- Email: [email protected]
Characterization of TiO2 fibers by combined electrospinning method and hydrothermal reaction
Materials Letters 106 (2013) 41–44
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Characterization of TiO2 fibers by combined electrospinning method and hydrothermal reaction Do-Young Choi a, Cheol-Ho Hwang b, Jae-Wook Lee c, In-Hwa Lee b, Il-Hong Oh b, Ju-Young Park d,n a
Department of Dental Materials, MRC Center, Chosun University, Gwangju 501-759, Republic of Korea Department of Environmental Engineering, Chosun University, Gwangju 501-759, Republic of Korea c Department of Chemical and Biochemical Engineering, Chosun University, Gwangju 501-759, Republic of Korea d Southwestern Research Institute of Green Energy, Mokpo-Si 530-400, Republic of Korea b
art ic l e i nf o
a b s t r a c t
Article history: Received 5 February 2013 Accepted 20 April 2013 Available online 30 April 2013
Crystalline TiO2 fibers were fabricated using a hydrothermal reaction or calcination treatment from titanium isopropoxide/poly(methyl methacrylate) fibers prepared using a sol–gel method and an electrospinning technique. The samples were characterized using thermogravimetric analysis, fieldemission scanning electron microscopy, and X-ray diffraction. The TiO2 fiber prepared by hydrothermal reaction than calcinations treatment could be obtained to anatase phase of the small crystallite size. The crystallites size of the hydrothermal-185, calcination-450, and calcination-500 were 6.28, 12.80, and 15.39 nm, respectively. These photocatalysts were evaluated based on the photodecomposition of methylene blue under ultraviolet light. The photocatalytic degradation rate followed a pseudo-firstorder equation. The kinetic constant (k1) of the hydrothermal-185, calcination-450, and calcination-500 samples were 7.40 10−3, 2.21 10−2, and 1.55 10−2, respectively. The TiO2 fibers prepared using calcination treatment had higher efficiencies than those prepared using a hydrothermal reaction, but the TiO2 fibers prepared without calcination treatment could be used as photocatalysts. & 2013 Elsevier B.V. All rights reserved.
Keywords: Electrospun TiO2 fibers Hydrothermal reaction Calcination treatment Photocatalyst
1. Introduction Electrospinning processes have several attractive advantages such as comparatively low cost, applicability to various materials, and the ability to generate relatively large-scale continuous films. Many inorganic micro/nanofibers have been fabricated using electrospinning techniques [1–4]. Many researchers have fabricated TiO2 nanofibers using sol–gel and electrospinning techniques [5–7]. Compared to conventional TiO2 particles, TiO2 fibers have greater surface-to-volume ratios, and their porous structures provide a higher number of surface active sites for effective photocatalysis [8–10]. However, the phase structure of the fibers is poorly controlled, so amorphous rather than crystalline fibers are obtained in most cases. To solve this problem, we have developed a simple and effective route that combines an electrospinning approach with a hydrothermal method for the fabrication of TiO2 fibers. Hydrothermal methods have many advantages, e.g., highly homogeneous crystalline products can be obtained directly at a relatively low reaction temperature (o150 1C), particle agglomeration is reduced, a narrow particle size distribution is obtained, phase homogeneity is achieved, and the particle morphology can be n
Corresponding author. Tel.: +82 010 3751 8812; fax: +82 61 287 8006. E-mail addresses: [email protected], [email protected] (J.-Y. Park).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.04.079
controlled. Hydrothermal methods also give a uniform composition, pure products, monodispersed particles, and control of the shape and size of the particles [11].
Fig. 1. Thermogravimetric analysis methacrylate) composite fibers.
of
titanium
isopropoxide/poly(methyl
42
D.-Y. Choi et al. / Materials Letters 106 (2013) 41–44
In general, crystalline TiO2 fibers were obtained by calcinations treatment for polymer removal from TIP/polymer fibers. However, to the best of our knowledge, there have been no reports on the preparation of crystalline TiO2 fiber by hydrothermal reaction instead of calcination treatment. In this work, titanium isopropoxide/poly(methyl methacrylate) (TIP/PMMA) fibers were successfully prepared using sol–gel and electrospinning techniques. Crystalline TiO2 fibers were obtained using a hydrothermal reaction or calcinations treatment. The effects of the production method on the crystal structures were examined, and the TiO2 fibers used to photocatalyst for decomposition of methylene blue. 2. Experimental To date, there have been a few reports of the formation of composite fibers by the electrospinning of precursor solutions [3,4].
