Oxygen-Induced Bi5+-Self-Doped Bi4V2O11 with a pân Homojunction

Subscriber access provided by NEW YORK UNIV

Article

Oxygen induced Bi5+ self-doped Bi4V2O11 with p–n homojunction towards promoted photocatalytic performance Chade Lv, Gang Chen, Xin Zhou, Congmin Zhang, Zukun Wang, Boran Zhao, and Danying Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b05302 • Publication Date (Web): 27 Jun 2017 Downloaded from http://pubs.acs.org on June 29, 2017

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 Applied Materials & Interfaces 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 28

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 Applied Materials & Interfaces

Oxygen induced Bi5+ self-doped Bi4V2O11 with p–n homojunction towards promoted photocatalytic performance Chade Lv, Gang Chen,* Xin Zhou,* Congmin Zhang, Zukun Wang, Boran Zhao and Danying Li MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology Harbin, P. R. China. ∗Corresponding author: Gang Chen, Xin Zhou; E-mail: [email protected]; [email protected]. Fax: (+86)-451-86413753.

ACS Paragon Plus Environment


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

ABSTRACT: Bi5+ self-doped Bi4V2O11 nanotubes with p–n homojunction are fabricated via oxygen inducing strategy. Calcinating the as-spun fibers with abundant oxygen plays the pivotal role in achieving Bi5+ self-doping. Density functional theory (DFT) calculation and experimental results indicate that the Bi5+ self-doping can narrow the bandgap of Bi4V2O11, which contribute to enhanced light-harvesting. Moreover, Bi5+ self-doping endows the Bi4V2O11 with n- and p-type semiconductor characteristics simultaneously, resulting in the construction of p–n homojunction for retarding rapid electron-hole recombination. Benefiting from these favorable properties, Bi5+ selfdoped Bi4V2O11 exhibits superior photocatalytic performance in contrast with pristine Bi4V2O11. Furthermore, this is the first report describing the achievement of p–n homojunction through self-doping, which gives full play to the advantages of selfdoping. KEYWORDS: self-doping, p–n homojunction, photocatalysis, Bi4V2O11, density functional theory


Page 2 of 28

Page 3 of 28

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


1. INTRODUCTION Thus far, unrelenting efforts have been devoted to the optimization of photocatalysts by various kinds of methods, such as doping,1 constructing heterojunctions2 and nano-structuring.3 Self-doping, as an exceptional element doping, is emerging as a promising strategy to improve the photocatalytic performance.4−7 Promoted transport of charge carriers can be achieved by selfdoping while the latent adverse impact stemmed from doping with adventitious species, for instance, undesirable thermal instability, can be avoided.8 In addition, it is conductive to strengthening light harvesting efficacy due to the narrowed bandgap or formation of intermediate levels between the conduction band (CB) and valence band (VB).9−11 Therefore, the self-doping holds the potential to exploit the utmost of the semiconductor photocatalysts. Motivated by these excellent properties, self-doping have been introduced into a variety of photocatalysts by elaborate approaches, especially through reduction treatment, which can result in low-valence self-doping with little hindrance.12,13 Despite great progresses have been achieved in introducing selfdoping by reduction treatment, it still remains limitations as follows: (a) due to the risk of forming metal rather than low-valence self-doping in some frequently-investigated catalysts, such as Bi-based semiconductors, which are considered as one category of the most active photocatalysts;14 (b) induced by reduction treatment, oxygen vacancies are generated accompanied with lowvalence self-doping, which might produce deep, localized, and filled states near the valence band maximum (VBM).15 States close to the VBM are fully occupied and therefore do not benefit for electron transport.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

Relative to reduction treatment, oxidation treatment will not give rise to the generation of oxygen vacancies, while oxygen atom can be introduced into lattice.16 This feature provides an alternative approach to realize high-valence self-doping though oxidation method. Very recently, Bi4V2O11 with intrinsic oxygen vacancies and layered structure has been regarded as an excellent photocatalyst for oxygen evolution and water purification.17−20 Inspired by its peculiar crystalline structure, it is conjectured that Bi4V2O11 possesses adequate space for introducing oxygen atoms to realize high-valence self-doping. Further, the n-p type transformation in Bi4V2O11 might occur because of the implanted oxygen, leading to the co-existence of n- and p-type domains.21 Thereby, the p–n type photochemical homojunction could be constructed, where the Fermi-level (Ef) alignment of the p- and n-type domains emerges, creating a built-in field.22 The photogenerated electrons and holes would separate effectively by means of migrating in opposite directions at the homojunction interface,23 ulteriorly promoting the photocatalysis.24 This far, aiming at constructing p–n homojunction, surface modification,22 element doping23 and electrodeposition25 are employed. Nevertheless, the construction of p–n homojunction achieved via self-doping is overlooked. And in view of the merits introduced by self-doping, we hypothesize that Bi5+ self-doped Bi4V2O11 could serve as a standout photocatalyst. In this work, oxygen induced Bi5+ self-doped Bi4V2O11 (Bi5+-BVO) is fabricated by tuning oxygen ambience during the heat treatment of as-spun fibers (Scheme 1). The electronic band structures, photoabsorption and photoinduced charge carriers transport properties of Bi5+-BVO are investigated by DFT calculation and systematic measurements. Enhanced photoabsorption


Page 4 of 28

Page 5 of 28

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


and boosted photoinduced charge carriers transport are realized in Bi5+-BVO. Furthermore, Bi5+ self-doping leads to the construction of p–n homojunction, which could facilitate the separation of photoinduced electrons and holes stemmed from as-created built-in field. Accordingly, above factors determine the superior photocatalytic performance of Bi5+-BVO for reduction of Cr(VI).

