A Generalized Synthesis of Metal Oxide Hollow Spheres Using a Hydrothermal Approach

Hollow spheres of crystalline metal oxides were synthesized in a simple one-pot synthesis via a hydrothermal approach. Various metal salts were dissolved together with carbohydrates in water, and the mixtures were heated to 180 °C in an autoclave. During the hydrothermal treatment, carbon spheres are formed with metal ions incorporated into their hydrophilic shell. The removal of carbon via calcination yields hollow metal oxide spheres. Using this process, we can produce a wide range of metal oxide hollow spheres that are not accessible via sol−gel chemistry. In this paper, we report the synthesis of Fe 2 O 3, NiO, Co 3 O 4, CeO 2, MgO, and CuO hollow spheres that are composed of nanoparticles. The surface area and thickness of the shell can be varied or controlled by the carbohydrate:metal salt concentration.