Defect Engineering-Driven Electron Spin Polarization and Charge Transfer in MOFs for Enhanced Sonocatalytic Therapy.

Sonocatalytic therapy (SCT) is a non-invasive tumor treatment modality that utilizes ultrasound (US)- activated sonocatalysts to generate reactive oxygen species (ROS), whose production critically dependent on the electronic structural properties of the catalytic sites. However, the spin state, which is a pivotal descriptor of electronic properties, remains underappreciated in SCT. Herein, a Ti-doped zirconium-based MOF (Ti-UiO-66, denoted as UTN) with ligand-deficient defects is constructed for SCT, revealing the important role of the electronic spin state in modulating intrinsic catalytic activity. The defect-driven sonocatalytic mechanism is elucidated as follows: 1) structural defects alleviate the limitations of ligand-metal charge transfer, achieving a 2.1-fold enhancement in charge transfer efficiency; 2) spin polarization at Ti active sites reconfigures the d-orbital electron distribution, thereby increasing the density of spin-polarized electronic states near the Fermi level. Furthermore, Ti 3d-O 2p orbital hybridization lowers the adsorption energies of H2O and O2 by 2.5-fold and 1.6-fold, respectively, thereby facilitating interfacial redox reactions and leading to enhanced ROS generation. Notably, UTN combined with US achieves 86.07% tumor inhibition efficiency. This work establishes novel insights into defect engineering, spin-state modulation, and surface interfacial adsorption in SCT, providing a theoretical paradigm framework for designing of high-performance sonocatalysts.