Bi Heterojunctions ... - ACS Publications

May 16, 2016 - •S Supporting Information. ABSTRACT: The homogeneous BiOBr/Bi heterojunctions photocatalyst was synthesized from {001} facet dominate...
1 downloads 15 Views 3MB Size
Subscriber access provided by ORTA DOGU TEKNIK UNIVERSITESI KUTUPHANESI

Article

Homogeneous {001}-BiOBr/Bi heterojunctions: facile controllable synthesis and morphology-dependent photocatalytic activity Yuxi Guo, Yihe Zhang, Hongwei Huang, and Na Tian ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00884 • Publication Date (Web): 16 May 2016 Downloaded from http://pubs.acs.org on May 16, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37

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

ACS Sustainable Chemistry & Engineering

Homogeneous

{001}-BiOBr/Bi

heterojunctions:

facile controllable synthesis and morphologydependent photocatalytic activity Yuxi Guo†, Yihe Zhang*,†, Na Tian†, Hongwei Huang*,† †

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, No.29 Xueyuan Street, Beijing 100083, China Corresponding Authors * Y. H. Zhang. E-mail: [email protected]. * H. W. Huang. E-mail: [email protected].

KEYWORDS. photocatalyst, BiOBr, metallic Bi, in situ reduction, PVP-assisted, plasmon resonance effect

ABSTRACT. The homogeneous BiOBr/Bi heterojunctions photocatalyst was synthesized from {001} facet dominated BiOBr flakes via a PVP-assisted in situ reduction reaction at room temperature. The high {001} facet exposure of BiOBr could induce the homogeneous distribution of metallic Bi on the surface of BiOBr. The introduction of PVP not only effectively protected the uniform structure, but also largely promoted the photocatalysis properties. Compared to the bare BiOBr, an obviously enhanced photochemical performance was achieved

ACS Paragon Plus Environment

1

ACS Sustainable Chemistry & Engineering

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 2 of 37

over the homogeneous BiOBr/Bi pertaining to Methyl Orange (MO) degradation and photocurrent generation. The highly enhanced photocatalytic activity can not only be attributed to the surface plasmon resonance effect and efficient separation of electron–hole pairs by the metallic Bi, but also largely depended on its uniform and regular structure. The present work provided a new approach to the development of attractive bismuth-based-photocatalysts/metallic Bi heterostructures with controllable structures and photocatalytic performance.

INTRODUCTION In view of making full use of the renewable solar energy source, the search of semiconductor photocatalysts for environment purification and energy production remains one of the most intense research interest.1-4 TiO2 is widely studied as an promising photocatalytic material.5-6 However, it requires UV light to be activated. Therefore, the development of novel visible-lightdriven (VLD) photocatalysts has drawn considerable attention among researchers.7-11 The tetragonal BiOX compounds has been widely applied as photocatalysts, pharmaceuticals, catalysts, ferroelectric materials.12-26 Among the bismuth oxyhalides, the BiOBr becomes attractive because it displays the visible-light responsive activity and good stability.

27-30

However, the light absorption of BiOBr with a band gap of 2.69 eV is still limited.31 Therefore, studies on further enhance its light responsive ability and photocatalytic efficiency is still important. Among various techniques, the surface plasmon resonance (SPR) noble-metal nanostructures have been proved to be effective to enhance the photocatalytic performance of the substrate semiconductors.32-42. Similar to noble metal, bismuth as a typical semimetal material, has also been discovered to exhibit plasmonic properties.43-44 In comparison to noble metals, the metallic

ACS Paragon Plus Environment

2

Page 3 of 37

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

ACS Sustainable Chemistry & Engineering

Bi is inexpensive. Concerning the unique properties of Bi, they can be perfect alternative SPR nanostructures in the photocatalytic process. The reported Bi-deposited semiconductor photocatalysts, including Bi/Bi2O3, Bi/(BiO)2CO3, all exhibit enhanced photocatalysis efficiency.45-49 Given the behavior of Bi, developing BiOBr/Bi structured nanocomposites to enhance photocatalytic activity has been attracting immense research efforts. Some groups synthesized BiOBr/Bi photocatalysts with improved visible photocatalytic activity, but they largely ignored the effect of Bi-rich {001}facet of BiOBr on the performance of Bi deposited and did not investigate further to gain uniform and regular morphology of samples.50-51 It is widely accepted that properties of composite photocatalytic materials are rather sensitive to their morphology. Until now, no research about controllable synthesis of desired morphology to improve BiOX/Bi’ photocatalysis has been reported. Herein, we report a novel PVP-assisted in situ reduction reaction strategy to synthesize uniform BiOBr/Bi heterojunctions from high {001} facets exposed BiOBr flakes at room temperature. During the reduction reaction, the precise control of distribution of metallic Bi was the key point in determining desirable physicochemical properties. Programming in the direction, we used the BiOBr flakes with high exposure of {001} facets which consist of [B2O2]2+ slabs as the substrates. As the Bi element is mainly contained in the [B2O2]2+ slabs on the {001} facets, the reduced metallic Bi may maximize its distribution area and form a homogeneous coating on the surface of the BiOBr crystals. Moreover, in order to control the synthesis process, we introduced PVP into the reaction system to maintain a peaceful reduction environment.

52-53

We

studied how to control the reaction condition for the formation of uniform and regular BiOBr/Bi structures. A possible mechanism for the formation of regular BiOBr/Bi samples was proposed.

ACS Paragon Plus Environment

3

ACS Sustainable Chemistry & Engineering

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 4 of 37

Moreover, the morphology-dependent photocatalytic activities of BiOBr/Bi was evaluated on the degradation of methyl orange under visible light (λ > 420nm) irradiation. EXPERIMENTAL SECTION Synthesis: The method for the synthesis of BiOBr flakes with high exposure of {001} facets is similar to that described in the previous work. 0.97g Bi(NO3)3•5H2O and 0.238g KBr was dispersed and dissolved into 25ml distilled water, respectively. The KBr solution was then added dropwise into the stirring Bi(NO3)3 suspension. After being stirred for 0.5 h at room temperature, the mixture was transferred into 100-mL Teflon-lined stainless autoclave and then heated at 120 ℃ for 24 hours. The resulting BiOBr precipitates were centrifuged, washed thoroughly with de-ionized water and ethanol and eventually dried at 60 ℃ for 12h. An in situ reduction was used to prepare Bi coated BiOBr flakes, as depicted in Scheme 1. 0.5 g of BiOBr flakes was dispersed in 20 mL of deionized water containing 7.5g PVP, to which 20 mL NaBH4 solution with different concentrations ranging from 5 to 30 mmol L-1 was dropped slowly under constant magnetic stirring. The BiOBr/Bi flakes prepared with different NaBH4 solutions were defined as BiOBr/Bi-5, BiOBr/Bi-10, BiOBr/Bi-15, BiOBr/Bi-20 and BiOBr/Bi30. The samples prepared with 5, 20 ,30 mmol L-1 without the use of PVP was named as NP BiOBr/Bi-5, NP BiOBr/Bi-20, NP BiOBr/Bi-30. After being reacted for 10 min, the obtained solid powder was collected by several centrifugation and washing steps and then dried at 60 ℃ for 12h. Characterization

