Defects lead to a massive enhancement in the UV-Vis-IR driven thermocatalytic activity of Co3O4 mesoporous nanorods

Abstract

A sample of Co₃O₄ mesoporous nanorods (Co₃O₄-MNR) with a considerable number of Co²⁺ vacancy defects was prepared by a facile method. Co₃O₄-MNR exhibits highly effective photothermocatalytic activity and excellent durability for the gas-phase oxidation of benzene (a recalcitrant poisonous air pollutant) under UV-visible-infrared illumination from a Xe lamp. It is discovered for the first time that the presence of Co²⁺ vacancies in Co₃O₄-MNR massively enhances the photothermocatalytic activity of Co₃O₄. Compared to a commercial Co₃O₄ sample (Aladdin) with a smaller number of Co²⁺ vacancies and TiO₂ (P25), the CO₂ production rate of Co₃O₄-MNR is massively increased by 165 and 309 times, respectively. Co₃O₄-MNR exhibits efficient photothermocatalytic activity for benzene oxidation even under the visible-infrared illumination of λ > 690 nm. The catalytic oxidation of benzene on Co₃O₄-MNR under the illumination of the Xe lamp follows a mechanism of solar-light-driven thermocatalysis. The experimental evidence of CO-TPR as well as theoretical evidence of density functional theory (DFT) calculations demonstrate that the presence of Co²⁺ vacancies in Co₃O₄-MNR significantly increases the activity of the lattice oxygen in Co₃O₄, thus massively promoting the thermocatalytic activity of Co₃O₄. Interestingly, a novel photoactivation on Co₃O₄, quite different from the conventional photocatalysis of semiconductor photocatalysts such as TiO₂, is discovered to considerably increase the solar-light-driven thermocatalytic activity of Co₃O₄-MNR. By combining the experimental evidence of isotope labeling, CO-TPR, and FTIR with the DFT calculations, we obtain a deep insight into the novel photoactivation: the illumination from the Xe lamp enhances the activity of the lattice oxygen in Co₃O₄-MNR, thus considerably promoting the solar-light-driven thermocatalytic activity of Co₃O₄-MNR.