Deeper understanding of advanced oxidation processes: identification/quantification of different oxidants in mono and...

The use of various oxidizing agents, including hydrogen peroxide (H₂O₂) and sulfate-based oxidants, has extended to a wide range of applications related to advanced oxidation processes (AOPs) for the degradation of organic compounds through pathways involving both radical and non-radical species, which are not yet fully understood. This paper proposes to study their interaction with suitable detection reagents (probes), revealing mechanistic information that resulted in the development of a combined luminescent/optical approach that allows their rapid differentiation and monitoring in mixtures. Sulfate-based oxidants (notably, peroxydisulfate, PDS) and H₂O₂-based oxidants are distinguished via light pathways using basic portable chemiluminescence (p-CL) and buffered electrochemiluminescence (ECL) with luminol, respectively. Peroxymonosulfate (PMS), in turn, produced a yellow compound under short-term buffered conditions without CL emission. This colored dark pathway, in which isosbestic points and singlet oxygen (¹O₂) were key elements in a redox reaction that can be electrochemically enhanced, was also obtained for PMS using p-aminobenzoic acid (PABA) as probe, confirming the interaction of the aniline ring. The yellow product was identified by FT-IR-ATR as a potentially aggregated quinonoid derivative. The resulting method was complemented with portable Raman and hydroquinone (HQ) UV-Vis spectroscopy for perborate (PB) and percarbonate (PC) speciation, respectively. It was tested using synthetic mixtures and samples containing one or two oxidants, with good results (RSD <5.3%, │Er│ < 7.6%).