ACS Paragon Plus Environment

4

Page 5 of 37

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

ACS Sustainable Chemistry & Engineering

The X-ray diffraction (XRD) (X/max-rA Advance diffractometer with Cu Kα radiation) were collected to analyze the crystal phase composition of samples. The nanostructure and size distribution of the as-obtained samples were observed by scanning electron microscopy (SEM) on a Hitachi S–4800. N2 adsorption–desorption isotherms were conducted to measure the specific BET surface areas of the BiOBr/Bi photocatalysts. The detailed information of the morphology was detected by the transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) using a JEOL JEM-2100. The optical properties of prepared hybrids were studied with a Varian Cary 5000 diffuse reflectance UV-vis spectrometer by employing BaSO4 as a standard. X-ray photoelectron spectra (XPS) (A VGMK II X-ray photoelectron spectrometer) were applied to explore surface elemental compositions and oxidation states of the sample. A Bruker ER200-SRC-10/12 electron paramagnetic resonance spectrometer equipped with visible-light irradiation system was operated to acquire the electron spin resonance (ESR) signals of radicals. The photoluminescence (PL) was recorded on a fluorescence

spectrophotometer

(RAMANLOG

6).

A

ChenhuaInstrument

CHI660C

electrochemical workstation was used to conduct the photoelectrochemical experiments by using a 300 W xenon lamp as the visible light source and 0.1 M Na2SO4 as supporting electrolyte. A carbon electrode and a platinum-saturated calomel electrode (SCE) served as the counter electrode and the reference electrode, respectively. The indium-tin oxide (ITO) glass coated with samples worked as the working electrode. All of the above measurements were conducted at room temperature. Photocatalytic Experiment. For the measurement of photocatalytical activity of the as-prepared samples, the degradation of MO under 500 W Xe arc lamp as the light source using a 420 nm cutoff filter. Typically, 50

ACS Paragon Plus Environment

5

ACS Sustainable Chemistry & Engineering

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 6 of 37

mg samples and 50 mL MO aqueous suspension were placed in a quartz test tube. Prior to irradiation, to reach the adsorption/desorption equilibrium the suspensions were fiercely magnetically stirred for 1 h in the dark. Then the visible light illumination was carried out. At given irradiation time intervals, 3 ml of the mixed solution was taken out and centrifuged, and the concentration of MO in the supernatant was monitored by a U-3010 UV-vis spectroscopic spectrophotometer by checking its characteristic absorbance at 464 nm. Determination of reactive species For investigating the active species that are responsible for the photocatalytic activity, severer scavengers, including 10 mmol L−1 isopropanol (IPA, •OH scavenger), 1 mmol L−1 1,4benzoquinone (BQ, •O2− scavenger), 1 mmol L−1 ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA-2Na, h+ scavenger), were individually added into the 50 mL MO solution. The testing was similar to the above photocatalytic experiment.

RESULTS AND DISCUSSION. TEM and HRTEM were performed on the as-synthesized pure BiOBr and BiOBr/Bi-20 photocatalyst to investigate the structure hybrid BiOBr/Bi (Figure 1). As displayed in Figure 1a, the surfaces of the pristine BiOBr flake were very smooth and neat. By mixing the BiOBr flakes with NaBH4 aqueous solution, an in situ reduction reaction was carried out instantly. From Figure 1c, we can obviously see that there was a layer of shell surrounding the BiOBr flake. From the enlarged TEM microscopy of BiOBr/Bi-20 in Figure 1d, the clear boundary between the BiOBr core and the shell was also observed, providing a strong evidence for the reduction of BiOBr surface. The HRTEM image of pure BiOBr sample was depicted in Figure 2a. The lattice

ACS Paragon Plus Environment

6

Page 7 of 37

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

ACS Sustainable Chemistry & Engineering

space was measured to be 0.277 nm, which corresponded to the (110) lattice plane of BiOBr, revealing that the prepared BiOBr was mainly enclosed by the {001} facets. The typical HRTEM image of BiOBr/Bi-20 was shown in Figure 2b, which was taken on the edge of a single flake. The fringe spacing was 0.294 nm, which was well indexed into the interplanar spacing of (111) of metallic Bi. It confirmed that the metallic Bi was formed on the surface around the BiOBr flakes as a result of partial reduction.

Figure 1. TEM images: (a) pure BiOBr flake before coating, (b) the magnified image,(c) BiOBr/Bi-20, (d) the magnified image of (c)

ACS Paragon Plus Environment

7

ACS Sustainable Chemistry & Engineering

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 8 of 37

Figure 2. (a) HRTEM images of pure BiOBr, (b) HRTEM images of edge of BiOBr/Bi-20.

The morphological information of the samples was also investigated by SEM. The pure BiOBr consisted of regular rectangle flakes with diameters of about 1.5 um and smooth surface (Figure 3a). Figure 3b–e showed the morphologies of the BiOBr/Bi composites with different NaBH4 concentrations of 10 (b), 15 (c), 20 (d) and 30 (e) mmol L-1. This samples are all prepared by adding 7.5 g PVP during the reduction process. We can see that all BiOBr/Bi samples still remained the regular rectangle flake structure. However, with the increase of the NaBH4 concentrations, the surface of the samples became more and more rough, indicating that the surface of BiOBr samples had been reduced by NaBH4. The schematic illustration under the SEM images clearly showed the change that occurred on the surface of these samples (Figure 3fj).

ACS Paragon Plus Environment

8

Page 9 of 37

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

ACS Sustainable Chemistry & Engineering

Figure 3. SEM images: (a) pure BiOBr, (b)BiOBr/Bi-10, (c) BiOBr/Bi-15, (d) BiOBr/Bi-20 and (e) BiOBr/Bi-30; (f-j) Schematic illustration of the surface of samples: (f) pure BiOBr, (g)BiOBr/Bi-10, (h) BiOBr/Bi-15, (i) BiOBr/Bi-20 and (j) BiOBr/Bi-30.

As a useful organic surfactant, PVP played very crucial roles in forming uniform BiOBr/Bi structure here. Figure 4 displayed the SEM images of the as-obtained BiOBr/Bi composites by in situ reduction process in 20 mmol L-1 NaBH4 solution with different amounts of PVP. As shown in Figure 4a and b, in the absence of PVP, the flakes suffered serious damage compared to the untreated pristine BiOBr and the surface of the BiOBr became extremely rough. Intriguingly, with the addition of PVP (From 2.5-7.5g) (Figure. 4b-f), the shape of the BiOBr became more and more regular and the surface of the sample gradually turned uniform. Accordingly, we supposed that it was the particular stabilization of PVP that enabled the formation of the resultant BiOBr/Bi flakes with a perfect and uniform structure.

