Liquid-Phase Exfoliation into Monolayered BiOBr Nanosheets for

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Liquid Phase Exfoliation into Monolayered BiOBr Nanosheets for Photocatalytic Oxidation and Reduction Hongjian Yu, Hongwei Huang, Kang Xu, Weichang Hao, Yuxi Guo, Shuobo Wang, Xiulin Shen, Shaofeng Pan, and Yihe Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02508 • Publication Date (Web): 12 Oct 2017 Downloaded from http://pubs.acs.org on October 13, 2017

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ACS Sustainable Chemistry & Engineering

Liquid Phase Exfoliation into Monolayered BiOBr Nanosheets for Photocatalytic Oxidation and Reduction †

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Hongjian Yu , Hongwei Huang*, , Kang Xu ,Weichang Hao , Yuxi Guo , Shuobo Wang , Xiulin Shen†, Shaofeng Pan†, Yihe Zhang*,† †

Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes,

National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China ‡

Center of Materials Physics and Chemistry and Department of Physics, Beihang University,

Beijing 100191, China *

Corresponding author. Tel.: +86-10-82322247.

E-mail: [email protected] (H. W. Huang); [email protected] (Y. H. Zhang)

ACS Paragon Plus Environment

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ABSTRACT: Monolayered photocatalytic materials have attracted huge research interests in terms of their large specific surface area and ample active sites. Sillén-structured layered BiOX (X=Cl, Br, I) casts great prospects owing to their strong photo-oxidation ability and high stability. Fabrication of monolayered BiOX by a facile, low-cost and scalable approach is highly challenging and anticipated. Herein, we describe the large-scale preparation of monolayered BiOBr nanosheets with a thickness of ~0.85 nm via a readily-achievable liquid phase exfoliation strategy with assistance of formamide at ambient conditions. The as-obtained monolayered BiOBr nanosheets are allowed diverse superiorities, such as enhanced specific area, promoted band structure and strengthened charge separation. Profiting from these benefits, the advanced BiOBr monolayers not only show excellent adsorption and photodegradation performance for treating contaminants, but also demonstrate a greatly promoted photocatalytic activity for CO2 reduction into CO and CH4. Additionally, monolayered BiOI nanosheets have also been obtained by the same synthetic approach. Our work offers a mild and general approach for preparation of monolayered BiOX, and may have huge potential to be extended to synthesis of other single-layer two-dimensional materials. KEYWORDS: BiOBr; monolayered nanosheets; liquid phase exfoliation; photodegradation; CO2 reduction


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INTRODUCTION Layered materials are considerable interest and widely applied in the fields of electronics,1 catalysis,2 energy generation and storage,3,4 biologies5 and so on. The layered feature enables these layered materials, such as graphene,6 layered double hydroxides (LDHs),7 bismuth semiconductor,8 C3N49 and transition metal dichalcogenides10, to be monolayered nanosheets by a variety of chemical methods. Especially, the preparation of single-layer or few-layers twodimensional (2D) photocatalytic materials is considered as a new promising method to improve the photocatalytic efficiency. Duo to the substantial exposing surfaces and numerous uncoordinated surface atoms, the monolayered nanosheets are endowed with large surface area and abundant catalytic sites for photocatalytic reactions. The ultrathin structure can also enable the photogenerated carriers to migrate fast from the inside of the particles to the surface, which greatly decreases the bulk recombination and promote the photocatalytic redox reaction.11, 12 As a series of layered ternary oxide semiconductor, Sillén structured BiOX (X=Cl, Br, I) have gained widespread attention, owing to their high activity, high stability, non-toxicity, and other advantages.13-16 Despite a great deal of efforts have been made to improve the photocatalytic activity of BiOX (X=Cl, Br, I), such as elemental doping,17 noble metal deposition,18 and heterojunction fabrication,19,20 it is still far from sufficient for potential applications and it is necessary to further improve the photocatalytic activity to meet the potential industrial applications. The crystal structure of BiOX (X=Cl, Br, I) belongs to PbFCltype tetragonal system with a space group of P4/nmm,21 where the layered structure is built by [Bi2O2] slabs stacked together by the weak nonbonding (van der Waals) interaction and slabs of double halogen atoms along the c axis direction. Because of the weak interaction between layers, it is possible to exfoliate BiOX into ultrathin nanosheets or even monolayered sheets.22 Though


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monolayer or few-layers of BiOX (X=Cl, Br, I) materials have been obtained 23-27, however, the reported synthetic techniques always require high temperature, high pressure, and complex procedures, which greatly confine their large-scale practical applications. Herein, we report the preparation of monolayered BiOBr nanosheets via a facile and scalable liquid phase exfoliation strategy with assistance of formamide at room temperature. Formamide molecules can react with the surface OH on bulk BiOBr, thereby rendering the formation of single-layer BiOBr. These BiOBr monolayers are found possessing large specific surface area, abundant active sites and oxygen vacancies, optimized band structure as well as promoted charge separation. Owing to these advantages, the monolayered BiOBr nanosheets show high adsorption capability, efficient photocatalytic degradation and CO2 reduction performance. The proposed strategy has huge potentials to be extended to preparation of other layered materials.

