- Email: [email protected]
Enhancement of the photocatalytic property of TiO2 columnar nanostructured films by changing deposition angle
Materials Research Bulletin 50 (2014) 68–72
Contents lists available at ScienceDirect
Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu
Enhancement of the photocatalytic property of TiO2 columnar nanostructured films by changing deposition angle Zhengcao Li *, Yi Teng, Liping Xing, Na Zhang, Zhengjun Zhang Advanced Materials Laboratory, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 January 2013 Received in revised form 16 September 2013 Accepted 13 October 2013 Available online 19 October 2013
Isolated and inclined columnar nanostructured TiO2 films were obtained by sputtering titanium with glancing angle deposition method and subsequently annealing in air. Compared with flat film, TiO2 film fabricated with this method has higher porosity; compared with TiO2 powder, it overcomes the obstacles of immobilization and recycling. The TiO2 photocatalysis was evaluated by the degradation of methyl orange under UV light. It was indicated that the photocatalytic performance increased with deposition angle, which changed the porosity of the films. The relationship between deposition angle (the angle between the target and substrate surface) and the TiO2 columnar inclination angle (the angle between TiO2 columnar and substrate normal) was discussed. Crown Copyright ß 2013 Published by Elsevier Ltd. All rights reserved.
Keywords: A. Oxides A. Nanostructures B Sputtering D. Catalytic properties D. Surface properties
1. Introduction Increasing concerns on the serious environmental pollution create a great demand for environment-friendly materials and techniques. In recent years, photocatalytic technique has drawn much attention because of its good performance in dealing with the environmental problems [1–3]. The degradation of organic pollutants in wastewater is an important procedure for environmental protection [4]. As a kind of promising photocatalyst, titanium dioxide (TiO2) performs effectively in degrading organic pollutants and therefore has been extensively investigated. In addition, TiO2 has many advantages such as non-toxicity, chemical and physical stability, a unique combination of optical and photochemical properties, which can be applied to disinfect, purify air and degrade organic compounds [5,6]. Much work studying photocatalytic properties of TiO2 indicates that TiO2 powders [5,7] and flat films fabricated by sol-gel method [8,9]. However, TiO2 powders have practical problems, such as immobilization and recycling. Meanwhile, flat films fabricated by sol-gel method perform a relatively low photocatalytic efficiency due to low porosity. As a result, more attention has been attracted to the fabrication of nanostructured TiO2 films [10–12] with enhanced specific surface area. In this study, TiO2 films were prepared by sputtering the Ti target in argon gas with glancing angle deposition method, and subsequently annealing in air.
* Corresponding author. Tel.: +86 10 62772233; fax: +86 10 62771160. E-mail address: [email protected] (Z. Li).
Isolated and inclined columnar nanostructures were obtained. The mainly used technique in this study to acquire columnar nanostructures is glancing angle deposition combined with magnetron sputtering in ultra-high vacuum [13]. Shadowing of incident adatoms tends to emphasize any random variation in growing film [10,14]. The incident flux cannot reach the shadowing area and therefore deposits on incident adatoms. This shadowing effect leads to columnar nanostructures exhibiting a high porosity (Fig. 1). TiO2 films fabricated in this study performed photocatalytic activity effectively toward methyl orange under UV light irradiation, which demonstrated the potential application for treatment of effluent and many other aspects. The objective of this study is to investigate the influence of deposition angles on photocatalytic activity and its mechanism. 2. Experimental details 2.1. Preparation The TiO2 films with columnar nanostructures were fabricated by sputtering Ti target with glancing angle deposition (GLAD) technique [13,15] in magnetron sputtering system and a subsequent two-step annealing treatment. All films were fabricated on quartz substrate. Sputtering Ti target by GLAD in magnetron sputtering system (JPG450), columnar nanostructure Ti films were obtained. The Ti target is a disk of 60 mm in diameter and 30 mm in thickness with purity of 99.99%. The base pressure and sputtering pressure were
0025-5408/$ – see front matter . Crown Copyright ß 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2013.10.021
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
69
Fig. 1. Shadowing effect of GLAD.
