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One-dimensional superfine Ni3(VO4)2 nanofibers with enhanced photoelectrocatalytic performance
Materials Letters 249 (2019) 13–16
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
One-dimensional superfine Ni3(VO4)2 nanofibers with enhanced photoelectrocatalytic performance Linbing Yao, Xue Li, Ke Sun, Mingzhi Wei, Qifang Lu ⇑ Shandong Provincial Key Laboratory of Processing and Testing Technology of Glass & Functional Ceramics, School of Material Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, PR China
a r t i c l e
i n f o
Article history: Received 15 February 2019 Received in revised form 11 April 2019 Accepted 12 April 2019 Available online 13 April 2019 Keywords: Ni3(VO4)2 Superfine nanofibers Electrospinning Photocatalyst Microstructure
a b s t r a c t One-dimensional superfine Ni3(VO4)2 nanofibers with diameter about 60 ± 5 nm have been successfully synthesized by simple and efficient electrospinning process. The construction and photoelectrochemistry performance of photocatalysts are characterized in detail. The relationships between the structures and photocatalytic activities are also discussed detailedly. Compared with Ni3(VO4)2 powders, superfine Ni3(VO4)2 nanofibers possess the excellent photoelectric properties, which could be attributed to the specific dimensional effect and large surface area. Moreover, the energy band structure, density of states and free energy of different crystal planes of Ni3(VO4)2 nanofibers have been simulated by density functional theory and explained in detail. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction In the past few decades, semiconductor photocatalysis has been considered as an effective approach to solve the problem of water pollution since the photocatalytic splitting of water on TiO2 electrode was reported [1]. However, the wide-band-gap semiconductor only takes on the photoresponse under UV light irradiation, which corresponds to just 5% of the sunlight that reaches the earth’s surface [2]. Therefore, exploring suitable narrow-bandgap semiconductor has grown up to be a pressing problem in the practical application of photocatalysts [3,4]. Orthorhombic Ni3(VO4)2, as a kind of visible-light-responsive photocatalyst, has attracted the tremendous attention due to its suitable electronic band structure (2.4 eV), high quantum yield and eximious photocatalytic activity [5]. It has been reported that the microstructures and exposed surfaces with different freeenergy of semiconductor directly affect the performance of photocatalyst [6]. Moreover, the size and morphology of semiconductor are closely related to its recycling performance. The nanofibers with one-dimensional (1D) effects could utilize sunlight more effectively and make the photogenerated electron-holes transfer to the surface of photocatalyst more quickly to participate in catalytic reaction due to large specific surface area [7–9]. In the present paper, 1D ultrafine Ni3(VO4)2 nanofibers with enhanced photoelectrocatalytic performance have been synthe⇑ Corresponding author. E-mail address: [email protected] (Q. Lu). https://doi.org/10.1016/j.matlet.2019.04.046 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
sized by designing the reasonable electrospinning and post treatment process. Moreover, energy band structure and partial/total density of states (PDOS/TDOS) for Ni3(VO4)2 nanofibers are elucidated by first-principle calculations to further understand the photocatalytic and photogenerated carrier transport mechanism in this work.
2. Experimental All chemical reagents were analytical grade and used without any purification. In a typical synthesis, 0.8 g polyvinylpyrrolidone (PVP K-90) as structure-directing agent was dissolved into 10 mL anhydrous ethanol with magnetic stirring. Simultaneously, 0.097 g (0.3 mmol) Ni(CH3COO)24H2O and 0.023 g (0.2 mmol) NH4VO3 were dissolved into the mixed solution of 3 mL deionized water and 1 mL acetic acid with magnetic stirring for 0.5 h, and then added into the structure-directing agent solution with magnetic stirring for 3 h to form the transparent and homogeneous precursor sols. The obtained precursor sols were totally placed in 20 mL plastic syringe attached to stainless steel needle with the inner diameter of 0.6 mm and then ejected from needle with an applied voltage of 20 kV. The distance between needle tip and aluminum foil collector was set to 20 cm, and the flow rate of the precursor sols was 2.26 mL h 1. The as-collected products were dried at 80 °C for 12 h and calcined at 500 °C for 2 h at a rate of 1 °C min 1 in the air atmosphere to obtain 1D ultrafine Ni3(VO4)2 nanofibers.