ACS Paragon Plus Environment

9

ACS Sustainable Chemistry & Engineering

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 10 of 37

Figure 4. SEM images of BiOBr/Bi prepared with different content of PVP, (a-b) 0g, (c-d) 2.5g, (e-f) 5g, (g-h) 7.5g.

ACS Paragon Plus Environment

10

Page 11 of 37

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

ACS Sustainable Chemistry & Engineering

Figure 5a displayed the unit cell of BiOBr. The [Bi2O2] layers are combined by two slabs of bromine to form a ‘sandwich’ structure along the c-axis. We can clearly see that the Bi elements are regularly distributed on the [Bi2O2] layers, and the arrangement of Bi atoms on this layer is the closest. In other words, the distribution density of Bi atoms is the largest and most homogeneous on [Bi2O2]2+ layer in the BiOBr crystal. As the {001} facets of BiOBr consists of [Bi2O2]2+ layers (Figure 5b), the metallic Bi can hence form an excellent coating on the BiOBr crystal with exposed {001} facets.

ACS Paragon Plus Environment

11

ACS Sustainable Chemistry & Engineering

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 12 of 37

Figure 5. (a) Atomic structure of the BiOBr sample, (b) Atomic structure of the (001) facets. (c) XRD patterns (d) the value intensity ratios of the (002) and (200) peaks of the samples: BiOBr, BiOBr/Bi-10, BiOBr/Bi-15, BiOBr/Bi-20 and BiOBr/Bi-30. XRD patterns of the pure BiOBr and BiOBr/Bi products synthesized in NaBH4 solution with different concentrations of 10, 15, 20, and 30 mmol/L were shown in Figure 5c. The diffraction peaks of as-prepared BiOBr were in perfectly good agreement with tetragonal phase of BiOBr (JCPDS 73-0733). Fascinatingly, comparing to the standard spectrum of BiOBr, the (001), (002), (003) and (004) peaks belonging to the {001} facets of as-prepared BiOBr/Bi displayed overwhelmingly higher relative intensities (Figure S1). The above results revealed that the main exposed surfaces of the as-prepared BiOBr were {001} facets. After being reduced by NaBH4 solution, all peaks of BiOBr/Bi samples can also be assigned to the BiOBr phase. However, probably because of its low amount, there were no characteristic peaks of metallic Bi detected in the XRD patterns. Meanwhile, no changes in the 2θ position of the peaks of BiOBr can be observed in the BiOBr/Bi samples, which implied that Bi appeared on the surface of BiOBr instead of entering its lattice. It can also be found that in the XRD patterns of the BiOBr/Bi, compared to the intensity of pure BiOBr, the relative intensity of (001), (002), (003) and (004) peaks decreased with the of NaBH4. The intensity ratios of the (002) versus (200) peaks were 4.54, 3.92, 3.58, 2.87 and 2.58 for pure BiOBr, BiOBr/Bi-10, BiOBr/Bi-15, BiOBr/Bi-20 and BiOBr/Bi-30, respectively(Figure 5d). This change in peak intensity also reflected the gradually decreased peaks of (001) series facets with increasing the NaBH4 content, confirming that the Bi nanoparticles were derived from the reduction of the exposed {001} facets of BiOBr.

ACS Paragon Plus Environment

12

Page 13 of 37

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

ACS Sustainable Chemistry & Engineering

The DRS spectra of the pure BiOBr, Bi simple substance and the as-prepared BiOBr/Bi samples were shown in Figure 6. The absorption edge of the pristine BiOBr was estimated to be at 450 nm. After reduction by NaBH4 solution, the BiOBr/Bi hybrids exhibited more absorption within the visible light range and the absorption of BiOBr/Bi samples was gradually close to that of pure Bi simple substance with increasing the amount of NaBH4. This significant enhancement of visible light absorption derived from the SPR effect of metallic Bi. Combined with the HRTEM result in Figure.2b it can be further confirmed the presence of Bi0 species on the surface of BiOBr flakes.

Figure 6. (a) UV–vis diffuse reflectance spectra of the samples.

XPS spectrogram was analyzed on BiOBr/Bi-20 to elucidate the surface elemental compositions and oxidation states of the sample. The XPS survey spectrum of the sample was displayed in Figure 7a. The binding energy peaks at 158 eV (Bi 4f), 529eV (O 1s) and 681 eV (Br 3d) can be assigned to Bi, O and Br, which were the dominant composition of the BiOBr/Bi20. The high-resolution XPS spectrum of Bi4f of the sample was shown in Figure 7b. The core

ACS Paragon Plus Environment

13

ACS Sustainable Chemistry & Engineering

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

level binding energies at 164.08 eV and 158.8 eV were the feature of Bi3+ in BiOBr.

Page 14 of 37

54

Apart

from the two peaks, there were two peaks that were located at 163.07 eV and 157.5 eV with low intensity, which can be assigned to the metallic Bi.55 The XPS result was consistent with that of DRS and TEM, proving the existence of metallic Bi as a result of in situ reduction of the surface of BiOBr flakes. As displayed in Figure 7c, the XPS spectra of the Br3d region can be fitted into two peaks at 68.9 eV and 67.9 eV.56 The O1s spectra of the BiOBr/Bi-20 (Figure. 7d) can be deconvoluted into two peaks. The peak located at 528.9 eV can be ascribed to the Bi-O bonds in the BiOBr layered structure and the binding energy value of 530.0 eV is attributed to hydroxyl groups on the surface. 19

ACS Paragon Plus Environment

14

Page 15 of 37

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

ACS Sustainable Chemistry & Engineering

Figure 7. XPS spectra of BiOBr/Bi-20 photocatalyst (a)survery pattern (b)Bi4f, (c) O1s and (d)Br3d.

Based on the above results, a potential reaction process was proposed to explain formation of uniform BiOBr/Bi structure, as illustrated is in Scheme 1. First, BiOBr flakes with exposed {001} facets were obtained by a modified hydrothermal method. When NaBH4 was added to the suspension of BiOBr flakes in the presence of the PVP, the redox reaction occurred between BiOBr and NaBH4, and the primary Bi nanocrystals nucleate firstly formed. PVP was known to play a significant role in the syntheses of metallic nanoparticles57. With the assistance and protection of PVP molecules acting as the capping agent, the damage to the surface of BiOBr by the reduction reaction was largely alleviated and the aggregation of nanoparticles was also suppressed. Thus, the metallic Bi homogeneously grew and coated in situ on the smooth surface of the BiOBr flakes. Scheme 1. Schematic Illustration of the Possible Formation Process of the uniform BiOBr/Bi structure