EXPERIMENTAL SECTION Materials synthesis All of the reagents used in this work were analytical grade and used as received without further purification. The bulk BiOBr was obtained by a sample hydrolysis method. 8 mmol Bi(NO3)3•5H2O (Sinopharm) was added to 50 mL deionized water, and dispersed by ultrasonic bath and magnetic stirring for 20 min. Meanwhile, 8 mmol KBr (Sinopharm) was dissolved in 50 mL deionized water. Then, the KBr solution was dropwise added into the Bi(NO3)3•5H2O suspension. The mixture was stirred for 8 h at room temperature. After that, the pale-yellow products were washed with deionized water for several times and dried at 60 oC for 12 hours in a vacuum drying oven. For synthesis of monolayered BiOBr nanosheets, 0.2g as-prepared BiOBr


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was added into 100 ml formamide (XiLong Scientific) solution in a three mouth flask, and then the mixture was stirred at a speed of 260 r/min for 6 hours under ultrasonic. Then, the suspension was centrifuged at the speed of 4000 r/min for 10 minutes to remove non-exfoliated materials. Finally, the supernatants were collected and centrifuged at the speed of 10000 r/min for 20 minutes, and the precipitates are monolayered BiOBr nanosheets. The color of monolayered BiOBr nanosheets is white (Fig. S1), and 0.2g bulk BiOBr can produce about 30-40 mg monolayered BiOBr nanosheets. Characterization AFM images were recorded using Oxford MFP-3D AFM (Oxford MFP-3D, UK). XRD of bulk BiOBr and monolayered BiOBr were carried out on a D8 Advance X-ray diffractometer (Bruker AXS, Germany) with Cu Kα radiation (λ = 1.5418 Å). Transmission electron microscopy (TEM) images were obtained by an electron microscopy (Hitachi H-8100, Japan). High-resolution transmission electron microscopy (HRTEM) images were acquired by a Tecnai F20 electron microscopy. The chemical compositions of the obtained materials were characterized by the X-ray photoelectron spectroscopy (XPS, ESCALAB 250 Xi ThermoFisher, UK). The room temperature X-ray Absorption Fine Structure (XAFS) data on the Bi L3-edge (13.419 keV) of bulk BiOBr and monolayered BiOBr were measured at the 16BM-D station of the High-Pressure Collaborative Access Team (HPCAT) at the Ad-vanced Phonon Source of Argonne National Laboratory. The data were processed and fitted with the program Athena28. Brunaure-Emmett-Teller (BET) surface area was recorded by nitrogen adsorption with a Micromeritics 3020 instrument. Zeta potential measurement was determined by a Zeta potential (Malvern ZS90, UK). The UV–Vis diffuse reflectance spectra (DRS) of prepared samples were determined on a UV-Vis spectrometer (Cary 5000 Varian, America) which can measure the


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optical properties of photocatalysts. The reflectance spectra of photocatalysts were collected at the range of 200–800 nm referenced to BaSO4. The PL spectra of the prepared materials were determined using a fluorescence spectrometer (F-4600 Hitachi, Japan). The photoelectrochemical properties of the obtained materials were measured by a three-electrode system and an electrochemical workstation (CHI660E, Chenhua Instruments Co. Shanghai, China). In this system, a saturated calomel electrode (SCE) was utilized as the reference electrode, and platinum wire was counter electrode, and the electrolyte solution was 0.1 M Na2SO4 solution. The sample films were coated on indium-tin oxide (ITO) sheet glass as the working electrode. A 300 W xenon lamp was used as the visible light source. There was no applied voltage between the electrodes. And all the measurements were collected at room temperature. The working electrode was sampled by a dip-coating method: Photocatalyst powder (30 mg) was dispersed in 2 mL of ethanol to obtain a uniform slurry. After that, the suspension was dropped on a indium– tin oxide (ITO) glass with size of 10 mm × 20 mm. Then, this working electrode was dried at 373 K for 10 h to eliminate ethanol. Photodegradation experiments The photocatalytic activities of as-prepared products were investigated by the degradation of methyl orange (MO) under simulated sunlight irradiation provided by a 500 W Xenon lamp. During the test, 30 mg sample powders were dispersed into 50 mL of 2×10−5 M methyl orange (MO) aqueous solution in a quartz tube. In order to ensure the adsorption–desorption equilibrium between solution and power, all the suspensions were stirred in the dark for 60 min before irradiation. After the Xe lamp was turned on, 3.0 mL of suspensions were taken at a certain interval of time. To remove the catalyst, the obtained liquids needed to be filtrated by a high


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speed centrifuge. Finally, the filtrates were tested on a Varian UV-Vis spectrophotometer (Shimadzu UV-5500PC, Japan) at wavelength 464 nm. Photocatalytic CO2 reduction test Photocatalytic reduction of CO2 experiments were conducted in a closed PLS-SXE300 Labsolar-IIIAG gas system with a 300 W Xe lamp (PLS-SXE300, China) as the light source. Then, the reactor was full of CO2 or argon to conduct the reaction with 200 mg photocatalyst powder. Afterward, the produced gases were analyzed by a gas chromatography (GC7900, Tianmei, Shanghai, TCD).

