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

Abstract

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.