“Gated” ion transport through hydrophobic protein domains in various cellular membranes was found widely, while these hydrophobic protein channels regulate ions transport through these membranes with both high selectivity and high flux. Hydrophobic and narrow carbon nanotubes (CNT) may serve as a simplified model to mimic these biological pores and thus reveal main properties of these hydrophobic nanochannels. Dense carbon nanotube (CNT) membranes with both 3-nm CNT and interstitial pores were prepared by a solvent-evaporation process. Ion diffusion through these membranes has an on/off behavior, which may be due to the sensitive water wettability of CNTs. At 298 K, ion diffusion through CNT membranes gradually stopped, but it increased dramatically when the temperature was increased 20 K or the membrane was subjected to ultrasound. Adsorption measurements show that water adsorption increased dramatically when the temperature was increased from 293 to 306 K, and this suggests that the adsorbed water forms a discontinuous phase at 293 K, but possibly a continuous layer at higher temperature in both the CNTs and the interstitial regions. When the ion diffusion channel was open, due to a continuous water phase, ions diffused through the CNT membranes at a rate similar to bulk diffusion in water.
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“Gated” Ion Transport through Dense Carbon Nanotube Membranes
“Gated” ion transport through hydrophobic protein domains in various cellular membranes was found widely, while these hydrophobic protein channels regulate ions transport through these membranes with both high selectivity and high flux. Hydrophobic and narrow carbon nanotubes (CNT) may serve as a simplified model to mimic these biological pores and thus reveal main properties of these hydrophobic nanochannels. Dense carbon nanotube (CNT) membranes with both 3-nm CNT and interstitial pores were prepared by a solvent-evaporation process. Ion diffusion through these membranes has an on/off behavior, which may be due to the sensitive water wettability of CNTs. At 298 K, ion diffusion through CNT membranes gradually stopped, but it increased dramatically when the temperature was increased 20 K or the membrane was subjected to ultrasound. Adsorption measurements show that water adsorption increased dramatically when the temperature was increased from 293 to 306 K, and this suggests that the adsorbed water forms a discontinuous phase at 293 K, but possibly a continuous layer at higher temperature in both the CNTs and the interstitial regions. When the ion diffusion channel was open, due to a continuous water phase, ions diffused through the CNT membranes at a rate similar to bulk diffusion in water.