2. EXPERIMENTAL 2.1 Preparation and Characterizations The fabrication of photocatalysts is similar to our previous work (details are presented in Supporting Information).20 To fabricate the Bi4V2O11 without Bi5+ doping (denoted as BVO), 0.5 g as-spun fibers were annealed in a covered crucible to furnish insufficient oxygen ambience as shown in Scheme 1. For Bi5+ self-doped Bi4V2O11 (denoted as Bi5+-BVO), 0.5 g as-spun fibers were calcinated in an uncovered crucible with sufficient oxygen. The crystalline structure of Bi5+-BVO and BVO was confirmed by X-ray diffraction (XRD) on Rigaku D/max-2000 diffractometer with Cu Kα radiation (λ = 0.15406 nm). Diffraction patterns were collected from 10° to 90° at a speed of 4 °C min-1 with a scan width of 0.02°. The morphology characterizations were observed by a HELIOS NanoLab 600i field emission scanning electron micro-scope (FE-SEM). Transmission electron microscopy (TEM) and highresolution TEM (HRTEM) were performed on FEI Tecnai G2 S-Twin operating at 300 kV. Brunauer–Emmett–Teller (BET) data were obtained with a Micromeritics ASAP 2020 (Accelerated Surface Area and Porosimetry System). UV-vis diffuse reflectance spectra were acquired by HITACHI UH4150. X-Ray photoelectron spectroscopy (XPS) was carried out using a Thermo



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 28

Scientific ESCALAB 250Xi X-ray photoelectron spectrometer with a pass energy of 20.00 eV and an Al Kα excitation source (1486.6 eV). Electron paramagnetic resonance (EPR) spectra were conducted on a Bruker A200 EPR Spectrometer operating at room temperature with micro frequency at 9.86 GHz. Photoluminescence (PL) spectra and time-resolved fluorescence decay spectra were obtained on HORIBA FluoroMax-4. 2.2 Photocatalytic and Photoelectrochemical Measurements. The photocatalytic Cr(VI) reduction is consistent with our previous work,20 The photocatalytic reduction of Cr(VI) was irradiated under visible light (> 400 nm) in the presence of citric acid. In a typical procedure, 0.05 g of photocatalyst was added into 100 mL of Cr(VI) solution (10 mg L-1, which was based on Cr in a dilute K2Cr2O7 solution). The photocatalyst was dispersed in the solution by ultrasonic treatment for 5 min. Then, the solution was stirred for 40 min in the dark to reach adsorption equilibrium. Prior to irradiation, 0.05 g citric acid was added into the solution. The photocatalyst was removed by centrifugation at given time intervals, and the Cr(VI) concentration was determined at 352 nm by using the HITACHI UH-5300 UV-vis spectrometer. The Mott–Schottky plots of Bi5+-BVO and BVO were measured by applying potentials in the range of 2.6 to 0.6 V versus an Ag/AgCl reference electrode. The light source employed was a 300 W Xe light source. Autolab electrochemical working station with a standard three-compartment cell was employed

to

measure

the

transient

photocurrent

response

and

the

electrochemical impedance spectroscopy (EIS) of the samples. FTO glass with photocatalysts coated was used as working electrode and a piece of Pt sheet, a


Page 7 of 28

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


Ag/AgCl electrode and 0.5 M sodium sulfate served as the counter electrode, reference electrode and electrolyte, respectively. 2.3 Computational Details All DFT calculations were performed using the Vienna Ab Initio Simulation Package (VASP) within the projector augmented wave formalism.26,

27

Projector-Augmented Wave (PAW)28 potentials for treating electron–ion interactions and Perdew–Burke–Ernzerhof (PBE) functional were employed. The cutoff energy of 400 eV and 6×4×6 k-point mesh centered at the G point was used for the plane-wave basis set. The convergence tolerance for selfconsistent energy is set at 10-5 eV, and all atomic structures were fully relaxed until the residual forces on all atoms were smaller than 0.01 eV/A. 3. RESULTS AND DISCUSSION In a typical synthesis, the first step is to electrospin precursor fibers (Scheme 1). Bi5+ self-doped Bi4V2O11 (Bi5+-BVO) is obtained by calcinating as-spun fibers in an uncovered crucible with sufficient oxygen. When the crucible is covered to isolate the as-spun fibers from sufficient oxygen ambience, Bi4V2O11 without Bi5+ doping (BVO) is fabricated.



