Regulating oxygen vacancies in ultrathin δ-MnO2 nanosheets with superior activity for gaseous ozone decomposition

Abstract

Ground-level ozone pollution is an environmental problem worldwide, and is hazardous to human health, especially the elderly, the children and the sensitive. It is a tough challenge to develop high-performance catalysts for thoroughly decomposing ozone under practical conditions because oxygen vacancies, i.e. reaction sites, tend to be occupied by water molecules or intermediate peroxides. Herein, ultrathin δ-MnO₂ nanosheets rich in oxygen vacancies were simply fabricated with the modulation of ammonium ions (NH₄⁺). Furthermore, regulating oxygen vacancies via NH₄⁺ ions was successfully implemented in ultrathin δ-MnO₂ nanosheets. The surface adsorbed NH₄⁺ ions facilitated the ozone adsorption and reduced the competitive adsorption of water molecules. In particular, the desorption of intermediates was accelerated by NH₄⁺ ions, as demonstrated by in situ Raman spectroscopy and DFT calculations. The as-synthesized catalyst exhibited rather excellent activity and stability for gaseous ozone decomposition under humid conditions, maintaining almost 100% conversion of 100 ppm ozone within 36 h at 50% relative humidity and a space velocity of 600 L g⁻¹ h⁻¹ at 25 °C. This work provides a facile, effective and scalable method to synthesize ultrathin δ-MnO₂ nanosheets and regulate oxygen vacancies and further develops a high-efficiency and low-cost catalytic material for ozone removal.