# Micro-Nanobubble Technology in Surface Cleaning and Defouling
## 2 Properties and Mechanisms of MNs  
NBs are distinct from larger bubbles owing to their special physical and chemical characteristics; their diameters are usually less than 1000 nm [6]. Their vast surface area, minimal rising velocity, high internal pressure, and capacity to produce ROS make them extremely adaptable to a wide range of applications such as industrial operations, water treatment, and cleaning [24]. Optimizing the performance of NBs in practical applications requires an understanding of their characteristics and workings. This section investigates their potential for radical generation, stability, surface contact, attachment mechanisms, and roles in cavitation and emulsion formation [25]. These features not only highlight the unique qualities of NBs but also show how they help progress defouling, surface cleaning, and other fields.  
The classification, analysis, and creation methods of MBs and NBs--also referred to as fine bubbles and ultrafine bubbles, respectively--have been the main subjects of the majority of research. The three primary methods for producing MBs and NBs are membranes, ultrasonication, and decompression [13]. At high pressure, a supersaturated state for gas dissolution is created for the decompression-form generator. Supersaturated gas is quite unstable at these kinds of pressures. As a result, it will generate MBs and NBs instantly according to the size parameters that are employed [9]. The decompression technique works well for quickly producing a large concentration of consistent bubbles. However, it uses a lot of energy and demands exact control over the pressure conditions.  
The membrane method involves injecting a gas into a liquid through a porous membrane, which causes bubbles to form between the liquid and the membrane surface. This method is reasonably easy to use and gives you precise control over the size and dispersion of the bubbles. Over time, membrane deterioration and blockage can lower the efficiency and raise maintenance needs [26]. By delivering ultrasonic waves to a solution and using the difference in the partially created pressure in the solution to evaporate the dissolved gas and produce bubbles, the ultrasonic technique produces cavitation. The ultrasonic technique works well for creating minuscule bubbles and can be applied to a wide range of situations. Because it requires specialized equipment and uses a lot of energy, it can be costly. Each technique and instrument creates a different number and size of bubbles [9; 13]. The potential for MBs and NBs to be scaled up and deployed at the industrial level has not received much attention lately [27].  
Figure 1: Microbubble and nanobubble technology in surface cleaning and defouling.  
[PERSON] et al. [28] reviewed several approaches to NB generation, contrasting the findings from different research groups and emphasizing differences between approaches. NBs with diameters less than 1000 nm are valuable for soil remediation, wastewater treatment, and metal recovery because of their special qualities, which include a long lifespan, high internal pressure, and minimal rising velocity. This study investigated several hydrodynamic techniques for creating NBs, such as ultrasonication, ejectors, spiral liquid flow, and venturi/nozzle-based generators, and analyzed the outcomes of various configurations. It highlighted how process variables such as flow regime, gas holdup, and material roughness could affect results. The electrolytic process was also discussed, although its industrial-scale use is restricted by its high energy costs. To improve the effectiveness of environmental processes, the review attempted to establish the groundwork for further studies on NB generation.