Tubular Titanates: Alkali-Metal Ion-Exchange Features and Carbon

Subscriber access provided by Drexel University Libraries

Materials and Interfaces

Tubular Titanates: Alkali-Metal Ion-Exchange Features and Carbon Dioxide Adsorption at Room Temperature Eri Uematsu, Atsushi Itadani, Hideki Hashimoto, Kazuyoshi Uematsu, Kenji Toda, and Mineo Sato Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05662 • Publication Date (Web): 11 Mar 2019 Downloaded from http://pubs.acs.org on March 19, 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 26 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

Industrial & Engineering Chemistry Research

Tubular Titanates: Alkali-Metal Ion-Exchange Features and Carbon Dioxide Adsorption at Room Temperature Eri Uematsu,† Atsushi Itadani,‡,* Hideki Hashimoto,¶ Kazuyoshi Uematsu,† Kenji Toda,† and Mineo Sato§,**

†

Graduate School of Science and Technology, Niigata University, 8050 Ikarashi, 2-no-cho,

Nishi-ku, Niigata, 950-2181, Japan ‡

Department of Human Sciences, Obihiro University of Agriculture and Veterinary Medicine,

Inada-cho, Obihiro, Hokkaido, 080-8555, Japan ¶

Department of Applied Chemistry, School of Advanced Engineering, Kogakuin University,

2665-1 Nakano-cho, Hachioji, Tokyo, 192-0015, Japan §

Department of Chemistry and Chemical Engineering, Niigata University, 8050 Ikarashi,

2-no-cho, Nishi-ku, Niigata, 950-2181, Japan

Corresponding authors: *

[email protected] (A. Itadani); **[email protected] (M. Sato)

1 ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 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

ABSTRACT: Tubular titanates (T-TiO2) are interesting materials considering their large specific surface area and ability for cationic substitution in the tubes. In this study, we systematically examined the alkali-metal ion-exchange features of T-TiO2 and clarified their CO2 adsorption properties at room temperature in details. Assuming the resulting ion exchange to be affected by hydration, T-TiO2 ion-exchange samples exhibited more intense exchange levels with an increasing alkali-metal ionic radius. Furthermore, the alkali-metal ions exchanged were confirmed from the EDS maps to be uniformly distributed in the samples. CO2 adsorption capabilities were found to decrease with increasing the ionic radius of the alkali-metal ions exchanged. We rationalized the electrostatic forces between CO2 and the alkali-metal ion-exchanged titanate nanotubes as the dominant driving force.

KEY WORDS: Titanate nanotube; Replacement ion; CO2; Infrared spectroscopy


Page 2 of 26

Page 3 of 26 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


INTRODUCTION After Kasuga et al. reported on a simple synthesis for producing tubular titanates (i.e., a hydrothermal treatment of titanium dioxide with an aqueous solution of NaOH),1,2 these materials have been extensively investigated targeting applications such as ion exchangers, catalysts, and adsorbents.3–16 Bavykin et al.7 and Ma et al.8 studied alkali-metal ion exchange into nanotubular titanates, and Sun and Li examined the transition-metal ion-exchange features of the tubular titanates.9 Kitano et al. and Wada et al. found that the protonated titanate nanotubes exhibit high catalytic activity for a reaction proceeding effectively under acidic conditions.10–12 Moreover, Bavykin et al. reported the adsorption of dihydrogen molecule into multilayered titania nanotubes,13 and Toledo-Antonio et al. studied the adsorption of carbon monoxide onto titania nanotubes.14 Particularly to carbon dioxide adsorption, Upendar et al. reported the use of sodium or potassium titanate nanotubes under low temperature conditions, and Bhattacharyya et al. employed titania nanotubes and platinized titania nanotubes.15,16 However, the capability of ion exchange with other cations for certain species (e.g., sodium and hydrogen cations) existing in the tubular titanates and/or the ability to adsorb different gaseous molecules on the ion-exchanged titanate nanotubes have not been elucidated completely despite the abovementioned reports describe the ion-exchange (or the intercalation) properties and the adsorption capabilities of tubular titanates. It is, therefore, important to clarify the ion-exchange features of tubular titanates as well as the effect of the exchanged cations on gas adsorption properties to infer about the potential applications of tubular titanates as ion exchangers and adsorbents. As such, the final goal of the present study is to gather further information related to the alkali-metal ion-exchange features of the sodium-form titanate nanotubes and to clarify the CO2 adsorption properties on the ion-exchanged titanate nanotubes at room temperature.

