Removal of diclofenac in solution by the E-Mn²⁺-PMS process via non-radical pathways

As water quality standards have improved and detection technology has advanced, the control of new pollutants has gradually become a research focus. The activation ability of divalent manganese toward peroxymonosulfate (PMS) was enhanced by the introduction of an electric field. The E-Mn²⁺-PMS synergistic process was developed for the removal of the refractory organic pollutant diclofenac (DCF) from water. Firstly, the effects of current density, PMS concentration, Mn²⁺ concentration, solution pH value and water matrix (NO₃^-、Cl^-、HA) on the removal of DCF in water were discussed, respectively. The results indicated that the synergy index of the E-Mn²⁺-PMS process was 10.88 within 20 min of reaction, and its reaction rate constant was 19.250×10^-2 min^-1. The mineralization rate of DCF was 67.4% within 180 min under the experimental conditions: current density was 11.42 mA/cm², PMS concentration was 1 mmol/L and Mn²⁺ concentration was 150 μmol/L. Acidic conditions facilitated the removal of DCF, and the optimal pH value was 3. NO₃^- had almost no effect on the removal of DCF, while Cl^- and HA promoted the removal of DCF significantly. Subsequently, it was demonstrated by radical scavenger experiments, electron paramagnetic resonance (EPR) tests, and analysis of manganese intermediate valence substances. The non-radical pathways (Mn (Ⅲ) oxidation and ¹O₂ oxidation) dominated in the E-Mn²⁺-PMS process. In comparison with the Mn²⁺-PMS process, the amorphous MnO₂ generated in situ under electric field conditions could quickly activate PMS to produce ¹O₂, achieving efficient removal of pollutants.