An efficient strategy for selective oxidation of ammonia nitrogen into N2 over BiOCl photocatalyst

[Display omitted] •NH4+-N denitrogenation under near-neutral pH and aerobic conditions.•NH4+-N conversion rate of ∼0.35 mg N L–1 min–1 and N2 selectivity of >97 %.•Efficient Cl− conversion into reactive chlorine species over BiOCl photocatalyst.•Cl−-mediated Mars-van Krevelen mechanism for reactive chlorine species production. Selective oxidation of ammonia nitrogen (NH4+-N) into N2 is critical to remove the superfluous nitrogen in the hydrosphere and control the fixed nitrogen inventory for the global nitrogen cycle. Herein, on the basis of chlorine radical chemistry, we report the photocatalytic denitrogenation over BiOCl with high N2 selectivity (>97 %). Efficient Cl– conversion into reactive chlorine species (RCS) is achieved, serving as the predominant reactive species for NH4+-N oxidation. According to the zero-order kinetics of Cl– for RCS generation, as well as the Cl– extraction/insertion over BiOCl, a Cl–-mediated Mars-van Krevelen mechanism is revealed, by which the catalytic performance shifts from the undesired deactivation (because of photocorrosion) towards the remarkably enhanced reactivity. This system exhibits great potential for the denitrogenation of saline wastewater, also provides an interesting strategy to activate inert chemical bond via the chlorine cycle.