Effects of Calcination Temperature on Morphology, Microstructure, and

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Effects of Calcination Temperature on Morphology, Microstructure, and Photocatalytic Performance of TiO Mesocrystals 2

Geun Chul Park, Tae Yang Seo, Chae hee Park, Jun Hyung Lim, and Jinho Joo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01920 • Publication Date (Web): 29 Jun 2017 Downloaded from http://pubs.acs.org on July 1, 2017

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Industrial & Engineering Chemistry Research

Effects of Calcination Temperature on Morphology, Microstructure, and Photocatalytic Performance of TiO2 Mesocrystals Geun Chul Park, Tae Yang Seo, Chae hee Park, Jun hyung Lim,* and Jinho Joo* School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, Korea Keywords: Calcination, Hydrothermal process, Mesocrystal, Photocatalyst, TiO2.

Corresponding Author *E-mail: [email protected]. Tel.: +82-31-290-7358. Fax: +82-31-299-4749. *E-mail: [email protected]. Tel.: +82-31-290-7358.

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ABSTRACT We synthesized TiO2 mesocrystals using a hydrothermal method, and investigated the effect of calcination temperature (100~800oC) on their morphology, crystallinity, and photocatalytic activity. While no appreciable changes in the shape, dimension, and crystal structure of the TiO2 nanoparticles (NPs) were observed as the calcination temperature increased to 300oC, the crystallinity improved with increasing temperature. The mesocrystal form of the NPs began to disappear at 400oC, and the specific surface area significantly decreased with increasing temperature owing to the reduced boundaries between the subunits and surface roughness of the NPs. The photocatalytic activity of the TiO2 NPs improved when the temperature increased to 300oC because of the enhanced crystallinity and elimination of by-products, on the other hand, it degraded at above 400oC due to the decreased surface area. These results suggest that controlling the calcination temperature is an effective way to tailor the morphology, crystallinity, and photocatalytic activity of TiO2 NPs.

1. INTRODUCTION Nano-sized photocatalysts have attracted attention for their effective use in the purification and disinfection of organic pollutants.1, 2 Of the materials being developed for photocatalytic applications, anatase TiO2 (a-TiO2) is the most widely used photocatalyst because of its high efficiency, low cost, chemical inertness, and photostability.3,4 It is well known that the photocatalytic activity of a-TiO2 nanoparticles (NPs) can be affected by the number of active sites on the surface that highly depend on their surface area and other structural characteristics such as crystal phase, crystallinity, crystallographic orientations, and crystal size.5,6 Considerable efforts have been made to enhance the photocatalytic activity of TiO2 NPs using morphology

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tuning, doping process, and deposition of noble metals or p-type semiconductors on TiO2 surface.7-9 In morphology tuning, a large specific surface area is important in order to provide more opportunities for the surface photochemical reaction. Although hierarchical and complex structures can induce more photocatalytic active sites due to their highly porous structure with its large specific surface area, they exhibit relatively poor crystallinity and large defects compared to mono-morphological structures, resulting in the rapid recombination of the photo-induced electron-hole pairs.10,11 It is thus desirable to find methods to increase the crystallinity and surface area simultaneously for practical photocatalytic applications. Recently, mesocrystals, a highly ordered superstructure of subunits with a mesoscopic size, have been of particular interest because they have an almost single crystalline nature and large specific surface area, which are major factors for superior photocatalytic performance.12 In the previous study, we synthesized a-TiO2 mesocrystals using the hydrothermal technique, and applied them to a photocatalyst.13 It was found that the presence of by-products, such as butyl acetate or remnant Ti complexes adsorbed on the subunits, caused a decrease in the number of actual photocatalytic active sites. The calcination process is a conventional and efficient method not only of removing the remnant organic materials, but also of improving crystallinity. Obtaining highly active a-TiO2 mesocrystals through the calcination process remains a major challenge because high calcination temperature significantly decreases the surface area of the mesocrystals by reducing porosity and can change the crystalline phase into rutile that has a lower photocatalytic activity than the a-TiO2.14 Hence, it is necessary to optimize the calcination temperature in order to achieve high crystallinity and large surface area without phase transition. Many studies have focused on controlling the calcination conditions (temperature, time, atmosphere, etc.) to enhance the photocatalytic property of conventional TiO2 particles for

