Unraveling the Dominant Role of Chlorine Vacancies in a BiOCl-Based Photocatalyst for Decabromodiphenyl Ether Debromination

Vacancy engineering is a powerful strategy to tune photocatalyst’s performance, but the divergent roles of different vacancies in photocatalytic reactions remain unclear. Herein, we systematically investigate the impacts of oxygen vacancies (VO) and chlorine vacancies (VCl) on visible-light-driven decabromodiphenyl ether (BDE209) debromination over a BiOCl-based iodine-chlorine solid-solution photocatalyst. A VO-enriched solid-solution catalyst (BiOCl0.8I0.2-VO) exhibited superior photoelectric properties, such as a broader light absorption range and higher photocurrent density, whereas VCl-enriched BiOCl0.8I0.2-x-VCl showed longer carrier lifetimes. Despite its weaker photoelectric response, BiOCl0.8I0.2-x-VCl achieved a much higher photocatalytic reaction rate for BDE209 debromination. After 50 min of photoreaction, ∼90% of BDE209 was removed, while the removal percentage was only 40% for BiOCl0.8I0.2-VO. The specific surface area-normalized rate constant in the BiOCl0.8I0.2-x-VCl was ∼8-fold superior to BiOCl0.8I0.2-VO. Also notably, BiOCl0.8I0.2-x-VCl exhibited a shorter induction period for BDE209 degradation than that for BiOCl0.8I0.2-VO. Further investigations revealed that VCl lowered the C–Br bond activation energy barrier and enabled efficient debromination with fewer photogenerated electrons. This work clarifies the divergent roles of VO and VCl in BiOCl for BDE209 debromination and photoelectric properties, offering insights into the rational design of vacancy-engineered photocatalysts for brominated pollutant remediation.