Reversible Switching of the Magnetic Orientation of Titanate

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Reversible Switching of the Magnetic Orientation of Titanate Nanosheets by Photochemical Reduction and Autoxidation Xiang Wang, Xiaoyu Li, Satoshi Aya, Fumito Araoka, Yasuhiro Ishida, Akiko Kikkawa, Markus Kriener, Yasujiro Taguchi, Yasuo Ebina, Takayoshi Sasaki, Shogo Koshiya, Koji Kimoto, and Takuzo Aida J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b09625 • Publication Date (Web): 16 Nov 2018 Downloaded from http://pubs.acs.org on November 16, 2018

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Journal of the American Chemical Society

Reversible Switching of the Magnetic Orientation of Titanate Nanosheets by Photochemical Reduction and Autoxidation Xiang Wang,†,‡,⊥ Xiaoyu Li,§,⊥ Satoshi Aya,‡ Fumito Araoka,‡ Yasuhiro Ishida,‡* Akiko Kikkawa,‡ Markus Kriener,‡ Yasujiro Taguchi,‡ Yasuo Ebina,∥ Takayoshi Sasaki,∥ Shogo Koshiya,∥ Koji Kimoto,∥ and Takuzo Aida†,‡* †

Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. ‡ RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. § School of Material Science and Technology, Beijing Institute of Technology, Beijing 100081, China. ∥National Institute

for Materials Science, International Center for Materials Nanoarchitectonics, 1-1 Namiki, Tsukuba, Ibaraki 305-

0044, Japan.

Supporting Information Placeholder ABSTRACT: Optical properties of aqueous colloidal disper-

sions of 2D electrolytes, if their aspect ratios are extra-large, can be determined by their orientation preferences. Recently, we reported that a colloidal dispersion of diamagnetic titanate(IV) nanosheets (TiIVNSs), when placed in a magnetic field, is highly anisotropic because TiIVNS anomalously orients its 2D plane orthogonal to the magnetic flux lines due to its large anisotropic magnetic susceptibility. Herein, we report a serendipitous finding that TiIVNSs can be in situ photochemically reduced into a paramagnetic species (TiIV/IIINSs), so that their preference of magnetic orientation changes from orthogonal to parallel. This transition distinctly alters the structural anisotropy and therefore optical appearance of the colloidal dispersion in a magnetic field. We also found that TiIV/IIINSs is autoxidized back to TiIVNSs under non-deaerated conditions. By using an elaborate setup, the dispersion of TiIVNSs serves as an optical switch remotely operable by magnet and light.

Colloidal systems composed of polyelectrolytes have extensively been studied but currently attract particular attention when such polyelectrolytes are low-dimensional and shape-persistent for suppressing entangling behaviors.1 In such a newly emerging field of colloidal sciences, main players are 2D materials including graphene oxides,1c,d metal oxide nanosheets,1e,f clays,1g inorganic layered double hydroxides,1h and disk-shaped phospholipid bilayer membranes.1i Physical properties of their colloidal dispersions are determined not only by the intrinsic properties of constituent 2D polyelectrolytes but also their relative orientation.2,3 In aqueous colloidal dispersions, van der Waals attraction and electrostatic repulsion serve as major long-range interactions,4 which are largely pronounced when shape-persistent

Figure 1. (a) Schematic structure of titanate(IV) nanosheet (TiIVNS). Counterions Me4N+ are omitted for clarity. ☐ = vacant site. (b) Atomic force microscopy (AFM) image of TiIVNS deposited on mica. (c) Schematic illustrations for the preferences of magnetic orientation: TiIVNS (left) and its reduced form containing Ti(III) species (TiIV/IIINS; right) orient their 2D planes orthogonal and parallel to the applied magnetic flux lines, respectively.

2D polyelectrolytes bear an extra-large aspect ratio. Methods for orienting such 2D polyelectrolytes include the utiliza-

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magnetic field, colloidally dispersed TiIVNSs align cofacially with one another since they anomalously prefer to orient their 2D plane orthogonal to the applied magnetic flux lines (Figure 1c, left).2b,3b,c Magnetic susceptibility is an intrinsic physical property of a substance and generally hard to change. However, the preference of TiIVNS for magnetic orientation would possibly be changed if diamagnetic TiIVNS can be converted into paramagnetic species (Figure 1c). TiIVNS is composed of a single-crystal-like 2D array of edge-sharing TiO6 octahedrons (Figure 1a), and characterized by its ultra-thin (0.75 nm) and extra-wide (~10 µm; Figure 1b) dimensions.9 TiIVNS carries dense negative charges (1.5 C m–2) and therefore can be well dispersed in aqueous media, where Me4N+ counterions wrap around the nanosheets to furnish an electric double layer.9d Similar to other titanium oxides,10 TiIVNS is semiconducting and can generate electron–hole pairs when photoexcited by UV light that is energetically equivalent to or greater than its band gap (~265 nm).11