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L. Yao et al. / Materials Letters 249 (2019) 13–16
All the characterization, computational details, photocatalytic and photoelectrochemical tests were provided in Supporting Information. 3. Results and discussion XRD pattern and raman spectrum were used to further analyze the phase and vibration of chemical bonds, respectively. As shown in Fig. 1a, all the diffraction peaks could be perfectly indexed to the orthorhombic Ni3(VO4)2 phase (JCPDS No. 741485), which is in agreement with analysis of raman spectrum (Fig. S1). The superfine Ni3(VO4)2 nanofibers with the diameter about 60 ± 5 nm have the rough surfaces and are made up of irregular nanoparticles interconnected with each other as observed in Fig. 1b-d. The highresolution TEM image (Fig. 1e) taken from a single Ni3(VO4)2 nanofiber demonstrates that the lattice fringes with d-spacing of 0.249 and 0.205 nm correspond to (1 2 2) and (1 5 1) planes of orthorhombic Ni3(VO4)2, respectively. Furthermore, the lattice planes of orthorhombic Ni3(VO4)2 identified by selected-area electron diffraction (SAED) prove the successful construction of orthorhombic Ni3(VO4)2. The surface area of superfine Ni3(VO4)2 nanofibers (35.8 m2 g 1) is about 2.6 times high than that of Ni3(VO4)2 powders (13.6 m2 g 1), which maybe come from the small diameter and dimensional effect of the nanofibers. In addition, the most probable pore size of nanofibers is mainly around 5– 10 nm (Fig. 1f). The increased specific surface area could provide more active sites for photocatalytic reaction, which is favorable for the efficient and fast transport of photo-induced carriers [10]. As can be seen from Fig. 2a, 1D superfine Ni3(VO4)2 nanofibers exhibit the stronger photoresponse and more red-shifted absorption than Ni3(VO4)2 powders, and the corresponding Eg value of superfine Ni3(VO4)2 nanofibers and powders is approximately 2.33 and 2.35 eV, respectively. As shown in Fig. S2, the calculated Eg of Ni3(VO4)2 nanofibers (2.12 eV) is smaller than experimental result (2.33 eV) due to the discontinuity of the exchange–correlation potential with respect to the particle number incorporated into the generalised Kohn-Sham single-particle Eigen values [8,11]. In addition, the energy band structures, TDOS and free energy of (1 2 2) and (1 5 1) planes of Ni3(VO4)2 nanofibers have
been comparatively discussed (Fig. S3). Additionally, the solid state EPR signal and PL intensity of Ni3(VO4)2 nanofibers are much higher than those of Ni3(VO4)2 powders, indicating the low recombination efficiency of photogenerated electron-holes in Ni3(VO4)2 nanofibers [12] (Fig. 2b and Fig. S4). After the simulated sunlight irradiation for 60 min, the degradation rate of Ni3(VO4)2 nanofibers toward tetracycline is 89.8%, about 2.8 times high than that of Ni3(VO4)2 powders (only 31.5%) due to the morphological advantage of the nanofibers (Fig. 2c and Fig. S5). However, the corresponding TOC removals of Ni3(VO4)2 nanofibers and powders is 75.7% and 26.8%, respectively, lower than the photocatalytic degradation attributable to the chromophore groups of tetracycline, which is inactive and not mineralized completely (Fig. 2d) [13]. Undoubtedly, the results of HPLC are consistent with those of photocatalytic degradation (Fig. 2e). The improved photodegradation activity may be attributed to 1D superfine fiber structure with large surface area, which can provide more active sites in the photocatalysis process [6]. In order to detect the recycling performance of Ni3(VO4)2 nanofibers, the cyclic degradation experiments are carried out. The Ni3(VO4)2 nanofibers still remain the superior photodegradation efficiency (84.7%), and crystal phase as well as nanofiber structure does not change after four consecutive photodegradation cycles (Fig. 2f and Fig. S6). To further confirm and identify the different free radical species in photocatalytic processes, trapping experiment of active species and EPR spectra were determined to explore the photocatalytic mechanism. As can be seen from Fig. 3a, e and O2 radicals are the primary active species. Moreover, the introduction of isopropanol into the reaction also inhibits the degradation, suggesting that OH radicals also participate in the degradation reaction. It is obvious that the EPR signals of Ni3(VO4)2 nanofibers are much higher than those of Ni3(VO4)2 powders, indicating that Ni3(VO4)2 nanofibers are beneficial to the production of O2 radicals (Fig. 3b). Equally important as superoxide radicals, the unique 1:2:2:1 quadruple peaks of hydroxyl radicals (OH) attributable to hydroxyl groups have been clearly identified (Fig. 3c). Similarly, EPR signals of OH radicals for Ni3(VO4)2 nanofibers are more obvious and easier to be captured than those for Ni3(VO4)2 powders. A series of photoelectric measurements have been implemented to
Fig. 1. XRD pattern (a), SEM images (b, c), HRTEM images (d, e) and SAED pattern (inset) of Ni3(VO4)2 nanofibers. N2 adsorption-desorption isotherms (f) and BJH pore size distribution curves (inset) of the different samples calcined at 500 °C for 2 h.
