BiOI Immobilized on Flexible Electrospun

Subscriber access provided by RMIT University Library

Article 3

4

Heterojunction of g-CN/BiOI Immobilized on Flexible Electrospun Polyacrylonitrile Nanofibers: Facile Preparation and Enhanced Visible Photocatalytic Activity for Floating Photocatalysis Xuejiao Zhou, Changlu Shao, Shu Yang, Xiaowei Li, Xiaohui Guo, Xiaoxiao Wang, Xinghua Li, and Yichun Liu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03760 • Publication Date (Web): 21 Dec 2017 Downloaded from http://pubs.acs.org on December 23, 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 Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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

ACS Sustainable Chemistry & Engineering

Heterojunction of g-C3N4/BiOI Immobilized on Flexible Electrospun

Polyacrylonitrile

Nanofibers:

Facile

Preparation and Enhanced Visible Photocatalytic Activity for Floating Photocatalysis

Xuejiao Zhou, Changlu Shao*, Shu Yang, Xiaowei Li, Xiaohui Guo, Xiaoxiao Wang, Xinghua Li*, Yichun Liu

Center for Advanced Optoelectronic Functional Materials Research, Key Laboratory of UV-Emitting Materials and Technology (Northeast Normal University), Ministry of Education, 5268 Renmin Street, Changchun 130024, People’s Republic of China

*Corresponding author: Email: [email protected]; Tel. 8643185098803. Email: [email protected]; Tel. 8643185098803.

1

ACS Paragon Plus Environment

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

Page 2 of 33

ABSTRACT: The heterojunction of g-C3N4/BiOI was uniformly immobilized on electrospun polyacrylonitrile (PAN) nanofibers via a facile in situ synthesis at room temperature. X-ray photoelectron spectra showed that both the C and N 1s peaks of PAN/g-C3N4/BiOI nanofibers shifted to higher binding energies than that of PAN/g-C3N4 nanofibers suggesting electron transfer from g-C3N4 to BiOI during the formation of heterojunctions. The enhanced photocurrent densities and significant decrease in photoluminescence intensity confirmed the effective charge separation at the heterojunction interfaces in PAN/g-C3N4/BiOI nanofibers. The efficient separation of the electron-hole pairs and their strong absorption in the visible region results in superior photocatalytic activities in the degradation of RhB dyes and toxic Cr (VI) ions under visible-light irradiation versus PAN/g-C3N4 and PAN/BiOI nanofibers. Moreover,

the

film-like

PAN/g-C3N4/BiOI

nanofibers

have

ultra-long

one-dimensional nanostructures and flexible self-supporting structures that can be used as useful floating photocatalysts. They can float easily on the liquid and are directly reused without separation during the photocatalytic reaction. These results demonstrate that flexible PAN/g-C3N4/BiOI nanofibers with high photocatalytic activity and excellent reusability have potential in wastewater treatment.

KEYWORDS: Electrospun nanofibers, Flexibility, g-C3N4/BiOI heterojunction, In situ synthesis, Visible photocatalytic activity

2


Page 3 of 33 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 Semiconductor-based photocatalysis technologies in the arena of environmental remediation and solar energy conversion have been extensively studied.1 Graphite carbon nitride (g-C3N4) is a new metal-free semiconductor photocatalyst that has recently been widely applied in the degradation of dye pollutants, the removal of toxic heavy metal ions, and the photocatalysis for hydrogen evolution during water splitting.2 It offers a suitable electronic structure (2.7 eV), high thermal and chemical stability, low cost, and excellent optical and photoelectrochemical properties.3 However, the photocatalytic activity of pure g-C3N4 is limited by the high recombination rate and low charge mobility rate of the photogenerated electron-hole pairs.4 Thus, many efforts have been made to reduce the recombination of photogenerated electron-hole pairs during photocatalytic reactions by constructing heterojunctions between g-C3N4 and another semiconductor with a suitable band potential including metallic oxide (TiO2, ZnO), metal sulfide (CdS, MoS2) or oxyhalide (BiOCl, BiOBr, BiOI), etc.5-10 Of these semiconductors, bismuth oxyiodide (BiOI) with the well matched band potentials, unique layered structure, and the stronger photoresponse in visible-light region (the band gap ~ 1.8 eV) is one of the most suitable semiconductors to form the heterojunction

with

g-C3N4.9

The

heterojunction

of

g-C3N4/BiOI

enables

photo-induced electrons from g-C3N4 to quickly transfer to the more positive conduction band (CB) of BiOI due to their strong internal electric field.11 This can induce effective separation of photo-generated electron-hole pairs to achieve high 3



Page 4 of 33

photocatalytic activity. Recently, many kinds of g-C3N4/BiOI heterojunctions and their nanostructures have been prepared and investigated because nanostructured photocatalysts with higher quantum yield and specific surface areas can improve the photocatalytic efficiency better than bulk material.9,12 However, nanostructured heterojunctions of g-C3N4/BiOI have poor dispersion in water and easily aggregate due to their higher surface energy.13,14 This leads to a remarkable reduction in their photocatalytic activities. Nanostructured heterojunctions of g-C3N4/BiOI also suffer some drawbacks as photocatalysts especially in the separation and recycling of the suspended small-sized nanoparticles. This may not satisfy large-scale practical applications. To solve these problems, the immobilization of nanostructured heterojunctions of g-C3N4/BiOI on an appropriate support might be a promising approach. Until now, different dimensional nanostructured materials have been used as supports

for

photocatalysts

such

as

zero-dimensional

nanoparticles

and

two-dimension nanofilms.15,16 However, the nanoparticle supports with a nanoscale size are easily lost during photocatalytic reaction and separation.17 This may cause secondary pollution. On the other hand, using two-dimensional nano-films as supports may dramatically reduce the interfacial contact between photocatalysts and pollutants due to their lower specific surface area.14,18 This also decreases photocatalytic performance. In contrast, one-dimensional nanofibers with a high surface area and high length-diameter ratios have high potential in overcoming these problems.19,20 In 4