ACS Paragon Plus Environment

15

ACS Sustainable Chemistry & Engineering

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 37

In our experiments, the visible light photocatalytic performances of these BiOBr/Bi samples were evaluated for degradation of MO dye (Figure 8a). The pseudo-first-order kinetics of pure BiOBr and BiOBr/Bi samples were compared in Figure 8b. After NaBH4 treatment, the photoactivities of BiOBr/Bi samples gradually improved with the increase of NaBH4 concentrations. When the concentration of NaBH4 reached to 20mmol L-1, the BiOBr/Bi-20 showed the highest photocatalytic activity with a degradation rate of 70% in 150 min, whereas only 26% of MO had been decomposed by the pure BiOBr in the same time. The photocatalytic efficiency of BiOBr/Bi-20 (0.0081 min−1) was about 4 times higher than that of pristine BiOBr (0.0021 min−1). Therefore, the appropriate amount of metallic Bi can act as an excellent nonnoble metal cocatalyst for the enhancement of the photocatalytic activity under visible light irradiation. With further increasing the concentration of NaBH4, a decrease of degradation rate was observed. The excessive Bi metals might become the recombination centers of photoinduced charge carriers, decreasing the photocatalytic activity.58-59 The photodegradation of colorless organic pollutant bisphenol A (BPA) of the above samples under visible light was also monitored (Figure S2). The BiOBr/Bi hybrides still exhibited much higher photocatalytic activity than the pure BiOBr. Therefore, the photosensitization role of MO during photocatalysis in the manuscript can be ruled out. To gain a deep insight about the relationship between the property and microstructure, the visible light photocatalytic activities of the BiOBr/Bi composites prepared with different PVP amount were investigated in terms of MO decomposition. From Figure 8c, we can see that a proportional correlation was found between the PVP amount and the photocatalytic efficiency of the BiOBr/Bi samples. When no PVP was added, the BiOBr/Bi sample displayed a poor photocatalytic performance and the degradation rate was only 29% after 150 min. It is because of

ACS Paragon Plus Environment

16

Page 17 of 37

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

ACS Sustainable Chemistry & Engineering

the severely damaged structure of BiOBr that led to the low photodegradation efficiency. The BiOBr/Bi hybrid with a uniform surface structure prepared in the presence of 7.5g PVP exhibited the best photocatalytic activity, which could degrade 71% of MO in 150 min. These results obviously elucidated that the photocatalytic activity of the obtained hybrids largely relied on the uniform structure. Evidently, the improved structure and properties were resulted from the use of PVP. The specific surface areas of our photocatalysts was measured via N2 adsorption– desorption isotherms. The BET-specific surface area for the as-obtained BiOBr/Bi composites by in situ reduction process in 20 mmol L-1 NaBH4 solution with different amounts of PVP is 9.58 m2/g (0g PVP), 9.44 m2/g (2.5g PVP), 8.93 m2/g (5g PVP), 8.51 m2/g (7g PVP), respectively. Even thought the specific surface area of samples increased with the decreased amount of PVP used in the preparation process, the BiOBr/Bi hybrid with a uniform surface structure prepared in the presence of 7.5g PVP still exhibited the best photocatalytic activity (see Figure 8c). This is because by adding PVP, the surface of BiOBr is protected to avoid further damage of the inner part of the BiOBr crystal. Therefore, the intact uniform BiOBr/Bi samples possess good performance than the damaged rough ones.

ACS Paragon Plus Environment

17

ACS Sustainable Chemistry & Engineering

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 37

Figure 8.(a) Photocatalytic degradation curves of MO for BiOBr/Bi samples prepared with different concentrations of NaBH4 under visible light irradiation (λ > 420 nm). (b) Apparent reaction rate constants for photocatalytic degradation of MO.(c) Photocatalytic degradation curves of MO for BiOBr/Bi samples with different amount of PVP under visible light irradiation (λ > 420 nm). (d) Photocurrent generation in the BiOBr and BiOBr/Bi-20 photocatalysts under visible-light irradiation (λ > 420 nm, [Na2SO4] = 0.1 M). The transient photocurrent generations were investigated for BiOBr flakes and BiOBr/Bi-20 electrodes to evaluate the mutual interaction between the metallic Bi and the BiOBr flakes. As shown in Figure 8d, under simulated solar irradiation a prompt and steady photocurrent generation was obtained during the on and off cycles. The BiOBr/Bi-20 sample exhibited much enhanced photocurrent intensity in comparison to the pure BiOBr. It was obvious that the in situ

ACS Paragon Plus Environment

18

Page 19 of 37

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

ACS Sustainable Chemistry & Engineering

deposition of metallic Bi resulted in the significant enhancement of the photocurrent. The apparently higher photocurrent meant the acceleration of photoinduced charge carriers transfer process in the BiOBr/Bi hybrid. In our study, PVP is indispensable to synthesize uniform BiOBr/Bi structure with desired photocatalytic activity. Figure 9 showed the the images of samples prepared by 5, 20 and 30 mmol L-1 NaBH4 with and without the use of PVP. From Figure 9, the powder colors shift from shallow yellow to grey and dark black with the increase of concentration of NaBH4 solution. This phenomenon could be attributed to the different amount of metallic Bi reduced on the surface of BiOBr. However, by using the same concentration NaBH4 solution the colors of the samples prepared without PVP were nearly the same as their counterpart prepared with PVP, indicating that the BiOBr/Bi samples prepared with the use of PVP and without PVP exhibited the similar light absorption. So the samples with and without the use of PVP should have similar amount of reduced metallic Bi on their surface. The color of sample prepared by using low concentration of NaBH4 solution (5 mmol L-1) was nearly the same as the pure BiOBr samples, which meant that there was not enough metallic Bi on the surface of samples to improve the photocatalytic activity. To confirm this, we also measured the photocatalytic activity of NP BiOBr/Bi-5. (Figure S3). The sample almost showed no improvement of photocatalytic activity in comparison with the pure BiOBr. The SEM images of the NP BiOBr/Bi-5 were shown in Figure S4. Although the surface of BiOBr was not severely damaged in the reduction process because of the low concentration of NaBH4 solution, the reduced metallic Bi was not enough to reach the desired photocatalytic activity. If more NaBH4 is needed in the reaction to gain more metallic Bi on the surface of BiOBr, PVP is indispensible to in the formation of homogeneous BiOBr/Bi heterojunctions.

