Monolayer Attachment of Metallic MoS2 on Restacked Titania

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Monolayer Attachment of Metallic MoS on Restacked Titania Nanosheets for Efficient Photocatalytic Hydrogen Generation Leanddas Nurdiwijayanto, Jinghua Wu, Nobuyuki Sakai, Renzhi Ma, Yasuo Ebina, and Takayoshi Sasaki ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b01319 • Publication Date (Web): 30 Nov 2018 Downloaded from http://pubs.acs.org on November 30, 2018

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ACS Applied Energy Materials

Monolayer Attachment of Metallic MoS2 on Restacked Titania Nanosheets for Efficient Photocatalytic Hydrogen Generation Leanddas Nurdiwijayanto†‡, Jinghua Wu†, Nobuyuki Sakai†, Renzhi Ma†, Yasuo Ebina†, Takayoshi Sasaki†‡* †International

Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for

Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan. ‡Graduate

School of Pure and Applied Sciences, University of Tsukuba, Tennodai 1-1-1, Tsukuba,

Ibaraki 305-8571, Japan.

ABSTRACT. Monolayer attachment of metallic MoS2 (1T) on restacked titania (Ti0.87O20.52) nanosheets was attained via a facile two-step flocculation process of their colloidal suspensions with the aid of the difference in critical H+ concentrations required for inducing flocculation of the respective nanosheets. The process produced porous flaky aggregates of restacked Ti0.87O20.52 nanosheets covered with monolayer MoS2, which serves as the electron collector and provides abundant catalytically active sites for proton reduction reaction. The MoS2-modified restacked-

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Ti0.87O20.52 nanosheets showed a remarkably high photocatalytic efficiency for hydrogen generation (1.2 mmol h-1 g-1), being superior to those of the restacked Ti0.87O20.52 nanosheets and P25-TiO2 nanoparticles conventionally modified with MoS2 (0.38, and 0.4 mmol h-1 g-1, respectively). The extensive molecular-level interfacial coupling of Ti0.87O20.52/MoS2 nanosheets facilitates efficient charge separation and fast electron transfer, resulting in the significantly enhanced photocatalytic activity.

KEYWORDS: 2D heterointerface, hydrogen evolution, monolayer co-catalyst, photocatalysis, two-step flocculation process.

INTRODUCTION Heterointerfaces, which involve two different materials, have historically been an important research subject.1–3 They have opened new pathways to artificial materials and systems with fascinating physical properties that emerge at the interfaces.4–6 A wide range of breakthroughs and innovations has been demonstrated from metal-semiconductor and semiconductor p-n junctions, which are important not only for electronic applications7–9 but also for the photocatalysis of H2/O2 evolution.10–12 The adoption of a heterointerface in photocatalytic materials is motivated by the need to overcome drawbacks, such as short lifetimes of the photogenerated electron-hole pairs. Photocatalysts studied so far have been mostly nanoparticle-based materials,13–16 and conventional impregnation methods of co-catalysts have not allowed fine control at nanoscale. The particlebased heterointerfaces employed in such studies usually fail to achieve sufficient interfacial contact at a molecular level, which ends at low separation efficiency of photogenerated carriers


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and unsatisfactory catalytic activities. On the other hand, the utilization of emerging twodimensional (2D) nanomaterials17–23 can be considered as a promising strategy, motivated by important benefits arising from their molecularly thin 2D nature, such as superior electron mobility, high specific surface area, abundant surface active sites, and excellent interfacial features (easy to achieve “face-to-face” contact).24 Recent advances in 2D nanomaterials have focused on the hetero-assembly of two different types of nanosheets, since such a simple process enables the organization of artificial materials through sophisticated tailorability and high freedom in material design, which cannot be attained from traditional synthetic methods.25–31 Integrating several 2D crystals into a vertical stack offers many opportunities to design/control functions originating from their interfacial interactions. Inspired by this aspect, we aim to develop a new class of photocatalytic materials via the hetero-assembly of molecularly thin 2D-based photocatalyst and co-catalyst such as titania (Ti1-O24) and metallic molybdenum disulfide (1T-phase MoS2) nanosheets, respectively. Ti1-O24 nanosheets are of particular interest for photocatalytic applications because they show efficient UV light absorption associated with their two-dimensionality.32,33 Meanwhile, 1T-phase MoS2 shows a high catalytic activity, particularly for H2 evolution, due to its excellent electrical conductivity34–36 and abundant catalytically active sites.37–39 Therefore, we may expect that proper design of the interfacial coupling between Ti1-O24 and 1T-phase MoS2 nanosheets will greatly enhance the photocatalytic activity towards hydrogen generation. Recently, it is noted that the hetero-assembly of layered 2D titania nanoplates and MoS2 layers has been reported via a hydrothermal method.40,41 However, precise control in the hybridization with MoS2 at a monolayer regime was hardly realized. The inadequate design brings a disadvantage for the separation of photogenerated carriers and transfer of electrons required for