Page 5 of 33 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


particular, electrospun polyacrylonitrile (PAN) nanofibers with an ultra-long one-dimensional nanostructure and good flexibility are a promising support for immobilizing the nanostructured heterojunctions of g-C3N4/BiOI. The PAN nanofibers have several advantages as a support: (1) the flexible PAN-based nanofibers have an open three-dimensional macroscopic structure and excellent hydrophobicity. This can minimize agglomeration and improve separation of the nanostructured heterojunctions of g-C3N4/BiOI in water for practical applications; (2) The PAN-based nanofibers have a higher special surface area than nanofilms. This improves the exposed active sites of the nanostructured photocatalysts and further enhances the activity in photocatalytic reactions; (3) more importantly, PAN-based nanofibers with a lower density makes them easily float on a liquid exposing them to light. This improves the irradiation efficiency of the light and maximizes their photocatalytic properties. However, there are no reports describing the immobilization of nanostructured heterojunctions of g-C3N4/BiOI on one-dimensional nanofibers. Based on the above consideration, heterojunctions of g-C3N4/BiOI were uniformly immobilized on the supports of electrospun PAN nanofibers via a soft and facile in situ synthesis. First, the PAN/g-C3N4/Bi(NO3)3 nanofibers were prepared by electrospinning a precursor that contained PAN, g-C3N4, and Bi(NO3)3. Thereafter, the PAN/g-C3N4/Bi(NO3)3 nanofibers were bathed in an aqueous solution of potassium iodide at room temperature for in situ synthesis of BiOI on the composite nanofibers. The PAN/g-C3N4/BiOI nanofibers were well characterized with strong interactions in the heterojunction via possible chemical bonding between BiOI and g-C3N4. The 5



PAN/g-C3N4/BiOI nanofibers had a markedly enhanced photocatalytic performance via the degradation of dye pollutants (RhB) and toxic heavy metal ions (Cr Ⅵ) via visible-light irradiation. The in situ synthesis of the heterojunction promoted the transfer of photo-induced electrons in the photocatalytic reaction. These results offer a novel and rational method for the immobilization of nanoscale photocatalysts on flexible supports. The obtained self-supporting photocatalysts could float easily and do not require separation for reuse in water purification and energy conversion.

EXPERIMENTAL SECTION Synthesis of the PAN/C3N4/Bi(NO3)3 nanofibers. All reagents were purchased from Beijing Chemicals (Beijing, China) and used without further purification. First, the g-C3N4 powder was prepared according to the literature.21 Next, 2.5 mmol of g-C3N4 powder was dissolved in 11 mL of N, N- dimethylformamide (DMF) and then further exfoliated by ultrasonic treatment for 1 h followed by 2.5 mmol of Bi(NO3)3·5H2O and 1.2 g of polyacrylonitrile (PAN) powders. After magnetic agitation for 48 h, the homogeneous precursor solution of PAN, g-C3N4, Bi(NO3)3 and DMF was obtained for electrospinning. A voltage of ~ 10 kV and a distance of ~ 16 cm were applied between the syringe tip and the counter electrode that was covered by aluminum foil. The nitrate-free PAN/g-C3N4 nanofibers were similarly prepared. Synthesis of the PAN/g-C3N4/BiOI nanofibers. PAN/g-C3N4/Bi(NO3)3 nanofibers (10 mg) were dipped into 100 mL KI aqueous solution (0.3 mM) for 10 min in Scheme 1. The color of the PAN/g-C3N4/Bi(NO3)3 nanofibers changed from white to 6


Page 6 of 33

Page 7 of 33 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


yellow indicating that the BiOI nanostructures were immobilized in situ on the PAN/g-C3N4 nanofibers. The obtained PAN/g-C3N4/BiOI nanofibers were washed with distilled water three times and dried at 60 °C for 8 h. The PAN/BiOI nanofibers were obtained by dipping PAN/Bi(NO3)3 nanofibers into aqueous KI. Detailed characterization of the products is found in the supporting information.

RESULTS AND DISCUSSION Morphology and structures analyses. The surface morphologies of the as-prepared samples were studied with scanning electron microscopy (SEM). The PAN/g-C3N4 nanofibers exhibit ultra-long one-dimensional nanostructures without severe agglomeration (Figure 1A). This is because the bulk g-C3N4 can be exfoliated into smaller nanostructures (~ 160 nm) through the ultrasonic exfoliation in precursors (Figure S1). The surface of the PAN/g-C3N4/Bi(NO3)3 nanofibers does not significantly change compared to the PAN/g-C3N4 nanofibers indicating that Bi ions can be uniformly dispersed in PAN/g-C3N4/Bi(NO3)3 nanofibers (Figure S2). After impregnation in the aqueous KI, the clear lamellar nanostructures were broadly dispersed on the PAN/g-C3N4/BiOI nanofibers (Figure 1C). Similar lamellar nanostructures were also observed on PAN/BiOI nanofibers by impregnating the PAN/Bi(NO3)3 nanofibers into aqueous KI (Figure 1E). Meanwhile, the surface color of the PAN/g-C3N4/BiOI and PAN/BiOI nanofibers both changed to yellow (inset of Figure 1C and E) versus the white PAN/g-C3N4 nanofibers (Figure 1A inset). This is attributed to the loading of BiOI nanostructures on the nanofibers. Notably, all these 7



