Ultrasound-Assisted Nanocasting Fabrication of Ordered Mesoporous MnO₂ and Co₃O₄ with High Surface Areas and Polycrystalline Walls

Highly ordered mesoporous MnO 2 and Co 3 O 4 are prepared by adopting an SBA-16-based nanocasting strategy under ultrasonic irradiation and characterized by means of numerous techniques. It is shown that the as-fabricated manganese and cobalt oxides possess well-ordered mesoporous architectures with polycrystalline pore walls. With the assistance of ultrasonic waves, the metal precursors can readily diffuse from the bulk solution to the inner pores of the silica template. The repeated four-step fabrication process, filling → filtration → washing → calcination, is beneficial for preventing the formation of manganese or cobalt oxide nanoparticles on the external surfaces of the template and facilitating more metal precursors to fill the mesopore channels of the template. After removal of the silica template by a 2 mol/L NaOH aqueous solution, the as-received highly ordered mesoporous MnO 2 and Co 3 O 4 exhibit a surface area of up to 266 and 313 m 2 /g, respectively, which is about 2−3 times higher than that reported in the literature. The mesoporous MnO 2 and Co 3 O 4 samples are more readily reduced at low temperatures and show much better catalytic performance for toluene complete oxidation than their bulk counterparts. The excellent performance of the mesoporous materials is ascribed to their ordered mesoporous structure, better reducibility, and high surface area.