Microporous Na-birnessite-type manganese oxides are synthesized by oxidation of Mn(OH)2 with K2S2O8 in strong alkaline environment. Subsequent ion-exchange reactions in aqueous solutions containing Sr, Ba promote their incorporation into the layered structural frameworks, which upon further hydration lead to the respective layered Buserites. Chemical composition and surface structure are assessed by X-ray powder diffraction, nitrogen- and argon- sorptiometry. Na-birnessites and Sr-buserites display good crystallinity. Ba-buserites consist mainly of nanocrystals. Their N2 adsorption/desorption isotherms of resemble IV-type isotherms. Integral and differential pore distribution curves obtained by N2-sorptiometry exhibit out-of-layers pores of 4-5 nm and 10-20 nm. Na-birnessites, Sr- and Ba-buserites possess external B.E.T surfaces of 75.6, 49.2 and 93.6 m2/g respectively. Considerable adsorption volumes of 14, 17 cm3/g for P/P0 = 0.05 for Na-birnessites and Ba-buserites are assessed by Ar-sorptiometry. Differential pore distribution curves confirm inner-layer micropores of 5 to 7 Å with a B.E.T specific area of 76.2 m²/g for Na-birnessites and 51.8 m²/g for Ba-buserites. Na-birnessites and Sr-, Ba-buserites possess enhanced ionic exchanging capacity, acting as a “sink” for heavy metal cations such as Fe2+, Fe3+, Co2+, Ni2+, As3+. The retention of U, Cs and Sr radioisotopes by them unfolds their salient anti-pollution potential for soil and subwater ecosystems.

Department of Chemistry Faculty of Natural Sciences Tirana Albania