- Email: [email protected]
Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 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 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity Yanhui Ao n, Hong Tang, Peifang Wang, Chao Wang Key laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing 210098, China
art ic l e i nf o
a b s t r a c t
Article history: Received 30 March 2014 Accepted 15 May 2014
Ag@AgCl nanoparticles were deposited on two dimensional (2D) square-like BiOCl nanoplates through an in-situ ultraviolet (UV) reduction method. In the method, CTAC was used as both Cl source and dispersant. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and UV–vis diffuse reflectance spectrum (DRS). Results showed that the Ag@AgCl–BiOCl hybrids exhibited an enhancement of photo-absorption in the visible and near infrared region owing to the surface plasmon resonance (SPR) of Ag. The activity of the obtained samples was investigated by the photodegradation of dye X-3B. Results showed that all the Ag@AgCl–BiOCl hybrids exhibited higher activity than pure BiOCl. The highest one showed five times enhancement in photoactivity compared to pure BiOCl. Furthermore, the mechanisms of sample growth and dye decomposition were proposed. & 2014 Published by Elsevier B.V.
Keywords: Nanoparticles Composite materials Photocatalysis Ag@AgCl BiOCl Visible light
1. Introduction Over the past decades, bismuth oxyhalides (BiOX, X¼ Cl, Br, I) attracted a large attention in the field of photocatalysis due to their unique properties and potential applications [1–4]. An's group prepared BiOX by a hydrolysis method, and found BiOCl had the highest activity for the decomposition of isopropanol [5]. As a layered compound, BiOCl showed high activity due to its efficient separation rate of photogenerated hole–electron pairs [6]. However, BiOCl can only be activated by the ultraviolet light (λo380 nm), which is about 4% of the solar spectrum. Therefore, some investigators tried to improve the visible light responsive activity of BiOCl by different methods [7,8]. Recently, AgXs (X¼Cl, Br, I) were reported to be good materials to improve the visible light responsive performance of some large band gap semiconductors [9–11]. Upon light illumination, AgX can form Ag@AgX due to its partial decomposition to Ag nanoparticles. Therefore, Ag@AgX exhibits efficient photocatalytic activity and good stability under visible light, owing to the surface plasmon resonance (SPR) of Ag nanoparticles [12–14]. Cheng's group synthesized an Ag/AgBr/BiOBr hybrid via an ion exchange method. The obtained samples showed good performance for pathogenic organism sterilization and dye degradation [11]. The flower-like Ag/AgCl/BiOCl composite also displayed enhanced visible-light photocatalytic activity [15]. n
Corresponding author. Tel./fax: þ 86 25 8378 7330. E-mail address: [email protected] (Y. Ao).
However, there is no work focused on the preparation and activity of Ag@AgX deposited two dimensional (2D) square-like BiOCl nanoplate. In this work, a novel type of Ag@AgCl–BiOCl hybrids with 2D square-like structure was prepared by an in-situ UV reduction method. The obtained hybrids exhibited a great enhancement in photocatalytic performance under visible light irradiation.
2. Experimental setup Synthesis: All chemicals involved were analytical grade and Q2 used without further purification. BiOCl nanosheet was prepared by a solvothermal method [16]. The Ag@AgCl–BiOCl hybrids were prepared by an in-situ ultraviolet reduction method. In a typical process, BiOCl nanoplate and hexadecyl trimethyl ammonium chloride (CTAC) were added into 150 ml ultrapure water. The suspension was ultrasonic treated for 5 min and stirred for 1.5 h. Afterwards, 4 ml of 0.1 M AgNO3 solution was quickly added into the above suspension, which was stirred for another 1.5 h. Then, it was irradiated by UV light for 10 min (or 20, 30, 45 min). The products were collected and washed thoroughly with deionised water. Finally, the samples were dried at 80 1C for 6 h. The obtained samples were defined as Ag@AgCl–BiOCl-1, Ag@AgCl– BiOCl-2, Ag@AgCl–BiOCl-3 and Ag@AgCl–BiOCl-4 for samples irradiated for 10, 20, 30 and 45 min, respectively. Characterization: The crystal form and crystallinity of the prepared samples were examined by X-ray diffraction (XRD).
http://dx.doi.org/10.1016/j.matlet.2014.05.083 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i
Y. Ao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
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 61 62 63 64 65 66
Fig. 1. (a) XRD patterns and (b) UV/vis diffuse reflectance spectra of pure BiOCl and Ag@AgCl–BiOCl hybrids.
