Room temperature synthesis of hierarchical SrCO₃ architectures by a surfactant-free aqueous solution route

Novel SrCO₃ architectures were prepared by a facile aqueous solution route at room temperature using SrCl₂, Na ₂CrO₄, and NaOH as the starting reaction reagents and distilled water as the solvent. The synthesized products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction and high-resolution transmission electron microscopy. The SrCO₃ architectures are in dandelion-like and flower-like morphologies with diameters of 5-10 μm and composed of numerous well-aligned single-crystalline nanorods of 20-40 nm in diameter and 1-2 μm in length. It is found that the morphology of the final products is strongly dependent on the experimental parameters, such as the concentration of aqueous NaOH solution and the reaction temperature. Various controlled synthetic experiments indicate that the growth process of SrCO₃ architectures involves the growth of single-crystalline SrCrO₄ nanowires, the formation of CO₃^2- ions through the reaction between CO₂ gas from air and aqueous NaOH solution, and finally the formation of SrCO₃ architectures through the reaction between SrCrO ₄ and CO₃^2- ions controlled by the difference of the solubility product. In addition, a "rod to dumbbell to sphere" mechanism is proposed for the formation of the SrCO₃ architectures.