Rapid Water Transportation through Narrow One-Dimensional

Jan 9, 2013 - ... Shinsyu University, 4-17-1 Wakasato, Nagano 380-8553, Japan. § .... by Endo et al.21 and Hata et al.,22 respectively, were found to...
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Rapid Water Transportation through Narrow One-Dimensional Channels by Restricted Hydrogen Bonds Tomonori Ohba,*,† Katsumi Kaneko,‡ Morinobu Endo,‡ Kenji Hata,§ and Hirofumi Kanoh† †

Graduate School of Science, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan Research Center for Exotic Nanocarbons, Shinsyu University, 4-17-1 Wakasato, Nagano 380-8553, Japan § Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi Tsukuba, Ibaraki 305-8565, Japan ‡

S Supporting Information *

ABSTRACT: Water plays an important role in controlling chemical reactions and bioactivities. For example, water transportation through water channels in a biomembrane is a key factor in bioactivities. However, molecular-level mechanisms of water transportation are as yet unknown. Here, we investigate water transportation through narrow and wide one-dimensional (1D) channels on the basis of water-vapor adsorption rates and those determined by molecular dynamics simulations. We observed that water in narrow 1D channels was transported 3−5 times faster than that in wide 1D channels, although the narrow 1D channels provide fewer free nanospaces for water transportation. This rapid transportation is attributed to the formation of fewer hydrogen bonds between water molecules adsorbed in narrow 1D channels. The water-transportation mechanism provides the possibility of rapid communication through 1D channels and will be useful in controlling reactions and activities in water systems.

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ray diffraction.7 Direct observation of water structures in CNTs has been conducted using environmental scanning electron microscopy and transmission electron microscopy (TEM): a rough water liquid−gas interface, nanosized cluster formation, and bubbling by electron beam heating have been observed.8 The direct observations of water structure in a CNT and a carbon nanopipe associated with MD simulation were reviewed in the preceding papers.9 The formation of water nanosized clusters in CNTs were observed by MC simulations, inducing a capillary-condensation-like pore filling.10 The simulations also show pore emptying or bubbles in a simulation box in the lowdensity region. Water filling in CNTs was observed in the above experiments and simulations, although both entropy and numbers of hydrogen bonds are expected to decrease when water is confined in CNTs. Pascal explained water filling on the basis of the entropy, enthalpy, and free energy obtained from MD simulations.11 The entropy terms of water confined in CNTs of diameter smaller than 1 nm provide significant stabilization of water. In CNTs larger than 1 nm in diameter, the enthalpy contributed to the water stability by formation of an ice-like phase. A stabilization mechanism by ice-like cluster formation in nanopores was also proposed based on molecular simulations.12 These unique structure formations of water in 1D channels have hardly been observed in bulk water, although the formation is partly similar to the mechanism in twodimensional nanopores and others.13

INTRODUCTION Water is one of the most ubiquitous, naturally occurring chemical substances. However, it has anomalous physical properties as a result of its constituent hydrogen bonds, and these properties have been extensively studied.1 Water transportation through a water channel in a biomembrane is another important research topic because water channels are involved in numerous physiological processes such as water metabolism, renal water conservation, digestion, homeostasis, and absorption of cerebrospinal fluid.2 Aquaporin water channels have hydrophobic quasi-one-dimensional (1D) channels that consist of widely distributed nanospaces; the channel size distribution is from 0.3 to 0.5 nm to nanometer order.3 Those researches provide significant improvement in understanding mechanism of water channels. However, a simple and rigid water-channel structure model is still necessary to investigate the mechanism from different aspects. A carbon nanotube (CNT) is believed to be an example of such a material because it has hydrophobic 1D channels into which molecules can penetrate.4 The behavior of water in CNTs has therefore been studied recently. Molecular dynamics (MD) simulations have predicted new ice phases in CNTs at high pressures, which are not seen in bulk ice.5 The predicted ice structure of water was also observed; pentagonal−octagonal ring formations of water below 190 K were observed using X-ray diffraction, and unusual hydrogen bonds of water confined in CNTs formed below 200 K were observed by infrared (IR) spectroscopic analysis associated with Monte Carlo (MC) simulations.6 Nanosized ice formation was also observed, even at room temperature, using electron radial distribution functions of X© XXXX American Chemical Society

