Synthesis, Spectral, Thermal and CO2 Absorption Studies on Birnessites Type Layered MnO6 Oxide

Abstract

Birnessite type layered MnO 6 oxides with increased crystallinity were synthesized from six carbohydrates and three dihydric phenols viz., dextrose, starch, fructose, galactose, maltose, lactose, catechol, resorcinol, quinol and KMnO 4 through the formation of a sol-gel. All of the MnO 6 oxides were characterized by powder XRD. The strong signal at 2h $ 12 corresponding to 7.4 Å refers to the Mn-Mn distance between the adjacent layers. The interlayer volume is dispersed with K + ions and H 2 O molecules. The presence of interlayer K + ions is indicated by a signal at 25°, corresponding to a distance of 3.5 Å . IR spectra of the oxides show signature bands at ca. 500 cm )1 due to the stretching modes occurring for MnO 6 entity. A broad band observed at ca. 3300 cm )1 is due to interlayer water molecules. Thermal analysis indicated three stage decomposition with the formation of MnO 2 at ca. 600°C through the intermediate formation of Mn(OH) n . The MnO 6 exhibited a remarkable CO 2 scrubbing ability, which has also been investigated.

Conditions for the formation of pure birnessite during the oxidation of Mn(II) cations in aqueous alkaline medium

“…Pure birnessite was also obtained by using H2O2 instead of O2 as oxidant [11,12] The second way to obtain birnessite relies on the reduction of MnO4in concentrated HCl medium [13,14]. Numerous organic reducing agents were used such as fumaric acid [15], sugars [16,17], alcohols [12,18], ethylene glycol [19] and more recently epoxypropane [20] and lactate [21]. This method could be constraining as it involved a relatively long time aging step [12,18], a calcination step at temperature above 400-450°C [16,17] or a hydrothermal treatment [20].…”

“…Numerous organic reducing agents were used such as fumaric acid [15], sugars [16,17], alcohols [12,18], ethylene glycol [19] and more recently epoxypropane [20] and lactate [21]. This method could be constraining as it involved a relatively long time aging step [12,18], a calcination step at temperature above 400-450°C [16,17] or a hydrothermal treatment [20].…”

Environmentally benign, recyclable nano hollandite and metal intercalated nano hollandites for hydrogen sulfide removal

“…CO 2 scrubbing by birnessite has been reported from our laboratory. 30 In this paper we report the scrubbing of H 2 S by hollandite and metal intercalated hollandites.…”

“…Bands around 734 (sh), 553, 558 (split bands) cm À1 are characteristic bands of manganese oxides with tunnel structure. 30 The observation signies the stabilization of the tunnel structure aer metal ion intercalation. IR of copper intercalated sample shows four medium intensity bands at 513, 602, 622 and 630 cm À1 indicating Cu-O interactions.…”

“…The observation shows that the 2 Â 2 tunnelled hollandite retains more water molecules in the lattice than the birnessite. 30 Fig. 7a and b depicts the representative infrared spectra (IR) of the hollandite and copper intercalated hollandites.…”