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

Scheme 1. Schematic illustration of fabricating Bi5+ self-doped Bi4V2O11 by tuning the oxygen ambience. The X-ray diffraction (XRD) analysis (Figure 1a) suggests that Bi4V2O11 (BVO) and Bi5+ self-doped Bi4V2O11 (Bi5+-BVO) consist of pure Bi4V2O11 (JCPDS No.42-0135).18,20 Tuning the oxygen ambience might have impacts on the crystalline structure of the samples. In magnified XRD patterns (Figure 1b), the peaks shift of Bi5+-BVO toward lower 2θ values can be observed. Because the ionic radius of Bi5+ (76 pm) is relatively smaller than that of Bi3+ (103 pm), the peaks shift could be due to the presence of defective Bi5+ in Bi4V2O11.29 Moreover, as displayed in schematic presentation of Bi4V2O11 crystalline structure (Figure 1c), the layered structure might furnish adequate space for introducing oxygen atoms to oxide Bi3+ into Bi5+.

Figure 1 XRD patterns of Bi5+-BVO and BVO samples at different ranges: (a) 10−60 °, (b) 27−30 °; (c) crystal structure of Bi4V2O11; XPS spectra of Bi5+BVO and BVO samples: (d) Bi 4f spectra, (e) V 2p spectra, (f) O 1s spectra.


Page 8 of 28

Page 9 of 28

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


To shed light on the defective structure, X-ray photoelectron spectroscopy (XPS) is carried out. In Bi 4f XPS spectra (Figure 1d), only two photoelectron peaks located at 159.2 eV and 164.5 eV are detected in BVO, which are corresponding to Bi3+ in Bi4V2O11.20,30 However, for Bi5+-BVO, except for Bi3+ peaks, two new peaks arise at 160.6 eV and 165.9 eV, which could be assigned to the Bi5+ defects.31,32 As for V 2p XPS spectra shown in Figure 1e, V peaks located at 516.7 eV and 524.3 eV belong to V5+, while no V4+ emerges, indicating only Bi5+ defects serve as self-doping element.20,30 From the observation in O 1s spectra (Figure 1f), two O 1s peaks could be clearly distinguished in BVO, which are located at 529.7 and 530.8 eV. The former corresponds to lattice oxygen (M-O), while the latter could originate from the intrinsic oxygen vacancy (Vo) in Bi4V2O11.33−35 Nevertheless, calcinated with abundant oxygen, the Vo peak disappears in Bi5+-BVO. Instead, two new peaks emerge located at 531.5 and 533.0 eV, which could be assigned to M−OH and H2O(l).36 Electron paramagnetic resonance (EPR) analysis (Figure S1) can also suggest the absence of oxygen vacancy in Bi5+-BVO, while the BVO possesses a typical signal of oxygen vacancies at g = 2.001.37 Based on above results, we can safely draw the conclusion that the Bi5+ self-doping is successfully induced by abundant oxygen, which accomplishes the achievement of self-doping relying on the presence of intrinsic oxygen vacancies. Moreover, the failure in introducing Bi5+ in other Bi-based photocatalysts (such as Bi2WO6 and Bi2MoO6) without intrinsic oxygen vacancies can further affirm above opinions.38, 39 Therefore, the doping equation could be described as follows: 2Bi + O → 2Bi•• + 2O


(1)


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

In addition to Bi5+ defect, Bi5+-BVO also possesses tubular structure, which is subjected to detailed morphology characterizations as below. The diameter of the nanotubes is approximately 60 nm (Figure 2a), and the insert image in Figure 2a is the magnified cross-section of the Bi5+-BVO nanotubes. Careful transmission electron microscope (TEM) (Figure 2b and Figure S2) and highangle annular dark-field (HAADF) (Figure 2c) observations can also confirm the tubular structure. The energy-dispersive X-ray (EDX) line profile (Figure 2d) indicates typical curve shape of a tubular structure. In addition, Bi, V and O are well-distributed throughout the nanotube with good homogeneity. As shown in HRTEM image (Figure 2e), the interplanar spacing of 0.28 nm corresponds to the (200) plane of the orthorhombic Bi4V2O11. SAED pattern also suggests the Bi5+-BVO is assigned to the orthorhombic phase.

Figure 2 SEM and TEM characterization of Bi5+-BVO: (a) SEM image; the insert is magnified cross-section, (b) TEM images, (c) HAADF image, (d) Line scan profile, (e) HRTEM image, (f) SAED pattern.


Page 10 of 28

Page 11 of 28

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


As shown above, with abundant oxygen ambience, we obtain Bi5+self-doped Bi4V2O11 with tubular structure, which is derived from solid as-spun fibers (Figure S3). In a sharp contrast, with the absence of abundant ambience, Bi4V2O11 nanofibers are fabricated with solid interior (Figure S4). These results imply that tuning the oxygen ambience not only induces the Bi5+ self-doping, but also results in the formation of tubular structure. To further affirm above viewpoint, the as-spun fibers are calcinated in O2 flow and H2/Ar atmosphere (denoted as Bi5+-BVO-O2 and H-BVO, respectively). When calcinated in O2 flow, the Bi5+ concentration in Bi5+-BVO-O2 dose not show obvious increase compared with Bi5+-BVO, indicating the self-doping of Bi5+ in Bi5+-BVO has already reached the upper-limit (Figure S5). The absence of tubular structure and Bi4V2O11 phase proves that sufficient oxygen atmosphere is the determinant factor for constructing Bi4V2O11 with tubular structure (Figure S6,7). Therefore, the oxygen inducing mechanism of Bi5+ self-doping and tubular structure is proposed (see Figure S8 and corresponding explanation in Supplemental Information). Moreover, as demonstrated by Brunauer–Emmett– Teller (BET) measurements (Figure S9), the tubular structure endows Bi5+BVO with higher surface area (7.09 m2 g-1) in relative to BVO possessing solid interior (3.52 m2 g-1). For the purpose of illuminating the impact of Bi5+ self-doping, UV-vis diffuse reflection spectra (DRS) are acquired to analyze the optical properties of the samples. As shown in Figure 3a, the BVO exhibits favorable visible light absorption and the absorption edge locates at approximately 550 nm. In contrast with BVO, the as-fabricated Bi5+-BVO has an extended absorption edge up to ca. 580 nm, indicating the light-harvesting ability is promoted after the