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various applications in the environmental and energy fields;14-16 however, variations in the morphology, crystallinity, and photocatalytic activity of a-TiO2 mesocrystals with calcination temperatures have rarely been reported. Herein, hydrothermally grown a-TiO2 mesocrystals were calcined at different temperatures (0~800oC), and applied to a photocatalyst. The effects of calcination temperature on the morphology, microstructure, chemical bonding structure, and photocatalytic property of the TiO2 NPs were evaluated. This study is expected to provide valuable information on the design, fabrication, and optimization of TiO2-based photocatalysts.

2. EXPERIMENTAL METHODS Titanium butoxide (Ti(OC4H9)4, 97%, Sigma-Aldrich) was used as a precursor for TiO2 mesocrystals. 0.4 M titanium butoxide was added drop wise to 30 mL acetic-acid (CH3CO2H, ≥99.7%, Sigma-Aldrich) with 0.5 mL deionized (DI) water while stirring at room temperature for 20 min. The solution was transferred to a Teflon-lined autoclave, and hydrothermally treated at 180oC for 12 h. After reaction, the precipitates were washed alternately with DI water and ethanol (C2H6O, 99.9%, Sigma-Aldrich) several times and dried at 80oC for 12 h in a vacuum oven. The calcination process was performed at temperatures of 100, 200, 300, 400, 600, and 800oC for 1 h in air. The crystallographic information was obtained by X-ray diffraction (XRD, Bruker-AXS, D8 Discover). The morphology and size distribution of the TiO2 NPs were observed using field emission scanning electron microscopy (FESEM, JEOL, JSM7000F) and high resolution transmission electron microscopy (HRTEM, JEOL, JEM ARM 200F). The average size of the NPs was determined by measuring their major axes from 30~40 samples using SEM. The

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chemical bonding structure was analyzed through X-ray photoelectron spectroscopy (XPS, VG Microtech, ECSA2000) using Al Kα (1468 eV). All the XPS spectra were referenced to a C 1s peak at 284.6 eV. The specific surface area was measured using the Brunauer-Emmett-Teller (BET) method with nitrogen adsorption (Micromeritics Gemeni 2360) and the average pore size was calculated through the Barrett–Joyner–Halenda (BJH) model. Photocatalytic activity was evaluated by the degradation of methylene blue (MB) as a function of time. In a typical measurement, 0.01 g of the samples was dispersed in 25 mg H2O with ultrasonication for 30 min. Then, 0.1 mL of the solution was mixed with 10 ppm MB solution (3.9 mL) in a cuvette and exposed to UV at 254 nm for 1 h using a 4 W UV-filtered lamp (Vilber, VL-4.LC). The degradation of MB was analyzed using UV-visible spectrophotometry (PG Instruments, T60 UV).

3. RESULTS AND DISCUSSION The phase structure and crystal quality of the as-grown and calcined TiO2 NPs were characterized using powder XRD as shown in Figure 1. The as-grown (non-calcined) TiO2 NPs corresponded to the anatase phase without any secondary phases such as rutile or brookite. No significant change was observed in the crystal structure of the NPs as the calcination temperature increased to 600oC. All the diffraction peaks for the 800oC sample exhibited not only anatase but also rutile phase, which suggests that the phase transition started above 600°C in our experimental condition. According to Lee et al., the phase transition of commercial p-25 and flame-synthesized TiO2 NPs occurred in the temperature ranges of 600°C-800°C and 1000°C1200oC, respectively.17 A slight difference in the transition temperature between the samples may be ascribed to the different particle sizes, impurities, and synthesis methods.18,19 As shown

