Accepted Manuscript AgI/TiO2 Nanocomposites: Ultrasound-Assisted Preparation, Visible-Light Induced Photocatalytic Degradation of Methyl Orange and Antibacterial Activity Bin Xue, Tao Sun, Ji-kui Wu, Fang Mao, Wei Yang PII: DOI: Reference:
S1350-4177(14)00146-1 http://dx.doi.org/10.1016/j.ultsonch.2014.04.021 ULTSON 2596
To appear in:
Ultrasonics Sonochemistry
Received Date: Revised Date: Accepted Date:
30 September 2013 29 March 2014 26 April 2014
Please cite this article as: B. Xue, T. Sun, J-k. Wu, F. Mao, W. Yang, AgI/TiO2 Nanocomposites: UltrasoundAssisted Preparation, Visible-Light Induced Photocatalytic Degradation of Methyl Orange and Antibacterial Activity, Ultrasonics Sonochemistry (2014), doi: http://dx.doi.org/10.1016/j.ultsonch.2014.04.021
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Title: AgI/TiO2 Nanocomposites: Ultrasound-Assisted Preparation, Visible-Light Induced Photocatalytic Degradation of Methyl Orange and Antibacterial Activity Author: Bin Xue, Tao Sun, Ji-kui Wu, Fang Mao, Wei Yang Affiliation: Department of Chemistry, College of Food Science and Technology, Shanghai Ocean University, China Corresponding author： ：Bin Xue Tel.: +86 21 61900363 E-mail: [email protected]; [email protected]
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AgI/TiO2 Nanocomposites: Ultrasound-Assisted Preparation, Visible-Light Induced Photocatalytic Degradation of Methyl Orange and Antibacterial Activity
Bin Xue *, Tao Sun, Ji-kui Wu, Fang Mao, Wei Yang Department of Chemistry, College of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China Abstract AgI/TiO2 nanocomposites were prepared by an ultrasound-assisted precipitation process and subsequent low-temperature (350 °C) calcination. The crystal phase, morphology and optical properties of the AgI/TiO2 nanocomposites were characterized by X-ray diffraction, transmission electron microscopy and UV–vis absorption spectroscopy. After calcination, the crystallite size of AgI nanoparticles in the AgI/TiO2 nanocomposites decreased, and visible light absorption intensity of the AgI/TiO2 nanocomposites was significantly enhanced. The AgI/TiO2 nanocomposites after calcination exhibited the superior photocatalytic activity for methyl orange degradation and killing of Escherichia coli under visible light irradiation. The improvement of photocatalytic activity could be attributed to two reasons, namely, reduced crystallite size and enhanced visible light absorption of AgI nanoparticles in calcined AgI/TiO2 nanocomposites. The trapping experiments demonstrated that superoxide radical (O2 ·-) and holes (h+) were the main reactive species for the photodegradation
of
methyl
orange
under
visible
light
irradiation.
The
ultrasound-assisted preparation approach is efficient and facile, which promotes large-scale production and application of AgI/TiO2 nanocomposites in photocatalytic degradation of organic pollutants, disinfection and other fields.
2
Keywords:
Nanocomposites;
Photocatalysis;
Semiconductors;
TiO2;
Ultrasound-assisted preparation; Visible-light induced
*Corresponding author. Tel.: +86 21 61900363. E-mail: [email protected]; [email protected].
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1. Introduction TiO2, an environmentally friendly semiconductor material, is widely used in photocatalytic degradation of organic pollutants, hydrogen production, antibacterial materials and solar cells due to its high activity, low-cost, stability and non-toxicity [1]. However, as first-generation photocatalysts, pristine TiO2 materials display very poor photocatalytic activity under visible light irradiation because of its wide band gap (e.g., 3.2 V for anatase and 3.0 V for rutile) and rapid recombination of photogenerated electron/hole pairs [1, 2]. The drawback seriously hinders practical applications of TiO2 materials in visible light driven photocatalytic process. Therefore, the design and preparation of visible light responsive TiO2 materials have attracted intense research interest [2]. In order to obtain second-generation TiO2 materials with visible light induced photocatalytic activity, elements (metal or non-metal) doping, coupling with narrow band gap semiconductor, and crystalline phase mixing are effective approaches [3-9]. The modified TiO2 materials obtained through the above approaches can significantly enhance the visible light induced photocatalytic activity due to extension of the photoresponse range as well as reduction of the recombination of photogenerated electron/hole pairs. Among these various modified approaches, coupling with narrow band gap semiconductors, such as silver halide (AgX), has attracted intense attention owing to highly activity and stability of product [10-17]. For example, Hu et al. prepared AgI/TiO2 (P25) with visible light induced photocatalytic activity of azo-dye degradation by the deposition-precipitation method [10]. Li et al. reported that AgBr-TiO2 nanotube films prepared via an immersion method showed highly efficient photodegradation of methyl orange (MO) under visible light irradiation [11]. Cao et al. synthesized novel composite AgI/AgCl/TiO2 photocatalysts by ion exchange
4
method [12]. However, the preparations of these AgX modified TiO2 nanocomposites usually require tedious procedures and long reaction times, which hinders large-scale production and extensive applications of the nanocomposites. In comparison to conventional methods, ultrasound-assisted preparation is efficient and facile for rapid preparation of nanostructured materials. The collapse of cavitation bubbles generates localized high temperature (about 104 K), pressure (about 105 kPa) and cooling rates (in excess of 109 K s-1) under ultrasonic condition, which can promote self-assembly and crystallization of nanostructured materials [18-22]. For instance, Meskin et al. synthesized nanocrystalline ZrO2, TiO2, NiFe2O4 and Ni0.5Zn0.5Fe2O4 powders by ultrasonic-hydrothermal treatment [23]. Shirsath et al. synthesized TiO2 nanoparticles doped with Fe and Ce using sonochemical approach [18]. Anandan et al. sonochemically prepared Au-TiO2 nanoparticles [24]. Nevertheless, to the best of our knowledge, little work has been made to the ultrasound-assisted preparation of AgX/TiO2 nanocomposites with visible-light responsive photocatalytic activity. In this paper, we report a facile ultrasound-assisted preparation of AgI/TiO2 nanocomposites. The crystal phase, morphology, UV–vis absorption spectrum, visible-light induced photocatalytic activity and mechanism, antibacterial effects of AgI/TiO2 nanocomposites were investigated. 2. Experimental All chemicals were of analytical grade except Ti(SO4)2, which was of chemically pure reagent. The preparation reaction mechanism illustrated in Scheme 1. In a typical preparation of TiO2 nanoparticles, 1.92 g of Ti(SO4)2, 0.30 g of NH4F and 0.96 g of urea were dissolved in 80 mL of deionized water under continuous stirring. The mixture was stirred for 30 min, then transferred into a 100 mL Teflon lined stainless
5