Figure 2. (a) Snapshots of 0.4 wt% aqueous dispersions of TiIVNSs (left) and their photochemically reduced species TiIV/IIINSs (right). (b–d) Electronic absorption spectra (b; 0.4 wt%), dynamic light scattering traces (c; DLS, 0.4 wt%), and electron paramagnetic resonance spectra (d; EPR, solid) of (i) TiIVNSs, (ii) TiIV/IIINSs, and (iii) their autoxidized species. (e) Change in absorbance at 500 nm of an aqueous dispersion of TiIVNSs (1.2 wt%) upon turning on and off UV light under non-deaerated conditions.

tion of electric5 and magnetic fields6 in addition to shear forces or laminar flows,7 among which former two are noninvasive and therefore appealing. In particular, unlike the orientation using electric fields that is occasionally accompanied by destruction of components, magnetic orientation is clean, reliable, and shape/size-independent. However, reported examples are not diverse. Colloidal assemblies of 2D polyelectrolytes would be more interesting if their magnetic orientation behaviors are manipulated spatiotemporally by the combination with other physical inputs.8 Here we report an unprecedented finding that diamagnetic titanate(IV) nanosheet (TiIVNS)9 can change its preference for magnetic orientation by in situ photochemical reduction, affording paramagnetic TiIV/IIINS. We recently found that TiIVNS possesses a unique diamagnetic susceptibility: In a

An aqueous dispersion of TiIVNSs (0.4 wt%) is colorless with a silky appearance (Figure 2a, left) because of the lack of absorption in the visible region (Figure 2b, i). Just coincidentally, we found that this colorless dispersion, while being irradiated with UV light (500 W xenon lamp) for 30 min exhibits a purple color (Figure 2a, right), displaying a broad absorption band at 500–800 nm (Figure 2b, ii and Figure S1a). The purple color is characteristic of Ti(III) species.12 Thus, Ti(IV) species in TiIVNS are photochemically reduced into Ti(III) species, affording titanate nanosheet TiIV/IIINS. Under non-deaerated conditions, the purple color gradually faded after the removal of UV irradiation and vanished within 10 min (Figure S1b), where the resulting absorption spectrum (Figure 2b, iii) was virtually identical to that of original TiIVNSs (Figure 2b, i), indicating that TiIV/IIINS, photochemically generated, is autoxidized back to TiIVNS. In fact, when the dispersion of TiIVNSs was bubbled with N2 beforehand for flushing out O2, the purple color lasted over a long period of time (>1 month) even after the removal of UV irradiation. The observed color-change cycle (i ➛ ii ➛ iii [i]) was repeatable multiple times (Figure 2e) without structural disruption of the nanosheets, as supported by dynamic light scattering (DLS) analysis (Figure 2c). The white- and purple-colored nanosheets are both negatively charged as determined by zeta potential measurements (–44 and –34 mV, respectively), so that both of them are well-dispersed in aqueous media, in consistency with their SAXS profiles (Figure S2). We confirmed that TiIV/IIINS is paramagnetic (vide infra). Electron paramagnetic resonance (EPR) spectroscopy of TiIV/IIINS (solid) showed an intense signal with a gvalue of 1.94 (Figure 2d, ii), which is attributable to the unpaired electrons in Ti(III) species.12d–g As expected, the autoxidation of TiIV/IIINS was accompanied by the disappearance of this characteristic EPR signal (Figure 2d, iii).