RESULTS AND DISCUSSION Fig. 1a shows the layered structure of bulk BiOBr built up by [Bi2O2] layers and Br slabs.29 When bulk BiOBr is exfoliated into monolayers, the BiOBr monolayer has three possible structures with different surface exposing atoms, namely Bi exposed surface, O exposed surface and Br exposed surface, as presented in Fig. 1c. According to density functional theory (DFT) calculations, the surface energy of the above three possible structures are calculated (Figure 1b). It is demonstrated that the surface energy of the crystal surface for the monolayered BiOBr structure with Br exposing atoms is the lowest among the three structures, indicating the higher thermodynamic stability. Therefore, the surface exposing atoms of monolayered BiOBr should be Br atoms.


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Figure 1. (a) Crystal structure of bulk BiOBr. (b) Surface energy of BiOBr with different surface exposing atoms.(c) Crystal structure of monolayered BiOBr with different surface exposing atoms. Atomic force microscopic (AFM) is employed to determine the thickness of BiOBr samples. The AFM images (Fig. 2a-d) show that the thickness of exfoliated BiOBr samples is approximately 0.85 nm, which agrees well with the thickness of monolayered BiOBr along the [001] direction. Clearly, this result illustrates that monolayered BiOBr nanosheets are successfully prepared by this simple liquid phase exfoliation route. The transmission electron microscopy (TEM) images (Fig. 2e and g) also demonstrate that the transparent BiOBr nanosheets are observed, which confirms the ultrathin structure and supports the AFM result.


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The selected area electron diffraction pattern displayed in the Fig. 2f reveals the [200] and [110] zone axis. The marked interplanar spacing of 0.28 nm corresponds to the (110) crystal plane of BiOBr (Fig 2h), which indicates that the exposed facet of monolayered BiOBr is (001) facet. Xray diffraction patterns of the bulk BiOBr and monolayer BiOBr samples are displayed in Fig. 2i. All of the diffraction peaks can be indexed to the tetragonal phase BiOBr with lattice parameters a=3.915 Å, b=3.915 Å and c=8.11 Å (JCPDS No. 73-2061). Notably, disappearance of the diffraction peak corresponding to the (001) plane of BiOBr surface, which reveals the drastic decrease in diffraction intensity of (001) direction, suggesting the successful exfoliation of BiOBr along this direction. The above results demonstrate that the monolayered BiOBr nanosheets were successfully obtained. Besides, the monolayered BiOI nanosheets have been prepared by the same synthetic route. The thickness of BiOI nanosheets is in the range of 0.8-1 nm (Fig. S2), which is consistent with the theoretical monolayered BiOI thickness (0.91 nm). It indicates the universality of the current synthetic strategy.


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Figure 2. (a,b,c,d) AFM images and corresponding height profiles of monolayered BiOBr nanosheets. (e, f) TEM image and the corresponding SAED pattern of superposition of multiple monolayer BiOBr. (g, h) TEM image and the corresponding HRTEM image of monolayered BiOBr. (i) XRD patterns of bulk BiOBr and monolayered BiOBr. (j) Crystal structure of monolayered BiOBr. To further reveal the interaction between atoms and get more information on the local structure evolution, XAFS on the Bi L3-edge (13.419 keV) of bulk BiOBr and monolayered BiOBr were carried out at room temperature. As shown in Fig. 3a, the Bi L-edge oscillation curves of bulk BiOBr and monolayered BiOBr present different profiles in the energy range of 13200-14200 eV, which illustrates the difference of local atomic arrangements in the catalysts. Fig. 3b displays the in situ Fourier transformed profiles of XAFS. It is obvious that there are three peaks in the range from 1 to 4 Å, which correspond to the Bi-O, Bi-Br and Bi-Bi distances, respectively. The radial distance of Bi-O in monolayered BiOBr is 0.04 Å shorter than bulk BiOBr, which revealed the presence of O vacancy30,31. The larger Bi-Br bond length in monolayered BiOBr than that in bulk BiOBr should be attributed to the exposing of surface Br atoms derived from monolayered structure. Compared to bulk BiOBr, the shorter Bi-Bi bonds in monolayer BiOBr should also be resulted from the lattice local contraction due to O vacancy. X-ray photoelectron spectroscopy (XPS) of the bulk BiOBr and monolayered BiOBr was conducted to analyze the surface composition and chemical states of related elements. Br 3d, Bi 4f and O 1s all can be found in the survey XPS spectra as displayed in Fig. 3c. For bulk BiOBr, the Bi 4f XPS spectra contain two peaks at binding energies of 159.5 and 164.8 eV, which belong to Bi 4f5/2 and Bi 4f7/2 in the [Bi2O2]2+ layer (Fig. 3d), respectively. Compared to bulk