fixed at 1.5 104 Pa and 0.15 Pa, respectively. Sputtering was performed in argon gas for 90 min. Argon gas flow was 20sccm in the beginning and kept 10sccm during the whole deposition process. The deposition power was about 160 W. The deposition angle, defined as the angle between the target and substrate surface, was set to 688, 738, 788, and 838, respectively. Annealing as-deposited Ti films in quartz tube furnace, TiO2 films with columnar nanostructures were obtained. Ti films were firstly annealed at 400 8C for 4 h to be oxidized partly, and then completely transformed into TiO2 by annealing at 550 8C for 1 h. A series of experiments with various combinations of annealing temperatures (300 8C, 400 8C, 450 8C, 500 8C, 550 8C, 600 8C and 700 8C) and annealing times (1 h, 2 h, 4 h and 6 h) were conducted to optimize the annealing treatment conditions. The experimental results showed that the columnar structure and the discreteness were destroyed at above 400 8C. Meanwhile, for the purpose of complete oxidation, annealing treatment had to last for more than 2 h at a temperature of higher than 550 8C [16]. As a result, such a two-step annealing treatment mentioned above was adopted to accomplish the transition from Ti to TiO2 completely while keeping columnar nanostructures by high temperature because of atom diffusion. 2.2. Characterization Nanostructure morphologies were observed with SEM and crystal phase characterizations were conducted by XRD. The parameters of XRD (U = 45 kV, I = 200 mA) were the same for all samples. Thickness of films was measured by a surface profile measuring instrument. Photocatalytic activities of prepared samples were characterized by degradation efficiency of diluted methyl orange under UV light irradiation [17]. A higher degradation rate indicates a better photocatalytic performance. Experiments of photodegradation were conducted as follows. Sample of TiO2 columnar nanostructured film on quartz substrate (15 mm 15 mm in size) was immersed in 6 mL diluted methyl orange solution (concentration was about 10 mmol/L). Then this setup was put under UV for 2 h. By characterizing the concentrations of methyl orange solution before and after UV irradiation, the degradation efficiency was calculated. According to Beer–Lambert law, the relationship between absorbance (A) and concentration (C) of a diluted solution is: C / A, and the relationship between absorbance (A) and transmittance (T) is: A = log T, so C / log T. The transmittance (T) at 460 nm of the spectra measured by a UV–vis spectrophotometer was used to calculate the degradation efficiency. The tests were repeated for the same 6 mL diluted methyl orange solution without sample under UV irradiation and with TiO2 sample without UV irradiation as control experiments.
of rutile phase according to the 21-1276 PDF Card, as determined by XRD (Fig. 2), which suggests that the phase was transformed to rutile TiO2 without residual Ti or other oxide. The results indicated that Ti completely transformed into TiO2 after the two-step annealing treatment. Thicknesses of TiO2 columnar nanostructure films deposited at deposition angles of 688, 738, 788, and 838 were approximately 530 nm, 520 nm, 500 nm, and 500 nm, respectively, measured by a surface profile measuring instrument. It seemed that thickness of TiO2 film decreased slightly with increasing deposition angles. The cross sections and surface morphologies of TiO2 columnar nanostructure films with different deposition angles were shown in Fig. 3. The columns were isolated and inclined in shape with a homogeneous distribution and high porosity consistent with films fabricated by GLAD at large deposition angles [13,14,18]. It is apparent from SEM surface images that the film with larger deposition angle had higher porosity, which could be due to increasing deposition angle enhanced shadowing effect. As a result, the porosity of TiO2 columnar nanostructured film increased with increasing the deposition angle [23]. It is well known that the photocatalytic reaction occurs on the surface and higher porosity results in higher photocatalytic activity [10,17,19]. So it could be expected that the films with larger deposition angles might perform photocatalytic decolorization more effectively. The columnar inclination angles of TiO2 films with different deposition angles were measured as indicated in Fig. 4. The columnar inclination angles were defined as the angles between the columns and the substrate normal in this article. Ten columns of every film were chosen to measure the inclination angle. The average inclination angle degrees of TiO2 films deposited at deposition angles of 688, 738, 788, and 838 were 248, 238, 218, and 228, respectively. There was little difference in the average
3. Results and discussion The TiO2 films with different deposition angles were all transparent and crystalline, with all peaks (2u = 27.68, 37.08, 41.48, 54.48, 56.68) corresponded to the known diffraction maxima
Fig. 2. XRD spectra of TiO2 columnar nanostructure films with different deposition angles of (a) 688, (b) 738, (c) 788, and (d) 838.
