Morphology-controlled synthesis of CeO2 nanocrystals and their facet-dependent gas sensing properties

Recently, the influence of polar facets on the gas sensing performance of metal oxides has drawn much attention, yet the facet-dependent gas sensing properties of rare earth oxides have not been reported so far. In this work, taking CeO2 as an example, uniform single-crystalline nanopolyhedra, nanorods and nanocubes of cubic CeO2 were selectively prepared by a hydrothermal method at different temperatures and NaOH concentrations, using Ce(NO3)3 as the cerium source. According to X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis, these CeO2 nanocrystals possess different exposed crystal planes: {111} and {100} for nanopolyhedra, {110} and {100} for nanorods, and {100} for nanocubes. Abundant defects were confirmed on the surface of three CeO2 nanocrystals by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and photoluminescence (PL). Notably, gas sensors based on these three CeO2 nanocrystals exhibited distinct response values towards dimethylamine vapor in the following order: nanocubes > nanorods > nanopolyhedra, while excluding the effects of characteristic dimension and specific surface area. The response order of CeO2 nanocrystals is primarily ascribed to the different content of surface defects and {100} polar facets instead of {111} and {110} nonpolar facets.