Room-Temperature\nOxidation of Formaldehyde by Layered\nManganese Oxide: Effect of Water

Abstract

Layered\nmanganese oxide, i.e., birnessite was prepared via the\nreaction of potassium permanganate with ammonium oxalate. The water\ncontent in the birnessite was adjusted by drying/calcining the samples\nat various temperatures (30 °C, 100 °C, 200 °C, 300\n°C, and 500 °C). Thermogravimetry-mass spectroscopy showed\nthree types of water released from birnessite, which can be ascribed\nto physically adsorbed H₂O, interlayer H₂O and\nhydroxyl, respectively. The activity of birnessite for formaldehyde\noxidation was positively associated with its water content, i.e.,\nthe higher the water content, the better activity it has. In-situ\nDRIFTS and step scanning XRD analysis indicate that adsorbed formaldehyde,\nwhich is promoted by bonded water via hydrogen bonding, is transformed\ninto formate and carbonate with the consumption of hydroxyl and bonded\nwater. Both bonded water and water in air can compensate the consumed\nhydroxyl groups to sustain the mineralization of formaldehyde at room\ntemperature. In addition, water in air stimulates the desorption of\ncarbonate via water competitive adsorption, and accordingly the birnessite\nrecovers its activity. This investigation elucidated the role of water\nin oxidizing formaldehyde by layered manganese oxides at room temperature,\nwhich may be helpful for the development of more efficient materials.