8 wt%, take 1 ml of the sodium zincate solution and dilute it to 5 ml with a concentration of 15.6 wt%, and mix the two and ultrasonicate for 4 minutes;

[0045] S5. Put it into a thermostatic heating magnetic stirrer with heat collection at 90 °C, heat and stir for 7 minutes;

[0046] S6. Centrifuge this solution at 10,000 revolutions for 2 hours (centrifugation temperature: 5 °C), pour off the excess liquid, leave the black-purple precipitate, collect the black-purple precipitate and freeze-dry it to obtain the Au / ZnO gas-sensitive material with a hollow structure.

[0047] Example 2:

[0048] S1. Put 34 mg of chloroauric acid and 100 ml of ultrapure water into a 200-ml transparent glass beaker, and stir well with a glass rod to obtain a chloroauric acid solution;

[0049] S2. Put the prepared chloroauric acid solution into a thermostatic heating magnetic stirrer with heat collection, then quickly add 2 ml (0.6%) of trisodium citrate solution, heat and stir at 100 °C for 2 minutes to obtain a colloidal Au nanoparticle solution;

[0050] S3. Take 21.9 mg of zinc acetate dihydrate and dissolve it in 10 ml of ultrapure water, add 1 ml (2 mol / L) of NaOH solution to form a white zinc hydroxide Zn(OH)₂ precipitate, and add 1 ml (2 mol / L) of NaOH solution to dissolve the white precipitate to form a sodium zincate solution;

[0051] S4. Take out 8 ml of the colloidal Au nanoparticle solution, dilute it to 40 ml with ultrapure water to a concentration of 4 wt%, take 1 ml of the sodium zincate solution and dilute it to 5 ml to a concentration of 11.2 wt%, and mix the two and sonicate for 4 minutes;

[0052] S5. Put it into a thermostatic heating magnetic stirrer with heat collection at 91 °C, heat and stir for 5 minutes;

[0053] S6. Centrifuge this solution at 10,000 revolutions for 2 hours (centrifugation temperature: 5 °C), pour off the excess liquid, leave the black-purple precipitate, collect the black-purple precipitate and freeze-dry it to obtain the Au / ZnO gas-sensitive material with a hollow structure.

[0054] Example 3:

[0055] The difference from Example 1 is only that the temperature in step S5 is 60 °C.

[0056] Example 4:

[0057] The difference from Example 1 is only that the temperature in step S5 is 120 °C.

[0058] Example 5:

[0059] The difference from Example 1 is only that the concentration of the colloidal Au nanoparticle solution is 1 wt%.

[0060] Example 6:

[0061] The only difference from Example 1 is that the concentration of the colloidal Au nanoparticle solution is 20 wt %.

[0062] Comparative Example 1:

[0063] S1. Dissolve 21.9 mg of zinc acetate dihydrate in 10 ml of ultrapure water, add 1 ml (2 mol / L) NaOH solution to form a white zinc hydroxide Zn(OH)2 precipitate;

[0064] S2, continue to add excess NaOH solution to dissolve the white precipitate to form sodium zincate Na2ZnO2 solution;

[0065] S3, dilute 1 ml of sodium zincate solution to 5 ml, add to 40 ml of ultrapure water, mix and sonicate for 4 minutes;

[0066] S4, put it into a heat collecting constant temperature heating magnetic stirrer, heat and stir at 91°C for 5 minutes;

[0067] S5. Centrifuge the solution at 10,000 rpm for 4 hours (centrifugation temperature: 5°C), pour off the excess liquid, leaving a white precipitate, collect the white precipitate and freeze-dry it to obtain a ZnO gas-sensitive material.

[0068] The gas-sensitive materials prepared in Examples 1-6 and Comparative Example 1 were dissolved in isopropanol, and the solution was fully dissolved into a suspension by ultrasonic treatment at a power of 120 W for 5 min, and then uniformly coated on the metal interdigital electrodes of the alumina ceramic substrate. The working temperature range was 200-350° C., according to Figure 1 As shown, a sensor is assembled by assembling honeycomb-shaped ceramics, an alumina substrate, gold interdigital electrodes, and a sensitive material layer on the surface of the gold interdigital electrodes.

[0069] Take 5 mg of iron oxide, cerium oxide, vanadium oxide, chromium oxide, aluminum oxide-supported palladium and zeolite powder respectively, put them into six 10 ml test tubes, add 2 ml of deionized water, and use ultrasonic processor to ultrasonicate for 5 minutes to obtain 6 different slurries. The six different slurries are injected into the holes of six honeycomb ceramics respectively and treated at 600℃ for 2 hours.

[0070] Sensor testing: The prepared sensor was placed in a temperature-controlled tube furnace. A digital mass flow controller was used to control the total gas flow rate at 200 sccm, and the background gas was 20% oxygen and 80% nitrogen. By introducing different flow rates of gas into the tube furnace, a digital source meter was used to monitor the resistance change of the sensor in real time under a 1V DC bias.

