Cascade Reaction for Efficient ¹O₂ Generation Enabled by Spatially Coupled Vacancy Pairs

Singlet oxygen (¹O₂) is a powerful nonradical oxidant for water purification, particularly in complex matrices. However, its spin-forbidden generation from triplet oxygen (³O₂) imposes significant thermodynamic barriers. This study reports a pulsed-laser synthesis strategy to create atomically adjacent vacancy pairs (V_Ti-O) on the surface of TiO₂, which function as a cooperative bifunctional redox nanoreactor for the sustainable generation of ¹O₂. The oxygen vacancy (V_O) serves as a reduction site for O₂ adsorption and activation, whereas the adjacent titanium vacancy (V_Ti), acting as an oxidation site, immediately converts superoxide (O₂ ^·-) into ¹O₂. The V_Ti-O pair shortens the migration path of O₂ ^·-, inhibits quenching, and enhances the overall reaction kinetics. In an integrated fixed-bed reactor operated under natural sunlight in a real water environment, this catalyst enables efficient pollutant degradation while maintaining aquatic biocompatibility, demonstrating its practical potential for low-energy, efficient ¹O₂ generation and wastewater treatment in sustainable solar-driven advanced oxidation processes.