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BiVO4 composite fibers with enhanced visible-light photocatalytic performance
Author’s Accepted Manuscript Facile synthesis of hollow and porous Ag+/Ag/BiVO4 composite fibers with enhanced visible-light photocatalytic performance Ke Wang, Limin Liang, Hui Liu, Xinjian Xie, Qiuyan Hao, Caichi Liu www.elsevier.com
PII: DOI: Reference:
S0167-577X(15)30502-4 http://dx.doi.org/10.1016/j.matlet.2015.08.145 MLBLUE19506
To appear in: Materials Letters Received date: 3 July 2015 Revised date: 27 August 2015 Accepted date: 29 August 2015 Cite this article as: Ke Wang, Limin Liang, Hui Liu, Xinjian Xie, Qiuyan Hao and Caichi Liu, Facile synthesis of hollow and porous Ag +/Ag/BiVO4 composite fibers with enhanced visible-light photocatalytic performance, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.08.145 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Facile synthesis of hollow and porous Ag+/Ag/BiVO4 composite fibers with enhanced visible-light photocatalytic performance Ke Wanga,b, Limin Lianga, Hui Liua, Xinjian Xiea,, Qiuyan Haoa, Caichi Liua, a. School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130, China b. Department of Mathematics and Physics, Hebei Institute of Architecture Civil Engineering, Zhangjiakou 075000, China Abstract: Novel hollow and porous Ag+/Ag/BiVO4 composite fibers were prepared by a one-step method using cotton fibers as templates. XRD and XPS results indicated that the sample is Ag+/Ag/BiVO4 composites. SEM and TEM results revealed that the sample is hollow fibers and the wall is porous. The UV-vis diffuse reflectance spectroscopy results demonstrated that the sample shows enhanced visible-light absorption. The investigation of the methylene blue degradation suggested that the sample has the most excellent photocatalytic activity as compared with the BiVO4 fibers and Ag/BiVO4 composite fibers. The synthesis procedure is also simple, rapid and practical. Keywords: Semiconductors; Ag+/Ag/BiVO4; Microstructure; Photocatalytic activity 1. Introduction With industrialization and population growth, the environmental contamination
Corresponding author. Tel.: +86 22 60202474, Fax: +86 22 60204129. Co-corresponding author. E-mail addresses: [email protected] (X. Xie), [email protected] (C. Liu).
1
caused by organic pollutants is becoming an increasing problem around the world. Thus, the development of renewable technologies for environmental remediation is highly desired. It is widely accepted that semiconductor photocatalysis has emerged as one of the most promising technologies because it represents an easy way to utilize the energy of solar light, abundantly available everywhere in the world. As one of the most important semiconductor photocatalysis, bismuth vanadate (BiVO4) has recently attracted considerable attention for its strong photocatalysis for pollutant decomposing and water splitting under visible light irradiation [1,2]. Therefore a variety of BiVO4 materials such as microspheres [3], microparticles [4], spindly microtubes [5], etc have been synthesized. However, the activity of BiVO4 materials is restricted by low efficiency in light absorption and serious recombination of charge carriers. In order to enhance the light-absorption efficiency hollow and/or porous BiVO4 were prepared [6,7]. Dopants such as Ag, Au and Pt are added to promote the separation of photogenerated charge carriers [8-10]. On the other hand, the natural materials exhibit a hierarchically built anatomy, optimized from nature in respect to their mechanical and functional properties by evolution over a long period of time, and they are also cheap, abundantly available and reproducible. Among them, cotton fibers have been proved to be a kind of vital template for preparing functional materials with hollow shape, especially single metal oxides [11]. However, to the best of our knowledge, there have been no reports of Ag+/Ag/BiVO4 composites with porous hollow fiber structure.
