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SiO2 composite with enhanced photocatalytic activity
Materials Letters 183 (2016) 175–178
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterization of a novel nanofibrous TiO2/SiO2 composite with enhanced photocatalytic activity Xuekun Tang a,b, Qiming Feng a,b, Kun Liu a,b,n, Yan Tan a a b
School of Minerals Processing & Bioengineering, Central South University, Changsha, 410083 China Key Laboratory for Mineral Materials and Application of Hunan Province, Central South University, Changsha, 410083 China
art ic l e i nf o
a b s t r a c t
Article history: Received 12 May 2016 Received in revised form 4 July 2016 Accepted 22 July 2016 Available online 22 July 2016
TiO2/chrysotile-based silica nanofibers composites (TiO2/SiO2NFs) were synthesized for the first time via a modified sol-gel method combining layer self-assembly procedure. In the composite, TiO2 nanoparticles are anatase structured and evenly dispersed without agglomeration on the surface of SiO2NFs in the form of monolayer. Compared to the commercial TiO2 (P25) and TiO2 prepared by similar sol-gel method, the TiO2/SiO2NFs composite exhibits much higher photocatalytic activity. The SiO2NFs in the composite not only provide a large adsorption capacity substrate, but also make TiO2 particles formed a well-dispersed monolayer to provide larger photocatalytic reaction surface area, resulting in the significantly increasing of photocatalytic activity. It is also found the TiO2/SiO2NFs prepared under 800 °C exhibits best photocatalytic activity due to the relatively optimum anatase crystalline phase fraction and crystallinity. & 2016 Elsevier B.V. All rights reserved.
Keywords: TiO2 monolayer Chrysotile-based SiO2 nanofibers Dispersion Photocatalytic activity
1. Introduction Titania dioxide (TiO2) is regarded as one of the most potential photocatalysts for organic pollution treatment due to its prominent advantages of high photocatalytic efficiency, high chemical resistance, economic availability and eco-friendly [1]. However, the TiO2 nanoparticles are easy to agglomerate, which significantly limits its photocatalytic activity due to the photocatalytic reactions take place on the surface of photocatalyst [2,3]. To solve these problems, a feasible way is to immobilize TiO2 particles on carrier with high surface area to form a well-dispersed layer [4]. The introduction of the carrier not only reduces the TiO2 particles agglomeration, but also improves the adsorption ability of the photocatalyst, which is an important criteria for efficient photocatalytic activity [5]. Up to now, wide variety of materials, such as diatomite [3], silica gels [6], activated carbons [7], etc, have been successfully applied as carriers. Nevertheless, these carriers are micrometer scale (such as the diatomite has a diameter of 5– 25 mm) and the TiO2 nanoparticles on carriers are partly agglomerated [8]. Thus, it can be speculated that the TiO2 nanoparticles will get a much better dispersion by using nanometer scale carrier. Previously, we reported a kind of amorphous silica nanofibers (SiO2NFs) prepared from chrysotile, whose diameter is 30–60 nm and length is several microns [9,10]. The SiO2NFs is a potential n
Corresponding author. E-mail address: [email protected] (K. Liu).
http://dx.doi.org/10.1016/j.matlet.2016.07.103 0167-577X/& 2016 Elsevier B.V. All rights reserved.
carrier due to its nano-size together with large specific surface area (nearly 400 m2/g) and adsorption ability [9,10]. In addition, researches have proved that the amorphous silica can significantly enhance the photocatalytic activity of TiO2 by preventing electronhole recombination in photocatalytic reaction [11]. Especially, to our best knowledge, application of SiO2NFs as photocatalyst carrier has never been reported before. In present paper, we immobilize TiO2 on SiO2NFs via a modified sol-gel method combining layer self-assembly procedure to form a novel photocatalyst composite. The as-prepared TiO2/SiO2NFs was characterized and the comparative photocatalytic activity studies were also carried out.
