Evolution of Oxyhalide Crystals under Electron Beam Irradiation: An in

Jul 10, 2018 - Synopsis. The structural evaluation of BiOCl crystals is triggered by electron beam irradiation and investigated in situ by transmissio...
0 downloads 0 Views 6MB Size
Download PDF
Article pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Evolution of Oxyhalide Crystals under Electron Beam Irradiation: An in Situ Method To Understand the Origin of Structural Instability Sujuan Wu,*,†,‡,§,⊥ Jianguo Sun,†,‡,⊥ Shi-Ze Yang,§,⊥ Qiongyao He,†,‡ Ling Zhang,†,‡ and Lidong Sun*,†,∥ †

College of Materials Science and Engineering, Chongqing University, Chongqing 400044, People’s Republic of China Electron Microscopy Center of Chongqing University, Chongqing University, Chongqing 400044, People’s Republic of China § Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States ∥ Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin 300071, People’s Republic of China

Downloaded via UNIV OF NEW ENGLAND on July 11, 2018 at 07:11:52 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: The oxyhalides have attracted growing interest because of their excellent photocatalytic performance. However, their structural instability hampers further development toward practical applications, a major challenge of current concerns. It is appealing to figure out the origin of structural instability and guide the design of advanced oxyhalide crystals for efficient photocatalysis. In this study, the decomposition of BiOCl crystals, a typical oxyhalide, is triggered by electron beam irradiation and investigated in situ by transmission electron microscopy. The results indicate that the instability originates from the unique layered structure of BiOCl crystals; the interlayer van der Waals bonds are easily broken under electron beam irradiation via the assistance of hydroxyl groups. This facilitates the formation of O/Cl-deficient BiO1−xCl1−y species, Bi metal nanoparticles, and nanobubbles (gaseous substance) that are confined between the adjacent layers. Surface reconstruction would be an effective way to stabilize the oxyhalide crystals.

■

VBi‴ and triple vacancy associates VBi‴VO••VBi‴ in ultrathin BiOCl nanosheets.15 Even though the defects usually lead on the one hand to an enhancement in photocatalytic activity,15−17 the unexpected instability on the other hand restricts the practical application of BiOCl crystals. Therefore, it is appealing to figure out the origin of instability of BiOCl crystals. Recently, the formation of nonstoichiometric BiO1−xCl1−y18 and Bi19,20 nanoparticles on the BiOCl surface was reported when they were employed as electrochemical electrodes. Similarly, oxygen vacancies were induced by UV light irradiation, whereas no such vacancies were observed under visible light.21,13 The difference is attributed to the large band gap energy of 3.45 eV for BiOCl crystals, in which electron− hole pairs can only be produced under UV light.12 This therefore suggests that the instability or decomposition of the BiOCl crystals may be related to electron injection. This is very similar to the electron radiolysis process, where the transition of a valence band electron to the conduction band leaves a hole in the original energy level.20,22 Subsequently anion vacancies, cation interstitials, new compounds, voids (empty regions),

INTRODUCTION Layered materials, such as atomically thick graphene, hexagonal boron nitrides, transition-metal dichalcogenides, transition-metal trichalcogenides, metal halides, perovskites, and graphitic carbon nitrides, have attracted growing interest for a variety of applications in electronics, catalysis, and energy storage.1−8 In particular, bismuth oxyhalides, BiOX (X = Cl, Br, I), are a new class of layered materials that are promising for photocatalytic energy conversion and environmental remediation.4,9,10 This is attributed to their excellent properties of charge separation and transport. With unique layeredstructure-mediated properties, bismuth oxychlorides (BiOCl) exhibit much higher photocatalytic activity in comparison to the commercial P25 (TiO2) toward pollutant degradation.11 The BiOCl crystals have a layered structure consisting of [Cl− Bi−O−Bi−Cl] units, where each Bi3+ ion is coordinated to four chlorine and four oxygen ions.12 It has been reported that the surface chlorine ions tend to dissociate from the BiOCl crystal via reaction with photogenerated charge carriers during photocatalysis, and oxygen vacancies (OVs) also emerge under UV light irradiation.13,14 A very recent work reported that the existence of hydroxyl groups is energetically favored in BiOCl, which participates in the generation of OVs and repair of BiOCl.14 Guan et al. confirmed the existence of isolated defects © XXXX American Chemical Society

