Formation and stability of bulk nanobubbles generated by gas–liquid mixing

doi:10.21203/rs.3.rs-1600295/v1

Download PDF

Article

Formation and stability of bulk nanobubbles generated by gas–liquid mixing

https://doi.org/10.21203/rs.3.rs-1600295/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

As the field of application of nanobubbles (NBs) expands, more in-depth research into NB generation techniques is required. In this study, the NB characteristics generated by gas–liquid mixing and an NB generation mechanism were investigated according to the different liquid volume fraction (LVF). In the gas–liquid mixing method, we confirmed that the important factors for NB generation are the shear force applied to the trapped bubbles and the amount of trapped bubbles in the liquid. Based on these factors, NBs were generated at more than 10×10⁸ NBs/ml and remained in a stable state for seven days. This study proposes a more specific NB generation mechanism and a valuable methodology for high-concentration NB generation through the gas–liquid mixing method.

Gas–liquid mixing

nanobubble

shear force

stability

zeta potential

Recently, due to the efforts of many researchers to prove the existence of bulk nanobubbles (BNBs) ^1–4, BNB-related technology has been actively reported. Nanobubbles (NBs) have extraordinary properties, such as a large specific surface area, surface electrical potential, and the ability to generate free radicals ^5–7. In addition, NBs in the stabilized state can exist in a liquid for a long time ^8,9, and transform the unique properties of liquids (e.g., surface tension, dissolved gas concentration, and hydrogen bonding force) ^1,10,11. Many researchers are leveraging these properties of NBs for application in various fields (e.g., fuel, wastewater treatment, acceleration of physiological activity in living organisms, and medical applications) ^9,12−14. Additionally, efforts are being made to find new application fields. However, most studies are limited to the lab-scale because of the limitations of NB generation methods (e.g., high concentration of NB generation, reduction of generation time, cost, and size adjustment), hindering the scale-up of NB-related industries. Following is a brief description of the most commonly used NB generation methods, which are classified according to the NB generation mechanism and apparatus used (e.g., membrane, decompression, gas–liquid mixing, and cavitation) ^15,16.

NB generation methods that are superior to conventional ones have recently been developed. For example, Kukijaki et al. ¹⁷ applied shear force onto the membrane surface by flowing a liquid instead of reducing the membrane pore size. Due to the application of shear force generated by the liquid flowing onto the membrane surface, the bubbles were detached from the membrane surface before growing into large-sized ones. Thus, relatively small-sized bubbles were generated. The authors generated NBs with diameters ranging from 360–720 nm using a Shirasu porous glass membrane and reported that the generated NBs were 8.6 times larger than the pore diameter of the porous membrane. The NB generating device developed by Alam et al. ¹⁸ applied a two-chamber swirling flow nozzle, which was designed to allow the gas–liquid mixture to rotate the inner wall of the cylinder at a faster speed, thereby generating a strong vortex near the cylinder output. They reported that the shear forces generated by the vortex broke up the gas–liquid mixture to create NBs. Wang et al. ¹⁹ developed an NB generating device that applied periodic pressure changes to closed containers filled with liquid and gas. They reported that it was possible to control the size of the generated NBs, including the generation of NBs itself, using this device. We have also developed a method for generating NBs by employing a linear actuator ²⁰. The linear actuator adopted the gas–liquid mixing method, converting rotational motion into linear motion and effectively mixing the gas and liquid in the container. The shear force induced by the continuous linear motion was transferred to the gas–liquid mixture formed in the container, and the trapped bubbles in the liquid split to generate NBs. We confirmed that NBs were effectively generated by using this linear actuator with CO₂ gas and distilled (DI) water. Fang et al. ²¹ applied a vortex oscillator similar to our study and reported that the NB concentration increased proportionally to the vibration frequency and time. Despite these efforts, the NB concentration generated by the NB generation methods reported until now has been low, and there are still many issues to be solved. Specifically, studies exploring the NB generation mechanism by the gas–liquid mixing method have not been clearly proved. In this study, the NB generation mechanism by using the gas–liquid mixing method was investigated using a lab-made NB generating device. The concentration of the generated NBs was investigated according to the different liquid volume fraction (LVF, which is expressed as the ratio of the liquid volume to the total container volume) and generation time. The characteristics of the generated NBs (e.g., mean diameter, size distribution, and surface potential) were then evaluated.