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the hydrogen evolution reaction.42 In addition, the decoration of thick MoS2 layers should impede the penetration of light into the photocatalyst, limiting the generation of electron-hole pairs. Therefore, in the present work, we report the design of 2D heterointerface structure via the monolayer attachment of 1T-phase MoS2 on the surface of restacked Ti0.87O20.52 nanosheets. The photocatalytic activity for hydrogen generation was examined by exposing UV light to the restacked products dispersed in an aqueous methanol solution. We expect that the modification of photocatalysts with monolayer MoS2 would be quite effective because of the limited damping of incident light to allow the activation of photocatalysts beneath it. In addition, the extensive coupling interfaces between the Ti0.87O20.52 and 1T-phase MoS2 nanosheets facilitate the facile migration of electrons to the surface active sites to promote photocatalytic reactions. Therefore, this structure may be regarded as an ideal candidate for photocatalytic hydrogen production with a large number of exposed active sites. Control samples, composed of restacked Ti0.87O20.52 nanosheets and P25-TiO2 nanoparticles conventionally modified with MoS2, were also fabricated and compared to illustrate the prominence of the 2D heterointerface.

RESULTS AND DISCUSSION Monolayer attachment of 1T-phase MoS2 on restacked Ti0.87O20.52 nanosheets was successfully attained via a facile two-step flocculation of their colloidal suspensions by controlling the amount of H+ ions in the solution. It was found that as much as a five-fold excess of H+ ions, used to restack Ti0.87O20.52 nanosheets, was needed to induce flocculation of 1T-phase MoS2. A colloidal suspension of Ti0.87O20.52 nanosheets was first flocculated with the addition of a specific amount of HCl (Figure 1), yielding a voluminous white precipitates. Some portions of the protons (~30%) was consumed to be accommodated in the restacked Ti0.87O20.52 nanosheets, being compatible


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with the increase of the zeta potential values from ca. 39 to 13 mV. A designated amount of 1Tphase MoS2 suspensions was subsequently added into the flocculated suspension of Ti0.87O20.52 nanosheets. The precipitates turned its color from white to black, indicating the successful modification with MoS2. The MoS2 nanosheets did not flocculate themselves, based on the flocculation control test on the MoS2 dispersion using an equivalent amount of HCl, which yielded no precipitates (Figure S3). The X-ray diffraction (XRD) pattern of the restacked Ti0.87O20.52 was basically composed of 0k0 and h0l reflections (Figure 2a), which are indicative of a lamellar structure. The diffraction peaks at 2 values of 8.24 and 16.5 can be indexed as the 010 and 020 planes of the basal series with an interlayer spacing of 1.07 nm. The sample exhibited 20 and 02 diffraction bands from the two-dimensional in-plane atomic arrangement of the Ti0.87O20.52 nanosheets, indicating that the 2D structure was maintained. After the addition of MoS2, the diffraction pattern remained practically unchanged except for a slight interlayer expansion of 0.04-0.1 nm. It should be noted that a peak attributable to the restacked MoS2 nanosheets expected to appear at 2 = ~14 was not detected over the entire MoS2 loadings, implying that the MoS2 nanosheets were attached as a monolayer form and the self-flocculation of the MoS2 was negligible. The attachment of MoS2 can be further confirmed from the progressive color changes of the dried products from pale yellow to dark greenish with increasing the MoS2 dose (Figure 2b), which are in accordance with the absorbance increase in the visible region due to the absorption from the metallic MoS2 (Figure 2c). On the other hand, physical mixtures of independently flocculated Ti0.87O20.52 and MoS2 nanosheets did not show uniform colors (Figure S4). The morphology of the samples showed the agglomeration of irregularly accumulated flaky particles (Figure S5). No microstructural changes were observed upon the addition of MoS2