Received: September 4, 2012 Revised: December 17, 2012

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The dynamic properties of water through CNTs have also been studied. Hummer evaluated the water dynamics in CNTs by MD simulations for confined water and osmotic water shifts.14 The MD simulations suggest a decrease in the binding energy of confined water in comparison with that in the bulk as well as significant thermal fluctuations and high flow rates. Holt experimentally showed fast water flow through vertically aligned CNT membranes rather than a flow of air.15 The CNT-membrane technique has been used for ion exclusion by inducing negative functional groups on the edges of CNTs.16 The transportation mechanism of an aqueous solution on the ion-repelling CNT membrane significantly promotes understanding of the ion-channel mechanism. Qin et al. also reported the advancement of water flow rate on a CNT.17 A CNT membrane is therefore an ideal model of a biological membrane with a water channel. The water-transportation mechanism in a model of a CNT membrane has been shown by MD simulations, as well as water transportation through such a CNT membrane, by imposing an osmotic pressure or electric field.18 Those studies demonstrated fast water transportation through CNTs. However, the MD simulations suggested that water transportation in CNTs was slower than that in bulk water as a result of an intermediate structure between a solid and a fluid.19 Water structure and transportation are strongly affected by CNT diameters smaller than 2 nm.5,6,11,17 Tube-diameter dependences of water flow in CNTs were evaluated in somewhere.18a,19,20 Faster water flow was observed for narrower CNTs in experiments, although water flow in MD simulations shows that wider CNTs provide faster water flow in the CNTs. Therefore, the mechanism of water flow in CNTs has to be continuously studied. Few experimental studies of water penetration through CNTs also have been conducted except for those by Holt’s group and Qin et al., as mentioned above. Furthermore, combined studies consisting of molecular simulations and experiments are necessary to understand the mechanism especially at the molecular level. Direct observations of water penetration through 1D channels of CNTs without other contaminants are desirable for improved understanding of the mechanism. Hence, further investigation of the mechanism of water transportation through well-defined CNTs is needed. Double- and single-walled CNTs synthesized by Endo et al.21 and Hata et al.,22 respectively, were found to have hydrophobic 1D channels, extremely high aspect ratios, and no metal catalysts. Thus, they have high potential for use in conducting fundamental studies on water transportation through their 1D channels. We used these narrow and wide 1D channels to investigate water transportation through 1D channels by examining water-vapor adsorption and vibrational changes in the OH stretching of adsorbed water and by conducting MD simulations. With the aim of understanding water-channel operation, we associated water flow in CNTs with hydrogen-bonding formation. Adsorption measurements of water in CNTs could fulfill the above-mentioned requirements because the amount of water penetrating through 1D channels can be directly evaluated from the adsorption increase of water vapor in CNTs without any special treatment of the CNTs. The adsorption rate is therefore related to the selfdiffusion coefficient of water in CNTs, which can be calculated using MD simulations.

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EXPERIMENTAL AND SIMULATED PROCEDURES

Experimental Section. The double-walled and single-walled CNTs provided by Endo’s and Hata’s groups were observed by high-resolution TEM using a JEM-2100F instrument (JEOL Co., Tokyo, Japan) at 120 kV. The samples were sonicated in ethanol solution and deposited on TEM grids. N2 adsorption isotherms at 77 K and water and SF6 adsorption isotherms at 303 K were measured using volumetric apparatuses (Autosorb-1, Quantachrome Co., and apparatus of our own design). Using our designed volumetric apparatus, we measured the adsorption rates of water vapor at 303 K every 50 ms as well as SF6 adsorption rates for comparison. Here, the measured adsorption rates were at equilibrium filling factors of 0.16 and 0.25. The CNTs were heated at 423 K and a pressure of less than 0.1 Pa for 2 h prior to measurements of adsorption isotherms and adsorption rates. Water-adsorbed 1D channels were prepared for FTIR spectroscopy (FT/IR-410; JASCO Co.) in a humidity-controlled cell with CaF2 windows. FT-IR measurements of water-adsorbed 1D channels and of 1D channels were conducted after introduction of saturated water vapor and vacuum evacuation, respectively. Simulation. MD simulations using the leapfrog Verlet integration algorithm with coupling to a thermal bath were performed to determine the water-transportation mechanism; the simulation model consisted of a 1D channel of infinite length and of diameter 1 or 2 nm placed in a unit cell of dimensions 4.0 × 4.0 × 12.0 nm3. The interaction potentials between water molecules and between a water molecule and a carbon wall were calculated using the TIP5P and Lennard-Jones potential models, respectively.23 A complete MD simulation (1000 ps) was performed at ∼303 K with an integration time of 0.1 fs (see Supporting Information for details). The Lorentz− Berthelot rules were applied for calculation of the Lennard-Jones potentials for different molecules. Ewald summation was used for accurate calculation of the Coulomb interactions of partial charges. Water self-diffusion was evaluated from water dynamics in the central part of 6 nm.