ACS Paragon Plus Environment

19

ACS Sustainable Chemistry & Engineering

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 20 of 37

Figure 9. Images of the BiOBr samples. (A) BiOBr/Bi-5; (B) BiOBr/Bi-20; (C) BiOBr/Bi-30; (D) NP BiOBr/Bi-5; (E) NP BiOBr/Bi-20; (F) NP BiOBr/Bi-30. Scavenger trapping experiments were carried out to detect the main active radicals in the degradation process. As illustrated in Figure 10, the degradation efficiency of MO was nearly not inhibited after addition of IPA (•OH scavenger), indicating that •OH was not the main active species responsible for the degradation of MO. By adding the MeOH (h+ scavegner), only 45% of MO was degraded after 150 min, less than the 73% degradation rate of MO without scavenger. This showed that the holes participated in the degradation process of MO, but it was still not the main active species. In the presence of BQ (•O2− scavenger), degradation efficiency of MO was significantly inhibited, suggesting that •O2− should be the main active species in MO oxidation. The electron spin resonance (ESR) analysis on BiOBr/Bi-20 and BiOBr was performed to investigate the production of active radical groups in the photocatalytic process. As shown in Figure 11 a and b, the typical ESR spectra of the DMPO-•O2- adduct and DMPO-•OH adduct were observed both in the light irradiated suspension of BiOBr/Bi and pure BiOBr. This indicated that the •O2- and •OH radicals were both produced in the photocatalytic process. As the •OH could not be formed on the VB of Bi-based photocatalyst60, the present •OH in this research

ACS Paragon Plus Environment

20

Page 21 of 37

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

ACS Sustainable Chemistry & Engineering

may be derived from superoxide anion radicals. However, according to the scavenger experiments, the degradation efficiency of MO is nearly not inhibited after addition of IPA, indicating that •OH is not active specie responsible for the degradation of MO. Theoretically, the standard redox potential of O2/•O2− is –0.28 eV, which is more negative than that of the CB edge potential of BiOBr (0.29 eV), the electrons on the edge of CB could not reduce the O2 to generate •O2−.61 However, this cannot exclude the formation of •O2− by photo-generated electrons from the higher conduction bands. This may due to the structural defects of BiOBr that help to transfer the electrons on the edge of the CB to the higher conduction bands. The reactants absorbed on the surface of the BiOBr may also lead to the movement of electrons from the edge of the CB to higher CB. Some previous literatures also reported the generation of •O2− over pure BiOBr.62-63 The intensity of the formed •O2- signals in BiOBr/Bi-20 were stronger than those in pure BiOBr, thus accounting for a better photocatalytic activity of BiOBr/Bi than BiOBr toward the degradation of MO. The increase of •O2- signal intensity in BiOBr/Bi also indicated that there are more electrons that react with the surface adsorbed O2 in the conduction band of BiOBr, which may come from the metalic Bi.

ACS Paragon Plus Environment

21

ACS Sustainable Chemistry & Engineering

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 22 of 37

Figure 10. (a) Plots of trapping experiment of active species of BiOBr/Bi-20 during the photocatalytic reaction of MO under visible light irradiation (λ > 420 nm). The typical Nyquist plots of BiOBr/Bi-20 and BiOBr before and after visible light irradiation were shown in Figure 11c. It was obvious that the arc radius of BiOBr/Bi-20 was smaller than the pure BiOBr. The smaller arc radius indicated the higher efficiency of separation and transfer process of photogenerated charge carriers, thus the photocatalytic activity of BiOBr/Bi was improved. As seen in Figure S5, the inverse minimum frequency of BiOBr/Bi electrode shifted to a lower frequency in comparison to the pure BiOBr sample. The effective lifetime of injected electrons (τ ) in the conduction band of semiconductor can be calculated by equation as follows: τ=1/2πf, where f is the inverse minimum frequency.

64

From this equation, the lifetime of

injected electron of the BiOBr/Bi (13 µs) is estimated about 1.4 times higher than that of the BiOBr (9 µs). This prolonged lifetime should be ascribed to fast charge transfer that can efficiently inhibit the recombination of electron-holes carriers.

ACS Paragon Plus Environment

22

Page 23 of 37

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

ACS Sustainable Chemistry & Engineering

Figure 11. ESR spectra: (a) DMPO–•O2− and (b) DMPO–•OH adducts on BiOBr/Bi photocatalyst under visible light irradiation (λ > 420 nm). (c) EIS Nynquist plots of pure BiOBr and BiOBr/Bi composites in the light on/off cycles under visible-light irradiation (λ > 420 nm, [Na2SO4] = 0.1 M) and (d) PL spectra of pure BiOBr and BiOBr/Bi composite. In a semiconducting material, the efficiency of charge migration and transfer can be reflected by the PL spectra. Figure 11d showed the comparison on PL spectra of BiOBr/Bi-20 and BiOBr under excitation wavelength of 233 nm. Compared with the bare BiOBr, the BiOBr/Bi sample showed obviously lower PL intensity, revealing its higher separation rate of the photoexcited charge carriers, thus the higher photocatalytic activity. Combined with the EIS results, the PL spectra analysis clearly demonstrated that the deposited metallic Bi can contribute to greatly inhibition in the recombination rate of charge carriers.47

ACS Paragon Plus Environment

23

ACS Sustainable Chemistry & Engineering

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 37

According to the above characterizations, a combination of mechanisms shown in Figure 12 had been proposed to justify the enhanced photocatalytic activity of BiOBr/Bi. Firstly, the SPR effect of deposited metallic Bi on the BiOBr enhanced the visible light absorption, as confirmed by the UV-vis DRS spectra. Meanwhile, the photoexcited electron–hole pairs of metallic Bi were preferentially formed by the SPR light absorption. Secondly, because the conduction band of BiOBr (0.29 eV) was lower than the Fermi level of Bi metal (–0.17 eV)48, the photoexcited electrons on the Bi surface would be injected to the conduction band of the adjacent BiOBr. The Bi shifted to more positive potentials to produce positive charges after the electrons were released. Then the metallic Bi would turn to its original state once it accepted the electrons from the valence band of BiOBr. This electron transfer process at the interface was beneficial to inhibit the recombination of photoinduced charge carriers. The photoexcited electrons on the higher conduction band of BiOBr, together with electrons from the metallic Bi, would react with the adsorbed O2 on the surface of BiOBr/Bi to generate more •O2−. Meanwhile, the holes generated at the valence band. The •O2− and holes then degraded the pollutants in the photocatalysis process .

ACS Paragon Plus Environment

24

Page 25 of 37

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

ACS Sustainable Chemistry & Engineering

Figure 12. Schematic diagram of the BiOBr/Bi hybrid photocatalyst under visible light illumination.

CONCLUSIONS In summary, homogeneous heterostructured BiOBr/Bi photocatalysts were fabricated by a facile PVP-assisted in situ reduction route from {001} facets dominated BiOBr flakes at room temperature. In the process, Bi3+ on the {001} facets of BiOBr was in situ reduced to metallic Bi

ACS Paragon Plus Environment

25

ACS Sustainable Chemistry & Engineering

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 37

by BH4- ions and then deposited on the surface of the BiOBr flakes. The introduction of PVP had a significant effect on the uniform morphology as well as the photocatalytic activities. The significantly improved visible light photocatalytic efficiency of as-prepared regular BiOBr/Bi is not only attributed to the combined contribution of SPR effect, efficient separation of charge carriers by Bi nanoparticles, but also largely dependent on the perfect homogeneous structural property. Our work not only provides a highly effective plasmon-induced BiOBr/Bi uniform structural hybrid photocatalyst, but also elucidates a designed approach to rational bismuthbased-photocatalysts/metallic Bi with controllable structures and photocatalytic performance.

Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.”

AUTHOR INFORMATION Corresponding Author *Y. H. Zhang. E-mail: [email protected]. *H. W. Huang. E-mail: [email protected]. Notes The authors declare no competing financial interest.