PAN-based composite nanofibers still exhibited high flexibility and macroscopic film-like structures. This may help design a new floating photocatalyst that does not need to be separated from wastewater during photocatalysis. In addition, energy dispersive X-ray (EDX) analysis showed that C, N, and O all existed in all the PAN-based composite nanofibers (Figure 1B, D and F). The Bi and I elements were only seen in PAN/g-C3N4/BiOI (Figure 1D) and PAN/BiOI nanofibers (Figure 1F). This further indicated that the BiOI nanostructures were immobilized in situ on PAN/g-C3N4 or PAN nanofibers at room temperature. A cross-sectional transmission electron microscopy (TEM) image was used to further study the microstructure of PAN/g-C3N4/BiOI nanofibers. The g-C3N4 nanostructures partially exposed in the nanofibers can be seen on their surface (Figure 2A). And, the small dark spots/sheets are easily seen in/on the PAN/g-C3N4/BiOI nanofiber. This indicates the uniform dispersion of BiOI nanostructures immobilized on the nanofiber. A high-resolution transmission electron microscopy (HRTEM) image of PAN/g-C3N4/BiOI nanofibers was obtained from the area marked with a rectangle in Figure 2A—this displays clear lattice fringes with a stacking distance of 0.325 nm (Figure 2B). This corresponds to the (0 0 2) lattice spacing of g-C3N4.22 The clear lattice fringes have a lattice spacing of 0.28 nm—this matched the spacing of the (1 1 0) crystal planes of tetragonal BiOI nanostructures.9 Moreover, the fast Fourier transform (FFT) pattern shows strong reflections associated with (1 1 0) planes demonstrating that the BiOI nanostructures are stacked along the (1 1 0) direction enforced by Van der Waals interactions (Figure 2B inset).23 These observations imply 8


Page 8 of 33

Page 9 of 33 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


that the g-C3N4 and BiOI nanostructures are present in the PAN/g-C3N4/BiOI nanofibers to form the g-C3N4/BiOI heterojunctions. The scanning TEM (STEM) and elemental mapping images of a representative individual PAN/g-C3N4/BiOI nanofiber contained in g-C3N4 are shown in Figure 2C-H. The Bi, O, and I elements derived from the BiOI nanostructures are well distributed on the selection area of PAN/g-C3N4/BiOI nanofibers. This further suggests that the BiOI samples with the smaller nanostructures could be easily immobilized on the PAN/g-C3N4/BiOI nanofibers. This was beneficial for the formation of uniform heterojunctions of g-C3N4/BiOI. The X-ray diffraction (XRD) patterns of pure g-C3N4 powders, PAN/g-C3N4 nanofibers, PAN/g-C3N4/BiOI nanofibers, and PAN/BiOI nanofibers are shown in Figure S3. The g-C3N4 powders have two characteristic peaks near 13.2° and 27.4°, corresponding to the periodic array of the in-plane tri-s-triazine and the interplanar stacking of aromatic systems.24,25 These are perfectly indexed as the (1 0 0) and (0 0 2) diffraction planes of the graphite-like g-C3N4, respectively.26 However, characteristic diffraction peaks of g-C3N4 were not observed in PAN/g-C3N4 or PAN/g-C3N4/BiOI nanofibers—probably due to the relatively low content of g-C3N4 in the these nanofibers. After impregnation in the KI aqueous solution, there were sharp diffraction peaks for BiOI nanostructures. This clearly illustrates the good crystallinity of the PAN/g-C3N4/BiOI and PAN/BiOI nanofibers, respectively. The diffraction peaks of the BiOI nanostructures in PAN/g-C3N4/BiOI or PAN/BiOI nanofibers are perfectly indexed as tetragonal BiOI (JCPDS No. 73-2062).11 9



Page 10 of 33

The characteristic signal peaks of the Fourier transform infrared (FTIR) spectrum are the most direct and effective evidence to confirm the presence of g-C3N4 in PAN/g-C3N4/BiOI nanofibers. The PAN/g-C3N4 and PAN/g-C3N4/BiOI nanofibers show typical stretching vibration modes for the CN heterocycles from the g-C3N4: 1319, 1567, and 1638 cm-1 (Figure 3A).27 The characteristic peaks at 809 cm-1 belong to the stretching vibration mode of the s-triazine ring unit derived from the g-C3N4.28 The characteristic absorption peaks at 2246, 1453, 1235, and 1736 cm-1 in all samples originated from the PAN supports—these were attributed to the vibrations of the cyano

groups,

carbon-hydrogen,

carbon-carbon,

and

carbon-oxygen

bonds,

respectively.14 The prominent peak at 539 cm-1 was attributed to the Bi-O stretching mode in the PAN/BiOI nanofibers.29 Notably, the characteristic peak derived from vibration of Bi-O bond in the PAN/g-C3N4/BiOI nanofibers was shifted to a larger wavenumber (Figure 3B). This probably derives from the structural distortion of the [Bi2O2]2+ slabs in the PAN/g-C3N4/BiOI nanofibers.9,29 These results suggest that an interfacial interaction between the g-C3N4 and BiOI might exist in the PAN/g-C3N4/BiOI nanofibers. This would enhance the photcatalytic activity. XPS analysis of the samples. The bonding configuration and chemical composition of the as-fabricated samples were further analyzed by X-ray photoelectron spectroscopy (XPS). Figure 4A shows the scanned XPS spectra of PAN/g-C3N4, PAN/g-C3N4/BiOI, and PAN/BiOI nanofibers. Versus pure PAN/g-C3N4 nanofibers, some new peaks derived from Bi and I elements were seen in PAN/g-C3N4/BiOI and PAN/BiOI nanofibers. This further demonstrates that the BiOI 10


Page 11 of 33 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


nanostructures exist in PAN/g-C3N4/BiOI and PAN/BiOI nanofibers. The binding energy of the C 1s peak at 284.6 eV is usually used to calibrate calibration the XPS measurements.30 The high-resolution XPS spectra of C and N 1s are presented in Figure 4B and C, respectively. The peaks at 287.6 eV and 397.6 eV were both attributed to the cyano group derived from the PAN supports.31,32 The typical binding energies of g-C3N4 are clearly seen at 288.6, 398.9, 400.4, and 401.8 eV for the PAN/g-C3N4 nanofibers. These correspond to the N-C=N, C=N-C, C-NHx, and N-(C)3 groups, respectively.21,27 However, the typical peaks of g-C3N4 noted above for PAN/g-C3N4/BiOI nanofibers obviously shifted to higher binding energies of 289.6, 399.1, 400.7, and 402.6 eV after the BiOI nanostructures are loaded. In addition, the XPS spectra of Bi 4f, I 3d, and O 1s for PAN/g-C3N4/BiOI and PAN/BiOI nanofibers were also given in Figure 4D-F, respectively. The splitting between Bi 4f7/2 and Bi 4f5/2 are both 5.3 eV for PAN/g-C3N4/BiOI and PAN/BiOI nanofibers.23 This suggests the normal state of Bi3+ in PAN/g-C3N4/BiOI and PAN/BiOI nanofibers (Figure 4D). The binding energies of Bi 4f, I 3d, and O 1s peak for PAN/g-C3N4/BiOI nanofibers all shift to lower binding energies versus PAN/BiOI nanofibers. Some previous studies have suggested that the internal electrical field could strongly affect the local binding energy of the g-C3N4 and BiOI in the heterojunction.11,29,33 The FT-IR data indicate strong interactions between g-C3N4 and BiOI molecules. Thus, when they are contact with each other and form heterojunctions, the electrons could transfer from g-C3N4 to BiOI because the Fermi 11



