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

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