Aggregation and disaggregation of Al2O3 nanoparticles: influence of solution pH, humic acid, and electrolyte cations.

Extensive use of Al2O3 nanoparticles in consumer and industrial products has led to concerns about their potential environmental impacts in the recent years. In most studies concerning Al2O3 aggregation and disaggregation, more was to consider the single factor that influences their environmental behaviors. Understanding the combined abiotic factors that influence the fate, transport, and stability of nanoparticles in a complex aquatic system has become extremely important. Here, we reported and analyzed the major abiotic factors such as typical solution pH, electrolyte cations in different valences (Na+ and Ca2+), and the presence of humic acid (HA) that influence the stability, aggregation, and disaggregation behaviors of Al2O3 nanoparticles in a complex aquatic system. Dynamic light scattering technique combined with fluorescence spectroscopic analysis was used to explore the aggregation mechanisms. Experimental results indicated that Al2O3 nanoparticle stability was mainly controlled by the steric hindrance, van der Walls, and electrostatic interactions between HA and Al2O3 nanoparticles. Aggregation kinetics and attachment efficiency studies induced by the addition of Na+ and Ca2+ cations confirmed that divalent electrolytes could reduce the large energy barrier between the charged colloidal particles more efficiently, and induce a more aggressive aggregation of the particles. Additionally, the bridging effect of HA with Ca2+ was also an important mechanism for the aggregation enhancement, which had been confirmed by the fluorescence excitation-emission matrix (EEM) spectra analysis. These findings are useful in understanding the environmental challenges of inorganic colloidal particles in natural environments. [ABSTRACT FROM AUTHOR]