Confinement Effect of Sub-Nanometer Difference on Melting Point of

Subscriber access provided by Karolinska Institutet, University Library

Article

Confinement Effect of Sub-Nanometer Difference on Melting Point of Ice-Nanotubes Measured by Photoluminescence Spectroscopy Shohei Chiashi, Yuta Saito, Takashi Kato, Satoru Konabe, Susumu Okada, Takahiro Yamamoto, and Yoshikazu Homma ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b06041 • Publication Date (Web): 22 Jan 2019 Downloaded from http://pubs.acs.org on January 24, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Confinement Effect of Sub-Nanometer Difference on Melting Point of Ice-Nanotubes Measured by Photoluminescence Spectroscopy Shohei Chiashi,∗,†,‡ Yuta Saito,¶ Takashi Kato,¶ Satoru Konabe,‡ Susumu Okada,‡,§ Takahiro Yamamoto,∥,‡ and Yoshikazu Homma∗,‡,¶ †Department of Mechanical Engineering, The University of Tokyo, Bunkyo, Tokyo 113-8656, Japan ‡Research Institute for Science & Technology, Tokyo University of Science, Shinjuku, Tokyo 162-8601, Japan ¶Department of Physics, Tokyo University of Science, Shinjuku, Tokyo 162-8601, Japan § Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan ∥Department of Liberal Arts, Faculty of Engineering, Tokyo University of Science, Katsushika, Tokyo 125-8585, Japan E-mail: [email protected]; [email protected]

Abstract Melting point is independent of size and shape in bulk materials but it exhibits the size dependence when material size is extremely small. In this study, we measured the melting point of water confined in single-walled carbon nanotubes (SWCNTs) with 16 different chiralities, which ranged 0.95 to 1.26 nm in diameter, and revealed the details of the SWCNT diameter dependence of the melting points. The melting point

1

ACS Paragon Plus Environment

ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

were probed by utilizing the change of photoluminescence (PL) emission wavelength of SWCNTs which encapsulated water, and the relation between the emission wavelength and the water phase was confirmed by the first-principles calculation. The periodicity of the melting point variation with SWCNT diameter came from the discrete change of ice-nanotube (ice-NT) diameter, and in addition even ice-NT with the identical diameter exhibited different melting point due to the slight difference of the inner space size of the encapsulating SWCNTs. The present results agreed with those of the molecular dynamics simulation (Takaiwa, D. et al., Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 39–43.). It was elucidated that the melting point of the nano-material changed sensitively to the atomic structure and the confinement space size.

KEYWORD: carbon nanotubes, water, encapsulation, confinement effects, melting point, spectroscopy, theoretical calculation

Bulk materials exhibit specific physical properties independent of the size and shape. By contrast, in nano-materials, the size effects on the physical properties appear, such as the Gibbs-Thomson effect in melting point and the quantum size effect in electronic band structure. The effect is monotonous and continuous on size as far as the atomic structure is unchanged, which means that it is possible to control the physical properties of nano-materials by precisely designing the size and morphology. When the size becomes in nano-scale, materials possibly possess a different atomic structure from that of bulk. In this case, the properties drastically depend on the atomic structure rather than the size. Most nano-materials do not exist alone, although the others are isolated in the vacuum space. They are usually supported on substrates, dispersed in solutions or suspended by supports. Since nano-materials have a large specific surface area, their properties are sensitive to surrounding materials. Therefore nano-materials exhibit an interesting variety in physical properties due to the size effects, the peculiar atomic structure and the environmental effects, 2


