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

[Display omitted] •A strategy of Al doping was proposed to enhance the excitonic effects of defective BiOCl and tailor O2 activation pathway.•O2 molecules were selectively activated to 1O2 with a boosted production through the energy transfer pathway.•Defective BiOCl with Al dopants can effectively degrade typical ECs in both simulated and real water matrices.•The crucial role of Al active sites in O2 activation and ECs degradation was revealed via experiments and theoretical calculations. Modulating excitonic effects enables the selective activation of O2 to singlet oxygen (1O2) for efficient degradation of emerging contaminants (ECs) in complex environmental systems. However, the lack of mechanistic investigation in excitonic effect modulation hinders the efficient O2 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 (BiOClOV) and tailor the O2 activation pathway for 1O2 generation. The Al dopants and surface oxygen vacancies (OVs) cooperatively promote O2 activation, where OVs mainly promote O2 absorption while Al mainly promote O2 activation. A new mechanism for 1O2 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 O2 to 1O2 by resonance energy transfer between triplet excitons and surface absorbed O2. Consequently, Al-doped BiOClOV 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 O2 to 1O2, offering valuable insights for the optimization of exciton-based photocatalysis through atomic-scale design strategies.