Received: April 10, 2018

A

DOI: 10.1021/acs.inorgchem.8b00953 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

BiOCl crystal but with lower image contrast (cf. FFT patterns of regions A and C in Figure 1c). High-resolution transmission electron microscopy (HRTEM) images disclose that no lattice distortion arises in region C with the single-crystalline feature of the BiOCl host still being maintained, as shown in Figure 1d, where an image contrast indeed exists. Figure S3a in the Supporting Information shows a high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) image of the bright area. It indicates that only changes in thickness by atom losses are reasonable under in situ conditions, as the image intensity is directly related to the atomic numbers of the elements present. The mapping of electron energy loss spectroscopy (Figure S3b,c) reveals that part of the Cl and O atoms are retained. This demonstrates that the crystal structure is maintained upon atom loss with the image contrast being reduced. In addition, the bright dots in region C are usually accompanied by a dark contrast, which may be attributed to the lattice strain, as indicated in Figure 1e and discussed below. Note that the dark and bright regions in Figure 1e (highlighted in regions i−iii) do not always line up in the same direction under the same imaging conditions, excluding the defocusing effect. A large number of the bright dots were focused and monitored in situ by TEM (beam current density of ∼9.8 nA/ cm2) to verify the decomposition process of BiOCl. It is found that the surface image is unstable and keeps blinking while the samples are focused at the very beginning. Once the imaging is completed, regions of lighter contrast with clear boundaries develop, as shown in Figure 1b. Movies were recorded for different bright dots, as selectively presented in Movies S1−S3 in the Supporting Information. Time-resolved TEM images were thus attained and are displayed in Figure 2, showing the

and nanobubbles (gaseous regions) are formed in the crystals through complicated redox reactions.8,23,24 The radiolysisinduced microstructure evolution can be tracked by electron microscopy. As such, the structure instability of BiOCl crystals is studied in situ with the assistance of transmission electron microscopy (TEM) in this work, which is fundamental toward practical applications.

■

RESULTS AND DISCUSSION Bismuth oxychloride nanosheets with a thickness of less than 100 nm were synthesized by the process stated in Methods, as presented in Figure S1 in the Supporting Information. Figure 1a shows a typical TEM image of a BiOCl single crystal

Figure 1. Characterization of a typical BiOCl crystal upon irradiation. TEM images of a BiOCl crystal under constant electron beam irradiation in less than 1 min (a) and for 16 min (b). Local HRTEM images in (b) showing three typical regions of different contrasts (region A, BiOCl crystal; region B, Bi nanocrystal; region C, nanobubbles/voids) and corresponding FFT patterns (c). Detailed examinations of the nanobubbles/voids patterned as small dots (d, e) in (b).

Figure 2. Structure evolution in BiOCl crystals. Time-resolved TEM images showing the evolution process of expanding (a), contracting (b), and coalescing (c) nanobubbles. The corresponding full movies are available in Movies S1−S3 in the Supporting Information.

(justified in Figure S2 in the Supporting Information) after immediate focusing, which is usually completed in 1 min. In other words, the obtained morphology has already been subjected to electron beam irradiation for about 1 min. Very interestingly, the crystal surface is patterned with small dots on the edge and long stripes in the center after irradiation for 16 min, as displayed in Figure 1b. Detailed examinations reveal three typical regions of different contrasts in Figure 1c: background (region A), dark dots (region B), and bright dots or stripes (region C). Corresponding FFT patterns indicate that region A belongs to the BiOCl single-crystal host, while region B is assigned to bismuth (Bi) nanocrystals. It is surprising that region C exhibits the same FFT pattern as the

typical evolution processes of expansion, contraction, and coalescence under continuous electron beam irradiation. Figure 2a,b shows the expanding and contracting processes of the bright dots, respectively. This is very similar to the nanobubbles emitted by chemical reactions in the liquid25 or implanted He bubbles in the metals.26 It is noteworthy that the contraction gives rise to an enhanced image contrast, indicating a condensed process (Figure 2b and Movie S2). The expansion, contraction, and coalescence behavior is a fingerprint of a gaseous substance. As the irradiation is prolonged, the small bright dots grow into larger dots through a coalescence process (Figure 2c) and evolve into irregular B

