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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.


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Illustrations of adsorption properties of MNBs in wastewater and of their quenching features. (a) The original wastewater (WW) includes both impurities (small dots) and several amounts of MNBs (B). Since a MNB sweeps impurities around it on the surface, the swept area is less polluted (white area around B) and the surface of the MNB is covered by impurities (small dots). When this solution is quenched and the replica samples are prepared on area (b), no MNBs with homogeneously dispersed impurities were observed. We can observe the TEM image of (b') fine particles homogeneously dispersing with a small ice crystallite (I) formed in the quenching process (related to Figure 4). In contrast, when the replica sample was prepared on area (c) including the MNB surrounded by purified water (PW), the observed TEM image was (c') the MNB adsorbing fine particles on its surface in smooth ice crystallites (related to Figure 5).
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Figure 6: Illustrations of adsorption properties of MNBs in wastewater and of their quenching features. (a) The original wastewater (WW) includes both impurities (small dots) and several amounts of MNBs (B). Since a MNB sweeps impurities around it on the surface, the swept area is less polluted (white area around B) and the surface of the MNB is covered by impurities (small dots). When this solution is quenched and the replica samples are prepared on area (b), no MNBs with homogeneously dispersed impurities were observed. We can observe the TEM image of (b') fine particles homogeneously dispersing with a small ice crystallite (I) formed in the quenching process (related to Figure 4). In contrast, when the replica sample was prepared on area (c) including the MNB surrounded by purified water (PW), the observed TEM image was (c') the MNB adsorbing fine particles on its surface in smooth ice crystallites (related to Figure 5).

Mentions: Compared to the fine particles observed in 1% NaCl solutions (Figure 3), the fine particles in the wastewater adsorbed on a MNB homogeneously. This may indicate that the fine particles on MNBs in the wastewater were not the precipitation of soluble impurities but the insoluble small particles originally existing in the solution. The homogeneous distribution of fine particles near the MNB surface (within 50 nm from the interface, see the extended figure of Figure 5a) seemed to suggest that fine particles in the wastewater tended to be attracted to the MNB. Based on these TEM images of replica samples from the wastewater (Figures 4 and 5), the impurity adsorption of MNBs in the wastewater can be described as follows (Figure 6). If the wastewater including both fine particles and soluble impurities at a relatively high concentration were solely quenched at liquid nitrogen temperature, fine particles could be fixed homogeneously in the glass state of the solution, and some ice crystallites would be formed by the freeze-condensed mechanism (Figure 6b, b'). Since the impurity concentration was high, the ice crystallite nucleation was limited, and its growth was slow enough to form the crystalline facets. This result is related to the fact that the area of the glass state with fine particles exceeded that of the ice crystallites. However, if the solution included MNBs, the insoluble particles would be collected on the MNBs by the attractive force between them in solutions (Figure 6c). The mobility of MNBs was not so high and the attractive force would only be present at limited distances, so the sweep area of a MNB in the solution was limited to only around the bubble (Figure 6a). Figure 5 depicts the quenched features of this condition (Figure 6c'). Therefore, it is conceivable that the application of MNBs to the engineering aspects is effective, but its total effectiveness would directly depend on the number concentration of MNBs and on their residence time.


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)

Illustrations of adsorption properties of MNBs in wastewater and of their quenching features. (a) The original wastewater (WW) includes both impurities (small dots) and several amounts of MNBs (B). Since a MNB sweeps impurities around it on the surface, the swept area is less polluted (white area around B) and the surface of the MNB is covered by impurities (small dots). When this solution is quenched and the replica samples are prepared on area (b), no MNBs with homogeneously dispersed impurities were observed. We can observe the TEM image of (b') fine particles homogeneously dispersing with a small ice crystallite (I) formed in the quenching process (related to Figure 4). In contrast, when the replica sample was prepared on area (c) including the MNB surrounded by purified water (PW), the observed TEM image was (c') the MNB adsorbing fine particles on its surface in smooth ice crystallites (related to Figure 5).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Illustrations of adsorption properties of MNBs in wastewater and of their quenching features. (a) The original wastewater (WW) includes both impurities (small dots) and several amounts of MNBs (B). Since a MNB sweeps impurities around it on the surface, the swept area is less polluted (white area around B) and the surface of the MNB is covered by impurities (small dots). When this solution is quenched and the replica samples are prepared on area (b), no MNBs with homogeneously dispersed impurities were observed. We can observe the TEM image of (b') fine particles homogeneously dispersing with a small ice crystallite (I) formed in the quenching process (related to Figure 4). In contrast, when the replica sample was prepared on area (c) including the MNB surrounded by purified water (PW), the observed TEM image was (c') the MNB adsorbing fine particles on its surface in smooth ice crystallites (related to Figure 5).
Mentions: Compared to the fine particles observed in 1% NaCl solutions (Figure 3), the fine particles in the wastewater adsorbed on a MNB homogeneously. This may indicate that the fine particles on MNBs in the wastewater were not the precipitation of soluble impurities but the insoluble small particles originally existing in the solution. The homogeneous distribution of fine particles near the MNB surface (within 50 nm from the interface, see the extended figure of Figure 5a) seemed to suggest that fine particles in the wastewater tended to be attracted to the MNB. Based on these TEM images of replica samples from the wastewater (Figures 4 and 5), the impurity adsorption of MNBs in the wastewater can be described as follows (Figure 6). If the wastewater including both fine particles and soluble impurities at a relatively high concentration were solely quenched at liquid nitrogen temperature, fine particles could be fixed homogeneously in the glass state of the solution, and some ice crystallites would be formed by the freeze-condensed mechanism (Figure 6b, b'). Since the impurity concentration was high, the ice crystallite nucleation was limited, and its growth was slow enough to form the crystalline facets. This result is related to the fact that the area of the glass state with fine particles exceeded that of the ice crystallites. However, if the solution included MNBs, the insoluble particles would be collected on the MNBs by the attractive force between them in solutions (Figure 6c). The mobility of MNBs was not so high and the attractive force would only be present at limited distances, so the sweep area of a MNB in the solution was limited to only around the bubble (Figure 6a). Figure 5 depicts the quenched features of this condition (Figure 6c'). Therefore, it is conceivable that the application of MNBs to the engineering aspects is effective, but its total effectiveness would directly depend on the number concentration of MNBs and on their residence time.

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