2. Experimental Synthetic processes of TiO2/SiO2NFs are as follow: First of all, the TiO2 precursor was prepared via a modified sol-gel method. 17.5 mL tetrabutyl orthotitanate was dissolved in 20 mL ethanol under string to obtain a solution (labeled as SA). Another solution (labeled as SB) was prepared containing 20 mL ethanol, 1.40 mL glacial acetic acid and 1.5 mL dilute nitric acid. SB was drop-wisely added into SA under vigorous stirring to obtain a TiO2 precursor colloid. Subsequently, the TiO2 particles were immobilized on the surface of SiO2NFs through a layer self-assembly procedure developed by ourselves. 0.25 g SiO2NFs was completely dispersed in 10 mL ethanol under ultrasonic and vigorous stirring to form a suspension. The suspension was rapidly mixed with the TiO2
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Fig. 1. X-ray diffraction patterns of the samples: (a) TiO2/SiO2NFs composites; (b) Sol-gel TiO2.
Fig. 2. TEM images of the SiO2NFs and TiO2/SiO2NFs composite (calcined under 800 °C).
precursor colloid, followed by vigorous stirring (for 4 min) and ultrasonic (for 1 min). Then, the suspension was filtered to separate the TiO2/SiO2NFs precursor and the colloid. Finally, The TiO2/ SiO2NFs precursor was dried (under 80 °C for 2 h) and calcined (for 2 h) to form the TiO2/SiO2NFs photocatalytic composite. The phase composition of the as-prepared samples was identified by X-ray powder diffractionmeter (XRD, Empyrean, Panalytical). The morphology was analyzed by transmission electron microscopy (TEM, JEM-2100F). The element composition was determined by X-ray fluorescence (Axios max, Panalytical). The photocatalytic activity was evaluated by degradation of rhodamine B (RhB) solution. The as-prepared 0.02 g TiO2/SiO2NFs (estimate composed of 0.013 g SiO2NFs and 0.007 g TiO2) was dispersed in 100 mL RhB (10 mg/L). The suspension was placed in dark and stirred continuously for 90 min to reach the adsorption-
desorption equilibrium. Subsequently, a 25 W ultraviolet lamp (emitting maximum intensity at 254 nm, Philips) was used as the light source. The residual RhB concentration was determined over an UV–vis spectrophotometer (UV-2600, Unico). In addition, the adsorption capacities and photocatalytic properties of single SiO2NFs (dosage is 0.013 g), commercial TiO2 (P25, produced by Degussa, dosage is 0.007 g) and sol-gel TiO2 (dosage is 0.007 g) were also evaluated for comparison.
3. Results and discussion Fig. 1 shows the XRD patterns of the SiO2NFs and TiO2/SiO2NFs composites. It can be seen in Fig. 1a that the pattern of SiO2NFs exhibits a broad diffraction peak between 15 and 30°, which is
X. Tang et al. / Materials Letters 183 (2016) 175–178
a
1.0
0.8
C/C0
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Sol-gel prepared TiO2 Commerical TiO2 (P25) SiO2NFs
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TiO2/SiO2NFs-700 TiO2/SiO2NFs-800
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1.2
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0
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c
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TiO2/SiO2NFs-800 0.025
TiO2/SiO2NFs-700 0.020
TiO2/SiO2NFs-900 0.015
P25 0.010
0.005
0.000
Prepared TiO2
Fig. 3. Degradation kinetics of RhB solution with different samples: (a) plots of C/C0 against reaction time under light off and light irradiation; (b) -ln(C/C0) versus light irradiation time; (c) reaction rate parameters.
