Strong Enhancement on the Degradation of Organic Contaminants by Base-Activated Peroxymonosulfate in Phosphate Buffer Solution

Alkali-activated peroxymonosulfate (PMS) exhibits low activation efficiency and high alkalinity consumption, and these limitations significantly hinder its practical application. In this study, it was established that the incorporation of phosphate buffered (PBS) could markedly increase the oxidation proficiency of Orange II (AO7) and Rhodamine B by PMS within the range of pH 6–11. At pH 9.0, the degradation efficiencies of AO7 and RhB in the PBS/PMS process are 24.4-fold and 16.5-fold higher than those in the alkali-activated PMS process, respectively. These efficiencies surpass those of previously reported alkali-activated PMS systems enhanced by pyrophosphate and NaHCO₃. The radical quenching studies demonstrated that SO₄^•− and •OH were the main responsible species in base-activated PMS in phosphate buffer solution rather than O₂^•− and ¹O₂ which have been previously reported. Furthermore, the predominant active species varied significantly under varying pH conditions. The incorporation of phosphate could markedly increase the oxidation proficiency of AO7 and RhB by PMS within the range of pH 6 to pH 11, with highest oxidation constant achieved at pH 9. The AO7 degradation rates increased with increasing phosphate concentrations, PMS doses, as well as higher temperature. The high removal efficiency of residue phosphate by CaCl₂ demonstrated that this method could be used as a pretreatment for wastewater treatment. The findings suggest that experiments on PMS-based advanced oxidation processes conducted in phosphate buffer solution (PBS) should account for the catalytic role of PBS in PMS activation.