Page 2 of 20

Page 3 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

and the investigation of nano-materials should be precisely performed considering these factors. Water confined in small pores is one of the well-known materials which exhibit the size effect of melting point. The melting point of water gradually decreases as the diameter of pores becomes smaller in micro scale. 1 In the range of nano-scale, the melting point of water has been investigated by using single-walled carbon nanotubes (SWCNTs) 2 as pores. SWCNTs are chemically stable and the hydrogen bonding among water molecules is much stronger than the interaction between a water molecule and an SWCNT. Therefore, SWCNTs are ideal nano-pores for water molecules. The encapsulation of water molecules in SWCNTs has been theoretically 3 and experimentally 4–12 studied. The simulation study points out the complex SWCNT diameter (dCNT ) dependence. 13 Water in the solid phase confined in SWCNTs forms a different atomic structure from bulk water, which is called ice-nanotube (ice-NT), and ice-NTs form different atomic structure which is characterized by an integer n (n-gonal ice-NT). 3 Even the ice-NTs with the same size n, exhibit the different melting point depending on dCNT . On the other hand, the most of experimental measurements to date have been conducted with ensembles (aggregated and bundled) of SWCNTs with different dCNT and chiralities (n, m), which have provided averaged rather than specific data. In addition, an analysis of an individual SWCNT is limited to a few chiralities and it is difficult to investigate a systematic analysis. Although XRD measurement 14 and Raman scattering spectroscopy 11 roughly show the dCNT dependence of the melting point, the interesting confinement effect on the melting point in nano-scale, which is theoretically predicted, is still unclear. In the present study, the dCNT dependence of melting point of ice-NT was investigated by performing photoluminescence (PL) spectroscopy for suspended SWCNTs with different chiralities. PL spectroscopy for SWCNTs 15,16 has sufficiently high sensitivity, and we have succeeded in revealing water encapsulation from only one suspended SWCNT by PL spectroscopy. 17 Because water enhances the dielectric constant surrounding the SWCNTs, ϵenv ,

3


ACS Nano

the encapsulation of water is detected as a change in the optical transition energy (Eii ) of SWCNTs. 18,19 The phase transition of water encapsulated in SWCNTs was detected by the PL measurement of individual SWCNTs and it was confirmed by first-principle calculation. The details of the dCNT dependence of the melting point was revealed by the combination of experimental and theoretical approaches. ;ĂͿ

;ďͿ

Emission Wavelength (nm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 20

1300

: opened : closed 1250 0 1000 2000 Water Vapor Pressure (Pa)

Figure 1: (Color online) Structure of suspended SWCNT and its water vapor dependence of PL emission wavelength. (a) SEM image of a suspended SWCNT between a pair of silica pillars. The length of the suspended SWCNT is 10 µm. (b) Dependence of emission wavelength on the water vapor pressure for an identical (9, 7) SWCNT before (closed-SWCNT) and after (opened-SWCNT) the oxidation treatment. The measurement was performed at 25 ◦ C.

Results and discussion Characterization of suspended and opened SWCNTs Figure 1(a) shows a scanning electron microscopy (SEM) image of an SWCNT suspended between silica pillars. Suspended and semi-conducting SWCNTs emit sharp and intensive PL spectra, even at room temperature. 16 If the SWCNTs are bundled or defective, their optical transition energies (Eii ) are modulated 20 or satellite peaks appear in the PL emission spectra, 21,22 respectively. Isolated (not bundled) and defect-free SWCNTs were carefully selected in advance from among suspended SWCNTs using PL spectroscopy. The Eii of the isolated and suspended SWCNTs changed with respect to molecular adsorption not only on the outer surface 23,24 but also on the inner space. 17 4


Page 5 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Figure 1(b) shows the water pressure dependence of emission wavelength, λem for (9, 7)SWCNT at 25 ◦ C before and after the oxidation treatment. Before the treatment, the SWCNTs are closed and water molecules can only adsorb on the outer surface, which corresponds to a rapid wavelength shift at an adsorption pressure around 250 Pa as shown in Figure 1(b). 24 The adsorption of water molecules increases ϵenv surrounding the SWCNTs, and decreases Eii . 18,19 On the other hand, after the oxidation treatment, the water vapor pressure dependence in Figure 1(b) showed an additional large shift at higher pressure. The additional shift of emission wavelength indicates the encapsulation of water molecules in the SWCNTs. 9,17 After oxidation treatment, SWCNTs lose their end-cap structure and they were opened. Water molecules smoothly enter and exit the opened SWCNTs.

PL spectra in the saturated water vapor Figure 2(a) shows PL spectra from an opened (9, 8) SWCNT measured in the saturated pressure at different temperatures. The wavelength of the emission peak at 20 ◦ C indicated that the opened SWCNT encapsulated water molecules. 17 When temperature decreased with keeping water vapor pressure saturated, the emission wavelength gradually blue-shifted. Because the blue-shift was never observed from closed SWCNTs, the shift originated from a change of the encapsulated water in SWCNT. The blue-shift of the PL emission peak indicates that ϵenv decreases. 18 If ϵenv in the solid phase is smaller than that in the liquid phase, as discussed below, then the blue-shift of the PL spectra can be explained as the liquid-solid transition of water in the SWCNT. The phase transition from liquid to solid phase of water in SWCNTs with temperature decrease is observed by XRD, 14 neutron scattering, 25 PL, 26 and Raman scattering spectroscopy measurements. 11 Here, we regard the blue-shift of the PL emission peak as the phase transition from liquid to solid phase. In Figure 2(b), the temperature dependence of E11 of opened (◦) and closed (•) SWCNTs 5


