12358
Ind. Eng. Chem. Res. 2010, 49, 12358–12364
Kinetic Modeling of Liquid Phase Photocatalysis on Supported TiO2 Nanoparticles in a Rectangular Flat-Plate Photoreactor A. R. Khataee,* M. Fathinia, and S. Aber Department of Applied Chemistry, Faculty of Chemistry, UniVersity of Tabriz, Tabriz, Iran
The photocatalytic degradation of C.I. Basic Blue 3 (BB3) in water on supported TiO2 nanoparticles was carried out in a rectangular flat-plate photoreactor. The photocatalytic degradation kinetic characteristics were experimentally investigated under different light intensities and initial dye concentrations. Calculating corresponding “apparent adsorption constants”, KS, and “apparent rate constants”, kr, of experimental results according to the Langmuir-Hinshelwood (L-H) model emphasized that the L-H constants varied with regard to the light intensity. A new kinetic model was developed on the basis of the intrinsic element reactions, which took into account the effect of light intensity, reaction intermediates, organic compound content, and first order reaction kinetics. The new kinetic model described the experimental results in a more accurate way and explained consistently the dependence of the apparent kinetic parameters kr and KS on the light intensity. 1. Introduction The heterogeneous photocatalytic process is a suitable technique for degrading organic water and air pollutants. As an example, many pesticides or dyes can be partially or completely mineralized in water,1-3 and odorous compounds can be destroyed in the gas phase.4,5 When the semiconductor, TiO2, is illuminated with λ < 390 nm light, an electron excites out of its energy level and consequently leaves a hole in the valence band. As electrons are promoted from the valence band to the conduction band, they generate electron-hole pairs. These charges can either recombine or participate in different reactions. Many studies have focused on the chemical pathways or the photodegradation kinetics, but there have been few reports based on the design of photocatalytic reactors.6-9 It is necessary to have a better knowledge of the optimal photocatalytic process conditions. TiO2 as a photocatalyst was employed in colloidal form or as an immobilized film.10,11 In photoreactors operated with TiO2 nanoparticles immobilized on the outer surface, the reaction rate is predominantly determined by the light intensity on the surface, the quantum efficiency of the catalyst, the adsorption properties of the reacting components in solution, and mass transfer from the bulk of the fluid to the catalyst surface.12-16 The challenge of photocatalysis consists in designing reactors with high efficiency. For this goal, it is important to have a better understanding of the affecting operational factors such as the initial pollutant concentration and light intensity on the degradation rate. The first-order kinetic expression has often been used due to its simplicity17 with good agreement for a certain initial organic content in photocatalytic processes: r)
-dC ) kappC dt
(1)
in which kapp is the apparent first-order rate constant (with the same restriction of C ) C0 at t ) 0, with C0 being the initial content in the bulk solution after dark adsorption and t the reaction time). The kinetic behavior, in which kapp of the firstorder kinetics is affected by the initial organic content, can be commonlydescribedintermsofamodifiedLangmuir-Hinshelwood * To whom correspondence should be addressed. Tel.: +98 411 3393165. Fax: +98 411 3340191. E-mail:
[email protected].
