ARTICLE pubs.acs.org/IECR
Template-Free Synthesis and Photocatalytic Application of Rutile TiO2 Hierarchical Nanostructures M. Ge,† J. W. Li,† L. Liu,*,† and Z. Zhou*,‡ †
Tianjin Key Laboratory of Environmental Remediation and Pollution Control, ‡Institute of New Energy Material Chemistry, and Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin 300071, P.R. China
bS Supporting Information ABSTRACT: A simple template-free hydrothermal method was employed to synthesize flower-shaped single-crystal rutile TiO2 hierarchical nanostructures without calcination process. Scanning electron microscope and transmission electron microscope images show that rutile TiO2 nanostructures with diameters of 11.5 μm are composed of nanorods with a wimble shape. The band gap of the as-prepared rutile TiO2 is about 3.02 eV by ultravioletvisible absorption spectrum. The photocatalytic performance of the as-obtained samples as catalysts for Rhodamine B (RhB) degradation under simulated solar light was greatly enhanced with the assistance of a small amount of H2O2. In the H2O2-containing system, the as-prepared rutile TiO2 photocatalyst was more efficient in the photodegradation of RhB than commercial P25. The stability and recycle of the rutile TiO2/H2O2 system were also investigated.
1. INTRODUCTION Dyes are severe organic pollutants in aquatic environments due to their huge production from the textile industry, their potential to form toxic aromatic amines, and their resistance to biodegradation.1,2 About 15% of the synthetic textile dyes are lost in waste streams during manufacturing or processing operations,2 which have potential harm to human beings. Actually, it is usually difficult to remove the dyes with biological and physical treatments. In the past decades, heterogeneous photocatalysis, as an advanced oxidation process (AOP), has been one of the promising and efficient alternatives to purify wastewater containing recalcitrant dye pollutants.35 It is well-known that TiO2 has been widely employed for photocatalytic applications because of its cheapness, nontoxicity, and stability.6,7 Generally, TiO2 exists in four phases: brookite, TiO2(B), anatase, and rutile. In contrast with the other three phases, rutile TiO2 is the most stable phase even in strongly acidic or basic conditions, and has been extensively used in lithium ion batteries8,9 and dye-sensitized solar cells.10 Yet, compared with anatase TiO2, rutile TiO2 receives little attention in photocatalytic degradation. Recently, it has been reported that rutile TiO2 with different morphologies showed efficient photocatalytic activity in photo-oxidation of organic pollutants under ultraviolet light or artificial solar light irradiation.1117 Hydrogen peroxide (H2O2) is an environmentally benign, inexpensive, and highly water-soluble oxidant; therefore, it is extensively employed in the AOPs, including O3/H2O2,18 UV/ H2O2,19 Fenton process,20 and photo-Fenton process.21 Recently, some studies disclosed the degradation of organic contaminations with enhanced activity using UV/H2O2/TiO2 or vis/H2O2/TiO2 photocatalysis.2225 Hence, one can deduce that UVvis/H2O2/TiO2 system will also have a high photocatalytic activity for oxidation of organic pollutants. Synthesis of hierarchical nanostructured semiconductor materials has attracted great research attention due to the excellent r 2011 American Chemical Society
physical and chemical properties and potential applications in various fields.2629 Herein, flower-shaped rutile TiO2 hierarchical nanostructures were synthesized by a facile one-step template-free hydrothermal method, by employing low-cost TiCl3, NaCl, and NaOH as the starting materials. Under simulated solar light irradiation, the photocatalytic performance of the asobtained rutile TiO2 nanostructures was investigated for degradation of Rhodamine B (RhB), which is a kind of organic dye that is chemically stable and difficult to degrade. The results revealed that the photocatalytic efficiency could be highly enhanced in the presence of H2O2. Also, the photo-oxidation of RhB investigated at different H2O2 amounts and the photostability of the rutile TiO2/H2O2 system were discussed.
