Superoxide generated by blue light photocatalysis of g-C3N4/TiO2 for selective conversion of amines

Abstract

Reactive oxygen species (ROS) are remarkably reactive chemical oxygen-containing molecules that not only occupy critical positions in cell signaling and homeostasis for regulating aerobic living organism's growth and development but also broadly participate in the environmental management as extraordinary oxidizing agents. Inspired by the behaviors of ROS, we designed an artful visible light photocatalytic system for the selective conversion of amines due to the activation of oxygen (O2) to superoxide (O2–) over g-C3N4/TiO2. Here, blue light was manipulated as a light source to circumvent the initiation of the strong nonselective hydroxyl radical (OH) that is often generated by valence band holes (hvb+) of TiO2. Aerial O2 was employed to achieve the long-lived, exclusive ROS, O2–, while acetonitrile, an aprotic solvent, was utilized to prolong the lifetime of O2–. Importantly, the g-C3N4/TiO2 possesses an exceptional capability for the generation of O2–. Based on the synergistic effect of two ingredients of the g-C3N4/TiO2 photocatalyst, the highly selective conversion of amines was achieved with superior conversions in comparison with the pristine TiO2 and g-C3N4. Furthermore, a mechanism dominated by O2– was proposed according to the kinetic studies, electron paramagnetic resonance (EPR), and ROS quenching experiments. This work highlights the importance of ROS in defining the desirable outcomes over semiconductor photocatalysts.