[0071] Attached Figure 2The TEM images of the Au nanoparticles and Au / ZnO prepared in Example 1 are presented. It can be seen from the TEM images that the sizes of the Au nanoparticles are relatively uniform and they have good dispersibility; Au / ZnO has a hollow structure.

[0072] Attached Figure 3 The in-situ XPS images of Au / ZnO prepared in Example 1 are given, where the proportion changes of lattice oxygen (O lat ), adsorbed oxygen (O ads ), and hydroxyl oxygen (O hyd ) at different temperatures show an obvious trend. Especially when the temperature is higher than 250 °C, the proportion of adsorbed oxygen (O ads ) decreases rapidly, so 250 °C is a critical temperature point. Among them, at 250 °C, the proportions of lattice oxygen (O lat ), adsorbed oxygen (O ads ), and hydroxyl oxygen (O hyd ) are 68.76%, 20.93%, and 10.31% respectively.

[0073] Attached Figure 4 The three-dimensional in-situ infrared spectra of Au / ZnO prepared in Example 1 are given, and it can be seen that with the increase of temperature, the surface functional groups of the Au / ZnO material change.

[0074] Attached Figure 5 Shows the responses of the Au / ZnO sensor prepared in Example 1 to different gases at 1 ppm from 200 °C to 350 °C. The response values of the sensor to formic acid at 1 ppm, 0.5 ppm, 0.1 ppm, 50 ppb, 10 ppb, 5 ppb, and 0.5 ppb at 250 °C reach 2015.52, 689.21, 72.22, 32.41, 12.95, 5.39, and 2.12 respectively. The gas sensitivity response is Ra / Rg, where Ra is the resistance of the sensor in air and Rg is the resistance of the sensor in the target gas. It can be seen that the sensor has the best response to gases at 250 °C.

[0075] Attached Figure 6 Shows the resistance change diagram of the Au / ZnO sensor prepared in Example 1 at 250 °C in different VOC gases and inorganic gases at a concentration of 1 ppm. Among them, the response to 1 ppm formic acid is 2015.52, and the response of the sensor is Ra / Rg (Ra is the stable resistance of the sensor in a background gas of 20% oxygen and 80% nitrogen, and Rg is the stable resistance of the sensor in the target gas). At the same time, the response values of the Au / ZnO sensor to acetic acid and propionic acid also reach 339.5 and 776.21, and the selectivity indexes of the sensor to formic acid / acetic acid and formic acid / propionic acid are 5.95 and 2.60 respectively. The selectivity index is calculated as

[0076] Appendix Figure 7 Figure 1 shows the resistance change graphs of the ZnO sensor prepared in Comparative Example 1 at 250 °C in different VOC gases and inorganic gases with a concentration of 1 ppm. The response of the ZnO sensor to 1 ppm formic acid is 55.21. The response of the sensor is Ra / Rg (Ra is the stable resistance of the sensor in a background gas of 20% oxygen and 80% nitrogen, and Rg is the stable resistance of the sensor in the target gas). It can be seen from the figure that the response of the ZnO sensor drops significantly. At the same time, the response values of the ZnO sensor to acetic acid and propionic acid also reach 4.49 and 39.51, and the selectivity indexes of the sensor to formic acid / acetic acid and formic acid / propionic acid are 15.5 and 1.4 respectively.

[0077] Appendix Figure 8 Figure 2 is the resistance change graph of the Au / ZnO sensor prepared in Example 1 at 250 °C in formic acid with a concentration ranging from 0.5 ppb to 1 ppm. It can be seen from the figure that Au / ZnO has high sensitivity, and the lowest detection limit can reach the ppt level.

[0078] Appendix Figure 9 Figure 3 is the resistance change graph of the Au / ZnO sensor prepared in Example 1 at 250 °C in 5 ppb formic acid under different humidity levels. It can be seen from the figure that humidity has a certain impact on the sensor response and will slightly reduce the sensor response.

[0079] Appendix Figure 10 Figure 4 is the long-term stability graph of the Au / ZnO sensor prepared in Example 1 at 250 °C for 100 ppb, 50 ppb, 10 ppb, and 5 ppb formic acid. It can be seen from the figure that the sensor has long-term stability.

[0080] Appendix Figure 11 XRD patterns of the catalytic materials: (a) Fe2O3; (b) V2O5; (c) CeO2; (d) Cr2O3; (e) Pd / Al2O3; (f) nanozeolite. It can be seen from the figure that these catalysts all have high crystallinity.

[0081] Appendix Figure 12 Figure 5 is the SEM pattern of the catalytic materials (a) SEM image of Fe2O3; (b) SEM image of V2O5; (c) SEM image of CeO2; (d) SEM image of Cr2O3; (e) SEM image of Pd / Al2O3; (f) SEM image of nanozeolite. It can be seen from the figure that the catalyst particle sizes are all in the micron level.