DOI: 10.1021/acs.inorgchem.8b00953 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

simulation in Figure 3d,e also implies that the evolution process of the BiOCl crystal should be different when it is observed from the side because of the layered structure. Further in situ examinations disclose that the formed gaseous substances are free to extend in the plane at the (001) facet when they are confined between layers, as shown in Movie S4 and Figure S4 in the Supporting Information, respectively. It is observed that the BiOCl crystals with hydroxyl groups decompose quickly under continuous electron beam irradiation (less than 1 min), whereas those with fewer hydroxyls remain stable under the same conditions (Figure S6). On the basis of previous reports7,14 that the hydroxyls act as active surface sites and facilitate the formation of photoinduced oxygen vacancies, it is thus speculated that the decomposition induced by a radiolysis reaction can also be ascribed to the presence of hydroxyl groups. When the hydroxyls adsorb on the surface, the vacancies, voids, and Bi nanoparticles would tend to form on the surface. When the hydroxyls are trapped inside, the resulting products may have a high possibility of being confined in the crystal, thereby generating a gaseous substance. As mentioned above and illustrated in Figure 3a, the BiOCl crystal has a layered structure, featuring a strong intralayer covalent bonding within each [Cl−Bi−O−Bi−Cl] slab while there are weak interlayer van der Waals interactions between neighboring slabs. This makes it feasible to partially substitute the Cl terminals with hydroxyls during synthesis and meanwhile maintain the crystal structure. To verify this hypothesis, the atomic structure of the (110) facet is investigated in detail below. Figure 4 displays the STEM images obtained in annular dark field and gives more details on the (110) facet of a

shapes due to the confinement of the surrounding solids (Figure S4 in the Supporting Information). This process takes place by mass transport from one dot to another across their interface, followed by shape adjustment. The coalescence proceeds in around 20 s, in good agreement with the nanobubbles coalescing under in situ TEM.25 The evolution process of the bright dots in region C (Figure 1c) is highly consistent with the mass transport in gas bubbles with unique features of expansion, contraction, and coalescence.27 Therefore, the bright dots in Figure 1b are assigned to either voids formed on the surface or nanobubbles confined in the BiOCl crystals with the assistance of electron beam irradiation in this study. In addition, the mean size of the bright dots is about 2.5 nm (see Figure S5 in the Supporting Information), which agrees well with the report that the critical radius of stable nanobubbles should be larger than 1.7 nm by molecular dynamic simulation.28 To get more insight into the structure evolution along with the decomposition process, the striped patterns in Figure 1b are dissected. It is reported that the BiOCl crystal exists as a layered structure, where the [Cl−Bi−O−Bi−Cl] monolayer stacks by van der Waals interactions between neighboring chlorine terminals along the c axis,12,17 as illustrated in Figure 3a. Figure 3b,c shows the details of the striped patterns that

Figure 3. Simulation of the atom loss in BiOCl crystals. (a) 3D illustration of the BiOCl crystal structure. (b, c) HRTEM images of the stripe patterns at the (001) facet. (d, e) Simulations of atomic arrangements on the (001), (010), and (100) facets of the BiOCl crystal structure after loss of Cl atoms along the [100] (d) and [010] (e) directions.

developed after electron beam irradiation for 16 min (see Figure 1b for patterns over a large scale), with an interstripe angle of 90°. Local magnification demonstrates a lattice spacing of 0.28 nm, corresponding to the (110) facet of the BiOCl crystal, and implies that the exposed facet is a (001) facet. Accordingly, it is deduced that the bright stripes are formed along the [100] and [010] directions in Figure 3d,e, respectively, on the basis of an angle of 135° between bright stripes and the lattice fringes. This further suggests that the loss of atoms proceeds on (100) and (010) facets, which may originate from the low cleavage energy.29 Figure 3d,e displays the simulation results of a BiOCl crystal after losing seven to eight consecutive planes of atoms in the (100) or (010) facet, where similar stripe patterns appear on the (001) facet with a stripe width of 1.55−1.75 nm, consistent with the critical radius of the stable bubble. This agrees well with the pattern features in Figure 3b,c, consolidating the proposed loss of atoms in (100) and (010) facets and the image contrast. The