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nanosheets, suggesting that the MoS2 should be intimately attached on the surface of the restacked Ti0.87O20.52 owing to the highly flexible nature of the individual nanosheets. The apparent lateral dimension of the flakes is larger (10-20 m) than that of the individual nanosheets, indicating that the flakes are agglomerates composed of several nanosheet stacks. This feature was also recognized from the transmission electron microscopy (TEM) observation (Figure 3a), where the restacked nanosheets could be distinguished by their edge regions. Close observation revealed the open and loose microstructure with a lamellar lath-like texture having a thickness of 10-15 nm (Figure 3b), corresponding to stacks of 10-15 nanosheets. The stacking thickness was much smaller than that for the starting titanate before exfoliation, K0.8Ti1.73Li0.27O2 (5-10 m), providing the high surface area. The presence of 1T-phase MoS2 on the restacked Ti0.87O20.52 was confirmed by electron diffraction (ED) analysis (Figure 3c), as indicated by in-plane diffraction rings of 11 and 32 based on a plausible 2D 31 superstructure.43,44 In contrast, high-resolution TEM only showed the lattice fringes from the restacked Ti0.87O20.52 with an average interlayer spacing of ~1 nm. We performed observations over 20 different locations and did not detect any restacked MoS2 nanosheets, which should show a smaller spacing of ~0.6 nm. The presence of MoS2 was further corroborated by X-ray photoelectron spectroscopy (XPS) (Figure 3d), showing the gradual increase in the spectral intensities of the Mo 3d and S 2p core levels with increasing the MoS2 loading. Furthermore, the energy dispersive X-ray spectroscopy (EDS) map indicated the uniform distribution of MoS2 on the restacked Ti0.87O20.52 (Figure 3e). To sum up, these results suggest that the MoS2 nanosheets attach only on the surface of restacked laths of Ti0.87O20.52 nanosheets. On the basis of structural considerations, we can estimate that a 18 wt% loading of MoS2 will result in the monolayer coverage (Supporting Information S6), assuming the individual lath of a


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15-layered nanosheet stack. Thus the loading range explored corresponds to a sub-monolayer coverage up to 55%. The photocatalytic activity of the obtained samples was examined for the hydrogen evolution reaction from an aqueous methanol solution under UV light irradiation (Figure 4a-b). The MoS2modified restacked-Ti0.87O20.52 exhibited H2 evolution activity up to ~1.2 mmol h-1 g-1 at a 2.5 wt% MoS2 loading, which is approximately 10 times higher than that of the restacked Ti0.87O20.52 itself and P25 nanoparticles (~0.15 and ~0.09 mmol h-1 g-1, respectively). In the case of nanoparticles, lesser degree of enhancement, typically 5-8 times, was reported upon loading of MoS2 nanosheets.45,46 The activity gradually decreased with further MoS2 loadings, which is the general trend for the co-catalyst modification. The enhancement of the photocatalytic activity can be ascribed to the extensive molecular-level interfacial contact of 2D nanosheets that can promote the injection of photogenerated electrons from Ti0.87O20.52 nanosheets to 1T-phase MoS2,47 facilitating the efficient separation of photogenerated carriers. Eventually, the transferred electrons can be effectively utilized for the hydrogen evolution reaction by taking advantages of the catalytic nature of metallic 1T MoS2. We also examined control samples of physical mixtures of independently flocculated Ti0.87O20.52 and MoS2 nanosheets and P25-nanoparticles modified with MoS2 under the identical experimental conditions (see the details in the Supporting Information S9-10). The former and the latter samples exhibited the activity up to ~0.38 and ~0.4 mmol h-1 g-1 (Figure 4c), respectively. The enhacement with respect to the materials without MoS2 is 2-4 folds, being much smaller than the sample in the present study. The lower photocatalytic activity may be attributed to the increase of the recombination rate of photogenerated carriers due to insufficient separation. This aspect can be understood because the physical mixture of independently flocculated Ti0.87O20.52 and MoS2


