Formation and Stability of Bulk Nanobubbles in Different Solutions

Abstract

The existence of bulk nanobubbles is still controversial in spite of their significance in a large range of applications. Here, we developed a new method of compression−decompression to produce controllably bulk nanobubbles. Then, we further investigated the generation of bulk nanobubbles in pure water, acid, alkaline, and salt solutions using nanoparticle tracking analysis. The results indicated that the concentration of bulk nanobubbles depends on the decompression time and would reach a maximum value when the decompression time is about 30 min for the pure water system. More importantly, we gave a relatively direct evidence of the existence of bulk nanobubbles by measuring the X-ray fluorescence intensity of Kr in acid, alkaline, and salt solutions. It is shown that the decrease tendency in intensity of Kr in alkaline solution is similar to that in the concentration of bulk nanobubbles with the deposited time, indicating that the bulk nanobubbles produced indeed have gas inside. Furthermore, the concentration and stability of bulk nanobubbles in an alkaline solution are greatest compared with other two solutions regardless of gas types. The concentration of bulk nanobubbles will decrease in the order alkaline > acid/pure water > salt solutions. We believe that our results should be very helpful in understanding the formation and stability of bulk nanobubbles in different solutions.

Investigating states of gas in water encapsulated between graphene layers

“…Total reflectance infrared spectroscopy of nanobubble solutions indicated the presence of hard hydrogen bonds equivalent to those found in ice and gas hydrates [39]. It has been reported that bulk nanobubbles 50-500 nm in diameter can be prepared by pressurizing gas in water and then decompressing the water to ambient pressure [40,41]. Thus, bulk nanobubbles may be present in the gas-supersaturated water that we prepared here.…”

“…The existence and stability of bulk nanobubbles have been highly debated. To date, numerous experimental studies have shown that bulk nanobubbles can be stable in water for hours or even weeks [3,[39][40][41]. Those studies mainly employed optical methods, which lack the resolution to see detailed structures in "nanobubbles".…”

Gas nanobubble dispersions as the important agent in environmental processes – generation methods review

“…DLS is most commonly used to determine the diameter of bubbles in liquid but allows only for the size distribution density measurement without the number concentration. NTA is potentially able to determine the concentration of bubbles (Oh et al ., 2015; Oh and Kim, 2017; Qiu et al ., 2017; Hu and Xia, 2018; Ke et al ., 2019). However, huge errors can be made using this method as the operator has to set the background level oneself.…”

Role of mineral flotation technology in improving bitumen extraction from mined Athabasca oil sands—II. Flotation hydrodynamics of water‐based oil sand extraction

“…Three common methods of exploring hydrodynamic cavitation are used to generate nanobubbles in flotation research: high intensity conditioning; fast liquid flow through a cavitation tube; and gas super‐saturation under dynamic conditions. While conventional particle size analyzers are used to detect the sizes of nanobubbles generated, the most commonly used method for estimating the population of nanobubbles is a nanoparticle tracking analysis (NTA) instrument, which is based on light scattering . In a high intensity agitation cell, the population of nanobubbles increased with increasing agitation speed, due to more intensified hydrodynamic cavitation at a higher agitation speed .…”

“…While conventional particle size analyzers are used to detect the sizes of nanobubbles generated, the most commonly used method for estimating the population of nanobubbles is a nanoparticle tracking analysis (NTA) instrument, which is based on light scattering. [142][143][144][145][146] In a high intensity agitation cell, the population of nanobubbles increased with increasing agitation speed, due to more intensified hydrodynamic cavitation at a higher agitation speed. [142,143] As shown in Figure 9, the size of nanobubbles generated dramatically decreased from 820 to 200 nm with an increasing agitation rate.…”