Syntheses and characterization of well-crystallized birnessite

A modified oxidation-deprotonation reaction (ODPR) was developed to synthesize well-crystallized birnessite. We compared the conventional methods for synthesis of birnessite with the ODPR approach. The structural chemistry of birnessite was evaluated by high-resolution transmission electron microscopy (HRTEM), using an energy-dispersive spectrometer (EDS) to determine the Na+ content. The average oxidation states (AOS) of birnessite were determined by potentiometric titration. Infrared spectrometric (IR) and X-ray diffraction (XRD) analytical techniques were used to characterize birnessite. The HRTEM lattice image and low Na+ content suggest that there are no vacancies in the octahedral layers of birnessite. The AOS values of birnessite ranged from 3.77 to 3.87 and the presence of IR bands at 1153 and 1084 cm(-1) were attributed to the Mn3+-OH deformation. The results show evidence for the presence of the Mn3+ or Mn2+ in the structure of birnessite.