ACS Paragon Plus Environment

26

Page 27 of 37

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

ACS Sustainable Chemistry & Engineering

ACKNOWLEDGMENT This work was jointly supported by National High Technology Research and Development Program (863 Program 2012AA06A109) of China, National Natural Science Foundations of China (Grant No. 51302251 and No. 51172245), Fundamental Research Funds for the Central Universities (2652013052),special co-construction project of Beijing city education committee, Key Project of Chinese Ministry of Education (No:107023).

REFERENCES 1. Yip, C. T.; Huang, H. T.; Zhou, L. M.; Xie, K. Y.; Wang, Y.; Feng, T. H.; Li, J. S.; Tam, W. Y. Direct and Seamless Coupling of TiO2 Nanotube Photonic Crystal to Dye-Sensitized Solar Cell: A Single-Step Approach. Adv. Mater. 2011, 23 (47), 5624-5628. 2. Shang, L.; Bian, T.; Zhang, B. H.; Zhang, D. H.; Wu, L. Z.; Tung, C. H.; Yin, Y. D.; Zhang, T. R. Graphene-Supported Ultrafine Metal Nanoparticles Encapsulated by Mesoporous Silica: Robust Catalysts for Oxidation and Reduction Reactions. Angew. Chem. Int. Edit. 2014, 53 (1), 250-254. 3. Huang, H. W.; He, Y.; Li, X. W.; Li, M.; Zeng, C.; Dong, F.; Du, X.; Zhang, T. R.; Zhang, Y. H. Non-Centrosymmetric Bi2O2(OH)(NO3) as a Desirable [Bi2O2]2+ Layered Photocatalyst: Strong Intrinsic Polarity, Rational Band Structure and {001} Active Exposing Facets CoBenefiting for Robust Photooxidating Capability, J. Mater. Chem. A, 2015, 3, 24547-24556. 4. 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

ACS Paragon Plus Environment

27

ACS Sustainable Chemistry & Engineering

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 37

Photocatalytic Activity under Simulated Solar Light Irradiation. J. Phys. Chem. C. 2013, 117 (44), 22986-22994. 5. Zhao, S. G.; Gong, P. F.; Bai, L.; Xu, X.; Zhang, S. Q.; Sun, Z. H.; Lin, Z. S.; Hong, M. C.; Chen, C. T.; Luo, J. H. Beryllium-free Li4Sr(BO3)2 for deep-ultraviolet nonlinear optical applications. Nat. Commun. 2014, 5,4019-4025. 6. Huang, H. W.; Liu, K.; Chen, K.; Zhang, Y. L.; Zhang, Y. H.; Wang, S. C. Ce and F Comodification on the Crystal Structure and Enhanced Photocatalytic Activity of Bi2WO6 Photocatalyst under Visible Light Irradiation. J. Phys. Chem. C. 2014, 118 (26), 14379-14387. 7. 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 MultiFunctional Applications of High-Performance CO32- Doped Bi2O2CO3. ACS Catalysis. 2015, 5, 4094-4103. 8. Zhang, Q. F.; Dandeneau, C. S.; Zhou, X. Y.; Cao, G. Z. ZnO Nanostructures for DyeSensitized Solar Cells. Adv. Mater. 2009, 21 (41), 4087-4108. 9. Tian, N.; Zhang, Y. H.; Huang, H. W.; He, Y.; Guo, Y. X. Influences of Gd Substitution on the Crystal Structure and Visible-Light-Driven Photocatalytic Performance of Bi2WO6. J. Phys. Chem. C. 2014, 118 (29), 15640-15648. 10. Briand, G. G.; Burford, N., Bismuth compounds and preparations with biological or medicinal relevance. Chem Rev 1999, 99 (9), 2601-2657.

ACS Paragon Plus Environment

28

Page 29 of 37

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

ACS Sustainable Chemistry & Engineering

11. Burch, R.; Chalker, S.; Loader, P.; Thomas, J. M.; Ueda, W. Investigation of Ethene Selectivity in the Methane Coupling Reaction on Chlorine-Containing Catalysts. Appl. Catal. aGen. 1992, 82 (1), 77-90. 12. Kijima, N.; Matano, K.; Saito, M.; Oikawa, T.; Konishi, T.; Yasuda, H.; Sato, T.; Yoshimura, Y. Oxidative catalytic cracking of n-butane to lower alkenes over layered BiOCl catalyst. Appl. Catal. a-Gen. 2001, 206 (2), 237-244. 13. Maile, F. J.; Pfaff, G.; Reynders, P. Effect pigments - past, present and future. Prog. Org. Coat. 2005, 54 (3), 150-163. 14. Lei, Y. Q.; Wang, G. H.; Song, S. Y.; Fan, W. Q.; Pang, M.; Tang, J. K.; Zhang, H. J. Room temperature, template-free synthesis of BiOI hierarchical structures: Visible-light photocatalytic and electrochemical hydrogen storage properties. Dalton. T. 2010, 39 (13), 32733278. 15. Huang, H. W.; Han, X.; Li, X. W.; Wang, S. C.; Chu, P. K.; Zhang, Y. H. Fabrication of Multiple Heterojunctions with Tunable Visible- Light-Active Photocatalytic Reactivity in BiOBr−BiOI Full-Range Composites Based on Microstructure Modulation and Band Structures. ACS Appl. Mater. Interfaces. 2015, 7, 482−492. 16. Zhang, K. L.; Liu, C. M.; Huang, F. Q.; Zheng, C.; Wang, W. D. Study of the electronic structure and photocatalytic activity of the BiOCl photocatalyst. Appl. Catal. B-Environ. 2006, 68 (3-4), 125-129. 17. Wang, W. D.; Huang, F. Q.; Lin, X. P.; Yang, J. H. Visible-fight-responsive photocatalysts xBiOBr-(1-x)BiOI. Catal. Commun. 2008, 9 (1), 8-12.