model. This model has been successfully used for heterogeneous photocatalytic degradation to determine the relationship between the apparent first-order rate constant and the initial content of the organic substrate,18,19 which is commonly expressed as eqs 2 and 3: r)-
krKSC dC ) ) kappC dt 1 + KSC0
(2)
C0 1 + krKS kr
(3)
1 kapp
)
where C0 is the initial organic content, kr is the reaction rate constant, and KS is the adsorption rate constant. Obviously, the reaction rate is dependent on the light intensity, organic compound content, and absorption performance of the catalyst.20,21 However, the rate constant kr and adsorption constant KS in the L-H model are independent of both factors. Although KS reflects the adsorptive affinity of a substrate on the catalyst surface, it should not vary with the light intensity, so the virtual meanings of the parameters (kr, KS) in the L-H model have not been clarified.22,23 In this way, if these points are included in the kinetic model, a novel apparent kinetic constant related to the light intensity and initial organic content would be realized. Therefore, in this paper, we investigated the kinetic characteristics of the photocatalytic degradation of BB3 at different initial concentrations of BB3 and light intensity in order to establish a kinetic model between the degradation rate, light intensity, and initial concentration of BB3. Meanwhile, the following work aims to test a new kinetic model and elucidate from the data obtained that the light intensity affected both constants (kr, KS) in the proposed kinetic model. Because modeling photocatalytic reactions requires a firm knowledge of the adsorption phenomena, we have presented a set of experiments for describing the dependency of the degradation rate on UV photon flow and the initial concentration of the dye. 2. Materials and Methods 2.1. Chemicals and Instruments. C.I. Basic Blue 3 (BB3), a commercial dye (Boyakhsaz Co., Tehran, Iran), was chosen as the model compound, whose characteristics are given in Table
10.1021/ie101997u 2010 American Chemical Society Published on Web 11/05/2010
Ind. Eng. Chem. Res., Vol. 49, No. 24, 2010
12359
Table 1. Characteristics of C.I. Basic Blue 3
1. The investigated photocatalyst was Millennium PC-500 (anatase: >99%; Millennium Inorganics, Brussels, Belgium) immobilized on nonwoven paper supplied by Ahlstrom Research & Services, Pont-Eveˆque, France. TiO2 nanoparticles were attached by a binder based on a suspension of colloidal SiO2 (EP1069950B1 European patent). According to the manufacturer’s specifications,24 the crystallites’ mean size was 5-10 nm, and the specific surface area was >300 m2 g-1. These characteristics were proved by our scanning electron microscopy (SEM), X-ray diffraction (XRD) analyses, and transmission electron microscopy (TEM), which are shown in Figures 1-3. Also, Figure 1 shows the SEM image of TiO2 nanoparticles deposited on nonwoven paper. The photocatalytic reactions were monitored by UV-vis spectrophotometry (WPA light wave S2000, England) in the range of 200-700 nm. Scanning electron microscopy was carried out on a Jeol TSM 330 (Jeol Europe SA, Croissy-sur-Seine, France) device after gold-plating of the samples. The samples used for TEM observations were prepared by dispersing the TiO2 powder in ethanol followed by ultrasonic vibration (Sonorex Bandelin Digi Tec, U.K.) for 15 min, then placing a drop of the dispersion onto a copper grid coated with
Figure 1. SEM image of TiO2 nanoparticles deposited on nonwoven paper.
Figure 2. XRD patter of Millennium PC-500 TiO2 nanoparticles.
Figure 3. TEM image of Millennium PC-500 TiO2 nanoparticles.
a layer of amorphous carbon. TEM was carried out on a Zeiss EM 900, Germany. To determine the crystal phase composition and average crystalline size of immobilized TiO2 nanoparticles sample, X-ray diffraction measurements were carried out at room temperature by using Siemens X-ray diffraction D5000, with Cu KR radiation. An accelerating voltage of 40 kV and an emission current of 30 mA were used. The average crystalline size of the samples was calculated according to the DebyeScherrer formula.11 It can be observed from Figure 2 that the peaks in XRD are at 2θ ) 25.3°, 37.8°, and 48.1°, which corresponded to anatase form TiO2. Artificial irradiation was provided by three 30 W UV-C lamp (Philips, The Netherlands) with peak intensity at 254 nm. 2.2. Photoreactor. The experimental setup is based on a rectangular photocatalytic reactor of workable area 15 × 90 cm2, made out of stainless steel (Figure 4). The reactor consists of several parts: a tank with a magnetic stirrer, three UV-C lamps, a peristaltic pump for circulating the dye solution, and an air pump for aeration. The catalytic support containing TiO2 nanoparticles was placed on the bottom of the reactor. Three 30 W UV-C lamps were placed over the immobilized TiO2 nanoparticles. The distance between the lamps and the immobilized TiO2 nanoparticles was adjusted in specific distance, and variation in the distance caused the change in light intensity. When three and two of the lamps were on, intensities of 47.2 and 26.3 W m-2 were provided. On the other hand, when just one of the lamps was on with a distance of 5 and 9 cm from the immobilized TiO2 nanoparticles, intensities of 19.7 and 12.3 W m-2 were provided, respectively. The radiation intensity was measured with a UV radiometer purchased from Cassy Lab Company (Germany). The reactor was washed after every run by circulating deionized water with a few drops of 30% hydrogen peroxide under UV irradiation, so that the immobilized photocatalyst was regenerated. Adsorption measurement of the dye on immobilized TiO2 was made using the same setup in the absence of irradiation. 2.3. Experimental Conditions for Kinetic Analysis. To probe the dependence of the kinetic characteristics of the photocatalytic degradation on the light intensity and initial organic content, a series of experiments were carried out at different photocatalytic conditions. The initial concentration of BB3 was varied from 2.5 to 20 mg L-1. The light intensity of UV lamps was 12.3, 19.7, 26.3, and 47.2 W m-2. The aerating rate of the air pump was constant for all experiments; the flow rate was set at 100 mL min-1. The samples were taken from the reactor at scheduled times, and the removal of the dye was followed by using a UV-vis spectrophotometer. For each group of experiments at a certain light intensity, six different BB3 concentrations were applied.