70
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
Fig. 3. Cross sections and surface morphologies of TiO2 columnar nanostructure films with different deposition angles of (a) 688, (b) 738, (c) 788, and (d) 838.
inclination angle degrees among those films within systematic error. The measured results did not agree with the relationship of the columnar inclination angle (b) and the deposition angle (a) with GLAD in electron beam evaporation system proposed by Tait [20]: b = a a sin[(1 cos a)/2], which indicated that b should increase with increasing a. The reason may be that the experiments of this study were conducted in magnetron sputtering system, and collimation of incident flux in magnetron sputtering system is not as good as that in electron beam evaporation system. The photocatalytic property is known as an important application of TiO2 [2,6,21,22]. Photocatalytic activities of prepared samples were evaluated by measuring the degradation efficiency of diluted methyl orange under UV light irradiation. The degradation efficiency was calculated using transmittance at a wavelength of 460 nm as mentioned in the last paragraph of
Section 2.2. The diluted methyl orange with the TiO2 sample was kept in dark for 2 h without UV irradiation as a control experiment. It was shown that the change of diluted methyl orange concentration before and after testing was negligible. Therefore the influence of nanostructure’s absorption on the decolorization of methyl orange was exempt. Transmittance spectra of origin methyl orange, methyl orange after 2 h UV irradiation without sample and with TiO2 samples deposited at deposition angles of 688, 738, 788, and 838, respectively were shown in Fig. 5. According to the transmittances at a wavelength of 460 nm and Beer–Lambert law, the calculated degradation efficiency of diluted methyl orange after 2 h UV radiation without sample and with TiO2 samples deposited at deposition angles of 688, 738, 788, and 838 were 11.6%, 22.1%, 29.6%, 35.1% and 37.8% as shown by the inset of Fig. 5. The result indicated
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
71
Fig. 4. The average inclination angle of TiO2 columnar nanostructure with different deposition angles of (a) 688, (b) 738, (c) 788, and (d) 838 respectively.
Fig. 5. Transmittance spectra of (a) origin methyl orange, (b) methyl orange after 2 h UV radiation without sample and with TiO2 samples deposited at deposition angles of (c) 688, (d) 738, (e) 788, and (f) 838 respectively (the inset shows the degradation rate changing with deposition angle).
that TiO2 films fabricated in this study all performed photocatalytic degradation effectively, and the photocatalytic activity increased with increasing the deposition angle.
4. Conclusions Isolated and inclined columnar nanostructure TiO2 films with high porosity obtained in this study all performed photocatalytic decolorization effectively under UV light irradiation. The crystal phase of the columnar nanostructure was rutile TiO2 without residual Ti or other oxide using the two-step annealing treatment. The average inclination angle is unchanged when the deposition angle varies from 688 to 838. Nevertheless, the photocatalytic efficiency was still increased with increasing the deposition angle, due to the enhanced shadowing effect and therefore higher porosity.
Acknowledgments The authors are grateful to the financial support by the National Natural Science Foundation of China (61076003 and 61176003), and the National Basic Research Program of China (973 program, 2010CB832900 and 2010CB731600). References [1] P. Saritha, C. Aparna, V. Himabindu, Y. Anjaneyulu, J. Hazard. Mater. 149 (2007) 609–614. [2] M.G. Neelavann, M. Revathi, C.A. Basha, J. Hazard. Mater. 149 (2007) 371–378. [3] B. Mounir, M.N. Pons, O. Zahraa, A. Yaacoubi, A. Benhammou, J. Hazard. Mater. 148 (2007) 513–520. [4] M. Farooq, I.A. Raja, A. Pervez, Sol. Energy 83 (2009) 1527–1533. [5] A. Fujishima, X.T. Zhang, D.A. Tryk, Surf. Sci. Rep. 63 (2008) 515–582. [6] P.K. Song, Y. Irie, Y. Shigesato, Thin Solid Films 496 (2006) 121–125. [7] S. Horikoshi, Y. Minatodani, H. Sakai, M. Abe, N. Serpone, J. Photochem. Photobiol. A 217 (2011) 191–200.
