Facet- and Size-Related Electrical Conductivity and Piezocatalytic Behaviors of Co3O4 Crystals from Lattice Deviation

Size-tunable Co3O4 cubes (136 and 276 nm), cuboctahedra (168 and 240 nm), and octahedra (180 and 258 nm) have been hydrothermally synthesized. Synchrotron X-ray diffraction (XRD) analysis suggests best fitting of peaks into bulk and surface layer lattice components for all the samples. Fast Fourier transform (FFT) processing of high-resolution transmission electron microscopy (HR-TEM) images shows a regular array of lattice points in the interior bulk but significant spot distortion in the surface layer. The surface lattice deviation patterns are distinct for different particle morphologies. Their band gaps can vary with particle size and shape. For the smaller crystals, an octahedron is electrically highly conductive, but a cube is nearly insulating from representative single-particle measurements. Cuboctahedra and octahedra also show higher piezoelectric responses than cubes do. Regardless of the particle shape, the smaller crystals are clearly more piezocatalytically effective at dye degradation than the larger ones. Active species generated in piezocatalysis have been identified. Lattice deviations from crystal shape control is a good way to enhance material properties.