L. Yao et al. / Materials Letters 249 (2019) 13–16
15
Fig. 2. UV–vis DRS (a) and Kubelka-Munk function plots (inset), solid state EPR spectra (b), photocatalytic activity (c) and TOC removal toward tetracycline (d) of different samples. HPLC chromatograms (e) of tetracycline solution at different time intervals and photodegradation recycling results (f) photocatalytically degraded by Ni3(VO4)2 nanofibers under simulated sunlight irradiation.
Fig. 3. Trapping experiment of active species during the photocatalytic degradation of tetracycline over Ni3(VO4)2 nanofibers (a) EPR spectra of DMPO-O2 (b) and DMPO-OH (c), transient photocurrent responses (d), CV curves (e) and EIS Nyquist curves (f) of Ni3(VO4)2 nanofibers and powders, respectively. Inset of Fig. 3f shows the equivalent circuit.
verify the performance of the samples and the results are displayed in Fig. 3d–f. In general, the increase in photocurrent intensity indicates a more efficient photoinduced charge carrier separation. It is clearly that compared with Ni3(VO4)2 powders, the Ni3(VO4)2 nanofibers show a more obvious and relatively stable photocurrent density under sunlight irradiation, suggesting the prolonged lifetime of photoinduced charge carriers (Fig. 3d). Fig. 3e is the CV curves of Ni3(VO4)2 nanofibers and powders at a scan rate of 1 mV s 1, respectively. Both the oxidative and reductive peaks of Ni3(VO4)2 nanofibers are higher than those of Ni3(VO4)2 powders, meaning that Ni3(VO4)2 nanofibers possess the more prominent photocatalytic performance compared with Ni3(VO4)2 powders [14]. The transmission resistance of photocarriers fitted by the
equivalent circuit can be determined by EIS Nyquist curves. The decreased arc radius in high frequency region indicates Ni3(VO4)2 nanofibers possess the enhanced charge transfer efficiency (Fig. 3f)[15]. 4. Conclusions In summary, 1D superfine Ni3(VO4)2 nanofibers were synthesized by electrospinning and calcination treatment for the first time, which exhibited the excellent photocatalytic performance for the removal of tetracycline under simulated sunlight irradiation. The small diameter and dimensional effect of the nanofibers were beneficial to ultrafast carrier separation and provided rich
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L. Yao et al. / Materials Letters 249 (2019) 13–16
catalytically active sites for photoeletrochemical reactions. The energy band structure, TDOS and free energy for Ni3(VO4)2 nanofibers were also simulated by DFT method. Thus, this work could serve a new guideline in the design of ultraviolet-visible-lightdriven photocatalysts for the environmental remediation.
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.04.046. References
Declaration of interest None.
Conflict of interest None. Acknowledgments This study was funded by the Shandong Provincial Natural Science Foundation (Grant No. ZR2016BM22 and ZR2018LF012).
Compliance with ethical standards The authors declare that they have no conflict of interest.