steel autoclave, kept at 180 °C for 12 h, and then cooled to room temperature. The resulting TiO2 nanoparticles were collected by filtration, washed using deionized water and dried at 80 °C for 12 h. The preparation procedure of AgI/TiO2 nanocomposites with 30 wt% AgI loding is as follows: 0.5 g of the as-prepared TiO2 nanoparticles and 0.103 g of KI were added to 50 mL of deionized water under continuous stirring. The mixture in a 100 mL glass beaker was stirred for 30 min and then sonicated for 30 min in the ultrasonic cleaning bath (KQ-300DE, 40 kHz, 300 W). Subsequently, 5 mL of 0.022 g mL-1 AgNO3 solution was rapidly injected to the mixture above. Finally, the mixture was further sonicated for 1 h. The product was collected by centrifugation, washed using deionized water and dried 12 h at 80 °C, and denoted as AgI/TiO2-UP. Then the as-prepared AgI/TiO2 nanocomposites were further calcinated at 350 °C for 2 h, and denoted as AgI/TiO2-UP-C. For comparison purposes, several control experiments with conventional precipitation process were performed. In these cases, the reaction mixture was stirred for 1 h after the injection of AgNO3 solution, while other preparation procedures are kept constant. The as-prepared sample was denoted as AgI/TiO2-CP. Then the as-prepared AgI/TiO2 -CP was further calcinated at 350 °C for 2 h, and denoted as AgI/TiO2-CP-C. The X-ray powder diffraction (XRD) patterns of the samples were recorded using a PANalytical X’Pert PRO diffractometer. Transmission electron microscopy (TEM) was performed on Hitachi H-800 microscope. UV–vis absorption spectra of the samples dispersed in ethanol (0.5 mg mL-1) were obtained on a UV–visible spectrophotometer (PERSEE, TU-1901). In a typical photocatalytic degradation test for organic pollutants, 50 mg of as-prepared AgI/TiO2-UP-C photocatalysts was added to 50 mL of a 10 mg L-1 MO
6
solution and then stirred in the dark for 30 min to ensure adsorption equilibrium. The suspension was then exposed to visible-light irradiation from a 250 W mercury blended lamp (4900 lumen of photon flux) with a filter (> 420 nm) at a distance of 20 cm. At given irradiation time intervals (20 min), the as-prepared AgI/TiO2-UP-C photocatalysts were removed by centrifugation and the MO solution concentrations were analyzed using a UV-Vis spectrophotometer (PERSEE, TU-1901). For detecting the reactive species during photocatalytic degradation of MO under visible light irradiation, different scavengers, such as triethanolamine (TEOA), isopropanol (IPA), p-benzoquinone (BQ), were introduced into photocatalytic reaction systems, the concentrations of the all scavengers are 1.0 mmol L-1 [25]. The method was similar to aforementioned photocatalytic degradation test. The antibacterial experiments were performed, similarly to the methods reported in the literatures [26-28]. In a typical photocatalytic antibacterial activity test, 44 mg of as-prepared AgI/TiO2-UP-C photocatalysts were added to 100 mL of 0.9 % saline solution in a flask under sonication for 1 h. Subsequently, 9.9 mL of the above mixture was sterilized by autoclaving at 121 °C for 20 min and mixed with 0.1 mL of the prepared Escherichia coli (E.coli) bacteria suspension (108 cfu mL-1) after cooling. The final photocatalysts and E.coli bacteria concentration in 10 mL of the reaction mixture were adjusted to 0.44 mg mL-1 and 106 cfu mL-1, respectively. To prevent settling of the photocatalysts, the reaction mixture in a Petri dish was stirred slowly with a magnetic stirrer. The reaction mixture was then exposed to visible-light irradiation from a 250 W mercury blended lamp (4900 lumen of photon flux) with a filter (> 420 nm) at a distance of 20 cm. 0.1 mL of the reaction mixture was collected 30 min later, immediately diluted with 0.9 % saline solution and then incubated at 37 °C for 24 h on a nutrient agar medium in dark.
7
3. Results and Discussion Fig. 1 shows the XRD patterns of the samples by ultrasound-assisted precipitation process. All the diffraction peaks of TiO2 component in three samples correspond to the anatase phase of TiO2 (JCPDS No. 21-1272). The diffraction peaks of AgI component supported on TiO2 nanoparticles attribute to β-AgI (JCPDS No. 09-0374). And no diffraction peaks of other impurities appear in the patterns. This indicates that the crystallization of AgI was rapidly performed through ultrasound-assisted precipitation. Furthermore, it is worth noting that the diffraction peaks of β-AgI component in the AgI/TiO2-UP-C nanocomposites are significantly broadening compared with XRD pattern of the AgI/TiO2 -UP nanocomposites. The phenomenon suggests that the crystallite size of AgI component in the AgI/TiO2 nanocomposites decreased after calcination. According to the literature [29], β-AgI exists below 147 °C, while above 147 °C β-AgI goes through a crystalline transition to α-AgI and the crystal phase transition is reversible. Therefore, the reduction of the crystallite size of AgI component in the AgI/TiO2-UP-C nanocomposites may be related to reversible crystal phase transition of AgI component during calcination. The XRD patterns of the samples by conventional precipitation process are shown in Fig. S1 (see supplementary data). Obviously, the intensity of diffraction peaks of AgI component in AgI/TiO2-CP nanocomposites is lower than that in AgI/TiO2-UP nanocomposites. This clearly indicates that the ultrasound process can improve the crystallinity of the product. Moreover, the sharpened diffraction peaks of β-AgI component in the AgI/TiO2-CP-C nanocomposites suggest that the crystallite size of β-AgI component in the AgI/TiO2-CP nanocomposites increased after calcination. This phenomenon may be attributed to the poor crystallinity of the AgI/TiO2 -CP nanocomposites. The change trend in β-AgI size of samples prepared by conventional precipitation process
8
after calcination is a contrast with that of samples prepared by ultrasound-assisted precipitation. It also reflects the differences between conventional precipitation and ultrasound-assisted precipitation. Fig. 2 is the TEM images of the samples by ultrasound-assisted precipitation process. Fig. 2a shows that the TiO2 consists of nanoparticles in the diameter of 10-20 nm. As shown in Fig. 2b, dark AgI nanoparticles with a size of 50-100 nm are coupled with TiO2 nanoparticles in AgI/TiO2-UP nanocomposites. Fig. 2c displays the morphology of AgI/TiO2-UP-C nanocomposites. Obviously, the crystallite size of dark AgI nanoparticles is reduced to 30-70 nm, but the crystallite size of TiO2 does not change apparently. The reduction of the crystallite size of AgI component after calcination is consistent with the aforementioned XRD analyst results. The small crystallite size of AgI component may be beneficial to the enhancement of photocatalytic activity of AgI/TiO2 nanocomposites owing to the reduction of the recombination of photogenerated electron/hole pairs. The TEM images of the samples by conventional precipitation process are shown in Fig. S2 (see supplementary data). It can be seen that the size of AgI nanoparticles (ca. 50 nm in diameter) in AgI/TiO2-CP significantly is smaller than that of AgI/TiO2-UP. The obvious agglomeration of AgI nanoparticles occurred in AgI/TiO2-CP-C. The size of the agglomeration is about 500-1000 nm. These results are consistent with the XRD analysis. The UV-vis absorption spectra of the samples by ultrasound-assisted precipitation process are shown in Fig. 3. The AgI/TiO2 -UP nanocomposites exhibit intense visible light absorption bands, which is distinctly different from the pristine TiO2 nanoparticles.