2. EXPERIMENTAL SECTION 2.1. Synthesis. All reagents were purchased from Tianjin Chemical Company and used as received. In a typical synthesis, 2.00 g of sodium chloride and an appropriate amount of sodium hydroxide were dissolved in distilled water (35 mL), and then 5 mL of titanium trichloride aqueous solution (1520 wt %) was added under stirring. The solution was then transferred to a 50mL Teflon-lined autoclave, which was maintained at 150 °C for 24 h, and then cooled to room temperature. The white precipitate was filtered off, washed with distilled water and absolute ethanol several times, and then dried at 100 °C in air for further use. The yield of rutile TiO2 nanostructures was over 95% (approximately 0.65 g). For comparison, P25 (nanoscale TiO2 powder, ∼80% anatase, ∼20% rutile; surface area, 50 m2 g1) was purchased from Degussa AG, Germany. Received: November 15, 2010 Accepted: April 29, 2011 Revised: April 27, 2011 Published: April 29, 2011 6681
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Figure 1. XRD pattern of the as-synthesized TiO2 sample.
Figure 3. TEM images of the as-synthesized TiO2 nanostructures: (a) low magnification TEM image, (b) high magnification TEM image, and (c) HRTEM image of a building unit.
3. RESULTS AND DISCUSSION
Figure 2. SEM images of the as-obtained flower shaped TiO2 nanostructures: (a) low magnification and (b) high magnification.
2.2. Characterization. The phase of the as-obtained product was characterized by X-ray diffraction (XRD) under a Rigaku D/ Max-2500 X-ray diffractometer employing Cu KR radiation, λ = 1.54056 Å. The size and morphology of the as-prepared product were characterized by using a field emission scanning electron microscope (FESEM, JEOL JSM-6700 at 10 kV) and a highresolution transmission electron microscope (HRTEM, FEI Tecnai G2 F20) operated at an acceleration voltage of 200 kV. UVvis diffuse reflectance spectra (DRS) were recorded in the range of 200800 nm with a UVvis spectrophotometer by using BaSO4 as the reference (Shimadzu, UV-3600). The N2 adsorptiondesorption measurement was performed on a Quantachrome NOVA2000 automatic analyzer at 77 K. The specific surface area was calculated by the BET method. 2.3. Photocatalytic Tests. The photocatalytic performance of the as-prepared rutile TiO2 was evaluated by the photodegradation of RhB at ambient temperature. The photocatalytic reaction was conducted in a cylindrical quartz reactor (250 mL) with water circulation facility. Rutile TiO2 nanostructures (0.100 g) and H2O2 (30 wt % in solution) were added to an aqueous RhB solution (1.0 105 M, 200 mL), which was stored in the dark for 30 min to ensure an adsorptiondesorption equilibrium. A 350 W Xe lamp was used as the simulated solar light source. Four mL of the sample solution was taken at given time intervals and separated through centrifugation (2500 rpm, 10 min). The concentration of RhB was measured by UVvis spectra (UV2550, Shimadzu). Total organic carbon (TOC) was measured with a Shimadzu TOC-V CPH analyzer.