[1] A. Fujishima, K. Honda, Nature 238 (1972) 37–38. [2] J. Li, M. Zhang, Q. Li, J. Yang, Appl. Surf. Sci. 391 (2016) 184–193. [3] F. Chen, Q. Yang, J. Sun, F. Yao, S. Wang, Y. Wang, X. Wang, X. Li, C. Niu, D. Wang, G. Zeng, ACS Appl. Mater. Interfaces 8 (2016) 32887–32900. [4] D. Xu, B. Cheng, S. Cao, J. Yu, Appl. Catal. B-Environ. 164 (2015) 380–388. [5] R. Kumar, P. Rai, A. Sharma, J. Mater. Chem. A 4 (2016) 9822–9831. [6] F. Opoku, K. Govender, C. van Sittert, P. Govender, Compos. Mater. Sci. 138 (2017) 462–473. [7] Q. Wang, K. Sun, Q. Lu, M. Wei, L. Yao, E. Guo, Dyes Pigm. 155 (2018) 194–201. [8] L. Yao, E. Guo, K. Sun, Q. Lu, Q. Wang, Mater. Lett. 231 (2018) 11–15. [9] Y. Zhou, L. Liu, T. Wu, G. Yuan, J. Li, Q. Ding, F. Qi, W. Zhu, X. OuYang, Y. Wang, RSC Adv. 48 (2018) 27073–27079. [10] X. Lin, D. Xu, J. Zheng, M. Song, G. Che, Y. Wang, Y. Yang, C. Liu, L. Zhao, L. Chang, J. Alloy. Compd. 688 (2016) 891–898. [11] R. Ponnusamy, B. Chakraborty, C. Rout, J. Phys. Chem. B 122 (2018) 2737–2746. [12] H. Wei, W.A. McMaster, J.Z.Y. Tan, L. Cao, D. Chen, R.A. Caruso, J. Phys. Chem. C 6 (2018) 7236–7245. [13] Y. Jin, X. Shen, Z. Liu, Z. Wang, B. Zhu, P. Xu, L. Luo, L. Zhang, New J. Chem. 42 (2018) 411–419. [14] S. Ma, S. Zhan, Y. Jia, Q. Zhou, ACS Appl. Mater. Interfaces 7 (2015) 10576– 10586. [15] S. Zhang, J. Li, M. Zeng, G. Zhao, J. Xu, W. Hu, X. Wang, ACS. Appl. Mater. Interfaces 5 (2013) 12735–12743.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
One-dimensional superfine Ni3(VO4)2 nanofibers with enhanced photoelectrocatalytic performance Linbing Yao, Xue Li, Ke Sun, Mingzhi Wei, Qifang Lu ⇑ Shandong Provincial Key Laboratory of Processing and Testing Technology of Glass & Functional Ceramics, School of Material Science and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, PR China
a r t i c l e
i n f o
Article history: Received 15 February 2019 Received in revised form 11 April 2019 Accepted 12 April 2019 Available online 13 April 2019 Keywords: Ni3(VO4)2 Superfine nanofibers Electrospinning Photocatalyst Microstructure
a b s t r a c t One-dimensional superfine Ni3(VO4)2 nanofibers with diameter about 60 ± 5 nm have been successfully synthesized by simple and efficient electrospinning process. The construction and photoelectrochemistry performance of photocatalysts are characterized in detail. The relationships between the structures and photocatalytic activities are also discussed detailedly. Compared with Ni3(VO4)2 powders, superfine Ni3(VO4)2 nanofibers possess the excellent photoelectric properties, which could be attributed to the specific dimensional effect and large surface area. Moreover, the energy band structure, density of states and free energy of different crystal planes of Ni3(VO4)2 nanofibers have been simulated by density functional theory and explained in detail. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction In the past few decades, semiconductor photocatalysis has been considered as an effective approach to solve the problem of water pollution since the photocatalytic splitting of water on TiO2 electrode was reported [1]. However, the wide-band-gap semiconductor only takes on the photoresponse under UV light irradiation, which corresponds to just 5% of the sunlight that reaches the earth’s surface [2]. Therefore, exploring suitable narrow-bandgap semiconductor has grown up to be a pressing problem in the practical application of photocatalysts [3,4]. Orthorhombic Ni3(VO4)2, as a kind of visible-light-responsive photocatalyst, has attracted the tremendous attention due to its suitable electronic band structure (2.4 eV), high quantum yield and eximious photocatalytic activity [5]. It has been reported that the microstructures and exposed surfaces with different freeenergy of semiconductor directly affect the performance of photocatalyst [6]. Moreover, the size and morphology of semiconductor are closely related to its recycling performance. The nanofibers with one-dimensional (1D) effects could utilize sunlight more effectively and make the photogenerated electron-holes transfer to the surface of photocatalyst more quickly to participate in catalytic reaction due to large specific surface area [7–9]. In the present paper, 1D ultrafine Ni3(VO4)2 nanofibers with enhanced photoelectrocatalytic performance have been synthe⇑ Corresponding author. E-mail address: [email protected] (Q. Lu). https://doi.org/10.1016/j.matlet.2019.04.046 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
sized by designing the reasonable electrospinning and post treatment process. Moreover, energy band structure and partial/total density of states (PDOS/TDOS) for Ni3(VO4)2 nanofibers are elucidated by first-principle calculations to further understand the photocatalytic and photogenerated carrier transport mechanism in this work.