EXPERIMENTAL Sodium-form titanate nanotubes were prepared via the hydrothermal treatment of 3 ACS Paragon Plus Environment


approximately 4 g of anatase-type titania (TiO2) with a purity of 98.5% (Kanto Chemical Co., Inc., Japan) in 100 cm3 of an aqueous solution of 10 M NaOH for 72 h at 413 K using a Teflon-lined autoclave, referring to the literature.1,2,17 The precipitate obtained was repeatedly washed with distilled water until the filtrate reached pH 7, followed by drying at 343 K. The thus synthesized sodium-form titanate nanotubes are hereafter designated as Na+-T-TiO2. The cation exchange of Na+ ions existing in the titanate nanotubes with other alkali-metal ions was performed as follows: approximately 1 g of Na+-T-TiO2 was dispersed in 100 cm3 of an aqueous solution of 0.005 M of LiCl, KCl, RbCl, or CsCl with stirring for 1 h at room temperature. This process was repeated several times to obtain the Li+-, K+-, Rb+-, or Cs+-T-TiO2 samples with different ion-exchange levels. These samples obtained were thoroughly washed with distilled water, followed by drying at 343 K. The contents of alkali-metal ions in the T-TiO2 samples were determined by atomic absorption spectrometry (AA-7000F, Shimadzu). The sample was dispersed in 50 cm3 of distilled water, followed by adding 60% perchloric acid (30 cm3). After the solution was stirred at 353 K for 10 min, the solution was filtered to prepare the 250 cm3 diluted solution by distilled water. The cation exchange levels of the samples were evaluated by assuming that one Na+ ion is exchanged by one Li+, K+, Rb+, or Cs+ ion: (the amount of decreased Na+)/(the amount of Na+ contained in the mother Na+-T-TiO2 sample) × 100 (%). Naturally, the ion-exchange levels evaluated were also consistent with the amounts of the Li+, K+, Rb+, or Cs+ ion contained in the samples. The samples prepared are represented as M +-T-TiO2(X) (M +

: exchanged alkali-metal ion; X: ion-exchange level in percentage). CO2 gas (purity of >99.995%) used as an adsorbate was purchased from Taiyo Nippon

Sanso Co., Ltd. The powder X-ray diffraction (XRD) profiles were collected using an MX-Labo (MAC Science Co. Ltd.) diffractometer with monochromatic Cu Kα radiation (λ = 0.154056 nm) under 25 mA and 40 kV. The adsorption and desorption isotherms of N2 at 77 K were measured with a Micromeritics TriStar II 3020 to evaluate the specific surface area and the pore structure of the samples. Prior to the N2 adsorption, each sample was degassed at room 4 ACS Paragon Plus Environment

Page 4 of 26

Page 5 of 26 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


temperature for 2 h. The specific surface areas of the samples were determined by applying the Brunauer–Emmett–Teller (BET) equation18 to the adsorption isotherms of N2 obtained. The pore-size distributions were evaluated from the desorption data using the Barrett–Joyner–Halenda (BJH) method.19 The thermogravimetry (TG) and differential thermal analysis for the samples were performed using an EXSTAR6000 (Seiko Instruments) at a heating rate of 10 K min–1 from room temperature to 1258 K under air atmosphere. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) measurements of the samples were performed using a JEOL JEM-2100F microscope coupled with an energy dispersive X-ray spectrometer (EDS, JED-2300T, JEOL). The CO2 adsorption experiment was performed at 298 K using a volumetric adsorption apparatus and the equilibrium pressure of the gas phase was monitored using an MKS Baratron pressure sensor. The samples were degassed at 673 K for 2 h. Fourier transform infrared (FT-IR) spectra (64 times were accumulated with a spectral resolution of 4 cm–1) were recorded at room temperature on a JASCO FT/IR-4200 spectrometer with a TGS detector. The samples were pressed into a 10-mm-diameter pellet and were placed in a cell made of quartz with KRS-5 windows, capable of in situ pretreatment and gas dosage.20

