Boosting exciton-based energy transfer for singlet oxygen generation in type-II heterojunction

The separation of photogenerated charge carriers has been widely investigated, but exciton effects in type-II heterojunctions are often overlooked. Herein, the Bi-bridge BiPO4/CdS type-II heterojunction (BiPO4/Bi/CdS) with oxygen vacancy was successfully fabricated. BiPO4/Bi/CdS displayed stronger phosphorescence emission than BiPO4/Bi, suggesting the higher efficiency of intersystem crossing. The effective intersystem crossing from singlet to triplet excitons facilitated the activation of O2 to singlet oxygen (1O2), which was the product of energy transfer from the triplet excitons to the ground-state O2 molecule. The synergies between oxygen vacancy, surface plasmon resonance of Bi and heterojunction-construction promoted charge carrier separation and the generation of 1O2. As a result, BiPO4/Bi/CdS exhibited excellent photocatalytic activity in ofloxacin degradation with 93% degradation efficiency and 55% mineralization efficiency under the joint action of 1O2 and h+ as reactive species. More importantly, the mechanism of BiPO4/Bi/CdS type-II heterojunction was set forth from the coupling of charge carriers and exciton effects. This work sheds new light on the regulation of excitonic effects in type-II heterojunction and provides unique insight into 1O2 production.