Magnesium manganese oxide nanoribbons: Synthesis, characterization, and catalytic application

A todorokite-type magnesium manganese oxide molecular sieve material with a morphology of nanoribbons has been synthesized using a combination of techniques consisting of a sol-gel process to synthesize a nanosized tetraethylammonium manganese oxide layered material, an ion-exchange method to prepare a thin-film Mg-buserite (Mg-OL-1) precursor, and a hydrothermal reaction to transform the Mg-buserite to nanoribbonlike Mg-todorokite (Mg-OMS-1) material. The transformation of the Mg-buserite thin films to Mg-todorokite nanoribbons has been studied using XRD and TEM. XRD data indicate that the structural transformation of Mg-OL-1 to Mg-OMS-1 is completed after hydrothermal heating at 150 °C for about 40 h and at 200 °C for less than 8 h. TEM data show that the nanoribbons form at an early stage of the hydrothermal treatment, followed by the appearance of lattice fringes. TEM data also indicate that the well-formed nanoribbonlike crystals have a uniform tunnel dimension along the a axis and a long-range-ordered 3 × 3 tunnel structure along the b axis. FESEM data show that the lengths of the nanoribbons range from a few micrometers to tens of micrometers and that the widths range from 20 to 100 nm. Elemental and average oxidation state analyses indicate a formula for the nanoribbon of Mg_2.11Mn_5.46O₁₂·_xH₂ O. According to TGA and TPD-MS data, these nanoribbons are thermally stable up to 500 °C. The BET surface area is 81 m²/g, which is higher than that of bulk todorokite synthesized using conventional methods. The catalytic performance of nanoribbonlike Mg-todorokite materials on convening benzyl alcohol to benzaldehyde was improved greatly as compared to that of bulk Mg-todorokite materials.