A novel method of ultraviolet/NaClO2-NH4OH for NO removal: Mechanism and kinetics.

The key step for nitric oxide (NO) removal using oxidation method is to efficiently oxidize NO. This study developed a novel advanced oxidation process (AOP) of ultraviolet light (UV) catalysis of chlorite (NaClO2) to oxidize NO. The production of nitric dioxide (NO2) and photo-production of chlorine dioxide (ClO2) were suppressed by adding ammonium hydroxide (NH4OH). The NO conversion efficiency was 98.1% using UV/NaClO2-NH4OH. Electron spin resonance (ESR) tests confirmed the roles of hydroxyl radical (HO) and oxychloride radical (ClO/Cl2O2) in the oxidation of NO. Kinetics analyses showed that NO flux was significantly enhanced by radical-induced (HO/ClO) oxidation of NO. In the presence of UV, the overall reaction rates (kov1*) were 3-8 times higher than those without UV. The Hatta number, namely the enhanced factor, was calculated in the range of 229-403 and 730-780 corresponding to without and with UV light, suggesting that NO oxidation belonged to fast and/or instantaneous reaction. Thus, the gas-film mass transfer resistance was the rate-determining step. N-containing product was determined as NH4+ and NO3- according to X-ray photoelectron spectroscopy (XPS).