Carbon growth process on the cobalt-based oxides

Abstract

In this work, cobalt-based oxides (CoO, NiCo2O4, ZnCo2O4)/carbon nanostructures were obtained in the atmosphere of C2H2/N2 at relatively low temperature (less than 500 °C). Cobalt-based oxides here were not used as catalysts but oxidants to participate the redox reaction during the carbon deposition. Time-dependent evolution experiments were carried out to investigate the carbon growth process on the cobalt-based oxides. By ex-situ observation of SEM and TEM, we found that on the CoO surface, carbon grew from carbon dots to crystalline carbon layer. But for NiCo2O4 and ZnCo2O4, carbon nanotubes were obtained. The growth process of carbon nanotube followed the procedure of carbon dots – crystalline carbon layer – carbon nanotube. Reasons for the difference between CoO and binary metal oxides might be due to the reducibility and morphology. This work gives a general method to synthesize cobalt-based oxides/carbon nanostructures and direct observation of carbon growth process, which would provide a guidance for future design of carbon/cobalt-based oxides nanostructures.