Abstract
The porous zinc oxide-nickel oxide (ZnO-NiO) composite nanosheets were synthesized via sputtering deposition of NiO thin film on the porous ZnO nanosheet templates. Various NiO film coverage sizes on porous ZnO nanosheet templates were achieved by changing NiO sputtering duration in this study. The microstructures of the porous ZnO-NiO composite nanosheets were investigated herein. The rugged surface feature of the porous ZnO-NiO composite nanosheets were formed and thicker NiO coverage layer narrowed the pore size on the ZnO nanosheet template. The gas sensors based on the porous ZnO-NiO composite nanosheets displayed higher sensing responses to ethanol vapor in comparison with the pristine ZnO template at the given target gas concentrations. Furthermore, the porous ZnO-NiO composite nanosheets with the suitable NiO coverage content demonstrated superior gas-sensing performance towards 50–750 ppm ethanol vapor. The observed ethanol vapor-sensing performance might be attributed to suitable ZnO/NiO heterojunction numbers and unique porous nanosheet structure with a high specific surface area, providing abundant active sites on the surface and numerous gas diffusion channels for the ethanol vapor molecules. This study demonstrated that coating of NiO on the porous ZnO nanosheet template with a suitable coverage size via sputtering deposition is a promising route to fabricate porous ZnO-NiO composite nanosheets with a high ethanol vapor sensing ability.
Highlights
Development of semiconductor oxide-based gas sensor has attracted much attention because of environmental problems associated with harmful air pollution
The sheet-like ZnO crystals are usually densely stacked by each other; the hierarchical structure may provide high spaces for target gases to diffuse into the inner region of the sensing material which improves their gas detection ability
The porous zinc oxide-nickel oxide (ZnO-NiO) composite nanosheets with two NiO coverage layer sizes were systemized by changing the deposition duration from 20 min to 40 min, which corresponded to the sample codes of ZnO-NiO-1 and ZnO-NiO-2, respectively
Summary
Development of semiconductor oxide-based gas sensor has attracted much attention because of environmental problems associated with harmful air pollution. ZnO in a form of nanostructure is of potential interest for the gas-sensing material application because nanostructured ZnO has a high specific surface area that can improve its gas-sensing performance towards target gases [5,6,7]. P-type Co3O4-decorated ZnO nanowires synthesized by a thermal evaporation method show superior ethanol and NO2 gas sensing performances than that of the pristine ZnO nanowires [15] These examples visibly demonstrate that the p-n heterojunction is beneficial to improve gas-sensing ability of the p-n composite structure. The gas-sensing response is highly associated with the microstructure of oxides; the fabrication of unique microstructure with porosity and large specific surface area is beneficial to improve the sensitivity of sheet-like ZnO sensing material. The ZnO-NiO composites with a suitable NiO crystallite loading content and a visible porous sheet structure demonstrate markedly improved gas-sensing performance towards ethanol vapor
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