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In order to further characterize TiIV/IIINS, we measured its selected-area electron diffraction (SAED; Figure 3b) as well

as that of TiIVNS (Figure 3a), and found that their SAED patterns resemble one another, commonly displaying a set of diffractions indexed as the (200), (202), and (002) faces characteristic of 2D single-crystalline structures.9c Only a noticeable difference between them is that TiIV/IIINS showed an electron diffraction attributable to the (100) face (Figure 3b and Figure S3b), whereas TiIVNS did not show the corresponding diffraction (Figure 3a and Figure S3a) due to the systematic extinction rule. In relation to these contrasting observations, one of our co-authors recently reported that, during the transmission electron microscopy (TEM) under a high electron dose, TiIVNS (Figure 3c) is reduced into a Ti(III) species (TiIIINS) showing an electron diffraction spot due to the (100) face.13 With the help of computational TEM simulations, TiIIINS was proposed to be a Ti2O3-type nanosheet with a particular structure shown in Figure 3d. We now assume that TiIV/IIINS, which is obtained by the photochemical reduction of TiIVNS, might contain TiIIINS as phase-separated domains (Figure S4). The following set of elementary reactions, based on the surface photochemistry of TiO2, represent a possible mechanism for the photochemical reduction of TiIVNS into TiIV/IIINS;12a–f TiO2 + hv → e−CB + h+VB

Figure 3. (a,b) SAED patterns of TiIVNS (a) and TiIIINS (Ti2O3-type nanosheet; b) deposited on a hydrophilized carbon-covered copper grid. (c,d) Schematic illustrations of TiIVNS (c) and TiIIINS (d) viewed along the directions orthogonal and parallel to the 2D plane.

(1)

+ Ti(IV) → Ti(III)

(2)

h+VB + O2−(Lattice) → O−•(Lattice)

(3)

e

−

CB

4h

+

VB

+ 2O

2−

(Lattice)

→ O2(Gas) + vacancy

(4)

Photoexcitation of TiO2 in aqueous media results in generating a pair of hole and electron (eq. 1), the latter of which reduces Ti(IV) into Ti(III) (eq. 2), while the former oxidizes O2– in the TiO2 lattice to afford O−• (eq. 3) or O2 (eq. 4).12a We believe that essentially the same sequence of reactions would occur when TiIVNS is photoexcited with UV light. When bulk TiO2 is used, the overall efficiency of the Ti(IV)-to-Ti(III) conversion is known to be very low.12c–f In sharp contrast, the photochemistry of TiIVNS is supposed to provide a much higher overall efficiency because this unilamellar titania is composed of only surface atoms that can be exposed to light (Figure 1a). In fact, by preliminary colorimetric titration of an aqueous dispersion of TiIV/IIINS with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) as an oxidant,12f we found that nearly 40% of the Ti species in TiIV/IIINS are trivalent.

Figure 4. (a,b) 2D SAXS images (upper) of aqueous dispersions of TiIVNSs (1.2 wt%; a) and TiIV/IIINSs (1.2 wt%; b) in a 10 T magnetic field and their azimuthal angle plots (lower). The incident X-ray beam was directed orthogonal to the applied magnetic field.

As already shown in Figure 2d, TiIV/IIINS contains unpaired electrons in the d orbital of Ti,12 thereby making its magnetization profile quite different from that of TiIVNS carrying no unpaired electrons. In fact, the superconducting quantum interference device (SQUID) profile of TiIV/IIINS, in regard to the magnetic field-dependency of the magnetization, is typical of paramagnetic species. In contrast, TiIVNS at 300 K (27 °C), consistently with our previous report,3b showed a magnetization curve with a negative slope, suggesting a dia-



magnetism-dominant nature of TiIVNS (Figure S5a, i). In sharp contrast, the magnetization curve of TiIV/IIINS showed a positive slope (Figure S5a, ii), characteristic of paramagnet-

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ic species. When TiIV/IIINS was cooled to 2 K (–271 °C), its paramagnetic nature became explicit (Figure S5b, ii). A detailed study on the temperature dependency of the magnetization profile revealed that TiIV/IIINS is neither ferromagnetic nor super-paramagnetic (Figures S6).14 Next, we employed 2D small angle X-ray scattering (2D SAXS) for investigating the orientation preference of TiIV/IIINSs in a magnetic field. The 2D SAXS image and its azimuthal angle plot in Figure 4b show that, when an aqueous dispersion of TiIV/IIINSs in a 10 T magnetic field was irradiated with an X-ray beam, TiIV/IIINSs scattered the incident X-ray beam exclusively in a direction orthogonal to the magnetic flux lines. Hence, TiIV/IIINSs orient their 2D plane parallel to an applied magnetic field. The order parameter was estimated to be 0.90. On the contrary to paramagnetic TiIV/IIINSs, diamagnetic TiIVNSs, as reported previously,3b orient their plane orthogonal to the applied magnetic field, where the incident X-ray beam was scattered exclusively in a direction parallel to the magnetic flux lines (Figure 4a). When TiIVNSs and TiIV/IIINSs are magnetically oriented, their aqueous dispersions are both optically anisotropic but they look differently. When an aqueous dispersion of TiIV/IIINSs in a 9 T magnetic field was viewed along the directions parallel and perpendicular to the applied magnetic field, the dispersion looked slightly opaque (Figure 5b, left) and highly opaque (Figure 5b, right), respectively, because TiIV/IIINS orients its 2D plane parallel to the magnetic field (Figure 5b, upper). Contrary to TiIV/IIINS, TiIVNS, as described above, orients its 2D plane orthogonal to the applied magnetic field. Therefore, the dispersion of TiIVNSs looked highly opaque (Figure 5a, left) and slightly opaque (Figure 5a, right) when viewed along the directions parallel and perpendicular to the applied magnetic field, respectively.

