This paper reports a convenient and facile preparation of single-crystalline palladium with controllable shape based on the reduction of kinetic control via hydrochloric acid oxidative etching. The concentration of HCl added to the reaction solution was found to be crucial for the shape evolution of palladium nanocrystals from nanocubes bounded by {100} facets to octahedrons by {111} facets. Palladium nanocubes can be readily obtained at a fast reduction rate without the involvement of additional HCl. With the introduction of a certain amount of HCl to the precursor solution, truncated nanocubes with {111} facets were formed, and the increase of HCl led to the slower reduction rate and the formation of palladium cuboctahedrons enclosed by six {100} facets and eight {111} facets at the expense of gradual shrinkage of {100} facets. The probable mechanism of morphological transformation was proposed upon a batch of experiments. The shape-dependent catalytic performances of as-obtained palladium nanocrystals were investigated by the structure-sensitive reaction of formic acid oxidation. It was found that catalytic activities of palladium nanocrystals displayed a strong dependence on the facets exposed on the surface, and cubic palladium exhibited the best catalytic performance compared with cubooctahedral and octahedral palladium nanocrystals.

Co3O4 nanocubes with perfect shape were synthesized by a simple hydrothermal route in which Co3O4 was directly prepared in the one-pot process with aging temperature set at 160 °C without a subsequent calcination. In this study, as the whole process is sintering free, this can successfully avoid the agglomeration of nanoparticles and protect the integrity of perfect crystal form to the maximum extent. Cubic Co3O4 nanoparticles were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. Important factors influencing the nanoparticles’ formation were discussed, which include temperature, molar ratio of Co(Ac)2 to NaOH, reactant concentration, and the use of surfactant. Optical property was investigated by Raman spectroscopy and UV–Vis spectroscopy. Magnetic property measurement indicated that the sample exhibited a low Néel temperature (33 K) and bulk antiferromagnetic coupling due to geometric confinement of antiferromagnetic order within the nanoparticles. Below TN, the noteworthy exchange bias interaction between ferromagnetically coupled surface spins and underlying antiferromagnet-like coupled surface spins has also been observed.

Hollow metal nanostructures have received increasing interest because they exhibit unique chemical and physical properties different from their solid counterparts. In this work, the autocatalytic-reduction approach based on the self-decomposing of metal hydroxides and oxides is reported, which is distinct from the traditional template methods. Under solution conditions of a reducing atmosphere, metal hydroxides can serve as both the autocatalytic reagent and the sacrificial templates in the reaction process. It is demonstrated that the autocatalytic-reduction method is a general approach to fabricate a series of metal hollow structures, including hollow Ni nanospheres (NSs), Ni nanotubes (NTs), bead-like Ni NSs, and hollow Cu microspheres. Moreover, the structural diversity of original M(OH)x or MOx/2 (M = metal) templates allows the preparation of size and shape-adjustable templates. A possible mechanism for hollow structure formation is also proposed.