Synthesis of Todorokite

Abstract

Todorokite of chemical composition (Mg(0.77)Na(0.03))(Mg(0.18)Mn(2+)(0.60)Mn(4+)(5.22)22) O(12).3.07 H(2)O was synthesized by a two-step procedure. First, sodium birnessite was synthesized and magnesium was exchanged for sodium to form magnesium birnessite, which was autoclaved under a saturated steam pressure at 155 degrees C for 8 hours to form well-crystallized todorokite. Synthesized todorokite particles consisted of fibers extending from a central plate. The plate itself was made of twinned fibers forming a trilling pattern. The infrared spectra and x-ray diffraction patterns were similar to those of natural todorokite samples. Calcium birnessite and nickel birnessite, when autoclaved under conditions similar to those for magnesium birnessite, yielded a todorokite structure. However, the formation of todorokite from calcium and nickel birnessite was less extensive.

Synthesis of manganese oxide octahedral molecular sieves containing cobalt, nickel, or magnesium, and the catalytic properties for hydration of acrylonitrile

“…Although todorokite in the natural form is a hydrated manganese oxide with impurities, the todorokite-type manganese oxide has been synthesized hydrothermally as a single-phase material [10][11][12][13]. Golden et al have reported a synthetic todorokite-type manganese oxide that was prepared by the hydrothermal treatment of Mg 2+ -exchanged birnessite-type manganese oxide [10].…”

Cr-hollandite: Breaking tradition with todorokite-type manganese oxides

“…Layered buserites with interlayer transition-metal cations were previously known only as precursors for todorokites. [8][9][10] Hollandites with interstitial transition metals are obtainable through ion exchange of K + in cryptomelane, but these substitution reactions are incomplete. [17,18] Indeed, only one other purely transition-metal hollandite, Aghollandite, has been reported to date [19][20][21] and none are known with transition-metal cations having charges greater than 1+.…”

“…When a divalent cation (Mg 2+ ) is substituted for interstitial Cr 3+ in the buserite precursor, Mg-buse(Cr), hydrothermal treatment produces the expected Mg-todo(Cr). [8][9][10][11][12] …”

“…[13] The appearance of Cr-hollandite is unique because divalent and trivalent transition metal cations were previously known only as templates for the todorokite structure. [8][9][10] Here we report further investigation into the formation of Cr-hollandite, including the influence of Cr 3+ both in tunnel and framework sites, as well as efforts to generate similar materials using other cations. We also examine the catalytic activity of Cr-hollandite in benzyl alcohol and carbon monoxide oxidation reactions.…”

“…Todorokite is typically generated with divalent metals as the templating cation, particularly Mg 2+ and cations of mid-late first-row transition metals. [8][9][10] Syntheses of hollandite and todorokite can also be designed for isomorphous doping of metal cations into the manganese oxide framework. [9][10][11][12] In a previous communication, we reported the synthesis under hydrothermal conditions of a hollandite-type manganese oxide with Cr 3+ in both interstitial and framework locations.…”