New layered double hydroxides containing intercalated manganese oxide species: synthesis and characterization.

Manganese oxide species (MnO(x)) have been intercalated within the gallery spaces of Mg-Al layered double hydroxides (LDHs). Synthesis of these materials was achieved by ion-exchange of the LDH-nitrate precursor with permanganate anion followed by reduction with organic reagents, such as glucose, ethanol, and ascorbic acid. Elemental analysis, X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, HR-TEM, and N(2) sorption analyses have been used to characterize these materials. TEM micrographs of LDH-MnO(x) materials revealed platelike morphology, characteristic of hydrotalcite-like compounds. Chemical analysis results showed that permanganate anions exchanged with nitrate anions. FT-IR and Raman spectroscopy confirmed the reduction of the permanganate anions after treatment with the organic reagents. The XRD diffraction patterns of LDH-MnO(x) revealed that the layer structure is maintained after all synthetic steps. The observed basal spacings of intercalates varied depending on the reducing agent; the largest expansion was 9.93A, corresponding to the use of ascorbic acid. The specific surface areas were also affected according to the organic reagent used, indicating that the structural modifications in the interlayer domain observed by X-ray diffraction also influence the microtextural properties.

Self-assembly of microporous manganese oxide octahedral molecular sieve hexagonal flakes into mesoporous hollow nanospheres.

Manganese oxide hollow nanospheres were prepared using a straightforward, template-free synthesis. The resulting material was mesoporous, crystalline, and of uniform diameter. The nanospheres were characterized by XRD, HR-SEM, and HR-TEM, and pore size distributions were calculated from nitrogen desorption. Unlike previous synthesis methods that use an inorganic template, this procedure requires no separation after synthesis to remove the template. The nanospheres are composed of hexagonal gamma-manganese oxide flakes and are approximately 400 nm in diameter. gamma-MnO2 is composed of a ramsdellite matrix (1 x 2 tunnels) with randomly distributed microdomains of pyrolusite (1 x 1 tunnels). These materials could have applications as cathodic battery materials, oxidation catalysts, catalyst supports, and adsorbents for pollutants.