We demonstrated that TIP (99.999% trace metal basis, Aldrich) can be added directly to a solution of PMMA (Mw ¼120,000, Sigma). To suppress hydrolysis of the sol–gel precursor, acetic acid as well as the PMMA solution in methylene chloride/ethanol (80/20, v/v) must be added. Acetic acid, methylene chloride, and ethanol were purchased from Daejung. TIP (6 mL) was mixed with 12 mL of acetic acid and 12 mL of ethanol. After 60 min, this solution was added to methylene chloride/ethanol (80/20, v/v) 50 g that contained 20 wt% PMMA, followed by magnetic stirring for 24 h. The mixture was immediately loaded into a glass syringe equipped with a 21-G stainlesssteel needle. The needle was connected to a high-voltage supply (DC power supply PS/ER 50R06 DM22, Glassman High Voltage Inc., USA). A voltage of 18 kV was applied between the needle and the collector. The distance between the needle and the target was 15 cm. The flow rate was controlled to 100 μL min-1 using a syringe.
Fig. 2. Field-emission scanning electron microscopy images of (a), (b) titanium isopropoxide/poly(methyl methacrylate) fibers. TiO2 fibers fabricated using an electrospinning method and (c), (d) calcination at 500 1C, and (e), (f) hydrothermal reaction.
D.-Y. Choi et al. / Materials Letters 106 (2013) 41–44
43
TIP/PMMA composite fibers prepared using the electrospinning process was subjected to calcination treatment or a hydrothermal reaction to crystallize the TiO2 grains. The fibers were suspended in 50 mL of ethanol/water solution (50/50, v/v) as the solvent. The hydrothermal reaction was carried out 185 1C for 12 h. Thermal gravimetric analysis (TGA) experiments were conducted on the TIP/Polymer composite fibers using a Metter Toedo DSC 823e thermal analyzer. The morphologies of the TiO2 nanofibers were observed by field-emission scanning electron microscopy (FE-SEM; S-4800, Hitachi, Tokyo, Japan). X-ray diffraction (XRD) patterns were recorded using a Philips (X'Pert PRO MPO) diffractometer (Cu Kα radiation). The photocatalytic degradation of a methylene blue solution was performed using the method by Park et al. [6].
3. Results and discussion Fig. 1 shows the thermogravimetric analysis diagram (TGA) for the electrospun TIP/PMMA composite fibers. The TGA curve of the electrospun TIP/PMMA fibers showed three steps and a total weight loss of ca. 18%. The first step, a weight loss of 7%, from 50 to 250 1C, could be attributed to the desorption of water, and the second significant weight loss of 64%, between 250 and 360 1C, was assigned to the decomposition of PMMA. From 360 to 500 1C, there was a weight loss of 7%. The TIP/PMMA composite fibers as-obtained from the electrospinning technique were smooth, without the presence of beads [Fig. 2(a) and (b)]. Fig. 2(c) and (d) shows SEM images of TiO2 fibers after calcination at 500 1C. The TiO2 fiber diameter decreased as a result of PMMA removal during calcination treatment, and we obtained TiO2 fibers with crystalline grains. The images of TiO2 fibers in Fig. 2(e) and (f) show TIP/PMMA fibers that were subjected to hydrothermal reaction for 12 h at 185 1C. The characteristics of the TiO2 fibers after calcination treatment of the TIP/PMMA fibers prepared by electrospinning were affected by the polymer. The crystalline size of the TiO2 fiber sample that was hydrothermally treated was therefore different from that of the calcined samples. Fig. 3 shows the XRD patterns of TiO2 fibers prepared under different conditions. The TiO2 fibers prepared using the hydrothermal reaction were anatase phase crystals [Fig. 3(a)]. As the calcination temperature increased, the anatase/rutile phase ratio decreased [Fig. 3(b)–(d)]. For a calcination temperature of 450 1C, both the anatase phase and the rutile phase were observed. In the case of a calcination temperature of 600 1C, rutile-phase TiO2 fibers were obtained. For TiO2 fibers prepared using the hydrothermal reaction, only the anatase phase was obtained, and the crystallinity was lower than those of the calcined TiO2 fibers, but we expected that they could be used as photocatalysts. Table 1 lists the anatase/rutile ratios and crystal sizes obtained from the XRD data. TiO2 fibers prepared using the hydrothermal reaction had crystallites size of 6.28 nm. Both hydrothermal-185 and calcination-400 were observed to be anatase phase, but the average crystal size of the calcination-400 sample was larger than that of the hydrothermal-185 sample. The crystallite size of the calcination-400, calcination-450, calcination-500, and calcination600 were 9.58, 12.80, 15.39, and 17.27 nm, respectively. In general, TiO2 particles prepared using the hydrothermal reaction was obtained as only the anatase phase [11]. The PMMA in TIP/PMMA fibers prepared by electrospinning acted as a template, and the polymer (PMMA) influenced the crystal formation and phase transitions [12]. TiO2 grains were obtained by PMMA removal during calcinations treatment. The hydrothermal reaction could provide TiO2 fibers with crystalline grains, as a result of the temperature and
Fig. 3. X-ray diffraction patterns of TiO2 fibers prepared under different conditions: (a) hydrothermal-185, (b) calcination-400, (c) calcination-450, (d) calcination-500, and (e) calcination-600.