12360
Ind. Eng. Chem. Res., Vol. 49, No. 24, 2010
Figure 4. The experimental setup of the rectangular photocatalytic reactor.
Figure 5. Effect of light intensity on the apparent rate constant kapp, for different concentrations of BB3.
3. Results and Discussion 3.1. Photocatalytic Degradation of BB3 in Water. In order to study the influence of the light intensity and the concentration of organic compound on the initial degradation rate, experiments were carried out with different light intensities and initial dye concentrations. Figure 5 shows the influence of the light intensity on the apparent first-order rate constant for different concentrations of BB3. The initial degradation rate increases with increasing photon flow. Figure 6 shows a plot of 1/kapp versus C0 for different light intensities. The values of the adsorption constant, KS, and the rate constant, kr, were obtained by linear regression of the points calculated through eq 3. The values of the kinetic parameter, kr, and the apparent adsorption parameter, KS, are plotted verses I0 (W m-2) in Figure 7. The results clearly show that kr, and KS depend on light intensity. As indicated by Ollis,25 the dependence of the apparent adsorption parameter with respect to light intensity creates flaws in the L-H slow step photocatalysis model. The dependence of the apparent adsorption parameter on intensity has been also reported for the photocatalytic degradation of phenol26 and acetophenone27 in the liquid phase.
Figure 6. Relation between 1/kapp and C0 with different light intensities (1, 47.2 W cm-2; 2, 26.3 W cm-2; 3, 19.7 W cm-2; 4, 12.3 W cm-2).
3.2. Kinetic Modeling of Photocatalytic Degradation. Under the mentioned experimental conditions, it can be assumed that the first step in the photocatalytic reaction is the adsorption of the BB3 molecule and its degradation products on the surface of immobilized TiO2, and the second step is the decomposition of all adsorbed substrates. Considering the above processes; the assumptions are as follows: (1) Photocatalytic oxidation is mainly completed via the hydroxyl groups absorbed on the surface of the immobilized TiO2, which attack the organic compounds and related intermediates on the catalyst surface. This is the rate-limiting step for the photocatalytic degradation process. (2) The combination of H2O/OH- with the photoinduced holes (h+) to form hydroxyl groups and the •OH radicals should be mainly formed from the adsorbed H2O molecules. (3) The combination rate of h+/e- is much more than the hydroxyl forming rate of the reaction between h+, H2O, and OH-. (4) The concentration of hydroxyl radicals is constant at a steady state (Bodenstein steady state assumption21). (5) The concentration of h+ is constant at a steady state (Bodenstein steady state assumption21).
