Gallic acid enhanced Cu(II)/H2O2 system for efficient degradation of naproxen: Insights into redox cycling and radical generation.

Previous studies have demonstrated that aqueous copper ions (Cu(II)) can activate hydrogen peroxide (H2O2) to generate hydroxyl radicals (HO•) for oxidative degradation of pharmaceuticals and personal care products (PPCPs). However, the treatment efficiency of this process is constrained by the kinetically limited reduction of Cu(Ⅱ) to Cu(I). In this study, introducing gallic acid (GA) into the Cu(II)/H2O2 system significantly enhanced the degradation efficiency of the model pharmaceutical compound naproxen (NPX) across a broad pH range (5.0-9.0). Under neutral conditions (initial pH 7.0, unadjusted), the GA/Cu(II)/H2O2 system achieved a high NPX degradation ratio of 92.0 % within 30 min, representing a 9.89-fold enhancement compared to the Cu(II)/H2O2 system alone. Mechanisms investigation revealed the simultaneous generation of Cu(III) and HO•, with quantitative analysis confirming HO• as the predominant reactive species. The modified performance is attributed to the formation of Cu(I)-GA complexes, which not only facilitate the Cu(II)/Cu(I) redox cycle but also lower the redox potential of the Cu(II)/Cu(I) couple, thereby promoting H2O2 activation. The system demonstrates excellent applicability for degrading diverse PPCPs, exhibits strong resistance to most common water matrix interferences, and maintains effective NPX removal and dissolved organic matter removal in real water samples including secondary water and lake water.