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RESULTS AND DISCUSSION As double-walled CNTs are in bundle form, the interstitial nanopores are not available for molecular adsorption.21,22 In other words, only the internal nanopores of double-walled CNTs are nanospaces for molecular adsorption. The internal nanopores of single-walled CNTs are also primary nanospaces for molecular adsorption because single-walled CNTs are in dispersed form. Hence, the internal nanopores of both types of CNT are dominant for molecular adsorption and work as 1D channels. The average internal tube diameters of double-walled and single-walled CNTs are 1 and 2 nm, respectively; these were evaluated using Raman spectroscopy, high-resolution TEM images, and N2 adsorption isotherms at 77 K in the preceding papers (see also the Supporting Information).23 As these average CNT diameters are carbon-center distances, the effective nanopore diameters of double-walled and single-walled CNTs for water penetration are 0.6 and 1.7 nm, corresponding to single- (or double-) and five-water-molecular sizes, respectively. Thus, the internal nanopores of double-walled and single-walled CNTs provide narrow and wide 1D channels for water molecules, although we could not obtain the CNT lengths because they are extremely long. In this manner, we named double-walled and single-walled CNTs as narrow and wide 1D channels. Figure 1 shows adsorption and desorption isotherms of water vapor at 303 K. Here, P0 is the saturated vapor pressure of water vapor, 4.2 kPa. A filling factor is defined as filling percentage of water to nanospaces, evaluated from the N2 adsorption isotherms. Water vapor was rarely adsorbed in the narrow and wide 1D channels below P/P0 = 0.5, whereas significant adsorption uptakes were observed above P/P0 = 0.5. As 1D channels are hydrophobic, water molecular affinities to B

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Figure 1. Water-vapor adsorption isotherms of narrow and wide 1D channels at 303 K. Filled and open symbols represent adsorption and desorption stages.

the hydrophobic nanopores are changed from hydrophobicity to hydrophilicity at P/P0 = 0.5, as mentioned in the previous study.12 The saturated adsorbed amounts of water vapor, which were evaluated from the intercepts of the desorption isotherms with P/P0 = 1.0, correspond to the micropore volume evaluated from N2 adsorption isotherms at 77 K (Table S1). Hence, 1D channels were sufficiently filled with water and liquid- or icelike structure of confined water was formed in the 1D channels, although vapor-phase water was introduced into the 1D channels. The liquid- and ice-like structures in the wide 1D channels were indeed reported in our preceding paper.7 The adsorption and desorption isotherms have significant hysteresis, indicating different water structures in the nanopores in the adsorption and desorption stages, as supposed by the preceding study.13 Here, we study the mechanism of water transportation in the adsorption stage. Figure 2 shows changes in the filling factors of water after water-vapor introduction and of SF6 for comparison. Here, the difference in the SF6 adsorption rates for both channels compensates for lack of knowledge of 1D channel lengths because SF6 is simply considered as a spherical molecule and a dispersion-interaction-dominant molecule.24 Hence, the filling changes of SF6 for both 1D channels should be apparently different when the effective 1D channel lengths are significantly different. Both adsorption progresses of water vapor and SF6 were rather slower than those diffusions in bulk phase. The SF6 adsorptions progressed relatively rapidly and were almost completed in 1 s. No differences between the adsorption rates in both 1D channels were observed. Thus, both channels provide the same transportation rates for a dispersioninteraction-dominant molecule such as SF6, indicating no influence of 1D channel lengths on adsorption rates. In contrast, a significant difference was observed between water adsorption rates for both 1D channels, as shown in Figure 2a, verifying a different mechanism of molecular transportation through 1D channels from a simple molecule. The adsorption delay of water vapor for wide1D channels was also observed at equilibrium filling factor 0.16, as shown in Figure S4a, whereas no adsorption delay of SF6 at filling factor 0.18 was observed in Figure S4b. Therefore, water adsorption delay cannot be explained by the Venturi effect, which is an effect of fast flow at a narrow cross section in a macroscopic system. A microscopic understanding is necessary in this system, and the difference of