2.1. Materials

The DI water was prepared by using a water purification system (Pure Power III+, Hunan, Korea), with an electrical conductivity of 0.31 ± 0.21 µs/cm, pH of 5.74 ± 0.21, and dissolved oxygen content of 8.26 ± 0.17 ppm. Highly pure oxygen gas (99.999%; Shinyoung Gas Co., Republic of Korea) and a 50 ml conical tube and cap (DH.W28005, Daihan Co., Republic of Korea) were used for NB generation. To eliminate the effects of impurities, all the conical tubes and caps used for this experiment were rinsed with methyl alcohol, washed in DI water, and dried by air jet before conducting the NB generation test.

2.2. NB generation using a lab-made NB generator

For the NB generation test, a new lab-made NB generating device was manufactured by redesigning our existing linear actuator ²⁰. This device comprised an electrical motor, a crank cam, a connecting rod, and a conical tube holder. The crank cam converted the rotational motion of the electric motor into linear motion and transmitted this linear motion to the connecting rod. The conical tube holder was connected to the top of the connecting rod and reciprocated vertically for a distance of 500 mm (117 strokes/min). This was the NB generating device used in the gas–liquid mixing method, which could generate the trapped bubbles (gas–liquid mixture) more effectively in the liquid. For preparing the test samples, DI water and oxygen gas were injected into the conical tube with different LVF (25, 50, 75, and 100%). The test samples were sealed with a parafilm and cap of conical tube to prevent the inflow and outflow of external air during the NB generation test. The prepared test samples were fixed in the conical tube holder of the NB generating device, and an NB generation test was performed according to the generation times of 5, 10, and 20 min.

2.3. NTA

For the quantitative analysis of NBs present in the liquid, an NB analysis was performed using a nanoparticle tracking analysis (NTA) system (NanoSight LM10-HSBFT14, Malvern, UK), with a blue polarized 405 nm laser that is widely being used in the NB research field. This NB visualization technique provides size, counts, and concentration measurements. The NTA instrument was equipped with a charge-coupled device (CCD) camera to capture dispersed light and the blue laser light source with a wavelength of 405 nm to excite fluorescence. The test solutions were placed in the sample chamber, which had a volume of 0.3 ml. With laser light illumination, the NBs appeared individually, as fast-moving dispersed dots of light (white dots) under Brownian motion, which were automatically tracked and recorded by the CCD camera. By analyzing these recorded images through NTA, the quantitative concentration of the particles could be obtained. The number of NBs per 1 ml of liquid was also calculated. Furthermore, the diameter of the NBs was calculated by substituting the diffusion coefficient (${D}_{t}$) into the Stokes–Einstein equation (Eq. (1)).

$${D}_{t}=\frac{{K}_{B}T}{3\pi \eta d}$$

where ${D}_{t}$, ${K}_{B}$, $T$, $\eta$, and $d$ are the diffusion coefficient, Boltzmann constant, absolute temperature, viscosity, and diameter of the nanoparticle, respectively. The NTA measurements for the generated NBs were performed five times.

2.4. Zeta-potential

A zeta potential analyzer (ZetaPALS, Brookhaven Instruments, USA) was used to measure the surface potential of NBs, which, when dispersed in liquid, could be used as an index to confirm the contamination of the liquid and degree of dispersion of NBs. To calculate the zeta potential of NB generated DI water, electrophoretic mobility was measured using the phase analysis light scattering method—a technique that measures electrophoretic mobility by detecting the phase shift of light proportional to the particle velocity. In addition, detecting the phase shift when measuring the zeta potential of transparent NBs is advantageous because it is more sensitive than the conventional method that detects the frequency shift. The zeta potential was calculated by substituting the measured electrophoretic mobility into the Henry equation (Eq. (2)).

$${U}_{E}=\frac{2ϵ\zeta f\left(ka\right)}{3\eta }$$

where ${U}_{E}$, $\epsilon$, $\zeta$, $\eta$, and $f\left(ka\right)$ are the electrophoretic mobility, dielectric constant, zeta potential, viscosity, and the Henry function, respectively. The zeta potential measurements for the generated NBs were also performed five times.