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BiOBr, the Bi 4f peak in the BiOBr monolayer exhibits an obvious shift with binding energies of 4f5/2and 4f7/2 are 158.8 and 164.3 eV, respectively. This difference showed that the chemical environment of surface Bi atoms in the monolayered BiOBr has changed, mainly due to the absence of some lattice oxygen atoms. Figure 3e shows the O 1s XPS spectra. The two peaks at 529.9 eV and 531.3 eV occurred for both bulk BiOBr and monolayered BiOBr, which correspond to lattice oxygen and surface hydroxyls, respectively. In comparison with bulk BiOBr, monolayered BiOBr has an evidently higher -OH amount. It may be owing to the absence of parts of surface Br atoms, resulting in more exposure of Bi atoms on the surface. The peak at 533.3 eV appeared in monolayered BiOBr is assigned to adsorbed water. This is because the surrounding water has strong interaction with open metal sites on the monolayer surfaces11,32 The peaks located at 68.6 eV belong to Br 3d, which are well consistent with those in BiOBr11. (Fig. 3f). In contrast to bulk BiOBr, the Br 3d peak of monolayered BiOBr also shifted, which further suggests the exposure of surface Bi atom. Obviously, these observations are in good agreement with the above XAFS results.


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Figure 3. (a) Normalized Bi L-edge XAFS spectra and (b) Fourier transformed profiles for Bi coordination environments of bulk and monolayered BiOBr. XPS spectra of (c) Survey, (d) highresolution Bi 4f, (e) O 1s and (f) Br 3d of bulk and monolayered BiOBr. According to the above observations, the formation mechanism for monolayered BiOBr was proposed as exhibited in Scheme 1. Similar to LDH exfoliation process, it is easy for formamide


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molecules to enter into the interlayers of bulk BiOBr and combine with the hydroxyl groups via hydrogen bond.33 With the increase of the amount of formamide molecules, the hydrogen bond between formamide molecules enlarges the interlayer distance of BiOBr, which weakens the interaction between layers. Under the action of mechanical agitation from stirring and ultrasonic, the BiOBr lamellas undergo lateral sliding, and bulk structures collapse, and finally large amount of monolayered BiOBr nanosheets are obtained. Scheme 1. Schematic illustration for formation of monolayered BiOBr nanosheets.

To inspect the change of optical absorption capability and band gap, UV/vis diffuse reflectance spectra (DRS) were measured and displayed in Fig. 4a. Compared to bulk BiOBr, the absorption edge of monolayered BiOBr nanosheets shows an obvious blue shift, which corresponds well to the nanosheet nature. The band gap energies of the as-obtained samples are calculated by the Kubelka−Munk (KM) expression: 34 αhν= A (hν – Eg) n/2

(1)

Where α, hν, A, and Eg represent the optical absorption coefficient, photonic energy, proportionality constant and band gap, respectively. BiOBr is an indirect semiconductor, so n is 4.35 The bandgap energy of monolayered BiOBr is 2.82 eV, which is 0.9 eV higher than the bulk BiOBr (2.73 eV) (Inset of Fig. 4a). Mott−Schottky plots are measured to provide the band


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structure information. As seen from Fig. 4b, the flat band potentials of bulk and monolayered BiOBr samples are -0.60 and -0.66 eV versus SCE, respectively. As the conduction band (CB) position is near the flat band potential, the CB position monolayered BiOBr is approximately 0.06 eV higher than that of bulk BiOBr. Combined with UV/vis DRS results, it is easy to know that the monolayered BiOBr has a more positive valence band (VB) position than bulk BiOBr by 0.03 eV. To confirm alteration in band energy levels, electronic band structures of the bulk and monolayer BiOBr were analyzed theoretically. As exhibited in Fig. 4d and e, the band structure evolution is resulted from the up-shift of CB position and down-shift of VB position, which agree well with the above experimental data. In general, the bandgaps calculated by DFT are smaller than that measured from the experimental determination,11,36,37 due to the band gap underestimate of DFT calculations. The plots of densities of states are illustrated in Fig. 4f and g. For bulk and monolayered BiOBr, the top of VB and the bottom of CB are both mainly composed of hybrid O 2p–Br 3p orbital and Bi 6p orbital, respectively. These results revealed that the monolayered BiOBr has stronger oxidation and reduction driving force,

38,39

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would contribute to the photocatalytic oxidation and reduction performance.