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nanosheets resulted in poor interfacial contact between self-flocculated aggregates of the two nanosheets. The use of P25 nanoparticles failed to attain wide-area intimate contact with MoS2 cocatalyst (Figure S11). These results are further supported by the Nyquist plots (Figure 4d). A smaller radius was observed for the MoS2-modified restacked-Ti0.87O20.52 electrode, suggesting a lower overall charge-transfer resistance.48,49 This result further demonstrates an eficient charge transfer across the electrode/electolyte interface upon the hybridization of monolayer MoS2 and Ti0.87O20.52 nanosheets. Thus, this comparison clearly underlines the merits of extensive coupling interfaces of 2D nanosheets, which definitely cannot be achieved with their nanoparticle or bulkscale counterparts. The restacked Ti0.87O20.52 nanosheets modified with monolayer co-catalyst of metallic MoS2 have demonstrated a remarkable enhancement of the photocatalytic activity for H2 evolution. There are three benefits that account for such an enhancement from the utilization of restacked nanosheets and their modification with a monolayer co-catalyst. First, the restacked flocculates are typically composed of 10-15 stacking layers. Thanks to such an ultrathin nature, even the Ti0.87O20.52 nanosheets at the deepest location in the the restacked flocculates can be photoactivated to generate electron-hole pairs.50 Second, the open and loose microstructure of the restacked nanosheets with high surface area (~40 m2 g-1, Figure S7) provides abundant active sites exposed, which should improve the surface contact with the water molecules and sacrificial reagents during the H2 evolution reaction. The third is the attachment of unilamellar MoS2. In general, co-catalysts are impregnated as a thick and dense body, significantly damping the penetration of light. Thus, photocatalysts beneath the co-catalyst become inactive. In that aspect, the unilamellar attachment of MoS2 can be regarded as the most favorable feature for the enhancement of the photocatalytic activity. Needless to say, the monolayer attachment provides a


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low shielding effect for the restacked Ti0.87O20.52. For example, the monolayer of MoS2 shows an absorbance of ~0.05 at  = 400 nm (equivalent to a ~10% damping of the incident light intensity). Thus, the restacked Ti0.87O20.52 nanosheets beneath the MoS2 can work even though they are covered with unilamellar MoS2 nanosheets, being exposed to abundant incident light. In addition, the electrons injected from Ti0.87O20.52 nanosheets can immediately migrate to the MoS2 surface, which are thus favorable for the efficient reduction of H+ into H2. If multilayer crystallite MoS2 as the co-catalyst is attached on the Ti0.87O20.52 surface, the electrons need to hop the multiple sheets until they reach the top-most surface.42 It is widely known that migration of carriers between the layers is slow and sluggish, which may lead to higher probability for electron-hole recombination.

CONCLUSION We have successfully attained the monolayer modification of restacked Ti0.87O20.52 nanosheets with 1T-phase MoS2 via a facile two-step flocculation process. The H+ concentration in the solution played a key role to allow the attachment of MoS2 nanosheets on restacked Ti0.87O20.52. The MoS2-modified restacked-Ti0.87O20.52 exhibited a highly efficient photocatalytic activity for hydrogen evolution, which is superior to those of physical mixtures of independently flocculated Ti0.87O20.52 and MoS2 nanosheets and P25-nanoparticles modified with MoS2, emphasizing the significant importance of molecular-level interfacial hybridization of 2D nanomaterials. Our synthetic strategy provides a facile and robust process for fabricating this type of heterostructure, which is beneficial for large-scale production thanks to its solution processability, room temperature operation, and no required additional energy in its process. We believe that this approach can open a promising avenue for a range of applications, not only for catalysis/photocatalysis but also for optoelectronics and energy storage.


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EXPERIMENTAL SECTION Materials. Reagents such as TiO2, K2CO3, and Li2CO3 were of 99.9% purity or higher (Rare Metallic Co., Japan). Bulk MoS2 crystals were purchased from Furuuchi Kagaku, Japan. nbutyllithium in hexane (1.6 M) was purchased from Wako Chemicals, Japan. Commercial TiO2 nanoparticles (P25), anatase:rutile = 70:30, was obtained from Japan Aerosil. All the other chemicals and solvents were of analytical grade and used without further purification. Ultrapure water (>18 M cm) filtered by a Milli-Q water filtration system was used throughout the experiments. Preparation of Ti0.87O20.52 and 1T-phase MoS2 nanosheets. The starting material for the nanosheets, K0.8Ti1.73Li0.27O2, was synthesized via a conventional solid-state calcination process.51 Reagents of K2CO3, TiO2, and Li2CO3 were mixed at a molar ratio of 0.4:1.73:0.135 and heated at 1173 K for an hour to be decarbonated. Then the powder was ground and calcined at 1273 K for 20 h. The obtained sample of K0.8Ti1.73Li0.27O2 (20 g) was treated with 1 dm3 of a HCl solution (1 mol dm-3) for 72 h. The HCl solution was replaced daily with a fresh solution by decantation. The product was recovered by filtration, washed with water, and air-dried. The resulting H+-exchanged phase, H1.07Ti1.73O4H2O (4 g), was exfoliated by treating with 1 dm3 of a 0.026 mol dm-3 tetrabutylammonium hydroxide solution under reciprocal shaking for 7 days.52,53 The resulting suspension contained monodisperse unilamellar Ti0.87O20.52 nanosheets having a lateral size of 0.3-2 m. 1T-phase MoS2 nanosheets were prepared through chemical exfoliation according to the literature.54 First, the starting crystals were pre-expanded by refluxing in N2H4 at 130 C for 24 h.55,56 The resulting powders were then lithiated by a 2.5-fold molar excess of the n-hexane solution


