A Novel Mesoporous Single-Crystal-Like Bi2WO6 with Enhanced

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A novel mesoporous single-crystal-like Bi2WO6 with enhanced photocatalytic activity for pollutants degradation and oxygen production Chunmei Li, Gang Chen, Jingxue Sun, Jiancun Rao, Zhonghui Han, Yidong Hu, and Yansong Zhou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b06995 • Publication Date (Web): 02 Nov 2015 Downloaded from http://pubs.acs.org on November 9, 2015

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ACS Applied Materials & Interfaces

A Novel Mesoporous Single-crystal-like Bi2WO6 with Enhanced Photocatalytic Activity for Pollutants Degradation and Oxygen Production Chunmei Li, † Gang Chen,*, † Jingxue Sun,*, † Jiancun Rao, ‡ Zhonghui Han, † Yidong Hu† and Yansong Zhou† † Department of Chemistry, Harbin Institute of Technology, 150001, P. R. China ‡ School of Materials Science and Engineering, Harbin Institute of Technology, 150001, P. R. China. ∗Corresponding author: E-mail: [email protected], [email protected], Fax: (+86)-451-86413753 ABSTRACT: The porous single-crystallike micro/nanomaterials exhibited splendid intrinsic performance in photocatalysts, dye-sensitized solar cells, gas sensors, lithium cells and many other application fields. Here, a novel mesoporous single-crystallike Bi2 WO6 tetragonal architecture was firstly achieved in the mixed molten salt system. Its crystal construction mechanism originated from the oriented attachment of nanosheet units accompanied by Ostwald ripening process. Additionally, the synergistic effect of mixed alkali metal nitrates and electrostatic attraction caused by internal electric field in crystal played a pivotal role in oriented attachment process of nanosheet units. The obtained sample displayed superior photocatalytic activity of both organic dye degradation and O2 evolution from water under visible light. We gained an insight into this unique architecture effect on the light absorption, photoelectricity and luminescent decay etc. physical properties that significantly influenced photocatalytic activity. KEYWORDS: single-crystallike Bi2 WO6 , mesoporous, construction mechanism, photocatalytic oxygen evolution, degrading organic pollutants

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1. INTRODUCTION During the past decades, many efforts have been focused on designing and constructing novel micro/nanomaterials intensively owing to the close correlation between their physical/chemical properties and micro/nano-structure.1-6 As far as photocatalytic materials are concerned, micro/nano-control of structure as well as crystallization is one of the preferred strategy to improve transfer and separation efficiency of charge carriers, adjust energy bandgap structure, increase surface active sites and shorten mo lecule diffusion routes etc..7-8 The traditional approach usually is preparing 3D hierarchical structure nanomaterials. Self-assembly of their basic building units is able to form abundant micro/nano-pores, which may facilitate molecules diffusion and transport inside sample9-10 as well as result in the large specific surface area, abundant reacting active sites and high light absorption ability at the same time11-14 . All of above characteristics would make the photocatalytic activity enhanced. However, the reported 3D polyporous photocatalysts are usually composed of building units with different crystallographic orientations, the majority of which exhibit polycrystalline struture. The interparticle boundaries related to defects generally may act as recombination centers of photogenerated charge carriers, leading to the activity discount of 3D polycrystalline structures photocatalysts.15-16 Recently, the mesoporous single-crystallike nanomaterials has caused increasing attention owing to its superior intrinsic performance in the various application fields, such as dye-sensitized solar cells,17 gas sensors,18 lithium storage19 etc.. Especially for photocatalysts, their single-crystallike structure can effectively reduce the quantity of defects of internal crystal to improve transfer and seperation ability of charge carriers, finally enhancing photocatalytic activity.20-21 For instance, the reported mesoporous single-crystallike TiO 2 photocatalysts prepared by soft/hard-templating methods exhibit more outstanding photocatalytic performance.22-23 However, the template agents may cause difficult complex production process and even secondary pollution. Meanwhile, TiO 2 is only excited by the ultraviolet light, lavishing most part of solar energy. Therefore, developing visible light driven mesoporous single-crystallike photocatalytic materials by a simple eco-friendly method may be one of the many candidate strategies for improving photocatalytic performance. Bi2 WO6 is one of the most attractive visible light driven photocatalysts applied to O2 evolution and organic pollutants degradation, 24-27 such as 3D microsphaeric,28 nanocages- like,29


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erythrocyte- like,30 nest- like,31 tyre/helix- like32 Bi2 WO6 and so forth. These 3D Bi2 WO6 hierarchical architectures present crystallization feature of polycrystalline and the properties of their pore are rarely described in detail, which are precisely two crucial factors that influence on improving photocatalytic activity. It is well known that the molten salt system is a unique reaction medium in favor of controlling crystals growth and pore structure, because it can directly influence intrinsic anisotropic growth owing to its lower flowability and diffusivity that usually result in relative slow crystal nucleation and growth rates. 33 Therefore, synthesizing mesoporous single-crystallike Bi2 WO6 using the green molten salt method may be a feasible techniques, relative investigations of which have not been reported up to now. In this work, a novel mesoporous single-crystallike Bi2 WO6 tetragonal architecture is firstly designed and prepared in a simple mixed molten salt system, which displays superior photocatalytic activity of both organic dye degradation and O2 evolution from water under visible light. We not only reveal that the construction mechanism results from the synergistic effect of mixed alkali metal nitrates and electrostatic attraction caused by internal electric field in crystal, but also get insight into the effect of the mesoporous single-crystallike structure on the light absorption, photoelectrochemistry, luminescent decay, physical properties etc. of Bi2 WO6 that influence photocatalytic activity significantly. 2. EXPERIMENTAL SECTION 2.1 Synthesis. All materials were purchased from commercial sources and used without further purification. In a typical procedure, firstly, 5 mL nitric acid solution was added into the bismuth nitrate (Bi(NO 3 )3 •5H2O, 20 mmol) solution to dissolve completely. Then sodium tungstate (Na2 WO4 •2H2O, 10 mmol) was added into the above solution drop by drop under vigorous magnetic stirring for 24 h. The generated suspension was performed by the centrifugal separation and washed adequately with deionized water. Bi2 WO6 precursor was finally obtained by drying at 80 °C for 20 h. Secondly, the mixed salt are prepared by the well mixed NaNO3 and KNO3 with a mole ratio of 1:1. Thirdly, the Bi2 WO6 precursor and NaNO3 -KNO 3 mixed salts are grinded evenly again with a weight ratio of 1:5. The mixture was put in corundum crucible and calcined at 350 °C for 4 h in the air. Finally, the single-crystallike mesoporous Bi2 WO6 (SCLBi2 WO6 ) sample was obtained by washing repeatedly with distilled water and drying at 80°C for


