Microwave hydrothermal synthesis of nanoporous cobalt oxides and their gas sensing properties

In this paper, the precursors were synthesized by microwave hydrothermal method using Co(NO3)2·6H2O as raw material, CO(NH2)2 and KOH as precipitants, respectively. The precursors and calcined products were characterized by XRD, FESEM, and BET–BJH. The results show that both constituent and synthetic condition can determine the products morphology. When using KOH as precipitant, hollow Co3O4 nanorings were obtained whose precursor was synthesized at 140 °C for 3 h and calcined at 500 °C in air for 2 h. While using CO(NH)2, Co3O4 like-nanochains were obtained whose precursor was synthesized at 110 °C for 1 h and calcined at 420 °C in air for 2 h, and Co3O4 nanosheets were obtained while their precursor was synthesized at 140 °C for 3 h and calcined at 500 °C in air for 2 h. The sensitivity test of Co3O4 to alcohol reveals that the hollow Co3O4 nanorings show the best sensitivity, porous Co3O4 like-nanochains are superior to that of the porous nanosheets.

Graphical abstractPhotographs taken at the field emission scanning electron microscope of (a) nanosheet-like Co3O4, (b) nanochain-like Co3O4 and (c) nanoring-like Co3O4.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► CO32− acts as an inhibitor that affects the growth rates of precursors in different crystal directions. ► Nanosheet-like Co3O4, nanochain-like Co3O4, and nanoring-like Co3O4 were obtained by microwave hydrothermal process under different precipitants and synthetic conditions. ► Specific surface area of nano Co3O4 with various morphologies plays an important role in gas sensitivity to alcohol.