Mechanisms on stability of bulk nanobubble and relevant applications: A review

The exceptional physicochemical properties of nanobubbles bestow them the potential for diverse applications, specially in water and wastewater treatment. These applications have stimulated new investigations into stability mechanisms —an essential prerequisite for their effective practical utilization. Producing nanobubbles with stable and measurable properties is a critical endeavour to broaden their applications. However, several challenges persist in the basic theoretical understanding of bulk nanobubble stability. Several bubble models and mechanisms of action remain uncertain and necessitate comprehensive exploration. This review aims to comprehensively analyze scientific information and experimental data reported in recent years on the mechanisms of nanobubble stability and related applications for aquatic environments. Empirical evidence has demonstrated that bulk nanobubbles can endure for notable spans of time —ranging from weeks to months-as verified through diverse characterization techniques. Nevertheless, this phenomenon poses a theoretical challenge to the conventional Young-Laplace equation. The mechanisms underlying this remarkable stability remain partially understood, creating a barrier to this pioneering technology's advancement and practical implementation. In this critical review, we thoroughly analyze the stability mechanisms of single nanobubble and clusters of nanobubbles, presenting these discussions distinctly. We precisely summarize and deliberate upon the impact of various controlling parameters within the aquatic environment that influence nanobubble stability. Moreover, we establish a cohesive link between the stability of bulk nanobubbles within aquatic environment applications, marking a novel assertion. Finally, this work proposes the most convincing stability mechanisms, highlights critical potential directions specially on stability-oriented and its applications for future research. This review will facilitate an in-depth understanding of the stability mechanism of nanobubbles and offer valuable insights of their potential applications in practical engineering. Additionally, it aims to contribute to the future design of nanobubble reactors.