Internal Electric Field Facilitates Facet-Dependent Photocatalytic Cl– Utilization on BiOCl in High-Salinity Wastewater for Ammonium Removal

High Cl– concentration in saline wastewater (e.g., landfill leachate) limits wastewater purification. Catalytic Cl– conversion into reactive chlorine species (RCS) arises as a sustainable strategy, making the salinity profitable for efficient wastewater treatment. Herein, aiming to reveal the structure–property relationship in Cl– utilization, bismuth oxychloride (BiOCl) photocatalysts with coexposed {001} and {110} facets are synthesized. With an increasing {001} ratio, the RCS production efficiency increases from 75.64 to 96.89 μg L–1 min–1. Mechanism investigation demonstrates the fast release of lattice Cl– as an RCS and the compensation of ambient Cl–. Correlation analysis between the internal electric field (IEF, parallel to [001]) and normalized efficiency on {110} (kRCS/S{110}, perpendicular to [001]) displays a coefficient of 0.86, validating that the promoted carrier dynamics eventually affects Cl– conversion on the open layered structure. The BiOCl photocatalyst is well behaved in ammonium (NH4+-N) degradation ranging from 20 to 800 mg N L–1 with different chlorinity (3–12 g L–1 NaCl). The sustainable Cl– conversion into RCS also realizes 85.4% of NH4+-N removal in the treatment of realistic landfill leachate (662 mg of N L–1 NH4+-N). The structure–property relationship provides insights into the design of efficient catalysts for environment remediation using ambient Cl–.