Figure 5. (a,b) Photos of 0.4 wt% aqueous dispersions of TiIVNSs (a) and TiIV/IIINSs (b) in a 10 × 10 mm quartz cuvette at 25 °C in a 9 T magnetic field. These photos were taken from the directions parallel (left) and orthogonal (right) to the applied magnetic field. (c,d) Photos of the transmitted 532 nm green laser beams (upper) through 0.4 wt% aqueous dispersions of TiIVNSs (c) and TiIV/IIINSs (d) in a 9 T magnetic field and their intensity profiles along the broken lines across the photos (lower). These photos were taken in a direction orthogonal to the applied magnetic field (Figure S7). (e) Change in transmittance of a 532 nm green laser beam through a 0.4 wt% aqueous dispersion of TiIVNSs upon turning on and off UV light under non-deaerated conditions. Although this optical change can be mainly due to the light reflection change of the nanosheets, the light absorption of TiIV/IIINS at 532 nm may also contribute to the optical change.

With the above observations in mind, a 532 nm green laser beam was allowed to transmit from an upper direction through a colloidal dispersion of magnetically oriented TiIVNSs, before and after their photochemical reduction into TiIV/IIINSs.15 For this purpose, a non-deaerated aqueous dispersion of TiIVNSs (0.4 wt%) in a 10 mm × 10 mm quartz cuvette was placed in the bore of a 9 T magnet such that the magnetic flux lines could be directed horizontally to the specimen (Figure 5c and Figure S7). With this configuration, TiIVNS oriented its 2D plane vertically, so that the green laser beam from the upper direction transmitted through the dispersion with a minimum optical interference. Then, the dispersion was irradiated by UV light, wherein TiIVNSs were photochemically reduced into TiIV/IIINSs. Because paramagnetic TiIV/IIINS thus generated oriented its 2D plane horizontally, the colloidal assembly of TiIV/IIINSs seriously interfered the transmittance of the green laser beam (Figure 5d). In this case, because the photoreduction of TiIVNSs was carried out under non-deaerated conditions, TiIV/IIINSs were autoxidized back into TiIVNSs after the removal of the UV irradiation. TiIVNSs thus recovered oriented their 2D plane


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vertically (Figure 5c), so that the serious optical interference, leading to a poor transmittance of the green laser beam, was attenuated spontaneously. As shown in Figure 5e, the dispersion can likewise open and close its optical window multiple times without deterioration. In summary, we found that diamagnetic TiIVNSs in an aqueous dispersion can be in situ photochemically reduced into paramagnetic TiIV/IIINSs. Under non-deaerated conditions, TiIV/IIINSs undergo autoxidation to return to TiIVNSs. When located in a magnetic field, TiIVNSs and TiIV/IIINSs in their aqueous dispersions orient their 2D planes orthogonal and parallel to the applied magnetic flux lines, respectively (Figure 1c). Because the aspect ratios of TiIVNSs and TiIV/IIINSs are extra-large, the structural anisotropies and optical appearances of their aqueous dispersions in a magnetic field are distinctly different from one another. Namely, the dispersion of TiIVNSs serves as an optical switch that is remotely operable by magnet and light. Extensive studies on physical and chemical properties of TiIV/IIINSs, a reduced form of TiIVNSs, are interesting subjects worthy of further investigation. ◼ ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. General; experimental procedures for the interconversion between TiIVNS and TiIV/IIINS; experimental details for the estimation of the amount of Ti(III) species in TiIV/IIINS; experimental details for evaluating the transmittances of a 532 nm green laser beam through aqueous dispersions of TiIVNSs and TiIV/IIINSs in a magnetic field; kinetic profiles of the conversion between TiIVNS and TiIV/IIINS; 1D SAXS profiles, TEM images, SAED patterns, and magnetization profiles of TiIVNS and TiIV/IIINS (PDF).