pressure, without PMMA removal. The hydrothermal-185 and Table 1 Anatase ratios and single-crystallite sizes for fibers obtained by the hydrothermal reaction and at different calcination treatment temperature. Sample name
Percentage of Size of anatase anatase crystalsb (nm) phasea
Hydrothermal-185 100 Calcination-400 100 Calcination-450 45 Calcination-500 7 Calcination-600 0 a b c
6.28 9.58 12.77 15.32
Size of rutile crystalsc (nm)
Average crystal size
12.83 15.39 17.26
6.28 9.58 12.80 15.39 17.26
Calculated based on the procedure described by Cullity et al. [14]. Calculated using the Scherrer equation [15]. Calculated using the Scherrer equation.
calination-400 samples therefore both contained the anatase phase, but the crystal size of the hydrothermal-185 sample was smaller than that of the calcination-400 sample because the PMMA controlled the grain formation. As the calcination temperature increased, the anatase/rutile ratio decreased, and the crystal size increased. The percentages of anatase phase in the calcination-450 and calcination-500 samples were 45% and 7%, respectively, and TiO2 fibers with crystal sizes of 12.8 and 15.39 nm, respectively, were obtained. Fig. 4 shows the changes in methylene blue concentration in the presence of the hydrothermal-185, calcination-450, and calcination-500 samples on UV irradiation. The concentration of methylene blue decreased significantly in all cases. We calculated the kinetic constant using a pseudo-first-order equation [Eq. (1)] and a simplified version of the Lagergren equation [Eq. (2)]. Lagergren [13] proposed a rate equation for the sorption of a solute from a liquid solution, based on the adsorption capacity. The Lagergren equation is the most widely used rate equation in liquid-phase sorption and this kinetic model
44
D.-Y. Choi et al. / Materials Letters 106 (2013) 41–44
4. Conclusions TIP/PMMA fibers were successfully prepared using sol–gel and electrospinning techniques. Crystalline TiO2 fibers were fabricated by a hydrothermal reaction or calcination from the prepared TIP/ PMMA fibers. The effects on the crystal structure of different preparation methods were examined, and the samples were used as photocatalysts in methylene blue decomposition. TiO2 fibers prepared using a hydrothermal reaction rather than calcination were anatase phase and small crystallite size. The photocatalytic degradation rate followed a pseudo-first-order equation. TiO2 fibers prepared by calcination treatment showed higher photocatalytic efficiencies than those of fibers prepared using a hydrothermal reaction, but the TiO2 fibers prepared without calcination treatment could be used as photocatalysts.
Acknowledgments
Fig. 4. Photocatalytic degradation and kinetic linear simulation curves of methylene blue under UV irradiation.
is expressed as dqt ¼ k1 ðqe −qt Þ dt
ð1Þ
Integrating the above equation for the boundary conditions t¼0 to t¼t and qt ¼qt gives lnðqe −qt Þ ¼ lnðqe −k1 tÞ
This work was supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea Government Ministry of Knowledge Economy (No. 201140100090). This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. R13-2008-010-00000-0).
