Aqueous solution synthesis of Cd(OH)2 hollow microspheres via Ostwald ripening and their conversion to CdO hollow microspheres

In this work we demonstrate that Cd(OH)(2) hollow microspheres could be prepared in high yield by a facile aqueous solution route from the mixture of aqueous solutions of CdCl2, Na2MoO4, and NaOH at room temperature. The synthesized products are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction, and the nitrogen adsorption-desorption isotherm technique. The Cd(OH)(2) hollow microspheres have an average diameter of 3 mu m and hollow interior of about 1.5 mu m. The shell consists of numerous single-crystalline nanoplates with thickness of about 100 nm and sizes of 400-700 nm. The controlled synthetic experiments indicate that the growth process of Cd(OH)(2) hollow microspheres involves first the formation of CdMoO4 solid microspheres and then the formation of Cd(OH)(2) solid microspheres through the reaction between CdMoO4 and OH- ions controlled by the difference of solubility product for CdMoO4 and Cd(OH)(2). The Ostwald ripening mechanism is proposed to account for the formation of Cd(OH)(2) hollow microspheres on the basis of scanning electron microscopy observations of intermediate products at different precipitation stages. Furthermore, the Cd(OH)(2) hollow microspheres can be easily converted to CdO semiconductors with similar morphology by calcining Cd(OH)(2) in air at 350 degrees C for 4 h.