Catalytic conversion of soluble aniline into insoluble N-phenylphenazine for wastewater treatments.

Aniline, a common pollutant in industrial wastewater, requires an effective treatment method with minimal chemical usage. In this study, a two-stage catalytic oligomerization process has been developed to address this issue by converting soluble aniline into insoluble oligomers for wastewater treatment. In the first stage, aniline is oxidized using hydrogen peroxide (H2O2) and a green catalyst, iron tetraamido macrocyclic ligand (Fe-TAML) to form aniline tetramers or pentamers. In the second stage, these oligoanilines undergo further oxidation with H2O2 alone at a higher temperature, resulting in the formation of N-phenylphenazine or its derivatives. These macrocyclic compounds precipitate from the wastewater due to π- π stacking, allowing easy separation through decantation or gravity filtration. After process optimization, only 3 mg/L of Fe-TAML and 2 g/L of H2O2 are required to treat 1 g/L of aniline, achieving a remarkable 96.8% aniline removal efficiency and a 62.5% precipitate yield. This two-stage oxidation approach shows promise for treating aniline and similar aromatic compounds in real industrial wastewater.