Influences of nanobubbles on particle–particle and bubble-particle interactions: A review

The investigation of the interactions between particles resulting from long-range hydrophobic forces has been thoroughly studied in the literature. The hydrophobic force is most likely a result of capillary forces that may occur when nanobubbles merge and create capillary bridges. Recent studies show that fine particle collection can be enhanced by introducing nanobubbles, which seems to be a positive indication of the existence of such capillary bridges. There has been a significant interest in nanobubble research in the past two decades due to their excellent stability and multitude of applications. Although this is an interesting research area, there is still a great debate about the extraordinary stability of nanobubbles. Arguably, much less is known about the underlying mechanisms responsible for their role in bubble-particle and particle–particle interactions that can potentially augment engineering processes. We aim to examine the underlying mechanisms of nanobubble interactions with particles and bubbles that can be conveniently utilized to explain the improved particle separation efficacy. This article also discusses the current understanding of the origin of nanobubbles, including their characterization methods, existing debates, and possible reconciliation of different theories. Finally, the review discusses areas that require further research to clarify some existing issues and provides a direction where further research in the area should be headed.