Ind. Eng. Chem. Res., Vol. 49, No. 24, 2010
12361
Owing to the fact that water is the solvent ([H2O] is constant), k4 [H2O][h+] . k3 [OH-]ads[h+] according to assumption (2). Consequently, [•OH]ads can be obtained according to the following equation: d[•OH]ads dt
k5[h+][OH-]ads + k4[h+][H2O] + k17[H2O2][e-]
)
+ k18[H2O2][O•2] + k19[H2O2]1/2[I]1/2 - k7[•OH]ads[C]ads - k8[•OH]ads[Sinactive] - k9[•OH]ads[int] - k10[•OH]ads - k11[•OH]ads[e-] ) 0
(8) with the following assumption: k7[•OH]ads[C]ads + k8[•OH]ads[Sinactive] + k9[•OH]ads[int] ) k7[C0 - Sinactive - int] + k8[C0 - Cads - int] - k9[C0 - Sinactive - Cads] ) k7[C]0 - k7[Sinactive - int] + k8[C]0 - k8[Cads - int] + k9[C]0 - k9[Sinactive - Cads] ) [C]0{k7 + k8 + k9} - k7[Sinactive - int] - k8[Cads - int] - k9[Sinactive - Cads] ) [C]0{kD} - k7[Sinactive - int] - k8[Cads - int] - k9[Sinactive - Cads] ) [C]0{kD}
(9) -k7[Sinactive - int] - k8[Cads - int] - k9[Sinactive - Cads] (10)
Figure 7. Relation between kr (a) and KS (b) in the L-H model with light intensity.
(6) The hydroxyl radicals can be deactivated by detrapping of the holes or via a reaction with surface electrons. Emeline et al.26 have considered the recombination of •OH radicals with surface electrons as the major pathway to explain the interdependence of the reaction rate with photon flow and the concentration of the target compound. Herein, we considered that recombination may occur through both processes. The elementary reaction equations are expressed in Table 2. According to assumption (1), the photocatalytic degradation rate (r) for the decomposition of BB3 on the immobilized TiO2 is represented as eq 4: r0 ) kD[•OH]ads[C]
(4)
where kD represents the rate constants of degradation products and [C] is the concentration of the organic compound. On the other hand, the concentration of photoinduced holes, [h+], can be obtained by applying assumption (5) as the following equation: +
d[h ] ) dt
k1I + k10[OH-]ads[h+] - k2[h+]2 +
+
-
The assumption is that expression 10 is rather low when compared to the expression [C]0{kD}, so eq 9 is valid. Equation 11 shows that water is solvent and its concentration is constant. k4[H2O] ) k'4
As a consequence, the concentration of [•OH]ads for a single compound can be obtained by using expression 7 as follows:
(6)
Consequently, [h+] has the form: [h+] )
( ) k1I k2
1/2
(7)
kD[C]0 + k10 + k11[e-]
)
k4′(k1 /k2)1/2I1/2
(12)
kD[C]0 + k10 + k11(k1 /k2)1/2I1/2
Including expression 12 in expression 4, the initial degradation rate is described by eq 13: r0 )
kDk4′(k1 /k2)1/2I1/2C kD[C]0 + k10 + k11(k1 /k2)1/2I1/2
(13)
Equation 13 can be transformed into eq 2 if kr ) k4′(k1 /k2)1/2I1/2 KS )
-k4[H2O][h ] - k5[h ][OH ]ads
k2[h+]2 . k4[h+][H2O] + k5[h+][OH-]ads
k4′[h+]
[•OH] )
(5)
Rothenberger et al.32 have applied laser pulse photolysis to determine the recombination rate coefficient of the separated e- and h+, in which k2 is much higher than k4. According to assumption (3):
(11)
kD k10 + k11(k1 /k2)1/2I1/2
(14) (15)
Hence, kr should be proportional to I1/2, and 1/KS should be proportional to I1/2, when k10 , k11 (k1/k2)1/2I1/2. So, eq 13 refers to all of the experimental dependencies of the apparent equilibrium constant and rate constant with regard to the light intensity in the liquid phase. Our results are in good agreement with the results of others research groups.26,27,32,33 On the other hand by dividing the numerator and the denominator of eq 13 by k10, the following expression is found: r0 )
(kDk4′(k1 /k2)1/2 /k10)I1/2C kD /k10[C]0 + 1 + (k11 /k10)(k1 /k2)1/2I1/2
(16)
12362
Ind. Eng. Chem. Res., Vol. 49, No. 24, 2010
Table 2. Elementary Reaction Equations Used for Kinetic Modeling1,28-31 a
Table 2. Continued -
k1
TiO2 + hν 98 e- + h+
(A1)
k15
HO•2 + O•2 98 HO2 + O2
k16
k2
e- + h+ 98 heat
(A2)
+ HO2 + H 98 H2O2
k17
k3
H2O + H+ + OH- + STiO2 98 H2Oads + OHads + H+
H2O2 + e- 98 •OHads + OH-
(A15)
(A16)
(A17)
(A3) k18
H2O2 + O•2 98 •OHads + OH- + O2 k4
h+ + H2Oads 98 •OHads + H+
(A4) k19
H2O2 + hν 98 2•OHads k5
h+ + OHads 98 •OHads + H+
(A18)
(A19)
(A5) a The subscript “ads” and STiO2 refer to the adsorbed species and the surface of immobilized TiO2 nanoparticles, respectively.
