Aluminum sites tailoring the molecular oxygen activation for singlet oxygen generation and emerging contaminant degradation: The underestimated role of excitonic effects

Modulating excitonic effects enables the selective activation of O 2 to singlet oxygen ( 1 O 2 ) for efficient degradation of emerging contaminants (ECs) in complex environmental systems. However, the lack of mechanistic investigation in excitonic effect modulation hinders the efficient O 2 activation towards generating preferred reactive oxygen species (ROS). Taking 2D BiOCl as a prototype, we herein propose a facile aluminum (Al) doping method to enhance the inherent excitonic effects of defective BiOCl (BiOCl OV ) and tailor the O 2 activation pathway for 1 O 2 generation. The Al dopants and surface oxygen vacancies (OVs) cooperatively promote O 2 activation, where OVs mainly promote O 2 absorption while Al mainly promote O 2 activation. A new mechanism for 1 O 2 generation driven by a strong excitonic effect has been proposed via experiments and theoretical investigations. Benefiting from the Al-mediated trapping state for singlet exciton, the intersystem crossing is promoted from singlet excitons to triplet excitons because of a lower singlet–triplet energy gap, thereby leading to a selective activation of O 2 to 1 O 2 by resonance energy transfer between triplet excitons and surface absorbed O 2 . Consequently, Al-doped BiOCl OV exhibits a superior activity and stability toward typical ECs degradation in both simulated and real water matrices. This study elucidates the role of the excitonic effect in selectively activating O 2 to 1 O 2 , offering valuable insights for the optimization of exciton-based photocatalysis through atomic-scale design strategies.