ACS Nano

Energy Diff. (meV)

0 1.08

1.07

Emission Energy (eV)

-5 °C

5

-40

-20 0 Temperature (°C)

-30 °C -

0

+

6 0

T mp=-32.1±3.6 (°C)

4 0.93

0.92

0.91

-40

-20 0 Temperature (°C) -

0

+

T mp

T mp

5

0

T mp=-17.1±0.61 (°C)

0.9

0.89

-40

0

15

1.01 1.00 0 20 Temperature (°C) 0

+

(9,8) T mp T mp 10 T 0mp= 8 -3.6±0.53 (°C) 6 4

T mp

0.91 0.90 0.89 -20 0 20 Temperature (°C) -

T mp

(11,6)

10

+

T mp=15.9±1.5 (°C)

20



Energy Diff. (meV)

T mp

0

20

-

(10,6)

8

-

T mp T mp (T mp )

(10,5)

-20



Energy Diff. (meV)

(T mp ) T mp T mp 1350 1400 Emission Wavelength (nm)

25

20

Energy Diff. (meV)

10 °C

(8,6)

10

Energy Diff. (meV)

20 °C


(9,8)

Energy Diff. (meV)

;ďͿ

;ĂͿ

Intensity (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 20

-20 0 20 Temperature (°C)

0

T mp

+

T mp

(12,5)

15 10 0

T mp=-16.14±0.59 (°C)

5 0.86 0.85 -40

-20 0 20 Temperature (°C)

Figure 2: (a) PL spectra from (9, 8) SWCNTs measured in the saturated water vapor at different temperatures. (b) Temperature dependence of E11 of SWCNTs with different chiralities measured in the saturated water vapor. In the lower panels, the filled (•) and opened (◦) circles represent the closed and opened SWCNTs, respectively. In the upper panels, the triangles (△) represent the energy difference between the closed and opened SWCNTs. The present data were fitted with hyperbolic tangent curves.

6


Page 7 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

are shown. The temperature dependence of the closed SWCNTs was slight and monotonous, and it did not show any transition features. On the other hands, some of the opened SWCNTs showed the clear blue-shift due to temperature decrease and the blue-shift was observed from SWCNTs with a diameter of 1.02 to 1.23 nm. The continuous phase transition was observed from SWCNTs with dCNT ∼ 1.1 nm in the MD simulation 13 and it was also measured in single-file chain of water molecules in (6,5) SWCNT by using PL spectroscopy. 26 In order to simplify the analysis, the temperature dependence of the energy difference of E11 between opened and closed SWCNTs was approximated by an hyperbolic tangent curve, as shown in Figure 2(b). The hyperbolic tangent curves represented the experimental data well. The 0 inflection point of the curve was defined as the middle melting point (Tmp ) of ice-NTs. In

the case of bulk materials, the melting point is a function of pressure and is determined uniquely for a given temperature. On the other hand, the melting point of ice-NTs was not + one temperature. In Figure 2(b), the upper and lower melting points were defined as Tmp − + − and Tmp , respectively. Tmp and Tmp are the temperatures corresponding to 12 and 88 % of

the total shift amount, respectively. In Figure 2(b), (8, 6) SWCNT did not show clear energy − + , respectively, because of and Tmp shift, and (10, 5) and (10, 6) SWCNTs did not show Tmp

the limitation of the measurement temperature range.

Phase dependence of PL emission wavelength Next, ϵin of encapsulated water in the solid and liquid phases in SWCNTs was estimated using first-principles calculations of DFT. Two types of water-molecule structures in SWCNTs were adopted. For SWCNTs with a diameter of 1.0 nm, the confined water molecules were assumed to form a pentagonal arrangement along the SWCNT circumference, 6 and to form a hydrogen-bond network, with the exception of edge molecules in the solid phase. Figure 3 shows the water-molecule structures used for the calculation. The solid phase of water molecules in an SWCNT is simulated by stacked pentagonal rings, in which each water molecule forms hydrogen bonds with those adjacent to it, with the exception of edge 7


ACS Nano

(a)

(b)

Figure 3: (Color online) Structural models of water for calculation of the electric polarization. (a) Water molecules with a pentagonal arrangement along the circumference of the SWCNT wall are connected to each other, which represents the structure of the solid phase. (b) Water molecules also form a pentagonal arrangement in which their dipole moments are aligned along the tube axis. Blue arrows indicate the direction of the dipole moment of the water molecules.