Page 12 of 33

level of g-C3N4 is higher than BiOI.34 The transfer and depletion of surface electrons from g-C3N4 will form a positive charge region on the g-C3N4. This will increase the binding energy of C and N during XPS testing. On the contrary, the negative charge region on BiOI will simultaneously reduce the binding energy of Bi, I, and O. This will lower their binding energies. Hence, the shifts of the binding energies for the heterojuction suggest that there is an effective charge transfer at the heterojunction interface. This might make charge separation easier during photocatalysis. Photocatalytic performance. The optical properties of PAN/g-C3N4, PAN/BiOI, and PAN/g-C3N4/BiOI nanofibers were seen in UV-vis diffuse reflectance spectroscopy (DRS) analysis. The PAN/g-C3N4 and PAN/BiOI nanofibers exhibit an absorption edge at ∼ 450 nm and 630 nm in the visible-light range, respectively (Figure S5). The band gap energies of PAN/g-C3N4 and PAN/BiOI nanofibers are described by the following equation35-37:

αhν = A(hν - Eg)n/2

(1)

where α, h, A, Eg are the absorption coefficient, photon energy, a constant and the band gap of semiconductor, respectively. The value of n depends on the characteristics of the transition in the semiconductor (g-C3N4 n=1; BiOI n=4). As shown in Figure S6, the band gap energies of g-C3N4 and BiOI are 2.7 and 1.94 eV, respectively. Of note, the optical absorption intensity of PAN/g-C3N4/BiOI nanofibers is higher than that of PAN/g-C3N4 and PAN/BiOI nanofibers. This might be due to the overlapping absorption characteristics of the heterojunction. The photocatalytic activity of the prepared samples was evaluated via degradation 12


Page 13 of 33 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


of RhB as a model pollutant in an aqueous solution under visible light. The UV-vis absorption spectra in Figure 5A indicate that all samples could reach saturated adsorption equilibrium within 30 minutes in the dark. Under visible-light, the self-degradation of RhB dye could be neglected.28 The degradation efficiency of RhB could reach 98.0, 68.7, and 42.0 % after irradiation for 90 min in the presence of PAN/g-C3N4/BiOI, PAN/BiOI and PAN/g-C3N4 nanofibers, respectively. The PAN/g-C3N4/BiOI nanofibers exhibit higher photocatalytic activity than PAN/BiOI or PAN/g-C3N4 nanofibers. To further determine the heterojunction effects in PAN/g-C3N4/BiOI nanofibers, a physical mixture of g-C3N4 powder and BiOI nanostructures was studied as a control. The corresponding mass of g-C3N4 and BiOI exist in PAN/g-C3N4/BiOI nanofibers was calculated via thermogravimetric analysis in the Supporting Information (Figure S4). As expected, the efficiency of RhB degradation over the PAN/g-C3N4/BiOI nanofibers (98.0 %) was also significantly enhanced relative to a physical mixture (76.9 %) of g-C3N4 powder and BiOI nanostructures. Versus the suspended powders in the physical mixture, the effective separation of electron-hole pairs at the heterojunction interface between g-C3N4 and BiOI in PAN/g-C3N4/BiOI nanofibers can enhance the photocatalytic activity. The apparent first-order rate constant of the photocatalytic reaction can evaluate the degradation rate of the photocatalyst as follows: ln(C0/C) = Kapp t.38,39

(2)

Here, Kapp is the apparent first-order rate constant (min-1), and C0 is the initial concentration (mg/L) of RhB. Terms C (mg/L) and t (min) are the concentration of 13



Page 14 of 33

RhB and the corresponding visible light irradiation time, respectively. Figure 5B shows that the apparent first-order rate constant of PAN/g-C3N4, PAN/g-C3N4/BiOI, and PAN/BiOI nanofibers for decomposing RhB under visible-light were 0.0043, 0.0399

and

0.0140 min-1,

respectively.

The

first-order rate

constant of

PAN/g-C3N4/BiOI nanofibers was 9.3-fold higher than PAN/g-C3N4 nanofibers and about 2.8 times of the PAN/BiOI nanofibers, respectively. These results indicate that the PAN/g-C3N4/BiOI nanofibers had better photocatalytic activity in the degradation of RhB. Thus, we conclude that the formation of a high-efficiency heterojunction in PAN/g-C3N4/BiOI nanofibers plays a key role in enhancing the interfacial charge transfer. Radical trapping was designed to study the contributory active species in the photocatalysis reaction (Figure 5C). The details of trapping experiments and the possible mechanism of the decomposing RhB were evaluated in Supporting Information. The results showed that the degradation of RhB is mainly driven by the participation of h+ radicals (Figure 5D). These h+ rapidly transfer to the g-C3N4 and directly react with adsorbed RhB dye to produce final degradation products. Thus, the effective

charge

separation

in

PAN/g-C3N4/BiOI

nanofibers

enhances

the

photocatalytic activities. Photoluminescence (PL) spectroscopy and photocurrent measurements are tools to study photoinduced interfacial charge transfer processes in PAN/g-C3N4/BiOI nanofibers. Figure 5E shows the photocurrent measurements for PAN/g-C3N4/BiOI, PAN/BiOI, and PAN/g-C3N4 nanofibers. The photocurrent intensity of the 14