◼ AUTHOR INFORMATION Corresponding Author *[email protected] *[email protected]

Author Contributions ⊥These authors equally contributed to this paper.

Notes The authors declare no competing financial interest.

◼ ACKNOWLEDGMENT This work was financially supported by a JSPS Grant-in-Aid for Scientific Research(S) (18H05260). We also acknowledge the ImPACT Program of the Council for Science, Technology and Innovation (Cabinet Office, Government of Japan). This study was supported by NIMS Nanofabrication Platform in Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. X.W. thanks the financial support from China Scholarship Council.

◼ REFERENCES (1) (a) de Gennes, P. G. The Physics of Liquid Crystals; Oxford University Press, London, 1974. (b) Smalyukh, I. I. Liquid Crystal Colloids. Annu. Rev. Condens. Matter Phys. 2018, 9, 207–226. (c) Kim, J.; Cote, L. J.; Huang, J. X. Two Dimensional Soft Material: New Faces of Graphene Oxide. Acc. Chem. Res. 2012, 45, 1356–1364. (d) Sasikala, S. P.; Lim, J.; Kim, I. H.; Jung, H. J.; Yun, T.; Han, T. H.; Kim, S. O. Graphene Oxide Liquid Crystals: A Frontier 2D Soft Material for Graphene-Based Functional Materials. Chem. Soc. Rev. 2018, 47, 6013–6045. (e) Wang, L.; Sasaki, T. Titanium Oxide Nanosheets: Graphene Analogues with Versatile Functionalities. Chem. Rev. 2014, 114, 9455−9486. (f) ten Elshof, J. E.; Yuan, H.; Rodriguez, P. G. Two‐Dimensional Metal Oxide and Metal Hydroxide Nanosheets: Synthesis, Controlled Assembly and Applications in Energy Conversion and Storage. Adv. Energy Mater. 2016, 6, 1600355. (g) Paineau, E.; Philippe, A. M.; Antonova, K.; Bihannic, I.; Davidson, P.; Dozov, I.; Gabriel, J. C. P.; Imperor-Clerc, M.; Levitz, P.; Meneau, F.; Michot, L. J. Liquid-Crystalline Properties of Aqueous Suspensions of Natural Clay Nanosheets. Liq. Cryst. Rev. 2013, 1, 110–126. (h) Wang, Q.; O’Hare, D. Recent Advances in the Synthesis and Application of Layered Double Hydroxide (LDH) Nanosheets. Chem. Rev. 2012, 112, 4124–4155. (i) Alipour, E.; Halverson, D.; McWhirter, S.; Walker, G. C. Phospholipid Bilayers: Stability and Encapsulation of Nanoparticles. Annu. Rev. Phys. Chem. 2017, 68, 261–283. (2) (a) de Azevedo, E. N.; Engelsberg, M.; Fossum, J. O.; de Souza, R. E. Anisotropic Water Diffusion in Nematic Self-Assemblies of Clay Nanoplatelets Suspended in Water. Langmuir, 2007, 23, 5100–5105. (b) Sano, K.; Kim, Y. S.; Ishida, Y.; Ebina, Y.; Sasaki, T.; Hikima, T.; Aida, T. Photonic Water Dynamically Responsive to External Stimuli Nature Commun. 