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 N-2 is a primary challenge for wastewater treatment. We present here a method to generate ClO center dot directionally for quick and efficient decomposition of NH4+ N to N-2. ClO center dot was produced and enhanced by a bifacial anode, a front WO3 photoanode and a rear Sb-SnO2 anode, in which HO center dot generated on WO3 reacts with HClO generated on Sb-SnO2 to form ClO center dot. 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 center dot with NH4+ N, which is 2.8 and 34.8 times than those of ClO center dot and HO center dot, respectively. The steady-state concentration of ClO center dot (2.5 x 10(-3) M) is 10(2) times those of HO center dot and Cl-center dot, 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 center dot generation and its application on ammonia wastewater treatment.