Average size and zeta potential of nanobubbles in different reagent solutions

In the present study, we analyzed the average size and zeta potential of nanobubbles (NBs) in chemical reagent solutions. Here, we proposed the possible mechanisms for the size growth and for negative and positive NB creation. NBs were produced by dispersing a supersaturated air-water mixture in a mixing chamber, and then causing the breakup of microbubbles in a Teflon hose. The size and zeta potential of the NBs were measured by dynamic light scattering. The NB size had no dependency on pH and grew over time. The proposed mechanism of the NBs’ size growth related to their coalescence in the solutions. The bubbles were charged negatively in the presence of glucose, ethylenediaminetetraacetic acid, and Na+, while they were charged positively in the addition of dimethyldioctadecylammonium bromide, Al3+, and Fe3+. The NB zeta potential decreased in all solutions, while their pH increased from 2 to 12. Zeta potential values remained stable for 150 min, proving the long-term permanence of bubbles in the bulk solutions. The charged NBs were created from the adsorbed species such as OH− and DODA+ and possible aqueous speciation (through the addition of metal ions) on its surface. Our results indicate that the type of chemical reagent solution can influence both the sign of the surface charge and the size of NBs, allowing them to be applicable in many treatment processes for water treatment.