Colloidal synthesis and formation mechanism of calcium molybdate notched microspheres

Abstract

A special structure, calcium molybdate (CaMoO₄) notched microspheres, were prepared by a solution-phase rapid-injection-based route using only CaCl₂, (NH₄)₆Mo₇O₂₄, and sodium dodecyl sulfate as reagents and ethylene glycol as a solvent. X-ray diffraction, scanning electron microscopy, transmission electronic microscopy and an X-ray energy dispersive spectrometer were used to characterize the obtained samples. The notched microspheres were uniform in size and shape, with each sphere containing one notch on its surface. The results show that the formation process of the CaMoO₄ notched microspheres is due to a “two-step” growth process, in which CaSO₄ nanorods are formed first and then CaMoO₄ microspheres are grown on the surfaces of the CaSO₄ nanorods. The reaction intermediate, the CaSO₄ nanorods, acts as a self-template for the formation of “CaMoO₄ sphere gripped CaSO₄ nanorod” structures, and finally produce very special structures – CaMoO₄ notched microspheres. The shape and size of the notched CaMoO₄ samples can be tuned from ellipses to spheres with diameters in the range of 0.1–1 μm by controlling the reaction conditions.