Brownian Dynamic Study of the Aggregation Process of TiO₂ Nanoparticles in Aqueous Suspensions

To fully comprehend the aggregation process of TiO₂ nanoparticles in aqueous suspensions, one must quantitatively characterize the size distribution and the number of aggregates during the aggregation process. A Brownian dynamics approach was applied to simulate the aggregation of TiO₂ nanoparticles in aqueous suspension. The well-known Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was utilized to describe the particle-particle interaction. The effect of particle size (10, 20, and 30 nm), pH (5.5, 7.0, and 9.0), and ionic strength (0.001, 0.01, and 0.1 M) on aggregation process was characterized using the number of aggregates, single TiO₂ nanoparticles, and size distribution of aggregates. Results indicated that aggregate size and degree of aggregation decreased with increase of pH, and increased with the increase of ionic strength. In comparison with pH and ionic strength, primary particle size probably played a critical role in the aggregation of the TiO₂ nanoparticles in aqueous suspension. The proportion of large aggregates that included more than 30 single TiO₂ nanoparticles in the 10 nm TiO₂ nanoparticles model system was 30.6%. Brownian dynamic simulation of the aggregation process of TiO₂ nanoparticle under different conditions is beneficial to adequately understand the fate of nanoparticles in environmental systems.