3.1. Structure and Morphology. The typical XRD pattern in Figure 1 reveals the phase and purity of the as-prepared TiO2 nanostructures. All the observed peaks can be indexed to a pure tetragonal rutile phase (JCPDS 21-1276). No characteristic peak was observed for other types, indicating the high purity and crystallinity of the product formed via the hydrothemal process. Figure 2 shows typical SEM images of the TiO2 nanostructures. The images at different magnifications reveal that the as-obtained rutile TiO2 sample is composed of flowershaped nanostructures with diameters in the range of 1.01.5 μm, and the microparticles can lead to a good precipitation performance compared with nanoparticles. TEM images clearly show that flower-shaped nanostructures are assembled by nanorods with a wimble shape (Figure 3a and 3b). HRTEM image indicates that the building units of the TiO2 nanostructures are single crystalline in nature (Figure 3c). The fringe spacing parallel to the c-axis of the nanorod building unit is estimated to be 0.32 nm, consistent with the d value of (110) lattice spacing, and the nanorods grow in the [001] direction, revealing that the growth in the [001] direction is faster than that in the [110] direction (Figure 3c), which is ascribed to the inherent growth pattern of rutile TiO2. 30 The same preferable growth along the [001] direction of rutile TiO2 was also reported previously.17,31,32 3.2. Optical Absorption Properties. For a semiconductor photocatalyst, its optical absorption property is relevant to its electronic structure, and the electronic structure feature is recognized as an important role of its photocatalytic performance. Figure 4 shows the UVvis diffuse reflectance spectra of the as-prepared rutile TiO2 nanostructures. The TiO2 sample has a strong light response in the ultraviolet region with an absorption edge of 409 nm. The band gap of TiO2 can be estimated 6682
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Figure 4. UVvis diffuse reflectance spectra of the rutile TiO2 nanostructures.
Figure 5. Nitrogen adsorptiondesorption isotherm and BJH pore size distribution (inset).
from the equation as below:33
Figure 7 demonstrates the evolution of RhB absorption spectra and the change of TOC at different irradiation times, from which we can see that the concentration of RhB decreased rapidly, and the total decomposition of RhB was achieved at about 80 min in the case of flower-shaped rutile TiO2 nanostructures and H2O2 (Figure 7a). In addition, the evolution of the colors of the RhB solutions before and after the photocatalytic reaction further indicated the high photocatalytic performance of the rutile TiO2/H2O2 system (inset of Figure 7a). The TOC value decreases by 37.9% after 120-min exposure to the simulated solar light, indicating that the mineralization of RhB occurred (Figure 7b). Furthermore, methyl orange (an anionic dye) was also chosen to evaluate the photocatalytic activity of the rutile TiO2/H2O2 system. Note that the concentration of methyl orange was determined according to the characteristic peak at ~464 nm. Nearly 100% of methyl orange was degraded after 80 min using simulated solar light in the rutile TiO2/H2O2 system (Figure S1, Supporting Information). The influence of the initial RhB concentration on the photodegradation rate was also investigated, and the results are shown in Figure 8. The LangmuirHinshelwood model is well established for photocatalysis when the concentration of pollutants is in the millimolar range.35 The relevant equations are listed as below:
1=2
REphoton ¼ AðEphoton Eg Þ
ð1Þ
where R, Ephoton, A, and Eg are absorption coefficient, discrete photo energy, proportionality constant, and the band gap, respectively. The band gap of TiO2 can be obtained from the plots of (RE)2 versus (E), as shown in the inset of Figure 4. The value of the band gap for the rutile TiO2 nanostructures was estimated to be 3.02 eV. 3.3. Nitrogen Sorption Analysis. The nitrogen adsorption desorption isotherm and BarretJoynerHalenda (BJH) pore size distribution of the as-synthesized rutile TiO2 nanostructures are shown in Figure 5. The isotherm is identified as type II, which is characteristic isotherm of macroporous materials. These pores presumably arise from the space among the nanorods within the flower-like TiO2 nanostructures.16 The BET surface area of the product is 60.2 m2 g1. 3.4. Photocatalytic Activity of Flower-Like TiO2 Nanostructures. Rhodamine B, a cationic dye, was chosen as the model pollutant to evaluate the photodegradation behaviors of rutile TiO2 hierarchical nanostructures under simulated solar light irradiation in the presence of H2O2. The photolysis of H2O2 is the cleavage of the molecule into hydroxyl radicals, which can attack the organic compounds.34 As is illustrated in Figure 6a, the decay of RhB was enhanced when the amount of H2O2 increased, which indicated that the photolysis of H2O2 occurred; however, the efficiency was relatively low even though 24.75 mM H2O2 was introduced. Without H2O2, 63% of RhB was degraded in the presence of rutile TiO2 nanostructures at 80 min (Figure 6b). The efficiency of the as-prepared rutile TiO2 nanostructures for RhB degradation using the simulated solar light was as high as other rutile TiO2 nanostructures in previous reports.16,17 Notably, the degradation rate of RhB was increased in the rutile TiO2/H2O2 system. Further increase of H2O2 to 4.9519.80 mM resulted in a progressive increase of the photodegradation rate; however, 24.75 mM H2O2 had the opposite effect and led to a decrease of degradation rate (Figure 6b). Therefore, the designed system with 19.80 mM of H2O2 showed the highest photodegradation rate (Figure 6b). This result revealed that the appropriate amount of H2O2 played an important role of the photooxidation of RhB under the simulated solar light irradiation.