The surface morphologies and microstructures were observed by scanning electron micrograph (SEM) and transmission electron microscope (TEM). The UV–vis absorption spectra were carried out on a spectrometer (UV3600, SHIMADZU). Photocatalytic activity measurement: Photocatalytic activities of the samples were evaluated by degradation of reactive brilliant red X-3B under the irradiation of visible light (λZ400 nm). The light source was a 300 W Xe lamp with a light filter. In every experiment, 0.01 g sample was added into 100 ml 40 ppm X-3B solution. The suspension was ultrasonic treated for 2 min, and then it was stirred for 30 min in dark to reach the adsorption–desorption equilibrium. At 15 min intervals in the irradiation process, about 2 ml suspension was sampled and examined.
3. Results and discussion The as-prepared samples were characterized by XRD. As shown in Fig. 1a, all the diffraction peaks of pure BiOCl could be indexed to the tetragonal phase of BiOCl (JCPDS no. 06-0249), suggesting the high purity. In addition to BiOCl diffraction peaks, there are some weak peaks observed in the XRD patterns of Ag@AgCl–BiOCl hybrids at about 2θ¼ 27.91, 32.21, 46.21, and 57.51, which can be indexed to the pattern of AgCl (JCPDS no. 85-1355). It is similar to the result reported by Zhang et al. [9]. However, no distinct diffraction peaks of metallic Ag could be found, probably due to its low content, high dispersity or small crystallite. Fig. 1b shows the UV/vis diffuse reflectance spectra of pure BiOCl and Ag@AgCl–BiOCl hybrids. All the samples had similar absorption edge at ca. 365 nm. Compared to pure BiOCl, Ag@AgCl– BiOCl hybrids exhibit stronger absorption ability in the visible light range. The remarkable enhancement in photoabsorption can be ascribed to the surface plasmon resonance (SPR) of Ag nanoparticles. Fig. 2a shows scheme of the synthetic procedure of the Ag@AgCl– BiOCl hybrid. Firstly, the square-like 2D BiOCl nanosheets were prepared by a hydrothermal process. The nanosheets have a thickness of 10–25 nm (Fig. 2b). Secondly, the BiOCl nanosheets are uniformly dispersed in the system with the assistant of CTAC. Simultaneously, AgCl nanoparticles uniformly grow on the surface of BiOCl nanosheets through the reaction between Ag þ and CTAC. Finally, AgCl are partially reduced to Ag0 species under UV light irradiation. Thus, the resultant Ag@AgCl nanoparticles are anchored on the BiOCl nanosheets uniformly, which can be seen from Fig. 2c–f, Ag@AgCl nanoparticles sized in 8–50 nm are observed. Apparently, CTAC can serve as both Cl source and dispersant. The photocatalytic activities of the samples were evaluated by photodegradation of the dye X-3B. As shown in Fig. 3a, Ag@AgCl– BiOCl hybrids all display superior photocatalytic performance than
pure BiOCl. The apparent rate constant was also chosen to compare the photocatalytic performance of different samples. And the results are shown in Fig. 3b, the obtained values are 0.0020, 0.0054, 0.011, 0.012 and 0.0043 for pure BiOCl, Ag@AgCl–BiOCl-1, Ag@AgCl–BiOCl-2, Ag@AgCl–BiOCl-3 and Ag@AgCl–BiOCl-4, respectively. A longer UV irradiation in the synthesis process would induce more Ag0 and stronger SPR. As a result, the time of light irradiation induce a notable difference in photocatalytic performance of the Ag@AgCl–BiOCl hybrids. The activity of the hybrids enhanced as the irradiation time increases when it is less than 30 min. However, the activity decreased when the irradiation time prolonged