Can or cannot green rust reduce chlorinated ethenes?

Green rusts (GRs) are Fe²⁺ , Fe³⁺ layered double hydroxides that are widely investigated for the reduction of inorganic and organic pollutants in soils and groundwaters. Of particular interest is the use of GRs for the reduction of chlorinated ethenes, but existing literature shows contrasting results. Here, we tested 4 GRs (with different interlayer and hydroxide sheet modifications) in reactions with 3 different chlorinated ethenes (tetra-, tri-, and cis-dichloroethylene) for up to 10 months. Our results show that none of the freshly synthesized and untreated GRs can reduce the here tested chlorinated ethenes to any significant extent, corroborated by the lack of degradation products after 10 months and the absence of any significant volatilization. This is in stark contrast to previous literature, which reported that GR can degrade these chlorinated ethenes. The absence of reaction in our experiments is explained by having equilibrated GR suspensions, where the affinity of chlorinated ethenes for GR surfaces is extremely low.