well in agreement with the amorphous SiO2. When the calcination temperature is 800 °C, the diffraction peaks of TiO2/SiO2NFs composites can be clearly indexed to the anatase phase and no other impurity peaks are observed. When the calcinations temperature reaches 900 °C, only weak diffraction peaks appear at 27.5° and 37.9°, which can be assigned to the (110) and (101) crystalline planes for rutile. In comparison, as presented in Fig. 1b, the sol-gel TiO2 (prepared by the similar sol-gel method) only
177
exhibits anatase peaks when the calcination temperature is 500 °C. However, when the calcination temperature rises above 700 °C, most of the pure TiO2 are transformed from anatase to rutile. Thus, it can be inferred that the SiO2NFs can acutely restrain the anatase-rutile phase transformation in TiO2. Clearly, The SiO2NFs and TiO2 junction system has much more thermal stability, which is benefit for the photocatalytic activities (because it is known that the anatase has higher photocatalytic activity than the rutile). According to the similar reports, this phenomenon is resulted from the formation of the Ti-O-Si bond between the amorphous SiO2 and anatase TiO2 under calcination treatment [12]. In addition, it indirectly indicates the successful immobilization of TiO2 on SiO2NFs. Fig. 2 shows the TEM images of initial SiO2NFs and TiO2/ SiO2NFs composites. It can be seen that the initial SiO2NFs is relatively uniform in morphology and has a smooth surface. In comparison, the TEM micrographs of the as-prepared TiO2/ SiO2NFs composites show a rough surface, which confirms the TiO2 particles are successfully supported on the surface of the SiO2NFs. The nano-structured TiO2 particles are evenly deposited around the SiO2NFs surface to form a monolayer. In addition, it is worth noting that the observed TiO2 particles on the surface of SiO2NFs are very tiny (less than 10 nm) and without agglomeration, which can make great enhancement for its photocatalytic activity [4]. The result of XRF analysis shows the ratio of each element in TiO2/SiO2NFs is Ti 22.49%, O 49.52%, Si 24.29%, C 2.21% and the others 1.49%. As a result, a theoretical value of Ti/Si weight percentage can be calculated as about 6/6.5, which is near to the actual value calculated by the weight of SiO2NFs before and after immobilizing with TiO2 (about 6/7). Overall, the results further confirm that the presence of TiO2 in the composite. Fig. 3a presents the plots of C/C0 against reaction time under light off and light irradiation (C0 and C are the RhB initial concentration and residual concentration at reaction time, respectively). Clearly, the TiO2/SiO2NFs shows a higher adsorption capacity and degradation rate. Fig. 3b presents the -ln(C/C0) versus light irradiation time. From the data, the photodegradation kinetic parameters are calculated and graphically presented in Fig. 3c for a better comparison. Similarity, TiO2/SiO2NFs photocatalytic degradation efficiency is also better than sol-gel TiO2 and P25. Besides, in Fig. 3a the single SiO2NFs shows the largest adsorption capacity. Thus, it can be inferred that the high adsorption capacity of TiO2/SiO2NFs is derived from the SiO2NFs, which would bring great enhancement to the photocatalytic performance of the composite [7]. Moreover, it is worth noting the sol-gel TiO2 has a very low photocatalytic activity. The reason is that the prepared TiO2 particles are in the form of serious agglomeration [13]. On the contrary, the TiO2 shows a high photocatalytic activity after been well-dispersed on SiO2NFs. Based on the facts, we also think the high photocatalytic activity is partly resulted from the better dispersion of the TiO2 particles, which leads to much larger adsorption and photocatalytic reaction surface area. Furthermore, comparatively, the TiO2/SiO2NFs prepared under 800 °C has the best photocatalytic activity. It may be due to the formation of relatively optimum anatase crystalline phase fraction and crystallinity in the TiO2/SiO2NFs [14].
4. Conclusions In summary, TiO2/SiO2NFs are successful synthesized via a modified sol-gel method combining layer self-assembly procedure for the first time. The as-prepared TiO2/SiO2NFs are anatase structured even under 800 °C. SiO2NFs can effectively improve the
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thermal stability of TiO2 and restrain the anatase-to-rutile phase transition. The microstructure of the TiO2/SiO2NFs shows that the TiO2 nanoparticles are well-dispersed to form a monolayer structure on the surface of the SiO2NFs. The TiO2/SiO2NFs exhibits high photocatalytic degradation rate and efficiency according to the comparative studies on degradation of RhB. The high photocatalytic activity of TiO2/SiO2NFs is not only related to the high adsorption capacity of SiO2NFs, but also resulted from the better dispersion of the TiO2 particles to provide the larger adsorption and photocatalytic reaction surface area. Moreover, the TiO2/ SiO2NFs prepared under 800 °C exhibits best photocatalytic activity due to the relatively optimum anatase crystalline phase fraction and crystallinity. In addition, this work also shows the good ability of one-dimension nano-scale materials used as photocatalyst carrier.
Acknowledgments This work was financially supported by the Teacher Research Foundation of Central South University (2015); the National Natural Science Foundation of China (No. 51104180); the Hunan Provincial Natural Science Foundation of China (No. 13JJ4015).
