Synthesis of cryptomelane- and birnessite-type manganese oxides at ambient pressure and temperature.

Cryptomelane-type octahedral molecular sieves (K-OMS-2) were successfully synthesized at ambient pressure and temperature by a simple one-step reaction pathway. We designed three synthesis mixes based on redox reactions of either MnSO4 or MnCl2 together with KMnO4 in aqueous solution. The synthesis products were characterized structurally (XRD, FTIR spectroscopy), morphologically (SEM, BET surface area), and chemically (SEM-EDX, ICP-OES). For all mixes, a precursor octahedral layered K-birnessite (K-OL-1) was formed after 1d that subsequently transformed into K-OMS-2. This transformation process depends on the pH of the reaction solution, the respective Mn(II) salt and time. We obtained K-OMS-2 materials with BET surface areas between 50.4 and 104.5 m(2) g(-1) and different crystallinities. The described method is reliable, reproducible, easy to handle and may be the basis to produce well defined Mn oxides that could be used for remediation and catalysis purposes.