Figure 4. Initiation of BiOCl decomposition. Scanning transmission electron microscopy (STEM) images in dark field showing the interfacial region (a) between a Bi nanocrystal (b) and BiOCl body (c). The square regions A and B in (a) are highlighted in (d) and (e), respectively. Insets in (b) and (c) are the corresponding FFT patterns for Bi and BiOCl crystals, respectively. The samples were irradiated for around 6 min. (f) Illustration of the decomposition process.

decomposed BiOCl. Figure 4a shows a clear interface between a Bi nanocrystal and BiOCl host, as evidenced in Figure 4b,c, respectively. The interfacial regions are highlighted in Figure 4d,e, with large space available for radiolysis products to reside. In light of the large electronegativity of the hydroxyls and the C

DOI: 10.1021/acs.inorgchem.8b00953 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry high irradiation sensitivity of the halides,20,30 it is plausible to initially produce the hydroxyl and Cl radicals under irradiation. The radiolysis products subsequently develop into a gaseous substance and then accumulate into nanobubbles, similar to the radiolysis reaction in the iron (hydr)oxide lattice.25 In parallel with the cleavage of O atoms, the adjacent Bi ions could be reduced under continuous irradiation, thus forming Bi nuclei. As the irradiation continues, the Bi nuclei grow gradually and develop into nanocrystals (see region B in Figure 1c) on the surface.19,20 Meanwhile, the loss of O and Cl/OH atoms in the BiOCl lattice results in the bending of the Bi atomic planes. Figure S7 in the Supporting Information displays magnified STEM images of a BiOCl crystal at the (110) facet. For the [Cl−Bi−O−Bi−Cl] slabs far from the interface, they exhibit a regular atomic arrangement. In contrast, for those near the interface, bending of the [Cl− Bi−O−Bi−Cl] slabs arises along different directions, as highlighted in Figure S7 (see arrows A−C). The causes by external forces are excluded because of the bending in opposite directions (cf. arrows A and B). We thereby infer that the existence of hydroxyls in the lattice cause the loss of atoms inside, which develops into the nucleation centers for nanobubbles. The lattice strain arises, accompanied by the loss of atoms, and drives the evolution processes of expansion, contraction, and coalescence of the radiolysis products under continuous electron beam irradiation. This is consistent with the phenomenon that the bright dots are always accompanied by dark shadows (see Figure 1e). Figure 4d presents that, at interfacial regions, Cl atoms are replaced by Bi atoms, with O atoms being lost. The rearrangement of Bi atoms subsequently gives rise to the formation of Bi nanocrystals, as exhibited in Figure 4e. A schematic diagram of the likely structural evolution process is illustrated in Figure 4f. In addition, it is also found that the contrast in square B of Figure 4a is much lower than that of the pristine BiOCl lattice, where the loss of Bi atoms leaves a large space for nanobubbles to reside inside or forms voids on the crystal surface. Electron beam irradiation imposed on the BiOCl crystals affects the structure in two important ways: collision and reduction. A large number of results show that, even under a mild process without collision such as light illumination or cyclic voltammetry, the BiOCl crystals are still unstable. As such, it is the reduction process induced by electron injection that affects the structure stability. Upon electron injection, the adsorbed hydroxyls act as active sites and trigger the formation of O/Cl-deficient species and Bi nanoparticles. Different from the photocatalysis, where the photoinduced electron−hole pairs participate in the redox reaction at the crystal surface, the electron radiolysis prefers to process inside the materials in view of the inelastic reaction, thus leading to the radicals and molecules (nanobubbles) that are confined between the adjacent layers. Therefore, to stabilize the crystal structure of oxyhalides in photocatalysis, it would be effective to restrict the adsorption of hydroxyls through surface reconstruction, which is currently under investigation in our group and will be reported in a separate study.

layers. Such a confinement induces the formation of nanobubbles, which is verified by the features of expansion, contraction, and coalescence. The evolution of the bubbles is accompanied by the formation of Bi nanocrystals. These findings shed light on the origin of the structure instability of BiOCl crystals and enable the design of advanced photocatalysts with high stability.