RESULTS AND DISCUSSION Characterization of Tubular Titanates. Initially, we confirmed from TEM pictures, XRD profiles, and N2 adsorption/desorption measurements that every sample displays a tubular structure. Shown in Figure 1 are representative TEM pictures of the mother Na+-T-TiO2 sample and its ion-exchanged form (here, Cs+-T-TiO2). The tubular structure of Na+-T-TiO2 is maintained after treatment with an ion-exchange solution, forming multilayer structures. The XRD patterns of the samples of Na+-T-TiO2 and their ion-exchanged forms are presented in Figure 2. For Na+-T-TiO2, the XRD peaks obtained at around 2θ = 10, 25, 28, and 48 degrees are responsible for the diffraction peaks at the (001), (110), (211), and (020) 5 ACS Paragon Plus Environment


planes, respectively.3,7,17 The ion-exchanged samples showed similar XRD patterns to that for Na+-T-TiO2, indicating that these samples retain their tubular structure even after ion-exchange operation. However, there is a clear shift of the peak at 2θ = 10 degrees (assigned to the (001) plane) toward a lower angle corresponding with increasing the ionic radius of alkali metal and ion-exchange level of the samples. When increasing the ion-exchange levels of the samples, in addition, the positions of the peaks at 2θ = 10 degrees were also clearly indicated to shift toward a lower angle (Figures S1–S4 in Supporting Information). We interpret these observations as a result of the titanate layers’ expansion due to the exchange of the larger size of the alkali-metal ion for Na+ ion into the layers. The peaks observed at around 2θ = 24 and 28 degrees change in terms of their intensities ratios, believed to be due to the distortion of the lattice structure on the tubular samples by the ion exchange.21,22 The specific surface area of Na+-T-TiO2 (ca. 180 m2 g–1) is much larger than that of the starting material, anatase-type TiO2 (ca. 20 m2 g–1) (Table 1 and Figure S5 in Supporting Information), evidencing the tubular characteristics of Na+-T-TiO2. Moreover, the ion-exchanged samples also showed large specific surface areas, with pore diameter sizes of ca. 3.5 nm for every sample (Table 1 and Figures S6–S10 in Supporting Information). For the specific surface areas and pore diameter sizes, a large difference was hardly confirmed between samples, regardless of the sizes of the exchanged alkali-metal ions. Figure 3 shows the Raman spectra for Na+-T-TiO2 and their ion-exchanged forms. Due to the tubular structure,23,24 the characteristic bands appear at around 270, 450, 660, 705, 820, and 910 cm–1 for all samples. Raman data also confirm that the ion-exchanged samples retain their tubular structure after the ion-exchange operation. The band at 450 cm–1 is assigned to the Ti–O–Ti framework vibration25,26 and the bands around 270 and 660 cm–1 are due to the Ti–O–M (here, M : alkali-metal ions) framework vibration in the titanate structure containing cation.27 The peak at around 270 cm–1 is found to split in two. We rationalized the latter observation as a result of local lattice distortions.28,29 The bands at 820 and 910 cm–1 are assigned to the cation species coordinated to oxygen and the Ti–O bond.25,30,31 Notably, the 6 ACS Paragon Plus Environment

Page 6 of 26

Page 7 of 26 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


bands at 820 and 910 cm–1 shift to lower wavenumbers with a decreasing ionic radius of the alkali metal.32,33 Since alkali-metal ions are monovalent, the attractiveness of the electron cloud of the framework oxygen of tubular titanate is expected to increase with the decrease in ionic radius. Consequently, the Ti–O bond weakens as the ionic radius decreases, and the bands at 820 and 910 cm–1 appear at lower wavenumbers. From the results discussed above, all samples indicate tubular structure. Illustrated in Figure 4 is the relationship between the number of exchange times performed and the ion-exchange level or the amount of the residual Na+ ions. For all alkali-metal ions, the ion-exchange levels increase steeply in the initial stage of the exchange, increasing with the increase of exchange times until they reach a saturation point. On the other hand, the residual Na+ ions in the samples decrease with increasing ion-exchange levels. As clearly seen in this figure, the ion-exchange level for the Na+-T-TiO2 sample is found to be larger with increasing the ionic radius of alkali-metal ions. This result indicates that the extent of the ion hydration influences the ion-exchange level in aqueous environments. The larger the ionic valence or the smaller the ionic radius, the greater is the number of water molecules attracted to the ion (solvation). Assuming solvation to influence the resulting interaction of the cation and the layers of Na+-T-TiO2, it is reasonable to expect greater ion-exchange levels for less hydrated ions, where a closer distance between material and ion is found. Such a view was supported from the water contents of the samples evaluated by the TG measurement. Study of CO2 Adsorption. The CO2 adsorption on Na+-T-TiO2 and their ion-exchanged forms were examined at 298 K. Here, we adopted the well-known process of CO2 adsorption to probe the active sites existing in the tubular titanates.34–36 The adsorption isotherms of CO2 obtained at 298 K on the respective tubular titanates are shown in Figure 5. For every sample, the adsorbed CO2 amounts increase steeply in the lower pressure region and linearly with increasing pressure. Therefore, the isotherms obtained seem to be of Langmuir-type at the lower pressure region and of Henry-type at the higher pressure. In addition, the adsorption amount is found to decrease with increasing the ionic radius of alkali-metal ions exchanged, except for the mother Na+-T-TiO2. The charge density of the alkali-metal ions increases with 7 ACS Paragon Plus Environment