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Figure 4. (a) UV-vis diffuse reflectance spectra (DRS) and band gap (inset) of bulk and monolayered BiOBr. (b) Mott–Schottky plots of bulk and monolayered BiOBr at afrequency of 1000 Hz (0.1 M Na2SO4). (c) Band structure diagrams of bulk and monolayered BiOBr. (d,e) Electronic band structures and (f, g) density of states (DOS) of bulk and monolayered BiOBr， respectively. To systematically assess the monolayered BiOBr, the photocatalytic oxidation and reduction performance is invesitgated. First, the as-prepared materials were monitored by testing the adsorption and photodegradation properties of MO. As presented in Fig. 5a, compared to bulk BiOBr, monolayered BiOBr shows a stronger adsorption capacity to MO. After the irradiation for 4h (Fig. 5b), 33% of MO can be removed by monolayered BiOBr, while for bulk BiOBr, the removal of MO was only 16.5%. It indicates that the monolayered BiOBr demonstrates more efficient photocatalytic oxidation ability. In order to further evaluate the photocatalytic activity of the monolayered BiOBr, CO2 reduction performance was monitored, as displayed in Fig. 5c-f. It is obvious that the generated amounts of CH4 and CO increase with irradiation time, and the production of CH4 and CO of monolayered BiOBr is almost 3 times higher than that of the bulk BiOBr. No gaseous products can be detected with purging argon, which eliminates the influence of residue organic impurities on the surface of monolayered BiOBr and demonstrates that CH4 and CO are truly produced in the photocatalytic CO2 reduction process.


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Figure 5. (a, b) Adsorption and photodegradation of MO over bulk and monolayered BiOBr materials under simulated sunlight. (c, d) CO and CH4 production curves and (e, f) corresponding rates over bulk and monolayered BiOBr under simulated sunlight. The photocatalytic activity of photocatalyst is always closely associated with band structure, specific surface area, and charge separation. Brunaure-Emmett-Teller (BET) N2 adsorption methods are employed to determine the surface area and porosity of the obtained materials, and


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the results are shown in Fig. 6a and b. The surface areas are 9.27 and 33.37 m2/g for the bulk BiOBr and monolayered BiOBr, respectively. Obviously, the monolayered BiOBr photocatalysts with higher BET surface area can absorb more reactants and generate more active species on their surface, enhancing the photocatalytic activity.12 Meanwhile, the Zeta potentials of bulk BiOBr and monolayered BiOBr are measured, which are +1.76 mV and +19.2 mV, respectively. Their Zeta potential difference is consistent with that of their surface areas. For photocatalytic materials, separation efficiency of charge carriers is a very important factor to affect the photocatalytic performance. As shown in Fig. 6c, monolayered BiOBr shows a photoluminescence emission peak with obviously lower intensity than bulk BiOBr, which illustrates that the recombination of photogenerated electrons and holes is depressed in monolayered BiOBr. Meanwhile, due to the nanosheet nature,39,40 the PL peak of monolayered BiOBr samples also display a clear blue shift, in accordance with the enlarged band gap. In order to further inspect the improved charge separation efficiency of monolayered BiOBr, photocurrent measurements are conducted as showed in Fig. 6d.41,42 The photocurrent intensity of monolayered BiOBr is higher than that of bulk BiOBr. This result further implies that more efficient charge separation occurred in the monolayered BiOBr.


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Figure 6. (a) Nitrogen absorption-desorption isotherms, (b) BET surface areas and Zeta potential, (c) Steady-state PL spectra and (d) Photocurrent density under simulated sunlight (0.1 M Na2SO4) of bulk BiOBr and monolayered BiOBr.

CONCLUSIONS In summary, monolayered BiOBr nanosheets with a thickness of ~0.85 nm have been synthesized by facile liquid phase exfoliation of bulk BiOBr under stirring and ultrasonic at ambient conditions. Compared to bulk BiOBr, monolayered BiOBr shows enhanced specific surface area, allowing more active sites. Monolayered BiOBr also possesses more negative


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conduction band position and more positive valence band position, offering stronger reduction and oxidation abilities, respectively. More importantly, a much strengthened charge separation efficiency was also achieved in monolayered BiOBr. The photocatalytic tests uncover that the monolayered BiOBr presents higher performance for adsorption, photodegradation and photocatalytic CO2 reduction into CO and CH4. Combining the photoelectrochemical and photocatalytic measurement results, enhanced charge separation in monolayered BiOBr should be the dominant factor for the increased photoactivity. Via the same synthetic route, monolayered BiOI nanosheets have been prepared as well, demonstrating the universality of the current strategy. Our study illustrates an easily-handled and efficient protocol for preparation of monolayered materials for environmental and energy applications.

■ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: The color of monolayered BiOBr, AFM images and the corresponding height profiles of monolayered BiOI nanosheets. (PDF)

■ AUSTHOR INFORMATION Corresponding Author *E-mail: [email protected]; Phone: +86-010-82332247 *E-mail: [email protected].


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Notes The authors declare no competing financial interest.

■ ACKNOWLEDGEMENTS This work was jointly supported by the National Natural Science Foundations of China (No. 51672258 and 51572246), the Fundamental Research Funds for the Central Universities (2652015296).

■ REFERENCES (1) Wang, X. C.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A Metal-Free Polymeric Photocatalyst for Hydrogen Production from Water under Visible Light. Nat. Mater. 2009, 8, 76-80. DOI:10.1038/nmat2317. (2) Wang, Q.H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S. Electronics and Optoelectronics of Two-Dimensional Transition Metal Dichalcogenides. Nat. Nanotechnol. 2012, 7, 699-712. DOI:10.1038/nnano.2012.193. (3) Lightcap, L. V.; Kosel, T. H.; Kamat, P. V. Anchoring Semiconductor and Metal Nanoparticles on a Two-Dimensional Catalyst Mat. Storing and Shuttling Electrons with Reduced Graphene Oxide. Nano. Lett. 2010, 10, 577-583. DOI: 10.1021/nl9035109.


