[Stability of Ferrihydrite and Goethite Nanoparticles Under Different Environmental Conditions]

Agglomeration and dispersion of nanoparticles control many important environmental processes. In this study, the particle size and zeta potential of ferrihydrite nanoparticles (FHNPs) and goethite nanoparticles (GTNPs) under different pH, ion, and organic matter conditions were measured. These data were used to calculate the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy between nanoparticles to further investigate the stability of two nanoparticles. The results showed that Na⁺ and Ca²⁺ promoted FHNPs and GTNPs agglomeration due to their ionic strength. The PO₄^3- with low-concentration (2 mmol·L^-1), humic acid and fulvic acid (2 mg·L^-1 and 10 mg·L^-1) loaded on iron mineral nanoparticles changed their surface charge and further improved the stability of FHNPs and GTNPs at medium and high pH. Although the PO₄^3- with high concentration (10 mmol·L^-1) also changed the electrical properties of iron mineral nanoparticles, it had little contribution to the GTNP stability due to its ionic strength. When the zeta potentials of FHNPs or GTNPs were close to 0, the primary barrier and secondary minima were nonexistent simultaneously. The two kinds of nanoparticles irreversibly agglomerated in primary minima. When the primary barrier and secondary minima coexisted, the proportion of reversible aggregation of FHNPs and GTNPs in secondary minima increased. The results provided support for further investigation of the environmental behavior of FHNPs and GTNPs, and iron mineral nanoparticle-facilitated transport of pollutants.