■

METHODS

■

ASSOCIATED CONTENT

Preparation of BiOCl Nanosheets. The bismuth oxychloride (BiOCl) nanosheets were synthesized according to previous reports.31 In a typical procedure, 5 g of Bi2O3 was dissolved in 20 mL of 37% HCl solution and the solution was then evaporated at 300 °C. The resulting products were washed with deionized water until the pH value reached 7 and then dried at 80 °C for 24 h. The resulting obtained powders were calcined in air at 200 °C for 2 h. Characterization. X-ray diffraction (XRD) patterns were recorded by an Empryean X-ray diffractometer with monochromatic Cu Kα radiation (λ = 1.5418 Å). Scanning electron microscopy (SEM) images were collected by using a field emission JEOL-SEM instrument (JSM-7800F). The high-resolution images were obtained from a TEM instrument, Zeiss LIBRA 200, with an acceleration voltage of 200 kV (0.24 nm point resolution). The atomic scale HAADF-STEM images and EELS mappings were obtained with a Nion Ultra STEM 200 instrument with sub-angstrom resolution at 200 kV. In situ observations were processed under a constant electron beam current density of 9.8 nA/cm2, from a JEOL 2100 transmission electron microscope at 200 kV with a LaB6 filament and a TVIPS F416 camera. It is noted that a stronger or longer electron beam irradiation introduces undesirable deformation and damage.23 The movies were recorded at five frames per second by the open-source software VirtualDub embedded in the DigitalMicrograph software. The as-recorded movie was compressed to reduce the file size (480 × 480 pixels), and Movie S1−S3 in the Supporting Information play 4 times faster than the original movies. All of the image analyses were carried out on the original images extracted from the movies. S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00953. Materials and methods, XRD, SEM, HAADF-STEM, and EELS (PDF) Structural evolution of BiOCl 1 (AVI) Structural evolution of BiOCl 2 (AVI) Structural evolution of BiOCl 3 (AVI) Structural evolution of BiOCl 4 (AVI)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail for S.W.: [email protected]. *E-mail for L.S.: [email protected]. ORCID

Sujuan Wu: 0000-0003-4390-2082 Jianguo Sun: 0000-0002-2222-2478 Shi-Ze Yang: 0000-0002-0421-006X Lidong Sun: 0000-0003-2247-4226

■

CONCLUDING REMARKS In conclusion, bismuth oxychloride crystals with a layered structure have been employed to study the structure evolution under electron beam irradiation. The decomposition is triggered by electron radiolysis with the assistance of hydroxyl groups, with the resulting species being confined between

Author Contributions ⊥

S.W., J.S., and S.-Z.Y. contributed equally to this work.

Author Contributions

S.W. and L.S. developed the concept. S.W. and J.S. synthesized the nanocatalysts and carried out sample physical characterizations and electrochemical measurements. S.W., J.S., Q.H., D

DOI: 10.1021/acs.inorgchem.8b00953 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

