Effects of humic acid and bovine serum albumin on the agglomeration and sedimentation of oxide nanoparticles

Abstract

To better understand the nanoparticle (NP) transport in the environment, the agglomeration and sedimentation of Al2O3, SiO 2, and TiO2 NPs were evaluated after being treated with bovine serum albumin (BSA) and a commercial humic acid (HA). The morphology of NP agglomerates was examined through a transmission electron microscope (TEM), and the agglomeration kinetics was evaluated using established time-resolved dynamic light scattering techniques. BSA treatments decreased the hydrodynamic diameters (d H) of the three NPs in both NaCl and CaCl2 electrolytes due to their steric repulsive forces caused by the BSA globular architecture. The treatments using HA induced the smallest d H of NPs in NaCl electrolyte, but the largest d H of NPs was found in CaCl2 electrolyte, because the HA bound to each other via calcium complexation and thereby enhanced the NP agglomeration. The zeta potentials of NPs were not the dominant factor to affect agglomeration. The NP sedimentation kinetics were studied through measuring the suspension optical absorbance. It was shown that the BSA treatments retarded the sedimentation in most situations; however, HA treatments accelerated the sedimentation greatly in CaCl 2 electrolyte, which was consistent with the measured changes in the d H values. The smallest d H of HA-treated NPs in NaCl electrolyte did not result in the lowest sedimentation rate, which indicated that the agglomeration size was not the only factor to affect the NP sedimentation. © 2014 Zhejiang University and Springer-Verlag Berlin Heidelberg.