Origin of sonocatalytic activity of fluorescent carbon dots

Although ultrasound-induced reactive oxygen species (ROS) have believed to be primary intermediates for the realization of sonodynamic therapy and sonocatalytic reactions, the mechanism of ROS production under ultrasound has not been well clarified till now. Here we discovered that ultrasound cavitation can break up oxygen-containing groups on the surface of carbon dots (CDs) to generate ROS, giving rise to a novel mechanism different from as-reported those. The bond cleavage of oxygen-containing groups contribute transient oxygen free radicals (•O−) that involve in the subsequent formation of ROS by quickly reacting with hydrogen ions and water, thereby leading to a twice higher sonocatalytic activity of CDs than TiO2. Moreover, the sonosensitizer function of CDs can be tuned by pH values of the surrounding environment that determine the generation and evolution reaction of oxygen free radicals under ultrasound irradiation. This finding paves a new way to design multifunctional sonosensitizers and utilize them in various fields.