ð2Þ
The kinetic constant k1 (min−1) can be determined by plotting ln(qe−qt) against t, or ln(qe−qt)/qe versus t. Note that the correlation coefficients (R2) of the pseudo-first-order model for the linear plots of the TiO2 fibers are very close to 1. This result implies that the photocatalytic degradation kinetics can be successfully described by the pseudo-first-order model. The kinetic constant (k1) of the hydrothermal-185, calcination-450, and calcination-500 samples were 7.40 10−3, 2.21 10−2 and 1.55 10−2, respectively. TiO2 fibers prepared by calcination treatment showed higher catalytic efficiencies than those of fibers prepared using the hydrothermal reaction, but the TiO2 fibers prepared without calcination treatment could be used as photocatalysts.
References [1] Li D, Xia Y. Nano Lett 2003;3 555–60. [2] Ramakrishna S, Fujihara K, Teo WE, Lim TC, Zuwei M. An introduction electrospinning and nanofibers. Singapore: World Scientific Publishing Company; 2005. [3] Park JY, Lee IH. J Nanosci Nanotechnol Res 2010;10:3402–5. [4] Ding B, Kim CK, Kim HY, Seo MK, Park SJ. Fiber Polym 2004;5:105–9. [5] Park JY, Yun JJ, Hwang CH, Lee IH. Mater Lett 2010;64:2692–5. [6] Park JY, Lee JH, Choi DY, Hwang CH, Lee JW. Mater Lett 2012;88:156–9. [7] Li H, Zhang W, Huang S, Pan W. Nanoscale 2012;4:801–6. [8] Park JY, Hwang KJ, Lee JW, Lee IH. J Mater Sci 2011;46:7240–6. [9] Malaguttl AR, Mourao HA, Garbin JR. Appl Catal B Environ 2009;90 205–12. [10] Libanori R, Giraldi TR, Longo E, Leite ER, Ribeiro C. J Sol-Gel Sci Technol 2009;49 95–100. [11] Wong CL, Tan YN, Mohamed AR. J Environ Manage 2011;92 1669–80. [12] Jin EM, Lee IH, Hwang CH, Park JY. J Adv Eng Technol 2011;4 487–90. [13] Lagergren S. Handlingar 1989;24:1–39. [14] Cullity BD, Stock SR. Elements of x-ray diffraction. 3rd ed. New Jersey: Prentice Hall; 2011 167–71. [15] Spurr RA, Myers H. Anal Chem 1957;29:760–2.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Characterization of TiO2 fibers by combined electrospinning method and hydrothermal reaction Do-Young Choi a, Cheol-Ho Hwang b, Jae-Wook Lee c, In-Hwa Lee b, Il-Hong Oh b, Ju-Young Park d,n a
Department of Dental Materials, MRC Center, Chosun University, Gwangju 501-759, Republic of Korea Department of Environmental Engineering, Chosun University, Gwangju 501-759, Republic of Korea c Department of Chemical and Biochemical Engineering, Chosun University, Gwangju 501-759, Republic of Korea d Southwestern Research Institute of Green Energy, Mokpo-Si 530-400, Republic of Korea b
art ic l e i nf o
a b s t r a c t
Article history: Received 5 February 2013 Accepted 20 April 2013 Available online 30 April 2013
Crystalline TiO2 fibers were fabricated using a hydrothermal reaction or calcination treatment from titanium isopropoxide/poly(methyl methacrylate) fibers prepared using a sol–gel method and an electrospinning technique. The samples were characterized using thermogravimetric analysis, fieldemission scanning electron microscopy, and X-ray diffraction. The TiO2 fiber prepared by hydrothermal reaction than calcinations treatment could be obtained to anatase phase of the small crystallite size. The crystallites size of the hydrothermal-185, calcination-450, and calcination-500 were 6.28, 12.80, and 15.39 nm, respectively. These photocatalysts were evaluated based on the photodecomposition of methylene blue under ultraviolet light. The photocatalytic degradation rate followed a pseudo-firstorder equation. The kinetic constant (k1) of the hydrothermal-185, calcination-450, and calcination-500 samples were 7.40 10−3, 2.21 10−2, and 1.55 10−2, respectively. The TiO2 fibers prepared using calcination treatment had higher efficiencies than those prepared using a hydrothermal reaction, but the TiO2 fibers prepared without calcination treatment could be used as photocatalysts. & 2013 Elsevier B.V. All rights reserved.