2016, 7, 12559. (c) Lu, X.; Feng, X.; Werber, J. R.; Chu, C.; Zucher, I.; Kim, J.-H.; Osuji, C. O.; Elimelech M. Enhanced Antibacterial Activity through the Controlled Alignment of Graphene Oxide Nanosheets. Proc. Natl. Acad. Sci. 2017, 114, 9793–9801. (d) Davidson, P.; Penisson, C.; Constantin, D.; Gabriel, J.-C. P. Isotropic, Nematic, and Lamellar Phases in Colloidal Suspensions of Nanosheets Proc. Natl. Acad. Sci. 2018, 115, 6662– 6667. (3) (a) Qiu, L.; Liu, J. Z.; Chang, S. L. Y.; Wu, Y.; Li, D. Biomimetic Superelastic Graphene-Based Cellular Monoliths Nature Commun. 2012, 3, 1241. (b) Liu, M.; Ishida, Y.; Ebina, Y.; Sasaki, T.; Hikima, T.; Takata, M.; Aida, T. An Anisotropic Hydrogel with Electrostatic Repulsion between Cofacially Aligned Nanosheets Nature 2015, 517, 68–72. (c) Kim, Y. S.; Liu, M.; Ishida, Y.; Ebina, Y.; Osada, M.; Sasaki, T.; Hikima, T.; Takata, M.; Aida, T. Thermoresponsive Actuation Enabled by Permittivity Switching in an Electrostatically Anisotropic Hydrogel. Nature Mater. 2015, 14, 1002– 1007. (d) Xia, Y.; Mathis, T. S.; Zhao, M. Q.; Anasori, B.; Dang, A.; Zhou, Z.; Cho, H.; Gogotsi, Y.; Yang, S. Thickness-Independent Capacitance of Vertically Aligned Liquid-Crystalline MXenes. Nature 2018, 557, 409–412. (4) (a) Derjaguin, B. A Theory of Interaction of Particles in Presence of Electric Double-Layers and the Stability of Lyophobe Colloids and Disperse Systems. Acta Phys. Chim. 1939, 10, 333–346. (b) Derjaguin, B.; Landau, L. D. Theory of the Stability of Strongly Charged Lyophobic Sols and of the Adhesion of Strongly Charged Particles in Solutions of Electrolytes. Acta Phys. Chim. 1941, 14, 633–662. (c) Verwey, E. J. W.; Overbeek, J. T. G. Theory of Stability of Lyophobic Colloids; Elsevier, Amsterdam, 1948. (5) (a) Paineau, E.; Antonova, K.; Baravian, C.; Bihannic, I.; Davidson, P.; Dozov, I.; Imperor-Clerc, M.; Levitz, P.; Madsen, A.; Meneau, F.; Michot, L. J. Liquid-Crystalline Nematic Phase in Aqueous Suspensions of a Disk-Shaped Natural Beidellite Clay. J. Phys. Chem. B 2009, 113, 15858– 15869. (b) Dozov, I.; Paineau, E.; Davidson, P.; Antonova, K.; Baravian, C.; Bihannic, I.; Michot, L. J. Electric-Field-Induced Perfect Anti-Nematic Order in Isotropic Aqueous Suspensions of a Natural Beidellite Clay. J. Phys. Chem. B 2011, 115, 7751–7765. (c) Nakato, T.; Nakamura, K.; Shimada, Y.; Shido, Y.; Houryu, T.; Iimura, Y.; Miyata, H. Electrooptic Response of Colloidal Liquid Crystals of Inorganic Oxide Nanosheets Prepared by Exfoliation of a Layered Niobate. J. Phys. Chem. C 2011, 115, 8934–8939.



