Aggregation of TiO₂–graphene nanocomposites in aqueous environment: Influence of environmental factors and UV irradiation

The aggregation kinetics of TiO₂–graphene nanocomposites in aqueous solution affected by solution pH, salt types (NaCl, CaCl₂) and concentrations of electrolytes, and stability induced by UV irradiation was investigated in this study. The zeta potentials and hydrodynamic diameter of the nanoparticles were used as bases to assess the aggregation behavior, and stability of nanocomposites exposed to UV irradiation was expressed in terms of supernatant concentration. The aggregation of TiO₂–graphene nanoparticles in aqueous media followed the colloidal theory. TiO₂–graphene nanoparticles were significantly aggregated in the presence of a diavalent cation compared with monovalent cation because the former was more capable of effective charge screening and neutralization. The calculated Hamaker constant of the TiO₂–graphene nanocomposites in aqueous solution prepared in the lab was 2.31 × 10⁻²⁰ J. The stability of this composite nanoparticles was between those of pure TiO₂ and graphene. A known intensity of UV irradiation was beneficial in the formation of TiO₂–graphene nanoparticle aggregates. However, prolonged UV irradiation may stabilize the nanoparticles. These results provided critical information about the colloidal properties of the new TiO₂–graphene nanocomposites and were useful in predicting the fate and transport of TiO₂–graphene nanocomposites in natural water environments. - Highlights: • This is the first study on the fate and transport of TiO₂–graphene in aqueous environment. • The Hamaker constant of TiO₂–graphene dispersed in aqueous solution was calculated. • The influence of UV irradiation on the stability of TiO₂–graphene was considered.