Formaldehyde Controlling the Synthesis of Multishelled SiO₂/Fe_xO_y Hollow Porous Spheres

A concise and facile sol–gel method to prepare multiple magnetic SiO2/FexOy hollow porous spheres was developed. A series of SiO2/FexOy hollow porous spheres consisting of single shell, yolk–shell, double shells, and triple shells could be obtained by simply adjusting the formaldehyde amount, as Fe(acac)3 was used as the shell-forming promoter. As the formaldehyde amount increases, the morphology of the as-prepared hollow spheres changed from single-shelled, yolk-shelled, double-shelled, to triple-shelled and then turned back. The spheres possess a large specific surface area (∼966 m2/g), uniform mesopores (∼4.5 nm), and large pore volume (1.37 cm3/g). Moreover, the yolk-shelled spheres have been successfully used in in situ adsorbing and reducing heavy metal ions in aqueous solution; the results suggested that it was an efficient adsorbent and convenient to concentrate from water.