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

introduction of Bi5+ self-doping. Such red shift for Bi5+-BVO results in a distinct color change from yellow (pristine Bi4V2O11) to orange red (Bi5+ selfdoped Bi4V2O11) (inset in Figure 3a). The band gaps of Bi5+-BVO and BVO are calculated to be 2.15 and 2.25 eV, respectively (Figure 3b).

Figure 3 (a) UV-vis diffuse reflectance spectra of Bi5+-BVO and BVO, (b) Plots of (αhν)n/2 vs hν (n=4). Aiming at exploring the impact of Bi5+ self-doping on the crystal structure and electronic structure of Bi5+-BVO, a full density functional theory (DFT) calculation is performed. Based on above proposed doping equation and experimental results, one oxygen atom is introduced to Bi4V2O11 and the model of Bi5+ self-doped Bi4V2O11 is constructed with six oxygen atoms surrounding the central Bi5+ ion to form a distorted octahedron BiO6 (Figure 4a, b). The calculated electronic band structure along the Brillouin zone path of orthorhombic lattice (ORC) and the density of state (DOS) plot of pristine Bi4V2O11 and Bi5+ self-doped Bi4V2O11 are shown in Figure 4c, d, e and f, respectively. Figure 4c show that the conduction band minimum (CBM) and valence band maximum (VBM) are located at the Г point with a direct band gap of 2.17 eV, which is consistent with the experimental and previous theoretical results.18 The DOS (Figure 4e) shows that the conduction band is


Page 12 of 28

Page 13 of 28

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


mainly contributed by O 2p and Bi3+ 6s,p states, while the valence band is composed primarily of V 3d and O 2p states, indicating a strong ionic bond character of Bi-O and V-O bond. With respect to Bi5+-BVO, Bi5+ and O-add states appearing in the conduction band (CB) and valence band (VB) near the Fermi level (Figure 4d, f) result in the lower of the CB and the increase of the VB, which leads to narrower band gap. The results are in good agreement with our experimental observation. Interestingly, for pristine Bi4V2O11, Fermi level occurs at the VBM, while the Bi5+ self-doping causes the VBM going upward and exceeding Fermi level, consequently leading to p-type Bi4V2O11. In contrast with the intrinsic n-type conductivities of Bi4V2O11, the introduction of Bi5+ self-doping might endow Bi4V2O11 with both n- and p-type conductivities, hence constructing p–n homojunction.



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

Figure 4 Crystal structure of BVO (a) and Bi5+-BVO (b), Electronic band structures of BVO (c) and Bi5+-BVO (d), DOS plots of BVO (e) and Bi5+-BVO (f), The insert in Figure 4f is corresponding magnified DOS plot. In order to corroborate above argument experimentally, the Mott−Schottky curves of Bi5+-BVO and BVO are performed (Figure 5a, b). As observed in Figure 5b, BVO exhibits intrinsic n-type characteristic due to the simple presence of a positive slope. Interestingly, in a sharp contrast with Bi5+-BVO, the straight lines with both positive and negative slopes can be observed in Bi5+-BVO simultaneously (Figure 5a), suggesting the Bi5+ self-doping endows the Bi4V2O11 with n- and p-type characteristics. Hence, p–n type homojunction is constructed ascribed to the co-existence of n- and p-type domains in Bi5+BVO, which meets above expectations. The construction of p–n type homojunction can introduce a built-in field at the interface stemmed from the Fermi-level (EF) alignment of the p- and n- type domains (Figure 5c).22 Attributed to the as-constructed p–n homojunction, the photoinduced charge carriers can separate and transport effectively to participate in photocatalysis reaction.22,24,25,40 And for all we know, this should be the first report on the construction of p–n homojunction induced by self-doping.

Figure 5. Mott–Schottky plots of Bi5+-BVO (a) and BVO (b), Illustration of charge transfer in the p–n homojunction of Bi5+-BVO (c).