Figure 2. Changes in filling factor of water vapor (a) and SF6 (b) in 1D channels.

water adsorption rate for narrow and wide 1D channels was intrinsic to water transportation through nanoscale channels. Water-vapor adsorption in both 1D channels began at 0.1 s; nearly complete adsorption equilibrium was achieved in 100 s. The filling factor of water vapor for narrow 1D channels increased rapidly from 0.5 to 10 s, whereas that for wide 1D channels increased gradually. Water transportation was almost completed in 16 and 49 s for narrow and wide 1D channels, respectively, at an equilibrium filling factor of 0.25. Water molecules were therefore transported 3−5 times faster through narrow 1D channels than through wide 1D channels, whereas SF6 transportations through narrow and wide 1D channels agreed well for both equilibrium filling factors. The differentials of the curves in Figure 2a were used to evaluate the adsorption rates of water vapor (Figure S4c); these rates directly represent the transportation of water vapor through narrow and wide 1D channels. We observed water-vapor adsorption to occur in three steps, namely extremely fast adsorption of water vapor for the first 0.2 s (second step in Figure S4c), relatively fast adsorption from 0.2 to 10 s (third step in Figure S4c), and gradual adsorption after 10 s (fourth step in Figure S4c), for both narrow and wide 1D channels. The schematic images of water adsorption are shown in Figure S 4d. The first step is attributed to the diffusion of water into the 1D channels. The second step results from transportation of water vapor through the 1D channels. The third step is a result of condensation in these 1D channels. We actually observed faster water transportation in the narrow 1D channels than in the wide 1D channels. The faster transportation in the narrow 1D channels is an unexpected result because the narrow 1D channels provide fewer free nanospaces for the transportation of water molecules, although the fast transportation was observed experimentally.15,17 C

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80 ps and then decreased. The times to attain the maximum transport diffusion coefficients almost correspond to the requisite filling times of water vapor: 13 and 51 ps, as shown in Figure 3. Water transportation in the narrow and wide 1D channels accelerates up to transport diffusion coefficients of 65 × 10−9 and 50 × 10−9 m2 s−1, respectively. The transport diffusion coefficient of bulk water was 75 × 10−9 m2 s−1 in the MD simulation of the 2 × 2 × 2 nm3 unit cell, which roughly corresponds with experimental thermal diffusivity 100 × 10−9 m2 s−1.25 Both channels therefore provide relatively rapid water transportation, despite the highly restricted nanospaces. A 1D channel also promotes water transportation to a considerable extent. The trends in the water-transportation properties in the narrow and wide 1D channels are consistent with the experimental adsorption rates shown in Figure 2; the difference in the water-transportation time scales is attributed to the different lengths of the 1D channels in the experiments and simulations. Intermolecular interaction of water should strongly influence water transportation. To investigate the reason for the rapid water transportation, we evaluated the average number of hydrogen bonds between water molecules from the MD simulations, as shown in Figure 4. The average number was

The MD simulations of water in narrow and wide 1D channels explain the anomalous nature of water transportation, as shown in Figure 3; the figure shows the changes in filling

Figure 3. Changes in filling factor of water molecules in 1D channels in MD simulations (a) and snapshots of water transporation in narrow and wide 1D channels (b). Water molecules flow from left to right in the nanospaces.

