Unexpected role of singlet oxygen generated in urea-modulated LaFeO3 perovskite heterogeneous Fenton system in denitrification: Mechanism and theoretical calculations

This study appears an unprecedented phenomenon that 1O2, generated in urea-modulated LaFeO3 (U-LaFeO3) perovskite heterogeneous Fenton system, is superior to OH• and O2•- in NO removal. The 2.5 U-LaFeO3/H2O2 system can remove 82.9% of NO, with a low H2O2/NO molar ratio (4.7) and high GHSV (30,800 h−1), along with good environmental adaptability and reusability. Urea modulation induced the formations of abundant La defects, O vacancies and Fe(IV), also improved the pore structure and surface area. The contribution order of different free radicals to NO removal is 1O2 > xO2•- > •OH. Characterization combined with theoretical calculation clarify that (i) H2O2 is inclined to derive HO2• on Fe sites; (ii) 1O2 is mainly generated from O2•- reaction with Fe(IV)/Fe(III); (iii) •OH is mainly produced by splitting of H2O2 on Fe site and decomposition of HO2• on OV site. The main denitrification paths are NO+1O2→NO2, NO2 + •OH→NO3- and NO+ •OH→NO2-.