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In the present work, hollow and porous Ag+/Ag/BiVO4 composite fibers were successfully synthesized by a one-step method using cotton fibers as templates. The synthesis procedure is simple, rapid and practical. The Ag+/Ag/BiVO4 composite fibers showed the most excellent photocatalytic activity as compared with the BiVO4 fibers and Ag/BiVO4 composite fibers prepared by a photoreduction method. 2. Experimental Preparation: AR-grade Bi(NO3)3·5H2O, NH4VO3 and AgNO3 were used in our experiment without further purification. In a typical process for the synthesis of Ag+/Ag/BiVO4 composite fibers, 2.4250g Bi(NO3)3·5H2O, 0.5850g NH4VO3 and 0.1529g AgNO3 were dissolved in 25.0 mL nitric acid aqueous solution with a concentration of 3 mol/L. 0.5000g cotton fibers were dipped into the solution, and then dried at 50°C for 2 h. Afterwards the precursors were calcinated at 500°C under air atmosphere for 2 h. The goal sample with fiber structure (labeled as S-2) was obtained finally. As references, BiVO4 fibers without the addition of AgNO3 (labeled as S-0) were prepared, and Ag/BiVO4 composite fibers (labeled as S-1) were prepared by immersing the BiVO4 fibers in AgNO3 solution and then irradiating with a 40 W UV lamp for 20 min according to the method reported by Zhang et al. [12]. Characterization: The crystal structures were recorded on an X-ray diffractometer (D/Max-Ultima IV, Rigaku, Japan). X-ray photoelectron spectroscopy (XPS) was performed on an Escalab 250Xi instrument (Thermo Scientific, USA). The microstructures were observed by a field emission scanning electron microanalyzer
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(FE-SEM, S4800, Hitachi, Japan) and a field emission transmission electron microscope (FE-TEM, Tecnai G2 F20, FEI, USA). The UV-vis diffuse reflectance spectra was analyzed on a UV-vis spectrophotometer (Cary 5000, Varian, USA). The photocatalytic reactivity of the as-prepared samples was evaluated using methylene blue (MB) as a probe molecule under visible-light irradiation. In a typical process, 100 mg BiVO4 samples were added to 100 mL of 10 mg/L MB solution and then stirred in the dark for 30 min. The solution was then exposed to visible light irradiation from a 300 W Xe lamp. After removal of the photocatalyst by centrifugation, the MB degradation was measured. 3. Results and discussions
Fig. 1. XRD patterns of the samples S-0, S-1 and S-2 Fig. 1 shows the XRD patterns of the as-prepared samples. It is clear that without the addition of AgNO3, the sample S-0 is BiVO4 of the monoclinic scheelite type (JCPDS 14-0688), and the peaks of these impurities Bi2O3 and V2O5 are not observed, indicating that BiVO4 with high purity could be obtained using this one-step method.
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When AgNO3 was added as a Ag source, peaks at 38.2° and 44.4° (marked with rounds) are observed over the samples S-1 and S-2, which are corresponding to (111) and (200) facets of Ag (JCPDS 04-0783), respectively. While an additional peak at 31.7° (marked with squares) over the sample S-2 ascribable to the hybrid metal oxide according to Zhou et al. [13] was observed obviously. Results indicated that the samples S-1 and S-2 contained Bi, O, V, Ag and C elements (Fig. 2a). The high-resolution XPS spectra (Fig. 2b) show that the peaks at binding energies of 374.1 and 368.1 eV of the sample S-1 could be ascribed to the Ag 3d3/2 and Ag 3d5/2 signals, respectively, suggesting the presence of metallic Ag. It is worth pointing out that the Ag 3d3/2 and Ag 3d5/2 signals of the sample S-2 shifted to slightly lower binding energies as compared with the sample S-1, possibly due to the presence of Ag+[13]. Based on the XRD and XPS results, one can conclude that the samples S-1 and S-2 are Ag/BiVO4 composites and Ag+/Ag/BiVO4 composites, respectively.
