Ultrafine Bi3TaO7 Nanodot-Decorated V, N Codoped TiO2

Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

Surfaces, Interfaces, and Applications

Ultrafine Bi3TaO7 Nanodots Decorated V, N CoDoped TiO2 Nanoblocks for Visible-Light Photocatalytic Activity: Interfacial Effect and Mechanism Insight Chengzhang Zhu, Yuting Wang, Zhifeng Jiang, Annai Liu, Yu Pu, Qiming Xian, Weixin Zou, and Cheng Sun ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b00903 • Publication Date (Web): 15 Mar 2019 Downloaded from http://pubs.acs.org on March 18, 2019

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 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 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.

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 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Ultrafine Bi3TaO7 Nanodots Decorated V, N Co-Doped TiO2 Nanoblocks for Visible-Light Photocatalytic Activity: Interfacial Effect and Mechanism Insight Chengzhang Zhu,† Yuting Wang,† Zhifeng Jiang,‡,§ Annai Liu,║ Yu Pu,║ Qiming Xian,*,† Weixin Zou,*,║ and Cheng Sun† †State

Key Laboratory of Pollution Control and Resource Reuse, School of the Environment,

Nanjing University, Nanjing 210023, PR China ‡School

of Life Sciences, The Chinese University of Hong Kong, Shatin, NT, PR China

§Institute ║Key

for Energy Research, Jiangsu University, Zhenjiang 212013, PR China

Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical

Engineering, Nanjing University, Nanjing 210023, PR China *Corresponding authors: Qiming Xian, Weixin Zou Tel/Fax: +86 25 89680259; E-mail address: [email protected], [email protected]

ABSTRACT: Bi3TaO7 is a potential photocatalyst due to its high chemical stability, defective fluorite-type structure and superior mobility of photoinduced holes. However, few studies have focused on the interfacial effects of Bi3TaO7-based photocatalysts. In this work, 0D Bi3TaO7 nanodots hybridized 3D V and N codoped TiO2 nanoblocks (B/VNT) composites were firstly synthesized for the photocatalytic removal of oxytetracycline hydrochloride, 2,4,6-trichlorophenol, and tetrabromobisphenol A. The fabricated B/VNT had superior photocatalytic performance to that of pristine components, and probable degradation pathways were proposed according to the primary intermediates identified by GC–MS. Interestingly, on B/VNT, the transfer of interfacial electrons was observed from V/N-TiO2 to Bi3TaO7, and the formed built-in electronic field led to a direct Z-scheme structure, rather than type II, as confirmed by the generated •OH and •O2− radicals and band structures from the DFT calculation. Therefore, the strong interfacial electronic interaction on

ACS Paragon Plus Environment 1

ACS Applied Materials & Interfaces 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 30

the B/VNT was significant, which drove faster photogenerated charge transfer, more visible light adsorption, active •OH and •O2− generation, and thus improving the photocatalytic activity. KEYWORDS: Bi3TaO7 nanodots, V/N-TiO2 nanoblocks, electronic interaction, Z-scheme, degradation pathways

INTRODUCTION Over the last few decades, the environmental problems (especially antibiotics, disinfection byproducts and brominated flame retardants) caused by the worldwide burgeoning industrialization have seriously threatened human health.1−4 Hence, the elimination of toxic pollutants becomes one of the most important emerging research fields, arousing tremendous attention. To date, various kinds of technologies, such as flocculation,5 membrane filtration,6 and biological technology,7 have been explored to address water pollution. Among the available methods, semiconductor photocatalysis is regarded as an attractive way for solving these issues because of the economical use of photocatalytic materials and solar energy.8−10 Since visible-light energy takes up most of the solar radiation, developing efficient visible-light-driven photocatalysts is highly required.11 With the advantages of suitable band gap (2.74−2.95 eV), excellent chemical stability and defect fluorite-type structure, bismuth tantalate (Bi3TaO7) has been demonstrated to be a promising photocatalyst for pollutants degradation.12,13 The hybridized valence band (VB) is primarily contributed by the Bi 6s and O 2p orbits, which not only favors an efficient utilization of visible light but also promotes the mobility of photogenerated holes and the oxidation reaction. However, the widespread use of Bi3TaO7 is severely limited owing to the rapid electron−hole recombination. To this end, massive effort has been dedicated to mitigate the above challenge. Coupling Bi3TaO7 with other semiconductor to form heterostructural photocatalytic system is an effective one, and with the aid of the unique heterostructure, the charge separation can be effectively achieved.14,15 In fact, for a type-II heterojunction, the photoinduction on the conduction band (CB) of one photocatalyst would transfer to the VB of another photocatalyst, during which the redox activity of ACS Paragon Plus Environment 2

Page 3 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


electrons and holes would be weakened, implying that the charge carriers may not possess sufficient redox ability to be practically applied in wastewater treatment.16 Previous reports have indicated that the direct Z-scheme heterojunction is a more valid alternative to the traditional type-II heterojunction.17,18 In a direct Z-scheme system, the reductive electrons in the higher CB and oxidative holes in the lower VB can be retained, leading to both high redox capacity and charge-separation efficiency.19 Moreover, with the strong electrostatic force between electrons and holes, the Z-scheme charge transfer behavior is more feasible in physical relative to that of the typical heterojunctions. Therefore, it is imperative to exploit a facial synthesis of Bi3TaO7-based Z-scheme heterojunctions with superior photocatalytic performance. As an industrially significant n-type semiconductor, titanium oxide (TiO2), with the merits of earth abundance, high refractive index, strong oxidizing power, and resistance to photocorrosion, has been the most extensively investigated photocatalyst.20−25 Intensive studies focused on band gap engineering, with the purpose of overcoming the defects inherent to TiO2.26,27 Doping with N or V can optimize the electronic structure of TiO2 to a narrowed band-gap, which remarkably improves the solar light harvesting of TiO2 and shallowly traps the initially photogenerated carriers to inhibit their rapid recombination.28−30 More importantly, considering the well-matched band structure between the two, it can be reasonably predicted that the doped TiO2 may be a good candidate for fabricating an interfacial Z-scheme heterojunction toward Bi3TaO7. Although researches on the photocatalytic activity of the Bi3TaO7-based Z-scheme composite have been reported, there is still some space to further study on optimizing morphology and interfacial interaction of photocatalytic composites, which are vital factors for enhanced photocatalytic performance. Herein, three-dimensional (3D) V/N-TiO2 nanoblocks (NBs) modified with zero-dimensional (0D) Bi3TaO7 nanodots (NDs) were prepared for the first time to form a 3D/0D Z-scheme structure for the use in toxic pollutants photodegradation. It was found that B/VNT heterojunctions with broad-spectrum photocatalytic capacities showed superior photocatalytic behavior to V/N-TiO2 and Bi3TaO7, mainly owing to the synergistic effect of the tiny size effect of the Bi3TaO7 NDs, the ACS Paragon Plus Environment 3


Page 4 of 30

incorporation of V and N species, and the constructed direct Z-scheme heterostructure. The results of ESR and the trapping experiments revealed that superoxide (•O2−) and hydroxyl (•OH) radicals were the main reactive species in the photocatalytic oxidation of Oxytetracycline. Combined with these produced oxidative species, the energy-level positions of V/N-TiO2 and Bi3TaO7, DFT, and XPS results clearly demonstrated strong interfacial effects and the interfacial charge-transfer path of 10% B/VNT, verifying that such a system works in the Z-scheme way. Furthermore, the diagram of electron−hole pairs separation and the reaction mechanism over the direct Bi3TaO7@V/N-TiO2 Z-scheme photocatalysts was also discussed in detail. This study might provide new insight into the rational design of Z-scheme heterojunction catalysts with strong interfacial interactions for environmental remediation.

