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Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater.

Uchida T, Oshita S, Ohmori M, Tsuno T, Soejima K, Shinozaki S, Take Y, Mitsuda K - Nanoscale Res Lett (2011)

Bottom Line: Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly.MNBs in pure water and in 1% NaCl solutions were spherical or oval.When we applied this technique to the observation of O2 MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface.PACS: 68.03.-g, 81.07.-b, 92.40.qc.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan. t-uchida@eng.hokudai.ac.jp.

ABSTRACT
Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly. We thus used a transmission electron microscope (TEM) with the freeze-fractured replica method to observe oxygen (O2) MNBs in solutions. MNBs in pure water and in 1% NaCl solutions were spherical or oval. Their size distribution estimated from TEM images close to that of the original solution is measured by light-scattered methods. When we applied this technique to the observation of O2 MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface.PACS: 68.03.-g, 81.07.-b, 92.40.qc.

No MeSH data available.


Related in: MedlinePlus

TEM images of freeze-fractured replica of 1% NaCl solution containing O2 MNBs. Scale bar indicates 200 nm. (a) Precipitated fine impurity particles (10 to 60 nm in diameter) and MNBs (200 and 300 nm in diameter) coexisted at the grain boundary of ice crystallites. Some fine particles were located around small MNBs but did not cover the entire bubble surface. (b) Replica sample of 1% NaCl solution without MNBs shown as a control.
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Figure 3: TEM images of freeze-fractured replica of 1% NaCl solution containing O2 MNBs. Scale bar indicates 200 nm. (a) Precipitated fine impurity particles (10 to 60 nm in diameter) and MNBs (200 and 300 nm in diameter) coexisted at the grain boundary of ice crystallites. Some fine particles were located around small MNBs but did not cover the entire bubble surface. (b) Replica sample of 1% NaCl solution without MNBs shown as a control.

Mentions: In order to examine the interaction between MNBs and additives in the solution, we observed a dilute NaCl solution containing O2 MNBs. The obvious difference in TEM images of these samples from those in pure MNB water was that fine particles (less than 100 nm in diameter) were observed on the grain boundary of ice crystallites (Figure 3a). These fine particles were also observed in the control (no MNB sample, Figure 3b). MNBs were also simultaneously trapped on the grain boundary in this figure. Based on the analogous features of disaccharide solutions [20,21], the ice crystallites were formed during the sample quenching process, and the fine particles were the agglomeration of condensed salts dissolved in the original solution due to the freeze-condensation mechanism. The remaining area in the grain boundary is considered to be the glass state of the solution. The shape and size of MNBs in 1% NaCl solution seemed to be similar to those in pure water. Its number concentration was slightly lower than that in pure water system, which may have resulted from the sample being prepared more than 1 week after aeration. This result is qualitatively consistent with the DLS measurements in pure water [19]. The addition of a small amount of NaCl is expected to play a positive role of stabilizing MNBs in engineering applications. However, we could not find obvious characteristics in our TEM images as reported for the sample with surfactants [17]. Since there are conflicting claims for the effect of ionic solutions on MNB stabilities [22], further systematic investigations are required for understanding the effect of additives on the lifetime of MNBs.


Transmission electron microscopic observations of nanobubbles and their capture of impurities in wastewater.

Uchida T, Oshita S, Ohmori M, Tsuno T, Soejima K, Shinozaki S, Take Y, Mitsuda K - Nanoscale Res Lett (2011)

TEM images of freeze-fractured replica of 1% NaCl solution containing O2 MNBs. Scale bar indicates 200 nm. (a) Precipitated fine impurity particles (10 to 60 nm in diameter) and MNBs (200 and 300 nm in diameter) coexisted at the grain boundary of ice crystallites. Some fine particles were located around small MNBs but did not cover the entire bubble surface. (b) Replica sample of 1% NaCl solution without MNBs shown as a control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211361&req=5

Figure 3: TEM images of freeze-fractured replica of 1% NaCl solution containing O2 MNBs. Scale bar indicates 200 nm. (a) Precipitated fine impurity particles (10 to 60 nm in diameter) and MNBs (200 and 300 nm in diameter) coexisted at the grain boundary of ice crystallites. Some fine particles were located around small MNBs but did not cover the entire bubble surface. (b) Replica sample of 1% NaCl solution without MNBs shown as a control.
Mentions: In order to examine the interaction between MNBs and additives in the solution, we observed a dilute NaCl solution containing O2 MNBs. The obvious difference in TEM images of these samples from those in pure MNB water was that fine particles (less than 100 nm in diameter) were observed on the grain boundary of ice crystallites (Figure 3a). These fine particles were also observed in the control (no MNB sample, Figure 3b). MNBs were also simultaneously trapped on the grain boundary in this figure. Based on the analogous features of disaccharide solutions [20,21], the ice crystallites were formed during the sample quenching process, and the fine particles were the agglomeration of condensed salts dissolved in the original solution due to the freeze-condensation mechanism. The remaining area in the grain boundary is considered to be the glass state of the solution. The shape and size of MNBs in 1% NaCl solution seemed to be similar to those in pure water. Its number concentration was slightly lower than that in pure water system, which may have resulted from the sample being prepared more than 1 week after aeration. This result is qualitatively consistent with the DLS measurements in pure water [19]. The addition of a small amount of NaCl is expected to play a positive role of stabilizing MNBs in engineering applications. However, we could not find obvious characteristics in our TEM images as reported for the sample with surfactants [17]. Since there are conflicting claims for the effect of ionic solutions on MNB stabilities [22], further systematic investigations are required for understanding the effect of additives on the lifetime of MNBs.

Bottom Line: Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly.MNBs in pure water and in 1% NaCl solutions were spherical or oval.When we applied this technique to the observation of O2 MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface.PACS: 68.03.-g, 81.07.-b, 92.40.qc.

View Article: PubMed Central - HTML - PubMed

Affiliation: Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan. t-uchida@eng.hokudai.ac.jp.

ABSTRACT
Unique properties of micro- and nanobubbles (MNBs), such as a high adsorption of impurities on their surface, are difficult to verify because MNBs are too small to observe directly. We thus used a transmission electron microscope (TEM) with the freeze-fractured replica method to observe oxygen (O2) MNBs in solutions. MNBs in pure water and in 1% NaCl solutions were spherical or oval. Their size distribution estimated from TEM images close to that of the original solution is measured by light-scattered methods. When we applied this technique to the observation of O2 MNBs formed in the wastewater of a sewage plant, we found the characteristic features of spherical MNBs that adsorbed surrounding impurity particles on their surface.PACS: 68.03.-g, 81.07.-b, 92.40.qc.

No MeSH data available.


Related in: MedlinePlus