decreasing their ionic radius and as a result, their polarization function is larger. Therefore, with decreasing ionic radius of alkali-metal ions, the static interaction between the cation and CO2 is stronger, consequently enhancing CO2 adsorption. We also prepared samples in which almost all Na+ ions in the mother nanotubes were exchanged for another alkali-metal ion by using high concentration (0.1 M) solutions. Every sample was evident to take the tubular structure (Figures S11–S14 in Supporting Information), as with the samples presented above. The TEM pictures of the ion-exchanged form (here, Cs+-T-TiO2) are shown in Figure 6. From the EDS maps, the cesium ions exchanged in the titanate tube were found to be uniformly distributed. Here, for these samples, we checked the CO2 adsorption properties using IR spectroscopy. Figure 7 shows the IR spectra for the asymmetric stretching (ν3) mode of the CO2 species adsorbed on the samples at room temperature. For all samples, a band appears at the region observed for the ν3 mode of CO2. The ν3 mode of the free CO2 is well-known to exhibit vibration at 2349 cm–1.34–37 The maximum wavenumber of absorption peak observed was 2354 cm–1 for Li+-T-TiO2(94), 2352 cm–1 for Na+-T-TiO2, 2346 cm–1 for K+-T-TiO2(89), 2344 cm–1 for Rb+-T-TiO2(82), and 2342 cm–1 for Cs+-T-TiO2(82). Clearly, maximum absorption shifts toward lower wavenumbers with an increasing ionic radius of the alkali-metal ions exchanged in the tubes. Here, we obtained a linear relationship between the ionic radius of alkali-metal ions exchanged and the values of the ν3 mode observed (Figure 8). Such tendency has also been observed for CO or CO2 adsorption onto alkali-metal ions exchanged zeolites.38–40 Bearing this in mind, we address electrostatic forces as the dominant driving force for the interaction of the alkali-metal ion-exchanged titanate nanotubes with CO2. In Figure 9, IR spectra taken for Li+-T-TiO2 exposed to CO2 at different equilibrium pressures are compared. Each IR spectrum observed was resolved into at least three components by curve-fitting techniques using the least-squares method: 2359, 2354, and 2347 cm–1. When exposing to 0.8 kPa CO2, the band at 2354 cm–1 increases in intensity, compared with the other two bands. The band at 2354 cm–1 is assigned to the linear-type complex Li+•••O=C=O.34–36 Referring to the literature,35 the appearance of the band at 2359 cm–1 8 ACS Paragon Plus Environment

Page 8 of 26

Page 9 of 26 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


suggests the existence of the double-coordinated CO2 molecule, and the band at 2347 cm–1 remains presently unknown. Finally, we describe the adsorption and desorption behavior of CO2 for the presented samples from the point of view of application (Figure S15 in Supporting Information). The absolute amount of CO2 adsorbed on the present samples was few, in comparison with that on other materials such as zeolites, carbon, and MOF studied recently.41–43 However, the present samples seem to strongly adsorb part of CO2, although many reports have been made for the physisorption feature of CO2. The CO2 adsorbed strongly on the present samples were completely desorbed by the evacuation at 673 K; the samples were completely recovered after re-evacuating the sample at 673 K. Furthermore, the samples were found to be stable, since the isotherm obtained after re-evacuating the sample at 673 K almost overlapped with the isotherm obtained after first evacuation at 673 K (initial state). Also, the CO2 capacity did not make much difference between the sample containing some water and the sample not containing the water (Figure S16 in Supporting Information). Therefore, it was indicated that the presented samples enough withstand repeated use.

CONCLUSIONS This study investigated the ion-exchange and CO2 adsorption properties of titanate nanotubes systematically. We clarified the relationship between the alkali-metal ion-exchange levels for the titanate nanotubes and the ionic radius of alkali-metal ions exchanged and/or between the CO2 adsorption features of titanate nanotubes and the ionic radius of alkali-metal ions exchanged. For the ion-exchange features of the sodium-form titanate nanotubes, the alkali-metal ion-exchange level increased as the ionic radius of the alkali-metal ions increased, considering that the extent of the hydration of the ion effects on the ion-exchange level. For the CO2 adsorption features, the amount of CO2 adsorbed on the samples decreased with increasing the ionic radius of alkali-metal ions exchanged. The static interaction between the metal ions and CO2 is weaker, and it was considered that the adsorption amounts of CO2 9 ACS Paragon Plus Environment


decrease. The present results may indicate potential for the development of new materials for CO2-separation or CO2-fixation.