EXPERIMENTAL SECTION Materials. Ammonium metavanadate (NH4VO3), ammonia (NH3), tantalum (V) chloride (TaCl5), bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), tetrabutyl titanate (TBT), potassium hydroxide (KOH), isopropyl alcohol ((CH3)2CHOH), and absolute ethanol (C2H5OH) purchased from Sinopharm Chemical Reagent Co., Ltd are of analytical grade. Oxytetracycline hydrochloride (OTTCH), 2,4,6-Trichlorophenol (2,4,6-TCP), and tetrabromobisphenol A (TBBPA) were obtained from Aladdin Reagent Co., Ltd. Ultrapure water (18.2 MΩ cm) was achieved by a Simplicity UV ultrapure water system (Merck Millipore). Synthesis of V and N Co-Doped TiO2 NBs. TBT was added dropwise into isopropyl alcohol and stirred for 30 min, in which a certain amount of NH4VO3 dispersed in the mixture containing ultrapure water (0.1 mL) and absolute ethanol (70 mL) was injected under a rate of 1.0 mL min−1. After refluxing at 80 °C for 5 h, the synthesized V-doped TiO2 were repeatedly washed with ethanol and fully dried in a vacuum oven at 60 °C, followed by thermal treatment in flowing NH3 at 600 °C. Upon cooling naturally to an ambient temperature, V and N co-doped TiO2 (denoted as V/N-TiO2) were ground to fine powder. ACS Paragon Plus Environment 4

Page 5 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Loading Bi3TaO7 NDs onto V/N-TiO2 NBs. The B/VNT photocatalysts were fabricated using a facile one-step solvothermal route. Typically, 0.15 g of newly prepared V/N-TiO2 NBs was ultrasonically dispersed in absolute ethanol (35 mL). Then, appropriate amounts of Bi(NO3)3·5H2O and TaCl5 were gradually added into the suspension with vigorous stirring. Subsequently, the pH value of the above homogeneous solution was adjusted to 10.0 with the addition of KOH solution (7 M). After that, the mixture was transferred to a Teflon autoclave and heated at 230 °C for 24 h. Finally, the final products were thoroughly washed with ultrapure water and ethanol in ultrasound for several times before being dried at 60 °C for 6 h. According to this method, different molar ratios of the Bi3TaO7 to V/N-TiO2 samples (i.e., 5%, 10%, 15%, and 20% Bi3TaO7/V/N-TiO2) were obtained and defined as 5% B/VNT, 10% B/VNT, 15% B/VNT, and 20% B/VNT, respectively. Characterization. X-ray diffraction (XRD) was characterized on a Philips X’Pert Pro diffractometer equipped with Ni-filtered Cu-Kα radiation (λ = 1.5418 nm). The morphologies and particle size of the synthesized catalysts were examined with transmission electron microscopy (TEM, JEM-200CX) at 200 kV. Atomic Force Microscopic (AFM, MFP-30) was utilized to determine the thickness of the product. Brunauer–Emmett–Teller (BET) surface areas were measured by nitrogen adsorption at 77 K on a Micromeritics ASAP 2010 adsorption apparatus. The optical properties of samples in the range of 200-800 nm were analyzed by a UV–vis spectrophotometer diffuse reflectance spectroscopy (DRS, UV-3600Plus) with BaSO4 as reference. X-ray photoelectron spectroscopy (XPS, ESCA PHI500) was employed to examine surface chemical composition and valence band (VB). Photoluminescence (PL) and time-resolved PL decay spectroscopy were obtained by a Horiba Fluorolog 3-22 type fluorescence spectrophotometer. Total organic carbon (TOC) analyses were carried out on a multi N/C 2100 (Analytik Jena AG) TOC analyzer. Electron spin resonance (ESR) signals of paramagnetic radicals (•OH and •O2−) spin-trapped by 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in water or methanol were detected by a Bruker model ESR JES-FA200 spectrometer.



Page 6 of 30

The photoelectrochemical measurements including electrochemical impedance spectroscopy (EIS) and photocurrent, were performed on an electrochemical workstation (CHI760E) with a standard three-electrode system in 0.2 M Na2SO4. The as-prepared photocatalysts were spin-coated onto the Indium Tin Oxide (ITO, 1 × 2 cm2) acted as the working electrode, while the saturated Ag/AgCl and platinum wire were served as the reference and counter electrodes, respectively. A 500 W Xe arc lamp was worked as irradiation in the electrochemical experiments. Photocatalytic Text. The photocatalytic experiments were performed in an open homemade thermostatic photoreactor (XPA-V, Xujiang, China, Nanjing) under an irradiation of a 1000 W Xenon lamp with a 420 nm cut-off filter. Prior to light illumination, a suspension containing 50 mg of catalyst and 50 mL of the model pollutants with the concentrations of OTTCH (20 mg L−1), TBBPA (10 mg L−1), and 2,4,6-TCP (10 mg L−1) were magnetically stirred in darkness for 1 h to achieve adsorption-desorption equilibrium between the two. During the irradiation, approximately 5 mL of the suspension was withdrawn at 20 min intervals and filtered through 0.22 µm Millipore filter to remove the photocatalyst, with the purpose of detecting the changes of the pollutant concentrations. Analytical Methods. The concentration of OTTCH was analyzed at its maximum absorption wavelength (356 nm) by a Lambda 750 UV–vis spectroscopy (PerkinElmer) with deionized water as the reference. The photodegradation rate was calculated by the following formula:

 ln(C/C 0 )  kapp t

(1)

Here, kapp is the apparent rate constant (min−1), C0 and C are the initial concentration and instant concentration of the target pollutants at time t, respectively. The concentrations of 2,4,6-TCP and TBBPA were determined by an Agilent 1200 high performance liquid chromatography (HPLC) instrument equipped with a C18 reversed phase column (4.6 mm × 250 mm × 5 μm) and UV detector set as 290 nm for 2,4,6-TCP and 220 nm for TBBPA. The mobile phase was the mixture of methanol-ultrapure water (85:15, v/v) with a flow rate of 1 mL min−1, and the column temperature was maintained at 30 °C during the sample analysis. ACS Paragon Plus Environment 6

Page 7 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The intermediate products of OTTCH were identified by gas chromatography–mass spectrometer (GC–MS) equipped with a TG-5SILMS column (30 m × 0.25 mm × 0.25 μm). Before GC–MS analysis, the reaction solution was filtered with a 0.22 µm Millipore filter, and was subsequently extracted with dichloromethane (5 mL) for three times. Afterward, the extracts were dried under flowing nitrogen and then dispersed in 1 mL acetonitrile. After that, trimethylsilylation was performed at 60 °C for 1 h using 100 μL of bis (trimethylsilyl) trifluoroacetamide (BSTFA). The column temperature program was set as follows: the initial temperature of GC was 50 °C for 3 min, then increased up to 300 °C with a heating rate of 5 °C min−1 and kept at this temperature for 2 min. The injector temperature was 250 °C. Helium was used as the carrier gas. Mass spectrometric detection was operated with 70 eV electron impact (EI) mode. Theoretical Calculation. Density functional theory (DFT) calculations were conducted using the Vienna Ab-initio Simulation Package (VASP). All-electron plane-wave basis sets with an energy cutoff of 400 eV, and a projector augmented wave (PAW) method were adopted. The samples were simulated using a surface model of p (2 × 2) unit cell periodicity. A (3 × 3 × 1) Monkhorst-Pack mesh was used for the Brillouin-zone integrations to be sampled. Electronic density-of states (DOS) of (2 × 2) supercells were calculated using a higher 9 × 9 × 1 K-point mesh. The conjugate gradient algorithm was used in the optimization. The convergence threshold was 1 × 10−4 eV in total energy and 0.05 eV/Å in force on each atom.

