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} ( k RCS / 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- .