22

Page 23 of 30

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


(4) Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Kim, K. S.; Ahn, J. H.; Kim, P.; Choi, J. Y.; Hong, B. H. Large-Scale Pattern Growth of Graphene Films for Stretchable Transparent Electrodes. Natrue. 2009, 457, 706. DOI: 10.1038/nature07719. (5) Park, H.; Li, Y. H.; Tsien, R.W. Influence of Synaptic Vesicle Position on Release Probability and Exocytotic Fusion Mode. Science. 2012, 335, 1362-1366. DOI: 10.1126/science.1216937. (6) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science, 2004, 306, 666-669. DOI: 10.1126/science.1102896. (7) Hibino, T.; Jones, W. New Approach to the Delamination of Layered Double Hydroxides. J. Mater. Chem. 2001, 11, 1321-1323. DOI: 10.1039/b101135i. (8) Liang, L.; Lei, F. C.; Gao, S.; Sun, Y. F.; Jiao, X. C.; Wu, J.; Qamar, S.; Xie, Y. Single Unit Cell Bismuth Tungstate Layers Realizing Robust Solar CO2 Reduction to Methanol. Angew. Chem. Int. Ed. 2015, 54, 13971. DOI: 10.1002/anie.201506966. (9) Dong, X.; Cheng, F. Recent Development in Exfoliated Two-Dimensional g-C3N4 Nanosheets for Photocatalytic Applications. J. Mater. Chem. A. 2015, 3, 23642-23652. DOI: 10.1039/c5ta07374j. (10) Shen, J. F.; He, Y. G.; Wu, J. J.; Gao, C. T.; Keyttal, K.; Zhang, X.; Yang, Y. C.; Yanng, M. G.; Vajtai, R.; Lou, J.; Ajayan, P. M. Liquid Phase Exfoliation of Two-Dimensional Materials by Directly Probing and Matching Surface Tension Components. Nano Lett. 2015, 15, 5449-5454. DOI: 10.1021/acs.nanolett.5b01842.


23


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 30

(11) Zhou, Y. G.; Zhang, Y. F.; Lin, M. S.; Long, J. L.; Zhang, Z. Z.; Lin, H. X.; Wu, J. C.-S.; Wang X. X. Monolayered Bi2WO6 Nanosheets Mimicking Heterojunction Interface with Open

Surfaces

for

Photocatalysis.

Nat.

Commun.

2015,

6,

8340.

DOI:

10.1038/ncomms9340. (12) Di, J.; Xia, J. X.; Ji, M. X.; Xu, L.; Yin, S.; Chen, Z. G.; Li, H. M. Bidirectional Acceleration of Carriers Separation Spatially via N-CQDs/atomically-thin BiOI Nanosheet Nanojunctions for Manipulating Active Species in Photocatalytic Process. J. Mater. Chem. A. 2016, 4, 5051-5061. DOI:10.1039/C6TA00284F. (13) Zhang, H. J.; Yang, Y. X.; Zhou, Z.; Zhao, Y. P.; Liu, L. Enhanced Photocatalytic Properties in BiOBr Nanosheets with Dominantly Exposed (102) Facets. J. Phys. Chem. C 2014, 118, 14662-14669. DOI: 10.1021/jp5035079. (14) Zhang, H. J.; Liu, L.; Zhou, Z. First-principles studies on facet-dependent photocatalytic properties of bismuth oxyhalides (BiOXs). RSC Adv. 2012, 2, 9224-9229. DOI: 10.1039/c2ra20881d. (15) Huang, H. W.; Han, X.; Li, X. W.; Wang, S. C.; Chu, P. K.; Zhang, Y. H. Fabrication of Multiple Heterojunctions with Tunable VisibleLight-Active Photocatalytic Reactivity in BiOBr−BiOI Full-Range Composites Based on Microstructure Modulation and Band Structures. ACS Appl. Mater. Inter. 2015, 7, 482−492. DOI: 10.1021/am5065409. (16) Guo, Y. X.; Zhang, Y. H.; Tian, N.; Huang, H. W. Homogeneous {001}-BiOBr/Bi Heterojunctions: Facile Controllable Synthesis and Morphology-Dependent Photocatalytic Activity.

ACS

Sustainable

Chem.

Eng.

2016,

4,

4003-4012.

DOI:

10.1021/acssuschemeng.6b00884.