to 45 min. Thus, 30 min is the optimum time to obtain the highest photocatalytic property in the present work. In contrast to the degradation percent of 11% by pure BiOCl in 1 h, Ag@AgCl–BiOCl-3 shows much higher degradation efficiency (five times faster than the pure BiOCl). This stems from the favorable crystallinity, excellent photoabsorption, good adsorption ability and some other factors. The SPR of Ag0 species may be the fundamental one above all. The reaction mechanism for the Ag@AgCl–BiOCl hybrid was illustrated in Fig. 3c. Photogenerated electron–hole (e –h þ ) pairs would be generated on the surface of Ag nanoparticles due to the SPR under visible light irradiation. The electrons would sequentially transfer to the conduction band (CB) of AgCl, and then migrate to that of BiOCl, which is more positive. And some of them may be trapped by dissolved O2 to generate d O2 , which is one of the primary active species. However, the electrons on the CB of BiOCl cannot react with O2 to produce d O2 radical (CB potential (BiOCl) ¼0.11 eV, E0 (O2/d O2 )¼ 0.046 eV) [17]. On the other hand, the h þ can react with OH and Cl in the solution and produce dOH and Cld respectively. These oxidative species will lead to the degradation of X-3B. Besides, Ag (h þ ) and the photoinduced h þ in the VB of BiOCl and AgCl can also oxidize X-3B molecules directly. The related equations are described in detail as follows [18,19]: Agþhν (vis)-Agn þ
n
Ag -Ag (h )þ e
e þ O2þ
d
O2
-
h þOH - OH þ
d
(1) (2) (3) (4)
h þCl -Cl
(5)
X-3B þ d O2
(6)
(dOH, Cld, h þ )-CO2 þ H2Oþ…
Such a plasmon-induced electron transfer process endows the asprepared Ag@AgCl–BiOCl hybrids efficient transfer of photoexcited electrons and light harvesting in the visible region. And result in the
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i
Y. Ao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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 61 62 63 64 65 66
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Fig. 2. (a) The schematic synthetic route to Ag@AgCl–BiOCl hybrid, SEM (b–e) and TEM (f) images of the samples: (b) pure BiOCl, (c) Ag@AgCl–BiOCl-1, (d) Ag@AgCl–BiOCl-2, and (e–f) Ag@AgCl–BiOCl-3.
Fig. 3. (a) Concentration variation of X-3B in the photocatalytic process, (b) apparent rate constants for different samples, and (c) schematic photocatalytic reaction process of Ag@AgCl–BiOCl hybrids on the degradation of X-3B under visible light irradiation.
enhanced photocatalytic property of visible-light-driven degradation toward reactive brilliant red X-3B.
4. Conclusions In summary, a series of Ag@AgCl–BiOCl nanosheets have been prepared via an in-situ ultraviolet reduction method. Results indicated that the method is feasible to obtain Ag@AgCl–BiOCl hybrid with excellent photocatalytic activity under visible irradiation. The longer UV irradiation time in the synthesis process can promote its property in a certain range (r30 min), and the optimal condition is 30 min in this work.
Acknowledgments We are grateful for grants from the National Science Fund for Distinguished Young Scholars (No. 51225901), the National Key Basic Research Development Program (“973” Project) of China
(No. 2010CB429006), the National Natural Science Foundation of Q3 China (No. 51108158), Research Fund for innovation team of Ministry of Education (IRT13061), the outstanding Youth Fund of Jiangsu Province (BK2012037), Fundamental Research Funds for the Central Universities (2013B32114 and 2013B14114).
