Metabisulfite as an Unconventional Reagent for Green Oxidation of Emerging Contaminants Using an Iron-Based Catalyst

In this work, contaminants of emergingconcern were catalytically degraded in the homogeneousphase with the use of unconventional green reagents. Threereagents, namely, sulfite, metabisulfite, and persulfate, weretested and compared with conventional hydrogen peroxide inthe degradation process activated by Fe-TAML. The latter is abiodegradable, homogeneous tetra-amido macrocyclic ligandcatalyst containing iron(III). Metabisulfite showed the highestefficiency among the three tested reagents, and its reactivitywas similar to that of H2O2. However, metabisulfite is a saferand cleaner reagent compared to H2O2. A comprehensivestudy of the activity of metabisulfite with Fe-TAML was carried out toward the oxidative degradation of eight contaminants ofemerging concern. The catalytic process was tested at different pH values (7, 9, and 11). Metabisulfite showed the highestactivity at pH 11, completely degrading some of the tested micropollutants, but in several cases, the system was active at pH 9 aswell. In particular, metabisulfite showed the best efficiency toward phenolic compounds. A preliminary study on the reactionmechanism and the nature of the active species in the Fe-TAML/metabisulfite system was also conducted, highlighting that ahigh-valent iron-oxo species might be involved in the degradation pathways.