Abiotic Transformation of Nitrobenzene by Zero Valent Iron under Aerobic Conditions: Relative Contributions of Reduction and Oxidation in the Presence of Ethylene Diamine Tetraacetic Acid

Abstract

Zero valent iron (ZVI) applications to remediation of shallow groundwaters can be affected by dissolved oxygen (DO) and organic ligands. To explore the intersection between these complicating factors, this study thoroughly characterized the reactions of nitrobenzene (NB) with ZVI in the presence DO and the model ligand ethylene diamine tetraacetic acid (EDTA). The results showed that NB is degraded by both ZVI reduction and ZVI-induced advanced oxidation under oxygen-limited conditions. The contribution of •OH to the degradation of NB increased with time so that nearly 39% of NB was oxidized by •OH at 15 min (pH = 3), but reduction was still the main pathway of NB transformation throughout. NB reduction products, such as aniline (AN), were also oxidized by •OH. The lower the pH, the greater the contribution of advanced oxidation, but DO was the limiting factor for •OH generation. Only 4.7% NB was fully degraded by ring opening and/or mineralization because the production of •OH was limited by low DO. After the transformation of NB and AN, other benzene ring and nitrogen-containing intermediates were identified (e.g., p-nitrophenol, p-aminophenol, hydroquinone, and p-benzoquinone). The removal of total organic carbon and total organic nitrogen was minimal. The results suggested that the relative doses of ZVI, DO, and iron-complexing ligands can be balanced for the optimal (rapid and deep) removal of organic contaminants.

Electrochemical Degradation of Nitrobenzene Wastewater: From Laboratory Experiments to Pilot-Scale Industrial Application

“…On the other hand, the nitro group of NB with strong electron-withdrawing characteristics could be electrophilic and attacked by •OH to form phenol. It is noteworthy that the reduction of NB also occurred on the cathode leading to the formation of aniline, which was also identified in other synchronistic oxidation and reduction systems [9,48]. Then, the substitution of -NH 2 by the -OH group could generate the product phenol with the release of NH 4 + .…”

Characteristics and application of iron-based materials in heterogeneous Fenton oxidation for wastewater treatment: a review

“…3 shows the different reactions that can occur when treating metals and metalloids with nZVI, including adsorption, reduction, oxidation, precipitation and mineralization on the surface. 31,70–72…”

“Doing More with Less”: Ni(II)@ORMOSIL, a Novel Sol-Gel Pre-Catalyst for the Reduction of Nitrobenzene

“…An alternative route to obtain aniline is via a condensation route, which is achieved by the condensation of NOB with PhNHOH [40]. NB reduction by ZVI as the reducing agent in aerobic media proceeds via the condensation route and results in azoxybenzene and azobenzene under oxygen-limited conditions [41]. ZVI-induced advanced oxidation of aniline yields azoxybenzene [41].…”

“…NB reduction by ZVI as the reducing agent in aerobic media proceeds via the condensation route and results in azoxybenzene and azobenzene under oxygen-limited conditions [41]. ZVI-induced advanced oxidation of aniline yields azoxybenzene [41]. NB reduction with NaBH 4 catalyzed by ZVI@ORMOSIL inhibits that possibility for obvious reasons.…”