Extremely Efficient Decomposition of Ammonia N to N 2 Using ClO • from Reactions of HO • and HOCl Generated in Situ on a Novel Bifacial Photoelectroanode

The conversion of excess ammonia N into harmless N 2 is a primary challenge for wastewater treatment. We present here a method to generate ClO • directionally for quick and efficient decomposition of NH 4 + N to N 2 . ClO • was produced and enhanced by a bifacial anode, a front WO 3 photoanode and a rear Sb–SnO 2 anode, in which HO • generated on WO 3 reacts with HClO generated on Sb–SnO 2 to form ClO • . Results show that the ammonia decomposition rate of Sb–SnO 2 /WO 3 is 4.4 times than that of WO 3 and 3.3 times than that of Sb–SnO 2, with achievement of the removal of NH 4 + N on Sb–SnO 2 /WO 3 and WO 3 being 99.2 and 58.3% in 90 min, respectively. This enhancement is attributed to the high rate constant of ClO • with NH 4 + 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 10 2 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–SnO 2 /WO 3 shows excellent total nitrogen removal (98.4%), which is more effective than WO 3 (47.1%) in 90 min. This study provides new insight on the directed ClO • generation and its application on ammonia wastewater treatment.