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12 h. The typical Bi2 WO6 is serving as a contrast is prepared by a traditional solid-state reaction methord referring to ref. 34 (SSR-Bi2 WO6 ). 2.2 Characterization. The phase of as-prepared Bi2 WO6 sample was characterized by powder X-ray diffractometer (XRD, RigakuD/max-2000) equipped with a Cu-Kα radiation at a scanning rate of 5°min-1 in the 2θ range of 10-90°. X-ray tube voltage and current were set at 45 kV and 50 mA, respectively. The morphologies of samples were characterized by field-emission scanning electron microscopy (FESEM, FEI QUANTA 200F). Transmission electron microscopy (TEM) and high-resolution TEM (HR-TEM) of samples were also carried out on FEI Tecnai G2 S-Twin and they are operated at 300 kV. X-ray photoelectron spectroscopy (XPS) analysis was measured on an American electronics physical system (HI5700ESCA) with X-ray photoelectron spectroscope using Al Kα (1486.6 eV) monochromatic X-ray radiation. The peak positions were corrected against the background carbon C 1s peak (284.6 eV). The UV- vis diffuse reflectance spectra (DRS) of the samples were recorded on a UV-vis spectrophotometer (PG, UH-4150) with BaSO 4 as the background between 250 nm and 900 nm at room temperature. The nitrogen adsorption and desorption isotherm, pore size distribution and specific surface area were measured using an AUTOSORB-1 surface area and pore size analyzer at 77K. The fluorescence decay spectra were measured by the FLUOROMAX-4C-TCSPC at room temperature. 2.3 Photocatalytic and Photoelectrochemical Measurement. The photocatalytic activities were evaluated by the organic pollutants degradation and oxygen evolution under visible light irradiation. The photodegradation of RhB (phenol) was performed at roo m temperature as follows: after the RhB (phenol) solution (100ml, 10 mg L-1 ) containing 0.05 g Bi2 WO6 was carried out about 5 min ultrasonic process, it was stirred 55 min in dark to achieve adsorptiondesorption equilibrium between photocatalysts and RhB (phenol). Then 0.1 ml H2 O2 was added to reactor before irradiation. Every 10 (20) min of time intervals, 3 mL mixture was collected from the suspension liquid, followed by centrifuged at 10 4 rpm for 3 min. The absorbance of the RhB (phenol) solution was measured at λ=554 nm (270 nm) with the UV- visible spectrophotometer (PG, TU-1901). The oxygen evolution was performed in a quartz reactor connected to a glass closed gas circulation system. The 0.1 g photocatalyst was suspended in 100 mL redistilled water and put into the quartz reactor after ultrasonic 20 min, then adding 0.1 M


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AgNO 3 as sacrificial agent. Xe lamp (300 W) with a filter (λ>400 nm) is served as visible light source. The reactive solution was continually stirred and maintained constant temperature by a water bath and vacuum environments during the O 2 evolution process. The evolved oxygen amount was measured by gas chromatography (Agilent 6820) with a thermal conductivity detector (TCD). The photoelectrochemical properties were measured in the CHI604C electrochemical working station employing a standard three-compartment cell under visible light assembled by a 300 W Xe lamp with a filter (λ>400 nm). The Bi2 WO6 samples coated at FTO glass, a kind of Ag/AgCl electrode, a piece of Pt sheet, and 0.01 M sodium carbonate were used as the working electrode, reference electrode, counter-electrode and electrolyte, respectively. 3. RESULTS AND DISCUSSION 3.1. Structure and Composition of SCL-Bi2 WO6 Photocatalysts. Figure 1 showed XRD pattern of the obtained single-crystallike Bi2 WO6 (SCL-Bi2 WO6 ), which corresponded to the orthorhombic phase of Bi2 WO6 (JCPDS Card No.39-0256). The sharp diffraction peaks and no other impurity phases were observed, indicating it had good purity and crystallinity. In addition, the surface chemical composition and valence states of SCL-Bi2 WO6 were analysed by XPS spectra. As shown the survey XPS spectrum in Figure 2a, the different binding energy was assigned to W 4f, Bi 4f, W 4d, C 1s, O 1s, Bi 4p states emission peaks, respectively. It demonstrated the as-prepared sample contained Bi, W and O elements, which was well in line with the result of EDS spectrum (Figure S1). Additionally, the high-resolution XPS spectra of the SCL-Bi2 WO6 sample were further performed. As shown in Figure 2b, the binding energy peak at 529.8 eV resulted from O 1s state. In addition, Figure 2c presented obvious binding energy peaks derived from W6+ 4f7/2 and 4f5/2 states at 35.4 eV and 37.5 eV. In the meantime, it produced two symmetrical binding energy peaks at 158.8 eV and 164.1 eV in Figure 2d, which was originated from Bi3+ 4f7/2 and 4f5/2 states, respectively.24,

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The results above further

demonstrated that the pure Bi2 WO6 sample was obtained. 3.2. Morphology of SCL-Bi2 WO6 Photocatalyst. FESEM technique was applied to investigate the micro- morphology features of SCL-Bi2 WO6 sample. FESEM image in Figure 3a showed that SCL-Bi2 WO6 exhibited uniformly distributed tetragonal morphology. FESEM image of the typical individual crystal in Figure 3b further identified that it had a well-defined tetragonal