(10) Sun, J.; Wu, S.; Yang, S.; Li, Q.; Xiong, J.; Yang, Z.; Lin, G.; Zhang, X.; Sun, L. Enhanced Photocatalytic Activity Induced by sp3 to sp2 Transition of Carbon Dopants in BiOCl Crystals. Appl. Catal., B 2018, 221, 467−472. (11) Li, H.; Qin, F.; Yang, Z.; Cui, X.; Wang, J.; Zhang, L. New Reaction Pathway Induced by Plasmon for Selective Benzyl Alcohol Oxidation on BiOCl Possessing Oxygen Vacancies. J. Am. Chem. Soc. 2017, 139, 3513−3521. (12) Zhang, K.; Liu, C.; Huang, F.; Zheng, C.; Wang, W. Study of the Electronic Structure and Photocatalytic Activity of the BiOCl Photocatalyst. Appl. Catal., B 2006, 68, 125−129. (13) Ye, L.; Deng, K.; Xu, F.; Tian, L.; Peng, T.; Zan, L. Increasing Visible-Light Absorption for Photocatalysis with Black BiOCl. Phys. Chem. Chem. Phys. 2012, 14, 82−85. (14) Wu, S.; Xiong, J.; Sun, J.; Hood, Z. D.; Zeng, W.; Yang, Z.; Gu, L.; Zhang, X.; Yang, S.-Z. Hydroxyl-Dependent Evolution of Oxygen Vacancies Enables the Regeneration of BiOCl Photocatalyst. ACS Appl. Mater. Interfaces 2017, 9, 16620−16626. (15) Guan, M.; Xiao, C.; Zhang, J.; Fan, S.; An, R.; Cheng, Q.; Xie, J.; Zhou, M.; Ye, B.; Xie, Y. Vacancy Associates Promoting SolarDriven Photocatalytic Activity of Ultrathin Bismuth Oxychloride Nanosheets. J. Am. Chem. Soc. 2013, 135, 10411−10417. (16) Jiang, J.; Zhang, L.; Li, H.; He, W.; Yin, J. J. Self-Doping and Surface Plasmon Modification Induced Visible Light Photocatalysis of BiOCl. Nanoscale 2013, 5, 10573. (17) Zhao, K.; Zhang, L.; Wang, J.; Li, Q.; He, W.; Yin, J. J. Surface Structure-Dependent Molecular Oxygen Activation of BiOCl SingleCrystalline Nanosheets. J. Am. Chem. Soc. 2013, 135, 15750−15753. (18) Fujishima, Y.; Okamoto, S.; Yoshiba, M.; Itoi, T.; Kawamura, S.; Yoshida, Y.; Ogura, Y.; Izumi, Y. Photofuel Cell Comprising Titanium Oxide and Bismuth Oxychloride (BiO1‑xCl1‑y) Photocatalysts That Uses Acidic Water as a Fuel. J. Mater. Chem. A 2015, 3, 8389−8404. (19) Wu, S.; Jiang, Y.; Hu, L.; Sun, J.; Wan, P.; Sun, L. SizeDependent Crystalline Fluctuation and Growth Mechanism of Bismuth Nanoparticles under Electron Beam Irradiation. Nanoscale 2016, 8, 12282−12288. (20) Chang, X.; Wang, S.; Qi, Q.; Gondal, M. A.; Rashid, S. G.; Gao, S.; Yang, D.; Shen, K.; Xu, Q.; Wang, P. Insights into the Growth of Bismuth Nanoparticles on 2D Structured BiOCl Photocatalysts: An In Situ TEM Investigation. Dalton Trans 2015, 44, 15888−15896. (21) An, H.; Du, Y.; Wang, T.; Wang, C.; Hao, W.; Zhang, J. Photocatalytic Properties of BiOX (X = Cl, Brand I). Rare Met. 2008, 27, 243−250. (22) Williams, D. B.; Carter, C. B. Transmission Electron Microscopy: A Textbook for Materials Science, 2nd ed.; Springer: New York, 2008. (23) Lian, J.; Wang, L. M.; Sun, K.; Ewing, R. C. In Situ TEM of Radiation Effects in Complex Ceramics. Microsc. Res. Tech. 2009, 72, 165−181. (24) Xu, W.; Zhang, Y.; Cheng, G.; Jian, W.; Millett, P. C.; Koch, C. C.; Mathaudhu, S. N.; Zhu, Y. In-Situ Atomic-Scale Observation of Irradiation-Induced Void Formation. Nat. Commun. 2013, 4, 2288. (25) Niu, K.; Frolov, T.; Xin, H. L.; Wang, J.; Asta, M.; Zheng, H. Bubble Nucleation and Migration in a Lead-Iron Hydr(Oxide) CoreShell Nanoparticle. Proc. Natl. Acad. Sci. U. S. A. 2015, 112, 12928− 12932. (26) Xie, D.-G.; Wang, Z.-J.; Sun, J.; Li, J.; Ma, E.; Shan, Z.-W. In Situ Study of the Initiation of Hydrogen Bubbles at the Aluminium Metal/Oxide Interface. Nat. Mater. 2015, 14, 899−903. (27) Shin, D.; Park, J. B.; Kim, Y.-J.; Kim, S. J.; Kang, J. H.; Lee, B.; Cho, S.-P.; Hong, B. H.; Novoselov, K. S. Growth Dynamics and Gas Transport Mechanism of Nanobubbles in Graphene Liquid Cells. Nat. Commun. 2015, 6, 6068. (28) Matsumoto, M. Surface Tension and Stability of a Nanobubble in Water: Molecular Simulation. J. Fluid Sci. Technol. 2008, 3, 922− 929. (29) Zhang, H.; Liu, L.; Zhou, Z. First-Principles Studies on FacetDependent Photocatalytic Properties of Bismuth Oxyhalides (BiOXs). RSC Adv. 2012, 2, 9224.

