Anoxic and oxic removal of humic acids with Fe@Fe2O3 core–shell nanowires: A comparative study

•Humic acids were removed by Fe@Fe2O3 core–shell nanowires via adsorption under anoxic condition.•The oxic removal of humic acids with Fe@Fe2O3 core–shell nanowires involved adsorption and oxidation.•The oxic humic acids removal rate was 2.5 times that of anoxic removal.

In this study we comparatively investigate the removal of humic acids with Fe@Fe2O3 core–shell nanowires under anoxic and oxic conditions. The products of humic acids after reacting with Fe@Fe2O3 core–shell nanowires under anoxic and oxic conditions were carefully examined with three-dimensional excitation emission matrix fluorescence spectroscopy and gas chromatography mass spectrometry. It was found that humic acids were removed by Fe@Fe2O3 core–shell nanowires via adsorption under anoxic condition. Langmuir adsorption isotherm was applicable to describe the adsorption processes. Kinetics of humic acids adsorption onto Fe@Fe2O3 core–shell nanowires was found to follow pseudo-second-order rate equation. By contrast, the oxic removal of humic acids with Fe@Fe2O3 core–shell nanowires involved adsorption and subsequent oxidation of humic acids because Fe@Fe2O3 core–shell nanowires could activate molecular oxygen to produce reactive oxygen species to oxidize humic acids. This subsequent oxidation of humic acids could improve the oxic removal rate to 2.5 times that of anoxic removal, accompanying with about 8.4% of mineralization. This study provides a new method for humic acids removal and also sheds light on the effects of humic acids on the pollutant removal by nano zero-valent iron.

Graphical abstractWe demonstrate that oxic removal of humic acids with Fe@Fe2O3 nanowires via adsorption and oxidation is more efficient than the counterpart anoxic removal only with adsorption.Figure optionsDownload full-size imageDownload high-quality image (191 K)Download as PowerPoint slide