r ¼
ln
dC kr KC ¼ dt 1 þ KC
ð2Þ
C0 ¼ kt C
ð3Þ
where r is the reaction rate, kr is the reaction rate constant, K is the adsorption coefficient, and C is the reactant concentration (eq 2). If C is very small, eq 3 is obtained. C0 and C are the concentration of reactant at time 0 and t, respectively, and k is the apparent firstorder rate constant. The apparent reaction rate constant (k) was obtained from the gradient of the graph of ln(C/C0) versus time. The apparent reaction rate constant was 0.045 and 0.011 min1 for the initial RhB concentrations of 1.0 105 M and 2.0 105 M, respectively. It can be observed that the photodegradation rate of RhB is much faster when the initial concentration is lower in the TiO2/H2O2 system. 6683
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Figure 6. (a) Photodegradation of RhB (1.0 105 M) under irradiation by different amounts of H2O2 and without the catalyst addition. (b) Degradation of RhB (1.0 105 M) with rutile TiO2 nanostructures under irradiation and with different amounts of H2O2.
Figure 7. (a) Absorption spectra of a solution of RhB (1.0 105 M) in the presence of the as-obtained rutile TiO2 nanostructures (0.5 g/L) and 19.80 mM of H2O2 under simulated solar light irradiation (inset: pictures of RhB solutions as the function of time). (b) Change of TOC with time in the presence of rutile TiO2 nanostructures and 19.80 mM of H2O2 under the simulated solar light.
Figure 9 demonstrates that the as-prepared rutile TiO2 hierarchical nanostructures have a higher photocatalytic activity than commercial P25 photocatalyst in the presence of 19.80 mM H2O2. This result may be attributed to the larger surface area of rutile TiO2 nanostructures than that of P25, and the more species generated on the surface of rutile TiO2 nanostructures than P25 in the solution containing H2O2 under the simulated solar light.36 Additionally, TiO2 hierarchical nanostructures can be easily separated from the photocatalytic reaction systems by sedimentation because of large particle size, while this is unachievable with P25. 3.5. Photocatalytic Mechanism. The addition of H2O2 to TiO2 suspensions can enhance the photocatalytic activity under UV light irradiation.37,38 In our designed photocatalytic system, photoinduced conduction band electrons (e) and valence band holes (hþ) were generated from TiO2 under the irradiation of simulated solar light (eq 4). These electrons and holes can further produce free radicals under the appropriate conditions (eqs 5 and 6). Actually, the recombination of electrons and holes occurred in the photocatalytic processes, which led to the decrease of photodegradation efficiency. When H2O2 was
present, which can accept a photogenerated electron from the conduction band to obtain OH 3 radicals and thus suppress the charge recombination (eq 7), which can lead to the enhancement of the photocatalytic performance. In addition, OH 3 radicals can form according to eq 8.39 TiO2 þ hν f e þ hþ
ð4Þ
e þ O2 f O2 •
ð5Þ
hþ þ OH f OH•
ð6Þ
H2 O2 þ e f OH þ OH•
ð7Þ
H2 O2 þ O2 • f OH þ OH• þ O2
ð8Þ
In general, TiO2 and H2O2 cannot absorb the visible light; however, some studies have proved that organic contaminations could be degraded in the H2O2 and TiO2 suspensions under visible light irradiation, because the complexes form on the TiO2 surfaces in the presence of H2O2, which leads to red shift 6684
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Figure 8. First-order plots for the photodegradation of RhB by TiO2 nanostructures. Line a: the initial RhB concentration, 1.0 105 M; 19.80 mM H2O2. Line b: the initial RhB concentration, 2.0 105 M; 19.80 mM H2O2. Figure 10. Cycling runs in photodegradation of RhB in the presence of the rutile TiO2 nanostructures under simulated solar light irradiation (the initial RhB concentration, 1.0 105 M; photocatalyst dose, 0.5 g/ L; in every run 19.80 mM H2O2 was added).