References [1] Su MH, He C, Zhu LF, Sun ZJ, Shan C, Zhang Q, et al. J Hazard Mater 2012;229– 230:72–82. [2] Ye P, Xie JJ, He YM, Zhang L, Wu TH, Wu Y. Mater Lett 2013;108:168–71. [3] Qin XY, Cheng HF, Wang WJ, Huang BB, Zhang XY, Dai Y. Mater Lett Q4 2013:285–8. [4] Wu SJ, Wang C, Cui YF, Hao WC, Wang TM, Brault P. Mater Lett 2011;65:1344–7. [5] An HZ, Du Y, Wang TM, Wang C, Hao WC, Zhang JY. Rare Met 2008;27:243–50. [6] Zhang KL, Liu CM, Huang FQ, Zheng C, Wang WD. Appl Catal B: Environ 2006;68:125–9. [7] Jiang J, Zhang LZ, Li H, He WW, Yin JJ. Nanoscale 2013;5:10573–81. [8] Cao J, Zhou CC, Lin HL, Xu BY, Chen SF. Appl Surf Sci 2013;284:263–9. [9] Zhang LS, Long TF, Yan CQ, He XC, Cheng ML, Zhong S. Adv Mater Res 2013;662:372–8.
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i
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[10] Kong L, Jiang Z, Lai HH, Nicholls RJ, Xiao TC, Jones MO, et al. J Catal 2012;293:116–25. [11] Cheng HF, Huang BB, Dai Y, Qin XY, Zhang XY. Langmuir 2010;26:6618–24. [12] Guo JF, Ma BW, Yin AY, Fan KN, Dai WL. J Hazard Mater 2012;211–212:77–82. [13] Abou Asi M, Zhu LF, He C, Sharma VK, Shu D, Li SZ, et al. Catal Today 2013;216:268–75.
[14] [15] [16] [17] [18] [19]
Cui WQ, Wang H, Liang YH, Liu L, Han BX. Catal Commun 2013;36:71–4. Xiong W, Zhao QD, Li XY, Zhang DK. Catal Commun 2011;16:229–33. Xiong JY, Cheng G, Li GF, Qin F, Chen R. RSC Adv 2011;1:1542–53. Ye LQ, Liu JY, Gong CQ, Tian LH, Peng TY, Zan L. ACS Catal 2012;2:1677–83. Zhou ZJ, Long MC, Cai WM, Cai J. Mol Catal A: Chem 2012;353–354:22–8. Cui WQ, Wang H, Liu L, Liang YH, McEvoy JG. Appl Surf Sci 2013;283:820–7.
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 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 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity Yanhui Ao n, Hong Tang, Peifang Wang, Chao Wang Key laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, Nanjing 210098, China
art ic l e i nf o
a b s t r a c t
Article history: Received 30 March 2014 Accepted 15 May 2014
Ag@AgCl nanoparticles were deposited on two dimensional (2D) square-like BiOCl nanoplates through an in-situ ultraviolet (UV) reduction method. In the method, CTAC was used as both Cl source and dispersant. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and UV–vis diffuse reflectance spectrum (DRS). Results showed that the Ag@AgCl–BiOCl hybrids exhibited an enhancement of photo-absorption in the visible and near infrared region owing to the surface plasmon resonance (SPR) of Ag. The activity of the obtained samples was investigated by the photodegradation of dye X-3B. Results showed that all the Ag@AgCl–BiOCl hybrids exhibited higher activity than pure BiOCl. The highest one showed five times enhancement in photoactivity compared to pure BiOCl. Furthermore, the mechanisms of sample growth and dye decomposition were proposed. & 2014 Published by Elsevier B.V.
Keywords: Nanoparticles Composite materials Photocatalysis Ag@AgCl BiOCl Visible light
1. Introduction Over the past decades, bismuth oxyhalides (BiOX, X¼ Cl, Br, I) attracted a large attention in the field of photocatalysis due to their unique properties and potential applications [1–4]. An's group prepared BiOX by a hydrolysis method, and found BiOCl had the highest activity for the decomposition of isopropanol [5]. As a layered compound, BiOCl showed high activity due to its efficient separation rate of photogenerated hole–electron pairs [6]. However, BiOCl can only be activated by the ultraviolet light (λo380 nm), which is about 4% of the solar spectrum. Therefore, some investigators tried to improve the visible light responsive activity of BiOCl by different methods [7,8]. Recently, AgXs (X¼Cl, Br, I) were reported to be good materials to improve the visible light responsive performance of some large band gap semiconductors [9–11]. Upon light illumination, AgX can form Ag@AgX due to its partial decomposition to Ag nanoparticles. Therefore, Ag@AgX exhibits efficient photocatalytic activity and good stability under visible light, owing to the surface plasmon resonance (SPR) of Ag nanoparticles [12–14]. Cheng's group synthesized an Ag/AgBr/BiOBr hybrid via an ion exchange method. The obtained samples showed good performance for pathogenic organism sterilization and dye degradation [11]. The flower-like Ag/AgCl/BiOCl composite also displayed enhanced visible-light photocatalytic activity [15]. n
Corresponding author. Tel./fax: þ 86 25 8378 7330. E-mail address: [email protected] (Y. Ao).
