Efficiency and Mechanism of Naproxen Degradation in the Mo/Fe3+/H2O2 System

Naproxen (NPX) is a widely occurring, refractory organic contaminant that cannot be removed by conventional water treatment processes. In response to the growing environmental pollution caused by NPX, an innovative and highly efficient green degradation method has been developed, designed on the principles of sustainability to promote long-term ecosystem health and advance a circular economy. In this study, using zero-valent molybdenum as a catalyst in combination with trivalent iron (Fe3+) and hydrogen peroxide (H2O2), we constructed a Mo/Fe3+/H2O2 system to treat NPX-contaminated water. The effects of solution pH, H2O2 concentration, Fe3+ concentration, Mo dosage, and co-existing water-matrix constituents (Cl−, HCO3−, PO43−, NO3−, and humic acid (HA)) on NPX removal were investigated; reactive species were identified; and the reusability of Mo as well as its performance under the continuous-flow condition were evaluated. The results showed that the optimal pH was 3 and the appropriate Fe3+ dosage is 100 µM. With 500 µM H2O2, 87.9% of NPX was removed within 7 min, and a moderate increase in Fe3+ concentration, together with a suitable H2O2 level, enhanced the removal efficiency. HCO3−, Cl−, and HA exerted slight inhibition, whereas PO43− markedly suppressed NPX degradation. Recycling tests and the 6 h continuous-flow treatment demonstrated excellent reusability and stability of Mo. Quenching experiments revealed that HO• and Fe(IV) were the dominant reactive species responsible for NPX degradation.