Intensity (arb. units)

solid phase (with ads.) liquid phase (with ads.) vapor phase (with ads.) empty (w/o ads.)

Dielectric Constant of Encapsulation, εin

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 20

10 5 0

1200

1250

Emission Wavelength, λem (nm)

Figure 4: (Color online) Dependence of PL emission wavelength of SWCNT on the adsorption and encapsulation states of water. (Upper panel) PL spectra measured in vacuum and under water vapor pressure at 360, 430, and 1200 Pa, and at 10 ◦ C. (Lower panel) Open circle (◦) and diamond (⋄) symbols represent the PL emission wavelength with and without an adsorption layer, respectively. Water-adsorbed SWCNTs (◦) are in three different states (empty, liquid water encapsulating, and solid water encapsulating). PL emission wavelength was experimentally measured, while ϵin was obtained by DFT calculation. The curve is calculated on the basis of the theoretical model using the Bethe-Salpeter and Poisson equations.

8


Page 9 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

molecules, as shown in Figure 3(a). ϵin was estimated by evaluation of the local potential profile along the SWCNT under an electric field, which gave ϵin as 5.46. To estimate the maximum value of ϵin in the liquid phase, the water-molecule structure with the dipole moment completely parallel to the tube axis was adopted (Figure 3(b)), which gave ϵin as 10.64. Note that in the case of bulk water, the extrapolated high-frequency permittivity, ϵ∞ is 3.1 in the solid phase 27 and ϵ∞ is 5.2-5.7 in the liquid phase. 28 Therefore, it is reasonable that ϵenv of confined water in the solid phase is smaller than in the liquid phase. In addition, the ϵenv dependence of Eii was simulated by solving the Bethe-Salpeter equation under the k·p approximation combined with the Poisson equation. 29 Figure 4 (lower panel) shows the relationship between emission wavelength and ϵin . We considered a model where a SWCNT is surrounded by a dielectric medium with an effective dielectric constant, ϵ∗out , and encapsulates a cylindrical dielectric medium (ϵin ) with diameter D. When the dielectric constant of the SWCNT (ϵtube ) was chosen as 3.25 and ϵ∗out = 1.26, the calculated emission wavelength corresponded well with that measured from the (10, 5) SWCNT in vacuum (⋄ symbol at ϵin = 1 in Figure 4) and that from a SWCNT with a water adsorption layer 24 (◦ symbol at ϵin = 1), respectively. The relationship between ϵin and the calculated emission wavelength with dCNT /D = 1.7 (solid curve) is shown in Figure 4. The experimental result and that from the two types of theoretical calculations are in excellent agreement. Therefore, we conclude that the peak shift as shown in Figure 2(a) corresponds to the solidliquid phase change.

Melting point of ice-NTs in SWCNTs 0 Tmp () of ice-NTs confined in SWCNTs with 11 different chiralities are shown in Figure 5. + − Because the phase transition was not sharp unlike bulk water, Tmp (H) and Tmp (N) are

also plotted. As reference, the melting points, which are obtained by XRD 14 (2) and Raman scattering spectroscopy 11 (}), and are calculated by molecular dynamics (MD) simulations 0 varied depending on dCNT and the variation was well consistent (◦ 13 and ∗ 30 ), are shown. Tmp

9


ACS Nano

RBM

400

XRD MD cal. MD cal.

(10,8)

(12,4)

PL + T mp

(9,8)

(10,6) (13,2)

(10,5)

(11,3) (8,7)

300

(12,1)

350 (8,6)

(11,7)

Tmp -

(15,2)

(12,5)

(11,6)

(9,7)

250

200

0

(14,3)

Temperature (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 20

Tmp not observed

10 11 12 13 14 SWCNT Tube Diameter (Å)

Figure 5: (Color online) Melting point of ice-NTs confined in SWCNTs with different diameter. Diamonds (), upward triangles (N) and downward triangles (H) represent the middle, lower and upper melting point, respectively. When these melting points were not observed, the cross marks (×) were plotted. The measurement temperature range was indicateed by a vertical dashed line. As references, the melting points measured by XRD (2 14 ), RBM (} 11 ), and calculated by MD simulation (◦ 13 and ∗ 30 ) are shown.

