The Fate of p-Nitrophenol in Goethite-Rich and Sulfide-Containing Dynamic Anoxic/Oxic Environments.

Reaction mechanisms between sulfide and iron (hydr)oxides are well-documented; however, the effect of sulfidation of iron (hydr)oxides on the fate of contaminants in dynamic anoxic/oxic environments is largely overlooked. Taking p-nitrophenol (p-NP) as a targeted contaminant, we studied its fate during the sulfidation of goethite in dynamic anoxic/oxic environments. In anoxic environments, the adsorbed p-NP on goethite was sharply released in the presence of S(-II) at two different concentrations (denoted as G1 and G2, respectively) due to lower affinity of p-NP on ═Fe-SH than ═Fe-OH. Then, the desorbed p-NP in the G1 system was completely reduced to p-aminophenol (p-AP), while negligible change of p-NP concentration occurred in the G2 system, which was ascribed to the generation of Fe(II)-bound goethite with high reactivity toward p-NP at G1. When the environments shifted to oxic conditions, the structural Fe(II) of FeS produced plenty of •OH in G1 and G2 through Fenton-like reaction, which attacked p-NP and p-AP toward complete degradation. Our study demonstrated that sulfidation of goethite and shift of redox conditions could be crucial factors in controlling the fate of p-NP, which needs to be considered when predicting the environmental fate of p-NP.