RESULTS AND DISCUSSION Structural, Compositional, and Morphological Information. The phase structures of Bi3TaO7, TiO2, V/N-TiO2 and B/VNT composites were investigated by XRD analysis. As shown in Figure 1a, bare TiO2 exhibited several diffraction peaks at ca. 25.3°, 37.8°, 47.9°, 54.0°, and 62.7°, perfectly indexed as the (101), (004), (200), (105), and (204) planes (JCPDS No. 21-1272), respectively.31,32 Notably, the anatase-to-rutile (110) phase transformation appeared, and the prominent (101) peak of both V/N-TiO2 and B/VNT composites slightly shifted to a lower diffraction angle relative to TiO2 ACS Paragon Plus Environment 7


(Figure 1b), which all suggested the incorporation of V and N into the TiO2 matrix. The results were consistent with those of XPS, in which the V 2p core level revealed that V4+ 2p2/3 (515.7 eV) and V5+ 2p2/3 (516.8 eV) ions were incorporated into the crystal lattice of TiO2 and formed a Ti-O-V bond (Figure S1a). Meanwhile, the occurrence of the N-Ti-O linkage (400.1 eV), Ti-O-N and Ti-O-N-O (401.4 eV) in the N 1s region further confirmed the successful doping of N species (Figure S1b).33 After loading Bi3TaO7 NDs onto the surface of V/N-TiO2, a series of crystal peaks corresponding to Bi3TaO7 (JCPDS No. 87-1256) phases occurred and gradually intensified as the Bi3TaO7 contents increased, indicating that Bi3TaO7 NDs had been coupled with V/N-TiO2 NBs. Moreover, all signals of V, N, Ta, Bi, Ti, and O appeared in the survey XPS spectrum of 10%

(220)

(111) (200)

(a)

(222)

B/VNT (Figure S2), further demonstrating its hybrid structure.

(b) A： Anatase

A： Anatase R： Rutile

R： Rutile

Bi3TaO7

15% B/VNT 10% B/VNT 5% B/VNT

R(110)

10

20

R(110)

30

A(105) A(200) A(204)

40

50

60

2-Theta (degree)

70

TiO2

(1

A(004)

01

)

V/N-TiO2

A

A(101)

Intensity (a.u.)

20% B/VNT

Intensity (a.u.)

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 30

24

80

28

32

2-Theta (degree)

Figure 1. (a) Normal and (b) partially enlarged XRD patterns of B/VNT in varying proportions, together with that of TiO2, V/N-TiO2, and Bi3TaO7.

The general morphology and microstructure of the samples were characterized by TEM and high-resolution TEM (HRTEM). It is apparent in Figure 2c that most of the V/N-TiO2 presented a relatively regular nanoblock morphology. The thickness of the nanoblocks is approximately 8.4 nm and 9.6 nm evidenced by the AFM image and height profile (Figure 2a,b). In addition, the typical diffused halo ring and dot patterns existed in the selected-area electron diffraction (SAED) pattern (inset in Figure 2c) demonstrated the polycrystalline property of V/N-TiO2 NBs. Figure 2d exhibits ACS Paragon Plus Environment 8

Page 9 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the TEM image of the resulting 10% B/VNT composite, in which V/N-TiO2 NBs employed as an excellent platform that was evenly and tightly decorated with Bi3TaO7 NDs. Well-dispersed ultrafine Bi3TaO7 NDs with an average sizes of about 4.92 nm (Figure 2e) could ensure sufficient contact with V/N-TiO2 NBs, and induce an interfacial interaction because of the quantum size effect, thereby facilitating the fast interfacial charge separation.34,35 From the HRTEM image (Figure 2f), a clear d-spacing of 0.351 nm obtained from V/N-TiO2 was consistent with the (101) planes, while the interplanar spacing of ca. 0.273 and 0.312 nm matched well with that of the (200) and (111) crystal facet of Bi3TaO7, which proved that the nanojunction was indeed constructed in the 10% B/VNT composite. Additionally, elemental mapping (Figure S3) of 10% B/VNT clearly displayed that the elements of Bi, Ta, Ti, O, N and V were homogeneously distributed in the heterojunction, further suggesting the formation of intimate interfaces between the two, rather than simply mixing.



Page 10 of 30

Figure 2. (a) AFM image, (b) height profile, (c) TEM image and corresponding SADE pattern (inset of (c)) of V/N-TiO2 NBs. (e) Size statistical analysis of Bi3TaO7 NDs. (d) TEM and (f) HRTEM images of 10% B/VNT heterojunction.

Nitrogen adsorption−desorption isotherms and the corresponding pore size distribution of Bi3TaO7, TiO2, V/N-TiO2, and 10% B/VNT are depicted in Figure S4. All of the samples exhibited similar type-IV isotherms with hysteresis loops, and the BET surface area trend followed the order of 10% B/VNT (62.9 m2/g) > V/N-TiO2 (46.3 m2/g) > TiO2 (38.5 m2/g) > Bi3TaO7 (23.7 m2/g), which revealed that V and N implantation suppressed crystalline growth, eventually increasing the surface area of TiO2. Simultaneously, the addition of Bi3TaO7 NDs also had a positive effect on the specific surface area, primarily due to the uniform dispersion of Bi3TaO7 NDs on the surface of V/N-TiO2 NBs. Therefore, an abundant interaction area between the above two moieties was achieved, which could shorten the distance of mass transfer and provide more surface-reactive sites for the degradation of toxic pollutants.36

Bandgap Structure. The DFT calculation was rationally employed to theoretically investigate the electronic structures of Bi3TaO7 and V/N-TiO2 theoretically. The schematic illustrations of Bi3TaO7 and V/N-TiO2 supercell models utilized in the calculations are presented in Figure 3a,b. It was observed that the valence band maximum (VBM) and conduction band minimum (CBM) of Bi3TaO7 were O 2p and Ta 4d orbitals, respectively. For V/N-TiO2, the VBM was the orbital mixture of O 2p and N 2p, whereas the CBM was the orbital mixture of V 3d and N 2p. Furthermore, the band energies of Bi3TaO7 and V/N-TiO2 were separately calculated to be 2.79 and 2.36 eV using the DFT method (Figure 3c,d), which were closed to the experimental results of Bi3TaO7 and V/N-TiO2 (Figure S5b), i.e., 2.84 and 2.52 eV, respectively. However, the theoretical band gap were moderately lower than the experimental values, which could be ascribed to the well-known restriction of the DFT calculation, i.e., the unknown exchange-correlation energy.37 ACS Paragon Plus Environment 10

Page 11 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Besides, the valence band maximum (VBM) of samples were also measured by the valence band X-ray photoelectron spectra (Figure 3e). As for single Bi3TaO7, the VBM was estimated to be 3.11 eV, while a blue shift occurred from 2.34 for TiO2 to 2.07 eV for V/N-TiO2, indicating that the existence of mid-gap band states between the VB and CB in V/N-TiO2. According to the formula of ECB = EVB – Eg, the corresponding conduction band minimum (CBM) edge position of Bi3TaO7, TiO2, and V/N-TiO2 would locate at ca. 0.27, –0.76, and –0.45 eV, respectively. Combined with the above results, the well-matched band structure of Bi3TaO7 and V/N-TiO2 was illustrated in Figure 3f, which might promote the separation of photogenerated carriers (electron and hole).