factor with time and snapshots of the MD simulation of water transportation through narrow and wide 1D channels (see also Figure S5). Here the snapshots were part of the unit cell, as described in the Supporting Information (Figure S2). The results clarify the mechanism of water-vapor transportation through narrow and wide 1D channels. At 0 ps, water molecules were located on the left side of the 1D channels in the snapshots (Figure 3b); they then began moving to the right side. In the narrow 1D channels, water moved rapidly to the right side, in contrast to water transportation in the wide 1D channels. Water transportation was completed in 13 and 51 ps in the narrow and wide 1D channels, respectively. Thus, the transportation rate of water through narrow 1D channels was 4 times faster than that through wide 1D channels, in agreement with the experimental transportation rate. Pascal et al. suggested that water in narrow 1D channels is dominated by the entropy terms rather than the enthalpy terms.11 Diffusion entropy changes might therefore be dominant for water transportation in such channels. The transport diffusion coefficients were also evaluated from the MD simulations every 2 ps (Figure S6). Here, we define the three-dimensional transport diffusion coefficient of water in 1D channels as ⟨Δ2⟩/2t. The transport diffusion coefficient of water vapor in the narrow 1D channel increased rapidly, whereas that in the wide 1D channel increased moderately. In the narrow 1D channel, the transport diffusion coefficient was relatively high, even below 1 ps; it reached 65 × 10−9 m2 s−1 at 10 ps and then slightly decreased above 10 ps. In contrast, the transport diffusion coefficient was significantly slower in the wide 1D channel; it gradually increased to 50 × 10−9 m2 s−1 at

Figure 4. Changes in the average number of hydrogen bonds between water molecules with time.

evaluated from the number of molecules with an intermolecular O−H distance shorter than 0.3 nm.26 In the narrow 1D channel, the number of hydrogen bonds increased to 0.6 at 10 ps and then remained roughly constant above that time. In the wide 1D channel, however, the number of hydrogen bonds increased to 2.0 after 10 ps. Water molecules in the narrow and wide 1D channels are therefore in monomeric and trimeric (or tetrameric) forms, respectively. Pascal et al. proposed that the numbers of hydrogen bonds of confined liquid water at 1 atm and 300 K were 2.5 in a narrow 1D channel and 3.4 in a wide 1D channel.11 The trend in the numbers of hydrogen bonds was similar, although the numbers obtained in this study were lower than those previously reported because of the low water density of 0.25 g dm−3 in this study. There was obvious difference between the hydrogen bonds in the two channels, as the difference in the number of hydrogen bonds for low-density water (in this study) was larger than that for high-density water (in the previous report). The water molecules are clearly unable to form sufficient hydrogen bonds in the narrow 1D channel, inducing weak intermolecular interactions of water. D

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channels agree with the results of the above MD simulations. These weak hydrogen bonds in the narrow 1D channels therefore facilitate water transportation. In other words, this limited hydrogen-bond formation promotes rapid transportation of water through narrow 1D channels.

The vibrational frequencies of OH stretching absorbance bands in Fourier transform IR (FT-IR) spectroscopy depend on the cluster number of water, as reported by Xantheas and Dunning, Jr.27 In other words, the OH stretching frequency of a water monomer at 3872 cm−1 decreases with formation of larger clusters, according to MP2-level calculations. The relationship between the differential frequency Δω from a monomer and the associated molecular number n of a water cluster is as follows: Δω = −100(n − 1). Hence, the above MD simulations predict that the frequency of adsorbed water in the wider 1D nanopores will exhibit a red-shift from that of water vapor, whereas that in the narrower 1D nanopores might be unchanged. Figure 5 shows the FT-IR spectra of water

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CONCLUSION In this study, we investigated the mechanism of water transportation through narrow and wide 1D channels by association of water flow with hydrogen bonds. Water vapor was found to move more quickly through narrow 1D channels than through wide 1D channels. The rapid transportation of water molecules in narrow 1D channels is attributed to the formation of fewer hydrogen bonds among water molecules in these narrow 1D channels. Water has to form 1D structures in narrow 1D channels, and this restricts the formation of hydrogen bonds, thereby promoting water transportation. This mechanism of anomalously fast transportation in 1D channels is helpful in clarifying the working mechanism of water channels and provides the possibility of rapid communication through water transportation.

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ASSOCIATED CONTENT

S Supporting Information *

TEM images, details of simulation procedure, characterization of nanospaces, details of water vapor adsorption rates, and snapshots in MD simulation. This material is available free of charge via the Internet at http://pubs.acs.org.

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Figure 5. FT-IR spectra of water adsorbed in wide and narrow 1D channels. The spectra of bulk liquid water and water vapor are shown for comparison.

AUTHOR INFORMATION

Corresponding Author

*E-mail [email protected]. Notes

The authors declare no competing financial interest.

