Role of dissolved iron ions in nanoparticulate zero-valent iron/H2O2 Fenton-like system

Nanoparticulate zero-valent iron (nZVI) was proved as an efficient Fenton-like catalyst and dissolved iron ions were more or less released into the studied water, but the role of these ions and its primary mechanisms in nZVI/H2O2 Fenton-like reaction process were little known. To address these issues, batch tests were conducted with nitrobenzene (NB) as a probe compound for comparing reaction efficiencies. It was found that, all the initial parameters included the initial concentrations of NB, H2O2 and dissolved oxygen (DO), pH, and nZVI dose-affected NB degradation in the nZVI/H2O2 system, and their optimum values were determined as 40.0mg/L, 4.0, 340.0mg/L, 112.0mg/L, and 5.0mg/L, respectively. Interestingly, each parameter worked at its optimum value, while the concentration of the iron ions was approximately 1.13mg/L in all the studied systems at the reaction time of 180min. The influences of these ions on the generation of the reactive oxygen species like hydroxyl radical (HO.), oxygen anion radical (O-2(-).), and perhydroxyl radical (HO2-.) depended on the concentration. When the concentration was lower than 1.13mg/L, HO. generating was enhanced, otherwise, HO. was inhibited and more O-2(-). and HO2-. were generation. These ions initiated homogeneous and heterogeneous reactions to degrade NB, shortened the time from about 120min to 60min to the NB degradation maximum rate, and the direct contribution of the former reaction was more than 20.0%. Therefore, adjusting the dissolved iron ions concentration close to its optimal value via controlling DO to no less than 5.0mg/L is a practical way to the maximum efficiency of nZVI/H2O2 system.