Page 14 of 28

Page 15 of 28

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


The Bi5+ self-doping induced band structure modulation leads to the construction of p–n homojunction as above. It is anticipated that this p–n homojunction is conductive to facilitating the separation and transport of photoinduced carriers transport during photocatalysis process. Further, the charge separation and transport dynamics of photoelectrons are examined by means of photocurrent responses.41 Figure 6a exhibits the current responses of Bi5+-BVO and BVO from 0.4 to 0.8 eV (vs. Ag/AgCl) under illumination of visible light. By contrast, enhanced photocurrent intensity could be discerned in Bi5+-BVO, while BVO shows faintish photocurrent response. It reveals that the rapid transport of photoinduced electron-hole pairs is realized in p–n homojunction of Bi5+-BVO.42



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

Figure 6. (a) Photocurrent response of Bi5+-BVO and BVO electrodes under visible-light illumination, (b) Electrochemical impedance spectra of Bi5+-BVO and BVO, (c) PL spectra and (d) Time-resolved fluorescence decay spectra of Bi5+-BVO and BVO; Photocatalysis measurements of BVO and Bi5+-BVO: (e) Cr(VI) reduction and (f) Cycling performance. Electrochemical impedance spectroscopy (EIS) experiments are utilized to monitor the electron generation and charge transport characteristics of Bi5+BVO and BVO.43, 44 From the observation in Figure 6b, the arc radius on the EIS Nyquist plot of Bi5+-BVO is much smaller compared to that of BVO,


Page 16 of 28

Page 17 of 28

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


implying promoted separation and transport efficiency of photoinduced charge carriers due to the construction of p–n homojunction in Bi5+-BVO. In order to further confirm the enhanced separation efficiency of photogenerated charge carriers in Bi5+-BVO, photoluminescence (PL) and timeresolved fluorescence decay spectra are performed.45 In contrast to the strong emission peaks for BVO (Figure 6c), the Bi5+-BVO displays rather weak PL peak, indicating that the p–n homojunction can effectively suppress the electron-hole

recombination.46

From

the

observation

in

time-resolved

fluorescence decay spectra (Figure 6d), the decay kinetics Bi5+-BVO of is relatively slow.47 The increased lifetimes of carriers in Bi5+-BVO could be ascribed to the promotion of the photoinduced charge carrier separation and transfer. As revealed by above analysis, the Bi5+ self-doping leads to the construction of p–n homojunction, therefore, the transport of photoinduced electron-hole pairs is effectively boosted. Stimulated by Bi5+ self-doping, which leads to enhanced photoabsorption and fantastic transport efficiency of photogenerated charge carriers, the asfabricated Bi5+-BVO could be conductive to being used as a promising catalyst for photocatalysis application. Figure 6e shows the photocatalytic reduction of Cr(VI) on Bi5+-BVO and BVO under visible light illumination. Compared to BVO, Bi5+-BVO exhibits better photocatalytic activity, reaching approximately 87% of Cr(VI) reduction after 100 min. However, only 47% of Cr(VI) can be reduced under the same condition. The comparable performance of both photocatalysts observed after 100 min discloses that introduction of Bi5+ selfdoping can dramatically enhance the photoreduction activity of Bi4V2O11. In addition, as the morphology of Bi5+-BVO is basically maintained after the



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

photocatalysis reaction (Figure S10), good cycling performance is achieved as displayed in Figure 6f. On the basis of the above analysis, there are three main reasons for the promoted visible-light photocatalytic activity of Bi5+-BVO. Remarkably, the narrow bandgap stemmed from Bi5+ doping expands the light harvesting, which can excite more photogenerated electrons and holes for participating in photocatalysis reactions (Figure S11). And secondly, enlarged surface area originated from tubular structure contributes to more active sites for photocatalysis. Last but not the least, attributed to Bi5+ self-doping, the construction of p–n homojunction is achieved, which can efficiently boost the separation and transfer of photogenerated electrons and holes. Consequently, abovementioned merits determine the superior photocatalytic performance of Bi5+ self-doped Bi4V2O11.


Page 18 of 28

Page 19 of 28

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


CONCLUSIONS In summary, oxygen induced Bi5+ self-doped Bi4V2O11 with promoted photocatalytic activity are fabricated by tuning the oxygen ambience during the heat treatment procedure. Density functional theory calculations results reveal that the Bi5+ self-doping can narrow bandgap realized by lowering the conduction

band

position

and increasing

the

valence

band

position

simultaneously. The enhanced light-harvesting ability is verified by UV-vis diffuse reflection spectra. Besides, p–n homojunction is constructed in Bi4V2O11 due to the Bi5+ self-doping, therefore, facilitated photoinduced charge carriers transport and retarded electron-hole recombination are realized as confirmed by photocurrent response, electrochemical impedance spectroscopy, photoluminescence and time-resolved fluorescence decay spectra. Hence, Bi5+ self-doped Bi4V2O11 shows enhanced photocatalytic properties for Cr(VI) in relative to pristine Bi4V2O11. Current findings might open up new ways for design and fabrication of self-doped photocatalysts with outstanding activity.



