Dithionite–zerovalent iron coupling drives Cu(II)/Cu(I) redox cycling for persulfate activation and PAH degradation in carbonate-rich water

Persulfate (PS)-based advanced oxidation of polycyclic aromatic hydrocarbons (PAHs) in carbonate-rich water is severely constrained by radical scavenging and surface passivation of iron-based activators. Here, a dithionite–zerovalent iron–copper (DTN–ZVI–Cu) ternary system was developed to promote persulfate activation toward predominantly non-radical oxidation under bicarbonate-rich conditions. DTN and ZVI accelerated Cu(II)-to-Cu(I) reduction while simultaneously regenerating the ZVI surface, thereby sustaining Cu-centered redox turnover and facilitating the formation of Cu(III)-like oxidizing species. In parallel, DTN promoted sulfur-centered conversion pathways that favored 1 O 2 generation. These non-radical oxidizing pathways are generally less susceptible to inorganic-anion scavenging than conventional sulfate and hydroxyl radicals. Under standard conditions, the system achieved 91% acenaphthene removal within 60 min ( k obs  = 0.039 min −1 ), an 8.7-fold kinetic enhancement over ZVI/PS alone. Moderate bicarbonate further promoted degradation, with k obs reaching 0.13 min −1  at 250 mg/L HCO 3 − , which is consistent with a plausible role of copper–carbonate complexation in stabilizing Cu redox cycling and favoring non-radical oxidation pathways. XPS analysis suggested that DTN–ZVI coupling elevated the reactive copper pool (Cu(I) + Cu(III)) to 57% of total surface copper. Applied to synthetic wastewaters, the system maintained 90–96% PAH removal at optimal dosages, indicating strong performance across complex saline matrices. This work demonstrates the feasibility of using coexisting Cu(II) as a catalytic resource for non-radical persulfate activation in carbonate-rich water.