Thin Films of Octahedral Molecular Sieves of Manganese Oxide

Abstract

Octahedral layered molecular sieve materials (OL-1) having the birnessite structure have been synthesized using sol−gel preparation methods. The sol obtained by redox reaction between sucrose and KMnO4 is then used to make films via (a) immersion, (b) spray coating, (c) spin coating, and (d) spatula coating. Crystalline OL-1 thin films have been prepared by methods a−c. Thin homogeneous films are most readily prepared by spray coating. Spin coating leads to noncrystalline and manganese-deficient films. The films have been characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and scanning Auger microscopy. The microscopy and Auger experiments show that there was no charging, implying these samples are good electrical conductors. The films are free from large amounts of impurity ions and carbonaceous deposits formed during the syntheses.

Nonaqueous Sol−Gel Syntheses of Microporous Manganese Oxides

“…Sol−gel chemistry has been used previously to prepare manganese oxide thin films, but with aqueous solvent. The reaction between KMnO 4 and sucrose has been shown to generate K−birnessite films on glass by immersion, spray, and spatula coating methods . These films had thickness on the order of 1 μm.…”

Manganese oxide thin films prepared by nonaqueous sol–gel processing: preferential formation of birnessite

“…This success is attributed to superior surface wetting afforded by nonaqueous sols, which promotes a more uniform coating. Aqueous sol-gel mixtures yield amorphous manganese oxide films when spin coated onto glass and Cu foil [16]. Crystallinity is achieved only for thicker films applied by immersion, spray, and spatula coating methods.…”

“…Aqueous sol-gel reactions of permanganate with saccharides and other polyalcohols reach the gel stage within two minutes of reactant mixing [9,16]. The useable time window for casting films before the onset of gelation is only about 30 seconds.…”

“…In particular, reactions between permanganate and organic reducing agents leave considerable carbon-containing residue in the xerogel, which can easily cause the film to fracture during drying and calcination. This situation is best illustrated in films prepared by aqueous sol-gel reactions using KMnO 4 and sucrose [16]. Such films are cast onto glass and Cu foil substrates by a variety of techniques including immersion, spray, spin, and spatula coating.…”

Shape-controlled synthesis of Mn2O3hollow structures and their catalytic properties

“…In contrast, reduction from high-valence Mn compounds is often used to synthesize low-valence and mixed-valence Mn compounds with different shapes. For the hydrothermal reduction reaction, natural organic macromolecules, such as glucose, [19][20][21][22] cyclodextrin 23 and sucrose, [24][25][26] have been used as reductants and capping agents to generate products with well-defined shapes, which cannot be obtained readily by precipitation. These natural organic macromolecules are often converted hydrothermally into carbon spheres.…”