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in Figure 1b, the full width at half maximum (FWHM) of the (101) main peak significantly reduced with increasing the calcination temperature. This implies that the crystallinity of the TiO2 NPs improved gradually with increasing calcination temperature. Figure 2 shows the FE-SEM images for the morphologies of the TiO2 NPs and their lateral dimensions (average length of major axis) with different calcination temperatures. The as-grown TiO2 NPs had a porous elliptical shape with the dimension of ~100 nm long (Figure 2a). No significant changes were observed in the shape and dimension (Figure 2h) of the NPs as the calcination temperature increased to 600oC. However, it is noted that the surface roughness of the NPs gradually decreased with increasing temperature probably due to the increased surface diffusion during the calcination process. As the calcination temperature was further increased to 800oC (Figure 2g), the morphology of the elliptical NPs dramatically changed to an irregular large NPs, which is probably because some NPs were sintered and bonded with each other. TEM analysis provided further insight into the detailed morphology and microstructure of the as-grown and calcined TiO2 NPS. Figures 3a-3g and their insets show the HR-TEM images and selected area electron diffraction (SAED) patterns of the samples. The sharp and bright dots in the SAED patterns demonstrated that all the samples had a single crystalline nature regardless of calcination temperature. The as-grown and 100°C-300oC calcined a-TiO2 NPs (Figures 3a-3d) exhibited a typical mesocrystal structure, consisting of self-assembled subunits arraying in the [001] direction. The subunit in the NPs had a truncated bipyramid shape with highly exposed {101} facets (as shown by the left inset of Figure 3a) and its size of the as-grown sample (17.3 nm) slightly increased with increasing temperature to 300oC (23.8 nm). It appears that at 400oC, the boundaries between the subunits became blurred and the mesocrystal form of the NP began to disappear. With increasing temperature from 400oC to 800oC, the crystallite size increased and

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the resultant number of subunits decreased, which may be ascribed to a coalescence of the oriented subunits in the NPs.12 At 800oC, the NP became a porous single-like crystal (the crystallite size was about 96.2 nm) rather than a mesocrystal form, and the morphology of the elliptical NP changed into an irregular shape which concurred with the FE-SEM observation. The crystallite (subunit) sizes, which were calculated from the Scherrer equation for the (101) main peak in the XRD patterns (Figure 1b), were 18.9, 19.8, 20.9, 22.6, 24.7, 31.7, and 49.5 nm for the as-grown, 100oC, 200oC, 300oC, 400oC, 600oC, and 800oC samples, respectively. The observed crystallite sizes in the TEM images showed similar trend to the calculated values from the XRD patterns, although Scherrer equation has a limited accuracy. Figure 3h shows the specific surface area of the samples measured using the BET method. The specific surface area of the as-grown, 100oC, 200oC, and 300oC samples were similar (86.8~89.8 m2/g). As the calcination temperature increased from 400oC to 800oC, the specific surface area of the samples significantly decreased from 53.8 to 2.5 m2/g. The pore size of the selected samples of the 200oC and 600oC were also calculated to be 3.4 and 25.2 nm, respectively, implying that the pores enlarged with increasing calcination temperature. This result is acceptable because the pore size increases while the porosity decreases in general as the crystallite grows. Therefore, the decreased surface area may be ascribed to the decreased boundaries between the subunits as a result of the enlarged subunit and pore sizes and the reduced surface roughness due to increased surface diffusion at high temperature. Considering the XRD and BET results, we expected that the photocatalytic performance would enhance with increasing calcination temperature to 300oC because the crystallinity of the NPs improved without a reduction in the specific surface area. The compositions and chemical bond configurations of the TiO2 NPs were evaluated by XPS. Figure 4a illustrates the wide scan XPS spectra of the samples, showing that all the Ti 2p3/2 and

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O 1s peaks were located at ~458.5 eV and ~529.5 eV, respectively, which suggests that all the samples were of TiO2 phase. The C 1s peak is related to the presence of C-based by-products such as butyl acetate or remnant Ti complexes. Figure 4b depicts the narrow scan O 1s peaks of the samples. The asymmetric peaks were deconvoluted into three types of oxygen levels. The low binding energy (OI) derives from the bonding between the O and Ti ions.20 The medium binding energy (OII) is associated with the hydroxyl group.21,22 The OII gradually decreased with increasing the temperature, which was probably due to the following chemical reaction taking place on the surface of TiO2 during calcination process:23-25

Ti-OH + HO-Ti → Ti-O-Ti + H2O

(1)

