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

Abstract

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 •OH, O2•−, 1O2 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.

Differences in the Oxidizing Species on the Surface of Metal-Doped Ferrihydrite and Hematite in the Alkaline S(IV)-O2 Solution

“…In the presence of CAT, the oxidized As­(III) is decreased by 32.3%, 57.1%, and 54.6% in the pure Fh, Cu-Fh, and Co-Fh systems, respectively (Figure a), whereas by 25.4%, 34.8%, and 29.9% in the pure Hem, Cu-Hem, and Co-Hem systems, respectively (Figure b), indicating that the doped Cu/Co apparently enhances the production of peroxo species. Dimethyl sulfoxide (DMSO) was also used as the probe to identify Fe­(IV)O oxo in the reaction systems in that it can selectively oxidize DMSO to dimethyl sulfone (DMSO 2 ). , Although DMSO can also react with ·OH to produce methyl sulfonic acid (CH 3 SOOH) and ethane, the absence of ·OH indicates that the consumption of DMSO is primarily due to reaction with Fe­(IV)O oxo (Figure S4). In the presence of 0.5 M DMSO, the oxidized As­(III) is decreased by 37.2%, 11.3%, and 12.5% as to pure Fh, Cu-Fh, and Co-Fh, respectively (Figure a), indicating that the doped Cu/Co reduces the production of Fe­(IV)O oxo in the Fh systems.…”

“…Dimethyl sulfoxide (DMSO) was also used as the probe to identify Fe(IV)�O oxo in the reaction systems in that it can selectively oxidize DMSO to dimethyl sulfone (DMSO 2 ). 21,22 Although DMSO can also react with •OH to produce methyl sulfonic acid (CH 3 SOOH) and ethane, 65 the absence of •OH indicates that the consumption of DMSO is primarily due to reaction with Fe(IV)�O oxo (Figure S4). In the presence of 0.5 M DMSO, the oxidized As(III) is decreased by 37.2%, 11.3%, and 12.5% as to pure Fh, Cu-Fh, and Co-Fh, respectively (Figure 6a), indicating that the doped Cu/Co reduces the production of Fe(IV)�O oxo in the Fh systems.…”

“…[9][10][11]19,20 In addition, our group also confirmed the presence of �Fe(III)-OOH peroxo on pyrite under oxic and alkaline conditions via selective oxidation of benzyl alcohol to benzaldehyde. 21,22 Until now, direct evidence for the presence of �Fe(IV)�O oxo and/or �Fe(III)-OOH peroxo on Fe (oxyhydr)oxides is still lacking.…”

“…Natural Fe (oxyhydr)­oxides are extensively distributed in lithosphere, biosphere, soil, and hydrosphere and play important roles in the removal of various contaminants given their large specific surface area, strong adsorption capacity, and high catalytic reactivity. , Previous studies suggested that Fe (oxyhydr)­oxides show high reactivity to react with H 2 O 2 or H 2 O–O 2 to form Fe­(IV)O oxo or Fe­(III)-OOH peroxo. , Density functional theory (DFT) calculations also indicate the likely formation of the Fe­(IV)O/Fe­(V)O oxo intermediates on the surface of hematite in the presence of O 2 and H 2 O. − By the means of selective oxidation of methyl phenyl sulfoxide (PMSO) to phenyl methyl sulfone (PMSO 2 ), previous studies confirmed the presence of highly reactive Fe­(IV)O oxo, which has been extensively used to determine the contribution of Fe­(IV)O oxo to various oxidation processes. − ,, In addition, our group also confirmed the presence of Fe­(III)-OOH peroxo on pyrite under oxic and alkaline conditions via selective oxidation of benzyl alcohol to benzaldehyde. , Until now, direct evidence for the presence of Fe­(IV)O oxo and/or Fe­(III)-OOH peroxo on Fe (oxyhydr)­oxides is still lacking.…”

Interaction of pyrite with zerovalent iron with superior reductive abilityviaFe(ii) regeneration

“…Pyrite (FeS 2 ) is a kind of mineral that widely exists in the crust or tailings. [37][38][39] With the composition of reducing groups, Fe(II) and S 2 2− , it has a strong reducing capacity and can effectively buffer the increase of pH via eqn (1). 40 For electron selectivity, pyrite is a more hydrophobic material and possesses a lower affinity to H due to its higher ratio of S. 16,20 Moreover, since FeS 2 can react with Fe 3+ , which is produced from the contaminant reduction by ZVI, to generate Fe 2+ , pyrite and ZVI show a synergistic effect on reduction to release more Fe(II).…”