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

ASSOCIATED CONTENT Supporting information for publication

EPR spectra of Bi5+-BVO and BVO (Figure S1), TEM images of Bi5+-BVO (Figure S2), SEM images of BVO (Figure S3), SEM images of as-spun fibers (Figure S4), XPS spectra of Bi5+-BVO and Bi5+-BVO-O2 (Figure S5). SEM images of H-BVO (Figure S6). XRD pattern of H-BVO (Figure S7). Formation mechanism of Bi5+ selfdoped Bi4V2O11 nanotubes and pristine Bi4V2O11 solid nanofibers. (Figure S8). BET measurements of Bi5+-BVO and BVO (Figure S9). SEM images of recycled Bi5+BVO catalyst (Figure S10). Photocatalysis Cr(VI) reduction plots of BVO and Bi5+BVO (> 550 nm) (Figure S11).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 Notes

The authors declare no competing financial interests. ACKNOWLEDGMENTS

This work was financially supported by the National Natural Science Foundation of China (21471040 and 21303030).


Page 20 of 28

Page 21 of 28

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


REFERENCES

(1). Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y. Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides. Science 2001, 293, 269–271. (2). Li, H. J.; Zhou, Y.; Tu, W. G.; Ye, J. H; Zou, Z. G. State-of-the-Art Progress in Diverse Heterostructured Photocatalysts toward Promoting Photocatalytic Performance. Adv. Funct. Mater. 2015, 25, 998–1013. (3). Osterloh, E. F. Inorganic Nanostructures for Photoelectrochemical and Photocatalytic Water Splitting. Chem. Soc. Rev. 2013, 42, 2294–2320. (4). Zuo, F.; Wang, L.; Wu, T.; Zhang, Z. Y.; Borchardt D.; Feng P. Y. Self-Doped Ti3+ Enhanced Photocatalyst for Hydrogen Production under Visible Light. J. Am. Chem. Soc. 2010, 132, 11856–11857. (5). Zuo, F.; Bozhilov, K.; Dillon, R. J.; Wang, L.; Smith, P.; Zhao, X. Active Facets on Titanium(III)-Doped TiO2: An Effective Strategy to Improve the Visible-Light Photocatalytic Activity. Angew. Chem. Int. Ed. 2012, 124, 6327–6330. (6). Zhang, X.; Zhang, L. Z. Electronic and Band Structure Tuning of Ternary Semiconductor Photocatalysts by Self Doping: The Case of BiOI. J. Phys. Chem. C 2010, 114, 18198–18206. (7). Dong, G. H.; Zhao, K.; Zhang, L. Z. Carbon Self-Doping Induced High Electronic Conductivity and Photoreactivity of g-C3N4. Chem. Commun. 2012, 48, 6178–6180. (8). Huang, H. W., Li, X. W.; Wang, J. J.; Dong, F.; Chu, P. K.; Zhang, T. R.; Zhang, Y. H. Anionic Group Self-Doping as a Promising Strategy: Band-Gap Engineering and Multi-Functional Applications of High-Performance CO32−Doped Bi2O2CO3. ACS Catal. 2015, 5, 4094−4103.



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

(9). Wang, J. Q.; Su, S. Y.; Liu, B.; Cao, M. H.; Hu, C. W. One-Pot, LowTemperature Synthesis of Self-Doped NaTaO3 Nanoclusters for Visible-LightDriven Photocatalysis. Chem. Commun., 2013, 49, 7830−7832. (10).

Ding, X.; Ho, W. K.; Shang, J.; Zhang, L. Z. Self Doping Promoted

Photocatalytic Removal of NO under Visible Light with Bi2MoO6: Indispensable Role of Superoxide Ions. Appl. Catal., B 2016, 182, 316–325. (11).

Yuan, X. T.; Wang, X.; Liu, X. Y.; Ge, H. X.; Yin, G. H.; Dong, C. L.; Huang,

F. Q. Ti3+-Promoted High Oxygen-Reduction Activity of Pd Nanodots Supported by Black Titania Nanobelts. ACS Appl. Mater. Interfaces 2016, 8, 27654–27660. (12).

Zhang, Y.; Xing, Z. P.; Liu, X. F.; Li, Z. Z.; Wu, X. Y.; Jiang, J. J.; Li, M.;

Zhu, Q.; Zhou, W. Ti3+ Self-Doped Blue TiO2(B) Single-Crystalline Nanorods for Efficient Solar-Driven Photocatalytic Performance. ACS Appl. Mater. Interfaces 2016, 8, 26851–26859. (13).

Zhou, C.; Zhao, Y. F.; Shang, L.; Cao, Y. H.; Wu, L. Z.; Tung, C. H.; Zhang,

T. R. Facile Preparation of Black Nb4+ Self-Doped K4Nb6O17 Microspheres with High Solar Absorption and Enhanced Photocatalytic Activity. Chem. Commun. 2014, 50, 9554–9556.

(14).

He, R. A.; Cao, S. W.; Zhou, P.; Yu, J. G. Recent Advances in Vsible Light Bi

‐Based Photocatalysts. Chin. J. Catal. 2014, 35, 989–1007. (15).

Socratous, J.; Banger, K. K.; Vaynzof, Y.; Sadhanala, A.; Brown, A. D.; Sepe,

A.; Steine, U.; Sirringhaus, H. Electronic Structure of Low-Temperature Solution-Processed Amorphous Metal Oxide Semiconductors for Thin-Film Transistor Applications. Adv. Funct. Mater. 2015, 25, 1873–1885.


Page 22 of 28

Page 23 of 28

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).