Figure 3. Crystal structures and calculated density of states of (a, c) Bi3TaO7 and (b, d) V/N-TiO2. Valence-band XPS spectra (e) and schematic of the electronic band structures (f) of Bi3TaO7, TiO2, and V/N-TiO2. ACS Paragon Plus Environment 11


Page 12 of 30

Optical and Photoelectrical Properties. Considering that the light-harvesting capacity played a crucial role in photocatalysis, the UV−vis DRS test was carried out (Figure S5a). The data showed that the absorption edge of Bi3TaO7 was 440 nm with a band gap of approximately 2.8 eV, while TiO2 only suffered photoabsorption in the ultraviolet region. It was noteworthy that the introduction of V and N extended the light absorption spectral range of TiO2 to the visible region, which might be ascribed to the introduced mid-gap states that result from the doping species.38 Moreover, the absorption edges of the B/VNT heterojunctions displayed an obvious red shift compared to V/N-TiO2 and Bi3TaO7, leading to more available visible light adsorption. This result implied that B/VNT could absorb more photons in the photocatalytic reaction. Generally, superior charge-separation property is of great significance to the photocatalytic efficiency of catalysts.39,40 Hence, steady-state photoluminescence (PL) of B/VNT composites excitated at 256 nm were employed to evaluate the charge separation and recombination (Figure S6a). Compared to TiO2, the higher photocurrent response of V/N-TiO2 could be ascribed to the improved light absorption that produces more electron−hole pairs and the codoped V and N that shallowly trap the charge carriers to prevent them from rapid recombination.21,41 Moreover, the fluorescence quenching via coupling Bi3TaO7 nanodots mainly results from improved interfacial charge transfer between Bi3TaO7 and V/N-TiO2, which could improve the separation of electron–hole pairs in the constructed heterojunction. Thereinto, 10% B/VNT exhibited the weakest emission intensity, matching well with the degradation results. To investigate the behavior of the photoinduced electrons and holes in depth, the time-resolved PL decay measurement was performed, as shown in Figure S6b. The results suggested that 10% B/VNT heterojunction showed the longest lifetime of free carriers with respect to that of Bi3TaO7 and V/N-TiO2, thereby leading to enhanced photocatalytic activity. The photocurrent and EIS were further performed to study both of the separation of electron−hole pairs and interfacial electron transfer. As depicted in Figure S7a, the sensitive photocurrent ACS Paragon Plus Environment 12

Page 13 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


response occurred once the light source was switched on, suggesting the rapid charge transport. When 10% B/VNT was spin-coated onto the pretreated ITO, the corresponding photocurrent density increased dramatically, rising up to 0.73 µA, which was approximately 2.9, 2.3, and 1.6-fold greater than TiO2, Bi3TaO7, and V/N-TiO2, respectively. This result manifested that the fabricated 10% B/VNT heterostructures with strong interfacial interactions could efficiently hinder the chance of electron−hole recombination and accelerate the charge transfer.42 As excepted, the EIS performances of Bi3TaO7, TiO2, V/N-TiO2, and 10% B/VNT exhibited similar variation trends (Figure S7b). Among them, 10% B/VNT displayed the shortest arc radius of the Nyquist circle, which reflected the minimum charge transfer resistance was obtained, again verifying that there was a higher efficiency of interfacial charge transport in the 10% B/VNT heterostructure.

Photocatalytic Activity and Degradation Pathways. The photocatalytic activity of different samples was first evaluated by the photodegradation of OTTCH (20 mg/L) under visible light illumination (λ > 420 nm). It could be observed in Figure 4a that the adsorption−desorption equilibrium between the catalysts and OTTCH molecules was reached within 60 min in darkness, and thus self-photolysis could be neglected. For bare TiO2 and Bi3TaO7, only 39.5% and 45.2% of OTTCH were decomposed after irradiation for 80 min because of the high recombination rate of photogenerated carriers. However, once the V and N dopants were incorporated into TiO2, the resulting V/N-TiO2 achieved more superior performance for OTTCH removal. All B/VNT photocatalysts realized improved degradation rate (DR) compared to the others, particularly the 10% B/VNT heterojunction. Nevertheless, the photocatalytic behavior started to decline with the further increase in Bi3TaO7 content, because excessive deposition of Bi3TaO7 NDs might reduce the light absorption and surface adsorption ability of catalysts, and occupy parts of available active sites on V/N-TiO2 NBs. Furthermore, the photocatalytic activity of physical mixture of Bi3TaO7 and V/N-TiO2 (B/VNT-PM) was substantially lower than 10% B/VNT, which implied that the strong heterojunction effect was formed on the interface between two moieties, rather than a simple mechanical mixture. As depicted in Figure 4b, the UV−vis characteristic absorption peak at 354 nm ACS Paragon Plus Environment 13


Page 14 of 30

quickly diminished, accompanied by a gradual blue shift as the irradiation proceeded, suggesting that the organic group of OTTCH was destroyed by 10% B/VNT.43 Moreover, the photocatalytic degradation followed the pseudo first-order kinetics and the reaction rate constants calculated from Figure 4c were presented in Table S1. In order to reduce the effect of specific surface area on the photoactivity, the degradation rates of the catalysts were normalized with their surface areas according to previous report,44 and the normalized rate constants (k’) were displayed in Table S2. It can be found that after normalized with respect to the specific surface area, the 10% B/VNT still showed the best degradation efficiency in all catalysts, followed the order of 10% B/VNT > Bi3TaO7 > V/N-TiO2 > TiO2. In addition, the k’ value of Bi3TaO7 was higher than that of V/N-TiO2, opposite to the order of reaction rate constant, which suggested that the specific surface area is also important to OTTCH photodegradation. Notably, the DR of OTTCH using 10% B/VNT is preferable to most of the reported Bi3TaO7-based or TiO2-based catalysts. Comparison of the results is listed (Table S3). To gain deeper insight into the photocatalytic properties of the as-prepared heterojunctions, the total organic carbon (TOC) measurement was conducted. Typically, the mineralization rate of TOC (70.4%) was lower than that of DR (93.7%) toward the removal of OTTCH (Figure 4d), suggesting that the structure of OTTCH could be effectively decomposed, however, the OTTCH molecules were more difficult to be mineralized into CO2 and H2O. Hence, some small intermediate products (this is proven later) were generated during the photodegradation process.45 The TOC removal curve displayed a similar variation trend to the DR curve of 10% B/VNT, which indicated the accurate evaluation of the photocatalytic activity. Simultaneously, the high TOC removal rate revealed that 10% B/VNT could be regarded as a potential candidate for environmental applications. TBBPA, a common brominated flame retardant that has been extensively used in textiles, circuit boards and thermoplastic plastics, may induce the disruption of cytotoxicity, immunotoxicity and neurotoxicity.46 In addition, 2,4,6-TCP, a chlorinated phenol that has been utilized as a fungicide, ACS Paragon Plus Environment 14

Page 15 of 30

herbicide and glue preservative in aquatic environments, can seriously threat the human health.47 Thus, efficient removal of 2,4,6-TCP and TBBPA using photocatalysis technology is of vital significance. Analogously, 10% B/VNT still showed optimal photocatalytic performance toward the degradation of TBBPA (DR, 69.9%) and 2,4,6-TCP (DR, 89.5%) within 80 min (Figure 4e), which suggested the broad-spectrum photodegradation capacities of the heterojunction material. Although the superior photocatalytic behavior of 10% B/VNT was verified, the stability with regard to practical applications is unclear. Therefore, cycle experiments for OTTCH degradation over Bi3TaO7 NDs, V/N-TiO2 NBs and 10% B/VNT were repeatedly performed for four times under identical reaction conditions (Figure 4f). No notable decrease of the degradation efficiency could be found after four recycles. Moreover, the XRD results (Figure S8) also exhibited that no noticeable change of the phase could be observed in the fresh and reused composites. These results indicated that 10% B/VNT was a highly efficient photocatalyst with broad photocatalytic spectrum and impressive stability. 0.8