Figure 9. Photodegradation of RhB (1.0 105 M) in two different reaction conditions under simulated solar light illumination.
extending to the visible region.40 In our experiments, we found that the white catalysts were turned light yellow after photocatalytic reaction. In the vis/TiO2/H2O2 process, the formed complexes on the rutile TiO2 surface can be excited by visible light to generate electrons, which are transferred to the conduction band of the rutile TiO2. These electrons combine with H2O2 to produce active OH 3 radicals (eq 7), which have strong oxidation ability to oxidize organic compounds adsorbed on the TiO2 surface.25 Based on the above discussion, addition of H2O2 to rutile TiO2 suspensions has an efficient degradation of organic compounds under simulated solar light irradiation (Figure 6b). However, when more than optimum H2O2 was introduced to the designed system, the photodegradation rate decreased. This is because H2O2 could consume hydroxyl radicals to form less reactive hydroperoxyl radicals and water according to eqs 9 and 10.41,42 H2 O2 þ OH• f H2 O þ HO2 •
ð9Þ
HO2 • þ OH• f H2 O þ O2
ð10Þ
3.6. Recycle and Stability Evaluation. The recycle experiments were carried out to evaluate the photostability of the rutile TiO2/H2O2 system under simulated solar light irradiation. After every 80-min photocatalytic reaction, the concentrated RhB
solution was injected and the separated photocatalysts were washed back into the reactor with distilled water in order to keep the initial concentration of RhB and photocatalysts constant.43 As illustrated in Figure 10, after five cycling runs of photodegradation of RhB, the photocatalytic activity of the TiO2/H2O2 system did not show any loss. In addition, after RhB photodegradation for 400 min, the crystal structure and the morphology of rutile TiO2 nanostructures were not changed, indicating that the catalysts are fairly stable (Figure S2, Supporting Information). Furthermore, the TiO2 nanostructures after five recycles completely precipitated after 3 h, demonstrating that the catalyst could be separated easily by sedimentation (Figure S3, Supporting Information). The recycle experiments, the comparison of the catalyst before and after reaction, and the sedimentation phenomenon indicate that the TiO2/H2O2 system is stable and does not photocorrode during the photodegradation of RhB. In addition, hydrogen peroxide extensively exists in natural water;44 thus, the TiO2/ H2O2 system has potential practical application in treating contaminated natural water.
4. CONCLUSION The rutile TiO2 hierarchical nanostructures have been prepared by a simple hydrothermal process. The as-synthesized TiO2 photocatalyst exhibited enhanced photocatalytic activity under simulated solar light irradiation when a small amount of H2O2 was added. Besides the enhanced photocatalytic performance, the photostability of the rutile TiO2/H2O2 system was also investigated. TiO2 hierarchical nanostructures can be easily separated from the reaction system by sedimentation, which can avoid separation problems. Due to facile synthetic process and low cost, the rutile TiO2/H2O2 system should have potential practical application to the removal of organic contaminants. ’ ASSOCIATED CONTENT
bS
Supporting Information. Change of methyl orange with time in the presence of rutile TiO2 nanostructures and H2O2 under simulated solar light irradiation, XRD patterns of rutile TiO2 naonstructures before and after cycling runs, SEM image of rutile TiO2 naonstructures after cycling runs, and sedimentation profile of rutile TiO2 naonstructures after cycling 6685
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’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected] (L.L.) or
[email protected] (Z.Z.).
