New mechanisms discovered to separate air molecules | 6/5/2018 | Staff
lhumara (Posted by) Level 3
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Nanoscale holes in graphene (called "nanowindows") can selectively choose which type of air molecules can pass through.

Scientists from Shinshu University and PSL University, France, theoretically proved the concerted motion of the nanowindow rim to selectively allow molecules to pass in a fast, energy-efficient way. This brings up new possibilities to create an advanced molecular separation membrane technology.

Vibration - Rim - Nanowidow - Size - Rim

The atomic vibration of the nanowindow rim changes the effective nanowidow size. When the rim of one side is deviated and the other is deviated to the opposite direction, the effective nanowindow size becomes larger than when the rim does not move. This effect is predominant for molecules of oxygen, nitrogen and argon, inducing an efficient separation of oxygen from air.

The study considered separation of the main components of air: oxygen, nitrogen and argon. The molecular sizes of oxygen, nitrogen and argon are 0.299, 0.305, and 0.363 nanometers (nm). The researchers compared the permeation of these molecules on six differently sized nanowindows (of 0.257 nm, 0.273 nm, 0.297 nm, 0.330 nm, 0.370 nm, and 0.378 nm).

Nanowindows - Oxidation - Treatment - Rims - Hydrogen

Nanowindows were prepared by oxidation treatment. Thus, their rims are passivated with hydrogen and oxygen atoms, which have an essential role for selective permeation.

Surprisingly, the molecules permeate through nanowindows even when the rigid nanowindow size is smaller than the target molecular size. For example, O2 permeates faster through 0.29 nm nanowindows than 0.33 nm nanowindows. The difference in permeation rate is associated with the interaction of the molecule with the nanowidow rim and graphene. The mechanism is explained...
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