10


Page 11 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

with that of the MD calculation result (◦). 13 The agreement validates that the corresponding of blue-shift of PL peaks, as shown in Figure 2, to the phase transition from liquid to solid phase. On the other hand, the melting point which is obtained by the shift of radial breathing mode peaks in Raman scattering spectra (}) 11 is different from our results. The difference comes from the different interpretation of water states on SWCNTs. K. V. Agrawal et al., found out the two peak shifts of RBM peaks with temperature change and they interpreted that they are caused by the water encapsulation (the vapor-liquid phase transition) and the liquid-solid phase transition, respectively. 11 However, the water adsorption on the outer surface of SWCNTs also shifts RBM peaks. 24 Although Agrawal et al., also observed the water adsorption and desorption effect on RBM peaks, they did not take account of it in the assignment of the RBM peak shifts. While we elucidate four different states of SWCNTs due to water adsorption and the phase transition as shown in Figure 4, Agrawal et al., only found three states at most. It suggests that what Agrawal et al., regarded as the liquidsolid phase transition corresponds to what we assigned as the encapsulation process (the vapor-liquid phase transition). Therefore, the melting point, which Agrawal et al., reported, is extremely higher than ours. In fact, the melting point of water in double-walled carbon nanotube (DWCNT) which Agrawal et al., reported (dCNT = 1.1 nm in Figure 5) agrees with our result, because the adsorption and desorption effect could be ignored in the DWCNT case. 0 According to the result of MD simulation, 13 the variation of Tmp comes from the diameter

difference between ice-NT and SWCNT. The circle marks connected with the dashed lines corresponds to the same n-gonal ice NT encapsulated in SWCNTs with different diameters in MD simulation. In Figure 5, melting point showed the local maximum around dCNT = 1.04, 1.13 and 1.25 nm and it indicates that ice-NTs with three different n values were observed in the present measurement. Based on the results of the MD simulation, 13 the melting points of n-gonal ice NTs were shown with different colors, although the border between different n-gonal ice NTs should be discussed.

11


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

As the MD simulation predicts, 13 the melting point of ice-NT varied with slight difference in dCNT . The PL measurement of an individual SWCNT experimentally revealed for the first time that the melting point of ice-NTs is sensitive to the dCNT change in the Angstrom scale. The melting point of ice-NT have been reported by XRD measurement and these results (2) are shown in Figure 5. In the XRD measurement, the SWCNT samples has diameter distribution, which is represented by the bar of x-axis. The large distribution of dCNT makes it difficult to observe the detailed features of the melting points.

Conclusions In the present study, the melting point of ice-NTs encapsulated in SWCNTs was measured and the precise dCNT dependence was experimentally revealed. The phase transition between solid and liquid phases was detected as the change of PL emission energy, which was confirmed by first-principle calculations. The melting point of ice-NTs clearly depended on dCNT and the dependence agreed with the results which have been reported by MD simulation. SWCNTs are ideal test tubes for the confinement effects and PL spectroscopy is the powerful tool for investigation of phase states of materials confined in SWCNTs. Precisely controlling dCNT in sub-nanometer resolution, the details of the confinement effects on the melting point of ice-NTs is elucidated.

Methods Synthesis of suspended and opened SWCNTs Suspended SWCNTs were directly grown between a pair of silica pillars. The silica pillar structure were fabricated using a lithographic technique with silica substrates, and a silicon layer was deposited with a thickness of 40 nm, except for the pillar top area. Cobalt with a nominal thickness of 0.01 nm was then deposited on the substrates with a vacuum evaporator.

12


Page 12 of 20

Page 13 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

The substrate was heated in an Ar/H2 mixed gas (H2 3% in volume), whereby the cobalt on the silicon layer formed CoSi2 , which was commensurate to the silicon lattice. 31 Cobalt nanoparticles were formed only on the pillar top area, and served as a catalyst. SWCNTs were synthesized by the alcohol catalytic chemical vapor deposition (CVD) method 32 using ethanol bubbled with Ar/H2 mixed gas (50 sccm at 93 kPa). The growth temperature was 870 ◦ C and the growth time was 10 min. SWCNTs were grown only from the pillar top area. In order to open SWCNTs, oxidation treatment was performed. Suspended SWCNTs were heated at 500 ◦ C in water vapor (1000 Pa).