2. Experimental All chemical reagents were analytical grade and used without any purification. In a typical synthesis, 0.8 g polyvinylpyrrolidone (PVP K-90) as structure-directing agent was dissolved into 10 mL anhydrous ethanol with magnetic stirring. Simultaneously, 0.097 g (0.3 mmol) Ni(CH3COO)24H2O and 0.023 g (0.2 mmol) NH4VO3 were dissolved into the mixed solution of 3 mL deionized water and 1 mL acetic acid with magnetic stirring for 0.5 h, and then added into the structure-directing agent solution with magnetic stirring for 3 h to form the transparent and homogeneous precursor sols. The obtained precursor sols were totally placed in 20 mL plastic syringe attached to stainless steel needle with the inner diameter of 0.6 mm and then ejected from needle with an applied voltage of 20 kV. The distance between needle tip and aluminum foil collector was set to 20 cm, and the flow rate of the precursor sols was 2.26 mL h 1. The as-collected products were dried at 80 °C for 12 h and calcined at 500 °C for 2 h at a rate of 1 °C min 1 in the air atmosphere to obtain 1D ultrafine Ni3(VO4)2 nanofibers.
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L. Yao et al. / Materials Letters 249 (2019) 13–16
All the characterization, computational details, photocatalytic and photoelectrochemical tests were provided in Supporting Information. 3. Results and discussion XRD pattern and raman spectrum were used to further analyze the phase and vibration of chemical bonds, respectively. As shown in Fig. 1a, all the diffraction peaks could be perfectly indexed to the orthorhombic Ni3(VO4)2 phase (JCPDS No. 741485), which is in agreement with analysis of raman spectrum (Fig. S1). The superfine Ni3(VO4)2 nanofibers with the diameter about 60 ± 5 nm have the rough surfaces and are made up of irregular nanoparticles interconnected with each other as observed in Fig. 1b-d. The highresolution TEM image (Fig. 1e) taken from a single Ni3(VO4)2 nanofiber demonstrates that the lattice fringes with d-spacing of 0.249 and 0.205 nm correspond to (1 2 2) and (1 5 1) planes of orthorhombic Ni3(VO4)2, respectively. Furthermore, the lattice planes of orthorhombic Ni3(VO4)2 identified by selected-area electron diffraction (SAED) prove the successful construction of orthorhombic Ni3(VO4)2. The surface area of superfine Ni3(VO4)2 nanofibers (35.8 m2 g 1) is about 2.6 times high than that of Ni3(VO4)2 powders (13.6 m2 g 1), which maybe come from the small diameter and dimensional effect of the nanofibers. In addition, the most probable pore size of nanofibers is mainly around 5– 10 nm (Fig. 1f). The increased specific surface area could provide more active sites for photocatalytic reaction, which is favorable for the efficient and fast transport of photo-induced carriers [10]. As can be seen from Fig. 2a, 1D superfine Ni3(VO4)2 nanofibers exhibit the stronger photoresponse and more red-shifted absorption than Ni3(VO4)2 powders, and the corresponding Eg value of superfine Ni3(VO4)2 nanofibers and powders is approximately 2.33 and 2.35 eV, respectively. As shown in Fig. S2, the calculated Eg of Ni3(VO4)2 nanofibers (2.12 eV) is smaller than experimental result (2.33 eV) due to the discontinuity of the exchange–correlation potential with respect to the particle number incorporated into the generalised Kohn-Sham single-particle Eigen values [8,11]. In addition, the energy band structures, TDOS and free energy of (1 2 2) and (1 5 1) planes of Ni3(VO4)2 nanofibers have
