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La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity
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Materials Letters journal homepage: www.elsevier.com/locate/matlet
New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity Jun Chen a,n, Shuangzhi Liu b, Li Zhang a, Na Chen a a b
School of Chemistry and Chemical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, China Chemistry and Engineering Department, Kaifeng University, Kaifeng 475004, China
art ic l e i nf o
a b s t r a c t
Article history: Received 31 January 2015 Accepted 28 February 2015
This work took the initiative to study the synthesis and photocatalytic properties of a new visible-lightactive SnS2/La2Ti2O7 heterojunction photocatalyst. SnS2/La2Ti2O7 nanoheterojunctions were synthesized via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets in deionized water at 130 1C for 6 h. The structure, composition, and optical property of the as-synthesized SnS2/La2Ti2O7 nanoheterojunctions were characterized by powder X-ray diffraction, wavelength dispersive X-ray fluorescence spectroscopy, transmission electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized SnS2/La2Ti2O7 nanoheterojunctions was tested in the reduction of aqueous Cr(VI) under visible-light (λ4 420 nm) irradiation, and compared with those of SnS2 nanoparticles and La2Ti2O7 nanosheets. It was observed that SnS2/La2Ti2O7 nanoheterojunctions exhibited much higher photocatalytic activity than SnS2 nanoparticles, whereas La2Ti2O7 nanosheets exhibited no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation. The reasons accounting for the photocatalytic results were also proposed. & 2015 Published by Elsevier B.V.
Keywords: Semiconductors Nanocomposites Powder technology Functional
1. Introduction The development of efficient visible-light-active photocatalysts is a prerequisite for practical application of photocatalysis technology in treating environmental pollutants [1–4]. Recently, SnS2 (Eg E2.2 eV) has been proved to be a relatively efficient and stable photocatalyst in the treatment of dyes and Cr(VI) in water under visible-light (λ 4400 nm) irradiation [5,6]. Nonetheless, for a single semiconductor, the rapid recombination of its photogenerated electrons and holes always reduces its photocatalytic efficiency [7–10]. La2Ti2O7 is a promising wide bandgap (Eg E3.8 eV) photocatalyst, by virtue of its flexibility to catalyze numerous photochemical reactions, low cost, low toxicity, and good stability [11–16]. Unfortunately, sole La2Ti2O7 can only be activated by UV light (λ o326 nm), which constitutes less than 5% of solar energy. Our theoretical calculation suggested that SnS2 and La2Ti2O7 have matched band potentials (Supplementary materials, Fig. S1), which render it possible for SnS2/La2Ti2O7 composite to possess higher visible-light-driven photocatalytic activity than SnS2 and La2Ti2O7. However, to the best of our knowledge, there is still no report on the study of SnS2/La2Ti2O7 composite as photocatalyst by far.
n
Corresponding author. Tel.: þ 86 13598692578. E-mail address: [email protected] (J. Chen).
In situ chemical methods are capable of synthesizing composite photocatalysts with heterojunction structures, which can provide tight heterointerfaces for charge transfer during photocatalytic use [7–10]. Herein, we report an in situ synthesis of SnS2/La2Ti2O7 nanoheterojunctions via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets in deionized water at 130 1C for 6 h. Furthermore, the photocatalytic activity of the assynthesized SnS2/La2Ti2O7 nanoheterojunctions was tested in the reduction of aqueous Cr(VI) under visible-light (λ4 420 nm) irradiation, and compared with those of SnS2 nanoparticles and La2Ti2O7 nanosheets.