PL Spectroscopy A Ti:sapphire laser was used as an excitation laser for photoluminescence (PL). The wavelength of the excitation laser ranged from 700 to 830 nm. The diameter and total power of the laser spot were approximately 18.4 µm and 6.25 µW, respectively. The low power density avoids additional heating of SWCNTs. Some SWCNTs, which were bundled with semiconducting SWCNTs, showed a red-shift of the optical transition energy. 20 Other SWCNTs exhibited a satellite peak in the lower energy side of the main emission peak, which indicated that hydrogen atoms were chemically adsorbed on them. 21 From among suspended SWCNTs, SWCNTs with a sharp and intensive PL emission peak at appropriate optical transition energies 33 and without any satellite peaks were selected. During PL measurement, the SWCNT samples was set in an environmental chamber. Through a quartz window of the chamber, the excitation laser irradiation was performed and scattering light was collected with an objective lens. In the chamber, the temperature of SWCNTs and water vapor was controlled with a Peltier temperature controller (from −40 to 25 ◦ C) and the water vapor pressure was controlled from 0 to 3000 Pa with a vacuum pump and a mass flow controller. The chirality of SWCNTs were determined by the combination of E22 and E11 . 33 In this 13


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

study, SWCNTs with 16 different chiralities were investigated ((8, 6), (12, 1), (11, 3), (8, 7), (10, 5), (9, 7), (10, 6), (13, 2), (12, 4), (9, 8), (11, 6), (12, 5), (10, 8), (14, 3), (11, 7) and (15, 2)), and the dCNT ranged from 0.95 to 1.26 nm.

Calculation of the environmental Effect In order to investigate the environmental effects on PL emission wavelength, the dielectric constant of encapsulated water was calculated. The dielectric constant of liquid and solid water confined in nanopores, ϵin , was estimated from first-principles calculations based on density functional theory (DFT). 34,35 Because of the time scale of exciton dynamics, 36 we can assume that only electronic polarization, which corresponds to the the extrapolated highfrequency permittivity (ϵ∞ ), contributes to ϵin . To investigate the static ϵin for tubular forms of liquid and solid water, the averaged local potential profiles along the water tubes were evaluated under an electric field running parallel to the nanotubes. The exchange-correlation energy of interacting electrons was treated in the local density approximation (LDA) with a functional form fitted to the Ceperley-Alder result. 37,38 Ultrasoft pseudopotentials 39 were used to describe the electron-ion interaction, in which the valence wave functions and charge density were expanded in terms of a plane-wave basis set with cutoff energies of 25 and 225 Ry, respectively. The external electric field was treated using the effective screening medium (ESM) method. 40

Acknowledgement A part of this work was financially supported by JSPS KAKENHI Grant Number JP16H02079. The authors aknowlege support from Nanocarbon Research Division and Water Frontier Science & Technology Research Center, Research Institute of Science & Technology, Tokyo University of Science.

14


Page 14 of 20

Page 15 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

References (1) Morishige, K.; Kawano, K. Freezing and Melting of Water in a Single Cylindrical pore: The Pore-Size Dependence of Freezing and Melting Behavior. J. Chem. Phys. 1999, 110, 4867–4872. (2) Iijima, S.; Ichihashi, T. Single-Shell Carbon Nanotubes of 1-nm Diameter. Nature 1993, 363, 603–605. (3) Koga, K.; Gao, G. T.; Tanaka, H.; Zeng, X. C. Formation of Ordered Ice Nanotubes Inside Carbon Nanotubes. Nature 2001, 412, 802–805. (4) Kolesnikov, A. I.; Zanotti, J. M.; Loong, C. K.; Thiyagarajan, P.; Moravsky, A. P.; Loutfy, R. O.; Burnham, C. J. Anomalously Soft Dynamics of Water in a Nanotube: A Revelation of Nanoscale Confinement. Phys. Rev. Lett. 2004, 93, 035503–1–035503–4. (5) Ghosh, S.; Ramanathan, K. V.; Sood, A. K. Water at Nanoscale Confined in SingleWalled Carbon Nanotubes Studied by NMR. Europhys. Lett. 2004, 65, 678–684. (6) 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. (7) Byl, O.; Liu, J. C.; Wang, Y.; Yim, W. L.; Johnson, J. K.; Yates-Jr., J. T. Unusual Hydrogen Bonding in Water-Filled Carbon Nanotubes. J. Am. Chem. Soc. 2006, 128, 12090–12097. (8) Cambré, S.; Wenseleers, W. Separation and Diameter-Sorting of Empty (End-Capped) and Water-Filled (Open) Carbon Nanotubes by Density Gradient Ultracentrifugation. Angew. Chem. Int. Ed. 2011, 50, 2764–2768. (9) Cambré, S.; Santos, S. M.; Wenseleers, W.; Nugraha, A. R. T.; Saito, R.; Cognet, L.;