ASSOCIATED CONTENT Supporting Information Figures S1–S4: XRD patterns of Li+-T-TiO2, K+-T-TiO2, Rb+-T-TiO2, and Cs+-T-TiO2. Figure S5: Adsorption-desorption isotherms of N2 at 77 K for Na+-T-TiO2 and anatase-type TiO2. Figure S6: Pore size distribution for Na+-T-TiO2. Figures S7–S10: Adsorption-desorption isotherms of N2 at 77 K and pore size distributions for Li+-T-TiO2, K+-T-TiO2, Rb+-T-TiO2, and Cs+-T-TiO2 with different ion-exchange levels. Figure S11: XRD patterns of Li+-T-TiO2, K+-T-TiO2, Rb+-T-TiO2, and Cs+-T-TiO2. Figure S12: Adsorption-desorption isotherms of N2 at 77 K for Li+-T-TiO2, K+-T-TiO2, Rb+-T-TiO2, and Cs+-T-TiO2. Figure S13: Pore size distributions for Li+-T-TiO2, K+-T-TiO2, Rb+-T-TiO2, and Cs+-T-TiO2. Figure S14: Raman spectra of Li+-T-TiO2, K+-T-TiO2, Rb+-T-TiO2, and Cs+-T-TiO2. Figure S15: Adsorption isotherms of CO2 at 298 K on Li+-T-TiO2(94). Figure S16: Adsorption isotherms of CO2 at 298 K on Na+-T-TiO2.

AUTHORS INFORMATION Corresponding Authors E-mail: [email protected] (A. I.); [email protected] (M. S.). Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was partly supported by The Uchida Energy Science Promotion Foundation. Our special thanks are due to Mr. Y. Oizumi at Office for Environment and Safety at Niigata 10 ACS Paragon Plus Environment

Page 10 of 26

Page 11 of 26 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


University for his cooperation in the atomic absorption spectrometry.



REFERENCES (1) Kasuga, T.; Hiramatsu, M.; Hoson, A.; Sekino, T.; Niihara, K. Formation of Titanium Oxide Nanotube. Langmuir 1998, 14, 3160. (2) Kasuga, T.; Hiramatsu, M.; Hoson, A.; Sekino, T.; Niihara, K. Titania, Nanotubes Prepared by Chemical Processing. Adv. Mater. 1999, 11, 1307. (3) Bavykin, D. V.; Friedrich, J. M.; Walsh, F. C. Protonated Titanates and TiO2 Nanostructured Materials: Synthesis, Properties, and Applications. Adv. Mater. 2006, 18, 2807. (4) Nian, J.-N.; Chen, S.-A.; Tsai, C.-C.; Teng, H. Structural Feature and Catalytic Performance of Cu Species Distributed over TiO2 Nanotubes. J. Phys. Chem. B 2006, 110, 25817. (5) Shankar, K.; Basham, J. I.; Allam, N. K.; Varghese, O. K.; Mor, G. K.; Feng, X.; Paulose, M.; Seabold, J. A.; Choi, K.-S.; Grimes, C. A. Recent Advances in the Use of TiO2 Nanotube and Nanowire Arrays for Oxidative Photoelectrochemistry. J. Phys. Chem. C 2009, 113, 6327. (6) Lee, K.; Mazare, A.; Schmuki, P. One-Dimensional Titanium Dioxide Nanomaterials: Nanotubes, Chem. Rev. 2014, 114, 9385. (7) Bavykin, D. V.; Walsh, F. C. Kinetics of Alkali Metal Ion Exchange into Nanotubular and Nanofibrous Titanates. J. Phys. Chem. C 2007, 111, 14644. (8) Ma, R.; Sasaki, T.; Bando, Y. Alkali Metal Cation Intercalation Properties of Titanate Nanotubes. Chem. Commun. 2005, 948. (9) Sun, X.; Li, Y. Synthesis and Characterization of Ion-Exchangeable Titanate Nanotubes. Chem. Eur. J. 2003, 9, 2229. (10) Kitano, M.; Nakajima, K.; Kondo, J. N.; Hayashi, S.; Hara, M. Protonated Titanate Nanotubes as Solid Acid Catalyst. J. Am. Chem. Soc. 2010, 132, 6622. (11) Kitano, M.; Wada, E.; Nakajima, K.; Hayashi, S.; Miyazaki, S.; Kobayashi, H.; Hara, M. Protonated Titanate Nanotubes with Lewis and Brønsted Acidity: Relationship between Nanotube Structure and Catalytic Activity. Chem. Mater. 2013, 25, 385. 12 ACS Paragon Plus Environment

