Facile synthesis of air-stable Prussian white microcubes via a hydrothermal method

Air-stable Prussian white (PW) microcubes were fabricated by the slow dissociation of K₄[Fe(CN)₆] under hydrothermal condition without the protection of inert atmosphere. Mössbauer spectra and Fourier transform infrared (FT-IR) spectrum were used to characterize the composition of PW. X-ray diffraction (XRD) identified the obtained PW was monoclinic, and the purity was high. Scanning electron microscopy (SEM) images indicated the cubes were composed by solid cubes and hollow cubes. The shape of crystals strongly depended on the concentration of K₄[Fe(CN)₆], the hydrothermal temperature as well as the reaction duration. The lower concentration and lower temperature resulted in perfect cubic crystals, while the higher concentration or the higher temperature resulted in irregular cubic crystals. After exposing in air for 2 months, no oxidation of PW occurred. To explain the formation of the PW microcubes, a layer-by-layer growth mechanism was put forward based on the low dissociation rate of K₄[Fe(CN) ₆]. The partially solubility of PW in water caused the formation of hollow cubes.