Biochar induced the decoupling of exciton dissociation and intersystem cross in BiOBr heterojunction for dual-channel boosted oxygen activation

This study showcased that introducing biochar to BiOBr heterojunction could decouple the exciton dissociation and intersystem cross (ISC) process. Nitrogen doped biochar (NBC) as an electron donor and shuttle reduced exciton binding energy. Moreover, Br-doped NBC became the novel ISC site to conduct energy transfer. This dual-channel O2 activation retained robust redox and anti-interference capabilities simultaneously, enabling superior purification of complex water matrix. [Display omitted] •NBC-BB enables the decoupling of exciton dissociation and intersystem cross.•NBC reduces the exciton binding energy of BB, enhancing carrier separation.•Br-doped NBC triggers a heavy atom effect, bolstering 1O2 formation.•Dual-channel O2 activation achieves robust water purification under visible light. Two-dimensional (2D) materials exhibit a strong propensity for exciton generation upon photoexcitation compared to bulk counterparts. However, as exciton relaxation processes, intersystem crossing (ISC) and exciton dissociation always compete in the carrier dynamics. This study presents a strategy to decouple exciton dissociation and ISC by introducing a nitrogen-doped biochar (NBC) as the ISC center to modify Z-scheme heterojunction (BiOBr/BiOIO3, BB). NBC-BB achieved a 1.75 times interfacial driving force compared to BB and suppressed the exciton binding energy (Eb) from 107 meV to 85 meV. Moreover, due to the spontaneous incorporation of Br into NBC during the preparation process, the singlet and triplet energy level difference (ΔEST) was shortened by 0.079 eV to intensify ISC on NBC. The constructive collaboration of exciton dissociation and ISC guaranteed the generation of reactive oxygen species (ROS) with strong redox potential and selectivity, achieving efficient removal of refractory organic pollutants under visible light. The bolstered oxygen adsorption indicated effective oxygen activation capability of NBC-BB, leading to a 1.4-fold and 3.1-fold increase in the generation efficiency of 1O2 and •O2−, respectively. This study also presented experiments on various influencing factors, cyclic stability, and a feasible continue-flow system, showcasing the stability and potential for the practical application.