The high binding energy (OIII) corresponds to the absorbed H2O molecules and by-products related bonds such as C=O, O-C-O, O=C-O. The intensities of both the C 1s peak (Figure 4a) and OIII in the O 1s peak (Figure 4b) reduced with increasing calcination temperature, which was attributed to the elimination of residual by-products. Particularly, the significant decrease in the 200oC sample suggests that the butyl acetate adsorbed on the TiO2 surface was almost evaporated at a higher calcination temperature than its boiling point (126oC).26 The photocatalytic performance of the TiO2 NPs was evaluated from the degradation ratio of the MB dye (C/Co) under UV irradiation as shown in Figure 5. The photocatalytic decomposition process of MB dye can be proposed as follows:

TiO2 + hν (UV) → TiO2 (ecb- + hvb+)

(2)

ecb- + O2 → •O2-

(3)

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hvb+ + OH- → •OH

(4)

hvb+ + H2O → H+ + •OH

(5)

O2- or H+ + organic dye → degradation products

(6)

•

The electrons (e−) in the valence band of TiO2 are excited and moved into conduction band, leaving behind holes (h+) in the valence band when the TiO2 NPs are irradiated by UV light with a photon energy higher than or equal to the band gap. The photo-induced electrons and holes can be readily trapped by electronic acceptors (O2) and donors (OH-) at the catalyst surface to yield superoxide radical anions (•O2-) and hydroxyl radicals (•OH), respectively.27 Both radicals serve as the major active species during the photocatalytic reaction. The degradation efficiency increased initially with increasing calcination temperature and reached the highest value at 300oC, followed by a decrease at a higher temperature (inset of Figure 5). The degradation efficiencies of the as-grown, 100, 200, and 300oC samples were about 61%, 80%, 84%, and 94% at an irradiation time of 60 min. This result is also coincident with the color change of the MB solution from blue to colorless as the irradiation time gradually increased (images are not shown here). The enhancement of the photocatalytic activity of the TiO2 NPs was attributed to the increased crystallinity and decreased by-products, resulting in the reduction of non-radiative recombination centers (electron/hole traps) and the increase of actual photocatalytic active sites, respectively. It is noted that the 300oC sample exhibited higher photocatalytic activity than the commercial p-25 TiO2. However, as the calcination temperature was further increased from 400oC to 800oC, the degradation efficiency of the sample significantly decreased because of the decreased surface area, despite the increased crystallinity and slightly decreased by-product. The significant degradation of photocatalytic efficiency at

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800oC was related to the morphology change of the TiO2 NPs from a mesocrystal to a porous single-like crystal which provided less active sites. These results imply that the photocatalytic activity was more affected by the surface area than by the other factors. Therefore, it is concluded that the synergetic effects of large surface area and high crystallinity were mainly responsible for the improvement in the photocatalytic properties of the TiO2 NPs.

4. CONCLUSIONS In this work, we synthesized a-TiO2 mesocrystals using a hydrothermal process, and the samples were calcined at diverse temperatures (100~800oC). The as-grown a-TiO2 had a porous elliptical shape, consisting of truncated bipyramidal subunits aligned to the [001] direction. With increasing calcination temperature to 300oC, no appreciable change in the morphology was observed, and the photocatalytic activity of the TiO2 NPs improved due to the increased crystallinity and reduced by-products. As the calcination temperature was increased from 400oC to 800oC, the NPs did not maintain a mesocrystal form, and the photocatalytic activity significantly degraded because of the decrease in specific surface area. The photocatalytic performance evaluation showed that the most effective calcination temperature was 300°C due to the synergetic effects of high crystallinity and large specific surface area. These results could facilitate understanding of the effect of calcination temperature on the morphology and microstructure of a-TiO2 mesocrystals and their application in the treatment of organic pollutants.

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Figure 1. (a) XRD patterns and (b) FWHM of the TiO2 NPs with respect to calcination temperatures.

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Figure 2. FE-SEM images of (a) as-grown and calcined TiO2 NPs at (b) 100oC, (c) 200oC, (d) 300oC, (e) 400oC, (f) 600oC, and (g) 800oC. (h) Variation of particle dimensions with calcination temperature (dimension of 800°C sample was not measured due to irregular shape of the NPs).