24

Page 25 of 30

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


(17) He, Y.; Zhang, Y. H.; Huang, H. W.; Li, X. W.; Tian, N.; Guo, Y. X.; Luo, Y. A Novel Bibased Oxybromide BaBiO2Br: Synthesis, Optical Property and Photocatalytic Activity. Colloid Surface A. 2015, 467, 195-200. DOI.org/10.1016/j.colsurfa.2014.11.007. (18) Yu, C. L.; Yu, J. C.; b, Fan, C. C.; Wen, H. R.; Hu, S. J. Synthesis and Characterization of Pt/BiOI Nanoplate Catalyst with Enhanced Activity under Visible Light irradiation. Mat. Sci. Eng. B. 2010, 166, 213-219. DOI: 10.1016/j.mseb.2009.11.029. (19) Guo, Y. X.; Huang, H. W.; He, Y.; Tian, N.; Zhang , Tierui.; Chu,P. K.; An, Q.; Zhang, Y. H. In Situ Crystallization for Fabrication of a Core–Satellite Structured BiOBr–CdS Heterostructure with Excellent Visible-Lightresponsive Photoreactivity. Nanoscale. 2015, 7, 11702. DOI.org/10.1016/j.colsurfa.2014.11.007. (20) Huang, H. W.; Xiao, K.; Liu, K.; Yu, S. X. Zhang, Y. H. In Situ Composition-Transforming Fabrication of BiOI/BiOIO3 Heterostructure: Semiconductor p−n Junction and Dominantly Exposed

Reactive

Facets.

Cryst.

Growth.

Des.

2016,

16,

221-228.

DOI:

10.1021/acs.cgd.5b01101. (21) Qian, Y. T. Introduction of Crystal Chemistry. Hefei : China Science and Technology University Press. 2005，，348-352. (22) Kijima , N.; Matano, K.; Saito, M.; Oikawab, T.; Konishib, To.; Yasudaa, H.; Satoa, T.; Yoshimuraa, Y. Oxidative Catalytic Cracking of n-butane to Lower Alkenes over Layered BiOCl Catalyst. Appl. Catal. A-Gen. 2001, 206, 237-244. DOI: 10.1016/S0926860X(00)00598-6.


25


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 26 of 30

(23) Guan, M. L.; Xiao, C.; Zhang, J.; Fan, S. J.; An, R.; Cheng, Q. M.; Xie, J. F.; Zhou, M.; Ye, B. J.; Xie, Y. Vacancy Associates Promoting Solar-Driven Photocatalytic Activity of Ultrathin Bismuth Oxychloride Nanosheets. J. Am. Chem. Soc. 2013, 135, 10411-10417. DOI: 10.1021/ja402956f. (24) Di, J.; Xia, J. X.; Ji, M. X.; Wang, B.; Li, X. W.; Zhang, Q.; Chen, Z. G.; Li, H. M. Nitrogen-Doped Carbon Quantum Dots/BiOBr Ultrathin Nanosheets: In Situ Strong Coupling and Improved Molecular Oxygen Activation Ability under Visible Light Irradiation.

ACS

Sustainable

Chem.

Eng.

2016,

4,

136-146.

DOI:

10.1021/acssuschemeng.5b00862. (25) Chen, J.; Guan, M. L.; Cai, W. Z.; Guo, J. J.; Xiao, C.; Zhang, G. K. The Dominant {001} Facet-Dependent Enhanced Visible-Light Photoactivity of Ultrathin BiOBr Nanosheets. Phys. Chem. Chem. Phys. 2014, 16, 20909. DOI: 10.1039/c4cp02972k. (26) Ye, L. Q.; Jin, X. L.; Liu, C.; Ding, C. H.; Xie, H. Q.; Chu, K. H.; Wong, P. K. ThicknessUltrathin and Bismuth-Rich Strategies for BiOBr to Enhance Photoreduction of CO2 into Solar

Fuels.

Appl.

Catal.

B-Environ.

2016,

187,

281-290.

DOI:

10.1016/j.apcatb.2016.01.044. (27) Jiang, Z. Y.; Liang, X. Z.; Liu, Y. Y.; Jing, T.; Wang, Z. Y.; Zhang, X. Y.; Qin, X. Y; Dai, Y.;Huang, B. B. Enhancing Visible Light Photocatalytic Degradation Performance and Bactericidal Activity of BiOI Via Ultrathin-Layer Structure. Appl. Catal. B-Environ. 2017, 211, 252–257. DOI: 10.1016/j.apcatb.2017.03.072. (28) Ravel, B.; Newville, M. Data Analysis for X-ray Absorption Spectroscopy Using IFEFFIT. J .Synchrotron. Radiat. 2005, 12, 537-541. DOI: 10.1107/S0909049505012719.