k6
C + STiO2 98 [C]ads
k7
•
OHads + [C]ads 98 [intermediate]
k8
•
OHads + Sinactive 98 inactive species
(A6) According to relations 2 and 9, expression 17 is obtained:
(A7)
r0 ) kappC )
kapp )
(A8)
βI1/2 C 1 + RI1/2 + η[C]0
βI1/2 1 + RI1/2 + η[C]0
(17)
(18)
where the constants can be obtained using expressions in eqs 19-21: •
k9
OHads + [intermediate] 98 degradation products
(A9) k10
•
OHads 98 OHads + h+
k11
•
OHads + e- 98 OHads
k12
-
O2 + e- 98 O•2
k13
-
O•2 + H+ 98 HO•2
k14
HO•2 + HO•2 98 H2O2 + O2
(A10)
(A11)
(A12)
(A13)
(A14)
k11(k1 /k2)1/2 k10
(19)
kDk'4(k1 /k2)1/2 k10
(20)
kD k10
(21)
R)
β)
η)
Equation 18 shows a pseudo-first-order reaction with respect to the BB3 concentration. The diagram of dispersion of the experimental versus calculated apparent reaction rate constants (kapp) for the photocatalytic degradation of BB3 is represented in Figure 8. According to Figure 8, the correlation coefficient (R2) value is 0.95, indicating that there is a strong significant correlation between the experimental apparent first-order rate constant and the fitted models based on relation 18. There is clear evidence that eq 18 is valid and confirms the interdependence of the rate with respect to intensity and concentration. The constants R, β, and η in the model were obtained by fitting kapp to [BB3]0 at different light intensities using the software package Matlab 7 and are listed in Table 3.
Ind. Eng. Chem. Res., Vol. 49, No. 24, 2010
Figure 8. A comparison between experimental and calculated apparent reaction rate constants obtained from expression 18, the new kinetic model. Table 3. Values of the Constants for the Correlation of eq 18 model kapp )
1/2
βI 1 + RI1/2 + η[CR]0
parameter
values
R
0.118
β
0.004
η
0.061
It can be seen in Figure 8 that the results obtained from the model are in good agreement with the experimental data. Conclusion The photocatalytic removal of BB3 using TiO2 nanoparticles supported on nonwoven paper was investigated in a flat-plate photoreactor. Kinetic characteristics of the photocatalytic degradation of BB3 were experimentally investigated with respect to the different initial BB3 concentrations and light intensities. The kinetic characteristics were ascertained to follow an L-H model; however, the dependence of the model constants KS and kr on the light intensity was observed. A new kinetic model based on the intrinsic element reactions was developed. The new model predicted that both kr and 1/KS were related to the reciprocal of the square root of the light intensity over a wide range. The validity of the model was proved by fitting it to experimental data obtained under various incident light intensities and initial organic contents. It was found that the results obtained from the model were in good agreement with the experimental data. Acknowledgment The authors thank the University of Tabriz, Iran for financial and other support. Literature Cited (1) Daneshvar, N.; Salari, D.; Niaei, A.; Khataee, A. R. Photocatalytic Degradation of the Herbicide Erioglaucine in the presence of Nanosized Titanium Dioxide: Comparison and Modeling of Reaction Kinetics. J. EnViron. Sci. Health, Part B 2006, 41, 1273. (2) Burrows, H. D.; Canle, L. M.; Santaballa, J. A.; Steenken, S. Reaction Pathways and Mechanisms of Photodegradation of Pesticides. J. Photochem. Photobiol. B 2002, 67, 71. (3) Khataee, A. R.; Pons, M. N.; Zahraa, O. Photocatalytic Degradation of Three Azo Dyes using Immobilized TiO2 Nanoparticles on Glass Plates Activated by UV Light Irradiation: Influence of Dye Molecular Structure. J. Hazard. Mater. 2009, 168, 451. (4) Obee, T. N.; Brown, R. T. TiO2 Photocatalysis for Indoor Air Applications: Effects of Humidity and Trace Contaminant Levels on the Oxidation Rates of Formaldehyde, Toluene, and 1,3-Butadiene. EnViron. Sci. Technol. 1995, 29, 1223.