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architecture with a rough surface and the size of ~2 µm. The internal micro-structural information of SCL-Bi2 WO6 was further investigated by TEM. Figure 3c-d showed TEM images of individual architecture at parallel and perpendicular direction, respectively, which precisely confirmed tetragonal micro-morphology characteristic. The high- magnification TEM images recorded on the edge of individual tetragonal architecture (Figure 3e- f) demonstrated that the architecture was actually built orderly by ultrathin nanosheet units with the thickness of ~9.6 nm. It was worth noting that SAED performed on an individual tetragonal architecture in Figure 3g displayed a set of symmetrical diffraction pattern with its spot- like appearance along the (010) zone axis of orthorhombic crystalline phase Bi2 WO6 . It implied the building nanosheet units of tetragonal architecture should be greatly oriented arrangement, which agreed well with the TEM images in Figure 3e- f. The above analyses indicated that the Bi2 WO6 sample exhibited singlecrystal- like structure characteristic. Moreover, the HRTEM image (Figure S2) displayed that lattice fringes among the adjacent nanosheets aligned to each other perfectly. Their orientations were also completely consistent and the interplanar spacing were all 0.272 nm corresponding to the (002) lattice plane of orthorhombic phase Bi2 WO6 , which further identified single-crystallike property. Furthermore, the HRTEM image in Figure 3h performed on nanosheet unit showed a clear 2D lattice fringes with an interplanar spacing of 0.273 nm and 0.272 nm, corresponding to the (200) and (002) lattice planes of orthorhombic phase Bi2 WO6 , respectively. Combining with SAED patterns, it suggested the formation of single-crystallike Bi2 WO6 with (010) lattice plane exposure. Meanwhile, we also investigated the TEM and the corresponding SAED characteristics of SSR-Bi2 WO6 sample (Figure S3). It turned out that SSR-Bi2 WO6 sample had random distribution and agglomeration morphology features as well as polycrystalline inherent quality. Obviously, the regular single-crystallike construction of SCL-Bi2 WO6 was more beneficial to the charge carriers transport and separation compared with the random SSRBi2 WO6 sample. This unique architecture of SCL-Bi2 WO6 sample may be attributed to their formation mechanism of the building crystals into self-similar crystals. 3.3 Formation Mechanis m of SCL-Bi2 WO6 Photocatalyst. It has been reported that when two or more initial sheets similar to aforementioned ultrathin nanosheets were close to each other in the low-fluidity medium, they tended to grow into each other and shared a planar interface in a common crystallographic orientation, thus presenting a single-crystallike characteristic.36 Therefore, here the construction of tetragonal mesoporous single-crystallike Bi2 WO6


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architecture might be directly related to the crystal growth process in the mixed molten salt system, which may be the oriented attachment occurred on the [010] crystal orientation of ultrathin nanosheet units. As shown in Scheme 1a, the Bi2 WO6 nanoparticle precursors firstly growed into ultrathin nanosheets based on layered structure feature of themselves in the initial reaction37 because of the relative low flowability and diffusivity in the mixed molten salt conditions (Step 1). The mixed molten salt could directly result in suppression effect of intrinsic anisotropic crystal growth owing to the relative slow nucleation and growth rates. So the nanosheets preferentially assembled along their [010] crystal orientation in the following process (Step 2). Finally, the tetragonal mesoporous single-crystallike Bi2 WO6 were formed after further orientated growth and Ostwald ripening process (Step 3). Based on the above analysis, this unique single-crystallike structural construction might be attributed to the synergistic effect of the following two points. Firstly, it was well known that Bi2 WO6 was constructed by alternating (Bi2 O 2 )n 2n+ and (WO 4 )n2n− layers along b axis, which usually produced an internal electric field paralleling to b axis (Scheme 1b). It further induced a certain amount of charges gathering on the surfaces of the nanosheet unit. Meanwhile, the electrostatic attraction among nanosheets with different charges might act as the driving force in the oriented attachment process, which guaranteed that nanosheets shared an identical crystallographic orientation. This is one of the two factors to finally construct tetragonal singlecrystal- like architecture. On the other hand, Alkali metal nitrates also played an important role for constructing tetragonal single-crystallike architecture, which provided a reaction medium in favor of the crystal growth exposing charged planes. 38-39 The report showed that if a crystalline structure containing charged planes was populated with anionic in molten Alkali nitrate flux, the layered crystal was preferentially exposed polar anionic-terminated planes, the growth way of which could decrease the free energy of charged planes in favor of their exposure.39 In addition, it was proved by theoretical study that the melt ions always left the space between the particle units in molten-salt system, which tended to form ordered layers between the particle unit facets.40 The above results proved that the mixed Alkali metal nitrates system was the essential factor for the oriented attachment along the [010] crystal orientation of Bi2 WO6 nanosheets. Therefore, the single-crystallike Bi2 WO6 tetragonal architecture construction after further ripening process was obtained in the mixed molten salt system owing to the synergistic effect of mixed alkali metal nitrates and electrostatic attraction caused by internal electric field in crystal.


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3.4 Mesoporous Property of SCL-Bi2 WO6 Photocatalyst. The mesoporous characteristic of SCL-Bi2 WO6 was indentified by the nitrogen adsorption-desorption experiment. Figure 4a displayed a typical character of IV-type isothermal curves with a hysteresis loop appeared in the range of 0.4-0.8 (P/P0 ), which suggested SCL-Bi2 WO6 had a mesoporous characteristic.41-42 Meanwhile, the corresponding pore diameter distribution (the insert of Figure 4a) centered at 3.8 nm confirmed that the formation of uniform mesoporous structures. In addition, the small angle XRD pattern of SCL-Bi2 WO6 was also carried out. As shown in Figure 4b, it appeared a distinct diffraction peak at ~2.1° in low two-theta angle. It indicated the pore distribution in SCLBi2 WO6 sample have highly uniform ordered mesoporous feature that might derive from the interlayer space of ultrathin nanosheet units.43 This unique micro-structure directly resulted in increasing the specific surface area. As measured, BET specific surface area of SCL-Bi2 WO6 reached to 15.26 m²g-1 and was 17.15 times higher than that of SSR-Bi2 WO6 (0.89 m2 g-1 ), which was in favor of improving its photocatalytic activity. 3.5 Photocatalytic Degradation Activity and Oxygen Production ove r As-prepared Samples. The photocatalytic activities of SCL-Bi2 WO6 and typical Bi2 WO6 sample prepared by solid-state reaction (SSR-Bi2 WO6 , XRD was shown in Figure S4) were firstly investigated by degrading organic pollutants under visible light (λ>400 nm). Figure 5a showed the dynamic curves of colored RhB dye degradation over the different samples. We found that H2 O2 could not decolorize or degrade RhB (Blank) in the absence of photocatalyst, as well as SCL-Bi2 WO6 and SSR-Bi2 WO6 displayed more intense photodegraded activity than Degussa P25 (TiO 2 ) at the same contents of H2 O 2. In particular, SCL-Bi2 WO6 presented the most splendid photocatalytic degradation ability, and completely decomposed RhB dye molecules within 50 min. By contrast, the removal rate of RhB dye over SSR-Bi2 WO6 and P25 was only ~43.3% and ~28.0% at the same reacting time, respectively. In addition, the kinetic characteristic of RhB degradation was also investigated by fitting its kinetic curve according to an approximated pseudo- first-order process.44 Figure 5b showed the plots of ln (C0 /C) versus irradiation time and the fitting results of these plots. The calculated removal rate constant k of RhB dye over SCL-Bi2 WO6 was 0.072 min-1 , which interestingly reached to 5.14 and 9.00 times as much as that of SSR-Bi2 WO6 (0.014 min-1 ) and P25 (0.008 min-1 ), respectively. Moreover, in the absence of H2 O 2 , the photodegradation of RhB dye activity over SCL-Bi2 WO6 was still higher than that of SSRBi2 WO6 (Figure S5), though the photocatalytic activity over both of them reduced a lot. Figure


