Fate and transport of nanomaterials in drinking water

The manufacture of significant quantities of nanomaterials will inevitably lead to the introduction of these materials into environment. The understanding on the characteristics and the fate of these nanomaterials in water is crucial to evaluate their environmental implication and potential risk for human exposure. This research investigated the characteristics, dispersion and stability of two important categories of nanomaterials, metal oxide nanoparticles and quantum dots (QDs) in different aquatic environment, as well as their propensity to be removed by portable water treatment. Lab-synthesized hematite was prepared as individual nanoparticles; whereas all commercial metal oxide nanoparticles were aggregates as received. Neither sonication nor dispersant could not break up these aggregates to primary nanoparticles. It may attribute to chemical bonding during the synthesis or storage. Except silica, metal oxide nanoparticle aggregates aggregated further in 0.01 M KCl solution. The stability of silica may be related to its low pH value of zero point of charge (pHzpc) and low Hamaker constant. Addition of 4 mg/L NOM could stabilize metal oxide nanoparticles by imparting negative charge to their surface and producing an increase in absolute surface potential. Compared with metal oxide nanoparticles, most QDs particles presented as individual nanoparticles, but they also contained a few aggregates. Due to carboxyl functional groups bound on QDs surface, QDs remained stable unless divalent or trivalent cations were introduced to from complexes with QDs. Portable water treatment studies showed that these nanoparticles were relatively difficult to be removed from water only by coagulation, flocculation and sedimentation processes and 0.45 μm filtration enhanced their removal.