Fig. 2. XPS spectra (a, b) of the samples S-1 and S-2. In the low magnified SEM image (Fig. 3a) of S-2, its fiber morphology, mimicking
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the shape of the cotton fiber, is observed. High magnified SEM (Fig. 3b) reveals that the fibers of the S-2 are hollow and porous, and the wall of the fiber also has a multi-structure with a thickness 800-1500 nm. Its hollow and porous morphology results from the combustion removal of the cotton fiber and the release of gases from the decomposition of the cotton fiber at an enough high temperature. The low-magnified TEM image (Fig. 3c) shows that the wall of the fiber is composed of irregular nanoparticles, and there are a number of holes between the nanoparticles, this may further confirm the porosity in the wall. It can also be seen in Fig. 3c that there are some tiny nanoparticles on the surfaces of larger nanoparticles. Fig. 3d represents HRTEM image recorded on the white rectangular area in Fig. 3c. The fringe spacing of 0.468 and 0.237 nm in the HRTEM image corresponds to the (011) and (111) planes of BiVO4 and metallic Ag, respectively.
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Fig. 3. SEM (a, b) and TEM (c, d) images of the sample S-2 Red-shift and enhancement of visible-light absorption in spectrum (Fig. 4a) were observed for the samples S-1 and S-2 compared to that of the sample S-0, which may due to a band-gap transition and charge-transfer transition between Ag and BiVO4 as reported by Sayama et al.[14]. The photocatalytic activities of the as-prepared samples were evaluated by the degradation of MB under the irradiation of visible light. As shown in Fig. 4b, the photodegradation efficiency of MB over the sample S-2 is near 94% within 120 min. The superior photocatalytic performance of the sample S-2 can be explained by its enhanced visible light absorption ability and the high separation efficiency of photogenerated charge carriers.
Fig. 4. (a) UV-vis absorption spectra and (b) photocatalytic activities of the samples S-0, S-1 and S-2 4. Conclusions For the first time, the Ag+/Ag/BiVO4 composites with porous hollow fiber structure were successfully prepared by a one-step method using cotton fibers as templates. The
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as-prepared Ag+/Ag/BiVO4 composite fibers have an enhanced visible light photocatalytic performance as compared with the BiVO4 fibers and Ag/BiVO4 composite fibers. This facile one-step method can be further extended to synthesize a vast mass of composite metal oxides with hollow and porous structures for great potential applications. References [1] Li JQ, Cui MM, Guo ZY, Liu ZX, Zhu ZF. Mater Lett 2015;151:75-78. [2] Kudo A, Ueda K, Kato H, Mikami I. Catal Lett 1998;53:229-230. [3] Li F, Yang CY, Li QG, Cao W, Li TH. Mater Lett 2015;145:52-55. [4] Tokunaga S, Kato H, Kudo A. Chem Mater 2001;13:4624-4628. [5] Liu W, Yu YQ, Cao LX, Su G, Liu XY, Zhang L, et al. J Hazard Mater 2010;181:1102-1108. [6] Jiang HY, Dai HX, Meng X, Ji KM, Zhang L, Deng JG. Appl Catal B: environmental 2011;105:326-334. [7] Li GS, Zhang DP, Yu JC. Chem Mater 2008;20:3983-3992. [8] Gao XM, Fu F, Zhang LP, Li WH. Physica B: Condensed Matter 2013;419:80-85. [9] Zhang AP, Zhang JZ. Journal of Alloys and Compounds 2010;491:631-635. [10] Ge L. Journal of Molecular Catalysis A: Chemical 2008;282:62-66. [11] Zhou XY, Huang B, Zou YL, Xie J, Yang J. Mater Lett 2014;120:279-82. [12] Zhang XF, Zhang YB, Quan X, Chen S. J Hazard Mater 2009;167:911-914. [13] Zhou B, Zhao X, Liu HJ, Qu JH, Huang CP. Sep Purif Technol 2011;77:275-282.
