Stability of Artificial Nano‐Hydroxyapatite in the Presence of Natural Colloids: Influence of Steric Forces and Chargeability

The stability of nano‐hydroxyapatite (nHAP) affects its fate in the environment. Few studies have compared the influence of colloids with different properties on the stability of nHAP. Fulvic acid, montmorillonite, and goethite were chosen as representative colloids. An ultraviolet–visible spectrophotometer and NanoBrook 90Plus phase analysis light scattering (PALS) were used to determine absorbance, zeta potential, and hydrodynamic diameter. Results showed that addition of fulvic acids could make nHAP more stable through electrostatic and steric effects, whereas montmorillonite affected the stability mainly by electrostatic effects. Goethite could adsorb onto nHAP particles and form goethite‐nHAP heteroaggregates at pH < pH pzc,goethite (i.e., pH at point of zero charge), and its addition enhanced the electrostatic repulsion forces at pH > pH pzc,goethite . Since fulvic acid has additional steric effects, its stability enhancement was greater than that of montmorillonite and goethite. Montmorillonite colloids were stronger than goethite colloids for enhancing the stability of nHAP, because montmorillonite had a higher absolute surface potential. The order in which organic and inorganic colloids were added affects the degree of stability of nHAP. Energy barriers calculated by extended Derjaguin–Landau–Verwey–Overbeek were in good agreement with the experimental results and implied that the nHAP particles were in the stage of reaction‐limited aggregation at pH 7 ± 0.1 and pH 9 ± 0.1. Our findings are important for understanding the cotransport of nanoparticles and colloids. Core Ideas Organic colloids enhance the stability of nHAP, mainly by steric effects. Organic colloids stabilize nHAP in the absence and presence of inorganic colloids. Montmorillonite and goethite stabilize nHAP particles, mainly by electrostatic forces. Energy barriers were calculated by extended Derjaguin–Landau–Verwey–Overbeek. Energy barriers showed the predominant role of steric effects.