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Figure 3. HR-TEM images of the TiO2 NPs as a function of calcination temperatures: (a) asgrown, (b) 100oC, (c) 200oC, (d) 300oC, (e) 400oC, (f) 600oC, (g) 800oC (left insets in Figure 3(a) and right top insets in Figures. 3(a)-3(g) show high-resolution images and SAED patterns, respectively), and (h) variation of specific surface area with calcination temperature. The red lines in the left inset of Figure 3(a) is guide for the eye.

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Figure 4. XPS spectra of the (a) wide scan and (b) deconvoluted O 1s of the TiO2 NPs at various calcination temperatures.

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Figure 5. Variation of photodegradation of the TiO2 NPs with different calcination temperatures. Co and C are the initial and residual concentrations of MB, respectively. The inset shows the C/Co of our samples and commercial p-25 at irradiation time of 60 min.

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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Tel.: +82-31-290-7358. Fax: +82-31-299-4749. *E-mail: [email protected]. Tel.: +82-31-290-7358.

ACKNOWLEDGMENT This research was supported by Basic Science Research Program through the National Research Foundation

of

Korea(NRF)

funded

by

the

Ministry

of

Education

(NRF-

2016R1A6A3A11934600).

REFERENCES (1) Li, Y.; Bastakoti, B. P.; Imura, M.; Hwang, S. M.; Sun, Z.; Kim, J. H.; Dou, S. X.; Yamauchi, Y. Synthesis of Mesoporous TiO2/SiO2 Hybrid Films as an Efficient Photocatalyst by Polymeric Micelle Assembly. Chem. Eur. J. 2014, 20, 6027-6032. (2) Oveisi, H.; Rahighi, S.; Jiang, X.; Nemoto, Y.; Beitollahi, A.; Wakatsuki, S.; Yamauchi, Y. Unusual Antibacterial Property of Mesoporous Titania Films: Drastic Improvement by Controlling Surface Area and Crystallinity. Chem. Asian J. 2010, 5, 1978-1983. (3) Zhang, J.; Zhou, P.; Liu, J.; Yu, J. New understanding of the difference of photocatalytic activity among anatase, rutile and brookite TiO2. Phys. Chem. Chem. Phys. 2014, 16, 2038220386. (4) Yu, J. C.; Yu, J.; Ho, W.; Jiang, Z.; Zhang, L. Effects of F-doping on the photocatalytic activity and microstructures of nanocrystalline TiO2 powders. Chem. Mater. 2002, 14, 38083816.

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Page 17 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Wu, N.; Wang, J.; Tafen de, N.; Wang, H.; Zheng, J. G.; Lewis, J. P.; Liu, X.; Leonard, S. S.; Manivannan, A. Shape-enhanced photocatalytic activity of single-crystalline anatase TiO2 (101) nanobelts. J. Am. Chem. Soc. 2010, 132, 6679-6685. (6) Yang, H. G.; Sun, C. H.; Qiao, S. Z.; Zou, J.; Liu, G.; Smith, S. C.; Cheng, H. M.; Lu, G. Q. Anatase TiO2 single crystals with a large percentage of reactive facets. Nature 2008, 453, 638641. (7) Chen, X.; Mao, S. S. Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications. Chem. Rev. 2007, 107, 2891-2959. (8) Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y. Visible-light photocatalysis in nitrogen-doped titanium oxides. Science 2001, 293, 269-271. (9) Subramanian, V.; Wolf, E.; Kamat, P. Catalysis with TiO2/gold nanocomposites. Effect of metal particle size on the Fermi level equilibration. J. Am. Chem. Soc. 2004, 126, 4943-4950. (10) Yu, J.; Zhang, L.; Cheng, B.; Su, Y. Hydrothermal preparation and photocatalytic activity of hierarchically sponge-like macro-/mesoporous titania. J. Phys. Chem. C 2007, 111, 1058210589. (11) Parlett, C. M.; Wilson, K.; Lee, A. F. Hierarchical porous materials: catalytic applications. Chem. Soc. Rev. 2013, 42, 3876-3893. (12) Ye, J.; Liu, W.; Cai, J.; Chen, S.; Zhao, X.; Zhou, H.; Qi, L. Nanoporous anatase TiO2 mesocrystals: additive-free synthesis, remarkable crystalline-phase stability, and improved lithium insertion behavior. J. Am. Chem. Soc. 2010, 133, 933-940. (13) Seo, T. Y.; Lee, S. M.; Choi, J. H.; Lee, C. M.; Park, G. C.; Jeong, S. H.; Jung, S.; Lim, J. H.; Joo, J. Effects of Hydrothermal Temperature on Crystallinity, Microstructure, and

