Unexpected Emergence of Carbon-Centered Radicals from Piezoelectric Effect in Oleic Acid-Capped BaTiO3

The utilization of alkyl radicals (•R) for hypoxic tumor therapy has great prospects due to its O2-independence and high reactivity. However, correlational initiators for in vivo activation remain scarce. Here, we report that ultrasound excitation of oleic acid-capped BaTiO3 (OA@BaTiO3) can result in an •R cascade and hence a means to conquer hypoxic tumors. Mechanistic studies find that the •R signal disappears when OA@BaTiO3 undergoes acid washing post-treatment, which is a common procedure for removing the unwanted byproduct BaCO3. Combined with the infrared spectrum analysis, acid treatment was proven to weaken the peaks at 2840–2970 cm–1 characteristic of -CH2- and terminal -CH3 stretching vibration of OA. There is compelling evidence that high temperature thermal oxidation of OA involves the generation of •R. Thus, acid washing is considered to remove the loosely bound yet catalytically active OA. And piezoelectric BaTiO3, a potential electron–hole redox catalyst, can sensitize these OA molecules and disintegrate them to •R. This unexpected discovery provides us with a distinctive mentality to seek diverse •R initiators for tumor ablation, as well as an additional perspective on the postprocessing of synthetic materials.