Birnessite-Type Manganese Dioxide Nanosheets on Metal-Organic Frameworks with High Catalytic Activity in Ozone Decomposition

Ground-level ozone (O3) poses a threat to both human health and ecosystems; the development of O3 decom-position catalysts is thus of fundamental and practical significance. In the past decades, metal oxides have been widely investigated for O3 elimination due to their low cost and high catalytic activity. Recently, it has been demonstrated that metal-organic frameworks (MOFs) could also show high performance in the removal of O3 and even other airborne gaseous pollutants at the same time. Herein, we report a facile synthetic method to prepare the composite of the well-known MOF, UiO-66-NH2, and birnessite-type manganese dioxide, namely, (5-MnO2, where the nanosheets of (5-MnO2 are vertically aligned and densely grown on the crystal surfaces of UiO-66-NH2. The (5-MnO2/UiO-66-NH2 composite could completely remove low-concentration O3 (5 ppm) in both dry and highly humid (RH = 80%) air at ambient temperature and pressure with a space velocity of 2000 L h-1 g-1. In contrast, a single-phase sample of (5-MnO2 or the typical O3 decomposition catalyst, a-MnO2, showed a much lower O3 removal efficiency under the same experimental conditions. Due to the ultrathin morphology (high surface area) and well-separated distribution (no aggregation) of (5-MnO2 nanosheets in the (5-MnO2/UiO-66-NH2 composite, there are rich Mn2+/Mn3+ atoms and oxygen vacancies on its surface, contributing to its high performance in catalytic O3 decomposition. This work demonstrated a facile method to prepare MOF-based composites with fascinating nanostructures and high catalytic activity in O3 decomposition, which are also potentially useful in other catalytic reactions.