Keywords: Electrospun TiO2 fibers Hydrothermal reaction Calcination treatment Photocatalyst
1. Introduction Electrospinning processes have several attractive advantages such as comparatively low cost, applicability to various materials, and the ability to generate relatively large-scale continuous films. Many inorganic micro/nanofibers have been fabricated using electrospinning techniques [1–4]. Many researchers have fabricated TiO2 nanofibers using sol–gel and electrospinning techniques [5–7]. Compared to conventional TiO2 particles, TiO2 fibers have greater surface-to-volume ratios, and their porous structures provide a higher number of surface active sites for effective photocatalysis [8–10]. However, the phase structure of the fibers is poorly controlled, so amorphous rather than crystalline fibers are obtained in most cases. To solve this problem, we have developed a simple and effective route that combines an electrospinning approach with a hydrothermal method for the fabrication of TiO2 fibers. Hydrothermal methods have many advantages, e.g., highly homogeneous crystalline products can be obtained directly at a relatively low reaction temperature (o150 1C), particle agglomeration is reduced, a narrow particle size distribution is obtained, phase homogeneity is achieved, and the particle morphology can be n
Corresponding author. Tel.: +82 010 3751 8812; fax: +82 61 287 8006. E-mail addresses: [email protected], [email protected] (J.-Y. Park).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.04.079
controlled. Hydrothermal methods also give a uniform composition, pure products, monodispersed particles, and control of the shape and size of the particles [11].
Fig. 1. Thermogravimetric analysis methacrylate) composite fibers.
of
titanium
isopropoxide/poly(methyl
42
D.-Y. Choi et al. / Materials Letters 106 (2013) 41–44
In general, crystalline TiO2 fibers were obtained by calcinations treatment for polymer removal from TIP/polymer fibers. However, to the best of our knowledge, there have been no reports on the preparation of crystalline TiO2 fiber by hydrothermal reaction instead of calcination treatment. In this work, titanium isopropoxide/poly(methyl methacrylate) (TIP/PMMA) fibers were successfully prepared using sol–gel and electrospinning techniques. Crystalline TiO2 fibers were obtained using a hydrothermal reaction or calcinations treatment. The effects of the production method on the crystal structures were examined, and the TiO2 fibers used to photocatalyst for decomposition of methylene blue. 2. Experimental To date, there have been a few reports of the formation of composite fibers by the electrospinning of precursor solutions [3,4].
We demonstrated that TIP (99.999% trace metal basis, Aldrich) can be added directly to a solution of PMMA (Mw ¼120,000, Sigma). To suppress hydrolysis of the sol–gel precursor, acetic acid as well as the PMMA solution in methylene chloride/ethanol (80/20, v/v) must be added. Acetic acid, methylene chloride, and ethanol were purchased from Daejung. TIP (6 mL) was mixed with 12 mL of acetic acid and 12 mL of ethanol. After 60 min, this solution was added to methylene chloride/ethanol (80/20, v/v) 50 g that contained 20 wt% PMMA, followed by magnetic stirring for 24 h. The mixture was immediately loaded into a glass syringe equipped with a 21-G stainlesssteel needle. The needle was connected to a high-voltage supply (DC power supply PS/ER 50R06 DM22, Glassman High Voltage Inc., USA). A voltage of 18 kV was applied between the needle and the collector. The distance between the needle and the target was 15 cm. The flow rate was controlled to 100 μL min-1 using a syringe.
Fig. 2. Field-emission scanning electron microscopy images of (a), (b) titanium isopropoxide/poly(methyl methacrylate) fibers. TiO2 fibers fabricated using an electrospinning method and (c), (d) calcination at 500 1C, and (e), (f) hydrothermal reaction.
D.-Y. Choi et al. / Materials Letters 106 (2013) 41–44
43
TIP/PMMA composite fibers prepared using the electrospinning process was subjected to calcination treatment or a hydrothermal reaction to crystallize the TiO2 grains. The fibers were suspended in 50 mL of ethanol/water solution (50/50, v/v) as the solvent. The hydrothermal reaction was carried out 185 1C for 12 h. Thermal gravimetric analysis (TGA) experiments were conducted on the TIP/Polymer composite fibers using a Metter Toedo DSC 823e thermal analyzer. The morphologies of the TiO2 nanofibers were observed by field-emission scanning electron microscopy (FE-SEM; S-4800, Hitachi, Tokyo, Japan). X-ray diffraction (XRD) patterns were recorded using a Philips (X'Pert PRO MPO) diffractometer (Cu Kα radiation). The photocatalytic degradation of a methylene blue solution was performed using the method by Park et al. [6].
