Synergistic dual-defect band engineering for highly efficient photocatalytic degradation of microplastics via Nb-induced oxygen vacancies in SnO2 quantum dots

The band structure is a crucial consideration in designing semiconductor photocatalysts, particularly as their size has been continuously decreasing over the past few decades. However, the bandgap of nanostructures is usually broadened due to quantum confinement effects, fundamentally inhibiting their photocatalytic performance. Herein, we demonstrate synergistic dual-defect band engineering in SnO2 quantum dots. Nb is incorporated to induce the creation of oxygen vacancies in the SnO2 crystal lattice. The synergistic mechanism between dual defects is elucidated through their interactive formation and collective contribution of the band structure. Nb impurities establish donor levels within the bandgap, while the gap between donor levels and the conduction band is filled by the induced oxygen vacancies, effectively extending the conduction band edge to the Fermi level. This design of dual-defect engineering not only narrows the bandgap but also provides abundant defect states for electron transitions and increases the lifetimes of photogenerated carriers, thereby facilitating highly efficient visible-light-driven photocatalytic degradation of microplastics, even in realistic aqueous environments. Furthermore, the intermediate products and photodegradation pathways of microplastics are comprehensively elucidated. The synergistic dual-defect band engineering not only achieves highly efficient visible-light-driven photocatalytic degradation of microplastics, but also introduces a comprehensive design framework for tuning band structures in nanoscale photocatalysts.