(a)

Light on

Dark

(b)

Bi3TaO7

Irradiation time

TiO2

0.6

Bi3TaO7 V/N-TiO2 0.4

B/VNT-PM 5% B/VNT 10% B/VNT 15% B/VNT 20% B/VNT photolysis

0.2

0.4

-40

-20

2.0

1.5

1.0

0.5

0

20

40

60

(d)

0.0

0.0 200

80

Time (min)

80

B/VNT-PM 5% B/VNT 10% B/VNT 15% B/VNT 20% B/VNT photolysis

0.2

0.0 -60

20 mg/L 0 min 20 min 40 min 60 min 80 min

-ln(C/C0)

Absorbance (a.u.)

0.8

V/N-TiO2

2.5

0.6

C/C0

(c)

TiO2

3.0

1.0

300

400

500

Wavelength (nm)

100

(e)

TBBPA 2,4,6-TCP

0

80

80

60

60

DR (%)

DR (%)

40

40

20

40

60

80

Time (min)

100

60

TOC (%)

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


(f)

1 st 2 nd 3 rd 4 th

40

20 20

0

20

0 0

20

40

Time (min)

60

80

Ti

O2 B

a i T3

O7 V

/N

i -T

O2

5%

B

/V

N

T

10

%

B

/V

N

T

15

%

B

/V

N

T

20

%

B

/V


N

T

0

Ta Bi 3

O7 V

/N

-T

iO

2

V

10

%

B/

N

T


Page 16 of 30

Figure 4. (a) Time-dependent concentration of OTTCH solution on exposure to visible light (λ > 420 nm) using the prepared photocatalysts, (b) temporal UV−vis absorption spectral changes during the OTTCH degradation in the presence of 10% B/VNT, (c) linear relationship of ln(C/C0) versus time, (d) TOC removal of OTTCH for 10% B/VNT by visible light irradiation for 80 min, (e) photocatalytic activity of TBBPA and 2,4,6-TCP with 10% B/VNT, (f) recycling photocatalytic tests for OTTCH degradation over pure Bi3TaO7, V/N-TiO2, and 10% B/VNT heterojunction.

As the structure of OTTCH molecules was decomposed, some intermediate products were generated. The intermediate products were identified by GC–MS analysis with EI full-scan patterns and the standard mass spectrum data of the U.S. National Institute of Standards and Technology.48 The retention time (min), molecular ion (m/z) and structure formula of the thirteen identified products are listed in Table 1. In particular, open-ring reactions and cleavages of the central carbon might be the two main reaction routes for OTTCH degradation. The intermediates (the second row in Figure 5) were primarily derived from the open-ring reactions, followed by the cleavage of the central carbon to form smaller organic molecules (the third row).49 With the introduction of reactive radicals caused by photogenerated electron–hole pairs, the ring was destroyed, after which CO2, H2O, and NH4+ were eventually involved in the photocatalytic oxidation reaction.50 Combined with these results, the proposed degradation pathways of OTTCH over 10% B/VNT are shown in Figure 5. Table 1. Identification of the Photodegradation Intermediates of OTTCH by GC–MS. Product

Retention Time/min

m/z

1

6.68

94

2

6.82

58

3

7.41

45

4

7.59

42


Structure Formula OH

OH

NH2

HN

C

NH

Page 17 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5

6

10.13

HO

O

O

OH

90

10.41

OH

116 O O

7

11.90

118

8

12.60

144

O

HO

OH

O OH

O O

9

16.43

230

O O

O

10

17.33

131

HO

NH O

OH

11

22.56

206

OH O

12

24.91

154

OH OH O

13

31.53

O

278

O O



H 3C

OTTCH

CH3

HO

OH

Page 18 of 30

CH3 N OH

NH2 OH OH

O

OH

O

O

O

O

OH O

O

OH

O

OH

O

O

OH

OH

O

O

O

O

O

OH

O

HO

OH

O

HO

O

O

OH

HO

NH

OH

HN

C

OH

NH

O

NH2

CO2, H2O, NH4+

Figure 5. Proposed photodegradation pathways of OTTCH irradiated by visible light.

Possible Photocatalytic Mechanism. In general, the optical/photoelectrical properties and photocatalytic performance were closely related to the interfacial electronic interaction of photocatalyst.51 Hence, XPS characterization was employed to investigate the interfacial effect. It is well known that an increase in the binding energies (BE) implies the weakened electron screening effect due to the decreased electron density, whereas the increment of electron density results in a lower BE value.52,53 As shown in Figure 6a−c, once Bi3TaO7 NDs were hybridized with V/N-TiO2 NBs, a notable BE shift was observed from the Bi 4f, Ta 4f and Ti 2p spectrum. In the XPS spectra of Bi 4f and Ta 4f, it was found that the BE were shifted to lower values on 10% B/VNT relative to Bi3TaO7, which suggested that the electron density was increased in the Bi and Ta elements of ACS Paragon Plus Environment 18

Page 19 of 30

B/VNT. Additionally, for the spectra of Ti 2p, it was observed that 10% B/VNT had a higher BE than that of V/N-TiO2 NBs, indicating that the electrons on Ti were reduced on B/VNT. Accordingly, it was deduced that on the B/VNT interface, the electrons transferred from V/N-TiO2 to Bi3TaO7, leading to the formation of the build-in electric field. In this case, the stronger electronic interaction on B/VNT interface drove photogenerated electrons transfer from CB (Bi3TaO7) to VB (V/N-TiO2). Therefore, a direct Z-scheme photocatalytic system was constructed in the B/VNT photocatalyst, instead of type II. (a)

Bi 2f7/2 158.9

164.2

25.4

(c)

Ta 4f

27.3

158.8

164.1

164

162

160

Bi3TaO7 25.3

27.1 28.5

10% B/VNT

10% B/VNT

158

156

31

30

29

28

27

Ti 2p

Ti 2p1/2 V/N-TiO2

458.7

464.5

26

25

24

Binding energy (eV)

Binding energy (eV)

Ti 2p3/2 458.6 464.3

28.7

Intensity (a.u.)

Bi3TaO7

166

(b)

Bi 4f

Intensity (a.u.)

Bi 2f5/2

Intensity (a.u.)

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

466

10% B/VNT

464

462

460

458

456

Binding energy (eV)

Figure 6. High-resolution XPS spectra of (a) Bi 4f, (b) Ta 4f, and Ti 2p region for Bi3TaO7, V/N-TiO2, and 10% B/VNT composite.

Moreover, the main active species involved in the photocatalytic oxidation of OTTCH were explored to validate the above Z-scheme photocatalytic structure. Different scavengers including 1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (TEMPOL), isopropanol (IPA) and ammonium oxalate (AO), were utilized as the scavengers of superoxide (•O2−), hydroxyl (•OH) and holes (h+), respectively. As illustrated in Figure 7a,b, the photodegradation efficiency of OTTCH was slightly depressed with the addition of AO, whereas an obvious change was observed when the IPA or TEMPOL was introduced. Consequently, it could be preliminarily inferred that the produced •O2− and •OH had a positive effects on OTTCH degradation. In addition, the generation of •O2− and •OH in the reaction system was further validated by the ESR spin-trap technology (Figure 7c,d). The ACS Paragon Plus Environment 19


Page 20 of 30

typical peaks corresponding to DMPO–•O2− and DMPO–•OH adducts were obviously observed under visible light illumination, and the peak intensity increased as irradiation time was prolonged. The ESR results indicated that both •O2− and •OH radicals were the dominant oxidative species in the photocatalytic process, which was in consistent with the results of trapping experiments.

