Superior Performance of the δ-MnO2 Ultrathin Nanoflower for Photocatalytic HCHO Oxidation.

Formaldehyde (HCHO) is carcinogenic and harmful upon prolonged exposure to human breathing. Most catalysts can eliminate HCHO at room temperature or above, but the full removal of HCHO through the catalytic process at low temperatures (<room temperature) is challenging. In this work, we developed a high-performance δ-MnO2 ultrathin nanoflower catalyst for the photo-oxidation of HCHO within 0-10 °C. Compared to γ- and β-MnO2, δ-MnO2 generates the highest densities of superoxide and OH group radicals upon irradiation, showing the highest oxidative ability for HCHO elimination below room temperature. Complete removal of 100 ppm of HCHO could be achieved at 10 °C, and 80% at 0 °C through the photocatalytic reaction over the δ-MnO2. Density functional theory calculations suggest that oxygen vacancies, superoxide radicals, and hydroxyl radicals present on δ-MnO2 play important roles in the photocatalytic process. This study develops efficient photocatalysts for HCHO oxidation below room temperature and expands the temperature range of HCHO elimination for practical applications.