Page 12 of 26

Page 13 of 26 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


(12) Wada, E.; Kitano, M.; Nakajima, K.; Hara, M. Effect of Preparation Conditions on the Structural and Acid Catalytic Properties of Protonated Titanate Nanotubes. J. Mater. Chem. A 2013, 1, 12768. (13) Bavykin, D. V.; Lapkin, A. A.; Plucinski, P. K.; Friedrich, J. M.; Walsh, F. C. Reversible Storage of Molecular Hydrogen by Sorption into Multilayered TiO2 Nanotubes. J. Phys. Chem. B 2005, 109, 19422. (14) Toledo-Antonio, J. A.; Capula, S.; Cortés-Jácome, M. A.; Angeles-Chávez, C.; López-Salinas, E.; Ferrat, G.; Navarrete, J.; Escobar, J. Low-Temperature FTIR Study of CO Adsorption on Titania Nanotubes. J. Phys. Chem. C 2007, 111, 10799. (15) Upendar, K.; Sri Hari Kumar, A.; Lingaiah, N.; Rama Rao, K. S.; Sai Prasad, P. S. Low-Temperature CO2 Adsorption on Alkali Metal Titanate Nanotubes. Int. J. Greenhouse Gas Control 2012, 10, 191. (16) Bhattacharyya, K.; Danon, A.; Vijayan, B. K.; Gray, K. A.; Stair, P. C.; Weitz, E. Role of the Surface Lewis Acid and Base Sites in the Adsorption of CO2 on Titania Nanotubes and Platinized Titania Nanotubes: An in Situ FT-IR Study. J. Phys. Chem. C 2013, 117, 12661. (17) Hirose, Y.; Mori, T.; Morishita, Y.; Itadani, A.; Kudoh, T.; Ohkubo, T.; Matsuda, T.; Kittaka, S.; Kuroda, Y. Visible-Light-Derived Photocatalyst Based on TiO2–δNδ with a Tubular Structure. Inorg. Chem. 2011, 50, 9948. (18) Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of Gases in Multimolecular Layers. J. Am. Chem. Soc. 1938, 60, 309. (19) Barrett, E. P.; Joyner, L. G.; Halenda, P. P. The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms. J. Am. Chem. Soc. 1951, 73, 373. (20) Kuroda, Y.; Maeda, H.; Morimoto, T. In Situ Sample Cell for EXAFS Measurements on Materials Treated at Elevated Temperatures in Vacuo. Rev. Sci. Instrum. 1989, 60, 3083. (21) Yoshida, R.; Suzuki, Y.; Yoshikawa, S. Effects of Synthetic Conditions and Heat-Treatment on the Structure of Partially Ion-Exchanged Titanate Nanotubes. Mater. Chem. Phys. 2005, 91, 409. 13 ACS Paragon Plus Environment