ACS Paragon Plus Environment

29

ACS Sustainable Chemistry & Engineering

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 30 of 37

18. Zhang, J.; Shi, F. J.; Lin, J.; Chen, D. F.; Gao, J. M.; Huang, Z. X.; Ding, X. X.; Tang, C. C. Self-assembled 3-D architectures of BiOBr as a visible light-driven photocatalyst. Chem. Mater. 2008, 20 (9), 2937-2941. 19. Ai, Z. H.; Ho, W. K.; Lee, S. C.; Zhang, L. Z. Efficient photocatalytic removal of NO in indoor air with hierarchical bismuth oxybromide nanoplate microspheres under visible light. Environ. Sci. Technol. 2009, 43 (11), 4143-4150. 20. Li, K.; Xu, Y. L.; He, Y.; Yang, C.; Wang, Y. L.; Jia, J. P. Photocatalytic fuel cell (PFC) and dye self-photosensitization photocatalytic fuel cell (DSPFC) with BiOCl/Ti photoanode under UV and visible light irradiation. Environ. Sci. Technol. 2013, 47 (7), 3490-3497. 21. Tian, H. T.; Li, J. W.; Ge, M.; Zhao, Y. P.; Liu, L. Removal of bisphenol A by mesoporous BiOBr under simulated solar light irradiation. Catal. Sci. Technol. 2012, 2 (11), 2351-2355. 22. Chen, F.; Liu, H. Q.; Bagwasi, S.; Shen, X. X.; Zhang, J. L. Photocatalytic study of BiOCl for degradation of organic pollutants under UV irradiation. J. Photoch. Photobio. A. 2010, 215 (1), 76-80. 23. Zhang, L.; Wang, W. Z.; Sun, S. M.; Sun, Y. Y.; Gao, E. P.; Xu, J. Water splitting from dye wastewater: A case study of BiOCl/copper(II) phthalocyanine composite photocatalyst. Appl. Catal. B-Environ. 2013, 132, 315-320. 24. Huang, W. L.; Zhu, Q. S. Structural and electronic properties of BiOX (X = F, Cl, Br, I) considering Bi 5f states. Comp. Mater. Sci. 2009, 46 (4), 1076-1084.

ACS Paragon Plus Environment

30

Page 31 of 37

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

ACS Sustainable Chemistry & Engineering

25. Zhang, K. L.; Liu, C. M.; Huang, F. Q.; Zheng, C.; Wang, W. D. Study of the electronic structure and photocatalytic activity of the BiOCl photocatalyst. Appl. Catal. B-Environ. 2006, 68 (3-4), 125-129. 26. Zhang, H. J.; Liu, L.; Zhou, Z. First-principles studies on facet-dependent photocatalytic properties of bismuth oxyhalides (BiOXs). Rsc. Adv. 2012, 2 (24), 9224-9229. 27. Yin, W. Z.; Wang, W. Z.; Zhou, L.; Sun, S. M.; Zhang, L. CTAB-assisted synthesis of monoclinic BiVO4 photocatalyst and its highly efficient degradation of organic dye under visible-light irradiation. J. Hazard. Mater. 2010, 173 (1-3), 194-199. 28 Shang, M.; Wang, W. Z.; Zhang, L. Preparation of BiOBr lamellar structure with high photocatalytic activity by CTAB as Br source and template. J. Hazard. Mater. 2009, 167 (1-3), 803-809. 29. Zhang, J.; Shi, F. J.; Lin, J.; Chen, D. F.; Gao, J. M.; Huang, Z. X.; Ding, X. X.; Tang, C. C. Self-assembled 3-D architectures of BiOBr as a visible light-driven photocatalyst. Chem. Mater. 2008, 20 (9), 2937-2941. 30. Wang, W. D.; Huang, F. Q.; Lin, X. P. xBiOI-(1-x)BiOCl as efficient visible-light-driven photocatalysts. Scripta. Mater. 2007, 56 (8), 669-672. 31. Lin, X. P.; Huang, F. Q.; Wang, W. D.; Shan, Z. C.; Shi, J. L. A series of Bi-based oxychlorides as efficient photocatalysts. Key. Eng. Mat. 2008, 368-372, 1503-1506. 32. Wang, P.; Huang, B. B.; Dai, Y.; Whangbo, M. H. Plasmonic photocatalysts: harvesting visible light with noble metal nanoparticles. Phys. Chem. Chem. Phys. 2012, 14 (28), 9813-9825.

ACS Paragon Plus Environment

31

ACS Sustainable Chemistry & Engineering

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 32 of 37

33. Zhou, X. M.; Liu, G.; Yu, J. G.; Fan, W. H. Surface plasmon resonance-mediated photocatalysis by noble metal-based composites under visible light. J. Mater. Chem. 2012, 22 (40), 21337-21354. 34. Linic, S.; Christopher, P.; Ingram, D. B. Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy. Nat. Mater. 2011, 10 (12), 911-921. 35. Clavero, C., Plasmon-induced hot-electron generation at nanoparticle/metal-oxide interfaces for photovoltaic and photocatalytic devices. Nat. Photonics. 2014, 8 (2), 95-103. 36. Wang, X. D.; Caruso, R. A. Enhancing photocatalytic activity of titania materials by using porous structures and the addition of gold nanoparticles. J. Mater. Chem. 2011, 21 (1), 20-28. 37. Yogi, C.; Kojima, K.; Takai, T.; Wada, N., Photocatalytic degradation of methylene blue by Au-deposited TiO2 film under UV irradiation. J. Mater. Sci. 2009, 44 (3), 821-827. 38. Arabatzis, I. M.; Stergiopoulos, T.; Andreeva, D.; Kitova, S.; Neophytides, S. G.; Falaras, P. Characterization and photocatalytic activity of Au/TiO2 thin films for azo-dye degradation. J. Catal. 2003, 220 (1), 127-135. 39. Cozzoli, P. D.; Curri, M. L.; Agostiano, A. Efficient charge storage in photoexcited TiO2 nanorod-noble metal nanoparticle composite systems. Chem. Commun. 2005, (25), 3186-3188. 40. Alvaro, M.; Cojocaru, B.; Ismail, A. A.; Petrea, N.; Ferrer, B.; Harraz, F. A.; Parvulescu, V. I.; Garcia, H. Visible-light photocatalytic activity of gold nanoparticles supported on template-synthesized mesoporous titania for the decontamination of the chemical warfare agent Soman. Appl. Catal. B-Environ. 2010, 99 (1-2), 191-197.

ACS Paragon Plus Environment

32

Page 33 of 37

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

ACS Sustainable Chemistry & Engineering

41. Kannaiyan, D.; Cha, M. A.; Jang, Y. H.; Sohn, B. H.; Huh, J.; Park, C.; Kim, D. H., Efficient photocatalytic hybrid Ag/TiO2 nanodot arrays integrated into nanopatterned block copolymer thin films. New. J. Chem. 2009, 33 (12), 2431-2436. 42. Fouad, D. M.; Mohamed, M. B. Comparative study of the photocatalytic activity of semiconductor nanostructures and their hybrid metal nanocomposites on the photodegradation of malathion. J. Nanomater. 2012, (2012), 1-8. 43. Toudert, J.; Serna, R.; de Castro, M. J. Exploring the optical potential of nano-bismuth: tunable surface plasmon resonances in the near ultraviolet-to-near infrared range. J. Phys. Chem. C. 2012, 116 (38), 20530-20539. 44. McMahon, J. M.; Schatz, G. C.; Gray, S. K. Plasmonics in the ultraviolet with the poor metals Al, Ga, In, Sn, Tl, Pb, and Bi. Phys. Chem. Chem. Phys. 2013, 15 (15), 5415-5423. 45. Liu, X. W.; Cao, H. Q.; Yin, J. F. Generation and photocatalytic activities of Bi@Bi2O3 microspheres. Nano. Res. 2011, 4 (5), 470-482. 46. Weng, S. X.; Chen, B. B.; Xie, L. Y.; Zheng, Z. Y.; Liu, P. Facile in situ synthesis of a Bi/BiOCl nanocomposite with high photocatalytic activity. J. Mater. Chem. A. 2013, 1 (9), 30683075. 47. Yu, Y.; Cao, C. Y.; Liu, H.; Li, P.; Wei, F. F.; Jiang, Y.; Song, W. G. A Bi/BiOCl heterojunction photocatalyst with enhanced electron-hole separation and excellent visible light photodegrading activity. J. Mater. Chem. A. 2014, 2 (6), 1677-1681.

