Engineering of Mn₃O₄@Ag microspheres assembled from nanosheets for superior O₃ decomposition

Manganese oxides have wide application in the ambient decomposition of ozone, although their activities are affected by many parameters. Morphology engineering and metal doping are, together, one of the most effective methods to enhance catalytic activity for O₃ decomposition. Herein, a topochemical transformation route to Mn₃O₄ nanospheres composed of 2D nanosheets is first provided by using layered β-MnOOH as the precursor. Then, silver nanoparticles are deposited over the Mn₃O₄ nanosheets via a redox reaction without any extra reducing agents. In comparison with Mn₃O₄ with a conventional octahedral morphology, the prepared Mn₃O₄ nanosphere (Mn₃O₄-NF), and its Ag-doped composite, Mn₃O₄@Ag (Mn₃O₄@Ag-NF), both retain the morphology of β-MnOOH, and display better reducibility and higher oxygen vacancies. The best catalytic performance for O₃ decomposition is found over Mn₃O₄@Ag-NF, which exhibits ∼88.5% removal efficiency within 24 h at a space velocity of 600 L g^-1 h^-1 and a relative humidity of 50% at room temperature. This work emphasizes the advantages of nanosheet morphology and metal doping in optimizing the catalytic activity for O₃ elimination of manganese oxide.