’ ACKNOWLEDGMENT This work was supported by Tianjin Municipal Science and Technology Commission (10SYSYJC27200) and China-US Center for Environmental Remediation and Sustainable Development. ’ REFERENCES (1) Raffainer, I. I.; Rudolf von Rohr, P. Promoted Wet Oxidation of the Azo Dye Orange II under Mild Conditions. Ind. Eng. Chem. Res. 2001, 40, 1083. (2) Bauer, C.; Jacques, P.; Kalt, A. Photooxidation of an Azo Dye Induced by Visible Light Incident on the Surface of TiO2. J. Photochem. Photobiol., A 2001, 140, 87. (3) Arslan, I.; Balcioglu, I. A.; Bahnemann, D. W. Heterogeneous Photocatalytic Treatment of Simulated Dyehouse Effluents Using Novel TiO2-photocatalysts. Appl. Catal., B 2000, 26, 193. (4) Vinodgopal, K.; Wynkoop, D. E.; Kamat, P. V. Environmental Photochemistry on Semiconductor Surfaces: Photosensitized Degradation of a Textile Azo Dye, Acid Orange 7, on TiO2 Particles Using Visible Light. Environ. Sci. Technol. 1996, 30, 1660. (5) Asilt€urk, M.; Sayılkan, F.; Erdemoglu, S.; Akarsu, M.; Sayılkan, H.; Erdemoglu, M.; Arpac, E. Characterization of the Hydrothermally Synthesized Nano-TiO2 Crystallite and the Photocatalytic Degradation of Rhodamine B. J. Hazard. Mater. 2006, 129, 164. (6) Linsebigle, A. L.; Lu, G. Q.; Yates, J. T. Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results. Chem. Rev. 1995, 95, 735. (7) Fujishima, A.; Rao, T. N.; Tryk, D. A. Titanium Dioxide Photocatalysis. J. Photochem. Photobiol., C 2000, 1, 1. (8) Zhang, H.; Li, G. R.; An, L. P.; Yan, T. Y.; Gao, X. P.; Zhu, H. Y. Electrochemical Lithium Storage of Titanate and Titania Nanotubes and Nanorods. J. Phys. Chem. C 2007, 111, 6143. (9) Gao, X. P.; Zhu, H. Y.; Pan, G. L.; Ye, S. H.; Lan, Y.; Wu, F.; Song, D. Y. Preparation and Electrochemical Characterization of Anatase Nanorods for Lithium-Inserting Electrode Material. J. Phys. Chem. B 2004, 108, 2868. (10) Park, N. G.; van de Lagemaat, J.; Frank, A. J. Comparison of Dye-Sensitized Rutile and Anatase-Based TiO2 Solar Cells. J. Phys. Chem. B 2000, 104, 8989. (11) Zhang, S.; Liu, C. Y.; Liu, Y.; Zhang, Z. Y.; Mao, L. Room Temperature Synthesis of Nearly Monodisperse Rodlike Rutile TiO2 Nanocrystals. J. Mater. Lett. 2009, 63, 127. (12) Li, X. X.; Xiong, Y. J.; Li, Z. Q.; Xie, Y. Large-Scale Fabrication of TiO2 Hierarchical Hollow Spheres. Inorg. Chem. 2006, 45, 3493. (13) Li, Y. Y.; Liu, J. P.; Jia, Z. J. Morphological Control and Photodegradation Behavior of Rutile TiO2 Prepared by a Low-temperature Process. Mater. Lett. 2006, 60, 1753. (14) Yang, S. W.; Gao, L. Fabrication and Characterization of Nanostructurally Flowerlike Aggregates of TiO2 via a Surfactant-free Solution Route: Effect of Various Reaction Media. Chem. Lett. 2005, 34, 1044. (15) Kandiel, T. A.; Dillert, R.; Feldhoff, A.; Bahnemann, D. W. Direct Synthesis of Photocatalytically Active Rutile TiO2 Nanorods Partly Decorated with Anatase Nanoparticles. J. Phys. Chem. C 2010, 114, 4909.