26

Page 27 of 30

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


(29) Li, J.; Yu, Y.; Zhang, L.Z. Bismuth Oxyhalide Nanomaterials: Layered Structures Meet Photocatalysis. Nanoscale. 2014, 6, 8473. DOI: 10.1039/c4nr02553a. (30) Huang, H. W.; Cao, R. R.; Yu, S. X.; Xu, K.; Hao, W. C.; Wang, Y. G.; Dong, F.; Zhang, T. R.; Zhang Y. H. Single-unit-cell layer established Bi2WO6 3D hierarchical archi-tectures: Efficient adsorption, photocatalysis and dye-sensitized photoelectrochemical performance. Appl. Catal. B-Environ. 2017, 219, 526-537. DOI: 10.1016/j.apcatb.2017.07.084. (31) Zhou, Y. N.; Wen, T.; Guo, Y. Z.; Yang, B. C.; Wang, Y. G. Controllable doping of nitrogen and tetravalent niobium affords yellow and black calcium niobate nanosheets for enhanced photocatalytic hydrogen evolution. RSC Adv. 2016, 6, 64930-64936. DOI: 10.1039/c6ra11407e. (32) Li, L. D.; Yan, J. Q.; Wang, T.; Zhao, Z. J.; Zhang, J.; Gong, J. L.; Guan, N. J. Sub-10 nm Rutile Titanium Dioxide Nanoparticles for Efficient Visible-Light-Driven Photocatalytic Hydrogen Production. Nat. Commun. 2015, 6, 5881. DOI: 10.1038/ncomms6881. (33) Hibino, T. Delamination of Layered Double Hydroxides Containing Amino Acids. Chem. Mater. 2004, 16, 5482-5488. DOI: 10.1021/cm048842a. (34) Li, H.; Shi, J. G.; Zhao, K.; Zhang, L. Z. Sustainable Molecular Oxygen Activation with Oxygen Vacancies on the {001} Facets of BiOCl Nanosheets under Solar Light. Nanoscale. 2014, 6, 14168-14173. DOI: 10.1039/c4nr04810e. (35) Huang, H. W.; Li, X. W.; Wang, J. J.; Dong, F.; Chu, P. K.; Zhang, T. R.; Zhang, Y. H. Anionic Group Self-Doping as a Promising Strategy: Band-Gap Engineering and Multi-


27


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 28 of 30

Functional Applications of High-Performance CO32–-Doped Bi2O2CO3. ACS Catal. 2015, 5, 4094-4103. DOI: 10.1021/acscatal.5b00444. (36) Yi, Z. G.; Ye, J. H.; Kikugawa, N.; Kako, T.; Ouyang, S. X.; Stuart-Williams, H.; Yang, H.; Cao, J. Y.; Luo, W. J; Li, Z. S.; Liu, Y.; Withers, R. L. An Orthophosphate Semiconductor with Photooxidation Properties under Visible-Light Irradiation. Nat. Mater. 2010, 9, 559-564. DOI: 10.1038/NMAT2780. (37) Huang, H. W.; He, Y.; Lin, Z. S.; Kang, L.; Zhang, Y. H. Two Novel Bi-Based Borate Photocatalysts: Crystal Structure, Electronic Structure, Photoelectrochemical Properties, and Photocatalytic Activity under Simulated Solar Light Irradiation. J. Phys. Chem. C 2013, 117, 22986-22994. DOI: 10.1021/jp4084184. (38) Zhang, X.; Li, B. H.; Wang, J. L.; Yuan, Y.; Zhang, Q. J.; Gao, Z. Z.; Liu Li. M.; Chen , L. The Stabilities and Electronic Structures of Single-Layer Bismuth Oxyhalides for Photocatalytic Water Splitting. Chem. Chem. Phys. 2014, 16, 25854-25861. DOI: 10.1039/c4cp03166k. (39)Xu, J.; Wang, Y. J.; Y. Zhu, F. Nanoporous Graphitic Carbon Nitride with Enhanced Photocatalytic Performance Langmuir. 2013, 29, 10566-10572. DOI: 10.1021/la402268u. (40) Cui, Y. J.; Zhang, J. S.; Zhang, G. G.; Huang, J. H.; Liu, P.;Antonietti, M.; Wang, X. C. Synthesis of Bulk and Nanoporous Carbon Nitride Polymers from Ammonium Thiocyanate for Photocatalytic Hydrogen Evolution. J. Mater. Chem. 2011, 21, 13032−13039. DOI: 10.1039/c1jm11961c


28

Page 29 of 30

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


(41) Huang, H. W.;

Tu, S. C.;

Zeng, C.; Zhang, T. R.; Reshak, A. H.; Zhang, Y. H.;

Macroscopic Polarization Enhancement Promoting Photo- and Piezoelectric-Induced Charge Separation and Molecular Oxygen Activation. Angew. Chem. Int. Ed. 2017, 56, 11860–11864. DOI: 10.1002/anie.201706549 (42) Tian, N.; Zhang, Y. H.; Li, X. W.; Xiao, K.; Du, X.; Dong, F.; Waterhouse, G. I.N.; Zhang, T. R.; Huang, H. W. Precursor-Reforming Protocol to 3D Mesoporous g-C3N4 Established by Ultrathin Self-Doped Nanosheets for Superior Hydrogen Evolution. Nano Energy. 2017, 38, 72-81. DOI: 10.1016/j.nanoen.2017.05.038


29


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Table of Content

Large-scale monolayered BiOBr nanosheets were prepared via a readily-achievable liquid phase exfoliation strategy with assistance of formamide at ambient conditions, which show excellent adsorption, photodegradation and photocatalytic CO2 reduction performance.


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Liquid-Phase Exfoliation into Monolayered BiOBr Nanosheets for

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