Figure 7. The photocatalytic performance (a) and degradation rate (b) of OTTCH with the addition of AO, TEMPOL, and IPA. DMPO spin-trapping ESR spectra with 0.1 mg/mL 10% B/VNT in the dark and under visible light irradiation (3 and 6 min) for DMPO–•OH in aqueous dispersion (c), and DMPO–•O2− in methanol dispersion (d). Illustration of the charge-transfer mechanisms for type II heterojunction (e).

However, if the type II structure was present in the B/VNT photocatalyst (Figure 7e), OH− could not be oxidized to generate •OH by h+ leaving in the VB of V/N-TiO2 because the EVB edge potential of V/N-TiO2 (2.07 V vs NHE) was more negative than E(•OH/OH−) (2.40 V vs NHE).54 Similarly, the ECB edge potential of Bi3TaO7 (0.27 V vs NHE) was more positive than E(O2/•O2−) (−0.046 V vs NHE), which suggested that the photoinduced electrons in the CB of Bi3TaO7 could not combine with dissolved O2 to form •O2−.15 Based on the generation of •OH and •O2−, we ACS Paragon Plus Environment 20

Page 21 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reasonably concluded that, instead of a type II structure, a direct Z-scheme photocatalytic system was constructed in B/VNT. Due to the built-in electronic field, the V/N-TiO2 acted as an electron reservoir to trap photogenerated electrons that were emitted from Bi3TaO7, preventing the electron-hole pairs recombination. The h+ in the VB of Bi3TaO7 oxidized OH− to •OH, and the e− in the CB of V/N-TiO2 reduced O2 to •O2−, which were consistent with the in situ ESR results. Moreover, the direct Z-scheme reaction mechanism for the enhanced photocatalytic activity over 10% B/VNT heterojunction (Figure 8) was proposed as follows: V/N-TiO2/Bi3TaO7 + hv → V/N-TiO2 (e− + h+)/Bi3TaO7 (e− + h+)

•O − 2

(2)

V/N-TiO2 (e−) + Bi3TaO7 (h+) → hv + heat

(3)

V/N-TiO2 (e−) + O2 → •O2−

(4)

Bi3TaO7 (h+) + H2O → •OH + OH−

(5)

(or •OH) + organic pollutants → degraded products

(6)

As a result, the superior photocatalytic behavior of 10% B/VNT could be ascribed to the following factors: (i) The incorporation of V and N species into the TiO2 matrix could be responsible for the enhanced visible-light absorption because of the mid-gap impurity levels formed between the CBM and VBM of V/N-TiO2, which not only narrowed the band gap (2.52 eV) but also increased the amount of the photoexcited electron−hole pairs, based on the UV-vis DRS and DFT calculation. Specifically, it was easier for electron transfer and reducing the recombination of electron−hole pairs, as confirmed by the results of transient photocurrent response and ESI. (ii) Compared to pristine components, the 10% B/VNT heterojunction with a higher surface areas was capable of shortening the distance of mass transfer and facilitating the adsorption of pollutant molecules for surface reactions.21 On the other hand, in addition to the matched energy-level positions (Bi3TaO7 and V/N-TiO2), a novel well-designed direct Z-scheme heterostructure with the strong interaction of built-in electric field was constructed, rather than the traditional type II heterojunction, thereby broadening visible light adsorption, boosting the charge separation ACS Paragon Plus Environment 21


Page 22 of 30

efficiency at intimate 3D/0D interfaces, and enabling the formation of more reactive oxygen species for the effective removal of organic pollutants (Figure 8).

Figure 8. Schematic diagram of photoinduced electron-hole separation process for 10% B/VNT Z-scheme heterojunction.

CONCLUSIONS In summary, 0D/3D heterostructures of B/VNT were successfully synthesized for the degradation of OTTCH, TBBPA, and 2,4,6-TCP under visible light irradiation. The 10% B/VNT composite showed superior photodegradation activity (93.7%) and TOC removal efficiency (70.4%) toward OTTCH degradation, and possible degradation pathways were proposed. Furthermore, at the interface of Bi3TaO7 and V/N-TiO2, a stronger electronic interaction, i.e., built-in electric field, resulted in the construction of Z-scheme heterojunction, which was beneficial for faster photo-generated charge transfer, the generation of more active radicals, and the enhanced degradation of toxic pollutants.

ASSOCIATED CONTENT Supporting Information High-resolution XPS spectra of V 2p, N1s region, XPS survey spectra, SEM images of 10% B/VNT (element-sensitive mapping images), BET, UV−vis DRS, PL, time-resolved fluorescence decay, transient photocurrent response and ESI Nyquist plots of samples, XRD spectra of 10% B/VNT ACS Paragon Plus Environment 22

Page 23 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


heterojunction after photocatalysis, pseudo-first-order constants (kapp) of different photocatalysts, comparison of the photodegradation activity, and the results of surface area, kapp, and rate constant normalized with the surface areas (k’).

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected].

Tel/Fax: +86 25 89680259 (Q.X.).

*E-mail: [email protected] (W.Z.). Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support from the Major Science and Technology Program for Water Pollution Control and Treatment (2017ZX07204004), National Natural Science Foundation of China (Grant 21876078, 51878331, 21707066), Jiangsu Key R&D Plan (BE2017711) and the Scientific Research Foundation of Graduate School of Nanjing University (2018CW08).

REFERENCES (1) Kudo, A.; Miseki, Y. Heterogeneous Photocatalyst Materials for Water Splitting. Chem. Soc. Rev. 2009, 38, 253−278. (2) Rossiter, S. E.; Fletcher, M. H.; Wuest, W. M. Natural Products as Platforms To Overcome Antibiotic Resistance. Chem. Rev. 2017, 117, 12415−12474. (3) Li, T.; Chen, Y.; Wan, P.; Fan, M.; Yang, X. J. Chemical Degradation of Drinking Water Disinfection Byproducts by Millimeter-Sized Particles of Iron-Silicon and Magnesium-Aluminum Alloys. J. Am. Chem. Soc. 2010, 132, 2500−2501. ACS Paragon Plus Environment 23