References [1] L. Elsellami, H. Lachheb, A. Houas, Mater. Sci. Semicond. Process. 36 (2015) 103–114. [2] K. Choi, W. Lee, S. Lee, C. Lim, Mater. Lett. 158 (2015) 36–39. [3] Y. Xia, F. Li, Y. Jiang, M. Xia, B. Xue, Y. Li, Appl. Surf. Sci. 303 (2014) 290–296. [4] Z. Sun, Z. Hu, Y. Yan, S. Zheng, Appl. Surf. Sci. 314 (2014) 251–259. [5] B. Wang, G. Zhang, X. Leng, Z. Sun, S. Zheng, J. Hazard. Mater. 285 (2015) 212–220. [6] D. Li, Q. Zhu, C. Han, Y. Yang, W. Jiang, Z. Zhang, J. Hazard. Mater. 285 (2015) 398–408. [7] X. Fu, H. Yang, G. Lu, Y. Tu, J. Wu, Mater. Sci. Semicond. Process. 39 (2015) 362–370. [8] S. Padmanabhan, S. Pal, E. Haq, A. Licciulli, Appl. Catal. A: Gen. 485 (2014) 157–162. [9] K. Liu, Q. Feng, Y. Yang, G. Zhang, L. Ou, Y. Lu, J. Non-Cryst. Solids 353 (2007) 1534–1539. [10] Y. Yang, Q. Feng, K. Liu, G. Zhang, L. Ou, Y. Lu. Proceedings of the XXIV International Mineral Processing Congress, vol. 3, Beijing, 2008, pp. 3311–3317. [11] S. Artkla, W. Kim, W. Choi, J. Wittayakun, Appl. Catal. B: Eviron. 91 (2015) 157–164. [12] H. Chang, S. Kim, H. Jang, S. Cho, Mater. Lett. 65 (2011) 3272–3274. [13] O. Elbanna, P. Zhang, M. Fujitsuka, T. Majima, Appl. Catal. B: Eviron. 192 (2016) 80–87. [14] K. Choi, W. Lee, S. Lee, C. Lim, Mater. Lett. 158 (2015) 36–39.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterization of a novel nanofibrous TiO2/SiO2 composite with enhanced photocatalytic activity Xuekun Tang a,b, Qiming Feng a,b, Kun Liu a,b,n, Yan Tan a a b
School of Minerals Processing & Bioengineering, Central South University, Changsha, 410083 China Key Laboratory for Mineral Materials and Application of Hunan Province, Central South University, Changsha, 410083 China
art ic l e i nf o
a b s t r a c t
Article history: Received 12 May 2016 Received in revised form 4 July 2016 Accepted 22 July 2016 Available online 22 July 2016
TiO2/chrysotile-based silica nanofibers composites (TiO2/SiO2NFs) were synthesized for the first time via a modified sol-gel method combining layer self-assembly procedure. In the composite, TiO2 nanoparticles are anatase structured and evenly dispersed without agglomeration on the surface of SiO2NFs in the form of monolayer. Compared to the commercial TiO2 (P25) and TiO2 prepared by similar sol-gel method, the TiO2/SiO2NFs composite exhibits much higher photocatalytic activity. The SiO2NFs in the composite not only provide a large adsorption capacity substrate, but also make TiO2 particles formed a well-dispersed monolayer to provide larger photocatalytic reaction surface area, resulting in the significantly increasing of photocatalytic activity. It is also found the TiO2/SiO2NFs prepared under 800 °C exhibits best photocatalytic activity due to the relatively optimum anatase crystalline phase fraction and crystallinity. & 2016 Elsevier B.V. All rights reserved.
