Manganese oxide nanomaterials hold promise for sustainable nanotechnologies given their utility for a variety of applications, the Earth’s abundance of manganese, and their low toxicity relative to other nanomaterials. However green scalable synthesis methods for such nanomaterials are needed. We report here a green room-temperature synthesis of polycrystalline Mn3O4 nanowires. In this procedure, aqueous Mn(II) is oxidized under circumneutral conditions by atmospheric oxygen in the presence of nanocrystalline iron oxide (α-Fe2O3), an inexpensive catalyst, and a classic biochemical Good’s buffer, PIPES (piperazine-N,NI-bis(2-ethanesulfonic acid). The synthesis method is novel due to its simplicity, minimal energy input and waste output, and potential scalability. The Mn3O4 nanowires have been characterized with a suite of electron microscopy techniques.