Etacheri, V.; Seery, M. K.; Hinder, S. J.; Pillai, S. C. Oxygen Rich Titania: A

Dopant Free, High Temperature Stable, and Visible-Light Active Anatase Photocatalyst. Adv. Funct. Mater. 2011, 21, 3744–3752. (17).

Chen, X. F.; Liu, J. B.; Wang, H.; Ding, Y. L.; Sun, Y. X.; Yan, H. One-Step

Approach to Novel Bi4V2O11 Hierarchical Hollow Microspheres with High Visible-Light-Driven Photocatalytic Activities. J. Mater. Chem. A 2013, 1, 877– 883. (18).

Jiang, Z. Y.; Liu, Y. Y.; Li, M. M.; Jing, T.; Huang, B. B.; Zhang, X. Y.; Qin

X. Y.; Dai, Y. One-Pot Solvothermal Synthesis of Bi4V2O11 as A New Solar Water Oxidation Photocatalyst. Sci. Rep. 2016, 6, 22727. (19).

Lv, C. D.; Chen, G.; Sun, J. X.; Zhou, Y. S.; Fan, S.; Zhang, C. M. Realizing

Nanosized Interfacial Contact via Constructing BiVO4/Bi4V2O11 Element-Copied Heterojunction Nanofibres for Superior Photocatalytic Properties. Appl. Catal., B 2015, 179, 54–60.

(20).

Lv, C. D.; Chen, G.; Sun, J. X.; Zhou, Y. S. Construction of α−β Phase

Junction on Bi4V2O11 via Electrospinning Retardation Effect and Its Promoted Photocatalytic Performance. Inorg. Chem. 2016, 55, 4782−4789. (21).

Xu, H.; Ye, H. T.; Coathup, D.; Mitrovic, I. Z.; Weerakkody, A. D.; Hu, X. J.

An Insight of p-Type to n-Type Conductivity Conversion in Oxygen IonImplanted Ultrananocrystalline Diamond Films by Impedance Spectroscopy. Appl. Phys. Lett. 2017, 110, 033102. (22).

Liu, G. G.; Zhao, G. X.; Zhou, W.; Liu, Y. Y.; Pang, H.; Zhang, H. B.; Hao,

D.; Meng, X. G.; Li, P.; Kako, T.; Ye, J. H. In Situ Bond Modulation of Graphitic Carbon Nitride to Construct p–n Homojunctions for Enhanced Photocatalytic Hydrogen Production. Adv. Funct. Mater. 2016, 26, 6822−6829.



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

(23).

Page 24 of 28

Liu, Y. D.; Cai, Y. Q.; Zhang, G.; Zhang, Y. W.; Ang, K. W. Al-Doped Black

Phosphorus p–n Homojunction Diode for High Performance Photovoltaic. Adv. Funct. Mater. 2017, 27, 1604638. (24).

Pan, L.; Wang, S. B.; Xie, J. W.; Wang, L.; Zhang, X. W.; Zou, J. J.

Constructing

TiO2

p-n

Homojunction

for

Photoelectrochemical

and

Photocatalytic Hydrogen Generation. Nano Energy 2016, 28, 296–303. (25).

Jiang, T. F.; Xie, T. F.; Yang, W. S.; Chen, L. P.; Fan, H. M.; Wang, D. J.

Photoelectrochemical and Photovoltaic Properties of p-n Cu2O Homojunction Films and Their Photocatalytic Performance. J. Phys. Chem. C 2013, 117, 4619−4624. (26).

Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations

for Metals and Semiconductors using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6, 15–50. (27).

Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50,

17953–17979. (28).

Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation

Made Simple. Phys. Rev. Lett. 1996, 77, 3865–3868. (29).

Ding, X.; Zhao K.; Zhang, L. Z. Enhanced Photocatalytic Removal of Sodium

Pentachlorophenate with Self-Doped Bi2WO6 under Visible Light by Generating More Superoxide Ions. Environ. Sci. Technol. 2014, 48, 5823−5831. (30).

Liu, Z. S.; Niu, J. N.; Feng, P. Z.; Sui, Y. W.; Zhu, Y. B. One-Pot Synthesis of

Bi24O31Br10/Bi4V2O11 Heterostructures and Their Photocatalytic Properties. RSC Adv. 2014, 4, 43399–43405.


Page 25 of 28

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


(31).

Ding, Y. B.; Yang, F.; Zhu, L. H.; Wang N.; Tang, H. Q. Bi3+ Self Doped

NaBiO3 Nanosheets: Facile Controlled Synthesis and Enhanced Visible Light Photocatalytic Activity. Appl. Catal., B 2015, 164, 151–158. (32).

Wang, W. J.; Chen, X. Q.; Liu, G.; Shen, Z. R.; Xia, D. H.; Wong P. K.; Yu, J.

C. Monoclinic Dibismuth Tetraoxide: a New Visible-Light-Driven Photocatalyst for Environmental Remediation. Appl. Catal., B 2015, 176–177, 444–453. (33).

Banger, K. K.; Yamashita, Y.; Mori, K.; Peterson, R. L.; Leedham, T.;

Rickard, J.; Sirringhaus, H. Low-Temperature, High-Performance SolutionProcessed Metal Oxide Thin-Film Transistors Formed by a ‘Sol–Gel on Chip’ Process. Nat. Mater. 2011, 10, 45–50. (34).