2. Experimental La2Ti2O7 nanosheets were synthesized via the hydrothermal reactions of equimolar La(NO3)3 6H2O and Ti(SO4)2 in 1 mol/L NaOH aqueous solution at 200 1C for 24 h [14], whereas other reagents were analytically pure and bought directly from Sinopharm Chemical Reagent Co., Ltd. Synthesis of SnS2/La2Ti2O7 nanoheterojunctions: 5 mmol SnCl4 5H2O, 20 mmol thioacetamide and 800 mg of La2Ti2O7 nanosheets were placed into a 50 mL Teflon jar, and 40.0 mL of deionized water was added with stirring. The mixture was further magnetically stirred for 40 min. Then, the Teflon jar was placed
http://dx.doi.org/10.1016/j.matlet.2015.02.134 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97
J. Chen et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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into a stainless steel autoclave, sealed and heated in an electric oven at 130 1C for 6 h. After the autoclave cooled down to room temperature naturally, the resultant precipitate was centrifuged, washed with deionized water and absolute ethanol, and dried in air at 80 1C for 12 h. For comparison, SnS2 nanoparticles were synthesized via the hydrothermal reactions of 5 mmol SnCl4 5H2O and 20 mmol thioacetamide in 40.0 mL of deionized water at 130 1C for 6 h. Characterization: The products were characterized by powder X-ray diffraction (XRD, German Bruker AXS D8 ADVANCE X-ray
diffractometer), wavelength dispersive X-ray fluorescence spectroscopy (WDXRF, Japan Shimadzu Corporation LAB CENTER XRF1800 WDXRF spectrometer), transmission electron microscopy (TEM, Holland Philips Tecnai-12 transmission electron microscopy), and UV–vis diffuse reflectance spectra (American Varian Cary 5000 ultraviolet–visible-near infrared spectrophotometer). Photocatalytic activities of the products (the dosage was 300 mg) were tested in the reduction of Cr(VI) in 300 mL of 50 mg/L K2Cr2O7 aqueous solution under visible-light (λ4420 nm) irradiation.
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2θ (deg.) Fig. 1. XRD patterns of (a) La2Ti2O7, (b) SnS2/La2Ti2O7 and (c) SnS2.
Fig. 1 shows the XRD patterns of the three products synthesized in this work. The XRD peaks of the product synthesized via the hydrothermal reactions of equimolar La(NO3)3 6H2O and Ti(SO4)2 in 1 mol/L NaOH aqueous solution at 200 1C for 24 h (Fig. 1(a)) can be indexed to pure monoclinic phase La2Ti2O7 (JCPDS card no. 811066), whereas those of the product synthesized via the hydrothermal reactions of SnCl4 5H2O and thioacetamide at 130 1C for 6 h (Fig. 1(c)) can be indexed to single hexagonal phase SnS2 (JCPDS card no. 89-3198). By contrast, the XRD peaks of the product synthesized via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets at 130 1C for 6 h (Fig. 1(b)) reveal the formation of SnS2/La2Ti2O7 composite. The content of La2Ti2O7 in the SnS2/La2Ti2O7 composite was determined to be 76.6 mass% by WDXRF.
Fig. 2. TEM images of (a) La2Ti2O7, (b) SnS2/La2Ti2O7 and (c) SnS2.
Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
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J. Chen et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Fig. 3. (a) UV–vis diffuse reflectance spectra of La2Ti2O7, SnS2/La2Ti2O7 and SnS2 in the absorbance mode, and (b) plots of (αhν)2 versus (hν) for estimating the Eg values of La2Ti2O7, SnS2/La2Ti2O7 and SnS2.
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nanoheterojunctions are irradiated by the incident visible-light (λ4420 nm), La2Ti2O7 has no photoabsorption, but SnS2 can absorb the incident visible-light. Thus, the electrons in the VB of SnS2 can be excited to its CB with simultaneous generation of an equal amount of holes in its VB. The photogenerated electrons (e ) can migrate from the CB of SnS2 to the CB of La2Ti2O7 via the interface of SnS2/La2Ti2O7 nanoheterojunctions, whereas the photogenerated holes (h þ ) still remain in the VB of SnS2. Consequently, the separation of e and h þ in SnS2 can be enhanced, and their recombination can be reduced. The more efficient separation of e and h þ can increase their lifetime and enhance the efficiency of their transfer to the target substrates (e.g., Cr(VI)) [8–10]. Moreover, La2Ti2O7 can be activated by the transferred e [15]. Therefore, SnS2/La2Ti2O7 nanoheterojunctions can exhibit higher photocatalytic activity than SnS2 nanoparticles.
