Phase Transition of Non-equilibrium Wurtzite CoO: Spontaneous Deposition of Sensing Material for Ultrasensitive Detection of Acetone

ABSTRACT A nanoscale sensing material was prepared in a facile manner via the phase transition of wurtzite CoO to spinel Co3O4, as a new gas sensor preparation platform. The combination of a h-CoO → β-Co(OH)2 phase transition followed by thermal oxidation led to the spontaneous deposition of Co3O4 on interdigitated electrodes. The prepared Co3O4 nanoplates exhibited good contact adhesion with the sensor substrate, which obviated the need for conventional film forming processes, and were shown to be suitable for direct gas sensing. Compared to other Co3O4 sensors, the phase-transitioned Co3O4 nanoplates showed very high sensitivity to acetone gas (12.5 for 1 ppm acetone) in the range 20–1000 ppb at an operating temperature of 200 ℃ and enhanced selectivity. The improved performance of the Co3O4 nanoplates was attributed to typical crystal facets with mainly exposed (111) planes as well as an enlarged surface area during phase transition. Therefore, it was concluded that phase transition methods can be applied to promising sensing substances to develop a variety of related ultrasensitive acetone sensors.