(6) (a) Kim, J. Y.; Osterloh, F. E.; Hiramatsu, H.; Dumas, R. K.; Liu, K. Synthesis and Real-Time Magnetic Manipulation of a Biaxial Superparamagnetic Colloid. J. Phys. Chem. B 2005, 109, 11151–11157. (b) Michot, L. J.; Bihannic, I.; Maddi, S.; Funari, S. S.; Baravian, C.; Levitz, P.; Davidson P. Liquid-Crystalline Aqueous Clay Suspensions. Proc. Natl. Acad. Sci. 2006, 103, 16101–16104. (c) Eguchi, M.; Angelone, M. S.; Yennawar, H. P.; Mallouk, T. E. Anisotropic Alignment of Lamellar Potassium Hexaniobate Microcrystals and Nanoscrolls in a Static Magnetic Field. J. Phys. Chem. C 2008, 112, 11280–11285. (d) Majewski, P. W.; Osuji, C. O. Controlled Alignment of Lamellar Lyotropic Mesophases by Rotation in a Magnetic Field. Langmuir 2010, 26, 8737–8742. (e) Kim, J. E.; Han, T. H.; Lee, S. H.; Kim, J. Y.; Ahn, C. W.; Yun, J. M.; Kim, S. O. Graphene Oxide Liquid Crystals. Angew. Chem. Int. Ed. 2011, 50, 3043–3047. (f) Sklute, E. C.; Eguchi, M.; Henderson, C. N.; Angelone, M. S.; Yennawar, H. P.; Mallouk, T. E. Orientation of Diamagnetic Layered Transition Metal Oxide Particles in 1-Tesla Magnetic Fields. J. Am. Chem. Soc. 2011, 133, 1824-1831. (g) Wu, L.; Ohtani, M.; Takata, M.; Saeki, A.; Seki, S.; Ishida, Y.; Aida, T. Magnetically Induced Anisotropic Orientation of Graphene Oxide Locked by in Situ Hydrogelation. ACS Nano 2014, 5, 4640–4649. (h) Ida S.; Ogata C.; Eguchi M.; Youngblood W. J.; Mallouk, T. E.; Matsumoto, Y. Photoluminescence of Perovskite Nanosheets Prepared by Exfoliation of Layered Oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: Lanthanide Ion). J. Am. Chem. Soc. 2008, 130, 7052–7059. (i) Osada M.; Ebina Y.; Fukuda K.; Ono K.; Takada K.; Yamaura K.; TakayamaMuromachi E.; Sasaki, T. Ferromagnetism in Two-Dimensional Ti0.8Co0.2O2 Nanosheets. Phys. Rev. B 2006, 73, 153301-1–153301-4. (7) (a) Schmidt, G.; Nakatani, A. I.; Butler, P. D.; Karim, A.; Han, C. C. Shear Orientation of Viscoelastic Polymer−Clay Solutions Probed by Flow Birefringence and SANS. Macromolecules 2000, 33, 7219–7222. (b) Schmidt, G.; Nakatani, A. I.; Butler, P. D; Han, C. C. Small-Angle Neutron Scattering from Viscoelastic Polymer−Clay Solutions. Macromolecules 2002, 35, 4725–4732. (c) Michot, L. J.; Bihannic, I.; Porsch, K.; Maddi, S.; Baravian, C.; Mougel, J.; Levitz, P. Phase Diagrams of Wyoming NaMontmorillonite Clay. Influence of Particle Anisotropy. Langmuir 2004, 20, 10829–10837. (d) Wang, X.; Gao, Y.; Mao, K.; Xue, G.; Chen, T.; Zhu, J.; Li, B.; Sun, P.; Jin, Q.; Ding, D. Unusual Rheological Behavior of Liquid Polybutadiene Rubber/Clay Nanocomposite Gels: The Role of Polymer−Clay Interaction, Clay Exfoliation, and Clay Orientation and Disorientation. Macromolecules 2006, 39, 6653–6660. (8) For dual control of nanoparticle assemblies by a magnetic field and light, see: (a) Vallooran, J. J.; Handschin, S.; Bolisetty, S.; Mezzenga, R. Twofold Light and Magnetic Responsive Behavior in Nanoparticle−Lyotropic Liquid Crystal Systems. Langmuir 2012, 28, 5589−5595. (b) Chovnik, O.; Balgley, R.; Goldman, J. R.; Klajn, R. J. Am. Chem. Soc. 2012, 134, 19564–19567. (c) Das, S.; Ranjan, P.; Maiti, P. S.; Singh, G.; Leitus, G.; Klajn, R. Dual-Responsive Nanoparticles and their SelfAssembly. Adv. Mater. 2013, 25, 422–426. (d) Sagebiel, S.; Stricker, L.; Engel, S.; Ravoo, B. J. Self-Assembly of Colloidal Molecules That Respond to Light and a Magnetic Field. Chem. Commun. 2017, 53, 9296–9299. (9) (a) Sasaki, T.; Watanabe, M.; Hashizume, H.; Yamada, H.; Nakazawa, H. Macromolecule-like Aspects for a Colloidal Suspension of an Exfoliated Titanate. Pairwise Association of Nanosheets and Dynamic Reassembling Process Initiated from It. J. Am. Chem. Soc. 1996, 118, 8329–8335. (b) Sasaki, T.; Kooli, F.; Iida, F.; Michiue, F.; Takenouchi, S.; Yajima, Y.; Izumi F.; Chakoumakos, B. C.; Watanabe, M. A Mixed Alkali Metal Titanate with the Lepidocrocite-like Layered Structure. Preparation, Crystal Structure, Protonic Form, and Acid−Base Intercalation Properties. Chem. Mater. 1998, 10, 4123–4128. (c) Sasaki, T.; Ebina, Y.; Kitami, Y.;