However, there is no work focused on the preparation and activity of Ag@AgX deposited two dimensional (2D) square-like BiOCl nanoplate. In this work, a novel type of Ag@AgCl–BiOCl hybrids with 2D square-like structure was prepared by an in-situ UV reduction method. The obtained hybrids exhibited a great enhancement in photocatalytic performance under visible light irradiation.
2. Experimental setup Synthesis: All chemicals involved were analytical grade and Q2 used without further purification. BiOCl nanosheet was prepared by a solvothermal method [16]. The Ag@AgCl–BiOCl hybrids were prepared by an in-situ ultraviolet reduction method. In a typical process, BiOCl nanoplate and hexadecyl trimethyl ammonium chloride (CTAC) were added into 150 ml ultrapure water. The suspension was ultrasonic treated for 5 min and stirred for 1.5 h. Afterwards, 4 ml of 0.1 M AgNO3 solution was quickly added into the above suspension, which was stirred for another 1.5 h. Then, it was irradiated by UV light for 10 min (or 20, 30, 45 min). The products were collected and washed thoroughly with deionised water. Finally, the samples were dried at 80 1C for 6 h. The obtained samples were defined as Ag@AgCl–BiOCl-1, Ag@AgCl– BiOCl-2, Ag@AgCl–BiOCl-3 and Ag@AgCl–BiOCl-4 for samples irradiated for 10, 20, 30 and 45 min, respectively. Characterization: The crystal form and crystallinity of the prepared samples were examined by X-ray diffraction (XRD).
http://dx.doi.org/10.1016/j.matlet.2014.05.083 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i
Y. Ao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
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 61 62 63 64 65 66
Fig. 1. (a) XRD patterns and (b) UV/vis diffuse reflectance spectra of pure BiOCl and Ag@AgCl–BiOCl hybrids.
The surface morphologies and microstructures were observed by scanning electron micrograph (SEM) and transmission electron microscope (TEM). The UV–vis absorption spectra were carried out on a spectrometer (UV3600, SHIMADZU). Photocatalytic activity measurement: Photocatalytic activities of the samples were evaluated by degradation of reactive brilliant red X-3B under the irradiation of visible light (λZ400 nm). The light source was a 300 W Xe lamp with a light filter. In every experiment, 0.01 g sample was added into 100 ml 40 ppm X-3B solution. The suspension was ultrasonic treated for 2 min, and then it was stirred for 30 min in dark to reach the adsorption–desorption equilibrium. At 15 min intervals in the irradiation process, about 2 ml suspension was sampled and examined.
