Photocatalytic degradation of NO by MnO catalyst: The decisive relationship between crystal phase, morphology and activity.

This study investigates the critical relationship between the crystal phase, morphology, and photocatalytic activity of MnO. The δ-MnO nanosheets, characterized by multiple exposed crystal planes forming junctions, exhibit optimized optical and electrical properties. Oxygen vacancy concentrations were observed in the order δ-MnO > γ-MnO > α-MnO, with corresponding increases in band gap width from 1.38 eV (δ-MnO₂) to 1.68 eV (α-MnO₂). The δ-MnO nanosheets achieved over 80 % NO removal efficiency and effectively suppressed the production of NO byproducts, outperforming α-MnO nanorods and γ-MnO nanospheres. The adsorption energy of O₂ followed the trend δ-MnO > γ-MnO > α-MnO, while the adsorption energy of NO was lowest on δ-MnO, facilitating its interaction with reactive species such as •O⁻ and •OH. For γ-MnO, NO directly reacted with •O⁻. The findings highlight the dependence of MnO photocatalytic performance on its crystal phase and morphology, with δ-MnO effectively inhibiting photogenerated electron-hole recombination due to its superior properties. This work presents a straightforward approach to designing high-performance transition metal photocatalysts through crystal phase and morphology control, offering valuable insights for future photocatalyst research.