Novel activated system of ferrate oxidation on organic substances degradation: Fe(VI) regeneration or Fe(VI) reduction

• NaClO could act with intermediate iron species to regenerate ferrate(VI); • Ferrate(VI) was reduced by NaClO 2 forming more intermediate iron species; • ·OH was involved into the degradation of organic substances in Fe(VI)/NaClO 2 ; • Fe(VI)/NaClO and Fe(VI)/NaClO 2 were both appropriate for authentic water; Ferrate(VI) oxidation has caught more attention because of its high-efficiency degradation capacity on organic substances, while previous studies overlooked the effect of NaClO and NaClO 2 on Fe(VI) oxidizability. This study discovered that NaClO could react with intermediate iron species, i.e., Fe(V) and Fe(IV), to regenerate Fe(VI), which reduced the unnecessary consumption of Fe(VI) by its self decomposition and thus improved the oxidizability of ferrate(VI) on organic substances. Then, the degradation content of sulfamethoxazole (SMX) and carbamazepine (CBZ) increased from 60.77% and 68.42% of 50 μM of Fe(VI) group to 100% and 73.21% of Fe(VI)/NaClO (50/5 μM) system within 30 min, respectively. However, NaClO 2 contributed to reducing Fe(VI) to form more intermediate iron species in the reaction system and then elevated the degradation rate of SMX and CBZ at the initial stage. NaClO 2 also further reduced intermediate iron species, leading to the decrease of active species. Besides, ·OH was involved into organics degradation in Fe(VI)/NaClO 2 system, due to the rapid decomposition of ferrate(VI). By frontier orbital theory analysis, Fe(VI) had the lowest E LUMO (-5.50 eV) so it was more liable to be reduced by NaClO 2 than intermediate iron species. Alpha orbital of Fe(V) possessed the highest E HOMO (-7.36 eV), which was more prone to be attacked by NaClO. Two coupling systems still achieved a synergistic effect on SMX degradation in authentic water. Meanwhile, the acute toxicity and disinfection by-products (DBPs) was further decreased in coupling systems. Therefore, Fe(VI)/NaClO and Fe(VI)/NaClO 2 system may be a viable method for abating micropollutants with their unique advantages in water treatment.