been comparatively discussed (Fig. S3). Additionally, the solid state EPR signal and PL intensity of Ni3(VO4)2 nanofibers are much higher than those of Ni3(VO4)2 powders, indicating the low recombination efficiency of photogenerated electron-holes in Ni3(VO4)2 nanofibers [12] (Fig. 2b and Fig. S4). After the simulated sunlight irradiation for 60 min, the degradation rate of Ni3(VO4)2 nanofibers toward tetracycline is 89.8%, about 2.8 times high than that of Ni3(VO4)2 powders (only 31.5%) due to the morphological advantage of the nanofibers (Fig. 2c and Fig. S5). However, the corresponding TOC removals of Ni3(VO4)2 nanofibers and powders is 75.7% and 26.8%, respectively, lower than the photocatalytic degradation attributable to the chromophore groups of tetracycline, which is inactive and not mineralized completely (Fig. 2d) [13]. Undoubtedly, the results of HPLC are consistent with those of photocatalytic degradation (Fig. 2e). The improved photodegradation activity may be attributed to 1D superfine fiber structure with large surface area, which can provide more active sites in the photocatalysis process [6]. In order to detect the recycling performance of Ni3(VO4)2 nanofibers, the cyclic degradation experiments are carried out. The Ni3(VO4)2 nanofibers still remain the superior photodegradation efficiency (84.7%), and crystal phase as well as nanofiber structure does not change after four consecutive photodegradation cycles (Fig. 2f and Fig. S6). To further confirm and identify the different free radical species in photocatalytic processes, trapping experiment of active species and EPR spectra were determined to explore the photocatalytic mechanism. As can be seen from Fig. 3a, e and O2 radicals are the primary active species. Moreover, the introduction of isopropanol into the reaction also inhibits the degradation, suggesting that OH radicals also participate in the degradation reaction. It is obvious that the EPR signals of Ni3(VO4)2 nanofibers are much higher than those of Ni3(VO4)2 powders, indicating that Ni3(VO4)2 nanofibers are beneficial to the production of O2 radicals (Fig. 3b). Equally important as superoxide radicals, the unique 1:2:2:1 quadruple peaks of hydroxyl radicals (OH) attributable to hydroxyl groups have been clearly identified (Fig. 3c). Similarly, EPR signals of OH radicals for Ni3(VO4)2 nanofibers are more obvious and easier to be captured than those for Ni3(VO4)2 powders. A series of photoelectric measurements have been implemented to
Fig. 1. XRD pattern (a), SEM images (b, c), HRTEM images (d, e) and SAED pattern (inset) of Ni3(VO4)2 nanofibers. N2 adsorption-desorption isotherms (f) and BJH pore size distribution curves (inset) of the different samples calcined at 500 °C for 2 h.
L. Yao et al. / Materials Letters 249 (2019) 13–16
15
Fig. 2. UV–vis DRS (a) and Kubelka-Munk function plots (inset), solid state EPR spectra (b), photocatalytic activity (c) and TOC removal toward tetracycline (d) of different samples. HPLC chromatograms (e) of tetracycline solution at different time intervals and photodegradation recycling results (f) photocatalytically degraded by Ni3(VO4)2 nanofibers under simulated sunlight irradiation.
Fig. 3. Trapping experiment of active species during the photocatalytic degradation of tetracycline over Ni3(VO4)2 nanofibers (a) EPR spectra of DMPO-O2 (b) and DMPO-OH (c), transient photocurrent responses (d), CV curves (e) and EIS Nyquist curves (f) of Ni3(VO4)2 nanofibers and powders, respectively. Inset of Fig. 3f shows the equivalent circuit.