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adsorbed in the wide and narrow 1D channels; the cluster sizes were evaluated from the differences between water-vaporadsorbed 1D channels and the 1D channels. The sharp absorption peaks in the range 3400−4000 cm−1 were assigned to the P and R branches of the symmetric and asymmetric stretching vibrations of water vapor at 3657 and 3790 cm−1, respectively. The broad absorption peak in liquid water was observed at 3392 cm−1. The shift in the OH stretching absorption band for water vapor from that of liquid water is the result of hydrogen-bond formation.27−29 The associated water number in liquid water was 3.6, from the relation between Δω and n. The absorbance bands in the narrow 1D channels were at similar positions to those of water vapor, but the absorbance intensities were significantly increased. The increase in absorbance intensities is a result of concentration of water vapor by water adsorption in the narrow 1D channels. In contrast, the broad peak was not observed. Thus, the hydrogenbonding structure of adsorbed water was similar to that of vapor. Water adsorbed in the narrow 1D channels is therefore monomeric, and the hydrogen-bonding networks should be weak, as in water vapor. In the case of wide 1D channels, the positions and intensities of the absorbance bands were similar to those of water vapor. However, a broad absorbance peak was also observed at 3450 cm−1. This peak could be related to the associated water number of adsorbed water, as mentioned above. The associated water number of adsorbed water in the wide 1D channels was 2.8. This indicates that adsorbed water forms trimers in the wide 1D channels. The hydrogen-bonding networks of water adsorbed in the narrow and wide 1D

ACKNOWLEDGMENTS This research was supported by a Research Fellowship from the Foundation for the JGC-S Scholarship Foundation, Promotion of Ion Engineering, Murata Science Foundation, Nippon Sheet Glass Foundation, Global COE Program, MEXT, Japan, as well as the JSPS Program “Strategic Young Researcher Overseas Visits Program for Accelerating Brain Circulation”.

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REFERENCES

(1) (a) Gragson, D. E.; Richmond, G. L. Investigations of the structure and hydrogen bonding of water molecules at liquid surfaces by vibrational sum frequency spectroscopy. J. Phys. Chem. B 1998, 102, 3847−3861. (b) Koop, T.; Luo, B.; Tsias, A.; Peter, T. Water activity as the determinant for homogeneous ice nucleation in aqueous solutions. Nature 2000, 406, 611−614. (c) Lee, H. M.; Suh, S. B.; Lee, J. Y.; Tarakeshwar, P.; Kim, K. S. Structures, energies, vibrational spectra, and electronic properties of water monomer to decamer. J. Chem. Phys. 2000, 112, 9759−9772. (d) Bellissent-Funnel, M.-C.; Sridi-Dorbez, R.; Bosio, L. X-ray and neutron scattering studies of the structure of water at a hydrophobic surface. J. Chem. Phys. 1996, 104, 10023−10029. (2) (a) Sui, H.; Han, B.-G.; Lee, J. K.; Walian, P.; Jap, B. K. Structural basis of water-specific transport through the AQP1 water channel. Nature 2001, 414, 872−878. (b) Hasegawa, H.; Ma, T.; Skach, W.; Matthay, M. A.; Verkman, A. S. Molecular cloning of a mercurialinsensitive water channel expressed in selected water-transporting tissues. J. Biol. Chem. 1994, 269, 5497−5500. (c) Kim, I.-B.; Oh, S.-J.; Nielsen, S.; Chun, M.-H. Immunocytochemical localization of Aquaporin 1 in the rat retina. Neurosci. Lett. 1998, 244, 52−54. E

