Improved Oxygen Activation over a Carbon/Co_3O_4 Nanocomposite for Efficient Catalytic Oxidation of Formaldehyde at Room Temperature

摘要

Oxygen activation is a key step in the catalytic oxidation of formaldehyde (HCHO) at room temperature. In this study, we synthesized a carbon/Co_3O_4 nanocomposite (C-Co_3O_4) as a solution to the insufficient capability of pristine Co_3O_4 (P- Co_3O_4) to activate oxygen for the first time. Oxygen activation was improved via carbon preventing the agglomeration of Co_3O_4 nanoparticles, resulting in small particles (approximately 7.7 nm) and more exposed active sites (oxygen vacancies and Co~(3+)). The removal efficiency of C-Co_3O_4 for 1 ppm of HCHO remained above 90%, whereas P-Co_3O_4 was rapidly deactivated. In static tests, the CO_2 selectivity of C-Co_3O_4 was close to 100%, far exceeding that of P-Co_3O_4 (42%). Various microscopic analyses indicated the formation and interaction of a composite structure between the C and Co_3O_4 interface. The carbon composite caused a disorder on the surface lattice of Co_3O_4, constructing more oxygen vacancies than P-Co_3O_4. Consequently, the surface reducibility of C-Co_3O_4was improved, as was its ability to continuously activate oxygen and H_2O into reactive oxygen species (ROS). We speculate that accelerated production of ROS helped rapidly degrade intermediates such as dioxymethylene, formate, and carbonate into CO_2. In contrast, carbonate accumulation on P-Co_3O_4 surfaces containing less ROS may have caused P-Co_3O_4 inactivation. Compared with noble nanoparticles, this study provides a transition metal-based nanocomposite for HCHO oxidation with high efficiency, high selectivity, and low cost, which is meaningful for indoor air purification.