verify the performance of the samples and the results are displayed in Fig. 3d–f. In general, the increase in photocurrent intensity indicates a more efficient photoinduced charge carrier separation. It is clearly that compared with Ni3(VO4)2 powders, the Ni3(VO4)2 nanofibers show a more obvious and relatively stable photocurrent density under sunlight irradiation, suggesting the prolonged lifetime of photoinduced charge carriers (Fig. 3d). Fig. 3e is the CV curves of Ni3(VO4)2 nanofibers and powders at a scan rate of 1 mV s 1, respectively. Both the oxidative and reductive peaks of Ni3(VO4)2 nanofibers are higher than those of Ni3(VO4)2 powders, meaning that Ni3(VO4)2 nanofibers possess the more prominent photocatalytic performance compared with Ni3(VO4)2 powders [14]. The transmission resistance of photocarriers fitted by the
equivalent circuit can be determined by EIS Nyquist curves. The decreased arc radius in high frequency region indicates Ni3(VO4)2 nanofibers possess the enhanced charge transfer efficiency (Fig. 3f)[15]. 4. Conclusions In summary, 1D superfine Ni3(VO4)2 nanofibers were synthesized by electrospinning and calcination treatment for the first time, which exhibited the excellent photocatalytic performance for the removal of tetracycline under simulated sunlight irradiation. The small diameter and dimensional effect of the nanofibers were beneficial to ultrafast carrier separation and provided rich
16
L. Yao et al. / Materials Letters 249 (2019) 13–16
catalytically active sites for photoeletrochemical reactions. The energy band structure, TDOS and free energy for Ni3(VO4)2 nanofibers were also simulated by DFT method. Thus, this work could serve a new guideline in the design of ultraviolet-visible-lightdriven photocatalysts for the environmental remediation.
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.04.046. References
Declaration of interest None.
Conflict of interest None. Acknowledgments This study was funded by the Shandong Provincial Natural Science Foundation (Grant No. ZR2016BM22 and ZR2018LF012).
Compliance with ethical standards The authors declare that they have no conflict of interest.
[1] A. Fujishima, K. Honda, Nature 238 (1972) 37–38. [2] J. Li, M. Zhang, Q. Li, J. Yang, Appl. Surf. Sci. 391 (2016) 184–193. [3] F. Chen, Q. Yang, J. Sun, F. Yao, S. Wang, Y. Wang, X. Wang, X. Li, C. Niu, D. Wang, G. Zeng, ACS Appl. Mater. Interfaces 8 (2016) 32887–32900. [4] D. Xu, B. Cheng, S. Cao, J. Yu, Appl. Catal. B-Environ. 164 (2015) 380–388. [5] R. Kumar, P. Rai, A. Sharma, J. Mater. Chem. A 4 (2016) 9822–9831. [6] F. Opoku, K. Govender, C. van Sittert, P. Govender, Compos. Mater. Sci. 138 (2017) 462–473. [7] Q. Wang, K. Sun, Q. Lu, M. Wei, L. Yao, E. Guo, Dyes Pigm. 155 (2018) 194–201. [8] L. Yao, E. Guo, K. Sun, Q. Lu, Q. Wang, Mater. Lett. 231 (2018) 11–15. [9] Y. Zhou, L. Liu, T. Wu, G. Yuan, J. Li, Q. Ding, F. Qi, W. Zhu, X. OuYang, Y. Wang, RSC Adv. 48 (2018) 27073–27079. [10] X. Lin, D. Xu, J. Zheng, M. Song, G. Che, Y. Wang, Y. Yang, C. Liu, L. Zhao, L. Chang, J. Alloy. Compd. 688 (2016) 891–898. [11] R. Ponnusamy, B. Chakraborty, C. Rout, J. Phys. Chem. B 122 (2018) 2737–2746. [12] H. Wei, W.A. McMaster, J.Z.Y. Tan, L. Cao, D. Chen, R.A. Caruso, J. Phys. Chem. C 6 (2018) 7236–7245. [13] Y. Jin, X. Shen, Z. Liu, Z. Wang, B. Zhu, P. Xu, L. Luo, L. Zhang, New J. Chem. 42 (2018) 411–419. [14] S. Ma, S. Zhan, Y. Jia, Q. Zhou, ACS Appl. Mater. Interfaces 7 (2015) 10576– 10586. [15] S. Zhang, J. Li, M. Zeng, G. Zhao, J. Xu, W. Hu, X. Wang, ACS. Appl. Mater. Interfaces 5 (2013) 12735–12743.