dx.doi.org/10.1021/la303570u | Langmuir XXXX, XXX, XXX−XXX

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Article

(3) (a) Agre, P.; Brown, S.; Nielsen, S. Aquaporin water channels: unanswered questions and unresolved controversies. Curr. Opin. Cell Biol. 1995, 7, 472−482. (b) Murata, K.; Mitsuoka, K.; Hirai, T.; Walz, T.; Agre, P.; Heymann, J. B.; Engel, A.; Fujiyoshi, Y. Structural determinants of water permeation through aquaporin-1. Nature 2000, 407, 599−605. (c) Agre, P.; Kozono, D. Aquaporin water channels: molecular mechanisms for human diseases. FEBS Lett. 2003, 555, 72− 78. (4) Sansom, M. S. P.; Biggin, P. C. Biophysics: water at the nanoscale. Nature 2001, 414, 156−157. (5) Koga, K.; Gao, G. T.; Tanaka, H.; Zeng, X. C. Formation of ordered ice nanotubes inside carbon nanotubes. Nature 2001, 412, 802−805. (6) (a) Maniwa, Y.; Kataura, H.; Abe, M.; Udaka, A.; Suzuki, S.; Achiba, Y.; Kira, H.; Matsuda, K.; Kadowaki, H.; Okabe, Y. Ordered water inside carbon nanotubes: formation of pentagonal to octagonal ice-nanotubes. Chem. Phys. Lett. 2005, 401, 534−538. (b) Byl, O.; Liu, J.-C.; Wang, Y.; Yim, W.-L.; Johnson, J. K., Jr.; Yates, J. T. Unusual hydrogen bonding in water-filled carbon nanotubes. J. Am. Chem. Soc. 2006, 128, 12090−12097. (7) Ohba, T.; Taira, S.; Hata, K.; Kaneko, K.; Kanoh, H. Predominant nanoice growth in single-walled carbon nanotubes by water-vapor loading. RSC Adv. 2012, 2, 3634−3637. (8) (a) Rossi, M. P.; Ye, H.; Gogotsi, Y.; Babu, S.; Ndungu, P.; Bradley, J.-C. Environmental scanning electron microscopy study of water in carbon nanopipes. Nano Lett. 2004, 4, 989−993. (b) Naguib, N.; Ye, H.; Gogotsi, Y.; Yazicioglu, A. G.; Megaridis, C. M.; Yoshimura, M. Observation of water confined in nanometer channels of closed carbon nanotubes. Nano Lett. 2004, 4, 2237−2243. (9) (a) Whitby, M.; Quirke, N. Fluid flow in carbon nanotubes and nanopipes. Nat. Nanotechnol. 2007, 2, 87−94. (b) Mattia, D.; Gogotsi, Y. Review: static and dynamic behavior of liquids inside carbon nanotubes. Microfluid. Nanofluid. 2008, 5, 289−305. (10) Striolo, A.; Gubbins, K. E.; Chialvo, A. A.; Cummings, P. T. Simulated water adsorption isotherms in carbon nanopores. Mol. Phys. 2004, 102, 243−251. (11) Pascal, T. A.; Goddard, W. A.; Jung, Y. Entropy and the driving force for the filling of carbon nanotubes with water. Proc. Natl. Acad. Sci. U. S. A. 2011, 108, 11794−11798. (12) Ohba, T.; Kanoh, H.; Kaneko, K. Affinity transformation from hydrophilicity to hydrophobicity of water molecules on the basis of adsorption of water in graphitic nanopores. J. Am. Chem. Soc. 2004, 126, 1560−1562. (13) (a) Do, D. D.; Do, H. D. A new adsorption-desorption model for water adsorption in activated carbon. Carbon 2000, 38, 767−773. (b) Alcaniz-Monge, J.; Linares-Solano, A.; Rand, B. Water adsorption on activated carbons: study of water adsorption in micro- and mesopores. J. Phys. Chem. B 2001, 105, 7998−8006. (c) Slasli, A. M.; Jorge, M.; Stoeckli, F.; Seaton, N. A. Water adsorption by activated carbons in relation to their microporous structure. Carbon 2003, 41, 479−486. (d) Desbiens, N.; Demachy, I.; Fuchs, A. H.; KirschRodeschini, H.; Soulard, M.; Patarin, J. Water condensation in hydrophobic nanopores. Angew. Chem., Int. Ed. 2005, 44, 5310−5313. (e) Ohba, T.; Kaneko, K. Cluster-associated filling of water molecules in slit-shaped graphitic nanopores. Mol. Phys. 2007, 105, 139−145. (14) (a) Hummer, G.; Rasaiah, J. C.; Noworyta, J. P. Water conduction through the hydrophobic channel of a carbon nanotube. Nature 2001, 414, 188−190. (b) Kalra, A.; Garde, S.; Hummer, G. Osmotic water transport through carbon nanotube membranes. Proc. Natl. Acad. Sci. U. S. A. 2003, 100, 10175−10180. (15) Holt, J. K.; Park, H. G.; Wang, Y.; Stadermann, M.; Artyukhin, A. B.; Grigoropoulos, C. P.; Noy, A.; Bakajin, O. Fast mass transport through sub-2-nanometer carbon nanotubes. Science 2006, 312, 1034− 1037. (16) Fornasiero, F.; Park, H. G.; Holt, J. K.; Stadermann, M.; Grigoropoulos, C. P.; Noy, A.; Bakajin, O. Ion exclusion by sub-2-nm carbon nanotube pores. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 17250−17255.

