Co3O4multilayer nanosheets were synthesized by a hydrothermal method and a post annealing treatment process. The effect of solution concentration and ratio on the morphology of Co3O4precursor was studied. The crystalline structure, morphology and elemental composition of Co3O4multilayer nanosheets were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy technologies. When exposed to reducing gas such as ethanol, resistance of Co3O4multilayer nanosheet sensor increases quickly, demonstrating that the Co3O4multilayer nanosheets are p-type conductivity. For 100 ppm alcohol at 240 °C, the sensor response is as high as 32, indicating that the powder of Co3O4multilayer nanosheets is a very promising low-powder gas sensing material.

For most resistive sensors, the change of carrier concentration usually dominates the conductivity change in the gas sensing process, while the role of carrier mobility change is difficult to reflect....

ZnO microspheres with complete and perforated morphologies were synthesized by a simple solvothermal method via regulating solvent composition. Material characterization has included XRD, SEM, XPS, Raman spectrum and Brunauer–Emmet–Teller (BET) methods. The introduction of ethanol into the solvent resulted in the morphology change from complete to perforated spheres, meanwhile generated more surface adsorption sites and larger specific surface area as demonstrated by XPS and BET analysis. A possible formation mechanism of ZnO microspheres is proposed to explain the perforation development process. The gas sensing performances of the sensors prepared using the complete and perforated spheres were compared to reveal the positive impact of morphology change.