Syntheses of Birnessites Using Alcohols as Reducing Reagents:  Effects of Synthesis Parameters on the Formation of Birnessites

This study shows that synthetic birnessite, an octahedral layered manganese oxide material called OL-1 can be synthesized with Na+, K+, Na+/Mg2+, or K+/Mg2+ ions as interlayer cations by redox reactions between permanganate and alcohols in a strong basic media. The synthesis processes were followed by powder X-ray diffraction (XRD) studies. OL-1 samples have been characterized by XRD, chemical analysis, average oxidation states measurements, and scanning electron microscopy studies. Results show that all OL-1 samples have an interlayer spacing of ∼7.0 Å. The average oxidation states of manganese fall in a range of 3.60−3.70. The chemical compositions for typical Na−OL-1 and K−OL-1 are Na4.7Mn14O27.7·8.7H2O and K4.6Mn14O27.9·6.6H2O, respectively. α-MnO(OH) coexists with Na−OL-1 in the synthesis where NaMnO4 aqueous solution is added to the solution containing ethanol, water, and sodium hydroxide. When Mg(MnO4)2 was used as the oxidant, more Mg2+ ions were accommodated in OL-1 than in previous reports. The interlayer space is propped opened by intercalating hexylammonium ions between the layers, confirming the layered structure.