Effects of interactions between humic acid and heavy metal ions on the aggregation of TiO nanoparticles in water environment.

Nanoparticles (NPs), heavy metal and natural organic matter (NOM) may simultaneously exist in the aquatic environment, where they will affect the behavior of each other and may enhance their toxicities. Studies on the influences of interactions between NOM and heavy metal ions on the behavior of NPs are scarce. In this study, combined effects of Pb and HA on the aggregation behavior of TiO NPs in water environment were investigated by Dynamic light scattering (DLS) and Nanoparticle tracking analysis (NTA). The results illustrated that interactions between Pb and HA could case the aggregation of TiO NPs obviously. The concurrence of Pb and HA resulted in decreased critical coagulation concentration (CCC) and increased attachment efficiencies. Meanwhile, we found that the addition sequences of HA and heavy metal clearly influenced the aggregation kinetics of TiO NPs. At different addition sequences, the complex reaction between Pb and HA changed the surface charge of TiO NPs, and caused the different aggregation behavior which depended on the complex locations and complex sites. Furthermore, the excitation-emission-matrix (EEM) fluorescence spectra was used to verify the significant effects of the complex interactions between Pb and HA on the aggregation of TiO NPs. Our results would be significant for interpreting TiO behavior in the complicated water system. The complexation between Pb and HA promoted the aggregation of TiO NPs, meanwhile, complex locations and complex sites played an important role.