Keywords: TiO2 monolayer Chrysotile-based SiO2 nanofibers Dispersion Photocatalytic activity
1. Introduction Titania dioxide (TiO2) is regarded as one of the most potential photocatalysts for organic pollution treatment due to its prominent advantages of high photocatalytic efficiency, high chemical resistance, economic availability and eco-friendly [1]. However, the TiO2 nanoparticles are easy to agglomerate, which significantly limits its photocatalytic activity due to the photocatalytic reactions take place on the surface of photocatalyst [2,3]. To solve these problems, a feasible way is to immobilize TiO2 particles on carrier with high surface area to form a well-dispersed layer [4]. The introduction of the carrier not only reduces the TiO2 particles agglomeration, but also improves the adsorption ability of the photocatalyst, which is an important criteria for efficient photocatalytic activity [5]. Up to now, wide variety of materials, such as diatomite [3], silica gels [6], activated carbons [7], etc, have been successfully applied as carriers. Nevertheless, these carriers are micrometer scale (such as the diatomite has a diameter of 5– 25 mm) and the TiO2 nanoparticles on carriers are partly agglomerated [8]. Thus, it can be speculated that the TiO2 nanoparticles will get a much better dispersion by using nanometer scale carrier. Previously, we reported a kind of amorphous silica nanofibers (SiO2NFs) prepared from chrysotile, whose diameter is 30–60 nm and length is several microns [9,10]. The SiO2NFs is a potential n
Corresponding author. E-mail address: [email protected] (K. Liu).
http://dx.doi.org/10.1016/j.matlet.2016.07.103 0167-577X/& 2016 Elsevier B.V. All rights reserved.
carrier due to its nano-size together with large specific surface area (nearly 400 m2/g) and adsorption ability [9,10]. In addition, researches have proved that the amorphous silica can significantly enhance the photocatalytic activity of TiO2 by preventing electronhole recombination in photocatalytic reaction [11]. Especially, to our best knowledge, application of SiO2NFs as photocatalyst carrier has never been reported before. In present paper, we immobilize TiO2 on SiO2NFs via a modified sol-gel method combining layer self-assembly procedure to form a novel photocatalyst composite. The as-prepared TiO2/SiO2NFs was characterized and the comparative photocatalytic activity studies were also carried out.
2. Experimental Synthetic processes of TiO2/SiO2NFs are as follow: First of all, the TiO2 precursor was prepared via a modified sol-gel method. 17.5 mL tetrabutyl orthotitanate was dissolved in 20 mL ethanol under string to obtain a solution (labeled as SA). Another solution (labeled as SB) was prepared containing 20 mL ethanol, 1.40 mL glacial acetic acid and 1.5 mL dilute nitric acid. SB was drop-wisely added into SA under vigorous stirring to obtain a TiO2 precursor colloid. Subsequently, the TiO2 particles were immobilized on the surface of SiO2NFs through a layer self-assembly procedure developed by ourselves. 0.25 g SiO2NFs was completely dispersed in 10 mL ethanol under ultrasonic and vigorous stirring to form a suspension. The suspension was rapidly mixed with the TiO2
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Fig. 1. X-ray diffraction patterns of the samples: (a) TiO2/SiO2NFs composites; (b) Sol-gel TiO2.
Fig. 2. TEM images of the SiO2NFs and TiO2/SiO2NFs composite (calcined under 800 °C).
precursor colloid, followed by vigorous stirring (for 4 min) and ultrasonic (for 1 min). Then, the suspension was filtered to separate the TiO2/SiO2NFs precursor and the colloid. Finally, The TiO2/ SiO2NFs precursor was dried (under 80 °C for 2 h) and calcined (for 2 h) to form the TiO2/SiO2NFs photocatalytic composite. The phase composition of the as-prepared samples was identified by X-ray powder diffractionmeter (XRD, Empyrean, Panalytical). The morphology was analyzed by transmission electron microscopy (TEM, JEM-2100F). The element composition was determined by X-ray fluorescence (Axios max, Panalytical). The photocatalytic activity was evaluated by degradation of rhodamine B (RhB) solution. The as-prepared 0.02 g TiO2/SiO2NFs (estimate composed of 0.013 g SiO2NFs and 0.007 g TiO2) was dispersed in 100 mL RhB (10 mg/L). The suspension was placed in dark and stirred continuously for 90 min to reach the adsorption-
desorption equilibrium. Subsequently, a 25 W ultraviolet lamp (emitting maximum intensity at 254 nm, Philips) was used as the light source. The residual RhB concentration was determined over an UV–vis spectrophotometer (UV-2600, Unico). In addition, the adsorption capacities and photocatalytic properties of single SiO2NFs (dosage is 0.013 g), commercial TiO2 (P25, produced by Degussa, dosage is 0.007 g) and sol-gel TiO2 (dosage is 0.007 g) were also evaluated for comparison.