Page 15 of 33 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


PAN/g-C3N4/BiOI nanofibers was significantly higher than that of PAN/g-C3N4 and PAN/BiOI nanofibers. This demonstrates that a more effective separation of photo-induced electron-hole pairs and faster interfacial charge transfer occurs on the heterojunction of PAN/g-C3N4/BiOI nanofibers. In addition, PL spectroscopy shows that the emission peak intensity of PAN/g-C3N4/BiOI nanofibers significantly decreased relative to PAN/g-C3N4 nanofibers (Figure 5F). This further suggests that the recombination of photo-induced electron-hole pairs was greatly inhibited by the interfacial charge transfer between g-C3N4 and BiOI nanostructures. Hence, the effective charge separation at the heterojunction interface on PAN/g-C3N4/BiOI nanofibers underlies their higher photocatalytic activity relative to PAN/g-C3N4 and PAN/BiOI nanofibers. Cr (VI) is toxic and is found in industrial wastewater. It is a serious threat to human health and is a model to evaluate the ability of the photocatalyst to transfer electrons. Thus, the photocatalytic activities and stability of our photocatalysts were also evaluated by reducing Cr (VI) ions converted into low-toxic Cr (III) in aqueous solution under visible-light irradiation. The self-oxidation of the K2Cr2O7 aqueous solution as well as the Cr (VI) adsorbed on the surface of the photocatalyst can be neglected in Figure 6A. The efficiency of Cr (VI) removal for PAN/g-C3N4, PAN/BiOI nanofibers, and PAN/g-C3N4/BiOI nanofibers were 24.6, 58.5 and 98.5 % at 150 min under visible-light irradiation, respectively. The UV-vis absorption spectra of Cr (VI) over PAN/g-C3N4/BiOI nanofibers show that the intensity of the primary peak at 540 nm decreased with increasing irradiation 15



Page 16 of 33

time (Figure S7). After only 150 min, the Cr (VI) had been completely reduced in an aqueous solution of K2Cr2O7. Moreover, kinetic analysis of photocatalytic reduction of Cr (VI) offers a better comparison on their photocatalytic activities (Figure 6B). The first-order rate constant of PAN/g-C3N4/BiOI nanofibers in the reduction of Cr (VI) was 0.0261 min−1. This was 15.4-fold higher than PAN/g-C3N4 nanofibers (0.0017 min-1) and 5.1 times that of the PAN/BiOI nanofibers (0.0051 min-1). Obviously, the PAN/g-C3N4/BiOI nanofibers exhibit higher photocatalytic activity for removing Cr (VI) than PAN/g-C3N4 and PAN/BiOI nanofibers. This indicates that the formation of heterojunctions on g-C3N4/BiOI on PAN nanofibers was crucial to their enhanced photocatalytic performance. Furthermore, the efficiency of Cr (VI) removal by PAN/g-C3N4/BiOI nanofibers was significantly enhanced relative to a purely physical mixture of g-C3N4 powder and BiOI nanostructures (64.4%). Versus the suspended powders in a physical mixture, the effective separation of electron-hole pairs at the heterojunction interface between g-C3N4 and BiOI in PAN/g-C3N4/BiOI nanofibers might results in obviously enhanced

photocatalytic

activity.

More

importantly,

the

heterojunction

of

g-C3N4/BiOI immobilized on the PAN nanofibers not only overcomes the unfavorable aggregation, but also avoids the loss of powder during photocatalysis. These results were consistent with the conclusions of the degradation of RhB and further indicate that PAN/g-C3N4/BiOI nanofibers have excellent photocatalytic properties in the degradation of RhB and the removal of Cr (VI) ions. Furthermore, discussions of the mechanism for the enhanced photocatalytic reduction of Cr (VI) by PAN/g-C3N4/BiOI 16


Page 17 of 33 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


nanofibers were shown in Supporting Information (Figure S8). Recyclability of PAN/g-C3N4/BiOI nanofibers. We also studied the stability of the photocatalytic activity over multiple recycling experiments. They could float on the surface of the solution to overcome challenges with subsidence and can maximize the absorption of visible light during photocatalysis (Figure 6C). After the photocatalytic reaction, the PAN/g-C3N4/BiOI nanofibers could be removed directly from the liquid for the next cycle. The PAN/g-C3N4/BiOI nanofibers have no obvious decrease in photocatalytic activity during recycling (Figure 6D). And, there was no appreciable change in their overall morphologies and constructions via SEM and XRD analysis of the PAN/g-C3N4/BiOI nanofibers after the photocatalytic reaction (Figure S9). Versus the powdery photocatalysts, the excellent stability of the PAN/g-C3N4/BiOI nanofibers is mainly attributed to their flexible self-supporting network structure, which benefits their reuse and overcomes challenges in agglomeration, subsidence, and loss during photocatalytic reactions.

CONCLUSIONS In summary, the heterojunction of g-C3N4/BiOI was successfully immobilized in situ on electrospun PAN nanofibers via a facile impregnation method at room temperature. The PAN/g-C3N4/BiOI nanofibers markedly enhance the photocatalytic activities during degradation of RhB dye and removal of toxic Cr (VI) ions under visible light irradiation compared to PAN/g-C3N4 and PAN/BiOI nanofibers. These improved photoactivities are attributed to effective charge transfer across the 17



heterojunction interface as evidenced by the increased photocurrent densities and the significant decrease in PL intensity studies combined with XPS and FTIR analysis. The PAN/g-C3N4/BiOI nanofibers have macroscopic network structures and flexible self-supporting structures that allowed them to easily float on the liquid and maximize the absorption of visible light for photocatalysis. Notably, these flexible floating photocatalysts can be directly reuse, i.e., without separation from the wastewater. This facilitates high efficiency utilization and industrialization. This work offers new insights into the design and fabrication of flexible self-supporting photocatalysts based on g-C3N4-based heterojunctions with high efficiency and practical performance.

