Achieving high catalytic performance with lower possible cost and higher energetic efficiency is critical for catalytic oxidation of volatile organic compounds (VOCs). However, traditional thermocatalysts generally undergo low catalytic activity and fewer active sites. Herein, this paper synthesizes nearly all-surface-atomic, ultrathin two-dimensional (2D) Co₃O₄ nanosheets to address these problems through offering a numerous active sites and high electron mobility. The 2D Co₃O₄ nanosheets (1.70 nm) exhibit catalyzation to the total oxidation of n-hexanal at the lower temperature of T_90% = 202 °C, and at the space velocity of 5.0 × 10⁴ h⁻¹. It is over 1.2 and 6 times higher catalytic activity than that of 2D CoO nanosheets (1.71 nm) and bulk Co₃O₄ counterpart, respectively. Transient absorption spectroscopy analysis shows that the oxygen vacancy defect traps electrons, thereby preventing the recombination with holes, increasing the lifetime of τ₁ electrons, and making electron–holes reach a non-dynamic equilibrium. The longer the electron lifetime is, the easier the oxygen vacancy defects capture electrons. Furthermore, the defects combine with oxygen to form active oxygen components. Compared with the lattice oxygen involved in the reaction of bulk Co₃O₄, the nanosheets change the catalytic reaction path, which effectively reduces the activation energy barrier from 34.07 to 27.15 kJ/mol. The changed surface disorder, the numerous coordinatively-unsaturated Co atoms and the high ratio of O_ads/O_lat on the surface of 2D Co₃O₄ nanosheets are responsible for the catalytic performance.

Catalytic oxidation of toluene over noble metal catalysts is a representative reaction for elimination of volatile organic compounds (VOCs). However, to fully understand the activation of molecular oxygen and the role of active oxygen species generated in this reaction is still a challenging target. Herein, MgO nanosheets and single-atom Pt loaded MgO (Pt SA/MgO) nanosheets were synthesized and used as catalysts in toluene oxidation. The activation process of molecular oxygen and oxidation performance on the two catalysts were contrastively investigated. The Pt SA/MgO exhibited significantly enhanced catalytic activity compared to MgO. The oxygen vacancies can be easily generated on the Pt SA/MgO surface, which facilitate the activation of molecular oxygen and the formation of active oxygen species. Based on the experimental data and theoretical calculations, an active oxygen species promoted oxidation mechanism for toluene was proposed. In the presence of H₂O, the molecular oxygen is more favorable to be dissociated to generate ^•OH on the oxygen vacancies of the Pt SA/MgO surface, which is the dominant active oxygen species. We anticipate that this work may shed light on further investigation of the oxidation mechanism of toluene and other VOCs over noble metal catalysts.