Extremely Efficient Decomposition of Ammonia N to N2 Using ClO• from Reactions of HO• and HOCl Generated in Situ on a Novel Bifacial Photoelectroanode

The conversion of excess ammonia N into harmless N₂ is a primary challenge for wastewater treatment. We present here a method to generate ClO^• directionally for quick and efficient decomposition of NH₄⁺ N to N₂. ClO^• was produced and enhanced by a bifacial anode, a front WO₃ photoanode and a rear Sb-SnO₂ anode, in which HO^• generated on WO₃ reacts with HClO generated on Sb-SnO₂ to form ClO^•. Results show that the ammonia decomposition rate of Sb-SnO₂/WO₃ is 4.4 times than that of WO₃ and 3.3 times than that of Sb-SnO₂, with achievement of the removal of NH₄⁺ N on Sb-SnO₂/WO₃ and WO₃ being 99.2 and 58.3% in 90 min, respectively. This enhancement is attributed to the high rate constant of ClO^• with NH₄⁺ N, which is 2.8 and 34.8 times than those of Cl^• and HO^•, respectively. The steady-state concentration of ClO^• (2.5 × 10^-13 M) is 10² times those of HO^• and Cl^•, and this is further confirmed by kinetic simulations. In combination with the Pd-Cu/NF cathode to form a denitrification exhaustion system, Sb-SnO₂/WO₃ shows excellent total nitrogen removal (98.4%), which is more effective than WO₃ (47.1%) in 90 min. This study provides new insight on the directed ClO^• generation and its application on ammonia wastewater treatment.