72
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
[8] D. Singh, N. Singh, S.D. Sharma, C. Kant, C.P. Sharma, R.R. Pandey, K.K. Saini, J. Sol– Gel Sci. Technol. 58 (2011) 269–276. [9] M. Lafjah, F. Djafri, A. Bengueddach, N. Keller, V. Keller, J. Hazard. Mater. 186 (2011) 1218–1225. [10] Y. Pihosh, I. Turkevych, J.H. Ye, M. Goto, A. Kasahara, M. Kondo, M. Tosa, J. Electrochem. Soc. 156 (2009) K160–K165. [11] F. Di Fonzo, C.S. Casari, V. Russo, M.F. Brunella, A.L. Bassi, C.E. Bottani, Nanotechnology (2009) 20. [12] Z.C. Li, L.P. Xing, Z.J. Zhang, Adv. Mater. Sci. Eng., 2012. [13] S.T. Chen, Z.C. Li, Z.J. Zhang, Nanoscale Res. Lett. 6 (2011) 326–330. [14] Q. Zhou, Z.C. Li, J. Ni, Z.J. Zhang, Mater. Trans. 52 (2011) 469–473. [15] Q. Zhou, Z.C. Li, Y. Yang, Z.J. Zhang, J. Phys. D Appl. Phys. (2008) 41.
[16] [17] [18] [19] [20] [21] [22] [23]
Z.C. Li, L.P. Xing, N. Zhang, Y. Yang, Z.J. Zhang, Mater. Trans. 52 (2011) 1939–1942. X.Z. Yu, Z.G. Shen, Vacuum 85 (2011) 1026–1031. Y.Q. Wang, Z.C. Li, X. Sheng, Z.J. Zhang, J. Chem. Phys. (2007) 126. Y.W. Dou, X. Feng, C. Yin, Adv. Manuf. Technol. 156–157 (Pts 1, 2) (2011) 1725–1729. R.N. Tait, T. Smy, M.J. Brett, Thin Solid Films 226 (1993) 196–201. Z.D. Meng, L. Zhu, J.G. Choi, M.L. Chen, W.C. Oh, J. Mater. Chem. 21 (2011) 7596– 7603. E. Murugan, R. Rangasamy, J. Biomed. Nanotechnol. 7 (2011) 225–228. L. Gonzalez-Garcia, G. Lozano, A. Barranco, H. Miguez, A.R. Gonzalez-Elipe, J. Mater. Chem. 20 (2010) 6408–6412.
Contents lists available at ScienceDirect
Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu
Enhancement of the photocatalytic property of TiO2 columnar nanostructured films by changing deposition angle Zhengcao Li *, Yi Teng, Liping Xing, Na Zhang, Zhengjun Zhang Advanced Materials Laboratory, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 11 January 2013 Received in revised form 16 September 2013 Accepted 13 October 2013 Available online 19 October 2013
Isolated and inclined columnar nanostructured TiO2 films were obtained by sputtering titanium with glancing angle deposition method and subsequently annealing in air. Compared with flat film, TiO2 film fabricated with this method has higher porosity; compared with TiO2 powder, it overcomes the obstacles of immobilization and recycling. The TiO2 photocatalysis was evaluated by the degradation of methyl orange under UV light. It was indicated that the photocatalytic performance increased with deposition angle, which changed the porosity of the films. The relationship between deposition angle (the angle between the target and substrate surface) and the TiO2 columnar inclination angle (the angle between TiO2 columnar and substrate normal) was discussed. Crown Copyright ß 2013 Published by Elsevier Ltd. All rights reserved.
Keywords: A. Oxides A. Nanostructures B Sputtering D. Catalytic properties D. Surface properties
1. Introduction Increasing concerns on the serious environmental pollution create a great demand for environment-friendly materials and techniques. In recent years, photocatalytic technique has drawn much attention because of its good performance in dealing with the environmental problems [1–3]. The degradation of organic pollutants in wastewater is an important procedure for environmental protection [4]. As a kind of promising photocatalyst, titanium dioxide (TiO2) performs effectively in degrading organic pollutants and therefore has been extensively investigated. In addition, TiO2 has many advantages such as non-toxicity, chemical and physical stability, a unique combination of optical and photochemical properties, which can be applied to disinfect, purify air and degrade organic compounds [5,6]. Much work studying photocatalytic properties of TiO2 indicates that TiO2 powders [5,7] and flat films fabricated by sol-gel method [8,9]. However, TiO2 powders have practical problems, such as immobilization and recycling. Meanwhile, flat films fabricated by sol-gel method perform a relatively low photocatalytic efficiency due to low porosity. As a result, more attention has been attracted to the fabrication of nanostructured TiO2 films [10–12] with enhanced specific surface area. In this study, TiO2 films were prepared by sputtering the Ti target in argon gas with glancing angle deposition method, and subsequently annealing in air.