15


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Lounis, B. Luminescence Properties of Individual Empty and Water-Filled SingleWalled Carbon Nanotubes. ACS Nano 2012, 6, 2649–2655. (10) Paineau, E.; Albouy, P.-A.; Rouzière, S.; Orecchini, A.; Rols, S.; Launois, P. X-ray Scattering Determination of the Structure of Water during Carbon Nanotube Filling. Nano Lett. 2013, 13, 1751–1756. (11) Agrawal, K. V.; Shimizu, S.; Drahushuk, L. W.; Kilcoyne, D.; Strano, M. S. Observation of Extreme Phase Transition Temperatures of Water Confined Inside Isolated Carbon Nanotubes. Nat. Nanotechnol. 2016, 12, 267–273. (12) Bernardina, S. D.; Paineau, E.; Brubach, J.-B.; Judeinstein, P.; Rouzière, S.; Launois, P.; Roy, P. Water in Carbon Nanotubes: The Peculiar Hydrogen Bond Network Revealed by Infrared Spectroscopy. J. Am. Chem. Soc. 2016, 138, 10437–10443. (13) Takaiwa, D.; Hatano, I.; Koga, K.; Tanaka, H. Phase Diagram of Water in Carbon Nanotubes. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 39–43. (14) Kyakuno, H.; Matsuda, K.; Yahiro, H.; Inami, Y.; Fukuoka, T.; Miyata, Y.; Yanagi, K.; Maniwa, Y.; Kataura, H.; Saito, T.; Yumura, M.; Iijima, S. Confined Water Inside Single-Walled Carbon Nanotubes: Global Phase Diagram and Effect of Finite Length. J. Chem. Phys. 2011, 134, 244501–1–244501–14. (15) Bachilo, S. M.; Strano, M. B.; Kittrell, C.; Hauge, R. H.; Smalley, R. E.; Weisman, R. B. Structure-Assigned Optical Spectra of Single-Walled Carbon Nanotubes. Science 2002, 298, 2361–2366. (16) Lefebvre, J.; Homma, Y.; Finnie, P. Bright Band Gap Photoluminescence from Unprocessed Single-Walled Carbon Nanotubes. Phys. Rev. Lett. 2003, 90, 217401–1–217401– 4.

16


Page 16 of 20

Page 17 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

(17) Chiashi, S.; Hanashima, T.; Mitobe, R.; Nagatsu, K.; Yamamoto, T.; Homma, Y. Water Encapsulation Control in Individual Single-Walled Carbon Nanotubes by Laser Irradiation. J. Phys. Chem. Lett. 2014, 5, 408–412. (18) Perebeinos, V.; Tersoff, J.; Avouris, P. Scaling of Excitons in Carbon Nanotubes. Phys. Rev. Lett. 2004, 92, 257402–1–257402–4. (19) Ohno, Y.; Iwasaki, S.; Murakami, Y.; Kishimoto, S.; Maruyama, S.; Mizutani, T. Chirality-Dependent Environmental Effects in Photoluminescence of Single-Walled Carbon Nanotubes. Phys. Rev. B 2006, 73, 235427–1–235427–5. (20) Lefebvre, J.; Finnie, P. Photoluminescence and Förster Resonance Energy Transfer in Elemental Bundles of Single-Walled Carbon Nanotubes. J. Phys. Chem. C 2009, 113, 7536–7540. (21) Nagatsu, K.; Chiashi, S.; Konabe, S.; Homma, Y. Brightening of Triplet Dark Excitons by Atomic Hydrogen Adsorption in Single-Walled Carbon Nanotubes Observed by Photoluminescence Spectroscopy. Phys. Rev. Lett. 2010, 105, 157403–1–157403–4. (22) Ghosh, S.; Bachilo, S. M.; Simonette, R. A.; Beckingham, K. M.; Weisman, R. B. Oxygen Doping Modifies Near-Infrared Band Gaps in Fluorescent Single-Walled Carbon Nanotubes. Science 2010, 330, 1656–1659. (23) Chiashi, S.; Watanabe, S.; Hanashima, T.; Homma, Y. Influence of Gas Adsorption on Optical Transition Energies of Single-Walled Carbon Nanotubes. Nano Lett. 2008, 8, 3097–3101. (24) Homma, Y.; Chiashi, S.; Yamamoto, T.; Kono, K.; Matsumoto, D.; Shitaba, J.; Sato, S. Photoluminescence Measurements and Molecular Dynamics Simulations of Water Adsorption on the Hydrophobic Surface of a Carbon Nanotube in Water Vapor. Phys. Rev. Lett. 2013, 110, 157402–1–157402–4.