12363
(5) Bouzaza, A.; Vallet, C.; Laplanche, A. Photocatalytic Degradation of Some VOCs in the Gas Phase using An Annular Flow Reactor: Determination of the Contribution of Mass Transfer and Chemical Reaction Steps in the Photodegradation Process. J. Photochem. Photobiol. A 2006, 177, 212. (6) Daneshvar, N.; Rasoulifard, M. H.; Khataee, A. R.; Hosseinzadeh, F. Removal of C.I. Acid Orange 7 from Aqueous Solution by UV Irradiation in the Presence of ZnO Nanopowder. J. Hazard. Mater. 2007, 143, 95. (7) Nanping, X.; Zaifeng, S.; Yiqun, F.; Junhang, D.; Jun, S.; Michael, Z. Effects of Particle Size of TiO2 on Photocatalytic Degradation of Methylene Blue in Aqueous Suspensions. Ind. Eng. Chem. Res. 1999, 38, 373. (8) Puma, G. L.; Yue, P. L. Modelling and Design of Thin-Film Slurry Photocatalytic Reactors for Water Purification. Chem. Eng. Sci. 2003, 58, 2269. (9) Sagawe, G.; Brandi, R. J.; Bahnemann, D.; Cassano, A. E. Photocatalytic Reactors for Treating Water Pollution with Solar Illumination. III: A Simplified Analysis for Recirculating Reactors. Sol. Energy 2004, 77, 471. (10) Legrini, O.; Oliveros, E.; Braun, A. M. Photochemical Processes for Water Treatment. Chem. ReV. 1993, 93, 671. (11) Khataee, A. R. Photocatalytic Removal of C.I. Basic Red 46 on Immobilized TiO2 Nanoparticles: Artificial Neural Network Modeling. EnViron. Technol. 2009, 30, 1155. (12) Khataee, A. R.; Pons, M. N.; Zahraa, O. Photocatalytic Decolorization and Mineralization of Orange Dyes on Immobilized Titanium Dioxide Nanoparticles. Water Sci. Technol. 2010, 62, 1112. (13) Levenspiel, O. Chemical Reaction Engineering; Wiley: New York, 1999. (14) Flury, M.; Wai, N. N. Dyes as Tracers for Vadose Zone Hydrology. ReV. Geophys. 2003, 41, 1002. (15) Fogler, S. H. Elements of Chemical Reaction Engineering; PrenticeHall International: New York, 1992. (16) Sahle-Demessie, E.; Bekele, S.; Pillaia, U. R. Residence Time Distribution of Fluids in Stirred Annular Photoreactor. Catal. Today 2003, 88, 61. (17) Rao, N. N.; Dubey, A. K.; Mohanty, S.; Khare, P.; Jain, R.; Kaul, S. N. Photocatalytic Degradation of 2-Chlorophenol: A Study of Kinetics, Intermediates and Biodegradability. J. Hazard. Mater. 2003, 101, 301. (18) Tennakone, K.; Tilakaratne, C. T. K.; Kottegoda, I. R. M. Photomineralization of Carbofuran by TiO2-Supported Catalyst. Water Res. 1997, 31, 1909. (19) Heredia, J. B.; Torregrosa, J.; Dominguez, J. R.; Peres, J. A. Oxidation of p-hydroxybenzoic Acid by UV Radiation and by TiO2/UV Radiation: Comparison and Modelling of Reaction Kinetic. J. Hazard. Mater. 2001, 83, 255. (20) Khataee, A. R.; Fathinia, M.; Aber, S.; Zarei, M. Optimization of Photocatalytic Treatment of Dye Solution on Supported TiO2 Nanoparticles by Central Composite Design: Intermediates IdentificationM. J. Hazard. Mater. 