* Corresponding author. Tel.: +86 10 62772233; fax: +86 10 62771160. E-mail address: [email protected] (Z. Li).
Isolated and inclined columnar nanostructures were obtained. The mainly used technique in this study to acquire columnar nanostructures is glancing angle deposition combined with magnetron sputtering in ultra-high vacuum [13]. Shadowing of incident adatoms tends to emphasize any random variation in growing film [10,14]. The incident flux cannot reach the shadowing area and therefore deposits on incident adatoms. This shadowing effect leads to columnar nanostructures exhibiting a high porosity (Fig. 1). TiO2 films fabricated in this study performed photocatalytic activity effectively toward methyl orange under UV light irradiation, which demonstrated the potential application for treatment of effluent and many other aspects. The objective of this study is to investigate the influence of deposition angles on photocatalytic activity and its mechanism. 2. Experimental details 2.1. Preparation The TiO2 films with columnar nanostructures were fabricated by sputtering Ti target with glancing angle deposition (GLAD) technique [13,15] in magnetron sputtering system and a subsequent two-step annealing treatment. All films were fabricated on quartz substrate. Sputtering Ti target by GLAD in magnetron sputtering system (JPG450), columnar nanostructure Ti films were obtained. The Ti target is a disk of 60 mm in diameter and 30 mm in thickness with purity of 99.99%. The base pressure and sputtering pressure were
0025-5408/$ – see front matter . Crown Copyright ß 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2013.10.021
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
69
Fig. 1. Shadowing effect of GLAD.
fixed at 1.5 104 Pa and 0.15 Pa, respectively. Sputtering was performed in argon gas for 90 min. Argon gas flow was 20sccm in the beginning and kept 10sccm during the whole deposition process. The deposition power was about 160 W. The deposition angle, defined as the angle between the target and substrate surface, was set to 688, 738, 788, and 838, respectively. Annealing as-deposited Ti films in quartz tube furnace, TiO2 films with columnar nanostructures were obtained. Ti films were firstly annealed at 400 8C for 4 h to be oxidized partly, and then completely transformed into TiO2 by annealing at 550 8C for 1 h. A series of experiments with various combinations of annealing temperatures (300 8C, 400 8C, 450 8C, 500 8C, 550 8C, 600 8C and 700 8C) and annealing times (1 h, 2 h, 4 h and 6 h) were conducted to optimize the annealing treatment conditions. The experimental results showed that the columnar structure and the discreteness were destroyed at above 400 8C. Meanwhile, for the purpose of complete oxidation, annealing treatment had to last for more than 2 h at a temperature of higher than 550 8C [16]. As a result, such a two-step annealing treatment mentioned above was adopted to accomplish the transition from Ti to TiO2 completely while keeping columnar nanostructures by high temperature because of atom diffusion. 2.2. Characterization Nanostructure morphologies were observed with SEM and crystal phase characterizations were conducted by XRD. The parameters of XRD (U = 45 kV, I = 200 mA) were the same for all samples. Thickness of films was measured by a surface profile measuring instrument. Photocatalytic activities of prepared samples were characterized by degradation efficiency of diluted methyl orange under UV light irradiation [17]. A higher degradation rate indicates a better photocatalytic performance. Experiments of photodegradation were conducted as follows. Sample of TiO2 columnar nanostructured film on quartz substrate (15 mm 15 mm in size) was immersed in 6 mL diluted methyl orange solution (concentration was about 10 mmol/L). Then this setup was put under UV for 2 h. By characterizing the concentrations of methyl orange solution before and after UV irradiation, the degradation efficiency was calculated. According to Beer–Lambert law, the relationship between absorbance (A) and concentration (C) of a diluted solution is: C / A, and the relationship between absorbance (A) and transmittance (T) is: A = log T, so C / log T. The transmittance (T) at 460 nm of the spectra measured by a UV–vis spectrophotometer was used to calculate the degradation efficiency. The tests were repeated for the same 6 mL diluted methyl orange solution without sample under UV irradiation and with TiO2 sample without UV irradiation as control experiments.