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[14] Sayama K, Nomura A, Arai T, Sugita T. J Phys Chem B 2006;110:11352-11360. Highlights
1. For the first time, the Ag+/Ag/BiVO4 composite fibers were prepared. 2. The composite fibers have an enhanced visible light photocatalytic performance. 3. The synthesis procedure is simple, rapid and practical.
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PII: DOI: Reference:
S0167-577X(15)30502-4 http://dx.doi.org/10.1016/j.matlet.2015.08.145 MLBLUE19506
To appear in: Materials Letters Received date: 3 July 2015 Revised date: 27 August 2015 Accepted date: 29 August 2015 Cite this article as: Ke Wang, Limin Liang, Hui Liu, Xinjian Xie, Qiuyan Hao and Caichi Liu, Facile synthesis of hollow and porous Ag +/Ag/BiVO4 composite fibers with enhanced visible-light photocatalytic performance, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.08.145 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Facile synthesis of hollow and porous Ag+/Ag/BiVO4 composite fibers with enhanced visible-light photocatalytic performance Ke Wanga,b, Limin Lianga, Hui Liua, Xinjian Xiea,, Qiuyan Haoa, Caichi Liua, a. School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130, China b. Department of Mathematics and Physics, Hebei Institute of Architecture Civil Engineering, Zhangjiakou 075000, China Abstract: Novel hollow and porous Ag+/Ag/BiVO4 composite fibers were prepared by a one-step method using cotton fibers as templates. XRD and XPS results indicated that the sample is Ag+/Ag/BiVO4 composites. SEM and TEM results revealed that the sample is hollow fibers and the wall is porous. The UV-vis diffuse reflectance spectroscopy results demonstrated that the sample shows enhanced visible-light absorption. The investigation of the methylene blue degradation suggested that the sample has the most excellent photocatalytic activity as compared with the BiVO4 fibers and Ag/BiVO4 composite fibers. The synthesis procedure is also simple, rapid and practical. Keywords: Semiconductors; Ag+/Ag/BiVO4; Microstructure; Photocatalytic activity 1. Introduction With industrialization and population growth, the environmental contamination
Corresponding author. Tel.: +86 22 60202474, Fax: +86 22 60204129. Co-corresponding author. E-mail addresses: [email protected] (X. Xie), [email protected] (C. Liu).
1
caused by organic pollutants is becoming an increasing problem around the world. Thus, the development of renewable technologies for environmental remediation is highly desired. It is widely accepted that semiconductor photocatalysis has emerged as one of the most promising technologies because it represents an easy way to utilize the energy of solar light, abundantly available everywhere in the world. As one of the most important semiconductor photocatalysis, bismuth vanadate (BiVO4) has recently attracted considerable attention for its strong photocatalysis for pollutant decomposing and water splitting under visible light irradiation [1,2]. Therefore a variety of BiVO4 materials such as microspheres [3], microparticles [4], spindly microtubes [5], etc have been synthesized. However, the activity of BiVO4 materials is restricted by low efficiency in light absorption and serious recombination of charge carriers. In order to enhance the light-absorption efficiency hollow and/or porous BiVO4 were prepared [6,7]. Dopants such as Ag, Au and Pt are added to promote the separation of photogenerated charge carriers [8-10]. On the other hand, the natural materials exhibit a hierarchically built anatomy, optimized from nature in respect to their mechanical and functional properties by evolution over a long period of time, and they are also cheap, abundantly available and reproducible. Among them, cotton fibers have been proved to be a kind of vital template for preparing functional materials with hollow shape, especially single metal oxides [11]. However, to the best of our knowledge, there have been no reports of Ag+/Ag/BiVO4 composites with porous hollow fiber structure.
