Oxygen‐Vacancy‐Rich Piezoelectric BiO _{2− x} Nanosheets for Augmented Piezocatalytic, Sonothermal, and Enzymatic Therapies

Abstract

Piezocatalytic therapy is a new‐emerging reactive oxygen species (ROS)‐enabled therapeutic strategy that relies on built‐in electric field and energy‐band bending of piezoelectric materials activated by ultrasound (US) irradiation. Despite becoming a hot topic, material development and mechanism exploration are still underway. Herein, as‐synthesized oxygen‐vacancy‐rich BiO _{2− x} nanosheets (NSs) demonstrate outstanding piezoelectric properties. Under US, a piezo‐potential of 0.25 V for BiO _{2− x} NSs is sufficient to tilt the conduction band to be more negative than the redox potentials of O ₂/ ^•O ₂ ⁻, ^•O ₂ ⁻/H ₂O ₂, and H ₂O ₂/ ^•OH, which initiates a cascade reaction for ROS generation. Moreover, the BiO _{2− x} NSs exhibit peroxidase and oxidase‐like activities to augment ROS production, especially in the H ₂O ₂‐overexpressed tumor microenvironment. Density functional theory calculations show that the generated oxygen vacancies in BiO _{2− x} NSs are favorable for H ₂O ₂ adsorption and increasing the carrier density to produce ROS. Furthermore, the quick movement of electrons enables an excellent sonothermal effect, for example, rapid rise in temperature to nearly 65 °C upon US with low power (1.2 W cm ⁻²) and short time (96 s). Therefore, this system realizes a multimode synergistic combination of piezocatalytic, enzymatic, and sonothermal therapies, providing a new direction for defect engineering‐optimized piezoelectric materials for tumor therapy.