3. Results and discussion Fig. 1 shows the XRD patterns of the SiO2NFs and TiO2/SiO2NFs composites. It can be seen in Fig. 1a that the pattern of SiO2NFs exhibits a broad diffraction peak between 15 and 30°, which is
X. Tang et al. / Materials Letters 183 (2016) 175–178
a
1.0
0.8
C/C0
0.6
Sol-gel prepared TiO2 Commerical TiO2 (P25) SiO2NFs
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TiO2/SiO2NFs-700 TiO2/SiO2NFs-800
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TiO2/SiO2NFs-900 Ultraviolet radiation
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TiO2/SiO2NFs-800 0.025
TiO2/SiO2NFs-700 0.020
TiO2/SiO2NFs-900 0.015
P25 0.010
0.005
0.000
Prepared TiO2
Fig. 3. Degradation kinetics of RhB solution with different samples: (a) plots of C/C0 against reaction time under light off and light irradiation; (b) -ln(C/C0) versus light irradiation time; (c) reaction rate parameters.
well in agreement with the amorphous SiO2. When the calcination temperature is 800 °C, the diffraction peaks of TiO2/SiO2NFs composites can be clearly indexed to the anatase phase and no other impurity peaks are observed. When the calcinations temperature reaches 900 °C, only weak diffraction peaks appear at 27.5° and 37.9°, which can be assigned to the (110) and (101) crystalline planes for rutile. In comparison, as presented in Fig. 1b, the sol-gel TiO2 (prepared by the similar sol-gel method) only
177
exhibits anatase peaks when the calcination temperature is 500 °C. However, when the calcination temperature rises above 700 °C, most of the pure TiO2 are transformed from anatase to rutile. Thus, it can be inferred that the SiO2NFs can acutely restrain the anatase-rutile phase transformation in TiO2. Clearly, The SiO2NFs and TiO2 junction system has much more thermal stability, which is benefit for the photocatalytic activities (because it is known that the anatase has higher photocatalytic activity than the rutile). According to the similar reports, this phenomenon is resulted from the formation of the Ti-O-Si bond between the amorphous SiO2 and anatase TiO2 under calcination treatment [12]. In addition, it indirectly indicates the successful immobilization of TiO2 on SiO2NFs. Fig. 2 shows the TEM images of initial SiO2NFs and TiO2/ SiO2NFs composites. It can be seen that the initial SiO2NFs is relatively uniform in morphology and has a smooth surface. In comparison, the TEM micrographs of the as-prepared TiO2/ SiO2NFs composites show a rough surface, which confirms the TiO2 particles are successfully supported on the surface of the SiO2NFs. The nano-structured TiO2 particles are evenly deposited around the SiO2NFs surface to form a monolayer. In addition, it is worth noting that the observed TiO2 particles on the surface of SiO2NFs are very tiny (less than 10 nm) and without agglomeration, which can make great enhancement for its photocatalytic activity [4]. The result of XRF analysis shows the ratio of each element in TiO2/SiO2NFs is Ti 22.49%, O 49.52%, Si 24.29%, C 2.21% and the others 1.49%. As a result, a theoretical value of Ti/Si weight percentage can be calculated as about 6/6.5, which is near to the actual value calculated by the weight of SiO2NFs before and after immobilizing with TiO2 (about 6/7). Overall, the results further confirm that the presence of TiO2 in the composite. Fig. 3a presents the plots of C/C0 against reaction time under light off and light irradiation (C0 and C are the RhB initial concentration and residual concentration at reaction time, respectively). Clearly, the TiO2/SiO2NFs shows a higher adsorption capacity and degradation rate. Fig. 3b presents the -ln(C/C0) versus light irradiation time. From the data, the photodegradation kinetic parameters are calculated and graphically presented in Fig. 3c for a better comparison. Similarity, TiO2/SiO2NFs photocatalytic degradation efficiency is also better than sol-gel TiO2 and P25. Besides, in Fig. 3a the single SiO2NFs shows the largest adsorption capacity. Thus, it can be inferred that the high adsorption capacity of TiO2/SiO2NFs is derived from the SiO2NFs, which would bring great enhancement to the photocatalytic performance of the composite [7]. Moreover, it is worth noting the sol-gel TiO2 has a very low photocatalytic activity. The reason is that the prepared TiO2 particles are in the form of serious agglomeration [13]. On the contrary, the TiO2 shows a high photocatalytic activity after been well-dispersed on SiO2NFs. Based on the facts, we also think the high photocatalytic activity is partly resulted from the better dispersion of the TiO2 particles, which leads to much larger adsorption and photocatalytic reaction surface area. Furthermore, comparatively, the TiO2/SiO2NFs prepared under 800 °C has the best photocatalytic activity. It may be due to the formation of relatively optimum anatase crystalline phase fraction and crystallinity in the TiO2/SiO2NFs [14].