17


ACS Nano 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(25) de Souza, N. R.; Kolesnikov, A. I.; Burnham, C. J.; Loong, C.-K. Structure and Dynamics of Water Confined in Single-Wall Carbon Nanotubes. J. Phys.: Condens. Matter 2006, 18, S2321–S2334. (26) Ma, X.; Cambré, S.; Wenseleers, W.; Doorn, S. K.; Htoon, H. Quasiphase Transition in a Single File of Water Molecules Encapsulated in (6,5) Carbon Nanotubes Observed by Temperature-Dependent Photoluminescence Spectroscopy. Phys. Rev. Lett. 2017, 118, 027402–1–027402–7. (27) Auty, R. P.; Cole, R. H. Dielectric Properties of Ice and Solid D2 O. J. Chem. Phys. 1952, 20, 1309–1314. (28) Kaatze, U. Complex Permittivity of Water as a Function of Frequency and Temperature. J. Chem. Eng. Data 1989, 34, 371–374. (29) Ando, T. Environment Effects on Excitons in Semiconducting Carbon Nanotubes. J. Phys. Soc. Jpn. 2010, 79, 024706–1–024706–10. (30) Raju, M.; van Duin, A.; Ihme, M. Phase Transitions of Ordered Ice in Graphene Nanocapillaries and Carbon Nanotubes. Sci. Rep. 2018, 8, 3851–1–3851–11. (31) Homma, Y.; Kobayashi, Y.; Ogino, T.; Takagi, D.; Ito, R.; Jung, Y. J.; Ajayan, P. M. Role of Transition Metal Catalysts in Single-Walled Carbon Nanotube Growth in Chemical Vapor Deposition. J. Phys. Chem. B 2003, 107, 12161–12164. (32) Maruyama, S.; Kojima, R.; Miyauchi, Y.; Chiashi, S.; Kohno, M. Low-Temperature Synthesis of High-Purity Single-Walled Carbon Nanotubes from Alcohol. Chem. Phys. Lett. 2002, 360, 229–234. (33) Lefebvre, J.; Finnie, P. Polarized Photoluminescence Excitation Spectroscopy of SingleWalled Carbon Nanotubes. Phys. Rev. Lett. 2007, 98, 167406–1–167406–4.

18


Page 18 of 20

Page 19 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

(34) Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136, B864– B871. (35) Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140, A1133–A1138. (36) Sarpkaya, I.; Zhang, Z.; Walden-Newman, W.; Wang, X.; Hone, J.; Wong, C. W.; Strauf, S. Prolonged Spontaneous Emission and Dephasing of Localized Excitons in Air-Bridged Carbon Nanotubes. Nat. Commun. 2013, 4, 2152–1–2152–8. (37) Perdew, J. P.; Zunger, A. Self-Interaction Correction to Density-Functional Approximations for Many-Electron Systems. Phys. Rev. B 1981, 23, 5048–5079. (38) Ceperley, D. M.; Alder, B. J. Ground State of the Electron Gas by a Stochastic Method. Phys. Rev. Lett. 1980, 45, 566–569. (39) Vanderbilt, D. Soft Self-Consistent Pseudopotentials in a Generalized Eigenvalue Formalism. Phys. Rev. B 1990, 41, 7892–7895. (40) Otani, M.; Sugino, O. First-Principles Calculations of Charged Surfaces and Interfaces: A Plane-Wave Nonrepeated Slab Approach. Phys. Rev. B 2006, 73, 115407–1–115407– 11.

19


ACS Nano

Graphical TOC Entry 300

Melting Point (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 20

&17 ZDWHU PROHFXOHV

PL XRD MD cal.

250

200

10

11

12

13

14

0HOWLQJ 3RLQW

LFH17

SWCNT Tube Diameter (Å)

20


Confinement Effect of Sub-Nanometer Difference on Melting Point of

Recommend Documents