[0082] Appendix Figure 13It is the response graph of the Au / ZnO sensor prepared in Example 1 under the catalytic conditions of Fe2O3, V2O5, CeO2, Cr2O3, Pd / Al2O3 and zeolite at 250°C in inorganic gases and VOC gases with a concentration of 1 ppm; it can be seen from the figure that after adding the catalyst, the sensor response drops significantly, but Fe2O3 improves the selectivity of the sensor to acetic acid and propionic acid. After the pre-positioned Fe2O3 catalyst, the responses of the Au / ZnO sensor to formic acid, acetic acid and propionic acid are 52.93, 2.01 and 2.14 respectively, and the selectivity indexes of the sensor to formic acid / acetic acid and formic acid / propionic acid are 51.4 and 45.6 respectively.

[0083] Table 1: Detection results of the performance of the sensors prepared in Examples 1-6 and Comparative Example 1

[0084]

[0085] In summary, the sensor prepared from the hollow zinc oxide composite material loaded with nano-gold according to the present invention shows extremely high sensitivity to formic acid at a working temperature of 250°C. For formic acid with a concentration of 1 ppm, the gas-sensing response value reaches 2015.52. However, in order to overcome the problem of poor selectivity of the sensor, a catalytic layer is installed at the front end of the sensor in the present invention. This improvement effectively improves the selective response of the sensor to formic acid, reduces the interference of other gas components, and does not affect the performance of the sensitive material itself.

[0086] In the embodiments here, for the points not exhausted in the midpoint values of the technical scope claimed by the present invention and for the new technical solutions formed by the equivalent replacement of single or multiple technical features in the technical solutions of the embodiments, they are also within the scope claimed by the present invention; at the same time, in all the exemplified or unexemplified embodiments of the present invention, the various parameters in the same embodiment only represent an example (i.e., a feasible solution) of its technical solution, and there is no strict cooperation and limitation relationship between the various parameters. Among them, the various parameters can be replaced with each other when not violating the axiom and the requirements of the present invention, except as otherwise specifically stated.

[0087] The technical means disclosed in the present invention are not limited to the technical means disclosed by the above technical means, but also include the technical solutions formed by any combination of the above technical features. The above is the specific implementation manner of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

[0088] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A hollow zinc oxide composite loaded with nano-gold, characterized in that, The composite material is loaded with nano-gold on hollow-structured zinc oxide. The particle size of the nano-gold particles is 5-10 nm, and the size of the hollow-structured zinc oxide is 500-1200 nm. The molar ratio of gold to zinc in the composite material is 1:0.1-3.

0.

2. A method for preparing a hollow zinc oxide composite loaded with nano-gold as described in claim 1, characterized in that, The method comprises the following steps: S1. Adding a colloidal Au nanoparticle solution into a sodium zincate solution, and mixing and ultrasonically treating; S2. Then performing high-temperature treatment, followed by solid-liquid separation, and finally performing drying treatment to obtain the nano-gold-loaded hollow zinc oxide composite material.

3. The preparation method of a hollow zinc oxide composite material loaded with nano-gold according to claim 2, characterized in that, The colloidal Au nanoparticle solution is prepared by heating a chloroauric acid solution at 80-120 °C for 1-5 min and adding a trisodium citrate solution for reaction.

4. The preparation method of a hollow zinc oxide composite material loaded with nano-gold according to claim 3, wherein, The mass ratio of chloroauric acid to trisodium citrate is 2.5-5:

1.

5. The preparation method of a hollow zinc oxide composite material loaded with nano-gold according to claim 2, characterized in that In step S1, the concentration of the sodium zincate solution is 2-6 wt%, and the concentration of the colloidal Au nanoparticle solution is 8-16 wt%.

6. The preparation method of the hollow zinc oxide composite material loaded with nano-gold according to claim 2, characterized in that, In step S1, the volume ratio of the sodium zincate solution to the colloidal Au nanoparticle solution is 3-15:

1.

7. The preparation method of a hollow zinc oxide composite material loaded with nano-gold according to claim 2, characterized in that, In step S2, the high-temperature treatment temperature is 80-100 °C, and the time is 3-8 min.

8. A sensitive material for a sensor, characterized in that, The sensitive material comprises the hollow zinc oxide composite material loaded with nano-gold as described in claim 1.

9. A sensor highly sensitive to formic acid, characterized in that, The sensor comprises the sensitive material as described in claim 8.

10. The sensor highly sensitive to formic acid according to claim 9, characterized in that, The sensor comprises a honeycomb ceramic, an alumina substrate, gold interdigitated electrodes, and a sensitive material layer on the surface of the gold interdigitated electrodes. The sensitive material layer is a hollow zinc oxide composite material loaded with nano-gold. The honeycomb ceramic is loaded with iron oxide particles, and the iron oxide particles cover the upstream of the gas flow of the sensor sensitive layer to form a catalytic layer.

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