Besides,
visible
absorption
intensity
of
AgI/TiO2-UP-C
nanocomposites further increases compared to that of AgI/TiO2 nanocomposites,
9
indicating the calcination can promote visible light absorption of AgI component. The intense
absorption
indicates
that
the
AgI/TiO2-UP
and
AgI/TiO2-UP-C
nanocomposites display high generation efficiency of electron/hole pairs under visible light irradiation [13]. Furthermore, the absorption band centred at 424 nm of the AgI/TiO2-UP-C nanocomposites is blue-shifted compared to the absorption band centred at 430 nm of the AgI/TiO2-UP nanocomposites. The phenomenon may be attributed to the quantum size effect of AgI component after calcination due to the decrease of the crystallite size. However, as shown in Fig. S3 (see supplementary data), blue-shift phenomenon of the absorption band centred at 430 nm did not happen in AgI/TiO2-CP-C nanocomposites. It shows that the preparation methods have significant effect on UV-vis absorption of AgI/TiO2 nanocomposites. The photocatalytic activity of the samples was evaluated by photocatalytic degradation of MO solution under visible light irradiation. The characteristic absorption of MO solution at 465 nm on the UV-Vis spectra was selected to determine its concentration. Fig. 4 shows time curves of photocatalytic degradation of MO solution for four different samples. A blank experiment indicates that there was almost no change in the concentration of MO solution. In three cases of pristine TiO2, AgI-UP and AgI-CP nanoparticles as photocatalysts, the concentration decreases of MO solution are very slow. Furthermore, the AgI/TiO2-UP, AgI/TiO2-CP and AgI/TiO2-CP-C
nanocomposites
exhibit
lower
photocatalytic
activity with
degradation rate of 28.3 %, 15.7 % and 19.2 %, respectively, after visible irradiation of 120 min. However, the AgI/TiO2-UP-C nanocomposites unexpectedly exhibit superior photocatalytic activity with degradation rate of 95.7 % under the same conditions. The results indicate that calcination could obviously improve the photocatalytic activity of AgI/TiO2 nanocomposites. The improvement effect could be
10
attributed to reduced crystallite size, enhanced visible light absorption of AgI nanoparticles and closer interaction between AgI and TiO2 in AgI/TiO2 nanocomposites after calcination [30]. In order to study the reactive species during photocatalytic degradation of MO under visible light irradiation, a series of trapping experiment were performed. The results are shown in Fig. 5. When TEOA (a quencher of h+) or BQ (a quencher of O2·-) introduced into photocatalytic reaction system prior to addition of the photocatalysts, the degradations of MO are significantly inhibited. However, the photodegradation of MO is not affected by the addition of IPA (a quencher of ·OH). This demonstrates that h+ and O2·- are the main reactive species during photocatalytic degradation of MO by the AgI/TiO2-UP-C nanocomposites under visible light irradiation [25]. According to the trapping experimental results, a possible photocatalytic reaction mechanism over the AgI/TiO2-UP-C nanocomposites was proposed. As shown in Fig. 6, under visible light irradiation, AgI can be excited to form photogenerated electron/hole pairs owing to narrow bandgap energy (2.8 eV) [31]. Furthermore, the conduction band (CB) potential of AgI (-0.42 eV) is more negative than that of TiO2 (-0.1 eV) [31]. Therefore, the photogenerated electrons of AgI can easily transfer to the surface of TiO2 and react with O2 to produce O2·- [1, 31]. The valence band (VB) edge of TiO2 (3.1 eV) is more positive than that of AgI (2.38 eV), but TiO2 can not be excited by visible light due to wide bandgap energy (3.2 eV), so the photogenerated holes of AgI remain in its VB [1, 31]. Further, organic pollutants are degraded by h+ and O2·-. The antibacterial activity of the AgI/TiO2-UP-C nanocomposites was evaluated by visible light induced photocatalytic disinfection of E. coli, a common Gram-negative bacterium. Fig. 7 shows the results of antibacterial experiments. Antibacterial
11
activities of the TiO2 and AgI/TiO2 -UP are not obvious, so the results are not given. Fig. 7a exhibits no bactericidal activity in the absence of the AgI/TiO2-UP-C nanocomposites and visible light irradiation. As shown in Fig. 7b, the AgI/TiO2-UP-C nanocomposites indicate low bactericidal activity in the absence of visible light irradiation. Moreover, as shown in Fig. 7c, visible light exhibits weak killing effect on E. coli in the absence of the AgI/TiO2-UP-C nanocomposites. However, as shown in Fig. 7d, the AgI/TiO2-UP-C nanocomposites exhibit obvious bactericidal activity under visible light irradiation. The results unambiguously show the antibacterial properties
of
the
AgI/TiO2-UP-C
nanocomposites.
Consequently,
the
AgI/TiO2-UP-C nanocomposites could be used in the field of water and air disinfection. 4. Conclusions We have successfully prepared AgI/TiO2 nanocomposites by an effective and facile ultrasound-assisted precipitation method and subsequent calcination. The AgI/TiO2 nanocomposites show many unique physicochemical properties different from the counterpart prepared by conventional precipitation process. The crystallite size of AgI nanoparticles in the AgI/TiO2 nanocomposites decreased through a crystalline transition during calcination. Coupling with AgI nanoparticles can obviously extend the photoresponse of the AgI/TiO2 nanocomposites to visible light range. Furthermore, the calcination process significantly enhanced visible light absorption intensity of the AgI/TiO2 nanocomposites. The AgI/TiO2 nanocomposites after calcination displayed superior visible light induced photocatalytic activity for MO degradation and killing of E. coli due to reduced crystalline size, enhanced visible light absorption of AgI nanoparticles and closer interaction between AgI and TiO2. The trapping experiment results suggested that O2·- and h+ were the main reactive
12
species for the photodegradation of MO under visible light irradiation. The AgI/TiO2 nanocomposites are expected for practical applications in photocatalysts, disinfection and so on. Acknowledgment This work was financially supported by Leading Academic Discipline Project of Shanghai Municipal Education Commission (Project Number: J50704), Funding of Shanghai Municipal Education Commission and Shanghai Ocean University (Project: B-5405-12-0019) and the Natural Science Foundation of Shanghai, China (no.11ZR1415400). References [1] B. Chen, S.S. Mao, Chem. Rev. 107 (2007) 2891. [2] N. Serpone, A.V. Emeline, J. Phys. Chem. Lett. 3 (2012) 673. [3] T.M. Triantis, T. Fotiou, T. Kaloudis, A.G. Kontos, P. Falaras, D.D. Dionysiou, M. Pelaez, A. Hiskia, J. Hazardous Mater. 211-212 (2012) 196. [4] H.L. Qin, G.B. Gu, S. Liu, Mater. Chem. Phys. 112 (2008) 346. [5] A. Hasanpour, M. Niyaifar, H. Mohammadpour, J. Amighian, J. Phys. Chem. Solids 73 (2012) 1066. [6] N. Ghows, M.H. Entezari, Ultrason Sonochem. 19 (2012) 1070. [7] N. Viriya-empikul, T. Charinpanitkul, N. Sano, A. Soottitantawat, T. Kikuchi, K. Faungnawakij, W. Tanthapanichakoon, Mater. Chem. Phys. 118 (2009) 254. [8] D. Nassoko, Y.F. Li, H. Wang, J.L. Li, Y.Z. Li, Y. Yu, J. Alloys Compd. 540 (2012) 228. [9] J.Q. Yan, G.J. Wu, N.J. Guan, L.D. Li, Z.X. Li, X.Z. Cao, Phys. Chem. Chem. Phys. 15 (2013) 10978.
