Preparative parameters and framework dopant effects in the synthesis of layer-structure birnessite by air oxidation

An air oxidation method has been used to synthesize a layer-structure birnessite (OL-1) by the oxidation of Mn2+. The synthesis was accomplished in a much shorter time than other methods such as the reduction of MnO4- and redox reactions between Mn2+ and MnO4-. Thorough investigations of preparative parameters such as the rate and extent of oxidation, the concentration of OH-, and the aging process were made to understand the synthesis of birnessite using air oxidation. Five metal (Fe, Co, Ni, Ca, and Cd) cations were added to the initial reactant solutions as framework dopants to study their effects on the synthesis and to modify the properties of the resulting birnessite. The crystal phases, average manganese oxidation states, surface areas, and thermal properties of birnessites prepared under different conditions were studied to understand the influence of these conditions on birnessite formation. Birnessite prepared by this air oxidation method was stable up to 500 degreesC.