A facile route to metal-oxide nanocrystals by direct pyrolysis of metal-organic frameworks

Metal-oxide nanoparticles (NPs) are of particular interest in various industrial applications. However, current liquid-phase synthetic routes for metal-oxide NPs generally involve complicated processes. Herein, we demon-strate a simple direct route to metal-oxide NPs through the pyrolysis of their metal-organic frameworks (MOFs). As illustrated by the synthesis of ZrO2 and CeO2 NPs, we employed Zr(IV)-and Ce(IV)-based CAU-24 MOFs as precursors, and pyrolysis was performed in both air and molten NaCl environments. Pure oxide NPs with sizes of less than 200 nm were obtained via both routes. Compared with direct pyrolysis in air, the use of molten salt as a liquid reaction medium leads to much smaller ZrO2 NPs but facilitates the growth of CeO2 NPs. The results can be explained by the presence of different phases in the nanocrystal growth process.