Enhancement of peroxymonosulfate activation for antibiotics removal by nano zero valent tungsten induced Cu(II)/Cu(I) redox cycles

Abstract

This work presented a new strategy to activate peroxymonosulfate (PMS) by the addition of nano-zero-valent tungsten (nZVT) via accelerating the redox cycles of Cu(II)/Cu(I), which induce the consecutive generation of highly reactive oxygen species ultimately. The oxidation capacity of the nZVT/Cu(II)/PMS process and the detailed mechanisms of PMS activation were investigated with tetracycline (TC) as the targeted pollutant. Our results indicated that about 70% TC removal was obtained in the nZVT/Cu(II)/PMS system in 15 min with an initial pH of 4.6. In addition, hydroxyl radicals (OH), sulfate radicals (SO4−), and superoxide radicals (O2−) were identified as the reactive oxygen species (ROSs) attributed to rapid TC decomposition according to the quenching studies and EPR technology. The effective component that was responsible for PMS activation and ROSs generation was ascertained to be the resulting Cu(I), which derived from the direct reduction pathway driven by epigenetic low valence tungsten species and the indirect reduction pathway driven by active hydrogen atoms. Further, the presence of Cu(II) significantly accelerated the corrosion of the nZVT powders, leading to the accumulation of low valence tungsten species and the decrease in the mean diameter of the ZVT nanoparticles. There was no obvious change of the composition and structure between the original and residual nZVT powders, as evidenced by XPS and XRD analysis. The degradation process of TC included the cleavage of specific functional groups, the ring-opening reactions and the hydroxylation process. This study provided theoretical significance in applying zero-valent metals to activate PMS through a cupric/cuprous redox cycling mechanism.