3. Results and discussion Fig. 1 shows the thermogravimetric analysis diagram (TGA) for the electrospun TIP/PMMA composite fibers. The TGA curve of the electrospun TIP/PMMA fibers showed three steps and a total weight loss of ca. 18%. The first step, a weight loss of 7%, from 50 to 250 1C, could be attributed to the desorption of water, and the second significant weight loss of 64%, between 250 and 360 1C, was assigned to the decomposition of PMMA. From 360 to 500 1C, there was a weight loss of 7%. The TIP/PMMA composite fibers as-obtained from the electrospinning technique were smooth, without the presence of beads [Fig. 2(a) and (b)]. Fig. 2(c) and (d) shows SEM images of TiO2 fibers after calcination at 500 1C. The TiO2 fiber diameter decreased as a result of PMMA removal during calcination treatment, and we obtained TiO2 fibers with crystalline grains. The images of TiO2 fibers in Fig. 2(e) and (f) show TIP/PMMA fibers that were subjected to hydrothermal reaction for 12 h at 185 1C. The characteristics of the TiO2 fibers after calcination treatment of the TIP/PMMA fibers prepared by electrospinning were affected by the polymer. The crystalline size of the TiO2 fiber sample that was hydrothermally treated was therefore different from that of the calcined samples. Fig. 3 shows the XRD patterns of TiO2 fibers prepared under different conditions. The TiO2 fibers prepared using the hydrothermal reaction were anatase phase crystals [Fig. 3(a)]. As the calcination temperature increased, the anatase/rutile phase ratio decreased [Fig. 3(b)–(d)]. For a calcination temperature of 450 1C, both the anatase phase and the rutile phase were observed. In the case of a calcination temperature of 600 1C, rutile-phase TiO2 fibers were obtained. For TiO2 fibers prepared using the hydrothermal reaction, only the anatase phase was obtained, and the crystallinity was lower than those of the calcined TiO2 fibers, but we expected that they could be used as photocatalysts. Table 1 lists the anatase/rutile ratios and crystal sizes obtained from the XRD data. TiO2 fibers prepared using the hydrothermal reaction had crystallites size of 6.28 nm. Both hydrothermal-185 and calcination-400 were observed to be anatase phase, but the average crystal size of the calcination-400 sample was larger than that of the hydrothermal-185 sample. The crystallite size of the calcination-400, calcination-450, calcination-500, and calcination600 were 9.58, 12.80, 15.39, and 17.27 nm, respectively. In general, TiO2 particles prepared using the hydrothermal reaction was obtained as only the anatase phase [11]. The PMMA in TIP/PMMA fibers prepared by electrospinning acted as a template, and the polymer (PMMA) influenced the crystal formation and phase transitions [12]. TiO2 grains were obtained by PMMA removal during calcinations treatment. The hydrothermal reaction could provide TiO2 fibers with crystalline grains, as a result of the temperature and
Fig. 3. X-ray diffraction patterns of TiO2 fibers prepared under different conditions: (a) hydrothermal-185, (b) calcination-400, (c) calcination-450, (d) calcination-500, and (e) calcination-600.
pressure, without PMMA removal. The hydrothermal-185 and Table 1 Anatase ratios and single-crystallite sizes for fibers obtained by the hydrothermal reaction and at different calcination treatment temperature. Sample name
Percentage of Size of anatase anatase crystalsb (nm) phasea
Hydrothermal-185 100 Calcination-400 100 Calcination-450 45 Calcination-500 7 Calcination-600 0 a b c
6.28 9.58 12.77 15.32
Size of rutile crystalsc (nm)
Average crystal size
12.83 15.39 17.26
6.28 9.58 12.80 15.39 17.26
Calculated based on the procedure described by Cullity et al. [14]. Calculated using the Scherrer equation [15]. Calculated using the Scherrer equation.
