pH-Dependent Structure-Activity Relationship of Polyaniline-Intercalated FeOCl for Heterogeneous Fenton Reactions

In this study, we prepared polyaniline-intercalated iron oxychloride (FeOCl-PANI) by aqueous intercalation method to use it as a Fenton-like catalyst that was then assessed in terms of behavior of intercalation, structural evolution, Fenton-like activity, and catalytic mechanism. Gel-permeation chromatography demonstrated that the molecular weight (polymerization extent) of polyaniline fragment gradually increased with the increase of intercalation time. Interestingly, the polyaniline-intercalated materials with varying intercalation times exhibited distinctly different Fenton-like activity trends under acidic (pH 4) and neutral (pH 7) conditions. Specifically, Fenton-like degradation is favored with a shorter intercalation time under acidic conditions, while it is preferred with a longer intercalation time under neutral pH values. We propose that an additional pH-dependent charging of FeOCl-PANI with different polymerization extents of the intercalated polyaniline promotes a switch in the contaminant degradation pathway, leading to opposite trends in observable activity at different pH values. As a class of typical layered metal chalcogenohalides (MeAX, A = O, S, Se, X = Cl, Br, I), FeOCl-PANI is expected to provide new insights into the development of other similar materials. This work could be useful to further understand the H₂O₂ heterogeneous activation behavior, which is of significance to the application of iron-based heterogeneous Fenton oxidation.