Oxygen Vacancies Promoted the Selective Photocatalytic Removal of NO with Blue TiO2 via Simultaneous Molecular Oxygen Activation and Photogenerated Hole Annihilation

Semiconductor photocatalytic technology has great potential for the removal of dilute gaseous NO in indoor and outdoor atmospheres but suffers from unsatisfactory NO-removal selectivity due to undesirable NO₂ byproduct generation. In this study, we demonstrate that the 99% selectivity of photocatalytic NO oxidation toward nitrate can be achieved over blue TiO₂ bearing oxygen vacancies (OVs) under visible-light irradiation. First-principles density functional theory calculation and experimental results suggested that the OVs of blue TiO₂ with localized electrons could facilitate the molecular oxygen activation through single-electron pathways to generate ·O₂^- and simultaneously promote the photogenerated hole annihilation. The generated ·O₂^- directly converted NO to nitrate, while the hole annihilation inhibited the side-reaction between holes and NO to avoid toxic NO₂ byproduct formation, resulting in the highly selective removal of NO. This study reveals the dual functions of OVs in defective photocatalysts and also provides fundamental guidance for the selective purification of NO with photocatalytic technology.