2010, 181, 886. (21) Meng, Y.; Huang, X.; Wu, Y.; Wang, X.; Qian, Y. Kinetic Study and Modeling on Photocatalytic Degradation of Para-Chlorobenzoate at Different Light Intensities. EnViron. Pollut. 2002, 117, 307. (22) Brosillan, S.; Ludovic, L.; Vallet, C.; Bouzaza, A.; Wolbert, D. Gas Phase Photocatalysis and Liquid Phase Photocatalysis: Interdependence and Influence of Substrate Concentration and Photon Flow on Degradation Reaction Kinetics. Appl. Catal., B 2008, 78, 232. (23) Li, Y.; Sun, S.; Ma, M.; Ouyang, Y.; Yan, W. Kinetic Study and Model of the Photocatalytic Degradation of Rhodamine B (RhB) by a TiO2Coated Activated Carbon Catalyst: Effects of Initial RhB Content, Light Intensity and TiO2 Content in the Catalyst. Chem. Eng. J. 2008, 142, 147. (24) Millennium Inorganic Chemicals, Certificated Analysis, PC 500 Lot No. 6293000124, 2007. (25) Ollis, D. F. Kinetics of Liquid Phase Photocatalyzed Reactions: An Illuminating Approach. J. Phys. Chem. B 2005, 109, 2439. (26) Emeline, A. V.; Ryabchuk, V.; Serpone, N. Factors Affecting the Efficiency of a Photocatalyzed Process in Aqueous Metal-Oxide Dispersions: Prospect of Distinguishing between Two Kinetic Models. J. Photochem. Photobiol. A 2000, 133, 89. (27) Xu, Y.; Langford, C. H. Variation of Langmuir Adsorption Constant Determined for TiO2-Photocatalyzed Degradation of Acetophenone under Different light Intensity. J. Photochem. Photobiol. A 2000, 133, 67. (28) Dutta, S.; Parsonsb, S. A.; Bhattacharjeea, C.; Jarvis, P.; Dattaa, S.; Bandyopadhyay, S. Kinetic Study of Adsorption and Photo-Decolorization of Reactive Red 198 on TiO2 Surface. Chem. Eng. J. 2009, 155, 674. (29) Daneshvar, N.; Salari, D.; Khataee, A. R. Photocatalytic Degradation of Azo Dye Acid Red 14 in Water: Investigation of the Effect of Operational Parameters. J. Photochem. Photobiol. A 2003, 157, 111.
12364
Ind. Eng. Chem. Res., Vol. 49, No. 24, 2010
(30) Khataee, A. R.; Kasiri, M. B. Photocatalytic Degradation of Organic Dyes in the Presence of Nanostructured Titanium dioxide: Influence of the Chemical Structure of Dyes. J. Mol. Catal. A: Chem. 2010, 328, 8. (31) Khataee, A. R.; Zarei, M.; Khameneh Asl, S. Photocatalytic Treatment of a Dye Solution using Immobilized TiO2 Nanoparticles Combined with Electro-Fenton Process: Optimization of Operational Parameters. J. Electroanal. Chem. 2010, 648, 143. (32) Rothenberger, G.; Moser, J.; Gratzel, M.; Serpone, N.; Sharma, D. K. Charge Carrier Trapping and Recombination Dynamics in Small Semiconductor Particles. J. Am. Chem. Soc. 1985, 107, 8054.
(33) Salvado-Estivill, I.; Hargreaves, D. M.; Puma, G. L. Evaluation of the Intrinsic Photocatalytic Oxidation Kinetics of Indoor Air Pollutants. EnViron. Sci. Technol. 2007, 41, 2028.
ReceiVed for reView April 25, 2010 ReVised manuscript receiVed October 21, 2010 Accepted October 21, 2010 IE101997U