Page 6 of 7

Watanabe, M.; Oidawa, T. Two-Dimensional Diffraction of Molecular Nanosheet Crystallites of Titanium Oxide. J. Phys. Chem. B 2001, 105, 6116–6121. (d) Yuan, H.; Lubbers, R.; Besselink, R.; Nijland, M.; ten Elshof, J. E. Improved Langmuir–Blodgett Titanate Films via in Situ Exfoliation Study and Optimization of Deposition Parameters. ACS Appl. Mater. Interfaces 2014, 6, 8567. (10) (a) Diebold, U. The Surface Science of Titanium Dioxide Surf. Sci. Rep. 2003, 48, 53–229. (b) Nazeeruddin, Md. K.; Humphry-Baker, R.; Liska, P.; Grätzel, M. Investigation of Sensitizer Adsorption and the Influence of Protons on Current and Voltage of a Dye-Sensitized Nanocrystalline TiO2 Solar Cell. J. Phys. Chem. B 2003, 107, 8981–8987. (c) Lu, X.; Wang, G.; Zhai, T.; Yu, M.; Gan, J.; Tong, Y.; Li, Y. Hydrogenated TiO2 Nanotube Arrays for Supercapacitors Nano Lett. 2012, 12, 1690–1696. (d) Qiu, B.; Xing, M.; Zhang, J. Mesoporous TiO2 Nanocrystals Grown in Situ on Graphene Aerogels for High Photocatalysis and Lithium-Ion Batteries. J. Am. Chem. Soc. 2014, 136, 5852–5855. (e) Low, J.; Cheng, B.; Yu, Surface Modification and Enhanced Photocatalytic CO2 Reduction Performance of TiO2: A Review. J. Appl. Surf. Sci. 2017, 392, 658–686. (11) (a) Sasaki, T.; Watanabe, M. Semiconductor Nanosheet Crystallites of Quasi-TiO2 and Their Optical Properties. J. Phys. Chem. B 1997, 101, 10159–10161. (b) Sakai, N.; Ebina, Y.; Takada, K.; Sasaki, T. Electronic Band Structure of Titania Semiconductor Nanosheets Revealed by Electrochemical and Photoelectrochemical Studies. J. Am. Chem. Soc. 2004, 126, 5851–5858. (c) Liu, M.; Ishida, Y.; Ebina, Y.; Sasaki, T.; Aida, T. Photolatently Modulable Hydrogels Using Unilamellar Titania Nanosheets as Photocatalytic Crosslinkers. Nat. Commun. 2013, 4, 2029. (12) (a) Fujishima, A.; Rao, T. N.; Tryk, D. A. Titanium Dioxide Photocatalysis. J. Photochem. Photobiol. C 2000, 1, 1–21. (b) Bityurin, N.; Znaidi, L.; Kanaev, A. Laser-Induced Absorption in Titanium Oxide Based Gels. Chem. Phys. Lett. 2003, 374, 95–99. (c) Kuznetsov, A. I.; Kameneva, O.; Alexandrov, A.; Bityurin, N.; Marteau, P.; Chhor, K.; Sanchez, C.; Kanaev, A. Light-Induced Charge Separation and Storage in Titanium Oxide Gels. Phys. Rev. E 2005, 71, 021403. (d) Kuznetsov, A. I.; Kameneva O.; Alexandrov A.; Bityurin N.; Chhor K.; Kanaev A. Chemical Activity of Photoinduced Ti3+ Centers in Titanium Oxide Gels. J. Phys. Chem. B. 2006, 110, 435–441. (e) Xiong, L.-B.; Li, J.-L.; Yang, B.; Yu, Y. Ti3+ in the Surface of Titanium Dioxide: Generation, Properties and Photocatalytic Application. J. Nanomater. 2012, 2012, 831524. (f) Schrauben, J. N.; Hayoun, R.; Valdez, C. N.; Braten, M.; Fridley, L.; Mayer, J. M. Titanium and Zinc Oxide Nanoparticles are Proton-Coupled Electron Transfer Agents. Science 2012, 336, 1298–1301. (g) Zuo, F.; Wang, L.; Wu, T.; Zhang, Z.; Borchardt, D.; Feng, P. Self-Doped Ti3+ Enhanced Photocatalyst for Hydrogen Production under Visible Light J. Am. Chem. Soc. 2010, 132, 11856–11857. (13) Ohwada, M.; Kimoto, K.; Suenaga, K.; Sato, Y.; Ebina, Y.; Sasaki, T. Synthesis and Atomic Characterization of a Ti2O3 Nanosheet. J. Phys. Chem. Lett. 2011, 2, 1820–1823. (14) As shown in Figure S6, the temperature-dependent magnetization profiles of TiIV/IIINS measured under field cooling (filled circles) and zerofield cooling (open circles) conditions were essentially identical to each other from 10 to 300 K and followed the Curie–Weiss behavior of paramagnetism. (15) For evaluating the transmittance, a 532-nm green laser beam was allowed to transmit through samples in a direction orthogonal to the applied magnetic field. TiIVNS and TiIV/IIINS were intact to the exposure to a 532 nm green laser beam.


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Reversible Switching of the Magnetic Orientation of Titanate

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