ASSOCIATED CONTENT Supporting Information. Characterization, photocatalytic and photocurrent measurements, trapping experiments: measurements, discussion of the photocatalytic mechanisms, SEM images of bulk g-C3N4 powders and PAN/g-C3N4/Bi(NO3)3 nanofibers, XRD patterns, UV-vis diffuse reflection spectra, TG curves, BET nitrogen adsorption/desorption isotherms, and EDX analysis of as-prepared samples.

ACKNOWLEDGMENTS The authors sincerely acknowledge Dr. Hancheng Zhu for supporting on the characterization of samples. The present work is supported financially by the National Natural Science Foundation of China (No. 51572045, 51272041, 61201107, 18


Page 18 of 33

Page 19 of 33 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


11604044, and 91233204), the National Basic Research Program of China (973 Program) (No. 2012CB933703), the 111 Project (No. B13013), the Natural Science Foundation of Jilin Province of China (20160101313JC), the Fundamental Research Funds for the Central Universities (2412017FZ009, 2412017QD007, 2412016KJ017), the China Postdoctoral Science Foundation (No. 2017M610188).

19



Page 20 of 33

REFERENCES (1) Ong, W.; Tan, L.; Ng, Y.; Yong, S.; Chai, S. Graphitic carbon nitride (g-C3N4)-based photocatalysts for artificial photosynthesis and environmental remediation: are we a step closer to achieving sustainability. Chem. Rev. 2016, 116 (12), 7159. DOI: 10.1021/acs.chemrev.6b00075 (2) Bian, J.; Li, Q.; Huang, C.; Li, J.; Guo, Y.; Zaw, M.; Zhang, R. Thermal vapor condensation of uniform graphitic carbon nitride films with remarkable photocurrent density for photoelectrochemical

applications.

Nano

Energy

2015,

15,

353.

DOI:

10.1016/j.nanoen.2015.04.012 (3) Wang, J.; Tang, L.; Zeng, G.; Liu, Y.; Zhou, Y.; Deng, Y.; Wang, J.; Peng, B. Plasmonic Bi metal deposition and g-C3N4 coating on Bi2WO6 microspheres for efficient visible-light photocatalysis.

ACS

Sustain.

Chem.

Eng.

2017,

5

(1),

1062.

DOI:

10.1021/acssuschemeng.6b02351 (4) Ma, L.; Fan, H.; Fu, K.; Lei, S.; Hu, Q.; Huang, H.; He, G. Protonation of graphitic carbon nitride (g-C3N4) for an electrostatically self-assembling carbon@g-C3N4 core-shell nanostructure toward high hydrogen evolution. ACS Sustain. Chem. Eng. 2017, 5 (8), 7093. DOI: 10.1021/acssuschemeng.7b01312 (5) Zhou, X.; Shao, C.; Li, X.; Wang, X.; Guo, X.; Liu, Y. Three dimensional hierarchical heterostructures of g-C3N4 nanosheets/TiO2 nanofibers: controllable growth via gas-solid reaction and enhanced photocatalytic activity under visible light. J. Hazard. Mater. 2018, 344, 113. DOI: 10.1016/j.jhazmat.2017.10.006 (6) Jo, W.; Selvam, N. C. Enhanced visible light-driven photocatalytic performance of ZnO–g-C3N4 coupled with graphene oxide as a novel ternary nanocomposite. J. Hazard. Mater. 2015, 299, 462. DOI: 10.1016/j.jhazmat.2015.07.042 (7) Zhang, J.; Wang, Y.; Jin, J.; Zhang, J.; Lin, Z.; Huang, F.; Yu, J. Efficient visible-light photocatalytic hydrogen evolution and enhanced photostability of core/shell CdS/g-C3N4 nanowires. ACS Appl. Mater. Interfaces 2013, 5 (20), 10317. DOI: 10.1021/am403327g (8) Wang, M.; Ju, P.; Li, J.; Zhao, Y.; Han, X.; Hao, Z. Facile synthesis of MoS2/g-C3N4/GO ternary heterojunction with enhanced photocatalytic activity for water splitting. ACS Sustain. Chem. Eng. 2017, 5 (9), 7878. DOI: 10.1021/acssuschemeng.7b01386 20


Page 21 of 33 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) Di, J.; Xia, J.; Yin, S.; Xu, H.; Xu, L.; Xu, Y.; He, M.; Li, H. Preparation of sphere-like g-C3N4/BiOI photocatalysts via a reactable ionic liquid for visible-light-driven photocatalytic degradation of pollutants. J. Mater. Chem. A 2014, 2 (15), 5340. DOI: 10.1039/c3ta14617k (10) Wang, X.; Wang, Q.; Li, F.; Yang, W.; Zhao, Y.; Hao, Y.; Liu, S. Novel BiOCl-C3N4 heterojunction photocatalysts: In situ preparation via an ionic-liquid-assisted solvent-thermal route and their visible-light photocatalytic activities. Chem. Eng. J. 2013, 234, 361. DOI: 10.1016/j.cej.2013.08.112 (11) Dai, K.; Lu, L.; Liang, C.; Zhu, G.; Liu, Q.; Geng, L.; He, J. A high efficient graphitic-C3N4/BiOI/graphene oxide ternary nanocomposite heterostructured photocatalyst with graphene oxide as electron transport buffer material. Dalt. Trans. 2015, 44 (17), 7903. DOI: 10.1039/c5dt00475f (12) Jiang, D.; Chen, L.; Zhu, J.; Chen, M.; Shi, W.; Xie, J. Novel p–n heterojunction photocatalyst constructed by porous graphite-like C3N4 and nanostructured BiOI: facile synthesis and

enhanced

photocatalytic

activity.

Dalt.

Trans.

2013,

42

(44),

15726.

DOI:

10.1039/c3dt52008k (13) Wang, K.; Shao, C.; Li, X.; Miao, F.; Lu, N.; Liu, Y. Heterojunctions of p-BiOI nanosheets/n-TiO2 nanofibers: preparation and enhanced visible-light photocatalytic activity. Materials. 2016, 9 (2), 1. DOI: 10.3390/ma9020090 (14) Chou, Y.; Shao, C.; Li, X.; Su, C.; Xu, H.; Zhang, M.; Zhang, P.; Zhang, X.; Liu, Y. BiOCl nanosheets immobilized on electrospun polyacrylonitrile nanofibers with high photocatalytic activity

and

reusable

property.

