Synthesis and Characterization of Birnessite and Cryptomelane Nanostructures in Presence of Hoffmeister Anions

Abstract

The effect of Hoffmeister anions , , and on the structure and morphology of birnessite and cryptomelane-type manganese dioxide nanostructures, produced by the reduction reaction of and in aqueous acidic media, was studied. The syntheses were based on the decomposition of aqueous in presence of HCl for birnessite-type and acidified for cryptomelane-type manganese dioxide under soft hydrothermal conditions. They were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM) techniques. XRD patterns show the formation of birnessite for the first synthesis and a mixture of cryptomelane and birnessite-types for the second synthesis. XRD data revealed that the Hoffmeister anions have a significant effect on the nanostructures of birnessite. The sulphate ion-treated birnessite has the smallest crystals, whereas the chloride ion-treated birnessite has the largest crystals. Their TEM and HRTEM studies revealed a transformation from nanoplatelet morphology for chloride-treated samples to nanofibrous morphology for sulphate-treated birnessite. For the cryptomelane nanostructures, Hoffmeister anions also show a profound effect on their crystalline structures as determined by XRD analyses revealing a transformation of the cryptomelane phase to birnessite phase of . This transformation is also supported by TEM and HRTEM studies.

Highly active manganese oxide catalysts for low-temperature oxidation of formaldehyde

“…It is well-known that catalytic activities are associated with the surface area, pore size and transition metal ion redox ability (surface reducibility) of the catalyst. Although a considerable number of strategies have been explored for tailoring their morphology, particle size, and framework substitution [16][17][18][19], to the best of our knowledge, there have been reported few birnessite materials, especially crystalline K-type birnessite materials with very high surface areas (>100 m 2 /g). In a very recent work, we reported a novel microemulsion method for synthesis of birnessite manganese oxides [20].…”

Microwave radiation influence on the thermal and spectroscopic properties of Na-birnessite-type material

“…4b), a total weight loss of 21.17% was identified. In the range of 25-225 °C, two endothermic peaks at 66 and 151 °C were observed and associated with the loss of adsorbed and interlamellar water of birnessite [29]. At 530 °C, an exothermic peak related to changes in the crystalline structure of the layered material for tunnel-type structure (OMS-2) was observed [30].…”

“…The low-frequency bands at ~177 and 294 cm -1 corresponded to the translational deviation of the [MnO 6 ] octahedrons and to the stretching modes of the NaO 6 interlayer groups [14]. The high frequency bands at 576 and 643 cm -1 corresponded to the symmetrical stretching of the oxygen atoms with respect to the manganese atoms ν 3 (Mn-O) along the octahedral chains in the basal plane of [MnO 6 ] sheets, and stretching vibrations ν 2 (Mn-O) perpendicular to the double chains of the [MnO 6 ] octahedron, respectively [29][30][31]. For untreated sample by MAH (BNa), the bands at 177 and 294 cm -1 were absent, while the Raman band around 576 cm -1 could be identified and related to the disordered birnessite.…”

Exploitation of KMnO4material as precursors for the fabrication of manganese oxide nanomaterials

“…− , on the structure and morphology of birnessite and cryptomelane-type manganese dioxide nanostructures was studied [126].…”