3.1. Effect of the gas–liquid ratio in the container

To confirm the effect of the LVF on NB generation in the container, the NB generation test was performed for 5 min using an NB generation device. Figure 1 shows an image of the generated NBs in DI water using the NTA apparatus; the black background represents liquid and the shiny dots are NBs. The generated NBs increased as the amount of liquid in the container decreased. The image analysis results obtained through the NTA software and the zeta potential values for the generated NBs are shown in Fig. 2. Furthermore, as seen in Fig. 2 (a), the concentration of NBs increased dramatically in inverse proportion to the amount of liquid in the container. The NB generation device used in this experiment was of the gas–liquid mixing type. The mechanism of NB generation is as follows. When the liquid in the container strongly collided with the bottom or top of the container, which had a vertical reciprocating motion, the bubbles were trapped in the liquid (inflow by collision between the droplets and stuck in the container’s edge) to form foam. At the same time, the trapped bubbles were refined by the shear force (generated by the turbulent flow of the liquid) caused by the impact of the liquid. This process occurred repeatedly in the container that continuously reciprocated vertically, resulting in the trapped bubbles being reduced to nano-size. Therefore, we assumed that the two most important factors affecting NB generation in this device were (1) the impulse of the liquid colliding with the container surface and (2) shear force (generated by turbulent flow). Based on these assumptions, a theoretical analysis was performed on the NB generation results (Fig. 2 (a)). Under each experimental condition (i.e, LVF), the impulse and shear force values upon the liquid colliding with the bottom or top of the container were derived, and the relationship between these values and the generated NB concentration was investigated. The value of impulse was greatest when the LVF was 50% and was calculated in the order of 75%, 25%, and 100% (LVF: 25%—4.05×10^− 3 kgžm/s; 50%—5.80 × 10^− 3 kgžm/s; 75%—5.40 × 10^− 3 kgžm/s; and 100%—0 kgžm/s). The Reynolds number of the liquid in the container was the largest at 25%, and it was confirmed that the conditions were sufficient to generate turbulence in the liquid in all cases except 100%. Therefore, when the LVF was 25%, strong turbulence occurred in the liquid in the container (magnitude of shear force—25% > 50% > 75% > 100%), and a high shear force was applied to the trapped bubbles. Although the above theoretical approaches were insufficient for analyzing quantitative values, it was assumed that comparing the rough magnitude (impulse, shear force) between the experimental conditions was not a problem. Based on this result, the magnitude of shear force applied to the liquid was proportional to the concentration of the generated NBs. In other words, the shear force applied to the trapped bubbles in the liquid played an important role in NB generation using the gas–liquid mixing method. However, since the NBs were generated not only at 25% but also at 50% and 75%, it was assumed that sufficient shear force was transmitted to generate NBs in all cases except 100%, meaning the amount of trapped bubbles (which are a prerequisite for NB generation) must be large to increase the concentration of NB generation. Regardless of the strength of shear force transmitted to the liquid in the container, if there were no bubbles trapped in the liquid, NBs could not be generated. When the container attached to the NB generation device descended at high speed, from the top position to the bottom position, the liquid in the container elongated (e.g., the head part of the sea wave) and collided with the bottom surface of the container. At this point, the gas was trapped inside the liquid to generate foam, and the amount of foam produced was proportional to the specific surface area of the liquid exposed to the gas when the liquid was elongated (Fig. 3). This phenomenon is similar to the generation of foam when sea waves break ²². Specifically, when the thickness of the head part of the wave was thin, a lot of foam was formed. Therefore, in this experiment, the amount of trapped foam increased at 25% with the smallest amount of liquid because the specific surface area of the liquid exposed to the gas was the largest (Fig. 3). Due to these reasons, it was assumed that the results of NB generation (Fig. 2 (a)) were caused by the amount of trapped bubbles and the shear force applied to the trapped bubbles. On the other hand, the mean diameter of the generated NBs was 200 nm or less, and there was no difference according to the LVF (Fig. 2 (b)). The zeta potential also exhibited a value between − 15–-20 mV in all cases except for the 100% gas–liquid ratio wherein NBs were not generated. Therefore, it can be assumed that the NBs generated through this NB generation technique were uniformly dispersed in liquid and existed in a relatively stable state.

