Harnessing Adsorption–Catalysis Synergy: Efficient Oxidative Removal of Gaseous Formaldehyde by a Manganese Dioxide/Metal–Organic Framework Nanocomposite at Room Temperature

Abstract

The potential utility of a transition metal oxide/metal–organic framework (MOF) nanocomposite has been explored using manganese dioxide (MnO2)/Universitetet i Oslo (UiO)-66-amine (NH2 (prototypical zirconium (Zr) MOF)) to develop an efficient adsorption–catalysis system for the removal of formaldehyde (FA) from the air. The room-temperature FA (100 ppm) conversion (XFA (%)), when tested using five different MnO2 (wt%) loadings in the nanocomposite, is estimated as: 1% MnO2 (88%) > 2% MnO2 (86%) > 4% MnO2 (84%) > 6% MnO2 (75%) > 20% MnO2 (47%). The FA removal performance is lowered as the active catalytic sites are covered with the increases in the MnO2 loading (e.g., >1 wt%). The FA and molecular oxygen species preferably adsorb (and activate) onto the Zr atoms attached to the NH2 groups. The oxidation of FA into carbon dioxide proceeds subsequently through the formation of intermediates (e.g., dioxymethylene and formate). The MnO2 nanoclusters act as secondary reactive adsorption sites to boost the capture, activation, and oxidation of the FA molecules at the Zr active centers. Accordingly, the MnO2/UiO-66-NH2 nanocomposite is demonstrated to effectively harness the adsorption–catalysis synergy for highly efficient removal of FA relative to other well-known catalysts (e.g., platinum and metal oxide-based nanomaterials).