3. Results and discussion The as-prepared samples were characterized by XRD. As shown in Fig. 1a, all the diffraction peaks of pure BiOCl could be indexed to the tetragonal phase of BiOCl (JCPDS no. 06-0249), suggesting the high purity. In addition to BiOCl diffraction peaks, there are some weak peaks observed in the XRD patterns of Ag@AgCl–BiOCl hybrids at about 2θ¼ 27.91, 32.21, 46.21, and 57.51, which can be indexed to the pattern of AgCl (JCPDS no. 85-1355). It is similar to the result reported by Zhang et al. [9]. However, no distinct diffraction peaks of metallic Ag could be found, probably due to its low content, high dispersity or small crystallite. Fig. 1b shows the UV/vis diffuse reflectance spectra of pure BiOCl and Ag@AgCl–BiOCl hybrids. All the samples had similar absorption edge at ca. 365 nm. Compared to pure BiOCl, Ag@AgCl– BiOCl hybrids exhibit stronger absorption ability in the visible light range. The remarkable enhancement in photoabsorption can be ascribed to the surface plasmon resonance (SPR) of Ag nanoparticles. Fig. 2a shows scheme of the synthetic procedure of the Ag@AgCl– BiOCl hybrid. Firstly, the square-like 2D BiOCl nanosheets were prepared by a hydrothermal process. The nanosheets have a thickness of 10–25 nm (Fig. 2b). Secondly, the BiOCl nanosheets are uniformly dispersed in the system with the assistant of CTAC. Simultaneously, AgCl nanoparticles uniformly grow on the surface of BiOCl nanosheets through the reaction between Ag þ and CTAC. Finally, AgCl are partially reduced to Ag0 species under UV light irradiation. Thus, the resultant Ag@AgCl nanoparticles are anchored on the BiOCl nanosheets uniformly, which can be seen from Fig. 2c–f, Ag@AgCl nanoparticles sized in 8–50 nm are observed. Apparently, CTAC can serve as both Cl source and dispersant. The photocatalytic activities of the samples were evaluated by photodegradation of the dye X-3B. As shown in Fig. 3a, Ag@AgCl– BiOCl hybrids all display superior photocatalytic performance than
pure BiOCl. The apparent rate constant was also chosen to compare the photocatalytic performance of different samples. And the results are shown in Fig. 3b, the obtained values are 0.0020, 0.0054, 0.011, 0.012 and 0.0043 for pure BiOCl, Ag@AgCl–BiOCl-1, Ag@AgCl–BiOCl-2, Ag@AgCl–BiOCl-3 and Ag@AgCl–BiOCl-4, respectively. A longer UV irradiation in the synthesis process would induce more Ag0 and stronger SPR. As a result, the time of light irradiation induce a notable difference in photocatalytic performance of the Ag@AgCl–BiOCl hybrids. The activity of the hybrids enhanced as the irradiation time increases when it is less than 30 min. However, the activity decreased when the irradiation time prolonged to 45 min. Thus, 30 min is the optimum time to obtain the highest photocatalytic property in the present work. In contrast to the degradation percent of 11% by pure BiOCl in 1 h, Ag@AgCl–BiOCl-3 shows much higher degradation efficiency (five times faster than the pure BiOCl). This stems from the favorable crystallinity, excellent photoabsorption, good adsorption ability and some other factors. The SPR of Ag0 species may be the fundamental one above all. The reaction mechanism for the Ag@AgCl–BiOCl hybrid was illustrated in Fig. 3c. Photogenerated electron–hole (e –h þ ) pairs would be generated on the surface of Ag nanoparticles due to the SPR under visible light irradiation. The electrons would sequentially transfer to the conduction band (CB) of AgCl, and then migrate to that of BiOCl, which is more positive. And some of them may be trapped by dissolved O2 to generate d O2 , which is one of the primary active species. However, the electrons on the CB of BiOCl cannot react with O2 to produce d O2 radical (CB potential (BiOCl) ¼0.11 eV, E0 (O2/d O2 )¼ 0.046 eV) [17]. On the other hand, the h þ can react with OH and Cl in the solution and produce dOH and Cld respectively. These oxidative species will lead to the degradation of X-3B. Besides, Ag (h þ ) and the photoinduced h þ in the VB of BiOCl and AgCl can also oxidize X-3B molecules directly. The related equations are described in detail as follows [18,19]: Agþhν (vis)-Agn þ
n
Ag -Ag (h )þ e
e þ O2þ
d
O2
-
h þOH - OH þ
d
(1) (2) (3) (4)
h þCl -Cl
(5)
X-3B þ d O2
(6)
(dOH, Cld, h þ )-CO2 þ H2Oþ…
Such a plasmon-induced electron transfer process endows the asprepared Ag@AgCl–BiOCl hybrids efficient transfer of photoexcited electrons and light harvesting in the visible region. And result in the
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i
Y. Ao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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 61 62 63 64 65 66
3
Fig. 2. (a) The schematic synthetic route to Ag@AgCl–BiOCl hybrid, SEM (b–e) and TEM (f) images of the samples: (b) pure BiOCl, (c) Ag@AgCl–BiOCl-1, (d) Ag@AgCl–BiOCl-2, and (e–f) Ag@AgCl–BiOCl-3.
