In a recent article, Jadhav and Barigou ( 2020, 36 (7), 1699-1708) investigated the question of the existence of stable bulk nanobubbles in water generated by hydrodynamic cavitation, ultrasound cavitation, and the addition of an organic compound (namely, ethanol) to water. They firmly conclude that these procedures result in stable bulk nanobubbles. However, a number of previous works documented that the nanoentities observed in water upon such procedures are not nanobubbles. Here, we analyze work of Jadhav and Barigou and show that conclusions regarding the nanobubble nature of the nanoentities are incorrect and are due to the choice of experimental techniques with weak sensitivity, methodical issues in the use of otherwise proper experimental techniques, and ambiguous outcomes of the rest of experiments.
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On the clustering of bulk nanobubbles and their colloidal stability.
J Colloid Interface Sci
November 2021
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom. Electronic address:
Bulk nanobubbles which are usually observed in pure water have a mean diameter typically around 100 nm. We use a combination of physical and chemical techniques to prove the hypothesis that the nanoentities observed in pure water are stable clusters of much smaller stable nanobubbles. The stability of bulk nanobubble clusters is affected by factors such as ionic strength or internal energy of the system.
View Article and Find Full Text PDFResponse to "Comment on Bulk Nanobubbles or Not Nanobubbles: That is the Question".
Langmuir
January 2021
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
Advanced techniques that combine high spatial resolution with chemical sensitivity to directly probe the observed nanoentities and provide direct evidence that they are truly gas-filled nanobubbles do not exist. Therefore, in our paper, we focused on providing, for the first time, multiple types of indirect evidence using a variety of physical and chemical techniques that the nanoentities are not due to contamination and, hence, they must be bulk nanobubbles (BNBs). It should be noted that such techniques require good experimental skills, sound protocols, good scientific expertise, and reliable equipment.
View Article and Find Full Text PDFComment on "Bulk Nanobubbles or Not Nanobubbles: That is the Question".
Langmuir
December 2020
Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovakia.
In a recent article, Jadhav and Barigou ( 2020, 36 (7), 1699-1708) investigated the question of the existence of stable bulk nanobubbles in water generated by hydrodynamic cavitation, ultrasound cavitation, and the addition of an organic compound (namely, ethanol) to water. They firmly conclude that these procedures result in stable bulk nanobubbles. However, a number of previous works documented that the nanoentities observed in water upon such procedures are not nanobubbles.
View Article and Find Full Text PDFCorrection: Proving and interpreting the spontaneous formation of bulk nanobubbles in aqueous organic solvent solutions: effects of solvent type and content.
Soft Matter
August 2020
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
Correction for 'Proving and interpreting the spontaneous formation of bulk nanobubbles in aqueous organic solvent solutions: effects of solvent type and content' by Ananda J. Jadhav et al., Soft Matter, 2020, 16, 4502-4511, DOI: 10.
View Article and Find Full Text PDFA Henry's law method for generating bulk nanobubbles.
Nanoscale
August 2020
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
A new technique for generating bulk nanobubble suspensions has been developed based on Henry's law which states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid. This principle which forms the basis of vacuum degasification has been exploited here to produce stable bulk nanobubbles in excess of 10 bubble mL in pure water, through successive expansion/compression strokes inside a sealed syringe. We provide evidence that the observed nano-entities must be gas-filled nanobubbles by showing that: (i) they cannot be attributed to organic or inorganic impurities; (ii) they disappear gradually over time whilst their mean size remains unchanged; (iii) their number density depends on the concentration of dissolved gas in water and its solubility; and (iv) added sparging of gas enhances process yield.
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