| As an important member of the sensor family,gas sensors can realize the quantitative and qualitative detection of gases by converting characteristics such as the component concentration of the measured gas into electrical signals,which plays an important role in the fields of industry,environmental protection and medical treatment.ZnO-based gas sensors are the earliest and most widely used branch of metal oxide semiconductor sensors.Since their discovery in the last century,they have attracted much attention because of their low cost,easy portability,simple preparation,and high sensitivity.Based on the widely used ZnO gas-sensitive materials,a series of ZnO-based composite nanomaterials were prepared by hydrothermal method,and the prepared ZnO-based composite nanomaterials were used as gas sensors.Gas-sensitive properties.The effects of the formation of heterostructures,noble metal doping,and nanometer size on the sensing properties of ZnO-based gas-sensitive materials were analyzed.The main research contents and results are as follows:1.A two-step hydrothermal method was used to synthesize a new composite nano-ZnO-ZnS-x(x=5,10,15,20)heterojunction with ZnS-modified ZnO nanowires and characterize its morphology and structure.The results show that as the concentration of Na2S solution increases,the content of ZnS in the formed heterojunction increases,and the ridgeline of the nanowires accompanying the ZnO-ZnS heterojunction changes from clear to fuzzy,indicating that the thickness of the ZnS shell structure increases.Gas sensitivity test results show that compared with pure ZnO-NWs,except for ZnO-ZnS-20,the response of ZnO-ZnS-x heterojunctions prepared with different concentrations of Na2S solution to H2S has significantly improved at different operating temperatures.Their best working temperature is 300℃.Among them,ZnO-ZnS-10 exhibits the highest gas sensitivity to H2S,and its response to 5 ppm of H2S(0.68)at a lower operating temperature of 150℃ and the response value of pure ZnO-NWs at 300℃(0.72).Indicating that the formation of ZnS shell structure with appropriate content can significantly enhance the response of ZnO-NWs to H2S at lower operating temperatures,realize the low temperature detection of H2S gas by the sensor,and effectively reduce the energy consumption of the sensor.After the sensor made of this material is left for 5 weeks,its response value changes little with time,showing good measurement stability.2.A simple one-step low-temperature hydrothermal method was used to synthesize ZnO nanowires with an average diameter of 150 nm,and then Pd-doped ZnO nanostructures were prepared by polyvinylpyrrolidone(PVP)-mediated photochemical deposition(PCD)method.The morphology and structure were characterized,and its sensitivity to acetone gas was studied.The results show that the amount of PVP added has a significant effect on the loading of Pd nanoparticles on the ZnO nanowires.When the amount of PVP added is 48 mg,the uniformity of the dispersion of Pd particles on the surface of ZnO-NWs is the best;In the range of 200-400℃,the response values of four Pd-ZnO-x(x=12,48,90,180)sensors with different Pd doping levels to acetone gas are higher than those of pure ZnO-NWs sensors,of which Pd-ZnO-48 has the best gas sensitivity performance among all Pd-ZnO-x;the optimal operating temperature of all sensors is 300℃,at which the Pd-ZnO-48 sensor’s response value to 20 ppm acetone gas is 0.6,It is about three times the response value(0.23)of pure ZnO-NWs under the same conditions.In the presence of eight interference gases of the same concentration,it was found that Pd-ZnO-48 has higher selectivity than pure ZnO-NWs.3.Using a simple low-temperature hydrothermal method,the ZnO-NWs with an average diameter of 50 nm were prepared by effectively controlling the size of the nanostructures by rationally adjusting the molar ratio,hydrothermal time,and hydrothermal temperature of the initial raw materials.PVP-mediated photochemical deposition(PCD)was used to dope Pd particles on ZnO-NWs to form Pd-ZnO-x(x=12,48,90,180)composite nanostructures,and characterize their morphology and structure.The effect of the size of Pd-ZnO composite nanostructures on its gas-sensitivity properties was described.The test results show that compared with 150 nm ZnO-NWs and Pd-ZnO-x,50 nm ZnO-NWs and Pd-ZnO-x sensors show greater advantages in sensitivity and selectivity.The 50nm Pd-ZnO-48 prepared at 48 mg of PVP has the highest response value,and its optimal operating temperature is 300℃.At this temperature,it has a good response to 1 ppm,3 ppm,5 ppm,10 ppm,and 20 ppm.The response values of acetone gas are as high as 0.28,0.45,0.52,0.66,and 0.89.This ultra-high sensitivity effect is not only due to the chemical sensitization and electron sublimation effects between Pd-ZnO,but also related to the nano-size effect of ZnO. |
