Topochemical formation of mesoporous MnO crystals

Heating hausmanite ZnMn2O4 in a reducing atmosphere results in the formation of rock salt MnO with significant Zn substitution. Further heating at elevated temperatures under reducing conditions results in Zn being reduced and expelled in the vapor phase, leaving behind nearly pure rock salt MnO. Used judiciously, the volume loss associated with such vapor-phase leaching can be employed for the formation of mesoporous MnO crystals with connected 30-60 nm pores, through a process of topochemical conversion. In this contribution we examine in detail the driving forces which induce vapor-phase leaching as well as the interplay between crystallography and crystal morphology which permit these unusual materials to be formed.