Nonradical Oxidation of Pollutants with Single-Atom-Fe(III)-Activated Persulfate: Fe(V) Being the Possible Intermediate Oxidant.

When applied for the remediation of polluted water/soil, peroxydisulfate (PDS) usually needs to be effectively activated to generate sulfate radical as the working oxidant. However, a significant part of the oxidation capacity of PDS is lost in this way because sulfate radical unselectively reacts with most of the substances in water/soil. PDS activation without generating radicals is preferred to maximize its oxidation capacity for targeted pollutants. Here, we report that single-atom Fe(III)- and nitrogen-doped carbon (Fe-N-C) can efficiently activate PDS to selectively remove some organic pollutants following an unreported nonradical pathway. The single-atom Fe(III) coordinated with pyridinic N atoms was confirmed to be the active site for the catalytic decomposition of PDS. However, the PDS decomposition did not produce radicals or reactive oxygen species. It is very likely that the coordinated Fe(III) is readily converted to Fe(V) through two-electron abstraction by PDS, and Fe(V) is responsible for the selective degradation of organic pollutants. The PDS/Fe-N-C-coupled process utilizes more oxidation capacity of PDS than both radical oxidation and other reported nonradical oxidation like PDS/CuO under the same experimental conditions. This process provides a new approach to selectively degrade some organic pollutants through PDS activation.