3.2. Effect of generation time

To confirm the effect of generation time, an NB generation test, based on the generation times of 5, 10, and 20 min, was performed. Figure 4 shows the NTA images captured in all cases. Figure 5 shows the analysis results of the captured images with the NTA software and the zeta potential value of the generated NBs. In addition, the quantitative values for Fig. 5 are outlined in Table 1. As confirmed in Section 3.1, NBs were abundant when the LVF was 25% for each generation time condition (5, 10, and 20 min), and the concentration of the generated NBs decreased as the liquid content in the container increased. In addition, the concentration of the generated NBs increased in proportion to the generation time in all cases except for 100%. Since this NB generation device performed a vertical reciprocating motion (117 strokes/min), it could be assumed that the number of bubbles trapped in the liquid and the number of shear forces applied to the initially trapped bubbles were 234 times per min. In other words, for each NB generation time, the shear force was applied 1,170 times for 5 min, 2,240 times for 10 min, and 4,680 times for 20 min. Therefore, the NB concentration significantly increased because more bubbles were trapped in the liquid and more shear forces were applied to the trapped bubbles as the generation time increased. The generation time also affected the size of the generated NBs. As can be seen in Fig. 5 (b), in all cases except for 100%, the mean diameter of the generated NBs decreased as the generation time increased. This phenomenon can be confirmed more clearly in the size distribution graph of the NBs (Fig. 6). As shown in Fig. 6, the peak (mode diameter) of the graph shifted to the left as the generation time increased. Considering that the difference in mode diameter of the generated NBs based on the LVF was negligible, the size of the generated NBs was thought to be more affected by the generation time (i.e., the number of shear forces applied to the trapped bubbles) than the LVF (i.e., the magnitude of shear force applied to the trapped bubbles). In addition, since the difference in zeta potential values of the generated NBs was negligible in all cases except 100%, it could be confirmed that the NBs generated by this method existed in a relatively stable state regardless of the generation time and the LVF.

Table 1

The results of characteristics evaluation after NB generation according to the LVF and generation time.
Generation time (min)	LVF (%)	Concentration (10⁸ NBs/ml)	Mean diameter (nm)	Zeta-potential (mV)
5	25	3.21 ± 0.13	187.33 ± 18.01	-18.80 ± 1.58
	50	1.48 ± 0.11	185.02 ± 14.73	-18.58 ± 1.80
	75	0.75 ± 0.08	190.66 ± 23.54	-16.80 ± 4.56
	100	0.10 ± 0.04	202.66 ± 13.05	-0.43 ± 0.44
10	25	6.56 ± 0.33	159.12 ± 12.16	-20.75 ± 2.22
	50	2.78 ± 0.18	160.33 ± 4.93	-18.72 ± 0.63
	75	1.23 ± 0.12	158.09 ± 11.35	-18.39 ± 1.45
	100	0.13 ± 0.06	207.33 ± 22.14	-1.19 ± 1.65
20	25	10.65 ± 1.07	149.03 ± 5.56	-20.80 ± 1.72
	50	5.01 ± 0.45	138.07 ± 9.53	-19.02 ± 2.15
	75	3.15 ± 0.32	144.66 ± 18.55	-19.98 ± 1.78
	100	0.12 ± 0.08	206.33 ± 25.69	-1.01 ± 0.61

3.3. NB stability

This study was designed to confirm the effect of the LVF and the generation time on NB generation and yielded meaningful results. In this section, we will investigate the long-term stability of the NBs generated by this device and the possibility of external contamination during the experiment.

First, the stability of the generated NBs was evaluated over time, for which the sample that generated the most NBs (LVF: 25%, generation time: 20 min) was used. NTA analysis and zeta potential measurements were then performed for seven days. In the NB research field, zeta potential is commonly used when discussing the stability of NBs because NBs with the same polarity repel each other and inhibit coalescence between neighboring bubbles ^8,23,24. As shown in Fig. 7 (a), the NB concentration decreased significantly for one day but showed a small decrease after seven days. Although the NB concentration decreased over time, there were still a large number of NBs (approximately 57.72% of the initial concentration) after seven days. On the other hand, the zeta potential of NBs was approximately − 20 mV, and no significant change during the seven days of stability evaluation was observed (Fig. 7 (c)). Therefore, the impact of reducing NB concentration due to coalescence between adjacent bubbles was regarded as insignificant because there was no change in the zeta potential values of NBs over time. This phenomenon was also observed in the mean diameter measurement results of the NBs (Fig. 7 (b)). Although the mean diameter of the NBs increased over time, the increase was not significant, approximately 20–30 nm only. If the coalescence between the adjacent bubbles had predominantly occurred, the mean diameter of the NBs measured after seven days should have been at least twice the initial diameter. Therefore, it was assumed that the decrease in NB concentration was due to the disappearance of some NBs, which were maintained in a relatively unstable state and diffused into the liquid, rather than the effect of coalescence.

