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

Abstract

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 reactionlimited aggregation at pH 7 ± 0.1 and pH 9 ± 0.1. Our findings are important for understanding the cotransport of nanoparticles and colloids.• 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.

The Effects of NaOH Concentration on the Hydrothermal Synthesis of a Hydroxyapatite–Zeolite Composite Using Blast Furnace Slag

“…As reported by Hansen et al [46], it was found that as the pH of the initial mixture increased, the aggregation of the synthesized hydroxyapatite crystals increased, which resulted in a decrease in both the specific surface area and adsorption capacity [47]. This phenomenon could be as a result of the surface energy of hydroxyapatite crystals [46,48]. The higher alkaline condition led to a higher surface energy of hydroxyapatite crystals, and it led to the aggregation of hydroxyapatite crystals [46,49].…”

Heteroaggregation and sedimentation of natural goethite and artificial Fe3O4 nanoparticles with polystyrene nanoplastics in water

“…Sedimentation of heteroaggregates of goethite and Fe 3 O 4 NP with PS NPs or montmorillonite suspensions in the cell was monitored by ultraviolet-visible spectroscopy using an 8453 UV-Vis spectrometer (Agilent Technologies, Santa Clara, CA, USA). Measurements were obtained from the time-resolved optical density (OD = C e [absorbance at different time intervals]/C 0 [initial absorbance]) of heteroaggregates of goethite and Fe 3 O 4 NP suspensions at 441 and 381 nm over 120 min time periods, respectively (Wu et al 2022a;Wu and Bi 2019).…”