(22) Ferreira, O. P.; Souza Filho, A. G.; Mendes, Filho, J.; Alves, O. L. Unveiling the Structure and Composition of Titanium Oxide Nanotubes through Ion Exchange Chemical Reactions and Thermal Decomposition Processes. J. Braz. Chem. Soc. 2006, 17, 393. (23) Ohsaka, T.; Izumi, F.; Fujiki, Y. Raman Spectrum of Anatase, TiO2. J. Raman Spectrosc. 1978, 7, 321. (24) Gao, T.; Fjellvåg, H.; Norby, P. Crystal Structures of Titanate Nanotubes: A Raman Scattering Study. Inorg. Chem. 2009, 48, 1423. (25) Kukovecz, Á; Hodos, M.; Kónya, Z.; Kiricsi, I. Complex-Assisted One-Step Synthesis of Ion-Exchangeable Titanate Nanotubes Decorated with CdS Nanoparticles. Chem. Phys. Lett. 2005, 411, 445. (26) Morgan, D. L.; Liu, H.-W.; Frost, R. L.; Waclawik, E. R. Implications of Precursor Chemistry on the Alkaline Hydrothermal Synthesis of Titania/Titanate Nanostructures. J. Phys. Chem. C 2010, 114, 101. (27) Hodos, M.; Horváth, E.; Haspel, H.; Kukovecz, Á; Kónya, Z.; Kiricsi, I. Photosensitization of Ion-Exchangeable Titanate Nanotubes by CdS Nanoparticles. Chem. Phys. Lett. 2004, 399, 512. (28) Hu, W.; Li, L.; Li, G.; Liu, Y.; Withers, R. L. Atomic-Scale Control of TiO6 Octahedra through Solution Chemistry towards Giant Dielectric Response. Sci. Rep. 2014, 4, 6582. (29) Ryu, J.; Kim, S.; Hong, H.-J.; Hong, J.; Kim, M.; Ryu, T.; Park, I.-S.; Chung, K.-S.; Jang, J. S.; Kim, B.-G. Strontium Ion (Sr2+) Separation from Seawater by Hydrothermally Structured Titanate Nanotubes: Removal vs. Recovery. Chem. Eng. J. 2016, 304, 503. (30) Zárate, R. A.; Fuentes, S.; Cabrera, A. L.; Fuenzalida, V. M. Structural Characterization of Single Crystals of Sodium Titanate Nanowires Prepared by Hydrothermal Process. J. Cryst. Growth 2008, 310, 3630. (31) Gajović, A.; Friščić, I.; Plodinec, M.; Iveković, D. High Temperature Raman Spectroscopy of Titanate Nanotubes. J. Mol. Struct. 2009, 924–926, 183. (32) Viana, B. C.; Ferreira, O. P.; Souza Filho, A. G.; Hidalgo, A. A.; Filho, J. M.; Alves, O. L. Alkali Metal Intercalated Titanate Nanotubes: A Vibrational Spectroscopy Study. Vib. 14 ACS Paragon Plus Environment

Page 14 of 26

Page 15 of 26 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


Spectrosc. 2011, 55, 183. (33) Viana, B. C.; Ferreira, O. P.; Souza Filho, A. G.; Rodrigues, C. M.; Moraes, S. G.; Filho, J. M.; Alves, O. L. Decorating Titanate Nanotubes with CeO2 Nanoparticles. J. Phys. Chem. C 2009, 113, 20234. (34) Bonelli, B.; Onida, B.; Fubini, B.; Areán, C. O.; Garrone, E. Vibrational and Thermodynamic Study of the Adsorption of Carbon Dioxide on the Zeolite Na-ZSM-5. Langmuir 2000, 16, 4976. (35) Bonelli, B.; Civalleri, B.; Fubini, B.; Ugliengo, P.; Areán, C. O.; Garrone, E. Experimental and Quantum Chemical Studies on the Adsorption of Carbon Dioxide on Alkali-Metal-Exchanged ZSM-5 Zeolite. J. Phys. Chem. B 2000, 104, 10978. (36) Bulánek, R.; Frolich, K.; Frýdová, E.; Čičmanec, P. Microcalorimetric and FTIR Study of the Adsorption of Carbon Dioxide on Alkali-Metal Exchanged FER Zeolites. Top. Catal. 2010, 53, 1349. (37) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed., John Wiley & Sons Inc.: New York, 1997. (38) Zecchina, A.; Bordiga, S.; Lamberti, C.; Spoto, G.; Carnelli, L.; Areán, C. O. Low-Temperature Fourier Transform Infrared Study of the Interaction of CO with Cations in Alkali-Metal Exchanged ZSM-5 Zeolites. J. Phys. Chem. 1994, 98, 9577. (39) Lamberti, C.; Bordiga, S.; Geobaldo, F.; Zecchina, A.; Areán, C. O. Stretching Frequencies of Cation-CO Adducts in Alkali-Metal Exchanged Zeolites: An Elementary Electrostatic Approach. J. Chem. Phys. 1995, 103, 3158. (40) Waghmode, S. B.; Vetrivel, R.; Hegde, S. G.; Gopinath, C. S.; Sivasanker, S. Physicochemical Investigations of the Basicity of the Cation Exchanged ETS-10 Molecular Sieves. J. Phys. Chem. B 2003, 107, 8517. (41) Yong, Z.; Mata, V.; Rodrigues, A. E. Adsorption of Carbon Dioxide at High Temperature—A Review. Separ. Purif. Technol. 2002, 26, 195. (42) Samanta, A.; Zhao, A.; Shimizu, G. K. H.; Sarkar, P.; Gupta, R. Post-Combustion CO2 Capture Using Solid Sorbents: A Review. Ind. Eng. Chem. Res. 2012, 51, 1438. 15 ACS Paragon Plus Environment


(43) Kumar, A.; Madden, D. G.; Lusi, M.; Chen, K.-J.; Daniels, E. A.; Curtin, T; Perry IV, J. J.; Zaworotko, M. J. Direct Air Capture of CO2 by Physisorbent Materials. Angew. Chem. Int. Ed. 2015, 54, 14372.