of rutile phase according to the 21-1276 PDF Card, as determined by XRD (Fig. 2), which suggests that the phase was transformed to rutile TiO2 without residual Ti or other oxide. The results indicated that Ti completely transformed into TiO2 after the two-step annealing treatment. Thicknesses of TiO2 columnar nanostructure films deposited at deposition angles of 688, 738, 788, and 838 were approximately 530 nm, 520 nm, 500 nm, and 500 nm, respectively, measured by a surface profile measuring instrument. It seemed that thickness of TiO2 film decreased slightly with increasing deposition angles. The cross sections and surface morphologies of TiO2 columnar nanostructure films with different deposition angles were shown in Fig. 3. The columns were isolated and inclined in shape with a homogeneous distribution and high porosity consistent with films fabricated by GLAD at large deposition angles [13,14,18]. It is apparent from SEM surface images that the film with larger deposition angle had higher porosity, which could be due to increasing deposition angle enhanced shadowing effect. As a result, the porosity of TiO2 columnar nanostructured film increased with increasing the deposition angle [23]. It is well known that the photocatalytic reaction occurs on the surface and higher porosity results in higher photocatalytic activity [10,17,19]. So it could be expected that the films with larger deposition angles might perform photocatalytic decolorization more effectively. The columnar inclination angles of TiO2 films with different deposition angles were measured as indicated in Fig. 4. The columnar inclination angles were defined as the angles between the columns and the substrate normal in this article. Ten columns of every film were chosen to measure the inclination angle. The average inclination angle degrees of TiO2 films deposited at deposition angles of 688, 738, 788, and 838 were 248, 238, 218, and 228, respectively. There was little difference in the average
3. Results and discussion The TiO2 films with different deposition angles were all transparent and crystalline, with all peaks (2u = 27.68, 37.08, 41.48, 54.48, 56.68) corresponded to the known diffraction maxima
Fig. 2. XRD spectra of TiO2 columnar nanostructure films with different deposition angles of (a) 688, (b) 738, (c) 788, and (d) 838.
70
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
Fig. 3. Cross sections and surface morphologies of TiO2 columnar nanostructure films with different deposition angles of (a) 688, (b) 738, (c) 788, and (d) 838.
inclination angle degrees among those films within systematic error. The measured results did not agree with the relationship of the columnar inclination angle (b) and the deposition angle (a) with GLAD in electron beam evaporation system proposed by Tait [20]: b = a a sin[(1 cos a)/2], which indicated that b should increase with increasing a. The reason may be that the experiments of this study were conducted in magnetron sputtering system, and collimation of incident flux in magnetron sputtering system is not as good as that in electron beam evaporation system. The photocatalytic property is known as an important application of TiO2 [2,6,21,22]. Photocatalytic activities of prepared samples were evaluated by measuring the degradation efficiency of diluted methyl orange under UV light irradiation. The degradation efficiency was calculated using transmittance at a wavelength of 460 nm as mentioned in the last paragraph of
Section 2.2. The diluted methyl orange with the TiO2 sample was kept in dark for 2 h without UV irradiation as a control experiment. It was shown that the change of diluted methyl orange concentration before and after testing was negligible. Therefore the influence of nanostructure’s absorption on the decolorization of methyl orange was exempt. Transmittance spectra of origin methyl orange, methyl orange after 2 h UV irradiation without sample and with TiO2 samples deposited at deposition angles of 688, 738, 788, and 838, respectively were shown in Fig. 5. According to the transmittances at a wavelength of 460 nm and Beer–Lambert law, the calculated degradation efficiency of diluted methyl orange after 2 h UV radiation without sample and with TiO2 samples deposited at deposition angles of 688, 738, 788, and 838 were 11.6%, 22.1%, 29.6%, 35.1% and 37.8% as shown by the inset of Fig. 5. The result indicated
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
71
Fig. 4. The average inclination angle of TiO2 columnar nanostructure with different deposition angles of (a) 688, (b) 738, (c) 788, and (d) 838 respectively.
Fig. 5. Transmittance spectra of (a) origin methyl orange, (b) methyl orange after 2 h UV radiation without sample and with TiO2 samples deposited at deposition angles of (c) 688, (d) 738, (e) 788, and (f) 838 respectively (the inset shows the degradation rate changing with deposition angle).
that TiO2 films fabricated in this study all performed photocatalytic degradation effectively, and the photocatalytic activity increased with increasing the deposition angle.