and L.Z. performed and supervised the in situ TEM measurements. S.-Y.Z. carried out the HAADF-STEM and EELS experiments. S.W., J.S., S.-Y.Z., and L.S. discussed the results and cowrote the paper. All of the authors have revised the manuscript. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We gratefully acknowledge helpful discussions with Prof. Michael S. Smith (Oak Ridge National Laboratory), Prof. Matthew F. Chisolm (Oak Ridge National Laboratory) and Prof. Xiaoxu Huang (Chongqing University and Technical University of Denmark). This research was financially supported by the National Natural Science Foundation of China (Nos. 51302329, 51501024, and 11227802), the Chongqing Research Program of Basic Research and Frontier Technology (No. cstc2015jcyjA90004), and the Fundamental Research Funds for the Central Universities (No. 2018CDQYCL0027). The transmission electron microscope (S.-Z.Y.) was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Divisio,n and through a user proposal supported by ORNL’s Center for Nanophase Materials Sciences, which is sponsored by the Scientific User Facilities Division of the U.S. Department of Energy. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI1053575.

■

REFERENCES

(1) Geim, A. K.; Grigorieva, I. V. Van Der Waals Heterostructures. Nature 2013, 499, 419−425. (2) Nicolosi, V.; Chhowalla, M.; Kanatzidis, M. G.; Strano, M. S.; Coleman, J. N. Liquid Exfoliation of Layered Materials. Science 2013, 340, 1226419−1226419. (3) Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The Chemistry of Two-Dimensional Layered Transition Metal Dichalcogenide Nanosheets. Nat. Chem. 2013, 5, 263−275. (4) Li, J.; Zhan, G.; Yu, Y.; Zhang, L. Superior Visible Light Hydrogen Evolution of Janus Bilayer Junctions via Atomic-Level Charge Flow Steering. Nat. Commun. 2016, 7, 11480. (5) Chen, Q.; Zhou, H.; Fang, Y.; Stieg, A. Z.; Song, T.-B.; Wang, H.-H.; Xu, X.; Liu, Y.; Lu, S.; You, J.; Sun, P.; McKay, J.; Goorsky, M. S.; Yang, Y. The Optoelectronic Role of Chlorine in CH3NH3PbI3(Cl)-Based Perovskite Solar Cells. Nat. Commun. 2015, 6, 7269. (6) Liu, Y.; Weiss, N. O.; Duan, X.; Cheng, H.-C.; Huang, Y.; Duan, X. Van Der Waals Heterostructures and Devices. Nat. Rev. Mater. 2016, 1, 16042. (7) Fabbri, E.; Nachtegaal, M.; Binninger, T.; Cheng, X.; Kim, B.-J.; Durst, J.; Bozza, F.; Graule, T.; Schäublin, R.; Wiles, L.; Pertoso, M.; Danilovic, N.; Ayers, K. E.; Schmidt, T. J. Dynamic Surface SelfReconstruction is the Key of Highly Active Perovskite NanoElectrocatalysts for Water Splitting. Nat. Mater. 2017, 16, 925−931. (8) Han, B.; Stoerzinger, K.; Tileli, V.; Gamalski, A.; Stach, E.; ShaoHorn, Y. Nanoscale Structural Oscillations in Perovskite Oxides Induced by Oxygen Evolution. Nat. Mater. 2017, 16, 121−126. (9) Li, J.; Yu, Y.; Zhang, L. Bismuth Oxyhalide Nanomaterials: Layered Structures Meet Photocatalysis. Nanoscale 2014, 6, 8473. E

DOI: 10.1021/acs.inorgchem.8b00953 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (30) Chen, F.; Liu, H.; Bagwasi, S.; Shen, X.; Zhang, J. Photocatalytic Study of BiOCl for Degradation of Organic Pollutants under UV Irradiation. J. Photochem. Photobiol., A 2010, 215, 76−80. (31) Jiang, Y.; Sun, J.; Wu, S. BiOCl Nanosheets with Controlled Exposed Facets and Improved Photocatalytic Activity. Catal. Lett. 2017, 147, 2006−2012.

F

DOI: 10.1021/acs.inorgchem.8b00953 Inorg. Chem. XXXX, XXX, XXX−XXX