Ammonium-treated birnessite-type MnO2 to increase oxygen vacancies and surface acidity for stably decomposing ozone in humid condition

Abstract Nowadays atmospheric ozone pollution increasingly occurs in summer in China developed areas. To improve catalytic stability of MnO2 for decomposing ozone in real humid environment, we developed a simple method to obtain the ammonium (NH4+) treated birnessite-type MnO2 (N-MnO2). NH4+ ions not only replaced K+ ions in the interlayer of MnO2 but also existed on the surface of MnO2, separating the original aggregated MnO2 nanoparticles into smaller ones. The N-MnO2 had much larger specific surface area than the original MnO2 (221 m2/g vs. 59 m2/g), leading to more oxygen vacancies and enhanced surface acidity. As a result, N-MnO2 exhibited excellent and stable activity for ozone decomposition in humid condition (relative humidity 50%) at room temperature, achieving 80% conversion of 115 ppm ozone under the space velocity as high as 600 L/gcat·h. In addition, N-MnO2 powder was successfully coated on the non-woven fabric. This composite material not only showed stable 60–80% conversion of 15 ppm ozone in a 7-day test, but also its air pressure-drop was only 3 Pa under the commonly used air filtration face velocity of 5.3 cm/s. Thus, as-synthesized N-MnO2 showed great potential in real building ventilation system to prevent ozone pollution from outdoor air.