4. Conclusions Isolated and inclined columnar nanostructure TiO2 films with high porosity obtained in this study all performed photocatalytic decolorization effectively under UV light irradiation. The crystal phase of the columnar nanostructure was rutile TiO2 without residual Ti or other oxide using the two-step annealing treatment. The average inclination angle is unchanged when the deposition angle varies from 688 to 838. Nevertheless, the photocatalytic efficiency was still increased with increasing the deposition angle, due to the enhanced shadowing effect and therefore higher porosity.
Acknowledgments The authors are grateful to the financial support by the National Natural Science Foundation of China (61076003 and 61176003), and the National Basic Research Program of China (973 program, 2010CB832900 and 2010CB731600). References [1] P. Saritha, C. Aparna, V. Himabindu, Y. Anjaneyulu, J. Hazard. Mater. 149 (2007) 609–614. [2] M.G. Neelavann, M. Revathi, C.A. Basha, J. Hazard. Mater. 149 (2007) 371–378. [3] B. Mounir, M.N. Pons, O. Zahraa, A. Yaacoubi, A. Benhammou, J. Hazard. Mater. 148 (2007) 513–520. [4] M. Farooq, I.A. Raja, A. Pervez, Sol. Energy 83 (2009) 1527–1533. [5] A. Fujishima, X.T. Zhang, D.A. Tryk, Surf. Sci. Rep. 63 (2008) 515–582. [6] P.K. Song, Y. Irie, Y. Shigesato, Thin Solid Films 496 (2006) 121–125. [7] S. Horikoshi, Y. Minatodani, H. Sakai, M. Abe, N. Serpone, J. Photochem. Photobiol. A 217 (2011) 191–200.
72
Z. Li et al. / Materials Research Bulletin 50 (2014) 68–72
[8] D. Singh, N. Singh, S.D. Sharma, C. Kant, C.P. Sharma, R.R. Pandey, K.K. Saini, J. Sol– Gel Sci. Technol. 58 (2011) 269–276. [9] M. Lafjah, F. Djafri, A. Bengueddach, N. Keller, V. Keller, J. Hazard. Mater. 186 (2011) 1218–1225. [10] Y. Pihosh, I. Turkevych, J.H. Ye, M. Goto, A. Kasahara, M. Kondo, M. Tosa, J. Electrochem. Soc. 156 (2009) K160–K165. [11] F. Di Fonzo, C.S. Casari, V. Russo, M.F. Brunella, A.L. Bassi, C.E. Bottani, Nanotechnology (2009) 20. [12] Z.C. Li, L.P. Xing, Z.J. Zhang, Adv. Mater. Sci. Eng., 2012. [13] S.T. Chen, Z.C. Li, Z.J. Zhang, Nanoscale Res. Lett. 6 (2011) 326–330. [14] Q. Zhou, Z.C. Li, J. Ni, Z.J. Zhang, Mater. Trans. 52 (2011) 469–473. [15] Q. Zhou, Z.C. Li, Y. Yang, Z.J. Zhang, J. Phys. D Appl. Phys. (2008) 41.
[16] [17] [18] [19] [20] [21] [22] [23]
Z.C. Li, L.P. Xing, N. Zhang, Y. Yang, Z.J. Zhang, Mater. Trans. 52 (2011) 1939–1942. X.Z. Yu, Z.G. Shen, Vacuum 85 (2011) 1026–1031. Y.Q. Wang, Z.C. Li, X. Sheng, Z.J. Zhang, J. Chem. Phys. (2007) 126. Y.W. Dou, X. Feng, C. Yin, Adv. Manuf. Technol. 156–157 (Pts 1, 2) (2011) 1725–1729. R.N. Tait, T. Smy, M.J. Brett, Thin Solid Films 226 (1993) 196–201. Z.D. Meng, L. Zhu, J.G. Choi, M.L. Chen, W.C. Oh, J. Mater. Chem. 21 (2011) 7596– 7603. E. Murugan, R. Rangasamy, J. Biomed. Nanotechnol. 7 (2011) 225–228. L. Gonzalez-Garcia, G. Lozano, A. Barranco, H. Miguez, A.R. Gonzalez-Elipe, J. Mater. Chem. 20 (2010) 6408–6412.