Interactions of iron-based nanoparticles with soil dissolved organic matter: adsorption, aging, and effects on hexavalent chromium removal

The interactions and mechanisms between soil dissolved organic matter (DOM) and three types of iron-based nanoparticles (NPs), i.e., nanoscale zero-valent iron (nZVI) particles, Fe2O3 NPs, and Fe3O4 NPs, were investigated in short-term exposure experiments. The adsorption results showed that soil DOM was rapidly adsorbed on the surface of the iron-based NPs with the adsorption rate varying according to Fe3O4 > Fe2O3 > nZVI. Spectral analysis results revealed that aromatic DOM fractions with high-molecular-weights were preferentially adsorbed. The binding mechanism was determined as hydrogen bonding and ligand exchange via Fourier transform infrared spectroscopy (FT-IR) analysis. Scanning electron microscopy, FT-IR, X-ray photoelectron spectroscopy, and X-ray diffraction were used to identify the corrosion products of the three iron-based NPs at the adsorption equilibrium. The results suggest that Fe3O4 and/or gamma-Fe2O3 and alpha-FeOOH were the main corrosion products of nZVIs and alpha-FeOOH was obtained as an aged product of Fe3O4 NPs. Results of Cr(VI) removal tests suggest that the aged nZVI achieved 79.87% of Cr(VI) removal and the Cr(VI) removal efficiency was significantly improved by coating DOM onto Fe2O3 NPs. The overall data indicate the fate and transformation of iron-based NPs and the enhancement for Cr(VI) removal after interactions between DOM and NPs.

Automated summary

The study investigated the interactions between soil dissolved organic matter and three types of iron-based nanoparticles, showing that the adsorption rate of soil DOM depended on the type of iron-based particles. Analysis revealed that aromatic DOM fractions with high molecular weights were preferentially adsorbed. Various methods were used to identify the corrosion products of the nanoparticles, revealing the fate and transformation of the nanoparticles and their enhanced ability for Cr(VI) removal after interacting with DOM.