Catalytic cross-coupling of aniline by pyrite and dissolved oxygen under alkaline conditions

Pyrite catalyzes oxidation of various organic contaminants by dissolved oxygen (DO) under acidic conditions; however, the catalytic mechanism under alkaline conditions is still not clear. In this study, we observe increased oxidation rates of aniline with increasing pHs (7.0-11.0). Electron paramagnetic resonance (EPR) analysis and quenching experiments rule out contributions of center dot OH, O-2(center dot-), O-1(2) and Fe (IV) to aniline oxidation and suggest that the Fe (III)-OOH peroxo and/or H2O2 are the primary oxidative species in the oxidation of aniline at pH 11.0. In addition, 200 mg L-1 H2O2 does not apparently increase the oxidation rate of aniline, which also rules out the predominant contribution of the produced H2O2 to aniline oxidation. We therefore suggest that the Fe (III)-OOH peroxo is indeed the primary oxidative species in the pyrite-DO system under alkaline conditions. Analyses of solid total organic carbon (TOC), gas chromatography-mass spectrometry and Fourier-transform infrared spectroscopy further reveal that more than 83.3% aniline has been polymerized to polyaniline, instead of being mineralized into CO2 and H2O, indicating that H-abstraction from aniline by the Fe (III)-OOH peroxo is an important step in the oxidation of aniline under alkaline conditions. This study provides new insight into the oxidative species in the pyrite-DO system, and opens a new door for organic degradations under alkaline conditions.