4. Conclusions In summary, TiO2/SiO2NFs are successful synthesized via a modified sol-gel method combining layer self-assembly procedure for the first time. The as-prepared TiO2/SiO2NFs are anatase structured even under 800 °C. SiO2NFs can effectively improve the
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thermal stability of TiO2 and restrain the anatase-to-rutile phase transition. The microstructure of the TiO2/SiO2NFs shows that the TiO2 nanoparticles are well-dispersed to form a monolayer structure on the surface of the SiO2NFs. The TiO2/SiO2NFs exhibits high photocatalytic degradation rate and efficiency according to the comparative studies on degradation of RhB. The high photocatalytic activity of TiO2/SiO2NFs is not only related to the high adsorption capacity of SiO2NFs, but also resulted from the better dispersion of the TiO2 particles to provide the larger adsorption and photocatalytic reaction surface area. Moreover, the TiO2/ SiO2NFs prepared under 800 °C exhibits best photocatalytic activity due to the relatively optimum anatase crystalline phase fraction and crystallinity. In addition, this work also shows the good ability of one-dimension nano-scale materials used as photocatalyst carrier.
Acknowledgments This work was financially supported by the Teacher Research Foundation of Central South University (2015); the National Natural Science Foundation of China (No. 51104180); the Hunan Provincial Natural Science Foundation of China (No. 13JJ4015).
References [1] L. Elsellami, H. Lachheb, A. Houas, Mater. Sci. Semicond. Process. 36 (2015) 103–114. [2] K. Choi, W. Lee, S. Lee, C. Lim, Mater. Lett. 158 (2015) 36–39. [3] Y. Xia, F. Li, Y. Jiang, M. Xia, B. Xue, Y. Li, Appl. Surf. Sci. 303 (2014) 290–296. [4] Z. Sun, Z. Hu, Y. Yan, S. Zheng, Appl. Surf. Sci. 314 (2014) 251–259. [5] B. Wang, G. Zhang, X. Leng, Z. Sun, S. Zheng, J. Hazard. Mater. 285 (2015) 212–220. [6] D. Li, Q. Zhu, C. Han, Y. Yang, W. Jiang, Z. Zhang, J. Hazard. Mater. 285 (2015) 398–408. [7] X. Fu, H. Yang, G. Lu, Y. Tu, J. Wu, Mater. Sci. Semicond. Process. 39 (2015) 362–370. [8] S. Padmanabhan, S. Pal, E. Haq, A. Licciulli, Appl. Catal. A: Gen. 485 (2014) 157–162. [9] K. Liu, Q. Feng, Y. Yang, G. Zhang, L. Ou, Y. Lu, J. Non-Cryst. Solids 353 (2007) 1534–1539. [10] Y. Yang, Q. Feng, K. Liu, G. Zhang, L. Ou, Y. Lu. Proceedings of the XXIV International Mineral Processing Congress, vol. 3, Beijing, 2008, pp. 3311–3317. [11] S. Artkla, W. Kim, W. Choi, J. Wittayakun, Appl. Catal. B: Eviron. 91 (2015) 157–164. [12] H. Chang, S. Kim, H. Jang, S. Cho, Mater. Lett. 65 (2011) 3272–3274. [13] O. Elbanna, P. Zhang, M. Fujitsuka, T. Majima, Appl. Catal. B: Eviron. 192 (2016) 80–87. [14] K. Choi, W. Lee, S. Lee, C. Lim, Mater. Lett. 158 (2015) 36–39.