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5c displayed the absorbance variation curves of RhB dye solutions over SCL-Bi2 WO6 , in which the absorption peaks of RhB dye at ultraviolet and visible region during degradation reaction process were all disappearing after reacting 40 min, indirectly proving that the RhB dye molecules were decomposed completely into the small organic/inorganic molecules or/and ions products.45 Meanwhile, the cycle runs of SCL-Bi2 WO6 were carried out owing to its importance in practical application. Figure 5d clearly presented that the photocatalytic activity of SCLBi2 WO6 was barely reduction after reusing five recycles, which implied that SCL-Bi2 WO6 had superior stability and reusability. Besides, the degradation of colourless phenol solution was also executed to further verify the photooxidation ability of SCL-Bi2 WO6 . The dynamic curves of photodegradation in Figure 6a showed that the phenol solution was decomposed more than 90% after 240 min over the SCL-Bi2 WO6 sample under visible light irradiation. The degradation degree was much higher than that of SSR-Bi2 WO6 and blank (without photocatalyst). The fitting removal rate constant k of SCL-Bi2 WO6 also reached 0.0085min-1 (Figure 6b), which reached to 4 times as much as that of SSR-Bi2 WO6 (0.0021 min-1 ). Furthermore, the photocatalytic activity of O 2 evolution from water under visible light was also performed to further evaluate photocatalytic activity of SCL-Bi2 WO6 . As shown in Figure 7, the O 2 evolution yield over SCLBi2 WO6 was ~471.1 µmol g-1 after reaction of 5 h, which was considerably higher than that of SSR-Bi2 WO6 (~155.6 µmol g-1 ). The average rate over SCL-Bi2 WO6 was further calculated to be ~84.8 µmol h-1 g-1 , which reached up to 2.48 times higher than that of SSR-Bi2 WO6 (~34.2 µmol h-1 g-1 ). All the above results demonstrated that the SCL-Bi2 WO6 sample served as an outstanding visible-light photocatalytic material for organic pollutants degradation and O 2 evolution from water. In general, the photocatalytic processes involved in surface reactions also greatly depend ing on micro- morphology and micro-structure feature of photocatalysts.46-47 To begin with, the mesoporous structure of SCL-Bi2 WO6 formed a large specific surface area, provided abundant reacting active sites, and produced a mass of molecule transport channels for the sufficient interaction between the reactive molecules and photocatalyst, thus improving photocatalytic performance. In addition, it was reported that the photogenerated charge carriers transport pathways were affected sensitively by crystal boundary of photocatalysts.17 Compared to polycrystalline SSR-Bi2 WO6 , the single-crystallike SCL-Bi2 WO6 had lesser crystal boundary, which facilitated long-range electron transport and also reduced the number of defects acting


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usually as recombination centers of photogenerated charge carriers, thus effectively increasing the lifetime of electrons and holes. Moreover, the high exposure percentage of (010) lattice plane for ultrathin nanosheet units in SCL-Bi2 WO6 architecture was conducive to making best use of internal electric field in favor of improving the transfer and separation efficiency of charge carriers as well as shortening transport distance paralleling to b axis direction, thus leading to the higher photocatalytic activity.48 3.6 Light Absorption, Photoelectroche mical and Luminescent Decay Properties of the AsPrepared Samples. Besides the own micro- morphology and micro-structure feature of SCLBi2 WO6 in favor of improving photocatalytic performance, in order to gain an insight into origins of improving photocatalytic activity, the mesoporous single-crystallike structure effect on the physical properties such as light absorption, photoelectricity and luminescent decay that influence photocatalytic activity significantly was investigated in detail. The light absorption ability of samples was evaluated by UV- vis DRS spectra. Figure 8 exhibited that the absorption ability of SCL-Bi2 WO6 was significantly enhanced compared with SSR-Bi2 WO6 , The absorbance edge of SCL-Bi2 WO6 (436.7 nm) took place distinct blue-shift of 8.7 nm relative to SSR-Bi2 WO6 (445.4 nm), and its steep shape indicated that the light absorption was due to the band-gap transition instead of the impurity level.49 The plots of (αhν)1/2 versus hν of SCLBi2 WO6 and SSR-Bi2 WO6 were further performed (the insert of Figure 8). The band gap value of SCL-Bi2 WO6 was identified to be 2.77 eV, which was obvious broadening compared with 2.73 eV of SSR-Bi2 WO6 . Moreover, the relative CB and VB positions of SCL-Bi2 WO6 and SSRBi2 WO6 were calculated (Table S1). The CB and VB positions of SCL-Bi2 WO6 shifted up and moved down 0.02 eV in comparison with that of SSR-Bi2 WO6 , respectively, which could enhance reduction ability of electrons and oxidizing ability holes, finally resulting in improvement of photocatalytic activity. The above results might be attributed to quantum size effect caused by ultrathin nanosheets, strong light reflection effect ca used by inner mesoporous and reduced light scatter effect caused by regularly ordered structure of SCL-Bi2 WO6 relative to SSR-Bi2 WO6 . We all knew that the photocatalytic activity improvement of photocatalysts was essentially attributed to increasing separation efficiency and lifetime of charge carriers. In general, the intense photocurrent response indicated that the sample had much strong generation, transfer and separation ability of charge carriers under light irradiation.50-51 As can be seen in Figure 9a, SCL-