4. Conclusions The TEM images of La2Ti2O7, SnS2/La2Ti2O7 and SnS2 are shown in Fig. 2(a)–(c), respectively. It can be seen from Fig. 2(a) and (c) that La2Ti2O7 and SnS2 comprise nanosheets and nanoparticles, respectively. On the other hand, Fig. 2(b) shows that SnS2/La2Ti2O7 consists of nanosheets decorated with nanoparticles, forming a heterojunction structure. Fig. 3(a) shows the UV–vis diffuse reflectance spectra of La2Ti2O7, SnS2/La2Ti2O7 and SnS2. It can be seen from Fig. 3(a) that La2Ti2O7 displays no absorption of visible-light, whereas both SnS2/La2Ti2O7 and SnS2 display distinct photoabsorption in the whole visible-light region. The bandgap (Eg) values of La2Ti2O7, SnS2/La2Ti2O7 and SnS2 were estimated to be 3.80, 2.20 and 2.05 eV, respectively, using the classic Tauc plot approach (Fig. 3(b)). Fig. 4 shows the photocatalytic reduction of aqueous Cr(VI) in the presence of La2Ti2O7, SnS2/La2Ti2O7 or SnS2 under visible-light (λ 4420 nm) irradiation. As is expected, La2Ti2O7 exhibits no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ4420 nm) irradiation, because it has no visiblelight-absorbing ability. In contrast, both SnS2/La2Ti2O7 and SnS2 exhibit photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation. However, the photocatalytic activity of SnS2/La2Ti2O7 is much higher that of SnS2. Upon visible-light (λ4420 nm) irradiation for 270 min, more than 95% of Cr(VI) can be reduced in the presence of SnS2/La2Ti2O7, whereas only 49% of Cr(VI) can be reduced in the presence of SnS2. Our theoretical calculation suggested that SnS2 and La2Ti2O7 have matched band potentials (Fig. S1), that is, the conduction band (CB) and valence band (VB) potentials of SnS2 are more negative than the CB and VB potentials of La2Ti2O7, respectively. When SnS2/La2Ti2O7
SnS2/La2Ti2O7 nanoheterojunctions were synthesized via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets in deionized water at 130 1C for 6 h. The SnS2/La2Ti2O7 nanoheterojunctions exhibited much higher photocatalytic activity than SnS2 nanoparticles, whereas La2Ti2O7 nanosheets exhibited no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ4420 nm) irradiation. The higher photocatalytic activity of SnS2/La2Ti2O7 nanoheterojunctions can be mainly attributed to the enhanced charge separation, which benefited from the matched band potentials of SnS2 and La2Ti2O7 as well as the heterojunction structure of the as-synthesized SnS2/La2Ti2O7 nanoheterojunctions.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2015.02.134. References [1] [2] [3] [4] [5] [6] [7] [8] [9]
Zhang YC, Yang M, Zhang G, Dionysiou DD. Appl Catal B 2013;142–143:249–58. Zhao Y, Zhang Y, Li J, Du X. Mater Lett 2014;130:139–42. Zhang Y, Zhang Q, Shi Q, Cai Z, Yang Z. Sep Purif Technol 2015;142:251–7. Zhang YC, Du ZN, Li SY, Zhang M. Appl Catal B 2010;95:153–9. Zhang YC, Li J, Zhang M, Dionysiou DD. Environ Sci Technol 2011;45: 9324–31. Zhang YC, Du ZN, Li KW, Zhang M. Sep Purif Technol 2011;81:101–7. Yang F, Han G, Fu D, Liu Z. Mater Lett 2013;99:24–7. Zhang YC, Li J, HY. Appl Catal B 2012;123–124:18–26. Zhang YC, Yao L, Zhang G, Dionysiou DD. Appl Catal B 2014;144:730–8.
Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
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[10] Zhang YC, Du ZN, Li KW, Zhang M, Dionysiou DD. ACS Appl Mater Interfaces 2011;3:1528–37. [11] Yang QL, Kang SZ, Chen H, Bu W, Mu J. Desalination 2011;266:149–53. [12] Wang Z, Teramura K, Hosokawa S, Tanaka T. Appl Catal B 2015;163:241–7. [13] Onozuka K, Kawakami Y, Imai H, Yokoi T, Tatsumi T. J Solid State Chem 2012;192:87–92.
[14] Li K, Wang Y, Wang H, Zhu M, Yan H. Nanotechnology 2006;17:4863–7. [15] Wang R, Xu D, Liu J, Li K, Wang H. Chem Eng J 2011;168:455–60. [16] Wu C, Zhang Y, Li S, Zheng H, Wang H, Liu J, et al. Chem Eng J 2011;178:468–74.
Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
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Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity Jun Chen a,n, Shuangzhi Liu b, Li Zhang a, Na Chen a a b
School of Chemistry and Chemical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, China Chemistry and Engineering Department, Kaifeng University, Kaifeng 475004, China
art ic l e i nf o
a b s t r a c t
Article history: Received 31 January 2015 Accepted 28 February 2015
This work took the initiative to study the synthesis and photocatalytic properties of a new visible-lightactive SnS2/La2Ti2O7 heterojunction photocatalyst. SnS2/La2Ti2O7 nanoheterojunctions were synthesized via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets in deionized water at 130 1C for 6 h. The structure, composition, and optical property of the as-synthesized SnS2/La2Ti2O7 nanoheterojunctions were characterized by powder X-ray diffraction, wavelength dispersive X-ray fluorescence spectroscopy, transmission electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized SnS2/La2Ti2O7 nanoheterojunctions was tested in the reduction of aqueous Cr(VI) under visible-light (λ4 420 nm) irradiation, and compared with those of SnS2 nanoparticles and La2Ti2O7 nanosheets. It was observed that SnS2/La2Ti2O7 nanoheterojunctions exhibited much higher photocatalytic activity than SnS2 nanoparticles, whereas La2Ti2O7 nanosheets exhibited no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation. The reasons accounting for the photocatalytic results were also proposed. & 2015 Published by Elsevier B.V.
Keywords: Semiconductors Nanocomposites Powder technology Functional
1. Introduction The development of efficient visible-light-active photocatalysts is a prerequisite for practical application of photocatalysis technology in treating environmental pollutants [1–4]. Recently, SnS2 (Eg E2.2 eV) has been proved to be a relatively efficient and stable photocatalyst in the treatment of dyes and Cr(VI) in water under visible-light (λ 4400 nm) irradiation [5,6]. Nonetheless, for a single semiconductor, the rapid recombination of its photogenerated electrons and holes always reduces its photocatalytic efficiency [7–10]. La2Ti2O7 is a promising wide bandgap (Eg E3.8 eV) photocatalyst, by virtue of its flexibility to catalyze numerous photochemical reactions, low cost, low toxicity, and good stability [11–16]. Unfortunately, sole La2Ti2O7 can only be activated by UV light (λ o326 nm), which constitutes less than 5% of solar energy. Our theoretical calculation suggested that SnS2 and La2Ti2O7 have matched band potentials (Supplementary materials, Fig. S1), which render it possible for SnS2/La2Ti2O7 composite to possess higher visible-light-driven photocatalytic activity than SnS2 and La2Ti2O7. However, to the best of our knowledge, there is still no report on the study of SnS2/La2Ti2O7 composite as photocatalyst by far.
n
Corresponding author. Tel.: þ 86 13598692578. E-mail address: [email protected] (J. Chen).
In situ chemical methods are capable of synthesizing composite photocatalysts with heterojunction structures, which can provide tight heterointerfaces for charge transfer during photocatalytic use [7–10]. Herein, we report an in situ synthesis of SnS2/La2Ti2O7 nanoheterojunctions via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets in deionized water at 130 1C for 6 h. Furthermore, the photocatalytic activity of the assynthesized SnS2/La2Ti2O7 nanoheterojunctions was tested in the reduction of aqueous Cr(VI) under visible-light (λ4 420 nm) irradiation, and compared with those of SnS2 nanoparticles and La2Ti2O7 nanosheets.