calination-400 samples therefore both contained the anatase phase, but the crystal size of the hydrothermal-185 sample was smaller than that of the calcination-400 sample because the PMMA controlled the grain formation. As the calcination temperature increased, the anatase/rutile ratio decreased, and the crystal size increased. The percentages of anatase phase in the calcination-450 and calcination-500 samples were 45% and 7%, respectively, and TiO2 fibers with crystal sizes of 12.8 and 15.39 nm, respectively, were obtained. Fig. 4 shows the changes in methylene blue concentration in the presence of the hydrothermal-185, calcination-450, and calcination-500 samples on UV irradiation. The concentration of methylene blue decreased significantly in all cases. We calculated the kinetic constant using a pseudo-first-order equation [Eq. (1)] and a simplified version of the Lagergren equation [Eq. (2)]. Lagergren [13] proposed a rate equation for the sorption of a solute from a liquid solution, based on the adsorption capacity. The Lagergren equation is the most widely used rate equation in liquid-phase sorption and this kinetic model
44
D.-Y. Choi et al. / Materials Letters 106 (2013) 41–44
4. Conclusions TIP/PMMA fibers were successfully prepared using sol–gel and electrospinning techniques. Crystalline TiO2 fibers were fabricated by a hydrothermal reaction or calcination from the prepared TIP/ PMMA fibers. The effects on the crystal structure of different preparation methods were examined, and the samples were used as photocatalysts in methylene blue decomposition. TiO2 fibers prepared using a hydrothermal reaction rather than calcination were anatase phase and small crystallite size. The photocatalytic degradation rate followed a pseudo-first-order equation. TiO2 fibers prepared by calcination treatment showed higher photocatalytic efficiencies than those of fibers prepared using a hydrothermal reaction, but the TiO2 fibers prepared without calcination treatment could be used as photocatalysts.
Acknowledgments
Fig. 4. Photocatalytic degradation and kinetic linear simulation curves of methylene blue under UV irradiation.
is expressed as dqt ¼ k1 ðqe −qt Þ dt
ð1Þ
Integrating the above equation for the boundary conditions t¼0 to t¼t and qt ¼qt gives lnðqe −qt Þ ¼ lnðqe −k1 tÞ
This work was supported by the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea Government Ministry of Knowledge Economy (No. 201140100090). This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No. R13-2008-010-00000-0).
ð2Þ
The kinetic constant k1 (min−1) can be determined by plotting ln(qe−qt) against t, or ln(qe−qt)/qe versus t. Note that the correlation coefficients (R2) of the pseudo-first-order model for the linear plots of the TiO2 fibers are very close to 1. This result implies that the photocatalytic degradation kinetics can be successfully described by the pseudo-first-order model. The kinetic constant (k1) of the hydrothermal-185, calcination-450, and calcination-500 samples were 7.40 10−3, 2.21 10−2 and 1.55 10−2, respectively. TiO2 fibers prepared by calcination treatment showed higher catalytic efficiencies than those of fibers prepared using the hydrothermal reaction, but the TiO2 fibers prepared without calcination treatment could be used as photocatalysts.
References [1] Li D, Xia Y. Nano Lett 2003;3 555–60. [2] Ramakrishna S, Fujihara K, Teo WE, Lim TC, Zuwei M. An introduction electrospinning and nanofibers. Singapore: World Scientific Publishing Company; 2005. [3] Park JY, Lee IH. J Nanosci Nanotechnol Res 2010;10:3402–5. [4] Ding B, Kim CK, Kim HY, Seo MK, Park SJ. Fiber Polym 2004;5:105–9. [5] Park JY, Yun JJ, Hwang CH, Lee IH. Mater Lett 2010;64:2692–5. [6] Park JY, Lee JH, Choi DY, Hwang CH, Lee JW. Mater Lett 2012;88:156–9. [7] Li H, Zhang W, Huang S, Pan W. Nanoscale 2012;4:801–6. [8] Park JY, Hwang KJ, Lee JW, Lee IH. J Mater Sci 2011;46:7240–6. [9] Malaguttl AR, Mourao HA, Garbin JR. Appl Catal B Environ 2009;90 205–12. [10] Libanori R, Giraldi TR, Longo E, Leite ER, Ribeiro C. J Sol-Gel Sci Technol 2009;49 95–100. [11] Wong CL, Tan YN, Mohamed AR. J Environ Manage 2011;92 1669–80. [12] Jin EM, Lee IH, Hwang CH, Park JY. J Adv Eng Technol 2011;4 487–90. [13] Lagergren S. Handlingar 1989;24:1–39. [14] Cullity BD, Stock SR. Elements of x-ray diffraction. 3rd ed. New Jersey: Prentice Hall; 2011 167–71. [15] Spurr RA, Myers H. Anal Chem 1957;29:760–2.