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Photocatalytic Activity of Anatase TiO2 Mesocrystals. J. Nanosci. Nanotechnol. 2016, 16, 11153-11157. (14) Yu, J.; Yu, H.; Cheng, B.; Zhao, X.; Yu, J.; Ho, W. The effect of calcination temperature on the surface microstructure and photocatalytic activity of TiO2 thin films prepared by liquid phase deposition. J. Phys. Chem. B 2003, 107, 13871-13879. (15) Zhang, Q.; Gao, L.; Guo, J. Effects of calcination on the photocatalytic properties of nanosized TiO2 powders prepared by TiCl4 hydrolysis. Appl. Catal. B: Environ. 2000, 26, 207215. (16) Ohno, T.; Mitsui, T.; Matsumura, M. Photocatalytic activity of S-doped TiO2 photocatalyst under visible light. Chem. Lett. 2003, 32, 364-365. (17) Lee, G. W.; Choi, S. M. Thermal stability of heat-treated flame-synthesized anatase TiO2 nanoparticles. J. Mater. Sci. 2008, 43, 715-720. (18) Pal, M.; Garcia Serrano, J.; Santiago, P.; Pal, U. Size-controlled synthesis of spherical TiO2 nanoparticles: morphology, crystallization, and phase transition. J. Phys. Chem. C 2007, 111, 96-102. (19) Li, J.; Wang, X.; Watanabe, K.; Ishigaki, T. Phase structure and luminescence properties of Eu3 -doped TiO2 nanocrystals synthesized by Ar/O2 radio frequency thermal plasma oxidation of liquid precursor mists. J. Phys. Chem. B 2006, 110, 1121-1127. (20) Chastain, J.; King, R. C.; Moulder, J. Handbook of X-ray photoelectron spectroscopy: a reference book of standard spectra for identification and interpretation of XPS data; Physical Electronics Eden Prairie, MN, 1995. (21) Beamson, G.; Briggs, D. High resolution XPS of organic polymers: the Scienta ESCA300 database. Wiley, 1992.

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(22) Kuznetsov, M. V.; Zhuravlev, J. F.; Gubanov, V. A. XPS analysis of adsorption of oxygen molecules on the surface of Ti and TiNx films in vacuum. J. Electron Spectrosc. Relat. Phenom. 1992, 58, 169-176. (23) Kolen’ko, Y. V.; Churagulov, B. R.; Kunst, M.; Mazerolles, L.; Colbeau-Justin, C. Photocatalytic properties of titania powders prepared by hydrothermal method. Appl. Catal. B: Environ. 2004, 54, 51-58. (24) Yu, J.; Zhao, X.; Zhao, Q. Effect of surface structure on photocatalytic activity of TiO2 thin films prepared by sol-gel method. Thin Solid Films 2000, 379, 7-14. (25) Lin, J.; Lin, Y.; Liu, P.; Meziani, M. J.; Allard, L. F.; Sun, Y. Hot-fluid annealing for crystalline titanium dioxide nanoparticles in stable suspension. J. Am. Chem. Soc. 2002, 124, 11514-11518. (26) Yang, C.; Qian, Y.; Zhang, L.; Feng, J. Solvent extraction process development and on-site trial-plant for phenol removal from industrial coal-gasification wastewater. Chem. Eng. J. 2006, 117, 179-185. (27) Xiang, Q.; Yu, J.; Wong, P. K. Quantitative characterization of hydroxyl radicals produced by various photocatalysts. J. Colloid. Interface. Sci. 2011, 357, 163-167.

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Effects of Calcination Temperature on Morphology, Microstructure, and

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