Page 24 of 30

(4) Koch, C.; Dundua, A.; Aragon-Gomez, J.; Nachev, M.; Stephan, S.; Willach, S.; Ulbricht, M.; Schmitz, O. J.; Schmidt, T. C.; Sures, B. Degradation of Polymeric Brominated Flame Retardants: Development of an Analytical Approach Using PolyFR and UV Irradiation. Environ. Sci. Technol. 2016, 50, 12912−12920. (5) Ahmed, B.; Ojha, A. K.; Singh, A.; Hirsch, F.; Fischer, I.; Patrice, D.; Materny, A. Well-controlled in-situ growth of 2D WO3 rectangular sheets on reduced graphene oxide with strong photocatalytic and antibacterial properties. J. Hazard. Mater. 2018, 347, 266−278. (6) Leo, C. V. D.; Luk-Cyr, J.; Liu, H.; Loeffel, K.; Al-Athel, K.; Anand, L. A New Methodology for Characterizing Traction-Separation Relations for Interfacial Delamination of Thermal Barrier Coatings. Acta. Mater. 2014, 71, 306−318. (7) Lan, H.; He, W.; Wang, A.; Liu, R.; Liu, H.; Qu, J.; Huang, C. P. An Activated Carbon Fiber Cathode for the Degradation of Glyphosate in Aqueous Solutions by the Electro-Fenton Mode: Optimal Operational Conditions and the Deposition of Iron on Cathode on Electrode Reusability. Water. Res. 2016, 105, 575−582. (8) Huang, Y.; Liu, Y.; Lin, Y.; Mao, Y.; Ouyang, G.; Liu, H.; Zhang, S.; Tong, Y. Cerium-Based Hybrid Nanorods for Synergetic Photo-Thermocatalytic Degradation of Organic Pollutants. J. Mater. Chem. A 2018, 6, 24740−24747. (9) Wen, M.; Mori, K.; Kuwahara, Y.; An, T.; Yamashita, H. Design and Architecture of Metal Organic Frameworks for Visible Light Enhanced Hydrogen Production. Appl. Catal. B 2017, 218, 555−569. (10) Zhou, X.; Liu, N.; Schmuki, P. Photocatalysis with TiO2 Nanotubes: “Colorful” Reactivity and Designing Site-Specific Photocatalytic Centers into TiO2 Nanotubes. ACS Catal. 2017, 7, 3210−3235. (11) Li, W.; Elzatahry, A.; Aldhayan, D.; Zhao, D.Y. Core-shell Structured Titanium Dioxide Nanomaterials for Solar Energy Utilization. Chem. Soc. Rev. 2018, 47, 8203−8237.


Page 25 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12) Luo, B.; Xu, D.; Li, D.; Wu, G.; Wu, M.; Shi, W.; Chen, M. Fabrication of a Ag/Bi3TaO7 Plasmonic Photocatalyst with Enhanced Photocatalytic Activity for Degradation of Tetracycline. ACS Appl. Mater. Interfaces 2015, 7, 17061−17069. (13) Zhang, G; Li, M.; Yu, S.; Zhang, S.; Huang, B.; Yu, J. Synthesis of Nanometer-Size Bi3TaO7 and Its Visible-Light Photocatalytic Activity for the Degradation of a 4BS Dye. J. Colloid Interface Sci. 2010, 345, 467−473. (14) Struzik, M.; Liu, X.; Abrahams, I.; Krok, F.; Malys, M.; Dygas, J. R. Defect Structure and Electrical Conductivity in the Pseudo-Binary System Bi3TaO7-Bi3NbO7. Solid State Ionics 2012, 218, 25−30. (15) Luo, B.; Chen, M.; Zhang, Z.; Xu, J.; Li, D.; Xu, D.; Shi, W. Highly Efficient Visible-Light-Driven Photocatalytic Degradation of Tetracycline by a Z-Scheme g-C3N4/Bi3TaO7 Nanocomposite Photocatalyst. Dalton Trans. 2017, 46, 8431−8438. (16) Zhou, P.; Yu, J.; Jaroniec, M. All-Solid-State Z-Scheme Photocatalytic Systems. Adv. Mater. 2014, 26, 4920−4935. (17) Maeda, K. Z-Scheme Water Splitting Using Two Different Semiconductor Photocatalysts. ACS Catal. 2013, 3, 1486−1503. (18) Guo, H.; Niu, C.; Zhang, L.; Wen, X.; Liang, C.; Zhang, X.; Guan, D.; Tang, N.; Zeng, G. Construction of Direct Z-Scheme AgI/Bi2Sn2O7 Nanojunction System with Enhanced Photocatalytic Activity: Accelerated Interfacial Charge Transfer Induced Efficient Cr(VI) Reduction, Tetracycline Degradation and Escherichia coli Inactivation. ACS Sustainable Chem. Eng. 2018, 6, 8003−8018. (19) Wang, X.; Liu, G.; Chen, Z. G.; Li, F.; Wang, L.; Lu, G. Q.; Chen, H. M. Enhanced Photocatalytic Hydrogen Evolution by Prolonging the Lifetime of Carriers in ZnO/CdS Heterostructures. Chem. Commun. 2009, 23, 3452−3454.



Page 26 of 30

(20) Gordon, T. R.; Cargnello, M.; Paik, T.; Mangolini, F.; Weber, R. T.; Fornasiero, P.; Murray, C. B. Nonaqueous Synthesis of TiO2 Nanocrystals Using TiF4 to Engineer Morphology, Oxygen Vacancy Concentration, and Photocatalytic Activity. J. Am. Chem. Soc. 2012, 134, 6751−6761. (21) Zhu, C.; Chen, X.; Ma, J.; Gu, C.; Xian, Q.; Gong, T.; Sun, C. Carbon Nitride-Modified Defective TiO2-x@Carbon Spheres for Photocatalytic H2 Evolution and Pollutants Removal: Synergistic Effect and Mechanism Insight. J. Phys. Chem. C 2018, 122, 20444−20458. (22) Liu, Y.; Wu, J. Synergistically Catalytic Activities of BiFeO3/TiO2 Core-Shell Nanocomposites for Degradation of Organic Dye Molecule through Piezophototronic Effect. Nano Energy 2019, 56, 74−81. (23) Jiang, W.; Bai, S.; Wang, L.; Wang, X.; Yang, L.; Li, Y.; Liu, D.; Wang, X.; Li, Z.; Jiang, J.; Xiong, Y. Integration of Multiple Plasmonic and Co-Catalyst Nanostructures on TiO2 Nanosheets for Visible-Near-Infrared Photocatalytic Hydrogen Evolution. Small 2016, 12, 1640−1648. (24) Fujishima, A.; Zhang, X.; Tryk, D. A. TiO2 Photocatalysis and Related Surface Phenomena. Surf. Sci. Rep. 2008, 63, 515−582. (25) Wu, F.; Yu, Y.; Yang, H.; German, L.; Li, Z.; Chen, J.; Yang, W.; Huang, L.; Shi, W.; Wang, L.; Wang, X. Simultaneous Enhancement of Charge Separation and Hole Transportation in a TiO2-SrTiO3 Core-Shell Nanowire Photoelectrochemical System. Adv. Mater. 2017, 29, 1701432. (26) Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y. Visible-Light Photocatalysis in Nitrogen-Doped Titanium Oxides. Science 2001, 293, 269–271. (27) Valero, J. M.; Obregón, S.; Colón, G. Active Site Considerations on the Photocatalytic H2 Evolution Performance of Cu-Doped TiO2 Obtained by Different Doping Methods. ACS Catal. 2014, 4, 3320–3329. (28) Wang, D. H.; Jia, L.; Wu, X. L.; Lu, L. Q.; Xu, A. W. One-Step Hydrothermal Synthesis of N-Doped TiO2/C Nanocomposites with High Visible Light Photocatalytic Activity. Nanoscale 2012, 4, 576–584.