Fig. 3. (a) Concentration variation of X-3B in the photocatalytic process, (b) apparent rate constants for different samples, and (c) schematic photocatalytic reaction process of Ag@AgCl–BiOCl hybrids on the degradation of X-3B under visible light irradiation.
enhanced photocatalytic property of visible-light-driven degradation toward reactive brilliant red X-3B.
4. Conclusions In summary, a series of Ag@AgCl–BiOCl nanosheets have been prepared via an in-situ ultraviolet reduction method. Results indicated that the method is feasible to obtain Ag@AgCl–BiOCl hybrid with excellent photocatalytic activity under visible irradiation. The longer UV irradiation time in the synthesis process can promote its property in a certain range (r30 min), and the optimal condition is 30 min in this work.
Acknowledgments We are grateful for grants from the National Science Fund for Distinguished Young Scholars (No. 51225901), the National Key Basic Research Development Program (“973” Project) of China
(No. 2010CB429006), the National Natural Science Foundation of Q3 China (No. 51108158), Research Fund for innovation team of Ministry of Education (IRT13061), the outstanding Youth Fund of Jiangsu Province (BK2012037), Fundamental Research Funds for the Central Universities (2013B32114 and 2013B14114).
References [1] Su MH, He C, Zhu LF, Sun ZJ, Shan C, Zhang Q, et al. J Hazard Mater 2012;229– 230:72–82. [2] Ye P, Xie JJ, He YM, Zhang L, Wu TH, Wu Y. Mater Lett 2013;108:168–71. [3] Qin XY, Cheng HF, Wang WJ, Huang BB, Zhang XY, Dai Y. Mater Lett Q4 2013:285–8. [4] Wu SJ, Wang C, Cui YF, Hao WC, Wang TM, Brault P. Mater Lett 2011;65:1344–7. [5] An HZ, Du Y, Wang TM, Wang C, Hao WC, Zhang JY. Rare Met 2008;27:243–50. [6] Zhang KL, Liu CM, Huang FQ, Zheng C, Wang WD. Appl Catal B: Environ 2006;68:125–9. [7] Jiang J, Zhang LZ, Li H, He WW, Yin JJ. Nanoscale 2013;5:10573–81. [8] Cao J, Zhou CC, Lin HL, Xu BY, Chen SF. Appl Surf Sci 2013;284:263–9. [9] Zhang LS, Long TF, Yan CQ, He XC, Cheng ML, Zhong S. Adv Mater Res 2013;662:372–8.
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i
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Y. Ao et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
[10] Kong L, Jiang Z, Lai HH, Nicholls RJ, Xiao TC, Jones MO, et al. J Catal 2012;293:116–25. [11] Cheng HF, Huang BB, Dai Y, Qin XY, Zhang XY. Langmuir 2010;26:6618–24. [12] Guo JF, Ma BW, Yin AY, Fan KN, Dai WL. J Hazard Mater 2012;211–212:77–82. [13] Abou Asi M, Zhu LF, He C, Sharma VK, Shu D, Li SZ, et al. Catal Today 2013;216:268–75.
[14] [15] [16] [17] [18] [19]
Cui WQ, Wang H, Liang YH, Liu L, Han BX. Catal Commun 2013;36:71–4. Xiong W, Zhao QD, Li XY, Zhang DK. Catal Commun 2011;16:229–33. Xiong JY, Cheng G, Li GF, Qin F, Chen R. RSC Adv 2011;1:1542–53. Ye LQ, Liu JY, Gong CQ, Tian LH, Peng TY, Zan L. ACS Catal 2012;2:1677–83. Zhou ZJ, Long MC, Cai WM, Cai J. Mol Catal A: Chem 2012;353–354:22–8. Cui WQ, Wang H, Liu L, Liang YH, McEvoy JG. Appl Surf Sci 2013;283:820–7.
Please cite this article as: Ao Y, et al. Deposition of Ag@AgCl onto two dimensional square-like BiOCl nanoplates for high visible-light photocatalytic activity. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.05.083i