Interpreting the interfacial and colloidal stability of bulk nanobubbles

Nirmalkar, Neelkanth; Pacek, Andrzej W.; Barigou, Mostafa

doi:10.1039/c8sm01949e

Cited by 163 publications

(221 citation statements)

References 49 publications

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“…These results seem to suggest, therefore, that a pure organic solvent acts as a gas sink removing any excess gas from the solution and, consequently, it does not form nanobubbles. Hence, since BNBs exist in pure water, as reported by a number of scientific reports including our own, 5,6,17,[48][49][50] then they should disappear at some organic solvent-water ratio, which is confirmed by the present results.…”

Section: Fundamental Questions Relating To the Existence And Behaviousupporting

confidence: 89%

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Proving and interpreting the spontaneous formation of bulk nanobubbles in aqueous organic solvent solutions: effects of solvent type and content

Jadhav

Barigou

2020

Soft Matter

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We show that the mixing of organic solvents with pure water leads to the spontaneous formation of suspended nano-entities which exhibit long-term stability on the scale of months. A wide range of solvents representing different functional groups are studied: methanol, ethanol, propanol, acetone, DMSO and formamide. We use various physical and chemical analytical techniques to provide compounded evidence that the nano-entities observed in all these aqueous solvent solutions must be gas-filled nanobubbles as they cannot be attributed to solvent nanodroplets, impurities or contamination. The nanobubble suspensions are characterized in terms of their bubble size distribution, bubble number density and zeta potential. The bubble number density achieved is a function of the type of solvent. It increases sharply with solvent content, reaching a maximum at an intermediate solvent concentration, before falling off to zero. We show that, whilst bulk nanobubbles can exist in pure water, they cannot exist in pure organic solvents and they disappear at some organic solvent-water ratio depending on the type of solvent. The gas solubility of the solvent relative to water as well as the molecular structure of the solvent are determining factors in the formation and stability of bulk nanobubbles. These phenomena are discussed and interpreted in the light of the experimental results obtained.

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Section: Fundamental Questions Relating To the Existence And Behaviousupporting

confidence: 89%

“…16 The present situation is exacerbated by the lack of a full rational explanation of the mechanism behind the long-term stability of BNBs. 6,[17][18][19] A number of speculative interpretations have been postulated but a complete physical model has yet to emerge.…”

Section: Introductionmentioning

confidence: 99%

Proving and interpreting the spontaneous formation of bulk nanobubbles in aqueous organic solvent solutions: effects of solvent type and content

Jadhav

Barigou

2020

Soft Matter

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“…The excessive negative surface charges destabilize the nanobubbles. 34 The collapse of nanobubbles has also been observed in previous studies. [15][16] However, as the electron beam dose rate significantly increases (see more details in Figure 3 as below), the growth of bubbles overcomes the shrinking of the bubbles, which is likely because of the enhanced pseudo-photocatalytic water splitting behavior.…”

Section: Resultssupporting

confidence: 71%

Visualization of facet-dependent pseudo-photocatalytic behavior of TiO2 nanorods for water splitting using In situ liquid cell TEM

et al. 2019

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We report an investigation of the pseudo-photocatalytic behavior of rutile TiO 2 nanorods for water splitting observed with liquid cell transmission electron microscopy (TEM). The electron beam serves as a "light" source to initiate the catalytic reaction and a "water-in-salt" aqueous solution is employed as the electrolyte. The observation reveals that bubbles are generated preferentially residing near the {110} facet of a rutile TiO 2 nanorod under a low electron dose rate (9.3-18.6 e -/Å 2 · s). These bubbles are ascribed to hydrogen gas generated from the pseudo-photocatalytic water splitting. As the electron beam current density increases to 93 e -/Å 2 · s, bubbles are also found at the {001} and {111} facets as well as in the bulk liquid solution, demonstrating the dominant effects of water electrolysis by electron beam under higher dose rates.The facet-dependent pseudo-photocatalytic behavior of rutile TiO 2 nanorods is further validated using density functional theory (DFT) calculation. Our work establishes a facile liquid cell TEM setup for the study of pseudo-photocatalytic water splitting and it may also be applied to investigation of other photo-activated phenomena occurring at the solid-liquid interfaces.

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“…A schematic representation of the formation of the hollow zinc phosphate nanoparticles is presented in Figure 6C. Because bulk nanobubbles are negatively charged, Zn +2 ions from zinc nitrate adsorb on the nanobubble surfaces and provide nucleation sites for the subsequent reaction between Zn +2 and PO 4 3− ions from ammonium phosphate at pH 8.5. Thus, zinc phosphate precipitates on the nanobubble surfaces forming hollow particles.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…32,39 Similarly, when generating bulk nanobubbles in pure water, another question that often arises is whether such nano-entities are oil droplets or solid nanoparticles which have detached from adjacent solid surfaces. 2,4,35 In this paper, we use different mechanical and chemical techniques [continuous high-shear rotor-stator (HSRS) device, acoustic cavitation, and water−ethanol mixing] to generate bulk nanobubbles. These techniques, between them, encompass the main possible sources of contamination behind the controversy in the literature.…”

Section: ■ Introductionmentioning

confidence: 99%

Bulk Nanobubbles or Not Nanobubbles: That is the Question

2020

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Bulk nanobubbles are a novel nanoscale bubble system with unusual properties which challenge our understanding of bubble behavior. Because of their extraordinary longevity, their existence is still not widely accepted as they are often attributed to the presence of supramolecular structures or contaminants. Nonetheless, bulk nanobubbles are attracting increasing attention in the literature, but reports generally lack objective evidence that the observed nano-entities are indeed nanobubbles. In this paper, we use various physical and chemical analytical techniques to provide multiple evidence that the nano-entities produced mechanically in pure water by a continuous high-shear rotor-stator device or acoustic cavitation and spontaneously by water−ethanol mixing are indeed gas-filled domains. We estimate that the results presented here combined provide conclusive proof that bulk nanobubbles do exist and they are stable. This paper should help close the debate about the existence of bulk nanobubbles and, hence, enable the scientific community to rather focus on developing the missing fundamental science in this area.

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Interpreting the interfacial and colloidal stability of bulk nanobubbles

Abstract: This paper elucidates parts of the mystery behind the interfacial and colloidal stability of the novel bubble system of bulk nanobubbles.

Cited by 163 publications

References 49 publications

Proving and interpreting the spontaneous formation of bulk nanobubbles in aqueous organic solvent solutions: effects of solvent type and content

Proving and interpreting the spontaneous formation of bulk nanobubbles in aqueous organic solvent solutions: effects of solvent type and content

Visualization of facet-dependent pseudo-photocatalytic behavior of TiO2 nanorods for water splitting using In situ liquid cell TEM

Bulk Nanobubbles or Not Nanobubbles: That is the Question

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