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Bi2 WO6 fabricated into film photoelectrode showed much higher photocurrent density than that of SSR-Bi2 WO6 film photoelectrode at the same bias under visible light (λ>400 nm), which demonstrated that the more effective separation of charge carriers and faster charge transfer through the SCL-Bi2 WO6 film photoelectrode interface. This result was also evidenced by the electrochemical impedance spectroscopy (EIS) of film photoelectrodes (Figure 9b). The arc radius of EIS coming from SCL-Bi2 WO6 film photoelectrode was much smaller than that of SSR-Bi2 WO6 film photoelectrode, which implied that SCL-Bi2 WO6 had lower resistance than that of SSR-Bi2 WO6 and contributed to the interfacial charge transfer. In addition, we further detected the ﬂuorescent lifetime of SCL-Bi2 WO6 and SSR-Bi2 WO6 . As displayed in Figure 10, the lifetime fitted from ﬂuorescent decay curve of SCL-Bi2 WO6 was 9.35 ns, which was more than twice of SSR-Bi2 WO6 (4.08 ns). It confirmed that the recombination probability of electronhole pairs could be inhibited in SCL-Bi2 WO6 . As a result, SCL-Bi2 WO6 exhibited the more superior photocatalytic performance. 3.7 Possible Photocatalytic Reaction Mechanis ms over SCL-Bi2 WO6 Sample. Based on the above analysis, the possible photocatalytic reaction mechanisms of organic pollutants degradation and oxygen evolution over SCL-Bi2 WO6 sample were shown in Scheme 2. When the photocatalyst was exposed to the visible light, electron-hole pairs were firstly produced on the sample surface. Then the electrons and holes separate and transfer to conduction band and valence band, respectively. In consequence, the photocatalytic reactions of RhB/phenol molecules were able to take place on the surface of SCL-Bi2 WO6 . As our previous reports,24 we proved the mainly reactive species was hole and superoxide radicals (∙O2-), but ∙O2- played a major role for the photodegradation of organic pollutants over Bi2 WO6 sample. When H2 O2 was added into the solutions, it could capture photogenerated electrons to improve separation efficiency of charge carriers, and yield abundant hydroxyl radicals (·OH) to removed RhB/phenol molecules thus enhancing photocatalytic activity. 30, 52-53 In the reaction process, a plenty of electrons reacted with H2 O 2 molecules to generate ∙OH and a small quantity of electrons were captured by the dissolved oxygen in water to produce ∙O 2 -. ∙OH, ∙O 2 - and holes all can degrade RhB/phenol molecules. However, without adding H2 O2 under same conditions, the photocatalytic activity of SCL-Bi2 WO6 and SCL-Bi2 WO6 samples was obvious lower (Figure S5). It indirectly indicated ∙OH was the main active species for degradation organic pollutant in the existence of H2 O 2 , which was in line with the previous report.53 In addition, the H2 O


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molecules absorbed on the sample surface could be directly oxidized by holes to generate O 2 . In this reaction, Ag+ ions as sacrificial agents were introduced into reacting system. It could not only capture photogenerated electrons to improve separation efficiency of charge carriers, but also make the generated Ag nanoparticles deposit on the sample surface that might induce surface plasmon resonance effect to improve light harvest ability, thus enhancing photocatalytic O2 evolution activity.

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4. CONCLUSIONS To sum up, the mesoporous single-crystallike Bi2 WO6 with integrated tetragonal architecture was firstly prepared in the mixed molten salt system, which exhibited the superior photocatalytic activity of organic pollutants degradation and oxygen evolution from water under visible light. The synergistic effect of mixed alkali metal nitrates and electro static attraction caused by internal electric field in crystal played a critical role for the construction of mesoporous single-crystallike Bi2 WO6 architecture. Besides its own structure feature in favor of improving photocatalytic activity, this unique architecture effectively adjusted physical properties to enhance separation efficiency and lifetime of electrons and holes. Giving insight into the construction mechanism of this mesoporous single-crystallike Bi2 WO6 architecture and its relationship with photocatalytic activity may open up the new opportunities to fabricate other micro/nanomaterials with a similar structure for improving functional performance. ASSOCIATED CONTENT Supporting Information for Publication EDS spectrum of SCL-Bi2 WO6 (Figure S1); HRTEM images of SCL-Bi2 WO6 (Figure S2); TEM and the corresponding SAED images of SSR-Bi2 WO6 (Figure S3); XRD pattern of SSR-Bi2 WO6 (Figure S4); Degradation dynamic curves of RhB solutions over SCL-Bi2 WO6 and SSR-Bi2 WO6 samples (Figure S5); X, Eg, ECB and EVB of SCL-Bi2 WO6 and SSR-Bi2 WO6 (Table S1). These materials are available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *Corresponding author: E-mail: [email protected], [email protected], Fax: (+86)-451-86413753


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Notes The authors declare no competing financial interests. ACKNOWLEDGMENTS This work was financially supported by projects of Natural Science Foundation of China (21501035, 21271055 and 21471040), the Fundamental Research Funds for the Central Universities (HIT. IBRSEM. A. 201410) and China Postdoctoral Science Foundation funded project (2015M570298). We acknowledge for the support by Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Techno logy (No.QAK201304), Program for Innovation Research of Science in Harbin Institute of Technology (PIRS of HIT B201412 and B201508). REFERENCES (1) Sun, Y. G.; Xia, Y. N. Shape-controlled Synthesis of Gold and Silver Nanoparticles. Science 2002, 298, 2176-2179. (2) Goto, T.; Ogawa, M. Visible-Light-Responsive Photocatalytic Flow Reactor Composed of Titania Film Photosensitized by Metal Complex-Clay Hybrid. ACS Appl. Mater. Interfaces 2015, 7, 12631-12634. (3) Crossland, E. J. W.; Noel, N.; Sivaram, V.; Leijtens, T.; Alexander-Webber, J. A.; Snaith, H. J. Mesoporous TiO 2 Single Crystals Delivering Enhanced Mobility and Optoelectronic Device Performance. Nature 2013, 495, 215-219. (4) Bera, R.; Kundu, S.; Patra, A. 2D Hybrid Nanostructure of Reduced Graphene Oxide-CdS Nanosheet for Enhanced Photocatalysis. ACS Appl. Mater. Interfaces 2015, 7, 13251-13259 (5) Bian, Z.; Zhu, J.; Wen, J.; Cao, F.; Huo, Y.; Qian, X.; Cao, Y.; Shen, M.; Li, H.; Lu, Y. Single-crystallike Titania Mesocages. Angew. Chem. Int. Ed. 2011, 50, 1105-1108. (6) Paramasivam, I.; Jha, H.; Liu, N.; Schmuki, P. A Review of Photocatalysis using Selforganized TiO 2 Nanotubes and Other Ordered Oxide Nanostructures. Small 2012, 8, 3073- 3103;


