A multi-technique approach for studying Na triclinic and hexagonal birnessites

Abstract Birnessite is a ubiquitous natural Mn oxide. This layered material is involved in a large variety of ion-exchange and redox reaction in soils and sediments. Synthetic Na-triclinic birnessite with a general formula [Mn III 0.35 Mn IV 0.65 O 2 ][Na + 0.35 0.7H 2 O] was converted into hexagonal birnessite by acidic treatment at pH = 3.5. Both solids were fully characterized by TEM, SEM, PXRD, FTIR, Raman scattering, 23 Na as well as the first 1 H MAS NMR birnessite spectra were reported. The surfaces of both forms were fully analyzed by XPS: a particular attention was paid to the determination of the oxidation state of Mn derived from the fitting of XPS Mn 3p or Mn 2p 3/2 features. An excess of reduced Mn at the surface in comparison to the bulk materials was evidenced.