2
In the present work, hollow and porous Ag+/Ag/BiVO4 composite fibers were successfully synthesized by a one-step method using cotton fibers as templates. The synthesis procedure is simple, rapid and practical. The Ag+/Ag/BiVO4 composite fibers showed the most excellent photocatalytic activity as compared with the BiVO4 fibers and Ag/BiVO4 composite fibers prepared by a photoreduction method. 2. Experimental Preparation: AR-grade Bi(NO3)3·5H2O, NH4VO3 and AgNO3 were used in our experiment without further purification. In a typical process for the synthesis of Ag+/Ag/BiVO4 composite fibers, 2.4250g Bi(NO3)3·5H2O, 0.5850g NH4VO3 and 0.1529g AgNO3 were dissolved in 25.0 mL nitric acid aqueous solution with a concentration of 3 mol/L. 0.5000g cotton fibers were dipped into the solution, and then dried at 50°C for 2 h. Afterwards the precursors were calcinated at 500°C under air atmosphere for 2 h. The goal sample with fiber structure (labeled as S-2) was obtained finally. As references, BiVO4 fibers without the addition of AgNO3 (labeled as S-0) were prepared, and Ag/BiVO4 composite fibers (labeled as S-1) were prepared by immersing the BiVO4 fibers in AgNO3 solution and then irradiating with a 40 W UV lamp for 20 min according to the method reported by Zhang et al. [12]. Characterization: The crystal structures were recorded on an X-ray diffractometer (D/Max-Ultima IV, Rigaku, Japan). X-ray photoelectron spectroscopy (XPS) was performed on an Escalab 250Xi instrument (Thermo Scientific, USA). The microstructures were observed by a field emission scanning electron microanalyzer
3
(FE-SEM, S4800, Hitachi, Japan) and a field emission transmission electron microscope (FE-TEM, Tecnai G2 F20, FEI, USA). The UV-vis diffuse reflectance spectra was analyzed on a UV-vis spectrophotometer (Cary 5000, Varian, USA). The photocatalytic reactivity of the as-prepared samples was evaluated using methylene blue (MB) as a probe molecule under visible-light irradiation. In a typical process, 100 mg BiVO4 samples were added to 100 mL of 10 mg/L MB solution and then stirred in the dark for 30 min. The solution was then exposed to visible light irradiation from a 300 W Xe lamp. After removal of the photocatalyst by centrifugation, the MB degradation was measured. 3. Results and discussions
Fig. 1. XRD patterns of the samples S-0, S-1 and S-2 Fig. 1 shows the XRD patterns of the as-prepared samples. It is clear that without the addition of AgNO3, the sample S-0 is BiVO4 of the monoclinic scheelite type (JCPDS 14-0688), and the peaks of these impurities Bi2O3 and V2O5 are not observed, indicating that BiVO4 with high purity could be obtained using this one-step method.
4
When AgNO3 was added as a Ag source, peaks at 38.2° and 44.4° (marked with rounds) are observed over the samples S-1 and S-2, which are corresponding to (111) and (200) facets of Ag (JCPDS 04-0783), respectively. While an additional peak at 31.7° (marked with squares) over the sample S-2 ascribable to the hybrid metal oxide according to Zhou et al. [13] was observed obviously. Results indicated that the samples S-1 and S-2 contained Bi, O, V, Ag and C elements (Fig. 2a). The high-resolution XPS spectra (Fig. 2b) show that the peaks at binding energies of 374.1 and 368.1 eV of the sample S-1 could be ascribed to the Ag 3d3/2 and Ag 3d5/2 signals, respectively, suggesting the presence of metallic Ag. It is worth pointing out that the Ag 3d3/2 and Ag 3d5/2 signals of the sample S-2 shifted to slightly lower binding energies as compared with the sample S-1, possibly due to the presence of Ag+[13]. Based on the XRD and XPS results, one can conclude that the samples S-1 and S-2 are Ag/BiVO4 composites and Ag+/Ag/BiVO4 composites, respectively.