2. Experimental La2Ti2O7 nanosheets were synthesized via the hydrothermal reactions of equimolar La(NO3)3 6H2O and Ti(SO4)2 in 1 mol/L NaOH aqueous solution at 200 1C for 24 h [14], whereas other reagents were analytically pure and bought directly from Sinopharm Chemical Reagent Co., Ltd. Synthesis of SnS2/La2Ti2O7 nanoheterojunctions: 5 mmol SnCl4 5H2O, 20 mmol thioacetamide and 800 mg of La2Ti2O7 nanosheets were placed into a 50 mL Teflon jar, and 40.0 mL of deionized water was added with stirring. The mixture was further magnetically stirred for 40 min. Then, the Teflon jar was placed
http://dx.doi.org/10.1016/j.matlet.2015.02.134 0167-577X/& 2015 Published by Elsevier B.V.
Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97
J. Chen et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
into a stainless steel autoclave, sealed and heated in an electric oven at 130 1C for 6 h. After the autoclave cooled down to room temperature naturally, the resultant precipitate was centrifuged, washed with deionized water and absolute ethanol, and dried in air at 80 1C for 12 h. For comparison, SnS2 nanoparticles were synthesized via the hydrothermal reactions of 5 mmol SnCl4 5H2O and 20 mmol thioacetamide in 40.0 mL of deionized water at 130 1C for 6 h. Characterization: The products were characterized by powder X-ray diffraction (XRD, German Bruker AXS D8 ADVANCE X-ray
diffractometer), wavelength dispersive X-ray fluorescence spectroscopy (WDXRF, Japan Shimadzu Corporation LAB CENTER XRF1800 WDXRF spectrometer), transmission electron microscopy (TEM, Holland Philips Tecnai-12 transmission electron microscopy), and UV–vis diffuse reflectance spectra (American Varian Cary 5000 ultraviolet–visible-near infrared spectrophotometer). Photocatalytic activities of the products (the dosage was 300 mg) were tested in the reduction of Cr(VI) in 300 mL of 50 mg/L K2Cr2O7 aqueous solution under visible-light (λ4420 nm) irradiation.
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2θ (deg.) Fig. 1. XRD patterns of (a) La2Ti2O7, (b) SnS2/La2Ti2O7 and (c) SnS2.
Fig. 1 shows the XRD patterns of the three products synthesized in this work. The XRD peaks of the product synthesized via the hydrothermal reactions of equimolar La(NO3)3 6H2O and Ti(SO4)2 in 1 mol/L NaOH aqueous solution at 200 1C for 24 h (Fig. 1(a)) can be indexed to pure monoclinic phase La2Ti2O7 (JCPDS card no. 811066), whereas those of the product synthesized via the hydrothermal reactions of SnCl4 5H2O and thioacetamide at 130 1C for 6 h (Fig. 1(c)) can be indexed to single hexagonal phase SnS2 (JCPDS card no. 89-3198). By contrast, the XRD peaks of the product synthesized via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets at 130 1C for 6 h (Fig. 1(b)) reveal the formation of SnS2/La2Ti2O7 composite. The content of La2Ti2O7 in the SnS2/La2Ti2O7 composite was determined to be 76.6 mass% by WDXRF.
Fig. 2. TEM images of (a) La2Ti2O7, (b) SnS2/La2Ti2O7 and (c) SnS2.
Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
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J. Chen et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Fig. 3. (a) UV–vis diffuse reflectance spectra of La2Ti2O7, SnS2/La2Ti2O7 and SnS2 in the absorbance mode, and (b) plots of (αhν)2 versus (hν) for estimating the Eg values of La2Ti2O7, SnS2/La2Ti2O7 and SnS2.