ARTICLE
(16) Wang, Y. W.; Zhang, L. Z.; Deng, K. J.; Chen, X. Y.; Zou, Z. G. Low Temperature Synthesis and Photocatalytic Activity of Rutile TiO2 Nanorod Superstructures. J. Phys. Chem. C 2007, 111, 2709. (17) Wu, J. M.; Qi, B. Low-Temperature Growth of Rutile Nanorod Thin Films and their Photon-Induced Property. J. Am. Ceram. Soc. 2008, 91, 3961. (18) Amir Tahmasseb, L.; Nelieu, S.; Kerhoas, L.; Einhorn, J. Ozonation of Chlorophenylurea Pesticides in Water: Reaction Monitoring and Degradation Pathways. J. Sci. Total Environ. 2002, 291, 33. (19) Javier Benitez, F.; Real, F. J.; Acero, J. L.; Garcia, C. Photochemical Oxidation Processes for the Elimination of Phenyl-urea Herbicides in Waters. J. Hazard. Mater. 2006, 138, 278. (20) Masomboon, N.; Ratanatamskul, C.; Lu, M. C. Chemical Oxidation of 2,6-Dimethylaniline in the Fenton Process. Environ. Sci. Technol. 2009, 43, 8629. (21) Kavitha, V.; Palanivelu, K. The Role of Ferrous Ion in Fenton and Photo-Fenton Processes for the Degradation of Phenol. Chemosphere 2004, 55, 1235. (22) Elmolla, E. S.; Chaudhuri, M. Photocatalytic Degradation of Amoxicillin, Ampicillin and Cloxacillin Antibiotics in Aqueous Solution Using UV/TiO2 and UV/H2O2/TiO2 Photocatalysis. Desalination 2010, 252, 46. (23) Coleman, H. M.; Vimonses, V.; Leslie, G.; Amal., R. Degradation of 1,4-dioxane in Water Using TiO2 Based Photocatalytic and H2O2/UV Processes. J. Hazard. Mater. 2007, 146, 496. (24) Rao, Y. F.; Chu, W. Reaction Mechanism of Linuron Degradation in TiO2 Suspension under Visible Light Irradiation with the Assistance of H2O2. Environ. Sci. Technol. 2009, 43, 6183. (25) Li, X. Z.; Chen, C. C.; Zhao, J. C. Mechanism of Photodecomposition of H2O2 on TiO2 Surfaces under Visible Light Irradiation. Langmuir 2001, 17, 4118. (26) Zhong, L. S.; Hu, J. S.; Liang, H. P.; Cao, A. M.; Song, W. G.; Wan, L. J. Self-Assembled 3D Flowerlike Iron Oxide Nanostructures and Their Application in Water Treatment. Adv. Mater. 2006, 18, 2426. (27) Liu, L.; Liu, H. J.; Zhao, Y. P.; Wang, Y. Q.; Duan, Y. Q.; Gao, G. D.; Ge, M.; Chen, W. Directed Synthesis of Hierarchical Nanostructured TiO2 Catalysts and their Morphology-Dependent Photocatalysis for Phenol Degradation. Environ. Sci. Technol. 2008, 42, 2342. (28) Li, H. B.; Duan, X. C.; Liu, G. C.; Jia, X. B.; Liu, X. Q. Morphology Controllable Synthesis of TiO2 by a Facile Hydrothermal Process. Mater. Lett. 2008, 62, 4035. (29) Ren, L.; Huang, X. T.; Sun, F. L.; He, X. Preparation and Characterization of Doped TiO2 Nanodandelion. Mater. Lett. 2007, 61, 427. (30) Li, W. J.; Shi, E. W.; Yin, Z. W. Growth Habit of Rutile and RAl2O3 Crystals. J. Cryst. Growth 