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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

Comparison of size distributions of O2 MNBs formed in pure water. The size distribution of MNBs obtained from TEM images of replica samples prepared just after aeration (solid circles with arbitrary unit, n = 114) is similar to that measured by a dynamic light scattering method (open diamonds with error bars and a smoothed line), which was reproduced from Ushikubo et al. [19].
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Figure 2: Comparison of size distributions of O2 MNBs formed in pure water. The size distribution of MNBs obtained from TEM images of replica samples prepared just after aeration (solid circles with arbitrary unit, n = 114) is similar to that measured by a dynamic light scattering method (open diamonds with error bars and a smoothed line), which was reproduced from Ushikubo et al. [19].

Mentions: TEM images indicated that most of the observed areas on the replica samples for the pure water including O2 MNBs were smooth, and that a small number of objects were observed. Based on the observation in an early study [20,21], the smooth area corresponded to the ice crystallite formed during quenching, and the objects were resulted from the textures formed during ice crystal growth or from the aggregation of a small amount of impurities included in the original solution. In addition, we found several spherical or oval holes in TEM images, which had relatively uniform sizes ranging from 10-6 to 10-7 m (Figure 1a, b). Since the number concentration of these holes was estimated to be 107 to 108 cm-3, which was obviously greater than that observed on the replica samples of pure water without aeration (as the control, see Figure 1c), most of these holes were considered to be MNBs that originally existed in solutions. This is supported by the facts that the number concentration of MNBs estimated from TEM images corresponded to the value expected from DLS measurements (107 cm-3), and that the size distributions of MNBs observed on the replica samples coincided qualitatively with those obtained in the original bulk MNB water [19] (Figure 2). The quantitative disagreement of the two distributions observed in this figure could be caused by that the size distribution from TEM images being slightly modified because the present observations were based on a limited amount of sample and observed TEM images were random but in small numbers (here n = 114). Therefore, we concluded that we could evaluate the existence of O2 MNBs formed in pure water by using our freeze-fractured replica method. This conclusion also supports the validity of the replica method for application to MNB studies as mentioned previously [16,17,18] and indicates that the lifetime of MNBs formed in pure water was long enough to prepare the samples with quenching.


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)

Comparison of size distributions of O2 MNBs formed in pure water. The size distribution of MNBs obtained from TEM images of replica samples prepared just after aeration (solid circles with arbitrary unit, n = 114) is similar to that measured by a dynamic light scattering method (open diamonds with error bars and a smoothed line), which was reproduced from Ushikubo et al. [19].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Comparison of size distributions of O2 MNBs formed in pure water. The size distribution of MNBs obtained from TEM images of replica samples prepared just after aeration (solid circles with arbitrary unit, n = 114) is similar to that measured by a dynamic light scattering method (open diamonds with error bars and a smoothed line), which was reproduced from Ushikubo et al. [19].
Mentions: TEM images indicated that most of the observed areas on the replica samples for the pure water including O2 MNBs were smooth, and that a small number of objects were observed. Based on the observation in an early study [20,21], the smooth area corresponded to the ice crystallite formed during quenching, and the objects were resulted from the textures formed during ice crystal growth or from the aggregation of a small amount of impurities included in the original solution. In addition, we found several spherical or oval holes in TEM images, which had relatively uniform sizes ranging from 10-6 to 10-7 m (Figure 1a, b). Since the number concentration of these holes was estimated to be 107 to 108 cm-3, which was obviously greater than that observed on the replica samples of pure water without aeration (as the control, see Figure 1c), most of these holes were considered to be MNBs that originally existed in solutions. This is supported by the facts that the number concentration of MNBs estimated from TEM images corresponded to the value expected from DLS measurements (107 cm-3), and that the size distributions of MNBs observed on the replica samples coincided qualitatively with those obtained in the original bulk MNB water [19] (Figure 2). The quantitative disagreement of the two distributions observed in this figure could be caused by that the size distribution from TEM images being slightly modified because the present observations were based on a limited amount of sample and observed TEM images were random but in small numbers (here n = 114). Therefore, we concluded that we could evaluate the existence of O2 MNBs formed in pure water by using our freeze-fractured replica method. This conclusion also supports the validity of the replica method for application to MNB studies as mentioned previously [16,17,18] and indicates that the lifetime of MNBs formed in pure water was long enough to prepare the samples with quenching.

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