13


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 14 of 27

(7) Yang, H. G.; Sun, C. H.; Qiao, S. Z.; Zou, J.; Liu, G.; Smith, S. C.; Cheng, H. M.; Lu, G. Q. Anatase TiO 2 Single Crystals with A Large Percentage of Reactive Facets. Nature 2008, 453, 638-641. (8) Wang, J. Q.; Cao, F. L.; Bian, Z. F.; Leung, M. K. H.; Li, H. X. Ultrafine Single-crystal TiOF2 Nanocubes with Mesoporous Structure, High Activity and Durability in Visible Light Driven Photocatalysis. Nanoscale 2014, 6, 897-902. (9) Yin, J. F.; Cao, H. Q.; Zhang, J. X.; Qu, M. Z.; Zhou, Z. F. Synthesis and Applications of gamma-Tungsten Oxide Hierarchical Nanostructures. Cryst. Growth Des. 2013, 13, 759-768 (10) Chen, D.; Ye, J. H. Hierarchical WO 3 Hollow Shells: Dendrite, Sphere, Dumbbell, and Their Photocatalytic Properties. Adv. Funct. Mater. 2008, 18, 1922-1928. (11) Muscas, G.; Singh, G.; Glomm, W. R.; Mathieu, R.; Kumar, P. A.; Concas, G.; Agostinelli, E.; Peddis, D. Tuning the Size and Shape of Oxide Nanoparticles by Controlling Oxygen Content in the Reaction Environment: Morphological Analysis by Aspect Maps. Chem. Mater. 2015, 6, 1982-1928. (12) Wang, J.; Ma, J. W.; Li, X. J.; Li, Y.; Zhang, G. L.; Zhang, F. B.; Fan, X. B. Cu2 O Mesoporous Spheres with A High Internal Diffusion Capacity and Improved Catalytic Ability for The Aza-Henry Reaction Driven by Visible Light. Chem. Commun. 2014, 50, 14237-14240. (13) Liu, G.; Zhao, Y.; Sun, C.; Li, F.; Lu, G. Q.; Cheng, H. M. Synergistic Effects of B/N Doping on The Visible- light Photocatalytic Activity of Mmesoporous TiO 2 . Angew. Chem. Int. Ed. 2008, 47, 4516-4520. (14) Zhou, W.; Li, W.; Wang, J. Q.; Qu, Y.; Yang, Y.; Xie, Y.; Zhang, K.; Wang, L.; Fu, H.; Zhao, D. Ordered Mesoporous Black TiO 2 as Highly Efficient Hydrogen Evolution Photocatalyst. J. Am. Chem. Soc. 2014, 136, 9280-9283. (15) Warren, S. C.; Voitchovsky, K.; Dotan, H.; Leroy, C. M.; Cornuz, M.; Stellacci, F.; Hebert, C.; Rothschild, A.; Gratzel, M. Identifying Champion Nanostructures for Solar Water-splitting. Nat. Mater. 2013, 12, 842-849.


14

Page 15 of 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


(16) Jiao, W.; Xie, Y. P.; Chen, R. Z.; Zhen, C.; Liu, G.; Ma, X. L.; Cheng, H. M. Synthesis of Mesoporous Single Crystal Rutile TiO 2 with Improved Photocatalytic And Photoelectrochemical Activities. Chem. Commun. 2013, 49, 11770-11772. (17) Adachi, M.; Murata, Y.; Takao, J.; Jiu, J. T.; Sakamoto, M.; Wang, F. M. Highly Efficient Dye-sensitized Solar Cells with A Titania Thin-film Electrode Composed of A Network Structure of Single-crystallike TiO 2 Nanowires Made by The "Oriented Attachment" Mechanism J. Am. Chem. Soc. 2004, 126, 14943-14949. (18) Fang, X. L.; Chen, C.; Jin, M. S.; Kuang, Q.; Xie, Z. X.; Xie, S. Y.; Huang, R. B.; Zheng, L. S. Single-crystallike Hematite Colloidal Nanocrystal Clusters: Synthesis and Applications in Gas Sensors, Photocatalysis and Water Treatment. J. Mater. Chem. 2009, 19, 6154-6160. (19) Zhang, D. Q.; Wen, M. C.; P.; Zhang, J. Zhu, G. Li, H. Li, Microwave-Induced Synthesis of Porous Single-Crystal-Like TiO 2 with Excellent Lithium Storage Properties. Langmuir 2012, 28, 4543-4547. (20) Yu, Y. F.; Zhang, J.; Wu, X.; Zhao, W. W.; Zhang, B. Nanoporous Single-Crystal-Like Cdx Zn1-x S Nanosheets Fabricated by the Cation-Exchange Reaction of Inorganic-Organic Hybrid ZnS-Amine with Cadmium Ions. Angew. Chem. Int. Ed. 2012, 51, 897-900. (21) Kuang, Q.; Yang, S. H. Template Synthesis of Single-Crystal-Like Porous SrTiO 3 Nanocube Assemblies and Their Enhanced Photocatalytic Hydrogen Evolution. ACS Appl. Mater. Interfaces 2013, 5, 3683-3690. (22) Zheng, X. L.; Kuang, Q.; Yan, K. Y.; Qiu, Y. C.; Qiu, J. H.; Yang, S. H. Mesoporous TiO 2 Single Crystals: Facile Shape-, Size-, and Phase-Controlled Growth and Efficient Photocatalytic Performance. ACS Appl. Mater. Interfaces 2013, 5, 11249-11257. (23) Sivaram, V.; Crossland, E. J. W.; Leijtens, T.; Noel, N. K.; Alexander-Webber, J.; Docampo, P.; Snaith, H. J. Observation of Annealing-Induced Doping in TiO 2 Mesoporous Single Crystals for Use in Solid State Dye Sensitized Solar Cells. J. Phys. Chem. C 2014, 118, 1821-1827.