Fig. 2. XPS spectra (a, b) of the samples S-1 and S-2. In the low magnified SEM image (Fig. 3a) of S-2, its fiber morphology, mimicking
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the shape of the cotton fiber, is observed. High magnified SEM (Fig. 3b) reveals that the fibers of the S-2 are hollow and porous, and the wall of the fiber also has a multi-structure with a thickness 800-1500 nm. Its hollow and porous morphology results from the combustion removal of the cotton fiber and the release of gases from the decomposition of the cotton fiber at an enough high temperature. The low-magnified TEM image (Fig. 3c) shows that the wall of the fiber is composed of irregular nanoparticles, and there are a number of holes between the nanoparticles, this may further confirm the porosity in the wall. It can also be seen in Fig. 3c that there are some tiny nanoparticles on the surfaces of larger nanoparticles. Fig. 3d represents HRTEM image recorded on the white rectangular area in Fig. 3c. The fringe spacing of 0.468 and 0.237 nm in the HRTEM image corresponds to the (011) and (111) planes of BiVO4 and metallic Ag, respectively.
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Fig. 3. SEM (a, b) and TEM (c, d) images of the sample S-2 Red-shift and enhancement of visible-light absorption in spectrum (Fig. 4a) were observed for the samples S-1 and S-2 compared to that of the sample S-0, which may due to a band-gap transition and charge-transfer transition between Ag and BiVO4 as reported by Sayama et al.[14]. The photocatalytic activities of the as-prepared samples were evaluated by the degradation of MB under the irradiation of visible light. As shown in Fig. 4b, the photodegradation efficiency of MB over the sample S-2 is near 94% within 120 min. The superior photocatalytic performance of the sample S-2 can be explained by its enhanced visible light absorption ability and the high separation efficiency of photogenerated charge carriers.
Fig. 4. (a) UV-vis absorption spectra and (b) photocatalytic activities of the samples S-0, S-1 and S-2 4. Conclusions For the first time, the Ag+/Ag/BiVO4 composites with porous hollow fiber structure were successfully prepared by a one-step method using cotton fibers as templates. The
7
as-prepared Ag+/Ag/BiVO4 composite fibers have an enhanced visible light photocatalytic performance as compared with the BiVO4 fibers and Ag/BiVO4 composite fibers. This facile one-step method can be further extended to synthesize a vast mass of composite metal oxides with hollow and porous structures for great potential applications. References [1] Li JQ, Cui MM, Guo ZY, Liu ZX, Zhu ZF. Mater Lett 2015;151:75-78. [2] Kudo A, Ueda K, Kato H, Mikami I. Catal Lett 1998;53:229-230. [3] Li F, Yang CY, Li QG, Cao W, Li TH. Mater Lett 2015;145:52-55. [4] Tokunaga S, Kato H, Kudo A. Chem Mater 2001;13:4624-4628. [5] Liu W, Yu YQ, Cao LX, Su G, Liu XY, Zhang L, et al. J Hazard Mater 2010;181:1102-1108. [6] Jiang HY, Dai HX, Meng X, Ji KM, Zhang L, Deng JG. Appl Catal B: environmental 2011;105:326-334. [7] Li GS, Zhang DP, Yu JC. Chem Mater 2008;20:3983-3992. [8] Gao XM, Fu F, Zhang LP, Li WH. Physica B: Condensed Matter 2013;419:80-85. [9] Zhang AP, Zhang JZ. Journal of Alloys and Compounds 2010;491:631-635. [10] Ge L. Journal of Molecular Catalysis A: Chemical 2008;282:62-66. [11] Zhou XY, Huang B, Zou YL, Xie J, Yang J. Mater Lett 2014;120:279-82. [12] Zhang XF, Zhang YB, Quan X, Chen S. J Hazard Mater 2009;167:911-914. [13] Zhou B, Zhao X, Liu HJ, Qu JH, Huang CP. Sep Purif Technol 2011;77:275-282.
8
[14] Sayama K, Nomura A, Arai T, Sugita T. J Phys Chem B 2006;110:11352-11360. Highlights
1. For the first time, the Ag+/Ag/BiVO4 composite fibers were prepared. 2. The composite fibers have an enhanced visible light photocatalytic performance. 3. The synthesis procedure is simple, rapid and practical.
9