Lability-specific enrichment of typical engineered metal (oxide) nanoparticles by surface-functionalized microbubbles...

Enrichment of metallic engineered nanoparticles (MENPs) from environmental waters is a prerequisite for their removal, reliable analyses, and environmental process interpretations. This work investigated the enrichment of typical MENPs with different degrees of lability using surface-functionalized microbbubles. During the process, the transformation/dissolution characteristics of MENPs were considered, and the impact of surfactant or coagulant dose, pH of MENP suspensions, and water matrix was systematically investigated. Results show that the colloidal gas aphrons (CGAs) were capable of enriching over 90.0% of ionic Ag(I) which ended up as AgBr and Ag₂CO₃ in floats when the pH of suspension was 6.0. The polyaluminum chloride-modified CGAs with positive surface charges were good at capturing the particulate ZnO-NPs (~84.8%) but failed to collect the ionic species. It should be noted that the total MENP enrichment efficiency closely related to the content proportions of different species. In the river water, both of the dissolved natural organic matter (fulvic acids) and the electrolytes might influence the enrichment process by affecting the species transformation of Ag-NPs and ZnO-NPs. For the stable TiO₂-NPs, 97.1% of the nanoparticles were captured by CGAs. FAs apparently reinforced the enrichment performance since the molecules acted as bridge and facilitated the attachment between TiO₂-NP and CGAs. This work contributes to establishing the robust microbubble-induced enrichment method considering the characteristics of MENP contaminants.