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of n-butyllithium in an Ar-filled dry box. The lithiated product was recovered by filtration and washed with hexane. Exfoliation was achieved by treating the lithiated product with water under ultrasonication and then centrifuging at 2000 rpm to remove the unexfoliated crystals. The successful formation of the 1T-type MoS2 nanosheets was confirmed as reported previously.43 Monolayer modification with MoS2. Attachment of 1T-phase MoS2 nanosheets onto restacked-Ti0.87O20.52 was conducted via a two-step flocculation process. Typically, 2 cm3 of a HCl solution (0.5 mol dm-3) was introduced into 200 cm3 of a colloidal suspension (0.2 g dm-3) of Ti0.87O20.52 nanosheets under continuous stirring. A designated amount of the 1T-phase MoS2 suspension was then added at a drop rate of 1 cm3 min-1. The resulting flocculate was collected by centrifugation, washed with water, and freeze dried. Fabrication of control samples: Physical mixtures of independently flocculated Ti0.87O20.52 and 1T-MoS2. A colloidal suspension of Ti0.87O20.52 nanosheets (0.2 g dm-3) was flocculated via addition of HCl solution. Metallic MoS2 was separately flocculated with a HCl solution at higher concentration. A designated amount of the flocculated MoS2 was then added to the solution of restacked Ti0.87O20.52 nanosheets under vigorous stirring. The resulting mixtures were then collected by centrifugation, washed with water, and freeze dried. P25-nanoparticles modified with 1T-MoS2. P25 nanoparticles and metallic 1T-phase MoS2 nanosheets was combined as follows. P25 nanoparticles were dispersed in water (0.2 g dm-3) followed by the addition of HCl (pH = ~2.3). The zeta potential value of the resulting dispersion was >30 mV. No sedimentation was observed after the addition of HCl, indicating that the agglomeration of P25 nanoparticles was not formed until this step. A designated amount of 1Tphase MoS2 was then added at a rate of 1 cm3 min-1, immediately forming precipitates of


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MoS2/P25-nanoparticles. The resulting mixtures were then collected by centrifugation, washed with water, and freeze dried. Characterizations. Topographic images of the nanosheets were obtained with a Hitachi SPA 400 atomic force microscope (AFM) in tapping mode using a Si-tip cantilever. Transmission electron microscopy (TEM) images and selected area electron diffraction (SAED) patterns were obtained with a JEOL JEM-3000F. The morphology of the restacked products was examined using a JEOL JSM-6010 LA scanning electron microscope (SEM) equipped with a Horiba energydispersive X-ray spectrometer (EDS). The specimens were coated with Pt to minimize the charging effect. The adsorption/desorption isotherm data of N2 were recorded using a Quantachrome Autosorb-1. A sample was outgassed under vacuum for 2 h at 423 K prior to each measurement. The BET surface area was calculated in a relative pressure range of 0.05 < P/P0 < 0.3. X-ray photoelectron spectroscopy (XPS) measurements were performed with a Thermo Scientific Theta Probe Thermo Electron spectrometer equipped with an Al K source. The spectra were calibrated relative to the C 1s binding energy at 284.8 eV. The UV-visible diffuse reflectance spectra of the obtained samples were recorded using a Shimadzu SolidSpec 3700 DUV. Powder X-ray diffraction (XRD) data were collected using a Rigaku Rint ULTIMA IV diffractometer with monochromatic Cu K radiation ( = 0.15405 nm). The zeta potential values of the suspensions were measured with an ELS-Z zeta potential analyzer. Photocatalytic tests. All photocatalytic tests were performed in an airtight quartz reaction cell (4 cm3 capacity), which was equipped with an outer jacket sealed with a PTFE tape. The photocatalyst powder (1 mg) was suspended in 2 cm3 of an aqueous 10 vol% methanol solution. Prior to each run, the reaction cell was bubbled with Ar gas for 30 min. To prevent air contamination, the Ar gas was circulated into the outer jacket during the test. Under constant