Appl.

Surf.

Sci.

2013,

285P,

509.

DOI:

10.1016/j.apsusc.2013.08.085 (15) Chen, T.; Chen, G.; Xing, S.; Wu, T.; Chen, H. Scalable routes to janus Au-SiO2 and ternary Ag-Au-SiO2 nanoparticles. Chem. Mater. 2010, 22 (13), 3826. DOI: 10.1021/cm101155v (16) Greco, F.; Zucca, A.; Taccola, S.; Menciassi, A.; Fujie, T.; Haniuda, H.; Takeoka, S.; Dario, P.; Mattoli, V. Ultra-thin conductive free-standing PEDOT/PSS nanofilms. Soft Matter 2011, 7 (22), 10642. DOI: 10.1039/c1sm06174g (17) Qin, D.; Lu, W.; Wang, X.; Li, N.; Chen, X.; Zhu, Z.; Chen, W. Graphitic carbon nitride from burial to re-emergence on polyethylene terephthalate nanofibers as an easily recycled photocatalyst for degrading antibiotics under solar irradiation. ACS Appl. Mater. Interface 2016, 8 21



(39), 25962. DOI: 10.1021/acsami.6b07680 (18) Zhang, X.; Shao, C.; Zhang, Z.; Li, J.; Zhang, P.; Zhang, M.; Mu, J.; Guo, Z.; Liang, P.; Liu, Y. In situ generation of well-dispersed ZnO quantum dots on electrospun silica nanotubes with high photocatalytic activity. ACS Appl. Mater. Interface 2012, 4 (2), 785. DOI: 10.1021/am201420b (19) Ma, Q.; Wang, J.; Dong, X.; Yu, W.; Liu, G.; Xu, J. Electrospinning preparation and properties of magnetic-photoluminescent bifunctional coaxial nanofiber. J. Mater. Chem. 2012, 22, 14438. DOI: 10.1039/C2JM32043F (20) Xi, X.; Wang, J.; Dong, X.; Ma, Q.; Yu, W.; Liu, G. Flexible Janus nanofiber: a new tactics to realize tunable and enhanced magnetic-luminescent bifunction. Chem. Eng. J. 2014, 254, 259. DOI: 10.1016/j.cej.2014.05.142 (21) Martin, D.; Qiu, K.; Shevlin, S.; Handoko, A.; Chen, X.; Guo, Z.; Tang, J. Highly efficient photocatalytic H2 evolution from water using visible light and structure-controlled graphitic carbon nitride. Angew. Chem. Int. Ed. 2014, 53, 9240. DOI: 10.1002/anie.201403375 (22) Yan, J.; Wu, H.; Chen, H.; Zhang, Y.; Zhang, F.; Liu, S. Fabrication of TiO2/C3N4 heterostructure for enhanced photocatalytic Z-scheme overall water splitting. Appl. Catal. B Environ. 2016, 191, 130. DOI: 10.1016/j.apcatb.2016.03.026 (23) Chang, C.; Zhu, L.; Wang, S.; Chu, X.; Yue, L. Novel Mesoporous graphite carbon nitride/BiOI heterojunction for enhancing photocatalytic performance under visible-light irradiation. ACS Appl. Mater. Interfaces 2014, 6 (7), 5083. DOI: 10.1021/am5002597 (24) Wang, X.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2009, 8 (1), 76. DOI: 10.1038/NMAT2317 (25) Han, Q.; Wang, B.; Gao, J.; Cheng, Z.; Zhao, Y.; Zhang, Z.; Qu, L. Atomically thin mesoporous nanomesh of graphitic C3N4 for high-efficiency photocatalytic hydrogen evolution. ACS Nano 2016, 10 (2), 2745. DOI: 10.1021/acsnano.5b07831 (26) Chen, X.; Wei, J.; Hou, R.; Liang, Y.; Xie, Z.; Zhu, Y.; Zhang, X.; Wang, H. Growth of g-C3N4 on mesoporous TiO2 spheres with high photocatalytic activity under visible light irradiation. Appl. Catal. B Environ. 2016, 188, 342. DOI: 10.1016/j.apcatb.2016.02.012 (27) Chen, Y.; Huang, W.; He, D.; Situ, Y.; Huang, H. Construction of heterostructured 22


Page 22 of 33

Page 23 of 33 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


g-C3N4/Ag/TiO2 microspheres with enhanced photocatalysis performance under visible-light irradiation. ACS Appl. Mater. Interfaces 2014, 6 (16), 14405. DOI: 10.1021/am503674e (28) Han, C.; Wang, Y.; Lei, Y.; Wang, B.; Wu, N.; Shi, Q.; Li, Q. In situ synthesis of graphitic-C3N4 nanosheet hybridized N-doped TiO2 nanofibers for efficient photocatalytic H2 production and degradation. Nano Res. 2015, 8 (4), 1199. DOI: 10.1007/s12274-014-0600-2 (29) Pan, C.; Xu, J.; Wang, Y.; Li, D.; Zhu, Y. Dramatic activity of C3N4/BiPO4 photocatalyst with core/shell structure formed by self-assembly. Adv. Funct. Mater. 2012, 22 (7), 1518. DOI: 10.1002/adfm.201102306 (30) Su, J.; Zhu, L.; Chen, G. Ultrasmall graphitic carbon nitride quantum dots decorated self-organized TiO2 nanotube arrays with highly efficient photoelectrochemical activity. Appl. Catal. B Environ. 2016, 186, 127. DOI: 10.1016/j.apcatb.2015.12.050 (31) Takahagi, T.; Shimada, I.; Fukuhara, M.; Morita, K.; Ishitani, A. XPS studies on the chemical structure of the stabilized polyacrylonitrile fiber in the carbon fiber production process. J. Polym. Sci. Part A Polym. Chem. 1986, 24, 3101. DOI: 10.1002/pola.1986.080241134 (32) Deng, S.; Bai, R.; Chen, J. Behaviors and mechanisms of copper adsorption on hydrolyzed polyacrylonitrile

fibers.