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[10] C. Hu, X.X. Hu, L.S. Wang, J.H. Qu, A.M. Wang, Environ. Sci. Technol. 40 (2006) 7903. [11] Q.Y. Li, Y.Y. Xing, R. Li, L.L. Zong, X.D. Wang, J.J. Yang, RSC Advances 2 (2012) 9781. [12] J. Cao, B.Y. Xu, B.D. Luo, H.L. Lin, S.F. Chen, Appl. Surf. Sci. 257 (2011) 7083. [13] Y.Z. Li, H. Zhang, Z.M. Guo, J.J. Han, X.J. Zhao, Q.N. Zhao, S.J. Kim, Langmuir 24 (2008) 8351. [14] W.X. Wang, L.Q. Jing, Y.C. Qu, Y.B. Luan, H.G. Fu, Y.C. Xiao, J. Hazardous Mater. 243 (2012) 169. [15] Y.J. Zang, R. Farnood, Appl. Catal. B 79 (2008) 334. [16] Y.Y. Xing, R. Li, Q.Y. Li, J.J. Yang, J. Nanopart. Res. 14 (2012) 1284. [17] J.F. Guo, B.W. Ma, A.Y. Yin, K.N. Fan, W.L. Dai, J. Hazardous Mater. 211-212 (2012) 77. [18] S.R. Shirsath, D.V. Pinjari, P.R. Gogate, S.H. Sonawane, A.B. Pandit, Ultrason. Sonochem. 20 (2013) 277. [19] P.R. Gogate, V.S. Sutkar, A.B. Pandit, Chem. Eng. J. 166 (2011) 1066. [20] V.S. Sutkar, P.R. Gogate, Chem. Eng. J. 158 (2010) 296. [21] V.S. Sutkar, P.R. Gogate, Chem. Eng. J. 155 (2009) 26. [22] D.V. Pinjari, K. Prasad, P.R. Gogate, S.T. Mhaske, A.B. Pandit, Chem. Eng. Process. 74 (2013) 178. [23] P.E. Meskin, V.K. Ivanov, A.E. Barantchikov, B.R. Churagulov, Y.D. Tretyakov, Ultrason. Sonochem. 13 (2006) 47. [24] S. Anandan, M. Ashokkumar, Ultrason. Sonochem. 16 (2009) 316.
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[25] L.Q. Ye, K.J. Deng, F. Xu, L.H. Tian, T.Y. Peng, L. Zan, Phys. Chem. Chem. Phys. 14 (2012) 82. [26] T.S. Wu, K.X Wang, G.D. Li, S.Y. Sun, J. Sun, J.S. Chen, ACS Appl. Mater. Interface 2 (2010) 544. [27] J.M. Yu, W.K. Ho, J.G. Yu, H.Y. Yip, P.K. Wong, J.C. Zhao, Environ. Sci. Technol. 39 (2005) 1175. [28] S. Sontakke, J. Modak, G. Madras, Chem. Eng. J. 165 (2010) 225. [29] W. Sun, Y.Z. Li, W.Q. Shi, X.J. Zhao, P.F. Fang, J. Mater. Chem. 21 (2011) 9263. [30] Q.Y. Li, Y.Y. Xing, R. Li, L.L. Zong, X.D. Wang, J.J. Yang, RSC Advances 2 （2012）9781. [31] H.L. Lin, J. Cao, B.D. Luo, B.Y. Xu, S.F. Chen, Catal. Comm. 21 (2012) 91.
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Scheme captions Scheme 1. Ultrasound-assisted preparation reaction mechanism of AgI/TiO2 nanocomposites. Figure captions Fig. 1. XRD patterns of the samples prepared by ultrasound-assisted precipitation process. Fig. 2. TEM images of the samples by ultrasound-assisted precipitation process: (a) TiO2, (b) AgI/TiO2-UP and (c) AgI/TiO2-UP-C. The insets of (b) and (c) are diameter distribution curves of AgI nanoparticles. Fig. 3. UV–vis absorption spectra of the samples by ultrasound-assisted precipitation process. Fig. 4. Photocatalytic activity of the samples. Fig. 5. Trapping experiment results of photogenerated reactive species in system of photodegradation of MO by the AgI/TiO2-UP-C under visible light irradiation. Fig. 6. Schematic diagram of the electron-hole separation and photocatalytic reaction process of the AgI/TiO2-UP-C under visible light irradiation. Fig. 7. The results of antibacterial testing: (a) and (c) without photocatalyst, (b) and (d) the AgI/TiO2-UP-C.
16
Scheme
Scheme 1.
17
Figures
Intensity (a.u.) (c)
(b)
(a)
10 20
β (100)
β (002)
A(101)
30 40
β (110)
β (112)
A(200)
60 A(204)
70
A(116) A(220) A(215) A(301)
A ~ Anatase
A(105) A(211)
β ~ β-AgI
50
2 Theta (degree)
Fig. 1.
A(103) A(004) A(112)
80
18
Fig. 2.
19
Absorbance (a.u.)
AgI/TiO2-UP-C AgI/TiO2-UP TiO2
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 3.
20
1.0 0.8 AgI/TiO2-UP-C
C/C0
0.6
AgI/TiO2-UP AgI/TiO2-CP-C AgI/TiO2-CP
0.4
TiO2 AgI-UP AgI-CP Blank
0.2 0.0 0
20
40
60
80
100
120
Time (min)
Fig. 4.
21
1.0
0.8
1-C/C0
0.6
0.4
0.2
0.0
No quencher
TEOA
IPA
BQ
Fig. 5.
22
Fig. 6.
23
No visible light irradiation
a
b
Under visible light irradiation
d
c
Fig. 7.
24
Research highlights ►A rapid and effective ultrasound-assisted precipitation preparation for AgI/TiO2 nanocomposites. ►Distinctive reduction of crystallite size of AgI nanoparticles after low-temperature calcination. ►Superior visible light induced photocatalytic activity of methyl orange and antibacterial activity.