Next, the inflow of contaminants (solid particles), which may have occurred during the experiment, was confirmed. Studies that have explored the possibility of contaminant inflow share a lot of similarities with those proving the existence of NBs. In fact, many researchers who insist that NBs cannot exist in a stable state in liquid regard NBs, recorded by an NTA apparatus, as solid particles flowing in from the outside. The existence of spherical NBs has recently been proved using scanning electron microscopy ¹, transmission electron microscopy ², and the mass spectrometry method ⁴, using a resonance cantilever and microfluidic channel, which can distinguish NBs from solid particles. In addition to these direct approaches, indirect approaches proving the existence of NBs by removing the NBs in the liquid have also been reported ^21,25,26. These studies exposed the NB solution to harsh environments (decompression, freezing, and thawing), causing the NBs to become unstable and diffuse into the liquid. Subsequently, NTA analysis was performed on an NB solution exposed to harsh environments, proving that the generated NBs were not solid particles. The freezing and thawing method was also used in this study to confirm the possibility of contaminant inflow. The test samples used for this experiment were selected from those applied for long-term stability evaluation (DI water, NB solution after generation, and NB solution after seven days). Each test sample was frozen in the freezer compartment of a home refrigerator for six hours and then left in the atmosphere until the temperature of the test sample became the same as room temperature. NTA analysis was performed on the test sample. The results are shown in Fig. 7 (d), where we can confirm that most of the initially present NBs disappeared in all the test samples after freezing and thawing. Therefore, it can be said that there was no possibility of inflow of contaminants from the outside during NB generation and the character evaluation that was performed in this study.

In this study, a method for generation NBs was proposed and the NB characteristics were investigated. For generating NBs, a lab-made NB generation device was used wherein the gas–liquid mixing method was applied among various NB generation methods. Through the NB generation test, a more specific NB generation process, based on the LVF and the generation time, was confirmed. The number of generated NBs increased as the amount of liquid in the container decreased in the concentration of generated NBs according to the LVF. For the cause analysis of these results, the main factors causing NB generation were assumed as the impulse and shear force based on the commonly known gas–liquid method. Theoretical calculations were subsequently performed. As a result, we confirmed that the shear force transmitted to the trapped bubble rather than the impulse of the liquid had a dominant effect on NB generation. In addition, it was confirmed that the amount of trapped bubbles, which is the prerequisite for NB generation, was also an important factor. In terms of the generated NB concentration based on the generation time, as the generation time increased, the concentration of generated NBs increased significantly due to the increase in the amount of trapped bubbles in the liquid and the number of shear forces applied to the trapped bubbles. It was also confirmed that the size of the NBs decreased due to the number of shear forces (i.e., generation time) applied to the trapped bubbles rather than the magnitude of shear force (i.e., LVF). In the aging test, 57.72% of the initial concentration of NBs generated by this device remained stable for seven days. This study devised a specific NB generation mechanism in the commonly known gas–liquid mixing method by using experimental and theoretical approaches and proposed a method for high-concentration NB generation under limited conditions. To generate high concentrations of NBs, the NB generation device or experimental setup must be designed such that (1) the amount of trapped bubbles in liquid should be large; (2) sufficient shear force should be transmitted to the trapped bubbles to refine the bubbles; and (3) the number of times shear force is transmitted to the trapped bubbles should be high.

Acknowledgements

This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT).(No. 2022R1A2C1010405)

Data availability

The datasets generated and analysed during the current study are available from the corresponding author upon a reasonable request.