J.

Colloid

Interface

Sci.

2003,

260

(2),

265.

DOI:

10.1016/S0021-9797(02)00243-6 (33) Wang, J.; Yao, H.; Fan, Z.; Zhang, L.; Wang, J.; Zang, S.; Li, Z. Indirect Z‑scheme BiOI/g ‑C3N4 photocatalysts with enhanced photoreduction CO2 activity under visible light irradiation. ACS Appl. Mater. Interfaces 2016, 8 (6), 3765. DOI: 10.1021/acsami.5b09901 (34) Lu, M.; Shao, C.; Wang, K.; Lu, N.; Zhang, X.; Zhang, P.; Zhang, M.; Li, X.; Liu, Y. p-MoO3 nanostructures/n-TiO2 nanofiber heterojunctions : controlled fabrication and enhanced photocatalytic properties. ACS Appl. Mater. Interfaces 2014, 6

(12), 9004. DOI:

10.1021/am5021155 (35) Cheng, H.; Huang, B.; Dai, Y.; Qin, X.; Zhang, X. One-step synthesis of the nanostructured AgI/BiOI composites with highly enhanced visible-light photocatalytic performances, Langmuir 2010, 26 (9), 6618. DOI: 10.1021/la903943s (36) Zhou, R.; Wu, J.; Zhang, J.; Tian, H.; Liang, P.; Zeng, T.; Lu, P.; Ren, J.; Huang, T.; Zhou, X.; Sheng, P. Photocatalytic oxidation of gas-phase Hg0 on the exposed reactive facets of BiOI/BiOIO3

heterostructures,

Appl.

Catal.

B

Environ.

23


2017,

204,

465.

DOI:


Page 24 of 33

10.1016/j.apcatb.2016.11.013 (37) Xiao, X.; Xing, C.; He, G.; Zuo, X.; Nan, J.; Wang, L. Solvothermal synthesis of novel hierarchical Bi4O5I2 nanoflakes with highly visible light photocatalytic performance for the degradation of 4-tert-butylphenol, Appl. Catal. B Environ. 2014, 148, 154. DOI: 10.1016/j.apcatb.2013.10.055 (38) Zhang, Z.; Huang, J.; Zhang, M.; Yuan, Q.; Dong, B. Ultrathin hexagonal SnS2 nanosheets coupled with g-C3N4 nanosheets as 2D/2D heterojunction photocatalysts toward high photocatalytic

activity.

Appl.

Catal.

B

Environ.

2015,

163,

298.

DOI:

10.1016/j.apcatb.2014.08.013 (39) Gao, S.; Zhang, Z.; Liu, K.; Dong, B. Environmental direct evidence of plasmonic enhancement on catalytic reduction of 4-nitrophenol over silver nanoparticles supported on flexible

fibrous

networks.

Appl.

Catal.

B

Environ.

10.1016/j.apcatb.2016.01.074

24


2016,

188,

245.

DOI:

Page 25 of 33 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 diagram PAN/g-C3N4/BiOI nanofiber synthesis.

25



Figure 1. (A) SEM images of PAN/g-C3N4, (C) PAN/g-C3N4/BiOI, and (E) PAN/BiOI nanofibers; EDX spectra of samples (B) PAN/g-C3N4, (D) PAN/g-C3N4/BiOI, and (F) PAN/BiOI nanofibers.

26


Page 26 of 33

Page 27 of 33 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 2. (A) Cross-sectional TEM and (B) the corresponding HRTEM images of the PAN/g-C3N4/BiOI nanofibers. FFT pattern of BiOI nanostructures in the PAN/g-C3N4/BiOI nanofibers (Figure 2B inset). (C) Cross-sectional STEM image and corresponding mappings of PAN/g-C3N4/BiOI nanofibers: (D) C element, (E) N element, (F) Bi element, (G) O element, and (H) I element. The two groups of parallel lines indicate representative composite nanofibers contained in the g-C3N4.

27



Figure 3. (A) FT-IR spectra of the PAN/g-C3N4, PAN/g-C3N4/BiOI, and PAN/BiOI nanofibers, and (B) the enlarged view of FT-IR spectra of PAN/g-C3N4/BiOI and PAN/BiOI nanofibers.

28


Page 28 of 33

Page 29 of 33 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. (A) XPS full-spectra, (B) C 1s and (C) N 1s core-level spectra for the as-synthesized samples of PAN/g-C3N4, PAN/g-C3N4/BiOI, and PAN/BiOI nanofibers. (D) Bi 4f, (E) I 3d, and (F) O 1s core-level spectra for PAN/g-C3N4/BiOI and PAN/BiOI nanofibers.

29



Figure 5. (A) Photocatalytic degradation and (B) kinetic linear simulation curves of RhB over the as-synthesized samples. (C) Effects of scavengers and (D) photocatalytic mechanism scheme for the photodegradation of RhB with PAN/g-C3N4/BiOI nanofibers under visible light irradiation (λ > 400 nm, I = 150 mW·cm-2). (E) Photocurrent spectra and (F) PL spectra of as-synthesized samples under visible light irradiation. 30


Page 30 of 33

Page 31 of 33 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) Photocatalytic degradation and (B) kinetic linear simulation curves of Cr (VI) over the as-synthesized samples. (C) Illustration of floating photocatalysis process for the degradation of RhB and the photoreduction of Cr (VI). (D) Cycling test and reusability of PAN/g-C3N4/BiOI nanofibers under visible light irradiation.

31



For Table of Contents Use Only.

The self-supporting PAN/g-C3N4/BiOI nanofibers with high photocatalytic activity do not require separation for reuse in water purification.

32


Page 32 of 33

Page 33 of 33 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 self-supporting PAN/g-C3N4/BiOI nanofibers with high photocatalytic activity do not require separation for reuse in water purification. 71x47mm (220 x 220 DPI)


BiOI Immobilized on Flexible Electrospun

Recommend Documents