Birnessite Reaction Lab Report

Summary for the H3O+ in the Birnessite (H-Bir) The presence of H3O+ in birenssite had been reported by Johnson1. In this paper, the author discussed that the hydrogen birnessite contained structural water and either hydroxyl hydronium (H3O+), or both. Interlayered H2O molecules inside the birnessite play an important role to the structure. The interlayer H2O is strongly bound to the interlayer molecules, like Na+, K+ or H+. Typically, the H-Bir could be synthesized vial by a co-precipitation method developed by Golden2. The reactant were MnCl2, HCl (pH =2), NaOH, and O2. The XRD for H-Bir was shown, it was similar to Na-Bir as well. 2The interlayer distance in c direction of H-Bir was shown ~ 7.29 Å which slight greater than Na+ (7.241 Å) and K+ (7.08 Å). In the Mid-IR data, the spectrum of H-Bir was showed sharp band at 1300 cm-1, 2300 cm-1, which didn’t appear in Na or K birnessite. From the infrared spectra, another band appeared at 4650 cm-1 was due to a combination mode of OH or H3O+. These bands confirmed the presence of hydroxyl or hydronuim, H3O+.

He synthesized the H-Bir with low PH, from pH 2 to pH 5. The (001) peaks of H-Bir were about 7.265, 7.196, 7.231 and 7.248 Å at the pH of 5, 4, 3, and 2, respectively. Comparing Na-Bir, some of the Mn3+ in the H-Bir showed disproportion and migration process to form Mn2+ and Mn4+. Then the H+, Mn2+ and Mn3+ cations compensated the negative layer charge, with the amount of interlayer Mn2+ cations decreasing at the lower pH. Drits4 and Silvester5 also addressed that Na-Bir synthesized at the low pH showed a significant migration of Mn2+ and M3+ cations into inlayer of HBi. Due to disproportion of Mn3+, the H-Bir had greater oxidation state range of Mn in the interlayer range compared to other synthetic birnessite. This implied that H-Bir had broadened absorption features in its interlayer