25
S1350-4177(14)00146-1 http://dx.doi.org/10.1016/j.ultsonch.2014.04.021 ULTSON 2596
To appear in:
Ultrasonics Sonochemistry
Received Date: Revised Date: Accepted Date:
30 September 2013 29 March 2014 26 April 2014
Please cite this article as: B. Xue, T. Sun, J-k. Wu, F. Mao, W. Yang, AgI/TiO2 Nanocomposites: UltrasoundAssisted Preparation, Visible-Light Induced Photocatalytic Degradation of Methyl Orange and Antibacterial Activity, Ultrasonics Sonochemistry (2014), doi: http://dx.doi.org/10.1016/j.ultsonch.2014.04.021
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 proof before it is published in its final 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.
Title: AgI/TiO2 Nanocomposites: Ultrasound-Assisted Preparation, Visible-Light Induced Photocatalytic Degradation of Methyl Orange and Antibacterial Activity Author: Bin Xue, Tao Sun, Ji-kui Wu, Fang Mao, Wei Yang Affiliation: Department of Chemistry, College of Food Science and Technology, Shanghai Ocean University, China Corresponding author： ：Bin Xue Tel.: +86 21 61900363 E-mail: [email protected]; [email protected]
1
AgI/TiO2 Nanocomposites: Ultrasound-Assisted Preparation, Visible-Light Induced Photocatalytic Degradation of Methyl Orange and Antibacterial Activity
Bin Xue *, Tao Sun, Ji-kui Wu, Fang Mao, Wei Yang Department of Chemistry, College of Food Science and Technology, Shanghai Ocean University, Shanghai 201306, China Abstract AgI/TiO2 nanocomposites were prepared by an ultrasound-assisted precipitation process and subsequent low-temperature (350 °C) calcination. The crystal phase, morphology and optical properties of the AgI/TiO2 nanocomposites were characterized by X-ray diffraction, transmission electron microscopy and UV–vis absorption spectroscopy. After calcination, the crystallite size of AgI nanoparticles in the AgI/TiO2 nanocomposites decreased, and visible light absorption intensity of the AgI/TiO2 nanocomposites was significantly enhanced. The AgI/TiO2 nanocomposites after calcination exhibited the superior photocatalytic activity for methyl orange degradation and killing of Escherichia coli under visible light irradiation. The improvement of photocatalytic activity could be attributed to two reasons, namely, reduced crystallite size and enhanced visible light absorption of AgI nanoparticles in calcined AgI/TiO2 nanocomposites. The trapping experiments demonstrated that superoxide radical (O2 ·-) and holes (h+) were the main reactive species for the photodegradation
of
methyl
orange
under
visible
light
irradiation.
The
ultrasound-assisted preparation approach is efficient and facile, which promotes large-scale production and application of AgI/TiO2 nanocomposites in photocatalytic degradation of organic pollutants, disinfection and other fields.
2
Keywords:
Nanocomposites;
Photocatalysis;
Semiconductors;
TiO2;
Ultrasound-assisted preparation; Visible-light induced
*Corresponding author. Tel.: +86 21 61900363. E-mail: [email protected]; [email protected].
3
1. Introduction TiO2, an environmentally friendly semiconductor material, is widely used in photocatalytic degradation of organic pollutants, hydrogen production, antibacterial materials and solar cells due to its high activity, low-cost, stability and non-toxicity [1]. However, as first-generation photocatalysts, pristine TiO2 materials display very poor photocatalytic activity under visible light irradiation because of its wide band gap (e.g., 3.2 V for anatase and 3.0 V for rutile) and rapid recombination of photogenerated electron/hole pairs [1, 2]. The drawback seriously hinders practical applications of TiO2 materials in visible light driven photocatalytic process. Therefore, the design and preparation of visible light responsive TiO2 materials have attracted intense research interest [2]. In order to obtain second-generation TiO2 materials with visible light induced photocatalytic activity, elements (metal or non-metal) doping, coupling with narrow band gap semiconductor, and crystalline phase mixing are effective approaches [3-9]. The modified TiO2 materials obtained through the above approaches can significantly enhance the visible light induced photocatalytic activity due to extension of the photoresponse range as well as reduction of the recombination of photogenerated electron/hole pairs. Among these various modified approaches, coupling with narrow band gap semiconductors, such as silver halide (AgX), has attracted intense attention owing to highly activity and stability of product [10-17]. For example, Hu et al. prepared AgI/TiO2 (P25) with visible light induced photocatalytic activity of azo-dye degradation by the deposition-precipitation method [10]. Li et al. reported that AgBr-TiO2 nanotube films prepared via an immersion method showed highly efficient photodegradation of methyl orange (MO) under visible light irradiation [11]. Cao et al. synthesized novel composite AgI/AgCl/TiO2 photocatalysts by ion exchange
4
method [12]. However, the preparations of these AgX modified TiO2 nanocomposites usually require tedious procedures and long reaction times, which hinders large-scale production and extensive applications of the nanocomposites. In comparison to conventional methods, ultrasound-assisted preparation is efficient and facile for rapid preparation of nanostructured materials. The collapse of cavitation bubbles generates localized high temperature (about 104 K), pressure (about 105 kPa) and cooling rates (in excess of 109 K s-1) under ultrasonic condition, which can promote self-assembly and crystallization of nanostructured materials [18-22]. For instance, Meskin et al. synthesized nanocrystalline ZrO2, TiO2, NiFe2O4 and Ni0.5Zn0.5Fe2O4 powders by ultrasonic-hydrothermal treatment [23]. Shirsath et al. synthesized TiO2 nanoparticles doped with Fe and Ce using sonochemical approach [18]. Anandan et al. sonochemically prepared Au-TiO2 nanoparticles [24]. Nevertheless, to the best of our knowledge, little work has been made to the ultrasound-assisted preparation of AgX/TiO2 nanocomposites with visible-light responsive photocatalytic activity. In this paper, we report a facile ultrasound-assisted preparation of AgI/TiO2 nanocomposites. The crystal phase, morphology, UV–vis absorption spectrum, visible-light induced photocatalytic activity and mechanism, antibacterial effects of AgI/TiO2 nanocomposites were investigated. 2. Experimental All chemicals were of analytical grade except Ti(SO4)2, which was of chemically pure reagent. The preparation reaction mechanism illustrated in Scheme 1. In a typical preparation of TiO2 nanoparticles, 1.92 g of Ti(SO4)2, 0.30 g of NH4F and 0.96 g of urea were dissolved in 80 mL of deionized water under continuous stirring. The mixture was stirred for 30 min, then transferred into a 100 mL Teflon lined stainless
5