Page 27 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(29) Eswar, N. K.; Ramamurthy, P. C.; Madras, G. Novel Synergistic Photocatalytic Degradation of Antibiotics and Bacteria Using V-N Doped TiO2 under Visible Light: the State of Nitrogen in V-Doped TiO2. New J. Chem. 2016, 40, 3464–3475. (30) Wang, T.; Shen, D.; Xu, T.; Jiang, R. Photocatalytic Degradation Properties of V-Doped TiO2 to Automobile Exhaust. Sci. Total. Environ. 2017, 586, 347–354. (31) Nie, L.; Yu, J.; Li, X.; Cheng, B.; Liu, G.; Jaroniec, M. Enhanced Performance of NaOH-Modified Pt/TiO2 toward Room. Environ. Sci. Technol. 2013, 47, 2777–2783. (32) Li, W.; Wang, F.; Liu, Y.; Wang, J.; Yang, J.; Zhang, L.; Elzatahry, A. A.; Al-Dahyan, D.; Xia, Y.; Zhao, D. General Strategy to Synthesize Uniform Mesoporous TiO2/Graphene/Mesoporous TiO2 Sandwich-Like Nanosheets for Highly Reversible Lithium Storage. Nano Lett. 2015, 15, 2186–2193. (33) Liu, J.; Han, R.; Zhao, Y.; Wang, H.; Lu, W.; Yu, T.; Zhang, Y. Enhanced Photoactivity of V-N Codoped TiO2 Derived from a Two-Step Hydrothermal Procedure for the Degradation of PCP-Na under Visible Light Irradiation. J. Phys. Chem. C 2011, 115, 4507–4515. (34) Yamashita, H.; Mori, K.; Kuwahara, Y.; Kamegawa, T.; Wen, M.; Verma, P.; Che, M. Single-site and nano-confined photocatalysts designed in porous materials for environmental uses and solar fuels. Chem. Soc. Rev. 2018, 26, 8072–8096. (35) Liu, J.; Zheng, M.; Shi, X.; Zeng, H.; Xia, H. Amorphous FeOOH Quantum Dots Assembled Mesoporous Film Anchored on Graphene Nanosheets with Superior Electrochemical Performance for Supercapacitors. Adv. Funct. Mater. 2016, 26, 919–930. (36) Jin, Y.; Jiang, D.; Li, D.; Chen, M. Construction of Ultrafine TiO2 Nanoparticle and SnNb2O6 Nanosheet 0D/2D Heterojunctions with Abundant Interfaces and Significantly Improved Photocatalytic Activity. Catal. Sci. Technol. 2017, 7, 2308−2317. (37) Liu, G.; Yin, L. C.; Wang, J.; Niu, P.; Zhen, C.; Xie, Y.; Cheng, H, M. A Red Anatase TiO2 Photocatalyst for Solar Energy Conversion. Energy Environ. Sci. 2012, 5, 9603−9610.



Page 28 of 30

(38) Choudhury, B.; Choudhury, A.; Borah, D. Interplay of Dopants and Defects in Making Cu Doped TiO2 Nanoparticle a Ferromagnetic Semiconductor. J. Alloy. Compd. 2015, 646, 692−698. (39) Huang, Y.; Li, K.; Lin, Y.; Tong, Y.; Liu, H. Enhanced Efficiency of Electron-Hole Separation in Bi2O2CO3 for Photocatalysis via Acid Treatment. ChemCatChem 2018, 10, 1982−1987. (40) Rosseler, O.; Shankar, M. V.; Du, M. K. L.; Schmidlin, L.; Keller, N.; Keller, V. Solar Light Photocatalytic Hydrogen Production from Water over Pt and Au/TiO2 (Anatase/Rutile) Photocatalysts: Influence of Noble Metal and Porogen Promotion. J. Catal. 2010, 269, 179−190. (41) Zhong, J.; Xu, J.; Wang, Q. Nitrogen and Vanadium Co-Doped TiO2 Mesosponge Layers for Enhancement in Visible Photocatalytic Activity, Appl. Surf. Sci. 2014, 315, 131−137. (42) Huang, Y.; Xu, H.; Yang, H.; Liu, Y.; Lin, Y. Efficient Charges Separation Using Advanced BiOI-Based Hollow Spheres Decorated with Palladium and Manganese Dioxide Nanoparticles, ACS Sustainable Chem. Eng. 2018, 6, 2751−2757. (43) Watanabe, T.; Takizawa, T.; Honda, K. Photocatalysis through Excitation of Adsorbates. 2. A Comparative Study of Rhodamine B and Methylene Blue on Cadmium Sulfide. J. Phys. Chem. 1977, 81, 1845−1851. (44) Su, K.; Ai, Z.; Zhang, L. Efficient Visible Light-Driven Photocatalytic Degradation of Pentachlorophenol with Bi2O3/TiO2−xBx. J. Phys. Chem. C 2012, 116, 17118−17123. (45) Zhang, G.; Guan, W.; Shen, H.; Zhang, X.; Fan, W.; Lu, C.; Bai, H.; Xiao, L.; Gu, W.; Shi, W. Organic Additives-Free Hydrothermal Synthesis and Visible-Light-Driven Photodegradation of Tetracycline of WO3 Nanosheets. Ind. Eng. Chem. Res. 2014, 53, 5443−5450. (46) Lilienthal, H.; Verwer, C. M.; van der Ven, L. T. M.; Piersma, A. H.; Vos, J. G. Exposure to Tetrabromobisphenol A (TBBPA) in Wistar Rats: Neurobehavioral Effects in Offspring from a One-Generation Reproduction Study. Toxicology 2008, 246, 45−54.


Page 29 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(47) Ji, H.; Chang, F.; Hu, X.; Qin, W.; Shen, J. Photocatalytic Degradation of 2,4,6-Trichlorophenol over g-C3N4 under Visible Light Irradiation. Chem. Eng. J. 2013, 218, 183−190. (48) Ding, S.; Mao, D.; Yang, S.; Wang, F.; Meng, L.; Han, M.; He, H.; Sun, C.; Xu, B. Graphene-Analogue h-BN Coupled Bi-Rich Bi4O5Br2 Layered Microspheres for Enhanced Visible-Light Photocatalytic Activity and Mechanism Insight. Appl. Catal. B 2017, 210, 386−399. (49) Yu, K.; Yang, S.; He, H.; Sun, C.; Gu, C.; Ju, Y. Visible Light-Driven Photocatalytic Degradation of Rhodamine B over NaBiO3: Pathways and Mechanism. J. Phys. Chem. A 2009, 113, 10024−10032. (50) Zhu, X.; Wang, Y.; Sun, R.; Zhou, D. Photocatalytic Degradation of Tetracycline in Aqueous Solution by Nanosized TiO2. Chemosphere 2013, 92, 925−932. (51) Zou, W.; Shao, Y.; Pu, Y.; Luo, Y.; Sun, J.; Ma, K.; Tang, C.; Gao, F.; Dong, L. Enhanced visible light photocatalytic hydrogen evolution via cubic CeO2 hybridized g-C3N4 composite. Appl. Catal. B 2017, 218, 51−59. (52) Zhu, M.; Sun, Z.; Fujitsuka, M.; Majima, T. Z-Scheme Photocatalytic Water Splitting on a 2D Heterostructure of Black Phosphorus/Bismuth Vanadate Using Visible Light. Angew. Chem. Int. Ed. 2018, 57, 2160−2164. (53) Zhao, X.; Feng, J.; Liu, J.; Lu, J.; Shi, W.; Yang, G.; Wang, G.; Feng, P.; Cheng, P. Metal-Organic

Framework-Derived

ZnO/ZnS

Heteronanostructures

for

Effcient

Visible-Light-Driven Photocatalytic Hydrogen Production. Adv. Sci. 2018, 5, 1700590. (54) Lv, T.; Li, D.; Hong, Y.; Luo, B.; Xu, D.; Chen, M.; Shi, W. Facile Synthesis of CdS/Bi4V2O11 Photocatalysts with Enhanced Visible-Light Photocatalytic Activity for Degradation of Organic Pollutants in Water. Dalton Trans. 2017, 46, 12675−12682.



Graphic


Page 30 of 30

Ultrafine Bi3TaO7 Nanodot-Decorated V, N Codoped TiO2

Recommend Documents