Page 16 of 26

Page 17 of 26 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


Table 1 Specific surface areas and pore diameters of samples obtained Specific surface area (m2 g–1) +

Na -T-TiO2

Pore diameter (nm)

178

3.3

Li -T-TiO2(12)

171

3.2

Li+-T-TiO2(28)

173

3.2

Li -T-TiO2(30)

163

3.6

Li+-T-TiO2(31)

156

3.2

K -T-TiO2(14)

187

3.3

K+-T-TiO2(31)

190

3.3

K -T-TiO2(37)

182

3.2

K+-T-TiO2(39)

181

3.3

Rb -T-TiO2(15)

168

3.3

Rb+-T-TiO2(32)

188

3.3

Rb -T-TiO2(42)

174

3.3

Rb+-T-TiO2(47)

180

3.4

Cs -T-TiO2(17)

172

3.3

Cs+-T-TiO2(35)

176

3.4

Cs -T-TiO2(48)

152

3.4

Cs+-T-TiO2(56)

164

3.4

+

+

+

+

+

+

+

+



Figure captions

Figure 1. TEM images of (a) Na+-T-TiO2 and (b) Cs+-T-TiO2(17).

Figure 2. XRD patterns of the samples.

Figure 3. Raman spectra of the samples.

Figure 4. Relationship between the number of exchange operation and (filled mark) the ion-exchange level or (open mark) the amount of the residual Na+ ions.

Figure 5. Adsorption isotherms of CO2 at 298 K on the samples.

Figure 6. (a) TEM image and (b) STEM image and EDS maps of Cs+-T-TiO2(82).

Figure 7. IR spectra for CO2 adsorbed on the samples at room temperature. Equilibrium pressure of CO2 was about 0.2 kPa for every case.

Figure 8. Relationship between the ionic radius of alkali-metal ions and the ν3 values observed.

Figure 9. IR spectra for Li+-T-TiO2(94) under the different CO2 equilibrium pressures. The spectra were resolved into three components, as shown by broken lines.


Page 18 of 26

Page 19 of 26 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


Figure 1 (a)

(b)



Figure 2

Intensity (a. u.)

Cs+-T-TiO2(56)

Rb+-T-TiO2(47)

K+-T-TiO2(39) Na+-T-TiO2 Li+-T-TiO2(31)

10

20

30

40 50 2theta (degree)

60

70

80

Figure 3

Cs+-T-TiO2(56)

Rb+-T-TiO2(47) Intensity (a. u.)

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 26

K+-T-TiO2(39)

Na+-T-TiO2

Li+-T-TiO2(31) 0

200

400

600

800

1000

-1

Raman shift (cm )


1200

Page 21 of 26

Figure 4

50

Exchange level (%)

2.5 40

30 2 20 (circles) (squares) (triangles) (diamonds)

10

Li+ K+ Rb+ Cs+

1.5

Amount of residual sodium ions (mmol g -1)

3

60

0 0

5

10

15

20

Number of exchange operation (times)

Figure 5 12 Na+-T-TiO2

Adsorbed amount (cm3 (S. T. P.) g-1)

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


10

8

6

4 (circle) (square) (triangle) (diamond)

2

Li+-T-TiO2(30) K+-T-TiO2(37) Rb+-T-TiO2(42) Cs+-T-TiO2(48)

0 0

2

4

6

8

10

Equilibrium pressure (kPa)


12

14


Page 22 of 26

Figure 6

(a)

(b)

Cs

O


Ti

Page 23 of 26

Figure 7

Cs+-T-TiO2(82)

Rb+-T-TiO2(82) Absorbance (a. u.)

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


K+-T-TiO2(89)

Na+-T-TiO2

Li+-T-TiO2(94) 0.1

2500

2450

2400

2300

2350

2250

Wave number (cm -1)


2200


Figure 8

2355 Li+ Na

v3 mode observed (cm-1)

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 24 of 26

+

2350

K+ 2345

Rb+ Cs+

2340 0.40

0.60

0.80

1.0

1.2

1.4

Ionic radius (angstrom)


1.6

1.8

Page 25 of 26

Figure 9

0.1

Absorbance (a. u.)

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


Pe = 0.8 kPa

Pe = 0.2 kPa

2400

2380

2360 2340 Wave number (cm -1)

2320


2300


TOC


Page 26 of 26

Tubular Titanates: Alkali-Metal Ion-Exchange Features and Carbon

Recommend Documents