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Irradiation time (min) Fig. 4. Photocatalytic reduction of aqueous Cr(VI) in the presence of La2Ti2O7, SnS2/ La2Ti2O7 or SnS2 under visible-light (λ 4420 nm) irradiation.
nanoheterojunctions are irradiated by the incident visible-light (λ4420 nm), La2Ti2O7 has no photoabsorption, but SnS2 can absorb the incident visible-light. Thus, the electrons in the VB of SnS2 can be excited to its CB with simultaneous generation of an equal amount of holes in its VB. The photogenerated electrons (e ) can migrate from the CB of SnS2 to the CB of La2Ti2O7 via the interface of SnS2/La2Ti2O7 nanoheterojunctions, whereas the photogenerated holes (h þ ) still remain in the VB of SnS2. Consequently, the separation of e and h þ in SnS2 can be enhanced, and their recombination can be reduced. The more efficient separation of e and h þ can increase their lifetime and enhance the efficiency of their transfer to the target substrates (e.g., Cr(VI)) [8–10]. Moreover, La2Ti2O7 can be activated by the transferred e [15]. Therefore, SnS2/La2Ti2O7 nanoheterojunctions can exhibit higher photocatalytic activity than SnS2 nanoparticles.
4. Conclusions The TEM images of La2Ti2O7, SnS2/La2Ti2O7 and SnS2 are shown in Fig. 2(a)–(c), respectively. It can be seen from Fig. 2(a) and (c) that La2Ti2O7 and SnS2 comprise nanosheets and nanoparticles, respectively. On the other hand, Fig. 2(b) shows that SnS2/La2Ti2O7 consists of nanosheets decorated with nanoparticles, forming a heterojunction structure. Fig. 3(a) shows the UV–vis diffuse reflectance spectra of La2Ti2O7, SnS2/La2Ti2O7 and SnS2. It can be seen from Fig. 3(a) that La2Ti2O7 displays no absorption of visible-light, whereas both SnS2/La2Ti2O7 and SnS2 display distinct photoabsorption in the whole visible-light region. The bandgap (Eg) values of La2Ti2O7, SnS2/La2Ti2O7 and SnS2 were estimated to be 3.80, 2.20 and 2.05 eV, respectively, using the classic Tauc plot approach (Fig. 3(b)). Fig. 4 shows the photocatalytic reduction of aqueous Cr(VI) in the presence of La2Ti2O7, SnS2/La2Ti2O7 or SnS2 under visible-light (λ 4420 nm) irradiation. As is expected, La2Ti2O7 exhibits no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ4420 nm) irradiation, because it has no visiblelight-absorbing ability. In contrast, both SnS2/La2Ti2O7 and SnS2 exhibit photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ 4420 nm) irradiation. However, the photocatalytic activity of SnS2/La2Ti2O7 is much higher that of SnS2. Upon visible-light (λ4420 nm) irradiation for 270 min, more than 95% of Cr(VI) can be reduced in the presence of SnS2/La2Ti2O7, whereas only 49% of Cr(VI) can be reduced in the presence of SnS2. Our theoretical calculation suggested that SnS2 and La2Ti2O7 have matched band potentials (Fig. S1), that is, the conduction band (CB) and valence band (VB) potentials of SnS2 are more negative than the CB and VB potentials of La2Ti2O7, respectively. When SnS2/La2Ti2O7
SnS2/La2Ti2O7 nanoheterojunctions were synthesized via hydrothermal treatment of SnCl4 5H2O, thioacetamide and La2Ti2O7 nanosheets in deionized water at 130 1C for 6 h. The SnS2/La2Ti2O7 nanoheterojunctions exhibited much higher photocatalytic activity than SnS2 nanoparticles, whereas La2Ti2O7 nanosheets exhibited no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ4420 nm) irradiation. The higher photocatalytic activity of SnS2/La2Ti2O7 nanoheterojunctions can be mainly attributed to the enhanced charge separation, which benefited from the matched band potentials of SnS2 and La2Ti2O7 as well as the heterojunction structure of the as-synthesized SnS2/La2Ti2O7 nanoheterojunctions.
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Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
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Please cite this article as: Chen J, et al. New SnS2/La2Ti2O7 heterojunction photocatalyst with enhanced visible-light activity. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.02.134i
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