steel autoclave, kept at 180 °C for 12 h, and then cooled to room temperature. The resulting TiO2 nanoparticles were collected by filtration, washed using deionized water and dried at 80 °C for 12 h. The preparation procedure of AgI/TiO2 nanocomposites with 30 wt% AgI loding is as follows: 0.5 g of the as-prepared TiO2 nanoparticles and 0.103 g of KI were added to 50 mL of deionized water under continuous stirring. The mixture in a 100 mL glass beaker was stirred for 30 min and then sonicated for 30 min in the ultrasonic cleaning bath (KQ-300DE, 40 kHz, 300 W). Subsequently, 5 mL of 0.022 g mL-1 AgNO3 solution was rapidly injected to the mixture above. Finally, the mixture was further sonicated for 1 h. The product was collected by centrifugation, washed using deionized water and dried 12 h at 80 °C, and denoted as AgI/TiO2-UP. Then the as-prepared AgI/TiO2 nanocomposites were further calcinated at 350 °C for 2 h, and denoted as AgI/TiO2-UP-C. For comparison purposes, several control experiments with conventional precipitation process were performed. In these cases, the reaction mixture was stirred for 1 h after the injection of AgNO3 solution, while other preparation procedures are kept constant. The as-prepared sample was denoted as AgI/TiO2-CP. Then the as-prepared AgI/TiO2 -CP was further calcinated at 350 °C for 2 h, and denoted as AgI/TiO2-CP-C. The X-ray powder diffraction (XRD) patterns of the samples were recorded using a PANalytical X’Pert PRO diffractometer. Transmission electron microscopy (TEM) was performed on Hitachi H-800 microscope. UV–vis absorption spectra of the samples dispersed in ethanol (0.5 mg mL-1) were obtained on a UV–visible spectrophotometer (PERSEE, TU-1901). In a typical photocatalytic degradation test for organic pollutants, 50 mg of as-prepared AgI/TiO2-UP-C photocatalysts was added to 50 mL of a 10 mg L-1 MO
6
solution and then stirred in the dark for 30 min to ensure adsorption equilibrium. The suspension was then exposed to visible-light irradiation from a 250 W mercury blended lamp (4900 lumen of photon flux) with a filter (> 420 nm) at a distance of 20 cm. At given irradiation time intervals (20 min), the as-prepared AgI/TiO2-UP-C photocatalysts were removed by centrifugation and the MO solution concentrations were analyzed using a UV-Vis spectrophotometer (PERSEE, TU-1901). For detecting the reactive species during photocatalytic degradation of MO under visible light irradiation, different scavengers, such as triethanolamine (TEOA), isopropanol (IPA), p-benzoquinone (BQ), were introduced into photocatalytic reaction systems, the concentrations of the all scavengers are 1.0 mmol L-1 [25]. The method was similar to aforementioned photocatalytic degradation test. The antibacterial experiments were performed, similarly to the methods reported in the literatures [26-28]. In a typical photocatalytic antibacterial activity test, 44 mg of as-prepared AgI/TiO2-UP-C photocatalysts were added to 100 mL of 0.9 % saline solution in a flask under sonication for 1 h. Subsequently, 9.9 mL of the above mixture was sterilized by autoclaving at 121 °C for 20 min and mixed with 0.1 mL of the prepared Escherichia coli (E.coli) bacteria suspension (108 cfu mL-1) after cooling. The final photocatalysts and E.coli bacteria concentration in 10 mL of the reaction mixture were adjusted to 0.44 mg mL-1 and 106 cfu mL-1, respectively. To prevent settling of the photocatalysts, the reaction mixture in a Petri dish was stirred slowly with a magnetic stirrer. The reaction mixture was then exposed to visible-light irradiation from a 250 W mercury blended lamp (4900 lumen of photon flux) with a filter (> 420 nm) at a distance of 20 cm. 0.1 mL of the reaction mixture was collected 30 min later, immediately diluted with 0.9 % saline solution and then incubated at 37 °C for 24 h on a nutrient agar medium in dark.
7
3. Results and Discussion Fig. 1 shows the XRD patterns of the samples by ultrasound-assisted precipitation process. All the diffraction peaks of TiO2 component in three samples correspond to the anatase phase of TiO2 (JCPDS No. 21-1272). The diffraction peaks of AgI component supported on TiO2 nanoparticles attribute to β-AgI (JCPDS No. 09-0374). And no diffraction peaks of other impurities appear in the patterns. This indicates that the crystallization of AgI was rapidly performed through ultrasound-assisted precipitation. Furthermore, it is worth noting that the diffraction peaks of β-AgI component in the AgI/TiO2-UP-C nanocomposites are significantly broadening compared with XRD pattern of the AgI/TiO2 -UP nanocomposites. The phenomenon suggests that the crystallite size of AgI component in the AgI/TiO2 nanocomposites decreased after calcination. According to the literature [29], β-AgI exists below 147 °C, while above 147 °C β-AgI goes through a crystalline transition to α-AgI and the crystal phase transition is reversible. Therefore, the reduction of the crystallite size of AgI component in the AgI/TiO2-UP-C nanocomposites may be related to reversible crystal phase transition of AgI component during calcination. The XRD patterns of the samples by conventional precipitation process are shown in Fig. S1 (see supplementary data). Obviously, the intensity of diffraction peaks of AgI component in AgI/TiO2-CP nanocomposites is lower than that in AgI/TiO2-UP nanocomposites. This clearly indicates that the ultrasound process can improve the crystallinity of the product. Moreover, the sharpened diffraction peaks of β-AgI component in the AgI/TiO2-CP-C nanocomposites suggest that the crystallite size of β-AgI component in the AgI/TiO2-CP nanocomposites increased after calcination. This phenomenon may be attributed to the poor crystallinity of the AgI/TiO2 -CP nanocomposites. The change trend in β-AgI size of samples prepared by conventional precipitation process
8
after calcination is a contrast with that of samples prepared by ultrasound-assisted precipitation. It also reflects the differences between conventional precipitation and ultrasound-assisted precipitation. Fig. 2 is the TEM images of the samples by ultrasound-assisted precipitation process. Fig. 2a shows that the TiO2 consists of nanoparticles in the diameter of 10-20 nm. As shown in Fig. 2b, dark AgI nanoparticles with a size of 50-100 nm are coupled with TiO2 nanoparticles in AgI/TiO2-UP nanocomposites. Fig. 2c displays the morphology of AgI/TiO2-UP-C nanocomposites. Obviously, the crystallite size of dark AgI nanoparticles is reduced to 30-70 nm, but the crystallite size of TiO2 does not change apparently. The reduction of the crystallite size of AgI component after calcination is consistent with the aforementioned XRD analyst results. The small crystallite size of AgI component may be beneficial to the enhancement of photocatalytic activity of AgI/TiO2 nanocomposites owing to the reduction of the recombination of photogenerated electron/hole pairs. The TEM images of the samples by conventional precipitation process are shown in Fig. S2 (see supplementary data). It can be seen that the size of AgI nanoparticles (ca. 50 nm in diameter) in AgI/TiO2-CP significantly is smaller than that of AgI/TiO2-UP. The obvious agglomeration of AgI nanoparticles occurred in AgI/TiO2-CP-C. The size of the agglomeration is about 500-1000 nm. These results are consistent with the XRD analysis. The UV-vis absorption spectra of the samples by ultrasound-assisted precipitation process are shown in Fig. 3. The AgI/TiO2 -UP nanocomposites exhibit intense visible light absorption bands, which is distinctly different from the pristine TiO2 nanoparticles.
