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 + /Mg 2+, or K + /Mg 2+ 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 Na 4.7 Mn 14 O 27.7 ·8.7H 2 O and K 4.6 Mn 14 O 27.9 ·6.6H 2 O, respectively. α-MnO(OH) coexists with Na−OL-1 in the synthesis where NaMnO 4 aqueous solution is added to the solution containing ethanol, water, and sodium hydroxide. When Mg(MnO 4 ) 2 was used as the oxidant, more Mg 2+ 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.