Lab. on Chemical Redox Acceleration Technologies for Water Quality
|Quantitative Photoelectrochemical Conversion of Ammonium to Dinitrogen Using Bromide-Mediated Redox Cycle|
|Year of publication||2021|
|Title of paper||Quantitative Photoelectrochemical Conversion of Ammonium to Dinitrogen Using Bromide-Mediated Redox Cycle|
|Author||Min Seok Koo, Seungmok Han, Kangwoo Cho, and Wonyong Choi*|
|Publication in journal||ACS Environmental Science & Technology Engineering|
|Status of publication||accepted|
Bromide ion (Br–) can be oxidized to reactive bromine species (RBS; Br•, Br2•–, and HOBr/OBr–) which can serve as an effective alternative to chlorine disinfectant. This study investigated the generation of RBS in a photoelectrochemical (PEC) system using an electrochromic TiO2 nanotube arrays (Blue-TNTs) electrode under UV light (λ > 320 nm) and demonstrated the effect of RBS on the direct conversion of ammonium (NH4+) to dinitrogen (N2) with near 100% efficiency. The PEC system utilizing in situ generated RBS not only removed NH4+ more efficiently than photocatalytic (PC) and electrochemical (EC) systems but also prevented the generation of unwanted products (i.e., NO2– and NO3–). In addition, compared with the PEC-Cl system, the PEC-Br system exhibited a superior ammonium removal efficiency (16% vs 95% for 120 min of reaction; under air-equilibrated condition). The PEC system also showed higher NH4+ removal efficiency and lower energy consumption when compared to an EC system (using a boron-doped diamond electrode). While bromate ions (BrO3–) are produced as a toxic byproduct of bromide oxidation in a typical ozonation system, the Blue-TNTs PEC-Br system fully hinders the bromate formation as long as ammonium is present in the solution because RBS rapidly reacts with NH4+ with little chance of further oxidation to bromate.