Besides,
visible
absorption
intensity
of
AgI/TiO2-UP-C
nanocomposites further increases compared to that of AgI/TiO2 nanocomposites,
9
indicating the calcination can promote visible light absorption of AgI component. The intense
absorption
indicates
that
the
AgI/TiO2-UP
and
AgI/TiO2-UP-C
nanocomposites display high generation efficiency of electron/hole pairs under visible light irradiation [13]. Furthermore, the absorption band centred at 424 nm of the AgI/TiO2-UP-C nanocomposites is blue-shifted compared to the absorption band centred at 430 nm of the AgI/TiO2-UP nanocomposites. The phenomenon may be attributed to the quantum size effect of AgI component after calcination due to the decrease of the crystallite size. However, as shown in Fig. S3 (see supplementary data), blue-shift phenomenon of the absorption band centred at 430 nm did not happen in AgI/TiO2-CP-C nanocomposites. It shows that the preparation methods have significant effect on UV-vis absorption of AgI/TiO2 nanocomposites. The photocatalytic activity of the samples was evaluated by photocatalytic degradation of MO solution under visible light irradiation. The characteristic absorption of MO solution at 465 nm on the UV-Vis spectra was selected to determine its concentration. Fig. 4 shows time curves of photocatalytic degradation of MO solution for four different samples. A blank experiment indicates that there was almost no change in the concentration of MO solution. In three cases of pristine TiO2, AgI-UP and AgI-CP nanoparticles as photocatalysts, the concentration decreases of MO solution are very slow. Furthermore, the AgI/TiO2-UP, AgI/TiO2-CP and AgI/TiO2-CP-C
nanocomposites
exhibit
lower
photocatalytic
activity with
degradation rate of 28.3 %, 15.7 % and 19.2 %, respectively, after visible irradiation of 120 min. However, the AgI/TiO2-UP-C nanocomposites unexpectedly exhibit superior photocatalytic activity with degradation rate of 95.7 % under the same conditions. The results indicate that calcination could obviously improve the photocatalytic activity of AgI/TiO2 nanocomposites. The improvement effect could be
10
attributed to reduced crystallite size, enhanced visible light absorption of AgI nanoparticles and closer interaction between AgI and TiO2 in AgI/TiO2 nanocomposites after calcination [30]. In order to study the reactive species during photocatalytic degradation of MO under visible light irradiation, a series of trapping experiment were performed. The results are shown in Fig. 5. When TEOA (a quencher of h+) or BQ (a quencher of O2·-) introduced into photocatalytic reaction system prior to addition of the photocatalysts, the degradations of MO are significantly inhibited. However, the photodegradation of MO is not affected by the addition of IPA (a quencher of ·OH). This demonstrates that h+ and O2·- are the main reactive species during photocatalytic degradation of MO by the AgI/TiO2-UP-C nanocomposites under visible light irradiation [25]. According to the trapping experimental results, a possible photocatalytic reaction mechanism over the AgI/TiO2-UP-C nanocomposites was proposed. As shown in Fig. 6, under visible light irradiation, AgI can be excited to form photogenerated electron/hole pairs owing to narrow bandgap energy (2.8 eV) [31]. Furthermore, the conduction band (CB) potential of AgI (-0.42 eV) is more negative than that of TiO2 (-0.1 eV) [31]. Therefore, the photogenerated electrons of AgI can easily transfer to the surface of TiO2 and react with O2 to produce O2·- [1, 31]. The valence band (VB) edge of TiO2 (3.1 eV) is more positive than that of AgI (2.38 eV), but TiO2 can not be excited by visible light due to wide bandgap energy (3.2 eV), so the photogenerated holes of AgI remain in its VB [1, 31]. Further, organic pollutants are degraded by h+ and O2·-. The antibacterial activity of the AgI/TiO2-UP-C nanocomposites was evaluated by visible light induced photocatalytic disinfection of E. coli, a common Gram-negative bacterium. Fig. 7 shows the results of antibacterial experiments. Antibacterial
11
activities of the TiO2 and AgI/TiO2 -UP are not obvious, so the results are not given. Fig. 7a exhibits no bactericidal activity in the absence of the AgI/TiO2-UP-C nanocomposites and visible light irradiation. As shown in Fig. 7b, the AgI/TiO2-UP-C nanocomposites indicate low bactericidal activity in the absence of visible light irradiation. Moreover, as shown in Fig. 7c, visible light exhibits weak killing effect on E. coli in the absence of the AgI/TiO2-UP-C nanocomposites. However, as shown in Fig. 7d, the AgI/TiO2-UP-C nanocomposites exhibit obvious bactericidal activity under visible light irradiation. The results unambiguously show the antibacterial properties
of
the
AgI/TiO2-UP-C
nanocomposites.
Consequently,
the
AgI/TiO2-UP-C nanocomposites could be used in the field of water and air disinfection. 4. Conclusions We have successfully prepared AgI/TiO2 nanocomposites by an effective and facile ultrasound-assisted precipitation method and subsequent calcination. The AgI/TiO2 nanocomposites show many unique physicochemical properties different from the counterpart prepared by conventional precipitation process. The crystallite size of AgI nanoparticles in the AgI/TiO2 nanocomposites decreased through a crystalline transition during calcination. Coupling with AgI nanoparticles can obviously extend the photoresponse of the AgI/TiO2 nanocomposites to visible light range. Furthermore, the calcination process significantly enhanced visible light absorption intensity of the AgI/TiO2 nanocomposites. The AgI/TiO2 nanocomposites after calcination displayed superior visible light induced photocatalytic activity for MO degradation and killing of E. coli due to reduced crystalline size, enhanced visible light absorption of AgI nanoparticles and closer interaction between AgI and TiO2. The trapping experiment results suggested that O2·- and h+ were the main reactive
12
species for the photodegradation of MO under visible light irradiation. The AgI/TiO2 nanocomposites are expected for practical applications in photocatalysts, disinfection and so on. Acknowledgment This work was financially supported by Leading Academic Discipline Project of Shanghai Municipal Education Commission (Project Number: J50704), Funding of Shanghai Municipal Education Commission and Shanghai Ocean University (Project: B-5405-12-0019) and the Natural Science Foundation of Shanghai, China (no.11ZR1415400). References [1] B. Chen, S.S. Mao, Chem. Rev. 107 (2007) 2891. [2] N. Serpone, A.V. Emeline, J. Phys. Chem. Lett. 3 (2012) 673. [3] T.M. Triantis, T. Fotiou, T. Kaloudis, A.G. Kontos, P. Falaras, D.D. Dionysiou, M. Pelaez, A. Hiskia, J. Hazardous Mater. 211-212 (2012) 196. [4] H.L. Qin, G.B. Gu, S. Liu, Mater. Chem. Phys. 112 (2008) 346. [5] A. Hasanpour, M. Niyaifar, H. Mohammadpour, J. Amighian, J. Phys. Chem. Solids 73 (2012) 1066. [6] N. Ghows, M.H. Entezari, Ultrason Sonochem. 19 (2012) 1070. [7] N. Viriya-empikul, T. Charinpanitkul, N. Sano, A. Soottitantawat, T. Kikuchi, K. Faungnawakij, W. Tanthapanichakoon, Mater. Chem. Phys. 118 (2009) 254. [8] D. Nassoko, Y.F. Li, H. Wang, J.L. Li, Y.Z. Li, Y. Yu, J. Alloys Compd. 540 (2012) 228. [9] J.Q. Yan, G.J. Wu, N.J. Guan, L.D. Li, Z.X. Li, X.Z. Cao, Phys. Chem. Chem. Phys. 15 (2013) 10978.