15


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 16 of 27

(24) Li, C. M.; Chen, G.; Sun, J. X.; Dong, H. J.; Wang, Y.; Lv, C. D. Construction of Bi2 WO6 Homojunction Via QDs Self-Decoration And Its Improved Separation Efficiency of Charge Carriers and Photocatalytic Ability. Appl. Catal. B: Environ. 2014, 160-161, 383-389. (25) Wang, D.; Guo, L.; Zhen, Y.; Yue, L.; Xue, G.; Fu, F. AgBr Quantum Dots Decorated Mesoporous Bi2 WO6 Architectures with Enhanced Photocatalytic Activities for Methylene Blue. J. Mater. Chem. A 2014, 2, 11716-11727. (26) Zhang, N.; Ciriminna, R.; M.; Pagliaro, Xu, Y. J. Nanochemistry-derived Bi2 WO6 Nanostructures: Towards Production of Sustainable Chemicals and Fuels Induced by Visible Light. Chem. Soc. Rev. 2014, 43, 5276-5287. (27) Tian Y. L.; Chang, B. B.; Lu, J. L.; Fu, J.; Xi, F. N.; Dong, X. P. Hydrothermal Synthesis of Graphitic Carbon Nitride-Bi2 WO6 Heterojunctions with Enhanced Visible Light Photocatalytic Activities. ACS Appl. Mater. Interfaces 2013, 5, 7079-7085. (28) Zhang, L. S.; Wang, W. Z.; Chen, Z. Q.; Zhou, L.; Xu, H. L.; Zhu, W. Fabrication of Flower- like Bi2 WO6 Superstructures As High Performance Visible- light Driven Photocatalysts. J. Mater. Chem. 2007, 17, 2526-2532. (29) Shang, M.; Wang, W. Z.; Xu, H. L. New Bi2 WO6 Nanocages with High Visible-LightDriven Photocatalytic Activities Prepared in Refluxing EG. Cryst. Growth Des. 2009, 9, 991-996. (30) Li, C. M.; Chen, G.; Sun, J. X.; Feng, Y. J.; Liu, J. J.; Dong, H. J. Ultrathin Nanoflakes Constructed Erythrocyte- like Bi2 WO6 Hierarchical Architecture Via Anionic Self-regulation Strategy for Improving Photocatalytic Activity and Gas-sensing Property. Appl. Catal. B: Environ. 2015, 163, 415-423. (31) Tian, Y.; Hua, G. M.; Li, N.; Fang, M.; Zhang, L. D. Bismuth Tungstate Nano/microstructures: Controllable Morphologies, Growth Mechanism and Photocatalytic Properties. J. Alloys Compd. 2011, 509, 724-730. (32) Zhang, L. S.; Wang, W. Z.; Zhou, L.; Xu, H. L. Bi2 WO6 Nano- And Microstructures: Shape Control And Associated Visible-Light-Driven Photocatalytic Activities. Small 2007, 3, 1618 1625.


16

Page 17 of 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


(33) Liu, X. F.; Fechler, N.; Antonietti, M. Salt Melt Synthesis of Ceramics, Semiconductors and Carbon Nanostructures. Chem. Soc. Rev. 2013, 42, 8237-8265. (34) Tang, J. W.; Zou, Z. G.; Ye, J. H. Photocatalytic Decomposition of Organic Contaminants by Bi2 WO6 under Visible Light Irradiation. Catal. Lett. 2004, 92, 53-56. (35) Long, B. H.; Huang, J. H.; Wang X. C. Photocatalytic Degradation of Benzene in Gas Phase by Nanostructured BiPO 4 Catalysts. Prog. Nat. Sci-Mater. 2012, 22, 644-653. (36) Yang, H. G.; Zeng, H. C. Self-construction of Hollow SnO 2 Octahedra Based on TwoDimensional Aggregation of Nanocrystallites. Angew. Chem. Int. Ed. 2004, 43, 5930-5933. (37) Zhang, L.; Wang, H.; Chen, Z.; Wong, P. K.; Liu, J. Bi2 WO6 Micro/nano-structures: Synthesis, Modifications And Visible-Light-Driven Photocatalytic Applications. Appl. Catal. B: Environ. 2011, 106, 1-3. (38) Afanasiev, P.; Aouine, M.; Deranlot, C.; Epicier, T. Ordered Arrays of Nanorods Obtained by Solid-Liquid Reactions of LaOCl Crystals. Chem. Mater. 2010, 22, 5411-5419. (39)Afanasiev, P. Snapshots of Zinc Oxide Formation in Molten Salt: Hollow Microtubules Generated by Oriented Attachment and the Kirkendall Effect. J. Phys. Chem. C 2012, 116, 23712381. (40) Sathiyanarayanan, R.; Alimohammadi, M.; Zhou, Y.; Fichthorn, K. A. Role of Solvent in the Shape-Controlled Synthesis of Anisotropic Colloidal Nanostructures. J. Phys. Chem. C 2011, 115, 18983-18990. (41) Tan, M. W.; Wang, X. G.; Wang, X. X.; Zou, X. J.; Ding, W. Z.; Lu, X. G. Formation of Magnesium Silicate on Surface of Silica for Steam Reforming of Liquefied Petroleum Gas. J. Catal. 2015, 329 , 151-166. (42) Wan, Z.; Zhang, G. K. Synthesis and Facet-dependent Enhanced Photocatalytic Activity of Bi2 SiO5 /AgI Nanoplate Photocatalysts. J. Mater. Chem. A 2015, 3, 16737-16745


17


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 18 of 27

(43) Zhou, W. J.; Guan, W. J.; Lu, C. Covalent Linking of Quantum Dots to Polymer for Inorganic-Inorganic Luminescence Films Via Layer-by-Layer Assembly with Clay. Chem. Commun. 2014, 50, 11370-11373. (44) Zhang, Z. J.; Wang, W. Z.; Yin, W. Z.; Shang, M.; Wang, L.; Sun, S. M. Inducing Photocatalysis By Visible Light Beyond the Absorption Edge: Effect of Upconversion Agent on The Photocatalytic Activity of Bi2 WO6 . Appl. Catal. B: Environ. 2010, 101, 68-73. (45) Dong, H. J.; Chen, G.; Sun, J. X.; Feng, Y. J.; Li, C. M.; Xiong, G. H.; Lv, C. D. HighlyEffective Photocatalytic Properties and Interfacial Transfer Efficiencies of Charge Carriers for The Novel Ag2 CO3 /AgX Heterojunctions Achieved by Surface Modification. Dalton Trans. 2014, 43, 7282-7289 (46) Chen, X.; Shen, S.; Guo, L.; Mao, S. S. Semiconductor-based Photocatalytic Hydrogen Generation. Chem. Rev. 2010, 110, 6503-6570. (47) Xiang, Q.; Yu, J.; Jaroniec, M. Synergetic Effect of MoS2 and Graphene as Cocatalysts for Enhanced Photocatalytic H2 -Production Activity of TiO 2 Nanoparticles. J. Am. Chem. Soc. 2012, 134, 6575-6578. (48) Li, J.; Yu, Y.; Zhang, L. Bismuth Oxyhalide Nanomaterials: Layered Structures Meet Photocatalysis. Nanoscale 2014, 6, 8473-8488. (49) Kudo, A.; Tsuji, I.; Kato, H. AgInZn7 S9 Solid Solution Photocatalyst for H2 Evolution from Aqueous Solutions under Visible Light Irradiation. Chem. Commun. 2002, 1958-1959. (50) Dong, H. J.; Chen, G.; Sun, J. X.; Feng, Y. J.; Li, C. M.; Lv, C. D. Stability, Durability and Regeneration Ability of A Novel Ag-based Photocatalyst, Ag2 Nb4O11 . Chem. Commun. 2014, 50, 6596-6599. (51) Zhang, Z. H.; Dua, R.; Zhang, L. B.; Zhu, H. B.; Zhang H. N.; Wang, P. Carbon-LayerProtected Cuprous Oxide Nanowire Arrays for Efficient Water Reduction. ACS Nano 2013, 7, 1709-1717.