ACS Paragon Plus Environment

33

ACS Sustainable Chemistry & Engineering

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 34 of 37

48. Dong, F.; Li, Q. Y.; Sun, Y. J.; Ho, W. K. Noble metal-like behavior of plasmonic Bi particles as a cocatalyst deposited on (BiO)2CO3 microspheres for efficient visible light photocatalysis. Acs. Catal. 2014, 4 (12), 4341-4350. 49. Chang, C.; Zhu, L. Y.; Fu, Y.; Chu, X. L. Highly active Bi/BiOI composite synthesized by one-step reaction and its capacity to degrade bisphenol A under simulated solar light irradiation. Chem. Eng. J. 2013, 233, 305-314. 50. Gao, M. C.; Zhang, D. F.; Pu, X. P.; Li, H.; Lv, D. D.; Zhang, B. B.; Shao, X. Facile hydrothermal synthesis of Bi/BiOBr composites with enhanced visible-light photocatalytic activities for the degradation of rhodamine B. Sep. Purif. Technol. 2015, 154, 211-216. 51. Ma, H.C.; Zhao, M.; Xing, H. M.; Fu, Y. H.; Zhang X. F.; Dong, X. L. Synthesis and enhanced photoreactivity of metallic Bi-decorated BiOBr composites with abundant oxygen vacancies, J. Mater. Sci. - Mater. Electron. 26 (2015) 10002-10011 52. Liu, H. L.; Ko, S. P.; Wu, J. H.; Jung, M. H.; Min, J. H.; Lee, J. H.; An, B. H.; Kim, Y. K. One-pot polyol synthesis of monosize PVP-coated sub-5nm Fe3O4 nanoparticles for biomedical applications. J. Magn. Magn. Mater. 2007, 310 (2), E815-E817. 53. Lee, H. Y.; Lee, S. H.; Xu, C. J.; Xie, J.; Lee, J. H.; Wu, B.; Koh, A. L.; Wang, X. Y.; Sinclair, R.; Xwang, S.; Nishimura, D. G.; Biswal, S.; Sun, S. H.; Cho, S. H.; Chen, X. Y. Synthesis and characterization of PVP-coated large core iron oxide nanoparticles as an MRI contrast agent. Nanotechnology. 2008, 19 (16), 1-6.

ACS Paragon Plus Environment

34

Page 35 of 37

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

ACS Sustainable Chemistry & Engineering

54. Shi, X. J.; Chen, X.; Chen, X. L.; Zhou, S. M.; Lou, S. Y.; Wang, Y. Q.; Yuan, L. PVP assisted hydrothermal synthesis of BiOBr hierarchical nanostructures and high photocatalytic capacity. Chem. Eng. J. 2013, 222, 120-127. 55. Li, L. L.; Zeng, C. M.; Ai, L. H.; Jiang, J. Synthesis of reduced graphene oxide-iron nanoparticles with superior enzyme-mimetic activity for biosensing application. J. Alloy. Compd. 2015, 639, 470-477. 56. Liu, Z. S.; Wu, B. T.; Zhu, Y. B.; Yin, D. G.; Wang, L. G. Fe-Ions Modified BiOBr Mesoporous Microspheres with Excellent Photocatalytic Property. Catal. Lett. 2012, 142 (12), 1489-1497. 57. Xiong, Y. J.; Washio, I.; Chen, J. Y.; Cai, H. G.; Li, Z. Y.; Xia, Y. N. Poly(vinyl pyrrolidone): A dual functional reductant and stabilizer for the facile synthesis of noble metal nanoplates in aqueous solutions. Langmuir. 2006, 22 (20), 8563-8570. 58. Ren, J.; Wang, W. Z.; Sun, S. M.; Zhang, L.; Chang, J. Enhanced photocatalytic activity of Bi2WO6 loaded with Ag nanoparticles under visible light irradiation. Appl. Catal. B-Environ. 2009, 92 (1-2), 50-55. 59. Young, C.; Lim, T. M.; Chiang, K.; Scott, J.; Amal, R. Photocatalytic oxidation of toluene and trichloroethylene in the gas-phase by metallised (Pt, Ag) titanium dioxide. Appl. Catal. BEnviron. 2008, 78 (1-2), 1-10. 60. Fu, H. B.; Pan, C. S.; Yao, W. Q.; Zhu, Y. F. Visible-light-induced degradation of rhodamine B by nanosized Bi2WO6. J. Phys. Chem. B. 2005, 109 (47), 22432-22439.

ACS Paragon Plus Environment

35

ACS Sustainable Chemistry & Engineering

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 36 of 37

61. Li, F. T.; Wang, Q.; Ran, J. R.; Hao, Y. J.; Wang, X. J.; Zhao, D. S.; Qiao, S. Z. Ionic liquid self-combustion synthesis of BiOBr/Bi24O31Br10 heterojunctions with exceptional visiblelight photocatalytic performances. Nanoscale. 2015, 7 (3), 1116-1126. 62. Ye, L. Q.; Liu, J. Y.; Jiang, Z.; Peng, T. Y.; Zan, L. Facets coupling of BiOBr-g-C3N4 composite photocatalyst for enhanced visible-light-driven photocatalytic activity. Appl. Catal BEnviron. 2013, 142, 1-7. 63.Jiang, G. H.; Wang, R. J.; Wang, X. H.; Xi, X. G.; Hu, R. B.; Zhou, Y.; Wang, S.; Wang, T.; Chen, W. X. Novel Highly Active Visible-Light-Induced Photocatalysts Based on BiOBr with Ti Doping and Ag Decorating. ACS applied materials & interfaces. 2012, 4 (9), 4440-4444. 64. Sun, S. M.; Wang, W. Z.; Zhang, L. Bi2WO6 quantum dots decorated reduced graphene oxide: improved charge separation and enhanced photoconversion efficiency. J. Phys. Chem. C. 2013, 117 (18), 9113-9120.

ACS Paragon Plus Environment

36

Page 37 of 37

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

ACS Sustainable Chemistry & Engineering

For Table of Contents Use Only Homogeneous

{001}-BiOBr/Bi

heterojunctions:

facile controllable synthesis and morphologydependent photocatalytic activity Yuxi Guo†, Yihe Zhang*,†, Na Tian†, Hongwei Huang*,†

Homogeneous {001}-BiOBr/Bi heterojunction are fabricated by facile controllable strategy and it shows morphology-dependent photocatalytic activity toward water purification.

ACS Paragon Plus Environment

37