Hsieh, P. T.; Chen, Y. C.; Kao, K. S.; Wang, C. M. Luminescence Mechanism

of ZnO Thin Film Investigated by XPS Measurement. Appl. Phys. A 2008, 90, 317–321. (35).

Chen, M.; Wang, X.; Yu, Y. H.; Pei, Z. L.; Bai, X. D.; Sun, C.; Huang, R. F.;

Wen, L. S. X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy Studies of Al-doped ZnO Films. Appl. Surf. Sci. 2000, 158, 134–140. (36).

Ali-Löytty, H.; Louie, M. W.; Singh, M. R.; Li, L.; Casalongue, H. G. S.;

Ogasawara, H.; Crumlin, E. J.; Liu, Z.; Bell, A. T.; Nilsson A.; Friebel, D. Ambient-Pressure XPS Study of a Ni−Fe Electrocatalyst for the Oxygen Evolution Reaction. J. Phys. Chem. C 2016, 120, 2247–2253. (37).

Li, H.; Shang, J.; Ai, Z. H.; Zhang, L. Z. Efficient Visible Light Nitrogen

Fixation with BiOBr Nanosheets of Oxygen Vacancies on the Exposed {001} Facets. J. Am. Chem. Soc. 2015, 137, 6393–6399. (38).

Liu, X. N.; Lu, Q. F.; Wei, M. Z.; Wang C. Q.; Liu, S. W. Facile

Electrospinning of CeO2/Bi2WO6 Heterostructured Nanofibers with Excellent



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

Visible-Light-Driven Photocatalytic Performance. Chem. Asian J. 2015, 10, 1710–1716. (39).

Zhao, J.; Lu, Q. F.; Wei, M. Z.; Wang, C. Q. Synthesis of One-Dimensional a-

Fe2O3/Bi2MoO6 Heterostructures by Electrospinning Process with Enhanced Photocatalytic Activity. J. Alloys Compd. 2015, 646, 417–424. (40).

He, Z. Q.; Shi, Y. Q.; Gao, C.; Wen, L. N.; Chen, J. M.; Song, S.

BiOCl/BiVO4 p-n Heterojunction with Enhanced Photocatalytic Activity under Visible-Light Irradiation. J. Phys. Chem. C 2014, 118, 389−398. (41).

Yan, J. Q.; Wang, T.; Wu, G. J.; Dai, W. L.; Guan, N. J.; Li L. D.; Gong, J. L.

Tungsten Oxide Single Crystal Nanosheets for Enhanced Multichannel Solar Light Harvesting, Adv. Mater. 2015, 27, 1580–1586. (42).

Zhou, Y. S.; Chen, G.; Yu, Y. G.; Zhao, L. C.; Sun, J. X.; He, F.; Dong, H. J.

A New Oxynitride-Based Solid State Z-Scheme Photocatalytic System for Efficient Cr(VI) Reduction and Water Oxidation. Appl. Catal., B 2016, 183, 176– 184. (43).

Lv, C. D.; Chen, G.; Sun, J. X.; Yan, C. S.; Dong, H. J.; Li, C. M. One-

Dimensional Bi2O3 QD-Decorated BiVO4 Nanofibers: Electrospinning Synthesis, Phase Separation Mechanism and Enhanced Photocatalytic Performance. RSC Adv. 2015, 5, 3767–3773. (44).

Yan, M.; Hua, Y. Q.; Zhu, F. F.; Gu, W.; Jiang, J. H.; Shen, H. Q.; Shi, W. D.

Appl. Catal., B 2017, 202, 518–527. (45).

He, F.; Chen, G.; Zhou, Y. S.; Yu, Y. G.; Li, L. Q.; Hao S. E.; Liu, B. ZIF-8

Derived Carbon (C-ZIF) as a Bifunctional Electron Acceptor and HER Cocatalyst for g-C3N4: Construction of a Metal-Free, All Carbon-Based Photocatalytic System for Efficient Hydrogen Evolution. J. Mater. Chem. A 2016, 4, 3822–3827.


Page 26 of 28

Page 27 of 28

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


(46).

Wu, Q. F.; Bao, S. Y.; Tian, B. Z.; Xiao Y. F., Zhang, J. L. Double-Diffusion-

Based Synthesis of BiVO4 Mesoporous Single Crystals with Enhanced Photocatalytic Activity for Oxygen Evolution. Chem. Commun. 2016, 52, 7478– 7481. (47).

He, F.; Chen, G.; Miao, J. W.; Wang, Z. X.; Su, D. M.; Liu, S.; Cai, W. Z.;

Zhang, L. P.; Hao S. E.; Liu, B. Sulfur-Mediated Self-Templating Synthesis of Tapered C-PAN/g-C3N4 Composite Nanotubes toward Efficient Photocatalytic H2 Evolution. ACS Energy Lett. 2016, 1, 969–975.



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

Table of Contents


Page 28 of 28

Oxygen-Induced Bi5+-Self-Doped Bi4V2O11 with a pân Homojunction

Recommend Documents

Oxygen-Induced Bi5+-Self-Doped Bi4V2O11 with a pân Homojunction