18

Page 19 of 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


(52) Li, C. M.; Chen, G.; Sun, J. X.; Feng, Y. J.; Dong, H. J.; Han, Z. H.; Hu, Y. D.; Lv, C. D. A Thin Empty-Shell Bismuth Tungstate Hierarchical Structure Constructed by The Acid Sculpture Effect with Improved Visible- light Photocatalytic Activity. New J. Chem. 2015, 39, 4384-4390. (53) He, Z.; Sun, C.; Yang, S. G.; Ding, Y. C.; He, H.; Wang, Z. L. Photocatalytic Degradation of Rhodamine B by Bi2 WO6 with Electron Accepting Agent Under Microwave Irradiation: Mechanism and Pathway J. Hazard. Mater. 2009, 162, 1477-1486. (54) Shimodaira, Y.; Kato, H.; Kobayashi, H; Kudo, A. Photophysical Properties and Photocatalytic Activities of Bismuth Molybdates under Visible Light Irradiation. J. Phys. Chem. B 2006, 110, 17790-17797. (55) Kho, Y. K.; Teoh W. Y.; Iwase, A.; Mädler, L.; Kudo, A.; Amal, R. Flame Preparation of Visible-Light-Responsive BiVO 4 Oxygen Evolution Photocatalysts with Subsequent Activation via Aqueous Route. ACS Appl. Mater. Interfaces 2011, 3, 1997-2004. (56) Obregón, S.; Colón, G. Improved O 2 Evolution from a Water Splitting Reaction over Er3+ and Y3+ Co-doped Tetragonal BiVO 4. Catal. Sci. Technol. 2014, 4, 2042-2050.


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FIGURE CAPTIONS Figure 1 XRD pattern of SCL-Bi2 WO6 sample. Figure 2 Survey (a) and high-resolution XPS spectra of O 1s (b), W 4f (c) and Bi 4f (d) for SCLBi2 WO6 sample. Figure 3 FESEM images (a, b), TEM images (c, d, e, f), SAED pattern (g) and HRTEM image (h) of SCL-Bi2 WO6 sample. Figure 4 N2 adsorption-desorption isothermal curves (a), pore size distribution (the insert of a) and small-angle XRD pattern (b) of SCL-Bi2 WO6 sample. Figure 5 Degradation dynamic curves (a), plots of ln (C0 /C) versus irradiation time and rate constant k of RhB solutions over different photocatalysts (b) under visible light (λ>400 nm), absorbance variation curves (c) and cycle runs (d) of RhB solutions over SCL-Bi2 WO6 sample under visible light (λ>400 nm). Figure 6 Degradation dynamic curves (a), plots of ln (C0 /C) versus irradiation time and rate constant k of Phenol solutions (b) over different samples under visible light (λ>400 nm). Figure 7 Photocatalytic O 2 evolution yield over SCL-Bi2 WO6 and SSR-Bi2 WO6 samples under visible light (λ>400 nm). Figure 8 UV-vis DRS spectra and plots of (αhν)1/2 versus hν (insert) of SCL-Bi2 WO6 and SSRBi2 WO6 samples. Figure 9 Photocurrent response (a) and EIS spectra (b) of SCL-Bi2 WO6 and SSR-Bi2 WO6 samples. Figure 10 Fluorescence decay curves of SCL-Bi2 WO6 and SSR-Bi2 WO6 samples.


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Figure 1 XRD pattern of SCL-Bi2 WO6 sample.

Figure 2 Survey (a) and high-resolution XPS spectra of O 1s (b), W 4f (c) and Bi 4f (d) for SCLBi2 WO6 sample.


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Figure 3 FESEM images (a, b), TEM images (c, d, e, f), SAED pattern (g) and HRTEM image (h) of SCL-Bi2 WO6 sample.

Figure 4 N2 adsorption-desorption isothermal curves (a), pore size distribution (the insert of a) and small-angle XRD pattern (b) of SCL-Bi2 WO6 sample.


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Figure 5 Degradation dynamic curves (a), plots of ln (C0 /C) versus irradiation time and rate constant k of RhB solutions over different photocatalysts (b) under visible light (λ>400 nm), absorbance variation curves (c) and cycle runs (d) of RhB solutions over SCL-Bi2 WO6 sample under visible light (λ>400 nm).

Figure 6 Degradation dynamic curves (a), plots of ln (C0 /C) versus irradiation time and rate constant k of Phenol solutions (b) over different samples under visible light (λ>400 nm).


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Figure 7 Photocatalytic O 2 evolution yield over SCL-Bi2 WO6 and SSR-Bi2 WO6 samples under visible light (λ>400 nm).

Figure 8 UV-vis DRS spectra and plots of (αhν)1/2 versus hν (insert) of SCL-Bi2 WO6 and SSRBi2 WO6 samples.


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Figure 9 Photocurrent response (a) and EIS spectra (b) of SCL-Bi2 WO6 and SSR-Bi2 WO6 samples.

Figure 10 Fluorescence decay curves of SCL-Bi2 WO6 and SSR-Bi2 WO6 samples.


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Schemes Scheme 1 Crystal growth mechanism of SCL-Bi2 WO6 (a), layered structure of Bi2 WO6 (b), and FESEM images of SCL-Bi2 WO6 at the different reaction time (c). Scheme 2 Possible photocatalytic mechanism of O 2 evolution and organic pollutant degradation over SCL-Bi2 WO6 sample..

Scheme 1 Crystal growth mechanism of SCL-Bi2 WO6 (a), layered structure of Bi2 WO6 (b), and FESEM images of SCL-Bi2 WO6 at the different reaction time (c).

Scheme 2 Possible photocatalytic mechanism of organic pollutant degradation and O2 evolution over SCL-Bi2 WO6 sample.


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Table of Contents Graphic


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A Novel Mesoporous Single-Crystal-Like Bi2WO6 with Enhanced

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