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stirring, the sample was irradiated using a UV light source (San-Ei electric XEF-501S,  = 300500 nm) with an intensity of 19 mW cm-2. The evolved H2 gas was determined using gas chromatography (Shimadzu GC-14, MS-5A column, Ar carrier, TDC), by collecting a headspace gas sample (0.05 cm3) using an airtight syringe. Commercial P25 nanoparticles (specific surface area of 55  15 m2 g-1) were used for comparative photocatalytic experiments. Electrochemical measurements. The electrochemical impedance spectroscopy (EIS) analysis was performed on a CH Instruments 760E electrochemical workstation using 0.5 mol dm-3 H2SO4 aqueous solution as an electrolyte, coiled platinum wire as a counter electrode, and Hg/Hg2SO4 electrode (= +0.657 V vs NHE) as a reference electrode. A 2.4 mg portion of photocatalyst powder was dispersed in a 0.01 cm-3 Nafion solution (10 wt%) and a 0.4 cm3 mixed solution of water and propanol (1:4, v/v). The working electrode was prepared by dropping 3  10-3 cm-3 of the mixture suspension onto a glassy carbon electrode (Ø = 3 mm), and dried at room temperature. The EIS measurements were performed in the dark under an Ar atmosphere by applying a sinusoidal AC voltage with 5 mV amplitude in a frequency range of 0.1 to 105 Hz at a current density of 10-2 mA cm-2.

ASSOCIATED CONTENT Supporting Information. AFM characterization of the Ti0.87O20.52- and 1T-phase MoS2 nanosheets, zeta potential data, morphology of the restacked products (SEM), BET surface area, time course of H2 evolution of P25 nanoparticles, and results of the control experiments of the restacked Ti0.87O20.52 nanosheets and P25-TiO2 nanoparticles conventionally modified with MoS2.


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AUTHOR INFORMATION Corresponding Author *T. Sasaki. Email: [email protected] Author Contributions L.N., J.W., and T.S. conceived the project and designed the experiment; L.N. and J.W. carried out the experiments, characterizations, photocatalytic tests, and electrochemical measurements; N.S., R.M., and Y.E. assisted with the characterizations and photocatalytic tests, and gave constructive advices on this work; L.N., assisted by J.W., wrote the original draft and T. S. completed it. L.N.

and J.W. contributed equally to this work.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the WPI-MANA, Ministry of Education, Culture, Sports, Science and Technology, Japan. T.S. acknowledges partial supports from the JSPS KAKENHI (15H02004, 16K13631) and CREST of the Japan Science and Technology Agency (JPMJCR17N1). N.S. acknowledges partial supports from the JSPS KAKENHI (16K14428).


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Figure 1. Schematic illustration for the restacking of Ti0.87O20.52 nanosheets and subsequent monolayer modification with MoS2 nanosheets.

Figure 2. a) XRD patterns, b) photographs, and c) UV-visible diffuse reflectance of restacked products with different MoS2 loadings.


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Figure 3. a,b) TEM images of restacked-Ti0.87O20.52/MoS2 (10 wt%), and c) corresponding ED pattern. d) XPS of samples at different MoS2 loadings. The intensities of the Mo 3d and S 2p spectra were normalized to those of the corresponding Ti 2p. e) EDS elemental mapping of 10 wt% sample.

Figure 4. a,b) Time course and rate of photocatalytic H2 evolution of MoS2-modified restackedTi0,87O20.52 at different MoS2 loadings. TF and MF are restacked Ti0.87O20.52 and 1T-phase MoS2


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alone, respectively. c) Photocatalytic activities in comparison with physical mixture of independently flocculated Ti0.87O20.52/MoS2 (blue trace) and P25-nanoparticles modified with MoS2 (green trace). d) Electrochemical impedance spectroscopy (EIS) Nyquist plots obtained in the dark.


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TABLE OF CONTENTS/ABSTRACT GRAPHIC


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Monolayer Attachment of Metallic MoS2 on Restacked Titania

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