Synergistic enhancement of ferrous ion with zero-valent copper/oxygen system: In-site formation and catalysis of H2O2

Zero-valent copper (ZVC) coupled with oxygen gas (O2) was extensively studied to degrade refractory contaminant, while the active dismutation reaction and low reactivity of Cu(I) refrained the performance at acid condition. In this study, ferrous ion (Fe(II)) was added to the ZVC/O2 system (ZVC/Fe(II)/O2 system) to enhance the degradation ability, the degradation rate of acid orange 7 in the ZVC/Fe(II)/O2 system was enhanced by 34.8% compared to the ZVC/O2 system, and the corresponding apparent rate constant was almost three times higher than that of the ZVC/O2 system. In the reactive species identification experiments, by electron spin resonance experiments and quenching experiments of nitrobenzene, tert butyl alcohol and methanol, hydroxyl radical was proven as primary reactive oxygen species rather than high-valent metal-Cu(III). In addition, the optimum ZVC dosage, Fe(II) concentration, pH and stirring rate were derived based on optimization experiments combined with economic applicability. In the ZVC/Fe(II)/O2 system, the mechanism was analyzed by detecting the variation of the concentration of H2O2, Cu(I) and total dissolved copper in the solution. In the degradation process, ZVC was corroded to form Cu(I) by H+, then Cu(I) reacted with O2 to generate hydrogen peroxide, the generated hydrogen peroxide was induced by Fe(II) and Cu(I) to produce hydroxyl radical, at the same time, ZVC and Cu(I) could reduce Fe(III) to Fe(II). The coexisting substances like carbonate ion, nitrate ion, sulfate ion and phosphate ion did not affect the demineralization of acid orange 7 in the ZVC/Fe(II)/O2 system, chloride ion remarkably accelerated the degradation rate of acid orange 7, while fulvic acid limited the acid orange 7 removal. The ZVC/Fe(II)/O2 system also showed excellent degradability in well water, lake water and tap water. Total dissolved copper concentration was controlled within 1 mg/L by the alkali precipitation method, which was within II-level environmental quality criteria in China. These facts suggested that Fe(II)-enhanced ZVC system had great development potential in water treatment.