Ohgaki, K., Khanh, N. Q., Joden, Y., Tsuji, A. & Nakagawa, T. Physicochemical approach to nanobubble solutions. Chem. Eng. Sci. 65, 1296–1300 (2010).
Uchida, T. et al. Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater. Nanoscale Res. Lett. 6, (2011).
Sugano, K., Miyoshi, Y. & Inazato, S. Study of Ultrafine Bubble Stabilization by Organic Material Adhesion. JAPANESE J. Multiph. FLOW 31, 299–306 (2017).
Kobayashi, H., Maeda, S., Kashiwa, M. & Fujita, T. Measurement and identification of ultrafine bubbles by resonant mass measurement method. Int. Conf. Opt. Part. Charact. (OPC 2014) 9232, 92320S (2014).
Takahashi, M. ζ Potential of Microbubbles in Aqueous Solutions: Electrical Properties of the Gas – Water Interface. J. Phys. Chem. B 109, 21858–21864 (2005).
Ushikubo, F. Y. et al. Zeta-potential of Micro- and/or Nano-bubbles in Water Produced by Some Kinds of Gases. IFAC Proc. Vol. 43, 283–288 (2010).
Liu, S. et al. Oxidative Capacity of Nanobubbles and Its Effect on Seed Germination. ACS Sustain. Chem. Eng. 4, 1347–1353 (2016).
Meegoda, J. N., Aluthgun Hewage, S. & Batagoda, J. H. Stability of nanobubbles. Environ. Eng. Sci. 35, 1216–1227 (2018).
Oh, S. H., Han, J. G. & Kim, J. M. Long-term stability of hydrogen nanobubble fuel. Fuel 158, 399–404 (2015).
Yasui, K., Tuziuti, T., Izu, N. & Kanematsu, W. Is surface tension reduced by nanobubbles (ultrafine bubbles) generated by cavitation? Ultrason. Sonochem. 52, 13–18 (2019).
Ushida, A. et al. Effect of Mixed Nanobubble and Microbubble Liquids on the Washing Rate of Cloth in an Alternating Flow. J. Surfactants Deterg. 15, 695–702 (2012).
Aluthgun Hewage, S., Batagoda, J. H. & Meegoda, J. N. Remediation of contaminated sediments containing both organic and inorganic chemicals using ultrasound and ozone nanobubbles. Environ. Pollut. 274, 116538 (2021).
Guo, Z. et al. Effects of nanobubble water on the growth of Lactobacillus acidophilus 1028 and its lactic acid production. RSC Adv. 9, 30760–30767 (2019).
Exner, A. A. & Kolios, M. C. Bursting microbubbles: How nanobubble contrast agents can enable the future of medical ultrasound molecular imaging and image-guided therapy. Curr. Opin. Colloid Interface Sci. 54, 101463 (2021).
Patel, A. K. et al. Advances in micro- and nano bubbles technology for application in biochemical processes. Environ. Technol. Innov. 23, 101729 (2021).
Lee, J. Il, Yim, B. S. & Kim, J. M. Effect of dissolved-gas concentration on bulk nanobubbles generation using ultrasonication. Sci. Rep. 10, (2020).
Kukizaki, M. & Goto, M. Size control of nanobubbles generated from Shirasu-porous-glass (SPG) membranes. J. Memb. Sci. 281, 386–396 (2006).
Alam, H. S., Sutikno, P., Soelaiman, T. A. F. & Sugiarto, A. T. Bulk Nanobubbles: generation using a two-chamber swirling flow nozzle and long-term stability in water. J. Flow Chem. (2021).
Wang, Q. et al. Generation and Stability of Size-Adjustable Bulk Nanobubbles Based on Periodic Pressure Change. Sci. Rep. 9, (2019).
Oh, S. H. & Kim, J. M. Generation and Stability of Bulk Nanobubbles. Langmuir 33, 3818–3823 (2017).
Fang, Z., Wang, X., Zhou, L., Zhang, L. & Hu, J. Formation and Stability of Bulk Nanobubbles by Vibration. Langmuir 36, 5 (2020).
Thorpe, S. A., Stubbs, A. R., Hall, A. J. & Turner, R. J. Wave-produced bubbles observed by side-scan sonar. Natur 296, 636–638 (1982).
Ulatowski, K., Sobieszuk, P., Mróz, A. & Ciach, T. Stability of nanobubbles generated in water using porous membrane system. Chem. Eng. Process. - Process Intensif. 136, 62–71 (2019).
Zhou, Y. et al. Long-Term Stability of Different Kinds of Gas Nanobubbles in Deionized and Salt Water. mdpi.com (2021).
Nirmalkar, N., Pacek, A. W. & Barigou, M. On the Existence and Stability of Bulk Nanobubbles. Langmuir 34, 10964–10973 (2018).
Agarwal, K., Trivedi, M. & Nirmalkar, N. Does salting-out effect nucleate nanobubbles in water: Spontaneous nucleation? Ultrason. Sonochem. 82, 105860 (2022).

No competing interests reported.

Download PDF

Version 1

posted

You are reading this latest preprint version

Formation and stability of bulk nanobubbles generated by gas–liquid mixing

Status:

Version 1

Abstract

Figures

1. Introduction

2. Experimental Details

2.1. Materials

2.2. NB generation using a lab-made NB generator

2.3. NTA

2.4. Zeta-potential

3. Results And Discussion

3.1. Effect of the gas–liquid ratio in the container

3.2. Effect of generation time

3.3. NB stability

4. Conclusions

Declarations

References

Additional Declarations

Status:

Version 1