(17) Qin, X.; Yuan, Q.; Zhao, Y.; Xie, S.; Liu, Z. Measurement of the rate of water translocation through carbon nanotubes. Nano Lett. 2011, 11, 2173−2177. (18) (a) Liu, B.; Li, X.; Li, B.; Xu, B.; Zhao, Y. Carbon nanotube based artificial water channel protein: membrane perturbation and water transportation. Nano Lett. 2009, 9, 1386−1394. (b) Li, J.; Gong, X.; Lu, H.; Li, D.; Fang, H.; Zhou, R. Electrostatic gating of a nanometer water channel. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 3687−3692. (19) Mashl, R. J.; Joseph, S.; Aluru, N. R.; Jakobsson, E. Anomalously immobilized water: a new water phase induced by confinement in nanotubes. Nano Lett. 2003, 3, 589−592. (20) Thomas, J. A.; McGaughey, J. H. Reassessing fast water transport through carbon nanotubes. Nano Lett. 2008, 8, 2788−2793. (21) (a) Miyamoto, J.; Hattori, Y.; Noguchi, D.; Tanaka, H.; Ohba, T.; Utsumi, S.; Kanoh, H.; Kim, Y. A.; Muramatsu, H.; Hayashi, T.; Endo, M.; Kaneko, K. Efficient H2 adsorption by nanopores of highpurity double-walled carbon nanotubes. J. Am. Chem. Soc. 2006, 128, 12636−12637. (b) Ohba, T.; Matsumura, T.; Hata, K.; Yumura, M.; Iijima, S.; Kanoh, H.; Kaneko, K. Nanoscale curvature effect on ordering of N2 molecules adsorbed on single wall carbon nanotube. J. Phys. Chem. C 2007, 111, 15660−15663. (22) (a) Hata, K.; Futaba, D. N.; Mizuno, K.; Namai, T.; Yumura, M.; Iijima, S. Water-assisted highly efficient synthesis of impurity-free single-walled carbon nanotubes. Science 2004, 306, 1362−1364. (b) Endo, M.; Muramatsu, H.; Hayashi, T.; Kim, Y. A.; Terrones, M.; Dresselhaus, M. S. Nanotechnology: “Buckypaper” from coaxial nanotubes. Nature 2005, 433, 476. (23) (a) Mahoney, M. W.; Jorgensen, W. L. A five-site model for liquid water and the reproduction of the density anomaly by rigid, nonpolarizable potential functions. J. Chem. Phys. 2000, 112, 8910− 8922. (b) Ohba, T.; Kaneko, K. Internal surface area evaluation of carbon nanotube with GCMC simulation-assisted N2 adsorption. J. Phys. Chem. B 2002, 106, 7171−7176. (24) Ihm, G.; Song, Y.; Mason, E. A new strong principle of corresponding states for nonpolar fluids. J. Chem. Phys. 1991, 94, 3839−3848. (25) Abramson, E. H.; Brown, J. M.; Slutsky, L. J. The thermal diffusivity of water at high pressures and temperatures. J. Chem. Phys. 2001, 115, 10461−10463. (26) Kalinichev, A. G.; Bass, J. D. Hydrogen bonding in supercritical water: a Monte Carlo simulation. Chem. Phys. Lett. 1994, 231, 301− 307. (27) Xantheas, S. S.; Dunning, T. H., Jr. Ab initio studies of cyclic water clusters (H2O)n, n = 1−6. I. Optimal structures and vibrational spectra. J. Chem. Phys. 1993, 99, 8774. (28) Schmidt, D. A.; Miki, K. Structural correlations in liquid water: a new interpretation of IR spectroscopy. J. Phys. Chem. A 2007, 111, 10119−10122. (29) Ohno, K.; Okimura, M.; Akai, N.; Katsumoto, Y. The effect of cooperative hydrogen bonding on the OH stretching-band shift for water clusters studied by matrix-isolation infrared spectroscopy and density functional theory. Phys. Chem. Chem. Phys. 2005, 7, 3005− 3014.

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dx.doi.org/10.1021/la303570u | Langmuir XXXX, XXX, XXX−XXX