Template-free solvothermal synthesis of hollow hematite spheres and their applications in gas sensors and Li-ion batteries

Magnetite (Fe3O4) hollow spheres were prepared by solvothermal reaction of ethanol solution containing Fe-acetate and L-lysine, and were subsequently transformed into hematite (Fe2O3) hollow spheres with nanoscale (20-30 nm) thin shells by heat treatment at 500 degrees C for 2 h. Both the as-prepared and heat-treated hollow spheres contained another small sphere within each shell, which was attributed to the following solvothermal self-assembly reactions: (1) the nucleation of Fe3O4 spheres, (2) lysine capping on the nuclei, (3) the growth of lysine-capped particles by cross-linking between lysine molecules, and (4) the formation of Fe shell layers by the interaction between Fe ions and outer lysine molecules. In the assembly reaction, L-lysine with amino and carboxyl radicals played the key role. The heat-treated Fe2O3 hollow spheres showed significantly enhanced C2H5OH sensing characteristics and promising Li-ion intercalation behaviors.