Emerging investigator series: Suspended air nanobubbles in water can shuttle polystyrene nanoplastics to air-water interface

Abstract

Nanoplastics in the environment are a great concern given their nanoscopic size, colloidal stability, and bio-recalcitrant and biomagnifying nature. They are detected ubiquitously in natural and built environments and pose harm to human and ecological health. In this study, we report the seminal evidence that suspended nanobubbles can remove nanoplastics when repulsive Coulombic forces between nanobubble and nanoplastic are subdued. Our findings showed 60% of 100 nm polystyrene latex was eliminated from the water column after stirring in nanobubble solution at the pHpzc of nanoplastics for 5 min whereas the controls with no nanobubbles showed no removal. Nanoparticle tracking analysis indicated a 61% decrease in number concentration and 27% increase in particle size in the subnatant due to plastic-bubble attachment. Additionally, the mass concentration of nanoplastics in the float after nanobubble flotation was 123% more than the concentration in the subnatant confirming an upward shuttling of plastic-bubble aggregate. This study paves the way forward for engineering systems where coagulation and flotation can deliberately contribute to the removal of nanoplastics with the utility of nanobubbles.