A facile low-temperature synthesis of hierarchical porous Co3O4 micro/nano structures derived from ZIF-67 assisted by ammonium perchlorate

Abstract

The thermolysis of metal–organic frameworks (MOFs) opens a new window for the fabrication of oxide semiconductors due to its simplicity, low cost and large-area uniformity of the resulting material. However, this approach usually requires high annealing temperatures over 350 °C. In this work, sub-micro hierarchical porous Co₃O₄ dodecahedra were synthesized by the thermolysis of zeolitic imidazolate frameworks 67 (ZIF-67) at a low temperature of 268 °C assisted by ammonium perchlorate (AP), in which ZIF-67 was employed as a metal source and a sacrificial template. The formation mechanism was probably attributable to the generation of Co–O bonds between the Co atom of ZIF-67 and the O atom of AP at lower temperatures which can accelerate the weakening of Co–N bonds of ZIF-67 and thus lead to an abrupt decomposition of ZIF-67 at 268 °C. More importantly, the generation of the Co–O bond and the weakening of the Co–N bond were identified using the FTIR, Raman and XPS results. As confirmed by DFT results, ZIF-67 can be decomposed into Co₃O₄ at lower temperatures assisted by AP than that in air. In addition, the obtained sub-micro hierarchical porous Co₃O₄ dodecahedra showed a very large specific surface area of 106.11 m² g⁻¹, much larger than that in previous reports. Therefore, this work can provide a novel atomic insight into the formation mechanism of Co₃O₄ hierarchical porous structures derived from ZIF-67 with AP at lower temperatures and also an energy-efficient method to synthesize porous metal oxide structures.