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[10] C. Hu, X.X. Hu, L.S. Wang, J.H. Qu, A.M. Wang, Environ. Sci. Technol. 40 (2006) 7903. [11] Q.Y. Li, Y.Y. Xing, R. Li, L.L. Zong, X.D. Wang, J.J. Yang, RSC Advances 2 (2012) 9781. [12] J. Cao, B.Y. Xu, B.D. Luo, H.L. Lin, S.F. Chen, Appl. Surf. Sci. 257 (2011) 7083. [13] Y.Z. Li, H. Zhang, Z.M. Guo, J.J. Han, X.J. Zhao, Q.N. Zhao, S.J. Kim, Langmuir 24 (2008) 8351. [14] W.X. Wang, L.Q. Jing, Y.C. Qu, Y.B. Luan, H.G. Fu, Y.C. Xiao, J. Hazardous Mater. 243 (2012) 169. [15] Y.J. Zang, R. Farnood, Appl. Catal. B 79 (2008) 334. [16] Y.Y. Xing, R. Li, Q.Y. Li, J.J. Yang, J. Nanopart. Res. 14 (2012) 1284. [17] J.F. Guo, B.W. Ma, A.Y. Yin, K.N. Fan, W.L. Dai, J. Hazardous Mater. 211-212 (2012) 77. [18] S.R. Shirsath, D.V. Pinjari, P.R. Gogate, S.H. Sonawane, A.B. Pandit, Ultrason. Sonochem. 20 (2013) 277. [19] P.R. Gogate, V.S. Sutkar, A.B. Pandit, Chem. Eng. J. 166 (2011) 1066. [20] V.S. Sutkar, P.R. Gogate, Chem. Eng. J. 158 (2010) 296. [21] V.S. Sutkar, P.R. Gogate, Chem. Eng. J. 155 (2009) 26. [22] D.V. Pinjari, K. Prasad, P.R. Gogate, S.T. Mhaske, A.B. Pandit, Chem. Eng. Process. 74 (2013) 178. [23] P.E. Meskin, V.K. Ivanov, A.E. Barantchikov, B.R. Churagulov, Y.D. Tretyakov, Ultrason. Sonochem. 13 (2006) 47. [24] S. Anandan, M. Ashokkumar, Ultrason. Sonochem. 16 (2009) 316.
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[25] L.Q. Ye, K.J. Deng, F. Xu, L.H. Tian, T.Y. Peng, L. Zan, Phys. Chem. Chem. Phys. 14 (2012) 82. [26] T.S. Wu, K.X Wang, G.D. Li, S.Y. Sun, J. Sun, J.S. Chen, ACS Appl. Mater. Interface 2 (2010) 544. [27] J.M. Yu, W.K. Ho, J.G. Yu, H.Y. Yip, P.K. Wong, J.C. Zhao, Environ. Sci. Technol. 39 (2005) 1175. [28] S. Sontakke, J. Modak, G. Madras, Chem. Eng. J. 165 (2010) 225. [29] W. Sun, Y.Z. Li, W.Q. Shi, X.J. Zhao, P.F. Fang, J. Mater. Chem. 21 (2011) 9263. [30] Q.Y. Li, Y.Y. Xing, R. Li, L.L. Zong, X.D. Wang, J.J. Yang, RSC Advances 2 （2012）9781. [31] H.L. Lin, J. Cao, B.D. Luo, B.Y. Xu, S.F. Chen, Catal. Comm. 21 (2012) 91.
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Scheme captions Scheme 1. Ultrasound-assisted preparation reaction mechanism of AgI/TiO2 nanocomposites. Figure captions Fig. 1. XRD patterns of the samples prepared by ultrasound-assisted precipitation process. Fig. 2. TEM images of the samples by ultrasound-assisted precipitation process: (a) TiO2, (b) AgI/TiO2-UP and (c) AgI/TiO2-UP-C. The insets of (b) and (c) are diameter distribution curves of AgI nanoparticles. Fig. 3. UV–vis absorption spectra of the samples by ultrasound-assisted precipitation process. Fig. 4. Photocatalytic activity of the samples. Fig. 5. Trapping experiment results of photogenerated reactive species in system of photodegradation of MO by the AgI/TiO2-UP-C under visible light irradiation. Fig. 6. Schematic diagram of the electron-hole separation and photocatalytic reaction process of the AgI/TiO2-UP-C under visible light irradiation. Fig. 7. The results of antibacterial testing: (a) and (c) without photocatalyst, (b) and (d) the AgI/TiO2-UP-C.
16
Scheme
Scheme 1.
17
Figures
Intensity (a.u.) (c)
(b)
(a)
10 20
β (100)
β (002)
A(101)
30 40
β (110)
β (112)
A(200)
60 A(204)
70
A(116) A(220) A(215) A(301)
A ~ Anatase
A(105) A(211)
β ~ β-AgI
50
2 Theta (degree)
Fig. 1.
A(103) A(004) A(112)
80
18
Fig. 2.
19
Absorbance (a.u.)
AgI/TiO2-UP-C AgI/TiO2-UP TiO2
200
300
400
500
600
700
800
Wavelength (nm)
Fig. 3.
20
1.0 0.8 AgI/TiO2-UP-C
C/C0
0.6
AgI/TiO2-UP AgI/TiO2-CP-C AgI/TiO2-CP
0.4
TiO2 AgI-UP AgI-CP Blank
0.2 0.0 0
20
40
60
80
100
120
Time (min)
Fig. 4.
21
1.0
0.8
1-C/C0
0.6
0.4
0.2
0.0
No quencher
TEOA
IPA
BQ
Fig. 5.
22
Fig. 6.
23
No visible light irradiation
a
b
Under visible light irradiation
d
c
Fig. 7.
24
Research highlights ►A rapid and effective ultrasound-assisted precipitation preparation for AgI/TiO2 nanocomposites. ►Distinctive reduction of crystallite size of AgI nanoparticles after low-temperature calcination. ►Superior visible light induced photocatalytic activity of methyl orange and antibacterial activity.
25
