Self-generated Schottky barriers in niobium carbide MXene nanocatalysts for theory-oriented sonocatalytic and NIR-II photonic hyperthermia tumor therapy

Two-dimensional (2D) transition metal carbides/nitrides (MXenes) have been extensively applied in biomedicine. However, the potential of MXene-based nanomedicine in sonodynamic therapy (SDT) has been rarely explored. Here, under the guidance of theoretical calculation, Nb2C MXenes are engineered as a high-performance sonocatalyst/sonosensitizer through mild in-situ self-oxidation. The work function values of Nb2C MXenes with different oxidation degrees are calculated to determine the optimized conditions to construct efficient Schottky heterojunction in the self-oxidized Nb2C MXenes. Experimentally, the niobium oxide clusters are homogeneously self-generated in-situ in Nb2C MXenes to form efficient Schottky barriers after the mild hydrothermal oxidation. The results reveal that the Schottky heterojunction can accelerate the separation of sono-triggered electron-hole pairs and inhibit their recombination, which profoundly augments the reactive oxygen species (ROS) generation efficiency of the in-situ self-oxidized Nb2C MXenes (denoted as Nb2C-Ox) under ultrasound (US) irradiation. The mild oxidation also allows the Nb2C-Ox to inherit the high photothermal performance of Nb2C MXenes in the second near-infrared (NIR-II) window. Accordingly, the developed Nb2C MXene-originated sonocatalyst/sonosensitizer can achieve high therapeutic efficacy based on the sonodynamic effect and NIR-II photonic hyperthermia. Therefore, this work proposes a theoretical calculation-oriented strategy to design and fabricate new MXene-based sonocatalysts/sonosensitizers for biomedical applications.