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

Abstract

In this work, contaminants of emerging concern were catalytically degraded in the homogeneous phase with the use of unconventional green reagents. Three reagents, namely, sulfite, metabisulfite, and persulfate, were tested and compared with conventional hydrogen peroxide in the degradation process activated by Fe-TAML. The latter is a biodegradable, homogeneous tetra-amido macrocyclic ligand catalyst containing iron(III). Metabisulfite showed the highest efficiency among the three tested reagents, and its reactivity was similar to that of H2O2. However, metabisulfite is a safer and cleaner reagent compared to H2O2. A comprehensive study of the activity of metabisulfite with Fe-TAML was carried out toward the oxidative degradation of eight contaminants of emerging concern. The catalytic process was tested at different pH values (7, 9, and 11). Metabisulfite showed the highest activity at pH 11, completely degrading some of the tested micropollutants, but in several cases, the system was active at pH 9 as well. In particular, metabisulfite showed the best efficiency toward phenolic compounds. A preliminary study on the reaction mechanism and the nature of the active species in the Fe-TAML/metabisulfite system was also conducted, highlighting that a high-valent iron-oxo species might be involved in the degradation pathways.

First evidence of a key role of the peroxymonosulfate radical (SO5•−) in a Fenton-like process based on metabisulfite

“…2b/c). This finding is consistent with our previous results (Farinelli et al 2019), that neither 2-PrOH nor t-BuOH are able to inhibit the degradation of PhOH under comparable conditions.…”

“…As neither 2-PrOH nor t-BuOH are reported to behave as effective quenchers for degradation by Fe-TAML/MBS (Farinelli et al 2019), we searched for alternative reaction quenchers.…”

“…In our previous work (Farinelli et al 2019), the ability of Fe-TAML to activate sulfite and metabisulfite (MBS) other than hydrogen peroxide was reported. The use of MBS in place of hydrogen peroxide in advanced oxidation processes is favourable, since MBS is much cheaper, safer, and almost equally efficient toward contaminant degradation compared to hydrogen peroxide (Farinelli et al 2021).…”

“…•− for the reasons explained above (inability of either 2-PrOH or t-BuOH to inhibit phenol degradation;Farinelli et al, 2019). Although different radicals could in principle account for EPR observations, simulations of the EPR spectra (see SM,…”

Developing an Ultrasensitive Colorimetric Assay for Low‐abundance Iron‐tetraamido Macrocyclic Ligand (Fe−TAML) Catalyst

“…Moreover, it can be used under a variety of working conditions, including variable pH, temperature, and solvent compositions. Due to these advantages, FeÀ TAML is widely regarded as a powerful green catalyst for many environmental friendly applications such as wastewater treatments, [3][4][5] water oxidation, [6,7] deactivation of bacterial spores, [8] biomass hydrolysis, [9] and cotton bleaching, [10] etc.…”