| ZnO is a n-type semiconductor oxides with energy gap of3.37eV, whichhas an excellent electronic mobility and chemical stability. In recent years, ZnOgas sensor has aroused majority of researchers’ attention. Doping noble metalelements in ZnO plays an extremetly important role of its performance, which isa focus in the study of ZnO gas sensors.In this paper, ZnO microstructures are prepared by hydrothermal method,and noble metallic oxide was doped and modificated to enhance the gas sensing.These morphologies and structures are characterized by scanning electronmicroscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy (XPS). The gas-sensingmeasurement was carried out based on the CGS-1TP, and the main conlusionscould be obtained as follows:(1) The rod-like ZnO microstructures with wurtzite hexagonal structurewere synthesized using hydrothermal method. The measured results showed thatthe the gas sensor held the maximum sensitivity of55.4%to200ppm methaneat5V which is the optimum operating voltage. Finally, the detection limit could down to1ppm.(2) The rod-like ZnO microstrictures were doped by different concentration(0.1,0.25,0.5, and1.0wt%) Pd element to improve the ethanol gas-sensingproperties. The characterization of the Pd/ZnO microstructures showed thatthere is no obvious change in the morphologies. Besides, the results of theethanol-sensitive properties detected in200ppm ethanol showed that the0.25wt%Pd/ZnO device has the utmost sensitivity. Simultaneously, the0.25wt%gas sensor shows better operating temperature (325℃) and lowerresponse/rescovery time (10/7s), which is superior to the pure one (400℃and17/24s).(3) The folwer-like ZnO microstructures with various concentration (0,0.5,1.0,3.0, and5.0wt%) dopant of Co were prepared by the hydrothermal method.The morphologies were changed significantly. The results of methane-sensitiveproperties showed that the Co/ZnO sensors have the best selectivity for methanethan the CO and H2. Then, when the amount of Co is1.0wt%, the optimumoperating temperature to methane is about140℃. In addition, the peak value ofthe sensitivity is about3.55, and the response/recovery time is about19/27s,repectively, which has an advatange over the one reported in other paper. Finally,its detecting limitation is as low as0.05ppm.(4) The adding of noble metal element promote the dissociation process ofmolecular oxygen on the surface of ZnO sensitive material, and theheterojunction accelerated the speed of carrier to enhance the gas sensing. And only appropriate noble metal element concentration can significantly improvethe gas sensing properties. |
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