2000, 208, 546. (31) Xiong, C. R.; Deng, X. Y.; Li, J. B. Preparation and Photodegradation Activity of High Aspect Ratio Rutile TiO2 Single Crystal Nanorods. Appl. Catal., B 2010, 94, 234. (32) Yang, K.; Zhu, J. M.; Zhu, J. J.; Huang, S. S.; Zhu, X. H.; Ma, G. B. Sonochemical Synthesis and Microstructure Investigation of Rodlike Nanocrystalline Rutile Titania. Mater. Lett. 2003, 57, 4639. (33) Huang, X. P.; Pan, C. X. Large-scale Synthesis of Singlecrystalline Rutile TiO2 Nanorods Via a One-step Solution Route. J. Cryst. Growth 2007, 306, 117. (34) Legrini, O.; Oliveros, E.; Braun, A. M. Photochemical Processes for Water Treatment. Chem. Rev. 1993, 93, 671. (35) Sakkas, V. A.; Arabatzis, I. M.; Konstantinou, I. K.; Dimou, A. D.; Albanis, T. A.; Falaras, P. Metolachlor Photocatalytic Degradation Using TiO2 Photocatalysts. Appl. Catal., B 2004, 49, 195. (36) Ohno, T.; Masaki, Y. J.; Hirayama, S.; Matsumura, M. TiO2Photocatalyzed Epoxidation of 1-Decene by H2O2 under Visible Light. J. Catal. 2001, 204, 163. (37) Poulios, I.; Micropoulou, E.; Panou, R.; Kostopoulou, E. Photooxidation of Eosin Y in the Presence of Semiconducting Oxides. Appl. Catal., B 2003, 41, 345. 6686
dx.doi.org/10.1021/ie1023113 |Ind. Eng. Chem. Res. 2011, 50, 6681–6687
Industrial & Engineering Chemistry Research
ARTICLE
(38) Aceituno, M.; Stalikas, C. D.; Lunar, L.; Rubio, S.; PerezBendito, D. H2O2/TiO2 Photocatalytic Oxidation of Metol. Identification of Intermediates and Reaction Pathways. Water Res. 2002, 36, 3582. (39) Kositzi, M.; Antoniadis, A.; Poulios, I.; Kiridis, I.; Malato, S. Solar Photocatalytic Treatment of Simulated Dyestuff Effluents. Solar Energy 2004, 77, 591. (40) Boonstra, A. H.; Mutsaers, C. A. H. A. Adsorption of Hydrogen Peroxide on the Surface of Titanium Dioxide. J. Phys. Chem. 1975, 79, 1940. (41) Yang, H. M.; Zhang, K.; Shi, R. R.; Li, X. W.; Dong, X. D.; Yu, Y. M. Sol-gel Synthesis of TiO2 Nanoparticles and Photocatalytic Degradation of Methyl orange in Aqueous TiO2 Suspensions. J. Alloys Compd. 2006, 413, 302. (42) Xiao, Q.; Zhang, J.; Xiao, C.; Tan, X. K. Photocatalytic Degradation of Methylene Blue over Co3O4/Bi2WO6 Composite under Visible Light Irradiation. Catal. Commun. 2008, 9, 1247. (43) Long, M. C.; Cai, W. M.; Cai, J.; Zhou, B. X.; Chai, X. Y.; Wu, Y. H. Efficient Photocatalytic Degradation of Phenol over Co3O4/BiVO4 Composite under Visible Light Irradiation. J. Phys. Chem. B 2006, 110, 20211. (44) Cooper, W. J.; Zika, R. G. Photochemical Formation of Hydrogen Peroxide in Surface and Ground Waters Exposed to Sunlight. Science 1983, 220, 711.
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